163 research outputs found
Star Formation in Dwarf Galaxies of the Nearby Centaurus A Group
We present Halpha narrow-band imaging of 17 dwarf irregular galaxies (dIs) in
the nearby Centaurus A Group. Although all large galaxies of the group have a
current or recent enhanced star formation episode, the dIs have normal star
formation rates and do not contain a larger fraction of dwarf starbursts than
other nearby groups. Relative distances between dIs and larger galaxies of the
group can be computed in 3D since most of them have now fairly accurately known
distances. We find that the dI star formation rates do not depend on local
environment, and in particular they do not show any correlation with the
distance of the dI to the nearest large galaxy of the group. There is a clear
morphology-density relation in the Centaurus A Group, similarly to the Sculptor
and Local Groups, in the sense that dEs/dSphs tend to be at small distances
from the more massive galaxies of the group, while dIs are on average at larger
distances. We find four transition dwarfs in the Group, dwarfs that show
characteristics of both dE/dSphs and dIs, and which contain cold gas but no
current star formation. Interestingly the transition dwarfs have an average
distance to the more massive galaxies which is intermediate between those of
the dEs/dSphs and dIs, and which is quite large: 0.54 +- 0.31 Mpc. This large
distance poses some difficulty for the most popular scenarios proposed for
transforming a dI into a dE/dSph (ram-pressure with tidal stripping or galaxy
harassment). If the observed transition dwarfs are indeed missing links between
dIs and dE/dSphs, their relative isolation makes it less likely to have been
produced by these mechanisms. We propose that an inhomogeneous IGM containing
higher density clumps would be able to ram-pressure stripped the dIs at such
large distances.Comment: 57 pages, 10 fi5gure
More galaxies in the Local Volume imaged in H-alpha
We have carried out an H-alpha flux measurement for 52 nearby galaxies as
part of a general H-alpha imaging survey for the Local Volume sample of
galaxies within 10 Mpc. Most of the objects are probable members of the groups
around Maffei 2/IC 342, NGC 672/IC 1727, NGC 784, and the Orion galaxy. The
measured H-alpha fluxes corrected for extinction are used to derive the galaxy
star formation rate (SFR). We briefly discuss some basic scaling relations
between SFR, hydrogen mass and absolute magnitude of the Local Volume galaxies.
The total SFR density in the local (z = 0) universe is estimated to be
(0.019+/-0.003) M_sun yr/Mpc^3.Comment: 29 pages, 6 figures, 7 tables (figures 2 and 3 is available at this
this http://una.sao.ru/halpha/articles/Maffield),Astronomical Journal,
accepte
Human Skeletal Muscle Mitochondrial Uncoupling Is Associated with Cold Induced Adaptive Thermogenesis
Background: Mild cold exposure and overfeeding are known to elevate energy expenditure in mammals, including humans. This process is called adaptive thermogenesis. In small animals, adaptive thermogenesis is mainly caused by mitochondrial uncoupling in brown adipose tissue and regulated via the sympathetic nervous system. In humans, skeletal muscle is a candidate tissue, known to account for a large part of the epinephrine-induced increase in energy expenditure. However, mitochondrial uncoupling in skeletal muscle has not extensively been studied in relation to adaptive thermogenesis in humans. Therefore we hypothesized that cold-induced adaptive thermogenesis in humans is accompanied by an increase in mitochondrial uncoupling in skeletal muscle. Methodology/Principal Findings: The metabolic response to mild cold exposure in 11 lean, male subjects was measured in a respiration chamber at baseline and mild cold exposure. Skeletal muscle mitochondrial uncoupling (state 4) was measured in muscle biopsies taken at the end of the respiration chamber stays. Mild cold exposure caused a significant increase in 24h energy expenditure of 2.8 % (0.32 MJ/day, range of 20.21 to 1.66 MJ/day, p,0.05). The individual increases in energy expenditure correlated to state 4 respiration (p,0.02, R 2 = 0.50). Conclusions/Significance: This study for the first time shows that in humans, skeletal muscle has the intrinsic capacity for cold induced adaptive thermogenesis via mitochondrial uncoupling under physiological conditions. This opens possibilitie
Further Support to the Uncoupling-to-Survive Theory: The Genetic Variation of Human UCP Genes Is Associated with Longevity
In humans Uncoupling Proteins (UCPs) are a group of five mitochondrial inner membrane transporters with variable tissue expression, which seem to function as regulators of energy homeostasis and antioxidants. In particular, these proteins uncouple respiration from ATP production, allowing stored energy to be released as heat. Data from experimental models have previously suggested that UCPs may play an important role on aging rate and lifespan. We analyzed the genetic variability of human UCPs in cohorts of subjects ranging between 64 and 105 years of age (for a total of 598 subjects), to determine whether specific UCP variability affects human longevity. Indeed, we found that the genetic variability of UCP2, UCP3 and UCP4 do affect the individual's chances of surviving up to a very old age. This confirms the importance of energy storage, energy use and modulation of ROS production in the aging process. In addition, given the different localization of these UCPs (UCP2 is expressed in various tissues including brain, hearth and adipose tissue, while UCP3 is expressed in muscles and Brown Adipose Tissue and UCP4 is expressed in neuronal cells), our results may suggest that the uncoupling process plays an important role in modulating aging especially in muscular and nervous tissues, which are indeed very responsive to metabolic alterations and are very important in estimating health status and survival in the elderly
Semiconductor Superlattices: A model system for nonlinear transport
Electric transport in semiconductor superlattices is dominated by pronounced
negative differential conductivity. In this report the standard transport
theories for superlattices, i.e. miniband conduction, Wannier-Stark-hopping,
and sequential tunneling, are reviewed in detail. Their relation to each other
is clarified by a comparison with a quantum transport model based on
nonequilibrium Green functions. It is demonstrated how the occurrence of
negative differential conductivity causes inhomogeneous electric field
distributions, yielding either a characteristic sawtooth shape of the
current-voltage characteristic or self-sustained current oscillations. An
additional ac-voltage in the THz range is included in the theory as well. The
results display absolute negative conductance, photon-assisted tunneling, the
possibility of gain, and a negative tunneling capacitance.Comment: 121 pages, figures included, to appear in Physics Reports (2001
The small G protein RAS2 is involved in the metabolic compensation of the circadian clock in the circadian model Neurospora crassa.
Accumulating evidence from both experimental and clinical investigations indicate a tight interaction between metabolism and circadian timekeeping; however, knowledge of the underlying mechanism is still incomplete. Metabolic compensation allows circadian oscillators to run with a constant speed at different substrate levels and therefore is a substantial criterion of a robust rhythm in a changing environment. Because previous data have suggested a central role of RAS2-mediated signaling in the adaptation of yeast to different nutritional environments, we examined the involvement of RAS2 in the metabolic regulation of the clock in the circadian model organism Neurospora crassa. We show that in a ras2-deficient strain, the period is longer than in the control. Moreover, unlike in wild type (wt), in Deltaras2 operation of the circadian clock was affected by glucose: compared with starvation conditions, the period was longer and the oscillation of expression of the frequency (frq) gene was dampened. In constant darkness the delayed phosphorylation of the FRQ protein and the long-lasting accumulation of FRQ in the nucleus were in accordance with the longer period and the less robust rhythm in the mutant. Whereas glucose did not affect the subcellular distribution of FRQ in wt, highly elevated FRQ levels were detected in the nucleus in Deltaras2. RAS2 interacted with the RAS-binding domain of the adenylate cyclase in vitro, and the cAMP analogue 8-Br-cAMP partially rescued the circadian phenotype in vivo. We propose therefore that RAS2 acts via a cAMP-dependent pathway and exerts significant metabolic control on the Neurospora circadian clock
Creating and curating an archive: Bury St Edmunds and its Anglo-Saxon past
This contribution explores the mechanisms by which the Benedictine foundation of Bury St Edmunds sought to legitimise and preserve their spurious pre-Conquest privileges and holdings throughout the Middle Ages. The archive is extraordinary in terms of the large number of surviving registers and cartularies which contain copies of Anglo-Saxon charters, many of which are wholly or partly in Old English. The essay charts the changing use to which these ancient documents were put in response to threats to the foundation's continued enjoyment of its liberties. The focus throughout the essay is to demonstrate how pragmatic considerations at every stage affects the development of the archive and the ways in which these linguistically challenging texts were presented, re-presented, and represented during the Abbey’s history
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