589 research outputs found
Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) model
In the context of non-supersymmetric SO(10) models, we analyze the
renormalization group equations for the fermions (including neutrinos) from the
GUT energy scale down to the electroweak energy scale, explicitly taking into
account the effects of an intermediate energy scale induced by a Pati--Salam
gauge group. To determine the renormalization group running, we use a numerical
minimization procedure based on a nested sampling algorithm that randomly
generates the values of 19 model parameters at the GUT scale, evolves them, and
finally constructs the values of the physical observables and compares them to
the existing experimental data at the electroweak scale. We show that the
evolved fermion masses and mixings present sizable deviations from the values
obtained without including the effects of the intermediate scale.Comment: Comments: 20 pages, 3 figures. Final version published in JHE
Energy Transfer and Spectra in Simulations of Two-dimensional Compressible Turbulence
We present results of high-resolution numerical simulations of compressible
2D turbulence forced at intermediate spatial scales with a solenoidal
white-in-time external acceleration. A case with an isothermal equation of
state, low energy injection rate, and turbulent Mach number
without energy condensate is studied in detail. Analysis of energy spectra and
fluxes shows that the classical dual-cascade picture familiar from the
incompressible case is substantially modified by compressibility effects. While
the small-scale direct enstrophy cascade remains largely intact, a large-scale
energy flux loop forms with the direct acoustic energy cascade compensating for
the inverse transfer of solenoidal kinetic energy. At small scales, the direct
enstrophy and acoustic energy cascades are fully decoupled at small Mach
numbers and hence the corresponding spectral energy slopes comply with
theoretical predictions, as expected. At large scales, dispersion of acoustic
waves on vortices softens the dilatational velocity spectrum, while the
pseudo-sound component of the potential energy associated with coherent
vortices steepens the potential energy spectrum.Comment: 10 pages, 6 figures. To appear in: Turbulence in Complex Conditions,
Proc. Euromech/Ercoftac Colloquium 589, ed. M. Gorokhovski, Springer, 201
Self-rated health among Mayan women participating in a randomised intervention trial reducing indoor air pollution in Guatemala
<p>Abstract</p> <p>Background</p> <p>Indoor air pollution (IAP) from solid fuels is a serious health problem in low-income countries that can be alleviated using improved stoves. Although women are the principal users, few studies have investigated the self-assessed impact of the stoves on their health and lives.</p> <p>Methods</p> <p>This study was conducted in rural highland Guatemala, involving 89 intervention and 80 control Mayan Indian young women (mean 27.8 years, SD 7.2). Outcomes were assessed after approximately 18 months use of the new stove. Our objectives were to compare self-rated health and change in health among women participating in a randomised control trial comparing a chimney stove with an open fire, to describe impacts on women's daily lives and their perceptions of how reduced kitchen smoke affects their own and their children's health.</p> <p>Results</p> <p>On intention-to-treat analysis, 52.8% of intervention women reported improvement in health, compared to 23.8% of control women (p < 0.001). Among 84 intervention women who reported reduced kitchen smoke as an important change, 88% linked this to improvement in their own health, particularly for non-respiratory symptoms (for example eye discomfort, headache); 57% linked reduced smoke to improvement in their children's health, particularly sore eyes.</p> <p>Conclusion</p> <p>Women's perception of their health was improved, but although smoke reduction was valued, this was linked mainly with alleviation of non-respiratory symptoms like eye discomfort and headache. More focus on such symptoms may help in promoting demand for improved stoves and cleaner fuels, but education about more severe consequences of IAP exposure is also required.</p
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
General preparation for Pt-based alloy nanoporous nanoparticles as potential nanocatalysts
Although Raney nickel made by dealloying has been used as a heterogeneous catalyst in a variety of organic syntheses for more than 80 years, only recently scientists have begun to realize that dealloying can generate nanoporous alloys with extraordinary structural characteristics. Herein, we achieved successful synthesis of a variety of monodisperse alloy nanoporous nanoparticles via a facile chemical dealloying process using nanocrystalline alloys as precursors. The as-prepared alloy nanoporous nanoparticles with large surface area and small pores show superior catalytic properties compared with alloyed nanoparticles. It is believed that these novel alloy nanoporous nanoparticles would open up new opportunities for catalytic applications
On-surface synthesis of graphene nanoribbons with zigzag edge topology
Graphene-based nanostructures exhibit a vast range of exciting electronic
properties that are absent in extended graphene. For example, quantum
confinement in carbon nanotubes and armchair graphene nanoribbons (AGNRs) leads
to the opening of substantial electronic band gaps that are directly linked to
their structural boundary conditions. Even more intriguing are nanostructures
with zigzag edges, which are expected to host spin-polarized electronic edge
states and can thus serve as key elements for graphene-based spintronics. The
most prominent example is zigzag graphene nanoribbons (ZGNRs) for which the
edge states are predicted to couple ferromagnetically along the edge and
antiferromagnetically between them. So far, a direct observation of the
spin-polarized edge states for specifically designed and controlled zigzag edge
topologies has not been achieved. This is mainly due to the limited precision
of current top-down approaches, which results in poorly defined edge
structures. Bottom-up fabrication approaches, on the other hand, were so far
only successfully applied to the growth of AGNRs and related structures. Here,
we describe the successful bottom-up synthesis of ZGNRs, which are fabricated
by the surface-assisted colligation and cyclodehydrogenation of specifically
designed precursor monomers including carbon groups that yield atomically
precise zigzag edges. Using scanning tunnelling spectroscopy we prove the
existence of edge-localized states with large energy splittings. We expect that
the availability of ZGNRs will finally allow the characterization of their
predicted spin-related properties such as spin confinement and filtering, and
ultimately add the spin degree of freedom to graphene-based circuitry.Comment: 15 pages, 4 figure
The <i>Pratylenchus penetrans</i> transcriptome as a source for the development of alternative control strategies:mining for putative genes involved in parasitism and evaluation of <i>in planta</i> RNAi
The root lesion nematode Pratylenchus penetrans is considered one of the most economically important species within the genus. Host range studies have shown that nearly 400 plant species can be parasitized by this species. To obtain insight into the transcriptome of this migratory plant-parasitic nematode, we used Illumina mRNA sequencing analysis of a mixed population, as well as nematode reads detected in infected soybean roots 3 and 7 days after nematode infection. Over 140 million paired end reads were obtained for this species, and de novo assembly resulted in a total of 23,715 transcripts. Homology searches showed significant hit matches to 58% of the total number of transcripts using different protein and EST databases. In general, the transcriptome of P. penetrans follows common features reported for other root lesion nematode species. We also explored the efficacy of RNAi, delivered from the host, as a strategy to control P. penetrans, by targeted knock-down of selected nematode genes. Different comparisons were performed to identify putative nematode genes with a role in parasitism, resulting in the identification of transcripts with similarities to other nematode parasitism genes. Focusing on the predicted nematode secreted proteins found in this transcriptome, we observed specific members to be up-regulated at the early time points of infection. In the present study, we observed an enrichment of predicted secreted proteins along the early time points of parasitism by this species, with a significant number being pioneer candidate genes. A representative set of genes examined using RT-PCR confirms their expression during the host infection. The expression patterns of the different candidate genes raise the possibility that they might be involved in critical steps of P. penetrans parasitism. This analysis sheds light on the transcriptional changes that accompany plant infection by P. penetrans, and will aid in identifying potential gene targets for selection and use to design effective control strategies against root lesion nematodes
Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) model
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