Showing papers by "University of California, San Diego published in 1968"

A quantitative analysis of the responding maintained by interval schedules of reinforcement

Abstract: Interval schedules of reinforcement maintained pigeons' key-pecking in six experiments. Each schedule was specified in terms of mean interval, which determined the maximum rate of reinforcement possible, and distribution of intervals, which ranged from many-valued (variable-interval) to single-valued (fixed-interval). In Exp. 1, the relative durations of a sequence of intervals from an arithmetic progression were held constant while the mean interval was varied. Rate of responding was a monotonically increasing, negatively accelerated function of rate of reinforcement over a range from 8.4 to 300 reinforcements per hour. The rate of responding also increased as time passed within the individual intervals of a given schedule. In Exp. 2 and 3, several variable-interval schedules made up of different sequences of intervals were examined. In each schedule, the rate of responding at a particular time within an interval was shown to depend at least in part on the local rate of reinforcement at that time, derived from a measure of the probability of reinforcement at that time and the proximity of potential reinforcements at other times. The functional relationship between rate of responding and rate of reinforcement at different times within the intervals of a single schedule was similar to that obtained across different schedules in Exp. 1. Experiments 4, 5, and 6 examined fixed-interval and two-valued (mixed fixed-interval fixed-interval) schedules, and demonstrated that reinforcement at one time in an interval had substantial effects on responding maintained at other times. It was concluded that the rate of responding maintained by a given interval schedule depends not on the overall rate of reinforcement provided but rather on the summation of different local effects of reinforcement at different times within intervals.

Problems of Optimal Structural Design

Abstract: Optimal sandwich structure design for stiffness, natural frequency, buckling load and safety through plasticity

Changes in Direction of Sea Floor Spreading

Abstract: Magnetic anomalies and fracture zones make distinctive patterns when the direction of sea floor spreading changes as has occurred repeatedly in the north-eastern Pacific. The mode of deformation is such that the spreading centres between transform faults become uniformly reoriented essentially perpendicular to the faults.

Extension of the Low Soft-Photon Theorem

Abstract: The Low theorem is applied to the radiative cross section for unpolarized particles. It is shown that the first two terms of an expansion in the photon energy depend on the unpolarized, nonradiative cross section only.

Photoreduction and photophosphorylation with tris-washed chloroplasts.

Abstract: The artificial electron donor compounds p-phenylenediamine (PD), N, N, N′, N′-tetramethyl-p-phenylenediamine (TMPD), and 2,6-dichlorophenol-indophenol (DCPIP) restored the Hill reaction and photophosphorylation in chloroplasts that had been inhibited by washing with 0.8 m tris (hydroxymethyl) aminomethane (tris) buffer, pH 8.0. The tris-wash treatment inhibited the electron transport chain between water and photosystem II and electron donation occurred between the site of inhibition and photosystem II. Photoreduction of nicotinamide adenine dinucleotide phosphate (NADP) supported by 33 μm PD plus 330 μm ascorbate was largely inhibited by 1 μm 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) while that supported by 33 μm TMPD or DCPIP plus ascorbate was relatively insensitive to DCMU. Experiments with the tris-washed chloroplasts indicated that electron donors preferentially donate electrons to photosystem II but in the presence of DCMU the donors (with the exception of PD at low concentrations) could also supply electrons after the DCMU block. The PD-supported photoreduction of NADP showed the relative inefficiency in far-red light characteristic of chloroplast reactions requiring photosystem II. With phosphorylating systems involving electron donors at low concentrations (33 μm donor plus 330 μm ascorbate) photophosphorylation, which occurred with P/e2 ratios approaching unity, was completely inhibited by DCMU but with higher concentrations of the donor systems, photophosphorylation was only partially inhibited.

Kinematics of Geomagnetic Secular Variation in a Perfectly Conducting Core

Abstract: The motions in the Earth’s electrically conducting fluid core which are the probable cause of the geomagnetic secular variations have time scales of the order of a few centuries or less. Seismic bounds on the kinematic molecular viscosity of the core and order-of-magnitude arguments about the eddy viscosity make plausible the hypothesis that at such short periods the core motion consists of a boundary layer of Ekman-Hartmann type close to the core mantle boundary, and an interior free-stream motion where the viscosity and resistivity can be set equal to zero. This boundary-layer approximation requires that the unknown vertical length scale of the poloidal geomagnetic field deep in the core be at least as long as the 600 km horizontal length scales inferred at the surface of the core from observations above the mantle. For periods shorter than a century the Ekman and magnetic boundary layers are probably thinner than 120 km. If magnetic flux diffusion is neglected (i.e. if electrical conductivity is considered infinite) in the free stream in the core then the external geomagnetic field is completely determined by the fluid motion at the top of the free stream. Therefore the hypothesis of negligible flux diffusion in the free stream has implications for the geomagnetic secular variation, and these implications can be used as a test of whether there is any motion of a perfectly conducting core which will produce the observed secular variation. If the observed secular variation passes this test, we can write down explicitly all ‘ eligible’ velocity fields, i.e. all velocity fields at the top of the free stream in the core which are capable of producing exactly the observed secular variation. The different eligible velocity fields are obtained by different choices of an arbitrary stream function on the surface of the core. We describe a method of selecting from among all eligible velocity fields those which are of particular geophysical interest, such as the one which is most nearly a rigid rotation (westward drift) or the one which is most nearly a latitude dependent westward drift with m degrees of freedom.

Orthomolecular Psychiatry Varying the concentrations of substances normally present in the human body may control mental disease

Abstract: The functioning of the brain is affected by the molecular concentrations of many substances that are normally present in the brain. The optimum concentrations of these substances for a person may differ greatly from the concentrations provided by his normal diet and genetic machinery. Biochemical and genetic arguments support the idea that orthomolecular therapy, the provision for the individual person of the optimum concentrations of important normal constituents of the brain, may be the preferred treatment for many mentally ill patients. Mental symptoms of avitaminosis sometimes are observed long before any physical symptoms appear. It is likely that the brain is more sensitive to changes in concentration of vital substances than are other organs and tissues. Moreover, there is the possibility that for some persons the cerebrospinal concentration of a vital substance may be grossly low at the same time that the concentration in the blood and lymph is essentially normal. A physiological abnormality such as decreased permeability of the blood-brain barrier for the vital substance or increased rate of metabolism of the substance in the brain may lead to a cerebral deficiency and to a mental disease. Diseases of this sort may be called localized cerebral deficiency diseases. It is suggested that the genes responsible for abnormalities (deficiencies) in the concentration of vital substances in the brain may be responsible for increased penetrance of the postulated gene for schizophrenia, and that the so-called gene for schizophrenia may itself be a gene that leads to a localized cerebral deficiency in one or more vital substances.

Some observations on the vertical migration ofdinoflagellates (1) (2).

Abstract: The technique of measuring chlorophyll concentration in vivo by fluorometric analysis has been adapted to studying the diurnal migration of dino-flagellates in the sea and also in a deep tank (3 m in diameter by 10 m deep). The downward migration of Ceratium furca was followed during a bloom off the California coast. The main band of cells migrated from the upper 2 m to a depth of 5 m about 2 hr after sunset, and was dispersed between 5 and 16 m 4.5 hr after sunset. Cultures of Gonyaulax polyedra and Cachonina niei both migrated to the surface of the deep lank during illumination and migrated downward during darkness at a rate of 1-2 mjhr. The downward migration was observed to begin before the light was turned off, indicating that migration is correlated with a cellular periodicity which is to some extent independent of the light regime. Further evidence for such a periodicity was afforded by observations that C. niei start to migrate up in the water column before start of the light period. Nitrogen-limited cells of G. polyedra showed no diurnal migration, but within 1 day after addition of a nitrogen source they recovered their full migratory ability. Cells of C. niei, however, continued to migrate during 5 days of N-starvation, although they did not concentrate in the upper 1/2 m as did the control cells.

How Mangroves Desalinate Seawater

Abstract: Water relations of a number of mangroves and other halophytes were studied. All mangroves had high negative pressure in the xylem (30 to 60 atm) which more than balances the osmotic pressure of the seawater (25 atm). Freezing a short stem section of an attached twig always resulted in wilting caused by eavitation of the tensile sap. Semipemeable membranes in the leaves remained functioning in spite of being iced or healed (50°C), or being poisoned by dinitrophenol and carbon monoxide (13 atm). Chloroform and ether ruptured the membranes. When some 40 atm pressure was applied to the root system of a decapitated seedling potted in seawater, a flow of nearly fresh water ensued. This separation kept on for hours in spile of chilling and poisoning with dinitrophenol or 20 atm carbon monoxide. A reversal of the gradient made roots lose water to the seawater. One may conclude, therefore, that mangroves separate fresh water from the sea by a simple non-metabolic ultrafiltration process, in a system where high tension obtains in the xylem and where turgor of the living cells is produced by an active maintenance of high solute pressure.

Localization and Regulation of Synthesis of Nitrate Reductase in Escherichia coli

Abstract: The nitrate reductase of Escherichia coli K-12 was localized in a particulate fraction of the cell and it sedimented as if it were bound to a large substructure that is subject to fragmentation during cell disruption procedures. Soluble enzyme, exhibiting a homogenous profile in sucrose gradients, was released from this fraction by an alkaline-heat treatment. Less than 1.5% of total active nitrate reductase apparently occurred in this soluble form during the course of formation of the particulate enzyme. Enzyme synthesis was repressed by aeration in the presence or absence of nitrate. Under anaerobic conditions, nitrate reductase was synthesized at a rate that could be increased 20-fold by the addition of nitrate. When enzyme synthesis was initiated by induction with nitrate or anaerobiosis, biphasic kinetics were obtained. We interpreted the results as evidence for the existence of a redox-sensitive repressor which mediates nitrate reductase regulation.

Inhibition of Chloroplasts by UV-Irradiation and Heat-Treatment

Abstract: The site of inhibition in UV-irradiated and heat-treated chloroplasts was examined by using artificial electron donor compounds such as p-phenylenediamine and hydroquinone which donated electrons specifically to photosystem II. In both cases the electron donors restored the photoreduction of nicotinamide adenine dinucleotide phosphate and the restored activity was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea. The fluorescence of variable yield was eliminated by both inhibitory treatments and was partially restored by the electron donors in the heat-treated but not the UV-irradiated chloroplasts. The results suggest that the sites of inhibition of UV-radiation and heat treatment are in the photosynthetic electron transport chain between water and photosystem II.

An Income-Net Worth Approach to Measuring Economic Welfare

Abstract: Economists and public policy-makers alike have long been concerned with the relative and absolute economic welfare of various segments of the population. This interest reflects an underlying concern both about the equity of the existing distribution and about our ability to explainand forecast more effectively the behavior of producers and consumers.' But given the many possible dimensions of a comprehensive measure of economic welfare, the single-dimensional, money-income measure so commonly used leaves much to be desired. The concern of this paper is with the development of an approach for measuring current economic welfare which is operationally feasible and broader in scope than the traditional money-income measure. The measure proposed is based on a combination of current income and current net worth (assets minus liabilities). These are made commensurable by converting net worth into an annuity value, which is added to current income. While this proposed measure stops well short of an "ideal"measure, we show that even this change leads to policy prescriptions rather different from those generated by the current income measure of economic welfare.

Alteration of the conformation of proteins in red blood cell membranes and in solution by fixatives used in electron microscopy.

Abstract: The effects of several commonly employed fixatives on the three-dimensional conformations of two soluble proteins and the protein of intact red blood cell membranes have been studied by means of circular dichroism measurements in the spectral region of the peptide absorption bands. The fixatives used produced significant and parallel conformational changes in all of the proteins, in the increasing order: glutaraldehyde; OsO4; glutaraldehyde followed by OsO4; and KMnO4. The last two treatments obliterated most of the helical character of the proteins. The significance of these observations to the preparation of specimens for electron microscopy is discussed.

Uptake of nitrate and nitrite by ditylum brightwellii-kinetics and mechanisms(1) (2).

Abstract: Ditylum brightwellii grown on NO2 - as a nitrogen source took up and assimilated NO2 - only in the light, apparently via a photosynthetic nitrite reductase. Assimilation was inhibited by dichlorophenyldimethylurea (DCMU), KCN, partially by 2,4 dinitrophenol, and by NO3 -. Kinetics of inhibition of NO2 - assimilation by NO3 - appeared to be "competitive." D. brightwellii cells grown on NO2 - took up NO3 - in both light and dark and in both cases the uptake was inhibited by p-chloromercuribenzoate, but not by DCMU, KCN, or by NO2 -. Most of the NO3 - taken up in the dark was recovered unchanged from the cells. However only 40% of NO3 - taken up in light was recovered from the cells and no NO2 - was found. This suggests that a photosynthetic nitrate reduction mechanism was active in these cells. DCMU inhibited the light-induced NO3 - reduction. This mechanism of NO3 - reduction is distinct from that involving NADH nitrate reductase in D. brightwellii since the concentration of the latter enzyme is very low in cells grown on NO2 -. Saturation kinetics were observed for NO2 - and NO3 - uptake. Half-saturation concentrations (Ks values) were 4 and 2 μM, respectively. These values are compared with those obtained for NO2 - and NO3 - assimilation by other unicellular algae. The comparisons show lower Ks values in oceanic species compared with tide-pool or freshwater algae and they support the idea that Ks values for NO3 - assimilation may provide a key to understanding species succession when this is due to declining: nitrate concentrations in the sea.

Pesticides: Transatlantic Movements in the Northeast Trades

Abstract: Concentrations of chlorinated hydrocarbons in airborne dust carried by the trade winds from the European-African land areas to Barbados range from less than 1 to 164 parts per billion. The lower limit of the average content of 1 cubic meter of air is 7.8 x 10-14 gram. The contributions of river-borne and atmospherically transported pesticides to parts of the marine environment are calculated approximately and comtpared. The amnounts of pesticides contributed to the tropical Atlantic by the trade winds appear to be comparable to those carried to the sea by major river systems.

Negative Magnetoresistivity in Dilute Alloys

Abstract: The negative magnetoresistivity of dilute alloys containing magnetic transition impurities is calculated in the second Born approximation using an $s\ensuremath{-}d$ exchange model. Physically the variation of the magnetoresistivity is the product of: (a) the field and temperature dependence of the conduction-electron scattering amplitudes, (b) the freezing out of the impurity's spin degree of freedom by the magnetic field. In zero field, the former contribution leads to the well-known Kondo logarithmic series in $T$, whereas the latter remains constant in temperature. But in the presence of a magnetic field and for $\frac{g{\ensuremath{\mu}}_{B}H}{{k}_{B}T}\ensuremath{\lesssim}2$, the freezing out of the spins, mainly described by the square of the magnetization, varies, and much more rapidly than the perturbation expansion of the scattering amplitudes. This is verified experimentally in $\mathrm{Cu}\mathrm{Mn}$ alloys (for $T\ensuremath{\gg}{T}_{\mathrm{Kondo}}$), and allows us to phenomenologically extend our results to $T\ensuremath{\approx}{T}_{\mathrm{Kondo}}$, for which we get the same good fit with experiments in $\mathrm{Cu}\mathrm{Fe}$ alloys. For $\frac{g{\ensuremath{\mu}}_{B}H}{{k}_{B}T}\ensuremath{\gtrsim}4$, the impurity spins are completely aligned with the field; the scattering amplitudes become the main source of variation in the magnetoresistivity. In this case, as in absence of field, an exact theory in needed.

The compton--getting effect.

Abstract: The differential current density and anisotropy seen by an observer moving relative to the frame of reference in which a flux of cosmic ray particles or photons is isotropic, is derived assuming that the observer's speed is small. The results are applied to examples relevant to the theory of cosmic ray modulation and the expected anisotropies of photons originating outside our galaxy.

A study of the near-miss involving Weber’s law and pure-tone intensity discrimination

Abstract: A study of pure-tone intensity discrimination is presented in which amplitude changes are detected in 1000 Hz tone bursts 15–20 msec in duration. The masking function (log detectable increment vs log background intensity) is found to have a slope of 9/10 when calculations are carried out via energy measurements. This near-miss to Weber’s law is in agreement with other data reported in the literature. The masking slope proves to be essentially independent of stimulus duration between 15 msec and 1.5 sec. Our stable slope parameter is interpreted as a detectability restriction generated by “mass-flow” phenomena in the auditory channel. These phenomena are thought to be similar to the fluctuations accompanying a noisy or turbulent stream of events. Pure-tone intensity discrimination is then analyzed as a special case of energy detection.

Statistical Theory of Nuclei

Abstract: The energy-density formalism is applied to finite nuclei. The total energy of the many-nucleon system is expressed as a functional $E(\ensuremath{\rho})$ of the local density $\ensuremath{\rho}(r)$, and the ground-state density distribution is found by minimization with respect to $\ensuremath{\rho}(r)$. The functional of the potential energy is directly derived from a nuclear-matter calculation with variable neutron excess by Brueckner et al. The density-gradient correction which takes care of the density variation at the nuclear surface contains an exchange- and a correlation-energy part. In a first attempt, proton and neutron densities are assumed proportional; therefore the present calculation is limited to light nuclei. The density distributions are found to be of the so-called modified Gaussian type with a cubic polynomial. Binding energy, radius, and surface thickness are in good agreement with experiment.

Marine Plankton Algae Grown with Light‐Dark Cycles.

Abstract: The diatoms Ditylum brightwellii and Nitzschia turgidula were grown in semi-continuous culture under various combinations of light intensity, temperature and daylength (photoperiod). Growth was strongly limited by light intensities below 0.03 cal/em2. min in both species. Above this intensity, light saturation of growth was rapidly approached in Nitzschia but only gradually so in Ditylum. The growth rate in continuous light was never significantly higher than with 16 hours of light plus 8 hours of dark. In Ditylum, continuous light above 0.03 cal/cm2. min caused a strong inhibition of growth at all temperatures. The chlorophyll concentration in the cells was greater the shorter the photopceriod. In cultures synchronised by different combinations of light intensity and photoperiod, cell division generally took place in the light. Synchrony was best under short photoperiods of bright light. Time courses are shown for chlorophyll synthesis and photosynthesis in synchronised cultures.