698 research outputs found
Renormalization of the Coulomb blockade gap due to extended tunneling in nanoscopic junctions
In this work we discuss the combined effects of finite-range
electron-electron interaction and finite-range tunneling on the transport
properties of ultrasmall tunnel junctions. We show that the Coulomb blockade
phenomenon is deeply influenced by the interplay between the geometry and the
screening properties of the contacts. In particular if the interaction range is
smaller than the size of the tunneling region a "weakly correlated" regime
emerges in which the Coulomb blockade gap \D is significantly reduced. In
this regime \D is not simply given by the conventional charging energy of the
junction, since it is strongly renormalized by the energy that electrons need
to tunnel over the extended contact.Comment: 7 pages, 5 figures. To appear in Phys. Rev.
Time-dependent quantum transport with superconducting leads: a discrete basis Kohn-Sham formulation and propagation scheme
In this work we put forward an exact one-particle framework to study
nano-scale Josephson junctions out of equilibrium and propose a propagation
scheme to calculate the time-dependent current in response to an external
applied bias. Using a discrete basis set and Peierls phases for the
electromagnetic field we prove that the current and pairing densities in a
superconducting system of interacting electrons can be reproduced in a
non-interacting Kohn-Sham (KS) system under the influence of different Peierls
phases {\em and} of a pairing field. An extended Keldysh formalism for the
non-equilibrium Nambu-Green's function (NEGF) is then introduced to calculate
the short- and long-time response of the KS system. The equivalence between the
NEGF approach and a combination of the static and time-dependent
Bogoliubov-deGennes (BdG) equations is shown. For systems consisting of a
finite region coupled to superconducting semi-infinite leads we
numerically solve the static BdG equations with a generalized wave-guide
approach and their time-dependent version with an embedded Crank-Nicholson
scheme. To demonstrate the feasibility of the propagation scheme we study two
paradigmatic models, the single-level quantum dot and a tight-binding chain,
under dc, ac and pulse biases. We provide a time-dependent picture of single
and multiple Andreev reflections, show that Andreev bound states can be
exploited to generate a zero-bias ac current of tunable frequency, and find a
long-living resonant effect induced by microwave irradiation of appropriate
frequency.Comment: 20 pages, 9 figures, published versio
Charge separation in donor-C60 complexes with real-time Green's functions: The importance of nonlocal correlations
We use the Nonequilibrium Green's Function (NEGF) method to perform real-time
simulations of the ultrafast electron dynamics of photoexcited donor-C60
complexes modeled by a Pariser-Parr-Pople Hamiltonian. The NEGF results are
compared to mean-field Hartree-Fock (HF) calculations to disentangle the role
of correlations. Initial benchmarking against numerically highly accurate
time-dependent Density Matrix Renormalization Group calculations verifies the
accuracy of NEGF. We then find that charge-transfer (CT) excitons partially
decay into charge separated (CS) states if dynamical non-local correlation
corrections are included. This CS process occurs in ~10 fs after
photoexcitation. In contrast, the probability of exciton recombination is
almost 100% in HF simulations. These results are largely unaffected by nuclear
vibrations; the latter become however essential whenever level misalignment
hinders the CT process. The robust nature of our findings indicate that
ultrafast CS driven by correlation-induced decoherence may occur in many
organic nanoscale systems, but it will only be correctly predicted by
theoretical treatments that include time-nonlocal correlations.Comment: 9 pages, 6 figures + supplemental information (4 pages)
MINT, the molecular interaction database: 2012 update
The Molecular INTeraction Database (MINT, http://mint.bio.uniroma2.it/mint/) is a public repository for protein-protein interactions (PPI) reported in peer-reviewed journals. The database grows steadily over the years and at September 2011 contains approximately 235,000 binary interactions captured from over 4750 publications. The web interface allows the users to search, visualize and download interactions data. MINT is one of the members of the International Molecular Exchange consortium (IMEx) and adopts the Molecular Interaction Ontology of the Proteomics Standard Initiative (PSI-MI) standards for curation and data exchange. MINT data are freely accessible and downloadable at http://mint.bio.uniroma2.it/mint/download.do. We report here the growth of the database, the major changes in curation policy and a new algorithm to assign a confidence to each interaction
Drop test simulation and validation of a full composite fuselage section of a regional aircraft
Abstract In the aircraft industry, the use of fiber reinforced materials for primary structural components over metallic parts has increased up to more than 50% in the recent years, because of their high strength and high modulus to weight ratios, high fatigue and corrosion resistance. Currently, the need of lowering weight and fuel consumption is pushing the world's largest aircraft manufacturers in the design and building of structures entirely made of composites. Fuselage structure plays an important role in absorbing the kinetic energy during a crash. Through the deformation, crushing and damage of fuselage sub-floor structure, a survivable space inside the cabin area should be preserved during and after a crash impact in order to minimize the risk of passengers' injuries. In this work, a Finite Element (FE) model of a full-scale 95% composites made fuselage section of a regional aircraft under vertical drop test is presented. The experiment, conducted by the Italian Aerospace Research Centre (CIRA) with an actual impact velocity of 9.14 m/s in according to the FAR/CS 25, has been numerically simulated. Two ATDs (Anthropomorphic Test Dummies), both 50th percentile, seats and belts have been modelled to reproduce the experimental setup. The results of the simulation, performed by using LS-DYNA® explicit FE code, have been validated by correlation with the experimental ones. Such comparisons highlight that a good agreement has been achieved. The presented FE model allows verifying the structural behavior under a dynamic load condition and also estimating the passive safety capabilities of the designed structure. Since the experiment is expensive and non-repeatable, a FE model can be used for Certification by Analysis purposes since, if established, it is able to virtually demonstrate the compliance to the airworthiness rules
Many-body current formula and current conservation for non-equilibrium fully interacting nanojunctions
We consider the electron transport properties through fully interacting
nanoscale junctions beyond the linear-response regime. We calculate the current
flowing through an interacting region connected to two interacting leads, with
interaction crossing at the left and right contacts, by using a non-equilibrium
Green's functions (NEGF) technique. The total current at one interface (the
left one for example) is made of several terms which can be regrouped into two
sets. The first set corresponds to a very generalised Landauer-like current
formula with physical quantities defined only in the interacting central region
and with renormalised lead self-energies. The second set characterises
inelastic scattering events occurring in the left lead. We show how this term
can be negligible or even vanish due to the pseudo-equilibrium statistical
properties of the lead in the thermodynamic limit. The expressions for the
different Green's functions needed for practical calculations of the current
are also provided. We determine the constraints imposed by the physical
condition of current conservation. The corresponding equation imposed on the
different self-energy quantities arising from the current conservation is
derived. We discuss in detail its physical interpretation and its relation with
previously derived expressions. Finally several important key features are
discussed in relation to the implementation of our formalism for calculations
of quantum transport in realistic systems
W=0 pairing in Hubbard and related models of low-dimensional superconductors
Lattice Hamiltonians with on-site interaction have W=0 solutions, that
is, many-body {\em singlet} eigenstates without double occupation. In
particular, W=0 pairs give a clue to understand the pairing force in repulsive
Hubbard models. These eigenstates are found in systems with high enough
symmetry, like the square, hexagonal or triangular lattices. By a general
theorem, we propose a systematic way to construct all the W=0 pairs of a given
Hamiltonian. We also introduce a canonical transformation to calculate the
effective interaction between the particles of such pairs. In geometries
appropriate for the CuO planes of cuprate superconductors, armchair
Carbon nanotubes or Cobalt Oxides planes, the dressed pair becomes a bound
state in a physically relevant range of parameters. We also show that W=0 pairs
quantize the magnetic flux like superconducting pairs do. The pairing mechanism
breaks down in the presence of strong distortions. The W=0 pairs are also the
building blocks for the antiferromagnetic ground state of the half-filled
Hubbard model at weak coupling. Our analytical results for the
Hubbard square lattice, compared to available numerical data, demonstrate that
the method, besides providing intuitive grasp on pairing, also has quantitative
predictive power. We also consider including phonon effects in this scenario.
Preliminary calculations with small clusters indicate that vector phonons
hinder pairing while half-breathing modes are synergic with the W=0 pairing
mechanism both at weak coupling and in the polaronic regime.Comment: 42 pages, Topical Review to appear in Journal of Physics C: Condensed
Matte
Patient and Family Involvement in Serious Incident Investigations From the Perspectives of Key Stakeholders: A Review of the Qualitative Evidence
Objectives
Investigations of healthcare harm often overlook the valuable insights of patients and families. Our review aimed to explore the perspectives of key stakeholders when patients and families were involved in serious incident investigations.
Methods
The authors searched three databases (Medline, PsycInfo, and CINAHL) and Connected Papers software for qualitative studies in which patients and families were involved in serious incident investigations until no new articles were found.
Results
Twenty-seven papers were eligible. The perspectives of patients and families, healthcare professionals, nonclinical staff, and legal staff were sought across acute, mental health and maternity settings. Most patients and families valued being involved; however, it was important that investigations were flexible and sensitive to both clinical and emotional aspects of care to avoid compounding harm. This included the following: early active listening with empathy for trauma, sincere and timely apology, fostering trust and transparency, making realistic timelines clear, and establishing effective nonadversarial communication. Most staff perceived that patient and family involvement could improve investigation quality, promote an open culture, and help ensure future safety. However, it was made difficult when multidisciplinary input was absent, workload and staff turnover were high, training and support needs were unmet, and fears surrounded litigation. Potential solutions included enhancing the clarity of roles and responsibilities, adequately training staff, and providing long and short-term support to stakeholders.
Conclusions
Our review provides insights to ensure patient and family involvement in serious incident investigations considers both clinical and emotional aspects of care, is meaningful for all key stakeholders, and avoids compounding harm. However, significant gaps in the literature remain
Right ventricular function in AL amyloidosis: characteristics and prognostic implication
AIM: The importance of right ventricle (RV) dysfunction in AL amyloidosis has been underestimated. This study was designed to comprehensively evaluate RV function and its prognostic role in patients with AL amyloidosis with and without echocardiographic evidence of cardiac involvement. METHOD AND RESULTS: Fifty-two biopsy-proven AL amyloidosis patients underwent a thorough echocardiographic evaluation. Twenty-seven patients (CA) met the international echocardiographic criteria for cardiac involvement [left ventricular (LV) wall thickness >/= 12 mm] and 25 patients had no cardiac amyloidosis features (NCA). Patients were compared with a sex- age-matched control group. Patients and controls underwent traditional, tissue Doppler (TDI), speckle-tracking left and RV echocardiographic evaluation. No difference was observed between groups in RV diastolic diameter, whereas CA patients showed increased RV free wall thickness (P< 0.0001). Compared with controls and NCA patients, traditional echocardiography, TDI, and speckle-tracking evaluation detected significantly (P< 0.0001) depressed RV longitudinal systolic function in CA patients. No difference was observed between groups at Doppler diastolic evaluation, whereas at tricuspidal annulus TDI analysis, CA subject showed significantly lower E' and A' values with increased E/E' ratio (P< 0.0001). Over a 19 months median follow-up period, 18 patients died. Cox multivariate analysis showed that N-terminal pro-Brain natriuretic peptide and RV longitudinal strain were the strongest death predictor. CONCLUSION: Our data show that in patients with AL amyloidosis, RV involvement develops later than LV amyloid deposition but when it occurs, prognosis dramatically worsens. Moreover RV longitudinal strain was the only echocardiographic predictor of prognosis. We suggest that RV function analysis should be performed routinely as a part of echocardiographic evaluation in these patients
Identification, isolation and in vitro expansion of human and nonhuman primate T stem cell memory cell
The T cell compartment is phenotypically and functionally heterogeneous; subsets of naive and memory cells have different functional properties, and also differ with respect to homeostatic potential and the ability to persist in vivo. Human stem cell memory T (TSCM) cells, which possess superior immune reconstitution and antitumor response capabilities, can be identified by polychromatic flow cytometry on the basis of the simultaneous expression of several naive markers together with the memory marker CD95. We describe here a protocol based on the minimum set of markers required for optimal identification of human and nonhuman primate (NHP) TSCM cells with commonly available flow cytometers. By using flow sorters, TSCM cells can thereby be isolated efficiently at high yield and purity. With the use of the 5.5-h isolation procedure, depending on the number of cells needed, the sorting procedure can last for 2-15 h. We also indicate multiple strategies for their efficient expansion in vitro at consistent numbers for functional characterization or adoptive transfer experiments
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