Showing papers by "University of Southern California published in 1992"

Optical Coherence Tomography

Abstract: Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease. OCT is an interferometric technique that detects reflected and backscattered light from tissue and is often described as the optical analogue to ultrasound. The inherent safety of the technology allows for in vivo use of OCT in patients. The main strength of OCT is the depth resolution. In dermatology, most OCT research has turned on non-melanoma skin cancer (NMSC) and non-invasive monitoring of morphological changes in a number of skin diseases based on pattern recognition, and studies have found good agreement between OCT images and histopathological architecture. OCT has shown high accuracy in distinguishing lesions from normal skin, which is of great importance in identifying tumour borders or residual neoplastic tissue after therapy. The OCT images provide an advantageous combination of resolution and penetration depth, but specific studies of diagnostic sensitivity and specificity in dermatology are sparse. In order to improve OCT image quality and expand the potential of OCT, technical developments are necessary. It is suggested that the technology will be of particular interest to the routine follow-up of patients undergoing non-invasive therapy of malignant or premalignant keratinocyte tumours. It is speculated that the continued technological development can propel the method to a greater level of dermatological use.

Generating fuzzy rules by learning from examples

Abstract: A general method is developed to generate fuzzy rules from numerical data. The method consists of five steps: divide the input and output spaces of the given numerical data into fuzzy regions; generate fuzzy rules from the given data; assign a degree of each of the generated rules for the purpose of resolving conflicts among the generated rules; create a combined fuzzy rule base based on both the generated rules and linguistic rules of human experts; and determine a mapping from input space to output space based on the combined fuzzy rule base using a defuzzifying procedure. The mapping is proved to be capable of approximating any real continuous function on a compact set to arbitrary accuracy. Applications to truck backer-upper control and time series prediction problems are presented. >

Power in Top Management Teams: Dimensions, Measurement, and Validation

Abstract: Top managers' power plays a key role in strategic decision making. However, although numerous scholars have recognized its importance, very few have attempted to measure the phenomenon. In this article, I present a set of dimensions measuring top managers' power and suggest a measurement methodology to facilitate empirical inquiry. Data from a group of 1,763 top managers in three industries were used to assess the validity and reliability of the power dimensions in three studies. Results demonstrate strong support for the proposed power dimensions.

Building an Information System Design Theory for Vigilant EIS

Abstract: This paper defines an information system design theory ISDT to be a prescriptive theory which integrates normative and descriptive theories into design paths intended to produce more effective information systems. The nature of ISDTs is articulated using Dubin's concept of theory building and Simon's idea of a science of the artificial. An example of an ISDT is presented in the context of Executive Information Systems EIS. Despite the increasing awareness of the potential of EIS for enhancing executive strategic decision-making effectiveness, there exists little theoretical work which directly guides EIS design. We contend that the underlying theoretical basis of EIS can be addressed through a design theory of vigilant information systems. Vigilance denotes the ability of an information system to help an executive remain alertly watchful for weak signals and discontinuities in the organizational environment relevant to emerging strategic threats and opportunities. Research on managerial information scanning and emerging issue tracking as well as theories of open loop control are synthesized to generate vigilant information system design theory propositions. Transformation of the propositions into testable empirical hypotheses is discussed.

A practical and theoretical guide to measurement invariance in aging research

Abstract: We describe mathematical and statistical models for factor invariance. We demonstrate that factor invariance is a condition of measurement invariance. In any study of change (as over age) measurement invariance is necessary for valid inference and interpretation. Two important forms of factorial invariance are distinguished: "configural" and "metric". Tests for factorial invariance and the range of tests from strong to weak are illustrated with multiple group factor and structural equation modeling analyses (with programs such as LISREL, COSAN, and RAM). The tests are for models of the organization and age changes of intellectual abilities. The models are derived from current theory of fluid (Gf) and crystallized (Gc) abilities. The models are made manifest with measurements of the WAIS-R in the standardization sample. Although this is a methodological paper, the key issues and major principles and conclusions are presented in basic English, devoid of technical details and obscure notation. Conceptual principles of multivariate methods of data analysis are presented in terms of substantive issues of importance for the science of the psychology of aging.

Criteria for the diagnosis of ischemic vascular dementia proposed by the State of California Alzheimer's Disease Diagnostic and Treatment Centers

Abstract: Accurate diagnosis of vascular dementia is important for the recognition of underlying pathophysiology and the institution of appropriate therapy. It is also important for the determination of the incidence and prevalence of not only vascular dementia but also Alzheimer's disease (AD), since differentiating between these two entities is often problematic. The State of California Alzheimer's Disease Diagnostic and Treatment Centers (ADDTC) herein propose criteria for the diagnosis of ischemic vascular dementia (IVD). These criteria broaden the conceptualization of vascular dementia, include the results of neuroimaging studies, emphasize the importance of neuropathologic confirmation, refine nosology, and identify areas that require further research. Parallel use of the proposed definitions of "possible" and "mixed" categories in the diagnosis of both AD and IVD would ensure compatibility between the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) criteria for AD and the ADDTC criteria for IVD. Uniform classification of subtypes of IVD will improve the generalizability of individual studies and aid in multicenter collaborations.

Fuzzy systems are universal approximators

Abstract: The author proves that fuzzy systems are universal approximators. The Stone-Weierstrass theorem is used to prove that fuzzy systems with product inference, centroid defuzzification, and a Gaussian membership function are capable of approximating any real continuous function on a compact set to arbitrary accuracy. This result can be viewed as an existence theorem of an optimal fuzzy system for a wide variety of problems. >

Whole genome amplification from a single cell: implications for genetic analysis

Abstract: We have developed an in vitro method for amplifying a large fraction of the DNA sequences present in a single haploid cell by repeated primer extensions using a mixture of 15-base random oligonucleotides. We studied 12 genetic loci and estimate that the probability of amplifying any sequence in the genome to a minimum of 30 copies is not less than 0.78 (95% confidence). Whole genome amplification beginning with a single cell, or other samples with very small amounts of DNA, has significant implications for multipoint mapping by sperm or oocyte typing and possibly for genetic disease diagnosis, forensics, and the analysis of ancient DNA samples.

Novel major archaebacterial group from marine plankton

Abstract: MARINE bacteria often dominate the plankton biomass1,2 and are responsible for much of the cycling of organic matter3, but bacterial diversity is poorly understood because conventional identification methods (requiring culturing) miss about 99% of the organisms4,5. Recent advances permit characterization of microbial communities by analysis of 16S ribosomal RNA gene sequences directly from biomass without the need to culture the organisms6; such studies from surface ocean samples have found only eubacteria7–10, not archaebacteria (or Archae11), which are profoundly different12. Here we report 16S rRNA sequences obtained from Pacific Ocean bacterioplankton samples collected from depths of 100 m and 500 m. Among these we found sequences only distantly related to those of any organisms previously characterized by 16S rRNA sequences, with similarities to the nearest such relatives (extreme thermophiles) approximately the same as those between animals and plants. We suggest that these sequences are from a previously undescribed archaebacterial group that may have diverged from the ancestors of characterized organisms very early in evolution.

A revised estimate of twin concordance in systemic lupus erythematosus

Abstract: Objective. Based on a small clinical series and previously published case reports, concordance for systemic lupus erythematosus (SLE) among monozygous (MZ) twins has been reported to be as high as 69%. Using a larger and less biased sample, we provide another estimate of this percentage. Methods. We established a registry of twins with SLE, based upon self-reports and information provided by the patients' physicians. We used DNA fingerprinting to validate the reported zygosity in a sample of these twins. Results. Of 107 twin pairs meeting the American College of Rheumatology 1982 revised criteria for the diagnosis of SLE, 24% of 45 MZ pairs and 2% of 62 dizygous (DZ) pairs were concordant. The frequency distributions of diagnostic criteria and disease symptoms in the SLE patients were similar to those in other published reports of SLE patients. Zygosity was confirmed by DNA fingerprinting in a subsample of 15 self-described MZ twins and 7 self-described DZ twins. AH individuals had correctly predicted their zygosity. Conclusion. MZ concordance for SLE is similar to that for other autoimmune diseases and is much lower than previously believed.

Normal polysomnographic values for children and adolescents.

Abstract: Although polysomnography is routinely performed to evaluate children and adolescents with sleep-disordered breathing, normal polysomnographic values for the pediatric age group have not yet been established. We therefore performed overnight polysomnography in 50 normal children and adolescents (mean age 9.7 +/- 4.6 SD yr, range 1.1 to 17.4 yr). Of the children 56% were male. Chest wall motion, ECG, oronasal airflow, end-tidal PCO2 (PETCO2), arterial oxygen saturation (SaO2), and electrooculogram were monitored. Children had 0.1 +/- 0.5 (range 0 to 3.1) obstructive apneas per hour of total sleep time, with only 18% of children having any obstructive apneas. No child had obstructive apneas > 10 s in duration. Of the children 30% had central apneas > or = 10 s in duration, and one child had a central apnea associated with SaO2 45 mm Hg) occurred for 7 +/- 19% total sleep time (range 0 to 91%). The SaO2 nadir was 96 +/- 2% (range 89 to 98%), with only one child desaturating below 90% in association with a central apnea. We conclude that polysomnographic results in the pediatric age group differ from those in adults. Recommendations for normal polysomnographic criteria are given.

Nonlinear control via approximate input-output linearization: the ball and beam example

Abstract: Approximate input-output linearization of nonlinear systems which fail to have a well defined relative degree is studied. For such systems, a method for constructing approximate systems that are input-output linearizable is provided. The analysis presented is motivated through its application to a common undergraduate control laboratory experiment-the ball and beam-where it is shown to be more effective for trajectory tracking than the standard Jacobian linearization. >

A pattern of accumulation of a somatic deletion of mitochondrial DNA in aging human tissues.

Abstract: An assay that selectively amplifies a specific deletion of the mitochondrial genome has been used to study the extent of the deletion's accumulation in a variety of human tissues. The deletion occurs at much higher levels in nervous and muscle tissues than in all other tissues studied. The variation in deletion level between the same tissues in different persons of similar age appears to be less than the variation among tissues within an individual. Tests for artifactual explanations of the level differences were each negative. Three cellular parameters that are correlated with the level of the deletion are identified. The preferential accumulation of deleterious mitochondrial mutations in a restricted subset of aging human tissues may compound deficiencies of function in those tissues that accrue with age.

Endoscopic sclerotherapy as compared with endoscopic ligation for bleeding esophageal varices.

Abstract: Background. Endoscopic sclerotherapy is an accepted treatment for bleeding esophageal varices, but it is associated with substantial local and systemic complications. Endoscopic ligation, a new form of endoscopic treatment for bleeding varices, may be safer. We compared the effectiveness and safety of the two techniques. Methods. In this randomized trial we compared endoscopic sclerotherapy and endoscopic ligation in 129 patients with cirrhosis who had proved bleeding from esophageal varices. Sixty-five patients were treated with sclerotherapy, and 64 with ligation. Initial treatment for acute bleeding was followed by elective retreatment to eradicate varices. The patients were followed for a mean of 10 months, during which we determined the incidence of complications and recurrences of bleeding, the number of treatments needed to eradicate varices, and survival. Results. Active bleeding at the first treatment was controlled by sclerotherapy in 10 of 13 patients (77 percent) and by ligation in 12...

Epstein-Barr virus-associated gastric adenocarcinoma.

Abstract: The Epstein-Barr virus (EBV) has been detected in certain types of lymphoma and some epithelial neoplasms including nasopharyngeal lymphoepithelioma, and rare lymphoepithelioma-like carcinomas occurring in a variety of organs including, most recently, the stomach. The authors investigated the possibility that EBV may be present not only in the rare gastric cancers that resemble nasopharyngeal lymphoepithelioma, but also in typical gastric adenocarcinoma. EBV sequences were detected in 22 of 138 (16%) cases of typical gastric adenocarcinoma by polymerase chain reaction and in situ hybridization (ISH) techniques. The EBV genomes were specifically present within the gastric carcinoma cells in an even distribution. The EBV genomes were also present in adjacent dysplastic epithelium but were absent in surrounding lymphocytes, other normal stromal cells, intestinal metaplasia, and normal gastric mucosa. The EBV genomes in the infected gastric carcinoma cells are expressed as EBV RNA was detected by ISH. EBV was most often detected in gastric tumors from men (21%) compared with women (3%). Thus some cases of gastric adenocarcinoma are EBV-associated.

Structural indexing: efficient 3-D object recognition

Abstract: The authors present an approach for the recognition of multiple 3-D object models from three 3-D scene data. The approach uses two different types of primitives for matching: small surface patches, where differential properties can be reliably computed, and lines corresponding to depth or orientation discontinuities. These are represented by splashes and 3-D curves, respectively. It is shown how both of these primitives can be encoded by a set of super segments, consisting of connected linear segments. These super segments are entered into a table and provide the essential mechanism for fast retrieval and matching. The issues of robustness and stability of the features are addressed in detail. The acquisition of the 3-D models is performed automatically by computing splashes in highly structured areas of the objects and by using boundary and surface edges for the generation of 3-D curves. The authors present results with the current system (3-D object recognition based on super segments) and discuss further extensions. >

Projections of the ventral subiculum to the amygdala, septum, and hypothalamus: A PHAL anterograde tract‐tracing study in the rat

Abstract: The projections of the ventral subiculum are organized differentially along the dorsoventral (or septotemporal) axis of this cortical field, with more ventral regions playing a particularly important role in hippocampal communication with the amygdala, bed nuclei of the stria terminalis (BST), and rostral hypothalamus. In the present study we re-examined the projection of the ventral subiculum to these regions with the Phaseolus vulgaris leucoagglutinin (PHAL) method in the rat. The results confirm and extend earlier conclusions based primarily on the autoradiographic method. Projections from the ventral subiculum course either obliquely through the angular bundle to innervate the amygdala and adjacent parts of the temporal lobe, or follow the alveus and fimbria to the precommissural fornix and medial corticohypothalamic tract. The major amygdalar terminal field is centered in the posterior basomedial nucleus, while other structures that appear to be innervated include the piriformamygdaloid area, the posterior basolateral, posterior cortical, posterior, central, medial, and intercalated nuclei, and the nucleus of the lateral olfactory tract. Projections from the ventral subiculum reach the BST mainly by way of the precommissural fornix, and provide rather dense inputs to the anterodorsal area as well as the transverse and interfascicular nuclei. The medial corticohypothalamic tract is the main route taken by fibers from the ventral subiculum to the hypothalamus, where they innervate the medial preoptic area, "shell" of the ventromedial nucleus, dorsomedial nucleus, ventral premammillary nucleus, and cell-poor zone around the medial mammillary nucleus. We also observed a rather dense terminal field just dorsal to the suprachiasmatic nucleus that extends dorsally and caudally to fill the subparaventricular zone along the medial border of the anterior hypothalamic nucleus and ventrolateral border of the paraventricular nucleus. The general pattern of outputs to the hypothalamus and septum is strikingly similar for the ventral subiculum and suprachiasmatic nucleus, the endogenous circadian rhythm generator.

Ecology of sea ice biota 2. Global significance.

Abstract: The sea ice does not only determine the ecology of ice biota, but it also influences the pelagic systems under the ice cover and at ice edges. In this paper, new estimates of Arctic and Antarctic production of biogenic carbon are derived, and differences as well as similarities between the two oceans are examined. In ice-covered seas, high algal concentrations (blooms) occur in association with several types of conditions. Blooms often lead to high sedimentation of intact cells and faecal pellets. In addition to ice-related blooms, there is progressive accumulation of organic matter in Arctic multi-year ice, whose fate may potentially be similar to that of blooms. A fraction of the carbon fixed by microalgae that grow in sea ice or in relation to it is exported out of the production zone. This includes particulate material sinking out of the euphotic zone, and also material passed on to the food web. Pathways through which ice algal production does reach various components of the pelagic and benthic food webs, and through them such top predators as marine mammals and birds, are discussed. Concerning global climate change and biogeochemical fluxes of carbon, not all export pathways from the euphotic zone result in the sequestration of carbon for periods of hundreds of years or more. This is because various processes, that take place in both the ice and the water column, contribute to mineralize organic carbon into CO2 before it becomes sequestered. Processes that favour the production and accumulation of biogenic carbon as well as its export to deep waters and sequestration are discussed, together with those that influence mineralization in the upper ice-covered ocean.

Dietary intake of fiber and decreased risk of cancers of the colon and rectum: Evidence from the combined analysis of 13 case-control studies

Abstract: BACKGROUND Colorectal cancer is a major public health problem in both North America and western Europe, and incidence and mortality rates are rapidly increasing in many previously low-risk countries. It has been hypothesized that increased intakes of fiber, vitamin C, and beta carotene could decrease the risk of colorectal cancer. PURPOSE The objective of this study was to examine the effects of fiber, vitamin C, and beta-carotene intakes on colorectal cancer risk in a combined analysis of data from 13 case-control studies previously conducted in populations with differing colorectal cancer rates and dietary practices. The study was designed to estimate risks in the pooled data, to test the consistency of the associations across the studies, and to examine interactions of the effects of the nutrients with cancer site, sex, and age. METHODS Original data records for 5287 case subjects with colorectal cancer and 10,470 control subjects without disease were combined. Logistic regression analysis was used to estimate relative risks and confidence intervals for intakes of fiber, vitamin C, and beta carotene, with the effects of study, sex, and age group being adjusted by stratification. RESULTS Risk decreased as fiber intake increased; relative risks were 0.79, 0.69, 0.63, and 0.53 for the four highest quintiles of intake compared with the lowest quintile (trend, P < .0001). The inverse association with fiber is seen in 12 of the 13 studies and is similar in magnitude for left- and right-sided colon and rectal cancers, for men and for women, and for different age groups. In contrast, after adjustment for fiber intake, only weak inverse associations are seen for the intakes of vitamin C and beta carotene. CONCLUSION This analysis provides substantive evidence that intake of fiber-rich foods is inversely related to risk of cancers of both the colon and rectum. IMPLICATIONS If causality is assumed, we estimate that risk of colorectal cancer in the U.S. population could be reduced about 31% (50,000 cases annually) by an average increase in fiber intake from food sources of about 13 g/d, corresponding to an average increase of about 70%.

A Conflict-Cooperation Scale for WEIS Events Data

Abstract: The problem of aggregating WEIS events data, coded as discrete events, into a continuous time series representing conflict or cooperation between two nations is discussed. Past literature on the su...

A prospective study of benign breast disease and the risk of breast cancer.

Abstract: Objective. —To examine the relation between proliferative benign breast disease with and without atypical hyperplasia and the subsequent risk of breast cancer. Design. —Case-control study nested within a prospective cohort study. Median follow-up after breast biopsy was 8 years (25th to 75th percentile, 5 to 14 years). Participants. —Selected from a prospective cohort of 121 700 US registered nurses followed up from 1976 to 1986. Cases were women with breast cancer who had a prior biopsy for benign breast disease. Controls were randomly selected and matched on year of biopsy and year of birth from among women in the cohort who had a benign breast biopsy but who did not develop breast cancer. Included in the analysis were 121 cases and 488 controls. Main Outcome Measure. —Development of breast cancer. Results. —Slides from the first benign breast biopsy were reviewed by two breast pathologists blinded to the outcome. The multiply adjusted relative risks (RRs) for breast cancer, relative to women with no proliferative disease, were 1.6 for proliferative disease without atypia (95% confidence interval [Cl], 1.0 to 2.5) and 3.7 for atypical hyperplasia (95% Cl, 2.1 to 6.8). Breast cancer risk was more strongly associated with atypical hyperplasia among premenopausal women (RR = 5.9; 95% Cl, 2.9 to 13.2) than postmenopausal women (RR = 2.3; 95% Cl, 0.9 to 5.9), but the association of breast cancer risk with proliferative disease without atypia did not differ across menopausal status. Conclusion. —These results confirm the marked increase in breast cancer risk among women with atypical hyperplasia, particularly in premenopausal women, and suggest that these women should be encouraged to undergo frequent breast cancer screening. (JAMA. 1992;267:941-944)