6,342 research outputs found
Maximum Distance Between the Leader and the Laggard for Three Brownian Walkers
We consider three independent Brownian walkers moving on a line. The process
terminates when the left-most walker (the `Leader') meets either of the other
two walkers. For arbitrary values of the diffusion constants D_1 (the Leader),
D_2 and D_3 of the three walkers, we compute the probability distribution
P(m|y_2,y_3) of the maximum distance m between the Leader and the current
right-most particle (the `Laggard') during the process, where y_2 and y_3 are
the initial distances between the leader and the other two walkers. The result
has, for large m, the form P(m|y_2,y_3) \sim A(y_2,y_3) m^{-\delta}, where
\delta = (2\pi-\theta)/(\pi-\theta) and \theta =
cos^{-1}(D_1/\sqrt{(D_1+D_2)(D_1+D_3)}. The amplitude A(y_2,y_3) is also
determined exactly
Antisite Domains in Double Perovskite Ferromagnets: Impact on Magnetotransport and Half-metallicity
Several double perovskite materials of the form A_2BB'O_6 exhibit high
ferromagnetic T_c, and significant low field magnetoresistance. They are also a
candidate source of spin polarized electrons. The potential usefulness of these
materials is, however, frustrated by mislocation of the B and B' ions, which do
not organise themselves in the ideal alternating structure. The result is a
strong dependence of physical properties on preparative conditions, reducing
the magnetization and destroying the half-metallicity. We provide the first
results on the impact of spatially correlated antisite disorder, as observed
experimentally, on the ferromagnetic double perovskites. The antisite domains
suppress magnetism and half-metallicity, as expected, but lead to a dramatic
enhancement of the low field magnetoresistance.Comment: 6 pages, pdflatex, EPL styl
Transitions through Critical Temperatures in Nematic Liquid Crystals
We obtain ‘dynamic’ estimates for critical nematic liquid crystal (LC) temperatures with a slowly varying temperature-dependent control variable. We focus on two critical temperatures : the supercooling temperature below which the isotropic phase loses stability and the superheating temperature above which the ordered nematic states do not exist. In contrast to the static problem, the isotropic phase exhibits a memory effect below the supercooling temperature. This delayed loss of stability is independent of the rate of change of temperature and depends purely on the initial value of the temperature
Persistence and Quiescence of Seismicity on Fault Systems
We study the statistics of simulated earthquakes in a quasistatic model of
two parallel heterogeneous faults within a slowly driven elastic tectonic
plate. The probability that one fault remains dormant while the other is active
for a time Dt following the previous activity shift is proportional to the
inverse of Dt to the power 1+x, a result that is robust in the presence of
annealed noise and strength weakening. A mean field theory accounts for the
observed dependence of the persistence exponent x as a function of
heterogeneity and distance between faults. These results continue to hold if
the number of competing faults is increased. This is related to the persistence
phenomenon discovered in a large variety of systems, which specifies how long a
relaxing dynamical system remains in a neighborhood of its initial
configuration. Our persistence exponent is found to vary as a function of
heterogeneity and distance between faults, thus defining a novel universality
class.Comment: 4 pages, 3 figures, Revte
Midpalatal implants vs headgear for orthodontic anchorage - a randomized clinical trial: Cephalometric results
OBJECTIVE: To compare the clinical effectiveness of the mid-palatal implant as a method of reinforcing anchorage during orthodontic treatment with that of conventional extra-oral anchorage.
DESIGN: A prospective, randomized, clinical trial
Setting: Chesterfield and North Derbyshire Royal Hospital NHS Trust and the Charles Clifford Dental Hospital, Sheffield.
SUBJECTS AND METHODS: 51 orthodontic patients between the ages of 12 and 39, with a class II division 1 malocclusion and ‘absolute anchorage’ requirements were randomly allocated to either receive a mid-palatal implant or headgear to reinforce orthodontic anchorage. The main outcome of the trial was to compare the mesial movement of the molars and incisors of the two treatment groups between T1 (start) and T2 (end of anchorage reinforcement) as measured from cephalometric radiographs.
RESULTS: The reproducibility of the measuring technique was acceptable. There were significant differences between the T1 and T2 measurements within the implant group for the position of the maxillary central incisor (p<0.001), position of the maxillary molar (p=0.009) and position of the mandibular molar (p<0.001). There were significant differences within the headgear group for the position of the mandibular central incisor (p<0.045), position of the maxillary molar (p=<0.001) and position of the mandibular molar (p<0.001). All the skeletal and dental points moved mesially more in the headgear group during treatment than in the implant group. These ranged from an average of 0.5mm more mesial for the mandibular permanent molar to 1.5mm more mesial for the maxillary molar and mandibular base. None of the treatment changes between the implant and headgear groups were statistically significant.
CONCLUSIONS: Mid-palatal implants are an acceptable technique for reinforcing anchorage in the orthodontic patient
Area Distribution of Elastic Brownian Motion
We calculate the excursion and meander area distributions of the elastic
Brownian motion by using the self adjoint extension of the Hamiltonian of the
free quantum particle on the half line. We also give some comments on the area
of the Brownian motion bridge on the real line with the origin removed. We will
stress on the power of self adjoint extension to investigate different possible
boundary conditions for the stochastic processes.Comment: 18 pages, published versio
Midpalatal implants vs headgear for orthodontic anchorage - a randomized clinical trial: Cephalometric results
OBJECTIVE: To compare the clinical effectiveness of the mid-palatal implant as a method of reinforcing anchorage during orthodontic treatment with that of conventional extra-oral anchorage.
DESIGN: A prospective, randomized, clinical trial
Setting: Chesterfield and North Derbyshire Royal Hospital NHS Trust and the Charles Clifford Dental Hospital, Sheffield.
SUBJECTS AND METHODS: 51 orthodontic patients between the ages of 12 and 39, with a class II division 1 malocclusion and ‘absolute anchorage’ requirements were randomly allocated to either receive a mid-palatal implant or headgear to reinforce orthodontic anchorage. The main outcome of the trial was to compare the mesial movement of the molars and incisors of the two treatment groups between T1 (start) and T2 (end of anchorage reinforcement) as measured from cephalometric radiographs.
RESULTS: The reproducibility of the measuring technique was acceptable. There were significant differences between the T1 and T2 measurements within the implant group for the position of the maxillary central incisor (p<0.001), position of the maxillary molar (p=0.009) and position of the mandibular molar (p<0.001). There were significant differences within the headgear group for the position of the mandibular central incisor (p<0.045), position of the maxillary molar (p=<0.001) and position of the mandibular molar (p<0.001). All the skeletal and dental points moved mesially more in the headgear group during treatment than in the implant group. These ranged from an average of 0.5mm more mesial for the mandibular permanent molar to 1.5mm more mesial for the maxillary molar and mandibular base. None of the treatment changes between the implant and headgear groups were statistically significant.
CONCLUSIONS: Mid-palatal implants are an acceptable technique for reinforcing anchorage in the orthodontic patient
Understanding Search Trees via Statistical Physics
We study the random m-ary search tree model (where m stands for the number of
branches of a search tree), an important problem for data storage in computer
science, using a variety of statistical physics techniques that allow us to
obtain exact asymptotic results. In particular, we show that the probability
distributions of extreme observables associated with a random search tree such
as the height and the balanced height of a tree have a traveling front
structure. In addition, the variance of the number of nodes needed to store a
data string of a given size N is shown to undergo a striking phase transition
at a critical value of the branching ratio m_c=26. We identify the mechanism of
this phase transition, show that it is generic and occurs in various other
problems as well. New results are obtained when each element of the data string
is a D-dimensional vector. We show that this problem also has a phase
transition at a critical dimension, D_c= \pi/\sin^{-1}(1/\sqrt{8})=8.69363...Comment: 11 pages, 8 .eps figures included. Invited contribution to
STATPHYS-22 held at Bangalore (India) in July 2004. To appear in the
proceedings of STATPHYS-2
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