We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.

Total and partial charge-changing cross sections have been measured for argon projectiles at 400 MeV/nucleon in carbon, aluminum, copper, tin and lead targets; cross sections for hydrogen were also obtained, using a polyethylene target. The validity of weak and strong factorization properties has been investigated for partial charge-changing cross sections; preliminary cross section values obtained for carbon, neon and silicon at 290 and 400 MeV/nucleon and iron at 400 MeV/nucleon, in carbon, aluminum, copper, tin and lead targets have been also used for testing these properties. Two different analysis methods were applied and both indicated that these properties are valid, without any significant difference between weak and strong factorization. The factorization parameters have then been calculated and analyzed in order to find some systematic behavior useful for modeling purposes.

The reaction between monomeric bis(1,2,4-tri-t-butylcyclopentadienyl)cerium hydride, Cp'2CeH, and several hydrofluorobenzene derivatives is described. The aryl derivatives that are the primary products, Cp'2Ce(C6H5-xFx) where x = 1,2,3,4, are thermally stable enough to be isolated in only two cases, since all of them decompose at different rates to Cp'2CeF and a fluorobenzyne; the latter is trapped by either solvent when C6D6 is used or by a Cp'H ring when C6D12 is the solvent. The trapped products are identified by GCMS analysis after hydrolysis. The aryl derivatives are generated cleanly by reaction of the metallacycle, Cp'((Me3C)2C5H2C(Me2)CH2)Ce, with a hydrofluorobenzene and the resulting arylcerium products, in each case, are identified by their 1H and 19F NMR spectra at 20oC. The stereochemical principle that evolves from these studies is that the thermodynamic isomer is the one in which the CeC bond is flanked by two ortho-CF bonds. This orientation is suggested to arise from the negative charge that is localized on the ipso-carbon atom due to Co(delta+)-Fo(delta-) polarization. The preferred regioisomer is determined by thermodynamic rather than kinetic effects; this is illustrated by the quantitative, irreversible solid-state conversion at 25oC over two months of Cp'2Ce(2,3,4,5-C6HF4) to Cp'2Ce(2,3,4,6-C6HF4), an isomerization that involves a CeC(ipso) for C(ortho)F …

A computational approach is presented for prediction and interpretation of core-level spectra of complex molecules. Applications are presented for several isolated organic molecules, sampling a range of chemical bonding and structural motifs. Comparison with gas phase measurements indicate that spectral lineshapes are accurately reproduced both above and below the ionization potential, without resort to ad hoc broadening. Agreement with experiment is significantly improved upon inclusion of vibrations via molecular dynamics sampling. We isolate and characterize spectral features due to particular electronic transitions enabled by vibrations, noting that even zero-point motion is sufficient in some cases.

Our previous atomic force microscopy (AFM) studies successfully visualized native Bacillus atrophaeus spore coat ultrastructure and surface morphology. We have shown that the outer spore coat surface is formed by a crystalline array of {approx}11 nm thick rodlets, having a periodicity of {approx}8 nm. We present here further AFM ultrastructural investigations of air-dried and fully hydrated spore surface architecture. In the rodlet layer, planar and point defects, as well as domain boundaries, similar to those described for inorganic and macromolecular crystals, were identified. For several Bacillus species, rodlet structure assembly and architectural variation appear to be a consequence of species-specific nucleation and crystallization mechanisms that regulate the formation of the outer spore coat. We propose a unifying mechanism for nucleation and self-assembly of this crystalline layer on the outer spore coat surface.

The relationship between pullback velocity and impact velocity is studied for different microstructures in Cu. A size distribution of potential nucleation sites is derived under the conditions of an applied stochastic stress field. The size distribution depends on flow stress leading to a connection between the plastic flow appropriate to a given microstructure and nucleation rate. The pullback velocity in turn depends on the nucleation rate resulting in a prediction for the relationship between pullback velocity and flow stress. The theory is compared to observations of Cu on Cu gas-gun experiments (10-50 GPa) for a diverse set of microstructures. The scaling law is incorporated into a 1D finite difference code and is shown to reproduce the experimental data with one adjustable parameter that depends only on a nucleation exponent, {Lambda}.

In a fusion reactor based on the Magnetized Target Fusion approach, the permanent power supply has to deliver currents up to a few mega-amperes to the target dropped into the reaction chamber. All the structures situated around the target will be destroyed after every pulse and have to be replaced at a frequency of 1 to 10 Hz. In this paper, an approach based on the use of spherical blanket surrounding the target, and pulsed plasma electrodes connecting the target to the power supply, is discussed. A brief physic analysis of the processes associated with creation of plasma electrodes is discussed.

The complexes [Ce(tmtaa)2], [Ce(tmtaa)(tmtaaH)]and[Ce2(tmtaa)3(thf)2]are obtained from Ce[N(SiMe3)2]3 and tmtaaH2, themacrocyclic ligand 6,8,15,17-tetramethyldibenzotetraaza[14]-annulene,depending on the stoichiometry, solvent and temperature. The crystalstructure of Ce(tmtaa)2 is isostructural with Zr(tmtaa)2, howevermagnetic susceptibility measurements in the range 5-300 K show thatCe(tmtaa)2 is not diamagnetic, but is a temperature-independentparamagnet (TIP), similar to Ce(cot)2, cerocene.

We examine ionizing radiation (IR) sensitivity and epistasisrelationships of several Saccharomyces mutants affectingpost-translational modifications of histones H2B and H3. Mutantsbre1delta, lge1delta, and rtf1delta, defective in histone H2B lysine 123ubiquitination, show IR sensitivity equivalent to that of the dot1deltamutant that we reported on earlier, consistent with published findingsthat Dot1p requires H2B K123 ubiquitination to fully methylate histone H3K79. This implicates progressive K79 methylation rather thanmono-methylation in IR resistance. The set2delta mutant, defective in H3K36 methylation, shows mild IR sensitivity whereas mutants that abolishH3 K4 methylation resemble wild type. The dot1delta, bre1delta, andlge1delta mutants show epistasis for IR sensitivity. The paf1deltamutant, also reportedly defective in H2B K123 ubiquitination, confers nosensitivity. The rad6delta, rad51null, rad50delta, and rad9deltamutations are epistatic to bre1? and dot1delta, but rad18delta andrad5delta show additivity with bre1delta, dot1delta, and each other. Thebre1delta rad18delta double mutant resembles rad6delta in sensitivity;thus the role of Rad6p in ubiquitinating H2B accounts for its extrasensitivity compared to rad18delta. We conclude that IR resistanceconferred by BRE1 and DOT1 is mediated through homologous recombinationalrepair, not postreplication repair, and confirm findings of a G1checkpoint role for the RAD6/BRE1/DOT1 pathway.

The configuration interaction (CI) approach to solving the nuclear many-body problem, also known as the interacting shell model, has proven to be powerful tool in understanding the structure of nuclei. The principal criticism of past applications of the shell model is the reliance on empirical tuning to interaction matrix elements. If an accurate description of nuclei far from the valley of stability, where little or no data is available, a more fundamental approach is needed. This starts with recent ab initio approaches with effective interactions in the no-core shell model (NCSM). Using effective-field theory for guidance, fully ab initio descriptions of nuclei up to {sup 16}O with QCD based NN, NNN, and NNNN interactions will be possible within the next five years. An important task is then to determine how to use these NCSM results to develop effective interactions to describe heavier nuclei without the need to resort to an empirical retuning with every model space. Thus, it is likely that more traditional CI applications utilizing direct diagonalization and more fundamental interactions will be applicable to nuclei with perhaps up to one hundred constituents. But, these direct diagonalization CI applications will always be computationally limited due to the rapid increase …

Passing an electron beam through an aperture can serve to reduce the beam current or change the transverse beam profile. For a sufficiently intense beam, space charge will drive a radial expansion of the beam, which may cause the current passing through the aperture to increase even though the current arriving at the aperture is decreasing. When a gridded electron gun is used, this may be expressed by stating that the transconductance of the apertured gun is negative. Here we explain this effect, and explore some of the key factors governing when it can occur and influencing its strength.

It is important to identify and control the operational and compositional variables that impact the important processing and performance properties of Saltstone grout mixes. The grout that is produced at the Saltstone Production Facility (SPF) is referred to as Saltstone and is a waste form that immobilizes low concentrations of radionuclides as well as certain toxic metals. The Saltstone will be disposed of in vaults at Savannah River Site (SRS). An effort referred to as the Saltstone Variability Study has been initiated to achieve this goal. The protocols developed in this variability study are also ideally suited as a tool to assess the impact of proposed changes to the processing flow sheet for Liquid Waste Operations at SRS. One such proposal that is currently under consideration is to introduce a leaching step in the treatment of the High Level Waste (HLW) sludge to remove aluminum prior to vitrification at the Defense Waste Processing Facility (DWPF). This leachate would significantly increase the soluble aluminate concentration in the salt feed that will be processed at the SPF. Consequently, an initial study of the impact of increased aluminate concentration on the Saltstone grout properties was performed. Prior work by Lukens (1) showed that …

As part of a small scale sequestration test (about 1500 tonsof CO2) in a saline aquifer, time-lapse borehole seismic surveys wereconducted to aid in characterization of subsurface CO2 distribution andmaterial property changes induced by the injected CO2. A VSP surveydemonstrated a large increase (about 75 percent) in seismic reflectivitydue to CO2 injection and allowed estimation of the spatial extent of CO2induced changes. A crosswell survey imaged a large seismic velocitydecrease (up to 500 m/s) within the injection interval and provided ahigh resolution image of this velocity change which maps the subsurfacedistribution of CO2 between two wells. Numerical modeling of the seismicresponse uses the crosswell measurements to show that this small CO2volume causes a large response in the seismic reflectivity. This resultdemonstrates that seismic detection of small CO2 volumes in salineaquifers is feasible and realistic.

We present the results of applying new object classification techniques to the supernova search of the Nearby Supernova Factory. In comparison to simple threshold cuts, more sophisticated methods such as boosted decision trees, random forests, and support vector machines provide dramatically better object discrimination: we reduced the number of nonsupernova candidates by a factor of 10 while increasing our supernova identification efficiency. Methods such as these will be crucial for maintaining a reasonable false positive rate in the automated transient alert pipelines of upcoming large optical surveys.

We propose and analyze a new tool to help solve sparse linear least-squares problems min{sub x} {parallel}Ax-b{parallel}{sub 2}. Our method is based on a sparse QR factorization of a low-rank perturbation {cflx A} of A. More precisely, we show that the R factor of {cflx A} is an effective preconditioner for the least-squares problem min{sub x} {parallel}Ax-b{parallel}{sub 2}, when solved using LSQR. We propose applications for the new technique. When A is rank deficient we can add rows to ensure that the preconditioner is well-conditioned without column pivoting. When A is sparse except for a few dense rows we can drop these dense rows from A to obtain {cflx A}. Another application is solving an updated or downdated problem. If R is a good preconditioner for the original problem A, it is a good preconditioner for the updated/downdated problem {cflx A}. We can also solve what-if scenarios, where we want to find the solution if a column of the original matrix is changed/removed. We present a spectral theory that analyzes the generalized spectrum of the pencil (A*A,R*R) and analyze the applications.

The self-assembly of tetradecylamine (C14) and of mixtures of tetradecyl and octadecylamine (C18) molecules from chloroform solutions on mica has been studied using atomic force microscopy(AFM). For pure components self-assembly proceeds more slowly for C14 than for C18. In both cases after equilibrium is reached islands of tilted molecules cover a similar fraction of the surface. Images of films formed by mixtures of molecules acquired before equilibrium is reached (short ripening time at room temperature) show only islands with the height corresponding to C18 with many pores. After a long ripening time, when equilibrium is reached, islands of segregated pure components are formed.

We derive lens distortion and magnification profiles of four well known clusters observed with Subaru. Each cluster is very well fitted by the general form predicted for Cold Dark Matter (CDM) dominated halos, with good consistency found between the independent distortion and magnification measurements. The inferred level of mass concentration is surprisingly high, 8 < c{sub vir} < 15 (<c{sub vir}> = 10.39 {+-} 0.91), compared to the relatively shallow profiles predicted by the {Lambda}CDM model, c{sub vir} = 5.06 {+-} 1.10 (for <M{sub vir}> = 1.25 x 10{sup 15} M{sub {circle_dot}}/h). This represents a 4{sigma} discrepancy, and includes the relatively modest effects of projection bias and profile evolution derived from N-body simulations, which oppose each other with little residual effect. In the context of CDM based cosmologies, this discrepancy implies some modification of the widely assumed spectrum of initial density perturbations, so clusters collapse earlier (z {ge} 1) than predicted (z < 0.5) when the Universe was correspondingly denser.

A new facility for high-pressure diffraction and spectroscopy using diamond anvil high-pressure cells has been built at the Advanced Light Source on Beamline 12.2.2. This beamline benefits from the hard X-radiation generated by a 6 Tesla superconducting bending magnet (superbend). Useful x-ray flux is available between 5 keV and 35 keV. The radiation is transferred from the superbend to the experimental enclosure by the brightness preserving optics of the beamline. These optics are comprised of: a plane parabola collimating mirror (M1), followed by a Kohzu monochromator vessel with a Si(111) crystals (E/{Delta}E {approx} 7000) and a W/B{sub 4}C multilayer (E/{Delta}E {approx} 100), and then a toroidal focusing mirror (M2) with variable focusing distance. The experimental enclosure contains an automated beam positioning system, a set of slits, ion chambers, the sample positioning goniometry and area detectors (CCD or image-plate detector). Future developments aim at the installation of a second end station dedicated for in situ laser-heating on one hand and a dedicated high-pressure single-crystal station, applying both monochromatic as well as polychromatic techniques.

The conversion efficiency of ultra short-pulse laser radiation to K-{alpha} x-rays has been measured for various chlorine-containing targets to be used as x-ray scattering probes of dense plasmas. The spectral and temporal properties of these sources will allow spectrally-resolved x-ray scattering probing with picosecond temporal resolution required for measuring the plasma conditions in inertial confinement fusion experiments. Simulations of x-ray scattering spectra from these plasmas show that fuel capsule density, capsule ablator density, and shock timing information may be inferred.

Based on the mineralogy and petrography, coarse-grained, igneous, anorthite-rich (Type C) calcium-aluminum-rich inclusions (CAIs) in the CV3 carbonaceous chondrite Allende have been recently divided into three groups: (i) CAIs with melilite and Al,Ti-diopside of massive and lacy textures (coarse grains with numerous rounded inclusions of anorthite) in a fine-grained anorthite groundmass (6-1-72, 100, 160), (ii) CAI CG5 with massive melilite, Al,Ti-diopside and anorthite, and (iii) CAIs associated with chondrule material: either containing chondrule fragments in their peripheries (ABC, TS26) or surrounded by chondrule-like, igneous rims (93) (Krot et al., 2007a,b). Here, we report in situ oxygen isotopic measurements of primary (melilite, spinel, Al,Ti-diopside, anorthite) and secondary (grossular, monticellite, forsterite) minerals in these CAIs. Spinel ({Delta}{sup 17}O = -25{per_thousand} to -20{per_thousand}), massive and lacy Al,Ti-diopside ({Delta}{sup 17}O = -20{per_thousand} to -5{per_thousand}) and fine-grained anorthite ({Delta}{sup 17}O = -15{per_thousand} to -2{per_thousand}) in 100, 160 and 6-1-72 are {sup 16}O-enriched relative spinel and coarse-grained Al,Ti-diopside and anorthite in ABC, 93 and TS26 ({Delta}{sup 17}O ranges from -20{per_thousand} to -15{per_thousand}, from -15{per_thousand} to -5{per_thousand}, and from -5{per_thousand} to 0{per_thousand}, respectively). In 6-1-72, massive and lacy Al,Ti-diopside grains are {sup 16}O-depleted ({Delta}{sup 17}O {approx} -13{per_thousand}) relative to spinel ({Delta}{sup 17}O = -23{per_thousand}). Melilite is the …

A laser-based, table-top instrument is constructed to perform femtosecond soft x-ray transient absorption spectroscopy. Ultrashort soft x-ray pulses produced via high-order harmonic generation of the amplified output of a femtosecond Ti:sapphire laser system are used to probe atomic core-level transient absorptions in atoms and molecules. The results provide chemically specific, time-resolved dynamics with sub-50-fs time resolution. In this setup, high-order harmonics generated in a Ne-filled capillary waveguide are refocused by a gold-coated toroidal mirror into the sample gas cell, where the soft x-ray light intersects with an optical pump pulse. The transmitted high-order harmonics are spectrally dispersed with a home-built soft x-ray spectrometer, which consists of a gold-coated toroidal mirror, a uniform-line spaced plane grating, and a soft x-ray CCD camera. The optical layout of the instrument, design of the soft x-ray spectrometer, and spatial and temporal characterization of the high-order harmonics are described. Examples of static and time-resolved photoabsorption spectra collected on this apparatus are presented.

The combination of lithography and self-assembly provides apowerful means of organizing solution-synthesized nanostructures for awide variety of applications. We have developed a fluidic assembly methodthat relies on the local pinning of a moving liquid contact line bylithographically produced topographic features to concentratenanoparticles at those features. The final stages of the assembly processare controlled first by long-range immersion capillary forces and then bythe short-range electrostatic and Van der Waal's interactions. We havesuccessfully assembled nanoparticles from 50 nm to 2 nm in size usingthis technique and have also demonstrated the controlled positioning ofmore complex nanotetrapod structures. We have used this process toassemble Au nanoparticles into pre-patterned electrode structures andhave performed preliminary electrical characterization of the devices soformed. The fluidic assembly method is capable of very high yield, interms of positioning nanostructures at each lithographically-definedlocation, and of excellent specificity, with essentially no particledeposition between features.

In the proposed E-166 experiment at SLAC, 50 GeV electrons pass through a helical undulator, and produce circularly polarized photons, which interact with a tungsten target and generate longitudinally polarized positrons. The background is an important issue for an experiment under consideration. To address this issue, simulations were performed with the code GEANT3 to model the production of secondary particles from high-energy electrons hitting an undulator. The energy density of photons generated at the target has been analyzed. Results of the simulations are presented and discussed.

The d+Au data from RHIC, including the pA results from the fixed-target CERN SPS pA data, suggest increased importance of initial-state shadowing and decreasing nuclear absorption with increasing energy. This is not surprising since smaller x is probed at higher energy while absorption due to multiple scattering is predicted to decrease with energy. The CERN SPS data suggest a J/{psi} absorption cross section of about 4 mb without shadowing, and a larger absorption cross section if it is included since the SPS x range is in the antishadowing region. The d+Au RHIC data support smaller absorption, {sigma}{sup J/{psi}}{sub abs} {approx} 0-2 mb. Thus our predictions for J/{psi} and {Upsilon} production in pPb and Pb+Pb interactions at the LHC are shown for initial-state shadowing alone with no absorption or dense matter effects. We note that including absorption would only move the calculated ratios down in proportion to the absorption survival probability since, at LHC energies, any rapidity dependence of absorption is at very large |y|, outside the detector acceptance.