Enhancement of thermoelectric properties of MBE grown un-doped ZnO by thermal annealing

Khalid, Mahmood,Asghar, Muhammad,Ali, Adnan,Ajaz-Un-Nabi, M.,Arshad, M. Imran,Amin, Nasir,Hasan, M.A. Techno-Press 2015 Advances in energy research Vol.3 No.2

In this paper, we have reported an enhancement in thermoelectric properties of un-doped zinc oxide (ZnO) grown by molecular beam epitaxy (MBE) on silicon (001) substrate by annealing treatment. The grown ZnO thin films were annealed in oxygen environment at $500^{\circ}C-800^{\circ}C$, keeping a step of $100^{\circ}C$ for one hour. Room temperature Seekbeck measurements showed that Seebeck coefficient and power factor increased from 222 to $510{\mu}V/K$ and $8.8{\times}10^{-6}$ to $2.6{\times}10^{-4}Wm^{-1}K^{-2}$ as annealing temperature increased from 500 to $800^{\circ}C$ respectively. This observation was related with the improvement of crystal structure of grown films with annealing temperature. X-ray diffraction (XRD) results demonstrated that full width half maximum (FWHM) of ZnO (002) plane decreased and crystalline size increased as the annealing temperature increased. Photoluminescence study revealed that the intensity of band edge emission increased and defect emission decreased as annealing temperature increased because the density of oxygen vacancy related donor defects decreased with annealing temperature. This argument was further justified by the Hall measurements which showed a decreasing trend of carrier concentration with annealing temperature.

Adaptive State-space Control of Under-actuated Systems Using Error-magnitude Dependent Self-tuning of Cost Weighting-factors

Omer Saleem,Khalid Mahmood-ul-Hasan 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.2

This article methodically constructs a novel adaptive self-tuning state-space controller that enhances the robustness of under-actuated systems against bounded exogenous disturbances. The generic Linear-Quadratic-Regulator (LQR) is employed as the baseline controller. The main contribution of this article is the formulation of a hierarchical online gain-adjustment mechanism that adaptively modulates the weighting-factors of LQR’s quadratic-performance-index by using pre-calibrated continuous hyperbolic scaling functions. The hyperbolic scaling functions are driven by the magnitude of system’s state-error variables. This augmentation dynamically updates the solution of the Matrix-Riccati-Equation which modifies the state-feedback gains after every sampling interval. The efficacy of the proposed adaptive controller is validated by conducting hardware-in-the-loop experiments on QNET Rotary Pendulum setup. The experimental outcomes show that the proposed adaptive control schemeyields stronger damping against oscillations and faster error-convergence rate, while maintaining the controller’s asymptotic-stability, under the influence of parametric uncertainties.

Unified Fault-Tolerant Control for Air-Fuel Ratio Control of Internal Combustion Engines with Advanced Analytical and Hardware Redundancies

Amin Arslan Ahmed,Mahmood-ul-Hasan Khalid 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.3

This paper proposes a Unifi ed Fault-Tolerant Control System (UFTCS) based on advanced analytical and hardware redundancies for Air-Fuel Ratio (AFR) control of Spark Ignition (SI) Internal Combustion (IC) engines. The advanced analytical redundancy part is termed the Hybrid Fault-Tolerant Control System (HFTCS) which consists of both active and passive types. The Lookup Tables (LTs) have been utilized in the active part and a robust proportional feedback controller of high gain with fuel throttle actuator has been implemented in the passive part. Since the failure of any two sensors at the same time or failure of a single actuator causes engine shutdown, an advanced hardware redundancy protocol Modifi ed Triple Modular Redundancy (MTMR) has been suggested for the sensors, and Dual Redundancy (DR) has been proposed for the actuators to prevent the tripping of the engine. MATLAB/Simulink simulation results indicate that the suggested UFTCS is highly robust to the sensor faults in both normal and noisy conditions. The probabilistic reliability analysis for various hardware redundancy schemes also proves the greater overall reliability of UFTCS. Finally, a comparison with the existing AFR control systems is carried out to demonstrate its superior performance

Hierarchical adaptive control of selfstabilizing electromechanical systems using artificial-immune self-tuning mechanism for state weighting-factors

Omer Saleem,Khalid Mahmood-ul-Hasan 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3

This article presents a novel self-adaptive linear-quadratic-regulator (LQR) architecture to improve the robustness of self-stabilizing electromechanical systems against exogenous disturbances. The main contribution of this article is to formulate a nonlinear-type artificial-immune adaptation mechanism that dynamically adjusts the state-weighting-factors of LQR’s quadratic-performance-index online. The Riccati-equation solver uses these updated state-weighting-factors to yield time-varying state-feedback gains. This hierarchical control procedure uses immunological computations to indirectly alter the LQR gains, which helps in flexibly reconfiguring the control trajectory under disturbances. The performance of the proposed immune-adaptive LQR is benchmarked against a conventional adaptive LQR and a fixed-gain LQR by conducting software simulations on the nominal model of the QNET rotary pendulum system. Credible real-time experiments are also conducted on the QNET rotary pendulum’s hardware setup to analyze each controller’s efficacy in the physical environment. The simulation and experimental results validate the superior disturbance-rejection capability of the proposed controller under every testing scenario.

High Diversity Transceiver for Low Power Differentially Encoded OFDM System

Faisal Nadeem,Muhammad Zia,Hasan Mahmood,Naeem Bhatti,Ihsan Haque 한국전자통신연구원 2016 ETRI Journal Vol.38 No.1

In this work, we investigate differentially encoded blind transceiver design in low signal-to-noise ratio (SNR) regimes for orthogonal frequency-division multiplexing (OFDM) signaling. Owing to the fact that acquisition of channel state information is not viable for short coherence times or in low SNR regimes, we propose a time-spread frequency-encoded method under OFDM modulation. The repetition (spreading) of differentially encoded symbols allows us to achieve a target energy per bit to noise ratio and higher diversity. Based on the channel order, we optimize subcarrier assignment for spreading (along time) to achieve frequency diversity of an OFDM modulated signal. We present the performance of our proposed transceiver design and investigate the impact of Doppler frequency on the performance of the proposed differentially encoded transceiver design. To further improve reliability of the decoded data, we employ capacity-achieving low-density parity-check forward error correction encoding to the information bits.

Anti-HIV Activity of Dehydroaltenusin-a Metabolite from a Streptomyces sp.

Abdul Jabbar,Ajude Prashad Shresta,Choudhury Mahmood Hasan,Mohammad Abdur Rashid 한국생약학회 1999 Natural Product Sciences Vol.5 No.4

Dehydroaltenusin (1) was isolated from the chloroform extract of the culture filtrate of a Streptomyces sp. and its structure was determined from spectral data as well as by comparison with published values. In an XTT-based in vitro anti-HIV assay, dehydroaltenusin effectively inhibited the cytopathic effects of HIV infection at a concentration of 1-5 ㎍/mL.

Antioxidant and Antimicrobial Activities of Iranian Mooseer (Allium hirtifolium Boiss) Populations

Hojat Ghahremani-majd,Farshad Dashti,Dara Dastan,Hasan Mumivand,Javad Hadian,Mahmood Esna-Ashari 한국원예학회 2012 Horticulture, Environment, and Biotechnology Vol.53 No.2

Mooseer or Persian shallot is a bulbous perennial herb belonging to the Alliaceae family. Antioxidant activities of 12 mooseer populations were determined using three assays including DPPH, FRAP, and ABTS. Antioxidant activities differed among all populations with the Sahneh and Nahavand population as the highest and the lowest, respectively. Antimicrobial activity of mooseer extracts were tested against six bacteria including Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae and two fungi including Candida albicans and Saccharomyces cerevisiae by disc diffusion method by determining their minimum inhibitory concentration values with all samples indicating moderate to high antimicrobial activity. For antimicrobial activity, Esfahan population showed the highest inhibitory effect on bacteria and fungi. According to the results of the study, mooseer has potential as a valuable dietary supplement.

Triangular Geometrized Sampling Heuristics for Fast Optimal Motion Planning

Qureshi, Ahmed Hussain,Mumtaz, Saba,Ayaz, Yasar,Hasan, Osman,Muhammad, Mannan Saeed,Mahmood, Muhammad Tariq SAGE Publications 2015 International Journal of Advanced Robotic Systems Vol.12 No.2

Bandwidth-Efficient Selective Retransmission for MIMO-OFDM Systems

Muhammad Zia,Nazar A. Saqib,Tariq Shah,Hasan Mahmood,Tamoor Kiani 한국전자통신연구원 2015 ETRI Journal Vol.37 No.1

In this work, we propose an efficient selective retransmission method for multiple-input and multiple-output (MIMO) wireless systems under orthogonal frequency-division multiplexing (OFDM) signaling. A typical received OFDM frame may have some symbols in error, which results in a retransmission of the entire frame. Such a retransmission is often unnecessary, and to avoid this, we propose a method to selectively retransmit symbols that correspond to poor-quality subcarriers. We use the condition numbers of the subcarrier channel matrices of the MIMO-OFDM system as a quality measure. The proposed scheme is embedded in the modulation layer and is independent of conventional hybrid automatic repeat request (HARQ) methods. The receiver integrates the original OFDM and the punctured retransmitted OFDM signals for more reliable detection. The targeted retransmission results in fewer negative acknowledgements from conventional HARQ algorithms, which results in increasing bandwidth and power efficiency. We investigate the efficacy of the proposed method for optimal and suboptimal receivers. The simulation results demonstrate the efficacy of the proposed method on throughput for MIMO-OFDM systems.

Profiling of Virulence-associated Factors in Shigella Species Isolated from Acute Pediatric Diarrheal Samples in Tehran, Iran

Sajad Yaghoubi,Reza Ranjbar,Mohammad Mehdi Soltan Dallal,Somayeh Yasliani Fard,Mohammad Hasan Shirazi,Mahmood Mahmoudi 질병관리본부 2017 Osong Public Health and Research Persptectives Vol.8 No.3

Objectives: The genus Shigella comprises the most infectious and diarrheagenic bacteria causing severe diseases, mostly in children under five years of age. This study aimed to detect nine virulence genes (ipaBCD, VirA, sen, set1A, set1B, ial, ipaH, stx, and sat) in Shigella species (spp.) using multiplex polymerase chain reaction (MPCR) and to determine the relation of Shigella spp. from pediatric diarrheal samples with hospitalization and bloody diarrhea in Tehran, Iran. Methods: Shigella spp. were isolated and identified using standard microbiological and serological methods. The virulence genes were detected using MPCR. Results: Seventy-five Shigella spp. (40 S. sonnei, 33 S. flexneri, 1 S. dysenteriae, and 1 S. boydii) were isolated in this study. The prevalence of ial, sen, sat, set1A, and set1B was 74.7%, 45.4%, 28%, 24%, and 24%, respectively. All S. flexneri isolates, while no S. sonnei, S. dysenteriae, or S. boydii isolates, contained sat, set1A, and set1B. All isolates were positive for ipaH, ipaBCD, and virA, while one (1.4%) of the isolates contained stx. The highest prevalence of virulence determinants was found in S. flexneri serotype IIa. Nineteen (57.6%) of 33 S. flexneri isolates were positive for ipaBCD, ipaH, virA, ial, and sat. The sen determinants were found to be statistically significantly associated with hospitalization and bloody diarrhea (p = 0.001). Conclusion: This study revealed a high prevalence of enterotoxin genes in S. flexneri, especially in serotype 2a, and has presented relations between a few clinical features of shigellosis and numerous virulence determinants of clinical isolates of Shigella spp.