Introduction: Usually osseointegration takes between three to six months after implant placement but patients are interested to have early loading. There are no definitive criteria for measuring bone mineral density (BMD), insertion torque (IT) (final torque force) and resonance frequency analysis (RFA) (primary implant stability) to determine exact loading time based on the relationship between the above-mentioned parameters. The aim of this study was to determine the relationship between IT, RFA and BMD in screw-type implants.Materials and Methods: This clinical trial was conducted on 18 patients who were candidates for ITI implant placement. Written consent was taken and jaw bone density was determined via a digital radiography technique before surgery. After implant placement, RFA and IT were measured. Fifty-five ITI implants of the total 62 implants placed were evaluated; the implants were 12 mm long with a diameter of 4.1 mm. Data was analyzed with Pearson’s test using SPSS.15 software (a=0.05).Results: There was a significant relationship between IT, RFA and BMD. Pearson’s test showed a correlation coefficient of 0.872 to 0.789 between the three parameters, indicating a strong relationship between them. The mean bone density was 1.468±0.042 g/cm2; the mean RFA was 66.01±2.2 ISQ and the mean IT was 34.62±3.33 N/cm2.Conclusion: Based on the results of the present study there is a significant relationship between, IT, RFA and BMD (p value=0.001).

Hypotension associated with spinal anesthesia for cesarean section is still a clinical problem. The role of crystalloid preloading to prevent hypotension associated with spinal anesthesia in parturients during cesarean section has been challenged. However, studies with crystalloids predict that fluid loading should be more efficacious if administered immediately after induction of spinal anesthesia. The effects of colloid loading after spinal anesthesia in cesarean section have not been studied enough. The aim of this study was to compare pre and co-loading of hetastarch for the prevention of hypotension following spinal anesthesia for cesarean delivery.Materials and Methods: This randomized clinical trial study was performed in 112 parturients (ASA I or II) undergoing elective cesarean section. Patients were randomly allocated to one of the two groups to receive rapid infusion of 500 ml of 6% hydroxyethylstarch (HES) before spinal anesthesia (preloading group, n=56), or rapid infusion of 500 ml of HES after induction of spinal anesthesia (co-loading group, n=56). The incidence of hypotension and the amount of vasopressor, (ephedrine 5 mg/mL+phenylephrine 25 micg/mL) were compared in the treatment of hypotension.Results: There was no significant difference in hypotension between the two groups (P=0.58). The preloading group used 2.2±1 ml of vasopressor mixture compared with 1.7±0.7 ml in the co-loading group (P=0.04) and the difference was significant.Conclusion: Colloid loading after induction of spinal anesthesia is as effective as preloading in reducing hypotension in cesarean section.

Carbon / epoxy composite is one of the most useful polymer matrix composites that has special properties such as high strength-to-weight ratio, high hardness, high corrosion resistance, resistance to nuclear radiation and etc. has high consumption in different industries such as aerospace industry. Therefor loading monitoring of this type of composite is important. In order to determine various failure mechanisms, acoustic emission method has more performance than other non-destructive methods. In this research acoustic emission method was used to study carbon/epoxy composite and evaluate frequency range of flexural loading. For this purpose bending behavior of composite and relation between acoustic signals had studied. Using both fast Fourier transform and wavelet transform analysis methods in this research, led to the same result with margin of 5%. By using FFT analysis, maximum frequency of 135 KHZ was determined while using wavelet transform, this amount led to 142 KHz. Time limits that events was occurred on the specimen, monitored by online diagrams that obtained from acoustical system. Energy distribution at failure mechanisms was obtained as 17%, 29% and 48% related to matrix fracture, debonding and fiber breakage respectively. Finally failure mechanisms of composite were confirmed by SEM images. Energy distribution amounts, time limits and ascending progress of diagrams validate bending diagram.

Introduction: Soil dynamic properties are used to evaluate the dynamic response of soils at different strain levels in geotechnical engineering. The shear modulus (G) and damping ratio (D) are among the most important dynamic properties of soils. In general, the factors affecting the dynamic behavior of soils are divided into two categories: first; soil type and characteristics such as water content, void ratio and soil plasticity and second; parameters of loads applied on the soil such as the number of loading cycles, loading frequency and loading waveform. Therefore, it is widely believed that the dynamic response of soils partially depends on the characteristics of the load. In this paper, 1-g shaking table tests were employed to investigate the effect of loading waveform and frequency content on dynamic properties of dry sands. The response obtained from soil samples during loading with different frequencies, input accelerations and waveforms were used to generate hysteresis loops of tested samples at different strain amplitudes. Then, hysteresis loops were used to determine the damping ratio and shear modulus at different strain levels. Finally, the effects of loading frequency and waveform on the changes of each parameter (G and D) were investigated. Material and methods: A hydraulic shaking table with a single degree of freedom, designed and constructed at the Crisis Management Center of Urmia University, was used to conduct the experiments. Firoozkuh No. 161 sand was used in all the experiments. The Firoozkuh sand gradation curve is similar to that of Toyoura sand. In this study, accelerometers were used to measure the acceleration of the input to the sample as well as to record the acceleration caused by the input excitation at different depths of the soil sample. The displacement transducers (LVDT sensors) were also used to measure linear displacement. Each soil sample was constructed using dry Firoozkuh sand poured uniformly into the container from four equal heights of 150 mm to reach a total height of 600 mm. During the compaction process, the accelerometers A1, A2, and A3 were placed at a depth of 150, 300 and 450 mm with respect to the bottom of container. Also, one accelerometer, A0, was attached rigidly to the container base to measure base acceleration. A displacement transducer (L1) was placed on the soil surface at a height of 600 mm from the floor of the container to measure the vertical displacement of the surface of the soil. In this study, 42 shaking table tests were performed to study the effect of loading frequency and waveform on dynamic properties of dry sand. The test samples were subjected to rectangular, sinusoidal and triangular loading at frequencies of 0. 5 to 9 Hz and at input acceleration of 0. 1g and 0. 3 g. Results and discussion: Given the importance of G-γ and D-γ curves in dynamic analyses, the changes in shear modulus with shear strain has been studied. The results show that the shear modulus increases as the frequency increases in all cases, and this increase is observed at lower frequencies and increases with increasing frequency. On the other hand, the shear modulus decreases with increasing shear strain. At a constant testing frequency, soil samples subjected to the rectangular waveform exhibited the largest shear modulus while the samples subjected to the triangular waveform showed the least shear modulus. The shear modulus of the samples under the sinusoidal waveform is barely more than the shear modulus of samples under triangular waveform. Moreover, by increasing the shear strain, the shear modulus values of samples with different waveforms have become closer and the waveform effect is reduced. As for the effect of input acceleration on the shear modulus, increasing the input acceleration increases the shear strain and consequently, decreases the shear modulus in all states (the values of shear modulus in various frequencies and the waveforms under the input acceleration of 0. 1 g are larger than the shear modulus values under the input acceleration of 0. 3g). In the case of the damping ratio, the results show that, in all cases, damping ratio increases with shear strain. At low strain levels, the damping ratio values at various frequencies and waveforms are low and yet very close. At higher strain levels, the increase in frequency increases the damping ratio. This increase is more significant at higher frequencies. Also, the effect of waveform on the damping ratio is more apparent at larger shear strains, and at such shear strain levels, soil samples under rectangular loading exhibit the largest damping ratio. The damping ratio associated with the sinusoidal and triangular loading are also close to each other and it is a slightly larger for sinusoidal loading. On the other hand, the damping ratio increases with input acceleration. In addition, the effect of increased input acceleration on the increase in the damping ratio is more obvious at higher frequencies mainly due to the increase in shear strain. Conclusion: In the present study, the effects of loading frequency and waveform on the dynamic properties of dry sand were investigated using shaking table tests. The following conclusions were drawn: The shear modulus increases with frequency. The trend is more obvious at larger frequencies. The effect of loading frequency on the damping ratio of the soil at low levels of strain is negligible, and at relatively large strain levels, damping ratio increases with loading frequency. Soil samples exhibit the highest shear modulus and damping ratio under rectangular loading. Therefore, in all the tested frequencies and input accelerations, the values of G and D for the rectangular waveforms are greater than those of the sinusoidal and triangular waveforms. The shear modulus and damping ratio for the sinusoidal waveforms are marginally greater than those of triangular waveforms, yet one can consider them practically similar. In all cases, the shear strain increased by increasing the amplitude of the input acceleration, and as a result, the shear modulus decreased and the damping ratio increased.

Every year, huge costs are spent on the maintenance of road pavements due to premature reflective deterioration of the road surface, a large part of which is related to road surface paving. Accordingly, in order to prevent the propagation of reflective cracks in newly coated pavements, various methods have been used and researched. The results have shown that all the adopted reflective crack control methods have only delayed the propagation of this type of crack. However, some methods have caused a greater impact on the appearance of reflective cracks and reducing the intensity of these cracks, and one of the best methods is the use of geosynthetic products and interlayers. In this research, the performance of 2 different types of geocomposite (with tensile strengths of 50 and 100 kN/m) in asphalt pavements in delaying the initiation of reflective cracks compared to control samples at different temperatures and loading frequencies was investigated. Based on the studies, it was observed that the use of type I geocomposite with high tensile strength is the most effective in increasing the fatigue life and among the mentioned factors, the temperature parameter will have the most negative effect on this performance. After the temperature, in order of the type of geocomposite used in terms of tensile strength and then the loading intensity, they will have the greatest effect on the fatigue life changes (about 53,000 cycles of loading difference, between the temperature of 40 and 0 degrees Celsius) on the reinforced asphalt coatings. Based on the results of variance analysis of the fatigue life model obtained in this research, the value of R² and Adjusted R² are equal to 0.987 and 0.981, respectively, which indicates the high accuracy of the presented model.

Today, the use of waste tires has been expanded in various geotechnical projects to absorb and reduce the vibration caused by seismic and dynamic loads, and therefore it is important to study the effect of different parameters on their behavior and dynamic characteristics in combination with soil. So this study examined the effects of loading frequency on dynamic properties of sand-tire powder mixtures such as shear modulus (G) and damping ratio (D). A series of 1-g shaking table tests were performed on sand-tire powder mixture. Tire powders were added to the sand with 5%, 10%, 15% and 20% in gravimetric basis and with a relative density of zero were subjected to sinusoidal loading at frequencies of 0. 5, 1, 2, 3, 5, 7 and 9 Hz and at input acceleration of 0. 1g and 0. 3g. The results showed that in all cases, the increase in frequency in the same cycles increased the shear modulus and the damping ratio. Also, with increasing shear strain, the shear modulus of the mixture decreased, but the damping ratio increased. On the other hand, by increasing the tire powder, the value of the shear modulus is reduced, but the amount of damping ratio is increased.