9,416 research outputs found
Rotating Leaks in the Stadium Billiard
The open stadium billiard has a survival probability, , that depends on
the rate of escape of particles through the leak. It is known that the decay of
is exponential early in time while for long times the decay follows a
power law. In this work we investigate an open stadium billiard in which the
leak is free to rotate around the boundary of the stadium at a constant
velocity, . It is found that is very sensitive to . For
certain values is purely exponential while for other values the
power law behaviour at long times persists. We identify three ranges of
values corresponding to three different responses of . It is
shown that these variations in are due to the interaction of the moving
leak with Marginally Unstable Periodic Orbits (MUPOs)
Lorentz-Invariant "Elements of Reality" and the Question of Joint Measurability of Commuting Observables
It is shown that the joint measurements of some physical variables
corresponding to commuting operators performed on pre- and post-selected
quantum systems invariably disturb each other. The significance of this result
for recent proofs of the impossibility of realistic Lorentz invariant
interpretation of quantum theory (without assumption of locality) is discussed.Comment: 15 page
Quantum Mechanical Interaction-Free Measurements
A novel manifestation of nonlocality of quantum mechanics is presented. It is
shown that it is possible to ascertain the existence of an object in a given
region of space without interacting with it. The method might have practical
applications for delicate quantum experiments.Comment: (revised file with no need for macro), 12, TAUP 1865-91
Area deprivation across the life course and physical capability in mid-life: findings from the 1946 British Birth Cohort
Physical capability in later life is influenced by factors occurring across the life course, yet exposures to area conditions have only been examined cross-sectionally. Data from the National Survey of Health and Development, a longitudinal study of a 1946 British birth cohort, were used to estimate associations of area deprivation (defined as percentage of employed people working in partly skilled or unskilled occupations) at ages 4, 26, and 53 years (residential addresses linked to census data in 1950, 1972, and 1999) with 3 measures of physical capability at age 53 years: grip strength, standing balance, and chair-rise time. Cross-classified multilevel models with individuals nested within areas at the 3 ages showed that models assessing a single time point underestimate total area contributions to physical capability. For balance and chair-rise performance, associations with area deprivation in midlife were robust to adjustment for individual socioeconomic position and prior area deprivation (mean change for a 1-standard-deviation increase: balance, −7.4% (95% confidence interval (CI): −12.8, −2.8); chair rise, 2.1% (95% CI: −0.1, 4.3)). In addition, area deprivation in childhood was related to balance after adjustment for childhood socioeconomic position (−5.1%, 95% CI: −8.7, −1.6). Interventions aimed at reducing midlife disparities in physical capability should target the socioeconomic environment of individuals—for standing balance, as early as childhood
Coupled valence and spin state transition in (Pr0.7Sm0.3)0.7Ca0.3CoO3
The coupled valence and spin state transition (VSST) taking place in
(Pr0.7Sm0.3)0.7Ca0.3CoO3 was investigated by soft x-ray absorption spectroscopy
(XAS) experiments carried out at the Pr-M4,5, Co-L2,3, and O-1s edges. This
VSST is found to be composed of a sharp Pr/Co valence and Co spin state
transition centered at T*=89.3 K, followed by a smoother Co spin-state
evolution at higher temperatures. At T < T*, we found that the praseodymium
displays a mixed valence Pr3+/Pr4+ with about 0.13 Pr4+/f.u., while all the
Co3+ is in the low-spin (LS) state. At T around T*, the sharp valence
transition converts all the Pr4+ to Pr3+ with a corresponding Co3+ to Co4+
compensation. This is accompanied by an equally sharp spin state transition of
the Co3+ from the low to an incoherent mixture of low and high spin (HS)
states. An involvement of the intermediate spin (IS) state can be discarded for
the Co3+. While above T* and at high temperatures the system shares rather
similar properties as Sr-doped LaCoO3, at low temperatures it behaves much more
like EuCoO3 with its highly stable LS configuration for the Co3+. Apparently,
the mechanism responsible for the formation of Pr4+ at low temperatures also
helps to stabilize the Co3+ in the LS configuration despite the presence of
Co4+ ions. We also found out that that the Co4+ is in an IS state over the
entire temperature range investigated in this study (10-290 K). The presence of
Co3+ HS and Co4+ IS at elevated temperatures facilitates the conductivity of
the material.Comment: 19 pages, 7 figures, Accepted in PR
Location of the Lee-Yang zeros and absence of phase transitions in some Ising spin systems
We consider a class of Ising spin systems on a set \Lambda of sites. The
sites are grouped into units with the property that each site belongs to either
one or two units, and the total internal energy of the system is the sum of the
energies of the individual units, which in turn depend only on the number of up
spins in the unit. We show that under suitable conditions on these interactions
none of the |\Lambda| Lee-Yang zeros in the complex z = exp{2\beta h} plane,
where \beta is the inverse temperature and h the uniform magnetic field, touch
the positive real axis, at least for large values of \beta. In some cases one
obtains, in an appropriately taken \beta to infinity limit, a gas of hard
objects on a set \Lambda'; the fugacity for the limiting system is a rescaling
of z and the Lee-Yang zeros of the new partition function also avoid the
positive real axis. For certain forms of the energies of the individual units
the Lee-Yang zeros of both the finite- and zero-temperature systems lie on the
negative real axis for all \beta. One zero-temperature limit of this type, for
example, is a monomer-dimer system; our results thus generalize, to finite
\beta, a well-known result of Heilmann and Lieb that the Lee-Yang zeros of
monomer-dimer systems are real and negative.Comment: Plain TeX. Seventeen pages, five figures from .eps files. Version 2
corrects minor errors in version
On relativistic elements of reality
Several arguments have been proposed some years ago, attempting to prove the
impossibility of defining Lorentz-invariant elements of reality. I find that a
sufficient condition for the existence of elements of reality, introduced in
these proofs, seems to be used also as a necessary condition. I argue that
Lorentz-invariant elements of reality can be defined but, as Vaidman pointed
out, they won't satisfy the so-called product rule. In so doing I obtain
algebraic constraints on elements of reality associated with a maximal set of
commuting Hermitian operators.Comment: Clarifications, reference added; published versio
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