Slope constrained topology optimization

The problem of minimum compliance topology optimization of an elastic continuum is considered. A general continuous density–energy relation is assumed, including variable thickness sheet models and artificial power laws. To ensure existence of solutions, the design set is restricted by enforcing pointwise bounds on the density slopes. A finite element discretization procedure is described, and a proof of convergence of finite element solutions to exact solutions is given, as well as numerical examples obtained by a continuation/SLP (sequential linear programming) method. The convergence proof implies that checkerboard patterns and other numerical anomalies will not be present, or at least, that they can be made arbitrarily weak. © 1998 John Wiley & Sons, Ltd.     

A combinatorial library of an {alpha}-helical bacterial receptor domain

The construction and characterization of a combinatorial libraryof a solvent-exposed surface of an -helical domain derived froma bacterial receptor is described. Using a novel solid-phaseapproach, the library was assembled in a directed and successivemanner utilizing single-stranded oligonucleotides containingmultiple random substitutions for the variegated segments ofthe gene fragment The simultaneous substitution of 13 residuesto all 20 possible amino acids was carried out in a region spanning81 nucleotides. The randomization was made in codons for aminoacids that were modelled to be solvent accessible at a surfacemade up from two of the three a-helices of a monovalent Fc-bindingdomain of staphylococcal protein A. After cloning of the PCR-amplifiedlibrary into a phagemid vector adapted for phage display ofthe mutants, DNA sequencing analysis suggested a random distributionof codons in the mutagenized positions. Four members of thelibrary with multiple substitutions were produced in Escherichiacoli as fusions to an albumin-binding affinity tag derived fromstreptococcal protein G. The fusion proteins were purified byhuman serum albumin affinity chromatography and subsequentlycharacterized by SDSelectrophoresis, CD spectroscopy and biosensoranalysis. The analyses showed that the mutant protein A derivativescould all be secreted as soluble full-length proteins. Furthermore,the CD analysis showed that all mutants, except one with a prolineintroduced into helix 2, have secondary structures in closeagreement with the wild-type domain. These results proved thatmembers of this -helical receptor library with multiple substitutionsin the solvent-exposed surface remain stable and soluble inE.coli. The possibility of using this library for a phenotypicselection strategy to obtain artificial antibodies with novelfunctions is discussed.     

Evaluation of image quality of lumbar spine images: a comparison between FFE and VGA

PURPOSE: The aim of the present study is to compare two different methods for evaluation of the quality of clinical X-ray images. METHODS: Based on fifteen lumbar spine radiographs, two new sets of images were created. A hybrid image set was created by adding two distributions of artificial lesions to each original image. The image quality parameters spatial resolution and noise were manipulated and a total of 210 hybrid images were created. A set of 105 disease-free images was created by applying the same combinations of spatial resolution and noise to the original images. The hybrid images were evaluated with the free-response forced error experiment (FFE) and the normal images with visual grading analysis (VGA) by nine experienced radiologists. RESULTS: In the VGA study, images with low noise were preferred over images with higher noise levels. The alteration of the MTF had a limited influence on the VGA score. For the FFE study, the visibility of the lesions was independent of the sharpness and the noise level. No correlation was found between the two image quality measures. CONCLUSIONS: FFE is a precise method for evaluation of image quality, but the results are only valid for the type of lesion used in the study, whereas VGA is a more general method for clinical image quality assessment. The results of the FFE study indicate that there might be a potential to lower the dose levels in lumbar spine radiography without losing important diagnostic information.     

Using mobile telephones: cognitive workload and attention resource allocation

Driver distraction is recognized as being one of the central causes of road traffic incidents and mobile telephones are tangible devices (among many other electronic devices) that can distract the driver through changes in workload. Forty participants completed a motorway route characterized by a low level of road complexity in the form of vehicle handling and information processing. A peripheral detection task (PDT) was employed to gauge mental workload. We compared effects of conversation type (simple versus complex) and telephone mode (hands-free versus handheld) to baseline conditions. The participants' reaction times increased significantly when conversing but no benefit of hands-free units over handheld units on rural roads/motorways were found. Thus, in regard to mobile telephones, the content of the conversation was far more important for driving and driver distraction than the type of telephone when driving on a motorway or similar type of road. The more difficult and complex the conversation, the greater the possible negative effect on driver distraction.     

Biogenic phosphorus in oligotrophic mountain lake sediments: differences in composition measured with NMR spectroscopy

Phosphorus (P) composition in alkaline sediment extracts from three Swedish oligotrophic mountain lakes was investigated using ³¹P-NMR spectroscopy. Surface sediments from one natural lake and two mature reservoirs, one of which has received nutrient additions over the last 3 years, were compared with respect to biogenic P composition. The results show significant differences in the occurrence of labile and biogenic P species in the sediments of the different systems. The P compound groups that varied most between these three systems were pyrophosphate and polyphosphates, compound groups known to play an important role in sediment P recycling. The content of these compound groups was lowest in the reservoirs and may indicate a coupling between anthropogenic disturbances (i.e., impoundment) to a water system and the availability of labile P species in the sediment. A statistical study was also conducted to determine the accuracy and reliability of using ³¹P-NMR spectroscopy for quantification of sediment P forms.     

Corrosion–microstructure interrelations in new low-lead and lead-free brass alloys

ABSTRACT

Stress-relieving heat treatment has been reported to deplete the corrosion resistance of new low-lead and lead-free brass alloys. How the heat treatment, processing and material composition relates to the microstructure and corrosion performance is not well understood. The present study aims to fill this knowledge gap by mapping stress-relieving annealing conditions and different standardised compositions to their respective microstructures and dezincification performance. It was found that loss of corrosion resistance was only the most severe for alloys with higher aluminium and iron content. These alloys displayed significant precipitation of intermetallic aluminium arsenide particles on grain boundaries, twins and lead particles, as well as the formation of β-phase along grain boundaries.

This paper is part of a Thematic Issue on Copper and its Alloys.     

Evacuation experiments in a virtual reality high‐rise building: exit choice and waiting time for evacuation elevators

The egress strategy in high‐rise buildings has traditionally been based on the sole use of stairs for evacuation. However, it is becoming more common to include evacuation elevators in the egress strategy in high‐rise buildings. Traditionally, evacuation elevators have not been allowed as an evacuation route, and people have been instructed to not use elevators in case of fire. This means that people might still not consider evacuation elevators even if they are designed to be safe in case of fire. Even if people choose evacuation elevators, they might not be willing to wait very long for an elevator to arrive. Virtual reality (VR) experiments were conducted to study exit choice and the waiting time for evacuation elevators in high‐rise buildings. The experiment was performed in a VR lab with a VR model of an existing high‐rise building. Results suggest that a simple way‐finding system using green flashing lights can influence people to more likely choose the elevator as their first evacuation choice. The results also show that the general trend is that people wait for either a limited time (<5 min) or a long time (>20 min). Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluation of different oxygen carriers for biomass tar reforming (I): Carbon deposition in experiments with toluene

In this work, an innovative method for gas conditioning in biomass gasification is analyzed. The objective is to remove tar by selectively reforming the unwanted hydrocarbons in the product gas with a chemical looping reformer (CLR), while minimizing the carbon formation during the process. Toluene, in a concentration of 600-2000 ppmv, was chosen as a tar model compound. Experiments were performed in a TGA apparatus and a fixed bed reactor. Four oxygen carriers (60% NiO/MgAl₂O₄ (Ni60), 40% NiO/NiAl₂O₄ (Ni40), 40% Mn₃O₄/Mg-ZrO₂ (Mn40) and FeTiO₃ (Fe)) were tested under alternating reducing/oxidizing cycles. Several variables affecting the reducing cycle were analyzed: temperature, time for the reduction step and H₂O/C₇H₈ molar ratio. Ni40 and Mn40 presented interesting characteristics for CLR of biomass tar. Both showed stable reactivity to C₇H₈ after a few cycles. Ni40 showed a high tendency to carbon deposition compared to Mn40, specially at high temperatures. Carbon deposition could be controlled by decreasing the temperature and the time for the reduction step. The addition of water also reduced the amount of carbon deposited, which was completely avoided working with a H₂O/C₇H₈ molar ratio of 26.4.     

Low-temperature aerosol flow reactor method for preparation of surface stabilized pharmaceutical nanocarriers

Nanoparticles can be used to improve the delivery of many drugs, especially peptides and proteins. Although several methods are available for polymeric nanoparticle preparation, there are few single-stage processes that produce dry, solid nanoparticles that can be easily re-dispersed in pharmaceutical vehicles. The aerosol flow reactor method is a single-stage process that has been used for the preparation of multicomponent, coated nanoparticles under uniform temperature and gas flow field. However, it is traditionally used with high synthesis temperatures. In the present study, the aerosol flow reactor method was further optimized for processing and surface stabilization of pharmaceutical nanoparticles containing temperature sensitive biomolecules. In the developed method, drug-loaded carrier nanoparticles consisting of a biodegradable polymer (Eudragit L100) and a drug (phenylephrine hydrochloride) were first produced by aerosol droplet drying and subsequently coated in the gas phase. The carrier particles were coated with l-leucine in order to inhibit agglomeration of the nanoparticles in solutions before administration. In the coating process, a side stream of l-leucine vapor was directed into the main aerosol flow containing the drug-loaded carriers. The mixing with the main flow at ambient temperature induced a supersaturation of l-leucine vapor and condensation on the carrier particles. The results demonstrate that solid, hydrodynamically stable drug-loaded polymeric nanoparticles can be produced with a thin l-leucine coating. The low process temperature enables the surface engineering of particles loaded with temperature sensitive drugs or bioactive materials to be utilized for drug delivery purposes.