674 research outputs found
In search of multipolar order on the Penrose tiling
Based on Monte Carlo calculations, multipolar ordering on the Penrose tiling,
relevant for two-dimensional molecular adsorbates on quasicrystalline surfaces
and for nanomagnetic arrays, has been analyzed. These initial investigations
are restricted to multipolar rotors of rank one through four - described by
spherical harmonics Ylm with l=1...4 and restricted to m=0 - positioned on the
vertices of the rhombic Penrose tiling. At first sight, the ground states of
odd-parity multipoles seem to exhibit long-range multipolar order, indicated by
the appearance of a superstructure in the form of the decagonal
Hexagon-Boat-Star tiling, in agreement with previous investigations of dipolar
systems. Yet careful analysis establishes that long-range multipolar order is
absent in all cases investigated here, and only short-range order exists. This
result should be taken as a warning for any future analysis of order in either
real or simulated arrangements of multipoles on quasiperiodic templates
Treatment of Linear and Nonlinear Dielectric Property of Molecular Monolayer and Submonolayer with Microscopic Dipole Lattice Model: I. Second Harmonic Generation and Sum-Frequency Generation
In the currently accepted models of the nonlinear optics, the nonlinear
radiation was treated as the result of an infinitesimally thin polarization
sheet layer, and a three layer model was generally employed. The direct
consequence of this approach is that an apriori dielectric constant, which
still does not have a clear definition, has to be assigned to this polarization
layer. Because the Second Harmonic Generation (SHG) and the Sum-Frequency
Generation vibrational Spectroscopy (SFG-VS) have been proven as the sensitive
probes for interfaces with the submonolayer coverage, the treatment based on
the more realistic discrete induced dipole model needs to be developed. Here we
show that following the molecular optics theory approach the SHG, as well as
the SFG-VS, radiation from the monolayer or submonolayer at an interface can be
rigorously treated as the radiation from an induced dipole lattice at the
interface. In this approach, the introduction of the polarization sheet is no
longer necessary. Therefore, the ambiguity of the unaccounted dielectric
constant of the polarization layer is no longer an issue. Moreover, the
anisotropic two dimensional microscopic local field factors can be explicitly
expressed with the linear polarizability tensors of the interfacial molecules.
Based on the planewise dipole sum rule in the molecular monolayer, crucial
experimental tests of this microscopic treatment with SHG and SFG-VS are
discussed. Many puzzles in the literature of surface SHG and SFG spectroscopy
studies can also be understood or resolved in this framework. This new
treatment may provide a solid basis for the quantitative analysis in the
surface SHG and SFG studies.Comment: 23 pages, 3 figure
Mechanical properties related to the relaxor-ferroelectric phase transition of titanium-doped lead magnesium niobate
2002-2003 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Vectorial Control of Magnetization by Light
Coherent light-matter interactions have recently extended their applications
to the ultrafast control of magnetization in solids. An important but
unrealized technique is the manipulation of magnetization vector motion to make
it follow an arbitrarily designed multi-dimensional trajectory. Furthermore,
for its realization, the phase and amplitude of degenerate modes need to be
steered independently. A promising method is to employ Raman-type nonlinear
optical processes induced by femtosecond laser pulses, where magnetic
oscillations are induced impulsively with a controlled initial phase and an
azimuthal angle that follows well defined selection rules determined by the
materials' symmetries. Here, we emphasize the fact that temporal variation of
the polarization angle of the laser pulses enables us to distinguish between
the two degenerate modes. A full manipulation of two-dimensional magnetic
oscillations is demonstrated in antiferromagnetic NiO by employing a pair of
polarization-twisted optical pulses. These results have lead to a new concept
of vectorial control of magnetization by light
Wettability of amorphous and nanocrystalline Fe78B13Si9 substrates by molten Sn and Bi
The wettability of amorphous and annealing-induced nanocrystalline Fe78B13Si9 ribbons by molten Sn and Bi at 600 K was measured using an improved sessile drop method. The results demonstrate that the structural relaxation and crystallization in the amorphous substrates do not substantially change the wettability with molten Bi because of their invariable physical interaction, but remarkably deteriorate the wettability and interfacial bonding with molten Sn as a result of changing a chemical interaction to a physical one for the atoms at the interface
Therapeutic targeting of Krüppel-like factor 4 abrogates microglial activation
<p>Abstract</p> <p>Background</p> <p>Neuroinflammation occurs as a result of microglial activation in response to invading micro-organisms or other inflammatory stimuli within the central nervous system. According to our earlier findings, Krüppel-like factor 4 (Klf4), a zinc finger transcription factor, is involved in microglial activation and subsequent release of proinflammatory cytokines, tumor necrosis factor alpha, macrophage chemoattractant protein-1 and interleukin-6 as well as proinflammatory enzymes, inducible nitric oxide synthase and cyclooxygenase-2 in lipopolysaccharide-treated microglial cells. Our current study focuses on finding the molecular mechanism of the anti-inflammatory activities of honokiol in lipopolysaccharide-treated microglia with emphasis on the regulation of Klf4.</p> <p>Methods</p> <p>For <it>in vitro </it>studies, mouse microglial BV-2 cell lines as well as primary microglia were treated with 500 ng/mL lipopolysaccharide as well as 1 μM and 10 μM of honokiol. We cloned full-length Klf4 cDNA in pcDNA3.1 expression vector and transfected BV-2 cells with this construct using lipofectamine for overexpression studies. For <it>in vivo </it>studies, brain tissues were isolated from BALB/c mice treated with 5 mg/kg body weight of lipopolysaccharide either with or without 2.5 or 5 mg/kg body weight of honokiol. Expression of Klf4, cyclooxygenase-2, inducible nitric oxide synthase and phospho-nuclear factor-kappa B was measured using immunoblotting. We also measured the levels of cytokines, reactive oxygen species and nitric oxide in different conditions.</p> <p>Results</p> <p>Our findings suggest that honokiol can substantially downregulate the production of proinflammatory cytokines and inflammatory enzymes in lipopolysaccharide-stimulated microglia. In addition, honokiol downregulates lipopolysaccharide-induced upregulation of both Klf4 and phospho-nuclear factor-kappa B in these cells. We also found that overexpression of Klf4 in BV-2 cells suppresses the anti-inflammatory action of honokiol.</p> <p>Conclusions</p> <p>Honokiol potentially reduces inflammation in activated microglia in a Klf4-dependent manner.</p
Improving "color rendering" of LED lighting for the growth of lettuce
Light plays a vital role on the growth and development of plant. On the base of white light with high color rendering to the benefit of human survival and life, we proposed to improve “color rendering” of LED lighting for accelerating the growth of lettuce. Seven spectral LED lights were adopted to irradiate the lettuces under 150 μmol·m−2·s−1 for a 16 hd−1 photoperiod. The leaf area and number profiles, plant biomass, and photosynthetic rate under the as-prepared LED light treatments were investigated. We let the absorption spectrum of fresh leaf be the emission spectrum of ideal light and then evaluate the “color rendering” of as-prepared LED lights by the Pearson product-moment correlation coefficient and CIE chromaticity coordinates. Under the irradiation of red-yellow-blue light with high correlation coefficient of 0.587, the dry weights and leaf growth rate are 2-3 times as high as the sharp red-blue light. The optimized LED light for lettuce growth can be presumed to be limited to the angle (about 75°) between the vectors passed through the ideal light in the CIE chromaticity coordinates. These findings open up a new idea to assess and find the optimized LED light for plant growth
Simple Metals at High Pressure
In this lecture we review high-pressure phase transition sequences exhibited
by simple elements, looking at the examples of the main group I, II, IV, V, and
VI elements. General trends are established by analyzing the changes in
coordination number on compression. Experimentally found phase transitions and
crystal structures are discussed with a brief description of the present
theoretical picture.Comment: 22 pages, 4 figures, lecture notes for the lecture given at the Erice
course on High-Pressure Crystallography in June 2009, Sicily, Ital
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