Localization of polymers in a finite medium with fixed random obstacles

In this paper we investigate the conformation statistics of a Gaussian chain embedded in a medium of finite size, in the presence of quenched random obstacles. The similarities and differences between the case of random obstacles and the case of a Gaussian random potential are elucidated. The connection with the density of states of electrons in a metal with random repulsive impurities of finite range is discussed. We also interpret the results obtained in some previous numerical simulations.Comment: 23 pages, 3 figures, revte

Polymers with self-avoiding interaction in random media: a localization-delocalization transition

In this paper we investigate the problem of a long self-avoiding polymer chain immersed in a random medium. We find that in the limit of a very long chain and when the self-avoiding interaction is weak, the conformation of the chain consists of many ``blobs'' with connecting segments. The blobs are sections of the molecule curled up in regions of low potential in the case of a Gaussian distributed random potential or in regions of relatively low density of obstacles in the case of randomly distributed hard obstacles. We find that as the strength of the self-avoiding interaction is increased the chain undergoes a delocalization transition in the sense that the appropriate free energy per monomer is no longer negative. The chain is then no longer bound to a particular location in the medium but can easily wander around under the influence of a small perturbation. For a localized chain we estimate quantitatively the expected number of monomers in the ``blobs'' and in the connecting segments.Comment: 20 pages, 2 figures, revtex

Localization of a polymer in random media: Relation to the localization of a quantum particle

In this paper we consider in detail the connection between the problem of a polymer in a random medium and that of a quantum particle in a random potential. We are interested in a system of finite volume where the polymer is known to be {\it localized} inside a low minimum of the potential. We show how the end-to-end distance of a polymer which is free to move can be obtained from the density of states of the quantum particle using extreme value statistics. We give a physical interpretation to the recently discovered one-step replica-symmetry-breaking solution for the polymer (Phys. Rev. E{\bf 61}, 1729 (2000)) in terms of the statistics of localized tail states. Numerical solutions of the variational equations for chains of different length are performed and compared with quenched averages computed directly by using the eigenfunctions and eigenenergies of the Schr\"odinger equation for a particle in a one-dimensional random potential. The quantities investigated are the radius of gyration of a free gaussian chain, its mean square distance from the origin and the end-to-end distance of a tethered chain. The probability distribution for the position of the chain is also investigated. The glassiness of the system is explained and is estimated from the variance of the measured quantities.Comment: RevTex, 44 pages, 13 figure

CHALLENGES AND CRITICAL SUCCESS FACTORS FOR E-PROCUREMENT ADOPTION IN ETHIOPIA

To ensure public procurement process fair, transparent, efficient and ethical, the Ethiopian Government implemented e-procurement adoption in selected pilot public organizations. This study intended to identify the major perceived challenges and critical success factors for e-procurement implementation and to ascertain strategies to mitigating the existing perceived challenges for e-procurement implementation in nine federal level organizations IN Ethiopia, selected as pilot scaled-down e-procurement implementation sites. Interview and structured questionnaire were used to collect primary data from purposively selected top managements and experts with directorate position from Finance, Procurement and ICT department from a total of 27and 54 employees, respectively and carried out analysis with 89 percent response rate. The result revealed that, man-power retention, inconsistent and disruptive infrastructure, integration with the legacy system, top management and employees’ commitment and attitude, supplier integration, security fear, weak and inconsistent support, poor monitoring and evaluation practices were found as the major challenges. While, training given to employees on how to use e-procurement tools and best procurement practices, the existence of change management programs for users on implementation of e-procurement through effective consultations and the high skill of procurement employees with IT perspective were found to be the major critical success factor

Domain wall roughening in dipolar films in the presence of disorder

We derive a low-energy Hamiltonian for the elastic energy of a N\'eel domain wall in a thin film with in-plane magnetization, where we consider the contribution of the long-range dipolar interaction beyond the quadratic approximation. We show that such a Hamiltonian is analogous to the Hamiltonian of a one-dimensional polaron in an external random potential. We use a replica variational method to compute the roughening exponent of the domain wall for the case of two-dimensional dipolar interactions.Comment: REVTEX, 35 pages, 2 figures. The text suffered minor changes and references 1,2 and 12 were added to conform with the referee's repor

Solvable model of a polymer in random media with long ranged disorder correlations

We present an exactly solvable model of a Gaussian (flexible) polymer chain in a quenched random medium. This is the case when the random medium obeys very long range quadratic correlations. The model is solved in $d$ spatial dimensions using the replica method, and practically all the physical properties of the chain can be found. In particular the difference between the behavior of a chain that is free to move and a chain with one end fixed is elucidated. The interesting finding is that a chain that is free to move in a quadratically correlated random potential behaves like a free chain with $R^2 \sim L$, where $R$ is the end to end distance and $L$ is the length of the chain, whereas for a chain anchored at one end $R^2 \sim L^4$. The exact results are found to agree with an alternative numerical solution in $d=1$ dimensions. The crossover from long ranged to short ranged correlations of the disorder is also explored.Comment: REVTeX, 28 pages, 12 figures in eps forma

Bacterial isolates and their antimicrobial susceptibility pattern among patients with external ocular infections at Borumeda hospital, Northeast Ethiopia

Background: Bacteria are major cause of ocular infections and possible loss of vision. The emergence of antimicrobial resistant bacteria increases the risk of treatment failure with potentially serious consequences. The aim of this study was to determine the prevalence of bacterial isolates and their antimicrobial susceptibility pattern among patients with external ocular infections. Methods: A cross sectional study was conducted among 160 patients with external ocular infections at Borumeda hospital, Northeast Ethiopia. Socio-demographic and clinical data were collected using structured questionnaire. External ocular specimens were collected using sterile swabs and inoculated on MacConkey agar, Chocolate agar and Blood agar culture Medias. Presumptive isolates were further identified by a series of biochemical tests. The antimicrobial susceptibility patterns of the isolates were determined by disk diffusion method. Result: The overall prevalence of bacterial pathogens among external ocular samples was 59.4 %. The majority of the isolates (93.7 %; 89/95) were Gram positive and the other 6.3 % (6/95) Gram negative bacteria. The proportion of coagulase negative Staphylococci among the Gram positive bacterial isolates was 53.7 % (n = 51/95). All Gram positive isolates were susceptible for vancomycin but 67.4 % (n = 60/95) of them were resistant against amoxicillin. Moreover, drug resistance to tetracycline, norfloxacylin, ceftriaxone and ciprofloxacin were observed among Gram negative bacteria isolates. Conclusion: The prevalence of bacterial pathogens among external ocular samples was high and the predominant isolate was coagulase negative Staphylococci. Exceptionally high amoxicillin resistance was observed among Gram positive bacterial isolates that may dictate to conduct drug susceptibility test routinely.Birtukan Shiferaw, Baye GelawEmail author, Abate Assefa, Yared Assefa and Zelalem Addi