418 research outputs found
An electromagnetic crystal Green function multiple scattering technique for arbitrary polarizations, lattices, and defects
Magnetic field in an apartment located above 10/0.4 kV substation: Levels and mitigation techniques
The paper presents a real case of non-ionising radiation testing in an apartment located directly above a 10/0.4 kV substation in Serbia. In order to check the compliance with national regulations on protection of population from non-ionising radiation, it was necessary to perform measurements of magnetic flux density in the apartment. After the first measurements were performed, the distribution company implemented a mitigation technique by placing a passive conductive shield inside the substation in order to decrease magnetic field levels in the apartment. Measurements performed after the mitigation technique had been implemented have shown that the applied shield had an impact on magnetic field reduction to a certain extent. However, since the obtained shielding factor was not very high, the authors analysed another possible shielding solution which would provide higher shielding factor and consequently lower magnetic field levels in the apartment. Both shielding solutions and the results they provide are presented and analysed
Enhanced diffraction by a rectangular grating made of a negative phase--velocity (or negative index) material
The diffraction of electromagnetic plane waves by a rectangular grating
formed by discrete steps in the interface of a homogeneous, isotropic, linear,
negative phase--velocity (negative index) material with free space is studied
using the semi--analytic C method. When a nonspecular diffracted order is of
the propagating type, coupling to that order is significantly larger for a
negative index material than for conventional material. The computed coupling
strengths reported here are in agreement with recent experiments, and
illustrate the role of evanescent fields localized at the grating interface in
producing this enhanced coupling.Comment: 12 pages, 4 figure
A spherical perfect lens
It has been recently proved that a slab of negative refractive index material
acts as a perfect lens in that it makes accessible the sub-wavelength image
information contained in the evanescent modes of a source. Here we elaborate on
perfect lens solutions to spherical shells of negative refractive material
where magnification of the near-field images becomes possible. The negative
refractive materials then need to be spatially dispersive with and . We concentrate on lens-like solutions for the
extreme near-field limit. Then the conditions for the TM and TE polarized modes
become independent of and respectively.Comment: Revtex4, 9 pages, 2 figures (eps
Life history parameters in acellular extrinsic fiber cementum microstructure
Life-history parameters such as pregnancies, skeletal trauma, and renal disease have previously been identified from hypomineralized growth layers (incremental lines) of acellular extrinsic fiber cementum (AEFC). The precise periodicity of these growth layers remains vaguely approximated, so causal life-history explanations using tooth cementum cannot yet be rigorously calculated or tested. On the other hand, we show how life history parameters in AEFC can be identified by two contrasting elemental detection methods. Based on our results we reject the possibility of accurate estimation of pregnancies and other life history parameters from cementum using scanning electron microscopy alone. Here, we propose a new methodological approach for cementum research, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), to measure degree and distribution of mineralization of cementum growth layers. Our results show that Tof-SIMS can significantly increase our knowledge of cementum composition and is therefore a powerful new tool for life history researchers
Prevention of coronary restenosis by stenting
Balloon angioplasty fails to provide acceptable long-term results for a significant proportion of patients. An intravascular mechanical support, developed with the aim of preventing restenosis and acute closure of diseased arteries after transluminal angioplasty, was implanted in 44 patients (39 male and five female), aged from 35 to 70 years (mean 56 years) with documented restenosis of native coronary artery (41 stents) and bypass grafts (12 stents). In the group of bypass graft patients there was no local restenosis and no major complication. In patients in whom stents were placed in native coronary arteries, the complication rate was higher (two patients died after coronary bypass surgery). One patient died suddenly at home. Except for one patient, in whom a new lesion developed proximally with extension into the stent, no case of restenosis could be observed. Despite the still relatively high complication rate, we feel that stenting may present a rational approach to the unresolved problem of restenosis after coronary angioplast
Temperature range of superconducting fluctuations above T_c in YBa_2Cu_3O_{7-\delta} single crystals
Microwave absorption measurements in magnetic fields from zero up to 16 T
were used to determine the temperature range of superconducting fluctuations
above the superconducting critical temperature T_c in YBa_2Cu_3O_{7-\delta}.
Measurements were performed on deeply underdoped, slightly underdoped, and
overdoped single crystals. The temperature range of the superconducting
fluctuations above T_c is determined by an experimental method which is free
from arbitrary assumptions about subtracting the nonsuperconducting
contributions to the total measured signal, and/or theoretical models to
extract the unknown parameters. The superconducting fluctuations are detected
in the ab-plane, and c-axis conductivity, by identifying the onset temperature
T'. Within the sensitivity of the method, this fluctuation regime is found only
within a fairly narrow region above T_c. Its width increases from 7 K in the
overdoped sample (T_c = 89 K), to at most 23 K in the deeply underdoped sample
(T_c = 57 K), so that T' falls well below the pseudogap temperature T*.
Implications of these findings are discussed in the context of other
experimental probes of superconducting fluctuations in the cuprates
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