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Mechanical Problems (mechanical + problem)
Selected AbstractsNumerical analysis of Augmented Lagrangian algorithms in complementary elastoplasticityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2004L. Contrafatto The main subject of the paper is the investigation of Augmented Lagrangian algorithms and update formulas in the solution of elastoplastic problems. A stress rate formulation for elastoplastic models with internal variables and its finite increment form is employed to state the mechanical problem. In this formulation the Augmented Lagrangian is used to enforce the constraint of plastic admissibility directly on the stresses and thermodynamic forces. This is not a limitation of the Augmented Lagrangian approach, and the same framework can be built on more classical displacement formulations as well. The meaning and the derivation of various first and second order Lagrangian multipliers update formulas and iterative schemes is shown. A new diagonal iteration algorithm and the introduction of a scale factor for the Augmented Lagrangian term are proposed. Numerical examples compare the efficiency of several forms of Augmented Lagrangian algorithms and illustrate the influence of the scale factor and of the penalty parameter. Copyright © 2004 John Wiley & Sons, Ltd. [source] Mechanical computation in neuronsDEVELOPMENTAL NEUROBIOLOGY, Issue 11 2009Jummi Laishram Abstract Growth cones are the main motile structures located at the tip of neurites and are composed of a lamellipodium from which thin filopodia emerge. In this article, we analyzed the kinetics and dynamics of growth cones with the aim to understand two major issues: first, the strategy used by filopodia and lamellipodia during their exploration and navigation; second, what kind of mechanical problems neurons need to solve during their operation. In the developing nervous system and in the adult brain, neurons constantly need to solve mechanical problems. Growth cones must decide how to explore the environment and in which direction to grow; they also need to establish the appropriate contacts, to avoid obstacles and to determine how much force to exert. Here, we show that in sparse cultures, filopodia grow and retract following statistical patterns, nearly optimal for an efficient exploration of the environment. In a dense culture, filopodia exploration is still present although significantly reduced. Analysis on 1271, 6432, and 185 pairs of filopodia of DRG, PC12 and Hippocampal neurons respectively showed that the correlation coefficient |,| of the growth of more than 50% of filopodia pairs was >0.15. From a computational point of view, filopodia and lamellipodia motion can be described by a random process in which errors are corrected by efficient feedback loops. This article argues that neurons not only process sensory signals, but also solve mechanical problems throughout their entire lifespan, from the early stages of embryogenesis to adulthood. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source] Smeared crack approach: back to the original trackINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2006M. Cervera Abstract This paper briefly reviews the formulations used over the last 40 years for the solution of problems involving tensile cracking, with both the discrete and the smeared crack approaches. The paper focuses on the smeared approach, identifying as its main drawbacks the observed mesh-size and mesh-bias spurious dependence when the method is applied ,straightly'. A simple isotropic local damage constitutive model is considered, and the (exponential) softening modulus is regularized according to the material fracture energy and the element size. The continuum and discrete mechanical problems corresponding to both the weak discontinuity (smeared cracks) and the strong discontinuity (discrete cracks) approaches are analysed and the question of propagation of the strain localization band (crack) is identified as the main difficulty to be overcome in the numerical procedure. A tracking technique is used to ensure stability of the solution, attaining the necessary convergence properties of the corresponding discrete finite element formulation. Numerical examples show that the formulation derived is stable and remarkably robust. As a consequence, the results obtained do not suffer from spurious mesh-size or mesh-bias dependence, comparing very favourably with those obtained with other fracture and continuum mechanics approaches. Copyright © 2006 John Wiley & Sons, Ltd. [source] Videotaped recording as a method of participant observation in psychiatric nursing researchJOURNAL OF ADVANCED NURSING, Issue 5 2000Eila Latvala RN PhD Videotaped recording as a method of participant observation in psychiatric nursing research This paper describes videotaped recording as a data collection method when conducting participant observation in a psychiatric nursing study. The videotaped episodes were part of the daily life of psychiatric nursing in a hospital environment. The advantages and limitations of using videotaped recording in nursing research will be discussed. This paper is based on two studies. The data consisted of 21 videotaped episodes of nursing report sessions or interdisciplinary team meetings in the psychiatric clinic of a university hospital. The participants consisted of patients, their significant others, nurses, doctors, social workers and physiotherapists. All videotaped material was transcribed verbatim. An essential advantage of videotaping is that most potentially useful interaction and behaviour can be captured. The advantage in terms of the credibility of videotaping was that the investigator was able to review the same videotaped situations again and again. Videotaped material is rich and provides several possibilities for analysing the data. In these studies data and source triangulation enabled the researchers to reduce personal influence on the results. The investigator must also be aware of the limitations concerning this method. The most essential limitations are mechanical problems and the influence of videotaping on behaviour. Careful ethical considerations are important concerning personal privacy, informed consent and respect for the self-determination of psychiatric patients. [source] Diagnosis and Treatment of Heel PainJOURNAL OF THE AMERICAN ACADEMY OF NURSE PRACTITIONERS, Issue 11 2003ANP-C, FAANP, Mary Jo Goolsby EdD The American College of Foot and Ankle Surgeons (ACFAC) clinical practice guideline (CPG) summarizes the literature on the assessment and diagnosis of heel pain. The framework classifies heel pain depending on whether the cause is mechanical, neurological, arthritic, traumatic, or from another origin. Treatment strategies are included for the most common form of heel pain that are caused by mechanical problems. [source] Safety and Efficacy of Intrathecal Baclofen Infusion by Implantable Pump for the Treatment of Severe Spinal Spasticity: A Spanish Multicenter StudyNEUROMODULATION, Issue 4 2000J Vidal MD Objective. To assess long-term efficacy, safety and functional benefit of intrathecal baclofen for severe spinal spasticity. Materials and Methods. This prospective multicenter study was performed in two stages: the first one consisted of an intrathecal bolus injection of baclofen, and the second of a continuous intrathecal baclofen infusion by means of an implantable pump. The sample consisted of 72 adult patients with severe spinal spasticity. Sixty-four were implanted and followed for 36 months. Muscular tone, spasms, and functional scales were evaluated before and periodically after administration of the drug, with a follow-up period of 36 months. Results. A very significant decrease in tone and spasms was observed in all cases (p < 0.001). Tolerance appeared during the first 12 months, increasing doses from a mean initial dose of 83.2 ,g (range 25,200 ,g) to a mean final dose of 270 ,g (range 25,800 ,g). Later on, efficacy remained stable, except in cases of mechanical problems of the infusion system. [source] Laser-Welded Titanium Frameworks Supported by Implants in the Partially Edentulous Mandible: A 10-Year Comparative Follow-Up StudyCLINICAL IMPLANT DENTISTRY AND RELATED RESEARCH, Issue 3 2008Anders Örtorp DDS, PhD/Odont Dr ABSTRACT Background: Comparative long-term knowledge of different framework materials in the partially edentulous implant patient is not available. Purpose: To report and compare 10-year data on free-standing implant-supported partial prostheses with laser-welded titanium (test) and conventional gold alloy (control) frameworks. Materials and Methods: Altogether, 52 partially edentulous patients were consecutively provided with laser-welded prostheses (n = 60) in the partially edentulous lower jaw (test group). A control group of 52 randomly selected patients with gold alloy castings (n = 60) was used for comparison. Clinical and radiographic 10-year data were retrospectively collected and evaluated for both groups. Results: The overall 10-year implant cumulative survival rate (CSR) was 93.0% (loaded implants, 96.4%), with a 10-year implant CSR of 91.5 and 94.7% for test and control implants, respectively (p > .05). Out of a total of 22 lost implants, 17 implants (77.3%) were shorter than 10 mm. The overall 10-year prosthesis CSR was 93.7%, with a corresponding 10-year CSR of 88.4 and 100% for test and control groups, respectively (p < .05). Average 10-year bone loss was 0.46 mm (SD 0.47) and 0.69 mm (SD 0.53) for the test and control groups (p < .001), respectively. Only 1% of the implants had >3 mm accumulated bone loss after 10 years. Altogether, 10 of the prostheses in both groups had implant component mechanical problems (8.3%). None of the frameworks or implants fractured, but more fractures of porcelain veneers were observed in the test group (p < .05). Conclusion: The protocol of implant treatment in the partially edentulous jaw functioned well during 10 years, although prosthodontic maintenance was required. However, laser-welded titanium frameworks presented more problems as compared with gold alloy frameworks. More loaded implants were lost (p < .05), and higher incidence of porcelain chipping was noted in the test group (p < .05). However, bone loss was on an average lower for the test group during the 10 years of follow-up (p < .001). [source] | |||||||||||||