A

One of the main problems posed by sand dunes is their encroachment on human habitats. Sand dunes move by different means, all of them aided by the wind. Sand dunes threaten buildings and crops in Africa, the Middle East, and China. Preventing sand dunes from overwhelming cities and agricultural areas has become a priority for the United Nations Environment Program. On the other hand, dune habitats provide niches for highly specialized plants and animals, including numerous rare and endangered species.

B

Sand is usually composed of hard minerals such as quartz that cannot be broken down into silt or clay. Yellow, brown and reddish shades of sand indicate their presence of iron compounds. Red sand is composed of quartz coated by a layer of iron oxide. White sands are nearly pure gypsum. Sand with a high percentage of silicate can be used in glassmaking. Sandstone is created by sand, mixed with lime, chalk or some other material that acts as a binding agent, that is deposited in layers at the bottom of a sea or other area and pressed together into rock by the great pressure of sediments that are deposited on top of it over thousands or millions of years.

C

The most common dune form on Earth and on Mars is crescentic. Crescent-shaped mounds are generally wider than they are long. The slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction, and they also are known as barchans or transverse dunes. Some types of crescentic dunes move more quickly over desert surfaces than any other type of dune. A group of dunes moved more than 100 metres per year between 1954 and 1959 the China’s Ningxia Province, and similar speeds have been recorded in the Western Desert of Egypt. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than 3 kilometres, are in China’s Taklamakan Desert.

D

Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on there or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 metres tall and may be the tallest dunes on Earth. Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. They may be more than 160 kilometres (99 mi) long. Some linear dunes merge to form Y-shaped compound dunes. Many forms in bidirectional wind regimes. The long axes of these dunes extend in the resultant direction of sand movement. Linear loess hills known as pahas are superficially similar.

E

Once sand begins to pile up, ripples and dunes can form. Wind continues to move sand up to the top of the pile until the pile is so steep that it collapses under its own weight. The collapsing sand comes to rest when it reaches just the right steepness to keep the dune stable. This angle, usually about 30-34°, is called the angle of repose. Every pile of loose particles has a unique angle of repose, depending upon the properties of the material it’s made of, such as the grain size and roundness. Ripples grow into dunes with the increase of wind and sand input.

F

The repeating cycle of sand inching up the windward side to the dune crest, then slipping down the dune’s slip face allows the dune to inch forward, migrating in the direction the wind blows. As you might guess, all of this climbing then slipping leaves its mark on the internal structure of the dune. The image on the right shows fossil sand dune structure preserved in the Merced Formation at Fort Funston, Golden Gate National Recreation Area. The sloping lines or laminations you see are the preserved slip faces of a migrating sand dune. This structure is called cross-bedding and can be the result of either wind or water currents. The larger the cross-bedded structure, however, the more likely it is to be formed by wind, rather than water.

G

Sand dunes can “sing” at a level up to 115 decibels and generate sounds in different notes. The dunes at Sand Mountain n Nevada usually sing in a low C but can also sing in B and C sharp. The La Mar de Dunas in Chile hum in F while those at the Ghord Lahmar in Morocco howl in G sharp. The sounds are produced by avalanches of sand generated by blowing winds. For a while, it was thought that the avalanches caused the entire dune to resonate like a flute or violin but if that were true then different size dunes would produce different notes. In the mid 2000s, American, French and Moroccan scientists visiting sand dunes in Morocco, Chile, China and Oman published a paper in the Physical Review Letters that determined the sounds were produced by collisions between grains of sand that caused the motions of the grains to become synchronized, causing the outer layer of a dune to vibrate like the cone of a loudspeaker, producing sound. The tone of the sounds depended primarily on the size of the grains.

H

Scientists performed a computer simulation on patterns and dynamics of desert dunes in laboratory. Dune patterns observed in deserts were reproduced. From the initial random state, stars and linear dunes are produced, depending on the variability of the wind direction. The efficiency in sand transport is calculated through the course of development. Scientists found that the sand transport is the most efficient in the linear transverse dune. The efficiency in sand transport always increased through the evolution, and the way it increases was stepwise. They also found that the shadow zone, the region where the sand wastes the chance to move, shrinks through the course of evolution, which greatly helps them build a model to simulate a sand move.

A

Americans today choose among more options in more parts of life than has ever been pos­sible before. To an extent, the opportunity to choose enhances our lives. It is only logical to think that if some choices are good, more is better; people who care about having infinite options will benefit from them, and those who do not can always just ignore the 273 versions of cereal they have never tried. Yet recent research strongly suggests that, psychologically, this assumption is wrong, with 5% lower percentage announcing they are happy. Although some choices are undoubtedly better than none, more is not always better than less.

B

Recent research offers insight into why many people end up unhappy rather than pleased when their options expand. We began by making a distinction between “maximizers” (those who always aim to make the best possible choice) and “satisficers” (those who aim for “good enough,” whether or not better selections might be out there).

C

In particular, we composed a set of statements—the Maximization Scale—to diagnose peo­ple’s propensity to maximize. Then we had several thousand people rate themselves from 1 to 7 (from “completely disagree” to “completely agree”) on such statements as “I never settle for second best.” We also evaluated their sense of satisfaction with their decisions. We did not define a sharp cutoff to separate maximizers from satisficers, but in general, we think of individuals whose average scores are higher than 4 (the scale’s midpoint) as maxi- misers and those whose scores are lower than the midpoint as satisficers. People who score highest on the test—the greatest maximizers—engage in more product comparisons than the lowest scorers, both before and after they make purchasing decisions, and they take longer to decide what to buy. When satisficers find an item that meets their standards, they stop looking. But maximizers exert enormous effort reading labels, checking out consumer magazines and trying new products. They also spend more time comparing their purchas­ing decisions with those of others.

D

We found that the greatest maximizers are the least happy with the fruits of their efforts. When they compare themselves with others, they get little pleasure from finding out that they did better and substantial dissatisfaction from finding out that they did worse. They are more prone to experiencing regret after a purchase, and if their acquisition disappoints them, their sense of well-being takes longer to recover. They also tend to brood or ruminate more than satisficers do.

E

Does it follow that maximizers are less happy in general than satisficers? We tested this by having people fill out a variety of questionnaires known to be reliable indicators of well­being. As might be expected, individuals with high maximization scores experienced less satisfaction with life and were less happy, less optimistic and more depressed than people with low maximization scores. Indeed, those with extreme maximization ratings had depression scores that placed them in the borderline of clinical range.

F

Several factors explain why more choice is not always better than less, especially for maxi­misers. High among these are “opportunity costs.” The quality of any given option cannot be assessed in isolation from its alternatives. One of the “costs” of making a selection is losing the opportunities that a different option would have afforded. Thus, an opportunity cost of vacationing on the beach in Cape Cod might be missing the fabulous restaurants in the Napa Valley. Early Decision Making Research by Daniel Kahneman and Amos Tversky showed that people respond much more strongly to losses than gains. If we assume that opportunity costs reduce the overall desirability of the most preferred choice, then the more alternatives there are, the deeper our sense of loss will be and the less satisfaction we will derive from our ultimate decision.

G

The problem of opportunity costs will be better for a satisficer. The latter’s “good enough” philosophy can survive thoughts about opportunity costs. In addition, the “good enough” standard leads to much less searching and inspection of alternatives than the maximizer’s “best” standard. With fewer choices under consideration, a person will have fewer opportu­nity costs to subtract.

H

Just as people feel sorrow about the opportunities they have forgone, they may also suffer regret about the option they settled on. My colleagues and I devised a scale to measure proneness to feeling regret, and we found that people with high sensitivity to regret are less happy, less satisfied with life, less optimistic and more depressed than those with low sensitivity. Not surprisingly, we also found that people with high regret sensitivity tend to be maximizers. Indeed, we think that worry over future regret is a major reason that individuals become maximizers. The only way to be sure you will not regret a decision is by making the best possible one. Unfortunately, the more options you have and the more opportunity costs you incur, the more likely you are to experience regret.

I

In a classic demonstration of the power of sunk costs, people were offered season subscrip­tions to a local theatre company. Some were offered the tickets at full price and others at a discount. Then the researchers simply kept track of how often the ticket purchasers actu­ally attended the plays over the course of the season. Full-price payers were more likely to show up at performances than discount payers. The reason for this, the investigators argued, was that the full-price payers would experience more regret if they did not use the tickets because not using the more costly tickets would constitute a bigger loss. To increase sense of happiness, we can decide to restrict our options when the decision is not crucial. For example, make a rule to visit no more than two stores when shopping for clothing.

The word 'guitar' was brought into English as an adaptation of the Spanish word 'guitarra', which was, in turn, derived from the Greek 'kithara'. Tracing the roots of the word further back into linguistic history, it seems to have been a combination of the Indo-European stem 'guit-', meaning music, and the root ’-tar’, meaning chord or string. The root '-tar' is actually common to a number of languages, and can also be found in the word ’sitar', also a stringed musical instrument. Although the spelling and pronunciation differ between languages, these key elements have been present in most words for 'guitar' throughout history.

While the guitar may have gained most of its popularity as a musical instrument during the modern era, guitar-like instruments have been in existence in numerous cultures throughout the world for more than 5,000 years. The earliest instruments that the modern eye and ear would recognise as a 'normal' acoustic guitar date from about 500 years ago. Prior to this time, stringed instruments were in use throughout the world, but these early instruments are known primarily from visual depictions, not from the continued existence of music written for them. The majority of these depictions show simple stringed instruments, often lacking some of the parts that define a modern guitar. A number of these instruments have more in common with the lute than the guitar.

There is some uncertainty about the exact date of the earliest six-string guitar. The oldest one still in existence, which was made by Gaetano Vinaccia, is dated 1779. However, the authenticity of six-string guitars alleged to have been made prior to 1790 is often suspect, as many fakes have been discovered dating to this era. The early nineteenth century is generally accepted as the time period during which six-string guitars began taking on their modern shape and dimensions. Thus for nearly two hundred years, luthiers, or guitar makers, have been producing versions of the modern acoustic guitar.

The first electric guitar was not developed until the early twentieth century. George Beauchamp received the first patent for an electric guitar in 1936, and Beauchamp went on to co-found Rickenbacker, originally known as the Electro String Instrument Company. Although Rickenbacker began producing electric guitars in the late 1930s, this brand received most of its fame in the 1960s, when John Lennon used a Rickenbacker guitar for the Beatles' debut performance on the Ed Sullivan show in 1964. George Harrison later bought a Rickenbacker guitar of his own, and the company later gave him one of their earliest 12-string electric guitars. Paul McCartney also used a Rickenbacker bass guitar for recording. The Beatles continued to use Rickenbacker guitars throughout their career, and made the instruments highly popular among other musicians of the era.

The Fender Musical Instruments Company and the Gibson Guitar Corporation were two other early electric guitar pioneers, both developing models in the early 1950s. Fender began with the Telecaster in 1950 and 1951, and the Fender Stratocaster debuted in 1954. Gibson began selling the Gibson Les Paul, based partially on assistance from jazz musician and guitar innovator Les Paul, in 1952. The majority of present day solid-body electric guitars are still based largely on these three early electric guitar designs.

Throughout the history of the guitar, an enormous number of individuals have made their mark on the way in which the instrument was built, played and perceived. Though some of these individuals are particularly well known, like the Beatles or Les Paul, the majority of these people are virtually invisible to most modern guitar fans. By looking at the entire history of the guitar, rather than just recent developments, largely confined to electric guitars, it is possible to see more of the contributions of earlier generations.