3,853 research outputs found
Spatial and temporal characterization of a Bessel beam produced using a conical mirror
We experimentally analyze a Bessel beam produced with a conical mirror,
paying particular attention to its superluminal and diffraction-free
properties. We spatially characterized the beam in the radial and on-axis
dimensions, and verified that the central peak does not spread over a
propagation distance of 73 cm. In addition, we measured the superluminal phase
and group velocities of the beam in free space. Both spatial and temporal
measurements show good agreement with the theoretical predictions.Comment: 5 pages, 6 figure
Starter culture technology: fermented foods
Practice of starter culture is an age old practice but without any scientific basis. With the awareness of need of microbial inoculations for regulation of fermentation process for quality production of desired quality foods innovative development have taken place. Development of new strains for elite strain which can improve the quality, stability, flavor, texture and phage resistant starter cultures are raised on a variety of medium depending organism as well as product to be developed. The starter culture are classified based on their composition growth requirement and methods of propagation. These starter cultures are preserved by different methods they can be available all the time. Though commercial strains are available their isolation and subsequent improvement through different genetical methods are desirable to get a novel strains with unique properties of commercial importance. Among different microorganisms such as lactic acid bacteria, yeast (Saccharomyce cerevisae, Penicillium camembertii, P. roquefortii) and Rhyzopus (R. oryzae, R. sojae) are extensively used for this purpose. Perfection in the preparation, storage and propagation need to be improved. Mixed starters with symbiotic activity have to be formulated
Fate and transport of volatile organic compounds in glacial till and groundwater at an industrial site in Northern Ireland
Volatile organic compound (VOC) contamination of subsurface geological material and groundwater was discovered on the Nortel Monkstown industrial site, Belfast, Northern Ireland. The objectives of this study were to (1) investigate the characteristics of the geological material and its influences on contaminated groundwater flow across the site using borehole logs and hydrological evaluations, and (2) identify the contaminants and examine their distribution in the subsurface geological material and groundwater using chemical analysis. This report focuses on the eastern car park (ECP) which was a former storage area associated with trichloroethene (TCE) degreasing operations. This is where the greatest amount of volatile organic compounds (VOCs), particularly TCE, were detected. The study site is on a complex deposit of clayey glacial till with discontinuous coarser grained lenses, mainly silts, sands and gravel, which occur at 0.45-7.82 m below ground level (bgl). The lenses overall form an elongated formation that acts as a small unconfined shallow aquifer. There is a continuous low permeable stiff clayey till layer beneath the lenses that performs as an aquitard to the groundwater. Highest concentrations of VOCs, mainly TCE, in the geological material and groundwater are in these coarser lenses at similar to 4.5-7 m bgl. Highest TCE measurements at 390,000 mu g L-1 for groundwater and at 39,000 mu g kg(-1) at 5.7 m for geological material were in borehole GA19 in the coarse lens zone. It is assumed that TCE gained entrance to the subsurface near this borehole where the clayey till was thin to absent above coarse lenses which provided little retardation to the vertical migration of this dense non-aqueous phase liquid (DNAPL) into the groundwater. However, TCE is present in low concentrations in the geological material overlying the coarse lens zone. Additionally, VOCs appear to be associated with poorly drained layers and in peat < 3.0 m bgl in the ECP. Some indication of natural attenuation as VOCs degradation products vinyl chloride (VC) and dichloromethane (DCM) also occur on the site
A balanced homodyne detector for high-rate Gaussian-modulated coherent-state quantum key distribution
We discuss excess noise contributions of a practical balanced homodyne
detector in Gaussian-modulated coherent-state (GMCS) quantum key distribution
(QKD). We point out the key generated from the original realistic model of GMCS
QKD may not be secure. In our refined realistic model, we take into account
excess noise due to the finite bandwidth of the homodyne detector and the
fluctuation of the local oscillator. A high speed balanced homodyne detector
suitable for GMCS QKD in the telecommunication wavelength region is built and
experimentally tested. The 3dB bandwidth of the balanced homodyne detector is
found to be 104MHz and its electronic noise level is 13dB below the shot noise
at a local oscillator level of 8.5*10^8 photon per pulse. The secure key rate
of a GMCS QKD experiment with this homodyne detector is expected to reach
Mbits/s over a few kilometers.Comment: 22 pages, 11 figure
Modelling stochastic bivariate mortality
Stochastic mortality, i.e. modelling death arrival via a jump process with stochastic intensity, is gaining increasing reputation as a way to represent mortality risk. This paper represents a first attempt to model the mortality risk of couples of individuals, according to the stochastic intensity approach.
On the theoretical side, we extend to couples the Cox processes set up, i.e. the idea that mortality is driven by a jump process whose intensity is itself a stochastic process, proper of a particular generation within each gender. Dependence between the survival times of the members of a couple is captured by an Archimedean copula.
On the calibration side, we fit the joint survival function by calibrating separately the (analytical) copula and the (analytical) margins. First, we select the best fit copula according to the methodology of Wang and Wells (2000) for censored data. Then, we provide a sample-based calibration for the intensity, using a time-homogeneous, non mean-reverting, affine process: this gives the analytical marginal survival functions. Coupling the best fit copula with the calibrated margins we obtain, on a sample generation, a joint survival function which incorporates the stochastic nature of mortality improvements and is far from representing independency.On the contrary, since the best fit copula turns out to be a Nelsen one, dependency is increasing with age and long-term dependence exists
Itinerant ferromagnetism in half-metallic CoS_2
We have investigated electronic and magnetic properties of the pyrite-type
CoS_2 using the linearized muffin-tin orbital (LMTO) band method. We have
obtained the ferromagnetic ground state with nearly half-metallic nature. The
half-metallic stability is studied by using the fixed spin moment method. The
non-negligible orbital magnetic moment of Co 3d electrons is obtained as in the local spin density approximation (LSDA). The calculated
ratio of the orbital to spin angular momenta / = 0.15 is
consistent with experiment. The effect of the Coulomb correlation between Co 3d
electrons is also explored with the LSDA + U method. The Coulomb correlation at
Co sites is not so large, eV, and so CoS_2 is possibly
categorized as an itinerant ferromagnet. It is found that the observed
electronic and magnetic behaviors of CoS_2 can be described better by the LSDA
than by the LSDA + U.Comment: 4 pages, 3 postscript figure
Genetic associations with learning over 100 days of practice
Cognitive performance is both heritable and sensitive to environmental inputs and sustained practice over time. However, it is currently unclear how genetic effects on cognitive performance change over the course of learning. We examine how polygenic scores (PGS) created from genome-wide association studies of educational attainment and cognitive performance are related to improvements in performance across nine cognitive tests (measuring perceptual speed, working memory, and episodic memory) administered to 131 adults (N = 51, ages = 20–31, and N = 80, ages = 65–80 years) repeatedly across 100 days. We observe that PGS associations with performance on a given task can change over the course of learning, with the specific pattern of change in associations differing across tasks. PGS correlations with pre-test to post-test scores may mask variability in how soon learning occurs over the course of practice. The associations between PGS and learning do not appear to simply reconstitute patterns of association between baseline performance and subsequent learning. Associations involving PGSs, however, were small with large confidence intervals. Intensive longitudinal research such as that described here may be of substantial value for clarifying the genetics of learning when implemented as far larger scale
The falling chain of Hopkins, Tait, Steele and Cayley
A uniform, flexible and frictionless chain falling link by link from a heap
by the edge of a table falls with an acceleration if the motion is
nonconservative, but if the motion is conservative, being the
acceleration due to gravity. Unable to construct such a falling chain, we use
instead higher-dimensional versions of it. A home camcorder is used to measure
the fall of a three-dimensional version called an -slider. After
frictional effects are corrected for, its vertical falling acceleration is
found to be . This result agrees with the theoretical
value of for an ideal energy-conserving -slider.Comment: 17 pages, 5 figure
Fermi surface of the colossal magnetoresistance perovskite La_{0.7}Sr_{0.3}MnO_{3}
Materials that exhibit colossal magnetoresistance (CMR) are currently the
focus of an intense research effort, driven by the technological applications
that their sensitivity lends them to. Using the angular correlation of photons
from electron-positron annihilation, we present a first glimpse of the Fermi
surface of a material that exhibits CMR, supported by ``virtual crystal''
electronic structure calculations. The Fermi surface is shown to be
sufficiently cubic in nature that it is likely to support nesting.Comment: 5 pages, 5 PS figure
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