1,931 research outputs found

    Structure and optical properties of high light output halide scintillators

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    Structural and optical properties of several high light output halide scintillators and closely related materials are presented based on first principles calculations. The optical properties are based on the Engel-Vosko generalized gradient approximation and the recently developed density functional of Tran and Blaha. The materials investigated are BaBr2_2, BaIBr, BaCl2_2, BaF2_2, BaI2_2, BiI3_3, CaI2_2, Cs2LiYCl_2LiYCl_6,CsBa, CsBa_2BrBr_5,CsBa, CsBa_2II_5,K, K_2LaBrLaBr_5,K, K_2LaClLaCl_5,K,K_2LaILaI_5,LaBr, LaBr_3,LaCl, LaCl_3,SrBr, SrBr_2,andYI, and YI_3.ForcomparisonresultsarepresentedfortheoxideCdWO. For comparison results are presented for the oxide CdWO_4.WefindthattheTranBlahafunctionalgivesgreatlyimprovedbandgapsandopticalpropertiesinthisclassofmaterials.Furthermore,wefindthatunlikeCdWO. We find that the Tran Blaha functional gives greatly improved band gaps and optical properties in this class of materials. Furthermore, we find that unlike CdWO_4$, most of these halides are highly isotropic from an optical point of view even though in many cases the crystal structures and other properties are not. This general result is rationalized in terms of halide chemistry. Implications for the development of ceramic halide scintillators are discussed

    Time-Resolved Measurement of a Charge Qubit

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    We propose a scheme for monitoring coherent quantum dynamics with good time-resolution and low backaction, which relies on the response of the considered quantum system to high-frequency ac driving. An approximate analytical solution of the corresponding quantum master equation reveals that the phase of an outgoing signal, which can directly be measured in an experiment with lock-in technique, is proportional to the expectation value of a particular system observable. This result is corroborated by the numerical solution of the master equation for a charge qubit realized with a Cooper-pair box, where we focus on monitoring coherent oscillations.Comment: 4 pages, 3 figure

    Analysis and characterization of ancillary service demand response strategies for variable air volume HVAC systems

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    Thesis (S.M. in Building Technology)--Massachusetts Institute of Technology, Dept. of Architecture, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 113-119).Output variability and prediction difficulties with respect to solar and wind electricity resources increase the requirement of grid-scale reserve capacity and add strain to existing firm generators used for reserves and other ancillary services. Residential and commercial buildings account for a large portion of the electricity consumed in the U.S. and can play a significant role in smart grids to help meet challenges brought about by intermittent renewable generation. High resolution power consumption and HVAC performance data measured in a real building was used to identify real-world operational qualities of VAV systems to be considered by building researchers and building practitioners. This includes the relative magnitude of building power loads, the direct and indirect relationships between environmental conditions and HVAC power consumption, the discrete operation of staged or cycled power loads, and the presence of HVAC operational faults. Also, three static pressure adjustment tests were performed over a one day period. Results showed that fan and terminal unit controllers responded within two minutes and system air flowrate was strongly related to power consumption. Dynamic models were created in order to simulate the performance of a VAV system providing spinning reserves by four different common demand response strategies: zone air dry bulb temperature setpoint adjustment (ZDBA), duct static pressure setpoint adjustment (SPA), supply air temperature adjustment (STA), and chilled water temperature adjustment (CWA). Simulations were run over ranges of implementation and cooling load intensities and the results were used to create characteristic curves for each strategy, which map performance in terms of system power consumption reduction, system airflow reduction, and zone temperature rise. Inflection points on the curves that delineate performance effectiveness are found to result from maximum or minimum terminal unit damper positions. In the future, the development of mathematical functional forms of these characterization curves could help predict and optimize the performance of VAV systems in providing ancillary services to electricity networks.by David H. Blum.S.M.in Building Technolog

    Neurogenetic interactions and aberrant behavioral co-morbidity of attention deficit hyperactivity disorder (ADHD): dispelling myths

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    BACKGROUND: Attention Deficit Hyperactivity Disorder, commonly referred to as ADHD, is a common, complex, predominately genetic but highly treatable disorder, which in its more severe form has such a profound effect on brain function that every aspect of the life of an affected individual may be permanently compromised. Despite the broad base of scientific investigation over the past 50 years supporting this statement, there are still many misconceptions about ADHD. These include believing the disorder does not exist, that all children have symptoms of ADHD, that if it does exist it is grossly over-diagnosed and over-treated, and that the treatment is dangerous and leads to a propensity to drug addiction. Since most misconceptions contain elements of truth, where does the reality lie? RESULTS: We have reviewed the literature to evaluate some of the claims and counter-claims. The evidence suggests that ADHD is primarily a polygenic disorder involving at least 50 genes, including those encoding enzymes of neurotransmitter metabolism, neurotransmitter transporters and receptors. Because of its polygenic nature, ADHD is often accompanied by other behavioral abnormalities. It is present in adults as well as children, but in itself it does not necessarily impair function in adult life; associated disorders, however, may do so. A range of treatment options is reviewed and the mechanisms responsible for the efficacy of standard drug treatments are considered. CONCLUSION: The genes so far implicated in ADHD account for only part of the total picture. Identification of the remaining genes and characterization of their interactions is likely to establish ADHD firmly as a biological disorder and to lead to better methods of diagnosis and treatment

    Phase II Study of Ifosfamide+Doxorubicin in Patients With Advanced Synovial Sarcomas (E1793): A Trial of the Eastern Cooperative Oncology Group

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    Purpose Because we had observed in the synovial sarcoma subgroup of a broad phase III advanced soft tissue sarcoma study a significantly greater objective regression rate from ifosfamide+doxorubicin (88%) than from doxorubicin alone (20%) (P = 0.02), the Eastern Cooperative Oncology Group (ECOG) decided to further assess this two drug combination in a subsequent Phase II study

    Use of a Robust Dehydrogenase from an Archael Hyperthermophile in Asymmetric Catalysis–Dynamic Reductive Kinetic Resolution Entry into (S)-Profens

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    Hyperthermophilic archaea are of great interest in evolutionary microbiology, owing to their ability to withstand high temperatures, and often extremes of pressure, pH and salinity. Enzymes from these organisms1 may offer particular opportunities for asymmetric synthesis, complementary to approaches with mesophilic enzymes,2 or those involving enzyme3 and pathway4 reengineering. However, perhaps due to a bias that hyperthermophilic enzymes have “narrow substrate specificities,”5 archaeal extremophiles remain a largely untapped resource in asymmetric synthesis.6 Herein, we disclose a remarkably general Dynamic Reductive Kinetic Resolution (DYRKR) entry into (S)-profens, including several important NSAIDs. The enzyme employed is alcohol dehydrogenase (ADH)-10, one of 13 annotated ADHs in the hyperthermophile Sulfolobus solfataricus. Protein phylogenetic analysis of this paralogous family indicates SsADH-10 is most closely related to homologues in distant taxa (Fig. 1). The highest identity between SsADH-10 and any other SsADHs is only 34%, suggesting that the SsADH family was established prior to the emergence of other archaeal lineages. Though not described as such, the SsADH-10 appears to be the only SsADH isozyme for which structural information is available in the pdb.

    Use of a Robust Dehydrogenase from an Archael Hyperthermophile in Asymmetric Catalysis–Dynamic Reductive Kinetic Resolution Entry into (S)-Profens

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    Hyperthermophilic archaea are of great interest in evolutionary microbiology, owing to their ability to withstand high temperatures, and often extremes of pressure, pH and salinity. Enzymes from these organisms1 may offer particular opportunities for asymmetric synthesis, complementary to approaches with mesophilic enzymes,2 or those involving enzyme3 and pathway4 reengineering. However, perhaps due to a bias that hyperthermophilic enzymes have “narrow substrate specificities,”5 archaeal extremophiles remain a largely untapped resource in asymmetric synthesis.6 Herein, we disclose a remarkably general Dynamic Reductive Kinetic Resolution (DYRKR) entry into (S)-profens, including several important NSAIDs. The enzyme employed is alcohol dehydrogenase (ADH)-10, one of 13 annotated ADHs in the hyperthermophile Sulfolobus solfataricus. Protein phylogenetic analysis of this paralogous family indicates SsADH-10 is most closely related to homologues in distant taxa (Fig. 1). The highest identity between SsADH-10 and any other SsADHs is only 34%, suggesting that the SsADH family was established prior to the emergence of other archaeal lineages. Though not described as such, the SsADH-10 appears to be the only SsADH isozyme for which structural information is available in the pdb.

    Roles of DnaK and RpoS in Starvation-Induced Thermotolerance of \u3ci\u3eEscherichia coli\u3c/i\u3e

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    DnaK is essential for starvation-induced resistance to heat, oxidation, and reductive division in Escherichia coli. Studies reported here indicate that DnaK is also required for starvation-induced osmotolerance, catalase activity, and the production of the RpoS-controlled Dps (PexB) protein. Because these dnaK mutant phenotypes closely resemble those of rpoS (o38) mutants, the relationship between DnaK and RpoS was evaluated directly during growth and starvation at 30°C in strains with genetically altered DnaK content. A starvation-specific effect of DnaK on RpoS abundance was observed. During carbon starvation, DnaK deficiency reduced RpoS levels threefold, while DnaK excess increased RpoS levels nearly twofold. Complementation of the dnaK mutation restored starvation-induced RpoS levels to normal. RpoS deficiency had no effect on the cellular concentration of DnaK, revealing an epistatic relationship between DnaK and RpoS. Protein half-life studies conducted at the onset of starvation indicate that DnaK deficiency significantly destabilized RpoS. RpoH (s32) suppressors of the dnaK mutant with restored levels of RpoS and dnaK rpoS double mutants were used to show that DnaK plays both an independent and an RpoS-dependent role in starvation-induced thermotolerance. The results suggest that DnaK coordinates sigma factor levels in glucose-starved E. coli

    Nonlocal Conductivity in the Vortex-Liquid Regime of a Two-Dimensional Superconductor

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    We have simulated the time-dependent Ginzburg-Landau equation with thermal fluctuations, to study the nonlocal dc conductivity of a superconducting film. Having examined points in the phase diagram at a wide range of temperatures and fields below the mean-field upper critical field, we find a portion of the vortex-liquid regime in which the nonlocal ohmic conductivity in real space is negative over a distance several times the spacing between vortices. The effect is suppressed when driven beyond linear response. Earlier work had predicted the existence of such a regime, due to the high viscosity of a strongly-correlated vortex liquid. This behavior is clearly distinguishable from the monotonic spatial fall-off of the conductivity in the higher temperature or field regimes approaching the normal state. The possibilities for experimental study of the nonlocal transport properties are discussed.Comment: 18 pages, revtex, 6 postscript figure
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