523 research outputs found

    Structural and behavioral characteristics of a commercial humic acid and natural dissolved aquatic organic matter

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    Dissolved organic matter (DOM) from two natural surface water sources and a commercial humic acid were analyzed using gel-permeation chromatography, high pressure reverse phase liquid chromatography, and 1H-NMR spectroscopy. Results from the chromatographic studies show that the DOM of two natural waters consisted primarily of relatively low molecular weight, polar organic constituents, while large and relatively nonpolar macromolecules comprised a significant fraction of the commercial humic acid. The 1H-NMR assays indicated that DOM from the two natural water samples was comprised of nonaromatic organic constituents, while the commercial humic acids tested contained both aromatic and aliphatic moieties. Based upon these composite results of the several different types of analysis employed, it is evident that the humic acid examined, and possibly others prepared in the same way, contain molecular structures which exhibit physical and chemical properties that do not reflect the true nature of DOM in real aquatic systems. Commercially available humic substances of this type may therefore not be suitable surrogates for naturally occurring DOM in laboratory investigations and analysis of geochemical and environmental transformation reactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28942/1/0000779.pd

    Signatures of Superfluidity in Dilute Fermi Gases near a Feshbach Resonance

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    We present a brief account of the most salient properties of vortices in dilute atomic Fermi superfluids near a Feshbach resonance.Comment: 6 pages, 1 figure, and jltp.cls. Several typos and a couple of inaccuracies have been correcte

    Kappa-symmetric Derivative Corrections to D-brane Dynamics

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    We show how the superembedding formalism can be applied to construct manifestly kappa-symmetric higher derivative corrections for the D9-brane. We also show that all correction terms appear at even powers of the fundamental length scale ll. We explicitly construct the first potential correction, which corresponds to the kappa-symmetric version of the 4F4\partial^4 F^4, which one finds from the four-point amplitude of the open superstring.Comment: 20 pages. Minor changes, added reference

    Revisiting the S-matrix approach to the open superstring low energy effective lagrangian

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    The conventional S-matrix approach to the (tree level) open string low energy effective lagrangian assumes that, in order to obtain all its bosonic αN{\alpha'}^N order terms, it is necessary to know the open string (tree level) (N+2)(N+2)-point amplitude of massless bosons, at least expanded at that order in α\alpha'. In this work we clarify that the previous claim is indeed valid for the bosonic open string, but for the supersymmetric one the situation is much more better than that: there are constraints in the kinematical bosonic terms of the amplitude (probably due to Spacetime Supersymmetry) such that a much lower open superstring nn-point amplitude is needed to find all the αN{\alpha'}^N order terms. In this `revisited' S-matrix approach we have checked that, at least up to α4{\alpha'}^4 order, using these kinematical constraints and only the known open superstring 4-point amplitude, it is possible to determine all the bosonic terms of the low energy effective lagrangian. The sort of results that we obtain seem to agree completely with the ones achieved by the method of BPS configurations, proposed about ten years ago. By means of the KLT relations, our results can be mapped to the NS-NS sector of the low energy effective lagrangian of the type II string theories implying that there one can also find kinematical constraints in the NN-point amplitudes and that important informations can be inferred, at least up to α4{\alpha'}^4 order, by only using the (tree level) 4-point amplitude.Comment: 34 pages, 3 figure, Submitted on Aug 4, 2012, Published on Oct 15, 201

    Weak reaction freeze-out constraints on primordial magnetic fields

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    We explore constraints on the strength of the primordial magnetic field based upon the weak reaction freeze-out in the early universe. We find that limits on the strength of the magnetic field found in other works are recovered simply by examining the temperature at which the rate of weak reactions drops below the rate of universal expansion (Γw\Gamma_{w} \le H). The temperature for which the n/pn/p ratio at freeze-out leads to acceptable helium production implies limits on the magnetic field. This simplifies the application of magnetic fields to other cosmological variants of the standard big-bang. As an illustration we also consider effects of neutrino degeneracy on the allowed limits to the primordial magnetic field.Comment: Submitted to Phys. Rev. D., 6 pages, 2 figure

    Higher order contributions to the effective action of N=4 super Yang-Mills

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    The one-loop low-energy effective action for non-Abelian N=4 supersymmetric Yang-Mills theory is computed to order F6F^6 by use of heat kernel techniques in N=1 superspace. At the component level, the F5F^5 terms are found to be consistent with the form of the non-Abelian Born-Infeld action computed to this order by superstring methods. The F6F^6 terms will be of importance for comparison with superstring calculations.Comment: 23 pages, JHEP style, references adde

    Role of mitochondrial raft-like microdomains in the regulation of cell apoptosis

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    Lipid rafts are envisaged as lateral assemblies of specific lipids and proteins that dissociate and associate rapidly and form functional clusters in cell membranes. These structural platforms are not confined to the plasma membrane; indeed lipid microdomains are similarly formed at subcellular organelles, which include endoplasmic reticulum, Golgi and mitochondria, named raft-like microdomains. In addition, some components of raft-like microdomains are present within ER-mitochondria associated membranes. This review is focused on the role of mitochondrial raft-like microdomains in the regulation of cell apoptosis, since these microdomains may represent preferential sites where key reactions take place, regulating mitochondria hyperpolarization, fission-associated changes, megapore formation and release of apoptogenic factors. These structural platforms appear to modulate cytoplasmic pathways switching cell fate towards cell survival or death. Main insights on this issue derive from some pathological conditions in which alterations of microdomains structure or function can lead to severe alterations of cell activity and life span. In the light of the role played by raft-like microdomains to integrate apoptotic signals and in regulating mitochondrial dynamics, it is conceivable that these membrane structures may play a role in the mitochondrial alterations observed in some of the most common human neurodegenerative diseases, such as Amyotrophic lateral sclerosis, Huntington's chorea and prion-related diseases. These findings introduce an additional task for identifying new molecular target(s) of pharmacological agents in these pathologies

    WNT signalling in prostate cancer

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    Genome sequencing and gene expression analyses of prostate tumours have highlighted the potential importance of genetic and epigenetic changes observed in WNT signalling pathway components in prostate tumours-particularly in the development of castration-resistant prostate cancer. WNT signalling is also important in the prostate tumour microenvironment, in which WNT proteins secreted by the tumour stroma promote resistance to therapy, and in prostate cancer stem or progenitor cells, in which WNT-β-catenin signals promote self-renewal or expansion. Preclinical studies have demonstrated the potential of inhibitors that target WNT receptor complexes at the cell membrane or that block the interaction of β-catenin with lymphoid enhancer-binding factor 1 and the androgen receptor, in preventing prostate cancer progression. Some WNT signalling inhibitors are in phase I trials, but they have yet to be tested in patients with prostate cancer

    Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pTp_T

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    We measured the longitudinal double spin asymmetries ALLA_{LL} for single hadron muo-production off protons and deuterons at photon virtuality Q2Q^2 < 1(GeV/c\it c)2^2 for transverse hadron momenta pTp_T in the range 0.7 GeV/c\it c to 4 GeV/c\it c . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/c\it c or 200 GeV/c\it c impinging on polarised 6LiD\mathrm{{}^6LiD} or NH3\mathrm{NH_3} targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation ΔG\Delta G inside the nucleon in the range of the nucleon momentum fraction carried by gluons 0.05<xg<0.20.05 < x_g < 0.2
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