Electro y dielectroforesis de nanopartículas por efecto fotovoltaico

El objetivo de esta tesis doctoral es la investigación del nuevo concepto de pinzas fotovoltaicas, es decir, del atrapamiento, ordenación y manipulación de partículas en las estructuras generadas en la superficie de materiales ferroeléctricos mediante campos fotovoltaicos o sus gradientes. Las pinzas fotovoltaicas son una herramienta prometedora para atrapar y mover las partículas en la superficie de un material fotovoltaico de una manera controlada. Para aprovechar esta nueva técnica es necesario conocer con precisión el campo eléctrico creado por una iluminación específica en la superficie del cristal y por encima de ella. Este objetivo se ha dividido en una serie de etapas que se describen a continuación. La primera etapa consistió en la modelización del campo fotovoltaico generado por iluminación no homogénea en substratos y guías de onda de acuerdo al modelo de un centro. En la segunda etapa se estudiaron los campos y fuerzas electroforéticas y dielectroforéticas que aparecen sobre la superficie de substratos iluminados inhomogéneamente. En la tercera etapa se estudiaron sus efectos sobre micropartículas y nanopartículas, en particular se estudió el atrapamiento superficial determinando las condiciones que permiten el aprovechamiento como pinzas fotovoltaicas. En la cuarta y última etapa se estudiaron las configuraciones más eficientes en cuanto a resolución espacial. Se trabajó con distintos patrones de iluminación inhomogénea, proponiéndose patrones de iluminación al equipo experimental. Para alcanzar estos objetivos se han desarrollado herramientas de cálculo con las cuales obtenemos temporalmente todas las magnitudes que intervienen en el problema. Con estas herramientas podemos abstraernos de los complicados mecanismos de atrapamiento y a partir de un patrón de luz obtener el atrapamiento. Todo el trabajo realizado se ha llevado a cabo en dos configuraciones del cristal, en corte X ( superficie de atrapamiento paralela al eje óptico) y corte Z ( superficie de atrapamiento perpendicular al eje óptico). Se ha profundizado en la interpretación de las diferencias en los resultados según la configuración del cristal. Todas las simulaciones y experimentos se han realizado utilizando como soporte un mismo material, el niobato de litio, LiNbO3, con el f n de facilitar la comparación de los resultados. Este hecho no ha supuesto una limitación en los resultados pues los modelos no se limitan a este material. Con respecto a la estructura del trabajo, este se divide en tres partes diferenciadas que son: la introducción (I), la modelización del atrapamiento electroforético y dielectroforético (II) y las simulaciones numéricas y comparación con experimentos (III). En la primera parte se fijan las bases sobre las que se sustentarán el resto de las partes. Se describen los efectos electromagnéticos y ópticos a los que se hará referencia en el resto de los capítulos, ya sea por ser necesarios para describir los experimentos o, en otros casos, para dejar constancia de la no aparición de estos efectos para el caso en que nos ocupa y justificar la simplificación que en muchos casos se hace del problema. En esta parte, se describe principalmente el atrapamiento electroforético y dielectroforético, el efecto fotovoltaico y las propiedades del niobato de litio por ser el material que utilizaremos en experimentos y simulaciones. Así mismo, como no debe faltar en ninguna investigación, se ha analizado el state of the art, revisando lo que otros científicos del campo en el que estamos trabajando han realizado y escrito con el fin de que nos sirva de cimiento a la investigación. Con el capítulo 3 finalizamos esta primera parte describiendo las técnicas experimentales que hoy en día se están utilizando en los laboratorios para realizar el atrapamiento de partículas mediante el efecto fotovoltaico, ya que obtendremos ligeras diferencias en los resultados según la técnica de atrapamiento que se utilice. En la parte I I , dedicada a la modelización del atrapamiento, empezaremos con el capítulo 4 donde modelizaremos el campo eléctrico interno de la muestra, para a continuación modelizar el campo eléctrico, los potenciales y las fuerzas externas a la muestra. En capítulo 5 presentaremos un modelo sencillo para comprender el problema que nos aborda, al que llamamos Modelo Estacionario de Separación de Carga. Este modelo da muy buenos resultados a pesar de su sencillez. Pasamos al capítulo 6 donde discretizaremos las ecuaciones que intervienen en la física interna de la muestra mediante el método de las diferencias finitas, desarrollando el Modelo de Distribución de Carga Espacial. Para terminar esta parte, en el capítulo 8 abordamos la programación de las modelizaciones presentadas en los anteriores capítulos con el fn de dotarnos de herramientas para realizar las simulaciones de una manera rápida. En la última parte, III, presentaremos los resultados de las simulaciones numéricas realizadas con las herramientas desarrolladas y comparemos sus resultados con los experimentales. Fácilmente podremos comparar los resultados en las dos configuraciones del cristal, en corte X y corte Z. Finalizaremos con un último capítulo dedicado a las conclusiones, donde resumiremos los resultados que se han ido obteniendo en cada apartado desarrollado y daremos una visión conjunta de la investigación realizada. ABSTRACT The aim of this thesis is the research of the new concept of photovoltaic or optoelectronic tweezers, i.e., trapping, management and manipulation of particles in structures generated by photovoltaic felds or gradients on the surface of ferroelectric materials. Photovoltaic tweezers are a promising tool to trap and move the particles on the surface of a photovoltaic material in a monitored way. To take advantage of this new technique is necessary to know accurately the electric field created by a specifc illumination in the crystal surface and above it. For this purpose, the work was divided into the stages described below. The first stage consisted of modeling the photovoltaic field generated by inhomogeneous illumination in substrates and waveguides according to the one-center model. In the second stage, electrophoretic and dielectrophoretic fields and forces appearing on the surface of substrates and waveguides illuminated inhomogeneously were studied. In the third stage, the study of its effects on microparticles and nanoparticles took place. In particular, the trapping surface was studied identifying the conditions that allow its use as photovoltaic tweezers. In the fourth and fnal stage the most efficient configurations in terms of spatial resolution were studied. Different patterns of inhomogeneous illumination were tested, proposing lightning patterns to the laboratory team. To achieve these objectives calculation tools were developed to get all magnitudes temporarily involved in the problem . With these tools, the complex mechanisms of trapping can be simplified, obtaining the trapping pattern from a light pattern. All research was carried out in two configurations of crystal; in X section (trapping surface parallel to the optical axis) and Z section (trapping surface perpendicular to the optical axis). The differences in the results depending on the configuration of the crystal were deeply studied. All simulations and experiments were made using the same material as support, lithium niobate, LiNbO3, to facilitate the comparison of results. This fact does not mean a limitation in the results since the models are not limited to this material. Regarding the structure of this work, it is divided into three clearly differentiated sections, namely: Introduction (I), Electrophoretic and Dielectrophoretic Capture Modeling (II) and Numerical Simulations and Comparison Experiments (III). The frst section sets the foundations on which the rest of the sections will be based on. Electromagnetic and optical effects that will be referred in the remaining chapters are described, either as being necessary to explain experiments or, in other cases, to note the non-appearance of these effects for the present case and justify the simplification of the problem that is made in many cases. This section mainly describes the electrophoretic and dielectrophoretic trapping, the photovoltaic effect and the properties of lithium niobate as the material to use in experiments and simulations. Likewise, as required in this kind of researches, the state of the art have been analyzed, reviewing what other scientists working in this field have made and written so that serve as a foundation for research. With chapter 3 the first section finalizes describing the experimental techniques that are currently being used in laboratories for trapping particles by the photovoltaic effect, because according to the trapping technique in use we will get slightly different results. The section I I , which is dedicated to the trapping modeling, begins with Chapter 4 where the internal electric field of the sample is modeled, to continue modeling the electric field, potential and forces that are external to the sample. Chapter 5 presents a simple model to understand the problem addressed by us, which is called Steady-State Charge Separation Model. This model gives very good results despite its simplicity. In chapter 6 the equations involved in the internal physics of the sample are discretized by the finite difference method, which is developed in the Spatial Charge Distribution Model. To end this section, chapter 8 is dedicated to program the models presented in the previous chapters in order to provide us with tools to perform simulations in a fast way. In the last section, III, the results of numerical simulations with the developed tools are presented and compared with the experimental results. We can easily compare outcomes in the two configurations of the crystal, in section X and section Z. The final chapter collects the conclusions, summarizing the results that were obtained in previous sections and giving an overview of the research.

A quantitative model for membrane fusion based on low-energy intermediates

The energetics of a fusion pathway is considered, starting from the contact site where two apposed membranes each locally protrude (as “nipples”) toward each other. The equilibrium distance between the tips of the two nipples is determined by a balance of physical forces: repulsion caused by hydration and attraction generated by fusion proteins. The energy to create the initial stalk, caused by bending of cis monolayer leaflets, is much less when the stalk forms between nipples rather than parallel flat membranes. The stalk cannot, however, expand by bending deformations alone, because this would necessitate the creation of a hydrophobic void of prohibitively high energy. But small movements of the lipids out of the plane of their monolayers allow transformation of the stalk into a modified stalk. This intermediate, not previously considered, is a low-energy structure that can reconfigure into a fusion pore via an additional intermediate, the prepore. The lipids of this latter structure are oriented as in a fusion pore, but the bilayer is locally compressed. All membrane rearrangements occur in a discrete local region without creation of an extended hemifusion diaphragm. Importantly, all steps of the proposed pathway are energetically feasible.

Russia's Clandestine War against the United States: The Resurrection of the KGB and Russian Organized Crime Post 9/11

As American leadership has narrowly focused on fighting global terror in Iraq and Afghanistan, the modern version of the KGB, now known as the FSB, has been conducting continuous clandestine warfare operations against the United States. These warfare operations include strategic economic and political partnerships with anti-American entities worldwide and direct embedding of double agents in the US intelligence community. This paper investigates the role of Russia's cultural history leading to the merger of the Russian Federal Security Service (FSB) and Russian Organized Crime (ROC). This paper concludes that the FSB is the most pervasive security threat to the United States and that employing Russian native and heritage speakers of Russian in the US intelligence community compromises US national security.

1794, Triennial catalogues annotated by William Winthrop, 1794-1812.

Leather and marbled hardcover binding. Substantially annotated. The volume consists of pages from the published catalogues pasted into a blank volume. The bulk of the volume is comprised of the printed list of graduate names found in the Triennial Catalogue accompanied by handwritten biographical information, usually a sentence in length. It begins with a handwritten section titled "Settled Ministers (in the first Parish in Cambridge)." The entries generally contain a residence, date of death (abbreviated ob), age of death (abbreviated ae), and professional information. While the 1794 Catalogue comprises the majority of the volume, names were added from Triennial Catalogues through the 1812 edition. An example of an entry, for John Hancock (Harvard AB 1754), reads “Rep. for Boston, Maj. Gen. Militia. Ob. Octo. 8. 1793 AE 57 Son of Rev. John of Brantree [sic]." A March 27, 1798 letter to Judge Richard Cranch (1726-1818) from Jeremy Belknap (1744-1798, Harvard AB 1762) pasted into the back of the volume. Written only two months before his death, Belknap describes his plan to "go thro’ the whole Catalogue of the graduates of Harvard College, & relate all that’s proper to be related." Four leaves of biographical notes for the classes of 1642-1686 towards the beginning of the volume are in a different hand with the note "Rev Dr. Holmes's handwriting."

IV. Essay, undated

The undated handwritten essay begins, "I bles god that I have bene born under the gospel..." The essay is a two page personal exploration into Christianity and belief, including the sentences "I believe that there is one god in three persons father son and holy god. I believe that Jesus Christ is the son of god and that he look upon him our nature and came into the world and dyed a miserable and cruel death for the sins of the elect."

Russia goes on the offensive ahead of the Eastern Partnership summit in Vilnius. OSW Commentary No. 115, 30.09.2013

In recent weeks, Russia has stepped up its efforts to prevent a group of former Soviet republics from tightening their relations with the European Union. The intensification of these efforts comes ahead of the upcoming Eastern Partnership summit, scheduled to take place in Vilnius on 28-29 November. It is expected that during the summit Kiev will sign the EU-Ukraine Association Agreement (AA) initialled in March 2012, including an agreement for a Deep and Comprehensive Free Trade Area (DCFTA). Meanwhile, Moldova, Armenia and Georgia are expected to initial similar documents, effectively accepting their terms and conditions, and paving the way for their official signing in the near future. Moscow has always viewed the relations between the EU and the post-Soviet states as a threat to its own influence in the region. Consequently, any attempts to tighten these relations have been actively opposed by Russia. The EU’s Eastern Partnership programme, launched in 2009, has posed a particular challenge to Moscow’s policies in the region.. Russia responded by rolling out a Eurasian integration project, which began in 2010 with the establishment of the Customs Union of Russia, Kazakhstan and Belarus, and is expected to culminate in the establishment of the Eurasian Economic Union by 2015. Moscow’s overarching objective has been to persuade the countries in the region, especially Ukraine, to adopt an unambiguously pro-Russian geopolitical stance and to join the integration project proposed by the Kremlin. The Russian government hopes that this would permanently place these states in Moscow’s sphere of influence and at the same time prevent them from developing closer relations with Brussels. Russia has regularly taken actions aimed at showcasing the benefits of integration with the Customs Union (particularly, by promising preferential pricing of Russian energy resources) and at the same time it has adopted measures highlighting the pitfalls of retaining a pro-European orientation (mainly by imposing occasional trade sanctions). The upcoming summit in Vilnius, during which Ukraine, Moldova, Armenia and Georgia could lock themselves on to a pro-European course, has spurred Moscow to intensify its efforts to torpedo a successful outcome of the Vilnius meeting, with a view to slowing down or even blocking the possibility of closer cooperation between the EU and the former Soviet republics.

The Putin doctrine: The formation of a conceptual framework for Russian dominance in the post-Soviet area. OSW Commentary No. 131, 28.03.2014

The statements made in recent weeks by Russian officials, and especially President Vladimir Putin, in connection with Moscow’s policy towards Ukraine, may suggest that the emergence of a certain doctrine of Russian foreign and security policy is at hand, especially in relation to the post-Soviet area. Most of the arguments at the core of this doctrine are not new, but recently they have been formulated more openly and in more radical terms. Those arguments concern the role of Russia as the defender of Russian-speaking communities abroad and the guarantor of their rights, as well as specifically understood good neighbourly relations (meaning in fact limited sovereignty) as a precondition that must be met in order for Moscow to recognise the independence and territorial integrity of post-Soviet states. However, the new doctrine also includes arguments which have not been raised before, or have hitherto only been formulated on rare occasions, and which may indicate the future evolution of Russia’s policy. Specifically, this refers to Russia’s use of extralegal categories, such as national interest, truth and justice, to justify its policy, and its recognition of military force as a legitimate instrument to defend its compatriots abroad. This doctrine is effectively an outline of the conceptual foundation for Russian dominance in the post-Soviet area. It offers a justification for the efforts to restore the unity of the ‘Russian nation’ (or more broadly, the Russian-speaking community), within a bloc pursuing close integration (the Eurasian Economic Union), or even within a single state encompassing at least parts of that area. As such, it poses a challenge for the West, which Moscow sees as the main opponent of Russia’s plans to build a new order in Europe (Eurasia) that would undermine the post-Cold War order.

Crimean Tatars after Russia's annexation of the Crimean Peninsula. OSW Commentary No. 141, 30.06.2014

After Russia’s annexation of Crimea, Crimean Tatars face the necessity of working out a modus vivendi to cope with the difficult situation which now confronts them. On the one hand, the desire to remain in their homeland, which they regained after exile in Soviet times, is an imperative encouraging them to accept the status quo, while on the other, the fear of Russia and the strong relations of Crimean Tatar elites with Kyiv would favour opposing the present state of affairs. Another fact pointing in favour of an agreement with Moscow is that Kyiv has not attempted to defend Crimea and has not been active in demanding its return to Ukraine, which has undermined Kyiv’s authority in the eyes of the Tatars. Therefore, the leaders of the Mejlis of Crimean Tatars (the national self-government) act carefully, trying to avoid actions which could be seen as provocative and thus liable to incite retribution. It could be expected that this course of action will continue, although it faces ever greater difficulties in the context of the Russian authorities’ adoption of a strongly anti-Tatar policy, which is likely to evoke more radical attitudes among the Crimean Tatars.

The Pro-Western Turn in Russia's Foreign Policy: Causes, Consequences and Prospects. OSW Point of View, September 2002

From Europe and Poland's point of view, one of the most important recent developments in international politics was the re-orientation of Russia's foreign policy. This paper aims to answer three important questions relating to this issue: 4. When and why did the "pro-Western turn" in the Russian Federation's policy take place? 5. Has it been profitable for Russia? 6. What goals will the Russian policy pursue in the future? An analysis of the last two years in Russia's foreign policy leads to the several conclusions, including those: 5. Clearly, the Russian leaders realise that in the longer term, Russia - in its desire for more influence in the world - will not be able to survive as an independent pole of power in international politics and it will have to join forces with the West (most likely, the European Union). 6. September 11 was not the cause of Russia's pro-Western turn, but rather a catalyst that put the process which started when Vladimir Putin took his office in sharp focus. 7. In the nearest future, this new direction of Russia's foreign policy seems not be challenged by internal opposition in Russia. 8. The "pro-Western turn" proved to be beneficial for Russia, although: d. Russia has not become a strategic ally of the US e. There has been no breakthrough in the relations between Russia and the European Union, and Moscow has not gained any real influence on NATO's important decisions. f. Russia has not become a major decision-maker of international politics. 5. Russia's closing to the West is in Poland's and Europe's interest.

How far do the borders of the west extend? Russian/Polish strategic conflicts in the period 1990-2010. OSW Report, 2010-03-18

From a historical perspective, the last two decades can almost be regarded as a 'golden age' of Polish-Russian relations. This is the first time in several centuries that a sovereign Poland and Russia have been able to develop mutual relations without resorting to force; moreover, they have established a bilateral legal basis and put into practice its provisions on "the inviolability of borders, territorial integrity, non-interference with internal affairs and the nations' right to self-determination. This does not change the fact that since 1990 the atmosphere between the two countries has much more often been chilly and tense. Contrary to the widely-held belief, Polish-Russian conflicts do not stem from genetic Russophobia on the part of Poland, or irrational prejudice on the part of Russia. Their substance is real and concerns strategic issues. At the deepest level, though, this is a dispute about how far the borders of the Western world extend, and about the Russian Federation's sphere of influence. However, it is not a clash between two states; moreover, Poland is certainly not the most important actor in this regard, although due to the historical context and its geographic location, it is one of the countries that lies closest to the 'line of contact', and is therefore particularly entangled in the disagreement.

The "Pro-Western Turn" in Russia's Foreign Policy: Causes, Consequences and Prospects. OSW Point of View (unspecified), September 2002

From Europe and Poland's point of view, one of the most important recent developments in international politics was the re-orientation of Russia's foreign policy. This paper aims to answer three important questions relating to this issue: 1. When and why did the "pro-Western turn" in the Russian Federation's policy take place? 2. Has it been profitable for Russia? 3. What goals will the Russian policy pursue in the future? An analysis of the last two years in Russia's foreign policy leads to the several conclusions, including those: a. Clearly, the Russian leaders realise that in the longer term, Russia - in its desire for more influence in the world - will not be able to survive as an independent pole of power in international politics and it will have to join forces with the West (most likely, the European Union). b. September 11 was not the cause of Russia's pro-Western turn, but rather a catalyst that put the process which started when Vladimir Putin took his office in sharp focus. 7. In the nearest future, this new direction of Russia's foreign policy seems not be challenged by internal opposition in Russia. c. The "pro-Western turn" proved to be beneficial for Russia, although: d. Russia has not become a strategic ally of the US e. There has been no breakthrough in the relations between Russia and the European Union, and Moscow has not gained any real influence on NATO's important decisions. f. Russia has not become a major decision-maker of international politics. g. Russia's closing to the West is in Poland's and Europe's interest.

An inexhaustible source of income? The significance of Belarusian refineries and the outlook for the future. OSW Commentary No. 81, 2012-06-20

Belarus generated a surplus at US$1.9 billion in foreign trade in goods and services in the first four months of 2012 as compared to a deficit of US$2.8 billion for the same timeframe a year earlier. Minsk owes this, its highest positive trade balance since 1991, mainly to a significant increase in exports of petroleum products manufactured by the refineries in Navapolatsk and Mazyr. This is a consequence of the favourable contract for supplies of Russian oil until 2015 which Belarus signed in December last year. This contract has resulted in a de facto resumption of Russia subsidising Belarus. The favourable conditions of Russian oil supplies will allow the Belarusian refineries to remain the driving force of the country’s economy, and the Belarusian government will not allow them to be privatised, which Russia has been seeking for years. The two refineries initiated an ambitious modernisation programme, which is aimed at increasing their output and improving the quality of their production. Owing to this, their share in the market of petroleum products in the region, including on the Polish market, may grow within the next few years.