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L Allen

Publications and source records attributed to L Allen.

At least 55 records · Page 3Linked to original sources
PubMed1995

Dichoptic and physical information combination: a comparison.

Two experiments, in which information from two different kinds of degraded (low-pass filtered and regionally averaged or blocked) visual stimuli (aircraft silhouettes) was combined, are reported. In the first experiment, the degraded images were perceptually combined by being separately presented to each eye in a dichoptic viewing situation. Both stimuli in both presentations were masked by identical random visual interference. When the two stimuli were visually fused, performance in a discrimination task was enhanced over that in control situations in which only one of the two stimuli was presented. In the second experiment the two degraded stimuli were physically superimposed prior to binocular presentation, with a similar result. The results of this hybrid (masking/binocular summation) experiment suggest that true advantageous information pooling occurs when these two types of degraded stimuli are combined either physically or dichoptically.

Attention↗
PubMed1995

Comprehensive appraisal of 239 + 240Pu in soils around Rocky Flats, Colorado.

Plutonium contamination of soils around Rocky Flats Environmental & Technology Site, near Golden, Colorado, resulted from past outdoor storage practices and subsequent remobilization due to inadequate cleanup practices. Until now human-health risk assessment has not been performed because of a lack of sufficient information regarding the spatial extent of 239 + 240Pu in soils. The purpose of this work was to elucidate the extent of plutonium contamination in surface soils, and to assess the uncertainty associated with the spatial distribution of 239 + 240Pu around Rocky Flats Environmental & Technology Site. Four data sets were collected or compiled for this investigation: (1) samples collected from 240 plots of 1.01- or 4.05-hectare by compositing 25 evenly-spaced samples from the upper 0.64 cm in each plot; (2) samples collected from the upper 5 cm of soil in 167 of the same 240 plots by compositing 10 samples from the center of each plot; (3) historical data compiled from samples collected between 1969 and 1973, considered to be the most indicative of the original release; and (4) the exhaustive data set that contains the samples from 1, 2, and 3 and other published data sets collected between 1974 and 1994. These latter samples varied in depth and method of sampling. Plutonium activity reported in the exhaustive data set ranged from 0.03 Bq kg-1 to 407,000 Bq kg-1 with a mean of 1,443 Bq kg-1, median of 6.6 Bq kg-1, standard deviation of 18,463 Bq kg-1, and a coefficient of variation of 12.6. The technique of nonparametric indicator kriging was used to model four conditional cumulative distribution functions of 239 + 240Pu in soils around Rocky Flats Environmental & Technology Site. Each of the conditional cumulative distribution functions was used to generate an E-type (mean of the conditional cumulative distribution functions) surface. The resulted surfaces were consistent with the hypothesis that the westerly winds were the dominant mechanism of plutonium dispersal. Other processes, such as downstream transport of sediment along local southeast-trending drainages, may have additionally moved small amounts of plutonium. The conditional cumulative distribution functions were also used to construct probability of exceedance maps of 239 + 240Pu in soils. For the purpose of this report two threshold values for the probability maps were selected: (1) the mean and the highest measured global fallout of plutonium (1.48 and 2.96 Bq kg-1, respectively); and (2) the programmatic preliminary remediation goal for residential occupancy scenario (126 Bq kg-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Colorado↗
PubMed1995

A type I cell-specific protein is a biochemical marker of epithelial injury in a rat model of pneumonia.

In this study we determined whether the alveolar fluid content of a specific epithelial type I cell protein, rTI40, can be used as a biochemical marker for lung injury. A model of alveolar epithelial injury was developed by instilling Pseudomonas aeruginosa bacteria (PA103) into the airspaces of anesthetized, ventilated rats. After 6 h, the alveolar fluid content of rTI40 from PA103-treated rats was increased over 80-fold in comparison to alveolar fluid from control rats (P < 0.05). This increase in rTI40 correlated with both morphological evidence of injury to alveolar epithelial type I cells and increased permeability of the alveolar epithelium to protein tracers. In contrast, the lactate dehydrogenase activity of alveolar fluid from PA103-treated rats was elevated only threefold over control values at 6 h (P < 0.05). In a second study using a less injurious strain of P. aeruginosa (PA103 exsA::omega), the alveolar fluid content of rTI40 was the same as control values. These findings indicate that the alveolar fluid content of a type I cell-specific protein can be used as a sensitive and specific biochemical marker of type I cell injury.

Animals↗
PubMed1995

Health and social characteristics and children's cognitive functioning: results from a national cohort.

OBJECTIVES: The purpose of this study was to examine the associations between cognitive functioning in children and sociodemographic, family, and health characteristics. METHODS: Data from phase 1 of the third National Health and Nutrition Examination Survey were used to evaluate performance on standardized cognitive tests in a representative sample of 2531 children 6 to 16 years of age. Multivariate analyses were used to assess independent associations between covariates and test performance. RESULTS: Lower income, minority status, and lower education of an adult reference person (one of the persons in the household who owned or rented the home) were independently associated with poorer performance on all cognitive subtests. To a lesser degree, general health status, history of birth complications, and sex also were independent predictors of performance for some of the subtests. CONCLUSIONS: These findings illustrate disparities in cognitive functioning across sociodemographic and health characteristics of children in the US population. They suggest the need for public health policies to take a multifaceted approach to optimizing childhood environments in order to overcome the effects of socioeconomic and minority status.

Adolescent↗
PubMed1995

The effect of combinations of image degradations in a discrimination task.

This paper explores the ways in which combinations of image degradations affect discrimination. Nine experiments are described that examine the discriminability of visual images that are degraded with three types of information reducing transformations: random punctate visual interference, low-pass spatial frequency filtering, and local area (i.e., block) averaging. The results of these experiments characterize a powerful visual ability to discriminate highly degraded stimuli unless that ability is severely challenged by relatively high levels of random visual interference. Discriminative commutativity of the orders in which the other two degradations are imposed is demonstrated. That is, the order in which the degradations are applied does not affect the final discriminative outcome. This result is in contrast to predictions from relevant mathematics and direct examination of the images produced by both orders of degradation. The commutativity is attributed to the particularly strong effect of the low-pass spatial frequency filtering degradation on the discrimination process. This study also demonstrates that combinations of degradations in a discrimination task always result in a reduction in performance, and never in the improvement that has been reported for recognition. This difference is attributed to the fact that form discrimination is mediated mainly by local features and high-frequency spatial components, whereas recognition is mediated mainly by global features and low-frequency spatial components.

Adult↗
PubMed1995

Combining image degradations in a recognition task.

Six experiments are reported that investigate the effect on form recognition performance of combining three kinds of stimulus degradations: local area averaging of intensities, low-pass spatial frequency filtering, and random dot visual interference. The effects are shown to be more complicated than previously reported in simple demonstrations. The complexity of the results suggests that models based on single stimulus attributes such as energy or spatial frequency spectrum probably cannot account for the data. Eclectic theories that invoke combinations of redundant processes may be necessary for describing visual recognition phenomena, even within the limited domain examined in this study.

Adult↗
PubMed1994

Wound complications in patients receiving adjuvant chemotherapy after mastectomy and immediate breast reconstruction for breast cancer.

A retrospective study was done to evaluate the frequency and severity of wound complications in 112 patients with breast cancer who received adjuvant chemotherapy following mastectomy with immediate breast reconstruction. Data on wound complications were available for 120 mastectomies. The rate of complications in 36 mastectomies treated with chemotherapy after mastectomy and immediate reconstruction was compared to that in 84 mastectomies not receiving adjuvant therapy. There were 25 wound complications (20.8%) in the entire group. The rate of wound complications was 27.8% (10 of 36 mastectomies) in the group treated with adjuvant chemotherapy and 17.9% (15 of 84 mastectomies) in the group that did not receive adjuvant therapy (P = 0.13). No patient had a delay in the initiation of adjuvant therapy because of wound complications secondary to immediate reconstruction. Logistic regression analysis found no correlation between age, type of operation, tumor pathology, stage, number of lymph nodes harvested, type of prosthesis or chemotherapy, and wound complications in patients undergoing immediate breast reconstruction after mastectomy. The frequency of wound complications was not increased in patients receiving adjuvant chemotherapy after mastectomy and immediate breast reconstruction. The administration of adjuvant chemotherapy does not need to be delayed in patients who have had immediate breast reconstruction following mastectomy for breast cancer.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

Psychophysical foundations of a model of amplified night vision in target detection tasks.

In this article we examine some of the basic psychophysics relevant to amplified night vision devices. These devices produce images that are substantially different from ordinary visual scenes. Distortions in contrast and luminance and the introduction of visual interference and geometrical artifacts contribute to unusual viewing conditions. We carried out experiments to determine the effect of these parameters of the image on a highly controlled visual target detection task simulated on a computer graphics system that closely models a night vision device. Our results indicate that display luminance and geometrical artifacts degrade detection performance only slightly, whereas contrast and visual interference have a substantial degrading effect.

Adult↗
PubMed1994

Decompression for dysthyroid ophthalmopathy via the orbital rim approach. Technical note.

A technique is described wherein the approach to the orbital cavity, with resection of its roof and lateral wall, is facilitated by a single burr hole and local en bloc removal of the lateral and supraorbital margins. A satisfactory decompression with reduction of proptosis of the orbital contents and a good cosmetic result is achieved without the need for a large dural exposure. The approach may be combined with removal of the anterior wall of the frontal sinus in cases where the lateral aspect extends appreciably laterally. Access to the orbital roof and lateral wall is straightforward and can be coupled with further removal of the floor lateral to the infraorbital nerve and medial wall. Advancement of the orbital rim upon bone replacement adds to orbital volume, creating better mechanical advantage for eyelid closure.

Adolescent↗
PubMed1994

The impact of school transitions in early adolescence on the self-system and perceived social context of poor urban youth.

This study examined the effects of the normative school transition (n = 580) during early adolescence on the self-system and perceived school and peer social contexts of poor, black (n = 161), white (n = 146), and Latino (n = 273) youth in the public school systems of 3 eastern urban cities. The results revealed negative effects of the school transition on the affective and behavioral domains of the self-system. These declines in self-esteem, class preparation, and grade-point average (GPA) were common across race/ethnicity and gender. Concurrently, the school transition was perceived to be associated with changes in the school and peer contexts. Daily hassles with the school increased, while social support and extracurricular involvement decreased over the transition. Daily hassles with peers decreased, and peer values were perceived as more antisocial. These changes in the school and peer microsystems were also common across race/ethnicity and gender. In addition, transition-associated school and peer changes and, in particular, changes in daily hassles with the school were associated with changes in the academic dimensions of the self-system, that is, academic efficacy expectations, class preparation, and GPA. The results are discussed within a developmental mismatch framework.

Adolescent↗
PubMed1993

Quantification and kinetics of 25-hydroxyvitamin D3 by isotope dilution liquid chromatography/thermospray mass spectrometry.

A liquid chromatography/thermospray mass spectrometry method has been developed and used to measure the plasma levels and half-life of 25-hydroxyvitamin D3 in adults. The mean plasma levels of 25-hydroxyvitamin D3 averaged 40 ng ml-1 (n = 4) in summer and 30 ng ml-1 (n = 6) in winter. The method was also used to determine the half-life of serum 25-hydroxyvitamin D3 in subjects maintained on either high or low-fiber diets who had been given an intravenous infusion of (6,19,19-2H3)25-hydroxyvitamin D3 sufficient to label 5% of their estimated body pools. The half-life was determined to be 10.4 days (n = 4), which is approximately 50% of the currently accepted value of 19 days, determined using radiolabeled methods. This difference may be due to kinetic isotope effects arising as a result of the tritiated compounds being labeled at sites that undergo Cyt-P450-catalyzed oxidations.

Adult↗