389 research outputs found
Genotoxicity of nitroso compounds and sodium dichromate in a model combining organ cultures of human nasal epithelia and the comet assay
Genotoxic effects of xenobiotics are a possible step in tumor initiation in the mucosa of the upper aerodigestive tract. Using the comet assay, detecting genotoxicity in human tissue has been restricted to single incubations in vitro, but in vivo most xenobiotics harm their target in a repetitive or chronic manner. Therefore, we propose a model, which provides repetitive incubations in human upper aerodigestive tract mucosa cultures. Samples of human inferior nasal turbinate mucosa (n = 25) were cultured according to a modified version of a technique originally described by Steinsvag. On day 1 fresh samples and on days 7, 9 and 11 organ cultures were incubated with N-nitrosodiethylamine (NDEA), sodium dichromate (Na2Cr2O7) and N'-methyl-N-nitro-N-nitrosoguanidine(MNNG). Mucosa samples and organ cultures, respectively, underwent a modified comet assay on days 1, 7 and 11. Genotoxicity could be shown for NDEA, Na2Cr2O7 and MNNG on days 1, 7 and 11. Duration of tissue culture and repetitive incubations did not significantly influence the results for NDEA. Nevertheless, Na2Cr2O7 and MNNG caused higher genotoxic effects on cultures subjected to the comet assay on day 11. This model may help to assess genotoxic hazards posed by environ mental pollutants that have a cumulative character in repetitive or chronic exposure in vivo. Copyright (C) 2001 S. Karger AG, Basel
Geometrical dependence of low frequency noise in superconducting flux qubits
A general method for directly measuring the low-frequency flux noise (below
10 Hz) in compound Josephson junction superconducting flux qubits has been used
to study a series of 85 devices of varying design. The variation in flux noise
across sets of qubits with identical designs was observed to be small. However,
the levels of flux noise systematically varied between qubit designs with
strong dependence upon qubit wiring length and wiring width. Furthermore,
qubits fabricated above a superconducting ground plane yielded lower noise than
qubits without such a layer. These results support the hypothesis that
localized magnetic impurities in the vicinity of the qubit wiring are a key
source of low frequency flux noise in superconducting devices.Comment: 5 pages, 5 figure
Excess Resistance Effect in a Normal Metal Contacting a Superconductor
In relatively pure normal samples contacting a superconductor we consider the
excess resistance effect (that is a decrease of the total electrical resistance
of the sample after transition of the superconducting part into the normal
state) and determine conditions under which the effect arises.Comment: 3 pages, 2 postscript figures all in uuencoded forma
Magnetic Response of a Single, Isolated Gold Loop
Measurements have been made of the low-temperature magnetic response of single, isolated, micron-size Au loops. The magnetic response is found to contain a component which oscillates with the applied magnetic flux with a fundamental period of Φ0=h/e. The amplitude of the oscillatory component corresponds to a persistent current of ≃(0.3–2.0)evF/L, 1 to 2 orders of magnitude larger than predicted by current theories
Probing Noise in Flux Qubits via Macroscopic Resonant Tunneling
Macroscopic resonant tunneling between the two lowest lying states of a
bistable RF-SQUID is used to characterize noise in a flux qubit. Measurements
of the incoherent decay rate as a function of flux bias revealed a Gaussian
shaped profile that is not peaked at the resonance point, but is shifted to a
bias at which the initial well is higher than the target well. The r.m.s.
amplitude of the noise, which is proportional to the decoherence rate 1/T_2^*,
was observed to be weakly dependent on temperature below 70 mK. Analysis of
these results indicates that the dominant source of low frequency (1/f) flux
noise in this device is a quantum mechanical environment in thermal
equilibrium.Comment: 4 pages 4 figure
Observation of Andreev Reflection Enhanced Shot Noise
We have experimentally investigated the quasiparticle shot noise in
NbN/MgO/NbN superconductor - insulator - superconductor tunnel junctions. The
observed shot noise is significantly larger than theoretically expected. We
attribute this to the occurrence of multiple Andreev reflection processes in
pinholes present in the MgO barrier. This mechanism causes the current to flow
in large charge quanta (Andreev clusters), with a voltage dependent average
value of m = 1+ 2 Delta/eV times the electron charge. Because of this charge
enhancement effect, the shot noise is increased by the factor m.Comment: 4 pages, 5 figures include
An unusual case of low-grade tubulopapillary adenocarcinoma of the sinonasal tract
<p>Abstract</p> <p>Background</p> <p>Low-grade papillary adenocarcinomas of the sinonasal tract are rare neoplasms. Over recent years, little doubt remains that this tumour represents a separate entity based on morphology, ultrastructural features and behaviour. We outline a case of this rare entity displaying a not hitherto described immunophenotype.</p> <p>Case presentation</p> <p>A 32 year old man presented recurrent epistaxis was evaluated with endoscopy which revealed a well circumscribed pedunculated mass lesion in left nares. The mass was arising from the nasal septum which was excised along with the mass. The biopsy revealed low-grade, non-intestinal type sinonasal tubulopapillary adenocarcinoma.</p> <p>Conclusion</p> <p>TTF-1 immunoreactivity in absence of thyroid or pulmonary primary in the present case remains an enigma. However, this raises the possibility of the utility of this antibody to predict a better clinical outcome in the subset of low grade non-intestinal sinonasal adenocarcinoma. More cases of similar morphological appearance may need to be examined for TTF-1 immunoreactivity and clinically followed up to establish this theory.</p
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