Finite-temperature Mott transitions in multi-orbital Hubbard model

We investigate the Mott transitions in the multi-orbital Hubbard model at half-filling by means of the self-energy functional approach. The phase diagrams are obtained at finite temperatures for the Hubbard model with up to four-fold degenerate bands. We discuss how the first-order Mott transition points $U_{c1}$ and $U_{c2}$ as well as the critical temperature $T_c$ depend on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations play a key role to control the Mott transitions in the multi-orbital Hubbard model.Comment: 8 pages, 7 figure

Representação Esparsa e Modelo de Esparsidade Conjunta no Reconhecimento de Faces

Resumo: O trabalho desenvolvido nesta dissertação propõe a utilização do modelo de esparsidade conjunta com complemento de matrizes (JSM-MC) para composição da base de treino no contexto de reconhecimento de faces utilizando o classificador baseado em representação esparsa (SRC). O método proposto visa trabalhar com imagens de faces em diferentes condições de iluminação e oclusão na base de teste e treino. Para oclusões nas imagens de teste, um modelo diferenciado é considerado para abordar o problema. Uma etapa de pré-processamento nas imagens de faces é realizada no intuito de reduzir os efeitos das variações de iluminações presentes nas imagens. Um agrupamento das imagens de treino é realizado visando um menor tempo de processamento. Além disso, uma proposta de modificação no algoritmo SRC é feita de forma a explorar a esparsidade dos coeficientes de representação esparsa. Ao final, os resultados são avaliados usando uma base de dados sujeita a variação de iluminação. Oclusões artificiais são inseridas a fim de investigar o desempenho do sistema nessas condições

Modeling the Formation of Giant Planet Cores I: Evaluating Key Processes

One of the most challenging problems we face in our understanding of planet formation is how Jupiter and Saturn could have formed before the the solar nebula dispersed. The most popular model of giant planet formation is the so-called 'core accretion' model. In this model a large planetary embryo formed first, mainly by two-body accretion. This is then followed by a period of inflow of nebular gas directly onto the growing planet. The core accretion model has an Achilles heel, namely the very first step. We have undertaken the most comprehensive study of this process to date. In this study we numerically integrate the orbits of a number of planetary embryos embedded in a swarm of planetesimals. In these experiments we have included: 1) aerodynamic gas drag, 2) collisional damping between planetesimals, 3) enhanced embryo cross-sections due to their atmospheres, 4) planetesimal fragmentation, and 5) planetesimal driven migration. We find that the gravitational interaction between the embryos and the planetesimals lead to the wholesale redistribution of material - regions are cleared of material and gaps open near the embryos. Indeed, in 90% of our simulations without fragmentation, the region near that embryos is cleared of planetesimals before much growth can occur. The remaining 10%, however, the embryos undergo a burst of outward migration that significantly increases growth. On timescales of ~100,000 years, the outer embryo can migrate ~6 AU and grow to roughly 30 Earth-masses. We also find that the inclusion of planetesimal fragmentation tends to inhibit growth.Comment: Accepted to AJ, 62 pages 11 figure

The effect of a natural, standardized bilberry extract (Mirtoselect (R)) in dry eye: a randomized, double blinded, placebo-controlled trial

OBJECTIVE: Dry eye, a chronic disease of lachrymal fluid and corneo-conjunctival epithelium, could significantly impact visual function, affects quality of life and work productivity. Beside several conventional treatments, nutritional supplements based on bilberry extract have been identified as effective contributors to eye health. Here, we aim at investigating the bioavailability of a standardized bilberry extract, its ability to alleviate dry eye symptoms and its antioxidant potential.MATERIALS AND METHODS: Either bilberry dried standardized extract derived from Vaccinium myrtillus L. fresh frozen fruits (Mirtoselect (R)) or a highly purified anthocyanin-rich extract, devoid of the non anthocyanin component and supported on maltodextrins, were each orally a dministrated to 5 male rats. Blood samples were collected at 5, 10, 15, 20, 30, 45, 60, 90, 120 minutes after treatment, processed and analyzed by UV spectrophotometric method. In a parallel analysis, 22 otherwise healthy subjects suffering from dry eye symptoms were enrolled randomly assigned to receive the more bioavailable bilberry extract or placebo. Ophthalmological and clinical examinations including Schirmer's test, pupil constriction, diacron-reactive oxygen metabolites (d-ROMs) test and biological antioxidant potential (BAP) test were performed at inclusion and after the 4-week study period.RESULTS: The area under the curve of plasmatic levels of anthocyanosides in rats resulted 202.34 +/- 24.23 mu g . min/ml for Mirtoselect (R) and 130.93 +/- 4.93 mu g . min/ml for the highly purified anthocyanin-rich bilberry extract, notwithstanding the fact that the highly purified anthocyanin-rich extract group received an anthocyanins dosage much higher than the Mirtoselect (R) group (354 mg/Kg in anthocyanosides vs. 136 mg/Kg in anthocyanosides). 21 subjects, 11 subjects in the bilberry extract (Mirtoselect (R)) group and 10 subjects in the placebo group completed the clinical study. Schirmer's test values indicating the volume of tear secretion were significantly improved in the bilberry extract group (p=0.019), whereas no significant changes were observed in the placebo group. A subset analysis revealed that Mirtoselect (R) could be more effective in subjects with higher tendency of dry eye. In terms of antioxidant potential, the bilberry extract produced significant improvement of BAP (p=0.003) and an increase of modified BAP/d-ROMs ratio, an indicator of overall balance between antioxidant potential and oxidative stress.CONCLUSIONS: Our results suggested that natural, standardized bilberry extract (Mirtoselect (R)) is a natural more bioavailable delivery form anthocyanins, suggesting a strong matrix effect exerted by the non-anthocyanin component. Furthermore, it can improve tear secretion and plasmatic antioxidant potential in subjects suffering from DED symptoms

Calculation of the average Green's function of electrons in a stochastic medium via higher-dimensional bosonization

The disorder averaged single-particle Green's function of electrons subject to a time-dependent random potential with long-range spatial correlations is calculated by means of bosonization in arbitrary dimensions. For static disorder our method is equivalent with conventional perturbation theory based on the lowest order Born approximation. For dynamic disorder, however, we obtain a new non-perturbative expression for the average Green's function. Bosonization also provides a solid microscopic basis for the description of the quantum dynamics of an interacting many-body system via an effective stochastic model with Gaussian probability distribution.Comment: RevTex, no figure

Heat Capacity and Magnetic Phase Diagram of the Low-Dimensional Antiferromagnet Y2_2BaCuO5_5

A study by specific heat of a polycrystalline sample of the low-dimensional magnetic system Y$_2$BaCuO$_5$ is presented. Magnetic fields up to 14 T are applied and permit to extract the ($T$,$H$) phase diagram. Below $\mu_0H^*\simeq2$ T, the N\'eel temperature, associated with a three-dimensional antiferromagnetic long-range ordering, is constant and equals $T_N=15.6$ K. Above $H^*$, $T_N$ increases linearly with $H$ and a field-induced increase of the entropy at $T_N$ is related to the presence of an isosbestic point at $T_X\simeq20$ K, where all the specific heat curves cross. A comparison is made between Y$_2$BaCuO$_5$ and the quasi-two-dimensional magnetic systems BaNi$_{2}$V$_{2}$O$_{8}$, Sr$_2$CuO$_2$Cl$_2$, and Pr$_2$CuO$_4$, for which very similar phase diagrams have been reported. An effective field-induced magnetic anisotropy is proposed to explain these phase diagrams.Comment: 14 pages, 7 figure

Planetesimal-driven planet migration in the presence of a gas disk

We report here on an extension of a previous study by Kirsh et al. (2009) of planetesimal-driven migration using our N-body code SyMBA (Duncan et al., 1998). The previous work focused on the case of a single planet of mass Mem, immersed in a planetesimal disk with a power-law surface density distribution and Rayleigh distributed eccentricities and inclinations. Typically 10^4-10^5 equal-mass planetesimals were used, where the gravitational force (and the back-reaction) on each planetesimal by the Sun and planetwere included, while planetesimal-planetesimal interactions were neglected. The runs reported on here incorporate the dynamical effects of a gas disk, where the Adachi et al. (1976) prescription of aerodynamic gas drag is implemented for all bodies. In some cases the Papaloizou and Larwood (2000) prescription of Type-I migration for the planet are implemented, as well as a mass distribution. In the gas-free cases, rapid planet migration was observed - at a rate independent of the planet's mass - provided the planet's mass was not large compared to the mass in planetesimals capable of entering its Hill sphere. In such cases, both inward and outward migrations can be self-sustaining, but there is a strong propensity for inward migration. When a gas disk is present, aerodynamic drag can substantially modify the dynamics of scattered planetesimals. For sufficiently large or small mono-dispersed planetesimals, the planet typically migrates inward. However, for a range of plausible planetesimal sizes (i.e. 0.5-5.0 km at 5.0 AU in a minimum mass Hayashi disk) outward migration is usually triggered, often accompanied by substantial planetary mass accretion. The origins of this behaviour are explained in terms of a toy model. The effects of including a size distribution and torques associated with Type-I migration are also discussed.Comment: 37 pages, 17 figures, Accepted for publication in Icaru

On the pressure of collisionless particle fluids. The case of solids settling in disks

Aims. Collections of dust, grains, and planetesimals are often treated as a pressureless fluid. We study the validity of neglecting the pressure of such a fluid by computing it exactly for the case of particles settling in a disk. Methods. We solve a modified collisionless Boltzmann equation for the particles and compute the corresponding moments of the phase space distribution: density, momentum, and pressure. Results. We find that whenever the Stokes number, defined as the ratio of the gas drag timescale to the orbital timescale, is more than 1/2, the particle fluid cannot be considered as pressureless. While we show it only in the simple case of particles settling in a laminar disk, this property is likely to remain true for most flows, including turbulent flows.Comment: Accepted for publication as a research note in Astronomy and Astrophysics. Language edite

Membranes, molecules and biophysics: enhancing monocyte derived dendritic cell (MDDC) immunogenicity for improved anti-cancer therapy

Despite great medical advancement in the treatment of cancer, cancer remains a disease of global significance. Chemotherapeutics can be very expensive and drain medical resources at a national level and in some cases the cost of treatment is so great that it prohibits their use by local health authorities. Drug resistance is also a major limiting factor to the successful treatment of cancer with many patients initially responding well but then becoming refractory to treatment with the same drug and in some case may become multi-drug resistant. The immune system is known to be important in the prevention of tumors by eliminating pre-cancerous or cancerous cells. This concept of immune surveillance has largely been super-ceded by the concept of immunoediting whereby the immune system imposes a selective pressure on tumor cells which may either control tumor growth or inadvertently select for tumor cells which have evolved to escape the immune response and which may induce tumor development. Stimulation of the immune system by vaccination offers many benefits in the treatment of cancer. It is highly cost effective and vaccines can be manipulated to include multi-antigens which in some cases may overcome equilibrium (and selective pressure) while also preventing the establishment of reactivated cancer cells, since cancer antigen-specific memory would be induced following the initial vaccination/booster phase. To date studies using vaccination as a treatment for cancer have been a little disappointing, probably due to insufficient level of immunogenicity. In this review we will discuss methods of manipulation of the immune system to increase the anti-cancer activity of dendritic cells in vivo and how monocyte derived dendritic cells may be manipulated ex vivo to provide more robust, patient-specific treatments

Electronic states around a vortex core in high-Tc superconductors based on the t-J model

Electronic states around vortex cores in high-Tc superconductors are studied using the two-dimensional t-J model in order to treat the d-wave superconductivity with short coherence length and the antiferromagnetic (AF) instability within the same framework. We focus on the disappearance of the large zero-energy peak in the local density of states observed in high-Tc superconductors. When the system is near the optimum doping, we find that the local AF correlation develops inside the vortex cores. However, the detailed doping dependence calculations confirm that the experimentally observed reduction of the zero-energy peak is more reasonably attributed to the smallness of the core size rather than to the AF correlation developed inside the core. The correlation between the spatial dependence of the core states and the core radius is discussed.Comment: 4 pages, 4 figure