819 research outputs found
The relation of the freezing procedure and the composition of the mixture to the physical and crystalline structure of ice cream
Publication authorized June 28, 1934."The data from this bulletin were taken from a paper submitted by the junior author in partial fulfillment of the requirements for the degree of Master of Arts in the Graduate School of the University of Missouri"--P. [3].Includes bibliographical references (page 20)
Composite Metal-hydrogen Electrodes for Metal-Hydrogen Batteries
The purpose of this project is to develop and conduct a feasibility study of metallic thin films (multilayered and alloy composition) produced by advanced sputtering techniques for use as anodes in Ni-metal hydrogen batteries. The anodes could be incorporated in thin film solid state Ni-metal hydrogen batteries that would be deposited as distinct anode, electrolyte and cathode layers in thin film devices. The materials could also be incorporated in secondary consumer batteries (i.e. type AF(4/3 or 4/5)) which use electrodes in the form of tapes. The project was based on pioneering studies of hydrogen uptake by ultra-thin Pd-capped metal-hydrogen ratios exceeding and fast hydrogen charging and Nb films, these studies suggested that materials with those of commercially available metal hydride materials discharging kinetics could be produced. The project initially concentrated on gas phase and electrochemical studies of Pd-capped niobium films in laboratory-scale NiMH cells. This extended the pioneering work to the wet electrochemical environment of NiMH batteries and exploited advanced synchrotron radiation techniques not available during the earlier work to conduct in-situ studies of such materials during hydrogen charging and discharging. Although batteries with fast charging kinetics and hydrogen-metal ratios approaching unity could be fabricated, it was found that oxidation, cracking and corrosion in aqueous solutions made pure Nb films-and multiiayers poor candidates for battery application. The project emphasis shifted to alloy films based on known elemental materials used for NiMH batteries. Although commercial NiMH anode materials contain many metals, it was found that 0.24 µm thick sputtered Zr-Ni films cycled at least 50 times with charging efficiencies exceeding 95% and [H]/[M] ratios of 0.7-1.0. Multilayered or thicker Zr-Ni films could be candidates for a thin film NiMH battery that may have practical applications as an integrated power source for modern electronic devices
Remnant Fermi surface in the presence of an underlying instability in layered 1T-TaS_2
We report high resolution angle-scanned photoemission and Fermi surface (FS)
mapping experiments on the layered transition-metal dichalcogenide 1T-TaS_2 in
the quasi commensurate (QC) and the commensurate (C) charge-density-wave (CDW)
phase. Instead of a nesting induced partially removed FS in the CDW phase we
find a pseudogap over large portions of the FS. This remnant FS exhibits the
symmetry of the one-particle normal state FS even when passing from the
QC-phase to the C-phase. Possibly, this Mott localization induced transition
represents the underlying instability responsible for the pseudogapped FS
Revised Stellar Properties of Kepler Targets for the Quarter 1-16 Transit Detection Run
We present revised properties for 196,468 stars observed by the NASA Kepler
Mission and used in the analysis of Quarter 1-16 (Q1-Q16) data to detect and
characterize transiting exoplanets. The catalog is based on a compilation of
literature values for atmospheric properties (temperature, surface gravity, and
metallicity) derived from different observational techniques (photometry,
spectroscopy, asteroseismology, and exoplanet transits), which were then
homogeneously fitted to a grid of Dartmouth stellar isochrones. We use
broadband photometry and asteroseismology to characterize 11,532 Kepler targets
which were previously unclassified in the Kepler Input Catalog (KIC). We report
the detection of oscillations in 2,762 of these targets, classifying them as
giant stars and increasing the number of known oscillating giant stars observed
by Kepler by ~20% to a total of ~15,500 stars. Typical uncertainties in derived
radii and masses are ~40% and ~20%, respectively, for stars with photometric
constraints only, and 5-15% and ~10% for stars based on spectroscopy and/or
asteroseismology, although these uncertainties vary strongly with spectral type
and luminosity class. A comparison with the Q1-Q12 catalog shows a systematic
decrease in radii for M dwarfs, while radii for K dwarfs decrease or increase
depending on the Q1-Q12 provenance (KIC or Yonsei-Yale isochrones). Radii of
F-G dwarfs are on average unchanged, with the exception of newly identified
giants. The Q1-Q16 star properties catalog is a first step towards an improved
characterization of all Kepler targets to support planet occurrence studies.Comment: 20 pages, 14 figures, 5 tables; accepted for publication in ApJS;
electronic versions of Tables 4 and 5 are available as ancillary files (see
sidebar on the right), and an interactive version of Table 5 is available at
the NASA Exoplanet Archive (http://exoplanetarchive.ipac.caltech.edu/
An Investigation of Equivalence Principle Violations Using Solar Neutrino Oscillations in a Constant Gravitational Potential
Neutrino oscillations induced by a flavor-dependent violation of the Einstein
Equivalence Principle (VEP) have been recently considered as a suitable
explanation of the solar electron-neutrino deficiency. Unlike the MSW
oscillation mechanism, the VEP mechanism is dependent on a coupling to the
local background gravitational potential . We investigate the differences
which arise by considering three-flavor VEP neutrinos oscillating against fixed
background potentials, and against the radially-dependent solar potential. This
can help determine the sensitivity of the gravitationally-induced oscillations
to both constancy and size (order of magnitude) of . In particular, we
consider the potential of the local superculster, , in
light of recent work suggesting that the varying solar potential has no effect
on the oscillations. The possibility for arbitrarily large background
potentials in different cosmologies is discussed, and the effects of one such
potential () are considered.Comment: 12pp, LaTeX; 12 figures (bitmapped postscript); Submitted to Phys Rev
Superconductivity in Cu_xTiSe_2
Charge density waves (CDWs) are periodic modulations of the conduction
electron density in solids. They are collective states that arise from
intrinsic instabilities often present in low dimensional electronic systems.
The layered dichalcogenides are the most well-studied examples, with TiSe_2 one
of the first CDW-bearing materials known. The competition between CDW and
superconducting collective electronic states at low temperatures has long been
held and explored, and yet no chemical system has been previously reported
where finely controlled chemical tuning allows this competition to be studied
in detail. Here we report how, upon controlled intercalation of TiSe_2 with Cu
to yield Cu_xTiSe_2, the CDW transition is continuously suppressed, and a new
superconducting state emerges near x = 0.04, with a maximum T_c of 4.15 K found
at x = 0.08. Cu_xTiSe_2 thus provides the first opportunity to study the CDW to
Superconductivity transition in detail through an easily-controllable chemical
parameter, and will provide new insights into the behavior of correlated
electron systems.Comment: Accepted to Nature Physic
Data and Safety Monitoring of COVID-19 Vaccine Clinical Trials
To speed the development of vaccines against SARS-CoV-2, the United States Federal Government has funded multiple phase 3 trials of candidate vaccines. A single 11-member data and safety monitoring board (DSMB) monitors all government-funded trials to ensure coordinated oversight, promote harmonized designs, and allow shared insights related to safety across trials. DSMB reviews encompass 3 domains: (1) the conduct of trials, including overall and subgroup accrual and data quality and completeness; (2) safety, including individual events of concern and comparisons by randomized group; and (3) interim analyses of efficacy when event-driven milestones are met. Challenges have included the scale and pace of the trials, the frequency of safety events related to the combined enrollment of over 100 000 participants, many of whom are older adults or have comorbid conditions that place them at independent risk of serious health events, and the politicized environment in which the trials have taken place
Specific heat and magnetic measurements in Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3 samples
We studied the magnetization as a function of temperature and magnetic field
in the compounds Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3. It allowed
us to identify the ferromagnetic, antiferromagnetic and charge ordering phases
in each case. The intrinsic magnetic moments of Nd3+ and Ho3+ ions experienced
a short range order at low temperatures. We also did specific heat measurements
with applied magnetic fields between 0 and 9 T and temperatures between 2 and
300 K in all three samples. Close to the charge ordering and ferromagnetic
transition temperatures the specific heat curves showed peaks superposed to the
characteristic response of the lattice oscillations. Below 10 K the specific
heat measurements evidenced a Schottky-like anomaly for all samples. However,
we could not successfully fit the curves to either a two level nor a
distribution of two-level Schottky anomaly. Our results indicated that the peak
temperature of the Schottky anomaly was higher in the compounds with narrower
conduction band.Comment: submitted to PR
Rotational and Cyclical Variability in gamma Cassiopeia
We report results of a nine-year monitoring effort on the unusual classical
Be with a robotic ground-based (APT) B,V-filtered telescope as well as
simultaneous observations in 2004 November with this instrument and the RXTE
(X-ray) telescope. Our observations disclosed no correlated optical response to
the rapid X-ray flares in this star, nor did the star show any sustained flux
changes during the course of either of the two monitored nights in either
wavelength regime. Our optical light curves reveal that gamma Cas undergoes
\~3%-amplitude cycles with lengths of 60--90 days. Over the nine days we
monitored the star with the RXTE, the X-ray flux varied in phase with its
optical cycle and with an amplitude predicted from correlated optical/X-ray
data from an earlier paper. The amplitudes of the V magnitude cycles are
30--40% larger than the B amplitudes, suggesting the seat of the cycles is
circumstellar. The cycle lengths constantly change and can damp or grow on
timescales as short as 13 days. We have also discovered a coherent period of
1.21581 +/-0.00002 days in all our data, which is consistent only with
rotation. The full amplitude of this variation is 0.0060 in both filters. The
derived waveform, somewhat surprisingly, is almost sawtooth in shape. This
variation probably originates on the star's surface. This circumstance hints at
the existence of a strong magnetic field with a complex topology and an
associated heterogeneous surface composition.Comment: 31 pages, 7 figures. Submitted to The Astrophysical Journa
X-ray and Optical Variations in the Classical Be Star gamma Cas
gamma Cas (B0.5e) is known to be a unique X-ray source because ot its
moderate L_x, hard X-ray spectrum, and light curve punctuated by ubiquitous
flares and slow undulations. Its X-ray peculiarities have led to a controversy
concerning their origin: either from wind infall onto a putative degenerate
companion, as for typical Be/X-ray binaries, or from the Be star per se. Recent
progress has been made to address this: (1) the discovery that gamma Cas is an
eccentric binary system (P = 203.59 d) with unknown secondary type, (2) the
accumulation of RXTE data at 9 epochs in 1996-2000, and (3) the collation of
robotic telescope B, V-band photometric observations over 4 seasons. The latter
show a 3%, cyclical flux variation with cycle lengths 55-93 days. We find that
X-ray fluxes at all 9 epochs show random variations with orbital phase. This
contradicts the binary accretion model, which predicts a substantial
modulation. However,these fluxes correlate well with the cyclical optical
variations. Also, the 6 flux measurements in 2000 closely track the
interpolated optical variations between the 2000 and 2001 observing seasons.
Since the optical variations represent a far greater energy than that emitted
as X-rays, the optical variability cannot arise from X-ray reprocessing.
However, the strong correlation between the two suggests that they are driven
by a common mechanism. We propose that this mechanism is a cyclical magnetic
dynamo excited by a Balbus-Hawley instability located within the inner part of
the circumstellar disk. In our model, variations in the field strength directly
produce the changes in the magnetically related X-ray activity. Turbulence
associated with the dynamo results in changes to the density distribution
within the disk and creates the observed optical variations.Comment: 30 dbl-spaced pages, Latex, plus 11 figures. Accepted by Ap
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