Low-Frequency Characterization of Switched dc-dc Converters

Averaging techniques are developed here to represent buck, boost, and buck-boost types of switched dc-dc converters by approximate continuous models. Simple analytical expressions in terms of the circuit components are derived for the characteristic transient and frequency responses of timeaveraged (continuous) power-stage models for use in designing and understanding the behavior of corresponding switched power stages. Novel conclusions include the dependence of effective circuit component values upon switch duty ratio and the existence of a real positive zero in certain transfer functions. Responses from analog computer simulations of the switched and averaged power stages agree well and, in turn, confirm the analytic predictions. High-order systems can be analyzed by the averaging technique without a commensurate increase in complexity

Can modeling and simulation really help power system designers?

The rap session provided an informal forum for dissemination of information on the state of the art in modeling and simulation of power processing systems. Merits of time domain and frequency domain approaches were debated and the use of these techniques for the prediction of performance and the optimization of a design were discussed. Although it appears that the present state of the art is somethat primative, interest is high and continued progress and improvement should be forthcoming

DECam integration tests on telescope simulator

The Dark Energy Survey (DES) is a next generation optical survey aimed at measuring the expansion history of the universe using four probes: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the survey, the DES Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera which will be mounted at the Blanco 4-meter telescope at the Cerro Tololo Inter- American Observatory. DES will survey 5000 square degrees of the southern galactic cap in 5 filters (g, r, i, z, Y). DECam will be comprised of 74 250 micron thick fully depleted CCDs: 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. Construction of DECam is nearing completion. In order to verify that the camera meets technical specifications for DES and to reduce the time required to commission the instrument, we have constructed a full sized telescope simulator and performed full system testing and integration prior to shipping. To complete this comprehensive test phase we have simulated a DES observing run in which we have collected 4 nights worth of data. We report on the results of these unique tests performed for the DECam and its impact on the experiments progress.Comment: Proceedings of the 2nd International Conference on Technology and Instrumentation in Particle Physics (TIPP 2011). To appear in Physics Procedia. 8 pages, 3 figure

Chemical Abundance Analysis of Tucana III, the Second rr-process Enhanced Ultra-Faint Dwarf Galaxy

We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally located in the core of the galaxy while the other two stars are located in the eastern and western tidal tails. The four stars have chemical abundance patterns consistent with the one previously studied star in Tucana III: they are moderately enhanced in $r$-process elements, i.e. they have $\approx +$0.4 dex. The non-neutron-capture elements generally follow trends seen in other dwarf galaxies, including a metallicity range of 0.44 dex and the expected trend in $\alpha$-elements, i.e., the lower metallicity stars have higher Ca and Ti abundance. Overall, the chemical abundance patterns of these stars suggest that Tucana III was an ultra-faint dwarf galaxy, and not a globular cluster, before being tidally disturbed. As is the case for the one other galaxy dominated by $r$-process enhanced stars, Reticulum II, Tucana III's stellar chemical abundances are consistent with pollution from ejecta produced by a binary neutron star merger, although a different $r$-process element or dilution gas mass is required to explain the abundances in these two galaxies if a neutron star merger is the sole source of $r$-process enhancement.Comment: 18 pages, 10 figures; accepted by Ap

Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy

The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled measurements. We describe a self-consistent reference mission design for building a Type Ia supernova Hubble diagram and for performing a wide-area weak gravitational lensing study. A 2-m wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The SNAP mission will obtain high-signal-to-noise calibrated light-curves and spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A wide-field survey covering one thousand square degrees resolves ~100 galaxies per square arcminute. If we assume we live in a cosmological-constant-dominated Universe, the matter density, dark energy density, and flatness of space can all be measured with SNAP supernova and weak-lensing measurements to a systematics-limited accuracy of 1%. For a flat universe, the density-to-pressure ratio of dark energy can be similarly measured to 5% for the present value w0 and ~0.1 for the time variation w'. The large survey area, depth, spatial resolution, time-sampling, and nine-band optical to NIR photometry will support additional independent and/or complementary dark-energy measurement approaches as well as a broad range of auxiliary science programs. (Abridged)Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.go

Radiofrequency multipole traps: Tools for spectroscopy and dynamics of cold molecular ions

Multipole radiofrequency ion traps are a highly versatile tool to study molecular ions and their interactions in a well-controllable environment. In particular the cryogenic 22-pole ion trap configuration is used to study ion-molecule reactions and complex molecular spectroscopy at temperatures between few Kelvin and room temperatures. This article presents a tutorial on radiofrequency ion trapping in multipole electrode configurations. Stable trapping conditions and buffer gas cooling, as well as important heating mechanisms, are discussed. In addition, selected experimental studies on cation and anion-molecule reactions and on spectroscopy of trapped ions are reviewed. Starting from these studies an outlook on the future of multipole ion trap research is given

Exploratory study of complexant concentrate waste processing

The purpose of this exploratory study, conducted by Pacific Northwest Laboratory for Westinghouse Hanford Company, was to determine the effect of applying advanced chemical separations technologies to the processing and disposal of high-level wastes (HLW) stored in underground tanks. The major goals of this study were to determine (1) if the wastes can be partitioned into a small volume of HLW plus a large volume of low-level waste (LLW), and (2) if the activity in the LLW can be lowered enough to meet NRC Class LLW criteria. This report presents the results obtained in a brief scouting study of various processes for separating radionuclides from Hanford complexant concentrate (CC) waste

Mannan Molecular Substructures Control Nanoscale Glucan Exposure in Candida

Cell wall mannans of Candida albicans mask β-(1,3)-glucan from recognition by Dectin-1, contributing to innate immune evasion. Glucan exposures are predominantly single receptor-ligand interaction sites of nanoscale dimensions. Candida species vary in basal glucan exposure and molecular complexity of mannans. We used super-resolution fluorescence imaging and a series of protein mannosylation mutants in C. albicans and C. glabrata to investigate the role of specific N-mannan features in regulating the nanoscale geometry of glucan exposure. Decreasing acid labile mannan abundance and α-(1,6)-mannan backbone length correlated most strongly with increased density and nanoscopic size of glucan exposures in C. albicans and C. glabrata, respectively. Additionally, a C. albicans clinical isolate with high glucan exposure produced similarly perturbed N-mannan structures and elevated glucan exposure geometry. Thus, acid labile mannan structure influences the nanoscale features of glucan exposure, impacting the nature of the pathogenic surface that triggers immunoreceptor engagement, aggregation, and signaling. Graus et al. find that N-mannan structural features regulated by Candida mannosyltransfersases control glucan exposure. Loss of mannan increased the frequency and size of glucan exposures and changed multivalent receptor engagement. Changes to mannan structure in a bloodstream isolate are associated with elevated glucan exposure at the nanoscale