4,283 research outputs found
A Turn-over in the Galaxy Luminosity Function of the Coma Cluster Core?
Our previous study of the faint end (R21.5) of the galaxy luminosity
function (GLF) was based on spectroscopic data in a small region near the Coma
cluster center. In this previous study Adami et al. (1998) suggested, with
moderate statistical significance, that the number of galaxies actually
belonging to the cluster was much smaller than expected. This led us to
increase our spectroscopic sample. Here, we have improved the statistical
significance of the results of the Coma GLF faint end study (R22.5) by
using a sample of 85 redshifts. This includes both new spectroscopic data and a
literature compilation. The relatively small number of faint galaxies belonging
to Coma that was suggested by Adami et al. (1998) and Secker et al. (1998) has
been confirmed with these new observations. We also confirm that the
color-magnitude relation is not well suited for finding the galaxies inside the
Coma cluster core, close to the center at magnitudes fainter than R19. We
show that there is an enhancement in the Coma line of sight of field galaxies
compared to classical field counts. This can be explained by the contribution
of groups and of a distant cluster along the line of sight. The
result is that the Coma GLF appears to turn-over or at least to become flat for
the faint galaxies. We suggest that this is due to environmental effects.Comment: 8 pages, 6 postscript figures, accepted in A&A, new table 1, updated
figure
Beyond Stereotypes of Adolescent Risk Taking: Placing the Adolescent Brain in Developmental Context
Recent neuroscience models of adolescent brain development attribute the morbidity and mortality of this period to structural and functional imbalances between more fully developed limbic regions that subserve reward and emotion as opposed to those that enable cognitive control. We challenge this interpretation of adolescent development by distinguishing risk-taking that peaks during adolescence (sensation seeking and impulsive action) from risk taking that declines monotonically from childhood to adulthood (impulsive choice and other decisions under known risk). Sensation seeking is primarily motivated by exploration of the environment under ambiguous risk contexts, while impulsive action, which is likely to be maladaptive, is more characteristic of a subset of youth with weak control over limbic motivation. Risk taking that declines monotonically from childhood to adulthood occurs primarily under conditions of known risks and reflects increases in executive function as well as aversion to risk based on increases in gist-based reasoning. We propose an alternative Lifespan Wisdom Model that highlights the importance of experience gained through exploration during adolescence. We propose, therefore, that brain models that recognize the adaptive roles that cognition and experience play during adolescence provide a more complete and helpful picture of this period of development
Multispeckle diffusing-wave spectroscopy: a tool to study slow relaxation and time-dependent dynamics
A multispeckle technique for efficiently measuring correctly
ensemble-averaged intensity autocorrelation functions of scattered light from
non-ergodic and/or non-stationary systems is described.
The method employs a CCD camera as a multispeckle light detector and a
computer-based correlator, and permits the simultaneous calculation of up to
500 correlation functions, where each correlation function is started at a
different time.
The correlation functions are calculated in real time and are referenced to a
unique starting time.
The multispeckle nature of the CCD camera detector means that a true ensemble
average is calculated; no time averaging is necessary.
The technique thus provides a "snapshot" of the dynamics, making it
particularly useful for non-stationary systems where the dynamics are changing
with time.
Delay times spanning the range from 1 ms to 1000 s are readily achieved with
this method.
The technique is demonstrated in the multiple scattering limit where
diffusing-wave spectroscopy theory applies.
The technique can also be combined with a recently-developed two-cell
technique that can measure faster decay times.
The combined technique can measure delay times from 10 ns to 1000 s.
The method is peculiarly well suited for studying aging processes in soft
glassy materials, which exhibit both short and long relaxation times,
non-ergodic dynamics, and slowly-evolving transient behavior.Comment: 11 pages 13 figures Accepted in Review of Scientific Instrument (june
02
Experimental realization of Lorentz boosts of space-time wave packets
It is now well-understood that a Lorentz boost of a spatially coherent
monochromatic optical beam yields a so-called space-time wave packet (STWP): a
propagation-invariant pulsed beam whose group velocity is determined by the
relative velocity between the source and observer. Moreover, the Lorentz boost
of an STWP is another STWP, whose group velocities are related by the
relativistic law for addition of velocities typically associated with massive
particles. We present an experimental procedure for testing this prediction in
both the subluminal and superluminal regimes that makes use of spatio-temporal
Fourier synthesis via a spatial light modulator. Our approach enables realizing
the change in temporal bandwidth, the invariance of the spatial bandwidth, the
concomitant change in the spatio-temporal wave-packet envelope, and the change
in group velocity that all accompany a Lorentz boost of a monochromatic optical
beam. The only consequence of the Lorentz boost not captured by this
methodology is the Doppler shift in the optical carrier. This work may provide
an avenue for further table-top demonstration of relativistic transformations
of optical fields.Comment: 13 pages, 10 figure
Alignment of patient and primary care practice member perspectives of chronic illness care: a cross-sectional analysis
Polly H. Noel and Luci K. Leykum are with the South Texas Veterans Health Care System, 7400 Merton Minter Blvd, San Antonio, TX 78229, USA -- Polly H. Noel, Ray F. Palmer, Raquel L. Romero, Luci K. Leykum, Holly J. Lanham, and Krista W. Bowers are with the Department of Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78229, USA -- Michael L. Parchman is with the MacColl Center for Healthcare Innovation, Group Health Research Institute, Group Health Cooperative, 1730 Minor Ave 1600, Seattle, WA 98101, USA -- Holly J. Leykum is with the The McCombs School of Business, The University of Texas at Austin, 2110 Speedway, Stop B6000, Austin, TX 78712, USA -- John E. Zeber is with the Central Texas Veterans Health Care System, 1901 S. 1st St, Temple, TX 76504, USA and Scott and White Healthcare Center for Applied Health Research, 2401 S. 31st St, Temple, TX 76508, USABackground: Little is known as to whether primary care teams’ perceptions of how well they have implemented the Chronic Care Model (CCM) corresponds with their patients’ own experience of chronic illness care. We examined the extent to which practice members’ perceptions of how well they organized to deliver care consistent with the CCM were associated with their patients’ perceptions of the chronic illness care they have received. Methods: Analysis of baseline measures from a cluster randomized controlled trial testing a practice facilitation intervention to implement the CCM in small, community-based primary care practices. All practice “members” (i.e., physician providers, non-physician providers, and staff) completed the Assessment of Chronic Illness Care (ACIC) survey and adult patients with 1 or more chronic illnesses completed the Patient Assessment of Chronic Illness Care (PACIC) questionnaire. Results: Two sets of hierarchical linear regression models accounting for nesting of practice members (N = 283) and patients (N = 1,769) within 39 practices assessed the association between practice member perspectives of CCM implementation (ACIC scores) and patients’ perspectives of CCM (PACIC). ACIC summary score was not significantly associated with PACIC summary score or most of PACIC subscale scores, but four of the ACIC subscales were consistently associated with PACIC summary score and the majority of PACIC subscale scores after controlling for patient characteristics. The magnitude of the coefficients, however, indicates that the level of association is weak. Conclusions: The ACIC and PACIC scales appear to provide complementary and relatively unique assessments of how well clinical services are aligned with the CCM. Our findings underscore the importance of assessing both patient and practice member perspectives when evaluating quality of chronic illness care.Information, Risk, and Operations Management (IROM)[email protected]
An extension of the SHARC survey
We report on our search for distant clusters of galaxies based on optical and
X-ray follow up observations of X-ray candidates from the SHARC survey. Based
on the assumption that the absence of bright optical or radio counterparts to
possibly extended X-ray sources could be distant clusters. We have obtained
deep optical images and redshifts for several of these objects and analyzed
archive XMM-Newton or Chandra data where applicable. In our list of candidate
clusters, two are probably galaxy structures at redshifts of z0.51 and
0.28. Seven other structures are possibly galaxy clusters between z0.3
and 1. Three sources are identified with QSOs and are thus likely to be X-ray
point sources, and six more also probably fall in this category. One X-ray
source is spurious or variable. For 17 other sources, the data are too sparse
at this time to put forward any hypothesis on their nature. We also
serendipitously detected a cluster at z=0.53 and another galaxy concentration
which is probably a structure with a redshift in the [0.15-0.6] range. We
discuss these results within the context of future space missions to
demonstrate the necessity of a wide field of view telescope optimized for the
0.5-2 keV range.Comment: Accepted in A&
Linear Momentum Density in Quasistatic Electromagnetic Systems
We discuss a couple of simple quasistatic electromagnetic systems in which
the density of electromagnetic linear momentum can be easily computed. The
examples are also used to illustrate how the total electromagnetic linear
momentum, which may also be calculated by using the vector potential, can be
understood as a consequence of the violation of the action-reaction principle,
because a non-null external force is required to maintain constant the
mechanical linear momentum. We show how one can avoid the divergence in the
interaction linear electromagnetic momentum of a system composed by an
idealization often used in textbooks (an infinite straight current) and a point
charge.Comment: 22 pages, 5 figures, to appear in Eur. J. Phy
Spectroscopic Observations of Optically Selected Clusters of Galaxies from the Palomar Distant Cluster Survey
We have conducted a redshift survey of sixteen cluster candidates from the
Palomar Distant Cluster Survey (PDCS) to determine both the density of PDCS
clusters and the accuracy of the estimated redshifts presented in the PDCS
catalog (Postman et. al. 1996). We find that the matched-filter redshift
estimate presented in the PDCS has an error sigma_z = 0.06 in the redshift
range 0.1 < z < 0.35 based on eight cluster candidates with three or more
concordant galaxy redshifts.
We measure the low redshift (0.1 < z < 0.35) space density of PDCS clusters
to be 31.3^{+30.5}_{-17.1} * E-06 h^3 Mpc^-3 (68% confidence limits for a
Poisson distribution) for Richness Class 1 systems. We find a tentative space
density of 10.4^{+23.4}_{-8.4}* E-06 h^3 Mpc^-3 for Richness Class 2 clusters.
These densities compare favorably with those found for the whole of the PDCS
and support the finding that the space density of clusters in the PDCS is a
factor of ~5 above that of clusters in the Abell catalog (Abell 1958; Abell,
Corwin, and Olowin 1989). These new space density measurements were derived as
independently as possible from the original PDCS analysis and therefore,
demonstrate the robustness of the original work. Based on our survey, we
conclude that the PDCS matched-filter algorithm is successful in detecting real
clusters and in estimating their true redshifts in the redshift range we
surveyed.Comment: 23 pages with 4 figures and 3 seperate tables. To be published in the
November Issue of the Astronomical Journa
Assessment of Connections Between Knowledge- Based Economy Characteristics and Selected Macroeconomic Categories in the European Union's Countries by Means of Panel Models
The aim of the article is to analyze the impact of knowledge-based economy variables on the selected macroeconomic categories - the share of total investments in GDP and the employment rate- in European Union's countries in the years 2000-2007, conducted with application of panel models.Celem artykułu jest analiza wpływu zmiennych opisujących gospodarkę opartą na wiedzy na podstawowe kategorie makroekonomiczne - udział całkowitych inwestycji w PKB i stopę zatrudnienia - w krajach Unii Europejskiej (z podziałem na kraje UE-15 i nowe kraje członkowskie UE) w latach 2000-2007, przeprowadzona w oparciu o modele panelowe
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