The prospects for 10 nm III-V CMOS

The increasing difficulties for further scaling down of Si CMOS is bringing to the fore the investigation of alternative channel materials. Among these, III-V compound semiconductors are very attractive due to their outstanding electron transport properties. This paper briefly reviews the prospects and the challenges for a III-V CMOS technology with gate lengths in the 10 nm range.Semiconductor Research CorporationIntel Corporatio

Probing Spin-Charge Separation in Tunnel-Coupled Parallel Quantum Wires

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.Comment: 9 pages, 3 figures, expanded version with many detail

Conductance oscillations in strongly correlated fractional quantum Hall line junctions

We present a detailed theory of transport through line junctions formed by counterpropagating single-branch fractional-quantum-Hall edge channels having different filling factors. Intriguing transport properties are exhibited when strong Coulomb interactions between electrons from the two edges are present. Such strongly correlated line junctions can be classified according to the value of an effective line-junction filling factor n that is the inverse of an even integer. Interactions turn out to affect transport most importantly for n=1/2 and n=1/4. A particularly interesting case is n=1/4 corresponding to, e.g., a junction of edge channels having filling factor 1 and 1/5, respectively. We predict its differential tunneling conductance to oscillate as a function of voltage. This behavior directly reflects the existence of novel Majorana-fermion quasiparticle excitations in this type of line junction. Experimental accessibility of such systems in current cleaved-edge overgrown samples enables direct testing of our theoretical predictions.Comment: 2 figures, 10 pages, RevTex4, v2: added second figure for clarit

The Dynamics and Evolutionary Potential of Domain Loss and Emergence

The wealth of available genomic data presents an unrivaled opportunity to study the molecular basis of evolution. Studies on gene family expansions and site-dependent analyses have already helped establish important insights into how proteins facilitate adaptation. However, efforts to conduct full-scale cross-genomic comparisons between species are challenged by both growing amounts of data and the inherent difficulty in accurately inferring homology between deeply rooted species. Proteins, in comparison, evolve by means of domain rearrangements, a process more amenable to study given the strength of profile-based homology inference and the lower rates with which rearrangements occur. However, adapting to a constantly changing environment can require molecular modulations beyond reach of rearrangement alone. Here, we explore rates and functional implications of novel domain emergence in contrast to domain gain and loss in 20 arthropod species of the pancrustacean clade. Emerging domains are more likely disordered in structure and spread more rapidly within their genomes than established domains. Furthermore, although domain turnover occurs at lower rates than gene family turnover, we find strong evidence that the emergence of novel domains is foremost associated with environmental adaptation such as abiotic stress response. The results presented here illustrate the simplicity with which domain-based analyses can unravel key players of nature's adaptational machinery, complementing the classical site-based analyses of adaptation

Parameter identification problems in the modelling of cell motility

We present a novel parameter identification algorithm for the estimation of parameters in models of cell motility using imaging data of migrating cells. Two alternative formulations of the objective functional that measures the difference between the computed and observed data are proposed and the parameter identification problem is formulated as a minimisation problem of nonlinear least squares type. A Levenberg–Marquardt based optimisation method is applied to the solution of the minimisation problem and the details of the implementation are discussed. A number of numerical experiments are presented which illustrate the robustness of the algorithm to parameter identification in the presence of large deformations and noisy data and parameter identification in three dimensional models of cell motility. An application to experimental data is also presented in which we seek to identify parameters in a model for the monopolar growth of fission yeast cells using experimental imaging data. Our numerical tests allow us to compare the method with the two different formulations of the objective functional and we conclude that the results with both objective functionals seem to agree

Mesoscopic effects in tunneling between parallel quantum wires

We consider a phase-coherent system of two parallel quantum wires that are coupled via a tunneling barrier of finite length. The usual perturbative treatment of tunneling fails in this case, even in the diffusive limit, once the length L of the coupling region exceeds a characteristic length scale L_t set by tunneling. Exact solution of the scattering problem posed by the extended tunneling barrier allows us to compute tunneling conductances as a function of applied voltage and magnetic field. We take into account charging effects in the quantum wires due to applied voltages and find that these are important for 1D-to-1D tunneling transport.Comment: 8 pages, 7 figures, improved Figs., added Refs. and appendix, to appear in Phys. Rev.

Análisis de la docencia universitaria por la influencia de la COVID-19: algunas lecciones aprendidas

La crisis sanitaria producida por el virus del SARS-COV-2 produjo un cambio drástico en la educación en marzo de 2020, cuando la enseñanza presencial se vio forzada a adaptarse a la telenseñanza. Esto produjo cambios en las metodologías docentes, los materiales didácticos y los métodos de evaluación. El objetivo de este estudio es determinar cuáles de estos cambios, implementados en la Universidad presencial, han sido positivos y deberían mantenerse en el tiempo. Para ello se ha realizado una encuesta a los alumnos de los distintos cursos de los grados impartidos en la E.T.S.I. Minas y Energía (E.T.S.I.M.E) de la Universidad Politécnica de Madrid que permite conocer cómo ha influido la pandemia en el uso de los nuevos materiales didácticos, qué tipo de modalidades de enseñanza prefieren los alumnos y qué recursos utilizan más durante el estudio. A pesar de que los apuntes y diapositivas de clase siguen siendo el recurso predilecto de los alumnos, se ha visto un gran interés por las grabaciones de clases. Otros materiales más tradicionales, como la bibliografía o las tutorías, son menos utilizados por los estudiantes. En cuanto a las modalidades de enseñanza, la opinión está polarizada. Por tanto, es necesario realizar un esfuerzo para combinar eficientemente las metodologías y recursos didácticos de telenseñanza a la docencia presencial, generando recursos asíncronos sin perjuicio de las actividades presenciales tradicionales

Análisis del impacto en el aprendizaje del entrenamiento mediante ejercicios con errores controlados

En este artículo se presenta la experiencia de innovación docente introducida en asignaturas impartidas en la E.T.S.I. Minas y Energía de la Universidad Politécnica de Madrid, basada en el entrenamiento con ejercicios que contienen errores controlados. Se analizan los resultados obtenidos con el empleo de esta metodología y su impacto en el aprendizaje. Se han preparado diversos ejercicios de entrenamiento que contienen errores comunes cometidos por los alumnos en tres asignaturas: Química, Gestión de Empresas y Expresión Gráfica. Los ejercicios de entrenamiento consisten en preguntas breves de respuesta rápida con cuatro posibles opciones de respuesta. Para el análisis del impacto en el aprendizaje se han tenido en cuenta los resultados obtenidos por los alumnos en las pruebas de evaluación y la percepción del alumnado consultándoles a través de una encuesta. En las dos primeras asignaturas, los ejercicios de evaluación no contenían errores, mientras que, en Expresión Gráfica éstos se basaron en la detección de errores controlados. En las asignaturas de Química y Gestión de Empresas, el entrenamiento con errores controlados ha mejorado las calificaciones obtenidas por el alumnado. Además, en el caso de Expresión Gráfica, los resultados muestran cómo el uso de errores controlados mejora la clasificación de los alumnos

Testing Bell's inequality using ballistic electrons in semiconductors

We propose an experiment to test Bell's inequality violation in condensed-matter physics. We show how to generate, manipulate, and detect entangled states using ballistic electrons in Coulomb-coupled semiconductor quantum wires. Due to its simplicity (only five gates are required to prepare entangled states and to test Bell's inequality), the proposed semiconductor-based scheme can be implemented with currently available technology. Moreover, its basic ingredients may play a role towards large-scale quantum-information processing in solid-state devices