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V Kozlov

Publications and source records attributed to V Kozlov.

14 recordsLinked to original sources
PubMed2006

Double-hadron leptoproduction in the nuclear medium.

The first measurements of double-hadron production in deep-inelastic scattering within the nuclear medium were made with the HERMES spectrometer at DESY HERA using a 27.6 GeV positron beam. By comparing data for deuterium, nitrogen, krypton, and xenon nuclei, the influence of the nuclear medium on the ratio of double-hadron to single-hadron yields was investigated. Nuclear effects on the additional hadron are clearly observed, but with little or no difference among nitrogen, krypton, or xenon, and with smaller magnitude than effects seen on previously measured single-hadron multiplicities. The data are compared with models based on partonic energy loss or prehadronic scattering and with a model based on a purely absorptive treatment of the final-state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter.

Journal Article↗
PubMed2005

Measurement of the tensor structure function b1 of the deuteron.

The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.

Journal Article↗
PubMed2005

Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target.

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.

Journal Article↗
PubMed2004

Flavor decomposition of the sea-quark helicity distributions in the nucleon from semiinclusive deep inelastic scattering.

Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.

Journal Article↗
PubMed2003

Evidence for quark-hadron duality in the proton spin asymmetry A1.

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A1. Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q2 between 1.2 and 12 GeV2 and values of W2 between 1 and 4 GeV2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q2 above 1.6 GeV2.

Journal Article↗
PubMed2003

Q2 dependence of nuclear transparency for exclusive rho0 production.

Exclusive coherent and incoherent electroproduction of the rho(0) meson from 1H and 14N targets has been studied at the HERMES experiment as a function of coherence length (l(c)), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon (-Q2). The ratio of 14N to 1H cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing l(c) for coherent (incoherent) rho(0) electroproduction. For fixed l(c), a rise of nuclear transparency with Q2 is observed for both coherent and incoherent rho(0) production, which is in agreement with theoretical calculations of color transparency.

Journal Article↗
PubMed2001

Correlation between nicotine-induced inhibition of hematopoiesis and decreased CD44 expression on bone marrow stromal cells.

This study demonstrates that in vivo exposure to cigarette smoke (CS) and in vitro treatment of long-term bone marrow cultures (LTBMCs) with nicotine, a major constituent of CS, result in inhibition of hematopoiesis. Nicotine treatment significantly delayed the onset of hematopoietic foci and reduced their size. Furthermore, the number of long-term culture-initiating cells (LTC-ICs) within an adherent layer of LTBMCs was significantly reduced in cultures treated with nicotine. Although the production of nonadherent mature cells and their progenitors in nicotine-treated LTBMCs was inhibited, this treatment failed to influence the proliferation of committed hematopoietic progenitors when added into methylcellulose cultures. Bone marrow stromal cells are an integral component of the hematopoietic microenvironment and play a critical role in the regulation of hematopoietic stem cell proliferation and self-renewal. Exposure to nicotine decreased CD44 surface expression on primary bone marrow-derived fibroblastlike stromal cells and MS-5 stromal cell line, but not on hematopoietic cells. In addition, mainstream CS altered the trafficking of hematopoietic stem/progenitor cells (HSPC) in vivo. Exposure of mice to CS resulted in the inhibition of HSPC homing into bone marrow. Nicotine and cotinine treatment resulted in reduction of CD44 surface expression on lung microvascular endothelial cell line (LEISVO) and bone marrow-derived (STR-12) endothelial cell line. Nicotine treatment increased E-selectin expression on LEISVO cells, but not on STR-12 cells. These findings demonstrate that nicotine can modulate hematopoiesis by affecting the functions of the hematopoiesis-supportive stromal microenvironment, resulting in the inhibition of bone marrow seeding by LTC-ICs and interfering with stem cell homing by targeting microvascular endothelial cells.

Animals↗
PubMed1998

Effects of oxysterols upon macrophage and lymphocyte functions in vitro.

Oxygenated derivatives of cholesterol (oxysterols), found in high concentrations in atherosclerotic lesions, are potent immunosuppressive agents inhibiting T-cell responses to different stimuli. The action of oxysterols on macrophage functions and macrophage-lymphocyte interaction has been poorly investigated. In this work, the effects of 25-hydroxycholesterol (25-OHCh) and 7-ketocholesterol (7-KCh) upon some functions of murine peritoneal macrophage (PM), such as generation of reactive oxygen intermediates (ROI), secretion of neopterin and interleukin-1 (IL-1)-like activity, Fc-receptor (FcR) activity, and murine and human lymphocyte functions, participating in lymphocyte-macrophage interactions, such as macrophage-activating factor (MAF) and Ia-inducing factor (IaIF) secretion, were studied in vitro. 7-KCh in concentration of 5 micrograms/mL culture medium only, but not 25-OHCh, significantly inhibited ROI generation by zymosan-stimulated PM. Pretreatment of PM for 22 h with 25-OHCh and 7-KCh led to the decrease of IL-1-like activity secretion. 25-OHCh and 7-KCh inhibited both FcR-dependent binding and phagocytosis of sheep red blood cells (SRBC). Oxysterols did not change both spontaneous and lipopolysaccharide-stimulated secretion of neopterin by PM. 25-OHCh dose-dependently and more efficiently than 7-KCh inhibited murine splenocyte secretion of MAF, which activity was determined by the ability of splenocyte-conditioned medium to stimulate ROI generation in PM. Both 25-OHCh and 7-KCh inhibited significantly proliferative activity of human mixed lymphocyte culture (MLC), as well as lymphocyte secretion of IaIF, which stimulates the expression of HLA antigens in cultured human monocytes. Purified Ch did not alter these parameters. These data showed, that some inflammatory functions of macrophages and lymphocytes may be modified by such environmental conditions as the presence of oxysterols.

Animals↗
PubMed1990

Some mechanisms involved in the prostaglandin E2 immunosuppressive effect in (CBA x C57BL)F1 mice in vivo.

The cellular mechanisms involved in the immunosuppressive effect of prostaglandin E2 (PGE2) multiple injections into (CBA x C57Bl)F1 mice in vivo have been studied. PGE2 injection increases the induction of specific T-suppressors. In addition, there is a decrease in macrophage phagocytic activity and in the phagocytosis index, apparently mediated by Fc gamma receptors (Fc gamma R) and not by the macrophage complement receptor (C3R). The induction of antibody synthesis by using "immune" macrophages injected into a syngeneic recipient results in considerable decrease in the accumulation of antibody-forming cells if the macrophage donor has been pretreated with exogenous PGE2 in comparison with untreated controls. These cellular mechanisms are possibly one part of the diverse way in which PGE2 exerts an immunosuppressive effect in vivo and contributes to humoral immune response suppression.

Animals↗