摘要:

Two guided modes in a grounded, thin, dielectric film waveguide having a periodic corrugation of the interface between the film and the cover can interact selectively in the neighborhood of a particular frequency. Five different theories exist for the investigation of this interaction. The first three are small amplitude theories which assume that the amplitude of the corrugation relative to the thickness of the film is small and the third and the fourth theories are large amplitude theories which do not make such an assumption. In the small amplitude theories, solutions are sought as a perturbation of ideal normal modes and boundary conditions are applied on the average flat surface. The first small amplitude theory makes use of quasioptical considerations and the other two small amplitude theories employ wave‐theoretical techniques. All three theories lead to identical coupled mode equations governing the interaction. The first large amplitude theory is based on an expansion in terms of local normal modes and is applicable for a grating with a smooth profile. The second large amplitude theory is applicable for a lamellar grating and it makes use of a model of a repetitively mismatched transmission line. The various intrinsic dephasing mechanisms are explained. The large amplitude theories are able to account for the dephasing effects due to the finite (nonvanishing) depth and the finite (noninfinite) length of the corrugations. Some aspects of passive devices and some theoretical considerations of active devices using corrugated waveguides are reviewed. The transmission line model is able to take into account the end effects. For the mode of operation considered, there are no end effects and the overall contribution of the vertical discontinuities vanish for the lamellar grating.

ISSN:0021-8979    

DOI:10.1063/1.340381

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We investigate the performance of a class of endoreversible‐combined refrigeration cycles operating between a low‐temperature heat reservoir atTLand a high‐temperature heat reservoir atTH, and derive the optimal configuration and the relation between the optimal coefficient of performance and the rate of refrigeration of these cycles. It is shown that the relation is similar to that of an optimal endoreversible refrigeration cycle. However, it is worth noticing that the overall heat resistance of a combined endoreversible refrigeration cycle is not identical with that of a single one, so that they are somewhat different from each other in performance. Simultaneously, it is pointed out that some performances of an endoreversible refrigeration cycle are quite different from those of an endoreversible power cycle.

ISSN:0021-8979    

DOI:10.1063/1.340470

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Fracture testing of silicon cantilever beams (thicknesses 10–20 &mgr;m) was performedinsituin a scanning electron microscope by means of an equipment specially designed for this purpose. Beams of various sizes and orientations (⟨011⟩ and ⟨001⟩) were manufactured in Si (100) wafers by two different micromachining procedures. The beams were tested by simple bending to fracture, and a number of fundamental fracture parameters were determined from an analytical model of elastic fracture. To verify its validity, the model was utilized to evaluate an experimentalEmodulus, which was found to agree well with previous results. Fracture limits, fracture strains, and initiating flaw sizes were determined. The maximum fracture limit was very high; about 10 GPa. The strengths of different beams scattered from this value down to practically zero strength, with an average close to 4 GPa. The corresponding fracture strains and initiating flaw sizes were 6% and 3 nm, respectively (maximum strength), and 2% and 17 nm (average strength). Finally, a simple fractography study was performed on the fractured beams.

ISSN:0021-8979    

DOI:10.1063/1.340471

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We propose a new technique for accurate measurement of ac voltages with Josephson junctions. Based on the counting of pulses generated by a Josephson junction, the method may be capable of precision at the ppm level for frequencies less than 100 kHz.

ISSN:0021-8979    

DOI:10.1063/1.340472

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Backsputtered material is demonstrated to be a major factor in determining gallium liquid metal ion source (LMIS) lifetimes andI‐Vcharacteristics during operation in ultrahigh vacuum. The behavior of LMIS emission current is extremely sensitive to the type of material backsputtered onto the source tip, shaft, and reservoir. The assimilation of sputtered material is important in maintaining stable ion emission and is found to depend on the miscibility of the contaminant material in gallium. Materials which do not form solid phases when mixed with liquid gallium have the least effect on ion currents.

ISSN:0021-8979    

DOI:10.1063/1.340473

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The wall relaxation time for optically pumped ⟨Sz⟩ polarized sodium atoms colliding with copper, stainless‐steel, and dry‐film coated surfaces has been measured as a function of an applied magnetic field. Results show that the mean number of wall collisions increases from one to about four before depolarization of sodium atoms occurs on a copper wall in a high (12 kG) magnetic field, whereas the atoms relax after a single collision on a stainless‐steel wall even in high fields. The relaxation time for a dry‐film coated surface, for the cell geometries used in our work, is dominated by the effusion of polarized sodium atoms from the cell. Our measurements also allow an estimate of the strength of the local magnetic field causing the ⟨Sz⟩ depolarization and of the correlation time of the depolarization interaction on the surface. The importance of these experimental results as applied to the performance of optically pumped polarized ion sources is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.340474

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The factors determining arrival time line shapes in ion drift tube devices are discussed. An analysis is presented for the line shape due to diffusive drift and its modification due to various boundary conditions. The modification of the line shape due to ion neutralization by randomly placed impurities within the drift area is considered.

ISSN:0021-8979    

DOI:10.1063/1.340475

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We find the formula &sgr;=&fgr;m[&sgr;&ohgr;+AQv/ (1+CQv/&sgr;w)] that embodies the fact that the rock conductivity &sgr; is a nonlinear function of water conductivity &sgr;w, can fit data on 140 cores rather well withm≊2,A=1.93×m(mho/m)(l/mol) andCQv=0.7 (mho/m). The observed curvature at low salinity is due to an interplay of tortuosity and water conductivity. Empirical correlation shows thatmincreases with the clay content, as the tortuosity increases with the clay content. Thus, the conductivity of a fully water saturated clay bearing (shaly) sand is completely determined from porosity &fgr;, charge densityQv, and water conductivity &sgr;w.

ISSN:0021-8979    

DOI:10.1063/1.340476

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new two‐photon method for recording holograms is presented. It is based on the fact that a first photon produces singlet oxygen by a photosensitization process; this species oxidizes a specific trap to produce a carbonyl compound. This latter is used as a conventional polymerization initiator and produces active species after the absorption of a second photon. The feasibility of this general process is demonstrated by using Methylene Blue (photosensitizer), diphenylisobenzofuranne (singlet oxygen trap), and a mixture of acrylamides (polymerizable compound). Finally, diffraction efficiencies higher than 2% are easily achieved with such systems. The influence of different experimental parameters was studied with a view to extending the sensitivity of the system to the infrared.

ISSN:0021-8979    

DOI:10.1063/1.340477

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The effects of unfocused 193‐ and 248‐nm laser radiation of 3–30 mJ/cm2on dc discharges of vinylchloride in helium are described. Laser‐initiated striking and quenching of the low‐current discharges are observed at pulse repetition rates of 10 to 0.001 s−1over a range of operating conditions. The apparent paradox of the coexistence of strike and quench conditions in the discharge gap for consecutive laser pulses is discussed.

ISSN:0021-8979    

DOI:10.1063/1.340478

出版商:AIP    

年代:1988

数据来源: AIP