Influence of Ga incorporation on photoinduced phenomena in Ge-S based glasses

To study the influence of Ga addition on photoinduced effect, GaGeS glasses with constant atomic ratio S/Ge = 2.6 have been prepared. Using Raman spectroscopy, we have reported the effect of Ga on the structural behavior of these glasses. An increase of the glass transition temperature T(g), the linear refractive index and the density have been observed with increasing gallium content. The photoinduced phenomena have been examined through the influence of time exposure and power density, when exposed to above light bandgap (3.53 eV). The correlation between photoinduced phenomena and Ga content in such glasses are shown hereby. (C) 2009 Elsevier B.V. All rights reserved.

Relaxation-chaos phenomena in celestial mechanics. I. On wisdom's model for the 3/1 kirkwood gap

Sudden eccentricity increases of asteroidal motion in 3/1 resonance with Jupiter were discovered and explained by J. Wisdom through the occurrence of jumps in the action corresponding to the critical angle (resonant combination of the mean motions). We pursue some aspects of this mechanism, which could be termed relaxation-chaos: that is, an unconventional form of homoclinic behavior arising in perturbed integrable Hamiltonian systems for which the KAM theorem hypothesis do not hold. © 1987.

On the equivalence of the mechanisms governing switching and hysteresis phenomena

The nucleation and growth model, which is usually applied to switching phenomena, is adapted for explaining surface potential measurements on the P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) copolymer obtained in a constant current corona triode. It is shown that the growth is one-dimensional and that the nucleation rate is unimportant, probably because surface potential measurements take much longer than the switching ones. The surface potential data can therefore be accounted for by a growth model in which the velocity of growth varies exponentially with the electric field. Since hysteresis loops can be obtained from surface potential measurements, it is suggested that similar mechanisms can be used when treating switching and hysteresis phenomena, provided that account is taken of the difference in the time scale of the measurements.

The effects of wet suits on physiological and biomechanical indices during swimming

The objectives of this study were to verify the effects of wet suits (WS) on the performance during 1500m swimming (V1500), on the velocity corresponding to the anaerobic threshold (VAT) and on the drag force (AD) as well as its coefficient (Cx). 19 swimmers randomly completed the following protocols on different days (with and without WS): 1) maximal performance of 1500m swimming; 2) VAT in field test, with fixed concentration of blood lactate (4 mM) and 3) determination of hydrodynamic indices (AD and Cx). The results demonstrated significant differences (p < 0.05) in the VAT (1.27±0.09; 1.21±0.06 m.s-1), and in the V1500 (1.21±0.08; 1.17±0.08 m.s-1), with and without WS, respectively. However the AD, and its Cx did not present significant differences (p>0.05) for the respective maximal speeds of swimming. In summary, we can conclude that WS allows swimmers to reach greater speeds in both, long- and short-course swims. This improvement can be related to the decrease of the AD, since with higher speeds (with WS) the subjects presented the same resistance, as they did when compared to speeds without a WS. Moreover, these data suggest that the methodology used in this study to determine the Cx is unable to detect the improvement caused by WS.

Treatment of mucus retention phenomena in children by the micro-marsupialization technique: case reports

The purpose of the present study was to emphasize the technique of micro-marsupialization as an alternative for the treatment of mucus retention phenomena. Out of 41 patients, 14 were selected for treatment by the micro-marsupialization technique on the basis of clinical criteria. Patient age ranged from 5-9 years. The technique was performed as follows: the area was disinfected with 0.1% iodine; a topical anesthetic was applied to cover the entire lesion for approximately 3 min; a 4.0 silk suture was passed through the internal part of the lesion along its widest diameter; and a surgical knot was made. Of the original 14 patients treated by the micro-marsupialization technique, 12 presented full regression one week after treatment. Recurrence occurred in two cases. It was possible to conclude that the micro-marsupialization technique is an alternative to be considered, especially in pediatric dentistry.

Interference phenomena, chiral bosons, and Lorentz invariance

We have studied the theory of gauged chiral bosons and proposed a general theory, a master action, that encompasses different kinds of gauge field couplings in chiral bosonized theories with first-class chiral constraints. We have fused opposite chiral aspects of this master action using the soldering formalism and applied the final action to several well-known models. The Lorentz rotation permitted us to fix conditions on the parameters of this general theory in order to preserve the relativistic invariance. We also have established some conditions on the arbitrary parameter concerned in a chiral Schwinger model with a generalized constraint, investigating both covariance and Lorentz invariance. The results obtained supplement the one that shows the soldering formalism as a new method of mass generation. ©2001 The American Physical Society.

The influence of diabetes mellitus and insulin therapy on biomechanical retention around dental implants: a study in rabbits.

The oral rehabilitation by dental implants in patients with diabetes remains a controversial issue. The aim of this study was to evaluate the influence of diabetes mellitus and insulin therapy on the bone healing around dental implants using torque removal. Twenty-seven rabbits were randomly divided into 3 groups with 9 animals each: control (C) group, induced diabetic (D) group, and insulin-treated diabetic (ITD) group (10 U/day). After 1 week, one implant was inserted at the tibial metaphysis of the animals. The glucose levels were periodically evaluated through the glucose-oxidase enzymatic method. The animals were killed at 4, 8, and 12 weeks after surgery and the biomechanical test was performed using a torque manometer. Statistically significant differences regarding the removal torque of the implant could not be found at 4 weeks (P = 0.2) among groups. Group C showed statistically higher values than groups D and ITD at the experimental periods of 8 (P = 0.0001 and P = 0.0002, respectively) and 12 weeks (P = 0.0053 and P = 0.001, respectively). There were no statistical differences between D and ITD groups in any of the experimental periods. Diabetes mellitus has negatively influenced the mechanical retention of implants placed at the tibial metaphysis of rabbits. Therapy with insulin did not induce any changes.

Effect of diclofenac sodium on the healing process of end-to-end anastomosis in carotid arteries of rabbits. Histopathological and biomechanical studies

Aim. Diclofenac sodium is a non-steroidal anti-inflammatory drug commonly used to attenuate painful inflammatory reactions in surgery. However, it may delay healing in the skin and gastrointestinal tract. The aim of this study was to evaluate the influence of Diclofenac in vascular healing. Methods. Ninety rabbits had their carotid arteries sectioned and reconstructed by end-to-end anastomosis with interrupted sutures. The animals were randomly allocated into 3 groups of 30 each and treated by intramuscular route with saline (control), 5 mg/kg/day of diclofenac sodium (DS-5), and 10 mg/kg/day of diclofenac sodium (DS-10). Treatment began on the day of surgery and lasted 4 days. Angiography, biomechanical properties (failure load, failure elongation, yield point, yield point elongation, and stiffness were obtained from the load/elongation curve), macroscopic and histological examinations (hematoxylin-eosin, Masson, Calleja, Picrossirius-red), and scanning electron microscopy were studied in both arteries on the 3rd and 15th postoperative days. Results. No significant differences in biomechanical properties were observed either in the 3 groups or the experimental times. The carotid artery healing process was similar in the 3 groups. Conclusion. Diclofenac sodium did not cause alterations nor delayed carotid artery healing.

The role of the oblique ligament in the mechanical behavior of the medial collateral ligament of the mongrel dog elbow joint - Some biomechanical aspects

This study investigated the oblique ligament mechanical contribution to the medial collateral ligament of the canine elbow joint. Fifteen dogs were used for the study of the failure load, displacement, and energy absorption of the medial collateral and oblique ligaments of the canine elbow joint, associate and separately in the joint. Medial collateral ligament failure load and energy absorption were significantly higher in relation to the isolated oblique ligament. When the ligaments were associated in the joint, they presented an increment in failure load, displacement and energy absorption in relation to the ligaments analyzed separately. It was concluded, therefore, that the oblique ligament could have an important paper in the stability of the canine elbow joint, as it favors the medial collateral ligament resistance to the tensile load, one of the main stabilizer of the elbow joint.

In vivo microbiological evaluation of the effect of biomechanical preparation of root canals using different irrigating solutions

The aim of this study was to evaluate the antimicrobial effect of biomechanical preparation using different irrigating solutions. Seventy-eight root canals from premolars of four dogs were used. After experimental induction of periapical lesions, the root canals were prepared using the following solutions for irrigation: Group 1) 2.5% sodium hypochlorite (NaOCl); Group 2) 2% chlorhexidine (CHX); Group 3) saline solution and Group 4) control group with no biomechanical preparation. The microbiological evaluation of the root canals was performed by counting the colony forming units (CFUs) using different culture mediums. Two absorbent paper cones were used in each root canal in order to collect the microbiological samples before, and thirty days after the biomechanical preparation. The culture plates were incubated in aerobic, anaerobic and microaerophilic environment. Statistical evaluation was carried out using analysis of variance, Tukey and Student tests. The results demonstrated that there was reduction in the number of microorganisms in the NaOCl and CHX groups (p<0.05). There was greater effectiveness in the chlorhexidine group. The group that used saline solution and the control group presented an increased number of microorganisms. It can be concluded that the use of antimicrobial irrigating solutions during biomechanical preparation promotes the reduction of endodontic microbiota. However, a considerable number of microorganisms were still observed.

Study of the phenomena of fatigue using the finite element method

About 99% of mechanical failures are consequence of the phenomena of fatigue, which consists on the progressive weakening of the resistant section of a mechanical component due to the growing of cracks caused by fluctuating loadings. A broad diversity of factors influences the fatigue life of a mechanical component, like the surface finishing, scale factors, among others, but none is as significantly as the presence of geometric severities. Stress concentrators are places where fatigue cracks have a greater probability to occur, and so on, the intuit of this work is to develop a consistent and trustfully methodology to determine the theoretical stress concentration factor of mechanical components. Copyright © 2007 SAE International.

Hindlimb unloading producing effects on bone biomechanical properties in mature male rats

Aging is associated with decline in muscle mass and strength and reduced bone density. Age-related bone loss is a primary factor in osteoporosis and all individuals are potential candidates for osteoporosis because bone loss with aging occurs in men and women, but less studied in men. To examine the appropriateness of hindlimb elevation, by tail suspension as a model for diminished mechanical loading, and to determine the influence of age on bone responsiveness to skeletal unloading, we use dual X ray absorptiometry (DXA) and digital radiographic images to analyze the response of the femur from mature rats to biomechanical loads. Femurs from male Wistar rats (9-mo-old) were scanned using DXA and DIGORA and measures obtained in ephipyseal and diaphyseal regions of interest. The mechanical testing was divided into compression load to fracture the head and a three-point bending load to fracture the femur middiaphysis. In femoral epiphysis from hindlimb unload (HU), animals presented significant differences between mineral bone content and density assessed by DXA. Detailed regions of femoral epiphysis (head, throcanteric fossa, throcanter and metaphysis) presented significant lower values from radiographic density. Only compressive load necessary to fracture the femoral head neck was also significantly diminished in HU animals. Disuse induced, as in elderly patients, deterioration of the trabecular bone architecture with critical effect on bone fragility. Rats with 21 days of hindlimb unloading can simulate disuse, suggesting that certain sub-regions of their aging bones are more susceptible to fracture, while other, i.e. diaphyses, are not.

SEM-EDS and biomechanical evaluation of implants with different surface treatments: An initial study

Aim: Alterations in implant surfaces can affect periimplant bone formation and shorten the healing time. The goal of the present study was a comparative scanning electron microscopy (SEM)/energy dispersive spectrometry (EDS) and biomechanical evaluation of implants subjected to different surface treatments. Materials and Methods: Four implant surfaces were analyzed in the present study: machined commercial implants (TU); porous-surfaced commercial implants blasted with Al2O3 microspheres and acid-etched (TJA); laser beam-irradiated experimental implants (Laser) and laser beam-irradiated experimental implants with hydroxyapatite coating (HA). One sample for each surface underwent pre-surgery SEM/EDS analysis. Thirty-two implants (8 for each surface treatment) were then inserted into the tibia of 4 rabbits. After 8 weeks, the animals were euthanized and the implants retrieved by reverse torque and processed for post-surgery SEM/EDS analysis. Results: HA implants presented higher removal torque values when compared to Laser, TJA and TU groups. Post-surgery SEM micrographs clearly showed bone formation on all the examined surfaces; however, in the TU group bone covered only some areas of the implant surface, while in TJA, Laser and HA groups the entire implant surfaces were overlaid by newly formed bone. EDS analysis supported the results obtained by SEM and removal torque, showing that concentration of Ca and P increased from TU to TJA, Laser and HA implants. Conclusions: Implants with surfaces modified by laser beam with or without apatite coating showed more promising results.

Evaluation of titanium implants with surface modification by laser beam. Biomechanical study in rabbit tibias

The purpose of the present study was to evaluate, using a biomechanical test, the force needed to remove implants with surface modification by laser (Nd:YAG) in comparison with implants with machined surfaces. Twenty-four rabbits received one implant with each surface treatment in the tibia, machined surface (MS) and laser-modified surface (LMS). After 4, 8 and 12 weeks of healing, the removal torque was measured by a torque gauge. The surfaces studied were analyzed according to their topography, chemical composition and roughness. The average removal torque in each period was 23.28, 24.0 and 33.85 Ncm for MS, and 33.0, 39.87 and 54.57 Ncm for LMS, respectively. The difference between the surfaces in all periods of evaluation was statistically significant (p < 0.05). Surface characterization showed that a deep and regular topography was provided by the laser conditioning, with a great quantity of oxygen ions when compared to the MS. The surface micro-topography analysis showed a statistical difference (p < 0.01) between the roughness of the LMS (R a = 1.38 ± 0.23 μm) when compared to that of the MS (R a = 0.33 ± 0.06 μm). Based on these results, it was possible to conclude that the LMS implants' physical-chemical properties increased bone-implant interaction when compared to the MS implants. © 2009 Sociedade Brasileira de Pesquisa Odontológica.