19,545 research outputs found
Introduction
This chapter will motivate why it is useful to consider the topic of derivations
and filtering in more detail. We will argue against the popular belief that
the minimalist program and optimality theory are incompatible theories in that the
former places the explanatory burden on the generative device (the computational
system) whereas the latter places it on the fi ltering device (the OT evaluator).
Although this belief may be correct in as far as it describes existing tendencies,
we will argue that minimalist and optimality theoretic approaches normally adopt
more or less the same global architecture of grammar: both assume that a generator
defines a set S of potentially well-formed expressions that can be generated on the
basis of a given input and that there is an evaluator that selects the expressions from
S that are actually grammatical in a given language L. For this reason, we believe
that it has a high priority to investigate the role of the two components in more detail
in the hope that this will provide a better understanding of the differences and similarities
between the two approaches. We will conclude this introduction with a brief
review of the studies collected in this book.
Universal measurement of quantum correlations of radiation
A measurement technique is proposed which, in principle, allows one to
observe the general space-time correlation properties of a quantized radiation
field. Our method, called balanced homodyne correlation measurement, unifies
the advantages of balanced homodyne detection with those of homodyne
correlation measurements.Comment: 4 pages, 4 figures, small misprints were corrected, accepted to Phys.
Rev. Let
Origin of non-exponential relaxation in a crystalline ionic conductor: a multi-dimensional 109Ag NMR study
The origin of the non-exponential relaxation of silver ions in the
crystalline ion conductor Ag7P3S11 is analyzed by comparing appropriate
two-time and three-time 109Ag NMR correlation functions. The non-exponentiality
is due to a rate distribution, i.e., dynamic heterogeneities, rather than to an
intrinsic non-exponentiality. Thus, the data give no evidence for the relevance
of correlated back-and-forth jumps on the timescale of the silver relaxation.Comment: 4 pages, 3 figure
Locating the source of projectile fluid droplets
The ill-posed projectile problem of finding the source height from spattered
droplets of viscous fluid is a longstanding obstacle to accident reconstruction
and crime scene analysis. It is widely known how to infer the impact angle of
droplets on a surface from the elongation of their impact profiles. However,
the lack of velocity information makes finding the height of the origin from
the impact position and angle of individual drops not possible. From aggregate
statistics of the spatter and basic equations of projectile motion, we
introduce a reciprocal correlation plot that is effective when the polar launch
angle is concentrated in a narrow range. The vertical coordinate depends on the
orientation of the spattered surface, and equals the tangent of the impact
angle for a level surface. When the horizontal plot coordinate is twice the
reciprocal of the impact distance, we can infer the source height as the slope
of the data points in the reciprocal correlation plot. If the distribution of
launch angles is not narrow, failure of the method is evident in the lack of
linear correlation. We perform a number of experimental trials, as well as
numerical calculations and show that the height estimate is insensitive to
aerodynamic drag. Besides its possible relevance for crime investigation,
reciprocal-plot analysis of spatter may find application to volcanism and other
topics and is most immediately applicable for undergraduate science and
engineering students in the context of crime-scene analysis.Comment: To appear in the American Journal of Physics (ms 23338). Improved
readability and organization in this versio
Electron Glass Dynamics
Examples of glasses are abundant, yet it remains one of the phases of matter
whose understanding is very elusive. In recent years, remarkable experiments
have been performed on the dynamical aspects of glasses. Electron glasses offer
a particularly good example of the 'trademarks' of glassy behavior, such as
aging and slow relaxations. In this work we review the experimental literature
on electron glasses, as well as the local mean-field theoretical framework put
forward in recent years to understand some of these results. We also present
novel theoretical results explaining the periodic aging experiment.Comment: Invited review to appear in Annual Review of Condensed Matter Physic
Characterization of the Dynamics of Glass-forming Liquids from the Properties of the Potential Energy Landscape
We develop a framework for understanding the difference between strong and
fragile behavior in the dynamics of glass-forming liquids from the properties
of the potential energy landscape. Our approach is based on a master equation
description of the activated jump dynamics among the local minima of the
potential energy (the so-called inherent structures) that characterize the
potential energy landscape of the system. We study the dynamics of a small
atomic cluster using this description as well as molecular dynamics simulations
and demonstrate the usefulness of our approach for this system. Many of the
remarkable features of the complex dynamics of glassy systems emerge from the
activated dynamics in the potential energy landscape of the atomic cluster. The
dynamics of the system exhibits typical characteristics of a strong supercooled
liquid when the system is allowed to explore the full configuration space. This
behavior arises because the dynamics is dominated by a few lowest-lying minima
of the potential energy and the potential energy barriers between these minima.
When the system is constrained to explore only a limited region of the
potential energy landscape that excludes the basins of attraction of a few
lowest-lying minima, the dynamics is found to exhibit the characteristics of a
fragile liquid.Comment: 13 pages, 6 figure
Illumination in symbiotic binary stars: Non-LTE photoionization models. II. Wind case
We describe a non-LTE photoionization code to calculate the wind structure
and emergent spectrum of a red giant wind illuminated by the hot component of a
symbiotic binary system. We consider spherically symmetric winds with several
different velocity and temperature laws and derive predicted line fluxes as a
function of the red giant mass loss rate, \mdot. Our models generally match
observations of the symbiotic stars EG And and AG Peg for \mdot about 10^{-8}
\msunyr to 10^{-7} \msunyr. The optically thick cross- section of the red giant
wind as viewed from the hot component is a crucial parameter in these models.
Winds with cross-sections of 2--3 red giant radii reproduce the observed
fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models
favor winds with acceleration regions that either lie far from the red giant
photosphere or extend for 2--3 red giant radii.Comment: 51 pages, LaTeX including three tables, requires 15 Encapsulated
Postscript figures, to appear in Ap
Strongly correlated photons generated by coupling a three- or four-level system to a waveguide
We study the generation of strongly correlated photons by coupling an atom to
photonic quantum fields in a one-dimensional waveguide. Specifically, we
consider a three-level or four-level system for the atom. Photon-photon bound
states emerge as a manifestation of the strong photon-photon correlation
mediated by the atom. Effective repulsive or attractive interaction between
photons can be produced, causing either suppressed multiphoton transmission
(photon blockade) or enhanced multiphoton transmission (photon-induced
tunneling). As a result, nonclassical light sources can be generated on demand
by sending coherent states into the proposed system. We calculate the
second-order correlation function of the transmitted field and observe bunching
and antibunching caused by the bound states. Furthermore, we demonstrate that
the proposed system can produce photon pairs with a high degree of spectral
entanglement, which have a large capacity for carrying information and are
important for large-alphabet quantum communication.Comment: 13+ pages, 7 figure
Environmental change within the Balkan region during the past ca. 50 ka recorded in the sediments from lakes Prespa and Ohrid
Lakes Prespa and Ohrid, in the Balkan region, are considered to be amongst the oldest lakes in Europe. Both lakes are hydraulically connected via karst aquifers. From Lake Ohrid, several sediment cores up to 15 m long have been studied over the last few years. Here, we document the first long sediment record from nearby Lake Prespa to clarify the influence of Lake Prespa on Lake Ohrid and the environmental history of the region. Radiocarbon dating and dated tephra layers provide robust age control and indicate that the 10.5 m long sediment record from Lake Prespa reaches back to 48 ka. Glacial sedimentation is characterized by low organic matter content and absence of carbonates in the sediments, which indicate oligotrophic conditions in both lakes. Holocene sedimentation is characterized by particularly high carbonate content in Lake Ohrid and by particularly high organic matter content in Lake Prespa, which indicates a shift towards more mesotrophic conditions in the latter. Long-term environmental change and short-term events, such as related to the Heinrich events during the Pleistocene or the 8.2 ka cooling event during the Holocene, are well recorded in both lakes, but are only evident in certain proxies. The comparison of the sediment cores from both lakes indicates that environmental change affects particularly the trophic state of Lake Prespa due to its lower volume and water depth
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