Physics and chemistry-based constitutive framework for thermo-chemically aged elastomer using phase-field approach

We propose a physics and chemistry-based constitutive framework to predict the stress responses of thermo-chemically aged elastomers and capture their brittle failure using the phase-field approach. High-temperature aging in the presence of oxygen causes the macromolecular network of elastomers to undergo complex chemical reactions inducing two main mechanisms: chain-scission and crosslinking. Chemical crosslinking contributes to the stiffening behavior characterizing the brittle response of aged elastomers. In this work, we first modify the Helmholtz free energy to incorporate the effect of thermo-chemically-driven crosslinking processes. Then, we equip the constitutive description with phase-field to capture the induced brittle failure via a strain-based criterion for fracture. We show that our proposed framework is self-contained and requires only four main material properties whose evolution due to thermo-chemical aging is characterized entirely by the change of the crosslink density obtained based on chemical characterization experiments. The developed constitutive framework is first solved analytically for the case of uniaxial tension in a homogeneous bar to highlight the interconnection between all four material properties. Then, the framework is numerically implemented within a finite element (FE) context via a user-element subroutine (UEL) in the commercial FE software Abaqus to simulate more complicated geometries and loading states. The framework is finally validated with respect to a set of experimental results available in the literature. The comparison confirms that the proposed constitutive framework can accurately predict the mechanical response of thermo-chemically aged elastomers. Further numerical examples are provided to demonstrate the effects of evolving material properties on the response of specimens containing pre-existing cracks

Can opium abuse be a risk factor for carotid stenosis in patients who are candidates for coronary artery bypass grafting?

Background: Over the centuries, opium has been the most frequent substance abused in the Middle East. There are many controversial aspects about the effects of opioids on the atherosclerosis process, which is still unclear. Methods: All patients who were candidates for coronary artery bypass graft in Tehran Heart Center were registered and evaluated for risk factors such as diabetes mellitus, hypertension, smoking status and duration, opium abuse, involved coronary arteries and left main branch lesion > 50%, carotid stenosis &#8805; 70%. Results: A total of 1,339 patients were enrolled in the study, of whom 400 (29.9%) were female and the other 939 (70.1%) male. Female patients were omitted from analysis due to the low numbers of female opium addicts. Our study revealed that in the addicted population, the risk of diabetes and hypertension was lower than in the non-addicted group (p < 0.05 for each variable) and fasting blood sugar tended to be less in addicted ones, but the number of involved coronary arteries, left main stenosis > 50% and extent of carotid stenosis was not significantly different between the two groups. Conclusions: Our investigations demonstrate that opium is not cardioprotective, as has been claimed by some previous studies, and does not even decelerate atherosclerosis of carotid arteries in opium-addicted patients, but more evidence is still needed to completely prove the case. (Cardiol J 2010; 17, 3: 254-258

A Data-Driven Approach to Full-Field Damage and Failure Pattern Prediction in Microstructure-Dependent Composites using Deep Learning

An image-based deep learning framework is developed in this paper to predict damage and failure in microstructure-dependent composite materials. The work is motivated by the complexity and computational cost of high-fidelity simulations of such materials. The proposed deep learning framework predicts the post-failure full-field stress distribution and crack pattern in two-dimensional representations of the composites based on the geometry of microstructures. The material of interest is selected to be a high-performance unidirectional carbon fiber-reinforced polymer composite. The deep learning framework contains two stacked fully-convolutional networks, namely, Generator 1 and Generator 2, trained sequentially. First, Generator 1 learns to translate the microstructural geometry to the full-field post-failure stress distribution. Then, Generator 2 learns to translate the output of Generator 1 to the failure pattern. A physics-informed loss function is also designed and incorporated to further improve the performance of the proposed framework and facilitate the validation process. In order to provide a sufficiently large data set for training and validating the deep learning framework, 4500 microstructural representations are synthetically generated and simulated in an efficient finite element framework. It is shown that the proposed deep learning approach can effectively predict the composites' post-failure full-field stress distribution and failure pattern, two of the most complex phenomena to simulate in computational solid mechanics

Propagating Relationship of Cerebral Oximetric Volume and the Clinical Outcome of Recombinant Tissue Plasminogen Activator (r-TPA) Therapy on Acute Cerebral Ischemic Stroke Patients

Introduction: Currently, the most available treatment for acute ischemic stroke (AIS) is thrombolytic therapy with recombinant tissue plasminogen activator (r-TPA). A challenge in r-TPA therapy is the prediction of recovery in each case.&nbsp;Objective: The aim was to find a possible relationship between the cerebral oximetry indexes and the clinical outcome of r-TPA therapy to assess the cerebral oximetry as a non-invasive monitoring agent for therapy.&nbsp;Methods: The inclusion criteria were all patients with AIS who received r-TPA. The neurologic status was evaluated based on the national institutes of health stroke scale (NIHSS) score at arrival, and after a period of 24 hours. In addition, the levels of brain oxygenation in both hemispheres were measured before and continuously over the first 24 hours after r-TPA injection, using an oximetric sensor in the frontal lobes. The clinical success was defined as a 4-point improvement from the baseline NIHSS.&nbsp;Results: Total 44 patients with the mean age of 58.2 ± 2.18 years were enrolled, of whom 68.18% were male. Twenty-eight patients remained clinically unimproved and 16 patients were improved. A significant difference was found in the mean surface area under the brain oximetric curve in the 24 hour, in the affected hemisphere in the improved group, compared to the unimproved group (P = 0.007). There was a significant difference between the mean increase in brain oxygenation within 24 hours in the improved and unimproved groups (P = 0.002).&nbsp;Conclusion: The cerebral oximetry could contribute to predict the likelihood of r-TPA prognosis in patients with AIS

The Relationship Between QT Interval and Intra-Hospital Mortality in patients with Spontaneous Intracranial Hemorrhage

Introduction: Repolarization abnormalities such as prolongation of QT interval and changes in ST segment and T wave are the most usual electrocardiogram (ECG) changes in patients with intracranial hemorrhage (ICH). It has recently been recommended that prolonged QTc interval raises the risk of death due to malignant ventricular arrhythmias or sudden cardiac death.&nbsp;Objective: The goal of this study was to evaluate the relationship between QT interval and death in patients with ICH.&nbsp;Method: This cross-sectional study was performed on patients with ICH who referred during 2015-2017 to Poursina Hospital, Rasht, Iran. The QT interval was manually measured based on the BAZETT formula. Max QT and Max QTc and QT dispersion were the variables evaluated by the ECG of the patients. The outcome under the study was the death or survival of patients during hospitalization.&nbsp;Results: Finally, 466 cases with the mean age of 69±12 years were studied of whom 68.7% were male. The average QT-Max interval was 350.4±56.5 milliseconds, and the average QTc-Max was 583.6±57.6 msec. Totally, 22.7% of the patients died. There was a significant statistical relationship between QTc-MAX and death (p=0.001). However, there was no statistically significant relationship between QT-MAX and the outcome (p=0.593).&nbsp;Conclusion: It is likely that, prolonged QT interval is correlated with in-hospital mortality of patients with ICH. Therefore, it can be expected that assessing ECG abnormalities, especially prolonged QTc could be valuable in these patients

Zinc status in Cardiovascular patients in the north of Islamic Republic of Iran

Studies have demonstrated that zinc plays an important role in development of cardiovascular diseases in Western populations. But there is little data for other racial groups. This study was aimed to investigate the association between serum zinc and coronary artery disease (CAD) in Iranian subjects.This study was conducted on 81 subjects,which referred to Heshmat Hospital of Guilan province , Iran, for routine coronary angiography from June to August 2011. Subjects were assigned into 2 groups; 41 CAD patients.case and 40 healthy subjects in control group. Data about smoking habit,physical activity, dietary intake and anthropometric indices were collected by questionnaire. Serum zinc was measured by atomic spectroscopy.The serum zinc concentrations were significantly lower in case group than control (p&lt;0.05). The mean serum zinc concentration in the case and control group was 73.50±1.61μg/dl and 78.47±1.66μg/dl, respectively. subjects  that lives in  rural area had 7.11-fold higher CAD risk in compare to subjects lives in urban  after adjustment for confounder factors,they also had lower zinc concentration than urban (p&lt;0.05). in our study With increasing in serum zinc concentration CAD risk decrease 0.94-fold.Zinc concentration had significant correlation with age (r= -0.23   p&lt;0.05), weight (r=0.26   p&lt;0.05)  and  Place for living (r=- 0.22  p= 0.04).There were no significant correlation between the dietary intake , Waist circumference ,smoking and serum zinc concentration in our study.Serum zinc concentration was significantly lower in the north of Islamic Republic of Iran patients with abnormal versus those with a normal angiogram. It seems Serum zinc concentration correlate with some risk factors for coronary artery diseas

Knowledge and practice regarding dental radiological waste disposal among dental specialists and general dentists in Amol and Babol cities

Introduction: The aim of this study was to assess dentists’ knowledge and practice about dental radiological wastes that are dangerous to the environment. Materials &Methods: This was a cross-sectional study was conducted in 2018-19. All participants completed a two sections’ (knowledge and practice) checklist. Data were analyzed using descriptive statistics, t-test and ANOVA. A value of P<0.05 was considered significant. Results: Totally, 204 (73.5% general dentists and 26.5% specialist) dentists from Amol (35.8%) and Babol (64.2%) participated. The mean age of participants was 39.2 (SD± 10.9) years, and 59.2% of them were female. The average percentage of dentists’ knowledge and practice about radiological waste disposal was 42.55 and 43.12% respectively. Gender, work experience, special or general degree, and city of clinical activity had no significant effect on dentists’ knowledge and practice (P>0.05). Conclusion: More than half of dentists had no correct knowledge and practice on how to dispose radiological wastes. It is necessary to develop specific approaches such as workshops and training classes

Late cardiac perconditioning by phenylephrine in an isolated rat heart model is mediated by mitochondrial potassium channels

The present study was designed to investigate the effect of early and late administration of phenylephrine during ischemia against regional ischemia–reperfusion injuries in an isolated rat heart model. All animals were randomly divided into experimental groups: (I) IR (Ischemic/ reperfusion): the hearts underwent 35 min of regional ischemia followed by 60 min of reperfusion; (II) 5HD-IR-0: the hearts were perfused for 5 min with 5HD (5-hydroxydecanoate, specific mKATP channel blocker, 100 µM) at the onset of regional ischemia; (III) 5HD-IR-20: the hearts were perfused for 5 min with 5HD 20 min after regional ischemia; (IV) PE-IR-10: the hearts were perfused for 5 min with phenylephrine 10 min after regional ischemia; (V) PE-IR-30: the hearts were perfused for 5 min with phenylephrine (100 µM) 30 min after regional ischemia; (VI) PE-5HD-IR-10 group: the hearts were perfused for 5 min with 5HD at the onset of regional ischemia after which phenylephrine was administrated as in group IV; and (VII) PE-5HD-IR-30: the hearts were perfused for 5 min with 5HD 20 min after the ischemia and then phenylephrine was administrated as in group V. The hemodynamic parameters were recorded throughout the experiment. Ischemia-induced arrhythmias, myocardial infarct size (IS), creatin kinase-MB isoenzyme (CK-MB), plasma lactate dehydrogenase (LDH) activities, and coronary blood flow (CBF) were measured in all animals. Perfusion of phenylephrine 30 min after the regional ischemia curtailed the myocardial infarct size, reduced CK-MB, and improved cardiac function and CBF. Administration of 5HD 30 min after the ischemia abolished cardioprotective effects of phenylephrine in the late phase. These results suggest the involvement of mKATP in the mechanism of phenylephrine-induced late preconditioning