A Simple Low-Vacuum Environmental Cell
The environmental cell device discussed in this paper provides a modest low-vacuum scanning electron microscopy (SEM) capability to a standard SEM without requiring additional pumping. This environmental cell confines a volume of low vacuum in contact with the sample surface using a container that has an aperture for admitting the primary electron beam. The aperture is large enough to permit a limited field of view of the sample, and small enough to limit the outflow of gas into the SEM chamber to that which can be accommodated by the standard SEM pumping system. This environmental cell also functions as a gaseous detector device.
Modeling the lung: Design and development of tissue engineered macro- and micro-physiologic lung models for research use
Respiratory tract specific cell populations, or tissue engineered in vitro grown human lung, have the potential to be used as research tools to mimic physiology, toxicology, pathology, as well as infectious diseases responses of cells or tissues. Studies related to respiratory tract pathogenesis or drug toxicity testing in the past made use of basic systems where single cell populations were exposed to test agents followed by evaluations of simple cellular responses. Although these simple single-cell-type systems provided good basic information related to cellular responses, much more can be learned from cells grown in fabricated microenvironments which mimic in vivo conditions in specialized microfabricated chambers or by human tissue engineered three-dimensional (3D) models which allow for more natural interactions between cells. Recent advances in microengineering technology, microfluidics, and tissue engineering have provided a new approach to the development of 2D and 3D cell culture models which enable production of more robust human in vitro respiratory tract models. Complex models containing multiple cell phenotypes also provide a more reasonable approximation of what occurs in vivo without the confounding elements in the dynamic in vivo environment. The goal of engineering good 3D human models is the formation of physiologically functional respiratory tissue surrogates which can be used as pathogenesis models or in the case of 2D screening systems for drug therapy evaluation as well as human toxicity testing. We hope that this manuscript will serve as a guide for development of future respiratory tract model systems as well as a review of conventional models.
Point anode proportional counters for the detection of soft X rays in microanalysis
An end-window (point anode) counter is described which has been designed for detecting soft X rays in an electron-probe microanalyser. An experimental evaluation of the counter showed that it had good resolution for the X-ray wavelength range encompassing CK, OK and AlK, provided that the needle-to-window distance and the X-ray aperture size were both suitably selected. The deterioration in counter performance when the optimum geometrical settings were not used was found to be due to a spread in mean pulse energies, which could reach 40%, arising from ionizations across the counter axis. The best resolution figures achieved during practical operation of this end-window counter, and a larger model of similar design, were σ/P = 20%, 42% and 64% for AlK, OK and CK X rays respectively, as compared with 15%, 35% and 46%, measured on a standard side-window design. These values are far inferior to suggested theoretical resolutions and methods of improving the counters are considered. It is concluded that a good side-window counter, with its superior resolution, is desirable for quantitative microanalysis using the network method, but other cases are discussed where the end-window counter may be preferred on account of its convenient geometry.