Angular displacement fiber-optic sensor: theoretical and experimental study

An optical-fiber sensor based on twist-induced optical activity has been developed for measuring angular displacements at low temperature. The sensing part is composed of a fiber coil rotated between two points, which induces a twist of two sections of fiber. A theoretical study of the evolution of a general input state of polarization in the sensor gave us its main characteristics. Then experimental investigations permitted the construction of a sensor to take angular measurements over a 100-deg range with an accuracy of 0.2 deg. The thermal sensitivity of this kind of sensor is also briefly reported.     

On the stabilizing behavior of zirconia: A Combined experimental and theoretical study

Reactive zirconia powder was synthesized by the complexation of zirconium metal from zirconium hydroxide using a solution of 8-hydroxiquinoline. The kinetics of zirconia crystallization was followed by X-ray diffraction, scanning electron microscopy and surface area measured by the nitrogen adsorption/desorption technique. The results indicated that zirconia with a surface area as high as 100 m²/g can be obtained by this method after calcination at 500°C. Zirconia presents three polymorphic phases (monoclinic, tetragonal and cubic), which are reversibly interconversible. The cluster model Zr₄O₈ and Zr₄O₇ ⁺² was used for a theoretical study of the stabilization process. The ab initio RHF method was employed with the Gaussian94 program and the total energies and the energy gap of the different phases were calculated and compared with the experimental energy gap. The theoretical results show good reproducibility of the energy gap for zirconia.     

Pore conductivity control at the hundred-nanometer scale: an experimental and theoretical study

We report on the observation of an unexpected mechanism that controls conductivity at the 100-nm scale on track-etched polycarbonate membranes. Transport measurements of positively charged methyl viologen performed by absorption spectroscopy under various pH conditions demonstrate that for 100-nm-diameter pores at pH 2 conductivity is blocked, while at pH 5 the ions move through the membrane according to diffusion laws. An oppositely charged molecular ion, naphthalene disulfonate, in the same membrane, shows the opposite trend: diffusion of the negative ion at pH 2 and very low conductivity at pH 5. The influence of parameters such as ionic strength and membrane surface coating are also investigated. A theoretical study of the system shows that at the 100-nm scale the magnitude of the electric field in the vicinity of the pores is too small to account for the experimental observations; rather, it is the surface trapping of the mobile ion (Cl- or Na+) that gives rise to the observed control of the conductivity. This surprising effect has potential applications for high-throughput separation of large molecules and bio-organisms.     

一种新型光学传感器的理论和实验研究

当多孔硅处于有机物蒸汽环境时,由于自身的多孔结构和巨大的比表面积,有机物蒸汽分子将迅速地吸附到多孔硅的表面,并在多孔硅的孔内发生毛细冷凝作用,这将引起多孔硅层有效折射率的变化,从而导致多孔硅微腔反射谱透射峰峰位的变化.本文主要利用Bruggeman介电常数近似理论与光子晶体传输矩阵的方法,建立了多孔硅微腔的理论传感模型.使用光学实验装置对多孔硅微腔进行了传感实验,证明多孔硅微腔可以实现对有机物蒸汽分子种类的检测,且分辨率较高,响应时间和恢复时间短,可重复性好.     

A theoretical and experimental study of chromatothermography at high concentrations

The concentration distribution produced by diffusion is examined; the differential equation has been solved numerically by computer to give working curves that define the physicochemical characteristics. An approximate analytical solution is also given.Translated from Inzhenerno Fizicheskii Zhurnal, Vol.27, No. 3, pp. 466–475, September, 1974.     

Osteogenic differentiation and mineralization in fibre-reinforced tubular scaffolds: theoretical study and experimental evidences

The development of composite scaffolds with well-organized architecture and multi-scale properties (i.e. porosity, degradation) represents a valid approach for achieving a tissue-engineered construct capable of reproducing the medium- and long-term in vitro behaviour of hierarchically complex tissues such as spongy bone. To date, the implementation of scaffold design strategies able to summarize optimal scaffold architecture as well as intrinsic mechanical, chemical and fluid transport properties still remains a challenging issue. In this study, poly ɛ-caprolactone/polylactid acid (PCL/PLA) tubular devices (fibres of PLA in a PCL matrix) obtained by phase inversion/salt leaching and filament winding techniques were proposed as cell instructive scaffold for bone osteogenesis. Continuous fibres embedded in the polymeric matrix drastically improved the mechanical response as confirmed by compression elastic moduli, which vary from 0.214 ± 0.065 to 1.174 ± 0.143 MPa depending on the relative fibre/matrix and polymer/solvent ratios. Moreover, computational fluid dynamic simulations demonstrated the ability of composite structure to transfer hydrodynamic forces during in vitro culture, thus indicating the optimal flow rate conditions that, case by case, enables specific cellular events—i.e. osteoblast differentiation from human mesenchymal stem cells (hMSCs), mineralization, etc. Hence, we demonstrate that the hMSC differentiation preferentially occurs in the case of higher perfusion rates—over 0.05 ml min^–1—as confirmed by the expression of alkaline phosphate and osteocalcin markers. In particular, the highest osteopontin values and a massive mineral phase precipitation of bone-like phases detected in the case of intermediate flow rates (i.e. 0.05 ml min^–1) allows us to identify the best condition to stimulate the bone extracellular matrix in-growth, in agreement with the hydrodynamic model prediction. All these results concur to prove the succesful use of tubular composite as temporary device for long bone treatment.     

A theoretical and experimental study of waveguide coupled SAWresonator filters

The coupling-of-modes (COM) formalism is extended to include coupled transducers and applied to the modelling of surface acoustic wave (SAW) coupled resonator filters. The models do not require the derivation of equivalent circuits and they accommodate finger reflections, electromagnetic feedthrough and external matching circuits. Frequency responses for waveguide-coupled devices are computed and compared to experimental results. Longitudinal mode profiles within the resonant cavities are presented     

New modal wave-front sensor: a theoretical analysis

We present a new design of a modal wave-front sensor capable of measuring directly the Zernike components of an aberrated wave front. The sensor shows good linearity for small aberration amplitudes and is particularly suitable for integration in a closed-loop adaptive system. We introduce a sensitivity matrix and show that it is sparse, and we derive conditions specifying which elements are necessarily zero. The sensor may be temporally or spatially multiplexed, the former using a reconfigurable optical element, the latter using a numerically optimized binary optical element. Different optimization schemes are discussed, and their performance is compared.     

Effects of conjugation on the properties of alkynylcarbazole compounds: experimental and theoretical study

Four novel dyes containing alkynylcarbazole, namely, 2-((9H-carbazol-3-yl)ethynyl)-9-ethyl-9H-carbazole, 3,6-bis((9-ethyl-9H-carbazol-2-yl)ethynyl)-9H-carbazole, 3-(phenylethynyl)-9H-carbazole and 3,6-bis(phenylethynyl)-9H-carbazole, were synthesized on the basis of single and double substitutes by following the Sonogashira coupling method. The synthesized dyes were then assessed as novel photosensitizers in visible-light photopolymerization to evaluate the effects of conjugation on the properties of aromatic compounds. A comparison between UV–vis and TD/DFT electron transition spectra shows that \(\lambda _{\mathrm{max}}\) in theoretical ultraviolet spectra matched well with the experimental spectra; every conjugated alkynylcarbazole dye exhibits a wide absorption band in the range of 300–400 mm. Moreover, conjugation enhancement by switching carbazoleacetylene moieties caused a red shift in the absorption bands. The theoretical study showed that the maxima \(\lambda \) of these molecules ranged from \(\sim \)330 to 370 mm, corresponding to \(\pi {\rightarrow }\pi ^{*}\) and \({n}{\rightarrow }\pi ^{*}\) electron transitions. Fluorescence spectroscopic data show that the strongest emission peaks exhibit a red shift because of the addition of conjugated acetylene groups. A combination of alkynyl dyes and iodonium under a halogen lamp atmosphere by visible-light photopolymerization displayed a positive response to the cationic polymerization of bisphenol-A epoxy resin A and free-radical polymerization of tripropylene glycol diacrylate.     

Absorption spectroscopy in tissue-simulating materials: a theoretical and experimental study of photon paths

A diffusion model of noninvasive absorption spectroscopy was used to determine how the change in signal resulting from a point absorber depends on the position of that absorber relative to the source and detector. This is equivalent to calculating the relative probability that a photon will visit a certain location in tissue before its detection. Experimental mapping of the point-target response in tissue-simulating materials confirmed the accuracy of the model. For steady-state spectroscopy a simple relation was derived between the mean depth visited by detected photons, the source-detector separation, and the optical penetration depth. It was also demonstrated theoretically that combining a pulsed source with time-gated detection provides additional control over the spatial distribution of the photon-visit probability.     

Piezoelectric behaviour of PZT doped with calcium: a combined experimental and theoretical study

An experimental and theoretical study on the piezoelectric behaviour of PZT doped with a range of calcium ion concentrations is presented. A systematic study of the effect on the piezoelectric properties of PZT doped with various concentrations of CaO at constant sintering temperature and sintering time was carried out. The remanent polarization, planar coupling factor and frequency–thickness constant increase with calcium concentration. Ab initio perturbed ion calculations show that the lattice energy decreases with calcium addition for both tetragonal and rhombohedral phases of PZT. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fracture analysis of V‐notched rubbers: An experimental and theoretical study

In this study, the rupture load in rubbers weakened by sharp V‐notch is investigated under mode I loading. To this end, first, mode I fracture tests are performed on V‐notched samples made of styrene‐butadiene rubbers and the corresponding rupture loads are obtained. Then, the effective stretch (ES) criterion, which was recently developed by the present authors for rupture assessment of cracked rubber parts, is extended and used for the V‐notched rubbers. It is shown that similar to cracked rubbers, the state of stress near the notch tip is also nearly uniaxial. By employing the ES criterion, the critical displacements corresponding to the rupture in the tested samples are calculated. Finally, the predictions of the criterion are compared with the corresponding experimental values, and good consistency is shown to exist.     

A theoretical and experimental study of the mobility of loose materials

The effect of external and internal parameters of loose materials on their mobility is investigated. A dimensionless equation describing the mobility of loose materials is obtained and confirmed by experimental data.M. V. Lomonosov Technological Institute of the Food Industry, Odessa, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 5–6, pp. 418–423, November–December, 1994.     

A theoretical and experimental study of a small-scale steam jet refrigerator

The paper provides the results of a theoretical and experimental study of a steam jet refrigerator. A small-capacity steam jet refrigerator has been tested with boiler temperatures in the range 120–140°C. The experimental data were found to be within 85% of the theoretical values. The experiments showed that choking of the secondary flow in the mixing chamber of the ejector plays an important role in the system performance. Maximum COP was obtained when the ejector was operated at its critical flow condition. Off-design performance characteristics of the system are provided.     

Determination of SBA-15 acidity through n-butyl amine TPD: a theoretical and experimental study

In this study, the interaction ways between n-butyl amine and SBA-15 molecular sieve were evaluated when the TPD technique is carried out to determine the total acidity of that solid. Experimental results (FTIR, TG/DTG, total acid, and catalytic activity) and theoretical calculations demonstrated that the n-butyl amine, used as probe molecule to total acidity determined by TPD, can act as acid or base depending on the nature and force of the active sites on SBA-15.     

ZnO controllable sized quantum dots produced by polyol method: An experimental and theoretical study

Zinc oxide quantum dots were prepared in diethyleneglycol using zinc acetate as a precursor compound and the particle size of the dried powders was determined using the X-ray diffraction method (XRD). It was found that quantum dot size ranges from 4 to 9 nm and is influenced by the initial zinc acetate concentration and the centrifugation speed. Theoretical predictions concerning quantum dot size by the potential morphing method showed good agreement with the measurements from XRD.     

Micromachined resonant temperature sensors: theoretical and experimental results

Describes the study of quartz temperature sensors based on new bulk acoustic wave microresonators operating in thickness modes. First, we compare the thermal sensitivity and the electromechanical coupling coefficients of singly or doubly rotated cuts. These investigations allow us to select some cuts with both a good thermal sensitivity and piezoelectric characteristics. In the second part, emphasis is placed on the micromachining of resonators suspended by four bridges. These two theoretical considerations lead to the choice of three cuts. Experimental measurements are then presented. The temperature-frequency characteristics of the resonators are measured over the range 20 to 100 degrees C. Motional resistances and Q factors are determined at room temperature.