Showing papers by "University of Pittsburgh published in 1968"

Reality of the Schwarzschild Singularity

Abstract: A spherically symmetric solution of the Einstein equations is presented that coincides with the exterior ($\mathcal{r}g2m$) Schwarzschild solution, but where the Schwarzschild "sphere" becomes a point singularity. The possible relevance of this solution to the question of gravitational collapse is discussed.

New Conservation Laws for Zero Rest-Mass Fields in Asymptotically Flat Space-Time

Abstract: Some recently discovered exact conservation laws for asymptotically flat gravitational fields are discussed in detail. The analogous conservation laws for zero rest-mass fields of arbitrary spin s(= 0, $\frac{1}{2}$, 1, $\ldots$) in flat or asymptotically flat space-time are also considered and their connexion with a generalization of Kirchoff's integral is pointed out. In flat space-time, an infinite hierarchy of such conservation laws exists for each spin value, but these have a somewhat trivial interpretation, describing the asymptotic incoming field (in fact giving the coefficients of a power series expansion of the incoming field). The Maxwell and linearized Einstein theories are analysed here particularly. In asymptotically flat space-time, only the first set of quantities of the hierarchy remain absolutely conserved. These are 4s + 2 real quantities, for spin s, giving a D(s, 0) representation of the Bondi-Metzner-Sachs group. But even for these quantities the simple interpretation in terms of incoming waves no longer holds good: it emerges from a study of the stationary gravitational fields that a contribution to the quantities involving the gravitational multipole structure of the field must also be present. Only the vacuum Einstein theory is analysed in this connexion here, the corresponding discussions of the Einstein-Maxwell theory (by Exton and the authors) and the Einstein-Maxwell-neutrino theory (by Exton) being given elsewhere. (A discussion of fields of higher spin in curved space-time along these lines would encounter the familiar difficulties first pointed out by Buchdahl.) One consequence of the discussion given here is that a stationary asymptotically flat gravitational field cannot become radiative and then stationary again after a finite time, except possibly if a certain (origin independent) quadratic combination of multipole moments returns to its original value. This indicates the existence of 'tails' to the outgoing waves (or back-scattered field), which destroys the stationary nature of the final field.

Effect of the Thyroid State on Myocardial Contractility and Ventricular Ejection Rate in Man

Abstract: Although the circulatory changes in various thyroid states are well known, the alterations of myocardial contractility of hypothyroidism and hyperthyroidism have remained controversial. The changes in the length of the ejection time (ET) and isovolumic contraction time (ICT) are used as indicative of alterations in inotropic state of the myocardium. Isovolumic contraction time, ejection time, and pre-ejection period were measured externally in 10 normal, 13 hyperthyroid, and five hypothyroid subjects. Cardiac outputs, mean rate of left ventricular ejection index, and predicted ejection times were calculated. More shortening of ICT and ET in hyperthyroid and more prolongation of these intervals in hypothyroid subjects than could be attributed to other factors were interpreted as indicative of increased and decreased myocardial contractility, respectively. Catecholamine depletion in hyperthyroid subjects with adequate administration of intramuscular reserpine induced no changes in cardiac output and oxygen ...

Nuclear Spin-Lattice Relaxation via Paramagnetic Centers

Abstract: The theory of nuclear spin-lattice relaxation via paramagnetic centers in diamagnetic crystals is investigated in terms of both the single-relaxation-center and the multirelaxation-center models. In this theory, the distances between centers are allowed to be finite. A new case is found for which the theory predicts a new dependence of the spin-lattice relaxation time upon the applied magnetic field, the concentration of the paramagnetic centers, and the magnitude of the diffusion constant. An adaptation of the theory to the rotating reference frame shows that under certain conditions the spin-lattice relaxation time in the rotating frame can be larger than in the laboratory frame.

Force, Active Principles, and Newton’s Invisible Realm

Abstract: In recent years, scholarship has made it possible to achieve a more extended interpretation of the development of Newton’s thought in the years following the publication of the Principia. It is now time to attempt the task of offering a framework within which the results of certain of these investigations can be linked together in a synoptic way. I shall concentrate on what I take to be one of the central problems which Newton attempted to solve in this later period, namely, the ontological problem of the causation of force.

Band Structure of Bismuth: Pseudopotential Approach

Abstract: The electronic band structure of bismuth is studied by means of a pseudopotential approach. The Lin-Kleinman pseudopotential was adopted; its parameters were adjusted slightly to bring the band structure into agreement with two known energy differences in bismuth. With this pseudopotential, the band structure along symmetry lines and planes is calculated and the effective masses of the carriers are studied. The band structure is in good agreement with optical data and with effective-mass anisotropies, but the magnitude of the effective masses may differ from experiment by a factor of 3. Using the experimental effective masses and $g$ factor of the holes, we infer the energy-level scheme at $T$ near ${E}_{F}$. Also, we have tentatively identified a higher-lying band which has been experimentally observed. A very efficient method of calculating nonlocal and spin-orbit coupling terms in $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{\ensuremath{\pi}}$ perturbation theory is presented.

Three-dimensional Fourier synthesis of horse oxyhaemoglobin at 2.8 A resolution: (1) x-ray analysis.

Abstract: The phase angles of 8,000 reflexions were determined by the method of isomorphous replacement, using crystals of native haemoglobin and of three heavy atom derivatives. The electron density maps show the positions of nearly all the amino-acid residues and some details of the haem groups. Next week the second part of this article—the atomic model—will appear.

Calcium metabolism in hela cells and the effects of parathyroid hormone

Abstract: Calcium metabolism was investigated in HeLa cells. 90% of the calcium of the cell monolayer is bound to an extracellular cell coat and can be removed by trypsin-EDTA. The calcium concentration of the naked cell, freed from its coat, is 0.47 mM. The calcium concentration of the medium does not affect the concentration of the naked cell calcium. However, the calcium of the cell coat is proportional to the calcium concentration in the medium. Calcium uptake into the cell coat increases with increasing calcium concentration of the medium, whereas uptake by the naked cell is independent of the calcium of the medium. Anaerobic conditions and metabolic inhibitors do not inhibit calcium uptake by the cell, a fact suggesting that this transfer is a passive phenomenon. The calcium in the extracellular cell coat, was not affected by parathyroid hormone. In contrast, the hormone increased the cellular calcium concentration by stimulating calcium uptake or by enhancing calcium binding to some cell components. These results suggest that, contrary to current thinking, parathyroid hormone influences the cellular calcium balance by mobilizing calcium from the extracellular fluids in order to increase its concentration in some cellular compartment. It is proposed that these effects can enhance calcium transport.

Serum antinuclear antibodies in progressive systemic sclerosis (scleroderma)

Abstract: Sera from 47 patients with PSS were studied for the presence of antinuclear antibodies. Antinuclear antibodies were present in 60 per cent of the sera in a titer of1:16 or greater. In most cases the titer was low, but a titer of1:256 or greater was present in sera from 6 patients. The pattern of nuclear fluorescence was most commonly that of fine or large speckles. Most sera contained both IgC and IgM antinuclear antibodies. There was no relation between duration of disease or severity of disease and the presence of antinuclear antibodies. Similarly, no correlation could be demonstrated between clinical findings and the immunoglobulin class, titer, or staining pattern of antinuclear antibody. The prevalence of high tilers of antinuclear antibodies was greater in patients with hypergammaglobulinemia than in those with normal levels of gamma globulin. Rheumatoid factor was present in 33 per cent of sera. Patients with high liters of rheumatoid factor tended to have high tilers of antinuclear antibodies. Antinuclear antibodies were found in low titer in 7 per cent of blood relatives less than 60 years of age. The number of sera with antinuclear antibodies was slightly higher in the non-aged relatives of patients with systemic lupus erythematosus (11 per cent), while the prevalence in relatives of patients with chronic discoid lupus (2 per cent) was similar to that of a group of healthy student nurses. The results reveal that antinuclear antibodies of a speckled pattern are commonly present in sera from patients with FSS and appear to be unrelated to the duration or severity of the disease. The peripheral pattern of nuclear fluorescence produced by sera from acutely ill patients with systemic lupus erythematosus was not observed with any of the sera of patients with PSS. These obs 3 ervations emphasize the fact that the presence of antinuclear antibodies in general is not diagnostic of any one disease, and indicate that the pattern of nuclear fluorescence produced by the antinuclear antibodies may aid in confirmation of clinical diagnosis.

Skeletal muscle involvement in progressive systemic sclerosis (scleroderma)

Abstract: 53 patients with typical PSS were examined for evidence of muscle weakness, abnormal serum enzymes, disturbances in urinary creatine and creatinine, and histopathologic alterations in skeletal muscle tissue. The majority was found to have clinical and biochemical features of primary myopathy. Microscopic involvement of muscle fibers or interstitium was present in 14 of 36 cases; the most consistent abnormality was interstitial fibrosis. This muscle involvement is considered an important feature in the course of PSS.

Severity of atherosclerosis in cerebral arteries, coronary arteries, and aortas*

Abstract: Physicians would like to be able to predict the severity of atherosclerosis in one artery by measuring the severity of atherosclerosis in another artery. I t is difficult, however, to measure atherosclerosis in one artery of a living patient; it is even more difficult to measure accurately atherosclerosis in two or more arteries by comparable methods in living patients. We have therefore investigated the correlation of atherosclerosis in various arteries of autopsied persons in whom most of the major arteries affected by atherosclerosis could be directly inspected and graded. The autopsied persons included in this study were from Oslo, Norway, and Guatemala, Central America, locations in which the average severity of atherosclerosis differs great1y.l Pathologists in these two areas submitted sets of arteries to the International Atherosclerosis Project, a cooperative survey of atherosclerosis in autopsied persons from many different populations.2 The results indicate that, on a group basis, severity of atherosclerosis in one artery parallels atherosclerosis in other arteries. However, on an individual case basis, severity of atherosclerosis in one artery does not predict closely severity of atherosclerosis in another artery except for bilateral cerebral arteries.

The site of calcium binding in relation to the activation of myofibrillar contraction.

Abstract: Skeletal muscle myofibrils, in the presence of 2 mM MgCl2 at pH 7.0, were found to have two classes of calcium-binding sites with apparent affinity constants of 2.1 x 106 M-1 (class 1) and ∼3 x 104 M-1 (class 2), respectively. At free calcium concentrations essential for the activation of myofibrillar contraction (∼10-6 M) there would be significant calcium binding only to the class 1 sites. These sites could bind about 1.3 µmoles of calcium per g protein. Extraction of myosin from the myofibrils did not alter their calcium-binding parameters. Myosin A, under identical experimental conditions, had little affinity for calcium. The class 1 sites are, therefore, presumed to be located in the I filaments. The class 1 sites could only be detected in F actin and myosin B preparations which were contaminated with the tropomyosin-troponin complex. Tropomyosin bound very little calcium. Troponin, which in conjunction with tropomyosin confers calcium sensitivity on actomyosin systems, could bind 22 µmoles of calcium per g protein with an apparent affinity constant of 2.4 x 106 M-1. In view of the identical affinity constants of the myofibrils and troponin and the much greater number of calcium-binding sites on troponin it is suggested that calcium activates myofibrillar contraction by binding to the troponin molecule.

Emission of Radiation from a System of Many Excited Atoms

Abstract: The Weisskopf-Wigner theory of the natural linewidth of a single isolated atom is extended to a system of $N(\ensuremath{\gg}1)$ identical nonoverlapping atoms which are all in the same excited state at time $t=0$. The positions ${\mathrm{X}}_{1}\ensuremath{\cdots}{\mathrm{X}}_{N}$ of the atoms are assumed to fill a volume $\mathcal{U}$ of given shape and size with macroscopically constant density. Emission of radiation from this system takes place only in the form of one narrow, but nonzero-width, bundle of nearly equal photons, which contains all the emitted radiation. If the density of atoms within $\mathcal{U}$ exceeds a certain threshold, the rate of emission of photons has the form of a typical spike. All effects depend sensitively on the shape and size of $\mathcal{U}$ and on the density of atoms within $\mathcal{U}$, and cannot be explained in conventional terms of spontaneous or stimulated emission of radiation.

The effect of steady-state increases in systemic arterial pressure on the duration of left ventricular ejection time

Abstract: The effect of steady-state increases in systemic arterial pressure on the duration of left ventricular ejection time was studied in 11 normal male subjects. Methoxamine, a pressor amine of predominantly vasoconstrictor activity but lacking significant inotropic effect, was administered intravenously resulting in an average increase in mean arterial pressure of 27 mm Hg. Heart rate was held constant by high right atrial pacing, and there was no significant change in cardiac output. During methoxamine infusion, when stroke volume, heart rate, and inotropic state were held constant, left ventricular ejection time increased as mean arterial pressure increased. There was a highly significant correlation between the increase in mean systolic blood pressure and the prolongation of left ventricular ejection time (r = 0.870). In one subject, an increase in mean systolic pressure of 75 mm Hg prolonged left ventricular ejection time 55 msec, producing paradoxical splitting of the second heart sound. The prolongation of left ventricular ejection time during infusion was not blocked by the prior intravenous administration of atropine sulfate or propranolol hydrochloride, thus ruling out both vagal inhibition of the left ventricle and reflex withdrawal of sympathetic tone as its cause. In three subjects, left ventricular end diastolic pressure was measured and found to be significantly increased. This finding suggests that the normal left ventricle maintains a constant stroke volume in the presence of an increased pressure load by the Frank Starling mechanism. This study concludes that arterial pressure must be included as a prime determinant of left ventricular ejection time along with stroke volume, heart rate, and inotropic state in intact man.

The syndrome of congenital adrenocortical unresponsiveness to ACTH. Report of six cases.

Abstract: Extract: Six patients with the syndrome of congenital adrenocortical unresponsiveness to ACTH are reported This syndrome is characterized by feeding problems early in life, hypoglycemic episodes and hyper-pigmentation of the skin (table I) Blood pressure and levels of electrolytes in serum were normal (table II) PPD and histoplasmin skin tests were negative, while antibodies to adrenal, thyroid, and gastric tissues were undetectable Urinary excretion of 17-hydroxycorticosteroids and cortisol production rates were low and did not respond to administration of ACTH (table III) While receiving a low sodium diet, the patients were able to conserve sodium (figs 2, 3 and 4) and to increase the rate of aldosterone secretion (tables IV and V) In one case, adrenal pathology showed a normal zona glomerulosa with atrophy of the zonae fasciculata and reticularis This isolated deficiency in cortisol secretion is not due to a defect in pituitary function or a deficiency of one of the enzymes directly involved in steroid biosynthesis The most probable pathogenesis is an abnormality at the site (or one of the sites) of ACTH action on cortisol biosynthesis Speculation: It is probable that some young infants in whom a diagnosis of Addison's disease is made do, in fact, have the syndrome of congenital adrenocortical unresponsiveness to ACTH Studies of cortisol secretion rates prior to and during ACTH administration and a determination of aldosterone secretion rates while receiving normal and low salt diets will permit differentiation of the two disorders

Single separable potential with attraction and repulsion.

Abstract: It is shown that a single separable potential can give both an attraction and a repulsion. This property is used to construct an interaction that fits the two-nucleon, $S$-wave phase shifts. For this potential, the important effects of the strong short-range repulsion can be included directly in existing three-body progams.

Structure of the tobacco mosaic virus particle; polymerization of tobacco mosaic virus protein.

Abstract: Publisher Summary The chapter describes a critical analysis of the molecular weight of tobacco mosaic virus (TMV) and with polymerization of TMV protein. TMV has a very high molecular weight and measurements of double refraction of flow led to the conclusion that the particles are rod-shaped. The molecular weight of TMV has been determined adequately by physicochemical methods and measurements with the electron microscope. These yielded with fair uniformity a value close to 40 million. A value of about 23 A for the pitch of the helix of the virus was determined from X-ray diffraction measurements, and pertains to the virus in wet gels. In the determination of molecular weight with the electron microscope, it is desirable to utilize a technique that does not depend upon the retention of the wet particle dimensions. Some of the earliest determinations of molecular weight were done by sedimentation and diffusion. Molecular weights obtained by this method do not depend on assumptions about the molecular configuration. Light scattering has been used extensively for the determination of particle weight. The method is particularly useful because of its sensitivity over a wide range of particle sizes and its ability to provide information on particle shape. Subsequent studies have established the correctness of the assumption that water is released upon polymerization. TMV, a protein seems to be a trimer of the chemical subunit. Its polymerization has been studied primarily by light scattering and osmotic pressure methods. Within certain limits, the polymerization can be interpreted quite accurately in terms of the mathematics of condensation polymerization. Accompanying the release of water molecules upon polymerization is an increase in partial specific volume. Hydrogen ions are bound during polymerization.

TSH-like Actions of Dibutyryl-cAMP on Isolated Bovine Thyroid Cells

Abstract: Isolated thyroid cells, prepared by tryptic dispersion of bovine thyroid glands, were incubated with TSH or with dibutyrylcyclic-3′,5′-AMP (DBC). Both these agents altered I--trapping in a biphasic manner; i.e., I--accumulation was depressed during the first hour, and then gradually augmented to abovenormal levels during the succeeding 6 hr. 131I-incorporation into thyroglobulin and into T4 was stimulated in essentially identical fashion by the TSH and DBC. Furthermore, stimulation of the incorporation of leucine-14C into protein and of the intracellular accumulation of 14C-αaminoisobutyrate was also demonstrated. The present findings in isolated thyroid cells, together with those showing that DBC and TSH both stimulate glucose oxidation and 32P-incorporation into phospholipid in thyroid slices, provide further indication of a role for the adenyl cyclasecAMP system in the mediation of TSH action. (Endocrinology 83: 877, 1968)

Periovulatory Progesterone Concentration in the Peripheral Plasma of the Rhesus Monkey with a Methodologic Note on the Detection of Ovulation

Abstract: Peripheral plasma progesterone concentrations were measured by competitive protein binding analysis in 23 normally cycling rhesus monkeys and related to the day of ovulation as established by direct observation during serial laparotomies. Plasma progesterone concentrations began to increase abruptly on the day prior to ovulation, reaching maximal values of approximately 4 mμg/ml 3–4 days after ovulation. On the day of ovulation some animalsshowed a decline in plasma progesterone concentration, others remained unchanged, and the remainder increased in continuous fashion. A rapid and simple method, based on a modification of the competitive protein binding technique for the measurement of progesterone, which permits the highly reliable determination of the day of ovulation in the rhesus monkey is described. (Endocrinology 82: 143, 1968)

Position of the occlusal plane in natural and artificial teeth

Abstract: A roentgenographic cephalometric investigation was conducted to compare the position of the occlusal plane of the artificial teeth with that of the natural teeth which existed before the remaining teeth were extracted. The occlusal plane of the trial dentures was first oriented to parallel the alatragus line and then modified so the occlusal surfaces of the second molars were placed at the level of the middle third of the retromolar pad. This location of the artificial occlusal plane was found to be at a lower level than the natural one in the posterior region. Hence, our findings indicate that the occlusal plane should be positioned so the second molars are placed at the level of the upper third of the retromolar pad.

Endogenous insulin and growth hormone response in children with newly diagnosed diabetes mellitus.

Abstract: Extract: Forty-five children with newly diagnosed diabetes mellitus were evaluated in terms of endogenous release of insulin and growth hormone using glucose, tolbutamide, arginine and glucagon as stimuli. The mean concentration of insulin in the plasma obtained from fasting diabetic children was found to be 10.0 μU/ml, a value significantly below the mean level of 15.3 μU/ml in the control group. Essentially no increase in the concentration of insulin in plasma resulted from stimulation with the above agents. The mean concentration of growth hormone in the plasma of fasting diabetics was found to be 3.8 mμg/ml, a value higher than but not significantly different from the value of 2.5 mμg/ml in the contrast patients. Following the intravenous infusion of arginine, however, the mean concentration of growth hormone in the plasma of diabetic children rose to 20.8 mμg/ml, a level significantly higher than the mean peak value of 7.4 mμg/ml in the nondiabetics. Although no change in the concentration of growth hormone followed glucagon injection in the nondiabetic children, a prompt, significant elevation to 9.4 mμg/ml occurred in the diabetics. Glucagon administration has not previously been reported to stimulate the release of growth hormone. Speculation: Insulin deficiency alone will not adequately explain the variability in clinical symptomatology and metabolic derangement seen in children with newly diagnosed diabetes mellitus. These data suggest that growth hormone may play an important role. The finding that glucagon administration stimulates release of growth hormone in the juvenile diabetic may indicate the presence of a previously unrecognized interrelation between glucagon-growth hormone and insulin.