The study of the physics of cometary nuclei

A semiannual progress report describing the work completed during the period 1 September 1975 to 29 February 1976 on the physics of cometary nuclei was given. The following items were discussed: (1) a paper entitled ""A speculation about comets and the earth'', (2) a chapter entitled"" The physics of comets'' for ""Reviews of Astronomy and Astrophysics'', (3) continuing work on split comets, and (4) results dealing with a new application of nongravitational solar-radial forces as a measure of comet nucleus dimensions and activity

Anomalously high potentials observed on ISEE

Data from two electric field experiments and from the plasma composition experiment on ISEE-1 are used to show that the spacecraft charged to close to -70 V in sunlight at 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely. Modeling of this event is required to determine if the barrier was produced by the presence of space charge

Moment Analysis of Magnetic Resonance Signals

A relation is given between the moments of a generalized convolution transform of a function, and the moments of the function itself. This relation is applied to the signal obtained with a field‐modulated EPR spectrometer, a consequence being that the integrated intensity of an absorption line may be obtained from first moment measurements at any modulation amplitude, regardless of line shape or various instrumental nonidealities. This result has been verified experimentally to within a few percent with a Varian EPR spectrometer. Extension to measurement of higher moments is discussed

SUPPLY CHAIN INTEGRATION IN THE FOOD AND CONSUMER GOODS INDUSTRIES

The interorganizational structures necessary to implement and achieve the logistical performance improvements identified in the Efficient Consumer Response (ECR) initiative and related supply chain management concepts are difficult to develop. Firms continue to struggle to implement integrated programs and techniques, particularly with respect to changing operating structures, relationships, and mindsets to facilitate true supply chain integration. This research explores the logistical strategies and structures used by selected food and consumer goods firms to integrate their supply chains. It illustrates effective integration strategies and identifies critical success factors and barriers to successful ECR implementation. A framework is used to guide managers in developing the competencies essential to integrating the supply chain and to establishing the relationships necessary to operate in an ECR environment. The framework, entitled Supply Chain 2000, depicts supply chain value creation as achieving synchronization and coordination across four critical supply chain flows: product/service; market accommodation; information; and cash.Industrial Organization,

Wind-shearing in gaseous protoplanetary disks and the evolution of binary planetesimals

One of the first stages of planet formation is the growth of small planetesimals. This early stage occurs much before the dispersal of most of the gas from the protoplanetary disk. Due to their different aerodynamic properties, planetesimals of different sizes and shapes experience different drag forces from the gas during this time. Such differential forces produce a wind-shearing (WISH) effect between close by, different size planetesimals. For any two planetesimals, a WISH radius can be considered, at which the differential acceleration due to the wind becomes greater than the mutual gravitational pull between the planetesimals. We find that the WISH radius could be much smaller than the Hill radius, i.e. WISH could play a more important role than tidal perturbations by the star. Here we study the WISH radii for planetesimal pairs of different sizes and compare the effects of wind and gravitational shearing (drag force vs. gravitational tidal force). We then discuss the role of WISH for the stability and survival of binary planetesimals. Binaries are sheared apart by the wind if they are wider than their WISH radius. WISH-stable binaries can inspiral and possibly coalesce due to gas drag. Here, we calculate the WISH radius and the gas drag-induced merger timescale, providing stability and survival criteria for gas-embedded binary planetesimals. Our results suggest that even WISH-stable binaries may merge in times shorter than the lifetime of the gaseous disk. This may constrain currently observed binary planetesimals to have formed far from the star or at a late stage after the dispersal of most of the disk gas. We note that the WISH radius may also be important for other processes such as planetesimal erosion and planetesimal encounters and collisions in a gaseous environment.Comment: ApJ, in pres

Evaluation of tantalum for mercury containment in the SNAP-8 boiler

Corrosion testing of tantalum for mercury containment in SNAP 8 boile

A new basic effect in retarding potential analyzers

The Retarding Potential Analyzer (RPA) is the standard instrument for in situ measurement of ion temperature and other ionospheric parameters. The fraction of incoming ions rejected by a RPA produces perturbations that reach well ahead of a thin Debye sheath, a feature common to all collisionless, hypersonic flows past ion-rejecting bodies. This phenomenon is here found to result in a correction to Whipple’s classical law for the current characteristic of an ideal RPA sheath thin; inverse ram ion Mach number M-1, and ram angle of RPA aperture u, small or moderately small

The Distance To The Hyades Cluster Based On Hubble Space Telescope Fine Guidance Sensor Parallaxes

Trigonometric parallax observations made with the Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) 3 of seven Hyades members in six fields of view have been analyzed along with their proper motions to determine the distance to the cluster. Knowledge of the convergent point and mean proper motion of the Hyades is critical to the derivation of the distance to the center of the cluster. Depending on the choice of the proper-motion system, the derived cluster center distance varies by 9%. Adopting a reference distance of 46.1 pc or m - M = 3.32, which is derived from the ground-based parallaxes in the General Catalogue of Trigonometric Stellar Parallaxes (1995 edition), the FK5/PPM proper-motion system yields a distance 4% larger, while the Hanson system yields a distance 2% smaller. The HST FGS parallaxes reported here yield either a 14% or 5% larger distance, depending on the choice of the proper-motion system. Orbital parallaxes (Torres et al.) yield an average distance 4% larger than the reference distance. The variation in the distance derived from the HST data illustrates the importance of the proper-motion system and the individual proper motions to the derivation of the distance to the Hyades center; therefore, a full utilization of the HST FGS parallaxes awaits the establishment of an accurate and consistent proper-motion system.NASA HST GTO, HF-1042.01-93A, HF-1046.01-93A, NAS526555Astronom

Neurology

Contains reports on four research projects.U. S. Public Health Service (B-3055-4)U. S. Public Health Service (B-3090-4)U. S. Public Health Service (MH-06175-02)U.S. Navy (Office of Naval Research (Nonr-1841 (70))U. S. Air Force (AF49(638)-1313

Meta-analysis & Review of Learner Performance & Preference: Virtual vs. Optical Microscopy

Background & Purpose: For nearly two decades, a wealth of literature has been published describing the various capabilities, uses, and adaptations of virtual microscopy (VM). Many studies have investigated the effects and benefits of VM on student learning compared to optical microscopy (OM). As such, this study statistically aggregated the findings of multiple comparative studies through a meta-analysis to summarize and substantiate the pedagogical efficacy of teaching with VM. Methods Using predefined eligibility criteria, teams of paired researchers screened the titles and abstracts of VM studies retrieved from seven different databases. After two rounds of screening, numerical and thematic data were extracted from the eligible studies for analysis. A summary effect size and estimate of heterogeneity were calculated to determine the effects of VM on learner performance and the amount of variance between studies, respectively. Trends in student perceptions were also analyzed and reported. Results: Of the 725 records screened, 72 studies underwent full-text review. In total, 12 studies were viable for meta-analysis and additional studies were reviewed to extract themes relating to learners’ perceptions of VM. The meta-analysis detected a small yet significant positive effect on learner performance (SMD=0.28, [CI=0.09, 0.47], p=0.003), indicating that learners experience marked knowledge gains when exposed to VM over OM. Variation among studies was evident as high heterogeneity was reported. An analysis of trends in learner perceptions noted that respondents favored VM over OM by a large margin. Conclusions: Despite many individual studies reporting non-significant findings when comparing VM to OM, the enhanced power afforded by meta-analysis revealed that the pedagogical approach of VM is modestly superior to OM and is preferred by learners