6,291 research outputs found
An independent test of the photometric selection of white dwarf candidates using LAMOST DR3
In Gentile Fusillo et al. (2015) we developed a selection method for white
dwarf candidates which makes use of photometry, colours and proper motions to
calculate a probability of being a white dwarf (Pwd). The application of our
method to the Sloan Digital Sky Survey (SDSS) data release 10 resulted in
nearly 66,000 photometrically selected objects with a derived Pwd,
approximately 21000 of which are high confidence white dwarf candidates. Here
we present an independent test of our selection method based on a sample of
spectroscopically confirmed white dwarfs from the LAMOST (Large Sky Area
Multi-Fiber Spectroscopic Telescope) survey. We do this by cross matching all
our 66,000 SDSS photometric white dwarf candidates with the over 4
million spectra available in the third data release of LAMOST. This results in
1673 white dwarf candidates with no previous SDSS spectroscopy, but with
available LAMOST spectra. Among these objects we identify 309 genuine white
dwarfs. We find that our Pwd can efficiently discriminate between confirmed
LAMOST white dwarfs and contaminants. Our white dwarf candidate selection
method can be applied to any multi-band photometric survey and in this work we
conclusively confirm its reliability in selecting white dwarfs without recourse
to spectroscopy. We also discuss the spectroscopic completeness of white dwarfs
in LAMOST, as well as deriving effective temperatures, surface gravities and
masses for the hydrogen-rich atmosphere white dwarfs in the newly identified
LAMOST sample.Comment: 10 pages, 7 figures. Accepted for publication in MNRAS. The full
catalogue presented in table 4 is available at
http://www2.warwick.ac.uk/fac/sci/physics/research/astro/catalogues/SDSS_WD_candidates_with_LAMOST_spectra.cs
Expression of bgt gene in transgenic birch (Betula platyphylla Suk.)
Study on the characteristics of integration and expression is the basis of genetic stability of foreign genes in transgenic trees. To obtain insight into the relationship of transgene copy number and expression level, we screened 22 transgenic birch lines. Southern blot analysis of the transgenic birch plants indicated that the copy number of bgt varies from one to four, of which 18.2% were single copy. Copy number of bgt and gus was different in 68% of transgenic birch plants, indicating that rearrangement or partial deletion appeared in the process of T-DNA integration. Transcriptional expression of bgt gene in transgenic birch plants was analyzed by Northern blot. TGS has been found in two transgenic lines with one and four copies of bgt. The ELISA result showed that the BGT protein expression level in the transgenic birch plants ranged from 0.000 to 0.283% of total soluble protein. In contrary to most studies, this research showed no significant correlation was found between copy number and expression level of bgt gene. Effective resistance of transgenic plants against Lymantria dispar was verified in feeding bioassays with the insects. Bioassays results were mostly consistent with the expression level of BGT insecticidal protein detected by ELISA and Western blot in transgenic birch. The paper showed transgenic birch had the high lethal effect on gypsy moth larvae (L. dispar). The practicality of this work will benefit not only the birch producers, but also the environment worldwide
Gear shift schedule design for multi-speed pure electric vehicles
© IMechE 2014. As pure electric vehicles are considered to be a major growth trend in the automotive industry, research into and development of efficient electric powertrain systems and related control technologies have become popular research topics. The growing importance and use of multi-speed transmissions in these vehicles make shift schedule design and research a crucial aspect of the powertrain systems design of pure electric vehicles. This paper provides a gear shift schedule calculation method for pure electric vehicles, which includes a dynamic shift schedule and an economic shift schedule calculation method, demonstrating how to optimize the shift points and to produce the upshift and downshift lines based on the motor efficiency map. Through the establishment of a pure electric vehicle model, simulation results show that a properly designed shift schedule can improve the working region of the motor and can refine the dynamic performance and the economic performance of the vehicle. Finally, rig testing results are demonstrated to be comparable with simulations and indicate the correctness of the method
Modelling and simulation of a two speed electric vehicle
Electric vehicles offer an alternative to hybrid and conventional vehicles through the use of electcric drive without fossil fuel consumption. This shifts green house gas production from the vehicle to power stations, but if power is supplied from renewable sources, such as wind power, zero emissions are generated. Practical vehicle design requires the consieration of competing demands of vehicle acceleration and performance against range and vehicle efficiency. Thus, considering requirements such as grade climbing and acceleration against vehicle range and power consumption, a two speed transmission is suggested for this vehicle study to increase motor operation at high torque and efficiency regions. To evaluate the application of such a transmission, a two speed electric vehicle powertrain is developed in Simulink®. Simulations are conducted to demonstrate the performance of the two speed electric vehicle. Results reveal the capability of the two speed vehicle to meet various performance criteria and provide an indication of effective range under different drive cycles
A comprehensive study of the open cluster NGC 6866
We present CCD photometry of the field of the open cluster NGC 6866.
Structural parameters of the cluster are determined utilizing the stellar
density profile of the stars in the field. We calculate the probabilities of
the stars being a physical member of the cluster using their astrometric data
and perform further analyses using only the most probable members. The
reddening and metallicity of the cluster were determined by independent
methods. The LAMOST spectra and the ultraviolet excess of the F and G type
main-sequence stars in the cluster indicate that the metallicity of the cluster
is about the solar value. We estimated the reddening
mag using the vs two-colour diagram. The distance modula, the
distance and the age of NGC 6866 were derived as mag,
pc and Myr, respectively, by fitting
colour-magnitude diagrams of the cluster with the PARSEC isochrones. The
Galactic orbit of NGC 6866 indicates that the cluster is orbiting in a slightly
eccentric orbit with . The mass function slope was
derived by using the most probable members of the cluster.Comment: 14 pages, including 16 figures and 7 tables, accepted for publication
in MNRAS. Table 4 in the manuscript will be published electronicall
Geometries for Possible Kinematics
The algebras for all possible Lorentzian and Euclidean kinematics with
isotropy except static ones are re-classified. The geometries
for algebras are presented by contraction approach. The relations among the
geometries are revealed. Almost all geometries fall into pairs. There exists correspondence in each pair. In the viewpoint of
differential geometry, there are only 9 geometries, which have right signature
and geometrical spatial isotropy. They are 3 relativistic geometries, 3
absolute-time geometries, and 3 absolute-space geometries.Comment: 40 pages, 7 figure
HP1 drives de novo 3D genome reorganization in early Drosophila embryos
Fundamental features of 3D genome organization are established de novo in the early embryo, including clustering of pericentromeric regions, the folding of chromosome arms and the segregation of chromosomes into active (A-) and inactive (B-) compartments. However, the molecular mechanisms that drive de novo organization remain unknown. Here, by combining chromosome conformation capture (Hi-C), chromatin immunoprecipitation with high-throughput sequencing (ChIP–seq), 3D DNA fluorescence in situ hybridization (3D DNA FISH) and polymer simulations, we show that heterochromatin protein 1a (HP1a) is essential for de novo 3D genome organization during Drosophila early development. The binding of HP1a at pericentromeric heterochromatin is required to establish clustering of pericentromeric regions. Moreover, HP1a binding within chromosome arms is responsible for overall chromosome folding and has an important role in the formation of B-compartment regions. However, depletion of HP1a does not affect the A-compartment, which suggests that a different molecular mechanism segregates active chromosome regions. Our work identifies HP1a as an epigenetic regulator that is involved in establishing the global structure of the genome in the early embryo
Reciprocal insulation analysis of Hi-C data shows that TADs represent a functionally but not structurally privileged scale in the hierarchical folding of chromosomes
Understanding how regulatory sequences interact in the context of chromosomal architecture is a central challenge in biology. Chromosome conformation capture revealed that mammalian chromosomes possess a rich hierarchy of structural layers, from multi-megabase compartments to sub-megabase topologically associating domains (TADs) and sub-TAD contact domains. TADs appear to act as regulatory microenvironments by constraining and segregating regulatory interactions across discrete chromosomal regions. However, it is unclear whether other (or all) folding layers share similar properties, or rather TADs constitute a privileged folding scale with maximal impact on the organization of regulatory interactions. Here, we present a novel algorithm named CaTCH that identifies hierarchical trees of chromosomal domains in Hi-C maps, stratified through their reciprocal physical insulation, which is a single and biologically relevant parameter. By applying CaTCH to published Hi-C data sets, we show that previously reported folding layers appear at different insulation levels. We demonstrate that although no structurally privileged folding level exists, TADs emerge as a functionally privileged scale defined by maximal boundary enrichment in CTCF and maximal cell-type conservation. By measuring transcriptional output in embryonic stem cells and neural precursor cells, we show that the likelihood that genes in a domain are coregulated during differentiation is also maximized at the scale of TADs. Finally, we observe that regulatory sequences occur at genomic locations corresponding to optimized mutual interactions at the same scale. Our analysis suggests that the architectural functionality of TADs arises from the interplay between their ability to partition interactions and the specific genomic position of regulatory sequences
Random Time-Dependent Quantum Walks
We consider the discrete time unitary dynamics given by a quantum walk on the
lattice performed by a quantum particle with internal degree of freedom,
called coin state, according to the following iterated rule: a unitary update
of the coin state takes place, followed by a shift on the lattice, conditioned
on the coin state of the particle. We study the large time behavior of the
quantum mechanical probability distribution of the position observable in
when the sequence of unitary updates is given by an i.i.d. sequence of
random matrices. When averaged over the randomness, this distribution is shown
to display a drift proportional to the time and its centered counterpart is
shown to display a diffusive behavior with a diffusion matrix we compute. A
moderate deviation principle is also proven to hold for the averaged
distribution and the limit of the suitably rescaled corresponding
characteristic function is shown to satisfy a diffusion equation. A
generalization to unitary updates distributed according to a Markov process is
also provided. An example of i.i.d. random updates for which the analysis of
the distribution can be performed without averaging is worked out. The
distribution also displays a deterministic drift proportional to time and its
centered counterpart gives rise to a random diffusion matrix whose law we
compute. A large deviation principle is shown to hold for this example. We
finally show that, in general, the expectation of the random diffusion matrix
equals the diffusion matrix of the averaged distribution.Comment: Typos and minor errors corrected. To appear In Communications in
Mathematical Physic
- …