1,186 research outputs found
Synthesis of Ligand free CdS Nanoparticles within a Sulfur Copolymer Matrix
Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high temperature solvents. These coordinating ligands help solubilize and stabilize the nanoparticles while in solution, and can influence the resulting size and reactivity of the nanoparticles during their formation. Despite the ubiquity of using ligands during synthesis, the presence of aliphatic ligands on the nanoparticle surface can result in a number of problems during the end use of the nanoparticles, necessitating further ligand stripping or ligand exchange procedures. We have developed a way to synthesize cadmium sulfide CdS nanoparticles using a unique sulfur copolymer. This sulfur copolymer is primarily composed of elemental sulfur, which is a cheap and abundant material. The sulfur copolymer has the advantages of operating both as a high temperature solvent and as a sulfur source, which can react with a cadmium precursor during nanoparticle synthesis, resulting in the generation of ligand free CdS. During the reaction, only some of the copolymer is consumed to produce CdS, while the rest remains in the polymeric state, thereby producing a nanocomposite material. Once the reaction is finished, the copolymer stabilizes the nanoparticles within a solid polymeric matrix. The copolymer can then be removed before the nanoparticles are used, which produces nanoparticles that do not have organic coordinating ligands. This nascent synthesis technique presents a method to produce metal sulfide nanoparticles for a wide variety of applications where the presence of organic ligands is not desired
Book Reviews
Book Review 1Book Title: Sharks and Rays of AustraliaBook Authors: P.R. Last & J.D. StevensPrinted and distributed by CSIRO, P.O. Box 89 East Melbourne. 3002 Australia, 1994. 612 pages and 84 colour plates.Book Review 2Book Title: The Ecology of Mangrove and Related Ecosystems. Proceedings of the International Symposium held at Mombasa, Kenya 24-30 September 1990Book Authors: Edited by Victor Jaccarini & Els MartensKluwer Academic Publishers, Dordrecht 1993. 272 pages. Hardbound. ISBN 0-7923-2049-2.Book Review 3Book Title: Rotifer Symposium VI. Proceedings of the Sixth International Rotifer Symposium, held in Banyoles, Spain, June 3-8, 1991Book Authors: Edited by J.J. Gilbert, E. Lubzens & M.R. MiracleReprinted from Hydrobiologia, vols 255-256, as Developments in Hydrobiology 83Kluwer Academic Publishers, Dordrecht /Boston /London. 572 pagesBook Review 4Book Title: Identification Guide to the Ant Genera of the WorldBook Author: Barry BoltonHarvard University Press, 1994. 224 pages, 522 SEM photographs. ISBN 0-674-44280-
Ultrafast carrier relaxation in GaN, In_(0.05)Ga_(0.95)N and an In_(0.05)Ga_(0.95)/In_(0.15)Ga_(0.85)N Multiple Quantum Well
Room temperature, wavelength non-degenerate ultrafast pump/probe measurements
were performed on GaN and InGaN epilayers and an InGaN multiple quantum well
structure. Carrier relaxation dynamics were investigated as a function of
excitation wavelength and intensity. Spectrally-resolved sub-picosecond
relaxation due to carrier redistribution and QW capture was found to depend
sensitively on the wavelength of pump excitation. Moreover, for pump
intensities above a threshold of 100 microJ/cm2, all samples demonstrated an
additional emission feature arising from stimulated emission (SE). SE is
evidenced as accelerated relaxation (< 10 ps) in the pump-probe data,
fundamentally altering the re-distribution of carriers. Once SE and carrier
redistribution is completed, a slower relaxation of up to 1 ns for GaN and
InGaN epilayers, and 660 ps for the MQW sample, indicates carrier recombination
through spontaneous emission.Comment: submitted to Phys. Rev.
Quantum electromagnetic field in a three dimensional oscillating cavity
We compute the photon creation inside a perfectly conducting, three
dimensional oscillating cavity, taking the polarization of the electromagnetic
field into account. As the boundary conditions for this field are both of
Dirichlet and (generalized) Neumann type, we analyze as a preliminary step the
dynamical Casimir effect for a scalar field satisfying generalized Neumann
boundary conditions. We show that particle production is enhanced with respect
to the case of Dirichlet boundary conditions. Then we consider the transverse
electric and transverse magnetic polarizations of the electromagnetic field.
For resonant frequencies, the total number of photons grows exponentially in
time for both polarizations, the rate being greater for transverse magnetic
modes.Comment: 11 pages, 1 figur
Interdisciplinary undergraduate learning modules in gerontechnology
As the older population grows rapidly worldwide, gerontechnology can play an increasingly crucial role in improving older people’s quality of life in an affordable and sustainable way. However, even with growing interests, gerontechnology has yet to be established as a widely available educational or research program. One root cause is the lack of a well-established curriculum to train new gerontechnologists and to help professionals in relevant fields to develop gerontechnological specialties. This paper summarizes our experience and insights gained from designing, instructing, and evaluating learning modules for gerontechnology in the past 2½ years, and outlines the learning materials and effective pedagogies for gerontechnology that can be adopted and further developed
Ground state of a polydisperse electrorheological solid: Beyond the dipole approximation
The ground state of an electrorheological (ER) fluid has been studied based
on our recently proposed dipole-induced dipole (DID) model. We obtained an
analytic expression of the interaction between chains of particles which are of
the same or different dielectric constants. The effects of dielectric constants
on the structure formation in monodisperse and polydisperse electrorheological
fluids are studied in a wide range of dielectric contrasts between the
particles and the base fluid. Our results showed that the established
body-centered tetragonal ground state in monodisperse ER fluids may become
unstable due to a polydispersity in the particle dielectric constants. While
our results agree with that of the fully multipole theory, the DID model is
much simpler, which offers a basis for computer simulations in polydisperse ER
fluids.Comment: Accepted for publications by Phys. Rev.
Epigenetic predictors of all-cause mortality are associated with objective measures of neighborhood disadvantage in an urban population
BACKGROUND: Neighborhood characteristics are robust predictors of overall health and mortality risk for residents. Though there has been some investigation of the role that molecular indicators may play in mediating neighborhood exposures, there has been little effort to incorporate newly developed epigenetic biomarkers into our understanding of neighborhood characteristics and health outcomes. METHODS: Using 157 participants of the Detroit Neighborhood Health Study with detailed assessments of neighborhood characteristics and genome-wide DNA methylation profiling via the Illumina 450K methylation array, we assessed the relationship between objective neighborhood characteristics and a validated DNA methylation-based epigenetic mortality risk score (eMRS). Associations were adjusted for age, race, sex, ever smoking, ever alcohol usage, education, years spent in neighborhood, and employment. A secondary model additionally adjusted for personal neighborhood perception. We summarized 19 neighborhood quality indicators assessed for participants into 9 principal components which explained over 90% of the variance in the data and served as metrics of objective neighborhood quality exposures. RESULTS: Of the nine principal components utilized for this study, one was strongly associated with the eMRS (β = 0.15; 95% confidence interval = 0.06-0.24; P = 0.002). This principal component (PC7) was most strongly driven by the presence of abandoned cars, poor streets, and non-art graffiti. Models including both PC7 and individual indicators of neighborhood perception indicated that only PC7 and not neighborhood perception impacted the eMRS. When stratified on neighborhood indicators of greenspace, we observed a potentially protective effect of large mature trees as this feature substantially attenuated the observed association. CONCLUSION: Objective measures of neighborhood disadvantage are significantly associated with an epigenetic predictor of mortality risk, presenting a potential novel avenue by which neighborhood-level exposures may impact health. Associations were independent of an individual's perception of their neighborhood and attenuated by neighborhood greenspace features. More work should be done to determine molecular risk factors associated with neighborhoods, and potentially protective neighborhood features against adverse molecular effects
Activity related energy expenditure, appetite and energy intake. Potential implications for weight management
The aim was to investigate relationships between activity related energy expenditure (AREE), appetite ratings and energy intake (EI) in a sample of 40 male (26.4years; BMI 23.5kg/m2) and 42 female (26.9years; BMI 22.4kg/m2) participants. AREE was expressed as the residual value of the regression between total daily EE (by doubly labeled water) and resting EE (by indirect calorimetry). EI was measured using an ad libitum buffet meal and visual analogue scales measured subjective appetite ratings before and after the meal. AREE was divided into low, middle and high sex-specific tertiles. General linear models were used to investigate differences in appetite ratings and EI across AREE tertiles. Before the meal, males in the high AREE tertile had significantly lower desire to eat and lower prospective food consumption and higher feelings of fullness compared to those in the low tertile. Males in the middle tertile had significantly higher satiety quotients after the meal and lower EI compared to the other tertiles. No significant differences across tertiles were found in females. Sex differences in relationships between AREE, appetite ratings and EI may lead to differing patterns of EI and subsequent weight maintenance
Topology of the ground state of two interacting Bose-Einstein condensates
We investigate the spatial patterns of the ground state of two interacting
Bose-Einstein condensates. We consider the general case of two different atomic
species (with different mass and in different hyperfine states) trapped in a
magnetic potential whose eigenaxes can be tilted with respect to the vertical
direction, giving rise to a non trivial gravitational sag. Despite the
complicated geometry, we show that within the Thomas-Fermi approximations and
upon appropriate coordinate transformations, the equations for the density
distributions can be put in a very simple form. Starting from this expressions
we give explicit rules to classify the different spatial topologies which can
be produced, and we discuss how the behavior of the system is influenced by the
inter-atomic scattering length. We also compare explicit examples with the full
numeric Gross-Pitaevskii calculation.Comment: RevTex4, 8 pages, 7 figure
Resonant photon creation in a three dimensional oscillating cavity
We analyze the problem of photon creation inside a perfectly conducting,
rectangular, three dimensional cavity with one oscillating wall. For some
particular values of the frequency of the oscillations the system is resonant.
We solve the field equation using multiple scale analysis and show that the
total number of photons inside the cavity grows exponentially in time. This is
also the case for slightly off-resonance situations. Although the spectrum of a
cavity is in general non equidistant, we show that the modes of the
electromagnetic field can be coupled, and that the rate of photon creation
strongly depends on this coupling. We also analyze the thermal enhancement of
the photon creation.Comment: 13 pages. New section on off-resonance motion is included. To appear
in Physical Review
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