11,424 research outputs found
Biosatellite attitude stabilization and control system
Design and operation of attitude stabilization and control system for Biosatellit
On the sharpness of the zero-entropy-density conjecture
The zero-entropy-density conjecture states that the entropy density, defined
as the limit of S(N)/N at infinity, vanishes for all translation-invariant pure
states on the spin chain. Or equivalently, S(N), the von Neumann entropy of
such a state restricted to N consecutive spins, is sublinear. In this paper it
is proved that this conjecture cannot be sharpened, i.e., translation-invariant
states give rise to arbitrary fast sublinear entropy growth. The proof is
constructive, and is based on a class of states derived from quasifree states
on a CAR algebra. The question whether the entropy growth of pure quasifree
states can be arbitrary fast sublinear was first raised by Fannes et al. [J.
Math. Phys. 44, 6005 (2003)]. In addition to the main theorem it is also shown
that the entropy asymptotics of all pure shift-invariant nontrivial quasifree
states is at least logarithmic.Comment: 11 pages, references added, corrected typo
Critical Langevin dynamics of the O(N)-Ginzburg-Landau model with correlated noise
We use the perturbative renormalization group to study classical stochastic
processes with memory. We focus on the generalized Langevin dynamics of the
\phi^4 Ginzburg-Landau model with additive noise, the correlations of which are
local in space but decay as a power-law with exponent \alpha in time. These
correlations are assumed to be due to the coupling to an equilibrium thermal
bath. We study both the equilibrium dynamics at the critical point and quenches
towards it, deriving the corresponding scaling forms and the associated
equilibrium and non-equilibrium critical exponents \eta, \nu, z and \theta. We
show that, while the first two retain their equilibrium values independently of
\alpha, the non-Markovian character of the dynamics affects the dynamic
exponents (z and \theta) for \alpha < \alpha_c(D, N) where D is the spatial
dimensionality, N the number of components of the order parameter, and
\alpha_c(x,y) a function which we determine at second order in 4-D. We analyze
the dependence of the asymptotic fluctuation-dissipation ratio on various
parameters, including \alpha. We discuss the implications of our results for
several physical situations
Universal parity effects in the entanglement entropy of XX chains with open boundary conditions
We consider the Renyi entanglement entropies in the one-dimensional XX
spin-chains with open boundary conditions in the presence of a magnetic field.
In the case of a semi-infinite system and a block starting from the boundary,
we derive rigorously the asymptotic behavior for large block sizes on the basis
of a recent mathematical theorem for the determinant of Toeplitz plus Hankel
matrices. We conjecture a generalized Fisher-Hartwig form for the corrections
to the asymptotic behavior of this determinant that allows the exact
characterization of the corrections to the scaling at order o(1/l) for any n.
By combining these results with conformal field theory arguments, we derive
exact expressions also in finite chains with open boundary conditions and in
the case when the block is detached from the boundary.Comment: 24 pages, 9 figure
The role of initial conditions in the ageing of the long-range spherical model
The kinetics of the long-range spherical model evolving from various initial
states is studied. In particular, the large-time auto-correlation and -response
functions are obtained, for classes of long-range correlated initial states,
and for magnetized initial states. The ageing exponents can depend on certain
qualitative features of initial states. We explicitly find the conditions for
the system to cross over from ageing classes that depend on initial conditions
to those that do not.Comment: 15 pages; corrected some typo
On entanglement evolution across defects in critical chains
We consider a local quench where two free-fermion half-chains are coupled via
a defect. We show that the logarithmic increase of the entanglement entropy is
governed by the same effective central charge which appears in the ground-state
properties and which is known exactly. For unequal initial filling of the
half-chains, we determine the linear increase of the entanglement entropy.Comment: 11 pages, 5 figures, minor changes, reference adde
Dynamical phase coexistence: A simple solution to the "savanna problem"
We introduce the concept of 'dynamical phase coexistence' to provide a simple
solution for a long-standing problem in theoretical ecology, the so-called
"savanna problem". The challenge is to understand why in savanna ecosystems
trees and grasses coexist in a robust way with large spatio-temporal
variability. We propose a simple model, a variant of the Contact Process (CP),
which includes two key extra features: varying external
(environmental/rainfall) conditions and tree age. The system fluctuates locally
between a woodland and a grassland phase, corresponding to the active and
absorbing phases of the underlying pure contact process. This leads to a highly
variable stable phase characterized by patches of the woodland and grassland
phases coexisting dynamically. We show that the mean time to tree extinction
under this model increases as a power-law of system size and can be of the
order of 10,000,000 years in even moderately sized savannas. Finally, we
demonstrate that while local interactions among trees may influence tree
spatial distribution and the order of the transition between woodland and
grassland phases, they do not affect dynamical coexistence. We expect dynamical
coexistence to be relevant in other contexts in physics, biology or the social
sciences.Comment: 8 pages, 7 figures. Accepted for publication in Journal of
Theoretical Biolog
Dynamic crossover in the global persistence at criticality
We investigate the global persistence properties of critical systems relaxing
from an initial state with non-vanishing value of the order parameter (e.g.,
the magnetization in the Ising model). The persistence probability of the
global order parameter displays two consecutive regimes in which it decays
algebraically in time with two distinct universal exponents. The associated
crossover is controlled by the initial value m_0 of the order parameter and the
typical time at which it occurs diverges as m_0 vanishes. Monte-Carlo
simulations of the two-dimensional Ising model with Glauber dynamics display
clearly this crossover. The measured exponent of the ultimate algebraic decay
is in rather good agreement with our theoretical predictions for the Ising
universality class.Comment: 5 pages, 2 figure
Knife River Indian Villages Archaeological Program: An Overview
The Knife River Indian Villages are located in North Dakota near the confluence of the Knife and Missouri Rivers, just north of the contemporary town of Stanton, North Dakota. They lie within the area between the Garrison Dam to the north and the Oahe Reservoir to the south, the last remaining unflooded segment of the Missouri River valley in the Dakotas. Within the area are river floodplains, terraces, dissected breaks and upland rolling terrain. Forests occur on the floodplain and lower terraces with a variety of native and exotic grasses found on the breaks and uplands. A number of relatively undisturbed archaeological sites occur along this stretch of river, an area which historical1y was the homeland of both the Hidatsa and Mandan Indians. The Knife River Indian Villages are the northernmost cluster of sites. They are the final major village complex representing the pinnacle of Hidatsa and Mandan cultural development in an unbroken occupational sequence spanning at least 500 years. They occur in an area that, even today, is considered only marginal1y suited for agriculture, yet they represent intensive occupation by semi-sedentary horticulturalists. This strategic location along the river also provided the villagers an opportunity to serve and prosper as key middleman traders between the Euro-Americans to the east and the Indians to the west, expanding upon a tradition which developed from earlier centuries of trading with their nomadic neighbors. Historically, the villages are rich in associations with prominent figures in the history of the American westward expansion as well as the earlier fur trade era. There is a wealth of historical data pertaining to the Lewis and Clark visits to the villages (1804-1806) and later documentation by the famous artists George Catlin and Karl Bodmer (1832-1834). Throughout this period the Hidatsa and Mandan were affected dramatically by the EuroAmerican influence resulting in unparal1eled change and innovation in both material culture and social organization. It was also this association that lead to the decimation of the Hidatsa and Mandan population through the spread of smal1pox through a series of outbreaks culminating in a major epidemic (1837) which forever altered these peoples\u27 culture
Priming access to natural-object and trait category hierarchies on pronunciation, lexical decision, and category verification tasks
Lexical decision, pronunciation, and category verification response times (RTs) to natural object and trait hierarchies were measured. Prime and target words consisted of both superordinate and subordinate object and trait category members. Trait words were categorized as desirable and undesirable (Hampson, et al., 1986). Subjects\u27 RTs to object and undesirable trait words displayed similar patterns. In all experiments, RTs to natural-object subordinate target words were significantly more rapid compared to superordinate words. This same pattern was also true for the undesirable traits, but reached significance in only the lexical decision task. The facilitation effect of the prime reached significance for the natural-objects in the category verification experiment and for the undesirable traits in the lexical decision experiment. This pattern of facilitation by the prime were consistent for natural-objects and undesirable traits across all experiments. In each experiment the opposite pattern of results were found for desirable traits. In the pronunciation and lexical decision experiments RTs to desirable superordinate trait words were significantly more rapid compared to desirable subordinate trait words. In all experiments the facilitation by desirable superordinate trait word primes was significantly greater compared to undesirable superordinate trait words. Post-experiment questionnaires indicated that subjects\u27 judgment of the logical hierarchy entailment asymmetries were highly consistent with the norms. Regression analysis of subjects\u27 judgments of the logical entailment between category stimulus pairs indicated no significant systematic relationship. Implications for research on attribution, category memory, and clinical research on cognitive assessment are discussed
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