Tan Delta Values Research Articles

Dynamic viscoelastic properties of processed soft denture liners: Part II—Effect of aging

The proper functioning of soft denture liners depends to a great extent on their mechanical properties. As with many polymers these materials are affected by aging. Twelve soft denture liners were processed by a laboratory according to the manufacturers' directions. Five specimens of each material were tested without aging. Five additional specimens of each material were subjected to 900 hours of accelerated aging in a Weather-Ometer instrument. These were tested with a dynamic viscoelastometer at three frequencies and two temperatures, and data for 37 degrees C and 1 Hz was obtained. Two of the ethyl methacrylate resins demonstrated the largest increases in storage (E') and loss moduli (E") after aging. These materials also showed the greatest overall E' and E". One denture liner material exhibited 673% and 488% increases in E' and E", and other materials showed smaller increases. The effects of aging on the damping factor (tan delta) were varied and five materials showed increased tan delta. Only two ethyl methacrylate resins developed lower tan delta. All the silicone and polyphosphazine rubbers showed small changes after aging and had the lowest tan delta values. Significance of differences between materials and treatments was tested with ANOVA, Scheffé intervals, and t-tests at a = 0.05. The ethyl methacrylate soft denture liners were affected the most by accelerated aging, and the silicones and polyphosphazine were least affected. The ethyl methacrylate resins also had the greatest values of E', E", and tan delta after aging.

The role of rheological properties in mucociliary transport by frog palate ciliated model.

The effect of viscoelastic properties on mucociliary transport rate was investigated using the frog palate ciliated model. Mucociliary transportability of several hydrophilic polymeric gels with widely different viscoelastic characteristics were tested on the frog palate mucociliary model. An apparent negative relationship is observed between the relative transport rate (TR) and storage (G1) or loss (G2) modulus. However, a minimum in relative transport rate is observed at an apparent loss tangent (tan delta) value of between 0.7 and 0.9. A theoretical model for mucociliary transport is presented. The model predicted a minimum in transport rate at tan delta equal to 1.74 after adjustment for primary variation due to storage modulus (G1), which is in agreement with the observed frog palate transport rate. The model isolates the loss tangent (tan delta) and the magnitude of the complex modulus (magnitude of G*) as the important viscoelastic parameters for mucociliary transport. Optimum rheological characteristics with respect to slow transport rate can be achieved by using hydrophilic polymer gels with a large complex modulus and simultaneously with a loss tangent equal to 1.74.

An experimental study on the replacement of the anterior cruciate ligament of the rabbit's knee using an augmented substitute

The mechanical properties of a reconstruction of the anterior cruciate ligament (ACL) using an augmented substitute were investigated in rabbits' knees. After total resection of the ACL, 25 knees were reconstructed with a patellar tendon alone (nonaugmented group) and 25 with a patella tendon augmented by a Leeds-Keio artificial ligament (augmented group). The rabbits were sacrificed for biomechanical testing at 0, 4, 8, 12 and 24 weeks, respectively, after operation. In the augmented group, the mean ultimate load was 48.8% of the original ACL load at 4 weeks, and this gradually increased to 65.6% at 8 weeks. That of the twenty-four-week specimens was restored to 71% of the original ACL load. In the nonaugmented group, the mean ultimate load decreased to 9.3% at 8 weeks, but increased to 37.5% at 24 weeks. The mean static stiffness in the augmented group was higher than in the nonaugmented group at all time periods. The differences between the augmented and nonaugmented groups were statistically significant in the 8 to 12 week period (p < 0.01). Tan delta values, exhibiting the magnitude of viscosity in a viscoelastic material, in the augmented group were significantly higher than those in the nonaugmented group at 8 weeks (p < 0.05) and 12 weeks (p < 0.01). The mean tan delta in the augmented group decreased to 0.08 +/- 0.04 at 24 weeks, but the values were higher than those of the original ACL. The mean dynamic elastic modulus in the augmented group was higher than in the nonaugmented group at all time periods. The difference between the augmented and nonaugmented groups was statistically significant in the 8th week (p < 0.05). The values of dynamic elastic modulus in both groups were increased at 24 weeks: 96.4 MPa in the augmented group, and 77.5 MPa in the nonaugmented group. It was demonstrated that the augmented ligaments used for anterior cruciate ligament reconstruction had greater strength and static stiffness than the patellar tendon autograft. As for dynamic properties, the augmented group showed higher viscosity group than ACL.

Biomechanical properties of the acromioclavicular joints

The purpose of this study was to investigate the biomechanical properties of the cartilagenous element of the acromioclavicular joint. Experimental specimens of the distal end of the clavicle were selected from operative excisions from patients with acromioclavicular joint dislocation. Dynamic stiffness, tan delta, cartilagenous thickness, elastic modulus and creep modulus were measured with a Biomechanical Spectrometer. The results were as follows: There was a negative correlation between age and values of dynamic stiffness as well as between age and the values of elastic modulus. The values of dynamic stiffness, tan delta, cartilagenous thickness, elastic modulus and creep modulus correlated significantly with the number of days after injury. The values for the anterior parts, excluding dynamic stiffness, were markedly higher than those for the other parts. Aging of the articular cartilage may be a factor in the lowering of dynamic stiffness and elastic modulus. Degenerative change is evidenced by a decrease in cartilaginous thickness and a softening of the articular cartilage. The anterior part of the articular surface showed good load-relaxation and viscoelastic properties. The anterior parts may act as the center of the rotational axis of the clavicle and the fulcrum of the horizontal adduction of the scapula when the arm is raised.

Design of a UHF applicator for rewarming of cryopreserved biomaterials.

The dielectric properties of cryopreserved biological tissue are discussed in relation to the problems which arise when EM fields are used for rapid rewarming. The UHF band is favored from two aspects: the avoidance of thermal runaway and the uniformity of heating inhomogeneous material. Various resonant cavity applicators are considered for efficient and uniform rewarming. The square-aspect TE 111 cylindrical applicator is favored principally because it allows variation of the E-field orientation as required during the warming profile. An appropriate kidney phantom organ is described. It is used to obtain measured values of the overall efficiency of a TE 111 applicator. The efficiency values are found to fall steadily with increasing temperature from 85% at -40 degrees C to 45% at the phase change, mainly due to the decreasing tan delta value of the phantom material.

Application of GPT to tan delta measuring apparatus for distribution cable in hot line

A hot line tan delta measuring apparatus which uses the secondary voltage of GPTs (grounding potential transformers) existing at substations and other facilities has been developed. An error vector circle diagram method which allows one to determine the value of tan delta to an accuracy of 0.1%, notwithstanding the phase difference existing between the primary and secondary voltages of a GPT, is described. The method was used in field experiments with favorable results. The method is especially superior in terms of safety and operability because no contact with high-voltage portions is required.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

上顎顎粘膜の動的粘弾性測定に関する研究

The purpose of this study is to investigate the viscoelastic properties of the oral mucosa. The handy apparatus which can easily show the rheological properties (i.e., G', G", tan delta) was made for the trial. The principle of this apparatus is to measure the stress and the phase difference produced when the constant sinusoidally oscillating shear deformation is loaded on the viscoelastic materials. This handy trial apparatus was found to be applicable in vivo, as evaluated by the dynamic spectrometers. The viscoelastic properties of the mucosa of the maxilla were investigated with this apparatus. The results were as follows: 1) Viscoelastic values varied in individual cases. 2) In the maxillary ridge area and the median portion, the values of modulus G and tan delta were low. In other words, the stiffness of these areas was low and the recovery from deformation was fast. 3) The values of modulus G and tan delta were high in the side region of the palate. The result showed that in this area there was a high stiffness and the recovery from deformation was slow. 4) In the incisive papilla and the area of flabby gum, the values of modulus G were low and the values of tan delta were high. The low stiffness and the slow recovery from deformation were shown in these areas.

Tracheal Mucus Rheology in Patients Undergoing Diagnostic Bronchoscopy: Interrelations with Smoking and Cancer

We examined the differences in tracheal mucus rheology between nonsmokers and smokers, and between smokers with and without lung cancer. Mucus was collected from patients undergoing diagnostic bronchoscopy without atropine by holding a cytology brush in contact with the tracheal mucosa for 10 to 15 s. Samples were obtained from 43 patients 24 to 79 yr of age: nine nonsmokers, 18 current smokers, and 16 exsmokers (greater than 6 months); 12 patients (nine smokers, three exsmokers) had lung cancer. Pulmonary function testing showed that the nonsmoker patients had significant restrictive lung disease, and the patients with cancer had significant irreversible airway obstruction. The viscoelastic properties of the mucus samples were determined by magnetic microrheometry. Two parameters are reported: G* (modulus of rigidity) and tan delta (loss tangent), each measured at 1 and 100 rad/s. G* is an index of overall deformability (elastic and viscous), and tan delta is the ratio of viscous to elastic deformability. For nonsmoker patients, the viscoelastic parameters were virtually identical to those found previously for normal volunteers. For smokers without cancer, the mucus had a lower value of tan delta 1 rad/s and therefore was predicted to be more easily transportable by ciliary action; for exsmokers without cancer, ciliary transportability as calculated from viscoelasticity was even higher because of both low tan delta and low G*. Mucus from patients with cancer was not significantly different from that of nonsmokers; however, the mucus was predicted to be less easily clearable by ciliary action than was that from smokers and exsmokers without cancer, mainly because of a higher tan delta at 1 rad/s.(ABSTRACT TRUNCATED AT 250 WORDS)

Surface component of vacuum absorption and resorption currents in polymers. III. A source of dielectric loss

For pt.II see ibid., vol.13, p.639 (1980). It is shown that, for a commercial co-polymer of hexafluoropropylene and tetrafluoroethylene, lateral charge transfer between the aluminium electrode edge and the immediately adjacent polymer surface dominates the dielectric loss currents in the frequency range 32 Hz-3.2 kHz. As a result the measured tan delta values vary with the electrode diameter. The variation decreases if the sample is allowed to age in air before dielectric loss measurements are made. This could be due to the formation of a thin oxide film on the aluminium electrode, and a decreasing probability of electron/hole tunnelling through the film as its thickness increases.

Dielectric loss in sodium nitrate crystals

The dielectric loss in NaNO3 crystals was studied as a function of frequency (0.1-100 KHz) at different temperatures (106-257 degrees C). The dipolar loss was analysed. The data for the temperatures below 140 degrees C were analysed using one Debye-type loss term. At higher temperatures, two Debye terms were found to be necessary. The first Debye peak has a value of tan delta of about 0.1 and its height is practically independent of temperature. It is ascribed to Maxwell-Wagner-type interfacial polarisation. The second peak (low frequency) which appears at temperatures higher than 140 degrees C increased in height with temperature. This is interpreted as due to intrinsic dipoles formed by cation vacancies and cation interstitials.

Detection of Hindered Rotations of 1,6-Diphenyl-1,3,5-Hexatriene in Lipid Bilayers by Differential Polarized Phase Fluorometry

Differential polarized phase fluorometry has been used to investigate the depolarizing motions of 1,6-diphenyl-1,3,5-hexatriene (DPH) in the isotropic solvent propylene glycol and in lipid bilayers of dimyristoyl-L-alpha-phosphatidylcholine (DMPC), dipalmitoyl-L-alpha-phosphatidylcholine (DPPC), and other phosphatidylcholines. Differential phase fluorometry is the measurement of differences in the phase angles between the parallel and perpendicular components of the fluorescence emission of a sample excited with sinusoidally modulated light. The maximum value of the tangent of the phase angle (tan Delta(max)) is known to be a function of the isotropy of the depolarizing motions. For DPH in propylene glycol the maximum tangent is observed at 18 degrees C, and this tangent value corresponds precisely with the value expected for an isotropic rotator. Additionally, the rotational rates determined by steady-state polarization measurements are in precise agreement with the differential phase measurements. These results indicate that differential phase fluorometry provides a reliable measure of the probe's rotational rate under conditions where these rotations are isotropic and unhindered.Rotational rates of DPH obtained from steady-state polarization and differential phase measurements do not agree when this probe is placed in lipid bilayers. The temperature profile of the tan Delta measurements of DPH in DMPC and DPPC bilayers is characterized by a rapid increase of tan Delta at the transition temperature (T(c)), followed by a gradual decline in tan Delta at temperatures above T(c). The observed tanDelta(max) values are only 62 and 43% of the theoretical maximum. This defect in tanDelta(max) is too large to be explained by any degree of rotational anisotropy. However, these defects are explicable by a new theory that describes the tan Delta values under conditions where the probe's rotational motions are restricted to a limiting anisotropy value, r(infinity). Theoretical calculations using this new theory indicate that the temperature dependence of the depolarizing motions of DPH in these saturated bilayers could be explained by a rapid increase in its rotational rate (R) at the transition temperature, coupled with a simultaneous decrease in r(infinity) at this same temperature. The sensitivity of the tan Delta values to both R and r(infinity) indicates that differential phase fluorometry will provide a method to describe more completely the depolarizing motion of probes in lipid bilayers.

Attenuation Characteristics of Circular Dielectric Waveguide at Millimeter Wavelengths

Experiments were done to determine the practicality of using circular dielectric waveguide for a low-loss transmission line at millimeter wavelengths. The lowest order mode on a circular dielectric guide will propagate regardless of how small the guide diameter is. Thus it is possible to make the attenuation factor of a circular dielectric guide arbitrarily small by reducing its diameter. Loss measurements for several different diameters of polystyrene and Teflon rods were made at 72.70 GHz. The measurements were made by directly probing long sections of dielectric guide and plotting the average power as a function of length on an X-Y plotter. Dielectric constants were measured from the standing wave patterns of polystyrene Teflon, and fused quartz rods at 71.0 GHz. Teflon rods exhibited attenuation factors from 0.8 dB/m to 2.2 dB/m depending on the diameter. This is an improvement over silver waveguide at this frequency. Polystyrene rods were found to have attenuation factors ranging from 3.9 dB/m to 12.5 dB/m, again depending on the diameter of the rod. The measured dielectric constants are consistent with previously published data. The various attenuation factors are related to the intrinsic loss tangent of the dielectric using the theory of the HE/sub 11/ mode. Values of tan delta derived from measurements of different rods are consistent indicating that the experimental results are valid. The problem of radiation from dielectric rods is discussed. The experimental results are not conclusive but it appears likely that radiation loss is negligible.

Dielectric properties and optical absorption of KTaO3single crystals and KTaO3.NaTaO mixed crystals

The dielectric constant K, loss tan delta and conductivity sigma of single crystals of pure KTaO3 and KTaO3. NaTaO3 mixed crystals (with 2, 12 and 35% Na) were determined as a function of frequency from 102 to 107 Hz and in the temperature range 30-350 degrees C. The dielectric constant at 30 degrees C decreases with frequency in all these samples. The tan delta values are below detection level at room temperature. The larger values of K at lower frequencies are attributed to crystal defects. The dielectric constant of all these samples decreases considerably with temperature at all frequencies but at 102 Hz, and from around 190 degrees C, it starts increasing with temperature This inversion temperature is found to increase with frequency but decrease with Na content. Dielectric loss is found to increase with temperature but decrease with frequency. Lg sigma plotted against 1/T for these samples shows that the intrinsic conductivity region is not reached even at 350 degrees C.