Hollow cathodes with BaO impregnated, porous tungsten inserts and tips

The technology of impregnated materials is described and some inherently advantageous characteristics of impregnated cathodes are discussed. Thermionic emission measurements are presented for oxide coated and impregnated cathodes. Five cathode configurations with barium oxide impregnated porous tungsten inserts and/or tips have been fabricated and tested. Reliability, durability, and stability of operation are characterized. One of the cathodes has accumulated over 9000 operational hours, another has been cycled on and off more than 800 times

Optical properties of ion beam textured metals

Copper, silicon, aluminum, titanium and 316 stainless steel were textured by 1000 eV xenon ions from an 8 cm diameter electron bombardment ion source. Simultaneously sputter-deposited tantalum was used to facilitate the development of the surface microstructure. Scanning electron microscopy of the ion textured surfaces revealed two types of microstructure. Copper, silicon, and aluminum developed a cone structure with an average peak-to-peak distance ranging from 1 micron for silicon to 6 microns for aluminum. Titanium and 316 stainless steel developed a serpentine ridge structure. The average peak-to-peak distance for both of these materials was 0.5 micron. Spectral reflectance was measured using an integrating sphere and a holraum reflectometer. Total reflectance for air mass 0 and 2, solar absorptance and total emittance normalized for a 425 K black body were calculated from the reflectance measurements

ArgR is an essential local transcriptional regulator of the arcABC-operon in Streptococcus suis and crucial for biological fitness in acidic environment

Streptococcus suis is one of the most important pathogens in pigs and can also cause severe infections in humans. Despite its clinical relevance very little is known about the factors contributing to its virulence. Recently, we identified a new putative virulence factor in Streptococcus suis, the arginine deiminase system (ADS), an arginine catabolic enzyme system encoded by the arcABC-operon, which enables Streptococcus suis to survive in acidic environment. In this study, we focused on ArgR, an ADS associated regulator belonging to the ArgR/AhrC arginine repressor family. Using an argR knock-out strain we could show that ArgR is essential for arcABC-operon expression and necessary for the biological fitness of Streptococcus suis. By cDNA expression microarray analyses and quantitative real time RT-PCR we found that the arcABC-operon is the only gene cluster regulated by ArgR, which is in contrast to many other bacteria. Reporter gene analysis with gfp under the control of the arcABC promoter demonstrated that ArgR is able to activate the arcABC promoter. Electrophoretic mobility shift assays with fragments of the arcABC promoter and recombinant ArgR, and chromatin immunoprecipitation with antibodies directed against ArgR revealed that ArgR interacts with the arcABC promoter in vitro and in vivo by binding to a region from -147 to 72 bp upstream of the transcriptional start point. Overall our results show that in Streptococcus suis ArgR is an essential, system specific transcriptional regulator of the ADS directly interacting with the arcABC promoter in vivo

Role of glucose and CcpA in capsule expression and virulence of Streptococcus suis

Streptococcus suis is one of the most important pathogens in pigs and is also an emerging zoonotic agent. After crossing the epithelial barrier, S. suis causes bacteraemia, resulting in meningitis, endocarditis and bronchopneumonia. Since the host environment seems to be an important regulatory component for virulence, we related expression of virulence determinants of S. suis to glucose availability during growth and to the sugar metabolism regulator catabolite control protein A (CcpA). We found that expression of the virulence-associated genes arcB, representing arcABC operon expression, cps2A, representing capsular locus expression, as well as sly, ofs, sao and epf, differed significantly between exponential and early stationary growth of a highly virulent serotype 2 strain. Deletion of ccpA altered the expression of the surface-associated virulence factors arcB, sao and eno, as well as the two currently proven virulence factors in pigs, ofs and cps2A, in early exponential growth. Global expression analysis using a cDNA expression array revealed 259 differentially expressed genes in early exponential growth, of which 141 were more highly expressed in the CcpA mutant strain 10¿ccpA and 118 were expressed to a lower extent. Interestingly, among the latter genes, 18 could be related to capsule and cell wall synthesis. Correspondingly, electron microscopy characterization of strain 10¿ccpA revealed a markedly reduced thickness of the capsule. This phenotype correlated with enhanced binding to porcine plasma proteins and a reduced resistance to killing by porcine neutrophils. Taken together, our data demonstrate that CcpA has a significant effect on the capsule synthesis and virulence properties of S. suis

The 63^{63}Ni(n,γ\gamma) cross section measured with DANCE

The neutron capture cross section of the s-process branch nucleus $^{63}$Ni affects the abundances of other nuclei in its region, especially $^{63}$Cu and $^{64}$Zn. In order to determine the energy dependent neutron capture cross section in the astrophysical energy region, an experiment at the Los Alamos National Laboratory has been performed using the calorimetric 4$\pi$ BaF$_2$ array DANCE. The (n,$\gamma$) cross section of $^{63}$Ni has been determined relative to the well known $^{197}$Au standard with uncertainties below 15%. Various $^{63}$Ni resonances have been identified based on the Q-value. Furthermore, the s-process sensitivity of the new values was analyzed with the new network calculation tool NETZ.Comment: 11 pages, 13 page

Loop-Corrected Compactifications of the Heterotic String with Line Bundles

We consider the E8 x E8 heterotic string theory compactified on Calabi-Yau manifolds with bundles containing abelian factors in their structure group. Generic low energy consequences such as the generalised Green-Schwarz mechanism for the multiple anomalous abelian gauge groups are studied. We also compute the holomorphic gauge couplings and induced Fayet-Iliopoulos terms up to one-loop order, where the latter are interpreted as stringy one-loop corrections to the Donaldson-Uhlenbeck-Yau condition. Such models generically have frozen combinations of Kaehler and dilaton moduli. We study concrete bundles with structure group SU(N) x U(1)^M yielding quasi-realistic gauge groups with chiral matter given by certain bundle cohomology classes. We also provide a number of explicit tadpole free examples of bundles defined by exact sequences of sums of line bundles over complete intersection Calabi-Yau spaces. This includes one example with precisely the Standard Model gauge symmetry.Comment: 47 pages, 6 figures, LaTeX, v2: stability discussion in sect. 2.1 slightly extended, refs. added, v3: normalization of Green-Schwarz term correcte

Supersymmetric (non-)Abelian Bundles in the Type I and SO(32) Heterotic String

We discuss perturbative four-dimensional compactifications of both the SO(32) heterotic and the Type I string on smooth Calabi-Yau manifolds endowed with general non-abelian and abelian bundles. We analyse the generalized Green-Schwarz mechanism for multiple anomalous U(1) factors and derive the generically non-universal one-loop threshold corrections to the gauge kinetic function as well as the one-loop corrected Fayet-Iliopoulos terms. The latter can be interpreted as a stringy one-loop correction to the Donaldson-Uhlenbeck-Yau condition. Applying S-duality, for the Type I string we obtain the perturbative Pi-stability condition for non-abelian bundles on curved spaces. Some simple examples are given, and we qualitatively discuss some generic phenomenological aspects of this kind of string vacua. In particular, we point out that in principle an intermediate string scale scenario with TeV scale large extra dimensions might be possible for the heterotic string.Comment: LaTeX, 32 pages, v2: refs adde

The Role of Deontic Logic in the Specification of Information Systems

In this paper we discuss the role that deontic logic plays in the specification of information systems, either because constraints on the systems directly concern norms or, and even more importantly, system constraints are considered ideal but violable (so-called `soft¿ constraints).\ud To overcome the traditional problems with deontic logic (the so-called paradoxes), we first state the importance of distinguishing between ought-to-be and ought-to-do constraints and next focus on the most severe paradox, the so-called Chisholm paradox, involving contrary-to-duty norms. We present a multi-modal extension of standard deontic logic (SDL) to represent the ought-to-be version of the Chisholm set properly. For the ought-to-do variant we employ a reduction to dynamic logic, and show how the Chisholm set can be treated adequately in this setting. Finally we discuss a way of integrating both ought-to-be and ought-to-do reasoning, enabling one to draw conclusions from ought-to-be constraints to ought-to-do ones, and show by an example the use(fulness) of this