Short-term power sources for tokamaks and other physical experiments

The Compass-D tokamak is being planned to move from UKAEA Culham (England) be and reinstalled in IPP Prague (Czech Republic). An overview of Compass-D energetics is described in short. The new power sources have to be designed. Alternative solutions of power sources have been investigated. Ignitrons and mechanical breakers can be replaced by modern high-power semiconductors. With respect to the need of accumulated energy, new technologies of energy storage - supercapacitors and high-speed flywheels, not applied up to now in similar fusion projects, are characterized in comparison with traditional ones - capacitors and big motor-flywheel generators. It is shown that these technologies enhance possibilities in arrangement of power supplies for tokamaks as well as for other high-power demanding experiments with pulse length from fraction to tens of seconds.     

A new approach to the preparation of large surface area poly(styrene-co-divinylbenzene) monoliths via knitting of loose chains using external crosslinkers and application of these monolithic columns for separation of small molecules

Poly(styrene-divinylbenzene) monoliths have been hypercrosslinked using a Fe³⁺ catalyzed Friedel–Crafts reaction involving three external crosslinkers (1) 4,4′-bis(chloromethyl)-1,1′-biphenyl, (2) α,α′-dichloro-p-xylene, and (3) formaldehyde dimethyl acetal. The first crosslinker was found to produce monoliths with the best chromatographic performance. The effects of a number of variables affecting the hypercrosslinking reaction were studied in detail. These variables included: (i) the temperature and time used for polymerization of the precursor monoliths, (ii) the amount and loading procedure of the external crosslinker and catalyst, and, (iii) the temperature and reaction time of the Friedel–Crafts alkylation. Polymers with extremely large surface areas reaching up to 900 m²/g were obtained using a precursor monolith polymerized for only 2.5 h, and hypercrosslinked with 4,4’-bis(chloromethyl)-1,1′-biphenyl. The increased performance of monoliths modified using this new procedure is comparable to the performance obtained with monolithic polymers containing chloromethylstyrene. However, the preparation of the poly(styrene-divinylbenzene) precursor is simpler than that of conterparts containing chloromethylstyrene. The hypercrosslinked monoliths in capillary columns were tested in an isocratic reversed phase liquid chromatography separation using a mixture comprised of acetone and six alkylbenzenes. Column efficiencies for retained analytes exceeded 70,000 plates/m.     

Multi-Scale Analysis of Vacuum Contact Drying

The modeling of the unit operation of vacuum contact drying is approached as a multi-scale problem. At the particle assembly length scale, effective transport properties (thermal conductivity, relative gas- and liquid-phase permeability) have been determined computationally by simulations on reconstructed porous media and verified by direct measurements. A distributed-parameter model of vacuum contact drying including liquid and vapor flow and differential energy balance has been formulated and used for the calculation of drying time as function of vacuum level, temperature, vessel diameter, and batch size at the unit operation length scale. Drying curves for a model system of sodium carbonate–isopropanol have been measured experimentally and compared with the model predictions. A very good agreement has been found.     

Label-free determination of picogram quantities of DNA by stripping voltammetry with solid copper amalgam or mercury electrodes in the presence of copper

Highly sensitive label-free techniques of DNA determination are particularly interesting in relation to the present development of the DNA sensors. We show that subnanomolar concentrations (related to monomer content) of unlabeled DNA can be determined using copper solid amalgam electrodes or hanging mercury drop electrodes in the presence of copper. DNA is first treated with acid (e.g., 0.5 M perchloric acid), and the acid-released purine bases are directly determined by the cathodic stripping voltammetry. Volumes of 5-3 microL of acid-treated DNA can easily be analyzed, thus making possible the determination of picogram and subpicogram amounts of DNA corresponding to attomole and subattomole quantities of 1000-base pair DNA. Application of this determination in DNA hybridization detection is demonstrated using surface H for the hybridization (superparamagnetic beads with covalently attached DNA probe) and the mercury electrodes only for the determination of DNA selectively captured at surface H.     

Physiology in daily hemodialysis in terms of the time average concentration/time average deviation concept

Quotidian or “daily" hemodialysis (DHD) is practiced in widely differing schedules. Yet all those schedules are reported to significantly ameliorate clinical outcome of patients. It is, however, not clear what is the actual cause of this amelioration. Rational possibilities include increased overall dialysis dose and increased weekly time. Conventional mathematical approaches (Kt/V_urea concept, equivalent renal clearance) cannot be used to study those issues because they do not consider number of dialysis per week and thus ignore the issue of treatment schedule “unphysiology.” The time average concentration/time average deviation (TAC/TAD) concept may well be used to visualize impact of treatment schedule on both plasma urea profile statics (TAC) and dynamics (TAD). The concept may further help to stratify studies for elucidation of the key factors of clinical outcome improvement seen on DHD. Actual physiologic mechanisms responsible for this improvement are to be sought among those with having derivative component (i.e., reacting to the rate of a change rather than to the magnitude of the change). It should, however, be kept in mind that the TAC/TAD concept is able to assess unphysiology of a treatment schedule, not unphysiology of a single treatment session.     

Czech results at criticality dosimetry intercomparison 2002

Two criticality dosimetry systems were tested by Czech participants during the intercomparison held in Valduc, France, June 2002. The first consisted of the thermoluminescent detectors (TLDs) (Al-P glasses) and Si-diodes as passive neutron dosemeters. Second, it was studied to what extent the individual dosemeters used in the Czech routine personal dosimetry service can give a reliable estimation of criticality accident exposure. It was found that the first system furnishes quite reliable estimation of accidental doses. For routine individual dosimetry system, no important problems were encountered in the case of photon dosemeters (TLDs, film badge). For etched track detectors in contact with the 232Th or 235U-Al alloy, the track density saturation for the spark counting method limits the upper dose at approximately 1 Gy for neutrons with the energy >1 MeV.     

Affinity capture and elution/electrospray ionization mass spectrometry assay of phosphomannomutase and phosphomannose isomerase for the multiplex analysis of congenital disorders of glycosylation types Ia and Ib

We report a new application of affinity capture-elution electrospray mass spectrometry (ACESI-MS) to assay the enzymes phosphomannomutase (PMM) and phosphomannose isomerase (PMI), which when deficient cause congenital disorders of glycosylation CDG-type Ia and type Ib, respectively. The novel feature of this mass-spectrometry-based assay is that it allows one to distinguish and quantify enzymatic products that are isomeric with their substrates that are present simultaneously in complex mixtures, such as cultured human cell homogenates. This is achieved by coupled assays in which the PMM and PMI primary products are in vitro subjected to another enzymatic reaction with yeast transketolase that changes the mass of the products to be detected by mass spectrometry. The affinity purification procedure is fully automated, and the mass spectrometric analysis is multiplexed in a fashion that is suitable for high-throughput applications.