1,574 research outputs found
Simple Combined Model for Nonlinear Excitations in DNA
We propose a new simple model for DNA denaturation bases on the pendulum
model of Englander\cite{A1} and the microscopic model of Peyrard {\it et
al.},\cite{A3} so called "combined model". The main parameters of our model
are: the coupling constant along each strand, the mean stretching
of the hydrogen bonds, the ratio of the damping constant and driven force
. We show that both the length of unpaired bases and the velocity
of kinks depend on not only the coupling constant but also the
temperature . Our results are in good agreement with previous works.Comment: 6 pages, 10 figures, submitted to Phys. Rev.
Obliquity Constraints on an Extrasolar Planetary-Mass Companion
We place the first constraints on the obliquity of a planetary-mass companion outside of the solar system. Our target is the directly imaged system 2MASS J01225093–2439505 (2M0122), which consists of a 120 Myr 0.4 M⊙ star hosting a 12–27 M_J companion at 50 au. We constrain all three of the system's angular-momentum vectors: how the companion spin axis, the stellar spin axis, and the orbit normal are inclined relative to our line of sight. To accomplish this, we measure projected rotation rates (v sin i) for both the star and the companion using new near-infrared high-resolution spectra with NIRSPEC at Keck Observatory. We combine these with a new stellar photometric rotation period from TESS and a published companion rotation period from Hubble Space Telescope to obtain spin-axis inclinations for both objects. We also fitted multiple epochs of astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b's orbital inclination. The three line-of-sight inclinations place limits on the true de-projected companion obliquity and stellar obliquity. We find that while the stellar obliquity marginally prefers alignment, the companion obliquity tentatively favors misalignment. We evaluate possible origin scenarios. While collisions, secular spin–orbit resonances, and Kozai–Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk—the scenario favored for brown dwarf companions to stars—appears promising
A TILLING by sequencing approach to identify induced mutations in sunflower genes
The Targeting Induced Local Lesions in Genomes (TILLING) technology is a reverse genetic strategy broadly applicable to every kind of genome and represents an attractive tool for functional genomic and agronomic applications. It consists of chemical random mutagenesis followed by high-throughput screening of point mutations in targeted genomic regions. Although multiple methods for mutation discovery in amplicons have been described, next-generation sequencing (NGS) is the tool of choice for mutation detection because it quickly allows for the analysis of a large number of amplicons. The aim of the present work was to screen a previously generated sunflower TILLING population and identify alterations in genes involved in several important and complex physiological processes. Twenty-one candidate sunflower genes were chosen as targets for the screening. The TILLING by sequencing strategy allowed us to identify multiple mutations in selected genes and we subsequently validated 16 mutations in 11 different genes through Sanger sequencing. In addition to addressing challenges posed by outcrossing, our detection and validation of mutations in multiple regulatory loci highlights the importance of this sunflower population as a genetic resource
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Editorial: summary for policymakers of the thematic assessment on pollinators, pollination and food production
Values of pollinators and pollination
1. Animal pollination plays a vital role as a regulating ecosystem service in nature. Globally, nearly 90 per cent of wild flowering plant species depend, at least in part, on the transfer of pollen by animals. These plants are critical for the continued functioning of ecosystems as they provide food, form habitats, and provide other resources for a wide range of other species.
2. More than three quarters of the leading types of global
food crops rely to some extent on animal pollination for yield and/or quality. Pollinator-dependent crops contribute to 35 per cent of global crop production volume.
3. Given that pollinator-dependent crops rely on animal pollination to varying degrees, it is estimated that 5–8 per cent of current global crop production is directly attributed to animal pollination with an annual market value of 577 billion (in 2015, United States dollars1) worldwide
Inferring the effective thickness of polyelectrolytes from stretching measurements at various ionic strengths: applications to DNA and RNA
By resorting to the thick-chain model we discuss how the stretching response
of a polymer is influenced by the self-avoidance entailed by its finite
thickness. The characterization of the force versus extension curve for a thick
chain is carried out through extensive stochastic simulations. The
computational results are captured by an analytic expression that is used to
fit experimental stretching measurements carried out on DNA and single-stranded
RNA (poly-U) in various solutions. This strategy allows us to infer the
apparent diameter of two biologically-relevant polyelectrolytes, namely DNA and
poly-U, for different ionic strengths. Due to the very different degree of
flexibility of the two molecules, the results provide insight into how the
apparent diameter is influenced by the interplay between the
(solution-dependent) Debye screening length and the polymers' ``bare''
thickness. For DNA, the electrostatic contribution to the effective radius,
, is found to be about 5 times larger than the Debye screening length,
consistently with previous theoretical predictions for highly-charged stiff
rods. For the more flexible poly-U chains the electrostatic contribution to
is found to be significantly smaller than the Debye screening length.Comment: iopart, 14 pages, 13 figures, to appear in J. Phys.: Condens. Matte
Random Scattering by Atomic Density Fluctuations in Optical Lattices
We investigate hitherto unexplored regimes of probe scattering by atoms
trapped in optical lattices: weak scattering by effectively random atomic
density distributions and multiple scattering by arbitrary atomic
distributions. Both regimes are predicted to exhibit a universal semicircular
scattering lineshape for large density fluctuations, which depend on
temperature and quantum statistics.Comment: 4 pages, 2 figure
Synthesis and Photocatalytic Activity for Toluene Removal of CDs/TiO2 - Zeolite Y
Hydrothermally synthesized carbon nanodots (CDs) were impregnated on TiO2. The product (CDs/TiO2) was mechanically mixed with zeolite Y for application in toluene photocatalytic oxidation reaction under UV radiation. Material properties of the samples were investigated by different methods. Toluene vapor was chosen as a typical volatile organic compound to investigate the performance of CDs/TiO2 – zeolite Y photocatalyst when these technological parameters were changed: toluene concentration, gas flow rate, humidity and UV light intensity. In each reaction, only one parameter was changed and the remaining conditions were fixed. The toluene concentrations at the beginning and the end of each reaction were analyzed with the use of gas chromatography (GC). The results of different reaction conditions show the trends for toluene treatment of the CDs/TiO2 – zeolite Y catalyst, thereby providing specific explanations for these trends. The experiments also show that toluene removal is highest when the toluene concentration in the inlet gas is 314 ppmv, the flow rate is 3 L/h, the humidity is 60%, and the catalyst (CDs/TiO2 – zeolite Y composite with 70% zeolite in weight) is illuminated by 4 UV lamps. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).
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