4,424 research outputs found
Generalization of the coupled dipole method to periodic structures
We present a generalization of the coupled dipole method to the scattering of
light by arbitrary periodic structures. This new formulation of the coupled
dipole method relies on the same direct-space discretization scheme that is
widely used to study the scattering of light by finite objects. Therefore, all
the knowledge acquired previously for finite systems can be transposed to the
study of periodic structures.Comment: 5 pages, 2 figures, and 1 tabl
Challenges of the preceptors working with new nurses: A phenomenological research study
© 2016. Introduction: Preceptors play an important role in the transition of new nurses to the practice setting, however, preceptorship experience has been perceived as stressful by preceptors. This study aimed to explore the lived experiences of nurse preceptors working with new nurses. Method: This qualitative study used the hermeneutic phenomenological design to explore the experiences of six nurse preceptors working with new nurses in a tertiary pediatric teaching hospital in Northwest of Iran, who were recruited by purposive sampling. Data were collected using in-depth semi-structured individual interviews between July 2014 and March 2015, and analyzed using the Diekelmann's seven-stage method. Results: Data analysis revealed three themes: 1) preceptorship as a challenging and stressful role; 2) lack of support; and 3) lack of appreciation. Preceptorship as 'a challenging and stressful role' was the constitutive pattern that unified the themes. Conclusion: The preceptorship of new nurses is challenging and stressful. Preceptors endure several roles concurrently, thus, their workload should be balanced appropriately in order not to compromise with one another and evade burnout. The preceptors need to be well supported and their contribution be appropriately recognized. Setting clear objectives and realistic expectations, and having clear policies and guidelines in place should help develop a preceptorship program that is more likely to bring about positive outcomes for both preceptors and new nurses
Tracking Multidecadal Lake Water Dynamics with Landsat Imagery and Topography/Bathymetry
An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.Water resource management is of critical importance due to its close relationship with nearly every industry, field, and lifeform on this planet. The success of future water management will rely upon having detailed data of current and historic water dynamics. This research leverages Google Earth Engine and uses Landsat 5 imagery in conjunction with bathymetry and Shuttle Radar Topography Mission digital elevation model data to analyze long‐term lake dynamics (water surface elevation, surface area, volume, volume change, and frequency) for Lake McConaughy in Nebraska, USA. Water surface elevation was estimated by extracting elevation values from underlying bathymetry and digital elevations models using 5,994 different combinations of water indices, water boundaries, and statistics for 100 time periods spanning 1985–2009. Surface elevation calculations were as accurate as 0.768 m root mean square error (CI95% [0.657, 0.885]). Water volume change calculations found a maximum change of 1.568 km3 and a minimum total volume of only 23.97% of the maximum reservoir volume. Seasonal and long‐term trends were identified, which have major affects regarding regional agriculture, local recreation, and lake water quality. This research fills an existing gap in optical remote sensing‐based monitoring of lakes and reservoirs, is more robust and outperforms other commonly used monitoring techniques, increases the number of water bodies available for long‐term studies, introduces a scalable framework deployable within Google Earth Engine, and enables data collection of both gauged and ungauged water bodies, which will substantially increase our knowledge and understanding of these critical ecosystems
Development of Digital Hysteresis Current Control with PLL Loop Gain Compensation Strategy for PWM Inverters with Constant Switching Frequency
Hysteresis current control is one of the simplest techniques used to control the magnitude and phase angle of motor current for motor drives systems. However, this technique presents several disadvantages such as operation at variable switching frequency which can reveal problems of filtering, interference between the phases in the case of the three-phase systems with insulated neutral connection or delta connection, and irregularity of the modulation pulses which especially causes an acoustic noise on the level of the machine for the high power drive. In this paper, a new technique is proposed for a variable-hysteresis-band controller based on dead beat control applied to three phase voltage source PWM inverters feeding AC motors. Its main aim is firstly ensure a constant switching frequency and secondly the synchronization of modulation pulses using the phase-locked-loop with loop gain compensation in order to ensure a better stability. The behavior of the proposed technique is verified by simulation
Selective nanomanipulation using optical forces
We present a detailed theoretical study of the recent proposal for selective
nanomanipulation of nanometric particles above a substrate using near-field
optical forces [Chaumet {\it et al.} Phys. Rev. Lett. {\bf 88}, 123601 (2002)].
Evanescent light scattering at the apex of an apertureless near-field probe is
used to create an optical trap. The position of the trap is controlled on a
nanometric scale via the probe and small objects can be selectively trapped and
manipulated. We discuss the influence of the geometry of the particles and the
probe on the efficiency of the trap. We also consider the influence of multiple
scattering among the particles on the substrate and its effect on the
robustness of the trap.Comment: 12 pages, 17 figure
Optical binding of particles with or without the presence of a flat dielectric surface
Optical fields can induce forces between microscopic objects, thus giving
rise to new structures of matter. We study theoretically these optical forces
between two spheres, either isolated in water, or in presence of a flat
dielectric surface. We observe different behavior in the binding force between
particles at large and at small distances (in comparison with the wavelength)
from each other. This is due to the great contribution of evanescent waves at
short distances. We analyze how the optical binding depends of the size of the
particles, the material composing them, the wavelength and, above all, on the
polarization of the incident beam. We also show that depending on the
polarization, the force between small particles at small distances changes its
sign. Finally, the presence of a substrate surface is analyzed showing that it
only slightly changes the magnitudes of the forces, but not their qualitative
nature, except when one employs total internal reflection, case in which the
particles are induced to move together along the surface.Comment: 8 pages, 9 figures, and 1 tabl
Out-of-equilibrium relaxation of the Edwards-Wilkinson elastic line
We study the non-equilibrium relaxation of an elastic line described by the
Edwards-Wilkinson equation. Although this model is the simplest representation
of interface dynamics, we highlight that many (not though all) important
aspects of the non-equilibrium relaxation of elastic manifolds are already
present in such quadratic and clean systems. We analyze in detail the aging
behaviour of several two-times averaged and fluctuating observables taking into
account finite-size effects and the crossover to the stationary and equilibrium
regimes. We start by investigating the structure factor and extracting from its
decay a growing correlation length. We present the full two-times and size
dependence of the interface roughness and we generalize the Family-Vicsek
scaling form to non-equilibrium situations. We compute the incoherent cattering
function and we compare it to the one measured in other glassy systems. We
analyse the response functions, the violation of the fluctuation-dissipation
theorem in the aging regime, and its crossover to the equilibrium relation in
the stationary regime. Finally, we study the out-of-equilibrium fluctuations of
the previously studied two-times functions and we characterize the scaling
properties of their probability distribution functions. Our results allow us to
obtain new insights into other glassy problems such as the aging behavior in
colloidal glasses and vortex glasses.Comment: 33 pages, 16 fig
Rheumatoid Arthritis Naive T Cells Share Hypermethylation Sites With Synoviocytes.
ObjectiveTo determine whether differentially methylated CpGs in synovium-derived fibroblast-like synoviocytes (FLS) of patients with rheumatoid arthritis (RA) were also differentially methylated in RA peripheral blood (PB) samples.MethodsFor this study, 371 genome-wide DNA methylation profiles were measured using Illumina HumanMethylation450 BeadChips in PB samples from 63 patients with RA and 31 unaffected control subjects, specifically in the cell subsets of CD14+ monocytes, CD19+ B cells, CD4+ memory T cells, and CD4+ naive T cells.ResultsOf 5,532 hypermethylated FLS candidate CpGs, 1,056 were hypermethylated in CD4+ naive T cells from RA PB compared to control PB. In analyses of a second set of CpG candidates based on single-nucleotide polymorphisms from a genome-wide association study of RA, 1 significantly hypermethylated CpG in CD4+ memory T cells and 18 significant CpGs (6 hypomethylated, 12 hypermethylated) in CD4+ naive T cells were found. A prediction score based on the hypermethylated FLS candidates had an area under the curve of 0.73 for association with RA case status, which compared favorably to the association of RA with the HLA-DRB1 shared epitope risk allele and with a validated RA genetic risk score.ConclusionFLS-representative DNA methylation signatures derived from the PB may prove to be valuable biomarkers for the risk of RA or for disease status
Proceeding of The International Seminar on Chemistry
Abstract Studies on the crude bark extract of Goniothalamus andersonii have enabled the isolation of stigmasterol, goniothalamin and two mixtures of sesquiterpenes.Their chemical structures were determined by using spectroscopic techniques like ¹H NMR, ¹³C NMR, GC-MS and Infrared spectroscopy.The crude n-hexane and etanol stem bark extracts of Goniothalamus andersonii were tested for their larvicidal activity against the larvae of Aedes aegypti. The n-hexane and methanol extracts of Goniothalamus andersonii were susceptible to the larvae with an LC50 value 42.3 µg/ml. This indicated very strong larvicidal activity. The ethanol extract showed larvicidal activity with an LC50 values of 58.1 µg/ml. This is also good larvicidal activity
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