123 research outputs found
Chirality Change in String Theory
It is known that string theory compactifications leading to low energy
effective theories with different chiral matter content ({\it e.g.} different
numbers of standard model generations) are connected through phase transitions,
described by non-trivial quantum fixed point theories.
We point out that such compactifications are also connected on a purely
classical level, through transitions that can be described using standard
effective field theory. We illustrate this with examples, including some in
which the transition proceeds entirely through supersymmetric configurations.Comment: 50 pages, 2 figure
Self-assembly of quantum dots: effect of neighbor islands on the wetting in coherent Stranski-Krastanov growth
The wetting of the homogeneously strained wetting layer by dislocation-free
three-dimensional islands belonging to an array has been studied. The array has
been simulated as a chain of islands in 1+1 dimensions. It is found that the
wetting depends on the density of the array, the size distribution and the
shape of the neighbor islands. Implications for the self-assembly of quantum
dots grown in the coherent Stranski-Krastanov mode are discussed.Comment: 4 pages, 6 figures, accepted version, minor change
Seasonal occurrence of vine pests in commercially treated vineyards in the Hex River Valley in the Western Cape Province, South Africa
Accurate Evaluation of the Cubic Lattice Green Functions Using Binomial Expansion Theorems
Magnetic field generation from non-equilibrium phase transitions
We study the generation of magnetic fields during the stage of particle
production resulting from spinodal instabilities during phase transitions out
of equilibrium. The main premise is that long-wavelength instabilities that
drive the phase transition lead to strong non-equilibrium charge and current
fluctuations which generate electromagnetic fields. We present a formulation
based on the non-equilibrium Schwinger-Dyson equations that leads to an exact
expression for the spectrum of electromagnetic fields valid for general
theories and cosmological backgrounds and whose main ingredient is the
transverse photon polarization out of equilibrium. This formulation includes
the dissipative effects of the conductivity in the medium. As a prelude to
cosmology we study magnetogenesis in Minkowski space-time in a theory of N
charged scalar fields to lowest order in the gauge coupling and to leading
order in the large N within two scenarios of cosmological relevance. The
long-wavelength power spectrum for electric and magnetic fields at the end of
the phase transition is obtained explicitly.
It follows that equipartition between electric and magnetic fields does not
hold out of equilibrium. In the case of a transition from a high temperature
phase, the conductivity of the medium severely hinders the generation of
magnetic fields, however the magnetic fields generated are correlated on scales
of the order of the domain size, which is much larger than the magnetic
diffusion length. Implications of the results to cosmological phase transitions
driven by spinodal unstabilities are discussed.Comment: Preprint no. LPTHE 02-55, 30 pages, latex, 2 eps figures. Added one
reference. To appear in Phys. Rev.
Effectiveness of sensor-augmented insulin-pump therapy in type 1 diabetes
BACKGROUND: Recently developed technologies for the treatment of type 1 diabetes mellitus include a variety of pumps and pumps with glucose sensors. METHODS: In this 1-year, multicenter, randomized, controlled trial, we compared the efficacy of sensor-augmented pump therapy (pump therapy) with that of a regimen of multiple daily insulin injections (injection therapy) in 485 patients (329 adults and 156 children) with inadequately controlled type 1 diabetes. Patients received recombinant insulin analogues and were supervised by expert clinical teams. The primary end point was the change from the baseline glycated hemoglobin level. RESULTS: At 1 year, the baseline mean glycated hemoglobin level (8.3% in the two study groups) had decreased to 7.5% in the pump-therapy group, as compared with 8.1% in the injection-therapy group (P<0.001). The proportion of patients who reached the glycated hemoglobin target (<7%) was greater in the pump-therapy group than in the injection-therapy group. The rate of severe hypoglycemia in the pump-therapy group (13.31 cases per 100 person-years) did not differ significantly from that in the injection-therapy group (13.48 per 100 person-years, P = 0.58). There was no significant weight gain in either group. CONCLUSIONS: In both adults and children with inadequately controlled type 1 diabetes, sensor-augmented pump therapy resulted in significant improvement in glycated hemoglobin levels, as compared with injection therapy. A significantly greater proportion of both adults and children in the pump-therapy group than in the injection-therapy group reached the target glycated hemoglobin level. (ClinicalTrials.gov number, NCT00417989.
Keeping It Real: Revisiting a Real-Space Approach to Running Ensembles of Cosmological N-body Simulations
In setting up initial conditions for ensembles of cosmological N-body
simulations there are, fundamentally, two choices: either maximizing the
correspondence of the initial density field to the assumed fourier-space
clustering or, instead, matching to real-space statistics and allowing the DC
mode (i.e. overdensity) to vary from box to box as it would in the real
universe. As a stringent test of both approaches, I perform ensembles of
simulations using power law and a "powerlaw times a bump" model inspired by
baryon acoustic oscillations (BAO), exploiting the self-similarity of these
initial conditions to quantify the accuracy of the matter-matter two-point
correlation results. The real-space method, which was originally proposed by
Pen 1997 and implemented by Sirko 2005, performed well in producing the
expected self-similar behavior and corroborated the non-linear evolution of the
BAO feature observed in conventional simulations, even in the
strongly-clustered regime (sigma8 >= 1). In revisiting the real-space method
championed by Sirko 2005, it was also noticed that this earlier study
overlooked an important integral constraint correction to the correlation
function in results from the conventional approach that can be important in
LambdaCDM simulations with Lbox == Lbox / 10.
Rectifying this shows that the fourier space and real space methods are about
equally accurate and efficient for modeling the evolution and growth of the
correlation function, contrary to previous claims. An appendix provides a
useful independent-of-epoch analytic formula for estimating the importance of
the integral constraint bias on correlation function measurements in LambdaCDM
simulations.Comment: 28 pages, 7 figures, substantial improvements throughou
Исследовательская деятельность эколого-биологической направленности в НОУ "Эврика" - эффективное средство профессиональной ориентации учащихся
В статье научно-исследовательская деятельность эколого-биологической направленности старшеклассников НОУ "Эврика" г. Нижнего Новгорода рассматривается как одна из значимых инновационных форм профессионального самоопределения. Материалом исследования послужил анализ программ конференции городского научного общества учащихся "Эврика" и судьбы выпускников данного общества. Отмечена тенденция роста популярности эколого-биологических исследований среди старшеклассников г. Нижнего Новгорода и успешное вхождение в профессию выпускников научного общества учащихся.In the article, the research activity of the ecology and biology of senior pupils of the scientific society of the pupils "Eureka" in Nizhny Novgorod is considered as one of the significant innovative forms of professional self-determination. The material of the study was the analysis of the programs of the conference of the city scientific society of the students "Eureka" and the fate of the graduates of this society. The tendency of growth of popularity of ecological and biological researches among senior pupils of Nizhny Novgorod and successful entry into the profession of graduates of the scientific society of students is noted
Genetic Sharing with Cardiovascular Disease Risk Factors and Diabetes Reveals Novel Bone Mineral Density Loci.
Bone Mineral Density (BMD) is a highly heritable trait, but genome-wide association studies have identified few genetic risk factors. Epidemiological studies suggest associations between BMD and several traits and diseases, but the nature of the suggestive comorbidity is still unknown. We used a novel genetic pleiotropy-informed conditional False Discovery Rate (FDR) method to identify single nucleotide polymorphisms (SNPs) associated with BMD by leveraging cardiovascular disease (CVD) associated disorders and metabolic traits. By conditioning on SNPs associated with the CVD-related phenotypes, type 1 diabetes, type 2 diabetes, systolic blood pressure, diastolic blood pressure, high density lipoprotein, low density lipoprotein, triglycerides and waist hip ratio, we identified 65 novel independent BMD loci (26 with femoral neck BMD and 47 with lumbar spine BMD) at conditional FDR < 0.01. Many of the loci were confirmed in genetic expression studies. Genes validated at the mRNA levels were characteristic for the osteoblast/osteocyte lineage, Wnt signaling pathway and bone metabolism. The results provide new insight into genetic mechanisms of variability in BMD, and a better understanding of the genetic underpinnings of clinical comorbidity
- …