Material Composition Of Objects Research Articles

Dual-energy computed tomography imaging with megavoltage and kilovoltage X-ray spectra.

Single-energy computed tomography (CT) often suffers from poor contrast yet remains critical for effective radiotherapy treatment. Modern therapy systems are often equipped with both megavoltage (MV) and kilovoltage (kV) X-ray sources and thus already possess hardware for dual-energy (DE) CT. There is unexplored potential for enhanced image contrast using MV-kV DE-CT in radiotherapy contexts. A single-line integral toy model was designed for computing basis material signal-to-noise ratio (SNR) using estimation theory. Five dose-matched spectra (3kV, 2 MV) and three variables were considered: spectral combination, spectral dose allocation, and object material composition. The single-line model was extended to a simulated CT acquisition of an anthropomorphic phantom with and without a metal implant. Basis material sinograms were computed and synthesized into virtual monoenergetic images (VMIs). MV-kV and kV-kV VMIs were compared with single-energy images. The 80kV-140kV pair typically yielded the best SNRs, but for bone thicknesses , the detunedMV-80kV pair surpassed it. Peak MV-kV SNR was achieved with dose allocated to the MV spectrum. In CT simulations of the pelvis with a steel implant, MV-kV VMIs yielded a higher contrast-to-noise ratio (CNR) than single-energy CT and kV-kV DE-CT. Without steel, the MV-kV VMIs produced higher contrast but lower CNR than single-energy CT. This work analyzes MV-kV DE-CT imaging and assesses its potential advantages. The technique may be used for metal artifact correction and generation of VMIs with higher native contrast than single-energy CT. Improved denoising is generally necessary for greater CNR without metal.

Object recognition via echoes: quantifying the crossmodal transfer of three-dimensional shape information between echolocation, vision, and haptics.

Active echolocation allows blind individuals to explore their surroundings via self-generated sounds, similarly to dolphins and other echolocating animals. Echolocators emit sounds, such as finger snaps or mouth clicks, and parse the returning echoes for information about their surroundings, including the location, size, and material composition of objects. Because a crucial function of perceiving objects is to enable effective interaction with them, it is important to understand the degree to which three-dimensional shape information extracted from object echoes is useful in the context of other modalities such as haptics or vision. Here, we investigated the resolution of crossmodal transfer of object-level information between acoustic echoes and other senses. First, in a delayed match-to-sample task, blind expert echolocators and sighted control participants inspected common (everyday) and novel target objects using echolocation, then distinguished the target object from a distractor using only haptic information. For blind participants, discrimination accuracy was overall above chance and similar for both common and novel objects, whereas as a group, sighted participants performed above chance for the common, but not novel objects, suggesting that some coarse object information (a) is available to both expert blind and novice sighted echolocators, (b) transfers from auditory to haptic modalities, and (c) may be facilitated by prior object familiarity and/or material differences, particularly for novice echolocators. Next, to estimate an equivalent resolution in visual terms, we briefly presented blurred images of the novel stimuli to sighted participants (N = 22), who then performed the same haptic discrimination task. We found that visuo-haptic discrimination performance approximately matched echo-haptic discrimination for a Gaussian blur kernel σ of ~2.5°. In this way, by matching visual and echo-based contributions to object discrimination, we can estimate the quality of echoacoustic information that transfers to other sensory modalities, predict theoretical bounds on perception, and inform the design of assistive techniques and technology available for blind individuals.

Quantitative uranium elemental reconstruction using spectral x-ray radiography

X-ray radiography offers the ability to noninvasively inspect the internal structure and material composition of objects. Dual-energy radiography allows material discrimination but is limited in quantitative material measurements due to the broad nature of the interrogating x-ray spectrum. Spectral radiography detectors provide an observation of not just the number of x rays that are transmitted through a sample but also the spectrum. Here, experimental validations of a method to use spectral x-ray radiography to accurately quantify the uranium mass in a powder are presented. An accurate system response model was developed, which includes a model of the incident x-ray source spectrum and a pixel-wise detector response that describes how the transmitted x rays were observed. Further, a calibration to account for the effect of partial x-ray attenuation was developed. The method is demonstrated to be capable of estimating the uranium mass in a variety of uranium oxide powders to a bias of −0.01±0.62%.

Survey of potentially hazardous object threat negation campaign options

Deflecting a potentially hazardous object (PHO) away from Earth is dependent on the amount of advance warning time, object material composition, trajectory, and the perturbing method. There are many proposed concepts that provide solutions to either deflect or fragment a PHO over a given amount of time. Each concept has its own advantages and disadvantages. Once a threat is established, an end-to-end PHO mitigation campaign design might include the use of various techniques and multiple phases. The purpose of this survey is to provide useful information to decision makers about the overall effort required to mitigate a threatening object with high reliability. Campaign and mission timelines, launch vehicle(s) and spacecraft, deflection option(s), and resource and technology requirements are some of the considerations that are addressed. A uniform rating scale is established and applied to a number of proposed deflection concepts. Several representative threat scenarios are defined and used to rank proposed deflection concepts based on a set of criteria, such as warning time and technology readiness. Multiple independent deflection attempts are considered as means to increase campaign effectiveness.

Collective remembering through the materiality and organization of war memorials

This article investigates how material objects fit into societal discourses of remembering; the authors focus on how the spatial and material composition of objects can affect subjects, thus suggesting particular meanings and engagements. In particular, they investigate war memorials as cultural objects and products of social discourses, but emphasize that the memorials are not reducible to these discourses. Rather, the materials used in the creation of war memorials as well as their holistic organization constitute vital aspects of the memorial site and its ability to engage individuals and groups in socially desirable and personally meaningful processes. The authors analyze the Massachusetts Vietnam Veterans Memorial, taking into account the holistic material organization, hyper-generalization of signs, symbolic functions, and social suggestions that the memorial provides for visitors passing through. They argue that, partially through its very materiality, the memorial guides the direction of viewers’ affective response, leading to particular interpretations and reactions.

Crinkling and crumpling: An auditory fMRI study of material properties

Knowledge of an object's material composition (i.e., what it is made of) alters how we interact with that object. Seeing the bright glint or hearing the metallic crinkle of a foil plate for example, confers information about that object before we have even touched it. Recent research indicates that the medial aspect of the ventral visual pathway is sensitive to the surface properties of objects. In the present functional magnetic resonance imaging (fMRI) study, we investigated whether the ventral pathway is also sensitive to material properties derived from sound alone. Relative to scrambled material sounds and non-verbal human vocalizations, audio recordings of materials being manipulated (i.e., crumpled) in someone's hands elicited greater BOLD activity in the right parahippocampal cortex of neurologically intact listeners, as well as a cortically blind participant. Additional left inferior parietal lobe activity was also observed in the neurologically intact group. Taken together, these results support a ventro-medial pathway that is specialized for processing the material properties of objects, and suggest that there are sub-regions within this pathway that subserve the processing of acoustically-derived information about material composition.

Use of Simulated Thermal Cues for Material Discrimination and Identification with a Multi-Fingered Display

Thermal cues provide information about the thermal properties of an object held in the hand. These cues can be simulated in a thermal display and used to assist in identifying the object. Two experiments were conducted using a thermal display that simulated the cues associated with contact with different materials. The thermal contact model was based on a semi-infinite body model that included thermal contact resistance and blood perfusion. Its performance was evaluated in two experiments, the first of which involved discriminating between simulated materials, and in the second, subjects were required to identify simulated materials based on the thermal cues presented to one, three, or five fingers. The results from the first experiment indicated that when the temperature profile associated with contact with a real material is presented to the finger, subjects can use this cue to discriminate between simulated materials. Their performance on this task is comparable to that achieved with real materials with similar thermal properties. In the second experiment, the accuracy with which subjects identified a simulated material based on thermal cues improved as the number of fingers stimulated increased, suggesting that spatial summation of cold occurs when the area stimulated is noncontiguous. However, most of the improvement in identifying materials occurred when the display presented thermal cues to three as compared to one finger, with little further enhancement in performance when five fingers were stimulated. These results indicate that thermal displays can be used effectively to present information about the material composition of objects in virtual environments.

Function from visual analysis and physical interaction: a methodology for recognition of generic classes of objects

This paper presents an overview of the GRUFF-I (Generic Recognition Using Form, Function and Interaction) system, a nonpart-based approach to generic object recognition which reasons about and generates plans for interaction with three-dimensional (3D) shapes from the categories furniture and dishes. The system operates as follows. A researcher selects an object and places it in an observation area. An initial intensity and range image are acquired. These are input to a three-stage recognition system. The first stage builds a 3D model. The second stage receives as input a 3D model and considers the shape-suggested functionality of this shape by applying concepts of physics and causation (e.g. to infer stability) to label the object's potential functionality. The third stage uses this labeling to instantiate a plan for interaction to confirm the object's functional use in a task by incorporating feedback from both visual and robotic sensors. Results of this work are presented for eighteen chair-like and cup-like objects. Major conclusions from this work include: (1) metrically accurate representations of the world can be built and used for higher level reasoning; (2) shape-based reasoning prior to interaction-based reasoning provides an efficient methodology for object recognition, in terms of the judicious use of system resources; and (3) interaction-based reasoning can be used to confirm the functionality of a categorized object without explicitly determining the object's material composition.