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N Katakura

Publications and source records attributed to N Katakura.

27 records · Page 2Linked to original sources
PubMed1981

[Viscoelastic behaviour of inlay waxes. (Part 2) Physical and dynamic viscoelastic properties for binary mixtures of waxes (author's transl)].

Binary mixtures of waxes added carnauba wax, beeswax or dammar to paraffin were investigated by measurements of X-ray diffraction, dilatometry, differential thermal analysis and dynamic viscoelasticity. The relationships between the viscoelastic behaviour and the physical properties of these waxes were discussed. Additions of carnauba wax to paraffin changed drastically viscoelastic properties of paraffin, that is, increased the dynamic modulus, G', and decreased the loss tangent, tan delta, in the region of higher temperatures including the crystal transition temperature region of paraffin. The possible explanation for this change of viscoelastic properties is that the presence of crystals of carnauba wax composed of longer chain molecules than that of paraffin rises interfacial interaction. The temperature dependence of viscoelastic properties for binary mixtures of paraffin and beeswax was approximately the same as that of paraffin. This is because paraffin and beeswax may form a sort of homogeneous phases. Additions of dammar to paraffin increased the elasticity of paraffin in the region of lower temperatures, but did not effected to change of G' and tan delta in the region of higher temperatures. Another effect of additions of dammar was to lower the thermal expansion of binary mixtures.

Elasticity↗
PubMed1981

[Viscoelastic behaviour of inlay waxes. (Part 3) Dynamic viscoelastic properties of ternary and quaternary mixtures of waxes (author's transl)].

The viscoelastic properties of ternary and quaternary mixtures added carnauba wax, dammar and beeswax to paraffin were investigated by measurement of dynamic viscoelasticity. The effects of the composition of waxes and the crystal transition temperature of paraffin to the viscoelastic behaviour of these waxes were discussed. The viscoelastic properties of ternary mixtures added carnauba wax and dammar to paraffin were similar to these of binary mixtures for paraffin and dammar in the region of lower temperatures, and similar to these of binary mixtures for paraffin and carnauba wax in the region of higher temperatures. In quaternary mixtures added carnauba wax, dammar and beeswax, tan delta was larger than that of ternary mixtures, so the effect of additions of dammar was disappeared in the region of lower temperatures. Additions of carnauba wax, like to the case of ternary mixtures, had an effect on the viscoelastic properties of quaternary mixtures, but the temperature dependence of G' and tan delta of these waxes were slightly broader than that of ternary mixtures in the region of higher temperature. For a same composition in ternary and quaternary mixtures, even if the paraffins with different transition temperature were used, the shapes of curves of G' and tan delta were so similar to one another that were approximately superposable.

Elasticity↗
PubMed1980

[Viscoelastic behaviour of inlay waxes (part 1). Physical and dynamic viscoelastic properties of several raw material waxes (author's transl)].

Several raw material waxes used in the inlay waxes, such as paraffins, carnauba wax, beeswax and dammar were investigated by measurements of X-ray diffraction, dilatometry, differential thermal analysis and dynamic viscoelasticity. The relationships between the viscoelastic behaviour and the physical properties of these waxes were discussed. The solid-solid phase transition from orthorhombic to hexagonal occurred in paraffins and the difference of the crystal transition temperature was observed between the kinds of paraffins. The viscoelastic properties and the thermal expansion of paraffins changed considerably in the crystal transition temperature region. Carnauba wax was an orthorhombic material, but such a crystal transition as paraffins did not appear. The dynamic modules of carnauba wax was greater than that of paraffin and decreased slowly to 70 degrees C and the loss tangent was small in this region. It was found, therefore, that carnauba wax had an elastic property in the crystal transition region of paraffin. Beeswax was also an orthorhombic material. The dynamic modulus of this was smallest in these waxes and the loss tangent increased relatively slowly with increases in temperature. Dammar was an amorphous solid. The dynamic modulus and the loss tangent were approximately constant in the low temperature region and changed greatly in the glass transition region. The thermal expansion of dammar was smallest in these waxes.

Bees↗
PubMed1980

[Thermal and viscoelastic properties and problems on measurement methods of JIS for inlay waxes (author's transl)].

The thermal and viscoelastic properties of commercial inlay waxes were investigated by measurements of JIS (Japanese Industrial Standard), differential thermal analysis, dilatometry and dynamic viscoelasticity. The crystal transition from orthorhombic to hexagonal caused by paraffin was observed in inlay waxes. The thermal expansion of waxes was influenced by crystal transition temperature. The cooling shrinkage of internal wax pattern is smaller in wax having larger expansion from 25 degrees C to 37 degrees C. The viscoelastic properties of inlay waxes shifted to low temperature region with decreasing in crystal transition temperature. The various properties of inlay waxes greatly changed at temperature of peak for loss tangent. There were some problems on measurement methods of JIS and the reexamination of thermal expansion and flow was suggested. Commercial inlay waxes, respectively, have various different properties, but from these results the qualities of waxes can not be determined so it's necessary to choose a suitable wax according to various conditions.

Elasticity↗
PubMed1977

[Rheological studies on deformation for dental waxes. 2. Stress relaxation behavior of inlay wax (author's transl)].

The rheological properties of inlay wax were investigated by experiment of stress relaxation, thermal expansion, thermal analysis and X-ray diffraction. The results obtained were as follows. The solid-solid phase transition caused by phase transition of paraffin was observed. The stress relaxation curves of inlay wax were obtained at various temperature, and from these curves the stress relaxation master curve was composed by application of time-temperature superposition principle. The temperature dependence of sift factor was devided into two regions of Arrhenius type, and the activation energy was about 60 kcal/mol at the temperature lower than 23 degrees C and 120 kcal/mol at higher temperature. This fact suggests that the relaxation mechanism of inlay wax can be classified into two different modes. The relaxation mechanism at lower temperature region is explained by crystalline relaxation, and at higher temperature is considered to depend upon the solid-solid phase transition process of inlay wax. Calculating from the activation energy, for each 2 degrees C rise in temperature, the rate of rheological change for inlay wax is approximately two-fold at lower temperature region, and about four-fold at higher temperature region.

Elasticity↗
PubMedDate not supplied

Flumazenil antagonizes the suppressive effect of midazolam on the somatosensory evoked potentials in the rat.

The effect of flumazenil, a specific benzodiazepine antagonist, on the midazolam-induced suppression of somatosensory evoked potentials (SEPs) following strong electrical stimulation of the upper lip was investigated in Wistar albino rats. The averaged SEPs were recorded from the contralateral surface of the skull in the temporal area. Each rat received midazolam in a dose of 10 mg/kg intraperitoneally. Five min after midazolam injection, the relative amplitude of the P1N1 wave of the SEPs was reduced significantly. A 0.5 mg dose of flumazenil or physiological saline was injected intraperitoneally 7.5 min after midazolam injection. The P1N1 amplitude recovered rapidly to the control value in the flumazenil group but not in the physiological saline group. No significant differences were found in the latencies of the P1 and N1 peaks before or after midazolam or flumazenil injection. It is suggested that flumazenil strongly antagonizes the midazolam-induced suppression of SEPs in the rat.

Anesthesia, Dental↗
PubMedDate not supplied

Midazolam does not affect the field potentials in the caudal part of the spinal trigeminal nucleus.

The effect of midazolam on the field potentials (FPs) in the caudal part of the spinal trigeminal nucleus following strong electrical stimulation of the upper lip was investigated in Wistar albino rats. The rats received i.p. dosages of 5, 10, or 20 mg/kg midazolam, or physiological saline. Relative amplitudes of the negative deflection were not suppressed after midazolam injection. No significant differences were found in the latencies of the potentials before and after midazolam injection. It is suggested that the main action site of midazolam may be located at a higher level than the spinal trigeminal nucleus.

Animals↗