Photoreflectance Studies of SIMOX Materials

Photoreflectance (PR) was used to study SIMOX materials produced under various fabrication conditions. The position, amplitude and shape of the 3.4 eV PR response were monitored for three different sets of samples which provided information about the crystalline quality of the top silicon layer. Each sample of the first set underwent different annealing conditions. A second set of six samples was arranged such that one sample was removed at a different step of the process involving three implantation-anneal cycles. A third set of four samples was implanted with different doses of oxygen. In the first case the PR signal improved with longer annealing times and higher temperatures; in the second case the PR signal appeared to deteriorate with each cycle undergone by the samples, while in the third case the degradation of the structure increased with the increased implantation dosage. Transmission electron microscopy (TEM) was also performed in the last two cases, and its results supported the PR conclusions.     

Categorization of novel animals by patients with Alzheimer's disease and corticobasal degeneration.

We taught a novel animal category by rule-based and similarity-based processes to participants with Alzheimer's disease (AD), corticobasal degeneration (CBD), and healthy age-matched participants. Healthy participants successfully categorized by either process. AD patients' rule-based categorization was impaired, while their similarity-based categorization resembled that of healthy participants. Correlations of AD patients' performance with measures of executive functioning suggested a deficit in the cognitive resources necessary for engaging rule-based categorization. The contribution of limited executive resources to categorization difficulty in AD was further demonstrated in a second experiment in which features determining category membership were of lower salience. CBD patients were relatively impaired at similarity-based processing, suggesting that qualitatively distinct categorization processes can be selectively compromised in patients with focal neurodegenerative diseases. Moreover, AD patients' impaired categorization correlated with performance on a measure of semantic memory, implicating this categorization deficit in AD patients' semantic memory difficulty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assessing visual memory disorders.

The Biber Figure Learning Test (BFLT) was administered to 19 patients with right- and 20 with left-hemisphere cerebrovascular accidents, 11 severe amnesics and 42 controls. Results indicate that the BFLT reliably assesses impairments in long-term visual memory independent of primary visuoperceptual, visuoconstructional, and language deficits. Healthy controls showed no effects of education and minimal age effects on the BFLT. Normal learning curves were found for cortical lesions patients, but their overall scores were below those of normals. Amnesics with subcortical-limbic pathology showed grossly impaired acquisition, retention, and recognition memory, but normal short-term visual memory and primary visuoperceptual/visuoconstructional abilities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Repetition of single words and nonwords in Alzheimer's disease

Repetition of single words and pronounceable nonwords (pseudowords) was assessed in Alzheimer's Disease (AD) patients to evaluate how lexical phonological processing might be accomplished when semantic and conceptual knowledge is impaired. AD patients performed significantly worse than healthy elderly controls on all repetition tasks. However, repetition abilities and dementia severity were not correlated, and AD patients produced the same distribution of error types as controls. Furthermore, despite their semantic problems, AD patients, like controls, showed a significant advantage for repeating real words compared to pseudowords, even when repeating low frequency phonologically complex words whose meaning is not likely to have been retained. The results support the postulated existence of a lexical phonological system that is used to repeat both known and novel words and that processes linguistic information independent of its meaning.     

Age, executive functions, and visuospatial functioning in healthy older adults.

Visuospatial test performance declines with age, whereas verbal test performance remains fairly constant. This pattern has been attributed to an age-related decline in either right-hemisphere functioning or executive functions (EFs), which may be associated with prefrontal cortical decline. Timed and untimed EF tests, and visuospatial tests requiring substantial integrative skill (I-VS) or little or no integrative skill (non-I-VS) were administered to young-old (aged 74 yrs and younger) and old-old (aged 75 yrs and older) healthy volunteers. Groups differed on I-VS tests and on many EF tests but not on non-I-VS tests. I-VS tests correlated highly with tests of EFs, but non-I-VS tests did not. These results are interpreted as supporting the proposal that an age-related decline in EF underlies the decline in visuospatial test performance observed with advancing age. Other issues regarding the relationship between age and EF are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failures in information processing in patients with Korsakoff''s syndrome

By means of a modified and simplified surgical and implantation technique, standardized values for visually evoked potentials (EP) from 7 brain structures (caudate nucleus, posterior hypothalamus, mesencephalic reticular formation, intra-laminar thalamic nuclei, amygdala, dorsal hippocampus and visual cortex) are obtained. The importance of a careful selection of the animal material, constant test conditions and the selection of test parameters as a prerequisite for the assessment of psychotropic drugs is emphasized and discussed. As an example of the specific influence on visually evoked potentials in the above named brain structures, the effects of haloperidol and amytriptyline on latencies and amplitudes of the individual parameters of EPs are described. It is assumed that the method described can be of great assistance for investigation and classification of newly developed substances.     

Psychiatric versus psychological opinion regarding personality disturbances.

Results of a survey "designed to determine, at least to some extent, the degree of diversity and disunity of opinion between" psychiatrists and psychologists are presented. An objective questionnaire, consisting of 100 "declarative statements covering the nature, cause, and treatment of disturbances to the mental life and behavior of individuals, with chief emphasis on characteristics usually identified as psychotic and neurotic" which were representative of current opinion, was used. 75 psychiatrists (32 working in mental hospitals in Pennsylvania and New Jersey and 43 practicing psychiatrists in 21 states and the District of Columbia) and 60 psychologists (in 23 states and the District of Columbia) were the Ss. "Only 19 statements of opinion, out of the 100 explored in this study, reveal statistically significant differences of opinion between psychiatrists and psychologists." Psychiatrists show a higher degree of acceptance on 14 items, psychologists a higher degree of acceptance on the other 5. The specific items on which differences were indicated are presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation spectroscopy as a tool for electronic material characterization

Modulation spectroscopy is an optical characterization tool that can be of great utility to the materials scientist. We present here numerous examples where a simple photo-reflectance and electroreflectance setup is used in our laboratory to determine such important material parameters as alloy composition and carrier concentration in a very short time. For determining alloy composition in semiconductors, contactless room temperature photoreflectance is nearly as sensitive as low temperature photoluminescence. Examples will be given on how to determine: the effects of surface preparation and implant damage; alloy composition and carrier homogeneity for large area wafers to better than 1%; the segregation coefficient of isoelectronic impurities in bulk semiconductors; the sub-band energies in quantum well structures; and the presence and homogeneity of built-in electric fields in MODFET structures. Particular emphasis will be placed on band edge and exciton effects on the photoreflectance and on the criteria used to distinguish between them. Materials studied included Si doped GaAs, Al_xGa_1-xAs for variousx grown by OMVPE and MBE, bulk InP doped with iso-electronic As and Sb, and MODFET structures.     

Determination of the E1 and E1+Δ1 energy bands by photoreflectance in AlxGa1−xAs in the region 0<x<0.55

The E₁ and E₁+Δ₁ energy bands of metal–organic chemical vapor deposition grown Al_xGa_1−xAs, with x in the range 0–0.55, have been determined using photoreflectance technique. The aluminum composition for each sample was determined using the energy of the room-temperature photoluminescence compensated peak value and a suitable fundamental band gap formula. The positions of the E₁ and E₁+Δ₁ peaks were determined from curve-fitting an appropriate theoretical model to our experimental data by a modified downhill simplex method. Using the results, we propose new E₁ and E₁+Δ₁ cubic expressions as functions of the aluminum composition, x, and compare them with the available reported expressions.     

Lexical semantic and associative priming in Alzheimer's disease.

Semantic memory impairment was investigated in patients with probable Alzheimer's disease (AD) using a threshold oral word reading task to assess priming of different lexical relationships. Healthy elderly controls showed significant priming for associatively related nouns (tempest-teapot) and also for nouns semantically related either because both designate basic-level exemplars of a common superordinate category (cousin-nephew) or because the target names the superordinate category of the prime (daughter-relative). AD patients, in contrast, showed preserved priming of lexical associates but impaired priming of certain semantic relationships. They showed no priming between words designating coordinate exemplars within a category, despite preserved priming of the superordinate category label. Findings are consistent with the view that at least part of the semantic deficit in AD is due to disruption of semantic knowledge that affects relationships among basic-level concepts, more than the relationships between these concepts and their corresponding superordinate category of membership. (PsycINFO Database Record (c) 2010 APA, all rights reserved)