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In this paper, a brief review is given of NASA's outer planet missions as performed with chemical propulsion systems. The Kuiper Express is discussed as an illustration of the integrated approach that should be used in mission and spacecraft design to maximize science return.
In this paper, analytic expressions are obtained for the design derivatives of eigenvalues and eigenfunctions of self-adjoint linear distributed parameter systems. Explicit treatment of boundary conditions is avoided by casting the eigenvalue equation into integral form. Results are expressed in terms of the linear operators defining the eigenvalue problem, and are therefore quite general. Sufficiency conditions appropriate to structural optimization of eigenvalues are obtained.
This paper presents a generalized and efficient method for quasi-static analysis of mooring systems, including complex scenarios such as when shared mooring lines interconnect multiple floating wind or wave energy devices. While quasi-static mooring models are well established, most published formulations are focused on specific applications, and no publicly available implementations provide efficient handling of large mooring system networks. The present formulation addresses these gaps by: (1) formulating solutions for edge cases not typically supported by quasi-static models; (2) creating a fully generalized model structure such that any combination of mooring lines, point masses, and floating bodies can be assembled; and (3) deriving analytic expressions for the system Jacobians (stiffness matrices) so that systems with many degrees of freedom can be solved efficiently. These techniques form the theory basis of MoorPy, an open-source mooring analysis library. The model is demonstrated on nine scenarios of increasing complexity with features of interest for offshore renewable energy applications. When compared with steady-state results from a lumped-mass dynamic model, the results show that the quasi-static formulation accurately calculates profiles and tensions and that its analytic approach provides more efficient and reliable computation of system stiffness matrices than finite-differencing methods. These results verify the accuracy of the MoorPy model.
Mathematical expressions for slew maneuver dynamics are presented. The total kinetic energy expression of the system is given as T = T(0) + T(1) + T(2), where T(0), T(1), and T(2) refer to the kinetic energies of the shuttle, the flexible beam, and the tip mass (the reflector), respectively. The specific equations for each of these are defined and integrated into the total energy expression. Using the chain rule in the Lagrange equations and an expression allowing the transformation of the orbiter angular velocity from the inertial frame to the body-fixed frame, the rotational equations are obtained. Finally, the vibration equations for the beam are derived, again using the Lagrange equations.
Assembly of International Space Station (ISS) is expected to be complete in 2010, with operations planned to continue through at least 2016. As we move nearer to assembly complete, replanning activities by NASA and ISS International Partners have been completed and the final complement of research facilities on ISS is becoming more certain. This paper will review pans for facilities in the US On-orbit Segment of ISS, including contributions from International Partners, to provide a vision of the research capabilities that will be available starting in 2010. At present, in addition to research capabilities in the Russian segment, the United States Destiny research module houses nine research facilities or racks. These facilities include five multi-purpose EXPRESS racks, two Human Research Facility (HRF) racks, the Microgravity Science Glovebox (MSG), and the Minus Eighty-degree Laboratory Freezer for ISS (MELFI), enabling a wide range of exploration-related applied as well as basic research. In the coming years, additional racks will be launched to augment this robust capability: Combustion Integrated Rack (CIR), Fluids Integrated Rack (FIR), Window Observation Rack Facility (WORF), Microgravity Science Research Rack (MSRR), Muscle Atrophy Research Exercise System (MARES), additional EXPRESS racks and possibly a second MELFI. In addition, EXPRESS Logistics Carriers (ELC) will provide attach points for external payloads. The European Space Agency s Columbus module will contain five research racks and provide four external attach sites. The research racks are Biolab, European Physiology Module (EPM), Fluid Science Lab (FSL), European Drawer System (EDS) and European Transport Carrier (ETC). The Japanese Kibo elements will initially support three research racks, Ryutai for fluid science, Saibo for cell science, and Kobairo for materials research, as well as 10 attachment sites for external payloads. As we look ahead to assembly complete, these new facilities represent a threefold increase from the current research laboratory infrastructure on ISS. In addition, the increase in resident crew size will increase from three to six in 2009, will provide the long-term capacity for completing research on board ISS. Transportation to and from ISS for crew and cargo will be provided by a fleet of vehicles from the United States, Russia, ESA and Japan, including accommodations for thermally-conditioned cargo. The completed ISS will have robust research accommodations to support the multidisciplinary research objective of scientists worldwide.
The Fisher Information Matrix provides the nucleus of a design procedure for obtaining parameter-insensitive feedback gains in Linear-Quadratic-Gaussian problems. The procedure minimizes a sum of performance and closed-loop sensitivity costs, the latter being related to the information content of the system response. Analytical expressions for the appended cost functional and its gradient with respect to the feedback gains are derived. These derivatives serve as the basis of a computationally efficient iterative algorithm that finds the optimal gains. Application of the technique is made to determine low sensitivity feedback gains for a C-5A wing loading alleviation system that has 15 states and three uncertain parameters.
Although expression of the small heat shock protein family member Hsp25 has been previously observed in the central nervous system (CNS), both constitutively and upon induction, its function in the CNS remains far from clear. In the present study we have characterized the spatial pattern of expression of Hsp25 in the normal adult mouse brain as well as the changes in expression patterns induced by subjecting mice to experimental hyperthermia or hypoxia. Immunohistochemical analysis revealed a surprisingly restricted pattern of constitutive expression of Hsp25 in the brain, limited to the facial, trigeminal, ambiguus, hypoglossal and vagal motor nuclei of the brainstem. After hyperthermia or hypoxia treatment, significant increases in the levels of Hsp25 were observed in these same areas and also in fibers of the facial and trigeminal nerve tracts. Immunoblot analysis of protein lysates from brainstem also showed the same pattern of induction of Hsp25. Surprisingly, no other area in the brain showed expression of Hsp25, in either control or stressed animals. The highly restricted expression of Hsp25 implies that this protein may have a specific physiological role in the orofacial motor nuclei, which govern precise coordination between muscles of mastication and the pharynx, larynx, and face. Its rapid induction after stress further suggests that Hsp25 may serve as a specific molecular chaperone in the lower cholinergic motor neurons and along their fibers under conditions of stress or injury. Copyright 1998 Elsevier Science B.V.
We propose a framework to learn the time-dependent Hartree–Fock (TDHF) inter-electronic potential of a molecule from its electron density dynamics. Although the entire TDHF Hamiltonian, including the inter-electronic potential, can be computed from first principles, we use this problem as a testbed to develop strategies that can be applied to learn a priori unknown terms that arise in other methods/approaches to quantum dynamics, e.g., emerging problems such as learning exchange–correlation potentials for time-dependent density functional theory. We develop, train, and test three models of the TDHF inter-electronic potential, each parameterized by a four-index tensor of size up to 60 × 60 × 60 × 60. Two of the models preserve Hermitian symmetry, while one model preserves an eight-fold permutation symmetry that implies Hermitian symmetry. Across seven different molecular systems, we find that accounting for the deeper eight-fold symmetry leads to the best-performing model across three metrics: training efficiency, test set predictive power, and direct comparison of true and learned inter-electronic potentials. All three models, when trained on ensembles of field-free trajectories, generate accurate electron dynamics predictions even in a field-on regime that lies outside the training set. To enable our models to scale to large molecular systems, we derive expressions for Jacobian-vector products that enable iterative, matrix-free training.
The critial luminosity at which the outward force of radiation balances the inward force of gravity plays an important role in many astrophysical systems. We present expressions for the radiation force on particles with arbitrary cross sections and analyze the radiation field produced by radiating matter, such as a disk, ring, boundary layer, or stellar surface, that rotates slowly around a slowly rotating gravitating mass. We then use these results to investigate the critical radiation flux and, where possible, the critical luminosity of such a system in genral relativity. We demonstrate that if the radiation source is axisymmetric and emission is back-front symmetric with repect to the local direction of motion of the radiating matter, as seen in the comoving frame, then the radial component of the radiation flux and the diagonal components of the radiation stress-energy tensor outside the source are the same, to first order in the rotation rates, as they would be if the radiation source and gravitating mass were not rotating. We argue that the critical radiation flux for matter at rest in the locally nonrotating frame is often satisfactory as an astrophysical benchmark flux and show that if this benchmark is adopted, many of the complications potentially introduced by rotation of the radiation source and the gravitating mass are avoided. We show that if the radiation field in the absence of rotation would be spherically symmetric and the opacity is independent of frequency and direction, one can define a critical luminosity for the system that is independent of frequency and direction, one can define a critical luminosity for the system that is independent of the spectrum and angular size of the radiation source and is unaffected by rotation of the source and mass and orbital motion of the matter, to first order. Finally, we analyze the conditions under which the maximum possible luminosity of a star or black hole powered by steady spherically symmetric radial accretion is the same in general relativity as in the Newtonian limit.
The Web-based Weather Expert System (WES) is a critical module of the Virtual Test Bed development to support 'go/no go' decisions for Space Shuttle operations in the Intelligent Launch and Range Operations program of NASA. The weather rules characterize certain aspects of the environment related to the launching or landing site, the time of the day or night, the pad or runway conditions, the mission durations, the runway equipment and landing type. Expert system rules are derived from weather contingency rules, which were developed over years by NASA. Backward chaining, a goal-directed inference method is adopted, because a particular consequence or goal clause is evaluated first, and then chained backward through the rules. Once a rule is satisfied or true, then that particular rule is fired and the decision is expressed. The expert system is continuously verifying the rules against the past one-hour weather conditions and the decisions are made. The normal procedure of operations requires a formal pre-launch weather briefing held on Launch minus 1 day, which is a specific weather briefing for all areas of Space Shuttle launch operations. In this paper, the Web-based Weather Expert System of the Intelligent Launch and range Operations program is presented.
In this paper we have reviewed the basics of tensor analysis in an attempt to clarify some misconceptions regarding contravariant and covariant vector components as used in fluid dynamics. We have indicated that contravariant components are components of a given vector expressed as a unique combination of the covariant base vector system and, vice versa, that the covariant components are components of a vector expressed with the contravariant base vector system. Mathematically, expressing a vector with a combination of base vector is a decomposition process for a specific base vector system. Hence, the contravariant velocity components are decomposed components of velocity vector along the directions of coordinate lines, with respect to the covariant base vector system. However, the contravariant (and covariant) components are not physical quantities. Their magnitudes and dimensions are controlled by their corresponding covariant (and contravariant) base vectors.
The determination of ignition or thermal explosion in an oxidizing porous body of material, as described by a dimensionless reaction-diffusion equation of the form .tu = .2u + .e-1/u over the bounded region O, is critically reexamined from a modern perspective using numerical methodologies. First, the classic stationary model is revisited to establish the proper reference frame for the steady-state solution space, and it is demonstrated how the resulting nonlinear two-point boundary value problem can be reexpressed as an initial value problem for a system of first-order differential equations, which may be readily solved using standard algorithms. Then, the numerical procedure is implemented and thoroughly validated against previous computational results based on sophisticated path-following techniques. Next, the transient nonstationary model is attacked, and the full nonlinear form of the reaction-diffusion equation, including a generalized convective boundary condition, is discretized and expressed as a system of linear algebraic equations. The numerical methodology is implemented as a computer algorithm, and validation computations are carried out as a prelude to a broad-ranging evaluation of the assembly problem and identification of the watershed critical initial temperature conditions for thermal ignition. This numerical methodology is then used as the basis for studying the relationship between the shape of the critical initial temperature distribution and the corresponding spatial moments of its energy content integral and an attempt to forge a fundamental conjecture governing this relation. Finally, the effects of dynamic boundary conditions on the classic storage problem are investigated and the groundwork is laid for the development of an approximate solution methodology based on adaptation of the standard stationary model.
We show that the tightly regulated tetracycline-sensitive Top10 promoter system (Weinmann et al. Plant J. 1994, 5, 559-569) is functional in Arabidopsis thaliana. A pure breeding A. thaliana line (JL-tTA/8) was generated which expressed a chimeric fusion of the tetracycline repressor and the activation domain of Herpes simplex virus (tTA), from a single transgenic locus. Plants from this line were crossed with transgenics carrying the ER-targeted green fluorescent protein coding sequence (mGFP5) under control of the Top10 promoter sequence. Progeny from this cross displayed ER-targeted GFP fluorescence throughout the plant, indicating that the tTA-Top10 promoter interaction was functional in A. thaliana. GFP expression was repressed by 100 ng ml-1 tetracycline, an order of magnitude lower than the concentration used previously to repress expression in Nicotiana tabacum. Moreover, the level of GFP expression was controlled by varying the concentration of tetracycline in the medium, allowing a titred regulation of transgenic activity that was previously unavailable in A. thaliana. The kinetics of GFP activity were determined following de-repression of the Top10:mGFP5 transgene, with a visible ER-targeted GFP signal appearing from 24 to 48 h after de-repression.
To meet the demands of the Beam Energy Scan phase-II (BES-II) program, the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) developed a dual real-time framework consisting of a High Level Trigger (HLT) and an Express Data Production system (xProduction). The HLT operates online within the Data Acquisition (DAQ) chain on a dedicated multi-core CPU cluster with the option to offload compute-intensive kernels to Xeon Phi coprocessors. It uses parallelized algorithms, such as the Cellular Automaton (CA) Track Finder, to perform rapid tracking, vertexing, and event filtering. This allows it to select events of interest in real time and provide immediate feedback on detector and beam conditions. In contrast, the xProduction workflow runs concurrently and independently of the DAQ loop. It applies near offline-quality calibration and reconstruction within hours of data collection. The xProduction input is the express data stream, whose content can be enriched by HLT trigger/priority selections under DAQ/HLT resource constraints, and it uses the STAR calibration/conditions framework, incorporating online calibration/QA information when available. This enables early preliminary physics analysis, including the reconstruction of rare signals, such as hyperons and hypernuclei. It also provides collaboration-wide access to analysis-ready datasets. Together, the HLT and xProduction systems form a complementary architecture: the HLT performs online event selection while the xProduction chain delivers high-quality results within a short amount of time. This integrated framework has enabled the prompt reconstruction of the $^5_Λ$ He hypernucleus with high statistical significance and the efficient processing of hundreds of millions of heavy-ion collision events. In conclusion, its demonstrated scalability and robustness establish a model for future high-luminosity experiments requiring both online event filtering and rapid access to analysis-quality data.
The Spacecraft Control and Operations System 2 (SCOSII) is the new generation of Mission Control Systems (MCS) to be used at ESOC. The system is generic because it offers a collection of standard functions configured through a database upon which a dedicated MCS is established for a given mission. An integral component of SCOSII is the support of a dedicated Operations Language (OL). The spacecraft operation engineers edit, test, validate, and install OL scripts as part of the configuration of the system with, e.g., expressions for computing derived parameters and procedures for performing flight operations, all without involvement of software support engineers. A layered approach has been adopted for the implementation centered around the explicit representation of a data model. The data model is object-oriented defining the structure of the objects in terms of attributes (data) and services (functions) which can be accessed by the OL. SCOSII supports the creation of a mission model. System elements as, e.g., a gyro are explicit, as are the attributes which described them and the services they provide. The data model driven approach makes it possible to take immediate advantage of this higher-level of abstraction, without requiring expansion of the language. This article describes the background and context leading to the OL, concepts, language facilities, implementation, status and conclusions found so far.
The deleterious effects that the Manchester (or Bi-phi) data asymmetry has on the performance of phase-modulated residual carrier communication systems are analyzed. Expressions for the power spectral density of an asymmetric Manchester data stream, the interference-to-carrier signal power ratio (I/C), and the error probability performance are derived. Since data asymmetry can cause undesired spectral components at the carrier frequency, the I/C ratio is given as a function of both the data asymmetry and the telemetry modulation index. Also presented are the data asymmetry and asymmetry-induced carrier tracking loop and the system bit-error rate to various parameters of the models.
Several muscles in the body exist mainly to work against gravity. Whether gravity is important in the development of these muscles is not known. By examining the basic proteins that compose muscle, questions about the role of gravity in muscle development can be answered. Myosin heavy chains (MHCs) are a family of proteins critically important for muscle contraction. Several types of MHCs exist (e.g., neonatal, slow, fast), and each type is produced by a particular gene. Neonatal MHCs are produced early in life. Slow MHCs are important in antigravity muscles, and fast MHCs are found in fast-twitch power muscles. The gene that is turned on or expressed will determine which MHC is produced. Early in development, antigravity skeletal muscles (muscles that work against gravity) normally produce a combination of the neonatal/embryonic MHCs. The expression of these primitive MHCs is repressed early in development; and the adult slow and fast MHC genes become fully expressed. We tested the hypothesis that weightbearing activity is critical for inducing the normal expression of the slow MHC gene typically expressed in adult antigravity muscles. Also, we hypothesized that thyroid hormone, but not opposition to gravity, is necessary for expressing the adult fast IIb MHC gene essential for high-intensity muscle performance. Groups of normal thyroid and thyroid-deficient neonatal rats were studied after their return from the 16-day Neurolab mission and compared to matched controls. The results suggest: (1) Weightlessness impaired body and limb skeletal muscle growth in both normal and thyroid-deficient animals. Antigravity muscles were impaired more than those used primarily for locomotion andor nonweightbearing activity. (2) Systemic and muscle expression of insulin-like growth factor-I (IGF-I), an important body and tissue growth factor, was depressed in flight animals. (3) Normal slow, type I MHC gene expression was markedly repressed in the normal thyroid flight group. (4) Fast IIb MHC gene expression was enhanced in fast-twitch muscles of normal thyroid animals exposed to spaceflight; however, thyroid deficiency markedly repressed expression of this gene independently of spaceflight. In summary, the absence of gravity, when imposed at critical stages of development, impaired body and skeletal muscle growth, as well as expression of the MHC gene family of motor proteins. This suggests that normal weightbearing activity is essential for establishing body and muscle growth in neonatal animals, and for expressing the motor gene essential for supporting antigravity functions.
A reference architecture is defined for an object-oriented implementation of domains, arrays, and distributions written in the programming language Chapel. This technology primarily addresses domains that contain arrays that have regular index sets with the low-level implementation details being beyond the scope of this discussion. What is defined is a complete set of object-oriented operators that allows one to perform data distributions for domain arrays involving regular arithmetic index sets. What is unique is that these operators allow for the arbitrary regions of the arrays to be fragmented and distributed across multiple processors with a single point of access giving the programmer the illusion that all the elements are collocated on a single processor. Today's massively parallel High Productivity Computing Systems (HPCS) are characterized by a modular structure, with a large number of processing and memory units connected by a high-speed network. Locality of access as well as load balancing are primary concerns in these systems that are typically used for high-performance scientific computation. Data distributions address these issues by providing a range of methods for spreading large data sets across the components of a system. Over the past two decades, many languages, systems, tools, and libraries have been developed for the support of distributions. Since the performance of data parallel applications is directly influenced by the distribution strategy, users often resort to low-level programming models that allow fine-tuning of the distribution aspects affecting performance, but, at the same time, are tedious and error-prone. This technology presents a reusable design of a data-distribution framework for data parallel high-performance applications. Distributions are a means to express locality in systems composed of large numbers of processor and memory components connected by a network. Since distributions have a great effect on the performance of applications, it is important that the distribution strategy is flexible, so its behavior can change depending on the needs of the application. At the same time, high productivity concerns require that the user be shielded from error-prone, tedious details such as communication and synchronization.