3,557 research outputs found
The Influence of Aerosol Hygroscopicity on Precipitation Intensity During a Mesoscale Convective Event
We examine how aerosol composition affects precipitation intensity using the Weather and Research Forecasting Model with Chemistry (version 3.6). By changing the prescribed default hygroscopicity values to updated values from laboratory studies, we test model assumptions about individual component hygroscopicity values of ammonium, sulfate, nitrate, and organic species. We compare a baseline simulation (BASE, using default hygroscopicity values) with four sensitivity simulations (SULF, increasing the sulfate hygroscopicity; ORG, decreasing organic hygroscopicity; SWITCH, using a concentration‐dependent hygroscopicity value for ammonium; and ALL, including all three changes) to understand the role of aerosol composition on precipitation during a mesoscale convective system (MCS). Overall, the hygroscopicity changes influence the spatial patterns of precipitation and the intensity. Focusing on the maximum precipitation in the model domain downwind of an urban area, we find that changing the individual component hygroscopicities leads to bulk hygroscopicity changes, especially in the ORG simulation. Reducing bulk hygroscopicity (e.g., ORG simulation) initially causes fewer activated drops, weakened updrafts in the midtroposphere, and increased precipitation from larger hydrometeors. Increasing bulk hygroscopicity (e.g., SULF simulation) simulates more numerous and smaller cloud drops and increases precipitation. In the ALL simulation, a stronger cold pool and downdrafts lead to precipitation suppression later in the MCS evolution. In this downwind region, the combined changes in hygroscopicity (ALL) reduces the overprediction of intense events (>70 mm d−1) and better captures the range of moderate intensity (30–60 mm d−1) events. The results of this single MCS analysis suggest that aerosol composition can play an important role in simulating high‐intensity precipitation events.Key PointsAerosol composition can affect spatial patterns of precipitationHygroscopicity and hydrometeor vertical distributions are sensitive to aerosol composition and impact precipitation processesAltering speciated aerosol hygroscopicity can influence the simulation of precipitation intensityPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141976/1/jgrd54341.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141976/2/jgrd54341_am.pd
Charge Ordering and Spin Dynamics in NaV2O5
We report high-resolution neutron inelastic scattering experiments on the
spin excitations of NaV2O5. Below Tc, two branches associated with distinct
energy gaps are identified. From the dispersion and intensity of the spin
excitation modes, we deduce the precise zig-zag charge distribution on the
ladder rungs and the corresponding charge order (about 0.6). We argue that the
spin gaps observed in the low-T phase of this compound are primarily due to the
charge transfer.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
From Skew-Cyclic Codes to Asymmetric Quantum Codes
We introduce an additive but not -linear map from
to and exhibit some of its interesting
structural properties. If is a linear -code, then is an
additive -code. If is an additive cyclic code then
is an additive quasi-cyclic code of index . Moreover, if is a module
-cyclic code, a recently introduced type of code which will be
explained below, then is equivalent to an additive cyclic code if is
odd and to an additive quasi-cyclic code of index if is even. Given any
-code , the code is self-orthogonal under the trace
Hermitian inner product. Since the mapping preserves nestedness, it can be
used as a tool in constructing additive asymmetric quantum codes.Comment: 16 pages, 3 tables, submitted to Advances in Mathematics of
Communication
Quantum internal modes of solitons in 1d easy-plane antiferromagnet in strong magnetic field
In presence of a strong external magnetic field the dynamics of solitons in a
one-dimensional easy-plane Heisenberg antiferromagnet exhibits a number of
peculiarities. Dynamics of internal soliton degrees of freedom is essentially
quantum, and they are strongly coupled to the "translational" mode of soliton
movement. These peculiarities lead to considerable changes in the response
functions of the system which can be detected experimentally.Comment: 8 pages, RevTeX, 6 figures, uses psfig.sty, submitted to PR
Quantum conformance test
We introduce a protocol addressing the conformance test problem, which consists in determining whether a process under test conforms to a reference one. We consider a process to be characterized by the set of end products it produces, which is generated according to a given probability distribution. We formulate the problem in the context of hypothesis testing and consider the specific case in which the objects can be modeled as pure loss channels. We demonstrate theoretically that a simple quantum strategy, using readily available resources and measurement schemes in the form of two-mode squeezed vacuum and photon counting, can outperform any classical strategy. We experimentally implement this protocol, exploiting optical twin beams, validating our theoretical results, and demonstrating that, in this task, there is a quantum advantage in a realistic setting
On the dynamics of coupled S=1/2 antiferromagnetic zig-zag chains
We investigate the elementary excitations of quasi one-dimensional S=1/2
systems built up from zig-zag chains with general isotropic exchange constants,
using exact (Lanczos) diagonalization for 24 spins and series expansions
starting from the decoupled dimer limit. For the ideal one-dimensional zig-zag
chain we discuss the systematic variation of the basic (magnon) triplet
excitation with general exchange parameters and in particular the presence of
practically flat dispersions in certain regions of phase space. We extend the
dimer expansion in order to include the effects of 3D interactions on the
spectra of weakly interacting zig-zag chains. In an application to KCuCl_3 we
show that this approach allows to determine the exchange interactions between
individual pairs of spins from the spectra as determined in recent neutron
scattering experiments.Comment: 8 pages, 9 figures; some changes, figure added; final versio
The aerosol-climate model ECHAM5-HAM
The aerosol-climate modelling system ECHAM5-HAM is introduced. It is based on a flexible microphysical approach and, as the number of externally imposed parameters is minimised, allows the application in a wide range of climate regimes. ECHAM5-HAM predicts the evolution of an ensemble of microphysically interacting internally- and externally-mixed aerosol populations as well as their size-distribution and composition. The size-distribution is represented by a superposition of log-normal modes. In the current setup, the major global aerosol compounds sulfate (SU), black carbon (BC), particulate organic matter (POM), sea salt (SS), and mineral dust (DU) are included. The simulated global annual mean aerosol burdens (lifetimes) for the year 2000 are for SU: 0.80 Tg(S) (3.9 days), for BC: 0.11 Tg (5.4 days), for POM: 0.99 Tg (5.4 days), for SS: 10.5 Tg (0.8 days), and for DU: 8.28 Tg (4.6 days). An extensive evaluation with in-situ and remote sensing measurements underscores that the model results are generally in good agreement with observations of the global aerosol system. The simulated global annual mean aerosol optical depth (AOD) is with 0.14 in excellent agreement with an estimate derived from AERONET measurements (0.14) and a composite derived from MODIS-MISR satellite retrievals (0.16). Regionally, the deviations are not negligible. However, the main patterns of AOD attributable to anthropogenic activity are reproduced
Spin dynamics in copper metaborate studied by muon spin relaxation
Copper metaborate CuBO was studied by muon spin relaxation
measurements in order to clarify its static and dynamic magnetic properties.
The time spectra of muon spin depolarization suggest that the local fields at
the muon site contain both static and fluctuating components in all ordered
phases down to 0.3 K. In the weak ferromagnetic phase (20 K~~9.3 K), the
static component is dominant. On the other hand, upon cooling the fluctuating
component becomes dominant in the incommensurate helix phase (9.3K > T > 1.4K).
The dynamical fluctuations of the local fields persist down to 0.3K, where a
new incommensurate phase (T < 1.4K) is expected to appear. This result suggests
that spins fluctuate even at T \to 0. We propose two possible origins of the
remnant dynamical spin fluctuations: frustration of the exchange interactions
and the dynamic behavior of the soliton lattice
Peierls-like transition induced by frustration in a two-dimensional antiferromagnet
We show that the introduction of frustration into the spin-1/2
two-dimensional (2D) antiferromagnetic Heisenberg model on a square lattice via
a next-nearest neighbor exchange interaction can lead to a Peierls-like
transition, from a tetragonal to an orthorhombic phase, when the spins are
coupled to adiabatic phonons. The two different orthorhombic ground states
define an Ising order parameter, which is expected to lead to a finite
temperature transition. Implications for , the first
realization of that model, will be discussed.Comment: 4 pages, to be published on Physical Review Letter
Cation distribution in manganese cobaltite spinels Co3−xMnxO4 (0 ≤ x ≤ 1) determined by thermal analysis
Thermogravimetric analysis was used in order to study the reduction in air of submicronic powders of Co3−x Mn x O4 spinels, with 0 ≤ x ≤ 1. For x = 0 (i.e. Co3O4), cation reduction occurred in a single step. It involved the CoIII ions at the octahedral sites, which were reduced to Co2+ on producing CoO. For 0 < x ≤ 1, the reduction occurred in two stages at increasing temperature with increasing amounts of manganese. The first step corresponded to the reduction of octahedral CoIII ions and the second was attributed to the reduction of octahedral Mn4+ ions to Mn3+. From the individual weight losses and the electrical neutrality of the lattice, the CoIII and Mn4+ ion concentrations were calculated. The distribution of cobalt and manganese ions present on each crystallographic site of the spinel was determined. In contrast to most previous studies that took into account either CoIII and Mn3+ or Co2+, CoIII and Mn4+ only, our thermal analysis study showed that Co2+/CoIII and Mn3+/Mn4+ pairs occupy the octahedral sites. These results were used to explain the resistivity measurements carried out on dense ceramics prepared from our powders sintered at low temperature (700–750 °C) in a Spark Plasma Sintering apparatus
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