Weinanalyse

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High gravity batch and continuous processes for beer production: Evaluation of fermentation performance and beer quality

This study deals with two innovative brewing processes, high gravity batch and complete continuous beer fermentation systems. The results show a significant influence of the variables such as concentration and temperature on the yield factor of the substrate into ethanol and consequently on the productivity of the high gravity batch process. The technological feasibility of continuous production of beer based on yeast immobilization on cheap alternative carriers was also demonstrated. The influence of process parameters on fermentation performance and quality of the obtained beers was studied by sensorial analysis. No significant difference in the degree of acceptance between the obtained products and some traditional market brands was found. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

The diameter of the acyclic Birkhoff polytope

In this work we give an interpretation of vertices and edges of the acyclic Birkhoff polytope, T_n=Ω_n(T), where T is a tree with n vertices, in terms of graph theory. We generalize a recent result relatively to the diameter of the graph G(T_n).     

Iridium and Rhodium as Permanent Chemical Modifiers for the Determination of Ag, As, Bi, Cd, and Sb by Electrothermal Atomic Absorption Spectrometry

Performance of graphite platforms coated with Ir, Rh, and a mixture of both, as permanent modifiers for Ag, As, Bi, Cd, and Sb, was evaluated. The coating process is very simple: a solution containing Ir, Rh, or a mixture of both is pipetted on the platform inserted in a graphite tube, and this is submitted to a temperature program. High pyrolysis temperatures are allowed, especially for As and Bi, 1400°C, in the Ir + Rh-coated platform. The sensitivity remains about the same for all analytes with different coatings, except for As in the Ir-coated platform, for which a remarkable gain was obtained in comparison to the other coatings. The lifetimes of the treated tubes were in the range 50 to more than 1000 cycles, being especially long for Sb and Ag in the Rh-coated platform, more than 600 and 1000 cycles, respectively. The Rh coating could not be used for Bi and Cd. Analysis of a certified reference water and of acid oyster tissue digests showed the absence of interference and good precision. Advantages of the permanent coatings are the possibility of low blanks byin situcleaning of the modifier and shorter analysis time.     

Flow-through solid-phase based optical sensor for the multisyringe flow injection trace determination of orthophosphate in waters with chemiluminescence detection

In this work, a novel flow-through solid-phase based chemiluminescence (CL) optical sensor is described for the trace determination of orthophosphate in waters exploiting the multisyringe flow injection analysis (MSFIA) concept with multicommutation. The proposed time-based injection flow system relies upon the in-line derivatisation of the analyte with ammonium molybdate in the presence of vanadate, and the transient immobilisation of the resulting heteropolyacid in a N-vinylpyrrolidone/divinylbenzene copolymer packed spiral shape flow-through cell located in front of the window of a photomultiplier tube. The simultaneous injection of well-defined slugs of luminol in alkaline medium and methanol solution towards the packed reactor is afterwards performed by proper switching of the solenoid valves. Then, the light emission from the luminol oxidation by the oxidant species retained onto the sorbent material is readily detected. At the same time, the generated molybdenum-blue compound is eluted by the minute amount of injected methanol, rendering the system prepared for a new measuring cycle. Therefore, the devised sensor enables the integration of the solid-phase CL reaction with elution and detection of the emitted light without the typical drawbacks of the molybdenum-blue based spectrophotometric procedures regarding the excess of molybdate anion, which causes high background signals due to its self-reduction. The noteworthy features of the developed CL-MSFIA system are the feasibility to accommodate reactions with different pH requirements and the ability to determine trace levels of orthophosphate in high silicate content samples (Si/P ratios up to 500). Under the optimised conditions, a dynamic linear range from 5 to 50 μg P l⁻¹ for a 1.8 ml sample, repeatability better than 3.0% and a quantification limit of 4 μg P l⁻¹ were attained. The flowing stream system handles 11 analysis h⁻¹ and has been successfully applied to the determination of trace levels of orthophosphate in environmental samples such as mineral, ground, tap and pond waters as well as samples from a water-steam cycle of an incineration plant. The t-test comparison of the means for the developed optical sensor and the molybdenum-blue spectrophotometric APHA/AWWA/WPCF reference method revealed that there is no evidence of significant differences between the obtained results at the 95% confidence level.     

Method to reduce the memory effect of mercury in the analysis of fish tissue using inductively coupled plasma mass spectrometry

The routine determination of mercury (Hg) by inductively coupled plasma mass spectrometry (ICP-MS) is affected by a pronounced memory effect in the sample introduction system. This results in long washout times for the analyte, which affects the accuracy and reliability of the analytical procedure. By using a combination of flow injection sample introduction and a sulfur-containing compound in the carrier solution, it was possible to decrease the memory effect of mercury to that for the internal standard (rhodium). The carrier solution contained 2-mercaptoethanol (2-ME) and the developed method was evaluated using three different fish tissue certified reference materials: CRM 464 (BCR, Brussels); DORM-1; and DORM-2 (NRC, Canada). The samples were mineralized using a combination of concentrated nitric acid and hydrogen peroxide and heating in a closed microwave oven. The developed flow injection ICP-MS procedure gave values for total mercury in all three CRM materials in agreement with the certified concentration range. Cold vapour atomic fluorescence spectrometry (CV-AFS) confirmed the results from the developed method. The developed flow injection method had a detection limit (defined as three times the standard deviation of the blank concentration) for mercury of 5.1 μg l⁻¹.     

Structural models in consumer credit

We propose a structural credit risk model for consumer lending using option theory and the concept of the value of the consumer’s reputation. Using Brazilian empirical data and a credit bureau score as proxy for creditworthiness we compare a number of alternative models before suggesting one that leads to a simple analytical solution for the probability of default. We apply the proposed model to portfolios of consumer loans introducing a factor to account for the mean influence of systemic economic factors on individuals. This results in a hybrid structural-reduced-form model. And comparisons are made with the Basel II approach. Our conclusions partially support that approach for modelling the credit risk of portfolios of retail credit.     

Innovative mechanical device for the post-tensioning of glass fiber reinforced polymer bars for masonry type retrofit applications

A mechanical device specially designed for the application of low-level post-tensioning forces to glass fiber reinforced polymer (GFRP) bars has been developed at the University of Missouri-Rolla. Some of the advantageous features of this device are that it is simple to assemble and the low-level post-tensioning forces can be applied manually and safely without the need for hydraulic jacks or heavy equipment. This device has been conceived with the main objective of retrofitting masonry buildings, some of which remain in service despite large, open cracks leading to considerable instability and serviceability concerns. According to the method derived in this paper, GFRP bars are installed in artificially imposed grooves and then post-tensioned with low-level stresses with the main objective to partially close these cracks, such that the serviceability and in-plane capacity of un-reinforced masonry (URM) buildings may be regained. In this paper we describe the mechanical components of this device, along with its advantageous features and potential application for the retrofit of URM walls.     

Interdiffusion at Sb/Ge interfaces induced in thin multilayer films by nanosecond laser irradiation

Thin films consisting of 3 or 4 Sb and Ge alternating layers are irradiated with single nanosecond laser pulses (12 ns, 193 nm). Real time reflectivity (RTR) measurements are performed during irradiation, and Rutherford backscattering spectrometry (RBS) is used to obtain the concentration depth profiles before and after irradiation. Interdiffusion of the elements takes place at the layer interfaces within the liquid phase. The reflectivity transients allow to determine the laser energy thresholds both to induce and to saturate the process being both thresholds dependent on the multilayer configuration. It is found that the energy threshold to initiate the process is lower when Sb is at the surface while the saturation is reached at lower energy densities in those configurations with thinner layers.     

Selective synthesis of some 5-hydrazono-5,6,7,8-tetrahydro-2H-1-benzopyran-2-ones

A simple, highly selective transformation of 5,6,7,8-tetrahydro-2H-1-benzopyran-2,5-diones 1–3 and 14 with some phenylhydrazines and heterocyclic hydrazines to 5-hydrazono-2H-1-benzopyran-2-ones 4–12 and 15–16 is described. Under more severe conditions the hydrazonoquinoline derivative 17 was obtained from the benzopyran derivative 3 and Phenylhydrazine.