955 research outputs found
Reform of United States Weapons Acquisition Policy: Competition, Teaming Agreements, and Dual- Sourcing
Attaining an adequate level of defense at an acceptable cost is as vital and elusive a goal as any the United States has pursued since World War II. No aspect of this goal has proven more vexing than the search for an effective process for purchasing armaments of reasonable price, satisfactory performance, and timely delivery. News accounts abound with reports of serious deficiencies in weapons projects that are central to this country\u27s defense. Recently, the Department of Defense (DOD) and the supplier community have been shaken by a flurry of disclosures and the first indictments emanating from the Department of Justice\u27s investigation of allegations of corruption in weapons acquisition- Operation Ill Wind. \u27 Accounts of inefficiency, poor system performance, and misconduct in individual programs are becoming so common that they obscure what is at stake. Quite simply, failure to solve the problems of weapons procurement will put both the country\u27s economic well-being and its physical security at risk
Galoisian Approach to integrability of Schr\"odinger Equation
In this paper, we examine the non-relativistic stationary Schr\"odinger
equation from a differential Galois-theoretic perspective. The main algorithmic
tools are pullbacks of second order ordinary linear differential operators, so
as to achieve rational function coefficients ("algebrization"), and Kovacic's
algorithm for solving the resulting equations. In particular, we use this
Galoisian approach to analyze Darboux transformations, Crum iterations and
supersymmetric quantum mechanics. We obtain the ground states, eigenvalues,
eigenfunctions, eigenstates and differential Galois groups of a large class of
Schr\"odinger equations, e.g. those with exactly solvable and shape invariant
potentials (the terms are defined within). Finally, we introduce a method for
determining when exact solvability is possible.Comment: 62 page
Spin excitations in the nematic phase and the metallic stripe spin-density wave phase of iron pnictides
We present a general study of the magnetic excitations within a weak-coupling
five-orbital model relevant to itinerant iron pnictides. As a function of
enhanced electronic correlations, the spin excitations in the symmetry broken
spin-density wave phase evolve from broad low-energy modes in the limit of weak
interactions to sharply dispersing spin wave prevailing to higher energies at
larger interaction strengths. We show how the resulting spin response at high
energies depends qualitatively on the magnitude of the interactions. We also
calculate the magnetic excitations in the nematic phase by including an orbital
splitting, and find a pronounced C_2 symmetric excitation spectrum right above
the transition to long-range magnetic order. Finally, we discuss the C_2 versus
C_4 symmetry of the spin excitations as a function of energy for both the
nematic and the spin-density wave phase.Comment: 10 pages, 10 figure
Urban AI in China: social control or hyper-capitalist development in the post-smart city?
Research and wider societal debates has explored the potentially transformative role of AI in extended social control and hyper-capitalist development in China. In this paper, we use those debates to reflect on experiments with Urban AI in China. The key issue is whether AI offers something distinctive or different compared with the logics and imaginaries of ideas of the smart city. Analysis of emblematic sites of urban AI management in the cities of Shanghai and Hangzhou demonstrates: the resonances and dissonances between urban AI and smart. But they also demonstrate distinctive and complex landscape of urban AI experiments that is not neatly captured in social control and free market applications perspectives on AI. Moreover, the urban experimental contexts in which AI is being rolled, reveal aspirations for creating new “digital empires,” exploring new limits on data power and potential social resistance. The paper makes a distinctive contribution by providing a new framework for comparing logics of computational urban management in the context of emerging AI applications. As such the paper provides a distinctive framework for situating future applications of urban AI management in China and identifies the future urban research priorities
de Sitter spacetime: effects of metric perturbations on geodesic motion
Gravitational perturbations of the de Sitter spacetime are investigated using
the Regge--Wheeler formalism. The set of perturbation equations is reduced to a
single second order differential equation of the Heun-type for both electric
and magnetic multipoles. The solution so obtained is used to study the
deviation from an initially radial geodesic due to the perturbation. The
spectral properties of the perturbed metric are also analyzed. Finally, gauge-
and tetrad-invariant first-order massless perturbations of any spin are
explored following the approach of Teukolsky. The existence of closed-form,
i.e. Liouvillian, solutions to the radial part of the Teukolsky master equation
is discussed.Comment: IOP macros, 10 figure
A novel isolator-based system promotes viability of human embryos during laboratory processing
In vitro fertilisation (IVF) and related technologies are arguably the most challenging of all cell culture applications. The starting material is a single cell from which one aims to produce an embryo capable of establishing a pregnancy eventually leading to a live birth. Laboratory processing during IVF treatment requires open manipulations of gametes and embryos, which typically involves exposure to ambient conditions. To reduce the risk of cellular stress, we have developed a totally enclosed system of interlinked isolator-based workstations designed to maintain oocytes and embryos in a physiological environment throughout the IVF process. Comparison of clinical and laboratory data before and after the introduction of the new system revealed that significantly more embryos developed to the blastocyst stage in the enclosed isolator-based system compared with conventional open-fronted laminar flow hoods. Moreover, blastocysts produced in the isolator-based system contained significantly more cells and their development was accelerated. Consistent with this, the introduction of the enclosed system was accompanied by a significant increase in the clinical pregnancy rate and in the proportion of embryos implanting following transfer to the uterus. The data indicate that protection from ambient conditions promotes improved development of human embryos. Importantly, we found that it was entirely feasible to conduct all IVF-related procedures in the isolator-based workstations
Differential expression of microRNAs and other small RNAs in muscle tissue of patients with ALS and healthy age-matched controls
Amyotrophic lateral sclerosis is a late-onset disorder primarily affecting motor neurons and leading to progressive and lethal skeletal muscle atrophy. Small RNAs, including microRNAs (miRNAs), can serve as important regulators of gene expression and can act both globally and in a tissue-/cell-type-specific manner. In muscle, miRNAs called myomiRs govern important processes and are deregulated in various disorders. Several myomiRs have shown promise for therapeutic use in cellular and animal models of ALS; however, the exact miRNA species differentially expressed in muscle tissue of ALS patients remain unknown. Following small RNA-Seq, we compared the expression of small RNAs in muscle tissue of ALS patients and healthy age-matched controls. The identified snoRNAs, mtRNAs and other small RNAs provide possible molecular links between insulin signaling and ALS. Furthermore, the identified miRNAs are predicted to target proteins that are involved in both normal processes and various muscle disorders and indicate muscle tissue is undergoing active reinnervation/compensatory attempts thus providing targets for further research and therapy development in ALS
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