BER Performance Analysis of Frequency-Hopping and Direct-Sequencing Spread Spectrum for Cognitive Radio Networks

Cognitive radio is an encouraging technology for future wireless communication networks. Due to the rapid increase in wireless services, the RF spectrum is going through a scarcity problem. This has forced mobile operators to participate in multi-million dollar auctions to reserve some spectrum resources. Cognitive radio tries to solve this scarcity problem by effectively using the unused portions of the spectrum. FHSS and DSSS are two spread spectrum technologies used for cognitive radios. In this paper, both techniques have been discussed extensively. DSSS accesses spectrum in a sequence whereas FHSS accesses spectrum by a hopping sequence and thus provide immunity to interference and jamming signals. Also, they have been concatenated to cognitive radio and analyzed to find which spread spectrum technology provides better communication. Simulations have been performed in MATLAB environment and results are shown in the form of number of error bits (BER) generated for a range of SNR values. DOI: 10.17762/ijritcc2321-8169.150514

Probabilistic Life Cycle Assessment of Safety Valves

The objective of this this thesis is to develop a probabilistic model for assessing the life cycle performance of safety valves used in the nuclear piping system. The life cycle performance is quantified in terms of reliability and life cycle cost in a given operating interval of the plant. A key input to the probabilistic lifecycle analysis is the lifetime distribution of the component in question. The second important element is the estimation of costs of inspection and in-service testing of components as well as costs of repairs and replacement of failed components. Based on this information, the life cycle analysis aims to predict the reliability and expected cost of operating a component in a future time interval. This study illustrates how to develop methods and algorithms for probabilistic assessment of the life cycle of safety valves used in the nuclear piping system. For statistically estimated parameters of the probability distributions of lifetime and various costs, historical operating data are required. This study uses about 20 years of historical data obtained from a group of temperature control valves used in the moderator system of a reactor. A maximum likelihood-based method is developed to estimate parameters of the lifetime distribution of a valve. The lifetime is defined as the time of first leakage in the valve since the time of installation. The ML method is based to consider complete and censored lifetime information. The distribution of repairs cost is also estimated by the ML method. The proposed method is applied to predict reliability and life cycle cost for various operating interval. This model can also be used to optimize the overhaul interval of the valve

MRI: an update and review on bio-effects and safety considerations

Diagnostic imaging technologies such as magnetic resonance (MR) are vital to catching signs of disease early and high quality diagnosis for treatment planning. However, some patients are unable to take advantage of its life saving capabilities. The procedures can be claustrophobic and the contraindications of MRI in patients having implants, pacemakers and also the risks associated with the use of cryogens, contrast agents etc. So this article provides an update on review on the bio effects and safety considerations for both patient and health practitioner with respect to the use of clinical MRI

Noise levels in a dental teaching institute: a matter of concern!

Objective: To measure and assess the noise levels produced by various dental equipments in different areas of a dental institution and to recommend improvements if noise levels are not within permissible limits. Materials and methods: Sound levels were measured at three different areas of a dental institution where learning and teaching activities are organized. The sound level was measured using a sound level meter known as 'decibulolmeter'. In each area the noise level was assessed at two positions-one, at 6 inches from the operators ear and second, at the chairside instrument trolley. Noise levels were also assessed from a central location of the clinic area when multiple equipments were in operation simultaneously. Results: Dental laboratory machine, dental hand-piece, ultrasonic scalers, amalgamators, high speed evacuation, and other items produce noise at different sound levels which is appreciable. The noise levels generated varied between 72.6 dB in pre-clinics and 87.2 dB in prosthesis laboratory. The results are comparable to the results of other studies which are conducted elsewhere. Although the risk to the dentists is lesser, but damage to the hearing is possible over prolonged periods. Conclusion: Higher noise levels are potentially hazardous to the persons working in such environments especially in the laboratory areas where noise levels are exceeding the permissible limits

Experimental evaluation of CO2 ejector cooling system for supermarkets at tropical zones

Cooling system for supermarkets, now-a-days in developing countries like India, mainly use man-made synthetic refrigerants/mixtures such as R134a, R404A and R410A (HFCs). These fluorinated refrigerants possess outrageous impact on the environment/ambient due of their high GWP and ODP. The EU F-gas regulation is formulated recently and came into force in 2014 in order to restrict the use of synthetic refrigerants for various HVAC applications. Under this regulation, it is also illegal to vent any such synthetic refrigerants to the atmosphere during the system servicing or end-of-life decommissioning. Sudden phase down of HFCs forced the present scenario to identify a potential replacement of these synthetic refrigerants. The influence of the same is comparatively high for developing countries. In the present study, the performance of a multi-ejector based supermarket cooling system is experimentally evaluated using natural refrigerant carbon dioxide (CO2). 33 kW cooling capacity of the system which is capable of maintaining three simultaneous different temperatures such as -29 °C for freezing, -6 °C for refrigeration and 7-11 °C for air-conditioning is examined at high ambient temperature context (up to 46 ºC gas cooler outlet temperature). The maximum COP of the supermarket cooling system appeared as 4.2. It is also observed that the maximum exergy efficiency of system is 0.316 obtained corresponding to 3.2 PIR of the system

Forearm bone mineral density in postmenopausal Indian women: correlation with calcium nutrition

Background: Osteoporosis is characterized by low bone mass with micro architectural deterioration of bone tissue leading to enhanced bone fragility, thus increasing the susceptibility to fracture. This study was conducted with the objective of measuring forearm bone mineral density in postmenopausal Indian women and to establish a correlation with indices of calcium nutrition i.e. dietary calcium intake, calcium supplements, serum calcium, serum phosphorus, serum alkaline phosphatase and serum intact parathyroid hormone.Methods: Fifty healthy, ambulatory postmenopausal women were selected and a prospective observational study was conducted to correlate the BMD with indices of calcium nutrition. Patient’s laboratory investigations (serum calcium, serum phosphorous, serum alkaline phosphatase and serum intact parathyroid hormone were done and BMD was assessed with dual-energy X-ray absorptiometry at non-dominant forearm; T-scores and Z-score were derived. Correlation analysis was done to investigate the relationship between indices of calcium nutrition and BMD.Results: The proportion of osteoporosis in forearm was 22%in the deficient group, 60% in the insufficient group and 18% in the sufficient group. Among the study group 15 subjects were osteoporotic by T score mid forearm where as 7 were osteoporotic with T score ultra distal forearm and 11 subjects had osteoporosis with T score total forearm.Conclusions: Out of all the indices of calcium nutrition, the correlation between the serum alkaline phosphatase and T score forearm was statistically significant

Dental Lasers: A Review of Safety Essentials

The laser technology offers a wide range of uses in dentistry with certain advantages to the general dental practitioner like bloodless surgery, minimal post-operative pain, reduction of operative time and high patient acceptance. Patient acceptance has also been demonstrated in various studies. Apart of these major advantages, safety regarding the use of lasers cannot be neglected and has become an important concern in this modern era of dentistry, as application of this technology is growing day by day. Potential hazards can be encountered while using lasers like ocular hazards, tissue injury, inhaling the vapor emitted by the laser procedure, fire and explosion hazards etc. The safe use of lasers includes all the individuals who might be exposed either deliberately or accidently while using lasers and effective measures that can be undertaken by clinicians and health professionals to minimize the injuries caused due to laser accidents. The present article serves to explore the risks involved in the use of lasers in dentistry and suggest some of the laser safety protocols/measures that can be established in the dental office for prevention of laser injuries

Energy efficient multiejector CO2 cooling system for high ambient temperature

Experimental evaluation of a multiejector CO2 cooling system of 33 kW cooling capacity is conducted for an Indian supermarket at high ambient temperature context. The test-rig is designed to depict the actual supermarket cooling requirements in India with three different cooling temperature levels simultaneously; freezing, medium refrigeration and air-conditioning. The rig is equipped with a novel design consisting of two multiejectors; low ejection ratio ejector (LERE) and high ejection ratio ejector (HERE), in a series configuration. It is observed that the maximum pressure lift of 5.5 bar is obtained with this new design. Moreover, improvement in the overall system performance with the support of the internal heat exchanger (IHX) is evaluated. Enhancements observed in the maximum COP and PIR are 7.2% and 6.2% respectively. Furthermore, the test-rig performance with the flooding and non-flooding of the medium temperature evaporator (refrigeration) is evaluated. It is observed that the evaporator flooding reduces its superheat at the exit by 83.84%, leading to the overall reduction of PIR by 6.51%. The performance of the proposed system is also compared with the reported field data obtained at a low ambient temperature context. The results projected that the proposed cooling system with series multiejector configuration is a reliable choice for higher ambient temperatures and it is expected to outperform the existing systems at lower ambient temperatures.acceptedVersio

Multiejector CO2 cooling system with evaporative gascooler for a supermarket application in tropical regions

In the present study, the performance of a 33 kW multiejector trans-critical CO2 cooling system is experimentally evaluated for a supermarket application with/without internal heat exchanger and evaporative cooling. In order to enhance the overall performance of the system for tropical regions, the testing is carried out at high ambient temperature (up to 46 °C) with 5 cm, 10 cm and 15 cm cooling pad thickness arrangements. The experimental results clearly projects that the evaporative cooler capacity reaches a maximum of 10 cm pad thickness. However, a minor improvement is observed in terms of Coefficient of Performance and Power Input Ratio beyond 10 cm pad thickness. Maximum improvement in COP with internal heat exchanger and evaporative cooler is 11% and 40% respectively. On the other hand, a maximum reduction in the system Power Input Ratio with internal heat exchanger and evaporative cooler is 8.5% and 26% respectively. However, a minor enhancement in Coefficient of Performance and Power Input Ratio of 4% and 6% are observed respectively with 15 cm cooling pad thickness. Furthermore, a comparative analysis is carried out with the existing and present experimental study to project the compatibility of an evaporative condenser in the ejector based CO2 cooling system. From the study, it is evident that the evaporative cooling arrangement for the gascooler of the CO2 system is suggested as a potential solution to the supermarket application at a high ambient temperature context. © 2021 Elsevier LtdacceptedVersio