Form und Intensität des Termitenangriffes an Hölzern verschiedener Struktur und Rohdichte Erste Mitteilung: Prüfungen an getrenntem Früh und Spätholz

Zusammenfassung An getrenntem Frühholz und Sp?tholz der Holzarten Kiefer, Fichte und Stieleiche wurden Fra?zwangsversuche mit der BodentermiteReticulitermes lucifugus Rossi durchgeführt. Es wurde beobachtet, da? die Termiten beim Holzangriff vornehmlich Radialfl?chen bevorzungen und in tangentialer Richtung weiterfressen. Der Holzabbau von Frühholz und Sp?tholz nimmt mit ansteigender Rohdichte ab.

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The way and intensity of termite attack on wood of different structure and density—Part I: Tests with separated spring: and summerwood

Summary Separated samples of springwood and summerwood of the species Scots pine, spruce and pedunculate oak were exposed to the attack of the soil-termite Reticulitermes lucifugus Rossi. When termites attack wood they mainly prefer radial sections and are going foreward in tangential direction. The portion of destroyed spring- and summerwood decreases when density increases.

     

Die in Schichten gleicher Dicke geschichtete Halbebene mit periodisch verteilter Randbelastung

Zusammenfassung In Erweiterung einer früheren Untersuchung über die reibungsfrei geschichtete, mit einer periodisch ver?nderlichen Druckbelastung beanspruchte Halbebene wurde nunmehr der gleiche Fall unter der Voraussetzung theoretisch untersucht, da? Reibungskr?fte zwischen den einzelnen Schichten auftreten. Der durch diese Kr?fte hervorgerufene Verschiebungswiderstand kann der Druckkraft proportional gesetzt werden. Eine bessere L?sung ergibt sich jedoch, wenn man Proportionalit?t zwischen der Schubspannung und der Relativverschiebung der Schichtr?nder annimmt. Es zeigt sich, da? bei vorhandener Reibung die von der Druckbelastung erzeugten Spannungen vom Rand der geschichteten Halbebene aus sehr viel schneller als in der reibungsfreien geschichteten Halbebene abklingen.     

Optical characteristics of silicon solar cells and of coatings for temperature control

Silicon photovoltaic cells, which are widely used in space vehicles for the direct conversion of solar radiation into electric power, exhibit an undesirable decrease in power output with increase in cell temperature. This article discusses the control of cell temperature in terms of the absorptance and the emittance of solar radiation by the cell surface. Using measured values of spectral reflectance to 25 microns, these parameters are determined for uncovered cells and for cells provided with glass filters and with silicon oxide films.     

PARTICLE SHAPE AND DIFFERENTIAL SHRINKAGE OF STEATITE TALC BODIES *

An attempt has been made to correlate the differential shrinkage of fired steatite pieces with the particle shape of the raw talc used in their manufacture. Various talcs of widely varying particle shape were used in making the steatite test pieces. It was found that the more irregular in shape the talc particles, the greater the differential shrinkage. A method is given for assigning arithmetical values to various particle shapes depending on their deviation from sphericity, this arithmetical value being known as specific shape factor. A direct relationship was found to exist between the differential shrinkage of a talc and its specific shape factor. As the talc particles became more irregular in shape, the “specific shape factor” value increased and the differential shrinkage was found to increase. The proper selection of the talc td be used and blends of various talcs were found to be helpful in the control of differential shrinkage.     

OPTICAL FLUOR-CROWN GLASSES*

The effect of variations in composition on optical properties was studied. The index of refraction is lowered by the substitution of fluorine and alumina for silica; the reciprocal dispersion, however, is increased by fluorine and lowered by alumina so that fluorine and alumina can be balanced against each other to give almost any desired optical properties within the field investigated, that is, in the range of 1.46 to 1.50 for index of refraction and 63 to 70 for the reciprocal dispersion.