1,181 research outputs found
Hybrid Superconducting Neutron Detectors
A new neutron detection concept is presented that is based on superconductive
niobium (Nb) strips coated by a boron (B) layer. The working principle of the
detector relies on the nuclear reaction 10B+n + 7Li ,
with and Li ions generating a hot spot on the current-biased Nb strip
which in turn induces a superconducting-normal state transition. The latter is
recognized as a voltage signal which is the evidence of the incident neutron.
The above described detection principle has been experimentally assessed and
verified by irradiating the samples with a pulsed neutron beam at the ISIS
spallation neutron source (UK). It is found that the boron coated
superconducting strips, kept at a temperature T = 8 K and current-biased below
the critical current Ic, are driven into the normal state upon thermal neutron
irradiation. As a result of the transition, voltage pulses in excess of 40 mV
are measured while the bias current can be properly modulated to bring the
strip back to the superconducting state, thus resetting the detector.
Measurements on the counting rate of the device are presented and the future
perspectives leading to neutron detectors with unprecedented spatial
resolutions and efficiency are highlighted.Comment: 8 pages 6 figure
Assessment of a quantum phase gate operation based on nonlinear optics
We analyze in detail the proposal for a two-qubit gate for travelling
single-photon qubits recently presented by C. Ottaviani \emph{et al}. [Phys.
Rev. A \textbf{73}, 010301(R) (2006)]. The scheme is based on an ensemble of
five-level atoms coupled to two quantum and two classical light fields. The two
quantum fields undergo cross-phase modulation induced by electromagnetically
induced transparency. The performance of this two-qubit quantum phase gate for
travelling single-photon qubits is thoroughly examined in the steady-state and
transient regimes, by means of a full quantum treatment of the system dynamics.
In the steady-state regime, we find a general trade-off between the size of the
conditional phase shift and the fidelity of the gate operation. However, this
trade-off can be bypassed in the transient regime, where a satisfactory gate
operation is found to be possible, significantly reducing the gate operation
time.Comment: 12 pages, 15 figure
A refined stable restriction theorem for vector bundles on quadric threefolds
Let E be a stable rank 2 vector bundle on a smooth quadric threefold Q in the
projective 4-space P. We show that the hyperplanes H in P for which the
restriction of E to the hyperplane section of Q by H is not stable form, in
general, a closed subset of codimension at least 2 of the dual projective
4-space, and we explicitly describe the bundles E which do not enjoy this
property. This refines a restriction theorem of Ein and Sols [Nagoya Math. J.
96, 11-22 (1984)] in the same way the main result of Coanda [J. reine angew.
Math. 428, 97-110 (1992)] refines the restriction theorem of Barth [Math. Ann.
226, 125-150 (1977)].Comment: Ann. Mat. Pura Appl. 201
Structurally-related (−)-epicatechin metabolites in humans: assessment using de novo chemically synthesized authentic standards
Accumulating data suggest that diets rich in flavanols and procyanidins are beneficial for human health. In this context, there has been a great interest in elucidating the systemic levels and metabolic profiles at which these compounds occur in humans. While recent progress has been made, there still exist considerable differences and various disagreements with regard to the mammalian metabolites of these compounds, which in turn is largely a consequence of the lack of availability of authentic standards that would allow for the directed development and validation of expedient analytical methodologies. In the present study, we developed a method for the analysis of structurally-related flavanol metabolites using a wide range of authentic standards. Applying this method in the context of a human dietary intervention study using comprehensively characterized and standardized flavanol- and procyanidin-containing cocoa, we were able to identify the structurally-related (−)-epicatechin metabolites (SREM) postprandially extant in the systemic circulation of humans. Our results demonstrate that (−)-epicatechin-3′-β-D-glucuronide, (−)-epicatechin-3′-sulfate, and a 3′-O-methyl(−)-epicatechin-5/7-sulfate are the predominant SREM in humans, and further confirm the relevance of the stereochemical configuration in the context of flavanol metabolism. In addition, we also identified plausible causes for the previously reported discrepancies regarding flavanol metabolism, consisting to a significant extent of inter-laboratory differences in sample preparation (enzymatic treatment and sample conditioning for HPLC analysis) and detection systems. Thus, these findings may also aid in the establishment of consensus on this topic
On Buchsbaum bundles on quadric hypersurfaces
Let be an indecomposable rank two vector bundle on the projective space
\PP^n, n \ge 3, over an algebraically closed field of characteristic zero. It
is well known that is arithmetically Buchsbaum if and only if and
is a null-correlation bundle. In the present paper we establish an analogous
result for rank two indecomposable arithmetically Buchsbaum vector bundles on
the smooth quadric hypersurface Q_n\subset\PP^{n+1}, . We give in
fact a full classification and prove that must be at most 5. As to
-Buchsbaum rank two vector bundles on , , we prove two
boundedness results.Comment: 22 pages, no figur
Weak localization and dimensional crossover in carbon nanotube systems
We investigate the effects of magnetic and electric fields on electron wavefunction
interactions in single walled carbon nanotube bundles. The magnetoresistance measurements
performed at 4.2Â K and the dependence of the data upon the electric field reveal good
agreement with weak localization theory. An electrical field conditioned characteristic
length is associated to ohmic-non ohmic transition, observed below 85Â K, in current
voltage characteristics. This length results equal to the average bundles diameter just at
T ≅ 85 K, indicating that 2D-3D crossover is responsible for the
observed conductance transition
Cross-cultural adaptation and validation of the voice handicap index into Italian
Objectives. To evaluate the internal consistency, reliability, and clinical validity of the Italian version of the Voice Handicap Index (VHI).
Study Design. Cross-sectional survey study was carried out.
Methods. One hundred and seventy-five patients with voice disorders, divided in four groups according to the etiology of the disease (neurogenic, structural, functional, and inflammatory), and 84 asymptomatic subjects were included in the study. Internal consistency was analyzed through Cronbach alpha coefficient. For the VHI test-retest reliability analysis, the Italian VHI was filled twice by 56 patients and 56 control subjects. The test-retest reliability was assessed through the Pearson correlation test. For the clinical validity assessment, the scores obtained in the pathological group were compared with those found in asymptomatic individuals through the Kruskal-Wallis test. Also, the correlation between VHI and the grade of voice disorder was assessed. Finally, the effect of age and gender on overall VHI and its three subscales was analyzed.
Results. Optimal internal consistency was found (alpha = 0.93); the test-retest reliability in both groups was high (r > 0.86). Nonparametric Kruskal-Wallis analysis of variance for the overall VHI score and its three domains revealed a significant main effect for group (P = 0.000). The control group scored significantly lower than the four groups of voice-disordered patients. The overall VHI score positively correlated with the grade of voice disorder (r = 0.43). In the voice-disorder group, age and gender were not correlated to the overall VHI score and to their three domains.
Conclusion. The Italian VHI is highly reproducible, and exhibits excellent clinical validity
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