Objects Of Various Sizes Research Articles

Target‐specific optimization of four‐dimensional cone beam computed tomography

Under-sampling artifacts are a major problem in four-dimensional cone-beam computed tomography (4D-CBCT) and may compromise evaluation of target motion. Several studies have addressed scan parameter selection for minimizing under-sampling artifacts; however, the role of the target characteristics in scan parameter selection has not been investigated. In this work, the authors evaluated 4D-CBCT performance by assessing the accuracy of target motion measurements for various target sizes and motions. The results may serve as patient-specific guidelines for scan parameters selection in 4D-CBCT. The authors acquired 4D-CBCT scans of a moving phantom consisting of six water-filled sphere targets of sizes 10-37 mm, using various scan times ranging from 30 s to 3 min., setting the motion to 3-s and 6-s periods. The authors used automatic image registration to extract the target motion trajectories and evaluated these measurements for various target sizes and motions over various combinations of scan parameters including scan time, detector configuration, number of respiration phases, and reconstruction filters. The most important object parameter to 4D-CBCT performance was the period of motion. Measurements for the 6-s motion were always systematically less accurate than measurements for the 3-s motion for 34 of 36 objects of various sizes and periods of motion. The 6-s motion required a greater scan time than the 3-s motion for equivalent measurement accuracy. The second most influential parameter was the target size. For the 3-s period of motion, objects larger than 13 mm were tracked with sub-millimeter accuracy with a 1-min scan time. For the 6-s period of motion, objects larger than 22-mm were tracked with sub-millimeter accuracy with a 1.5-min scan time. For all sizes and motions, temporal blurring was observed when the number of phases was fewer than 8. Offset detector configuration provided the same performance as centered detector except for small targets (20 mm.) at short scan times (≤1 min). Finally, reconstruction filtering and number of respiratory phases did not affect performance. Scan time should be set according to target size and motion. The authors have provided figures that provide the minimum scan time needed to achieve the particular motion measurement accuracy for a particular size and motion period.

Near-Earth objects from the cometary flux

AbstractWe analyze the orbital distribution of objects captured to near-Earth space from the flux of comets coming from the outer Solar system. For this purpose, we use the model of the cometary cloud developed earlier (Emelfyanenko, Asher, Bailey, 2007). This model is consistent with the broad dynamical characteristics of observed near-parabolic comets, short-period comets, Centaurs and high-eccentricity trans-Neptunian objects. We show that the observed distributions of both large and small near-Earth objects are different from the modeled distribution formed dynamically by the action of planetary perturbations. In particular, while the distributions of arguments of perihelion for observed Jupiter-family comets and modeled cometary asteroids follow a sinusoidal law with pronounced maxima around 0 and 180 degrees, it is not the case for observed cometary asteroids of any size. We conclude that there exist many unobserved extinct short-period comets among near-Earth objects of various sizes.

Imparting functionality to a metal–organic framework material by controlled nanoparticle encapsulation

Microporous metal-organic frameworks (MOFs) that display permanent porosity show great promise for a myriad of purposes. The potential applications of MOFs can be developed further and extended by encapsulating various functional species (for example, nanoparticles) within the frameworks. However, despite increasing numbers of reports of nanoparticle/MOF composites, simultaneously to control the size, composition, dispersed nature, spatial distribution and confinement of the incorporated nanoparticles within MOF matrices remains a significant challenge. Here, we report a controlled encapsulation strategy that enables surfactant-capped nanostructured objects of various sizes, shapes and compositions to be enshrouded by a zeolitic imidazolate framework (ZIF-8). The incorporated nanoparticles are well dispersed and fully confined within the ZIF-8 crystals. This strategy also allows the controlled incorporation of multiple nanoparticles within each ZIF-8 crystallite. The as-prepared nanoparticle/ZIF-8 composites exhibit active (catalytic, magnetic and optical) properties that derive from the nanoparticles as well as molecular sieving and orientation effects that originate from the framework material.

Discovering Thematic Objects in Image Collections and Videos

Given a collection of images or a short video sequence, we define a thematic object as the key object that frequently appears and is the representative of the visual contents. Successful discovery of the thematic object is helpful for object search and tagging, video summarization and understanding, etc. However, this task is challenging because 1) there lacks a priori knowledge of the thematic objects, such as their shapes, scales, locations, and times of re-occurrences, and 2) the thematic object of interest can be under severe variations in appearances due to viewpoint and lighting condition changes, scale variations, etc. Instead of using a top-down generative model to discover thematic visual patterns, we propose a novel bottom-up approach to gradually prune uncommon local visual primitives and recover the thematic objects. A multilayer candidate pruning procedure is designed to accelerate the image data mining process. Our solution can efficiently locate thematic objects of various sizes and can tolerate large appearance variations of the same thematic object. Experiments on challenging image and video data sets and comparisons with existing methods validate the effectiveness of our method.

Saliency Density Maximization for Efficient Visual Objects Discovery

Detection of salient objects in an image remains a challenging problem despite extensive studies in visual saliency, as the generated saliency map is usually noisy and incomplete. In this paper, we propose a new method to discover the salient object without prior knowledge on its shape and size. By searching the sub-image, i.e., a bounding box of maximum saliency density, the new formulation can automatically crop the salient objects of various sizes in spite of the cluttered background, and is capable to handle different types of saliency maps. A global optimal solution is obtained by the proposed density-based branch-and-bound search. The proposed method can apply to both images and videos. Experimental results on a public dataset of 5000 images show that our unsupervised detection approach is comparable to the state-of-the-art learning-based methods. Promising results are also observed in the salient object detection for videos with a good potential in video retargeting.

Limited-angle x-ray luminescence tomography: methodology and feasibility study

X-ray luminescence tomography (XLT) has recently been proposed as a new imaging modality for biological imaging applications. This modality utilizes phosphor nanoparticles which luminesce near-infrared light when excited by x-ray photons. The advantages of this modality are that it uniquely combines the high sensitivity of radioluminescent nanoparticles and the high spatial localization of collimated x-ray beams. Currently, XLT has been demonstrated using x-ray spatial encoding to resolve the imaging volume. However, there are applications where the x-ray excitation may be limited by geometry, where increased temporal resolution is desired, or where a lower dose is mandatory. This paper extends the utility of XLT to meet these requirements by incorporating a photon propagation model into the reconstruction algorithm in an x-ray limited-angle (LA) geometry. This enables such applications as image-guided surgery, where the ability to resolve lesions at depths of several centimeters can be the key to successful resection. The hybrid x-ray/diffuse optical model is first formulated and then demonstrated in a breast-sized phantom, simulating a breast lumpectomy geometry. Both numerical and experimental phantoms are tested, with lesion-simulating objects of various sizes and depths. Results show localization accuracy with median error of 2.2 mm, or 4% of object depth, for small 2–14 mm diameter lesions positioned from 1 to 4.5 cm in depth. This compares favorably with fluorescence optical imaging, which is not able to resolve such small objects at this depth. The recovered lesion size has lower size bias in the x-ray excitation direction than the optical direction, which is expected due to the increased optical scatter. However, the technique is shown to be quite invariant in recovered size with respect to depth, as the standard deviation is less than 2.5 mm. Sensitivity is a function of dose; radiological doses are found to provide sufficient recovery for µg ml−1 concentrations, while therapy dosages provide recovery for ng ml−1 concentrations. Experimental phantom results agree closely with the numerical results, with positional errors recovered within 8.6% of the effective depth for a 5 mm object, and within 5.2% of the depth for a 10 mm object. Object-size median error is within 2.3% and 2% for the 5 and 10 mm objects, respectively. For shallow-to-medium depth applications where optical and radio-emission imaging modalities are not ideal, such as in intra-operative procedures, LAXLT may be a useful tool to detect molecular signatures of disease.

A Self-Sensing Microgripper Module With Wide Handling Ranges

A compliant two-fingered microgripper is designed, fabricated, and demonstrated. To mimic human finger actuation, the proposed finger is distributively actuated by a shape memory alloy (SMA) wire. An SMA-actuated finger model is presented to predict SMA strain and finger motion given its contraction force. Based on this model, the finger shape and SMA wire dimension are optimally designed. The gripper is shown to have a wide handling range, high mechanical advantage, and sufficient out-of-plane stiffness; thus, it can accommodate objects of various sizes and weights. To control its motion, the SMA contraction force is estimated by using the proposed force to electrical resistance model. Gained from the simple driving electronics and self-sensing of SMA, the fabricated gripper can be made compact and lightweight. Finally, a self-powered gripper module is attached to a robot arm to perform several illustrative manipulations.

Human rostral dorsal premotor cortex mediates graspability judgment of external objects by evaluating hand motor capability

Humans can judge whether an object is graspable or not by merely glancing at it. This judgment is possible because of the brain's pragmatic function that links action with perception, i.e., the spatial property of the object is immediately associated with the motor capability of hands. In this study, we investigated the neural correlates of this cognitive-motor process by conducting an event-related functional magnetic resonance imaging experiment. Healthy right-handed participants were made to judge whether they could grasp visually presented objects with their right hand without generating any actual movements [motor evaluation (ME) task]. Objects of various sizes were presented to the participants in front of their hands; they judged the graspability of the object as soon as possible. For the control, the participants simply compared the size of the presented object and the static size of their fists [size comparison (SC) task]. Thus, only in the former task, the participants had to evaluate their motor capability by briefly simulating their range of hand motion. Rostral parts of the dorsal premotor cortices (prePMd) were activated bilaterally only during the ME task, and the activities were positively correlated with the duration of the evaluation. The prePMd participates in the judgment of graspability for external objects by evaluating hand motor capability. This function may assure a basic premise for the selection of an appropriate motor option when our hands interact with a variety of external objects.

Magnetic micro-manipulations to probe the local physical properties of porous scaffolds and to confine stem cells

The in vitro generation of engineered tissue constructs involves the seeding of cells into porous scaffolds. Ongoing challenges are to design scaffolds to meet biochemical and mechanical requirements and to optimize cell seeding in the constructs. In this context, we have developed a simple method based on a magnetic tweezer set-up to manipulate, probe, and position magnetic objects inside a porous scaffold. The magnetic force acting on magnetic objects of various sizes serves as a control parameter to retrieve the local viscosity of the scaffolds internal channels as well as the stiffness of the scaffolds pores. Labeling of human stem cells with iron oxide magnetic nanoparticles makes it possible to perform the same type of measurement with cells as probes and evaluate their own microenvironment. For 18 μm diameter magnetic beads or magnetically labeled stem cells of similar diameter, the viscosity was equivalently equal to 20 mPa s in average. This apparent viscosity was then found to increase with the magnetic probes sizes. The stiffness probed with 100 μm magnetic beads was found in the 50 Pa range, and was lowered by a factor 5 when probed with cells aggregates. The magnetic forces were also successfully applied to the stem cells to enhance the cell seeding process and impose a well defined spatial organization into the scaffold.

Development of a flexure-based, force-sensing microgripper for micro-object manipulation

This paper presents the design and development of a flexure-based microgripper, accompanied with a real-time, vision-based force sensing system to handle objects of various sizes ranging from 100 µm to 1 mm. A simulation-based design methodology is adopted to develop an initial microgripper design, which is then optimized using theoretical modeling. The final prototype developed generated a large stroke length of over 500 µm with high-deflection magnification (ratio of the end deflection (output) to the input deflection) of 3.52. A spring system has been incorporated into the microgripper for easy measurement and control of the gripping forces. The web-camera-based visual system enables real-time force measurement with a resolution of 2.37 mN and can be operated in both manual and automatic modes to control the applied forces. The system has successfully demonstrated gripping of a variety of micro-objects including a 100 µm human hair and a 1 mm steel rod with forces as small as 43 mN and 159 mN, respectively.

Contrast sensitivity of digital imaging display systems: Contrast threshold dependency on object type and implications for monitor quality assurance and quality control in PACS

The American Association of Physicists in Medicine Task Group 18 has published standards and quality control (QC) guidelines to ensure consistency and optimal quality for digital image display systems (DIDSs). In many of these recommended QC tests, static test patterns that contain low-contrast objects are often used to assess and validate the quality of a DIDS. These low-contrast objects often have the shape of circular disks or squares with sharp edges, neither of which resemble most of the diagnostic findings in medical images. On the other hand, circular objects with fuzzy boundaries bear a closer resemblance to lung nodules in chest radiography and masses in mammography; thus, they may be more clinically relevant in assessing display system quality. In this article human observers' contrast sensitivities of circular objects with sharp edges and those with fuzzy ones were investigated. The contrast thresholds of human viewers using a consumer-grade color LCD monitor and a medical-grade monochrome LCD monitor were measured for objects of various sizes displayed against uniform backgrounds with various luminance levels. Contrast-detail curves for circular objects with sharp edges and those with fuzzy boundaries were measured and compared. It was found that contrast thresholds for objects with fuzzy boundaries were higher (i.e., the objects were more difficult to detect) than those with sharp edges. Objects with fuzzy boundaries were potentially more sensitive in distinguishing quality differences among image display devices and thus may be a better QC measurement in detecting subtle deterioration in image display devices.

Measurement of Grasp Position by Humans for Soft-Fingered Robotic Hands

Abstract In this study, we investigate how humans decide the grasping position for contacting objects of various sizes and shapes using two fingers. We propose a grasp criterion that yields the best grasping position for a two soft-fingered robotic hands. The relationship between the grasp direction/angle and the grasping position in a situation where a vertex object is grasped is analyzed numerically by minimizing a proposed performance function. Results show that many observed grasping positions used by humans correspond to a set of weighting coefficients that equally weigh all the factors in the criterion. We set up the hypothesis “The human might like grasping position in which the finger was not greatly intuitively expanded”. This is verified by the numerical optimization and experiments by ten subjects.

Lidar-based Mapping of Forest Volume and Biomass by Taxonomic Group Using Structurally Homogenous Segments

This study evaluated the potential of an object-oriented approach to forest type classification as well as volume and biomass estimation using small-footprint, multiple return lidar data. The approach was applied to coniferous, deciduous, and mixed forest stands in the Virginia Piedmont, U.S.A. A multiresolution, hierarchical segmentation algorithm was applied to a canopy height model (CHM) to delineate objects ranging from 0.035 to 5.632 ha/average object. Per-object lidar point (per return height and intensity) and CHM distributional parameters were used as input to a discriminant classification of 2-class (deciduous-coniferous) and 3-class (deciduous-coniferous-mixed) forest definitions. Lidar point-height-based and CHM classifications yielded overall accuracies of 89 percent and 79 percent, respectively. Volume and biomass estimates exhibited differences of no more than 5.5 percent compared to field estimates, while showing distinctly improved precisions (up to 45.5 percent). There were no significant differences between accuracies for varying object sizes, which implies that reducing the lidar point coverage would not affect classification accuracy. These results lead to the conclusion that a lidar-based approach to forest type classification and volume/biomass assessment has the potential to serve as a single-source inventory tool.

大きな把持力が得られる直動機構

This paper proposes a linear motion mechanism for a robot gripper that can exert a large grasp force. A robot gripper requires speed when opening and closing its jaws, and force when grasping an object. The proposed linear motion mechanism can drive its output quickly to an object and can generate a large grasp force by using a lever. The mechanism has two feed screws with different pitches along one screw shaft. Initially a gear is fastened on the feed screw with the smaller pitch to rotate the shaft. The feed screw with the larger pitch enables quick motion of the output nut. After the output makes contact with an object, the rotation of the shaft stops. By further driving the gear, it becomes loosened and begins to move axially by the feed screw. The gear pushes the lever, which generates a large fingertip force. We have developed an 86g gripper with this mechanism and experimentally verified that it can grasp objects of various sizes and can exert a large grasp force over 200N. It is also experimentally verified that the gripper can grasp and ungrasp an object reliably over 5000 times if machine lubricant is properly supplied.

Identification of land cover alterations in the Alta Murgia National Park (Italy) with VHR satellite imagery

Landcoverexertsagreatinfluenceonmanybasicenvironmentalprocessesandconsequentlyanytransformation in it may have a marked impact on the environment from the local to the global scales. In multidisciplinary research contexts, satellite remote sensing offers opportunities both to evaluate the effects of these processes and to provide one of the information layers needed for designing national strategies oriented to protection and sustainableuseofourresources.Theadventofrecentsatelliteimageryhasincreasedthepossibilitytoinvestigate large-scale areas in great detail. Together with an increase in spatial and radiometric resolution, there is, usually, an increase in the variability within land parcels, generating a decrease in the accuracy of land use classification on a per-pixel basis. In order to avoid such negative impacts, an object-oriented classification methodology on IKONOS multispectral data has been implemented on the test area of the Alta Murgia National Park, in the Apulia region (Italy), where soil adaptation for agricultural practices, through rock breaking, has taken place over the last 20 years. The analysis has been conducted with a classification strategy that is able to distinguish land use functions on the basis of differences in spatial distribution and pattern of land cover forms. It consists of two phases: segmentation of the image into meaningful multipixel objects of various sizes, based on both spectral and spatial characteristics of groups of pixels; then, assignment of the segments (objects) to classes using fuzzy logic and a hierarchical decision key.

Movement kinematics in prehension are affected by grasping objects of different mass

Previous research has identified that prehension is composed of a reach and a grasp component and that the position and size of the object can independently affect each. However, no effects on prior to contact prehension kinematics have been reported for manipulations in object mass. We felt that this 'lack of a finding' was surprising, as a more accurate grip position on heavier objects would prevent slippage and rotation when lifting the object. Therefore, we hypothesized that increased object mass would effect the grasp component movement kinematics prior to contact in preparation for a stable final grip placement on the object. We report two experiments in which participants reached, grasped and lifted objects of various size and mass, and their movement kinematics were recorded using a motion tracking system. The results showed that the mass of the object significantly influenced prior-to-contact grasp kinematics. Both studies showed that the heavy compared to light objects caused increased peak grasp aperture, a final finger and thumb placement on the object that more closely passed through the object centre of mass, increased lift delay and reduced peak lift velocity. The data are discussed in terms of how object mass influences the reach, grasp and lift components of prehensile movement.

Microtubule depolymerization can drive poleward chromosome motion in fission yeast

Prometaphase kinetochores interact with spindle microtubules (MTs) to establish chromosome bi-orientation. Before becoming bi-oriented, chromosomes frequently exhibit poleward movements (P-movements), which are commonly attributed to minus end-directed, MT-dependent motors. In fission yeast there are three such motors: dynein and two kinesin-14s, Pkl1p and Klp2p. None of these enzymes is essential for viability, and even the triple deletion grows well. This might be due to the fact that yeasts kinetochores are normally juxtapolar at mitosis onset, removing the need for poleward chromosome movement during prometaphase. Anaphase P-movement might also be dispensable in a spindle that elongates significantly. To test this supposition, we have analyzed kinetochore dynamics in cells whose kinetochore-pole connections have been dispersed. In cells recovering from this condition, the maximum rate of poleward kinetochore movement was unaffected by the deletion of any or all of these motors, strongly suggesting that other factors, like MT depolymerization, can cause such movements in vivo. However, Klp2p, which localizes to kinetochores, contributed to the effectiveness of P-movement by promoting the shortening of kinetochore fibers.

Computation of lower bounds on the network cost in location problems subject to distance constraints

Methods for the computation of lower bounds on the cost of the connecting network for the continuous and discrete variants of the problem of location of interconnected objects subject to minimal or maximal distances between them are proposed. For the continuous variant, the bound is found by solving a linear programming problem. For the discrete variant, an assignment problem with a rectangular matrix containing forbidden entries is constructed. An application of the assignment problem for locating objects of various sizes is described.

A superelastic alloy microgripper with embedded electromagnetic actuators andpiezoelectric force sensors: a numerical and experimental study

This paper presents the analysis, design, and characterization of a superelastic alloy (NiTi)microgripper with integrated electromagnetic actuators and piezoelectric force sensors. Themicrogripper, fabricated by electro-discharge machining, features force sensing capability,large force output, and large displacements to accommodate objects of various sizes. Thedesign parameters for the embedded electromagnetic actuators were selected on the basis offinite element sensitivity analysis. In order to make the microgripper capable of resolvinggripping forces, piezoelectric force sensors were fabricated and integrated into themicrogripper. The performance of the microgripper, the integrated force sensors,and the electromagnetic actuators was experimentally evaluated. A satisfactorymatch between experimental results and finite element simulations was obtained.Furthermore, comparison studies demonstrated that the superelastic alloy (NiTi)microgripper was capable of producing larger displacement than a stainless steelmicrogripper. Finally, experimental results of optical fiber alignment and themanipulation of tiny biological tissues with the superelastic microgripper were presented.

Short-term plasticity of the visuomotor map during grasping movements in humans

During visually guided grasping movements, visual information is transformed into motor commands. This transformation is known as the "visuomotor map." To investigate limitations in the short-term plasticity of the visuomotor map in normal humans, we studied the maximum grip aperture (MGA) during the reaching phase while subjects grasped objects of various sizes. The objects seen and the objects grasped were physically never the same. When a discrepancy had been introduced between the size of the visual and the grasped objects, and the subjects were fully adapted to it, they all readily interpolated and extrapolated the MGA to objects not included in training trials. In contrast, when the subjects were exposed to discrepancies that required a slope change in the visuomotor map, they were unable to adapt adequately. They instead retained a subject-specific slope of the relationship between the visual size and MGA. We conclude from these results that during reaching for grasping, normal subjects are unable to abandon a straight linear function determining the relationship between visual object size and MGA. Moreover, the plasticity of the visuomotor map is, at least in short term, constrained to allow only offset changes, that is, only "rigid shifts" are possible between the visual and motor coordinate systems.