Scientists at NASA and Columbia University in New York have used computer modeling to successfully reproduce an abrupt climate change that took place 8,200 years ago. At that time -- the beginning of the current warm period -- climate changes were caused by a massive flood of fresh water into the North Atlantic.
This work is the first to consistently re-create the event by computer modeling, and the first time that the model results have been confirmed by comparison to the climate record, which includes ice-core and tree-ring data.
"We only have one example of how the climate reacts to changes -- the past," said Gavin A. Schmidt, a researcher at the NASA Goddard Institute for Space Studies (GISS) and co-author on the study. "If we're going to accurately simulate the Earth's future, we need to be able to replicate past events. This was a real test of the model's skill."
The study was led by Allegra LeGrande, a graduate student in the department of earth and environmental sciences at Columbia. The results appeared in the journal Proceedings of the National Academy of Sciences in January.
The group used an atmosphere-ocean coupled climate computer model known as GISS Model E-R to simulate the climate impact of a massive freshwater flood into the North Atlantic that happened after the end of the last Ice Age. Retreating glaciers opened a route for two ancient meltwater lakes, known as Agassiz and Ojibway, to suddenly drain from the middle of the North American continent.
According to the model, temperatures in the North Atlantic and Greenland showed the largest decrease, with slightly less cooling over parts of North America and Europe. The rest of the Northern Hemisphere, however, experienced very little effect, and temperatures in the Southern Hemisphere remained largely unchanged. Moreover, ocean circulation, which initially dropped by half after the simulated flood, appears to have rebounded within 50 to 150 years.
Difference engines: Move over Mr. Turing
Proving the old adage that a good idea has many fathers, some scholars believe that one of the fathers of computing is Panini, an ancient Sanskrit grammarian who, according to commonly accepted estimates, lived in the fifth century B.C. Almost nothing is known for certain about Panini's life. Tradition has it that he was born near the Indus River in what's now Pakistan.
Panini's grammar for Sanskrit is highly systematized and technical. Inherent in its analytic approach are the concepts of the phoneme, the morpheme and the root, not recognized by Western linguists until some two millennia later. His rules have a reputation of perfection -- that is, they are claimed to fully describe Sanskrit morphology, without any redundancy. A consequence of his grammar's focus on brevity is its highly nonintuitive structure, reminiscent of contemporary "machine language" (as opposed to "human-readable" programming languages).
Panini uses metarules, transformations and recursions with such sophistication that his grammar has the computing power equivalent to that of a Turing machine. In this sense, Panini may, indeed, be considered the father of computing machines. His work was also the forerunner to modern formal-language theory. Paninian grammars have also been devised for non-Sanskrit languages. The Backus-Naur form (sometimes called the Panini-Backus form), or BNF, grammars used to describe modern programming languages are similar to Panini's grammar rules.
It's not even known whether Panini used writing for the composition of his work. Some historians argue that a work of such complexity would have been impossible to compile without written notes, while others allow for the possibility that he might have composed it with the help of a group of students whose memories served him as "notepads."
Groves of academe: answers without questions
By combining quantum computation and quantum interrogation, scientists at the University of Illinois at Urbana-Champaign have found an exotic way of determining an answer to an algorithm -- without ever running the algorithm.
Using an optical-based quantum computer, a research team led by physicist Paul Kwiat has presented the first demonstration of "counterfactual computation," inferring information about an answer even though the computer did not run. The researchers reported their work in the Feb. 23 issue of Nature.
Quantum computers could solve certain types of problems much faster than classical computers. Speed and efficiency are gained because quantum bits can be placed in superpositions of one and zero, as opposed to classical bits, which can only be either one or zero. Moreover, the logic behind the coherent nature of quantum information processing often deviates from intuitive reasoning, leading to some surprising effects.
"It seems absolutely bizarre that counterfactual computation -- using information that is counter to what must have actually happened -- could find an answer without running the entire quantum computer," said Kwiat.
Sometimes called interaction-free measurement, quantum interrogation uses wave-particle duality (in this case, of photons) to search a region of space without actually entering that region.
Using two optical interferometers nested within a third, Kwiat's team succeeded in counterfactually searching a four-element database using Lov Grover's quantum algorithm for searching unsorted databases. "By placing our photon in a quantum superposition of running and not running the search algorithm, we obtained information about the answer even when the photon did not run the search algorithm," said graduate student Onur Hosten, lead author of the paper.
"In a sense, it is the possibility that the algorithm could run which prevents the algorithm from running," Kwiat said. "That is at the heart of quantum interrogation schemes, and to my mind, quantum mechanics doesn't get any more mysterious than this."
E-mail 2006
22 percent of the global e-mail user population resides in North America.
44 percent of worldwide e-mail users are under the age of 29.
35 percent of the corporate e-mail installed base is related to small business.
69 percent is the projected growth rate in the installed base in the unified communications segment of the telecom market from 2006 to 2009.