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Nascent polypeptide chains exit the ribosome in the same relative position in both eucaryotes and procaryotes.
We located the polypeptide nascent chain as it leaves cytoplasmic ribosomes from the plant Lemna gibba by immune electron microscopy using antibodies against the small subunit of the enzyme ribulose-1,5-bisphosphate carboxylase. Similar studies with Escherichia coli ribosomes, using antibodies directed against the enzyme beta-galactosidase, show that the polypeptide nascent chain emerges in the same relative position in plants and bacteria. The eucaryotic ribosomal exit site is on the large subunit, approximately 75 A from the interface between subunits and nearly 160 A from the central protuberance, the presumed site for peptidyl transfer. This is the first functional site on both the eucaryotic and procaryotic ribosomes to be determined
Job Satisfaction and Psychological Health of Long Distance Drivers in Benin City
This cross-sectional analytical study was designed to assess the level of and factors affecting job satisfaction andpsychological health among long distance drivers in Benin City, Edo, Nigeria. A 21-item Job satisfaction questionnaire and the Golberg’s General Health Questionnaire (GHQ 28) were used for data collection from 168 consenting drivers. Data was analysed with SPSS version 15. Results showed that an appreciable number of drivers were satisfied with their job (85%). Factors linked with satisfaction included flexibility of periods designated as resting hours (91.6%), company administration and management (84.6%), self- perception of being valued by the company (79.7%), and remuneration (74.1%). Sources of dissatisfaction included lack of training on the job (82%) and frequent arassment by law enforcement officers (77%). Psychological morbidity was rare. Overall, the drivers showed high level satisfaction towards their job, though there were areas of dissatisfaction that need to be addressed in the interest and safety of passengers and other road users.Keywords: Drivers, Health, Job Satisfaction, Long distance, Psychologica
Protostellar accretion traced with chemistry. High resolution C18O and continuum observations towards deeply embedded protostars in Perseus
Context: Understanding how accretion proceeds is a key question of star
formation, with important implications for both the physical and chemical
evolution of young stellar objects. In particular, very little is known about
the accretion variability in the earliest stages of star formation.
Aims: To characterise protostellar accretion histories towards individual
sources by utilising sublimation and freeze-out chemistry of CO.
Methods: A sample of 24 embedded protostars are observed with the
Submillimeter Array (SMA) in context of the large program "Mass Assembly of
Stellar Systems and their Evolution with the SMA" (MASSES). The size of the
CO emitting region, where CO has sublimated into the gas-phase, is
measured towards each source and compared to the expected size of the region
given the current luminosity. The SMA observations also include 1.3 mm
continuum data, which are used to investigate whether a link can be established
between accretion bursts and massive circumstellar disks.
Results: Depending on the adopted sublimation temperature of the CO ice,
between 20% and 50% of the sources in the sample show extended CO
emission indicating that the gas was warm enough in the past that CO sublimated
and is currently in the process of refreezing; something which we attribute to
a recent accretion burst. Given the fraction of sources with extended CO
emission, we estimate an average interval between bursts of 20000-50000 yr,
which is consistent with previous estimates. No clear link can be established
between the presence of circumstellar disks and accretion bursts, however the
three closest known binaries in the sample (projected separations <20 AU) all
show evidence of a past accretion burst, indicating that close binary
interactions may also play a role in inducing accretion variability.Comment: Accepted for publication in A&A, 21 pages, 13 figure
MISALIGNED DISKS IN THE BINARY PROTOSTAR IRS 43
Recent high angular resolution (0.2") ALMA observations of the 1.1 mm
continuum and of HCO+ J=3-2 and HCN J=3-2 gas towards the binary protostar IRS
43 reveal multiple Keplerian disks which are significantly misaligned (
60), both in inclination and position angle and also with respect to
the binary orbital plane. Each stellar component has an associated
circumstellar disk while the binary is surrounded by a circumbinary disk.
Together with archival VLA measurements of the stellar positions over 25 years,
and assuming a circular orbit, we use our continuum measurements to determine
the binary separation, a = 74 4 AU, and its inclination, i
30. The misalignment in this system suggests that turbulence has likely
played a major role in the formation of IRS 43.Comment: 7 pages, 4 figure
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of multiple protostar systems in the Perseus molecular cloud previously
detected by the Karl G. Jansky Very Large Array (VLA). We observed 17 close
(600~AU separation) multiple systems at 1.3~mm in continuum and five
molecular lines (i.e., \twco, \cateo, \thco, HCO, SO) to characterize the
circum-multiple environments in which these systems are forming. We detect at
least one component in the continuum for the 17 multiple systems. In three
systems, one companion is not detected, and for two systems the companions are
unresolved at our observed resolution. We also detect circum-multiple dust
emission toward 8 out of 9 Class 0 multiples. Circum-multiple dust emission is
not detected toward any of the 8 Class I multiples. Twelve systems are detected
in the dense gas tracers toward their disks/inner envelopes. For these 12
systems, we use the dense gas observations to characterize their formation
mechanism. The velocity gradients in the circum-multiple gas are clearly
orthogonal to the outflow directions in 8 out of the 12 systems, consistent
with disk fragmentation. Moreover, only two systems with separations 200~AU
are \textit{inconsistent} with disk fragmentation, in addition to the two
widest systems (500~AU). Our results suggest that disk fragmentation via
gravitational instability is an important formation mechanism for close
multiple systems, but further statistics are needed to better determine the
relative fraction formed via this method.Comment: 48 Pages, 26 Figures, 7 Tables, Accepted by Ap
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