Strong enhancement of the chemiluminescence of the Cu(II)-H<Subscript>2</Subscript>O<Subscript>2</Subscript> system on addition of carbon nitride quantum dots,and its application to the detection of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose

The authors report that carbon nitride quantum dots (CN QDs) exert a strong enhancing effect on the Cu(II)/H₂O₂ chemiluminescent system. Chemiluminescence (CL) intensity is enhanced by CN QDs by a factor of ~75, while other carbon nanomaterials have a much weaker effect. The possible mechanism of the effect was evaluated by recording fluorescence and CL spectra and by examining the effect of various radical scavengers. Emitting species was found to be excited-state CN QDs that produce green CL peaking at 515 nm. The new CL system was applied to the sensitive detection of H₂O₂ and glucose (via glucose oxidase-catalyzed formation of H₂O₂) with detection limits (3σ) of 10 nM for H₂O₂ and 100 nM for glucose. The probe was employed for glucose determination in human plasma samples with satisfactory results.

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Graphical abstract The effect of carbon nitride quantum dots (CN QDs) on Cu(II)-H₂O₂ chemiluminescence reaction was studied and the new CL system was applied for sensitive detection of glucose based on the glucose oxidase (GOx)-catalyzed formation of H₂O₂.

     

Microwave hall field inertia due to dielectric relaxation time

The magnetoresistive e.m.f. caused by microwave was measured as a function of _m in wide (3 cm – 4mm) range wave length. It has been found that Maxwell relaxation time does not influence the microwave Hall field lag in semiconductors. The discussion of these results is presented.     

On the Riemann-Hilbert's boundary value problem, for flow through porous inhomogeneous media

The present paper is an extension of other results concerning Emile Picard's Great Theorem [2], [3] used for the study of plane, stationary flow with free and seepage surfaces in porous inhomogeneous media of second type.     

Stability of an incompressible fluid acted on by surface-tension forces. Case of a doubly connected equilibrium surface

The stability of the equilibrium position of a volume of incompressible fluid is considered; it is bounded by the rigid walls of the vessel and two equilibrium surfaces. The stability conditions are expressed in terms of parameters determined for each of the surfaces by independent solution of the eigenvalue problem. The stability of an arbitrary volume of incompressible fluid having spherical segments as the two equilibrium surfaces is investigated as an example.     

Traveling liquid bridges in unsaturated fractured porous media

Interplay between capillary, gravity and viscous forces in unsaturated fractures gives rise to a range of complex flow phenomena. Evidence of highly intermittent fluxes, preferential and sustainable flow pathways lead to potentially significant flow focusing of concern for regulatory and management of water resources in fractured rock formations. In previous work[Ghezzehei TA,Or D.: Water Resour. Res. In Review(2005)] we developed mechanistic models for formation, growth and detachment of liquid bridges in geometrical irregularities within fractures. Such discrete and intermittent flows present a challenge to standard continuum theories. Our focus here is on predicting travel velocities of detached liquid elements and their interactions with fracture walls. The scaling relationships proposed by Podgorski et al. [Podgorski, T., et al.: Phys. Rev. Lett. 8703(3), 6102-NIL_95 (2001)] provide a general framework for processes affecting travel velocities of discrete liquid elements in fractures, tubes, and in coarse porous media. Comparison of travel velocity and distance by discrete bridges relative to equivalent continuous film flow reveal significantly faster and considerably larger distances traversed by liquid bridges relative to liquid films. Coalescence and interactions between liquid bridges result in complex patterns of travel times and distances. Mass loss on rough fracture surfaces shortens travel distances of an element; however, results show that such retardation provides new opportunities for coalescence of subsequent liquid elements traveling along the same path, resulting in mass accumulation and formation of larger liquid elements traveling larger distances relative to smooth fracture surfaces. Such flow focusing processes may be amplified considering a population of liquid bridges within a fracture plane and mass accumulation in fracture intersections.     

Preparation and multi-properties of insulated single-phase BiFeO3 ceramics

Six types of BiFeO₃ ceramic samples, with subtle differences in synthesis conditions, were prepared. The comparison of their phases, electrical resistivity, and porosity revealed that the use of Bi₂O₃ and Fe₂O₃ powders of <1 μm size and a rapid liquid-phase sintering process of 855 °C for 5 min at 100 °C/s is beneficial to synthesize poreless single-phase BiFeO₃ samples with high electrical resistivity of ∼5×10¹² Ω cm. Deoxygenated Bi_xFe_yO_{1.5x+1.5y−δ} (x≠y, δ≥0) impurities were identified and found to be the main cause of low electrical resistivity and high porosity in the multi-phase samples. Large saturation polarization of 16.6 μC/cm² and low leakage current density of 30 mA/m², both at a high electric field of 145 kV/cm, were measured in the optimized single-phase samples at room temperature besides a large piezoelectric d₃₃ coefficient of 27 pC/N and an obvious canted antiferromagnetic behavior.     

Bands of Localized Electromagnetic Waves in 3D Random Media

Anderson localization of electromagnetic waves in three-dimensional disordered dielectric structures is studied using a simple yet realistic theoretical model. An effective approach based on analysis of probability distributions, not averages, is developed. The disordered dielectric medium is modeled by a system of randomly distributed electric dipoles. Spectra of certain random matrices are investigated and the possibility of appearance of the continuous band of localized waves emerging in the limit of an infinite medium is indicated. It is shown that localization could be achieved without tuning the frequency of monochromatic electromagnetic waves to match the internal (Mie-type) resonances of individual scatterers. A possible explanation for the lack of experimental evidence for strong localization in 3D as well as suggestions how to make localization experimentally feasible are also given. Rather peculiar requirements for setting in localization in 3D as compared to 2D are indicated.     

Subharmonic and asymmetric convection rolls

Summary A new class of steady solutions is derived describing convection rolls which do not reflect the symmetry of the physical conditions of the convection layer. As does the class of mixed solutions considered by Segel (1962) and by Knobloch and Guckenheimer (1983) the new class arises from a wavelength doubling bifurcation. The new class is distinguished by a tilt of the convection rolls which gives rise to a finite mean horizontal component of vorticity. An analytic theory is derived for small amplitudes of motion in the case of stress-free boundaries. The theory is extended to higher amplitudes by numerical computations. The new solution shares with the solution of Segel, Knobloch and Guckenheimer the property that it is unstable for large Prandtl numbersP with respect to disturbances which tend to establish the wellknown symmetric solutions, but becomes stable with respect to these disturbances for Prandtl numbers .

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Zusammenfassung Eine neue Klasse von Lösungen wird abgeleitet, welche Konvektionsrollen beschreibt, die nicht der Symmetrie der physikalischen Bedingungen der Schicht entsprechen. Ebenso wie die von Segel (1962) und von Knobloch und Guckenheimer (1983) abgeleitete Klasse von gemischten Lösungen geht die neue Klasse von Lösungen aus einer Verzweigung mit Wellenlängenverdopplung hervor. Die neue Klasse zeigt eine Schrägstellung der Rollen, die zu einer endlichen gemittelten horizontalen Komponente der Wirbelstärke führt. Eine analytische Theorie wird für den Fall kleiner Amplituden der Bewegung bei spannungsfreien Randbedingungen abgeleitet. Durch numerische Rechnungen wird die Theorie zu höheren Amplituden hin erweitert. Die neue Lösung hat mit der Lösung von Segel, Knobloch und Guckenheimer die Eigenschaft gemeinsam, daß sie instabil ist für große PrandtlzahlenP gegenüber Störungen, welche zu den bekannten symmetrischen Lösungen führen; für Prandtlzahlen ist sie aber stabil gegenüber diesen Störungen.