A finite element method for thermo-mechanical coupling analysis of shape memory alloys

Due to strong thermo-mechanical coupling in shape memory alloys (SMAs), heat generation/absorption during forward/reverse phase transformation can cause temperature variations in the material; influencing its mechanical behaviour. It is usually assumed that this coupling is only affected by the loading rate. But, recently studies have shown that the size of the structure and the boundary conditions are also important. Therefore, only the definition of quasistatic or slow loading rate can not guarantee an isothermal process and so further considerations need to be made. Based on the powerful model, proposed by Lagoudas et al. [1] and later improved for computer programming using the return mapping algorithm by Qidwai and Lagoudas [2], this contribution presents a three-dimensional thermo-mechanically coupled extension which describes two important typical phenomena of material model of SMAs: superelasticity and superplasticity (shape memory effect). An algorithm is then proposed to implement the coupled model into a finite element code. Performed simulations with different boundary conditions demonstrate that the both loading rate and the size dependency can be captured within the proposed framework. The results are in good agreement with available data in the literature

The effects of extremely low frequency pulsed electromagnetic field on collagen synthesis of rat skin: A biochemical and histoligical approach

The efficacious effects of pulsed electromagnetic field (PEMF) under the certain field parameters like frequency and the field intensity have been reported for various tissue and molecules. Since collagen is found abundantly in most tissue structures, this research was designed to further investigate the effects of extremely low frequency (ELF) PEMF on the synthesis of the epidermal collagen. To do the task, six groups of animals each consisting of eight mature male rats were selected randomly as one group for the control and five for the test. The field was generated by using a parallel set of Helmholtz coil. The first set of experiments was carried out at the peak intensity of 2 mT (milli Tesla) for different frequencies of 25, 50 and 100 Hz. Since the most effective frequency turned out to be 25 Hz, another set of experiment was conducted using this frequency and two different field intensities of 1 and 4 mT. The field was applied for 2.5 h/day lasting for 8 days, keeping the same procedure for the control group except for the field turned off. On the ninth day, the rats were sacrificed and the skin samples from the dorsal region were taken for biochemical assessment of collagen by measuring hydroxyproline content using Stegeman-Stalder method and histological assessment. The data indicated that pulsed electromagnetic field of 2 mT at 25 Hz increased the collagen synthesis (P<0.05). The other intensities and frequency setting did not have much distinguishable effect, however, at the frequency of 25 Hz and 4 mT, the field effect on the collagen increase was also noticeable. It was concluded that applying the field parameters of 25 Hz and 2 mT peak intensity for 2.5 h/day during eight days rendered a significant increase in collagen synthesis in rat skin. Histological observations were consistent with the biochemical findings

M-fractional derivative under interval uncertainty: theory, properties and applications

In the recent years some efforts were made to propose simple and well-behaved fractional derivatives that inherit the classical properties from the first order derivative. In this regards, the truncated M-fractional derivative for α-differentiable function was recently introduced that is a generalization of four fractional derivatives presented in the literature and has their important features. In this research, we aim to generalize this novel and effective derivative under interval uncertainty. The concept of interval truncated M-fractional derivative is introduced and some of the distinguished properties of this interesting fractional derivative such as Rolle’s and mean value theorems, are developed for the interval functions. In addition, the existence and uniqueness conditions of the solution for the interval fractional differential equations (IFDEs) based on this new derivative are also investigated. Finally, we present the applicability of this novel interval fractional derivative for IFDEs based on the notion of w-increasing (w-decreasing) by solving a number of test problems

A Gradient Weighted Moving Finite-Element Method with Polynomial Approximation of Any Degree

A gradient weighted moving finite element method (GWMFE) based on piecewise polynomial of any degree is developed to solve time-dependent problems in two space dimensions. Numerical experiments are employed to test the accuracy and effciency of the proposed method with nonlinear Burger equation

A cephalometric comparison of twin block and bionator appliances in treatment of class II malocclusion

Class II malocclusion is one of the most common orthodontic problems. In cases of class II malocclusion with mandibular deficiency, functional appliances often are used with the intent of stimulating mandibular growth. Bionator and twin block are two of the more popular functional appliances. The aim of this study was to compare the treatment outcomes of these two appliances using cephalometric radiographs. Cephalometric radiographs of 33 patients who had class II division I malocclusion, before and after treatment were digitalized. The mean changes in twin block and bionator groups were compared using independent t test. Twin block and bionator showed no statistically significant differences in cephalometric parameters except for ANB, NA-Pog, Basal and Ar-Go-Me angles. There were no statistically significant differences in dentoalveolar and mandibular position between twin block and bionator (p>0.1). Twin block was more efficient in inhibition of forward movement of maxilla (p<0.1)

Improvement of Secondary Sedimentation Tanks in the Presence of a Baffle

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

An eigenvalue-eigenvector method for solving a system of fractional differential equations with uncertainty

A new method is proposed for solving systems of fuzzy fractional differential equations (SFFDEs) with fuzzy initial conditions involving fuzzy Caputo differentiability. For this purpose, three cases are introduced based on the eigenvalue-eigenvector approach; then it is shown that the solution of system of fuzzy fractional differential equations is vector of fuzzy-valued functions. Then the method is validated by solving several examples

Acoustic phonon scattering in a low density, high mobility AlGaN/GaN field effect transistor

We report on the temperature dependence of the mobility, $\mu$, of the two-dimensional electron gas in a variable density AlGaN/GaN field effect transistor, with carrier densities ranging from 0.4$\times10^{12}$ cm$^{-2}$ to 3.0$\times10^{12}$ cm$^{-2}$ and a peak mobility of 80,000 cm$^{2}$/Vs. Between 20 K and 50 K we observe a linear dependence $\mu_{ac}^{-1} = \alpha$T indicating that acoustic phonon scattering dominates the temperature dependence of the mobility, with $\alpha$ being a monotonically increasing function of decreasing 2D electron density. This behavior is contrary to predictions of scattering in a degenerate electron gas, but consistent with calculations which account for thermal broadening and the temperature dependence of the electron screening. Our data imply a deformation potential D = 12-15 eV.Comment: 3 pages, 2 figures, RevTeX. Submitted to Appl Phys Let

Impact of exercise in high-humidity on heart rate variability and salivary oxidative stress in obese and lightweight asthmatic children

BACKGROUND: Asthma and obesity are becoming increasingly common among children. Such conditions are known to negatively affect both cardiac autonomic function and oxidative stress. We therefore investigated the heart rate variability (HRV) and oxidative (malondialdehyde, MDA) response to exercise within a high humidity environment (similar to 65%) in obese and lightweight asthmatic children. METHODS: Forty-two children participated in this study and were categorized into four groups: obese asthmatic (OA, N.=10), obese non-asthmatic (ONA, N.=15), lightweight asthmatic (LA, N.=10), and lightweight non-asthmatic (LNA, N.=7). Time-domain and nonlinear indices of HRV were assessed at rest, during, and immediately after exercise. Further, saliva samples were collected immediately before and after exercise and analyzed for the determination of MDA. RESULTS: HRV significantly decreased during and after exercise compared to baseline (P<0.05) with short-term fractal scaling exponent (alpha 1) for the LNA group significantly smaller than the OA group after exercise (P<0.05). In contrast, the long-term fractal scaling exponent (alpha 2) was greater after exercise compared to baseline and during exercise for all groups (P<0.05). MDA significantly decreased after exercise compared to baseline (P<0.05). We also found significant correlations after exercise between salivary levels of MDA with HRV components (i.e., RMSSD, SD1, and alpha 2) in asthmatic groups (all P<0.05). CONCLUSIONS: Our findings showed that exercise in high humidity environment does not significantly differentiate the autonomic response among children with various conditions (i.e., obese, asthmatic and healthy). However, a significant relationship was found between HRV and MDA in asthmatic children after exercise, highlighting the inter-relationship between oxidative stress markers and autonomic function in asthmatic children

Differences in maladaptive schemas between patients suffering from chronic and acute posttraumatic stress disorder and healthy controls

War, as a stressor event, has a variety of acute and chronic negative consequences, such as posttraumatic stress disorder (PTSD). In this context, early maladaptive schema-based problems in PTSD have recently become an important research area. The aim of this study was to assess early maladaptive schemas in patients with acute and chronic PTSD.; Using available sampling methods and diagnostic criteria, 30 patients with chronic PTSD, 30 patients with acute PTSD, and 30 normal military personnel who were matched in terms of age and wartime experience were selected and assessed with the Young Schema Questionnaire-Long Form, Beck Depression Inventory second version (BDI-II), the Beck Anxiety Inventory (BAI), and the Impact of Events Scale (IES).; Both acute and chronic PTSD patients, when compared with normal military personnel, had higher scores for all early maladaptive schemas. Additionally, veterans suffering from chronic PTSD, as compared with veterans suffering from acute PTSD and veterans without PTSD, reported more impaired schemas related, for instance, to Self-Control, Social Isolation, and Vulnerability to Harm and Illness.; The results of the present study have significant preventative, diagnostic, clinical, research, and educational implications with respect to PTSD