95 research outputs found
Nereid: Light Curve for 1999-2006 and a Scenario for its Variations
Nereid is a small irregular moon of Neptune that displays large-, moderate-,
and small-amplitude photometric variations on both fast and slow time scales.
The central mystery of Nereid is now to explain the physical mechanism of these
unique brightness changes and why they change with time. To characterize
Nereid's variability, we have been using the SMARTS telescopes on Cerro Tololo
for synoptic monitoring from 1999 to 2006. We present a well-sampled
photometric time series of 493 magnitudes on 246 nights mostly in the V-band.
In combination with our earlier data (for 774 magnitudes over 362 nights), our
20-year data set is the most comprehensive for any small icy body in our Solar
System. Our yearly light curves show that Nereid displays various types of
behaviors: large amplitude brightenings and fadings (1987 to 1990);
moderate-amplitude variation about the average phase curve (1993-1997, 2003,
2005), moderate-amplitude variation and systematically brighter by roughly
one-quarter magnitude throughout the entire season (2004); and nearly constant
light curves superimposed on a surprisingly large-amplitude opposition surge
(1998, 1999, 2000, 2006). Other than in 2004, Nereid's variations were closely
centered around a constant phase curve that is well fit with a Hapke model for
the coherent backscattering opposition surge mechanism with angular scale of
0.7+-0.1 degrees. In our entire data set from 1987-2006, we find no significant
periodicity. We propose that the year-to-year changes in the variability of
Nereid are caused by forced precession (caused by tidal forces from Neptune) on
the spin axis of a nonspherical Nereid, such that cross-sectional areas and
average albedos change as viewed from Earth.Comment: Icarus in press, 45 manuscript page
Crystal chemistry of ferric-rich fayalites
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1983.Microfiche copy available in Archives and ScienceBibliography: leaves 122-125.by Martha Williams Schaefer.Ph.D
The Youthful Appearance of the 2003 EL61 Collisional Family
We present new solar phase curve observations of the 2003 EL61 collisional
family showing that all the members have light-scattering properties similar to
the bright icy satellites and dwarf planets. Compared to other Kuiper Belt
objects, the five family members we observe (2003 EL61, 2002 TX300, 2003 OP32,
2005 RR43, and 1995 SM55) have conspicuously neutral color (V-I = 0.6-0.8 mag)
and flat phase curves at small phase angles (phase coefficients of 0.0 - 0.1
mag deg-1). Comparing the phase curves we observe for other icy Kuiper Belt
objects to the phase curves of icy satellites, we find that the flat phase
curves of the 2003 EL61 family are an indication they have high albedo surfaces
coated with fresh ice in the last ~100 Myr. We examine possible resurfacing
processes and find none that are plausible. To avoid the influence of cosmic
radiation that darkens and reddens most icy surfaces on times scales > ~100
Myr, the family members must be unusually depleted in carbon, or else the
collision that created the family occurred so recently that the parent body and
fragments have not had time to darken. We also find a rotation period of 4.845
(+/- 0.003) h with amplitude 0.26 (+/- 0.04) mags for 2003 OP32.Comment: 12 pages, 3 tables, 4 figure
Monitoring of lung edema by microwave reflectometry during lung ischemia-reperfusion injury in vivo
It is still unclear whether lung edema can be monitored by microwave reflectometry and whether the measured changes in lung dry matter content (DMC) are accompanied by changes in PaO(2) and in pro-to anti-inflammatory cytokine expression (IFN-gamma and IL-10). Right rat lung hili were cross-clamped at 37 degrees C for 0, 60, 90 or 120 min ischemia followed by 120 min reperfusion. After 90 min (DMC: 15.9 +/- 1.4%; PaO(2): 76.7 +/- 18 mm Hg) and 120 min ischemia (DMC: 12.8 +/- 0.6%; PaO(2): 43 +/- 7 mm Hg), a significant decrease in DMC and PaO(2) throughout reperfusion compared to 0 min ischemia (DMC: 19.5 +/- 1.11%; PaO(2): 247 +/- 33 mm Hg; p < 0.05) was observed. DMC and PaO(2) decreased after 60 min ischemia but recovered during reperfusion (DMC: 18.5 +/- 2.4%; PaO(2) : 173 +/- 30 mm Hg). DMC values reflected changes on the physiological and molecular level. In conclusion, lung edema monitoring by microwave reflectometry might become a tool for the thoracic surgeon. Copyright (c) 2006 S. Karger AG, Basel
Phase Curves of Nine Trojan Asteroids over a Wide Range of Phase Angles
We have observed well-sampled phase curves for nine Trojan asteroids in B-,
V-, and I-bands. These were constructed from 778 magnitudes taken with the
1.3-m telescope on Cerro Tololo as operated by a service observer for the
SMARTS consortium. Over our typical phase range of 0.2-10 deg, we find our
phase curves to be adequately described by a linear model, for slopes of
0.04-0.09 mag/deg with average uncertainty less than 0.02 mag/deg. (The one
exception, 51378 (2001 AT33), has a formally negative slope of -0.02 +- 0.01
mag/deg.) These slopes are too steep for the opposition surge mechanism to be
shadow hiding (SH), so we conclude that the dominant surge mechanism must be
coherent backscattering (CB). In a detailed comparison of surface properties
(including surge slope, B-R color, and albedo), we find that the Trojans have
surface properties similar to the P and C class asteroids prominent in the
outer main belt, yet they have significantly different surge properties (at a
confidence level of 99.90%). This provides an imperfect argument against the
traditional idea that the Trojans were formed around Jupiter's orbit. We also
find no overlap in Trojan properties with either the main belt asteroids or
with the small icy bodies in the outer Solar System. Importantly, we find that
the Trojans are indistinguishable from other small bodies in the outer Solar
System that have lost their surface ices (such as the gray Centaurs, gray
Scattered Disk Objects, and dead comets). Thus, we find strong support for the
idea that the Trojans originally formed as icy bodies in the outer Solar
System, were captured into their current orbits during the migration of the gas
giant planets, and subsequently lost all their surface ices.Comment: Icarus, in pres
Balancing the Cost of Leaving with the Cost of Living: Drivers of Long-Term Retention of Health Workers: An Explorative Study in Three Rural Districts in Eastern Uganda
Background: Health worker retention in rural and underserved areas remains a persisting problem in many low and middle income countries, and this directly affects the quality of health services offered. Objective: This paper explores the drivers of long-term retention and describes health worker coping mechanisms in rural Uganda. Methods: A descriptive qualitative study explored the factors that motivated health workers to stay, in three rural districts of Uganda: Kamuli, Pallisa, and Kibuku. In-depth interviews conducted among health workers who have been retained for at least 10 years explored factors motivating the health workers to stay within the district, opportunities, and the benefits of staying. Results: Twenty-one health workers participated. Ten of them male and 11 female with the age range of 33–51 years. The mean duration of stay among the participants was 13, 15, and 26 years for Kamuli, Kibuku, and Pallisa respectively. Long-term retention was related to personal factors, such as having family ties, community ties, and opportunities to invest. The decentralization policy and pension benefits also kept workers in place. Opportunities for promotion or leadership motivated long stay only if they came with financial benefits. Workload reportedly increased over the years, but staffing and emoluments had not increased. Multiple job, family support, and community support helped health workers cope with the costs of living, and holding a secure pensionable government job was valued more highly than seeking uncertain job opportunities elsewhere. Conclusion: The interplay between the costs of leaving and the benefit of staying is demonstrated. Family proximity, community ties, job security, and pension enhance staying, while higher costs of living and an unpredictable employment market make leaving risky. Health workers should be able to access investment opportunities in order to cope with inadequate remuneration. Promotions and leadership opportunities only motivate if accompanied by financial benefits
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Effects of Immunization With the Soil-Derived Bacterium Mycobacterium vaccae on Stress Coping Behaviors and Cognitive Performance in a "Two Hit" Stressor Model
Previous studies demonstrate that Mycobacterium vaccae NCTC 11659 (M. vaccae), a soil-derived bacterium with anti-inflammatory and immunoregulatory properties, is a potentially useful countermeasure against negative outcomes to stressors. Here we used male C57BL/6NCrl mice to determine if repeated immunization with M. vaccae is an effective countermeasure in a "two hit" stress exposure model of chronic disruption of rhythms (CDR) followed by acute social defeat (SD). On day -28, mice received implants of biotelemetric recording devices to monitor 24-h rhythms of locomotor activity. Mice were subsequently treated with a heat-killed preparation of M. vaccae (0.1 mg, administered subcutaneously on days -21, -14, -7, and 27) or borate-buffered saline vehicle. Mice were then exposed to 8 consecutive weeks of either stable normal 12:12 h light:dark (LD) conditions or CDR, consisting of 12-h reversals of the LD cycle every 7 days (days 0-56). Finally, mice were exposed to either a 10-min SD or a home cage control condition on day 54. All mice were exposed to object location memory testing 24 h following SD. The gut microbiome and metabolome were assessed in fecal samples collected on days -1, 48, and 62 using 16S rRNA gene sequence and LC-MS/MS spectral data, respectively; the plasma metabolome was additionally measured on day 64. Among mice exposed to normal LD conditions, immunization with M. vaccae induced a shift toward a more proactive behavioral coping response to SD as measured by increases in scouting and avoiding an approaching male CD-1 aggressor, and decreases in submissive upright defensive postures. In the object location memory test, exposure to SD increased cognitive function in CDR mice previously immunized with M. vaccae. Immunization with M. vaccae stabilized the gut microbiome, attenuating CDR-induced reductions in alpha diversity and decreasing within-group measures of beta diversity. Immunization with M. vaccae also increased the relative abundance of 1-heptadecanoyl-sn-glycero-3-phosphocholine, a lysophospholipid, in plasma. Together, these data support the hypothesis that immunization with M. vaccae stabilizes the gut microbiome, induces a shift toward a more proactive response to stress exposure, and promotes stress resilience.
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Early Devonian (Late Emsian) shark fin remains (Chondrichthyes) from the Paraná Basin, southern Brazil
This is an open-access article distributed under the terms of the Creative Commons Attribution License [Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)]. The attached file is the published version of the article
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