12,081 research outputs found
The Measure of Poverty: A Boston Indicators Project Special Report
Examines Boston's poverty rate by race/ethnicity, family structure, education, and geography; income inequality; demand for safety-net programs; and how the high cost of living and budget cuts affect vulnerable households and those below the poverty line
City of Ideas: Reinventing Boston's Innovation Economy: The Boston Indicators Report 2012
Analyzes indicators of the city's economic, social, and technological progress; potential for creating innovative solutions to global and national challenges; and complexities, disparities, and weaknesses in the indicators and innovation economy paradigm
Formation of the First Stars by Accretion
The process of star formation from metal-free gas is investigated by
following the evolution of accreting protostars with emphasis on the properties
of massive objects. The main aim is to establish the physical processes that
determine the upper mass limit of the first stars. Although the consensus is
that massive stars were commonly formed in the first cosmic structures, our
calculations show that their actual formation depends sensitively on the mass
accretion rate and its time variation. Even in the rather idealized case in
which star formation is mainly determined by dot{M}acc, the characteristic mass
scale of the first stars is rather uncertain. We find that there is a critical
mass accretion rate dot{M}crit = 4 10^{-3} Msun/yr that separates solutions
with dot{M}acc> 100 Msun can form,
provided there is sufficient matter in the parent clouds, from others
(dot{M}acc > dot{M}crit) where the maximum mass limit decreases as dot{M}acc
increases. In the latter case, the protostellar luminosity reaches the
Eddington limit before the onset of hydrogen burning at the center via the
CN-cycle. This phase is followed by a rapid and dramatic expansion of the
radius, possibly leading to reversal of the accretion flow when the stellar
mass is about 100Msun. (abridged)Comment: 34 pages, 12 figures. ApJ, in pres
A DMRG Study of Low-Energy Excitations and Low-Temperature Properties of Alternating Spin Systems
We use the density matrix renormalization group (DMRG) method to study the
ground and low-lying excited states of three kinds of uniform and dimerized
alternating spin chains. The DMRG procedure is also employed to obtain
low-temperature thermodynamic properties of these systems. We consider a 2N
site system with spins and alternating from site to site and
interacting via a Heisenberg antiferromagnetic exchange. The three systems
studied correspond to being equal to and
; all of them have very similar properties. The ground state is found
to be ferrimagnetic with total spin . We find that there is
a gapless excitation to a state with spin , and a gapped excitation to
a state with spin . Surprisingly, the correlation length in the ground
state is found to be very small for this gapless system. The DMRG analysis
shows that the chain is susceptible to a conditional spin-Peierls instability.
Furthermore, our studies of the magnetization, magnetic susceptibility
and specific heat show strong magnetic-field dependences. The product
shows a minimum as a function of temperature T at low magnetic fields; the
minimum vanishes at high magnetic fields. This low-field behavior is in
agreement with earlier experimental observations. The specific heat shows a
maximum as a function of temperature, and the height of the maximum increases
sharply at high magnetic fields. Although all the three systems show
qualitatively similar behavior, there are some notable quantitative differences
between the systems in which the site spin difference, , is large
and small respectively.Comment: 16 LaTeX pages, 13 postscript figure
Electronic structure of the molecule based magnet Cu PM(NO3)2 (H2O)2
We present density functional calculations on the molecule based S=1/2
antiferromagnetic chain compound Cu PM(NO3)2 (H2O)2; PM = pyrimidine. The
properties of the ferro- and antiferromagnetic state are investigated at the
level of the local density approximation and with the hybrid functional B3LYP.
Spin density maps illustrate the exchange path via the pyrimidine molecule
which mediates the magnetism in the one-dimensional chain. The computed
exchange coupling is antiferromagnetic and in reasonable agreement with the
experiment. It is suggested that the antiferromagnetic coupling is due to the
possibility of stronger delocalization of the charges on the nitrogen atoms,
compared to the ferromagnetic case. In addition, computed isotropic and
anisotropic hyperfine interaction parameters are compared with recent NMR
experiments
Boston's Education Pipeline: A Report Card
Assesses the city's progress in creating an effective and equitable education pipeline from early childhood through college or postsecondary training. Examines demographic and outcome data and risk and prevention factors, and notes areas for improvement
Semiclassical corrections to the interaction energy of a hard-sphere Boltzmann gas
Quantum effects in statistical mechanics are important when the thermal
wavelength is of the order of, or greater than, the mean interatomic spacing.
This is examined at depth taking the example of a hard-sphere Boltzmann gas.
Using the virial expansion for the equation of state, it is shown that the
interaction energy of a classical hard-sphere gas is exactly zero. When the
(second) virial coefficient of such a gas is obtained quantum mechanically,
however, the quantum contribution to the interaction energy is shown to be
substantial. The importance of the semiclassical corrections to the interaction
energy shows up dramatically in such a system.Comment: 9 pages, 3 figures, submitted to Eur. J. Phy
Assessing health and well-being among older people in rural South Africa
Background: The population in developing countries is ageing, which is likely to increase the burden of noncommunicable diseases and disability.
Objective: To describe factors associated with self-reported health, disability and quality of life (QoL) of older people in the rural northeast of South Africa.
Design: Cross-sectional survey of 6,206 individuals aged 50 and over. We used multivariate analysis to examine relationships between demographic variables and measures of self-reported health (Health Status), functional ability (WHODASi) and quality of life (WHOQoL).
Results: About 4,085 of 6,206 people eligible (65.8%) completed the interview. Women (Odds Ratio (OR)
1.30, 95% CI 1.09, 1.55), older age (OR2.59, 95% CI 1.97, 3.40), lower education (OR1.62, 95% CI 1.31,2.00), single status (OR1.18, 95% CI 1.01, 1.37) and not working at present (OR1.29, 95% CI 1.06, 1.59) were associated with a low health status. Women were also more likely to report a higher level of disability (OR1.38, 95% CI 1.14, 1.66), as were older people (OR2.92, 95% CI 2.25, 3.78), those with no education (OR1.57, 95% CI 1.26, 1.97), with single status (OR1.25, 95% CI 1.06, 1.46) and not working at present (OR1.33, 95% CI 1.06, 1.66). Older age (OR1.35, 95% CI 1.06, 1.74), no education (OR1.39, 95% CI
1.11, 1.73), single status (OR1.28, 95% CI 1.10, 1.49), a low household asset score (OR1.52, 95% CI 1.19,
1.94) and not working at present (OR1.32; 95% CI 1.07, 1.64) were all associated with lower quality of life.
Conclusions: This study presents the first population-based data from South Africa on health status, functional ability and quality of life among older people. Health and social services will need to be restructured to provide effective care for older people living in rural South Africa with impaired functionality and other health problems
When do high and low status group members support confrontation? The role of perceived pervasiveness of prejudice
This paper examines how perceived pervasiveness of prejudice differentially affects high and low status group members' support for a low status group member who confronts. In Experiment 1 (N=228), men and women read a text describing sexism as rare or as pervasive and subsequently indicated their support for a woman who confronted or did not confront a sexist remark. Experiment 2 (N=324) specified the underlying process using a self-affirmation manipulation. Results show that men were more supportive of confrontation when sexism was perceived to be rare than when it was pervasive. By contrast, women tended to prefer confrontation when sexism was pervasive relative to when it was rare. Personal self-affirmation decreased men's and increased women's support for confrontation when prejudice was rare, suggesting that men's and women's support for confrontation when prejudice is rare is driven by personal impression management considerations. Implications for understanding how members of low and high status groups respond to prejudice are discussed.info:eu-repo/semantics/submittedVersio
Tropical thin cirrus and relative humidity observed by the Atmospheric Infrared Sounder
International audienceGlobal observations of cloud and humidity distributions in the upper troposphere within all geophysical conditions are critically important in order to monitor the present climate and to provide necessary data for validation of climate models to project future climate change. Towards this end, tropical oceanic distributions of thin cirrus optical depth (?), effective diameter (De), and relative humidity with respect to ice (RHi) within cirrus (RHic) are simultaneously derived from the Atmospheric Infrared Sounder (AIRS). Corresponding increases in De and cloud temperature are shown for cirrus with ?>0.25 that demonstrate quantitative consistency to other surface-based, in situ and satellite retrievals. However, inferred cirrus properties are shown to be less certain for increasingly tenuous cirrus. In-cloud supersaturation is observed for 8?12% of thin cirrus and is several factors higher than all-sky conditions; even higher frequencies are shown for the coldest and thinnest cirrus. Spatial and temporal variations in RHic correspond to cloud frequency while regional variability in RHic is observed to be most prominent over the N. Indian Ocean basin. The largest cloud/clear sky RHi anomalies tend to occur in dry regions associated with vertical descent in the sub-tropics, while the smallest occur in moist ascending regions in the tropics. The characteristics of RHic frequency distributions depend on ? and a peak frequency is located between 60?80% that illustrates RHic is on average biased dry. The geometrical thickness of cirrus is typically less than the vertical resolution of AIRS temperature and specific humidity profiles and thus leads to the observed dry bias, shown with coincident cloud vertical structure obtained from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The joint distributions of thin cirrus microphysics and humidity derived from AIRS provide unique and important regional and global-scale insights on upper tropospheric processes not available from surface, in situ, and other contemporary satellite observing platforms
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