摘要:

Arrays of thermopile detectors arranged on flat panels were used to measure stray radiation from high‐power transmission lines at 140 GHz in the FTU tokamak electron cyclotron resonance heating experiment. These instruments are insensitive to polarization and to the direction of propagation within ±40° off normal incidence. They have a time constant of 120 ms, therefore amplification and synchronous detection are required for the measurement of short radiation pulses. No special measurement techniques are required with long pulses or cw radiation. The typical sensitivity is 2 mV cm2/mW in long pulse operation and 47 &mgr;V cm2/mW for 1 ms pulses. The detectors are sensitive to light and adequate filtering should be added to suppress it if necessary. These characteristics are adequate for the measurement of human exposure levels to electromagnetic radiation in the millimeter wave range. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147581

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have previously observed that cytosolic free calcium ([Ca2+]i) is increased in HL‐60 cells after exposure to an extremely low frequency (ELF) magnetic field. To facilitate the investigation of the time dependence of this effect, we built a magnetic field exposure system in which four samples of cells could be kept at constant temperature and maintained in suspension with constant mixing. Fluorimetric measurements of [Ca2+]ifrom these samples were made in real time using a periscopic optical system attached to a fluorescence spectrophotometer. This design feature eliminated possible confounding influences of the applied magnetic field on the light detection electronics, and isolated the cell samples against stray magnetic fields from electronic equipment. The operation of the instrument was computerized. This permitted the precise definition and replication of experimental conditions such as the properties of the applied magnetic field, the rate of sample mixing, and the instant at which an agonist was added to the cells. It also provided a time‐resolved record of sample temperature and fluorescence for each experiment. Characterization of the instrument enabled us to rule out potential confounding influences on fluorimetric [Ca2+]imeasurements, such as temperature and mechanical vibration, and to have confidence in the accuracy and precision of the applied ELF and static magnetic fields. Experiments with HL‐60 and Jurkat cells verified that the instrument could measure [Ca2+]iin live cells and follow large rapid changes in [Ca2+]iafter activation with an agonist. This instrument will provide an ideal tool with which to investigate in greater detail the effect of ELF magnetic fields on [Ca2+]iin HL‐60 cells. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147521

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

To check and measure the converse piezoelectric effect in bone samples, we had to detect displacements in the range of 1–100 pm with three kinds of restrictions: (1) the biological nature of the samples imposes severe limits in selecting a suitable device and method; (2) such a method has to take into account some clinical applications to which the experiment is devoted; (3) the piezoelectric behavior of bone samples is particularly interesting at low frequencies, around 1 Hz. For such reasons we modified an existing dilatometer based on a microwave differential spectrometer. A 14 GHz klystron, linearly modulated in frequency by a triangular 50 Hz voltage applied to the repeller, is connected, via magic T, to two identical cavities tunable around 14 GHz and whose resonance curves are recorded by crystal detectors. When one of the two cavities changes its height according to the length variations of the sample, its resonance frequency varies resulting in a shift of the resonant curve with respect to the resonance curve of the other cavity acting as reference. The comparison between the cavities’ responses is performed by a pulse technique transforming the frequency shifts into time intervals, that are then converted into dc voltages. The differential character of this measurement avoids the need for the microwave source stabilization. The relative shift in frequency is measured with an accuracy better than 500 Hz. This accuracy allows us to measure displacements smaller than 7 nm in the cavity’s height. After 2 h of warmup, thanks to the differential arrangement of the system, thermal or other drifts are not detectable within a lapse of time of 12 h. This feature allows coherent signal averaging over long periods. With a piezoelectric ceramic stack moving 100 pm in square wave fashion at 50 mHz we found that the signal to noise ratio was 20 dB after 1000 cycles of signal averaging, when our bandpass filter was tuned at 1 Hz. In conclusion, this system can detect periodic displacements as small as 1 pm in a short time and reliably. Due to the operational simplicity and stability, at room temperature and humidity, the device is suitable for dilatometric measurements on biological samples. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147535

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this article, we describe the architecture of the 3 m suspended Michelson interferometer prototype for gravitational wave detection which is operational in Napoli. The characteristic which makes this interferometer different from the existing ones is the digital implementation of the control system, the monitoring system, the data acquisition system, and the archiving system. This architecture makes this interferometer a good test bench for the study, the development, and the test of general techniques for the automatic control of interferometers for gravitational wave detection. In particular, it is now being used for the development and the test of some subsystems of the very long baseline interferometric VIRGO antenna for gravitational wave detection. [The Virgo Project, Final Design of the Italian–French large base interferometric antenna Virgo for gravitational wave detection of which the authors are proponents and in whose construction the Authors are collaborating (INFN, Italy, and CNRS, France, 1989, 1992, 1995).] ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147536

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The new sediment trap has a 0.5 m2aperture, a funnel slope of 34° and is capable of collecting 21 samples at programmed intervals (1 min–1 year) during deployment in the deep ocean. The trap has been designed to allow reliable data on trace inorganic and organic components (such as trace elements,n‐alkanes, PCBs, PAHs, amino/fatty acids) in addition to the standard biogeochemical variables in the collected particles. Due to the exclusive use of synthetic (such as fiberglass, PVC, PTFE, or POM‐Delrin®) and highly resistant metallic materials contamination problems have been eliminated for these species. Blank values determined in several tests in the open ocean were as low as 1% or even less of the amounts present in trap material, even at low particulate loadings. Another major aim was the elimination of loss of dissolved components from the sample cups into seawater. Microbial and chemical processes modify the collected particles, thereby mobilizing originally particulate species into solution. It is thus essential to avoid greater losses of dissolved species through diffusion into the surrounding seawater after collection. This was achieved by means of an especially designed sealing mechanism. Tests with tracer substances during field studies proved that losses of dissolved components from supernatants during one year of deployment are as low as 10%. Additionally, the relationship between flow characteristics around the traps and their excursions from the vertical position in a bottom‐tethered array was studied during a one‐year deployment in the North Atlantic. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147582

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A stainless‐steel chamber has been constructed and interfaced to a Fourier transform infrared spectrometer for the purpose of studying laboratory simulated atmospheric aerosols and clouds. The chamber is cylindrical in design and is comprised of a double‐walled inner assembly that resides within an outer vacuum jacket. The volume of the aerosol sample region is 28 L. By circulating refrigerated methanol between the double walls of the inner assembly, constant temperature control of the sample region can be maintained between 187 and 300 K. A study of temperature uniformity within the chamber at 291, 240, and 187 K revealed a standard deviation in temperature of 1.6 K as determined from measurements made using five copper–constantan thermocouples. Good agreement is obtained between thermocouple measured temperatures and rotational temperatures computed from infrared absorption spectra of methane gas. The chamber described here has been used to examine heterogeneous chemistry of solid powder samples. A technique of generating an aerosol sample by rapidly dispersing a solid powder in a gas is presented. The half‐life of a &ggr;‐alumina aerosol sample was measured to be 25 min. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147537

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This article describes a user‐controlled detector simulator to aid development of the grazing incidence spectrometer (GIS), which forms part of the coronal diagnostic spectrometer on‐board the solar and heliospheric observatory. The simulator was a vital element in carrying out full range tests of the GIS processing electronics in the absence of real detectors, including extreme conditions not easily achievable by other means. With a large degree of flexibility, the simulator provides a wide range of characteristics of output events of realistic shapes. Although the simulator was designed specifically to simulate the spiral anode as used by the GIS, the design is applicable to any three channel detector system and has since been used for theFONEMAinstrument for the Russian Mars96 mission. The simulator functionality, performance parameters, software and hardware design, and the overall grounding scheme are presented. The simulator performance with some test results are also discussed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147538

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A general, nonlinear least‐squares, direct‐search strategy for the analysis of the time‐dependence of single or multicomponent spectral data sets is described. The generic procedure is named component resolved (CORE) spectroscopy, and has previously been successfully applied to the special case of Fourier transform pulsed field gradient spin‐echo NMR data (FT‐PGSE). The main purpose of the CORE processing is to improve the quality of evaluated data through its intrinsic S/N enhancement, and to confidently allow studies on multicomponent data sets characterized by either or both of (a) extensive spectral overlap and (b) only minor differences in (for example) individual component kinetic decay rates. The generality of the CORE approach is here illustrated through examples from chemical kinetics and time‐resolved fluorescence. Unlike previous strategies for the same purpose, CORE can easily be adapted to a large variety of data set types, that can be of almost unlimited size. As a consequence of its direct approach to the underlying problem, the minimization approach is also perfectly stable. The generic CORE strategy also does appear to lend itself nicely to parallel processing, which would speed up the data processing by one or two orders of magnitude in future implementations. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147539

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A simple but effective approach to inversion of the Poisson transform is described. The use of cubic splines to approximate the inverse function automatically provides a degree of regularization which helps to overcome the ill‐conditioned nature of the problem. Representative tests of the method are presented. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147540

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The measurement system transfer characteristic is an unsteady, nonlinear function that depends upon time and ambient conditions. The article presents a method of tracking the real characteristic by using periodic autocalibration of the real characteristic and by applying a tangent method to the ideal characteristic. The efficiency of the algorithm has been verified for dc current generation. Periodic autocalibration fixes the current state of the measurement system characteristic by measuring internal references. The correction of a quantity at the input of the current generator is calculated from measurement of its output quantity and by using a tangent method applied to the ideal current generator characteristic. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147541

出版商:AIP    

年代:1996

数据来源: AIP