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We have obtained a subarcsecond image of the disk associated with the T Tauri star HL Tau at a wavelength of 2.7 mm using the new high-resolution capability of the BIMA Array. The disk is elongated with a deconvolved Gaussian source size of 10 ± 02 × 05 ± 02, implying a semimajor axis of 70 ± 15 AU for a distance of 140 pc; the minor axis may be unresolved. The position angle of the major axis (125° ± 10°) is orthogonal to the axis of the optical jet. The disk centroid is coincident with the VLA λ = 3.6 cm source position and nearly coincident with recent measurements of the near-infrared emission peak. The λ = 2.7 mm images, along with previous interferometric measurements at λ = 0.87 mm and flux measurements from 10 μm to 1.3 cm, are well fitted by a simple power-law disk model with a shallow radial dependence to the surface density [Σ(r) ∝ r0 to r-1], an outer radius between 90 and 160 AU, and a dust opacity law proportional to ν1.

The Allen Telescope Array, a joint project between the SETI Institute and the Radio Astronomy Laboratory at the University of California Berkeley, is currently under development and construction at the Hat Creek Radio Observatory in northern California. It will consist of 350 6.1-m offset Gregorian antennas in a fairly densely packed configuration, with minimum baselines of less than 10 m and a maximum baseline of about 900 m. The dual-polarization frequency range spans from about 500 MHz to 11 GHz, both polarizations of which are transported back from each antenna. The first generation processor will provide 32 synthesized beams of 104 MHz bandwidth, eight at each of four tunings, as well as outputs for a full-polarization correlator at two of the tunings at the same bandwidth. This paper provides a general description of the Allen Telescope Array.

The Berkeley Illinois Maryland Association (BIMA) array consists of 6 antennas, each 6 meters in diameter, operating at a wavelength of 3 mm. The telescope control is fully automated, allowing round-the-clock observing with little or no supervision. The array can also be controlled from a remote site. One of the major challenges of automated operation is the ability to tune multiple receivers to the desired operating frequency in a reliable manner. The large tuning range required at millimeter wavelengths (85 to 115 GHz), the nonlinear response of the microwave cavities and oscillator phase lock problems have been stumbling blocks for remote receiver tuning. At BIMA, we have developed an automated system capable of tuning all the receivers to any observing frequency within a few minutes. The system uses a Sun workstation in conjunction with dedicated hardware to control the receivers. Large disparities between receiver characteristics are handled in an efficient manner through the use of lookup tables. We describe the system design in detail, and discuss the problems encountered along with appropriate solutions. The generation of lookup tables in the laboratory is also presented.

We describe the characteristics of the BIMA millimeter wave array at Hat Creek, California. The array is an aperture synthesis instrument consisting of 9 6-meter diameter antennas which may be deployed in three differenet configurations, with spacings ranging from 7 meters up to 1.3 km. At an observing frequency of 100 GHz these configurations yield maps with angular resolutions of 5", 2", and 0.4", over a 2' field. Larger fields may be mapped by using multiple pointings. For all but the oldest telescopes, the surface accuracy is ≤ 30 microns rms, and the aperture efficiency is 77% at 100 GHz. Background emission from antenna losses and spillover is very low, about 5 K after subtraction of the cosmic Bv(2.7K). Each antenna contains a single dewar which accommodates up to four separate receivers. SIS mixers are cooled to 3.2 K with novel Gifford-McMahon cycle refrigerators. Both the upper and lower sidebands of the first local oscillator are received and separated, providing two bands extending from 70-900 MHz on each side of the first local oscillator. The correlation spectrometer covers a bandwidth of up to 800 MHz, and provides up to 2048 channels for each antenna pair. There are four independently tunable spectral windows (in each sideband), allowing simultaneous observations of several different spectral lines. The spectral resolution ranges from 6 kHz to 3 MHz. For a single 8 hour track in one configuration, the sensitivity is approximately 1 mJy/beam in the 800 MHz wide continuum. Measurements of atmospheric phase fluctuations as functions of both time and baseline have been made; these indicate that routine imaging at angular resolutions of less than 1" at 100 GHz is possible only if self-calibration or some other means of phase correction can be applied. Examples of a few recent results are included. We note that 30% of the observing time on the array is granted to visitors.

SiO emission in both a strong maser transition in the first excited vibrational state and in a weaker transition in the ground vibrational state both arise from the same small region in the Kleinmann-Low Nebula in Orion. Within the errors, the source position coincides with that of the infrared source IRc2.

We have determined the triple-point temperature of high-purity gallium to be 29.77406°C using three standard platinum resistance thermometers (SPRTs) calibrated on the IPTS-68 and using samples of gallium from three commercial sources. All data obtained on the highest purity sample have a standard deviation of ±0.00011°C. The overall systematic uncertainty is estimated to be +0.6-1.1 m°C. The day-to-day irreproducibility of a single melt of each gallium cell was found to be < ±15 μ°C, while over a period of 7 months the irreproducibility among melts of each gallium cell was ≤ ±0.00011°C. These limits on the reproducibility appear to be largely instrumental since every time an SPRT was left in a gallium cell for several days there was no change in the indicated temperature of the triple-point to within the instrumental resolution of ±1.5 μ°C. The pressure dependence was measured and determined to be dT/dP = -2.011 ± 0.001 m°C/atm.

A phase-locked second harmonic Gunn oscillator, mechanically tunable from 65 to 115 GHz, has been developed for use as a Iocal oscillator (LO) in millimeter radio astronomy. The oscillator's output power is greater than 2 mW over most of its operating range, and exceeds 10 mW from 80 to 102 GHz. Its frequency can be electronically tuned approximately +-200 MHz by varying the bias voltage on the Gunn diode it is phase locked by exploiting this bias tuning. The oscillator consists of a commercially available, packaged GaAs Gunn diode which is mounted in a coaxial resonator of adjustable length. Descriptions of the mechanical design and phase-lock circuit are given. Extensive experimental measurements of the tuning range and power output for oscillators with different resonator dimensions also are reported.

(1969). A Comparison of Controlled Grazing and Manual Hoeing as a Means of Reducing the Incidence of Cymbopogon Afronardus Stapf in Ankole Pastures, Uganda. East African Agricultural and Forestry Journal: Vol. 35, No. 2, pp. 154-159.

The magnetic susceptibility, heat capacity, and optical-absorption spectrum of Dy P${\mathrm{O}}_{4}$ have been measured as a function of temperature and magnetic field. The optical-absorption spectrum indicates that the magnetic interactions in Dy P${\mathrm{O}}_{4}$ have the form of the Ising interaction and occur primarily between nearest neighbors. The magnetic-susceptibility and heat-capacity measurements have been compared with exact series expansions for a diamond lattice assuming an Ising system with nearest-neighbor interactions. The theoretical calculations are in agreement with the measurements. The nature of the divergence of the heat capacity at the critical point is examined. Our data do not permit us to distinguish between the applicability of the logarithmic and power-law divergencies since they are indistinguishable in the region of our measurements. The temperature dependence of the critical field for the metamagnetic phase transition has also been determined and compared with the calculated value for the critical field at 0 K obtained from the spectroscopic measurements.

Summary Coincident with the shooting out of hippopotamus in May 1958 20 permanent 30.46 m line intercept transects were established on the denuded grassland of the Mweya Peninsula, Queen Elizabeth National Park, western Uganda, to assess botanical changes in basal cover, species composition and frequency. Between May 1958 and May 1959, grass basal cover (GBC) decreased from 14.7% to 5.3% and bare ground increased from 78.3% to 83.6%. After four years total ground cover was 10.9% GBC, 27.2% litter, 1.3% dicotyledons and 60.6% bare ground. Changes occurred in grass species composition. The perennial carpet grass, Chrysochloa orientalis, declined from 37.7% GBC (transect frequency 100%) to 6.6% (87%) by May 1962. Bunch grasses showed marked recovery: Sporobolus pyramidalis increased from 8.0% GBC (60%) to 27.6% (100% frequency). Cynodon dactylon, initially prominent in two lakeside transects only, declined from 9.2% GBC to 2.1%, then became re-established in inland localities and recovered to 11.7% GBC. The variable rainfall (714 mm annual average) and its influence on plant growth is discussed and the advantage of mechanically increasing effective rainfall mentioned. Authorities for plant names are given in Table 3.

SUMMARYStocking rates of 3, 6 and 9 acres per 2- to 3-year old steer on Acacia-Cymbopogonj Themeda complex pasture in Ankole, Uganda, demonstrated that 3 acres per head gave significantly lower individual live-weight gains, but that there was little difference between 6 and 9 acres over a 6-year period. Although cattle grazed at 3 acres averaged only 175 lb per head per annum, compared with 207 lb at 6 acres per head, the income was Sh. 34 per acre compared to only Sh. 20–50 at 6 acres per head. At 9 acres/head the return was Sh. 13–50 an acre.A comparison of a 2 paddock/1 herd system with continuous grazing revealed no differences in production, despite the heavier capital investment involved in the former system. Growth rates at all three stocking rates were similar for most of the year, but in the dry season when all the cattle lost weight those stocked at 3 acres per head suffered the greatest losses (50–60 lb) and those at 9 acres per head the least (20–30 lb).

The eclipse of the moon on December 31, 1963, was observed at a wavelength of 8.35 mm. A decrease in the brightness temperature at the center of the disk of 3.5°K was measured. From this result, a value of 2×10−4 for the combination α(K/pc)½ is deduced for a homogeneous lunar subsoil. α is the power attenuation coefficient for radio waves in the subsoil; K, ρ, and c are, respectively, the thermal conductivity, density, and specific heat capacity of the subsoil in cgs units.

Ammonia gas molecules in interstellar medium, discussing detection in direction of galactic center by means of microwave emission

A high sensitivity vibrating sample magnetometer for use at very low temperatures is described. It can be made extremely compact by the use of a piezoelectric element as the vibrator. The complete magnetometer can be placed in the cryostat between the poles of an electromagnet and can be operated at high applied magnetic fields.

Water in interstellar regions detected by microwave emission from 6 sub 16 to 5 sub 23 rotational transition

We have made magnetic susceptibility, electron spin resonance, and Mossbauer measurements on two different amphiboles, (Fe, Mg)7Si8O22(OH)2, and crocidolite, Na2Fe5Si8O22 (OH)2, which indicate that these materials are ordered antiferromagnetically at liquid helium temperatures. Amphibole minerals are characterized structurally by long double chains of linked silicate tetrahedra. The metal anions are ’sandwiched’ between pairs of double silicate chains to form long narrow ribbons relatively well separated from each other. In amosite the only magnetic species present is Fe2+. This has been confirmed for our samples by the Mossbauer measurements. The ac magnetic susceptibility measurements on oriented fibers indicate that there are two antiferromagnetic transitions in amosite; one around 22 K associated with an easy axis perpendicular to the fiber axis, and one around 7 K associated with an easy axis parallel with the fiber axis. The Mossbauer spectra support this interpretation. Both Mossbauer and spin resonance indicate that any magnetic impurities must be less than one percent.

The sharpness and reproducibility of the gallium melting point were studied and the melting temperature of gallium in terms of IPTS-68 was determined. Small melting-point cells designed for use with thermistors are described. Nine gallium cells including three levels of purity were used in 68 separate determinations fo the melting point. The melting point of 99.99999% pure gallium in terms of IPTS-68 is found to be 29.771(4) +/- 0.001(4) degree C; the melting range is less than 0.0005 degree C and is reproducible to +/- 0.0004 degree C.

GdAs04 and GdV04 are Heisenberg antiferromagnets with relatively large anisotropy fields, about half of which is dipolar in origin. The ratios of the anisotropy to the exchange fields for the salts, based on the molecular field theory and using the published values of the interaction constants, indicate that both salts should have spin‐flop phases. We have measured the magnetization and its derivative of GdV04 and GdAs04 as a function of applied magnetic field for various temperatures below TN and derived their magnetic phase diagrams. GdV04 (TV = 2.50 K) is a textbook type example of a system having a spin‐flop phase with T3 = 1.37 K. The critical field for the transition from the antiferromagnetic to the spin‐flop phase is 10.5 kG and that for the transition from the spin‐flop to the ferromagnetic (or saturated paramagnetic) phase is 21.8 kG. GdAs04 (TN = 1.26 K) does not have a simple spin‐flop phase but undergoes transitions to two intermediate phases before undergoing a transition to the ferromagneti...

The low temperature magnetic susceptibilities of five asbestos minerals have been measured. Amosite and crocidolite are antiferromagnetic in the liquid helium temperature range. Canadian chrysotile has Curie law behavior between 1 and 4 K. Anthophyllite and Rhodesian chrysotile have Curie-Weiss law behavior between 1 and 4 K.

(1960). The Estimation of Ankole and Zebu Cattle Weights by Girth Measurement. East African Agricultural and Forestry Journal: Vol. 26, No. 2, pp. 140-141.

The hydrate transition temperatures of Na(2)SO(4)·10H(2)O to Na(2)SO(4), KF·2H(2)O to KF, and Na(2)HPO(4)·7H(2)O to Na(2)HPO(4)·2H(2)O were established using ACS grade salts as 32.374 °C, 41.422 °C, and 48.222 °C, respectively. A simple and reliable procedure involving inexpensive materials was used to realize these transitions as temperature fixed points. Each transition temperature was attained within 30 minutes of hydrate initiation and remained constant to within ±0.002 °C for more than 10 hours if the mixture was stirred. The established transition temperatures were sensitive at the 0.001 °C level to the amount of impurities, so the materials used should be of the highest quality available. These systems fill a gap in the existing spectrum of temperature standards and should be useful in biomedical laboratories for calibrating thermometers.

A hybrid analog-digital spectrometer has been built and is installed at Hat Creek Observatory on the millimeter-wave interferometer (Welch et al. 1977). The analog portion of the instrument comprises the filters; the digital part consists of a three-level correlator. The correlator serves three baselines, providing 512 complex channels for each. The bandwidth of the digital portion of the correlator is 40 MHz. The correlator may be partitioned in a flexible way, so that each part is fed by one sideband of a filtered portion of the band; in this way a total bandwidth of 320 MHz may be achieved. Other configurations are possible.