487 research outputs found
Identification of wheat varieties and glutenin subunits: capillary electrophoresis and computer-assisted interpretation of results
Established and supported under the Australian Government’s Cooperative Research Centre Progra
Cosmological inference including massive neutrinos from the matter power spectrum: biases induced by uncertainties in the covariance matrix
Data analysis from upcoming large galaxy redshift surveys, such as Euclid and
DESI will significantly improve constraints on cosmological parameters. To
optimally extract the information from these galaxy surveys, it is important to
control with a high level of confidence the uncertainty and bias arising from
the estimation of the covariance that affects the inference of cosmological
parameters. In this work, we are addressing two different but closely related
issues: (i) the sampling noise present in a covariance matrix estimated from a
finite set of simulations and (ii) the impact on cosmological constraints of
the non-Gaussian contribution to the covariance matrix of the power spectrum.
We focus on the parameter estimation obtained from fitting the matter power
spectrum in real space, using the DEMNUni N-body simulations. Regarding the
first issue, we adopt two different approaches to reduce the sampling noise in
the precision matrix that propagates in the parameter space: on the one hand
using an alternative estimator of the covariance matrix based on a non-linear
shrinkage, NERCOME; and on the other hand employing a method of fast generation
of approximate mock catalogs, COVMOS. We find that NERCOME can significantly
reduce the noise induced on the posterior distribution of parameters, but at
the cost of a systematic overestimation of the error bars on the cosmological
parameters. We show that using a COVMOS covariance matrix estimated from a
large number of realisations (10~000) results in unbiased cosmological
constraints. Regarding the second issue, we quantify the impact on cosmological
constraints of the non-Gaussian part of the power spectrum covariance purely
coming from non-linear clustering. We find that when this term is neglected,
both the errors and central values of the estimated parameters are affected for
a scale cut \kmax > 0.2\ \invMpc.Comment: 21 pages, 2 appendices, 20 figures. Submitted to A&
Acetate Acetylacetonate Ampy Ruthenium(II) Complexes as Efficient Catalysts for Ketone Transfer Hydrogenation
The mixed acetate acetylacetonate (acac) ruthenium(II) phosphine complexes Ru(OAc)(acac)P2 [P2=(PPh3)2, Ph2P(CH2)4PPh2 (dppb)] were prepared by protonation of Ru(OAc)2(PPh3)2 with acetylacetone in dichloromethane. Reaction of the dppb derivative with 2-(aminomethyl)pyridine (ampy) affords the complex Ru(OAc)(acac)(ampy)(dppb), which converts to [Ru(acac)(ampy)(dppb)](OAc) in toluene at 90 \ub0C. In the former derivative the ampy ligand is monodentate and coordinates through the NH2-moiety. The isolated acac complexes are active catalysts for the transfer hydrogenation of ketones with loadings as low as 0.01 mol%, the ampy having a strong accelerating effect. Several aromatic and aliphatic ketone substrates are converted to their corresponding alcohols, and different electronic influences through substituents on acetophenone are tolerated
Preparation of Neutral trans - Cis [Ru(O2CR)2P2(NN)], Cationic [Ru(O2CR)P2(NN)](O2CR) and Pincer [Ru(O2CR)(CNN)P2] (P = PPh3, P2= diphosphine) Carboxylate Complexes and their Application in the Catalytic Carbonyl Compounds Reduction
The diacetate complexes trans-[Ru(\u3ba1-OAc)2(PPh3)2(NN)] (NN = ethylenediamine (en) (1), 2-(aminomethyl)pyridine (ampy) (2), 2-(aminomethyl)pyrimidine (ampyrim) (3)) have been isolated in 76-88% yield by reaction of [Ru(\u3ba2-OAc)2(PPh3)2] with the corresponding nitrogen ligands. The ampy-type derivatives 2 and 3 undergo isomerization to the thermodynamically most stable cationic complexes [Ru(\u3ba1-OAc)(PPh3)2(NN)]OAc (2a and 3a) and cis-[Ru(\u3ba1-OAc)2(PPh3)2(NN)] (2b and 3b) in methanol at RT. The trans-[Ru(\u3ba1-OAc)2(P2)2] (P2 = dppm (4), dppe (5)) compounds have been synthesized from [Ru(\u3ba2-OAc)2(PPh3)2] by reaction with the suitable diphosphine in toluene at 95 \ub0C. The complex cis-[Ru(\u3ba1-OAc)2(dppm)(ampy)](6) has been obtained from [Ru(\u3ba2-OAc)2(PPh3)2] and dppm in toluene at reflux and reaction with ampy. The derivatives trans-[Ru(\u3ba1-OAc)2P2(NN)] (7-16; NN = en, ampy, ampyrim, 8-aminoquinoline; P2 = dppp, dppb, dppf, (R)-BINAP) can be easily synthesized from [Ru(\u3ba2-OAc)2(PPh3)2] with a diphosphine and treatment with the NN ligands at RT. Alternatively these compounds have been prepared from trans-[Ru(OAc)2(PPh3)2(NN)] by reaction with the diphosphine in MEK at 50 \ub0C. The use of (R)-BINAP affords trans-[Ru(\u3ba1-OAc)2((R)-BINAP)(NN)] (NN = ampy (11), ampyrim (15)) isolated as single stereoisomers. Treatment of the ampy-type complexes 8-15 with methanol at RT leads to isomerization to the cationic derivatives [Ru(\u3ba2-OAc)P2(NN)]OAc (8a-15a; NN = ampy, ampyrim; P2 = dppp, dppb, dppf, (R)-BINAP). Similarly to 2, the dipivalate trans-[Ru(\u3ba1-OPiv)2(PPh3)2(ampy)] (18) is prepared from [Ru(\u3ba2-OPiv)2(PPh3)2] (17) and ampy in CHCl3. The pincer acetate [Ru(\u3ba1-OAc)(CNNOMe)(PPh3)2] (19) has been synthesized from [Ru(\u3ba2-OAc)2(PPh3)2] and HCNNOMe ligand in 2-propanol with NEt3 at reflux. In addition, the dppb pincer complexes [Ru(\u3ba1-OAc)(CNN)(dppb)] (CNN = AMTP (20), AMBQPh (21)) have been obtained from [Ru(\u3ba2-OAc)2(PPh3)2], dppb, and HAMTP or HAMBQPh with NEt3, respectively. The acetate NN and pincer complexes are active in transfer hydrogenation with 2-propanol and hydrogenation with H2 of carbonyl compounds at S/C values of up to 10000 and with TOF values of up to 160000 h-1
Expanded Vandermonde powers and sum rules for the two-dimensional one-component plasma
The two-dimensional one-component plasma (2dOCP) is a system of mobile
particles of the same charge on a surface with a neutralising background.
The Boltzmann factor of the 2dOCP at temperature can be expressed as a
Vandermonde determinant to the power . Recent advances in
the theory of symmetric and anti-symmetric Jack polymonials provide an
efficient way to expand this power of the Vandermonde in their monomial basis,
allowing the computation of several thermodynamic and structural properties of
the 2dOCP for values up to 14 and equal to 4, 6 and 8. In this
work, we explore two applications of this formalism to study the moments of the
pair correlation function of the 2dOCP on a sphere, and the distribution of
radial linear statistics of the 2dOCP in the plane
One Hundred Years of Observations of the Be Star HDE 245770 (the X-ray Binary A0535+26/V725 Tau): The End of an Active Phase
UBV observations of the X-ray binary system A0535+26/V725 Tau at the Crimean
Station of the Sternberg Astronomical Institute in 1980-1998 are presented.
Based on our and published data, we analyze the photometric history of the star
from 1898.Comment: Translated from Pis'ma Astronomicheskii Zhurnal, Vol. 26, No. 1,
2000, pp. 13-2
Jack superpolynomials with negative fractional parameter: clustering properties and super-Virasoro ideals
The Jack polynomials P_\lambda^{(\alpha)} at \alpha=-(k+1)/(r-1) indexed by
certain (k,r,N)-admissible partitions are known to span an ideal I^{(k,r)}_N of
the space of symmetric functions in N variables. The ideal I^{(k,r)}_N is
invariant under the action of certain differential operators which include half
the Virasoro algebra. Moreover, the Jack polynomials in I^{(k,r)}_N admit
clusters of size at most k: they vanish when k+1 of their variables are
identified, and they do not vanish when only k of them are identified. We
generalize most of these properties to superspace using orthogonal
eigenfunctions of the supersymmetric extension of the trigonometric
Calogero-Moser-Sutherland model known as Jack superpolynomials. In particular,
we show that the Jack superpolynomials P_{\Lambda}^{(\alpha)} at
\alpha=-(k+1)/(r-1) indexed by certain (k,r,N)-admissible superpartitions span
an ideal {\mathcal I}^{(k,r)}_N of the space of symmetric polynomials in N
commuting variables and N anticommuting variables. We prove that the ideal
{\mathcal I}^{(k,r)}_N is stable with respect to the action of the
negative-half of the super-Virasoro algebra. In addition, we show that the Jack
superpolynomials in {\mathcal I}^{(k,r)}_N vanish when k+1 of their commuting
variables are equal, and conjecture that they do not vanish when only k of them
are identified. This allows us to conclude that the standard Jack polynomials
with prescribed symmetry should satisfy similar clustering properties. Finally,
we conjecture that the elements of {\mathcal I}^{(k,2)}_N provide a basis for
the subspace of symmetric superpolynomials in N variables that vanish when k+1
commuting variables are set equal to each other.Comment: 36 pages; the main changes in v2 are : 1) in the introduction, we
present exceptions to an often made statement concerning the clustering
property of the ordinary Jack polynomials for (k,r,N)-admissible partitions
(see Footnote 2); 2) Conjecture 14 is substantiated with the extensive
computational evidence presented in the new appendix C; 3) the various tests
supporting Conjecture 16 are reporte
Kondo Effect in Systems with Spin Disorder
We consider the role of static disorder in the spin sector of the one- and
two-channel Kondo models. The distribution functions of the disorder-induced
effective energy splitting between the two levels of the Kondo impurity are
derived to the lowest order in the concentration of static scatterers. It is
demonstrated that the distribution functions are strongly asymmetric, with the
typical splitting being parametrically smaller than the average rms value. We
employ the derived distribution function of splittings to study the temperature
dependence of the low-temperature conductance of a sample containing an
ensemble of two-channel Kondo impurities. The results are used to analyze the
consistency of the two-channel Kondo interpretation of the zero-bias anomalies
observed in Cu/(Si:N)/Cu nanoconstrictions.Comment: 16 pages, 5 figures, REVTe
Skeletal muscle contraction. The thorough definition of the contractile event requires both load acceleration and load mass to be known
<p>Abstract</p> <p>Background</p> <p>The scope of this work is to show that the correct and complete definition of the system of muscle contraction requires the knowledge of both the mass and the acceleration of the load.</p> <p>Results</p> <p>The aim is achieved by making use of a model of muscle contraction that operates into two phases. The first phase considers the effects of the power stroke in the absence of any hindrance. In the second phase viscous hindrance is introduced to match the experimental speed and yield of the contraction. It is shown that, at constant force of the load, changing load acceleration changes the time course of the pre-steady state of myofibril contraction. The decrease of the acceleration of the load from 9.8 m.s<sup>-2 </sup>to 1 m.s<sup>-2 </sup>increases the time length of the pre-steady state of the contraction from a few microseconds to many hundreds of microseconds and decreases the stiffness of the active fibre.</p> <p>Conclusions</p> <p>We urge that in the study of muscle contraction both the mass and the acceleration of the load are specified.</p
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