Search

This paper explores the chaotic dynamics of a piezoelectrically laminated initially curved microbeam resonator subjected to fringing-field electrostatic actuation, for the first time. The resonator is fully clamped at both ends and is coated with two piezoelectric layers, encompassing both the top and bottom surfaces. The nonlinear motion equation which is obtained by considering the nonlinear fringing-field electrostatic force, includes geometric nonlinearities due to the mid-plane stretching and initial curvature. The motion equation is discretized using Galerkin method and the reduced order system is numerically integrated over the time for the time response. The variation of the first three natural frequencies with respect to the applied electrostatic voltage is determined and the frequency response curve is obtained using the combination of shooting and continuation methods. The bifurcation points have been examined and their types have been clarified based on the loci of the Floquet exponents on the complex plane. The period-doubled branches of the frequency response curves originating from the period doubling (PD) bifurcation points are stablished. It's demonstrated that the succession PD cascades leads to chaotic behavior. The chaotic behavior is identified qualitatively by constructing the corresponding Poincaré section and analyzing the response's associated frequency components. The bifurcation diagram is obtained for a wide range of excitation frequency and thus the exact range in which chaotic behavior occurs for the system is determined. The chaotic response of the system is regularized and controlled by applying an appropriate piezoelectric voltage which shifts the frequency response curve along the frequency axis. [ABSTRACT FROM AUTHOR]

The friction coefficient resulting from the road surface condition directly affects the vehicle braking condition and distance. In the American Association of State Highway and Transportation Officials (AASHTO), the braking distance for different speeds, upgrades, and downgrades is recommended. However, the effects of the variations in the friction coefficient, type, and weight of vehicles are not directly taken into account. Therefore, the present study firstly examines the effects of the variations in vehicle speed, friction coefficient, longitudinal grade (upgrade and downgrade) in AASHTO 2018, and the vehicle type on braking distance. Secondly, a nonlinear analytical approach is considered to estimate braking distance and determine a critical friction coefficient that causes decreases in the braking distance. The findings indicate that under dry road surface conditions (with a friction coefficient of 0.6), the weight of the vehicle predominantly influences braking distance, resulting in heavier vehicles having shorter braking distances than lighter vehicles across all selected grades, except at a − 6%. However, when the road surface friction coefficient decreases from 0.6 to 0.18, the impact of vehicle weight surpasses the effect of the longitudinal grade, leading to an increase in braking distance. Consequently, when designing a road, it's essential to consider not only the technical road parameters and vehicle dimensions but also the vehicle weight and the road surface conditions in areas prone to snowfall, among other factors. If we wish to account for snowy and icy conditions, in addition to AASHTO's classification of wet conditions, in order to refine predictions of braking distance, the results of this study can provide valuable insights for road designers. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear dynamics of a piezoelectrically sandwiched initially curved microbeam subjected to fringing-field electrostatic actuation is investigated. The governing motion equation is derived by minimizing the Hamiltonian over the time and discretized to a reduced-order model using the Galerkin technique. The modelling accounts for nonlinearities due to the fringing-field electrostatic force, initial curvature and mid-plane stretching. The electrostatic force is numerically computed using finite element simulation. The nonlinear dynamics of the microbeam in the vicinity of primary resonance is investigated, and the bifurcation types are determined by investigating the location of the Floquet exponents and their configuration with respect to the unit circle on the complex plane. The branches on the frequency–response curves, which originate from the period-doubling bifurcation points, are introduced, and the transition from period-1 to period-2 response is demonstrated by slight sweep of the excitation frequency over the time. The effect of DC and AC electrostatic excitation and the piezoelectric excitation on the response of the system are examined, and their effect on the bifurcation types is determined. The force response curves assuming the AC voltage as the bifurcation parameter are also introduced; it is illustrated that in contrast to in-plane electrostatic excitation, in fringing field-based resonators the resonator is not limited by pull-in instability, which is substantially confining the amplitude of the motion in in-plane resonators. [ABSTRACT FROM AUTHOR]

The static and dynamic behavior of a curved single-walled carbon nanotube which is under twist-bending couple based on nonlocal theory is analyzed. The nonlocal theory is used to model the mechanical behavior of structure in small scale. The obtained differential equations are solved using a simply supported boundary condition and Navier analytical method. Moreover the twisted vibration and bending of curved nanotube is analyzed and also the armchair model is assumed in this study. The following parameters were studied in this paper: the effect of nonlocal parameter, the curved nanotube's opening angel, the Young's modulus and the mode number is studied. The results were verified with the previous literature which showed an excellent agreement. The results of this paper can be used as a benchmark for future investigations. [ABSTRACT FROM AUTHOR]

Current evidences indicated that a group of soluble mediators called chemokines is involved in tumor growth and metastasis. The association of IL-8 with tumor cell migration was previously found, and its expression was related to angiogenesis, tumor progression, and metastasis in many kinds of carcinomas in human and animal models. Furthermore, it has been showed that IL-17 plays its role as either a proteome of tumor progression or antitumor indifferent cancer models. To investigate the messenger RNA (mRNA) expressions of IL-8 and IL-17 in patients with colorectal cancer (CRC) and non-tumor tissue, quantitative real-time PCR was used in the study. Our results showed that expression of IL-8 mRNA was significantly increased in tumor tissues (mean ± SD 3.84 ± 0.08) compared with adjacent normal mucosa (mean ± SD 1.17 ± 0.75, P = 0.001). Furthermore, a higher expression of IL-17 mRNA was found in tumor tissues (mean ± SD 2.73 ± 0.69) when compared with normal tissues (mean ± SD 1.06 ± 0.07, P = 0.001). Our findings indicated that advanced tumor-node-metastasis (TNM) stage ( P = 0.024) and histological grade (poorly differentiated, P = 0.013) and distant metastasis ( P = 0.001) were correlated with expression of IL-8. Moreover, high expression of IL-17 showed significant association with early stage CRC (TNM) ( P = 0.038). In conclusion, the expression of IL-8 and IL-17 mRNAs was significantly increased in tumor tissues compared with adjacent normal tissues. We found that advanced TNM stage and histological grade and distant metastasis were correlated with expression of IL-8, while high expression of IL-17 showed significant association with early stage CRC (TNM) stage and overexpression of IL-8 may be associated with progression of CRC. [ABSTRACT FROM AUTHOR]

In order to evaluate the correlation of B7-H4 and B7-H1 with renal cell carcinoma (RCC), we analyzed B7-H1 and B7-H4 expressions and their clinical significance by immunohistochemical method. Our result indicated that B7-H4-positive staining was detected in 58.13 % of RCC tissues (25 tissues tumors), and there were 18 tissues of patients without detectable B7-H4. Furthermore, 21 cases (48.83 %) were B7-H1-positive. Positive tumor expressions of B7-H4 and B7-H1 were markedly related to advanced TNM stage ( P = 0.001; P = 0.014), high grade ( P = 0.001; P = 002), and larger tumor size ( P = 0.002; P = 024) in RCC tissues than patients with B7-H4-negative and B7-H1-negative in RCC tissues. The patients with B7-H1 and B7-H4-positive expressions were found to be markedly correlated with the overall survival of the patients ( P < 0.05) and tended to have an increased risk of death when compared with negative expression groups. Univariate analysis showed that B7-H4 and B7-H1 expressions, TNM stage, high grade, and tumor size were significantly related to the prognosis of RCC. Furthermore, multivariate analysis showed that B7-H4 and B7-H1 expressions decreased overall survival. The adjusted HR for B7-H1 was 2.83 (95 % CI 1.210-2.971; P = 0.031) and also was 2.918 (95 % CI 1.243-3.102; P = 0.006) for B7-H4 that showed these markers were independent prognostic factors in RCC patients. The expressions of B7-H1 and B7-H4 in RCC patients indicate that these markers may be as a predictor of tumor development and death risk. Further investigations can be helpful to confirm B7-H1 and B7-H4 roles as an independent predictor of clinical RCC outcome. [ABSTRACT FROM AUTHOR]

Current evidences have indicated that osteosarcoma is strongly associated with abnormal genetic and epigenetic changes that lead to the abnormal expression of oncogenes or methylation of tumor suppressor genes. In the present study, MACC1 and CDC5L mRNA levels in the patients with osteosarcoma were evaluated using quantitative real-time PCR. Our results demonstrated that CDC5L mRNA levels were higher in tumor tissues than in adjacent normal tissues (2.713 ± 0.738 vs. 1.071 ± 0.629; P < 0.05). Moreover, MACC1 was upregulated in tumor bone tissues than in adjacent normal tissues (3.221 ± 0. 624 vs. 1.427 ± 0.456; P < 0.05). Our result demonstrated that high expression of CDC5L was significantly related to advanced TNM stage ( P = 0.032). No significant difference was determined between CDC5L mRNA expression and other clinicopathological parameters including age, gender, tumor diameter, location, tumor grade, and histological type. In addition, overexpression of MACC1 was strongly correlated with advanced TNM stage ( P = 0.027) and high tumor grade ( P = 0.035). Our findings indicated that mRNA level of CDC5L is correlated with advanced TNM stage, and MACC1 may be involved in progression of osteosarcoma. [ABSTRACT FROM AUTHOR]

In this paper, thermoelectric-mechanical buckling behavior of the piezoelectric nanobeams is investigated based on the nonlocal theory and Euler-Bernoulli beam theory. The electric potential is assumed linear through the thickness of the nanobeam and the governing equations are derived by Hamilton's principle. The governing equations are solved analytically for different boundary conditions. The effects of the nonlocal parameter, temperature change, and external electric voltage on the critical buckling load of the piezoelectric nanobeams are discussed in detail. This study should be useful for the design of piezoelectric nanodevices. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to assess the frequency of different histopathological findings obtained from dilatation and curettage (D&C) specimens in patients with abnormal uterine bleeding (AUB). Methods: In a retrospective review of 591 specimens, the included subjects were all women with AUB who underwent D&C between 2002 and 2006 in Be'sat Hospital, Tehran, Iran. The pathological diagnoses were analyzed in four groups from normal to malignant endometrium. The pathological groups were evaluated for patients' characteristics including demographic data and medical history. Results: The majority of patients (61.6 %) were in the 41-50 year age group. Totally, 81.4 % of patients had normal pathology. The disordered proliferative endometrium/polyps, hyperplasia, and malignant pathology were found in 15.4, 2.5, and 0.7 % of specimens, respectively. The abnormal pathologies were seen more among patients with postmenopausal status, nulli-/primigravid women, and those with hypertension, diabetes, hypothyroidism, and polycystic ovary syndrome. Conclusions: The proliferative endometrium and secretory endometrium were the most common histopathological observations in AUB patients in our region, and except normal endometrium, disordered proliferative endometrium was the most common cause of AUB. [ABSTRACT FROM AUTHOR]