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## Head injuries related to the use of baby walkers.

Stoffman, J M; Bass, M J; Fox, A M
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.39%
To determine what proportion of head injuries in children under 24 months of age who presented to an emergency department were related to the use of baby walkers, we reviewed the charts of 52 such children. Walkers were involved in 42% of the head injuries in the children under 12 months of age and in none of those in the children aged 12 to 24 months. All walker-related injuries, including skull fractures in three children, involved stairs (p less than 0.001). Questionnaires were also sent to all families with children aged 3 to 18 months attending a private pediatric practice to determine the prevalence of falls involving baby walkers among these children and the factors associated with such falls. Of the 152 responding families 82% reported using or having used a walker. Thirty-six percent of the families reported that their child had a fall while in a walker, with 8.8% of the falls resulting in contact with a doctor. Walker-related falls were directly associated with time spent in the walker (p less than 0.001) and with a previous fall from the walker by an older sibling (p less than 0.03). Since there is no demonstrated benefit of walkers, their use should not be encouraged, and parents should be advised of their potential danger.

## Risks of Baby Walkers and Options for Prevention

Aziz, Alnoor; McIntyre, Lynn; Khazen, Roch
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.53%
Recent studies have reported fatal head injuries associated with baby walkers. Skull fractures and hospital admissions are significantly higher for infants who have received head injuries while using a walker. Thirty to 50% of infants regularly placed in walkers experience an accident or injury related to the device. Most injuries are minor cuts, abrasions and contusions. While there are many hazards, no benefits have been documented. The walkers do not help children learn to walk. Options for preventing injury including banning baby walkers, product design regulations, and public education about the risks. An outright ban would be difficult, because walkers are not considered inherently dangerous; they become so when parental supervision is lacking. Although design specifications will decrease some walker-related injuries, they will not prevent severe or fatal head injuries associated with falls down stairs. Public awareness of hazards from baby walkers and discouragement of their use are recommended preventive measures at this time.

## Hydrogel Walkers with Electro-Driven Motility for Cargo Transport

Yang, Chao; Wang, Wei; Yao, Chen; Xie, Rui; Ju, Xiao-Jie; Liu, Zhuang; Chu, Liang-Yin
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.47%
In this study, soft hydrogel walkers with electro-driven motility for cargo transport have been developed via a facile mould-assisted strategy. The hydrogel walkers consisting of polyanionic poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylamide) exhibit an arc looper-like shape with two “legs” for walking. The hydrogel walkers can reversibly bend and stretch via repeated “on/off” electro-triggers in electrolyte solution. Based on such bending/stretching behaviors, the hydrogel walkers can move their two “legs” to achieve one-directional walking motion on a rough surface via repeated “on/off” electro-triggering cycles. Moreover, the hydrogel walkers loaded with very heavy cargo also exhibit excellent walking motion for cargo transport. Such hydrogel systems create new opportunities for developing electro-controlled soft systems with simple design/fabrication strategies in the soft robotic field for remote manipulation and transportation.

## Moments of vicious walkers and M\"obius graph expansions

Katori, Makoto; Komatsuda, Naoaki
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.28%
A system of Brownian motions in one-dimension all started from the origin and conditioned never to collide with each other in a given finite time-interval $(0, T]$ is studied. The spatial distribution of such vicious walkers can be described by using the repulsive eigenvalue-statistics of random Hermitian matrices and it was shown that the present vicious walker model exhibits a transition from the Gaussian unitary ensemble (GUE) statistics to the Gaussian orthogonal ensemble (GOE) statistics as the time $t$ is going on from 0 to $T$. In the present paper, we characterize this GUE-to-GOE transition by presenting the graphical expansion formula for the moments of positions of vicious walkers. In the GUE limit $t \to 0$, only the ribbon graphs contribute and the problem is reduced to the classification of orientable surfaces by genus. Following the time evolution of the vicious walkers, however, the graphs with twisted ribbons, called M\"obius graphs, increase their contribution to our expansion formula, and we have to deal with the topology of non-orientable surfaces. Application of the recent exact result of dynamical correlation functions yields closed expressions for the coefficients in the M\"obius expansion using the Stirling numbers of the first kind.; Comment: REVTeX4...

## Vicious accelerating walkers

Xu, S. -L. -Y.; Schwarz, J. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.47%
A vicious walker system consists of N random walkers on a line with any two walkers annihilating each other upon meeting. We study a system of N vicious accelerating walkers with the velocity undergoing Gaussian fluctuations, as opposed to the position. We numerically compute the survival probability exponent, {\alpha}, for this system, which characterizes the probability for any two walkers not to meet. For example, for N = 3, {\alpha} = 0.71 \pm 0.01. Based on our numerical data, we conjecture that 1/8N(N - 1) is an upper bound on {\alpha}. We also numerically study N vicious Levy flights and find, for instance, for N = 3 and a Levy index {\mu} = 1 that {\alpha} = 1.31 \pm 0.03. Vicious accelerating walkers relate to no-crossing configurations of semiflexible polymer brushes and may prove relevant for a non-Markovian extension of Dyson's Brownian motion model.; Comment: 7.5 pages, 5 figures

## Vicious walkers, friendly walkers and Young tableaux II: With a wall

Krattenthaler, Christian; Guttmann, Anthony J.; Viennot, Xavier G.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.39%
We derive new results for the number of star and watermelon configurations of vicious walkers in the presence of an impenetrable wall by showing that these follow from standard results in the theory of Young tableaux, and combinatorial descriptions of symmetric functions. For the problem of $n$-friendly walkers, we derive exact asymptotics for the number of stars and watermelons both in the absence of a wall and in the presence of a wall.; Comment: 35 pages, AmS-LaTeX; Definitions of n-friendly walkers clarified; the statement of Theorem 4 and its proof were corrected

## Vicious Walkers in a Potential

Bray, Alan J.; Winkler, Karen
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.53%
We consider N vicious walkers moving in one dimension in a one-body potential v(x). Using the backward Fokker-Planck equation we derive exact results for the asymptotic form of the survival probability Q(x,t) of vicious walkers initially located at (x_1,...,x_N) = x, when v(x) is an arbitrary attractive potential. Explicit results are given for a square-well potential with absorbing or reflecting boundary conditions at the walls, and for a harmonic potential with an absorbing or reflecting boundary at the origin and the walkers starting on the positive half line. By mapping the problem of N vicious walkers in zero potential onto the harmonic potential problem, we rederive the results of Fisher [J. Stat. Phys. 34, 667 (1984)] and Krattenthaler et al. [J. Phys. A 33}, 8835 (2000)] respectively for vicious walkers on an infinite line and on a semi-infinite line with an absorbing wall at the origin. This mapping also gives a new result for vicious walkers on a semi-infinite line with a reflecting boundary at the origin: Q(x,t) \sim t^{-N(N-1)/2}.; Comment: 5 pages

## A Reflection Principle for Three Vicious Walkers

Chen, William Y. C.; Dou, Donna Q. J.; Zhang, Terence Y. J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.47%
We establish a reflection principle for three lattice walkers and use this principle to reduce the enumeration of the configurations of three vicious walkers to that of configurations of two vicious walkers. In the combinatorial treatment of two vicious walkers, we make connections to two-chain watermelons and to the classical ballot problem. Precisely, the reflection principle leads to a bijection between three walks $(L_1, L_2, L_3)$ such that $L_2$ intersects both $L_1$ and $L_3$ and three walks $(L_1, L_2, L_3)$ such that $L_1$ intersects $L_3$. Hence we find a combinatorial interpretation of the formula for the generating function for the number of configurations of three vicious walkers, originally derived by Bousquet-M\'elou by using the kernel method, and independently by Gessel by using tableaux and symmetric functions.; Comment: 12 pages, 5 figures

## Random walk on a population of random walkers

Agliari, E.; Burioni, R.; Cassi, D.; Neri, F. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.28%
We consider a population of $N$ labeled random walkers moving on a substrate, and an excitation jumping among the walkers upon contact. The label $\mathcal{X}(t)$ of the walker carrying the excitation at time $t$ can be viewed as a stochastic process, where the transition probabilities are a stochastic process themselves. Upon mapping onto two simpler processes, the quantities characterizing $\mathcal{X}(t)$ can be calculated in the limit of long times and low walkers density. The results are compared with numerical simulations. Several different topologies for the substrate underlying diffusion are considered.; Comment: 16 pages, 9 figures

## Exact distributions of the number of distinct and common sites visited by N independent random walkers

Kundu, Anupam; Majumdar, Satya N.; Schehr, Gregory
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.28%
We study the number of distinct sites S_N(t) and common sites W_N(t) visited by N independent one dimensional random walkers, all starting at the origin, after t time steps. We show that these two random variables can be mapped onto extreme value quantities associated to N independent random walkers. Using this mapping, we compute exactly their probability distributions P_N^d(S,t) and P_N^d(W,t) for any value of N in the limit of large time t, where the random walkers can be described by Brownian motions. In the large N limit one finds that S_N(t)/\sqrt{t} \propto 2 \sqrt{\log N} + \widetilde{s}/(2 \sqrt{\log N}) and W_N(t)/\sqrt{t} \propto \widetilde{w}/N where \widetilde{s} and \widetilde{w} are random variables whose probability density functions (pdfs) are computed exactly and are found to be non trivial. We verify our results through direct numerical simulations.; Comment: 5 pages, 3 figures

## Maximum Distance Between the Leader and the Laggard for Three Brownian Walkers

Majumdar, Satya N.; Bray, Alan J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.39%
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.

## Arrival statistics and exploration properties of mortal walkers

Yuste, Santos B.; Abad, E.; Lindenberg, Katja
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.39%
We study some of the salient features of the arrival statistics and explo- ration properties of mortal random walkers, that is, walkers that may die as they move, or as they wait to move. Such evanescence or death events have profound consequences for quantities such as the number of distinct sites visited which are relevant for the computation of encounter- controlled rates in chemical kinetics. We exploit the observation that well-known methods developed decades ago for immortal walkers are widely applicable to mortal walkers. The particular cases of exponential and power-law evanescence are considered in detail. Finally, we discuss the relevance of our results to the target problem with mortal traps and a particular application thereof, namely, the defect di?usion model. Evanescence of defects is postulated as a possible complementary contri- bution or perhaps even an alternative to anomalous di?usion to explain observed stretched exponential relaxation behavior.

## Exact encounter times for many random walkers on regular and complex networks

Sanders, David P.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.28%
The exact mean time between encounters of a given particle in a system consisting of many particles undergoing random walks in discrete time is calculated, on both regular and complex networks. Analytical results are obtained both for independent walkers, where any number of walkers can occupy the same site, and for walkers with an exclusion interaction, when no site can contain more than one walker. These analytical results are then compared with numerical simulations, showing very good agreement.; Comment: 11 pages, 4 figures. Submitted for publication

## Caught Active Walkers

Schoellmann, S.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.28%
A discrete implementation on a lattice of the Active Walker Model is presented. After the model's validity is shown in simple simulations, more complex simulations of walkers passing consecutively a lattice from an arbitrary starting point at the left border to a random destination on the right border are presented. It is found that walkers may be caught at a certain position by bouncing back and forth between two contiguous lattice sites. The statistical characteristics of this catchment effect are being studied. The probability distribution of the number of walkers having passed the lattice before the catchment occurred shows a exponential decrease to higher numbers. Furthermore, the influence of some parameters of the model on the catchment phenomenon is discussed. Position and height of the maxima of these distributions show a linear dependency on a parameter.; Comment: 8 pages, 10 figures

## Vicious Random Walkers and a Discretization of Gaussian Random Matrix Ensembles

Nagao, Taro; Forrester, Peter J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.28%
The vicious random walker problem on a one dimensional lattice is considered. Many walkers take simultaneous steps on the lattice and the configurations in which two of them arrive at the same site are prohibited. It is known that the probability distribution of N walkers after M steps can be written in a determinant form. Using an integration technique borrowed from the theory of random matrices, we show that arbitrary k-th order correlation functions of the walkers can be expressed as quaternion determinants whose elements are compactly expressed in terms of symmetric Hahn polynomials.; Comment: LaTeX, 15 pages, 1 figure, minor corrections made before publication in Nucl. Phys. B

## Vicious walkers, friendly walkers and Young tableaux III: Between two walls

Krattenthaler, Christian; Guttmann, Anthony J.; Viennot, Xavier G.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.28%
We derive exact and asymptotic results for the number of star and watermelon configurations of vicious walkers confined to lie between two impenetrable walls, as well as for the analogous problem for $\infty$-friendly walkers. Our proofs make use of results from symmetric function theory and the theory of basic hypergeometric series.; Comment: 15 pages, LaTeX; several typos in Section 3 corrected

## Quantum Walk-based Generation of Entanglement Between Two Walkers

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.39%
Quantum walks can be used either as tools for quantum algorithm development or as entanglement generators, potentially useful to test quantum hardware. We present a novel algorithm based on a discrete Hadamard quantum walk on a line with one coin and two walkers whose purpose is to generate entanglement between walkers. We provide several classical computer simulations of our quantum algorithm in which we show that, although the asymptotical amount of entanglement generated between walkers does not reach the highest degree of entanglement possible at each step for either coin measurement outcome, the entanglement ratio (entanglement generated/highest value of entanglement possible, for each step) tends to converge, and the actual convergence value depends on the coin initial state and on the coin measurement outcome. Furthermore, our numerical simulations show that, for the quantum walks used in our algorithm, the value towards which entanglement ratio converges also depends on the position probability distribution symmetry of a quantum walk computed with one single walker and the same coin initial state employed in the corresponding quantum walk with two walkers.; Comment: 8 pages, 15 figures

## Scaling Limit of Vicious Walkers, Schur Function, and Gaussian Random Matrix Ensemble

Katori, M.; Tanemura, H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.53%
We consider the diffusion scaling limit of the vicious walkers and derive the time-dependent spatial-distribution function of walkers. The dependence on initial configurations of walkers is generally described by using the symmetric polynomials called the Schur functions. In the special case in the scaling limit that all walkers are started from the origin, the probability density is simplified and it shows that the positions of walkers on the real axis at time one is identically distributed with the eigenvalues of random matrices in the Gaussian orthogonal ensemble. Since the diffusion scaling limit makes the vicious walkers converge to the nonintersecting Brownian motions in distribution, the present study will provide a new method to analyze intersection problems of Brownian motions in one-dimension.; Comment: 4 pages,revtex,no figures

## Fraction of uninfected walkers in the one-dimensional Potts model

O'Donoghue, S. J.; Bray, A. J.