Growth of diamond crystals by combustion synthesis

Abstract

Low-pressure synthesis of diamond by activated chemical vapour deposition processes is attractive for producing diamond films for optical and electronic (i.e. non-abrasive) applications because of the ability of these processes to produce these films in large dimensions. The low growth rate (about 1 μm h^?1) has, however, precluded these processes for abrasive grain production on simple economic grounds. With the introduction of combustion synthesis of diamond at growth rates exceeding 100μmh^?1, this barrier seems less formidable than it once did. The synthesis of large (about 200 μm) well formed single crystals of diamond by the combustion process with growth rates of about 100μm h^?1, reported here, offers an opportunity to explore the potential of this process for abrasive grain production.     

High-speed photography of low-velocity impact cracking of solid spheres

Results from a high-speed photographic study of low-velocity impact cracking of optically transparent acrylic resin and poly(methyl methacrylate) spheres of 12.7mm diameter are described. It is shown that, in a sphere undergoing an impact, cracking occurs after the sphere has been plastically deformed. The point of initiation of cracking is shown to be located at the circle of contact between the sphere and the impacting platen. The cracking then develops throughout the sphere, with cracks attaining velocities of 600-800ms^-1. It has been suggested that crack initiation at the contact circle is caused by the tensile circumferential stress, which is generated owing to the plastic flow of the sphere.     

Kinematic analysis of goal-directed aims made against early and late perturbations: an investigation of the relative influence of two online control processes

Examination of goal-directed movements has evidenced two processes of visually regulated online control: early trajectory control that operates to make movement adjustments on the basis of limb velocity comparisons to internally generated models of the expected limb velocity, and late trajectory control that uses allocentric information about the limb and target positions. The results of experiments using illusory perturbations suggest that the two systems have an additive influence on movement outcome, and are relatively independent. In this theoretical context, three experiments were conducted in which actual perturbations to the aiming limb dynamics and the tasks demands were introduced. Compressed air expulsed through a stylus, in the direction of, or opposite to, that of the movement was used to impact limb velocity and the target location was moved at movement initiation to impact late evaluation of target and limb position. The results of the compressed air-only and moving target-only conditions replicated the previous evidence of early and late control, respectively. Interestingly, movement accuracy measures yielded an interactive effect of the two perturbations when presented in tandem. It appears that the perturbations prompted parallel operation of the two control processes.     

Spectroscopic studies of a thermochromic centre in synthetic diamonds grown by the temperature-gradient method

Abstract

Synthetic diamonds grown by the temperature-gradient method at temperatures just above the melting point of the solvent-catalyst often have an unattractive dull-green colour. This green colour, which is prominent at room-temperature, disappears if the diamond is cooled to below 120 K and is restored on warming the crystal back to room temperature. We show that the behaviour of the absorption band responsible for the colour is consistent with the transition occurring from the upper level of a centre with a split ground state, for which transitions from the lower level are forbidden. Temperature-dependence measurements indicate that the energy splitting in the ground state is about 50 meV. The broad featureless absorption band, with a maximum near 1·9eV, is assumed to be vibronic in origin. The absence of structure in the band indicates that the electronic transition is strongly coupled to the lattice and, as expected, the zero-phonon line, estimated to be at around 1eV, is too weak to detect. The same absorption band is also shown to be present in some individual crystals of synthetic diamond abrasive grit.     

调节聚焦对高中生毅力水平的影响:学业情绪的中介作用

对644名高一、高二学生进行调节聚焦、毅力和学业情绪的问卷调查,以探讨高中生毅力水平与调节聚焦和学业情绪之间的关系。结果显示:(1)高中男生的毅力水平显著高于女生,高一年级学生的毅力水平显著高于高二年级;(2)高中生的调节聚焦并不完全直接导致毅力的增强或降低,而是通过学业情绪作为中介而间接影响毅力的。促进定向通过高兴的中介作用而增强毅力,通过沮丧的中介作用而降低毅力;预防定向通过生气的中介作用而降低毅力,但是满足的中介作用不显著。     

Passion,grit, and mindset in undergraduate sport sciences students

The aim of this study was two-fold: (i) to compare passion, grit and mindset between sexes; and (ii) to analyze the relationships between passion, grit and mindset. Fifty-eight men (age: 20.10 ± 2.70 years old) and forty-eight women (age: 19.27 ± 4.10 years old) sports sciences undergraduate students voluntarily participated in this study. A cross-sectional survey design was followed. The passion scale, grit scale and mindset scale were provided to participants. Comparisons in the passion, grit and mindset items revealed no significant differences between sexes (p > 0.05). Relationships between passion, grit and mindset were tested. Overall (both sexes considered), correlations presented small magnitudes in the pair's passion*grit (r = 0.28; 95%CI [-0.07; 0.31]; p = 0.004), passion*mindset (r = 0.203; 95%CI [0.01; 0.38]; p = 0.043) and grit*mindset (r = 0.06; 95%CI [-0.14; 0.25]; p = 0.574). As conclusions, the present study did not find significant differences in passion, grit and mindset between sexes in undergraduate sports sciences students. Additionally, it was verified that relationships between passion, grit and mindset are small in this population.     

Secondary defects induced by ion and electron irradiation of GaSb

Secondary defects induced by ion and electron irradiation up to 6?dpa (displacements per atom) at liquid-nitrogen temperature in GaSb thin films are compared. For Sn ion (60?keV) irradiation, voids were observed. However, for high-energy electron (2?MeV) irradiation, interstitial-type dislocation loops were produced. The densities of voids and interstitial-type dislocation loops were almost equivalent (8?×?10¹⁴?voids/m² and 3?×?10¹⁴?loops/m²) after irradiations at the same damage level of 6?dpa. It is concluded that the formation of voids by ion irradiation follows the creation of localised vacancy defects in cascade damage.     

Task-dependent modulation of word processing mechanisms during modified visual search tasks

During visual search for words, the impact of the visual and semantic features of words varies as a function of the search task. This event-related potential (ERP) study focused on the way these features of words are used to detect similarities between the distractor words that are glanced at and the target word, as well as to then reject the distractor words. The participants had to search for a target word that was either given literally or defined by a semantic clue among words presented sequentially. The distractor words included words that resembled the target and words that were semantically related to the target. The P2a component was the first component to be modulated by the visual and/or semantic similarity of distractors to the target word, and these modulations varied according to the task. The same held true for the later N300 and N400 components, which confirms that, depending on the task, distinct processing pathways were sensitized through attentional modulation. Hence, the process that matches what is perceived with the target acts during the first 200?ms after word presentation, and both early detection and late rejection processes of words depend on the search task and on the representation of the target stored in memory.     

Speed-Accuracy Characteristics of Saccadic Eye Movements

Speed-accuracy trade-off characteristic of horizontal saccadic eye movements were examined in this study. Unlike limb movements, saccadic eye movements are preprogrammed, unidimensional, and do not involve target impact. Hence, they provide an optimal test of the impulse variability account of the speed-accuracy trade-off in rapid movements. Subjects were required to alternately look at two target lights as fast and as accurately as possible for a period of 10 s. Target lights subtended angles of 5,10,15, and 20°. By restricting target distances to less than 20° of arc, the speed-accuracy relation was examined for single horizontal saccadic movements of the eye. Movement of the dominant eye was tracked with an infra-red eye monitoring device. Fifty saccadic movements of the eye were recorded for each target distance and used to compute the average amplitude, duration, and velocity of eye movements, as well as, movement endpoint variability. An increase in both average velocity and movement endpoint variability with increasing movement amplitude was found. This, together with the unique features of the eye movement system, support the impulse variability account of the speed-accuracy trade-off in rapid movements.     

Tuning characteristics of the top-down attentional setting

Previous studies of top-down attentional guidance have focused generally on the attentional prioritization of a single target feature. The present study focused on how the attentional system would be configured when the target possesses several unique features. These features were perfectly correlated, which meant that monitoring just one of them would be an adequate strategy. The experiments addressed the following questions: (a) If the target is a singleton, would the attentional system be set to monitor the target’s unique features, or would the search strategy default to singleton detection? (b) Can the target’s static and dynamic features be prioritized simultaneously? (c) Are all of the target’s features prioritized, or only those features that are diagnostic of targethood? The results revealed an attentional system that can be flexibly tuned to multiple target features across static and dynamic dimensions. This system can simultaneously be narrowly tuned to monitor a specific target feature and broadly tuned to detect singletons. Finally, the attentional system monitors only those features that are diagnostic of targethood.     

Fortune and reversals of fortune in visual search: Reward contingencies for pop-out targets affect search efficiency and target repetition effects

Rewards have long been known to modulate overt behavior. But their possible impact on attentional and perceptual processes is less well documented. Here, we study whether the (changeable) reward level associated with two different pop-out targets might affect visual search and trial-to-trial target repetition effects (see Maljkovic & Nakayama, 1994). Observers searched for a target diamond shape with a singleton color among distractor diamond shapes of another color (e.g., green among red or vice versa) and then judged whether the target had a notch at its top or bottom. Correct judgments led to reward, with symbolic feedback indicating this immediately; actual rewards accumulated for receipt at study end. One particular target color led to a higher (10:1) reward for 75% of its correct judgments, whereas the other singleton target color (counterbalanced over participants) yielded the higher reward on only 25% of the trials. We measured search performance in terms of inverse efficiency (response time/proportion correct). The reward schedules not only led to better performance overall for the more rewarding target color, but also increased trial-to-trial priming for successively repeated targets in that color. The actual level of reward received on the preceding trial affected this, as did (orthogonally) the likely level. When reward schedules were reversed within blocks, without explicit instruction, corresponding reversal of the impact on search performance emerged within around 6 trials, asymptoting at around 15 trials, apparently without the observers’ explicit knowledge of the contingency. These results establish that pop-out search and target repetition effects can be influenced by target reward levels, with search performance and repetition effects dynamically tracking changes in reward contingency.     

Characterization of platelet-related infrared luminescence in diamond

Characterization of the platelet-related infrared emission in diamond using photoluminescence (PL) and PL excitation techniques is reported. It is suggested that the emission originates from the radiative recombination of electrons and holes at platelet-induced bands of electron states separated by a gap of about 1.7eV.     

The Impact of Real and Illusory Perturbations on the Early Trajectory Adjustments of Goal-Directed Movements

Examinations of goal-directed movements reveal a process of control that operates to make adjustments on the basis of the expected visual afference associated with the limb's movement. This experiment examined the impact of perturbations to the perceived and actual velocity of aiming movements when each was presented alone or in tandem with the other. Perturbations to perceived velocity were achieved by translating the background over which aiming movements were performed. An aiming stylus that discharged air either in the direction of the movement or in the direction opposite the movement generated the actual velocity perturbations. Kinematic analyses of the aiming movements revealed that only the actual perturbation influenced the control of early movement trajectories. The results are discussed with respect to the influence that visual information has on the control exerted against physical perturbations. Speculations are raised regarding how potential for perturbations influences the strategies adopted for minimizing their impact.     

Multiple liquid impact of single-crystal lithium fluoride

Lithium fluoride in its single-crystal form is an interesting material for investigating the development of fracture by multiple liquid impact owing to its well characterized crystal structure. The development of fracture during liquid impact is attributed to the extension of short circumferential cracks produced around the loaded area by the passing Rayleigh stress wave after the impact event. The damage threshold of single-crystal lithium fluoride is developed using the Cavendish Laboratory's multiple impact jet apparatus as a result of identifying the characteristic fracture annulus associated with liquid impact during a controlled experimental procedure. The observation of damage produced in solids by liquid impact has practical significance in the problems with supersonic aircraft flying through rain and in the erosion of turbine blades moving at high speeds through wet steam.     

Grit and academic performance among first-year university students: A brief report

This study examined grit and academic performance among a sample of South African university students (n = 121, mean age = 19.55, SD = 1.77, female = 57.85%). Data were collected using the Grit Scale and academic performance was assessed over one academic semester. Simple regression analysis was computed to predict students’ academic achievement from components of their self-reported grit. The grit component of consistency of interest accounted for 3% of the variance in the student’s academic achievement scores. Similarly, the grit component of perseverance of effort explained 9% of the variance in scores. Students who scored high on the Grit Scale also obtained higher academic marks compared to participants who scored low on the same instrument. The findings suggest that grit is an important personal resource for higher education students.     

The conditioned anticipation of people (CAP) model of driving in urban spaces

Despite significant gains in overall collision rates, pedestrian and bicycle safety in complete street environments remains an on-going challenge. However, urban areas with the most risk exposure for pedestrians continue to maintain lower incident rates than their suburban counterparts (“Dangerous by Design” 2021). Under most driving circumstances, the over-rehearsed nature of driving leads to a psychological state similar to self-hypnosis, where attention is subconsciously maintained on the driving task while metacognitive awareness is minimized or eliminated. This state continues until some type of conflict, uncertainty, and/or novel stimulus is presented. The primary difference in driver attention in urban environments is postulated to result from the Conditioned Anticipation of People (CAP). Based on the human neurological predisposition to recognize and fixate on human faces and figures, we hypothesize that in areas where drivers have been conditioned to expect human presence, low-level metacognition is preemptively re-engaged to address their presence, resulting in higher attentional resource expenditure and increased distraction management. Such conditioning may be generated by contextual features common to pedestrian-friendly environments but, necessarily, must be reinforced over time by the Actual Presence of People (APP). CAP driver engagement is limited by the perceptual abilities of the driver such that at higher speeds or within wider corridors, the presence of pedestrians is more difficult to perceive. This results in a non-CAP attention pattern, exhibiting minimal metacognitive activity, high levels of automaticity, and reduced attention. This model was generated based on the observation that vulnerable user presence and the roadway contextual features that support the driver's ability to see vulnerable users were related to attention data measured during the SHRP2 Naturalistic Driving Study. Visually discernable features that were associated with vulnerable user presence had relationships with attention and large effect sizes (η² > 0.5). Contextual features that had relationships with vulnerable user presence, but minimal visual impact or interfered with the driver’s ability to see vulnerable users had no relationship to driver attention. This behavioral pattern provides supportive evidence for the proposed model.     

Speed-accuracy characteristics of saccadic eye movements

Speed-accuracy trade-off characteristic of horizontal saccadic eye movements were examined in this study. Unlike limb movements, saccadic eye movements are preprogrammed, unidimensional, and do not involve target impact. Hence, they provide an optimal test of the impulse variability account of the speed-accuracy trade-off in rapid movements. Subjects were required to alternately look at two target lights as fast and as accurately as possible for a period of 10 s. Target lights subtended angles of 5, 10, 15, and 20 degrees. By restricting target distances to less than 20 degrees of arc, the speed-accuracy relation was examined for single horizontal saccadic movements of the eye. movement of the dominant eye was tracked with an infra-red eye monitoring device. Fifty saccadic movements of the eye were recorded for each target distance and used to compute the average amplitude, duration, and velocity of eye movements, as well as, movement endpoint variability. An increase in both average velocity and movement endpoint variability with increasing movement amplitude was found. This, together with the unique features of the eye movement system, support the impulse variability account of the speed-accuracy trade-off in rapid movements.     

Grit Applied Within: Identity and Well-being

This study investigates how grit, perseverance in the face of challenges and focus on achieving goals, relates to identity development and how identity development mediates the relationship between grit and well-being. Emerging adult college students (N = 232) indicated their grit, identity status, and well-being by completing an online questionnaire. Grit-perseverance of effort was associated with all identity statuses. Grit-consistency of interest was associated most identity statuses. Commitment and ruminative exploration mediated the relationship between grit and happiness and self-esteem, respectively.     

EELS analysis of vacuum arc-deposited diamond-like films

Abstract

Electron energy-loss spectroscopy measurements have been made on amorphous diamond-like carbon films produced by condensing the plasma stream from a filtered vacuum arc. The results are compared with spectra from diamond, graphitized carbon and amorphous carbon. Although the energy-loss spectra reveal the presence of a small quantity of sp²-bonded material in the diamond-like film, the high plasmon frequency and shape of the K-edge show that the material is essentially an amorphous form of diamond. The fraction of sp²- bonded carbon was quantified and found to be of the order of 15%. It was not possible to determine if the sp² carbon was on the surface or throughout the bulk.     

The game is afoot: A response to three insightful commentaries

This is an author response to commentaries on our original article (Wu, Sheppard & Mitchell, 2016). We abstract two main themes from the commentaries, and they are as follows: (1) What kind of clues in target behaviour allow perceivers to infer target EQ? And related with this, by what process do perceivers infer the target's EQ? (2) Do features of the target group naturally lead to a U‐shaped function, whereby it is easy for perceivers to identify those at the extremes but not those in the middle of the continuum?