Showing papers by "University of Ljubljana published in 1984"

NMR relaxation study of the H-bonded glass Rb 1 − x ( N H 4 ) x H 2 P O 4

Abstract: The existence of a minimum in the temperature dependence of the $^{87}\mathrm{Rb}$ spin-lattice relaxation time ${T}_{1}$ in ${\mathrm{Rb}}_{1\ensuremath{-}x}{(\mathrm{N}{\mathrm{H}}_{4})}_{x}{\mathrm{H}}_{2}\mathrm{P}{\mathrm{O}}_{4}$ with $x=0.35$ indicates a tremendous progressive slowing down of the proton intrabond (O-H\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}O) jump motion from ~ ${10}^{\ensuremath{-}11}$ to ~ ${10}^{\ensuremath{-}7}$ sec not found in ${\mathrm{RbH}}_{2}$${\mathrm{PO}}_{4}$ or other members of the ${\mathrm{KH}}_{2}$${\mathrm{PO}}_{4}$ family exhibiting ferro- or antiferroelectric transitions. The occurrence of a linewidth broadening together with the ${T}_{1}$ minimum exhibits a wide distribution of correlation times that develops near the onset of the low-frequency dielectric dispersion and loss characteristic of the glass state. The results can be described in terms of a cluster freeze-out model originally developed for spin-glasses. The ${\mathrm{NH}}_{4}$ reorientations freeze out much before the low-temperature glass state has been reached.

A metabolic osmotic model of human erythrocytes.

Abstract: A metabolic osmotic model of red blood cells is presented which takes into account the main reaction steps of glycolysis and the passive and active fluxes of ions across the cell membrane. Cellular energy metabolism and osmotic behaviour are linked by the ATP consumption for the active transport of cations as well as by the osmotic action of the glycolytic intermediate 2,3-diphosphoglycerate (2,3-DPG). The model is based on a system of differential equations describing the metabolic reactions and transport processes. Further, two algebraic conditions for the osmotic equilibrium and the electroneutrality of the cell are considered. Using realistic system parameters the model allows the calculation of a great number of dependent variables, among them the cell volume, the concentrations of metabolites and ions and the transmembrane potential. Only stationary states are considered. The parameter dependence of important model variables is characterized by control coefficients. The main results are: (a) The volume of erythrocytes is mainly determined by the permeabilities of the leak fluxes of cations, the content of hemoglobin and the activity of the hexokinase-phosphofructokinase system of glycolysis; (b) Changes of volume affect the glycolytic rate mainly by changing the concentration of ATP which is a regulator of glycolysis; (c) A change in the membrane area may affect the other cell properties only if it is connected with variations of the number of active and leak sites of the membrane.

Dynamics of spastic knee joint.

Abstract: Goniometric records of a swinging lower leg (pendulum test) provide useful information in assessing the level of hypertonia in normals, spinal cord injured (SCI) patients and hemiparetic patients. A linearised second-order dynamic model without forcing function is proposed for a normal and hypotonic paraplegic leg Forces which appear in the quadriceps muscle in spastic patients are simulated with hypertonia torquest Th. A combined biomechanical and neural model is proposed to facilitate qualitative discussion of the observed phenomena. Large variability of goniograms in spastic patients as well as lack of detailed knowledge regarding the neurophysiology of spasticity prevents further development of realistic models which should be time varying and nonlinear.

Δ2-1,2,3-Triazolines

Abstract: Publisher Summary The 1,2,3-triazolines were first discovered during their studies on the action of organic azides on quinones. Triazolines have assumed considerable importance as intermediates in a number of organic syntheses and recently as a new class of potential anticonvulsant drugs. This chapter presents a comprehensive, unified survey of the methods of synthesis and reactions of Δ 2 -1,2,3-Triazolines. The chemistry of mono-, bi-, and polycyclic triazolines, and that of spiro- and bistriazolines, is considered. A brief account of the chemistry of Δ 3 - and Δ 4 -1,2,3-triazolines is given. Triazoline aromatization to triazoles is achieved by oxidation, isomerization reactions, and elimination of stable molecular fragments, all of which require the presence of free hydrogen at position 4 and/or 5 of the triazoline ring. The aromatization reaction affords a selective, synthetic route for the preparation of triazoles of definitive structure, in as much as azide addition to acetylenes is not regioselective.

13C NMR in ferroelectric smectic liquid crystals

Abstract: The temperature dependence of the 13C NMR chemical shifts has been measured in the isotropic, the smectic A and the smectic C* phases of chiral DOBAMBC (p-decyloxybenzylidene p′-amino 2-methyl butyl cinnamate) and HOBACPC (hexyloxybenzylidene p′-amino 2-chloro α propyl cinnamate). The measurements allowed for a microscopic determination of the temperature dependence of the molecular tilt angle and the dipolar ordering of the C=O groups-i.e. the in-plane spontaneous polarization-without destroying the helical structure.

Temperature dependence of the pitch of the helix in a chiral ferroelectric smectic liquid crystal

Abstract: The temperature dependence of the helical pitch in the ferroelectric liquid crystal DOBAMBC near the C*-A transition (T c ) has been measured with a high temperature resolution. The pitch strongly decreases with temperature near the transition but reaches a finite value at T c. The consistency of the data with different theoretical models is studied.

Stefan's measurement of the thermal conductivity of air

Abstract: Stefan's measurement of the thermal conductivity of gases, the first experiment to confirm results of the kinetic theory of gases, is considered in a historical setting. The measurement of the thermal conductivity of air and its independence of pressure is repeated using a somewhat adapted form of Stefan's 'diathermometer'. The method is not demanding and is suitable for use in student's laboratories.

Some evidence for the ampullary organs in the European cave salamander Proteus anguinus (Urodela, Amphibia).

Abstract: The multicellular epithelial organs in Proteus anguinus, which Bugnion (1873) assumed to be developing neuromasts, have been analyzed by lightand electron-microscopy. Their fundamental structure consists of single ampullae with sensory and accessory cells with apical parts that extend into the pit of the ampulla, and of a short jelly-filled canal connecting the ampulla pit with the surface of the skin. The organs are located intra-epithelially and are supported by a tiny dermal papilla. The cell elements of sensory epithelium are apically linked together by tight junctions. The free apical surface of the sensory cell bears several hundred densely packed stereocilia-like microvilli whereas the basal surface displays afferent neurosensory junctions with a pronounced round synaptic body. The compact uniform organization of the apical microvillous part shows a hexagonal pattern. A basal body was found in some sensory cells whereas a kinocilium was observed only in a single cell. The accessory cells have their free surface differentiated in a sparsely distributed and frequently-forked microvilli. The canal wall is built of two or three layers of tightly coalescent flat cells bordering on the lumen with branching microvilli. The ultrastructure of the content of the ampulla pit is presented.

Self-tuning deadbeat controllers

Abstract: A deterministic self-tuning deadbeat control scheme is presented which is extremely simple to implement in the single-variable and multivariable cases. Its convergence properties are analysed by straightforward application of de Larminat's convergence results.

Onsager symmetries in field-dependent flows of rarefied molecular gases

Abstract: Investigations of field effects upon transport phenomena in molecular gases have recently been extended from the hydrodynamic to trasition and Knudsen regimes. In the steady state of a binary mixture between parallel plates the average flow velocity, diffusive flux aand heat flux linearly depend upon small gradients of pressure, concentration and temperature. The relation is specified by a matrix of field- and pressure-dependent coefficients L αβ , each of which may be a tensor. The Onsager reciprocity, L αβ ( B )= L βα† (- B , is verified by a derivation from the linearized Boltzmann equation, by taking account of the symmetries of intermolecular and gas-surface collision operators. A more detailed analysis is possible at moderate rarefaction, when the fluxes can be split into bulk and boundary-layer parts, the latter involving field-dependent slip coefficients.

Effect of electrical stimulation on spasticity in hemiparetic patients

Abstract: Cyclical electrical stimulation has been applied to 10 hemiparetic patients with clinical signs of knee joint spasticity. The programme included 30 minutes of stimulation to the hamstrings followed by another 30 minutes of stimulation to the hamstrings and quadriceps. None of the patients experienced increased spasticity. The reduction in spasticity ranged from none to substantial with some other beneficial side-effects. No conclusions could be drawn as to whether hamstring stimulation is preferred to combined stimulation or to quadriceps stimulation alone. It is suggested that small portable stimulators be introduced for chronic use in spastic patients after an optimum stimulation regimen is individually established for each patient.

Elemental analysis of Celtic coins

Abstract: Surface compositions of silver Celtic coins discovered in Slovenia were determined by PIXE. Bulk values were measured for some examples cut to half of their thickness. Thick target analysis avoided the use of standards; an iterative procedure was used in order to deduce concentrations.

Mass transfer in aerated fermentation broths in a stirred tank reactor

Abstract: The volumetric mass transfer coefficients, kLa, measured in a pilot plant (0.1 m3) and an industrial (67.5 m3) fermentor during an actual fermentation process are presented. Problems related to the estimation of the phsyical properties as well as to the correlation of experimental data and to scale up procedures are discussed. Although the scale up factor was rather high, both sets of data could be represented by single correlation. Comparison of the experimental data with several available correlations demonstrated the need for pilot plant experiments and scale up procedures, since it is almost impossible to take into account all relevant system properties. On presente des coefficients volumetriques de transfert de masse (kLa) mesures dans une usine-pilote (0,1 m3) et un fermenteur industriel (67,5 m3), au cours d'un veritable procede de fermentation. On discute les problemes qui ont trait a l'estimation des proprietes physiques, a la correlation des resultats experimentaux et au passage a l'echelle des procedes de fermentation. Bien que le facteur de changement d'echelle ait ete plutǒt eleve, on a pu representer les deux series de resultats au moyen d'une seule correlation. La comparaison entre les resultats experimentaux et plusieurs correlations disponibles a montre la necessite d'experimenter en usine-pilote et d'utiliser des procedures de passage a l'echelle industrielle, etant donne qu'il est presqu'impossible de tenir compte de toutes les proprietes pertinentes du systeme.

Microscopic Model for the Ferroelastic Transition in KLiSO4

Abstract: A microscopic model for the ferroelastic transition in KLiSO4 at Tc = 190 K is proposed. The model is based on the ordering of the “top” SO4 oxygen into one of the three off-centre sites below Tc. It yields a transition of first order and agrees with the predictions of the Landau theory for the hexagonal-orthorhombic equitranslational transition. Ein mikroskopisches Modell fur den ferroelastischen Ubergang in KLiSO4 bei Tc = 190 K wird vorgeschlagen. Das Modell beruht auf dem Einfrieren des „obersten” SO4-Sauerstoffs in einen der drei „Off-Center”-Platze unterhalb Tc. Es liefert einen Ubergang erster Ordnung und stimmt mit Vorhersagen der Landauschen Theorie fur hexagonal-rhombische Aquitranslationsubergange uberein.

The analysis of thick target metal alloys

Abstract: The application of proton induced X-ray emission (PIXE) for elemental analysis of metal alloys was studied. A simple correction function is introduced, which takes into account thick target effects. Calibration standards are thus avoided and the concentrations are obtained from X-ray production cross sections. The method was tested and good agreement was found between the reference and measured concentrations.

Radiochemical neutron activation analysis in standardization of trace elements in biological reference materials at the nanogram level

Abstract: Results for up to 12 trace elements in some newer biological materials of the NBS Washington (Citrus Leaves, New Bovine Liver, Wheat and Rice Flours, Milk Powder, Stabilized Wine) are reported using radiochemical neutron activation analysis. A discussion of the techniques and problems of standardization and the correct use of standards is included.

Measurements of proton induced L shell X-ray cross sections on thin Lu, W, Au, Tl, Pb, Th and U targets

Abstract: The L X-ray production cross sections induced by 0.5–0.9 MeV protons in the elements Lu, W, Au, Tl, Pb, Th and U were measured. Special attention was paid to the determination of X-ray yields originating from the transitions to the different L-subshells. According to the asymmetric response of the intrinsic Ge detector to the monochromatic X-ray radiation, a Gaussian fit corrected for an exponential tail under the peak energy was proposed. When this more realistic approach was applied, significant differences were obtained at particular line intensities. The X-ray production cross sections for different transitions were used in the determination of L-subshell ionization cross sections.

Nasopharyngeal rhabdomyoma. Report of case (light and electron microscopic studies) and review of the literature.

Abstract: Summary Rhabdomyoma is an extremely rare benign tumor originating from the skeletal or cardiac muscle cells. Only 87 cases of rhabdomyoma have been reported to date, 70% occuring in the head and neck areas. The authors present the fourth case of rhabdomyoma of the nasopharynx. The tumor appeared in an 18 year old woman with hypacusis. Examination of the epipharynx showed a 2 X 1,5 em tumor, extending from torus tubarius down to the soft palate. Light microscopy disclosed areas and islands of polymorphous large cells with abundant eosinophilic cytoplasm. Cross striations were focally visible with special PT AH staining. Electron microscopy revealed parallel and haphazardly arranged fibrillar bands (myofibrils) with irregularly and periodically arranged densities corresponding to Z lines. The pecularities of our case were abundant cystically dilated rough endoplasmatic reticulum and the absence of cytoplasmatic glycogen.

The effect of adrenocorticotropin on histamine and 5-hydroxytryptamine secretion from rat mast cells

Abstract: Characteristics of histamine (Hi) and 5-hydroxytryptamine (5-HT) release from rat peritoneal mast cells in response to the polypeptide adrenocorticotropin (ACTH) were studied. During a 15 min incubation at 37 degrees C, ACTH evoked Hi as well as 5-HT release from rat mast cells at concentrations of 1 X 10(-4) M-1 X 10(-3) M. The release was dose-dependent and very rapid. After 15 sec the amount of the amines released was the same as after 4.5 min. In most experiments, the percentage of Hi release was slightly but significantly higher than the percentage of 5-HT release. Hi and 5-HT release induced by ACTH also took place in a calcium-free medium. However, the release of the amines was decreased when calcium was omitted. Comparison of the effects of ACTH, compound 48/80 and substance P on mast cell secretion showed that ACTH is about 100 times less active then substance P which was in turn about 100 times less active than compound 48/80. When both ACTH and compound 48/80 were used together as liberators , the release was significantly higher than with either liberator alone. Our results indicate that there are receptor sites for the endogenous polypeptide ACTH on the mast cell membrane which mediate Hi and 5-HT release. This release was found to resemble that evoked by the basic secretogogue compound 48/80 but in some aspects to be different from that evoked by substance P.

The effect of group selective reagents N-ethylmaleimide and dithiothreitol on histamine H1-receptor binding sites in the vascular smooth muscle membranes.

Abstract: The chemical nature of the histamine H1-receptors of beef aortic membranes has been elucidated by introducing two group selective reagents in the [3H]-mepyramine binding studies: dithiothreitol (DTT), a protein-disulphide group reducing reagent, and N-ethylmaleimide (NEM), a protein-thiol group alkylating agent. In the binding experiments, NEM independently inhibits [3H]-mepyramine binding. The inhibition is time and concentration dependent. DTT on the other hand potentiates the binding of the radioligand to its receptor and changes the affinity of histamine in competing for [3H]-mepyramine binding site. In the DTT-pretreated membranes (100 microM), histamine shows a higher affinity for [3H]-mepyramine binding (Ki 0.35 microM) than in the untreated membranes (Ki 3.7 microM). Comparison of the pharmacological studies on the DTT-treated rabbit aortic strips and above binding studies, revealed a good correlation between the changes in the affinity of histamine for its receptor, when DTT was present. The results suggest an important role of the S-S and SH groups in the function of aortic histamine H1-receptor.