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Beta-Phosphinoethylboranes as Ambiphilic Ligands in Nickel-Methyl Complexes

Description: The ambiphilic {beta}-phosphinoethylboranes Ph{sub 2}PCH{sub 2}CH{sub 2}BR{sub 2} (BR{sub 2} = BCy{sub 2} (1a), BBN (1b)), which feature a ethano spacer CH{sub 2}CH{sub 2} between the Lewis acidic boryl and Lewis basic phosphino groups, were synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds 1a and 1b were fully characterized by elemental analysis, and by NMR and IR spectroscopy. X-ray crystallographic studies of compound 1b revealed infinite helical chains of the molecules connected through P{hor_ellipsis}B donor-acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors and acceptors was highlighted by their reactions with (dmpe)NiMe{sub 2}. Zwitterionic complexes (dmpe)NiMe(Ph{sub 2}PCH{sub 2}CH{sub 2}BCy{sub 2}Me) (2a) and (dmpe)NiMe(Ph{sub 2}PCH{sub 2}CH{sub 2}[BBN]Me) (2b) were generated via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray crystallography. Furthermore, B(C{sub 6}F{sub 5}){sub 3} abstracts the methyl group of a coordinated borate ligand to generate a free, 3-coordinate borane center in [(dmpe)NiMe(1a)]{sup +}[MeB(C{sub 6}F{sub 5}){sub 3}]{sup -} (3).
Date: October 28, 2007
Creator: Fischbach, Andreas; Bazinet, Patrick R.; Waterman, Rory & Tilley, T. Don
Partner: UNT Libraries Government Documents Department

The Simplest Double Slit: Interference and Entanglement in Double Photoionization of H2

Description: The wave nature of particles is rarely seen in nature. One reason is their very short de Broglie wavelengths in most situations. However, even with wavelengths close to the size of their surroundings, they couple to their environment, e.g. by gravity, Coulomb interaction, or thermal radiation. These couplings shift the phase of the waves, often in an uncontrolled way, hence yielding varying amounts of decoherence i.e. loss of phase integrity. Decoherence is thought to be a main cause of the transition from quantum to classical behavior. How much interaction is necessary and how big an environment is needed to induce the onset of classical behavior? Here we show that a photoelectron and two protons form a minimum particle/slit system, and that a minimum environment can be no more than a single additional electron. We observe interference 'fringes' in the angular distribution of a single electron and the loss of fringe visibility caused by its Coulomb interaction with a second electron. While, at the same time, the correlated momenta of the entangled electron pair continue to exhibit quantum interference.
Date: September 18, 2007
Creator: Akoury , D.; Kreidi, K.; Jahnke , T.; Weber, Th.; Staudte , A.; Schoffler, M. et al.
Partner: UNT Libraries Government Documents Department

Spin Spectrometer at the ALS and APS

Description: A spin-resolving photoelectron spectrometer, the"Spin Spectrometer," has been designed and built. It has been utilized at both the Advanced Light Source in Berkeley, CA, and the Advanced Photon Source in Argonne, IL. Technical details and an example of experimental results are presented here.
Date: April 20, 2007
Creator: Laboratory, Lawrence Livermore National; Missouri-Rolla, University of; Technologies, Boyd; Morton, Simon A; Morton, Simon A; Tobin, James G et al.
Partner: UNT Libraries Government Documents Department

Stable SUSY breaking model with O(10) eV gravitino from combined D-term gauge mediation and U(1)' mediation

Description: We show a calculable example of stable supersymmetry (SUSY) breaking modelswith O(10) eV gravitino mass based on the combination of D-term gauge mediationand U(1)' mediation. A potential problem of the negative mass squared for theSUSY standard model (SSM) sfermions in the D-term gauge mediation is solvedby the contribution from the U(1)' mediation. On the other hand, the splittingbetween the SSM gauginos and sfermions in the U(1)' mediation iscircumvented bythe contributions from the D-term gauge mediation. Since the U(1)' mediation doesnot introduce any new SUSY vacua, we achieve a completely stable model underthermal effects. Our model, therefore, has no cosmological difficulty.
Date: December 17, 2007
Creator: Nakayama, Yu & Nakayama, Yu
Partner: UNT Libraries Government Documents Department

Quantum geometry and gravitational entropy

Description: Most quantum states have wavefunctions that are widely spread over the accessible Hilbert space and hence do not have a good description in terms of a single classical geometry. In order to understand when geometric descriptions are possible, we exploit the AdS/CFT correspondence in the half-BPS sector of asymptotically AdS_5 x S5 universes. In this sector we devise a"coarse-grained metric operator" whose eigenstates are well described by a single spacetime topology and geometry. We show that such half-BPS universes have a non-vanishing entropy if and only if the metric is singular, and that the entropy arises from coarse-graining the geometry. Finally, we use our entropy formula to find the most entropic spacetimes with fixed asymptotic moments beyond the global charges.
Date: May 29, 2007
Creator: Simon, Joan; Balasubramanian, Vijay; Czech, Bart Iomiej; Larjo, Klaus; Marolf, Donald & Simon, Joan
Partner: UNT Libraries Government Documents Department

A Proposal to Upgrade the Silicon Strip Detector

Description: The STAR Silicon Strip Detector (SSD) was built by a collaboration of Nantes, Strasbourg and Warsaw collaborators. It is a beautiful detector; it can provide 500 mu m scale pointing resolution at the vertex when working in combination with the TPC. It was first used in Run 4, when half the SSD was installed in an engineering run. The full detector was installed for Run 5 (the Cu-Cu run) and the operation and performance of the detector was very successful. However, in preparation for Run 6, two noisy ladders (out of 20) were replaced and this required that the SSD be removed from the STAR detector. The re-installation of the SSD was not fully successful and so for the next two Runs, 6 and 7, the SSD suffered a cooling system failure that allowed a large fraction of the ladders to overheat and become noisy, or fail. (The cause of the SSD cooling failure was rather trivial but the SSD could not be removed betweens Runs 6 and 7 due to the inability of the STAR detector to roll along its tracks at that time.)
Date: November 5, 2007
Creator: Matis, Howard; Michael, LeVine; Jonathan, Bouchet; Stephane, Bouvier; Artemios, Geromitsos; Gerard, Guilloux et al.
Partner: UNT Libraries Government Documents Department

Proton hexality from an anomalous flavor U(1) and neutrino masses--Linking to the string scale

Description: We devise minimalistic gauged U(1)_X Froggatt-Nielsen models which at low-energy give rise to the recently suggested discrete gauge Z_6 symmetry, proton hexality, thus stabilizing the proton. Assuming three generations of right-handed neutrinos, with the proper choice of X-charges, we obtain viable neutrino masses. Furthermore, we find scenarios such that no X-charged hidden sector superfields are needed, which from a bottom-up perspective allows the calculation of g_string, g_X and G_SM's Kac-Moody levels. The only mass scale apart from M_grav is m_soft.
Date: August 7, 2007
Creator: Murayama, Hitoshi; Dreiner, Herbi K.; Luhn, Christoph; Murayama, Hitoshi & Thormeiere, Marc
Partner: UNT Libraries Government Documents Department

Mixing and CP violation in the D0 and B0(s) systems

Description: Recent developments for mixing and CP violation in the D0 and Bs systems are reviewed, including (i) the recently emerging evidence for D0-D0bar mixing and the interpretations of the measurements; (ii) the theoretical status of the calculations of Delta(Gamma_D) and Delta(m_D); (iii) some implications of the measurement of Bs mixing for new physics.
Date: May 7, 2007
Creator: Ligeti, Zoltan & Ligeti, Zoltan
Partner: UNT Libraries Government Documents Department

Readout of TPC Tracking Chambers with GEMs and Pixel Chip

Description: Two layers of GEMs and the ATLAS Pixel Chip, FEI3, have been combined and tested as a prototype for Time Projection Chamber (TPC) readout at the International Linear Collider (ILC). The double-layer GEM system amplifies charge with gain sufficient to detect all track ionization. The suitability of three gas mixtures for this application was investigated, and gain measurements are presented. A large sample of cosmic ray tracks was reconstructed in 3D by using the simultaneous timing and 2D spatial information from the pixel chip. The chip provides pixel charge measurement as well as timing. These results demonstrate that a double GEM and pixel combination, with a suitably modified pixel ASIC, could meet the stringent readout requirements of the ILC.
Date: December 21, 2007
Creator: Kadyk, John; Kim, T.; Freytsis, M.; Button-Shafer, J.; Kadyk, J.; Vahsen, S.E. et al.
Partner: UNT Libraries Government Documents Department

Influence of projectile neutron number on cross section in cold fusion reactions

Description: Elements 107-112 [1,2] have been discovered in reactions between {sup 208}Pb or {sup 209}Bi targets and projectiles ranging from {sup 54}Cr through {sup 70}Zn. In such reactions, the compound nucleus can be formed at excitation energies as low as {approx}12 MeV, thus this type of reaction has been referred to as 'cold fusion'. The study of cold fusion reactions is an indispensable approach to gaining a better understanding of heavy element formation and decay. A theoretical model that successfully predicts not only the magnitudes of cold fusion cross sections, but also the shapes of excitation functions and the cross section ratios between various reaction pairs was recently developed by Swiatecki, Siwek-Wilczynska, and Wilczynski [3,4]. This theoretical model, also referred to as Fusion by Diffusion, has been the guide in all of our cold fusion studies. One particularly interesting aspect of this model is the large predicted difference in cross sections between projectiles differing by two neutrons. The projectile pair where this difference is predicted to be largest is {sup 48}Ti and {sup 50}Ti. To test and extend this model, {sup 208}Pb({sup 48}Ti,n){sup 255}Rf and {sup 208}Pb({sup 50}Ti,n){sup 257}Rf excitation functions were recently measured at the Lawrence Berkeley National Laboratory's (LBNL) 88-Inch Cyclotron utilizing the Berkeley Gas-filled Separator (BGS). The {sup 50}Ti reaction was carried out with thin lead targets ({approx}100 {micro}g/cm{sup 2}), and the {sup 48}Ti reaction with both thin and thick targets ({approx}470 {micro}g/cm{sup 2}). In addition to this reaction pair, reactions with projectile pairs {sup 52}Cr and {sup 54}Cr [5], {sup 56}Fe and {sup 58}Fe [6], and {sup 62}Ni [7] and {sup 64}Ni [8] will be discussed and compared to the Fusion by Diffusion predictions. The model predictions show a very good agreement with the data.
Date: September 1, 2007
Creator: Dragojevic, Irena; Dragojevic, I.; Gregorich, K.E.; Dullmann, Ch.E.; Folden III, C.M.; Garcia, M.A. et al.
Partner: UNT Libraries Government Documents Department

Dissecting Biological Dark Matter: Single Cell Genetic Analysis of TM7, a Rare and Uncultivated Microbe from the Human Mouth

Description: We have developed a microfluidic device that allows the isolation and genome amplification of individual microbial cells, thereby enabling organism-level genomic analysis of complex microbial ecosystems without the need for culture. This device was used to perform a directed survey of the human subgingival crevice and to isolate bacteria having rod-like morphology. Several isolated microbes had a 16S rRNA sequence that placed them in candidate phylum TM7, which has no cultivated or sequenced members. Genome amplification from individual TM7 cells allowed us to sequence and assemble >1,000 genes, providing insight into the physiology of members of this phylum. This approach enables single-cell genetic analysis of any uncultivated minority member of a microbial community.
Date: July 1, 2007
Creator: Fenner, Marsha W; Marcy, Yann; Ouverney, Cleber; Bik, Elisabeth M.; Losekann, Tina; Ivanova, Natalia et al.
Partner: UNT Libraries Government Documents Department

DNA Repair Decline During Mouse Spermiogenesis Results in the Accumulation of Heritable DNA Damage

Description: The post-meiotic phase of mouse spermatogenesis (spermiogenesis) is very sensitive to the genomic effects of environmental mutagens because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage. We hypothesized that repeated exposures to mutagens during this repair-deficient phase result in the accumulation of heritable genomic damage in mouse sperm that leads to chromosomal aberrations in zygotes after fertilization. We used a combination of single or fractionated exposures to diepoxybutane (DEB), a component of tobacco smoke, to investigate how differential DNA repair efficiencies during the three weeks of spermiogenesis affected the accumulation of DEB-induced heritable damage in early spermatids (21-15 days before fertilization, dbf), late spermatids (14-8 dbf) and sperm (7-1 dbf). Analysis of chromosomal aberrations in zygotic metaphases using PAINT/DAPI showed that late spermatids and sperm are unable to repair DEB-induced DNA damage as demonstrated by significant increases (P<0.001) in the frequencies of zygotes with chromosomal aberrations. Comparisons between single and fractionated exposures suggested that the DNA repair-deficient window during late spermiogenesis may be less than two weeks in the mouse and that during this repair-deficient window there is accumulation of DNA damage in sperm. Finally, the dose-response study in sperm indicated a linear response for both single and repeated exposures. These findings show that the differential DNA repair capacity of post-meioitic male germ cells has a major impact on the risk of paternally transmitted heritable damage and suggest that chronic exposures that may occur in the weeks prior to fertilization because of occupational or lifestyle factors (i.e, smoking) can lead to an accumulation of genetic damage in sperm and result in heritable chromosomal aberrations of paternal origin.
Date: December 1, 2007
Creator: Marchetti, Francesco; Marchetti, Francesco & Wyrobek, Andrew J.
Partner: UNT Libraries Government Documents Department

D-dualized D-brane

Description: We further investigate the dimensional duality (D-duality) proposed in arXiv: 0705.0550 by mainly focusing on the properties of D-branes in this background. We derive the world-sheet correspondence of static D-branes, and discuss the fate of non-static D-branes from the world-sheet viewpoint. The quantum string production with or without D-branes is also studied fromthe time-like Liouville theory. We find that the closed string production from the background is much larger than that from D-branes decaying into nothing.
Date: June 6, 2007
Creator: Nakayama, Yu & Nakayama, Yu
Partner: UNT Libraries Government Documents Department

Flavorful supersymmetry

Description: Weak scale supersymmetry provides elegant solutions to many of the problems of the standard model, but it also generically gives rise to excessive flavor and CP violation. We show that, if the mechanism that suppresses the Yukawa couplings also suppresses flavor changing interactions in the supersymmetry breaking parameters, essentially all the low energy flavor and CP constraints can be satisfied. The standard assumption of flavor universality in the supersymmetry breaking sector is not necessary. We study signatures of this framework at the LHC. The mass splitting among different generations of squarks and sleptons can be much larger than in conventional scenarios, and even the mass ordering can be changed. We find that there is a plausible scenario in which the next-to-lightest superparticle is a long-lived right-handed selectron or smuon which decays into the lightest superparticle, a gravitino. This leads to the spectacularsignature of monochromatic electrons or muons in a stopper detector, providing strong evidence for the framework.
Date: December 13, 2007
Creator: Nomura, Yasunori; Nomura, Yasunori; Papucci, Michele & Stolarski, Daniel
Partner: UNT Libraries Government Documents Department

Field Theory On the World Sheet: Mean Field Expansion And Cutoff Dependence

Description: Continuing earlier work, we apply the mean field method to the world sheet representation of a simple field theory. In particular, we study the higher order terms in the mean field expansion, and show that their cutoff dependence can be absorbed into a running coupling constant. The coupling constant runs towards zero in the infrared, and the model tends towards a free string. One cannot fully reach this limit because of infrared problems, however, one can still apply the mean field method to the high energy limit (high mass states) of the string.
Date: January 10, 2007
Creator: Bardakci, Korkut
Partner: UNT Libraries Government Documents Department

Geometric metastability, quivers and holography

Description: We use large N duality to study brane/anti-brane configurations on a class of Calabi-Yau manifolds. With only branes present, the Calabi-Yau manifolds in question give rise to N=2 ADE quiver theories deformed by superpotential terms. We show that the large N duality conjecture of hep-th/0610249 reproduces correctly the known qualitative features of the brane/anti-brane physics. In the supersymmetric case, the gauge theories have Seiberg dualities which are represented as flops in the geometry. Moreover, the holographic dual geometry encodes the whole RG flow of the gauge theory. In the non-supersymmetric case, the large N duality predicts that the brane/anti-brane theories also enjoy such dualities, and allows one to pick out the good description at a given energy scale.
Date: September 6, 2007
Creator: Aganagic, Mina; Aganagic, Mina; Beem, Christopher & Freivogel, Ben
Partner: UNT Libraries Government Documents Department

Geometric transitions and D-term SUSY breaking

Description: We propose a new way of using geometric transitions to study metastable vacua in string theory and certain confining gauge theories. The gauge theories in question are N=2 supersymmetric theories deformed to N=1 by superpotential terms. We first geometrically engineer supersymmetry-breaking vacua by wrapping D5 branes on rigid 2-cycles in noncompact Calabi-Yau geometries, such that the central charges of the branes are misaligned. In a limit of slightly misaligned charges, this has a gauge theory description, where supersymmetry is broken by Fayet-Iliopoulos D-terms. Geometric transitions relate these configurations to dual Calabi-Yaus with fluxes, where H_RR, H_NS and dJ are all nonvanishing. We argue that the dual geometry can be effectively used to study the resulting non-supersymmetric, confining vacua
Date: November 5, 2007
Creator: Aganagic, Mina; Aganagic, Mina & Beem, Christopher
Partner: UNT Libraries Government Documents Department

Geometry of non-supersymmetric three-charge bound states

Description: We study the smooth non-supersymmetric three-charge microstatesof Jejjala, Madden, Ross and Titchener using Kaluza-Klein reductions of the solutions to five and four dimensions. Our aim is to improve our understanding of the relation between these non-supersymmetric solutions and the well-studied supersymmetric cases. We find some surprising qualitative differences. In the five-dimensional description, the solution has orbifold fixed points which break supersymmetry locally, so the geometries cannot be thought of as made up of separate half-BPS centers. In the four-dimensional description, the two singularities in the geometry are connected by a conical singularity, which makes it impossible to treat them independently and assign unambiguous brane charges to these centers.
Date: May 14, 2007
Creator: Gimon, Eric; Gimon, Eric G.; Levi, Thomas S. & Ross, Simon F.
Partner: UNT Libraries Government Documents Department

Gauge mediation with D-term SUSY breaking

Description: We construct a gauge-mediation model with a D-term supersymmetry (SUSY) breaking. R-symmetry breaking necessary for generating the SUSY standard-model gaugino masses is given by gaugino condensation of a strongly coupled gauge theory in the hidden sector. The energy scale of the strong dynamics of the hidden sector gauge theory should be around the messenger mass scale M, or otherwise perturbative calculations would be reliable and would lead to negative soft mass squared for squarks and sleptons. Thus, all the mass scales are controlled by a virtually single parameter, \sqrt{D}/M. This model covers a very wide range of gravitino mass, m_{3/2} \simeq 1 eV--100 TeV. Possible embeddings of the model in string theory are also discussed.
Date: May 7, 2007
Creator: Watari, Taizan; Nakayama, Y.; Taki, Masato; Watari, Taizan & Yanagida, T.T.
Partner: UNT Libraries Government Documents Department

The Genetically Remote Pathogenic Strain NVH391-98 of the Bacillus cereus Group Represents the Cluster of Thermophilic Strains

Description: Bacteria of the Bacillus cereus group are known to cause food poisoning. A rare phylogenetically remote strain, NVH391-98, was recently characterized to encode a particularly efficient cytotoxin K presumably responsible for food poisoning. This pathogenic strain and its close relatives can be phenotypically distinguished from other strains of the B. cereus group by the inability to grow at temperatures below 17 degrees C and by the ability to grow at temperatures from 48 to 53 degrees C. A temperate phage, phBC391A2, residing in the genome of NVH391-98 allows us to distinguish the three known members of this thermophilic strain cluster.
Date: October 2, 2007
Creator: Auger, Sandrine; Galleron, Nathalie; Bidnenko, Elena; Ehrlich, S. Dusko; Lapidus, Alla & Sorokin, Alexei
Partner: UNT Libraries Government Documents Department

The Genome of the Epsilonproteobacterial Chemolithoautotroph Sulfurimonas dentrificans

Description: Sulfur-oxidizing epsilonproteobacteria are common in a variety of sulfidogenic environments. These autotrophic and mixotrophic sulfur-oxidizing bacteria are believed to contribute substantially to the oxidative portion of the global sulfur cycle. In order to better understand the ecology and roles of sulfur-oxidizing epsilonproteobacteria, in particular those of the widespread genus Sulfurimonas, in biogeochemical cycles, the genome of Sulfurimonas denitrificans DSM1251 was sequenced. This genome has many features, including a larger size (2.2 Mbp), that suggest a greater degree of metabolic versatility or responsiveness to the environment than seen for most of the other sequenced epsilonproteobacteria. A branched electron transport chain is apparent, with genes encoding complexes for the oxidation of hydrogen, reduced sulfur compounds, and formate and the reduction of nitrate and oxygen. Genes are present for a complete, autotrophic reductive citric acid cycle. Many genes are present that could facilitate growth in the spatially and temporally heterogeneous sediment habitat from where Sulfurimonas denitrificans was originally isolated. Many resistance-nodulation-development family transporter genes (10 total) are present; of these, several are predicted to encode heavy metal efflux transporters. An elaborate arsenal of sensory and regulatory protein-encoding genes is in place, as are genes necessary to prevent and respond to oxidative stress.
Date: August 8, 2007
Creator: Class, USF Genomics; Sievert, Stefan M.; Scott, Kathleen M.; Klotz, Martin G.; Chain, Patrick S.G.; Hauser, Loren J. et al.
Partner: UNT Libraries Government Documents Department

Genome-wide experimental determination of barriers to horizontal gene transfer

Description: Horizontal gene transfer, in which genetic material is transferred from the genome of one organism to another, has been investigated in microbial species mainly through computational sequence analyses. To address the lack of experimental data, we studied the attempted movement of 246,045 genes from 79 prokaryotic genomes into E. coli and identified genes that consistently fail to transfer. We studied the mechanisms underlying transfer inhibition by placing coding regions from different species under the control of inducible promoters. Their toxicity to the host inhibited transfer regardless of the species of origin and our data suggest that increased gene dosage and associated increased expression is a predominant cause for transfer failure. While these experimental studies examined transfer solely into E. coli, a computational analysis of gene transfer rates across available bacterial and archaeal genomes indicates that the barriers observed in our study are general across the tree of life.
Date: September 24, 2007
Creator: Rubin, Edward; Sorek, Rotem; Zhu, Yiwen; Creevey, Christopher J.; Francino, M. Pilar; Bork, Peer et al.
Partner: UNT Libraries Government Documents Department

The Genomes On Line Database (GOLD) in 2007: status of genomic and metagenomic projects and their associated metadata

Description: The Genomes On Line Database (GOLD) is a comprehensive resource of information for genome and metagenome projects world-wide. GOLD provides access to complete and ongoing projects and their associated metadata through pre-computed lists and a search page. The database currently incorporates information for more than 2900 sequencing projects, of which 639 have been completed and the data deposited in the public databases. GOLD is constantly expanding to provide metadata information related to the project and the organism and is compliant with the Minimum Information about a Genome Sequence (MIGS) specifications.
Date: December 31, 2007
Creator: Fenner, Marsha W; Liolios, Konstantinos; Mavromatis, Konstantinos; Tavernarakis, Nektarios & Kyrpides, Nikos C.
Partner: UNT Libraries Government Documents Department