omniomni/omni-engineering huggingface dataset:
Lehman's laws of software evolution. In software engineering, the laws of software evolution refer to a series of laws that Lehman and Belady formulated starting in 1974 with respect to software evolution.
The laws describe a balance between forces driving new developments on one hand, and forces that slow down progress on the other hand.  Over the past decades the laws have been revised and extended several times.

Context

Observing that most software is subject to change in the course of its existence, the authors set out to determine laws that these changes will typically obey, or must obey for the software to survive.

In his 1980 article, Lehman qualified the application of such laws by distinguishing between three categories of software:
 An S-program is written according to an exact specification of what that program can do. For example, a program to find solutions to the eight queens puzzle would be an S-program. These programs are mostly static and shouldn't evolve much.
 A P-program is written to implement certain procedures that completely determine what the program can do (the example mentioned is a program to play chess)
 An E-program is written to perform some real-world activity; how it should behave is strongly linked to the environment in which it runs, and such a program needs to adapt to varying requirements and circumstances in that environment
The laws are said to apply only to the last category of systems.

The laws

All told, eight laws were formulated:

 (1974) "Continuing Change" — an E-type system must be continually adapted or it becomes progressively less satisfactory.
 (1974) "Increasing Complexity" — as an E-type system evolves, its complexity increases unless work is done to maintain or reduce it.
 (1974) "Self Regulation" — E-type system evolution processes are self-regulating with the distribution of product and process measures close to normal.
 (1978) "Conservation of Organisational Stability (invariant work rate)" — the average effective global activity rate in an evolving E-type system is invariant over the product's lifetime.
 (1978) "Conservation of Familiarity" — as an E-type system evolves, all associated with it, developers, sales personnel and users, for example, must maintain mastery of its content and behaviour to achieve satisfactory evolution. Excessive growth diminishes that mastery. Hence the average incremental growth remains invariant as the system evolves.
 (1991) "Continuing Growth" — the functional content of an E-type system must be continually increased to maintain user satisfaction over its lifetime.
 (1996) "Declining Quality" — the quality of an E-type system will appear to be declining unless it is rigorously maintained and adapted to operational environment changes.
 (1996) "Feedback System" (first stated 1974, formalised as law 1996) — E-type evolution processes constitute multi-level, multi-loop, multi-agent feedback systems and must be treated as such to achieve significant improvement over any reasonable base.

References
 

Software maintenance
Reaction Engines Scimitar. The Reaction Engines Scimitar is a derivative of the SABRE engine technology, but intended for jet airliners (the Reaction Engines LAPCAT A2 concept), rather than space launch applications. Consequently, most of the Scimitar engine technology is similar to SABRE but designed for much longer life. Both engines are designed around existing ramjet technology, but the Scimitar engine lacks the rocket features and has high bypass features for greater efficiency. The engines burn liquid hydrogen as fuel.

The incorporation of lightweight heat exchangers in the main thermodynamic cycles of these engines is a new feature to aerospace propulsion. Similar studies of intercoolers used on jet engines show significant improvement of efficiency.

References

Aircraft engines
Engine technology
Italair Pegaso. The Italair F.20 Pegaso was a twin-engine utility aircraft designed by Stelio Frati and built in Italy in 1971.

Design and development
It had the sleek lines typical of Frati's designs and was a conventional low-wing cantilever monoplane with retractable tricycle undercarriage. Construction throughout was of metal, and the aircraft was notable at the time for its high speed, much greater than that of its competitors. The prototype Pegaso was exhibited at the 1973 Paris Air Show. Before arrangements could be made to produce the aircraft in series, however, Italair ran out of money, and the rights to the design reverted to Frati.

In the early 1980s, Frati designed a modernised version of the aircraft, powered by Allison 250 turboprop engines in place of the Pegaso's piston engines and equipped with a large sliding bubble canopy. 
Built by Frati's own company, General Avia, and named the F.20TP Condor, this version first flew on 7 May 1983. Frati hoped that this version might attract military buyers who could use it for training, maritime patrol, or even ground attack, and the prototype was equipped with two pylons under each wing to demonstrate its capacity to carry external stores. Although exhibited at the Paris Air Show in 1985, development of the Condor was postponed in favour of the Promavia Jet Squalus that Frati was working on at the time, and was eventually abandoned.

Specifications (F.20 Pegaso)

References

Further reading

 
 
 

1970s Italian civil utility aircraft
Low-wing aircraft
Aircraft first flown in 1971
Twin piston-engined tractor aircraft
John Donkin. John Donkin (1802–1854) was a British engineer. He was a son of Bryan Donkin and worked in this father's company in Bermondsey, primarily on paper-making equipment.  He married Caroline Hawes, granddaughter of William Hawes, notable as founder of the Royal Humane Society.  Caroline Hawes was the sister of Sir Benjamin Hawes, brother-in-law of Isambard Kingdom Brunel.

John Donkin was the father of Bryan Donkin Junior and grandfather of Sydney Donkin.  He was first cousin of William Fishburn Donkin.

Sources
 
  Grace's Guide Accessed 28 June 2013

Engineers from London
1802 births
1854 deaths
British mechanical engineers
People from Bermondsey
Grob G 116. The Grob G 116 was a civil utility aircraft developed in Germany in the late 1980s. It was an enlarged and more powerful four-seat version of the two-seat Grob G 115. Like its predecessor, it was a conventional low-wing cantilever monoplane with fixed tricycle undercarriage. Also like the G 115, construction throughout was of composite materials.

Grob commenced displaying a highly realistic mock-up of the design in 1987, and a prototype flew the following year. However, by 1989 the firm became uncertain about the commercial viability of the aircraft in the face of heavy competition in the four-seat sector, and the project was first postponed and finally cancelled.

Specifications

References
 
 
 
 
 
 

1980s German civil utility aircraft
Grob aircraft
Low-wing aircraft
Single-engined tractor aircraft
Aircraft first flown in 1988
Grob GF 200. The Grob GF 200 was a business aircraft of unorthodox design developed in Germany during the 1990s.

Design and development
The GF 200 was a low-wing cantilever monoplane with retractable tricycle undercarriage and a highly streamlined fuselage. The engine was mounted within the fuselage, to the rear of the passenger cabin, and drove the pusher propeller via a driveshaft. The GF 200 has a T-tail, but also a large ventral fin beneath the fuselage. Like other Grob designs, construction throughout was of composite materials, in the case of this particular aircraft, including the driveshaft.

Development commenced in 1983 but was postponed due to concerns about achieving certification for the composite design. However, with financial support from the German government, development commenced in earnest by the end of the decade. The project officially launched at the Hannover Show in May 1988, at which a mockup of the design was displayed and a hope expressed to have the aircraft flying within two years.

Operational history

As it transpired, the prototype was rolled out in March 1991, in the hope of a first flight by May, and which finally took place on 26 November.
The aircraft made its first public appearance at the Berlin Air Show in 1992. Initial flight tests revealed problems with engine cooling and excessive noise. The former concern was addressed by a redesign of the engine air intakes.

The prototype was intended as a test aircraft and technology demonstrator, and lacked many of the refinements that would have been incorporated into a production aircraft, including cabin pressurisation, de-icing equipment, and even a complete cabin interior. When Grob was unable to find financial backing to take the design further, the company embarked on the construction of a more "true-to-life" prototype in 1997, the GF 250, in the belief that this would prove more attractive to potential business partners.

Further planned developments included the turboshaft-powered GF 300, and the GF 350 with twin turboshaft engines driving a common propeller.

Specifications (GF 200)

See also

References

Citations

Bibliography

 
 
 
 
 
 
 
 
 
 
 

GF200
1990s German business aircraft
Single-engined pusher aircraft
Low-wing aircraft
Aircraft first flown in 1991
Leaching (pedology). In pedology, leaching is the removal of soluble materials from one zone in soil to another via water movement in the profile. It is a mechanism of soil formation distinct from the soil forming process of eluviation, which is the loss of mineral and organic colloids. Leached and eluviated materials tend to be lost from topsoil and deposited in subsoil.  A soil horizon accumulating leached and eluviated materials is referred to as a zone of illuviation.

Laterite soil, which develops in regions with high temperature and heavy rainfall, is an example of this process in action.

See also
Bioleaching
Biomineralisation
Dissolved load
Leaching (agriculture)
Groundwater recharge
Soil salinity control

References

Economic geology
Sedimentology
Soil science
HAL Krishak. The HAL HAOP-27 Krishak ('Farmer') was a military observation aircraft produced in India in the 1960s. It was initially developed by Hindustan Aeronautics as an enlarged, four-seat version of the HAL Pushpak light aircraft.

Two prototypes were built, with the first flying in November 1959 and the second in November 1960. With no interest from buyers, the project was shelved until the Indian Army issued a requirement in the early 1960s for an aircraft to replace the Auster AOP.6 and AOP.9s then serving in the observation role. The original Krishak design was slightly revised to meet the new specification, and the type was adopted into service in 1965. The Krishak was phased out in the mid-1970s when it was replaced by the HAL Cheetah.

Variants
Krishak Used a Continental 190 hp engine
Krishak Mk.2 Used a Continental 225 hp engine

Operators

Indian Army

Specifications (Krishak Mk.2)

See also

Notes

References

 
 

1950s Indian civil utility aircraft
Krishak
Single-engined tractor aircraft
Aircraft first flown in 1959
Halberstadt D.I. The Halberstadt D.I was a prototype fighter aircraft built in Germany in 1916 as a scaled down version of the firm's earlier B.II two seater. It was a conventional, two-bay biplane with staggered wings of nearly equal span and fixed, tailskid undercarriage. The engine was the same Mercedes D.I that was fitted to the B.II, and a single machine gun was fitted. Two prototypes were evaluated by the Idflieg, their performance being found inadequate. The modifications required to bring the aircraft up to an acceptable standard would result in the Halberstadt D.II later the same year.

Specifications

References

 
 
 
 

1910s German fighter aircraft
D.I
Single-engined tractor aircraft
Biplanes
Aircraft first flown in 1915
Prioria (company). Prioria, formally known as Prioria Robotics Inc., was an American corporation that originally focused on designing embedded sensor processing products and services. Established in Gainesville, Florida in 2003, Prioria transitioned from embedded systems to the design and development of unmanned aircraft. The company would go on to develop multiple Unmanned aircraft platforms as well as offering commercial services.

The first unmanned aircraft developed, sold, and supported the Maveric Unmanned Aerial Vehicle (also called an autonomous Micro Air Vehicle), while also maintaining a services division focused on defense focused research and development of embedded sensor processing systems. After Maveric, the Company developed Leviathan, a larger fixed wing UAS and the Hex Rotor. In 2014 the company transitioned to offering commercial services.

Prioria had a few key contributions to field of unmanned system:

 Maveric was the first drone to offer autonomous vision based collision avoidance processed on board the aircraft.
 Prioria was the first company to be Aerovironment in a Program of Record for small UAS. Though Aerovironment would win it back in the next cycle.

Notable Technologies

Bendable wing

Maveric benefited from a bendable wing technology that Prioria licensed from the University of Florida. Developed by Dr Peter Ifju

Onboard collision avoidance

Prioria developed an onboard collision avoidance system 

Prioria filed for bankruptcy in February 2018 after losing a major program of record for the Leviathan aircraft to Lockheed Martin in the fall of 2018.

References

External links
Prioria Inc.

Prioria Inc.
Defunct aircraft manufacturers of the United States
Manufacturing companies established in 2003
Companies based in Gainesville, Florida
Electric vehicle manufacturers
Companies that filed for Chapter 7 bankruptcy in 2018
2003 establishments in Florida
American companies established in 2003
Manufacturing companies disestablished in 2018
2018 disestablishments in Florida
American companies disestablished in 2018
Edwin Augustus Stevens Jr.. Edwin Augustus Stevens Jr. (March 14, 1858 – March 8, 1918) was an army officer, marine engineer, and naval architect.  He was among the founders of Cox & Stevens in 1905, which became an influential and successful New York design firm.

Early life
Stevens was born in Philadelphia in 1858, the son of Martha Bayard Dod (1831–1899) and Edwin Augustus Stevens (1795–1868), a well-known designer and founder of the Stevens Institute of Technology, and nephew of John Cox Stevens, founder of the New York Yacht Club and a driving force in the design of the yacht America and the competition for the America's Cup.

He attended St. Paul's School in Concord, New Hampshire and then entered Princeton University, graduating with an A.B. degree in 1879. He then enrolled at the Stevens Institute of Technology, graduating as an engineer.

Career
His most notable personal achievement was the propeller driven double ended ferry, which is the most typical vehicle ferry in use today.  The significance of his design was a shaft which could control propellers at both ends of the craft.  Among the advantages was superior braking of the vessels, since paddle wheel propulsion systems could not effectively be reversed to slow the craft.  Prior to propeller drives, double ended ferries had less usable width because of side wheel propulsion.

Cox & Stevens began in 1905 as a yacht design and commercial brokerage in New York City.   The original principal partners were Daniel H. Cox, Irving Cox, and Edwin Augustus Stevens Jr.  The firm continued under various names until the 1970s.

Personal life
On October 28, 1879, he married Emily Contee Lewis (1857–1931) of Virginia.  She was the great-granddaughter of Lawrence Lewis (1767-1839), George Washington's nephew, and Eleanor Parke Custis Lewis, Washington's adopted daughter and step-granddaughter. Together, they had eight children:

 John Stevens VI (1881–1932), who died unmarried.
 Edwin Augustus Stevens III (1882–1954), who died unmarried.
 Washington Lewis Stevens (1883–1946), who married Nannie Nye Jackson in 1905.
 Bayard Stevens (1885–1927)
 Martha Bayard Stevens (1886–1888), who died young.
 Basil Martiau Stevens (1888–1957), who married Helen Conro Ward (1891–1943)
 Lawrence Lewis Stevens (1889–1958), who became an actuary and who married Anne D. Malpass (1890–1974).
 Emily Custis Lewis Stevens (1896–1963), who died unmarried.

Stevens died in 1918, six days before his 60th birthday, in Washington, D.C., where he was serving as a shipyard inspector under appointment by President Woodrow Wilson.

References

Further reading
 First Family of Inventors History of the Stevens family
 Cox and Stevens Collection Mystic Seaport Museum
 Hoboken Museum
 The Encyclopedia of Yacht Designers, by Lucia Del Sol Knight (Editor), Daniel Bruce MacNaughton (Editor) W. W. Norton & Company 2005
 The Golden Century: Classic Motor Yachts, 1830–1930, by Ross Mactaggart, W. W. Norton & Company  2001

External links

1858 births
1918 deaths
Princeton University alumni
People from Hoboken, New Jersey
American naval architects
America's Cup yacht designers
Members of the New York Yacht Club
Chew Men Leong. Chew Men Leong is a Singaporean former two-star rear-admiral who served as Chief of Navy between 2007 and 2011.

Education
Chew received his pre-university education in Raffles Junior College and graduated in 1985. He was awarded the Singapore Armed Forces Overseas Scholarship in 1987. He graduated with a bachelor's degree (first class honours) in electrical and electronic engineering from Imperial College London in 1990. He was awarded the Singapore Armed Forces Postgraduate Scholarship in 2001 and went on to obtain a Master of Science in management from Stanford University in 2002.

Military career
Chew enlisted in the Singapore Armed Forces (SAF) in 1985. Throughout his military career, he held various appointments, including: Executive Officer, RSS Sea Lion (1992–1994); Commanding Officer, RSS Vigour (1998–2000); Commanding Officer, 188 Squadron (2000); Commander, 1st Flotilla (2001); Head, Joint Plans and Transformation Department (2002–2004); Fleet Commander (2004–2005); Head, Naval Operations Department (2006); Chief of Staff, Naval Staff (2006–2007).

Chew succeeded Ronnie Tay as the Chief of Navy on 31 August 2007. He left the SAF on 29 March 2011 and relinquished his appointment to Ng Chee Peng.

Post-military career
After retiring from the military, Chew became the Chief Executive Officer of the Public Utilities Board (PUB), Singapore's national water agency on 8 December 2011 to 30 September 2014. Subsequently, he was appointed as Chief Executive of the Land Transport Authority from 1 October 2014 to 11 November 2016 until his resignation from the public service.
He also sits on the board of Jurong Port Pte Ltd and is also a member of the Singapore Quality Award Governing Council.

Awards
 Public Administration Medal (Military) (Gold), in 2008.
 Officer, Legion of Honour, in 2011.

References

 

Living people
Singaporean people of Chinese descent
Raffles Institution alumni
Raffles Junior College alumni
Alumni of Imperial College London
Stanford University alumni
Officers of the Legion of Honour
Chiefs of the Republic of Singapore Navy
1967 births
Charing Cross (District line) tube crash. The Charing Cross (District line) tube crash occurred on 17 May 1938 at about 09:55 hours, between Charing Cross (now Embankment) and Temple stations. Six people were killed when a Circle line service ran into the rear of a District line service held at an automatic signal. A wiring error had caused the preceding signal to incorrectly display a green aspect.

Preliminary events
The track circuits connected to the signal cabin at Charing Cross had been converted to alternating current on the morning of 8 May. As a result, there was some wiring which needed to be secured. This work was carried out during the engineering hours on 17 May.

Signal fault
The signal wiring engineer had secured and reconnected all wires between the various circuit breakers in the cabin. However, one wire, which linked circuit breaker number 8 to circuit breaker number 9 had been put on the wrong terminal of circuit breaker number 9. This caused signal EH9, the eastbound starter signal, to clear even though the section ahead was occupied by a train held at automatic signal number 823.

The cabin was put into automatic mode as this was how it was normally set, but no testing was carried out, and traffic began with no observation from the engineers. Manual working was only used when a train was to be reversed at Charing Cross.

Problem reported
The problem did not appear until the line became busy. On arrival at Temple at 09:40, a motorman reported that he had nearly run into the train ahead.

The message was conveyed to Charing Cross but no action was taken despite further reports that the signal was working incorrectly. By the time it became clear that there was a significant problem, it was too late to prevent the collision.

Allocation of blame
The Ministry of Transport report held the Signal Installer and Chief Lineman responsible for the wiring error and the failure to test the signals thoroughly. The Station Foreman, Porter and Inspector were responsible for not acting promptly to prevent a collision.

Similar accident
A similar accident involving a signal wiring error had occurred near the same station on the Northern line on 10 March 1938. These wrong-side failures are extremely rare and it was a remarkable coincidence for two such failures to occur in the same year near the same station, albeit on different lines.

References
"Report to Ministry of Transport into the accident at Charing Cross on 17 May 1938", from the Railways Archive. Accessed 14 April 2008.

Disasters on the London Underground
1938 in London
Railway accidents in 1938
1938 disasters in the United Kingdom
May 1938 in the United Kingdom
Train collisions in England
Schuetze reagent. Schuetze reagent, also written as Schütze reagent, is made up of iodine pentoxide (I2O5) and sulfuric acid on granular silica gel. It is used to convert carbon monoxide (CO) into carbon dioxide (CO2) at room temperature. This can be used as a method for assaying carbon content in quality control of the production of uranium carbide fuel for nuclear reactors.

References

Oxidizing mixtures
Iodine compounds
Oxides
Acidic oxides
Hilaire de Chardonnet. Louis-Marie Hilaire Bernigaud de Grange, Count (Comte) de Chardonnet (1 May 1839 – 11 March 1924) was a French engineer and industrialist from Besançon, and inventor of artificial silk.

In the late 1870s, Chardonnet was working with Louis Pasteur on a remedy to the epidemic that was destroying French silkworms. Failure to clean up a spill in the darkroom resulted in Chardonnet's discovery of nitrocellulose as a potential replacement for real silk. Realizing the value of such a discovery, Chardonnet began to develop his new product.

He called his new invention "Chardonnet silk" (soie de Chardonnet) and displayed it in the Paris Exhibition of 1889. Unfortunately, Chardonnet's material was extremely flammable, and was subsequently replaced with other, more stable materials.

He was the first to patent artificial silk, although Georges Audemars had invented a variety called rayon in 1855.

See also 
 Cellatex

References

1839 births
1924 deaths
Businesspeople from Besançon
19th-century French engineers
19th-century French inventors
George D. Fowler. George D. Fowler (1860 – October 14, 1909) was a Pennsylvania Railroad official. He was considered an authority on golf. He was President of the American Society of Signal Engineers.

He was born in 1860 in Alexandria, Virginia.  He was closely related to George Washington and was a brother-in-law of Fitzhugh Lee.

He became president of the American Society of Signal Engineers.

He died of heart disease on October 14, 1909, at the Rittenhouse Club in Philadelphia, Pennsylvania.

References

1860 births
1909 deaths
20th-century American railroad executives
Businesspeople from Alexandria, Virginia
Businesspeople from Philadelphia
19th-century American businesspeople