Photoemission studies of Ga1−x_{1-x}Mnx_{x}As: Mn-concentration dependent properties

Using angle-resolved photoemission, we have investigated the development of the electronic structure and the Fermi level pinnning in Ga$_{1-x}$Mn$_{x}$As with Mn concentrations in the range 1--6%. We find that the Mn-induced changes in the valence-band spectra depend strongly on the Mn concentration, suggesting that the interaction between the Mn ions is more complex than assumed in earlier studies. The relative position of the Fermi level is also found to be concentration-dependent. In particular we find that for concentrations around 3.5--5% it is located very close to the valence-band maximum, which is in the range where metallic conductivity has been reported in earlier studies. For concentration outside this range, larger as well as smaller, the Fermi level is found to be pinned at about 0.15 eV higher energy.Comment: REVTeX style; 7 pages, 3 figure

Radikale onkologische Chirurgie als Therapieprinzip beim Pankreaskarzinom

Zusammenfassung: Grundlagen: Mit den heutigen tiefen Morbiditäts-und Mortalitätsraten für Pankreasresektionen ist die Indikationsstellung für eine Standard- oder pyloruserhaltende Whipple-Operation weniger restriktiv zu stellen. Methodik: Pankreasresektionen für Karzinome sollten deshalb in kurativer oder palliativer Absicht, wenn immer möglich, durchgeführt werden. Verlangt werden dafür erfahrene Chirurgen mit über 10 Pankreaseingriffen pro Jahr und einer Mortalität von unter 10%. Als Standard gilt eine 2reihige Pankreatikojejunostomie mit Y-Roux-Rekonstruktion sowie die peri- und postoperative Therapie mit Octreotid während 7 Tagen. Ergebnisse: Innerhalb von 32 Monaten wurden 113 Patienten mit Pankreaskarzinom behandelt. Die Resektionsrate lag bei 50%, bei der Mehrzahl der Fälle wurde eine pyloruserhaltende Whipple-Operation durchgeführt (30/57). Die postoperative Morbidität lag bei 22,3%, kein Patient verstarb. Schlußfolgerungen: Die erweiterte (radikale) Duodenopankreatektomie wird ihren Wert im Vergleich zur Standard- oder pyloruserhaltenden Duodenopankreatektomie in prospektivrandomisierten Studien erst noch belegen müssen. Die Wirksamkeit einer adjuvanten Chemo- und/oder Radiotherapie bedarf weiterer Überprüfung mittels prospektiver Studie

Eta invariants for flat manifolds

Using H. Donnelly result from the article "Eta Invariants for G-Spaces" we calculate the eta invariants of the signature operator for almost all 7-dimensional flat manifolds with cyclic holonomy group. In all cases this eta invariants are an integer numbers. The article was motivated by D. D. Long and A. Reid article "On the geometric boundaries of hyperbolic 4-manifolds, Geom. Topology 4, 2000, 171-178Comment: 18 pages, a new version with referees comment

Analysis of the commutation error of filtering operators for the double-averaged equations of flows in porous media in a LES formalism

The continuum approach employing porous media models is an attractive solution method in the area of Computational Fluid Dynamics (CFD) simulation of fixed-bed reactors due to its robustness and efficiency. This paper applies the double-averaging methodology to refine the mathematical basis for the continuum approach, opening a way to alleviate its main limitations: space-invariant averaging volume and inaccurate treatment of the porous/non-porous interface. The averaging operator is recast as a general space-time filter and a detailed analysis of commutation errors is performed, using a classic Large Eddy Simulation (LES) formalism. An explicit filtering framework has been implemented in the open-source CFD library OpenFOAM to carry out an a-posteriori evaluation of the unclosed terms appearing in the Double-Averaged Navier-Stokes (DANS) equations also considering a space-varying filter width. Two resolved simulations have been performed. First, the flow around a single, stationary particle has been considered and used to validate derived equations and the filtering procedure. Second, an LES of the turbulent flow in a channel partly occupied with a porous medium has been conducted. The results have been filtered, and the commutation error at the porous-fluid interface has been evaluated and compared to the prediction of two models. The significance of the commutation error terms is also discussed and assessed. Finally, the solver for DANS equations has been developed and used to simulate both of the studied geometries. The magnitude of the error associated with neglecting the commutation errors has been investigated and an LES simulation combined with a porous drag model was performed. Very encouraging results have been obtained indicating that the inaccuracy of the drag closure overshadows the error related to the commutation of operators.Comment: This material has been submitted to Physics of Fluids. It contains 33 pages and 21 Figure

EFFECTS OF REARING ENVIRONMENT ON BEHAVIOR OF CAPTIVE-REARED WHOOPING CRANES

Whooping cranes (Grus americana) are 1 of the most endangered bird species in North America. In 1999 the Whooping Crane Eastern Partnership was formed to establish a migratory population of whooping cranes in eastern North America. These efforts have been extremely successful in terms of adult survival but reproductive success post-release has been low. One hypothesis developed to explain such low reproductive success is that captive-rearing techniques fail to prepare the birds to be effective parents. Captive-reared whooping cranes at the U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel, Maryland, are either reared by humans in crane costumes or by surrogate conspecific adults. We hypothesized that the 2 captive-rearing techniques differentially shaped chick behavior. To test this, we measured chick behavior daily as well as when chicks were placed in novel environments. Twice per day, every day, 5-minute focal observations were conducted on each chick. When they were introduced to a novel environment, 10-minute focal observations were conducted within 1 hour of introduction. The 2 groups differed significantly: costume-reared chicks were, on average, more stationary than parent-reared birds. These data suggest that future research should be done to determine whether or not rearing technique could have longterm effects on post-release behavior and reproductive success

Die pyloruserhaltende Whipple-Operation: eine Alternative oder heutiger Standard beim Pankreaskarzinom?

Zusammenfassung: Grundlagen: Während die pyloruserhaltende Whipple-Operation eine gute Alternative zur klassischen Operation bei periampullären Tumoren darstellt, ist das Verfahren beim Pankreaskopfkarzinom umstritten. Methodik: Wir haben die Daten von 70 Patienten mit Pankreaskopfkarzinom prospektiv im Hinblick auf die Vorteile des operativen Vorgehens und in bezug auf Lebensqualität und Überlebenszeit untersucht. Ergebnisse: Bei 44 Patienten wurde eine pyloruserhaltende Resektion durchgeführt, bei 26 Fällen eine klassische Whipple-Operation (WO) mit Lymphadenektomie. Es gab bezüglich Alter, Geschlecht und Tumorstadium keine Unterschiede in den beiden Patientengruppen. Die Mittelwerte für die Operationszeit, Blutverlust und Hospitalisationsdauer betrugen bei der pyloruserhaltenden WO 382 min, 1125 ml und 18,3 Tage und bei der klassischen WO 460 min (p<0,05), 1650 ml (p<0,05) und 22 Tage. Die mediane Überprüfzeit betrug 17 Monate (Range 2 bis 28 Monate). In den ersten 3 Monaten postoperativ war der Gewichtsverlauf bei den Patienten mit pyloruserhaltender WO deutlich besser. Die mediane Überlebenszeit war nicht signifikant verschieden mit 12,2 Monaten für die Patienten mit pyloruserhaltender WO und 12,9 Monaten bei den Patienten mit klassischer WO. Schlußfolgerungen: Bei Patienten mit Pankreaskarzinom war die Lebensqualität und Gewichtszunahme postoperativ besser bei solchen mit pyloruserhaltender partieller Duodenopankreatektomie im Vergleich zur klassischen WO. Aufgrund dieser Ergebnisse, der intraoperativen Vorteile und bei gleicher Überlebenszeit sollte dieses Operationsverfahren beim Pankreaskarzinom, wenn immer möglich, bevorzugt werde

Ripples Make Waves: Binding Structured Activity and Plasticity in Hippocampal Networks

Establishing novel episodic memories and stable spatial representations depends on an exquisitely choreographed, multistage process involving the online encoding and offline consolidation of sensory information, a process that is largely dependent on the hippocampus. Each step is influenced by distinct neural network states that influence the pattern of activation across cellular assemblies. In recent years, the occurrence of hippocampal sharp wave ripple (SWR) oscillations has emerged as a potentially vital network phenomenon mediating the steps between encoding and consolidation, both at a cellular and network level by promoting the rapid replay and reactivation of recent activity patterns. Such events facilitate memory formation by optimising the conditions for synaptic plasticity to occur between contingent neural elements. In this paper, we explore the ways in which SWRs and other network events can bridge the gap between spatiomnemonic processing at cellular/synaptic and network levels in the hippocampus

Dependence of Curie Temperature on the Thickness of Epitaxial (Ga,Mn)As Film

We present the magnetotransport properties of very thin (5 to 15 nm) single (Ga,Mn)As layers grown by low temperature molecular beam epitaxy. A lower (Ga,Mn)As thickness limit of 5 nm for the ferromagnetic phase and the dependence of the Curie temperature on (Ga,Mn)As thickness are determined from electrical transport measurements. The Curie temperature is determined to be 97 K for the thinnest ferromagnetic sample and is found to decrease for increasing layer thickness. A carrier density of ~7.1$\times10^{20}$ cm$^{-3}$ for the 5 nm thick (Ga,Mn)As layer is determined from Hall measurements. Differences between magnetotransport properties of thick and thin (Ga,Mn)As layers are observed and discussed.Comment: 6 pages, 4 figure

Termination dependent topological surface states of the natural superlattice phase Bi4_4Se3_3

We describe the topological surface states of Bi$_4$Se$_3$, a compound in the infinitely adaptive Bi$_2$-Bi$_2$Se$_3$ natural superlattice phase series, determined by a combination of experimental and theoretical methods. Two observable cleavage surfaces, terminating at Bi or Se, are characterized by angle resolved photoelectron spectroscopy and scanning tunneling microscopy, and modeled by ab-initio density functional theory calculations. Topological surface states are observed on both surfaces, but with markedly different dispersions and Kramers point energies. Bi$_4$Se$_3$ therefore represents the only known compound with different topological states on differently terminated surfaces.Comment: 5 figures references added Published in PRB: http://link.aps.org/doi/10.1103/PhysRevB.88.08110