251 research outputs found
Preservice teachers’ pictorial strategies for a multistep multiplicative fraction problem
Previous research has documented that preservice teachers (PSTs) struggle with under- standing fraction concepts and operations, and misconceptions often stem from their understanding of the referent whole. This study expands research on PSTs’ understanding of wholes by investigating pictorial strategies that 85 PSTs constructed for a multistep fraction task in a multiplicative context. The results show that many PSTs were able to construct valid pictorial strategies, and the strategies were widely diverse with respect to how they made sense of an unknown referent whole of a fraction in multiple steps, how they represented the wholes in their drawings, in which order they did multiple steps, and which type of model they used (area or set). Based on their wide range of pictorial strategies, we discuss potential benefits of PSTs’ construction of their own representations for a word problem in developing problem solving skills
Higgs Phenomenology with CPsuperH
The MSSM contains CP-violating phases that may have important observable
effects in Higgs physics. We review recent highlights in Higgs phenomenology
obtained with the code CPsuperH, a useful tool for studies of the production,
mixing and decay of a coupled system of the neutral Higgs bosons at future high
energy colliders such as the LHC, ILC (LC), and a muon collider (MC).
CPsuperH implements the constraints from upper limits on electric dipole
moments, and may be extended to include other related low-energy observables,
such as b -> s \gamma and B -> K l l, and to compute the relic abundance of the
lightest neutralino.Comment: 20 pages, LaTeX, 7 figures, invited article by Modern Physics Letters
A (review section
High-performance Si microwire photovoltaics
Crystalline Si wires, grown by the vapor–liquid–solid (VLS)
process, have emerged as promising candidate materials for lowcost, thin-film photovoltaics. Here, we demonstrate VLS-grown Si microwires that have suitable electrical properties for high-performance photovoltaic applications, including long minority-carrier diffusion lengths (L_n » 30 µm) and low surface recombination velocities (S « 70 cm·s^(-1)). Single-wire radial p–n junction solar cells were fabricated with amorphous silicon and silicon nitride
surface coatings, achieving up to 9.0% apparent photovoltaic efficiency, and exhibiting up to ~600 mV open-circuit voltage with over 80% fill factor. Projective single-wire measurements and optoelectronic simulations suggest that large-area Si wire-array solar cells have the potential to exceed 17% energy-conversion efficiency, offering a promising route toward cost-effective crystalline Si photovoltaics
B --> Phi K_S and Supersymmetry
The rare decay B --> Phi K_S is a well-known probe of physics beyond the
Standard Model because it arises only through loop effects yet has the same
time-dependent CP asymmetry as B --> Psi K_S. Motivated by recent data
suggesting new physics in B --> Phi K_S, we look to supersymmetry for possible
explanations, including contributions mediated by gluino loops and by Higgs
bosons. Chirality-preserving LL and RR gluino contributions are generically
small, unless gluinos and squarks masses are close to the current lower bounds.
Higgs contributions are also too small to explain a large asymmetry if we
impose the current upper limit on B(B_s --> mu mu). On the other hand,
chirality-flipping LR and RL gluino contributions can provide sizable effects
and while remaining consistent with related results in B --> Psi K_S, Delta
M_s, B --> X_s gamma and other processes. We discuss how the LR and RL
insertions can be distinguished using other observables, and we provide a
string-based model and other estimates to show that the needed sizes of mass
insertions are reasonable.Comment: 33 pages, 32 figures, Updated version for PRD. Includes discussions
of other recent works on this topic. Added discussions & plots for gluino
mass dependence and effects of theoretical uncertaintie
Development of a Spirometry \u3cem\u3eT\u3c/em\u3e-score in the General Population
Background and objective: Spirometry values may be expressed as T-scores in standard deviation units relative to a reference in a young, normal population as an analogy to the T-score for bone mineral density. This study was performed to develop the spirometry T-score.
Methods: T-scores were calculated from lambda-mu-sigma-derived Z-scores using a young, normal age reference. Three outcomes of all-cause death, respiratory death, and COPD death were evaluated in 9,101 US subjects followed for 10 years; an outcome of COPD-related health care utilization (COPD utilization) was evaluated in 1,894 Korean subjects followed for 4 years.
Results: The probability of all-cause death appeared to remain nearly zero until -1 of forced expiratory volume in 1 second (FEV1) T-score but increased steeply where FEV1 T-score reached below -2.5. Survival curves for all-cause death, respiratory death, COPD death, and COPD utilization differed significantly among the groups when stratified by FEV1 T-score (P \u3c 0.001). The adjusted hazard ratios of the FEV1 T-score for the four outcomes were 0.54 (95% confidence interval, 0.48–0.60), 0.43 (95% CI: 0.37–0.50), 0.30 (95% CI: 0.24–0.37), and 0.69 (95% CI: 0.59–0.81), respectively, adjusting for covariates (P \u3c 0.001).
Conclusion: The spirometry T-score could predict all-cause death, respiratory death, COPD death, and COPD utilization
Probing MSSM Higgs Sector with Explicit CP Violation at a Photon Linear Collider
The CP properties of Higgs bosons can be probed through their s-channel
resonance productions via photon-photon collisions by use of circularly and/or
linearly polarized backscattered laser photons at a TeV-scale linear e^+ e^-
collider. Exploiting this powerful tool, we investigate in detail the Higgs
sector of the minimal supersymmetric Standard Model with explicit CP violation.Comment: 18 pages, 5 figures. Some comments added and typos corrected. To
appear in Phys. Rev.
B(d) --> phi K(S) CP asymmetries as an important probe of supersymmetry
The decay is a special probe of physics beyond the
Standard Model (SM), since it has no SM tree level contribution. Motivated by
recent data suggesting a deviation from the SM for its time-dependent CP
asymmetry, we examine supersymmetric explanations. Chirality preserving
contributions are generically small, unless gluino is relatively light. Higgs
contributions are also too small to explain a large asymmetry. Chirality
flipping and gluino contributions actually can provide sizable
effects without conflict with all related results. We discuss how various
insertions can be distinguished, and argue the needed sizes of mass insertions
are reasonable.Comment: 5 pages, 4 figures. A few typos in the abstract are corrected. This
is a shortened version of hep-ph/021209
Common Variants in the Glycerol Kinase Gene Reduce Tuberculosis Drug Efficacy
Despite the administration of multiple drugs that are highly effective in vitro, tuberculosis (TB) treatment requires prolonged drug administration and is confounded by the emergence of drug-resistant strains. To understand the mechanisms that limit antibiotic efficacy, we performed a comprehensive genetic study to identify Mycobacterium tuberculosis genes that alter the rate of bacterial clearance in drug-treated mice. Several functionally distinct bacterial genes were found to alter bacterial clearance, and prominent among these was the glpK gene that encodes the glycerol-3-kinase enzyme that is necessary for glycerol catabolism. Growth on glycerol generally increased the sensitivity of M. tuberculosis to antibiotics in vitro, and glpK-deficient bacteria persisted during antibiotic treatment in vivo, particularly during exposure to pyrazinamide-containing regimens. Frameshift mutations in a hypervariable homopolymeric region of the glpK gene were found to be a specific marker of multidrug resistance in clinical M. tuberculosis isolates, and these loss-of-function alleles were also enriched in extensively drug-resistant clones. These data indicate that frequently observed variation in the glpK coding sequence produces a drug-tolerant phenotype that can reduce antibiotic efficacy and may contribute to the evolution of resistance.
IMPORTANCE: TB control is limited in part by the length of antibiotic treatment needed to prevent recurrent disease. To probe mechanisms underlying survival under antibiotic pressure, we performed a genetic screen for M. tuberculosis mutants with altered susceptibility to treatment using the mouse model of TB. We identified multiple genes involved in a range of functions which alter sensitivity to antibiotics. In particular, we found glycerol catabolism mutants were less susceptible to treatment and that common variation in a homopolymeric region in the glpK gene was associated with drug resistance in clinical isolates. These studies indicate that reversible high-frequency variation in carbon metabolic pathways can produce phenotypically drug-tolerant clones and have a role in the development of resistance
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