Defocus image contrast in hexagonally-ordered mesoporous material.

A transmission electron microscope was used to characterize a powder form of hexagonally-ordered mesoporous silica material. The structural symmetry built into this amorphous material allowed one to obtain three characteristic images, i.e. a hexagonal honey-comb structure and wide/narrow parallel lines. These images were found to originate primarily from phase contrast, which changed sensitively with defocusing. To further understand the contrast behaviour of these images, an analytical form of the defocus contrast theory was developed and applied to the simulation of the characteristic wide/narrow parallel line images. The simulation was found to be in good qualitative agreement with experiments, where changes in focus conditions and specimen thickness were predicted to alter the contrast in the resulting parallel-line type images.

Quantitative TEM analysis of a hexagonal mesoporous silicate structure.

TEM analysis of mesoporous materials is generally undertaken to give qualitative results. Accurate quantitative analysis is demonstrated in this study. A systematic image analysis of a powder form of a hexagonal mesoporous material known as KIT-6 is conducted using a transmission electron microscope (TEM). Three types of image contrast typically appear in this material (a hexagonal honeycomb structure, wide and narrow parallel lines). The honeycomb face is used to characterise this material in terms of a conventional 2-D hexagonal structure and the d-spacings for the (100) and (110) planes are experimentally measured in varying focus conditions. A tilting experiment is conducted to determine how the angle of tilt affects the line spacing and their visibility. Tilting has very little effect on the line spacing, whereas it affects the visibility of both the wide and narrow lines by limiting an angle range of visibility. The hexagonal lattice structure parameter determined by TEM method is found to be approximately 7% lower than that calculated by low-angle X-ray diffraction. Thus we conclude that TEM data can be used to determine the geometry and dimensions of hexagonal mesoporous silica materials, with a small error in the hexagonal lattice parameter.

Detection of ferricyanide as a probe for the effect of hematocrit in whole blood biosensors.

Measurement of the concentration of an analyte in whole blood can be influenced by a range of factors; the red cell content or hematocrit (Hct) of the sample, the distribution and rate of movement of analyte between red cells and plasma, the amount of protein in solution, the viscosity of the sample and fouling of the sensor. The effect of the red cells is the major factor that must be taken into account. Using the analyte molality rather than the analyte molarity, the theoretical response for a range of analytes which are found in plasma and in the red cells can be calculated. For an analyte which is found in plasma alone, the effect of hematocrit is significant, with a bias of -1% per %Hct; if the analyte can freely and rapidly diffuse between the red cells and plasma, this bias is reduced to zero. Using ferrocyanide as a model analyte, the effects of fouling and reduced sample viscosity were measured to be -0.2% per %Hct, giving an overall bias of -1.2% per %Hct, a level of bias which is not clinically acceptable. This bias can be negated by measuring the hematocrit separately and incorporating it into the measurement algorithm. Such a correction is essential for the correct measurement of the concentration of an analyte in whole blood.

Proving sexual assault.

The framework provided by therapeutic jurisprudence is used to examine the rules of evidence that govern sexual assault trials. The concern is with the impact of the trial process on the accusing witness. In the first part a personal narrative is used to put the legal rules in context. Psychological sources are used in discussing the reasons for presenting such a narrative. In the second part, the effect of statutory changes to the common law rules as effected in NSW in 1981 is analyzed. Drawing upon the Heroines of Justice report the paper suggests that the intention of reducing the trauma of the victim has not yet been achieved. It is suggested that this failure is not unique. A change in attitude on the part of those involved in the trial process is necessary, and the hope is that this paper might contribute to such a change.

Trends in electrochemical biosensors.

The development of electrochemically based biosensors is discussed in the context of what has been learned from the successful development of glucose biosensors. Some future trends are discussed.

Would reading an account of an event refresh your memory?

Witnesses to an event who have prepared an account of it may be given an opportunity to review this account or to read another account before testifying. The authors investigated the effects of this procedure by using participant accounts and both accurate and misleading experimenter-prepared accounts. Another experimental group did not review any account. Participants given no opportunity to refresh memory were less accurate in free recall than participants who refreshed memory, but they were equally accurate in answering direct questions. Measures of consistency between performance on testing sessions showed that the opportunity to review a self-produced account resulted in more consistent performance than nonreview. Results of this study have important implications in pretrial witness preparation.

The oxidation of chiral alcohols catalyzed by catalase in organic solvents.

The catalytic properties of bovine liver catalase have been investigated in organic solvents. In tetrahydrofuran, dioxane, and acetone (all containing 1% to 3% of water), the enzyme breaks down tert-butyl hydroperoxide several fold faster than in pure water. Furthermore, the rate of catalase-catalyzed production of tert-butanol from tert-butyl hydroperoxide increases more than 400-fold upon transition from aqueous buffer to ethanol as the reaction medium. The mechanistic rationale for this striking effect is that in aqueous buffer the rate-limiting step of the enzymatic process involves the reduction of catalase's compound I by tert-butyl hydroperoxide. In ethanol, and additional step in the reaction scheme becomes available in which ethanol, greatly outcompeting the hydroperoxide, is oxidized by compound I regenerating the free enzyme. In solvents, such as acetonitrile or tetrahydrofuran, which themselves are not oxidizable by compound I, catalase catalyzes the oxidation of numerous primary and secondary alcohols with tert-butyl hydroperoxide to the corresponding aldehydes or ketones. The enzymatic oxidation of some chiral alcohols (2,3-butanediol, citronellol, and menthol) under these conditions occurs enantioselectively. Examination of the enantioselectivity for the oxidation of 2,3-butanediol in a series of organic solvents reveals a considerable solvent dependence. (c) 1995 John Wiley & Sons, Inc.

Photochemical generation and reactions of heme cation radicals in heme proteins.

A novel approach is described for generating reactive oxidizing centers in heme proteins, with zinc hemoglobin (Zn Hb) and zinc cytochrome c (Zn cyt c) used as examples. The reaction of 3Zn* Hb with [CoIII(NH3)5 Cl]2+, and of 3Zn* cyt c with methyl viologen are described. In the case of Zn Hb the cation radical produced decays with a rate constant of k3 = 2400s-1. Using this value the rate of the reaction (formula; see text) can be calculated to be 4500s-1.