1,772 research outputs found
The phase diagram of L\'evy spin glasses
We study the L\'evy spin-glass model with the replica and the cavity method.
In this model each spin interacts through a finite number of strong bonds and
an infinite number of weak bonds. This hybrid behaviour of L\'evy spin glasses
becomes transparent in our solution: the local field contains a part
propagating along a backbone of strong bonds and a Gaussian noise term due to
weak bonds. Our method allows to determine the complete replica symmetric phase
diagram, the replica symmetry breaking line and the entropy. The results are
compared with simulations and previous calculations using a Gaussian ansatz for
the distribution of fields.Comment: 20 pages, 7 figure
Terahertz superlattice parametric oscillator
We report a GaAs/AlAs superlattice parametric oscillator. It was pumped by a
microwave field (power few mW) and produced 3rd harmonic radiation (frequency
near 300 GHz). The nonlinearity of the active superlattice was due to Bragg
reflections of conduction electrons at the superlattice planes. A theory of the
nonlinearity indicates that parametric oscillation should be possible up to
frequencies above 10 THz. The active superlattice may be the object of further
studies of predicted extraordinary nonlinearities for THz fields.Comment: 10 pages, 4 figure
Microscopic study of the He2-SF6 trimers
The He2-SF6 trimers, in their different He isotopic combinations, are studied
both in the framework of the correlated Jastrow approach and of the Correlated
Hyperspherical Harmonics expansion method. The energetics and structure of the
He-SF6 dimers are analyzed, and the existence of a characteristic rotational
band in the excitation spectrum is discussed, as well as the isotopic
differences. The binding energies and the spatial properties of the trimers, in
their ground and lowest lying excited states, obtained by the Jastrow ansatz
are in excellent agreement with the results of the converged CHH expansion. The
introduction of the He-He correlation makes all trimers bound by largely
suppressing the short range He-He repulsion.
The structural properties of the trimers are qualitatively explained in terms
of the shape of the interactions, Pauli principle and masses of the
constituents.Comment: 17 pages, 5 figures. Submitted to PR
Pairing in low-density Fermi gases
We consider pairing in a dilute system of Fermions with a short-range
interaction. While the theory is ill-defined for a contact interaction, the BCS
equations can be solved in the leading order of low-energy effective field
theory. The integrals are evaluated with the dimensional regularization
technique, giving analytic formulas relating the pairing gap, the density, and
the energy density to the two-particle scattering length.Comment: 12 pages, 2 EPS-figures, uses psfig.sty, eq.(9) correcte
The Three-Boson System at Next-To-Next-To-Leading Order
We discuss effective field theory treatments of the problem of three
particles interacting via short-range forces (range R >> a_2, with a_2 the
two-body scattering length). We show that forming a once-subtracted scattering
equation yields a scattering amplitude whose low-momentum part is
renormalization-group invariant up to corrections of O(R^3/a_2^3). Since
corrections of O(R/a_2) and O(R^2/a_2^2) can be straightforwardly included in
the integral equation's kernel, a unique solution for 1+2 scattering phase
shifts and three-body bound-state energies can be obtained up to this accuracy.
We use our equation to calculate the correlation between the binding energies
of Helium-4 trimers and the atom-dimer scattering length. Our results are in
excellent agreement with the recent three-dimensional Faddeev calculations of
Roudnev and collaborators that used phenomenological inter-atomic potentials.Comment: 20 pages, 3 eps figure
Distinguishing African bovids using Zooarchaeology by Mass Spectrometry (ZooMS): new peptide markers and insights into Iron Age economies in Zambia
Assessing past foodways, subsistence strategies, and environments depends on the accurate identification of animals in the archaeological record. The high rates of fragmentation and often poor preservation of animal bones at many archaeological sites across sub-Saharan Africa have rendered archaeofaunal specimens unidentifiable beyond broad categories, such as “large mammal” or “medium bovid”. Identification of archaeofaunal specimens through Zooarchaeology by Mass Spectrometry (ZooMS), or peptide mass fingerprinting of bone collagen, offers an avenue for identification of morphologically ambiguous or unidentifiable bone fragments from such assemblages. However, application of ZooMS analysis has been hindered by a lack of complete reference peptide markers for African taxa, particularly bovids. Here we present the complete set of confirmed ZooMS peptide markers for members of all African bovid tribes. We also identify two novel peptide markers that can be used to further distinguish between bovid groups. We demonstrate that nearly all African bovid subfamilies are distinguishable using ZooMS methods, and some differences exist between tribes or sub-tribes, as is the case for Bovina (cattle) vs. Bubalina (African buffalo) within the subfamily Bovinae. We use ZooMS analysis to identify specimens from extremely fragmented faunal assemblages from six Late Holocene archaeological sites in Zambia. ZooMS-based identifications reveal greater taxonomic richness than analyses based solely on morphology, and these new identifications illuminate Iron Age subsistence economies c. 2200–500 cal BP. While the Iron Age in Zambia is associated with the transition from hunting and foraging to the development of farming and herding, our results demonstrate the continued reliance on wild bovids among Iron Age communities in central and southwestern Zambia Iron Age and herding focused primarily on cattle. We also outline further potential applications of ZooMS in African archaeology.Introduction Faunal identifications and key research questions ZooMS in African archaeology Materials & methods Collagen extraction and digestion Peptide mass fingerprinting LC-MS/MS Biomarker identification and confirmation Identification of archaeological samples Results and discussion - Data quality control - Distinguishing among bovid groups Comparison with published markers ZooMS analysis and archaeofaunal identifications Herding economies and the persistence of hunting in Iron Age Zambia Conclusio
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