746 research outputs found

    Nanorotors and self-assembling macromolecular machines: The torque ring of the bacterial flagellar motor

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    The bacterial flagellar motor (BFM) is a self-assembling rotary nanomachine. It converts a flux of cations into the mechanical rotation of long filaments that propel bacteria through viscous media. The BFM contains a torque-generating ring that is complete with molecular machinery known as the switch complex that allows it to reverse directions. With four billion years of optimization, the BFM probably offers the pinnacle of sophisticated nanorotor design. Moreover as one of the best-characterized large biomolecular complexes, it offers the potential for convergence between nanotechnology and biology, which requires an atomic level understanding of BFM structure and function. This review focuses on current molecular models of the reversible BFM and the strategies used to derive them

    Essential trauma management training: addressing service delivery needs in active conflict zones in eastern Myanmar

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    <p>Abstract</p> <p>Introduction</p> <p>Access to governmental and international nongovernmental sources of health care within eastern Myanmar's conflict regions is virtually nonexistent. Historically, under these circumstances effective care for the victims of trauma, particularly landmine injuries, has been severely deficient. Recognizing this, community-based organizations (CBOs) providing health care in these regions sought to scale up the capacity of indigenous health workers to provide trauma care.</p> <p>Case description</p> <p>The Trauma Management Program (TMP) was developed by CBOs in cooperation with a United States-based health care NGO. The goal of the TMP is to improve the capacity of local health workers to deliver effective trauma care. From 2000 to the present, international and local health care educators have conducted regular workshops to train indigenous health workers in the management of landmine injuries, penetrating and blunt trauma, shock, wound and infection care, and orthopedics. Health workers have been regularly resupplied with the surgical instruments, supplies and medications needed to provide the care learnt through TMP training workshops.</p> <p>Discussion and Evaluation</p> <p>Since 2000, approximately 300 health workers have received training through the TMP, as part of a CBO-run health system providing care for approximately 250 000 internally displaced persons (IDPs) and war-affected residents. Based on interviews with health workers, trauma registry inputs and photo/video documentation, protocols and procedures taught during training workshops have been implemented effectively in the field. Between June 2005 and June 2007, more than 200 patients were recorded in the trauma patient registry. The majority were victims of weapons-related trauma.</p> <p>Conclusion</p> <p>This report illustrates a method to increase the capacity of indigenous health workers to manage traumatic injuries. These health workers are able to provide trauma care for otherwise inaccessible populations in remote and conflicted regions. The principles learnt during the implementation of the TMP might be applied in similar settings.</p

    Quantum and classical vibrational relaxation dynamics of N-methylacetamide on ab initio potential energy surfaces

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    Employing extensive quantum-chemical calculations at the DFT/B3LYP and MP2 level, a quartic force field of isolated N-methylacetamide is constructed. Taking into account 24 vibrational degrees of freedom, the model is employed to perform numerically exact vibrational configuration interaction calculations of the vibrational energy relaxation of the amide I mode. It is found that the energy transfer pathways may sensitively depend on details of the theoretical description. Moreover, the exact reference calculations were used to study the applicability and accuracy of (i) the quasiclassical trajectory method, (ii) time-dependent second-order perturbation theory, and (iii) the instantaneous normal mode description of frequency fluctuations. Based on the results, several strategies to describe vibrational energy relaxation in biomolecular systems are discussed.Comment: 18 pages, 6 figures, submitted to J. Phys. Chem.

    The quantum critical point in CeRhIn_5: a resistivity study

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    The pressure--temperature phase diagram of CeRhIn_5 has been studied under high magnetic field by resistivity measurements. Clear signatures of a quantum critical point has been found at a critical pressure of p_c = 2.5 GPa. The field induced magnetic state in the superconducting state is stable up to the highest field. At p_c the antiferromagnetic ground-state under high magnetic field collapses very rapidly. Clear signatures of p_c are the strong enhancement of the resistivity in the normal state and of the inelastic scattering term. No clear T2 temperature dependence could be found for pressures above T_c. From the analysis of the upper critical field within a strong coupling model we present the pressure dependence of the coupling parameter lambda and the gyromagnetic ratio g. No signatures of a spatially modulated order parameter could be evidenced. A detailed comparison with the magnetic field--temperature phase diagram of CeCoIn_5 is given. The comparison between CeRhIn_5 and CeCoIn_5 points out the importance to take into account the field dependence of the effective mass in the calculation of the superconducting upper critical field H_c2. It suggests also that when the magnetic critical field H_(0) becomes lower than H_c2 (0)$, the persistence of a superconducting pseudo-gap may stick the antiferromagnetism to H_c2 (0).Comment: 15 pages, 20 figures, to be published in J. Phys. Soc. Jp

    Event-by-Event Fluctuations of Particle Ratios in Central Pb+Pb Collisions at 20 to 158 AGeV

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    In the vicinity of the QCD phase transition, critical fluctuations have been predicted to lead to non-statistical fluctuations of particle ratios, depending on the nature of the phase transition. Recent results of the NA49 energy scan program show a sharp maximum of the ratio of K+ to Pi+ yields in central Pb+Pb collisions at beam energies of 20-30 AGeV. This observation has been interpreted as an indication of a phase transition at low SPS energies. We present first results on event-by-event fluctuations of the kaon to pion and proton to pion ratios at beam energies close to this maximum.Comment: 4 pages, 4 figures, Quark Matter 2004 proceeding

    Multiplicity fluctuations in nuclear collisions at 158 A GeV

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    System size dependence of multiplicity fluctuations of charged particles produced in nuclear collisions at 158 A GeV was studied in the NA49 CERN experiment. Results indicate a non-monotonic dependence of the scaled variance of the multiplicity distribution with a maximum for semi-peripheral Pb+Pb interactions with number of projectile participants of about 35. This effect is not observed in a string-hadronic model of nuclear collision HIJING.Comment: Presented at "Focus on Multiplicity", 17-19 of June, Bari, Ital

    System size and centrality dependence of the balance function in A+A collisions at sqrt[sNN]=17.2 GeV

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    Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at sqrt[sNN]=17.2 GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions

    Antiferromagnetism and Superconductivity in Cerium based Heavy Fermion Compounds

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    The study of competing ground states is a central issue in condensed matter physic. In this article we will discuss the interplay of antiferromagnetic order and unconventional superconductivity in Ce based heavy-fermion compounds. In all discussed examples superconductivity appears at the border of magnetic order. Special focus is given on the pressure-temperature-magnetic field phase diagram of CeRhIn5 and CeCoIn5 which allows to discuss microscopic coexistence of magnetic order and superconductivity in detail. A striking point is the similarity of the phase diagram of different classes of strongly correlated systems which is discussed briefly. The recently discovered non-centrosymmetric superconductors will open a new access with the possible mixing of odd and even parity pairing.Comment: 38 pages, 22 figures, to be published in Comptes rendues - Physiqu
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