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131.
Vasile Georgescu Gianina Dobrescu Florica Papa Niculae I. Ionescu 《Reaction Kinetics and Catalysis Letters》2008,94(2):345-350
Benzene total oxidation on a Cu-Cr supported catalyst was investigated using the work function method. Above 300°C, the majority
of the oxygen species on the surface was O2− in the absence or in the presence of hydrocarbon. 相似文献
132.
We analyse the evolution of a system of finite faults by considering the non‐linear eigenvalue problems associated to static and dynamic solutions on unbounded domains. We restrict our investigation to the first eigenvalue (Rayleigh quotient). We point out its physical significance through a stability analysis and we give an efficient numerical algorithm able to compute it together with the corresponding eigenfunction. We consider the anti‐plane shearing on a system of finite faults under a slip‐dependent friction in a linear elastic domain, not necessarily bounded. The static problem is formulated in terms of local minima of the energy functional. We introduce the non‐linear (static) eigenvalue problem and we prove the existence of a first eigenvalue/eigenfunction characterizing the isolated local minima. For the dynamic problem, we discuss the existence of solutions with an exponential growth, to deduce a (dynamic) non‐linear eigenvalue problem. We prove the existence of a first dynamic eigenvalue and we analyse its behaviour with respect to the friction parameter. We deduce a mixed finite element discretization of the non‐linear spectral problem and we give a numerical algorithm to approach the first eigenvalue/eigenfunction. Finally we give some numerical results which include convergence tests, on a single fault and a two‐faults system, and a comparison between the non‐linear spectral results and the time evolution results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
133.
I. A. Atanasiu und Th. Ionescu 《Fresenius' Journal of Analytical Chemistry》1932,90(7-8):288-289
Ohne Zusammenfassung 相似文献
134.
P. J. van Ekeren L. D. Ionescu V. B. F. Mathot J. C. van Miltenburg 《Journal of Thermal Analysis and Calorimetry》2000,59(3):683-697
Specific heat capacities of a homogeneous ethylene-1-octene copolymer were measured by adiabatic calorimetry in the temperature
range from 5 to 400 K (stepwise heating at averaged rates of approximately 1 to 34 K h–1, after cooling at rates in the range from 8 K h–1 to 4 K min–1). The glass transition takes place from roughly 205 to225 K and is centred around approximately 215 K. At the latter temperature,
also the temperature drifts during the stabilisation periods are at maximum. Clearly, with devitrification above 215 K also
melting sets in. Using two sets of reference data (one for branched and linear polyethylenes, BPE, and the other for strictly
linear polyethylene, LPE)for completely crystalline and for completely amorphous material, the crystallinity of the polymer
was calculated as a function of temperature, within the two-phase model. In heating, the crystallinity decreased from 0.254
to zero in the temperature range from 220 to 360 K, confirming earlier DSC heat capacity measurements. During the stabilisation
periods, below325 K, negative drifts were observed, related to endothermic effects caused by melting. However, in the temperature
range from 325 K up to the end melting temperature, 360 K, positive drifts were measured, reflecting exothermic effects. These
are attributed to recrystallisation phenomena. The occurrence and amount of recrystallisation depend on the thermal history
of the sample: slower cooling and a longer time spent at a temperature of annealing clearly diminish recrystallisation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
135.
J. Rosen P. O. Å. Persson M. Ionescu J. Pigott D. R. McKenzie M. M. M. Bilek 《Plasma Chemistry and Plasma Processing》2007,27(5):599-608
The effect of gas entry point on the plasma chemistry, ion energy distributions and resulting alumina thin film growth have
been investigated for a d.c. cathodic arc with an aluminum cathode operated in an oxygen/argon atmosphere. Ions of aluminum,
oxygen and argon, as well as ions originating from the residual gas are investigated, and measurements for gas entry at both
the cathode and close to the substrate are compared. The latter was shown to result in higher ion flux, lower levels of ionised
residual gas, and lower ion energies, as compared to gas inlet at the cathode. These plasma conditions that apply when gas
entry at the substrate is used result in a higher film deposition rate, less residual gas incorporation, and more stoichiometric
alumina films. The results show that the choice of gas entry point is a crucial parameter in thin film growth using reactive
PVD processes such as reactive cathodic arc deposition. 相似文献
136.
We derive in this paper necessary and sufficient conditions for the
existence of the stabilizing solution to the differential Riccati equation, with
indefinite sign quadratic term. The key object of the present approach is
the Popov operator, associated with a controlled exponentially dichotomic
evolution and a quadratic cost. Special attention is paid to the classical positivity
theory and a time-varying version of the celebrated Kalman-Yakubovich-
Popov Lemma is given under relaxed assumptions. 相似文献
137.
Adriana Samide B. Tutunaru Catalina Ionescu P. Rotaru Luminita Simoiu 《Journal of Thermal Analysis and Calorimetry》2014,118(2):631-639
Aminophylline (AMF) was studied as corrosion inhibitor for carbon steel in 1.0 mol L?1 HCl solution using electrochemical measurements associated with UV–Vis spectrophotometry and optical microscopy. Simultaneous thermogravimetry/derivative thermogravimetry and differential scanning calorimetry analysis was performed in order to determine the temperature range in which AMF is an effective inhibitor, without the decomposition risk that could change the inhibition mechanism. Thermal behaviour restricts AMF application as corrosion inhibitor for carbon steel in 1.0 mol L?1 HCl solution at temperatures ≤45 °C where there are no significant modifications of the adsorption mechanism. According to the results of electrochemical measurements, in association with UV–Vis spectrophotometry and optical microscopy techniques, AMF is a mixed-type inhibitor for carbon steel corrosion in 1.0 mol L?1 HCl solution, simultaneously suppressing the anodic and cathodic processes and acting via spontaneous physisorption on the metal surfaces. 相似文献
138.
J. Ray Runyon Lars Nilsson Matilda Ulmius Alejandra Castro Ruxandra Ionescu Claes Andersson Christoph Schmidt 《Analytical and bioanalytical chemistry》2014,406(6):1597-1605
The purpose of this study was to assess the stability of the polyfructan levan under different pH solution conditions by monitoring changes in the levan physicochemical properties, such as molar mass (M), root mean square radius (r rms ), hydrodynamic radius (r h ), structure factor (r rms /r h ), and aggregation state with respect to solution pH and hydrolysis time. A commercial levan produced from Z. Mobilis was characterized using asymmetric flow field-flow fractionation (AF4) in combination with online multiangle light scattering (MALS) and differential refractive index (dRI) detection. Under neutral pH solution conditions the levan was found to have a M ranging from 105 to 5?×?107 g/mol, a r rms ranging from ~25 to 100 nm and a r h from ~3 to 151 nm. Two populations were observed in the sample. One population with a M less than 106 g/mol which represented ~60 % of the sample and a second population with an ultrahigh M up to 5?×?107 g/mol, which comprised ~40 % of the sample. The measured r rms /r h structure factor decreased from 1.8 to 0.65 across the AF4 fractogram indicating that early eluting low M levan species had a random coil configuration and late eluting high M species had more homogeneous spherical structures. The measured apparent density values decreased from 80 to 10 kg/m3 across the elution profile and suggest that the observed second population also contains aggregates. The stability of levan in different pH conditions ranging from 1.3 to 8.5 was assessed by tracking changes in the average M and r h , and monitoring the formation of fructose over 1 week. The onset of levan acid hydrolysis was observed to occur sooner at lower pH conditions and no hydrolysis was observed for pH 5.5 and higher. 相似文献
139.
Flexoelectricity of pure Azpac (an HOAB-palladium complex) was studied using planar nematic layers under an in-plane electric field. Longitudinal domains were observed with a period inversely proportional to the applied d.c. electric field. These domains were considered as a first experiment manifestation of the theoretical prediction of R. B. Meyer (1969) and their study has permitted the evaluation of the difference in flexo-coefficientse1z - e3x. Their appearance can also be followed for the non-complexed HOAB, using instant video-microscopy frames.
Mixtures of Azpac, up to 10wt%, and MBBA were oriented homeotropically and band flexoelectric deformations were observed, both in d.c. and in a.c. (1 to 1000 Hz) electric fields normal to the director. The dynamics of director reorientation were studied by the method of flexoelectric light modulation. A system comprising a He-Ne laser and a lock-in amplifier interfaced by a PC was developed. By operating this in a frequency sweep regime, viscoelastic spectra of director dynamics were recorded. These spectra were excited using a linear flexoelectric coupling mechanism. Breaks in the spectra were observed in the range 200 to 600 Hz, indicating a cross-over from bulk to surface dissipation of energy. For the first time, a surface viscosity of 2.6 × 10-8Jsm-2 was determined for MBBA homeotropically anchored on a DMOAP-coated glass surface.
In concentrations at low as 2.5 wt%, Azpac was found to cancel the bend flexo-coefficient of MBBA and at higher concentrations, a steep rise in the flexo-coefficient of the mixture was observed, but with an opposite sign. Thus, the application of Azpac as an effective additive for adjustment of the value and sign of the flexo-coefficient in flexoelectro-optic displays or light modulators could be suggested. 相似文献
Mixtures of Azpac, up to 10wt%, and MBBA were oriented homeotropically and band flexoelectric deformations were observed, both in d.c. and in a.c. (1 to 1000 Hz) electric fields normal to the director. The dynamics of director reorientation were studied by the method of flexoelectric light modulation. A system comprising a He-Ne laser and a lock-in amplifier interfaced by a PC was developed. By operating this in a frequency sweep regime, viscoelastic spectra of director dynamics were recorded. These spectra were excited using a linear flexoelectric coupling mechanism. Breaks in the spectra were observed in the range 200 to 600 Hz, indicating a cross-over from bulk to surface dissipation of energy. For the first time, a surface viscosity of 2.6 × 10-8Jsm-2 was determined for MBBA homeotropically anchored on a DMOAP-coated glass surface.
In concentrations at low as 2.5 wt%, Azpac was found to cancel the bend flexo-coefficient of MBBA and at higher concentrations, a steep rise in the flexo-coefficient of the mixture was observed, but with an opposite sign. Thus, the application of Azpac as an effective additive for adjustment of the value and sign of the flexo-coefficient in flexoelectro-optic displays or light modulators could be suggested. 相似文献
140.