9,592 research outputs found
Two-Photon Polarization Interference for Pulsed SPDC in a PPKTP Waveguide
We study the spectral properties of Spontaneous Parametric Down Conversion in
a periodically poled waveguided structure of KTP crystal pumped by ultra-short
pulses. Our theoretical analysis reveals a strongly multimode and asymmetric
structure of the two-photon spectral amplitude for type-II SPDC. Experimental
evidence, based on Hong-Ou-Mandel polarization interference with narrowband
filtering, confirms this result.Comment: Submitted for publicatio
Magnetization reversal in mixed ferrite-chromite perovskites with non magnetic cation on the A-site
In this work, we have performed Monte Carlo simulations in a classical model
for RFeCrO with R=Y and Lu, comparing the numerical simulations
with experiments and mean field calculations. In the analyzed compounds, the
antisymmetric exchange or Dzyaloshinskii-Moriya (DM) interaction induced a weak
ferromagnetism due to a canting of the antiferromagnetically ordered spins.
This model is able to reproduce the magnetization reversal (MR) observed
experimentally in a field cooling process for intermediate values and the
dependence with of the critical temperatures. We also analyzed the
conditions for the existence of MR in terms of the strength of DM interactions
between Fe and Cr ions with the x values variations.Comment: 8 pages, 7 figure
Characterization of Navassa National Wildlife Refuge: A preliminary report for NF-06-05 (NOAA ship "Nancy Foster", April 18-30, 2006)
Navassa is a small, undeveloped island in the Windward Passage between Jamaica and Haiti. It was designated a National Wildlife Refuge under the jurisdiction of the U.S. Fish and Wildlife Service in 1999, but the remote location makes management and enforcement challenging, and the area is regularly fished by artisanal fishermen from Haiti. In April 2006, the NOAA Center for Coastal Fisheries and Habitat Research conducted a research cruise to Navassa. The cruise produced the first high-resolution multibeam bathymetry for the area, which will facilitate habitat mapping and assist in refuge management. A major emphasis of the cruise was to study the impact of Haitian fishing gear on benthic habitats and fish communities; however, in 10 days on station only one small boat was observed with five fishermen and seven traps. Fifteen monitoring stations were established to characterize fish and benthic communities along the deep (28-34 m) shelf, as these areas have been largely unstudied by previous cruises. The fish communities included numerous squirrelfishes, triggerfishes, and parrotfishes. Snappers and grouper were also present but no small individuals were observed. Similarly, conch surveys indicated the population was in low abundance and was heavily skewed towards adults. Analysis of the benthic photoquadrats is currently underway. Other cruise activities included installation of a temperature logger network, sample collection for stable isotope analyses to examine trophic structure, and drop camera surveys to ground-truth habitat maps and overhead imagery. (PDF contains 58 pages
Evolution of Preprofessional Pharmacy Curricula
Objectives. To examine changes in preprofessional pharmacy curricular requirements and trends, and determine rationales for and implications of modifications. Methods. Prerequisite curricular requirements compiled between 2006 and 2011 from all doctor of pharmacy (PharmD) programs approved by the Accreditation Council of Pharmacy Education were reviewed to ascertain trends over the past 5 years. An online survey was conducted of 20 programs that required either 3 years of prerequisite courses or a bachelorâs degree, and a random sample of 20 programs that required 2 years of prerequisites. Standardized telephone interviews were then conducted with representatives of 9 programs. Results. In 2006, 4 programs required 3 years of prerequisite courses and none required a bachelorâs degree; by 2011, these increased to 18 programs and 7 programs, respectively. Of 40 programs surveyed, responses were received from 28 (70%), 9 (32%) of which reported having increased the number of prerequisite courses since 2006. Reasons given for changes included desire to raise the level of academic achievement of students entering the PharmD program, desire to increase incoming student maturity, and desire to add clinical sciences and experiential coursework to the pharmacy curriculum. Some colleges and schools experienced a temporary decrease in applicants. Conclusions. The preprofessional curriculum continues to evolve, with many programs increasing the number of course prerequisites. The implications of increasing prerequisites were variable and included a perceived increase in maturity and quality of applicants and, for some schools, a temporary decrease in the number of applicants
DIRECT ESTIMATION OF ABOVEGROUND FOREST PRODUCTIVITY THROUGH HYPERSPECTRAL REMOTE SENSING OF CANOPY NITROGEN
The concentration of nitrogen in foliage has been related to rates of net photosynthesis across a wide range of plant species and functional groups and thus represents a simple and biologically meaningful link between terrestrial cycles of carbon and nitrogen. Although foliar N is used by ecosystem models to predict rates of leafâlevel photosynthesis, it has rarely been examined as a direct scalar to standâlevel carbon gain. Establishment of such relationships would greatly simplify the nature of forest C and N linkages, enhancing our ability to derive estimates of forest productivity at landscape to regional scales. Here, we report on a highly predictive relationship between wholeâcanopy nitrogen concentration and aboveground forest productivity in diverse forested stands of varying age and species composition across the 360â000âha White Mountain National Forest, New Hampshire, USA. We also demonstrate that hyperspectral remote sensing can be used to estimate foliar N concentration, and hence forest production across a large number of contiguous images. Together these data suggest that canopyâlevel N concentration is an important correlate of productivity in these forested systems, and that imaging spectrometry of canopy N can provide direct estimates of forest productivity across large landscapes
Identification of a novel polyprenylated acylphloroglucinolâderived SIRT1 inhibitor with cancerâspecific anti-proliferative and invasion-suppressing activities
SIRT1, a class III histone deacetylase, plays a critical role in regulating cancer cell growth, migration and invasion, which makes it a potential target for cancer therapeutics. In this study, we screened derivatives of several groups of natural products and identified a novel SIRT1 inhibitor JQ-101, a synthetic derivative of the polyprenylated acylphloroglucinol (PPAP) natural products, with an IC(50) for SIRT1 of 30 ”M in vitro, with 5-fold higher activity for SIRT1 vs. SIRT2. Exposure of tumor cells to JQ-101 significantly enhanced acetylation of p53 and histone H4K16 at known sites of SIRT1 deacetylation, validating SIRT1 as its cellular target. JQ-101 suppressed cancer cell growth and survival by targeting SIRT1, and also exhibited selective cytotoxicity towards a panel of human tumor cell lines, while producing no toxicity in two normal human cell types at comparable concentrations. JQ-101 induced both apoptosis and cell senescence, and suppressed cancer cell invasion in vitro. In summary, we have identified JQ-101 as a new SIRT1 inhibitor which may have potential application in cancer treatment through its ability to induce tumor cell apoptosis and senescence and suppress cancer cell invasion.CA164245 - NCI NIH HHS; R01 CA101992 - NCI NIH HHS; R21 CA129046 - NCI NIH HHS; R21 CA141036 - NCI NIH HHS; P50 GM067041 - NIGMS NIH HHS; UL1RR025771 - NCRR NIH HHS; CA101992 - NCI NIH HHS; UL1 RR025771 - NCRR NIH HHS; GM-073855 - NIGMS NIH HHS; CA129046 - NCI NIH HHS; R21 CA164245 - NCI NIH HHS; GM-067041 - NIGMS NIH HHS; CA141036 - NCI NIH HHS; R01 GM073855 - NIGMS NIH HH
Photocatalytic hydrogen production using polymeric carbon nitride with a hydrogenase and a bioinspired synthetic Ni catalyst.
Solar-light-driven H2 production in water with a [NiFeSe]-hydrogenase (H2ase) and a bioinspired synthetic nickel catalyst (NiP) in combination with a heptazine carbon nitride polymer, melon (CN(x)), is reported. The semibiological and purely synthetic systems show catalytic activity during solar light irradiation with turnover numbers (TONs) of more than 50,000â
molâH2(molâH2ase)(-1) and approximately 155â
molâH2â(molâNiP)(-1) in redox-mediator-free aqueous solution at pHâ
6 and 4.5, respectively. Both systems maintained a reduced photoactivity under UV-free solar light irradiation (λ>420â
nm).This is the final version. It was first published in Angewandte Chemie International Edition at http://onlinelibrary.wiley.com/doi/10.1002/anie.201406811/abstract
Dissipative versus Conditional Generation of Gaussian Entanglement and Spin Squeezing
Spin squeezing of collective atomic spins can be achieved conditionally via
probing with light and subsequent homodyne detection, as is done in a Quantum
Nondemolition measurement. Recently it has been shown that squeezing can also
be created unconditionally by a properly designed dissipative dynamics. We
compare the two approaches in a Gaussian description, and optimize over all
Gaussian light-matter interactions. We find that in the optimal unconditional
scheme based on dissipation the level of squeezing scales as . In
contrast, the optimal conditional scheme based on measurement of light -- which
in fact is not a Quantum Nondemolition measurement -- can provide squeezing
which scales as in the most relevant regime of moderate optical
depths. Our results apply directly also to the creation of entanglement in the
form of non-local spin squeezing of two atomic ensembles.Comment: 9 pages, 7 figure
Plant and root endophyte assembly history: interactive effects on native and exotic plants
Funded by Society for Conservation Biology; National Research Initiative of the USDA Cooperative State Research, Education and Extension Service; Terman Fellowship of Stanford UniversityDifferences in the arrival timing of plants and soil biota may result in different plant communities through priority effects, potentially affecting the success of native vs. exotic plants, but experimental evidence is largely lacking. We conducted a greenhouse experiment to investigate whether the assembly history of plants and fungal root endophytes could interact to influence plant emergence and biomass. We introduced a grass species and eight fungal species from one of three land-use types (undisturbed,
disturbed, or pasture sites in a Florida scrubland) in factorial combinations. We then introduced all plants and fungi from the other land-use types 2 weeks later. Plant emergence was monitored for 6 months, and final plant biomass and fungal species composition
assessed. The emergence and growth of the exotic Melinis repens and the native Schizacharyium niveum were affected negatively when introduced early with their âhomeâ fungi, but early introduction of a different plant species or fungi from a different site type
eliminated these negative effects, providing evidence for interactive priority effects. Interactive effects of plant and fungal arrival history may be an overlooked determinant of plant community structure and may provide an effective management tool to inhibit biological invasion and aid ecosystem restoration
Magnetoelectric coupling in polycrystalline FeVO4
We report coupling between magnetic and electric orders for antiferromagnetic
polycrystalline FeVO4 in which magnetism-induced polarization has been recently
found in noncollinear antiferromagnetic state below the second
antiferromagnetic phase transition at TN2=15.7K. In this low symmetry phase
space group P-1, the magnetic field dependence of electric polarization
evidences a clear magnetoelectric coupling in the noncollinear spin-configured
antiferromagnetic phase. The discontinuity of magnetodielectric effect observed
at the vicinity of the polar to nonpolar transition evidences competition
between different magnetodielectric couplings in the two different
antiferromagnetic states. The existence of thermal expansion anomaly near TN2
and magnetostriction effect support magnetoelastically mediated scenario of the
observed magnetoelectric effect.Comment: 4 pages, 6 figures, Phys. Rev. B 80, 172103 (2009
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