On apparent breaking the second law of thermodynamics in quantum transport studies

We consider a model for stationary electronic transport through a one-dimensional chain of two leads attached to a perturbed central region (quantum dot) in the regime where the theory proposed recently by Capek for a similar model of phonon transport predicts the striking phenomenon of a permanent current between the leads. This result based on a rigorous but asymptotic Davies theory is at variance with the zero current yielded by direct transport calculations which can be carried out in the present model. We find the permanent current to be within the error of the asymptotic expansion for finite couplings, and identify cancelling terms of the same order.Comment: 5 pages, 3 figure

Inelastic quantum transport in superlattices: success and failure of the Boltzmann equation

Electrical transport in semiconductor superlattices is studied within a fully self-consistent quantum transport model based on nonequilibrium Green functions, including phonon and impurity scattering. We compute both the drift velocity-field relation and the momentum distribution function covering the whole field range from linear response to negative differential conductivity. The quantum results are compared with the respective results obtained from a Monte Carlo solution of the Boltzmann equation. Our analysis thus sets the limits of validity for the semiclassical theory in a nonlinear transport situation in the presence of inelastic scattering.Comment: final version with minor changes, to appear in Physical Review Letters, sceduled tentatively for July, 26 (1999

Coherent Transport through an interacting double quantum dot: Beyond sequential tunneling

Various causes for negative differential conductance in transport through an interacting double quantum dot are investigated. Particular focus is given to the interplay between the renormalization of the energy levels due to the coupling to the leads and the decoherence of the states. The calculations are performed within a basis of many-particle eigenstates and we consider the dynamics given by the von Neumann-equation taking into account also processes beyond sequential tunneling. A systematic comparison between the levels of approximation and also with different formalisms is performed. It is found that the current is qualitatively well described by sequential processes as long as the temperature is larger than the level broadening induced by the contacts.Comment: 11 pages, 5 figures included in tex

Theory and measurements of harmonic generation in semiconductor superlattices with applications in the 100 GHz to 1 THz range

This manuscript describes harmonic generation in semiconductor superlattices, starting from a Nonequilibrium Green's functions input to relaxation rate-type analytical approximations for the Boltzmann Equation in which imperfections in the structure lead to asymmetric current flow and scattering processes under forward and reverse bias. The resulting current-voltage curves and the predicted consequences on harmonic generation, notably the development of even harmonics are in good agreement with experiments. Significant output for frequencies close to 1 THz (7th harmonic) at room temperature, after excitation by a 141 GHz input signal, demonstrate the potential of superlattice devices for GHz-THz applications

Theory of traveling filaments in bistable semiconductor structures

We present a generic nonlinear model for current filamentation in semiconductor structures with S-shaped current-voltage characteristics. The model accounts for Joule self-heating of a current density filament. It is shown that the self-heating leads to a bifurcation from static to traveling filament. Filaments start to travel when increase of the lattice temperature has negative impact on the cathode-anode transport. Since the impact ionization rate decreases with temperature, this occurs for a wide class of semiconductor systems whose bistability is due to the avalanche impact ionization. We develop an analytical theory of traveling filaments which reveals the mechanism of filament motion, find the condition for bifurcation to traveling filament, and determine the filament velocity.Comment: 13 pages, 5 figure

Unhiding the audiovisual past at Columbia University Libraries

As part of a larger hidden collections initiative, Columbia University Libraries initiated plans in 2018 to digitize their unique audiovisual holdings over seven years. In order to meet an ambitious target within a limited timeframe, staff across divisions and departments had to collaboratively develop shared workflows and efficiencies to maximize output while ensuring a high level of quality. Due to the unique challenges of working with audio and video collections, this collaborative effort was truly unprecedented in the history of Columbia Libraries. This project represented an excellent opportunity to test new functionalities of our locally developed digital asset management system Hyacinth and find robust methods to improve digital curation and preservation using tools like Archivematica digital preservation system. The scope of the project required that we develop efficiencies in our cataloging and metadata enhancement workflows including task automation in OpenRefine, sync metadata between systems including our Voyager ILS and Hyacinth, and plan for new initiatives such as the implementation of a rights management module and integration of crosswalks to ArchivesSpace. One additional outcome of the project’s first year is a deeper analysis of project statistics and workflows using project management methods to inform the future development and planning of the project for years 2-7. This presentation will examine the development of these shared workflows across curatorial, preservation, metadata, and digital technology units, challenges overcome, and lessons learned

Future Proof: Preserving and Providing Access to Columbia's Audio Visual Collections

As part of a larger hidden collections initiative, in 2018, Columbia University Libraries embarked on a seven year project to digitize their unique audiovisual holdings. In order to meet an ambitious target within a limited timeframe, staff across divisions and departments had to collaboratively develop shared workflows and efficiencies to maximize output while ensuring a high level of quality. Due to the unique challenges of working with analog film/video collections, this collaborative effort was truly unprecedented in the history of Columbia Libraries. This project represented an excellent opportunity to test new functionalities of our locally developed digital asset management system Hyacinth and find robust methods to improve digital curation and preservation using tools like Archivematica digital preservation system. The scope of the project required that we develop efficiencies in our cataloging and metadata enhancement workflows including task automation in OpenRefine, sync both published and unpublished metadata between systems including our Voyager ILS and Hyacinth, and plan for an exponential increase in how digital media collections would be used by both patrons and staff. This presentation will examine the development, implementation, and lessons learned of these cross-departmental workflows as they pertain to the complex landscape of large-scale digital media preservation and access within research libraries

Delirium e demência no idoso: existem fatores de risco comuns?

Delirium is a neurobehavioral syndrome caused by the transient disruption of cerebral homeostasis, which is invariably subsequent to systemic or central nervous system insults. In general medical settings, the occurrence of delirium is also associated with a higher incidence of post-operative complications, longer hospital stays, and poor functional recovery. Ageing and cognitive decline are known risk factors for the occurrence of delirium. In elderly patients, delirium has been shown to be associated with pre-existing dementia. Conversely, non-demented elderly subjects who develop a new delirium episode display an increased incidence of dementia in the long-term outcome. Prospective case-control studies have demonstrated a significant association between the previous diagnosis of delirium and the development of dementia. The association between delirium and dementia may be even higher among the eldest elderly. After reviewing the relevant literature on the association between delirium and dementia, we hypothesize that the occurrence of delirium in non-demented elderly individuals is predictive of a worse cognitive outcome, and increased risk of dementia, in the long-term follow-up. We further discuss the biological nature of this association in the light of the cholinergic deficit observed in the pathophysiology of both delirium and Alzheimer's disease.Delirium é uma síndrome neurocomportamental decorrente da quebra transitória da homeostase cerebral. Deve-se, invariavelmente, a perturbações sistêmicas ou do sistema nervoso central. No contexto médico geral, a ocorrência de delirium está associada à maior incidência de complicações clínico-cirúrgicas, maior tempo de permanência hospitalar e pior recuperação funcional. O envelhecimento e o comprometimento cognitivo são fatores de risco conhecidos para o delirium. Em pacientes idosos, a ocorrência aumenta o reconhecimento de quadros demenciais preexistentes. Em contrapartida, indivíduos idosos não-demenciados que desenvolvem um episódio de delirium durante uma dada internação hospitalar têm incidência aumentada de demência na evolução em longo prazo. Estudos prospectivos e controlados demonstraram uma associação significativa entre o diagnóstico prévio de delirium e o ulterior desenvolvimento de síndromes demenciais. Essa associação parece ser ainda maior em indivíduos muito idosos. O presente estudo de revisão aborda criticamente a natureza da associação entre delirium e demência. Hipotetiza-se que a sua ocorrência em indivíduos idosos cognitivamente preservados é fator preditivo de deterioração cognitiva, e de risco aumentado para o desenvolvimento de demência, no seguimento de longo termo. As bases neurobiológicas da associação entre delirium e demência são discutidas à luz da hipótese colinérgica da doença de Alzheimer, uma vez que o comprometimento da neurotransmissão colinérgica é denominador comum a essas duas perturbações neuropsíquicas

Delirium: uma perspectiva histórica

Delirium remained a stable psychiatric category until the early 19th century when it underwent etiological and phenomenological redefinition, precipitating the transformation of the functional insanities into psychoses. Confusion, introduced by French workers during the second half of the century, referred to a syndrome wider than (but including) delirium. It emphasized chaotic thinking and cognitive failure. The notion of clouding of consciousness (and temporo-spatial disorientation) established a common denominator for the two concepts, while Chaslin and Bonhoeffer redefined confusion and delirium as the stereotyped manifestations of acute brain failure.O delirium corresponde a uma das primeiras doenças mentais descritas na literatura médica, há mais de 2.500 anos. Nas classificações psiquiátricas, permaneceu como categoria nosológica independente até o final do século XIX, quando foi redefinida com base nos seus aspectos fenomenológicos e etiológicos, precipitando a reclassificação das insanidades funcionais em psicoses. os estados confusionais passaram a se referir a uma síndrome mais ampla que incluía o delirium, enfatizando a desorganização dos processos cognitivos e do pensamento, e tendo no turvamento da consciência e na desorientação temporoespacial a condição de base. Com o objetivo de descrever a evolução histórica do conceito de delirium, foram realizados levantamentos da literatura médica através do sistema Medline, além da pesquisa em publicações literárias específicas sobre os temas história da medicina e história da psiquiatria. Partiu-se de algumas observações dogmáticas praticadas na Antigüidade e Idade Média, para atingir as definições e práticas atuais, oferecendo uma análise crítica dos critérios diagnósticos vigentes (DSM-III, DSM-IIIR, DSM-IV e CID-10). Não obstante a evolução conceitual, o delirium continua sendo mal compreendido, do ponto de vista fisiopatológico e são poucas as opções terapêuticas. o diagnóstico de delirium é ato eminentemente clínico: baseia-se na observação cautelosa das manifestações psíquicas e comportamentais dos pacientes acometidos, além da análise dos fatores predisponentes e precipitantes. É freqüente o seu subdiagnóstico em contextos clínicos e cirúrgicos. o diagnóstico do delirium é estabelecido em apenas 30% a 50% dos pacientes, sendo a omissão diagnóstica menos freqüente em serviços que contam com a interconsulta psiquiátrica. o delirium é uma das complicações mais comuns entre pacientes idosos hospitalizados e está associado a maior morbimortalidade. Isso sustenta a importância do seu pronto reconhecimento e manejo

Effects of impurity scattering on electron-phonon resonances in semiconductor superlattice high-field transport

A non-equilibrium Green's function method is applied to model high-field quantum transport and electron-phonon resonances in semiconductor superlattices. The field-dependent density of states for elastic (impurity) scattering is found non-perturbatively in an approach which can be applied to both high and low electric fields. I-V curves, and specifically electron-phonon resonances, are calculated by treating the inelastic (LO phonon) scattering perturbatively. Calculations show how strong impurity scattering suppresses the electron-phonon resonance peaks in I-V curves, and their detailed sensitivity to the size, strength and concentration of impurities.Comment: 7 figures, 1 tabl