Parameter Estimation for Viscoplastic Material Modeling

A key ingredient in the design of engineering components and structures under general thermomechanical loading is the use of mathematical constitutive models (e.g. in finite element analysis) capable of accurate representation of short and long term stress/deformation responses. In addition to the ever-increasing complexity of recent viscoplastic models of this type, they often also require a large number of material constants to describe a host of (anticipated) physical phenomena and complicated deformation mechanisms. In turn, the experimental characterization of these material parameters constitutes the major factor in the successful and effective utilization of any given constitutive model; i.e., the problem of constitutive parameter estimation from experimental measurements

GVIPS Models and Software

Two reports discuss, respectively, (1) the generalized viscoplasticity with potential structure (GVIPS) class of mathematical models and (2) the Constitutive Material Parameter Estimator (COMPARE) computer program. GVIPS models are constructed within a thermodynamics- and potential-based theoretical framework, wherein one uses internal state variables and derives constitutive equations for both the reversible (elastic) and the irreversible (viscoplastic) behaviors of materials. Because of the underlying potential structure, GVIPS models not only capture a variety of material behaviors but also are very computationally efficient. COMPARE comprises (1) an analysis core and (2) a C++-language subprogram that implements a Windows-based graphical user interface (GUI) for controlling the core. The GUI relieves the user of the sometimes tedious task of preparing data for the analysis core, freeing the user to concentrate on the task of fitting experimental data and ultimately obtaining a set of material parameters. The analysis core consists of three modules: one for GVIPS material models, an analysis module containing a specialized finite-element solution algorithm, and an optimization module. COMPARE solves the problem of finding GVIPS material parameters in the manner of a design-optimization problem in which the parameters are the design variables

Production and characterization of antimicrobial active substance from some macroalgae collected from Abu- Qir bay (Alexandria) Egypt

The antimicrobial activity of three different macroalgal species [Jania rubens (Linnaeus) Lamouroux; Ulva fasciata Delile and Sargassum vulgare C. Agardh] belonging to Rhodophyta, Chlorophyta and Phaeophyceae, respectively, were collected seasonally in 2007 to 2008 from Abu-Qir bay (Alexandria, Egypt). The different macroalgal species were tested against pathogenic microbes such as Bacillus subtilis, Staphylococcus aureus and Streptococcus aureus as gram-positive bacteria, Escherichia coli, Salmonella typhi and Klebsiella pneumoniae as gram-negative bacteria and one yeast strain, Candida albicans. The influence of sampling season on the antimicrobial activity of the collected seaweeds showed strong activity in spring followed by winter, summer and autumn, respectively. However, the strongest antimicrobial activity was recorded in 70% acetone extract of U. fasciata collected during winter against all the tested microorganisms. This extract was purified using column chromatography (CC) and thin layer chromatography (TLC). The nature of this purified antimicrobial material was detected using different chemical analysis (UV, IR,1H NMR and MS) which indicated that it is an aromatic compound and has different active groups (-NH2, -C=O, -NO2, phenyl ring and -CH3). The molecular weight of the compound was determined (662) and its structure was characterized as a derivative of phthalate ester [(E)-1-(10-acetamido-2-nitrodec-9-enyl) 2-(10-acetamido-2-nitrodecyl) 4-methylphthalate]. This is the first evidence of the isolation of phthalate esters derivative from green seaweeds (U. fasciata) that has broad antimicrobial activity.Key words: Antimicrobial, pathogenic microbes, season, seaweeds

Optimum joint profile for constrained motion of a planar rigid-flexible manipulator

Dynamic system performance of a constrained rigid-flexible manipulator in contact with a circular surface is considered here. A dynamic model with zero tip deformation constraint is derived using extended Hamilton’s principle. An analytical approach for vibration of the flexible link using the assumed modes technique is presented. The effect the force exerted at the end-effector and the required joint torque is investigated through the solution of the inverse dynamics problem. Optimum system performance is suggested for the circular contact surfaces considered in this study using the minimum energy criteria for three joint motion profiles

Robust Integration Schemes for Generalized Viscoplasticity with Internal-State Variables

The scope of the work in this presentation focuses on the development of algorithms for the integration of rate dependent constitutive equations. In view of their robustness; i.e., their superior stability and convergence properties for isotropic and anisotropic coupled viscoplastic-damage models, implicit integration schemes have been selected. This is the simplest in its class and is one of the most widely used implicit integrators at present

In vitro screening of antimicrobial activity of extracts of some macroalgae collected from Abu-Qir bay Alexandria, Egypt

Ethanol, methanol and acetone extracts of nine marine macroalgae (Rhodophyta, Chlorophyta and Phaeophyta) from Abu-Qir bay (Alexandria, Egypt) were evaluated for antimicrobial activity by agar well diffusion methods against pathogenic microbes (Bacillus subtilis, Staphylococcus aureus and Streptococcus aureus as gram-positive bacteria, and (Escherichia coli, Salmonella typhi and Klebsiella pneumoniae as gram-negative bacteria) and one yeast strain Candida albicans. All pathogenic microorganisms were obtained from Culture Collection of Botany Department, Faculty of Science, Tanta University. The best results were obtained by acetone extracts with inhibition activity (36.7%), followed by the methanol extracts (32.9%), and then ethanol extracts (30.2%) for all tested microorganisms. The tested species of Chlorophyta were the most active followed by Rhodophyta and Phaeophyta. The most active seaweeds was Ulva fasciata (chlorophyceae) against all tested microorganisms.Key words: Seaweeds, antimicrobial activity, extracts, pathogenic microbes

Adverse effects of energy drink on rat pancreas and the therapeutic role of each of bone marrow mesenchymal stem cells and Nigella Sativa oil

Background: Energy drinks have been observed to threaten public health leading to many medical problems. Bone marrow-derived mesenchymal stem cells (BMSCs) have broad prospects in tissue regeneration. Nigella Sativa (NS) possess great therapeutic properties for the treatment of a wide range of diseases. Materials and methods: Forty adult male albino rats were divided into: control group and treated group. The treated group was further subdivided into: energy drink subgroup 2a, BMSCs-injected subgroup 2b, NS-injected subgroup 2c. Histological, immunohistochemical and biochemical assessment was performed. Results: Administration of energy drink revealed that it adversely affected the pancreatic cytoarchitecture. BMSCs and NS have been similarly observed to significantly ameliorate the histological, biochemical and immunohistochemical changes induced by energy drink. Conclusions: The extent of pancreatic regeneration, exerted by each of BMSCs and NS oil, is nearly similar but the effect of BMSCs is more superior; however, NS could be privileged to BMSCs as a line of treatment being easily accessible and of lower cost

Factors influencing ICTs acceptance and usage for e-government services in public organizations in Jordan

E-government in public organisations in Jordan has been in existence for more than two decades. However, there is still lack of studies in discovering the aspects of attitude and behavior of public organisation employees towards e government services. Therefore, this study aims to investigate the determinants of the ICT usage from the perspective of attitude and behavior of the employees in the e-government services. This study employed the Model of Readiness for Organizational Change proposed by Holt as the underpinning theory and further enhanced it to the technology acceptance model III proposed by Venkatesh, and Bala as the additional predictors of ICT acceptance via the intervening effect of attitude towards intention to use for e-government. The study setting was based on three main public organizations from Jordan, namely; Municipality of Zarqa, Municipality of Irbid, Municipality of Mafraq and systematic random sampling of data collection was done through self-administered questionnaire and analysis was done by using the PLS structural equation modelling as the statistical tool. The findings show that principal supports, motivation valence, appreciation, perceived ease of use, perceived usefulness and current usage have a positive significant effect on current usage of e-government services. The findings further reveal that attitude to change positively intervene through current usage and intention to use of ICT acceptance and usage for e-government services. These results are immeasurably valuable to practitioners for managing and executing their strategies in public organisations. Furthermore, it contributes and enriches knowledge pertaining to the predictors of e-government usage