Concurrent filtering and smoothing: A parallel architecture for real-time navigation and full smoothing

We present a parallelized navigation architecture that is capable of running in real-time and incorporating long-term loop closure constraints while producing the optimal Bayesian solution. This architecture splits the inference problem into a low-latency update that incorporates new measurements using just the most recent states (filter), and a high-latency update that is capable of closing long loops and smooths using all past states (smoother). This architecture employs the probabilistic graphical models of factor graphs, which allows the low-latency inference and high-latency inference to be viewed as sub-operations of a single optimization performed within a single graphical model. A specific factorization of the full joint density is employed that allows the different inference operations to be performed asynchronously while still recovering the optimal solution produced by a full batch optimization. Due to the real-time, asynchronous nature of this algorithm, updates to the state estimates from the high-latency smoother will naturally be delayed until the smoother calculations have completed. This architecture has been tested within a simulated aerial environment and on real data collected from an autonomous ground vehicle. In all cases, the concurrent architecture is shown to recover the full batch solution, even while updated state estimates are produced in real-time.

Cisplatin induces neuronal activation and increases central AMPA and NMDA receptor subunit gene expression in mice

Although rats and mice do not vomit, these species are widely studied as models of energy balance and sickness behavior. Previous work has shown that rats exhibit similar neuroanatomical activation of brain and visceral afferent pathways following cisplatin chemotherapy compared to vomiting species. However, the neural response to cisplatin in mice is understudied. Here, food intake, body weight, and central c-Fos immunofluorescence were analyzed in the hindbrains of male C57BL/6 mice following IP saline or cisplatin (5mg/kg, and 20mg/kg doses). As glutamate receptor signaling is classically linked to inhibitory feeding pathways in the rodent, gene expression of selected α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartic acid (NMDA) receptor subunits were assessed in the dorsal vagal complex (DVC), parabrachial nucleus (PBN), amygdala, and bed nucleus of the stria terminalis (BNST). Our results show dose-dependent reductions in food intake and body weight following cisplatin treatment, as well as increases in cisplatin-induced c-Fos in the PBN and throughout the DVC. Quantitative PCR analysis shows cisplatin-induced increases in NMDA receptor subunit expression, particularly NR2B, in the DVC, PBN, BNST, and amygdala. In addition, upregulation of AMPA receptor subunits (GluA1 and/or GluA2) were observed in all regions examined except the amygdala. Taken together, these results suggest similar neural pathways mediating cisplatin effects in mice compared to other well-studied species, which are likely mediated by central upregulation of AMPA and NMDA receptors.

The MIT Stata Center dataset

This paper presents a large scale dataset of vision (stereo and RGB-D), laser and proprioceptive data collected over an extended duration by a Willow Garage PR2 robot in the 10 story MIT Stata Center. As of September 2012 the dataset comprises over 2.3 TB, 38 h and 42 km (the length of a marathon). The dataset is of particular interest to robotics and computer vision researchers interested in long-term autonomy. It is expected to be useful in a variety of research areas—robotic mapping (long-term, visual, RGB-D or laser), change detection in indoor environments, human pattern analysis, long-term path planning. For ease of use the original ROS ‘bag’ log files are provided and also a derivative version combining human readable data and imagery in standard formats. Of particular importance, this dataset also includes ground-truth position estimates of the robot at every instance (to typical accuracy of 2 cm) using as-built floor-plans—which were carefully extracted using our software tools. The provision of ground-truth for such a large dataset enables more meaningful comparison between algorithms than has previously been possible.

Advanced perception, navigation and planning for autonomous in-water ship hull inspection

Inspection of ship hulls and marine structures using autonomous underwater vehicles has emerged as a unique and challenging application of robotics. The problem poses rich questions in physical design and operation, perception and navigation, and planning, driven by difficulties arising from the acoustic environment, poor water quality and the highly complex structures to be inspected. In this paper, we develop and apply algorithms for the central navigation and planning problems on ship hulls. These divide into two classes, suitable for the open, forward parts of a typical monohull, and for the complex areas around the shafting, propellers and rudders. On the open hull, we have integrated acoustic and visual mapping processes to achieve closed-loop control relative to features such as weld-lines and biofouling. In the complex area, we implemented new large-scale planning routines so as to achieve full imaging coverage of all the structures, at a high resolution. We demonstrate our approaches in recent operations on naval ships.

iSAM2: Incremental smoothing and mapping using the Bayes tree

We present a novel data structure, the Bayes tree, that provides an algorithmic foundation enabling a better understanding of existing graphical model inference algorithms and their connection to sparse matrix factorization methods. Similar to a clique tree, a Bayes tree encodes a factored probability density, but unlike the clique tree it is directed and maps more naturally to the square root information matrix of the simultaneous localization and mapping (SLAM) problem. In this paper, we highlight three insights provided by our new data structure. First, the Bayes tree provides a better understanding of the matrix factorization in terms of probability densities. Second, we show how the fairly abstract updates to a matrix factorization translate to a simple editing of the Bayes tree and its conditional densities. Third, we apply the Bayes tree to obtain a completely novel algorithm for sparse nonlinear incremental optimization, named iSAM2, which achieves improvements in efficiency through incremental variable re-ordering and fluid relinearization, eliminating the need for periodic batch steps. We analyze various properties of iSAM2 in detail, and show on a range of real and simulated datasets that our algorithm compares favorably with other recent mapping algorithms in both quality and efficiency.

Cooperative AUV Navigation using a Single Maneuvering Surface Craft

In this paper we describe the experimental implementation of an online algorithm for cooperative localization of submerged autonomous underwater vehicles (AUVs) supported by an autonomous surface craft. Maintaining accurate localization of an AUV is difficult because electronic signals, such as GPS, are highly attenuated by water. The usual solution to the problem is to utilize expensive navigation sensors to slow the rate of dead-reckoning divergence. We investigate an alternative approach that utilizes the position information of a surface vehicle to bound the error and uncertainty of the on-board position estimates of a low-cost AUV. This approach uses the Woods Hole Oceanographic Institution (WHOI) acoustic modem to exchange vehicle location estimates while simultaneously estimating inter-vehicle range. A study of the system observability is presented so as to motivate both the choice of filtering approach and surface vehicle path planning. The first contribution of this paper is to the presentation of an experiment in which an extended Kalman filter (EKF) implementation of the concept ran online on-board an OceanServer Iver2 AUV while supported by an autonomous surface vehicle moving adaptively. The second contribution of this paper is to provide a quantitative performance comparison of three estimators: particle filtering (PF), non-linear least-squares optimization (NLS), and the EKF for a mission using three autonomous surface craft (two operating in the AUV role). Our results indicate that the PF and NLS estimators outperform the EKF, with NLS providing the best performance.

The effect of steady-state increases in systemic arterial pressure on the duration of left ventricular ejection time

The effect of steady-state increases in systemic arterial pressure on the duration of left ventricular ejection time was studied in 11 normal male subjects. Methoxamine, a pressor amine of predominantly vasoconstrictor activity but lacking significant inotropic effect, was administered intravenously resulting in an average increase in mean arterial pressure of 27 mm Hg. Heart rate was held constant by high right atrial pacing, and there was no significant change in cardiac output. During methoxamine infusion, when stroke volume, heart rate, and inotropic state were held constant, left ventricular ejection time increased as mean arterial pressure increased. There was a highly significant correlation between the increase in mean systolic blood pressure and the prolongation of left ventricular ejection time (r = 0.870). In one subject, an increase in mean systolic pressure of 75 mm Hg prolonged left ventricular ejection time 55 msec, producing paradoxical splitting of the second heart sound. The prolongation of left ventricular ejection time during infusion was not blocked by the prior intravenous administration of atropine sulfate or propranolol hydrochloride, thus ruling out both vagal inhibition of the left ventricle and reflex withdrawal of sympathetic tone as its cause. In three subjects, left ventricular end diastolic pressure was measured and found to be significantly increased. This finding suggests that the normal left ventricle maintains a constant stroke volume in the presence of an increased pressure load by the Frank Starling mechanism. This study concludes that arterial pressure must be included as a prime determinant of left ventricular ejection time along with stroke volume, heart rate, and inotropic state in intact man.

Effects of age of cattle, turning technology and compost environment on disappearance of bone from mortality compost

As residual bones in mortality compost negatively impact subsequent tillage, two studies were performed. For the first study, windrows of mature cattle or calves were placed on a base of barley straw and covered with beef manure. Windrows were divided into two sections and turned at 3-month intervals. Approximately 5000 kg of finished compost per windrow was passed through a 6mm trommel screen, with bones collected and weighed. Bone weight was 0.66% of mature cattle compost and 0.38% of calf compost on a dry matter basis, but did not differ after adjustment for weights of compost ingredients. In a subsequent study, four windrows were constructed containing mortalities, straw and beef manure (STATC) or straw, manure and slaughter waste (STATW). Also, straw, beef manure and slaughter waste was added to an 850 L rolling drum composter (DRUMW). Fresh bovine long-bones from calves were collected, weighed and embedded in the compost. Bones were retrieved and weighed when windrows were turned, or with DRUMW, after 8 weeks. Temperatures achieved followed the order STATW>STATC>DRUMW (p<0.05). Rate of bone disappearance followed a pattern identical to temperature, with the weight of bones in STATW declining by 53.7% during 7 weeks of composting. For STATC, temperatures were uniform over three composting periods, but bone disappearance was improved (p<0.05) when compost dry matter was lower (46%), as compared to 58%. Using a ratio of five parts manure to one part mortalities, results of this study demonstrated that residual bone was <1% of cured cattle compost and may be reduced by maintaining a high compost temperature and moisture content.

Cooperative Localization for Autonomous Underwater Vehicles

This paper describes an algorithm for distributed acoustic navigation for Autonomous Underwater Vehicles (AUVs). Whereas typical AUV navigation systems utilize pre-calibrated arrays of static transponders, our work seeks to create a fully mobile network of AUVs that perform acoustic ranging and data exchange with one another to achieve cooperative positioning for extended duration missions over large areas. The algorithm enumerates possible solutions for the AUV trajectory based on dead-reckoning and range-only measurements provided by acoustic modems that are mounted on each vehicle, and chooses the trajectory via minimization of a cost function based on these constraints. The resulting algorithm is computationally efficient, meets the strict bandwidth requirements of available AUV modems, and has potential to scale well to networks of large numbers of vehicles. The method has undergone extensive experimentation, and results from three different scenarios are reported in this paper, each of which utilizes MIT SCOUT Autonomous Surface Craft (ASC) as convenient platforms for testing. In the first experiment, we utilize three ASCs, each equipped with a Woods Hole acoustic modem, as surrogates for AUVs. In this scenario, two ASCs serve as Communication/Navigation Aids (CNAs) for a third ASC that computes its position based exclusively on GPS positions of the CNAs and acoustic range measurements between platforms. In the second scenario, an undersea glider is used in conjunction with two ASCs serving as CNAs. Finally, in the third experiment, a Bluefin12 AUV serves as the target vehicle. All three experiments demonstrate the successful operation of the technique with real ocean data.

Influence of carbon and buffer amendment on ammonia volatilization in composting

Laboratory-scale experiments were carried out to test a mathematical model of the nitrogen dynamics in a composting process. The main ingredients of composting materials were wheat straw and dairy manure. The influence of (a) two carbon amendments, i.e. molasses and office paper, and (b) two chemicals forming buffer solutions on ammonia volatilization were investigated. Nitrogen losses amounted to 12-25% of initial nitrogen, in which ammonia volatilization accounted for 60-99%. Addition of molasses, a readily available form of carbon, reduced cumulative ammonia emissions substantially, but office paper, i.e. cellulose, had only a small influence. The addition of buffering chemicals did not significantly reduce ammonia volatilization.

Effect of peptide concentration and temperature on leuprolide stability in dimethyl sulfoxide

The effects of temperature and concentration on leuprolide degradation in dimethyl sulfoxide (DMSO) were explored. Leuprolide degradation products were analyzed by reverse phase high-performance liquid chromatography (RP-HPLC), size exclusion chromatography (SEC) and structurally characterized by mass spectrometry. Leuprolide solution stability in DMSO was characterized at 50, 100, 200, 400 mg/ml at 37-80 degrees C for 2 months to 3 years. Leuprolide degradation products were identified by mass spectrometry and could generally be attributed to isomerization, hydrolysis, oxidation, or aggregation. The hydrolytic degradation products consisted primarily of backbone cleavage C-terminal to Trp(3), Ser(4), Tyr(5), Leu(6) and Leu(7), and oxidation of Trp(3) and beta-elimination of Ser(4) were identified. Leuprolide degradation at 50 degrees C, 65 degrees C and 80 degrees C proceeded in an exponential fashion (E(a)=22. 6+/-1.2 kcal/mol); however, leuprolide degradation plateau'd after approximately 6 months at 37 degrees C. Upon closer examination, degradation product peak areas were seen to vary with temperature. For example, aggregation products did not increase with time at 37 degrees C, but aggregation peak intensities increased sharply with time at 80 degrees C. Increasing the temperature also increased the proportion of leuprolide degrading via isomerization/hydrolytic pathways, and decreased the proportion degrading via oxidation. These variations suggested that solvent dielectric, free H(+) in an aprotic solvent, oxygen solubility, impurities and residual moisture may play a role. Leuprolide solubilized in DMSO yields adequate stabililty for a 1 year implantable osmotic delivery system, where use of a dry aprotic solvent results in conditions similar to solid state stability.

Characterization and comparison of leuprolide degradation profiles in water and dimethyl sulfoxide

The effect of solvent on the rate of leuprolide degradation and on the structure of the degradation products was explored. Leuprolide solutions (370 mg/mL) were prepared in water and dimethyl sulfoxide (DMSO) for delivery in DUROS osmotic implants. Both solvent systems demonstrated better than 90% stability after 1 year at 37 degrees C, where the DMSO formulation afforded better stability than the aqueous formulation and was used in subsequent clinical trials. The rate of leuprolide degradation in DMSO was also observed to accelerate with increasing moisture content, indicating that the aprotic solvent minimized chemical degradation. Interestingly, leuprolide degradation products varied with formulation vehicle. The proportions of leuprolide degradation products observed to form in water and DMSO at 37 degrees C were hydrolysis > aggregation > isomerization > oxidation and aggregation > oxidation > hydrolysis > isomerization, respectively. Specifically, more N-terminal hydrolysis and acetylation were observed under aqueous conditions, and increased Trp oxidation and Ser beta-elimination were seen under non-aqueous conditions. Furthermore, the major chemical degradation pathway changed with temperature in the DMSO formulation (decreasing oxidation with increasing temperature), but not in the aqueous formulation.

Surgical intervention in acute myocardial infarction: an historical perspective

Acute myocardial infarction is an evolving event that lends itself well to surgical intervention. An historical review of surgery of acute myocardial infarction, with specific emphasis on the Spokane data, shows that this can be done safely and efficiently with myocardial salvage. Those people who were operated on within 6 hours of the onset of symptoms of acute myocardial infarction had a clear reduction in hospital mortality incidence and a better long-term result. The conclusion of our review is that emergency coronary artery bypass grafting for acute evolving myocardial infarction should be considered as a therapeutic option in every patient. All other modalities of therapy should be compared with the results of acute bypass surgery.

Adult cardiology and the expanding supply of physicians

The number of cardiologists can be projected with considerable accuracy into the next century. The total cardiology pool of physicians will increase until the year 2015 at which time those entering and leaving the pool will come into equilibrium. At that time the ratio of active cardiologists to the population will have greatly increased. This nation's future need for cardiologists is difficult to assess with any degree of precision. Therefore, this is the time for updating practice profile studies. Such studies today could be formulated in a manner to provide more detailed information on the cardiologist's daily activities. In addition, a data base developed through methodology such as the consensus formation approach must be developed and updated on a periodic basis. Through such analyses it will be possible to quantitate the future needs of cardiovascular manpower.