Superfluidity of isotopically doped parahydrogen clusters

It is shown by computer simulations that superfluid {\it para}-hydrogen clusters of more than 22 molecules can be turned insulating and "solidlike" by the replacement of as few as one or two molecules, with ones of the heavier {\it ortho}-deuterium isotope. A much smaller effect is observed with substitutional {\it ortho}-hydrogen. Substitutional {\it ortho}-deuterium molecules prevalently sit in the inner part of the cluster, whereas {\it ortho}-hydrogen impurities reside primarily in the outer shell, near the surface. Implications on the superfluidity of pure {\it para}-hydrogen clusters are discussed.Comment: 4 pages, 5 figure

The nature of CuA in cytochrome c oxidase

The isolation and purification of yeast cytochrome c oxidase is described. Characterization of the purified protein indicates that it is spectroscopically identical with cytochrome c oxidase isolated from beef heart. Preparations of isotopically substituted yeast cytochrome c oxidase are obtained incorporating [1,3-15N2]histidine or [beta,beta- 2H2]cysteine. Electron paramagnetic resonance and electron nuclear double resonance spectra of the isotopically substituted proteins identify unambiguously at least 1 cysteine and 1 histidine as ligands to CuA and suggest that substantial spin density is delocalized onto a cysteine sulfur in the oxidized protein to render the site Cu(I)-S

Carbon and nitrogen assimilation in the Bering Sea clams Nuculana radiata and Macoma moesta

We analyzed bulk carbon and nitrogen stable isotope values (delta C-13 and delta N-15) of the benthic clams Nuculana radiata and Macoma moesta from the Bering Sea during controlled feeding experiments (spring of 2009 and 2010) using isotopically labeled sea ice algae. The aim was to determine the ability of these clam species to assimilate carbon and nitrogen from sea ice algae. Specimens were collected in the Bering Sea and placed into jars without sediment (2009, N. radiata only) or into natural sediment cores (2010, both species). The clams were offered isotopically enriched (both C and N) or non-enriched algal feeds for time periods of 42 (2009) and 18 d (2010). Isotopic assimilation rates for carbon and nitrogen were calculated using the change in the isotope ratios of the clams over the experimental time. N. radiata in the jar experiments had slow isotopic assimilation rates (0.01 to 0.23 parts per thousand d(-1)), with solvent-extractable organic matter/lipids taking up both of the isotope markers fastest and muscle tissue the slowest. Lipids may thus be particularly suitable to track the immediate ingestion of sea ice algal production in benthic consumers. M. moesta showed 30% higher isotopic assimilation compared to N. radiata in sediment cores, likely reflecting the different feeding behaviors of these two species. Based on our results, N. radiata is likely better able to utilize food sources buried in the sediment and may be more competitive over the sediment surface feeding M. moesta under conditions of reduced ice algal production in the northern Bering Sea. (C) 2012 Elsevier B.V. All rights reserved.This project was undertaken as a part of the National Science Foundation funded Bering Sea Ecosystem Study (BEST Project) #0732767awarded to R. Gradinger, K. Iken, and B. Bluhm at the University of Alaska Fairbanks. Additional research funding to J. Weems was provided by the UAF Center for Global Change Student Research Grant with funds from the Cooperative Institute for Alaska Research and the Harland and Genevieve Emerson Foundation of Adel, Iowa. Bering Sea field support and operations in 2009 and 2010 were provided by chief scientists L. Cooper, J. Grebmeier, and C. Ashjian, and the vessels and crews of the United States Coast Guard Cutters Healy and Polar Sea. Additionally, field and laboratory aid was provided by B. Bluhm, M. Kaufman, B. McConnell, M. Schuster, and J. von Meltzer. Services rendered by the Alaska Stable Isotope Facility and its staff, N. Haubenstock and T. Howe, were very much appreciated. Academic support for J. Weems was provided by the School of Fisheries and Ocean Sciences at the University of Alaska Fairbanks. We thank M. Castellini and two anonymous reviewers for comments on earlier versions of this manuscript. Support for the fatty acid analyses and partial support forWooller came from NSF grant ARC 0902177 awarded to (Gradinger, Iken and Wooller). [ST]Ye

Effect of nucleon exchange on projectile multifragmentation in the reactions of 28Si + 112Sn and 124Sn at 30 and 50 MeV/nucleon

Multifragmentation of quasiprojectiles was studied in reactions of 28Si beam with 112Sn and 124Sn targets at projectile energies 30 and 50 MeV/nucleon. The quasiprojectile observables were reconstructed using isotopically identified charged particles with Z_f <= 5 detected at forward angles. The nucleon exchange between projectile and target was investigated using isospin and excitation energy of reconstructed quasiprojectile. For events with total reconstructed charge equal to the charge of the beam (Z_tot = 14) the influence of beam energy and target isospin on neutron transfer was studied in detail. Simulations employing subsequently model of deep inelastic transfer, statistical model of multifragmentation and software replica of FAUST detector array were carried out. A concept of deep inelastic transfer provides good description of production of highly excited quasiprojectiles. The isospin and excitation energy of quasiprojectile were described with good overall agreement. The fragment multiplicity, charge and isospin were reproduced satisfactorily. The range of contributing impact parameters was determined using backtracing procedure.Comment: 11 pages, 8 Postscript figures, LaTeX, to appear in Phys. Rev. C ( Dec 2000

Thermal Conductivity of Isotopically Enriched 28Si Revisited

The thermal conductivity of isotopically enriched 28Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of 4 samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched 28Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 10&#61617;2 %. This finding is in disagreement with an earlier report by Ruf et al. At &#61566;26 K the thermal conductivity of 28Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of &#61566;8 for a 99.982% 28Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be &#61566;3% lower than the values recommended in the literature

Correlated Microscale Isotope and Scanning Transmission X-Ray Analyses of Isotopically Anomalous Organic Matter from the CR2 Chondrite EET 92042

We discuss correlated examinations of organic matter from the CR2 chondrite EET 92042, using SIMS, STXM and other methods. We found a large, isotopically highly anomalous region of probable presolar origin that is C- and 13C-poor and 15N-rich