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XMM-Newton observed SAX J2103.5+4545 on January 6, 2003, while RXTE was monitoring the source. Using RXTE-PCA dataset between December 3, 2002 and January 29, 2003, the spin period and average spin-up rate during the XMM-Newton observations were found to be $354.7940\pm0.0008$ s and $(7.4\pm0.9)\times10^{-13}$Hz s$^{-1}$ respectively. In the power spectrum of the 0.9-11 keV EPIC-PN lightcurve, we found quasi periodic oscillations around 0.044 Hz (22.7 s) with an rms fractional amplitude $\sim $6.6 %. We interpreted this QPO feature as the Keplerian motion of inhomogenuities through the inner disk. In the X-ray spectrum, in addition to the power law component with high energy cutoff and $\sim6.4$ keV fluorescent iron emission line (Baykal et al., 2002), we discovered a soft component consistent with a blackbody emission with ${\rm{kT}}\sim1.9$keV. The pulse phase spectroscopy of the source revealed that the blackbody flux peaked at the peak of the pulse with an emission radius $\sim 0.3$ km, suggesting the polar cap on the neutron star surface as the source of blackbody emission. The flux of the iron emission line at $\sim 6.42$ keV was shown to peak at the off-pulse phase, supporting the idea that this feature arises from fluorescent emission of the circumstellar material around the neutron star rather than the hot region in the vicinity of the neutron star polar cap., Comment: 16 pages 4 figures. Major revisions present. Accepted for publication in ApJ

We measured Doppler shifts of three bright spectral lines in the X-ray emission from Cygnus X-3 as recorded by the Chandra X-Ray Observatory. Doppler shifts of lines associated with Si XIV and S XVI exhibit orbital modulation. The magnitude and phasing of this modulation relative to the orbital ephemeris indicate the location of the source of this emission within the wind emanating from the compact object's companion. These observations enable us to make an indirect measurement of the separation of the two stars. Under certain assumptions our observation of a line associated with Fe XXV also limits the mass of the compact object M < 3.6 MSun., 7 pages, 3 figures, Accepted for publication in The Astrophysical Journal Letters

The November 1999 outburst of the transient pulsar SAX J2103.5+4545 was monitored with the large area detectors of the Rossi X-Ray Timing Explorer until the pulsar faded after a year. The 358 s pulsar was spun up for 150 days, at which point the flux dropped quickly by a factor of 7, the frequency saturated and, as the flux continued to decline, a weak spin-down began. The pulses remained strong during the decay and the spin-up/flux correlation can be fit to the Ghosh and Lamb derivations for the spin-up caused by accretion from a thin, pressure-dominated disk, for a distance 3.2 kpc and a surface magnetic field 1.2 10^{13} Gauss. During the bright spin-up part of the outburst, the flux was subject to strong orbital modulation, peaking 3 days after periastron of the eccentric 12.68 day orbit, while during the faint part, there was little orbital modulation. The X-ray spectra were typical of accreting pulsars, describable by a cut-off power-law, with an emission line near the 6.4 keV of K alpha fluorescence from cool iron. The equivalent width of this emission did not share the orbital modulation, but nearly doubled during the faint phase, despite little change in the column density. The outburst could have been caused by an episode of increased wind from a Be star, such that a small accretion disk is formed during each periastron passage. A change in the wind and disk structure apparently occurred after 5 months such that the accretion rate was no longer modulated or the diffusion time was longer. The distance estimate implies the X-ray luminosity observed was between 1 10^{36} ergs s^{-1} and 6 \times 10^{34} ergs s^{-1}, with a small but definite correlation of the intrinsic power-law spectral index., Accepted for publication in Astrophysical Journal

We analysed the RXTE archival data of 1E 1048.1-5937 covering a time span of more than one year. The spin down rate of this source decreases by 30 percent during the observation. We could not resolve the X-ray flux variations because of contamination by Eta Carinae. We find that the level of pulse frequency fluctuations of 1E 1048.1-5937 is consistent with typical noise levels of accretion powered pulsars. Recent RXTE observations of 1E 2259+586 have shown a constant spin down with a very low upper limit on timing noise. We used the RXTE archival X-ray observations of 1E 2259+586 to show that the intrinsic X-ray luminosity times series is also stable, with an rms fractional variation of less than 15 percent. The source could have been in a quiet phase of accretion with a constant X-ray luminosity and spin down rate.

This paper presents the highlights and key findings of 10 years of use and study of Ada and object-oriented design in NASA Goddard's Flight Dynamics Division (FDD). In 1985, the Software Engineering Laboratory (SEL) began investigating how the Ada language might apply to FDD software development projects. Although they began cautiously using Ada on only a few pilot projects, they expected that, if the Ada pilots showed promising results, the FDD would fully transition its entire development organization from FORTRAN to Ada within 10 years. However, 10 years later, the FDD still produced 80 percent of its software in FORTRAN and had begun using C and C++, despite positive results on Ada projects. This paper presents the final results of a SEL study to quantify the impact of Ada in the FDD, to determine why Ada has not flourished, and to recommend future directions regarding Ada. Project trends in both languages are examined as are external factors and cultural issues that affected the infusion of this technology. The detailed results of this study were published in a formal study report [1] in March of 1995. This paper supersedes the preliminary results of this study that were presented at the Eighteenth Annual Software Engineering Workshop in 1993 [2].

We observe glitches in the arrival times of X-ray pulses from GRO J1744-28 associated with the large X-ray bursts observed from this source. In early observations, the pulse arrival time becomes delayed by 28 ms (6% of the 467 ms pulsar period) following bursts while the shape of the nearly sinusoidal light curve is essentially unchanged. This arrival-time lag decays exponentially over the next ~1000 s. In later observations, the observed phase lags are smaller, and eventually, some bursts appear to be accompanied by a small phase advance. While explanations of these observations that rely upon changes in the postburst accretion flow are natural, our observations present some problems for these explanations. It may be that this behavior can be understood by analogy with glitches in spinning-down radio pulsars, though this explanation has its own problems. Explained as a glitch, the phase shift is the result of coupling of the neutron star's crust to the crustal superfluid, which is spun up more slowly than the rest of the star, and the recovery is due to coupling between the crust and the core of the neutron star.

In this Letter, we provide an introduction to the main features seen in a series of observations of the bursting pulsar GRO J1744-28. The observations were made from 1996 January through May with the proportional counter array on the Rossi X-Ray Timing Explorer spacecraft. In the 2-10 keV band, GRO J1744-28 emitted large bursts of ~10 s duration at a rate of about 2 per hour. The peak flux during these bursts was ~6-40 times greater than that in the quiescent, or nonbursting, periods. For the earliest bursts, the inferred peak luminosity approaches 100 times the Eddington limit, which is suggestive of some kind of beaming mechanism. A range of smaller bursts and quasi-periodic oscillation features were also seen. All this activity was superposed on an almost perfect sinusoidal modulation at a frequency of 2.14 Hz with an amplitude of ~10% of the nonbursting flux. The source's persistent flux declined in a roughly linear trend from late January until mid-May, by which time its intensity was confused with several other sources.

This article examines the premise that object-oriented technology (OOT) is the most significant technology ever examined by the Software Engineering Laboratory (SEL). The evolution of the use of OOT in the SEL “Experience Factory” is described in terms of the SEL's original expectations, focusing on how successive generations of projects have used OOT. General conclusions are drawn on how the usage of the technology has evolved in this environment.

This article summarizes a workshop organized and conducted by the authors on April 1 and 2, 1993, under the auspices of Portland State University and the Oregon Center for Advanced Technology Education. This workshop provided a uniquely comprehensive and realistic look at the state of the art and practice of object-oriented programming. Issues discussed at the workshop and summarized here include the naturalness of object-oriented technology, reuse potential, programming support and evaluation tools, and the cost of converting to an object-oriented design technology. The findings should be of interest to researchers, organizations, and individuals who are exploring and/or using the object-oriented approach to software development. The article concludes by offering some recommendations for the use of objectoriented technology.

Data taken with the CYGNUS detector between 1989 September and 1993 January have been used to search for 1 s bursts of ultrahigh-energy gamma rays from point sources at arbitrary locations in the northern sky. We find no evidence for such bursts. We set a theory-dependent upper limit on the rate-density of evaporating black holes of 8.5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ ${\mathrm{pc}}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{yr}}^{\mathrm{\ensuremath{-}}1}$ at the 99% C.L. When the same emission spectrum is used to recalculate previous upper limits based on direct searches, this limit is the most restrictive by nearly 2 orders of magnitude.

Abstract In 2006 Enterprise developed a 16-inch oil export system from Shenzi field located in Green Canyon Block 653 in the Gulf of Mexico, approximately 120 nautical miles offshore in approximately 4,375 ft of water depth. The oil export system is attached to the Shenzi TLP host facility. The 16-inch oil export SCR system is subject to the CVA (Certified Verification Agent) verification required by MMS (Minerals Management Service) 30 CFR Part 250 [Ref. 1]. NTL No. 2007-G14 [Ref. 2] was issued pursuant to 30 CFR 250.103 to provide clarification and guidance for pipeline riser design, fabrication, and installation under the platform verification program specified in 30 CFR 250.909 through 918. This paper summarizes the 16-inch oil export SCR CVA verification procedure. This paper presents a systematic SCR CVA verification procedure. The CVA verification procedure includes SCR CVA verification preparation, and verification of SCR design, fabrication, and installation. The verification procedure and table formats developed are unique and applicable to other types of pipeline risers in the Gulf of Mexico. Introduction The Shenzi field is located in the deepwater central Gulf of Mexico approximately 120 miles from the Louisiana coast. The field comprises Green Canyon Blocks 609, 610, 653, and 654. Water depth at the site is approximately 4,300 ft. Figure 1 presents the Shenzi Field layout [Ref. 3]. The Shenzi Oil Export Pipeline and SCR will transport crude oil from BHP Billiton's Tension Leg Platform (TLP) in Green Canyon Block 653 in approximately 4500 fsw to the Ship Shoal 332B Platform in approximately 435 fsw. Figure 2 presents an artist's rendering of the Shenzi TLP [Ref. 3]. 30 CFR Part 250 was published in the Federal Register on July 19, 2005. The rule became effective on August 18, 2005. 30 CFR 250.909 through 250.918 applies to new pipeline risers attached to the floating platforms in the Gulf of Mexico. The rule defines the CVA nomination, CVA's primary responsibilities, CVA's primary duties during the design phase, CVA's primary duties during the fabrication phase, and the CVA's primary duties during the installation phase. The detailed engineering design of Shenzi 16-inch oil export SCR started at the beginning of 2006. So it was one of the earliest SCRs subjected to the CVA program. This paper presents a systematic SCR CVA verification procedure developed during Shenzi 16-inch oil export SCR CVA verification project. The verification procedure includes SCR CVA verification preparation, SCR design CVA verification, SCR fabrication CVA verification, and SCR installation CVA verification. The verification procedure and table formats developed are unique and applicable to other types of pipeline risers in the Gulf of Mexico. SCR Design Data SCR Data The API 5L X-65 steel grade has been selected for the oil export SCR. Table 1 summarizes the oil export SCR data, pipe wall thickness tolerances, corrosion allowance, SCR coating data, and VIV suppression device data. Internal Fluid, Design Pressure and Temperature Design pressure and temperature are 3,540 psig and 140 ?F. For normal operating condition, the pressure and temperature are 3,220 psig and 120 ?F. For hurricane shut-down condition, the pressure and temperature are 3,540 psig and 120 ?F. The oil density is 54.0 pcf and the pressure reference elevation is 200 ft above mean sea level for all conditions.

In recent years, most fluid produced or exported has been transported using steel catenary risers (SCRs) attached to deepwater floating structures. The SCRs are terminated at the floating structures using Top Termination Units (TTUs) such as flexible joints or tapered stress joints. The flexible joints are usually designed to allow the riser to rotate with the floating structure motion and reduce the amount of moments transferred to the hull structure. The flexible joints depend on the flexibility and compressibility of the elastomer layers to allow for the rotation of the SCR. The stress joints, alternatively, provide fixed support at the hull and thus larger bending moment that has to be accounted for in the hull design. The stress joints can be made of steel or titanium material. The SCR TTU’s receptacle, which will be welded to the hull porch and contains the TTU basket, has to be designed to meet the force and reaction requirements associated with the selected TTU type. However, in some cases which could be due to failure of the TTU to meet the expected life or the operational requirements, the operators may have to replace the damaged TTU with another one or with a different TTU type. A few examples are available in the Gulf of Mexico. Recently the Flexible Joint TTU of the Independent Hub 20-inch export SCR had an operational problem. During the course of investigating the related issues and studying possible solutions, one option considered was the feasibility of replacing the Flexible Joint (FJ) with Titanium Tapered Stress Joint (TSJ). This paper highlights the issues that have to be considered in the design of the FJ existing receptacle to accommodate the force reactions of a Titanium TSJ. These issues are addressed and the results of the detailed finite element analysis performed are provided. The analysis conclusions, which are related to the feasibility of the existing receptacle to receive the loads imposed by TSJ and the modifications required to achieve this, are presented.Copyright © 2009 by ASME

Abstract Described herein is a chronology for developing a deepwater pipeline repair system and cooperative ownership group for affecting emergency repairs of damaged pipelines. Using a Joint Industry Project (JIP) funding model, technology development started in 2004, and continued as Hurricanes Katrina and Rita hit in 2005, and resulted in the formation of DW RUPE - Pipelines Co-Ownership Group in May of 2007. Included in this paper is a description of the repair methods developed, and repair tools being procured and developed for affecting 10 to 24 inch ANSI pipeline repairs in 1,000 to 10,000 feet of water. A recently-developed spreadsheet-based pipe lifting analysis laptop computing tool is described for use in planning pipe lifting and cutting operations for a specific emergency pipeline repair operation in deep water. Background on the Formation of DW RUPE In 2004 Phase 1 of a JIP was formed to develop a low CAPEX emergency repair capability for pipelines and flowlines in water depths in the 1,000-10,000 ft range, in the US Gulf of Mexico. Stress Subsea, Inc. (SSI) performed a Failure Mode and Effects Analysis, conducted interviews with suppliers and operators and included input from the JIP Steering Committee. Phase 1 JIP Conclusions As a result from DW RUPE, Phase 1, the following conclusions were drawn for export pipelines:The probability of needing a deepwater repair is low, but the consequences resulting from pipeline damage are high. Because of this, the project agreed upon pursuing a low CAPEX repair solution, recognizing the need to minimize capital expenditures since the probabilities of occurrence are low.The most likely damage types are wet and dry buckles caused by anchor snags (the DW RUPE shallower water depth range is 1,000 ft., hence anchoring damage is still a consideration).Potential repair solutions for a low CAPEX pipeline repair and a low CAPEX flowline repair are different.Traditionally a leak clamp and a spool piece connector set are needed for each pipe size. The project pursued a new paradigm of adapting and employing full structural clamps in place of connectors. This allows two clamps to be used in a spool piece repair or one of the structural clamps to be used alone for a pinhole leak from a cracked weld. Two clamps serve the same function as two connectors and a clamp (Pipeline Repair), thus reducing the CAPEX investment for inventory.Cracked welds are the most likely cause for pinhole leaks. Full structural clamps are advised to arrest crack propagation (Pipeline Repair).

SAX J2103.5+4545 has been continuously monitored for $\sim $ 900 days by Rossi X-ray Timing Explorer (RXTE) since its outburst in July 2002. Using these observations and previous archival RXTE observations of SAX J2103.5+4545, we refined the binary orbital parameters and find the new orbital period as P= (12.66536 $\pm $ 0.00088) days and the eccentricity as 0.4055$\pm$ 0.0032. With these new orbital parameters, we constructed the pulse frequency and pulse frequency derivative histories of the pulsar and confirmed the correlation between X-ray flux and pulse frequency derivative presented by Baykal, Stark and Swank (2002). We constructed the power spectra for the fluctuations of pulse frequency derivatives and found that the power law index of the noise spectra is 2.13 $\pm$ 0.6. The power law index is consistent with random walk in pulse frequency derivative and is the steepest among the HMXRBs. X-ray spectra analysis confirmed the inverse correlation trend between power-law index and X-ray flux found by Baykal, Stark and Swank (2002)., Comment: 23 pages, 7 figures, revised version accepted for publication in MNRAS

We present the calibration and background model for the Proportional Counter Array (PCA) aboard the Rossi X-ray Timing Explorer (RXTE). The energy calibration is systematics limited below 10 keV with deviations from a power-law fit to the Crab nebula plus pulsar less than 1%. Unmodelled variations in the instrument background amount to less than 2% of the observed background below 10 keV and less than 1% between 10 and 20 keV. Individual photon arrival times are accurate to 4.4 micro-seconds at all times during the mission and to 2.5 micro-seconds after 29 April 1997. The peak pointing direction of the five collimators is known to a precision of a few arc-seconds, 77 pages, 34 figures. accepted by Ap J Supplement for April 2006 issue. This paper and additional calibration information are available from http://universe.gsfc.nasa.gov/xrays/programs/rxte/pca/ pcapage.html. Revised version contains minor changes to match accepted version

The strengths of product line engineering have been described before. But how can an organization make the move from developing one-of products to product line engineering without major interruptions in the day-today work? This paper describes how to perform the transition to product line engineering and lists the various strategies for such a transition. It also describes how to create an adoption plan and how to institutionalize product line engineering in an organization.

Software product lines promise benefits like development and maintenance effort reduction, time to market decrease, and quality improvement, all resulting from planned and systematic reuse of common core assets. However, very little quantitative data has been measured so far to prove these promises. This paper formulates and discusses 7 hypotheses on howthe promised advantages would look like in a quantitative way. It is meant to be a starting point for discussion on how to quantify which product line benefits and how they can be measured.

Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we carried out pulse timing analysis of the transient X-ray pulsar SAX J2103.5+4545. An outburst was detected by All Sky Monitor (ASM) October 25 1999 and reached a peak X-ray brightness of 27 mCrab October 28. Between November 19 and December 27, the RXTE/PCA carried out pointed observations which provided us with pulse arrival times. These yield an eccentric orbit (e= 0.4 \pm 0.2) with an orbital period of 12.68 \pm 0.25 days and light travel time across the projected semimajor axis of 72 \pm 6 sec. The pulse period was measured to be 358.62171 \pm 0.00088 s and the spin-up rate (2.50 \pm 0.15) \times 10^{-13} Hz s^{-1}. The ASM data for the February to September 1997 outburst in which BeppoSAX discovered SAX J2103.5+4545 (Hulleman, in't Zand and Heise 1998) are modulated at time scales close to the orbital period. Folded light curves of the 1997 ASM data and the 1999 PCA data are similar and show that the intensity increases at periastron passages., To appear in The Astrophysical Journal (Letters)

The Bursting Pulsar, GRO J1744-28, has been observed with the Rossi X-ray Timing Explorer (RXTE) regularly since the launch of the satellite in December 1995. This accretion driven pulsar has undergone two outbursts which have been accompanied by significant spin-up of the pulsar. Between these two outbursts, the pulsar was detectable during each observation down to fluxes perhaps one thousandth of the persistent flux at the peak of the first outburst. We observe evidence of a change in the sign of the frequency derivative during the faintest period but the relationship between the observed luminosity and the frequency derivative is complex., 4 pages, 2 figures, AIP Proceedings LaTex format, to appear in "Accretion Processes in Astrophysical Systems", Proc. of the 8th Annual Astrophysics Conference in Maryland, S. S. Holt & T. Kallman (eds.)

The Rossi X-ray Timing Explorer (RXTE) has been monitoring the Bursting Pulsar, GRO J1744-28, since Jan. 1996. Large deadtimes in the proportional counter array (PCA) have made measurements of the peak flux during bursts problematic, therefore the value α, of the ratio of time averaged persistent luminosity to time averaged burst luminosity, has not been well determined. The value of α has important implications for understanding the nature of the bursts. Some RXTE observations begun after the recent reemergence of GRO J1744-28 in Dec. 1996 were performed with the source offset from the axis of peak PCA response. This reduces the deadtime in the PCA and allows a more precise determination of burst peak fluxes and thus α. These observations provide an understanding of the deadtime processes during periods when the source was viewed at peak response. Between 17–24 January 1997 we estimate that α was ≈34. Based on similarity of the overall lightcurve and countrate, this value is also appropriate for the peri...

The proportional counter array (PCA) is designed to perform microsecond timing of bright galactic sources and broad band, confusion limited, studies of faint extragalactic sources in the 2 - 60 keV x-ray band. The PCA was launched as part of the Rossi X-ray Timing Explorer (RXTE) satellite into a circular orbit of altitude 580 km and 23 degrees inclination on December 30, 1995. The mission contains three experiments: a set of large area xenon proportional counters sensitive from 2 - 60 keV (proportional counter array: PCA), a set of large area sodium iodide scintillators sensitive from 15 - 200 keV (high energy x-ray timing experiment: HEXTE), and three wide field of view scanning detectors which monitor most of the sky each orbit (all sky monitor: ASM). The goals of the mission are summarized by Swank et al. We present performance and calibration data on the measured and predicted in-orbit background, energy response, relative and absolute timing performance, and the operational possibilities made available with the high performance experiment data system (EDS) designed and built by MIT.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper examines the premise that object-oriented technology (OOT) is the most significant technology ever examined by the Software Engineering Laboratory. The evolution of the use of OOT in the Software Engineering Laboratory (SEL) 'Experience Factory' is described in terms of the SEL's original expectations, focusing on how successive generations of projects have used OOT. General conclusions are drawn on how the usage of the technology has evolved in this environment.

Data from an extensive air shower detector of ultrahigh-energy cosmic rays shows shadowing of the cosmic-ray flux by the Moon and the Sun with significance of 4.9 standard deviations. This is the first observation of such shadowing. The effect has been used to determine that the angular resolution of the detector is 0.75{degree} {sub {minus}0.90{degree}}{sup +0.13{degree}}.

The 11 ‘‘in‐phase’’ source events from the 1986 muon‐rich bursts associated with Hercules X‐1 (previously reported by this group) have been studied for indications of further anomalous behavior. The most significant effect observed resulted from an analysis of the showerfront time‐structures of these events. This analysis was then applied a priori to the rest of the source day, where an additional ∼9 signal events are expected to remain. The same effect was observed at a chance probability level of ∼0.1%.

A new method of searching for UHE point source has been developed. With a data sample of 150 million events, we have surveyed the sky for point sources over 3314 locations (1.4°

A small pilot experiment to examine the use of the water‐Cerenkov technique for air shower detection was installed near the center of the CYGNUS air shower array. Preliminary results showing general agreement with simulations are presented. Thus, the technique promises to offer significant advances for VHE‐UHE γ‐ray astronomy.

A preliminary search is made for continuously pulsed, and burst, emission from the Crab pulsar or its nebula at ultra‐high energies using the CYGNUS air shower experiment. No evidence is found for pulsed emission over the entire data set of 1,075 days searched. A 90% confidence upper limit for the flux of cosmic rays at the interpulse phase is 6.9×10−14 cm−2s−1 above 50 TeV. A single day (JD=2447644.5,UTC=66700s to JD=2447645.5,UTC=11200s), is found to have a 4.1 σ excess corresponding to a chance probability of 2.2%; no evidence of the pulsar period is found on this day.

We report here the preliminary results of our observations of the sporadic X‐binary system 4U0115+63. The CYGNUS air shower array has been collecting data since April 1986. No significant excess is seen from the direction of this source, nor any correlation with its 24‐day orbital period. A 90% confidence‐level upper limit on the flux from 4U0115+63 is 2.8×10−13 cm−2 s−1 above 50 TeV. This flux limit is considerably lower than those reported by other UHE experiments. Search for periodicity at the neutron star frequency is in progress.

Data from the CYGNUS extensive air shower experiment at Los Alamos, NM has been analyzed to study the angular resolution of the array, and to search for point sources in the galaxy. Results on searches for steady emission from Cyg X‐3, Her X‐1 and the Crab nebula are presented.

A unique feature of Cygnus X-3 is that occasionally it has large radio outbursts that begin very abruptly and last for several days. Several experiments in the past have claimed to observe signals above 1 TeV correlated with these radio bursts; the most recent bursts occurred in June and July 1989. No significant signal was observed by the CYGNUS experiment over time scales longer than a day during this time; a 90%-confidence-level limit of 3.0{times}10{sup {minus}13} cm{sup {minus}2} s{sup {minus}1} is placed on the flux above 50 TeV during the period from 15 May to 31 July 1989.

The CYGNUS air-shower array has been used to search for emission of ultra-high-energy gamma radiation from 13 active galactic nuclei (AGNs) that were detected by EGRET. The data set spans the period 1986 April 2 to 1993 January 1. The data set has been searched for continuous emission, for emission on the time scale of 1 week, and for emission on the time scale of 1 day. No evidence for emission from any of the AGNs on any of the time scales examined was found. The 90% Confidence Level (CL) upper limit to the continuous flux from Mrk 421 above 50 TeV is 7.5×10 -14 cm -1 s -1

A search has been made for steady emission or ultra-high-energy radiation from individual point sources over most or the northern sky. Over 2×10 8 air showers induced by primary particles or energy greater than about 10 TeV were recorded from 1986 April until 1991 May by the CYGNUS air shower array. No statistically significant excess above the background from the isotropic flux or cosmic rays was found for any direction in the sky from 0° to 80° declination. In addition, 49 specific potential sources were examined, and none showed a statistically significant excess or events

An object is an abstract software model of a problem domain entity. Objects are packages of both data and operations of that data (Goldberg 83, Booch 83). The Ada (tm) package construct is representative of this general notion of an object. Object-oriented design is the technique of using objects as the basic unit of modularity in systems design. The Software Engineering Laboratory at the Goddard Space Flight Center is currently involved in a pilot program to develop a flight dynamics simulator in Ada (approximately 40,000 statements) using object-oriented methods. Several authors have applied object-oriented concepts to Ada (e.g., Booch 83, Cherry 85). It was found that these methodologies are limited. As a result a more general approach was synthesized with allows a designer to apply powerful object-oriented principles to a wide range of applications and at all stages of design. An overview is provided of this approach. Further, how object-oriented design fits into the overall software life-cycle is considered.