Three-axis attitude determination via Kalman filtering of magnetometer data

A three-axis Magnetometer/Kalman Filter attitude determination system for a spacecraft in low-altitude Earth orbit is developed, analyzed, and simulation tested. The motivation for developing this system is to achieve light weight and low cost for an attitude determination system. The extended Kalman filter estimates the attitude, attitude rates, and constant disturbance torques. Accuracy near that of the International Geomagnetic Reference Field model is achieved. Covariance computation and simulation testing demonstrate the filter's accuracy. One test case, a gravity-gradient stabilized spacecraft with a pitch momentum wheel and a magnetically-anchored damper, is a real satellite on which this attitude determination system will be used. The application to a nadir pointing satellite and the estimation of disturbance torques represent the significant extensions contributed by this paper. Beyond its usefulness purely for attitude determination, this system could be used as part of a low-cost three-axis attitude stabilization system

Autonomous Magnetic Navigation for Earth Orbiting Spacecraft

The strength and orientation of the Earth\u27s magnetic field varies as a function of the location of the observations, which means that the magnetic field measurements contains position information. Many artificial satellites carry a magnetometer on-board. The local magnetic field measurements could be used to provide navigation information. Such a navigation method has the advantage of requiring only data from low cost on-board instruments and has applications in low budget operation of satellite systems. Furthermore if processing can be performed on-board, this method leads to the possibility of fully autonomous long term navigation. In many systems magnetic navigation could be an effective back-up. To study the feasibility and potential performance of spacecraft magnetic navigation, the concept was investigated using two possible approaches. In a first configuration the magnetic field orientation is assumed to be complemented by measurements of the Nadir direction provided by an Earth horizon sensor on board; the two vectors form the basis of a space sextant. In the second configuration magnetic field magnitude is the sole source of external information

Active Magnetic Control System for Gravity Gradient Stabilized Spacecraft

Active magnetic control is studied as a means to improve the capabilities and performance of gravity gradient stabilized spacecraft. Active magnetic control eliminates the need for a passive damper and can reduce significantly the costs and complexity of other functional parts of the spacecraft. The system under study includes three magnetic torquers, one three-axis magnetometer, and a control processor. It does not require any moving parts, and provides for rapid libration damping, tighter stabilization and active control of the yaw angle. Control algorithms are defined. Results of the analysis of the control laws and computer simulations, including high-order models of the geomagnetic field and atmospheric disturbance torques, are presented. The algorithms perform well within a wide range of orbital inclinations and attitude angles and allow maneuverability and stabilization around the yaw axis. A Kalman Filter is used to provide estimates of the attitude angles, the angular rates, and a global disturbance torque, based on measurements from the magnetometer. Results of simulations, including the attitude estimator in the control loop, are presented. The possibility of a fully autonomous acquisition, deployment, and stabilization sequence using the magnetic control system is discussed

The dual nature of identity fusion : a unifying force or a source of division?

Identity plays a key role in determining what matters to people and what they are willing to fight for. Identity fusion, an extreme form of identification where one's personal self is unified with an abstraction (a group, cause, or other individual), predicts extreme behaviors in defense of the target of fusion. In the face of a perceived threat to one's fused group, fused individuals often react harshly against the source of the threat, such as by endorsing violence against outgroups. However, identity fusion does not necessitate hostility toward outgroups. Indeed, some work suggests that in the absence of threat, fused individuals can be benign towards outgroup members. The demarcation between when fusion might have prosocial outcomes for the larger society as opposed to antisocial outcomes against perceived outgroup members is in need of further exploration, especially in the highly divided modern American political landscape. Therefore, the purpose of this dissertation is to further investigate the nature of identity fusion and when fusion might have a unifying influence as opposed to a divisive one. Across four lines of research, the current work examined (1) whether identity fusion is a more potent predictor of extreme behaviors in the political sphere than rival constructs such as moral convictions or sacred values (Chapter 2), (2) whether fusion with a partisan identity such as a political party positively predicts extreme behaviors that could potentially increase the power of the partisan group, but may be detrimental to the larger society (Chapters 3-5), and (3) whether fusion with a superordinate group such as one's nation or even all of humanity negatively predicts behaviors that may harm the larger society, even if such behaviors might myopically benefit one's political party. Findings from Chapter 2 provide evidence that identity fusion is the strongest predictor of extreme behavior on behalf of a political cause. Findings from Chapters 3-5 show that fusion with a political party or candidate positively predicts support for authoritarian actions against the opposing party, while fusion with the US negatively predicts the same authoritarianism. In Chapter 5, writing about a patriotic memory increased fusion with the US among Republicans, and fusion with the US marginally interacted with the patriotic prime manipulation to predict decreased support for authoritarianism among both Republicans and Democrats. Taken together, these findings shed valuable insight into the dual nature of identity fusion as both a unifying force and a source of division.Psycholog

The Space System for the High Energy Transient Experiment

The High Energy Transient Experiment (HETE) is an astrophysics project funded by NASA and led by the Center for Space Research (CSR) at the Massachusetts Institute of Technology (MIT). It has for principal goal the detection and precise localization of the still mysterious sources of gamma ray bursts. The project is original in many respects. HETE will provide simultaneous observations of bursts in the gamma, X-ray and UV ranges from the same small (250 Ibms) space platform. A network of ground stations around the world will diffuse in real time key information derived from HETE observations to many ground observatories, allowing quick follow-on observations with ground instruments. The whole project is entirely managed by MIT, under top level NASA supervision, and satellite and ground stations will be remotely operated from CSA. The HETE system development is conducted with a small budget and under a short schedule

Remote Access Observatories in Low Earth Orbit -A Low-Cost Concept for a Small Scientific Spacecraft

In parallel with the evolution of large observatory spacecraft such as the Einstein, Copernicus, and IUE, and the yet-to-be-Iaunched Hubble Space Telescope and Gamma Ray Observatory, Increasingly large ground telescopes are in construction which will allow ground astronomy to compete favorably with elaborate and expensive space systems in the quest for new discoveries. Sometimes overlooked in this pursuit of new discoveries, with the limited observational time on the space Instruments, or the oversubscribed large ground Instruments, Is the recent development of smaller, low-cost robotic ground observatories designed for routine - but vital - collection of synoptic data. High-quality stellar observations are now being made by exploitation of new computer and detector technologies in unattended remote ground observatories, typically by modest aperture Instruments tailored to the Job. These Instruments operate in modes similar to those employed in the observatory spacecraft. Recent developments In the small satellite technology, some being reported at this conference, allow a reduced cost of payload delivery Into orbit and suggest that another look Is deserved at the 1960s\u27 concept of small astronomical satellites, which would be operable by simple command systems to conduct monitoring of variable, flare, and cataclysmic stars, perhaps limited only to precision filter photometry or simple Imaging In wavelengths not accessible from the ground. These would allow conduct of bread-and-butter astronomy at and accuracies wavelengths available only In space on objects Identified by the larger research Instruments, undertaking science too costly to pursue over long periods with multi-billion dollar systems. This paper will explore small spacecraft provided with low-cost attitude systems (LCAS) for stabilization, modest telescope optics, and low-power communications and spacecraft computer sub-systems which could perform autonomous celestial acquisitions and photometric data collection

Development and Validation of a Predictive Risk Score for Blood Transfusion in Patients Undergoing Curative-Intent Surgery for Intrahepatic Cholangiocarcinoma

Background and Objectives: Among patients undergoing liver resection for intrahepatic cholangiocarcinoma (ICC), perioperative bleeding requiring blood transfusion is a common complication, yet preoperative identification of patients at risk for transfusion remains challenging. The objective of this study was to develop a preoperative risk score for blood transfusion requirement during surgery for ICC. Methods: Patients undergoing curative-intent liver surgery for ICC (1990–2020) were identified from a multi-institutional database. A predictive model was developed and validated. An easy-to-use risk calculator was made available online. Results: Among 1420 patients, 300 (21.1%) received an intraoperative transfusion. Independent predictors of transfusion included severe preoperative anemia (OR = 1.65, 95% CI 1.10–2.47), T2 category or higher (OR = 2.00, 95% CI 1.36–3.02), positive lymph nodes (OR = 1.75, 95% CI 1.32–2.32) and major resection (OR = 2.56, 95%CI 1.85–3.58). Receipt of blood transfusion significantly correlated with worse outcomes. The model showed good discriminative ability in both training (AUC = 0.68, 95% CI 0.66–0.72) and bootstrapping validation (C-index = 0.67, 95% CI 0.65–0.70) cohorts. An online risk calculator of blood transfusion requirement was developed (https://catalano-giovanni.shinyapps.io/TransfusionRisk). Conclusions: Intraoperative blood transfusion was significantly associated with poor postoperative outcomes among patients undergoing surgery for ICC. The identification of patients at high risk of transfusion could improve perioperative patient care and blood resources allocation.</p

Early Onset Intrahepatic Cholangiocarcinoma:Clinical Characteristics, Oncological Outcomes, and Genomic/Transcriptomic Features

Introduction: Data on clinical characteristics and disease-specific prognosis among patients with early onset intrahepatic cholangiocarcinoma (ICC) are currently limited. Methods: Patients undergoing hepatectomy for ICC between 2000 and 2020 were identified by using a multi-institutional database. The association of early (≤50 years) versus typical onset (&gt;50 years) ICC with recurrence-free (RFS) and disease-specific survival (DSS) was assessed in the multi-institutional database and validated in an external cohort. The genomic and transcriptomic profiles of early versus late onset ICC were analyzed by using the Total Cancer Genome Atlas (TCGA) and Memorial Sloan Kettering Cancer Center databases. Results: Among 971 patients undergoing resection for ICC, 22.7% (n = 220) had early-onset ICC. Patients with early-onset ICC had worse 5-year RFS (24.1% vs. 29.7%, p &lt; 0.05) and DSS (36.5% vs. 48.9%, p = 0.03) compared with patients with typical onset ICC despite having earlier T-stage tumors and lower rates of microvascular invasion. In the validation cohort, patients with early-onset ICC had worse 5-year RFS (7.4% vs. 20.5%, p = 0.002) compared with individuals with typical onset ICC. Using the TCGA cohort, 652 and 266 genes were found to be upregulated (including ATP8A2) and downregulated (including UTY and KDM5D) in early versus typical onset ICC, respectively. Genes frequently implicated as oncogenic drivers, including CDKN2A, IDH1, BRAF, and FGFR2 were infrequently mutated in the early-onset ICC patients. Conclusions: Early-onset ICC has distinct clinical and genomic/transcriptomic features. Morphologic and clinicopathologic characteristics were unable to fully explain differences in outcomes among early versus typical onset ICC patients. The current study offers a preliminary landscape of the molecular features of early-onset ICC.</p

Effects of fro and HzO on andesite phase relations between 2 and 4 kbar

International audienceExperimentalp hasee quilibriah ave been investigatedo n three medium-K silicic andesite (60-61 wt % SiO2) samples from Mount Pelhe at 2-4 kbar, 850-1040øC, under both vapor-saturatedC O2-freea nd vapor-saturatedC O2-bearingc onditions.M ost experiments were crystallizatione xperimentsu singd ry glassesp reparedf rom the naturalr ocks.B oth normal-a nd rapidq uenche xperimentsw ere performed.T wo rangeso f oxygenf ugacity( fo2) were investigatedN: NO (Ni-NiO buffer) to NNO + 1 and NNO + 2 to NNO + 3. At 2 kbar for moderatelyo xidizing conditionsp, lagioclase( pl) and magnetite( mt) are the liquidus phases, followed by low-Ca pyroxene (opx); these three phases coexist over a large temperature( T)-H20 range( 875-950øC and 5-7 wt % H20 in melt). Amphibole (am) is stable undern ear vapor-saturatedC O2-freec onditionsa t 876øC. At 900øC, ilmenite (ilm) is found only in experimentsle sst hano r equalt o NNO. Upon increasingp ressure( P) underv aporsaturatedC O2-freec onditionsp, l + mt is replacedb y am + mt on the liquidusa bove3 .5 kbar. For highly oxidizingc onditionsm, t is the solel iquidusp hasea t 2 kbar, followed by pl and opx, except in the most H20-rich part of the diagram at 930øC, where opx is replaced by Carich pyroxene( cpx) and am. Compositionso f ferromagnesianp hasess ystematicallyc orrelate with changingfo2E xperimentalg lassesr angef rom andesitict hroughd acitict o rhyolitic, showings ystematicc ompositionavl ariationsw ith pl + opx + mt fractionation( increaseo f SiO2a ndK 20,d ecreasoef A1203C, aO,F eOt, andM gO).F eO*/MgOm oderateilnyc reases with increasingS iO2.F orfo2 conditionst ypical of calk-alkalinem agmatism( approximately NNO + 1), magnetite is either a liquidus or a near-liquidus phase in hydrous silicic andesite magmas,a nd this shoulds timulater eexaminationfo r the mechanismso f generationo f andesitesb y fractionationf rom basalticp arents

Barrett's esophagus: clinical features, obesity, and imaging

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87127/1/j.1749-6632.2011.06044.x.pd