摘要:

In conventional coincident‐current magnetic storage systems, a specific storage element is selected by simultaneously applying, to two or more intersecting wires, currents of magnitudes such that their sum will produce a magnetic field sufficient to switch the element and such that the presence of any one of the selecting currents alone will not cause the element to switch. In the system described here, a coincident summation of magnetic flux causes the element to switch, and the magnitudes of the currents inducing the flux are not critical. This allows the switching time to be freed of the current‐selection‐ratio limitation typical of the coincident‐current selection systems. In the coincident‐flux system, one may use selecting flux densities representing fields very much greater than the coercive field, giving very fast switching times.

ISSN:0021-8979    

DOI:10.1063/1.1722248

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The role of crack propagation velocity in the cleavage of crystals and aggregates is emphasized in this paper. The available data on crack propagation in elastic media are summarized, showing that this phenomenon is adequately understood at present. For inelastic media, it is postulated that in addition to the Griffith Criterion two critical velocity conditions must be satisfied or crack propagation cannot occur. One critical velocity pertains to propagation through a crystal, and the other to propagation through an aggregate. The first critical velocity depends on the rate at which plastic glide can absorb energy at a crack tip and the number and size of cleavage steps that a crack front contains. These quantities are estimated. The second critical velocity accounts for the dependence of fracture stress on grain size in aggregates and interprets other experimental behaviors of aggregates which contradict previous interpretations.

ISSN:0021-8979    

DOI:10.1063/1.1722249

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Specimens of U‐9, ‐10.5, ‐12, and ‐13.5 w/o (weight percent) Mo and U‐10 w/o Nb, heat treated to retain the metastable gamma phase at room temperature and also to transform this phase to the room temperature stable phases, were irradiated in the Materials Testing Reactor (MTR) at maximum temperatures of less than 200°C. Electrical resistivity, temperature coefficient of electrical resistivity, hardness, and density measurements as well as x‐ray diffraction patterns indicated that the stable phases at room temperature reverted to the metastable gamma phase during irradiation. No apparent changes in the microstructures of thermally transformed specimens were observed after irradiation. Lack of observable microstructural changes was attributed to the development of a ghost structure. X‐ray line broadening measurements indicated essentially complete homogenization of thermally transformed U‐Mo alloy specimens during irradiation. The mechanism of the phase reversal was explained on the basis of the displacement spike hypothesis.

ISSN:0021-8979    

DOI:10.1063/1.1722250

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A mathematical treatment of the Bennett‐type rf mass spectrometer has been developed which is appreciably simpler to handle when dealing with a multistage analyzer. This simplification is a result of changing the point of reference in the tube from that previously used. The resulting form of the equation is soluble by the use of a very simple analog computer which is described.

ISSN:0021-8979    

DOI:10.1063/1.1722251

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Effects of crystal growth rate and growth direction on the density of random dislocations and on the minority carrier lifetime have been observed. The dislocation density increases rapidly with growth rate above a rate of about 0.15 in. per minute and varies somewhat with growth direction. The capture efficiency per unit length of dislocation decreases at high growth rates and it is suggested that this effect is caused by the failure of impurity atoms to segregate at dislocations or by the clustering of dislocations.

ISSN:0021-8979    

DOI:10.1063/1.1722252

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The variance of the number of zeros of a Gaussian signal on a short time interval was derived in a recent paper by Steinberg,et al. This result is generalized to include the covariance of the number of zeros of a Gaussian signal at the values &thgr;1and &thgr;2, using a somewhat different mathematical approach. A special case with &thgr;1=&thgr;2=&thgr; gives the variance of the number of times the signal equals &thgr; on a given time interval.

ISSN:0021-8979    

DOI:10.1063/1.1722253

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A general method is developed to allow calculation of the critical buckling of an assemblage of fissile regions coupled by neutron leakage. Consideration is given both to regions embedded in vacuum and in material media. Several cases of simple geometry are further developed to illustrate the theory.

ISSN:0021-8979    

DOI:10.1063/1.1722254

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

An investigation has been made of the electrostatic charge produced in vacuum on several inorganic insulators when they are put into rolling contact with nickel, platinum, and copper surfaces. The primary role of relative motion is to increase the area on the insulator that ultimately undergoes contact, thereby increasing the total charge separated. With quartz, all evidence favors electron transfer which occurs because the nonconductor has a higher effective work function than the metal. Field emission‐induced back leakage of electrons during separation of the charged surfaces is considered to reduce the charge originally separated to that actually measured. Little difference is seen between the charging properties of quartz cleaned chemically in room air and quartz subsequently outgassed at 700°Cin vacuobetter than 10−8mm Hg. No difference in electron affinity is found between fused and monocrystalline quartz. No evidence directly supporting electron transfer is found for the other insulators tested, synthetic single crystals of Al2O3, MgO, NaCl, KCl, KBr, and KI; and the possibility of ion transfer is considered. All charge against nickel much less vigorously and less reproducibly than does quartz. The alkali halides and MgO which contains excess Mg or O as a bulk impurity charge positively, while stoichiometric MgO charges negatively. With Al2O3, there is a strong dependence of charge density on crystallographic orientation. Alteration of charging properties by surface and/or bulk conduction is found to be negligible for all insulators tested, within the reproducibility of the charging measurements.

ISSN:0021-8979    

DOI:10.1063/1.1722255

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Some simple methods of preparing MgO thin films on Mg&sngbnd;Ag alloy with high secondary emission ratios are discussed. The oxidation procedure and a discussion of the underlying phenomena are presented. Films with a secondary yield of 12 at 600 v may be produced by oxidation in either oxygen or carbon dioxide. Results of a study of some of the factors influencing the life of a secondary emitter are given. These include the effects on the secondary emitting characteristics of evaporation products from an oxide‐coated cathode and the deterioration of the thin film under electron bombardment.

ISSN:0021-8979    

DOI:10.1063/1.1722256

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

To reduce the physical and chemical complexity of the oxide coated cathode, the support metal and interface were eliminated by applying the (BaSr)O layer to a MgO ceramic which is electrically and chemically inert to (BaSr)O. The three interacting chemical phases of the usual oxide coated cathode are thereby reduced to a single phase—the oxide coat alone. At 1000°K, thermionic emission, measured by a pulse technique, is about 1 order of magnitude less than from modern commercial cathodes but considerably greater than from any other cathode system. The emission capability is unaffected by treatment in either atomic hydrogen or methane, which reduce BaO to Ba metal and thereby increase the Ba content of the oxide. The experiments were an attempt to test the usual assumption that emission in conventional oxide coated cathodes is determined by the composition of the (BaSr)O phase. The results suggest strongly that much of the complexity of practical cathodes is in the oxide layer itself and that factors other than the content of excess Ba are decisive for thermionic emission.

ISSN:0021-8979    

DOI:10.1063/1.1722257

出版商:AIP    

年代:1956

数据来源: AIP