Multiassignment for tracking a large number of overlapping objects[and application to fibroblast cells]

In this paper we present a new technique for data association using multiassignment for tracking a large number of closely spaced (and overlapping) objects. The algorithm is illustrated on a biomedical problem, namely the tracking of a group of fibroblast (tissue) cells from an image sequence, which motivated this work. Because of their proximity to one another and due to the difficulties in segmenting the images accurately from a poor-quality image sequence, the cells are effectively closely spaced objects (CSOs). The algorithm presents a novel dichotomous, iterated approach to multiassignment using successive one-to-one assignments of decreasing size with modified costs. The cost functions, which are adjusted depending on the “depth” of the current assignment level and on the tracking results, are derived. The resulting assignments are used to form, maintain and terminate tracks with a modified version of the probabilistic data association (PDA) filter, which can handle the contention for a single measurement among multiple tracks in addition to the association of multiple measurements to a single track. Estimation results are given and compared with those of the standard 2D one-to-one assignment algorithm. It is shown that iterated multiassignment results in superior measurement-to-track association. The algorithms presented can be used for other general tracking problems, including dense air traffic surveillance and control     

Sedimentable amyloplasts in starch sheath cells of woody stems of Japanese cherry.

We examined whether sedimentable amyloplasts act as statolith in the perception of gravity in woody stems using the elongated internodes of Japanese cherry (Prunus jamasakura Sieb. ex Koidz.). In the internode of the seedlings grown on earth, amyloplasts were found sedimented at the distal end of each cell of the endodermal starch sheath tissue. In the internode grown on three-dimensional (3-D) clinostat, amyloplasts were dispersed throughout the cell matrix in the endodermal starch sheath tissue. After changing the positions of the internode from vertical to horizontal, re-sedimentation of amyloplasts toward the direction of gravity was completed in 1h, whereas the bending of the internode was observed after 12 days. We propose that sedimentable amyloplasts in the endodermal starch sheath cells may play a role in gravity perception leading to secondary xylem formation in the secondary thickening growth and eccentric growth in gravi-bending of tree stems.     

Software approach to access UWB interference on GPS receivers

Ever since the FCC approved the use of UWB devices in commercial and federal bands, various agencies whose operations and/or products rely on the integrity of signals within certain "restricted" radio frequency bands have voiced concerns over the potential impact of the UWB interference. GPS signals are among these "restricted" bands. Several groups in the GPS community have conducted experimental studies concerning the impact of UWB interference on the performance of various grades of commercial and aviation GPS receivers. In this paper, we present a software approach to simulate and evaluate UWB interference on GPS receivers. The software approach provides greater flexibility in the design of testing scenarios, such as the inclusion of a large number of aggregated UWB devices, the generation of new UWB signals and modulation schemes, and the possibility of extending the study to new GPS signals. The paper discusses a general framework for developing algorithms to evaluate UWB and GPS interference under a wide variety of hardware and software conditions. This framework consists of three classes of components: input, processing, and analysis. The input components are responsible for the generation of UWB signal waveforms and modulation schemes, and GPS signals. The processing components include a simulated model of GPS RF front end and software implementation of GPS processing blocks, such as acquisition, tracking, and post-processing. The analysis components focus on the study of specific receiver processing component outputs. Both real and simulated UWB signals can be used in the study. The real UWB signals are primarily used to validate the simulation procedure, whereas the simulated UWB signals are used to allow the immediate incorporation of new UWB waveforms and modulations in the evaluations. This paper presents details of the software components developed and the preliminary results achieved     

Hard X-ray focusing optics up to 80 keV for the future missions

X-ray telescopes have been providing high sensitivity X-ray observations in numerous missions. For X-ray telescopes in the future, one of the key technologies is to expand the energy band beyond 10 keV. We designed depth-graded multilayer, so-called supermirrors, for a hard X-ray telescope in the energy band up to 40 keV using lightweight thin-foil optics. They were successfully flown in a balloon flight and obtained a hard X-ray image of Cyg X-1 in the 20–40 keV band. Now supermirrors are promising to realize a hard X-ray telescope. We have estimated the performance of a hard X-ray telescope using a platinum–carbon supermirror for future satellite missions, such as NeXT (Japan) and XEUS (Europe). According to calculations, they will have a significant effective area up to 80 keV, and their effective areas will be more than 280 cm² even at 60 keV. Limiting sensitivity will be down to 1.7 × 10⁻¹³ erg cm⁻² s⁻¹ in the 10–80 keV band at a 100 ks observation. In this paper, we present the results of the balloon experiment with the first supermirror flown and projected effective areas of hard X-ray telescopes and action items for future missions.     

New assignment-based data association for tracking move-stop-move targets

We present a new assignment-based algorithm for data association in tracking ground targets employing evasive move-stop-move maneuvers using ground moving target indicator (GMTI) reports obtained from an airborne sensor. To avoid detection by the GMTI sensor, the targets deliberately stop for some time before moving again. The sensor does not detect a target when the latter's radial velocity (along the line-of-sight from the sensor) falls below a certain minimum detectable velocity (MDV). Even in the absence of move-stop-move maneuvers, the detection has a less-than-unity probability (P/sub D/<1) due to obscuration and thresholding. Then, it is of interest, when a target is not detected, to develop a systematic technique that can distinguish between lack of detection due to P/sub D/<1 and lack of detection due to a stop (or a near stop). Previously, this problem was solved using a variable structure interacting multiple model (VS-IMM) estimator with a stopped target model (VS-IMM-ST) without explicitly addressing data association. We develop a novel "two-dummy" assignment approach for move-stop-move targets that considers both the problem of data association as well as filtering. Typically, in assignment-based data association a "dummy" measurement is used to denote the nondetection event. The use of the standard single-dummy assignment, which does not handle move-stop-move motion explicitly, can result in broken tracks. The new algorithm proposed here handles the evasive move-stop-move motion by introducing a second dummy measurement to represent nondetection due to the MDV. We also present a likelihood-ratio-based track deletion scheme for move-stop-move targets. Using this two-dummy data association algorithm, the track corresponding to a move-stop-move target is kept "alive' during missed detections both due to MDV and due to P/sub D/<1. In addition, one can obtain reductions in both rms estimation errors as well as the total number of track breakages.     

Longevity in space; experiment on the life span of Paramecium cell clone in space.

Life span is the most interesting and also the most important biologically relevant time to be investigated on the space station. As a model experiment, we proposed an investigation to assess the life span of clone generation of the ciliate Paramecium. In space, clone generation will be artificially started by conjugation or autogamy, and the life span of the cell populations in different gravitational fields (microgravity and onboard 1 x g control) will be precisely assessed in terms of fission age as compared with the clock time. In order to perform the space experiment including long-lasting culture and continuous measurement of cell division, we tested the methods of cell culture and of cell-density measurement, which will be available in closed environments under microgravity. The basic design of experimental hardware and a preliminary result of the cultivation procedure are described.     

Retinal photoreceptor and related gene expression in normal and clinostat-treated fish embryos

Medaka fish had performed mating behavior successfully in space for the first time among vertebrate, and the eggs which were laid in space developed normally, and hatched during the space travel of 15 days aboard the space shuttle in the second International Microgravity Laboratory (IML-2) mission in 1994 (Ijiri 1994). But there has been few studies whether microgravity affects the development of rather complex tissues in this fish. Investigating this problem, we focused on the organogenetic events in the retina in developing Medaka under normal and simulated microgravity conditions (by a three-dimensional clinostat, 3D-clinostat). Our results showed that both normal and 3D-clinostat-treated Medaka embryos developed on almost equal time course. Moreover, we investigated the development of the retina in normal and 3D-clinostat-treated embryos, but there were no differences in organogenesis of their retina. Lamination of retina occurred almost at equal timing and the expressions of opsin genes in the 3D-clinostat-treated group also began almost at the same time as control. Our observations suggest that there were no definite effects of simulated microgravity on the organizations of a complex tissue such as retina in developing fish embryos.     

Arctic — Antarctic night airglow comparisons

Airglow observations from Eureka, Canada (80° N) and South Pole (90° S) observatories have been made through the winters during the past 1/2 solar cycle. Seasonal and solar activity changes are evident. The intensities also show temporal variations due to wave activity, with periods from 6 hours to 15 days, particularly in the Arctic OI and Na emissions. Comparisons are made of the OH intensities measured at Eureka and South Pole during their respective winters.     

The structure of Kelvin–Helmholtz vortices with super-sonic flow

We have done two-dimensional simulations of the Kelvin–Helmholtz instability (KHI) with super-sonic flow using the CIP method. The linear analyses of a simple uniform density case show that the KHI cannot grow vigorously when the velocity jump is more than twice the sound speed (when the flow speed relative to the vortex is super-sonic). In this study, by situating a high density contrast across the shear layer, we set the flow in only one of the sides to be super-sonic and then show that the KHI does grow and rolls up a vortex. The formation of a shock is essential for the KHI vigorous growth and the structure of the vortex is strongly influenced by the shock geometry. The results should have substantial implications to velocity shear layer dynamics involving large density jump, such as planetary magnetospheric boundary layers.