Set Of Test Objects Research Articles

Calibration Dependencies and Accuracy Assessment of a Silicone Rubber 3D Printer

Silicone rubbers are relatively new in additive manufacturing, with only a few commercial printing services and reports on custom-built printers available. Publications and standards on calibration and accuracy assessment are especially lacking. In this study, the printhead calibration process of a custom-built silicone printer is explained, and a set of test objects is proposed and evaluated. The printer in use is based on an open-source filament printer, capable of multi-material printing with silicone rubbers and thermoplastic polymers. Three different high-viscosity single-component liquid silicone rubbers and one polylactic acid thermoplastic filament were used as printing materials. First, the calibration process of the silicone printhead was conducted, and the dependency of the dosing accuracy on silicone viscosity, nozzle diameter and extrusion speed was evaluated. Second, various test specimens were proposed and printed to characterize the accuracy and geometric limitations of this printer. These test parts contained features such as thin walls, slender towers, small holes and slots, unsupported overhangs and bridges. It was concluded that silicone viscosity strongly affects geometric inaccuracies. Design recommendations were deducted from the results, advising for wall thicknesses above 1 mm, slenderness ratios below 2, bridging lengths below 2 mm and unsupported overhang angles below 30°.

Preserved category-based inferences for word learning in school-aged children with developmental language disorder

ABSTRACT Word learning difficulties are often found in children with Developmental Language Disorder (DLD). Lexical patterns of difficulties appear to be well described in the context of DLD but very little research focuses on their underlying causes. Word learning is known to be an inference-based process, constrained by categorization, which helps the extension of new words to unfamiliar referents and situations. These processes appear integrated in Bayesian models of cognition, which supposes that learning relies on an inductive inference process that recruits prior knowledge and principles of statistical learning (detection of regularities). Taken together, these mechanisms remain underexplored in DLD. Our study aims to define whether children with DLD can draw inductive inferences in a word learning context using categorization. Twenty children with DLD (between 6;0 and 12;6), and 20 language-matched and 16 age-matched controls were exposed to a word learning task where they were given exemplars of objects associated with pseudo-words. The objects belonged to six categories spread across three hierarchical levels. For each item, the children chose which one(s), among a set of test objects from the same categories, could be labelled the same way (word extension). Results showed that school-aged children with DLD could extend new words to broader categories as well as their typically developing (TD) peers. Nevertheless, none of the DLD or TD children showed a specification of their categorization of familiar instances that referred to more restricted instances. Our study suggests preserved abilities in using conceptual knowledge in order to learn new words, which could be used as a compensative strategy in the context of therapy. Further studies are needed to investigate this ability in more complex learning contexts.

3D Object Recognition Based on Point Clouds in Underwater Environment with Global Descriptors: A Survey.

This paper addresses the problem of object recognition from colorless 3D point clouds in underwater environments. It presents a performance comparison of state-of-the-art global descriptors, which are readily available as open source code. The studied methods are intended to assist Autonomous Underwater Vehicles (AUVs) in performing autonomous interventions in underwater Inspection, Maintenance and Repair (IMR) applications. A set of test objects were chosen as being representative of IMR applications whose shape is typically known a priori. As such, CAD models were used to create virtual views of the objects under realistic conditions of added noise and varying resolution. Extensive experiments were conducted from both virtual scans and from real data collected with an AUV equipped with a fast laser sensor developed in our research centre. The underwater testing was conducted from a moving platform, which can create deformations in the perceived shape of the objects. These effects are considerably more difficult to correct than in above-water counterparts, and therefore may affect the performance of the descriptor. Among other conclusions, the testing we conducted illustrated the importance of matching the resolution of the database scans and test scans, as this significantly impacted the performance of all descriptors except one. This paper contributes to the state-of-the-art as being the first work on the comparison and performance evaluation of methods for underwater object recognition. It is also the first effort using comparison of methods for data acquired with a free floating underwater platform.

Picking, grasping, or scooping small objects lying on flat surfaces: A design approach

Grasping in constrained environments is, to this day, an ongoing research topic. Objects can rarely be grasped from arbitrary directions, hence the need to study the options available to grasp them. This paper proposes a gripper capable of grasping small or thin objects that cannot be directly pinch-grasped. The focus is placed on objects that lie on hard surfaces. The proposed approach uses a quasistatic method referred to as scooping while implementing a passive thumb to compensate for manipulator positioning errors. Hence, the robot arm does not need to be moved while the gripper is grasping an object, similarly to a human hand performing a precision grasp. The design approach is presented and the main design choice, namely the use of epicyclic gear trains instead of conventional revolute joints, is explained. The implementation of the proposed approach to the gripper design is shown. We explain how parallel pinch grasps and large grasping forces are achieved even though the mechanism does not follow the usual parallelogram four-bar implementation of parallel pinch mechanisms. The experimental validation of the proposed concept is then presented by picking up a set of test objects in sequence and demonstrating some variants of the method that expand on the concept.

Bidirectional Symbolic Analysis for Effective Branch Testing

Structural coverage metrics, and in particular branch coverage, are popular approaches to measure the thoroughness of test suites. Unfortunately, the presence of elements that are not executable in the program under test and the difficulty of generating test cases for rare conditions impact on the effectiveness of the coverage obtained with current approaches. In this paper, we propose a new approach that combines symbolic execution and symbolic reachability analysis to improve the effectiveness of branch testing. Our approach embraces the ideal definition of branch coverage as the percentage of executable branches traversed with the test suite, and proposes a new bidirectional symbolic analysis for both testing rare execution conditions and eliminating infeasible branches from the set of test objectives. The approach is centered on a model of the analyzed execution space. The model identifies the frontier between symbolic execution and symbolic reachability analysis, to guide the alternation and the progress of bidirectional analysis towards the coverage targets. The experimental results presented in the paper indicate that the proposed approach can both find test inputs that exercise rare execution conditions that are not identified with state-of-the-art approaches and eliminate many infeasible branches from the coverage measurement. It can thus produce a modified branch coverage metric that indicates the amount of feasible branches covered during testing, and helps team leaders and developers in estimating the amount of not-yet-covered feasible branches. The approach proposed in this paper suffers less than the other approaches from particular cases that may trap the analysis in unbounded loops.

Ensuring Interoperability for the Internet of Things: Experience with CoAP Protocol Testing

Constrained Application Protocol (CoAP) is a specialized web transfer protocol, designed for realizing interoperation with constrained networks and nodes for machine to machine applications like smart energy, building automation, etc. As an important ubiquitous application protocol for the future Internet of Things, CoAP will be potentially implemented by a wide range of smart devices to achieve cooperative services. Therefore, a high level of interoperability of CoAP implementations is crucial. In this context, CoAP Plugtest—the first formal CoAP interoperability testing event was held in Paris, March 2012 to motivate vendors to verify the interoperability of their equipments. The event turned to be successful due to our contribution, including the test method and tool. This paper presents the testing method and procedure for the CoAP Plugtest event. To carry out the tests, a set of test objectives concerning the most important properties of CoAP have been selected and used to measure the interoperability of CoAP implementations. The process of verification has been automated by implementing a test validation tool based on the technique of passive testing. By using the test tool, a number of devices were successfully tested.

High-resolution neutron radiography with microchannel plates: Proof-of-principle experiments at PSI

With the appearance of highly collimated and intense neutron beamlines, the resolution of radiographic experiments is often limited by the parameters of the neutron imaging detector. Neutron-sensitive microchannel plates (MCPs) proved to be very efficient for conversion of a thermal or cold neutron into an electron pulse of up to 10 6 electrons preserving location of the neutron absorption within ∼15 μm. In this paper, we present the results of preliminary measurements performed with neutron-sensitive MCPs coupled with a Medipix2/Timepix active pixel sensor. A set of test objects was imaged at both thermal and cold neutron imaging beamlines of Paul Scherrer Institute. The spatial resolution of the detector operating at high counting rate mode was confirmed to be limited by the 55 μm pixel size of the Medipix2 readout. At the same time, event centroiding applied to the charge values measured with Timepix readout allowed individual neutron counting with spatial resolution on the scale of MCP pore spacing (11 μm in the present measurements). The ongoing improvement of the speed of the readout electronics should eliminate the low counting rate limitation of the latter high-resolution imaging.

Attunement, Calibration, and Exploration in Fast Haptic Perceptual Learning

Often, a relatively small number of trials suffices to enhance one's task-specific perceptual capability. In the present experiment, fast perceptual learning was investigated with respect to the perception of the heights or widths of wielded nonvisible rectangular objects. In that haptic perceptual task, inertial differences (mass and moments of inertia) are the basis for perceived size differences. The authors hypothesized that rapid improvement might occur in attunement (attending to the task-relevant inertial variable), calibration (scaling spatial extent to the task-relevant inertial variable), and exploratory behavior (wielding so as to differentiate the task-relevant inertial variable). Twenty-four students performed 25 trials with a set of practice objects; those trials were followed and preceded by 18 trials with a set of test objects. Practice, with knowledge of results (KR), improved both attunement, as measured by regression of perceived spatial extent on the inertial variables, and calibration, as measured by constant and variable error. Of the preceding measures, only variable error improved with practice in the absence of KR. In both KR conditions, however, exploratory behavior decreased in duration and complexity, as measured by recurrence quantification analysis. The present results suggest that the mechanisms involved in fast perceptual learning are more varied and complex than are those encompassed by current accounts.

The prevalence and the weakness of an early name mapping preference.

An empirical puzzle regarding toddlers' fast mapping motivated the current investigation. Whereas children between 1;10 and 2;1 have shown only a modest rate of mapping novel nouns onto unfamiliar rather than familiar objects, a very high rate has been observed in those between 1;4 and 1;8 (Mervis & Bertrand, 1991). Study 1 examined whether young two-year-olds (N = 40, mean age = 2;1) might map at a higher rate when tested with procedures unique to Mervis & Bertrand's assessment--strong corrective feedback rather than mild positive non-contingent feedback; large sets of test objects rather than pairs; presentation of easier tests first. Only the first variable affected performance in a manner that could solve the puzzle. Unfamiliar kinds were selected at a much higher rate under corrective (0.86) than non-contingent (0.57) feedback. Although nearly every child in the non-contingent group chose correctly on the first trial, many failed to do so thereafter. In Study 2, rather than presenting a test word to the children (N = 16, mean age = 2;2), the experimenter merely asked for 'the one I want'. Unfamiliar kinds were selected much less often than in Study 1, suggesting that at least one lexical principle proposed in the literature underlies the noun mapping preference. Changes over trials in the two studies indicated that the noun mapping preference is quite prevalent, but unless initial choices are strongly reinforced, an increase in the salience of familiar kinds after the first trial lures some children into error. Consistent with this analysis, toddlers in Study 3 (N = 24, mean age = 2:1) who received non-contingent strong acceptance for their noun mapping decisions, selected unfamiliar kinds more often than those who had received non-contingent mild acceptance in Study 1.

II. Performance assessment and quality control in MRI by Eurospin test objects and protocols

As part of its work, the European Concerted Action “Tissue Characterisation by MRS and MRI” (COMAC-BME) has expended considerable effort in the field of magnetic resonance imaging (MRI) quality control. A set of test objects—the Eurospin set—have been designed and rigorously tested in many systems throughout Europe. The full history of this development is described, together with a detailed presentation of the types of measurements that are achievable with such test objects and examples of the results. Further, the principles of more complex Stage II tests (which involve invasive interaction with the system) are introduced. Finally, simplified methods of quantifying the overall performance are discussed and the levels of MRI quality control from acceptance testing to routine quality assurance outlined.

A set of test objects for quality assurance in diagnostic radiology

A set of test objects for quality assurance in diagnostic radiology

A set of X-ray test objects for image quality control in digital subtraction fluorography. II: Application and interpretation of results.

In the previous article we introduced a set of test objects for quality control of digital subtraction fluorography (DSF) systems. These test objects have been evaluated using several commercial DSF systems in their clinical environment. In this second article we present test images and results obtained during these trails and explain how the test objects can be used to analyse the imaging performance of DSF systems.

Taxonomic Repeatability: An Experimental Approach

Moss, W. W. (Div. Entomol, U. Calif., Berkeley 94720). 1971. Taxonomic repeatability: an experimental approach. Syst. Zoo/., 20:309–330.—Two groups of workers from two universities assigned phenetic similarities, intuitively and numerically, to two sets of test objects (Caminalcules). The results of these studies were analyzed for correspondence and relative variability, and contrasted in various ways.

The Production and Calibration of Foucault Test Objects of Various Contrasts*

A method is described for the production and calibration of resolution test objects of a type similar to those introduced by Foucault. These test objects consist of alternate white and gray bands of equal width. The targets are photographic copies of impressions made from inked ruled zinc plates. In order to compensate for the lateral diffusion of the white bands in the photographic processes, the zinc plates are ruled to produce black bands twenty percent wider than the white bands. In the copying process each photograph consists of alternate exposures to the zinc plate impression and to a white card, such that the total exposure for each photograph is constant. A series of such photographic copies is simultaneously printed on one sheet of photographic paper. These prints constitute a set of test objects of various contrasts in which the white and gray bands are practically equal in width. The test objects are calibrated by means of a photoelectric mechanism which records the reflectivity of the white and gray bands and indicates the number of white bands per inch. Using the method outlined above, test objects have been produced and calibrated in which the number of lines varied up to 120 per inch and which had contrasts as low as 1 percent.