1,768 research outputs found
Terahertz superlattice parametric oscillator
We report a GaAs/AlAs superlattice parametric oscillator. It was pumped by a
microwave field (power few mW) and produced 3rd harmonic radiation (frequency
near 300 GHz). The nonlinearity of the active superlattice was due to Bragg
reflections of conduction electrons at the superlattice planes. A theory of the
nonlinearity indicates that parametric oscillation should be possible up to
frequencies above 10 THz. The active superlattice may be the object of further
studies of predicted extraordinary nonlinearities for THz fields.Comment: 10 pages, 4 figure
Interface electronic states and boundary conditions for envelope functions
The envelope-function method with generalized boundary conditions is applied
to the description of localized and resonant interface states. A complete set
of phenomenological conditions which restrict the form of connection rules for
envelope functions is derived using the Hermiticity and symmetry requirements.
Empirical coefficients in the connection rules play role of material parameters
which characterize an internal structure of every particular heterointerface.
As an illustration we present the derivation of the most general connection
rules for the one-band effective mass and 4-band Kane models. The conditions
for the existence of Tamm-like localized interface states are established. It
is shown that a nontrivial form of the connection rules can also result in the
formation of resonant states. The most transparent manifestation of such states
is the resonant tunneling through a single-barrier heterostructure.Comment: RevTeX4, 11 pages, 5 eps figures, submitted to Phys.Rev.
Extracts of Feijoa Inhibit Toll-Like Receptor 2 Signaling and Activate Autophagy Implicating a Role in Dietary Control of IBD
Inflammatory bowel disease (IBD) is a heterogeneous chronic inflammatory disease affecting the gut with limited treatment success for its sufferers. This suggests the need for better understanding of the different subtypes of the disease as well as nutritional interventions to compliment current treatments. In this study we assess the ability of a hydrophilic feijoa fraction (F3) to modulate autophagy a process known to regulate inflammation, via TLR2 using IBD cell lines
QSAR-Driven Discovery of Novel Chemical Scaffolds Active against Schistosoma mansoni.
Schistosomiasis is a neglected tropical disease that affects millions of people worldwide. Thioredoxin glutathione reductase of Schistosoma mansoni (SmTGR) is a validated drug target that plays a crucial role in the redox homeostasis of the parasite. We report the discovery of new chemical scaffolds against S. mansoni using a combi-QSAR approach followed by virtual screening of a commercial database and confirmation of top ranking compounds by in vitro experimental evaluation with automated imaging of schistosomula and adult worms. We constructed 2D and 3D quantitative structure-activity relationship (QSAR) models using a series of oxadiazoles-2-oxides reported in the literature as SmTGR inhibitors and combined the best models in a consensus QSAR model. This model was used for a virtual screening of Hit2Lead set of ChemBridge database and allowed the identification of ten new potential SmTGR inhibitors. Further experimental testing on both shistosomula and adult worms showed that 4-nitro-3,5-bis(1-nitro-1H-pyrazol-4-yl)-1H-pyrazole (LabMol-17) and 3-nitro-4-{[(4-nitro-1,2,5-oxadiazol-3-yl)oxy]methyl}-1,2,5-oxadiazole (LabMol-19), two compounds representing new chemical scaffolds, have high activity in both systems. These compounds will be the subjects for additional testing and, if necessary, modification to serve as new schistosomicidal agents
First Experimental Characterization of Microwave Emission from Cosmic Ray Air Showers
We report the first direct measurement of the overall characteristics of
microwave radio emission from extensive air showers. Using a trigger provided
by the KASCADE-Grande air shower array, the signals of the microwave antennas
of the CROME (Cosmic-Ray Observation via Microwave Emission) experiment have
been read out and searched for signatures of radio emission by high-energy air
showers in the GHz frequency range. Microwave signals have been detected for
more than 30 showers with energies above 3*10^16 eV. The observations presented
in this Letter are consistent with a mainly forward-directed and polarised
emission process in the GHz frequency range. The measurements show that
microwave radiation offers a new means of studying air showers at energies
above 10^17 eV.Comment: Accepted for publication in PR
Multifractal analysis of the electronic states in the Fibonacci superlattice under weak electric fields
Influence of the weak electric field on the electronic structure of the
Fibonacci superlattice is considered. The electric field produces a nonlinear
dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the
nonlinearity is explained in terms of energy levels anticrossings. The
multifractal formalism is applied to investigate the effect of weak electric
field on the statistical properties of electronic eigenfunctions. It is shown
that the applied electric field does not remove the multifractal character of
the electronic eigenfunctions, and that the singularity spectrum remains
non-parabolic, however with a modified shape. Changes of the distances between
energy levels of neighbouring eigenstates lead to the changes of the inverse
participation ratio of the corresponding eigenfunctions in the weak electric
field. It is demonstrated, that the local minima of the inverse participation
ratio in the vicinity of the anticrossings correspond to discontinuity of the
first derivative of the difference between marginal values of the singularity
strength. Analysis of the generalized dimension as a function of the electric
field shows that the electric field correlates spatial fluctuations of the
neighbouring electronic eigenfunction amplitudes in the vicinity of
anticrossings, and the nonlinear character of the scaling exponent confirms
multifractality of the corresponding electronic eigenfunctions.Comment: 10 pages, 9 figure
Essential versus accessory aspects of cell death: recommendations of the NCCD 2015
Cells exposed to extreme physicochemical or mechanical stimuli die in an uncontrollable manner, as a result of their immediate structural breakdown. Such an unavoidable variant of cellular demise is generally referred to as ‘accidental cell death’ (ACD). In most settings, however, cell death is initiated by a genetically encoded apparatus, correlating with the fact that its course can be altered by pharmacologic or genetic interventions. ‘Regulated cell death’ (RCD) can occur as part of physiologic programs or can be activated once adaptive responses to perturbations of the extracellular or intracellular microenvironment fail. The biochemical phenomena that accompany RCD may be harnessed to classify it into a few subtypes, which often (but not always) exhibit stereotyped morphologic features. Nonetheless, efficiently inhibiting the processes that are commonly thought to cause RCD, such as the activation of executioner caspases in the course of apoptosis, does not exert true cytoprotective effects in the mammalian system, but simply alters the kinetics of cellular demise as it shifts its morphologic and biochemical correlates. Conversely, bona fide cytoprotection can be achieved by inhibiting the transduction of lethal signals in the early phases of the process, when adaptive responses are still operational. Thus, the mechanisms that truly execute RCD may be less understood, less inhibitable and perhaps more homogeneous than previously thought. Here, the Nomenclature Committee on Cell Death formulates a set of recommendations to help scientists and researchers to discriminate between essential and accessory aspects of cell death
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