18,143 research outputs found
Synthesis, Crystal Structure and Photophysical Properties of Lanthanide Coordination Polymers of 4- 4-(9H-Carbazol-9-Yl)Butoxy Benzoate: The Effect of Bidentate Nitrogen Donors on Luminescence
A new aromatic carboxylate ligand, 4-[4-(9H-carbazol-9-yl)butoxy]benzoic acid (HL), has been synthesized by the replacement of the hydroxyl hydrogen of 4-hydroxy benzoic acid with a 9-butyl-9H-carbazole moiety. The anion derived from HL has been used for the support of a series of lanthanide coordination compounds [Ln = Eu (1), Gd (2) and Tb (3)]. The new lanthanide complexes have been characterized by a variety of spectroscopic techniques. Complex 3 was structurally authenticated by single-crystal X-ray diffraction and found to exist as a solvent-free 1D coordination polymer with the formula [Tb(L)(3)](n). The structural data reveal that the terbium atoms in compound 3 reside in an octahedral ligand environment that is somewhat unusual for a lanthanide. It is interesting to note that each carboxylate group exhibits only a bridging-bidentate mode, with a complete lack of more complex connectivities that are commonly observed for extended lanthanide-containing solid-state structures. Examination of the packing diagram for 3 revealed the existence of two-dimensional molecular arrays held together by means of CH-pi interactions. Aromatic carboxylates of the lanthanides are known to exhibit highly efficient luminescence, thus offering the promise of applicability as optical devices. However, due to difficulties that arise on account of their polymeric nature, their practical application is somewhat limited. Accordingly, synthetic routes to discrete molecular species are highly desirable. For this purpose, a series of ternary lanthanide complexes was designed, synthesized and characterized, namely [Eu(L)(3)(phen)] (4), [Eu(L)(3)(tmphen)] (5), [Tb(L)(3)(phen)] (6) and [Tb(L)(3)(tmphen)] (7) (phen = 1,10-phenanthroline and tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline). The photophysical properties of the foregoing complexes in the solid state at room temperature have been investigated. The quantum yields of the ternary complexes 4 (9.65%), 5 (21.00%), 6 (14.07%) and 7 (32.42%), were found to be significantly enhanced in the presence of bidentate nitrogen donors when compared with those of the corresponding binary compounds 1 (0.11%) and 3 (1.45%). Presumably this is due to effective energy transfer from the ancillary ligands.Council of Scientific and Industrial Research (CSIR-TAPSUN Project) SSL, NWP-55CSIR, New DelhiRobert A. Welch Foundation F-0003Chemistr
Electronic screening and damping in magnetars
We calculate the screening of the ion-ion potential due to electrons in the
presence of a large background magnetic field, at densities of relevance to
neutron star crusts. Using the standard approach to incorporate electron
screening through the one-loop polarization function, we show that the magnetic
field produces important corrections both at short and long distances. In
extreme fields, realized in highly magnetized neutron stars called magnetars,
electrons occupy only the lowest Landau levels in the relatively low density
region of the crust. Here our results show that the screening length for
Coulomb interactions between ions can be smaller than the inter-ion spacing.
More interestingly, we find that the screening is anisotropic and the screened
potential between two static charges exhibits long range Friedel oscillations
parallel to the magnetic field. This long-range oscillatory behavior is likely
to affect the lattice structure of ions, and can possibly create rod-like
structures in the magnetar crusts. We also calculate the imaginary part of the
electron polarization function which determines the spectrum of electron-hole
excitations and plays a role in damping lattice phonon excitations. We
demonstrate that even for modest magnetic fields this damping is highly
anisotropic and will likely lead to anisotropic phonon heat transport in the
outer neutron star crust.Comment: 14 pages, 5 Figure
Reinterpreting Shock Wave Structure Predictions using the Navier-Stokes Equations
Classical Navier-Stokes equations fail to predict shock wave profiles
accurately. In this paper, the Navier-Stokes system is fully transformed using
a velocity variable transformation. The transformed equations termed the
re-casted Navier-Stokes equations display physics not initially included. We
then analyse the stationary shock structure problem in a monatomic gas by
solving both the classical and the re-casted Navier-Stokes equations
numerically using a finite difference global solution (FDGS) scheme. The
numerical results are presented for different upstream Mach numbers ranging
from supersonic to hypersonic flows. We found that the re-casted Navier-Stokes
equations show better agreements with the experimentally measured density and
reciprocal shock thickness profiles
Experimental Evidence of Time Delay Induced Death in Coupled Limit Cycle Oscillators
Experimental observations of time delay induced amplitude death in a pair of
coupled nonlinear electronic circuits that are individually capable of
exhibiting limit cycle oscillations are described. In particular, the existence
of multiply connected death islands in the parameter space of the coupling
strength and the time delay parameter for coupled identical oscillators is
established. The existence of such regions was predicted earlier on theoretical
grounds in [Phys. Rev. Lett. 80, 5109 (1998); Physica 129D, 15 (1999)]. The
experiments also reveal the occurrence of multiple frequency states, frequency
suppression of oscillations with increased time delay and the onset of both
in-phase and anti-phase collective oscillations.Comment: 4 aps formatted RevTeX pages; 6 figures; to appear in Phys. Rev. Let
Dust extinction from Balmer decrements of star-forming galaxies at 0.75<z<1.5 with HST/WFC3 spectroscopy from the WISP survey
Spectroscopic observations of Halpha and Hbeta emission lines of 128
star-forming galaxies in the redshift range 0.75<z<1.5 are presented. These
data were taken with slitless spectroscopy using the G102 and G141 grisms of
the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of
the WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust
extinction is measured from stacked spectra that cover the Balmer decrement
(Halpha/Hbeta). We present dust extinction as a function of Halpha luminosity
(down to 3 x 10^{41} erg/s), galaxy stellar mass (reaching 4 x 10^{8} Msun),
and rest-frame Halpha equivalent width. The faintest galaxies are two times
fainter in Halpha luminosity than galaxies previously studied at z~1.5. An
evolution is observed where galaxies of the same Halpha luminosity have lower
extinction at higher redshifts, whereas no evolution is found within our error
bars with stellar mass. The lower Halpha luminosity galaxies in our sample are
found to be consistent with no dust extinction. We find an anti-correlation of
the [OIII]5007/Halpha flux ratio as a function of luminosity where galaxies
with L_{Halpha}<5 x 10^{41} erg/s are brighter in [OIII]5007 than Halpha. This
trend is evident even after extinction correction, suggesting that the
increased [OIII]5007/Halpha ratio in low luminosity galaxies is likely due to
lower metallicity and/or higher ionization parameters.Comment: 11 pages, 9 figures, 2 tables; version addressing the referee
comment
Effect of Level Statistics on Local Magnetism in Nanoscale Metallic Grains
Effect of level statistics on local electronic states and local magnetism in
nanoscale metallic grains with transition-metal impurity in the ballistic
regime is studied. It is shown that the mean occupation of local electron and
the local magnetic moment in nanoscale metallic grains with odd conduction
electrons are larger than those with even conduction electrons. The effect of
even-odd parity on the condition for the occurrence of local magnetic moment is
also discussed, it is found that the critical value for the
formation of local moment in nanoscale metallic grains is much smaller than
that in bulks. The dependences of the local spin susceptibility on size and the
Coulomb interaction are obtained. These results show that the level statistics
plays an important role for the local magnetism, it distinguishes the
properties of nanoscale metallic grains from those of small clusters and bulks.Comment: Latex, 6 figures in Postscrip
The Classification of Obsessive–Compulsive and Related Disorders in the ICD-11
Background To present the rationale for the new Obsessive–Compulsive and Related Disorders (OCRD) grouping in the Mental and Behavioural Disorders chapter of the Eleventh Revision of the World Health Organization’s International Classification of Diseases and Related Health Problems (ICD-11), including the conceptualization and essential features of disorders in this grouping. Methods Review of the recommendations of the ICD-11 Working Group on the Classification for OCRD. These sought to maximize clinical utility, global applicability, and scientific validity. Results The rationale for the grouping is based on common clinical features of included disorders including repetitive unwanted thoughts and associated behaviours, and is supported by emerging evidence from imaging, neurochemical, and genetic studies. The proposed grouping includes obsessive–compulsive disorder, body dysmorphic disorder, hypochondriasis, olfactory reference disorder, and hoarding disorder. Body-focused repetitive behaviour disorders, including trichotillomania and excoriation disorder are also included. Tourette disorder, a neurological disorder in ICD-11, and personality disorder with anankastic features, a personality disorder in ICD-11, are recommended for cross-referencing. Limitations Alternative nosological conceptualizations have been described in the literature and have some merit and empirical basis. Further work is needed to determine whether the proposed ICD-11 OCRD grouping and diagnostic guidelines are mostly likely to achieve the goals of maximizing clinical utility and global applicability. Conclusion It is anticipated that creation of an OCRD grouping will contribute to accurate identification and appropriate treatment of affected patients as well as research efforts aimed at improving our understanding of the prevalence, assessment, and management of its constituent disorders
Neutrino Propagation In Color Superconducting Quark Matter
We calculate the neutrino mean free path in color superconducting quark
matter, and employ it to study the cooling of matter via neutrino diffusion in
the superconducting phase as compared to a free quark phase. The cooling
process slows when quark matter undergoes a second order phase transition to a
superconducting phase at the critical temperature . Cooling subsequently
accelerates as the temperature decreases below . This will directly impact
the early evolution of a newly born neutron star should its core contain quark
matter. Consequently, there may be observable changes in the early neutrino
emission which would provide evidence for superconductivity in hot and dense
matter.Comment: 12 pages, 5 figure
Is deep venous thrombosis a common complication in patients treated with Ilizarov external fixator?
Background: Determining the incidence of deep venous thrombosis (DVT), a prospective study, in patients treated with Ilizarov external fixators for lower extremity fractures, fracture non unions or deformity correction.Methods: A Prospective, observational and cross sectional study. 49 Patients with complex lower extremity injuries, deformities and non-union of fractures were treated with Ilizarov external fixator application, were assessed clinically and radiological (Venous Doppler) at regular intervals- 6 days post-surgery then at 6 weeks, 12 weeks and between 4 to 6 months post-operative. None were given chemoprophylaxis for the prevention of DVT and everyone were assessed pre operatively with a questionnaire and wells criteria was taken for assessment of high risk for developing venous thrombosis. There were 41 men and 8 women, 85.75% of the study group is of age 30 to 60 years.Results: Only 1 of 49 patients developed radiological evident DVT within 6 days of surgery. Patients who underwent application of Ilizarov external fixator electively for deformity correction, osteomyelitis and non-union showed no clinical or radiological evident signs of DVT.Conclusions: The incidence of DVT and PTE is minimal when patients without chemoprophylaxis underwent lower limb Ilizarov external fixator application for acute trauma and electively for deformity correction, treatment of non-union and osteomyelitis. However further comparative and randomized studies need to be done to confirm our results
Realistic Neutrino Opacities for Supernova Simulations With Correlations and Weak Magnetism
Advances in neutrino transport allow realistic neutrino interactions to be
incorporated into supernova simulations. We add tensor couplings to
relativistic RPA calculations of neutrino opacities. Our results reproduce
free-space neutrino-nucleon cross sections at low density, including weak
magnetism and recoil corrections. In addition, our opacities are
thermodynamically consistent with relativistic mean field equations of state.
We find antineutrino mean free paths that are considerably larger then those
for neutrinos. This difference depends little on density. In a supernova, this
difference could lead to an average energy of that is larger than
that for by an amount that is comparable to the energy difference
between and Comment: 15 pages, 10 figures, submitted to PRC, minor changes to figs. (9,10
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