Effects of crystalline anisotropy on resonant acoustic loss of torsional quartz viscometers.

Vibrational modes of unrestrained elastic cylinders of trigonal crystals are studied using Ritz-based polynomial approximations for displacements formulated in rectangular Cartesian coordinates. The selected orientation of the threefold trigonal axis is perpendicular to the cylinder axis, corresponding to the configuration employed in torsional quartz viscometry (TQV) for characterizing Newtonian fluids. A revised working equation for TQV is derived, incorporating effects of crystalline anisotropy, and Ritz results are used to numerically quantify effects of acoustic radiation from surface-normal displacements and viscous loss from nontorsional surface-parallel displacements of resonant modes corresponding to the purely torsional modes of isotropic cylinders traditionally employed as an approximation in TQV analysis. For a cylinder typical of TQV, with 3 mm diameter and 50 mm length, the anisotropy-related correction to the extracted fluid viscosity is a positive shift of 36 ppm relative to the isotropic approximation, if radiative losses are neglected. This contribution is independent of fluid properties. Radiative losses depend on the properties of the fluid and reduce the extracted viscosity. The total magnitude of corrections varies between several tens of parts per million for low density gases to values on the order of 0.01% for normal liquids near atmospheric pressure and 0.06% for superfluid helium.

Transport and Electromechanical Properties of Ca3TaGa3Si2O14 Piezoelectric Crystals at Extreme Temperatures.

Transport mechanisms in structurally ordered piezoelectric Ca3TaGa3Si2O14 (CTGS) single crystals are studied in the temperature range of 1000-1300 °C by application of the isotope 18O as a tracer and subsequent analysis of diffusion profiles of this isotope using secondary ion mass spectrometry (SIMS). Determined oxygen self-diffusion coefficients enable calculation of oxygen ion contribution to the total conductivity, which is shown to be small. Since very low contributions of the cations have to be expected, the total conductivity must be dominated by electron transport. Ion and electron conductivities are governed by different mechanisms with activation energies (1.9±0.1) eV and (1.2±0.07) eV, respectively. Further, the electromechanical losses are studied as a function of temperature by means of impedance spectroscopy on samples with electrodes and a contactless tone-burst excitation technique. At temperatures above 650 °C the conductivity-related losses are dominant. Finally, the operation of CTGS resonators is demonstrated at cryogenic temperatures and materials piezoelectric strain constants are determined from 4.2 K to room temperature.

Sensing bacterial vibrations and early response to antibiotics with phase noise of a resonant crystal.

The speed of conventional antimicrobial susceptibility testing (AST) is intrinsically limited by observation of cell colony growth, which can extend over days and allow bacterial infections to advance before effective antibiotics are identified. This report presents an approach for rapidly sensing mechanical fluctuations of bacteria and the effects of antibiotics on these fluctuations. Bacteria are adhered to a quartz crystal resonator in an electronic bridge that is driven by a high-stability frequency source. Mechanical fluctuations of cells introduce time-dependent perturbations to the crystal boundary conditions and associated resonant frequency, which translate into phase noise measured at the output of the bridge. In experiments on nonmotile E. coli exposed to polymyxin B, cell-generated frequency noise dropped close to zero with the first spectra acquired 7 minutes after introduction of the antibiotic. In experiments on the same bacterial strain exposed to ampicillin, frequency noise began decreasing within 15 minutes of antibiotic introduction and proceeded to drop more rapidly with the onset of antibiotic-induced lysis. In conjunction with cell imaging and post-experiment counting of colony-forming units, these results provide evidence that cell death can be sensed through measurements of cell-generated frequency noise, potentially providing a basis for rapid AST.

High-temperature electroacoustic characterization of Y-cut and singly-rotated Ca3TaGa3Si2O14 resonators.

Synthetic piezoelectric crystals in the P321 crystal class have been a focus of substantial research that is largely driven by applications in high-temperature resonant BAW and SAW sensing. Fully ordered crystals in this class, such as Ca3TaGa3Si2O14 (CTGS), have been suggested as offering the potential of electroacoustic performance that is superior to more extensively studied langasite (LGS) and langatate (LGT), which are partially disordered. In this study, the resonant frequencies, acoustic damping, and electrical conductivity of CTGS bulk acoustic resonators with Y-cut and (YXl)-30° crystal orientations and fundamental frequencies near 5 MHz are investigated at temperatures between ambient and 1100°C. (YXl)-30° resonators are found to have turnover temperatures near 200°C for the third and fifth overtones, in contrast to a monotonic decrease in resonant frequencies of Y-cut crystals with increasing temperature. The maximum temperature derivative of fractional changes in fifth-overtone frequency of (YXl)-30° CTGS is 40 × 10-6K-1 (near 1100°C), and this value is not greatly different from the temperature derivative of Y-cut CTGS frequencies over a broader range of temperatures. At ambient temperatures, the acoustic loss Q-1 of CTGS with both crystal orientations is found to be greater than the lowest values previously reported for LGS and LGT. The electrical conductivity of the CTGS specimens between 500°C and 1100°C is substantially lower than that previously reported for LGS. Corresponding to this lower conductivity, the piezoelectric/conductive contribution to Q-1 at elevated temperatures is reduced. Additional anelastic relaxation peaks observed between 100°C and 700°C are similar to those previously reported for LGS and LGT.

Continuum-based free vibration of circular trigonal and isotropic plates.

The free vibration behavior of completely unrestrained elastic circular plates with trigonal and isotropic material symmetry is studied with an approach involving approximate continuum solutions to the three-dimensional theory of linear elasticity. Of primary interest are (1) the influence of trigonal material symmetry on the modes of free vibration and (2) the accuracy of thin plate theory relative to the more exact three-dimensional theory. Resonant frequencies are calculated from the weak form of the equations of motion for the plate through the use of approximation functions and the Ritz method formulated in cylindrical coordinates. This approach enables the resulting eigenvalue problem to be split through group-theoretical symmetry analysis. Representative examples are given and quantitative limits are discussed.

Vibrational modes of nanolines.

Brillouin-light-scattering spectra previously have been shown to provide information on acoustic modes of polymeric lines fabricated by nanoimprint lithography. Finite-element methods for modeling such modes are presented here. These methods provide a theoretical framework for determining elastic constants and dimensions of nanolines from measured spectra in the low gigahertz range. To make the calculations feasible for future incorporation in inversion algorithms, two approximations of the boundary conditions are employed in the calculations: the rigidity of the nanoline/substrate interface and sinusoidal variation of displacements along the nanoline length. The accuracy of these approximations is evaluated as a function of wavenumber and frequency. The great advantage of finite-element methods over other methods previously employed for nanolines is the ability to model any cross-sectional geometry. Dispersion curves and displacement patterns are calculated for modes of polymethyl methacrylate nanolines with cross-sectional dimensions of 65 nm × 140 nm and rectangular or semicircular tops. The vibrational displacements and dispersion curves are qualitatively similar for the two geometries and include a series of flexural, Rayleigh-like, and Sezawa-like modes.

Osmotic tolerance and membrane permeability characteristics of rhesus monkey (Macaca mulatta) spermatozoa.

Biophysical characteristics of the plasma membrane, such as osmotic sensitivity and water and cryoprotectant permeability are important determinants of the function of spermatozoa after cryopreservation. A series of experiments was conducted with rhesus macaque spermatozoa at 23 degrees C to determine their: (1) cell volume and osmotically inactive fraction of the cell volume; (2) permeability coefficients for water and the cryoprotectants dimethyl sulfoxide, glycerol, propylene glycol, and ethylene glycol; (3) tolerance to anisosmotic conditions; and (4) motility after a one step addition and removal of the four cryoprotectants. An electronic particle counter and computer aided semen analysis were used to determine the cell volume and permeability coefficients, and motility, respectively. Rhesus spermatozoa isosmotic cell volume was 27.7+/-3.0 microm3 (mean+/-SEM) with an osmotically inactive cell fraction of 51%. Hydraulic conductivity in the presence of dimethyl sulfoxide, glycerol, propylene glycol, and ethylene glycol was 1.09+/-0.30, 0.912+/-0.27, 1.53+/-0.53, and 1.94+/-0.47 microm/min/atm, respectively. Cryoprotectant permeability was 1.39+/-0.31, 2.21+/-0.32, 3.38+/-0.63, and 6.07+/-1.1 (x10(-3)cm/min), respectively. Rhesus sperm tolerated all hyposmotic exposures. However, greater than 70% motility loss was observed after exposure to solutions of 600 mOsm and higher. A one step addition and removal of all four cryoprotectants did not cause significant motility loss. These data suggest that rhesus sperm are tolerant to hyposmotic conditions, and ethylene glycol may be the most appropriate cryoprotectant for rhesus sperm cryopreservation, as it has the highest permeability coefficient of the tested cryoprotectants.

Chimpanzee (Pan troglodytes) spermatozoa osmotic tolerance and cryoprotectant permeability characteristics.

Osmotic properties of chimpanzee spermatozoa were studied at 22 degrees C. An electronic particle counter was used to determine the isosmotic cell volume, and the volume response after exposure to four commonly used cryoprotectants: dimethyl sulfoxide, glycerol, propylene glycol, and ethylene glycol. The data were analyzed to determine the hydraulic conductivity and the permeability coefficients for the four cryoprotectants. The osmotically inactive volume fraction was determined using a Boyle van't Hoff plot of cells exposed to sodium chloride solutions. A computer-assisted semen analysis system was used to determine the osmotic tolerance of chimp spermatozoa, as well as the effects of a one-step addition and removal of 1 M permeating cryoprotectant on sperm motility. The isosmotic volume of chimpanzee sperm is 27.7 microm3. The osmotically inactive cell fraction is 69%. Hydraulic conductivity was higher in the presence of ethylene glycol: 4.09 +/- 0.76 (mean +/- SEM) and propylene glycol: 3.91 +/- 0.71 as compared to dimethyl sulfoxide: 3.49 +/- 0.79 and glycerol: 2.83 +/- 0.40 microm/min per atmosphere. The permeability of chimpanzee sperm in ethylene glycol (2.18 +/- 0.40 x 10(-3) cm/min) and propylene glycol (1.75 +/- 0.17 x 10(-3) cm/min) was higher than in glycerol (1.42 +/- 0.12 x 10(-3) cm/min) and dimethyl sulfoxide (0.82 +/- 0.015 x 10(-3) cm/min). Although chimpanzee sperm tolerated osmotic stress in the range of 169-400 mOsm very well, loss of motility was observed as the solution concentrations diverged from isosmotic condition. Exposure to the four cryoprotectants at 1 M did not cause a significant reduction in sperm motility. This information on membrane permeability characteristics and cryoprotectant tolerance will aid in designing more reliable cryopreservation protocols for chimpanzee sperm.

Traction-free vibrations of finite trigonal elastic cylinders.

The unrestrained, traction-free vibrations of finite elastic cylinders with trigonal material symmetry are studied using two approaches, based on the Ritz method, which formulate the weak form of the equations of motion in cylindrical and rectangular coordinates. Elements of group theory are used to divide approximation functions into orthogonal subsets, thus reducing the size of the computational problem and classifying the general symmetries of the vibrational modes. Results for the special case of an isotropic cylinder are presented and compared with values published by other researchers. For the isotropic case, the relative accuracy of the formulations in cylindrical and rectangular coordinates can be evaluated, because exact analytical solutions are known for the torsional modes. The calculation in cylindrical coordinates is found to be more accurate for a given number of terms in the series approximation functions. For a representative trigonal material, langatate, calculations of the resonant frequencies and the sensitivity of the frequencies on each of the elastic constants are presented. The dependence on geometry (ratio of length to diameter) is briefly explored. The special case of a transversely isotropic cylinder (with the elastic stiffness C14 equal to zero) is also considered.

Symmetrization of Ritz approximation functions for vibrational analysis of trigonal cylinders.

In the Ritz method of calculating vibrational normal modes, a set of finite series approximation functions provides a matrix eigenvalue equation for the coefficients in the series and the resonant frequency. The matrix problem usually can be block-diagonalized by grouping the functions into subsets according to their properties under the symmetry operations that are common to the specimen geometry and crystal class. This task is addressed, in this study, for the case of cylindrical specimens of crystals belonging to one of the higher trigonal crystal classes. The existence of doubly degenerate resonant modes significantly complicates the analysis. Group-theoretical projection operators are employed to extract, from series approximation functions in cylindrical coordinates, the terms that transform according to each irreducible representation of the point group. This provides a complete symmetry-based block diagonalization and categorization of the modal symmetries. Off-diagonal projection operators are used to provide relations between the displacement patterns of degenerate modes. The method of analysis is presented in detail to assist in its application to other geometries, crystal structures, and/or forms of Ritz approximation functions.

Blastocyst transfer: a useful tool for reduction of high-order multiple gestations in a human assisted reproduction program.

OBJECTIVE: We evaluated the efficacy of blastocyst transfer in decreasing the incidence of high-order multiple gestations after in vitro fertilization. STUDY DESIGN: We conducted a retrospective analysis of 218 patients who were undergoing in vitro fertilization and by our criteria of three 8-cell embryos on day 3 could receive either a day 3 transfer of cleaved embryos or a day 5 transfer of blastocysts. Ongoing pregnancy rates, implantation rates (determined by the total number of visualized gestational sacs), and multiple pregnancy rates were compared between the 2 groups. RESULTS: Respective day 3 and day 5 ongoing pregnancy rates (61% and 51%) and implantation rates (35% and 33%) were not significantly different. There were 9 triplet or higher gestations in the day 3 group and 0 in the day 5 group. CONCLUSION: Blastocyst transfer can be used to reduce the number of embryos transferred and the resultant incidence of high-order multiple pregnancies while maintaining high pregnancy rates.

Use of intrauterine devices (IUDs) for contraception in the common chimpanzee (Pan troglodytes).

The common chimpanzee (Pan troglodytes) is a species phylogenetically very close to man. It was not many years ago that the captive population of chimpanzees (P. troglodytes) was considered at risk because of perceived problems with reproductive success. With the potential need for many individuals for research in a variety of areas, particularly in the areas of parasitic and viral infections, an NIH-funded program was established to promote the breeding of the species. That program, the 'National Chimpanzee Breeding and Research Program', was highly successful, so successful, in fact, that there is now a surplus of animals available for current research programs. This situation has prompted the use of intrauterine devices (IUDs) as a method of fertility control. Overall, this method is successful and associated with a failure (of pregnancy) rate similar to that reported in the human. Physical and logistic constraints, however, render the method less than ideal for situations where a pregnancy rate of zero is desired.