Photothermal deflection measurement on heat transport in GaAs epitaxial layers

In this paper, we report the in-plane and cross-plane measurements of the thermal diffusivity of double epitaxial layers of n-type GaAs doped with various concentrations of Si and a p-type Be-doped GaAs layer grown on a GaAs substrate by the molecular beam epitaxial method, using the laser-induced nondestructive photothermal deflection technique. The thermal diffusivity value is evaluated from the slope of the graph of the phase of the photothermal deflection signal as a function of pump-probe offset. Analysis of the data shows that the cross-plane thermal diffusivity is less than that of the in-plane thermal diffusivity. It is also seen that the doping concentration has a great influence on the thermal diffusivity value. Measurement of p-type Be-doped samples shows that the nature of the dopant also influences the effective thermal diffusivity value. The results are interpreted in terms of a phonon-assisted heat transfer mechanism and the various scattering process involved in the propagation of phonons.

Photothermal deflection measurement on heat transport in GaAs epitaxial layers

In this paper, we report the in-plane and cross-plane measurements of the thermal diffusivity of double epitaxial layers of n-type GaAs doped with various concentrations of Si and a p-type Be-doped GaAs layer grown on a GaAs substrate by the molecular beam epitaxial method, using the laser-induced nondestructive photothermal deflection technique. The thermal diffusivity value is evaluated from the slope of the graph of the phase of the photothermal deflection signal as a function of pump-probe offset. Analysis of the data shows that the cross-plane thermal diffusivity is less than that of the in-plane thermal diffusivity. It is also seen that the doping concentration has a great influence on the thermal diffusivity value. Measurement of p-type Be-doped samples shows that the nature of the dopant also influences the effective thermal diffusivity value. The results are interpreted in terms of a phonon-assisted heat transfer mechanism and the various scattering process involved in the propagation of phonons

Photothermal deflection measurement on heat transport in GaAs epitaxial layers

In this paper, we report the in-plane and cross-plane measurements of the thermal diffusivity of double epitaxial layers of n-type GaAs doped with various concentrations of Si and a p-type Be-doped GaAs layer grown on a GaAs substrate by the molecular beam epitaxial method, using the laser-induced nondestructive photothermal deflection technique. The thermal diffusivity value is evaluated from the slope of the graph of the phase of the photothermal deflection signal as a function of pump-probe offset. Analysis of the data shows that the cross-plane thermal diffusivity is less than that of the in-plane thermal diffusivity. It is also seen that the doping concentration has a great influence on the thermal diffusivity value. Measurement of p-type Be-doped samples shows that the nature of the dopant also influences the effective thermal diffusivity value. The results are interpreted in terms of a phonon-assisted heat transfer mechanism and the various scattering process involved in the propagation of phonons

Full complex Fresnel holograms displayed on liquid cristal displays

We propose a method to display full complex Fresnel holograms by adding the information displayed on two analogue ferroelectric liquid crystal spatial light modulators. One of them works in real-only configuration and the other in imaginary-only mode. The Fresnel holograms are computed by backpropagating an object at a selected distance with the Fresnel transform. Then, displaying the real and imaginary parts on each panel, the object is reconstructed at that distance from the modulators by simple propagation of light. We present simulation results taking into account the specifications of the modulators as well as optical results. We have also studied the quality of reconstructions using only real, imaginary, amplitude or phase information. Although the real and imaginary reconstructions look acceptable for certain distances, full complex reconstruction is always better and is required when arbitrary distances are used.

The Cold Tongue in the South China Sea during Boreal Winter and Its Interaction with the Atmosphere

A distinct cold tongue has recently been noticed in the South China Sea during the winter monsoon, with the cold tongue temperature minimum occurring in the January or February. This cold tongue shows signi¯cant links with the Maritime Continent's rainfall during the winter period. The cold tongue and its interaction with the Maritime Continent's weather were studied using Reynolds SST data, wind ¯elds from the NCEP{NCAR reanalysis dataset and the quikSCAT dataset. In addition, rainfall from the GOES Precipitation Index (GPI) for the periods 2000 to 2008 was also used. The propagation of the cold tongue towards the south is explained using wind dynamics and the western boundary current. During the period of strong cold tongue, the surface wind is strong and the western boundary current advects the cold tongue to the south. During the period of strong winds the zonal gradient of SST is high [0.5±C (25 km)¡1]. The cold tongue plays an important role in regulating the climate over the Maritime Continent. It creates a zonal/meridional SST gradient and this gradient ultimately leads in the formation of convection. Hence, two maximum precipitation zones are found in the Maritime Continent, with a zone of relatively lower precipitation between, which coincides with the cold tongue's regions. It was found that the precipitation zones have strong links with the intensity of the cold tongue. During stronger cold tongue periods the precipitation on either side of the cold tongue is considerably greater than during weaker cold tongue periods. The features of convection on the eastern and western sides of the cold tongue behave di®erently. On the eastern side convection is preceded by one day with SST gradient, while on the western side it is four days.

Etablierung neuer Methoden zur in vitro Kultivierung der Baumart Fraxinus excelsior L. und Entwicklung von Verfahren zur Kryokonservierung von in vitro Sprossspitzen

Die hier vorliegende Arbeit wurde im Rahmen eines europäischen Projektes mit dem Titel „Improving Fraxinus (Ash) productivity for European needs by testing, selection, propagation and promotion of improved genetic resources“ an der Niedersächsischen Forstlichen Versuchsanstalt, Abteilung Waldgenressourcen erstellt. Im Rahmen des Projektes wurden 62 Plusbäume aus einem 15 Jahre alten europäischen Herkunfts-/ Nachkommenschaftsversuch in den Niedersächsischen Forstämtern Bovenden und Dannenberg nach den Kriterien Stammform und Wuchsleistung für die vegetative Vermehrung ausgewählt. Ziel dieser Arbeit war die Optimierung bestehender in vitro Protokolle sowie die Entwicklung eines bisher noch nicht existierenden Kryokonservierungsprotokolls für in vitro Sprossspitzen. Im ersten Teil dieser Arbeit wird die Entwicklung des in vitro Protokolls für Fraxinus excelsior dargestellt. Die Optimierung der Methoden zur Etablierung, Vermehrung und Bewurzelung erfolgte durch Versuchsreihen mit unterschiedlichen Klonen, so dass insgesamt 26 der selektierten Plusbäume erfolgreich in vitro etabliert werden konnten. Achselknospen frischer Triebe der Pfropflinge der Mutterbäume stellten die beste Explantatquelle dar. Die Explantate wurden mit 0,2 % Quecksilberchlorid (HgCl2) oberflächensterilisiert bevor sie auf hormonfreies Woody Plant Medium (WPM) transferiert wurden. Nach zwei Wochen erfolgte ein Transfer auf WPM mit 4 mg/l 6-Benzylaminopurine (BAP) und 0,15 mg/l Indole-3-butyric acid (IBA). Die besten Vermehrungsraten wurden auf WPM mit 4 mg/l BAP, 0,15 mg/l IBA und 0,01 mg/l TDZ und 0,7 % Agar in Honiggläsern mit einem Plastikdeckel erzielt. Als Bewurzelungsmedium wurde 0,5 konzentriertes Murashige und Skoog (MS) Medium mit 2 mg/l IBA, 0,25 mg/l BAP und 0,8 % Agar verwandt. Im zweiten Teil der Arbeit werden die Versuchsreihen zur Entwicklung des Kryokonservierungsprotokolls von in vitro Sprossspitzen dargestellt. Zur Entwicklung der Methode wurden die Vorbehandlungsbedingungen verbessert und zwei Techniken, die Alginat- / Dehydrati-onsmethode und die Vitrifikationsmethode mit Hilfe der sogenannten PVS2-Lösung (Plant Vitrification solution number 2) getestet. Die optimierte PVS2-Methode erwies sich als die für Esche besser geeignete Technik und ließ sich erfolgreich zur Kryokonservierung juveniler und adulter Kulturen anwenden. Die Regenerationsraten lagen zwischen 50 und 100 % für juvenile bzw. 50 und 80 % für adulte Kulturen.

Optimizing Robust Quantum Gates in Open Quantum Systems

We are currently at the cusp of a revolution in quantum technology that relies not just on the passive use of quantum effects, but on their active control. At the forefront of this revolution is the implementation of a quantum computer. Encoding information in quantum states as “qubits” allows to use entanglement and quantum superposition to perform calculations that are infeasible on classical computers. The fundamental challenge in the realization of quantum computers is to avoid decoherence – the loss of quantum properties – due to unwanted interaction with the environment. This thesis addresses the problem of implementing entangling two-qubit quantum gates that are robust with respect to both decoherence and classical noise. It covers three aspects: the use of efficient numerical tools for the simulation and optimal control of open and closed quantum systems, the role of advanced optimization functionals in facilitating robustness, and the application of these techniques to two of the leading implementations of quantum computation, trapped atoms and superconducting circuits. After a review of the theoretical and numerical foundations, the central part of the thesis starts with the idea of using ensemble optimization to achieve robustness with respect to both classical fluctuations in the system parameters, and decoherence. For the example of a controlled phasegate implemented with trapped Rydberg atoms, this approach is demonstrated to yield a gate that is at least one order of magnitude more robust than the best known analytic scheme. Moreover this robustness is maintained even for gate durations significantly shorter than those obtained in the analytic scheme. Superconducting circuits are a particularly promising architecture for the implementation of a quantum computer. Their flexibility is demonstrated by performing optimizations for both diagonal and non-diagonal quantum gates. In order to achieve robustness with respect to decoherence, it is essential to implement quantum gates in the shortest possible amount of time. This may be facilitated by using an optimization functional that targets an arbitrary perfect entangler, based on a geometric theory of two-qubit gates. For the example of superconducting qubits, it is shown that this approach leads to significantly shorter gate durations, higher fidelities, and faster convergence than the optimization towards specific two-qubit gates. Performing optimization in Liouville space in order to properly take into account decoherence poses significant numerical challenges, as the dimension scales quadratically compared to Hilbert space. However, it can be shown that for a unitary target, the optimization only requires propagation of at most three states, instead of a full basis of Liouville space. Both for the example of trapped Rydberg atoms, and for superconducting qubits, the successful optimization of quantum gates is demonstrated, at a significantly reduced numerical cost than was previously thought possible. Together, the results of this thesis point towards a comprehensive framework for the optimization of robust quantum gates, paving the way for the future realization of quantum computers.

Electrical Design: A Problem for Artificial Intelligence Research

This report outlines the problem of intelligent failure recovery in a problem-solver for electrical design. We want our problem solver to learn as much as it can from its mistakes. Thus we cast the engineering design process on terms of Problem Solving by Debugging Almost-Right Plans, a paradigm for automatic problem solving based on the belief that creation and removal of "bugs" is an unavoidable part of the process of solving a complex problem. The process of localization and removal of bugs called for by the PSBDARP theory requires an approach to engineering analysis in which every result has a justification which describes the exact set of assumptions it depends upon. We have developed a program based on Analysis by Propagation of Constraints which can explain the basis of its deductions. In addition to being useful to a PSBDARP designer, these justifications are used in Dependency-Directed Backtracking to limit the combinatorial search in the analysis routines. Although the research we will describe is explicitly about electrical circuits, we believe that similar principles and methods are employed by other kinds of engineers, including computer programmers.

A Conservative Front Tracking Algorithm

The discontinuities in the solutions of systems of conservation laws are widely considered as one of the difficulties in numerical simulation. A numerical method is proposed for solving these partial differential equations with discontinuities in the solution. The method is able to track these sharp discontinuities or interfaces while still fully maintain the conservation property. The motion of the front is obtained by solving a Riemann problem based on the state values at its both sides which are reconstructed by using weighted essentially non oscillatory (WENO) scheme. The propagation of the front is coupled with the evaluation of "dynamic" numerical fluxes. Some numerical tests in 1D and preliminary results in 2D are presented.

Augmented state Kalman filtering for AUV navigation

Addresses the problem of estimating the motion of an autonomous underwater vehicle (AUV), while it constructs a visual map ("mosaic" image) of the ocean floor. The vehicle is equipped with a down-looking camera which is used to compute its motion with respect to the seafloor. As the mosaic increases in size, a systematic bias is introduced in the alignment of the images which form the mosaic. Therefore, this accumulative error produces a drift in the estimation of the position of the vehicle. When the arbitrary trajectory of the AUV crosses over itself, it is possible to reduce this propagation of image alignment errors within the mosaic. A Kalman filter with augmented state is proposed to optimally estimate both the visual map and the vehicle position

La globalización del miedo

Un rasgo importante del actual proceso de globalización consiste en que los sentimientos de miedo acosan cada vez con más fuerza a los habitantes de la aldea global. El incremento del terrorismo, las amenazas ambientales, los riesgos asociados al desarrollo de nuevas tecnologías y, en general, la atmósfera de inestabilidad que caracteriza la vida contemporánea, se traducen en una creciente propagación del miedo. En este artículo examinaremos primero las principales causas por las cuales la sociedad actual resulta tan vulnerable frente al miedo, especialmente el derivado del terrorismo. Luego, veremos de qué modo los medios de comunicación acrecientan esta vulnerabilidad. Al final, mostraremos en qué sentido estamos asistiendo al surgimiento de una sociedad global en estado de miedo permanente.

La valoración de la prueba testimonial; el paradigmático caso del Coronel Luis Alfonso Plazas Vega

De acuerdo a la coyuntura social por la que atraviesa actualmente la administración de justicia colombiana, en cuanto a la proliferación de injusticias y errores judiciales causados por la valoración probatoria positiva de los falsos testigos, nace nuestro estudio y la respectiva crítica a la estimación superficial que se realiza a la prueba testimonial por parte de algunos de nuestros jueces, y la aceptación sin mayor control que efectúa la Fiscalía General de la Nación. En ese sentido, se realiza una exhaustiva pero concisa investigación al respecto de todos y cada uno de los factores relevantes a la hora de valorar al deponente y su testimonio como medio probatorio, de suerte que establece los diferentes requisitos formales y sustanciales de los cuales debe gozar, tanto el testigo como su declaración, para que puedan ser tomados en cuenta a la hora de tomar una decisión judicial en materia penal. Con base en lo anterior, nuestra monografía consta de una parte teórica y una parte teóricopractica, en la cual se tomó como ejemplo principal, el paradigmático caso del Coronel ® Luis Alfonso Plazas Vega, toda vez que es un proceso que actualmente se encuentra en sede de casación, y aun no tiene un pronunciamiento definitivo por parte de la honorable Corte Suprema de Justicia, por lo cual es posible realizar una crítica constructiva y propia en lo que concierne a la valoración de la prueba testimonial, en el entendido en que no existe una decisión inequívoca. Finalmente, lo que se pretende con este trabajo es explicar de una manera sencilla y de fácil entendimiento la labor que deben realizar los jueces de la República y la Fiscalía, que aunque no es la que toma la decisión, también debería realizar un mínima valoración, o por lo menos una verificación al momento de aportar y darle credibilidad a testigos que son favorables a su teoría del caso. De forma tal que, la administración de justicia debe llevar a cabo una valoración probatoria, específicamente encaminada al estándar probatorio que se le debe atribuir al testimonio, teniendo en cuenta los factores externos e internos que afecten la declaración, y por los cuales se vea influenciada la misma; todo esto, con el fin de evitar los errores judiciales que se han generado a lo largo de nuestra historia, los cuales han conllevado a innumerables injusticias creando gran polémica y un desasosiego por parte de la sociedad civil.

Social Media Analytics: Trust and Power

In this lecture for a second year interdisciplinary course (part of the curriculum innovation programme) We explore the scope of social media analytics and look at two aspects in depth: Analysing for influence (looking at factors such as network structure, propagation of content and interaction), and analysing for trust (looking at different methods including policy, provenance and reputation - both local and global). The lecture notes include a number of short videos, which cannot be included here for copy-write reasons.

Genotipificación de HLA-B en pacientes colombianos afectados por el síndrome Stevens-Johnson y la Necrólisis Epidérmica Tóxica

Las reacciones alérgicas a medicamentos cutáneas severas (RAM) como el Síndrome Stevens Johnson (SJS) y la Necrólisis Epidérmica Tóxica (NET),caracterizadas por exantema, erosión de la piel y las membranas mucosas, flictenas, desprendimiento de la piel secundario a la muerte de queratinocitos y compromiso ocular. Son infrecuentes en la población pero con elevada morbi-mortalidad, se presentan luego de la administración de diferentes fármacos. En Asia se ha asociado el alelo HLA-B*15:02 como marcador genético para SJS. En Colombia no hay datos de la incidencia de estas RAM, ni de la relación con medicamentos específicos o potenciales y tampoco estudios de aproximación genómica de genes de susceptibilidad.

Virus infection speeds: theory versus experiment

In order to explain the speed of Vesicular Stomatitis Virus VSV infections, we develop a simple model that improves previous approaches to the propagation of virus infections. For VSV infections, we find that the delay time elapsed between the adsorption of a viral particle into a cell and the release of its progeny has a very important effect. Moreover, this delay time makes the adsorption rate essentially irrelevant in order to predict VSV infection speeds. Numerical simulations are in agreement with the analytical results. Our model satisfactorily explains the experimentally measured speeds of VSV infections