Energy and exergy analyses of vacuum cooling as experimental assessment: case study for boiled cauliflower (Brassica Oleracea Var)

Journal of Thermal Analysis and Calorimetry - Thermodynamic properties and glass transition temperature (Tg) of heat pump dried scallop adductors with (SA-C) and without (SA) sodium alginate...     

Determination of Hg on poly(vinylferrocenium) (PVF)-modified platinum electrode

A new surface based on poly(vinylferrocenium) (PVF⁺)-modified platinum electrode was developed for determination of Hg²⁺ ions in aqueous solutions. The polymer was electrodeposited on platinum electrode by constant potential electrolysis as PVF⁺ClO₄⁻. Cl⁻ ions were then attached to the polymer matrix by anion exchange and the modified electrode was dipped into Hg²⁺ solution. Hg²⁺ was preconcentrated at the polymer matrix by adsorption and also complexation reaction with Cl⁻. Detection of Hg²⁺ was carried out by differential pulse anodic stripping voltammetry (DPASV) after reduction of Hg²⁺. Mercury ions as low as 5 × 10⁻¹⁰ M could be detected with the prepared electrode and the relative standard deviation was calculated as 6.35% at 1 × 10⁻⁶ M concentration (n = 6). Interferences of Ag⁺, Pb²⁺ and Fe³⁺ ions were also studied at two different concentration ratios with respect to Hg²⁺. The developed electrode was applied to the determination of Hg²⁺ in water samples.     

Ostrowski Type Inequality for Double Integrals on Time Scales

We prove the Ostrowski type inequality for double integrals on time scales and thus unify corresponding continuous and discrete versions from the literature. We also apply the Ostrowski inequality for double integrals to the quantum time scales.     

Insights into the isomerization of photochromic oxazines from the excitation dynamics of BODIPY-oxazine dyads

We synthesized five BODIPY-oxazine dyads in one to four synthetic steps from known precursors. They differ in the nature of the unsaturated spacer linking the oxazine photochrome to either the conjugated framework or the boron center of the BODIPY fluorophore. Despite the π-character of the linkers, the two functional components are electronically isolated in the ground state and the BODIPY fluorophore maintains its absorption and, with one exception, emission properties unaltered. Instead, the photochemical response of the photochromic component is completely suppressed within all dyads. Rather than the expected opening of the oxazine ring, the laser excitation of these molecular assemblies results in the effective population of the BODIPY triplet in four of the five dyads. Control experiments with appropriate model compounds indicate that the local excitation of the oxazine component results first in intersystem crossing and then energy transfer to the BODIPY component. In fact, the transfer of energy from the triplet state of the former to the triplet state of the latter competes successfully with the opening of the oxazine ring and prevents the isomerization of the photochromic component. These observations demonstrate, for the very first time, that the photoinduced opening of these photochromic oxazines occurs along the potential energy surface of their triplet state. Such valuable mechanistic insights into their excitation dynamics can guide the design of novel members of this family of photochromic compounds with improved photochemical properties.     

Preparation of polyethyleneglycol (PEG) coatings for microencapsulation of charcoal

Polyethyleneglycols (PEGs) with their high solubility in water cannot normally be used as a coating material in aqueous solutions such as blood. A λ-radiation procedure was therefore applied after coating charcoal granules with PEG in a non-aqueous phase, and an 80–90% insoluble polymer matrix on charcoal was obtained. PEGs with different molecular weights from 4000 to 300,000 were used for coating. The performance of this system was determined by using several test solutes, namely creatinine, uric acid, and vitamin B-12. It was observed that the pore size and structure of these membranes can be adjusted by changing the irradiation time and by using PEGs with different molecular weights. Thus, very high mass transfer rates can be achieved.     

Nanostructured magnetic cuprate cluster: synthesis,structure, UV-Vis spectroscopy,and magnetic properties of a new copper(II) arsenate NaCuAsO4 containing discrete [Cu4O16]24- clusters

Crystals of copper(II) arsenate NaCuAsO(4) were grown by conventional high-temperature, solid-state methods in molten-salt media. The compounds were characterized by single crystal X-ray diffraction, UV-vis spectroscopy, and magnetic susceptibility measurements. NaCuAsO(4) crystallizes in a monoclinic lattice with a = 6.002 (1) A, b = 10.853 (2) A, c = 10.373 (2) A, beta = 91.50 (3) degrees, and V = 675.4(2) A(3); P2(1)/c (No. 14); Z = 8. The newly isolated sodium copper(II) arsenate reveals a pseudo-one-dimensional channel structure where the sodium cations reside. The extended framework contains nanostructured [Cu(4)O(16)](24-) magnetic clusters that are interlinked by closed-shell, nonmagnetic AsO(4)(3-) oxy anions via sharing vertex oxygen atoms of the CuO(5) and AsO(4) polyhedral units. Each [Cu(4)O(16)](24-) cluster consists of four CuO(5) square pyramidal units in a chair configuration centered by a center of inversion. The two crystallographically independent Cu(2+) cations adopt the [4 + 1] CuO(5) Jahn-Teller distortion giving rise to an intense d-d transition in UV-vis absorption spectra. The magnetic susceptibility measurements reveal that the title compound is antiferromagnetic. At high temperatures, the data follows a pure Curie law, suggesting noninteracting spins, but with a rapid suppression of the effective spin below T = 70 K. At low temperature, the susceptibility collapses, indicating spin gap formation as the magnetic-cluster material settles into the lowest energy magnetic singlet state. The current work in the exploratory synthesis of oxy compounds containing nanostructured transition-metal-oxide magnetic clusters leads to new materials for experimental and theoretical developments of magnetic models.     

High performance AlxGa1−xN-based avalanche photodiodes

We report high performance solar-blind photodetectors with reproducible avalanche gain as high as 820 under ultraviolet illumination. The solar-blind photodetectors have a sharp cut-off around 276 nm. We improved the device performance by designing different epitaxial wafer structure with thinner active multiplication layer. We compare the resulting fabricated devices from these wafers in terms of dark current, photoresponse, avalanche gain performances.