9,630 research outputs found
Inhomogeneity and transverse voltage in superconductors
Voltages parallel and transverse to electric current in slightly
inhomogeneous superconductors can contain components proportional to the field
and temperature derivatives of the longitudinal and Hall resistivities. We show
that these anomalous contributions can be the origin of the zero field and
even-in-field transverse voltage occasionally observed at the superconductor to
normal state transition. The same mechanism can also cause an anomaly in the
odd-in-field transverse voltage interfering the Hall effect signal.Comment: 6 pages, 7 figure
A Geometric Model of Arbitrary Spin Massive Particle
A new model of relativistic massive particle with arbitrary spin
(()-particle) is suggested. Configuration space of the model is a product
of Minkowski space and two-dimensional sphere, . The system describes Zitterbewegung at the classical level.
Together with explicitly realized Poincar\'e symmetry, the action functional
turns out to be invariant under two types of gauge transformations having their
origin in the presence of two Abelian first-class constraints in the Hamilton
formalism. These constraints correspond to strong conservation for the
phase-space counterparts of the Casimir operators of the Poincar\'e group.
Canonical quantization of the model leads to equations on the wave functions
which prove to be equivalent to the relativistic wave equations for the massive
spin- field.Comment: 25 pages; v2: eq. (45.b) correcte
Massive spinning particle on anti-de Sitter space
To describe a massive particle with fixed, but arbitrary, spin on
anti-de Sitter space , we propose the point-particle model with
configuration space , where the sphere
corresponds to the spin degrees of freedom. The model possesses two gauge
symmetries expressing strong conservation of the phase-space counterparts of
the second- and fourth-order Casimir operators for . We prove that the
requirement of energy to have a global positive minimum over the
configuration space is equivalent to the relation , being the
particle's spin, what presents the classical counterpart of the quantum massive
condition. States with the minimal energy are studied in detail. The model is
shown to be exactly solvable. It can be straightforwardly generalized to
describe a spinning particle on -dimensional anti-de Sitter space ,
with the corresponding configuration
space.Comment: 23 pages, LaTe
Rigorous Dynamics and Radiation Theory for a Pauli-Fierz Model in the Ultraviolet Limit
The present paper is devoted to the detailed study of quantization and
evolution of the point limit of the Pauli-Fierz model for a charged oscillator
interacting with the electromagnetic field in dipole approximation. In
particular, a well defined dynamics is constructed for the classical model,
which is subsequently quantized according to the Segal scheme. To this end, the
classical model in the point limit is reformulated as a second order abstract
wave equation, and a consistent quantum evolution is given. This allows a study
of the behaviour of the survival and transition amplitudes for the process of
decay of the excited states of the charged particle, and the emission of
photons in the decay process. In particular, for the survival amplitude the
exact time behaviour is found. This is completely determined by the resonances
of the systems plus a tail term prevailing in the asymptotic, long time regime.
Moreover, the survival amplitude exhibites in a fairly clear way the Lamb shift
correction to the unperturbed frequencies of the oscillator.Comment: Shortened version. To appear in J. Math. Phy
Genetic and Environmental Contributions to Body Mass Index: Comparative Analysis of Monozygotic Twins, Dizygotic Twins and Same-Age Unrelated Siblings
Background—Earlier studies have established that a substantial percentage of variance in obesity-related phenotypes is explained by genetic components. However, only one study has used both virtual twins (VTs) and biological twins and was able to simultaneously estimate additive genetic, non-additive genetic, shared environmental and unshared environmental components in body mass index (BMI). Our current goal was to re-estimate four components of variance in BMI, applying a more rigorous model to biological and virtual multiples with additional data. Virtual multiples share the same family environment, offering unique opportunities to estimate common environmental influence on phenotypes that cannot be separated from the non-additive genetic component using only biological multiples.
Methods—Data included 929 individuals from 164 monozygotic twin pairs, 156 dizygotic twin pairs, five triplet sets, one quadruplet set, 128 VT pairs, two virtual triplet sets and two virtual quadruplet sets. Virtual multiples consist of one biological child (or twins or triplets) plus one same-aged adoptee who are all raised together since infancy. We estimated the additive genetic, non-additive genetic, shared environmental and unshared random components in BMI using a linear mixed model. The analysis was adjusted for age, age2, age3, height, height2, height3, gender and race.
Results—Both non-additive genetic and common environmental contributions were significant in our model (P-values \u3c 0.0001). No significant additive genetic contribution was found. In all, 63.6% (95% confidence interval (CI) 51.8–75.3%) of the total variance of BMI was explained by a non-additive genetic component, 25.7% (95% CI 13.8–37.5%) by a common environmental component and the remaining 10.7% by an unshared component.
Conclusion—Our results suggest that genetic components play an essential role in BMI and that common environmental factors such as diet or exercise also affect BMI. This conclusion is consistent with our earlier study using a smaller sample and shows the utility of virtual multiples for separating non-additive genetic variance from common environmental variance
Fixed Price Approximability of the Optimal Gain From Trade
Bilateral trade is a fundamental economic scenario comprising a strategically
acting buyer and seller, each holding valuations for the item, drawn from
publicly known distributions. A mechanism is supposed to facilitate trade
between these agents, if such trade is beneficial. It was recently shown that
the only mechanisms that are simultaneously DSIC, SBB, and ex-post IR, are
fixed price mechanisms, i.e., mechanisms that are parametrised by a price p,
and trade occurs if and only if the valuation of the buyer is at least p and
the valuation of the seller is at most p. The gain from trade is the increase
in welfare that results from applying a mechanism; here we study the gain from
trade achievable by fixed price mechanisms. We explore this question for both
the bilateral trade setting, and a double auction setting where there are
multiple buyers and sellers. We first identify a fixed price mechanism that
achieves a gain from trade of at least 2/r times the optimum, where r is the
probability that the seller's valuation does not exceed the buyer's valuation.
This extends a previous result by McAfee. Subsequently, we improve this
approximation factor in an asymptotic sense, by showing that a more
sophisticated rule for setting the fixed price results in an expected gain from
trade within a factor O(log(1/r)) of the optimal gain from trade. This is
asymptotically the best approximation factor possible. Lastly, we extend our
study of fixed price mechanisms to the double auction setting defined by a set
of multiple i.i.d. unit demand buyers, and i.i.d. unit supply sellers. We
present a fixed price mechanism that achieves a gain from trade that achieves
for all epsilon > 0 a gain from trade of at least (1-epsilon) times the
expected optimal gain from trade with probability 1 - 2/e^{#T epsilon^2 /2},
where #T is the expected number of trades resulting from the double auction
Spectrum Generating Algebras for the free motion in
We construct the spectrum generating algebra (SGA) for a free particle in the
three dimensional sphere for both, classical and quantum descriptions. In
the classical approach, the SGA supplies time-dependent constants of motion
that allow to solve algebraically the motion. In the quantum case, the SGA
include the ladder operators that give the eigenstates of the free Hamiltonian.
We study this quantum case from two equivalent points of view.Comment: 29 pages, 1 figur
Gender, war and militarism: making and questioning the links
The gender dynamics of militarism have traditionally been seen as straightforward, given the cultural mythologies of warfare and the disciplining of ‘masculinity’ that occurs in the training and use of men's capacity for violence in the armed services. However, women's relation to both war and peace has been varied and complex. It is women who have often been most prominent in working for peace, although there are no necessary links between women and opposition to militarism. In addition, more women than ever are serving in many of today's armies, with feminists rather uncertain on how to relate to this phenomenon. In this article, I explore some of the complexities of applying gender analyses to militarism and peace work in sites of conflict today, looking most closely at the Israeli feminist group, New Profile, and their insistence upon the costs of the militarized nature of Israeli society. They expose the very permeable boundaries between the military and civil society, as violence seeps into the fears and practices of everyday life in Israel. I place their work in the context of broader feminist analysis offered by researchers such as Cynthia Enloe and Cynthia Cockburn, who have for decades been writing about the ‘masculinist’ postures and practices of warfare, as well as the situation of women caught up in them. Finally, I suggest that rethinking the gendered nature of warfare must also encompass the costs of war to men, whose fundamental vulnerability to psychological abuse and physical injury is often downplayed, whether in mainstream accounts of warfare or in more specific gender analysis. Feminists need to pay careful attention to masculinity and its fragmentations in addressing the topic of gender, war and militarism
- …