1,697 research outputs found
Multicanonical Parallel Tempering
We present a novel implementation of the parallel tempering Monte Carlo
method in a multicanonical ensemble. Multicanonical weights are derived by a
self-consistent iterative process using a Boltzmann inversion of global energy
histograms. This procedure gives rise to a much broader overlap of
thermodynamic-property histograms; fewer replicas are necessary in parallel
tempering simulations, and the acceptance of trial swap moves can be made
arbitrarily high. We demonstrate the usefulness of the method in the context of
a grand-multicanonical ensemble, where we use multicanonical simulations in
energy space with the addition of an unmodified chemical potential term in
particle-number space. Several possible implementations are discussed, and the
best choice is presented in the context of the liquid-gas phase transition of
the Lennard-Jones fluid. A substantial decrease in the necessary number of
replicas can be achieved through the proposed method, thereby providing a
higher efficiency and the possibility of parallelization.Comment: 8 pages, 3 figure, accepted by J Chem Phy
A point is normal for almost all maps ÎČx+α mod 1 or generalized ÎČ-transformations
We consider the map Tα,ÎČ(x):=ÎČx+αmod1, which admits a unique probability measure Όα,ÎČ of maximal entropy. For x[0,1], we show that the orbit of x is Όα,ÎČ-normal for almost all (α,ÎČ)[0,1)Ă(1,â) (with respect to Lebesgue measure). Nevertheless, we construct analytic curves in [0,1)Ă(1,â) along which the orbit of x=0 is Όα,ÎČ-normal at no more than one point. These curves are disjoint and fill the set [0,1)Ă(1,â). We also study the generalized ÎČ-transformations (in particular, the tent map). We show that the critical orbit x=1 is normal with respect to the measure of maximal entropy for almost all
Ătude du colmatage de membranes d'osmose inverse utilisĂ©es pour la prĂ©paration des eaux de dialyse rĂ©nale
L'osmose inverse est l'Ă©lĂ©ment clef de la production d'eau ultrapure servant dans la prĂ©paration du liquide de dialyse rĂ©nale. Le vieillissement des membranes d'osmose inverse se traduit par une dĂ©rive croissante de la conductivitĂ© en sortie de membrane et par une augmentation de la teneur en bactĂ©ries dans le permĂ©at dĂ©livrĂ© en sortie d'osmose inverse, entraĂźnant un risque de contamination pour le patient.Les suivis en conductivitĂ© et numĂ©rations bactĂ©riennes dans la chaĂźne de production d'eau osmosĂ©e de l'HĂŽpital de Colmar (France) montre un fort dysfonctionnement au niveau des prĂ©traitements et notamment du charbon actif, siĂšge d'une importante prolifĂ©ration bactĂ©rienne (2.3 103 colonies pour 100 ml en amont du charbon actif , 1.1 105 pour 100 ml en aval). Une Ă©tude de corrĂ©lations entre entrĂ©e et sortie d'osmoseurs montre que la forte teneur en germes en sortie du charbon actif est directement responsable de la prĂ©sence des bactĂ©ries dans le permĂ©at.Des tests hydrauliques effectuĂ©s sur les membranes aprĂšs quatre annĂ©es d'utilisation intensive (6500 heures par an), permettent d'identifier les mĂ©canismes prĂ©pondĂ©rants de vieillissement et de colmatage des membranes utilisĂ©es Ă l'hĂŽpital de Colmar (compaction, formation d'un dĂ©pĂŽt et altĂ©ration de structure).Afin d'identifier les substances colmatantes non retenues par le prĂ©traitement, le film colmatant est analysĂ© par analyse Ă©lĂ©mentaire, spectrophotomĂ©trie infrarouge, diffraction X et zĂȘtamĂ©trie, ce qui nous a permis de mettre en Ă©vidence la prĂ©sence notamment d'argiles, de silice et de substances humiques.The use of reverse osmosis to produce ultrapure water for kidney patients is very prevalent at the present time. About 20000 patients are treated every day in France and the cost of treatment is estimated at 10 thousand million French francs. The patients are provided with a permeate which in principle contains neither ions nor bacteria, which can cause disease and irreversible alteration of the upper-arm articulations. After several months of utilization, the presence of a foulant deposit and biofilm proliferation is often noted on the thin layered active surface of the polyamide membranes. In many cases, the membrane may become irreversibly fouled and require replacement.The aim of this work was to determine the causes of membrane fouling at a reverse osmosis plant in "HĂŽpital Pasteur" (Colmar, France). First we analyzed the ion-rejection capacity of membranes and the evolution of conductivity over 200 weeks. We observed an increasing drift in conductivity, which could not be halted by cleaning and regeneration procedures. In the second phase of the study, we carried out microbiological studies at many sampling points of the ultrapure water plant in "HĂŽpital Pasteur". We noted a very important proliferation of bacteria downstream of the pretreatments. The activated charcoal unit is responsible for this problem (2.3 x 103 UFC / 100 mL upstream from the activated charcoal bed, 1.1 x 105 UFC / 100 mL downstream). We noted an important dysfunction in the pretreatment, essentially attributable to the activated charcoal (bacteria) and the resins (silica).We performed tests with x-ray diffraction as a rapid method to determine the crystalline forms present. In the foulant deposits, we found quartz and clay. Infrared spectroscopy is useful in determining the type of organic constituents; in our deposits we noted the presence of humic materials. The analysis of those deposits gave essentially carbon and silicon. The foulant deposits were of organic and crystalline origins
Experiences of LNU Neophyte Teachers: Cues for a Viable Mentoring Program
The usefulness of teachersâ mentoring program cannot be underestimated. Some universities and colleges in the Philippines have been implementing this kind of program with different approaches, content, and scope. The extent of mentoring programs to improve teaching careers has been studied here and abroad. Results remain inconclusive. This case study with a phenomenological peg has explored the lived experiences of neophyte teachers through semi-structured interviews and focus group discussions. Their experiences in the first years of teaching were characterized by uncertainties, anxieties, struggles, and difficulties emanating from their lack of expertise on various aspects related to teaching practice, lack of knowledge about the culture and context of the university in which they were teaching, and lack of knowledge about the learners. With these specific inadequacies identified and the novice teachersâ implicit desire to be mentored, cues for a viable neophyte teacherâs mentoring program are drawn in the context of a teacher-training university
A model of interacting Navier-Stokes singularities
We introduce a model of interacting singularities of Navier-Stokes, named
pin\,cons. They follow a Hamiltonian dynamics, obtained by the condition that
the velocity field around these singularities obeys locally Navier-Stokes
equations. This model can be seen of a generalization of the vorton model of
Novikov, that was derived for the Euler equations. When immersed in a regular
field, the pin\,cons are further transported and sheared by the regular field,
while applying a stress onto the regular field, that becomes dominant at a
scale that is smaller than the Kolmogorov length. We apply this model to
compute the motion of a dipole of pin\,cons. When the initial relative
orientation of the dipole is inside the interval (0, pi/2), a dipole made of
pin\,con of same intensity exhibits a transient collapse stage, following a
scaling with dipole radius tending to 0 like (tc - t) power 0.63. For long
time, the dynamics of the dipole is however repulsive, with both components
running away from each other to infinity.Comment: 24 pages 13 figure
Pair distribution function and structure factor of spherical particles
The availability of neutron spallation-source instruments that provide total
scattering powder diffraction has led to an increased application of real-space
structure analysis using the pair distribution function. Currently, the
analytical treatment of finite size effects within pair distribution refinement
procedures is limited. To that end, an envelope function is derived which
transforms the pair distribution function of an infinite solid into that of a
spherical particle with the same crystal structure. Distributions of particle
sizes are then considered, and the associated envelope function is used to
predict the particle size distribution of an experimental sample of gold
nanoparticles from its pair distribution function alone. Finally, complementing
the wealth of existing diffraction analysis, the peak broadening for the
structure factor of spherical particles, expressed as a convolution derived
from the envelope functions, is calculated exactly for all particle size
distributions considered, and peak maxima, offsets, and asymmetries are
discussed.Comment: 7 pages, 6 figure
Time-Delay Interferometry
Equal-arm interferometric detectors of gravitational radiation allow phase
measurements many orders of magnitude below the intrinsic phase stability of
the laser injecting light into their arms. This is because the noise in the
laser light is common to both arms, experiencing exactly the same delay, and
thus cancels when it is differenced at the photo detector. In this situation,
much lower level secondary noises then set overall performance. If, however,
the two arms have different lengths (as will necessarily be the case with
space-borne interferometers), the laser noise experiences different delays in
the two arms and will hence not directly cancel at the detector. In order to
solve this problem, a technique involving heterodyne interferometry with
unequal arm lengths and independent phase-difference readouts has been
proposed. It relies on properly time-shifting and linearly combining
independent Doppler measurements, and for this reason it has been called
Time-Delay Interferometry (or TDI). This article provides an overview of the
theory and mathematical foundations of TDI as it will be implemented by the
forthcoming space-based interferometers such as the Laser Interferometer Space
Antenna (LISA) mission. We have purposely left out from this first version of
our ``Living Review'' article on TDI all the results of more practical and
experimental nature, as well as all the aspects of TDI that the data analysts
will need to account for when analyzing the LISA TDI data combinations. Our
forthcoming ``second edition'' of this review paper will include these topics.Comment: 51 pages, 11 figures. To appear in: Living Reviews. Added conten
Parity and Time Reversal in the Spin-Rotation Interaction
A recently reported discrepancy between experimental and theoretical values
of the muon's g-2 factor is interpreted as due to small violations of the
conservation of P and T in the spin-rotation coupling. The experiments place an
upper limit on these violations and on the weight change of spinning
gyroscopes.Comment: 3 page
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