Vortex ring generation due to the coalescence of a water drop at a free surface

 Results are presented of an experimental investigation of vortex ring formation by a fluid drop contacting a free surface with negligible velocity. The pool fluid is mixed with fluorescein dye, and a laser sheet is used to illuminate a plane of the flow. A series of representative images is recorded by a CCD camera and speculation is made regarding specific sources of vorticity flux through the free surface. Two scaling analyses previously presented by other investigators are demonstrated to be equivalent under the assumptions of this experiment, and they provide the motivation for a series of test runs in which the duration of the coalescence process, τ_*, is related to variations in drop diameter L and fluid surface tension σ. Experimental results are in agreement with the analyses, showing τ_*∼σ^-1/2 and τ_*∼L ^3/2. Received: 22 December 1995 / Accepted: 15 October 1996     

Study of trace elements in milk by nuclear analytical techniques

This work is part of a project with the IAEA, in a coordinated program on Trace Elements in Human and Bio-Environmental Systems to evaluate their nutritional requirements, interrelations and the role of trace elements in health, metabolism, etc. Cow's milk being regarded as one of the most important and nutritious foodstuffs consumed by people. Hence as a first step, an elemental analysis for milk was carried out for this purpose; a few samples of pasteurized milk and local sample were investigated for essential and toxic trace elements. The secondary aim of this project was the assessment of various analytical techniques involved. However, in the present work, the methods involved were AAS, PIXE and NAA. The latter method was applied both instrumentally and radiochemically. Although the results pertaining to the various methods employed are not in good agreement. there is, however, some justification to clarify this internal inconsistency. The precision of NAA and AAS allows a greater degree of acceptance. Although PIXE is very fast and rather routine, the technique for trace element analysis needs certain adaptations and development.     

Bioavailability of essential trace elements in the presence of phytate, fiber and calcium

Summary Bioavailability and/or homeostasis of some essential trace elements such as zinc, iron, etc., in the presence of phytate, fiber and calcium are subject to alteration. These factors were measured in this study for Iranian diets in a frame of a Coordinated Research Project (CRP). However, the most prominent dietary factor in this regard is phytate. The phytate effect on zinc homeostasis is a chemical phenomenon dependent physiologically on pH in the gastrointestinal tract at or near the sites of absorption. Calcium is a synergistic coprecipitating factor in the complexation of zinc by phytate. Fiber has also a tendency to absorb insoluble compounds in gastrointestinal tract including zinc, iron and many other trace elements. One of the most known clinical observations regarding zinc deficiency was found in the rural area of the Fars province of Iran in the late 1950s at Shiraz University. However, the molar ratio of [phytate] : [zinc] and [calcium] [phytate] : [zinc] in Iranian Diets in a recent study are 7-17 and 150-800, respectively. The critical ratios of [phytate] : [zinc] of 10 or less will provide adequate zinc to sustain homeostasis.     

Protein-X,Pancreatic Stone-, Pancreatic thread-, reg-protein,P19, lithostathine,and now what? Characterization,structural analysis and putative function(s) of the major non-enzymatic protein of pancreatic secretions

Reg protein was first found in pancreatic stones. It was named Pancreatic Stone Protein and later renamed lithostathine, as it was assumed to prevent stone formation. The 144 amino acid protein is O-glycosylated on Thr-5. The glycan chain is variable in length and in charge. Lithostathine 3-D organization is of the C-lectin type, even though it is unlikely to have any functional calcium-binding site. The Arg11-Ile12 bond is readily cleaved by trypsin; the resulting C-terminal polypeptide precipitates at physiological pH and tends to form fibrils. The protein was more recently found in the regenerating endocrine pancreas and it was named Reg (for regenerating) protein. Numerous proteins related to Reg have been identified successively in several mammalian species. They constitute the Reg superfamily. Reg genes show the same organization and are located in the same chromosome region. These genes are therefore likely to derive from a common ancestor gene by duplication. In the course of evolution, they may have diverged in tissue-related expression and function. In the endocrine pancreas, Reg protein stimulates islet beta-cell growth and reduces experimental diabetes via the activation of a high affinity receptor. The role of the protein produced by the exocrine pancreas, however, is controversial. Not only is Reg/lithostathine unlikely to be a physiologically relevant pancreatic stone inhibitor, but it may contribute to stone formation. We suggest that it might help prevent the harmful activation of protease precursors in the pancreatic juice. The protein provides a useful model for examining the conformational changes associated with globular to fibril transformation.     

Spectroscopic studies of the electronic and vibrational spectra of tetramethylammonium fluorochromate(VI)

The electronic and vibrational spectra of tetramethylammonium fluorochromate(VI) have been measured. The observed electronic transitions correlated simply and directly with those of CrO ₄ ²⁻ . The electronic spectrum shows a weak band at about 450 nm and the edge of a very strong, broad band which extends beyond 344 nm. The intervening band has been identified with o oxygen-to-chromium charge transfer. This band exhibits a partially resolved vibrational progression or vibronic coupling due to excitation of a symmetric stretching mode in the CrO₃ group. This vibronic coupling is analyzed completely due to spectral correlation and symmetry of transitions, the Duschinsky effect, vibronic-spin-orbit coupling, environmental effect, anharmonicity order, vibrational intervals, and electronic rearrangement. The text was submitted by the authors in English.     

Catalytic Method for Synthesis of Aspirin by a Green,Efficient and Recyclable Solid Acid Catalyst (Preyssler's Anion) at Room Temperature

Synthesis of aspirin at room temperature via O‐acetylation of salicylic acid in the presence of Preyssler type heteropolyacids has been investigated in order to contribute toward clean technology, which is the most important need of the society. All of the catalysts are recyclable and reusable.     

Complexes of pyrimidine DNA bases with thallium(I)

The stability constants of complexes of a thallium(I) ion with cytosine and thymine were determined in aqueous solution at 25°C and 0.1 mol dm⁻³ ionic media, using a combination of potentiometric and spectrophotometric techniques. Sodium perchlorate was used to maintain the ionic strength. The composition of the formed complexes was determined and it was shown that thallium(I) forms two mononuclear 1:1 species with cytosine of the type TIHL⁺ and TIL, and a mononuclear 1:1 complex species with thymine in the form TIHL, in the pH range of study (1–11), where L represents the fully dissociated ligand. The cumulative stability constants, β _xyz, of the complexes, [(thallium)_x(H)_y(ligand)_z], were calculated by a nonlinear fitting method and their distributions were presented as a function of-log[H⁺]. This text was submitted by the authors in English.     

Optimization of cadmium adsorption from aqueous solutions by functionalized graphene and the reversible magnetic recovery of the adsorbent using response surface methodology

Novel functionalized graphene adsorbent was prepared and characterized using different techniques. The prepared adsorbent was applied for the removal of cadmium ions from aqueous solution. A response surface methodology was used to evaluate the simple and combined effects of the various parameters, including adsorbent dosage, pH, and initial concentration. Under the optimal conditions, the cadmium removal performance of 70% was achieved. A good agreement between experimental and predicted data in this study was observed. The experimental results revealed of cadmium adsorption with high linearity follow Langmuir isotherm model with maximum adsorption capacity of 502 mg g^?1, and the adsorption data fitted well into pseudo‐second order model. Thermodynamic studies showed that adsorption process has exothermic and spontaneous nature. The recommended optimum conditions are: cadmium concentration of 970 mg L^?1, adsorbent dosage of 1 g L^?1, pH of 6.18, and T = 25 °C. The magnetic recovery of the adsorbent was performed using a magnetic surfactant to form a noncovalent magnetic functionalized graphene. After magnetic recovery of the adsorbent both components (adsorbent and magnetic surfactant) were recycled by tuning the surface charges through changing the pH of the solution. Desorption behavior studied using HNO₃ solution indicated that the adsorbent had the potential for reusability.