Effect of Te doping on thermal diffusivity of Bi2Se3 crystals: A study using open cell photoacoustic technique

An open cell configuration has been employed for the photoacoustic measurement of the thermal diffusivity of undoped Bi2Se3 crystals and Bi2Se3 crystals doped with various concentrations of Te. The amplitude of the photoacoustic signal obtained under heat transmission configuration as a function of chopping frequency is used to evaluate the numerical value of thermal diffusivity, α. Doped samples show a substantial reduction in the value of α compared to undoped samples. The variations in the thermal diffusivity of the doped samples are explained in terms of the phonon assisted heat transfer mechanism. It is seen that α is very sensitive to structural variations arising from doping. The experimentally observed results are correlated with X-ray diffraction studies.

Highly conductive and transparent ZnO thin film using Chemical Spray Pyrolysis technique: Effect of doping and deposition parameters

In the present work we report the preparation details studies on ZnO thin films. ZnO thin films are prepared using cost effective deposition technique viz., Chemical Spray Pyrolysis (CSP). The method is very effective for large area preparation of the ZnO thin film. A new post-deposition process could also be developed to avoid the adsorption of oxygen that usually occurs after the spraying process i.e., while cooling. Studies were done by changing the various deposition parameters for optimizing the properties of ZnO thin film. Moreover, different methods of doping using various elements are also tried to enhance the conductivity and transparency of the film to make these suitable for various optoelectronic applications.

Size effects in the magneto-optical response of Co nanoparticles

A study of the magneto-optical (MO) spectral response of Co nanoparticles embedded in MgO as a function of their size and concentration in the spectral range from 1.4 to 4.3 eV is presented. The nanoparticle layers were obtained by sputtering at different deposition temperatures. Transmission electron microscopy measurements show that the nanoparticles have a complex structure which consists of a crystalline core having a hexagonal close-packed structure and an amorphous crust. Using an effective-medium approximation we have obtained the MO constants of the Co nanoparticles. These MO constants are different from those of continuous Co layers and depend on the size of the crystalline core. We associate these changes with the size effect of the intraband contribution to the MO constants, related to a reduction of the relaxation time of the electrons into the nanoparticles.

Ab initio study of MF2 (M=Mn, Fe, Co, Ni) rutile-type compounds using the periodic unrestricted Hartree-Fock approach

The ab initio periodic unrestricted Hartree-Fock method has been applied in the investigation of the ground-state structural, electronic, and magnetic properties of the rutile-type compounds MF2 (M=Mn, Fe, Co, and Ni). All electron Gaussian basis sets have been used. The systems turn out to be large band-gap antiferromagnetic insulators; the optimized geometrical parameters are in good agreement with experiment. The calculated most stable electronic state shows an antiferromagnetic order in agreement with that resulting from neutron scattering experiments. The magnetic coupling constants between nearest-neighbor magnetic ions along the [001], [111], and [100] (or [010]) directions have been calculated using several supercells. The resulting ab initio magnetic coupling constants are reasonably satisfactory when compared with available experimental data. The importance of the Jahn-Teller effect in FeF2 and CoF2 is also discussed.

Effect of preparation on magnetic properties of Mn-Zn ferrite

Mixed ferrites belonging to the type Mn0.9Zn0.1Fe2O4 have been prepared by the double sintering method and by the chemical co-precipitation for comparing their magnetic properties. Sintered and precipitated ferrites exhibit different characteristics, especially in their magnetic properties like magnetization (Ms), coercive field (Hc) and Curie temperature (Tc). The sintered particles were size reduced in order to compare with the nanosized co-precipitated particles. The effect of grinding has also been studied. Particles have been collected at regular intervals of grinding and their properties have been studied. The increase in the coercive field has been recorded by a hysteresis curve tracer confirming size reduction. X-ray diffraction studies confirmed the structure and consequent size reduction

Tailoring Magnetic Properties of Co-Fe Thin Films by Topographical Modifications Using Thermal Annealing and Swift Heavy Ion Irradiation and Fabrication of Magnetoelectric Multilayers for Device Applications

Magnetism and magnetic materials have been playing a lead role in improving the quality of life. They are increasingly being used in a wide variety of applications ranging from compasses to modern technological devices. Metallic glasses occupy an important position among magnetic materials. They assume importance both from a scientific and an application point of view since they represent an amorphous form of condensed matter with significant deviation from thermodynamic equilibrium. Metallic glasses having good soft magnetic properties are widely used in tape recorder heads, cores of high-power transformers and metallic shields. Superconducting metallic glasses are being used to produce high magnetic fields and magnetic levitation effect. Upon heat treatment, they undergo structural relaxation leading to subtle rearrangements of constituent atoms. This leads to densification of amorphous phase and subsequent nanocrystallisation. The short-range structural relaxation phenomenon gives rise to significant variations in physical, mechanical and magnetic properties. Magnetic amorphous alloys of Co-Fe exhibit excellent soft magnetic properties which make them promising candidates for applications as transformer cores, sensors, and actuators. With the advent of microminiaturization and nanotechnology, thin film forms of these alloys are sought after for soft under layers for perpendicular recording media. The thin film forms of these alloys can also be used for fabrication of magnetic micro electro mechanical systems (magnetic MEMS). In bulk, they are drawn in the form of ribbons, often by melt spinning. The main constituents of these alloys are Co, Fe, Ni, Si, Mo and B. Mo acts as the grain growth inhibitor and Si and B facilitate the amorphous nature in the alloy structure. The ferromagnetic phases such as Co-Fe and Fe-Ni in the alloy composition determine the soft magnetic properties. The grain correlation length, a measure of the grain size, often determines the soft magnetic properties of these alloys. Amorphous alloys could be restructured in to their nanocrystalline counterparts by different techniques. The structure of nanocrystalline material consists of nanosized ferromagnetic crystallites embedded in an amorphous matrix. When the amorphous phase is ferromagnetic, they facilitate exchange coupling between nanocrystallites. This exchange coupling results in the vanishing of magnetocrystalline anisotropy which improves the soft magnetic properties. From a fundamental perspective, exchange correlation length and grain size are the deciding factors that determine the magnetic properties of these nanocrystalline materials. In thin films, surfaces and interfaces predominantly decides the bulk property and hence tailoring the surface roughness and morphology of the film could result in modified magnetic properties. Surface modifications can be achieved by thermal annealing at various temperatures. Ion irradiation is an alternative tool to modify the surface/structural properties. The surface evolution of a thin film under swift heavy ion (SHI) irradiation is an outcome of different competing mechanism. It could be sputtering induced by SHI followed by surface roughening process and the material transport induced smoothening process. The impingement of ions with different fluence on the alloy is bound to produce systematic microstructural changes and this could effectively be used for tailoring magnetic parameters namely coercivity, saturation magnetization, magnetic permeability and remanence of these materials. Swift heavy ion irradiation is a novel and an ingenious tool for surface modification which eventually will lead to changes in the bulk as well as surface magnetic property. SHI has been widely used as a method for the creation of latent tracks in thin films. The bombardment of SHI modifies the surfaces or interfaces or creates defects, which induces strain in the film. These changes will have profound influence on the magnetic anisotropy and the magnetisation of the specimen. Thus inducing structural and morphological changes by thermal annealing and swift heavy ion irradiation, which in turn induce changes in the magnetic properties of these alloys, is one of the motivation of this study. Multiferroic and magneto-electrics is a class of functional materials with wide application potential and are of great interest to material scientists and engineers. Magnetoelectric materials combine both magnetic as well as ferroelectric properties in a single specimen. The dielectric properties of such materials can be controlled by the application of an external magnetic field and the magnetic properties by an electric field. Composites with magnetic and piezo/ferroelectric individual phases are found to have strong magnetoelectric (ME) response at room temperature and hence are preferred to single phasic multiferroic materials. Currently research in this class of materials is towards optimization of the ME coupling by tailoring the piezoelectric and magnetostrictive properties of the two individual components of ME composites. The magnetoelectric coupling constant (MECC) (_ ME) is the parameter that decides the extent of interdependence of magnetic and electric response of the composite structure. Extensive investigates have been carried out in bulk composites possessing on giant ME coupling. These materials are fabricated by either gluing the individual components to each other or mixing the magnetic material to a piezoelectric matrix. The most extensively investigated material combinations are Lead Zirconate Titanate (PZT) or Lead Magnesium Niobate-Lead Titanate (PMNPT) as the piezoelectric, and Terfenol-D as the magnetostrictive phase and the coupling is measured in different configurations like transverse, longitudinal and inplane longitudinal. Fabrication of a lead free multiferroic composite with a strong ME response is the need of the hour from a device application point of view. The multilayer structure is expected to be far superior to bulk composites in terms of ME coupling since the piezoelectric (PE) layer can easily be poled electrically to enhance the piezoelectricity and hence the ME effect. The giant magnetostriction reported in the Co-Fe thin films makes it an ideal candidate for the ferromagnetic component and BaTiO3 which is a well known ferroelectric material with improved piezoelectric properties as the ferroelectric component. The multilayer structure of BaTiO3- CoFe- BaTiO3 is an ideal system to understand the underlying fundamental physics behind the ME coupling mechanism. Giant magnetoelectric coupling coefficient is anticipated for these multilayer structures of BaTiO3-CoFe-BaTiO3. This makes it an ideal candidate for cantilever applications in magnetic MEMS/NEMS devices. SrTiO3 is an incipient ferroelectric material which is paraelectric up to 0K in its pure unstressed form. Recently few studies showed that ferroelectricity can be induced by application of stress or by chemical / isotopic substitution. The search for room temperature magnetoelectric coupling in SrTiO3-CoFe-SrTiO3 multilayer structures is of fundamental interest. Yet another motivation of the present work is to fabricate multilayer structures consisting of CoFe/ BaTiO3 and CoFe/ SrTiO3 for possible giant ME coupling coefficient (MECC) values. These are lead free and hence promising candidates for MEMS applications. The elucidation of mechanism for the giant MECC also will be the part of the objective of this investigation.

From evolution to co-evolution – An empirical study of the role of innovation, policy and public research in industrial dynamics

In the past decades since Schumpeter’s influential writings economists have pursued research to examine the role of innovation in certain industries on firm as well as on industry level. Researchers describe innovations as the main trigger of industry dynamics, while policy makers argue that research and education are directly linked to economic growth and welfare. Thus, research and education are an important objective of public policy. Firms and public research are regarded as the main actors which are relevant for the creation of new knowledge. This knowledge is finally brought to the market through innovations. What is more, policy makers support innovations. Both actors, i.e. policy makers and researchers, agree that innovation plays a central role but researchers still neglect the role that public policy plays in the field of industrial dynamics. Therefore, the main objective of this work is to learn more about the interdependencies of innovation, policy and public research in industrial dynamics. The overarching research question of this dissertation asks whether it is possible to analyze patterns of industry evolution – from evolution to co-evolution – based on empirical studies of the role of innovation, policy and public research in industrial dynamics. This work starts with a hypothesis-based investigation of traditional approaches of industrial dynamics. Namely, the testing of a basic assumption of the core models of industrial dynamics and the analysis of the evolutionary patterns – though with an industry which is driven by public policy as example. Subsequently it moves to a more explorative approach, investigating co-evolutionary processes. The underlying questions of the research include the following: Do large firms have an advantage because of their size which is attributable to cost spreading? Do firms that plan to grow have more innovations? What role does public policy play for the evolutionary patterns of an industry? Are the same evolutionary patterns observable as those described in the ILC theories? And is it possible to observe regional co-evolutionary processes of science, innovation and industry evolution? Based on two different empirical contexts – namely the laser and the photovoltaic industry – this dissertation tries to answer these questions and combines an evolutionary approach with a co-evolutionary approach. The first chapter starts with an introduction of the topic and the fields this dissertation is based on. The second chapter provides a new test of the Cohen and Klepper (1996) model of cost spreading, which explains the relationship between innovation, firm size and R&D, at the example of the photovoltaic industry in Germany. First, it is analyzed whether the cost spreading mechanism serves as an explanation for size advantages in this industry. This is related to the assumption that the incentives to invest in R&D increase with the ex-ante output. Furthermore, it is investigated whether firms that plan to grow will have more innovative activities. The results indicate that cost spreading serves as an explanation for size advantages in this industry and, furthermore, growth plans lead to higher amount of innovative activities. What is more, the role public policy plays for industry evolution is not finally analyzed in the field of industrial dynamics. In the case of Germany, the introduction of demand inducing policy instruments stimulated market and industry growth. While this policy immediately accelerated market volume, the effect on industry evolution is more ambiguous. Thus, chapter three analyzes this relationship by considering a model of industry evolution, where demand-inducing policies will be discussed as a possible trigger of development. The findings suggest that these instruments can take the same effect as a technical advance to foster the growth of an industry and its shakeout. The fourth chapter explores the regional co-evolution of firm population size, private-sector patenting and public research in the empirical context of German laser research and manufacturing over more than 40 years from the emergence of the industry to the mid-2000s. The qualitative as well as quantitative evidence is suggestive of a co-evolutionary process of mutual interdependence rather than a unidirectional effect of public research on private-sector activities. Chapter five concludes with a summary, the contribution of this work as well as the implications and an outlook of further possible research.

The effect of Ponzi schemes on crime: Evidence from the colombian case

This paper estimates the impact of a massive negative income shock led by the simultaneous crash down of several Ponzi schemes (also known as financial ``pyramids"") in Colombia on crime rates at the municipal level. Using novel data on the spatial incidence of the latest wave of Colombian pyramids and their crash down date, I estimate difference-in-differences models with both monthly and yearly frequency. I find that the negative income shock of the pyramids" crash down differentially exacerbates crime in affected municipalities compared to those with no presence of Ponzi schemes. This is true for minor offenses like commercial theft or residential burglary, but not for major crimes as murder or terrorism.

Economic crisis and the financial system amplification effect

A well informed and cautious financial system can improves the welfare outcome of an economy by driving lenders surplus to borrow-ers. Nevertheless in a crisis situation the financial system cautious behavior can become a crisis amplifier given that the credit approval conditions are hardly meet, so there could be a credit crunch even in a low interest rates environment. This paper illustrates the previous by developing a general equilibrium model where the collateral credit condition defines the prudential behavior of the financial sys-tem. This and some other conditions amplify the magnitude of a negative productivity shock.

The differential effect on dropout of increasing grades' supply by integrating or expanding schools: evidence from a quasi-experiment in Bogotá

En el año 2002, la Secretaría de Educación de Bogotá estipuló la Resolución 2101 que tenía por objeto asegurar el ciclo de la educación completo en los colegios públicos. El propósito de este trabajo es evaluar el impacto de los mecanismos seguidos a la aplicación de esta política sobre la tasa de deserción escolar. Las escuelas tenían tres mecanismos diferentes para alcanzar el objetivo de la presente resolución: expandir los grados escolares ofertados, integrarse con otros colegios de la zona, o ambos. Para ello, utilizo variables instrumentales para resolver el sesgo causado por el hecho de que los colegios que siguen determinada estrategia eran los que tenían altas tasas de deserción inicialmente. Usando datos sobre las características institucionales y las características socio-demográficas de la población cerca del colegio, evalúo el impacto de estos tres mecanismos sobre las tasas de deserción escolar. Los resultados sugieren que las instituciones que aumentaron los grados experimentan un aumento en el número de estudiantes que abandonan el colegio en 12.1 puntos porcentuales, mientras que las instituciones que complementaron este mecanismo con la integración de un colegio próximo pre existente mostraron una reducción en la tasa de deserción escolar de 9.8 puntos porcentuales.

Estudio Costo-Efectividad de Lidocaína tópica como adyuvante a Pregabalina y Gabapentina en dolor neuropático periférico en una I.P.S de Bogotá 2011.

Introducción: el dolor neuropático es una patología de considerable prevalencia e impacto socio-económico en la población latinoamericana, la evidencia clínica sugiere que los ligandos de canales de calcio y el parche de Lidocaína pueden tratar exitosamente el dolor neuropático periférico y localizado. Metodología: se realizo una evaluación económica tipo costo-efectividad, observacional y retrospectiva con datos extraídos de las historias clínicas de pacientes atendidos en la clínica de dolor de la IPS. La variable primaria de efectividad fue la mejoría del dolor medida mediante escala visual análoga. Resultados: se estudiaron 94 pacientes tratados con: Gabapentina (G) 21, Pregabalina (P) 24, Gabapentina+ lidocaína (G/P) 24, Pregabalina + Lidocaína (P/L) 25, los costos asociados al tratamiento son los siguientes COP$114.070.835, COP$105.855.920, COP$88.717.481 COP$89.854.712 respectivamente, el número de pacientes con mejoría significativa de dolor fue: 8,10,9 y 21 pacientes respectivamente. El ICER de G/L con respecto a G fue: COP$ -25.353.354. El ICER de P/L con respecto a P fue: COP$ -1.454.655. Conclusiones: la adición del parche de lidocaína a la terapia regular con P/L represento una disminución de consumo de recursos en salud como uso de medicamentos co-analgésicos, analgésicos de rescate y fármacos para controlar reacciones adversas, de la misma forma que consultas a profesionales de la salud. Cada paciente manejado con P/L representa un ahorro de COP $1.454.655 al contrario si se manejase con el anticonvulsivante de manera exclusiva, en el caso de G/L este ahorro es de COP $ 25.353.354 frente a G sola.

Apendicitis aguda perforada en adultos; aproximación a las inequidades sociales en salud, Bogotá 2012

La perforación del apéndice es una complicación temprana de la apendicitis aguda, demoras en el diagnóstico o tratamiento incrementan la tasa de perforación. Se desconoce si la perforación dl apéndice es un reflejo de inequidades sociales. Se pretendió determinar la asociación de la apendicitis aguda perforada en adultos y la equidad en acceso a salud. Estudio tipo cohorte retrospectivo documental, de historias clínicas de pacientes con apendicitis aguda; el análisis se realizó con Stata 11.1 y Epi-info. Los resultados se presentaron en tablas y figuras. Se incluyeron 540 casos (292 hombre y 248 mujeres), el grupo de edad que aporto más datos fue el de 18 a 49 años (391 pacientes); el tiempo medio de síntomas a consulta fue de 37,45 horas, y de 5,3 horas para el paso a cirugía desde el ingreso, fueron solicitadas 76 ecografías y 53 tomografías, 50 interconsultas a urología y 10 a ginecología hasta el diagnostico. El grupo de mayores de 49 años, el estrato socioeconómico tres y la tomografía fueron factores de riesgo independientes para perforación del apéndice. El análisis multivariado mostró asociación lineal entre el estrato socioeconómico y tiempo de síntomas al ingreso, tiempo para paso a cirugía, solicitud de ayudas diagnósticas e interconsultas, con buena significación estadística. La apendicitis aguda perforada en adultos, podría ser un indicador de inequidad en salud. Se requiere de estudios multi-céntricos, con mayor tiempo de evaluación y muestra para demostrar si el apéndice perforado es un trazador de inequidades en salud en Colombia.

Experiencia en nefrectomía: serie de casos de cuatro años

Introducción: Las indicaciones por las cuales un paciente requiere una nefrectomía son múltiples: las neoplasias, la hidronefrosis y la exclusión funcional son las principales. En manos expertas la nefrectomía es un procedimiento seguro, especialmente porque en la actualidad el abordaje por excelencia es realizar una técnica mínimamente invasiva con conservación de nefronas. Se presenta el análisis de la experiencia en Mederi, Hospital Universitario Mayor en esta intervención. Metodología: Se realizó una serie de casos de pacientes llevados a nefrectomía entre mayo de 2008 y mayo de 2012. Se incluyeron la totalidad de los casos. Resultados: Se analizaron 72 registros, 49 mujeres y 25 hombres; 13 de ellas fueron laparoscópicas. La edad promedio fue de 58,6 años. El tiempo medio operatorio fue 169,23 minutos (118-220 minutos). El sangrado operatorio promedio fue de 680,63 ml (IC95%: 2,83-1358 ml). El tiempo de hospitalización promedio fue de 4,88 días IC95%. La mayoría de los pacientes se distribuyeron en estadios medios de la enfermedad tumoral, con poco compromiso ganglionar y metástasis; el diagnóstico histológico y estadio dominante fueron el carcinoma de células renales grado 3 de Fuhrman respectivamente. Se reportan 13 casos de compromiso de la capsula de Gerota y 11 con compromiso del hilio. Discusión: La experiencia en nefrectomía de la institución es muy positiva por el bajo número de mortalidad y complicaciones. En cuanto a la técnica, es importante promover la técnica laparoscópica

Caracterización y ajuste del factor de magnificación para radiología digital de cadera

Introducción. Las imágenes obtenidas mediante rayos X, determinan una conducta clínica en ortopedia y son analizadas por parte del cirujano en el momento previo a realizar un acto quirúrgico. El planeamiento pre quirúrgico basado en radiografías de cadera, permite predecir el tamaño de los componentes protésicos a utilizar en un reemplazo de cadera. Con el advenimiento de las radiografías digitales, existe la falsa percepción de que estas tienen corregido el factor de magnificación. La corrección de dicho factor requiere un protocolo de calibración de imágenes, aún no implementado en la Fundación Santa Fe de Bogotá (FSFB). Como consecuencia, las radiografías de cadera actualmente resultan magnificadas. Materiales y métodos. Fueron seleccionados 73 pacientes con reemplazo articular total de la cadera intervenidos en la FSFB. Para cada paciente, se estableció la dimensión de la cabeza protésica en la radiografía de cadera obtenida mediante el sistema de radiología digital (PACS-IMPAX) y su tamaño fue comparado con el de la cabeza femoral implantada. Resultados. La concordancia entre los dos observadores al medir la dimensión radiológica de los componentes protésicos fue excelente y el coeficiente de magnificación promedio de 1.2 (20%). Este será introducido al PACS-IMPAX para ajustar el tamaño definitivo de la radiografía. Conclusión. El ajuste del PACS-IMPAX permite obtener radiografías en las cuales se refleja con mayor precisión el tamaño de los segmentos anatómicos y de los componentes protésicos.

Eficacia del plasma rico en plaquetas en procedimientos médicos estéticos faciales . Evaluación en contorno de ojos.

Introducción: En la actualidad se están implementando nuevas técnicas, para el tratamiento de líneas de expresión facial. El Plasma Rico en Plaquetas (PRP) utiliza factores de crecimiento humano autólogos con fines médicos estéticos. El objetivo de este trabajo fue evaluar el tratamiento con plasma rico en plaquetas en el manejo del rejuvenecimiento periocular. Materiales y métodos: Estudio descriptivo retrospectivo en una cohorte de 27 pacientes entre 30 a 70 años de ambos sexos,tratados con PRP sin tratamientos médicos estéticos previos . Se compararon fotografías del sistema VISIA®, previo y posterior el PRP, para determinar los cambios del área periocular. Con análisis comparativo de medias utilizando pruebas t de student. Resultados: De 27 historias clínicas revisadas 96,3% eran mujeres, la edad promedio fue de 52.67 años. Se observaron cambios clínicos satisfactorios en el manejo del foto envejecimiento periocular con mejoría estadísticamente significativa entre el promedio inicial y el post tratamiento en arrugas, textura y porfirinas (p: 0.000). No se observaron diferencias estadísticamente significativas entre los grupos de edad (p = 0,62). Los pacientes analizados posterior al tratamiento se encuentran en mejor estado que el 63,78% de la población de su mismo sexo, edad y fototipo de piel. Los eventos adversos fueron disminuyendo en su frecuencia en cada una de las sesiones siguientes. Discusión: El PRP proporciona una mejoría global en los parámetros de envejecimiento periocular lo cual se correlaciono con los estudios previos in vitro. Conclusiones: El PRP es seguro y eficaz en contorno de ojos.