William Kingdon Clifford  (4 May 18453 March 1879) was an English mathematician and philosopher. Building on the work of Hermann Grassmann, he introduced what is now termed geometric algebra, a special case of the Clifford algebra named in his honour. The operations of geometric algebra have the effect of mirroring, rotating, translating, and mapping the geometric objects that are being modelled to new positions. Clifford algebras in general and geometric algebra in particular have been of ever increasing importance to mathematical physics, geometry, and computing. Clifford was the first to suggest that gravitation might be a manifestation of an underlying geometry. In his philosophical writings he coined the expression mind-stuff.

Biography
Born at Exeter, William Clifford showed great promise at school. He went on to King's College London (at age 15) and Trinity College, Cambridge, where he was elected fellow in 1868, after being second wrangler in 1867 and second Smith's prizeman. Being second was a fate he shared with others who became famous scientists, including William Thomson (Lord Kelvin) and James Clerk Maxwell. In 1870, he was part of an expedition to Italy to observe the solar eclipse of 22 December 1870. During that voyage he survived a shipwreck along the Sicilian coast.

In 1871, he was appointed professor of mathematics and mechanics at University College London, and in 1874 became a fellow of the Royal Society.  He was also a member of the London Mathematical Society and the Metaphysical Society.

Clifford married Lucy Lane on 7 April 1875, with whom he had two children. Clifford enjoyed entertaining children and wrote a collection of fairy stories, The Little People.

Death and legacy
In 1876, Clifford suffered a breakdown, probably brought on by overwork. He taught and administered by day, and wrote by night. A half-year holiday in Algeria and Spain allowed him to resume his duties for 18 months, after which he collapsed again. He went to the island of Madeira to recover, but died there of tuberculosis after a few months, leaving a widow with two children.

Clifford and his wife are buried in London's Highgate Cemetery, near the graves of George Eliot and Herbert Spencer, just north of the grave of Karl Marx.

The academic journal Advances in Applied Clifford Algebras publishes on Clifford's legacy in kinematics and abstract algebra.

Mathematics

The discovery of non-Euclidean geometry opened new possibilities in geometry in Clifford's era. The field of intrinsic differential geometry was born, with the concept of curvature broadly applied to space itself as well as to curved lines and surfaces. Clifford was very much impressed by Bernhard Riemann's 1854 essay "On the hypotheses which lie at the bases of geometry". In 1870, he reported to the Cambridge Philosophical Society on the curved space concepts of Riemann, and included speculation on the bending of space by gravity. Clifford's translation of Riemann's paper was published in Nature in 1873. His report at Cambridge, "On the Space-Theory of Matter", was published in 1876, anticipating Albert Einstein's general relativity by 40 years. Clifford elaborated elliptic space geometry as a non-Euclidean metric space. Equidistant curves in elliptic space are now said to be Clifford parallels.

Clifford's contemporaries considered him acute and original, witty and warm. He often worked late into the night, which may have hastened his death. He published papers on a range of topics including algebraic forms and projective geometry and the textbook Elements of Dynamic. His application of graph theory to invariant theory was followed up by William Spottiswoode and Alfred Kempe.

Algebras
In 1878, Clifford published a seminal work, building on Grassmann's extensive algebra. He had succeeded in unifying the quaternions, developed by William Rowan Hamilton, with Grassmann's outer product (aka the exterior product). He understood the geometric nature of Grassmann's creation, and that the quaternions fit cleanly into the algebra Grassmann had developed. The versors in quaternions facilitate representation of rotation. Clifford laid the foundation for a geometric product, composed of the sum of the inner product and Grassmann's outer product. The geometric product was eventually formalized by the Hungarian mathematician Marcel Riesz. The inner product equips geometric algebra with a metric, fully incorporating distance and angle relationships for lines, planes, and volumes, while the outer product gives those planes and volumes vector-like properties, including a directional bias.

Combining the two brought the operation of division into play. This greatly expanded our qualitative understanding of how objects interact in space. Crucially, it also provided the means for quantitatively calculating the spatial consequences of those interactions. The resulting geometric algebra, as he called it, eventually realized the long sought goal of creating an algebra that mirrors the movements and projections of objects in 3-dimensional space.

Moreover, Clifford's algebraic schema extends to higher dimensions. The algebraic operations have the same symbolic form as they do in 2 or 3-dimensions. The importance of general Clifford algebras has grown over time, while their isomorphism classes - as real algebras - have been identified in other mathematical systems beyond simply the quaternions.

The realms of real analysis and complex analysis have been expanded through the algebra H of quaternions, thanks to its notion of a three-dimensional sphere embedded in a four-dimensional space. Quaternion versors, which inhabit this 3-sphere, provide a representation of the rotation group SO(3). Clifford noted that Hamilton's biquaternions were a tensor product  of known algebras, and proposed instead two other tensor products of H: Clifford argued that the "scalars" taken from the complex numbers C might instead be taken from split-complex numbers D or from the dual numbers N. In terms of tensor products,  produces split-biquaternions, while  forms dual quaternions. The algebra of dual quaternions is used to express screw displacement, a common mapping in kinematics.

Philosophy

As a philosopher, Clifford's name is chiefly associated with two phrases of his coining, mind-stuff and the tribal self. The former symbolizes his metaphysical conception, suggested to him by his reading of Baruch Spinoza, which Clifford (1878) defined as follows:

Regarding Clifford's concept, Sir Frederick Pollock wrote:

Tribal self, on the other hand, gives the key to Clifford's ethical view, which explains conscience and the moral law by the development in each individual of a 'self,' which prescribes the conduct conducive to the welfare of the 'tribe.' Much of Clifford's contemporary prominence was due to his attitude toward religion. Animated by an intense love of his conception of truth and devotion to public duty, he waged war on such ecclesiastical systems as seemed to him to favour obscurantism, and to put the claims of sect above those of human society. The alarm was greater, as theology was still unreconciled with Darwinism; and Clifford was regarded as a dangerous champion of the anti-spiritual tendencies then imputed to modern science. There has also been debate on the extent to which Clifford's doctrine of 'concomitance' or 'psychophysical parallelism' influenced John Hughlings Jackson's model of the nervous system and, through him, the work of Janet, Freud, Ribot, and Ey.

Ethics

In his 1877 essay, The Ethics of Belief, Clifford argues that it is immoral to believe things for which one lacks evidence. He describes a ship-owner who planned to send to sea an old and not well built ship full of passengers. The ship-owner had doubts suggested to him that the ship might not be seaworthy: "These doubts preyed upon his mind, and made him unhappy." He considered having the ship refitted even though it would be expensive. At last, "he succeeded in overcoming these melancholy reflections." He watched the ship depart, "with a light heart…and he got his insurance money when she went down in mid-ocean and told no tales."

Clifford argues that the ship-owner was guilty of the deaths of the passengers even though he sincerely believed the ship was sound: "[H]e had no right to believe on such evidence as was before him." Moreover, he contends that even in the case where the ship successfully reaches the destination, the decision remains immoral, because the morality of the choice is defined forever once the choice is made, and actual outcome, defined by blind chance, doesn't matter. The ship-owner would be no less guilty: his wrongdoing would never be discovered, but he still had no right to make that decision given the information available to him at the time.

Clifford famously concludes with what has come to be known as Clifford's principle: "it is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence."

As such, he is arguing in direct opposition to religious thinkers for whom 'blind faith' (i.e. belief in things in spite of the lack of evidence for them) was a virtue. This paper was famously attacked by pragmatist philosopher William James in his "Will to Believe" lecture. Often these two works are read and published together as touchstones for the debate over evidentialism, faith, and overbelief.

Premonition of relativity
Though Clifford never constructed a full theory of spacetime and relativity, there are some remarkable observations he made in print that foreshadowed these modern concepts:
In his book Elements of Dynamic (1878), he introduced "quasi-harmonic motion in a hyperbola". He wrote an expression for a parametrized unit hyperbola, which other authors later used as a model for relativistic velocity. Elsewhere he states:

The geometry of rotors and motors…forms the basis of the whole modern theory of the relative rest (Static) and the relative motion (Kinematic and Kinetic) of invariable systems.

This passage makes reference to biquaternions, though Clifford made these into split-biquaternions as his independent development.
The book continues with a chapter "On the bending of space", the substance of general relativity. Clifford also discussed his views in On the Space-Theory of Matter in 1876.

In 1910, William Barrett Frankland quoted the Space-Theory of Matter in his book on parallelism: "The boldness of this speculation is surely unexcelled in the history of thought. Up to the present, however, it presents the appearance of an Icarian flight." Years later, after general relativity had been advanced by Albert Einstein, various authors noted that Clifford had anticipated Einstein. Hermann Weyl (1923), for instance, mentioned Clifford as one of those who, like Bernhard Riemann, anticipated the geometric ideas of relativity.

In 1940, Eric Temple Bell published The Development of Mathematics, in which he discusses the prescience of Clifford on relativity:

Bolder even than Riemann, Clifford confessed his belief (1870) that matter is only a manifestation of curvature in a space-time manifold. This embryonic divination has been acclaimed as an anticipation of Einstein's (1915–16) relativistic theory of the gravitational field. The actual theory, however, bears but slight resemblance to Clifford's rather detailed creed. As a rule, those mathematical prophets who never descend to particulars make the top scores. Almost anyone can hit the side of a barn at forty yards with a charge of buckshot.

John Archibald Wheeler, during the 1960 International Congress for Logic, Methodology, and Philosophy of Science (CLMPS) at Stanford, introduced his geometrodynamics formulation of general relativity by crediting Clifford as the initiator.

In The Natural Philosophy of Time (1961), Gerald James Whitrow recalls Clifford's prescience, quoting him in order to describe the Friedmann–Lemaître–Robertson–Walker metric in cosmology.

Cornelius Lanczos (1970) summarizes Clifford's premonitions:

[He] with great ingenuity foresaw in a qualitative fashion that physical matter might be conceived as a curved ripple on a generally flat plane. Many of his ingenious hunches were later realized in Einstein's gravitational theory. Such speculations were automatically premature and could not lead to anything constructive without an intermediate link which demanded the extension of 3-dimensional geometry to the inclusion of time. The theory of curved spaces had to be preceded by the realization that space and time form a single four-dimensional entity.

Likewise, Banesh Hoffmann (1973) writes:

Riemann, and more specifically Clifford, conjectured that forces and matter might be local irregularities in the curvature of space, and in this they were strikingly prophetic, though for their pains they were dismissed at the time as visionaries.

In 1990, Ruth Farwell and Christopher Knee examined the record on acknowledgement of Clifford's foresight. They conclude that "it was Clifford, not Riemann, who anticipated some of the conceptual ideas of General Relativity." To explain the lack of recognition of Clifford's prescience, they point out that he was an expert in metric geometry, and "metric geometry was too challenging to orthodox epistemology to be pursued." In 1992, Farwell and Knee continued their study of Clifford and Riemann:[They] hold that once tensors had been used in the theory of general relativity, the framework existed in which a geometrical perspective in physics could be developed and allowed the challenging geometrical conceptions of Riemann and Clifford to be rediscovered.

Selected writings
 1872. On the aims and instruments of scientific thought, 524–41.
 1876 [1870]. On the Space-Theory of Matter.
 1877. "The Ethics of Belief." Contemporary Review 29:289.
 1878. Elements of Dynamic: An Introduction to the Study of Motion And Rest In Solid And Fluid Bodies.
Book I: "Translations"
Book II:  "Rotations"
Book III: "Strains"
 1878. "Applications of Grassmann's Extensive Algebra." American Journal of Mathematics 1(4):353.
 1879: Seeing and Thinking—includes four popular science lectures:
"The Eye and the Brain"
"The Eye and Seeing"
"The Brain and Thinking"
"Of Boundaries in General"
 1879. Lectures and Essays I & II, with an introduction by Sir Frederick Pollock.
 1881. "Mathematical fragments" (facsimiles).
 1882. Mathematical Papers, edited by Robert Tucker, with an introduction by Henry J. S. Smith.
 1885. The Common Sense of the Exact Sciences, completed by Karl Pearson.
 1887. Elements of Dynamic 2.

Quotations

See also
 Bessel–Clifford function
 Clifford's principle
 Clifford analysis
 Clifford gates
 Clifford bundle
 Clifford module
 Clifford number
 Motor
 Rotor
 Simplex
 Split-biquaternion
 Will to Believe Doctrine

References

Notes

Citations

Further reading

  (The on-line version lacks the article's photographs.)

  (See especially pages 78–91)
Madigan, Timothy J. (2010). W.K. Clifford and "The Ethics of Belief Cambridge Scholars Press, Cambridge, UK 978-1847-18503-7.
  (See especially Chapter 11)

External links

 William and Lucy Clifford (with pictures)

 Clifford, William Kingdon, William James, and A.J. Burger (Ed.), The Ethics of Belief.
 Joe Rooney William Kingdon Clifford, Department of Design and Innovation, the Open University, London.

1845 births
1879 deaths
19th-century deaths from tuberculosis
19th-century British philosophers
19th-century English mathematicians
English atheists
Algebraists
British relativity theorists
Alumni of Trinity College, Cambridge
Fellows of Trinity College, Cambridge
Alumni of King's College London
Academics of University College London
Fellows of the Royal Society
Burials at Highgate Cemetery
Second Wranglers
Panpsychism
Scientists from Exeter
Tuberculosis deaths in Portugal
Epistemologists

William Kingdon Clifford


Interstate 78 (I-78) is an east–west route stretching from Union Township, Lebanon County, Pennsylvania, to New York City. In New Jersey, I-78 is called the Phillipsburg–Newark Expressway and the Newark Bay–Hudson County Extension of the New Jersey Turnpike. The highway runs for  in the northern part of the state of New Jersey from the I-78 Toll Bridge over the Delaware River at the Pennsylvania state line in Phillipsburg, Warren County, east to the Holland Tunnel under the Hudson River at the New York state line in Jersey City, Hudson County. The Phillipsburg–Newark Expressway portion of I-78, formally called the Lightning Division Memorial Highway, runs from the Phillipsburg area east across rural areas of western New Jersey before entering suburban areas in Somerset County. The road crosses the Watchung Mountains, widening into a local–express lane configuration at Route 24 as it continues through urban areas to Newark. Here, I-78 intersects the mainline of the New Jersey Turnpike (I-95) and becomes the Newark Bay Extension, crossing the Newark Bay Bridge and continuing to Jersey City. The route, along with Route 139, follows a one-way pair of surface streets to the Holland Tunnel.

In 1927, Route 11 was legislated as a high-speed bypass of US Route 22 (US 22) between Whitehouse and Warren Township but was never built. The earliest parts of I-78 to be built were the Holland Tunnel in 1927 and the Newark Bay Extension. With the creation of the Interstate Highway System in the 1950s, a highway was planned along US 22 through northern New Jersey, becoming I-78 in 1958. The highway between Phillipsburg and Newark was built in various stages from the 1960s to 1989, with the final segment opening at the I-78 Toll Bridge. The section of highway through the Watchung Mountains and across Newark garnered opposition from environmentalists and residents who were worried about the effects of the highway. In addition, there was opposition to building I-78 through Phillipsburg, which resulted in the alignment to the south of the Lehigh Valley. In the 2000s, I-78 was completely rebuilt between Route 24 and the Garden State Parkway. In addition, missing movements between the parkway and I-78 were completed in 2010.

Route description

Warren and Hunterdon counties

I-78 enters New Jersey from Pennsylvania on the I-78 Toll Bridge over the Delaware River and the Belvidere and Delaware River Railway, heading into Phillipsburg, Warren County. The highway heads south into agricultural areas as a six-lane freeway that is maintained by the Delaware River Joint Toll Bridge Commission (DRJTBC), entering Pohatcong Township a short distance after the river. The freeway makes a turn to the east as it briefly passes through a corner of Alpha before coming back into Pohatcong Township. Bypassing the center of Alpha to the south, I-78 passes under Norfolk Southern Railway's Lehigh Line and has two more segments that enter the Alpha borough limits before coming to an interchange with US 22 and the western terminus of Route 173. At this point, US 22 forms a concurrency with I-78 and the road comes into Greenwich Township. At this point, the New Jersey Department of Transportation (NJDOT) takes over maintenance of the road. I-78/US 22 continue east through Greenwich Township, coming to a westbound exit and eastbound entrance with County Route 637 (CR 637). The road turns southeast and has an eastbound exit and westbound entrance with CR 632 in Franklin Township. Within the ramps for this interchange, there are weigh stations in both directions.

A short distance after this interchange, I-78/US 22 crosses the Musconetcong River into Bloomsbury, Hunterdon County. In Bloomsbury, the road has an interchange with Route 173. After this interchange, the freeway enters Bethlehem Township, with Route 173 closely running to the north of I-78/ US22. The road comes to a bridge over Norfolk Southern Railway's Central Running Track line and has rest areas in both directions before it passes over Norfolk Southern Railway's Lehigh Line and turns southeast to cross Musconetcong Mountain. As the freeway crosses Jugtown Mountain, there is an automatic deicing spray, the first such to be installed in New Jersey.

The freeway turns east again and enters Union Township, coming to an interchange with CR 614 and Route 173. From here, I-78/US 22 continue east directly to the south of Route 173, coming to another interchange with that route as well as CR 625. Entering more commercial areas, Route 173 merges onto I-78/US 22 at exit 13. At exit 15, the highway interchanges with CR 513, and Route 173 splits from I-78/US 22 by heading north on CR 513. At this point, the freeway enters Franklin Township briefly at exit 15 and then enters Clinton where it crosses the South Branch Raritan River. I-78/US 22 turns northeast and leaves Clinton for Clinton Township, where it has an eastbound exit and westbound entrance for Route 173 that also provides access to Route 31. Immediately after is the interchange with Route 31. At the next interchange near the community of Annandale, US 22 splits from I-78 onto a four-lane surface highway, heading closely to the south of that route.

Immediately after the split, I-78 passes over NJ Transit's Raritan Valley Line and runs through rural areas with increasing suburban development. The freeway runs through Lebanon, where an exit for CR 639 provides access to the town and the Round Valley Recreation Area. After running through Clinton Township again and into Readington Township, US 22 turns southeast while I-78 continues a due east course. In Tewksbury Township, there is an interchange with CR 523 that also provides access to CR 517. After this exit, the highway crosses back into Readington Township.

Somerset and Union counties

After crossing the Lamington River, I-78 comes into Bedminster, Somerset County, continuing east through more woods and farms with some suburban residential areas. Upon entering Somerset County, there is an exit for CR 665 (signed as CR 523 Spur). The next interchange, exit 29, is called the Vincent R. Kramer Interchange. It is at I-287, which serves as a bypass around New York City. At this point, I-78 carries four eastbound lanes and three westbound lanes as the median widens. The road enters wooded suburban areas and crosses Second Watchung Mountain, running through a corner of Bridgewater Township, where there is a westbound scenic overlook, before coming into Bernards Township. The eastbound direction narrows back to three lanes before the interchange with CR 525, at which point the freeway crosses into Warren Township. The road heads east along the southern bank of the Dead River, coming to exit 36 for CR 651. I-78 heads farther south of the Dead River as it comes to the CR 531 interchange. Past CR 531, the highway turns to the northeast and comes to an interchange with Drift Road/Dale Road that provides access to US 22. At this point, I-78 runs across Second Watchung Mountain again into Watchung.

The freeway crosses Green Brook into Berkeley Heights, Union County, reaching exits for CR 655 and CR 640. The latter is an eastbound exit and entrance that also provides access to parallel CR 527. At this point, I-78 runs between Second Watchung Mountain to the northwest and the Watchung Reservation to the southeast. Along the reservation border, the road passes under Nikesite Road before coming into Summit, where there is an overpass that serves as a wildlife crossing. There is an eastbound exit and westbound entrance with CR 527 as it heads away from the Watchung Reservation and into more suburban surroundings. It briefly forming the border between Summit to the northwest and Mountainside to the southeast  before coming into Springfield Township. The freeway passes near First Watchung Mountain before coming to the Route 24 interchange, where suburban development becomes more dense.

At Route 24, I-78 divides into local–express lanes, with three express and three local lanes eastbound and two express and three local lanes westbound. In this section of the highway, most access is via the local lanes, though the next exit for Route 124 includes a direct westbound onramp to the express lanes. Before Route 124, I-78 briefly runs east through Millburn in Essex County and Springfield Township again before entering Union Township at the interchange. Past Route 124, I-78 carries a 3-2-2-3–lane configuration and comes to partial interchanges with CR 630 and CR 633. The next interchange along the highway provides access to the Garden State Parkway along the border of Union Township and Hillside. The road turns northeast again into Hillside, heading into more urbanized settings. In Hillside, I-78 passes under Conrail Shared Assets Operations' (CSAO) Irvington Industrial Track line and has an eastbound exit and westbound entrance to Winans Avenue.

Essex and Hudson counties

I-78 briefly passes through a corner of Irvington in Essex County before continuing into Newark. Upon entering Newark, the road has an interchange serving CR 602 and Wainwright Street. Following this, the freeway passes near urban neighborhoods before coming to exit 56. This large semi-directional T interchange was originally meant to serve the unbuilt Route 75, which would have connected to I-280. The large flyover ramps constructed were converted to exit ramps to Irvine Turner Boulevard with full access to the local and express lanes. Past this, the roadway passes over CSAO's Lehigh Line (which also carries NJ Transit's Raritan Valley Line), Route 27, and Amtrak's Northeast Corridor. The final interchange on the free part of I-78 is the massive complex to the north of the Newark Liberty International Airport, called the Newark Airport Interchange, with ramps to and from US 1/9, US 22, Route 21, and many local roads. Several ramps provide access to the express lanes. Just to the east, the local and express lanes rejoin at the toll gate for the New Jersey Turnpike, at which point I-78 becomes maintained by the New Jersey Turnpike Authority (NJTA), following the Newark Bay Extension of the New Jersey Turnpike. An interchange just beyond the toll booth provides full access to I-95, the mainline of the New Jersey Turnpike. I-78 here becomes a four-lane highway, heading over the New Jersey Turnpike and CSAO's Chemical Coast Secondary and Corbin Street Lead lines before passing by the Port Newark–Elizabeth Marine Terminal.

I-78 crosses the Newark Bay on the Newark Bay Bridge into Bayonne, Hudson County. As it enters Jersey City, exit 14A, numbered as part of the New Jersey Turnpike, provides access to Route 440. Within this interchange, the road passes over CSAO's Bayonne Industrial Track and Greenville Industrial Track lines. From here, the freeway turns northeast on an elevated alignment and passes industrial areas of Jersey City, with CSAO's National Docks Branch line parallel to the northwest. The next interchange, exit 14B, is for Bayview Avenue and provides access to Liberty State Park. After this interchange, I-78 comes to exit 14C, the number given to the toll plaza at the end of the turnpike extension. After the toll plaza, there is an exit for a park and ride lot at the Liberty State Park station along NJ Transit's Hudson–Bergen Light Rail line. Continuing north, the road passes over the Hudson–Bergen Light Rail line before there is an exit for Columbus Drive and Montgomery Street. Past this interchange, the highway crosses PATH's Newark–World Trade Center line. I-78 heads down to surface level and passes over CSAO's National Docks Branch line twice before it merges with the Route 139 freeway.

From here, I-78 and Route 139 pass through business areas as a one-way pair that follows six-lane 12th Street eastbound and six-lane 14th Street westbound. This segment of the route is under the jurisdiction of the Port Authority of New York and New Jersey (PANYNJ) and is also known as Boyle Plaza. It runs on surface streets with traffic lights, an example of a non–limited-access section of Interstate Highway. The first intersection is with Jersey Avenue, which heads to Downtown Jersey City and Hoboken. It intersects with the one-way northbound CR 633 (Erie Street) next before crossing one-way southbound CR 635 (Grove Street). After Grove Street, the road crosses CR 637 (Luis Muñoz Marín Boulevard) near Newport Centre just to the south. Past this intersection, the eastbound direction comes to the toll plaza for the Holland Tunnel. From here, the concurrency enters the Holland Tunnel under the Hudson River, which carries two lanes in each direction. Route 139 ends at the New Jersey–New York state line within the tunnel and I-78 continues into the New York City borough of Manhattan.

History

The oldest section of I-78, the Holland Tunnel, was built in September 1927. The tunnel pre-dated the Interstate Highway System, as a commuter route linking Jersey City, New Jersey and Lower Manhattan. Six months after it was opened, 3.66 million passengers had used the tunnel. In 1927, Route 11 had legislatively approved as a high-speed bypass of US 22, running from Route 28 in Whitehouse east to Route 29 in Warren Township, roughly following the alignment of present-day I-78; it was never built.

The Newark Bay Extension of the New Jersey Turnpike was the first limited-access section of I-78 to be built in the state of New Jersey. The  long expressway was opened in 1956 to provide access from the New Jersey Turnpike mainline to the Holland Tunnel. At this time, the Interstate Highway System was established and a route was planned to run east–west from the Harrisburg, Pennsylvania, area to New York City, running across the northern part of New Jersey from Phillipsburg to Jersey City along the US 22 corridor. This freeway was originally planned as FAI Corridor 102 and I-80 before it became I-78 in 1958.

The part of I-78 between exit 3 and exit 13 opened in the 1960s; this segment runs concurrent with US 22 with the old alignment of US 22 becoming Route 173. In building the road between CR 614 and exit 13, the eastbound lanes of US 22 became westbound I-78 and the westbound lanes of US 22 became the Route 173 frontage road. By 1969, I-78 had also been completed between exit 13 and CR 525. In July 1963, New Jersey Governor Richard J. Hughes approved a plan to build I-78 through the city of Newark at a cost of $205 million (equivalent to $ in ). This plan had been opposed by several communities along the route. The section of I-78 between Route 24 and the New Jersey Turnpike was completed in the mid-1970s. Along this stretch, exit 56 was to connect to the proposed Route 75 freeway, which was never built.

The section of freeway between CR 525 and Drift Road (exit 41) in Watchung was completed in 1974. The section from Drift Road to Route 24 (exit 48) in Springfield Township was delayed because of environmental impacts to the Watchung Reservation. In order to mitigate opposition to the original plan, that was shifted closer to the northern edge of the Reservation, which required extensive cuts into the Second Watchung Mountain. Extra land was added to the Nikesite Road overpass and a separate elevated wildlife crossing was built to allow for animal migration. The road was also designed to use a narrower right-of-way with no median strip and just a Jersey barrier dividing the highway, to minimize the amount of rock to be removed. This stretch of I-78 opened in 1986.

A section of I-78 in Newark was closed off in August 1989 when a debris pile under a bridge caught fire and damaged the elevated highway. The road was opened nine days after the fire occurred. The westernmost section of I-78 in New Jersey opened in November 1989 after a more northerly alignment along present day US 22 through Phillipsburg was rejected due to community opposition. This led to I-78 being rerouted to the south of the Lehigh Valley in Pennsylvania and New Jersey. The additional length of roadway that resulted from this rerouting is the reason exit numbers 3 through 52 (which were assigned before this westernmost section opened) are mismatched by approximately  when compared to their corresponding milemarker.

I-78, like many other highways in New Jersey, once had solar powered emergency callboxes every , however, with the advent of cellphones, the usage of these callboxes became extremely limited. To save on maintenance costs, the NJDOT removed these call boxes in 2005.

From 2006 to 2007, the highway between Route 24 (exit 48) and the Garden State Parkway (exit 52) was rebuilt. This included redecking of bridge decks and covering the deteriorated concrete pavement with an asphalt overlay. Exit 52 was reconstructed due to missing ramps from the Garden State Parkway and I-78 since the I-278 connection was canceled. Construction began in June 2008, with the ramp from the northbound Garden State Parkway to westbound I-78 being completed in September 2009. The connection between the southbound Garden State Parkway and eastbound I-78 was completed in December 2010. In 2012–2013, the deteriorating concrete surface of I-78 between the Garden State Parkway (exit 52) and US 1/9 and US 22 (exit 57) was resurfaced with an asphalt overlay; this had been the last section of I-78 within New Jersey that was still concrete.

In the early 2020s, the NJTA announced plans to widen its section of I-78, between I-95 and Jersey City, from four to six lanes. Preliminary studies for the project began in 2021; at the time, the project was slated to begin in 2023 and be complete in 2026. The project faced significant opposition from residents of neighboring communities. The project, originally budgeted at $4.7 billion, had increased to $10.6 billion by late 2022.

Exit list

See also

References

External links

I-78 in New Jersey Exits
Photos of Interstate 78 at New Jersey Roads
Speed Limits for New Jersey State Roads: Interstate 78
A history of the building of I-78 in NJ
I-78 (Greater New York Roads)

 New Jersey
78
Transportation in Warren County, New Jersey
Transportation in Hunterdon County, New Jersey
Transportation in Somerset County, New Jersey
Transportation in Union County, New Jersey
Transportation in Essex County, New Jersey
Transportation in Hudson County, New Jersey
New Jersey Turnpike
Holland Tunnel

Interstate 78 in New Jersey


Lee Joseph Bracegirdle is an Australian-American composer, horn player and conductor.

He was born in Houston, Texas, US, and grew up in Bucks County, near Philadelphia, Pennsylvania.  He resides in Sydney, Australia and his compositions are published by C.F. Peters.

After studies in French horn at the Philadelphia Musical Academy with Joseph DeAngelis, he studied at the Juilliard School with James Chambers and John Cerminaro, and privately with Carmine Caruso and Roy Stevens.

In New York he free-lanced with the New York City Symphony Orchestra, the Brooklyn Philharmonia, and with jazz musicians Clark Terry, Ornette Coleman, Stanley Clark, Teo Macera and Dave Brubeck.

His principal horn positions included México's Orquesta Filarmónica de la UNAM (OFUNAM), the Chamber Orchestra of México City, and the Hof Symphony Orchestra (Hofer Symphoniker) (1977–1980), where he co-founded the quintet Rekkenze Brass. In 1980 he became Associate Principal Horn with the Sydney Symphony Orchestra, where he worked until his retirement in 2012. His recordings made through the Australian Broadcasting Corporation include the sonatas of Paul Hindemith. In 1981 he co-founded the Australian Brass Quintet.

He wrote and edited horn etudes for the International Music Company and 3-C Musikverlag, and has hosted master classes at the Salzburg Mozarteum, the Juilliard School, the Curtis Institute, the University of Illinois, the Chopin University of Music (Warsaw), and the Conservatorio Esteban Salas (Santiago de Cuba).

He studied conducting with Michael Gielen and Jorge Rotter at the Salzburg Mozarteum, and made his conducting debut in 1991 with the Orchestra of the Mozarteum.  Since 1996 he has been Musical Director and Composer-in-Residence of the Australian Chamber Ballet.

He began composing orchestral music in the late 1990s, many of his works being commissioned by the Sydney Symphony Orchestra and the American Wind Symphony Orchestra. He holds an honorary diploma from the Kodaly Academy in Chicago, and has been composer-in-Residence at Bundanon (Australia) and the Brahmshaus (Baden-Baden).

Major compositions:
 Divertimento for Orchestra (1998)
 Variations for Orchestra (2000), (C.F. Peters, catalogue #EP68263R)
 Eat Pianist (ballet) (2002)
 Prometheus and Pandora (ballet) (2003)
 Ammerseelieder (2005), (C.F. Peters, catalogue #EP68264R)
 Threnos (2007), (C.F. Peters, catalogue #EP68187)
 Euphonium Concerto (2007), (C.F. Peters, catalogue #EP68262-S)
 Landscape Visions (2010)
 Passacaglia and Gigues (2011)
 Legends of the Old Castle (2012), (C.F. Peters, catalogue #EP68414R)
 Violin Concerto (2012)
 Shoalhaven-Lieder (2015)
 ''Triptych for saxophone and orchestra (2017)

References

1952 births
Living people
American jazz composers
American classical horn players
Musicians from Houston
University of the Arts (Philadelphia) alumni
Juilliard School alumni
American jazz horn players
Jazz musicians from Texas
Classical musicians from Texas
American male jazz composers

Lee Bracegirdle


Each winner of the 1966 Governor General's Awards for Literary Merit was selected by a panel of judges administered by the Canada Council for the Arts.

Winners

English Language
Fiction: Margaret Laurence, A Jest of God
Poetry or Drama: Margaret Atwood, The Circle Game
Non-Fiction: George Woodcock, The Crystal Spirit: A Study of George Orwell

French Language
Fiction: Claire Martin, La joue droite.
Poetry or Drama: Réjean Ducharme, L'avalée des avalés.
Non-Fiction: Marcel Trudel, Le comptoir, 1604–1627.

Governor General's Awards
Governor General's Awards
Governor General's Awards

1966 Governor General's Awards


Bosra (), formerly Bostra () and officially called Busra al-Sham (), is a town in southern Syria, administratively belonging to the Daraa District of the Daraa Governorate and geographically part of the Hauran region.

According to the Syria Central Bureau of Statistics (CBS), Bosra had a population of 19,683 in the 2004 census. It is the administrative center of the nahiyah ("subdistrict") of Bosra which consisted of nine localities with a collective population of 33,839 in 2004. Bosra's inhabitants are predominantly Sunni Muslim, although the town has a small Shia Muslim community.

Bosra has an ancient history and during the Roman era it was a prosperous provincial capital and Metropolitan Archbishopric, under the jurisdiction of Eastern Orthodox Patriarchate of Antioch and All the East. It continued to be administratively important during the Islamic era, but became gradually less prominent during the Ottoman era. It also became a Latin Catholic titular see and the episcopal see of a Melkite Catholic Archeparchy. Today, it is a major archaeological site and has been declared by UNESCO as a World Heritage Site.

History

Bosra was the first Nabatean city in the 2nd century BC. The Nabatean Kingdom was conquered by Cornelius Palma, a general of Trajan, in 106 AD.

According to John Malalas, it was called Bostra () after Bostras, a Roman general who was sent into the country.

Roman and Byzantine era

Under the Roman Empire Bosra was renamed Nova Trajana Bostra and was the residence of the legio III Cyrenaica. It was made capital of the Roman province of Arabia Petraea. The city flourished and became a major metropolis at the juncture of several trade routes, in particular the Via Traiana Nova, a Roman road that connected Damascus to the Red Sea. It became an important centre for food production and during the reign of Emperor Philip the Arab Bosra began to mint its own coins. The two Councils of Arabia were held at Bosra in 246 and 247 AD.

By the Byzantine period, which began in the 5th century, Christianity became the dominant religion in Bosra (Βόσρα in Greek-Byzantine). The city became a Metropolitan archbishop's seat (see below) and a large cathedral was built in the 6th century. Bosra was conquered by the Sasanian Persians in the early 7th century but was recaptured during the Byzantine reconquest.

Islamic era
Bosra played an important part in the early life of Muhammad, as described in the entry for the Christian monk Bahira.  The forces of the Rashidun Caliphate under general Khalid ibn Walid captured the city from the Byzantines in the Battle of Bosra in 634. Throughout Islamic rule, Bosra would serve as the southernmost outpost of Damascus, its prosperity being mostly contingent on the political importance of that city. Bosra held additional significance as a center of the pilgrim caravan between Damascus and the Muslim holy cities of Mecca and Medina, the destinations of the annual hajj pilgrimage. Early Islamic rule did not alter the general architecture of Bosra, with only two structures dating to the Umayyad era (721 and 746) when Damascus was the capital of the Caliphate. As Bosra's inhabitants gradually converted to Islam the Roman-era holy sites were utilized for Muslim practices. In the 9th-century Ya'qubi wrote that Bosra was the capital of the Hauran province.

After the end of the Umayyad era in 750, major activity in Bosra ceased for around 300 years until the late 11th-century. In the last years of Fatimid rule, in 1068, a number of building projects were commissioned. With the advent of Seljuk rule in 1076, increasing focus was paid to Bosra's defenses. In particular, the Roman theater was transformed into a fortress, with a new floor added to the interior staircase tower. With the coming to power of the Burid dynasty in Damascus, the general Kumushtakin was allotted the entire Hauran plain as a fief by the atabeg Tughtakin. Under Kumushtakin, efforts to enhance the Muslim nature of the city increased with the construction of a number of Islamic edifices. Of these projects was the restoration of the Umari Mosque, which had been built by the Umayyads in 721. Another mosque commissioned was the smaller al-Khidr Mosque built at the northwestern part of the city, which was established under Kumushtakin, in 1134. Kumushtakin also had a madrasa constructed alongside the Muslim shrine honoring the mabrak an-naqa ("camel's knees"), which marked the imprints of the camel the prophet Muhammad rode on when he entered Bosra in the early 7th-century. In 1147, King Baldwin III of Jerusalem led a Crusader force to capture the city, however, his attempt was thwarted, as the Damascene army led by Mu'in ad-Din Unur managed to garrison into Bosra's citadel.

A golden age of political and architectural activity in Bosra began during the reign of Ayyubid sultan al-Adil I (1196–1218). One of the first architectural developments in the city was the construction of eight large external towers in the Roman theater-turned-fortress. The project began in 1202 and were completed in 1253, towards the end of the Ayyubid period. The two northern corner towers alone occupied more space than the remaining six. After al-Adil's death in 1218, his son as-Salih Ismail inherited the fief of Bosra who resided in its newly fortified citadel. During Ismail's rule, Bosra gained political prominence. Ismail used the city as his base when he claimed the sultanate in Damascus on two separate occasions, reigning between 1237–38 and 1239–45.

Ottoman era
In 1596 Bosra appeared in the Ottoman tax registers as Nafs Busra, being part of the nahiyah of Bani Nasiyya in the Qada of Hauran. It had a Muslim population consisting of 75 households and 27 bachelors, and a Christian population of 15 households and 8 bachelors. Taxes were paid on wheat, barley, summer crops, fruit- or other trees,  goats and/or beehives and water mill.

Modern era
Today, Bosra is a major archaeological site, containing ruins from Roman, Byzantine, and Muslim times, its main feature being the well preserved Roman theatre. Every year there is a national music festival hosted in the main theatre.

Significant social and economic changes have affected Bosra since the end of the French Mandate in 1946. While up until the 1950s the shopkeepers of Bosra were from Damascus, since then most shop owners are residents of the town. In the late Ottoman era and the French Mandate period, the agricultural relationship was between the small landowner and the sharecroppers, since agrarian reforms in the late 1950s and 1960s, the relevant relationship has been between the landowners and the wage laborers. Many of its residents have found work in the Gulf Cooperation Council states, sending proceeds to their relatives in Bosra. Social changes together with increased access to education have largely diminished the traditional clan life according to historian Hanna Batatu.

During the presidency of Hafez al-Assad (1970–2000), Bosra and the surrounding villages were left largely outside of government interference and, for the most part, were politically dominated by members of the prominent al-Mokdad clan who served as intermediaries of sorts between the residents of the town and the governor of Daraa and the Ba'ath Party branch secretary.

On October 14, 2012, there was intense gunfire from government forces stationed at checkpoints on the main road running through the town. On 13 November 2012, fierce fighting was reported in the east side of the town. By January 2013, after 22 months of conflict amid the ongoing Syrian Civil War, some refugees fleeing Bosra spoke of ever-escalating violence with many bodies being left in the streets during the violence. On 15 January 2013, it was reported that the citadel was used by the army to shell the town on a daily basis. Since the beginning of February 2014 the city was under the control of the Syrian Army. However, on 31 January 2015, the Army's 5th Division confronted a contingent from the rebels near the famous Roman theater – fierce firefights broke out between the groups. On 1 February 2015, the Army forces shelled areas in the eastern neighborhood of the town. On 25 March 2015, Syrian rebels seized the town, ousting Syrian soldiers and allied militiamen after four days of intense battle.

Bosra was recaptured by the Syrian Arab Army on 2 July 2018, following the surrender of the rebel forces. The recapture was a part of the Daraa Offensive, which has involved the surrender and/or reconciliation of many rebel groups in the area.

Main sights

Of the city which once counted 80,000 inhabitants, there remains today only a village settled among the ruins. The 2nd century Roman theater, constructed probably under Trajan, is the only monument of this type with its upper gallery in the form of a covered portico which has been integrally preserved. It was fortified between 481 and 1231.

Further, Nabatean and Roman monuments, Christian churches, mosques and Madrasahs are present within the half-ruined enceinte of the city. The structure of the cathedral, a central plan with eastern apses flanked by 2 sacristies, exerted a decisive influence on the evolution of Christian architectural forms, and to a certain extent on Islamic style. Al-Omari Mosque of Bosra is one of the oldest surviving mosques in Islamic history.

Close by are the Kharaba Bridge and the Gemarrin Bridge, both Roman bridges.

Climate
Bosra has a cold semi-arid climate (Köppen climate classification BSk). Rainfall is higher in winter than in summer. The average annual temperature in Bosra is . About  of precipitation falls annually.

Demographics
In the late 1990s, Bosra had an estimated population of 12,000. Its population increased to 19,683 according to the 2004 census by the Syria Central Bureau of Statistics. The population of its metropolitan area was 33,839.

Bosra's inhabitants are predominantly Sunni Muslims and are mostly divided between eight major clans. The leading clan is the al-Mokdad, said to be descended from Prophet Muhammad's companion Miqdad ibn Aswad. The clan interestingly has many members of which have blond hair and blue eyes. However, the oldest clan of Bosra are the Hamd,  They claim to be descendants of the ancient Roman governor of Bosra, although other townspeople believe they are of Crusader and Jewish origins. Regarding land ownership, the Hamd clan owns around 1,000 hectares in the town while the al-Mokdad clan owns roughly 12,000. The latter's members were historically influential in the Hauran region and beyond, having had one of their own in the Ottoman parliament of Abdul Hamid II in Constantinople during the Young Turks period and in the Syrian parliament during the French Mandate period. As of the late 1990s, members of the al-Miqdad clan occupied the positions of mayor, the chief imam of the main al-Omari Mosque, the chief of the town's bureau of antiquities as well as manager of Bosra's carpet workshop and the owner of the principal coffeehouse. While their members traditionally resided in the eastern quarter of old Bosra, they are currently prevalent throughout the town.

Bosra also has a small Shia Muslim community of some fifty families. According to Palestinian American historian Hanna Batatu, the Shia inhabitants of Bosra were "relatively recent arrivals," and immigrated to the town from the city of Nabatieh in South Lebanon. Most of the working members of the Shia community are artisans or laborers. Batatu also asserts that social changes in Bosra since Syrian independence have led to tribal diffusion, with intermarriage between the clans and between the Sunni and Shia communities having increased significantly.

People
 Saint Timon the Deacon, 1st century, Christian proto-deacon and bishop of Bosra
 Beryllus of Bostra, 3rd century, Bishop
 Shimon ben Lakish, 3rd century, amora of the second generation and rabbi
 Titus of Bostra, fl. 4th century, Christian theologian
 Saint Antipater of Bostra, fl. 5th century, Christian bishop
 Bahira, c. 600, Assyrian monk
 Ibn Kathir (1301–1373), Islamic scholar

References

Sources

External links

 Catholic Encyclopedia on Bosra
 Official website of Bosra city
 Extensive photo site about Bosra
 Photo Gallery of Bosra
 GCatholic Latin titular see
  Map of the town, Google Maps
  Bosra-map; 22M
 Eastern Orthodox Archdiocese of Bosra, Horan and Jabal al-Arab
 Brief History of the Archdiocese of Bosra-Hauran

Cities in Syria
Nabataea
Populated places in Daraa District
Shia Muslim communities in Syria
Archaeological sites in Daraa Governorate
World Heritage Sites in Danger
Nabataean architecture

Bosra


A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. These compressors are common in industrial applications and replace more traditional piston compressors where larger volumes of compressed gas are needed, e.g. for large refrigeration cycles such as chillers, or for compressed air systems to operate air-driven tools such as jackhammers and impact wrenches. For smaller rotor sizes the inherent leakage in the rotors becomes much more significant, leading to this type of mechanism being less suitable for smaller compressors than piston compressors.

The screw compressor is identical to the screw pump except that the pockets of trapped material get progressively smaller along the screw, thus compressing the material held within the pockets. Thus the screw of a screw compressor is asymmetrical along its length, while a screw pump is symmetrical all the way.

The gas compression process of a rotary screw is a continuous sweeping motion, so there is very little pulsation or surging of flow, as occurs with piston compressors. This also allows screw compressors to be significantly quieter and produce much less vibration than piston compressors, even at large sizes, and produces some benefits in efficiency.

Working

Rotary-screw compressors use two very closely meshing spiral rotors to compress the gas. In a dry-running rotary-screw compressor, timing gears ensure that the male and female rotors maintain precise alignment without contact which would produce rapid wear.  In an oil-flooded rotary-screw compressor, lubricating oil bridges the space between the rotors, both providing a hydraulic seal and transferring mechanical energy between the rotors, allowing one rotor to be entirely driven by the other.

Gas enters at the suction side and moves through the threads as the screws rotate.  The meshing rotors force the gas through the compressor, and the gas exits at the end of the screws. The working area is the inter-lobe volume between the male and female rotors. It is larger at the intake end, and decreases along the length of the rotors until the exhaust port. This change in volume is the compression.

The intake charge is drawn in at the end of the rotors in the large clearance between the male and female lobes. At the intake end the male lobe is much smaller than its female counterpart, but the relative sizes reverse proportions along the lengths of both rotors (the male becomes larger and the female smaller) until (tangential to the discharge port) the clearance space between each pair of lobes is much smaller. This reduction in volume causes compression of the charge before being presented to the output manifold.

The effectiveness of this mechanism is dependent on precisely fitting clearances between the spiral rotors and between the rotors and the chamber for sealing of the compression cavities. However, some leakage is inevitable, and high rotational speeds must be used to minimize the ratio of leakage flow rate over effective flow rate.

In contrast to Roots blowers, modern screw compressors are made with different profiles on the two rotors: the male rotor has convex lobes which mesh with the concave cavities of the female rotor. Usually the male rotor has fewer lobes than the female rotor, so that it rotates faster. Originally, screw compressors were made with symmetrical rotor cavity profiles, but modern versions use asymmetrical rotors, with the exact rotor designs being the subject of patents.

Size

The capacities of rotary-screw compressors are typically rated in horsepower (HP), Standard Cubic Feet per Minute (SCFM)* and pounds per square inch gauge (PSIG.)  For units in the 5 through 30 HP range the physical size of these units are comparable to a typical two-stage compressor.  As horsepower increases, there is a substantial economy of scale in favor of the rotary-screw compressors.  As an example, a 250 HP compound compressor is a large piece of equipment that generally requires a special foundation, building accommodations and highly trained riggers to place the equipment.  On the other hand, a 250 HP rotary-screw compressor can be placed on an ordinary shop floor using a standard forklift.  Within industry, a 250 HP rotary-screw compressor is generally considered to be a compact piece of equipment.

Rotary-screw compressors are commonly available in the 5 through 500 HP range and can produce air flows in excess of 2500 SCFM. While the pressure produced by a single-stage screw compressor is limited to 250 PSIG, a two-stage screw compressor can deliver pressures of up to 600 PSIG.

Rotary-screw compressors tend to be smooth running with limited vibration, thus not requiring a specialized foundation or mounting system. Normally, rotary-screw compressors are mounted using standard rubber isolation mounts designed to absorb high-frequency vibrations.  This is especially true in rotary-screw compressors that operate at high rotational speeds.

*To a lesser extent, some compressors are rated in Actual Cubic Feet per Minute (ACFM).  Still others are rated in Cubic Feet per Minute (CFM). Using CFM to rate a compressor is incorrect because it represents a flow rate that is independent of a pressure reference.  i.e. 20 CFM at 60 PSI.

History
The screw compressor was first patented in 1878 by Heinrich Krigar in Germany, however the patent expired without a working machine being built.

The modern helical lobe screw compressor was developed in Sweden by Alf Lysholm who was the chief engineer at Ljungstroms Angturbin. Lysholm developed the screw compressor while looking for a way to overcome compressor surge in gas turbines. Lysholm first considered a roots type blower but found this was unable to generate a high enough pressure ratio. In 1935, Ljungstroms patented a helical lobe screw compressor which was then widely licensed to other manufacturers. Ljungstroms Angturbin AB was renamed Svenska Rotor Maskiner (SRM) in 1951.

In 1952, the first Holroyd cutting machine was used, by the Scottish engineering company Howden, to produce helical lobe compressor rotors greatly reducing both cost and manufacturing time.

In 1954, Howden and SRM jointly developed the first oil flooded screw compressor.  Flooding provided both cooling, which allowed higher pressure ratios, and the elimination of timing gears.  The first commercially available flooded screw air compressor was introduced in 1957 by Atlas Copco.

Slot valves were developed by SRM in the 1950s, allowing for improvements in capacity control which had been a limiting factor for screw compressor application.

Asymmetric rotors were first patented by SRM and subsequently introduced commercially by Sullair in 1969.  The introduction of asymmetric rotors improved sealing, further increasing the types efficiency.

Applications
Rotary-screw compressors are generally used to supply compressed air for larger industrial applications.  They are best applied in applications that have a continuous air demand such as food packaging plants and automated manufacturing systems although a large enough number of intermittent demands, along with some storage, will also present a suitably continuous load. In addition to fixed units, rotary-screw compressors are commonly mounted on tow-behind trailers and powered with small diesel engines.  These portable compression systems are typically referred to as construction compressors.  Construction compressors are used to provide compressed air to jack hammers, riveting tools, pneumatic pumps, sand blasting operations and industrial paint systems. They are commonly seen at construction sites and on duty with road repair crews throughout the world.

Screw air compressors are also commonly used on Rotary, DTH and RC drill rigs used in mining production and exploration drilling applications and in oil and gas pipeline services such as pneumatic testing or air pigging.

Oil-free
In an oil-free compressor, the air is compressed entirely through the action of the screws, without the assistance of an oil seal.  They usually have lower maximal discharge pressure capability as a result. However, multi-stage oil-free compressors, where the air is compressed by several sets of screws, can achieve pressures of over  and output volume of over .

Oil-free compressors are used in applications where entrained oil carry-over is not acceptable, such as medical research and semiconductor manufacturing.  However, this does not preclude the need for filtration, as hydrocarbons and other contaminants ingested from the ambient air must also be removed prior to the point of use.  Consequently, air treatment identical to that used for an oil-flooded screw compressor is frequently required to ensure quality compressed air.

In small piston compressors carpenters homeowners sometimes use "oil free" compressors in which oil free is a reference to not using oil but Teflon type of coatings permanently adhered to wear surfaces.

Oil-injected

In an oil-injected rotary-screw compressor, oil is injected into the compression cavities to aid sealing and provide cooling for the gas charge. The oil is separated from the discharge stream, cooled, filtered and recycled. The oil captures non-polar particulates from the incoming air, effectively reducing the particle loading of compressed-air particulate filtration. It is usual for some entrained compressor oil to carry into the compressed-gas stream downstream of the compressor. In many applications, this is rectified by coalescer/filter vessels. Refrigerated compressed air dryers with internal cold coalescing filters are rated to remove more oil and water than coalescing filters that are downstream of air dryers, because after the air is cooled and the moisture is removed, the cold air is used to pre-cool the hot entering air, which warms the exiting air. In other applications, this is rectified by the use of receiver tanks that reduce the local velocity of compressed air, allowing oil to condense, drop out of the air stream, and to be removed from the compressed-air system by condensate-management equipment.

Oil flooded screw compressors are used in a wide variety of applications including air compression, gas refrigeration, hydrocarbon processing and power utilization from low-grade heat sources. Sizes range from small workshop air compressors to  heavy industrial compressors with output pressures as high as . New oil flooded screw air compressors release <5 mg/m3 of oil carryover.

Lubricants, polyalkylene glycol (PAG), polyalphaolefin (PAO), mineral oils
PAG oil is polyalkylene glycol which is also called polyglycol. PAG oil burns off cleanly, leaving no residue, and have been used as a carrier oil for solid lubricants for high-temperature chain lubrication. Some versions are food grade and biodegradable. PAG lubricants are used by the two largest U.S. air compressor OEMs in rotary screw air compressors. PAG oil-injected compressors are not used to spray paint, because PAG oil dissolve paints. Reaction-hardening two-component epoxy resin paints are resistant to PAG oil.

Polyglycols are not compatible with mineral oil based greases. A mixture of polyglycols with mineral oils results is a gelatinous, gooey mess. Silicon grease does tolerate Polyglycols. One pneumatic controls manufacturer puts silicon grease on the seals and gaskets.

Mineral oil (but not polyalkylene glycol oil) lubricated compressors are recommended for mineral oil greases coated seals, such as pneumatic high speed 4-way valves and air cylinders that operate without mineral oiler lubricators. One manufacturer has rated its pneumatic high speed 4-way valves with a life of 50 million cycles, if not exposed to polyglycol oils.

Polyalphaolefin PAO oil is compatible with mineral oil greases.

Conical screw compressor

The relatively recently developed conical screw compressor is in effect a conical spiral extension of a gerotor.  It does not have the inherent "blow-hole" leakage path which, in well designed screw compressors, is responsible for significant leakage through the assembly.  This allows much smaller rotors to have practical efficiency since at smaller sizes the leakage area does not become as large a portion of the pumping area as in straight screw compressors.  In conjunction with the decreasing diameter of the cone shaped rotor this also allows much higher compression ratios in a single stage with lower output pulsation.

Control schemes

Among rotary-screw compressors, there are multiple control schemes, each with differing advantages and disadvantages.

Start/stop

In a start/stop control scheme, compressor controls actuate relays to apply and remove power to the motor according to compressed air needs. Significant storage is required in most usage cases if the load is intermittent or is poorly matched to the compressor, the storage required will often be larger than the compressor itself.

Load/unload

In a load/unload control scheme, the compressor remains continuously powered. However, when the demand for compressed air is satisfied or reduced, instead of disconnecting power to the compressor, a device known as a slide valve is activated.  This device uncovers part of the rotor and proportionately reduces capacity of the machine down to typically 25% of the compressor's capability, thereby unloading the compressor. This reduces the number of start/stop cycles for electric motors over a start/stop control scheme in electrically-driven compressors, improving equipment service life with a minimal change in operating cost. When a load/unload control scheme is combined with a timer to stop the compressor after a predetermined period of continuously unloaded operation, it is known as a dual-control or auto-dual scheme. This control scheme still requires storage since there are only two production rates available to match consumption, although significantly less than a start/stop scheme.

Modulation

Instead of starting and stopping the compressor, a slide valve as described above continuously modulates capacity to the demand rather than being controlled in steps.  While this yields a consistent discharge pressure over a wide range of demand, overall power consumption may be higher than with a load/unload scheme, resulting in approximately 70% of full-load power consumption when the compressor is at a zero-load condition.

Due to the limited adjustment in compressor power consumption relative to compressed-air output capacity, modulation is a generally inefficient method of control when compared to variable-speed drives. However, for applications where it is not readily possible to frequently cease and resume operation of the compressor (such as when a compressor is driven by an internal-combustion engine and operated without the presence of a compressed-air receiver), modulation is suitable. The continuously variable production rate also eliminates the need for significant storage if the load never exceeds the compressor capacity.

Variable displacement

Utilized by compressor companies Quincy Compressor, Kobelco, Gardner Denver, Kaishan USA, and Sullair, variable displacement alters the percentage of the screw compressor rotors working to compress air by allowing air flow to bypass portions of the screws. While this does reduce power consumption when compared to a modulation control scheme, a load/unload system can be more effective with large amounts of storage (10 gallons per CFM).  If a large amount of storage is not practical, a variable-displacement system can be very effective, especially at greater than 70% of full load.

One way that variable displacement may be accomplished is by using multiple lifting valves on the suction side of the compressor, each plumbed to a corresponding location on the discharge.  In automotive superchargers, this is analogous to the operation of a bypass valve.

Variable speed

While an air compressor powered by a variable-speed drive can offer the lowest operating-energy cost without any appreciable reduction in service life over a properly maintained load/unload compressor, the variable-frequency power inverter of a variable-speed drive typically adds significant cost to the design of such a compressor, reducing its economic benefits over a properly sized load/unload compressor if air demand is constant.  However, a variable-speed drive provides for a nearly linear relationship between compressor power consumption and free air delivery allowing the most efficient operation over a very wide range of air demand. The compressor will still have to enter start/stop mode for very low demand as efficiency still drops off rapidly at low production rates due to rotor leakage.  In harsh environments (hot, humid or dusty) the electronics of variable-speed drives may have to be protected to retain expected service life.

Superchargers

The twin-screw type supercharger is a positive displacement type device that operates by pushing air through a pair of meshing close-tolerance screws similar to a set of worm gears. Twin-screw superchargers are also known as Lysholm superchargers (or compressors) after their inventor, Alf Lysholm.
Each rotor is radially symmetrical, but laterally asymmetric. By comparison, conventional "Roots" type blowers have either identical rotors (with straight rotors) or mirror-image rotors (with helixed rotors).
The Whipple-manufactured male rotor has three lobes, the female five lobes. The Kenne-Bell male rotor has four lobes, the female six lobes. Females in some earlier designs had four. By comparison, Roots blowers always have the same number of lobes on both rotors, typically 2, 3 or 4.

Comparative advantages
The rotary screw compressor has low leakage levels and low parasitic losses vs. Roots type. The supercharger is typically driven directly from the engine's crankshaft via a belt or gear drive. Unlike the Roots type supercharger, the twin-screw exhibits internal compression which is the ability of the device to compress air within the housing as it is moved through the device instead of relying upon resistance to flow downstream of the discharge to establish an increase of pressure.

The requirement of high-precision computer-controlled manufacturing techniques makes the screw type supercharger a more expensive alternative to other forms of available forced induction. With later technology, manufacturing cost has been lowered while performance increased.

All supercharger types benefit from the use of an intercooler to reduce heat produced during pumping and compression.

A clear example of the technology applied by the twin-screw in companies like Ford, Mazda, Mercedes and Mercury Marine can also demonstrate the effectiveness of the twin screw. While some centrifugal superchargers are consistent and reliable, they typically do not produce full boost until near peak engine rpm, while positive displacement superchargers such as Roots type superchargers and twin-screw types offer more immediate boost. In addition to this, twin-screw superchargers can keep the reasonable boost to higher rpm better than other positive displacement supercharges.

Related terms
The term "blower" is commonly used to define a device placed on engines with a functional need for additional airflow, such as a 2-stroke Diesel engine, where positive intake pressure is needed to "scavenge", or clear spent exhaust gasses from the cylinder and force a fresh intake charge into the cylinder before the compression stroke. The term "blower" is applied to rotary screw, roots-type, and centrifugal compressors when utilized as part of an automotive forced induction system. The term 'cabin blower' is also used for the pressurisation of aircraft for high altitude flight, which used Roots type compressors particularly in the 1950s (see Marshall supercharger).

See also
Gas compressor
Guided-rotor compressor
Reciprocating compressor
Vapor-compression refrigeration
Variable-speed air compressor

References

Gas compressors

Rotary-screw compressor


The Bolesław Śmiały coal mine is a large mine in the south of Poland in Łaziska Górne, Silesian Voivodeship, 172 km south-west of the capital, Warsaw. Bolesław Śmiały represents one of the largest coal reserve in Poland having estimated reserves of 50 million tonnes of coal. The annual coal production is around 2.13 million tonnes.

References

External links
 Official site

Coal mines in Poland
Mikołów County

Bolesław Śmiały Coal Mine


A folding door is a type of door which opens by folding back in sections or so-called panels.  Folding doors are also known as 'bi-fold doors', in spite of them most often having more than two panels. Another term is 'concertina' doors, inspired by the musical instrument of the same name.

Folding doors can be used as internal or external room dividers and are made from a variety of materials. Most folding doors are glazed and the panels have frames of either wood, aluminium or upvc. They can open up and fold either internally or externally and are widely used in modern extensions.

Opposed to a conventional door with a standard aperture of 700-900 mm, most modern folding door (sets) can be up to several meters in width, and thereby considerably increase both physical and visual accessibility between either two internal rooms or an internal room and an outside space.

Historically folding doors were already known by the Romans as excavations in Pompeii have revealed. Peter Connolly writes in his book 'Pompeii' that the Romans 'disliked single-leaf doors and wherever possible, both inside and out, they used double or even folding doors'.

See also
Folding bus doors

Doors

Folding door