71 research outputs found
Near-threshold Lambda(1520) production by the gamma p -> K+Lambda(1520) reaction at forward K+ angles
Differential cross sections and photon-beam asymmetries for the gamma p -> K+
Lambda(1520) reaction have been measured with linearly polarized photon beams
at energies from the threshold to 2.4 GeV at 0.6<cos(theta)<1. A new bump
structure was found at W=2.11 GeV in the cross sections. The bump is not well
reproduced by theoretical calculations introducing a nucleon resonance with
J<=3/2. This result suggests that the bump might be produced by a nucleon
resonance possibly with J>=5/2 or by a new reaction process, for example an
interference effect with the phi photoproduction having a similar bump
structure in the cross sections.Comment: 5 pages, 4 figures, published in Phys. Rev. Let
Measurement of the Reaction at Backward Angles
Cross sections for the have been measured at
backward angles using linearly polarized photons in the range 1.50 to 2.37 GeV.
In addition, the beam asymmetry for this reaction has been measured for the
first time at backward angles. The was detected at forward angles in
the LEPS spectrometer via its decay to and the K^+ was inferred using
the technique of missing mass. These measurements, corresponding to kaons at
far backward angles in the center-of-mass frame, complement similar CLAS data
at other angles. Comparison with theoretical models shows that the reactions in
these kinematics provide further opportunities to investigate the reaction
mechanisms of hadron dynamics.Comment: 6 figures, submitted to PRC rapid communication
Backward-angle photoproduction of mesons on the proton at = 1.5--2.4 GeV
Differential cross sections and photon beam asymmetries for
photoproduction have been measured at = 1.5--2.4 GeV and at the
scattering angles, --1 cos --0.6. The
energy-dependent slope of differential cross sections for -channel
production has been determined. An enhancement at backward angles is found
above = 2.0 GeV. This is inferred to be due to the -channel
contribution and/or resonances. Photon beam asymmetries have been obtained for
the first time at backward angles. A strong angular dependence has been found
at 2.0 GeV, which may be due to the unknown high-mass resonances.Comment: 12 pages, 4 figures, submitted to PL
Forward coherent -meson photoproduction from deuterons near threshold
Differential cross sections and decay asymmetries for coherent -meson
photoproduction from deuterons were measured for the first time at forward
angles using linearly polarized photons at = 1.5-2.4 GeV. This
reaction offers a unique way to directly access natural-parity Pomeron dynamics
and gluon exchange at low energies. The cross sections at zero degrees increase
with increasing photon energy. The decay asymmetries demonstrate a complete
dominance of natural-parity exchange processes, showing that isovector
unnatural-parity -meson exchange is small. Nevertheless the deduced cross
sections of -mesons from nucleons contributed by isoscalar t-channel
exchange processes are not well described by the conventional Pomeron model.Comment: 14 pages, 6 figures. Final published versio
An analysis of Methylenetetrahydrofolate reductase and Glutathione S-transferase omega-1 genes as modifiers of the cerebral response to ischemia
<p>Abstract</p> <p>Background</p> <p>Cerebral ischemia involves a series of reactions which ultimately influence the final volume of a brain infarction. We hypothesize that polymorphisms in genes encoding proteins involved in these reactions could act as modifiers of the cerebral response to ischemia and impact the resultant stroke volume. The final volume of a cerebral infarct is important as it correlates with the morbidity and mortality associated with non-lacunar ischemic strokes.</p> <p>Methods</p> <p>The proteins encoded by the methylenetetrahydrofolate reductase (<it>MTHFR</it>) and glutathione S-transferase omega-1 (<it>GSTO-1</it>) genes are, through oxidative mechanisms, key participants in the cerebral response to ischemia. On the basis of these biological activities, they were selected as candidate genes for further investigation. We analyzed the C677T polymorphism in the <it>MTHFR </it>gene and the C419A polymorphism in the <it>GSTO-1 </it>gene in 128 patients with non-lacunar ischemic strokes.</p> <p>Results</p> <p>We found no significant association of either the <it>MTHFR </it>(p = 0.72) or <it>GSTO-1 </it>(p = 0.58) polymorphisms with cerebral infarct volume.</p> <p>Conclusion</p> <p>Our study shows no major gene effect of either the <it>MTHFR </it>or <it>GSTO-1 </it>genes as a modifier of ischemic stroke volume. However, given the relatively small sample size, a minor gene effect is not excluded by this investigation.</p
Single Cell Analysis Facilitates Staging of Blimp1-Dependent Primordial Germ Cells Derived from Mouse Embryonic Stem Cells
The cell intrinsic programming that regulates mammalian primordial germ cell (PGC) development in the pre-gonadal stage is challenging to investigate. To overcome this we created a transgene-free method for generating PGCs in vitro (iPGCs) from mouse embryonic stem cells (ESCs). Using labeling for SSEA1 and cKit, two cell surface molecules used previously to isolate presumptive iPGCs, we show that not all SSEA1+/cKit+ double positive cells exhibit a PGC identity. Instead, we determined that selecting for cKitbright cells within the SSEA1+ fraction significantly enriches for the putative iPGC population. Single cell analysis comparing SSEA1+/cKitbright iPGCs to ESCs and embryonic PGCs demonstrates that 97% of single iPGCs co-express PGC signature genes Blimp1, Stella, Dnd1, Prdm14 and Dazl at similar levels to e9.5â10.5 PGCs, whereas 90% of single mouse ESC do not co-express PGC signature genes. For the 10% of ESCs that co-express PGC signature genes, the levels are significantly lower than iPGCs. Microarray analysis shows that iPGCs are transcriptionally distinct from ESCs and repress gene ontology groups associated with mesoderm and heart development. At the level of chromatin, iPGCs contain 5-methyl cytosine bases in their DNA at imprinted and non-imprinted loci, and are enriched in histone H3 lysine 27 trimethylation, yet do not have detectable levels of Mvh protein, consistent with a Blimp1-positive pre-gonadal PGC identity. In order to determine whether iPGC formation is dependent upon Blimp1, we generated Blimp1 null ESCs and found that loss of Blimp1 significantly depletes SSEA1/cKitbright iPGCs. Taken together, the generation of Blimp1-positive iPGCs from ESCs constitutes a robust model for examining cell-intrinsic regulation of PGCs during the Blimp1-positive stage of development
Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)Sigma0 reactions at Egamma=1.5-2.4 GeV
Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0
reactions are measured for the first time for Egamma=1.5-2.4 GeV and
0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the
Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are
positive and gradually increase with rising photon energy. The data are not
consistent with theoretical predictions based on tree-level effective
Lagrangian approaches. Including the new results in the development of the
models is, therefore, crucial for understanding the reaction mechanism and to
test the presence of baryon resonances which are predicted in quark models but
are sofar undiscovered
The gamma + p to K+ + Lambda and gamma + p to K+ + Sigma0 reactions at forward angles with photon energies from 1.5 to 2.4 GeV
Differential cross sections and photon beam asymmetries for the gamma p
rightarrow K+ Lambda and gamma p rightarrow K+ Sigma0 reactions have been
measured in the photon energy range from 1.5 GeV to 2.4 GeV and in the angular
range from Theta_{cm} = 0 to 60 of the K+ scattering angle in the center of
mass system at the SPring-8/LEPS facility. The photon beam asymmetries for both
the reactions have been found to be positive and to increase with the photon
energy. The measured differential cross sections agree with the data measured
by the CLAS collaboration at cosTheta_{cm}<0.9 within the experimental
uncertainties, but the discrepancy with the SAPHIR data for the K+Lambda
reaction is large at cosTheta_{cm}>0.9. In the K+Lambda reaction, the
resonance-like structure found in the CLAS and SAPHIR data at W=1.96 GeV is
confirmed. The differential cross sections at forward angles suggest a strong
K-exchange contribution in the t-channel for the K+Lambda reaction, but not for
the K+Sigma0 reaction.Comment: 13 pages, 18 figures, submitted to Physical Review
Diffractive -meson photoproduction on proton near threshold
Photoproduction of -meson on protons was studied by means of linearly
polarized photons at forward angles in the low-energy region from threshold to
= 2.37 GeV. The differential cross sections at do
not increase smoothly as increases, but show a local maximum at
around 2.0 GeV. The angular distributions demonstrate that -mesons are
photo-produced predominantly by helicity-conserving processes, and the local
maximum is not likely due to unnatural-parity processes.Comment: 6 pages, error on the cross sections were corrected, accepted for
publication in Phys. Rev. Let
phi photo-production from Li, C, Al, and Cu nuclei at Egamma=1.5 - 2.4 GeV
The photo-production of mesons from Li, C, Al, and Cu at forward
angles has been measured at =1.5--2.4 GeV. The number of events for
incoherent phi photo-production is found to have a target mass number
dependence of in the kinematical region of
. The total cross section of the -nucleon interaction,
, has been estimated as mb using the
-dependence of the photo-production yield and a Glauber-type multiple
scattering theory. This value is much larger than in free
space, suggesting that the properties might change in the nuclear
medium.Comment: 12 pages 4 figures, submitted to Phys. Lett.
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