232 research outputs found
Exact exchange-correlation potential of a ionic Hubbard model with a free surface
We use Lanczos exact diagonalization to compute the exact
exchange-correlation (xc) potential of a Hubbard chain with large binding
energy ("the bulk") followed by a chain with zero binding energy ("the
vacuum"). Several results of density functional theory in the continuum
(sometimes controversial) are verified in the lattice. In particular we show
explicitly that the fundamental gap is given by the gap in the Kohn-Sham
spectrum plus a contribution due to the jump of the xc-potential when a
particle is added. The presence of a staggered potential and a nearest-neighbor
interaction V allows to simulate a ionic solid. We show that in the ionic
regime in the small hopping amplitude limit the xc-contribution to the gap
equals V, while in the Mott regime it is determined by the Hubbard U
interaction. In addition we show that correlations generates a new potential
barrier at the surface
Testing gravity using galaxy-galaxy lensing and clustering amplitudes in KiDS-1000, BOSS, and 2dFLenS
The physics of gravity on cosmological scales affects both the rate of assembly of large-scale structure and the gravitational lensing of background light through this cosmic web. By comparing the amplitude of these different observational signatures, we can construct tests that can distinguish general relativity from its potential modifications. We used the latest weak gravitational lensing dataset from the Kilo-Degree Survey, KiDS-1000, in conjunction with overlapping galaxy spectroscopic redshift surveys, BOSS and 2dFLenS, to perform the most precise existing amplitude-ratio test. We measured the associated E_{G} statistic with 15 - 20% errors in five Îz = 0.1 tomographic redshift bins in the range 0.2 < z < 0.7 on projected scales up to 100â h^{-1} Mpc. The scale-independence and redshift-dependence of these measurements are consistent with the theoretical expectation of general relativity in a Universe with matter density Ω_{m} = 0.27 ± 0.04. We demonstrate that our results are robust against different analysis choices, including schemes for correcting the effects of source photometric redshift errors, and we compare the performance of angular and projected galaxy-galaxy lensing statistics
The catalog-to-cosmology framework for weak lensing and galaxy clustering for LSST
We present TXPipe, a modular, automated and reproducible pipeline for
ingesting catalog data and performing all the calculations required to obtain
quality-assured two-point measurements of lensing and clustering, and their
covariances, with the metadata necessary for parameter estimation. The pipeline
is developed within the Rubin Observatory Legacy Survey of Space and Time
(LSST) Dark Energy Science Collaboration (DESC), and designed for cosmology
analyses using LSST data. In this paper, we present the pipeline for the
so-called 3x2pt analysis -- a combination of three two-point functions that
measure the auto- and cross-correlation between galaxy density and shapes. We
perform the analysis both in real and harmonic space using TXPipe and other
LSST-DESC tools. We validate the pipeline using Gaussian simulations and show
that it accurately measures data vectors and recovers the input cosmology to
the accuracy level required for the first year of LSST data under this
simplified scenario. We also apply the pipeline to a realistic mock galaxy
sample extracted from the CosmoDC2 simulation suite (Korytov et al. 2019).
TXPipe establishes a baseline framework that can be built upon as the LSST
survey proceeds. Furthermore, the pipeline is designed to be easily extended to
science probes beyond the 3x2pt analysis.Comment: 20+11 pages, 10+11 figures. Version accepted in The Open Journal of
Astrophysic
Consistent lensing and clustering in a low-S8 Universe with BOSS, DES Year 3, HSC Year 1, and KiDS-1000
We evaluate the consistency between lensing and clustering based on measurements from Baryon Oscillation Spectroscopic Survey combined with galaxy-galaxy lensing from Dark Energy Survey (DES) Year 3, Hyper Suprime-Cam Subaru Strategic Program (HSC) Year 1, and Kilo-Degree Survey (KiDS)-1000. We find good agreement between these lensing data sets. We model the observations using the DARK EMULATOR and fit the data at two fixed cosmologies: Planck (S8 = 0.83), and a Lensing cosmology (S8 = 0.76). For a joint analysis limited to large scales, we find that both cosmologies provide an acceptable fit to the data. Full utilization of the higher signal-to-noise small-scale measurements is hindered by uncertainty in the impact of baryon feedback and assembly bias, which we account for with a reasoned theoretical error budget. We incorporate a systematic inconsistency parameter for each redshift bin, A, that decouples the lensing and clustering. With a wide range of scales, we find different results for the consistency between the two cosmologies. Limiting the analysis to the bins for which the impact of the lens sample selection is expected to be minimal, for the Lensing cosmology, the measurements are consistent with A = 1; A = 0.91 ± 0.04 (A = 0.97 ± 0.06) using DES+KiDS (HSC). For the Planck case, we find a discrepancy: A = 0.79 ± 0.03 (A = 0.84 ± 0.05) using DES+KiDS (HSC). We demonstrate that a kinematic Sunyaev-Zeldovich-based estimate for baryonic effects alleviates some of the discrepancy in the Planck cosmology. This analysis demonstrates the statistical power of small-scale measurements; however, caution is still warranted given modelling uncertainties and foreground sample selection effects
Recent visible light and metal free strategies in [2+2] and [4+2] photocycloadditions
When aiming to synthesize molecules with elevated molecular complexity starting from relatively simple starting materials, photochemical transformations represent an open avenue to circumvent analogous multistep procedures. Specifically, light-mediated cycloadditions remain as powerful tools to generate new bonds begotten from non-very intuitive disconnections, that alternative thermal protocols would not offer. In response to the current trend in both industrial and academic research pointing towards green and sustainable processes, several strategies that meet these requirements are currently available in the literature. This Minireview summarizes [2+2] and [4+2] photocycloadditions that do not require the use of metal photocatalysts by means of alternative strategies. It is segmented according to the cycloaddition type in order to give the reader a friendly approach and we primarily focus on the most recent developments in the field carried out using visible light, a general overview of the mechanism in each case is offered as wellFinancial support was provided by the European Research Council (ERC-CoG, Contract Number: 647550), the Spanish Government (RTI2018-095038-B-I00), the âComunidad de Madridâ and European Structural Funds (S2018/NMT-4367). R. I. R thanks FundaciĂłn Carolina for a graduate fellowshi
Noncovalent Interactions of Hydrated DNA and RNA Mapped by 2D-IR Spectroscopy
Biomolecules couple to their aqueous environment through a variety of
noncovalent interactions. Local structures at the surface of DNA and RNA are
frequently determined by hydrogen bonds with water molecules, complemented by
non-specific electrostatic and many-body interactions. Structural fluctuations
of the water shell result in fluctuating Coulomb forces on polar and/or ionic
groups of the biomolecular structure and in a breaking and reformation of
hydrogen bonds. Two-dimensional infrared (2D-IR) spectroscopy of vibrational
modes of DNA and RNA gives insight into local hydration geometries, elementary
molecular dynamics, and the mechanisms behind them. In this chapter, recent
results from 2D-IR spectroscopy of native and artificial DNA and RNA are
presented, together with theoretical calculations of molecular couplings and
molecular dynamics simulations. Backbone vibrations of DNA and RNA are
established as sensitive noninvasive probes of the complex behavior of hydrated
helices. The results reveal the femtosecond fluctuation dynamics of the water
shell, the short-range character of Coulomb interactions, and the strength and
fluctuation amplitudes of interfacial electric fields.Comment: To appear as Chapter 8 of Springer Series in Optical Sciences:
Coherent Multidimensional Spectroscopy -- Editors: Cho, Minhaeng (Ed.), 201
Methods to Quantify Nanomaterial Association with, and Distribution across, the Blood-Brain Barrier in Vivo
The role and functional anatomy of the blood-brain barrier (BBB) is summarized to enable the investigator to appropriately address evaluation of nanomaterial interaction with, and distribution across, it into brain tissue (parenchyma). Transport mechanisms across the BBB are presented, in relation to nanomaterial physicochemical properties. Measures and test substances to assess BBB integrity/disruption/permeation are introduced, along with how they are used to interpret the results obtained with the presented methods. Experimental pitfalls and misinterpretation of results of studies of brain nanomaterial uptake are briefly summarized, that can be avoided with the methods presented in this chapter. Two methods are presented. The in situ brain perfusion technique is used to determine rate and extent of nanomaterial distribution into the brain. The capillary depletion method separates brain parenchymal tissue from the endothelial cells that contribute to the BBB. It is used to verify nanomaterial brain tissue entry. These methods are best used together, the latter refining the results obtained with the former. Details of the materials and equipment needed to conduct these methods, and description of the procedures and data interpretation, are provided
Strong detection of the CMB lensingxgalaxy weak lensingcross-correlation from ACT-DR4,PlanckLegacy and KiDS-1000
We measure the cross-correlation between galaxy weak lensing data from the
Kilo Degree Survey (KiDS-1000, DR4) and cosmic microwave background (CMB)
lensing data from the Atacama Cosmology Telescope (ACT, DR4) and the Planck
Legacy survey. We use two samples of source galaxies, selected with photometric
redshifts, and , which produce a
combined detection significance of the CMB lensing/weak galaxy lensing
cross-spectrum of . With the lower redshift galaxy sample, for which
the cross-correlation is detected at a significance of , we present
joint cosmological constraints on the matter density parameter, , and the matter fluctuation amplitude parameter, , marginalising
over three nuisance parameters that model our uncertainty in the redshift and
shear calibration, and the intrinsic alignment of galaxies. We find our
measurement to be consistent with the best-fitting flat CDM
cosmological models from both Planck and KiDS-1000. We demonstrate the capacity
of CMB-weak lensing cross-correlations to set constraints on either the
redshift or shear calibration, by analysing a previously unused high-redshift
KiDS galaxy sample , with the cross-correlation detected at
a significance of . This analysis provides an independent assessment
for the accuracy of redshift measurements in a regime that is challenging to
calibrate directly owing to known incompleteness in spectroscopic surveys.Comment: 13 pages, 9 figures, 1 tables, submitted to A&
The CPLEAR detector at CERN
The CPLEAR collaboration has constructed a detector at CERN for an extensive programme of CP-, T- and CPT-symmetry studies using and produced by the annihilation of 's in a hydrogen gas target. The and are identified by their companion products of the annihilation which are tracked with multiwire proportional chambers, drift chambers and streamer tubes. Particle identification is carried out with a liquid Cherenkov detector for fast separation of pions and kaons and with scintillators which allow the measurement of time of flight and energy loss. Photons are measured with a lead/gas sampling electromagnetic calorimeter. The required antiproton annihilation modes are selected by fast online processors using the tracking chamber and particle identification information. All the detectors are mounted in a 0.44 T uniform field of an axial solenoid of diameter 2 m and length 3.6 m to form a magnetic spectrometer capable of full on-line reconstruction and selection of events. The design, operating parameters and performance of the sub-detectors are described.
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