Influence of annealing on the photoluminescence of nanocrystalline ZnO synthesized by microwave processing

Zinc oxide (ZnO) nanoparticles have been synthesized by a microwave heating method. The resulting powders were annealed at temperatures from 400°C to 800°C for 4?h. The annealed powders were characterized in terms of their structural, morphological, and optical properties by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and room-temperature photoluminescence (PL) spectroscopy, respectively. The XRD patterns of the samples revealed the formation of phase-pure ZnO, apparently without any impurities. However, FT-IR spectra revealed the presence of carboxylate impurities, the signals of which disappear as the annealing temperatures are increased from 400°C to 800°C. SEM pictures showed increasing size ZnO nanoparticles with increase in annealing temperature. The powder annealed at 800°C is identified as hexagonal wurzite ZnO. The improved PL spectral performance of the ZnO powder correlates well with the improved crystalline quality of the nanoparticles, as revealed by the XRD and PL. Sharp ultraviolet (UV) band edge luminescence has been observed at 375?nm, which is suitable for application in UV light emitting devices. The results also showed that the excitation wavelength dependence of the luminescence arises from quantum confinement effects.     

Morphological and magnetic response of copper-substituted nickel ferrite nanoparticles

Ferrite nanoparticles are interesting materials owing to their unique physical and chemical properties. The metal-doped ferrites have well-defined structures and magnetic response, such as high permeability for a specific frequency range. In this study, copper-substituted nickel ferrite (Ni_1?xCu_xFe₂O₄) nanoparticles with a compositional range of 0?≤?x?≤?0.3 were synthesised through a co-precipitation technique. Metal chlorides were used as precursors and NaOH as a precipitating agent for the growth of ferrite nanoparticles. To minimise the internal stresses and maximise the magnetic response, ferrite nanoparticles were annealed in a furnace at 700°C for 6 h. The structural and magnetic response of Ni_1?xCu_xFe₂O₄ ferrite with different values of x were investigated using Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FT-IR), Vibrating Sample Magnetometer (VSM) and X-ray Diffraction (XRD) techniques. XRD analysis confirmed the formation of cubic spinel structure of single phase for all the compositions. The lattice constant decreased with increase in the value of x. FT-IR study showed two main metal oxygen bonds in the range 500–700 cm^?1 confirming the formation of a single-phase cubic inverse structure of Cu-substituted Ni ferrite. VSM results revealed the formation of ferrimagnetic nanoparticles. The optical and magnetic response of the ferrite nanoparticles changed with Cu content.     

Shape from shading from images rendered with various surface types and light fields

Shape constancy is referred to as the tendency for the perceived shape of an object to remain unchanged even under changed viewing and illumination conditions. We investigated, in two experiments, whether shape constancy would hold for images of 3-D solid objects defined by shading only, whose renderings differed in terms of surface material type (bi-directional reflectance distribution functions), light field, light direction, shape, and specularity. Observers were presented with the image of a sphere or an ellipsoid and required to set perceived orientation and cross-section profile on designated points of the image. Results showed that shape judgments varied with all the aforementioned variables except specularity. Shape estimates were more precise with specular than asperity scattering surfaces, collimated than hemispherical diffuse lighting conditions, lower than higher elevations, spherical than ellipsoidal shapes, but not different between surfaces having differing specularity. These results suggest that shape judgments are made largely on the basis of the overall intensity distribution of shading, and that the portions of intensity distribution that are due to nonstructural variables such as surface material type or light field are not excluded in the process of shape estimation, as if being due to structural components. It is concluded that little constancy is expected in the perception of shape from shading.     

The role of convexity in perception of symmetry and in visual short-term memory

Visual perception of shape is affected by coding of local convexities and concavities. For instance, a recent study reported that deviations from symmetry carried by convexities were easier to detect than deviations carried by concavities. We removed some confounds and extended this work from a detection of reflection of a contour (i.e., bilateral symmetry), to a detection of repetition of a contour (i.e., translational symmetry). We tested whether any convexity advantage is specific to bilateral symmetry in a two-interval (Experiment 1) and a single-interval (Experiment 2) detection task. In both, we found a convexity advantage only for repetition. When we removed the need to choose which region of the contour to monitor (Experiment 3) the effect disappeared. In a second series of studies, we again used shapes with multiple convex or concave features. Participants performed a change detection task in which only one of the features could change. We did not find any evidence that convexities are special in visual short-term memory, when the to-be-remembered features only changed shape (Experiment 4), when they changed shape and changed from concave to convex and vice versa (Experiment 5), or when these conditions were mixed (Experiment 6). We did find a small advantage for coding convexity as well as concavity over an isolated (and thus ambiguous) contour. The latter is consistent with the known effect of closure on processing of shape. We conclude that convexity plays a role in many perceptual tasks but that it does not have a basic encoding advantage over concavity.     

Unconscious fantasy: a reconsideration of the concept

Despite general agreement about the clinical importance of unconscious fantasy, the concept itself has remained unclear. After reviewing Freud's work on the subject, the conceptual dilemma is specified: where in current psychoanalytic theory do we place this important, dynamically repressed, structuralized mental content? Three conceptual paths have been followed in attempting to deal with this problem. The first emphasizes the structural, tripartite model, discarding topographic concepts. The second replaces the structural model with a schema model borrowed from academic psychology. The third combines the structural and topographic models. None of these approaches is entirely satisfactory and without problems. Because of their central role in mental life, unconscious fantasies deserve careful definition. They should be distinguished from conscious fantasies and daydreams as well as from the process of fantasizing. They are differentiated from other varieties of unconscious content by their enduring quality and their organized, storylike quality reflecting the distortions typical of the primary process. As dynamically unconscious templates from the childhood past, they shape subsequent compromise formations and are relatively impervious to new experience. The development of psychoanalytic theory from a macrostructural to a microstructural emphasis is discussed in relation to the unconscious fantasy concept.     

Rules vs. analogy in English past tenses: a computational/experimental study

Are morphological patterns learned in the form of rules? Some models deny this, attributing all morphology to analogical mechanisms. The dual mechanism model (Pinker, S., & Prince, A. (1998). On language and connectionism: analysis of a parallel distributed processing model of language acquisition. Cognition, 28, 73-193) posits that speakers do internalize rules, but that these rules are few and cover only regular processes; the remaining patterns are attributed to analogy. This article advocates a third approach, which uses multiple stochastic rules and no analogy. We propose a model that employs inductive learning to discover multiple rules, and assigns them confidence scores based on their performance in the lexicon. Our model is supported over the two alternatives by new "wug test" data on English past tenses, which show that participant ratings of novel pasts depend on the phonological shape of the stem, both for irregulars and, surprisingly, also for regulars. The latter observation cannot be explained under the dual mechanism approach, which derives all regulars with a single rule. To evaluate the alternative hypothesis that all morphology is analogical, we implemented a purely analogical model, which evaluates novel pasts based solely on their similarity to existing verbs. Tested against experimental data, this analogical model also failed in key respects: it could not locate patterns that require abstract structural characterizations, and it favored implausible responses based on single, highly similar exemplars. We conclude that speakers extend morphological patterns based on abstract structural properties, of a kind appropriately described with rules.     

Shape constancy: The effects of changing shape orientation and the effects of changing the position of focal features

Five experiments examined the time taken to judge that two consecutive elongated geometrical shapes had the same structure, irrespective of their orientation. Shape transformations either changed the orientation of the principal axis while maintaining the relative locations of focal features or maintained the orientation of the principal axis while changing the relative locations of focal features, or they changed both. Experiment 1 demonstrated that changes in the orientation of the principal axis were more detrimental to matching than were changes in the locations of the shape’s focal features. Indeed, the time taken to match same-orientation shapes was the same as that taken to match shapes that maintained the same position in the visual field. Further experiments showed that this result was not due to differential apparent motion in the transformation conditions, that it was not due to response bias, and that it generalized across shapes. However, the result was different when subjects could predict the location of the to-be-matched stimulus. In this case, performance was principally affected by the position of the focal feature of the shape and not by the shape’s orientation. It is suggested that the results reflect the efficiency with which subjects can construct matching representations for the stimuli When subjects cannot predict stimulus locations, they generate representations by describing shape structure relative to the shape’s principal axis. When the axis of the to-be-matched shapes is constant, subjects can use the same procedure in generating this representation for both shapes, facilitating matching relative to the case in which the orientation of the axis changes. When subjects can predict the stimulus location, they selectively attend to the focal features of shapes, minimizing the effects of shape orientation.     

Morphological patterns and their colour

This study analyzed qualitative aspects in perception, particularly the relationship between morphological aspects of biological shapes and colour. The experiment reported by the study assessed the functional relation between shape and colour and, in particular, the relations among the patterns of shapes appearing in perceptual configurations, as well as certain characteristics of colour. Participants were shown 32 natural images and were asked to match them with a colour. The results indicated that some figures were more frequently associated (positively or negatively) with some colours instead of others. Type of shape, texture, and three-dimensionality were important elements in the participants' choices. Rounded figures and non-holed figures had positive matches with red; elongated figures were associated with colours between blue and green; and holed figures showed positive matches with colours between green and yellow. Type of shape and texture also exhibited a relationship with the warmth of the colour.     

Language comprehenders mentally represent the shapes of objects

We examined the prediction that people activate perceptual symbols during language comprehension. Subjects read sentences describing an animal or object in a certain location. The shape of the object or animal changed as a function of its location (e.g., eagle in the sky, eagle in a nest). However, this change was only implied by the sentences. After reading a sentence, subjects were presented with a line drawing of the object in question. They judged whether the object had been mentioned in the sentence (Experiment 1) or simply named the object (Experiment 2). In both cases, responses were faster when the pictured object's shape matched the shape implied by the sentence than when there was a mismatch. These results support the hypothesis that perceptual symbols are routinely activated in language comprehension.     

Creating names for things

Ten subjects rendered names for each of 168 novel entities. The entities were quite varied. Naming strategies in this task situation were assessed with several dependent measures: (1) the structural form of the name expression (compound noun, lexically modified noun, etc.), (2) the content analysis of the name (i.e., into morphological patterns that directly convey content properties of referents), (3) statistical measures (number of syllables), and (4) comments and ratings elicited from participants. Several general strategies were induced.This is a shortened version of Carroll (1979a).     

Implicit learning for probable changes in a visual change detection task

Previous research demonstrates that implicitly learned probability information can guide visual attention. We examined whether the probability of an object changing can be implicitly learned and then used to improve change detection performance. In a series of six experiments, participants completed 120–130 training change detection trials. In four of the experiments the object that changed color was the same shape (trained shape) on every trial. Participants were not explicitly aware of this change probability manipulation and change detection performance was not improved for the trained shape versus untrained shapes. In two of the experiments, the object that changed color was always in the same general location (trained location). Although participants were not explicitly aware of the change probability, implicit knowledge of it did improve change detection performance in the trained location. These results indicate that improved change detection performance through implicitly learned change probability occurs for location but not shape.     

材料的几何属性差异对3—7岁儿童分类标准影响的研究

以７３名３—７岁儿童为被试,通过变换分类材料的几何属性（形状或大小）的差异程度,采用自由分类方法,探讨材料差异程度的变换对儿童分类标准的影响。结果表明：３—７岁儿童的分类标准均受分类材料几何属性差异变化的影响。３岁儿童的分类标准几乎完全随分类材料的变换而改变;４—５岁儿童的分类标准主要表现为随分类材料的变换而改变;６—７岁儿童的分类标准虽然有随分类材料的变换而改变的趋势,但已经表现出比较稳定的按形状分类;５—６岁是儿童分类能力发展的质的飞跃阶段。     

Morphological Processing in Adult Dyslexia

This study employed the masked-priming paradigm [Forster and Davis (J Exp Psychol bearn Mem Cogn 10: 680–698, 1984).], along with traditional methods of evaluation of morphological awareness and phonological processing, to obtain a finer-grained picture of the relationship between morphological abilities and reading in adult dyslexic readers. Participants were 21 dyslexic and 21 normally reading native Hebrew-speaking male college students. The results with masked priming demonstrated almost normal status of morphological knowledge in adult dyslexic readers with the presence of characteristic processing slowness. Phonological processing and morphological awareness were also shown to contribute primarily to word decoding in the regular and dyslexic group alike. At the same time, the contribution of different phonological skills to morphological priming effects (for pattern and root) dropped to zero. The findings demonstrated that weakness of dyslexic readers in morphological awareness tasks cannot be explained either by hypotheses on the structural deficit of morphological knowledge in dyslexia or by phonological deficit hypotheses. The explanation for this phenomenon seems to lie in the specific deficit of morphological processing, or even, more generally, in metalinguistic processing deficiency in dyslexia.     

Development of the perception of invariants: substance and shape

Three experiments investigated the perception of substance and shape as invariant properties of objects by three-month-old infants. In experiment 1, infants were habituated to two differently shaped objects undergoing a rigid motion. After habituation of the infants, the objects were presented undergoing a different rigid motion, or undergoing a deforming motion, or undergoing the same rigid motion. Habituation was maintained to the new rigid motion, indicating that the two rigid motions were perceived as sharing an invariant property. Dishabituation, on the other hand, occurred when a deforming motion followed a rigid one. In experiment 2, infants were habituated to one shape undergoing two different rigid motions. After habituation, the shape was changed but the same two motions continued. Dishabituation occurred, compared to a group with no shape change, indicating that shape is distinguished as an invariant property over two rigid motions. In experiment 3, habituation to a shape undergoing two rigid motions was followed by a new shape presented motionless, or the same shape presented motionless. Cessation of motion did not prevent recognition of shape as invariant. Two properties of an object, substance and shape, thus appear to be detectable as invariant in an event sequence, an instance of "phenomenal doubling" at an early age.     

小学低年级汉语儿童语素意识、汉字识别和词汇知识的发展关系——交叉滞后研究

以146名小学一年级儿童为研究对象, 进行了历时2年的3次追踪测试, 考察小学生从一到三年级的语素意识、汉字识别和词汇知识之间发展关系的变化。在控制了语音意识、快速命名、正字法意识、一般认知能力和自回归效应后, 结果发现：(1)一年级时的汉字识别显著预测二年级的同音语素意识和同形语素意识; (2)一年级时的词汇知识显著预测二年级的复合语素意识和汉字识别; (3)二年级时的汉字识别和词汇知识对三年级的同音语素意识、同形语素意识和复合语素意识均有显著预测作用; (4)二年级时的同形语素意识对三年级的词汇知识具有显著预测作用。结果表明, 小学一至三年级的汉字识别和词汇知识对语素意识具有预测作用; 三种语素意识对汉字识别和词汇知识的预测作用中, 只有同形语素意识能够显著预测词汇知识; 三种语素意识、汉字识别和词汇知识的发展关系存在变化且具有阶段性特点。     

Secondary task modality, expectancy, and the measurement of attentional capacity

Previous studies have obtained conflicting evidence regarding the effect of probe modality when a secondary probe task is used to measure attentional demands of a primary letter-matching task. The present experiments found no difference in the shape of the probe reaction time functions for auditory and visual probes as long as probe modality was known. When probes "unexpectedly" occurred in the modality that was different from the majority of the probes, differences were obtained. Only the unexpected auditory function changed, shape relative to the others, with reaction time to probes that occurred early in the matching task sequence being increased. The results are interpreted as supporting a role of attentional capacity in the activation of structures that accept relevant sensory input.     

Investigating metrical and structural aspects of visual completion: Priming versus searching

Earlier research on visual occlusion showed some flexibility in the formation of visual completions, as long as the structural aspects (e.g., symmetry) of the visible part of the partly occluded shape were preserved in the completion (de Wit & van Lier, ). In this study, we examined whether changing the overall size of the occluded shape would preserve the overall structure. In Experiment 1, using the primed‐matching paradigm, we found evidence for relative size invariance in the completion process. To investigate whether changes in the structural aspects of shape are generally more salient than those of size, we employed the same stimuli in visual search and change detection paradigms. Experiment 2 demonstrated effects of completion in both paradigms. Experiment 3 showed that the metrical aspects of the shapes used in Experiment 1 are nevertheless detected faster than the structural aspects under search conditions. Because the variation in structural aspects is not more salient than in metrical aspects, we conclude that for these shapes, visual completion is indeed size‐invariant. The relations between performances in the three paradigms are discussed.     

Influence of Zn incorporation on the microstructural and magnetic properties of La0.67Sr0.33Mn1−xZnxO3 nanoparticles synthesised by the sol–gel method

Perovskite manganite nanoparticles with the chemical formula La_0.67Sr_0.33Mn_1?xZn_xO₃ (x = 0, 0.1 and 0.2) were prepared by the sol–gel process and the influence of Zn substitution on their microstructural and magnetic properties studied in detail. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed for crystal structure determination and microstructural analysis. The results of XRD analysis confirmed the polycrystalline nature and rhombohedral crystal structure with space group R(-3c) for all compositions. SEM micrographs of the samples revealed an agglomeration/well-connected appearance of the particles. The composition and uniform distribution of all the elements were established by energy-dispersive spectroscopy. TEM images clearly confirmed an almost spherical shape of the nanoparticles with an average particle size of about 11, 14 and 13 nm for the 0, 10 and 20% Zn-doped samples, respectively. The magnetic behaviour of the nanoparticles was studied at room temperature with a vibrating sample magnetometer (VSM) up to a field of 1.8 Tesla. These measurements established a superparamagnetic nature with a variation in the saturation magnetization (M_s) with Zn content.