Search

We apply a canonical transformation Hubble’s law to turn it into a quantum equation and derive its solutions in a homogenous universe (assumptions analogous to the FLRW universe). The eigenfunctions of Hubble’s law are also stationary states (eigenfunctions of the Hamiltonian). The study of these solutions reveals many striking results, including: 1) By enforcing boundary conditions at the cosmic horizon, we derive a fundamental lower limit to the uncertainty in any rest mass (or measurement thereof) . This implies a lower limit also to the mean particle mass which we call the mass quantum . 2) We postulate that particles with finite mass can be regarded as a composition of a large number of mass quanta and deduce a relation between mass uncertainty and mass m0: . 3) This uncertainty leads naturally to localization of the composite mass, with the radius of localization proportional to the inverse square root of mass . We associate this localization with the classical localization of a massive particle. 4) We derive an expression for the critical mass where there is a crossover from quantum behavior to classical behavior , where is the material mass density. The classical sizes derived in 4) are consistent with empirical results for our universe. We note the theory described here has no free parameters, hence it points to a new fundamental equation of the universe, essentially defining the mass quantum. It is a pure quantum theory that does not invoke general relativity at any stage, and the derivation uses mathematics accessible to an upper level undergraduate student in physics.

The Allen Telescope Array was used to search for signals with characteristics similar to the “Wow” signal, the best candidate for an extraterrestrial radio signal found during Ohio State University’s (OSU’s) seven-year 21 cm 10-kHz channel sky survey for signals possibly due to extraterrestrial intelligence. While previous follow-up searches have reported null results, our observations covered a 5 deg2 field of view that extends well beyond the locus of all consistent directions of arrival (DOAs) of the original signal, and covered a 10 MHz bandwidth four times wider than the widest prior follow-up observations, using 12.8 kHz channels approximating OSU’s 10 kHz resolution. Approximately 100 hours of data were accumulated, considerably more time than any previous follow-up campaigns. We used interferometric imaging with an angular resolution of approximately 007 and automated feature-finding to search for point-like features mimicking a Wow repetition, obtaining single-channel sensitivity of ∼1.2 Jy for one minute averages. This allows identification of the DOA of a very brief repetition, with strong discrimination from radio interference, and eliminates the usual constraint that the signal must persist for long periods of time (around one hour) before the true DOA can be verified (because interfering signals from the horizon sometimes masquerade as coming from the look direction). No point-like features significantly exceeding the noise were found inside the full width at half maximum of the OSU fields of view, although one 26σ point-like feature was detected during one 10 second integration about 1/3° away.

Last year, the SETI Institute in collaboration with IBM, lead an effort to apply convolutional neural networks to the problem of identifying the class of unknown signals in simulated single-dish radio telescope data, with much success. In this paper we look at a different problem in radio astronomy, the construction of high fidelity images from stored correlator visibility files. This work is motivated by the amazing recent successes of CNN autoencoders developed for photographic image processing in the machine learning community. The second half of a photographic autoencoder has a structure very similar to what would be required for image generation from raw radio interferometer data (visibilities). In this paper, we argue that a deep convolutional neural network (CNN) can be a highly (computationally) effective approach to radio interferometer image generation starting from raw visibilities and producing high fidelity, cleaned (deconvolved) images as an output. We consider the linear and nonlinear operations performed in image generation and how they have analogs in a standard CNN. We also discuss the potential computational cost savings that might be had by replacing our complicated image processing pipelines with neural networks. A toy model CNN is developed and initial results will be presented.

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <, 19 pages, 8 figures, accepted for publication in ApJL

Note: This is a revised version of the paper that _corrects_a_calculation_error in translating observed Jansky units to EIRP in Watts. Mistakes are labeled below. Motivated by the hypothesis that Oumuamua could conceivably be an interstellar probe, we used the Allen Telescope Array to search for radio transmissions that would indicate a non-natural origin for this object. Observations were made at radio frequencies between 1 and 10 GHz using the Array's correlator receiver with a channel bandwidth of 100 kHz. In frequency regions not corrupted by man-made interference, we find no signal flux with frequency-dependent lower limits of 0.01 Jy at 1 GHz and 0.1 Jy at 7 GHz. For a putative isotropic object, these limits correspond to transmitter powers of (was mistakenly 30 mW) 10 W and (was mistakenly 300 mW) 100 W, respectively. In frequency ranges that are heavily utilized for satellite communications, our sensitivity to weak signals is badly impinged, but we can still place an upper limit of (was mistakenly 10 W) 3 kW for a transmitter on the asteroid. For comparison and validation should a transmitter be discovered, contemporaneous measurements were made on the solar system asteroids 2017 UZ and 2017 WC with comparable sensitivities. Because they are closer to Earth, we place upper limits on transmitter power to be 0.1 and 0.001 times the limits for Oumuamua, respectively., Comment: 10 pages, 5 figures, submitted to Astrophysical Journal

We have developed a new generation of low noise, broadband feeds for the Allen Telescope Array at the Hat Creek Observatory in Northern California. The new feeds operate over the frequency range 0.9 to 14 GHz. The noise temperatures of the feeds have been substantially improved by cooling the entire feed structure as well as the low noise amplifiers to 70 K. To achieve this improved performance, the new feeds are mounted in glass vacuum bottles with plastic lenses that maximize the microwave transmission through the bottles. Both the cooled feeds and their low noise amplifiers produce total system temperatures that are in the range 25-30 K from 1 GHz to 5 GHz and 40-50 K up to 12.5 GHz., Comment: 16 pages, 11 figures, accepted to Publications of the Astronomical Society of the Pacific

著者人数: 87名, Accepted: 2011-02-08, 資料番号: SA1004099000

The systematic search for extraterrestrial intelligence (SETI) has been ongoing for slightly more than half the century that this journal has been in print, and the topic has been of human interest through recorded history. Are we any closer to detecting cosmic company or knowing whether it should be there? This paper takes a look at what has been done, what we are currently doing, and briefly speculates about what the future of SETI research may look like as well as the implications of a successful detection.

The Search for ExtraTerrestrial Intelligence (SETI) finally has its own full-time telescope. The Allen telescope array (ATA) in Northern California was dedicated on October 11, 2007. This array, which will eventually be composed of 350 small radio antennas, each 6.1 m in diameter, is being built as a partnership between the SETI Institute and the University of California Radio Astronomy Laboratory. Last October, Paul G. Allen (who provided the funds for the technology development and the first phase of array construction) pushed a silver button and all 42 antennas of the current ATA-42 slewed to point in the direction of the distant galaxy M81. Specialized electronic backend detectors attached to the ATA began making a radio map of that galaxy and simultaneously began SETI observations of HIP48573, a G5V star near M81 on the sky and a distance of 264 light years from Earth. The Allen telescope array will greatly improve the speed of conducting SETI searches over the next few decades, and it will allow a suite of different search strategies to be undertaken. This paper summarizes some of the earliest SETI observations from the array, and describes the search strategies currently being planned.

We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch (12 visits), 690 deg(2) radio image and catalog at 1.4 GHz. The survey is designed to detect rare, very bright transients as well as to verify the capabilities of the ATA to form large mosaics. The combined image using data from all 12 ATATS epochs has rms noise sigma = 3.94 mJy beam(-1) and dynamic range 180, with a circular beam of 150 '' FWHM. It contains 4408 sources to a limiting sensitivity of 5 sigma = 20 mJy beam(-1). We compare the catalog generated from this 12 epoch combined image to the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency, and find that we can measure source positions to better than similar to 20 ''. For sources above the ATATS completeness limit, the median flux density is 97% of the median value for matched NVSS sources, indicative of an accurate overall flux calibration. We examine the effects of source confusion due to the effects of differing resolution between ATATS and NVSS on our ability to compare flux densities. We detect no transients at flux densities greater than 40 mJy in comparison with NVSS and place a 2 sigma upper limit of 0.004 deg(-2) on the transient rate for such sources. These results suggest that the greater than or similar to 1 Jy transients reported by Matsumara et al. may not be true transients, but rather variable sources at their flux density threshold.

We report radio SETI observations on a large number of known exoplanets and other nearby star systems using the Allen Telescope Array (ATA). Observations were made over about 19000 hours from May 2009 to Dec 2015. This search focused on narrow-band radio signals from a set totaling 9293 stars, including 2015 exoplanet stars and Kepler objects of interest and an additional 65 whose planets may be close to their Habitable Zone. The ATA observations were made using multiple synthesized beams and an anticoincidence filter to help identify terrestrial radio interference. Stars were observed over frequencies from 1- 9 GHz in multiple bands that avoid strong terrestrial communication frequencies. Data were processed in near-real time for narrow-band (0.7- 100 Hz) continuous and pulsed signals, with transmitter/receiver relative accelerations from -0.3 to 0.3 m/s^2. A total of 1.9 x 10^8 unique signals requiring immediate follow-up were detected in observations covering more than 8 x 10^6 star-MHz. We detected no persistent signals from extraterrestrial technology exceeding our frequency-dependent sensitivity threshold of 180 - 310 x 10^-26 W / m^2., Comment: 225 pages including very long table, 9 figures, 7 tables, resubmitted to Astrophysical Journal

We report a novel radio autocorrelation (AC) search for extraterrestrial intelligence (SETI). For selected frequencies across the terrestrial microwave window (1-10 GHz) observations were conducted at the Allen Telescope Array to identify artificial non-sinusoidal periodic signals with radio bandwidths greater than 4 Hz, which are capable of carrying substantial messages with symbol-rates from 4-1000000 Hz. Out of 243 observations, about half (101) were directed toward sources with known continuum flux > ~1 Jy over the sampled bandwidth (quasars, pulsars, supernova remnants, and masers), based on the hypothesis that they might harbor heretofore undiscovered natural or artificial, repetitive, phase or frequency modulation. The rest of the targets were mostly toward exoplanet stars with no previously discovered continuum flux. No signals attributable to extraterrestrial technology were found in this study. We conclude that the maximum probability that future observations like the ones described here will reveal repetitively modulated emissions is less than 1% for continuum sources and exoplanets, alike. The paper concludes by describing a new approach to expanding this survey to many more targets and much greater sensitivity using archived data from interferometers all over the world., 33 pages, 4 figures, 3 tables

The technique of plasma enhanced chemical vapor deposition has been used to synthesize Fe nanoparticles in an amorphous boron carbide matrix. The nanoparticles range in size from approximately 0.7 to 4.5 nm. It has been demonstrated that the size of the nanoparticles is proportional to the density of the Fe precursor (ferrocene) in the vapor. The matrix films have been found to be extremely hygroscopic. Upon absorption of moisture the films buckle and delaminate from the Si substrate. The buckling is a consequence of induced strain arising from the transformation of the Fe nanoparticles into α-Fe2O3. The formation of α-Fe2O3 has been verified by electron diffraction and near edge x-ray absorption fine structure measurements. Examination of the magnetic properties of the α-Fe2O3 using the technique of magnetic circular dichroism indicate that the nanoparticles are not ferromagnetic.

The wave vector dependence of Rayleigh and higher order Sezawa elastic waves in single crystalline epitaxial face-centered-cubic (fcc) Co layers are measured by Brillouin light scattering at room temperature. The dispersion of the mode velocities allows the independent elastic constants to be determined for this cubic phase of cobalt. These results compare very favorably to previous determinations of the elastic constants measured above 700 K from the high-temperature fcc phase of pure Co. Deviations from theoretical estimates are discussed.

The structure and magnetic properties of Fe/Ni(001) multilayers are studied using x-ray diffraction, magneto-optical Kerr effect magnetometry, and x-ray magnetic circular dichroism. Multilayers are deposited with constant Fe layers (12 {Angstrom}) and wedged Ni layers (0{endash}30 {Angstrom}), repeated 20 times, to explore the magnetic moment and the structure dependence upon thickness of Ni (t{sub Ni}). Up to t{sub Ni}{approx}16 {Angstrom} (11 ML), both the Fe and the Ni have a bct structure, similar to the bulk structure of bcc Fe. The magnetic moments of Ni in the bct region are nearly constant at 0.85{mu}{sub B} for a Ni thickness t{sub Ni} in the range 3 {Angstrom}{lt}t{sub Ni}{lt}16 {Angstrom}. This represents a significant enhancement over the moment in bulk fcc Ni (0.59{mu}B). The Fe/Ni multilayer undergoes a crystalline phase transition between 16 {Angstrom}{lt}t{sub Ni}{lt}23 {Angstrom}, beyond which both the Fe and Ni have an fct structure. In the fct region, the Ni magnetic moment is close to its bulk value and the Fe magnetic moment drops to 1.5{mu}{sub B}, which is {approximately}70{percent} of its bulk value. The crystalline phase transition is also accompanied by a rotation of the magnetic easy axis by 45{degree} in the plane of the film. {copyright} {italmore » 1999} {ital The American Physical Society}« less

The layer-averaged magnetic moments of Co and Rh have been measured in sputter deposited Co/Rh (001) multilayer thin films using the x-ray magnetic circular dichroism. The Rh moments were measured at both the $L$ and $M$ absorption edges, where we find that the Rh moment decreases as a function of increasing Rh layer thickness ${(t}_{\mathrm{Rh}}).$ The decline of the layer-averaged Rh moment is well described in terms of a simple dilution, implying that the Rh moment is confined to the interfacial region. We find that the Co moment remains largely unaffected, maintaining a bulklike value of $1.7{\ensuremath{\mu}}_{B}$ in the region preceding the first antiferromagnetic coupling peak where ${t}_{\mathrm{Rh}}$ ranges from 0 to 4 \AA{}. We also find, via application of the dichroism sum rules, that the ratio $〈{L}_{z}〉/〈{S}_{z}〉$ for Co increases $\ensuremath{\approx}10%$ for this same region. Finally, we contrast the magnetic behavior of the Co/Rh (001) and Fe/Rh (001) multilayer systems.

It is demonstrated that x-ray magnetic linear dichroism (XMLD) in absorption spectroscopy is a viable technique for element-specific magnetic characterization of metallic thin films and multilayers. XMLD is measured at the Fe, Co, Cr, and V ${L}_{2,3}$ edges, and varies from 1--11% of the edge jump in the absorption coefficient, with a magnitude that scales with the square of the magnetic moment. The XMLD spectra show satisfactory agreement with first principles calculations of this effect.

The structure and magnetic properties of Fe/Ru(001) multilayers are studied using x-ray diffraction, magneto-optical Kerr-effect magnetometry, and x-ray magnetic circular dichroism. The Fe layer thickness is maintained constant at 7.5 \AA{}, while the nominal Ru layer thickness ${t}_{\mathrm{Ru}}$ is variable. For ${t}_{\mathrm{Ru}}l3.5$ \AA{}, the multilayer has a body-centered-tetragonal structure with a perpendicular lattice constant that varies linearly with Ru thickness. In this region, the Fe has a bulklike magnetic moment. The Ru has a monotonically decreasing moment with increasing thickness. The Ru moments are of order $0.5{\ensuremath{\mu}}_{B}$ in this region. Beyond ${t}_{\mathrm{Ru}}\ensuremath{\approx}3.5 \mathrm{\AA{}},$ the crystal structure of the multilayer transforms to an hcp (102) orientation and the magnetic moments of both the Fe and Ru disappear. These results are compared and contrasted with those from Fe/Rh(001) multilayers.

Epitaxial Fe/V(001) multilayers are studied both experimentally and by theoretical calculations. Sputter-deposited epitaxial films are characterized by x-ray diffraction, magneto-optical Kerr effect, and x-ray magnetic circular dichroism. These results are compared with first-principles calculations modeling different amounts of interface interdiffusion. The exchange coupling across the V layers is observed to oscillate, with antiferromagnetic peaks near the V layer thicknesses ${t}_{V}\ensuremath{\approx}22$, 32, and 42 \AA{}. For all films including superlattices and alloys, the average V magnetic moment is antiparallel to that of Fe. The average V moment increases slightly with increasing interdiffusion at the Fe/V interface. Calculations modeling mixed interface layers and measurements indicate that all V atoms are aligned with one another for ${t}_{V}\ensuremath{\lesssim}15$ \AA{}, although the magnitude of the V moment decays toward the center of the layer. This ``transient ferromagnetic'' state arises from direct $(d$-$d)$ exchange coupling between V atoms in the layer. It is argued that the transient ferromagnetism suppresses the first antiferromagnetic coupling peak between Fe layers, expected to occur at ${t}_{V}\ensuremath{\approx}12$ \AA{}.

We present details of the crystal structure and magnetic behavior of Fe/Rh (001) sputter deposited multilayer thin films. We find that the films undergo a structural phase transformation from a body-centered-tetragonal (bct) to a face-centered-tetragonal (fct) lattice which is concomitant with a magnetic transformation from a ferromagnetic to a nonferromagnetic state. We identify the Rh spacer thickness where both bct and fct phases first coexist as the critical thickness (tcrit). In the region prior to the critical thickness, both Fe and Rh are ferromagnetic with Rh moments of at least 1μB and Fe moments enhanced as much as 30% relative to their bulk value. In the postcritical region, we find the films to be nonferromagnetic. The experimental results are compared with theoretical calculations on similar structures.

Element-specific magnetic moments in Fe/V superlattices are studied using x-ray magnetic circular dichroism (XMCD). Superlattices are simultaneously deposited with the epitaxial orientations (100), (211), and (110), to explore the orientation dependence of these moments. The layer-averaged vanadium moments are antiparallel to those of the Fe and are larger than those observed in alloys with similar composition. The V moments decay monotonically and relatively slowly with distance from the Fe interface (exponential decay length: ) in qualitative agreement with recent calculations. In contrast to calculations, the magnitudes of the V moments fall on a universal curve for the three orientations.

The relationship between indirect exchange coupling and interlayer d-electron magnetic moments is studied using magnetometry and x-ray magnetic circular dichroism (XMCD) in Fe/Cr multilayers. Multilayers are simultaneously prepared with growth axes along different crystallographic orientations to determine the orientation dependence of these properties. We find the Cr moments are antiparallel to the Fe, and that a Cr thickness (${\mathrm{t}}_{\mathrm{Cr}}$) of 1 ML has a moment of \ensuremath{\approx}-0.7${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$, 50% larger than the Cr moment developed in Fe-based dilute Cr alloys. For larger ${\mathrm{t}}_{\mathrm{Cr}}$ the Cr moment decays very quickly with distance from the Fe interface, while the Fe moment remains bulklike at all Cr thicknesses. It is found that for ${\mathrm{t}}_{\mathrm{Cr}}$10 \AA{} there are slight differences in the indirect (oscillatory) exchange coupling between Fe layers depending on crystallographic orientation. Intuitively, one would also expect an orientation dependence to the induced Cr moments, but we find them to be orientation independent. The orientation independence of the Cr moments correlates well with the orientation independent coupling which has been previously observed for ${\mathrm{t}}_{\mathrm{Cr}}$g10 \AA{}.

Results are presented detailing the crystallographic quality of a number of metal films deposited by epitaxial sputter deposition. Such films have single-orientation f.c.c., h.c.p., b.c.c. and hybrid crystals structures, and include the elements Ag, Au, Co, Cr, Cu, Fe, Rh, Ru, Pd and V. The crystal structure was characterized using X-ray diffraction analysis.

We report on a search for the presence of signals from extraterrestrial intelligence in the direction of the star system KIC 8462852. Observations were made at radio frequencies between 1-10 GHz using the Allen Telescope Array. No narrowband radio signals were found at a level of 180-300 Jy in a 1 Hz channel, or medium band signals above 10 Jy in a 100 kHz channel., Comment: 9 pages, 3 figures

The induced magnetic moment of Rh atoms in ${\mathrm{Co}}_{\mathit{x}}$${\mathrm{Rh}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$ alloys (x=77,49) is investigated by x-ray magnetic circular dichroism (XMCD) at the Rh ${\mathit{M}}_{2,3}$ absorption edge. By comparing with the XMCD signal observed in an ${\mathrm{Fe}}_{77}$${\mathrm{Rh}}_{23}$ alloy where the Rh magnetic moment is known, the value of the Rh magnetic moment in Co alloys can be determined (0.6${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for x=77 and 0.1${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for x=51). We find that the Rh moment is about 1/3 the Fe or Co moment for the alloys studied. Analogous measurements of XMCD from a ${\mathrm{Co}}_{71}$${\mathrm{Ru}}_{29}$ alloy show Ru behavior very different from that of Rh, with an induced Ru moment 1/14 the Co moment.

The existence or not of oscillatory interlayer exchange coupling of ferromagnetic layers via (111) oriented copper spacer layers is controversial. We present evidence from magnetic and giant magnetoresistance studies of well-defined antiferromagnetic interlayer coupling in single crystalline (111) permalloy/Au multilayers. Four oscillations in the coupling are observed as the Au spacer layer thickness is increased. The oscillation period is \ensuremath{\simeq}10 \AA{} which is significantly shorter than the period of \ensuremath{\simeq}11.5 \AA{} predicted in Ruderman-Kittel-Kasuya-Yosida based models.

We address some of the recent controversies regarding the interpretation of Auger electron diffraction patterns by simulating those from the 64 eV M2,3VV and the 914 eV L3VV lines from a Cu(001) surface. The lower‐energy diffraction pattern, in particular, is found to be strongly dependent on the angular momentum l of the emitted Auger electrons, in line with the observations of some other authors. However, we find that both peaks and dips are observed on the same diffraction pattern at the projections of different atomic rows, indicating that the angular momentum of the source wave cannot be the only determinant of these features. We find that the distance of the scatterer from the source, as well as overlap and interference effects from scatterers in other atomic rows to be an equally important determining factor. On comparing our simulations with experimental diffraction patterns, we find that, for an l=3 source wave, our simulations agree remarkably well with the data from both Auger lines.

We examine the effect of Co-cluster morphology on giant magnetoresistance (MR) in phase-separated Co-Cu films. The Co clusters were characterized through grazing incidence, anomalous, small-angle x-ray scattering. With thermal annealing the Co cluster diameter increases from 21 to \ensuremath{\sim}250 \AA{} with a concomitant drop from \ensuremath{\sim}35% to 1% in the 4.2 K MR. The MR scales approximately as the inverse cluster size. Comparison with theory indicates that interfacial spin-dependent electron scattering is the dominant scattering mechanism underlying giant MR for cluster diameters up to at least 250 \AA{}.

This review considers recent developments in MBE growth of artificially-layered magnetic-metal structures on both semiconductors and insulating substrates. It is seen that the ability to seed specific orientations of such structures and to probe their structural and chemical properties with a variety of in situ probes is a key advantage of MBE over more conventional deposition techniques. In particular, interface formation can be probed during growth. This is helpful in developing a realistic picture of interfaces in such structures and in relating magnetic properties to interface structural and chemical properties. Furthermore, the growth of epitaxial structures permits the detailed characterization of atomic and interface structure with X-ray diffraction and electron microscopy.

A full multiple-scattering method is described for the calculation of angle-resolved photoelectron, Auger-electron, and Kikuchi-electron diffraction patterns. The method is particularly useful for the range of electron kinetic energies from about 50 eV to a few thousand eV. Approximations that take advantage of the finite experimental angular resolution, and, for the higher electron kinetic energies, the dominant electron forward scattering, are implemented, and may be used to improve computational efficiency. Comparisons of calculations with an experimental LVV Auger diffraction pattern from a Cu(001) surface show excellent agreement

The X-ray absorption near-edge structures from the Si 2p edge have been measured at high resolution, and compared to a theoretical calculation using a cluster multiple-scattering model. The absorption features near threshold are shown to be sensitive to the degree of short-range crystalline order, over a range of up to 40 AA. The real-space scattering cluster calculation establishes the connection between the short-range order, as reflected in cluster size or final-state electron damping, and the line-widths of sharp absorption features near the 2p edge. Results are shown for amorphous and crystalline Si, and silicon oxides in the form of quartz, obsidian, and thin films on single-crystal Si substrates.

Giant magnetoresistance is reported in As-grown, epitaxial Co-Cu and Co-Ag alloy layers. The (111)- and (001)-oriented films were deposited onto (0001) sapphire and (001) rocksalt substrates, respectively, by co-evaporation in ultrahigh vacuum. Phase separation of the Co and Cu or Ag was obtained without any annealing after growth. The magnetoresistance at 4.2 K exceeded 50% and 70% in Co-Cu and Co-Ag films, respectively, and for films deposited at 250 °C a significant perpendicular magnetic anisotropy was observed in both magnetoresistance and magnetization studies. Grazing-incidence small-angle X-ray scattering indicates that the characteristic diameter and separation of Co clusters are approximately 25 A and 76 A, respectively, in (111) Co-Ag films grown at 250 °C.

The relationship of the growth and structure of highly oriented (111) Co/Cu superlattices to their magnetotransport properties is discussed. To eliminate changes in growth parameters between different samples, wedged superlattice structures were prepared in which uniform Co layers are separated by Cu layers whose thickness is varied by more than a factor of 2 across the substrate. Smooth variations in magnetoresistance (MR) as a function of Cu-layer thickness were obtained. No evidence for oscillations in MR was found with the exception of a peak in MR for thin Cu layers centered at about 10 A

We present a procedure for the growth of (110) oriented Pt and Cu on SrTiO 3 (110). This procedure provides excellent single crystal quality for both the Pt and the Cu films. We study the homoepitaxial behavior of Pt(110) and Cu(110) using low energy electron diffraction, X-ray photoelectron diffraction, and scanning electron microscopy. The Pt(110) surface is unstable to homoepitaxy at 600 o C, resulting in a faceted surface exposing (111) terraces which are thousands of angstroms long and ≤100 A wide. The Cu(110) surface undergoes spontaneous roughening below 300 o C during homoepitaxy

Circularly polarized soft x-rays have been used with an imaging photoelectron microscope to record images of magnetic domains at a spatial resolution of 1 micrometer. The magnetic contrast, which can be remarkably large, arises from the fact that the x-ray absorption cross section at inner-shell absorption edges of aligned magnetic atoms depends on the relative orientation of the photon spin and the local magnetization direction. The technique is element-specific, and, because of the long mean free paths of the x-rays and secondary electrons, it can record images of buried magnetic layers.

The 1959 Nature article by Giuseppe Cocconi and Phil Morrison1 provided the theoretical underpinnings for SETI, accompanied in 1960 by Project Ozma2, the first radio search for signals by Frank Drake at the National Radio Astronomy Observatory (NRAO). Well over 100 search programs have been conducted since that time, primarily at radio and optical wavelengths, (see www.seti.org/searcharchives) without any successful signal detection. Some have suggested that this means humans are alone in the cosmos. But that is far too strong a conclusion to draw from far too small an observational sampling. Instead of concluding that intelligent life on Earth is unique, it is more appropriate to note that in 50 years our ability to search for electromagnetic signals has improved by at least 14 orders of magnitude and that these improvements are still occurring at an exponential rate. At the SETI Institute we are in the process of reinventing the way we search in order to fully utilize these technological enhancements. We are now building the setiQuest community and we intend to get the world involved in making our searches better. We need to find ways to harness the intelligence of all Earthlings in order to better seek out extraterrestrial intelligence. If we do it right, we just might succeed, and we might also change how we see ourselves, and make our own world a better place.

The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array. PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky with an emphasis on synoptic observations that measure the static and time-variable properties of the sky. During the 2.5-year campaign, PiGSS will twice observe ~250,000 radio sources in the 10,000 deg^2 region of the sky with b > 30 deg to an rms sensitivity of ~1 mJy. Additionally, sub-regions of the sky will be observed multiple times to characterize variability on time scales of days to years. We present here observations of a 10 deg^2 region in the Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The PiGSS image was constructed from 75 daily observations distributed over a 4-month period and has an rms flux density between 200 and 250 microJy. This represents a deeper image by a factor of 4 to 8 than we will achieve over the entire 10,000 deg^2. We provide flux densities, source sizes, and spectral indices for the 425 sources detected in the image. We identify ~100$ new flat spectrum radio sources; we project that when completed PiGSS will identify 10^4 flat spectrum sources. We identify one source that is a possible transient radio source. This survey provides new limits on faint radio transients and variables with characteristic durations of months., Accepted for publication in ApJ; revision submitted with extraneous figure removed

We present the first X-ray secondary (photoelectron) emission microscopy (XSEM) pictures and video microimages of an uncoated and unstained neuron specimen. This novel kind of synchrotron radiation microscopy is suitable for local chemical analysis with a lateral resolution in the micron range. We explored the details of the neuron system, demonstrated chemical contrast by scanning the photon energy, studied in real time the photoelectron emitting properties of the specimen's components, and made preliminary tests of the radiation damage. These results significantly enhance the potential role of photoemission techniques in the life sciences and specifically in neurobiology.

An x‐ray photoemission microscope is described that is designed for x‐ray absorption imaging and spectroscopy with 1‐μm spatial resolution. The energy resolution of x‐ray absorption near‐edge structures microspectroscopy is determined only by the bandpass of the monochromator, and not by the photoemission microscope detector.

Experimental and theoretically simulated Auger electron diffraction patterns are studied to determine the effects of several experimental parameters on the holographic images generated from these patterns. Among the parameters examined are the experimental angular resolution, electron kinetic energy, and total collection solid angle of the diffraction pattern. Several techniques of combining the images from diffraction patterns taken at different kinetic energies are critically analyzed and compared. The origin of small radius “forward scattering artifacts” in the holographic images is discussed. A technique for removing these artifacts is introduced which requires no prior knowledge of the structure being studied.

Forward-scattering diffraction patterns from single-crystal Cu(111) substrates and an epitaxial film of FCC Cu/Ir(111) have been analyzed to produce real-space images of the atomic lattice by Fourier-transform holography. The accuracy of atomic positions is found to be better in the single-crystal holograms than in the ultrathin film of copper. The angular dependence of the atomic scattering factor produces a shift in the position of atoms in the holographic image, and causes the atom image to be asymmetric. Model calculations reproduce the atom shift and asymmetry. A modified Fourier-transform algorithm is shown to correct for both the atom-shift and the image asymmetry.

In this report, we demonstrate the observation of visible cathodoluminescence (CL) of Er-doped amorphous AlN films produced by sputtering. Optical transmission studies point out that the films are highly transparent and the band gap is about 5.61 eV. Elemental analysis by Rutherford backscattering spectrometry shows that AlN films are stoichiometric. X-ray diffraction measurements reveal that the films retain the amorphous structure even after annealing in N2 ambient at 1000 °C. The sharp characteristic emission lines in the CL spectra correspond to Er3+ intra-4fn shell transitions and are observed over the temperature range of 9–330 K. The results indicate the suitability of Er-doped amorphous AlN films for light-emitting device applications.

Des cliches de diffraction des electrons d'Auger de photoemission a deux dimensions contiennent un cliche d'interference. On l'interprete comme un hollogramme pour determiner la structure atomique tridimensionnelle entourant un atome d'une espece chimique particuliere

X‐ray absorption near edge structure (XANES) spectra are measured from silicon oxides using a photoemission microscope. Native oxide overlayers on Si(100) and Si(111) crystals are studied at various stages of the thermal desorption process. Because of the very high energy resolution inherent in the microscope, we are able to resolve for the first time the spin–orbit splitting of the core exciton structure in SiO2. The spectroscopic signature of this transition is unique, and it has enabled us to identify the core exciton XANES structures of two intermediate oxidation states of silicon (Si2+ and Si3+). We have found the Si2+ and Si3+ states existing at the Si–SiO2 interface. We have also found, for the first time, that Si2+ can exist independently on the silicon surface apart from any SiO2.

The electronic structure of oxide thin films on silicon single crystals has been measured with high spatial resolution by x-ray absorption near edge spectroscopy (XANES) using a photoelectron microscope and monochromatic synchrotron radiation. Native oxide overlayers on Si(100) and Si(111) crystals were studied at various stages during thermal desorption of the oxide. The spatial resolution capability of the microscope is used to perform selected-area XANES measurements of silicon and silicon oxides, which reveal for the first time the absorption characteristics of intermediate oxidation states of silicon (Si2+ and Si3+), and identify the spin-orbit splitting of the silicon 2p core-exciton structure in Si2+, Si3+, and SiO2. Our results confirm photoemission measurements which find Si2+ and Si3+ states existing at vertical interfaces between Si and SiO2. Unlike the photoemission spectra, however, selected-area XANES can resolve the spectroscopic signatures of these intermediate oxidation states in laterally inhomogeneous interfaces.

Fe 10 A /V tV (001) superlattices are prepared by magnetron sputter deposition and characterized using x-ray diffraction (XRD), magneto-optical Kerr effect (MOKE) magnetometry, and x-ray magnetic circular dichroism (XMCD). MOKE loops show three peaks in saturation field as a function of tV, indicating RKKY induced AF coupling at tV =22 A, 32 A, and 42 A. The expected AF coupling peak at 12 A, however, is missing. XMCD measurements show that the V layers carry a relatively large magentic moment which extends surprisingly far from the Fe/V interface. Such 'transient ferromagentism' suggests a strong V-V direct exchange coupling within the V layer. We argue that the V-V direct exchange coupling suppresses the 12 A AF coupling peak, but since direct exchange coupling decays more quickly than RKKY coupling, the AF peaks at 22, 32, and 42 A are observed.