17,597 research outputs found
The difluoromethylene (CF2) group in aliphatic chains : synthesis and conformational preference of palmitic acids and nonadecane containing CF2 groups
Funding: ERC Advanced Investigator Grant (D.O'H).The syntheses of palmitic acids and a nonadecane are reported with CF2 groups located 1,3 or 1,4 to each other along the aliphatic chain. Specifically 8,8,10,10- and 8,8,11,11-tetrafluorohexadecanoic acids (6b and 6c) are prepared as well as the singly modified analogue 8,8-difluorohexadecanoic acid (6a). Also 8,8,11,11-tetrafluorononadecane (27) is prepared as a pure hydrocarbon containing a 1,4-di-CF2 motif. The modified palmitic acids are characterized by differential scanning calorimetry (DSC) to determine melting points and phase behaviour relative to palmitic acid (62.5 degrees C). It emerges that 6c, with the CF2 groups placed 1,4- to each other, has a significantly higher melting point (89.9 degrees C) when compared to the other analogues and palmitic acid itself. It is a crystalline compound and the structure reveals an extended anti-zig-zag chain. Similarly 8,8,11,11-tetrafluorononadecane (27) adopts an extended anti-zig-zag structure. This is rationalized by dipolar relaxation between the two CF2 groups placed 1,4 to each other in the extended anti-zig-zag chain and suggests a design modification for long chain aliphatics which can introduce conformational stability.Publisher PDFPublisher PDFPeer reviewe
Nearby, Thermally Emitting Neutron Stars
We describe a sample of thermally emitting neutron stars discovered in the
ROSAT All-Sky Survey. We discuss the basic observational properties of these
objects and conclude that they are nearby, middle-aged pulsars with moderate
magnetic fields that we see through their cooling radiation. While these
objects are potentially very useful as probes of matter at very high densities
and magnetic fields, our lack of understanding of their surface emission limits
their current utility. We discuss this and other outstanding problems: the
spectral evolution of one sources and the relation of this population to the
overall pulsar population.Comment: 9 pages, one table, 3 figures. To appear in the proceedings of "40
Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17,
2007, McGill University, Montreal, Canad
The Critical Role of Public Charging Infrastructure
Editors: Peter Fox-Penner, PhD, Z. Justin Ren, PhD, David O. JermainA decade after the launch of the contemporary global electric vehicle (EV) market, most cities face a major challenge preparing for rising EV demand. Some cities, and the leaders who shape them, are meeting and even leading demand for EV infrastructure. This book aggregates deep, groundbreaking research in the areas of urban EV deployment for city managers, private developers, urban planners, and utilities who want to understand and lead change
Structural and electronic origin of the magnetic structures in hexagonal LuFeO
Using combined theoretical and experimental approaches, we studied the
structural and electronic origin of the magnetic structure in hexagonal
LuFeO. Besides showing the strong exchange coupling that is consistent with
the high magnetic ordering temperature, the previously observed spin
reorientation transition is explained by the theoretically calculated magnetic
phase diagram. The structural origin of this spin reorientation that is
responsible for the appearance of spontaneous magnetization, is identified by
theory and verified by x-ray diffraction and absorption experiments.Comment: 5 pages, 2 tables and 4 figures, Please contact us for the
supplementary material. Accepted in Phys. Rev. B, in productio
The SMC Condensin Complex Is Required for Origin Segregation in Bacillus subtilis
SummarySMC condensin complexes play a central role in organizing and compacting chromosomes in all domains of life [1, 2]. In the bacterium Bacillus subtilis, cells lacking SMC are viable only during slow growth and display decondensed chromosomes, suggesting that SMC complexes function throughout the genome [3, 4]. Here, we show that rapid inactivation of SMC or its partner protein ScpB during fast growth leads to a failure to resolve newly replicated origins and a complete block to chromosome segregation. Importantly, the loss of origin segregation is not due to an inability to unlink precatenated sister chromosomes by Topoisomerase IV. In support of the idea that ParB-mediated recruitment of SMC complexes to the origin is important for their segregation, cells with reduced levels of SMC that lack ParB are severely impaired in origin resolution. Finally, we demonstrate that origin segregation is a task shared by the condensin complex and the parABS partitioning system. We propose that origin-localized SMC constrains adjacent DNA segments along their lengths, drawing replicated origins in on themselves and away from each other. This SMC-mediated lengthwise condensation, bolstered by the parABS system, drives origin segregation
Analysis of electromagnetic interference from power system processing and transmission components for Space Station Freedom
The goal of this research project was to analyze the potential effects of electromagnetic interference (EMI) originating from power system processing and transmission components for Space Station Freedom. The approach consists of four steps: (1) developing analytical tools (models and computer programs); (2) conducting parameterization (what if?) studies; (3) predicting the global space station EMI environment; and (4) providing a basis for modification of EMI standards
Table-like magnetocaloric effect in Gd56Ni15Al27Zr2 alloy and its field independence feature
In order to obtain “table-like” magnetocaloric effect (MCE), multiple-phase Gd56Ni15Al27Zr2 alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd2Al and GdNiAl further broadened the relatively wider magnetic entropy change (−ΔSM) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5 K to 77.5 K. The plateau feature of the MCE was found to be nearly independent of the applied magnetic field from 3 T to 5 T. The maximum −ΔSMvalue of the MCE platforms is 6.0 J/kg K under applied magnetic field change of 5 T. Below 3 T, the field independence of the table-like feature disappears. The relatively large constant values of −ΔSM for the respective applied magnetic fields have promising applications in magnetic refrigeration using regenerative Ericsson cycle
Bacillus Subtilis SMC Complexes Juxtapose Chromosome Arms as They Travel from Origin to Terminus
Structural maintenance of chromosomes (SMC) complexes play critical roles in chromosome dynamics in virtually all organisms, but how they function remains poorly understood. In the bacterium Bacillus subtilis, SMC-condensin complexes are topologically loaded at centromeric sites adjacent to the replication origin. Here we provide evidence that these ring-shaped assemblies tether the left and right chromosome arms together while traveling from the origin to the terminus (>2 megabases) at rates >50 kilobases per minute. Condensin movement scales linearly with time, providing evidence for an active transport mechanism. These data support a model in which SMC complexes function by processively enlarging DNA loops. Loop formation followed by processive enlargement provides a mechanism by which condensin complexes compact and resolve sister chromatids in mitosis and by which cohesin generates topologically associating domains during interphase. Keywords: SMC; ParB; condensin; cohesion; loop extrusion; TADNational Institutes of Health (U.S.) (Grant GM082899
Roughening transitions of driven surface growth
A model of surface growth given by a two-dimensional discrete, driven, damped sine-Gordon
equation is studied using Langevin dynamics. Our large-scale simulations show that the equilibrium
Kosterlitz-Thouless roughening transition splits into two crossovers (or transitions) under the
external force of, e.g., vapor-surface chemical potential difference. Three different regimes are characterized
in terms of roughness, growth rate, and height-height correlations-the onset of a rough
phase is accompanied by the suppresion of oscillatory growth. Our results are interpreted consistently
within a renormalization group framework. We discuss the generality of our conclusions and
propose specific comparisons with experimentsPartially supported by DGICyT (Spain) Grant No. PB92-0248, by MEC (Spain)/Fulbright, and by the European Union Network ERBCHRXCT930413. Work at Los Alamos is performed under the auspices of the U.S. DOE.Publicad
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