Characterization of Alkali Metal Dispensers and Non-Evaporable Getter Pumps in Ultra-High Vacuum Systems for Cold Atomic Sensors

A glass ultrahigh vacuum chamber with rubidium alkali metal dispensers and non-evaporable getter pumps has been developed and used to create a cold atomic sample in a chamber that operates with only passive vacuum pumps. The ion-mass spectrum of evaporated gases from the alkali metal dispenser has been recorded as a function of dispenser current. The efficacy of the non-evaporable getter pumps in promoting and maintaining vacuum has been characterized by observation of the Rb vapor optical absorption on the D2 transition at 780 nm and vacuum chamber pressure rate of rise tests. We have demonstrated a sample of laser-cooled Rb atoms in this chamber when isolated and operating without active vacuum pumps

Processing deficits in monitoring analog and digital displays: Implications for attentional theory and mental-state estimation research

Subjects performed short term memory tasks, involving both spatial and verbal components, and a visual monitoring task involving either analog or digital display formats. These two tasks (memory vs. monitoring) were performed both singly and in conjunction. Contrary to expectations derived from multiple resource theories of attentional processes, there was no evidence that when the two tasks involved the same cognitive codes (i.e., either both spatial or both verbal/linguistics) there was more of a dual task performance decrement than when the two tasks employed different cognitive codes/processes. These results are discussed in terms of their implications for theories of attentional processes and also for research in mental state estimation

Stabilization of grid frequency through dynamic demand control

Frequency stability in electricity networks is essential to the maintenance of supply quality and security. This paper investigates whether a degree of built-in frequency stability could be provided by incorporating dynamic demand control into certain consumer appliances. Such devices would monitor system frequency (a universally available indicator of supply-demand imbalance) and switch the appliance on or off accordingly, striking a compromise between the needs of the appliance and the grid. A simplified computer model of a power grid was created incorporating aggregate generator inertia, governor action and load-frequency dependence plus refrigerators with dynamic demand controllers. Simulation modelling studies were carried out to investigate the system's response to a sudden loss of generation, and to fluctuating wind power. The studies indicated a significant delay in frequency-fall and a reduced dependence on rapidly deployable backup generation

Timescape cosmology with radiation fluid

The timescape cosmology represents a potentially viable alternative to the standard homogeneous cosmology, without the need for dark energy. Although average cosmic evolution in the timescape scenario only differs substantially from that of Friedmann-Lemaitre model at relatively late epochs when the contribution from the energy density of radiation is negligible, a full solution of the Buchert equations to incorporate radiation is necessary to smoothly match parameters to the epoch of photon decoupling and to obtain constraints from cosmic microwave background data. Here we extend the matter-dominated solution found in earlier work to include radiation, providing series solutions at early times and an efficient numerical integration strategy for generating the complete solution. The numerical solution is used to directly calculate the scale of the sound horizon at decoupling, and at the baryon drag epoch. The constraints on these scales from the Planck satellite data yield bounds on the timescape cosmological parameters, which are found to also agree with the best-fit values from a recent analysis of SDSS-II supernova data, while avoiding the problem of a primordial lithium-7 abundance anomaly.Comment: 21 pages, 6 figures; v2: small additions, accepted by Class. Quantum Gra

The Influence of Medicare Home Health Payment Incentives: Does Payer Source Matter?

During the late 1990s, an interim payment system (IPS) was instituted to constrain Medicare home health care expenditures. Previous research has largely focused on the implications of the IPS for Medicare patients, but our study broadens the analysis to consider patients with other payer sources. Using the National Home and Hospice Care Survey, we found similar effects of the IPS across payer types. Specifically, the IPS was associated with a decrease in access to care for the sickest patients, less agency assistance with activities of daily living, and shorter length-of-use. However, these changes did not translate into worse discharge outcomes.Medicare, health, incentives

Model of Transcriptional Activation by MarA in Escherichia coli

We have developed a mathematical model of transcriptional activation by MarA in Escherichia coli, and used the model to analyze measurements of MarA-dependent activity of the marRAB, sodA, and micF promoters in mar-rob- cells. The model rationalizes an unexpected poor correlation between the mid-point of in vivo promoter activity profiles and in vitro equilibrium constants for MarA binding to promoter sequences. Analysis of the promoter activity data using the model yielded the following predictions regarding activation mechanisms: (1) MarA activation of the marRAB, sodA, and micF promoters involves a net acceleration of the kinetics of transitions after RNA polymerase binding, up to and including promoter escape and message elongation; (2) RNA polymerase binds to these promoters with nearly unit occupancy in the absence of MarA, making recruitment of polymerase an insignificant factor in activation of these promoters; and (3) instead of recruitment, activation of the micF promoter might involve a repulsion of polymerase combined with a large acceleration of the kinetics of polymerase activity. These predictions are consistent with published chromatin immunoprecipitation assays of interactions between polymerase and the E. coli chromosome. A lack of recruitment in transcriptional activation represents an exception to the textbook description of activation of bacterial sigma-70 promoters. However, use of accelerated polymerase kinetics instead of recruitment might confer a competitive advantage to E. coli by decreasing latency in gene regulation.Comment: 30 pages, 2 figure

Extending electron orbital precession to the molecular case: Can orbital alignment be used to observe wavepacket dynamics?

The complexity of ultrafast molecular photoionization presents an obstacle to the modelling of pump-probe experiments. Here, a simple optimized model of atomic rubidium is combined with a molecular dynamics model to predict quantitatively the results of a pump-probe experiment in which long range rubidium dimers are first excited, then ionized after a variable delay. The method is illustrated by the outline of two proposed feasible experiments and the calculation of their outcomes. Both of these proposals use Feshbach 87Rb2 molecules. We show that long-range molecular pump-probe experiments should observe spin-orbit precession given a suitable pump-pulse, and that the associated high-frequency beat signal in the ionization probability decays after a few tens of picoseconds. If the molecule was to be excited to only a single fine structure state state, then a low-frequency oscillation in the internuclear separation would be detectable through the timedependent ionization cross section, giving a mechanism that would enable observation of coherent vibrational motion in this molecule.Comment: 9 pages, 10 figures, PRA submissio

Finding cool subdwarfs using a V-J reduced proper-motion diagram: Stellar parameters for 91 candidates

We present the results of a search for cool subdwarfs for which our candidates were drawn from a V-J reduced proper-motion diagram constructed by Salim & Gould (2002). Kinematic (U, V, and W) and self-consistent stellar parameters (Teff, log g, [Fe/H], and V_t) are derived for 91 candidate subdwarfs based on high resolution spectra. The observed stars span 3900K < Teff < 6200K and -2.63 < [Fe/H] < 0.25 including only 3 giants (log g < 4.0). Of the sample, 77 stars have MgH lines present in their spectra. With more than 56% of our candidate subdwarfs having [Fe/H] < -1.5, we show that the V-J reduced proper-motion diagram readily identifies metal-poor stars.Comment: PASP (in press

Exotic Axions

We show that axion phenomenology may be significantly different than conventionally assumed in theories which exhibit late phase transitions (below the QCD scale). In such theories one can find multiple pseudoscalars with axion-like couplings to matter, including a string scale axion, whose decay constant far exceeds the conventional cosmological bound. Such theories have several dark matter candidates.Comment: 5 pages, 1 figure, References adde