464 research outputs found
Bremsstrahlung Spectrum in alpha Decay
Using our previous approach to electromagnetic emission during tunneling, an
explicit, essentially classical, formula describing the bremsstrahlung spectrum
in alpha decay is derived. The role of tunneling motion in photon emission is
discussed. The shape of the spectrum is a universal function of the ratio Eg/Eo
, where Eg is the photon energy and Eo is a characteristic energy depending
only on the nuclear charge and the energy of the alpha particle.Comment: 8 pages, 3 figure
Dynamical suppression of telegraph and 1/f noise due to quantum bistable fluctuator
We study dynamical decoupling of a qubit from non gaussian quantum noise due
to discrete sources, as bistable fluctuators and 1/f noise. We obtain analytic
and numerical results for generic operating point. For very large pulse
frequency, where dynamic decoupling compensates decoherence, we found universal
behavior. At intermediate frequencies noise can be compensated or enhanced,
depending on the nature of the fluctuators and on the operating point. Our
technique can be applied to a larger class of non-gaussian environments.Comment: Revtex 4, 5 pages, 3 figures. Title revised and some other minor
changed. Final version as published in PR
Qubits as devices to detect the third moment of current fluctuations
Under appropriate conditions controllable two-level systems can be used to
detect the third moment of current fluctuations. We derive a Master Equation
for a quantum system coupled to a bath valid to the third order in the coupling
between the system and the environment. In this approximation the reduced
dynamics of the quantum system depends on the frequency dependent third moment.
Specializing to the case of a controllable two-level system (a qubit) and in
the limit in which the splitting between the levels is much smaller than the
characteristic frequency of the third moment, it is possible to show that the
decay of the qubit has additional oscillations whose amplitude is directly
proportional to the value of the third moment. We discuss an experimental setup
where this effect can be seen.Comment: 10 pages, 7 figure
Tree-Ring-Reconstructed Summer Temperatures from Northwestern North America during the Last Nine Centuries*
Northwestern North America has one of the highest rates of recent temperature increase in the world, but the putative âdivergence problemâ in dendroclimatology potentially limits the ability of tree-ring proxy data at high latitudes to provide long-term context for current anthropogenic change. Here, summer temperatures are reconstructed from a Picea glauca maximum latewood density (MXD) chronology that shows a stable relationship to regional temperatures and spans most of the last millennium at the Firth River in northeastern Alaska. The warmest epoch in the last nine centuries is estimated to have occurred during the late twentieth century, with average temperatures over the last 30 yr of the reconstruction developed for this study [1973â2002 in the Common Era (CE)] approximately 1.3° ± 0.4°C warmer than the long-term preindustrial mean (1100â1850 CE), a change associated with rapid increases in greenhouse gases. Prior to the late twentieth century, multidecadal temperature fluctuations covary broadly with changes in natural radiative forcing. The findings presented here emphasize that tree-ring proxies can provide reliable indicators of temperature variability even in a rapidly warming climate
Detection of antibacterial activity of essential oil components by TLC-bioautography using luminescent bacteria
The aim of the present study was the chemical characterization of some medically relevant essential oils (tea tree, clove, cinnamon bark, thyme and eucalyptus) and the investigation of antibacterial effect of the components of these oils by use of a direct bioautographic method. Thin layer chromatography (TLC) was combined with biological detection in this process. The chemical composition of the oils was determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Eucalyptol (84.2%) was the main component of the essential oil of eucalyptus, eugenol (83.7%) of clove oil, and trans-cinnamic aldehyde (73.2%), thymol (49.9%) and terpinen-4-ol (45.8%) of cinnamon bark, thyme and tea tree oils, respectively. Antibacterial activity of the separated components of these oils, as well as their pure main components (eucalyptol, eugenol, trans-cinnamic aldehyde and thymol) was observed against the Gram-negative luminescence tagged plant pathogenic bacterium Pseudomonas syringae pv. maculicola (Psmlux) and the Gram-negative, naturally luminescent marine bacterium Vibrio fischeri. On the whole, the antibacterial activity of the essential oils could be related to their main components, but the minor constituents may be involved in this process. Trans-cinnamic aldehyde and eugenol were the most active compounds in TLC-bioautography.
The sensitivity of TLC-bioautographic method can be improved with using luminescent test bacteria. This method is more cost-effective and provides more reliable results in comparison with conventional microbiological methods, e.g. disc-diffusion technique
Bremsstrahlung in Decay
A quantum mechanical analysis of the bremsstrahlung in decay of
Po is performed in close reference to a semiclassical theory. We
clarify the contribution from the tunneling, mixed, outside barrier regions and
from the wall of the inner potential well to the final spectral distribution,
and discuss their interplay. We also comment on the validity of semiclassical
calculations, and the possibility to eliminate the ambiguity in the nuclear
potential between the alpha particle and daughter nucleus using the
bremsstrahlung spectrum.Comment: 6 pages, 3 figures, submitted to PR
Investigation of the impact of neutron irradiation on SiC power MOSFETs lifetime by reliability tests
High temperature reverse-bias (HTRB), High temperature gate-bias (HTGB) tests and electrical DC characterization were performed on planar-SiC power MOSFETs which survived to accelerated neutron irradiation tests carried out at ChipIr-ISIS (Didcot, UK) facility, with terrestrial neutrons. The neutron test campaigns on the SiC power MOSFETs (manufactered by ST) were con-ducted on the same wafer lot devices by STMicroelectronics and Airbus, with different neutron tester systems. HTGB and HTRB tests, which characterise gate-oxide integrity and junction robustness, show no difference between the non irradiated devices and those which survived to the neutron irradiation tests, with neutron fluence up to 2 Ă 1011 (n/cm2). Electrical characterization performed pre and post-irradiation on different part number of power devices (Si, SiC MOSFETs and IGBTs) which survived to neutron irradiation tests does not show alteration of the data-sheet electrical parameters due to neutron interaction with the device
Three-body correlations in Borromean halo nuclei
Three-body correlations in the dissociation of two-neutron halo nuclei are
explored using a technique based on intensity interferometry and Dalitz plots.
This provides for the combined treatment of both the n-n and core-n
interactions in the exit channel. As an example, the breakup of 14Be into
12Be+n+n by Pb and C targets has been analysed and the halo n-n separation
extracted. A finite delay between the emission of the neutrons in the reaction
on the C target was observed and is attributed to 13Be resonances populated in
sequential breakup.Comment: 5 pages, 4 figures, submitted to PR
Use of high hydrostatic pressure (HHP) to obtain an ingredient rich in bioactive compounds from cv. Tempranillo red pomace
With the aim to obtain an ingredient rich in bioactive compounds to be used in meat products, a red grape pomace (RGP) cv. Tempranillo, was subjected to the application of different hydrostatic high pressure (HHP) treatments: i) 600 MPa/1s; ii) 600 MPa/300s and two others treatments of 2 cycles of HHP, iii) 2 cycles of 600MPa/1s and iv) 1 first cycle of 400 MPa/1s and second cycle 600 MPa/1s. The microbiological population and polyphenoloxidase activity (PPO) of treated RGP was studied immediately after the treatments and at 270 days after the treatments at temperatures of 4 and 20 ÂșC respect a control sample untreated. The treatments significantly reduced the microbial population; the effect of HHP3 and HHP4 (two cycles) did not differ from those of HHP1 and HHP2 (1 cycle). Phenolic compounds (anthocyanins, flavanols, flavonols, phenolic acids and stilbenes) were extracted from GRP, identified and quantified by HPLC. The values of all these phenolic families were maintained immediately after HHP with exception of a decrease of anthocyanins in HHP3. However, the HHP treatments did not affect the polyphenoloxidase enzyme, since the phenolic compounds were notably reduced during storage although phenolic compounds were better well-preserved at refrigeration than at room temperature
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