Crystallite size determination for supported metal catalysts by single X-ray profile fourier analysis

An X-ray diffraction method is presented capable of determining the average particle size, microstrains, the probability of faults as well as a particle size distribution function in crystalline materials. The method is based on the Fourier analysis of a single X-ray diffraction profile. Results obtained on supported platinum catalysts used in H/D isotopic exchange reactions are reported. On the basis of experimental spectra and our XRLINE1 code all structural parameters could be obtained.     

Extraction of chlorinated hydrocarbons from fish with sulphuric acid

A method is described for extraction of chlorinated hydrocarbons (DDTs and PCBs) from fish samples with sulphuric acid of various concentrations. The results are better than those obtained by an official method using Soxhiet extraction with n-hexane, especially with 9.5-13M sulphuric acid. The relative standard deviation is about 12% for analysis of portions of a homogenized single sample taken from the dorsal flesh of the same fish. Drawbacks and advantages in comparison with other methods are discussed.     

Hybrid junctions of zinc(II) and magnesium(II) phthalocyanine with wide-band-gap semiconductor nano-oxides: spectroscopic and photoelectrochemical characterization

The optical properties of zinc phthalocyanine (ZnIIPc) and magnesium phthalocyanine (MgIIPc) in DMSO and DMF solutions have been extensively investigated, and the photoelectrochemical behaviors of layer-by-layer hybrid junctions formed of the two metallo(II) phthalocyanines (MIIPcs) and wide-band-gap colloidal semiconductors, namely, ZnO and TiO2 nanocrystals (NCs), have been probed. Different experimental conditions, such as the Pc center metal ion, dye concentration, and solvent identity, were investigated in order to elucidate their effects on the photoelectrochemical performances of the prepared heterojunctions. Finally, thermal treatment of either dye and NC films and control of the NC shape and surface chemistry were also studied and, interestingly, were found to be critical in affecting the performance of photochemical sensitization processes, occurring at the dye/oxide and oxide/solution interfaces.     

Computational Mechanics: Pattern and Prediction, Structure and Simplicity

Computational mechanics, an approach to structural complexity, defines a process's causal states and gives a procedure for finding them. We show that the causal-state representation—an -machine—is the minimal one consistent with accurate prediction. We establish several results on -machine optimality and uniqueness and on how -machines compare to alternative representations. Further results relate measures of randomness and structural complexity obtained from -machines to those from ergodic and information theories.     

Some aspects of radioactive contamination after Chernobyl accident in Romania

After the Chernobyl disaster, the radioactive cloud passage over Romania beginning with the April 30th, 1986 caused fall-out of different intensities in different regions.. The principal contributors to the radioactive exposure during the month of May and rest of 1986 were the short and medium half-live radionuclides: ¹³²Te+¹³²I, ¹³¹I, ¹⁴⁰Ba+¹⁴⁰La, ¹⁰³Ru+¹⁰³Rh, ¹⁰⁶Ru+¹⁰⁶Rh, ⁹⁵Zr+⁹⁵Nb, ¹³⁶Cs, ¹³⁴Cs, ¹⁴¹Ce, ¹⁴⁴Ce and ¹²⁵Sb. After four-five years only ¹³⁷Cs and ⁹⁰Sr remained significant radioactive contaminants. During May 1986 the grass was the mostly affected component of the environment and it contaminated rapidly the majority of foods. Measurements made on the daily gathered pollen samples and eggs during May 1986 clearly indicated that these samples can be used as bioindicators of radioactive contamination of the atmospheric air and, respectively, for soil and grass. Regarding soil contamination, the higher ^134+137Cs deposits in Romania following the northeast-southwest direction were measured, some of these being above 80 kBq/m². This direction is the same with the cloud passage over Romania during the first week of May 1986 and it was confirmed by measurements in the former Yugoslavia, Albania, Greece, and south of Italy.     

Design of a high-sensitivity negative ion source time-of-flight mass analyzer assembly created by cylindrical electrodes with a common axis

The new design incorporates the negative ion source and the mass analyzer, both constructed from cylindrical electrodes. The ion source is formed by three gridded cylindrical electrodes: a pulsed grid, the intermediate grid and the final accelerating grid. During a first time lapse, the electrons penetrate through the pulsed grid into the retarding field between this grid and the intermediate grid. The electrons are turning at some depth inside this intergrid space, where the attachment to neutral molecules most probably occurs. Next, the pulsed grid becoming strongly negative and ions are extracted towards the final acceleration grid. The ions from the cylindrical surface where they were created concentrate on the common axis of the electrodes (lateral focusing). The source lateral and time focus are coincident. A cylindrical electrostatic mirror is fitted to the source. The design, with a single stage, ensures also lateral focusing of the ions diverging from the common axis of the electrodes. The mirror electric and geometric parameters were selected to ensure both lateral and time focusing on the final detector with subsequent high luminosity. The basic parameters of the specific negative ion source time-of-flight mass analyzer design proposed here, are ion source final acceleration, intermediate, pulsed cylindrical grid radii 10, 20 and 30 mm, respectively, electrostatic mirror earthed grid and ion turning points surface radii 0.6 and 0.8 m, respectively. Ion packet smearing by the ion energy spread (resulting from the initial electron energy spread as electrons are turning at different depths inside the ionization region, from the moment when ions were created, being accelerated towards the pulsed grid during ionization) and by the turnaround time inside the cylindrical field was accounted for. Maintaining very high sensitivity, a resolution of the order of 100 is expected.     

13C separation by IRMPD of CF2HCL molecules with a powerful CO2-TEA laser

The single pulse separation parameters in IRMPD of CF₂HCL molecules have been obtained in relation with the laser fluence, the number of laser pulses, and the gas pressure. The measurements have been carried out using a fixed laser line (9P22) and an ordinary shape of the laser pulses.     

Gamma-ray spectrometric analysis of neutron irradiated golden sands

A nondestructive method has been used for the qualitative and quantitative determination of elements such as Au, Cu, Ag in minerals and especially in golden sand. The induced radioactivity has been analyzed with a high resolution gamma spectrometer containing a Ge(Li) semiconductor detector type and a multichannel analyzer. The samples have been collected from the alluvia of the Mure? and Some?ul Mic river basins, proving the presence of gold and copper in small concentrations. These results have been correlated to previous data showing the existence of some gold mines in these zones. This nondestructive, rapid and highly sensitive method can be used for industrial processes [1] control and prospections. The use of a NaI(Tl) scintillation crystal for routine measurements of the ¹⁹⁸Au radioisotope type and the interferences by copper, silver and indium in the irradiated samples are discussed.     

Phototoxicity and cytotoxicity of chlorophyll a/cyclodextrins complexes on Jurkat cells

The aggregation status of chlorophyll a (Chl a) and the ability of four cyclodextrins, hydroxypropyl-beta-cyclodextrin (HP-beta-CD), hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD), heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DIMEB), and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TRIMEB), to solubilize the pigment in the complete cellular medium RPMI 1640 was estimated by means of UV-Vis absorption and static resonance light scattering (RLS) measurements. The results indicate that the pigment interacts with cyclodextrins in the cellular medium differently to that observed in water. The cytotoxic and phototoxic activity of these complexes towards human leukemia T-lymphocytes (Jurkat cells) was tested by means of experiments aimed to discriminate between the intrinsic toxicity and the toxicity induced by light. The overall data indicate that the HP-beta-CD is the cyclodextrins having the best characteristics to form with Chl a a potential supramolecular system for the photodynamic therapy.     

Calibration of NaI(TI) spectrometer for radiocesium volume-samples. Some results from Transylvania region

A four-channel NP-424 type gamma analyzer coupled with a large NaI(Tl) scintillator was calibrated using a¹³⁷Cs point source. The volume-samples were plexiglas cylindrical boxes (D=76mm, H=40mm) directly placed on the NaI(Tl) detector. Measurements for 64 indoor positions at full-662 keV-peak were made. Sample selfabsorbtion was determined considering a linear attenuation for gamma rays and measuring the absorption factor for maximum thickness of the volume sample (h0=40mm). The obtained results for two types of environmental samples (soil and milk-powder) are compared with the data acquired from other Romanian laboratories, in the frame of the Environmental Radioactivity Action (ERA) which standardized such types of measurements. The same samples were measured with a calibrated GeLi detector (INAN-Louvain la Neuve) and the results were in good agreement with our measurements. Using this NaI(Tl) calibrated spectrometer some radiocesium deposits (56 localities) from Transylvanian region were measured. The results show that a large deposit exists in the direction NE-SW in connection with the radioactive cloud passing. For Alba region were measured more than 40 kBq/m² of cesium deposit.