omniomni/omni-engineering huggingface dataset:
Zig-zag bridge. A zig-zag bridge is a pedestrian bridge composed of short segments, each set at an angle relative to its neighbors and usually with an alternating right and left turn required when traveling across the bridge. It is used in standard crossings for structural stability; and in traditional and contemporary Asian and Western landscape design  across water gardens.

When constructed of wood, each segment is formed from planks and is supported by posts. When constructed of stone, the bridge will use short or long rectilinear slabs set upon stone footings.

Garden and ceremonial bridge

A zig-zag bridge is  often seen in the Chinese garden, Japanese garden, and Zen rock garden. It may be made of stone slabs or planks as part of a pond design and is frequently seen in rustic gardens.  It is also used in high art modern fountain gardens, often in public urban park and botanic garden landscapes.

The objective in employing such a bridge, constructed according to Zen philosophy and teachings, is to focus the walker's attention to the mindfulness of the current place and time moment – "being here, now". As it often has no railings, it is quite possible for an inattentive walker to simply fall off an end into the water.

The zig-zag of paths and bridges also follows a principle of Chinese Feng Shui.

Standard bridge
The post and plank version has an advantage when employed as a crossing of a muddy bottom or marsh: It is structurally stable, where a straight bridge might tend to tip due to the posts moving in the soft mud. Each segment of walkway mutually supports the next from twisting and tipping by being securely fastened to it. This is the same advantage possessed by a zig-zag split rail fence.

See also
Footbridge
Moon bridge
S bridge
Step-stone bridge

References

External links

Footbridges
Stone bridges
Garden features
Stonemasonry
Chinese gardening styles
Japanese style of gardening
Bridges
BDS C. BDS C (or the BD Software C Compiler) is a compiler for a sizeable subset of the C programming language, that ran on and generated code for the Intel 8080 and Zilog Z80 processors. It was the first C compiler for CP/M. It was written by Leor Zolman and first released in 1979 when he was 20 years old. "BDS" stands for "Brain Damage Software."

BDS C was popular and influential among CP/M users and developers. It ran much faster than other Z80-hosted compilers. It was possible to run BDS C on single-floppy machines with as little as 30K of RAM in comparison to most other commercial compilers which required many passes and the writing of intermediate files to disk. 

Weak points of BDS C were that the floating point math routines and the file access functions were incompatible with the C compiler used on UNIX, and that its relocatable object files were incompatible with the Microsoft MACRO-80 assembler, making it more difficult to integrate C code with assembly language.

BDS C was bundled with a subset of the Unix system written in about 1980, called MARC (Machine Assisted Resource Coordinator). This effort in some ways resembled GNU, though MARC was to be able to run CP/M software through emulation. Unfortunately MARC's author, Ed Ziemba, perished in a snorkeling accident before he could complete the project.

In 2002, Leor Zolman released the 8080 assembly language source code for BDS C, along with the sources of 8080 assembler and linking tool, into the public domain.

Reception
Around 75,000 copies were sold, including a stripped down Japanese version.

A number of commercial CP/M products were written in the BDS C subset of the C language, including PeachText from PeachTree Software, MINCE and Scribble from Mark of the Unicorn, and most of the software in the Perfect Software suite including Perfect Writer, PerfectCalc, PerfectSpeller, and PerfectFiler (which suite was bundled with the Kaypro).

See also

Small-C

References

External links
BD Software download page
MUF Mastery - historical note about Leor Zolman and BDS C
Interview with Leor Zolman
BDS C Users Group

1979 software
C (programming language) compilers
CP/M software
Free and open source compilers
Formerly proprietary software
Public-domain software with source code
Assembly language software
Supersonic fracture. Supersonic fractures are fractures where the fracture propagation velocity is higher than the speed of sound in the material. This phenomenon was first discovered by scientists from the Max Planck Institute for Metals Research in Stuttgart (Markus J. Buehler and Huajian Gao) and IBM Almaden Research Center in San Jose, California (Farid F. Abraham).

The issues of intersonic and supersonic fracture become the frontier of dynamic fracture mechanics. The work of Burridge initiated the exploration for intersonic crack growth (when the crack tip velocity V is between the shear in wave speed C^8 and the longitudinal wave speed C^1.

Supersonic fracture was a phenomenon totally unexplained by the classical theories of fracture. Molecular dynamics simulations by the group around Abraham and Gao have shown the existence of intersonic mode I and supersonic mode II cracks. This motivated a continuum mechanics analysis of supersonic mode III cracks by Yang. Recent progress in the theoretical understanding of hyperelasticity in dynamic fracture has shown that supersonic crack propagation can only be understood by introducing a new length scale, called χ; which governs the process of energy transport near a crack tip. The crack dynamics is completely dominated by material properties inside a zone surrounding the crack tip with characteristic size equal to χ. When the material inside this characteristic zone is stiffened due to hyperelastic properties, cracks propagate faster than the longitudinal wave speed. The research group of Gao has used this concept to simulate the Broberg problem of crack propagation inside a stiff strip embedded in a soft elastic matrix. These simulations confirmed the existence of an energy characteristic length. This study also had implications for dynamic crack propagation in composite materials. If the characteristic size of the composite microstructure is larger than the energy characteristic length, χ; models that homogenize the materials into an effective continuum would be in significant error. The challenge arises of designing experiments and interpretative simulations to verify the energy characteristic length. Confirmation of the concept must be sought in the comparison of experiments on supersonic cracks and the predictions of the simulations and analysis. While much excitement rightly centres on the relatively new activity related to intersonic cracking, an old but interesting possibility remains to be incorporated in the modern work: for an interface between elastically dissimilar materials, crack propagation that is subsonic but exceeds the Rayleigh wave speed has been predicted for at least some combinations of the elastic properties of the two materials.

See also
Characteristic energy length scale

References

Fracture mechanics
Melonite. Melonite is a telluride of nickel; it is a metallic mineral. Its chemical formula is NiTe2.  It is opaque and white to reddish-white in color, oxidizing in air to a brown tarnish.  

It was first described from the Melones and Stanislaus mine in Calaveras County, California in 1866, by Frederick Augustus Genth.

Melonite occurs as trigonal crystals, which cleave in a (0001) direction. It has a specific gravity of 7.72 and a hardness of 1–1.5 (very soft).

See also
 List of minerals
 Tenifer and Melonite finish

References

 D. M. Chizhikov and V. P. Shchastlivyi, 1966, Tellurium and Tellurides, Nauka Publishing, Moscow

External links 
 
 

Nickel minerals
Telluride minerals
Trigonal minerals
Minerals in space group 164
Transition metal dichalcogenides
Minerals described in 1866
Return to Flight. Return to Flight can refer to:

 Apollo 7, NASA's first mission after the Apollo 1 fire
 Apollo 14, NASA's first mission after the failure of Apollo 13
 Falcon 9 Flight 20
 Space Shuttle mission STS-26, NASA's first mission after the Space Shuttle Challenger disaster
 Space Shuttle mission STS-114, NASA's first test mission after the Space Shuttle Columbia disaster
 Space Shuttle mission STS-121, NASA's second test mission following the Columbia disaster
 ISRO's successful launch of GSLV-D5 with indigenously developed CE-7.5 cryogenic rocket engine
Real Programmers Don't Use Pascal. "Real Programmers Don't Use Pascal" (a parody of the bestselling 1982 tongue-in-cheek book on stereotypes about masculinity Real Men Don't Eat Quiche) is an essay about computer programming written by Ed Post of Tektronix, Inc., and published in July 1983 as a reader's contribution in Datamation.

History
Widely circulated on Usenet in its day, and well known in the computer software industry, the article compares and contrasts real programmers, who use punch cards and write programs in FORTRAN or assembly language, with modern-day "quiche eaters" who use programming languages such as Pascal which support structured programming and impose restrictions meant to prevent or minimize common bugs due to inadvertent programming logic errors.  Also mentioned are feats such as Seymour Cray, the inventor of the Cray-1 supercomputer, using manual control switches to load the first operating system for the CDC 7600 without notes.

The next year Ed Nather’s The Story of Mel, also known as The realest programmer of all, extended the theme. Immortalized in the piece is Mel Kaye of the Royal McBee Computer Corporation. As the story famously puts it, "He wrote in machine code—in 'raw, unadorned, inscrutable hexadecimal numbers. Directly.'"

Since then, the computer folklore term Real Programmer has come to describe the archetypical "hardcore" programmer who eschews the modern languages and tools of the day in favour of more direct and efficient (for the machine, decidedly not for the programmer) solutions—closer to the hardware. The term is used in many subsequent articles, webcomics and in-jokes—although the alleged defining features of a "Real Programmer" differ with time and place.

See also

References

Notes

External links
Real Programmers Don't Use Pascal (full original)

Computer folklore
Pascal (programming language)
1983 essays
1983 in computing
Parodies of literature
Computer humour
Azobisisobutyronitrile. Azobisisobutyronitrile (abbreviated AIBN) is an organic compound with the formula . This white powder is soluble in alcohols and common organic solvents but is insoluble in water. It is often used as a foamer in plastics and rubber and as a radical initiator. 

As an azo initiator, radicals resulting from AIBN have multiple benefits over common organic peroxides. For example, they do not have oxygenated byproducts or much yellow discoloration. Additionally, they do not cause too much grafting and therefore are often used when making adhesives, acrylic fibers, detergents, etc.

Mechanism of decomposition
In its most characteristic reaction, AIBN decomposes,  eliminating a molecule of nitrogen gas to form two 2-cyanoprop-2-yl radicals:

Because azobisisobutyronitrile readily gives off free radicals, it is often used as a radical initiator. This happens at temperatures above 40 °C, but in experiments is more commonly done at temperatures between 66 °C and 72 °C. This decomposition has a ΔG‡ of 131 kJ/mol and results in two 2-cyano-2-propyl (carbon) radicals and a molecule of nitrogen gas. The release of nitrogen gas pushes this decomposition forward due to the increase in entropy. And the 2-cyano-2-propyl radical is stabilized by the −CN group.

Chemical reactions 
These radicals formed by the decomposition of AIBN can initiate free-radical polymerizations and other radical-induced reactions. For instance, a mixture of styrene and maleic anhydride in toluene will react if heated, forming the copolymer upon addition of AIBN. Another example of a radical reaction that can be initiated by AIBN is the anti-Markovnikov hydrohalogenation of alkenes. AIBN has also been used as the radical initiator for Wohl–Ziegler bromination.  The AIBN-derived 2-cyano-2-propyl radical abstracts the hydrogen from tributyltin hydride. The resulting tributyltin radical can be used for removal of a bromine atom.

AIBN-derived radicals abstract a hydrogen from HBr to give a bromine radical, which can add to alkenes. This type of hydrohalogenation of an alkene proceeds with anti-Markovnikov selectivity.

Production and analogues
AIBN is produced in two steps from acetone cyanohydrin. Reaction with hydrazine gives the substituted dialkylhydrazine.  In the second step, the hydrazine is oxidized to the azo derivative:

Related azo compounds behave similarly, such as 1,1′-azobis(cyclohexanecarbonitrile). Water-soluble azo initiators are also available.

Safety
AIBN is safer to use than benzoyl peroxide (another radical initiator) because the risk of explosion is far less. However, it is still considered as an explosive compound, decomposing above 65 °C.  A respirator dust mask, protective gloves and safety glasses are recommended. Pyrolysis of AIBN without a trap for the formed 2-cyanopropyl radicals results in the formation of tetramethylsuccinonitrile, which is highly toxic.

References

External links

Azo compounds
Radical initiators
Acentric factor. The acentric factor  is a conceptual number introduced by Kenneth Pitzer in 1955, proven to be useful in the description of fluids. It has become a standard for the phase characterization of single and pure components, along with other state description parameters such as molecular weight, critical temperature, critical pressure, and critical volume (or critical compressibility). The acentric factor is also said to be a measure of the non-sphericity (centricity) of molecules. 

Pitzer defined  from the relationship
 
where
 is the reduced saturation vapor pressure, and 
 is the reduced temperature.

Pitzer developed this factor by studying the vapor-pressure curves of various pure substances. Thermodynamically, the vapor-pressure curve for pure components can be mathematically described using the Clausius–Clapeyron equation.

The integrated form of equation is mainly used for obtaining vapor-pressure data mathematically. This integrated version shows that the relationship between the logarithm of vapor pressure and the reciprocal of absolute temperature is approximately linear.

For a series of fluids, as the acentric factor increases the vapor curve is "pulled" down, resulting in higher boiling points. For many monatomic fluids,  at  which leads to . In many cases,  lies above the boiling temperature of liquids at atmosphere pressure.

Values of  can be determined for any fluid from accurate experimental vapor-pressure data. The definition of  gives values close to zero for the noble gases argon, krypton, and xenon.  is also very close to zero for molecules which are nearly spherical. Values of  correspond to vapor pressures above the critical pressure and are non-physical.

The acentric factor can be predicted analytically from some equations of state. For example, it can be easily shown from the above definition that a van der Waals fluid has an acentric factor of about −0.302024, which if applied to a real system would indicate a small, ultra-spherical molecule.

Values of some common gases

See also

 Equation of state
 Reduced pressure
 Reduced temperature

References 

Gas laws
Susan Dumais. Susan Dumais (born August 11, 1953) is an American computer scientist who is a leader in the field of information retrieval, and has been a significant contributor to Microsoft's search technologies.
According to Mary Jane Irwin, who heads the Athena Lecture awards committee, “Her sustained contributions have shaped the thinking and direction of human-computer interaction and information retrieval."

Biography
Susan Dumais is a Technical Fellow at Microsoft and Managing Director of the Microsoft Research Northeast Labs, inclusive of MSR New England, MSR New York and MSR Montreal. Her research at Microsoft has focused on gaze-enhanced interaction, the temporal dynamics of information systems, user modeling and personalization, novel interfaces for interactive retrieval, and search evaluation. She is also an Affiliate Professor at the University of Washington Information School, where she was the Ph.D. advisor for computer science professor Jeff Huang.

Before joining Microsoft in 1997, Dumais was a researcher at Bellcore (now Telcordia Technologies), where she and her colleagues conducted research into what is now called the vocabulary problem in information retrieval. Their study demonstrated, through a variety of experiments, that different people use different vocabulary to describe the same thing, and that even choosing the "best" term to describe something is not enough for others to find it.  One implication of this work is that because the author of a document may use different vocabulary than someone searching for the document, traditional information retrieval methods will have limited success.

Dumais and the other Bellcore researchers then began investigating ways to build search systems that avoided the vocabulary problem. The result was their invention of Latent Semantic Indexing.

Awards
In 2006, Dumais was inducted as a Fellow of the Association for Computing Machinery. In 2009, she received the Gerard Salton Award, an information retrieval lifetime achievement award. In 2011, she was inducted to the National Academy of Engineering for innovation and leadership in organizing, accessing, and interacting with information. In 2014, Dumais received the Athena Lecturer Award for "fundamental contributions to computer science." and the Tony Kent Strix award for "sustained contributions that are both innovative and practical" with "significant impact".
In 2015, she was inducted into the American Academy of Arts and Sciences. In 2020 she received the SIGCHI Lifetime Research Award and inducted into the ACM SIGIR Academy in 2021.

References

External links
 Home page at Microsoft Research

2006 fellows of the Association for Computing Machinery
Microsoft employees
Microsoft Research people
Living people
American women computer scientists
American computer scientists
University of Washington faculty
Information retrieval researchers
Microsoft technical fellows
American women academics
1953 births
21st-century American women scientists
20th-century American women scientists
Wet sump. Within piston engines, a wet sump is part of a lubrication system whereby the crankcase sump is used as an integral oil reservoir. An alternative system is the dry sump, whereby oil is pumped from a shallow sump into an external reservoir.

Piston engines are lubricated by oil which is pumped into various bearings, and thereafter allowed to drain to the base of the engine under gravity.  In most production automobiles and motorcycles, which use a wet sump system, the oil is collected in a  capacity pan at the base of the engine, known as the sump or oil pan, where it is pumped back up to the bearings by the  internal oil pump.

A wet sump offers the advantage of a simple design, using a single pump and no external reservoir.  Since the sump is internal, there is no need for hoses or tubes connecting the engine to an external sump which may leak.  An internal oil pump is generally more difficult to replace, but that is dependent on the engine design.

A wet sump design can be problematic in a racing car, as the large g force pulled by drivers going around corners causes the oil in the pan to slosh, gravitating away from the oil pick-up, briefly starving the system of oil and damaging the engine.  However, on a motorcycle this difficulty does not arise, as a bike leans into corners and the oil is not displaced sideways.  Nevertheless, racing motorcycles usually benefit from dry sump lubrication, as the shallow sump allows the engine to be mounted lower in the frame; and a remote oil tank can allow for improved lubricant cooling. On some dry sump motorcycles, such as the Yamaha TRX850 and the Yamaha TDM, the oil tank is integral to the engine, sitting atop the gearbox.
 
Early stationary engines employed a small scoop on the extremity of the crankshaft or connecting rod to assist with the lubrication of the cylinder walls by means of a splashing action.  Modern small engines, such as those used in lawnmowers, use a "slinger" (basically a paddle wheel) to perform the same function.

Two-stroke and four-stroke engines 
Small two-stroke engines, such as in motorcycles and lawnmowers, have total loss lubrication. Such engines use crankcase compression to feed the fuel/air mixture through the crankcase. This precludes the use of both wet sump and dry sump systems, as excess oil here would contaminate the mixture, leading to excess oil being burned in the engine and so excessive hydrocarbon emissions. These small engines run on specifically prepared fuel, a mixture of gasoline and two-stroke oil in a ratio recommended by the manufacturer. In some engines this mixture may also be independently pre-injected into the engine cylinders and bearings by a pump.

Four-stroke engines and large (non-petrol) two-stroke engines used in locomotives and ships may have either wet or dry sumps. Large two-stroke engines do not use crankcase compression; instead they use a mechanical blower or a turbocharger to aspirate air.

Types of wet sump 
 Splash lubrication
 Splash and pressure 
 Full pressure feed

References

Engine lubrication systems