Showing papers by "Ben-Gurion University of the Negev published in 1975"

Statistical Black Hole Thermodynamics

Abstract: Traditional methods from statistical thermodynamics, with appropriate modifications, are used to study several problems in black-hole thermodynamics. Jaynes's maximum-uncertainty method for computing probabilities is used to show that the earlier-formulated generalized second law is respected in statistically averaged form in the process of spontaneous radiation by a Kerr black hole discovered by Hawking, and also in the case of a Schwarzschild hole immersed in a bath of black-body radiation, however cold. The generalized second law is used to motivate a maximum-entropy principle for determining the equilibrium probability distribution for a system containing a black hole. As an application we derive the distribution for the radiation in equilibrium with a Kerr hole (it is found to agree with what would be expected from Hawking's results) and the form of the associated distribution among Kerr black-hole solution states of definite mass. The same results are shown to follow from a statistical interpretation of the concept of black-hole entropy as the natural logarithm of the number of possible interior configurations that are compatible with the given exterior black-hole state. We also formulate a Jaynes-type maximum-uncertainty principle for black holes, and apply it to obtain the probability distribution among Kerr solution states for an isolated radiating Kerr hole.

Water Vapor Isotherms and Heat of Immersion of Na/Ca-Montmorillonite Systems—I: Homoionic Clay

Abstract: Adsorption isotherms for water vapor, c-spacing and heat of immersion in water of Na- and Ca-montmorillonite were measured at 25°C at various r.h. The amount of water adsorbed as a function of the r.h. increased gradually, whereas the c-spacing increased, and the heat of immersion (per mole of adsorbed water) decreased in steps. There was good agreement between the calorimetric data, the heat calculated from the isotherms by use of BET equation, and the calculations from the ion-dipole model. A model is presented to describe the hydration of sodium and calcium montmorillonite.

On the mechanism of glow discharge detection of microwave and millimeter-wave radiation

Abstract: A simplified and unified model of glow-discharge detection of microwave/millimeter wave radiation, compatible with experimental data reported to date, is presented. Emphasis is placed on the roles of the potential gradient and the electrode geometry.

The Role of Abscisic Acid in Cross-Adaptation of Tobacco Plants

Abstract: Tobacco plants (Nicotiana rustica L) pre-exposed to leaf dehydration, mineral deprivation, salination, or BO33− toxicity exhibited increased resistance to subzero temperature and to reduced oxygen in the root medium The stressed plants all showed an elevated content of leaf abscisic acid Upon transfer of mineral deprived and salinated plants to prestress conditions, a decline in leaf abscisic acid content to prestress levels took place together with a loss of the increased resistance to subzero temperature and to deprivation of root oxygen Treatment with abscisic acid by direct application to the leaves or by addition to the root medium improved leaf resistance to subzero temperature and to deprivation of root oxygen A common hormone-regulation mechanism involving abscisic acid is suggested for this phenomenon of “cross-adaptation” by which a given stress confers increased resistance to other, apparently unrelated stresses

Nonsingular general-relativistic cosmologies

Abstract: According to the "singularity theorems" of Penrose, Hawking, and Geroch, all general-relativistic cosmological models must have a singularity. However, the energy condition assumed by the theorems is not satisfied by all known forms of matter. (A notable exception is the massive Klein-Gordon field.) Our object here is to construct exact isotropic cosmological models without singularities by exploiting a violation of the energy condition which arises naturally from the basic physics, rather than being introduced ad hoc via an equation of state. We accomplish this with models in which the matter, envisaged as dust, interacts with a conformal scalar field whose field equation and stress-energy tensor come from an action principle. All the equations that govern the evolution of the models are solved exactly. For all possible topologies of the universe, the singularity can be avoided for a certain range of the parameters of the model, but only for the closed universe is the required range physically appealing.

The aetiology of senile osteoporosis: secondary hyperparathyroidism due to renal failure.

Abstract: The aetiology of senile osteoporosis was investigated in a series of elderly normal persons (mean age 76.8 years) who were compared to 18–19 year old normal controls. Osteoporosis was estimated by standard radiological morphometric and densitometric techniques, in the metacarpals and thoraco-lumbar vertebrae. Serum parathyroid hormone levels were significantly higher in the elderly group, and correlated well with morphometric and densometric measurements of osteoporosis. Creatinine clearance was reduced in seven out of nine of the elderly group, and correlated well with the degree of osteoporosis. Serum thyrocalcitonin levels were reduced in the elderly. Tubular reabsorption of phosphate and TmP/GFR were in the hyperparathyroid range in the elderly group and correlated well with the degree of osteoporosis. The hypothesis is advanced that the osteoporosis of old age is a result of parathryoid overactivity, caused by asymptomatic chronic renal failure. The suggestion is made that a diet low in phosphorus might reduce the incidence of osteoporosis in old age by reducing the parathyroid overactivity.

The Northern Termination of the Andes

Abstract: In terms of topography, the northernmost extensions of the Andes branch into long fingerlike ranges separated by low-lying sediment-filled basins. Geologic definition of the northern Andes is a far more complex problem. For many, the term “Andes” has the connotation of Tertiary block uplifts or Germano-type orogeny, in contrast to the orogenic model associated with island arcs. It is common practice, therefore, to regard the Southern Caribbean Mountains, i.e., the coastal ranges of northern Venezuela and Trinidad, as having affinities with the Caribbean Island Arc, whereas the Merida ranges are classed as Andean. There are others such as Gansser (1973) who include all ranges on the continental mainland as Andean and consider the Caribbean Island Arc to begin at the southernmost of the Lesser Antilles. On the gross scale of this report, the two kinds of orogenic belt are closely associated in space: With allowance for major lateral offsets, one may claim geologic continuity from the lesser Antilles into the northern ranges of Trinidad-Venezuela and thence into the Guajira Peninsula and the northwestern apex of the Santa Marta block continuing into the Cordillera Central (cf. Alvarez, 1971). It has been an arbitrary decision on my part to exclude from discussion here the northern ranges of Trinidad-Venezuela and the Guajira Peninsula. For convenience, the southern limit of the region under discussion has been set at the latitude of Bogota (4°40’ N).

Seasonal and diurnal courses of water relations of the arido-active plant Hammada scoparia in the Negev desert

Abstract: The photosynthesizing branches of Hammada scoparia, one of the typical dwarf shrubs of the Negev desert, undergo a seasonal change from succulent to xeromorphic anatomy. This trend is accompanied by a marked decrease of water content and of total water Ψ plant and osmotic Ψ π plant potential. Irrigated plants do not show such transitions. The daily courses of Ψ plant and Ψ π plant showed minima around noon and a tendency for maxima before sunrise. Turgor pressure Ψ plant reached minima around noon and became negative (until ca.-10 bars). Generally, Ψ plant decreases with increasing water vapour concentration difference between plant and air (WD) in the first half of the day, and in the second half the reversal of this trend occurs. Mostly smaller increments of Ψ plant were correlated with larger increases in WD which lead to the conclusion that stomates closed enough to maintain transpiration at a constant value. Non-irrigated and irrigated plants showed different hysteresis loops of relation between Ψ plant and WD. Regulatory reduction of transpiration appears largely independently of Ψ plant which is in spring and with irrigated plants on a high level, with non-irrigated plants in summer on a low level. In summer the continous but decreasing drop of Ψ plant with increasing WD was interpreted as caused by a change in soil or root resistance. Independent of the seasonal state and of the Ψ plant level, H. scoparia regulates its water status within limited ranges of Ψ plant changes: the irrigated plants on a higher level, the non-irrigated on a lower level of Ψ plant . The water contents of the tissues of H. scoparia are linearily related to Ψ plant as well as Ψ plant . Steeper slopes with non-irrigated plants in summer than with spring palnts and with irrigated plants during the whole season signify that in the latter a certain increment in turgor pressure corresponds to a large gain in water content while in the non-irrigated summer plants it varies only little for an identical change in Ψ plant . This behaviour of non-irrigated wild plants apparently is due to the change of the elastic properties of the tissues in the assimilating branches.

Effect of litter size on milk yield in the rat.

Abstract: The amount of milk removed from rats during 1 hour's suckling after a separation period of 8 hours was estimated by weighing their pups. In the 1st experiment litters of 9 pups were suckled by all rats. At test sucklings held daily on days 6-15 of lactation, pups were reallocated to give 3, 6, 9, 12 or 15 pups per dam. The largest amount of milk was removed at suckling by groups of 12 pups. In a 2nd experiment, rats were constantly sucked by litters of either 3, 6, 9, 12 or 15 pups from birth to slaughter at 15 days post partum. Rats with 12 and 15 pups yielded the most milk, nearly twice as much as those suckling only 6 or 9 pups. Litters of 3 pups consumed less than 1/3 of the amount consumed by litters of 6 or 9 pups.

The Role of Abscisic Acid in Senescence of Detached Tobacco Leaves

Abstract: The role of abscisic acid in the regulation of senescence was investigated in detached tobacco leaves (Nicotiana rustica L.). Leaves senesced in darkness showed a sharp rise in abscisic acid level in the early stage of aging, followed by a rapid decline later. The same trend was found when leaves were aged in light, but the rise in abscisic acid occurred four days later than in darkness. Senescence was slower in light than in darkness, while salt stress accelerated the processes. Leaves treated with kinetin which senesced in light and darkness, did not show an increase in abscisic acid. Application of kinetin led to a transformation from free to bound ABA. These results may indicate that ABA and cytokinin are involved in a trigger mechanism which regulates senescence; the stage at which this trigger is activated determines the rate of senescence.

Raman study on several smectic phases in terephtal- bis -butylaniline (TBBA)

Abstract: Raman investigation on the lattice modes (8-200 ${\mathrm{cm}}^{\ensuremath{-}1}$) of several smectic phases in terephtal-bis-butylaniline (TBBA) reveals significant spectral differences. Softening of the lowest lattice 19-${\mathrm{cm}}^{\ensuremath{-}1}$ mode, observed very near to the solid-smectic-$B$ phase transition, is correlated with the gradual release of the smectic inter-layer glide motion. The Raman spectra add new insight into the ordering within the layers of the metastable smectic phases and also indicate the existence of molecular dynamic rotations in the smectic-$B$ phase.

On intensity perturbations in vibronically induced radiative transitions

Abstract: Intensity perturbations in forbidden radiative transitions due to cubic anharmonic mixing involving the inducing mode and a totally symmetric progression-forming mode are discussed. It is shown that such mixing will lead to deviations from mirror symmetry of the absorption and fluorescence structure because the destructive-constructive interference pattern which prevails in absorption is different to that in emission. This analysis is applied to intensities in the 2600 A system of benzene. Moderate cubic coupling energies (ca. 10 cm-1) have marked effects on intensity distributions even when the interacting levels are 200 cm-1 apart. The splitting of the progressions 10 n 61 2 and 1 n 062 1 into two sub-progressions (l=0, 2) is linearly dependent on the extent of vibronic excitation in the a 1g mode v 1. These effects are amenable to experimental detection.

Elevated microviscosity in membranes of erythrocytes affected by hereditary spherocytosis.

Abstract: Summary. Erythrocytes affected by hereditary spherocytosis (HS), obtained from several splenectomized patients, showed a varying degree of elevated osmotic fragility. In order to evaluate a possible role of the crythrocyte membrane lipids in HS, microviscosity of the membrane lipid core was measured by a fluorescence-polarization technique. Intact HS-affected red cells, as well as their ghost membranes and liposomes prepared from their lipid extract, all showed a distinctly higher microviscosity than the respective normal control. The increased microviscosity correlated with the severity of HS. The data support the proposition that the defect in HS-affected red cells is associated, at least in part, with alterations in the membrane lipids.

Spin rotation in ternary Ho 0.6 Tb 0.4 Fe 2

Abstract: The spin rotation which takes place in the ternary cubic Laves phase compound ${\mathrm{Ho}}_{0.6}$${\mathrm{Tb}}_{0.4}$${\mathrm{Fe}}_{2}$ was studied by means of neutron diffraction and M\"ossbauer-effect spectroscopy. The neutron diffraction measurements were carried out on an aligned powder sample as a function of temperature (4.2-300 K) and external magnetic field (0-8 kOe). M\"ossbauer spectra of $^{57}\mathrm{Fe}$ were obtained over a 77-200-K temperature range. The spin rotation in ${\mathrm{Ho}}_{0.6}$${\mathrm{Tb}}_{0.4}$${\mathrm{Fe}}_{2}$ is found to take place over the temperature interval 90-140 K. The experimental results enable the determination of the direction of the ferrimagnetic axis as a function of temperature within the spin-rotation interval.

Behavior of Kibbutz and urban children receiving an injection.

Abstract: This study attempted to demonstrate the usefulness of uncomplicated psychophysiological measures applied in a real-life setting involving stress. The Ss were 17 Kibbutz girls and 19 Urban girls who received immunization needles in varied contexts. Measures of the 12-yr-olds included heart rates (HR) taken at the wrist and finger sweat prints (FS) recorded one day before, immediately before, and one week after Ss received their needles. Supplementary verbal rating scales and behavioral observations added validity to the physiological indices. A lower HR of Kibbutz Ss immediately before their injections (p<01) accurately predicted their more relaxed behavior to needle penetration (p<.001). FS was of limited validity being masked completely by ambient temperature. Simple physiological measures, it was concluded, can be predictive in applied contexts.

Enzyme Content of Plant Microbodies as Affected by Experimental Procedures

Abstract: The content of specific enzymes in microbodies isolated from tobacco Nicotiana rustica, L. leaves may vary according to the procedure followed during the isolation of the organelles. The type of homogenizing medium, its ionic components and the ratio of medium to tissue during homogenization, affect the over-all yield and relative distribution of each microbody enzyme in different ways. The type of density gradient and the initial acceleration of the centrifuge rotor affect also the enzyme content of sedimenting microbodies. These observations explain some of the conflicting results obtained on the determination of the intracellular location of several enzymes.

Laser induced isotropic holes in nematic liquid crystals

Abstract: The possibility of producing isotropic “holes” in thin films of nematic liquid crystals, whose sizes are controllable by the laser power, is demonstrated. The potential applicability of this effect for display devices is discussed.

Studies on the intracellular location of enzymes of the photosynthetic carbon-reduction cycle.

Abstract: Homogenates of dark-pretreated leaves yield two particulate fractions in density gradient centrifugation: one contains chlorophyll (chloroplasts) while a second fraction contains ribulose-1, 5-bisphophate carboxylase, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase and catalase. Addition of a microbody-rich pellet to chloroplasts isolated from dark-pretreated plants largely enhances both oxygen evolution and CO2-fixation into organic compounds. The pathway of CO2 reduction may be part of a membrane system which, under suitable conditions, may separate from the chloroplast as a distinct cytoplasmic entity, having physical properties similar to those of microbodies.