451 research outputs found
Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators
Whispering gallery resonators (WGR's), based on total internal reflection,
possess high quality factors in a broad spectral range. Thus, nonlinear optical
processes in such cavities are ideally suited for the generation of broadband
or tunable electromagnetic radiation. Experimentally and theoretically, we
investigate the tunability of optical parametric oscillation in a radially
structured WGR made of lithium niobate. With a 1.04 /mum pump wave, the signal
and idler waves are tuned from 1.78 to 2.5 \mum - including the point of
degeneracy - by varying the temperature between 20 and 62 {\deg}C. A weak
off-centering of the radial domain structure extends considerably the tuning
capabilities. The oscillation threshold lies in the mW-power range.Comment: 4 pages, 5 figure
Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in Transverse Magnetic Field
We report on magnetization, sound velocity, and magnetocaloric-effect
measurements of the Ising-like spin-1/2 antiferromagnetic chain system
BaCoVO as a function of temperature down to 1.3 K and applied
transverse magnetic field up to 60 T. While across the N\'{e}el temperature of
K anomalies in magnetization and sound velocity confirm the
antiferromagnetic ordering transition, at the lowest temperature the
field-dependent measurements reveal a sharp softening of sound velocity
and a clear minimum of temperature at T,
indicating the suppression of the antiferromagnetic order. At higher fields,
the curve shows a broad minimum at T, accompanied by a
broad minimum in the sound velocity and a saturation-like magnetization. These
features signal a quantum phase transition which is further characterized by
the divergent behavior of the Gr\"{u}neisen parameter . By contrast, around the critical field, the
Gr\"{u}neisen parameter converges as temperature decreases, pointing to a
quantum critical point of the one-dimensional transverse-field Ising model.Comment: Phys. Rev. Lett., to appea
Immigration into the mainstream: Conflicting ideological streams, strategic reasoning and party competition
A surprising discovery:five pedagogical skills outdoor and experiential educators might offer more mainstream educators in this time of change
Mechanical land clearing to promote establishment of coastal sandplain grassland and shrubland communities
Author Posting. Β© The Author(s), 2005. This is the author's version of the work. It is posted here by permission of Blackwell Publishing for personal use, not for redistribution. The definitive version was published in Restoration Ecology 14 (2006): 220-232, doi:10.1111/j.1526-100X.2006.00124.x.The decline in grasslands and other species-rich early-successional habitats on the coastal sandplains of the northeastern U.S. has spurred management to increase the area of these declining plant communities. We mechanically removed overstory oak and applied seed from a nearby sandplain grassland on the island of Marthaβs Vineyard, Massachusetts to evaluate this technique for creating an open oak community able to support sandplain herbaceous species. We compared vegetation structure and composition before and after clearing in an area of total tree removal (clearcutting), an area where 85% of tree basal area was removed (savanna cutting) and in adjacent coastal oak forest. Plant responses to clearcutting and savanna cutting were similar. Sandplain herbs colonized at high frequencies after seeding and increasing herbaceous cover from <7% before clearing to 22-38% three growing seasons later. Carex pensylvanica (Pennsylvania sedge) increased in cover ~ 6-fold, accounting for 84-90% of the increased herbaceous cover. Other native ruderals, and exotic herbs reached 6%, 2%, and 1%, cover respectively, after three years. Species richness across cleared treatments increased from 30 to 79 species. All forest species were retained. Forest shrubs and trees initially declined from their dominant cover, but rebounded after three years. Tree clearing plus seeding appeared to be a viable management practice for increasing cover of herbaceous sandplain species while causing minimal increases in exotic herbaceous cover. The long-term persistence of sandplain herbs may require periodic disturbances that limit woody regrowth.This work was funded by grants from the A. W. Mellon Foundation and the Massachusetts Environmental Trust to MBL and from the Kohlberg Foundation to TNC
The Mast Cell Degranulator Compound 48/80 Directly Activates Neurons
Background
Compound 48/80 is widely used in animal and tissue models as a βselectiveβ mast cell activator. With this study we demonstrate that compound 48/80 also directly activates enteric neurons and visceral afferents.
Methodology/Principal Findings
We used in vivo recordings from extrinsic intestinal afferents together with Ca++ imaging from primary cultures of DRG and nodose neurons. Enteric neuronal activation was examined by Ca++ and voltage sensitive dye imaging in isolated gut preparations and primary cultures of enteric neurons. Intraluminal application of compound 48/80 evoked marked afferent firing which desensitized on subsequent administration. In egg albumen-sensitized animals, intraluminal antigen evoked a similar pattern of afferent activation which also desensitized on subsequent exposure to antigen. In cross-desensitization experiments prior administration of compound 48/80 failed to influence the mast cell mediated response. Application of 1 and 10 Β΅g/ml compound 48/80 evoked spike discharge and Ca++ transients in enteric neurons. The same nerve activating effect was observed in primary cultures of DRG and nodose ganglion cells. Enteric neuron cultures were devoid of mast cells confirmed by negative staining for c-kit or toluidine blue. In addition, in cultured enteric neurons the excitatory action of compound 48/80 was preserved in the presence of histamine H1 and H2 antagonists. The mast cell stabilizer cromolyn attenuated compound 48/80 and nicotine evoked Ca++ transients in mast cell-free enteric neuron cultures.
Conclusions/Significance
The results showed direct excitatory action of compound 48/80 on enteric neurons and visceral afferents. Therefore, functional changes measured in tissue or animal models may involve a mast cell independent effect of compound 48/80 and cromolyn
DISC1 genetics, biology and psychiatric illness
Psychiatric disorders are highly heritable, and in many individuals likely arise from the combined effects of genes and the environment. A substantial body of evidence points towards DISC1 being one of the genes that influence risk of schizophrenia, bipolar disorder and depression, and functional studies of DISC1 consequently have the potential to reveal much about the pathways that lead to major mental illness. Here, we review the evidence that DISC1 influences disease risk through effects upon multiple critical pathways in the developing and adult brain
Chitosan-Graft-Branched Polyethylenimine Copolymers: Influence of Degree of Grafting on Transfection Behavior
BACKGROUND: Successful non-viral gene delivery currently requires compromises to achieve useful transfection levels while minimizing toxicity. Despite high molecular weight (MW) branched polyethylenimine (bPEI) is considered the gold standard polymeric transfectant, it suffers from high cytotoxicity. Inversely, its low MW counterpart is less toxic and effective in transfection. Moreover, chitosan is a highly biocompatible and biodegradable polymer but characterized by very low transfection efficiency. In this scenario, a straightforward approach widely exploited to develop effective transfectants relies on the synthesis of chitosan-graft-low MW bPEIs (Chi-g-bPEI(x)) but, despite the vast amount of work that has been done in developing promising polymeric assemblies, the possible influence of the degree of grafting on the overall behavior of copolymers for gene delivery has been largely overlooked. METHODOLOGY/PRINCIPAL FINDINGS: With the aim of providing a comprehensive evaluation of the pivotal role of the degree of grafting in modulating the overall transfection effectiveness of copolymeric vectors, we have synthesized seven Chi-g-bPEI(x) derivatives with a variable amount of bPEI grafts (minimum: 0.6%; maximum: 8.8%). Along the Chi-g-bPEI(x) series, the higher the degree of grafting, the greater the ΞΆ-potential and the cytotoxicity of the resulting polyplexes. Most important, in all cell lines tested the intermediate degree of grafting of 2.7% conferred low cytotoxicity and higher transfection efficiency compared to other Chi-g-bPEI(x) copolymers. We emphasize that, in transfection experiments carried out in primary articular chondrocytes, Chi-g-bPEI(2.7%) was as effective as and less cytotoxic than the gold standard 25 kDa bPEI. CONCLUSIONS/SIGNIFICANCE: This work underlines for the first time the pivotal role of the degree of grafting in modulating the overall transfection effectiveness of Chi-g-bPEI(x) copolymers. Crucially, we have demonstrated that, along the copolymer series, the fine tuning of the degree of grafting directly affected the overall charge of polyplexes and, altogether, had a direct effect on cytotoxicity
Prox1 Is Required for Granule Cell Maturation and Intermediate Progenitor Maintenance During Brain Neurogenesis
The transcription factor Prox1 plays a crucial role in intermediate progenitor maintenance and hippocampal neuron differentiation during adult neurogenesis in the dentate gyrus region of the hippocampus
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