Bioactive ceramic-reinforced composites for bone augmentation

Biomaterials have been used to repair the human body for millennia, but it is only since the 1970s that man-made composites have been used. Hydroxyapatite (HA)-reinforced polyethylene (PE) is the first of the ‘second-generation’ biomaterials that have been developed to be bioactive rather than bioinert. The mechanical properties have been characterized using quasi-static, fatigue, creep and fracture toughness testing, and these studies have allowed optimization of the production method. The in vitro and in vivo biological properties have been investigated with a range of filler content and have shown that the presence of sufficient bioactive filler leads to a bioactive composite. Finally, the material has been applied clinically, initially in the orbital floor and later in the middle ear. From this initial combination of HA in PE other bioactive ceramic polymer composites have been developed

Bosonic spectral density of epitaxial thin-film La1.83Sr0.17CuO4 superconductors from infrared conductivity measurements

We use optical spectroscopy to investigate the excitations responsible for the structure in the optical self-energy of thin epitaxial films of La1.83Sr0.17CuO4. Using Eliashberg formalism to invert the optical spectra we extract the electron-boson spectral function and find that at low temperature it has a two component structure closely matching the spin excitation spectrum recently measured by magnetic neutron scattering. We contrast the temperature evolution of the spectral density and the two-peak behavior in La2-xSrxCuO4 with another high temperature superconductor Bi2Sr2CaCu2O8+d. The bosonic spectral functions of the two materials account for the low Tc of LSCO as compared to Bi-2212

Early plaque formation on fibre-reinforced composites in vivo.

AbstractIn the present study, two different fibre-reinforced composites (FRCs) (glass and polyethylene FRC), dental ceramic and restorative composite were compared with respect to early plaque formation in vivo. Disc-shaped specimens were randomly distributed among the upper first and second molars of 14 healthy adult volunteers. Plaque samples were collected 24 h after the attachment of the specimens. Mutans streptococci (MS), non-mutans streptococci and total facultative bacteria were cultured. The plaque recovered from polyethylene FRC harboured significantly more MS than the plaque of ceramic, restorative composite and glass FRC. For the counts of non-mutans streptococci and total facultative bacteria, polyethylene FRC showed the highest counts, and ceramic showed a trend towards lower counts. The amount of plaque accumulation showed an association to the earlier reported surface roughness values of the studied materials. It was concluded that in the oral environment, polyethylene FRC promotes plaque accumulation and adhesion of MS more than glass FRC, restorative composite and dental ceramic. Glass FRC resembles restorative composite with respect to plaque accumulation and the adherence of MS.</div

Spectral statistics for unitary transfer matrices of binary graphs

Quantum graphs have recently been introduced as model systems to study the spectral statistics of linear wave problems with chaotic classical limits. It is proposed here to generalise this approach by considering arbitrary, directed graphs with unitary transfer matrices. An exponentially increasing contribution to the form factor is identified when performing a diagonal summation over periodic orbit degeneracy classes. A special class of graphs, so-called binary graphs, is studied in more detail. For these, the conditions for periodic orbit pairs to be correlated (including correlations due to the unitarity of the transfer matrix) can be given explicitly. Using combinatorial techniques it is possible to perform the summation over correlated periodic orbit pair contributions to the form factor for some low--dimensional cases. Gradual convergence towards random matrix results is observed when increasing the number of vertices of the binary graphs.Comment: 18 pages, 8 figure

The unusual thickness dependence of superconductivity in α\alpha-MoGe thin films

Thin films of $\alpha$-MoGe show progressively reduced $T_{c}$'s as the thickness is decreased below 30 nm and the sheet resistance exceeds 100 $\Omega/\Box$. We have performed far-infrared transmission and reflection measurements for a set of $\alpha$-MoGe films to characterize this weakened superconducting state. Our results show the presence of an energy gap with ratio $2\Delta_0/k_BT_{c} = 3.8 \pm 0.1$ in all films studied, slightly higher than the BCS value, even though the transition temperatures decrease significantly as film thickness is reduced. The material properties follow BCS-Eliashberg theory with a large residual scattering rate except that the coherence peak seen in the optical scattering rate is found to be strongly smeared out in the thinner superconducting samples. A peak in the optical mass renormalization at $2\Delta_0$ is predicted and observed for the first time

Slowly cycling Rho kinase-dependent actomyosin cross-bridge slippage explains intrinsic high compliance of detrusor smooth muscle

Biological soft tissues are viscoelastic because they display timeindependent pseudoelasticity and time-dependent viscosity. However, there is evidence that the bladder may also display plasticity, defined as an increase in strain that is unrecoverable unless work is done by the muscle. In the present study, an electronic lever was used to induce controlled changes in stress and strain to determine whether rabbit detrusor smooth muscle (rDSM) is best described as viscoelastic or viscoelastic plastic. Using sequential ramp loading and unloading cycles, stress-strain and stiffness-stress analyses revealed that rDSM displayed reversible viscoelasticity, and that the viscous component was responsible for establishing a high stiffness at low stresses that increased only modestly with increasing stress compared with the large increase produced when the viscosity was absent and only pseudoelasticity governed tissue behavior. The study also revealed that rDSM underwent softening correlating with plastic deformation and creep that was reversed slowly when tissues were incubated in a Ca2+ -containing solution. Together, the data support a model of DSM as a viscoelastic-plastic material, with the plasticity resulting from motor protein activation. This model explains the mechanism of intrinsic bladder compliance as slipping cross bridges, predicts that wall tension is dependent not only on vesicle pressure and radius but also on actomyosin cross-bridge activity, and identifies a novel molecular target for compliance regulation, both physiologically and therapeutically

Optical Response for the d-density wave model

We have calculated the optical conductivity and the Raman response for the d-density wave model, proposed as a possible explanation for the pseudogap seen in high Tc cuprates. The total optical spectral weight remains approximately constant on opening of the pseudogap for fixed temperature. This occurs because there is a transfer of weight from the Drude peak to interband transitions across the pseudogap. The interband peak in the optical conductivity is prominent but becomes progressively reduced with increasing temperature, with impurity scattering, which distributes it over a larger energy range, and with ineleastic scattering which can also shift its position, making it difficult to have a direct determination of the value of the pseudogap. Corresponding structure is seen in the optical scattering rate, but not necessarily at the same energies as in the conductivity.Comment: 14 pages, 15 figures, final revised version published in PR

Simulation of truncated normal variables

We provide in this paper simulation algorithms for one-sided and two-sided truncated normal distributions. These algorithms are then used to simulate multivariate normal variables with restricted parameter space for any covariance structure.Comment: This 1992 paper appeared in 1995 in Statistics and Computing and the gist of it is contained in Monte Carlo Statistical Methods (2004), but I receive weekly requests for reprints so here it is

Detailed design of a resonantly-enhanced axion-photon regeneration experiment

A resonantly-enhanced photon-regeneration experiment to search for the axion or axion-like particles is described. This experiment is a shining light through walls study, where photons travelling through a strong magnetic field are (in part) converted to axions; the axions can pass through an opaque wall and convert (in part) back to photons in a second region of strong magnetic field. The photon regeneration is enhanced by employing matched Fabry-Perot optical cavities, with one cavity within the axion generation magnet and the second within the photon regeneration magnet. Compared to simple single-pass photon regeneration, this technique would result in a gain of (F/pi)^2, where F is the finesse of each cavity. This gain could feasibly be as high as 10^(10), corresponding to an improvement in the sensitivity to the axion-photon coupling, g_(agg), of order (F/pi)^(1/2) ~ 300. This improvement would enable, for the first time, a purely laboratory experiment to probe axion-photon couplings at a level competitive with, or superior to, limits from stellar evolution or solar axion searches. This report gives a detailed discussion of the scheme for actively controlling the two Fabry-Perot cavities and the laser frequencies, and describes the heterodyne signal detection system, with limits ultimately imposed by shot noise.Comment: 10 pages, 5 figure