Extensive continuum analyses are carried out to estimate the influence of matrix stiffness, a small length scale, and intertubular
radial displacements on free vibrations of an individual double-walled carbon nanotybe. The analyses are based on both local
and classical Euler–Bernoulli and Timoshenko elasticity theories with concentricity and nonconcentricity assumptions. The
effect of a small length scale is incorporated in the formulations. New intertubular resonant frequencies are calculated based
on these theories. Detailed results are demonstrated for the resonant frequencies as functions of matrix stiffness and the
small length scale. The results indicate that the internal radial displacement and the stiffness of the surrounding matrix
can greatly affect the resonant frequencies, especially at higher frequencies, and thus the latter does not keep the otherwise
concentric structure at ultrahigh frequencies. More over, at high frequencies and small aspect ratios, the effect of the small
length scale be comes more significant. 相似文献
Herein, we propose a scheme for the realization of two-dimensional atomic localization in aλ-type three-level atomic medium such that the atom interacts with the two orthogonal standing-wave fields and a probe field. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be obtained by monitoring the probe transmission spectra of the weak probe field for the first time. A single and double sharp localized peaks are observed in the one-wavelength domain. We have theoretically archived high-resolution and high-precision atomic localization within a region smaller thanλ/25×λ/25. The results may have potential applications in the field of nano-lithography and advance laser cooling technology. 相似文献
We have theoretically investigated two-dimensional atom localization using the absorption spectra of birefringence beams of light in a single wavelength domain.The atom localization is controlled and modified through tunneling effect in a conductive chiral atomic medium with absorption spectra of birefringent beams.The significant localization peaks are investigated in the left and right circularly polarized beam.Single and double localized peaks are observed in different quadrants with minimum uncertainty and significant probability.The localized probability is modified by controlling birefringence and tunneling conditions.These results may be useful for the capability of optical microscopy and atom imaging. 相似文献
The oxidative coupling reaction between hydroquinone or catechols and various sodium benzenesulfinates was investigated using the laccase from Trametes versicolor, in the presence of O2 in a phosphate buffer solution at room temperature to afford sulfonyl benzenediols in 75–95% yield. 相似文献
Simple and rapid spectrophotometric methods have been developed for the microdetermination of fluoxetine HCl. The proposed
methods are based on the formation of ion-pair complexes between fluoxetine and bromophenol blue (BPB), bromothymol blue (BTB),
bromocresol green (BCG), and bromocresol purple (BCP) which can be measured at optimum λmax. Optimization of reaction conditions was investigated. Beerșs law was obeyed in the concentration ranges of 0.5–8.0 μg mL−1, whereas optimum concentration as adopted from the Ringbom plots was 0.7–7.7 μg mL−1. The molar absorptivity, Sandell sensitivity, and detection limit were also calculated. The most optimal and sensitive method
was developed using BCG. The correlation coefficient was 0.9988 (n = 6) with a relative standard deviation of 1.25, for six determinations of 4.0 μg mL−1. The proposed methods were successfully applied to the determination of fluoxetine hydrochloride in its dosage forms and
in biological fluids (spiked plasma sample) using the standard addition technique. 相似文献
A highly sensitive spectrophotometric method for palladium determination using piroxicam and tenoxicam as new chromogenic
reagents has been developed. In the presence of sodium lauryl sulfate (SLS), palladium reacts with piroxicam (PX) or tenoxicam
(TX) to form stable yellow orange complexes in an acetate buffer solution of pH 5.0 at 424 nm and 426 nm with molar absorptivity
of 7.16 × 104 L mol−1 cm−1 and 1.20 × 105 L mol−1 cm−1, respectively. Sandell sensitivity, detection, and quantitation limits were also calculated. Optimum conditions were evaluated
considering pH, reagent concentration, time, temperature, and surfactant concentration. The complex system conforms to Beer’s
law over the range of 0.07–1.28 μg mL−1 palladium. The stoichiometric ratio and stability constant were also evaluated. Tolerance limits of many cations and anions
were determined. Finally, the proposed method was applied successfully in the determination of palladium in jewellery, anode
mud, synthetic mixtures, catalysts, and alloy samples. 相似文献
Quinones are known producers of reactive oxygen species (ROS) that may be toxic in natural aquatic environments. In this study, the effects of parent quinones and their photodegradation products on bacterial growth were determined, and photochemical ROS formation rates were measured. Using (3)H-leucine incorporation to measure growth of the bacterium Pseudomonas aeruginosa and natural seawater bacterioplankton, growth inhibition was observed when samples were exposed to dichlone, chloranil and sodium anthraquinone-2-sulfonate (AQ2S). For seawater, compared with other quinones tested, dichlone showed the greatest toxicity in the dark, and AQ2S toxicity was greatest during simultaneous exposure to sunlight. Photodegraded chloranil and dichlone showed decreased toxicity compared with nonirradiated samples. For P. aeruginosa, AQ2S and its photodegradation products showed the greatest toxicity during simultaneous exposure to sunlight. Chloranil photodegradation products showed reduced toxicity compared with the parent compound during simultaneous exposure to sunlight. Dichlone was the only compound to show any toxicity to P. aeruginosa in the dark, and its photodegradation products were more toxic than the parent compound. Based on the results of dark and light controlled experiments measuring bacterial growth and estimated ROS production rates, ROS alone does not account for relative differences in toxicity between these quinones. 相似文献
The removal of metal ions from aqueous solutions by biosorption plays an important role in water pollution control. In this
study, dried leaves and branches of poplar trees were studied for removing some toxic elements (cadmium, lead, and uranium)
from aqueous solutions. The equilibrium experiments were systematically carried out in a batch process, covering various process
parameters that include agitation time, adsorbent size and dosage, initial cadmium, lead and uranium concentration, and pH
of the aqueous solution. Adsorption behavior was found to follow Freundlich and Langmuir isotherms. The results have shown
that both dried leaves and branches can be effectively used for removing uranium, while only branches were found to remove
lead and cadmium completely from the aqueous solution. The maximum biosorption capacity of leaves for uranium was found to
be 2.3 mg g−1 and 1.7 mg g−1 and 2.1 mg g−1 for lead and cadmium on branches, respectively. In addition, the studied biomass materials were used in removing lead and
cadmium from contaminated water and the method was found to be effective. 相似文献
In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT−GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, ks, and the charge transfer coefficient, α, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4 ± 0.5 s−1 and 0.51, respectively at pH = 7.0. The obtained results indicate that hydrazine peak potential at OMWCNT−GCE shifted for 14, 109, and 136 mV to negative values as compared with oxadiazole-modified GCE, MWCNT−GCE, and activated GCE surface, respectively. The electron transfer coefficient, α, and the heterogeneous rate constant, k′, for the oxidation of hydrazine at OMWCNT−GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0 μM and 10.0 to 400.0 μM and detection limit of 0.17 μM for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT−GCE was shown to be successfully applied to determine hydrazine in various water samples.
A unified approximation method is derived to illustrate the effect of electro-mechanical coupling on vibration-based energy harvesting systems caused by variations in damping ratio and excitation frequency of the mechanical subsystem. Vibrational energy harvesters are electro-mechanical systems that generate power from the ambient oscillations. Typically vibration-based energy harvesters employ a mechanical subsystem tuned to resonate with ambient oscillations. The piezoelectric or electromagnetic coupling mechanisms utilized in energy harvesters, transfers some energy from the mechanical subsystem and converts it to an electric energy. Recently the focus of energy harvesting community has shifted toward nonlinear energy harvesters that are less sensitive to the frequency of ambient vibrations. We consider the general class of hybrid energy harvesters that use both piezoelectric and electromagnetic energy harvesting mechanisms. Through using perturbation methods for low amplitude oscillations and numerical integration for large amplitude vibrations we establish a unified approximation method for linear, softly nonlinear, and bi-stable nonlinear energy harvesters. The method quantifies equivalent changes in damping and excitation frequency of the mechanical subsystem that resembles the backward coupling from energy harvesting. We investigate a novel nonlinear hybrid energy harvester as a case study of the proposed method. The approximation method is accurate, provides an intuitive explanation for backward coupling effects and in some cases reduces the computational efforts by an order of magnitude. 相似文献