Showing papers by "University of Illinois at Urbana–Champaign published in 1969"

Measurements of Subnanosecond Fluorescence Lifetimes with a Cross-Correlation Phase Fluorometer

Abstract: The methods for the direct determination of fluorescence lifetimes may be discussed by considering each single fluorescent species as a detector in which the response to an infinitely narrow pulse of light decays in time, t, according to the exponential law I ( t ) = I(0) x exp (kt) . From the relations of the exciting light with the light emitted by such exponential detector, the rate constant k or its reciprocal T, the lifetime of the excited state may be determined. FIGURE 1 shows the Fourier spectrum characteristic of an exponential detector (cf. McLachlan, 1963). The detector responds without attenuation or change of phase to all frequencies from zero to those approaching k, while frequencies of this order or exceeding k are progressively more attenuated. The phase of the emitted light lags behind that of the excitation by 4.5\" when o = k, and tends to 90\" lag towards complete attenuation. It follows that, for the determination of k, the fluorescence must be excited by light of one or more frequencies in the neighborhood of k (hatched area of FIGURE 1 ) . The former is practically realized by excitation with sinusoidally modulated light, and the latter by excitation with light pulses the frequency spectrum of which is made up of a narrow band of frequencies. Classical electrodynamics shows that, for emission in the visible and ultraviolet regions of the spectrum, k is of the order of los sec-1 (or T of order 10-8 sec). Therefore, the frequencies to be employed in the excitation must be of the order of l O s / 2 ~ or in the region of 1-50 MHz. Light modulated at a single frequency in this range may be produced by various electro-optical methods, (Gaviola, 1927; Maerks, 1938; Bauer & Rozwadowski, 1959; Miiller et al., 1965), whereas techniques for the production of approximately Gaussian pulses of half-width 0.3 to 3 nsec (D'Alessio et al. 1964, Hundley et al. 1967) have been described. Each type of method has its own advantages and disadvantages. The pulse method is particularly useful when several modes of decay are possible, although the methods employing a single frequency are undoubtedly the more accurate because of the extreme frequency selection attainable by electronic techniques. They are also better adapted to the measurement of lifetimes in the subnanosecond region, and because we had this object in mind we have chosen to employ sinusoidally modulated light of fixed frequency in our measurements. The theory of the fluorometer, so named by Gaviola who constructed the first apparatus of this kind in 1926, has been given in detail by Dushinsky (1933). If a fluorescent species is illuminated with light modulated with frequency f, describable by the expression E(t) = A + B cos 27rft * This research was supported by United States Public Health Service Grant GM 11223.

Superfluidity in neutron stars

Abstract: Possible states of superfluidity in the liquid interiors of neutron stars, including neutron pairing, proton pairing and pion condensation are described, and recent work on the subject is reviewed.

Spin up in neutron stars: the future of the vela pulsar.

Abstract: Assuming that the speed up of the Vela pulsar was caused by a “starquake”, a number of predictions can be made, and the event can be taken as evidence that the interior of the pulsar is a superfluid.

Evaluation of factor analytic research procedures by means of simulated correlation matrices.

Abstract: In order to study the effectiveness of factor analytic methods, a procedure was developed for computing simulated correlation matrices which are more similar to real data correlation matrices than are those matrices computed from the factor analysis structural model. In the present investigation, three methods of factor extraction were studied as applied to 54 simulated correlation matrices which varied in proportion of variance derived from a major factor domain, number of factors in the major domain, and closeness of the simulation procedure to the factor analysis structural model. While the factor extraction methods differed little from one another in quality of results for matrices more dissimilar to the factor analytic model, major differences in quality of results were associated with fewer factors in the major domain, higher proportion of variance from the major domain, and closeness of the simulation procedure to the factor analysis structural model.

A token reinforcement program in a public school: a replication and systematic analysis.

Abstract: A base rate of disruptive behavior was obtained for seven children in a second-grade class of 21 children. Rules, Educational Structure, and Praising Appropriate Behavior while Ignoring Disruptive Behavior were introduced successively; none of these procedures consistently reduced disruptive behavior. However, a combination of Rules, Educational Structure, and Praise and Ignoring nearly eliminated disruptive behavior of one child. When the Token Reinforcement Program was introduced, the frequency of disruptive behavior declined in five of the six remaining children. Withdrawal of the Token Reinforcement Program increased disruptive behavior in these five children, and reinstatement of the Token Reinforcement Program reduced disruptive behavior in four of these five. Follow-up data indicated that the teacher was able to transfer control from the token and back-up reinforcers to the reinforcers existing within the educational setting, such as stars and occasional pieces of candy. Improvements in academic achievement during the year may have been related to the Token Program, and attendance records appeared to be enhanced during the Token phases. The Token Program was utilized only in the afternoon, and the data did not indicate any generalization of appropriate behavior from the afternoon to the morning.

An ultrastructural and cytological study of preimplantation development of the mouse.

Abstract: Each stage of preimplantation development in the mouse from the fertilized egg to the blastocyst stage (including the unfertilized egg) was studied cytologically and ultrastructurally. Observations were made on the appearance and elaboration of several cellular organelles, inclusions and cell surface specilizations. The fertilized egg exhibits many intranuclear annulate lamellae, an increase in cytoplasmic vesicle number when compared to the unfertilized egg, and small amounts of crystalloids; mitochondria are vacuolated and small. The 2-cell stage is very similar to the fertilized egg but shows an increase in the number of cytoplasmic vesicles. The 4-cell stage is characterized by many changes: functional nucleoli appear, vacuolated mitochondria enlarge, cytoplasmic vesicles continue to increase in number, rough endoplasmic reticulum appears (as mitochondria-associated sacs), and some ribosomes are localized near the plasma membrane. At the 8-cell stage, large numbers of free ribosomes are observed in the cytoplasm, but clusters (polysomes) predominate at the 16-cell stage (morula). Morulae develop junctional complexes and exhibit differences in cytoplasmic basophilia between cells, which may be a prelude to differentiation. At the blastocyst stage, nucleoli change to an elongate form and differences in cytoplasmic background density can be observed ultrastructurally. Observations suggest that the contents of the blastocoel may be derived from the cytoplasmic vesicles, which increase in number and size subsequent to fertilization and discharge their contents into the intercellular spaces; the blastocoel arises as these fluid-filled spaces become confluent and enlarge.

Taste versus calories: sensory and metabolic signals in the control of food intake.

Abstract: In this paper we would like to discuss the role of sensory and metabolic signals in the control of food intake. The problem can be defined by perusing FIGURE 1, which presents a simplified version of a previously published schema outlining the control of intake in flow chart form (Jacobs, 1962). The initial conditions assume an animal already eating food. We shall not be concerned with the particular causes initiating the meal. Starting with the top of the FIGURE 1, then, we may ask classical question of physiologists analyzing intake regulation: What does the diet contain that can act as a signal to monitor subsequent intake? This signal can increase intake in a short-term positive feedback loop, as seen in the lower right side of the Figure, or decrease it in a negative feedback loop. The latter case we have called satiety. The two classes of physicochemical stimuli which interest us are labeled calories and taste. Both sets of signals are initiated in specialized receptor systems and relayed to the central nervous system (CNS) by nervous and/or humoral paths. It should be pointed out that our choice of the terms, taste and calories, is an oversimplification of the actual situation, which is at least hinted at in FIGURE 2. This diagram shows the same system, with the physicochemical stimuli expanded. What we have called calories are in fact only one of a large number of potential metabolic signals, and taste, only one of a number of potential seniory signals. The metabolic class includes all of the classical factors that physiologists have implicated in food intake. When a single factor is singled out and perhaps overemphasized, we have a “theory” of intake, as in the classical glucostatic and thermostatic hypotheses. Some would also consider a lipostatic or perhaps an “aminostatic” theory as well. Most people working in this area now accept Edward Adolph’s dictum that food intake is under multiple factor control, and that some combination of all of the metabolic signals is involved. The sensory category summarizes the classes of stimuli contained in food which have been of interest to the sensory psychologist, but which, for the most part, have been ignored by the regulatory physiologist. FIGURE 2 suggests many interesting problems, e.g. which receptor system responds to which classes of stimuli? Where are the latter located? Are they independent? For the purpose of this discussion, we can ignore these complexities. Returning to the simpler case (FIGURE 1 ) , we can now point out that the terms,

Evaluation of our thoughts on secondary plant substances

Abstract: The paper presents and evaluates modern concepts about the role of the secondary plant substances in the host selection of phytophagous insects. It deals with the following main topics: A. The role of nutrients in host selection. B. The concept of utilization in this context. C. The role of the secondary substances as attractants. D. The role of the secondary substances as repellents. The conclusion is reached that host selection is principally guided by the presence and/or absence of secondary substances, and that qualitatively and quantitatively nutrients can play only a very minor part, if one at all, in this context. ZUSAMMENFASSUNG BEWERTUNG UNSERER VORSTELLUNGEN UBER SEKUNDARE PFLANZENSTOFFE Die Arbeit bringt und beurteilt moderne Auffassungen uber die Rolle der sekundaren Pflanzeninhaltsstoffe bei der Wirtswahl phytophager Insekten. Sie enthalt die folgenden Hauptabschnitte: A. Die Rolle der Nahrstoffe bei der Wirtswahl. B. Die Auffassung der Ausnutzung in diesem Zusammenhang. C. Die Rolle der sekundaren Pflanzenstoffe als Attraktants. D. Die Rolle der sekundaren Pflanzenstoffe als Repellents. Es wird die Schlusfolgerung gezogen, das die Wirtspflanzenwahl grundsatzlich von der Gegenwart und/oder dem Fehlen sekundarer Pflanzenstoffe bestimmt wird, und Nahrstoffe, wenn uberhaupt, in diesem Zusammenhang, quantitativ und qualitativ nur eine sehr untergeordnete Rolle spielen konnen.

Spontaneous Mutation: Genetic Control of Mutation Rates in Bacteriophage T4

Abstract: The following two articles are concerned with the genetic control of mutation rate. The first describes the anti-mutagenic effect of some DNA polymerase mutations on phage T4 mutation rates, and discusses the implications they hold for the mechanism of action of DNA polymerase. The second compares spontaneous mutation rates in different species, and considers the biological factors which may determine these rates.

Numerical solution for the flow around a cylinder at Reynolds numbers of 40, 200 and 500

Abstract: Finite difference solutions for the time dependent equations of motion have been carried out in order to extend the range of available data on steady flow around a cylinder to larger Reynolds numbers. At the termination of the calculations for R = 40 and 200, the separation angle, the drag coefficient and the pressure and vorticity distributions around the surface of the cylinder were very close to their steady-state values. For R = 500 the separation angle and drag coefficient were very close to their steady-state values but the pressure distribution and vorticity distribution at the rear of the cylinder were still changing slightly. The results at R = 500 were found to be quite different from those at R = 200 so it is not clear how closely we approximated the steady solution for R → ∞. The forces on the cylinder due to viscous drag and due to pressure drag are found to be smaller for steady flow than for laboratory experiments where the wake is unsteady.

Velocity gradients at the wall for flow around a cylinder at Reynolds numbers from 5 × 10 3 to 10 5

Abstract: Electrochemical techniques have been used to measure the velocity gradients at the surface of a cylinder for Reynolds numbers from 5 × 103 to 105. This is a companion study to that already reported by Dimopoulos & Hanratty (1968) for a Reynolds number range of 60–360. The use of a specially designed sandwich electrode enabled the direction of the velocity gradient as well as its magnitude to be measured. Of particular interest is the region of definite length after separation where the velocity gradient is negative, followed by an ill-defined region where the flow moves in the positive direction. Still farther downstream the direction of flow changes with time in an irregular fashion. The measured velocity gradients prior to separation are described satisfactorily by boundary-layer theory. The presence of a splitter plate in the rear of the cylinder eliminates periodic fluctuations in the wake and has a significant effect on the boundary layer prior to separation.

Ethiopia: A center of diversity

Abstract: “ Encompassed on all sides by the enemies of their religion, the Aethio pians slept near a thousand years, forgetful of the world by whom they were forgotten≓ (6).

Methodology for Experimental Studies of Young Children in Natural Settings

Abstract: A method for the experimental study of young children in natural settings is described. These settings include the home, institution, school, and clinic as well as the behavior of parents, peers, and professional workers. Dominant stimulus and response events are assessed in preliminary observations which typically involve written accounts of the child’s behavior and the conditions under which it occurs. Subsequently, a behavioral code which specifies these events is constructed. The adequacy of the code is then tested and revised until independent observers reliably agree on the occurrence of the events. The training of observers, methods of calculating reliability coefficients, and the frequency of observations are discussed. The experimental design is a single subject strategy in which data are collected on individual children under four or more conditions to evaluate the functional relationships between behavior and environmental stimuli. During the first of these conditions, the baseline period, the field situation is left unchanged. Next, the variable of interest is manipulated to assess its effect on the behavior being observed. When response frequency has again stabilized, the conditions are changed to those that were in effect during the baseline period. In the fourth phase, the conditions of the first experimental period are reinstated. Ways of analyzing the data and interpreting the findings are also discussed.

Rhodopseudomonas acidophila, sp. n., a New Species of the Budding Purple Nonsulfur Bacteria

Abstract: A succinate-mineral salts medium of pH 5.2 provided selective enrichment conditions for Rhodomicrobium vannielii and for a new species belonging to the Athiorhodaceae, described herein as Rhodopseudomonas acidophila. Seven strains of the new species have been isolated from different sources in the United States and Germany. The cells are rod-shaped or ovoid, 1.0 to 1.3 mum wide and 2 to 5 mum long, and motile by means of polar flagella. Multiplication occurs by budding. The photopigments consist of bacteriochlorophyll a and carotenoids of the spirilloxanthin series, together with new carotenoids. All strains can grow either under anaerobic conditions in the light or under microaerophilic to aerobic conditions in the dark. No growth factors are required. The range of simple organic substrates photo-assimilated resembles that characteristic of Rhodomicrobium. Good photolithotrophic growth is possible at the expense of molecular hydrogen; thiosulfate and sulfide are not utilized.

Structure of vortex lines in pure superconductors

Abstract: A method is given for solving the Bogoliubov equations for quasiparticle excitations in superconductors in the WKBJ approximation. It is applied to calculate the excitation spectrum and the scattering states of an isolated vortex line in a type-II superconductor. The pair potential and magnetic field in the vicinity of the core are determined by a variational method. For values of the Ginzburg-Landau parameter $\ensuremath{\kappa}$ near 1, the energy so calculated is about 10% too high and the critical $\ensuremath{\kappa}$ for type-II superconductivity about 25% too high, indicating that the variational functions used are only approximately of the correct form. The energy of the bound states depends on the magnetic quantum number like a Landau energy; the effective magnetic field is of the order of the upper critical field ${H}_{c2}$ for all values of $\ensuremath{\kappa}$.

Note on a Criterion for the Number of Common Factors.

Abstract: LINN (1968) has published the results of a, Monte Carlo approach to the number of factors problem involving the use of random normal deviates as additional variables in correlational matrices from which principal components are extracted. Horn (1966) has made use of an independent component analysis of random normal deviates, parallel to the analysis of the &dquo;real&dquo; variables, in order to correct the Kaiser criterion (see Horn) which assumes population values of the correlations, for capitalization on chance in the sample. This note briefly presents some results obtained from another, and more promising, variation on their procedures. Linn found that his mean square ratios, analogous to F-ratios with data from the latent roots of real variables in the numerator and of random variables in the denomination, fluctuated widely

Tolerance of Cold and Bergmann's Rule

Abstract: As size is well known to affect the energy relations between an endotherm and its environment, one would expect that size may also influence or be related to geographic distribution. Bergmann's Rule postulates that geographic races of small size are generally found in the warmer parts of a species' range and races of larger size in the cooler parts. This rule has been attacked by Scholander (1955, 1956) and Irving (1957) on the grounds that the differences in size involved are too small to provide significant heat conservation and that adaptation to cold depends mainly on improved insulation (Scholander et al., 1950a). The rule has been defended by Mayr (1956) and Hamilton (1961) on empirical grounds, and recently from a theoretical basis by LeFebvre and Raveling (1967). Good comparative data on the weights of different races of a species are difficult to find, but variations of the order of 10 to 100+ per cent exist between extreme northern and southern forms. If we assume that standard metabolism in the zone of thermal neutrality, or the energy requirements of the bird at complete rest and in a post absorptive condition, increases with weight (W) as W0724 (Lasiewski and Dawson, 1967) and surface area as W0.667, then a 50 per cent increase in weight would reduce the rate of heat loss per unit area body surface only 2.4 per cent. This advantage might well be offset by the 34 per cent increase in the birds' standard metabolism and hence energy requirements. The importance of size on a bird's tolerance of cold may be analyzed in a more significant manner by comparing the standard metabolism for species in the zone of thermal neutrality with their standard metabolism at 0?C. The lower limit of temperature tolerance for several small tropical resident and migrant passerine species and temperate zone permanent residents in the summer is 0?C or slightly below (Table 2). Winter residents in temperate regions and migrants to the Arctics, however, are able to tolerate much lower temperatures. Equations for the regression of standard metabolism (M = kcal/bird-day) on ambient temperature below the zone of thermal neutrality have been compiled for a number of species from data available in the literature (Table 1). These equations make possible the drawing of regression lines for standard metabolism in relation to weight (W = grams) both for the zone of thermal neutrality and for 0?C (Figure 1). The equations for these lines are as follows: