Monday, September 29, 2008

Bluetooth 1.1

  • Ratified as IEEE Standard 802.15.1-2002.
  • Many errors found in the 1.0B specifications were fixed.
  • Added support for non-encrypted channels.
  • Received Signal Strength Indicator (RSSI).

Tuesday, September 23, 2008

Lorenz

In the 1930s German radio engineers developed a new system, called the "Ultrakurzwellen-Landefunkfeuer" (LFF), or simply "Leitstrahl" (guiding beam) but referred to outside Germany as Lorenz, the name of the company manufacturing the equipments. In Lorenz two signals were broadcast on the same frequencies from highly directional antennas with beams a few degrees wide. One was pointed slightly to the left of the other, with a small angle in the middle where they overlapped. The signals were chosen as dots and dashes, timed so that when the aircraft was in the small area in the middle the sound was continuous. Planes would fly into the beams by listening to the signal to identify which side of middle they were on, and then corrected until they were in the center.

Originally developed as a night and bad-weather landing system, in the late 1930s they also started developing long-range versions for night bombing. In this case a second set of signals were broadcast at right angles to the first, and indicated the point at which to drop the bombs. The system was highly accurate and a battle of the beams broke out when United Kingdom intelligence services attempted, and then succeeded, in rendering the system useless.

In the post-war era similar systems were widely deployed, notably in the United States where a system of long range "airways" was created spanning the country with stations about 200 miles (320km) apart. The signals were chosen as the A and N letters from morse code, dot-dash and dash-dot respectively. However, new developments soon rendered these systems obsolete.

Tuesday, September 16, 2008

Definition of sense

There is no firm agreement among neurologists as to the number of senses because of differing definitions of what constitutes a sense. One definition states that an exteroceptive sense is a faculty by which outside stimuli are perceived.The traditional five senses are sight, hearing, touch, smell, taste: a classification attributed to Aristotle.Humans also have at least six additional senses (a total of eleven including interoceptive senses) that include: nociception (pain), equilibrioception (balance), proprioception & kinesthesia (joint motion and acceleration), sense of time, thermoception (temperature differences), and in some a weak magnetoception (direction)

One commonly recognized catagorisation for human senses is as follows: chemoreception; photoreception; mechanoreception; and thermoception. Indeed, all human senses fit into one of these four categories.

Monday, September 08, 2008

Palaeobiogeography

Paleobiogeography goes one step further to include paleogeographic data and considerations of plate tectonics. Using molecular analyses and corroborated by fossils, it has been possible to demonstrate that perching birds evolved first in the region of Australia or the adjacent Antarctic (which at that time lay somewhat further north and had a temperate climate). From there, they spread to the other Gondwanan continents and Southeast Asia - the part of Laurasia then closest to their origin of dispersal - in the late Paleogene, before achieving a global distribution in the early Neogene . Not knowing the fact that at the time of dispersal, the Indian Ocean was much narrower than it is today, and that South America was closer to the Antarctic, one would be hard pressed to explain the presence of many "ancient" lineages of perching birds in Africa, as well as the mainly South American distribution of the suboscines.

Tuesday, September 02, 2008

Generalized anxiety disorder

Generalized anxiety disorder is a common chronic disorder that affects twice as many women as men and can lead to considerable impairment (Brawman-Mintzer & Lydiard, 1996, 1997). As the name implies, generalized anxiety disorder is characterized by long-lasting anxiety that is not focused on any particular object or situation. In other words it is unspecific or free-floating. People with this disorder feel afraid of something but are unable to articulate the specific fear. They fret constantly and have a hard time controlling their worries. Because of persistent muscle tension and autonomic fear reactions, they may develop headaches, heart palpitations, dizziness, insomnia and chest pain. These physical symptoms, combined with the intense, long-term anxiety, make it difficult to cope with normal daily activities.