Electrostatics

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Electrostatics

Foam peanuts clinging to a cat's fur due to static electricity. The electric field of the charged fur causes polarization of the molecules of the foam due to electrostatic induction, resulting in a slight attraction of the light plastic pieces to the fur. This effect is also the cause of static cling in clothes.

Electrostatics is a branch of physics that studies slow-moving or stationary electric charges.

Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber, ἤλεκτρον (ḗlektron), was thus the source of the word 'electricity'. Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described by Coulomb's law.

There are many examples of electrostatic phenomena, from those as simple as the attraction of plastic wrap to one's hand after it is removed from a package, to the apparently spontaneous explosion of grain silos, the damage of electronic components during manufacturing, and photocopier & laser printer operation. Electrostatic forces play a large role at the nanoscale; for instance, the force between an electron and a proton, which together make up a hydrogen atom, is about 36 orders of magnitude stronger than the gravitational force acting between them. Because they are large at small scales, Coulomb forces between electrons and the positively charged nuclei play a very large role in how atoms and molecules behave.

Coulomb's law

Main article: Coulomb's law

Coulomb's law states that:

'The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.'

The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different signs, the force between them is attractive.

If ${\displaystyle r}$ is the distance (in meters) between two charges, then the force (in newtons) between two point charges ${\displaystyle q}$ and ${\displaystyle Q}$ (in coulombs) is:

${\displaystyle F=\frac{1}{4\pi {\epsilon }_0}\frac{qQ}{r^2}=k_{\text{e}}\frac{qQ}{r^2},}$

where ε₀ is the vacuum permittivity, or permittivity of free space:

${\displaystyle {\epsilon }_0\approx 8.854187817\times {10}^{-12}{\mathrm{C}}^2\cdot {\mathrm{N}}^{-1}\cdot {\mathrm{m}}^{-2}.}$

The SI units of ε₀ are equivalently A²⋅s⁴ ⋅kg⁻¹⋅m⁻³ or C²⋅N⁻¹⋅m⁻² or F⋅m⁻¹. The Coulomb constant is:

${\displaystyle k_{\text{e}}=\frac{1}{4\pi {\epsilon }_0}\approx 8.987551792\times {10}^9\mathrm{N}\cdot {\mathrm{m}}^2\cdot {\mathrm{C}}^{-2}.}$

A single proton has a charge of e, and the electron has a charge of −e, where,

${\displaystyle e=1.602176634\times {10}^{-19}\mathrm{C}.}$

These physical constants (ε₀, k_e, e) are currently defined so that e is exactly defined, and ε₀ and k_e are measured quantities.

Electric field

Main article: Electric field

The electrostatic field (lines with arrows) of a nearby positive charge (+) causes the mobile charges in conductive objects to separate due to electrostatic induction. Negative charges (blue) are attracted and move to the surface of the object facing the external charge. Positive charges (red) are repelled and move to the surface facing away. These induced surface charges are exactly the right size and shape so their opposing electric field cancels the electric field of the external charge throughout the interior of the metal. Therefore, the electrostatic field everywhere inside a conductive object is zero, and the electrostatic potential is constant.

The electric field, ${\displaystyle \overrightarrow{E}}$, in units of Newtons per Coulomb or volts per meter, is a vector field that can be defined everywhere, except at the location of point charges (where it diverges to infinity). It is defined as the electrostatic force ${\displaystyle \overrightarrow{F}}$ in newtons on a hypothetical small test charge at the point due to Coulomb's Law, divided by the magnitude of the charge ${\displaystyle q}$ in coulombs

${\displaystyle \overrightarrow{E}=\frac{\overrightarrow{F}}{q}}$

Electric field lines are useful for visualizing the electric field. Field lines begin on positive charge and terminate on negative charge. They are parallel to the direction of the electric field at each point, and the density of these field lines is a measure of the magnitude of the electric field at any given point.

Consider a collection of ${\displaystyle N}$ particles of charge ${\displaystyle Q_i}$, located at points ${\displaystyle {\overrightarrow{r}}_i}$ (called source points), the electric field at ${\displaystyle \overrightarrow{r}}$ (called the field point) is:

${\displaystyle \overrightarrow{E}(\overrightarrow{r})=\frac{1}{4\pi {\epsilon }_0}\sum _{i=1}^N\frac{{\hat{\mathcal{R}}}_i{Q}_i}{{\Vert {\overrightarrow{\mathcal{R}}}_i\Vert }^2},}$

where ${\displaystyle {\overrightarrow{\mathcal{R}}}_i=\overrightarrow{r}-{\overrightarrow{r}}_i,}$ is the displacement vector from a source point ${\displaystyle {\overrightarrow{r}}_i}$ to the field point ${\displaystyle \overrightarrow{r}}$, and ${\displaystyle {\hat{\mathcal{R}}}_i={\overrightarrow{\mathcal{R}}}_i/\Vert {\overrightarrow{\mathcal{R}}}_i\Vert }$ is a unit vector that indicates the direction of the field. For a single point charge at the origin, the magnitude of this electric field is ${\displaystyle E=k_{\text{e}}Q/{\mathcal{R}}^2,}$ and points away from that charge if it is positive. The fact that the force (and hence the field) can be calculated by summing over all the contributions due to individual source particles is an example of the superposition principle. The electric field produced by a distribution of charges is given by the volume charge density ${\displaystyle \rho (\overrightarrow{r})}$ and can be obtained by converting this sum into a triple integral:

${\displaystyle \overrightarrow{E}(\overrightarrow{r})=\frac{1}{4\pi {\epsilon }_0}\iiint \frac{\overrightarrow{r}-\overrightarrow{r}{}^{\prime }}{{\Vert \overrightarrow{r}-\overrightarrow{r}{}^{\prime }\Vert }^3}\rho (\overrightarrow{r}{}^{\prime }){\mathrm{d}}^{3}r{}^{\prime }}$

Gauss' law

Main articles: Gauss' law and Gaussian surface

Gauss's law states that "the total electric flux through any closed surface in free space of any shape drawn in an electric field is proportional to the total electric charge enclosed by the surface." Many numerical problems can be solved by considering a Gaussian surface around a body. Mathematically, Gauss's law takes the form of an integral equation:

${\displaystyle {\oint }_S\overrightarrow{E}\cdot \mathrm{d}\overrightarrow{A}=\frac{1}{{\epsilon }_0}{Q}_{\text{enclosed}}={\int }_V\frac{\rho }{{\epsilon }_0}\cdot {\mathrm{d}}^{3}r,}$

where ${\displaystyle {\mathrm{d}}^{3}r=\mathrm{d}x\mathrm{d}y\mathrm{d}z}$ is a volume element. If the charge is distributed over a surface or along a line, replace ${\displaystyle \rho {\mathrm{d}}^{3}r}$ by ${\displaystyle \sigma \mathrm{d}A}$ or ${\displaystyle \lambda \mathrm{d}\ell }$. The divergence theorem allows Gauss's Law to be written in differential form:

${\displaystyle \overrightarrow{\mathrm{\nabla }}\cdot \overrightarrow{E}=\frac{\rho }{{\epsilon }_0}.}$

where ${\displaystyle \overrightarrow{\mathrm{\nabla }}\cdot }$ is the divergence operator.

Poisson and Laplace equations

Main articles: Poisson's equation and Laplace's equation

The definition of electrostatic potential, combined with the differential form of Gauss's law (above), provides a relationship between the potential Φ and the charge density ρ:

${\displaystyle {\mathrm{\nabla }}^2\varphi =-\frac{\rho }{{\epsilon }_0}.}$

This relationship is a form of Poisson's equation. In the absence of unpaired electric charge, the equation becomes Laplace's equation:

${\displaystyle {\mathrm{\nabla }}^2\varphi =0,}$

Electrostatic approximation

The validity of the electrostatic approximation rests on the assumption that the electric field is irrotational:

${\displaystyle \overrightarrow{\mathrm{\nabla }}\times \overrightarrow{E}=0.}$

From Faraday's law, this assumption implies the absence or near-absence of time-varying magnetic fields:

${\displaystyle \frac{\mathrm{\partial }\overrightarrow{B}}{\mathrm{\partial }t}=0.}$

In other words, electrostatics does not require the absence of magnetic fields or electric currents. Rather, if magnetic fields or electric currents do exist, they must not change with time, or in the worst-case, they must change with time only very slowly. In some problems, both electrostatics and magnetostatics may be required for accurate predictions, but the coupling between the two can still be ignored. Electrostatics and magnetostatics can both be seen as non-relativistic Galilean limits for electromagnetism

Electrostatic potential

Main article: Electrostatic potential

As the electric field is irrotational, it is possible to express the electric field as the gradient of a scalar function, ${\displaystyle \varphi }$, called the electrostatic potential (also known as the voltage). An electric field, ${\displaystyle E}$, points from regions of high electric potential to regions of low electric potential, expressed mathematically as

${\displaystyle \overrightarrow{E}=-\overrightarrow{\mathrm{\nabla }}\varphi .}$

The gradient theorem can be used to establish that the electrostatic potential is the amount of work per unit charge required to move a charge from point ${\displaystyle a}$ to point ${\displaystyle b}$ with the following line integral:

${\displaystyle -{\int }_a^b\overrightarrow{E}\cdot \mathrm{d}\overrightarrow{\ell }=\varphi (\overrightarrow{b})-\varphi (\overrightarrow{a}).}$

From these equations, we see that the electric potential is constant in any region for which the electric field vanishes (such as occurs inside a conducting object).

Electrostatic energy

Main articles: Electric potential energy and Energy density

A test particle's potential energy, ${\displaystyle U_{\mathrm{E}}^{\text{single}}}$, can be calculated from a line integral of the work, ${\displaystyle q_n\overrightarrow{E}\cdot \mathrm{d}\overrightarrow{\ell }}$. We integrate from a point at infinity, and assume a collection of ${\displaystyle N}$ particles of charge ${\displaystyle Q_n}$, are already situated at the points ${\displaystyle {\overrightarrow{r}}_i}$. This potential energy (in Joules) is:

${\displaystyle U_{\mathrm{E}}^{\text{single}}=q\varphi (\overrightarrow{r})=\frac{q}{4\pi {\epsilon }_0}\sum _{i=1}^N\frac{Q_i}{\Vert {\overrightarrow{\mathcal{R}}}_{\mathcal{i}}\Vert }}$

where ${\displaystyle \overrightarrow{{\mathcal{R}}_{\mathcal{i}}}=\overrightarrow{r}-{\overrightarrow{r}}_i}$ is the distance of each charge ${\displaystyle Q_i}$ from the test charge ${\displaystyle q}$, which situated at the point ${\displaystyle \overrightarrow{r}}$, and ${\displaystyle \varphi (\overrightarrow{r})}$ is the electric potential that would be at ${\displaystyle \overrightarrow{r}}$ if the test charge were not present. If only two charges are present, the potential energy is ${\displaystyle k_{\text{e}}{Q}_1{Q}_2/r}$. The total electric potential energy due a collection of N charges is calculating by assembling these particles one at a time:

${\displaystyle U_{\mathrm{E}}^{\text{total}}=\frac{1}{4\pi {\epsilon }_0}\sum _{j=1}^N{Q}_j\sum _{i=1}^{j-1}\frac{Q_i}{r_{ij}}=\frac{1}{2}\sum _{i=1}^N{Q}_i{\varphi }_i,}$

where the following sum from, j = 1 to N, excludes i = j:

${\displaystyle {\varphi }_i=\frac{1}{4\pi {\epsilon }_0}\sum _{\stackrel{j=1}{j\ne i}}^N\frac{Q_j}{r_{ij}}.}$

This electric potential, ${\displaystyle {\varphi }_i}$ is what would be measured at ${\displaystyle {\overrightarrow{r}}_i}$ if the charge ${\displaystyle Q_i}$ were missing. This formula obviously excludes the (infinite) energy that would be required to assemble each point charge from a disperse cloud of charge. The sum over charges can be converted into an integral over charge density using the prescription $\sum (\cdots )\to \int (\cdots )\rho {\mathrm{d}}^{3}r$:

${\displaystyle U_{\mathrm{E}}^{\text{total}}=\frac{1}{2}\int \rho (\overrightarrow{r})\varphi (\overrightarrow{r}){\mathrm{d}}^{3}r=\frac{{\epsilon }_0}{2}\int {\left|\mathbf{E}\right|}^2{\mathrm{d}}^{3}r,}$

This second expression for electrostatic energy uses the fact that the electric field is the negative gradient of the electric potential, as well as vector calculus identities in a way that resembles integration by parts. These two integrals for electric field energy seem to indicate two mutually exclusive formulas for electrostatic energy density, namely $\frac{1}{2}\rho \varphi$ and $\frac{1}{2}{\epsilon }_0{E}^2$; they yield equal values for the total electrostatic energy only if both are integrated over all space.

Electrostatic pressure

On a conductor, a surface charge will experience a force in the presence of an electric field. This force is the average of the discontinuous electric field at the surface charge. This average in terms of the field just outside the surface amounts to:

${\displaystyle P=\frac{{\epsilon }_0}{2}{E}^2,}$

This pressure tends to draw the conductor into the field, regardless of the sign of the surface charge.

Gerontology

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Gerontology

Older adults playing cards in Amsterdam, 1970

Gerontology (/ˌdʒɛrənˈtɒlədʒi/ JERR-ən-TOL-ə-jee) is the study of the social, cultural, psychological, cognitive, and biological aspects of aging. The word was coined by Ilya Ilyich Mechnikov in 1903, from the Greek γέρων (gérōn), meaning "old man", and -λογία (-logía), meaning "study of". The field is distinguished from geriatrics, which is the branch of medicine that specializes in the treatment of existing disease in older adults. Gerontologists include researchers and practitioners in the fields of biology, nursing, medicine, criminology, dentistry, social work, physical and occupational therapy, psychology, psychiatry, sociology, economics, political science, architecture, geography, pharmacy, public health, housing, and anthropology.

The multidisciplinary nature of gerontology means that there are a number of sub-fields which overlap with gerontology. There are policy issues, for example, involved in government planning and the operation of nursing homes, investigating the effects of an aging population on society, and the design of residential spaces for older people that facilitate the development of a sense of place or home. Dr. Lawton, a behavioral psychologist at the Philadelphia Geriatric Center, was among the first to recognize the need for living spaces designed to accommodate the elderly, especially those with Alzheimer's disease. As an academic discipline the field is relatively new. The USC Leonard Davis School of Gerontology created the first PhD, master's and bachelor's degree programs in gerontology in 1975.

History

In the medieval Islamic world, several physicians wrote on issues related to Gerontology. Avicenna's The Canon of Medicine (1025) offered instruction for the care of the aged, including diet and remedies for problems including constipation. Arabic physician Ibn Al-Jazzar Al-Qayrawani (Algizar, c. 898–980) wrote on the aches and conditions of the elderly. His scholarly work covers sleep disorders, forgetfulness, how to strengthen memory, and causes of mortality. Ishaq ibn Hunayn (died 910) also wrote works on the treatments for forgetfulness.

While the number of aged humans, and the life expectancy, tended to increase in every century since the 14th, society tended to consider caring for an elderly relative as a family issue. It was not until the coming of the Industrial Revolution that ideas shifted in favor of a societal care-system. Some early pioneers, such as Michel Eugène Chevreul, who himself lived to be 102, believed that aging itself should be a science to be studied. Élie Metchnikoff coined the term "gerontology" in 1903.

Modern pioneers like James Birren began organizing gerontology as its own field in the 1940s, later being involved in starting a US government agency on aging – the National Institute on Aging – programs in gerontology at the University of Southern California and University of California, Los Angeles, and as past president of the Gerontological Society of America (founded in 1945).

With the population of people over 60 years old expected to be some 22% of the world's population by 2050, assessment and treatment methods for age-related disease burden – the term geroscience emerged in the early 21st century.

Aging demographics

The world is forecast to undergo rapid population aging in the next several decades. In 1900, there were 3.1 million people aged 65 years and older living in the United States. However, this population continued to grow throughout the 20th century and reached 31.2, 35, and 40.3 million people in 1990, 2000, and 2010, respectively. Notably, in the United States and across the world, the "baby boomer" generation began to turn 65 in 2011. Recently, the population aged 65 years and older has grown at a faster rate than the total population in the United States. The total population increased by 9.7%, from 281.4 million to 308.7 million, between 2000 and 2010. However, the population aged 65 years and older increased by 15.1% during the same period. It has been estimated that 25% of the population in the United States and Canada will be aged 65 years and older by 2025. Moreover, by 2050, it is predicted that, for the first time in United States history, the number of individuals aged 60 years and older will be greater than the number of children aged 0 to 14 years. Those aged 85 years and older (oldest-old) are projected to increase from 5.3 million to 21 million by 2050. Adults aged 85–89 years constituted the greatest segment of the oldest-old in 1990, 2000, and 2010. However, the largest percentage point increase among the oldest-old occurred in the 90- to 94-year-old age group, which increased from 25.0% in 1990 to 26.4% in 2010.

With the rapid growth of the aging population, social work education and training specialized in older adults and practitioners interested in working with older adults are increasingly in demand.

Gender differences with age

There has been a considerable disparity between the number of men and women in the older population in the United States. In both 2000 and 2010, women outnumbered men in the older population at every single year of age (e.g., 65 to 100 years and over). The sex ratio, which is a measure used to indicate the balance of males to females in a population, is calculated by taking the number of males divided by the number of females, and multiplying by 100. Therefore, the sex ratio is the number of males per 100 females. In 2010, there were 90.5 males per 100 females in the 65-year-old population. However, this represented an increase from 1990 when there were 82.7 males per 100 females, and from 2000 when the sex ratio was 88.1. Although the gender gap between men and women has narrowed, women continue to have a greater life expectancy and lower mortality rates at older ages relative to men. For example, the Census 2010 reported that there were approximately twice as many women as men living in the United States at 89 years of age (361,309 versus 176,689, respectively).

Geographic distribution of older adults in the United States

The number and percentage of older adults living in the United States vary across the four different regions (Northeast, Midwest, West, and South) defined by the United States census. In 2010, the South contained the greatest number of people aged 65 years and older and 85 years and older. However, proportionately, the Northeast contains the largest percentage of adults aged 65 years and older (14.1%), followed by the Midwest (13.5%), the South (13.0%), and the West (11.9%). Relative to the Census 2000, all geographic regions demonstrated positive growth in the population of adults aged 65 years and older and 85 years and older. The most rapid growth in the population of adults aged 65 years and older was evident in the West (23.5%), which showed an increase from 6.9 million in 2000 to 8.5 million in 2010. Likewise, in the population aged 85 years and older, the West (42.8%) also showed the fastest growth and increased from 806,000 in 2000 to 1.2 million in 2010. It is worth highlighting that Rhode Island was the only state that experienced a reduction in the number of people aged 65 years and older, and declined from 152,402 in 2000 to 151,881 in 2010. Conversely, all states exhibited an increase in the population of adults aged 85 years and older from 2000 to 2010.

Sub-fields

As with many disciplines, over the course of the 20th and 21st century the field of gerontology has sub-divided into multiple specific disciplines focused on increasingly narrow aspects of the aging process.

Biogerontology

Main article: Biogerontology

The hand of an older adult

Biogerontology is the special sub-field of gerontology concerned with the biological aging process, its evolutionary origins, and potential means to intervene in the process. Aim of biogerontology is to prevent age-related disease by intervening in aging processes or even eliminate aging per se. Some argue that aging fits the criteria of disease, therefore aging is disease and should be treated as disease. In 2008 Aubrey de Grey said that in case of suitable funding and involvement of specialists there is a 50% chance, that in 25–30 years humans will have technology saving people from dying of old age, regardless of the age at which they will be at that time. His idea is to repair inside cells and between them all that can be repaired using modern technology, allowing people to live until time when technology progress will allow to cure deeper damage. This concept got the name "longevity escape velocity".

A meta analysis of 36 studies concluded that there is an association between age and DNA damage in humans, a finding consistent with the DNA damage theory of aging.

Social gerontology

Social gerontology is a multi-disciplinary sub-field that specializes in studying or working with older adults. Social gerontologists may have degrees or training in social work, nursing, psychology, sociology, demography, public health, or other social science disciplines. Social gerontologists are responsible for educating, researching, and advancing the broader causes of older people.

Because issues of life span and life extension need numbers to quantify them, there is an overlap with demography. Those who study the demography of the human life span differ from those who study the social demographics of aging.

Social theories of aging

Several theories of aging are developed to observe the aging process of older adults in society as well as how these processes are interpreted by men and women as they age.

Activity theory

Activity theory was developed and elaborated by Cavan, Havighurst, and Albrecht. According to this theory, older adults' self-concept depends on social interactions. In order for older adults to maintain morale in old age, substitutions must be made for lost roles. Examples of lost roles include retirement from a job or loss of a spouse.

Activity is preferable to inactivity because it facilitates well-being on multiple levels. Because of improved general health and prosperity in the older population, remaining active is more feasible now than when this theory was first proposed by Havighurst nearly six decades ago. The activity theory is applicable for a stable, post-industrial society, which offers its older members many opportunities for meaningful participation. Weakness: Some aging persons cannot maintain a middle-aged lifestyle, due to functional limitations, lack of income, or lack of a desire to do so. Many older adults lack the resources to maintain active roles in society. On the flip side, some elders may insist on continuing activities in late life that pose a danger to themselves and others, such as driving at night with low visual acuity or doing maintenance work to the house while climbing with severely arthritic knees. In doing so, they are denying their limitations and engaging in unsafe behaviors.

Disengagement theory

Disengagement theory was developed by Cumming and Henry. According to this theory, older adults and society engage in a mutual separation from each other. An example of mutual separation is retirement from the workforce. A key assumption of this theory is that older adults lose "ego-energy" and become increasingly self-absorbed. Additionally, disengagement leads to higher morale maintenance than if older adults try to maintain social involvement. This theory is heavily criticized for having an escape clause - namely, that older adults who remain engaged in society are unsuccessful adjusters to old age.

Gradual withdrawal from society and relationships preserves social equilibrium and promotes self-reflection for elders who are freed from societal roles. It furnishes an orderly means for the transfer of knowledge, capital, and power from the older generation to the young. It makes it possible for society to continue functioning after valuable older members die.

Age stratification theory

According to this theory, older adults born during different time periods form cohorts that define "age strata". There are two differences among strata: chronological age and historical experience. This theory makes two arguments. 1. Age is a mechanism for regulating behavior and as a result determines access to positions of power. 2. Birth cohorts play an influential role in the process of social change.

Life course theory

According to this theory, which stems from the life course perspective aging occurs from birth to death. Aging involves social, psychological, and biological processes. Additionally, aging experiences are shaped by cohort and period effects.

Also reflecting the life course focus, consider the implications for how societies might function when age-based norms vanish—a consequence of the deinstitutionalization of the life course— and suggest that these implications pose new challenges for theorizing aging and the life course in postindustrial societies. Dramatic reductions in mortality, morbidity, and fertility over the past several decades have so shaken up the organization of the life course and the nature of educational, work, family, and leisure experiences that it is now possible for individuals to become old in new ways. The configurations and content of other life stages are being altered as well, especially for women. In consequence, theories of age and aging will need to be reconceptualized.

Cumulative advantage/disadvantage theory

According to this theory, which was developed beginning in the 1960s by Derek Price and Robert Merton and elaborated on by several researchers such as Dale Dannefer, inequalities have a tendency to become more pronounced throughout the aging process. A paradigm of this theory can be expressed in the adage "the rich get richer and the poor get poorer". Advantages and disadvantages in early life stages have a profound effect throughout the life span. However, advantages and disadvantages in middle adulthood have a direct influence on economic and health status in later life.

Environmental gerontology

Environmental gerontology is a specialization within gerontology that seeks an understanding and interventions to optimize the relationship between aging persons and their physical and social environments.

The field emerged in the 1930s during the first studies on behavioral and social gerontology. In the 1970s and 1980s, research confirmed the importance of the physical and social environment in understanding the aging population and improved the quality of life in old age. Studies of environmental gerontology indicate that older people prefer to age in their immediate environment, whereas spatial experience and place attachment are important for understanding the process.

Some research indicates that the physical-social environment is related to the longevity and quality of life of the elderly. Precisely, the natural environment (such as natural therapeutic landscapes, therapeutic garden) contributes to active and healthy aging in the place.

Jurisprudential gerontology

Jurisprudential gerontology (sometimes referred to as "geriatric jurisprudence") is a specialization within gerontology that looks into the ways laws and legal structures interact with the aging experience. The field started from legal scholars in the field of elder law, which found that looking into legal issues of older persons without a broader inter-disciplinary perspective does not provide the ideal legal outcome. Using theories such as therapeutic jurisprudence, jurisprudential scholars critically examined existing legal institutions (e.g. adult guardianship, end of life care, or nursing homes regulations) and showed how law should look more closely to the social and psychological aspects of its real-life operation. Other streams within jurisprudential gerontology also encouraged physicians and lawyers to try to improve their cooperation and better understand how laws and regulatory institutions affect health and well-being of older persons.

Heavy bomber

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Heavy_bomber

USAAF B-29 Superfortress, a heavy bomber.

Heavy bombers are bomber aircraft capable of delivering the largest payload of air-to-ground weaponry (usually bombs) and longest range (takeoff to landing) of their era. Archetypal heavy bombers have therefore usually been among the largest and most powerful military aircraft at any point in time. In the second half of the 20th century, heavy bombers were largely superseded by strategic bombers, which were often even larger in size, had much longer ranges and were capable of delivering nuclear bombs.

Because of advances in aircraft design and engineering — especially in powerplants and aerodynamics — the size of payloads carried by heavy bombers has increased at rates greater than increases in the size of their airframes. The largest bombers of World War I, the Zeppelin-Staaken Riesenflugzeuge of Germany, could carry a payload of up to 4,400 pounds (2,000 kg) of bombs; by the latter half of World War II, the Avro Lancaster (introduced in 1942) routinely delivered payloads of 14,000 pounds (6,400 kg) (and sometimes up to 22,000 lb (10,000 kg)) and had a range of 2,530 miles (4,070 km), while the B-29 (1944) delivered payloads in excess of 20,000 pounds (9,100 kg) and had a range of 3,250 miles (5,230 km). By the late 1950s, the jet-powered Boeing B-52 Stratofortress, travelling at speeds of up to 650 miles per hour (1,050 km/h) (more than double that of a Lancaster), could deliver a payload of 70,000 pounds (32,000 kg), over a combat radius of 4,480 miles (7,210 km).

During World War II, mass production techniques made available large, long-range heavy bombers in such quantities as to allow strategic bombing campaigns to be developed and employed. This culminated in August 1945, when B-29s of the United States Army Air Forces dropped atomic bombs over Hiroshima and Nagasaki in Japan.

The arrival of nuclear weapons and guided missiles permanently changed the nature of military aviation and strategy. After the 1950s intercontinental ballistic missiles and ballistic missile submarines began to supersede heavy bombers in the strategic nuclear role. Along with the emergence of more accurate precision-guided munitions ("smart bombs") and nuclear-armed missiles, which could be carried and delivered by smaller aircraft, these technological advancements eclipsed the heavy bomber's once-central role in strategic warfare by the late 20th century. Heavy bombers have, nevertheless, been used to deliver conventional weapons in several regional conflicts since World War II (for example, B-52s in the Vietnam War).

Heavy bombers are now operated only by the air forces of the United States, Russia and China. They serve in both strategic and tactical bombing roles.

World War I

The British produced Short Bomber

The first heavy bomber was designed as an airliner. Igor Sikorsky, an engineer educated in St Petersburg, but born in Kiev of Polish-Russian ancestry designed the Sikorsky Ilya Muromets to fly between his birthplace and his new home. It did so briefly until August 1914, when the Russo-Balt wagon factory converted to a bomber version, with British Sunbeam Crusader V8 engines in place of the German ones in the passenger plane. By December 1914 a squadron of 10 was bombing German positions on the Eastern Front and by summer 1916 there were twenty. It was well-armed with nine machine guns, including a tail gun and initially was immune to German and Austro-Hungarian air attack. The Sikorsky bomber had a wingspan just a few feet shorter than, with a bomb load only 3% of, a World War II Avro Lancaster.

The Handley Page Type O/100 owed a lot to Sikorsky's ideas; of similar size, it used just two Rolls-Royce Eagle engines and could carry up to 2,000 lb (910 kg) of bombs. The O/100 was designed at the beginning of the war for the Royal Navy specifically to sink the German High Seas Fleet in Kiel: the Navy called for “a bloody paralyser of an aircraft” Entering service in late 1916 and based near Dunkirk in France, it was used for daylight raids on naval targets, damaging a German destroyer. But after one was lost, the O/100 switched to night attacks.

The uprated Handley Page Type O/400 could carry a 1,650 lb (750 kg) bomb, and wings of up to 40 were used by the newly formed, independent Royal Air Force from April 1918 to make strategic raids on German railway and industrial targets. A single O/400 was used to support T. E. Lawrence's Sinai and Palestine Campaign.

The Imperial German Air Service operated the Gotha bomber, which developed a series of marques. The Gotha G.IV operated from occupied Belgium from the Spring of 1917. It mounted several raids on London beginning in May 1917. Some reached no further than Folkestone or Sheerness on the Kent Coast. But on June 13, Gothas killed 162 civilians, including 18 children in a primary school, and injured 432 in East London. Initially, defence against air attack was poor, but by May 19, 1918, when 38 Gothas attacked London, six were shot down and another crashed on landing.

German aircraft companies also built a number of giant bombers, collectively known as the Riesenflugzeug. Most were produced in very small numbers from 1917 onwards and several never entered service. The most numerous were the Zeppelin-Staaken R.VI of which 13 saw service, bombing Russia and London: four were shot down and six lost on landing. The R.VIs were larger than the standard Luftwaffe bombers of World War II.

The Vickers Vimy, a long-range heavy bomber powered by two Rolls-Royce Eagle engines, was delivered to the newly formed Royal Air Force too late to see action (only one was in France at time of the Armistice with Germany). The Vimy's intended use was to bomb industrial and railway targets in western Germany, which it could reach with its range of 900 miles (1,400 km) and a bomb load of just over a ton. The Vickers Vimy is best known as the aircraft that made the first Atlantic crossing from St John's Newfoundland to Clifden in Ireland piloted by the Englishman John Alcock and navigated by Scot Arthur Whitten Brown on June 14, 1919.

Strategic bomber theory

The Douglas B-18 Bolo on take off

Between the wars, aviation opinion fixed on two tenets. The first was that “the bomber will always get through.” The speed advantage of biplane fighters over bombers was insignificant, and it was believed that they would never catch them. Furthermore, there was no effective method of detecting incoming bombers at sufficiently long range to scramble fighters on an interception course. In practice, a combination of new radar technology and advances in monoplane fighter design eroded this disadvantage. Throughout the war, bombers continually managed to strike their targets, but suffered unacceptable losses in the absence of careful planning and escort fighters. Only the later de Havilland Mosquito light bomber was fast enough to evade fighters. Heavy bombers needed defensive armament for protection, which reduced their effective bomb payload.

The second tenet was that strategic bombing of industrial capacity, power generation, oil refineries, and coal mines could win a war. This was certainly vindicated by the firebombing of Japanese cities and the two atomic bombs dropped on Hiroshima and Nagasaki in August 1945, as Japan's fragile housing and cottage industry made themselves easily vulnerable to attack, thus completely destroying Japanese industrial production (see Air Raids on Japan). It was less evident that it held true for the bombing of Germany. During the war, German industrial production actually increased, despite a sustained Allied bombing campaign.

As the German Luftwaffe's main task was to support the army, it never developed a successful heavy bomber. The prime proponent of strategic bombing, Luftwaffe Chief of Staff General Walther Wever, died in an air crash in 1936 on the very day that the specification for the Ural bomber (later won by the Heinkel He 177 which saw only limited use against the Soviet Union and the United Kingdom) was published. After Wever's death, Ernst Udet, development director at the Air Ministry steered the Luftwaffe towards dive bombers instead.

World War II

Main article: Strategic bombing during World War II

The USAAF B-24 Liberator

When Britain and France declared war on Germany in September 1939, the RAF had no heavy bomber yet in service; heavy bomber designs had started in 1936 and ordered in 1938.

The Handley Page Halifax and Avro Lancaster both originated as twin-engine "medium" bombers, but were rapidly redesigned for four Rolls-Royce Merlin engines and rushed into service once the technical problems of the larger Rolls-Royce Vulture emerged in the Avro Manchester. The Halifax joined squadrons in November 1940 and flew its first raid against Le Havre on the night of 11–12 March 1941. British heavy bomber designs often had three gun turrets with a total of 8 machine guns.

In January 1941, the Short Stirling reached operational status and first combat missions were flown in February. It was based on the successful Short Sunderland flying boat and shared its Bristol Hercules radial engines, wing, and cockpit with a new fuselage. It carried up to 14,000 lb (6,400 kg) of bombs—almost twice the load of a Boeing B-17 Flying Fortress—but over just a 300-mile (480 km) radius. Due to its thick, short wing it was able to out-turn the main German night fighters, the Messerschmitt Bf 110 and the Junkers Ju 88. Heavy bombers still needed defensive armament for protection, even at night. The Stirling's low operational ceiling of just 12,000 ft (3,700 m)—also caused by the thick wing—meant that it was usually picked on by night fighters; within five months, 67 of the 84 aircraft in service had been lost. The bomb bay layout limited the size and types of bombs carried and it was relegated to secondary duties such as tug and paratrooper transport.

Due to the absence of British heavy bombers, 20 United States Army Air Corps Boeing B-17 Flying Fortresses were lent to the RAF, which during July 1941 commenced daylight attacks on warships and docks at Wilhelmshaven and Brest. These raids were complete failures. After eight aircraft were lost due to combat or breakdown and with many engine failures, the RAF stopped daylight bombing by September. It was clear that the B-17C model was not combat ready and that its five machine guns provided inadequate protection.

Combat feedback enabled Boeing engineers to improve the aircraft; when the first model B-17E began operating from English airfields in July 1942, it had many more defensive gun positions including a vitally important tail gunner. Eventually, U.S. heavy bomber designs, optimized for formation flying, had 10 or more machine guns and/or cannons in both powered turrets and manually operated flexible mounts to deliver protective arcs of fire. These guns were located in tail turrets, side gun ports either just behind the bombardier's clear nose glazing as "cheek" positions, or midway along the rear fuselage sides as "waist" positions. U.S. bombers carried .50 caliber machine gun, and dorsal (spine/top of aircraft) and ventral (belly/bottom of aircraft) guns with powered turrets. All of these machine guns could defend against attack when beyond the range of fighter escort; eventually, a total of 13 machine guns were fitted in the B-17G model. In order to assemble combat boxes of several aircraft, and later combat wings formed of a number of boxes, assembly ships were used to speed up formation.

Even this extra firepower, which increased empty weight by 20% and required more powerful versions of the Wright Cyclone engine, was insufficient to prevent serious losses in daylight. Escort fighters were needed but the RAF interceptors such as the Supermarine Spitfire had very limited endurance. An early raid on Rouen-Sotteville rail yards in Brittany on August 17, 1942, required four Spitfire squadrons outbound and five more for the return trip.

The USAAF chose to attack aircraft factories and component plants. On August 17, 1943, 230 Fortresses attacked a ball-bearing plant in Schweinfurt and again two months later, with 291 bombers, in the second raid on Schweinfurt. The works was severely damaged but at a huge cost: 36 aircraft lost in the first raid, 77 in the second. Altogether 850 airmen were killed or captured; only 33 Fortresses returned from the October raid undamaged

With the arrival of North American P-51 Mustangs and the fitting of drop tanks to increase the range of the Republic P-47 Thunderbolt for the Big Week offensive, between February 20–25, 1944, bombers were escorted all the way to the target and back. Losses were reduced to 247 out of 3,500 sorties, still devastating but accepted at the time.

The Consolidated B-24 Liberator and later version of the Fortress carried even more extensive defensive armament fitted into Sperry ball turrets. This was a superb defensive weapon that rotated a full 360 degrees horizontally with a 90-degree elevation. Its twin M2 Browning machine guns had an effective range of 1,000 yards (910 m). The Liberator was the result of a proposal to assemble Fortresses in Consolidated plants, with the company returning with its own design of a longer-range, faster and higher-flying aircraft that could carry an extra ton of bombs. Early orders were for France (delivered to the RAF after the fall of France) and Britain, already at war, with just a batch of 36 for the USAAF.

Neither the USAAF nor the RAF judged the initial design suitable for bombing and it was first used on a variety of VIP transport and maritime patrol missions. Its long range, however, persuaded the USAAF to send 177 Liberators from Benghazi in Libya to bomb the Romanian oilfields on August 1, 1943, in Operation Tidal Wave. Due to navigational errors and alerted German flak batteries and fighters, only half returned to base although a few landed safely at RAF bases in Cyprus and some in Turkey, where they were interned. Only 33 were undamaged. Damage to the refineries was soon repaired and oil production actually increased

By October 1942, a new Ford Motor Company plant at Willow Run Michigan was assembling Liberators. Production reached a rate of over one an hour in 1944 helping the B-24 to become the most produced US aircraft of all time. It became the standard heavy bomber in the Pacific and the only one used by the RAAF. The SAAF used Liberators to drop weapons and ammunition during the Warsaw Uprising in 1944.

The Avro Manchester was a twin-engine bomber powered by the ambitious 24-cylinder Rolls-Royce Vulture, but was rapidly redesigned for four Rolls-Royce Merlin engines due to technical problems with the Vulture which caused the aircraft to be unreliable, under-powered and hastened its withdrawal from service. Reaching squadrons early in 1942, the redesigned bomber with four Merlin engines and longer wings was renamed Avro Lancaster; it could deliver a 14,000 lb (6,400 kg) load of bombs or up to 22,000 lb (10,000 kg) with special modifications. The Lancaster's bomb bay was undivided, so that bombs of extraordinary size and weight such as the 10-ton Grand Slam could be carried.

Barnes Wallis, deputy chief aircraft designer at Vickers, spent much time thinking about weapons that might shorten the war. He conceived his “Spherical Bomb, Surface Torpedo” after watching his daughter flip pebbles over water. Two versions of the 'bouncing bomb' were developed: the smaller Highball was to be used against ships and attracted essential British Admiralty funding for his project. A 1,280 lb (580 kg) flying torpedo, of which half was Torpex torpedo explosive, it was developed specifically to sink the Tirpitz which was moored in Trondheim fjord behind torpedo nets. Development delays in the 'bouncing bomb' meant that another Barnes Wallis invention, the 5-ton Tallboy was deployed instead; two Tallboys dropped by Avro Lancasters from 25,000 ft (7,600 m) altitude hit at near-supersonic speed and capsized the Tirpitz on November 12, 1944. Upkeep, the larger version of the bouncing bomb, was used to destroy the Mohne and Eder dams by Lancasters from the specially recruited and trained No. 617 Squadron RAF, often known as "the Dam Busters", under Wing Commander Guy Gibson.

In March and April 1945, as the war in Europe was ending, Lancasters dropped Grand Slams and Tallboys on U-boat pens and railway viaducts across north Germany. At Bielefeld more than 100 yards (91 m) of railway viaduct was destroyed by Grand Slams creating an earthquake effect, which shook the foundations.

The Boeing B-29 Superfortress was a development of the Fortress, but a larger design with four Wright R-3350 Duplex-Cyclone engines of much greater power, enabling it to fly higher, faster, further and with a bigger bomb load. The mammoth new Wright radial engines were susceptible to overheating if anything malfunctioned, and technical problems with the powerplant seriously delayed the B-29's operational service debut. The aircraft had four remotely operated twin-gun turrets on its fuselage, controlled through an analog computer sighting system; the operator could use any of a trio of Perspex ball stations. Only the tail gunner manually controlled his gun turret station in the rear of the airplane.

B-29s were initially deployed to bases in India and China, from which they could reach Japan; but the logistics (including transport of fuel for the B-29 fleet over the Himalayan range) of flying from these remote, primitive airfields were complicated and costly. The island of Saipan in the Marianas was assaulted to provide Pacific air bases from which to bomb Japanese cities. Initial high-level, daylight bombing raids using high-explosive bombs on Japanese cities with their wood and paper houses produced disappointing results; the bombers were then switched to low-level, nighttime incendiary attacks for which they had not originally been designed (one variant, the B-29B was specially modified for low altitude night missions by removal of armament and other equipment). Japan burned furiously from the B-29 incendiary raids. On August 6, 1945, B-29 Enola Gay dropped an atomic bomb on Hiroshima. Three days later, B-29 Bockscar dropped another on Nagasaki. The war ended when Japan announced its surrender to the Allies on August 15, and the Japanese government subsequently signed the official instrument of surrender on September 2, 1945.

After World War II

The Soviet Air Force Tu-95 heavy bomber

Line-up of Soviet Cold War heavy bombers of Soviet Strategic Aviation, from Tu-4 to Tu-22M

After World War II, the name strategic bomber came into use, for aircraft that could carry aircraft ordnances over long distances behind enemy lines. They were supplemented by smaller fighter-bombers with less range and lighter bomb load, for tactical strikes. Later these were called strike fighters, attack aircraft and multirole combat aircraft.

When North Korea attacked South Korea in 1950 the USAF responded with daylight bomber raids on supply lines through North Korea. B-29 Superfortresses flew from Japan on behalf of the United Nations, but the supply line for North Korea's army from the Soviet Union was physically and politically out of reach: North Korea for the most part lacked worthwhile strategic targets of its own. The Soviet-backed Northern forces easily routed the South Korean army. The distance to North Korea was too great for fighter escorts based in Japan, so the B-29s flew alone. In November, Mikoyan-Gurevich MiG-15s flown by Soviet pilots started to intercept the US bombers over North Korea. The MiG-15 was specifically designed to destroy US heavy bombers; it could out-perform any fighter deployed by United Nations air forces until the capable F-86 Sabre was produced in greater numbers and brought to Korea. After 28 B-29s were lost, the bombers were restricted to night interdiction and concentrated on destroying supply routes, including the bridges over the Yalu river into China.

By the 1960s, manned heavy bombers could not match the intercontinental ballistic missile in the strategic nuclear role. More accurate precision-guided munitions ("smart bombs"), nuclear-armed missiles or bombs were able to be carried by smaller aircraft such as fighter-bombers and multirole fighters. Despite these technological innovations and new capabilities of other contemporary military aircraft, large strategic bombers such as the B-1, B-52 and B-2 have been retained for the role of carpet bombing in several conflicts. The most prolific example (in terms of total bomb tonnage) is the U.S. Air Force B-52 Stratofortress during the 1960s–early 1970s Vietnam War era, in Operation Menu, Operation Freedom Deal, and Operation Linebacker II. In 1987 the Soviet Tu-160—the heaviest supersonic bomber/aircraft currently in active service—entered service; it can carry twelve long-range cruise missiles.

The 2010 New START agreement between the United States of America and the Russian Federation defined a "heavy bomber" by two characteristics:

• range greater than 8,000 kilometres (5,000 mi)
• equipped for long-range nuclear "air-launched cruise missiles" (ALCMs), defined as an air-to-surface cruise missile of a type flight-tested from an aircraft or deployed on a bomber after 1986.