2008年12月1日 星期一

Computer

A computer is a machine that manipulates data according to a list of instructions.
The first devices that resemble modern computers date to the mid-20th century (1940–1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers (PC).Modern computers are based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space.Today, simple computers may be made small enough to fit into a wristwatch and be powered from a watch battery. Personal computers, in various forms, are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and children's toys.
The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity.

It is difficult to identify any one device as the earliest computer, partly because the term "computer" has been subject to varying interpretations over time. Originally, the term "computer" referred to a person who performed numerical calculations (a human computer), often with the aid of a mechanical calculating device.
The history of the modern computer begins with two separate technologies - that of automated calculation and that of programmability.
Examples of early mechanical calculating devices included the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC). Hero of Alexandria (c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when. This is the essence of programmability.
The "castle clock", an astronomical clock invented by Al-Jazari in 1206, is considered to be the earliest programmable analog computer.It displayed the zodiac, the solar and lunar orbits, a crescent moon-shaped pointer travelling across a gateway causing automatic doors to open every hour, and five robotic musicians who play music when struck by levers operated by a camshaft attached to a water wheel. The length of day and night could be re-programmed every day in order to account for the changing lengths of day and night throughout the year.
The end of the Middle Ages saw a re-invigoration of European mathematics and engineering, and Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers. However, none of those devices fit the modern definition of a computer because they could not be programmed.
In 1801, Joseph Marie Jacquard made an improvement to the textile loom that used a series of punched paper cards as a template to allow his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.
It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine".Due to limited finances, and an inability to resist tinkering with the design, Babbage never actually built his Analytical Engine.

Earthship

An Earthship is a type of passive solar home made of natural and recycled materials. Designed and marketed by Earthship Biotecture of Taos, NM, the homes are primarily constructed to work autonomously and are generally made of earth-filled tires, utilising thermal mass construction to naturally regulate indoor temperature. They also usually have their own special natural ventilation system. Earthships are a type of off-grid home, which minimizes their reliance on public utilities and fossil fuels.
Earthships are built to utilize the available local resources, especially energy from the sun. For example, windows on the sunny side admit light and heat, and the buildings are often horseshoe-shaped to maximize southern (or northern in the southern hemisphere) sunlight and warmth in the colder months. Likewise, the thick, dense outer walls provide effective insulation against summer heat.
Internal, non-load-bearing walls are often made of a "honey comb" of recycled cans joined by concrete and are referred to as tin can walls. These walls are usually thickly plastered with adobe or stucco.
The Earthship, as it exists today, began to take shape in the 1970s. Mike Reynolds, founder of Earthship Biotecture, a company that specializes in designing and building Earthships, wanted to create a home that would do three things; first, it would be sustainable, using material indigenous to the entire planet as well as recycled materials wherever possible. Second, the homes would rely on natural energy sources and be independent from the “grid”, therefore being less susceptible to natural disasters and free from the electrical and water lines that Reynolds considered unsightly and wasteful. Finally, it would be economically feasible for the average person with no specialized construction skills to be able to create.
Eventually, Reynolds' vision took the form of the common U-shaped earth-filled tire homes seen today. As a concept, the Earthship was not limited to tires - any dense material with a potential for thermal mass, such as concrete, adobe, or stone could theoretically be used to create an Earthship. However, the earth-rammed tire version of the Earthship is now the most common design, and is usually the only structure referred to as “Earthship”.
Unlike other materials, rammed-earth tires are more accessible to the average person. Scrap tires are ubiquitous around the world and easy to come by; there are an estimated 2 billion tires throughout the United States. According to the Scrap Tire Management Council, as many as 253 million scrap tires are generated each year in the United States and of those 253 million tires only 53% are reclaimed by the scrap tire market[citation needed]. In addition to the availability of scrap tires, the method by which they are converted into usable "bricks", the ramming of the earth, is simple and affordable.
The earth rammed tires of an Earthship are usually assembled by teams of two people working together as part of a larger construction team. One member of the two person team shovels dirt, which usually comes from the building site, placing it into the tire one scoop at a time. The second member, who stands on the tire, uses a sledge hammer to pack the dirt in. The second person moves in a circle around the tire to keep the dirt even and avoid warping the tire. All tires in an Earthship are made in place because, when properly made, they weigh as much as 300 pounds and can be very difficult to relocate.
Additional benefits of the rammed earth tire are its great load-bearing capacity and its resistance to fire.
A fully rammed tire, which is about 2 feet 8 inches wide, is massive enough to surpass conventional requirements for structural load distribution to the earth. Because the tire is full of soil, it does not burn when exposed to fire. In 1996 after a fire swept through many conventional homes in New Mexico, an Earthship discovered in the aftermath was relatively unharmed.Only the south-facing wall and the roof had burned away, compared to the total destruction of the conventional homes. After testing the walls of an Earthship in Ridgway, Colorado, engineer Tom Griepentrog said, “It is my opinion that the construction method is equivalent to or better than the general quality, strength, effectiveness, fire resistance, durability and safety that is required by the uniform building code.”Currently, Earthships are in use in almost every state in the United States, as well as many countries in Europe. The use of insulation on the outside of tire walls, which was not common in early designs, is improving the viability of Earthships in every climate without compromising their durability. In the year 2000, Mike Reynolds, in partnership with Daren Howarth, launched Earthship Biotecture Europe, an organization that aims to explore and evolve the concept of the Earthship within a European context. Two more directors were appointed to Earthship Biotecture Europe in July 2006 - Kevan Trott and Kirsten Jacobsen.

Dishwasher


Unlike manual dishwashing, which relies largely on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot (55–65 degrees Celsius or 130–150 degrees Fahrenheit) water on the dishes. First detergent-added water is used for cleaning purposes, then clean water to remove the detergent residue. Some dishwashers have multiple wash and rinse periods within the complete cycle. In some dishwashers, a rinsing aid can be added to the rinse cycle. As there is no human contact during the process, strong detergents may be used which would be too alkaline for habitual exposure to the skin. Many dishwashers have a heating element to achieve fast drying and sanitation of the dishes. In some models, this element can also be used to heat cold water to the desired wash temperature.

Human dishwashers
The word dishwasher may also refer to a person who washes dishes in a commercial setting. These employees rinse dishes, load them into a stainless steel dishwasher, unload them, and stack them into their respective dish holders. Pots and pans are also washed by hand by scrubbing them in a soap and water mix, immersing them in a rinse of plain water, and then immersing them in a water/sanitizer solution for a period. Silverware is washed by placing loose silverware in a tray, washing them several times like this, then sorting them into circular holders, and washing them again in the dishwasher.

History
The first reports of a mechanical dishwashing device are of an 1850 patent by Joel Houghton of a hand-powered device.
Modern dishwashers are descended from the 1886 invention of Josephine Cochrane, also hand-powered, which she unveiled at the 1893 Chicago World's Fair. Cochrane was quite wealthy and was the granddaughter of John Fitch, the inventor of the steamboat. She never washed dishes herself and only invented the dishwasher as her servants were chipping her fine china.
Models installed with permanent plumbing arrived in the 1920s. In 1937, William Howard Livens invented a small dishwasher suitable for home. It had all the features of a modern dishwasher, including a front door for loading, a wire rack to hold crockery and a rotating sprayer. Electric drying elements were added in 1940.
Adoption was greatest at first in commercial environments, but by the 1970s dishwashers had become commonplace in domestic residences in the US.

Capacity
The international standard for the capacity of a dishwasher is expressed as standard place settings. Dishes or plates of irregular sizes may not fit properly in a dishwasher's cleaning compartment, so it is advisable to check for compatibility before buying a dishwasher.
Commercial dishwashers are rated as plates per hour. The rating is based on standard sized plates of the same size. The same can be said for commercial glass washers, they are based on standard glasses, normally pint glasses.

Size
Dishwashers that are installed into standard kitchen cabinets have a standard width and depth of 60 cm (Europe) or 24 inches (US), and most dishwashers must be installed into a hole a minimum of 86 cm (Europe) or 34 inches (US) tall. Portable dishwashers exist in 45 and 60 cm (Europe) 18 and 24 inch (US) widths, with casters and attached countertops. Dishwashers may come in standard or tall tub designs; standard tub dishwashers have a service kickplate beneath the dishwasher door that allows for simpler maintenance and installation, but tall tub dishwashers have approximately 20% more capacity and better sound dampening from having a continuous front door.

Geomagnetically induced current

Geomagnetically induced currents (GIC), affecting the normal operation of long technological conductor systems, are a manifestation at ground level of space weather. During space weather events (or geomagnetic storms) Earth's near space current systems experience large spatiotemporal variations reflected also in the variations of the Earth’s geomagnetic field. These variations induce currents (GIC) in conductors operated at the surface of Earth. Electric transmission grids and buried pipelines are common examples of such conductor systems. GIC can cause problems such as increased corrosion of pipeline steel and damaged high-voltage power transformers. GIC are one possible consequence of geomagnetic storms, which may also affect geophysical exploration surveys and oil and gas drilling operations.
The Risk to Ground Infrastructures from Geomagnetically Induced Currents

The basic principle for the generation of GIC: variations of the ionospheric currents (I(t)) generate an electric field (E(t)) driving GIC. Shown are also real GIC recordings from the Finnish natural gas pipeline.
A time-varying magnetic field external to the Earth induces electric currents in the conducting ground. These currents create a secondary (internal) magnetic field. As a consequence of Faraday's law of induction, an electric field at the surface of the Earth is induced associated with time variations of the magnetic field. The surface electric field causes electrical currents, known as geomagnetically induced currents (GIC), to flow in any conducting structure, for example, a power or pipeline grid grounded in the Earth. This electric field, measured in V/km, acts as a voltage source across networks.
Examples of conducting networks are electrical power transmission grids, oil and gas pipelines, undersea communication cables, telephone and telegraph networks and railways. GIC are often described as being quasi direct current (DC), although the variation frequency of GIC is governed by the time variation of the electric field. For GIC to be a hazard to technology, the current has to be of a magnitude and occurrence frequency that makes the equipment susceptible to either immediate or cumulative damage. The size of the GIC in any network is governed by the electrical properties and the topology of the network. The largest magnetospheric-ionospheric current variations, resulting in the largest external magnetic field variations, occur during geomagnetic storms and it is then that the largest GIC occur. Significant variation periods are typically from seconds to about an hour, so the induction process involves the upper mantle and lithosphere. Since the largest magnetic field variations are observed at higher magnetic latitudes, GIC have been regularly measured in Canadian, Finnish and Scandinavian power grids and pipelines since the 1970s. GIC of tens to hundreds of Amperes have been recorded. GIC have also been recorded at mid-latitudes during major storms. There may even be a risk to low latitude areas, especially during a storm commencing suddenly because of the high, short-period rate of change of the field that occurs on the dayside of the Earth.
GIC have been known since the mid-1800s when it was noted that electrical telegraph systems could sometimes run without power during geomagnetic storms, described at the time as operating on the “celestial battery”, while at other times they were completely inoperative . See also: Aurora (astronomy)

GIC in power grids
Modern electric power transmission systems consist of generating plants inter-connected by electrical circuits that operate at fixed transmission voltages controlled at substations. The grid voltages employed are largely dependent on the path length between these substations and 200kV-700kV system voltages are common. There is a trend towards higher voltages and lower line resistances to reduce transmission losses over longer and longer path lengths. Low line resistances produce a situation favourable to the flow of GIC. Power transformers have a magnetic circuit that is disrupted by the quasi-DC GIC: the field produced by the GIC offsets the operating point of the magnetic circuit and the transformer may go into half-cycle saturation. This produces a harmonic-rich AC waveform, localised heating and leads to high reactive power demands, inefficient power transmission and possible mis-operation of protective measures. Balancing the network in such situations requires significant additional reactive power capacity . The magnitude of GIC that will cause significant problems to transformers varies with transformer type. Modern industry practice is to specify GIC tolerance levels on new transformers.
On 13 March 1989 a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protection relays tripped in a cascading sequence of events . Six million people were left without power for nine hours, with significant economic loss. Since 1989 power companies in North America, the UK, Northern Europe and elsewhere have invested in evaluating the GIC risk and in developing mitigation strategies.
GIC risk can, to some extent, be reduced by capacitor blocking systems, maintenance schedule changes, additional on-demand generating capacity, and ultimately, load shedding. These options are expensive and sometimes impractical. The continued growth of high voltage power networks results in higher risk. This is partly due to the increase in the interconnectedness at higher voltages; connections in terms of power transmission to grids in the auroral zone, and grids operating closer to capacity than in the past.
To understand the flow of GIC in power grids and to advise on GIC risk, analysis of the quasi-DC properties of the grid is necessary . This must be coupled with a geophysical model of the Earth that provides the driving surface electric field, determined by combining time-varying ionospheric source fields and a conductivity model of the Earth. Such analyses have been performed for North America, the UK and in Northern Europe. The complexity of power grids, the source ionospheric current systems and the 3D ground conductivity make an accurate analysis difficult . By being able to analyse major storms and their consequences we can build a picture of the weak spots in a transmission system and run hypothetical event scenarios.
Grid management is also aided by space weather forecasts of major geomagnetic storms. This allows for mitigation strategies to be implemented. Solar observations provide a 1-3 day warning of an Earth-bound coronal mass ejection (CME), depending on CME speed. Following this, detection of the solar wind shock that precedes the CME in the solar wind, by spacecraft at the Lagrangian L1 point, gives a definite 20-60 minutes warning of a geomagnetic storm (again depending on local solar wind speed). The magnitude and arrival time of a CME after detection is unknown, although there is much research and model development within the space weather community.

Electric blanket


An electric blanket is a blanket with an integrated electrical heating device usually placed above the top bed sheet. Another variation of the electric blanket is the electric mattress pad, which is placed below the bottom bed sheet. Electric blankets usually have a control unit which adjusts the amount of heat the blanket produces. Blankets for larger sized beds often have separate controls for each side of the bed. The electric blanket may be used to pre-heat the bed before use or to keep the occupant warm while in bed.
Modern electric blankets have carbon fibre wires that are barely noticeable and produce heat in the far infra-red part of the spectrum, penetrating through other clothes. These blankets usually work on 24 volts instead of the 110/240 volts. Therefore, they are advertised as being a safer, more efficient and more comfortable alternative.

Safety concerns
Due to the combination of heat, electricity, the abundance of flammable bedding material, and a sleeping occupant, the use of electric blankets is of concern to fire safety officials internationally. Of primary concern are blankets that are older than 10 years and/or have been subject to damage, by creasing, flexing, fraying, or ordinary wear and tear. In the UK, it is estimated that 5,000 fires per year are caused by faulty electric blankets, of which 99% are believed to have been caused by blankets 10 years or older.
Electric blankets also present a burn risk to those who cannot feel pain or are unable to react to it. Individuals included in this group are small children, diabetics, and the elderly.

Popular culture
An anthropomorphic-faced cartoon electrical blanket named "Blanky" was portrayed in the 1987 film The Brave Little Toaster .


mini coffee grinder


keyring led light


12V Battery Charger


dual fuel generator


car backup sensor


air cooled condenser


gas engine scooter


automotive rocker switch


Optical Wired Mouse


digital fishing scales


Conveyor Roller Bearing


Mirror Ball Motor


Portable Cassette Radio


Wireless Speaker Amplifier


Car Amplifier Installation


Laser Diode Pump


TFT-LCD Color TV


Power Window Regulator


Steam Bath Generator


adhesive vinyl sheets


hydraulic pressure regulator


Machine Tig Welding


hydraulic piston cylinder


Power Splitter Cable


electric valve actuator


glass solar collector


ozone generator water


Mechanical Pump Seal


electric mini scooters


Laser Wire Stripping

2008年11月10日 星期一

Tall bike

A tall bike is an unusually tall bicycle, typically built for the purpose of fun and recreation, though with occasional practical use.

Modern tall bikes are most commonly constructed by individuals from spare parts. Two conventional bicycle frames are connected, by welding, brazing, or other means, one atop the other. The drive train is reconfigured to connect to the upper set of pedals, and the controls are moved to the upper handlebar area.

Alternatively, a bicycle can be built by inverting the frame, and inserting the forks from the 'wrong side', flipping the rear wheel, and adding a long gooseneck and tall handlebars, then welding a long seatpost tube to the 'bottom' (now the top) of the frame. This type of tall bike is made with only one bike frame, and is often called an upside-down bike rather than a tall bike, though the seat can be quite high, depending on the frame shape used. This type can be somewhat safer, as there is less tubing between the rider's legs and dismounting in a hurry can be easily accomplished.

Tall bikes are a popular mode of transportation for modern 'bicycle clubs' (SCUL, Rat Patrol, Zoobomb, Black Label Bike Club, The Winking Circle, Dead Baby Bikes, C.h.u.n.k. 666, Cyclecide, etc.) and activist groups. They are also a mainstay among builders of Clown bikes, art bikes, Clown alleys and parade groups. Bicycle modification is considered a fun and cheap hobby, and never fails to attract a lot of attention. Most modern cities contain large quantities of unused or abandoned bicycles that provide the raw materials for tall bikes and other mutant cycles.
Practical uses

Tall bikes can be used for general transportation and recreation, just like other bicycles. Regular tall-bike commuters note that both their increased visibility and the simple 'wow factor' give them a safety advantage in automobile traffic over 'short bikes.'

A Giraffe Lamplighter Bicycle, manufactured in 1898.

Historically, one of the first practical uses of the tall bike was as a late 1800s lamp lighting system, by which a worker would mount a specialized tall bicycle while equipped with a torch for lighting gas lamps. As the worker rode to each lamp, they would lean against the lamp post, light the lamp, and then ride to the next. Upon completing the circuit of lamps, an assistant would help the rider dismount.

In Bugbrooke, Northamptonshire, England The Clark Brothers in the 1950s built tall bikes to get to work when it flooded. These bikes they called 'Flood Bikes'. They have been on BBC TV and even did a Welsh language programme on them. They are currently in a museum somewhere.

Sporting

Tall bike jousting is a popular sport among bicycle hackers, and is commonly considered to have been introduced by Jake Houle and Lil' Bob of the Hard Times/Black Label Bike Club. Combatants arm themselves with lances, and attempt to score points by dislodging the other rider. Rules vary by area, and with the mood of the combatants. Like all jousting games, participants consider it a sport where honor plays a role and dishonorable wins are frowned upon.

Jousters create lances that vary from simple PVC pipe and foam devices that are flexible, soft, and relatively safe, up to wooden or metal lances that may be quite dangerous. Regional rules vary, some specifying flaming lances for effect, or glass containers attached to the end, the goal being to break the glass container in order to score points.

Design considerations

Tall bikes present some interesting design considerations, and different localities tend to have different methods of dealing with them.

One consistent issue is that the seat tends to end up in line with, or behind, the rear axle, which creates a powerful tendency to lift the front wheel of the bicycle on acceleration. Some bicycle builders simply accept this tendency, but others solve the problem by moving the seat post forward, lowering the handlebars, or by using a smaller wheel in front, typically a 24" instead of a 26".

Stability can also be negatively affected, and enhancements such as extended wheelbase by welding extensions on the front and rear dropouts can benefit stability. Contest holders often place restrictions on such modification to prevent unfair advantages.

See the bicycle and motorcycle geometry and bicycle and motorcycle dynamics articles for more on these issues.


Bamboo Table Set


mirror wall tile


Ride On Motorbike


Socket Tool Set


embroidered denim jeans


Plastic Ball Valve


foam folding chair


decorative glass bottle


blister packaging machinery


vinyl acetate monomer


Impact Screw Driver


Bicycle Spare Parts


AA Battery Case


iron stepping stone


cotton tote bags


Portable Car Lifts


european leather sofa


electric soldering iron


VoIP USB Handset


Heavy Duty Webbing


solenoid valve coil


key selector switch


Floating Ball Light


Yarn Dyed Shirt


USB DVB Stick


bathroom wall panel


metal engraving machine


electric heating pad


Black CRT Monitor


acrylic paper weight

Electric motor

An electric motor uses electrical energy to produce mechanical energy. The reverse process, that of using mechanical energy to produce electrical energy, is accomplished by a generator or dynamo. Traction motors used on locomotives and some electric and hybrid automobiles often perform both tasks if the vehicle is equipped with dynamic brakes. Electric motors are found in household appliances such as fans, refrigerators, washing machines, pool pumps, floor vacuums, and fan-forced ovens. They are also found in many other devices such as computer equipment, in its disk drives, printers, and fans; and in some sound and video playing and recording equipment as DVD/CD players and recorders, tape players and recorders, and record players. Electric motors are also found in several kinds of toys such as some kinds of vehicles and robotic toys.

The principle of conversion of electrical energy into mechanical energy by electromagnetic means was demonstrated by the British scientist Michael Faraday in 1821 and consisted of a free-hanging wire dipping into a pool of mercury. A permanent magnet was placed in the middle of the pool of mercury. When a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a circular magnetic field around the wire. This motor is often demonstrated in school physics classes, but brine (salt water) is sometimes used in place of the toxic mercury. This is the simplest form of a class of electric motors called homopolar motors. A later refinement is the Barlow's Wheel. These were demonstration devices, unsuited to practical applications due to limited power.

The first real electric motor, using electromagnets for both stationary and rotating parts, was demonstrated by Ányos Jedlik in 1828 Hungary. He built an electric-motor propelled vehicle in 1828.

The first English commutator-type direct-current electric motor capable of a practical application was invented by the British scientist William Sturgeon in 1832. Following Sturgeon's work, a commutator-type direct-current electric motor made with the intention of commercial use was built by the American Thomas Davenport and patented in 1837. Although several of these motors were built and used to operate equipment such as a printing press, due to the high cost of primary battery power, the motors were commercially unsuccessful and Davenport went bankrupt. Several inventors followed Sturgeon in the development of DC motors but all encountered the same cost issues with primary battery power. No electricity distribution had been developed at the time. Like Sturgeon's motor, there was no practical commercial market for these motors.

The modern DC motor was invented by accident in 1873, when Zénobe Gramme connected the dynamo he had invented to a second similar unit, driving it as a motor. The Gramme machine was the first electric motor that was successful in the industry.

In 1888 Nikola Tesla invented the first practicable AC motor and with it the polyphase power transmission system. Tesla continued his work on the AC motor in the years to follow at the Westinghouse company.


Bamboo Table Set


mirror wall tile


Ride On Motorbike


Socket Tool Set


embroidered denim jeans


Plastic Ball Valve


foam folding chair


decorative glass bottle


blister packaging machinery


vinyl acetate monomer


Impact Screw Driver


Bicycle Spare Parts


AA Battery Case


iron stepping stone


cotton tote bags


Portable Car Lifts


european leather sofa


electric soldering iron


VoIP USB Handset


Heavy Duty Webbing


solenoid valve coil


key selector switch


Floating Ball Light


Yarn Dyed Shirt


USB DVB Stick


bathroom wall panel


metal engraving machine


electric heating pad


Black CRT Monitor


acrylic paper weight