1,006 research outputs found
Loop homology of spheres and complex projective spaces
In his Inventiones paper, Ziller (Invent. Math: 1-22, 1977) computed the
integral homology as a graded abelian group of the free loop space of compact,
globally symmetric spaces of rank 1. Chas and Sullivan (String Topology,
1999)showed that the homology of the free loop space of a compact closed
orientable manifold can be equipped with a loop product and a BV-operator
making it a Batalin-Vilkovisky algebra. Cohen, Jones and Yan (The loop homology
algebra of spheres and projective spaces, 2004) developed a spectral sequence
which converges to the loop homology as a spectral sequence of algebras. They
computed the algebra structure of the loop homology of spheres and complex
projective spaces by using Ziller's results and the method of Brown-Shih (Ann.
of Math. 69:223-246, 1959, Publ. Math. Inst. Hautes \'Etudes Sci. 3: 93-176,
1962). In this note we compute the loop homology algebra by using only spectral
sequences and the technique of universal examples. We therefore not only obtain
Zillers' and Brown-Shihs' results in an elementary way, we also replace the
roundabout computations of Cohen, Jones and Yan (The loop homology algebra of
spheres and projective spaces, 2004) making them independent of Ziller's and
Brown-Shihs' work. Moreover we offer an elementary technique which we expect
can easily be generalized and applied to a wider family of spaces, not only the
globally symmetric ones.Comment: 10 pages, 8 figure
Loop space homology associated with the mod 2 Dickson invariants
Peer reviewedPublisher PD
Probing renal blood volume with magnetic resonance imaging
Damage to the kidney substantially reduces life expectancy. Renal tissue hypoperfusion and hypoxia are key elements in the pathophysiology of acute kidney injury and its progression to chronic kidney disease. In vivo assessment of renal haemodynamics and tissue oxygenation remains a challenge. Blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) is sensitive to changes in the effective transversal relaxation time (T(2)*) in vivo, is non-invasive and indicative of renal tissue oxygenation. However, the renal T(2)* to tissue pO(2) relationship is not governed exclusively by renal blood oxygenation, but is affected by physiological confounders with alterations in renal blood volume fraction (BVf) being of particular relevance. To decipher this interference probing renal BVf is essential for the pursuit of renal MR oximetry. Superparamagnetic iron oxide nanoparticle (USPIO) preparations can be used as MRI visible blood pool markers for detailing alterations in BVf. This review promotes the opportunities of MRI based assessment of renal BVf. Following an outline on the specifics of renal oxygenation and perfusion, changes in renal BVf upon interventions and their potential impact on renal T(2)* are discussed. We also describe the basic principles of renal BVf assessment using ferumoxytol enhanced MRI in the equilibrium concentration regime. We demonstrate that ferumoxytol does not alter control of renal haemodynamics and oxygenation. Preclinical applications of ferumoxytol enhanced renal MRI as well as considerations for its clinical implementation for examining renal BVf changes are provided alongside practical considerations. Finally, we explore the future directions of MRI based assessment of renal BVf
New transit observations for HAT-P-30 b, HAT-P-37 b, TrES-5 b, WASP-28 b, WASP-36 b, and WASP-39 b
We present new transit light curves for planets in six extrasolar planetary
systems. They were acquired with 0.4-2.2 m telescopes located in west Asia,
Europe, and South America. When combined with literature data, they allowed us
to redetermine system parameters in a homogeneous way. Our results for
individual systems are in agreement with values reported in previous studies.
We refined transit ephemerides and reduced uncertainties of orbital periods by
a factor between 2 and 7. No sign of any variations in transit times was
detected for the planets studied.Comment: Submitted to Acta Astronomic
Outbreak of encephalitic listeriosis in red-legged partridges (Alectoris rufa)
An outbreak of neurological disease was investigated in red-legged partridges between 8 and 28 days of age. Clinical signs included torticollis, head tilt and incoordination and over an initial eight day period approximately 30–40 fatalities occurred per day. No significant gross post mortem findings were detected. Histopathological examination of the brain and bacterial cultures followed by partial sequencing confirmed a diagnosis of encephalitis due to Listeria monocytogenes. Further isolates were obtained from follow-up carcasses, environmental samples and pooled tissue samples of newly imported day-old chicks prior to placement on farm. These isolates had the same antibiotic resistance pattern as the isolate of the initial post mortem submission and belonged to the same fluorescent amplified fragment length polymorphism (fAFLP) subtype. This suggested that the isolates were very closely related or identical and that the pathogen had entered the farm with the imported day-old chicks, resulting in disease manifestation in partridges between 8 and 28 days of age. Reports of outbreaks of encephalitic listeriosis in avian species are rare and this is to the best of our knowledge the first reported outbreak in red-legged partridges
Constraining the Distribution of L- & T-Dwarfs in the Galaxy
We estimate the thin disk scale height of the Galactic population of L- &
T-dwarfs based on star counts from 15 deep parallel fields from the Hubble
Space Telescope. From these observations, we have identified 28 candidate L- &
T- dwarfs based on their (i'-z') color and morphology. By comparing these star
counts to a simple Galactic model, we estimate the scale height to be 350+-50
pc that is consistent with the increase in vertical scale with decreasing
stellar mass and is independent of reddening, color-magnitude limits, and other
Galactic parameters. With this refined measure, we predict that less than 10^9
M_{sol} of the Milky Way can be in the form L- & T- dwarfs, and confirm that
high-latitude, z~6 galaxy surveys which use the i'-band dropout technique are
97-100% free of L- & T- dwarf interlopers.Comment: 4 pages, 4 figures, accepted to ApJ
Recommended from our members
Highly Specific, Bi-substrate-Competitive Src Inhibitors from DNA-Templated Macrocycles
Protein kinases are attractive therapeutic targets, but their high sequence and structural conservation complicates the development of specific inhibitors. We recently discovered from a DNA-templated macrocycle library inhibitors with unusually high selectivity among Src-family kinases. Starting from these compounds, we developed and characterized in molecular detail potent macrocyclic inhibitors of Src kinase and its cancer-associated gatekeeper mutant. We solved two co-crystal structures of macrocycles bound to Src kinase. These structures reveal the molecular basis of the combined ATP- and substrate peptide-competitive inhibitory mechanism and the remarkable kinase specificity of the compounds. The most potent compounds inhibit Src activity in cultured mammalian cells. Our work establishes that macrocycles can inhibit protein kinases through a bi-substrate competitive mechanism with high potency and exceptional specificity, reveals the precise molecular basis for their desirable properties, and provides new insights into the development of Src-specific inhibitors with potential therapeutic relevance.Chemistry and Chemical Biolog
Extrinsic intestinal denervation modulates tumor development in the small intestine of ApcMin/+ mice
Background Innervation interacts with enteric immune responses. Chronic
intestinal inflammation is associated with increased risk of colorectal
cancer. We aimed to study potential extrinsic neuronal modulation of
intestinal tumor development in a mouse model. Methods Experiments were
performed with male ApcMin/+ or wild type mice (4 weeks old, body weight
approximately 20 g). Subgroups with subdiaphragmatic vagotomy (apcV/wtV),
sympathetic denervation of the small intestine (apcS/wtS) or sham operated
controls (apcC/wtC) were investigated (n = 6-14 per group). Three months after
surgical manipulation, 10 cm of terminal ileum were excised, fixed for 48 h in
4% paraformaldehyde and all tumors were counted and their area determined in
mm2 (mean ± standard error of the mean (SEM)). Whole mounts of the muscularis
of terminal ileum and duodenum (internal positive control) were also stained
for tyrosine hydroxylase to confirm successful sympathetic denervation.
Results Tumor count in ApcMin/+ mice was 62 ± 8 (apcC), 46 ± 11 (apcV) and 54
± 8 (apcS) which was increased compared to wildtype controls with 4 ± 0.5
(wtC), 5 ± 0.5 (wtV) and 5 ± 0.6 (wtS; all p < 0.05). For ApcMin/+ groups,
vagotomized animals showed a trend towards decreased tumor counts compared to
sham operated ApcMin/+ controls while sympathetic denervation was similar to
sham ApcMin/+. Area covered by tumors in ApcMin/+ mice was 55 ± 10 (apcC), 31
± 8 (apcV) and 42 ± 8 (apcS) mm2, which was generally increased compared to
wildtype controls with 7 ± 0.6 (wtC), 7 ± 0.4 (wtV) and 7 ± 0.6 (wtS) mm2 (all
p < 0.05). In ApcMin/+ groups, tumor area was decreased in vagotomized animals
compared to sham operated controls (p < 0.05) while sympathetically denervated
mice showed a minor trend to decreased tumor area compared to controls.
Conclusions Extrinsic innervation of the small bowel is likely to modulate
tumor development in ApcMin/+ mice. Interrupted vagal innervation, but not
sympathetic denervation, seems to inhibit tumor growth
Transit Timing Analysis in the HAT-P-32 system
We present the results of 45 transit observations obtained for the transiting
exoplanet HAT-P-32b. The transits have been observed using several telescopes
mainly throughout the YETI network. In 25 cases, complete transit light curves
with a timing precision better than min have been obtained. These light
curves have been used to refine the system properties, namely inclination ,
planet-to-star radius ratio , and the ratio between
the semimajor axis and the stellar radius . First analyses by
Hartman et al. (2011) suggest the existence of a second planet in the system,
thus we tried to find an additional body using the transit timing variation
(TTV) technique. Taking also literature data points into account, we can
explain all mid-transit times by refining the linear ephemeris by 21ms. Thus we
can exclude TTV amplitudes of more than min.Comment: MNRAS accepted; 13 pages, 10 figure
- …