Re-evaluation of correction factors of a primary standard graphite calorimeter in 60Co gamma ray beams as a basis for the appointment of the BEV absorbed dose rate to water reference value

The graphite calorimeter of the Federal Office of Metrology and Surveying (BEV-Bundesamt für Eich- und Vermessungswesen) was established in the 1980s as the primary standard for the absorbed dose to water for (60)Co gamma ray beams. To maintain the primary standard at an international level the graphite calorimeter and its corresponding components had to undergo a refurbishment and modernisation process. The correction factors of the graphite calorimeter were re-evaluated with Monte Carlo and experimental methods to obtain improved values. These are the correction for the effect of the gaps (1.0061), the scaling correction (0.9998), the correction for the difference in air attenuation (0.9971) and the corrections for the effective measurement depths in the graphite phantom for the graphite calorimeter (0.9886) and the CC01-105 ionisation chamber (0.9913). Consequently, it was necessary to change the reference value for the absorbed dose rate to water of the (60)Co teletherapy unit used for the calibration of secondary standard dosemeters.     

Semi-natural Forested Landscape under a Bark Beetle Outbreak: A case study of the Bohemian Forest (Czech Republic)

Long-term and lasting human interference in forest ecosystems in the Bohemian Forest has resulted in the loss of some equilibrium mechanisms and hence increased susceptibility to ecological disturbances. Two methods for estimating bark beetle outbreaks in spruce forests are reported: an assessment of the susceptibility of individual trees to attack according to crown structure characteristics; and the use of remotely sensed data and image processing techniques to quantify changes in forest cover. The results document a significant increase in the area of highly damaged and dead forest classes, from 1% in 1987 to 16% in 1998, and a decrease in the area of healthy and moderately damaged spruce classes from 71% in 1987 to 52% in 1998. A possible approach to managing mountain Norway spruce ecosystems invaded by bark beetle in the Bohemian Forest is proposed.     

Model-based scale-up of vacuum contact drying of pharmaceutical compounds

An integrated methodology for the scale-up of vacuum contact drying with intermittent agitation is described in this work. The methodology combines a mathematical model of vacuum contact drying, based on differential transient heat and energy balances, and a small-scale experimental apparatus for model validation and parameter estimation. The validated model was used for the estimation of drying times of six different pharmaceutical compounds at the pilot and manufacturing scale over a range of drying conditions – pressure 15–200 mbar, temperature 45–70 °C, solvents: acetone, water, methanol, n-propanol, and isopropyl acetate. The mean difference between predicted and actual drying times for the six compounds was less than 9%, which is considered a significant improvement over current semi-empirical approaches to vacuum contact drying scale-up.     

Surface characterization of palladium-copper bimetallic catalysts by FTIR spectroscopy and test reactions

Different bi-metallic palladium-copper catalysts have been prepared according to different sequences of impregnation of a commercial alumina. CO adsorption followed by FTIR spectroscopy was performed in order to identify the nature of the superficial sites. Two test reactions were also used to characterize the nature of the active surface site: gas phase toluene hydrogenation was selected in order to show the hydrogenating activity of metallic palladium, whereas the reaction of decomposition of ethanol, which exhibits 100% selectivity in the formation of ethanal on pure copper catalysts, was also studied on this series of catalysts. The results obtained by both methods are complementary. By comparison with the behaviour of pure palladium or copper based catalysts, they allow to propose hypotheses on the surface composition: separated phases, alloys or a phase covered by the other one.     

Direct assay of enzymes in heme biosynthesis for the detection of porphyrias by tandem mass spectrometry. Porphobilinogen deaminase

We report a new assay of human porphobilinogen deaminase (PBGD). Deficiency in this enzyme activity causes acute intermittent porphyria, the most common disorder of heme biosynthesis. The assay involves incubation of blood erythrocyte lysate with porphobilinogen, the natural PBGD substrate. Two subsequent enzymes in the heme biosynthetic pathway, uroporphyrinogen III synthase and uroporphyrinogen decarboxylase, are deactivated by heating so that their activity does not interfere with the PBGD assay. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) is used to monitor the production of uroporphyrinogen I and thus measure the PGBD activity. A simple and efficient workup using liquid-liquid extraction with >90% product recovery was employed to avoid separation by liquid chromatography. The assays show good reproducibility (+/-3.3%) and linear dependence of the uroporphyrinogen I formation on incubation time and protein amount. The Km of PGBD for porphobilinogen was measured as 11.2 +/- 0.5 microM with Vmax of 0.0041 +/- 0.0002 microM/(min.mg of hemoglobin). The coefficient of variation of PBGD activity among several unaffected individuals (12%) is significantly lower than the decrease due to acute intermittent porphyria (50%).     

Direct assay of enzymes in heme biosynthesis for the detection of porphyrias by tandem mass spectrometry. Uroporphyrinogen decarboxylase and coproporphyrinogen III oxidase

We report new assays of enzymes uroporphyrinogen decarboxylase (UROD) and coproporphyrinogen III oxidase (CPO) in the heme biosynthetic pathway. The assays were developed for use in clinical diagnostics of inherited disorders porphyria cutanea tarda and hereditary coproporphyria, respectively. Electrospray ionization tandem mass spectrometry is used to monitor the decarboxylation of pentaporphyrinogen I or uroporphyrinogen III catalyzed by UROD and to determine the enzyme activity in human erythrocytes by measuring the production of coproporphyrinogen I or III. The Km value for pentaporphyrinogen I was measured as 0.17 +/- 0.03 microM. A mass spectrometric assay was also developed for the two-step decarboxylative oxidation of coproporphyrinogen III to protoporphyrinogen IX catalyzed by CPO in mitochondria from human lymphocytes (Km = 0.066 +/- 0.009 microM). The assays show good reproducibility, use simple workup by liquid-liquid extraction of enzymatic products, and employ commercially available substrates and internal standards.     

Routine individual monitoring of aircraft crew exposure: Czech experience and results since 1998

ICRP Publication 60 recommended that the radiation exposure due to the cosmic component at high altitudes be considered when appropriate as part of occupational exposure to the radiation. The recommendation was incorporated to the Czech regulation in 1997, and the studies on how to perform individual dosimetry of Czech companies aircraft crew started immediately. The individual monitoring values were calculated using the Transport code CARI. The results obtained since the beginning have been recalculated, now with the version 6. The information on the flight schedules and the participation of aircraft crew in the flight were received from the air company. Routine individual dosimetry had started in 1998. Main results for the period 1998-2003 are as follows: both relative frequencies, as well as, average annual effective doses vary with the company and with the year, without any evident general tendency; the average annual values of E were between 1.5 and 2 mSv; and collective effective dose increased regularly, from approximately 1.5 manSv to >2.2 manSv. More detailed analysis is presented, including the verification of the procedure by a series of onboard experimental measurements.     

Adhesion and growth of vascular smooth muscle cells in cultures on bioactive RGD peptide-carrying polylactides

The surface of poly(l-lactide) (PLLA) films deposited on glass coverslips was modified with poly(dl-lactide) (PDLLA), or 1:4 mixtures of PDLLA and PDLLA-b-PEO block copolymers, in which either none, 5% or 20% of the copolymer molecules carried a synthetic extracellular matrix-derived ligand for integrin adhesion receptors, the GRGDSG oligopeptide, attached to the end of the PEO chain. The materials, perspective for vascular tissue engineering, were seeded with rat aortic smooth muscle cells (11,000 cells/cm²) and the adhesion, spreading, DNA synthesis and proliferation of these cells was followed on inert and bioactive surfaces. In 24-h-old cultures in serum-supplemented media, the number of cells adhering to the PDLLA-b-PEO copolymer was almost eight times lower than that on the control PDLLA surface. On the surfaces containing 5% and 20% GRGDSG-PEO-b-PDLLA copolymer, the number of cells increased 6- and 3-fold respectively, compared to the PDLLA-b-PEO copolymer alone. On PDLLA-b-PEO copolymer alone, the cells were typically round and non-spread, whereas on GRGDSG-modified surfaces the cell spreading areas approached those found on PDLLA, reaching values of 991 μm² and 611 μm² for 5% and 20% GRGDSG respectively, compared to 958 μm² for PDLLA. The cells on GRGDSG-grafted copolymers were able to form vinculin-containing focal adhesion plaques, to synthesize DNA and even proliferate in a serum-free medium, which indicates specific binding to the GRGDSG sequences through their adhesion receptors.     

Room-temperature bonding for plastic high-pressure microfluidic chips

A generic method for the rapid, reproducible, and robust bonding of microfluidic chips fabricated from plastics has been developed and optimized. One of the bonding surfaces is exposed to solvent vapor prior to bringing the mating parts into contact and applying a load. Nanoindentation measurements performed by atomic force microscopy show that a reversible material softening occurs upon exposure to solvent vapor. Subsequent exposure of the bonded chip to UV light then strengthens the bond between mating parts and increases the burst pressure by 50% due to partial cross-linking and chain scission reactions as measured by size exclusion chromatography-multiangle light scattering (SEC-MALS). Performing all steps of this procedure at room temperature eliminates channel distortion observed during thermal bonding and affords channels with highly uniform cross-sectional dimensions. Our technique enables chips resistant to pressures as high as 34.6 MPa.