Irregular Contact Research Articles

The geochemistry of archaean clastic metasediments in relation to crustal evolution, Northeastern Yilgarn Block, Western Australia

Abstract Clastic rudaceous metasedimentary rocks range from arkose to ultramafic para-schist in lithology and have high Na, Rb, Ni, Cr and V contents, except for pure arkose which has low Ni, Cr and V. The various arkoses are not comparable chemically with analyses of any Archaean or younger arkose or greywacke. The distinctive geochemistry and immature sedimentology of this clastic sequence (Jones Creek Conglomerate) results from: (a) derivation from sodic granitoid, low-K basaltic, peridotitic and gneissic source areas, (b) sedimentation in a high energy environment close to source areas, and (c) a lack of major post-depositional chemical alteration. Pebbles in the Conglomerate also attest to the local derivation of detritus from both sides of its very elongate outcrop. Following the emplacement (at 2689 ± 17 Ma) and unroofing of a sodic granitoid pluton, the Conglomerate was rapidly deposited in a graben-like basin. An irregular unconformable contact between the Conglomerate and this pluton is preserved locally. Elsewhere contacts with granitoid or supracrustal rocks are tectonised, but the petrology of the Conglomerate indicates that these contacts were unconformities also. Contrary to previous suggestions, it is considered unlikely that the Conglomerate stratigraphically separates an older from a younger supracrustal sequence in this area. The Conglomerate probably represents the last depositional event before the onset of deformation and protracted regional metamophism to the greenschist—amphibolite facies transition. Crustal evolution from the emplacement of the sodic pluton to the cessation of metamorphism probably occupied some 100 Ma rather than 60 Ma as proposed elsewhere.

Suppression of demand mechanism by inactive myocardial electrodes.

A 14 year old girl, at age 8, had had a bipolar pulse generator implanted with myocardial leads. Because one of the myocardial leads fractured near the electrode, a second pair of myocardial leads were implanted. Thus, the patient had two pairs of myocardial leads and one demand pulse generator implanted. When the patient was readmitted to the hospital because of light-headedness, the ECG monitor revealed frequent suppression of pulse generator pulses when hand pressure was exerted over the pulse generator site. Converting the pulse generator into the asynchronous mode with a magnet prevented inhibition. The pacemaker pocket was reopened. The pulse generator could not be inhibited either by pulling on the active myocardial leads or by moving the pulse generator, but the pulse generator could be inhibited by manipulation of the inactive leads which produced electrical signals having amplitudes and frequencies which were in the bandwidth of the sensing circuit. The probable cause of the electrical signals was the irregular contact of the terminals of the inactive leads with the patient's abdominal muscles. Replacement of the demand pulse generator by an asynchronous type resulted in cessation of the patient's light-headedness.

The influence of thermal expansion on the friction and wear process

Experimental results are presented for temperatures of two metal surfaces in sliding contact. Considerable fluctuations are observed. It is suggested that temperature gradients, set up by irregular heating at the surface, cause local thermal expansion at the areas of contact, thus perpetuating the irregular contact conditions. The system is limited by the wear at the areas of contact which eventually reduces the level of the contact areas to that of the surrounding surface. Subsequent cooling causes contraction and produces depressions which correspond to the wear volume during the cycle. Further experiments to confirm this explanation show good agreement.

Interpretation of the specific heat of various graphites at very low temperatures

The difference in the specific heat between various graphites observed recently by van der Hoeven and Keesom in the temperature range 0.4° ~ 2.0°K is explained satisfactorily on the basis of the theory presented previously by the author; smaller values of rc 33 and c 44 are assumed for specimens with higher degree of stacking faults. The possibility of explaining the observed difference in terms of the surface modes of vibration of particles is therefore to be precluded. A model is proposed for graphite specimens that particles are in irregular but close contact with each other and long wavelength phonons can almost freely propagate through their contact surfaces.

Stratigraphic Relations of the Shakopee Dolomite and the St. Peter Sandstone in Southwestern Wisconsin

The sharply undulating surface that separates the Shakopee dolomite from the overlying St. Peter sandstone was studied in southwestern Wisconsin and contiguous areas in Iowa. It is characterized by irregularly dipping beds, evidence of much subsurface solution directly below the contact, and a varied thickness of intercalated green and maroon shale and sandstone in the contact zone. The contact has relief of as much as 170 feet. Data from detailed examination of outcrops and from subsurface studies of churn-drill samples and diamond-drill cores indicate that the irregular contact is due primarily to compaction of Shakopee lime muds over relatively rigid masses, probably biogenic, accentuated by subsurface solution and accompanying compaction under the weight of younger sediments. No compelling reason was found to assign any of the irregularity at the contact to subaerial erosion of an emergent Shakopee surface in pre-St. Peter time.

A Means of Applying Diathermy to Irregular Surfaces of the Body and Inside the Mouth

Hitherto there has been no pre-eminently satisfactory method of applying diathermy to an irregular surface such as the face, the elbow or the ankle. The difficulty has been to obtain a sufficiently close and even fit of the electrode over the surface; the result of irregular contact is that certain spots are overheated. The following technique arose out of that which I developed for intra-oral treatment. The electrode for external use consists of a rigid insulated sheet of vulcanite or bakelite roughly moulded to form a casing over the area to be treated. A shape for a special part is shown in Fig. 1. It is held in place by means of rubber bands attached to studs embedded in the material in suitable places (Fig. 2). The base is totally lined on the tissue side with metal foil, which is connected to an external terminal. When required for use, the metal surface of the electrode is thickly coated with Diatol I, a plastic conducting material (Fig. 3).