Showing papers by "University of Groningen published in 1969"

Magnetic semiconductors

Abstract: Both semiconductors and magnetic materials exhibit interesting properties that can be used in electronic devices. A material that combines these properties, i.e., a magnetic semiconductor, could show interesting cross effects, such as a large magnetoresistance, or hysteresis and the associated memory phenomena introduced in the semiconductive properties. The discovery of ferromagnetic semiconductors (EuSe, CdCr 2 Se 4 , etc.) and the subsequent study of their properties has shown that a strong interaction between charge carriers and magnetic properties indeed exists. In this paper the available experimental information on cross effects between electric and magnetic properties is reviewed. The observed phenomena are discussed on the basis of a simple model with an exchange interaction between the charge carriers and the magnetic moments. Finally, the possibilities for observing the Gunn effect in magnetic semiconductors is discussed.

Some ternary uranium chalcogenides

Abstract: The synthesis and crystal structures of the ternary uranium compounds UYX, where Y = Si , Ge , Sn , Sb , and X = S , Se , Te , are reported. USiS, UGeS, USnTe, USbS, USbTe and also UTe 2 − x are isotypic with ZrSiS which has a distorted PbFCl-type structure. USiSe, UGeSe and UGeTe have structures of a new type, closely related to that of ZrSiS. The compounds USiTe, USnS and USnSe could not be prepared. The instability of these compounds and the occurence of ZrSiS and UGeTe-type compounds are discussed.

The system niobium-sulfur

Abstract: The following phases have been found in the system niobium-sulfur: NbS3, 2s-NbS2, 3s-NbS2, 2s-Nb1 + xS2, 3s-Nb1 + xS2, Nb3S4, h.t.-Nb1 − xS, l.t.-Nb1 − xS, Nb21S8. While NbS3 is a diamagnetic semiconductor, the other niobium sulfides are metallic with nearly temperature-independent paramagnetism. H.t.-Nb1 − xS, stable above 780 °C, has an orthorhombic structure of the MnP type with infinite zigzag Nb-Nb chains. The low-temperature form of Nb1 − xS has a hexagonal superstructure of the NiAs type with triangular Nb3 clusters. The structures of the other niobium sulfides that had been reported previously, were confirmed.

Nuclear Magnetic Resonance Measurements on a Macroscopically Ordered Smectic Liquid Crystalline Phase

Abstract: OF the three types of liquid crystalline phases, the smectic type can be formed in some compounds by either varying the temperature (thermotropic mesophases) or the solvent concentration (lyotropic mesophases). The system we used belongs to the latter type and consisted of a solution of potassium oleate (KO) in D2O. According to Luzzati et al.1, a concentration above 72 per cent by weight of KO in water yields a smectic mesophase at room temperature (20° C). In such a system the soap-like molecules can form a lamellar domain structure, and in these domains the direction of the molecular maximum and minimum polarizability perpendicular to the molecular chains is at random. This results in an ordered structure with an optical uniaxial character having its optical axis perpendicular to the lamellae.

Psychophysiological Studies in Newborn Infants

Abstract: Publisher Summary In a characteristic psychophysiological study, the independent variable (usually the behavioral one) is systematically manipulated, while changes in the dependent (usually the physiological) variables are recorded. The permanent record of such a study is usually in the form of a polygraph tracing, because in most psychophysiological studies several dependent variables are simultaneously recorded. This chapter concerns with a number of problems specific to psychophysiological studies of human newborns. It considers some of the biological determinants of postnatal behavior in human infants. The endogenous physiological activity of the neonate have been described and some of the implications of this activity for psychophysiological studies have been considered. To illustrate specific problems, the chapter treats a limited number of studies in detail, rather than attempt a systematic review of the several hundred relevant articles. Some of the main trends in the neonatal psychophysiological literature have been summarized.

A bacteriocinogenic factor of Enterobacter cloacae.

Abstract: Enterobacter cloacae strain DF13 produces a bacteriocin which is able to kill other strains of Enterobacter and Klebsiella. This property can be transmitted to Enterobacter cloacae strain O 2 (up to 90% of the acceptor population became bacteriocinogenic), to E. coli K12F- and E. coli K 12 Hfr. Transfer of chromosome material was never observed, suggesting that the production of the bacteriocin is determined by a plasmid. However all attempts to eliminate this plasmid failed. The plasmid F′ trp cys Col B Col V could be transferred from E. coli into Ent. cloacae DF13 and subsequently it could be eliminated by acridine orange treatment. Ent. cloacae DF13 harbours in addition two independently transferable R-factors, one determining resistance against streptomycin and sulfanilamide and the other resistance against penicillin. Most but not all Ent. cloacae O2 recombinants which have received only the bacteriocinogenic factor upon conjugation with Ent. cloacae DF 13, can transfer this property to Ent. cloacae O2 but not to E. coli. E. coli F- recombinants, which have received only the bacteriocinogenic factor cannot transfer this property. The results suggest that the bacteriocinogenic factor cannot mediate its own transfer, but can be transferred when another transmissible plasmid is present. This may be the R(str sul) factor, the F-factor in E. coli Hfr or a transfer factor (Δ) in Ent. cloacae O2. Closed circular DNA molecules were selectively isolated from these strains and investigated by electron microscopy and velocity sedimentation. Ent. cloacae DF13 harbours small closed circular DNA molecules ranging from 0.5 to 3.2 μ in contour length, 98% of which corresponds to a size class of 0.7±0.1 μ. Ent. cloacae O2 also harbours closed circular DNA ranging from 0.8 to 3.0 μ in contour length, with major size classes of 0.9 μ and 1.4 μ respectively. Circular DNA of a contour length of 3.0±0.2 μ (S20,w=26 S) corresponding to a molecular weight of 6.0×106 daltons was transferred to E. coli and Ent. cloacae O 2 concomitantly with the ability to produce the bacteriocin. A significant difference was observed in the number of copies of the plasmid between Ent. cloacae and E. coli.

Muscle co-ordination of the respiratory pump of the carp (Cyprinus Carpio L.).

Abstract: 1. An analysis has been made of the pattern of activity of the muscles of the head of the carp, in relation to respiratory movements and pressures generated in the buccal and opercular cavity, during normal respiration and during coughing. 2. From comparison with the results of analyses carried out on other species of fish it is suggested that the respiratory movements of free-swimming teleosts in general conform to the following principles: the lateral expansions and contractions of the buccal and opercular cavities are always synchronous, but the lowering of the floor of the mouth may be synchronous with, or may precede, the lateral expansion. 3. In the carp the levator operculi muscle, although it inserts on the opercular bone, does not participate in the opercular pump but is the abductor of the lower jaw.

On the polymorphism of tantalum diselenide

Abstract: The structure of a new polymorph of tantalum diselenide, 4s(c)-TaSe2, has been determined by X-ray diffraction. In this form the metal has trigonal-prismatic coordination, as in 2s(a)-TaSe2, 3s-TaSe2 and 4s(a)-TaSe2. In Is-TaSe2 the coordination of the metal is octahedral, while in 4s(b)-TaSe2 and 6s-TaSe2 the two types of coordination coexist. The thermal relations between the various polymorphic forms have been studied. It is found that octahedral coordination is stable above 880 °C, trigonal-prismatic coordination below 800 °C, while the two coordinations coexist at intermediate temperatures. The transitions Is →3 6s →3 2s and Is →3 4s(b) →3 4s(c) are reversible, but the high-temperature forms can be retained at room temperature by quenching. Heating of quenched Is- or 6s-TaSe2 gives the metastable 3s form. A mechanism is proposed for the irreversible transitions (occurring at 200 °–225 °C) which explains these observations.

Functional Anatomy and Movement Co-Ordination of the Respiratory Pump of the Carp (Cyprinus Carpio L.)

Abstract: 1. An anatomical description of the head skeleton of the carp ( Cyprinus carpio ) is given. The description is limited to what is relevant for the functioning of the respiratory pumps. 2. An anatomical description of the head muscles of the carp is given. 3. The result of the contraction of most of the head muscles through coupling of skeletal elements spreads farther over the respiratory system than only to the bones to which the muscles are attached directly. It is through this that in the first place all the muscles producing laterad movements, with the exception only of the dilator operculi, influence the volume of both the buccal and opercular cavities, and in the second place that contraction of the hypobranchial muscles not only results in vertical movements of the floor of all the respiratory cavities, but also in laterad movements of their side walls. The hyoid arch plays a central role in the coupling system because it interconnects almost all the other elements. 4. The functional significance of the interaction through couplings is integration of the respiratory movements through which during low-intensity breathing whole muscles can cease to be active and during high-intensity respiration whole muscles can be recruited without seriously affecting the co-ordination of the movements and hence the hydrodynamic efficiency of the pumps.

Histochemical demonstration of enzymes related to NADPH-dependent hydroxylating systems in rat liver after phenobarbital treatment.

Abstract: Male rats were given 100mg phenobarbital for three days intraperitoneally. Biochemically an increase was found in activity of nitro-anisole demethylation and in the content of cytochrome P-450. Enzymhistochemically an increase in activity was noted for NADPH tetr. red., G6PD, ICD, and Naftol AS-D-esterase; a decrease was seen in G6Pase and glycogen, but no difference was found in NADH tetr. red. From these results it has been suggested that NADPH tetr. red. is directly involved in the hydroxylation chain, while G6PD and ICD are more indirectly involved.

An electron‐microscopical study of the plasmodesmata in the roots of young barley seedlings*

Abstract: SUMMARY Many plasmodesmata can be found in the walls of the cells of the endodermis and the pericycle of the roots. A mutual symplasmatic contact is thus established between the cells of the pericycle, endodermis and the innermost layer of the cortex. The radial walls of the endodermal cells are very thin and tend to become folded as a result of the fixation and embedding procedure. Virtually no plasmodesmata could be observed in these walls nor any striking feature which could be related to the presence of a Casparian strip. The plasmodesmata are spindle-shaped and lined by a membrane, which is a continuation of the plasmalemma. They all possess a central osmophilic strand. The pores on either end of the plasmodesmata are closed by the contact between plasmalemma and this strand. The substructure of the strand and its relationship to the endoplasmatic reticulum is discussed. Some rough calculations with respect to the role these structures may play in the process of intercellular transport are given and the significance of the plasmalemma for this type of transport is emphasized.