Theoretical analysis of a quartz-enhanced photoacoustic spectroscopy sensor

Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors are based on a recent approach to photoacoustic detection which employs a quartz tuning fork as an acoustic transducer. These sensors enable detection of trace gases for air quality monitoring, industrial process control, and medical diagnostics. To detect a trace gas, modulated laser radiation is directed between the tines of a tuning fork. The optical energy absorbed by the gas results in a periodic thermal expansion which gives rise to a weak acoustic pressure wave. This pressure wave excites a resonant vibration of the tuning fork thereby generating an electrical signal via the piezoelectric effect. This paper describes a theoretical model of a QEPAS sensor. By deriving analytical solutions for the partial differential equations in the model, we obtain a formula for the piezoelectric current in terms of the optical, mechanical, and electrical parameters of the system. We use the model to calculate the optimal position of the laser beam with respect to the tuning fork and the phase of the piezoelectric current. We also show that a QEPAS transducer with a particular 32.8 kHz tuning fork is 2–3 times as sensitive as one with a 4.25 kHz tuning fork. These simulation results closely match experimental data.     

Renormalized solution for Stefan type problems: existence and uniqueness

We consider a class of nonlinear degenerate problems of Stefan type: $u_t- \Delta w -\nabla F(u,w)= g(\cdot,u), \ w\in \beta(u)$ where β is a maximal monotone graph in ${\mathbb{R}^2,}We consider a class of nonlinear degenerate problems of Stefan type:

ut- Dw -?F(u,w) = g(·,u),  w ? b(u)u_t- \Delta w -\nabla F(u,w)= g(\cdot,u), \ w\in \beta(u)      994. Minimization of Gerstewitz functionals extending a scalarization by Pascoletti and Serafini      Petra Weidner 《Optimization》2018,67(7):1121-1141 Scalarization in vector optimization is often closely connected to the minimization of Gerstewitz functionals. In this paper, the minimizer sets of Gerstewitz functionals are investigated. Conditions are given under which such a set is nonempty and compact. Interdependencies between solutions of problems with different parameters or with different feasible point sets are shown. Consequences for the parameter control in scalarization methods are proved. It is pointed out that the minimization of Gerstewitz functionals is equivalent to an optimization problem which generalizes the scalarization by Pascoletti and Serafini. The results contain statements about minimizers of certain Minkowski functionals and norms. Some existence results for solutions of vector optimization problems are derived.      995. Reduction of ostazine dyes’ photodynamic effect by Fenton reaction      Tomáš Mackuľak  Miroslava Smolinská  Petra Olejníková  Josef Prousek  Alžbeta Takáčová 《Chemical Papers》2012,66(2):156-160 The aim of this work was to evaluate the influence of ostazine dyes on the microbial population in environment. These dyes act as photosensitizers after irradiation by visible light. The photodynamic effect was induced in this way. The effect of irradiated water solutions of ostazine green, ostazine yellow, and ostazine blue on the Escherichia coli growth was tested. Furthermore, the effect of these dyes (at c = 3.5 μg mL−1) on bacterial growth was evaluated after their pretreatment by the Fenton reaction. Dramatic changes in dyes’ toxicity were observed after coloured solutions were pretreated by the Fenton reaction.      996. Influence of surface topography on the interactions between nanostructured hydrophobic surfaces      Hansson PM  Swerin A  Schoelkopf J  Gane PA  Thormann E 《Langmuir : the ACS journal of surfaces and colloids》2012,28(21):8026-8034 Nanostructured particle coated surfaces, with hydrophobized particles arranged in close to hexagonal order and of specific diameters ranging from 30 nm up to 800 nm, were prepared by Langmuir-Blodgett deposition followed by silanization. These surfaces have been used to study interactions between hydrophobic surfaces and a hydrophobic probe using the AFM colloidal probe technique. The different particle coated surfaces exhibit similar water contact angles, independent of particle size, which facilitates studies of how the roughness length scale affects capillary forces (previously often referred to as "hydrophobic interactions") in aqueous solutions. For surfaces with smaller particles (diameter < 200 nm), an increase in roughness length scale is accompanied by a decrease in adhesion force and bubble rupture distance. It is suggested that this is caused by energy barriers that prevent the motion of the three-phase (vapor/liquid/solid) line over the surface features, which counteracts capillary growth. Some of the measured force curves display extremely long-range interaction behavior with rupture distances of several micrometers and capillary growth with an increase in volume during retraction. This is thought to be a consequence of nanobubbles resting on top of the surface features and an influx of air from the crevices between the particles on the surface.      997. Comparison of tunneling times in isotropic and anisotropic media      Jelena Radovanovi?  Igor Ili?  Petra P. Beli?ev  Vitomir Milanovi?  Ljup?o Had?ievski 《Applied Physics A: Materials Science & Processing》2012,109(4):997-1006 We present a comparative analysis of the tunneling times of electromagnetic (EM) waves propagating in isotropic and anisotropic media. First, suitable expressions for the tunneling times in a layered periodic material, with anisotropic properties originating from its structure, are derived, followed by numerical calculations performed for a new type of anisotropic semiconductor metamaterial. In the first case, we have considered a layered structure which contains two differently doped In0.53Ga0.47As semiconductor layers. The second structure under investigation is made of alternately placed layers of doped In0.53Ga0.47As and undoped Al0.48Ga0.52As. The investigation of the dwell time as a function of incident wave frequency has revealed the existence of two peaks, one of which may be interpreted as a consequence of anisotropy, while the other one corresponds to the peak related to the absorption and the group delay. Both of these two peaks are affected by variations of layers?? doping densities. Furthermore, at increased incident angles of incoming EM waves, the dwell time peak occurs at the upper boundary of the frequency interval, for which the structure exhibits negative refractive index.      998. Thermal analysis of doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>      Petra Šulcová  Jan Večeřa  Pavel Bystrzycki 《Journal of Thermal Analysis and Calorimetry》2012,108(2):525-529 New environmentally inorganic pigments based on Bi2O3 doped by metal ions, such as Zr4+ and Dy3+ have been developed and characterized using the methods thermal analysis, X-ray powder diffraction, and spectral reflectance data. The compounds having formula Bi2−x Dy x/2Zr3x/8O3 (x = 0.2, 0.6, 1.0, and 1.2) were prepared by the solid state reaction. Methods of thermal analysis were used for determination of the temperature region of the pigment formation and thermal stability of compounds. The incorporation of doped ions in Bi2O3 changes the color from yellow to orange and also contributes to a growth of their thermal stability. This property gives a direction for coloring ceramic glazes.      999. Hydration of humic and fulvic acids studied by DSC      Ji?í Ku?erík  Petra Bursáková  Alena Pr??ová  Lucie Grebíková  Gabriele Ellen Schaumann 《Journal of Thermal Analysis and Calorimetry》2012,110(1):451-459 Qualitative and quantitative aspects of hydration of four humic acids (HA) and three fulvic acids (FA) originating from different sources were investigated. DSC experiments at subambient temperatures were carried out in order to monitor differences in ice behavior originating from freezable water surrounding humic molecules. It was found that kinetic effects play a significant role in hydration processes of both HA and FA. In fact, the hydration took part over 21?days which was detected as a progressive decrease in ice melting enthalpy. Simultaneously, the peak shapes and positions changed indicating structural changes in the physical structure of the humic substances. In case of FA, the dependency of melting enthalpy on water concentration showed a linear trend resembling a complete hydration previously observed for water-soluble hydrophilic polymers. In contrast, the melting enthalpy of some HA increased in a step-like way with increasing water content, suggesting preservation of original hydrophobic scaffold during the hydration. The differences between the rather young FA and the rather old HA lead to the conclusion that water can play a significant role in processes of humification. We assume that separation of hydrophobic and hydrophilic domains and thus increase in nanoscale heterogeneity represents an important physical contribution to the overall humification process. It was also demonstrated that the higher content of oxygen in humic molecules is not the only indicator of higher water holding capacity. Instead the porosity of humic matrix seems to contribute as additional parameter into these processes.      1000. Study of doped CeO<Subscript>2</Subscript> prepared by different synthesis      Petra Šulcová  Jan Večeřa  Lucie Strnadlová 《Journal of Thermal Analysis and Calorimetry》2012,108(2):519-523 The compounds based on CeO2 belong to the group of high-temperature pigments. The principal of these pigments makes the host lattice of the CeO2, which is doped by terbium and zirconium ions, that lead to obtaining of the interesting dark orange colour. The research is focused on three different methods of synthesis. The pigments have been prepared by the classical dry proces (i.e. solid-state reaction) in the temperature range from 1,200 to 1,600 °C, by the precipitation and as the last method a simulation of ‘Mixer Dryer Reactor’(MDR) under laboratory conditions (two-step process) was used. The aim was to improve and optimize the synthesis conditions of studied pigments. The compounds were also evaluated from the point of view of their colour properties and structure.      [首页] « 上一页 [95] [96] [97] [98] [99] 100 下一页 » 末  页»

Minimization of Gerstewitz functionals extending a scalarization by Pascoletti and Serafini

Scalarization in vector optimization is often closely connected to the minimization of Gerstewitz functionals. In this paper, the minimizer sets of Gerstewitz functionals are investigated. Conditions are given under which such a set is nonempty and compact. Interdependencies between solutions of problems with different parameters or with different feasible point sets are shown. Consequences for the parameter control in scalarization methods are proved. It is pointed out that the minimization of Gerstewitz functionals is equivalent to an optimization problem which generalizes the scalarization by Pascoletti and Serafini. The results contain statements about minimizers of certain Minkowski functionals and norms. Some existence results for solutions of vector optimization problems are derived.     

Reduction of ostazine dyes’ photodynamic effect by Fenton reaction

The aim of this work was to evaluate the influence of ostazine dyes on the microbial population in environment. These dyes act as photosensitizers after irradiation by visible light. The photodynamic effect was induced in this way. The effect of irradiated water solutions of ostazine green, ostazine yellow, and ostazine blue on the Escherichia coli growth was tested. Furthermore, the effect of these dyes (at c = 3.5 μg mL⁻¹) on bacterial growth was evaluated after their pretreatment by the Fenton reaction. Dramatic changes in dyes’ toxicity were observed after coloured solutions were pretreated by the Fenton reaction.     

Influence of surface topography on the interactions between nanostructured hydrophobic surfaces

Nanostructured particle coated surfaces, with hydrophobized particles arranged in close to hexagonal order and of specific diameters ranging from 30 nm up to 800 nm, were prepared by Langmuir-Blodgett deposition followed by silanization. These surfaces have been used to study interactions between hydrophobic surfaces and a hydrophobic probe using the AFM colloidal probe technique. The different particle coated surfaces exhibit similar water contact angles, independent of particle size, which facilitates studies of how the roughness length scale affects capillary forces (previously often referred to as "hydrophobic interactions") in aqueous solutions. For surfaces with smaller particles (diameter < 200 nm), an increase in roughness length scale is accompanied by a decrease in adhesion force and bubble rupture distance. It is suggested that this is caused by energy barriers that prevent the motion of the three-phase (vapor/liquid/solid) line over the surface features, which counteracts capillary growth. Some of the measured force curves display extremely long-range interaction behavior with rupture distances of several micrometers and capillary growth with an increase in volume during retraction. This is thought to be a consequence of nanobubbles resting on top of the surface features and an influx of air from the crevices between the particles on the surface.     

Comparison of tunneling times in isotropic and anisotropic media

We present a comparative analysis of the tunneling times of electromagnetic (EM) waves propagating in isotropic and anisotropic media. First, suitable expressions for the tunneling times in a layered periodic material, with anisotropic properties originating from its structure, are derived, followed by numerical calculations performed for a new type of anisotropic semiconductor metamaterial. In the first case, we have considered a layered structure which contains two differently doped In_0.53Ga_0.47As semiconductor layers. The second structure under investigation is made of alternately placed layers of doped In_0.53Ga_0.47As and undoped Al_0.48Ga_0.52As. The investigation of the dwell time as a function of incident wave frequency has revealed the existence of two peaks, one of which may be interpreted as a consequence of anisotropy, while the other one corresponds to the peak related to the absorption and the group delay. Both of these two peaks are affected by variations of layers?? doping densities. Furthermore, at increased incident angles of incoming EM waves, the dwell time peak occurs at the upper boundary of the frequency interval, for which the structure exhibits negative refractive index.     

Thermal analysis of doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

New environmentally inorganic pigments based on Bi₂O₃ doped by metal ions, such as Zr⁴⁺ and Dy³⁺ have been developed and characterized using the methods thermal analysis, X-ray powder diffraction, and spectral reflectance data. The compounds having formula Bi_2−x Dy _x/2Zr_3x/8O₃ (x = 0.2, 0.6, 1.0, and 1.2) were prepared by the solid state reaction. Methods of thermal analysis were used for determination of the temperature region of the pigment formation and thermal stability of compounds. The incorporation of doped ions in Bi₂O₃ changes the color from yellow to orange and also contributes to a growth of their thermal stability. This property gives a direction for coloring ceramic glazes.     

Hydration of humic and fulvic acids studied by DSC

Qualitative and quantitative aspects of hydration of four humic acids (HA) and three fulvic acids (FA) originating from different sources were investigated. DSC experiments at subambient temperatures were carried out in order to monitor differences in ice behavior originating from freezable water surrounding humic molecules. It was found that kinetic effects play a significant role in hydration processes of both HA and FA. In fact, the hydration took part over 21?days which was detected as a progressive decrease in ice melting enthalpy. Simultaneously, the peak shapes and positions changed indicating structural changes in the physical structure of the humic substances. In case of FA, the dependency of melting enthalpy on water concentration showed a linear trend resembling a complete hydration previously observed for water-soluble hydrophilic polymers. In contrast, the melting enthalpy of some HA increased in a step-like way with increasing water content, suggesting preservation of original hydrophobic scaffold during the hydration. The differences between the rather young FA and the rather old HA lead to the conclusion that water can play a significant role in processes of humification. We assume that separation of hydrophobic and hydrophilic domains and thus increase in nanoscale heterogeneity represents an important physical contribution to the overall humification process. It was also demonstrated that the higher content of oxygen in humic molecules is not the only indicator of higher water holding capacity. Instead the porosity of humic matrix seems to contribute as additional parameter into these processes.     

Study of doped CeO<Subscript>2</Subscript> prepared by different synthesis

The compounds based on CeO₂ belong to the group of high-temperature pigments. The principal of these pigments makes the host lattice of the CeO₂, which is doped by terbium and zirconium ions, that lead to obtaining of the interesting dark orange colour. The research is focused on three different methods of synthesis. The pigments have been prepared by the classical dry proces (i.e. solid-state reaction) in the temperature range from 1,200 to 1,600 °C, by the precipitation and as the last method a simulation of ‘Mixer Dryer Reactor’(MDR) under laboratory conditions (two-step process) was used. The aim was to improve and optimize the synthesis conditions of studied pigments. The compounds were also evaluated from the point of view of their colour properties and structure.