454 research outputs found
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 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 , where is the end to end distance and is the length of the
chain, whereas for a chain anchored at one end . The exact
results are found to agree with an alternative numerical solution in
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
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