bluuebunny/crossref_metadata_2025 huggingface dataset:
Labour Mobility in Construction: European Implications of the Laval un Partneri Dispute with Swedish Labour
Authors: Woolfson Charles , Sommers Jeff
Published: March 2006

The accession to the European Union of new member states from central and eastern Europe, with weak trade union movements, poorly developed social dialogue and inferior working conditions, has been viewed as a threat to regulated labour standards in the EU-15. This article examines a high-profile labour dispute arising from the conditions of Latvian construction contract labour in Sweden. The dispute exposes weaknesses in the protective floor of minimum standards offered by the posted workers Directive. It also goes to the core of the debate about the preservation of a ‘European social model’ and the proposed Services Directive.
Observer-based Control of Variable Dynamic Structures
Authors: Terro Mohamad J. , Boukas El-Kebir , Hassan Mohamad F.
Published: March 2006

This paper deals with the control of structures with variable dynamic properties. The variability in the dynamic properties emanates from changes during the lifetime of the structures due to factors such as aging or possible modification. This variability may cause an inappropriate response if we still use the controller designed for the original structure. The control that eliminates the effects of such variability is of interest. Modeling the variable changes as norm-bounded uncertainties, an observer-based controller is designed to robustly stabilize the structure. The conditions that determine the controller are in the linear matrix inequality (LMI) setting, making the results tractable even for high dimension systems. A numerical example is provided to show the effectiveness of the developed approach.
Identi cation of the Dynamic Models of Machine Tool Supporting Systems. Part I: An Algorithm of the Method
Authors: Berczyński Stefan , Gutowski Pawe
Published: March 2006

In this paper we present an original algorithm for the identification of dynamic models of machine tool supporting systems on the basis of limited information about an object contained in the experimentally determined frequency response characteristics obtained for a given excitation. We have described the way of creating models that are later to be identified. The models have been built in the convention of the rigid finite element method, which is complemented by the added option that allows us to model slideway joints. Any stiffness and damping coefficients of any spring–damping elements of a given model can be estimated by means of the elaborated method. In order to select decision variables, we have used a sensitivity analysis of the frequency response characteristics on changes in the values of a model's parameters. The Fisher's model of uncertainty has been adopted for the algorithm. The minimization of the identification criterion has been carried out using gradient methods. In order to assess the uniqueness of the obtained solutions the Cramer– Rao information inequality has been used. On the basis of the presented algorithm a computer program IDENT has been elaborated. It enables an effective estimation of parameters of machine tool supporting systems. The numerical tests have confirmed both the reliability of the algorithm and the high effectiveness of the IDENT program. In this paper we present both the results and the commentary of one such test.
Proteasome inhibitors induce a terminal unfolded protein response in multiple myeloma cells
Authors: Obeng Esther A. , Carlson Louise M. , Gutman Delia M. , Harrington William J. , Lee Kelvin P. , Boise Lawrence H.
Published: March 2006

Multiple myeloma (MM) is an incurable plasma cell malignancy. The 26S proteasome inhibitor, bortezomib, selectively induces apoptosis in MM cells; however, the nature of its selectivity remains unknown. Here we demonstrate that 5 different MM cell lines display similar patterns of sensitivity to 3 proteasome inhibitors (PIs) but respond differently to specific NF-κB inhibition. We further show that PIs initiate the unfolded protein response (UPR), a signaling pathway activated by the accumulation of misfolded proteins within the endoplasmic reticulum (ER). Consistent with reports that prosurvival/physiologic UPR components are required for B-cell differentiation into antibody-secreting cells, we found that MM cells inherently expressed the ER chaperones GRP78/Bip and GRP94/gp96. However, bortezomib rapidly induced components of the proapoptotic/terminal UPR, including PERK, the ER stress–specific eIF-2α kinase; ATF4, an ER stress–induced transcription factor; and its proapoptotic target, CHOP/GADD153. Consistent with our hypothesis that PIs induce the accumulation of misfolded ER-processed proteins, we found that the amount of immunoglobulin subunits retained within MM cells correlated with their sensitivity to PIs. These findings suggest that MM cells have a lower threshold for PI-induced UPR induction and ER stress–induced apoptosis because they constitutively express ER stress survival factors to function as secretory cells.
The role of KAHRP domains in knob formation and cytoadherence of P falciparum-infected human erythrocytes
Authors: Rug Melanie , Prescott Stuart W. , Fernandez Kate M. , Cooke Brian M. , Cowman Alan F.
Published: March 2006

Surface protrusions of Plasmodium falciparum-infected erythrocytes, called knobs, display focal aggregates of P falciparum erythrocyte membrane protein 1 (PfEMP1), the adhesion ligand binding endothelial-cell receptors. The resulting sequestration of infected erythrocytes in tissues represents an important factor in the course of fatalities in patients with malaria. The main component of knobs is the knob-associated histidine-rich protein (KAHRP), and it contributes to altered mechanical properties of parasite-infected erythrocytes. The role of KAHRP domains in these processes is still elusive. We generated stable transgenic P falciparum-infected erythrocytes expressing mutant versions of KAHRP. Using atomic force and electron microscopy we show that the C-terminal repeat region is critical for the formation of functional knobs. Elasticity of the membrane differs dramatically between cells with different KAHRP mutations. We propose that the 5′ repeat region of KAHRP is important in cross-linking to the host-cell cytoskeleton and this is required for knob protrusion and efficient adhesion under physiologic flow conditions. (Blood. 2006;108:370-378)
Ribosomes and marrow failure: coincidental association or molecular paradigm?
Authors: Liu Johnson M. , Ellis Steven R.
Published: March 2006

Gene products mutated in the inherited bone marrow failure syndromes dyskeratosis congenita (DC), cartilage-hair hypoplasia (CHH), Diamond-Blackfan anemia (DBA), and Shwachman-Diamond syndrome (SDS) are all predicted to be involved in different aspects of ribosome synthesis. At this moment, however, it is unclear whether this link indicates a causal relationship. Although defective ribosome synthesis may contribute to each of these bone marrow failure syndromes (and perhaps others), precisely which feature of each disease is a consequence of failure to produce adequate amounts of ribosomes is obscured by the tendency of each gene product to have extraribosomal functions. Delineation of the precise role of each gene product in ribosomal biogenesis and in hematopoietic development may have both therapeutic and prognostic importance and perhaps even direct the search for new bone marrow failure genes.
Notch1-dependent lymphomagenesis is assisted by but does not essentially require pre-TCR signaling
Authors: Campese Antonio F. , Garbe Annette I. , Zhang Fangrong , Grassi Fabio , Screpanti Isabella , von Boehmer Harald
Published: March 2006

Overexpression of intracellular Notch plays an important role in the generation of human acute lymphoblastic T cell leukemia (T-ALL). In mouse models, it was shown that Notch-dependent T-ALL required pre-TCR signaling. Here we show that pre-TCR signaling is required to condition mice for Notch-dependent transformation but that it is not required to sustain malignant growth of T-ALL. In contrast to previous studies, we found that disease development does not require pre-TCR but that it can be accelerated in Rag2-/- mice by transient mimicking of pre-TCR signals. (Blood. 2006;108:305-310)
Understanding of Genetic Information in Higher Secondary Students in Northeast India and the Implications for Genetics Education
Authors: Chattopadhyay Ansuman
Published: March 2006

Since the work of Watson and Crick in the mid-1950s, the science of genetics has become increasingly molecular. The development of recombinant DNA technologies by the agricultural and pharmaceutical industries led to the introduction of genetically modified organisms (GMOs). By the end of the twentieth century, reports of animal cloning and recent completion of the Human Genome Project (HGP), as well techniques developed for DNA fingerprinting, gene therapy and others, raised important ethical and social issues about the applications of such technologies. For citizens to understand these issues, appropriate genetics education is needed in schools. A good foundation in genetics also requires knowledge and understanding of topics such as structure and function of cells, cell division, and reproduction. Studies at the international level report poor understanding by students of genetics and genetic technologies, with widespread misconceptions at various levels. Similar studies were nearly absent in India. In this study, I examine Indian higher secondary students' understanding of genetic information related to cells and transmission of genetic information during reproduction. Although preliminary in nature, the results provide cause for concern over the status of genetics education in India. The nature of students' conceptual understandings and possible reasons for the observed lack of understanding are discussed.
Survey of Undergraduate Research Experiences (SURE): First Findings
Authors: Lopatto David
Published: March 2006

In this study, I examined the hypothesis that undergraduate research enhances the educational experience of science undergraduates, attracts and retains talented students to careers in science, and acts as a pathway for minority students into science careers. Undergraduates from 41 institutions participated in an online survey on the benefits of undergraduate research experiences. Participants indicated gains on 20 potential benefits and reported on career plans. Over 83% of 1,135 participants began or continued to plan for postgraduate education in the sciences. A group of 51 students who discontinued their plans for postgraduate science education reported significantly lower gains than continuing students. Women and men reported similar levels of benefits and similar patterns of career plans. Ethnic groups did not significantly differ in reported levels of benefits or plans to continue with postgraduate education.
The Use of a Knowledge Survey as an Indicator of Student Learning in an Introductory Biology Course
Authors: Bowers Nancy , Brandon Maureen , Hill Cynthia D.
Published: March 2006

A knowledge survey (KS) is a series of content-based questions sequenced in order of presentation during a course. Students do not answer the questions; rather, they rank their confidence in their ability to answer each question. A 304-question KS was designed and implemented for a multisection, multi-instructor introductory biology course to determine whether this tool could be used to assess student learning. The KS was administered during the first 2 wk and the last 2 wk of the semester online via WebCT. Results were scored using one point for each “not confident” response (level 1), two points for each “possibly confident” response (level 2), and three points for each “confident” response (level 3). We found that scores increased significantly between the pre- and post-KS, indicating that student confidence in their knowledge of the course material increased over the semester. However, the correlation between student confidence and final grades was negligible or low, and chi-square tests show that KS scores and matched exam questions were not significantly related. We conclude that under the conditions implemented in our study, the KS does not reliably measure student learning as measured by final grades or exam questions.
Information Literacy in Biology Education: An Example from an Advanced Cell Biology Course
Authors: Porter John R.
Published: March 2006

Information literacy skills are critically important for the undergraduate biology student. The ability to find, understand, evaluate, and use information, whether from the scientific literature or from Web resources, is essential for a good understanding of a topic and for the conduct of research. A project in which students receive information literacy instruction and then proceed to select, update, and write about a current research topic in an upper-level cell biology course is described. Students research the chosen topic using paper and electronic resources, generate a list of relevant articles, prepare abstracts based on papers read, and, finally, prepare a“ state-of-the-art” paper on the topic. This approach, which extends over most of one semester, has resulted in a number of well-researched and well-written papers that incorporate some of the latest research in cell biology. The steps in this project have also led to students who are prepared to address future projects on new and complex topics. The project is part of an undergraduate course in cell biology, but parts of the assignments can be modified to fit a variety of subject areas and levels.
A continuous 5300-yr Holocene cryptotephrostratigraphic record from northern New Zealand and implications for tephrochronology and volcanic hazard assessment
Authors: Gehrels Maria J. , Lowe David J. , Hazell Zoë J. , Newnham Rewi M.
Published: March 2006

A continuous ∼5280 calendar (cal.) yr long cryptotephrostratigraphic record of a peat core from northern New Zealand demonstrates that cryptotephra studies can enhance conventional tephra records by extending the known distribution of ash fall and enabling re-assessment of volcanic hazards. A systematic sampling strategy was used to locate peaks in glass-shard concentrations and to determine loci of individual geochemical populations, and a palynological method involving spiking samples with Lycopodium spores was adapted to facilitate accurate counting of glass-shard concentrations. Using glass shard major element compositions, and a core chronology based on eight AMS 14C ages and two visible macroscopic tephra layers, Taupo Tephra (Unit Y) (1688-1748 cal. BP) and Tuhua Tephra (6800-7230 cal. BP) (2cr-age ranges), four cryptotephras were correlated with known eruptions: Whakaipo (Unit V) (2743-2782 cal. BP), Stent (Unit Q) (4240-4510 cal. BP), and Unit K (4970-5290 cal. BP), erupted from Taupo Volcanic Centre, and Whakatane Tephra (5470-5600 cal. BP) erupted from Okataina Volcanic Centre. Mixed glass populations were found in the core, most likely an artefact of post-depositional remobilization of shards vertically (both up and down) in the peat or on its surface by wind, or a result of closely spaced eruption events, or a combination of these. A secondary glass population identified within the macroscopic Taupo Tephra was tentatively attributed to either an earlier phase within that eruption or to mixing with a slightly older Taupo-derived eruptive or (less likely) a currently unknown Okataina-derived eruptive. These results indicate that, in the absence of continuous cryptotephrostratigraphic analysis, a peak in shard concentrations may not in itself be indicative of the ‘true’ stratigraphic (ie, isochronous) level of a tephra layer. For cryptotephra studies of peat cores, we recommend (1) using a detailed sampling strategy for the analysis of distal tephra-derived glass to detect and account for any mixed populations and possible vertical spread of glass shards through the peat, and (2) analysing more shards from larger samples to help ‘capture’ sparsely represented cryptic andesitic tephra deposits.
The effect of climate variability on pollen productivity, AD 1975-2000, recorded in a Sphagnum peat hummock
Authors: Sjögren Per , van Leeuwen Jacqueline F.N. , van der Knaap W. O. , van der Borg Klaas
Published: March 2006

Pollen accumulation rates and pollen percentages from a Sphagnum peat hummock in the Jura Mountains were used to determine past pollen deposition. Post-bomb calibrated radiocarbon dates allowed estimations of annual variability in pollen productivity AD 1975-2000. Percentages of abundant taxa were modified (downweighted) to reduce the influence of plant cover, mean pollen productivity, and interdependence of the variables. Significant correlations with seasonal climatic parameters (tested with simple linear regression) were found both for pollen accumulation rates and for modified pollen percentages. Winter temperature is an important factor for pollen productivity of several tree species. The climatic effect on the modified pollen assemblage is best explained by a wet/warm to cold/dry gradient, but seasonal influence is considerable (ordination by PCA, RDA). Modified pollen percentages showed similarities in annual fluctuations between sites in the Jura Mountains, the Western Alps and the Eastern Alps.
Cupressus dupreziana: a dendroclimatic record for the middle-late Holocene in the central Sahara
Authors: Cremaschi Mauro , Pelfini Manuela , Santilli Maurizio
Published: March 2006

Dendroclimatology of Cupressus dupreziana, the Tassili cypress, has been attempted on samples obtained from the door beams of the old cities of Ghat and Barkat located at the foot of the Tassili, where the cypress still lives. The tree rings of 20 samples were measured and dated by 24 AMS 14C dates. A mean ring-width chronology has thus been obtained, spanning, though discontinuously, 5220 to 100 14C BP (5990-65 cal. BP). As the tree-ring width in dry lands depends mainly on water availability, the mean ring-width chronology represents a detailed record of changes in rainfall on a decade scale for the middle and late Holocene of the central Sahara. It indicates main drought spells at 5200-5000 14C BP (5900-5760 cal. BP) and at 4350 BP (5120 cal. BP), followed by phases of enhanced precipitation and by the onset of extreme arid conditions at 1550 14C BP (1500 cal. BP).
Hypomania in clinical practice
Authors: Smith Daniel J. , Ghaemi S. Nassir
Published: March 2006

Recent work suggests that a broad clinical spectrum of bipolar disorder is more common than previously thought and that the disorder may affect up to 5% of the population. The correct definition and diagnosis of hypomania is central to the identification of bipolar disorder. In this review we focus on recent diagnostic and clinical advances relating to bipolar disorder, with particular reference to hypomanic states. We also highlight some of the controversies in this field and discuss ways in which clinicians might improve their detection of bipolar disorders.
Assessing professional and clinical competence: the way forward†
Authors: Brown Nick , Doshi Monica
Published: March 2006

Recent developments in postgraduate medical education for the training of junior doctors in the UK necessitate changes in all parts of the curriculum, including the assessment system. There is a move away from the limited, traditional one-off assessment towards multidimensional, broader assessments of a doctor's longer-term performance. This is accompanied by the rapid development of assessment tools, collectively termed workplace-based assessments, and is in keeping with an outcome-based approach to medical education and its increasing professionalisation. In addition to clinical skills, other aspects of being a good practitioner are being assessed, including team-working, working with colleagues and patients, probity and communication skills. Using a combination of tools gives the assessment process high validity. Of the many challenges posed by these changes is the need for data on their reliability in psychiatry. There must be a clear process for applying assessments, national standardisation and training for those using asessment tools.
New Trends in Astrodynamics and Applications: Optimal Trajectories for Space Guidance
Authors: AZIMOV DILMURAT , BISHOP ROBERT
Published: March 2006

Abstract: This paper represents recent results on the development of optimal analytic solutions to the variation problem of trajectory optimization and their application in the construction of on‐board guidance laws. The importance of employing the analytically integrated trajectories in a mission design is discussed. It is assumed that the spacecraft is equipped with a power‐limited propulsion and moving in a central Newtonian field. Satisfaction of the necessary and sufficient conditions for optimality of trajectories is analyzed. All possible thrust arcs and corresponding classes of the analytical solutions are classified based on the propulsion system parameters and performance index of the problem. The solutions are presented in a form convenient for applications in escape, capture, and interorbital transfer problems. Optimal guidance and neighboring optimal guidance problems are considered. It is shown that the analytic solutions can be used as reference trajectories in constructing the guidance algorithms for the maneuver problems mentioned above. An illustrative example of a spiral trajectory that terminates on a given elliptical parking orbit is discussed.
Trajectory Design for Space Missions to Libration Point L2
Authors: DI SALVO ALESSIO
Published: March 2006

Abstract: This work is focused on the detection and computation of “free” transfer trajectories from parking orbits around the Earth to quasiperiodic orbits around the collinear libration point L2, in the Sun‐Earth system; no correction or insertion maneuvers into the final orbits have been considered. The circular restricted three‐body problem is the mathematical model used to describe the motion of a spacecraft, in the gravitational field of the two primaries, computed by integrating the nonlinearized equations of motion. A shooting method has been designed and developed to determine the increment of velocity required for the perigee maneuver, which injects a spacecraft into its transfer trajectory: first the velocity boundary for the Earth escape/capture condition is detected and then an iterative bisection method is applied until the burnout velocity, tangential to the parking orbit, leads the spacecraft to its final Lissajous orbit. For a launch from Kourou at local noon, Ariane5 GTO and Soyuz GTO “equivalent” have been studied and compared, considering fuel minimization for the transfer maneuver and general mission constraints, as maximum excursion of the final Lissajous orbit from the ecliptic plane and eclipses avoidance during the mission. This analysis highlights advantages and drawbacks of various parking orbits. Mission goals are the key factor for the tradeoff among orbit selection, launch options, and the other constraints, fixed by mission requirements.
Recent Gravity‐Assist Trajectories for Interplanetary and Solar Exploration
Authors: DUNHAM DAVID W. , FARQUHAR ROBERT W. , McADAMS JAMES V.
Published: March 2006

Abstract: This paper describes how lunar and planetary gravity assists have been used to design trajectories that have enabled challenging missions, currently flying or in development, at the Applied Physics Laboratory (APL) of Johns Hopkins University, to explore the Sun, and the planets closest to and farthest from it. This is a continuation of a paper presented at the first New Trends in Astrodynamics and Applications conference, January 2003. That paper concentrated on the Third International Sun‐Earth Explorer (ISEE‐3) halo orbit mission, later known as the International Cometary Explorer, or ICE, and the Near Earth Asteroid Rendezvous (NEAR) mission of APL, and the ground‐breaking orbits that those spacecraft used to accomplish their ambitious goals. This paper gives much more information about current APL missions, MESSENGER, STEREO, and New Horizons, which were only briefly described in the previous paper.
Teleoperation Support for Early Human Planetary Missions
Authors: GENTA GIANCARLO , PERINO MARIA ANTONIETTA
Published: March 2006

Abstract: A renewed interest in human exploration is flourishing among all the major spacefaring nations. In fact, in the complex scene of planned future space activities, the development of a Moon base and the human exploration of Mars might have the potential to renew the enthusiasm in expanding the human presence beyond the boundaries of Earth. Various initiatives have been undertaken to define scenarios and identify the required infrastructures and related technology innovations. The typical proposed approach follows a multistep strategy, starting with a series of precursor robotic missions to acquire further knowledge of the planet and to select the best potential landing sites, and evolving toward more demanding missions for the development of a surface infrastructure necessary to sustain human presence. The technologies involved in such a demanding enterprise range from typical space technologies, like transportation and propulsion, automation and robotics, rendezvous and docking, entry/reentry, aero‐braking, navigation, and deep space communications, to human‐specific issues like physiology, psychology, behavioral aspects, and nutritional science for long‐duration exposure, that go beyond the traditional boundaries of space activities. Among the required elements to support planetary exploration, both for the precursor robotic missions and to sustain human exploration, rovers and trucks play a key role. A robust level of autonomy will need to be secured to perform preplanned operations, particularly for the surface infrastructure development, and a teleoperated support, either from Earth or from a local base, will enhance the in situ field exploration capability.
Hamilton‐Jacobi Modelling of Relative Motion for Formation Flying
Authors: KOLEMEN EGEMEN , KASDIN N JEREMY , GURFIL PINI
Published: March 2006

Abstract: A precise analytic model for the relative motion of a group of satellites in slightly elliptic orbits is introduced. With this aim, we describe the relative motion of an object relative to a circular or slightly elliptic reference orbit in the rotating Hill frame via a low‐order Hamiltonian, and solve the Hamilton‐Jacobi equation. This results in a first‐order solution to the relative motion identical to the Clohessy‐Wiltshire approach; here, however, rather than using initial conditions as our constants of the motion, we utilize the canonical momenta and coordinates. This allows us to treat perturbations in an identical manner, as in the classical Delaunay formulation of the two‐body problem. A precise analytical model for the base orbit is chosen with the included effect of zonal harmonics (J2, J3, J4). A Hamiltonian describing the real relative motion is formed and by differing this from the nominal Hamiltonian, the perturbing Hamiltonian is obtained. Using the Hamilton equations, the variational equations for the new constants are found. In a manner analogous to the center manifold reduction procedure, the non‐periodic part of the motion is canceled through a magnitude analysis leading to simple boundedness conditions that cancel the drift terms due to the higher order perturbations. Using this condition, the variational equations are integrated to give periodic solutions that closely approximate the results from numerical integration (1 mm/per orbit for higher order and eccentricity perturbations and 30 cm/per orbit for zonal perturbations). This procedure provides a compact and insightful analytic description of the resulting relative motion.
NEO Impact Projections
Authors: REMO JOHN L.
Published: March 2006

Abstract: The concept of a near‐Earth object (NEO) impact projection metric (PM) based on the ratio of the observation time to the impact time, ρ(t), for a projected NEO impact is developed. The PM can assist NEO mitigation decision‐making that is based on the discontinuously changing cumulative impact probability and help mitigate false alarms of NEO impact with Earth that have undermined public perception toward the veracity of predicting NEO threats.
Variational Methods for Periodic Solutions of NewtonianN‐Body Problems
Authors: SHIQING ZHANG
Published: March 2006

Abstract:We survey some recent results on periodic solutions forN‐body problems that were obtained by variational minimization methods.
Decentralized Formation Flying Control in a Multiple‐Team Hierarchy
Authors: MUELLER JOSEPH B. , THOMAS STEPHANIE J.
Published: March 2006

Abstract: In recent years, formation flying has been recognized as an enabling technology for a variety of mission concepts in both the scientific and defense arenas. Examples of developing missions at NASA include magnetospheric multiscale (MMS), solar imaging radio array (SIRA), and terrestrial planet finder (TPF). For each of these missions, a multiple satellite approach is required in order to accomplish the large‐scale geometries imposed by the science objectives. In addition, the paradigm shift of using a multiple satellite cluster rather than a large, monolithic spacecraft has also been motivated by the expected benefits of increased robustness, greater flexibility, and reduced cost. However, the operational costs of monitoring and commanding a fleet of close‐orbiting satellites is likely to be unreasonable unless the onboard software is sufficiently autonomous, robust, and scalable to large clusters. This paper presents the prototype of a system that addresses these objectives—a decentralized guidance and control system that is distributed across spacecraft using a multiple team framework. The objective is to divide large clusters into teams of “manageable” size, so that the communication and computation demands driven by N decentralized units are related to the number of satellites in a team rather than the entire cluster. The system is designed to provide a high level of autonomy, to support clusters with large numbers of satellites, to enable the number of spacecraft in the cluster to change post‐launch, and to provide for on‐orbit software modification. The distributed guidance and control system will be implemented in an object‐oriented style using a messaging architecture for networking and threaded applications (MANTA). In this architecture, tasks may be remotely added, removed, or replaced post launch to increase mission flexibility and robustness. This built‐in adaptability will allow software modifications to be made on‐orbit in a robust manner. The prototype system, which is implemented in Matlab, emulates the object‐oriented and message‐passing features of the MANTA software. In this paper, the multiple team organization of the cluster is described, and the modular software architecture is presented. The relative dynamics in eccentric reference orbits is reviewed, and families of periodic, relative trajectories are identified, expressed as sets of static geometric parameters. The guidance law design is presented, and an example reconfiguration scenario is used to illustrate the distributed process of assigning geometric goals to the cluster. Next, a decentralized maneuver planning approach is presented that utilizes linear‐programming methods to enact reconfiguration and coarse formation keeping maneuvers. Finally, a method for performing online collision avoidance is discussed, and an example is provided to gauge its performance.
Horsing Around on Saturn
Authors: VANDERBEI ROBERT J.
Published: March 2006

Abstract: On the basis of simple statistical mechanical models, the prevailing view of the rings of Saturn is that they are unstable and must therefore have been formed rather recently. In this paper, we argue that the Saturn rings and inner moons are in much more stable orbits than previously thought and, therefore, that they likely formed together as part of the initial formation of the solar system. To make this argument, we give a detailed description of so‐called horseshoe orbits and show that this horseshoeing phenomenon greatly stabilizes the rings of Saturn. This paper is part of a collaborative effort with E. Belbruno and J.R. Gott III. For a description of their part of the work, see their papers in these proceedings.
Metrics on the Relative Spacecraft Motion Invariant Manifold
Authors: GURFIL P , KHOLSHEVNIKOV KONSTANTIN V.
Published: March 2006

Abstract: This paper establishes a methodology for obtaining the general solution to the spacecraft relative motion problem by utilizing Cartesian configuration space in conjunction with classical orbital elements. The geometry of the relative motion configuration space is analyzed, and the relative motion invariant manifold is determined. Most importantly, the geometric structure of the relative motion problem is used to derive useful metrics for quantification of the minimum, maximum, and mean distance between spacecraft for commensurable and non‐commensurable mean motions. A number of analytic solutions, as well as useful examples, are provided, illustrating the calculated bounds. A few particular cases are given that yield simple solutions.
Robust Mission Design Through Evidence Theory and Multiagent Collaborative Search
Authors: VASILE MASSIMILIANO
Published: March 2006

Abstract: In this paper, the preliminary design of a space mission is approached by introducing uncertainties on the design parameters and formulating the resulting reliable design problem as a multiobjective optimization problem. Uncertainties are modelled through evidence theory and the belief, or credibility, that the successful achievement of mission goals is maximized along with the reliability of constraint satisfaction. The multiobjective optimization problem is solved through a novel algorithm based on the collaboration of a population of agents in search for the set of highly reliable solutions. Two typical problems in mission analysis are used to illustrate the proposed methodology.
Earth‐to‐Moon Low Energy Transfers Targeting L1 Hyperbolic Transit Orbits
Authors: TOPPUTO FRANCESCO , VASILE MASSIMILIANO , BERNELLI‐ZAZZERA FRANCO
Published: March 2006

Abstract: In the frame of the lunar exploration, numerous future space missions will require maximization of payload mass, and simultaneously achieving reasonable transfer times. To fulfill this request, low energy non‐Keplerian orbits could be used to reach the Moon instead of high energetic transfers. The low energy solutions can be separated into two main categories depending on the nature of the trajectory approaching the Moon: low energy transit orbits that approach the Moon from the interior equilibrium point L1 and weak stability boundary transfers that reach the Moon after passing through L2. This paper proposes an alternative way to exploit the opportunities offered by L1 transit orbits for the design of Earth‐Moon transfers. First, in a neighborhood of the L1 point, the three‐body dynamics is linearized and written in normal form; then the entire family of nonlinear transit orbits is obtained by selecting the appropriate nontrivial amplitudes associated with the hyperbolic part. The L1‐Earth arc is close to a 5:2 resonant orbit with the Moon, whose perturbations cause the apogee to rise. In a second step, two selected low altitude parking orbits around the Earth and the Moon are linked with the transit orbit by means of two three‐body Lambert arcs, solutions of two two‐point boundary value problems. The resulting Earth‐to‐Moon trajectories prove to be very efficient in the Moon captured arc and save approximately 100 m/sec in Δv cost when compared to the Hohmann transfer. Furthermore, such solutions demonstrate that Moon capture could be obtained in the frame of the Earth‐Moon R3BP neglecting the presence of the Sun.
Relative Equilibria for General Gravity Fields in the Sphere‐Restricted Full Two‐Body Problem
Authors: SCHEERES D J
Published: March 2006

Abstract: Equilibrium conditions for a mutually attracting general mass distribution and point mass are stated. The equilibrium conditions can be reduced to six equations in six unknowns, plus the existence of integrals of motion consisting of the total angular momentum and energy of the system. The equilibrium conditions are further reduced to two independent equations, and their theoretical properties are studied. We state a set of necessary and sufficient conditions for an equilibrium that is well suited to the computation of certain classes of equilibria. These equations are solved for nonsymmetric gravity fields of interest, using a real asteroid shape model for the general gravity fields. The stability of the resulting equilibria are also noted.
Growth Hormone Treatment and Aortic Dimensions in Turner Syndrome
Authors: Bondy Carolyn A. , Van Phillip L. , Bakalov Vladimir K. , Ho Vincent B.
Published: March 2006

Background: In recent years many girls with Turner syndrome (TS) have been treated with supraphysiological doses of GH to increase adult height. In addition to promoting statural growth, GH may have direct effects on the cardiovascular system.

Objective: We sought to determine whether GH treatment affects aortic diameter in girls with TS because there is an increased risk for aortic dilation and dissection in this syndrome.

Methods: In a retrospective, cross-sectional study, we compared ascending and descending aortic diameters measured by magnetic resonance imaging in GH-treated (n = 53) vs. untreated (n = 48) patients with TS participating in a National Institutes of Health protocol between 2001 and 2004.

Results: The average duration of GH treatment was 4.7 with se 0.4 yr (range 2–11 yr). The two groups were similar in age and weight, but GH-treated subjects were on average 8 cm taller (P = 0.002). The diameter of the ascending aorta was increased by 7.3% and descending aorta by 8.9% in the GH-treated group. However, after correction for age, height, weight, and presence of bicuspid aortic valve and coarctation, using a multiple regression, neither history of GH treatment nor the length of GH treatment had an effect on the aortic diameter. Weight (P = 0.02), height (P = 0.001), and presence of bicuspid aortic valve (P = 0.0001) were associated with larger ascending aortic diameter, whereas age (P = 0.008), height (P = 0.02), and history of coarctation (P = 0.006) were associated with larger descending aortic diameter.

Conclusions: GH treatment of girls with TS does not seem to affect ascending or descending aortic diameter above the increase related to the larger body size.
Functional genomics inDictyostelium: MidA, a new conserved protein, is required for mitochondrial function and development
Authors: Torija Patricia , Vicente Juan J. , Rodrigues Tiago B. , Robles Alicia , Cerdán Sebastián , Sastre Leandro , Calvo Rosa M. , Escalante Ricardo
Published: March 2006

Genomic sequencing has revealed a large number of evolutionary conserved genes of unknown function. In the absence of characterized functional domains, the discovery of the role of these genes must rely on experimental approaches. We have selected 30 Dictyostelium discoideum genes of unknown function that showed high similarity to uncharacterized human genes and were absent in the complete proteomes from Saccharomyces cerevisiae and S. pombe. No putative functional motifs were found in their predicted encoded proteins. Eighteen genes were successfully knocked-out and three of them showed obvious phenotypes. A detailed analysis of one of them, midA, is presented in this report. Disruption of midA in Dictyostelium leads to pleiotropic defects. Cell size, growth rate, phagocytosis and macropinocytosis were affected in the mutant. During development, midA- cells showed an enhanced tendency to remain at the slug stage, and spore viability was compromised. The expression of MidA fused to GFP in midA- strain rescued the phenotype and the fused protein was located in the mitochondria. Although cellular oxygen consumption, mitochondrial content and mitochondrial membrane potential were similar to wild type, the amount of ATP was significantly reduced in the mutant suggesting a mitochondrial dysfunction. Metabolomic analysis by natural-abundance 13C-nuclear magnetic resonance has shown the lack of glycogen accumulation during growth. During starvation, mutant cells accumulated higher levels of ammonia, which inhibited normal development. We hypothesize that the lack of MidA reduces mitochondrial ATP synthetic capacity and this has an impact in some but not all energy-dependent cellular processes. This work exemplifies the potential of Dictyostelium as a model system for functional genomic studies.
Single-molecule analysis of chemoattractant-stimulated membrane recruitment of a PH-domain-containing protein
Authors: Matsuoka Satomi , Iijima Miho , Watanabe Tomonobu M. , Kuwayama Hidekazu , Yanagida Toshio , Devreotes Peter N. , Ueda Masahiro
Published: March 2006

Molecular mechanisms of chemotactic response are highly conserved among many eukaryotic cells including human leukocytes and Dictyostelium discoideum cells. The cells can sense the differences in chemoattractant concentration across the cell body and respond by extending pseudopods from the cell side facing to a higher concentration. Pseudopod formation is regulated by binding of pleckstrin homology (PH)-domain-containing proteins to phosphatidylinositol 3,4,5-trisphosphates [PtdIns(3,4,5)P3] localized at the leading edge of chemotaxing cells. However, molecular mechanisms underlying dynamic features of a pseudopod have not been fully explained by the known properties of PH-domain-containing proteins. To investigate the mechanisms, we visualized single molecules of green fluorescent protein tagged to Crac (Crac-GFP), a PH-domain-containing protein in D. discoideum cells. Whereas populations of Crac molecules exhibited a stable steady-state localization at pseudopods, individual molecules bound transiently to PtdIns(3,4,5)P3 for ∼120 milliseconds, indicating dynamic properties of the PH-domain-containing protein. Receptor stimulation did not alter the binding stability but regulated the number of bound PH-domain molecules by metabolism of PtdIns(3,4,5)P3. These results demonstrate that the steady-state localization of PH-domain-containing proteins at the leading edge of chemotaxing cells is dynamically maintained by rapid recycling of individual PH-domain-containing proteins. The short interaction between PH domains and PtdIns(3,4,5)P3 contributes to accurate and sensitive chemotactic movements through the dynamic redistributions. These dynamic properties might be a common feature of signaling components involved in chemotaxis.
Cadherin Cad99C is required for normal microvilli morphology in Drosophila follicle cells
Authors: Schlichting Karin , Wilsch-Bräuninger Michaela , Demontis Fabio , Dahmann Christian
Published: March 2006

Microvilli are actin-filled membranous extensions common to epithelial cells. Several proteins have been identified that localize to microvilli. However, most of these proteins are dispensable for the normal morphogenesis of microvilli. Here, we show by immunoelectron microscopy that the non-classical cadherin Cad99C localizes to microvilli of Drosophila ovarian follicle cells. Loss of Cad99C function leads to disorganized and abnormal follicle cell microvilli. Conversely, overexpression of Cad99C in follicle cells results in large bundles of microvilli. Furthermore, altered microvilli morphology correlates with defects in the assembly of the vitelline membrane, an extracellular layer secreted by follicle cells that is part of the eggshell. Finally, we provide evidence that Cad99C is the homolog of vertebrate protocadherin 15. Mutations in the gene encoding protocadherin 15 lead to the disorganization of stereocilia, which are microvilli-derived extensions of cochlear hair cells, and deafness (Usher syndrome type 1F). Our data suggest an essential role for Cad99C in microvilli morphogenesis that is important for follicle cell function. Furthermore, these results indicate that insects and vertebrates use related cadherins to organize microvilli-like cellular extensions.
Potential dual molecular interaction of theDrosophila7-pass transmembrane cadherin Flamingo in dendritic morphogenesis
Authors: Kimura Hiroshi , Usui Tadao , Tsubouchi Asako , Uemura Tadashi
Published: March 2006

Seven-pass transmembrane cadherins (7-TM cadherins) play pleiotropic roles in epithelial planar cell polarity, shaping dendritic arbors and in axonal outgrowth. In contrast to their role in planar polarity, how 7-TM cadherins control dendritic and axonal outgrowth at the molecular level is largely unknown. Therefore, we performed extensive structure-function analysis of the Drosophila 7-TM cadherin Flamingo (Fmi) and investigated the activities of individual mutant forms mostly in dendritogenesis of dendritic arborization (da) neurons. One of the fmi-mutant phenotypes was overgrowth of branches in the early stage of dendrite development. In da neurons but not in their adjacent non-neuronal cells, expression of a truncated form (ΔN) that lacks the entire cadherin repeat sequence, rescues flies - at least partially - from this phenotype. Another phenotype is observed at a later stage, when dendritic terminals outgrowing from the contralateral sides meet and then avoid each other. In the fmi mutant, by contrast, those branches overlapped. Overexpression of the ΔN form on the wild-type background phenocopied the overlap phenotype in the mutant, and analysis in heterologous systems supported the possibility that this effect might be because the Fmi-Fmi homophilic interaction is inhibited by ΔN. We propose that a dual molecular function of Fmi play pivotal roles in dendrite morphogenesis. In the initial growing phase, Fmi might function as a receptor for a sofar-unidentified ligand and this hypothetical heterophilic interaction would be responsible for limiting branch elongation. At a later stage, homophilic Fmi-binding at dendro-dendritic interfaces would elicit avoidance between dendritic terminals.
DrosophilaIncenp is required for cytokinesis and asymmetric cell division during development of the nervous system
Authors: Chang Chih-Jui , Goulding Sarah , Adams Richard R. , Earnshaw William C. , Carmena Mar
Published: March 2006

The chromosomal passenger protein complex has emerged as a key player in mitosis, with important roles in chromatin modifications, kinetochore-microtubule interactions, chromosome bi-orientation and stability of the bipolar spindle, mitotic checkpoint function, assembly of the central spindle and cytokinesis. The inner centromere protein (Incenp; a subunit of this complex) is thought to regulate the Aurora B kinase and target it to its substrates. To explore the roles of the passenger complex in a developing multicellular organism, we have performed a genetic screen looking for new alleles and interactors of Drosophila Incenp. We have isolated a new null allele of Incenp that has allowed us for the first time to study the functions of the chromosomal passengers during development. Homozygous incenpEC3747 embryos show absence of phosphorylation of histone H3 in mitosis, failure of cytokinesis and polyploidy, and defects in peripheral nervous system development. These defects are consistent with depletion of Aurora B kinase activity. In addition, the segregation of the cell-fate determinant Prospero in asymmetric neuroblast division is abnormal, suggesting a role for the chromosomal passenger complex in the regulation of this process.
A Theoretical Interpretation of Remarkable Enhancement of Intermolecular Binding at the Lipid-Water Interface
Authors: Sakurai Minoru , Tamagawa Hirohisa , Furuki Takao , Inoue Yoshio , Ariga Katsuhiko , Kunitake Toyoki
Published: March 2006

A multidielectric model combined with quantum chemical calculation was applied to interpretate intermolecular binding at the lipid-water interface. The calculation well reproduced the observed binding energy between guanidium cation and AMP.