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Search Results: 1 - 10 of 2487 matches for " Deborah Governale "
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Abdominal Compartment Syndrome: Risk Factors, Diagnosis, and Current Therapy
Gina M. Luckianow,Matthew Ellis,Deborah Governale,Lewis J. Kaplan
Critical Care Research and Practice , 2012, DOI: 10.1155/2012/908169
Abstract: Abdominal compartment syndrome’s manifestations are difficult to definitively detect on physical examination alone. Therefore, objective criteria have been articulated that aid the bedside clinician in detecting intra-abdominal hypertension as well as the abdominal compartment syndrome to initiate prompt and potentially life-saving intervention. At-risk patient populations should be routinely monitored and tiered interventions should be undertaken as a team approach to management. 1. Introduction The concepts of intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are pervasive, but the objective criteria by which to diagnose each of these entities are often misunderstood [1]. IAH and ACS occur in both medical and surgical Intensive Care Units (ICU), the general ward, and may even occur the Emergency Department. Successful outcomes rely on early and accurate diagnosis combined with timely therapy [2–4]. Herein we describe these conditions, identify the at-risk patient populations, review diagnostic techniques as well as tiered medical management strategies, acute surgical therapy and long-term interventions to improve patient safety, optimize survival, and decrease morbidity. 2. Epidemiology Changes in fluid resuscitation paradigms, such as Early Goal Directed Therapy (EGDT) in the medical realm, and “damage control resuscitation” in the trauma realm, have increased patient survival [5, 6]. As a result of vigorous fluid resuscitation, however, each has also been associated with an unanticipated and undesired consequence—intra-abdominal hypertension and abdominal compartment syndrome (ACS). Given the detrimental effects of ACS (organ failure and death), heightened awareness surrounding the recognition of IAH and its progression to ACS, as well as the reporting of ACS, is paramount for optimal patient care. IAH is estimated to occur in 32.1% of ICU patients, and ACS has been reported in up to 4.2% of patients requiring critical care [7]. In order to identify each of these, one must be familiar with their definitions. 3. Definitions According to the World Society of the Abdominal Compartment Syndrome (WSACS), ACS may be defined as sustained intra-abdominal pressure (IAP) of >20?mm?Hg with the presence of an attributable organ failure [8]. While the WSACS has defined the parameters of ACS, it is important to delineate ACS from its predecessor, intra-abdominal hypertension. Absent from any disease processes, the average intra-abdominal pressure ranges from 5 to 7?mm?Hg with a normal upper limit of 12?mm?Hg [8]. Thus, a sustained IAP
Quantum dots with Rashba spin-orbit coupling
M. Governale
Physics , 2002, DOI: 10.1103/PhysRevLett.89.206802
Abstract: We present results on the effects of spin-orbit coupling on the electronic structure of few-electron interacting quantum dots. The ground-state properties as a function of the number of electrons in the dot $N$ are calculated by means of spin density functional theory. We find a suppression of Hund's rule due to the competition of the Rashba effect and exchange interaction. Introducing an in-plane Zeeman field leads to a paramagnetic behavior of the dot in a closed shell configuration, and to spin texture in space.
Spin Accumulation in Quantum Wires with Strong Rashba Spin-Orbit Coupling
M. Governale,U. Zuelicke
Physics , 2002, DOI: 10.1103/PhysRevB.66.073311
Abstract: We present analytical and numerical results for the effect of Rashba spin-orbit coupling on band structure, transport, and interaction effects in quantum wires when the spin precession length is comparable to the wire width. In contrast to the weak-coupling case, no common spin-quantization axis can be defined for eigenstates within a single-electron band. The situation with only the lowest spin-split subbands occupied is particularly interesting because electrons close to Fermi points of the same chirality can have approximately parallel spins. We discuss consequences for spin-dependent transport and effective Tomonaga-Luttinger descriptions of interactions in the quantum wire.
Probing Spin-Charge Separation in Tunnel-Coupled Parallel Quantum Wires
U. Zuelicke,M. Governale
Physics , 2001, DOI: 10.1103/PhysRevB.65.205304
Abstract: Interactions in one-dimensional (1D) electron systems are expected to cause a dynamical separation of electronic spin and charge degrees of freedom. A promising system for experimental observation of this non-Fermi-liquid effect consists of two quantum wires coupled via tunneling through an extended uniform barrier. Here we consider the minimal model of an interacting 1D electron system exhibiting spin-charge separation and calculate the differential tunneling conductance as well as the density-density response function. Both quantities exhibit distinct strong features arising from spin-charge separation. Our analysis of these features within the minimal model neglects interactions between electrons of opposite chirality and applies therefore directly to chiral 1D electron systems realized, e.g., at the edge of integer quantum-Hall systems. Physical insight gained from our results is useful for interpreting current experiment in quantum wires as our main conclusions still apply with nonchiral interactions present. In particular, we discuss the effect of charging due to applied voltages, and the possibility to observe spin-charge separation in a time-resolved experiment.
Gauge invariant grid discretization of Schr?dinger equation
M. Governale,C. Ungarelli
Physics , 1998, DOI: 10.1103/PhysRevB.58.7816
Abstract: Using the Wilson formulation of lattice gauge theories, a gauge invariant grid discretization of a one-particle Hamiltonian in the presence of an external electromagnetic field is proposed. This Hamiltonian is compared both with that obtained by a straightforward discretization of the continuous Hamiltonian by means of balanced difference methods, and with a tight-binding Hamiltonian. The proposed Hamiltonian and the balanced difference one are used to compute the energy spectrum of a charged particle in a two-dimensional parabolic potential in the presence of a perpendicular, constant magnetic field. With this example we point out how a "naive" discretization gives rise to an explicit breaking of the gauge invariance and to large errors in the computed eigenvalues and corresponding probability densities; in particular, the error on the eigenfunctions may lead to very poor estimates of the mean values of some relevant physical quantities on the corresponding states. On the contrary, the proposed discretized Hamiltonian allows a reliable computation of both the energy spectrum and the probability densities.
A magnetic barrier in confined two-dimensional electron gases: Nanomagnetometers and magnetic switches
Michele Governale,Daniel Boese
Physics , 2000, DOI: 10.1063/1.1325396
Abstract: We investigate the conductance properties of a hybrid ferromagnet-semiconductor structure consisting of a confined two-dimensional electron gas and a transverse ferromagnetic strip on top. Within the framework of the Landauer-B\"uttiker model, we develop an alternative way to consider magnetic fields. Our method describes devices ranging from a recently realized nanomagnetometer down to quasi one-dimensional quantum wires. We provide a rigorous way to relate the measured resistance to the actual magnetization of the strip. Regarding the quasi one-dimensional wires we propose a new device application, a tunable magnetic switch.
Rashba spin splitting in quantum wires
M. Governale,U. Zuelicke
Physics , 2004, DOI: 10.1016/j.ssc.2004.05.047
Abstract: This article presents an overview of results pertaining to electronic structure, transport properties, and interaction effects in ballistic quantum wires with Rashba spin splitting. Limits of weak and strong spin--orbit coupling are distinguished, and spin properties of the electronic states elucidated. The case of strong Rashba spin splitting where the spin--precession length is comparable to the wire width turns out to be particularly interesting. Hybridization of spin--split quantum--wire subbands leads to an unusual spin structure where the direction of motion for electrons can fix their spin state. This peculiar property has important ramifications for linear transport in the quantum wire, giving rise to spin accumulation without magnetic fields or ferromagnetic contacts. A description for interacting Rashba--split quantum wires is developed, which is based on a generalization of the Tomonaga--Luttinger model.
Static polarizability of two-dimensional hole gases
T. Kernreiter,M Governale,U. Zuelicke
Physics , 2010, DOI: 10.1088/1367-2630/12/9/093002
Abstract: We have calculated the density-density (Lindhard) response function of a homogeneous two-dimensional (2D) hole gas in the static (omega=0) limit. The bulk valence-band structure comprising heavy-hole (HH) and light-hole (LH) states is modeled using Luttinger's kdotp approach within the axial approximation. We elucidate how, in contrast to the case of conduction electrons, the Lindhard function of 2D holes exhibits unique features associated with (i) the confinement-induced HH-LH energy splitting and (ii) the HH-LH mixing arising from the charge carriers' in-plane motion. Implications for the dielectric response and related physical observables are discussed.
Momentum-Resolved Tunneling into Fractional Quantum Hall Edges
U. Zuelicke,E. Shimshoni,M. Governale
Physics , 2002, DOI: 10.1103/PhysRevB.65.241315
Abstract: Tunneling from a two-dimensional contact into quantum-Hall edges is considered theoretically for a case where the barrier is extended, uniform, and parallel to the edge. In contrast to previously realized tunneling geometries, details of the microscopic edge structure are exhibited directly in the voltage and magnetic-field dependence of the differential tunneling conductance. In particular, it is possible to measure the dispersion of the edge-magnetoplasmon mode, and the existence of additional, sometimes counterpropagating, edge-excitation branches could be detected.
Finite-frequency noise in a quantum dot with normal and superconducting leads
Stephanie Droste,Janine Splettstoesser,Michele Governale
Physics , 2014, DOI: 10.1103/PhysRevB.91.125401
Abstract: We consider a single-level quantum dot tunnel-coupled to one normal and one superconducting lead. We employ a diagrammatic real-time approach to calculate the finite-frequency current noise for subgap transport. The noise spectrum gives direct access to the internal dynamics of the dot. In particular the noise spectrum shows sharp dips at the frequency of the coherent oscillations of Cooper pairs between dot and superconductor. This feature is most pronounced when the superconducting correlation is maximal. Furthermore, in the quantum-noise regime, $\omega> k_\text{B}T,\mu_\text{N}$, the noise spectrum exhibits steps at frequencies equal to the Andreev addition energies. The height of these steps is related to the effective coupling strength of the excitations. The finite-frequency noise spectrum hence provides a full spectroscopy of the system.
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