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  • American Association for the Advancement of Science (AAAS)
  • Cambridge University Press
  • American Institute of Physics (AIP)
  • 1
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    Optimization of an exchange-correlation density functional for water (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-06-10
    Description: We describe a method, that we call data projection onto parameter space (DPPS), to optimize an energy functional of the electron density, so that it reproduces a dataset of experimental magnitudes. Our scheme, based on Bayes theorem, constrains the optimized functional not to depart unphysically from existing ab initio functionals. The resulting functional maximizes the probability of being the “correct” parameterization of a given functional form, in the sense of Bayes theory. The application of DPPS to water sheds new light on why density functional theory has performed rather poorly for liquid water, on what improvements are needed, and on the intrinsic limitations of the generalized gradient approximation to electron exchange and correlation. Finally, we present tests of our water-optimized functional, that we call vdW-DF-w, showing that it performs very well for a variety of condensed water systems.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Characterizing solid-state ignition of runaway chemical reactions in Ni-Al nanoscale multilayers under uniform heating (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-08
    Description: Nanoscale layers of nickel and aluminum can mix rapidly to produce runaway reactions. While self-propagating high temperature synthesis reactions have been observed for decades, the solid-state ignition of these reactions has been challenging to study. Particularly elusive is characterization of the low-temperature chemical mixing that occurs just prior to the ignition of the runaway reaction. Characterization can be challenging due to inhomogeneous microstructures, uncontrollable heat losses, and the nonuniform distribution of heat throughout the material prior to ignition. To reduce the impact of these variables, we heat multilayered Ni/Al foils in a highly uniform manner and report ignition temperatures as low as 245 °C for heating rates ranging from 2000 °C/s to 50 000 °C/s. Igniting in this way reveals that there are four stages before the reaction is complete: heating to an ignition temperature, low temperature solid-state mixing, a separate high temperature solid-state mixing, and liquid-state mixing. Multiple bilayer spacings, heating rates, and heating times are compared to show that the ignition temperature is a function of the bilayer spacing. A symmetric numerical diffusion model is used to show that there is very little chemical mixing in the first 10 ms of heating but significant mixing after 50 ms. These predictions suggest that ignition temperatures should increase for the slowest heating rates but this trend could not be identified clearly. The modeling was also used to examine the kinetic parameters governing the early stages of solid-state diffusion and suggest that grain boundary diffusion is dominant.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Highly textured oxypnictide superconducting thin films on metal substrates (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-31
    Description: Highly textured NdFeAs(O,F) thin films have been grown on ion beam assisted deposition-MgO/Y 2 O 3 /Hastelloy substrates by molecular beam epitaxy. The oxypnictide coated conductors showed a superconducting transition temperature ( T c ) of 43 K with a self-field critical current density ( J c ) of 7.0 × 10 4   A / cm 2 at 5 K, more than 20 times higher than powder-in-tube processed SmFeAs(O,F) wires. Albeit higher T c as well as better crystalline quality than Co-doped BaFe 2 As 2 coated conductors, in-field J c of NdFeAs(O,F) was lower than that of Co-doped BaFe 2 As 2 . These results suggest that grain boundaries in oxypnictides reduce J c significantly compared to that in Co-doped BaFe 2 As 2 and, hence biaxial texture is necessary for high J c.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Spectral encoding method for measuring the relative arrival time between x-ray/optical pulses (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-08-29
    Description: The advent of few femtosecond x-ray light sources brings promise of x-ray/optical pump-probe experiments that can measure chemical and structural changes in the 10–100 fs time regime. Widely distributed timing systems used at x-ray Free-Electron Laser facilities are typically limited to above 50 fs fwhm jitter in active x-ray/optical synchronization. The approach of single-shot timing measurements is used to sort results in the event processing stage. This has seen wide use to accommodate the insufficient precision of active stabilization schemes. In this article, we review the current technique for “measure-and-sort” at the Linac Coherent Light Source at the SLAC National Accelerator Laboratory. The relative arrival time between an x-ray pulse and an optical pulse is measured near the experimental interaction region as a spectrally encoded cross-correlation signal. The cross-correlation provides a time-stamp for filter-and-sort algorithms used for real-time sorting. Sub-10 fs rms resolution is common in this technique, placing timing precision at the same scale as the duration of the shortest achievable x-ray pulses.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    The creation of large-volume, gradient-free warm dense matter with an x-ray free-electron laser (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-03-25
    Description: The efficiency and uniformity of heating induced by hard x-ray free-electron laser pulse is investigated for 0.5  μ m silver foils using the X-ray Pump Probe instrument at the Linac Coherent Light Source facility. Intense 8.9 keV x-ray pulses of 60 fs duration deposit energy predominantly via inner-shell ionization to create a non-equilibrium Ag solid density plasma. The x-ray pulses are focused to 14 × 17  μ m 2 by means of beryllium lenses and by varying the total beam energy, the energy deposition is varied over a range of irradiances from 4.4 to 6.5 × 10 15  W/cm 2 . Two time-and-space resolved interferometers simultaneously probed the expansion of the front and rear sample surfaces and find evidence of a nearly symmetric expansion pointing to the uniformity of energy deposition over the full target thickness. The experimental results are compared with two different hydrodynamic simulations of the sample expansion. The agreement between experimental and theoretical results yields an estimate of the temperature evolution as a function of x-ray irradiance that varies from 8 to 10 eV for the x-ray irradiances studied.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Performance of a beam-multiplexing diamond crystal monochromator at the Linac Coherent Light Source (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-06-07
    Description: A double-crystal diamond monochromator was recently implemented at the Linac Coherent Light Source. It enables splitting pulses generated by the free electron laser in the hard x-ray regime and thus allows the simultaneous operations of two instruments. Both monochromator crystals are High-Pressure High-Temperature grown type-IIa diamond crystal plates with the (111) orientation. The first crystal has a thickness of ∼100 μm to allow high reflectivity within the Bragg bandwidth and good transmission for the other wavelengths for downstream use. The second crystal is about 300 μm thick and makes the exit beam of the monochromator parallel to the incoming beam with an offset of 600 mm. Here we present details on the monochromator design and its performance.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Translating biomolecular recognition into nanomechanics (2000)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2000-04-15
    Description: We report the specific transduction, via surface stress changes, of DNA hybridization and receptor-ligand binding into a direct nanomechanical response of microfabricated cantilevers. Cantilevers in an array were functionalized with a selection of biomolecules. The differential deflection of the cantilevers was found to provide a true molecular recognition signal despite large nonspecific responses of individual cantilevers. Hybridization of complementary oligonucleotides shows that a single base mismatch between two 12-mer oligonucleotides is clearly detectable. Similar experiments on protein A-immunoglobulin interactions demonstrate the wide-ranging applicability of nanomechanical transduction to detect biomolecular recognition.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fritz, J -- Baller, M K -- Lang, H P -- Rothuizen, H -- Vettiger, P -- Meyer, E -- Guntherodt, H -- Gerber, C -- Gimzewski, J K -- New York, N.Y. -- Science. 2000 Apr 14;288(5464):316-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉IBM Research, Zurich Research Laboratory, Saumerstrasse 4, CH-8803 Ruschlikon, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10764640" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antibody Specificity ; Base Pair Mismatch ; Base Pairing ; Chemistry, Physical ; Goats ; Gold/*chemistry ; Hydrogen Bonding ; Immunoglobulin Constant Regions/*chemistry ; Ligands ; *Nucleic Acid Hybridization ; Oligodeoxyribonucleotides/*chemistry ; Physicochemical Phenomena ; Rabbits ; Silicon/*chemistry ; Staphylococcal Protein A/*chemistry ; Static Electricity ; Stress, Mechanical ; Thionucleotides/chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    The history of South American tropical precipitation for the past 25,000 years (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-02-07
    Description: Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Baker, P A -- Seltzer, G O -- Fritz, S C -- Dunbar, R B -- Grove, M J -- Tapia, P M -- Cross, S L -- Rowe, H D -- Broda, J P -- New York, N.Y. -- Science. 2001 Jan 26;291(5504):640-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Duke University, Division of Earth and Ocean Sciences, Durham, NC 27708, USA. pbaker@geo.duke.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11158674" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Atmosphere ; Bolivia ; Diatoms ; *Fresh Water ; *Geologic Sediments ; Peru ; Plankton ; *Rain ; Temperature ; Time ; *Tropical Climate
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Early warming of tropical South America at the last glacial-interglacial transition (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-06-01
    Description: Glaciation in the humid tropical Andes is a sensitive indicator of mean annual temperature. Here, we present sedimentological data from lakes beyond the glacial limit in the tropical Andes indicating that deglaciation from the Last Glacial Maximum led substantial warming at high northern latitudes. Deglaciation from glacial maximum positions at Lake Titicaca, Peru/Bolivia (16 degrees S), and Lake Junin, Peru (11 degrees S), occurred 22,000 to 19,500 calendar years before the present, several thousand years before the Bolling-Allerod warming of the Northern Hemisphere and deglaciation of the Sierra Nevada, United States (36.5 degrees to 38 degrees N). The tropical Andes deglaciated while climatic conditions remained regionally wet, which reflects the dominant control of mean annual temperature on tropical glaciation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Seltzer, G O -- Rodbell, D T -- Baker, P A -- Fritz, S C -- Tapia, P M -- Rowe, H D -- Dunbar, R B -- New York, N.Y. -- Science. 2002 May 31;296(5573):1685-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, USA. goseltze@syr.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12040193" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    Zebrafish hox clusters and vertebrate genome evolution (1998)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1998-11-30
    Description: HOX genes specify cell fate in the anterior-posterior axis of animal embryos. Invertebrate chordates have one HOX cluster, but mammals have four, suggesting that cluster duplication facilitated the evolution of vertebrate body plans. This report shows that zebrafish have seven hox clusters. Phylogenetic analysis and genetic mapping suggest a chromosome doubling event, probably by whole genome duplication, after the divergence of ray-finned and lobe-finned fishes but before the teleost radiation. Thus, teleosts, the most species-rich group of vertebrates, appear to have more copies of these developmental regulatory genes than do mammals, despite less complexity in the anterior-posterior axis.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Amores, A -- Force, A -- Yan, Y L -- Joly, L -- Amemiya, C -- Fritz, A -- Ho, R K -- Langeland, J -- Prince, V -- Wang, Y L -- Westerfield, M -- Ekker, M -- Postlethwait, J H -- P01HD22486/HD/NICHD NIH HHS/ -- R01RR10715/RR/NCRR NIH HHS/ -- New York, N.Y. -- Science. 1998 Nov 27;282(5394):1711-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9831563" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Chromosome Mapping ; Chromosomes/genetics ; *Evolution, Molecular ; Gene Duplication ; *Genes, Homeobox ; *Genome ; Models, Genetic ; *Multigene Family ; Phylogeny ; Pseudogenes ; Zebrafish/*genetics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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