September, 2012

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Wiegand

Wiegand is an old German surname. It originated from the Old High German verb wgan, meaning to fight, through the past participle form wgant, meaning the fighter. The word comes from wîg (battle/war). The name was in use by the Middle Ages, also as a first name.

People with the name Wiegand or von Wiegand:

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Wiegand effect

The Wiegand effect is a nonlinear magnetic effect, named after its discoverer John R. Wiegand, produced in specially annealed and hardened wire called Wiegand wire.

Wiegand wire is low-carbon Vicalloy, an alloy of cobalt, iron, and vanadium, which is ferromagnetic. Initially, the wire is fully annealled. In this state the alloy is “soft” in the magnetic sense – that is, it is attracted to magnets and so magnetic field lines will divert preferentially into the metal, but the metal retains only a very small residual field when the external field is removed.

During manufacture, to give the wire its unique magnetic properties, it is subjected to a series of twisting and untwisting operations, to cold-work the outside shell of the wire, while retaining a soft core within the wire, and then the wire is aged. The result is that the magnetic coercivity of the outside shell is much larger than the inner core. This high coercivity outer shell will retain an external magnetic field even when the field’s original source is removed.

The wire now exhibits a very large magnetic hysteresis loop – if a magnet is brought near the wire, the high coercivity outer shell excludes the magnetic field from the inner soft core until the magnetic threshold is reached, at which point the entire wire (both the outer shell and inner core) rapidly switches magnetisation polarity. This switchover occurs in a few microseconds, and is termed the Wiegand effect.

The value of the Wiegand effect is that the switchover speed is sufficiently fast that a significant voltage can be output from a solenoid using a Wiegand-wire core. Because the voltage induced by a changing magnetic field is proportional to the rate of change of the field, a Wiegand-wire core can increase the output voltage of a magnetic field sensor by several orders of magnitude as compared to a similar coil with a non-Wiegand core. This higher voltage can easily be detected electronically, and when combined with the high repeatability threshold of the magnetic field switching, making the Wiegand effect useful for positional sensors.

Once the Wiegand wire has flipped magnetization, it will retain that magnetization until flipped in the other direction. Sensors and mechanisms that use the Wiegand effect must take this retention into account.

The Wiegand effect is a macroscopic extension of the Barkhausen effect as the special treatment of the Wiegand wire causes the wire to act macroscopically as a single large magnetic domain. The numerous small high-coercivity domains in the Wiegand wire outer shell switch in an avalanche, generating the Wiegand effect’s rapid magnetic field change.

Besides sensors, the Wiegand effect is used for security keycard door locks.  The plastic keycard has a series of short lengths of Wiegand wire embedded in it, which encodes the key by the presence or absence of wires. A second track of wires provides a clock track. The card is read by pulling it through a slot in a reader device, which has a fixed magnetic field and a sensor coil. As each length of wire passes through the magnetic field, its magnetic state flips which indicates a 1, and this is sensed by the coil. The absence of a wire indicates a 0. The resulting Wiegand protocol digital code is then sent to a host controller to determine whether to electrically unlock the door.

Wiegand cards are more durable and difficult to counterfeit than barcode or magnetic stripe cards. Since the keycode is permanently set into the card at manufacture by the positions of the wires, Wiegand cards can’t be erased by magnetic fields or reprogrammed as magnetic stripe cards can.

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Snakehead: Invasive species being caught in waterways throughout S.J.

chl 0901 snakehead fishing
Adam Mihara of Maple Shade fishes in Stewart Lake in Woodbury. The snakehead fish has been caught in this body of water and is known for its ability to survive on land for a few hours.

SNAKEHEAD FACTS

• Averages 2 feet long
• 7-13 pounds
• Color and size vary
• 28 varieties of the species

 

It might be one of the ugliest fish you’d ever want to see lurking in local ponds and streams. Brown with dark blotches, beady eyes atop its flattened head, the northern snakehead is coming up on the end of more and more reels across South Jersey.

And local fishermen claim the creature, dubbed “Frankenfish” for its ability to survive and even slither on land for considerable distances, is being caught here at an alarming rate.

“They’re exploding,” Rick Sayers, owner of Big Timber Bait and Tackle in Brooklawn, said of the species, which is not native to South Jersey. “They’re all over the place now.”

Snakeheads, which originally came from China and once were sold in this country at pet stores, are of great concern to scientists across the Mid-Atlantic region. The federal government banned the transport of live specimens in 2002.

The media had a feeding frenzy when snakeheads were found in a pond in South Philadelphia’s FDR Park in the summer of 2004. The park is near the Schuylkill River and that’s how authorities believe they’ve managed to swim as far south as Raccoon Creek in Logan and as far north as Bordentown.

The state Department of Environmental Protection was first alerted to their presence in New Jersey in 2009, when the species surfaced in Stewart Lake in Woodbury.

“They were once thought of as mostly a warm-water fish, but they love our habitat around here and they’ve shown that they do well in cold water,” said Christopher Smith, principal fish biologist for the DEP.

“They produce a large amount of offspring…. snakeheads grow pretty quick, faster than a bass does. They’re also resilient in that they can live out of water for, literally, five or six hours.”

Snakehead, which feed on native species like frogs, small reptiles and often small birds and mammals, are on the state’s Aquatic Invasive Species list. Officials fear their presence could disrupt the area’s ecosystem.

“In theory, any time you introduce a large predator to a population, you’re going to have competition for food and space, so there’s definitely the potential for impact,” Smith said. “Really, only time will tell.”

It might be one of the ugliest fish you’d ever want to see lurking in local ponds and streams. Brown with dark blotches, beady eyes atop its flattened head, the northern snakehead is coming up on the end of more and more reels across South Jersey.

And local fishermen claim the creature, dubbed “Frankenfish” for its ability to survive and even slither on land for considerable distances, is being caught here at an alarming rate.

“They’re exploding,” Rick Sayers, owner of Big Timber Bait and Tackle in Brooklawn, said of the species, which is not native to South Jersey. “They’re all over the place now.”

Snakeheads, which originally came from China and once were sold in this country at pet stores, are of great concern to scientists across the Mid-Atlantic region. The federal government banned the transport of live specimens in 2002.

The media had a feeding frenzy when snakeheads were found in a pond in South Philadelphia’s FDR Park in the summer of 2004. The park is near the Schuylkill River and that’s how authorities believe they’ve managed to swim as far south as Raccoon Creek in Logan and as far north as Bordentown.

The state Department of Environmental Protection was first alerted to their presence in New Jersey in 2009, when the species surfaced in Stewart Lake in Woodbury.

“They were once thought of as mostly a warm-water fish, but they love our habitat around here and they’ve shown that they do well in cold water,” said Christopher Smith, principal fish biologist for the DEP.

“They produce a large amount of offspring…. snakeheads grow pretty quick, faster than a bass does. They’re also resilient in that they can live out of water for, literally, five or six hours.”

Snakehead, which feed on native species like frogs, small reptiles and often small birds and mammals, are on the state’s Aquatic Invasive Species list. Officials fear their presence could disrupt the area’s ecosystem.

“In theory, any time you introduce a large predator to a population, you’re going to have competition for food and space, so there’s definitely the potential for impact,” Smith said. “Really, only time will tell.”

 

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