4,627 research outputs found
Multi-Player Diffusion Games on Graph Classes
We study competitive diffusion games on graphs introduced by Alon et al. [1]
to model the spread of influence in social networks. Extending results of
Roshanbin [8] for two players, we investigate the existence of pure Nash
equilibria for at least three players on different classes of graphs including
paths, cycles, grid graphs and hypercubes; as a main contribution, we answer an
open question proving that there is no Nash equilibrium for three players on (m
x n) grids with min(m, n) >= 5. Further, extending results of Etesami and Basar
[3] for two players, we prove the existence of pure Nash equilibria for four
players on every d-dimensional hypercube.Comment: Extended version of the TAMC 2015 conference version now discussing
hypercube results (added details for the proof of Proposition 1
Detecting periodicity in experimental data using linear modeling techniques
Fourier spectral estimates and, to a lesser extent, the autocorrelation
function are the primary tools to detect periodicities in experimental data in
the physical and biological sciences. We propose a new method which is more
reliable than traditional techniques, and is able to make clear identification
of periodic behavior when traditional techniques do not. This technique is
based on an information theoretic reduction of linear (autoregressive) models
so that only the essential features of an autoregressive model are retained.
These models we call reduced autoregressive models (RARM). The essential
features of reduced autoregressive models include any periodicity present in
the data. We provide theoretical and numerical evidence from both experimental
and artificial data, to demonstrate that this technique will reliably detect
periodicities if and only if they are present in the data. There are strong
information theoretic arguments to support the statement that RARM detects
periodicities if they are present. Surrogate data techniques are used to ensure
the converse. Furthermore, our calculations demonstrate that RARM is more
robust, more accurate, and more sensitive, than traditional spectral
techniques.Comment: 10 pages (revtex) and 6 figures. To appear in Phys Rev E. Modified
styl
Time transfer between the Goddard Optical Research Facility and the U.S. Naval Observatory using 100 picosecond laser pulses
A horizontal two-way time comparison link in air between the University of Maryland laser ranging and time transfer equipment at the Goddard Optical Research Facility (GORF) 1.2 m telescope and the Time Services Division of the U.S. Naval Observatory (USNO) was established. Flat mirrors of 25 cm and 30 cm diameter respectively were placed on top of the Washington Cathedral and on a water tower at the Beltsville Agricultural Research Center. Two optical corner reflectors at the USNO reflect the laser pulses back to the GORF. Light pulses of 100 ps duration and an energy of several hundred microjoules are sent at the rate of 10 pulses per second. The detection at the USNO is by means of an RCA C30902E avalanche photodiode and the timing is accomplished by an HP 5370A computing counter and an HP 1000 computer with respect to a 10 pps pulse train from the Master Clock
Individual psychological therapy in an acute inpatient setting : service user and psychologist perspectives
Objectives
The acute inpatient setting poses potential challenges to delivering oneâtoâone psychological therapy; however, there is little research on the experiences of both receiving and delivering therapies in this environment. This qualitative study aimed to explore service usersâ and psychologistsâ experiences of undertaking individual therapy in acute inpatient units. It focused on the relationship between service users and psychologists, what service users found helpful or unhelpful, and how psychologists attempted to overcome any challenges in delivering therapy.
Design
The study used a qualitative, interviewâbased design.
Methods
Eight service users and the six psychologists they worked with were recruited from four acute inpatient wards. They participated in individual semiâstructured interviews eliciting their perspectives on the therapy. Service usersâ and psychologistsâ transcripts were analysed together using Braun and Clarke's (2006, Qualitative Research in Psychology, 3, 77) method of thematic analysis.
Results
The accounts highlighted the importance of forming a âhumanâ relationship â particularly within the context of the inpatient environment â as a basis for therapeutic work. Psychological therapy provided valued opportunities for meaningâmaking. To overcome the challenges of acute mental health crisis and environmental constraints, psychologists needed to work flexibly and creatively; the therapeutic work also extended to the wider context of the inpatient unit, in efforts to promote a shared understanding of service usersâ difficulties.
Conclusions
Therapeutic relationships between service users and clinicians need to be promoted more broadly within acute inpatient care. Psychological formulation can help both service users and ward staff in understanding crisis and working collaboratively. Practiceâbased evidence is needed to demonstrate the effectiveness of adapted psychological therapy models
Enhancement of spontaneous and stimulated emission of a rhodamine 6G dye by an Ag aggregate
We have demonstrated that by adding the solution of aggregated silver nanoparticles to the solution of rhodamine 6G dye, one can enhance the efficiency of spontaneous and stimulated emission. We attribute an increase of the spontaneous emission intensity of dye to the increase of the absorption efficiency caused by the field enhancements in metallic nanostructures associated with surface plasmons. The enhancement of the stimulated emission of dye, which has the same nature as the enhancement of absorption, was observed in the pump-probe and laser experiments
Evolution of accretion disks around massive black holes: constraints from the demography of active galactic nuclei
Observations have shown that the Eddington ratios (the ratio of the
bolometric luminosity to the Eddington luminosity) in QSOs/active galactic
nuclei (AGNs) cover a wide range. In this paper we connect the demography of
AGNs obtained by the Sloan Digital Sky Survey with the accretion physics around
massive black holes and propose that the diversity in the Eddington ratios is a
natural result of the long-term evolution of accretion disks in AGNs. The
observed accretion rate distribution of AGNs (with host galaxy velocity
dispersion sigma~70-200 km/s) in the nearby universe (z<0.3) is consistent with
the predictions of simple theoretical models in which the accretion rates
evolve in a self-similar way. We also discuss the implications of the results
for the issues related to self-gravitating disks, coevolution of galaxies and
QSOs/AGNs, and the unification picture of AGNs.Comment: 18 pages, 2 figures; revised, main conclusions not changed; to appear
in ApJ, Oct., 200
The Local Universe as Seen in Far-Infrared and in Far-Ultraviolet: A Global Point of View on the Local Recent Star Formation
We select far-infrared (FIR-60 microns) and far-ultraviolet (FUV-1530 A)
samples of nearby galaxies in order to discuss the biases encountered by
monochromatic surveys (FIR or FUV). Very different volumes are sampled by each
selection and much care is taken to apply volume corrections to all the
analyses. The distributions of the bolometric luminosity of young stars are
compared for both samples: they are found to be consistent with each other for
galaxies of intermediate luminosities but some differences are found for high
(>5 10^{10} L_sun) luminosities. The shallowness of the IRAS survey prevents us
from securing comparison at low luminosities (<2 10^9 L_sun). The ratio of the
total infrared (TIR) luminosity to the FUV luminosity is found to increase with
the bolometric luminosity in a similar way for both samples up to 5 10^{10}
L_sun. Brighter galaxies are found to have a different behavior according to
their selection: the L_TIR/L_FUV ratio of the FUV-selected galaxies brighter
than 5 10^{10} L_sun reaches a plateau whereas L_TIR/L_FUV continues to
increase with the luminosity of bright galaxies selected in FIR. The
volume-averaged specific star formation rate (SFR per unit galaxy stellar mass,
SSFR) is found to decrease toward massive galaxies within each selection. The
SSFR is found to be larger than that measured for optical and NIR-selected
sample over the whole mass range for the FIR selection, and for masses larger
than 10^{10} M_sun for the FUV selection. Luminous and massive galaxies
selected in FIR appear as active as galaxies with similar characteristics
detected at z ~ 0.7.Comment: 32 pages, 9 figures, to be published in the Astrophysical Journal
Supplement series dedicated to GALEX result
Peculiar Broad Absorption Line Quasars found in DPOSS
With the recent release of large (i.e., > hundred million objects),
well-calibrated photometric surveys, such as DPOSS, 2MASS, and SDSS,
spectroscopic identification of important targets is no longer a simple issue.
In order to enhance the returns from a spectroscopic survey, candidate sources
are often preferentially selected to be of interest, such as brown dwarfs or
high redshift quasars. This approach, while useful for targeted projects, risks
missing new or unusual species. We have, as a result, taken the alternative
path of spectroscopically identifying interesting sources with the sole
criterion being that they are in low density areas of the g - r and r - i
color-space defined by the DPOSS survey. In this paper, we present three
peculiar broad absorption line quasars that were discovered during this
spectroscopic survey, demonstrating the efficacy of this approach. PSS
J0052+2405 is an Iron LoBAL quasar at a redshift z = 2.4512 with very broad
absorption from many species. PSS J0141+3334 is a reddened LoBAL quasar at z =
3.005 with no obvious emission lines. PSS J1537+1227 is a Iron LoBAL at a
redshift of z = 1.212 with strong narrow Mgii and Feii emission. Follow-up high
resolution spectroscopy of these three quasars promises to improve our
understanding of BAL quasars. The sensitivity of particular parameter spaces,
in this case a two-color space, to the redshift of these three sources is
dramatic, raising questions about traditional techniques of defining quasar
populations for statistical analysis.Comment: 27 pages, 13 figures, Accepted to the Astronomical Journa
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