摘要:

Experimental measurements are made for the steady‐state frequency response of a supported thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for both a supported one material wire (typeK) and a two material wire (typeT) with unequal material properties across the junction. The data for the amplitude ratio and phase angle are correlated to within 10% with the theoretical predictions of Fralick and Forney (1992) for a laser‐heated junction with no bead. This is accomplished by choosing a natural frequency &ohgr;nfor the wire data to correlate the first‐order response at large gas temperature frequencies. Moreover, it is found that a large bead size (roughly twice the wire diameter) will increase the amplitude ratio at low frequencies and distort the phase angle. In the latter case, it is necessary to increase the thermocouple wire length by 20% in the theory to correlate the data when the junctions have beads (silver soldered).

ISSN:0034-6748    

DOI:10.1063/1.1144080

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An ultrahigh vacuum (UHV) surface analysis chamber coupled with a visible light‐scattering apparatus is described. This combination of UHV surface analysis capabilities and bidirectional reflectance distribution function measurements permits investigation of effects of various surface treatments such as gas adsorption and ion bombardment on optical scatter. Stray light reflections from the UHV windows and components are temporally rejected by use of a picosecond pulsed laser source and synchronized, time‐gated detector. This system allows measurement of optical scatter levels in the range of 10−7sr−1.

ISSN:0034-6748    

DOI:10.1063/1.1144081

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe a method for measuring and controlling the temperature of thin ceramic plates which are used as substrates for the deposition of thin films in high vacuum. The ceramic plates have an embedded platinum resistor which acts as both heating element and thermometer. The temperature of the substrate is controlled by an electronic feedback circuit. This arrangement enables accurate measurements of the thin‐film temperature. In addition, the system has a fast response time and excellent long‐term temperature stability. We describe an application where the temperature control system is combined with ac resistance measurements to study the kinetics of a solid‐state interdiffusion reaction in Ni‐Zr multilayers.

ISSN:0034-6748    

DOI:10.1063/1.1144082

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The design and construction of a 1‐kW induction heating supply is described. The system was optimized for applications in which the power is coupled into a graphite susceptor which is the substrate holder for samples placed in the reaction chamber of a chemical vapor deposition system. The supply draws power from a 120‐V, 20‐A service outlet and delivers a 10‐kHz output which is proportional to the magnitude of a 0–5 Vdc control signal. Presently available powern‐metal‐oxide‐semiconductor field‐effect transistors permit the construction of a compact unit which is small enough to be installed inside of a deposition cabinet.

ISSN:0034-6748    

DOI:10.1063/1.1144083

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe the construction and operation of a liquid‐phase reaction cell designed in our laboratory that is attached to an ultrahigh‐vacuum (UHV) chamber equipped with the traditional surface science techniques for structure and composition analysis. The sample surface can be prepared and characterized in the UHV chamber prior to transfer in the liquid‐phase reaction cell. The transfer has been designed so that there is no loss of the UHV chamber vacuum integrity, as few parts as possible come into contact with the liquid, the surface stays clean during the transfer. The liquid‐phase reaction cell itself is designed to study liquid‐phase hydrogenation reactions at pressures up to 2 atm and temperatures up to 70 °C. A 1‐mm‐diam liquid jet with a velocity up to 6 m/s is produced by a gear pump that is incident on the sample surface to allow good mass transfer at the liquid‐solid interface. The progress of the reaction is followed by gas chromatography. We report the reaction rate data for the hydrogenation of cyclohexene on a platinum foil.

ISSN:0034-6748    

DOI:10.1063/1.1144084

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have designed and constructed a sealed, temperature‐controlled Couette‐type shear cell which allows us to carry outinsitusynchrotron x‐ray scattering studies of the nonequilibrium structures of complex fluids under flow, probing lengths ranging from the nanometer to the semimacroscopic micron scale. The sealed design allows the cell to be tilted, facilitating the scanning of all directions in reciprocal space. In contrast to existing neutron shear cells, we access the shear plane containing the velocity and the velocity gradient. The temperature control of the cell enables us to carry out phase transition studies far from equilibrium. The complex fluid systems which may be studied with this cell include thermotropic and lyotropic liquid crystals, microemulsions, and polymeric fluids. Recent results on the nematic and smectic‐Aphases of a liquid crystal, and the disordered bicontinuousL3phases of surfactant membranes in the vicinity of the ordered lamellarL&agr;phase under flow, are presented.

ISSN:0034-6748    

DOI:10.1063/1.1144085

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For detection of weak signals, and for use on ultralow temperature experiments, it would be useful to have a robust superconducting quantum interference device (SQUID) amplifier that works below 1 K. We report on a test of a commercial SQUID amplifier that has lower noise than others we have tested, and works well while attached to a 50‐mK chamber. The SQUID noise was improved only modestly when cooled from 4 K to 50 mK. The best energy resolution measured was 2200 ℏ.

ISSN:0034-6748    

DOI:10.1063/1.1144086

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A surface tensiometer has been devised which is based on the mathematical solution, as a function of the surface tension of a liquid, of the profile of a cylindrical meniscus formed against a flat plate brought into contact with the free surface of a quiescent pool of the liquid. Only the angles of inclination of the meniscus at two arbitrary points are to be actually measured; the angle at each point is known accurately by observing the angle of reflection of a laser beam vertically irradiated onto the point. No knowledge of the contact angle on the plate is required. The tensiometer is suitable for the study of surface adsorption or of insoluble monolayers just the same as in the Wilhelmy plate method, but it is still superior to the Wilhelmy plate tensiometers and other conventional surface balances in its applicability to the measurements in an atmosphere completely insulated from the laboratory air. An apparatus is demonstrated that has been constructed primarily for the measurements of surface tensions of aqueous lithium bromide (LiBr) solutions with higher alcohol additives, i.e., working fluids of absorption heat pumps, under reduced pressures and elevated temperatures.

ISSN:0034-6748    

DOI:10.1063/1.1144087

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The investigation of the servo control of the position of the bottom mass in a balanced two‐stage pendulum vibration isolation system is reported. Experimental results for a simple prototype system and predictions based on a model presented in this paper are in good agreement. The application of such a system to a high‐sensitivity laser interferometric gravity wave detector is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144088

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A wideband (dc to 2 kHz) highly sensitive seismometer using a Michelson laser interferometer has been developed. The horizontal acceleration of the ground is sensed by a suspended mirror; its position is then detected as the fringe signal of the light in the interferometer. The minimum measurable displacement with this seismometer is 3×10−11m/&sqrt;Hz at 1 Hz (limited by the thermal fluctuation of air and the frequency noise of the laser) and 2×10−15m/&sqrt;Hz above 2 kHz (limited by the shot noise of the light). One application of this seismometer is to use it for very sensitive vibration measurements, such as in seismic noise investigations of possible sites for a large‐scale laser‐interferometric gravitational wave detector.

ISSN:0034-6748    

DOI:10.1063/1.1144089

出版商:AIP    

年代:1993

数据来源: AIP