Thermally activated barrier crossing and stochastic resonance of a flexible polymer chain in a piecewise linear bistable potential

We study the stochastic resonance (SR) of a flexible polymer chain crossing over a piecewise linear bistable potential. The dependence of signal to noise ratio $SNR$ on noise intensity $D$, coupling constant $k$ and polymer length $N$ is studied via two state approximation. We find that the response of signal to the background noise strength is significant at optimum values of $D_{opt}$, $k_{opt}$ and $N_{opt}$ which suggests novel means of manipulating proteins or vesicles. Furthermore, the thermally activated barrier crossing rate $r_{k}$ for the flexible polymer chain is studied. We find that the crossing rate $r_{k}$ exhibits an optimal value at an optimal coupling constant $k_{opt}$; $k_{opt}$ decreases with $N$. As the chain length $N$ increases, the escape rate for the center of mass $r_{k}$ monotonously decreases. On the other hand, the crossing rate for the portion of polymer segment $r_s$ increases and saturates to a constant rate as $N$ steps up.Comment: 16 pages, 9 figure

Energetics of a simple microscopic heat engine

We model a microscopic heat engine as a particle hopping on a one-dimensional lattice in a periodic sawtooth potential, with or without load, assisted by the thermal kicks it gets from alternately placed hot and cold thermal baths. We find analytic expressions for current and rate of heat flow when the engine operates at steady state. Three regions are identified where the model acts either as a heat engine or as a refrigerator or as neither of the two. At quasistatic limit both efficiency of the engine and coefficient of performance of the refrigerator go to that for Carnot engine and Carnot refrigerator, respectively. We investigate efficiency of the engine at two operating conditions (at maximum power and at optimum value with respect to energy and time) and compare them with those of the endoreversible and Carnot engines.Comment: 6 pages and 8 figure

Diagnosis of Early Infant HIV Infection among Sero-Positive Mother in Jimma Zone, Southern West Ethiopia, Jimma

Back ground: Ethiopia is among the country most affected by the HIV with adult prevalence of 1.5%; majority of children acquired HIV from their mother through vertical transmission. WHO estimate that about 3.2 million children were living with HIV at the end of 2013 worldwide. HIV-related mortality rates remain high in sub-Saharan Africa despite growing access to ART. Ethiopian government has launched fee based ART treatment in 2003 and free ART in 2005. The aim of current study is to determine the prevalence of HIV infection among HIV-exposed infant from their HIV positive mothers in Jimma zone. Methods: A retrospective study was carried out at JUSH on 225 infants born from HIV seropositive mothers. The relevant data were retrieved from molecular laboratory result record. Data were collected by the investigator. Collected data were tallied and processed by manually and computer tools.  Data was entered in to excel sheet for statistical analysis. The quality of data was controlled. Ethical issue was taken into account.Results: The study revealed that 5.3% (12/225) of the infants born from HIV seropositive mothers were found to be HIV positive. From a total of 225 infants born from HIV seropositive mothers and had been tested for HIV by DNA PCR, 120(53.3%) were males and 105(46.7%) were females. With regard to the time of diagnosis of infants born from HIV positive mothers, the majority 210 (93.3%) had their DBS tested at or after 7 weeks. While only 15 (6.7%) infants were tested at the right time, which is at 6 weeks.Conclusion: The vertical transmission rate was (5.3%) in the present study, reflects the using of prevention of mother to child transmission (PMTCT) strategy needed to be strengthen and further activities has to be continued. Keywords: HIV, Early infant diagnosis, HAART, DB