Showing papers by "Boston University published in 1989"

Stable Adaptive Systems

Abstract: Stability theory simple adaptive systems adaptive observers the control problem persistent excitation error models robust adaptive control the control problem - relaxation of assumptions multivariable adaptive systems applications of adaptive control.

Effect sizes for interpreting changes in health status.

Abstract: Health status measures are being used with increasing frequency in clinical research. Up to now the emphasis has been on the reliability and validity of these measures. Less attention has been given to the sensitivity of these measures for detecting clinical change. As health status measures are app

T-cell receptor cross-linking transiently stimulates adhesiveness through LFA-1

Abstract: Effective interaction between T cells and their targets requires that recognition of specific antigen be coordinated with increased cell-cell adhesion. We show that antigen-receptor cross-linking increases the strength of the adhesion mechanism between lymphocyte function-associated molecule-1 (LFA-1) and intercellular adhesion molecules (ICAMs), with intracellular signals transmitted from the T-cell antigen receptor to the LFA-1 adhesion molecule. The increase in avidity is rapid and transient, providing a dynamic mechanism for antigen-specific regulation of lymphocyte adhesion and de-adhesion.

How Do Self-Attributed and Implicit Motives Differ?.

Abstract: From the beginning of the work on the achievement motive (McClelland, Atkinson, Clark, & Lowell, 1953), it has been apparent that motive dispositions as coded in imaginative thought from stories written to pictures differ from motive dispositions with the same name as measured in self-reported desires or interests. The authors of the studies on achievement motivation wanted to demonstrate that the variable they had identified in fantasy functioned like an animal drive in the sense that it energized, directed, and selected behavior. In this tradition (cf. Melton, 1952) it was particularly important to show that a motivational disposition that these authors labeled n Achievement (for the need to achieve) would select behavior or facilitate learning just as hunger would facilitate a rat's learning a maze. When McClelland et al. examined a self-reported desire for achievement, they observed that it did not facilitate learning in the same way that n Achievement did and so concluded that self-reported desires do not function like motives. An early study (deCharms, Morrison, Reitman, & McClelland, 1955) showed that the two measures of achievement motivation were uncorrelated and that their behavioral correlates were different. For these reasons deCharms et al. urged that the two measures be distinguished in future research by referring to the variable identified in fantasy as n Achievement (for the need to achieve) and the self-reported desire for achievement as v Achievement (for valuing achievement).

A hard-core predicate for all one-way functions

Abstract: A central tool in constructing pseudorandom generators, secure encryption functions, and in other areas are “hard-core” predicates b of functions (permutations) ƒ, discovered in [Blum Micali 82]. Such b(x) cannot be efficiently guessed (substantially better than 50-50) given only ƒ(x). Both b, ƒ are computable in polynomial time.[Yao 82] transforms any one-way function ƒ into a more complicated one, ƒ*, which has a hard-core predicate. The construction applies the original ƒ to many small pieces of the input to ƒ* just to get one “hard-core” bit. The security of this bit may be smaller than any constant positive power of the security of ƒ. In fact, for inputs (to ƒ*) of practical size, the pieces effected by ƒ are so small that ƒ can be inverted (and the “hard-core” bit computed) by exhaustive search.In this paper we show that every one-way function, padded to the form ƒ(p, x) = (p, g(x)), VVpVV = VxV, has by itself a hard-core predicate of the same (within a polynomial) security. Namely, we prove a conjecture of [Levin 87, sec. 5.6.2] that the scalar product of Boolean vectors p, x is a hard-core of every one-way function ƒ(p, x) = (p, g(x)). The result extends to multiple (up to the logarithm of security) such bits and to any distribution on the x's for which ƒ is hard to invert.

Impaired neurogenic and endothelium-mediated relaxation of penile smooth muscle from diabetic men with impotence.

Abstract: Relaxation of the smooth muscle of the corpora cavernosa of the penis is necessary for penile erection. To determine the relation of impaired relaxation to impotence in diabetic patients, we performed an in vitro examination of corpus cavernosum tissue obtained at the time of implantation of a penile prosthesis in 21 diabetic and 42 nondiabetic men with impotence. Contraction was induced in isolated strips of corporal smooth muscle by norepinephrine; then relaxation was assessed with electrical stimulation of autonomie nerves and with the administration of three agents: acetylcholine, which is known to be mediated by endothelium-derived relaxing factor; papaverine; and sodium nitroprusside. The latter two act directly on smooth muscle (i.e., they are endothelium-independent). Autonomically mediated relaxation with electrical stimulation was less pronounced in the smooth muscle from diabetic men (n = 18) than in the smooth muscle from nondiabetic men (n = 24; P = 0.001). The degree of impairment i...

Architecture and intrinsic connections of the prefrontal cortex in the rhesus monkey.

Abstract: An investigation of the architectonic organization and intrinsic connections of the prefrontal cortex was conducted in rhesus monkeys. Cytoarchitectonic analysis indicates that in the prefrontal cortex there are two trends of gradual change in laminar characteristics that can be traced from limbic periallocortex towards isocortical areas. The stepwise change in laminar features is characterized by the emergence and gradual increase in the width of granular layer IV, by an increase in the size of pyramidal cells in layers III and V, and by a higher cell-packing density in the supragranular layers. Myeloarchitectonic analysis reveals that the limbic areas are poorly myelinated, adjacent areas have a diffuse myelin content confined to the deep layers, and in isocortices the myelinated fibers are distributed in organized horizontal bands (of Bail-larger) and a vertical plexus. Using the above architectonic criteria, we observed that one of the architectonic trends takes a radial basoventral course from the periallocortex in the caudal orbitofrontal region to the adjacent proisocortex and then to area 13. The next stage of architectonic regions includes orbital areas 12, 11, and 14, which is followed by area 10, lateral area 12, and the rostral part of ventral area 46. The last group includes the caudal part of ventral area 46 and ventral area 8. The other trend takes a mediodorsal course from the periallocortex around the rostral portion of the corpus callosum to the adjacent proisocortical areas 24, 25, and 32 and then to the medially situated isocortical areas 9, 10, and 14. The next stage includes lateral areas 10 and 9 and the rostral part of dorsal area 46. The last group includes the caudal part of dorsal area 46 and dorsal area 8. The interconnections of subdivisions of the basoventral and mediodorsal cortices were studied with the aid of anterograde and retrograde tracers. Within each trend a given area projects in two directions: to adjoining regions belonging to succeeding architectonic stages on the one hand, and to nearby regions from the preceding architectonic stage on the other. In each direction there is more than one region involved in this projection system, paralleling the radial nature of architectonic change. Periallo- and proisocortices have widespread intrinsic connections, whereas isocortices situated at a distance from limbic areas, such as area 8, have restricted connections. Most interconnections are limited to areas within the same architectonic trend. However, there are links between cortices from the two trends, and these seem to occur between areas that are at a similar stage of architectonic differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)

Pseudo-random generation from one-way functions

Abstract: We show that the existence of one-way functions is necessary and sufficient for the existence of pseudo-random generators in the following sense. Let ƒ be an easily computable function such that when x is chosen randomly: (1) from ƒ(x) it is hard to recover an x1 with ƒ(x1) = ƒ(x) by a small circuit, or; (2) ƒ has small degeneracy and from ƒ(x) it is hard to recover x by a fast algorithm. From one-way functions of type (1) or (2) we show how to construct pseudo-random generators secure against small circuits or fast algorithms, respectively, and vice-versa. Previous results show how to construct pseudo-random generators from one-way functions that have special properties ([Blum, Micali 82], [Yao 82], [Levin 85], [Goldreich, Krawczyk, Luby 88]).We use the results of [Goldreich, Levin 89] in an essential way.

Multivitamin/Folic Acid Supplementation in Early Pregnancy Reduces the Prevalence of Neural Tube Defects

Abstract: We examined the relation of multivitamin intake in general, and folic acid in particular, to the risk of neural tube defects in a cohort of 23 491 women undergoing maternal serum α-fetoprotein screening or amniocentesis around 16 weeks of gestation. Complete questionnaires and subsequent pregnancy outcome information was obtained in 22 776 pregnancies, 49 of which ended in a neural tube defect. The prevalence of neural tube defect was 3.5 per 1000 among women who never used multivitamins before or after conception or who used multivitamins before conception only. The prevalence of neural tube defects for women who used folic acid-containing multivitamins during the first 6 weeks of pregnancy was substantially lower—0.9 per 1000 (prevalence ratio, 0.27; 95% confidence interval, 0.12 to 0.59 compared with never users). For women who used multivitamins without folic acid during the first 6 weeks of pregnancy and women who used multivitamins containing folic acid beginning after 7 or more weeks of pregnancy, the prevalences were similar to that of the nonusers and the prevalence ratios were close to 1.0. ( JAMA . 1989;262:2847-2852)

Is the Extended Family Altruistically Linked? Direct Tests Using Micro Data

Abstract: What is the basic economic decision-making unit? Is it the household or the extended family? This question is fundamental to economic analysis and policy design. The answer given by the Life Cycle and Keynesian models is that the economic unit is the household. According to these models, members of particular households act selfishly and do not fully share resources with extended family members in other households. Hence, altering the distribution of resources across households within the extended family will alter the consumption and labor supply of those households who acquire or lose resources. In contrast to the Life Cycle and Keynesian models, the altruism model implies that the extended family is the basic economic decision-making unit. According to this model the extended family is linked through altruism and, as a result, acts as if it fully shares resources. In the altruism model nondistortionary changes in the distribution of resources across households within the extended family will have no effect on the consumption or labor supply of any of its members. Despite its importance, the boundaries of economic decision-making units have not, to our knowledge, been examined directly with micro data. Stated differently, the altruism model has not been tested against the Life Cycle and Keynesian alternatives with such data. This paper uses matched data on parents and their adult children, contained in the Panel Study of Income Dynamics, to perform such a test. In essence our test asks whether the distribution of consumption and labor supply across households within the extended family depends on the distribution of resources across households within the extended family. Our findings provide quite strong evidence against the altruism model. The distribution of resources across households within the extended family is a highly significant (statistically and economically) determinant of the distribution of onsumption within the extended family. This finding holds for the entire sample as well as the subsample consisting of rich parents and poor children. In addition to showing that the distribution of extended family resources matters for extended family consumption, we test the life cycle model by asking whether only own resources matter, i.e., whether the resources of extended family members have no affect on a household's consumption. Our results indicate that extended family member resources have, at most, a modest effect on household consumption after one has controlled for the fact that extended family resources help predict a household's own permanent income.

Physical performance measures in aging research.

Abstract: Evaluation of physical functioning plays a valuable role in clinical geriatrics as well as in aging research. Physical functioning has generally been assessed through self- or proxy-report. An important addition to this form of assessment is the use of performance measures of physical function, in which individuals are asked to actually perform specific tasks and are evaluated using standardized criteria. Although there has been limited methodological work on physical performance instruments, this approach offers a number of potential advantages. Several performance assessments have been developed that correlate highly with other measures of health status and predict need for long-term care and mortality. It is suggested that more widespread use be made of physical performance assessments and that they be evaluated as measures of functioning in cross-national studies, as indicators of change in functioning over time, as endpoints in intervention studies, as tools for identifying persons functioning at high levels, and as sources of relevant information for the clinician.

Lumbar Muscle Fatigue and Chronic Lower Back Pain

Abstract: There currently is a clinical need for an objective technique to assess muscle dysfunction associated with chronic lower back pain. A Back Analysis System for objectively measuring local fatigue in the back extensor muscles is presented. The reliability and validity of this technique was evaluated by testing chronic low-back pain patients and control subjects without back pain. Concurrent surface electromyograms (EMG) were detected from multiple back muscles during sustained isometric contractions at different force levels of trunk extension. Median frequency parameters of the EMG power density spectrum were monitored to quantify localized muscle fatigue. Results indicated: 1) high reliability estimates for repeated trials; 2) significant differences (P less than 0.05) in median frequency parameters between lower back pain patients and control subjects for specific combinations of contractile force level and muscle site tested; 3) Median Frequency parameters correctly classified lower back pain and control subjects using a two-group discriminant analysis procedure. The applicability of this technique as a treatment outcome measure and diagnostic screening method for lower back pain patients is discussed.

Flexibility: The Next Competitive Battle: The Manufacturing Futures Survey

Abstract: Over the past 4 years research teams from INSEAD (Fontainebleau), Boston University and Waseda University (Tokyo) have administered a yearly survey on the manufacturing strategy of the large manufacturers of the three industrialized regions of the world In this paper the results for the 1986 survey are compared One of the most striking results of that year's survey is the emphasis some of the more advanced manufacturers put on their efforts to overcome the trade-off between flexibility and cost efficiency In particular for the Japanese respondents these attempts become clear Europeans and North Americans are not yet seizing the opportunity to cut costs through rapid production and design changes, and are focusing more on traditional cost reduction programmes and the improvement of quality This might mean that they are preparing the basis on which they can built to obtain added value from flexible automation If this is the case then the Japanese are clearly ahead

Skin aging and photoaging: An overview

Abstract: As the population ages, common skin disorders of the elderly demand greater attention Moreover, the many clinical, histologic, and physiologic changes that characterize old skin are increasingly implicated in its vulnerability to environmental injury and certain diseases Thus it behooves dermatologists to study the basic biologic process of aging in the skin and the separable process of photoaging, which itself is a major clinical problem To date studies at the cellular level have demonstrated major functional losses, particularly in proliferative capacity between infancy and adulthood, with definite further loss between early and late adulthood and as a result of chronic sun exposure Continued careful, quantitative assessment of aging and photoaging in human skin both in vivo and in vitro will be critical to a better understanding of these processes and particularly to their successful therapeutic modification

Ordering due to disorder in a frustrated vector antiferromagnet.

Abstract: In many continuous spin systems, competing interactions give nontrivial degeneracies of the classical ground states. Degeneracy-breaking free-energy terms arise from thermal (or quantum) fluctuations, which select for collinear states, and from dilution, which selects for anticollinear (yet long-range ordered) states. They are explicitly computed for an XY square-lattice antiferromagnet dominated by second-neighbor antiferromagnetic exchange. The predicted phase diagram agrees qualitatively with simulations.

Transitional Dynamics and Economic Growth in the Neoclassical Model

Abstract: An understanding of the qualitative nature of the transitional dynamics of the neociassical model - the process of convergence from an initial capital stock to a steady state growth path - is a key part of the shared knowledge of most economists. It forms the basis, for example, of the widespread interest in hypotheses about convergence of levels of national economic activity. Based on several quantitative experiments undertaken in the 1960s with fixed savings rates versions of the neoclassical model, many economists further believe that the transition process can be lengthy, potentially rationalizing differences in growth rates across countries that are sustained for decades. In this paper, we undertake a systematic quantitative investigation of transitional dynamics within the most widely employed versions of the neoclassical model with interteorally optimizing households. Lengthy transitional episodes arise only if there is very low intertemporal substitution. But, more important, we find that the simplest neoclassical model inevitably generates a central implication that is traced to the production technology. Whenever we try to use it to explain major growth episodes, the model produces a rate of return that is counterfactually high in the early stages of development. For example, in seeking to account for U.S-Japan differences in post war growth as a consequence of differences in end-of-war capital, we find that the immediate postwar rate of return in Japan would have had to exceed 500% per annum. Frequently employed variants of the basic neoclassical model - those that introduce adjustment costs, separate production and consumption sectors, and international capital mobility - can potentially sweep this marginal product implication under the rug. However, such alterations necessarily cause major discrepancies to arise in other areas. With investment adjustment costs, for example, the implications resurface in counterfactual variations in Tobin's Q. We interpret our results as illustrating two important principles. First, systematic quantitative investigation of familiar models can provide surprising new insights into their practical operation. Second, explanation of sustained cross country differences in growth rates will require departure from the familiar neoclassical environment.

Genetic prediction of nonresponse to hepatitis B vaccine.

Abstract: In previous studies of the antibody response to hepatitis B vaccine in 598 subjects who received a full course of vaccination, we observed a bimodal response, with about 14 percent producing less than approximately 1000 radioimmunoassay (RIA) units. An analysis of the major histocompatibility complex (MHC) HLA and complement types of 20 of the subjects with the lowest responses indicated a greater-than-expected number of homozygotes for the extended or fixed MHC haplotype [HLA-B8, SC01, DR3]. This finding suggested that the lack of a normal response was a recessive MHC-linked trait. In this study, we prospectively vaccinated five homozygotes and nine heterozygotes for this haplotype in the expectation that the homozygotes would produce much lower levels of antibody than the heterozygotes. When the antibody response was assessed two months after the third injection, four of the five homozygotes had produced very low levels (approximately 1000 units or less) of antibody (mean, 467 RIA units; range, less than 8 to 1266), whereas all nine heterozygotes produced more than 2500 RIA units (mean, 15,608; range, 2655 to 28,900) (P less than 0.01). We conclude that the usual response to hepatitis B surface antigen is due to the presence of a dominant immune-response gene in the MHC and that a low response is due to the absence of such a gene and the presence on both chromosomes of MHC haplotypes (such as [HLA-B8, SC01, DR3]) that indicate such a response.

Sunlight Regulates the Cutaneous Production of Vitamin D3 by Causing Its Photodegradation

Abstract: Exposure to sunlight initiates the formation of vitamin D3 in skin as the UV B radiation in the solar spectrum causes the photoconversion of 7-dehydrocholesterol to previtamin D3 A heat-induced isomerization then converts previtamin D3 to vitamin D3 over a period of days A number of irradiation products of vitamin D3 are known to form upon irradiation with high intensity UV radiation, but the effect of subsequent exposures to sunlight on the vitamin D3 formed in skin is not known To investigate this phenomenon, human skin containing vitamin D3 was exposed to sunlight in Boston A model system of [3H]vitamin D3 in methanol was also used to study the effects of sunlight on vitamin D3 throughout the year Vitamin D3 proved to be exquisitely sensitive to sunlight, and once formed in the skin, exposure to sunlight resulted in its rapid photodegradation to a variety of photoproducts, including 5,6-transvitamin D3, suprasterol I, and suprasterol II

Blood pressure as a risk factor for cardiovascular disease. The Framingham Study--30 years of follow-up.

Abstract: Data from 30 years of follow-up of the original Framingham Study cohort of 5,070 men and women aged 30-62 years who were first examined during the period 1948-1952 and who were free of cardiovascular disease reveal that blood pressure is a strong and consistent predictor of the development of coronary heart disease, stroke, transient ischemic attack, and congestive heart failure. Other factors related to blood pressure like obesity, left ventricular hypertrophy as demonstrated on electrocardiograms, and heart enlargement as shown by x-ray radiography made several selective additional independent contributions to risk; heart enlargement by x-ray radiography was the best predictor of congestive heart failure.

Objective Assessment of Vocal Hyperfunction: An Experimental Framework and Initial Results

Abstract: This report describes the experimental design and initial results of an ongoing clinical investigation of voice disorders. Its major focus is the development and use of quantitative measures to provide objective descriptions of conditions referred to as "vocal hyperfunction." The experimental design for this project is based on a descriptive theoretical framework, which holds that there are different types and stages of hyperfunctionally related voice disorders. Data consist of indirect measures derived from noninvasive aerodynamic and acoustic recordings including (a) parameters derived from inverse filtered approximations of the glottal air flow waveform; (b) estimates of transglottal pressure, average glottal air flow, glottal resistance and vocal efficiency; and (c) measures of vocal intensity and fundamental frequency. Initial results (based on comparisons among 15 voice patients and 45 normal speakers) support major assumptions that underlie the theoretical framework, and indicate that the measurement approach being utilized is capable of differentiating hyperfunctional from normal voices and hyperfunctional conditions from one another. Organic manifestations of vocal hyperfunction (nodules, polyps, contact ulcers) are accompanied by abnormally high values for the glottal waveform parameters of AC flow and maximum flow declination rate, suggesting increased potential for vocal fold trauma due to high vocal fold closure velocities and collision forces. In contrast, nonorganic manifestations of hyperfunction (functional disorders) tend to be associated with abnormally high levels of unmodulated DC flow, without high values for AC flow and maximum flow declination rate, suggesting reduced potential for vocal fold trauma. Measures also suggest different underlying mechanisms for nodules and polyps as compared to contact ulcers. Results are discussed relative to predictions based on the theoretical framework for vocal hyperfunction.

Politeness Theory and Shakespeare's Four Major Tragedies.

Abstract: Penelope Brown and Stephen Levinson (1987) have proposed that power (P), distance (D), and the ranked extremity (R) of a face-threatening act are the universal determinants of politeness levels in dyadic discourse. This claim is tested here for Shakespeare's use of Early Modern English in Hamlet, King Lear, Macbeth, and Othello. The tragedies are used because: (1) dramatic texts provide the best information on colloquial speech of the period; (2) the psychological soliloquies in the tragedies provide the access to inner life that is necessary for a proper test of politeness theory; and (3) the tragedies represent the full range of society in a period of high relevance to politeness theory. The four plays are systematically searched for pairs of minimally contrasting dyads where the dimensions of contrast are power (P), distance (D), and intrinsic extremity (R). Whenever such a pair is found, there are two speeches to be scored for politeness and a prediction from theory as to which should be more polite. The results for P and for R are those predicted by theory, but the results for D are not. The two components of D, interactive closeness and affect, are not closely associated in the plays. Affect strongly influences politeness (increased liking increases politeness and decreased liking decreases politeness); interactive closeness has little or no effect on politeness. The uses of politeness for the delineation of character in the tragedies are illustrated. (Politeness theory, speech act theory, pragmatics, sociolinguistics, theory of literature, Shakespeare studies)

Impaired vision and hip fracture. The Framingham Study.

Abstract: Falls affect a large proportion of the elderly and can result in a variety of injuries, including hip fractures. Several studies have suggested that visual impairment contributes to falls, but studies have not used standardized definitions of visual impairment and have not examined injurious falls or fractures. We looked at the risk of hip fracture associated with visual impairment in those members of the Framingham Study Cohort who took part in the Framingham Eye Study in 1973–75. Of 2,633 subjects followed for 10 years after the eye exam, 110 sustained hip fractures. The fracture rates in those with moderately impaired (20/30 to 20/80) vision (8.5%) and poor (20/100 or worse) vision (11.3%) were higher than in those with good (20/25 or better) vision (3.0%). After adjustment for age, sex, weight, alcohol consumption, and (in women) estrogen use, the relative risk of fracture in those with moderate impairment was 1.54 (95% CI = 0.95–2.49), while for those with poor vision, the relative risk was 2.17 (95% CI = 1.24–3.80). Of note, those with moderately impaired vision in one eye and good vision in the other had a higher risk of fracture (relative risk = 1.94) than those with a similar degree of binocular impairment (relative risk = 2.11). Poor vision in one or both eyes was linked to an elevated fracture risk. This suggests that good stereoscopic vision may be necessary to prevent falls. The risk of fracture with poor and moderately impaired vision combined was increased in women (relative risk = 1.96, 95% CI = 1.23–3.11) but not in men (relative risk = 0.79, 95% CI = 0.23–2.72). 17.5% (17/97) of women with poor vision in at least one eye sustained a hip fracture during the 10 years of the study. Cataracts were the most common cause of fracture-related visual impairment, but neither cataracts nor other common eye diseases had an independent effect on fracture risk after adjustment for visual acuity. In sum, visual impairment is an important risk factor for hip fracture, especially among elderly women.