Inverse photoemission in strongly correlated electron systems

Based on exact results for small clusters of 2D t-J model we demonstrate the existence of several distinct `channels' in its inverse photoemission (IPES) spectrum. Hole-like quasiparticles can either be annihilated completely, or leave behind a variable number of spin excitations, which formed the `dressing cloud' of the annihilated hole. In the physical parameter regime the latter processes carry the bulk of IPES weight and although the Fermi surface takes the form of hole pockets, the distribution of spectal weight including these `magnon-bands' in the IPES spectrum is reminiscent of free electrons. The emerging scenario for Fermiology and spectral weight distribution is shown to be consistent with photoemission, inverse photemission and de Haas--van Alphen experiments on cuprate superconductors.Comment: Revtex file, 4 PRB pages + three figures appended as uu-encoded postscript. Hardcopies of figures (or the entire manuscript) can also be obtained by e-mail request to: [email protected]

Temperature dependent band structure of the Kondo insulator

We present a Qantum Monte Carlo (QMC) study of the temperature dependent dynamics of the Kondo insulator. Working at the so-called symmetrical point allows to perform minus-sign free QMC simulations and thus reach temperatures of less than 1% of the conduction electron bandwidth. Study of the temperature dependence of the single particle Green's function and dynamical spin correlation function shows a surprisingly intricate low temperature band structure and gives evidence for two characteristic temperatures, which we identify with the Kondo and coherence temperature, respectively. In particular, the data show a temperature induced metal-insulator transition at the coherence temperature.Comment: RevTex-file, 4 PRB pages with 4 eps figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]

Hole photoproduction in insulating copper oxide

Basing on t-J model we calculate the k-dependence of a single hole photoproduction probability for CuO2 plane at zero doping. We also discuss the radiation of spin-waves which can substantially deform the shape of photoemission spectra.Comment: latex 8 pages, 3 figure

Composici?n corporal y condici?n f?sica en los estudiantes de educaci?n b?sica secundaria y media de la Instituci?n Educativa San Antonio del municipio de Cunday Tolima

140 p. Recurso Electr?nicoIntroducci?n: La composici?n corporal y otros componentes de la condici?n f?sica han demostrado ser importantes indicadores de salud. Es por ello que se plantea el siguiente objetivo: Analizar los niveles de composici?n corporal y condici?n f?sica en los estudiantes de educaci?n b?sica secundaria y media de la instituci?n educativa San Antonio del municipio de Cunday-Tolima. Adem?s fueron utilizados los siguientes materiales y m?todos: participaron 323 estudiantes con una muestra de 165 (hombres: 82 y mujeres: 83), con un rango de edad de 11 a 18 a?os. Se aplicaron las pruebas f?sicas de la bater?a Alpha Fitness Test, versi?n extendida. Se evalu? ?ndice de masa corporal (IMC), Per?metro de Cintura y Porcentaje de Grasa. Dando como Resultados: Se encontraron diferencias de g?nero en las variables estudiadas, con mayor IMC y porcentaje graso en los ni?os y adolescentes (20,9 kg/m2 vs. 19,6kg/ m2 y 12,9 % vs 23 %, respectivamente); tambi?n, el per?metro de cintura fue mayor en los hombres (64,8 cm vs. 62,5 cm), ellos presentaron niveles m?s elevados de masa corporal, porcentaje de grasa y per?metro de cintura, con diferencias significativas (p<0.05). Adem?s alcanzaron niveles m?s elevados para la capacidad aer?bica, el salto con pies juntos y la velocidad, con diferencias estad?sticamente significativas en el VO2m?x y el salto (p<0.05). Se hallaron correlaciones medias y considerables entre algunas variables estudiadas. Lo que permiti? llegar a las siguientes conclusiones: El 73,3% (n1=121) de los estudiantes poseen peso normal, seguido por el 25,5% (n2=42) con riesgo de sobrepeso por ?ltimo, s?lo el 1,2% (n3=2) de los escolares tienen sobrepeso. Los hombres muestran mejores niveles de capacidad aer?bica, capacidad musculo-esquel?tica y capacidad motora. Palabras Claves: Composici?n Corporal, Capacidades F?sicas Condicionales, Instituci?n Educativa.Introduction: The body insertion and other components of the physical condition are important witnesses of health. That is why the following objective is posed: To analyze the levels of body composition and physical condition in the secondary and middle school students of the San Antonio educational institution in the municipality of Cunday-Tolima. In addition, the following materials and methods were used: 323 students participated with a sample of 165 (men: 82 and women: 83), with an age range of 11 to 18 years. The physical tests of the Alpha Fitness Test battery, extended version, were applied. Body mass index (BMI), waist circumference and percentage of fat were evaluated. Giving as Results: Gender differences were found in the variables studied, with higher BMI and fat percentage in children and adolescents (20.9 kg / m2 vs. 19.6 kg / m2 and 12.9% vs 23%, respectively); also, the waist circumference was higher in men (64.8 cm vs. 62.5 cm), they presented higher levels of body mass, fat percentage and waist circumference, with significant differences (p<0.05). They also reached higher levels for aerobic capacity, jumping with feet together and speed, with statistically significant differences in VO2max and jump (p<0.05). Mean and considerable correlations were found between some variables studied. What allowed to reach the following conclusions: 73.3% (n1 = 121) of the students possess but normal, followed by 25.5% (n2 = 42) with risk of overweight last, only 1.2% (n3 = 2) of Schoolchildren are overweight. Men show better levels of aerobic capacity, musculoskeletal capacity and motor ability. Keywords: Corporal Composition, Physical Conditional Capacities, Educational Institution

Anomalous low doping phase of the Hubbard model

We present results of a systematic Quantum-Monte-Carlo study for the single-band Hubbard model. Thereby we evaluated single-particle spectra (PES & IPES), two-particle spectra (spin & density correlation functions), and the dynamical correlation function of suitably defined diagnostic operators, all as a function of temperature and hole doping. The results allow to identify different physical regimes. Near half-filling we find an anomalous `Hubbard-I phase', where the band structure is, up to some minor modifications, consistent with the Hubbard-I predictions. At lower temperatures, where the spin response becomes sharp, additional dispersionless `bands' emerge due to the dressing of electrons/holes with spin excitatons. We present a simple phenomenological fit which reproduces the band structure of the insulator quantitatively. The Fermi surface volume in the low doping phase, as derived from the single-particle spectral function, is not consistent with the Luttinger theorem, but qualitatively in agreement with the predictions of the Hubbard-I approximation. The anomalous phase extends up to a hole concentration of 15%, i.e. the underdoped region in the phase diagram of high-T_c superconductors. We also investigate the nature of the magnetic ordering transition in the single particle spectra. We show that the transition to an SDW-like band structure is not accomplished by the formation of any resolvable `precursor bands', but rather by a (spectroscopically invisible) band of spin 3/2 quasiparticles. We discuss implications for the `remnant Fermi surface' in insulating cuprate compounds and the shadow bands in the doped materials.Comment: RevTex-file, 20 PRB pages, 16 figures included partially as gif. A full ps-version including ps-figures can be found at http://theorie.physik.uni-wuerzburg.de/~eder/condmat.ps.gz Hardcopies of figures (or the entire manuscript) can also be obtained by e-mail request to: [email protected]

Dynamics of spin ladders

We derive an approximate theory for Heisenberg spin ladders with two legs by mapping the spin dynamics onto the problem of hard-core `bond-Bosons'. The parameters of the Bosonic Hamiltonian are obtained by matching anomalous Green's functions to Lanczos results and we find evidence for a strong renormalization due to quantum fluctuations. Various dynamical spin correlation functions are calculated and found to be in good agreement with Lanczos results. We then enlarge the effective Hamiltonian to describe the coupling of the bond-Bosons to a single hole injected into the system and treat the hole-dynamics within the `rainbow-diagram' approximation by Schmidt-Rink et. al. Theoretical predictions for the single hole spectral function are obtained and found to be in good agreement with Lanczos results.Comment: RevTex-file, 10 PRB pages with 7 eps files. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]

Assessing metric structures on GPGPU environments

Similarity search consists on retrieving objects within a database that are similar or relevant to a particular query. It is a topic of great interest to scientific community because of its many fields of application, such as searching for words and images on the World Wide Web, pattern recognition, detection of plagiarism, multimedia databases, among others. It is modeled through metric spaces, in which objects are represented in a black-box that contains only the distance between objects; calculating the distance function is costly and search systems operate at a high query rate. Metrical structures have been developed to optimize this process; such structures work as indexes and preprocess data to decrease the distance evaluations during the search. Processing large volumes of data makes unfeasible the use of such structures without using parallel processing environments. Technologies based on multi- CPU and GPU architectures are among the most force due to its costs and performance.XV Workshop de Procesamiento Distribuido y Paralelo (WPDP)Red de Universidades con Carreras en Informática (RedUNCI

Implementation and Performance Analysis of a Low Resolution OFDM System Prototype With Low Cost Hardware

The present work focus on the implementation and analyze of performance of a low-resolution OFDM system prototype with low-cost hardware. A software defined radio (SDR) system was chosen in this implementation due to its various advantages over a traditional radio system. Among the options of SDR devices available, the use of universal software radio peripherals (USRP) was avoided due to its high cost, despite its popularity in this field of research. Alternatively, a combination of two low-cost SDRs, "Hackrf One" and "RTL- SDR Blog V3" with the GNU Radio, a popular, free and open source radio software, were used. Thus, it was possible to emulate the behavior of a low resolution ADC in the receiver, characterize its performance and estimate its energy savings. This allowed us to determine the feasibility of building a component with the analog-to-digital conversion function with few bits of resolution. We conclude that the performance of an ADC with at least 5 bits of resolution is pretty reasonable and that this reduction in the number of bits, in comparison to 8-bit ADC, represents a fairly expressive energy saving

Assessing metric structures on GPGPU environments

Similarity search consists on retrieving objects within a database that are similar or relevant to a particular query. It is a topic of great interest to scientific community because of its many fields of application, such as searching for words and images on the World Wide Web, pattern recognition, detection of plagiarism, multimedia databases, among others. It is modeled through metric spaces, in which objects are represented in a black-box that contains only the distance between objects; calculating the distance function is costly and search systems operate at a high query rate. Metrical structures have been developed to optimize this process; such structures work as indexes and preprocess data to decrease the distance evaluations during the search. Processing large volumes of data makes unfeasible the use of such structures without using parallel processing environments. Technologies based on multi- CPU and GPU architectures are among the most force due to its costs and performance.XV Workshop de Procesamiento Distribuido y Paralelo (WPDP)Red de Universidades con Carreras en Informática (RedUNCI