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Search Results: 1 - 10 of 150133 matches for " H Kremer "
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The use of high–sensitivity sapphire cells in high pressure NMR spectroscopy and its application to proteins
W. Kremer,M. R. Arnold,N. Kachel,H. R. Kalbitzer
Spectroscopy: An International Journal , 2004, DOI: 10.1155/2004/407619
Abstract: The application of high pressure in bioscience and biotechnology has become an intriguing field in un/refolding and misfolding processes of proteins. NMR spectroscopy is the only generally applicable method to monitor pressure–induced structural changes at the atomic level in solution. Up to now the application of most of the multidimensional NMR experiments is impossible due to the restricted volume of the high pressure glass cells which causes a poor signal–to–noise ratio. Here we present high strength single crystal sapphire cells which double the signal–to–noise ratio. This increased signal–to–noise ratio is necessary to perform, for example, phophorus NMR spectroscopy under variable pressures. To understand the effect of pressure on proteins, we need to know the pressure dependence of 1H chemical shifts in random coil model tetrapeptides. The results allow distinguishing structural changes from the pressure dependence of the chemical shifts. In addition, the influence of pressure on the buffer system was investigated. Since high pressure was shown to populate intermediate amyloidogenic states of proteins the investigation of pressure effects on proteins involved in protein conformational disorders like Alzheimer's Disease (AD) and Transmissible Spongiform Encephalopathies (TSE) is of keen interest. 1H–15N–TROSY–spectra were acquired to study the effects of pressure and temperature on chemical shifts and signal volumes of the human prion protein. These measurements show identical pressure sensitivity of huPrP(23–230) and huPrP(121–230). First results suggest a folding intermediate for the human prion protein which can be populated by high hydrostatic pressure.
On the Origin of the Metallic and Anisotropic Magnetic Properties of Na_xCoO_2 (x~~0.75)
M. -H. Whangbo,D. Dai,R. K. Kremer
Physics , 2006,
Abstract: Non-stoichiometric NaxCoO2 (0.5 < x < 1) consists of CoO2 layers made up of edge-sharing CoO6 octahedra, and exhibits strongly anisotropic magnetic susceptibilities as well as metallic properties. A modified Curie-Weiss law was proposed for systems containing anisotropic magnetic ions to analyze the magnetic susceptibilities of NaxCoO2 (x ~~ 0.75), and implications of this analysis were explored. Our study shows that the lowspin Co4+ (S = 1/2) ions of NaxCoO2 generated by the Na vacancies cause the anisotropic magnetic properties of NaxCoO2, and suggests that the six nearest-neighbor Co3+ ions of each Co4+ ion adopt the intermediate-spin electron configuration thereby behaving magnetically like low-spin Co4+ ions. The Weiss temperature of NaxCoO2 is more negative along the direction of the lower g-factor (i.e., Theta_parallel < Theta_perp < 0, and g_parallel < g_perp). The occurrence of intermediate-spin Co3+ ions surrounding each Co4+ ion account for the apparently puzzling magnetic properties of NaxCoO2 (x ~~ 0.75), i.e., the large negative Weiss temperature, the three-dimensional antiferromagnetic ordering below ~22 K, and the metallic properties. The picture of the magnetic structure derived from neutron scattering studies below ~22 K are in apparent conflict with that deduced from magnetic susceptibility measurements between ~50 - 300 K. These conflicting pictures are resolved by noting that the spin exchange between Co3+ ions is more strongly antiferromagnetic than that between Co4+ and Co3+ ions.
Reply to: Comment by S.-L. Drechsler et al. (arXiv:1006.5070v2)
M. Enderle,B. Fak,H. -J. Mikeska,R. K. Kremer
Physics , 2011,
Abstract: In a comment on arXiv:1006.5070v2, Drechsler et al. claim that the frustrated ferromagnetic spin-1/2 chain LiCuVO4 should be described by a strong rather than weak ferromagnetic nearest-neighbor interaction, in contradiction with their previous work. Their comment is based on DMRG and ED calculations of the magnetization curve and the magnetic excitations. We show that their parameters are at odds with the magnetic susceptibility and the magnetic excitation spectrum, once intensities are taken into account, and that the magnetization curve cannot discriminate between largely different parameter sets within experimental uncertainties. We further show that their new exact diagonalization results support the validity of the RPA-approach, and strongly reinforce our conclusion on the existence of a four-spinon continuum in LiCuVO4, see Enderle et al., Phys. Rev. Lett. 104 (2010) 237207.
Social Network and Inter-Organizational Learning: The Case of a Brazilian Cooperative of Fish-Farmers  [PDF]
Andreia Maria Kremer, Edson Talamini
Social Networking (SN) , 2013, DOI: 10.4236/sn.2013.22010
Abstract: The inter-organizational learning approach has shown considerable growth in recent years. The concepts of trust and cooperation between individuals present in the New Economic Sociology (NES) approach of social relations emerge with great emphasis and are gaining prominence as a facilitator and propellant mechanism in transferring knowledge inside networks. This study aims to analyze the learning networks formed by fish-farmers organized into a cooperative to identify the characteristics of the network through structural analysis and identification of its critical actors. The study was performed with thirteen fish-farmers of a cooperative headquartered inMundo Novocounty, which is located inMato Grosso do Sulstate in the Midwest region of Brazil. Questionnaires and interviews with closed and open questions were used to collect the data. Measures of centrality (for individuals), density and reciprocity (in relations between individuals) were obtained from ORA software. The findings revealed that experience exchanges between fish-farmers, events participation, meetings attendance, speech audience and technical advice are the main forms of inter-organizational learning. Results suggest that the network has low levels of cohesion and that it is not taking advantage of its full potential. It was also found that there is a subgroup within the network that presents a high level of cohesion and shared learning based on cooperative informal relationships. Grounded in findings, suggestions for future research are presented.
Investigation of the strongly correlated one-dimensional magnetic behavior of NiTa2O6
J. M. Law,H. -J. Koo,M. -H. Whangbo,E. Bruecher,V. Pomjakushin,R. K. Kremer
Physics , 2014, DOI: 10.1103/PhysRevB.89.014423
Abstract: The magnetic properties of NiTa$_2$O$_6$ were investigated by magnetic susceptibility, specific heat, electron paramagnetic resonance, neutron powder diffraction and pulse field magnetization measurements. Accompanying \textit{ab initio} DFT calculations of the spin-exchange constants complemented and supported our experimental findings that NiTa$_2$O$_6$ must be described as a quasi-1D Heisenberg $S$ = 1 spin chain system with a nearest-neighbor only anti-ferromagnetic spin-exchange interaction of 18.92(2) K. Inter-chain coupling is by about two orders of magnitude smaller. Electron paramagnetic resonance measurements on Mg$_{1-x}$Ni$_x$Ta$_2$O$_6$ ($x \approx$ $1\%$) polycrystalline samples enabled us to estimate the single-ion zero-field splitting of the $S$ = 1 states which amounts to less than $4\%$ of the nearest-neighbor spin-exchange interaction. At 0 T NiTa$_2$O$_6$ undergoes long-range anti-ferromagnetic ordering at 10.3(1) K evidenced by a $\lambda$-type anomaly in the specific heat capacity. On application of a magnetic field the specific heat anomaly is smeared out. We confirmed the magnetic structure by neutron powder diffraction measurements and at 2.00(1) K refined a magnetic moment of 1.93(5) $\mu_{\rm{B}}$ per Ni$^{2+}$ ion. Additionally, we followed the magnetic order parameter as a function of temperature. Lastly we found saturation of the magnetic moment at 55.5(5) T with a $g$-factor of 2.14(1), with an additional high field phase above 12.8(1) T. The onset of the new high field phase is not greatly effected by temperature, but rather smears out as one approaches the long-range ordering temperature.
?A qué llamamos salud y enfermedad mental en pediatría?: una mirada reflexiva sobre los diagnósticos psiquiátricos y su relación con nuevas teorías de subjetivación en el ni?o
Archivos argentinos de pediatr?-a , 2011, DOI: 10.5546/aap.2011.412
Abstract: conceptual basis for infant and juvenile psychiatry are discussed taking into account the clear differences in the definition of health and mental illness. it is emphasized that the mind is not simply a biological phenomenon and, thus, there is a need for assessment parameters that include subjective states, as well as a shift from lineal thoughts to complex forms that include the value of experience, fate, and event, amongst other ideas. this allows a change of perspective: the acknowledgement of the positive indicators of mental health and not only the absence of symptoms or disorders.
Polymer dynamics: long time simulations and topological constraints
Kremer, Kurt;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000500007
Abstract: topological constraints, entanglements, dominate the viscoelastic behavior of high molecular weight polymeric liquids. to give a microscopic foundation of the phenomenological tube, recently a method for identifying the so called primitive path mesh that characterizes the microscopic topological state of (computer generated) conformations of long-chain polymer networks, melts and solutions was introduced. here we give a short account of this approach and compare this to long time simulations.
Los límites de la cosa juzgada en el Derecho de la Unión Europea
Revista de derecho (Valparaíso) , 2010, DOI: 10.4067/S0718-68512010000200006
Abstract: this article aims at answering the question whether there is, and if so, to what extent, a limitation to the res iudicata of the national decisions of the member states of the european union. for this, certain important rulings, dating back to the past years, handed down by the court of justice of the european union will be reviewed.
Rorty and Normativity
Alexander Kremer
Human Affairs , 2007, DOI: 10.2478/v10023-007-0007-8
Abstract: The paper summarizes some of the main ideas in Rorty's philosophy and indicates the views he holds on normativity. As a neopragmatic thinker, Rorty wants as little normativity as possible, but this does not mean that he rejects all types of normativity.
Rorty on Science and Politics
Alexander Kremer
Human Affairs , 2009, DOI: 10.2478/v10023-009-0022-z
Abstract: In my paper I will prove my overall thesis that Rorty consistently enforces his politically saturated liberal ironic standpoint in the fields of science and politics from his "Contingency" book (1989). As a neopragmatist thinker he gives priority to politics in the sense of a liberal democracy over everything else. Even philosophy as "cultural politics" serves this purpose. He did not want to create a detailed political philosophy, but the main motive of his philosophy is political. He is charged with complacency, relativism and misinterpreting traditional pragmatism, but I show that this is mistaken. Rorty offers "only" a non-systematic, but logical and permanently developed interpretation of our present world on the basis of knowledge he appropriated and improved by building bridges between pragmatism, analytic and continental philosophy. I will analyze briefly in the first part his neo-pragmatist thoughts on science in connection with his political views. In the second part I will interpret Rorty as a liberal ironist who regards almost everything as contingent, except democracy. He outlines a liberal utopia that means first of all a just society in a Rawlsian sense, but he also develops his idea further in a neo-pragmatic way.
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