A gang signal is a visual or verbal way gang members identify their affiliation. This can take many forms including hand signs and colored clothing. Many of these slogans and hand signs, have become part of popular culture; the wearer favors, or is in, that particular gang. With symbols, graffiti is a large symbol displayed on trains. "Throwing up" a gang sign with the hands is one of the most known and obvious forms of "claiming". It is used in many situations where other identifiers may not be possible or appropriate, it can show that a gang member is in the area to "do business" as opposed to just passing through; these signs are made by formation of the fingers on one or both hands to make some sort of symbol or letter. It can serve to relay more specific information, such as what set they represent within a larger gang or in which activities they are taking part. Individual letters can be used to tell stories when flashed in rapid succession, each representing a word beginning with that letter.
These signs, because they are displayed only when wanted, are the most consistent across various areas. Many of these hand signals are quite close to other common hand signs, this can cause confusion among gang members, non-gang members, anti-gang authorities. Another identifier that can be displayed only when desired is a gang handshake, which includes some component of the gang hand signs and/or other hand and finger symbols. Clothing is a strong signal; the clothing gangs wear allows rival gangs to identify, friend and, foe. For example, the uniforms for many Hispanic gangs are standard and recognizable. Gangs such as the Latin Kings would wear long white T-shirts, baggy pants, either a bandana or a hat, sometimes both. Black gang members are more individualistic with their clothing; the gang would wear a specific clothing and certain accessories that would match their crew's colors. Examples include the Bloods, whose gang colour is red, the Crips, who wear blue. Most gang members wear Levi's.
Bandanas can be worn in various types of ways. This is done by gang members to signify; the most popular bandana colors are red, black, white and yellow. It is worn on the head or in the left or right back pockets of gang members. Gang colors
Reflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite or Tovex blast, a specialized air gun or a seismic vibrator known by the trademark name Vibroseis. Reflection seismology is similar to echolocation; this article is about surface seismic surveys. Reflections and refractions of seismic waves at geologic interfaces within the Earth were first observed on recordings of earthquake-generated seismic waves; the basic model of the Earth's deep interior is based on observations of earthquake-generated seismic waves transmitted through the Earth’s interior. The use of human-generated seismic waves to map in detail the geology of the upper few kilometers of the Earth's crust followed shortly thereafter and has developed due to commercial enterprise the petroleum industry. Seismic reflection exploration grew out of the seismic refraction exploration method, used to find oil associated with salt domes.
Ludger Mintrop, a German mine surveyor, devised a mechanical seismograph in 1914 that he used to detect salt domes in Germany. He applied for a German patent in 1919, issued in 1926. In 1921 he founded the company Seismos, hired to conduct seismic exploration in Texas and Mexico, resulting in the first commercial discovery of oil using the refraction seismic method in 1924; the 1924 discovery of the Orchard salt dome in Texas led to a boom in seismic refraction exploration along the Gulf Coast, but by 1930 the method had led to the discovery of most of the shallow Gulf Coast salt domes, the refraction seismic method faded. The Canadian inventor Reginald Fessenden was the first to conceive of using reflected seismic waves to infer geology, his work was on the propagation of acoustic waves in water, motivated by the sinking of the Titanic by an iceberg in 1912. He worked on methods of detecting submarines during World War I, he applied for the first patent on a seismic exploration method in 1914, issued in 1917.
Due to the war, he was unable to follow up on the idea. John Clarence Karcher discovered seismic reflections independently while working for the United States Bureau of Standards on methods of sound ranging to detect artillery. In discussion with colleagues, the idea developed that these reflections could aid in exploration for petroleum. With several others, many affiliated with the University of Oklahoma, Karcher helped to form the Geological Engineering Company, incorporated in Oklahoma in April, 1920; the first field tests were conducted near Oklahoma City, Oklahoma in 1921. Early reflection seismology was viewed with skepticism by many in the oil industry. An early advocate of the method commented: "As one who tried to introduce the method into general consulting practice, the senior writer can recall many times when reflections were not considered on a par with the divining rod, for at least that device had a background of tradition."The Geological Engineering Company folded due to a drop in the price of oil.
In 1925, oil prices had rebounded, Karcher helped to form Geophysical Research Corporation as part of the oil company Amerada. In 1930, Karcher helped to found Geophysical Service Incorporated. GSI was one of the most successful seismic contracting companies for over 50 years and was the parent of an more successful company, Texas Instruments. Early GSI employee Henry Salvatori left that company in 1933 to found another major seismic contractor, Western Geophysical. Many other companies using reflection seismology in hydrocarbon exploration, engineering studies, other applications have been formed since the method was first invented. Major service companies today include CGG, ION Geophysical, Petroleum Geo-Services, Polarcus, TGS and WesternGeco. Most major oil companies have conducted research into seismic methods as well as collected and processed seismic data using their own personnel and technology. Reflection seismology has found applications in non-commercial research by academic and government scientists around the world.
Seismic waves are mechanical perturbations that travel in the Earth at a speed governed by the acoustic impedance of the medium in which they are travelling. The acoustic impedance, Z, is defined by the equation: Z = V ρ,where V is the seismic wave velocity and ρ is the density of the rock; when a seismic wave travelling through the Earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time taken for the waves to travel from the source, reflect off an interface and be detected by an array of receivers at the surface. Knowing the travel times from the source to various receivers, the velocity of the seismic waves, a geophysicist attempts to reconstruct the pathways of the waves in order to build up an image of the subsurface. In common with other geophysical methods, reflection seismology may be seen as a type of inverse problem.
That is, given a set of data collected by experimentation and the physical laws that apply to the experiment, the experimenter wishes to develop an abstract model of the physical system being studied. In the case of refle
Sport stacking known as cup stacking or speed stacking, is an individual and team sport that involves stacking 9 or 12 specially designed cups in pre-determined sequences as fast as you can. The cups are specially designed to allow for faster times. Participants of sport stacking stack cups in specific sequences, by aligning the inside left lateral adjunct of each cup with that of the next. Sequences are pyramids of 3, 6, or 10 cups. Players compete against another player; the governing body setting the rule is the World Sport Stacking Association. While working for the Boys & Girls Club of Oceanside, California in 1981, Wayne Godinet came up with the idea for sport stacking; when the children he was working with were tired of playing traditional sports, he took paper cups and asked them to stack the cups as fast as they could. The sport was well received, so Godinet decided to acquire plastic cups to be used by his club, he discovered that his new plastic cups would stick together, so Godinet modified the cups by adding a hole to the bottom of the cups.
He formed his own company, Karango Cupstack Co. which manufactured and distributed these modified cups in a variety of colors. By the end of the decade, Godinet estimated he had sold 25,000 sets of cups. During the 1980s, Godinet hosted the annual National Cupstacking Championship in Oceanside. One of the national champions was Matt Adame, a member of Godinet's club, the "Professional Cupstack Drill Team". In November 1990, Adame and his teammates were featured on The Tonight Show Starring Johnny Carson. After the sport received national attention on The Tonight Show, Bob Fox, a physical education teacher from Colorado, introduced stacking to his students. Fox's enthusiasm led to the creation of the annual Colorado state tournament in 1997. In 1998, together with Larry Goers, created a line of proprietary sport stacking products including the patented timing system known as the StackMat. Fox started traveling across the country in 2000 to promote Speed Stacks full-time. In 2001 Fox founded the World Cup Stacking Association to formalize the sport's rules and sanction competitions worldwide.
As the sport began to spread to neighboring states, the WCSA hosted the first Rocky Mountain Cup Stacking Championships, where Fox's daughter, Emily Fox, broke her own world record by completing the cycle in 7.43 seconds. The next year, the first WCSA World Championship took place at the Denver Coliseum and has since been held annually; the WCSA formally titled the sport "sport stacking" and changed their name to the World Sport Stacking Association in 2005. The WSSA cited the public recognition that stacking is considered a sport as the reason for the name change. Official sport stacking cups are specially designed to prevent sticking and to allow the competitor to go faster; the cups are reinforced with several ribs on the inside which separate the cups when they are nestled. The exterior's textured to allow better grip; the insides are smooth and slide past each other easily. The tops of the cups have 1-4 holes. One special line of cups has cups without tops to further decrease air resistance.
One can purchase the specially designed "stacking mats" called "stack mats," which are mats connected to a sensitive timer. These are used for official tournament timing, as well as casual play practice timing. Special weighted training cups, called "Super Stacks," are made from metal and are most used directly before competing; the added weight is intended to make the regular cups feel lighter. Jumbo Stacks are a bigger version of the original speed stacks cups, they are used more in P. E. classes rather than at home. There are three sequences stacked in official sport stacking events, that are defined by the rule book handed out by the WSSA: 3-3-3: Uses nine cups; this sequence consists of three sets of three cups each. The three sets must be stacked going from left-to-right or right-to-left, down-stacked into their original positions in the same order as the up-stack. 3-6-3: Uses 12 cups. This sequence is similar to the 3-3-3; each pile of cups is stacked up from left-to-right or right-to-left, the down-stack occurs in the same order.
Cycle: Uses 12 cups. This is a sequence of stacks in the following order: a 3-6-3 stack, a 6-6 stack and a 1-10-1 stack, finishing in a down stacked 3-6-3. Common for all sequences are these major rules: You may not up-stack two pyramids at the same time, but in the down-stack, it is okay to touch two stacks at the same time. If a stack is not completed you must correct it immediately; the only exception to this rule is. If this happens, the player may continue the down-stack and correct the fallen stack when you reach it. There are three main categories of competing that WSSA-sanctioned tournaments offer: Individual: Each competitor is allowed two warm-ups and three timed tries for each sequence; the best time for each sequence is compared with other competitors. In the case of a tie, the second-best times are used. Doubles: Two competitors stand side-by-side to complete the stack, with one competitor using only his or her right hand while the other using only his or her left hand; the same rules for individuals apply here.
The only official doubles. Relay: Four competitors
In chemistry, pi stacking refers to attractive, noncovalent interactions between aromatic rings, since they contain pi bonds. These interactions are important in nucleobase stacking within DNA and RNA molecules, protein folding, template-directed synthesis, materials science, molecular recognition, although new research suggests that pi stacking may not be operative in some of these applications. Despite intense experimental and theoretical interest, there is no unified description of the factors that contribute to pi stacking interactions; the benzene dimer is the prototypical system for the study of pi stacking, is experimentally bound by 8–12 kJ/mol in the gas phase with a separation of 4.96 Å between the centers of mass for the T-shaped dimer. The small binding energy makes the benzene dimer difficult to study experimentally, the dimer itself is only stable at low temperatures and is prone to cluster. Other evidence for pi stacking comes from X-ray crystal structures. Perpendicular and offset parallel configurations can be observed in the crystal structures of many simple aromatic compounds.
Similar offset parallel or perpendicular geometries were observed in a survey of high-resolution x-ray protein crystal structures in the Protein Data Bank. Analysis of the aromatic amino acids phenylalanine, tyrosine and tryptophan indicates that dimers of these side chains have many possible stabilizing interactions at distances larger than the average van der Waals radii; the preferred geometries of the benzene dimer have been modeled at a high level of theory with MP2-R12/A computations and large counterpoise-corrected aug-cc-PVTZ basis sets. The two most stable conformations are the parallel displaced and T-shaped, which are isoenergetic and represent energy minima. In contrast, the sandwich configuration maximizes overlap of the pi system, is least stable, represents an energetic saddle point; this finding is consistent with a relative rarity of this configuration in x-ray crystal data. The relative binding energies of these three geometric configurations of the benzene dimer can be explained by a balance of quadrupole/quadrupole and London dispersion forces.
While benzene does not have a dipole moment, it has a strong quadrupole moment. The local C–H dipole means that there is positive charge on the atoms in the ring and a correspondingly negative charge representing an electron cloud above and below the ring; the quadrupole moment is reversed for hexafluorobenzene due to the electronegativity of fluorine. The benzene dimer in the sandwich configuration is stabilized by London dispersion forces but destabilized by repulsive quadrupole/quadrupole interactions. By offsetting one of the benzene rings, the parallel displaced configuration reduces these repulsive interactions and is stabilized; the large polarizability of aromatic rings lead to dispersive interactions as major contribution to stacking effects. These play a major role for interactions of nucleobases e.g. in DNS. The T-shaped configuration enjoys favorable quadrupole/quadrupole interactions, as the positive quadrupole of one benzene ring interacts with the negative quadrupole of the other.
The benzene rings are furthest apart in this configuration, so the favorable quadrupole/quadrupole interactions evidently compensate for diminished dispersion forces. The ability to fine-tune pi stacking interactions would be useful in numerous synthetic efforts. One example would be to increase the binding affinity of a small-molecule inhibitor to an enzyme pocket containing aromatic residues; the effects of substituents on pi stacking interactions is difficult to model and a matter of debate. An early model for the role of substituents in pi stacking interactions was proposed by Hunter and Sanders, they used a simple mathematical model based on sigma and pi atomic charges, relative orientations, van der Waals interactions to qualitatively determine that electrostatics are dominant in substituent effects. According to their model, electron-withdrawing groups reduce the negative quadrupole of the aromatic ring and thereby favor parallel displaced and sandwich conformations. Contrastingly, electron donating groups increase the negative quadrupole, which may increase the interaction strength in a T-shaped configuration with the proper geometry.
Based on this model, the authors proposed a set of rules governing pi stacking interactions which prevailed until more sophisticated computations were applied. Experimental evidence for the Hunter–Sanders model was provided by Siegel et al. using a series of substituted syn- and anti-1,8-di-o-tolylnaphthalenes. In these compounds the aryl groups "face-off" in a stacked geometry due to steric crowding, the barrier to epimerization was measured by nuclear magnetic resonance spectroscopy; the authors reported that aryl rings with electron-withdrawing substituents had higher barriers to rotation. The interpretation of this result was that these groups reduced the electron density of the aromatic rings, allowing more favorable sandwich pi stacking interactions and thus a higher barrier. In other words, the electron-withdrawing groups resulted in "less unfavorable" electrostatic interactions in the ground state. Hunter et al. applied a more sophisticated chemical double mutant cycle with a hydrogen-bonded "zipper" to the issue of substituent effects in pi stacking interactions.
This technique has been used to study a multitude of noncovalent interactions. The single mutation, in this case changing a substituent on an aromatic ring, results in secondary effects such as a change in hydrogen bond strength; the double mutation quantifies these secondary interactions, such that a weak interaction of interest can be dissected from the array. Their results indicate that more electron-withdrawing substituents have l
The guard is a ground grappling position in which one combatant has their back to the ground while attempting to control the other combatant using their legs. In pure grappling combat sports, the guard is considered an advantageous position, because the bottom combatant can attack with various joint locks and chokeholds, while the top combatant's priority is the transition into a more dominant position, a process known as passing the guard. In the sport of mixed martial arts, as well as hand-to-hand combat in general, it is possible to strike from the top in the guard though the bottom combatant exerts some control. There are various types of guard, with their own disadvantages; the guard is a key part of Brazilian Jiu-Jitsu. It is used, but not formally named, in Judo though it is sometimes referred to as dō-osae in Japanese, meaning "trunk hold", it is called the "front body scissor" in catch wrestling. Transitioning directly from standing to the guard position is known as pulling guard. Tsunetane Oda, a judo groundwork specialist who died in 1955, demonstrated the technique on video.
Sometimes referred to as full guard, the closed guard is the typical guard position. In this guard the legs are hooked behind the back of the opponent, preventing them from standing up or moving away; the opponent needs to open the legs up to be able to improve positioning. The bottom combatant might transit between the open and closed guard, as the open guard allows for better movement, but has a bigger risk of the opponent passing the guard; the open guard is used to perform various joint locks and chokeholds. The legs can be used to move the opponent, to create leverage; the open guard allows the opponent to stand up or try to pass the guard, so this position is used temporarily to set up sweeps or other techniques. Open guard is a general term that encompasses a large number of guard positions where the legs are used to push, wrap or hook the opponent without locking the ankles together around them; the butterfly guard involves both of the legs being hooked with the ankles in between the opponents legs, against the inside of the opponents thighs.
The opponent is controlled using both arms. The leverage in the butterfly guard allows powerful sweeps; the guard allows one to elevate or set the opponent off balance and because of this it is useful in avoiding damage and allows transitions to other dominant positions. The analogous technique in wrestling and catch wrestling is called double elevator; the X-guard is an open guard where one of the combatants is standing up and the other is on their back. The bottom combatant uses the legs to entangle one of the opponent's legs, which creates opportunities for powerful sweeps; the X-guard is used in combination with butterfly and half guard. In a grappling match, this is an advantageous position for the bottom combatant, but in general hand-to-hand combat, the top combatant can attack with stomps or soccer kicks. Skilled use of the x-guard can prevent the opponent from attempting a kick, or throw them off balance should they raise a leg; the x-guard has been used in Judo before being popularised by Marcelo Garcia.
The spider guard comprises a number of positions all of which involve controlling the opponents arms while using the soles of the feet to control the opponent at the biceps, thighs or a combination of them. It is most effective; the spider guard can be used for sweeps and to set up joint chokeholds. The De la Riva guard is an open guard, used in Judo before being popularized in Brazilian Jiu-Jitsu by black belt Ricardo de la Riva Goded, successful with it in competition; the guard consists of one of the legs wrapped behind the opponent's leg from the outside, the ankle held with one hand, the other hand grips one of their sleeves. The De la Riva guard offers a number of sweeps and submissions, is more used in combination with spider guard; the rubber guard a position. Similar positions have been seen in Judo before being used in Brazilian jiu-jitsu by Nino Schembri popularized and made a system by Eddie Bravo. Many techniques have been developed from this position including sweeps and striking defense.
By using a leg to hold an opponent down, one arm is free to work on submissions, sweeps or to strike the opponent's trapped head. The 50-50 guard is a position popularized by Roberto “Gordo” Correa and extensively used by the Mendes Brothers and Guilherme Mendes, Bruno Frazzato, Ryan Hall and Ramon Lemos from the Atos Jiu-Jitsu Team. In other grappling systems such as catch wrestling and Sambo, it is a form of the "outside leg triangle" type of leg control. In this position, the fighter on the bottom crosses a triangle on the opponent's leg, which allows for the leg to be dominated while leaving the arms free to work on sweeps and submissions; this position has been criticized for use in competitions with restricted use of leglocks due to the potential of stalling a match when the fighter on top cannot pass the guard and the fighter on the bottom cannot perform a sweep. In order to overcome the primary defense of one's opponent, their guard, attain a more dominant position, such as side mount, full mount, or knee on stomach a practitioner must pass the guard.
There are several ways of doing so. Examples of this type of action would be digging the practitioner's forearms into the inner thigh of
Focus stacking is a digital image processing technique which combines multiple images taken at different focus distances to give a resulting image with a greater depth of field than any of the individual source images. Focus stacking can be used in any situation where individual images have a shallow depth of field. Focus stacking can be useful in landscape photography. Focus stacking offers flexibility: since it is a computational technique, images with several different depths of field can be generated in post-processing and compared for best artistic merit or scientific clarity. Focus stacking allows generation of images physically impossible with normal imaging equipment. Alternative techniques for generating images with increased or flexible depth of field include wavefront coding and light-field cameras; the starting point for focus stacking is a series of images captured at different focal depths. While none of these images has the sample in focus they collectively contain all the data required to generate an image which has all parts of the sample in focus.
In-focus regions of each image may be detected automatically, for example via edge detection or Fourier analysis, or selected manually. The in-focus patches are blended together to generate the final image; this processing is called z-stacking, focal plane merging. Getting sufficient depth of field can be challenging in macro photography, because depth of field is smaller for objects nearer the camera, so if a small object fills the frame, it is so close that its entire depth cannot be in focus at once. Depth of field is increased by stopping down aperture, but beyond a certain point, stopping down causes blurring due to diffraction, which counteracts the benefit of being in focus, it reduces the luminosity of the image. Focus stacking allows the depth of field of images taken at the sharpest aperture to be increased; the images at right illustrate the increase in DOF that can be achieved by combining multiple exposures. The Mars Science Laboratory mission has a device called Mars Hand Lens Imager, which can take photos that can be focus stacked.
In microscopy high numerical apertures are desirable to capture as much light as possible from a small sample. A high numerical aperture gives a shallow depth of field. Higher magnification objective lenses have shallower depth of field; when observing a sample directly the limitations of the shallow depth of field are easy to circumvent by focusing up and down through the sample. Atomic resolution scanning transmission electron microscopy encounters similar difficulties, where specimen features are much larger than the depth of field. By taking a through-focal series, the depth of focus can be reconstructed to create a single image in focus. Brenizer Method Deep focus Focus bracketing Frazier lens High dynamic range imaging Image stitching Image fusion Microscopy#Deconvolution Johnson, Dave. 2008. How to Do Everything: Digital Camera. 5th ed. New York: McGraw-Hill Osborne Media. ISBN 978-0-07-149580-6. Ray, Sidney. 2002. Applied Photographic Optics. 3rd ed. Oxford: Focal Press. ISBN 0-240-51540-4. Media related to Focus stacking at Wikimedia Commons