2,105 research outputs found
DHCR7 mutations linked to higher vitamin D status allowed early human migration to Northern latitudes
PMCID: PMC3708787This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
Parametrization of Quintessence and Its Potential
We develop a theoretical method of constructing the quintessence potential
directly from the effective equation of state function , which describes
the properties of the dark energy. We apply our method to four parametrizations
of equation of state parameter and discuss the general features of the
resulting potentials. In particular, it is shown that the constructed
quintessence potentials are all in the form of a runaway type.Comment: 6 pages, 2 figures, LaTeX2
Parametrizations of the Dark Energy Density and Scalar Potentials
We develop a theoretical method of constructing the scalar (quintessence or
phantom) potential directly from the dimensionless dark energy function X(z),
the dark energy density in units of its present value. We apply our method to
two parametrizations of the dark energy density, the quiessence-Lambda ansatz
and the generalized Chaplygin gas model, and discuss some features of the
constructed potentials.Comment: 8 pages, 2 figures, ws-mpla.cls, Accepted for publication in Mod.
Phys. Lett.
Two-Field Quintom Models in the w-w' Plane
The w-w' plane, defined by the equation of state parameter for the dark
energy and its derivative with respect to the logarithm of the scale factor, is
useful to the study of classifying the dynamical dark energy models. In this
note, we examine the evolving behavior of the two-field quintom models with w
crossing the w=-1 barrier in the w-w' plane. We find that these models can be
divided into two categories, type A quintom in which w changes from >-1 to <-1
and type B quintom in which w changes from -1 as the universe expands.Comment: 5 pages, 2 figures, RevTeX, Accepted for publication as a Brief
Report in Physical Review
Site-selective protein modification via disulfide rebridging for fast tetrazine/trans-cyclooctene bioconjugation
An inverse electron demand DielsâAlder reaction between tetrazine and trans-cyclooctene (TCO) holds great promise for protein modification and manipulation. Herein, we report the design and synthesis of a tetrazine-based disulfide rebridging reagent, which allows the site-selective installation of a tetrazine group into disulfide-containing peptides and proteins such as the hormone somatostatin (SST) and the antigen binding fragment (Fab) of human immunoglobulin G (IgG). The fast and efficient conjugation of the tetrazine modified proteins with three different TCO-containing substrates to form a set of bioconjugates in a site-selective manner was successfully demonstrated for the first time. Homogeneous, well-defined bioconjugates were obtained underlining the great potential of our method for fast bioconjugation in emerging protein therapeutics. The formed bioconjugates were stable against glutathione and in serum, and they maintained their secondary structure. With this work, we broaden the scope of tetrazine chemistry for site-selective protein modification to prepare well-defined SST and Fab conjugates with preserved structures and good stability under biologically relevant conditions
Probing the Coupling between Dark Components of the Universe
We place observational constraints on a coupling between dark energy and dark
matter by using 71 Type Ia supernovae (SNe Ia) from the first year of the
five-year Supernova Legacy Survey (SNLS), the cosmic microwave background (CMB)
shift parameter from the three-year Wilkinson Microwave Anisotropy Probe
(WMAP), and the baryon acoustic oscillation (BAO) peak found in the Sloan
Digital Sky Survey (SDSS). The interactions we study are (i) constant coupling
delta and (ii) varying coupling delta(z) that depends on a redshift z, both of
which have simple parametrizations of the Hubble parameter to confront with
observational data. We find that the combination of the three databases
marginalized over a present dark energy density gives stringent constraints on
the coupling, -0.08 < delta < 0.03 (95% CL) in the constant coupling model and
-0.4 < delta_0 < 0.1 (95% CL) in the varying coupling model, where delta_0 is a
present value. The uncoupled LambdaCDM model (w_X = -1 and delta = 0) still
remains a good fit to the data, but the negative coupling (delta < 0) with the
equation of state of dark energy w_X < -1 is slightly favoured over the
LambdaCDM model.Comment: 9 pages, 7 figures, RevTeX, minor corrections, references added,
accepted for publication in Phys. Rev.
Subcritical Flow at Open Channel Structures Bridge Constructions
The techniques previously employed by the writers for describing subcritical flow at open channel constrictions have been found valid for analyzing nonuniform flow in open channels. Combining the nonuniform flow analysis with the submerged flow ratings for various bridge geometrics has provided an analytical means for determining the backwater due to the bridge constrictions under âabnormal stage â dischargeâ conditions
- âŠ