3,816 research outputs found
Phonon-Mediated High-Temperature Superconductivity in Few-Hydrogen Metal-Bonded Perovskite up to 54 K under Ambient Pressure
Multi-hydrogen lanthanum hydrides have shown the highest critical temperature
at 250-260 K under 170-200 GPa. However, such high pressure is a great
challenge for sample preparation and practical application. To address this
challenge, we propose a novel design strategy for high- superconductors by
constructing new few-hydrogen metal-bonded perovskite hydrides at ambient
pressure, such as , with better ductility than the well-known
multi-hydrogen, cuprate and iron-based superconductors. Based on the
Migdal-Eliashberg theory, we predict that the structurally stable
has a favorable high up to 54 K under atmospheric pressure, similar to
SmOFeAs.Comment: 6 pages, 4 figure
SAHARA: A Simplified AtmospHeric Correction AlgoRithm for Chinese gAofen Data: 1. Aerosol Algorithm.
The recently launched Chinese GaoFen-4 (GF4) satellite provides valuable information to obtain geophysical parameters describing conditions in the atmosphere and at the Earth’s surface. The surface reflectance is an important parameter for the estimation of other remote sensing parameters linked to the eco-environment, atmosphere environment and energy balance. One of the key issues to achieve atmospheric corrected surface reflectance is to precisely retrieve the aerosol optical properties, especially Aerosol Optical Depth (AOD). The retrieval of AOD and corresponding atmospheric correction procedure normally use the full radiative transfer calculation or Look-Up-Table (LUT) methods, which is very time-consuming. In this paper, a Simplified AtmospHeric correction AlgoRithm for gAofen data (SAHARA) is presented for the retrieval of AOD and corresponding atmospheric correction procedure. This paper is the first part of the algorithm, which describes the aerosol retrieval algorithm. In order to achieve high-accuracy analytical form for both LUT and surface parameterization, the MODIS Dark-Target (DT) aerosol types and Deep Blue (DB) similar surface parameterization have been proposed for GF4 data. Limited Gaofen observations (i.e., all that were available) have been tested and validated. The retrieval results agree quite well with MODIS Collection 6.0 aerosol product, with a correlation coefficient of R2 = 0.72. The comparison between GF4 derived AOD and Aerosol Robotic Network (AERONET) observations has a correlation coefficient of R2 = 0.86. The algorithm, after comprehensive validation, can be used as an operational running algorithm for creating aerosol product from the Chinese GF4 satellite.N/
Achievable Rate Region and Path-Based Beamforming for Multi-User Single-Carrier Delay Alignment Modulation
Delay alignment modulation (DAM) is a novel wideband transmission technique
for mmWave massive MIMO systems, which exploits the high spatial resolution and
multi-path sparsity to mitigate ISI, without relying on channel equalization or
multi-carrier transmission. In particular, DAM leverages the delay
pre-compensation and path-based beamforming to effectively align the multi-path
components, thus achieving the constructive multi-path combination for
eliminating the ISI while preserving the multi-path power gain. Different from
the existing works only considering single-user DAM, this paper investigates
the DAM technique for multi-user mmWave massive MIMO communication. First, we
consider the asymptotic regime when the number of antennas Mt at BS is
sufficiently large. It is shown that by employing the simple delay
pre-compensation and per-path-based MRT beamforming, the single-carrier DAM is
able to perfectly eliminate both ISI and IUI. Next, we consider the general
scenario with Mt being finite. In this scenario, we characterize the achievable
rate region of the multi-user DAM system by finding its Pareto boundary.
Specifically, we formulate a rate-profile-constrained sum rate maximization
problem by optimizing the per-path-based beamforming. Furthermore, we present
three low-complexity per-path-based beamforming strategies based on the MRT,
zero-forcing, and regularized zero-forcing principles, respectively, based on
which the achievable sum rates are studied. Finally, we provide simulation
results to demonstrate the performance of our proposed strategies as compared
to two benchmark schemes based on the strongest-path-based beamforming and the
prevalent OFDM, respectively. It is shown that DAM achieves higher spectral
efficiency and/or lower peak-to-average-ratio, for systems with high spatial
resolution and multi-path diversity.Comment: 13 pages, 5 figure
Quality assurance plan for China collection 2.0 aerosol datasets
The inversion of atmospheric aerosol optical depth (AOD) using satellite data has always been a challenge topic in atmospheric research. In order to solve the aerosol retrieval problem over bright land surface, the Synergetic Retrieval of Aerosol Properties (SRAP) algorithm has been developed based on the synergetic using of the MODIS data of TERRA and AQUA satellites [1, 2]. In this paper we describe, in details, the quality assessment or quality assurance (QA) plan for AOD products derived using the SRAP algorithm. The pixel-based QA plan is to give a QA flag to every step of the process in the AOD retrieval. The quality assessment procedures include three common aspects: 1) input data resource flags, 2) retrieval processing flags, 3) product quality flags [3]. Besides, all AOD products are assigned a QA ‘confidence’ flag (QAC) that represents the aggregation of all the individual QA flags. This QAC value ranges from 3 to 0, with QA = 3 indicating the retrievals of highest confidence and QA = 2/QA = 1 progressively lower confidence [4], and 0 means ‘bad’ quality. These QA (QAC) flags indicate how the particular retrieval process should be considered. It is also used as a filter for expected quantitative value of the retrieval, or to provide weighting for aggregating/averaging computations [5]. All of the QA flags are stored as a “bit flag” scientific dataset array in which QA flags of each step are stored in particular bit positions
(E)-Ethyl N′-(3-hydroxybenzylidene)hydrazinecarboxylate dihydrate
The asymmetric unit of the title compound, C10H12N2O3·2H2O, contains two organic molecules with similar conformations and four water molecules. Each organic molecule is close to planar (r.m.s. deviations = 0.035 and 0.108 Å) and adopts a trans conformation with respect to its C=N bond. In the crystal, the components are linked into a three-dimensional network by N—H⋯O, O—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds, some of which are bifurcated. An R
2
2(8) loop occurs between adjacent organic molecules
An atmospheric correction algorithm for FY3/MERSI data over land in China
Feng-Yun (FY-3) is the second generation of the Chinese Polar Orbiting Meteorological Satellites with global, three-dimensional, quantitative, and multispectral capabilities. Medium Resolution Spectral Imager (MERSI) has 20 channels onboard the FY-3A and FY-3B satellites, including five channels (four VIS and one thermal IR) with a spatial resolution of 250m. The top of the atmosphere signal are necessary to be radiometrically calibrated and corrected for atmospheric effects based on surface reflectance, especially in land surface remote sensing and applications. This paper presents an atmospheric correction algorithm for FY3/MERSI data over land in China, taking into account the directional properties of the observed surface by a kernel-based Bi-directional Reflectance Distribution Function (BRDF) model. The comparison with MODGA and ASD reflectance showed that there is a good agreement. Therefore, FY3/MERSI can serve a reliable and new data source for quantifying global environment change
Post calibration of channel 1 of NOAA-14 AVHRR: Implications on aerosol optical depth retrieval
In order to produce long-term aerosol optical depth (AOD) dataset over land from the Advanced Very High Resolution Radiometer (AVHRR), AVHRR data quality in terms of radiometric calibration must be maintained. A vicarious calibration method have been developed by incorporating well calibrated Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) radiance data over several pseudo-invariant targets to inter-calibrate the channel 1 of AVHRR based on Bidirectional Reflectance Distribution Functions (BRDFs) and spectral band adjustment factor (SBAF) models for different targets. Comparison of our calibration coefficients with those of Pathfinder Atmospheres Extended (PATMOS-x) indicate the calibration accuracy to be within 2.5%. The operational L1B and recalibrated AVHRR radiance are applied to derive AOD maps over East America (dark surface) and West Africa (bright surface) using the land aerosol and bidirectional reflectance inversion by times series technique (LABITS) algorithm. Preliminary comparisons show that significant difference in the retrieved AOD from the two different calibration is expected, while the spatial distribution of AOD difference is
complicated due to different surface brightness and deficiencies of numeric solutions
Probing Primordial Gravitational Waves: Ali CMB Polarization Telescope
In this paper, we will give a general introduction to the project of Ali CMB
Polarization Telescope (AliCPT), which is a Sino-US joint project led by the
Institute of High Energy Physics (IHEP) and has involved many different
institutes in China. It is the first ground-based Cosmic Microwave Background
(CMB) polarization experiment in China and an integral part of China's
Gravitational Waves Program. The main scientific goal of AliCPT project is to
probe the primordial gravitational waves (PGWs) originated from the very early
Universe.
The AliCPT project includes two stages. The first stage referred to as
AliCPT-1, is to build a telescope in the Ali region of Tibet with an altitude
of 5,250 meters. Once completed, it will be the worldwide highest ground-based
CMB observatory and open a new window for probing PGWs in northern hemisphere.
AliCPT-1 telescope is designed to have about 7,000 TES detectors at 90GHz and
150GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with
the number of detectors more than 20,000.
Our simulations show that AliCPT will improve the current constraint on the
tensor-to-scalar ratio by one order of magnitude with 3 years' observation.
Besides the PGWs, the AliCPT will also enable a precise measurement on the CMB
rotation angle and provide a precise test on the CPT symmetry. We show 3 years'
observation will improve the current limit by two order of magnitude.Comment: 11 pages, 7 figures, 2 table
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