Showing papers by "Harvard University published in 1981"
TL;DR: In this paper, a large data set consisting of about 1000 normal mode periods, 500 summary travel time observations, 100 normal mode Q values, mass and moment of inertia have been inverted to obtain the radial distribution of elastic properties, Q values and density in the Earth's interior.
9,266 citations
TL;DR: It is shown that sympathetic and parasympathetic nervous activity make frequency-specific contributions to the heart rate power spectrum, and that renin-angiotensin system activity strongly modulates the amplitude of the spectral peak located at 0.04 hertz.
Abstract: Power spectrum analysis of heart rate fluctuations provides a quantitative noninvasive means of assessing the functioning of the short-term cardiovascular control systems. We show that sympathetic and parasympathetic nervous activity make frequency-specific contributions to the heart rate power spectrum, and that renin-angiotensin system activity strongly modulates the amplitude of the spectral peak located at 0.04 hertz. Our data therefore provide evidence that the renin-angiotensin system plays a significant role in short-term cardiovascular control in the time scale of seconds to minutes.
5,088 citations
TL;DR: An integrated review of the transfer of optical radiation into human skin is presented, aimed at developing useful models for photomedicine.
2,499 citations
TL;DR: The haemagglutinin glycoprotein of influenza virus is a trimer comprising two structurally distinct regions: a triple-stranded coiled-coil of α-helices extends 76 Å from the membrane and a globular region of antiparallel β-sheet is positioned on top of this stem.
Abstract: The haemagglutinin glycoprotein of influenza virus is a trimer comprising two structurally distinct regions: a triple-stranded coiled-coil of alpha-helices extends 76 A from the membrane and a globular region of antiparallel beta-sheet, which contains the receptor binding site and the variable antigenic determinants, is positioned on top of this stem. Each subunit has an unusual loop-like topology, starting at the membrane, extending 135 A distally and folding back to enter the membrane.
2,444 citations
TL;DR: In this paper, the authors present the rationale and procedures for conducting a process analysis in evaluation research, which attempts to identify the process that mediates the effects of some treatment, by estimating the parameters of a causal chain between the treatment and some outcome variable.
Abstract: This article presents the rationale and procedures for conducting a process analysis in evaluation research. Such an analysis attempts to identify the process that mediates the effects of some treatment, by estimating the parameters of a causal chain between the treatment and some outcome variable. Two different procedures for estimating mediation are discussed. In addition we present procedures for examining whether a treatment exerts its effects, in part, by altering the mediating process that produces the outcome. Finally, the benefits of process analysis in evaluation research are underlined.
2,349 citations
01 May 1981
TL;DR: It is shown that it is possible to automatically synthesize the synchronization skeleton of a concurrent program from a Temporal Logic specification and it is believed that this approach may in the long run turn out to be quite practical.
Abstract: We have shown that it is possible to automatically synthesize the synchronization skeleton of a concurrent program from a Temporal Logic specification We believe that this approach may in the long run turn out to be quite practical Since synchronization skeletons are, in general, quite small, the potentially exponential behavior of our algorithm need not be an insurmountable obstacle Much additional research will be needed, however, to make the approach feasible in practice
2,333 citations
TL;DR: In this paper, the solution of the non-LTE optically thick transfer equations for hydrogen, carbon, and other constituents to determine semi-empirical models for six components of the quiet solar chromosphere was investigated.
Abstract: The described investigation is concerned with the solution of the non-LTE optically thick transfer equations for hydrogen, carbon, and other constituents to determine semiempirical models for six components of the quiet solar chromosphere. For a given temperature-height distribution, the solution is obtained of the equations of statistical equilibrium, radiative transfer for lines and continua, and hydrostatic equilibrium to find the ionization and excitation conditions for each atomic constituent. The emergent spectrum is calculated, and a trial and error approach is used to adjust the temperature distribution so that the emergent spectrum is in best agreement with the observed one. The relationship between semiempirical models determined in this way and theoretical models based on radiative equilibrium is discussed by Avrett (1977). Harvard Skylab EUV observations are used to determine models for a number of quiet-sun regions.
2,205 citations
TL;DR: In this article, the authors construct an explicit realistic SU(5) model in which softly broken supersymmetry is used to protect the Higgs doublets from quadratic mass renormalization.
1,916 citations
TL;DR: A model for the photochemistry of the global troposphere constrained by observed concentrations of H2O, O3, CO, CH4, NO, NO2, and HNO3 is presented in this paper.
Abstract: A model for the photochemistry of the global troposphere constrained by observed concentrations of H2O, O3, CO, CH4, NO, NO2, and HNO3 is presented. Data for NO and NO2 are insufficient to define the global distribution of these gases but are nonetheless useful in limiting several of the more uncertain parameters of the model. Concentrations of OH, HO2, H2O2, NO, NO2, NO3, N2O5, HNO2, HO2NO2, CH3O2, CH3OOH, CH2O, and CH3CCl3 are calculated as functions of altitude, latitude, and season. Results imply that the source for nitrogen oxides in the remote troposphere is geographically dispersed and surprisingly small, less than 107 tons N yr−1. Global sources for CO and CH4 are 1.5 × 109 tons C yr−1 and 4.5 × 108 tons C yr−1, respectively. Carbon monoxide is derived from combustion of fossil fuel (15%) and oxidation of atmospheric CH4 (25%), with the balance from burning of vegetation and oxidation of biospheric hydrocarbons. Production of CO in the northern hemisphere exceeds that in the southern hemisphere by about a factor of 2. Industrial and agricultural activities provide approximately half the global source of CO. Oxidation of CO and CH4 provides sources of tropospheric O3 similar in magnitude to loss by in situ photochemistry. Observations of CH3CCl3 could offer an important check of the tropospheric model and results shown here suggest that computed concentrations of OH should be reliable within a factor of 2. A more definitive test requires better definition of release rates for CH3CCl3 and improved measurements for its distribution in the atmosphere.
1,762 citations
TL;DR: In this article, a study was performed in three groups of male Munich-Wistar rats 1 wk after surgery: group I, eight control rats that underwent laparotomy and were fed a normal diet.
Abstract: Micropuncture studies were performed in three groups of male Munich-Wistar rats 1 wk after surgery: group I, eight control rats that underwent laparotomy and were fed a normal diet; group II, nine rats that underwent right nephrectomy and segmental infarction of five-sixths of the left kidney and were fed a normal diet; and group III, seven rats that underwent the same renal ablative procedure and were fed a low protein diet. Single nephron glomerular filtration rate (SNGFR) was higher in the remnant kidney of group II rats compared with group I rats due to higher average values for mean glomerular transcapillary hydraulic pressure difference (delta P) and initial glomerular plasma flow rate (QA) in group II. Glomeruli in remnant kidneys of group II showed striking alterations in morphology, including epithelial cell protein reabsorption droplets, foot process fusion, and mesangial expansion. Group III rats demonstrated a mean SNGFR not statistically different from that of group I, but significantly less than that of group II rats. This lack of absolute hyperfiltration in remnant glomeruli of group III rats relative to group I obtained because QA and delta P did not increase above values found in group I. The glomerular structural lesions seen in group II were also largely attenuated in group III. These studies demonstrate that alterations in glomerular hemodynamics associated with renal ablation are accompanied by structural lesions and suggest that sustained single nephron hyperfiltration may have maladaptive consequences by damaging remnant glomeruli.
1,753 citations
TL;DR: A murine monoclonal antibody (OC125) has been developed that reacts with each of six epithelial ovarian carcinoma cell lines and with cryopreserved tumor tissue from 12 of 20 ovarian cancer patients, but does not bind to a variety of nonmalignant tissues, including adult and fetal ovary.
Abstract: A murine monoclonal antibody (OC125) has been developed that reacts with each of six epithelial ovarian carcinoma cell lines and with cryopreserved tumor tissue from 12 of 20 ovarian cancer patients. By contrast, the antibody does not bind to a variety of nonmalignant tissues, including adult and fetal ovary. OC125 reacts with only 1 of 14 cell lines derived from nonovarian neoplasms and has failed to react with cryostat sections from 12 nonovarian carcinomas.
TL;DR: Four ‘antigenic sites’ on the three-dimensional structure of the influenza haemagglutinin are identified and at least one amino acid substitution in each site seems to be required for the production of new epidemic strains between 1968 and 1975.
Abstract: Four 'antigenic sites' on the three-dimensional structure of the influenza haemagglutinin are identified. At least one amino acid substitution in each site seems to be required for the production of new epidemic strains between 1968 and 1975.
TL;DR: Natural selection has now made its case, but similar delays in recognizing the role of selection in the other fields could deprive us of valuable help in solving the problems which confront us.
Abstract: Selection by consequences is a causal mode found only in living things, or in machines made by living things. It was first recognized in natural selection, but it also accounts for the shaping and maintenance of the behavior of the individual and the evolution of cultures. In al three of these fields, it replaces explanations based on the causal modes of classical mechanics. The replacement is strongly resisted. Natural selection has now made its case, but similar delays in recognizing the role of selection in the other fields could deprive us of valuable help in solving the problems which confront us.
TL;DR: In this paper, the reliability and validity of measures of organizational characteristics used in previous marketing studies in the areas of strategic planning and distribution channels are examined, and the authors examine the reliability of these measures.
Abstract: The author examines the reliability and validity of measures of organizational characteristics used in previous marketing studies in the areas of strategic planning and distribution channels. Key i...
TL;DR: The traditional Bain/Mason paradigm of industrial organization (IO) offered strategic management a systematic model for assessing competition within an industry, yet the model was seldom used in the business policy (BP) field.
Abstract: The traditional Bain/Mason paradigm of industrial organization (IO) offered strategic management a systematic model for assessing competition within an industry, yet the model was seldom used in the business policy (BP) field. IO and BP differed in their frames of reference (public vs. private), units of analysis (industry vs. firm), views of the decision maker and stability of structure, and in other significant respects. Development of IO theory during the 1970s has narrowed the gap between the two fields, to the extent that IO should now be of central concern to policy scholars.
TL;DR: Insulin infusion increases sympathetic nervous system activity in the absence of changes in blood glucose in nonobese young men using glucose clamp techniques.
Abstract: Recent studies indicate a link between carbohydrate intake and the functional state of the sympathetic nervous system. Fasting or carbohydrate restriction decreases sympathetic activity, while glucose ingestion or dietary supplementation with sucrose increases sympathetic nerve activity. To examine the potential contributions of hyperglycemia and hyperinsulinemia to sympathetic stimulation, sympathetic activity was assessed by measurement of plasma norepinephrine (NE) levels and concomitant cardiovascular indices in nonobese young men during glucose and insulin infusions using glucose clamp techniques. In the insulin infusion studies (euglycemic glucose clamp), insulin was administered at 2 mU/kg/min and 5 mU/kg/min for 2 h while blood glucose was maintained at basal levels by a variable rate of glucose infusion. In the hyperglycemic studies, blood glucose was raised 125 mg/dl above basal and maintained at that level for 2h. In response to both insulin infusions, plasma NE rose progressively over the course of the study, increasing 50% with the 2-mU infusion (from mean basal value of 240 ± 34 pg/ml to 360 ± 41 at 150 min, P
TL;DR: In this paper, the authors present a primarily psychological point of view and a relatively microanalysis of the verbal and nonverbal exchange between the deceiver and the lie detector, and explore methodological issues, channel effects in the detection of deception and other factors affecting the accuracy of lie detection.
Abstract: Publisher Summary Lying and lie detection are the two components that, together, make up the exchange called as the “communication of deception.” Deception is an act that is intended to foster in another person a belief or understanding that the deceiver considers false. This chapter presents a primarily psychological point of view and a relatively microanalysis of the verbal and nonverbal exchange between the deceiver and the lie detector. The chapter discusses the definition of deception. It describes the deceiver's perspective in lie-detection, including the strategies of deception and behaviors associated with lie-telling. The lie-detector's perspective is also discussed in the chapter, and it has described behaviors associated with the judgments of deception and strategies of lie detection. The chapter discusses the outcomes of the deceptive communication process—that is, the accuracy of lie detection—and explores methodological issues, channel effects in the detection of deception, and other factors affecting the accuracy of lie detection.
Book•
01 Jan 1981TL;DR: Algorithms, complexity analysis, and algorithmic ideas are introduced informally in Chapter 1, and are pursued throughout the book, each section is followed by problems.
Abstract: From the Publisher:
Lewis and Papadimitriou present this long awaited Second Edition of their best-selling theory of computation. The authors are well-known for their clear presentation that makes the material accessible to a a broad audience and requires no special previous mathematical experience. In this new edition, the authors incorporate a somewhat more informal, friendly writing style to present both classical and contemporary theories of computation. Algorithms, complexity analysis, and algorithmic ideas are introduced informally in Chapter 1, and are pursued throughout the book. Each section is followed by problems.
TL;DR: This paper presents a heuristic for this problem in which an assignment of customers to vehicles is obtained by solving a generalized assignment problem with an objective function that approximates delivery cost and shows that it has outperformed the best existing heuristics on a sample of standard test problems.
Abstract: : We consider a common variant of the vehicle routing problem in which a vehicle fleet delivers products stored at a central depot to satisfy customer orders. Each vehicle has a fixed capacity, and each order uses a fixed portion of vehicle capacity. The routing decision involves determining which of the demands will be satisfied by each vehicle and what route each vehicle will follow in servicing its assigned demand in order to minimize total delivery cost. We present a heuristic for this problem in which an assignment of customers to vehicles is obtained by solving a generalized assignment problem with an objective function that approximates delivery cost. This heuristic has many attractive features. It has outperformed the best existing heuristics on a sample of standard test problems. It will always find a feasible solution if one exists, something no other existing heuristic can guarantee. It can be easily adapted to accommodate many additional problem complexities. By parametrically varying the number of vehicles in the fleet, our method can be used to optimally solve the problem of finding the minimum size fleet that can feasibly service the specified demand.
TL;DR: Living skin-equivalent grafts consisting of fibroblasts cast in collagen lattices and seeded with epidermal cells were successfully grafted onto the donors of the cells.
Abstract: Living skin-equivalent grafts consisting of fibroblasts cast in collagen lattices and seeded with epidermal cells were successfully grafted onto the donors of the cells. The grafts were vascularized, did not evoke a homograft reaction, inhibited wound contraction, filled the wound space, and persisted.
TL;DR: It is confirmed that the natural gait at any speed indeed entails the smallest possible energy expenditure, and rates of oxygen consumption as an indicator of rates of energy consumption are used.
Abstract: It seems reasonable that quadrupeds should change gait from a walk to a trot to a gallop in such a way as to minimize their energy consumption, as human beings are known1 to change from a walk to a run at a particular speed (2.4 m s−1) below which walking requires less energy than running and above which the opposite is true. Thus by changing gait, human beings keep the energy cost of locomotion to a minimum as their speed increases. One reason this relation holds is that in humans, metabolic rate increases curvilinearly with walking speed1. If metabolism were a curvilinear function of speed within each of the gaits used by quadrupeds, it would support the hypothesis that they also change gait to minimize energetic cost. There is an old controversy about whether metabolic rate increases linearly or curvilinearly in running humans1,2 but all previous reports have suggested that metabolic rate increases linearly with speed in quadrupeds. Extended gaits were an important experimental tool in the study of human gait changes; thus we have trained three small horses (110–170 kg) to walk, trot and gallop on a motorized treadmill, and to extend their gaits on command. We report here that, using measurements of rates of oxygen consumption as an indicator of rates of energy consumption, we have confirmed that the natural gait at any speed indeed entails the smallest possible energy expenditure.
TL;DR: The variable portion of an immunoglobulin heavy chain gene is assembled from at least three discontinuous segments of DNA, the V, D and J regions, and the large number of human J region genes and, hence, their greater potential for generating diversity as compared to the that of the mouse J regions appears to result from recent genetic duplications.
TL;DR: In this article, the theoretical existence of the quasifirm in the construction industry is discussed and empirical evidence from a field study of homebuilders is presented in support of this argument.
Abstract: Construction projects are executed by general contractors who retain the services of special trade subcontractors. This form of organization is preferable to vertically integrating these trades because of the transaction cost implications of construction technology. The general contractor and special trade subcontractors can form a stable organizational unit when conditions permit. This organizational form, called here the ‘quasifirm’, is analogous to the ‘inside contracting system’ discussed by Williamson (1975) . This paper uses Williamson, 1975 , Williamson, 1979 transaction cost approach to argue the theoretical existence of the quasifirm in the construction industry. Empirical evidence from a field study of homebuilders is presented in support of this argument.
TL;DR: In this article, a significant relationship was found between the market value of a firm and its intangible capital, proxied by past R&D expenditures and the number of patents, based on a time-series cross-section analysis of data for large U.S. firms.
TL;DR: The fetal calf serum supplement of cell-culture medium contains enough of the vitamin to affect the differentiation of cultured keratinocytes derived from epidermis and from other stratified squamous epithelia.
TL;DR: A general technique applicable to Gram-negative prokaryotes for site-directed mutagenesis of cloned DNA fragments which is applied to the study of the symbiotic nitrogen fixation genes of Rhizobium meliloti is reported.
Abstract: The genetic analysis of genes from prokaryotic species for which experimental genetic systems have not yet been developed is often limited by the difficulty of producing mutations in those genes. We report here a general technique applicable to Gram-negative prokaryotes for site-directed mutagenesis of cloned DNA fragments which we have applied to the study of the symbiotic nitrogen fixation genes of Rhizobium meliloti. In particular, we mutagenized cloned R. meliloti restriction fragments in Escherichia coli with transposon Tn5 and then replaced the wild-type parental DNA sequences with the mutant DNA sequences in the R. meliloti genome. Using this method we show that an R. meliloti DNA restriction fragment, cloned previously on the basis of homology to Klebsiella pneumoniae nif genes1, contains gene(s) essential for symbiotic nitrogen fixation. In addition, we use this method to construct a physical genetic map of a subset of the R. meliloti nif genes.
TL;DR: Solitary fibrous tumors of the pleura are not associated with asbestos and nuclear pleomorphism and a high mitotic rate are seen in larger tumors but do not necessarily indicate a poor prognosis if the tumor is circumscribed.
Abstract: Three-hundred-sixty cases of solitary fibrous tumor of the pleura from the literature are analyzed, and eight new cases are described. Of patients reported on prior to 1972, 72% had symptoms due to the tumor at the time of diagnosis, but only 54% of patients reported on since then were symptomatic. This probably reflects earlier diagnosis as a result of increased use of chest radiographs in asymptomatic populations. Cough, chest pain, dyspnea, and/or pulmonary osteoarthropathy are each found in at least one-third of patients who have symptoms. Approximately 80% of solitary fibrous tumors of the pleura originate in the visceral and 20% in the parietal pleura. In the literature and in this experience these tumors are on the whole circumscribed. They range in size from 1–36 cm with a mean of 6 cm. Many are pedunculated on pleural-based pedicles that contain hypertrophic arteries and veins. Histologic examination of the tumor usually discloses cellular areas alternating with hyalinized and/or necrotic areas. Spindle-shaped cells typically have minimal nuclear pleomorphism and rare or absent mitoses. Numerous thin-walled vessels constitute an additional feature of large tumors. Electron microscopical examination reveals features of both fibroblasts and mesothelial cells. Solitary fibrous tumors behave in a benign fashion in 88% of cases after surgical resection. In 12% of the cases the tumor is responsible for the patient's death because of its extensive intrathoracic growth, by virtue of either late diagnosis or unresectable recurrence. No single histologic feature allows a definite prognosis. The best indicator of a good prognosis is the presence of a pedicle supporting the tumor. Also favorable is circumscription of the tumor without invasion of lung, mediastinum, or chest wall. Nuclear pleomorphism and a high mitotic rate are seen in larger tumors but do not necessarily indicate a poor prognosis if the tumor is circumscribed. Solitary fibrous tumors of the pleura are not associated with asbestos.
Posted Content•
TL;DR: In this article, a rational expectations equilibrium in a discretionary environment where the policymaker pursues a "reasonable" objective, but where precommitments on monetary growth are precluded is established.
Abstract: Natural-rate models suggest that the systematic parts of monetary policy will not have important consequences for the business cycle. Nevertheless, we often observe high and variable rates of monetary growth, and a tendency for monetary authorities to pursue countercyclical policies. This behavior is shown to be consistent with a rational expectations equilibrium in a discretionary environment where the policymaker pursues a "reasonable" objective, but where precommitments on monetary growth are precluded. At each point in time, the policymaker optimizes subject to given inflationary expectations, which determine a Phillips Curve-type tradeoff between monetary growth/inflation and unemployment. Inflationary expectations are formed with the knowledge that policymakers will be in this situation. Accordingly, equilibrium excludes systematic deviations between actual and expected inflation, which means that the equilibrium unemployment rate ends up independent of "policy" in our model. However, the equilibrium rates of monetary growth/inflation depend on various parameters, including the slope of the Phillips Curve, the costs attached to unemployment versus inflation, and the level of the natural unemployment rate. The monetary authority determines an average inflation rate that is "excessive," and also tends to behave countercyclically. Outcomes are shown to improve if a costlessly operating rule is implemented in order to precomrnit future policy choices in the appropriate manner. The value of these precommitments -- that is, of long-term agreements between the government and the private sector -- underlies the argument for rules over discretion. Discretion is the sub-set of rules that provides no guarantees about the government's future behavior.
TL;DR: This paper examined the extent to which fixation duration and probability of fixating the target word was influenced by contextual constraint and the misspelling and found that when subjects did fixate the target, the fixation duration was shorter in the high-constraint passages.