2,770 research outputs found
Lifelongα-tocopherol supplementation increases the median life span of C57BL/6 mice in the cold but has only minor effects on oxidative damage
The effects of dietary antioxidant supplementation on oxidative stress and life span are confused. We maintained C57BL/6 mice at 7 ± 2°C and supplemented their diet with α-tocopherol from 4 months of age. Supplementation significantly increased (p = 0.042) median life span by 15% (785 days, n = 44) relative to unsupplemented controls (682 days, n = 43) and also increased maximum life span (oldest 10%, p = 0.028). No sex or sex by treatment interaction effects were observed on life span, with treatment having no effect on resting or daily metabolic rate. Lymphocyte and hepatocyte oxidative DNA damage and hepatic lipid peroxidation were unaffected by supplementation, but hepatic oxidative DNA damage increased with age. Using a cDNA macroarray, genes associated with xenobiotic metabolism were significantly upregulated in the livers of female mice at 6 months of age (2 months supplementation). At 22 months of age (18 months supplementation) this response had largely abated, but various genes linked to the p21 signaling pathway were upregulated at this time. We suggest that α-tocopherol may initially be metabolized as a xenobiotic, potentially explaining why previous studies observe a life span extension generally when lifelong supplementation is initiated early in life. The absence of any significant effect on oxidative damage suggests that the life span extension observed was not mediated via any antioxidant properties of α-tocopherol. We propose that the life span extension observed following α-tocopherol supplementation may be mediated via upregulation of cytochrome p450 genes after 2 months of supplementation and/or upregulation of p21 signaling genes after 18 months of supplementation. However, these signaling pathways now require further investigation to establish their exact role in life span extension following α-tocopherol supplementation
Superconformal Multi-Black Hole Moduli Spaces in Four Dimensions
Quantum mechanics on the moduli space of N supersymmetric Reissner-Nordstrom
black holes is shown to admit 4 supersymmetries using an unconventional
supermultiplet which contains 3N bosons and 4N fermions. A near-horizon limit
is found in which the quantum mechanics of widely separated black holes
decouples from that of strongly-interacting, near-coincident black holes. This
near-horizon theory is shown to have an enhanced D(2,1;0) superconformal
symmetry. The bosonic symmetries are SL(2,R) conformal symmetry and SU(2)xSU(2)
R-symmetry arising from spatial rotations and the R-symmetry of N=2
supergravity.Comment: 23 pages, harvmac. v2: many typos fixe
The linear multiplet and ectoplasm
In the framework of the superconformal tensor calculus for 4D N=2
supergravity, locally supersymmetric actions are often constructed using the
linear multiplet. We provide a superform formulation for the linear multiplet
and derive the corresponding action functional using the ectoplasm method (also
known as the superform approach to the construction of supersymmetric
invariants). We propose a new locally supersymmetric action which makes use of
a deformed linear multiplet. The novel feature of this multiplet is that it
corresponds to the case of a gauged central charge using a one-form potential
not annihilated by the central charge (unlike the standard N=2 vector
multiplet). Such a gauge one-form can be chosen to describe a variant nonlinear
vector-tensor multiplet. As a byproduct of our construction, we also find a
variant realization of the tensor multiplet in supergravity where one of the
auxiliaries is replaced by the field strength of a gauge three-form.Comment: 31 pages; v3: minor corrections and typos fixed, version to appear in
JHE
Superconducting p-branes and Extremal Black Holes
In Einstein-Maxwell theory, magnetic flux lines are `expelled' from a black
hole as extremality is approached, in the sense that the component of the field
strength normal to the horizon goes to zero. Thus, extremal black holes are
found to exhibit the sort of `Meissner effect' which is characteristic of
superconducting media. We review some of the evidence for this effect, and do
present new evidence for it using recently found black hole solutions in string
theory and Kaluza-Klein theory. We also present some new solutions, which arise
naturally in string theory, which are non-superconducting extremal black holes.
We present a nice geometrical interpretation of these effects derived by
looking carefully at the higher dimensional configurations from which the lower
dimensional black hole solutions are obtained. We show that other extremal
solitonic objects in string theory (such as p-branes) can also display
superconducting properties. In particular, we argue that the relativistic
London equation will hold on the worldvolume of `light' superconducting
p-branes (which are embedded in flat space), and that minimally coupled zero
modes will propagate in the adS factor of the near-horizon geometries of
`heavy', or gravitating, superconducting p-branes.Comment: 22 pages, 2 figure
Internal Monitoring of Acoustic Emission in Graphite-Epoxy Composites Using Imbedded Optical Fiber Sensors
The monitoring of acoustic emission (AE) is an important technique for the nondestructive characterization of strained materials because time and frequency domain analyses of AE events yield information about the type, geometry, and location of defects, as well as how material failure may occur. The quantitative interpretation of AE event signatures is critically dependent upon the faithfulness of the acoustic transduction and signal processing system in reproducing localized stress wave amplitude as a function of time. Although the usual sensor for acoustic emission is the piezoelectric transducer, several investigators have considered the application of interferometric optical sensing techniques which offer good spatial resolution and frequency response [1,2]. These techniques typically focus one beam of a modified Michelson interferometer to a small spot on the surface of a specimen and measure the time-dependent normal component of surface displacement at the location of that spot
Vacua of M-theory and string theory
We argue that supersymmetric higher-dimension operators in the effective
actions of M-theory and IIB string theory do not affect the maximally
supersymmetric vacua: and in M-theory and
in IIB string theory. All these vacua are described in
superspace by a fixed point with all components of supertorsion and
supercurvature being supercovariantly constant. This follows from 32 unbroken
supersymmetries and allows us to prove that such vacua are exact.Comment: 16 pages, late
A family history of breast cancer will not predict female early onset breast cancer in a population-based setting
ABSTRACT: BACKGROUND: An increased risk of breast cancer for relatives of breast cancer patients has been demonstrated in many studies, and having a relative diagnosed with breast cancer at an early age is an indication for breast cancer screening. This indication has been derived from estimates based on data from cancer-prone families or from BRCA1/2 mutation families, and might be biased because BRCA1/2 mutations explain only a small proportion of the familial clustering of breast cancer. The aim of the current study was to determine the predictive value of a family history of cancer with regard to early onset of female breast cancer in a population based setting. METHODS: An unselected sample of 1,987 women with and without breast cancer was studied with regard to the age of diagnosis of breast cancer. RESULTS: The risk of early-onset breast cancer was increased when there were: (1) at least 2 cases of female breast cancer in first-degree relatives (yes/no; HR at age 30: 3.09; 95% CI: 128-7.44), (2) at least 2 cases of female breast cancer in first or second-degree relatives under the age of 50 (yes/no; HR at age 30: 3.36; 95% CI: 1.12-10.08), (3) at least 1 case of female breast cancer under the age of 40 in a first- or second-degree relative (yes/no; HR at age 30: 2.06; 95% CI: 0.83-5.12) and (4) any case of bilateral breast cancer (yes/no; HR at age 30: 3.47; 95%: 1.33-9.05). The positive predictive value of having 2 or more of these characteristics was 13% for breast cancer before the age of 70, 11% for breast cancer before the age of 50, and 1% for breast cancer before the age of 30. CONCLUSION: Applying family history related criteria in an unselected population could result in the screening of many women who will not develop breast cancer at an early age
Apraxia and motor dysfunction in corticobasal syndrome
Background: Corticobasal syndrome (CBS) is characterized by multifaceted motor system dysfunction and cognitive disturbance; distinctive clinical features include limb apraxia and visuospatial dysfunction. Transcranial magnetic stimulation (TMS) has been used to study motor system dysfunction in CBS, but the relationship of TMS parameters to clinical features has not been studied. The present study explored several hypotheses; firstly, that limb apraxia may be partly due to visuospatial impairment in CBS. Secondly, that motor system dysfunction can be demonstrated in CBS, using threshold-tracking TMS, and is linked to limb apraxia. Finally, that atrophy of the primary motor cortex, studied using voxel-based morphometry analysis (VBM), is associated with motor system dysfunction and limb apraxia in CBS. Methods: Imitation of meaningful and meaningless hand gestures was graded to assess limb apraxia, while cognitive performance was assessed using the Addenbrooke's Cognitive Examination - Revised (ACE-R), with particular emphasis placed on the visuospatial subtask. Patients underwent TMS, to assess cortical function, and VBM. Results: In total, 17 patients with CBS (7 male, 10 female; mean age 64.4+/2 6.6 years) were studied and compared to 17 matched control subjects. Of the CBS patients, 23.5% had a relatively inexcitable motor cortex, with evidence of cortical dysfunction in the remaining 76.5% patients. Reduced resting motor threshold, and visuospatial performance, correlated with limb apraxia. Patients with a resting motor threshold <50% performed significantly worse on the visuospatial sub-task of the ACE-R than other CBS patients. Cortical function correlated with atrophy of the primary and pre-motor cortices, and the thalamus, while apraxia correlated with atrophy of the pre-motor and parietal cortices. Conclusions: Cortical dysfunction appears to underlie the core clinical features of CBS, and is associated with atrophy of the primary motor and pre-motor cortices, as well as the thalamus, while apraxia correlates with pre-motor and parietal atrophy
Warm Dust and Spatially Variable PAH Emission in the Dwarf Starburst Galaxy NGC 1705
We present Spitzer observations of the dwarf starburst galaxy NGC 1705
obtained as part of SINGS. The galaxy morphology is very different shortward
and longward of ~5 microns: short-wavelength imaging shows an underlying red
stellar population, with the central super star cluster (SSC) dominating the
luminosity; longer-wavelength data reveals warm dust emission arising from two
off-nuclear regions offset by ~250 pc from the SSC. These regions show little
extinction at optical wavelengths. The galaxy has a relatively low global dust
mass (~2E5 solar masses, implying a global dust-to-gas mass ratio ~2--4 times
lower than the Milky Way average). The off-nuclear dust emission appears to be
powered by photons from the same stellar population responsible for the
excitation of the observed H Alpha emission; these photons are unassociated
with the SSC (though a contribution from embedded sources to the IR luminosity
of the off-nuclear regions cannot be ruled out). Low-resolution IRS
spectroscopy shows moderate-strength PAH emission in the 11.3 micron band in
the eastern peak; no PAH emission is detected in the SSC or the western dust
emission complex. There is significant diffuse 8 micron emission after scaling
and subtracting shorter wavelength data; the spatially variable PAH emission
strengths revealed by the IRS data suggest caution in the interpretation of
diffuse 8 micron emission as arising from PAH carriers alone. The metallicity
of NGC 1705 falls at the transition level of 35% solar found by Engelbracht and
collaborators; the fact that a system at this metallicity shows spatially
variable PAH emission demonstrates the complexity of interpreting diffuse 8
micron emission. A radio continuum non-detection, NGC 1705 deviates
significantly from the canonical far-IR vs. radio correlation. (Abridged)Comment: ApJ, in press; please retrieve full-resolution version from
http://www.astro.wesleyan.edu/~cannon/pubs.htm
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