437 research outputs found
Uniaxial pressure dependence of magnetic order in MnSi
We report comprehensive small angle neutron scattering (SANS) measurements
complemented by ac susceptibility data of the helical order, conical phase and
skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all
crystallographic orientations uniaxial pressure favours the phase for which a
spatial modulation of the magnetization is closest to the pressure axis.
Uniaxial pressures as low as 1kbar applied perpendicular to the magnetic field
axis enhance the skyrmion lattice phase substantially, whereas the skyrmion
lattice phase is suppressed for pressure parallel to the field. Taken together
we present quantitative microscopic information how strain couples to magnetic
order in the chiral magnet MnSi.Comment: 23 pages, includes supplemen
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Diversity of felodipine solvates: Structure and physicochemical properties
Solvates of the calcium-channel blocking agent felodipine with three structurally related common organic
solvents, acetone (ATN), dimethyl sulfoxide (DMSO) and acetophenone (APN), are described. A
relationship between the felodipine packing arrangement in all known solvates and the van der Waals volume of the solvent molecule is established. Intermolecular interaction energies in the crystals are
examined using the PIXEL approach in order to rationalize the difference between alternative molecule
packing arrangements. DSC studies show that the desolvation onset temperatures of the solvates are
closely comparable, despite the large difference in the boiling points of the solvent molecules. The
enthalpies of formation derived from the calorimetric data for the solvates are also found to be similar, despite the difference in the van der Waals volume of the solvent molecules.This work was supported by a grant from the President of the
Russian Federation no. МК- 67.2014.3 and Russian Foundation
for Basic Research (project № 14-03-31001).This is the accepted manuscript. The final version is available at http://pubs.rsc.org/en/Content/ArticleLanding/2015/CE/C5CE00350D#!divAbstract
Cimetidine, C10H16N6S, formC: crystal structure and modelling of polytypes using suoperspace approach
An efficient method for modelling a polytypic family is presented with the example of cimetidine in the form C polymorph. The method exploits the (3 + 1)-dimensional superspace model, which is a powerful tool for the description, prediction and understanding of polytype modifications in small-molecule crystallography, as illustrated with this pharmaceutical example
Band structure of helimagnons in MnSi resolved by inelastic neutron scattering
A magnetic helix realizes a one-dimensional magnetic crystal with a period
given by the pitch length . Its spin-wave excitations -- the
helimagnons -- experience Bragg scattering off this periodicity leading to gaps
in the spectrum that inhibit their propagation along the pitch direction. Using
high-resolution inelastic neutron scattering the resulting band structure of
helimagnons was resolved by preparing a single crystal of MnSi in a single
magnetic-helix domain. At least five helimagnon bands could be identified that
cover the crossover from flat bands at low energies with helimagnons basically
localized along the pitch direction to dispersing bands at higher energies. In
the low-energy limit, we find the helimagnon spectrum to be determined by a
universal, parameter-free theory. Taking into account corrections to this
low-energy theory, quantitative agreement is obtained in the entire energy
range studied with the help of a single fitting parameter.Comment: 5 pages, 3 figures; (v2) slight modifications, published versio
X-ray observations of highly obscured 9.7 micron sources: an efficient method for selecting Compton-thick AGN ?
Spitzer/IRS has revealed many sources with very deep Si features at 9.7micron
(tau>1). We set out to investigate whether a strong Si absorption feature is a
good indicator for the presence of a heavily obscured AGN. We compile X-ray
spectroscopic observations available in the literature on the
optically-thick,tau(9.7)>1 sources from the IRAS Seyfert sample. We find that
the majority of the high-tau optically confirmed Seyferts (6/9) in this sample
are probably CT. Thus we provide direct evidence for a connection between
mid-IR optically-thick galaxies and CT AGN, with the success rate being close
to 70% in the local Universe. This is at least comparable, if not better, than
other rates obtained with photometric information in the mid to far-IR, or even
mid-IR to Xray. However, this technique cannot provide complete CT AGN
samples,ie there are many CT AGN which do not show significant Si absorption,
with the most notable example being N1068. Having assessed the validity of the
high 9.7micron technique locally, we attempt to construct a sample of candidate
CT AGN at higher redshifts. We compile a sample of 7 high-tau sources in the
GOODS and 5 in the Spitzer FLS. All these have been selected to have no PAH
features EW(6.2)<0.3 in order to maximize the probability that they are AGN. 6
out of 7 sources in the GOODS have been detected in X-rays, while for the five
FLS sources only X-ray flux upper limits are available. The high X-ray
luminosities of the detected GOODS sources corroborates that these are AGN. For
FLS, ancillary optical spectroscopy reveals hidden nuclei in two more sources.
SED fitting can support the presence of an AGN in the vast majority of sources.
We cannot derive useful X-ray spectroscopy constraints on whether these are CT.
However, the low LX/L6 ratios, suggest that at least 4 out of the 6 detected
sources in GOODS may be associated with CT AGN.Comment: 12 pages, to appear in A&A; version after language editin
Searching for Compton-thick active galactic nuclei at z~0.1
Using a suite of X-ray, mid-IR and optical active galactic nuclei (AGN)
luminosity indicators, we search for Compton-thick (CT) AGNs with intrinsic
L_X>10^42erg/s at z~0.03-0.2, a region of parameter space which is currently
poorly constrained by deep narrow-field and high-energy (E>10keV) all-sky X-ray
surveys. We have used the widest XMM-Newton survey (the serendipitous source
catalogue) to select a representative sub-sample (14; ~10%) of the 147 X-ray
undetected candidate CT AGNs in the Sloan Digital Sky Survey (SDSS) with
f_X/f_[OIII]<1; the 147 sources account for ~50% of the overall Type-2 AGN
population in the SDSS-XMM overlap region. We use mid-IR spectral decomposition
analyses and emission-line diagnostics, determined from pointed Spitzer-IRS
spectroscopic observations of these candidate CT AGNs, to estimate the
intrinsic AGN emission (predicted L_X,2-10keV (0.2-30)x10^42erg/s). On the
basis of the optical [OIII], mid-IR [OIV] and 6um AGN continuum luminosities we
conservatively find that the X-ray emission in at least 6/14 (>43%) of our
sample appear to be obscured by CT material with N_H>1.5x10^24cm^-2. Under the
reasonable assumption that our 14 AGNs are representative of the overall X-ray
undetected AGN population in the SDSS-XMM parent sample, we find that >20% of
the optical Type-2 AGN population are likely to be obscured by CT material.
This implies a space-density of log(Phi) >-4.9Mpc^-3 for CT AGNs with
L_X>10^42erg/s at z~0.1, which we suggest may be consistent with that predicted
by X-ray background synthesis models. Furthermore, using the 6um continuum
luminosity to infer the intrinsic AGN luminosity and the stellar velocity
dispersion to estimate M_BH, we find that the most conservatively identified CT
AGNs in this sample may harbour some of the most rapidly growing black holes
(median M_BH~3x10^7M_o) in the nearby Universe, with a median Eddington ratio
of ~0.2.Comment: 16 pages, 2 tables, 6 figures. Accepted for publication in MNRA
Direct Compression Behavior of Low- and High-Methoxylated Pectins
The objective of this study was to evaluate possible usefulness of pectins for direct compression of tablets. The deformation behavior of pectin grades of different degree of methoxylation (DM), namely, 5%, 10%, 25%, 35%, 40%, 50%, and 60% were, examined in terms of yield pressures (YP) derived from Heckel profiles for both compression and decompression and measurements of elastic recovery after ejection. All pectin grades showed a high degree of elastic recovery. DM 60% exhibited most plastic deformation (YP 70.4 MPa) whereas DM 5% (104.6 MPa) and DM 10% (114.7 MPa) least. However, DM 60% gave no coherent tablets, whereas tablet tensile strengths for DM 5% and DM 10% were comparable to Starch 1500®. Also, Heckel profiles were similar to Starch 1500®. For sieved fractions (180–250 and 90–125 μm) of DM 25% and DM 40% originating from the very same batch, YPs were alike, indicating minor effects of particle size. These facts indicate that DM is important for the compaction behavior, and batch-to-batch variability should also be considered. Therefore, pectins of low degree of methoxylation may have a potential as direct compression excipients
Measurement of the Decay Amplitudes of B0 --> J/psi K* and B0s --> J/psi phi Decays
A full angular analysis has been performed for the pseudo-scalar to
vector-vector decays, B0 --> J/psi K* and B_s --> J/psi phi, to determine the
amplitudes for decays with parity-even longitudinal and transverse polarization
and parity-odd transverse polarization. The measurements are based on 190 B0
candidates and 40 B_s candidates collected from a data set corresponding to 89
inverse pb of pbarp collisions at root(s) = 1.8 TeV at the Fermilab Tevatron.
In both decays the decay amplitude for longitudinal polarization dominates and
the parity-odd amplitude is found to be small.Comment: 7 pages, 3 figures, 1 tabl
Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV
We present results of searches for diphoton resonances produced both
inclusively and also in association with a vector boson (W or Z) using 100
pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on
the product of cross section times branching ratio for both p\bar
p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive
production to the expectations from heavy sgoldstinos we derive limits on the
supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the
sgoldstino mass and the choice of other parameters. Also, using a NLO
prediction for the associated production of a Higgs boson with a W or Z boson,
we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we
set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which
couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82
GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure
Measurement of the Strong Coupling Constant from Inclusive Jet Production at the Tevatron Collider
We report a measurement of the strong coupling constant, ,
extracted from inclusive jet production in collisions at
1800 GeV. The QCD prediction for the evolution of with
jet transverse energy is tested over the range 40<<450 GeV using
for the renormalization scale. The data show good agreement with QCD in
the region below 250 GeV. In the text we discuss the data-theory comparison in
the region from 250 to 450 GeV. The value of at the mass of the
boson averaged over the range 40<<250 GeV is found to be
. The associated theoretical uncertainties are mainly due to the choice
of renormalization scale (^{+6%}_{-4%}) and input parton distribution
functions (5%).Comment: 7 pages, 3 figures, using RevTeX. Submitted to Physical Review
Letter
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