Neutron detection by measuring capture gammas in a calorimetric approach

The neutron capture detector (NCD) is introduced as a novel detection scheme for thermal and epithermal neutrons that could provide large-area neutron counters by using common detector materials and proven technologies. The NCD is based on the fact that neutron captures are usually followed by prompt gamma cascades, where the sum energy of the gammas equals to the total excitation energy of typically 6-9 MeV. This large sum energy is measured in a calorimetric approach and taken as the signature of a neutron capture event. An NCD consists of a neutron converter, comprising of constituents with large elemental neutron capture cross-section like cadmium or gadolinium, which is embedded in common scintillator material. The scintillator must be large and dense enough to absorb with reasonable probability a portion of the sum energy that exceeds the energy of gammas emitted by common (natural, medical, industrial) radiation sources. An energy window, advantageously complemented with a multiplicity filter, then discriminates neutron capture signals against background. The paper presents experimental results obtained at the cold-neutron beam of the BER II research reactor, Helmholtz-Zentrum Berlin, and at other neutron sources with a prototype NCD, consisting of four BGO crystals with embedded cadmium sheets, and with a benchmark configuration consisting of two separate NaI(Tl) detectors. The detector responses are in excellent agreement with predictions of a simulation model developed for optimizing NCD configurations. NCDs could be deployed as neutron detectors in radiation portal monitors (RPMs). Advanced modular scintillation detector systems could even combine neutron and gamma sensitivity with excellent background suppression at minimum overall expense.     

Influence of flow stress accuracy on the results of metal forming processes

During the determination of flow stress measuring errors in the range of ± 10% may easily occur. These measuring errors are transmitted to a greater or lesser extent to the FEM analysis. An evaluation of the influence of stress-strain curve errors in the FEM calculation of forming processes and its results was made using the ABAQUS programme package for the simulation of the rolling process and using the FINEL programme package for the simulation of the upsetting process. Both programmes describe force and equivalent stress with the same accuracy as the stress-strain curve does. Lateral and longitudinal flow behaviour appears relatively insensitive to measuring errors in the determination in the stress-strain curve, as does local strain. Attention should be payed, however, to the calculation of individual stress components. In these cases the errors may be compounded during the calculation.     

Characterization and evaluation of β-glucan formulations as injectable implants for protein and peptide delivery

Context: Injectable implants are biodegradable, syringeable formulations that are injected as liquids, but form a gel inside the body due to a change in pH, ions or temperature. Objective: To investigate the effect of polymer concentration, pH, ions and temperature on the gel formation of β-glucan, a natural cell-wall polysaccharide derived from barley, with particular emphasis on two-phase system formation after addition of dextran or PEG. Materials and methods: Oscillation viscometry was used to evaluate the gel character by measuring flow index (N), storage (G') and loss (G″) moduli. Two-phase systems were further characterized for hardness and syringeability using a texture analyzer. Finally, in vitro release characteristics were determined using Franz diffusion cells. Results: Oscillation viscometry revealed that only addition of dextran or PEG resulted in distinct gel formation. This was seen by a decrease in N after polymer addition. Moreover, hardness (in g) of the gels increased significantly (p?相似文献   

Plant genetic factors for iron homeostasis affect iron bioavailability in Caco-2 cells

The Caco-2 cell model is standardised for testing Fe uptake capacities of human epithelial cells from various food sources. Here, we used this system to study the impact of plant genetic Fe homeostasis factors on Fe bioavailability. The tomato fer mutant produces yellow Fe-deficient leaves due to the inability of the plant mutant to acquire Fe from soil. The chloronerva mutant lacks the metal chelator nicotianamine that is necessary for proper distribution and internal mobilization of Fe within the plant. We found that Fe uptake by Caco-2 cells was significantly compromised when mutant fer and chloronerva tomato leaf extracts had been supplied as Fe source. However after supplementation with Fe, no difference in Fe uptake were observed between fer and wild type tomato samples, whereas increased Fe uptake was obtained for chloronerva samples.Hence, our work suggests that genetic factors for plant Fe contents are important determinants for food quality.     

Finite dose skin penetration: a comparison of concentration-depth profiles from experiment and simulation

In this paper we present a mathematical diffusion model describing the transient transdermal penetration of two non-volatile substances, the lipophilic flufenamic acid and the hydrophilic caffeine, after finite dosing in an aqueous vehicle system. A striking feature of this microscopic diffusion model is its ability to predict concentration-depth profiles. Relevant input parameters are obtained from a previously published infinite dose study (Naegel et?al in Eur J Pharm Biopharm 68:368?C379, 2008; Hansen et?al in Eur J Pharm Biopharm 68:352?C367, 2008). The quality of the model has been evaluated by comparing the concentration-depth profiles in stratum corneum (SC) and deeper skin layers of the experiment with those of the simulation. The results from the experiment and the simulation are in good agreement. The study addresses benefits and shortcomings of the model, and discusses future perspectives such as incorporating different morphological regions of the SC.     

Untersuchungen zur Standsicherheit von Basaltpfeilern in Mendig (Deutschland)

As a relict of former subsurface basalt mining activities within the municipal area of the city of Mendig (Germany) an area of about 200,000 m² of disused pillar-supported mining openings still exists at about 15–20 m below the current ground surface. After the shut-down of mining, numerous pillars experienced brittle deformation and several surface collapses occurred. To prevent any further harmful damages, a risk assessment with modeling of relevant parts of the mining openings is carried out currently. The geomechanical input data for modeling are based on the results of numerous laboratory tests. The test results indicate, that pillar failure is strongly influenced by a combination of particular pillar properties such as geomechanical properties (uniaxial compression strength) as well as geometric properties (width-height-ratio, inclination of pillar longitudinal axis).     

Nanoparticles made of fluorescence-labelled Poly(L-lactide-co-glycolide): preparation, stability, and biocompatibility

Nanoparticles have recently been demonstrated in a rat model to be a promising tool for targeting inflamed areas of the intestinal mucosa in inflammatory bowel diseases whilst concentrating anti-inflammatory drugs at their site of action. Still, however, this novel concept has to be proven in vivo in humans. As a first step biodegradable and biocompatible fluorescent nanoparticles were prepared and characterized to serve as markers for successful inflammation targeting in future clinical trials. To achieve stable fluorescence labelling, fluoresceinamine was covalently bound to poly(L-lactide-co-glycolide) (PLGA) as described by Horisawa et al. The modification rate of carboxyl-end groups of the PLGA chains determined by 1H NMR was 65%. From this modified polymer, nanoparticles (FA-PLGA nanoparticles) of approximately 270 nm size were prepared via nanoprecipitation. Apart from an initial burst effect, most of the label (> 88%) appeared to be strongly bound and was leaked only slowly from the particles. In contrast, we found an immediate leakage of encapsulated sodium fluorescein with nanoparticles prepared by a double emulsion method. In degradation experiments we studied and visualized the changes in morphology and elastic properties of the FA-PLGA nanoparticles within 15 weeks using atomic force microscopy. When FA-PLGA nanoparticles were applied on an in vitro model of the intestinal mucosa (Caco-2 cell culture), only minor amounts of their fluorescent degradation products (approximately 0.02% after 6 h) were transported. In a cytotoxicity study with Caco-2 cells, FA-PLGA nanoparticles yielded an IC50 value as for plain PLGA nanoparticles. In conclusion, the polymer modification method allows to prepare fluorescently labelled nanoparticles from a well-known biodegradable pharmaceutical polymer with sufficient stability to be monitored over a period of several days. Some initial leakage of fluorescence label appears to be unavoidable but negligible with respect to potential absorption and cytotoxicity when applied in vivo.