This paper assesses the impacts of the severe vertical irregularity, particularly the discontinuity in lateral force resisting system (LFRS), on the seismic behavior of high-rise buildings at various performance levels. Two 50-story high-rise buildings are selected to represent a regular structure and an irregular building. The reference buildings are designed using modern seismic design provisions. Verified fiber based simulation models are developed and forty natural earthquake records representing two seismic scenarios are selected to assess the seismic vulnerability of the severe vertical irregularity. The results indicate that, although a proper overstrength factor is employed in the design of the irregular building, it is significantly more vulnerable at different earthquake intensities than the regular counterpart. The limit state exceedance probabilities reflect the substantial increase in seismic losses with the discontinuity in LFRS. This confirms the need for mitigation actions to reduce the seismic losses of structures exhibiting this severe irregularity.
The period elongation of modern multi-story buildings under seismic loads is assessed in this paper. Ten reference structures of low, medium and high-rise buildings are selected and fully designed to represent the contemporary buildings in the UAE. The selected structures vary in height from 2 to 100 stories with three different lateral force resisting systems, namely flat slab-columns (FSC), shear walls (SW) and tube in tube (TIT) systems. The elastic and elongated periods are estimated using eigenvalue and time history analyses. It is concluded that the average period elongation at the life safety limit state is 2.2, 1.6 and 1.1 for the FSC, SW and TIT systems, respectively. At the collapse prevention performance level, the period elongation for the above-mentioned systems is 2.8, 2.0 and 1.3, respectively. The study proposes an effective stiffness of 0.5EI, 0.8EI and 1.0EI for the vertical members of the FSC, SW and TIT systems, respectively.
High Peak-to-Average-Power Ratio (PAPR) of transmitted signals is the most commonly encountered impediment in broadband telecommunication systems that use orthogonal frequency division multiplexing (OFDM) modulation scheme. Companding techniques have been recently used to alleviate the high PAPR of OFDM signal, which detrimentally affects the efficiency and linearity of power amplifiers. The proposed research is meant to develop a smart fully adaptive Tx-Rx link for an OFDM based system. Under this structure, a concurrent companding and bias control techniques are introduced to enhance the efficiency of the power amplifier; particularly the overall DC/RF power conversion. The companding algorithm is presented with an adaptive behavior at the baseband level to reduce PAPR. PAPR/BER tradeoff optimization is required to improve the system efficiency and complexity. In this paper, performance evaluation of most commonly companding schemes is presented. The system performance is evaluated over two standard metrics; the CCDF of PAPR and BER.
An S-band digital radar testbed implemented using discrete microwave components is presented. By utilizing multiple receiver channels, digital array radars (DAR) are able to perform several functions such as tracking a specific target in space, while rejecting jammers from a certain angular location, which is of interest in high clutter environments. The proposed digital radar testbed possess the unique attributes of having high (>50 dB) dynamic range over a wide (600 MHz) instantaneous bandwidth to improve the radar's range resolution (0.25 m). The ultimate goal of this study is to produce DAR on printed circuit boards (PCB), using commercial surface mount components, to reduce the cost and physical size while maintaining the radar's specifications. The limitations and constraints of such design transfer should be studied in order to achieve the best system performance in smaller scales.
In this work, an S-Band radar system based on stretch processing technique is developed at the chip level. The novelty in this work lies in providing a compact and miniaturized radar system chipset. The radar has many characteristics that ensure high performance: a wide bandwidth signal (600 MHz) that provides high resolution to distinguish between close objects, stretch processing technique that dramatically reduces the required sampling rates and relaxes the specifications of analog to digital converters, high dynamic range that allows weak signals to be detected from targets masked by high levels of clutter (such as snow and rain), multiple receiver channels that enable digital antenna beamforming at the receiver to mitigate any strong interferer, and finally operation in the S-Band (2-4 GHz) that provides high immunity against clutter in long range surveillance applications.
In wireless communication systems, multipath and interference effects degrade the SNR and increase the BER of received signals, which can be improved using beamforming algorithms. In the adaptive beamforming where signal-path gains are changed in real time based on statistics of the received signals, the SNR is improved and BER is decreased, but power dissipation undergoes unpredictable transients during the gain adaptation process which are detrimental to battery-based power management systems in mobile applications. In this paper, we propose an FPGA-based power analysis methodology which can result in selection of energy-efficient adaptive beamforming algorithm. We used simple four-channel Least-Mean-Squares (LMS) beamformer and prototyping it on Xilinx's Virtex 7 FPGA. Iterating through proposed methodology guarantees the selection of adaptive algorithm design point which represents best tradeoff between parameter convergence, machine precision and energy-efficiency for the embedded array signal processor.
To improve the performance of CO2 absorption/stripping in gas liquid membrane contactor module a relatively new idea, enhanced CO2 desorption (based on pH-shift) was studied. In this study the pH values were changed by using asymmetric solutions of glycine and KOH (i.e. solutions containing different molar amounts of amino acid and base). Lower pH decreases the CO2 solubility of the solvent and promotes the hydrolysis of the carbamate species. Consequently at lower pH the CO2 reaction equilibrium shifts towards the release of CO2 enhancing the partial pressure of CO2. Hence higher molar ratios of glycine/KOH shows better stripping and reduced absorption performance. Subsequently in continuous operation of absorption and followed up by stripping, the stripping performance was controlled by reduced absorption performance because of resultant low initial CO2 concentrations. Thus for the net effect the molar ratio has to be optimized to achieve both good absorption and subsequent stripping performance.
9-Ethenylanthracenes and 9-phenyl-10-ethenylanthracenes have been prepared by solventless Wittigolefination and Suzuki coupling. The crystal structures of two ethyl (E)-3- [anthran-9-yl]propenoates have been measured
This study extends an ongoing evaluation of a chemical process which uses desalination brine to convert CO2 into useful Sodium bicarbonate while partially treating the brine in the process. The focus of this present paper is a sensitivity analysis of the CO2 absorption step of the process. Important process parameters such as temperature, brine concentration and amine concentration are varied to see their impact on a key process performance index which is the percent sodium removal from the brine. The results showed that the CO2 absorption step is significantly improved at lower temperatures, high brine concentrations and moderate amine concentration. When the amine used in the process is 2-Amino, 2-methyl, propanol (AMP), the optimum concentration was found to be 30 weight%.
Magnetic water treatment has been a subject of dispute for quite some time now. This work attempts to ascertain the effects of magnetic treatment on the precipitates formed from hard water. The crystals formed were characterized using scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). The findings indicate that aragonite is preferentially formed after magnetic field treatment, while calcite is the predominant form of calcium carbonate precipitated when there was no magnetic treatment of the solution.
