A geometric parameter study of piezoelectric coverage on a rectangular cantilever energy harvester

This paper proposes a versatile model for optimizing the performance of a rectangular cantilever beam piezoelectric energy harvester used to convert ambient vibrations into electrical energy. The developed model accounts for geometric changes to the natural frequencies, mode shapes and damping in the structure. This is achieved through the combination of finite element modelling and a distributed parameter electromechanical model, including load resistor and charging capacitor models. The model has the potential for use in investigating the influence of numerous geometric changes on harvester performance, and incorporates a model for accounting for changes in damping as the geometry changes. The model is used to investigate the effects of substrate and piezoelectric layer length, and piezoelectric layer thickness on the performance of a microscale device. Findings from a parameter study indicate the existence of an optimum sample length due to increased mechanical damping for longer beams and improved power output using thicker piezoelectric layers. In practice, harvester design is normally based around a fixed operating frequency for a particular application, and improved performance is often achieved by operating at or near resonance. To achieve unbiased comparisons between different harvester designs, parameter studies are performed by changing multiple parameters simultaneously with the natural frequency held fixed. Performance enhancements were observed using shorter piezoelectric layers as compared to the conventional design, in which the piezoelectric layer and substrate are of equal length

Optimization of piezoelectric cantilever energy harvesters including non-linear effects

This paper proposes a versatile non-linear model for predicting piezoelectric energy harvester performance. The presented model includes (i) material non-linearity, for both substrate and piezoelectric layers, and (ii) geometric non-linearity incorporated by assuming inextensibility and accurately representing beam curvature. The addition of a sub-model, which utilizes the transfer matrix method to predict eigenfrequencies and eigenvectors for segmented beams, allows for accurate optimization of piezoelectric layer coverage. A validation of the overall theoretical model is performed through experimental testing on both uniform and non-uniform samples manufactured in-house. For the harvester composition used in this work, the magnitude of material non-linearity exhibited by the piezoelectric layer is 35 times greater than that of the substrate layer. It is also observed that material non-linearity, responsible for reductions in resonant frequency with increases in base acceleration, is dominant over geometric non-linearity for standard piezoelectric harvesting devices. Finally, over the tested range, energy loss due to damping is found to increase in a quasi-linear fashion with base acceleration. During an optimization study on piezoelectric layer coverage, results from the developed model were compared with those from a linear model. Unbiased comparisons between harvesters were realized by using devices with identical natural frequencies—created by adjusting the device substrate thickness. Results from three studies, each with a different assumption on mechanical damping variations, are presented. Findings showed that, depending on damping variation, a non-linear model is essential for such optimization studies with each model predicting vastly differing optimum configurations

Synthesis and antimicrobial studies on novel sulfonamides containing 4-azidomethyl coumarin

A series of new and novel coumarin-6-sulfonamides with a free C4-azidomethyl group have been synthesized as antimicrobials in three steps starting from 7-methyl-4-bromomethylcoumarin 1. The reaction of 1 with chlorosulfonic acid was found to yield the corresponding 6-sulfonylchloride 2, which when treated with sodium azide led to intermediate 3. The title sulfonamides 5a-y were obtained from the reaction of 3 with various aromatic amines 4 in refluxing benzene. The chemical structures of the compounds were elucidated by IR, NMR and LC-MS spectral data. All the synthesized compounds have been screened for their in vitro anti-bacterial and anti-fungal activities. Some of the compounds have been found to be active against both bacterial species at a concentration of 1 μg/mL. © 2009 Elsevier Masson SAS. All rights reserved

The body constitution of patients and intubation scales as predictors of difficult intubation considered in relation to the experience of the intubator

The aims of the study were to identify factors that may result in difficulties in intubation, and to compare the results obtained when an experienced and when a less experienced anaesthesiologist was involved. The 96 patients included in the study were evaluated for difficult intubation according to the following scales: Mallampati, upper lip bite test (ULBT) and Patil. The mobility of the cervical segments of the vertebral column, the distance between the jugular notch of the sternum and the chin and the anatomical constitution of the body were other factors that were taken into consideration. Statistical analysis was performed in order to identify factors that may result in difficulties in intubation for an experienced and for a less experienced anaesthesiologist

Physical Characteristics of Al/n-CdS Thin-Film Schottky Diode at High Temperatures

Cadmium sulphide (CdS), a member of group II-VI semiconductors, is a promising material based on its applications. The present investigations describe the preparation and electrical characterization of CdS thin films. CdS thin films with thickness of 1000 nm were deposited by vacuum evaporation at room temperature. Characteristic parameters of Schottky junctions formed by a thermal vapor deposition of 500 nm of Al films on pre-coated CdS glass substrates were obtained experimentally from the I-V characteristics in the temperature range of 303–393 K. Diode parameters, such as the zero-bias barrier height ?b0, flat band barrier height ?bf, ideality factor ?, and series resistance RS were investigated using the thermionic emission method

In-hospital mortality of non-st segment elevation myocardial infarction in a Puerto Rican population

Introduction: Currently, there is limited published information on in-hospital mortality regarding ST segment elevation and non-ST segment elevation myocardial infarction. This information is even scarcer on the Hispanic population. We aim to study if there is a difference on in-hospital mortality between ST elevation myocardial infarction (STEMI) and non-ST elevation myocardial infarction (NSTEMI) in a mostly Hispanic population. Methods: A secondary data analysis of a non-concurrent prospective study was performed using the Puerto Rican Heart Attack study database. Dependent variable was in-hospital mortality and independent variable was type of myocardial infarction (STEMI or NSTEMI). We conducted, sequentially, a descriptive, bivariate and multivariate analysis. The chi-squared test was used to compare categorical variables and t-test for continuous variables. Finally, a logistic regression model was used to perform the multivariate analysis. Results: From the 838 Puerto Rican patients hospitalized with ST classification, 310 (37%) were diagnosed with STEMI. Patients with STEMI were younger (65 years vs 68 years; p=0.008), more likely to receive invasive treatment (47.9% vs 27.5%, p<0.001), and less likely to have a history of hypertension (72.5% vs 79.0%, p=0.033) compared to NSTEMI patients. For every 1- year increase in age, there is a 4% increase in in-hospital mortality. Patients with hyperlipidemia were approximately two times more likely to die in the hospital compared to patients without hyperlipidemia. In the unadjusted analysis, there was no significant association between STEMI and NSTEMI patients and in-hospital mortality. After adjusting for confounders, patients with STEMI had twice the risk of dying than those with NSTEMI. Conclusions: Findings from this study suggest that Puerto Ricans with STEMI have double the risk of in-hospital mortality than NSTEMI patients. Our findings were similar to those reported in the literature. A timely recognition of at-risk patients, especially among STEMI patients, may help reduce short-term morality among patients hospitalized with acute myocardial infarction in Puerto Rico

Density functional theory of spin-polarized disordered quantum dots

Using density functional theory, we investigate fluctuations of the ground state energy of spin-polarized, disordered quantum dots in the metallic regime. To compare to experiment, we evaluate the distribution of addition energies and find a convolution of the Wigner-Dyson distribution, expected for noniteracting electrons, with a narrower Gaussian distribution due to interactions. The tird moment of the total distribution is independent of interactions, and so is predicted to decrease by a factor of 0.405 upon application of a magnetic field which transforms from the Gaussian orthogonal to the Gaussian unitary ensemble.Comment: 13 pages, 2 figure

Synthesis, structural and physical properties of δ′\delta'-FeSe1−x_{1-x}

We report on synthesis, structural characterization, resistivity, magnetic and thermal expansion measurements on the as yet unexplored $\delta'$-phase of FeSe$_{1-x}$, here synthesized under ambient- (AP) and high-pressure (HP) conditions. We show that in contrast to $\beta$-FeSe$_{1-x}$, monophasic superconducting $\delta'$-FeSe$_{1-x}$ can be obtained in off-stoichiometric samples with excess Fe atoms preferentially residing in the van der Waals gap between the FeSe layers. The AP $\delta'$-FeSe$_{1-x}$ sample studied here ($T_c$ $\simeq$ 8.5\,K) possesses an unprecedented residual resistivity ratio RRR $\simeq$ 16. Thermal expansion data reveal a small feature around $\sim$90\,K, which resembles the anomaly observed at the structural and magnetic transitions for other Fe-based superconductors, suggesting that some kind of "magnetic state" is formed also in FeSe. %indicative of a fluctuating magnetic ordering. For HP samples (RRR $\simeq$ 3), the disorder within the FeSe layers is enhanced through the introduction of vacancies, the saturated magnetic moment of Fe is reduced and only spurious superconductivity is observed.Comment: 7 pages, 8 figures, published versio

Charge dynamics through pi-stacked arrays of conjugated molecules: effect of dynamic disorder in different transport/transfer regimes

We provide further computational evidence that the electronic coupling between pi-stacked molecules is strongly modulated by the thermal motions at room temperature, not only in supramolecular flexible systems (like DNA) but also in molecular crystals. The effect of this modulation on the charge dynamics is different for different transfer/transport mechanisms and depends on the modulation timescale. In the case of charge transfer (CT) between a donor and an acceptor, the effect of electronic coupling fluctuations introduces a corrective term in the expression of the rate constant (different for adiabatic and non-adiabatic CT). For the transport in molecular crystals, this fluctuation can be the limiting factor for the charge mobility. Although the fluctuation of the electronic coupling is similar in magnitude for all systems containing molecular pi-stacking, its importance for the charge dynamics increases with the decrease of the reorganization energy