2,389 research outputs found
Current and noise correlations in a double dot Cooper pair beam splitter
We consider a double quantum dot coupled to two normal leads and one
superconducting lead, modeling the Cooper pair beam splitter studied in two
recent experiments. Starting from a microscopic Hamiltonian we derive a general
expression for the branching current and the noise crossed correlations in
terms of single and two-particle Green's function of the dot electrons. We then
study numerically how these quantities depend on the energy configuration of
the dots and the presence of direct tunneling between them, isolating the
various processes which come into play. In absence of direct tunneling, the
antisymmetric case (the two levels have opposite energies with respect to the
superconducting chemical potential) optimizes the Crossed Andreev Reflection
(CAR) process while the symmetric case (the two levels have the same energies)
favors the Elastic Cotunneling (EC) process. Switching on the direct tunneling
tends to suppress the CAR process, leading to negative noise crossed
correlations over the whole voltage range for large enough direct tunneling
Current correlations in the interacting Cooper-pair beam-splitter
We propose an approach allowing the computation of currents and their
correlations in interacting multiterminal mesoscopic systems involving quantum
dots coupled to normal and/or superconducting leads. The formalism relies on
the expression of branching currents and noise crossed correlations in terms of
one- and two-particle Green's functions for the dots electrons, which are then
evaluated self-consistently within a conserving approximation. We then apply
this to the Cooper-pair beam-splitter setup recently proposed [L. Hofstetter et
al. Nature (London) 461 960 (2009); Phys. Rev. Lett. 107 136801 (2011); L. G.
Herrmann et al. Phys. Rev. Lett. 104 026801 (2010)], which we model as a double
quantum dot with weak interactions, connected to a superconducting lead and two
normal ones. Our method not only enables us to take into account a local
repulsive interaction on the dots, but also to study its competition with the
direct tunneling between dots. Our results suggest that even a weak Coulomb
repulsion tends to favor positive current cross correlations in the
antisymmetric regime (where the dots have opposite energies with respect to the
superconducting chemical potential)
Gamma-ray burst contributions to constraining the evolution of dark energy
We explore the gamma-ray bursts' (GRBs') contributions in constraining the
dark energy equation of state (EOS) at high () and at middle
redshifts () and estimate how many GRBs are needed to get
substantial constraints at high redshifts. We estimate the constraints with
mock GRBs and mock type Ia supernovae (SNe Ia) for comparisons. When
constraining the dark energy EOS in a certain redshift range, we allow the dark
energy EOS parameter to vary only in that redshift bin and fix EOS parameters
elsewhere to -1. We find that it is difficult to constrain the dark energy EOS
beyond the redshifts of SNe Ia with GRBs unless some new luminosity relations
for GRBs with smaller scatters are discovered. However, at middle redshifts,
GRBs have comparable contributions with SNe Ia in constraining the dark energy
EOS.Comment: 3 pages, 5 figures. Published in Astronomy and Astrophysics.
Corrected referenc
Off-diagonal long-range order, cycle probabilities, and condensate fraction in the ideal Bose gas
We discuss the relationship between the cycle probabilities in the
path-integral representation of the ideal Bose gas, off-diagonal long-range
order, and Bose--Einstein condensation. Starting from the Landsberg recursion
relation for the canonic partition function, we use elementary considerations
to show that in a box of size L^3 the sum of the cycle probabilities of length
k >> L^2 equals the off-diagonal long-range order parameter in the
thermodynamic limit. For arbitrary systems of ideal bosons, the integer
derivative of the cycle probabilities is related to the probability of
condensing k bosons. We use this relation to derive the precise form of the
\pi_k in the thermodynamic limit. We also determine the function \pi_k for
arbitrary systems. Furthermore we use the cycle probabilities to compute the
probability distribution of the maximum-length cycles both at T=0, where the
ideal Bose gas reduces to the study of random permutations, and at finite
temperature. We close with comments on the cycle probabilities in interacting
Bose gases.Comment: 6 pages, extensive rewriting, new section on maximum-length cycle
Growth and optical properties of GaN/AlN quantum wells
We demonstrate the growth of GaN/AlN quantum well structures by
plasma-assisted molecular-beam epitaxy by taking advantage of the surfactant
effect of Ga. The GaN/AlN quantum wells show photoluminescence emission with
photon energies in the range between 4.2 and 2.3 eV for well widths between 0.7
and 2.6 nm, respectively. An internal electric field strength of
MV/cm is deduced from the dependence of the emission energy on the well width.Comment: Submitted to AP
Josephson effect through an anisotropic magnetic molecule
We study the Josephson effect through a magnetic molecule with anisotropic
properties. Performing calculations in the tunneling regime, we show that the
exchange coupling between the electron spin on the molecule and the molecular
spin can trigger a transition from the state to the 0 state, and we study
how the spin anisotropy affects this transition. We show that the behavior of
the critical current as a function of an external magnetic field can give
access to valuable information about the spin anisotropy of the molecule
A comprehensive strategy to detect the fraudulent adulteration of herbs: The oregano approach
AbstractFraud in the global food supply chain is becoming increasingly common due to the huge profits associated with this type of criminal activity. Food commodities and ingredients that are expensive and are part of complex supply chains are particularly vulnerable. Both herbs and spices fit these criteria perfectly and yet strategies to detect fraudulent adulteration are still far from robust. An FT-IR screening method coupled to data analysis using chemometrics and a second method using LC-HRMS were developed, with the latter detecting commonly used adulterants by biomarker identification. The two tier testing strategy was applied to 78 samples obtained from a variety of retail and on-line sources. There was 100% agreement between the two tests that over 24% of all samples tested had some form of adulterants present. The innovative strategy devised could potentially be used for testing the global supply chains for fraud in many different forms of herbs
Interventional oncology at the time of COVID-19 pandemic: Problems and solutions.
The COVID-19 pandemic has deeply impacted the activity of interventional oncology in hospitals and cancer centers. In this review based on official recommendations of different international societies, but also on local solutions found in different expert large-volume centers, we discuss the changes that need to be done for the organization, safety, and patient management in interventional oncology. A literature review of potential solutions in a context of scarce anesthesiologic resources, limited staff and limited access to hospital beds are proposed and discussed based on the literature data
Design of a Polarised Positron Source Based on Laser Compton Scattering
We describe a scheme for producing polarised positrons at the ILC from
polarised X-rays created by Compton scattering of a few-GeV electron beam off a
CO2 or YAG laser. This scheme is very energy effective using high finesse laser
cavities in conjunction with an electron storage ring.Comment: Proposal submitted to the ILC workshop, Snowmass 2005. v2: note
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Gated cardiac CT in infants: What can we expect from deep learning image reconstruction algorithm?
ECG-gated cardiac CT is now widely used in infants with congenital heart disease (CHD). Deep Learning Image Reconstruction (DLIR) could improve image quality while minimizing the radiation dose.
To define the potential dose reduction using DLIR with an anthropomorphic phantom.
An anthropomorphic pediatric phantom was scanned with an ECG-gated cardiac CT at four dose levels. Images were reconstructed with an iterative and a deep-learning reconstruction algorithm (ASIR-V and DLIR). Detectability of high-contrast vessels were computed using a mathematical observer. Discrimination between two vessels was assessed by measuring the CT spatial resolution. The potential dose reduction while keeping a similar level of image quality was assessed.
DLIR-H enhances detectability by 2.4% and discrimination performances by 20.9% in comparison with ASIR-V 50. To maintain a similar level of detection, the dose could be reduced by 64% using high-strength DLIR in comparison with ASIR-V50.
DLIR offers the potential for a substantial dose reduction while preserving image quality compared to ASIR-V
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