6,958 research outputs found
Moving Five-Branes in Low-Energy Heterotic M-Theory
We construct cosmological solutions of four-dimensional effective heterotic
M-theory with a moving five-brane and evolving dilaton and T modulus. It is
shown that the five-brane generates a transition between two asymptotic
rolling-radii solutions. Moreover, the five-brane motion always drives the
solutions towards strong coupling asymptotically. We present an explicit
example of a negative-time branch solution which ends in a brane collision
accompanied by a small-instanton transition. The five-dimensional origin of
some of our solutions is also discussed.Comment: 16 pages, Latex, 3 eps figure
Statistical periodicity in driven quantum systems: General formalism and application to noisy Floquet topological chains
Much recent experimental effort has focused on the realization of exotic
quantum states and dynamics predicted to occur in periodically driven systems.
But how robust are the sought-after features, such as Floquet topological
surface states, against unavoidable imperfections in the periodic driving? In
this work, we address this question in a broader context and study the dynamics
of quantum systems subject to noise with periodically recurring statistics. We
show that the stroboscopic time evolution of such systems is described by a
noise-averaged Floquet superoperator. The eigenvectors and -values of this
superoperator generalize the familiar concepts of Floquet states and
quasienergies and allow us to describe decoherence due to noise efficiently.
Applying the general formalism to the example of a noisy Floquet topological
chain, we re-derive and corroborate our recent findings on the noise-induced
decay of topologically protected end states. These results follow directly from
an expansion of the end state in eigenvectors of the Floquet superoperator.Comment: 13 pages, 5 figures. This is the final, published versio
Stochastic delocalization of finite populations
Heterogeneities in environmental conditions often induce corresponding
heterogeneities in the distribution of species. In the extreme case of a
localized patch of increased growth rates, reproducing populations can become
strongly concentrated at the patch despite the entropic tendency for population
to distribute evenly. Several deterministic mathematical models have been used
to characterize the conditions under which localized states can form, and how
they break down due to convective driving forces. Here, we study the
delocalization of a finite population in the presence of number fluctuations.
We find that any finite population delocalizes on sufficiently long time
scales. Depending on parameters, however, populations may remain localized for
a very long time. The typical waiting time to delocalization increases
exponentially with both population size and distance to the critical wind speed
of the deterministic approximation. We augment these simulation results by a
mathematical analysis that treats the reproduction and migration of individuals
as branching random walks subject to global constraints. For a particular
constraint, different from a fixed population size constraint, this model
yields a solvable first moment equation. We find that this solvable model
approximates very well the fixed population size model for large populations,
but starts to deviate as population sizes are small. The analytical approach
allows us to map out a phase diagram of the order parameter as a function of
the two driving parameters, inverse population size and wind speed. Our results
may be used to extend the analysis of delocalization transitions to different
settings, such as the viral quasi-species scenario
Identification of a functional genetic variant driving racially dimorphic platelet gene expression of the thrombin receptor regulator, PCTP.
Platelet activation in response to stimulation of the Protease Activated Receptor 4 (PAR4) receptor differs by race. One factor that contributes to this difference is the expression level of Phosphatidylcholine Transfer Protein (PCTP), a regulator of platelet PAR4 function. We have conducted an expression Quantitative Trait Locus (eQTL) analysis that identifies single nucleotide polymorphisms (SNPs) linked to the expression level of platelet genes. This analysis revealed 26 SNPs associated with the expression level of PCTP at genome-wide significance (p \u3c 5Ă—10(-8)). Using annotation from ENCODE and other public data we prioritised one of these SNPs, rs2912553, for functional testing. The allelic frequency of rs2912553 is racially-dimorphic, in concordance with the racially differential expression of PCTP. Reporter gene assays confirmed that the single nucleotide change caused by rs2912553 altered the transcriptional potency of the surrounding genomic locus. Electromobility shift assays, luciferase assays, and overexpression studies indicated a role for the megakaryocytic transcription factor GATA1. In summary, we have integrated multi-omic data to identify and functionalise an eQTL. This, along with the previously described relationship between PCTP and PAR4 function, allows us to characterise a genotype-phenotype relationship through the mechanism of gene expression
Experimental Determination of the Lorenz Number in Cu0.01Bi2Te2.7Se0.3 and Bi0.88Sb0.12
Nanostructuring has been shown to be an effective approach to reduce the
lattice thermal conductivity and improve the thermoelectric figure of merit.
Because the experimentally measured thermal conductivity includes contributions
from both carriers and phonons, separating out the phonon contribution has been
difficult and is mostly based on estimating the electronic contributions using
the Wiedemann-Franz law. In this paper, an experimental method to directly
measure electronic contributions to the thermal conductivity is presented and
applied to Cu0.01Bi2Te2.7Se0.3, [Cu0.01Bi2Te2.7Se0.3]0.98Ni0.02, and
Bi0.88Sb0.12. By measuring the thermal conductivity under magnetic field,
electronic contributions to thermal conductivity can be extracted, leading to
knowledge of the Lorenz number in thermoelectric materials
Perancangan Fidget Device Berbasis Internet of Things
Increasing stress level among the people is rising a concern. Fidget devices are proposed as a way to help relieve stress. They are easy to use and can be carried everywhere. Two of most commonly used fidget devices are fidget spinner and fidget cube. These fidget devices are believed to cope with anxiety so that users can focus their nervous energy on fidget devices. In this research, the fidget device to be discussed is the fidget cube, since it is considered as safer and has various button than the fidget spinner. Not only stress relievers, IoT-based fidget cube also has the ability to send data to a web server. It aims to see a trend or data about the user\u27s behavior, which buttons are often used by users and the frequency of using fidget cube in daily life. This data can later be used in other scientific fields.Tingkat stress di dunia mengalami kenaikan dari tahun ke tahun. Oleh karena itu, teknologi semakin berkembang menciptakan alat pengurang stres yang mudah digunakan dan dibawa kemanapun. Salah satu alat pengurang stres adalah fidget devices. Saat ini, ada dua bentuk fidget devices yang umum digunakan, yaitu fidget spinner dan fidget cube. Kedua fidget devices ini dipercaya untuk mengatasi kegelisahan sehingga pengguna dapat memusatkan kegelisahannya ke fidget devices. Dalam perancangan kali ini, fidget device yang akan dibahas adalah fidget cube karena fidget cube dirasa lebih aman dan lebih bervariasi jika dibandingkan fidget spinner. Tak hanya penghilang stres, fidget cube berbasis IoT juga memiliki kemampuan untuk mengirim data ke web server. Hal ini bertujuan untuk melihat suatu trend atau data mengenai perilaku si pengguna, tombol mana saja yang sering digunakan oleh pengguna dan frekuensi penggunaan fidget cube pada kehidupan sehari-hari. Data ini nantinya dapat digunakan dalam bidang keilmuan lainnya
Classification and Moduli Kahler Potentials of G_2 Manifolds
Compact manifolds of G_2 holonomy may be constructed by dividing a
seven-torus by some discrete symmetry group and then blowing up the
singularities of the resulting orbifold. We classify possible group elements
that may be used in this construction and use this classification to find a set
of possible orbifold groups. We then derive the moduli Kahler potential for
M-theory on the resulting class of G_2 manifolds with blown up co-dimension
four singularities.Comment: 30 pages, Latex, references adde
G_2 Domain Walls in M-theory
M-theory is considered in its low-energy limit on a G_2 manifold with
non-vanishing flux. Using the Killing spinor equations for linear flux, an
explicit set of first-order bosonic equations for supersymmetric solutions is
found. These solutions describe a warped product of a domain wall in
four-dimensional space-time and a deformed G_2 manifold. It is shown how these
domain walls arise from the perspective of the associated four-dimensional N=1
effective supergravity theories. We also discuss the inclusion of membrane and
M5-brane sources.Comment: 30 pages, Late
- …