808 research outputs found
Einstein's "Zur Elektrodynamik..." (1905) Revisited, with Some Consequences
Einstein, in his "Zur Elektrodynamik bewegter Korper", gave a physical
(operational) meaning to "time" of a remote event in describing "motion" by
introducing the concept of "synchronous stationary clocks located at different
places". But with regard to "place" in describing motion, he assumed without
analysis the concept of a system of co-ordinates. In the present paper, we
propose a way of giving physical (operational) meaning to the concepts of
"place" and "co-ordinate system", and show how the observer can define both the
place and time of a remote event. Following Einstein, we consider another
system "in uniform motion of translation relatively to the former". Without
assuming "the properties of homogeneity which we attribute to space and time",
we show that the definitions of space and time in the two systems are linearly
related. We deduce some novel consequences of our approach regarding
faster-than-light observers and particles, "one-way" and "two-way" velocities
of light, symmetry, the "group property" of inertial reference frames, length
contraction and time dilatation, and the "twin paradox". Finally, we point out
a flaw in Einstein's argument in the "Electrodynamical Part" of his paper and
show that the Lorentz force formula and Einstein's formula for transformation
of field quantities are mutually consistent. We show that for faster-than-light
bodies, a simple modification of Planck's formula for mass suffices. (Except
for the reference to Planck's formula, we restrict ourselves to Physics of
1905.)Comment: 55 pages, 4 figures, accepted for publication in "Foundations of
Physics
Differentiating normal and problem gambling: a grounded theory approach.
A previous study (Ricketts & Macaskill, 2003) delineated a theory of problem gambling based on the experiences of treatment seeking male gamblers and allowed predictions to be made regarding the processes that differentiate between normal and problem gamblers. These predictions are the focus of the present study, which also utilised a grounded theory approach, but with a sample of male high frequency normal gamblers. The findings suggest that there are common aspects of gambling associated with arousal and a sense of achievement. The use of gambling to manage negative emotional states differentiated normal and problem gambling. Perceived self-efficacy , emotion management skills and perceived likelihood of winning money back were intervening variables differentiating problem and normal gamblers.</p
Detection of relic gravitational waves in the CMB: Prospects for CMBPol mission
Detection of relic gravitational waves, through their imprint in the cosmic
microwave background radiation, is one of the most important tasks for the
planned CMBPol mission. In the simplest viable theoretical models the
gravitational wave background is characterized by two parameters, the
tensor-to-scalar ratio and the tensor spectral index . In this paper,
we analyze the potential joint constraints on these two parameters, and
, using the potential observations of the CMBPol mission, which is
expected to detect the relic gravitational waves if . The
influence of the contaminations, including cosmic weak lensing, various
foreground emissions, and systematical errors, is discussed.Comment: 26 pages, 19 figures, 4 tables; JCAP in pres
Endogenous steroid profiling by gas chromatography-tandem mass spectrometry and multivariate statistics for the detection of natural hormone abuse in cattle
Independence of , Poincare Invariance and the Non-Conservation of Helicity
A relativistic constituent quark model is found to reproduce the recent data
regarding the ratio of proton form factors, . We show that
imposing Poincare invariance leads to substantial violation of the helicity
conservation rule, as well as an analytic result that the ratio
for intermediate values of .Comment: 13 pages, 7 figures, to be submitted to Phys. Rev. C typos corrected,
references added, 1 new figure to show very high Q^2 behavio
Using multimedia and peer assessment to promote collaborative e-learning
Collaborative e-learning is increasingly appealing as a pedagogical approach that can positively affect student learning. We propose a didactical model that integrates multimedia with collaborative tools and peer assessment to foster collaborative e-learning. In this paper, we explain it and present the results of its application to the “International Seminars on Materials Science” online course. The proposed didactical model consists of five educational activities. In the first three, students review the multimedia resources proposed by the teacher in collaboration with their classmates. Then, in the last two activities, they create their own multimedia resources and assess those created by their classmates. These activities foster communication and collaboration among students and their ability to use and create multimedia resources. Our purpose is to encourage the creativity, motivation, and dynamism of the learning process for both teachers and students
Competing orders in a magnetic field: spin and charge order in the cuprate superconductors
We describe two-dimensional quantum spin fluctuations in a superconducting
Abrikosov flux lattice induced by a magnetic field applied to a doped Mott
insulator. Complete numerical solutions of a self-consistent large N theory
provide detailed information on the phase diagram and on the spatial structure
of the dynamic spin spectrum. Our results apply to phases with and without
long-range spin density wave order and to the magnetic quantum critical point
separating these phases. We discuss the relationship of our results to a number
of recent neutron scattering measurements on the cuprate superconductors in the
presence of an applied field. We compute the pinning of static charge order by
the vortex cores in the `spin gap' phase where the spin order remains
dynamically fluctuating, and argue that these results apply to recent scanning
tunnelling microscopy (STM) measurements. We show that with a single typical
set of values for the coupling constants, our model describes the field
dependence of the elastic neutron scattering intensities, the absence of
satellite Bragg peaks associated with the vortex lattice in existing neutron
scattering observations, and the spatial extent of charge order in STM
observations. We mention implications of our theory for NMR experiments. We
also present a theoretical discussion of more exotic states that can be built
out of the spin and charge order parameters, including spin nematics and phases
with `exciton fractionalization'.Comment: 36 pages, 33 figures; for a popular introduction, see
http://onsager.physics.yale.edu/superflow.html; (v2) Added reference to new
work of Chen and Ting; (v3) reorganized presentation for improved clarity,
and added new appendix on microscopic origin; (v4) final published version
with minor change
Association of baseline inflammatory markers and the development of negative symptoms in individuals at clinical high risk for psychosis
Negative symptoms are common in individuals at clinical high-risk (CHR) for psychosis and are associated with worse functional outcomes. Inflammation may be one mechanism underlying negative symptoms. Inflammatory markers are altered in individuals at CHR and are associated with negative symptoms in patients with schizophrenia. We thus hypothesized that baseline inflammatory markers would predict the development of negative symptoms in individuals at CHR for psychosis. Thirty seven individuals from the North American Prodromal Longitudinal Study who met CHR criteria were included in the study. Inflammatory cytokines, including interferon (IFN)-λ, Interleukin (IL)-1β, IL-1 receptor antagonist (IL-1RA), IL-4, IL-6, IL-8, IL-10, and tumor necrosis factor (TNF) were measured at baseline. Negative symptoms as measured by the Scale of Prodromal Symptoms, were measured at baseline and six and twelve months. Associations between inflammatory markers and the trajectory of negative symptoms (slope) over the first year of follow-up, were assessed using linear regression models controlling for age, sex, race and depressive symptom severity (as assessed by the Calgary Depression Scale for Schizophrenia). Baseline TNF (beta = 0.361, p = 0.007) and IL-6 (beta = −0.306, p = 0.026) predicted negative symptoms slopes, along with depressive symptom severity at baseline (beta = −0.596, p = 0.000). These findings demonstrate that inflammatory cytokines may underlie the development of negative symptoms in some individuals at CHR for psychosis. TNF predicted the development of negative symptoms independent of baseline depression. Given the heterogeneity of the CHR population, the comorbidity of negative symptoms and depression in this population, and the particular challenges in treating negative symptoms, immune markers could represent potential biomarkers that underlie the development of negative symptoms, representing a potential treatment target
Utilização de parte da região codificadora da glicoproteína b na diferenciação do herpesvírus bovino 1.1, herpesvírus bovino 1.2 e herpesvírus bovino 5
Diverse Beliefs and Time Variability of Risk Premia
Why do risk premia vary over time? We examine this problem theoretically and empirically by studying the effect of market belief on risk premia. Individual belief is taken as a fundamental primitive state variable. Market belief is observable; it is central to the empirical evaluation and we show how to measure it. Our asset pricing model is familiar from the noisy REE literature but we adapt it to an economy with diverse beliefs. We derive equilibrium asset prices and implied risk premium. Our approach permits a closed form solution of prices; hence we trace the exact effect of market belief on the time variability of asset prices and risk premia. We test empirically the theoretical conclusions. Our main result is that, above the effect of business cycles on risk premia, fluctuations in market belief have significant independent effect on the time variability of risk premia. We study the premia on long positions in Federal Funds Futures, 3- and 6-month Treasury Bills (T-Bills). The annual mean risk premium on holding such assets for 1-12 months is about 40-60 basis points and we find that, on average, the component of market belief in the risk premium exceeds 50% of the mean. Since time variability of market belief is large, this component frequently exceeds 50% of the mean premium. This component is larger the shorter is the holding period of an asset and it dominates the premium for very short holding returns of less than 2 months. As to the structure of the premium we show that when the market holds abnormally favorable belief about the future payoff of an asset the market views the long position as less risky hence the risk premium on that asset declines. More generally, periods of market optimism (i.e. "bull" markets) are shown to be periods when the market risk premium is low while in periods of pessimism (i.e. "bear" markets) the market's risk premium is high. Fluctuations in risk premia are thus inversely related to the degree of market optimism about future prospects of asset payoffs. This effect is strong and economically very significant
- …