OCDs in Group Divisible Design Set-Up

A (group) divisible design is a tactical configuration for which the v points are split into m classes of n each, such that points have joining number λ (resp. λ2) if and only if they are in the same (resp. in different) classes. We are interested in such designs with a nice automorphism group. We first investigate divisible designs with equally many points and blocks admitting an automorphism group acting regularly on all points and on all blocks, i.e., with a Singer group (Singer [50] obtained the first result in this direction for the finite projective spaces).As in the case of block designs, one may expect a divisible design with a Singer group to be equivalent to some sort of difference set; as it turns out, one here obtains a generalisation of the relative difference sets of Butson and Elliott [11] and [20].

Download Full-text

The Effects of Drying Techniques on Clay-Rich Soil Texture

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052341 ◽

1974 ◽

Vol 32 ◽

pp. 466-467

Author(s):

T. G. Naymik

Keyword(s):

Critical Point ◽

Liquid Nitrogen ◽

Liquid Nitrogen Temperature ◽

Drying Methods ◽

Air Drying ◽

Freeze Dried ◽

Critical Point Drying ◽

Set Up ◽

The Relationship ◽

Quartz Grains

Three techniques were incorporated for drying clay-rich specimens: air-drying, freeze-drying and critical point drying. In air-drying, the specimens were set out for several days to dry or were placed in an oven (80°F) for several hours. The freeze-dried specimens were frozen by immersion in liquid nitrogen or in isopentane at near liquid nitrogen temperature and then were immediately placed in the freeze-dry vacuum chamber. The critical point specimens were molded in agar immediately after sampling. When the agar had set up the dehydration series, water-alcohol-amyl acetate-CO2 was carried out. The objectives were to compare the fabric plasmas (clays and precipitates), fabricskeletons (quartz grains) and the relationship between them for each drying technique. The three drying methods are not only applicable to the study of treated soils, but can be incorporated into all SEM clay soil studies.

Download Full-text

Evaluation of Freezing Methods by Low Temperature X-Ray Diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100079176 ◽

1977 ◽

Vol 35 ◽

pp. 330-333

Author(s):

T. Gulik-Krzywicki ◽

M.J. Costello

Keyword(s):

Biological Materials ◽

Molecular Organization ◽

X Ray Diffraction ◽

Glass Capillary ◽

X Ray ◽

Rate Dependent ◽

Before And After ◽

Freeze Etching ◽

Diffraction Patterns ◽

Set Up

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.

Download Full-text

Eels Under Standing Wave Conditions

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100054911 ◽

1982 ◽

Vol 40 ◽

pp. 492-495

Author(s):

O.L. Krivanek ◽

J. TaftØ

Keyword(s):

Standing Wave ◽

Wave Conditions ◽

Set Up ◽

A Site ◽

Complex Crystal

It is well known that a standing electron wavefield can be set up in a crystal such that its intensity peaks at the atomic sites or between the sites or in the case of more complex crystal, at one or another type of a site. The effect is usually referred to as channelling but this term is not entirely appropriate; by analogy with the more established particle channelling, electrons would have to be described as channelling either through the channels or through the channel walls, depending on the diffraction conditions.

Download Full-text

Low-Loss Images in a Stem/Tem Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010009244x ◽

1976 ◽

Vol 34 ◽

pp. 496-497 ◽

Cited By ~ 1

Author(s):

David C. Joy ◽

Dennis M. Maher

Keyword(s):

High Resolution ◽

Surface Topography ◽

Beam Direction ◽

Low Loss ◽

Specimen Holder ◽

Glancing Angle ◽

High Resolution Images ◽

Set Up ◽

Conventional Manner ◽

Objective Type

High-resolution images of the surface topography of solid specimens can be obtained using the low-loss technique of Wells. If the specimen is placed inside a lens of the condenser/objective type, then it has been shown that the lens itself can be used to collect and filter the low-loss electrons. Since the probeforming lenses in TEM instruments fitted with scanning attachments are of this type, low-loss imaging should be possible.High-resolution, low-loss images have been obtained in a JEOL JEM 100B fitted with a scanning attachment and a thermal, fieldemission gun. No modifications were made to the instrument, but a wedge-shaped, specimen holder was made to fit the side-entry, goniometer stage. Thus the specimen is oriented initially at a glancing angle of about 30° to the beam direction. The instrument is set up in the conventional manner for STEM operation with all the lenses, including the projector, excited.

Download Full-text

UHV-TEM studies of laser-induced damage

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087471 ◽

1991 ◽

Vol 49 ◽

pp. 632-633

Author(s):

T.S. Savage ◽

R. Ai ◽

D. Dunn ◽

L.D. Marks

Keyword(s):

Surface Science ◽

Rapid Heating ◽

Local Heating ◽

Routine Practice ◽

Transmission Electron ◽

Northwestern University ◽

Laser Induced Damage ◽

Set Up ◽

Focusing Lens ◽

Diffusion Of Impurities

The use of lasers for surface annealing, heating and/or damage has become a routine practice in the study of materials. Lasers have been closely looked at as an annealing technique for silicon and other semiconductors. They allow for local heating from a beam which can be focused and tuned to different wavelengths for specific tasks. Pulsed dye lasers allow for short, quick bursts which can allow the sample to be rapidly heated and quenched. This short, rapid heating period may be important for cases where diffusion of impurities or dopants may not be desirable.At Northwestern University, a Candela SLL - 250 pulsed dye laser, with a maximum power of 1 Joule/pulse over 350 - 400 nanoseconds, has been set up in conjunction with a Hitachi UHV-H9000 transmission electron microscope. The laser beam is introduced into the surface science chamber through a series of mirrors, a focusing lens and a six inch quartz window.

Download Full-text