4,247 research outputs found
The Starburst Nature of Lyman-Break Galaxies: Testing UV Extinction with X-rays
We derive the bolometric to X-ray correlation for a local sample of normal
and starburst galaxies and use it, in combination with several UV reddening
schemes, to predict the 2--8 keV X-ray luminosity for a sample of 24
Lyman-break galaxies in the HDF/CDF-N. We find that the mean X-ray luminosity,
as predicted from the Meurer UV reddening relation for starburst galaxies,
agrees extremely well with the Brandt stacking analysis. This provides
additional evidence that Lyman-break galaxies can be considered as scaled-up
local starbursts and that the locally derived starburst UV reddening relation
may be a reasonable tool for estimating the UV extinction at high redshift. Our
analysis shows that the Lyman-break sample can not have far-IR to far-UV flux
ratios similar to nearby ULIGs, as this would predict a mean X-ray luminosity
100 times larger than observed, as well as far-IR luminosities large enough to
be detected in the sub-mm. We calculate the UV reddening expected from the
Calzetti effective starburst attenuation curve and the radiative transfer
models of Witt & Gordon for low metallicity dust in a shell geometry with
homogeneous or clumpy dust distributions and find that all are consistent with
the observed X-ray emission. Finally, we show that the mean X-ray luminosity of
the sample would be under predicted by a factor of 6 if the the far-UV is
unattenuated by dust.Comment: 7 pages, 3 figures. Accepted for publication in A
Large Radius Hagedorn Regime in String Gas Cosmology
We calculate the equation of state of a gas of strings at high density in a
large toroidal universe, and use it to determine the cosmological evolution of
background metric and dilaton fields in the entire large radius Hagedorn
regime, (ln S)^{1/d} << R << S^{1/d} (with S the total entropy). The pressure
in this regime is not vanishing but of O(1), while the equation of state is
proportional to volume, which makes our solutions significantly different from
previously published approximate solutions. For example, we are able to
calculate the duration of the high-density "Hagedorn" phase, which increases
exponentially with increasing entropy, S. We go on to discuss the difficulties
of the scenario, quantifying the problems of establishing thermal equilibrium
and producing a large but not too weakly-coupled universe.Comment: 12 pages, 4 figures, more details presented in string thermodynamics
section, to be published in Physical Review
Epidural Analgesia Decreases Narcotic Requirements in Low Level Spina Bifida Patients Undergoing Urologic Laparotomy for Neurogenic Bladder and Bowel
Purpose
Concern of anatomical anomalies and worsening neurologic symptoms has prevented widespread use of epidural catheters in patients with low level spina bifida (LLSB). We hypothesize that thoracic epidural placement in the T9-T10 interspace is safe and decreases narcotic requirements in LLSB patients following major open lower urinary tract reconstruction (LUTR).
Materials and Methods
We reviewed consecutive LLSB patients who had LUTR and epidurals for post-operative pain control. Controls were LLSB patients who received single shot transversus abdominis plane (TAP) blocks with similar procedures. Complications from epidural placement, including changes in motor and sensory status were recorded. Opioid consumption was calculated utilizing equivalent IV morphine doses. Mean and maximum pain scores on post-operative day (POD) 0-3 were calculated.
Results
10 LLSB patients who had lower urinary tract reconstruction and epidurals were matched to 10 LLSB patients who had lower urinary tract reconstruction and transverse abdominis plane blocks. Groups were demographically similar. All had full abdominal sensation and functional levels at or below L3. No epidural complications or changes in neurological status were noted. The epidural group had decreased opioid consumption on POD 0-3 (0.75 mg/kg vs. 1.29 mg/kg, p=0.04). Pain scores were similar or improved in the epidural group.
Conclusions
Thoracic epidural analgesia appears to be a safe and effective opioid sparing option to assist with post-operative pain management following lower urinary tract reconstruction in LLSB patients
Extended Kalman filter for integrating tracking data from ground-based radar and airborne global positioning system
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (leaf 89).by Mark P. Green.M.S
Brief Communication: Sexual dimorphic expression of myostatin and follistatin like-3 in a rat trans-generational under-nutrition model
The detrimental effects of maternal under-nutrition during gestation on fetal development are well known with an increased propensity of metabolic disorders identified in the adult offspring. Understanding exactly how and by which molecular pathways inadequate nutrition can impact upon offspring phenotype is critical and necessary for the development of treatment methods and ultimately prevention of any negative health effects. Myostatin, a negative regulator of muscle development, has recently been shown to effect glucose homeostasis and fat deposition. The involvement of myostatin in glucose metabolism and adipogenesis thus supports its ability to act in the continued alterations to the postnatal phenotype of the offspring. This hypothesis was examined in the current study using a trans-generational gestationally under-nourished rat model exposed to a high-fat (HF) diet post-weaning. The body weight, body fat, plasma glucose and insulin concentrations of the offspring, both male and female, were investigated in relation to the protein expression of myostatin and its main inhibitor; follistatin like-3 (FSTL-3), in skeletal muscle of mature offspring. Sexual dimorphism was clearly evident in the majority of these measures, including myostatin and FSTL-3 expression. Generally males displayed higher (P < 0.05) myostatin precursor and dimer expression than females, which was especially apparent (P < 0.01) in both chow and HF trans-generationally undernourished (UNAD) groups. In females only, myostatin precursor and dimer expression was altered by both trans-generational under-nutrition and postnatal diet. Overall FSTL-3 expression did not differ between sexes, although difference between sexes within certain treatments and diets were evident. Most notably, HF fed UNAD females had higher (P < 0.05) FSTL-3 expression than HF fed UNAD males. The former group also displayed higher (P < 0.01) FSTL-3 expression compared to all other female groups. In summary, myostatin may prove to be a key mediator of the effects of inadequate prenatal nutrition, independently or in combination with a high-fat postnatal diet on offspring phenotype. Consequently, further study of myostatin may provide a novel therapeutic pathway for the treatment of metabolic disorders; however, it is vital that the influence of nutrition and gender should be taken into consideration
Inclusive fitness forces of selection in an age-structured population
Hamilton’s force of selection acting against age-specific mortality is constant and maximal prior to the age of first reproduction, before declining to zero at the age of last reproduction. The force of selection acting on age-specific reproduction declines monotonically from birth in a growing or stationary population. Central to these results is the assumption that individuals do not interact with one another. This assumption is violated in social organisms, where an individual’s survival and/or reproduction may shape the inclusive fitness of other group members. Yet, it remains unclear how the forces of selection might be modified when inclusive fitness, rather than population growth rate, is considered the appropriate metric for fitness. Here, we derive such inclusive fitness forces of selection, and show that selection on age-specific survival is not always constant before maturity, and can remain above zero in post-reproductive age classes. We also show how the force of selection on age-specific reproduction does not always decline monotonically from birth, but instead depends on the balance of costs and benefits of increasing reproduction to both direct and indirect fitness. Our theoretical framework provides an opportunity to expand our understanding of senescence across social species
Inverted orbital polarization in strained correlated oxide films
Manipulating the orbital occupation of valence electrons via epitaxial strain
in an effort to induce new functional properties requires considerations of how
changes in the local bonding environment affect the band structure at the Fermi
level. Using synchrotron radiation to measure the x-ray linear dichroism of
epitaxially strained films of the correlated oxide CaFeO3, we demonstrate that
the orbital polarization of the Fe valence electrons is opposite from
conventional understanding. Although the energetic ordering of the Fe 3d
orbitals is confirmed by multiplet ligand field theory analysis to be
consistent with previously reported strain-induced behavior, we find that the
nominally higher energy orbital is more populated than the lower. We ascribe
this inverted orbital polarization to an anisotropic bandwidth response to
strain in a compound with nearly filled bands. These findings provide an
important counterexample to the traditional understanding of strain-induced
orbital polarization and reveal a new method to engineer otherwise unachievable
orbital occupations in correlated oxides
Combined bezafibrate and medroxyprogesterone acetate: potential novel therapy for acute myeloid leukaemia
Background: The majority of acute myeloid leukaemia (AML) patients are over sixty years of age. With current treatment regimens, survival rates amongst these, and also those younger patients who relapse, remain dismal and novel therapies are urgently required. In particular, therapies that have anti-leukaemic activity but that, unlike conventional chemotherapy, do not impair normal haemopoiesis.
Principal Findings: Here we demonstrate the potent anti-leukaemic activity of the combination of the lipid-regulating drug bezafibrate (BEZ) and the sex hormone medroxyprogesterone acetate (MPA) against AML cell lines and primary AML cells. The combined activity of BEZ and MPA (B/M) converged upon the increased synthesis and reduced metabolism of prostaglandin D2 (PGD2) resulting in elevated levels of the downstream highly bioactive, anti-neoplastic prostaglandin 15-deoxy Δ12,14 PGJ2 (15d-PGJ2). BEZ increased PGD2 synthesis via the generation of reactive oxygen species (ROS) and activation of the lipid peroxidation pathway. MPA directed prostaglandin synthesis towards 15d-PGJ2 by inhibiting the PGD2 11β -ketoreductase activity of the aldo-keto reductase AKR1C3, which metabolises PGD2 to 9α11β-PGF2α. B/M treatment resulted in growth arrest, apoptosis and cell differentiation in both AML cell lines and primary AML cells and these actions were recapitulated by treatment with 15d-PGJ2. Importantly, the actions of B/M had little effect on the survival of normal adult myeloid progenitors.
Significance: Collectively our data demonstrate that B/M treatment of AML cells elevated ROS and delivered the anti-neoplastic actions of 15d-PGJ2. These observations provide the mechanistic rationale for the redeployment of B/M in elderly and relapsed AML
Deep three-dimensional solid-state qubit arrays with long-lived spin coherence
Nitrogen-vacancy centers (NVCs) in diamond show promise for quantum computing, communication, and sensing. However, the best current method for entangling two NVCs requires that each one is in a separate cryostat, which is not scalable. We show that single NVCs can be laser written 6–15-µm deep inside of a diamond with spin coherence times that are an order of magnitude longer than previous laser-written NVCs and at least as long as naturally occurring NVCs. This depth is suitable for integration with solid immersion lenses or optical cavities and we present depth-dependent T2 measurements. 200 000 of these NVCs would fit into one diamond
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