627,047 research outputs found
Dynamics and zeta functions on conformally compact manifolds
In this note, we study the dynamics and associated zeta functions of
conformally compact manifolds with variable negative sectional curvatures. We
begin with a discussion of a larger class of manifolds known as convex
co-compact manifolds with variable negative curvature. Applying results from
dynamics on these spaces, we obtain optimal meromorphic extensions of weighted
dynamical zeta functions and asymptotic counting estimates for the number of
weighted closed geodesics. A meromorphic extension of the standard dynamical
zeta function and the prime orbit theorem follow as corollaries. Finally, we
investigate interactions between the dynamics and spectral theory of these
spaces
Counting the ions surrounding nucleic acids.
Nucleic acids are strongly negatively charged, and thus electrostatic interactions-screened by ions in solution-play an important role in governing their ability to fold and participate in biomolecular interactions. The negative charge creates a region, known as the ion atmosphere, in which cation and anion concentrations are perturbed from their bulk values. Ion counting experiments quantify the ion atmosphere by measuring the preferential ion interaction coefficient: the net total number of excess ions above, or below, the number expected due to the bulk concentration. The results of such studies provide important constraints on theories, which typically predict the full three-dimensional distribution of the screening cloud. This article reviews the state of nucleic acid ion counting measurements and critically analyzes their ability to test both analytical and simulation-based models
The Number of Nowhere-Zero Flows on Graphs and Signed Graphs
A nowhere-zero -flow on a graph is a mapping from the edges of
to the set \{\pm1, \pm2, ..., \pm(k-1)\} \subset \bbZ such that, in
any fixed orientation of , at each node the sum of the labels over the
edges pointing towards the node equals the sum over the edges pointing away
from the node. We show that the existence of an \emph{integral flow polynomial}
that counts nowhere-zero -flows on a graph, due to Kochol, is a consequence
of a general theory of inside-out polytopes. The same holds for flows on signed
graphs. We develop these theories, as well as the related counting theory of
nowhere-zero flows on a signed graph with values in an abelian group of odd
order. Our results are of two kinds: polynomiality or quasipolynomiality of the
flow counting functions, and reciprocity laws that interpret the evaluations of
the flow polynomials at negative integers in terms of the combinatorics of the
graph.Comment: 17 pages, to appear in J. Combinatorial Th. Ser.
Counting geodesic loops on surfaces of genus at least 2 without conjugate points
In this paper we prove asymptotic estimates for closed geodesic loops on
compact surfaces with no conjugate points. These generalize the classical
counting results of Huber and Margulis and sector theorems for surfaces of
strictly negative curvature. We will also prove more general sector theorems,
generalizing results of Nicholls and Sharp for special case of surfaces of
strictly negative curvature
UriSed 3 PRO automated microscope in screening bacteriuria at region-wide laboratory organization
Background and aims: We assessed the possibility to rule out negative urine cultures by counting with UriSed 3 PRO (77 Elektmnika, Hungary) at Helsinki and Uusimaa Hospital District. Materials and methods: Bacteria counting of the UriSed 3 PRO automated microscope was verified with reference phase contrast microscopy against growth in culture. After acceptance into routine, results of bacteria and leukocyte counting from 56 426 specimens with eight UriSed 3 PRO instruments were compared against results from parallel samples cultured on chromogenic agar. Laboratory data including preanalytical details were accessed through the regional database of the Helsinki and Uusimaa Hospital District. Results: A combined sensitivity of 87-92% and a negative predictive value of 90-96% with a specificity of 54-50% was reached, depending on criteria. Preanalytical data (incubation time in bladder) combined with the way of urine collection would improve these figures if reliable. Conclusions: Complex patient populations, regional logistics and data interfases, and economics related to increased costs of additional particle counts against costs of screening cultures of all samples, did not support adaptation of a screening process of urine cultures. This conclusion was made locally, and may not be valid elsewhere.Peer reviewe
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