Anomalous Hall Effect in three ferromagnets: EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30

The Hall resistivity (Rho_xy), resistivity (Rho_xx), and magnetization of three metallic ferromagnets are investigated as a function of magnetic field and temperature. The three ferromagnets, EuFe4Sb12 (Tc = 84 K), Yb14MnSb11 (Tc = 53 K), and Eu8Ga16Ge30 (Tc = 36 K) are Zintl compounds with carrier concentrations between 1 x 10^21 cm^-3 and 3.5 x 10^21 cm^-3. The relative decrease in Rho_xx below Tc [Rho_xx(Tc)/Rho_xx(2 K)] is 28, 6.5, and 1.3 for EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30 respectively. The low carrier concentrations coupled with low magnetic anisotropies allow a relatively clean separation between the anomalous (Rho_'xy), and normal contributions to the measured Hall resistivity. For each compound the anomalous contribution in the zero field limit is fit to alpha Rho_xx + sigma_xy rho_xx^2 for temperatures T < Tc. The anomalous Hall conductivity, sigma_xy, is -220 +- 5 (Ohm^-1 cm^-1), -14.7 +- 1 (Ohm^-1 cm^-1), and 28 +- 3 (Ohm^-1 cm^-1) for EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30 respectively and is independent of temperature for T < Tc if the change in spontaneous magnetization (order parameter) with temperature is taken into account. These data are consistent with recent theories of the anomalous Hall effect that suggest that even for stochiometric ferromagnetic crystals, such as those studied in this article, the intrinsic Hall conductivity is finite at T = 0, and is a ground state property that can be calculated from the electronic structure.Comment: 22 pages, 13 figures Submitted to PR

Depletion-Isolation Effect in Vertical MOSFETs During the Transition From Partial to Fully Depleted Operation

A simulation study is made of floating-body effects (FBEs) in vertical MOSFETs due to depletion isolation as the pillar thickness is reduced from 200 to 10 nm. For pillar thicknesses between 200–60 nm, the output characteristics with and without impact ionization are identical at a low drain bias and then diverge at a high drain bias. The critical drain bias Vdc for which the increased drain–current is observed is found to decrease with a reduction in pillar thickness. This is explained by the onset of FBEs at progressively lower values of the drain bias due to the merging of the drain depletion regions at the bottom of the pillar (depletion isolation). For pillar thicknesses between 60–10 nm, the output characteristics show the opposite behavior, namely, the critical drain bias increases with a reduction in pillar thickness. This is explained by a reduction in the severity of the FBEs due to the drain debiasing effect caused by the elevated body potential. Both depletion isolation and gate–gate coupling contribute to the drain–current for pillar thicknesses between 100–40 nm

THE ANALYSIS OF THE CLOSEOUT PROCESS AND RECOMMENDATIONS FOR REDUCING BACKLOG

Each year, more contracts are added to the Department of Defense Virtual Contracting Enterprise (VCE) database as overaged contracts. The purpose of this research is to analyze the Federal Acquisition Regulation (FAR) for the contract closeout process. This research assesses U.S. Government Accountability Office (GAO) reports and evaluates a survey from a contracting agency to offer recommendations that would reduce the current contract closeout backlog and allow organizations to improve overall closeout rates. The primary question we addressed is, How can contracting agencies prepare and prioritize the number of overage contracts for closeouts? The secondary question is, How can contracting agencies prevent a backlog of contracts requiring closeout requirements in the future? This report determined that the government does not provide the resources required to effectively manage the process of contract closeouts at an institutional level. The suggestions provided are intended to increase the prioritization of the contract closeout process while capitalizing on the limited tools and resources available.Major, United States ArmyMajor, United States ArmyApproved for public release. Distribution is unlimited

Integrating aerodynamics and structures in the minimum weight design of a supersonic transport wing

An approach is presented for determining the minimum weight design of aircraft wing models which takes into consideration aerodynamics-structure coupling when calculating both zeroth order information needed for analysis and first order information needed for optimization. When performing sensitivity analysis, coupling is accounted for by using a generalized sensitivity formulation. The results presented show that the aeroelastic effects are calculated properly and noticeably reduce constraint approximation errors. However, for the particular example selected, the error introduced by ignoring aeroelastic effects are not sufficient to significantly affect the convergence of the optimization process. Trade studies are reported that consider different structural materials, internal spar layouts, and panel buckling lengths. For the formulation, model and materials used in this study, an advanced aluminum material produced the lightest design while satisfying the problem constraints. Also, shorter panel buckling lengths resulted in lower weights by permitting smaller panel thicknesses and generally, by unloading the wing skins and loading the spar caps. Finally, straight spars required slightly lower wing weights than angled spars

Optical interferometer in space

The present design concepts for a Laser Gravitational Wave Observatory in Space are described. Laser heterodyne distance measurements are made between test masses located in three spacecraft separated by roughly 10(exp 6) km. The major technology issues are: the reduction of spurious acceleration noise for the test masses to below 2 x 10(exp -15) cm/sq sec/Hz(0.5) from 10(exp -5) to 10(exp -3) Hz; and the measurement of changes in the difference of the antenna arm lengths to 5 x 10(exp -11) cm/Hz(0.5) from 10(exp -3) to 1 Hz with high reliability. The science objectives are: to measure discrete sinusoidal gravitational wave signals from individual sources with periods of 1 second to 1 day; to measure the stochastic background due to unresolved binaries; and to search for gravitational wave pulses with periods longer than 1 sec from possible exotic sources such as gravitational collapse of very massive objects

Winter Observations of Mammals and Birds, St. Matthew Island

Remore and uninhabited St. Matthew Island, lying 60 30 N, 172 30 W, on the continental shelf of the Bering Sea, is infrequently visited in summer and very rarely seen in the winter. The only signs of past human habitation are the wind-torn remains of a World War II naval observation station and the rectangular depressions of a couple of Eskimo house pits, of undetermined age, on the southwest side of the island. The last known visit to the island was during the summer of 1966. Our opportunity came on 6 and 7 February 1970, as a result of an oceanographic cruise aboard the U.S. Coast Guard icebreaker Northwind to study winter conditions in the ice-covered Bering Sea. At that time the island was covered with crusted, wind-glazed snow and locked in sea ice, with open water only along the south shore where large leads had opened up in the lee of the island. The weather was cold and very windy, temperatures ranging from 10&deg;F to -20&deg;F with a wind velocity averaging 30 to 40 knots, from the north. The afternoon of the 6th was clear, permitting a helicopter survey of the entire island. Most of the daylight hours of the 7th were occupied by ground investigations of the island under worsening weather conditions (overcast sky and 40-knot wind). The mammal population of the island is sparse .... We saw only arctic fox and reindeer, with no evidence of small mammals though they are known to exist there. ... Species observed on or in the vicinity of St. Matthew: Arctic Fox (Alopex lagopus), Reindeer (Rangifer tarandus), Walrus (Odobenus rosmarus), Ringed Seal (Phoca hispida,) Snowy Owl (Nyctea scandiaca), Thick-billed Murre (Uria lomvia), Harlequin (Histrionicus histrionicus), Common Eider (Somateria mollissima), King Eider (Somateria spectabilis), Old squaw (Clangula hyemalis), Pelagic Cormorant (Phalacrocorax pelagicus), Slaty-backed Gull (Larus schistisagus), Glaucous-winged Gull (Larus glaucescens), Glaucous Gull (Larus hyperboreus), Ivory Gull (Pagophila eburnea). We found a single herd of 32 reindeer at the southeast corner of the island. The animals were large and appeared to be in good condition, with impressive antlers. They are the remnant of a reindeer population introduced in 1944 that experienced a spectacular increase to 6,000 animals before crashing to 42 in the winter of 1963-64. Klein visited St. Matthew in the summer of 1966 to study the remaining reindeer and collected 10 animals, including the last male. He left 32 animals, all thought to be female, and all of which survived the intervening three and a half years up to the time of our arrival on the island. The observed marine mammal populations in the vicinity of St. Matthew proved to be disappointing. ... Ringed and bearded seals and walrus were observed some distance to the east of St. Matthew, in the edge of the sea ice in Bristol Bay; walrus were seen in large numbers north of the island, in the vicinity of St. Lawrence, so it seems likely that there should be marine mammals present in the area. ... The bird fauna of St. Matthew and vicinity was more diverse than that of the mammal. Twelve species were seen around the island, all of which, with the exception of a snowy owl, were marine and were observed in the leads and polynyas of the sea ice. Most common were murres, harlequins, and oldsquaws. ... As the ship proceeded westward from St. Matthew toward the Siberian coast, murres, black guillemots, and 4 species of gulls were seen. Several slaty-backed and glaucous-winged gulls were seen, and 3 glaucous and 2 ivory gulls observed near 60&deg;N, 175&deg;W. [Interestingly] ... of all the gulls seen, the slaty-back was by far the most common. This species is not considered common in Alaska

Laminin enhances the growth of human neural stem cells in defined culture media

<p>Abstract</p> <p>Background</p> <p>Human neural stem cells (hNSC) have the potential to provide novel cell-based therapies for neurodegenerative conditions such as multiple sclerosis and Parkinson's disease. In order to realise this goal, protocols need to be developed that allow for large quantities of hNSC to be cultured efficiently. As such, it is important to identify factors which enhance the growth of hNSC. <it>In vivo</it>, stem cells reside in distinct microenvironments or niches that are responsible for the maintenance of stem cell populations. A common feature of niches is the presence of the extracellular matrix molecule, laminin. Therefore, this study investigated the effect of exogenous laminin on hNSC growth.</p> <p>Results</p> <p>To measure hNSC growth, we established culture conditions using B27-supplemented medium that enable neurospheres to grow from human neural cells plated at clonal densities. Limiting dilution assays confirmed that neurospheres were derived from single cells at these densities. Laminin was found to increase hNSC numbers as measured by this neurosphere formation. The effect of laminin was to augment the proliferation/survival of the hNSC, rather than promoting the undifferentiated state. In agreement, apoptosis was reduced in dissociated neurospheres by laminin in an integrin β1-dependent manner.</p> <p>Conclusion</p> <p>The addition of laminin to the culture medium enhances the growth of hNSC, and may therefore aid their large-scale production.</p

Closing the Nuclear Fuel Cycle with a Simplified Minor Actinide Lanthanide Separation Process (ALSEP) and Additive Manufacturing

Expanded low-carbon baseload power production through the use of nuclear fission can be enabled by recycling long-lived actinide isotopes within the nuclear fuel cycle. This approach provides the benefits of (a) more completely utilizing the energy potential of mined uranium, (b) reducing the footprint of nuclear geological repositories, and (c) reducing the time required for the radiotoxicity of the disposed waste to decrease to the level of uranium ore from one hundred thousand years to a few hundred years. A key step in achieving this goal is the separation of long-lived isotopes of americium (Am) and curium (Cm) for recycle into fast reactors. To achieve this goal, a novel process was successfully demonstrated on a laboratory scale using a bank of 1.25-cm centrifugal contactors, fabricated by additive manufacturing, and a simulant containing the major fission product elements. Americium and Cm were separated from the lanthanides with over 99.9% completion. The sum of the impurities of the Am/Cm product stream using the simulated raffinate was found to be 3.2 × 10−3 g/L. The process performance was validated using a genuine high burnup used nuclear fuel raffinate in a batch regime. Separation factors of nearly 100 for 154Eu over 241Am were achieved. All these results indicate the process scalability to an engineering scale

Fgf-dependent glial cell bridges facilitate spinal cord regeneration in Zebrafish

Adult Zebrafish show a remarkable capacity to regenerate their spinal column after injury, an ability that stands in stark contrast to the limited repair that occurs within the mammalian CNS post-injury. The reasons for this interspecies difference in regenerative capacity remain unclear. Here we demonstrate a novel role for Fgf signaling during glial cell morphogenesis in promoting axonal regeneration after spinal cordinjury. Zebrafish glia are induced by Fgf signaling, to form anelongated bipolarmorphology that formsabridge between the two sides of the resected spinal cord, over which regenerating axons actively migrate. Loss of Fgf function inhibits formation of this "glial bridge" and prevents axon regeneration. Despite the poor potential for mammalian axonal regeneration, primate astrocytes activated by Fgf signaling adopt a similar morphology to that induced in Zebrafish glia. This suggests that differential Fgf regulation, rather than intrinsic cell differences, underlie the distinct responses of mammalian and Zebrafish glia to injury