1,942 research outputs found
Topographically specific effects of ELF-1 on retinal axon guidance in vitro and retinal axon mapping in vivo
Peer reviewedPublisher PD
A Push-Button Molecular Switch
The preparation, characterization, and switching mechanism of a unique single-station mechanically switchable hetero[2]catenane are reported. The facile synthesis utilizing a âthreading-followed-by-clippingâ protocol features Cu^(2+)-catalyzed Eglinton coupling as a mild and efficient route to the tetrathiafulvalene-based catenane in high yield. The resulting mechanically interlocked molecule operates as a perfect molecular switch, most readily described as a âpush-buttonâ switch, whereby two discrete and fully occupied translational states are toggled electrochemically at incredibly high rates. This mechanical switching was probed using a wide variety of experimental techniques as well as quantum-mechanical investigations. The fundamental distinctions between this single-station [2]catenane and other more traditional bi- and multistation molecular switches are significant
Are rotating strange quark stars good sources of gravitational waves?
We study the viscosity driven (Jacobi-like) bar mode instability of rapidly
rotating strange stars in general relativity. A triaxial, "bar shaped" compact
star could be an efficient source of continuous wave gravitational radiation in
the frequency range of the forthcoming interferometric detectors. We locate the
secular instability point along several constant baryon mass sequences of
uniformly rotating strange stars described by the MIT bag model. Contrary to
neutron stars, strange stars with T/|W| (the ratio of the rotational kinetic
energy to the absolute value of the gravitational potential energy) much lower
than the corresponding value for the mass-shed limit can be secularly unstable
to bar mode formation if shear viscosity is high enough to damp out any
deviation from uniform rotation. The instability develops for a broad range of
gravitational masses and rotational frequencies of strange quark stars. It
imposes strong constraints on the lower limit of the frequency at the innermost
stable circular orbit around rapidly rotating strange stars. The above results
are robust for all linear self-bound equations of state assuming the growth
time of the instability is faster than the damping timescale. We discuss
astrophysical scenarios where triaxial instabilities (r-mode and viscosity
driven instability) could be relevant in strange stars described by the
standard MIT bag model of normal quark matter. Taking into account actual
values of viscosities in strange quark matter and neglecting the magnetic field
we show that Jacobi-like instability cannot develop in any astrophysicaly
interesting temperature windows. The main result is that strange quark stars
described by the MIT bag model can be accelerated to very high frequency in Low
Mass X-ray binaries if the strange quark mass is ~ 200 MeV or higher.Comment: 15 pages, 10 figures, to appear in Astronomy and Astrophysic
Pricing Options in Incomplete Equity Markets via the Instantaneous Sharpe Ratio
We use a continuous version of the standard deviation premium principle for
pricing in incomplete equity markets by assuming that the investor issuing an
unhedgeable derivative security requires compensation for this risk in the form
of a pre-specified instantaneous Sharpe ratio. First, we apply our method to
price options on non-traded assets for which there is a traded asset that is
correlated to the non-traded asset. Our main contribution to this particular
problem is to show that our seller/buyer prices are the upper/lower good deal
bounds of Cochrane and Sa\'{a}-Requejo (2000) and of Bj\"{o}rk and Slinko
(2006) and to determine the analytical properties of these prices. Second, we
apply our method to price options in the presence of stochastic volatility. Our
main contribution to this problem is to show that the instantaneous Sharpe
ratio, an integral ingredient in our methodology, is the negative of the market
price of volatility risk, as defined in Fouque, Papanicolaou, and Sircar
(2000).Comment: Keywords: Pricing derivative securities, incomplete markets, Sharpe
ratio, correlated assets, stochastic volatility, non-linear partial
differential equations, good deal bound
Recommended from our members
Yeast require redox switching in DNA primase
Eukaryotic DNA primases contain a [4Fe4S] cluster in the C-terminal domain of the p58 subunit (p58C) that affects substrate affinity but is not required for catalysis. We show that, in yeast primase, the cluster serves as a DNA-mediated redox switch governing DNA binding, just as in human primase. Despite a different structural arrangement of tyrosines to facilitate electron transfer between the DNA substrate and [4Fe4S] cluster, in yeast, mutation of tyrosines Y395 and Y397 alters the same electron transfer chemistry and redox switch. Mutation of conserved tyrosine 395 diminishes the extent of p58C participation in normal redox-switching reactions, whereas mutation of conserved tyrosine 397 causes oxidative cluster degradation to the [3Fe4S]^+ species during p58C redox signaling. Switching between oxidized and reduced states in the presence of the Y397 mutations thus puts primase [4Fe4S] cluster integrity and function at risk. Consistent with these observations, we find that yeast tolerate mutations to Y395 in p58C, but the single-residue mutation Y397L in p58C is lethal. Our data thus show that a constellation of tyrosines for protein-DNA electron transfer mediates the redox switch in eukaryotic primases and is required for primase function in vivo
Parents' reported preference scores for childhood atopic dermatitis disease states
BACKGROUND: We sought to elicit preference weights from parents for health states corresponding to children with various levels of severity of atopic dermatitis. We also evaluated the hypothesis that parents with children who had been diagnosed with atopic dermatitis would assign different preferences to the health state scenarios compared with parents who did not have a child with atopic dermatitis. METHODS: Subjects were parents of children aged 3 months to 18 years. The sample was derived from the General Panel, Mommies Sub-Panel, and Chronic Illness Sub-Panel of Harris Interactive. Participants rated health scenarios for atopic dermatitis, asthma, and eyeglasses on a visual analog scale, imagining a child was experiencing the described state. RESULTS: A total of 3539 parents completed the survey. Twenty-nine percent had a child with a history of atopic dermatitis. Mean preference scores for atopic dermatitis were as follows: mild, 91 (95% confidence interval [CI], 90.7 to 91.5); mild/moderate, 84 (95%CI, 83.5 to 84.4); moderate, 73 (95%CI, 72.5 to 73.6); moderate/severe, 61 (95%CI, 60.6 to 61.8); severe, 49 (95% CI, 48.7 to 50.1); asthma, 58 (95%CI, 57.4 to 58.8); and eyeglasses, 87(95%CI, 86.3 to 87.4). CONCLUSIONS: Parents perceive that atopic dermatitis has a negative effect on quality of life that increases with disease severity. Estimates of parents' preferences can provide physicians with insight into the value that parents place on their children's treatment and can be used to evaluate new medical therapies for atopic dermatitis
Kinetic model of DNA replication in eukaryotic organisms
We formulate a kinetic model of DNA replication that quantitatively describes
recent results on DNA replication in the in vitro system of Xenopus laevis
prior to the mid-blastula transition. The model describes well a large amount
of different data within a simple theoretical framework. This allows one, for
the first time, to determine the parameters governing the DNA replication
program in a eukaryote on a genome-wide basis. In particular, we have
determined the frequency of origin activation in time and space during the cell
cycle. Although we focus on a specific stage of development, this model can
easily be adapted to describe replication in many other organisms, including
budding yeast.Comment: 10 pages, 6 figures: see also cond-mat/0306546 & physics/030615
- âŠ