End Plane Research Articles

Crystal Structure Determination of Glycerol-Containing Lipids from Electron Diffraction Data. Use of Analog Compounds Based upon Configurational Isomers of Cyclopentane-1, 2, 3-TRIOL

Lipids containing long polymethylene chains were among the first compounds subjected to electron diffraction structure analysis. It was only recently realized, however, that various distortions of thin lipid microcrystal plates, e.g. bends, polar group and methyl end plane disorders, etc. (1-3), restrict coherent scattering to the methylene subcell alone, particularly if undistorted molecular layers have well-defined end planes. Thus,ab initiocrystal structure determination on a given single uncharacterized natural lipid using electron diffraction data can only hope to identify the subcell packing and the chain axis orientation with respect to the crystal surface. In lipids based on glycerol, for example, conformations of long chains and polar groups about the C-C bonds of this moiety still would remain unknown.One possible means of surmounting this difficulty is to investigate structural analogs of the material of interest in conjunction with the natural compound itself. Suitable analogs to the glycerol lipids are compounds based on the three configurational isomers of cyclopentane-1,2,3-triol shown in Fig. 1, in which three rotameric forms of the natural glycerol derivatives are fixed by the ring structure (4-7).

1.16 Extremely uniform thin films by vacuum deposition from a ‘tube source’

Abstract A vacuum deposition device without moving parts called ‘tube source’ has been developed which is capable of producing from a small area source on plane extended fixed substrates thin films with 10 times less thickness variation than a film would show deposited from the same small area source as the one used with the ‘tube source’ at the same distance but without the tube source arrangement. For example, using the tube source, a film deposited on a flat circular substrate of 10.4 cm diameter shows a thickness variation less than ± 0.4% at a substrate to source distance of 23.2 cm. The tube source consists of a wide cylinder. At one end on the axis of the cylinder there is a small area source, for example, a 1 2 in. commercial dimple boat electrically heated and filled with the material to be deposited; from the other end flat substrates were positioned in a plane perpendicular to the cylinder axis at varying distances. A disc with its plane also perpendicular to the axis and its center on it was suspended with three very thin stretched wires inside the tube in such a way that no vapor atoms could hit the substrate directly, in other words the disc forms a shadow for the source on the substrate. Hereby, the arrival of vapor atoms can be made much more random depending on the geometry (distance of substrate from top end plane of cylinder, distance of source from bottom end plane, a.o.). The tube could be heated by nichrome wire wrapped around it to change the reflectivity of the vapor atoms. Optimum thickness distributions on the substrate were determined by Monte Carlo methods using a computer as well as analytically.

Space-charge-limited currents in electron-irradiated dielectrics

This paper develops the theory of steady-state currents generated in a dielectric placed between positively or negatively biased electrodes and irradiated with a partially penetrating electron beam. The dielectric is divided into an irradiated region (IR), which extends from the electrode of incidence to the extrapolated range of the beam, and a nonirradiated region (NIR). In the IR the primary beam generates an electron-hole plasma. Its end plane acts as a virtual electrode embedded in the dielectric. Currents are space-charge limited in the NIR and Ohmic in the IR which is characterized by a uniform radiation-induced conductivity. Depending on the polarity of the electrode bias, electrons or holes are drawn from the IR into the NIR. The theory correctly predicts an apparent threshold effect for the inset of steady-state currents: the current amplitudes remain small as long as the electron range is smaller than half the sample thickness, and increase strongly only afterwards. Calculated current curves for different beam energies are in satisfactory agreement with experimental results. The role of the electron beam as a virtual electrode is discussed.

Small-hole coupling of resonant cavities and waveguides

General formulas and equivalent circuits are given for a resonant cavity coupled to the end plane of a wave guide, inserted between two waveguides, and coupled to the sidewall of a waveguide. The aperture, the cavity and the waveguides are of arbitrary shape.

Ultrasonic Grinding of Natural Graphite

FINE grinding of graphite is usually carried out in a mortar or in a ball mill. The reduction of the particle size proceeds rather slowly due to the lubricating action of the grain surfaces, and the ground crystals contain various kinds of lattice imperfections including stacking faults—the extent of the imperfections being subject to the period and method of grinding. Recently, Bacon1 and others2–5 studied this phenomenon, both using an electron microscope and X-rays. I myself carried out some experiments on similar lines with Madagascar graphite ground in a cell excited with ultrasonic waves. The original powder was 50–65 mesh graphite crushed in a mortar. The slurry containing the powder was treated with 20-kc/s, 150 V amp ultrasonic radiation in a cylindrical cell 26 mm in diameter. The slurry entered the cell through a pipe attached on the face of the cylinder and flowed out through another pipe attached on the opposite side, and it was circulated slowly with a gear pump. The ultrasonic power was supplied through the top of the cell which was the end plane of the oscillator horn. The height of the cell was adjustable. In the range of height from 1 to 10 mm the change of grinding speed was not marked. The following media were used: Pure water, 1 per cent aqueous solution of tannic acid or detergent, glycerine, paraffin oil and dense bromoform (specific gravity 2.8). The bromoform seemed to have superior grinding powers, but was troublesome in extended use due to its corrosiveness and irritating vapour. The glycerine was found to be unsuitable for the purpose. Aqueous solution of tannic acid or detergent wetted the graphite particles, and the powder was uniformly dispersed after several passes through the cell. Crushing then proceeded continuously, although pure water did not wet it and the agglomerated powder floated on it for a long time without becoming dispersed in it. When ultrasonic vibration was applied in an open cell containing the slurry, for example by simply inserting the horn end in a beaker, the graphite particles were expelled from the horn and floated on the liquor surface even in water containing tannic acid or detergent. Paraffin oil was inferior to the aqueous solutions.

A ROTA-WEDGE TECHNIC FOR THERAPY WITH HIGH-ENERGY RADIATION BEAMS.

Wedge filters designed to modify the shape of the isodose curves obtained with a medium voltage x-ray generator were first described by Ellis and Miller (4). Ellis, Shanks, Kemp, and Oliver (5) more fully reported their clinical use. During the past decade, wedge filters have been used extensively with high-energy machines, ranging from cobalt-60 teletherapy units to a 22-Mevp betatron (Tulley, 9; Tranter, 8; van Roosenbeek and Grimm, 6; Cohen, Burns, and Sear, 1). One of the main attractions of wedge filters is that tumors situated close to one surface of the body may be uniformly irradiated with wedge-filtered fields directed exclusively through that same side of the body; i.e., treatment of eccentrically placed lesions may be carried out from the homolateral side only, without the excessive irradiation of contralateral normal tissue. This is often inevitable when two or more normal fields are used in a cross-fire technic. Figure 1 illustrates a site commonly treated with wedge filters, namely, the maxillary antrum. The considerations that follow, however, are not limited to this site but have a general application. The tumor is uniformly irradiated to a high dose, while there is a rapid fall-off beyond the tumor region; in the example quoted, this would imply a low dose to the eye on the opposite side. At the same time, the. entry portals are confined to the diseased sections of the head. Such treatment plans, obtainable with wedge filters, are simple, elegant, and effective if the therapist is able to execute them accurately. For this to be possible, skilled workshop facilities are essential because the isodose distribution in Figure 1 is valid only if the space between the curved contour of the patient and the end plane of the collimator (i.e., the dotted areas in Fig. 1) is filled with bolus material. In practice, bolus material in contact with the skin would sacrifice the skin-sparing effect which is one of the significant advantages of high-energy radiations. Consequently, bolus should be replaced by a compensator of some sort, displaced from the skin as described by Ellis, Hall, and Oliver (3) or by Cohen, Burns, and Sear (1960). The compensator is equivalent to bolus material as far as absorption is concerned and effectively converts the irregular contour of the patient into a plane surface. Since it is sited more than 15 cm. from the skin, however, electron build-up and the associated skin-sparing effect are preserved. Similar technics are used routinely in many departments but require an active and well staffed workshop to tailor-make compensators for individual patients. Such facilities simply do not exist in many smaller institutions. Rotating cobalt units are a common feature, however, and arc therapy is frequently chosen to treat tumors in the region of the head and neck, similar to that illustrated in Figure 1.

The use of standard isodose distributions with high energy radiation beams--the accuracy of a compensator technique in correcting for body contours.

The standard isodose curves used in radiotherapy are based on measurements in a phantom of unit density material with a plane surface at right angles to the central axis of the beam. In order that these isodose curves may be applied accurately in practice, some method is needed to convert the irregular contours of a patient into a plane surface at right angles to the central axis of the treatment beam. This is particularly important where standard multifield techniques are used, for example, two wedge fields at right angles. A method widely used for 250 kV therapy is to fill the space between the irregular contour of the patient and the end plane of the applicator with a bolus material of unit density. This method is, in general, undesirable for high-energy beams, because it sacrifices the important skin-sparing advantage which follows from the fact that the maximum dose “build-up” is reached at a significant depth below the surface. However, with a cobalt 60 unit, the required effect has been obtained us...

Rectangular-Hexahedoral Photometer for Linear source of Light

It is Possible to mesure the total luminous flux from a fluorescent lomp by a rectangular hexa-hedoron when a substitution method is employed, ouly if it has the same type, the same colour, and the same light distribution curve.If we should like to measure the performance of a fluorecent lamp by a hexahedoral photometer, its measurement may contain some error due to unlike light distribution. The unsuitable relation between the size of hexahedoron and lamp length may make a factor of error, so that the sensitivities from the different parts of a lamp are not constant.The coefficient of relative sensitivity that contributes to the estimation of the preceeding error is defined and the measurement of the coefficient is described in this paper.From the point of view of the coefficient of relative sensitivity a cubic flux integrator contains the smallist error among the other rectangular hexahedorous, and the longer the length of an integrator is, the larger its error tends to be.It must be determind by the demanded precision of measurement what is the allowable length of integrator.The best position of the screen is the center of the whole distance between the lamp and the window, from the standpoint of the coefficient of relative sensitivity, the illumination of the window. and the relative diffused illumination by unlike light distribution.It is better to put the window on the side plane than on the end plane, because the latter occupies larger space than the former.