El efecto Hall consiste en la aparición de un campo eléctrico en un conductor cuando es atravesado por un campo magnético. A este campo eléctrico se le llama campo Hall. Llamado efecto Hall en honor a su descubridor Edwin Duntey Hall Cuando por un material conductor o semiconductor, circula una corriente eléctrica, y estando este mismo material en el seno de un campo magnético, se comprueba que aparece una fuerza magnética en los portadores de carga que los reagrupa dentro del material, esto es, los portadores de carga se desvían y agrupan a un lado del material conductor o semiconductor, apareciendo así un campo eléctrico perpendicular al campo magnético y al propio campo eléctrico generado por la batería (Fm). Este campo eléctrico es el denominado campo Hall (EH), y ligado a él aparece la tensión Hall
Fuente: http://es.wikipedia.org/wiki/The_Hall_Effect
Ronny j duarte C
sábado, 29 de mayo de 2010
El Nanogenerador
Científicos del Colegio de Materiales de la Ciencia ("School of Materials Science") del Instituto de Tecnología de Georgia, acaban de demostrar un generador a nano escala el cual podría entregar electricidad a maquinarias microscópicas al obtenerla del medioambiente que lo rodea, el cual es construido usando una matriz de nanofilamentos de óxido de zinc, de acuerdo a Zhong Lin Wang, Profesor del School of Materials Science"Este es un gran paso hacia la energización de dispositivos a nano escala usando una tecnología económica, adaptable y portátil. Ha existido un gran interés en crear nanodispositivos pero, generalmente, no se piensa en cómo energizarlos. Nuestro nanogenerador nos permite obtener o reciclar la energía de muchas fuentes para entregársela a esos dispositivos."
Fuente: http://foros.gxzone.com/96417-cientificos_crean_un_nanogenerador.html
Ronny j duarte C
Tipos de cuasiparticulas
• Los fonones, modos vibratorios en una estructura cristalina.
• Los excitones, que son la superposición de un electrón y un hueco.
• Los plasmones, conjunto de excitaciones coherentes de un plasma.
• Los polaritones son la mezcla de un fotón y otra de las cuasipartículas de ésta lista.
• Los polarones, que son cuasipartículas cargadas en movimiento que están rodeadas de iones en un material.
• Los magnones son excitaciones coherentes de los espines de los electrones en un material.
ronny j duarte c
• Los excitones, que son la superposición de un electrón y un hueco.
• Los plasmones, conjunto de excitaciones coherentes de un plasma.
• Los polaritones son la mezcla de un fotón y otra de las cuasipartículas de ésta lista.
• Los polarones, que son cuasipartículas cargadas en movimiento que están rodeadas de iones en un material.
• Los magnones son excitaciones coherentes de los espines de los electrones en un material.
ronny j duarte c
Cuasipartícula
En la física de la materia condensada El concepto de cuasipartícula es uno de los más importantes debido a que es una de las pocas formas de simplificar el problema de los muchos cuerpos de mecánica cuántica. Este tipo particular son posibles de identificar en ciertos sistemas físicos en el cual las partículas están interactuando entre si, esta particula se puede cnsiderar como una única partícula moviéndose a través del sistema, rodeada por una nube de otras partículas que se están apartando de su camino o arrastradas por su movimiento
Fuente: http://en.wikipedia.org/wiki/Quasiparticle
Ronny j duarte C
Autorreplicación
Es el proceso por el cual una cosa puede hacer una copia de sí misma. Las células, en ambientes adecuados, se reproducen por división celular. Un ejemplo de ello es el ADN el cual se replica y puede transmitirse a la descendencia durante la reproducción, los virus informáticos se reproducen utilizando el hardware y el software ya presentes en los ordenadores, las Memes se reproducen usando la mente humana y la cultura como su mecanismo de reproducción.
Fuente: http://en.wikipedia.org/wiki/Self-replication
Fuente: http://en.wikipedia.org/wiki/Self-replication
Autoensamblaje
Este fenómeno se puede ser comparado al de la formación de cristales minerales partiendo de sus átomos o iones constitutivos, el autoensamblaje es básicamente la asociación espontánea de moléculas para formar estructuras de gran tamaño, las cuales son llamadas supramoléculas, estas presentan a su vez una interacción entre las moléculas y las estructuras celulares, las estructuras se forman por un número considerable de subunidades de igual o distinta naturaleza molecular, y pueden obtenerse in vitro a partir de sus constituyentes purificados.
Aplicaciones:
En una de las aplicaciones que se le ha dado al autoensamblaje de origen natural se encuentra la fabricación chips de ordenador. En los chips de prueba en los laboratorios, los investigadores han demostrado que, al emplear esta técnica, las señales eléctricas en los chips pueden fluir un 35 por ciento más rápido, o que los chips pueden consumir un 15 por ciento menos energía comparada con los más avanzados que utilizan técnicas convencionales.
Fuente: http://en.wikipedia.org/wiki/Self-assembly
ronny j duarte c
Aplicaciones:
En una de las aplicaciones que se le ha dado al autoensamblaje de origen natural se encuentra la fabricación chips de ordenador. En los chips de prueba en los laboratorios, los investigadores han demostrado que, al emplear esta técnica, las señales eléctricas en los chips pueden fluir un 35 por ciento más rápido, o que los chips pueden consumir un 15 por ciento menos energía comparada con los más avanzados que utilizan técnicas convencionales.
Fuente: http://en.wikipedia.org/wiki/Self-assembly
ronny j duarte c
Ángulo de contacto
Se refiere al ángulo que forma la superficie de un líquido justo en el momento que entra en contacto con un solido, el valor del ángulo depende principalmente de la relación que existe entre las fuerzas adhesivas entre el líquido y el sólido y las fuerzas cohesivas del líquido, por ejemplo si considere una gota líquida en una superficie sólida. Si el líquido se atrae demasiado fuerte a la superficie sólida provocando que la gotita se separará totalmente hacia fuera en la superficie sólida el ángulo del contacto estará cerca de 0°, pero en los sólidos menos fuertemente hidrofílicos tendrán un ángulo del contacto hasta 90°.
Fuente: http://www.worldlingo.com/ma/enwiki/es/Contact_angle
Puntos cuánticos o 'átomos artificiales'
Son nanoestructuras creadas en el laboratorio que miden millonésimas de milímetros, es decir, nanómetros, tienen una diversidad de aplicaciones en distinta áreas como las telecomunicaciones, la computación cuántica, la seguridad o la biomedicina.
Una En la escala macroscópica, los puntos cuánticos pueden tener el aspecto de una simple pastilla plana. Nadie sospecharía que esa sustancia ha sido construida en el laboratorio partiendo de unos pocos átomos, con técnicas que manipulan la materia a escalas de nanómetros. A esas dimensiones el material se convierte en una matriz sobre la que han crecido estructuras, como pirámides o montañas, esas estructuras son los puntos cuánticos. En estos puntos cuánticos los electrones están obligados a permanecer atrapados
Una utilidad de los puntos cuánticos o átomos artificiales seria la visión futurista de nanorobots que patrullan por el torrente sanguíneo sanando células cancerosas o detectando virus, además, a los puntos cuánticos, que tienen más o menos el tamaño de las proteínas, se les puede pegar anticuerpos capaces de reconocer compuestos, células o virus. Muchos investigadores planean usarlos como marcadores de células cancerosas, a las que se podría seguir a medida que se multiplican o migran.
Fuente: <a href="http://www.worldlingo.com/ma/enwiki/es/Contact_angle">http://www.worldlingo.com/ma/enwiki/es/Contact_angle</a>
Una En la escala macroscópica, los puntos cuánticos pueden tener el aspecto de una simple pastilla plana. Nadie sospecharía que esa sustancia ha sido construida en el laboratorio partiendo de unos pocos átomos, con técnicas que manipulan la materia a escalas de nanómetros. A esas dimensiones el material se convierte en una matriz sobre la que han crecido estructuras, como pirámides o montañas, esas estructuras son los puntos cuánticos. En estos puntos cuánticos los electrones están obligados a permanecer atrapados
Una utilidad de los puntos cuánticos o átomos artificiales seria la visión futurista de nanorobots que patrullan por el torrente sanguíneo sanando células cancerosas o detectando virus, además, a los puntos cuánticos, que tienen más o menos el tamaño de las proteínas, se les puede pegar anticuerpos capaces de reconocer compuestos, células o virus. Muchos investigadores planean usarlos como marcadores de células cancerosas, a las que se podría seguir a medida que se multiplican o migran.
Fuente: <a href="http://www.worldlingo.com/ma/enwiki/es/Contact_angle">http://www.worldlingo.com/ma/enwiki/es/Contact_angle</a>
Faces de la física de la materia concentrada
Modificando sus condiciones de temperatura o presión a cualquier sustancia o elemento material, pueden obtenerse distintos estados o fases, denominados estados de agregación de la materia, estos estados tienen propiedades y características diferentes, y aunque los más conocidos son cuatro: fase solida, fase liquida, fase gaseosa y face plasmática.
La fase solida: calificados generalmente como duros y resistentes, y en ellos las fuerzas de atracción son mayores que las de repulsión, se presentan como cuerpos de forma compacta.
Fase liquida: tienen la capacidad de fluir y adaptarse a la forma del recipiente que lo contiene
Fase gaseosa: Las moléculas del gas se encuentran prácticamente libres de manera que tienen la capacidad de distribuirse por todo el espacio en el cual son contenidos.
Fase plasmática: Es un estado parecido al gas pero formado por electrones y cationes (iones con carga positiva), separados entre sí y libres, por eso es un excelente conductor. Un ejemplo muy claro es el sol.
La fase solida: calificados generalmente como duros y resistentes, y en ellos las fuerzas de atracción son mayores que las de repulsión, se presentan como cuerpos de forma compacta.
Fase liquida: tienen la capacidad de fluir y adaptarse a la forma del recipiente que lo contiene
Fase gaseosa: Las moléculas del gas se encuentran prácticamente libres de manera que tienen la capacidad de distribuirse por todo el espacio en el cual son contenidos.
Fase plasmática: Es un estado parecido al gas pero formado por electrones y cationes (iones con carga positiva), separados entre sí y libres, por eso es un excelente conductor. Un ejemplo muy claro es el sol.
¿Que es la física de la materia condensada?
La física de la materia condensada se ocupa de las características físicas macroscópicas de la materia. La física de la materia concentrada se refiere particularmente a las faces condensadas. Los ejemplos más comunes de la materia condensada son los sólidos y los líquidos. La Física de la Materia Condensada se considera como el campo más extenso de la física contemporánea. Como reseña histórica se puede señalar que la física de la materia condensada nació a partir de la física del estado sólido, que ahora es considerado como uno de sus subcampos principales. El término "física condensada de la materia" fue acuñado, al parecer, por Philip Anderson. El nombre física condensada se debe porque muchos de los conceptos y técnicas desarrollados para estudiar sólidos se aplican también a sistemas fluidos.
fuente: http://en.wikipedia.org/wiki/Condensed_matter_physics
fuente: http://en.wikipedia.org/wiki/Condensed_matter_physics
Statistical Physics and Condensed Matter
Non-equilibrium & Disordered Systems
In a disordered system, because of the presence of impurities or of other forms of structural disorder, the interactions between the degrees of freedom are given by frozen random variables. At low temperature, certain disordered systems, such as spin glasses, display slow dynamics which is due to a complex energy landscape with many metastable states. Such slow dynamics prevent the system from reaching a Boltzmann thermal equilibrium during the time it is observed. It thus keeps a certain memory of its history: we say that it ages. During the last decade, numerous works have been devoted to non-equilibrium systems: the structure of excitations and chaos in spin glasses, the violation of the fluctuation-dissipation theorem, the concept of effective temperature, the study of exactly soluble kinetic models, the statistics of metastable states, the extrema and saddle points of random energy landscapes, etc.
Growth of ferromagnetic domains.
Quantum Systems & Condensed Matter Physics
Condensed matter physics displays remarkable quantum phenomena: superconductivity, the fractional Hall effect, Bose-Einstein condensation, the Kondo effect... Field theory can be used to study the behavior of real systems: vortex models for the description of superconducting properties of mesoscopic systems, as well as Laughlin quasi-particles carrying fractional electric charge; dimer lattice models for the description of incompressible quantum liquids with topological order and fractional excitations. Supersymmetric models can describe phase diagrams of certain strongly correlated electron systems in which both fermionic metallic phases and bosonic magnetic phases coexist (e.g. a Kondo impurity in a metal). Various out-of-equilibrium quantum systems are also studied, ranging from the formation of a Bose-Einstein condensate to the dynamics of quantum dots in which a small number of electrons are trapped by potential barriers.
Hofstadter spectrum of an electron on a frustrated lattice
Soft Matter & Biological Systems
Polymers are physical realizations of stochastic processes such as Brownian motion or self-avoiding random walks. Certain universal aspects of membranes (flexible films, biological membranes) are related to random geometries which are studied in string theory and quantum gravity. When the objects are charged (poly-electrolytes, charged membranes) or when they possess internal degrees of freedom, their physical and geometric properties are deeply modified: new phases appear. The physics of disordered systems governs the complex interactions between chemically different monomers in biological polymers. One can study this way the denaturation of DNA or the folding of proteins and of RNA. The classification of the possible forms of the latter can be made with the help of topological tools (the Euler characteristic or the genus). At a more macroscopic scale, the interactions of proteins and genes are modeled with the help of biological lattices, and the study of their connectivity properties yields a better understanding of cellular metabolism.
Protein interaction with an RNA molecule
Fluid Dynamics
The study of hydrodynamic instabilities allows us to understand the mechanisms which can lead to turbulence. Thermal convection is a typical instability present in our environment. Alone, or coupled to other mechanisms, it creates motion in the atmosphere and in oceans. The modeling of the dynamo effect aims at understanding of the generation and the maintenance of the magnetic field inside the earth, the planets and stars. Shearing flow modes, the instabilities of which are modified by rotation or stratification, are studied in relation to laboratory experiments and as possible sources of turbulence in accretion disks and in astrophysics
Magnetic field induced by the dynamo effect in a cylinder
Asignatura: CRF
Dirección: http://ipht.cea.fr/en/Phocea-SPhT/ast_visu_spht.php?id_ast=233
Ver Blog: http://franklinqcrf.blogspot.com/
Condensed Matter Physics
Solid materials are an aspect of physics which pervade everyday life. Condensed Matter Physics (CMP) has been at the heart of all the developments in materials which have taken place in the past 100 years and which have transformed our society. A fundamental understanding of the underlying physical properties allows the tailoring of materials with specified properties and functionality. The recently developed capability to design and probe collections of condensed atoms and molecules from the mesoscale (~microns) down to nanoscale (~nm) size scales is set to become one of the key technologies of the 21st century. On these length-scales, the bulk properties of matter give way to altered behaviour due to quantum mechanical interactions. Research in CMP is increasingly critical as industrial components such as transistors for computer memories, and magnetic particles for hard disks, are pushed smaller and faster, where they encounter quantum effects. Basic research in condensed matter physics is the key to future discoveries which can overcome these fundamental quantum limitations.
The current research interests in the group fall into the following areas:
•Nanoscale and Surface Physics
•Cellular and Molecular Biophysics
•Magnetism
•Nanoscale and Surface Physics
•Cellular and Molecular Biophysics
•Magnetism
Nombre: Franklin J. Quintero C.
Asignatura: CRF
Direccion: http://www.liv.ac.uk/physics/cmp/
Ver Blog: http://franklinqcrf.blogspot.com/
Theoretical Condensed Matter Physics
What makes Condensed Matter Physics a fascinating subject is the fact that a wide range of physical phenomena and properties of matter emerge from the relatively simple interaction laws that govern the behavior of electrons and atoms - the basic building blocks of the "ordinary" matter around us. Can we understand the variety of emergent phases and the transitions between them? Which of the properties are peculiar to the microscopic details of interactions and which are universal for wide classes of physical systems? How does disorder, surfaces, confining geometry (e.g. nanostructures) affect these properties? These are some of the fundamental questions that condensed matter theory addresses
The Condensed Matter Theory Group at the UCR Department of Physics is represented by Professors Vivek Aji, Leonid Pryadko, Kirill Shtengel, Shan-Wen Tsai, Chandra Varma and Roya Zandi. The research interests of the group include both "hard" and "soft" condensed matter physics. The former category refers to the studies of quantum phenomena in condensed matter, particularly in the strongly correlated systems. The research topics include superconductivity, quantum phase transitions, the physics of novel materials and nanostructures, and quantum computation. The soft condensed matter physics includes classical statistical mechanics and its applications to the physics of polymers and biological systems.
The interests of the members of the group are briefly described below:
Professor Leonid Pryadko is interested the physics of disordered and strongly-correlated, mostly low-dimensional systems. This includes two-dimensional electron systems (2DES's) in semiconductors and on the surface of liquid Helium, both in zero magnetic field and under the conditions of quantum Hall effect, layered high-transition temperature (high-Tc) cuprate superconductors and related materials, various one-dimensional systems (self-organized quasi-1D systems like stripes in cuprates, chiral edge channels in quantum Hall samples, quasi-one-dimensional organics, carbon nanotubes, etc), "zero"-dimensional systems (quantum dots, tunneling junctions, Kondo spins, etc). His most recent projects include quantum coherent control and quantum computation, high-temperature superconductivity, cold atoms in optical lattices, and transport phenomena in disordered correlated systems.
Professor Kirill Shtengel's current research involves studying solid state systems with frustration, both classical and quantum. Effects of frustration tend to suppress conventional ordered phases. This, in turn, may give way to the appearance of new, unconventional phases at low enough temperatures. One fascinating possibility is so-called fractionalized phases. As the name suggests, the excitations in such systems carry fractions of "normal" particles' charge and spin and have other unusual properties, such as fractional exchange statistics which makes them very attractive candidates for some interesting schemes of fault-tolerant quantum computation. He is also interested in statistical mechanics of frustrated systems.
Professor Shan-Wen Tsai's research focuses on such topics as properties of novel materials and nanostructures where the presence of strong interactions and disorder lead to a wide range of macroscopic quantum effects. Current and recent projects involve investigation of the electronic properties of a d-wave superconducting quantum wire, study of the behavior of correlated electrons in a high magnetic field and the magnetotransport properties of graphite and bismuth, development of a renormalization-group method for studying interacting electrons coupled to bosonic excitations such as phonons and its application to electron-phonon systems in one and two-dimensions, and to Bose-Fermi mixtures in artificial lattices of cold atoms.
Professor Roya Zandi is doing research in the fields of statistical mechanics and soft condensed matter physics, which has given her the opportunity to work in broad interdisciplinary areas: she has conducted research in the statistical mechanics of both neutral and charged polymers, the dynamics of the passage of polymers through membrane pores, knot theory and Casimir forces in superfluid films. Her most recent research focuses on statistical mechanics of virus assembly, both equilibrium and nonequilibrium aspects. She has investigated the physical basis for the icosahedral structures observed in spherical viruses. She is currently examining the role of the genome (RNA or DNA) in the equilibrium viral structure and in the dynamics of the self-assembly process.
Nombre: Franklin J. Quintero C.
Asignatura: CRF
Dirección: http://www.physics.ucr.edu/research/tcmp.html
Ver Blog: http://franklinqcrf.blogspot.com/
Condensed matter physics
Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter. In particular, it is concerned with the "condensed" phases that appear whenever the number of constituents in a system is extremely large and the interactions between the constituents are strong. The most familiar examples of condensed phases are solids and liquids, which arise from the electromagnetic forces between atoms. More exotic condensed phases include the superconducting phase exhibited by certain materials at low temperature, the ferromagnetic and antiferromagnetic phases of spins on atomic lattices, and the Bose-Einstein condensate found in certain ultracold atomic systems.
The aim of condensed matter physics is to understand the behavior of these phases by using well-established physical laws, in particular those of quantum mechanics, electromagnetism and statistical mechanics. The diversity of systems and phenomena available for study makes condensed matter physics by far the largest field of contemporary physics. By one estimate,[citation needed] one third of all United States physicists identify themselves as condensed matter physicists. The field has a large overlap with chemistry, materials science, and nanotechnology, and there are close connections with the related fields of atomic physics and biophysics. Theoretical condensed matter physics also shares many important concepts and techniques with theoretical particle and nuclear physics.
Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields. The name of the field was apparently[citation needed] coined in 1967 by Philip Anderson and Volker Heine when they renamed their research group in the Cavendish Laboratory of the University of Cambridge from "Solid-State Theory" to "Theory of Condensed Matter". In 1978, the Division of Solid State Physics at the American Physical Society was renamed as the Division of Condensed Matter Physics.[1] One of the reasons for this change is that many of the concepts and techniques developed for studying solids can also be applied to fluid systems. For instance, the conduction electrons in an electrical conductor form a Fermi liquid, with similar properties to conventional liquids made up of atoms or molecules. Even the phenomenon of superconductivity, in which the quantum-mechanical properties of the electrons lead to collective behavior fundamentally different from that of a classical fluid, is closely related to the superfluid phase of liquid helium.
Condensed matter physics
Nombre: Franklin J. Quintero C.
Asignatura: CRF
Dirección: http://www.answers.com/topic/condensed-matter-physics
Ver Blog: http://franklinqcrf.blogspot.com/
State of matter
States of matter are the distinct forms that different phases of matter take on. Historically, the distinction is made based on qualitative differences in bulk properties. Solid is the state in which matter maintains a fixed volume and shape; liquid is the state in which matter maintains a fixed volume but adapts to the shape of its container; and gas is the state in which matter expands to occupy whatever volume is available.
More recently, distinctions between states have been based on differences in molecular interrelationships. Solid is the state in which intermolecular attractions keep the molecules in fixed spatial relationships. Liquid is the state in which intermolecular attractions keep molecules in proximity, but do not keep the molecules in fixed relationships. Gas is that state in which the molecules are comparatively separated and intermolecular attractions have relatively little effect on their respective motions. Plasma is a highly ionized gas that occurs at high temperatures. The intermolecular forces created by ionic attractions and repulsions give these compositions distinct properties, for which reason plasma is described as a fourth state of matter.
Forms of matter that are not composed of molecules and are organized by different forces can also be considered different states of matter. Fermionic condensate and the quark–gluon plasma are examples.
Although solid, gas and liquid are the most common states of matter on Earth, much of the baryonic matter of universe is in the form of hot plasma, both as rarefied interstellar medium and as dense stars.
States of matter may also be defined in terms of phase transitions. A phase transition indicates a change in structure and can be recognized by an abrupt change in properties. By this definition, a distinct state of matter is any set of states distinguished from any other set of states by a phase transition. Water can be said to have several distinct solid states. The appearance of superconductivity is associated with a phase transition, so there are superconductive states. Likewise, liquid crystal states and ferromagnetic states are demarcated by phase transitions and have distinctive properties.
This diagram shows the nomenclature for the different phase transitions.
Nombre: Franklin J. Quintero C.
Asignatura: CRF
Dirección: http://www.answers.com/topic/state-of-matter-1
Ver Blog: http://franklinqcrf.blogspot.com/
Liquid Crystals
The focus of our research activities is the physical chemistry of the liquid-crystalline state of matter. Classical topics of physical chemistry like the relation between structure and properties, thermodynamics and kinetics of phase transitions, electrical and optical properties of matter as well as structure and dynamics of low-dimensional and biological systems can be studied by means of liquid-crystalline systems in an excellent way. The following sections should deliver introductory insight into the research field of liquid crystals and its technical application.
Liquid crystals are liquids with long-range orientational order (anisotropic fluids), which combine the fluidity of ordinary liquids with the interesting electrical and optical properties of crystalline solids. They are observed as thermodynamically stable phases between the crystalline solid and ordinary isotropic liquid states (thermotropic liquid crystals). Liquid-crystalline structures result from self-organization of strongly anisometric molecules (Figure 1): The majority of liquid crystals are formed by rod-like (calamitic) molecules with a length of approximately 20 to 40 Ångströms. However disc-like (discotic) molecules, such as Phthalocyanincomplexes, Phospholipids as well as rigid DNA-double-helices also form liquid-crystalline systems.
Figure 1: Example of the self-organization of anisometric molecules in liquid-crystalline phases. On the left: rod-like molecules form a nematic liquid, in which the longitudinal axes of the molecules are parallelly aligned to a common preferred direction ("director"). On the right: disc-like (discotic) molecules arrange to molecule-stacks (columns), in which the longitudinal axes are also aligned parallely to the director. As a result of their orientational order, liquid crystals exhibit anisotropic physical properties, just like crystals.
Figure 2: Polarizing microscope picture of the formation of a nematic liquid crystal upon cooling out of the isotropic melt. Because of its optical anisotropy (birefringence) the liquid crystal appears bright between the crossed polarizers of the microscope. In the black areas (left side) we still have an optical isotropic melt.
A fascinating and characteristic feature of liquid-crystalline systems is, that they change their molecular and supermolecular organization drastically as an effect of very small external perturbations: The molecules in liquid crystal displays for instance are reoriented by relatively weak electrical fields. If one dissolves a small amount of chiral molecules in an achiral liquid-crystalline host phase, this results in remarkable macroscopic chirality effects, ranging from helical superstructures to the appearence of ferroelectricity. For this and other reasons liquid crystals - combined with polymers and colloids - are therefore summed up under the generic term ''Soft Matter" and treated under the branch of physical chemistry of condensed matter.
Figure 3: In liquid-crystalline systems elastic deformations are already induced by relatively weak perturbations (e.g. an electric field E). The scale of length of those deformations lies within the range of optical wave lenghts.
Figure 4: Schematic classification of the branch of "liquid crystals" into the physical chemistry of condensed matter.
Nombre: Franklin J. Quintero C.
Asignatura: CRF
Dirección:http://www.ipc.unistuttgart.de/~giesselm/AG_Giesselmann/Forschung/Fluessigkristalle/Fluessigkristalle.html
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Condensed Matter Physics
Condensed matter physics is the study of materials in the solid or liquid state, including their structure and mechanical, electrical, magnetic, thermal, optical and chemical properties. In addition to presenting rich and fascinating questions about the physical world, it is an area of physics with many real-world applications in such areas as microelectronics, information storage and communication, chemistry and the development and use of new materials. Students with strong backgrounds in condensed matter physics are often well qualified for research and engineering positions in industry, as well as for academic careers.
Experimental condensed matter physics at Tufts focuses on crystal structure and phase transitions in polymers and biopolymers, interactions of atoms and molecules with metal surfaces, ultrafast nonlinear optics and photonics, and the study of nanometer-scale biophysical systems. On-site facilities are housed in the modern Science and Technology Center, and include X-ray diffractometers, infrared spectrometers, ultrahigh vacuum surface analysis equipment, femtosecond lasers, scanning calorimeters, and atomic force microscopes. Researchers at Tufts also collaborate widely, including using facilities at Brookhaven National Laboratory.
Theoretical work at Tufts is concerned with the dynamic behavior of spin systems, including transitions caused both by thermally activated processes and by quantum tunneling.
Nombre: Franklin J. Quintero C.
Asignatura: CRF
Dirección: https://wikis.uit.tufts.edu/confluence/display/cmp/Home
Ver Blog: http://franklinqcrf.blogspot.com/
Experimental Polymer Physics
The polymer physics group conducts research on thermal and electrical properties of macromolecules in relation to structure. Macromolecules exhibit a wide variety of organizational structures, including disordered liquid phases, thermotropic liquid crystals, and true three-dimensional crystals. The liquid-to-solid state phase transformations in liquid crystalline polymers and polymer melts is investigated using dielectric relaxation spectroscopy, and wide and small angle X-ray scattering. Our research group travels to the Brookhaven National Laboratory several times a year to conduct scattering experiments using the high intensity X-radiation at the National Synchrotron Light Source.
In-house research facilities in the polymer physics group at Tufts include systems for measuring spatially resolved optical retardance, electric dipole relaxation, heat capacity and thermal properties. Wide angle X-ray diffraction and molecular modeling capabilties also exist in the polymer physics group. One fundamental problem we are studying is the kinetics of phase transformation in polymers, and the competition between ordering (eg., isotropic-to-nematic-to-crystal) and phase separation under the influence of external fields. In another project in the nano-technology area, we are investigating the effects of restricted dimensionality on the phase transformation kinetics in crystallizable thin films. The research in this group is interdisciplinary in nature, combining solid state physics with materials science.
The polymer physics group collaborates with researchers in the Biomedical Engineering Dept. at Tufts, and has shared facilities including the Biomaterials Characterization Laboratory. We are studying silk and silk-inspired diblock copolymers. Our model system consists of protein sequences found in native spider dragline silk and we use genetic variants of these sequences to provide the copolymer building blocks in order to assess relationships between block sequence and morphological and structural features. Target applications included drug delivery and medical implants based on silks which are biocompatible.
Recent students graduating with the Ph. D. from our group have been employed at Exxon Research Center, Michelin Americas Research Center, Assumption College, and Cisco Systems.
Nombre: Franklin J. Quintero C.
Asignatura: CRFDirección: https://wikis.uit.tufts.edu/confluence/display/cmp/Polymer+Physics
Ver Blog: http://franklinqcrf.blogspot.com/
The Inelastic Neutron Scattering Spectrum Of Nicotinic Acid And Its Assignment By Solid-State Density Functional Theory
Accepted in Chemical Physics Letters. What began as a reasonably straightforward inelastic neutron scattering (INS) assignment was expanded upon reviewer request to include an analysis of the potential for in-cell nicotinic acid (or niacin, depending on who you ask. Not to be confused with this Niacin, which would be another post altogether) prototropic tautomerization (technically, one might consider this just proton migration along the chain of the nicotinic acid molecules in the solid-state, which might just be more supported as, providing the punch line early, proton migration does not seem to occur in this system), a point that was mentioned in the paper as a possibility within the crystal cell but not originally examined as part of the spectral assignment. In the crystal cell picture shown below, tautomerization would result in proton H5 migrating to N', yielding a chain (if it propagated down the entire one-dimensional chain of nicotinic acid molecules in the solid-state) of zwitterions (molecules with both positive and negative charges on the covalent framework). Anyone with experience in the solid-state study of amino acids knows that zwitterions are not only stable species in the solid-state, but they can also the dominant species in the solid-state, as ionic interactions and the dipole alignment that results from the alignment of, in this case, zwitterions, can yield greater stability than the neutral species, where only hydrogen bonding and dispersions forces occur in the crystal packing arrangement.
The inelastic neutron scattering assignment by solid-state density functional theory (DFT) strongly supports that, at the 25 K temperature of the neutron experiment, the crystal cell is of the neutral, non-zwitterionic form (as shown below, which labels the possible arrangements of hydrogens in the Z=4 crystal cell). Furthermore, despite the existence of several potentially stable proton arrangements in the crystal cell (the three additional forms shown below), the nicotinic acid crystal cell seems to prefer the neutral form even through room temperature. Fortunately, previous studies using other spectroscopic methods seem to agree. As has been the case for the vast majority of all of the previous INS studies, the solid-state DFT calculations were performed with DMol3 and the INS simulated spectra generated with Dr. A. J. Ramirez-Cuesta's most excellent aClimax program.
Matthew R. Hudson, Damian G. Allis, and Bruce S. Hudson
Department of Chemistry, 1-014 Center for Science and Technology, Syracuse University, Syracuse, NY 13244-4100, USA
Keywords: nicotinic acid, niacin, vitamin B3, inelastic neutron scattering spectroscopy, solid-state density functional theory
Abstract: The 25 K inelastic neutron scattering (INS) spectrum of nicotinic acid has been measured and assigned by solid-state density functional theory (DFT). Vibrational mode energies involving the carboxylic acid proton are found to be significantly altered due to intermolecular hydrogen-bonding. There is good overall agreement between experiment and simulation in all regions of the spectrum, with identified deviations considered in detail by spectral region: phonon (25 – 300 cm-1), molecular (300 – 1600 cm-1), and high-frequency (>2000 cm-1). The relative energies, geometries, and vibrational spectra associated with hypothesized tautomerization in the solid-state have also been investigated.
Nombre: Franklin J. Quintero C.
Asignatura: CRFDirección: http://www.somewhereville.com/?p=563
Ver Blog: http://franklinqcrf.blogspot.com/
What is theoretical condensed matter physics, and why is it interesting?
Condensed Matter Physics is the study of the structure and behaviour of the matter that makes up most of the usual (and unusual) stuff that surrounds us every day. It is not the study of the very small (particle theory) or of the very large (astrophysics and cosmology) but of the things in between. It takes for granted that most of these are made up of electrons and nuclei interacting according to the well-established laws of electromagnetism and quantum mechanics, and tries to explain their properties.
What makes it an interesting and fundamental branch of physics? It turns out that large assemblies of electrons and nuclei in a condensed state often exhibit so-called cooperative behaviour which is quite different from that of the individual parts. Superconductivity, for example. And the study of this new behaviour requires theoretical methods which can be every bit as sophisticated as those of particle theory or relativity. In fact, mathematically they often have a lot in common. But while there is (we hope) only one `theory of everything' which describes the building blocks of matter, at intermediate scales there are any number of `effective' theories which account for the wealth of phenomena which we observe. Thus the subject is very diverse.
In condensed matter physics, experiment and observation play a key role. As compared with particle physics, most experiments are much easier to carry out, generally much more precise, and take far less time. So the link between experiment and theory is that much stronger.
Condensed matter physics is both fast-moving and outward looking. Developments come from fresh theoretical ideas, from ideas transplanted to a novel context, and from (sometimes serendipitous) experimental discoveries. Some of these developments involve topics at the interface between condensed matter physics and other fields - examples include atomic physics and biology.
Condensed matter physics is also very important because it often uncovers phenomena which are technologically important. As well as solid state devices, the whole field of polymers, complex fluids and other so-called `soft' condensed matter systems has all sorts of applications. More recently, the methods which condensed matter theorists use to study interacting systems with many degrees of freedom have been used to attack problems in such diverse fields as economics and the life sciences.
As a study in itself, as well as being a sound basis for any career where quantitative skills and problem-solving are at a premium, an apprenticeship in condensed matter theory is fascinating and invaluable.
Nombre: Franklin J. Quintero C.
Asignatura: CRFDirección: http://www-thphys.physics.ox.ac.uk/research/condensedmatter/intro.php
Ver Blog: http://franklinqcrf.blogspot.com/
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