Two interacting diffusing particles on low-dimensional discrete structures

In this paper we study the motion of two particles diffusing on low-dimensional discrete structures in presence of a hard-core repulsive interaction. We show that the problem can be mapped in two decoupled problems of single particles diffusing on different graphs by a transformation we call 'diffusion graph transform'. This technique is applied to study two specific cases: the narrow comb and the ladder lattice. We focus on the determination of the long time probabilities for the contact between particles and their reciprocal crossing. We also obtain the mean square dispersion of the particles in the case of the narrow comb lattice. The case of a sticking potential and of 'vicious' particles are discussed.Comment: 9 pages, 6 postscript figures, to appear in 'Journal of Physics A',-January 200

Exact time-dependent correlation functions for the symmetric exclusion process with open boundary

As a simple model for single-file diffusion of hard core particles we investigate the one-dimensional symmetric exclusion process. We consider an open semi-infinite system where one end is coupled to an external reservoir of constant density $\rho^\ast$ and which initially is in an non-equilibrium state with bulk density $\rho_0$. We calculate the exact time-dependent two-point density correlation function $C_{k,l}(t)\equiv -$ and the mean and variance of the integrated average net flux of particles $N(t)-N(0)$ that have entered (or left) the system up to time $t$. We find that the boundary region of the semi-infinite relaxing system is in a state similar to the bulk state of a finite stationary system driven by a boundary gradient. The symmetric exclusion model provides a rare example where such behavior can be proved rigorously on the level of equal-time two-point correlation functions. Some implications for the relaxational dynamics of entangled polymers and for single-file diffusion in colloidal systems are discussed.Comment: 11 pages, uses REVTEX, 2 figures. Minor typos corrected and reference 17 adde

Facilitators and Barriers to Participation in a Peer Support Intervention for Veterans With Chronic Pain

OBJECTIVE: To understand facilitators and barriers to participation in a peer support intervention for self-management of chronic pain. METHODS: After completing a pilot intervention study, peer coaches and their veteran patients took part in a qualitative, semistructured interview to explore their experiences with the intervention. Data were analyzed using an immersion/crystallization approach. RESULTS: Three facilitators and 2 barriers to patient participation in a peer support intervention for veterans with chronic pain emerged. Facilitators were (1) having a shared identity as veterans, (2) being partnered with a person who also has chronic pain, and (3) support from the study staff. Barriers were (1) logistical challenges, and (2) challenges to motivation and engagement in the intervention. DISCUSSION: Awareness of facilitators and barriers to participation in a peer-supported self-management program for chronic pain, as well as strategies to capitalize on facilitators and mitigate barriers, are essential for further study and ultimate clinical implementation of such a program

Correlates of Attendance in Psychiatric Services: A Critical Review

poster abstractAttendance and dropout are concerning problems in the mental health field. With dropout rates averaging around 50%, mental health agencies lose money and resources invested in missed appointments and under-attended groups, providers lose valuable time, and consumers do not receive recommended levels of services. While there is research on consumer, provider, and agency factors that affect attendance, it has not been integrated and reviewed in the context of community services for those with psychotic disorders. The authors conducted a critical review of literature examining correlates of attendance in community services provided to samples with psychotic disorders as the most prominent diagnostic category. Twenty-two studies were identified that met inclusion criteria. Over 100 unique correlates of attendance were tested; the authors categorized these into eight content areas: demographics, current functioning, history (psychiatric/functional), neurocognitive functioning, services/treatment, social functioning, self-stigma/insight, and symptoms/psychopathology. Correlates were also sorted according to how often they were examined and how many times they were found to be significantly related to consumer attendance. The category containing the most unique correlates was symptoms/psychopathology. Demographic correlates were researched the most, with three unique correlates examined in over ten studies (age, sex, and living situation). Of these demographic correlates, all but two were found significant 25% of the time or less, and none exceeded 40%. Alternatively, some correlates have been investigated few times, but with promising results and theoretical connections to attendance, such as baseline illness severity, which has been found significant in 75% of analyses. There is evidence that researchers are examining correlates for which there is little empirical evidence of a connection to attendance. This may lead to missed opportunities to maximize attendance, use of services, and resources. Implications for future research in the area are discussed

An interacting spin flip model for one-dimensional proton conduction

A discrete asymmetric exclusion process (ASEP) is developed to model proton conduction along one-dimensional water wires. Each lattice site represents a water molecule that can be in only one of three states; protonated, left-pointing, and right-pointing. Only a right(left)-pointing water can accept a proton from its left(right). Results of asymptotic mean field analysis and Monte-Carlo simulations for the three-species, open boundary exclusion model are presented and compared. The mean field results for the steady-state proton current suggest a number of regimes analogous to the low and maximal current phases found in the single species ASEP [B. Derrida, Physics Reports, {\bf 301}, 65-83, (1998)]. We find that the mean field results are accurate (compared with lattice Monte-Carlo simulations) only in the certain regimes. Refinements and extensions including more elaborate forces and pore defects are also discussed.Comment: 13pp, 6 fig

p-species integrable reaction-diffusion processes

We consider a process in which there are p-species of particles, i.e. A_1,A_2,...,A_p, on an infinite one-dimensional lattice. Each particle $A_i$ can diffuse to its right neighboring site with rate $D_i$, if this site is not already occupied. Also they have the exchange interaction A_j+A_i --> A_i+A_j with rate $r_{ij}.$ We study the range of parameters (interactions) for which the model is integrable. The wavefunctions of this multi--parameter family of integrable models are found. We also extend the 2--species model to the case in which the particles are able to diffuse to their right or left neighboring sites.Comment: 16 pages, LaTe

Subjective Experiences of the Benefits and Key Elements of a Cognitive Behavioral Intervention Focused on Community Work Outcomes in Persons With Mental Illness

New research suggests that group-based cognitive behavioral therapy (CBT) may help improve employment outcomes in persons with mental illness, yet the effects and potential key elements facilitating change in such interventions are unclear. Using a mixed methods approach, this study examined the perspectives of persons with mental illness after participating in a pilot study of the “CBT for Work Success” intervention. Findings demonstrate that participants valued the intervention and perceived that it assisted them in achieving work goals. Therapeutic effects included improved self-efficacy, work motivation, enhanced sense of self as workers, and increased beliefs that work success is attainable. CBT for Work Success elements perceived to be important in facilitating work goals included cognitive restructuring, behavioral coping strategies, problem solving work barriers, meaningful reflection on oneself as a worker, and important factors associated with the group process. The authors discuss the implications of these findings and future research directions

Persistence in the One-Dimensional A+B -> 0 Reaction-Diffusion Model

The persistence properties of a set of random walkers obeying the A+B -> 0 reaction, with equal initial density of particles and homogeneous initial conditions, is studied using two definitions of persistence. The probability, P(t), that an annihilation process has not occurred at a given site has the asymptotic form $P(t) -> const + t^{-\theta}$, where $\theta$ is the persistence exponent (``type I persistence''). We argue that, for a density of particles $\rho >> 1$, this non-trivial exponent is identical to that governing the persistence properties of the one-dimensional diffusion equation, where $\theta \approx 0.1207$. In the case of an initially low density, $\rho_0 << 1$, we find $\theta \approx 1/4$ asymptotically. The probability that a site remains unvisited by any random walker (``type II persistence'') is also investigated and found to decay with a stretched exponential form, $P(t) \sim \exp(-const \rho_0^{1/2}t^{1/4})$, provided $\rho_0 << 1$. A heuristic argument for this behavior, based on an exactly solvable toy model, is presented.Comment: 11 RevTeX pages, 19 EPS figure

Asymmetric exclusion process with next-nearest-neighbor interaction: some comments on traffic flow and a nonequilibrium reentrance transition

We study the steady-state behavior of a driven non-equilibrium lattice gas of hard-core particles with next-nearest-neighbor interaction. We calculate the exact stationary distribution of the periodic system and for a particular line in the phase diagram of the system with open boundaries where particles can enter and leave the system. For repulsive interactions the dynamics can be interpreted as a two-speed model for traffic flow. The exact stationary distribution of the periodic continuous-time system turns out to coincide with that of the asymmetric exclusion process (ASEP) with discrete-time parallel update. However, unlike in the (single-speed) ASEP, the exact flow diagram for the two-speed model resembles in some important features the flow diagram of real traffic. The stationary phase diagram of the open system obtained from Monte Carlo simulations can be understood in terms of a shock moving through the system and an overfeeding effect at the boundaries, thus confirming theoretical predictions of a recently developed general theory of boundary-induced phase transitions. In the case of attractive interaction we observe an unexpected reentrance transition due to boundary effects.Comment: 12 pages, Revtex, 7 figure