230 research outputs found
Irreversible reorganization in a supercooled liquid originates from localised soft modes
The transition of a fluid to a rigid glass upon cooling is a common route of
transformation from liquid to solid that embodies the most poorly understood
features of both phases1,2,3. From the liquid perspective, the puzzle is to
understand stress relaxation in the disordered state. From the perspective of
solids, the challenge is to extend our description of structure and its
mechanical consequences to materials without long range order. Using computer
simulations, we show that the localized low frequency normal modes of a
configuration in a supercooled liquid are causally correlated to the
irreversible structural reorganization of the particles within that
configuration. We also demonstrate that the spatial distribution of these soft
local modes can persist in spite of significant particle reorganization. The
consequence of these two results is that it is now feasible to construct a
theory of relaxation length scales in glass-forming liquids without recourse to
dynamics and to explicitly relate molecular properties to their collective
relaxation.Comment: Published online: 20 July 2008 | doi:10.1038/nphys1025 Available from
http://www.nature.com/nphys/journal/v4/n9/abs/nphys1025.htm
Community-based intervention to promote breast cancer awareness and screening: The Korean experience
<p>Abstract</p> <p>Background</p> <p>There are many differences in culture, community identity, community participation, and ownership between communities in Western and Asian countries; thus, it is difficult to adopt the results of community intervention studies from Western countries. In this study, we conducted a multicity, multicomponent community intervention trial to correct breast cancer myths and promote screening mammography for women living in an urban community in Korea.</p> <p>Methods</p> <p>A 6-month, 2-city community intervention trial was conducted. In the intervention city, 480 women were surveyed at baseline and 7 months later to evaluate the effects of the intervention program. Strategies implemented in the intervention city included community outreach and clinic and pharmacy-based in-reach strategies.</p> <p>Results</p> <p>This study showed a 20.4-percentage-point decrease in myths about the link between cancer and breast size, a 19.2-percentage-point decrease in myths concerning mammography costs, and a 14.1-percentage-point increase in intention to undergo screening mammography. We also saw a 23.4-percentage-point increase in the proportion of women at the action stage of the transtheoretical model in the intervention city. In the comparison city, smaller decreases and increases were observed.</p> <p>Conclusions</p> <p>Our study showed the value of an intervention study aimed at reducing belief in breast cancer myths in an urban community in Korea. The invention also made women more likely to undergo mammography in future.</p
HIV research in Australia: linking basic research findings with clinical and public health outcomes
Despite a population of only 20 million and sustained low prevalence of HIV infection in Australia, Australian researchers have provided many substantial original findings to the fields of HIV pathogenesis, treatment and prevention. More recently, Australian clinicians and scientists have turned their attention to assisting other countries in developing effective responses, particularly within the Asia-Pacific region. It is therefore fitting that the 4th International AIDS Society (IAS) Conference on HIV Pathogenesis, Treatment and Prevention will be held in Sydney in July 2007. The meeting is expected to attract over 5000 participants and will have a dynamic and innovative programme within the three major themes of HIV basic science, clinical research and biomedical prevention
Access to Sterile Syringes through San Francisco Pharmacies and the Association with HIV Risk Behavior among Injection Drug Users
Increased options for syringe acquisition and disposal have been associated with reductions in high-risk behaviors. This study determined the extent of pharmacy uptake in accessing syringes among injection drug users (IDUs) and estimated associations between pharmacy uptake and safer injection/disposal practices. Two years after the implementation of California’s Disease Prevention Demonstration Project, which removed restrictions to non-prescription syringe sales through pharmacies with local authorization, IDUs were recruited through street outreach in San Francisco and interviewed regarding recent syringe acquisition, use, and disposal. The sample of 105 persons included a high proportion of men (67%), people of color (49%), and homeless persons (71%). The most common syringe source was a syringe exchange program (SEP) (80%), with pharmacies being accessed by 39% of respondents. The most commonly cited source of disposal was a SEP (65%), with very few reports of pharmacy disposal (2%). Adjusted analysis showed that unsuccessful attempts to purchase syringes at a pharmacy increased the odds of both injecting with a used syringe and giving away a used syringe. Using a SEP decreased the odds of unsafe injection and disposal practices. Thus, 2 years after the initiation of the California Disease Prevention Demonstration Project, results from this small study suggest that SEPs still provide the majority of syringe distribution and disposal services to San Francisco IDUs; however, pharmacies now augment syringe access. In addition, unsafe injection behavior is reported more often among those who do not use these syringe sources. These results are consistent with prior studies in suggesting that increasing the availability of syringes through SEPs and pharmacies, and developing bridges between them, may further reduce syringe-related risk
A mathematical and computational review of Hartree-Fock SCF methods in Quantum Chemistry
We present here a review of the fundamental topics of Hartree-Fock theory in
Quantum Chemistry. From the molecular Hamiltonian, using and discussing the
Born-Oppenheimer approximation, we arrive to the Hartree and Hartree-Fock
equations for the electronic problem. Special emphasis is placed in the most
relevant mathematical aspects of the theoretical derivation of the final
equations, as well as in the results regarding the existence and uniqueness of
their solutions. All Hartree-Fock versions with different spin restrictions are
systematically extracted from the general case, thus providing a unifying
framework. Then, the discretization of the one-electron orbitals space is
reviewed and the Roothaan-Hall formalism introduced. This leads to a exposition
of the basic underlying concepts related to the construction and selection of
Gaussian basis sets, focusing in algorithmic efficiency issues. Finally, we
close the review with a section in which the most relevant modern developments
(specially those related to the design of linear-scaling methods) are commented
and linked to the issues discussed. The whole work is intentionally
introductory and rather self-contained, so that it may be useful for non
experts that aim to use quantum chemical methods in interdisciplinary
applications. Moreover, much material that is found scattered in the literature
has been put together here to facilitate comprehension and to serve as a handy
reference.Comment: 64 pages, 3 figures, tMPH2e.cls style file, doublesp, mathbbol and
subeqn package
Assessing seasonality of travel distance to harm reduction service providers among persons who inject drugs
BACKGROUND: Prior research has examined access to syringe exchange program (SEP) services among persons who inject drugs (PWID), but no research has been conducted to evaluate variations in SEP access based on season. This is an important gap in the literature given that seasonal weather patterns and inclement weather may affect SEP service utilization. The purpose of this research is to examine differences in access to SEPs by season among PWID in the District of Columbia (DC). FINDINGS: A geometric point distance estimation technique was applied to records from a DC SEP that operated from 1996 to 2011. We calculated the walking distance (via sidewalks) from the centroid point of zip code of home residence to the exchange site where PWID presented for services. Analysis of variance (ANOVA) was used to examine differences in walking distance measures by season. Differences in mean walking distance measures were statistically significant between winter and spring with PWID traveling approximately 2.88 and 2.77 miles, respectively, to access the SEP during these seasons. CONCLUSIONS: The results of this study suggest that seasonal differences in SEP accessibility may exist between winter and spring. PWID may benefit from harm reduction providers adapting their SEP operations to provide a greater diversity of exchange locations during seasons in which inclement weather may negatively influence engagement with SEPs. Increasing the number of exchange locations based on season may help resolve unmet needs among injectors
Postpartum-specific anxiety as a predictor of infant-feeding outcomes and perceptions of infant-feeding behaviours: new evidence for childbearing specific measures of mood
Studies of pregnancy-specific anxiety suggest that it is a distinct construct which predicts perinatal outcomes more effectively than other general measures of anxiety. In response, a novel measure of postpartum-specific anxiety (PSAS) has been developed and validated, but it is not yet clear whether it possesses the same predictive power as its pregnancy-specific counterparts. The aim of this short-term prospective study was to (a) test the predictive validity of the PSAS in the context of one specific perinatal outcome, infant-feeding, and (b) examine whether the PSAS may be more efficacious at predicting infant-feeding outcomes and behaviours than the more commonly used general measures. Eight hundred mothers of infants aged between 0 and 6 months completed the PSAS alongside general measures of anxiety and depression at baseline. A subsample (n = 261) returned to complete a follow-up questionnaire examining infant-feeding outcomes and behaviours two weeks later. Hierarchical regression models revealed that the PSAS was associated with lower odds of breastfeeding exclusively, and breastfeeding in any quantity in the first 6 months postpartum. PSAS scores were also significantly associated with infant-feeding behaviours including a lower perceived enjoyment of food, and greater perceived food responsiveness and satiety responsiveness in the infant. As hypothesised, the PSAS was a stronger predictor of infant-feeding outcomes and behaviours than general anxiety and depression. The findings provide evidence for the predictive validity of the PSAS and call for the use of childbearing specific measures of mood when attempting to predict perinatal outcomes. Replication of these findings across other indices of maternal and infant health is now necessary
Assessing Syringe Exchange Program Access among Persons Who Inject Drugs (PWID) in the District of Columbia
Prior research has explored spatial access to syringe exchange programs (SEPs) among persons who inject drugs (PWID), but these studies have been based on limited data from short periods of time. No research has explored changes in spatial access to SEPs among PWID longitudinally. The purpose of this research is to examine spatial access to SEPs among PWID who accessed services at a SEP in Washington, District of Columbia (DC), from 1996 to 2010. The geometric point distance estimation technique was used to calculate the mean walking distance PWID traveled from the centroid point of their zip code of home residence to the mobile exchange site where they accessed SEP services. Analysis of variance (ANOVA) was used to examine differences in walking distance measures by year. The results of this research suggest that the distance DC PWID traveled to access SEP services remained relatively constant (approximately 2.75 mi) from 2003 to 2008, but increased to just over 4 mi in 2010. This research provides support for expanding SEP operations such that PWID have increased access to their services. Increasing SEP accessibility may help resolve unmet needs among injectors
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
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