Science History Institute
The Science History Institute is an institution that preserves and promotes understanding of the history of science. Located in Philadelphia, Pennsylvania, it includes a library, archive, research center and conference center, it was founded in 1982 as a joint venture of the American Chemical Society and the University of Pennsylvania, as the Center for the History of Chemistry. The American Institute of Chemical Engineers became a co-founder in 1984, it was renamed the Chemical Heritage Foundation in 1992, moved two years to the institution's current location, 315 Chestnut Street in Old City. On December 1, 2015, CHF merged with the Life Sciences Foundation, creating an organization that covers "the history of the life sciences and biotechnology together with the history of the chemical sciences and engineering." As of February 1, 2018, the organization was renamed the Science History Institute, to reflect its wider range of historical interests, from chemical sciences and engineering to the life sciences and biotechnology.
The Institute focuses not only on the history of chemistry but on the history of science, the history of technology, trends in research and development, the impact of science on society, relationships between science and art, among other subjects. It supports a community of an oral history program; as of 2012, it was the largest US grantor of research fellowships for the history of science. The idea of creating "a library of reference and a chemical museum" in the United States can be found in the Proceedings of the first meeting of the American Chemical Society in 1876. Impetus for the creation of the Science History Institute dates to 1976, when the nation's bicentennial and the centennial of the American Chemical Society stimulated interest in both history and chemistry. John H. Wotiz of the Division of the History of Chemistry of the ACS organized a session on the history of chemistry as part of the ACS centennial activities and was a strong proponent of a national center for historical chemistry.
In 1979, the ACS formed a task force chaired by Ned D. Heindel to investigate the possibility of creating a national center for the history of chemistry. Arnold Thackray, a professor in the Department of History and Sociology of Science at the University of Pennsylvania, curator of the Edgar Fahs Smith Memorial Collection on the history of chemistry at the University of Pennsylvania, argued for the formation of such a center in Philadelphia, he was able to obtain promises of private support from chemist John C. Haas, institutional support from the Dow Chemical Company and DuPont. In December 1981 the ACS approved the establishment of the Center for the History of Chemistry, with support of $50,000 per year for five years, in cooperation with the University of Pennsylvania, to provide an equivalent in goods and services. An agreement to create the Center for the History of Chemistry was signed by officers of the American Chemical Society and the University of Pennsylvania on January 22 and 26, 1982.
A policy council was appointed by the sponsoring institutions to oversee routine operations of the center, Arnold Thackray was appointed part-time director of the center on April 29, 1982. The official inauguration of the center was held on March 11, 1983; the Center's first home was in several vacant basement rooms on the University of Pennsylvania campus. Its "immediate aims" included gathering oral histories of important chemists and inventorying papers and manuscripts in repositories throughout the country to map "the unexplored territory of the history of chemistry and chemical technology."A National Advisory Board was formed from a wide-ranging group of people in academia and industry. In 1982, its members included John C. Haas, historians Margaret W. Rossiter and Alfred D. Chandler, Jr. and at least three Nobel Prize winners, Christian B. Anfinsen, Herbert C. Brown, Glenn T. Seaborg; the American Institute of Chemical Engineers became a co-founder of the Center, signing an agreement on August 27 and 28, 1984.
In addition, the institution began to establish relationships with affiliated organizations such as The Chemists' Club, the American Society for Biochemistry and Molecular Biology, the American Association of Textile Chemists and Colorists, the Electrochemical Society and the American Society for Mass Spectrometry. As early as 1983, the Center for the History of Chemistry expressed an interest in "The Conservation of Historic American Chemical Instruments", in discussions of a possible joint project with the Smithsonian. However, the center did not yet have exhibition or collections space to allow for the acquisition of any but the most limited quantities of documents; the center did curate a number of traveling exhibitions by collaborating with other organizations, including "Joseph Priestley: Enlightened Chemist", "Polymers and People", "Scaling Up", "Chemical Education in the United States". During the 1980s, the center came to the attention of Arnold Orville Beckman; the Arnold and Mabel Beckman Foundation provided a $2 million challenge grant in 1986 to stimulate expansion of the center as a research institute, the Arnold and Mabel Beckman Center for the History of Chemistry.
Beckman challenged the center to define its mission more broadly, reaching out to academic and trade organizations, including biochemistry, materials science, petrochemicals and instrumentation within its mandate. The National Foundation for History of Chemistry was established in 1987 as a supporting Pennsylvania nonprofit; the renamed Beckman Center began a major capital campaign, listing as its needs "offices, an exhibit gallery, a reading room, library stacks, archives and storage areas." It celebrated its
Entrepreneurship is the process of designing and running a new business, initially a small business. The people who create these businesses are called entrepreneurs. Entrepreneurship has been described as the "capacity and willingness to develop and manage a business venture along with any of its risks in order to make a profit". While definitions of entrepreneurship focus on the launching and running of businesses, due to the high risks involved in launching a start-up, a significant proportion of start-up businesses have to close due to "lack of funding, bad business decisions, an economic crisis, lack of market demand—or a combination of all of these. A broader definition of the term is sometimes used in the field of economics. In this usage, an Entrepreneur is an entity which has the ability to find and act upon opportunities to translate inventions or technology into new products: "The entrepreneur is able to recognize the commercial potential of the invention and organize the capital and other resources that turn an invention into a commercially viable innovation."
In this sense, the term "Entrepreneurship" captures innovative activities on the part of established firms, in addition to similar activities on the part of new businesses. Entrepreneurship is the act of being an entrepreneur, or "the owner or manager of a business enterprise who, by risk and initiative, attempts to make profits". Entrepreneurs oversee the launch and growth of an enterprise. Entrepreneurship is the process by which either an individual or a team identifies a business opportunity and acquires and deploys the necessary resources required for its exploitation. Early-19th-century French economist Jean-Baptiste Say provided a broad definition of entrepreneurship, saying that it "shifts economic resources out of an area of lower and into an area of higher productivity and greater yield". Entrepreneurs create something new, something different—they change or transmute values. Regardless of the firm size, big or small, they can partake in entrepreneurship opportunities; the opportunity to become an entrepreneur requires four criteria.
First, there must be situations to recombine resources to generate profit. Second, entrepreneurship requires differences between people, such as preferential access to certain individuals or the ability to recognize information about opportunities. Third, taking on risk is a necessity. Fourth, the entrepreneurial process requires the organization of resources; the entrepreneur is a factor in and the study of entrepreneurship reaches back to the work of Richard Cantillon and Adam Smith in the late 17th and early 18th centuries. However, entrepreneurship was ignored theoretically until the late 19th and early 20th centuries and empirically until a profound resurgence in business and economics since the late 1970s. In the 20th century, the understanding of entrepreneurship owes much to the work of economist Joseph Schumpeter in the 1930s and other Austrian economists such as Carl Menger, Ludwig von Mises and Friedrich von Hayek. According to Schumpeter, an entrepreneur is a person, willing and able to convert a new idea or invention into a successful innovation.
Entrepreneurship employs what Schumpeter called "the gale of creative destruction" to replace in whole or in part inferior innovations across markets and industries creating new products including new business models. In this way, creative destruction is responsible for the dynamism of industries and long-run economic growth; the supposition that entrepreneurship leads to economic growth is an interpretation of the residual in endogenous growth theory and as such is hotly debated in academic economics. An alternative description posited by Israel Kirzner suggests that the majority of innovations may be much more incremental improvements such as the replacement of paper with plastic in the making of drinking straws; the exploitation of entrepreneurial opportunities may include: Developing a business plan Hiring the human resources Acquiring financial and material resources Providing leadership Being responsible for both the venture's success or failure Risk aversionEconomist Joseph Schumpeter saw the role of the entrepreneur in the economy as "creative destruction" – launching innovations that destroy old industries while ushering in new industries and approaches.
For Schumpeter, the changes and "dynamic disequilibrium brought on by the innovating entrepreneur the norm of a healthy economy". While entrepreneurship is associated with new, for-profit start-ups, entrepreneurial behavior can be seen in small-, medium- and large-sized firms and established firms and in for-profit and not-for-profit organizations, including voluntary-sector groups, charitable organizations and government. Entrepreneurship may operate within an entrepreneurship ecosystem which includes: Government programs and services that promote entrepreneurship and support entrepreneurs and start-ups Non-governmental organizations such as small-business associations and organizations that offer advice and mentoring to entrepreneurs Small-business advocacy organizations that lobby governments for increased support for entrepreneurship programs and more small business-friendly laws and regulations Entrepreneurship resources and facilities Entrepreneurship education and training programs offered by schools and universities Financing In the 2000s, usage of the term "entrepreneurship" expanded to include how and why some individuals ide
A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light, such as flat-white paint; the most familiar type of mirror is the plane mirror. Curved mirrors are used, to produce magnified or diminished images or focus light or distort the reflected image. Mirrors are used for personal grooming or admiring oneself, for viewing the area behind and on the sides on motor vehicles while driving, for decoration, architecture. Mirrors are used in scientific apparatus such as telescopes and lasers and industrial machinery. Most mirrors are designed for visible light. There are many types of glass mirrors, each representing a different manufacturing process and reflection type.
An aluminium glass mirror is made of a float glass manufactured using vacuum coating, i.e. aluminium powder is evaporated onto the exposed surface of the glass in a vacuum chamber and coated with two or more layers of waterproof protective paint. A low aluminium glass mirror is manufactured by coating silver and two layers of protective paint on the back surface of glass. A low aluminium glass mirror is clear, light transmissive and reflects accurate natural colors; this type of glass is used for framing presentations and exhibitions in which a precise color representation of the artwork is essential or when the background color of the frame is predominantly white. A safety glass mirror is made by adhering a special protective film to the back surface of a silver glass mirror, which prevents injuries in case the mirror is broken; this kind of mirror is used for furniture, glass walls, commercial shelves, or public areas. A silkscreen printed glass mirror is produced using inorganic color ink that prints patterns through a special screen onto glass.
Various colors and glass shapes are available. Such a glass mirror is durable and more moisture resistant than ordinary printed glass and can serve for over 20 years; this type of glass is used for decorative purposes. A silver glass mirror is an ordinary mirror, coated on its back surface with silver, which produces images by reflection; this kind of glass mirror is produced by coating a silver, copper film and two or more layers of waterproof paint on the back surface of float glass, which resists acid and moisture. A silver glass mirror provides clear and actual images, is quite durable, is used for furniture and other decorative purposes. Decorative glass mirrors are handcrafted. A variety of shades and glass thickness are available. A beam of light reflects off a mirror at an angle of reflection equal to its angle of incidence; that is, if the beam of light is shining on a mirror's surface, at a θ ° angle vertically it reflects from the point of incidence at a θ ° angle, vertically in the opposite direction.
This law mathematically follows from the interference of a plane wave on a flat boundary. In a plane mirror, a parallel beam of light changes its direction as a whole, while still remaining parallel. In a concave mirror, parallel beams of light become a convergent beam, whose rays intersect in the focus of the mirror. Known as converging mirror In a convex mirror, parallel beams become divergent, with the rays appearing to diverge from a common point of intersection "behind" the mirror. Spherical concave and convex mirrors do not focus parallel rays to a single point due to spherical aberration. However, the ideal of focusing to a point is a used approximation. Parabolic reflectors resolve this. Parabolic reflectors are not suitable for imaging nearby objects because the light rays are not parallel. Objects viewed in a mirror will appear not vertically inverted. However, a mirror does not "swap" left and right any more than it swaps top and bottom. A mirror reverses the forward/backward axis. To be precise, it reverses the object in the direction perpendicular to the mirror surface.
Because left and right are defined relative to front-back and top-bottom, the "flipping" of front and back results in the perception of a left-right reversal in the image. Looking at an image of oneself with the front-back axis flipped results in the perception of an image with its left-right axis flipped; when reflected in the mirror, your right hand remains directly opposite your real right hand, but it is perceived as the left hand of your image. When a person looks into a mirror, the image is front-back reversed, an effect similar to the holl
Chemical engineering is a branch of engineering that uses principles of chemistry, mathematics and economics to efficiently use, produce and transport chemicals and energy. A chemical engineer designs large-scale processes that convert chemicals, raw materials, living cells and energy into useful forms and products. Chemical engineers are involved in many aspects of plant design and operation, including safety and hazard assessments, process design and analysis, control engineering, chemical reaction engineering, biological engineering, construction specification, operating instructions. Chemical engineering degree is directly linked with all the majors of various engineering disciplines. A 1996 British Journal for the History of Science article cites James F. Donnelly for mentioning an 1839 reference to chemical engineering in relation to the production of sulfuric acid. In the same paper however, George E. Davis, an English consultant, was credited for having coined the term. Davis tried to found a Society of Chemical Engineering, but instead it was named the Society of Chemical Industry, with Davis as its first Secretary.
The History of Science in United States: An Encyclopedia puts the use of the term around 1890. "Chemical engineering", describing the use of mechanical equipment in the chemical industry, became common vocabulary in England after 1850. By 1910, the profession, "chemical engineer," was in common use in Britain and the United States. Chemical engineering emerged upon the development of unit operations, a fundamental concept of the discipline of chemical engineering. Most authors agree that Davis invented the concept of unit operations if not developed it, he gave a series of lectures on unit operations at the Manchester Technical School in 1887, considered to be one of the earliest such about chemical engineering. Three years before Davis' lectures, Henry Edward Armstrong taught a degree course in chemical engineering at the City and Guilds of London Institute. Armstrong's course failed because its graduates were not attractive to employers. Employers of the time would have rather hired mechanical engineers.
Courses in chemical engineering offered by Massachusetts Institute of Technology in the United States, Owens College in Manchester and University College London suffered under similar circumstances. Starting from 1888, Lewis M. Norton taught at MIT the first chemical engineering course in the United States. Norton's course was contemporaneous and similar to Armstrong's course. Both courses, however merged chemistry and engineering subjects along with product design. "Its practitioners had difficulty convincing engineers that they were engineers and chemists that they were not chemists." Unit operations was introduced into the course by William Hultz Walker in 1905. By the early 1920s, unit operations became an important aspect of chemical engineering at MIT and other US universities, as well as at Imperial College London; the American Institute of Chemical Engineers, established in 1908, played a key role in making chemical engineering considered an independent science, unit operations central to chemical engineering.
For instance, it defined chemical engineering to be a "science of itself, the basis of which is... unit operations" in a 1922 report. Meanwhile, promoting chemical engineering as a distinct science in Britain led to the establishment of the Institution of Chemical Engineers in 1922. IChemE helped make unit operations considered essential to the discipline. In 1940s, it became clear that unit operations alone were insufficient in developing chemical reactors. While the predominance of unit operations in chemical engineering courses in Britain and the United States continued until the 1960s, transport phenomena started to experience greater focus. Along with other novel concepts, such as process systems engineering, a "second paradigm" was defined. Transport phenomena gave an analytical approach to chemical engineering while PSE focused on its synthetic elements, such as control system and process design. Developments in chemical engineering before and after World War II were incited by the petrochemical industry, advances in other fields were made as well.
Advancements in biochemical engineering in the 1940s, for example, found application in the pharmaceutical industry, allowed for the mass production of various antibiotics, including penicillin and streptomycin. Meanwhile, progress in polymer science in the 1950s paved way for the "age of plastics". Concerns regarding the safety and environmental impact of large-scale chemical manufacturing facilities were raised during this period. Silent Spring, published in 1962, alerted its readers to the harmful effects of DDT, a potent insecticide; the 1974 Flixborough disaster in the United Kingdom resulted in 28 deaths, as well as damage to a chemical plant and three nearby villages. The 1984 Bhopal disaster in India resulted in 4,000 deaths; these incidents, along with other incidents, affected the reputation of the trade as industrial safety and environmental protection were given more focus. In response, the IChemE required safety to be part of every degree course that it accredited after 1982. By the 1970s, legislation and monitoring agencies were instituted in various countries, such as France and the United States.
Advancements in computer science found applications designing and managing plants, simplifying calculations and drawings that had to be done manually. The c
The Moon is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, the largest among planetary satellites relative to the size of the planet that it orbits; the Moon is after Jupiter's satellite Io the second-densest satellite in the Solar System among those whose densities are known. The Moon is thought to have formed not long after Earth; the most accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. The Moon is in synchronous rotation with Earth, thus always shows the same side to Earth, the near side; the near side is marked by dark volcanic maria that fill the spaces between the bright ancient crustal highlands and the prominent impact craters. After the Sun, the Moon is the second-brightest visible celestial object in Earth's sky, its surface is dark, although compared to the night sky it appears bright, with a reflectance just higher than that of worn asphalt.
Its gravitational influence produces the ocean tides, body tides, the slight lengthening of the day. The Moon's average orbital distance is 1.28 light-seconds. This is about thirty times the diameter of Earth; the Moon's apparent size in the sky is the same as that of the Sun, since the star is about 400 times the lunar distance and diameter. Therefore, the Moon covers the Sun nearly during a total solar eclipse; this matching of apparent visual size will not continue in the far future because the Moon's distance from Earth is increasing. The Moon was first reached in September 1959 by an unmanned spacecraft; the United States' NASA Apollo program achieved the only manned lunar missions to date, beginning with the first manned orbital mission by Apollo 8 in 1968, six manned landings between 1969 and 1972, with the first being Apollo 11. These missions returned lunar rocks which have been used to develop a geological understanding of the Moon's origin, internal structure, the Moon's history. Since the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft.
Both the Moon's natural prominence in the earthly sky and its regular cycle of phases as seen from Earth have provided cultural references and influences for human societies and cultures since time immemorial. Such cultural influences can be found in language, lunar calendar systems and mythology; the usual English proper name for Earth's natural satellite is "the Moon", which in nonscientific texts is not capitalized. The noun moon is derived from Old English mōna, which stems from Proto-Germanic *mēnô, which comes from Proto-Indo-European *mḗh₁n̥s "moon", "month", which comes from the Proto-Indo-European root *meh₁- "to measure", the month being the ancient unit of time measured by the Moon; the name "Luna" is used. In literature science fiction, "Luna" is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of Earth's moon; the modern English adjective pertaining to the Moon is lunar, derived from the Latin word for the Moon, luna. The adjective selenic is so used to refer to the Moon that this meaning is not recorded in most major dictionaries.
It is derived from the Ancient Greek word for the Moon, σελήνη, from, however derived the prefix "seleno-", as in selenography, the study of the physical features of the Moon, as well as the element name selenium. Both the Greek goddess Selene and the Roman goddess Diana were alternatively called Cynthia; the names Luna and Selene are reflected in terminology for lunar orbits in words such as apolune and selenocentric. The name Diana comes from the Proto-Indo-European *diw-yo, "heavenly", which comes from the PIE root *dyeu- "to shine," which in many derivatives means "sky and god" and is the origin of Latin dies, "day"; the Moon formed 4.51 billion years ago, some 60 million years after the origin of the Solar System. Several forming mechanisms have been proposed, including the fission of the Moon from Earth's crust through centrifugal force, the gravitational capture of a pre-formed Moon, the co-formation of Earth and the Moon together in the primordial accretion disk; these hypotheses cannot account for the high angular momentum of the Earth–Moon system.
The prevailing hypothesis is that the Earth–Moon system formed after an impact of a Mars-sized body with the proto-Earth. The impact blasted material into Earth's orbit and the material accreted and formed the Moon; the Moon's far side has a crust, 30 mi thicker than that of the near side. This is thought to be; this hypothesis, although not perfect best explains the evidence. Eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, Jeff Taylor challenged fellow lunar scientists: "You have eighteen months. Go back to your Apollo data, go back to your computer, do whatever you have to, but make up your mind. Don't come to our conference unless you have something to say about the Moon's birth." At the 1984 conference at Kona, the giant impact hypothesis emerged as the most consensual theory. Before the conference, there were parti
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti
Elmer is a small lunar impact crater, located to the south of Mare Smythii, near the eastern limb of the Moon. This crater is seen at a oblique angle from Earth, the visibility is affected by libration. Elmer lies southwest of the crater Kreiken, east-southeast of the larger Dale; this is a circular, bowl-shaped crater with an interior floor that occupies about half the total diameter