Statistical repulsion/attraction of electrons in graphene in a magnetic field

The aim of this work is to describe the thermodynamic properties of an electron gas in graphene placed in a constant magnetic field. The electron gas is constituted by $N$ Bloch electrons in the long wavelength approximation. The partition function is analyzed in terms of a perturbation expansion of the dimensionless constant $(\sqrt{eB}L)^{-1}$. The statistical repulsion/attraction potential for electrons in graphene is obtained in the respective case in which antisymmetric/symmetric states in the coordinates are chosen. Thermodynamic functions are computed for different orders in the perturbation expansion and the different contributions are compared for symmetric and antisymmetric states, showing remarkable differences between them due to the spin exchange correlation. A detailed analysis of the statistical potential is done, showing that, although electrons satisfy Fermi statistics, attractive potential at some interparticle distances can be found.Comment: Physica B, 201

Valley properties of doped graphene in a magnetic field

The aim of this work is to describe the electronic properties of graphene in a constant magnetic field in the long wavelength approximation with random binary disorder, by solving the Soven equation self-consistently. Density of state contributions for different valleys in each sublattice sites are obtained for different values of magnetic field strength showing remarkable differences between K and K' valleys. A band gap is obtained by an asymmetric on-site impurity concentration and the graphene electrons acquire an anomalous magnetic moment, which is opposite in different valleys, which depend highly in the interplay between the impurity band, the band edges and the broadening of the Landau levels. In turn, magnetization as a function of B for different on-site random impurities is computed showing that by decreasing the on-site impurity energy values, maximum magnetization is shifted towards higher values of B which can be used to create and manipulate polarized valley currents. Finally, conductivity and local vertex function are obtained as a function of energy showing that scattering contributions from A and B sublattices differ significantly. Effective medium local two-irreducible vertex is computed showing that scattering from sublattices A and B do not contribute equally, which can be related to weak anti-localization. From these results, it could be possible to explore how the valley pseudospin can be used to create polarized currents by populating asymmetrically the sublattice sites, where the population can be tuned with the applied magnetic field strength

Landau level transitions indoped graphene in a time dependent magnetic field

The aim of this work is to describe the Landau levels transitions of Bloch electrons in doped graphene with an arbitrary time dependent magnetic field in the long wavelength approximation. In particular, transitions from the m Landau level to the m + 1 and m + 2 Landau levels are studied using time-dependent perturbation theory. Time intervals are computed in which transition probabilities tend to zero at low order in the coupling constant. In particular, Landau level transitions are studied in the case of Bloch electrons travelling in the direction of the applied magnetic force and the results are compared with classical and revival periods of electrical current in graphene. Finally, current probabilities are computed for the n = 0 and n = 1 Landau levels showing expected oscillating behavior with modified cyclotron frequency.Comment: 18 pages, 7 figure

Dynamical diffusion and renormalization group equation for the Fermi velocity in doped graphene

The aim of this work is to study the electron transport in graphene with impurities by introducing a generalization of linear response theory for linear dispersion relations and spinor wave functions. Current response and density response functions are derived and computed in the Boltzmann limit, showing that in the former case, a minimum conductivity appears in the no-disorder limit. In turn, from the generalization of both functions, an exact relation can be obtained that relates both. Combining this result with the relation given by the continuity equation, it is possible to obtain general functional behavior of the diffusion pole. Finally, a dynamical diffusion is computed in the quasistatic limit using the definition of relaxation function. A lower cutoff must be introduced to regularize infrared divergences, which allow us to obtain a full renormalization group equation for the Fermi velocity, which is solved up to order O(h^2).Comment: 20 pages, 2 figure

Ballistic transport properties in pristine-doped-pristine graphene junctions

We investigate the ballistic electron transport in a monolayer graphene with configurational averaged impurities, located between two clean graphene leads. It is shown that the electron transmission are strongly dependent on the concentration of impurities and the incident energy. In turn, the conductance computed using the Landauer formalism shows a similar behavior to those found in experimental works as a function of the applied voltage for different concentrations of impurities in the limit of low temperatures. In the limit of zero bias voltage, the conductance shows a minimum value which reduces to zero for high concentration of impurities which disentangle graphene sublattices. These results can be very helpful for exploring the tunneling mechanism of electrons through doped thermodynamically stable graphene

Deprea auccana and Deprea physalidicalyx (Solanaceae), two new species from Northeastern Peru

Se describe e ilustra en detalle Deprea auccana S. Leiva, Barboza & Deanna y D. physalidicalyx S. Leiva, Barboza & Deanna (Solanaceae), dos nuevas especies del noreste de Perú. Deprea auccana es propia de la Reserva Privada Abra Patricia (ECOAN; ruta Pomacochas-Nueva Cajamarca, Distrito Yambrasbamba, Prov. Bongará, Dpto. Amazonas, Perú). Se caracteriza principalmente por la forma y tamaño de sus hojas, el número de flores por nudo, la longitud de los lóbulos calicinos, estambres homodínamos y los frutos erectos, con el cáliz fructífero acrescente y bipartido a la madurez. Deprea physalidicalyx S. Leiva, Barboza & Deanna habita en la Catarata de Aguashiyacu (ruta Tarapoto-Juanjuí, Prov. Tarapoto, Dpto. San Martín, Perú). Se caracteriza por los lóbulos de la corola lila intenso en la superficie central y cremoso en los bordes interiormente, estambres homodínamos, baya cremosa a la madurez y por el cáliz fruticoso muy acrescente e inflado que envuelve flojamente a la baya en toda su longitud, de 3,5-4 cm de largo por 2,3-2,7 cm de diámetro. Se incluyen datos sobre su distribución geográfica, ecología, fenología, estado de conservación y diferencias con especies afines.Deprea auccana S. Leiva, Barboza & Deanna and D. physalidicalyx Leiva, Barboza & Deanna (Solanaceae) are described and illustrated. Deprea auccana inhabits Abra Patricia Private Reserve (ECOAN, Pomacochas-Nueva Cajamarca road, Yambrasbamba District, Bongara Prov., Amazonas Dept., Peru). This species is distinguished by the shape and size of its leaves, number of flowers per node, length of calyx lobes, homodynamous stamens and its erect fruits with an accrescent and bipartite fruiting calyx when mature. Deprea physalidicalyx S. Leiva, Barboza & Deanna inhabits in the Aguashiyacu waterfall (Tarapoto-Juanjui road, Tarapoto Prov., San Martin Dept., Peru) and it is characterized by the corolla lobes deep purple on the middle and cream on the margins internally, homodynamous stamens and the creamy berry when mature, loosely enveloped by a fruiting calyx very accrescent and inflated, 3.5-4 cm long, 2.3-2.7 cm diameter. Data about geographic distribution, ecology, phenology, conservation assessment and differences with related species are included.Fil: Leiva Gonzalez, Segundo. Universidad Privada Antenor Orrego de Trujillo; PerúFil: Barboza, Gloria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina. Universidad Nacional de Córdoba; ArgentinaFil: Deanna, Rocío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina. Universidad Nacional de Córdoba; Argentin

Response of the Femur to Exercise During Recovery Between Two Bouts of Hindlimb Unloading in Adult Male Rats

Mechanical unloading with microgravity exposure during spaceflight induces bone loss in weight bearing bones. Combined with loss of bone due to aging, this disuse bone loss puts astronauts at increased risk of fracture upon returning to 1G conditions. It is important to study countermeasures, such as exercise, to mitigate or prevent this bone loss. This study utilized the hindlimb unloaded (HU) rat model to characterize the effects of resistance exercise on recovery dynamics in-between two bouts of HU. In the larger project adult male Sprague-Dawley rats, six months of age, were divided into the following groups: baseline (sacrificed at 6 months of age); aging cage controls (did not undergo any treatment, sacrificed at 7, 8, 9, 10, and 12 months of age); 1HU7 (one month of HU at 6 months of age followed by three months of ambulatory recovery); 2HU10 (one month of HU at 6 months of age, ambulatory recovery for two months, one month HU at 9 months of age, and final two month ambulatory recovery); 1HU10 (one month HU at 9 months of age and two month ambulatory recovery); and 2HU+Ex (One month HU at 6 months of age, two month resistance exercise recovery, and a 2nd bout of HU at 9 months of age). This thesis focused on the 2HU+Ex data, while utilizing data from other groups for comparisons. The data in this thesis includes ex vivo densitometric and biomechanical properties at the femoral neck (FN), femur midshaft diaphysis (FD), and distal femur metaphysis (DFM). All compartments of BMC increased following exercise recovery above AC at the FN and DFM. Ambulatory recovery values revealed incomplete recovery in total and cortical BMC at the DFM and full recovery in other parameters. DFM and FD vBMD data indicated there were further benefits of exercise during recovery. Geometric data revealed periosteal apposition at the DFM and FN following exercise recovery. FD mechanical properties did not produce benefits of exercise. However, FN maximum force increased above all other groups after exercise recovery. Elastic modulus of the DFM showed benefits of exercise recovery in the response to the 2nd HU

Raising the Efficiency Limit of the GaAs-based Intermediate Band Solar Cell Through the Implementation of a Mololithic Tandem with an AlGaAs top Cell.

The high efficiency limit of the intermediate band solar cell (IBSC) corresponds to the case of using as intermediate band (IB) host material a semiconductor with gap in the range of 2 eV. Traditional photovoltaic materials, such as Si and GaAs, are not appropriate to produce IB devices because their gaps are too narrow. To overcome this problem, we propose the implementation of a multi-junction device consisting of an IBSC combined with a single gap cell. We calculate the efficiency limits using the detailed balance model and conclude that they are very high (> 60% under maximum concentration) for any fundamental bandgap from 0.7 to 3.6 eV in the IBSC inserted in the tandem. In particular, the two-terminal tandem of a GaAs-based IBSC current matched to an optimized AlGaAs top cell has an efficiency limit as high as 64%

Análisis de necesidades de formación de recursos humanos para el año 2010

El Instituto Colombiana para el fomento de al Educación Superior ICFES, en coordinación con el instituto colombiano de Crédito Educativo y Estudios Técnicos en el Exterior ICETEX y la mayoría de las Universidades del país, está desarrollando este estudio prospectivo

Exercise Ameliorates Endocrine Pancreas Damage Induced by Chronic Cola Drinking in Rats

Purpose: This study evaluates whether the daily practice of an exercise routine might protect from endocrine pancreas damage in cola drinking rats. Methods: Forty-eight Wistar rats were randomly assigned to 4 groups depending on a) beverage consumption ad libitum, water (W) or cola beverage (C), and b) physical activity, sedentary (S) or treadmill running (R). Accordingly, 4 groups were studied: WS (water sedentary), WR (water runner), CS (cola sedentary) and CR (cola runner). Body weight, nutritional data, plasma levels of glucose, creatinine, total cholesterol and cholesterol fractions, and triglycerides (enzymocolorimetry), and systolic blood pressure (plethysmography) were measured. After 6 months, euthanasia was performed (overdose sodium thiopental). Pancreatic tissue was immediately excised and conventionally processed for morphometrical and immunohistochemical determinations. Results: The effects of running and chronic cola drinking on pancreas morphology showed interaction (p<0.001) rather than simple summation. Cola drinking (CS vs WS) reduced median pancreatic islet area (-30%, 1.8 104 μm2 vs 2.58 104 μm2, p<0.0001) and median β-cell mass (-43%, 3.81 mg vs 6.73 mg, p<0.0001), and increased median α/β ratio (+49%, 0.64 vs 0.43, p< 0.001). In water drinking rats (WR vs WS), running reduced median α-cell mass (-48%, 1.48 mg vs 2.82 mg, p<0.001) and α/β ratio (-56%, 0.19 vs 0.43, p<0.0001). Differently, in cola drinking rats (CR vs CS), running partially restored median islet area (+15%, 2.06 104 μm2 vs 1.79 104 μm2, p<0.05), increased median β-cell mass (+47%, 5.59 mg vs 3.81 mg, p <0.0001) and reduced median α/β ratio (-6%, 0.60 vs 0.64, p<0.05). Conclusion: This study is likely the first reporting experimental evidence of the beneficial effect of exercise on pancreatic morphology in cola-drinking rats. Presently, the increase of nearly 50% in β cells mass by running in cola drinking rats is by far the most relevant finding. Moderate running, advisably indicated in cola consumers and patients at risk of diabetes, finds here experimental support.Fil: Otero-Losada, Matilde Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; ArgentinaFil: Gonzalez, Julian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; ArgentinaFil: Muller, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; ArgentinaFil: Ottaviano, Graciela Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; ArgentinaFil: Cao, Gabriel Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; ArgentinaFil: Azzato, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; ArgentinaFil: Ambrosio, Giuseppe. Università di Perugia; ItaliaFil: Milei, Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; Argentin