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Search Results: 1 - 10 of 5550 matches for " Sam Cohen "
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Chemical accuracy from quantum Monte Carlo for the Benzene Dimer
Sam Azadi,R. E. Cohen
Physics , 2015, DOI: 10.1063/1.4930137
Abstract: We report an accurate study of interactions between Benzene molecules using variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo (DMC) methods. We compare these results with density functional theory (DFT) using different van der Waals (vdW) functionals. In our QMC calculations, we use accurate correlated trial wave functions including three-body Jastrow factors, and backflow transformations. We consider two benzene molecules in the parallel displaced (PD) geometry, and find that by highly optimizing the wave function and introducing more dynamical correlation into the wave function, we compute the weak chemical binding energy between aromatic rings accurately. We find optimal VMC and DMC binding energies of -2.3(4) and -2.7(3) kcal/mol, respectively. The best estimate of the CCSD(T)/CBS limit is -2.65(2) kcal/mol [E. Miliordos et al, J. Phys. Chem. A 118, 7568 (2014)]. Our results indicate that QMC methods give chemical accuracy for weakly bound van der Waals molecular interactions, comparable to results from the best quantum chemistry methods.
Environmental Influences on the Distribution of Mangroves on Bahamas Island
Ayron M Strauch,Sam Cohen,George S Ellmore
Journal of Wetlands Ecology , 2012, DOI: 10.3126/jowe.v6i0.6081
Abstract: Mangrove forests provide valuable ecosystem services but are declining in many tropical locations. The abundance of mangrove species in coastal fringe forests is related to biotic processes such as species succession or competition and abiotic factors, including nutrient availability, physiochemical water quality, soil composition, and tidal inundation. We examined the abundance of Rhizophora mangle and Avicennia germinans relative to environmental factors, including porewater chemistry, soil substrate, and distance from the ocean, on Bahamas Island. In this system, R. mangle were primarily found in litter-dominated soils and abundances were positively related to distance from the ocean, while A. germinans was only found in sandy soils closest to the ocean. Although phosphate, alkalinity, and salinity in porewater did not explain the distribution of species, free chloride varied significantly with distance from the ocean. These results suggest that soil conditions and tidal inundation may help determine the distribution of mangrove species on Caribbean islands. DOI: http://dx.doi.org/10.3126/jowe.v6i0.6081 J Wet Eco 2012 (6): 16-24
The Neural Correlates of Religious and Nonreligious Belief
Sam Harris, Jonas T. Kaplan, Ashley Curiel, Susan Y. Bookheimer, Marco Iacoboni, Mark S. Cohen
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0007272
Abstract: Background While religious faith remains one of the most significant features of human life, little is known about its relationship to ordinary belief at the level of the brain. Nor is it known whether religious believers and nonbelievers differ in how they evaluate statements of fact. Our lab previously has used functional neuroimaging to study belief as a general mode of cognition [1], and others have looked specifically at religious belief [2]. However, no research has compared these two states of mind directly. Methodology/Principal Findings We used functional magnetic resonance imaging (fMRI) to measure signal changes in the brains of thirty subjects—fifteen committed Christians and fifteen nonbelievers—as they evaluated the truth and falsity of religious and nonreligious propositions. For both groups, and in both categories of stimuli, belief (judgments of “true” vs judgments of “false”) was associated with greater signal in the ventromedial prefrontal cortex, an area important for self-representation [3], [4], [5], [6], emotional associations [7], reward [8], [9], [10], and goal-driven behavior [11]. This region showed greater signal whether subjects believed statements about God, the Virgin Birth, etc. or statements about ordinary facts. A comparison of both stimulus categories suggests that religious thinking is more associated with brain regions that govern emotion, self-representation, and cognitive conflict, while thinking about ordinary facts is more reliant upon memory retrieval networks. Conclusions/Significance While religious and nonreligious thinking differentially engage broad regions of the frontal, parietal, and medial temporal lobes, the difference between belief and disbelief appears to be content-independent. Our study compares religious thinking with ordinary cognition and, as such, constitutes a step toward developing a neuropsychology of religion. However, these findings may also further our understanding of how the brain accepts statements of all kinds to be valid descriptions of the world.
Dimensionality Reduction for k-Means Clustering and Low Rank Approximation
Michael B. Cohen,Sam Elder,Cameron Musco,Christopher Musco,Madalina Persu
Computer Science , 2014,
Abstract: We show how to approximate a data matrix $\mathbf{A}$ with a much smaller sketch $\mathbf{\tilde A}$ that can be used to solve a general class of constrained k-rank approximation problems to within $(1+\epsilon)$ error. Importantly, this class of problems includes $k$-means clustering and unconstrained low rank approximation (i.e. principal component analysis). By reducing data points to just $O(k)$ dimensions, our methods generically accelerate any exact, approximate, or heuristic algorithm for these ubiquitous problems. For $k$-means dimensionality reduction, we provide $(1+\epsilon)$ relative error results for many common sketching techniques, including random row projection, column selection, and approximate SVD. For approximate principal component analysis, we give a simple alternative to known algorithms that has applications in the streaming setting. Additionally, we extend recent work on column-based matrix reconstruction, giving column subsets that not only `cover' a good subspace for $\bv{A}$, but can be used directly to compute this subspace. Finally, for $k$-means clustering, we show how to achieve a $(9+\epsilon)$ approximation by Johnson-Lindenstrauss projecting data points to just $O(\log k/\epsilon^2)$ dimensions. This gives the first result that leverages the specific structure of $k$-means to achieve dimension independent of input size and sublinear in $k$.
Psychology as an Associational Science: A Methodological Viewpoint  [PDF]
Sam S. Rakover
Open Journal of Philosophy (OJPP) , 2012, DOI: 10.4236/ojpp.2012.22023
Abstract: Unlike the sciences (physics), psychology has not developed in any of its areas (such as perception, learning, cognition) a top-theory like Newtonian theory, the theory of relativity, or quantum theory in physics. This difference is explained by a methodological discrepancy between the sciences and psychology, which centers on the measurement procedure: in psychology, measurement units similar to those in physics have not been discovered. Based on the arguments supporting this claim, a methodological distinction is made between the sciences and psychology as an associational science. It is suggested that that these two kinds of science generate two different classes of technologies. The possibility that in psychology there is a connection between the issue of measurement and the unsolved consciousness/brain problem is discussed.
A Case of Meningitis? What’s Your Diagnosis?  [PDF]
Pollach Gregor, Kampondeni Sam
Open Journal of Modern Neurosurgery (OJMN) , 2012, DOI: 10.4236/ojmn.2012.24014
Abstract: The five year old, somnolent girl from Mozambique with no medical history was presented with fever, neckstiffness, headaches, an almost complete paraplegia and a septic picture. Malaria parasites and HIV testing was negative. The lumbal puncture revealed staphylococcus. Subsequently a MRI scan showed no sign of meningitis but an extensive posterior epidural collection from C3 to the level of S1. Moreover it showed a vertebral osteomyelitis at L1. Bacteria in CSF were seen as an artefact and the child was treated by multilevel (purely) epidural punctures with drainage, rinsing and instillation of ceftriaxon. The epidural puncture proved acid fast bacilli in the pus, so that an anti-tuberculotic therapy was given. The child recovered quickly from sepsis and was able to walk several steps without help after three months.
HIV, Stigma, and Rates of Infection: More Complicated than Reidpath and Chan Suggest
Sam Singer
PLOS Medicine , 2007, DOI: 10.1371/journal.pmed.0040051
The Interaction Between Dietary Valine and Tryptophan Content and Their Effect on the Performance of Piglets
Sam Millet
Animals , 2012, DOI: 10.3390/ani2010076
Abstract: Four experimental diets for newly weaned pigs were formulated: (1) low valine and low tryptophan; (2) low valine and high tryptophan; (3) high valine and low tryptophan and (4) high valine and high tryptophan. Dietary standardized ileal digestible (SID) lysine content was 1.06 g/kg. The SID valine to SID lysine ratio was 0.58 and 0.67 for the low and high valine diets, respectively, and SID tryptophan to SID lysine ratios were 0.19 and 0.22 for the low and high tryptophan diets, respectively. In total, 64 pens of 6 pigs (3 barrows and 3 gilts) were divided over the four experimental treatments. No interaction between dietary supply of valine and tryptophan was observed ( P > 0.1 for all parameters). Increasing the dietary valine content increased the daily feed intake, daily gain and gain:feed ( P < 0.001 for all three parameters). Increasing the dietary tryptophan content improved gain:feed during the first 2 weeks ( P < 0.05) and overall ( P < 0.05). Valine supply had a greater effect on performance results than tryptophan supply. It may thus be beneficial to provide a diet with an optimal dietary concentration of valine even if other amino acids are at suboptimal dietary levels.
Analysis of 44 Cases before the Landlord and Tenant Board Involving Bed Bug Infestations in Ontario, Canada: Focus on Adjudicator Decisions Based on Entomological/Pest Management Evidence and Accountability under the Residential Tenancy Act and Other Applicable Legislation
Sam Bryks
Insects , 2011, DOI: 10.3390/insects2030343
Abstract: The resurgence of bed bugs in major urban centres in North America has resulted in conflict between landlords and tenants. This is commonly focused on attribution of blame for source of infestation, on responsibility, on costs for preparation, treatment and losses, and for compensation as rent abatement and/or alternative temporary housing. In Ontario, Canada, these issues are often decided by adjudicators at the Landlord and Tenant Board hearing claims, counter-claims and defense by legal representation (lawyers and paralegals) as well as through mediation. Evidence in these hearings may include photographs, invoices for costs as well as testimony by tenants, landlords and “expert witnesses” who are most often pest control firms representing their landlord clients. A total of 44 Landlord and Tenant Board adjudicated cases available online were analyzed. The analysis included elements of the decisions such as adjudicator, claimant (landlord or tenant), basis of claim, review of evidence, amount of claim, amount awarded, and evaluation of the quality of the evidence. The results of the analysis of these findings are discussed. Recommendations for improvement of adjudicator decisions on the basis of knowledge of bed bug biology and Integrated Pest Management best practices are presented as well as the importance of education of tenants and landlords to a process of mutual trust, support and accountability.
Good news on rotavirus vaccine?
Sam Jaffe
Genome Biology , 2004, DOI: 10.1186/gb-spotlight-20040713-01
Abstract: In July of 1999, the Centers for Disease Control issued an alert about what appeared to be a statistically significant increase in intussusception - a potentially dangerous condition in which the small intestine collapses in on itself - that occurred in the days following vaccination. A cluster of 15 cases of intussusception was identified in infants who recently had the vaccine.According to data analyzed by Lone Simonsen, a National Institutes of Health researcher, more than 80% of all cases of intussusception events that were associated with the vaccine happened with babies who received the vaccine after 4 months of age, which was at the far end of the manufacturer's recommendations. That's because, Simonsen told us, when the vaccine first appeared, many doctors were "catching up" with older babies who didn't have a chance to get the vaccine in the months before its approval. "You can't talk about the intussusception risks of RotaShield without talking about the age of the child at first dose," Simonsen told attendees at the Sixth International Rotavirus Symposium here on Wednesday (July 7) when she presented the as-yet unpublished data.Another important element in Simonsen's appraisal of the 4-year-old data is the fact that overall intussusception rates of children given the rotavirus vaccine were the same as the baseline expectation of otherwise healthy children in the first year of life - about 1 in 3000. That suggests that RotaShield was "shaking the apple tree," Simonsen said. "RotaShield appears to have triggered an intussusception response in infants who probably would have had it anyway," Simonsen said. "It just shook out all the bad apples earlier."The data caused some doctors in the audience to reassess their view of RotaShield. "If a vaccine triggers intussusception in infants who are going to get it anyway, that means it's not only preventing rotavirus but it's providing much safer and more watchful conditions for the intussusception to occur," Paul Of
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