Predicting the whispering gallery mode spectra of microresonators

The whispering gallery modes (WGMs) of optical resonators have prompted intensive research efforts due to their usefulness in the field of biological sensing, and their employment in nonlinear optics. While much information is available in the literature on numerical modeling of WGMs in microspheres, it remains a challenging task to be able to predict the emitted spectra of spherical microresonators. Here, we establish a customizable Finite- Difference Time-Domain (FDTD)-based approach to investigate the WGM spectrum of microspheres. The simulations are carried out in the vicinity of a dipole source rather than a typical plane-wave beam excitation, thus providing an effective analogue of the fluorescent dye or nanoparticle coatings used in experiment. The analysis of a single dipole source at different positions on the surface or inside a microsphere, serves to assess the relative efficiency of nearby radiating TE and TM modes, characterizing the profile of the spectrum. By varying the number, positions and alignments of the dipole sources, different excitation scenarios can be compared to analytic models, and to experimental results. The energy flux is collected via a nearby disk-shaped region. The resultant spectral profile shows a dependence on the configuration of the dipole sources. The power outcoupling can then be optimized for specific modes and wavelength regions. The development of such a computational tool can aid the preparation of optical sensors prior to fabrication, by preselecting desired the optical properties of the resonator.Comment: Approved version for SPIE Photonics West, LASE, Laser Resonators, Microresonators and Beam Control XV

Method for predicting whispering gallery mode spectra of spherical microresonators

A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source. This provides a guide for experiments that rely on efficient coupling to the modes of microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from a variety of possible collection regions, such as a disk-shaped region. The customizability of the technique allows one to consider a variety of mode excitation scenarios, which are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.Comment: Published 10 Apr 2015 in Opt. Express Vol. 23, Issue 8, pp. 9924-9937; The FDTD toolkit supercomputer scripts are hosted at: http://sourceforge.net/projects/npps/files/FDTD_WGM_Simulator

Comparison of Isolated Anterior Cruciate Ligament Tearing with Anterior Cruciate Ligament Tearing Associated with Displaced Lateral Femoral Condyle Fracture in Knee Arthrosis Formation

Abstract: Introduction: The etiology of posttraumatic arthritis has not been studied well. Although it has long been assumed that articular incongruity leads to post traumatic arthritis, clinical and basic sciences evidence to support such claim are not sufficient. On the other hand, the relationship of instability due to anterior cruciate ligament deficiency and Arthrosis has not been clearly defined and the relative importance of instability and incongruity is unknown. Method: ACL tearing were created in right knees of 9 rabbits (group A) and ACL tearing and displaced lateral condylar fracture with 1 mm step were created in another 9 rabbits (group B). After 6 months, osteoarthritis changes were compared between control knee and injured knee of each rabbit and between the two groups. Results: In both groups, osteoarthritis changes in injured knees were more comparing to the control knee and in whole osteoarthritis changes were significantly more in group B compared to group A. Conclusion: The unstable knee due to ACL deficiency goes toward osteoarthritis faster than normal knee. Incongruity in unstable joint increases intensity of osteoarthritis changes. It shows the importance of achieving anatomic reduction in intra articular fractures before ligament reconstruction. Keywords: Incongruity, Instability, Arthritis, Anterior cruciate ligamen

The Effect of Platelet Rich Plasma Dressing on Healing Diabetic Foot Ulcers

Background: Some of the studies confirmed the effectiveness of platelet rich plasma (PRP) in the treatment of diabetic foot ulcers (DFU). However, these studies had small sample size and used different methods such as PRP gel or PRP injections. The results are also contraversial. Objectives: This study aimed to investigate the effect of PRP dressing on healing of DFUs. Patients and Methods: A randomized, controlled trial was conducted on 50 patients with DFUs referred to Kashan’s Shahid Beheshti hospital. Patients were randomly allocated to control (n = 25) and experimental (n = 25) groups. Data collection instrument consisted of two checklists; one for gathering demographic information and the other one included questions about ulcer characteristics and its treatment. After surgical debridement, ulcers depth and surface area were measured. Then, the ulcers of the control group were irrigated and dressed with sterile gauzes. However, in the intervention group, ulcers were dressed with sterile gauzes impregnated with PRP. Ulcers depth and surface area of all ulcers were measured on the days 0, 7, 14 and 21 after debridement. Independent-samples t-test, Mann–Whitney U and repeated measures analysis of variance were used to analyze data. Results: At baseline, the mean ulcer depth were 15.08 ± 10.43 and 19.08 ± 14.01 mm in the control and intervention groups, respectively (P = 0.26), which decreased to 13.03 ± 14.1 and 4.560 ± 5.76 after three weeks (P = 0.04). Moreover, the mean ulcer surface area were 14.17 ± 8.52 and 12.791 ± 14.86 mm2 in control and intervention groups respectively (P = 0.69), which decreased to 11.88 ± 13.65 and 2.68 ± 5.94 after three weeks (P = 0.03). Conclusions: PRP dressing could significantly decrease the depth and surface area of DFUs in a three-week period

On massive gravitons in 2+1 dimensions

The Fierz-Pauli (FP) free field theory for massive spin 2 particles can be extended, in a spacetime of (1+2) dimensions (3D), to a generally covariant parity-preserving interacting field theory, in at least two ways. One is "new massive gravity" (NMG), with an action that involves curvature-squared terms. Another is 3D "bigravity", which involves non-linear couplings of the FP tensor field to 3D Einstein-Hilbert gravity. We review the proof of the linearized equivalence of both "massive 3D gravity" theories to FP theory, and we comment on their similarities and differences.Comment: 6 pages, to appear in the proceedings of the Spanish Relativity Meeting ERE2009, Bilbao; minor changes, reference adde

Creep in oak material from the Vasa ship: verification of linear viscoelasticity and identification of stress thresholds

Creep deformation is a general problem for large wooden structures, and in particular for shipwrecks in museums. In this study, experimental creep data on the wooden cubic samples from the Vasa ship have been analysed to confirm the linearity of the viscoelastic response in the directions where creep was detectable (T and R directions). Isochronous stress-strain curves were derived for relevant uniaxial compressive stresses within reasonable time spans. These curves and the associated creep compliance values justify that it is reasonable to assume a linear viscoelastic behaviour within the tested ranges, given the high degree of general variability. Furthermore, the creep curves were fitted with a one-dimensional standard linear solid model, and although the rheological parameters show a fair amount of scatter, they are candidates as input parameters in a numerical model to predict creep deformations. The isochronous stress-strain relationships were used to define a creep threshold stress below which only negligible creep is expected. These thresholds ranges were 0.3-0.5 MPa in the R direction and 0.05-0.2 MPa in the T direction