391 research outputs found
Analysis, Design and Fabrication of centimeter-wave Dielectric Fresnel Zone Plate Lens and reflector
Fresnel lens has a long history in optics. This concept at non-optical
wavelengths is also applicable. In this paper we report design and fabrication
of a half and quarter wave dielectric Fresnel lens made of Plexiglas, and a
Fresnel reflector at 11.1 GHz frequency. We made two lenses and one reflector
at same frequency and compare their gain and radiation pattern to simulated
results. Some methods for better focusing action will be introduced
Response to tilted magnetic fields in Bi2Sr2CaCu2O8 with columnar defects: Evidence for transverse Meissner effect
The transverse Meissner effect (TME) in the highly layered superconductor
Bi2Sr2CaCu2O(8+y) with columnar defects is investigated by transport
measurements. We present detailed evidence for the persistence of the
Bose-glass phase when H is tilted at an angle theta < theta_c (T) away from the
column direction: (i) the variable-range vortex hopping process for low
currents crosses over to the half-loops regime for high currents; (ii) in both
regimes near theta_c(T) the energy barriers vanish linearly with tan(theta) ;
(iii) the transition temperature is governed by T_{BG}(0) -T_{BG}(theta) sim
|tan(theta)|^{1/\nu_{\perp}} with \nu_{\perp}=1.0 +/- 0.1. Furthermore, above
the transition as theta->\theta_c+, moving kink chains consistent with a
commensurate-incommensurate transition scenario are observed. These results
thereby clearly show the existence of the TME for theta < theta_c(T).Comment: 4 pages, RevTeX, 5 EPS figure
Effect of field tilting on the vortices in irradiated Bi-2212
We report on transport measurements in a Bi-2212 single crystal with columnar
defects parallel to the c-axis. The tilt of the magnetic field away from the
direction of the tracks is studied for filling factors f=B_z/B_phi<1. Near the
Bose Glass transition temperature T_BG, the angular scaling laws are verified
and we find the field independent critical exponents nu'=1.1 and z'=5.30.
Finally, above H_perpC we evidence the signature of a smectic-A like vortex
phase. These experimental results provide support for the Bose Glass theory.Comment: 2 pages LaTeX, 2 EPS figures, uses fleqn and espcrc2 style macros.
Submitted to Proceedings of M2S-HTSC-V
Huge Seebeck coefficients in non-aqueous electrolytes
The Seeebeck coefficients of the non-aqueous electrolytes tetrabutylammonium
nitrate, tetraoctylphosphonium bromide and tetradodecylammonium nitrate in
1-octanol, 1-dodecanol and ethylene-glycol are measured in a temperature range
from T=30 to T=45 C. The Seebeck coefficient is generally of the order of a few
hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here
we report huge values of 7 mV/K at 0.1M concentration for tetrabutylammonium
nitrate in 1-dodecanol. These striking results open the question of
unexpectedly large kosmotrope or "structure making" effects of
tetraalkylammonium ions on the structure of alcohols.Comment: Submitted to J. Chem. Phy
Infrared study of the phonon modes in PrMnO and CaMnO
The infrared (IR) reflectivity spectra of orthorhombic manganese perovskites
PrMnO and CaMnO are studied in the frequency range of optical phonon
modes at temperatures varying from 300 to 4 K. The IR phonon spectra of these
two materials are analyzed by a fitting procedure based on a Lorentz model, and
assigned to definite vibrational modes of structures by comparison with
the results of lattice dynamical calculations. The calculations have been
performed in the framework of a shell model using short range
Born-Mayer-Buckingham and long range Coulomb potentials, whose parameters have
been optimized in order that the calculated Raman and IR active phonon
frequencies, and lattice parameters match with their experimental values. We
find a close correspondence between the values of the IR phonon frequencies of
PrMnO and CaMnO, which shows that the substitution of the Pr
ions with Ca results in a reduction of the frequency of medium- and
high-energy IR phonons, and an increase of the frequency of those of
low-energy. Nevertheless, the experimentally obtained IR phonon amplitudes of
the two materials appear to be unrelated. A comparative study of the
vibrational patterns of these modes reveals that most of them correspond to
complex atomic vibrations significantly different from PrMnO to CaMnO
which cannot be assigned only to a given type of vibration (external, bending,
or stretching modes). In particular, these results confirm that the structure
of CaMnO is quite far from the ideal (cubic) perovskite structure.Comment: 10 pages, 6 figure
Multiple time-scale approach for a system of Brownian particles in a non-uniform temperature field
The Smoluchowsky equation for a system of interacting Brownian particles in a
temperature gradient is derived from the Kramers equation by means of a
multiple time-scale method. The interparticle interactions are assumed to be
represented by a mean-field description. We present numerical results that
compare well with the theoretical prediction together with an extensive
discussion on the prescription of the Langevin equation in overdamped systems.Comment: 8 pages, 2 figure
Vegetal diamine oxidase alleviates histamine-induced contraction of colonic muscles
Excess of histamine in gut lumen generates a pronounced gastrointestinal discomfort, which may include diarrhea and peristalsis dysfunctions. Deleterious effects of histamine can be alleviated with antihistamine drugs targeting histamine receptors. However, many antihistamine agents come with various undesirable side effects. Vegetal diamine oxidase (vDAO) might be a relevant alternative owing to its histaminase activity. Mammalian intestinal mucosa contains an endogenous DAO, yet possessing lower activity compared to that of vDAO preparation. Moreover, in several pathological conditions such as inflammatory bowel disease and irritable bowel syndrome, this endogenous DAO enzyme can be lost or inactivated. Here, we tested the therapeutic potential of vDAO by focusing on the well-known effect of histamine on gut motility. Using ex vivo and in vitro assays, we found that vDAO is more potent than commercial anti-histamine drugs at inhibiting histamine-induced contraction of murine distal colon muscles. We also identified pyridoxal 5′-phosphate (the biologically active form of vitamin B6) as an effective enhancer of vDAO antispasmodic activity. Furthermore, we discovered that rectally administered vDAO can be retained on gut mucosa and remain active. These observations make administration of vDAO in the gut lumen a valid alternative treatment for histamine-induced intestinal dysfunctions
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