2,561 research outputs found
The effect of sequence correlation on bubble statistics in double-stranded DNA
No full textDNA exists stably in the double-stranded structure at physiological temperatures, but base pairs are observed to unbind locally, giving way to bubbles (i.e., locally denatured states) due to thermal fluctuation. In this study, we consider the effect of sequence on the bubble statistics. On the basis of the Edwards equation description [W. Sung and J.-H. Jeons, Phys. Rev. E 69, 031902 (2004) ], we develop a stochastic model incorporating the sequence randomness as a dichotomic noise, where the bubble and its size are identified as a returning random walk and its first passage time, respectively. By simulating the model Langevin equation, we obtain the bubble size distribution and show how it is affected by the sequence correlation. We find that the bubble size distribution of DNA with finite sequence correlation deviates from the Poland-Scheraga-type distribution. In particular, the formation of large bubbles is dramatically enhanced as sequence correlation length gets longer. (c) 2006 American Institute of Physics.open1177sciescopu
Rumphellolide G, a new caryophyllane-type tetrahydropyran norsesquiterpenoid from the gorgonian coral Rumphella antipathies (Gorgoniidae)
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Book Discussion : PJ Powers
No full textThe UJ Campus Health Services and the Student Affairs Division in partnership with the UJ Library invite you to meet PJ Powers (Thandeka) the co-author of the book HERE I AM About the book: Here I Am, written with Marianne Thamm, is an intimate and hilarious account of the life and times of one of this country’s most recognisable and enduring performers. From the dizzying heights of international stardom to the dark depths of her struggle with alcohol, this is a must-read to explore the heady mix of politics and music of the time. More than just a story about the personal journey of one of South Africa’s most beloved music icons, this extraordinary memoir of PJ Powers – or Thandeka, as she was affectionately renamed by Soweto crowds – is set against the turbulent backdrop of South Africa’s recent political history. It features a gallery of political leaders and international celebrities, including the likes of Nelson Mandela, Graça Machel, Chris Hani, Joaquim Chissano, Queen Elizabeth II, Brenda Fassie, Sharon Stone and Robert De Niro. Facilitator: Prof Alban Burke, Director – PsyCad, University of Johannesburg PJ Powers will also perform a few songs on the day. Date: 27 August 2015 Time: 16:30 for 17:00 Venue: Auditorium (6th Floor), APK Library, University of Johannesburg (corner Kingsway and University Road, Auckland Park) RSVP: By Wednesday, 26 August 2015 to Theodorah Modise on [email protected] / 011 559 226
Book Discussion : PJ Powers
No full textThe UJ Campus Health Services and the Student Affairs Division in partnership with the UJ Library invite you to meet PJ Powers (Thandeka) the co-author of the book HERE I AM About the book: Here I Am, written with Marianne Thamm, is an intimate and hilarious account of the life and times of one of this country’s most recognisable and enduring performers. From the dizzying heights of international stardom to the dark depths of her struggle with alcohol, this is a must-read to explore the heady mix of politics and music of the time. More than just a story about the personal journey of one of South Africa’s most beloved music icons, this extraordinary memoir of PJ Powers – or Thandeka, as she was affectionately renamed by Soweto crowds – is set against the turbulent backdrop of South Africa’s recent political history. It features a gallery of political leaders and international celebrities, including the likes of Nelson Mandela, Graça Machel, Chris Hani, Joaquim Chissano, Queen Elizabeth II, Brenda Fassie, Sharon Stone and Robert De Niro. Facilitator: Prof Alban Burke, Director – PsyCad, University of Johannesburg PJ Powers will also perform a few songs on the day. Date: 27 August 2015 Time: 16:30 for 17:00 Venue: Auditorium (6th Floor), APK Library, University of Johannesburg (corner Kingsway and University Road, Auckland Park) RSVP: By Wednesday, 26 August 2015 to Theodorah Modise on [email protected] / 011 559 226
Polymer translocation induced by adsorption
No full textWe study the translocation of a flexible polymer through a pore in a membrane induced by its adsorption on the trans side of the membrane. When temperature T is higher than T-c, the adsorption-desorption transition temperature, the attractive interaction between polymer and membrane plays little role in affecting polymer conformation, leading to translocation time that scales as tau similar to L-3, where L is the polymer contour length. When T<T-c, however, the translocation time undergoes a sharp crossover to tau similar to L-2 for sufficiently long polymers, following the second-order conformational (adsorption) transition. The translocation time is found to exhibit the crossover around T=T-c', which is lower than T-c for polymers shorter than a critical length (N < N-c). (C) 1998 American Institute of Physics.open11100sciescopu
Dynamics of pore growth in membranes and membrane stability
No full textPores can form and grow in biomembranes because of factors such as thermal fluctuation, transmembrane electrical potential, and cellular environment. We propose a new statistical physics model of the pore growth treated as a non-Markovian stochastic process, with a free energy barrier and memory friction from the membrane matrix treated as a quasi-two-dimensional viscoelastic and dielectric fluid continuum. On the basis of the modern theory of activated barrier crossing, an analytical expression for membrane lifetime and the phase diagram for membrane stability are obtained. The memory effect due to membrane viscoelasticity and the elasticity due to cytoskeletal network are found to induce sharp transitions to membrane stability against pore growth and compete with other factors to manifest rich dynamic transitions over the membrane lifetime.open1130sciescopu
Polymer release out of a spherical vesicle through a pore
No full textTranslocation of a polymer out of a curved surface or membrane is studied via the mean first passage time approach. Membrane curvature gives rise to a constraint on polymer conformation, which effectively drives the polymer to the outside of confinement, where the available volume of the polymer conformational fluctuation is larger. Considering a polymer release out of a spherical vesicle, the polymer translocation time tau is changed to the scaling behavior tau similar to L-2 for R<R-G, from tau similar to L-3 for R much greater than R-G, where L is the polymer contour length, and R and R-G are the vesicle radius and polymer radius of gyration, respectively. Also, the polymer capture into a spherical bud is studied, and a possible apparatus for easy capture is suggested.open1161sciescopu
Statistical mechanics of membrane protein conformation: A homopolymer model
No full textThe conformation and the phase diagram of a membrane protein are investigated via grand canonical ensemble approach using a homopolymer model. We discuss the nature and pathways of alpha-helix integration into the membrane that result depending upon membrane permeability and polymer adsorptivity. For a membrane with the permeability larger than a critical value, the integration becomes the second order transition that occurs at the same temperature as that of the adsorption transition. For a nonadsorbing membrane, the integration is of the first order due to the aggregation of alpha helices.open1120sciescopu
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