1,647 research outputs found
Red-giant stars in eccentric binaries
The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to improved understanding of red-giant stars and binary stars. We discuss the characterization of known eccentric system, containing a solar-like oscillating red-giant primary component. We also report several new binary systems that are candidates for hosting an oscillating companion. A powerful approach to study binary stars is to combine asteroseimic techniques with light curve fitting. Seismology allows us to deduce the properties of red giants. In addition, by modeling the ellipsoidal modulations we can constrain the parameters of the binary system. An valuable independent source are ground-bases, high-resolution spectrographs
The fatigue performance of electrofusion tapping tees subject to contamination
Electrofusion jointing is a common joint process used to weld polyethylene (PE) water pipe in the UK. For many years, the UK Water Industry has experienced a small number of premature failures of electrofusion fittings; this inevitably causes leakage. The common causes of critical failures have been highlighted and as a result of this, a testing programme was designed and implemented to assess the fatigue performance of electrofusion tapping tees if they were to be installed by ‘bad practice’. A fine china talc was used to replicate contamination in the field. The results suggest that failures associated with fatigue are possible in a relatively short space of time on tapping tees when they are subject to contamination. The pressure ranges used in the fatigue regime aimed to replicate the potential magnitude of surge pressures that can be experienced in water distribution mains
Experiment and modelling of birefringent flows using commercial CFD code
It is well-known that certain fluids are birefringent and when flows are viewed in polarised light interference fringes are observed. The fringes are caused by a phase shift in the light passing through the fluid and are proportional to the integral of the maximum shear strains in the fluid. In order to understand what is happening within the three dimensional flow and overcome the difficulties due to this integration, additional computational or experimental information is needed. In this work, a commercially available computer code (Fluent) is used for the first time to model the flows. The flow data are then exported to a spreadsheet where the shear rates are integrated across the field and then banded for graphical output. The results from this are then compared to results generated from birefringent flow experiments and the agreement is found to be good since the modelled fringes show the same patterns as those in the experiment. This novel use of computational and experimental techniques together will allow quantitative analysis of three-dimensional flows in the future. Currently, there are still a lot of empirical variables involved in fitting the computational fringes to the experiment, but the results of this preliminary study show that this is a promising approach to this type of problem
Finding non-eclipsing binaries through pulsational phase modulation
We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire four-year light curves to accurately mea- sure the frequencies of the strongest pulsation modes, then track the pulsation phases at those frequencies in 10-d segments. This produces a series of time-delay measurements in which binarity is apparent as a periodic modulation whose amplitude gives the projected light travel time across the orbit. Fourier analysis of this time-delay curve provides the pa- rameters of the orbit, including the period, eccentricity, angle of ascending node and time
of periastron passage. Differentiating the time-delay curve yields the full radial-velocity
curve directly from the Kepler photometry, without the need for spectroscopy. We show examples with delta Scuti stars having large numbers of pulsation modes, including one system in which both components of the binary are pulsating. The method is straightfor- ward to automate, thus radial velocity curves can be derived for hundreds of non-eclipsing binary stars from Kepler photometry alone.
This contribution is based largely upon the work by Murphy et al. [1], describing the phase-modulation method in detail
The inverse moment problem for convex polytopes
The goal of this paper is to present a general and novel approach for the
reconstruction of any convex d-dimensional polytope P, from knowledge of its
moments. In particular, we show that the vertices of an N-vertex polytope in
R^d can be reconstructed from the knowledge of O(DN) axial moments (w.r.t. to
an unknown polynomial measure od degree D) in d+1 distinct generic directions.
Our approach is based on the collection of moment formulas due to Brion,
Lawrence, Khovanskii-Pukhikov, and Barvinok that arise in the discrete geometry
of polytopes, and what variously known as Prony's method, or Vandermonde
factorization of finite rank Hankel matrices.Comment: LaTeX2e, 24 pages including 1 appendi
Streaming algorithms for 2-coloring uniform hypergraphs
We consider the problem of two-coloring n-uniform hypergraphs. It is known that any such hypergraph with at most 1/10√n/ln n 2n hyperedges can be two-colored [7]. In fact, there is an efficient (requiring polynomial time in the size of the input) randomized algorithm that produces such a coloring. As stated [7], this algorithm requires random access to the hyperedge set of the input hypergraph. In this paper, we show that a variant of this algorithm can be implemented in the streaming model (with just one pass over the input), using space O(|V|B), where V is the vertex set of the hypergraph and each vertex is represented by B bits. (Note that the number of hyperedges in the hypergraph can be superpolynomial in |V|, and it is not feasible to store the entire hypergraph in memory.) We also consider the question of the minimum number of hyperedges in non-two-colorable n-uniform hypergraphs. Erdos showed that there exist non-2-colorable n-uniform hypegraphs with O(n2 2n) hyperedges and Θ(n2) vertices. We show that the choice Θ(n2) for the number of vertices in Erdös's construction is crucial: any hypergraph with at most 2n2/t vertices and 2nexp(t/8) hyperedges is 2-colorable. (We present a simple randomized streaming algorithm to construct the two-coloring.) Thus, for example, if the number of vertices is at most n1.5, then any non-2-colorable hypergraph must have at least 2n exp(√n/8) » n22n hyperedges. We observe that the exponential dependence on t in our result is optimal up to constant factors
Effective action approach and Carlson-Goldman mode in d-wave superconductors
We theoretically investigate the Carlson-Goldman (CG) mode in two-dimensional
clean d-wave superconductors using the effective ``phase only'' action
formalism. In conventional s-wave superconductors, it is known that the CG mode
is observed as a peak in the structure factor of the pair susceptibility
only just below the transition temperature T_c and only
in dirty systems. On the other hand, our analytical results support the
statement by Y.Ohashi and S.Takada, Phys.Rev.B {\bf 62}, 5971 (2000) that in
d-wave superconductors the CG mode can exist in clean systems down to the much
lower temperatures, . We also consider the manifestations of
the CG mode in the density-density and current-current correlators and discuss
the gauge independence of the obtained results.Comment: 23 pages, RevTeX4, 12 EPS figures; final version to appear in PR
Dynamical model and nonextensive statistical mechanics of a market index on large time windows
The shape and tails of partial distribution functions (PDF) for a financial
signal, i.e. the S&P500 and the turbulent nature of the markets are linked
through a model encompassing Tsallis nonextensive statistics and leading to
evolution equations of the Langevin and Fokker-Planck type. A model originally
proposed to describe the intermittent behavior of turbulent flows describes the
behavior of normalized log-returns for such a financial market index, for small
and large time windows, both for small and large log-returns. These turbulent
market volatility (of normalized log-returns) distributions can be sufficiently
well fitted with a -distribution. The transition between the small time
scale model of nonextensive, intermittent process and the large scale Gaussian
extensive homogeneous fluctuation picture is found to be at a 200 day
time lag. The intermittency exponent () in the framework of the
Kolmogorov log-normal model is found to be related to the scaling exponent of
the PDF moments, -thereby giving weight to the model. The large value of
points to a large number of cascades in the turbulent process. The
first Kramers-Moyal coefficient in the Fokker-Planck equation is almost equal
to zero, indicating ''no restoring force''. A comparison is made between
normalized log-returns and mere price increments.Comment: 40 pages, 14 figures; accepted for publication in Phys Rev
A Prospective Multicenter SPOG 2003 FN Study of Microbiologically Defined Infections in Pediatric Cancer Patients with Fever and Neutropenia.
BACKGROUND: Fever and neutropenia (FN) often complicate anticancer treatment and can be caused by potentially fatal infections. Knowledge of pathogen distribution is paramount for optimal patient management.
METHODS: Microbiologically defined infections (MDI) in pediatric cancer patients presenting with FN by nonmyeloablative chemotherapy enrolled in a prospective multi-center study were analyzed. Effectiveness of empiric antibiotic therapy in FN episodes with bacteremia was assessed taking into consideration recently published treatment guidelines for pediatric patients with FN.
RESULTS: MDI were identified in a minority (22%) of pediatric cancer patients with FN. In patients with, compared to without MDI, fever (median, 5 [IQR 3-8] vs. 2 [IQR1-3] days, p < 0.001) and hospitalization (10 [6-14] vs. 5 [3-8] days, p < 0.001) lasted longer, transfer to the intensive care unit was more likely (13 of 95 [14%] vs. 7 of 346 [2.0%], p < 0.001), and antibiotics were given longer (10 [7-14] vs. 5 [4-7], p < 0.001). Empiric antibiotic therapy in FN episodes with bacteremia was highly effective if not only intrinsic and reported antimicrobial susceptibilities were considered but the purposeful omission of coverage for coagulase negative staphylococci and enterococci was also taken into account (81% [95%CI 68 - 90] vs. 96.6% [95%CI 87 - 99.4], p = 0.004) CONCLUSIONS: MDI were identified in a minority of FN episodes but they significantly affected management and the clinical course of pediatric cancer patients. Compliance with published guidelines was associated with effectiveness of empiric antibiotic therapy in FN episodes with bacteremia
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