2,516 research outputs found
Variational theory of flux-line liquids
We formulate a variational (Hartree like) description of flux line liquids
which improves on the theory we developed in an earlier paper [A.M. Ettouhami,
Phys. Rev. B 65, 134504 (2002)]. We derive, in particular, how the massive term
confining the fluctuations of flux lines varies with temperature and show that
this term vanishes at high enough temperatures where the vortices behave as
freely fluctuating elastic lines.Comment: 10 pages, 1 postscript figur
Open-Ended Evolutionary Robotics: an Information Theoretic Approach
This paper is concerned with designing self-driven fitness functions for
Embedded Evolutionary Robotics. The proposed approach considers the entropy of
the sensori-motor stream generated by the robot controller. This entropy is
computed using unsupervised learning; its maximization, achieved by an on-board
evolutionary algorithm, implements a "curiosity instinct", favouring
controllers visiting many diverse sensori-motor states (sms). Further, the set
of sms discovered by an individual can be transmitted to its offspring, making
a cultural evolution mode possible. Cumulative entropy (computed from ancestors
and current individual visits to the sms) defines another self-driven fitness;
its optimization implements a "discovery instinct", as it favours controllers
visiting new or rare sensori-motor states. Empirical results on the benchmark
problems proposed by Lehman and Stanley (2008) comparatively demonstrate the
merits of the approach
Applicability of the Fisher Equation to Bacterial Population Dynamics
The applicability of the Fisher equation, which combines diffusion with
logistic nonlinearity, to population dynamics of bacterial colonies is studied
with the help of explicit analytic solutions for the spatial distribution of a
stationary bacterial population under a static mask. The mask protects the
bacteria from ultraviolet light. The solution, which is in terms of Jacobian
elliptic functions, is used to provide a practical prescription to extract
Fisher equation parameters from observations and to decide on the validity of
the Fisher equation.Comment: 5 pages, 3 figs. include
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Study of the hovering period and bubble size in fully developed pool nucleate boiling of saturated liquid with a time-dependent heat source
In this paper, the bubble behavior in saturated pool boiling with a time-dependent heat source is analyzed. The study is restricted to the period from fully developed nucleate boiling until critical heat flux occurs. The hovering period and the departure volume of the bubble are selected as the characteristic parameters for bubble behavior. These parameters are quantified by solving the equation of motion for an idealized bubble. This equation is solved for cases in which the surface heat flux changes linearly and exponentially as a function of time. After nondimensionalization, the results are compared directly with the results of the steady-state problem. The comparison shows that the transient heat input has practically no effect on the hovering period. However, the transient heat flux causes a decreased volume at bubble departure. The volume decrease is dependent on the severity of the transient. These results are in qualitative agreement with the experimental observation quoted in the literature
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Explosive morphology from fractal analysis of micrographs
The effect of particle size on the details of the initiation and detonation of condensed explosives has long been known. The effect of the three-dimensional nature of explosive particles as a neat pressings (with voids), or as dispersed in a second (or third) phase (with or without voids), has been the subject of many investigations of detonation phenomena. However, succinct and accurate descriptions of the compacts and pressings are difficult to achieve because the morphology and size distributions are generally altered by processing into useful configurations and densities. Three-dimensional measurements of near-full-density pressings are not easy and have not been done with great accuracy. The authors explore the analysis of various particle-size and morphological measurements using the formalisms of fractal geometry. They intend to show, by a combination of modeling and data analysis, that a three-dimensional description of the explosive, the binder, and the voids can be constructed from one- and two-dimensional measurements of surface. In the long term, they hope to correlate these descriptions with the measurements of explosive behavior
The cubic period-distance relation for the Kater reversible pendulum
We describe the correct cubic relation between the mass configuration of a
Kater reversible pendulum and its period of oscillation. From an analysis of
its solutions we conclude that there could be as many as three distinct mass
configurations for which the periods of small oscillations about the two pivots
of the pendulum have the same value. We also discuss a real compound Kater
pendulum that realizes this property.Comment: 25 pages 4figure
Worldwide delineation of multi-tier city–regions
Urban centers are pivotal in shaping societies, yet a systematic globalanalysis of how countries are organized around multiple urban centers islacking. We enhance understanding by delineating city–regions worldwide,classifying over 30,000 urban centers into four tiers—town, small,intermediate and large city—based on population size and mapping theircatchment areas based on travel time, differentiating between primaryand secondary city–regions. Here we identify 1,403 primary city–regionsemploying a 3 h travel time cutoff and increasing to 4,210 with a 1 h cutoff,which is more indicative of commuting times. Our findings reveal substantialinterconnectedness among urban centers and with their surrounding areas,with 3.2 billion people having physical access to multiple tiers within anhour and 4.7 billion within 3 h. Notably, among people living in or closest totowns or small cities, twice as many have easier access to intermediate thanto large cities, underscoring intermediate cities’ crucial role in connectingsurrounding populations. This systematic identification of city–regionsglobally uncovers diverse organizational patterns across urban tiers,influenced by geography, level of development and infrastructure, offeringa valuable spatial dataset for regional planning, economic development andresource management
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Low-level radioactive waste management at Argonne National Laboratory-East
This paper is an overview of the low-level radioactive waste management practices and treatment systems at Argonne National Laboratory - East (ANL-E). It addresses the systems, processes, types of waste treated, and the status and performance of the systems. ANL-E is a Department of Energy laboratory that is engaged in a variety of research projects, some of which generate radioactive waste, in addition a significant amount of radioactive waste remains from previous projects and decontamination and decommissioning of facilities where this work was performed
High precision and continuous field measurements of δ 13C and δ 18O in carbon dioxide with a cryogen-free QCLAS
The present paper describes a compact and cryogen-free, quantum cascade laser based absorption spectrometer (QCLAS) designed for in situ, continuous and high precision isotope ratio measurements of atmospheric CO2. The mobile instrument incorporates several new features including a novel astigmatic multi-pass cell assembly, a quasi-room temperature quantum cascade laser, thermoelectrically cooled detectors as well as a new retrieval approach. The combination of these features now makes it possible to measure isotope ratios of ambient CO2 with a precision of 0.03 and 0.05‰ for δ13C and δ18O, respectively, using a 100s integration time. A robust and optimized calibration procedure was developed to bring the retrieved isotope ratios on an absolute scale. This assures an accuracy better than 0.1‰ under laboratory conditions. The instrument performance was also assessed in a field campaign in which the spectrometer operated autonomously and provided mixing ratio values for the main three CO2 isotopologues at one second time resolution. An accuracy of 0.2‰ was routinely obtained for both isotope ratios during the entire period. The results were in excellent agreement with the standard laboratory-based isotope ratio mass spectrometer measurements made on field-collected flask samples. A few illustrative examples are used to depict the potential of this optical method in atmosphere-biosphere researc
Vortex wandering in a forest of splayed columnar defects
We investigate the scaling properties of single flux lines in a random
pinning landscape consisting of splayed columnar defects. Such correlated
defects can be injected into Type II superconductors by inducing nuclear
fission or via direct heavy ion irradiation. The result is often very efficient
pinning of the vortices which gives, e.g., a strongly enhanced critical
current. The wandering exponent \zeta and the free energy exponent \omega of a
single flux line in such a disordered environment are obtained analytically
from scaling arguments combined with extreme-value statistics. In contrast to
the case of point disorder, where these exponents are universal, we find a
dependence of the exponents on details in the probability distribution of the
low lying energies of the columnar defects. The analytical results show
excellent agreement with numerical transfer matrix calculations in two and
three dimensions.Comment: 11 pages, 9 figure
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