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Atomic force microscopy has been used to measure adhesion and friction forces at the interface between an oxidized metal probe tip and amorphous carbon films of varying hydrogen contents (12.3–39.0 atomic percent hydrogen). The interface of an oxide surface and a hard carbon coating models the unlubricated head-disk interface of current hard disk products. Adhesion forces normalized by the radius of curvature of the contacting tip range from 1.09 to 8.53 N/m. Coefficients of friction values, measured as the slope of the friction versus load plot, range from 0.33 to 0.87. A trend of increasing adhesion forces and coefficients of friction is observed for increasing hydrogen content in the films. We attribute the increase in adhesion and friction to increases in the surface free energy of the carbon films with the incorporation of hydrogen.

Wind variability in OB stars may be ubiquitous and a connection between projected stellar rotation velocity and wind activity is well established. However, the origin of this connection is unknown. To probe the nature of the rotation connection, several of the attendees at the workshop on Instability and Variability of Hot-Star Winds drafted an IUE observing proposal. The goal of this program was to follow three stars for several rotations to determine whether the rotation connection is correlative or causal. The stars selected for monitoring all have rotation periods less than or equal to 5 days. They were HD 50896 (WN5), HD 64760 (BO.5 Ib), and HD 66811 (zeta Pup; 04 If(n)). During 16 days of nearly continuous observations in 1995 January (dubbed the 'MEGA' campaign), 444 high-dispersion IUE spectra of these stars were obtained. This Letter presents an overview of the results of the MEGA campaign and provides an introduction to the three following Letters, which discuss the results for each star.

The tropopause, typically at 16 to 18 km altitude at the lower latitudes, dips to 8 km in the polar regions. This makes the cold, dry and nonturbulent lower stratosphere accessible to tethered aerostats. Tethered aerostats can fly as high as 12 km and are extremely reliable, lasting for many years. In contrast to free-flying balloons, they can stay on station for weeks at a time, and payloads can be safely recovered for maintenance and adjustment and relaunched in a matter of hours. We propose to use such a platform, located first in the Arctic (near Fairbanks, Alaska) and, potentially, later in the Antarctic, to operate a new technology 6-meter, diluted aperture telescope with diffraction-limited performance in the near infrared. Thanks to the low ambient temperature (220 K), thermal emission from the optics is of the same order as that of the zodiacal light in the 2 to 3 micron band. Since this wavelength interval is the darkest part of the zodiacal light spectrum from optical wavelengths to 100 microns, the combination of high resolution images and a very dark sky make it the spectral region of choice for observing the redshifted light from galaxies and clusters of galaxies at moderate to high redshifts.

Nanoindentation and nanoscratching experiments have been performed to assess the mechanical properties of several carbon thin films with potential application as wear resistant coatings for magnetic disks. These include three hydrogenated-carbon films prepared by sputter deposition in a H2/Ar gas mixture (hydrogen contents of 20, 34, and 40 atomic %) and a pure carbon film prepared by cathodic-arc plasma techniques. Each film was deposited on a silicon substrate to thickness of about 300 nm. The hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients. The results show that the hardness, elastic modulus, and scratch resistance of the 20% and 34% hydrogenated films are significantly greater than the 40% film, thereby showing that there is a limit to the amount of hydrogen producing beneficial effects. The cathodic-arc film, with a hardness of greater than 59 GPa, is considerably harder than any of the hydrogenated films and has a superior scratch resistance.

57 Background: A woman with a known BRCA mutation has a lifetime risk for the development of breast cancer of up to 80%. Carolinas Medical Center cares for approximately 600 breast cancer patients annually with genetic testing offered to those patients whose history meets commonly established criteria. This study seeks to document the follow-up patients with BRCA mutations most commonly undertake at our facility. Methods: This study is a retrospective review of all patients who underwent genetic testing at Carolinas Medical Center and who were found to be positive for a mutation in the BRCA gene. Since 1996 our genetics group has tested 2056 individuals, of these 246 (12%) carry a mutation of the BRCA-1 and/or BRCA-2 gene. 102 of these 246 patients (41%) had no evidence of cancer at the time of genetic testing. 144 of these 246 patients (59%) did carry a diagnosis of cancer at the time of genetic testing. Results: Of the 246 patients who tested positive for a deleterious mutation in the BRCA gene 204 (83%) had documented follow-up after their diagnosis. 140 of those 204 patients (69%) had documented initial follow-up appointments to discuss their diagnosis. 63 patients of the 140 (45%) who sought initial consultation met with a surgeon. 73 of these 140 patients (52%) had their initial consultation with a Gyn/Oncologist. 3 patients had their initial consultation with a medical oncologist and the remaining patient with their primary care physician. Documentation was available for 131 of the 204 patients (64%) in regards to follow up related to their risk of breast cancer development, 129 of those patients were being followed by a high risk breast provider. 126 of the 204 patients (62%) with long term follow-up were being followed by a Gyn/Oncologist secondary to their increased risk for ovarian cancer. This data includes all patients regardless of the decisions they made concerning surveillance or prophylactic surgery. Conclusions: The majority of the patients at Carolinas Medical Center who have tested positive for a BRCA mutation have sought long term follow-up with both a high risk breast provider and a Gyn/Oncologist in regards to their increased risk for the development of both breast and ovarian cancer.

The Richardson-Lucy iteration (also known as the EM iteration for image restoration with Poisson statistics) is the most widely used image restoration technique for optical astronomical data. Like all maximum likelihood methods, it suffers from noise amplification in the restored images. Previously suggested methods for dealing with this problem (stopping the iteration early or smoothing the final image) have serious drawbacks for astronomical applications. This paper describes a new image restoration iteration based on the RL method that reduces noise amplification. The method is based on a modified form of the Poisson likelihood function that is flatter in the vicinity of a good fit. The resulting iteration is very similar to the RL iteration, but includes a new spatially adaptive damping factor that prevents noise amplification in regions of the image where a smooth model provides an adequate fit to the data; thus, I call this the `damped Richardson-Lucy iteration.' The damped iteration converges more rapidly than the RL method and can be accelerated using the same techniques as the standard RL iteration. Results are shown for both simulated data and Hubble Space Telescope images.

The lower stratosphere in the polar regions offers conditions for observation in the near-infrared comparable to those obtained from space. We describe a concept for a 6-meter, diluted aperture, near-infrared telescope carried by a tethered aerostat flying at 12 km altitude, to serve as a testbed for future space astronomical observatories while producing frontier science.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An image compression algorithm has ben developed that is well-suited to astronomical images. The method has 3 steps: an intensity mapping to generate an image that has roughly constant noise in each pixel, an orthonormal wavelet transform, and quadtree coding of the bit-planes of the wavelet coefficients. The quadtree values may be further compressed by an standard compression technique, such as Huffman or arithmetic coding. If the 2D Haar transform is used, the calculations can be carried out using integer arithmetic, and the method can be used for both lossy and lossless compression. The Haar transform basis functions are well-suited to most astronomical images because they are highly localized. The performance of the algorithm using smoother, longer range wavelets is also shown; they can give slightly better lossy compression at the cost of an increase in artifacts around point sources, but they are not effective for lossless compression using this scheme. This technique has also been used as the basis of a progressive image transmission system that can be used for either remote observing or access to remote image archives. After less than 1% of the data have been received, the image is visually similar to the original, so it is possible to assess the quality of images very quickly. If necessary, the entire compressed data set can be sent so that the original image is recovered exactly.

Nonthermal radio emission has been observed from some of the most luminous hot star winds. It is understood to be synchrotron radiation of the relativistic electrons in the winds. To understand how the electrons are accelerated to such high energies and to correctly explain the observed radio flux and spectra require an exhaustive investigation of all the relevant physical processes involved and possibly point to a complex wind structure. In this paper we discuss the logical path toward a comprehensive model of the nonthermal radio emission from hot star winds. Based on the available observational data and fundamental theoretical considerations, we found that the only physically viable and self-consistent scenario is:the nonthermal radio emission is synchrotron radiation of relativistic electrons ⇌ the electrons are accelerated by shocks via the first-order Fermi mechanism ⇌ the acceleration has to be in situ in the radio emitting region ⇌ the shocks formed at the base of the winds have to propagate to beyond the radio photosphere).

We present the discovery of only the second radio-selected, z ~ 6 quasar. We identified SDSS J222843.54+011032.2 (z=5.95) by matching the optical detections of the deep Sloan Digital Sky Survey (SDSS) Stripe 82 with their radio counterparts in the Stripe82 VLA Survey. We also matched the Canadian-France-Hawaiian Telescope Legacy Survey Wide (CFHTLS Wide) with the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey but have yet to find any z ~ 6 quasars in this survey area. The discovered quasar is optically-faint, z = 22.3 and M_{1450} ~ -24.5, but radio-bright, with a flux density of f$_{1.4GHz, peak}$ = 0.31mJy and a radio-loudness of R ~ 1100 (where R = f_{5GHz}/f_{2500}). The i-z color of the discovered quasar places it outside the color selection criteria for existing optical surveys. We conclude by discussing the need for deeper wide-area radio surveys in the context of high-redshift quasars., Comment: 20 pages, 6 figures, and ApJ accepted

We have investigated the effects of SiNx overcoat on bulk magnetic properties and recording performances in perpendicular media. Difference in recording parameters between disks with SiNx and carbon overcoats is mainly due to the difference in writeability caused by coercivity change during SiNx overcoat deposition. The bulk magnetic properties of the cap in the recording layer are affected by the reaction with silicon and nitrogen. Although SiNx overcoat changes writeability, it does not alter the intrinsic dependence of recording parameters on writeabilty.

The Hubble Space Telescope image quality is degraded significantly as a result of the spherical aberration in the primary mirror. Although the forthcoming HST servicing mission will deploy corrective optics systems and a second-generation camera with built-in correctors, the current and archival images for the past three years require the use of restoration techniques in order to achieve the full scientific potential of the HST mission. In addition, we expect that the restoration techniques now being developed will continue to be utilized on post- servicing mission imagery in order to remove the remaining diffraction features and optimize dynamic range. A variety of well-known image restoration techniques, such as Wiener filters, Richardson-Lucy, Jansson-van Cittert, CLEAN, and maximum entropy, have been applied to HST imaging with reasonable success. However, all techniques have been hampered by incomplete knowledge of the point spread function and the space variance of the PSF in the Wide Field/Planetary Camera, HST's most frequently used imager. The best restoration results to date have been obtained by utilizing observed PSFs (an optimal exposure which minimizes noise and image defects) on small enough subsets of the total field of view so that the PSF variation can be ignored.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Results of a systematic investigation of the Raman, hardness, and resistivity properties of sputtered amorphous carbon films on silicon substrates for hydrogen stoichiometries between 14% and 39% are presented. Frequency shift and line broadening effects of the Raman active graphite-like vibrations are consistent with a model of both harness and strain present in the amorphous network being independently controlled by the unprotonated sp3 carbon-carbon bonding fraction and the hydrogen concentration. Comparison to constraint counting models for covalent random networks indicates that the hardness of hydrogenated amorphous carbon follows the degree of network strain. We find no evidence for phonon confinement effects in micro crystals consistent with a random network structure without predominating microcrystals. Resistivity data indicate that the vibrational properties are largely independent of strong variations in the electronic properties with stoichiometry.

The effect of residual stress on the scratch adhesion critical load has been measured for sputtered tantalum films. In this single metallurgical system, six different failure modes could be observed, ranging from ductile ploughing to extensive spallation. For tantalum films deposited on silicon substrates, a 15% decrease in critical load was observed as the film residual stress increased from -1.1 GPa to +1.0 GPa. A larger percentage decrease (50%) was observed for films deposited on softer AIMg/NiP substrates. Film spallation was more extensive for films deposited over a thin carbon layer and for these films critical loads increased slightly with film stress. These results are substantially in contradiction with existing quantitative models for the scratch adhesion test and indicate that failure by shear at the film-substrate interface can be more important than failure by compressive buckling.

The spherical aberration of the primary mirror of the Hubble Space Telescope has seriously reduced the sensitivity and degraded the resolution of images and spectra from the instruments onboard the satellite. In this paper, we describe the nature of the aberration problem and the resulting point-spread functions for both the imaging and spectrographic detectors. A number of image restoration algorithms have been evaluated for use on HST data, including both linear and non-linear techniques, and sample results are shown for a modified Richardson- Lucy method. The best prospects for obtaining improvements in the restored images are likely to derive from developing techniques for adaptive regularization.

The Hubble Space Telescope High Speed Photometer has four image dissector tubes, two with UV sensitive photocathodes, two sensitive to the near UV and to visual light, and a single red sensitive photomultiplier tube. The HSP is capable of photometric measurements from 1200 to 7500 A with time resolution of 11 microseconds and has no moving parts. An initial analysis of the on-orbit engineering performance of the HSP is presented with changes in operating procedures resulting from the primary mirror spherical aberration and experience gained during the verification period.

In the early 1970s Richardson1 and Lucy2 published an iterative method for recovering images of objects that appear blurred. Their method has been rediscovered by Shepp and Vardi3 for imaging radionuclides. The connection between these two seemingly disparate fields of science—restoring optical imagery and radionuclide imaging—occurs because they are inverse-problems having a common mathematical description. The purpose of this paper is to note some implications for restoring optical imagery of recent developments in radionuclide imaging.3-5 These developments yield extensions of the Richardson-Lucy iteration that have proved to be powerful for restoring images from quantum-limited data. An application to images acquired with the Hubble Space Telescope is given.

Carbon overcoat films are used extensively in thin film disk applications to provide wear resistance. A nano-indentation technique and wafer curvature measurements have been used to study the mechanical properties of carbon films sputtered under various processing conditions. Specifically, the effects of substrate/target spacing, power, pressure, and substrate bias have been studied for films sputtered in an argon plasma. The relationship of these properties to contact start-stop performance of hydrocarbon lubricated disks is further described. The frictional performance during the test can be related to film hardness, while the durability can be affected by the residual film stress.

Extensive clinical experience has shown that systemic interleukin (IL)-2 administration can induce complete or partial regression of renal cell cancer (RCC) metastases in 15 to 20 % of patients. Since IL-2 has no direct anti-cancer effects, it is believed that cancer regression is mediated either by a direct modulation of immune cell effector functions or through the mediation of soluble factors released as a result of IL-2 administration. We previously observed that transcriptional and protein changes induced by systemic IL-2 administration affect predominantly mononuclear phagocytes with little effect, particularly within the tumor microenvironment, on T cell activation, localization and proliferation. It further appeared that mononuclear phagocyte activation could be best explained by the indirect mediation of a secondary release of cytokines by IL-2 responsive cells either in the circulation or in peripheral tissues. To better characterize the cytokine outburst that follows systemic IL-2 administration we followed the serum levels of 68 soluble factors in ten patients with RCC undergoing high dose (720,000 IU/kg intravenously every 8 hours) IL-2 therapy. Serum was collected before therapy, 3 hours after the 1st and 4th dose and assayed on a multiplexed protein array platform. This study demonstrated that 1) the serum concentration of more than half the soluble factors studied changed significantly during therapy; 2) changes became more dramatic with increasing doses; 3) subclasses of soluble factors displayed different kinetics and 4) cytokine patterns varied quantitatively among patients. This study shows that the cytokine storm that follows systemic IL-2 administration is complex and far-reaching inclusive of soluble factors with disparate, partly redundant and partly contrasting effects on immune function. Therefore comparing in parallel large number of soluble factors, it sets a comprehensive foundation for further elucidation of "cytokine storm" in larger patient pools. Based on this analysis, we propose a prospective collection of serum samples in a larger cohort of patients undergoing IL-2 administration with the purpose of discerning patterns predictive of clinical outcome and toxicity.

Objective. —To determine whether an organized intervention including data feedback, training in continuous quality improvement techniques, and site visits to other medical centers could improve the hospital mortality rates associated with coronary artery bypass graft (CABG) surgery. Design. —Regional intervention study. Patient demographic and historical data, body surface area, cardiac catheterization results, priority of surgery, comorbidity, and status at hospital discharge were collected on CABG patients in Northern New England between July 1, 1987, and July 31, 1993. Setting. —This study included all 23 cardiothoracic surgeons practicing in Maine, New Hampshire, and Vermont during the study period. Patients. —Data were collected on 15 095 consecutive patients undergoing isolated CABG procedures in Maine, New Hampshire, and Vermont during the study period. Interventions. —A three-component intervention aimed at reducing CABG mortality was fielded in 1990 and 1991. The interventions included feedback of outcome data, training in continuous quality improvement techniques, and site visits to other medical centers. Main Outcome Measure. —A comparison of the observed and expected hospital mortality rates during the postintervention period. Results. —During the postintervention period, we observed the outcomes for 6488 consecutive cases of CABG surgery. There were 74 fewer deaths than would have been expected. This 24% reduction in the hospital mortality rate was statistically significant ( P =.001). This reduction in mortality rate was relatively consistent across patient subgroups and was temporally associated with the interventions. Conclusion. —We conclude that a multi-institutional, regional model for the continuous improvement of surgical care is feasible and effective. This model may have applications in other settings. ( JAMA . 1996;275:841-846)

Several imaging devices are characterized by a space-variant point-spread function (PSF), such as the wide-field/planetary camera of the Hubble Space Telescope (HST). Several techniques for image recovery that use data from such imagers approximate the space-variant PSF by a space-invariant PSF. A modified Richardson-Lucy method is implemented that accommodates the space-variant PSF of the HST as well as corrections for background counts, nonuniform flat field, and readout noise. The implementation runs on the DEC mppl2000 Sx/Model 200 massively parallel computer. Restorations of simulated HST images are obtained with a space-variant PSF and, for comparison, with a space-invariant approximation. Results of these processing methods are compared, and it is found that a residual artifact appears in restorations when a space-invariant PSF is used owing to the mismatch of the PSF kernel used in the restoration and the space-variant one underlying the image acquired with the telescope. This residual artifact is effectively eliminated when the processing is based on the space-variant PSF.

We report on an observation of the youngest Crab-like supernova remnant, 3C 58, undertaken with the {ital ROSAT} high-resolution imager. The presence of a compact X-ray source at the center of the remnant, suggested by earlier observations, is confirmed, although aspect problems with the Observatory allow us to set only an upper limit on the size of the source of less than 10{double_prime}. We describe an efficient new algorithm for conducting period searches on sparsely sampled data with a relatively small number of photons, and use it to set an upper limit on the pulsed fraction of this source of 50{percent}. We show that the diffuse X-ray emission from the remnant is cospatial with the nonthermal radio emission and constrain the spectral parameters of the X-ray power-law fit. We go on to explore several models for the compact source, showing that Crab-like nonthermal pulses and thermal emission from the entire stellar surface are unlikely to explain the emission. Polar caps heated by magnetospheric discharges could be responsible for the observed X-rays. We conclude that the low X-ray pulsed fraction, inferred emitting area and temperature for the compact source, nebular luminosities in the X-ray and radio bands, and the known agemore » can all be reconciled if {ital P}{approximately}200 ms, {dot {ital P}}{approximately}4000{times}10{sup {minus}15} s s{sup {minus}1}, and {ital B}{approximately}3{times}10{sup 13} G, which would make this the highest magnetic field pulsar known. {copyright} {ital 1995 The American Astronomical Society.}« less

The FIRST survey to produce Faint Images of the Radio Sky at Twenty centimeters is now underway using the NRAO Very Large Array. We describe here the scientific motivation for a large-area sky survey at radio frequencies which has a sensitivity and angular resolution comparable to the Palomar Observatory Sky Survey, and we recount the history that led to the current survey project. The technical design of the survey is covered in detail, including a description and justification of the grid pattern chosen, the rationale behind the integration time and angular resolution selected, and a summary of the other considerations which informed our planning for the project. A comprehensive description of the automated data analysis pipeline we have developed is presented. We also report here the results of the first year of FIRST observations. A total of 144 hr of time in 1993 April and May was used for a variety of tests, as well as to cover an initial strip of the survey extending between 07{sup h}15{sup m} and 16{sup h}30{sup m} in a 2{sq_bullet}8 wide declination zone passing through the local zenith (28.2{lt}{delta}{lt}31.0). A total of 2153 individual pointings yielded an image database containing 1039 merged images 46{sq_bullet}5{times}34{sq_bullet}5more » in extent with 1{center_dot}{double_prime}8 pixels and a typical rms of 0.13 mJy. A catalog derived from this 300 deg{sup 2} region contains 28,000 radio sources. We have performed extensive tests on the images and source list in order to establish the photometric and astrometric accuracy of these data products. We find systematic astrometric errors of {lt}0{center_dot}{double_prime}05; individual sources down to the 1 mJy survey flux density threshold have 90{percent} confidence error circles with radii of {lt}1{double_prime}. CLEAN bias introduces a systematic underestimate of point-source flux densities of {approximately}0.25 mJy; the bias is more severe for extended sources. (Abstract Truncated)« less

HD 193793=WR 140 is a W-R+O binary system with a 7.9 yr, highly elliptical ({ital e}=0.85) orbit. It shows variable, nonthermal radio emission over its orbital period that is explained as synchrotron radiation from relativistic electrons accelerated in the shock between the W-R and O winds. Although we now know of quite a few W-R+O star binary systems, only HD 193793 is well studied across the entire electromagnetic spectrum; hence, it affords us the best opportunity to test various models for the system against a wealth of observational data. HD 193793 is an ideal laboratory for studying the properties of hot star winds and the physics of particle acceleration by strong shocks in those winds. In this paper we present the results of 8 years of monitoring the radio flux density from HD 193793 with the VLA. This database is unique both in terms of its dense coverage of an entire binary cycle and because it extends the radio coverage to 2 cm wavelength, a shorter wavelength than previously available. With these data we are able to simultaneously solve for the time-dependent attenuation in the system and the intrinsic radio luminosity. The standard model of spherically symmetric colliding winds facesmore » severe difficulties in explaining the observations. We conclude that the radio data are most readily interpreted if we adopt a new model of the system in which the W-R star wind is strongly equatorially enhanced, so that most of the mass loss is confined to a plane. This model for the W-R wind also provides a natural explanation for the sudden formation of dust that causes an infrared outburst just after periastron. {copyright} {ital 1995 The American Astronomical Society.}« less

We have developed several algorithms for classifying objects in astronomical images. These algorithms have been used to label stars, galaxies, cosmic rays, plate defects, and other types of objects in sky surveys and other image databases. Our primary goal has been to develop techniques that classify with high accuracy, in order to ensure that celestial objects are not stored in the wrong catalogs. In addition, classification time must be fast due to the large number of classifications and to future needs for on-line classification systems. This paper reports on our results from using decision tree classifiers to identify cosmic ray hits in Hubble Space Telescope images. This method produces classifiers with over 95% accuracy using data from a single, upaired image. Our experiments indicate that this accuracy will get even higher if methods for eliminating background noise improve.

Data acquired with a CCD camera are modeled as an additive Poisson–Gaussian mixture, with the Poisson component representing cumulative counts of object-dependent photoelectrons, object-independent photoelectrons, bias electrons, and thermoelectrons and the Gaussian component representing readout noise. Two methods are examined for compensating for readout noise. One method relies on approximating the Gaussian readout noise by a Poisson noise and then using a modified Richardson–Lucy algorithm to effect the compensation. This method has been used for restoring images acquired with CCD’s in the original Wide-Field/Planetary Camera aboard the Hubble Space Telescope. The second method directly uses the expectation-maximization algorithm derived for the Poisson–Gaussian mixture data. This requires the determination of the conditional-mean estimate of the Poisson component of the mixture, which is accomplished by the evaluation of a nonlinear function of the data. The second method requires more computation than the first but is more accurate mathematically and yields modest improvements in the quality of the restorations, particularly for fainter objects. As a specific example, we compare the two methods in restorations of images representative of those acquired with that camera; they contain excess blurring that is due to spherical aberration and a rms readout noise level of 13 electrons.

Hubble Space Telescope Wide Field/Planetary Camera UBV images of three massive, compact multiple systems with the SNR 30 Dor B/NGC 2060 and 30 Dor C/NGC 2044 are discussed and illustrated. In two cases, WN+OB objects have been resolved into additional components to those previously known from ground-based observations, substantially reducing the luminosities of the WN stars and rendering them currently unidentified; in the third case, the components of a B+K composite-spectrum object have been clearly identified. The results are of significance for evolutionary interpretations of these massive stars and for determinations of the upper IMF in extragalactic systems.

We have used the Very Large Array (VLA) to survey the inner Galaxy (absolute value of b less than 0.4 deg, l = 350-40 deg) at 5 GHz to a limiting sensitivity of between 2.5 and 10 mJy. The survey has resulted in a catalog of 1272 discrete sources (including 100 sources outside the formal survey area) of which we have temtatively identified approximately 450 as ultracompact H II regions and approximately 45 as planetary nebulae. Approximately 30% of the radio sources are detected in the Infrared Astronomy Satellite (IRAS) Point source Catalog. The results confirm a scale height of only 30 pc for ultracompact H II regions. We show that source lists generated from the IRAS Point Source Catalog alone suffer serious selection effects; the combination of the IRAS and radio surveys allows us to produce a much more complete census of the regions of massive star formation in our Galaxy.

A model for data acquired with the use of a charge-coupled-device camera is given and is then used for developing a new iterative method for restoring intensities of objects observed with such a camera. The model includes the effects of point spread, photoconversion noise, readout noise, nonuniform flat-field response, nonuniform spectral response, and extraneous charge carriers resulting from bias, dark current, and both internal and external background radiation. An iterative algorithm is identified that produces a sequence of estimates converging toward a constrained maximum-likelihood estimate of the intensity distribution of an imaged object. An example is given for restoring images from data acquired with the use of the Hubble Space Telescope.

We have discovered two high-redshift (z abs =3.388 and 2.908) damped Lyα absorption systems and a third possible damped system (z abs =3.080) while obtaining spectra of optical counterparts from a sample of flat spectrum radio sources. These three systems all have higher redshifts than any previously known damped Lyα absorption systems in the spectra of radio-loud quasars, and they are among the highest redshift damped Lyα systems known. It is unlikely that we would have found as many as two or three damped Lyα absorption systems among our sample unless there is a significant increase in the area-weighted comoving density of damped systems for z≥3

HST/GHRS ultraviolet spectrograms of the individual O3 If*/WN6-A object Mk 42 in 30 Dor and the adjacent, central multiple system R136a are compared with each other and with an appropriate sequence of O3 If* and WN6-A standards from the IUE archive. The analogous spectral montages covering the blue-violet regino, based on new, homogeneous, digital observations of the same stars with the CTIO 4 m telescope, are also presented. These comparisons show clearly the intermediate O3/WN nature of the Mk 42 spectrum, in terms of both emission-line strength (increasing with envelope density) and stellar-wind velocity (decreasing with envelope density). It is also shown that R136a possesses stronger WN spectral characteristics than Mk 42, in agreement with HST narrow-band imaging by the WF/PC Team.

Using the Green Bank 1.4 GHz Northern Sky Survey, a catalog of 30239 sources over the declination range of -5° to 82° to a flux density limit of 100 mJy has been generated. Spectral indices were found for over 90% of these sources based on flux densities at 0.365 or 4.85 GHz taken from other catalogs. Flux densities at all three frequencies are available for 20000 sources. The spectral properties of 1.4 GHz sources are discussed along with the selection effects induced by the idiosyncracies of the various catalogs

We propose that the chaotic stellar winds from massive stars are potential π 0 -decay γ-ray sources. A small fraction of the thermal ions is first-order Fermi accelerated to high energies by the shocks embedded in the highly unstable radiatively driven winds. These particles interact with the thermal ions to produce γ-rays peaked around 0.1 GeV via π 0 -decay. When the mass-loss rate of an early-type star is high enough, the wind becomes opaque to the ion-ion interactions and a substantial fraction of the nonthermal ions' energy is emitted in γ-rays

We have surveyed a 140 deg strip along the Galactic plane with the VLA for OH masers. Fifty OH masers, including 14 new sources, were detected. The masers have a very narrow distribution in Galactic latitude and are probably Population I objects. A study of the IRAS counterparts of OH masers from this and other surveys reveals a strong correlation between the infrared colors of OH masers and Galactic latitude

An estimate of the possible γ-ray luminosity from winds around hot stars is given and it is shown that the predicted photon flux below 1 MeV from nearby stars can be greater than the detection threshold of the Oriented Scintillation Spectrometer Experiment on the Gamma Ray Observatory. Charged particles are first-order Fermi accelerated to relativistic energies by strong isothermal shocks generated by radiatively driven instabilities in the winds. Low-energy γ-rays of luminosity ∼10 33 ergs/s are emitted by the relativistic electrons via inverse Compton scattering of the stellar UV photons and are predicted to be well correlated with the hard X-ray component observed by the Solid State Spectrometer of the Einstein Observatory from some nearby hot stars

The paper describes X-ray and optical observations with the Einstein Observatory of two SNRs which are examples of a group of SNRs that have centrally peaked X-ray surface brightness distributions and limb-brightened radio morphologies. X-ray and optical spectra confirm that they are located along lines of sight with substantial intervening absorption, as is the case of other objects that have these morphological characteristics. The hydrogen column density along the line of sight to both remnants is established at (7-11) x 10 to the 21st/sq cm. A thermal origin is proposed as the most likely explanation for the X-ray morphology. It is demonstrated that these SNRs do not have a density and temperature distribution which resembles that of a point explosion in a uniform-density medium, even when the overburden of absorption is considered.

A new similarity solution that describes the evolution of an SNR expanding into a cloudy interstellar medium is expounded. The solution incorporates a reasonable model of the conductive evaporation of cold clouds embedded in the hot gas behind the shock. The model has two new parameters in addition to those describing the usual Sedov solution for a uniform interstellar medium. The X-ray, infrared, and optical luminosities of remnants with evaporating clouds are calculated, and some of the expected spectral characteristics in the various wavebands are discussed. The effects described may explain the class of remnants observed to have centrally peaked X-ray emission and shell-like radio emission. The total H-alpha luminosity from evaporating clouds predicted by this model is less than that observed for SNRs with centrally peaked thermal X-ray emission. A detailed calculation of the X-ray and optical line emission from evaporating clouds would be very useful in testing this model against the observations.

The IRAS Point Source Catalog has been compared with the 20 cm Galactic plane survey (GPS) of Zoonematkermani S. et al. (1990, Astrophys. J. Sup. Ser., 74). A new technique for distinguishing chance from true coincidences using the bands at which the IRAS sources are detected is developed. For each match, an estimate of the probability that the match represents a true association is derived. Of the 1992 radio sources, 330 have high probability associations, with most having reliabilities above 90%. The GPS/IRAS sources are clearly Galactic: they have a very restricted distribution in both Galactic latitude and longitude.

The mechanisms responsible for the hard X-ray emission of OB supergiants (OBSGs) are investigated theoretically, modifying the periodic-shock model of Lucy (1982). The physical processes discussed include (1) the particle acceleration (PA) mechanism and its effect on the structure of individual shocks, (2) the energy cutoff and spectral index of the relativistic electrons and ions, and (3) the efficiency of PA by shocks and its implications for the number densities of relativistic particles. The model is used to predict the spectrum and intensity of the dominant nonthermal X-ray emission source from OBSGs, and the results are shown to be in good agreement with Einstein Observatory Solid-State Spectrometer observations of three OBSGs in Orion (Cassinelli and Swank, 1983). It is inferred that the surface magnetic fields of OBSGs are no greater than a few G, and that the PA rates are significantly lower than generally predicted for collisionless astrophysical shocks. 66 refs.

It has been proposed that a single preoperative dose of a corticosteroid may protect the myocardium from ischemic injury during open heart surgery. To test this hypothesis, a prospective, randomized, double blind study was carried out in ninety-five patients undergoing coronary bypass surgery using intermittent ischemic arrest with systemic and local hypothermia. Half the patients received 2 gm (approximately 30 mg/kg) of methylprednisolone 2 hours prior to the initiation of cardiopulmonary bypass and the other half received a placebo. Postoperative electrocardiograms and blood levels of serum creatine phosphokinase (CPK), lactic dehydrogenase (LDH), and serum glutamic oxalacetic transaminase (SGOT) were compared in the two groups. No apparent difference was noted in the number of patients with significantly elevated levels of CPK, LDH, or SGOT or in the number with positive isoenzyme patterns of CPK and LDH. Moreover, there was no significant difference in the mean values of CPK, LDH, or SGOT between the two groups. The number of patients with electrocardiographic evidence of myocardial injury (10 per cent) was the same in both groups and no difference was noted in (1) the ease with which patients could be weaned from cardiopulmonary bypass, (2) postoperative arrhythmias, (3) postoperative bleeding, (4) postoperative respiratory insufficiency, and (5) length of hospital stay. It is concluded that a single preoperative dose of 2 gm of methylprednisolone offers no demonstrable protection to the myocardium from the effects of ischemia during coronary artery bypass surgery.

A consecutive and comparative reading of the biographies of F. Scott Fitzgerald not only provides a cumulative portrait of the biographical figure but also suggests that such a reading reveals something about our own collective psychological and critical response to that figure. In works by Mizener, Graham, Turnbull, Latham, Buttita, Milford, and Mayfield, Fitzgerald emerges as an accessible and appealing figure who, inspite of his willing participation in the role of literary celebrity, remained remarkably representative of a common experience that is familar to most of us.