375 research outputs found
Er-doped Tellurite glasses for planar waveguide power amplifier with extended gain bandwidth
Tellurite glass compositions doped with erbium and erbium/ytterbium optimised to support extended gain bandwidth with significant amplification have been fabricated, and their thermal, optical absorption, excitation and luminescence properties investigated. Each rare-earth dopant concentration was set at 1x1020/cm3. Broad emission cross-section bandwidths up to 50nm FWHM were observed, with fluorescence lifetimes of ~3ms. Collinear pump probe measurements on ~4mm thick bulk samples revealed peak gains of up to 2.1dB/cm at a wavelength of 1535nm in the co-doped material, with an incident pump intensity of only Iinc~8kW/cm2 at a wavelength of 974nm. At equivalent absorbed pump powers between co-doped and single doped materials the relative gain was 1.25dB/cm (Iinc~4kW/cm2) and 0.9dB/cm (Iinc~8kW/cm2) respectively, demonstrating efficient energy transfer from the ytterbium to erbium ions. Excited state absorption at longer wavelengths was observed and characterised and its implication on realising sufficient gain in the wavelength band of interest is discussed
Self-shielding effect of a single phase liquid xenon detector for direct dark matter search
Liquid xenon is a suitable material for a dark matter search. For future
large scale experiments, single phase detectors are attractive due to their
simple configuration and scalability. However, in order to reduce backgrounds,
they need to fully rely on liquid xenon's self-shielding property. A prototype
detector was developed at Kamioka Observatory to establish vertex and energy
reconstruction methods and to demonstrate the self-shielding power against
gamma rays from outside of the detector. Sufficient self-shielding power for
future experiments was obtained.Comment: 8 pages, 8 figure
Kinetics of water flow through polymer gel
The water flow through the poly(acrylamide) gel under a constant water
pressure is measured by newly designed apparatus. The time evolution of the
water flow in the gel, is calculated based on the collective diffusion model of
the polymer network coupled with the friction between the polymer network and
the water. The friction coefficient are determined from the equilibrium
velocity of water flow. The Young modulus and the Poisson's ratio of the rod
shape gels are measured by the uni-axial elongation experiments, which
determine the longitudinal modulus independently from the water flow
experiments. With the values of the longitudinal modulus and of the friction
determined by the experiments, the calculated results are compared with the
time evolution of the flow experiments. We find that the time evolution of the
water flow is well described by a single characteristic relaxation time
predicted by the collective diffusion model coupled with the water friction.Comment: 7 pages, 5 figures, 27 references, Eqs adde
Looking into the matter of light-quark hadrons
In tackling QCD, a constructive feedback between theory and extant and
forthcoming experiments is necessary in order to place constraints on the
infrared behaviour of QCD's \beta-function, a key nonperturbative quantity in
hadron physics. The Dyson-Schwinger equations provide a tool with which to work
toward this goal. They connect confinement with dynamical chiral symmetry
breaking, both with the observable properties of hadrons, and hence provide a
means of elucidating the material content of real-world QCD. This contribution
illustrates these points via comments on: in-hadron condensates; dressed-quark
anomalous chromo- and electro-magnetic moments; the spectra of mesons and
baryons, and the critical role played by hadron-hadron interactions in
producing these spectra.Comment: 11 pages, 7 figures. Contribution to the Proceedings of "Applications
of light-cone coordinates to highly relativistic systems - LIGHTCONE 2011,"
23-27 May, 2011, Dallas. The Proceedings will be published in Few Body
System
Surface state atoms and their contribution to the surface tension of quantum liquids
We investigate the new type of excitations on the surface of liquid helium.
These excitations, called surfons, appear because helium atoms have discrete
energy level at the liquid surface, being attracted to the surface by the van
der Waals force and repulsed at a hard-core interatomic distance. The
concentration of the surfons increases with temperature. The surfons propagate
along the surface and form a two-dimensional gas. Basing on the simple model of
the surfon microscopic structure, we estimate the surfon activation energy and
effective mass for both helium isotopes. We also calculate the contribution of
the surfons to the temperature dependence of the surface tension. This
contribution explains the great and long-standing discrepancy between theory
and experiment on this temperature dependence in both helium isotopes. The
achieved agreement between our theory and experiment is extremely high. The
comparison with experiment allows to extract the surfon activation energy and
effective mass. The values of these surfon microscopic parameters are in a
reasonable agreement with the calculated from the proposed simple model of
surfon structure.Comment: 10 pages, 6 figure
OsHKT1;4-mediated Na+ transport in stems contributes to Na+ exclusion from leaf blades of rice at the reproductive growth stage upon salt stress
Background: Na+ exclusion from leaf blades is one of the key mechanisms for glycophytes to cope with salinity stress. Certain class I transporters of the high-affinity K+ transporter (HKT) family have been demonstrated to mediate leaf blade-Na+ exclusion upon salinity stress via Na+-selective transport. Multiple HKT1 transporters are known to function in rice (Oryza sativa). However, the ion transport function of OsHKT1;4 and its contribution to the Na+ exclusion mechanism in rice remain to be elucidated. Results: Here, we report results of the functional characterization of the OsHKT1;4 transporter in rice. OsHKT1;4 mediated robust Na+ transport in Saccharomyces cerevisiae and Xenopus laevis oocytes. Electrophysiological experiments demonstrated that OsHKT1;4 shows strong Na+ selectivity among cations tested, including Li+, Na+, K+, Rb+, Cs+, and NH4 +, in oocytes. A chimeric protein, EGFP-OsHKT1;4, was found to be functional in oocytes and targeted to the plasma membrane of rice protoplasts. The level of OsHKT1;4 transcripts was prominent in leaf sheaths throughout the growth stages. Unexpectedly however, we demonstrate here accumulation of OsHKT1;4 transcripts in the stem including internode II and peduncle in the reproductive growth stage. Moreover, phenotypic analysis of OsHKT1;4 RNAi plants in the vegetative growth stage revealed no profound influence on the growth and ion accumulation in comparison with WT plants upon salinity stress. However, imposition of salinity stress on the RNAi plants in the reproductive growth stage caused significant Na+ overaccumulation in aerial organs, in particular, leaf blades and sheaths. In addition, 22Na+ tracer experiments using peduncles of RNAi and WT plants suggested xylem Na+ unloading by OsHKT1;4. Conclusions: Taken together, our results indicate a newly recognized function of OsHKT1;4 in Na+ exclusion in stems together with leaf sheaths, thus excluding Na+ from leaf blades of a japonica rice cultivar in the reproductive growth stage, but the contribution is low when the plants are in the vegetative growth stage
Scintillation yield of liquid xenon at room temperature
The intensity of scintillation light emission from liquid xenon at room
temperature was measured. The scintillation light yield at 1 deg. was measured
to be 0.64 +/- 0.02 (stat.) +/- 0.06 (sys.) of that at -100 deg. Using the
reported light yield at -100 deg. (46 photons/keV), the measured light yield at
1 deg. corresponds to 29 photons/keV. This result shows that liquid xenon
scintillator gives high light yield even at room temperature.Comment: 16pages,12figure
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
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