762 research outputs found
On a modified-Lorentz-transformation based gravity model confirming basic GRT experiments
Implementing Poincar\'e's `geometric conventionalism' a scalar
Lorentz-covariant gravity model is obtained based on gravitationally modified
Lorentz transformations (or GMLT). The modification essentially consists of an
appropriate space-time and momentum-energy scaling ("normalization") relative
to a nondynamical flat background geometry according to an isotropic,
nonsingular gravitational `affecting' function Phi(r). Elimination of the
gravitationally `unaffected' S_0 perspective by local composition of space-time
GMLT recovers the local Minkowskian metric and thus preserves the invariance of
the locally observed velocity of light. The associated energy-momentum GMLT
provides a covariant Hamiltonian description for test particles and photons
which, in a static gravitational field configuration, endorses the four `basic'
experiments for testing General Relativity Theory: gravitational i) deflection
of light, ii) precession of perihelia, iii) delay of radar echo, iv) shift of
spectral lines. The model recovers the Lagrangian of the Lorentz-Poincar\'e
gravity model by Torgny Sj\"odin and integrates elements of the precursor
gravitational theories, with spatially Variable Speed of Light (VSL) by
Einstein and Abraham, and gravitationally variable mass by Nordstr\"om.Comment: v1: 14 pages, extended version of conf. paper PIRT VIII, London,
2002. v2: section added on effective tensorial rank, references added,
appendix added, WEP issue deleted, abstract and other parts rewritten, same
results (to appear in Found. Phys.
Cigarette ignition propensity, smoking behavior, and toxicant exposure: A natural experiment in Canada
<p>Abstract</p> <p>Background</p> <p>This study used a 'pre-post' research design to measure the impact of the Canadian reduced ignition propensity law on cigarette toxicity and smoking behavior among Canadian smokers.</p> <p>Method</p> <p>The study was conducted in Ontario, Canada over a ten-month period in 2005-2006, consisting of 4 laboratory visits (baseline N = 61, final N = 42). At Visit 1, questionnaire data and biospecimens were collected. During the following 24 hours, participants smoked 5 cigarettes <it>ad libitum </it>through a topography recording device and collected their cigarette butts. Visit 2 consisted of a questionnaire and smoking one cigarette to measure laboratory topography values. After ten months, these procedures were repeated.</p> <p>Results</p> <p>Generalized estimating equations, with law status (pre and post) as a fixed within-subject factor, were used to determine changes in behavior and biomarker exposure. Overall, there were no significant differences in smoking topography, breath carbon monoxide, and saliva cotinine pre-post law (<it>p</it>>0.1). However, analyses revealed a significant increase in the summed concentrations of hydroxyfluorene metabolites (N = 3),, and 1-hydroxypyrene in urine, with at notable increase in hydroxyphenanthrene metabolites (N = 3) (<it>p</it><sub>Σhydroxyfluorene </sub>= 0.013, 22% increase; <it>p<sub>1-hydroxypyrene </sub></it>= 0.018, 24% increase; <it>p</it><sub>Σhydroxyphenanthrene </sub>= 0.061, 17% increase).</p> <p>Conclusion</p> <p>While the results suggest no change in topography variables, data showed increases in exposure to three PAH biomarkers following reduced ignition propensity implementation in Canada. These findings suggest that human studies should be considered to evaluate policy impacts.</p
Politics by other means?:STS and research in education
Science and Technology Studies (STS) has been surprisingly slow to become widely known and deployed in the field of education. Yet STS has a rich array of concepts and analytical methods to offer to studies of: knowledge practices and epistemic cultures; the interrelationship between states and knowledge; regulatory practices, governance and institutions; and classrooms, pedagogy, teaching and learning. Most importantly, it provides a fresh perspective on how power operates in ordering societies, disciplining actors and promoting ideas and practices. In this paper, we provide an introduction to STS and elaborate what it offers education scholars. Using examples from the emerging body of STS work in the field of education, and in particular from the papers in this special issue, we argue that STS is not only useful, but an exciting and generative form of critique–one that is especially suited to investigating contemporary issues in education policies and practices
Population-level consequences of heterospecific density-dependent movements in predator-prey systems
In this paper we elucidate how small-scale movements, such as those associated with searching for food and avoiding predators, affect the stability of predator-prey dynamics. We investigate an individual-based Lotka-Volterra model with density dependent movement, in which the predator and prey populations live in a very large number of coupled patches. The rates at which individuals leave patches depend on the local densities of heterospecifics, giving rise to one reaction norm for each of the two species. Movement rates are assumed to be much faster than demographics rates. A spatial structure of predators and prey emerges which affects the global population dynamics. We derive a criterion which reveals how demograhic stability depends on the relationships between the per capita covariance and densities of predators and prey. Specifically we establish that a positive relationship with prey density and a negative relationship with predator density tend to be stabilizig. On a more mechanistic level we show how these relationships are linked to the movement reaction norms of predators and prey. Numerical results show that these findings hold both for local and global movements, i.e., both when migration is biased towards neighboring patches and when all patches are reached with equal probability
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Gestational Exposure to Endocrine-Disrupting Chemicals and Reciprocal Social, Repetitive, and Stereotypic Behaviors in 4- and 5-Year-Old Children: The HOME Study
Background: Endocrine-disrupting chemicals (EDCs) may be involved in the etiology of autism spectrum disorders, but identifying relevant chemicals within mixtures of EDCs is difficult. Objective: Our goal was to identify gestational EDC exposures associated with autistic behaviors. Methods: We measured the concentrations of 8 phthalate metabolites, bisphenol A, 25 polychlorinated biphenyls (PCBs), 6 organochlorine pesticides, 8 brominated flame retardants, and 4 perfluoroalkyl substances in blood or urine samples from 175 pregnant women in the HOME (Health Outcomes and Measures of the Environment) Study (Cincinnati, OH). When children were 4 and 5 years old, mothers completed the Social Responsiveness Scale (SRS), a measure of autistic behaviors. We examined confounder-adjusted associations between 52 EDCs and SRS scores using a two-stage hierarchical analysis to account for repeated measures and confounding by correlated EDCs. Results: Most of the EDCs were associated with negligible absolute differences in SRS scores (≤ 1.5). Each 2-SD increase in serum concentrations of polybrominated diphenyl ether-28 (PBDE-28) (β = 2.5; 95% CI: –0.6, 5.6) or trans-nonachlor (β = 4.1; 95% CI: 0.8–7.3) was associated with more autistic behaviors. In contrast, fewer autistic behaviors were observed among children born to women with detectable versus nondetectable concentrations of PCB-178 (β = –3.0; 95% CI: –6.3, 0.2), β-hexachlorocyclohexane (β = –3.3; 95% CI: –6.1, –0.5), or PBDE-85 (β = –3.2; 95% CI: –5.9, –0.5). Increasing perfluorooctanoate (PFOA) concentrations were also associated with fewer autistic behaviors (β = –2.0; 95% CI: –4.4, 0.4). Conclusions: Some EDCs were associated with autistic behaviors in this cohort, but our modest sample size precludes us from dismissing chemicals with null associations. PFOA, β-hexachlorocyclohexane, PCB-178, PBDE-28, PBDE-85, and trans-nonachlor deserve additional scrutiny as factors that may be associated with childhood autistic behaviors. Citation: Braun JM, Kalkbrenner AE, Just AC, Yolton K, Calafat AM, Sjödin A, Hauser R, Webster GM, Chen A, Lanphear BP. 2014. Gestational exposure to endocrine-disrupting chemicals and reciprocal social, repetitive, and stereotypic behaviors in 4- and 5-year-old children: the HOME Study. Environ Health Perspect 122:513–520; http://dx.doi.org/10.1289/ehp.130726
Adaptation strategies of the Icelandic horse with induced forelimb lameness at walk, trot and tölt
Background and objective Lameness assessment in the gaited Icelandic horse is complex. We aimed to describe their kinematic and temporal adaptation strategies in response to forelimb lameness at walk, trot and tolt.Study designIn vivo experiment.Methods Ten clinically non-lame Icelandic horses were measured before and after reversible forelimb lameness induction. Upper body and limb kinematics were measured using 11 inertial measurement units mounted on the poll, withers, pelvis (tubera sacrale) and all four limbs and hoofs (Equimoves (R), 500 Hz). Horses were measured on a straight line at walk and trot in-hand and at walk, trot and tolt while ridden. Linear mixed models were used to compare baseline and lame conditions (random factor = 'horse'), and results are presented as the difference in estimated marginal means or percentage of change.Results Lameness induction significantly (p < 0.05) increased head vertical movement asymmetry at walk (HDmin/HDmaxHAND: 18.8/5.7 mm, HDmin/HDmaxRIDDEN: 9.8/0.3 mm) and trot (HDmin/HDmaxHAND: 18.1/7.8 mm, HDmin/HDmaxRIDDEN: 24.0/9.3 mm). At the tolt, however, HDmin did not change significantly (1.1 mm), but HDmax increased by 11.2 mm (p < 0.05). Furthermore, pelvis vertical movement asymmetry (PDmax) increased by 4.9 mm, sound side dissociation decreased (-8.3%), and sound diagonal dissociation increased (6.5%). Other temporal stride variables were also affected, such as increased stance duration of both forelimbs at walk, tolt and in-hand trot.Main limitations Only one degree of lameness (mild) was induced with an acute lameness model.Conclusions Classical forelimb lameness metrics, such as vertical head and withers movement asymmetry, were less valuable at tolt compared to walk and trot, except for HDmax. Therefore, it is advised to primarily use the walk and trot to detect and quantify forelimb lameness in the Icelandic horse
Business models in servitization
This chapter sheds light on the different business models of manufacturing companies that have servitized their business operations. This chapter presents four distinctive yet simultaneously pursued business models for servitized manufacturers: (1) the product business model, (2) the service-agreement business model (3) the process-oriented business model, and (4) the performance-oriented business model. Depending on the direction taken, dedicated customer needs targeted, value propositions adopted, and services and solutions provided, a servitized manufacturer should decide which business model(s) the firm will adopt with different customers.fi=vertaisarvioitu|en=peerReviewed
A spatially-VSL gravity model with 1-PN limit of GRT
A scalar gravity model is developed according the 'geometric conventionalist'
approach introduced by Poincare (Einstein 1921, Poincare 1905, Reichenbach
1957, Gruenbaum1973). In principle this approach allows an alternative
interpretation and formulation of General Relativity Theory (GRT), with
distinct i) physical congruence standard, and ii) gravitation dynamics
according Hamilton-Lagrange mechanics, while iii) retaining empirical
indistinguishability with GRT. In this scalar model the congruence standards
have been expressed as gravitationally modified Lorentz Transformations
(Broekaert 2002). The first type of these transformations relate quantities
observed by gravitationally 'affected' (natural geometry) and 'unaffected'
(coordinate geometry) observers and explicitly reveal a spatially variable
speed of light (VSL). The second type shunts the unaffected perspective and
relates affected observers, recovering i) the invariance of the locally
observed velocity of light, and ii) the local Minkowski metric (Broekaert
2003). In the case of a static gravitation field the model retrieves the
phenomenology implied by the Schwarzschild metric. The case with proper source
kinematics is now described by introduction of a 'sweep velocity' field w: The
model then provides a hamiltonian description for particles and photons in full
accordance with the first Post-Newtonian approximation of GRT (Weinberg 1972,
Will 1993).Comment: v1: 11 pages, GR17 conf. paper, Dublin 2004, v2: WEP issue solved,
section on acceleration transformation added, text improved, more references,
same results, v3: typos removed, footnotes, added and references updated, v4:
appendix added, improved tex
Gestational Exposure to Polybrominated Diphenyl Ethers and Social Skills and Problem Behaviors in Adolescents: The Home Study
Background: Polybrominated diphenyl ethers (PBDEs) are persistent environmental pollutants used as flame retardants. Gestational PBDE exposure has been associated with a variety of behavior problems in children, but little is known about its impact into adolescence, particularly on social skills, which are important for achieving social competence, establishing identity, and forming lasting relationships. Objective: We investigated associations between gestational exposure to PBDEs and social skills and problem behaviors in early adolescence in a longitudinal pregnancy and birth cohort in Cincinnati, Ohio (recruited 2003–2006). Methods: We measured maternal serum concentrations of five PBDE congeners during gestation. At age 12, we measured social skills and problem behaviors scores for 243 adolescents using self- and caregiver-report on the Social Skills Improvement System (SSiS). We used multivariable linear regression models to estimate associations between maternal PBDE concentrations and SSiS scores, controlling for potential covariates. We report associations for the five congeners and a summary exposure variable (∑5BDE: the sum of BDE- 28, 47, 99, 100, and 153, n = 197). Results: We found sex-specific associations of ∑5BDE concentrations with adolescent-reported Problem Behaviors (∑5BDE × sex pint = 0.02) and caregiver-reported Social Skills (∑5BDE × sex pint = 0.02). In sex-stratified models, log10 transformed data revealed increased maternal ∑5BDE concentration among males was associated with decreased caregiver-reported Social Skills composite score (β = -10.2, 95% CI: −19.5, −1.0), increased adolescent-reported Problem Behaviors composite score (β = 12.1, 95% CI: 5.4, 18.8), and increased caregiver-reported Problem Behaviors composite score (β = 6.2, 95% CI: 0.7, 11.7). Further analysis on SSiS subscales revealed similar patterns in significant associations among males. There were no statistically significant associations in stratified models among females despite higher ∑5BDE exposure (Female GM=40.15 ng/g lipid, GSE=1.10; Male GM=35.30 ng/g lipid, GSE=1.09). Discussion: We found gestational PBDE exposure in males was associated with poorer behavioral outcomes, extending previous findings among this cohort into early adolescence
Time on a Rotating Platform
Traditional clock synchronisation on a rotating platform is shown to be
incompatible with the experimentally established transformation of time. The
latter transformation leads directly to solve this problem through noninvariant
one-way speed of light. The conventionality of some features of relativity
theory allows full compatibility with existing experimental evidence.Comment: 12 pages, Latex, no figure. Copies available at [email protected]
accepted for publication in Found. Phys. Let
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