Ternary erbium chromium sulfides : structural relationships and magnetic properties

Single crystals of four erbium-chromium sulfides have been grown by chemical vapor transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er(3)CrS(6) octahedral sites are occupied exclusively by Cr(3+) cations, leading to one-dimensional CrS(4)(5-) chains of edge-sharing octahedra, while in Er(2)CrS(4), Er(3+), and Cr(2+) cations occupy the available octahedral sites in an ordered manner. By contrast, in Er(6)Cr(2)S(11) and Er(4)CrS(7), Er(3+) and Cr(2+) ions are disordered over the octahedral sites. In Er(2)CrS(4), Er(6)Cr(2)S(11), and Er(4)CrS(7), the network of octahedra generates an anionic framework constructed from M(2)S(5) slabs of varying thickness, linked by one-dimensional octahedral chains. This suggests that these three phases belong to a series in which the anionic framework may be described by the general formula [M(2n+1)S(4n+3)](x-), with charge balancing provided by Er(3+) cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er(4)CrS(7), Er(6)Cr(2)S(11), and Er(2)CrS(4) may thus be considered as the n = 1, 2, and infinity members of this series. While Er(4)CrS(7) is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er(3)CrS(6) (T(C)(Cr) = 30 K; T(C)(Er) = 11 K) and Er(2)CrS(4) (T(N)(Cr) = 42 K, T(N)(Er) = 10 K) whereas Er(6)Cr(2)S(11) exhibits ordering of the chromium sub-lattice only (T(N) = 11.4 K)

Gravitational-wave versus binary-pulsar tests of strong-field gravity

Binary systems comprising at least one neutron star contain strong gravitational field regions and thereby provide a testing ground for strong-field gravity. Two types of data can be used to test the law of gravity in compact binaries: binary pulsar observations, or forthcoming gravitational-wave observations of inspiralling binaries. We compare the probing power of these two types of observations within a generic two-parameter family of tensor-scalar gravitational theories. Our analysis generalizes previous work (by us) on binary-pulsar tests by using a sample of realistic equations of state for nuclear matter (instead of a polytrope), and goes beyond a previous study (by C.M. Will) of gravitational-wave tests by considering more general tensor-scalar theories than the one-parameter Jordan-Fierz-Brans-Dicke one. Finite-size effects in tensor-scalar gravity are also discussed.Comment: 23 pages, REVTeX 3.0, uses epsf.tex to include 5 postscript figures (2 paragraphs and a 5th figure added at the end of section IV + minor changes

Properties of the T8.5 Dwarf Wolf 940 B

We present 7.5-14.2um low-resolution spectroscopy, obtained with the Spitzer Infrared Spectrograph, of the T8.5 dwarf Wolf 940 B, which is a companion to an M4 dwarf with a projected separation of 400 AU. We combine these data with previously published near-infrared spectroscopy and mid-infrared photometry, to produce the spectral energy distribution for the very low-temperature T dwarf. We use atmospheric models to derive the bolometric correction and obtain a luminosity of log L/Lsun = -6.01 +/- 0.05. Evolutionary models are used with the luminosity to constrain the values of effective temperature (T_eff) and surface gravity, and hence mass and age for the T dwarf. We further restrict the allowed range of T_eff and gravity using age constraints implied by the M dwarf primary, and refine the physical properties of the T dwarf by comparison of the observed and modelled spectroscopy and photometry. This comparison indicates that Wolf 940 B has a metallicity within 0.2 dex of solar, as more extreme values give poor fits to the data - lower metallicity produces a poor fit at lambda > 2um while higher metallicity produces a poor fit at lambda < 2um. This is consistent with the independently derived value of [m/H] = +0.24 +/- 0.09 for the primary star, using the Johnson & Apps (2008) M_K:V-K relationship. We find that the T dwarf atmosphere is undergoing vigorous mixing, with an eddy diffusion coefficient K_zz of 10^4 to 10^6 cm^2 s^-1. We derive an effective temperature of 585 K to 625 K, and surface gravity log g = 4.83 to 5.22 (cm s^-2), for an age range of 3 Gyr to 10 Gyr, as implied by the kinematic and H alpha properties of the M dwarf primary. The lower gravity corresponds to the lower temperature and younger age for the system, and the higher value to the higher temperature and older age. The mass of the T dwarf is 24 M_Jupiter to 45 M_Jupiter for the younger to older age limit.Comment: 24 pages which include 5 Figures and 3 Tables. Accepted for publication in the Astrophysical Journal July 2 201

Mechano-chemical kinetics of DNA replication: identification of the translocation step of a replicative DNA polymerase

[EN] During DNA replication replicative polymerases move in discrete mechanical steps along the DNA template. To address how the chemical cycle is coupled to mechanical motion of the enzyme, here we use optical tweezers to study the translocation mechanism of individual bacteriophage Phi29 DNA polymerases during processive DNA replication. We determine the main kinetic parameters of the nucleotide incorporation cycle and their dependence on external load and nucleotide (dNTP) concentration. The data is inconsistent with power stroke models for translocation, instead supports a loose-coupling mechanism between chemical catalysis and mechanical translocation during DNA replication. According to this mechanism the DNA polymerase works by alternating between a dNTP/PPi-free state, which diffuses thermally between pre- and post-translocated states, and a dNTP/PPi-bound state where dNTP binding stabilizes the post-translocated state. We show how this thermal ratchet mechanism is used by the polymerase to generate work against large opposing loads (~50 pN).We thank Stephan Grill laboratory (MPI-CBG, Dresden) for help with data collection and E. Galburt, M. Manosas and M. De Vega for critical reading of the manuscript. Spanish Ministry of Economy and Competitiveness [BFU2011-29038 to J.L.C., BFU2013-44202 to J.M.V., BFU2011-23645 to M.S., FIS2010-17440, GR35/10-A920GR35/10-A-911 to F.J.C., MAT2013-49455-EXP to J.R.A.-G. and BFU2012-31825 to B.I.]; Regional Government of Madrid [S2009/MAT 1507 to J.L.C. and CDS2007-0015 to M.S.]; European Molecular Biology Organization [ASTF 276-2012 to J.M.L.]. Funding for open access charge: Spanish Ministry of Economy and Competitiveness [BFU2012-31825 to B.I.].Morin, J.; Cao, F.; Lázaro, J.; Arias-Gonzalez, JR.; Valpuesta, J.; Carrascosa, J.; Salas, M.... (2015). Mechano-chemical kinetics of DNA replication: identification of the translocation step of a replicative DNA polymerase. Nucleic Acids Research. 43(7):3643-3652. https://doi.org/10.1093/nar/gkv204S36433652437Steitz, T. A., & Steitz, J. A. (1993). A general two-metal-ion mechanism for catalytic RNA. Proceedings of the National Academy of Sciences, 90(14), 6498-6502. doi:10.1073/pnas.90.14.6498Nakamura, T., Zhao, Y., Yamagata, Y., Hua, Y., & Yang, W. (2012). Watching DNA polymerase η make a phosphodiester bond. Nature, 487(7406), 196-201. doi:10.1038/nature11181Kohlstaedt, L., Wang, J., Friedman, J., Rice, P., & Steitz, T. (1992). Crystal structure at 3.5 A resolution of HIV-1 reverse transcriptase complexed with an inhibitor. Science, 256(5065), 1783-1790. doi:10.1126/science.1377403Steitz, T. A. (2006). Visualizing polynucleotide polymerase machines at work. The EMBO Journal, 25(15), 3458-3468. doi:10.1038/sj.emboj.7601211Zhang, H., Cao, W., Zakharova, E., Konigsberg, W., & De La Cruz, E. M. (2007). Fluorescence of 2-aminopurine reveals rapid conformational changes in the RB69 DNA polymerase-primer/template complexes upon binding and incorporation of matched deoxynucleoside triphosphates. Nucleic Acids Research, 35(18), 6052-6062. doi:10.1093/nar/gkm587Wang, W., Wu, E. Y., Hellinga, H. W., & Beese, L. S. (2012). Structural Factors That Determine Selectivity of a High Fidelity DNA Polymerase for Deoxy-, Dideoxy-, and Ribonucleotides. Journal of Biological Chemistry, 287(34), 28215-28226. doi:10.1074/jbc.m112.366609Berezhna, S. Y., Gill, J. P., Lamichhane, R., & Millar, D. P. (2012). Single-Molecule Förster Resonance Energy Transfer Reveals an Innate Fidelity Checkpoint in DNA Polymerase I. Journal of the American Chemical Society, 134(27), 11261-11268. doi:10.1021/ja3038273Hariharan, C., Bloom, L. B., Helquist, S. A., Kool, E. T., & Reha-Krantz, L. J. (2006). Dynamics of Nucleotide Incorporation:  Snapshots Revealed by 2-Aminopurine Fluorescence Studies†. Biochemistry, 45(9), 2836-2844. doi:10.1021/bi051644sJoyce, C. M., Potapova, O., DeLucia, A. M., Huang, X., Basu, V. P., & Grindley, N. D. F. (2008). Fingers-Closing and Other Rapid Conformational Changes in DNA Polymerase I (Klenow Fragment) and Their Role in Nucleotide Selectivity†. Biochemistry, 47(23), 6103-6116. doi:10.1021/bi7021848Vande Berg, B. J., Beard, W. A., & Wilson, S. H. (2000). DNA Structure and Aspartate 276 Influence Nucleotide Binding to Human DNA Polymerase β. Journal of Biological Chemistry, 276(5), 3408-3416. doi:10.1074/jbc.m002884200Showalter, A. K., & Tsai, M.-D. (2002). A Reexamination of the Nucleotide Incorporation Fidelity of DNA Polymerases†. Biochemistry, 41(34), 10571-10576. doi:10.1021/bi026021iShah, A. M., Li, S.-X., Anderson, K. S., & Sweasy, J. B. (2001). Y265H Mutator Mutant of DNA Polymerase β. Journal of Biological Chemistry, 276(14), 10824-10831. doi:10.1074/jbc.m008680200Rothwell, P. J., Mitaksov, V., & Waksman, G. (2005). Motions of the Fingers Subdomain of Klentaq1 Are Fast and Not Rate Limiting: Implications for the Molecular Basis of Fidelity in DNA Polymerases. Molecular Cell, 19(3), 345-355. doi:10.1016/j.molcel.2005.06.032Patel, S. S., Wong, I., & Johnson, K. A. (1991). Pre-steady-state kinetic analysis of processive DNA replication including complete characterization of an exonuclease-deficient mutant. Biochemistry, 30(2), 511-525. doi:10.1021/bi00216a029Luo, G., Wang, M., Konigsberg, W. H., & Xie, X. S. (2007). Single-molecule and ensemble fluorescence assays for a functionally important conformational change in T7 DNA polymerase. Proceedings of the National Academy of Sciences, 104(31), 12610-12615. doi:10.1073/pnas.0700920104Joyce, C. M., & Benkovic, S. J. (2004). DNA Polymerase Fidelity:  Kinetics, Structure, and Checkpoints†. Biochemistry, 43(45), 14317-14324. doi:10.1021/bi048422zFiala, K. A., & Suo, Z. (2004). Mechanism of DNA Polymerization Catalyzed bySulfolobus solfataricusP2 DNA Polymerase IV†. Biochemistry, 43(7), 2116-2125. doi:10.1021/bi035746zCramer, J., & Restle, T. (2005). Pre-steady-state Kinetic Characterization of the DinB Homologue DNA Polymerase ofSulfolobus solfataricus. Journal of Biological Chemistry, 280(49), 40552-40558. doi:10.1074/jbc.m504481200Choi, J.-Y., & Guengerich, F. P. (2005). Adduct Size Limits Efficient and Error-free Bypass Across Bulky N2-Guanine DNA Lesions by Human DNA Polymerase η. Journal of Molecular Biology, 352(1), 72-90. doi:10.1016/j.jmb.2005.06.079Olsen, T. J., Choi, Y., Sims, P. C., Gul, O. T., Corso, B. L., Dong, C., … Weiss, G. A. (2013). Electronic Measurements of Single-Molecule Processing by DNA Polymerase I (Klenow Fragment). Journal of the American Chemical Society, 135(21), 7855-7860. doi:10.1021/ja311603rAllen, W. J., Rothwell, P. J., & Waksman, G. (2008). An intramolecular FRET system monitors fingers subdomain opening in Klentaq1. Protein Science, 17(3), 401-408. doi:10.1110/ps.073309208Johnson, S. J., & Beese, L. S. (2004). Structures of Mismatch Replication Errors Observed in a DNA Polymerase. Cell, 116(6), 803-816. doi:10.1016/s0092-8674(04)00252-1Yin, Y. W., & Steitz, T. A. (2004). The Structural Mechanism of Translocation and Helicase Activity in T7 RNA Polymerase. Cell, 116(3), 393-404. doi:10.1016/s0092-8674(04)00120-5Golosov, A. A., Warren, J. J., Beese, L. S., & Karplus, M. (2010). The Mechanism of the Translocation Step in DNA Replication by DNA Polymerase I: A Computer Simulation Analysis. Structure, 18(1), 83-93. doi:10.1016/j.str.2009.10.014Zhang, C., & Burton, Z. F. (2004). Transcription Factors IIF and IIS and Nucleoside Triphosphate Substrates as Dynamic Probes of the Human RNA Polymerase II Mechanism. Journal of Molecular Biology, 342(4), 1085-1099. doi:10.1016/j.jmb.2004.07.070Nedialkov, Y. A., Gong, X. Q., Hovde, S. L., Yamaguchi, Y., Handa, H., Geiger, J. H., … Burton, Z. F. (2003). NTP-driven Translocation by Human RNA Polymerase II. Journal of Biological Chemistry, 278(20), 18303-18312. doi:10.1074/jbc.m301103200Gong, X. Q., Zhang, C., Feig, M., & Burton, Z. F. (2005). Dynamic Error Correction and Regulation of Downstream Bubble Opening by Human RNA Polymerase II. Molecular Cell, 18(4), 461-470. doi:10.1016/j.molcel.2005.04.011Guajardo, R., & Sousa, R. (1997). A model for the mechanism of polymerase translocation 1 1Edited by A. R. Fersht. Journal of Molecular Biology, 265(1), 8-19. doi:10.1006/jmbi.1996.0707Thomen, P., Lopez, P. J., & Heslot, F. (2005). Unravelling the Mechanism of RNA-Polymerase Forward Motion by Using Mechanical Force. Physical Review Letters, 94(12). doi:10.1103/physrevlett.94.128102Larson, M. H., Zhou, J., Kaplan, C. D., Palangat, M., Kornberg, R. D., Landick, R., & Block, S. M. (2012). Trigger loop dynamics mediate the balance between the transcriptional fidelity and speed of RNA polymerase II. Proceedings of the National Academy of Sciences, 109(17), 6555-6560. doi:10.1073/pnas.1200939109Bar-Nahum, G., Epshtein, V., Ruckenstein, A. E., Rafikov, R., Mustaev, A., & Nudler, E. (2005). A Ratchet Mechanism of Transcription Elongation and Its Control. Cell, 120(2), 183-193. doi:10.1016/j.cell.2004.11.045Bai, L., Fulbright, R. M., & Wang, M. D. (2007). Mechanochemical Kinetics of Transcription Elongation. Physical Review Letters, 98(6). doi:10.1103/physrevlett.98.068103Abbondanzieri, E. A., Greenleaf, W. J., Shaevitz, J. W., Landick, R., & Block, S. M. (2005). Direct observation of base-pair stepping by RNA polymerase. Nature, 438(7067), 460-465. doi:10.1038/nature04268Dangkulwanich, M., Ishibashi, T., Liu, S., Kireeva, M. L., Lubkowska, L., Kashlev, M., & Bustamante, C. J. (2013). Complete dissection of transcription elongation reveals slow translocation of RNA polymerase II in a linear ratchet mechanism. eLife, 2. doi:10.7554/elife.00971Lieberman, K. R., Dahl, J. M., Mai, A. H., Cox, A., Akeson, M., & Wang, H. (2013). Kinetic Mechanism of Translocation and dNTP Binding in Individual DNA Polymerase Complexes. Journal of the American Chemical Society, 135(24), 9149-9155. doi:10.1021/ja403640bLieberman, K. R., Dahl, J. M., Mai, A. H., Akeson, M., & Wang, H. (2012). Dynamics of the Translocation Step Measured in Individual DNA Polymerase Complexes. Journal of the American Chemical Society, 134(45), 18816-18823. doi:10.1021/ja3090302Dahl, J. M., Mai, A. H., Cherf, G. M., Jetha, N. N., Garalde, D. R., Marziali, A., … Lieberman, K. R. (2012). Direct Observation of Translocation in Individual DNA Polymerase Complexes. Journal of Biological Chemistry, 287(16), 13407-13421. doi:10.1074/jbc.m111.338418Rodriguez, I., Lazaro, J. M., Blanco, L., Kamtekar, S., Berman, A. J., Wang, J., … de Vega, M. (2005). A specific subdomain in  29 DNA polymerase confers both processivity and strand-displacement capacity. Proceedings of the National Academy of Sciences, 102(18), 6407-6412. doi:10.1073/pnas.0500597102Morin, J. A., Cao, F. J., Valpuesta, J. M., Carrascosa, J. L., Salas, M., & Ibarra, B. (2012). Manipulation of single polymerase-DNA complexes: A mechanical view of DNA unwinding during replication. Cell Cycle, 11(16), 2967-2968. doi:10.4161/cc.21389Morin, J. A., Cao, F. J., Lazaro, J. M., Arias-Gonzalez, J. R., Valpuesta, J. M., Carrascosa, J. L., … Ibarra, B. (2012). Active DNA unwinding dynamics during processive DNA replication. Proceedings of the National Academy of Sciences, 109(21), 8115-8120. doi:10.1073/pnas.1204759109Ibarra, B., Chemla, Y. R., Plyasunov, S., Smith, S. B., Lázaro, J. M., Salas, M., & Bustamante, C. (2009). Proofreading dynamics of a processive DNA polymerase. The EMBO Journal, 28(18), 2794-2802. doi:10.1038/emboj.2009.219Bustamante, C., Chemla, Y. R., Forde, N. R., & Izhaky, D. (2004). Mechanical Processes in Biochemistry. Annual Review of Biochemistry, 73(1), 705-748. doi:10.1146/annurev.biochem.72.121801.161542Jahnel, M., Behrndt, M., Jannasch, A., Schäffer, E., & Grill, S. W. (2011). Measuring the complete force field of an optical trap. Optics Letters, 36(7), 1260. doi:10.1364/ol.36.001260Soengas, M. S., Esteban, J. A., Lázaro, J. M., Bernad, A., Blasco, M. A., Salas, M., & Blanco, L. (1992). Site-directed mutagenesis at the Exo III motif of phi 29 DNA polymerase; overlapping structural domains for the 3′-5′ exonuclease and strand-displacement activities. The EMBO Journal, 11(11), 4227-4237. doi:10.1002/j.1460-2075.1992.tb05517.xSoengas, M. S., Gutiérrez, C., & Salas, M. (1995). Helix-destabilizing Activity of φ29 Single-stranded DNA Binding Protein: Effect on the Elongation Rate During Strand Displacement DNA Replication. 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Binary separation in very thin nematic films: thickness and phase coexistence

The behavior as a function of temperature of very thin films (10 to 200 nm) of pentylcyanobiphenyl (5CB) on silicon substrates is reported. In the vicinity of the nematic/isotropic transition we observe a coexistence of two regions of different thicknesses: thick regions are in the nematic state while thin ones are in the isotropic state. Moreover, the transition temperature is shifted downward following a 1/h^2 law (h is the film thickness). Microscope observations and small angle X-ray scattering allowed us to draw a phase diagram which is explained in terms of a binary first order phase transition where thickness plays the role of an order parameter.Comment: 5 pages, 3 figures, submitted to PRL on the 26th of Apri

The Implications of Family Size on Students Educational Attainment in Cameroon

The purpose of this study is to find out the implications of family size on students educational attainment in Cameroon. To this effects educational attainment was capture through various levels of child education. The ordered probit model was use to estimate our result while data was Demographic Health Survey. The result shows that family size negatively and significantly affects child educational attainment while a child is more likely to attain primary education but less likely to attain both secondary and higher education relative a child from small family size. We recommend that the ministry of planning and urban development should passed a law limiting the number of children one should have so that more resources will be allocated per child which will go a long way to increase child quality

Binary Cosmic Strings

The properties of cosmic strings have been investigated in detail for their implications in early-universe cosmology. Although many variations of the basic structure have been discovered, with implications for both the microscopic and macroscopic properties of cosmic strings, the cylindrical symmetry of the short-distance structure of the string is generally unaffected. In this paper we describe some mechanisms leading to an asymmetric structure of the string core, giving the defects a quasi-two-dimensional character. We also begin to investigate the consequences of this internal structure for the microscopic and macroscopic physics.Comment: 19 pages; uses harvmac (not included

Prevalence and Associated Factors of Hypertension Among Civil Servants Working in Arba Minch Town, South Ethiopia

Despite Hypertension is a global public health challenge and a leading modifiable risk factor for cardiovascular disease and death attention was not given in developing countries. Therefore measuring the prevalence and identifying predictors of Hypertension is very important. Institution based cross sectional study design was employed from March–April, 2016 by taking 319 randomly selected civil servants working in in Arba Minch town. Data was collected using structured questionnaire and standardized instruments for physical examination by 5 trained nurses. SPSS version 20 was used for data analysis. Bi-variable and Multivariate logistic regression was employed for analysis of risk factors. The mean SBP and DBP of study participants were 120.87 + 14.15 mmHg and 80.28 + 8.8 mmHg, respectively. The prevalence of hypertension was found to be 27.8% (95% CI = 22.9-32.7%). Civil servants of age 50 years and above [AOR = 13.3], age 40-49 years [AOR = 5], age 30-39 years [AOR = 3.5], abdominal obesity [AOR=12.2], general obesity [AOR = 4.2], stress status [AOR = 12.3], current alcohol drink [AOR = 3.3], ex-drinker [AOR = 8.9] and family history of hypertension [AOR = 5.6] were found to be significantly associated with hypertension. The prevalence indicates that it is hidden epidemic in this population; therefore for screening and risk reduction program are needed

Search for Gravitational Waves from Low Mass Compact Binary Coalescence in LIGO's Sixth Science Run and Virgo's Science Runs 2 and 3

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009 and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25 solar masses; this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90%-confidence rate upper limits of the binary coalescence of binary neutron star, neutron star- black hole and binary black hole systems are 1.3 x 10^{-4}, 3.1 x 10^{-5} and 6.4 x 10^{-6} Mpc^{-3}yr^{-1}, respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.Comment: 11 pages, 5 figures. For a repository of data used in the publication, go to: . Also see the announcement for this paper on ligo.org at: <http://www.ligo.org/science/Publication-S6CBCLowMass/index.php