882 research outputs found
Incremental expansions for Hubbard-Peierls systems
The ground state energies of infinite half-filled Hubbard-Peierls chains are
investigated combining incremental expansion with exact diagonalization of
finite chain segments. The ground state energy of equidistant infinite Hubbard
(Heisenberg) chains is calculated with a relative error of less than for all values of using diagonalizations of 12-site (20-site)
chain segm ents. For dimerized chains the dimerization order parameter as a
function of the onsite repulsion interaction has a maximum at nonzero
values of , if the electron-phonon coupling is lower than a critical
value . The critical value is found with high accuracy to be
. For smaller values of the position of the maximum of is
approximately , and rapidly tends to zero as approaches from
below. We show how our method can be applied to calculate breathers for the
problem of phonon dynamics in Hubbard-Peierls systems.Comment: 4 Pages, 3 Figures, REVTE
An Artificial SEI Layer Based on an Inorganic Coordination Polymer with Self-Healing Ability for Long-Lived Rechargeable Lithium-Metal Batteries
Upon immersion of a lithium (Li) anode into a diluted 0.05 to 0.20â
M dimethoxyethane solution of the phosphoric-acid derivative (CFCHO)P(O)OH (HBFEP), an artificial solid-electrolyte interphase (SEI) is generated on the Li-metal surface. Hence, HBFEP reacts on the surface to the corresponding Li salt (LiBFEP), which is a Li-ion conducting inorganic coordination polymer. This film exhibits â due to the reversibly breaking ionic bonds â self-healing ability upon cycling-induced volume expansion of Li. The presence of LiBFEP as the major component in the artificial SEI is proven by ATR-IR and XPS measurements. SEM characterization of HBFEP-treated Li samples reveals porous layers on top of the Li surface with at least 3â
ÎŒm thickness. LiâLi symmetrical cells with HBFEP-modified Li electrodes show a three- to almost fourfold cycle-lifetime increase at 0.1â
mAâcm in a demanding model electrolyte that facilitates fast battery failure (1â
M LiOTf in TEGDME). Hence, the LiBFEP-enriched layer apparently acts as a Li-ion conducting protection barrier between Li and the electrolyte, enhancing the rechargeability of Li electrodes
Synthesis of poly(methyl methacrylate)-poly(poly(ethylene glycol) methacrylate)-polyisobutylene ABCBA pentablock copolymers by combining quasiliving carbocationic and atom transfer radical polymerizations and characterization thereof
Novel, unique
amphiphilic
pentab
lock terpolymers consisting of the highly hydrophobic
polyisobutylene
(PIB)
mid
-
segment attached to the hydrophilic combshaped
poly(poly(ethylene
glycol
) methacrylate)
(PPEGMA) polymacromonomer chains, which are
coupled to poly(methyl methacrylate) (PMMA)
outer segments were synthesized by the
combination of quasiliving carbocationic polymerization and
atom transfer radical
polymerization (
ATRP
)
. First,
a
bifunctional PIB macroinitiator w
as
prepared by quasiliving
carbocationic polymerization and subsequent
quantitative chain end derivatizations. ATRP of
PEGMAs with different molecular weights (M
n
= 188, 300 and 475 g/mol) led to triblock
copolymers which were further reacted with MMA under ATRP conditions to obtain P
MMA
-
PPE
G
MA
-
PIB
-
PPEGMA
-
PMMA
AB
CB
A
-
type pen
ta
block copolymers
. It was found that
slow initi
ation takes place between the PIB macroinitiator and PEGMA macromonomers with
higher molecular weights via ATRP
.
ATRP of MMA with the
resulting
block copolymers
composed of PIB and PPEGMA chain segments led t
o the desired block copolymers with
high initiating efficiency. Investigations of the resulting
pentablock copolymers by DSC,
SAXS and phase mode AFM revealed that
nanophase separation occurs in these new
macromolecular structures with average domain dista
nces of 11
-
14 nm, and local lamellar
self
-
assembly takes place in the pentablocks with PPEGMA polymacromonomer segments of
PEGMAs with M
n
of 118 g/mol and 300
g/mol
,
while disordered nanophases are observed in
the block copolymer with PEGMA having molecula
r weight of 475 g/mol. These new
amphiphilic block copolymers composed of biocompatible chain segments can find
applications in a variety of advanced fields
On the Navier-Stokes equations with rotating effect and prescribed outflow velocity
We consider the equations of Navier-Stokes modeling viscous fluid flow past a
moving or rotating obstacle in subject to a prescribed velocity
condition at infinity. In contrast to previously known results, where the
prescribed velocity vector is assumed to be parallel to the axis of rotation,
in this paper we are interested in a general outflow velocity. In order to use
-techniques we introduce a new coordinate system, in which we obtain a
non-autonomous partial differential equation with an unbounded drift term. We
prove that the linearized problem in is solved by an evolution
system on for . For this we use
results about time-dependent Ornstein-Uhlenbeck operators. Finally, we prove,
for and initial data , the
existence of a unique mild solution to the full Navier-Stokes system.Comment: 18 pages, to appear in J. Math. Fluid Mech. (published online first
Direct measurements of the energy flux due to chemical reactions at the surface of a silicon sample interacting with a SF6 plasma
Energy exchanges due to chemical reactions between a silicon surface and a
SF6 plasma were directly measured using a heat flux microsensor (HFM). The
energy flux evolution was compared with those obtained when only few reactions
occur at the surface to show the part of chemical reactions. At 800 W, the
measured energy flux due to chemical reactions is estimated at about 7
W.cm\^{-2} against 0.4 W.cm\^{-2} for ion bombardment and other contributions.
Time evolution of the HFM signal is also studied. The molar enthalpy of the
reaction giving SiF4 molecules was evaluated and is consistent with values
given in literature.Comment: 3 page
WeightâofâEvidence Approach for Assessing Removal of Metals from the Water Column for Chronic Environmental Hazard Classification
The United Nations and the European Union have developed guidelines for the assessment of longâterm (chronic) chemical environmental hazards. This approach recognizes that these hazards are often related to spillage of chemicals into freshwater environments. The goal of the present study was to examine the concept of metal ion removal from the water column in the context of hazard assessment and classification. We propose a weightâofâevidence approach that assesses several aspects of metals including the intrinsic properties of metals, the rate at which metals bind to particles in the water column and settle, the transformation of metals to nonavailable and nontoxic forms, and the potential for remobilization of metals from sediment. We developed a test method to quantify metal removal in aqueous systems: the extended transformation/dissolution protocol (T/DPâE). The method is based on that of the Organisation for Economic Coâoperation and Development (OECD). The key element of the protocol extension is the addition of substrate particles (as found in nature), allowing the removal processes to occur. The present study focused on extending this test to support the assessment of metal removal from aqueous systems, equivalent to the concept of âdegradabilityâ for organic chemicals. Although the technical aspects of our proposed method are different from the OECD method for organics, its use for hazard classification is equivalent. Models were developed providing mechanistic insight into processes occurring during the T/DPâE method. Some metals, such as copper, rapidly decreased (within 96 h) under the 70% threshold criterion, whereas others, such as strontium, did not. A variety of method variables were evaluated and optimized to allow for a reproducible, realistic hazard classification method that mimics reasonable worstâcase scenarios. We propose that this method be standardized for OECD hazard classification via round robin (ring) testing to ascertain its intraâ and interlaboratory variability. Environ Toxicol Chem 2019;38:1839â1849. © 2019 SETAC.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151334/1/etc4470_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151334/2/etc4470.pd
Angle-dependent normalization of neutron-proton differential cross sections
Systematic errors in the database of differential cross sections below
350 MeV are studied. By applying angle-dependent normalizations with the help
of the energy-dependent Nijmegen partial-wave analysis PWA93 the
-values of some seriously flawed data sets can be reduced significantly
at the expense of a few degrees of freedom. It turns out that in these special
cases the renormalized data sets can be made statistically acceptable such that
they do not have to be discarded any longer in partial-wave analyses of the
two-nucleon scattering data.Comment: 11 pages, 1 figure; expanded versio
KAM for the quantum harmonic oscillator
In this paper we prove an abstract KAM theorem for infinite dimensional
Hamiltonians systems. This result extends previous works of S.B. Kuksin and J.
P\"oschel and uses recent techniques of H. Eliasson and S.B. Kuksin. As an
application we show that some 1D nonlinear Schr\"odinger equations with
harmonic potential admits many quasi-periodic solutions. In a second
application we prove the reducibility of the 1D Schr\"odinger equations with
the harmonic potential and a quasi periodic in time potential.Comment: 54 pages. To appear in Comm. Math. Phy
Solid polymer fuel cell synthesis by low pressure plasmas: a short review
In this review, we report on the use of low pressure plasmas for elaborating materials at the heart of solid polymer fuel cells (SPFC), especially electrodes and the membrane electrolyte. Electrodes are formed using plasma sputtering techniques while the ion conducting membranes are built up using plasma polymerization. Fuel cell performance will be improved by these approaches. The electrode catalyst profile is optimized while membrane working temperature is increased and methanol crossover is lowered compared to conventional PEM fuel cells.We gratefully thank GdR 2479 PACEM, Université d'Orléans,
SPI-CNRS, ACI ECD 2004 (Ministry of Research) for grants
and constant support
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