Constitutional law of the United States

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https://en.wikipedia.org/wiki/Constitutional_law_of_the_United_States

The constitutional law of the United States is the body of law governing the interpretation and implementation of the United States Constitution. The subject concerns the scope of power of the United States federal government compared to the individual states and the fundamental rights of individuals. The ultimate authority upon the interpretation of the Constitution and the constitutionality of statutes, state and federal, lies with the Supreme Court of the United States.

The Supreme Court

Judicial review

Early in its history, in Marbury v. Madison, 5 U.S. 137 (1803) and Fletcher v. Peck, 10 U.S. 87 (1810), the Supreme Court of the United States declared that the judicial power granted to it by Article III of the United States Constitution included the power of judicial review, to consider challenges to the constitutionality of a State or Federal law. The holding in these cases empowered the Supreme Court to strike down enacted laws that were contrary to the Constitution. In this role, for example, the Court has struck down state laws for failing to conform to the Contract Clause (see, e.g., Dartmouth College v. Woodward), the Equal Protection Clause (see, e.g., Brown v. Board of Education), or the Commerce Clause of the Constitution (see, e.g., United States v. Lopez).

Scope and effect

The Supreme Court's interpretations of constitutional law are binding on the legislative and executive branches of the federal government, on the lower courts in the federal system, and on all state courts. This system of binding interpretations or precedents evolved from the common law system (called "stare decisis"), where courts are bound by their own prior decisions and by the decisions of higher courts. Neither English common law courts nor continental civil law courts had the power to declare legislation unconstitutional, the United States Supreme Court has long held the power to declare federal or state legislation unconstitutional.

Justiciability

Federal courts consider other doctrines before allowing a lawsuit to go forward:

• Actual dispute - the lawsuit concerns a "case or controversy" under the meaning of Article III, Section 2 of the U.S. Constitution
• Standing - the party bringing the suit must have (1) a particularized and concrete injury, (2) a causal connection between the complained-of conduct and that injury, and (3) a likelihood that a favorable court decision will redress the injury
• Ripeness - a party will lack standing where his/her case raises abstract, hypothetical or conjectural questions.
• Mootness - a party is seeking redress over a case that no longer has a basis for dispute, though there are limited exceptions
• Political question - the issues raised in the suit are unreviewable because the Constitution relegates it to another branch of government.

The Supreme Court prohibits itself from issuing advisory opinions where there is no actual case or controversy before them.(See Muskrat v. United States, 219 U.S. 346 (1911)).

Differing views on the role of the Court

There are a number of ways that commentators and Justices of the Supreme Court have defined the Court's role, and its jurisprudential method:

• Originalism is a family of similar theories that hold that the Constitution has a fixed meaning from an authority contemporaneous with its ratification, and that it should be construed in light of that authority. Generally, originalism stands for the principle that the Constitution should be interpreted according to its meaning in the late 18th Century. Prominent adherents include Antonin Scalia and Clarence Thomas.
• Purposivism is "an approach that places more emphasis on statutory purpose and congressional intent," practiced notably by Stephen Breyer.
• Judicial restraint is the idea that the Supreme Court should decide as few cases as possible and on the narrowest possible grounds in order to allow the democratic process to play out without judicial interference wherever possible. Oliver Wendell Holmes Jr. and Felix Frankfurter are often associated this approach.
• Instrumentalism is the approach that society and the law complement and ought to reflect each other, generally leading to the law shifting with public opinion. Ruth Bader Ginsburg was a notable jurist who utilized this philosophy.

Federalism

Political power in the United States is divided under a scheme of federalism, in which multiple units of government exercise jurisdiction over the same geographical area. This manner of distributing political power was a compromise between two extremes feared by the framers: the efficiency of tyranny when power is overly centralized, as under the British monarchy, on one end of the spectrum, and the ineffectiveness of an overly decentralized government, as under the Articles of Confederation, on the other. Supporters of federalism believed that a division of power between federal and state governments would decrease the likelihood of tyranny. The framers felt the states were in the best position to restrict such movements. Another value of federalism is that the states are much closer to the people, so that they can be more responsive to and effective in resolving the localized concerns of the public. Federalism represented a middle ground by dividing power between the governments of the individual states and the centralized federal government.

The Constitution assigns the powers of the federal government to the legislative (Article I), executive (Article II), and judicial (Article III) branches, and the Tenth Amendment provides that those powers not expressly delegated to the federal government are reserved by the States or the people.

Legislative powers committed to the U.S. Congress (Article I)

Article I, Section 8 of the Constitution contains the enumerated powers of Congress.

The federal commerce power

Congress is authorized to "regulate commerce with foreign nations, and among the several states, and with the Indian tribes" under Article I, Section 8, Clause 3 of the Constitution.

Important early cases include United States v. E.C. Knight Co. (1895) which held that the federal Sherman Act could not be applied to manufacture of sugar because the authority of the commerce clause was insufficient to affect the manufacture of goods. Further limitation continued in cases such as Schecter Poultry v. United States, in which the Court invalidated a federal statute seeking to enforce labor conditions at a slaughterhouse for chickens; the Court held the relationship between labor conditions and chickens was too indirect - that chickens come to rest upon arrival at the slaughterhouse (thereby ending the stream of commerce), so whatever happened in the slaughterhouse was not Congress's business.

In Stafford v. Wallace, the Court articulated a "stream of commerce" test; if a transaction affected commerce in a transition that was local, but supported interstate commerce, then Congress could regulate those transactions under the commerce clause. The judgement in Stafford began the Court's increased deference to Congress in matters regarding interpretation of its powers. Further expansion of Congress's commerce clause power continued with Wickard v. Filburn in 1942 involving a farmer's refusal to comply with a federal quota. Wickard articulated the aggregation principle: that effects of the entire class matter rather than composites of the class, so even if the single farmer did not substantially affect interstate commerce, all farmers - the class to which he belonged - do - they compete with the national market. This case largely ended challenges to laws based upon the extent of power bestowed by the commerce clause until United States v. Lopez (1995).

In 1995, the Court held that the Crime Control Act of 1990, which the Gun-Free School Zones Act was a part of, was unconstitutional because it was an "impermissible extension of congressional power under the Commerce Clause." Lopez remains the central case regarding the authority of Congress under the commerce power.

The spending power

Clause 1 of Article I, § 8 grants Congress the power to levy and collect taxes provided that they are uniform across the nation. Notable cases and challenges to the power of Congress include McCray v. United States (1904), Flint v. Stone Tracy & Co. (1911), and Printz v. United States (1997).

Other enumerated powers

Other federal powers specifically enumerated by Section 8 of Article I of the United States Constitution (and generally considered exclusive to the federal government) are:

• to coin money, and to regulate its value;
• to establish laws governing bankruptcy;
• to establish post offices (although Congress may allow for the establishment of non-governmental mail services by private entities);
• to control the issuance of copyrights and patents (although copyrights and patents may also be enforced in state courts);
• to govern the District of Columbia and all other federal properties;
• to control naturalization (and, implicitly, the immigration) of aliens;
• to enforce "by appropriate legislation" the Thirteenth, Fourteenth, and Fifteenth Amendments to the United States Constitution (a function of the Constitution's Necessary and Proper clause);
• to propose, by a two-thirds vote, constitutional amendments for ratification by three-fourths of the states pursuant to the terms of Article V.

Members of the Senate and of the House of Representatives have immunity for all statements made on the floor of Congress except in cases of "Treason, Felony, or Breach of the Peace "(Art. I Sec. 6).

Executive powers committed to the President of the United States (Article II)

Article II, Section 1, vests the executive power in the President of the United States of America. Unlike the commitment of authority in Article I, which refers Congress only specifically enumerated powers "herein granted" and such powers as may be necessary and proper to carry out the same, Article II is all-inclusive in its commitment of the executive power in a President of the United States of America.

Enumerated powers of the President Several important powers are expressly committed to the President under Article II, Section 2. These include:

• Commander-in-chief of the armed forces;
• Power to pardon offenses against the United States;
• Power to make treaties (with consent of the Senate); and the
• Power to appoint judges, ambassadors, and other officers of the United States (with the advice and consent of the Senate);

The Presentment Clause (Article I, Section 7, cl. 2–3) grants the president the power to veto Congressional legislation and Congress the power to override a presidential veto with a supermajority. Under the clause, once a bill has been passed in identical form by both houses of Congress, with a two thirds majority in both houses, it becomes federal law.

The president approves or rejects a bill in its entirety; he is not permitted to veto specific provisions. In 1996, Congress passed, and President Bill Clinton signed, the Line Item Veto Act of 1996, which gave the president the power to veto individual items of budgeted expenditures in appropriations bills. The Supreme Court subsequently declared the line-item veto unconstitutional as a violation of the Presentment Clause in Clinton v. City of New York, 524 U.S. 417 (1998). The Court held that the Constitution's silence on the subject of such a procedure as "an express prohibition," and that statutes may only be enacted "in accord with a single, finely wrought and exhaustively considered, procedure", and that a bill must be approved or rejected by the president in its entirety.

Foreign affairs and war powers

Article I grants congress the power to declare war, raise, and support the armed forces of the United States, while, Article II grants the president the power of the commander-in-chief of the armed forces. The Supreme Court rarely addresses the issue of the president's use of troops, and have been dismissed on grounds that their use is a political question.

Appointment and removal of executive personnel

Article II, Section 2 grants the President the power, with the "advice and consent of the Senate," to appoint "ambassadors,... judges of the Supreme Court, and all other officers of the United States, whose appointments are not otherwise provided for" in the Constitution. This includes members of the cabinet, top-level agency officials, Article III judges, US Attorneys, and the Chairman of the Joint Chiefs, among many other positions. Under the modern interpretation of "advice and consent," a presidential appointment must be confirmed by majority vote in the Senate in order to take effect.

Article II, Section 2 gives Congress the discretion to vest the appointment of "inferior officers" in either the President alone, the heads of departments, or the lower federal courts.

The President has the authority to remove most high-level executive officers at will. Congress, however, may place limitations on the removal of certain executive appointees serving in positions where independence from the presidency is considered desirable, such as stipulating that removal may only be for cause.

Executive Immunity

Sitting presidents enjoyed immunity from civil suit for damages arising from actions taken while in office, but this rule was significantly curtailed by the Supreme Court's decision in Clinton v. Jones, which held that sitting Presidents could be sued for actions before taking office or unrelated to the discharge of executive powers.

Judiciary structure and jurisdiction of the federal courts (Article III)

Article Three of the United States Constitution vests the judicial power of the federal government in the Supreme Court. The Judiciary Act of 1789 implemented Article III by creating a hierarchy under which circuit courts consider appeals from the district courts and the Supreme Court has appellate authority over the circuit courts. The Judiciary Act of 1789 provided that the Supreme Court would consist of one chief justice and five associate justices; there have been nine justices since 1869.

Powers reserved to the states

Some of the more important powers reserved to the states by the Constitution are:

• the power, by "application of two-thirds of the legislatures of the several states," to require Congress to convene a constitutional convention for the purpose of proposing amendments to or revising the terms of the Constitution (see Article V).
• The Tenth Amendment establishes the system of dual sovereignty by reserving "the powers not delegated to the United States by the Constitution, nor prohibited by it to the States...to the States respectively, or to the people."

Suits against states: effect of the 11th Amendment

Main article: Eleventh Amendment to the United States Constitution

The Eleventh Amendment to the United States Constitution defines the scope of when and in what circumstances a state may be taken to federal court. Taken literally, the Amendment prohibits a citizen from suing a state in federal court through the sovereign immunity doctrine. However, the Court has articulated three exceptions: 1) Particular state officials may be sued, 2) States can waive immunity or consent to suit, and 3) Congress may authorize suits against a state through the abrogation doctrine. However, concerning this latter exception, the Supreme Court has held in Seminole Tribe v. Florida that Congress may not, outside of the Fourteenth Amendment, authorize federal lawsuits against states in abrogation of the Eleventh Amendment's guarantee of sovereign state immunity.

The United States government, its agencies and instrumentalities, are immune from state regulation that interferes with federal activities, functions, and programs. State laws and regulations cannot substantially interfere with an authorized federal program, except for minor or indirect regulation, such as state taxation of federal employees, a practice established in McCulloch v. Maryland (1819).

Intergovernmental immunities and interstate relations

Main article: Intergovernmental immunity (United States)

The United States government, its agencies and instrumentalities, are immune from state regulation that interferes with federal activities, functions, and programs. State laws and regulations cannot substantially interfere with an authorized federal program, except for minor or indirect regulation, such as state taxation of federal employees, a practice established in McCulloch v. Maryland (1819).

Rights of individuals

Bill of Rights

First Amendment

Freedom of expression

Main article: Freedom of speech in the United States

The freedom of speech has been widely controversial throughout American history, with cases such as Schenck v. United States (1919) and Brandenburg v. Ohio (1969) establishing the extent to which government can legally restrict speech. The freedom of speech does not extend to libel, but New York Times Co. v. Sullivan (1964) established a higher level of protection for the press.

Freedom of religion

Main article: Freedom of Religion in the United States

In the United States, freedom of religion is a constitutionally protected right provided in the religion clauses of the First Amendment. Freedom of religion is also closely associated with separation of church and state, a concept advocated by Colonial founders such as Dr. John Clarke, Roger Williams, William Penn and later Founding Fathers such as James Madison and Thomas Jefferson.

The long-term trend has been towards increasing secularization of the government. The remaining state churches were disestablished in 1820 and teacher-led public school prayer was abolished in 1962, but the military chaplaincy remains to the present day. Notable cases include Tennessee v. Scopes, Engel v. Vitale, Abington School District v. Schempp, Georgetown College v. Jones, Lemon v. Kurtzman, Goldman v. Weinberger, County of Allegheny v. ACLU, and Rosenberger v. University of Virginia.

Second Amendment

Main articles: Second Amendment to the United States Constitution and Right to keep and bear arms

The Second Amendment states that “a well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed,”. It has been one of the most controversial rights in the Bill of Rights-notable cases consist of United States v. Miller (1934), Printz v. United States (1997), District of Columbia v. Heller (2008), and McDonald v. City of Chicago (2010).

Third Amendment

Main article: Third Amendment to the United States Constitution

The Third Amendment prohibits the quartering of soldiers in private residences and has never been the basis of a decision by the Supreme Court. Engblom v. Carey is the case most often mentioned involving Third Amendment claims.

Fourth Amendment

Main article: Fourth Amendment to the United States Constitution

The Fourth Amendment prohibits the unreasonable search and seizure of one's effects and requires a warrant for both searches and arrests based upon probable cause. Important cases include Coolidge v. New Hampshire, Payton v. New York, United States v. Watson, Michigan v. Summers, and New York v. Harris.

Fifth Amendment

Main article: Fifth Amendment to the United States Constitution

The Takings Clause

Generally speaking, the Fifth Amendment prevents the government from taking private property "for public use without just compensation." This prohibition on takings is applicable to the states via incorporation.

Due Process

The Fifth Amendment ensures that no person will be deprived of "life, liberty, or property, without due process of law" and protects oneself against self incrimination. The Miranda warning was a result of Miranda v. Arizona. Other notable cases include Michigan v. Tucker, Rhode Island v. Innis, Edwards v. Arizona, and Kuhlmann v. Wilson.

Sixth Amendment

Main article: Sixth Amendment to the United States Constitution

The Sixth Amendment guarantees the right to a speedy, public trial, the power to compel witnesses, the right to counsel, and the right to an impartial jury. Cases concerning its interpretation include Baldwin v. New York, Barker v. Wingo, Crawford v. Washington, Duncan v. Louisiana, and Melendez-Diaz v. Massachusetts.

Seventh Amendment

Main article: Seventh Amendment to the United States Constitution

The Seventh Amendment guarantees a jury trial in civil cases in addition to the guarantee of a jury in a criminal trial provided by the Sixth Amendment. Its guarantees are not incorporated to the states via the Fourteenth Amendment, although most state constitutions contain similar provisions. Hardware Dealers Mutual Fire Insurance Co. of Wisconsin v. Glidden Co. (1931) is the most recent significant case regarding the Amendment's interpretation.

Eighth Amendment

Main article: Eighth Amendment to the United States Constitution

The Eighth Amendment prohibits the imposition of excessive bail, excessive fines, and cruel and unusual punishment. The Supreme Court declared the death penalty unconstitutional in Furman v. Georgia (1972) under the Eighth Amendment. It was later reinstated in Gregg v. Georgia. Other notable cases include Malloy v. Hogan, Witherspoon v. Illinois, Gideon v. Wainwright, and Woodson v. North Carolina.

Metallocene

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Metallocene 

General chemical structure of a metallocene compound, where M is a metal cation

A metallocene is a compound typically consisting of two cyclopentadienyl anions (C
₅H⁻
₅, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C₅H₅)₂M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride or vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp₂ZrCH₃]⁺ catalyze olefin polymerization.

Some metallocenes consist of metal plus two cyclooctatetraenide anions (C
₈H²⁻
₈, abbreviated cot²⁻), namely the lanthanocenes and the actinocenes (uranocene and others).

Metallocenes are a subset of a broader class of compounds called sandwich compounds. In the structure shown at right, the two pentagons are the cyclopentadienyl anions with circles inside them indicating they are aromatically stabilized. Here they are shown in a staggered conformation.

History

Ferrocene

The first metallocene to be classified was ferrocene, and was discovered simultaneously in 1951 by Kealy and Pauson, and Miller et al. Kealy and Pauson were attempting to synthesize fulvalene through the oxidation of a cyclopentadienyl salt with anhydrous FeCl₃ but obtained instead the substance C₁₀H₁₀Fe At the same time, Miller et al reported the same iron product from a reaction of cyclopentadiene with iron in the presence of aluminum, potassium, or molybdenum oxides. The structure of "C₁₀H₁₀Fe" was determined by Geoffrey Wilkinson et al. and by Ernst Otto Fischer et al. These two were awarded the Nobel Prize in Chemistry in 1973 for their work on sandwich compounds, including the structural determination of ferrocene. They determined that the carbon atoms of the cyclopentadienyl (Cp) ligand contributed equally to the bonding and that bonding occurred due to the metal d-orbitals and the π-electrons in the p-orbitals of the Cp ligands. This complex is now known as ferrocene, and the group of transition metal dicyclopentadienyl compounds is known as metallocenes. Metallocenes have the general formula [(η⁵-C₅H₅)₂M]. Fischer et al. first prepared the ferrocene derivatives involving Co and Ni. Often derived from substituted derivatives of cyclopentadienide, metallocenes of many elements have been prepared.

One of the very earliest commercial manufacturers of metallocenes was Arapahoe Chemicals in Boulder, Colorado

Definition

Ball-and-stick model of a metallocene molecule where the cyclopentadienyl anions are in a staggered conformation. The purple ball in the middle represents the metal cation.

The general name metallocene is derived from ferrocene, (C₅H₅)₂Fe or Cp₂Fe, systematically named bis(η⁵-cyclopentadienyl)iron(II). According to the International Union of Pure and Applied Chemistry definition, a metallocene contains a transition metal and two cyclopentadienyl ligands coordinated in a sandwich structure, i.e., the two cyclopentadienyl anions are on parallel planes with equal bond lengths and strengths. Using the nomenclature of "hapticity", the equivalent bonding of all 5 carbon atoms of a cyclopentadienyl ring is denoted as η⁵, pronounced "pentahapto". There are exceptions, such as uranocene, which has two cyclooctatetraene rings sandwiching a uranium atom.

In metallocene names, the prefix before the -ocene ending indicates what metallic element is between the Cp groups. For example, in ferrocene, iron(II), ferrous iron is present.

In contrast to the more strict definition proposed by International Union of Pure and Applied Chemistry, which requires a d-block metal and a sandwich structure, the term metallocene and thus the denotation -ocene, is applied in the chemical literature also to non-transition metal compounds, such as barocene (Cp₂Ba), or structures where the aromatic rings are not parallel, such as found in manganocene or titanocene dichloride (Cp₂TiCl₂).

Some metallocene complexes of actinides have been reported where there are three cyclopentadienyl ligands for a monometallic complex, all three of them bound η⁵.

Classification

There are many (η⁵-C₅H₅)–metal complexes and they can be classified by the following formulas:

Formula	Description
[(η5-C5H5)2M]	Symmetrical, classical 'sandwich' structure
[(η5-C5H5)2MLx]	Bent or tilted Cp rings with additional ligands, L
[(η5-C5H5)MLx]	Only one Cp ligand with additional ligands, L ('piano-stool' structure)

Metallocene complexes can also be classified by type:

1. Parallel
2. Multi-decker
3. Half-sandwich compound
4. Bent metallocene or tilted
5. More than two Cp ligands

Synthesis

Three main routes are normally employed in the formation of these types of compounds:

Using a metal salt and cyclopentadienyl reagents

Sodium cyclopentadienide (NaCp) is the preferred reagent for these types of reactions. It is most easily obtained by the reaction of molten sodium and dicyclopentadiene. Traditionally, the starting point is the cracking of dicyclopentadiene, the dimer of cyclopentadiene. Cyclopentadiene is deprotonated by strong bases or alkali metals.

MCl₂ + 2 NaC₅H₅ → (C₅H₅)₂M + 2 NaCl            (M = V, Cr, Mn, Fe, Co; solvent = THF, DME, NH₃)

CrCl₃ + 3 NaC₅H₅ → [(C₅H₅)₂Cr] + 1⁄2 "C₁₀H₁₀" + 3 NaCl

NaCp acts as a reducing agent and a ligand in this reaction.

Using a metal and cyclopentadiene

This technique provides using metal atoms in the gas phase rather than the solid metal. The highly reactive atoms or molecules are generated at a high temperature under vacuum and brought together with chosen reactants on a cold surface.

M + C₅H₆ → MC₅H₅ + 1⁄2 H₂            (M = Li, Na, K)

M + 2 C₅H₆ → [(C₅H₅)₂M] + H₂            (M = Mg, Fe)

Using cyclopentadienyl reagents

A variety of reagents have been developed that transfer Cp to metals. Once popular was thallium cyclopentadienide. It reacts with metal halides to give thallium chloride, which is poorly soluble, and the cyclopentadienyl complex. Trialkyltin derivatives of Cp⁻ have also been used.

Many other methods have been developed. Chromocene can be prepared from chromium hexacarbonyl by direct reaction with cyclopentadiene in the presence of diethylamine; in this case, the formal deprotonation of the cyclopentadiene is followed by reduction of the resulting protons to hydrogen gas, facilitating the oxidation of the metal centre.

Cr(CO)₆ + 2 C₅H₆ → Cr(C₅H₅)₂ + 6 CO + H₂

Metallocenes generally have high thermal stability. Ferrocene can be sublimed in air at over 100 °C with no decomposition; metallocenes are generally purified in the laboratory by vacuum sublimation. Industrially, sublimation is not practical so metallocenes are isolated by crystallization or produced as part of a hydrocarbon solution. For Group IV metallocenes, donor solvents like ether or THF are distinctly undesirable for polyolefin catalysis. Charge-neutral metallocenes are soluble in common organic solvents. Alkyl substitution on the metallocene increases the solubility in hydrocarbon solvents.

Structure

A structural trend for the series MCp₂ involves the variation of the M-C bonds, which elongate as the valence electron count deviates from 18.

M(C5H5)2	rM–C (pm)	Valence electron count
Fe	203.3	18
Co	209.6	19
Cr	215.1	16
Ni	218.5	20
V	226	15

In metallocenes of the type (C₅R₅)₂M, the cyclopentadienyl rings rotate with very low barriers. Single crystal X-ray diffraction studies reveal both eclipsed or staggered rotamers. For non-substituted metallocenes the energy difference between the staggered and eclipsed conformations is only a few kJ/mol. Crystals of ferrocene and osmocene exhibit eclipsed conformations at low temperatures, whereas in the related bis(pentamethylcyclopentadienyl) complexes the rings usually crystallize in a staggered conformation, apparently to minimize steric hindrance between the methyl groups.

Spectroscopic properties

Vibrational (infrared and Raman) spectroscopy of metallocenes

Infrared and Raman spectroscopies have proved to be important in the analysis of cyclic polyenyl metal sandwich species, with particular use in elucidating covalent or ionic M–ring bonds and distinguishing between central and coordinated rings. Some typical spectral bands and assignments of iron group metallocenes are shown in the following table:

Spectral frequencies of group 8 metallocenes

	Ferrocene (cm−1)	Ruthenocene (cm−1)	Osmocene (cm−1)
C–H stretch	3085	3100	3095
C–C stretch	1411	1413	1405
Ring deformation	1108	1103	1096
C–H deformation	1002	1002	995
C–H out-of-plane bend	811	806	819
Ring tilt	492	528	428
M–ring stretch	478	446	353
M–ring bend	170	185	–

NMR (¹H and ¹³C) spectroscopy of metallocenes

Nuclear magnetic resonance (NMR) is the most applied tool in the study of metal sandwich compounds and organometallic species, giving information on nuclear structures in solution, as liquids, gases, and in the solid state. ¹H NMR chemical shifts for paramagnetic organotransition-metal compounds is usually observed between 25 and 40 ppm, but this range is much more narrow for diamagnetic metallocene complexes, with chemical shifts usually observed between 3 and 7 ppm.

Mass spectrometry of metallocenes

Mass spectrometry of metallocene complexes has been very well studied and the effect of the metal on the fragmentation of the organic moiety has received considerable attention and the identification of metal-containing fragments is often facilitated by the isotope distribution of the metal. The three major fragments observed in mass spectrometry are the molecular ion peak, [C₁₀H₁₀M]⁺, and fragment ions, [C₅H₅M]⁺ and M⁺.

Derivatives

Main article: Sandwich compound

After the discovery of ferrocene, the synthesis and characterization of derivatives of metallocene and other sandwich compounds attracted researchers’ interests.

Metallocenophanes

Metallocenophanes feature linking of the cyclopentadienyl or polyarenyl rings by the introduction of one or more heteroannular bridges. Some of these compounds undergo thermal ring-opening polymerizations to give soluble high molecular weight polymers with transition metals in the polymer backbone. Ansa-metallocenes are derivatives of metallocenes with an intramolecular bridge between the two cyclopentadienyl rings.

Polynuclear and heterobimetallic metallocenes

• Ferrocene derivatives: biferrocenophanes have been studied for their mixed valence properties. Upon one-electron oxidation of a compound with two or more equivalent ferrocene moieties, the electron vacancy could be localized on one ferrocene unit or completely delocalized.
• Ruthenocene derivatives: in the solid state biruthenocene is disordered and adopts the transoid conformation with the mutual orientation of Cp rings depending on the intermolecular interactions.
• Vanadocene and rhodocene derivatives: vanadocene complexes have been used as starting materials for the synthesis of heterobimetallic complexes. The 18 valence electron ions [Cp₂Rh]⁺ are very stable, unlike the neutral monomers Cp₂Rh which dimerize immediately at room temperature and they have been observed in matrix isolation.

Multi-decker sandwich compounds

Nickel triple-decker sandwich complex

Triple-decker complexes are composed of three Cp anions and two metal cations in alternating order. The first triple-decker sandwich complex, [Ni₂Cp₃]⁺, was reported in 1972. Many examples have been reported subsequently, often with boron-containing rings.

Metallocenium cations

The most famous example is ferrocenium, [Fe(C₅H₅)₂]⁺, the blue iron(III) complex derived from oxidation of orange iron(II) ferrocene (few metallocene anions are known).

Applications

Many derivatives of early metal metallocenes are active catalysts for olefin polymerization. Unlike traditional and still dominant heterogeneous Ziegler–Natta catalysts, metallocene catalysts are homogeneous. Early metal metallocene derivatives, e.g. Tebbe's reagent, Petasis reagent, and Schwartz's reagent are useful in specialized organic synthetic operations.

Potential applications

The ferrocene/ferrocenium biosensor has been discussed for determining the levels of glucose in a sample electrochemically through a series of connected redox cycles.

Metallocene dihalides [Cp₂MX₂] (M = Ti, Mo, Nb) exhibit anti-tumor properties, although none have proceeded far in clinical trials.

Affective computing

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Affective_computing 

Affective computing is the study and development of systems and devices that can recognize, interpret, process, and simulate human affects. It is an interdisciplinary field spanning computer science, psychology, and cognitive science. While some core ideas in the field may be traced as far back as to early philosophical inquiries into emotion, the more modern branch of computer science originated with Rosalind Picard's 1995 paper on affective computing and her book Affective Computing published by MIT Press. One of the motivations for the research is the ability to give machines emotional intelligence, including to simulate empathy. The machine should interpret the emotional state of humans and adapt its behavior to them, giving an appropriate response to those emotions.

Areas

Detecting and recognizing emotional information

Detecting emotional information usually begins with passive sensors that capture data about the user's physical state or behavior without interpreting the input. The data gathered is analogous to the cues humans use to perceive emotions in others. For example, a video camera might capture facial expressions, body posture, and gestures, while a microphone might capture speech. Other sensors detect emotional cues by directly measuring physiological data, such as skin temperature and galvanic resistance.

Recognizing emotional information requires the extraction of meaningful patterns from the gathered data. This is done using machine learning techniques that process different modalities, such as speech recognition, natural language processing, or facial expression detection. The goal of most of these techniques is to produce labels that would match the labels a human perceiver would give in the same situation: For example, if a person makes a facial expression furrowing their brow, then the computer vision system might be taught to label their face as appearing "confused" or as "concentrating" or "slightly negative" (as opposed to positive, which it might say if they were smiling in a happy-appearing way). These labels may or may not correspond to what the person is actually feeling.

Emotion in machines

Another area within affective computing is the design of computational devices proposed to exhibit either innate emotional capabilities or that are capable of convincingly simulating emotions. A more practical approach, based on current technological capabilities, is the simulation of emotions in conversational agents in order to enrich and facilitate interactivity between human and machine.

Marvin Minsky, one of the pioneering computer scientists in artificial intelligence, relates emotions to the broader issues of machine intelligence stating in The Emotion Machine that emotion is "not especially different from the processes that we call 'thinking.'"

Technologies

In psychology, cognitive science, and in neuroscience, there have been two main approaches for describing how humans perceive and classify emotion: continuous or categorical. The continuous approach tends to use dimensions such as negative vs. positive, calm vs. aroused.

The categorical approach tends to use discrete classes such as happy, sad, angry, fearful, surprise, disgust. Different kinds of machine learning regression and classification models can be used for having machines produce continuous or discrete labels. Sometimes models are also built that allow combinations across the categories, e.g. a happy-surprised face or a fearful-surprised face.

The following sections consider many of the kinds of input data used for the task of emotion recognition.

Emotional speech

Various changes in the autonomic nervous system can indirectly alter a person's speech, and affective technologies can leverage this information to recognize emotion. For example, speech produced in a state of fear, anger, or joy becomes fast, loud, and precisely enunciated, with a higher and wider range in pitch, whereas emotions such as tiredness, boredom, or sadness tend to generate slow, low-pitched, and slurred speech. Some emotions have been found to be more easily computationally identified, such as anger or approval.

Emotional speech processing technologies recognize the user's emotional state using computational analysis of speech features. Vocal parameters and prosodic features such as pitch variables and speech rate can be analyzed through pattern recognition techniques.

Speech analysis is an effective method of identifying affective state, having an average reported accuracy of 70 to 80% in research from 2003 and 2006. These systems tend to outperform average human accuracy (approximately 60%) but are less accurate than systems which employ other modalities for emotion detection, such as physiological states or facial expressions. However, since many speech characteristics are independent of semantics or culture, this technique is considered to be a promising route for further research.

Algorithms

The process of speech/text affect detection requires the creation of a reliable database, knowledge base, or vector space model, broad enough to fit every need for its application, as well as the selection of a successful classifier which will allow for quick and accurate emotion identification.

As of 2010, the most frequently used classifiers were linear discriminant classifiers (LDC), k-nearest neighbor (k-NN), Gaussian mixture model (GMM), support vector machines (SVM), artificial neural networks (ANN), decision tree algorithms and hidden Markov models (HMMs). Various studies showed that choosing the appropriate classifier can significantly enhance the overall performance of the system. The list below gives a brief description of each algorithm:

• LDC – Classification happens based on the value obtained from the linear combination of the feature values, which are usually provided in the form of vector features.
• k-NN – Classification happens by locating the object in the feature space, and comparing it with the k nearest neighbors (training examples). The majority vote decides on the classification.
• GMM – is a probabilistic model used for representing the existence of subpopulations within the overall population. Each sub-population is described using the mixture distribution, which allows for classification of observations into the sub-populations.
• SVM – is a type of (usually binary) linear classifier which decides in which of the two (or more) possible classes, each input may fall into.
• ANN – is a mathematical model, inspired by biological neural networks, that can better grasp possible non-linearities of the feature space.
• Decision tree algorithms – work based on following a decision tree in which leaves represent the classification outcome, and branches represent the conjunction of subsequent features that lead to the classification.
• HMMs – a statistical Markov model in which the states and state transitions are not directly available to observation. Instead, the series of outputs dependent on the states are visible. In the case of affect recognition, the outputs represent the sequence of speech feature vectors, which allow the deduction of states' sequences through which the model progressed. The states can consist of various intermediate steps in the expression of an emotion, and each of them has a probability distribution over the possible output vectors. The states' sequences allow us to predict the affective state which we are trying to classify, and this is one of the most commonly used techniques within the area of speech affect detection.

It is proved that having enough acoustic evidence available the emotional state of a person can be classified by a set of majority voting classifiers. The proposed set of classifiers is based on three main classifiers: kNN, C4.5 and SVM-RBF Kernel. This set achieves better performance than each basic classifier taken separately. It is compared with two other sets of classifiers: one-against-all (OAA) multiclass SVM with Hybrid kernels and the set of classifiers which consists of the following two basic classifiers: C5.0 and Neural Network. The proposed variant achieves better performance than the other two sets of classifiers.

Databases

The vast majority of present systems are data-dependent. This creates one of the biggest challenges in detecting emotions based on speech, as it implicates choosing an appropriate database used to train the classifier. Most of the currently possessed data was obtained from actors and is thus a representation of archetypal emotions. Those so-called acted databases are usually based on the Basic Emotions theory (by Paul Ekman), which assumes the existence of six basic emotions (anger, fear, disgust, surprise, joy, sadness), the others simply being a mix of the former ones. Nevertheless, these still offer high audio quality and balanced classes (although often too few), which contribute to high success rates in recognizing emotions.

However, for real life application, naturalistic data is preferred. A naturalistic database can be produced by observation and analysis of subjects in their natural context. Ultimately, such database should allow the system to recognize emotions based on their context as well as work out the goals and outcomes of the interaction. The nature of this type of data allows for authentic real life implementation, due to the fact it describes states naturally occurring during the human–computer interaction (HCI).

Despite the numerous advantages which naturalistic data has over acted data, it is difficult to obtain and usually has low emotional intensity. Moreover, data obtained in a natural context has lower signal quality, due to surroundings noise and distance of the subjects from the microphone. The first attempt to produce such database was the FAU Aibo Emotion Corpus for CEICES (Combining Efforts for Improving Automatic Classification of Emotional User States), which was developed based on a realistic context of children (age 10–13) playing with Sony's Aibo robot pet. Likewise, producing one standard database for all emotional research would provide a method of evaluating and comparing different affect recognition systems.

Speech descriptors

The complexity of the affect recognition process increases with the number of classes (affects) and speech descriptors used within the classifier. It is, therefore, crucial to select only the most relevant features in order to assure the ability of the model to successfully identify emotions, as well as increasing the performance, which is particularly significant to real-time detection. The range of possible choices is vast, with some studies mentioning the use of over 200 distinct features. It is crucial to identify those that are redundant and undesirable in order to optimize the system and increase the success rate of correct emotion detection. The most common speech characteristics are categorized into the following groups.

1. Frequency characteristics
   • Accent shape – affected by the rate of change of the fundamental frequency.
   • Average pitch – description of how high/low the speaker speaks relative to the normal speech.
   • Contour slope – describes the tendency of the frequency change over time, it can be rising, falling or level.
   • Final lowering – the amount by which the frequency falls at the end of an utterance.
   • Pitch range – measures the spread between the maximum and minimum frequency of an utterance.
2. Time-related features:
   • Speech rate – describes the rate of words or syllables uttered over a unit of time
   • Stress frequency – measures the rate of occurrences of pitch accented utterances
3. Voice quality parameters and energy descriptors:
   • Breathiness – measures the aspiration noise in speech
   • Brilliance – describes the dominance of high Or low frequencies In the speech
   • Loudness – measures the amplitude of the speech waveform, translates to the energy of an utterance
   • Pause Discontinuity – describes the transitions between sound and silence
   • Pitch Discontinuity – describes the transitions of the fundamental frequency.

Facial affect detection

The detection and processing of facial expression are achieved through various methods such as optical flow, hidden Markov models, neural network processing or active appearance models. More than one modalities can be combined or fused (multimodal recognition, e.g. facial expressions and speech prosody, facial expressions and hand gestures, or facial expressions with speech and text for multimodal data and metadata analysis) to provide a more robust estimation of the subject's emotional state.

Facial expression databases

Main article: Facial expression databases

Creation of an emotion database is a difficult and time-consuming task. However, database creation is an essential step in the creation of a system that will recognize human emotions. Most of the publicly available emotion databases include posed facial expressions only. In posed expression databases, the participants are asked to display different basic emotional expressions, while in spontaneous expression database, the expressions are natural. Spontaneous emotion elicitation requires significant effort in the selection of proper stimuli which can lead to a rich display of intended emotions. Secondly, the process involves tagging of emotions by trained individuals manually which makes the databases highly reliable. Since perception of expressions and their intensity is subjective in nature, the annotation by experts is essential for the purpose of validation.

Researchers work with three types of databases, such as a database of peak expression images only, a database of image sequences portraying an emotion from neutral to its peak, and video clips with emotional annotations. Many facial expression databases have been created and made public for expression recognition purpose. Two of the widely used databases are CK+ and JAFFE.

Emotion classification

Main article: Emotion classification

By doing cross-cultural research in Papua New Guinea, on the Fore Tribesmen, at the end of the 1960s, Paul Ekman proposed the idea that facial expressions of emotion are not culturally determined, but universal. Thus, he suggested that they are biological in origin and can, therefore, be safely and correctly categorized. He therefore officially put forth six basic emotions, in 1972:

• Anger
• Disgust
• Fear
• Happiness
• Sadness
• Surprise

However, in the 1990s Ekman expanded his list of basic emotions, including a range of positive and negative emotions not all of which are encoded in facial muscles. The newly included emotions are:

1. Amusement
2. Contempt
3. Contentment
4. Embarrassment
5. Excitement
6. Guilt
7. Pride in achievement
8. Relief
9. Satisfaction
10. Sensory pleasure
11. Shame

Facial Action Coding System

Main article: Facial Action Coding System

A system has been conceived by psychologists in order to formally categorize the physical expression of emotions on faces. The central concept of the Facial Action Coding System, or FACS, as created by Paul Ekman and Wallace V. Friesen in 1978 based on earlier work by Carl-Herman Hjortsjö are action units (AU). They are, basically, a contraction or a relaxation of one or more muscles. Psychologists have proposed the following classification of six basic emotions, according to their action units ("+" here mean "and"):

Emotion	Action units
Happiness	6+12
Sadness	1+4+15
Surprise	1+2+5B+26
Fear	1+2+4+5+20+26
Anger	4+5+7+23
Disgust	9+15+16
Contempt	R12A+R14A

Challenges in facial detection

As with every computational practice, in affect detection by facial processing, some obstacles need to be surpassed, in order to fully unlock the hidden potential of the overall algorithm or method employed. In the early days of almost every kind of AI-based detection (speech recognition, face recognition, affect recognition), the accuracy of modeling and tracking has been an issue. As hardware evolves, as more data are collected and as new discoveries are made and new practices introduced, this lack of accuracy fades, leaving behind noise issues. However, methods for noise removal exist including neighborhood averaging, linear Gaussian smoothing, median filtering, or newer methods such as the Bacterial Foraging Optimization Algorithm.

Other challenges include

• The fact that posed expressions, as used by most subjects of the various studies, are not natural, and therefore algorithms trained on these may not apply to natural expressions.
• The lack of rotational movement freedom. Affect detection works very well with frontal use, but upon rotating the head more than 20 degrees, "there've been problems".
• Facial expressions do not always correspond to an underlying emotion that matches them (e.g. they can be posed or faked, or a person can feel emotions but maintain a "poker face").
• FACS did not include dynamics, while dynamics can help disambiguate (e.g. smiles of genuine happiness tend to have different dynamics than "try to look happy" smiles.)
• The FACS combinations do not correspond in a 1:1 way with the emotions that the psychologists originally proposed (note that this lack of a 1:1 mapping also occurs in speech recognition with homophones and homonyms and many other sources of ambiguity, and may be mitigated by bringing in other channels of information).
• Accuracy of recognition is improved by adding context; however, adding context and other modalities increases computational cost and complexity

Body gesture

Main article: Gesture recognition

Gestures could be efficiently used as a means of detecting a particular emotional state of the user, especially when used in conjunction with speech and face recognition. Depending on the specific action, gestures could be simple reflexive responses, like lifting your shoulders when you don't know the answer to a question, or they could be complex and meaningful as when communicating with sign language. Without making use of any object or surrounding environment, we can wave our hands, clap or beckon. On the other hand, when using objects, we can point at them, move, touch or handle these. A computer should be able to recognize these, analyze the context and respond in a meaningful way, in order to be efficiently used for Human–Computer Interaction.

There are many proposed methods to detect the body gesture. Some literature differentiates 2 different approaches in gesture recognition: a 3D model based and an appearance-based. The foremost method makes use of 3D information of key elements of the body parts in order to obtain several important parameters, like palm position or joint angles. On the other hand, appearance-based systems use images or videos to for direct interpretation. Hand gestures have been a common focus of body gesture detection methods.

Physiological monitoring

This could be used to detect a user's affective state by monitoring and analyzing their physiological signs. These signs range from changes in heart rate and skin conductance to minute contractions of the facial muscles and changes in facial blood flow. This area is gaining momentum and we are now seeing real products that implement the techniques. The four main physiological signs that are usually analyzed are blood volume pulse, galvanic skin response, facial electromyography, and facial color patterns.

Blood volume pulse

Overview

A subject's blood volume pulse (BVP) can be measured by a process called photoplethysmography, which produces a graph indicating blood flow through the extremities. The peaks of the waves indicate a cardiac cycle where the heart has pumped blood to the extremities. If the subject experiences fear or is startled, their heart usually 'jumps' and beats quickly for some time, causing the amplitude of the cardiac cycle to increase. This can clearly be seen on a photoplethysmograph when the distance between the trough and the peak of the wave has decreased. As the subject calms down, and as the body's inner core expands, allowing more blood to flow back to the extremities, the cycle will return to normal.

Methodology

Infra-red light is shone on the skin by special sensor hardware, and the amount of light reflected is measured. The amount of reflected and transmitted light correlates to the BVP as light is absorbed by hemoglobin which is found richly in the bloodstream.

Disadvantages

It can be cumbersome to ensure that the sensor shining an infra-red light and monitoring the reflected light is always pointing at the same extremity, especially seeing as subjects often stretch and readjust their position while using a computer. There are other factors that can affect one's blood volume pulse. As it is a measure of blood flow through the extremities, if the subject feels hot, or particularly cold, then their body may allow more, or less, blood to flow to the extremities, all of this regardless of the subject's emotional state.

The corrugator supercilii muscle and zygomaticus major muscle are the 2 main muscles used for measuring the electrical activity, in facial electromyography.

Facial electromyography

Main article: Facial electromyography

Facial electromyography is a technique used to measure the electrical activity of the facial muscles by amplifying the tiny electrical impulses that are generated by muscle fibers when they contract. The face expresses a great deal of emotion, however, there are two main facial muscle groups that are usually studied to detect emotion: The corrugator supercilii muscle, also known as the 'frowning' muscle, draws the brow down into a frown, and therefore is the best test for negative, unpleasant emotional response.↵The zygomaticus major muscle is responsible for pulling the corners of the mouth back when you smile, and therefore is the muscle used to test for a positive emotional response.

Here we can see a plot of skin resistance measured using GSR and time whilst the subject played a video game. There are several peaks that are clear in the graph, which suggests that GSR is a good method of differentiating between an aroused and a non-aroused state. For example, at the start of the game where there is usually not much exciting game play, there is a high level of resistance recorded, which suggests a low level of conductivity and therefore less arousal. This is in clear contrast with the sudden trough where the player is killed as one is usually very stressed and tense as their character is killed in the game.

Galvanic skin response

Main article: Galvanic skin response

Galvanic skin response (GSR) is an outdated term for a more general phenomenon known as [Electrodermal Activity] or EDA. EDA is a general phenomena whereby the skin's electrical properties change. The skin is innervated by the [sympathetic nervous system], so measuring its resistance or conductance provides a way to quantify small changes in the sympathetic branch of the autonomic nervous system. As the sweat glands are activated, even before the skin feels sweaty, the level of the EDA can be captured (usually using conductance) and used to discern small changes in autonomic arousal. The more aroused a subject is, the greater the skin conductance tends to be.

Skin conductance is often measured using two small silver-silver chloride electrodes placed somewhere on the skin and applying a small voltage between them. To maximize comfort and reduce irritation the electrodes can be placed on the wrist, legs, or feet, which leaves the hands fully free for daily activity.

Facial color

Overview

The surface of the human face is innervated with a large network of blood vessels. Blood flow variations in these vessels yield visible color changes on the face. Whether or not facial emotions activate facial muscles, variations in blood flow, blood pressure, glucose levels, and other changes occur. Also, the facial color signal is independent from that provided by facial muscle movements.

Methodology

Approaches are based on facial color changes. Delaunay triangulation is used to create the triangular local areas. Some of these triangles which define the interior of the mouth and eyes (sclera and iris) are removed. Use the left triangular areas’ pixels to create feature vectors. It shows that converting the pixel color of the standard RGB color space to a color space such as oRGB color space or LMS channels perform better when dealing with faces. So, map the above vector onto the better color space and decompose into red-green and yellow-blue channels. Then use deep learning methods to find equivalent emotions.

Visual aesthetics

Aesthetics, in the world of art and photography, refers to the principles of the nature and appreciation of beauty. Judging beauty and other aesthetic qualities is a highly subjective task. Computer scientists at Penn State treat the challenge of automatically inferring the aesthetic quality of pictures using their visual content as a machine learning problem, with a peer-rated on-line photo sharing website as a data source. They extract certain visual features based on the intuition that they can discriminate between aesthetically pleasing and displeasing images.

Potential applications

Education

Affection influences learners' learning state. Using affective computing technology, computers can judge the learners' affection and learning state by recognizing their facial expressions. In education, the teacher can use the analysis result to understand the student's learning and accepting ability, and then formulate reasonable teaching plans. At the same time, they can pay attention to students' inner feelings, which is helpful to students' psychological health. Especially in distance education, due to the separation of time and space, there is no emotional incentive between teachers and students for two-way communication. Without the atmosphere brought by traditional classroom learning, students are easily bored, and affect the learning effect. Applying affective computing in distance education system can effectively improve this situation. 

Healthcare

Social robots, as well as a growing number of robots used in health care benefit from emotional awareness because they can better judge users' and patient's emotional states and alter their actions/programming appropriately. This is especially important in those countries with growing aging populations and/or a lack of younger workers to address their needs.

Affective computing is also being applied to the development of communicative technologies for use by people with autism. The affective component of a text is also increasingly gaining attention, particularly its role in the so-called emotional or emotive Internet.

Video games

Affective video games can access their players' emotional states through biofeedback devices. A particularly simple form of biofeedback is available through gamepads that measure the pressure with which a button is pressed: this has been shown to correlate strongly with the players' level of arousal; at the other end of the scale are brain–computer interfaces. Affective games have been used in medical research to support the emotional development of autistic children.

Other applications

Other potential applications are centered around social monitoring. For example, a car can monitor the emotion of all occupants and engage in additional safety measures, such as alerting other vehicles if it detects the driver to be angry. Affective computing has potential applications in human–computer interaction, such as affective mirrors allowing the user to see how he or she performs; emotion monitoring agents sending a warning before one sends an angry email; or even music players selecting tracks based on mood.

One idea put forth by the Romanian researcher Dr. Nicu Sebe in an interview is the analysis of a person's face while they are using a certain product (he mentioned ice cream as an example). Companies would then be able to use such analysis to infer whether their product will or will not be well received by the respective market.

One could also use affective state recognition in order to judge the impact of a TV advertisement through a real-time video recording of that person and through the subsequent study of his or her facial expression. Averaging the results obtained on a large group of subjects, one can tell whether that commercial (or movie) has the desired effect and what the elements which interest the watcher most are.

Cognitivist vs. interactional approaches

Within the field of human–computer interaction, Rosalind Picard's cognitivist or "information model" concept of emotion has been criticized by and contrasted with the "post-cognitivist" or "interactional" pragmatist approach taken by Kirsten Boehner and others which views emotion as inherently social.

Picard's focus is human–computer interaction, and her goal for affective computing is to "give computers the ability to recognize, express, and in some cases, 'have' emotions". In contrast, the interactional approach seeks to help "people to understand and experience their own emotions" and to improve computer-mediated interpersonal communication. It does not necessarily seek to map emotion into an objective mathematical model for machine interpretation, but rather let humans make sense of each other's emotional expressions in open-ended ways that might be ambiguous, subjective, and sensitive to context.

Picard's critics describe her concept of emotion as "objective, internal, private, and mechanistic". They say it reduces emotion to a discrete psychological signal occurring inside the body that can be measured and which is an input to cognition, undercutting the complexity of emotional experience.

The interactional approach asserts that though emotion has biophysical aspects, it is "culturally grounded, dynamically experienced, and to some degree constructed in action and interaction". Put another way, it considers "emotion as a social and cultural product experienced through our interactions".