Since the discovery of nerve growth factor, it has been thought that neurotrophic factors are released or secreted from target cells. However, more recently it has been suggested that a specific neurotrophic factor known as brain-derived neurotrophic factor (BDNF) may reach target cells directly from pre-synaptic axons. It has not been known how these molecules get from the neuron in which they are produced to the target cells. Keigo Kohara, Akihiko Kitamura, Mieko Morishima, and Tadaharu Tsumoto have demonstrated that BDNF is transported anterogradely from presynaptic neurons to target neurons.

Recently on the microscopy list server, a question came up as to how to compensate for charging in SEM micrographs. Several good answers were suggested. Some of them were 1) recoating the sample to prevent the build up of charge on the sample in the first place, and image it again, 2) use an environmental SEM (ESEM) in the “wet” mode to eliminate the charging phenomena, 3) use a different detector, such as a backscattered electron detector, which is much less sensitive to charging phenomena, and 4) apply adjustments to the digital image using software such as Adobe PhotoshopÆ to minimize the effect of the charging problem.

If we accept that the optical layouts of single-beam laser scanning confocals are generally quite similar, the most important variable is “Photon Efficiency” (PE): the fraction of photons leaving the focal plane that actually contribute to the number stored in the image memory. Unfortunately, this parameter is a function of a very large number of operator settings, design decisions and optical performance specifications (BioTechniques The 39 Steps; A Cautionary Tale about “quantitative” 3D fluorescence microscopy, April 2000 28:884-7). As a result, although all manufactures claim excellent “Photon Efficiency” none actually provide any specifications. We have to determine the PE ourselves.

This article is the third of a series transcribed from the discussion taped during the Core Facility Management session. Buileted paragraphs indicate comments by individuals attending the session.

D. Sherman: The next topic we are going to deal with has to do with calibration of electron microscopes. This became very important in my situation because we started dealing with people with nanotubes and nanovesicles and with very small things where they needed to have accurate size both in the SEM and the TEM magnification range. My own frustrations dealing with calibration, especially in the in between magnification, spurred me on to ask a couple of experts to give us some insight on what we should be doing with calibration - the problems associated with this and some general information about how to go about doing this in our standard facilities where money is short.

Spherical debris particles in spalled areas of bearing raceways have been attributed to motions of the crack faces during spall generation. This note suggests an alternative generation mechanism for the particles.

Figure 1, from Failure Atlas for Hertz Contact Machine Elements, shows a spherical debris particle lying on the spalled surface of a bearing raceway. The atlas characterizes the spheroids as characteristic of spalling fatigue, and attributes the spheroids to alternating micro-motions between crack faces, but qualifies by saying that the specific mechanism of their generation is not understood. The spheroid measures about 50 microns and consists of bearing steel, oxidized at the surface.

The properties and performance of electronic devices are crucially dependent on interface-related phenomena. The presence of interfaces can enable electronic device functionality (p-n diodes, solar cells); alternatively, non-functional interfaces can degrade device performance (ohmic vs. non-ohmic contacts). The most versatile tools for semiconductor interface characterization are ac (impedance spectroscopy, C-V) and dc (I-V) transport measurements. However, due to the lack of spatial resolution, these methods often cannot separate the contributions from electroactive interfaces and contacts. This is especially true for the non-traditional electronic materials such as semiconductive oxides, nitrides, conductive polymers, etc. Combined with the tendency towards miniaturization of electronic devices, this clearly necessitates spatially resolved ac and dc transport measurements.

Immediately following the bioterror associated anthrax cases in September, there were an unprecedented number of reports of “suspicious white powdery substances” nationwide. Some of these reports were hoaxes. Others were honest cases of mistaken identity. A very few involved anthrax spores.

An incident on our campus caused the temporary closing of a portion of a dormitory building and disrupted the activities of a large number of students, faculty, and staff. When campus officials contacted the FBI for assistance in evaluating the suspect material they were advised that the bureau was so overwhelmed by reports of suspicious substances that they were unable to respond effectively unless additional circumstances suggested a credible biohazard threat. The material in our incident eventually proved to be laundry detergent.

First, the OEM is obligated to service contract customers first. Without a could go to the bottom of the list. This would not be all that different with a third party firm—although they might try a little harder to be timely. With service contracts, payment has been made up front (or at least committed up front) for a entire year. This is guaranteed income and includes a guaranteed liability (for the OEM) “to maintain the instrument/system to its original specifications”. Service organizations must and do take this responsibility seriously. This liability doesn't exist with biliable customers, and work will be done to the best of the OEM's ability and only to the limit of the specific purchase order.

First, it is important to know whether the objective of the analysis is to measure the total amount of the two metals in the assembly as a whole, or to measure their proportions in each of the different areas; the tin solder, the intermetallic layers and so on. The purpose to which the results are to be put is also important. To some extent the answer depends on knowing this, as a biased but highly repeatable measure of something is often useful for internal purposes.

For Au/Sn intermetallic compounds which have quite specific compositions, the absorption/enhancement effects will be different than for a low-concentration solid solution of either of the metals in the other.

According to the International Standards Organization (ISO), for companies that are in compliance with ISO-9000 or QS-9000, traceable measurements shall be made when products or processes require dimensional measurements be made to a known uncertainty. These measurements are often made with a traceable ruler or micrometer. For magnification (the ratio of object size to image size) to be traceable, both the image and object size must be measured with calibration standards that have traceable dimensions. In the current ISO jargon the “uncertainty” of the instruments used to make the measurements must be known. The word “accuracy” is now only considered to be a subjective term and shall remain dimensionless.