23,593 research outputs found
Mangiferin: A Promising Anticancer Bioactive
Of late, several biologically active antioxidants from natural products have been investigated by the researchers in order to combat the root cause of carcinogenesis, i.e., oxidative stress. Mangiferin, a therapeutically active C-glucosylated xanthone, is extracted from pulp, peel, seed, bark and leaf of Mangifera indica. These polyphenols of mangiferin exhibit antioxidant properties and tend to decrease the oxygen-free radicals, thereby reducing the DNA damage. Indeed, its capability to modulate several key inflammatory pathways undoubtedly helps in stalling the progression of carcinogenesis. The current review article emphasizes an updated account on the patents published on the chemopreventive action of Mangiferin, apoptosis induction made on various cancer cells, along with proposed antioxidative activities and patent mapping of other important therapeutic properties. Considering it as promising polyphenol, this paper would also summarize the diverse molecular targets of Mangiferin
Enhanced dynamic nuclear polarization via swept microwave frequency combs
Dynamic Nuclear Polarization (DNP) has enabled enormous gains in magnetic
resonance signals and led to vastly accelerated NMR/MRI imaging and
spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the
full electron spectrum are appealing since they allow direct participation of
all electrons in the hyperpolarization process. Such methods typically entail
sweeps of microwave radiation over the broad electron linewidth to excite DNP,
but are often inefficient because the sweeps, constrained by adiabaticity
requirements, are slow. In this paper we develop a technique to overcome the
DNP bottlenecks set by the slow sweeps, employing a swept microwave frequency
comb that increases the effective number of polarization transfer events while
respecting adiabaticity constraints. This allows a multiplicative gain in DNP
enhancement, scaling with the number of comb frequencies and limited only by
the hyperfine-mediated electron linewidth. We demonstrate the technique for the
optical hyperpolarization of 13C nuclei in powdered microdiamonds at low
fields, increasing the DNP enhancement from 30 to 100 measured with respect to
the thermal signal at 7T. For low concentrations of broad linewidth electron
radicals, e.g. TEMPO, these multiplicative gains could exceed an order of
magnitude.Comment: Contains supplementary inf
Ge quantum dot arrays grown by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface: nucleation, morphology and CMOS compatibility
Issues of morphology, nucleation and growth of Ge cluster arrays deposited by
ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered.
Difference in nucleation of quantum dots during Ge deposition at low (<600 deg
C) and high (>600 deg. C) temperatures is studied by high resolution scanning
tunneling microscopy. The atomic models of growth of both species of Ge
huts---pyramids and wedges---are proposed. The growth cycle of Ge QD arrays at
low temperatures is explored. A problem of lowering of the array formation
temperature is discussed with the focus on CMOS compatibility of the entire
process; a special attention is paid upon approaches to reduction of treatment
temperature during the Si(001) surface pre-growth cleaning, which is at once a
key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array
formation process. The temperature of the Si clean surface preparation, the
final high-temperature step of which is, as a rule, carried out directly in the
MBE chamber just before the structure deposition, determines the compatibility
of formation process of Ge-QD-array based devices with the CMOS manufacturing
cycle. Silicon surface hydrogenation at the final stage of its wet chemical
etching during the preliminary cleaning is proposed as a possible way of
efficient reduction of the Si wafer pre-growth annealing temperature.Comment: 30 pages, 11 figure
Positive Semidefiniteness and Positive Definiteness of a Linear Parametric Interval Matrix
We consider a symmetric matrix, the entries of which depend linearly on some
parameters. The domains of the parameters are compact real intervals. We
investigate the problem of checking whether for each (or some) setting of the
parameters, the matrix is positive definite (or positive semidefinite). We
state a characterization in the form of equivalent conditions, and also propose
some computationally cheap sufficient\,/\,necessary conditions. Our results
extend the classical results on positive (semi-)definiteness of interval
matrices. They may be useful for checking convexity or non-convexity in global
optimization methods based on branch and bound framework and using interval
techniques
Averaging approximation to singularly perturbed nonlinear stochastic wave equations
An averaging method is applied to derive effective approximation to the
following singularly perturbed nonlinear stochastic damped wave equation \nu
u_{tt}+u_t=\D u+f(u)+\nu^\alpha\dot{W} on an open bounded domain
\,, \,. Here is a small parameter
characterising the singular perturbation, and \,, \,, parametrises the strength of the noise. Some scaling transformations
and the martingale representation theorem yield the following effective
approximation for small , u_t=\D u+f(u)+\nu^\alpha\dot{W} to an error of
\ord{\nu^\alpha}\,.Comment: 16 pages. Submitte
Pressure shift of the superconducting T_c of LiFeAs
The effect of hydrostatic pressure on the superconductivity in LiFeAs is
investigated up to 1.8 GPa. The superconducting transition temperature, T_c,
decreases linearly with pressure at a rate of 1.5 K/GPa. The negative pressure
coefficient of T_c and the high ambient pressure T_c indicate that LiFeAs is
the high-pressure analogue of the isoelectronic SrFe_2As_2 and BaFe_2As_2.Comment: 3 pages, 2 figure
Infrared stability of ABJ-like theories
We consider marginal deformations of the superconformal ABJM/ABJ models which
preserve N=2 supersymmetry. We determine perturbatively the spectrum of fixed
points and study their infrared stability. We find a closed line of fixed
points which is IR stable. The fixed point corresponding to the ABJM/ABJ models
is stable under marginal deformations which respect the original SU(2)xSU(2)
invariance, while deformations which break this group destabilize the theory
which then flows to a less symmetric fixed point. We discuss the addition of
flavor degrees of freedom. We prove that in general a flavor marginal
superpotential does not destabilize the system in the IR. An exception is
represented by a marginal coupling which mixes matter charged under different
gauge sectors. Finally, we consider the case of relevant deformations which
should drive the system to a strongly coupled IR fixed point recently
investigated in arXiv:0909.2036 [hep-th].Comment: 1+11 pages, 4 figures; v2: minor correction
Electron doping evolution of the neutron spin resonance in NaFeCoAs
Neutron spin resonance, a collective magnetic excitation coupled to
superconductivity, is one of the most prominent features shared by a broad
family of unconventional superconductors including copper oxides, iron
pnictides, and heavy fermions. In this work, we study the doping evolution of
the resonances in NaFeCoAs covering the entire superconducting
dome. For the underdoped compositions, two resonance modes coexist. As doping
increases, the low-energy resonance gradually loses its spectral weight to the
high-energy one but remains at the same energy. By contrast, in the overdoped
regime we only find one single resonance, which acquires a broader width in
both energy and momentum, but retains approximately the same peak position even
when drops by nearly a half compared to optimal doping. These results
suggest that the energy of the resonance in electron overdoped
NaFeCoAs is neither simply proportional to nor the
superconducting gap, but is controlled by the multi-orbital character of the
system and doped impurity scattering effect.Comment: accepted by PR
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