Paul Horowitz

A Scanning X-Ray Microscope Using Synchrotron Radiation

Focused synchrotron radiation collimated by means of a pinhole has been used to construct a scanning x-ray microscope capable of making stereoscopic element-discriminating pictures of relatively thick specimens in an atmospheric environment.

Scanning Proton-Induced X-ray Microspectrometry in an Atmospheric Environment

Collimated million-electron-volt proton beams, brought out into air, can be used as a scanning microprobe to examine specimens with a spatial resolution of the order of 1 micrometer. Trace elements at concentrations as low as 1 part per million can be detected. Some preliminary results based on the use of this simple method are presented.

Ellipsoidal and bent cylindrical condensing mirrors for synchrotron radiation

Abstract A simple description is given of the intensity profile of X-rays reflected at glancing incidence from an ellipsoidal or bent cylindrical condensing mirror. Results obtained with a quartz mirror at the Cambridge Electron Accelerator are shown.

The diverse chemical forms of heavy metals in tissue extracts of some metallophytes from Shaba Province, Zaïre

Abstract Copper and cobalt were determined in tissue extracts of five metallophytes from Shaba Province, Zaire. About 4O% of the cobalt and copper was extractable into deionized water and a further 4O% was extractable in 0.2M hydrochloric acid. It was concluded that copper and cobalt are bound to several different ligands instead of a single ligand as in the case of nickel hyperaccumulators. Proton microprobe studies on the cobalt accumulator Haumaniastrum robertii showed a strong inverse correlation between the spatial distributions of cobalt and potassium, as well as a direct relationship between cobalt and calcium. It is suggested that some of the cobalt may be immobilized with calcium in oxalate crystals.

Five years of Project META - An all-sky narrow-band radio search for extraterrestrial signals

We have conducted a five-year search of the northern sky (delta between 30 and 60 deg) for narrow-band radio signals near the 1420 MHz line of neutral hydrogen, and its second harmonic, using an 8.4 x 10 exp 6 channel Fourier spectrometer of 0.05 Hz resolution and 400 kHz instantaneous bandwidth. The observing frequency was corrected both for motions with respect to three astronomical inertial frames, and for the effect of Earths rotation, which provides a characteristic changing Doppler signature for narrow-band signals of extraterrestrial origin. Among the 6 x 10 exp 13 spectral channels searched, we have found 37 candidate events exceeding the average detection threshold of 1.7 x 10 exp -23 W/sq m, none of which was detected upon reobservation. The strongest of these appear to be dominated by rare processor errors. However, the strongest signals that survive culling for terrestrial interference lie in or near the Galactic plane. We describe the search and candidate events, and set limits on the prevalence of supercivilizations transmitting Doppler-precompensated beacons at H I or its second harmonic. We conclude with recommendations for future searches, based upon these findings, and a description of our next-generation search system.

Targeted and all-sky search for nanosecond optical pulses at Harvard-Smithsonian

We have built a system to detect nanosecond pulsed optical signals from a target list of some 10,000 sun-like stars, and have made some 20,000 observations during its two years of operation. A beamsplitter feeds a pair of hybrid avalanche photodetectors at the focal plane of the 1.5m Cassegrain at the Harvard/Smithsonian Oak Ridge Observatory (Agassiz Station), with a coincidence triggering measurement of pulse width and intensity at sub-nanosecond resolution. A flexible web-enabled database, combined with mercifully low background coincidence rates (approximately 1 event per night), makes it easy to sort through far-flung data in search of repeated events from any candidate star. An identical system will soon begin observations, synchronized with ours, at the 0.9m Cassegrain at Princeton University. These will permit unambiguous identification of even a solitary pulse. We are planning an all-sky search for optical pulses, using a dedicated 1.8m f/2.4 spherical glass light bucket and an array of pixelated photomultipliers deployed in a pair of matched focal planes. The sky pixels, 1.5 arcmin square, tessellate a 1.6 by 0.2 degree patch of sky in transit mode, covering the Northern sky in approximately 150 clear nights. Fast custom IC electronics will monitor corresponding pixels for coincident optical pulses of nanosecond timescale, triggering storage of a digitized waveform of the light flash.

A Search for Ultra-Narrowband Signals of Extraterrestrial Origin

Nearly 200 nearby stars similar to the sun were observed at the 21-centimeter neutral hydrogen wavelength (in the heliocentric frame) with a bandwidth of 1 kilohertz and a resolution of 0.015 hertz, using the Arecibo 305-meter antenna. At this resolution the effects of terrestrial interference are so slight that the detection limit of 4 x 10–27 watt per square meter was set by receiver noise alone. No evidence of artificial signals was found.

The Art of Electronics

At long last, here is the thoroughly revised and updated third edition of the hugely successful The Art of Electronics. It is widely accepted as the best single authoritative book on electronic circuit design. In addition to new or enhanced coverage of many topics, the third edition includes 90 oscilloscope screenshots illustrating the behavior of working circuits, dozens of graphs giving highly useful measured data of the sort that is often buried or omitted in datasheets but which you need when designing circuits, and 80 tables (listing some 1650 active components), enabling intelligent choice of circuit components by listing essential characteristics (both specified and measured) of available parts. The new Art of Electronics retains the feeling of informality and easy access that helped make the earlier editions so successful and popular. It is an indispensable reference and the gold standard for anyone, student or researcher, professional or amateur, who works with electronic circuits.

OPTICAL SEARCH FOR PULSATIONS FROM PULSATING RADIO SOURCE CP 1919.

Optical observations of the 18th magnitude blue star and of the faint red object in the approximate location of the pulsating radio source CP 1919 disclose no pulsations of visible light, in a mode similar to that of the radio pulsations, of more than 0.4 percent or 0.8 percent, respectively, of the total visible output; or, for a sinusoidal modulation with the same period, no more than a 4-percent, or 8-percent, root-mean-square intensity fluctuation.

Spatially resolved X-ray energy analysis

Abstract We have constructed a proton-induced X-ray emission (PIXE) analysis system that performs one- or two-dimensional scans of a sample and stores energy spectra at each point for later analysis. This system permits examination of the spectra or the spatial distribution of a selected element as data is being gathered, and allows versatile imaging and graphing analysis later. The boundaries of the region under study can easily be altered, both for one-dimensional line scans and two-dimensional rasters. The system includes provisions for beam-current normalization and baseline removal.