Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 40
Filtrar
1.
Rev Sci Instrum ; 87(2): 02B921, 2016 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-26932093

RESUMEN

Francium is the heaviest species among the alkali elements. Due to its properties, francium is said to be of advantage in measurements of tiny observations, such as atomic parity violation and electric dipole moment. Before executing experiments with francium, it must be produced artificially because it is one of the most unstable elements. We produced francium with the nuclear fusion reaction of an oxygen beam and gold target, ionized the produced francium through a thermal ionization process, and extracted the ion with electrostatic fields. However, the thermal ionization process is known to ionize not only an objective atom but also other atomic species. Therefore, a Wien filter was installed to analyze the composition of the ion beam and purify the beam. This allowed us to improve the beam purity from ∼10(-6) to ∼10(-3).

2.
Appl Opt ; 55(5): 1164-9, 2016 Feb 10.
Artículo en Inglés | MEDLINE | ID: mdl-26906392

RESUMEN

We demonstrate frequency offset locking between two laser sources using a waveguide-type electro-optic modulator (EOM) with 10th-order sidebands for magneto-optical trapping of Fr atoms. The frequency locking error signal was successfully obtained by performing delayed self-homodyne detection of the beat signal between the repumping frequency and the 10th-order sideband component of the trapping light. Sweeping the trapping-light and repumping-light frequencies with keeping its frequency difference of 46 GHz was confirmed over 1 GHz by monitoring the Doppler absorption profile of I2. This technique enables us to search for a resonance frequency of magneto-optical trapping of Fr.

3.
Int J Sports Med ; 36(7): 519-25, 2015 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-25760149

RESUMEN

One distinctive trait of kendo, the Japanese martial art of fencing, is the execution of sustained, high-effort vocalizations during actions. The purpose of this study was to determine the effect of these vocalizations on respiratory functions. First, the intensity of 3 kendo exercises was quantified by measuring oxygen uptake (V̇O2) and comparing it with V̇O2max measured during treadmill tests of 8 university kendo athletes. Respiratory variables of these 8 athletes were then analyzed using a portable breath gas analyzer during the most intensive kendo exercise, kakari-keiko, with and without vocalization. Breathing frequency (fB) increased regardless of vocalization, but in trials with vocalization, fB and ventilation were significantly lower, and expiration time was significantly longer. Components of expired gases were also affected by vocalization. Although there was no significant difference in oxygen uptake, vocalization yielded a reduction in carbon dioxide output (V̇CO2) and an increase in fraction of end-tidal carbon dioxide (FetCO2). We thus conclude that these vocalizations greatly affect expiration breathing patterns in kendo. Moreover, repetition of kakari-keiko caused a reduction in V̇CO2 and an increase in FetCO2 and CO2 storage. We consider the possibility that the sustained high-effort vocalizations of kendo also increase cerebral blood flow.


Asunto(s)
Dióxido de Carbono/metabolismo , Ejercicio Físico/fisiología , Artes Marciales/fisiología , Voz/fisiología , Adolescente , Pruebas Respiratorias/métodos , Prueba de Esfuerzo , Humanos , Masculino , Oxígeno/metabolismo , Respiración , Adulto Joven
4.
J Sports Med Phys Fitness ; 55(7-8): 797-804, 2015.
Artículo en Inglés | MEDLINE | ID: mdl-25369277

RESUMEN

AIM: This randomized controlled study was designed to examine the effects of reduced coenzyme Q10 (ubiquinol; CoQ10) supplementation on blood pressure (BP) and exercise-induced muscle damage in kendo athletes during a 4-day kendo training camp. METHODS: In a double-blinded manner, 32 young kendo athletes were randomly assigned to supplement with either placebo or CoQ10 (600 mg) daily for 11 days from 1 week prior to camp to end of camp. BP was measured every morning after waking up during the training camp. Blood samples were taken at 3 time points; 1 week and 1 day prior and upon completion of training camp at 17:30. Statistical analysis was performed by repeated-measures analysis of variance followed by Bonferroni/Dunn post-hoc tests. RESULTS: Before the training camp started, there were no differences in diastolic BP between these groups. However, after kendo training started, diastolic BP in the CoQ10 group was significantly lower than that in the placebo group (P<0.05). Plasma creatine kinase (CK) and myoglobin (Mb) concentrations were significantly increased in both groups during the camp (P<0.05), whereas there were no significant differences in CK and Mb between CoQ10 and placebo groups (CK: P=0.82, Mb: P=0.69). CONCLUSION: Oral supplementation with reduced form of CoQ10 (ubiquinol; Kaneka QHTM) showed a significant hypotensive effect in young male kendo athletes during a 4-day kendo training camp, although it did not significantly ameliorate kendo exercise-induced muscle damage.


Asunto(s)
Presión Sanguínea/efectos de los fármacos , Artes Marciales/fisiología , Músculo Esquelético/efectos de los fármacos , Ubiquinona/análogos & derivados , Biomarcadores/sangre , Creatina Quinasa/sangre , Suplementos Dietéticos , Método Doble Ciego , Humanos , Masculino , Mioglobina/sangre , Educación y Entrenamiento Físico , Ubiquinona/administración & dosificación , Adulto Joven
5.
J Chem Phys ; 141(13): 134201, 2014 Oct 07.
Artículo en Inglés | MEDLINE | ID: mdl-25296799

RESUMEN

We present here the first evidence of photodesorption induced by low-intensity non-resonant light from an yttrium thin foil, which works as a neutralizer for Rb and Fr ions beam. Neutral atoms are suddenly ejected from the metal surface in a pulsed regime upon illumination with a broadband flash light and then released in the free volume of a pyrex cells. Here atoms are captured by a Magneto-Optical Trap (MOT), which is effectively loaded by the photodesorption. Loading times of the order of the flash rise time are measured. Desorption is also obtained in the continuous regime, by exploiting CW visible illumination of the metallic neutralizer surface. We demonstrate that at lower CW light intensities vacuum conditions are not perturbed by the photodesorption and hence the MOT dynamics remains unaffected, while the trap population increases thanks to the incoming desorbed atoms flux. Even with the Y foil at room temperature and hence with no trapped atoms, upon visible illumination, the number of trapped atoms reaches 10(5). The experimental data are then analyzed by means of an analytical rate equation model, which allows the analysis of this phenomenon and its dynamics and allows the determination of critical experimental parameters and the test of the procedure in the framework of radioactive Francium trapping. In this view, together with an extensive investigation of the phenomenon with (85)Rb, the first demonstration of the photodesorption-aided loading of a (210)Fr MOT is shown.

6.
Phys Rev Lett ; 113(10): 102501, 2014 Sep 05.
Artículo en Inglés | MEDLINE | ID: mdl-25238351

RESUMEN

The direct 3α decay branch from the 02+ state at Ex=7.65 MeV in 12C, which is known as the Hoyle state, is considered to affect the triple-α reaction rate strongly and to give crucial information on its structure. We have performed a high-precision measurement of the 3α decay from this state using the 12C(12C,3α)12C reaction at E12C=110 MeV. The branching ratio of the direct 3α decay was under the detection limit in the present experiment. By comparing with Monte Carlo simulations for three decay mechanisms as the sequential decay through the ground state of ^{8}Be, the direct decay with equal energies of three α particles, and the direct decay to the phase space uniformly, we have obtained the upper limit of 0.2% on the direct 3α decay.

7.
J Oral Rehabil ; 31(1): 74-80, 2004 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-15125601

RESUMEN

This study evaluates the light-attenuating effects of enamel on the properties of light-cured restorative resins using simple experimental filters. Three filters were designed to replicate the light transmittance characteristics of 0.5, 1.0 and 1.5 mm thick human enamel. The bending strength, depth of cure, and levels of residual monomer for 12 shades of three commercial light-cured composite resins were examined. These resins were cured either using direct irradiation from a light source or irradiation through one of the filters. For all materials, the bending strength and depth of cure of specimens irradiated through a filter were lower and the levels of residual monomer were higher than those found in specimens irradiated directly. The results indicate that the light-attenuating effect of enamel reduces the polymerization efficiency, resulting in poorer mechanical properties of light-cured composite resins.


Asunto(s)
Resinas Compuestas , Esmalte Dental , Luz , Análisis del Estrés Dental/métodos , Humanos , Ensayo de Materiales/métodos , Dispersión de Radiación
8.
J Oral Rehabil ; 31(2): 166-71, 2004 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-15009602

RESUMEN

The polymethylmethacrylate (PMMA) resins containing gamma-methacryloxypropyltrimethoxysilane (gamma -MPS) of 0, 2, 4, 6, 10, 15, 20 and 30 mo1%, added to methylmethacrylate, were prepared using a monomer-polymer technique and stored in air or water at 37 +/- 0.5 degrees C for 28 days. The flexural strength and flexural modulus of the PMMA resins containing gamma -MPS of 20 and 30 mo1% were significantly smaller than those containing 2-6 mo1% and the same statements were true for the adhesive strength to porcelain tooth. However, its value of adhesive strength to Co-Cr alloy was remarkably less than to porcelain tooth. By contrast, there was no significant difference among the Knoop hardness of the PMMA resins examined. On the other hand, the thermal expansion had an increasing tendency with an increase of a gamma -MPS content. The dynamic shear modulus within a temperature measured (20-140 degrees C) decreased s1ightly as the gamma -MPS content of the PMMA resins increased, and the peak temperature of mechanical loss tangent also tended to decrease. These results indicated that the PMMA resin containing gamma -MPS of 6 mol% was the best composition from the standpoint of an excellent adhesive strength against porcelain, although its water absorption was 1.9 times that of PMMA.


Asunto(s)
Resinas Compuestas/química , Recubrimientos Dentinarios , Metacrilatos/química , Polimetil Metacrilato/química , Silanos/química , Porcelana Dental , Bases para Dentadura , Humanos , Ensayo de Materiales/métodos
9.
J Oral Rehabil ; 29(9): 827-34, 2002 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-12366536

RESUMEN

In order to investigate the thermal stability, the physical and mechanical, and dynamic viscoelastic properties of glass-fibre reinforced composite materials were measured. The G' of the seven materials examined was within 5;20 +/- 14; 55 and 4;50-14; 35 GPa for dry and wet specimens in air at 37 degrees C, respectively, and decreased with increasing temperature. The G' values of dry specimens decreased by 7;74-15;4% when heated to 60 degrees C. The value of tan delta ranged from 0;0102 to 0;0295 and from 0.0181 to 0.0406 for dry and wet specimens in air at 37 degrees C, respectively. The coefficient of linear thermal expansion between 30 and 60 degrees C ranged from 0;557 to 3; 95 x 10-5/ degrees C. Moreover, the filler content ranged from 56; 36 to 88; 87 wt%. These results showed that the magnitudes of G', tan delta, and the coefficient of linear thermal expansion and water absorption depend on the inorganic filler or glass-fibre content; i.e. the amount of resin matrix. Moreover, for all the materials examined, the G' values were thermostable in the temperature range encountered in the oral cavity.


Asunto(s)
Resinas Compuestas/química , Vidrio , Absorción , Coronas , Análisis del Estrés Dental , Dentadura Parcial Fija , Análisis Diferencial Térmico , Elasticidad , Ensayo de Materiales , Tamaño de la Partícula , Resistencia al Corte , Viscosidad , Agua
10.
J Oral Rehabil ; 29(8): 744-8, 2002 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-12220341

RESUMEN

Nine photo-activated acrylic-type (EPL) soft lining materials were produced experimentally to examine their durability. The purpose of this study was to investigate the effect of photo-irradiation on the hardness of experimental soft lining materials. The hardness (Hex) of the nine EPLs was increased 4.3-170.1% by exposing them to light. The effect of irradiation on the Hex of the EPLs was remarkable when the material contained much ethylmethacrylate, together with smaller amounts of di-n-butyl phthalate. Moreover, the Hex tended to increase for EPLs in which the liquid portion contained less di-n-butyl phthalate or more ethanol (Et). The weight change ratio (Wc) was greater for EPL specimens containing less Et. The Wcs ranged from 0.118 to 0.661% after 8 weeks. These results showed that the Hexs of six of the EPLs were approximately equal to those of four commercially available soft lining materials, and these six EPLs may have properties favouring their use in clinical dentistry.


Asunto(s)
Resinas Acrílicas/efectos de la radiación , Bases para Dentadura , Alineadores Dentales , Absorción , Análisis de Varianza , Dibutil Ftalato/efectos de la radiación , Etanol/efectos de la radiación , Dureza/efectos de la radiación , Luz , Ensayo de Materiales , Metilmetacrilatos/efectos de la radiación , Fotoquímica , Fármacos Fotosensibilizantes , Polimetil Metacrilato/efectos de la radiación , Agua/química
11.
J Oral Rehabil ; 29(8): 770-6, 2002 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-12220345

RESUMEN

We studied changes in the hardness, relaxation modulus [Er(t)], and weight change ratio (Wc) of experimental photo-activated acrylic soft lining materials (EPLs) stored in three aqueous solutions [distilled water (DW), physiological saline solution (PS), and artificial saliva (AS)] at 37 degrees C for 8 weeks. The hardness of the EPLs increased markedly during the first 4 days of storage, and subsequently changed little. The greatest hardness occurred in the EPL specimen containing the largest amount of ethanol (Et). The relaxation modulus [Er(8)] of the EPLs ranged from 1.35 to 1.66 MPa immediately before storage, and from 1.43 to 2.21 MPa after an 8-week immersion. Like hardness, the increase in [Er(t)] was greatest when the EPL contained large amounts of Et. The Wc ranged from 0.118 to 0.661% after storage for 8 weeks, and increased most for the EPL specimen containing the smallest amount of Et. Furthermore, 3-7 days after the start of immersion many hollows were observed in the surface of specimens with a high Et content. The results indicate that Wc and hollow formation are sensitive to the Et content of the EPL, and that Et content is closely tied to the change in hardness and relaxation modulus with time.


Asunto(s)
Resinas Acrílicas/química , Alineadores Dentales , Etanol/química , Análisis de Varianza , Almacenaje de Medicamentos , Elasticidad , Dureza , Luz , Ensayo de Materiales , Fotoquímica , Porosidad , Saliva Artificial/química , Cloruro de Sodio/química , Agua/química
12.
J Am Chem Soc ; 123(2): 203-9, 2001 Jan 17.
Artículo en Inglés | MEDLINE | ID: mdl-11456505

RESUMEN

Oxide ion conductivity in La(2)GeO(5)-based oxide was investigated and it was found that La-deficient La(2)GeO(5) exhibits oxide ion conductivity over a wide range of oxygen partial pressure. The crystal structure of La(2)GeO(5) was estimated to be monoclinic with P2(1)/c space group. Conductivity increased with increasing the amount of La deficiency and the maximum value was attained at x = 0.39 in La(2 - x)GeO(5 - delta). The oxide ion transport number in La(2)GeO(5)-based oxide was estimated to be unity by the electromotive force measurement in H(2)-O(2) and N(2)-O(2) gas concentration cells. At a temperature higher than 1000 K, the oxide ion conductivity of La(1.61)GeO(5 - delta) was almost the same as that of La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(3 - delta) or Ce(0.85)Gd(0.15)O(2 - delta), which are well-known fast oxide ion conductors. On the other hand, a change in the activation energy for oxide ion conductivity was observed at 973 K, and at intermediate temperature, the oxide ion conductivity of La(1.61)GeO(5 - delta) became much smaller than that of these well-known fast oxide ion conductors. The change in the activation energy of the oxide ion conductivity seems to be caused by a change in the local oxygen vacancy structure. However, doping a small amount of Sr for La in La(2)GeO(5) was effective to stabilize the high-temperature crystal structure to low temperature. Consequently, doping a small amount of Sr increases the oxide ion conductivity of La(2)GeO(5)-based oxide at low temperature.

13.
J Oral Rehabil ; 28(4): 320-7, 2001 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-11350584

RESUMEN

The setting times of seven commercially available elastomeric impression materials were determined using Wilson's reciprocating rheometer at temperatures 23 +/- 0.5 or 32 +/- 0.5 degrees C. The surface compressive strength and depression of these materials after setting time were measured using a rheometer (Fudoh). Each material was mixed according to the mixing proportion (base/accelerator or catalyst ratio) recommended by the manufacturer. The surface compressive strength and the depression of each material were measured by using a method which pressed the material to the edge of a sensitive rod (2.0 mm in diameter) connected to a load cell. In the case of silicone impression materials (additional type) at a temperature of 23 +/- 0.5 degrees C, the surface compressive strength and the depression of these materials were extremely stable after the setting time. However, the surface compressive strength of other materials except additional type materials increased markedly after setting time and the depression corresponding to the surface compressive strength decreased. These increased largely with the increase, in pressing speed to the sensitive rod. At 450 s from the setting time of all materials, there was an adequate correlation (r = 0.84) between measured values and theoretical values derived using the theory of elasticity.


Asunto(s)
Materiales de Impresión Dental/química , Fuerza Compresiva , Elasticidad , Elastómeros/química , Éteres/química , Ensayo de Materiales , Reología/instrumentación , Siliconas/química , Sulfuros/química , Propiedades de Superficie , Factores de Tiempo
14.
J Psychol ; 134(5): 571-6, 2000 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-11034136

RESUMEN

Doctoral recipients in clinical psychology scored higher than doctoral recipients in counseling psychology on the national licensing exam, the Examination for Professional Practice in Psychology. The largest discrepancies between the 2 groups were on Subtest I (diagnosis), Subtest II (intervention), and Subtest III (research). The differences were less large for Subtest IV (professional/ethical/legal issues) and for Subtest V (social application). The authors recommend that both counseling and clinical psychology graduate students take more course work in the department of the other discipline.


Asunto(s)
Consejo/educación , Práctica Profesional , Psicología Clínica/educación , Evaluación Educacional , Humanos
15.
Dent Mater ; 16(2): 150-8, 2000 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-11203537

RESUMEN

OBJECTIVES: The present investigation was undertaken to determine the reinforcing effect of woven glass fibers on deflection, flexural strength, flexural modulus and impact strength of acrylic denture base polymer. METHODS: Three silanized or unsilanized woven glass fibers were used. Specimens were made by heating the denture cure resin dough containing glass fibers, which were sheathed in the dough. Specimens with four different thicknesses and of five different types were made, incorporating the glass fiber. Three-point flexural test and flywheel type impact test were employed to determine the flexural properties and impact strength. RESULTS: When specimens contained unsilanized glass fiber, the flexural strength in specimens of 1 and 2 mm thickness and the impact strength in specimens of 2 mm thickness were higher than those of specimens without glass fiber (p < 0.01). On the contrary, the flexural strength and deflection in specimens reinforced with silanized glass fiber of 1 mm thickness were significantly higher (p < 0.01, p < 0.05) than those of unreinforced specimens. Further, the impact strength in specimens reinforced with silanized glass fiber of 2 mm thickness was significantly higher (p < 0.01) than that of unreinforced specimens. Statistically significant differences were found in the flexural strength (p < 0.05) and in the impact strength (p < 0.01) when specimens of 4 mm thickness were reinforced with two or three unsilanized glass fibers. SIGNIFICANCE: The reinforcement with glass fiber was effective in thin specimens, and the reinforcing effect increased with the increase of the number of glass fibers in the case of thick specimens.


Asunto(s)
Resinas Acrílicas/química , Bases para Dentadura , Vidrio/química , Algoritmos , Análisis de Varianza , Elasticidad , Furanos/química , Humanos , Ensayo de Materiales , Metacrilatos/química , Metilmetacrilato/química , Microscopía Electrónica de Rastreo , Docilidad , Polimetil Metacrilato/química , Silanos/química , Dióxido de Silicio/química , Solubilidad , Solventes/química , Estrés Mecánico , Propiedades de Superficie
16.
Dent Mater J ; 19(4): 329-37, 2000 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-11816362

RESUMEN

The adhesive strength of porcelain artificial teeth and polymethylmethacrylates (PMMAs), which contained silanes with various number of vinyl or ethoxy groups, and the mechanical and physical properties of the PMMAs were measured. Four types of PMMAs with silanes showed high adhesive shear strength and caused fractures in the porcelain. Water absorption of the PMMAs increased with the addition of silane, but that of one type with silane was almost the same as the PMMA only type. The flexural strengths of the PMMAs with silane, except for one type, showed no significant differences compared with that of PMMA (p < 0.05). The Tg levels of all PMMAs with silane fell less than that of PMMA. From these results, it was found that PMMA with silane from three vinyl groups and one ethoxy group showed excellent chemical bonding to porcelain and low water absorption.


Asunto(s)
Resinas Acrílicas/química , Recubrimiento Dental Adhesivo , Materiales Dentales/química , Bases para Dentadura , Polimetil Metacrilato/química , Silanos/química , Absorción , Adhesividad , Análisis de Varianza , Porcelana Dental , Elasticidad , Ensayo de Materiales , Docilidad , Estadísticas no Paramétricas , Diente Artificial , Agua/química
17.
Dent Mater J ; 19(4): 338-45, 2000 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-11816363

RESUMEN

The purpose of this study was to investigate a method for evaluating color stability of light-cured composite resins using an experimental filter that simulates human enamel. The light transmission coefficients and their spectral distributions from 400 to 600 nm of twelve enamel specimens were measured. The experimental filter was designed so that its light transmittance characteristics were similar to those of enamel. Color stability tests for ten shades of two light-cured composite resins, which were irradiated directly and indirectly through the experimental filter with a light source, were performed. Despite different irradiation procedures, most materials exhibited significant color changes in the color stability test. Although the differences were small, the group of specimens irradiated indirectly through the filter showed significantly higher color differences in comparison with those irradiated directly. Our results indicate that the light attenuating effect of enamel affects the color stability of light-cured composite resins.


Asunto(s)
Resinas Compuestas/química , Materiales Dentales/química , Coloración de Prótesis , Color , Esmalte Dental/química , Filtración/instrumentación , Humanos , Luz , Fotoquímica
18.
J Psychol ; 133(4): 369-75, 1999 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-10412218

RESUMEN

The present research is an examination of the parameters and correlates of kanashibari, operationally defined as being unable to move upon awakening or before falling asleep. Nonclinical Japanese individuals (N = 720), 34% of whom reported an experience of kanashibari at least once, were administered D. I. Templer's (1970) Death Anxiety Scale, R. Brown's (1990) Locus of Control Scale, and a questionnaire devised by the authors to collect information about kanashibari. The results showed that the kanashibari experience was positively correlated with death anxiety, with being a woman, and with external-other locus of control; this last measure assessed the extent to which these individuals felt that their lives were determined by fate, good luck, or chance.


Asunto(s)
Actitud Frente a la Muerte , Actitud Frente a la Salud/etnología , Control Interno-Externo , Trastornos del Sueño-Vigilia/psicología , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Susceptibilidad a Enfermedades/etnología , Susceptibilidad a Enfermedades/psicología , Disnea/etnología , Disnea/psicología , Femenino , Humanos , Japón/epidemiología , Masculino , Persona de Mediana Edad , Prevalencia , Pruebas Psicológicas , Factores Sexuales , Trastornos del Sueño-Vigilia/etnología
19.
Dent Mater J ; 18(4): 430-6, 1999 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-10786164

RESUMEN

To elucidate the effects of thermal cycling on the viscoelastic properties of four commercial resins for crown and bridge, dynamic shear modulus (G'), mechanical loss tangent (tan delta), Knoop hardness, water sorption and appearance of specimen surfaces before and after thermal cycling test were determined. The changes of G' and tan delta for two materials were insignificant with increased repetitions of thermal cycling. Those of the other two materials were statistically significant: in particular, G' at temperatures above 60 degrees C was inclined to increase slightly and tan delta decreased considerably. While the Knoop hardness of the materials was a little decreased over a number of 75,000 thermal cycles, the water sorption almost attained an equilibrium in uptake after 14,000 thermal cycles. Furthermore, cracks on the specimen surface were observed after 37,500 to 75,000 thermal cycles. From these results, the deterioration of materials was observed as damage to the specimen surface. Moreover, it could be presumed that the materials would be further polymerized during the period of thermal cycling.


Asunto(s)
Resinas Compuestas/química , Coronas con Frente Estético , Análisis de Varianza , Elasticidad , Dureza , Calor , Ensayo de Materiales , Polímeros/química , Estadísticas no Paramétricas , Propiedades de Superficie , Viscosidad , Humectabilidad
20.
J Dent Res ; 77(11): 1874-80, 1998 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-9823725

RESUMEN

In this study, we examined the rheological properties of elastomeric impression materials, both before and during setting, to assess the clinical significance of certain key characteristics such as viscosity, pseudoplasticity, and the rate of development of elasticity. The hypothesis to be tested was that monitoring the change in tan delta is the most appropriate means of monitoring the setting characteristics of elastomers. The loss tangent (tan delta) and the dynamic viscosity (eta') for five impression materials (both unmixed pastes and mixed/setting materials) were measured by means of a controlled-stress rheometer in a cone/plate configuration. For unmixed pastes, tests were performed at various frequencies (0.1 to 10 Hz) and torques (from 1 to 50 x 10(-4) Nm), while testing on setting materials was performed at constant frequency (1 Hz) and torque (3 x 10(-3) Nm). Most base and catalyst pastes were pseudoplastic before being mixed. Immediately after being mixed, the polyether (tan delta = 9.85) and polysulfide (tan delta = 9.54) elastomers showed tan delta markedly higher than those of other mixed materials (tan delta = 4.96 to 3.01). The polyvinylsiloxane elastomers showed lower initial tan delta, which rapidly reduced even further with time. This suggests that these materials should be used as soon as possible after being mixed. The polyether elastomer had a comparatively long induction period during which the tan delta remained at a high value. These characteristics are thought to be key factors in controlling clinical efficacy and therefore support the hypothesis that monitoring tan delta is an appropriate method for evaluating the setting characteristics of elastomers. One limitation was that the controlled-stress rheometer was unable to monitor rheological properties through to completion of setting.


Asunto(s)
Materiales de Impresión Dental/química , Elastómeros de Silicona/química , Ensayo de Materiales/instrumentación , Ensayo de Materiales/métodos , Ensayo de Materiales/estadística & datos numéricos , Pomadas , Reología/instrumentación , Reología/métodos , Reología/estadística & datos numéricos , Torque , Viscosidad
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...