1,681 research outputs found
The Proper Motion of PSR J0205+6449 in 3C 58
We report on sensitive phase-referenced and gated 1.4-GHz VLBI radio
observations of the pulsar PSR J0205+6449 in the young pulsar-wind nebula 3C
58, made in 2007 and 2010. We employed a novel technique where the ~105-m Green
Bank telescope is used simultaneously to obtain single-dish data used to
determine the pulsar's period as well as to obtain the VLBI data, allowing the
VLBI correlation to be gated synchronously with the pulse to increase the
signal-to-noise. The high timing noise of this young pulsar precludes the
determination of the proper motion from the pulsar timing. We derive the
position of the pulsar accurate at the milliarcsecond level, which is
consistent with a re-determined position from the Chandra X-ray observations.
We reject the original tentative optical identification of the pulsar by
Shearer and Neustroev (2008), but rather identify a different optical
counterpart on their images, with R-band magnitude ~24. We also determine an
accurate proper motion for PSR J0205+6449 of (2.3 +- 0.3) mas/yr, corresponding
to a projected velocity of only (35 +- 6) km/s for a distance of 3.2 kpc, at
p.a. -38 deg. This projected velocity is quite low compared to the velocity
dispersion of known pulsars of ~200 km/s. Our measured proper motion does not
suggest any particular kinematic age for the pulsar.Comment: 10 pages, 7 figures; accepted for publication in MNRA
Full spin switch effect for the superconducting current in a superconductor/ferromagnet thin film heterostructure
Superconductor/ferromagnet (S/F) proximity effect theory predicts that the
superconducting critical temperature of the F1/F2/S or F1/S/F2 trilayers for
the parallel orientation of the F1 and F2 magnetizations is smaller than for
the antiparallel one. This suggests a possibility of a controlled switching
between the superconducting and normal states in the S layer. Here, using the
spin switch design F1/F2/S theoretically proposed by Oh et al. [Appl. Phys.
Lett. 71, 2376 (1997)], that comprises a ferromagnetic bilayer separated by a
non-magnetic metallic spacer layer as a ferromagnetic component, and an
ordinary superconductor as the second interface component, we have successfully
realized a full spin switch effect for the superconducting current.Comment: 5 pages, 4 figure
Urea hydration from dielectric relaxation spectroscopy: Old findings confirmed, new insights gained
© the Owner Societies 2016. We report results on urea hydration obtained by dielectric relaxation spectroscopy (DRS) in a broad range of concentrations and temperatures. In particular, the effective hydration number and dipole moment of urea have been determined. The observed changes with composition and temperature were found to be insignificant and mainly caused by the changing number density of urea. Similarly, solute reorientation scaled simply with viscosity. In contrast, we find that water reorientation undergoes substantial changes in the presence of urea, resulting in two water fractions. The first corresponds to water molecules strongly bound to urea. These solvent molecules follow the reorientational dynamics of the solute. The second fraction exhibits only a minor increase of its relaxation time (in comparison with pure water) which is not linked to solution viscosity. Its activation energy decreases significantly with urea concentration, indicating a marked decrease of the number of H-bonds among the H2O molecules belonging to this fraction. Noncovalent interactions (NCI) analysis, capable to estimate the strength of the interactions within a cluster, shows that bound water molecules are most probably double-hydrogen bonded to urea via the oxygen atom of the carbonyl group and a cis-hydrogen atom. Due to the increased H-bond strength compared to the water dimer and the rigid position in the formed complex the reorientation of these bound H2O molecules is strongly impeded
Manifestation of New Interference Effects in Superconductor/Ferromagnet Spin Valve
Superconductor/ferromagnet (S/F) spin valve effect theories based on the S/F
proximity phenomenon assume that the superconducting transition temperature Tc
of F1/F2/S or F1/S/F2 trilayers for parallel magnetizations of the F1- and
F2-layers (TcP) are smaller than for the antiparallel orientations (TcAP).
Here, we report for CoOx/Fe1/Cu/Fe2/In multilayered systems with varying
Fe2-layer thickness the sign-changing oscillating behavior of the spin valve
effect \Delta Tc=TcAP-TcP. Our measurements revealed the full direct spin valve
effect with TcAP>TcP for Fe2-layer thickness dFe2<1 nm and the full inverse
(TcAP<TcAP) spin valve effect for dFe2>=1 nm. Interference of Cooper pair wave
functions reflected from both surfaces of the Fe2-layer appear as the most
probable reason for the observed behavior of \Delta Tc.Comment: Accepted for publication in PR
Hydration and self-aggregation of a neutral cosolute from dielectric relaxation spectroscopy and MD simulations: The case of 1,3-dimethylurea
© the Owner Societies 2017.The influence of the amphiphile 1,3-dimethylurea (1,3-DMU) on the dynamic properties of water was studied using dielectric relaxation spectroscopy. The experiment provided evidence for substantial retardation of water reorientation in the hydration shell of 1,3-DMU, leading to a separate slow-water relaxation in addition to contributions from bulk-like and fast water as well as from the solute. From the amplitudes of the resolved water modes effective hydration numbers were calculated, showing that each 1,3-DMU molecule effectively freezes the reorientation of 1-2 water molecules. Additionally, a significant amount of solvent molecules, decreasing from ∼39 at infinite dilution to ∼3 close to the solubility limit, is retarded by a factor of ∼1.4 to 2.3, depending on concentration. The marked increase of the solute amplitude indicates pronounced parallel dipole alignment between 1,3-DMU and its strongly bound H2O molecules. Molecular dynamics (MD) simulations of selected solutions revealed a notable slowdown of water rotation for those solvent molecules surrounding the methyl groups of 1,3-DMU and strong binding of ∼2H2O by the hydrophilic carbonyl group, corroborating thus the experimental results. Additionally, the simulations revealed 1,3-DMU self-aggregates of substantial lifetime
消化器内科この一年
© the Owner Societies 2017.The influence of the amphiphile 1,3-dimethylurea (1,3-DMU) on the dynamic properties of water was studied using dielectric relaxation spectroscopy. The experiment provided evidence for substantial retardation of water reorientation in the hydration shell of 1,3-DMU, leading to a separate slow-water relaxation in addition to contributions from bulk-like and fast water as well as from the solute. From the amplitudes of the resolved water modes effective hydration numbers were calculated, showing that each 1,3-DMU molecule effectively freezes the reorientation of 1-2 water molecules. Additionally, a significant amount of solvent molecules, decreasing from ∼39 at infinite dilution to ∼3 close to the solubility limit, is retarded by a factor of ∼1.4 to 2.3, depending on concentration. The marked increase of the solute amplitude indicates pronounced parallel dipole alignment between 1,3-DMU and its strongly bound H2O molecules. Molecular dynamics (MD) simulations of selected solutions revealed a notable slowdown of water rotation for those solvent molecules surrounding the methyl groups of 1,3-DMU and strong binding of ∼2H2O by the hydrophilic carbonyl group, corroborating thus the experimental results. Additionally, the simulations revealed 1,3-DMU self-aggregates of substantial lifetime
Role of alkali cations for the excited state dynamics of liquid water near the surface
Time-resolved liquid jet photoelectron spectroscopy was used to explore the excited state dynamics at the liquid water surface in the presence of alkali cations. The data were evaluated with the help of ab initio calculations on alkali-water clusters and an extension of these results on the basis of the dielectric continuum model: 160nm, sub-20fs vacuum ultraviolet pulses excite water molecules in the solvent shell of Na + or K + cations and evolve into a transient hydrated complex of alkali-ion and electron. The vertical ionization energy of this transient is about 2.5eV, significantly smaller than that of the solvated electron. ??? 2012 American Institute of Physics.open1
Role of the atypical chemoattractant receptor CRAM in regulating CCL19 induced CCR7 responses in B-cell chronic lymphocytic leukemia
BACKGROUND: The non-signalling chemokine receptors, including receptors DARC, D6 and CCX-CKR, have recently been shown to be involved in chemokine clearance and activity regulation. The human chemokine receptor CRAM (also known as HCR or CCRL2) is the most recently identified member of this atypical group. CRAM is expressed on B cells in a maturation-stage dependent manner and absent on T cells. We have recently shown that it competitively binds CCL19. CCL19 and its signalling receptor CCR7 are critical components involved in cell recruitment to secondary lymphoid organs and in maturation. B cell Chronic Lymphocytic Leukemia (B-CLL) is a low-grade lymphoma characterized by proliferative centres (or pseudofollicles). Proliferative centres develop due to abnormal cellular localisation and they are involved in the development of malignant cells. CCR7 is highly expressed on B cells from CLL patients and mediates migration towards its ligands CCL19 and CCL21, while CRAM expression and potential interferences with CCR7 are yet to be characterized. RESULTS: In this study, we show that B cells from patients with B-CLL present highly variable degrees of CRAM expression in contrast to more consistently high levels of CCR7. We investigated the hypothesis that, similar to the atypical receptor DARC, CRAM can modulate chemokine availability and/or efficacy, resulting in the regulation of cellular activation. We found that a high level of CRAM expression was detrimental to efficient chemotaxis with CCL19. MAP-kinase phosphorylation and intracellular calcium release induced by CCL19 were also altered by CRAM expression. In addition, we demonstrate that CRAM-induced regulation of CCL19 signalling is maintained over time. CONCLUSIONS: We postulate that CRAM is a factor involved in the fine tuning/control of CCR7/CCL19 mediated responses. This regulation could be critical to the pivotal role of CCL19 induced formation of proliferation centres supporting the T/B cells encounter as well as disease progression in B-CLL
- …