31,703 research outputs found
Asteroseismology of the Scuti star HD 50844
Aims. We aim to probe the internal structure and investigate more detailed
information of the Scuti star HD 50844 with asteroseismology. Methods.
We analyse the observed frequencies of the Scuti star HD 50844
obtained by Balona (2014), and search for possible multiplets based on the
rotational splitting law of g-mode. We tried to disentangle the frequency
spectra of HD 50844 by means of the rotational splitting only. We then compare
them with theoretical pulsation modes, which correspond to stellar evolutionary
models with various sets of initial metallicity and stellar mass, to find the
best-fitting model. Results. There are three multiplets including two complete
triplets and one incomplete quintuplet, in which mode identifications for
spherical harmonic degree and azimuthal number are unique. The
corresponding rotational period of HD 50844 is found to be
2.44 days. The physical parameters of HD 50844 are well
limited in a small region by three modes identified as nonradial ones
(, , and ) and by the fundamental radial mode
(). Our results show that the three nonradial modes (, ,
and ) are all mixed modes, which mainly represent the property of the
helium core. The fundamental radial mode () mainly represents the
property of the stellar envelope. In order to fit these four pulsation modes,
both the helium core and the stellar envelope must be matched to the actual
structure of HD 50844. Finally, the mass of the helium core of HD 50844 is
estimated to be 0.173 0.004 for the first time. The physical
parameters of HD 50844 are determined to be 1.81 0.01 ,
0.008 0.001. 7508 125 K, log 3.658
0.004, 3.300 0.023 , 30.98 2.39 .Comment: 11 pages, 7 figures, 6 tables, accepted for publication in A&
Two-dimensional viscous flow computations of hypersonic scramjet nozzle flowfields at design and off-design conditions
The PARC2D code has been selected to analyze the flowfields of a representative hypersonic scramjet nozzle over a range of flight conditions from Mach 3 to 20. The flowfields, wall pressures, wall skin friction values, heat transfer values and overall nozzle performance are presented
The construction and evaluation of a word pronunciation test for grades four, five, and six
Thesis (Ed.M.)--Boston Universit
Binary Induced Neutron-Star Compression, Heating, and Collapse
We analyze several aspects of the recently noted neutron star collapse
instability in close binary systems. We utilize (3+1) dimensional and spherical
numerical general relativistic hydrodynamics to study the origin, evolution,
and parametric sensitivity of this instability. We derive the modified
conditions of hydrostatic equilibrium for the stars in the curved space of
quasi-static orbits. We examine the sensitivity of the instability to the
neutron star mass and equation of state. We also estimate limits to the
possible interior heating and associated neutrino luminosity which could be
generated as the stars gradually compress prior to collapse. We show that the
radiative loss in neutrinos from this heating could exceed the power radiated
in gravity waves for several hours prior to collapse. The possibility that the
radiation neutrinos could produce gamma-ray (or other electromagnetic) burst
phenomena is also discussed.Comment: 17 pages, 7 figure
Improved targeted outdoor advertising based on geotagged social media data
With as many as 4 million passenger journeys within the London Underground system every weekday, the advertisement spaces across the stations hold considerable potential. However, the planning of specific advertisements across time and space is difficult to optimize as little is known about passers-by. Therefore, in order to generate detailed and quantifiable spatio-temporal information which is particular to each station area, we have explored local social media data. This research demonstrates how local interests can be mined from geotagged Tweets by using Latent Dirichlet Allocation, an unsupervised topic modelling method. The relative popularity of each of the key topics is then explored spatially and temporally between the station areas. Overall, this research demonstrates the value of using Geographical Information System and text-mining techniques to generate valuable spatio-temporal information on popular interests from Twitter data
Exterior optical cloaking and illusions by using active sources: a boundary element perspective
Recently, it was demonstrated that active sources can be used to cloak any
objects that lie outside the cloaking devices [Phys. Rev. Lett. \textbf{103},
073901 (2009)]. Here, we propose that active sources can create illusion
effects, so that an object outside the cloaking device can be made to look like
another object. invisibility is a special case in which the concealed object is
transformed to a volume of air. From a boundary element perspective, we show
that active sources can create a nearly "silent" domain which can conceal any
objects inside and at the same time make the whole system look like an illusion
of our choice outside a virtual boundary. The boundary element method gives the
fields and field gradients (which can be related to monopoles and dipoles) on
continuous curves which define the boundary of the active devices. Both the
cloaking and illusion effects are confirmed by numerical simulations
Dynamic Range Majority Data Structures
Given a set of coloured points on the real line, we study the problem of
answering range -majority (or "heavy hitter") queries on . More
specifically, for a query range , we want to return each colour that is
assigned to more than an -fraction of the points contained in . We
present a new data structure for answering range -majority queries on a
dynamic set of points, where . Our data structure uses O(n)
space, supports queries in time, and updates in amortized time. If the coordinates of the points are integers,
then the query time can be improved to . For constant values of , this improved query
time matches an existing lower bound, for any data structure with
polylogarithmic update time. We also generalize our data structure to handle
sets of points in d-dimensions, for , as well as dynamic arrays, in
which each entry is a colour.Comment: 16 pages, Preliminary version appeared in ISAAC 201
General-relativistic coupling between orbital motion and internal degrees of freedom for inspiraling binary neutron stars
We analyze the coupling between the internal degrees of freedom of neutron
stars in a close binary, and the stars' orbital motion. Our analysis is based
on the method of matched asymptotic expansions and is valid to all orders in
the strength of internal gravity in each star, but is perturbative in the
``tidal expansion parameter'' (stellar radius)/(orbital separation). At first
order in the tidal expansion parameter, we show that the internal structure of
each star is unaffected by its companion, in agreement with post-1-Newtonian
results of Wiseman (gr-qc/9704018). We also show that relativistic interactions
that scale as higher powers of the tidal expansion parameter produce
qualitatively similar effects to their Newtonian counterparts: there are
corrections to the Newtonian tidal distortion of each star, both of which occur
at third order in the tidal expansion parameter, and there are corrections to
the Newtonian decrease in central density of each star (Newtonian ``tidal
stabilization''), both of which are sixth order in the tidal expansion
parameter. There are additional interactions with no Newtonian analogs, but
these do not change the central density of each star up to sixth order in the
tidal expansion parameter. These results, in combination with previous analyses
of Newtonian tidal interactions, indicate that (i) there are no large
general-relativistic crushing forces that could cause the stars to collapse to
black holes prior to the dynamical orbital instability, and (ii) the
conventional wisdom with respect to coalescing binary neutron stars as sources
of gravitational-wave bursts is correct: namely, the finite-stellar-size
corrections to the gravitational waveform will be unimportant for the purpose
of detecting the coalescences.Comment: 22 pages, 2 figures. Replaced 13 July: proof corrected, result
unchange
Single sample pathway analysis in metabolomics: performance evaluation and application
Background Single sample pathway analysis (ssPA) transforms molecular level omics data to the pathway level, enabling the discovery of patient-specific pathway signatures. Compared to conventional pathway analysis, ssPA overcomes the limitations by enabling multi-group comparisons, alongside facilitating numerous downstream analyses such as pathway-based machine learning. While in transcriptomics ssPA is a widely used technique, there is little literature evaluating its suitability for metabolomics. Here we provide a benchmark of established ssPA methods (ssGSEA, GSVA, SVD (PLAGE), and z-score) alongside the evaluation of two novel methods we propose: ssClustPA and kPCA, using semi-synthetic metabolomics data. We then demonstrate how ssPA can facilitate pathway-based interpretation of metabolomics data by performing a case-study on inflammatory bowel disease mass spectrometry data, using clustering to determine subtype-specific pathway signatures. Results While GSEA-based and z-score methods outperformed the others in terms of recall, clustering/dimensionality reduction-based methods provided higher precision at moderate-to-high effect sizes. A case study applying ssPA to inflammatory bowel disease data demonstrates how these methods yield a much richer depth of interpretation than conventional approaches, for example by clustering pathway scores to visualise a pathway-based patient subtype-specific correlation network. We also developed the sspa python package (freely available at https://pypi.org/project/sspa/), providing implementations of all the methods benchmarked in this study. Conclusion This work underscores the value ssPA methods can add to metabolomic studies and provides a useful reference for those wishing to apply ssPA methods to metabolomics data
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