Comparison of real time suspended sediment transport measurements in river environment by LISST instruments in stationary and moving operation mode

Suspended sediment and particle size measurements were in this study performed with two instruments based on laser diffraction. The measurements were conducted in the river Danube during a 1-year flood, which enabled measurements in a large scale and under conditions with high sediment load. The aim of this study was to compare LISST-SL stationary measurements with LISST-SL moving measurements to gain knowledge for extensive field surveys of large areas. The moving measurements were performed in four different depths along a transect and compared with stationary measurements in five verticals in the same depths. The results showed that the measured suspended sediment concentrations are smaller for the moving measurements compared to the stationary measurements. In addition thus the d₅₀ was smaller for the moving measurements, which is an indicator for the phenomena of non-isokinetic sampling. A comparison of the pump speed of the two operation modes proofed that during LISST-SL moving measurements a non-isokinetic sampling effect occurred. Hence, a suction effect happened, resulting in an underestimation of particles >63 µm. Beside the LISST-SL simultaneously a LISST-STX was used during the field survey to investigate the behavior and the results of the instrument under conditions where it is originally not designed for. However, the predominant suspended sediment concentrations in the river influenced the measurements and thus multiple scattering occurred. As a consequence the measurements of the suspended sediment concentrations showed lower values for the measured suspended sediment concentrations compared to the LISST-SL stationary measurements. It could also be seen that due to the high amount of fine particles, which were transported during the flood event, a re-scattering of light occurred also in case of measurements where the value for the optical transmission was with 0.38 above the standardized used limit of 0.3.     

Microwave-assisted dechlorination of polychlorobenzenes by hypophosphite anions in aqueous alkaline media in the presence of Pd-loaded active carbon

Microwave-assisted dechlorination of chlorobenzene and the three dichlorobenzenes takes place in the presence of the hypophosphite (NaH(2)PO(2)) reductant and Pd-loaded activated carbon (Pd/C) in alkaline media at relatively low temperatures. The extent of loss/dechlorination at 90 degrees C followed the order: o-DCB approximately m-DCB>CB>p-DCB. Detected final products were mostly benzene and phenol. Dechlorination of pentachlorobenzene (PeCB) through reduction was slight even when both NaH(2)PO(2) and Pd/C were simultaneously employed in the absence of NaOH, nor when NaH(2)PO(2) alone was present in excess. The generated HCl proved to be an inhibitor, thus the need for the presence of NaOH to enhance dechlorination. Conventional heating of the reacting mixture above 90 degrees C to a reaction temperature of 180 degrees C led to no further dechlorination of the PeCB. Intermediate products of dechlorination of PeCP were the tetrachlorobenzenes with final products being benzene and phenol (GC-FID spectral analyses). Both salicylic acid (a constituent of humic acid) and l(+)-ascorbic acid used as possible promoters proved to be rather ineffective. The simultaneous presence of NaH(2)PO(2), Pd-loaded activated carbon and NaOH was crucial in the dechlorination of PeCB by microwave dielectric heating with maximal reduction of PeCB being ca. 75% under these conditions.     

A crossed photon-atom beam method for absolute measurement of total photoionization cross sections on isolated metal atoms: Measurements on Ba and Eu atoms

A crossed photon-atom beam apparatus has been constructed for absolute measurement of total photoionization cross sections of isolated and neutral metallic atoms. The main purpose is to establish the technique which can be used as widely as possible for the metallic elements. Using this apparatus, measurements on Ba and Eu atoms have been made at selected energies in their 4d giant resonance regions 110-140 eV and 140-180 eV, respectively. A monochromatized synchrotron radiation was used as a light source. The target-atom density in the interaction section was determined with accuracy of 9% using the accumulation rate of metallic atoms on a quartz crystal sensor and the average velocity of the atoms obtained by a time-of-flight method combined with a pulsed electron gun. The number of photons was determined with use of a double-ion chamber preferably. The entire systematic errors have been estimated to be 20% for Ba and 27% for Eu. The comparison of the measured cross-section values with previous experimental and theoretical results is reasonable, indicating that the crossed photon-atom beam method is fairly promising technique.     

Enhanced remediation of simulated wastewaters contaminated with 2-chlorophenol and other aquatic pollutants by TiO2-photoassisted ozonation in a sunlight-driven pilot-plant scale photoreactor

Solar photoassisted remediation of a simulated wastewater contaminated with 2-chlorophenol (2-CP) was carried out by various advanced oxidation processes in a pilot-plant-scale Pyrex glass tubular-type photoreactor using solar cell derived electricity to drive the whole setup. The UV-assisted degradation and mineralization (loss of total organic carbon, TOC) of 2-CP in the co-presence of TiO₂ and ozone (UV/TiO₂/O₃) was enhanced significantly compared with ozonation alone (UV/O₃) and conventional TiO₂ photocatalysis in oxygenated dispersions (UV/TiO₂/O₂). The mineralization process was monitored by TOC assays and chloride ion analyzes. The utilization of immobilized TiO₂ was also examined with a TiO₂-coated glass photoreactor and compared with dispersed TiO₂ in aqueous media. In addition, simulated wastewaters contaminated with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), the endocrine disruptor bisphenol-A (BPA), the anionic surfactants sodium dodecylbenzenesulfonate (DBS) and sodium butylnaphthalenesulfonate (BNS), together with the cationic benzyldodecyldimethyl- ammonium bromide (BDDAB) surfactant were also efficiently remediated under otherwise identical conditions. The TiO₂-photoassisted ozonation of organic wastewater contaminants is a promising synergistic methodology to accelerate the remediation of such wastewaters, even when the TiO₂ is immobilized which can lead to reduced costs of operation.     

Enzymatic Synthesis and Structural Confirmation of Novel Oligosaccharide,D-Fructofuranose-linked Chitin Oligosaccharide

Utilizing transglycosylation reaction catalyzed by β- N -acetylhexosaminidase of Stenotrophomonas maltophilia , β-D-fructofuranosyl-(2↔1)-α- N , N ´diacetylchitobioside (GlcNAc ₂ -Fru) was synthesized from N -acetylsucrosamine and N , N ´-diacetylchitobiose (GlcNAc ₂ ), and β-D-fructofuranosyl-(2↔1)-α- N , N ´, N ´´-triacetylchitotrioside (GlcNAc ₃ -Fru) was synthesized from GlcNAc ₂ -Fru and GlcNAc ₂ . Through purification by charcoal column chromatography, pure GlcNAc ₂ -Fru and GlcNAc ₃ -Fru were obtained in molar yields of 33.0 % and 11.7 % from GlcNAc ₂ , respectively. The structures of these oligosaccharides were confirmed by comparing instrumental analysis data of fragments obtained by enzymatic hydrolysis and acid hydrolysis of them with known data of these fragments.     

Diffusion along migrating and stationary grain boundaries in the CuAg system

The diffusion along a migrating random grain boundary of a Cu-3.8 at.% Ag bicrystal has been investigated by discontinuous precipitation and dissolution. The measurements have been carried out over an extensive temperature range. The reaction front velocities varied between 1.8 × 10⁻¹⁰ and 2.7 × 10⁻⁶ m/s. The values of sδD_b (s = segregation factor, δ = grain boundary width and D_b = grain boundary diffusion coefficient) have been determined from the precipitation data according to different models. All of the four models applied yield sδD_b values which are of the same order of magnitude as the sδD_b values of stationary grain boundaries. The best correspondence is given by the model of Turnbull resulting in the following Arrhenius parameters: pre-exponential factor (sδD_b)₀ = 5.80 × 10⁻¹¹ m³/s and effective activation energy Q^ef_b = 144.1 kJ/mol. Based on the numerous available data which permit a relevant comparison, we conclude that the diffusivities of migrating, sliding and stationary grain boundaries in the CuAg system are of the same order of magnitude. This conclusion is in accord with the general behavior of other binary systems.