5,692 research outputs found
Computing the distribution of a tree metric
The Robinson-Foulds (RF) distance is by far the most widely used measure of dissimilarity between trees. Although the distribution of these distances has been investigated for twenty years, an algorithm that is explicitly polynomial time has yet to be described for computing this distribution (which is also the dis- tribution of trees around a given tree under the popular Robinson-Foulds metric). In this paper we derive a polynomial-time algorithm for this distribution. We show how the distribution can be approximated by a Poisson distribution determined by the proportion of leaves that lie in âcherriesâ of the given tree. We also describe how our results can be used to derive normalization constants that are required in a recently-proposed maximum likelihood approach to supertree construction
A Frobenius variant of Seshadri constants
We define and study a version of Seshadri constant for ample line bundles in
positive characteristic. We prove that lower bounds for this constant imply the
global generation or very ampleness of the corresponding adjoint line bundle.
As a consequence, we deduce that the criterion for global generation and very
ampleness of adjoint line bundles in terms of usual Seshadri constants holds
also in positive characteristic.Comment: 16 page
Flux control of cytochrome c oxidase in human skeletal muscle
In the present work, by titrating cytochrome c oxidase (COX) with the specific inhibitor KCN, the flux control coefficient and the metabolic reserve capacity of COX have been determined in human saponin-permeabilized muscle fibers. In the presence of the substrates glutamate and malate, a 2.3 ± 0.2-fold excess capacity of COX was observed in ADP-stimulated human skeletal muscle fibers. This value was found to be dependent on the mitochondrial substrate supply. In the combined presence of glutamate, malate, and succinate, which supported an approximately 1.4-fold higher rate of respiration, only a 1.4 ± 0.2-fold excess capacity of COX was determined. In agreement with these findings, the flux control of COX increased, in the presence of the three substrates, from 0.27 ± 0.03 to 0.36 ± 0.08. These results indicate a tight in vivo control of respiration by COX in human skeletal muscle. This tight control may have significant implications for mitochondrial myopathies. In support of this conclusion, the analysis of skeletal muscle fibers from two patients with chronic progressive external ophthalmoplegia, which carried deletions in 11 and 49% of their mitochondrial DNA, revealed a substantially lowered reserve capacity and increased flux control coefficient of COX, indicating severe rate limitations of oxidative phosphorylation by this enzyme
The GTC exoplanet transit spectroscopy survey. VI. A spectrally-resolved Rayleigh scattering slope in GJ 3470b
Aims. As a sub-Uranus-mass low-density planet, GJ 3470b has been found to
show a flat featureless transmission spectrum in the infrared and a tentative
Rayleigh scattering slope in the optical. We conducted an optical transmission
spectroscopy project to assess the impacts of stellar activity and to determine
whether or not GJ 3470b hosts a hydrogen-rich gas envelop. Methods. We observed
three transits with the low-resolution OSIRIS spectrograph at the 10.4 m Gran
Telescopio Canarias, and one transit with the high-resolution UVES spectrograph
at the 8.2 m Very Large Telescope. Results. From the high-resolution data, we
find that the difference of the Ca II H+K lines in- and out-of-transit is only
0.67 +/- 0.22%, and determine a magnetic filling factor of about 10-15%. From
the low-resolution data, we present the first optical transmission spectrum in
the 435-755 nm band, which shows a slope consistent with Rayleigh scattering.
Conclusions. After exploring the potential impacts of stellar activity in our
observations, we confirm that Rayleigh scattering in an extended
hydrogen/helium atmosphere is currently the best explanation. Further
high-precision observations that simultaneously cover optical and infrared
bands are required to answer whether or not clouds and hazes exist at
high-altitude.Comment: 12 pages, 11 figures, accepted for publication in A&
Asymmetric gate induced drain leakage and body leakage in vertical MOSFETs with reduced parasitic capacitance
Vertical MOSFETs, unlike conventional planar MOSFETs, do not have identical structures at the source and drain, but have very different gate overlaps and geometric configurations. This paper investigates the effect of the asymmetric source and drain geometries of surround-gate vertical MOSFETs on the drain leakage currents in the OFF-state region of operation. Measurements of gate-induced drain leakage (GIDL) and body leakage are carried out as a function of temperature for transistors connected in the drain-on-top and drain-on-bottom configurations. Asymmetric leakage currents are seen when the source and drain terminals are interchanged, with the GIDL being higher in the drain-on-bottom configuration and the body leakage being higher in the drain-on-top configuration. Band-to-band tunneling is identified as the dominant leakage mechanism for both the GIDL and body leakage from electrical measurements at temperatures ranging from ?50 to 200?C. The asymmetric body leakage is explained by a difference in body doping concentration at the top and bottom drainâbody junctions due to the use of a p-well ion implantation. The asymmetric GIDL is explained by the difference in gate oxide thickness on the vertical (110) pillar sidewalls and the horizontal (100) wafer surface
General approach for studying first-order phase transitions at low temperatures
By combining different ideas, a general and efficient protocol to deal with
discontinuous phase transitions at low temperatures is proposed. For small
's, it is possible to derive a generic analytic expression for appropriate
order parameters, whose coefficients are obtained from simple simulations. Once
in such regimes simulations by standard algorithms are not reliable, an
enhanced tempering method, the parallel tempering -- accurate for small and
intermediate system sizes with rather low computational cost -- is used.
Finally, from finite size analysis, one can obtain the thermodynamic limit. The
procedure is illustrated for four distinct models, demonstrating its power,
e.g., to locate coexistence lines and the phases density at the coexistence.Comment: 5 page
Rotating Boson Stars in 5 Dimensions
We study rotating boson stars in five spacetime dimensions. The boson fields
consist of a complex doublet scalar field. Considering boson stars rotating in
two orthogonal planes with both angular momenta of equal magnitude, a special
ansatz for the boson field and the metric allows for solutions with nontrivial
dependence on the radial coordinate only. The charge of the scalar field equals
the sum of the angular momenta. The rotating boson stars are globally regular
and asymptotically flat. For our choice of a sixtic potential the rotating
boson star solutions possess a flat spacetime limit. We study the solutions in
flat and curved spacetime.Comment: 17 pages, 6 figure
Estimating fixed effects: perfect prediction and bias in binary response panel models, with an application to the hospital readmissions reduction program
The maximum likelihood estimator for the regression coefficients, ÎČ, in a panel binary response model with fixed effects can be severely biased if N is large and T is small, a consequence of the incidental parameters problem. This has led to the development of conditional maximum likelihood estimators and, more recently, to estimators that remove the O(Tâ1) bias in ÎČ^. We add to this literature in two important ways. First, we focus on estimation of the fixed effects proper, as these have become increasingly important in applied work. Second, we build on a bias-reduction approach originally developed by Kosmidis and Firth (2009) for cross-section data, and show that in contrast to other proposals, the new estimator ensures finiteness of the fixed effects even in the absence of within-unit variation in the outcome. Results from a simulation study document favourable small sample properties. In an application to hospital data on patient readmission rates under the 2010 Affo
O(N) and RP^{N-1} Models in Two Dimensions
I provide evidence that the 2D model for is equivalent
to the -invariant non-linear -model in the continuum limit. To
this end, I mainly study particular versions of the models, to be called
constraint models. I prove that the constraint and models are
equivalent for sufficiently weak coupling. Numerical results for their
step-scaling function of the running coupling are
presented. The data confirm that the constraint model is in the samei
universality class as the model with standard action. I show that the
differences in the finite size scaling curves of i and models
observed by Caracciolo et al. can be explained as a boundary effect. It is
concluded, in contrast to Caracciolo et al., that and models
share a unique universality class.Comment: 14 pages (latex) + 1 figure (Postscript) ,uuencode
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