Athermal Nonlinear Elastic Constants of Amorphous Solids

We derive expressions for the lowest nonlinear elastic constants of amorphous solids in athermal conditions (up to third order), in terms of the interaction potential between the constituent particles. The effect of these constants cannot be disregarded when amorphous solids undergo instabilities like plastic flow or fracture in the athermal limit; in such situations the elastic response increases enormously, bringing the system much beyond the linear regime. We demonstrate that the existing theory of thermal nonlinear elastic constants converges to our expressions in the limit of zero temperature. We motivate the calculation by discussing two examples in which these nonlinear elastic constants play a crucial role in the context of elasto-plasticity of amorphous solids. The first example is the plasticity-induced memory that is typical to amorphous solids (giving rise to the Bauschinger effect). The second example is how to predict the next plastic event from knowledge of the nonlinear elastic constants. Using the results of this paper we derive a simple differential equation for the lowest eigenvalue of the Hessian matrix in the external strain near mechanical instabilities; this equation predicts how the eigenvalue vanishes at the mechanical instability and the value of the strain where the mechanical instability takes place.Comment: 17 pages, 2 figures

Stochastic model of transcription factor-regulated gene expression

We consider a stochastic model of transcription factor (TF)-regulated gene expression. The model describes two genes: Gene A and Gene B which synthesize the TFs and the target gene proteins respectively. We show through analytic calculations that the TF fluctuations have a significant effect on the distribution of the target gene protein levels when the mean TF level falls in the highest sensitive region of the dose-response curve. We further study the effect of reducing the copy number of Gene A from two to one. The enhanced TF fluctuations yield results different from those in the deterministic case. The probability that the target gene protein level exceeds a threshold value is calculated with a knowledge of the probability density functions associated with the TF and target gene protein levels. Numerical simulation results for a more detailed stochastic model are shown to be in agreement with those obtained through analytic calculations. The relevance of these results in the context of the genetic disorder haploinsufficiency is pointed out. Some experimental observations on the haploinsufficiency of the tumour suppressor gene, Nkx3.1, are explained with the help of the stochastic model of TF-regulated gene expression.Comment: 17 pages, 11 figures. Accepted for publication in Physical Biolog

Extended states in 1D lattices: application to quasiperiodic copper-mean chain

The question of the conditions under which 1D systems support extended electronic eigenstates is addressed in a very general context. Using real space renormalisation group arguments we discuss the precise criteria for determining the entire spertrum of extended eigenstates and the corresponding eigenfunctions in disordered as well as quasiperiodic systems. For purposes of illustration we calculate a few selected eigenvalues and the corresponding extended eigenfunctions for the quasiperiodic copper-mean chain. So far, for the infinite copper-mean chain, only a single energy has been numerically shown to support an extended eigenstate [ You et al. (1991)] : we show analytically that there is in fact an infinite number of extended eigenstates in this lattice which form fragmented minibands.Comment: 10 pages + 2 figures available on request; LaTeX version 2.0

Isometric handgrip strength of agricultural workers from northeast region of India

Handgrip strength is considered as one of the most important factors for performing various agricultural tasks related to torqueing, lifting, pulling, pushing, etc. Hand tools and equipment which are designed based on anthropometric/strength data of different population, may not be suitable for any particular targeted user group. As a result work related musculoskeletal disorders (WMSDs) at upper extremity may occur very often. Lack of strength data of Assamese population (people of Assam, a state in northeast India), motivated present authors to conduct a survey on isometric handgrip strength data of 200 agricultural workers (130 male and 70 female, aged 17-62 years) from the Kamrup district of the state. Maximal isometric handgrip strength was determined using a handheld handgrip dynamometer with standard testing position, protocol and instructions. Descriptive statistics such as mean, standard deviation (SD), percentiles etc. were summarized. Results of student’s t-tests showed significant differences (

Isometric muscular strength data of Indian agricultural workers for equipment design: Critical analysis

Abstract: Human muscular strength is extensively used in Indian agriculture for operating various push-pull type farm tools and equipment.  Incompatibility between operators’ physical capabilities (anthropometric and biomechanical) and demands of physical task to operate tools/equipment often leads to poor performance, low productivity and safety problems.  Although anthropometric data are generally being considered, an inadvertent negligence of using strength database for agricultural tools/equipment design is very common in developing countries like India.  Therefore, in present paper an attempt has been made to statistically analyze available strength data (pooled and regional/state wise data) of male and female Indian agricultural workers to understand nature of variability of those data in terms of difference between pooled Indian data vs. individual state data; difference between male vs. female data across various states of India; and for determining safe operational force limits for handling various agricultural tools/equipment.  Critical evaluation of male and female strength data revealed that there are significant differences (p<0.01 or p<0.05) between mean values of pooled Indian data vs. individual state data for almost all strength variables under study.  It has also been observed that average muscular strength of female is significantly lower (in general 2/3rd of male) than their male counter parts across all states.  Thus, present study concluded that regional variations and gender variation of isometric strength data are crucial ergonomic consideration for using percentile strength data during calculation of operational force limits for designing various agricultural tools/equipment to be used by targeted user populations from various parts of a country like India with huge ethnic diversity.   Keywords: ergonomics, muscular strength, tools and equipment, agricultural workers, Indi

Photo-reduced route of polyaniline nanofiber synthesis with embedded silver nanoparticles

AbstractThis work presents a method on the preparation and performance of four silver (Ag) concentrations in polyaniline (PANI) and polyvinyl alcohol (PVA) nanocomposite blend (PNPAg). The synthesis of Ag nanoparticles is first performed by photo reduction and then aniline is polymerized in Ag-PVA matrix. Morphological analysis by SEM and TEM reveals formation of nanoparticles with diameter 30–70nm. Nanocomposites with lower Ag concentrations have highly aligned PNPAg nanofibers of diameter 50–80nm and agglomeration for the one with higher concentrations. In addition, FTIR spectra show a systematic change in its characteristic peaks with increase in Ag contents. The crystallinity study depicts the tetragonal crystal structure of metallic nanocomposites having same particle sizes as obtained in SEM and TEM. In order to explore the possible applications of these nanocomposites in electronic industry, their electrical properties are investigated. The in-plane I-V characteristics indicate a transition of polymer nanocomposites from non-ohmic to ohmic material with increase of Ag content. The room temperature electrical conductivities are found to be in the range of 4.74×10−4 to 3.96×10−2S/m with no major difference in activation energy for all nanocomposites