American Association for the Advancement of Science (AAAS)
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Pathways to a Protein Folding Intermediate Observed in a 1-Microsecond Simulation in Aqueous Solution An implementation of classical molecular dynamics on parallel computers of increased efficiency has enabled a simulation of protein folding with explicit representation of water for 1 microsecond, about two orders of magnitude longer than the longest simulation of a protein in water reported to date. Starting with an unfolded state of villin headpiece subdomain, hydrophobic collapse and helix formation occur in an initial phase, followed by conformational readjustments. A marginally stable state, which has a lifetime of about 150 nanoseconds, a favorable solvation free energy, and shows significant resemblance to the native structure, is observed; two pathways to this state have been found.
American Association for the Advancement of Science (AAAS) - Tập 282 Số 5389 - Trang 740-744 - 1998
A Glimpse of the Holy Grail?
American Association for the Advancement of Science (AAAS) - Tập 282 Số 5389 - Trang 642-643 - 1998
Remobilization in the Cratonic Lithosphere Recorded in Polycrystalline Diamond Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere.
American Association for the Advancement of Science (AAAS) - Tập 289 Số 5482 - Trang 1182-1185 - 2000
Water in Earth's Mantle: The Role of Nominally Anhydrous Minerals
Most minerals of Earth's upper mantle contain small amounts of hydrogen, structurally bound as hydroxyl (OH). The OH concentration in each mineral species is variable, in some cases reflecting the geological environment of mineral formation. Of the major mantle minerals, pyroxenes are the most hydrous, typically containing ∼200 to 500 parts per million H
2
O by weight, and probably dominate the water budget and hydrogen geochemistry of mantle rocks that do not contain a hydrous phase. Garnets and olivines commonly contain ∼1 to 50 parts per million. Nominally anhydrous minerals constitute a significant reservoir for mantle hydrogen, possibly accommodating all water in the depleted mantle and providing a possible mechanism to recycle water from Earth's surface into the deep mantle.
American Association for the Advancement of Science (AAAS) - Tập 255 Số 5050 - Trang 1391-1397 - 1992
Prospective representation of navigational goals in the human hippocampus Brain activity to represent the future
How do humans navigate from A to B? Brown
et al.
developed a virtual reality task to investigate the neural representations that support human navigational planning. Highly specific activity of the hippocampus and related brain areas represented the future locations to which participants eventually moved. Network-level interactions of the hippocampus with the prefrontal cortex thus enable flexible representation of planned destinations.
Science
, this issue p.
1323
American Association for the Advancement of Science (AAAS) - Tập 352 Số 6291 - Trang 1323-1326 - 2016
Perceiving Real-World Scenes When a briefly presented real-world scene was jumbled, the accuracy of identifying a single, cued object was less than that when the scene was coherent. Jumbling remained an effective variable even when the subject knew where to look and what to look for. Thus an object's meaningful context may affect the course of perceptual recognition and not just peripheral scanning or memory.
American Association for the Advancement of Science (AAAS) - Tập 177 Số 4043 - Trang 77-80 - 1972
Do 15-Month-Old Infants Understand False Beliefs? For more than two decades, researchers have argued that young children do not understand mental states such as beliefs. Part of the evidence for this claim comes from preschoolers' failure at verbal tasks that require the understanding that others may hold false beliefs. Here, we used a novel nonverbal task to examine 15-month-old infants' ability to predict an actor's behavior on the basis of her true or false belief about a toy's hiding place. Results were positive, supporting the view that, from a young age, children appeal to mental states—goals, perceptions, and beliefs—to explain the behavior of others.
American Association for the Advancement of Science (AAAS) - Tập 308 Số 5719 - Trang 255-258 - 2005
Theory of Mind Is Independent of Episodic Memory Theory of mind (ToM) to infer other people's current mental states and episodic memory of personal happenings have been assumed to be closely related. We report two participants with severely impaired episodic memory who perform indistinguishably from healthy controls on objective ToM tests. These results suggest that ToM can function independently of episodic memory.
American Association for the Advancement of Science (AAAS) - Tập 318 Số 5854 - Trang 1257-1257 - 2007
Prospection: Experiencing the Future All animals can predict the hedonic consequences of events they've experienced before. But humans can predict the hedonic consequences of events they've never experienced by simulating those events in their minds. Scientists are beginning to understand how the brain simulates future events, how it uses those simulations to predict an event's hedonic consequences, and why these predictions so often go awry.
American Association for the Advancement of Science (AAAS) - Tập 317 Số 5843 - Trang 1351-1354 - 2007
Pyrimidine Starvation Induced by Adenosine in Fibroblasts and Lymphoid Cells: Role of Adenosine Deaminase
In the presence of 10
-4
to 10
-5
molar adenosine, established cell lines of fibroblastic or lymphoid origin die of pyrimidine starvation. Less than lethal concentrations inhibit cell growth. Over a broad concentration range, the effects of adenosine are prevented by providing a suitable pyrimidine source. We suggest that the recently described immune deficiency disease associated with absence of adenosine deaminase may be the result of pyrimidine starvation induced by adenosine nucleotides in cells of the lymphoid system.
American Association for the Advancement of Science (AAAS) - Tập 182 Số 4114 - Trang 836-837 - 1973
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