The post-buckling behaviour of anisotropic stiffened panels with initial imperfections is investigated. Since buckling of the skin between the stiffeners often occurs first, a non-linear analysis is developed for symmetric panels under biaxial compression in order to obtain the out-of-plane panel deflection in the post-buckling range. The non-linear differential equations are expressed in terms of the out-of-plane displacement and the Airy function. They are solved with the Galerkin method for various boundary conditions by imposing an edge displacement control. The theoretical and experimental results obtained by the present analysis show that the transverse load can greatly influence the buckling loads and halfwave number. Since no experimental results have been found in the literature, several tests have been carried out on graphite/epoxy blade stiffened panels 900 mm long and 620 mm wide applying simultaneously biaxial compression loads with several combined ratios. An eccentricity results between longitudinal and transverse load, because the longitudinal compression is applied along the centroidal axes of the stiffened section while the transverse compression is applied to the skin panel. The correlation between the experimental and analytical results has been quite good; the experimental results demonstrate the influence of eccentricity of the transverse load on panel deflection in the pre- and post-buckling range. 相似文献
The aim of this work was to demonstrate that various types of nanostructures provide different gains in terms of sensitivity or detection limit albeit providing the same gain in terms of increased area. Commercial screen printed electrodes (SPEs) were functionalized with 100 µg of bismuth oxide nanoparticles (Bi2O3 NPs), 13.5 µg of gold nanoparticles (Au NPs), and 4.8 µg of multi-wall carbon nanotubes (MWCNTs) to sense hydrogen peroxide (H2O2). The amount of nanomaterials to deposit was calculated using specific surface area (SSA) in order to equalize the additional electroactive surface area. Cyclic voltammetry (CV) experiments revealed oxidation peaks of Bi2O3 NPs, Au NPs, and MWCNTs based electrodes at (790 ± 1) mV, (386 ± 1) mV, and (589 ± 1) mV, respectively, and sensitivities evaluated by chronoamperometry (CA) were (74 ± 12) µA mM?1 cm?2, (129 ± 15) ±A mM?1 cm?2, and (54 ± 2) ±A mM?1 cm?2, respectively. Electrodes functionalized with Au NPs showed better sensing performance and lower redox potential (oxidative peak position) compared with the other two types of nanostructured SPEs. Interestingly, the average size of the tested Au NPs was 4 nm, under the limit of 10 nm where the quantum effects are dominant. The limit of detection (LOD) was (11.1 ± 2.8) ±M, (8.0 ± 2.4) ±M, and (3.4 ± 0.1) ±M for Bi2O3 NPs, Au NPs, and for MWCNTs based electrodes, respectively. 相似文献
Narrow‐linewidth lasers are key elements in optical metrology and spectroscopy. Spectral purity of these lasers determines accuracy of the measurements and quality of collected data. Solid state and fiber lasers are stabilized to relatively large and complex external optical cavities or narrow atomic and molecular transitions to improve their spectral purity. While this stabilization technique is rather generic, its complexity increases tremendously moving to longer wavelenghts, to the infrared (IR) range. Inherent increase of losses of optical materials at longer wavelengths hinders realization of compact, room temperature, high finesse IR cavities suitable for laser stabilization. In this paper, we report on demonstration of quantum cascade lasers stabilized to high‐Q crystalline mid‐IR microcavities. The lasers operating at room temperature in the 4.3‐4.6 μm region have a linewidth approaching 10 kHz and are promising for on‐chip mid‐IR and IR spectrometers.
A novel technique, based on low intensity ultrasonic wave propagation, has been applied to investigate the gelation of a waxy
crude oil, caused by the crystallization of paraffin fractions as the temperature reduces below a threshold value, called
WAT (wax appearance temperature). Because this phenomenon significantly affects the rheological behavior of crude oils, the
knowledge of the conditions under which it occurs, during oil storage and/or transportation, is a topical issue in the oil
industry. In this work, an ultrasonic equipment has been set up, able to propagate longitudinal waves in the MHz range and
to display in real time the behavior of ultrasonic velocity and attenuation when the crude oil sample is subjected to heating
and cooling cycles. When the ultrasonic probes alternatively rotate as parallel plates of a conventional rheometer, low intensity
longitudinal waves (in the megahertz range), and shear oscillations (in the hertz range) are simultaneously applied on the
sample, thus widely broadening the frequency range of investigation. On cooling, the crystallization of paraffin fractions
and the consequent formation of a network structure in the oil matrix are responsible of the development and growth of the
crude oil elastic response, which becomes dominant over the viscous response. This process can be reliably detected by dynamic
mechanical analysis and by ultrasonic analysis through the increase of the storage modulus G′ and longitudinal velocity, respectively.
The growth and further association between wax crystals causes a dissipation of acoustic energy, which is indicated by the
increase of the wave attenuation. The combination of rheological and ultrasonic methods has provided a better insight both
on the gel transition of crude oils and the viscoelastic behavior of gelled samples. The ultrasonic wave propagation has demonstrated
to be a powerful tool for monitoring the sol–gel transition in waxy crude oils. Finally, the effect of ultrasonic waves with
different intensity on the gel build-up has been also evaluated. A reduction of the gel strength with increasing wave intensity
has been observed and the recovery of elastic response after removing ultrasonic irradiation has been monitored.
This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006. 相似文献
We study the problem of drift estimation for two-scale continuous time series. We set ourselves in the framework of overdamped Langevin equations, for which a single-scale surrogate homogenized equation exists. In this setting, estimating the drift coefficient of the homogenized equation requires pre-processing of the data, often in the form of subsampling; this is because the two-scale equation and the homogenized single-scale equation are incompatible at small scales, generating mutually singular measures on the path space. We avoid subsampling and work instead with filtered data, found by application of an appropriate kernel function, and compute maximum likelihood estimators based on the filtered process. We show that the estimators we propose are asymptotically unbiased and demonstrate numerically the advantages of our method with respect to subsampling. Finally, we show how our filtered data methodology can be combined with Bayesian techniques and provide a full uncertainty quantification of the inference procedure.
Summary An optical observer in the space-time manifoldV4 is defined as a time-like world linea carrying an orthonormal tetrad of vector fields e(i) (i=0, 1, 2, 3) with e(0) always tangent toa. To the world linea we associate the congruence of null geodesics outgoing from points ofa and directed towards the past. The resulting geometrical structure is analysed in detail.
Sommario Un osservatore ottico nella varietà spaziotempoV4 è definito come linea di universoa, dotata di una tetrade ortonormale di campi vettoriali e(i) (i=0, 1, 2, 3), con e(0) sempre tangente ada Alla linea di universoa è associata la congruenza di geodetiche nulle uscenti da punti dia e dirette verso il passato. La struttura geometrica che ne risulta è esaminata in dettaglio.
Work performed under the auspices of the «Gruppo Nazionale per la Fisica Matematica» (C.N.R.). 相似文献
Ethanol extracts of Stachys glutinosa L. (Lamiaceae) were investigated for antioxidative properties, as well as antiproliferative action on various cell lines. The antioxidant activities were investigated by ABTS (2,2′-azinobis-3-ethylbenzothiazoline-6-sulphonic acid) assay, DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging, β-carotene/linoleic acid assay, scavenging of hydrogen peroxide (horseradish peroxidase test), superoxide anion scavenging, and hypochlorous acid scavenging (taurine test). The antioxidant activity was reported as IC50 and reveals antioxidant effects. Antiproliferative effects were measured in vitro on three cell lines: HepG2 (human hepatocarcinoma), MCF7 (breast human adenocarcinoma) and C2C12 (mouse myoblast) cell lines by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The ethanol extract induced variations in cell viability on all cell lines tested. At 200 μg/mL, the effects on cell viability were ? 23%, ? 27% and ? 37%, respectively, for C2C12, MCF7 and HepG2. 相似文献
We present a quantum cellular automaton model in one space-dimension which has the Dirac equation as emergent. This model, a discrete-time and causal unitary evolution of a lattice of quantum systems, is derived from the assumptions of homogeneity, parity and time-reversal invariance. 相似文献
Hydroxypropyl methylcellulose (HPMC) and polyvinyl alcohol (PVA) are important polymers in pharmaceutical, food and other industries being largely used as encapsulation agents. The characterization of two reference grades of HPMC (Pharmacoat? 603 and Pharmacoat? 615) and one reference grade of PVA (Mowiol? 4-98), through X-ray diffraction (XRD) and thermogravimetry (TG) is described. Specific analyses were performed by means of dynamic vapour sorption analysis of water adsorption/desorption from vapours at 10, 25, 40, 55 and 70?°C. Guggenheim?CAnderson?Cde Boer (GAB), Brunauer?CEmmett?CTeller (BET), Park and n-layer BET models were successfully used to fit the experimental data. The glass transition temperature as function of water content was measured by means of differential scanning calorimetry (DSC). The experimental data were analysed according to Linear, Gordon?CTaylor, Fox and Roos equations. XRD studies revealed amorphous structure for the Pharmacoat??603 and Pharmacoat??615 and crystalline for Mowiol??4-98. Single and multi-step temperature degradation point was found for Pharmacoat??603 and Pharmacoat??615 and Mowiol??4-98, respectively. The water uptake is higher for Pharmacoat??603 and Pharmacoat??615 than Mowiol??4-98. The influence of temperature on water uptake is opposite for the two types of polymers. GAB and n-layer BET were found to better model Pharmacoat??603 and Pharmacoat??615 and Mowiol??4-98 data, respectively. The water makes the glass transition to decrease quite drastically. Gordon?CTaylor is better fitting the experimental data both for Pharmacoat??603 and Pharmacoat??615 and Mowiol??4-98. 相似文献