1,100 research outputs found
Analyses of mean and turbulent motion in the tropics with the use of unequally spaced data
Wind velocities from 25 km to 60 km over Ascension Island, Fort Sherman and Kwajalein for the period January 1970 to December 1971 are analyzed in order to achieve a better understanding of the mean flow, the eddy kinetic energy and the Eulerian time spectra of the eddy kinetic energy. Since the data are unequally spaced in time, techniques of one-dimensional covariance theory were utilized and an unequally spaced time series analysis was accomplished. The theoretical equations for two-dimensional analysis or wavenumber frequency analysis of unequally spaced data were developed. Analysis of the turbulent winds and the average seasonal variance and eddy kinetic energy of the turbulent winds indicated that maximum total variance and energy is associated with the east-west velocity component. This is particularly true for long period seasonal waves which dominate the total energy spectrum. Additionally, there is an energy shift for the east-west component into the longer period waves with altitude increasing from 30 km to 50 km
Resolving the decades-long transient FIRST J141918.9+394036: an orphan long gamma-ray burst or a young magnetar nebula?
Ofek (2017) identified FIRST J141918.9+394036 (hereafter FIRST J1419+3940) as
a radio source sharing similar properties and host galaxy type to the compact,
persistent radio source associated with the first known repeating fast radio
burst, FRB 121102. Law et al. (2018) showed that FIRST J1419+3940 is a
transient source decaying in brightness over the last few decades. One possible
interpretation is that FIRST J1419+3940 is a nearby analogue to FRB 121102 and
that the radio emission represents a young magnetar nebula (as several
scenarios assume for FRB 121102). Another interpretation is that FIRST
J1419+3940 is the afterglow of an `orphan' long gamma-ray burst (GRB). The
environment is similar to where most such events are produced. To distinguish
between these hypotheses, we conducted radio observations using the European
VLBI Network at 1.6 GHz to spatially resolve the emission and to search for
millisecond-duration radio bursts. We detect FIRST J1419+3940 as a compact
radio source with a flux density of (on 2018
September 18) and a source size of (i.e. given the angular diameter distance of ).
These results confirm that the radio emission is non-thermal and imply an
average expansion velocity of . Contemporaneous
high-time-resolution observations using the 100-m Effelsberg telescope detected
no millisecond-duration bursts of astrophysical origin. The source properties
and lack of short-duration bursts are consistent with a GRB jet expansion,
whereas they disfavor a magnetar birth nebula.Comment: 8 pages, 4 figures, accepted for publication in ApJ
Near-equilibrium isotope fractionation during planetesimal evaporation
Silicon and Mg in differentiated rocky bodies exhibit heavy isotope
enrichments that have been attributed to evaporation of partially or entirely
molten planetesimals. We evaluate the mechanisms of planetesimal evaporation in
the early solar system and the conditions that controlled attendant isotope
fractionations. Energy balance at the surface of a body accreted within ~1 Myr
of CAI formation and heated from within by 26Al decay results in internal
temperatures exceeding the silicate solidus, producing a transient magma ocean
with a thin surface boundary layer of order < 1 meter that would be subject to
foundering. Bodies that are massive enough to form magma oceans by radioisotope
decay (ge 0.1%) can retain hot rock vapor even in the absence of ambient
nebular gas. We find that a steady-state rock vapor forms within minutes to
hours and results from a balance between rates of magma evaporation and
atmospheric escape. Vapor pressure buildup adjacent to the surfaces of the
evaporating magmas would have inevitably led to an approach to equilibrium
isotope partitioning between the vapor phase and the silicate melt. Numerical
simulations of this near-equilibrium evaporation process for a body with a
radius of ~ 700 km yield a steady-state far-field vapor pressure corresponding
to 95% saturation. Approaches to equilibrium isotope fractionation between
vapor and melt should have been the norm during planet formation due to the
formation of steady-state rock vapor atmospheres and/or the presence of
protostellar gas. We model the Si and Mg isotopic composition of bulk Earth and
show that the best fit is for a carbonaceous chondrite-like source material
with about 12% loss of Mg and 15% loss of Si resulting from near-equilibrium
evaporation into the solar protostellar disk of hydrogen gas on timescales of
10,000 to 100,000 years.Comment: 35 pages, 15 figure
Resolving the decades-long transient FIRST J141918.9+394036: an orphan long gamma-ray burst or a young magnetar nebula?
Ofek (2017) identified FIRST J141918.9+394036 (hereafter FIRST J1419+3940) as
a radio source sharing similar properties and host galaxy type to the compact,
persistent radio source associated with the first known repeating fast radio
burst, FRB 121102. Law et al. (2018) showed that FIRST J1419+3940 is a
transient source decaying in brightness over the last few decades. One possible
interpretation is that FIRST J1419+3940 is a nearby analogue to FRB 121102 and
that the radio emission represents a young magnetar nebula (as several
scenarios assume for FRB 121102). Another interpretation is that FIRST
J1419+3940 is the afterglow of an `orphan' long gamma-ray burst (GRB). The
environment is similar to where most such events are produced. To distinguish
between these hypotheses, we conducted radio observations using the European
VLBI Network at 1.6 GHz to spatially resolve the emission and to search for
millisecond-duration radio bursts. We detect FIRST J1419+3940 as a compact
radio source with a flux density of (on 2018
September 18) and a source size of (i.e. given the angular diameter distance of ).
These results confirm that the radio emission is non-thermal and imply an
average expansion velocity of . Contemporaneous
high-time-resolution observations using the 100-m Effelsberg telescope detected
no millisecond-duration bursts of astrophysical origin. The source properties
and lack of short-duration bursts are consistent with a GRB jet expansion,
whereas they disfavor a magnetar birth nebula.Comment: 8 pages, 4 figures, accepted for publication in ApJ
EFFECT OF MATERNAL DIETARY ENERGY SOURCE ON GLUCOSE HOMEOSTASIS, LIVER GLYCOGEN AND CARCASS LIPID IN THE NEONATAL PIG
Two experiments were conducted to determine the effects of supplementary dietary energy (carbohydrate versus fat) fed to sows during late gestation on energy storage and glucose homeostasis in neonatal pigs. In the first experiment, 28 crossbred sows received one of two dietary treatments that were initiated on day 100 of gestation. The control group was fed daily 1.82 kg of a corn-soybean meal-based diet plus an additional .18 kg of cornstarch. Their counterparts were fed 1.82 kg of a cornsoybean meal diet containing 8% bleachable fancy tallow. The effect of maternal dietary energy source during late gestation on glucose homeostasis was evaluated by fasting pigs from birth (t0), whereas the gestation-lactation effect was evaluated by fasting pigs after they had nursed the sow for 24 hr (t24). Pigs on the tallow treatment responded differently to the to fast, as determined by the patterns of plasma glucose (treatment x time, P\u3c.05) and free fatty acids (treatment x time, P\u3c.10). The tallow group maintained a slightly higher glucose concentration during the initial 24 hr, after which no difference was observed. Control pigs reached a peak free fatty acid (FFA) concentration by 12 hr, whereas the tallow group reached a maximum by 24 hr, which corresponded with declining glucose concentration. Pigs on the t24 tallow treatment maintained a slightly higher plasma glucose concentration during the initial 24 hr of fasting (12 hr - 68.3 vs 63.2 mg/l00 ml; 24 hr - 67.1 vs 56.3 mg/100 ml); however, no significant treatment effect or treatment x time interaction was observed. Pigs on the tallow treatment maintained a higher, although not significantly different, plasma FFA concentration during the fast (144 / μeq/liter) than pigs in the control group (126 / μeq/liter). In the second experiment, progeny of 12 sows were sacrificed immediately after birth. The respective carcass lipid (percentage) and liver glycogen (milligrams/ gram) concentrations for pigs from sows fed the control and tallow diets were 1.48, 229.1 vs 1.50, 234.9. The liver glycogen to body weight ratio (milligrams:gram) was 7.1 and 7.8 for the control and tallow groups, respectively
Response of Different Genetic Lines of Boars to Varying Levels of Dietary Calcium and Phosphorus
Two experiments were conducted to determine the effect of various levels of dietary calcium (Ca) and phosphorus (P) on performance, soundness and blood and bone parameters of different genetic lines of boars fed under variable environmental conditions. The first experiment compared different genetic lines of boars fed two levels of dietary Ca and P. Forty purebred (Large White) and Nebraska Gene Pool boars were allotted by breed and initial weight to two levels of dietary Ca and P (.65 Ca/.50% P and 1.3% Ca/1.0% P)
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