摘要:

The specific heats of NdP5O14and PrP5O14were measured with a differential scanning calorimeter over the temperature range 385–440 °K. The ferroelastic phase transition was confirmed to be second order. The ferroelastic transition temperatures for NdP5O14and PrP5O14were 426.5 and 416.5 °K, respectively. A second thermal anomaly was observed in both materials approximately 20 °K below the ferroelastic transition.

ISSN:0003-6951    

DOI:10.1063/1.89863

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Spatial‐period (320‐nm) square‐wave gratings fabricated on amorphous SiO2substrates were used to produce uniform alignment of the director in nematic and smectic liquid‐crystal layers. This demonstrates that molecular alignment can be achieved using surface structures fabricated by a planar process. A novel method of producing twisted‐nematic liquid‐crystal displays using surface gratings is described.

ISSN:0003-6951    

DOI:10.1063/1.89864

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Surface‐acoustic‐wave (SAW) characteristics of a lead potassium niobate (Pb2KNb5O15) single crystal have been calculated. It is predicted that SAW on this material has very strong electromechanical coupling 2&Dgr;v/vof more than 10% in the stiffened Rayleigh mode in theX‐axis boule andY‐cut plate and as high as 28.5% in the Bleustein‐Gulyaev mode in theZ‐axis cylinder.

ISSN:0003-6951    

DOI:10.1063/1.89865

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A new method for generation and detection of acoustic volume waves in nonpiezoelectric dielectrics is described. The acoustic intensity is sensitive to band‐gap illumination. Acoustic conversion is observed on inserting the sample in a reentrant cavity, in contact with the center post during application of rf pulses. The induced conversion efficiency builds up with a time constant in the range of seconds to minutes depending on the nature of the metal dielectric contact and on rf pulse repetition rate. Acoustic signals of 75 dB above noise have been generated in KTaO3. Very long storage times are observed. A model for the transducer action based on induced space charge and a surface barrier is proposed, similar to the model of Fossheim and Bjerkan for surface‐wave generation in nonpiezoelectric dielectrics. The estimated electromechanical coupling coefficient is comparable to that of piezoelectric LiNbO3and LiTaO3.

ISSN:0003-6951    

DOI:10.1063/1.89866

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Electron attachment to Br2and HBr has been studied over a range ofE/Pvalues using a high‐pressure electron‐beam‐sustained gas‐discharge apparatus. Experiments were performed in gas mixtures containing the attaching species and a large excess (⩾99%) of N2which was included to control the electron temperature. Values of the dissociative attachment rate constants at an average electron energy near 1.0 eV for Br2and HBr were found to be 1.0×10−10and 8×10−10cm3/sec, respectively. Using the known electron energy dependence of the dissociative attachment cross section, the magnitude of the dissociative attachment cross section for HBr was estimated.

ISSN:0003-6951    

DOI:10.1063/1.89867

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The absorption of 10.6‐&mgr; and 2.8‐&mgr; radiation by inverse bremsstrahlung in an electron‐beam‐sustained discharge is measured in several gases as a function ofE/N. The experimentally derived absorption cross sections are compared with theoretical predictions and good agreement is shown.

ISSN:0003-6951    

DOI:10.1063/1.89868

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A preliminary experiment was performed to investigate conversion of 10.6‐&mgr;m laser energy to electrical energy via a laser‐sustained argon plasma. Short‐circuit currents of 0.7 A were measured between thoriated‐tungsten emitter and collector electrodes immersed in the laser‐sustained argon plasma. Open‐circuit voltages of ∼1.5 V were inferred from the current‐voltage load characteristics. The dominant mechanism of laser energy conversion is uncertain at this time. Much higher output powers appear possible.

ISSN:0003-6951    

DOI:10.1063/1.89869

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Using a simple time‐of‐flight technique, we have measured the electron drift velocity in helium with 0.1–1% fluorine additive. Our results in a 0.1% mixture are in close agreement with data in pure helium. The measured drift velocity increases with increasing fluorine concentration.

ISSN:0003-6951    

DOI:10.1063/1.89870

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The influence of anode and cathode plasma upon the behavior of low‐impedance REB diodes is investigated by acquiring data with anodes and cathodes heated to 1000 and 200 °C, respectively. These data indicate a reduction in impedance collapse which is consistent with a 20% reduction in the anode‐cathode plasma gap closure velocity and a factor of 2.5 reduction in ion current. The ion current is reduced for heated anodes because then the ion current is primarily attributed to weakly ionized carbon and higher atomic number ions rather than protons.

ISSN:0003-6951    

DOI:10.1063/1.89860

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We have considered the interaction between a laser‐produced plasma and a grounded conducting cylindrical aperture. Space‐charge effects both within and beyond the aperture are treated in an approximate analysis. We apply our results to recent ion pinhole measurements to show that space‐charge effects can account for the data obtained.

ISSN:0003-6951    

DOI:10.1063/1.89861

出版商:AIP    

年代:1978

数据来源: AIP