3,125 research outputs found
Perturbation solution of hollow-fiber membrane module for pure gas permeation
No full textThis study presents an analytic solution for permeation of a pure gas in a hollow-fiber module, based on regular perturbation method. It is assumed that pressure drop due to frictional loss should be proportional to velocity, and that mass transfer be mainly convective with the permeation through the fiber membrane. Four governing equations are characterized by five parameters depending on the design specifications and operating conditions of the module. When the parameter characterizing pressure drop is small, regular perturbation method is capable of providing the analytic solution. Compared with numerical simulation, the analytic solution is found to be sufficiently precise when the parameter is far less than the other parameters characterizing the mass transfer and pressure difference between permeate and reject streams. (C) 1998 Elsevier Science B.V
Effect of pressure drop on performance of hollow-fiber membrane module for gas permeation
No full textThe pressure drop mainly due to viscous friction inside hollow fibers is taken into consideration by nondimensionalization and numerical simulation of governing equations. For pure gas, the permeation pressure and velocity of actual situations with a viscous fluid deviate significantly from those of the corresponding inviscid or no-pressure-drop cases. The apparent permeability estimated from the relation of permeate now rate and pressure difference is considerably underestimated in actual situations, and more severely for the region of small pressure difference and large module length. Numerical simulation shows that the estimated permeability behaves as if it were an increasing function of pressure difference for a constant permeability and roughly a constant for a dual-sorption-type permeability, respectively. For binary-mixture permeation the cut ratio and purity of permeate stream are mainly governed by two dimensionless parameters standing for pressure drop and permeability, respectively. The cut ratio and corresponding product composition are predictable without the rigorous simulation of the governing equations
Letter to F.D. Moon from A. Mitchell Salone regarding information about and photos of the Colored School in Wewoka
No full textLetter to F.D. Moon regarding a book being written on African American schools. The author asks for photos of the school and shows appreciation for how he runs the school
Counterfactual Fairness with Disentangled Causal Effect Variational Autoencoder
No full textThe problem of fair classification can be mollified if we develop a method to remove the embedded sensitive information from the classification features. This line of separating the sensitive information is developed through the causal inference, and the causal inference enables the counterfactual generations to contrast the what-if case of the opposite sensitive attribute. Along with this separation with the causality, a frequent assumption in the deep latent causal model defines a single latent variable to absorb the entire exogenous uncertainty of the causal graph. However, we claim that such structure cannot distinguish the 1) information caused by the intervention (i.e., sensitive variable) and 2) information correlated with the intervention from the data. Therefore, this paper proposes Disentangled Causal Effect Variational Autoencoder (DCEVAE) to resolve this limitation by disentangling the exogenous uncertainty into two latent variables: either 1) independent to interventions or 2) correlated to interventions without causality. Particularly, our disentangling approach preserves the latent variable correlated to interventions in generating counterfactual examples. We show
that our method estimates the total effect and the counterfactual effect without a complete causal graph. By adding a fairness regularization, DCEVAE generates a counterfactual fair dataset while losing less original information. Also, DCEVAE generates natural counterfactual images by only flipping sensitive information. Additionally, we theoretically show the differences in the covariance structures of DCEVAE and prior works from the perspective of the latent disentanglement
We Reach the Moon. Title page inscribed by the author.
No full textOn 20 July 1969, Neil Armstrong and Buzz Aldrin became the first humans to land on the moon. The achievement inspired a host of products and memorabilia. On display from the publishing collection of Seymour Lawrence is both the German and American editions of the children’s 1969 picture book Journey to the Moon by artist Erich Fuchs who depicts the eight-day voyage with cubist modernism. The author of We Reach the Moon was the New York Times science reporter, and he inscribed his paperback to Mississippi writer Willie Morris and family.https://egrove.olemiss.edu/space_exhibit_2020/1012/thumbnail.jp
Neutralizing Gender Bias in Word Embeddings with Latent Disentanglement and Counterfactual Generation
No full textRecent research demonstrates that word embeddings, trained on the human-generated corpus, have strong gender biases in embedding spaces, and these biases can result in the discriminative results from the various downstream tasks. Whereas the previous methods project word embeddings into a linear subspace for debiasing, we introduce a Latent Disentanglement method with a siamese auto-encoder structure with an adapted gradient reversal layer. Our structure enables the separation of the semantic latent information and gender latent information of given word into the disjoint latent dimensions. Afterwards, we introduce a Counterfactual Generation to convert the gender information of words, so the original and the modified embeddings can produce a gender-neutralized word embedding after geometric alignment regularization, without loss of semantic information. From the various quantitative and qualitative debiasing experiments, our method shows to be better than existing debiasing methods in debiasing word embeddings. In addition, Our method shows the ability to preserve semantic information during debiasing by minimizing the semantic information losses for extrinsic NLP downstream tasks
On lunar collision orbits: New methodologies for Moon-to-Moon transfer design
No full textMany interplanetary missions massively leverage the lunar gravitational pull in the so-called low-energy regime to converge to their aim, saving consistent amount of fuel. Among these, two future Japanese spacecraft are expected to repeatedly encounter the Moon along their trajectories to either facilitate the escape from the Earth–Moon system or opportunely target a specific region in its neighbourhood. Although never actively employed for preliminary trajectory design, lunar collision orbits have shown a rich dynamical structure and an applicability for both medium- and low-energy regimes. These characteristics, together with their intrinsic nature of being close to trajectories experiencing lunar fly-by, have encouraged this research. In this work, lunar collision orbits are employed to delineate a method for obtaining ballistic transfers between two successive lunar encounters, briefly addressed as Moon-to-Moon. This study is first carried out with the assumptions of the autonomous Circular Restricted Three-Body Problem, subsequently extended to the nonautonomous Bi-circular Restricted Four-Body Problem, including the solar gravitational influence.Poincaré cuts are extensively used as a dimensionality reductant for lunar collision orbits: this allows to ascertain their similar behaviour with trajectories flybying the Moon, whose characteristics are partly foreseen by determining the associated intersection with the same cut. A patching is performed at the cut to obtain both single and multiple ballistic Moon-to-Moon transfers. The strict bond of lunar collision orbits with the invariant manifolds of simple periodic orbits about Lagrangian points is confirmed and exploited to design ballistic itineraries connecting highly elliptic orbits about the Earth to horizontal Lyapunov orbits of the Earth–Moon system, via a single Moon-to-Moon transfer. With the usage of the lunar collision orbits and the Poincaré cut, a simple optimization technique is implemented to retrieve a properly defined Moon-to-Moon transfer from a trajectory missing a second fly-by with the Moon. Including the presence of the Sun, a similar method for obtaining single and multiple Moon-to-Moon transfers is developed. A classification of lunar double-collision transfers is then performed within the same framework, highlighting their similarity with other studies in past literature, eventually leading to the construction of a database of Moon-to-Moon transfers. The latter, conceived as an improvement with respect to the former version by adding the lunar gravitational influence, shows its applicability in real preliminary trajectory design.Aerospace Engineerin
Moon Dog [Translation]
No full textA Japanese to English translation of the poem Moon Dog originally written by Mizuho Ishid
New solar-sail orbits for polar observation of the earth and moon
No full textIn this paper, a new family of solar-sail periodic orbits with adequate properties for polar observation of the Earth and moon is developed under the simplified but nonautonomous dynamics of the solar-sail augmented Earth–moon circular restricted three-body problem. The novel orbits, termed “distant-circular orbits,” are found through differential correction and continuation and employ a simple sun-facing steering law for the solar sail. A basic coverage analysis shows that one of the distant-circular orbits is capable of providing continuous coverage of both the Earth’s and lunar north (or south) poles with just a single sailcraft at a minimum elevation angle of 14 deg and an average range of six Earth–moon distances. Moreover, simple transfer trajectories between orbits of the family are found, so that the sailcraft can switch between observing the northern and southern latitudes of the Earth and moon during a single mission. Subsequently, using multiple-shooting differential correction, all results are migrated to a higher-fidelity dynamic framework that considers, among others, the eccentricity of the moon’s orbit. The perturbations cause the periodicity of the orbits to break, turning them into seemingly quasi-periodic orbits, but it is shown that the coverage capabilities are maintained. Finally, an active control strategy is developed to counteract part of the perturbing effects such that, by appropriately steering the sail, the apparent quasi-periodicity of the orbits is enhanced and the deviation from the unperturbed orbits is reduced.Accepted Author ManuscriptAstrodynamics & Space Mission
Semimetallic features in thermoelectric transport properties of 2H-3R phase niobium diselenide
No full textIn two-dimensional van der Waals crystals, the interlayer stacking sequence often leads to a change in crystal symmetry and, thus, new polymorphs, leading to an abundant array of physical properties. In this paper, we report the polymorphic form of 2H–3R–NbSe2 that exhibits a substantial difference in terms of the gate dependence of semimetallic behavior and Seebeck coefficient, compared to the well-known 2H–NbSe2 with metallic transport behavior. The semimetallic features of 2H–3R–NbSe2 indicate the presence of minor carriers, confirmed through theoretical calculations, which is in good agreement with the transport behavior. Our results reveal perspectives for understanding the metastable 2H–3R phase NbSe2, which is not far from equilibrium, and for engineering the materials necessary for efficient energy harvesting. © 2020 Elsevier Ltd1
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