369 research outputs found
Evaluation of Increased Vitamin D Fortification in High-Temperature, Short-Time–Processed 2% Milk, UHT-Processed 2% Fat Chocolate Milk, and Low-Fat Strawberry Yogurt
The objective of this study was to determine the effect of increased vitamin D fortification (250 IU/serving) of high-temperature, short-time (HTST)–processed 2% fat milk, UHT-processed 2% fat chocolate milk, and low-fat strawberry yogurt on the sensory characteristics and stability of vitamin D during processing and storage. Three replicates of HTST pasteurized 2% fat milk, UHT pasteurized 2% fat chocolate milk, and low-fat strawberry yogurt were manufactured. Each of the 3 replicates for all products contained a control (no vitamin D fortification), a treatment group with 100 IU vitamin D/serving (current level of vitamin D fortification), and a treatment group with 250 IU vitamin D/serving. A cold-water dispersible vitamin D3 concentrate was used for all fortifications. The HTST-processed 2% fat milk was stored for 21 d, with vitamin D analysis done before processing and on d 0, 14, and 21. Sensory analysis was conducted on d 14. The UHT-processed 2% fat chocolate milk was stored for 60 d, with vitamin D analysis done before processing and on d 0, 40, and 60. Sensory analysis was conducted on d 40. Low-fat strawberry yogurt was stored for 42 d, with vitamin D analysis done before processing, and on d 0, 28, and 42. Sensory analysis was conducted on d 28. Vitamin D levels in the fortified products were found to be similar to the target levels of fortification (100 and 250 IU vitamin D per serving) for all products, indicating no loss of vitamin D during processing. Vitamin D was also found to be stable over the shelf life of each product. Increasing the fortification of vitamin D from 100 to 250 IU/serving did not result in a change in the sensory characteristics of HTST-processed 2% fat milk, UHT-processed 2% fat chocolate milk, or low-fat strawberry yogurt. These results indicate that it is feasible to increase vitamin D fortification from 100 to 250 IU per serving in these products
Bimodal distribution of the autocorrelation function in gamma-ray bursts
Autocorrelation functions (ACFs) are studied for a sample of 16 long
gamma-ray bursts (GRBs) with known redshift z, that were observed by the BATSE
and Konus experiments. When corrected for cosmic time dilation, the ACF shows a
bimodal distribution. A narrow width class (11 bursts) has at half-maximum a
mean width of 1.6 s with a relative dispersion of 32%, while a broad width
class (5 bursts) has a width of 7.5 s with a 4% dispersion. The separation
between the two mean values is highly significant (> 7 standard deviations).
This temporal property could be used on the large existing database of GRBs
with unknown redshift. The broad width set shows a very good linear correlation
between width at half-maximum and (1+z), with a correlation coefficient R=0.995
and a probability of chance alignment <0.0004. The potential application of
this correlation to cosmology studies is discussed, using it in combination
with recently proposed luminosity indicators.Comment: 7 pages, 7 figures. Accepted for publication in A&
Implementation of P-Controller in Computational Fluid Dynamics (CFD) Simulation of a Pilot Scale Outlet Temperature Controlled Spray Dryer
[EN] Most of the CFD simulations of spray dryers reported in the literature utilizes a fixed air inlet temperature numerical framework. In this paper, a numerical framework was introduced to model spray drying as an outlet air temperature controlled process. A P-controller numerical framework was introduced which allows the inlet temperature to be automatically adjusted based on the required outlet temperature set point. This numerical framework was evaluated with a simulation of a two-stage pilot scale spray drying system at the Davis Dairy Plant (South Dakota State University) which is used for commercial contract spray drying operation.Afshar, S.; Jubaer, H.; Metzger, L.; Patel, H.; Selomulya, C.; Woo, MW. (2018). Implementation of P-Controller in Computational Fluid Dynamics (CFD) Simulation of a Pilot Scale Outlet Temperature Controlled Spray Dryer. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 155-162. https://doi.org/10.4995/IDS2018.2018.7536OCS15516
The effect of metallicity on the Cepheid Period-Luminosity relation from a Baade-Wesselink analysis of Cepheids in the Galaxy and in the Small Magellanic Cloud
(ABRIDGED) We have applied the near-IR Barnes-Evans realization of the
Baade-Wesselink method as calibrated by Fouque & Gieren (1997) to five
metal-poor Cepheids with periods between 13 and 17 days in the Small Magellanic
Cloud as well as to a sample of 34 Galactic Cepheids to determine the effect of
metallicity on the period-luminosity (P-L) relation. For ten of the Galactic
Cepheids we present new accurate and well sampled radial-velocity curves. The
Baade-Wesselink analysis provides accurate individual distances and
luminosities to the Cepheids in the two samples, allowing us to constrain
directly, in a purely differential way, the metallicity effect on the Cepheid
P-L relation. For the Galactic Cepheids we provide a new set of P-L relations
which have zero-points in excellent agreement with astrometric and
interferometric determinations. These relations can be used directly for the
determination of distances to solar-metallicity samples of Cepheids in distant
galaxies, circumventing any corrections for metallicity effects on the
zero-point and slope of the P-L relation. We find evidence for both such
metallicity effects in our data. Comparing our two samples of Cepheids at a
mean period of about 15 days, we find a weak effect of metallicity on the
luminosity similar to that adopted by the HST Key Project on the Extragalactic
Distance Scale.Comment: 23 pages, 9 figures, accepted for publication in A&
Optical and X-ray Transients from Planet-Star Mergers
We evaluate the prompt observational signatures of the merger between a
massive close-in planet (a `hot Jupiter') and its host star, events with an
estimated Galactic rate of ~0.1-1/yr. Depending on the ratio of the mean
density of the planet rho_p to that of the star rho_star, a merger results in
three possible outcomes. If rho_p/rho_star > 5, then the planet directly
plunges below the stellar atmosphere before being disrupted by tidal forces.
Dissipation of orbital energy creates a hot wake behind the planet, producing a
EUV/soft X-ray transient as the planet sinks below the stellar surface. The
peak luminosity L_X ~ 1e36 erg/s is achieved weeks-months prior to merger,
after which the stellar surface is enshrouded by an outflow. The final inspiral
is accompanied by an optical transient powered by the recombination of hydrogen
in the outflow, which peaks at L~1e37-38 erg/s on a timescale ~days. If instead
rho_planet/rho_star < 5, then Roche Lobe overflow occurs above the stellar
surface. For rho_p/rho_star < 1, mass transfer is stable, resulting the planet
being accreted on a relatively slow timescale. However, for 1 < rho_p/rho_star
< 5, mass transfer may instead be unstable, resulting in the planet being
dynamically disrupted into an accretion disk around the star. Super-Eddington
outflows from the disk power an optical transient with L~1e37-38 erg/s and
characteristic duration ~week-months. The disk itself becomes visible once the
accretion rate become sub-Eddington, resulting in a bolometric brightening and
spectral shift to the UV. Optical transients from planet merger events may
resemble classical novae, but are distinguished by lower ejecta mass and
velocity ~100s km/s, and by hard pre- and post-cursor emission, respectively.
Promising search strategies include combined optical, UV, and X-ray surveys of
nearby massive galaxies with cadences from days to months.Comment: 20 pages, 11 figures, 2 tables, submitted to MNRA
Calibrating the Cepheid Period-Luminosity relation from the infrared surface brightness technique I. The p-factor, the Milky Way relations, and a universal K-band relation
We determine Period-Luminosity relations for Milky Way Cepheids in the
optical and near-IR bands. These relations can be used directly as reference
for extra-galactic distance determination to Cepheid populations with solar
metallicity, and they form the basis for a direct comparison with relations
obtained in exactly the same manner for stars in the Magellanic Clouds,
presented in an accompanying paper. In that paper we show that the metallicity
effect is very small and consistent with a null effect, particularly in the
near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC
and SMC to form a best relation. We employ the near-IR surface brightness
(IRSB) method to determine direct distances to the individual Cepheids after we
have recalibrated the projection factor using the recent parallax measurements
to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC
should be independent of pulsation period. We confirm our earlier finding that
the projection factor for converting radial velocity to pulsational velocity
depends quite steeply on pulsation period, p=1.550-0.186*log(P) in disagrement
with recent theoretical predictions. We delineate the Cepheid PL relation using
111 Cepheids with direct distances from the IRSB analysis. The relations are by
construction in agreement with the recent HST parallax distances to Cepheids
and slopes are in excellent agreement with the slopes of apparent magnitudes
versus period observed in the LMC.Comment: Accepted for publication by Astronomy and Astrophysics. 15 pages, 11
figure
Baade-Wesselink distances and the effect of metallicity in classical cepheids
The aim of this paper is to investigate the metallicity dependence of the
-relation in and based on a sample of 68 Galactic Cepheids with
individual Baade-Wesselink distances (some of the stars also have an HST-based
parallax) and individually determined metallicities from high-resolution
spectroscopy. Literature values of the -band, -band and radial velocity
data have been collected for a sample of 68 classical cepheids that have their
metallicity determined in the literature from high-resolution spectroscopy.
Based on a surface-brightness relation and a projection factor derived
in a previous paper, distances have been derived from a Baade-Wesselink
analysis. - and -relations in and are derived. The effect of
the adopted dependence of the projection factor on period is investigated. The
change from a constant -factor to one recently suggested in the literature
with a mild dependence on results in a less steep slope by 0.1 unit,
which is about the 1-sigma error bar in the slope itself. The observed slope in
the -relation in in the LMC agrees with both hypotheses. In the
difference between the Galactic and LMC slope is larger and would favour a mild
period dependence of the -factor. The dependence on metallicity in and
is found to be marginal, and independent of the choice of -factor on
period. This result is severely limited by the small range in metallicity
covered by the Galactic Cepheids.Comment: A&A accepte
Open Questions in GRB Physics
Open questions in GRB physics are summarized as of 2011, including
classification, progenitor, central engine, ejecta composition, energy
dissipation and particle acceleration mechanism, radiation mechanism, long term
engine activity, external shock afterglow physics, origin of high energy
emission, and cosmological setting. Prospects of addressing some of these
problems with the upcoming Chinese-French GRB mission, SVOM, are outlined.Comment: 27 pages. To appear in a special issue of Comptes Rendus Physique
"GRB studies in the SVOM era", Eds. F. Daigne, G. Dubu
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
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