198 research outputs found
High-Energy and High-Power-Density Potassium Ion Batteries Using Dihydrophenazine-Based Polymer as Active Cathode Material
Polymeric aromatic amines were shown to be very promising cathodes for lithium-ion batteries. Surprisingly, these materials are scarcely used for designing post-lithium batteries. In this Letter, we investigate the application of the high-voltage poly(N-phenyl-5,10-dihydrophenazine) (p-DPPZ) cathodes for K-ion batteries. The designed batteries demonstrate an impressive specific capacity of 162 mAh g-1 at the current density of 200 mA g-1, operate efficiently at high current densities of 2-10 A g-1, enabling charge and discharge within ∼1-4 min, and deliver the specific capacity of 125-145 mAh g-1 with a retention of 96 and 79% after 100 and 1000 charge-discharge cycles, respectively. Finally, these K-ion batteries with polymeric p-DPPZ cathodes showed rather outstanding specific power of >3 × 104 W kg-1, thus paving a way to the design of ultrafast and durable high-capacity metal-ion batteries matching the increasing demand for high power and high energy density electrochemical energy storage devices. © 2019 American Chemical Society.Government Council on Grants, Russian Federation: 02.Russian Science Foundation, RSF: 16-13-00111This work was supported by Russian Science Foundation, project 16-13-00111. We acknowledge the support of Dr. A. Mumyatov with FTIR spectroscopy measurements. The XPS measurements were supported by the Government of Russian Federation (Act 211, Agreement No. 02.A03.21.0006) and Theme “Electron” (no. AAAA-A18-118020190098-5)
Pseudogap phase formation in the crossover from Bose-Einstein condensation to BCS superconductivity
A phase diagram for a 2D metal with variable carrier density has been
derived. It consists of a normal phase, where the order parameter is absent; a
so-called ``abnormal normal'' phase where this parameter is also absent but the
mean number of composite bosons (bound pairs) exceeds the mean number of free
fermions; a pseudogap phase where the absolute value of the order parameter
gradually increases but its phase is a random value, and finally a
superconducting (here Berezinskii-Kosterlitz-Thouless) phase. The
characteristic transition temperatures between these phases are found. The
chemical potential and paramagnetic susceptibility behavior as functions of the
fermion density and the temperature are also studied. An attempt is made to
qualitatively compare the resulting phase diagram with the features of
underdoped high- superconducting compounds above their critical
temperature.Comment: 26 pages, revtex, 5 EMTeX figures; more discussion and references
added; to be published in JET
Essential and checkpoint functions of budding yeast ATM and ATR during meiotic prophase are facilitated by differential phosphorylation of a meiotic adaptor protein, Hop1
A hallmark of the conserved ATM/ATR signalling is its ability to mediate a wide range of functions utilizing only a limited number of adaptors and effector kinases. During meiosis, Tel1 and Mec1, the budding yeast ATM and ATR, respectively, rely on a meiotic adaptor protein Hop1, a 53BP1/Rad9 functional analog, and its associated kinase Mek1, a CHK2/Rad53-paralog, to mediate multiple functions: control of the formation and repair of programmed meiotic DNA double strand breaks, enforcement of inter-homolog bias, regulation of meiotic progression, and implementation of checkpoint responses. Here, we present evidence that the multi-functionality of the Tel1/Mec1-to-Hop1/Mek1 signalling depends on stepwise activation of Mek1 that is mediated by Tel1/Mec1 phosphorylation of two specific residues within Hop1: phosphorylation at the threonine 318 (T318) ensures the transient basal level Mek1 activation required for viable spore formation during unperturbed meiosis. Phosphorylation at the serine 298 (S298) promotes stable Hop1-Mek1 interaction on chromosomes following the initial phospho-T318 mediated Mek1 recruitment. In the absence of Dmc1, the phospho-S298 also promotes Mek1 hyper-activation necessary for implementing meiotic checkpoint arrest. Taking these observations together, we propose that the Hop1 phospho-T318 and phospho-S298 constitute key components of the Tel1/Mec1- based meiotic recombination surveillance (MRS) network and facilitate effective coupling of meiotic recombination and progression during both unperturbed and challenged meiosis
The GALAH survey: accurate radial velocities and library of observed stellar template spectra
GALAH is a large-scale magnitude-limited southern stellar spectroscopic survey. Its second data release (GALAH DR2) provides values of stellar parameters and abundances of 23 elements for 342 682 stars (Buder et al.). Here we add a description of the public release of radial velocities with a typical accuracy of 0.1 km s−1 for 336 215 of these stars, achievable due to the large wavelength coverage, high resolving power, and good signal-to-noise ratio of the observed spectra, but also because convective motions in stellar atmosphere and gravitational redshift from the star to the observer are taken into account. In the process we derive medians of observed spectra that are nearly noiseless, as they are obtained from between 100 and 1116 observed spectra belonging to the same bin with a width of 50 K in temperature, 0.2 dex in gravity, and 0.1 dex in metallicity. Publicly released 1181 median spectra have a resolving power of 28 000 and trace the well-populated stellar types with metallicities between −0.6 and +0.3. Note that radial velocities from GALAH are an excellent match to the accuracy of velocity components along the sky plane derived by Gaia for the same stars. The level of accuracy achieved here is adequate for studies of dynamics within stellar clusters, associations, and streams in the Galaxy. So it may be relevant for studies of the distribution of dark matter.TZ, GT, and KC acknowledge financial support of ˇ
the Slovenian Research Agency (research core funding No. P1-0188
and project N1-0040). TZ acknowledges the grant from the distinguished visitor programme of the RSAA at the Australian National
University. JK is supported by a Discovery Project grant from the
Australian Research Council (DP150104667) awarded to J. BlandHawthorn and T. Bedding. ARC acknowledges support through
the Australian Research Council through grant DP160100637. LD,
KF, and Y-ST are grateful for support from Australian Research
Council grant DP160103747. SLM acknowledges support from
the Australian Research Council through grant DE140100598. LC
is the recipient of an ARC Future Fellowship (project number
FT160100402). Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number
CE17010001
RASSF1A–LATS1 signalling stabilizes replication forks by restricting CDK2-mediated phosphorylation of BRCA2
Genomic instability is a key hallmark of cancer leading to tumour heterogeneity and therapeutic resistance. BRCA2 has a fundamental role in error-free DNA repair but also sustains genome integrity by promoting RAD51 nucleofilament formation at stalled replication forks. CDK2 phosphorylates BRCA2 (pS3291-BRCA2) to limit stabilizing contacts with polymerized RAD51; however, how replication stress modulates CDK2 activity and whether loss of pS3291-BRCA2 regulation results in genomic instability of tumours are not known. Here we demonstrate that the Hippo pathway kinase LATS1 interacts with CDK2 in response to genotoxic stress to constrain pS3291-BRCA2 and support RAD51 nucleofilaments, thereby maintaining genomic fidelity during replication stalling. We also show that LATS1 forms part of an ATR-mediated response to replication stress that requires the tumour suppressor RASSF1A. Importantly, perturbation of the ATR–RASSF1A–LATS1 signalling axis leads to genomic defects associated with loss of BRCA2 function and contributes to genomic instability and ‘BRCA-ness’ in lung cancers
Ginzburg-Landau theory of superconductors with short coherence length
We consider Fermions in two dimensions with an attractive interaction in the
singlet d-wave channel of arbitrary strength. By means of a
Hubbard-Stratonovich transformation a statistical Ginzburg-Landau theory is
derived, which describes the smooth crossover from a weak-coupling BCS
superconductor to a condensate of composite Bosons. Adjusting the interaction
strength to the observed slope of H_c2 at T_c in the optimally doped high-T_c
compounds YBCO and BSCCO, we determine the associated values of the
Ginzburg-Landau correlation length xi and the London penetration depth lambda.
The resulting dimensionless ratio k_F xi(0) approx 5-8 and the Ginzburg-Landau
parameter kappa=lambda xi approx 90-100 agree well with the experimentally
observed values. These parameters indicate that the optimally doped materials
are still on the weak coupling side of the crossover to a Bose regime.Comment: 12 pages, RevTeX, 6 postscript figures, resubmitted with minor
changes in section III, to appear in Physical Review
Beyond Gaia DR3: tracing the [{\alpha}/M]-[M/H] bimodality from the inner to the outer Milky Way disc with Gaia RVS and Convolutional Neural-Networks
Gaia DR3 has provided the community with about one million RVS spectra
covering the CaII triplet region. In the next Gaia data releases, we anticipate
the number of RVS spectra to successively increase from several 10 million
spectra to eventually more than 200M spectra. Thus, stellar spectra are
produced on an "industrial scale" with numbers well above those for current and
anticipated ground based surveys. However, many of these spectra have low S/N
(from 15 to 25 per pixel), such that they pose problems for classical spectral
analysis pipelines and therefore alternative ways to tap into these large
datasets need to be devised. We aim to leverage the versatility/capabilities of
machine learning techniques for supercharged stellar parametrization, by
combining Gaia RVS spectra with the full set of Gaia products and
high-resolution, high-quality spectroscopic reference data sets. We develop a
hybrid Convolutional Neural-Network (CNN) which combines the Gaia DR3 RVS
spectra, photometry (G, Bp, Rp), parallaxes, and XP coefficients to derive
atmospheric parameters (Teff, log(g), and overall [M/H]) and chemical
abundances ([Fe/H] and [/M]). We trained the CNN with a high-quality
training sample based on APOGEE DR17 labels. With this CNN, we derived
homogeneous atmospheric parameters and abundances for 841300 stars, that
remarkably compared to external data-sets. The CNN is robust against noise in
the RVS data, and very precise labels are derived down to S/N=15. We managed to
characterize the [/M]-[M/H] bimodality from the inner regions to the
outer parts of the Milky Way, which has never been done using RVS spectra or
similar datasets. This work is the first to combine machine-learning with such
diverse datasets (spectroscopy, astrometry, and photometry), and paves the way
for the large scale machine-learning analysis of Gaia-RVS spectra from future
data releases.Comment: 24 pages, 24 figures, submitted to A&
Budding yeast ATM/ATR control meiotic double-strand break (DSB) levels by down-regulating Rec114, an essential component of the DSB-machinery
An essential feature of meiosis is Spo11 catalysis of programmed DNA double strand breaks (DSBs). Evidence suggests that the number of DSBs generated per meiosis is genetically determined and that this ability to maintain a pre-determined DSB level, or "DSB homeostasis", might be a property of the meiotic program. Here, we present direct evidence that Rec114, an evolutionarily conserved essential component of the meiotic DSB-machinery, interacts with DSB hotspot DNA, and that Tel1 and Mec1, the budding yeast ATM and ATR, respectively, down-regulate Rec114 upon meiotic DSB formation through phosphorylation. Mimicking constitutive phosphorylation reduces the interaction between Rec114 and DSB hotspot DNA, resulting in a reduction and/or delay in DSB formation. Conversely, a non-phosphorylatable rec114 allele confers a genome-wide increase in both DSB levels and in the interaction between Rec114 and the DSB hotspot DNA. These observations strongly suggest that Tel1 and/or Mec1 phosphorylation of Rec114 following Spo11 catalysis down-regulates DSB formation by limiting the interaction between Rec114 and DSB hotspots. We also present evidence that Ndt80, a meiosis specific transcription factor, contributes to Rec114 degradation, consistent with its requirement for complete cessation of DSB formation. Loss of Rec114 foci from chromatin is associated with homolog synapsis but independent of Ndt80 or Tel1/Mec1 phosphorylation. Taken together, we present evidence for three independent ways of regulating Rec114 activity, which likely contribute to meiotic DSBs-homeostasis in maintaining genetically determined levels of breaks
The GALAH survey: Multiple stars and our Galaxy. I. A comprehensive method for deriving properties of FGK binary stars
Binary stellar systems form a large fraction of the Galaxy's stars. They are
useful as laboratories for studying the physical processes taking place within
stars, and must be correctly taken into account when observations of stars are
used to study the structure and evolution of the Galaxy. We present a sample of
12760 well-characterised double-lined spectroscopic binaries that are
appropriate for statistical studies of the binary populations. They were
detected as SB2s using a t-distributed stochastic neighbour embedding (t-SNE)
classification and a cross-correlation analysis of GALAH spectra. This sample
consists mostly of dwarfs, with a significant fraction of evolved stars and
several dozen members of the giant branch. To compute parameters of the primary
and secondary star (, , [Fe/H], ,
, , , and ), we used a
Bayesian approach that includes a parallax prior from Gaia DR2, spectra from
GALAH, and apparent magnitudes from APASS, Gaia DR2, 2MASS, and WISE. The
derived stellar properties and their distributions show trends that are
expected for a population of close binaries (a 10 AU) with mass ratios . The derived metallicity of these binary stars is statistically
lower than that of single dwarf stars from the same magnitude-limited sample.Comment: Accepted for publication in A&
Nonperturbative XY-model approach to strong coupling superconductivity in two and three dimensions
For an electron gas with delta-function attraction we investigate the
crossover from weak- to strong-coupling supercoductivity in two and three
dimensions. We derive analytic expressions for the stiffness of phase
fluctuations and set up effective XY-models which serve to determine
nonperturbatively the temperature of phase decoherence where superconductivity
breaks down. We find the transition temperature T_c as a monotonous function of
the coupling strength and carrier density both in two and three dimensions, and
give analytic formulas for the merging of the temperature of phase decoherence
with the temperature of pair formation in the weak-coupling limit.Comment: Few typos corrected. Emails that were sent to the address
[email protected] in June and July 1999 were lost in a computer crash, so if
your comments were not answered please send them once mor
- …