STM observation of steps and terraces on tungsten (211) surface

Thermally cleaned W(211) surface with 0.7 degrees miscut consists of (211) terraces separated by monoatomic steps. When the surface is exposed to oxygen and subsequently annealed at 1100-1900 K, the width of (211) terraces increases and multilayer steps are formed. Similar step bunching is observed during routine cleaning of the sample by annealing in oxygen and thermal flashing in ultra high vacuum. During such cleaning procedure islands of c(6 x 4) reconstruction are observed.     

Preservation of high resolution protein structure by cryo-electron microscopy of vitreous sections

We have quantitated the degree of structural preservation in cryo-sections of a vitrified biological specimen. Previous studies have used sections of periodic specimens to assess the resolution present, but preservation before sectioning was not assessed and so the damage due particularly to cutting was not clear. In this study large single crystals of lysozyme were vitrified and from these X-ray diffraction patterns extending to better than 2.1 Å were obtained. The crystals were high pressure frozen in 30% dextran, and cryo-sectioned using a diamond knife. In the best case, preservation to a resolution of 7.9 Å was shown by electron diffraction, the first observation of sub-nanometre structural preservation in a vitreous section.     

Thermo-mechanical characteristics of UV-irradiated polyurethane elastomers extended with α, ω-alkane diols

A series of polyurethane elastomers were prepared by the reaction of poly ε-caprolactone and 4,4′-diphenylmethane diisocyanate. The prepolymer was extended using α, ω-alkane diols as chain extenders having 2-10 methylene units in their structure. The synthesized samples were irradiated for 50, 100 and 200 h in an ultra violet (UV) exposure unit. Modifications in the chemical structure before and after irradiation were characterized using Fourier Transform Infrared spectroscopy. The thermal and mechanical properties were affected by the ultra violet irradiation time and the number of methylene units in the chain extenders. The experimental results indicated that the morphological structure changed during irradiation as a consequence of hard segment and soft segment degradation.     

Liquid crystalline polyethers based on conformational isomerism

Summary Nonradiative singlet energy transfer has been used to monitor the formation of micelles by diblock copolymers of poly(styrene) and poly(oxyethylene). The acceptor is placed at the junction between the two blocks in sample A1. The donor is placed either at the junction point between the blocks (D1) or free end of the block of poly(styrene) (D2). The experiment finds similar efficiencies of nonradiative singlet energy transfer in micelles formed by D1 and A1, and micelles formed by D2 and A1. This result implies that the free ends of the insoluble blocks do not seek out the center of mass of the micelle, but instead have a distribution throughout the micelle that is similar to the distribution of the junction points. Therefore the result confirms a crucial prediction from a recent simulation of the internal structure of the micelle formed by diblock copolymers in a selective solvent.     

Preservation of fatty duck liver by high pressure treatment

Fatty liver samples from duck were treated with high pressures and packaged in multilayer films. Microbiological analysis, permeability of the films to oxygen and fat loss, caused by melting, were assessed after pressure or thermal treatment. Microbiological analysis showed a noteworthy reduction in the total aerobic mesophilic flora and eradication of the coliform flora, whichever film or treatment was used. Nevertheless, a significant bacterial flora was observed during storage at 4 °C from 42 days with a polyethylene/polyamide/polyethylene film and a sample which had been treated with pressure. But, treatment at 550 MPa for 55 °C and 20 min, in combination with two low oxygen permeability films (ethylene and vinyl alcohol copolymer) gave a product with long storage life (90 days) at 4 °C and a significant reduction in the melting of lipids.     

Visualization of crust formation during hot-air-drying via micro-CT

Abstract

Nowadays, hot-air-drying (HAD) is the most common process for the production of dried fruits and vegetables till now. It is well known that HAD has a big influence on product structure leading to effects like shrinkage or case-hardening. While shrinkage has already been documented throughout the drying process, case-hardening or the formation of a crust has only been shown for the dried product. In this study, a three-step approach consisting of a HAD-, a freezing-, and a freeze-drying step is used to show the development of a crust of carrot discs throughout a HAD process. With this method, the crust structures created during HAD were preserved and could be analyzed in a dry state with cone-beam micro-CT measurements. Crust thickness increased significantly during HAD and crust formation started before a relative moisture content of X/X₀ = 0.5.     

Morphological determinants of bite force capacity in insects: a biomechanical analysis of polymorphic leaf-cutter ants

The extraordinary success of social insects is partially based on division of labour, i.e. individuals exclusively or preferentially perform specific tasks. Task preference may correlate with morphological adaptations so implying task specialization, but the extent of such specialization can be difficult to determine. Here, we demonstrate how the physical foundation of some tasks can be leveraged to quantitatively link morphology and performance. We study the allometry of bite force capacity in Atta vollenweideri leaf-cutter ants, polymorphic insects in which the mechanical processing of plant material is a key aspect of the behavioural portfolio. Through a morphometric analysis of tomographic scans, we show that the bite force capacity of the heaviest colony workers is twice as large as predicted by isometry. This disproportionate ‘boost’ is predominantly achieved through increased investment in muscle volume; geometrical parameters such as mechanical advantage, fibre length or pennation angle are likely constrained by the need to maintain a constant mandibular opening range. We analyse this preference for an increase in size-specific muscle volume and the adaptations in internal and external head anatomy required to accommodate it with simple geometric and physical models, so providing a quantitative understanding of the functional anatomy of the musculoskeletal bite apparatus in insects.     

Evaluation of the usefulness of serial combination processes for drying of apples

Abstract

Serial combination drying processes are currently studied as alternatives to conventional drying processes. Compared to freeze-drying (FD), serial combination drying appears to be faster and less expensive, while providing better product quality than hot-air drying (HAD) and microwave-vacuum drying (MVD) as previously demonstrated for carrots. Using the example of carrots, it has also been shown that the drying front moves radially outwards over the course of FD. This unexpected behavior was suggested to originate from the carrots’ heterogeneous structure. It was hypothesized that apple pieces behave differently. Here, this hypothesis was proven by using micro-computed tomography measurements of partly freeze-dried apple pieces. In order to improve the drying process of apple pieces, several single and combination drying processes were carried out. Processes were evaluated by using drying time and sample quality as relevant parameters. Sample quality was determined by analyzing the 3D-structure, rehydration behavior, color, and ingredient retention. Results showed that single MVD is a well suitable drying technique for apple pieces, producing dried products of equal quality to FD. Different from carrots, serial combinations are not necessary to improve the quality of dried apple pieces. Nonetheless, especially a combination of HAD and MVD was useful to obtain specific structures such as puffed pores that did not result from single MVD.