828 research outputs found
Matrix isolation technique for the study of some factors affecting the partitioning of trace elements
The factors that affect the preferred positions of cations in ionic solid solutions were investigated utilizing vibrational spectroscopy. Solid solutions of the sulfate and chromate ions codoped with La(+3) and Ca(+2) in a KBr host lattice were examined as a function of the polyvalent cation concentration. The cation-anion pairing process was found to be random for Ca(+2), whereas the formation of La(+3)-SO4(-2) ion pairs with a C2 sub v bonding geometry is highly preferential to any type of La(+3)-CrO4(-2) ion pair formation. The relative populations of ion pair site configurations are discussed in terms of an energy-entropy competition model which can be applied to the partition of trace elements during magmatic processes
Bialoruska autokefaliczna cerkiew prawoslawna na emigracji i udzial w jej dzialalnosci duchowienstwa ukrainskiego (Belarusian Autocephalous Orthodox Church in exile and participation in its activity of the Ukrainian clergy )
Po zakończeniu II wojny światowej na Zachodzie znalazła się pewna liczba Białorusinów. Za
sprawą emigrantów białoruskich w 1948 roku na terytorium Niemiec doszło do reaktywacji Białoruskiej
Autokefalicznej Cerkwi Prawosławnej. Jej parafie istniały w krajach Europy Zachodniej, obu Ameryk i
Australii. Niebagatelny udział zarówno w reaktywacji, jak i dalszej działalności BAPC wzięło duchowieństwo
ukraińskie. Przede wszystkim w działania na rzecz BAPC czynnie zaangażował się biskup Sergiusz
(Ochotenko), którego działalność jest oceniana bardzo różnie w dostępnej literaturze przedmiotu (After World War II, in the West was a number of Belarusians. Thanks to Belarusian emigrants in 1948,
in Germany came to a reactivation of the Belarusian Autocephalous Orthodox Church. Its parishes were
in Western Europe, America and Australia. A substantial share in both reactivation as well as further
activities of the Belarusian Autocephalous Orthodox Church took Ukrainian clergy. First of all, Bishop
Sergij (Ochotenko) was actively involved to actions for the Belarusian Autocephalous Orthodox Church
with whose activity is assessed very differently in the available literature
Direct vs. indirect optical recombination in Ge films grown on Si substrates
The optical emission spectra from Ge films on Si are markedly different from
their bulk Ge counterparts. Whereas bulk Ge emission is dominated by the
material's indirect gap, the photoluminescence signal from Ge films is mainly
associated with its direct band gap. Using a new class of Ge-on-Si films grown
by a recently introduced CVD approach, we study the direct and indirect
photoluminescence from intrinsic and doped samples and we conclude that the
origin of the discrepancy is the lack of self-absorption in thin Ge films
combined with a deviation from quasi-equilibrium conditions in the conduction
band. The latter is confirmed by a simple model suggesting that the deviation
from quasi-equilibrium is caused by the much shorter recombination lifetime in
the films relative to bulk Ge
Yukawa potentials in systems with partial periodic boundary conditions II : Lekner sums for quasi-two dimensional systems
Yukawa potentials may be long ranged when the Debye screening length is
large. In computer simulations, such long ranged potentials have to be taken
into account with convenient algorithms to avoid systematic bias in the
sampling of the phase space. Recently, we have provided Ewald sums for
quasi-two dimensional systems with Yukawa interaction potentials [M. Mazars,
{\it J. Chem. Phys.}, {\bf 126}, 056101 (2007) and M. Mazars, {\it Mol. Phys.},
Paper I]. Sometimes, Lekner sums are used as an alternative to Ewald sums for
Coulomb systems. In the present work, we derive the Lekner sums for quasi-two
dimensional systems with Yukawa interaction potentials and we give some
numerical tests for pratical implementations. The main result of this paper is
to outline that Lekner sums cannot be considered as an alternative to Ewald
sums for Yukawa potentials. As a conclusion to this work : Lekner sums should
not be used for quasi-two dimensional systems with Yukawa interaction
potentials.Comment: 25 pages, 5 figures and 1 tabl
Optical coherence tomography in patients with chronic migraine: Literature review and update
Migraine is a chronic disease characterized by unilateral, pulsating, and often moderate-to-severe recurrent episodes of headache with nausea and vomiting. It affects approximately 15% of the general population, yet the underlying pathophysiological mechanisms are not fully understood. Optical coherence tomography (OCT) is a safe and reproducible diagnostic technique that utilizes infrared wavelengths and has a sensitivity of 8-10 µm. It can be used to measure thinning of the retinal nerve fiber layer (RNFL) in some neurological disorders. Although ophthalmologists are often the first specialists to examine patients with migraine, few studies have addressed the involvement of the optic nerve and retino-choroidal structures in this group. We reviewed the literature on the etiological and pathological mechanisms of migraine and the relationship between recurrent constriction of cerebral and retrobulbar vessels and ischemic damage to the optic nerve, retina, and choroid. We also assessed the role of OCT for measuring peripapillary RNFL thickness and macular and choroidal changes in migraine patients. There is considerable evidence of cerebral and retrobulbar vascular involvement in the etiology of migraine. Transitory and recurrent constriction of the retinal and ciliary arteries may cause ischemic damage to the optic nerve, retina, and choroid in patients with migraine. OCT to assess the thickness of the peripapillary RNFL, macula, and choroid might increase our understanding of the pathophysiology of migraine and facilitate diagnosis of retino-choroidal compromise and follow-up of therapy in migraine patients. Future studies should determine the usefulness of OCT findings as a biomarker of migraine
Saturation of front propagation in a reaction-diffusion process describing plasma damage in porous low-k materials
We propose a three-component reaction-diffusion system yielding an asymptotic
logarithmic time-dependence for a moving interface. This is naturally related
to a Stefan-problem for which both one-sided Dirichlet-type and von
Neumann-type boundary conditions are considered. We integrate the dependence of
the interface motion on diffusion and reaction parameters and we observe a
change from transport behavior and interface motion \sim t^1/2 to logarithmic
behavior \sim ln t as a function of time. We apply our theoretical findings to
the propagation of carbon depletion in porous dielectrics exposed to a low
temperature plasma. This diffusion saturation is reached after about 1 minute
in typical experimental situations of plasma damage in microelectronic
fabrication. We predict the general dependencies on porosity and reaction
rates.Comment: Accepted for publication in Phys. Rev.
Scaling of viscous dynamics in simple liquids:theory, simulation and experiment
Supercooled liquids are characterized by relaxation times that increase
dramatically by cooling or compression. Many liquids have been shown to obey
power-law density scaling, according to which the relaxation time is a function
of density to some power over temperature. We show that power-law density
scaling breaks down for larger density variations than usually studied. This is
demonstrated by simulations of the Kob-Andersen binary Lennard-Jones mixture
and two molecular models, as well as by experimental results for two van der
Waals liquids. A more general form of density scaling is derived, which is
consistent with results for all the systems studied. An analytical expression
for the scaling function for liquids of particles interacting via generalized
Lennard-Jones potentials is derived and shown to agree very well with
simulations. This effectively reduces the problem of understanding the viscous
slowing down from being a quest for a function of two variables to a search for
a single-variable function.Comment: 7 pages, 5 figure
The role of vitamin A and its CSF metabolites in supporting a novel mechanism of idiopathic intracranial hypertension
Swarming in shallow waters
A swarm is a collection of separate objects that move autonomously in the same direction in a concerted fashion. This type of behavior is observed in ensembles of various organisms but has proven inherently difficult to realize in artificial chemical systems, where the components have to self-assemble dynamically and, at the same time, propel themselves. This paper describes a class of systems in which millimeter-sized components interact hydrodynamically and organize into dissipative structures that swarm in thin fluid layers. Depending on the geometry of the particles, various types of swarms can be engineered, including ensembles that rotate, follow a "leader", or are pushed in front of a larger particle
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