2,730 research outputs found
The Edge Electric Field of a Pyroelectric and its Applications
Following a change of temperature of a pyroelectric (PE), a depolarizing
electric field appears both inside the PE, as well as outside its edges, the
edge depolarizing electric field (EDEF). The EDEF extends outwards up to a
distance of the order of magnitude of the PE width. The mapping and the
strength of the EDEF have been calculated and analyzed for the case of a
semi-infinite pyroelectric plate. This strong EDEF (104-105 V/cm), when
penetrating into the surrounding medium, creates a variety of physical effects:
inducing electrical current in a semiconductor and affecting its resistance,
accelerating charged and neutral particles in vacuum or in a gas, generating
electromagnetic waves, modifying optical characteristics by electrooptical and
photoelasic effects, generating piezoelectric deformation and more. We show
that these EDEF induced effects could serve as a basis for the development of
various applications and devices.Comment: 27 pages including 13 figure
Electric Field Effect Analysis of Thin PbTe films on high-epsilon SrTiO3 Substrate
Thin PbTe films (thickness 500 - 600 angstrom), deposited on SrTiO3, have
been investigated by electric field effect (EFE). The high resistivity of such
thin films warrants a high sensitivity of the EFE method. The SrTiO3 substrate
serves as the dielectric layer in the Gate-Dielectric-PbTe structure. Due to
the large dielectric constant of SrTiO3, particularly at low temperatures, the
electric displacement D in the film reaches the high value of about 10^8 V/cm,
and the EFE introduced charge into the PbTe film amounts to ~ 8 microC/cm2. The
high D permits to measure the EFE resistance and Hall constant over a wide
region of D, revealing the characteristic features of their D-dependence. An
appropriate theoretical model has been formulated, showing that, for such
films, one can measure the dependence of the Fermi level on D. In fact, we
demonstrate that shifting the Fermi level across the gap by varying D, the
density-of-states of the in-gape states can be mapped out. Our results show,
that the PbTe layers studied, possess a mobility gap exceeding the gap of bulk
PbTe.Comment: 27 pages, 12 figure
Time domain Dielectric Spectroscopy Study of Human Cells. II. Normal and Malignant White Blood Cells
open access articleThe dielectric properties of human lymphocyte suspensions were studied by time domain dielectric spectroscopy (TDDS). Nine populations of malignant and normal lymphocytes were investigated. Analysis of the dielectric parameters of cell structural parts were performed in the framework of Maxwell^Wagner mixture formula and the double-shell model of cell. The specific capacitance of the cell membranes was estimated by the Hanai^Asami^Koisumi formula. It was shown that the dielectric permittivity, capacitance and conductivity values of cell membranes are higher for normal lymphocytes than for the malignant ones. The difference of the same parameters for normal B- and T-cells is also discussed
Non-Fermi liquid behavior of SrRuO_3 -- evidence from infrared conductivity
The reflectivity of the itinerant ferromagnet SrRuO_3 has been measured
between 50 and 25,000 cm-1 at temperatures ranging from 40 to 300 K, and used
to obtain conductivity, scattering rate, and effective mass as a function of
frequency and temperature. We find that at low temperatures the conductivity
falls unusually slowly as a function of frequency (proportional to
\omega^{-1/2}), and at high temperatures it even appears to increase as a
function of frequency in the far-infrared limit. The data suggest that the
charge dynamics of SrRuO_3 are substantially different from those of
Fermi-liquid metals.Comment: 4 pages, 3 postscript figure
Non-Typhi Salmonella gastroenteritis in children presenting to the emergency department: characteristics of patients with associated bacteraemia
ABSTRACTThe records of children with Salmonella gastroenteritis only (n = 97), and those with associated bacteraemia (n = 64), seen in one medical centre during a 12-year period, were analysed retrospectively. Mean patient age was 2.24 ± 2.8 years (range, 0.05–16 years), and 49% were male. Children with bacteraemia presented after a longer duration of symptoms (7.0 ± 6.9 vs. 3.9 ± 4.6 days, p 0.0002), and had higher erythrocyte sedimentation rates (45 ± 22 vs. 33 ± 22 mm/h, p < 0.02) and lactate dehydrogenase values (924 ± 113 vs. 685 ± 165 IU/L, p 0.001). There was a trend in bacteraemic children towards immunosuppression (6.3% vs. 1.0%, p 0.08) and a lower number of siblings (2.9 ± 1.9 vs. 3.8 ± 2.7, p 0.063). Non-bacteraemic children had a more severe clinical appearance, and a higher percentage had a moderate to bad general appearance (51.5 vs. 29.7%, p < 0.01), with dehydration (37.1 vs. 18.8%, p 0.02) and vomiting (58.8 vs. 39.0%, p 0.02). Laboratory dehydration indicators were also markedly worse in non-bacteraemic children, with urine specific gravity of 1020 ± 9.4 vs. 1013 ± 9.0 (p 0.0002), base excess of −4.2 ± 3.0 vs. −2.5 ± 3.4 mEq/L (p 0.01), and blood urea nitrogen of 10.1 ± 7.0 vs. 7.4 ± 4.5 mg% (p 0.002). Thus, the clinical presentation of bacteraemic children was more gradual, and associated gastroenteritis and dehydration was less pronounced. These findings may contribute in part to the inadvertent discharge of bacteraemic children from the emergency department
The Rossiter-McLaughlin effect and analytic radial velocity curves for transiting extrasolar planetary systems
A transiting extrasolar planet sequentially blocks off the light coming from
the different parts of the disk of the host star in a time dependent manner.
Due to the spin of the star, this produces an asymmetric distortion in the line
profiles of the stellar spectrum, leading to an apparent anomaly of the radial
velocity curves, known as the Rossiter - McLaughlin effect. Here, we derive
approximate but accurate analytic formulae for the anomaly of radial velocity
curves taking account of the stellar limb darkening. The formulae are
particularly useful in extracting information of the projected angle between
the planetary orbit axis and the stellar spin axis, \lambda, and the projected
stellar spin velocity, V sin I_s. We create mock samples for the radial curves
for the transiting extrasolar system HD209458, and demonstrate that constraints
on the spin parameters (V sin I_s, \lambda) may be significantly improved by
combining our analytic template formulae and the precision velocity curves from
high-resolution spectroscopic observations with 8-10 m class telescopes. Thus
future observational exploration of transiting systems using the Rossiter -
McLaughlin effect is one of the most important probes to better understanding
of the origin of extrasolar planetary systems, especially the origin of their
angular momentum.Comment: 39 pages, 16 figures, Accepted to ApJ. To match the published version
(ApJ 623, April 10 issue
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