4,573 research outputs found
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 and as well as the critical temperature 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 YBaCuO
A study by specific heat of a polycrystalline sample of the low-dimensional
magnetic system YBaCuO is presented. Magnetic fields up to 14 T are
applied and permit to extract the (,) phase diagram. Below
T, the N\'eel temperature, associated with a
three-dimensional antiferromagnetic long-range ordering, is constant and equals
K. Above , increases linearly with and a
field-induced increase of the entropy at is related to the presence of an
isosbestic point at K, where all the specific heat curves cross.
A comparison is made between YBaCuO and the quasi-two-dimensional
magnetic systems BaNiVO, SrCuOCl, and
PrCuO, 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
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