1,112 research outputs found
Tuneable molecular doping of corrugated graphene
Density functional theory (DFT) modeling of the physisorption of four
different types of molecules (toluene, bromine dimmer, water and nitrogen
dioxide) over and above graphene ripples has been performed. For all types of
molecules changes of charge transfer and binding energies in respect to flat
graphene is found. The changes in electronic structure of corrugated graphene
and turn of {\pi}-orbitals of carbon atoms in combination with chemical
structure of adsorbed molecules are proposed as the causes of difference with
the perfect graphene case and variety of adsorption properties of different
types of the molecules. Results of calculation suggest that the tops of the
ripples are more attractive for large molecules and valley between ripples for
small molecules. Stability of molecules on the ripples and energy barriers for
migration over flat and corrugated graphene is also discussed.Comment: 15 pages, 5 figures, accepted in Surface Scienc
Analytical and clinical evaluation of an electrochemiluminescence immunoassay for the determination of CA 125
The CA 125 II assay on the Elecsys(R) 2010 analyzer was evaluated in an
international multicenter trial. Imprecision studies yielded within-run
CVs of 0.8-3.3% and between-day CVs of 2.4-10.9%; CVs for total
imprecision in the manufacturer's laboratory were 2.4-7.8%. The linear
range of the assay extended to at least 4500 kilounits/L (three decades).
Interference from triglycerides (10.3 mmol/L), bilirubin (850 micromol/L),
hemoglobin (1.1 mmol/L), anticoagulants (plasma), and several widely used
drugs was undetectable. Method comparisons with five other CA 125 II
assays showed good correlation but differences in standardization. A 95th
percentile cutoff value of 35 kilounits/L was calculated from values
measured in 593 apparently healthy (pre- and postmenopausal) women. In 95%
of patients with benign gynecological diseases CA 125 was </=190
kilounits/L; 63% of patients with newly diagnosed ovarian carcinoma had
values >190 kilounits/L. A comparison of CA 125 values obtained with the
Elecsys test and with other common CA 125 tests in monitored patients
being treated for ovarian cancer showed identical patterns. In conclusion,
the Elecsys CA 125 II assay is linear over a broad range, yields precise
and accurate results, is free from interferences, and compares well with
other assays
Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time
We present a model for structure formation, melting, and optical properties
of gold/DNA nanocomposites. These composites consist of a collection of gold
nanoparticles (of radius 50 nm or less) which are bound together by links made
up of DNA strands. In our structural model, the nanocomposite forms from a
series of Monte Carlo steps, each involving reaction-limited cluster-cluster
aggregation (RLCA) followed by dehybridization of the DNA links. These links
form with a probability which depends on temperature and particle
radius . The final structure depends on the number of monomers (i. e. gold
nanoparticles) , , and the relaxation time. At low temperature, the
model results in an RLCA cluster. But after a long enough relaxation time, the
nanocomposite reduces to a compact, non-fractal cluster. We calculate the
optical properties of the resulting aggregates using the Discrete Dipole
Approximation. Despite the restructuring, the melting transition (as seen in
the extinction coefficient at wavelength 520 nm) remains sharp, and the melting
temperature increases with increasing as found in our previous
percolation model. However, restructuring increases the corresponding link
fraction at melting to a value well above the percolation threshold. Our
calculated extinction cross section agrees qualitatively with experiments on
gold/DNA composites. It also shows a characteristic ``rebound effect,''
resulting from incomplete relaxation, which has also been seen in some
experiments. We discuss briefly how our results relate to a possible sol-gel
transition in these aggregates.Comment: 12 pages, 10 figure
Anisotropic dark energy stars
A model of compact object coupled to inhomogeneous anisotropic dark energy is
studied. It is assumed a variable dark energy that suffers a phase transition
at a critical density. The anisotropic Lambda-Tolman-Oppenheimer-Volkoff
equations are integrated to know the structure of these objects. The anisotropy
is concentrated on a thin shell where the phase transition takes place, while
the rest of the star remains isotropic. The family of solutions obtained
depends on the coupling parameter between the dark energy and the fermion
matter. The solutions share several features in common with the gravastar
model. There is a critical coupling parameter that gives non-singular black
hole solutions. The mass-radius relations are studied as well as the internal
structure of the compact objects. The hydrodynamic stability of the models is
analyzed using a standard test from the mass-radius relation. For each
permissible value of the coupling parameter there is a maximum mass, so the
existence of black holes is unavoidable within this model.Comment: 12 pages, 6 figures, final manuscript, Accepted for publication in
Astrophysics & Space Scienc
Neutrino Mass from R-parity Violation in Split Supersymmetry
We investigate how the observed neutrino data can be accommodated by R-parity
violation in Split Supersymmetry. The atmospheric neutrino mass and mixing are
explained by the bilinear parameters inducing the neutrino-neutralino
mixing as in the usual low-energy supersymmetry. Among various one-loop
corrections, only the quark-squark exchanging diagrams involving the order-one
trilinear couplings can generate the solar neutrino mass
and mixing if the scalar mass is not larger than GeV. This scheme
requires an unpleasant hierarchical structure of the couplings, e.g.,
, and . On the other hand, the model has a distinct collider
signature of the lightest neutralino which can decay only to the final states,
and , arising from the bilinear mixing. Thus, the
measurement of the ratio; would provide a clean probe of the small reactor and
large atmospheric neutrino mixing angles as far as the neutralino mass is
larger than 62 GeV.Comment: 10 pages, 3 figures, version submitted to JHE
Proteome profiling outperforms transcriptome profiling for coexpression based gene function prediction
Coexpression of mRNAs under multiple conditions is commonly used to infer cofunctionality of their gene products despite well-known limitations of this "guilt-by-association" (GBA) approach. Recent advancements in mass spectrometry-based proteomic technologies have enabled global expression profiling at the protein level; however, whether proteome profiling data can outperform transcriptome profiling data for coexpression based gene function prediction has not been systematically investigated. Here, we address this question by constructing and analyzing mRNA and protein coexpression networks for three cancer types with matched mRNA and protein profiling data from The Cancer Genome Atlas (TCGA) and the Clinical Proteomic Tumor Analysis Consortium (CPTAC). Our analyses revealed a marked difference in wiring between the mRNA and protein coexpression networks. Whereas protein coexpression was driven primarily by functional similarity between coexpressed genes, mRNA coexpression was driven by both cofunction and chromosomal colocalization of the genes. Functionally coherent mRNA modules were more likely to have their edges preserved in corresponding protein networks than functionally incoherent mRNA modules. Proteomic data strengthened the link between gene expression and function for at least 75% of Gene Ontology (GO) biological processes and 90% of KEGG pathways. A web application Gene2Net (http://cptac.gene2net.org) developed based on the three protein coexpression networks revealed novel gene-function relationships, such as linking ERBB2 (HER2) to lipid biosynthetic process in breast cancer, identifying PLG as a new gene involved in complement activation, and identifying AEBP1 as a new epithelial-mesenchymal transition (EMT) marker. Our results demonstrate that proteome profiling outperforms transcriptome profiling for coexpression based gene function prediction. Proteomics should be integrated if not preferred in gene function and human disease studies
Reionization by active sources and its effects on the cosmic microwave background
We investigate the possible effects of reionization by active sources on the
cosmic microwave background. We concentrate on the sources themselves as the
origin of reionization, rather than early object formation, introducing an
extra period of heating motivated by the active character of the perturbations.
Using reasonable parameters, this leads to four possibilities depending on the
time and duration of the energy input: delayed last scattering, double last
scattering, shifted last scattering and total reionization. We show that these
possibilities are only very weakly constrained by the limits on spectral
distortions from the COBE FIRAS measurements. We illustrate the effects of
these reionization possibilities on the angular power spectrum of temperature
anisotropies and polarization for simple passive isocurvature models and simple
coherent sources, observing the difference between passive and active models.
Finally, we comment on the implications of this work for more realistic active
sources, such as causal white noise and topological defect models. We show for
these models that non-standard ionization histories can shift the peak in the
CMB power to larger angular scales.Comment: 21 pages LaTeX with 11 eps figures; replaced with final version
accepted for publication in Phys. Rev.
Effects of Large CP violating phases on g_{\m}-2 in MSSM
Effects of CP violation on the supersymmetric electro-weak correction to the
anomalous magnetic moment of the muon are investigated with the most general
allowed set of CP violating phases in MSSM. The analysis includes contributions
from the chargino and the neutralino exchanges to the muon anomaly. The
supersymmetric contributions depend only on specific combinations of CP phases.
The independent set of such phases is classified. We analyse the effects of the
phases under the EDM constraints and show that large CP violating phases can
drastically affect the magnitude of the supersymmetric electro-weak
contribution to and may even affect its overall sign.Comment: 26 pages Latex file including 4 figure
Possible origins of macroscopic left-right asymmetry in organisms
I consider the microscopic mechanisms by which a particular left-right (L/R)
asymmetry is generated at the organism level from the microscopic handedness of
cytoskeletal molecules. In light of a fundamental symmetry principle, the
typical pattern-formation mechanisms of diffusion plus regulation cannot
implement the "right-hand rule"; at the microscopic level, the cell's
cytoskeleton of chiral filaments seems always to be involved, usually in
collective states driven by polymerization forces or molecular motors. It seems
particularly easy for handedness to emerge in a shear or rotation in the
background of an effectively two-dimensional system, such as the cell membrane
or a layer of cells, as this requires no pre-existing axis apart from the layer
normal. I detail a scenario involving actin/myosin layers in snails and in C.
elegans, and also one about the microtubule layer in plant cells. I also survey
the other examples that I am aware of, such as the emergence of handedness such
as the emergence of handedness in neurons, in eukaryote cell motility, and in
non-flagellated bacteria.Comment: 42 pages, 6 figures, resubmitted to J. Stat. Phys. special issue.
Major rewrite, rearranged sections/subsections, new Fig 3 + 6, new physics in
Sec 2.4 and 3.4.1, added Sec 5 and subsections of Sec
Dimers, Effective Interactions, and Pauli Blocking Effects in a Bilayer of Cold Fermionic Polar Molecules
We consider a bilayer setup with two parallel planes of cold fermionic polar
molecules when the dipole moments are oriented perpendicular to the planes. The
binding energy of two-body states with one polar molecule in each layer is
determined and compared to various analytic approximation schemes in both
coordinate- and momentum-space. The effective interaction of two bound dimers
is obtained by integrating out the internal dimer bound state wave function and
its robustness under analytical approximations is studied. Furthermore, we
consider the effect of the background of other fermions on the dimer state
through Pauli blocking, and discuss implications for the zero-temperature
many-body phase diagram of this experimentally realizable system.Comment: 18 pages, 10 figures, accepted versio
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