Archive for July, 2007

Through-hole technology

Saturday, July 28th, 2007

Through-hole technology, also spelled “thru-hole”, refers to the mounting scheme used for electronic components that involves the use of pins on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side.

While through-hole mounting provides strong mechanical bonds when compared to surface-mount technology techniques, the additional drilling required makes the boards more expensive to produce. They also limit the available routing area for signal traces on layers immediately below the top layer on multilayer boards since the holes must pass through all layers to the opposite side. To that end, through-hole mounting techniques are now usually reserved for bulkier components such as electrolytic capacitors or semiconductors in larger packages such as the TO220 that require the additional mounting strength.

Design engineers often prefer the larger through-hole to surface mount parts when prototyping because they are easier to handle, insert, and solder. A rule of thumb for creating a through-hole on a PCB is to make the drill diameter 0.008” larger then the part’s lead. The installation of discrete through-hole parts (e.g. resistor, capacitors, and diodes ), is done by bending the leads 90 degrees in the same direction, inserting part in the board, bending leads located on the back of the board in opposing directions to improve the part’s mechanical strength; finally, soldering the leads such that the solder seeps through to both sides of the board.

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Kaare Klint

Thursday, July 26th, 2007

Kaare Klint (Born December 15, 1888 in Copenhagen<ref name=Brit>[1] Britannica online</ref> — March 28, 1954) was a Danish architect and furniture designer. He was a Lecturer in furniture design at the Royal Academy of Fine Arts in Copenhagen 1924.
Style epitomized by clean, pure lines, the best materials of his time and superb craftsmanship.

The designs of Klint were based on neo-classical designs, and were simple and elegant. He was interested in ergonomy, and his furniture was designed to fit human proportions as well as possible. He was an influential proponent of the modern Scandavian style, and emphasized ergonomics in design. <ref name=Brit/>


References

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Caning (furniture)

Tuesday, July 24th, 2007

In the context of furniture, caning is a method of weaving chair seats and other furniture. Caning material is derived from the skin of rattan vines grown mostly in Indonesia, the Philippines and Malaysia. Some vines reach 500 feet in length. One of the earliest woven chair seats is in the Metropolitan Museum of Art collection. It was owned by Reni-seneb, a scribe of Dynasty 18 (1539 - 1295 BC). A wood chair with ivory inlay, it had a string mesh seat which has been reconstructed. Caning or cane is a term which is incorrectly generically used to describe any woven seat.

Other kinds of woven chair seats include Rush (natural and paper), Danish Cord, Shaker Tape, Binder Cane, Flat Reed and Splint.

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Jake Kaner

Tuesday, July 24th, 2007

Professor Jake Kaner (born 1959) is Professor of Furniture at Buckinghamshire Chilterns University College, and a member of the Institute of Conservation.
He was recently awarded a grant by Arts and Humanities Research Council to create an Electronic Furniture Archive of High Wycombe. In 2004, he was called upon to create replica furniture for the 78 Derngate Charles Rennie Mackintosh project in Northampton of certain Mackintosh originals.

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Carnation (heraldry)

Thursday, July 19th, 2007

In heraldry, carnation is a tincture, the colour of European human skin (i.e., pale pink). It is not used in English heraldry but quite frequent on the continent, in France in particular, derived from widespread use in German heraldry.

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Garapa

Tuesday, July 17th, 2007

Garapa (var. Guarapa) is the Brazilian Portuguese term for the juice of raw sugar cane (in some Southern states garapa is better known as “caldo de cana” (cane juice). Also known as “guarapo” or “guarapo de caña” in Spanish, it is a very popular drink in several countries of tropical Latin America and among Latin American communities in Southern Florida. Sugar cane juice is especially popular among the Cuban expatriate community in Miami, where it is found in abundance at many locations in Little Havana. Sugar cane juice is obtained by crushing peeled sugar cane in a small hand- or electric mill. The drink is often served cold with a squeeze of lemon (in Cuba and Brazil) or pineapple (Brazil). Due to its high sugar content it is rich in calories. Garapa juice is the primary source of sugar cane derivatives such as raw sugar (obtained by evaporation and refining), cachaça or “caninha” and ethanol.


Etymology

The origin of the word is unclear. There are two hypotheses:

  1. African origin, it means “fermented drink” in West Africa, and was brought into Brazil and the rest of Latin America by slaves from Cabo Verde islands, then to the Madeira islands.
  2. Tupí-Guaraní origin, from guarab, meaning a fermented drink laced with honey

In Brazilian Portuguese, garapa is also used figuratively as meaning a good thing, easy to get. Garapa doida (crazy garapa) is also the name given to cachaça in the Amazon region.


Health risk

Raw sugar cane juice can be a health risk to drinkers, mostly because of the unhygienic conditions under which it is prepared in rural areas. Since it is very sugary, it is an ideal culture medium to all kinds of microorganisms, so it should not be stored outside a refrigerator. In fact, it is almost always consumed as a freshly prepared drink. Pasteurization is required if the juice is to be bottled and sold as such, and a date of validity should be stamped on the container.

Garapa has been recently involved in a widely publicized episode in the state of Santa Catarina, Brazil [1], when at least 49 tourists were infected with Chagas disease by drinking garapa most likely produced at roadside stalls. The sugar cane used for it most probably was contaminated with feces of the insect vector, a Reduviid.

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Jeremy Broun

Wednesday, July 11th, 2007

Jeremy Broun is a British woodworker, furniture designer maker, speaker, and writer.

Broun’s furniture is innovative in the use of technique and form. His Caterpillar Rocking chair
in 1984 ‘is visually stunning, a good combination of colour, structure and practicality… and has the advantage of being a truly original idea : just as Saarinen and his pedestal chairs converted four chairlegs into one’ (An Encyclopedia of Chairs - The Apple Press).

He won a Winston Churchill Travel Scholarship to Sweden, Finland and Italy in 1979 and in the same year was elected a Fellow of The Society of Designer Craftsmen, the original Arts and Crafts Exhibition Society founded by William Morris. Since 1980 he has been a member of the Crafts Council Index of Selected Makers. He has exhibited extensively including The Royal Society of Arts and the Ars Nova Museum in Finland.
His work was included in the ‘First Sale of Contemporary British Crafts’ at Sotheby’s in 1980 and in 2002 at the Centenary exhibition celebrating the Hill House designed by Charles Rennie Mackintosh.

In 1989 he gained The Worshipful Company of Furniture Makers Ambrose Heal Award for his craft documentary films. He has written numerous articles on woodworking and design including “Furniture Today” and “A History of (Furniture) Designer Makers” in 2005.


List of selected books by Jeremy Broun

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Behold

Tuesday, July 10th, 2007

Behold is a brand of Furniture Polish produced by the Sara Lee Corporation. Behold furniture polish and Endust dusting aid were previously produced by Drackett. When Drackett was sold to S. C. Johnson & Son in 1992, these two products were sold off to avoid anti-trust concerns. S.C.Johnson produces Pledge, a similar product to Behold, as well as other waxes.

William R. Johnson, now president of H.J. Heinz, was assistant brand manager for Behold at Drackett, 1974-1977.

The NIH household products database lists Behold as containing propane and butane and naphtha. Isopropane and butane blends are used as propellants for household cleaners.

Aerosol furniture polishes apply a thin layer of silicon oils, rather than the thicker, more durable layer of solid waxes. Fine furniture craftsmen warn that the silicon oils can penetrate through tiny cracks in the finish and make eventual refinishing very difficult. [1].


External links

  • NIH Product Safety Database
  • FTC orders divestiture of Behold
  • McComb’s Alumni Profile
  • Furniture care

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Sectional curvature

Sunday, July 8th, 2007

In Riemannian geometry, the sectional curvature is one of the ways to describe the curvature of Riemannian manifolds. The sectional curvature <math>K(\sigma_p)</math> depends on a two-dimensional plane <math>\sigma_p</math> in the tangent space at p. It is the Gaussian curvature of that section — the surface which has the plane <math>\sigma_p</math> as a tangent plane at p, obtained from geodesics which start at p in the directions of <math>\sigma_p</math> (in other words, the image of <math>\sigma_p</math> under the exponential map at p). Formally, the sectional curvature is a smooth real-valued function on the 2-Grassmannian bundle over the manifold.

The sectional curvature determines the curvature tensor completely and is a very useful geometric notion.


Definition

Given a Riemannian manifold and two linearly independent tangent vectors at the same point, <math>u</math> and <math>v</math>, we can define

<math>K(u,v)={\langle R(u,v)v,u\rangle\over \langle u,u\rangle\cdot\langle v,v\rangle-\langle u,v\rangle^2}</math>

Here <math>R</math> is the Riemann curvature tensor.

It can be shown that <math>K(u,v)</math> depends only on the 2-plane <math>\sigma</math> spanned by <math>u</math> and <math>v</math>. It is called sectional curvature of the 2-plane <math>\sigma</math>.


Manifolds with constant sectional curvature

Riemannian manifolds with constant sectional curvature are the most simple. These are called space forms. By rescaling the metric there are three possible cases

  • negative curvature −1, hyperbolic geometry
  • zero curvature, Euclidean geometry
  • positive curvature +1, elliptic geometry

The model manifolds for the three geometries are hyperbolic space, Euclidean space and a unit sphere. They are the only complete, simply connected Riemannian manifolds of given sectional curvature. All other complete constant curvature manifolds are quotients of those by some group of isometries.


Properties

  • A complete Riemannian manifold has non-negative sectional curvature if and only if the function <math>f_p(x)=dist^2(p,x)</math> is 1-concave for all points p.
  • A complete simply connected Riemannian manifold has non-positive sectional curvature if and only if the function <math>f_p(x)=dist^2(p,x)</math> is 1-convex.


Manifolds with non-positive sectional curvature

Cartan showed that if M is a complete and simply connected manifold with non-positive sectional curvature, then it is diffeomorphic to a Euclidean space. Therefore the topological structure of a complete non-positively curved manifold is determined by its fundamental group.


Manifolds with positive sectional curvature

There is still known little about the structure of positively curved manifolds. It follows from the soul theorem that a complete non-compact non-negatively curved manifold is diffeomorphic to a normal bundle over a compact non-negatively curved manifold. As for compact positively curved manifolds, there are two classical results:

  • It follows from the Myers theorem that the fundamental group of such manifold is finite.
  • It follows from the Synge theorem that the fundamental group of such manifold in even dimensions is 0, if orientable and <math>\Bbb Z_2</math> otherwise. In odd dimensions a positively curved manifold is always orientable.

Moreover, there are relatively few examples of compact positively curved manifolds, leaving a lot of conjectures (e.g. the Hopf conjecture on whether there is a metric of positive sectional curvature on <math>\Bbb S^2\times\Bbb S^2</math>). The most typical way of constructing new examples is the following corollary from the O’Neill curvature formulas: if <math>(M,g)</math> is a Riemannian manifold admitting a free isometric action of a Lie group G, and M has positive sectional curvature on all 2-planes ortogonal to the orbits of G, then the manifold <math>M/G</math> with the quotient metric has positive sectional curvature. This fact allows to construct the classical positively curved spaces, being spheres and projective spaces, as well as these examples:

  • The Berger spaces <math>B^7=SO(5)/SO(3)</math> and <math>B^{13}=SU(5)/Sp(2)\cdot\Bbb S^1</math>.
  • The Wallach spaces (or the homogeneous flag manifolds): <math>W^6=SU(3)/T^2</math>, <math>W^{12}=Sp(3)/Sp(1)^3</math> and <math>W^{24}=F_4/Spin(8)</math>.
  • The Aloff-Wallach spaces <math>W^7_{p,q}=SU(3)/diag(z^p,z^q,\overline{z}^{p+q})</math>.
  • The Eschenburg spaces <math>E_{k,l}=diag(z^{k_1},z^{k_2},z^{k_3})\backslash SU(3)/diag(z^{l_1},z^{l_2},z^{l_3})^{-1}</math>.
  • The Bazaikin spaces <math>B^{13}_p=diag(z_1^{p_1},\dots,z_1^{p_5})\backslash U(5)/diag(z_2A,1)^{-1}</math>, where <math>A\in Sp(2)\subset SU(4)</math>.


References

  • J. Milnor, Morse Theory


External Links

  • Wolfgang Ziller, Examples of manifolds with non-negative sectional curvature


See also

  • Riemann curvature tensor
  • curvature of Riemannian manifolds
  • curvature

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Sunlounger

Sunday, July 8th, 2007

A sunlounger is an article of swimming pool or beach-side furniture, often fashioned from white plastic which is designed for people to lie down, or sit upon, whilst relaxing. Somewhat bed-like in nature, a part of the surface can be propped up to allow the user to sit up and read, or it can be fully reclined to a flat surface to allow snoozing in the horizontal position.

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Booty call (slang)

Friday, July 6th, 2007

A booty call is a telephone call, other communication, or visitation made with the sole intent of engaging in sex with the person being contacted. Traditionally this social practice, especially the term booty call, is associated with a person calling another person for a sexual encounter after having already established either a casual or more serious relationship involving sexual relations.

In most instances, a booty call is made when the prospect of a traditional romantic date is highly unlikely (e.g., late in the evening, after midnight or in the pre-dawn hours), thus making it obvious that the intent of the call is for the sole purpose of obtaining and engaging in sexual intercourse.

Most notably, the booty call is an alternative type of sexual relation between people. One can look at the booty call as sexual intercourse taking place between the social constructs of marriage, dating and prostitution. The lure in this case is the mutual satisfaction and pleasure of sex outside a traditional relationship (with all its complexities and commitments). A booty call is typically looked at with the singular purpose of sexual pleasure and is not engaged upon to replace traditional relationships. As such, a booty call can take place with two (or more people) already involved in a relationship, but without the intent of breaking the relationship. However, as an alternate framework for sexual relations, the booty call can meet the urge for intimacy in a period of time or situation that allows for little or no sexual fulfillment otherwise. As such, the booty call becomes a gratifying and efficient option to a drastic change in a social situation, i.e., breaking an otherwise good relationship due to unsatisfying sex.

The phrase originated in a comedic routine by stand-up comedian Bill Bellamy in the early 1990s. It is used by persons of either gender, and many ethnicities, to request sexual favors by calling an acquaintance that may or may not be romantically linked to the caller.

Booty calls can also be used by one partner of an ended relationship to obtain sex from the ex-partner, due to lingering emotions and feelings of a need for continued physical connection, without feeling compelled to continue dating that person. This may be referred to as “ex sex.”

The term itself is more likely to be used by the person answering the call or others in his/her company than the person making the call. For example, “Did John take off?”, “Yeah, he had to answer a booty call.” It is not considered derisive.

Although traditionally the telephone is used for a booty call, the last ten years have seen the rise of IM, chat, e-mail, and text message booty calling.

The term has since evolved to refer to one or the other party to the relationship, e.g. “She’s my booty call.”


See also

  • Booty
  • Drunk dialing
  • Casual relationship
  • Casual sex

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Lebanon, Colorado

Wednesday, July 4th, 2007

Lebanon, Colorado is a small, unincorporated community in Montezuma County, Colorado located north of Cortez, Colorado and is served by the Dolores Post Office, Zip Code 81323.

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