Stress Concentration on PDMS: An evaluation of three numerical constitutive models using digital image correlation

The examination of hyperelastic materials’ behavior, such as polydimethylsiloxane (PDMS), is crucial for applications in areas as biomedicine and electronics. However, the limitations of hyperelastic models for specific stress scenarios, with stress concentration, are not well explored on the literature. To address this, firstly, three constitutive models were evaluated (Neo-Hookean, Mooney-Rivlin, and Ogden) using numerical simulations and Digital Image Correlation (DIC) analysis during a uniaxial tensile test. The samples were made of PDMS with stress concentration geometries (center holes, shoulder fillets, and edge notches). Results of ANOVA analysis showed that any of the three models can be chosen for numerical analysis of PDMS since no significant differences in suitability were found. Finally, the Ogen model was chosen to obtain the stress concentration factors for these geometries, a property which characterize how discontinuities change the maximum stress supported by an element. Our study provides new values for variables needed to analyze and design hyperelastic elements and produce a foundation for understanding PDMS stress-strain behavior.The authors acknowledge the projects EXPL/EME-EME/0732/2021 and 2022.06207.PTDC for the financial support, through national funds (OE), within the scope of the Scientific Research and Technological Development Projects (IC&DT) program in all scientific domains (PTDC), PORTUGAL 2020 Partnership Agreement, European Regional Development Fund (FEDER), via the Foundation for Science and Technology, I.P. (FCT, I.P) and the R&D Units projects (UIDB/00690/2020 and UIDP/00690/2020) (CIMO), SusTEC (LA/P/0007/2020), UIDB/ 04077/2020, UIDP/04077/2020, UIDB/04436/2020 and UIDB/00532/ 2020. Andrews Souza acknowledges FCT for the Ph.D. scholarship 2021.07961.BD.info:eu-repo/semantics/publishedVersio

Clinical correlation between N-terminal pro-b-type natriuretic peptide and angiographic coronary atherosclerosis

OBJECTIVES: This study aimed to investigate the clinical correlation between angiographic coronary atherosclerosis and N-terminal pro-B-type natriuretic peptide along with other known correlated factors. METHODS: In total, 153 patients with a diagnostic hypothesis of stable angina, unstable angina or acute myocardial infarction were classified as group A (patients with angiographically normal coronary arteries) or group B (patients with angiographic coronary atherosclerosis). The two groups were analyzed with respect to the following factors: gender, age, body mass index, abdominal circumference, smoking, diabetes mellitus, arterial hypertension, early family history of atherosclerosis, statin use, the presence of metabolic syndrome, clinical presentation and biochemical factors, including cholesterol, creatinine and fibrinogen plasma concentrations, monocyte counts and N-terminal pro-B-type natriuretic peptide. RESULTS: Univariate analyses comparing the two groups revealed that group B patients more frequently had diabetes, used statins and had systolic dysfunction, N-terminal pro-B-type natriuretic peptide levels ≥250 pg/mL, fibrinogen levels >;500 mg/dL and ≥501 monocytes/mm3 compared with group A patients (

New drugs from traditional medicines: pharmacological evaluation of plant extracts from Chapada Diamantina (Brazil)

Plants are rich sources of medicines and Brazil is among the most biodiverse nations in the world.info:eu-repo/semantics/publishedVersio

Self-avoiding walks and connective constants in small-world networks

Long-distance characteristics of small-world networks have been studied by means of self-avoiding walks (SAW's). We consider networks generated by rewiring links in one- and two-dimensional regular lattices. The number of SAW's $u_n$ was obtained from numerical simulations as a function of the number of steps $n$ on the considered networks. The so-called connective constant, $\mu = \lim_{n \to \infty} u_n/u_{n-1}$, which characterizes the long-distance behavior of the walks, increases continuously with disorder strength (or rewiring probability, $p$). For small $p$, one has a linear relation $\mu = \mu_0 + a p$, $\mu_0$ and $a$ being constants dependent on the underlying lattice. Close to $p = 1$ one finds the behavior expected for random graphs. An analytical approach is given to account for the results derived from numerical simulations. Both methods yield results agreeing with each other for small $p$, and differ for $p$ close to 1, because of the different connectivity distributions resulting in both cases.Comment: 7 pages, 5 figure

Bulk Viscous LRS Biachi-I Universe with variable GG and decaying Λ\Lambda

The present study deals with spatially homogeneous and totally anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological model with variable $G$ and $\Lambda$ in presence of imperfect fluid. To get the deterministic model of Universe, we assume that the expansion $(\theta)$ in the model is proportional to shear $(\sigma)$. This condition leads to $A=\ell B^{n}$, where $A$,\;$B$ are metric potential. The cosmological constant $\Lambda$ is found to be decreasing function of time and it approaches a small positive value at late time which is supported by recent Supernovae Ia (SN Ia) observations. Also it is evident that the distance modulus curve of derived model matches with observations perfectly.Comment: 11 pages, 4 figures and 1 table, Accepted for publication in Astrophysics and Space Scienc

M-Theory Moduli Space and Cosmology

We conduct a systematic search for a viable string/M-theory cosmology, focusing on cosmologies that include an era of slow-roll inflation, after which the moduli are stabilized and the Universe is in a state with an acceptably small cosmological constant. We observe that the duality relations between different cosmological backgrounds of string/M-theory moduli space are greatly simplified, and that this simplification leads to a truncated moduli space within which possible cosmological solutions lie. We review some known challenges to four dimensional models in the "outer", perturbative, region of moduli space, and use duality relations to extend them to models of all of the (compactified) perturbative string theories and 11D supergravity, including brane world models. We conclude that cosmologies restricted to the outer region are not viable, and that the most likely region of moduli space in which to find realistic cosmology is the "central", non-perturbative region, with coupling and compact volume both of order unity, in string units.Comment: 42 pages, 3 figure