摘要:

Characteristic x‐ray diffraction patterns produced by transverse, radial and tangential sections of wood fibers have been discussed. There are two fundamental types of orientation of the micelles or fibrils in wood fibers: A, parallel to the fiber axis; B, parallel to each other, but on a spiral at a definite slope to the fiber axis. The deviation from either type may be qualitatively estimated from the diffraction pattern. For type B, the slope of the spiral may be measured with considerable accuracy. When large angles of slope of the micelles are indicated most wood fibers differ fundamentally from cotton. In wood fibers the average slope is at a definite angle to the fiber axis; the deviation is from Type B. In cotton fibers the average slope approaches 0°; the deviation is from Type A.

ISSN:0021-8979    

DOI:10.1063/1.1745174

出版商:AIP    

年代:1933

数据来源: AIP

摘要:

The temperature dependence of the piezoelectric strain constantd14was investigated in mixed crystals isomorphous with Rochelle salt. Crystals oriented for utilization of Voigt's theory of the converse piezoelectric effect in the hemihedral class of the orthorhombic system were grown at constant temperature from supersaturated solutions of Rochelle salt containing isomorphous impurities C4H4O6Na NH4·4H2O or C4H4O6Na Tl·4H2O and measurements of the strain resulting from an applied electric field were made in the range 10 to 35°C. Hysteresis and saturation occur in the range of large piezoelectric activity whered14evaluated from the straight portion of the strain curve is approximately 5 × 10−4in both the pure salt and mixed crystal, a value several times as large as that reported from measurements of the direct effect in Rochelle salt. The critical temperature for a mixed crystal lies below that of pure Rochelle salt (25+273°K) and the shift observed compares favorably in magnitude with the value calculated from the dipole theory of dielectrics. The region in whichd14decreases to about 10−5covers 3°C. The value ofd14diminishes further as the temperature is raised.d14is defined as twice the change in length per cm length of a narrow crystal cut at 45° with theYandZaxes when unit electrostatic field is applied in theXdirection.

ISSN:0021-8979    

DOI:10.1063/1.1745175

出版商:AIP    

年代:1933

数据来源: AIP

摘要:

The sensitivity to voltage, measured in volts per mm scale deflection, of a direct‐current thermionic amplifier (simple circuit) is taken as inversely proportional to the mutual conductance divided by the plate current of the valve employed. The mutual conductance is found to decrease less rapidly than the plate current, as the filament and plate potentials are lowered. The most sensitive operating value of the plate potential of a UX 222 is found to be 1.5 volts giving a voltage sensitivity of 8×10−4volt/mm in the simple circuit with no plate current compensation. By suitable use of the screen grid, a grid‐filament resistance of 1014ohms may be obtained giving a current sensitivity of 8×10−15amp./mm with an input resistor of 1011ohms.

ISSN:0021-8979    

DOI:10.1063/1.1745176

出版商:AIP    

年代:1933

数据来源: AIP

摘要:

The rise, into an ideal uniform soil, of liquid, under the action of capillary forces, differs from the steady flow across the soil. The steady transmission of fluids takes place through the continuous capillaries extending across the soil; the rise, under capillary forces, of liquid is from cell to cell. The hexagonal scheme of grains spaced at a distance (2r+d), wheredis a function of porosity, is used as a statistical representation of the soil; and the problem discussed from the standpoint of this packing. The fluid, in its passage through the long capillaries, flows through a cyclic capillary showing definite maxima and minima in each element; and likewise, the rise, from cell to cell, under capillary forces, is through a channel with definite maxima and minima. The minimum opening, of a cell, is the section defined by the plane of centers; the greatest is the section defined by the plane, parallel to the plane of centers, tangent to the grains of the cell immediately over the first cell. The greatest rise, occurs when the minimum opening holds the meniscus and is observed by allowing the liquid to fall through the soil; the least rise should occur when the maximum opening holds the meniscus and should be observed by allowing the liquid to rise through the soil. Wetting phenomena introduce, however, complications affecting the minimum rise. Rings of liquid form, just above the meniscus, around the point of contact of each pair of grains, and carry the rising liquid higher until it attains a position where it is no longer able to reach the rings so formed; equilibrium then prevails at a rise intermediate to the two extremes just defined. The exact conditions controlling the rise phenomena are determined; the approximation, developed for the capillary equation, in an earlier paper, is then used, with these conditions, to calculate the minimum rise. The results are compared with the data given in the earlier paper; good agreement, within the experimental error, is obtained.

ISSN:0021-8979    

DOI:10.1063/1.1745177

出版商:AIP    

年代:1933

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1745178

出版商:AIP    

年代:1933

数据来源: AIP

摘要:

From the skip distances of radio waves measured in temperate latitudes during 1927 and 1928 the average day ionization is calculated to be at about 200 km above sea level with a maximum electron density of 7.5×105and 5.6×105for a summer and winter day, respectively, which agree with the observed virtual heights from radio echo experiments and the longest wave which at normal incidence pierces through the ionized layer. The ratio 1.33 of summer to winter day electron density agrees with the ratio 1.42 calculated from ionization by the ultraviolet light of the sun. An average night ionization of 2.5×105and 1×105for summer and winter at 160 km is in rough accord with the radio facts as far as they are known, but within limits a more dense ionization at a higher level, or a less dense at a lower level, would accord equally well. The average day ionization for 1927 and 1928 is 6.5×105electrons cm−3which, when compared with the value 4.3×105calculated from the skip distances of 1923 and 1924, shows thatthe ionization increased by about 50 percent from minimum to maximum solar activity.

ISSN:0021-8979    

DOI:10.1063/1.1745179

出版商:AIP    

年代:1933

数据来源: AIP