Determination of the chemical oxygen demand (COD) using a copper electrode: a clean alternative method

A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater. The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l⁻¹ COD with detection limit of 20.3 mg l⁻¹ COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate) COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end products do not contain toxic metals.     

Uranium determination at ppb levels by X-ray fluorescence after its preconcentration on polyurethane foam

A sensitive method based on the preconcentration of uranium on powdered polyurethane foam (PUF) has been developed to determinate this element in water samples by X-ray florescence. Uranium at ppb levels was sorbed as the salicylate complex on powdered PUF at pH 4.0. The resulting PUF was filtered through a filter paper and used for X-ray fluorescence measurements. For 50 μg/l of uranium the coefficient of variation for five measurements is 5% and the detection limit is 5.5 μg/l. The interference level of various ions and ligands was studied and optimum conditions were developed to determine uranium in reference materials, waste water, mine drainage, and sea water.     

Characterization of a crystal grown from Ocimum Basilicum leaves and branches

Leaves and branches of Ocimum Basilicum were dried, reduced to coarse powder and extracted in aqueous metanol and aqueous hexane. This paper discusses the X‐ray diffraction and FT‐Raman spectra measured at room temperature. The data obtained have been used to propose a general assignment of the vibrational fundamentals on the base of frequencies assigned in other related single crystals. From the results we can conclude that the crystal has a high symmetry. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transport and thermodynamic properties of a 2DEG in the presence of tilted magnetic field: the influence of Rashba interaction

The effects of Rashba spin-orbit coupling on the physical properties of a non-interacting two-dimensional electron gas (2DEG) in presence of a tilted magnetic field are investigated. The spin-orbit and Zeeman interactions depend on the intensity and direction of the external magnetic field and we study their influence on the physical properties of the system. We obtain the energy spectrum, the density of states, the Fermi energy, and we analyze the combined effect of the Zeeman and Rashba Spin-Orbit Interaction on the transport and thermodynamic properties.     

Shock wave formation in hot nuclear matter

Assuming that nuclear matter can be treated as a perfect fluid, we study the propagation of perturbations in the baryon density at high temperature. The equation of state is derived from the non-linear Walecka model. The expansion of the Euler and continuity equations of relativistic hydrodynamics around equilibrium configurations lead to the breaking wave equation for the density perturbation. We solve it numerically for this perturbation and follow the propagation of the initial pulses.     

Low-Temperature Raman Spectra of l-Histidine Crystals

We present a Raman spectroscopy investigation of the vibrational properties of l-histidine crystals at low temperatures. The temperature dependence of the spectra show discontinuities at 165 K, which we identify with modifications in the bonds associated to both the NH₃ ⁺ and CO₂ ^? motifs indicative of a conformational phase transition that changes the intermolecular bonds. Additional evidence of such a phase transition is provided by differential scanning calorimetry measurements, which identified an enthalpic anomaly at ～165 K.     

A General Solution of the Fokker-Planck Equation

The Fokker-Planck equation is useful to describe stochastic processes. Depending on the force acting in the system, the solution of this equation becomes complicated and approximate or numerical solutions are needed. The relation with the Schrödinger equation allows building a method to obtain solutions of the Fokker-Planck equation. However, this approach has been limited to the study of confined potentials, restricting its applicability. In this work, we suggest a general treatment for non-confining potentials through the use of series of functions based on the solution of the Schrödinger equation, with part of discrete spectrum and part of continuum spectrum. Two examples, the Rosen-Morse potential and a limited harmonic potential, are analyzed using the suggested approach.     

Range and range straggling of 15 to 350 keV 69Ga in amorphous silicon

Depth distribution profiles of 15 to 350 keV ⁶⁹Ga+ implanted at room temperature in amorphized silicon have been measured by ⁴He ion Rutherford backscattering. The measured projected ranges and range stragglings are in excellent agreement with the predictions calculated via realistic Monte Carlo simulations, TRIM code.