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Dynamic stretching

Aishani Ghosal, Binny J Cherayil
This paper is broadly concerned with the dynamics of a polymer confined to a rectangular slit of width D and deformed by a planar elongational flow of strength γ̇. It is interested, more specifically, in the nature of the coil-stretch transition that such polymers undergo when the flow strength γ̇ is varied, and in the degree to which this transition is affected by the presence of restrictive boundaries. These issues are explored within the framework of a finitely extensible Rouse model that includes pre-averaged surface-mediated hydrodynamic interactions...
August 14, 2017: Journal of Chemical Physics
Shuangshuang Zhang, Shuanhu Qi, Leonid I Klushin, Alexander M Skvortsov, Dadong Yan, Friederike Schmid
Using Brownian dynamics, we study the dynamical behavior of a polymer grafted onto an adhesive surface close to the mechanically induced adsorption-stretching transition. Even though the transition is first order (in the infinite chain length limit, the stretching degree of the chain jumps discontinuously), the characteristic relaxation time is found to grow according to a power law as the transition point is approached. We present a dynamic effective interface model which reproduces these observations and provides an excellent quantitative description of the simulation data...
August 14, 2017: Journal of Chemical Physics
Heather E Bailey, Yong-Lei Wang, Michael D Fayer
The orientational dynamics and microscopic liquid structure of a protic ionic liquid, 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide (EhimNTf2), and its aprotic analogue, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2), were studied at various water concentrations using optical heterodyne-detected optical Kerr Effect (OHD-OKE) spectroscopy, linear infrared spectroscopy, and atomistic simulations. The OHD-OKE experiments essentially measure the orientational relaxation of the Ehim+ and Emim+ cations...
August 15, 2017: Journal of Physical Chemistry. B
Maria Ekimova, Wilson Quevedo, Lukasz Szyc, Marcella Iannuzzi, Philippe Wernet, Michael Odelius, Erik T J Nibbering
In a multi-facetted investigation combining local soft-x-ray and vibrational spectroscopic probes with ab initio molecular dynamics simulations, hydrogen-bond interactions of two key principal amine compounds in aqueous solution, ammonia (NH3) and ammonium ion (NH4+), are quantitatively assessed in terms of electronic structure, solvation structure, and dynamics. From the x-ray measurements and from the complementary determination of the IR-active hydrogen stretching and bending modes of NH3 and NH4+ in aqueous solution, the picture emerges of a comparatively strongly hydrogen-bonded NH4+ ion via N-H donating interactions, whereas NH3 has a strong accepting hydrogen bond with one water molecule at the nitrogen lone pair but only weak N-H donating hydrogen bonds...
August 15, 2017: Journal of the American Chemical Society
Yishuo Guo, Jun Liu, Youping Wu, Liqun Zhang, Zhao Wang, Ying Li
Through united-atom molecular dynamics simulations, we build a series of graphene (GP) reinforced cis-1,4-polybutadiene (cis-PB) models with two novel GP structures, intercalated and stacked GP structures, to investigate the effect of different GP packing patterns on the chain structure, chain dynamics, uniaxial tension and visco-elastic behaviors, and correlate the microscopic mechanism with macroscopic mechanical properties. Simulation results show that the interlayer polymer chains in the void of intercalated GPs are strongly confined, leading to higher bond orientation of polymer chains during the stretch process compared with monodisperse systems...
August 15, 2017: Physical Chemistry Chemical Physics: PCCP
Sandro R Freitas, Bruno Mendes, Guillaume Le Sant, Ricardo J Andrade, Antoine Nordez, Zoran Milanovic
PURPOSE: It is recognized that stretching is an effective method to chronically increase the joint range of motion. However, the effects of stretching training on the muscle-tendon structural properties remain unclear. This systematic review with meta-analysis aimed to determine whether chronic stretching alter the muscle-tendon structural properties. METHODS: Published papers regarding longitudinal stretching (static, dynamic and/or PNF) intervention (either randomized or not) in humans of any age and health status, with more than 2 weeks in duration and at least 2 sessions per week, were searched in PubMed, PEDro, ScienceDirect and ResearchGate databases...
August 12, 2017: Scandinavian Journal of Medicine & Science in Sports
Lin Wang, Tatsuya Ishiyama, Akihiro Morita
Using the flexible and polarizable model in the preceding paper I, we performed comprehensive analysis of C-H stretching vibrations of ethanol and partially deuterated ones by molecular dynamics (MD) simulation. The overlapping band structures of C-H stretching region including (i) methyl and methylene, (ii) number of modes with Fermi resonances, and (iii) different trans/gauche conformers are disentangled by various analysis methods, such as isotope exchange, empirical potential parameter shift analysis, and separate calculations of conformers...
August 11, 2017: Journal of Physical Chemistry. A
Raphael Thon, Wutharath Chin, Didier Chamma, Jean-Pierre Galaup, Aimeric Ouvrard, Bernard Bourguignon, Claudine Crépin
Methane solids present more than one accessible crystalline phase at low temperature at zero pressure. We trap W(CO)6 in CH4 and CD4 matrices between 8 and 35 K to probe the interaction between an impurity and its surrounding molecular solid under various physical conditions. Linear and nonlinear vibrational spectroscopies of W(CO)6 highlight different kinds of interaction and reveal new and remarkable signatures of the phase transition of methane. The structures in the absorption band of the antisymmetric CO stretching mode exhibit a clear modification at the transition between phase II and phase I in CH4 and motional narrowing is observed upon temperature increase...
December 7, 2016: Journal of Chemical Physics
Kenneth S Schweizer, Daniel M Sussman
We employ a first-principles-based, force-level approach to construct the anharmonic tube confinement field for entangled fluids of rigid needles, and also for chains described at the primitive-path (PP) level in two limiting situations where chain stretch is assumed to either be completely equilibrated or unrelaxed. The influence of shear and extensional deformation and polymer orientation is determined in a nonlinear elastic limit where dissipative relaxation processes are intentionally neglected. For needles and PP-level chains, a self-consistent analysis of transverse polymer harmonic dynamical fluctuations predicts that deformation-induced orientation leads to tube weakening or widening...
December 7, 2016: Journal of Chemical Physics
Tamal Roy, Kai Szuttor, Jens Smiatek, Christian Holm, Steffen Hardt
We study the effect of pressure-driven flow on a single surface-tethered DNA molecule confined between parallel surfaces. The influence of flow and channel parameters as well as the length of the molecules on their extension and orientation is explored. In the experiments the chain conformations are imaged by laser scanning confocal microscopy. We find that the fractional extension of the tethered DNA molecules mainly depends on the wall shear stress, with effects of confinement being very weak. Experiments performed with molecules of different contour length show that the fractional extension is a universal function of the product of the wall shear stress and the contour length, a result that can be obtained from a simple scaling relation...
August 11, 2017: Soft Matter
Lili Li, Jie Yang
Molecular dynamics simulation with the Stillinger-Weber potential is employed to study the mechanical behaviors of single-layer black phosphorus (SLBP) at different temperatures. The SLBP is initially loaded by a uniaxial tensile/compressive prestrain in either armchair or zigzag direction then stretched or compressed in the direction that is orthogonal to the direction of the prestrain. It is found that overall, mechanical properties such as tensile/compressive Young's modulus, tensile/compressive strength and yield strength are enhanced by a compressive prestrain but are reduced by a tensile prestrain, and that an armchair-oriented prestrain can improve mechanical properties more significantly than a zigzag-oriented prestrain...
August 10, 2017: Nanotechnology
Xi Zhang, Lei Bao, Yuan-Yan Wu, Xiao-Long Zhu, Zhi-Jie Tan
The radial distribution of the end-to-end distance Ree is crucial for quantifying the global size and flexibility of a linear polymer. For semiflexible polymers, several analytical formulas have been derived for the radial distribution of Ree ignoring the stretching flexibility. However, for semiflexible oligomers, such as DNA or RNA, the stretching flexibility can be rather pronounced and can significantly affect the radial distribution of Ree. In this study, we obtained an extended formula that includes the stretch modulus to describe the distribution of Ree for semiflexible oligomers on the basis of previous formulas for semiflexible polymers without stretching flexibility...
August 7, 2017: Journal of Chemical Physics
Ruaridh Forbes, Andrey E Boguslavskiy, Iain Wilkinson, Jonathan G Underwood, Albert Stolow
We present an experimental femtosecond time-resolved study of the 399 nm excited state dynamics of nitrogen dioxide using channel-resolved above threshold ionization (CRATI) as the probe process. This method relies on photoelectron-photoion coincidence and covariance to correlate the strong-field photoelectron spectrum with ionic fragments, which label the channel. In all ionization channels observed, we report apparent oscillations in the ion and photoelectron yields as a function of pump-probe delay. Further, we observe the presence of a persistent, time-invariant above threshold ionization comb in the photoelectron spectra associated with most ionization channels at long time delays...
August 7, 2017: Journal of Chemical Physics
K Gope, V S Prabhudesai, N J Mason, E Krishnakumar
We report the molecular dynamics of dissociative electron attachment to sulfur dioxide (SO2) by measuring the momentum distribution of fragment anions using the velocity slice imaging technique in the electron energy range of 2-10 eV. The S(-) channel results from symmetric dissociation which exhibits competition between the stretch mode and bending mode of vibration in the excited parent anion. The asymmetric dissociation of parent anions leads to the production of O(-) and SO(-) channels where the corresponding neutral fragments are formed in their ground as well as excited electronic states...
August 7, 2017: Journal of Chemical Physics
Ritu Gothwal, Shashidhar Thatikonda
Development of antibiotic resistance in environmental bacteria is a direct threat to public health. Therefore, it becomes necessary to understand the fate and transport of antibiotic and its resistant bacteria. This paper presents a mathematical model for spatial and temporal transport of fluoroquinolone and its resistant bacteria in the aquatic environment of the river. The model includes state variables for organic matter, fluoroquinolone, heavy metals, and susceptible and resistant bacteria in the water column and sediment bed...
August 5, 2017: Environmental Science and Pollution Research International
Lukas S Stelzl, Nicole Erlenbach, Marcel Heinz, Thomas F Prisner, Gerhard Hummer
The conformational dynamics of DNA is essential in the functioning of the genetic machinery. Experiments have revealed that the classical description of DNA as an elastic rod neglects the complex dynamics crucial in protein-DNA interactions. Pulsed electron-electron double resonance (PELDOR/DEER) experiments of nucleic acids with rigid spin labels provide highly accurate distance and orientation information. Here we combine PELDOR experiments with molecular dynamics (MD) simulations to arrive at an atomistic view of the conformational dynamics of DNA...
August 4, 2017: Journal of the American Chemical Society
Peter J Thul, Kirsten Tschapalda, Petra Kolkhof, Abdou Rachid Thiam, Monika Oberer, Mathias Beller
Lipid droplets (LDs) are the principal organelles of lipid storage. They consist of a hydrophobic core of storage lipids, surrounded by a phospholipid monolayer with proteins attached. While some of these proteins are essential to regulate cellular and organismic lipid metabolism, key questions concerning LD protein function, such as their targeting to LDs, are still unanswered. Intriguingly, some proteins are restricted to LD subsets by an as yet unknown mechanism. This finding makes LD targeting even more complex...
August 3, 2017: Journal of Cell Science
Martin W Scheeler, Wim M van Rees, Hridesh Kedia, Dustin Kleckner, William T M Irvine
Helicity, a topological measure of the intertwining of vortices in a fluid flow, is a conserved quantity in inviscid fluids but can be dissipated by viscosity in real flows. Despite its relevance across a range of flows, helicity in real fluids remains poorly understood because the entire quantity is challenging to measure. We measured the total helicity of thin-core vortex tubes in water. For helical vortices that are stretched or compressed by a second vortex, we found conservation of total helicity. For an isolated helical vortex, we observed evolution toward and maintenance of a constant helicity state after the dissipation of twist helicity by viscosity...
August 4, 2017: Science
William J Chopik, Robin S Edelstein, Kevin J Grimm
Research on individual differences in attachment-and their links to emotion, cognition, and behavior in close relationships-has proliferated over the last several decades. However, the majority of this research has focused on children and young adults. Little is known about mean-level changes in attachment orientation beyond early life, in part due to a dearth of longitudinal data on attachment across the life span. The current study used a Q-Sort-based measure of attachment to examine mean-level changes in attachment orientation from age 13 to 72 using data from the Block and Block Longitudinal Study, the Intergenerational Studies, and the Radcliffe College Class of 1964 Sample (total N = 628)...
August 3, 2017: Journal of Personality and Social Psychology
Aryesh Mukherjee, Shreyas Mandre, L Mahadevan
Birdsong is the product of the controlled generation of sound embodied in a neuromotor system. From a biophysical perspective, a natural question is that of the difficulty of producing birdsong. To address this, we built a biomimetic syrinx consisting of a stretched simple rubber tube through which air is blown, subject to localized mechanical squeezing with a linear actuator. A large static tension on the tube and small dynamic variations in the localized squeezing allow us to control transitions between three states: a quiescent state, a periodic state and a solitary wave state...
August 2017: Journal of the Royal Society, Interface
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