Oblique evaporation waves

Evaporation waves are processes that may occur under certain conditions in which a metastable or superheated liquid undergoes a sudden phase transition in a narrow and observable region, which resembles a shock wave. It is inferred from photographic documentation that in certain liquid jet flashing regimes the phenomenon is present. The evaporation wave discontinuity has been successfully modeled in a similar way as a deflagration wave in a combusting gas. One-dimensional laboratory experiments have demonstrated the existence of the (lower) Chapman-Jouguet solution for the cases where the liquid were at a high degree of metastability. Subsonic solutions were also observed for less pronounced degree of metastability (Hill 1991, Sim oes-Moreira 1994). In this paper, the fundamental theory is briefly revised and compared with some of the experimental results obtained for the cases operating at the C-J condition. Next, the paper presents the extension of the one-dimensional theory to include the oblique evaporation wave geometry. Relationships between upstream and downstream flow properties are discussed ant further consequences of these relationships are analyzed. Received 12 October 1999 / Accepted 21 March 2000     

Inexact subgradient methods for quasi-convex optimization problems

In this paper, we consider a generic inexact subgradient algorithm to solve a nondifferentiable quasi-convex constrained optimization problem. The inexactness stems from computation errors and noise, which come from practical considerations and applications. Assuming that the computational errors and noise are deterministic and bounded, we study the effect of the inexactness on the subgradient method when the constraint set is compact or the objective function has a set of generalized weak sharp minima. In both cases, using the constant and diminishing stepsize rules, we describe convergence results in both objective values and iterates, and finite convergence to approximate optimality. We also investigate efficiency estimates of iterates and apply the inexact subgradient algorithm to solve the Cobb–Douglas production efficiency problem. The numerical results verify our theoretical analysis and show the high efficiency of our proposed algorithm, especially for the large-scale problems.     

Indium-incorporation-induced transformation of optical, photoluminescence and lasing properties of InGaN epilayers

A comparative combined study of photoluminescence (PL), PL kinetics, stimulated emission (SE) and photoreflectance (PR) properties in In_xGa_1−xN epilayers is carried out in the composition range 0≤x≤0.19. In-incorporation up to 4% leads to the sufficient longer radiative recombination decay time due to the decrease in non-radiative recombination channels, which are peculiar to GaN, and band-to-band optical transitions predominate the spontaneous PL spectrum. Further In-incorporation (x>4%) leads to the localization of carriers and/or excitons at band-tails in the In-rich areas. Correlation between the position of dominant low-energy PR oscillation due to the main band gap and SE peak position shows that band-to-band transitions are responsible for lasing and dominate the PL spectrum in all highly pumped In_xGa_1−xN samples.     

Joins of n-degenerate graphs and uniquely (m,n)-partitionable graphs

The Lick-White point-partition numbers generalize the chromatic number and the point-arboricity. Similarly, uniquely (m, n)-partitionable graphs generalize uniquely m-colorable graphs.Theorem 1 gives a method for constructing uniquely (m, n)-partitionable graphs as well as a sufficient condition for a join of mn-degenerate graphs to be uniquely (m, n)-partitionable. For the case n = 1, we obtain a necessary and sufficient condition (Lemma 1). As a consequence, an embedding result for uniquely (m, 1)-partitionable graphs is obtained (Theorem 2). Finally, uniquely (m, n)-partitionable graphs with minimal connectivity are constructed (Theorem 3).     

The characteristic exponents of the falling ball model

We study the characteristic exponents of the Hamiltonian system ofn (>=2) point massesm ₁,...,m _n freely falling in the vertical half line {q|q>=0} under constant gravitation and colliding with each other and the solid floorq=0 elastically. This model was introduced and first studied by M. Wojtkowski. Hereby we prove his conjecture: All relevant characteristic (Lyapunov) exponents of the above dynamical system are nonzero, provided thatm ₁>= ...>=m _n (i.e. the masses do not increase as we go up) andm ₁≠m ₂. Research partially supported by the Hungarian National Foundation for Scientific Research, No. 16425.     

Evolution of ochratoxin A content from must to wine in Port Wine microvinification

To study the evolution of ochratoxin A (OTA) content from must to wine during the making of Port Wine, grapes from the five most common varieties of Port Wine were harvested and combined in equal percentages in order to perform microvinifications. Three sets of assays were studied: a blank (A), where the most common Port Wine-making process was used; in the second (B), a solution of OTA was added to the initial must; in the third (C), the grapes were aspersed with an inoculating solution of OTA-producing fungi. Samples were collected, in duplicate, on four different occasions throughout the process. The influence of the addition of SO₂ to the must was also assessed in each set. The quantification of OTA was based on the standard reference method for wines (European Standard prEN 14133), which includes clean-up via immunoaffinity columns and HPLC with fluorescence detection. The limits of detection were 0.076 g/l for wine and 0.114 g/l for must. The method was validated by assessing the precision, accuracy and by obtaining an estimate of the global uncertainty. Overall, the levels of OTA observed during the vinifications dropped by up to 92%, and no grapes used in this work were contaminated naturally.     

Aminopyridine-benzoxanthene enantioselective receptor for sulfonylamino acids

Combination of a cis-tetrahydrobenzoxanthene skeleton with a benzoxazole and an amidopyridine provides an enantioselective receptor for sulfonylamino acids with chiral recognitions of up to 18. The structure of the complex between receptor 1 and the leucine triflate is known by X-ray analysis. The receptor racemic mixture can be suitably resolved through crystalization in the presence of leucine triflate as guest. Receptor 1 can be used for the enantioselective extraction of sulfonylamino acids from aqueous solutions of their salts.