The first detailed measurement of the dependence on target nuclear mass of the average squared transverse momentum 〈pt2〉 of π+, π−, and K+ mesons from deep-inelastic lepton scattering is obtained as ...a function of several kinematic variables. The data were accumulated at the Hermes experiment at Desy, in which the Hera 27.6 GeV lepton beam was scattered off several nuclear gas targets. The average squared transverse momentum was clearly observed to increase with atomic mass number. The effect increases as a function of Q2 and x and remains constant as a function of both the virtual photon energy ν and the fractional hadron energy z, except that it vanishes as z approaches unity.
Azimuthal asymmetries in exclusive electroproduction of a real photon from a longitudinally polarized deuterium target are measured with respect to target polarization alone and with respect to ...target polarization combined with beam helicity and/or beam charge. The asymmetries appear in the distribution of the real photons in the azimuthal angle
ϕ around the virtual photon direction, relative to the lepton scattering plane. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe–Heitler process. The results for the beam-charge and beam-helicity asymmetries from a tensor polarized deuterium target with vanishing vector polarization are shown to be compatible with those from an unpolarized deuterium target, which is expected for incoherent scattering dominant at larger momentum transfer. Furthermore, the results for the single target-spin asymmetry and for the double-spin asymmetry are found to be compatible with the corresponding asymmetries previously measured on a hydrogen target. For coherent scattering on the deuteron at small momentum transfer to the target, these findings imply that the tensor contribution to the cross section is small. Furthermore, the tensor asymmetry is found to be compatible with zero.
Azimuthal asymmetries in exclusive electroproduction of a real photon from an unpolarized deuterium target are measured with respect to beam helicity and charge. They appear in the distribution of ...these photons in the azimuthal angle
ϕ around the virtual-photon direction, relative to the lepton scattering plane. The extracted asymmetries are attributed to either the deeply virtual Compton scattering process or its interference with the Bethe–Heitler process. They are compared with earlier results on the proton target. In the measured kinematic region, the beam-charge asymmetry amplitudes and the leading amplitudes of the beam-helicity asymmetries on an unpolarized deuteron target are compatible with the results from unpolarized protons.
Cephalosporin acid synthetase (CASA) is responsible for specific to synthesis of cephalosporin-acids, its expression in Escherichia coli cells is accompanied by accumulation of unprocessed insoluble ...precursor. In order to optimize conditions of recombinant CASA production we have studied the effects of several parameters of strain cultivation, including growth media composition, temperature, and inoculation dose. Also plasmids for production of CASA variants with the signal sequence of Erwinia carotovora L-asparaginase (ansCASA) and "leaderless" CASA were created in search of more efficient expression constructs. Removal of the N-terminal secretion signal sequence reduced the production of functionally active CASA more than 10-fold and inhibited strain growth. Insertion of the L-asparaginase signal sequence increased the specific enzyme activity in the resultant recombinant strain. The ansCASA producing strain was used to develop the method of immobilization of the recombinant enzyme on an epoxy-activated macroporous acrylic support. The resultant biocatalyst performed effective synthesis of cefazolin from 3-(5-methyl-1,3,4-thiadiazol-2-il)-thiomethyl-7- aminocephalosporanic acid (MMTD-7-ACA) and methyl ester of 1(H)-tetrazolilacetic acid (МETzAA), under mild conditions a transformation level of MMTD-7-ACA to cefazolin of 95% is reached.
Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive
ρ
0
electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized ...hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1<
Q
2
<7 GeV
2
, 3.0<
W
<6.3 GeV, and −
t
<0.4 GeV
2
. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on
Q
2
and
t
are presented, as well as the longitudinal-to-transverse
ρ
0
electroproduction cross-section ratio as a function of
Q
2
. A small but statistically significant deviation from the hypothesis of
s
-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism.
Polarizations of the secondary protons from the (p,2p) reactions on 7Li nucleus at 1 GeV of the initial proton energy have been measured in a kinematically complete experiment. Two final protons from ...the reaction were detected in coincidence by means of a two-arm magnetic spectrometer at nonsymmetric scattering angles Θ1=15°÷26° and Θ2=58.6° in the momentum range of the residual nucleus up to 175 MeV/c. Both arms of the spectrometer were equipped with multiwire proportional chamber polarimeters. The resolution of the spectrometer on separation energy of 4.5 MeV (FWHM) was enough to reliably separate S- and P-shell recoil protons.
The experimental data shows a strong deviation from a simple Impulse Approximation expectation, both for S- and P-shell (p,2p) events. Analysis in the framework of the the Distorted Wave Impulse Approximation has been done in combination with depolarization factors, the latter being found by fits to the data. Simple estimations show that the experimentally found depolarization, in particular for the protons detected in the high-energy arm of the spectrometer, is too large. A significant reduction of the both detected proton polarizations might be explained in the frame of a recently developed approach based on modification of the pp-scattering amplitude in nuclear medium.
The influence of the nuclear medium on lepto-production of hadrons was studied in the HERMES experiment at DESY in semi-inclusive deep-inelastic scattering of 27.6 GeV positrons off deuterium, ...nitrogen and krypton targets. The differential multiplicity for krypton relative to that of deuterium has been measured for the first time for various identified hadrons (π+, π−, π0, K+, K−, p and p̄) as a function of the virtual photon energy ν, the fraction z of this energy transferred to the hadron, and the hadron transverse momentum squared pt2. The multiplicity ratio is strongly reduced in the nuclear medium at low ν and high z, with significant differences among the various hadrons. The distribution of the hadron transverse momentum is broadened towards high pt2 in the nuclear medium, in a manner resembling the Cronin effect previously observed in collisions of heavy ions and protons with nuclei.
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