2,687 research outputs found
Separation and Quantification of 1,4-benzodiazepines: HPLC versus CZE
The goal of the present study was to separate a set of benzodiazepines, namely bromazepam,
oxazepam, nitrazepam, chlordiazepoxide, flunitrazepam, lormetazepam and diazepam by analytical scale
HPLC and CZE. The both methods for separation of these seven compounds from the 1,4-benzodiazepine
group were optimized and compared. LODs and LOQs were determined under the optimized conditions in
the both methods. The corresponding LOD and LOQ values are approximately three orders of magnitude
lower in HPLC than in CZE. As expected, elution order was found to be different for the both techniques.
As a result of a critical collation of all the parameters considered, RP-HPLC was found to be more suitable
for determination of the set of benzodiazepines. A real sample analysis was performed under optimized
conditions to demonstrate applicability of the proposed analytical methods. (doi: 10.5562/cca1738
Coupled Negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8
The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline
compound has been measured as function of temperature and magnetic field up to
14T. It is found that the application of an external magnetic field suppresses
the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic
field dependence reveals a negative magnetocapacitance which is proportional to
the magnetic susceptibility, suggesting a common magnetostrictive origin for
the magnetic field dependence of the two quantities. This result is very
different from that obtained from the isostructural compound Ni3V2O8 that
presents a peak in the dielectric constant at the incommensurate magnetic phase
transition coupled to a sign change of the magnetocapacitance
The influence of the Hall force on the vortex dynamics in type II superconductors
The effect of the Hall force on the pinning of vortices in type II
superconductors is considered. A field theoretic formulation of the pinning
problem allows a non-perturbative treatment of the influence of quenched
disorder. A self-consistent theory is constructed using the diagrammatic
functional method for the effective action, and an expression for the pinning
force for independent vortices as well as vortex lattices is obtained. We find
that the pinning force for a single vortex is suppressed by the Hall force at
low temperatures while it is increased at high temperatures. The effect of the
Hall force is more pronounced on a single vortex than on a vortex lattice. The
results of the self-consistent theory are shown to be in good agreement with
numerical simulations.Comment: 9 pages, 4 figures, published in Physical Review
Sulfo- and Oxy-analogues of Arginine: Synthesis, Analysis and Preliminary Biological Screening
A novel methodology for the synthesis of sulfo- and oxy-modified amino acid analogues of
arginine (Arg) has been developed using both conventional and polymer assisted synthesis from ready
available amino acid precursor. Introduction of guanidine group was made also by the MWA synthesis.
The in vitro inhibitory effect of the amino acid analogues on the growth of murine erythroleukemia cells,
clone F4N in culture was also studied. (doi: 10.5562/cca1780
Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks
The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth\u27s climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO2 uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO2 uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycleâclimate models
Enantioseparation of Dansylated Amino Acids by Ligand-exchange Capillary Electrophoresis Using L-phenylalaninamide, L-lysine or L-threonine as Chiral Selector
In recent years enantioseparation of both active pharmaceutical ingredients and bio molecules
such as amino acids became more and more necessary because in most cases the two stereo forms exhibit
different pharmacological effects. This article deals with the chiral separation of dansylated amino acids
by ligand-exchange capillary electrophoresis using L-phenylalaninamide, L-lysine and L-threonine as chiral
selectors. Experiments with different central metal ions such as Cu(II), Co(II), Cd(II), Ni(II) and Zn(II)
were carried out. Optimal conditions were found out by studying the effect of the pH and the selector molarity
on the chiral resolution. Best separation was obtained for the Cu(II)/L-lysine complex, showing a
chiral resolution up to 17 for Dns-DL-Met. (doi: 10.5562/cca1762
Open Luttinger liquids
We study the problem of Luttinger liquids interacting with an active
environment. We are particularly interested in how dissipation affects the
response and correlation functions of non-isolated Luttinger liquids. We show
that the exchange of particles, energy, and momentum lead to changes in the
exponents characterizing the various correlations functions. We discuss the
importance of the zero mode physics in this context.Comment: Revtex, 4 pages. Final version published in PR
The Trans-Planckian Problem of Inflationary Cosmology
In most current models of inflation based on a weakly self-coupled scalar
matter field minimally coupled to gravity, the period of inflation lasts so
long that, at the beginning of the inflationary period, the physical
wavelengths of comoving scales which correspond to the present large-scale
structure of the Universe were smaller than the Planck length. Thus, the usual
computations of the spectrum of fluctuations in these models involve
extrapolating low energy physics (both in the matter and gravitational sector)
into regions where this physics is not applicable. In this paper we demonstrate
that the usual predictions of inflation for the spectrum of cosmological
fluctuations do indeed depend on the hidden assumptions about super-Planck
scale physics. We introduce a class of modified dispersion relations to mimic
possible effects of super-Planck scale physics, and show that in some cases
important deviations from the usual predictions of inflation are obtained. Some
implications of this result for the unification of fundamental physics and
early Universe cosmology are discussed.Comment: 16 pages, 2 figures. One important correction in the Corley/Jacobson
case with b_m>0 and some misprints corrected. Version published in PR
Correlations in two-component log-gas systems
A systematic study of the properties of particle and charge correlation
functions in the two-dimensional Coulomb gas confined to a one-dimensional
domain is undertaken. Two versions of this system are considered: one in which
the positive and negative charges are constrained to alternate in sign along
the line, and the other where there is no charge ordering constraint. Both
systems undergo a zero-density Kosterlitz-Thouless type transition as the
dimensionless coupling is varied through . In
the charge ordered system we use a perturbation technique to establish an
decay of the two-body correlations in the high temperature limit.
For , the low-fugacity expansion of the asymptotic
charge-charge correlation can be resummed to all orders in the fugacity. The
resummation leads to the Kosterlitz renormalization equations.Comment: 39 pages, 5 figures not included, Latex, to appear J. Stat. Phys.
Shortened version of abstract belo
Quantum Collective Creep: a Quasiclassical Langevin Equation Approach
The dynamics of an elastic medium driven through a random medium by a small
applied force is investigated in the low-temperature limit where quantum
fluctuations dominate. The motion proceeds via tunneling of segments of the
manifold through barriers whose size grows with decreasing driving force .
In the limit of small drive, at zero-temperature the average velocity has the
form . For strongly
dissipative dynamics, there is a wide range of forces where the dissipation
dominates and the velocity--force characteristics takes the form
, with the
action for a typical tunneling event, the force dependence being determined by
the roughness exponent of the -dimensional manifold. This result
agrees with the one obtained via simple scaling considerations. Surprisingly,
for asymptotically low forces or for the case when the massive dynamics is
dominant, the resulting quantum creep law is {\it not} of the usual form with a
rate proportional to ; rather we find corresponding to and , with the naive scaling exponent for massive
dynamics. Our analysis is based on the quasi-classical Langevin approximation
with a noise obeying the quantum fluctuation--dissipation theorem. The many
space and time scales involved in the dynamics are treated via a functional
renormalization group analysis related to that used previously to treat the
classical dynamics of such systems. Various potential difficulties with these
approaches to the multi-scale dynamics -- both classical and quantum -- are
raised and questions about the validity of the results are discussed.Comment: RevTeX, 30 pages, 8 figures inserte
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