摘要:

One way to classify performance indices of irreversible heat engines is according to how the indices change when one engine is replaced by two (or more) of the same kind in series. We investigate the performance of two endoreversible engines (i.e., heat engines with the only irreversibility being heat resistance to the surroundings) which are put in series to form a single engine, whose power output is maximized. In this unconstrained optimization the interface between the two stages, which for the present model is the intermediate temperature and the relative timing of the two engines, is arbitrary and can be used to satisfy other, nonthermodynamic constraints. Adding any constraint on the volume of the working gas does not lift this indeterminacy. The optimum composite system is equivalent to a single endoreversible engine, thus displaying a sequencing property similar to Carnot engines.

ISSN:0021-8979    

DOI:10.1063/1.331592

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

We determine the solution to the prototype problem: Given a finite amount of time, what is the optimal motion of a piston fitted to a cylinder containing a gas pumped with a given heating rate and coupled to a heat bath? The optimal motion is such as to maximize the work obtained via the piston in a specified period of time. This problem is solved for various end‐point constraints, including constraints on final volume, final energy, or final volume and energy. We consider several associated problems including constraints on the rate of change of volume, piston friction, piston mass, and inertial effects of the gas. Explicit thermodynamic analyses of the solutions are carried out for various examples. The efficiency and the gain over nonoptimal paths are studied. Significant improvement over the bound on the efficiency is obtained as calculated by (infinite time, reversible) thermodynamics. The nature of the limit of the optimal solution as the time approaches infinity is determined. For a finite heating rate the optimal path is irreversible even as the time approaches infinity.

ISSN:0021-8979    

DOI:10.1063/1.329960

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Using the Pontryagin maximum principle we optimize the operating conditions of a model external‐combustion engine to obtain maximal efficiency. The model engine consists of a cylinder equipped with a piston containing a gas, pumped with a given time‐dependent rate of heating, and coupled to a heat bath. We consider a fully cyclic engine, wherein both the volume and the energy of the working fluid are periodic. Such engines possess a finite optimal compression ratio. The gain in efficiency over nonoptimal paths is significant. We demonstrate the results with a numerical example, and we perform a thermodynamic analysis.

ISSN:0021-8979    

DOI:10.1063/1.329931

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

We apply the method of optimal control theory to determine the optimal piston trajectory for successively less idealized models of the Otto cycle. The optimal path has significantly smaller losses from friction and heat leaks than the path with conventional piston motion and the same loss parameters. The resulting increases in efficiency are of the order of 10%.

ISSN:0021-8979    

DOI:10.1063/1.329894

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Charge trapping in the intervening oxide layers of electrically‐alterable read‐only memories has been studied for different device configurations incorporating a dual electron injector structure (DEIS). The degradation of the write/erase capability of these devices is associated with electron capture in neutral trapping centers present in both chemical‐vapor‐deposited and thermal oxides. Annealing the exposed DEIS stack at 1000 °C in N2results in better cycling capability. The dominant traps in unannealed samples were found to have capture cross sections of &sgr;c0x≊10−16−10−17cm2, while those in annealed samples have &sgr;c0x≊10−17−10−18cm2.

ISSN:0021-8979    

DOI:10.1063/1.329908

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A scheme is proposed for coherent detection and real time Fourier processing of optical signals. In this scheme an input signal is photomixed at one photodetector with a variable (chirped) frequency output of a tunable diode last (TDL). Part of the TDL radiation is photomixed at a second photodetector with a fixed frequency output of a stable laser. The electrical signals from the two detectors are convolved by a surface scoustic wave convolver. After proper filtering and envelope detection, the convolver output can be shown to give the power spectrum of the input signal. This scheme may be used for spectroscopy in the infrared.

ISSN:0021-8979    

DOI:10.1063/1.329951

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Point‐contact Josephson junctions with a submicron contact diameter have been used as high‐frequency mixers (170–220 GHz) under high thermal background conditions. The junction is formed across a full height (0.56×1.06 mm2) waveguide between a 3–5‐&mgr;m thick Nb whisker and a 0.2‐mm diam Nb center conductor of a coaxial line. The best single‐side band mixer‐noise temperature that was measured is 165 K (± 25%) with a corresponding single‐side band conversion efficiency of 0.36±0.03 (a loss of 4.5 ±0.4 dB) at a signal frequency of 185 GHz, including losses in the coupling horn and the waveguide. The performance was measured with the hot‐cold source technique. The effects of nonheterodyne response in that situation were investigated in detail. The junctions have been operated in a coherent receiver that can be used on a telescope with only small adaptations. The instantaneous bandwidth of the receiver is about 20 GHz.

ISSN:0021-8979    

DOI:10.1063/1.329957

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Electron impact collision strengths and transition rates for manganese ions of the Li I through F I isoelectronic sequence are calculated for transitions between levels of the configurations 2s22pk, 2s2pk+1, and 2pk+2. The excitation rate coefficients and transition rates obtained from these data are used to calculate level populations at temperatures of maximum abundance of the ions. The proton excitation rates for fine structure levels are also included in the level population calculations. The relative intensities of allowed lines are calculated and the calculated wavelengths are compared with the recent observations of the TFR group. The wavelengths of the forbidden and intersystem lines are also given and compared with the observations where available.

ISSN:0021-8979    

DOI:10.1063/1.329964

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The possible Auger recombination mechanisms in direct‐gap semiconductors are investigated. These include band‐to‐band processes, phonon‐assisted processes, and Auger recombination via shallow traps. The band‐to‐band Auger rates are calculated including Fermi statistics, nonparabolic bands, and screening effects both forn‐type andp‐type semiconductors. The nonparabolicity is calculated using the Kane‐band model. The band‐to‐band Auger processes are characterized by a strong temperature dependence, the Auger rate decreasing rapidly with decreasing temperature. The phonon‐assisted and the trap processes do not exhibit such a strong temperature dependence. This is because the additional momentum conservation for the four‐particle states in band‐to‐band processes gives rise to a ’’threshold energy’’ for the process. For the same reason, the band‐to‐band Auger rate decreases rapidly with increasing band gap. In large‐band‐gap semiconductors the weakly temperature‐dependent phonon‐assisted processes are expected to dominate. The Auger recombination rate via shallow‐trap levels increases with increasing trap depth. A numerical computation is carried out for the quaternary alloy In1−xGaxAsyP1−y. We find that the calculated Auger rate is significant enough to account for the observed temperature dependence of threshold current of 1.3‐ and 1.55‐&mgr;m InGaAsP‐InP double heterostructure lasers.

ISSN:0021-8979    

DOI:10.1063/1.329942

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The loss characteristics of hollow‐core, oxide‐glass‐cladding, middle infrared (near 1000 cm−1) optical waveguide is calculated numerically for TE01, TM01, and HE11modes. The oxide‐glass cladding used has its refractive indexnrless than unity; their transmission losses of the waveguide are relatively small due to total reflection effect. The necessity condition of complex refractive indexnr‐ikof the cladding is clarified to be used with such hollow‐core optical waveguides.

ISSN:0021-8979    

DOI:10.1063/1.329961

出版商:AIP    

年代:1982

数据来源: AIP