摘要:

Algorithms based on Prony’s method are proposed for the estimation of exponential time constants of a double exponential fluorescence–decay process. The performance of these algorithms is evaluated, using Monte Carlo simulations, the results of which are presented showing that the performance of Prony’s method can be greatly improved with the selection of an optimized observation window width and a few algorithm-related parameters. The applications of these noniterative algorithms in real-time, quasidistributed temperature sensor systems are discussed where the material decay may not approximate to a single exponential, or multimaterial sensors are used with a single, simple pump source and a single detector. Applications to quasidistributed sensor systems are considered and, thus, experimental results are presented to justify the use of the algorithms in Prony’s method in practical double exponential fluorescence decay sensor analysis. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147755

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe in detail a high-temperature octopole/collision cell apparatus for studying ion–molecule reactions involving nonvolatile target species, including metals. The system can be operated at temperatures up to ∼1200 K and features coaxially heated octopole rods and a heated collision cell in which the vapor of a nonvolatile target material is generated by evaporation from a bulk sample contained therein. The poles are heated independently of the cell and are maintained at a higher temperature to prevent condensation of the sample on the poles. This ensures a well characterized operating temperature that is necessary for absolute cross-section measurements. The apparatus design permits two independent methods for the determination of the target vapor density. The absolute Na+N2+charge transfer cross section has been measured for collision energies in the range 0.1–2.25 eV. These results represent the first guided-ion beam measurement of an absolute ion–metal atom reaction cross section, and are compared to earlier studies conducted with other methods. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147591

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Apparatus and techniques were developed to electrodynamically trap and manipulate groups of microparticles. The equipment consists of a vibrating orifice aerosol generator, an inductive particle charger, a plenum chamber, and a double-ring electrodynamic balance. Salt particles (NaNO3) of controllable and measurable mass and charge were produced and introduced into the balance in nitrogen at flow rates up to 25 cm3/min. Ordered arrays of any number of particles up to 26 were assembled and manipulated. Methods for compressing the arrays are presented, and controlled ejection of single particles from a trapped array is demonstrated. Particles of opposite polarity were successfully levitated and kept apart, and aggregation of these particles was then induced by changing the electric field. Raman spectra were recorded for multiple salt particles, each having a diameter of 3.5 &mgr;m, by aligning them in a laser beam. The enhanced Raman signal is compared with that from a single particle isolated from the array. From the results, a detection limit of 0.4 pg per particle was estimated. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147682

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A compact 2.45 GHz surface-wave ion source has been developed for the production of stable beams from gaseous feed materials. The source has been operated with two different geometries of surface wave generation, that is, a dielectric disk on ground plane structure and a dielectric disk between the parallel plate structure with a holey top plate. The designer can control the intensity of the emitted microwave simply by varying the thickness of the dielectric plate. The sources have been operated with three different thicknesses of the dielectric plate:td=10,15, and 20 mm.td=10mm is the optimum coupling condition. Moreover, the ion beam current of the holey-plate structure is 1.5 times as high as that of the dielectric disk structure. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147746

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By combining optical fibers with piezoelectric scanning Fabry–Perot interferometer, the profiles of H&agr;and D&agr;have been determined simultaneously in a single Tokamak discharge. Consequently, the ratio of hydrogen to deuterium and ion temperature are obtained. Not only is the uncertainty of shot-to-shot avoided, the results of the experiment indicate that this instrumentation has the advantage of rapid wavelength scanning, large dispersion, high resolution, and good adaptability of working in adverse circumstances such as at a Tokamak site. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147704

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured the temperature dependent change ∂&Fgr;/∂Tin the flux signal of a superconducting quantum interference device (SQUID) operating in a flux locked loop. Thin film niobium dc SQUIDs were used for these investigations. One and the same device could be operated either as dc or rf SQUID allowing one to compare the effect of temperature variation in both modes of operation. We have found that relaxation of trapped flux appears to be the dominant result of temperature variation. The asymmetry of the two critical junction currents in dc SQUID operation could be seen, as well as an influence of an external magnetic field on ∂&Fgr;/∂T. This influence was an order of magnitude smaller when the device was operated as an rf SQUID, compared to dc SQUID operation. By the use of a high frequency demagnetization process, ∂&Fgr;/∂Tcould be reduced from typical values of about 0.3&Fgr;0/K to less than0.05&Fgr;0/K in certain cases. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147709

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Newly developed equipment is described for measuring specific heat between 0.5 and 60 K in magnetic fields up to 17.5 T, using the traditional semi-adiabatic method in combination with a mechanical heat switch. The lower limit found for the heat capacity of sample plus holder amounts to 0.04 mJ/K at 500 mK. Under these conditions, the absolute accuracy is better than 1 &mgr;J/K. Some recent data obtained with this equipment on an UNiAl single crystal are given as an example. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147761

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new method that fits the whole temperature response of a heat-pulse calorimeter for heat capacity is developed. Analyzing the thermal response of a heat-pulse calorimeter on a model that was used by the relaxation method, the authors derived some useful relations and further utilized the numeric method of the general linear least squares to determine the heat capacity of a sample. Absolute accuracy of the proposed method was verified by determining the heat capacity of a 0.249 76 g copper sample (purity 99.999&percent;) on a self-designed and fully automated calorimetric system from 4.5 to 80 K. Comparing the result with the literature, the deviation in average was 1.2&percent; from 4.5 to 20 K and 2.0&percent; from 20 to 80 K. It is found that the proposed method is capable of measuring heat capacity regardless if the sample is adiabatically or nonadiabatically isolated. The size of the specimen is not critical for the application of the method and the temperature range of measurement can be expanded. It also deals with the &tgr;2effect. Details of the employed calorimetric system are described. Stability, inherent limitations, and further improvement of the system are also discussed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147722

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The stress dependence of ultrasonic velocities is used as the physical basis for a device that measures large forces. A solid aluminum cylinder serves as a load-bearing element, and noncontacting electromagnetic-acoustic transducers are used to excite and detect resonant vibrational modes. The problem of vibrational damping at the ends of the cylinder is solved by making the diameter slightly larger in a central section, so that certain resonant modes are “trapped,” with negligible amplitude at the ends. Nearly complete temperature compensation is achieved by taking the ratio of two resonant frequencies with approximately the same temperature dependence but with much different stress dependencies. The measurement of force with vibrational spectroscopy provides several advantages over conventional resistive strain gages, including greater resolution, insensitivity to transducer and bond degradation, durability in harsh environments, and insensitivity to bending moments. The resolution in strain is approximately4×10−8.The upper limit of measurable stresses approaches the yield strength of the aluminum cylinder; this is approximately 325 MPa, which corresponds to a strain of4×10−3.

ISSN:0034-6748    

DOI:10.1063/1.1147779

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An omega (&OHgr;) filter has been designed to satisfy the following four constraints: (1) the dispersion at 200 kV is larger than 1 &mgr;m/eV, (2) the principal second-order aberration coefficientsA&ggr;&ggr;&ggr;,B&ggr;&dgr;&dgr;are less than 1000 mm, (3) all of the inclination angles of the entrance and the exit faces of the sector magnets are within 0–45° (positive), and (4) the drift length between the first and the second magnet (or between the third and the fourth magnet) is less than the radius of the largest magnet. The latter two are practical requirements and are important for the experimental adjustment of the optical axis. The optimization of filter dimensions was made using a numerical electron trajectory method as follows: (1) The optical axis was found by calculating the central electron trajectories using a table of the fringing field distribution and a constant field strength inside the magnet. (2) The stigmatic focus condition was found by changing the inclination angles of the faces of the magnets. (3) The 18 secondary aberration coefficients [H. Rose, Optik51, 15 (1978)] were numerically calculated. A three-dimensional trajectory calculation was made for the selected filter shape. A filter with a 1.3 &mgr;m/eV dispersion at 200 kV has been designed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147797

出版商:AIP    

年代:1997

数据来源: AIP