10,023 research outputs found
Comparison of reusable insulation systems for cryogenically-tanked earth-based space vehicles
Three reusable insulation systems concepts were developed for use with cryogenic tanks of earth-based space vehicles. Two concepts utilized double-goldized Kapton (DGK) or double-aluminized Mylar (DAM) multilayer insulation (MLI), while the third utilized a hollow-glass-microsphere, loadbearing insulation (LBI). Thermal performance measurements were made under space-hold (vacuum) conditions for insulating warm boundary temperatures of approximately 291 K. The resulting effective thermal conductivity was approximately 0.00008 W/m-K (W = weight,Kg; m = measured; K = temperature) for the MLI systems (liquid hydrogen test results) and 0.00054 W/m-K for the LBI system (liquid nitrogen test results corrected to liquid hydrogen temperature)
Effects of the pyrethroid insecticide gamma-cyhalothrin on aquatic invertebrates in laboratory and outdoor microcosm tests
The sensitivity of a range of freshwater lentic invertebrates to gamma-cyhalothrin (GCH), a single enantiomer of the synthetic pyrethroid lambda-cyhalothrin, was assessed in single species laboratory tests and an outdoor multi-species ecosystem test. The most sensitive species in the laboratory single species tests with GCH was Chaoborus obscuripes (96 h EC50: 3.8 ng/l). The species sensitivity distribution curve, based on the laboratory 96 h EC50 acute toxicity data for eight species, gave a median HC5 value for GCH of 2.12 ng/l. The NOECcommunity derived from the multi-species ecosystem test was 5 ng/l, and the insects Chaoborus sp. and Caenis sp. were identified as the most sensitive species. The results indicate that the median HC5, based on eight species selected to include those known to be sensitive to pyrethroids, provided a good estimation of the NOECcommunity for GCH. Furthermore, the results for GCH indicated that the endpoints typically used in higher-tier risk assessments for pesticides in Europe (HC5 and NOECcommunity) were consistent with expectations when compared to the equivalent endpoints for the racemate LC
Quasiperiodic spin-orbit motion and spin tunes in storage rings
We present an in-depth analysis of the concept of spin precession frequency
for integrable orbital motion in storage rings. Spin motion on the periodic
closed orbit of a storage ring can be analyzed in terms of the Floquet theorem
for equations of motion with periodic parameters and a spin precession
frequency emerges in a Floquet exponent as an additional frequency of the
system. To define a spin precession frequency on nonperiodic synchro-betatron
orbits we exploit the important concept of quasiperiodicity. This allows a
generalization of the Floquet theorem so that a spin precession frequency can
be defined in this case too. This frequency appears in a Floquet-like exponent
as an additional frequency in the system in analogy with the case of motion on
the closed orbit. These circumstances lead naturally to the definition of the
uniform precession rate and a definition of spin tune. A spin tune is a uniform
precession rate obtained when certain conditions are fulfilled. Having defined
spin tune we define spin-orbit resonance on synchro--betatron orbits and
examine its consequences. We give conditions for the existence of uniform
precession rates and spin tunes (e.g. where small divisors are controlled by
applying a Diophantine condition) and illustrate the various aspects of our
description with several examples. The formalism also suggests the use of
spectral analysis to ``measure'' spin tune during computer simulations of spin
motion on synchro-betatron orbits.Comment: 62 pages, 1 figure. A slight extension of the published versio
Slow dynamics at the smeared phase transition of randomly layered magnets
We investigate a model for randomly layered magnets, viz. a three-dimensional
Ising model with planar defects. The magnetic phase transition in this system
is smeared because static long-range order can develop on isolated rare spatial
regions. Here, we report large-scale kinetic Monte Carlo simulations of the
dynamical behavior close to the smeared phase transition which we characterize
by the spin (time) autocorrelation function. In the paramagnetic phase, its
behavior is dominated by Griffiths effects similar to those in magnets with
point defects. In the tail region of the smeared transition the dynamics is
even slower: the autocorrelation function decays like a stretched exponential
at intermediate times before approaching the exponentially small asymptotic
value following a power law at late times. Our Monte-Carlo results are in good
agreement with recent theoretical predictions based on optimal fluctuation
theory.Comment: 7 pages, 6 eps figures, final version as publishe
Composition-tuned smeared phase transitions
Phase transitions in random systems are smeared if individual spatial regions
can order independently of the bulk system. In this paper, we study such
smeared phase transitions (both classical and quantum) in substitutional alloys
AB that can be tuned from an ordered phase at composition to
a disordered phase at . We show that the ordered phase develops a
pronounced tail that extends over all compositions . Using optimal
fluctuation theory, we derive the composition dependence of the order parameter
and other quantities in the tail of the smeared phase transition. We also
compare our results to computer simulations of a toy model, and we discuss
experiments.Comment: 6 pages, 4 eps figures included, final version as publishe
Understanding fish populations
Editorial to special issue
Strength of Higher-Order Spin-Orbit Resonances
When polarized particles are accelerated in a synchrotron, the spin
precession can be periodically driven by Fourier components of the
electromagnetic fields through which the particles travel. This leads to
resonant perturbations when the spin-precession frequency is close to a linear
combination of the orbital frequencies. When such resonance conditions are
crossed, partial depolarization or spin flip can occur. The amount of
polarization that survives after resonance crossing is a function of the
resonance strength and the crossing speed. This function is commonly called the
Froissart-Stora formula. It is very useful for predicting the amount of
polarization after an acceleration cycle of a synchrotron or for computing the
required speed of the acceleration cycle to maintain a required amount of
polarization. However, the resonance strength could in general only be computed
for first-order resonances and for synchrotron sidebands. When Siberian Snakes
adjust the spin tune to be 1/2, as is required for high energy accelerators,
first-order resonances do not appear and higher-order resonances become
dominant. Here we will introduce the strength of a higher-order spin-orbit
resonance, and also present an efficient method of computing it. Several
tracking examples will show that the so computed resonance strength can indeed
be used in the Froissart-Stora formula. HERA-p is used for these examples which
demonstrate that our results are very relevant for existing accelerators.Comment: 10 pages, 6 figure
Improving Gaussian mixture latent variable model convergence with Optimal Transport
Generative models with both discrete and continuous latent variables are highly motivated by the structure of many real-world data sets. They present, however, subtleties in training often manifesting in the discrete latent variable not being leveraged. In this paper, we show why such models struggle to train using traditional log-likelihood maximization, and that they are amenable to training using the Optimal Transport framework of Wasserstein Autoencoders. We find our discrete latent variable to be fully leveraged by the model when trained, without any modifications to the objective function or significant fine tuning. Our model generates comparable samples to other approaches while using relatively simple neural networks, since the discrete latent variable carries much of the descriptive burden. Furthermore, the discrete latent provides significant control over generation
This Is the Way: Faculty on the Camino de Santiago
Excerpt from book chapter: For nearly a millennium, pilgrims have made their way to Santiago de Compostela to visit the tomb of Saint James. These pilgrims initially journeyed from the Iberian Peninsula and then greater Europe, establishing over a dozen routes to reach the northwestern city in modern-day Galicia, a province of Spain. These routes followed established pathways connecting urban hubs, ports, and trade channels. While the number of pilgrims rose steadily in the Middle Ages through the Renaissance, the popularity of pilgrimage mirrored that of the Catholic Church and began to wane with the onset of the Enlightenment. It is not until the late twentieth century that we begin to see the Camino\u27s revitalization and then a boom in participation in the first decades of this century...https://scholarworks.wm.edu/educationbookchapters/1055/thumbnail.jp
Organic and Inorganic Fertilizers in Food Production System in Nigeria
Food production systems must operate to be socially acceptable, environmentally sustainable and economically viable. As the availability of land and water resources is rapidly declining, there is need to increase the productivity of remaining natural resources, including energy while at the same time observing nutritional and environmental needs of our people. The single most efficient and cost-effective input that can increase the productivity of land in Nigeria is fertilizer-be it organic or inorganic. Fertilizer can increase food, root/tuber, nuts/vegetables and grain production, release marginal lands from production and reduce environmental degradation including the risk and uncertainty associated with the production of agricultural products. Efficient management of plant nutrients ensures that fertilizers are used in the most environmentally acceptable and sustainable way and that crops are supplied with all essential plant nutrients at the appropriate time and in the required quantity to avert environmental pollution. Site specific nutrient use, integrated plant nutrient supply, nutrient placement including fertigation and synchronizing nutrient supply with demand, etc are some of the means by which fertilizers can be used more efficiently. All these will help to make more economical the use of natural resources, protect the environment and improve public image of farming and the fertilizer industry in Nigeria especially now that the land fallow systems which helped in building soil fertility have reduced to one or two year rotation
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