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Three dimensional motion analysis and vibration characteristics of dynamically scaled model of asymmetrically clustered launch vehicle
One of the most exciting plasma physics investigations of recent years has been connected with the understanding of a new strong turbulent plasma state excited by propagating electron beams. This new state is initiated on the linear level by parametric instabilities (OTS, modulational, etc.) and results in a very dynamic state composed of collective clusters of modes called solitons, cavitons, spikons, etc. Introduction of these concepts into the classic beam-plasma interaction problem has rendered quasi-linear and weak turbulence theories inapplicable over most of the interesting parameter range, and helped explain many paradoxes connected with the propagation of beams in the laboratory and space. Following a brief review of these nonlinear notions, the means by which their application to type III solar radiobursts has revolutionized understanding of their propagation, radioemission and scaling properties and has guided the in situ observations towards a more complete understanding are demonstrated. A particular burst (May 16, 1971) is analyzed in detail and compared with numerical predictions.
Recently protocols were introduced that enable the integration of synchronous traffic (voice or video) and asynchronous traffic (data) and extend the size of local area networks without loss in speed or capacity. One of these is DRAMA, a multiband protocol based on broadband technology. It provides dynamic allocation of bandwidth among clusters of nodes in the total network. A number of traffic placement policies for such networks are proposed and evaluated. Metrics used for performance evaluation include average network access delay, degree of fairness of access among the nodes, and network throughput. The feasibility of the DRAMA protocol is established through simulation studies. DRAMA provides effective integration of synchronous and asychronous traffic due to its ability to separate traffic types. Under the suggested traffic placement policies, the DRAMA protocol is shown to handle diverse loads, mixes of traffic types, and numbers of nodes, as well as modifications to the network structure and momentary traffic overloads.
A twi-dimensional kinematic model has been used to diagnose the thermodynamic, water vapor, and hydrometeor fields of the stratiform clouds associated with a mesoscale tropical cloud cluster. The model incorporates ice- and water-cloud microphysics, visible and infrared radiation, and convective adjustment. It is intended to determine the relative contributions of radiation, mycrophysics, and turbulence to diabatic heating, and the effects that radiation has on the water budget of the cluster in the absence of dynamical interactions. The model has been initialized with thermodynamic fields and wind velocities diagnosed from a GATE tropical squall line. It is found that radiation does not directly affect the water budget of the stratiform region, and any radiative effect on hydrometeors must involve interaction with dynamics.
The hierarchical triple system containing the millisecond pulsar PSR B1620-26 in M4 is the first star system ever detected in a globular cluster. Such systems should form in globular clusters as a result of dynamical interactions between binaries. We propose that the triple system containing PSR B1620-26 formed through an exchange interaction between a wide primordial binary and a pre-existing binary millisecond pulsar. This scenario would have the advantage of reconciling the approximately 10(exp 9) yr timing age of the pulsar with the much shorter lifetime of the triple system in the core of M4.
We present the results of N-body simulations of tidally limited star clusters with an initial population of 0%-20% binaries. We find that (1) if enough binaries are initially present, the binary fraction may fall to a minimum value, then increase at late times; (2) the cluster evaporation timescale is quite insensitive to the details of the initial binary distribution; (3) the cluster core radius stabilizes at a few percent of the half-mass radius when binaries are present, just as in the case of isolated clusters; and (4) there may be a marked difference between the spatial distribution of low-energy and high-energy binaries as the cluster evolves. Specifically, the spatial distribution of the lower energy systems is often substantially more extended than that of the more tightly bound pairs. At no time are our simulated clusters well described by simple dynamical models that neglect the close coupling between the binding energies and the center-of-mass energies of the binaries they contain.
We have studied colloidal aggregation in a model colloid plus polymer system with short-range attractive interactions. By varying the colloid concentration and the strength of the attraction, we explored regions where the equilibrium phase is expected to consist of colloidal crystallites in coexistance with colloidal gas (i.e. monomers). This occurs for moderate values of the potential depth, U approximately equal to 2-5 kT. Crystallization was not always observed. Rather, over an extended sub-region two new metastable phases appear, one fluid-like and one solid-like. These were examined in detail with light scattering and microscopy techniques. Both phases consist of a near uniform distribution of small irregular shaped clusters of colloidal particles. The dynamical and structural characteristics of the ergodic-nonergodic transition between the two phases share much in common with the colloidal hard sphere glass transition.
The bullfrog saccule, a sensor of gravity and substrate-borne vibration, is a model system for hair cell transduction. Saccular hair cells also increase in number throughout adult life and rapidly recover after hair cell damage, making this organ an ideal system for studying hair cell development, repair, and regeneration. We have used of hair cell and supporting cell immunocytochemical markers to identify damaged hair cells and hair cell precursors in organotypic cultures of the bullfrog saccule. We then used an innovative combination of confocal, electron, and time-lapse microscopy to study the fate of damaged hair cells and the origin of new hair cells after gentamicin ototoxicity in normal and mitotically blocked saccular cultures. These studies have shown that gentamicin ototoxicity produces both lethal and sublethal hair cell damage. They have also shown that hair cell recovery in this organ takes place by both the repair of sublethally damaged hair cells and by the replacement of lost hair cells by mitotic regeneration. In parallel studies, we have used biophysical and molecular biological techniques to study the differentiation and innervation of developing, repairing, and regenerating hair cells. More specifically, we have used RT-PCR to obtain the bullfrog homologues of L-type voltage- gated calcium (L-VGCC) and large-conductance Ca(2+)-activated potassium (BK) channel genes. We have then obtained probes for these genes and, using in situ hybridization, begun to examine their expression in the bullfrog saccule and amphibian papilla. We have also used fluorescent-labeled channel toxins and channel toxin derivatives to determine the time of appearance of L-type voltage-gated calcium (L-VGCC) and Ca(2+)-activated potassium (BK) channels and to study dynamic changes in the number, distribution, and co-localization of these proteins in developing, repairing, and regenerating hair cells. Using time-lapse microscopy, we are also studying the dynamic relationship between ion channel clustering and synaptic formation in hair cells and afferent neurons. In future studies, we will determine when hair cell precursors acquire electrical tuning, and, using whole-cell patch-clamp techniques, identify and characterize their L-VGCC and BK currents. We will also use biophysical techniques to determine the number of L-VGCC and BK channels and the size and gating kinetics of their underlying L-VGCC and BK conductances, correlating these variables with the amplitude and frequency of membrane oscillations produced by intracellular current steps. We expect these studies to determine how hair cells regulate ion channel expression to achieve specific physiological responses.
Radiative and turbulent surface exchanges of heat and moisture across the atmosphere-ocean interface are fundamental components of the Earth s energy and water balance. Characterizing the spatiotemporal variability of these exchanges of heat and moisture is critical to understanding the global water and energy cycle variations, quantifying atmosphere-ocean feedbacks, and improving model predictability. These fluxes are integral components to tropical ocean-atmosphere variability; they can drive ocean mixed layer variations and modify the atmospheric boundary layer properties including moist static stability, thereby influencing larger-scale tropical dynamics. Non-parametric cluster-based classification of atmospheric and ocean surface properties has shown an ability to identify coherent weather regimes, each typically associated with similar properties and processes. Using satellite-based observational radiative and turbulent energy flux products, this study investigates the relationship between these weather states and surface energy processes within the context of tropical climate variability. Investigations of surface energy variations accompanying intraseasonal and interannual tropical variability often use composite-based analyses of the mean quantities of interest. Here, a similar compositing technique is employed, but the focus is on the distribution of the heat and moisture fluxes within their weather regimes. Are the observed changes in surface energy components dominated by changes in the frequency of the weather regimes or through changes in the associated fluxes within those regimes? It is this question that the presented work intends to address. The distribution of the surface heat and moisture fluxes is evaluated for both normal and non-normal states. By examining both phases of the climatic oscillations, the symmetry of energy and water cycle responses are considered.
The Purpose of the Inflight Parachute Measurement Challenge is to solicit potential measurement solutions that can result in successful parachute loading assumption validation, along with validation of Fluid-Structure Interaction (FSI) simulations. A parachute system contains many components which see various loading conditions including tension and aerodynamic pressure forces. While measurements can be made in wind tunnels, significant limitations exist as compared to flight testing which include scaling, dynamic pressure time history, and cluster behavior. Traditional flight test instrumentation is difficult due the flexible nature of parachute components, packing requirements, and high forces and chaos during deployment. The Objectives of this challenge are to (1) describe the anatomy and behavior of parachute systems, (2) identify measurements of particular interest to the parachute design and analysis community, (3) identify additional uses of measurements such as FSI validation.
This grant provided for the demonstration of coupled controls, body dynamics, and fluids computations in a workstation cluster environment; and an investigation of the impact of peer-peer communication on flow solver performance and robustness. The findings of these investigations were documented in the conference articles.The attached publication, 'Towards Distributed Fluids/Controls Simulations', documents the solution and scaling of the coupled Navier-Stokes, Euler rigid-body dynamics, and state feedback control equations for a two-dimensional canard-wing. The poor scaling shown was due to serialized grid connectivity computation and Ethernet bandwidth limits. The scaling of a peer-to-peer communication flow code on an IBM SP-2 was also shown. The scaling of the code on the switched fabric-linked nodes was good, with a 2.4 percent loss due to communication of intergrid boundary point information. The code performance on 30 worker nodes was 1.7 (mu)s/point/iteration, or a factor of three over a Cray C-90 head. The attached paper, 'Nonlinear Fluid Computations in a Distributed Environment', documents the effect of several computational rate enhancing methods on convergence. For the cases shown, the highest throughput was achieved using boundary updates at each step, with the manager process performing communication tasks only. Constrained domain decomposition of the implicit fluid equations did not degrade the convergence rate or final solution. The scaling of a coupled body/fluid dynamics problem on an Ethernet-linked cluster was also shown.
The current dynamic state and rate of destruction for the system of globular clusters in the Galaxy are modeled. It is found that gravitational shocks due to the central bulge of the Galaxy are very efficient in destroying clusters on highly radial orbits. This effect, extrapolated at the present unweighted destruction rate over 10 to the 10th yr, can account for the observed difference between the velocity distribution of globular clusters and other tracers of the halo population.
A total of 663 galaxies with known redshifts in a 12 deg x 12 deg field centered on A2634, including 211 new measurements, are used to study in detail the structure of the region. In it we find six main galaxy concentrations: the nearby clusters A2634 and A2666, two groups in the vicinity of A2634, and two distant clusters at approximately 18,000 (A2622) and approximately 37,000 km/s seen in projection near the core of A2634. For A2634, the most richly sampled of those concentrations, we are able to apply strict cluster membership criteria. Two samples - one containing 200 galaxies within 2 deg from the cluster center and a second, magnitude-limited, of 118 galaxies within the central half degree - are used to examine the structure, kinematics, dynamics, and morphological segregation of the cluster. We show that early type galaxies appear to be a relaxed system, while the spiral population eschews the center of the cluster and exhibits both a multimodal velocity distribution and a much larger velocity dispersion that the ellipticals. We propose that the spiral galaxies of A2634 represent a dynamically young cluster population. For the galaxy component of A2634, we find no evidence of significant substructure in the central regions. We also conclude that the adoption of lenient membership criteria that ignore the dynamical complexity of A2634 are unlikely to be responsible for the conflicting results reported on the motion of this cluster with respect ot the CMB. The kinematical and dynamical analysis is extended to A2634's close companion, A2666, and the two distant background clusters.
The masses of galaxy clusters are dominated by dark matter, and a robust determination of their temperatures and masses has the potential of indicating how much dark matter exists on large scales in the universe, and the cosmological parameter Omega. X-ray observations of galaxy clusters provide a direct measure of both the gas mass in the intra-cluster medium, and also the total gravitating mass of the cluster. We used new and archival ASCA and ROSAT observations to measure these quantities for a sample of intermediate redshift clusters which have also been subject to intensive dynamical studies, in order to compare the mass estimates from different methods. We used data from 12 of the CNOC cluster sample at 0.18 less than z less than 0.55 for this study. A direct comparison of dynamical mass estimates from Carlberg, Yee & Ellingson (1997) yielded surprisingly good results. The X-ray/dynamical mass ratios have a mean of 0.96+/- 0.10, indicating that for this sample, both methods are probably yielding very robust mass estimates. Comparison with mass estimates from gravitational lensing studies from the literature showed a small systematic with weak lensing estimates, and large discrepancies with strong lensing estimates. This latter is not surprising, given that these measurements are made close to the central core, where optical and Xray estimates are less certain, and where substructure and the effects of individual galaxies will be more pronounced. These results are presented in Lewis, Ellingson, Morris \& Carlberg, 1998, submitted to the Astrophysical Journal.
A multiple one-body Monte Carlo code is used to investigate the evolution of galaxies in a steady cluster potential under the influence of dynamical friction, two-body relaxation, tidal stripping, and galaxy mergers. The basic assumptions, estimated time scales, method and computer program, and effects of uncertainties in galaxy encounter physics are addressed. Numerical experiments in which the mass initially carried by galaxies and the mass function are varied are reported. It is shown that the formation of a very massive cluster galaxy depends critically on the number of galaxies, the initial division of cluster material between galaxies and a smooth intracluster medium, the mass spectrum of the galaxies, and chance. By the end of all simulations, less than half of the mass in the central regions of the cluster is bound to galaxies. It appears possible to produce any of the Bautz-Morgan classes from very similar initial conditions.
The precise positions of the luminous X-ray sources in eight globular clusters have been measured with the Einstein X-Ray Observatory. When combined with similarly precise measurements of the dynamical centers and core radii of the globular clusters, the distribution of the X-ray source mass is determined to be in the range 0.9-1.9 solar mass. The X-ray source positions and the detailed optical studies indicate that (1) the sources are probably all of similar mass, (2) the gravitational potentials in these high-central density clusters are relatively smooth and isothermal, and (3) the X-ray sources are compact binaries and are probably formed by tidal capture.
This article reviews the prevailing paradigm for how galaxies and larger structures formed in the universe: gravitational instability. Basic observational facts are summarized to motivate the standard cosmological framework underlying most detailed investigations of structure formation. The observed univers approaches spatial uniformity on scales larger than about 10(exp 26) cm. On these scales gravitational dynamics is almost linear and therefore relatively easy to relate to observations of large-scale structure. On smaller scales cosmic structure is complicated not only by nonlinear gravitational clustering but also by nonlinear nongravitational gas dynamical processes. The complexity of these phenomena makes galaxy formation one of the grand challenge problems of the physical sciences. No fully satisfactory theory can presently account in detail for the observed cosmic structure. However, as this article summarizes, significant progress has been made during the last few years.
Sensing platforms must advance in scale and sophistication in order to support increasingly ambitious missions across Earth and space science; intelligence, surveillance, and reconnaissance (ISR); and planetary exploration. Distributed, persistent observation platforms have the potential to play a pivotal role in next generation missions through improved area coverage, enhanced situational awareness, and faster identification of trends and changes. The Multi-Agent Clusters for Persistent Observations from Space (MACPOS) project at NASA Langley Research Center is developing key technologies for the autonomous, heterogeneous formations that will comprise such platforms. Research thrusts include dynamic formation negotiation for self-assembling clusters of agents, distributed motion planning, and coordinated trajectory execution. Adaptive leader-follower formation negotiation allows agents to cluster and break off as necessary to adapt to both nominal and new mission objectives. Coordinated motion planning and execution maintain the formation while ensuring safe separation distances among agents and obstacles in the environment. These capabilities align MACPOS with NASA’s initiative for space and surface in-situ assembly through fundamental technology development for autonomous multi-agent systems. This paper presents an overview and early progress for the MACPOS project. We describe the system architecture for both individual agents and the overall fleet. Design considerations are given for the planning, control, and metrology subsystems. Finally, we discuss planned project milestones and the expected course of development.