Nonlinear viscoelastic modeling of soft polymers

A one‐dimensional phenomenological constitutive model, representing the nonlinear viscoelastic behavior of polymers is developed in this study. The proposed model is based on a modification of the well‐known three element standard solid model. The linear dashpot is replaced by an Eyring type one, while the nonlinearity is enhanced by a nonlinear, strain dependent spring constant. The new constitutive model was proved to be capable of capturing the main aspects of nonlinear viscoelastic response, namely, monotonic and cyclic loading, creep and stress relaxation, with the same parameter values. Model validation was tested on the experimental results at various modes of deformation for two elastomeric type materials, performed elsewhere. A very good agreement between model simulations and experimental data was obtained in all cases. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42141.     

RF characterization and isolation properties of mesoporous Si by on-chip coplanar waveguide measurements

We report on the broadband electrical characterization of thick mesoporous silicon layers used as RF microplates for on-chip integration of high-Q passive devices in a CMOS-compatible process. To measure the RF losses of the microplate we have fabricated several designs of Coplanar Waveguides (CPWs), for form-factors relevant to the sizes of on-chip passive RF devices, on thick mesoporous Si layers (RF microplates) of various thicknesses, and we compared the results with those obtained from similar CPWs integrated directly on the p-type Si substrate. For maximum measurement sensitivity of the loss, the CPWs were designed to be very good transmission lines matched to 50 Ω port impedances. We also characterized the grown mesoporous Si by performing electromagnetic simulations of the structure and identifying the measured and simulated S-parameters over a broadband frequency region, for the appropriate simulator input of complex permittivity. The measured results show that, for CPW features commensurate with the scale of on-chip RF passive devices, a 50-μm-thick mesoporous Si layer on the Si substrate reduces the losses to 1/6th–1/4th of the values corresponding to a p-type Si substrate, showing that mesoporous Si is an excellent material for CMOS-compatible on-chip integration of high-Q passive devices.     

Highly ordered hexagonally arranged nanostructures on silicon through a self-assembled silicon-integrated porous anodic alumina masking layer

A combined process of electrochemical formation of self-assembled porous anodic alumina thin films on a Si substrate and Si etching through the pores was used to fabricate ideally ordered nanostructures on the silicon surface with a long-range, two-dimensional arrangement in a hexagonal close-packed lattice. Pore arrangement in the alumina film was achieved without any pre-patterning of the film surface before anodization. Perfect pattern transfer was achieved by an initial dry etching step, followed by wet or electrochemical etching of Si at the pore bottoms. Anisotropic wet etching using tetramethyl ammonium hydroxide (TMAH) solution resulted in pits in the form of inverted pyramids, while electrochemical etching using a hydrofluoric acid (HF) solution resulted in concave nanopits in the form of semi-spheres. Nanopatterns with lateral size in the range 12-200?nm, depth in the range 50-300?nm and periodicity in the range 30-200?nm were achieved either on large Si areas or on pre-selected confined areas on the Si substrate. The pore size and periodicity were tuned by changing the electrolyte for porous anodic alumina formation and the alumina pore widening time. This parallel large-area nanopatterning technique shows significant potential for use in Si technology and devices.     

Parents' job insecurity affects children's academic performance through cognitive difficulties.

The authors developed and tested a model in which children who perceive their parents to be insecure about their jobs are distracted cognitively, which in turn affects their academic performance negatively. Participants were 102 female and 18 male undergraduates (mean age?=?18 years), their fathers (mean age?=?49 years), and their mothers (mean age?=?47 years). Students completed questionnaires measuring perceived parental job insecurity, identification with parents, and cognitive difficulties; 3 months later, they also reported their midyear grades. Fathers and mothers each completed questionnaires assessing their job insecurity. Support for the model was obtained using LISREL 8, and as predicted, children's identification with their mothers and fathers moderated the relationship between their perceptions of their mothers' and fathers' job insecurity and their own cognitive difficulties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of p53 mutants derived from lung carcinomas on the p53-responsive element (p53RE) of the MDM2 gene

The present study represents a continuation of previous works in which we observed that lung carcinomas co-expressing MDM2 protein and p53 mutants (mt p53) exhibited more aggressive behaviour. In the above studies, we suggested a 'gain of function' mechanism of mt p53 proteins based on the fact that the MDM2 gene possesses a p53-responsive element (MDM2-p53RE). In this study, to prove our hypothesis, we selected 12 cases from a series of 51 bronchogenic carcinomas. In these 12 cases, we examined the ability of the expressed mt p53 to bind the MDM2-p53RE and correlated the findings with MDM2 expression. Furthermore, we constructed four of these p53 mutants and studied their transactivation properties by co-transfecting them with a reporter plasmid carrying MDM2-p53RE in the p53 null non-small-cell lung carcinoma cell line (NSCLC) H1299. We observed mutant p53 protein DNA-binding activity, which depended on the nature and the position of the amino acid substitution. The fact that the cases with DNA-binding activity were accompanied with MDM2 protein isoforms' overexpression is indicative of a 'gain of function' phenotype. This hypothesis was enforced by the findings of the transfection experiments, which revealed that certain p53 mutants enhanced the expression of the luciferase reporter gene either directly or indirectly via a dominant positive effect on the wild-type p53. In conclusion, this work is one first attempt to examine if the deregulation of the p53/MDM2 autoregulatory feedback loop is due to novel properties of certain p53 mutants in the specific environment of a subset of bronchogenic carcinomas.     

High-Performance Work Systems and Occupational Safety.

Two studies were conducted investigating the relationship between high-performance work systems (HPWS) and occupational safety. In Study 1, data were obtained from company human resource and safety directors across 138 organizations. LISREL VIII results showed that an HPWS was positively related to occupational safety at the organizational level. Study 2 used data from 189 front-line employees in 2 organizations. Trust in management and perceived safety climate were found to mediate the relationship between an HPWS and safety performance measured in terms of personal-safety orientation (i.e., safety knowledge, safety motivation, safety compliance, and safety initiative) and safety incidents (i.e., injuries requiring first aid and near misses). These 2 studies provide confirmation of the important role organizational factors play in ensuring worker safety. (PsycINFO Database Record (c) 2010 APA, all rights reserved)