51 research outputs found
Performance of hemielliptic dielectric lens antennas with optimal edge illumination
The role of edge illumination in the performance of compact-size dielectric
lens antennas (DLAs) is studied in accurate manner using a highly efficient
algorithm based on the combination of the Muller boundary integral equations
and the method of analytical regularization. The analysis accounts for the
finite size of the lens and directive nature of the primary feed placed close
to the center of the lens base. The problem is solved in a two-dimensional
formulation for both E- and H-polarizations. It is found that away from
internal resonances that spoil the radiation characteristics of DLAs made of
dense materials, the edge illumination has primary importance. The proper
choice of this parameter helps maximize DLA directivity, and its optimal value
depends on the lens material and feed polarization. Index Terms: Beam
collimation, dielectric lens antenna, directivity improvement, edge
illumination, edge taper, hemielliptic lens.Comment: 5 pages, 9 figure
Whispering-gallery and Luneburg-lens effects in a beam-fed circularly-layered dielectric cylinder
The whispering-gallery mode (WGM) excitation and Luneburg lens (LL) effect
are studied for a lossy circularly-layered dielectric cylinder illuminated by a
beam field. The latter is simulated by the Complex Source-Point (CSP) beam.
Exact series solution to the wave scattering problem is used to obtain the
far-field patterns and directivity. The WG mode effect is shown to undermine
the LL performance. Index Terms: Layered circular dielectric cylinder, Complex
source point beam, Whispering-gallery modes, Luneburg lens.Comment: 5 pages, 7 figure
Optical and modal features of hemielliptic dielectric lenses
Any dielectric lens has a finite closed boundary and therefore is, in fact,
an open dielectric resonator capable of supporting resonant modes whose
Q-factor depends of the lens parameters (size, shape, and material). The
hemielliptic lens, that is an essential building block of many mm-wave and THz
antennas, is not an exception: it supports the so-called halfbowtie (HBT)
resonances that can strongly affect performance of such antennas. In this paper
we illustrate the interplay between the optical and modal features in the
electromagnetic behaviour of hemielliptic lenses and highlight the drastic
influence of the HBT resonances on radiation characteristics of lens antennas.
We also discuss the difficulties associated with accurate description of the
resonant phenomena in compact-size hemielliptic lenses with conventional
techniques and provide recommendations on how to minimize the parasitic impact
of HBT resonances on the antenna performance.Comment: 5 pages 6 figure
Assessment of the diversity of vascular plants in phytocenoses with a share of Quercus mongolica on the territory of Relic Oaks State Reserve
In this paper, we assess the diversity of vascular plants in phytocenoses with Quercus mongolica (family Fagaceae) on the territory of the Relic Oaks State Reserve (Eastern Siberia, Transbaikal region), where Q. mongolica is located at the northwestern boundary of the areal. The descriptions of phytocenoses have been processed in the PAST3 application. The similarity of species composition has been determined using the Jaccard index. The resulting tree diagram shows two groups of descriptions at a similarity level of 0.14-0.15. The first group includes the descriptions of mixed forest quadrats, in which Q. mongolica is a co-edificator. The second group of descriptions presents the communities where Q. mongolica is the only species in the tree layer. The analysis of the tree diagram shows the dependence of species richness within the phytocenoses on the surface patterns and edaphoclimatic conditions. The phytocenoses located on steep southern slopes show less diversity
Mechanism of Inhibition of Enveloped Virus Membrane Fusion by the Antiviral Drug Arbidol
The broad-spectrum antiviral arbidol (Arb) inhibits cell entry of enveloped viruses by blocking viral fusion with host cell membrane. To better understand Arb mechanism of action, we investigated its interactions with phospholipids and membrane peptides. We demonstrate that Arb associates with phospholipids in the micromolar range. NMR reveals that Arb interacts with the polar head-group of phospholipid at the membrane interface. Fluorescence studies of interactions between Arb and either tryptophan derivatives or membrane peptides reconstituted into liposomes show that Arb interacts with tryptophan in the micromolar range. Interestingly, apparent binding affinities between lipids and tryptophan residues are comparable with those of Arb IC50 of the hepatitis C virus (HCV) membrane fusion. Since tryptophan residues of membrane proteins are known to bind preferentially at the membrane interface, these data suggest that Arb could increase the strength of virus glycoprotein's interactions with the membrane, due to a dual binding mode involving aromatic residues and phospholipids. The resulting complexation would inhibit the expected viral glycoprotein conformational changes required during the fusion process. Our findings pave the way towards the design of new drugs exhibiting Arb-like interfacial membrane binding properties to inhibit early steps of virus entry, i.e., attractive targets to combat viral infection
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