Natural frequency of beams with embedded piezoelectric sensors and actuators

A mathematical model is developed to study the natural frequency of beams with embedded piezoelectric sensors and actuators. The piezoelectric sensors/actuators in a non-piezoelectric matrix (host beam) are analyzed as two inhomogeneity problems by using Eshelby’s equivalent inclusion method. The natural frequency of the beam is determined from the variational principle in Rayleigh quotient form, which is expressed as functions of the elastic strain energy and dielectric energy of the piezoelectric sensors/actuators. The Euler-Bernoulli beam theory and Rayleigh-Ritz approximation technique are used in the present analysis. Parametric studies show that the size, volume fraction and location of the piezoelectric inclusions significantly influence the natural frequency of the beam

Novel indolylarylsulfone derivatives as covalent HIV-1 reverse transcriptase inhibitors specifically targeting the drug-resistant mutant Y181C

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are widely used in combination therapies against HIV-1. However, emergent and transmitted drug resistance compromise their efficacy in the clinical setting. Y181C is selected in patients receiving nevirapine, etravirine and rilpivirine, and together with K103N is the most prevalent NNRTI-associated mutation in HIV-infected patients. Herein, we report on the design, synthesis and biological evaluation of a novel series of indolylarylsulfones bearing acrylamide or ethylene sulfonamide reactive groups as warheads to inactivate Cys181-containing HIV-1 RT via a Michael addition reaction. Compounds I-7 and I-9 demonstrated higher selectivity towards the Y181C mutant than against the wild-type RT, in nucleotide incorporation inhibition assays. The larger size of the NNRTI binding pocket in the mutant enzyme facilitates a better fit for the active compounds, while stacking interactions with Phe227 and Pro236 contribute to inhibitor binding. Mass spectrometry data were consistent with the covalent modification of the RT, although off-target reactivity constitutes a major limitation for further development of the described inhibitors.by grants PID2019-104176RB-I00/AEI/10.13039/501100011033) (Spanish Ministry of Science and Innovation) and 2019AEP001 (CSIC), as well as an institutional grant of Fundación Ramón Areces (awarded to the CBMSO)

The First Data Release of the Beijing-Arizona Sky Survey

The Beijing-Arizona Sky Survey (BASS) is a new wide-field legacy imaging survey in the northern Galactic cap using the 2.3m Bok telescope. The survey will cover about 5400 deg$^2$ in the $g$ and $r$ bands, and the expected 5$\sigma$ depths (corrected for the Galactic extinction) in the two bands are 24.0 and 23.4 mag, respectively. BASS started observations in January 2015, and has completed about 41% of the whole area as of July 2016. The first data release contains both calibrated images and photometric catalogs obtained in 2015 and 2016. The depths of single-epoch images in the two bands are 23.4 and 22.9 mag, and the full depths of three epochs are about 24.1 and 23.5 mag, respectively.Comment: 16 pages, published by A

Mechanical properties of carbon nanotubes reinforced ultra high molecular weight polyethylene

Carbon nanotubes have been shown to enhance the engineering properties of plastic fibers in ballistic-resistant garments enabling the garments to withstand very high impact forces while remaining to be lightweight. Previous study shows that by reinforcing ultra high molecular weight polyethylene (UHMWPE) fibers with a small amount of carbon nanotubes, the fibers are simultaneously toughened and strengthened. In this paper, we study the mechanical properties of carbon nanotube reinforced ultra high molecular weight polyethylene (UHMWPE) by using micromechanics-based Mori-Tanaka model. Results show that the addition of small amount of carbon nanotubes as reinforcement can substantially improve the mechanical properties of the UHMWPE fibers

Vibrations of multiple delaminated beams

The free vibrations of beams with two enveloping delaminations have been solved analytically without resorting to numerical approximation. The multiple delaminated beam is analyzed as several interconnected Euler–Bernoulli beams. The differential stretching and the bending–extension coupling are considered in the formulation. The influence of the sizes and locations of the delaminations on the primary and secondary frequencies and mode shapes of a beam are investigated. For clamped–clamped beams, the primary frequency shows a high sensitivity for the long delamination but a low sensitivity for the second short delamination, while for the secondary frequency, the sensitivity is high for both delaminations. For cantilever beams, the primary and secondary frequencies show a high sensitivity for the long delamination but low sensitivity for the second short delamination. Results are compared with the analytical and experimental data reported in the literature to verify the validity of the present model

Vibration of beams with two overlapping delaminations in prebuckled states

An analytical solution for the free vibrations of beams with two overlapping delaminations in prebuckled states is presented. The delaminated beam is analyzed as seven interconnected Euler–Bernoulli beams. The continuity and boundary conditions are satisfied between adjoining beams. Both the ‘free mode’ and the ‘constrained mode’ assumption in delamination buckling and vibration are used. A parametric study is performed to investigate the influence of the axial compressive load on the natural frequency and the mode shape of the delaminated beam. A monotonic relation between the natural frequency and the compressive load is observed. Comparisons with the analytical results reported for delamination buckling and vibration verify the validity of the present solution

Free vibration analysis of delaminated bimaterial beams

Non-dimensional parameters, namely, axial stiffness ratio and bending stiffness ratio, are introduced to study the vibration of bimaterial beams with a single delamination. The use of these parameters provide a better understanding on the influence of the axial stiffness and bending stiffness of the delaminated layers on the vibration of a delaminated beam. Both the ‘free mode’ and ‘constrained mode’ models in the study of the vibration of delaminated beams are used in the present analysis. A relative slenderness ratio specific for delamination vibration is further introduced, which is shown to dominate the vibration characteristics of the beam. For lower slenderness ratios, the influence of the delamination decreases and a global vibration mode dominates. For higher slenderness ratios, the influence of the delamination increases and a local vibration mode prevails

Vibration of beams with embedded piezoelectric sensors and actuators

This paper presents a micromechanics approach to the study of the vibration of beams with embedded piezoelectric sensors and actuators. The natural frequency of the beam is determined from the variational principle in Rayleigh quotient form. The piezoelectric sensors and actuators embedded in the beam are analysed using Eshelby's equivalent inclusion method. In addition, the Euler–Bernoulli beam theory and Rayleigh–Ritz approximation technique are used in the analysis. Results show that the size, volume fraction and location of the piezoelectric inclusions significantly influence the natural frequency of the beam. The results of the present model agree well with the theoretical results presented in the literature

The performance of 1-3 piezoelectric composites with a porous non-piezoelectric matrix

A micromechanics-based method is developed to evaluate the performance of 1–3 piezoelectric composites with a porous non-piezoelectric matrix. The classical Mori–Tanaka method is first used to analyze the porous polymer matrix, then the Mori–Tanaka method for piezoelectric composites is used to analyze the porous polymer matrix with embedded piezoceramic fibers. A parametric study is conducted to investigate the influence of the volume fraction, shape and orientation of the pores on the mechanical properties of the polymer matrix and the performance of the 1–3 piezoelectric composites. The results of the study show that the performance of the piezoelectric composites is significantly enhanced by the presence of pores in the matrix, particularly by cylindrical pores perpendicular to the piezoceramic fibers