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Search Results: 1 - 10 of 208071 matches for " W K nig "
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Ideal mixture approximation of cluster size distributions at low density
S. Jansen,W. Knig
Statistics , 2011, DOI: 10.1007/s10955-012-0499-5
Abstract: We consider an interacting particle system in continuous configuration space. The pair interaction has an attractive part. We show that, at low density, the system behaves approximately like an ideal mixture of clusters (droplets): we prove rigorous bounds (a) for the constrained free energy associated with a given cluster size distribution, considered as an order parameter, (b) for the free energy, obtained by minimising over the order parameter, and (c) for the minimising cluster size distributions. It is known that, under suitable assumptions, the ideal mixture has a transition from a gas phase to a condensed phase as the density is varied; our bounds hold both in the gas phase and in the coexistence region of the ideal mixture. The present paper improves our earlier results by taking into account the mixing entropy.
Precision calculation of the quartet-channel p-d scattering length
Sebastian Knig,H. -W. Hammer
Physics , 2013, DOI: 10.1103/PhysRevC.90.034005
Abstract: We present a fully perturbative calculation of the quartet-channel proton--deuteron scattering length up to next-to-next-to-leading order in pionless effective field theory. We use a framework that consistently extracts the Coulomb-modified effective range function for a screened Coulomb potential in momentum space and allows for a clear linear extrapolation back to the physical limit without screening. Our result of (10.9 +/- 0.4) fm agrees with older experimental determinations of this quantity but deviates from potential-model calculations and a more recent result from Black et al., which find larger values around 14 fm. As a possible resolution to this discrepancy, we discuss the scheme dependence of Coulomb subtractions in a three-body system.
Constraints on a possible dineutron state from pionless EFT
H. W. Hammer,Sebastian Knig
Physics , 2014, DOI: 10.1016/j.physletb.2014.07.015
Abstract: We investigate the sensitivity of the three-nucleon system to changes in the neutron-neutron scattering length to next-to-leading order in the pionless effective field theory, focusing on the the triton-3He binding energy difference and neutron-deuteron elastic scattering. Due to the appearance of an electromagnetic three-body counterterm at this order, the triton-3He binding energy difference remains consistent with the experimental value even for large positive neutron-neutron scattering lengths while the elastic neutron-deuteron scattering phase shifts are insensitive. We conclude that a bound dineutron cannot be excluded to next-to-leading order in pionless EFT.
Low-energy p-d scattering and He-3 in pionless EFT
Sebastian Knig,H. -W. Hammer
Physics , 2011, DOI: 10.1103/PhysRevC.83.064001
Abstract: We calculate low-energy proton--deuteron scattering in the framework of pionless effective field theory. In the quartet channel, we calculate the elastic scattering phase shift up to next-to-next-to-leading order in the power counting. In the doublet channel, we perform a next-to-leading order calculation. We obtain good agreement with the available phase shift analyses down to the scattering threshold. The phase shifts in the region of non-perturbative Coulomb interactions are calculated by using an optimised integration mesh. Moreover, the Coulomb contribution to the 3He-3H binding energy difference is evaluated in first order perturbation theory. We comment on the implications of our results for the power counting of subleading three-body forces.
Prevalence of the molecular marker of chloroquine resistance (pfcrt 76) in Nigeria 5 years after withdrawal of the drug as first-line antimalarial: A cross-sectional study
M Efunshile, T Runsewe-Abiodun, B Ghebremedhin, W K nig, B K nig
South African Journal of Child Health , 2011,
Abstract: Background. In line with the World Health Organization (WHO) guideline on chloroquine (CQ) resistance, CQ was withdrawn as the first-line antimalarial drug in Nigeria in 2005 as a result of widespread resistance. It was expected that its sensitivity and clinical usefulness ould be restored with time. This study therefore aimed to determine the level of CQ resistance in Nigerian children aged less than 60 months. Methods. We monitored the resistance pattern 5 years after withdrawal of CQ, using the pfcrt K76T mutation as a molecular marker for CQ resistance. Results. Of 98 Plasmodium falciparum-positive blood samples, 95 (96.9%) showed the K76T mutation. Twenty-seven (27.6%) of the children had been treated with CQ at home before presentation at the clinic, while 50 (51.0%) had taken other antimalarials. Conclusion. Our results indicate that there is an urgent need to re-evaluate antimalarial drug policy in Nigeria, especially when 27.6% of our study population still use CQ at home despite its withdrawal as first-line antimalarial. This may require effective legislation against the manufacture, importation and use of CQ in Nigeria, if the purpose behind its withdrawal is to be achieved.
The proton-deuteron system in pionless EFT revisited
Sebastian Knig,Harald W. Grie?hammer,H. -W. Hammer
Physics , 2014, DOI: 10.1088/0954-3899/42/4/045101
Abstract: We provide a detailed discussion of the low-energy proton-deuteron system in pionless effective field theory, considering both the spin-quartet and doublet S-wave channels. Extending and amending our previous work on the subject, we calculate the 3He-3H binding energy difference both perturbatively (using properly normalized trinucleon wave functions) and non-perturbatively by resumming all O(alpha) Coulomb diagrams in the doublet channel. Our nonperturbative result agrees well with a calculation that involves the full off-shell Coulomb T-matrix. Carefully examining the cutoff-dependence in the doublet channel, we present numerical evidence for a new three-nucleon counterterm being necessary at next-to-leading order if Coulomb effects are included. Indeed, such a term has recently been identified analytically. We furthermore make a case for a simplified Coulomb power counting that is consistent throughout the bound-state and scattering regimes. Finally, using a "partially screened" full off-shell Coulomb T-matrix, we investigate the importance of higher-order Coulomb corrections in low-energy quartet-channel scattering.
Non-relativistic bound states in a finite volume
Sebastian Knig,Dean Lee,H. -W. Hammer
Physics , 2011, DOI: 10.1016/j.aop.2011.12.015
Abstract: We derive general results for the mass shift of bound states with angular momentum l >= 1 in a periodic cubic box in two and three spatial dimensions. Our results have applications to lattice simulations of hadronic molecules, halo nuclei, and Feshbach molecules. The sign of the mass shift can be related to the symmetry properties of the state under consideration. We verify our analytical results with explicit numerical calculations. Moreover, we comment on the relations connecting the effective range parameter, the binding momentum of a given state and the asymptotic normalization coefficient of the corresponding wave function. We give explicit expressions for this relation in the shallow binding limit.
Volume Dependence of Bound States with Angular Momentum
Sebastian Knig,Dean Lee,H. -W. Hammer
Physics , 2011, DOI: 10.1103/PhysRevLett.107.112001
Abstract: We derive general results for the mass shift of bound states with angular momentum l >= 1 in a finite periodic volume. Our results have direct applications to lattice simulations of hadronic molecules as well as atomic nuclei. While the binding of S-wave bound states increases at finite volume, we show that the binding of P-wave bound states decreases. The mass shift for D-wave bound states as well as higher partial waves depends on the representation of the cubic rotation group. Nevertheless, the multiplet-averaged mass shift for any angular momentum l can be expressed in a simple form, and the sign of the shift alternates for even and odd l. We verify our analytical results with explicit numerical calculations. We also show numerically that similar volume corrections appear in three-body bound states.
Causality, universality, and effective field theory for van der Waals interactions
Serdar Elhatisari,Sebastian Knig,Dean Lee,H. -W. Hammer
Physics , 2013, DOI: 10.1103/PhysRevA.87.052705
Abstract: We analyze low-energy scattering for arbitrary short-range interactions plus an attractive 1/r^6 tail. We derive the constraints of causality and unitarity and find that the van der Waals length scale dominates over parameters characterizing the short-distance physics of the interaction. This separation of scales suggests a separate universality class for physics characterizing interactions with an attractive 1/r^6 tail. We argue that a similar universality class exists for any attractive potential 1/r^{alpha} for alpha >= 2. We also discuss the extension to multi-channel systems near a magnetic Feshbach resonance. We discuss the implications for effective field theory with attractive singular power law tails.
Causality constraints for charged particles
Sebastian Knig,Dean Lee,H. -W. Hammer
Physics , 2012, DOI: 10.1088/0954-3899/40/4/045106
Abstract: In quantum systems with short-range interactions, causality imposes nontrivial constraints on low-energy scattering parameters. We investigate these causality constraints for systems where a long-range Coulomb potential is present in addition to a short-range interaction. The main result is an upper bound for the Coulomb-modified effective range parameter. We discuss the implications of this bound to the effective field theory for nuclear halo systems. In particular, we consider several examples of proton--nucleus and nucleus--nucleus scattering. For the bound-state regime, we find relations for the asymptotic normalization coefficients (ANCs) of nuclear halo states. As an application of these relations, we extract the ANCs of the excited 2+ and 1- states in O-16 from alpha--C-12 scattering data.
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