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Orbit
Kinds of Orbit Terms modified by Orbit Selected AbstractsDesigned protein G core variants fold to native-like structures: Sequence selection by ORBIT tolerates variation in backbone specificationPROTEIN SCIENCE, Issue 2 2001Scott A. Ross Abstract The solution structures of two computationally designed core variants of the ,1 domain of streptococcal protein G (G,1) were solved by 1H NMR methods to assess the robustness of amino acid sequence selection by the ORBIT protein design package under changes in protein backbone specification. One variant has mutations at three of 10 core positions and corresponds to minimal perturbations of the native G,1 backbone. The other, with mutations at six of 10 positions, was calculated for a backbone in which the separation between G,1's ,-helix and ,-sheet was increased by 15% relative to native G,1. Exchange broadening of some resonances and the complete absence of others in spectra of the sixfold mutant bespeak conformational heterogeneity in this protein. The NMR data were sufficiently abundant, however, to generate structures of similar, moderately high quality for both variants. Both proteins adopt backbone structures similar to their target folds. Moreover, the sequence selection algorithm successfully predicted all core ,1 angles in both variants, five of six ,2 angles in the threefold mutant and four of seven ,2 angles in the sixfold mutant. We conclude that ORBIT calculates sequences that fold specifically to a geometry close to the template, even when the template is moderately perturbed relative to a naturally occurring structure. There are apparently limits to the size of acceptable perturbations: In this study, the larger perturbation led to undesired dynamic behavior. [source] Experience with Delay-Tolerant Networking from orbit,INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 5-6 2010W. Ivancic Abstract We describe the first use from space of the Bundle Protocol for Delay-Tolerant Networking (DTN) and lessons learned from experiments made and experience gained with this protocol. The Disaster Monitoring Constellation (DMC), constructed by Surrey Satellite Technology Ltd (SSTL), is a multiple-satellite Earth-imaging low-Earth-orbit sensor network in which recorded image swaths are stored onboard each satellite and later downloaded from the satellite payloads to a ground station. Store-and-forward of images with capture and later download gives each satellite the characteristics of a node in a disruption-tolerant network. Originally developed for the ,Interplanetary Internet,' DTNs are now under investigation in an Internet Research Task Force (IRTF) DTN research group (RG), which has developed a ,bundle' architecture and protocol. The DMC is technically advanced in its adoption of the Internet Protocol (IP) for its imaging payloads and for satellite command and control, based around reuse of commercial networking and link protocols. These satellites' use of IP has enabled earlier experiments with the Cisco router in Low Earth Orbit (CLEO) onboard the constellation's UK-DMC satellite. Earth images are downloaded from the satellites using a custom IP-based high-speed transfer protocol developed by SSTL, Saratoga, which tolerates unusual link environments. Saratoga has been documented in the Internet Engineering Task Force (IETF) for wider adoption. We experiment with the use of DTNRG bundle concepts onboard the UK-DMC satellite, by examining how Saratoga can be used as a DTN ,convergence layer' to carry the DTNRG Bundle Protocol, so that sensor images can be delivered to ground stations and beyond as bundles. Our practical experience with the first successful use of the DTNRG Bundle Protocol in a space environment gives us insights into the design of the Bundle Protocol and enables us to identify issues that must be addressed before wider deployment of the Bundle Protocol. Published in 2010 by John Wiley & Sons, Ltd. [source] Theatre in the Sky: a ubiquitous broadband multimedia-on-demand service over a novel constellation composed of quasi-geostationary satellitesINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 3 2006Tarik Taleb Abstract To meet an ever-growing demand for wideband multimedia services and electronic connectivity across the world, development of ubiquitous broadband multimedia systems is gaining a tremendous interest at both commercial and academic levels. Satellite networks will play an indispensable role in the deployment of such systems. A significant number of satellite communication constellations have been thus proposed using Geostationary (GEO), Medium Earth Orbit (MEO), or Low Earth Orbit (LEO) satellites. These constellations, however, either require a potential number of satellites or are unable to provide data transmission with high elevation angles. This paper proposes a new satellite constellation composed of Quasi-GeoStationary Orbit (Quasi-GSO) satellites. The main advantage of the constellation is in its ability to provide global coverage with a significantly small number of satellites while, at the same time, maintaining high elevation angles. Based on a combination of this Quasi-GSO satellites constellation and terrestrial networks, the paper proposes also an architecture for building a global, large-scale, and efficient Video-on-Demand (VoD) system. The entire architecture is referred to as a ,Theatre in the Sky'. Copyright © 2006 John Wiley & Sons, Ltd. [source] Stability analysis of an adaptive packet access scheme for mobile communication systems with high propagation delaysINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2003Giovanni Giambene Abstract In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time-Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot-code resource. This protocol is named Adaptive Time Code-Packet Reservation Multiple Access (ATC-PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)- Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High-Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC-PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC-PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd. [source] Surgical Anatomy Around the Orbit,The System of ZonesCLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 3 2007Article first published online: 11 APR 200 No abstract is available for this article. [source] Powdery mildew resistance in Czech and Slovak barley cultivarsPLANT BREEDING, Issue 3 2000A. Dreiseitl Abstract Fifteen powdery mildew resistance genes and the gene MlaN81 derived from ,Nepal 81'were found in 76 Czech and Slovak spring and winter barley cultivars when tested for reaction to a set of powdery mildew isolates. Nine cultivars (,Donum', ,Expres', ,Jubilant', ,Orbit', ,Primus', ,Progres', ,Stabil', ,Vladan' and ,Zlatan') are composed of lines with different resistance genes. The Mlat gene is present in nine cultivars and was transferred from the Anatolian landrace ,A-516,. The resistances derived from ,KM-1192'and ,CI 7672'were identical and designated Ml(Kr). Five winter barley cultivars possess the Ml(Bw) resistance. The winter barley line ,KM-2099'carries the mlo gene. The parental cultivar ,Palestine 10'was also tested in which the genes Mlk1, MlLa were identified. The German cultivar ,Salome', a parent of seven cultivars tested, probably carries the gene MlLa in addition to mlo and Mla7. The gene mlo6 may be present in the cultivar ,Heris'. Most of the results were confirmed by the pedigrees of the cultivars. [source] Periodic Orbits near equilibriaCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 9 2010Luis Barreira Lyapunov, Weinstein, and Moser obtained remarkable theorems giving sufficient conditions for the existence of periodic orbits emanating from an equilibrium point of a differential system with a first integral. Using averaging theory, we establish a similar result for a differential system without assuming the existence of a first integral. Our result can also be interpreted as a kind of special Hopf bifurcation. © 2010 Wiley Periodicals, Inc. [source] Tension pneumo-orbitus and pneumocephalus induced by a nasal oxygen cannula: Report on two paediatric casesJOURNAL OF PAEDIATRICS AND CHILD HEALTH, Issue 5 2000Bj O'Brien Abstract: The present paper highlights the potential dangers of misplaced nasopharyngeal oxygen cannulae causing secondary pneumo-orbitus and pneumocephalus in two paediatric patients. While this complication is uncommon, early recognition allows prompt and appropriate intervention, with cessation of nasal oxygen, cannula removal, early investigation with computed tomography (CT) head/orbit scan and orbital or cranial decompression, if required. Early CT imaging identifies medial orbital or paranasal sinus fractures, the presence of sinusitis, associated intracranial air and assessment of the degree of orbital or intracranial tension. Antibiotics are not usually required for this type of clean injury unless pre-existing sinusitis is identified. In both cases, direct orbital decompression was performed with excellent results after identification of marked unilateral tense exophthalmos, delayed pupillary reactions to light and ophthalmopegia. [source] Accumulation Process of High-Z Impurity in Toroidal Rotating Tokamak PlasmaCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010K. Hoshino Abstract The accumulation process of high-Z impurity in toroidal rotating tokamak plasma is investigated. A new inward pinch of high-Z impurity due to the ionization/recombination processes is derived using an analytic model. This inward pinch is driven by the large deviation of a drift orbit from a magnetic surface and the resultant variation of the charge state along the drift orbit. The pinch velocity increases with increasing toroidal rotation speed in both the co-direction and the ctr-direction. The inward pinch expected by the analytic model is really observed in the numerical simulation using the IMPGYRO code (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] "Going to War in Buses": The Anglo-American Clash over Leyland Sales to Cuba, 1963,1964DIPLOMATIC HISTORY, Issue 5 2010Christopher Hull The sale of buses by the Leyland Motor Company to Cuba proved contentious, not only in the realm of Anglo-American relations, but also in the domestic sphere of a behind the scenes inter-departmental disagreement within the British government. This is because the bus exports pitted political against economic interests at the height of the Cold War and in the midst of a British export drive. As Her Majesty's Government readily recognized, Washington was particularly sensitive over any issue related to Cuba, which by 1963 was firmly in the communist orbit of the Soviet bloc and which the United States was determined to isolate economically through the application of a trade blockade. The decision to approve the sales came at the end of the Macmillan and Kennedy administrations, and clouded the short-lived partnership of Prime Minister Alec Douglas-Home and President Lyndon B. Johnson. The bus exports became an election issue in the campaigns of both leaders in 1964, assuming a political significance that belied the buses' seemingly innocuous function and outward appearance. [source] Control of eye orientation: where does the brain's role end and the muscle's begin?EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2004Dora E. Angelaki Abstract Our understanding of how the brain controls eye movements has benefited enormously from the comparison of neuronal activity with eye movements and the quantification of these relationships with mathematical models. Although these early studies focused on horizontal and vertical eye movements, recent behavioural and modelling studies have illustrated the importance, but also the complexity, of extending previous conclusions to the problems of controlling eye and head orientation in three dimensions (3-D). An important facet in understanding 3-D eye orientation and movement has been the discovery of mobile, soft-tissue sheaths or ,pulleys' in the orbit which might influence the pulling direction of extraocular muscles. Appropriately placed pulleys could generate the eye-position-dependent tilt of the ocular rotation axes which are characteristic for eye movements which follow Listing's law. Based on such pulley models of the oculomotor plant it has recently been proposed that a simple two-dimensional (2-D) neural controller would be sufficient to generate correct 3-D eye orientation and movement. In contrast to this apparent simplification in oculomotor control, multiple behavioural observations suggest that the visuo-motor transformations, as well as the premotor circuitry for saccades, pursuit eye movements and the vestibulo-ocular reflexes, must include a neural controller which operates in 3-D, even when considering an eye plant with pulleys. This review summarizes the most recent work and ideas on this controversy. In addition, by proposing directly testable hypotheses, we point out that, in analogy to the previously successful steps towards elucidating the neural control of horizontal eye movements, we need a quantitative characterization first of motoneuron and next of premotor neuron properties in 3-D before we can succeed in gaining further insight into the neural control of 3-D motor behaviours. [source] Outcome of sinonasal melanoma: Clinical experience and review of the literature,HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 10 2010Thomas N. Roth MD Abstract Background. Primary sinonasal malignant melanoma (SNMM) is a rare clinical entity. There is neither a classification nor a staging system nor an evidence-based treatment concept established. Our objective was to find potential risk factors predicting the outcome. Methods. Twenty-five patients with histologically confirmed SNMM were consecutively included and retrospectively analyzed. Staging methods were nasal endoscopy, CT, MRI, and positron emission tomography (PET) scan. Patients were selected for a curative or palliative concept. All patients had postoperative follow-up with control-MRI at 3 and 6 months. Restaging was performed when local recurrence occurred. Results. Nineteen patients underwent primary surgery with curative intention; in 16 cases with tumor free margins. Thirteen patients (68%) had transnasal endoscopic surgery, 4 lateral rhinotomy, and 2 transfacial approach with orbital exenteration. Six patients (32%) had palliative therapy and 7 patients (37%) had adjuvant radiotherapy. Despite radical operations, 6 patients (37%) showed local recurrence and 8 patients (50%) developed distant metastasis. In 2 patients with incomplete surgery, regional metastasis was noted. The median disease-free interval was 18 months, and the median overall survival rate was 23 months. Conclusion. SNMMs of the ethmoid and maxillary sinuses have a worse prognosis than other localizations in the nasal cavity; infiltration into the skull base, orbit, or facial soft tissue correlates with a very poor outcome corresponding to the palliative situations. Furthermore, local recurrence insinuates aggressive disease with short survival rate. A main difference from its cutaneous counterpart seems to be a primary tendency to hematogenic spread. Further research is needed to confirm these findings. © 2010 Wiley Periodicals, Inc. Head Neck, 2010 [source] Complications of craniofacial resection for malignant tumors of the skull base: Report of an International Collaborative Study,HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 6 2005Ian Ganly MD Abstract Background. Advances in imaging, surgical technique, and perioperative care have made craniofacial resection (CFR) an effective and safe option for treating malignant tumors involving the skull base. The procedure does, however, have complications. Because of the relative rarity of these tumors, most existing data on postoperative complications come from individual reports of relatively small series of patients. This international collaborative report examines a large cohort of patients accumulated from multiple institutions with the aim of identifying patient-related and tumor-related predictors of postoperative morbidity and mortality and set a benchmark for future studies. Methods. One thousand one hundred ninety-three patients from 17 institutions were analyzed for postoperative mortality and complications. Postoperative complications were classified into systemic, wound, central nervous system (CNS), and orbit. Statistical analyses were carried out in relation to patient characteristics, extent of disease, prior radiation treatment, and type of reconstruction to determine factors that predicted mortality or complications. Results. Postoperative mortality occurred in 56 patients (4.7%). The presence of medical comorbidity was the only independent predictor of mortality. Postoperative complications occurred in 433 patients (36.3%). Wound complications occurred in 237 (19.8%), CNS-related complications in 193 (16.2%), orbital complications in 20 (1.7%), and systemic complications in 57 (4.8%) patients. Medical comorbidity, prior radiation therapy, and the extent of intracranial tumour involvement were independent predictors of postoperative complications. Conclusions. CFR is a safe surgical treatment for malignant tumors of the skull base, with an overall mortality of 4.7% and complication rate of 36.3%. The impact of medical comorbidity and intracranial tumor extent should be carefully considered when planning therapy for patients whose tumors are amenable to CFR. © 2005 Wiley Periodicals, Inc. Head Neck27: XXX,XXX, 2005 [source] Anterior cranial base reconstruction using free tissue transfer: Changing trends,HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 2 2003Joseph Califano MD Abstract Introduction. A consecutive series of 135 patients undergoing resection for malignant tumors involving the anterior cranial base between 1976 and 1999 was reviewed. Patient and Methods. In the years from 1976,1991, free-tissue transfer was used in 5 of 76 or 6.6% of cases, whereas free-tissue reconstruction was used in 24 of 59 or 40% of cases in the years 1992,1999. Of those cases reconstructed with free-tissue transfer in 1976,1991, 60% (three of five) underwent a complex resection defined as involving dura, brain, or more than one major structure adjacent to skull base. Of those patients reconstructed with conventional (pericranial or pericranial/galeal) pedicled flaps in this time period, 35% (25 of 71) underwent a complex resection. From 1992,1999, 75% (18 of 24) of patients reconstructed with free-tissue transfer received a complex resection, whereas only 6% (2 of 35) of patients reconstructed by other means received a complex resection. Outcomes. For those patients reconstructed by free-tissue transfer, there were no instances of flap loss. Comparison of these two time periods was notable for a similar patient composition in terms of age, histologic findings, and extent of resection. Major complication rates for patients who are reconstructed with free-tissue transfer for anterior cranial base resections (31%) are similar compared with patients who have been reconstructed with conventional pedicled flaps (35%). This was noted despite an increased extent and complexity of resection in those patients who underwent free-tissue transfer reconstruction (72%) compared with those patients reconstructed by more conventional means (26%) p < .001. Conclusion. In our institution, the use of vascularized, free-tissue transfer has replaced pedicled flaps as the preferred modality for reconstructing complex anterior cranial base defects involving resection of dura, brain, or multiple major structures adjacent to local skull base, including the orbit, palate, and other structures. Complication rates for patients reconstructed with free-tissue transfer techniques is similar to those patients reconstructed by conventional techniques, despite an increase in complexity of resection in this group. © 2002 Wiley Periodicals, Inc. Head Neck 24: 000,000, 2002 [source] Malignant tumors of the nasal cavity and paranasal sinuses,HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 9 2002Teri S. Katz MD Abstract Purpose To evaluate the role of radiation therapy in patients with nasal cavity and paranasal sinus tumors. Materials and Methods Between October 1964 and July 1998, 78 patients with malignant tumors of the nasal cavity (48 patients), ethmoid sinus (24 patients), sphenoid sinus (5 patients), or frontal sinus (1 patient) were treated with curative intent by radiation therapy alone or in the adjuvant setting. There were 25 squamous cell carcinomas, 14 undifferentiated carcinomas, 31 minor salivary gland tumors (adenocarcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma), 8 esthesioneuroblastomas, and 1 transitional cell carcinoma. Forty-seven patients were treated with irradiation alone, 25 with surgery and postoperative irradiation, 2 with preoperative irradiation and surgery, and 4 with chemotherapy in combination with irradiation with or without surgery. Results The 5-year actuarial local control rate for stage I (limited to the site of origin; 22 patients) was 86%; for stage II (extension to adjacent sites (eg, adjacent sinuses, orbit, pterygomaxillary fossa, nasopharynx; 21 patients) was 65%; and for stage III (destruction of skull base or pterygoid plates, or intracranial extension; 35 patients) was 34%. The 5-year actuarial local control rate for patients receiving postoperative irradiation was 79% and for patients receiving irradiation alone was 49% (p = .05). The 5-, 10-, 15-, and 20-year ultimate local control rates for all 78 patients were 60%, 56%, 48%, and 48%, respectively. The 5-, 10-, 15-, and 20-year cause-specific survival rates for all 78 patients were 56%, 45%, 39%, and 39%, respectively. The 5-, 10-, 15-, and 20-year absolute survival rates for all 78 patients were 50%, 31%, 21%, and 16%, respectively. Of the 67 (86%) patients who were initially seen with node-negative disease, 39 (58%) received no elective neck treatment, and 28 (42%) received elective neck irradiation. Of the 39 patients who received no elective neck treatment, 33 (85%) did not experience recurrence in the neck compared with 25 (89%) of 28 patients who received elective neck irradiation. Most patients who received elective neck irradiation (57%) had stage III disease. Twenty-one (27%) of 78 patients had unilateral blindness develop secondary to radiation retinopathy or optic neuropathy; the complication was anticipated in most of these patients, because the ipsilateral eye was irradiated to a high dose. Four patients (5%) unexpectedly had bilateral blindness develop because of optic neuropathy. All four of these patients received irradiation alone. Conclusion Surgery and postoperative radiation therapy may result in improved local control, absolute survival, and complications when compared with radiation therapy alone. Elective neck irradiation is probably unnecessary for patients with early-stage disease. © 2002 Wiley Periodicals, Inc. Head Neck 24: 821,829, 2002 [source] Computational NMR Spectroscopy of Transition-Metal/Nitroimidazole Complexes: Theoretical Investigation of Potential RadiosensitizersHELVETICA CHIMICA ACTA, Issue 10 2005Teodorico The computed chemical shifts of transition-metal complexes with dimetridazole (=,1,2-dimethyl-5-nitro-1H -imidazole; 1), a prototypical nitro-imidazole-based radiosensitizer, are reported at the GIAO-BP86 and -B3LYP levels for BP86/ECP1-optimized geometries. These complexes comprise [MCl2(1)2] (M,=,Zn, Pd, Pt), [RuCl2(DMSO)2(1)2], and [Rh2(O2CMe)4(1)2]. Available ,(1H) and ,(15N) values, and ,,(1H) and ,,(15N) coordination shifts are well-reproduced theoretically, provided solvation and relativistic effects are taken into account by means of a polarizable continuum model and suitable methods including spin,orbit (SO) coupling, respectively. These effects are particularly important for the metal-coordinated N-atom, where the contributions from solvation and relativity can affect ,(15N) and ,,(15N) values up to 10,20,ppm. The 195Pt chemical shifts of cis - and trans -[PtCl2(1)2] are well-reproduced using the zero-order regular approximation including SO coupling (ZORA-SO). Predictions are reported for 99Ru and 103Rh chemical shifts, which suggest that these metal centers could be used as additional, sensitive NMR probes in their complexes with nitro-imidazoles. [source] Central nervous system dissemination in immunocompetent patients with aggressive lymphomas: incidence, risk factors and therapeutic optionsHEMATOLOGICAL ONCOLOGY, Issue 2 2009Andrés J. M. Ferreri Abstract Central nervous system (CNS) dissemination is a rare (4,5%) but usually fatal complication of aggressive lymphomas. Prophylaxis modalities to prevent CNS dissemination in aggressive lymphomas cannot be widely applied to every lymphoma patient since it is associated with increased risk of neurotoxicity. Therefore, identification of high-risk patients as the best candidates to receive CNS prophylaxis constitutes a major endpoint in the management of these malignancies. Various risk factors and models for CNS recurrence have been described. Parameters reflecting the extent and proliferation of the disease, like elevated serum lactate dehydrogenase levels, involvement of multiple extranodal sites, advanced stage and high age-adjusted International Prognostic Index (IPI) score, as well as the involvement of specific anatomic sites, like testes, orbit, paranasal sinuses, have been identified and confirmed as important to predict CNS dissemination. Management of this complication in aggressive lymphomas with conventional-dose chemotherapy is associated with disappointing results, while some preliminary but encouraging experiences suggest a potential role of high-dose chemotherapy and stem cell transplantation. The analysis of recent clinical studies could lead to advancement in the prognosis of aggressive lymphomas, but several questions regarding the optimum chemotherapy combination, the best conditioning regimen and the role of radiation therapy and intrathecal chemotherapy remain still unanswered. The purposes of the present review are to critically analyse current data on the risk of CNS dissemination in aggressive lymphomas, the clinical presentation of secondary CNS lymphomas and the efficacy of CNS prophylaxis as well as to discuss the available therapeutic options for this devastating event. Copyright © 2009 John Wiley & Sons, Ltd. [source] On the orbital motion of a rotating inner cylinder in annular flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2007Shunxin Feng Abstract In this paper, numerical calculations have been performed to analyse the influence of the orbital motion of an inner cylinder on annular flow and the forces exerted by the fluid on the inner cylinder when it is rotating eccentrically. The flow considered is fully developed laminar flow driven by axial pressure gradient. It is shown that the drag of the annular flow decreases initially and then increases with the enhancement of orbital motion, when it has the same direction as the inner cylinder rotation. If the eccentricity and rotation speed of the inner cylinder keep unchanged (with respect to the absolute frame of reference), and the orbital motion is strong enough that the azimuthal component (with respect to the orbit of the orbital motion) of the flow-induced force on the inner cylinder goes to zero, the flow drag nearly reaches its minimum value. When only an external torque is imposed to drive the eccentric rotation of the inner cylinder, orbital motion may occur and, in general, has the same direction as the inner cylinder rotation. Under this condition, whether the inner cylinder can have a steady motion state with force equilibrium, and even what type of motion state it can have, is related to the linear density of the inner cylinder. Copyright © 2006 John Wiley & Sons, Ltd. [source] Development and Simulation of an Embedded Hydrogen Peroxide Catalyst Chamber in Low-Temperature Co-Fired CeramicsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2007Donald Plumlee Satellites in the range of 10,50 kg require small propulsion devices to perform station-keeping tasks in orbit. Low-temperature co-fired ceramic structures provide a unique platform to produce a reliable, low-cost micropropulsion system. The design uses microchannels embedded in the ceramic substrate to create a nozzle and embedded catalyst chamber. A hydrogen peroxide monopropellant is injected into a silver-coated catalyst chamber structure. The monopropellant decomposes into hot gas, which is expelled through the nozzle producing thrust. A thermal energy balance and a kinetic model is presented along with performance testing. [source] Performance of delay-sensitive traffic in multi-layered satellite IP networks with on-board processing capabilityINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2007Suzan Bayhan Abstract In this article, performance of delay-sensitive traffic in multi-layered satellite Internet Protocol (IP) networks with on-board processing (OBP) capability is investigated. With OBP, a satellite can process the received data, and according to the nature of application, it can decide on the transmission properties. First, we present a concise overview of relevant aspects of satellite networks to delay-sensitive traffic and routing. Then, in order to improve the system performance for delay-sensitive traffic, specifically Voice over Internet Protocol (VoIP), a novel adaptive routing mechanism in two-layered satellite network considering the network's real-time information is introduced and evaluated. Adaptive Routing Protocol for Quality of Service (ARPQ) utilizes OBP and avoids congestion by distributing traffic load between medium-Earth orbit and low-Earth orbit layers. We utilize a prioritized queueing policy to satisfy quality-of-service (QoS) requirements of delay-sensitive applications while evading non-real-time traffic suffer low performance level. The simulation results verify that multi-layered satellite networks with OBP capabilities and QoS mechanisms are essential for feasibility of packet-based high-quality delay-sensitive services which are expected to be the vital components of next-generation communications networks. Copyright © 2007 John Wiley & Sons, Ltd. [source] Age-associated changes in the amount of subcutaneous tissue in the face evaluated in the ultrasonic B modeINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2005M. Satoh In this study, age-associated changes in facial skin, cosmetologically critical factors, were studied in terms of local subcutaneous fat tissue. The subjects were 98 Japanese females evenly chosen from their teens to 70s. On each subject, the thickness of subcutaneous tissue was determined by the ultrasonic B mode method on four facial sites, forehead, orbit, cheek, and mandible. Age-association of the tissue thickness was facial site-dependent. In the orbit, the subcutaneous tissue became thicker with age, whereas it showed a tendency of thinning in the forehead. No clear age-association was observed in the cheek or the mandible. To analyze the age-association further, the data were stratified into ,lean group' and ,obese group' based on their BMI, and subjected to multiple regression analysis. The age-association in the orbit was much more distinctive in the lean group than in the obese group. [source] Wegener's granulomatosis presenting as pyoderma gangrenosumINTERNATIONAL JOURNAL OF DERMATOLOGY, Issue 11 2003Hajnal Irén Szőcs MD A 59-year-old male patient developed a necrotizing ulceration on the right shin. Both clinical and histopathologic examinations suggested pyoderma gangrenosum. After temporary improvement of skin symptoms under peroral glucocorticoid treatment, a hemorrhagic-purulent discharge started from the nose, he began to have fever, malaise, cough, and a chest X-ray revealed inflammation in the lung. Cerebral CT and MRI disclosed midline bone loss within the nasal septum and granulomatosus tissue masses protruding into the right orbit. The c-ANCA test was positive, serum IgA was elevated, and he had microhaematuria and proteinuria. In this severe case of Wegener's granulomatosis prolonged methylprednisone and cyclophosphamide treatment was initiated. Both the skin symptoms and the granulomatosus infiltrations resolved. [source] Image reconstruction with a shift-variant filtration in circular cone-beam CT,INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 5 2004Lifeng Yu Abstract It is well known that cone-beam data acquired with a circular orbit are insufficient for exact image reconstruction. Despite this, because a cone-beam scanning configuration with a circular orbit is easy to implement in practice, it has been widely employed for data acquisition in, e.g., micro-CT and CT imaging in radiation therapy. The algorithm developed by Feldkamp, Davis, and Kress (FDK) and its modifications, such as the Tent,FDK (T-FDK) algorithm, have been used for image reconstruction from circular cone-beam data. In this work, we present an algorithm with spatially shift-variant filtration for image reconstruction in circular cone-beam CT. We performed computer-simulation studies to compare the proposed and existing algorithms. Numerical results in these studies demonstrated that the proposed algorithm has resolution properties comparable to, and noise properties better than, the FDK algorithm. As compared to the T-FDK algorithm, our proposed algorithm reconstructs images with an improved in-plane spatial resolution. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 213,221, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20026 [source] Non-diagonal MIMO QFT controller design reformulationINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 9 2009Mario Garcia-Sanz Abstract This paper presents a reformulation of the full-matrix quantitative feedback theory (QFT) robust control methodology for multiple-input,multiple-output (MIMO) plants with uncertainty. The new methodology includes a generalization of previous non-diagonal MIMO QFT techniques; avoiding former hypotheses of diagonal dominance; simplifying the calculations for the off-diagonal elements, and then the method itself; reformulating the classical matrix definition of MIMO specifications by designing a new set of loop-by-loop QFT bounds on the Nichols Chart, which establish necessary and sufficient conditions; giving explicit expressions to share the load among the loops of the MIMO system to achieve the matrix specifications; and all for stability, reference tracking, disturbance rejection at plant input and output, and noise attenuation problems. The new methodology is applied to the design of a MIMO controller for a spacecraft flying in formation in a low Earth orbit. Copyright © 2008 John Wiley & Sons, Ltd. [source] Adaptive output feedback tracking control of spacecraft formationINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 2-3 2002Hong Wong Abstract In this paper, an adaptive, output feedback control design methodology is presented for a spacecraft formation flying (SFF) system. A Lagrangian derivation of the SFF model is considered to produce position dynamics for follower spacecraft #n relative to follower spacecraft #(n,1), where n is an arbitrary positive integer, assuming that the leader spacecraft in the formation follows a no-thrust, natural, elliptical orbit. Next, a control law is designed to provide a filtered velocity measurement and a desired adaptive compensation with semi-global, asymptotic, relative position tracking. To show the efficacy of the control algorithm, all desired trajectories are generated online by numerically solving the unperturbed nonlinear SFF dynamics with initial conditions satisfying a no-thrust, natural orbit constraint equation. The proposed control law is simulated for the case of two and three spacecraft and is shown to yield semi-global, asymptotic tracking of the relative position in addition to the convergence of disturbance parameter estimates. Copyright © 2002 John Wiley & Sons, Ltd. [source] Experience with Delay-Tolerant Networking from orbit,INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 5-6 2010W. Ivancic Abstract We describe the first use from space of the Bundle Protocol for Delay-Tolerant Networking (DTN) and lessons learned from experiments made and experience gained with this protocol. The Disaster Monitoring Constellation (DMC), constructed by Surrey Satellite Technology Ltd (SSTL), is a multiple-satellite Earth-imaging low-Earth-orbit sensor network in which recorded image swaths are stored onboard each satellite and later downloaded from the satellite payloads to a ground station. Store-and-forward of images with capture and later download gives each satellite the characteristics of a node in a disruption-tolerant network. Originally developed for the ,Interplanetary Internet,' DTNs are now under investigation in an Internet Research Task Force (IRTF) DTN research group (RG), which has developed a ,bundle' architecture and protocol. The DMC is technically advanced in its adoption of the Internet Protocol (IP) for its imaging payloads and for satellite command and control, based around reuse of commercial networking and link protocols. These satellites' use of IP has enabled earlier experiments with the Cisco router in Low Earth Orbit (CLEO) onboard the constellation's UK-DMC satellite. Earth images are downloaded from the satellites using a custom IP-based high-speed transfer protocol developed by SSTL, Saratoga, which tolerates unusual link environments. Saratoga has been documented in the Internet Engineering Task Force (IETF) for wider adoption. We experiment with the use of DTNRG bundle concepts onboard the UK-DMC satellite, by examining how Saratoga can be used as a DTN ,convergence layer' to carry the DTNRG Bundle Protocol, so that sensor images can be delivered to ground stations and beyond as bundles. Our practical experience with the first successful use of the DTNRG Bundle Protocol in a space environment gives us insights into the design of the Bundle Protocol and enables us to identify issues that must be addressed before wider deployment of the Bundle Protocol. Published in 2010 by John Wiley & Sons, Ltd. [source] Fade correlation and diversity effects in satellite broadcasting to mobile users in S-bandINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 5 2008Albert Heuberger Abstract In this paper, we present measurement results for fade correlation in time and space of signals from two satellites in geostationary orbit with 30° separation. Fade data for urban, residential and rural environments are analyzed. In addition to fade cumulative distribution function, rice factor and coherence length of individual fade signals, also the joint probability density function and the cross-correlation for the fade from the two satellites are presented. The coherence length of single satellite fades extends to about 18,m in the urban area and is around 2,m in the rural area. The correlation coefficient of dual satellite fades is below 0.3 in the residential and rural area. In the urban area larger correlations around 0.7 occur. Based on the measured fade data the diversity gain for various network configurations are determined by simulation for a forward error correction scheme using concatenated codes in combination with random interleavers. Network configurations of interest are single-satellite space diversity, two-satellite space diversity, one-satellite time diversity and two-satellite space and time diversity. For short interleavers of 5,m the diversity gain is in the residential area of 2.3,dB for the two-satellite space diversity, 0.3,dB for one-satellite time diversity and 4.1,dB for two-satellite space and time diversity. Copyright © 2008 John Wiley & Sons, Ltd. [source] A novel QoS routing protocol for LEO and MEO satellite networksINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2007Yunhui Zhou Abstract The rapid advance of communication and satellite technology pushes broadband satellite networks to carry on multimedia traffic. However, the function of onboard routing cannot be provided in existing satellite networks with inter-satellite links, and quality of service (QoS) of satellite networks cannot be reliably guaranteed because of great difficulties in processing of long distance-dependent traffic. In this paper, a two-layered low-Earth orbit and medium-Earth orbit satellite network (LMSN) is presented. A novel hierarchical and distributed QoS routing protocol (HDRP) is investigated, and an adaptive bandwidth-constrained minimum-delay path algorithm is developed to calculate routing tables efficiently using the QoS metric information composed of delays and bandwidth. The performance of LMSN and HDRP is also evaluated through simulations and theoretical analysis. Copyright © 2007 John Wiley & Sons, Ltd. [source] Relay communications for Mars explorationINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2007Charles D. Edwards Telecommunication is an essential and challenging aspect of planetary exploration. For Mars landers, the constraints of mass, volume, power and energy typically limit their communications capabilities on the long-distance link back to Earth. By deploying relay spacecraft in Martian orbit, these landers can achieve much greater data return and can obtain contact opportunities at times when Earth is not in view. Currently, both NASA and European Space Agency (ESA) have pursued this strategy, deploying relay payloads on their Mars science orbiters. This relay infrastructure has significantly benefited the science return from the 2003 Mars Exploration Rovers and is poised to support the Phoenix Lander and Mars Science Laboratory missions later this decade. Longer-term plans call for continued growth in relay capability, greatly increasing data return from the Martian surface to enable exciting new Mars exploration concepts and advance our understanding of our planetary neighbour. Copyright © 2007 John Wiley & Sons, Ltd. [source] Freezing height distribution in the tropicsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2003Merhala Thurai Abstract The calculation of fade margins required to meet the user-specified availability criteria needs to take into consideration a number of meteorological factors specific to the earth-station location. One such factor is the annual average of the freezing level height. Information on this height is available in ITU-R Recommendation P. 839-3, which provides contours that are generated on a 1.5° by 1.5° latitude by longitude resolution grid. This paper compares these heights with the bright-band heights (BBH) obtained from the precipitation radar on-board the TRMM (Tropical Rainfall Measuring Mission) satellite. Four years of TRMM radar data have been analysed, and their averages are compared within the latitude range covered by the satellite orbit (35°N to 35°S). Comparisons show that the radar bright-band heights typically occur 300 m below the 0°C isotherm heights. However, results also indicate that this difference may be latitude dependent. Also examined are the year-to-year variability and the seasonal variation. In the former case, only 1998 showed BBH values which are somewhat higher in tropical regions, this year having had one of the strongest El Nińo events recorded. In the latter case, results show significant seasonal variation, becoming more pronounced at higher latitudes. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||