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A single crystal, (110)-oriented dilute antiferromagnet (AF) Fe0.82Zn0.18F2 film was grown via molecular beam epitaxy on a (110)-MgF2 substrate by codepositing FeF2 and ZnF2, followed by 1.0 nm pure FeF2 and 18 nm Co layers. The exchange bias (HE) and coercivity (HC) of the Co film strongly depend on the cooling field (HCF) and temperature. For 0⩽HCF 0 for T

We report the observation of ferromagnetism at over 900K in Cr-GaN and Cr-AlN thin films. The saturation magnetization moments in our best films of Cr-GaN and Cr-AlN at low temperatures are 0.42 and 0.6 u_B/Cr atom, respectively, indicating that 14% and 20%, of the Cr atoms, respectively, are magnetically active. While Cr-AlN is highly resistive, Cr-GaN exhibits thermally activated conduction that follows the exponential law expected for variable range hopping between localized states. Hall measurements on a Cr-GaN sample indicate a mobility of 0.06 cm^2/V.s, which falls in the range characteristic of hopping conduction, and a free carrier density (1.4E20/cm^3), which is similar in magnitude to the measured magnetically-active Cr concentration (4.9E19/cm^3). A large negative magnetoresistance is attributed to scattering from loose spins associated with non-ferromagnetic impurities. The results indicate that ferromagnetism in Cr-GaN and Cr-AlN can be attributed to the double exchange mechanism as a result of hopping between near-midgap substitutional Cr impurity bands., Comment: 14 pages, 4 figures, submitted to APL

We have developed an instrument which simultaneously measures the thermal conductivity κ, Seebeck coefficient α, and electrical resistivity ρ of a sample, thereby determining the thermoelectric figure of merit Z = α2/(κρ). A Quantum Design Physical Property Measurement System (PPMS) provides the temperature control from 1.9 - 390 K and applied magnetic fields of up to 14 tesla. Two small probes mounted along the sample each contain thin film Cernox chip thermometers as well as electrical contacts to monitor the temperature and voltage drops across the sample. A third probe attached to the end of the sample provides a heater and current source to stimulate the sample both thermally and electrically. The sample's response to cyclic heat pulses is analyzed in real time using DSP techniques. A nonlinear least-squares fit is used, employing a two time-constant model to determine both the thermal conductivity and the Seebeck coefficient for the material. Data acquisition using these ac techniques are expedited since we can sweep both temperature and field during a measurement. Adaptive algorithms continually adjust the thermal and electrical stimuli applied to the sample, optimizing the speed and accuracy of the measurement. We present results from some of the materials measured so far, including thermal conductivity standards and Pb in the superconducting state.

This randomized trial compared a strategy of direct stenting without predilatation (n = 39) with conventional stenting with predilatation (n = 42) in patients with suitable lesions in native vesselsor = 2. 5-mm diameter to be covered by either a 9- or 16-mm-length NIR Primo stent. Equipment cost [mean (median) +/- SD] was less in those with direct stenting [$1,199 (979) +/- 526] than in those with predilatation [$1,455 (1,285) +/- 401, P0.001]. There was no significant difference in contrast use or fluoroscopy time. Procedural time was shorter in the direct stenting group. The clinical outcome at 1 month was satisfactory in both groups. In selected patients, a strategy of direct stenting is feasible, costs less, and is quicker to perform than the conventional strategy of stenting following predilatation.

Doppler echocardiographic studies have previously documented abnormalities of mitral flow during acute rejection similar to those seen in patients with "restrictive" physiology. As central venous flow is known to be abnormal in such patients, it was proposed that examination of superior vena caval flow with Doppler echocardiography might be useful for the detection of acute cardiac rejection.Thirty orthotopic cardiac transplant patients, 15 of whom had acute cardiac rejection diagnosed by endomyocardial biopsy, were studied within 36 hours of biopsy. Superior vena caval Doppler flow velocities as well as mitral and tricuspid flow velocities were recorded using a Hewlett-Packard Sonos 500/1000 echocardiograph system. Examinations were performed blinded to the biopsy result. Mitral and tricuspid peak early flow velocities in the nonrejector group were similar to those seen in normal subjects (mitral, 70 +/- 5 cm/sec; tricuspid midexpiratory apnea, 50 +/- 11 cm/sec). Superior vena caval flow was abnormal with 13 of 15 patients demonstrating a biphasic pattern of forward flow with dominant diastolic flow. In the 15 patients with acute cardiac rejection, both mitral and tricuspid flow velocities developed a "restrictive"-type pattern with increased peak early flow velocities (mitral, 89 +/- 24 cm/sec; tricuspid midexpiratory apnea, 63 +/- 19 cm/sec; por = 0.05 versus nonrejectors) and decreased mitral early flow-velocity deceleration times (rejectors, 97 +/- 26 msec; nonrejectors, 144 +/- 41 msec; por = 0.05). The pattern of superior vena caval flow became markedly abnormal with a virtually complete loss of forward systolic flow (rejectors, 4.4 +/- 6.6 cm/sec; nonrejectors, 26.1 +/- 8.8 cm/sec at midexpiratory apnea; por = 0.0001). In 10 of 15 patients, systolic forward flow was absent. If acute rejection was defined as forward systolic flowor = 17 cm/sec, then sensitivity was 100%, specificity was 80%, and predictive accuracy was 90%.During acute cardiac rejection, forward systolic superior vena caval flow is markedly diminished compared with nonrejectors. This is accompanied by other Doppler echocardiographic features consistent with the development of "restrictive" physiology. It is postulated that the loss of forward systolic flow in the superior vena cava is due to diminished long-axis shortening of the right ventricle associated with acute cardiac rejection.

Ten Ss rated perceived depth and contour clarity of figures containing binocularly disparate subjective contours. There was no tendency for stereoscopic depth cues to enhance the perceived clarity of subjective contours. Disparity cues that were incompatible with monocular depth cues reduced the depth sensation but did not affect contour clarity. Although subjective contours can be perceived stereoscopically, they are seen in less depth than real contours with the same degree of horizontal disparity.

Bornstein’s hypothesis that there is a loss of color discrimination in tropical areas was not supported in earlier research in the Cook Islands. Using a more sensitive color vision test (the Farnsworth-Munsell 100-Hue Test), a loss of color discrimination in the red-purple and blue-green regions of the spectrum was found. The lack of sex differences in this color discrimination loss supports a physiological rather than a genetic explanation of the observed decrement.

The effects of qualitative labels on the judgment of gustatory dissimilarities were examined in the situation where the S was required to memorise the salient characteristics of one stimulus in a pair before judging its dissimilarity to the other. Systematic shifts in judgments occurred under various labelling conditions, suggesting that verbal cues play an important part in the perception of stimulus relations.

A system comprising a weakly connected superconducting ring inductively coupled to a resonant L‐C circuit has been studied using an analog computer. The weak link was characterized either by a current‐phase relation of the form I = Ic sinφ or by ``supercurrent breakdown,'' and the results were compared. The effects of a normal resistance shunting the junction were investigated, as well as the effects of thermal current noise in the ring. Some criteria for achieving optimum coupling to the superconducting ring are discussed.

Scales whose categories are labeled with ranges of ratio values are compared with verbal category scales and magnitude estimation. Relative perceived intensities of Eugenol odor were scaled by power law methods, using 102 Ss, five scaling methods-one verbal, two numerical, and two magnitude estimation-and making comparisons against two alternate odor reference standards. Variations in the psychophysical exponent values derived under each condition were examined. Comparisons between scale types were made: numerical ratio-range category scales may behave as magnitude estimations or as category scales depending on the way responses are scored by the experimenter.

We have fabricated small‐area tunnel junctions of a lead‐tellurium‐lead structure. These have been used in conjunction with bulk superconductors to make hybrid quantum interference devices. We have successfully operated these devices at bias frequencies of 30 MHz, 300 MHz, and 10 GHz.

We describe the design, operation, and performance of a superconducting quantum interference device (SQUID) which operates at a frequency of 9 GHz. It is sensitive to variations of magnetic field in a frequency band from 0 to 1 GHz.

We have designed and tested a model for a 3 kHz receiver using a superconducting antenna circuit and a SQUID (Superconducting QUantum Interference Device) amplifier. Q factors as high as 6400 have been demonstrated for the resonant antenna, giving it an extremely low intrinsic noise voltage. We have anlayzed and solved various problems of matching between antenna and SQUID, as well as measuring noise, contributed by materials in the surrounding cryostat. We have been able to use feedback from the SQUID amplifier into the antenna to effectively broaden the 3 dB bandwidth to 1200 Hz without raising the noise level of the system significantly. By scaling the results obtained with our model receiver to an antenna volume of .022 M-cubed we have been able to estimate that a noise level of 2.4 x 10 to the -17th power T/(sq.rt. Hz) could be obtained in a 100 Hz bandwidth. (Author)

SQUID based instruments have been commercially manufactured in the United States for over six years. However, until about three years ago these systems were only suitable to be used by low temperature physicists and other researchers who were willing to become initiated into the somewhat black art of SQUID operation. The early instruments presented users with a choice between temperamental point-contact junctions and temperature sensitive thin-film bridges. It was often up to the user to piece his system together from various suppliers, and then have to worry about RFI (radio frequency interference), slew rate limitations, mysterious flux jumping, ground loops and a host of other distracting problems. There were no comprehensive research contracts let to industry for the systematic development of SQUID systems, so that out of necessity the development work was done in a piecemeal fashion. The terms “special” and “optional” have sometimes been used as euphemisms for “untried” when soliciting fixed-price contracts. These practices have resulted in some desperately heroic development feats. They have also, on occasion, left the customer with the task of salvaging a less than successful design.

Descriptions of the taste qualities of a nucleotide, disodium-5′-guanylate, are reported under two different response sets, lenient and stringent. Control comparison stimuli were de-ionized water and weak sodium chloride, and near threshold taste concentrations were used. Twenty subjects, 10 under each response set, participated. D5′G has a complex taste, and induces a marked false positive detection response pattern which resembles its own taste. The implications for methodology in gustatory psychophysics are noted.

The energy sensitivity of a direct current (dc) superconducting quantum interference device (SQUID) can be improved if it is operated in a two-stage configuration. Employing this technique, a commercial dc SQUID system was modified and made competitive with other sensors especially designed for very low noise applications. We report the noise measurements performed in the temperature range 4.2 K–25 mK. At 4.2 K, the coupled energy sensitivity obtained with the two-stage dc SQUID was approximately ten times better than with a conventional readout electronics. The noise energy decreases linearly until approximately 300 mK, in good agreement with theoretical previsions. At lower temperature the hot-electron effect produces a saturation and the best energy sensitivity measured with open input coil is 35 ℏ.

Reactive MBE growth was used to synthesize ferromagnetic Cr-doped GaN and AlN thin films with Curie temperatures above 900K. 2% Cr-doped GaN and 7% Cr-doped AlN were found to have a saturation magnetization moment of 0.42 and 0.6 μB/Cr atom, indicating that ∼14% and ∼20% of the Cr, respectively, are magnetically active. Structural characterization using X-ray diffraction (XRD) and transmission electron microscopy (TEM) did not find evidence of a ferromagnetic secondary phase. Electrical characterization indicate that the resistivity of the Cr-doped GaN films depends exponentially on temperature as R=Roexp[(To/T)1/2], characteristic of variable range hopping. In contrast, Cr-doped AlN films are highly resistive. Local spin density functional calculations predict that Cr forms a deep level defect in both systems and the t2 level falls approximately at midgap. Our theoretical and experimental results indicate that ferromagnetism in Cr-doped GaN and AlN arises as a result of the double exchange mechanism within the partially filled Cr t2 band.

The quantization of magnetic flux in a superconducting circuit can serve for the measurement of electrical quantities in the same way that we use the wavelength of light to measure length. We report a demonstration of this function in the measurement of attenuation ratio at a frequency of 30 MHz.