37 results on '"Mahdi Alqahtani"'
Search Results
2. MXene-GaN van der Waals metal-semiconductor junctions for high performance multiple quantum well photodetectors
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Lingzhi Luo, Yixuan Huang, Keming Cheng, Abdullah Alhassan, Mahdi Alqahtani, Libin Tang, Zhiming Wang, and Jiang Wu
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Applied optics. Photonics ,TA1501-1820 ,Optics. Light ,QC350-467 - Abstract
A MXene-GaN van der Waals Metal-Semiconductor Junctions based High Performance Multiple Quantum Well Photodetector was demonstrated, which shows great potential for underwater wireless optical communication and turbidity sensing.
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- 2021
- Full Text
- View/download PDF
3. Using a Deep Learning Method and Data from Two-Dimensional (2D) Marker-Less Video-Based Images for Walking Speed Classification
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Tasriva Sikandar, Mohammad F. Rabbi, Kamarul H. Ghazali, Omar Altwijri, Mahdi Alqahtani, Mohammed Almijalli, Saleh Altayyar, and Nizam U. Ahamed
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2D image ,marker-less video ,walking speed pattern ,walking speed classification ,quasi-periodic pattern ,LSTM ,Chemical technology ,TP1-1185 - Abstract
Human body measurement data related to walking can characterize functional movement and thereby become an important tool for health assessment. Single-camera-captured two-dimensional (2D) image sequences of marker-less walking individuals might be a simple approach for estimating human body measurement data which could be used in walking speed-related health assessment. Conventional body measurement data of 2D images are dependent on body-worn garments (used as segmental markers) and are susceptible to changes in the distance between the participant and camera in indoor and outdoor settings. In this study, we propose five ratio-based body measurement data that can be extracted from 2D images and can be used to classify three walking speeds (i.e., slow, normal, and fast) using a deep learning-based bidirectional long short-term memory classification model. The results showed that average classification accuracies of 88.08% and 79.18% could be achieved in indoor and outdoor environments, respectively. Additionally, the proposed ratio-based body measurement data are independent of body-worn garments and not susceptible to changes in the distance between the walking individual and camera. As a simple but efficient technique, the proposed walking speed classification has great potential to be employed in clinics and aged care homes.
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- 2021
- Full Text
- View/download PDF
4. Ensemble-Based Machine Learning Algorithms for Classifying Breast Tissue Based on Electrical Impedance Spectroscopy.
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Sam Matiur Rahman, Md. Asraf Ali, Omar Altwijri, Mahdi Alqahtani, Nasim Ahmed, and Nizam Uddin Ahamed
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- 2019
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5. Gender Effects in Surface Electromyographic Activity of the Biceps Brachii Muscle During Prolonged Isometric Contraction.
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Nizam Uddin Ahamed, Zulkifli Bin Md Yusof, Mahdi Alqahtani, Omar Altwijri, S. A. M. Matiur Rahman, and Kenneth Sundaraj
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- 2015
- Full Text
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6. MXene-GaN van der Waals metal-semiconductor junctions for high performance multiple quantum well photodetectors
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Zhiming Wang, Yixuan Huang, Libin Tang, Jiang Wu, Lingzhi Luo, Keming Cheng, Mahdi Alqahtani, and Abdullah I. Alhassan
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Photocurrent ,Materials science ,Optoelectronic devices and components ,business.industry ,Photodetector ,Photodetection ,QC350-467 ,Orders of magnitude (numbers) ,Specific detectivity ,Optics. Light ,Article ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,TA1501-1820 ,Responsivity ,symbols.namesake ,symbols ,Optoelectronics ,Applied optics. Photonics ,van der Waals force ,business ,Applied optics ,Dark current - Abstract
A MXene-GaN-MXene based multiple quantum well photodetector was prepared on patterned sapphire substrate by facile drop casting. The use of MXene electrodes improves the responsivity and reduces dark current, compared with traditional Metal-Semiconductor-Metal (MSM) photodetectors using Cr/Au electrodes. Dark current of the device using MXene-GaN van der Waals junctions is reduced by three orders of magnitude and its noise spectral intensity shows distinct improvement compared with the traditional Cr/Au–GaN–Cr/Au MSM photodetector. The improved device performance is attributed to low-defect MXene-GaN van der Waals interfaces. Thanks to the high quality MXene-GaN interfaces, it is possible to verify that the patterned substrate can locally improve both light extraction and photocurrent collection. The measured responsivity and specific detectivity reach as high as 64.6 A/W and 1.93 × 1012 Jones, respectively, making it a potential candidate for underwater optical detection and communication. The simple fabrication of MXene-GaN-MXene photodetectors spearheaded the way to high performance photodetection by combining the advantages of emerging 2D MXene materials with the conventional III-V materials., A MXene-GaN van der Waals Metal-Semiconductor Junctions based High Performance Multiple Quantum Well Photodetector was demonstrated, which shows great potential for underwater wireless optical communication and turbidity sensing.
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- 2021
7. Depth Dependent Variations in Human Achilles Tendon as a Result of Active Smoking: An Elastographic Study
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Rimsha Siddiqui, Mahdi Alqahtani, Mohammed Almijalli, Eraj Humayun Mirza, and Ravish Javed
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musculoskeletal diseases ,medicine.medical_specialty ,Achilles tendon ,medicine.anatomical_structure ,business.industry ,Ophthalmology ,Depth dependent ,Medicine ,Health Informatics ,Radiology, Nuclear Medicine and imaging ,Active smoking ,musculoskeletal system ,business - Abstract
Current study was set to determine the impact of active smoking on Achilles Tendon (AT) as soft tissue using an elastographic technique. This study comprises of 54 male individuals having sedentary lifestyle. Volunteers were categorized into two groups of smokers (n = 20) and non-smokers (n = 34). Body composition analysis was performed to evaluate the physiological changes in human body mass indexes. Ultrasound Strain Elastog-raphy (USE) technique was used to find the stiffness along with anatomical images to envisage the anomalous status of Achilles tendon. Statistical analysis of data obtained through body composition, tendon anatomy and Strain Elastography (SE) was used to scrutinize the physiological, anatomical and elasticity variations within the tendon. A reduction in Fat Free Mass Index (FFMI) was observed among smokers with a significant difference (P = 0.042). Further, an increased significant difference (P = 0.029) was found in AT Strain Ratios (SR) of smokers as compared to non-smokers. Lightening in tendon mass and dilution in tendon stiffness indicates that smoking mechanism may generate excessive apoptosis and decrease the density of tenocytes. Nicotine is the key element that inhibits the functional capacity of Tendon Stem Cells and is highly responsible for tendinopathy, eventually leading to tendon rupture and injury.
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- 2021
8. Influence of body mass index and weight lifting on bicep brachii muscle and distal bicep tendon stiffness evaluated using ultrasound elastography
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Omar Altuwaijri, Majed Z. Al-Enezi, Meteb Altaf, Mahmoud M. A. Abulmeaty, Ravish Javed, and Mahdi Alqahtani
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Adult ,Male ,lcsh:Medical technology ,Weight Lifting ,Bicep brachii ,Concentric ,Strain ratio ,Tendons ,Young Adult ,03 medical and health sciences ,0302 clinical medicine ,Ultrasound ,Humans ,Medicine ,Eccentric ,Radiology, Nuclear Medicine and imaging ,Prospective Studies ,Muscle, Skeletal ,Body mass index ,Sedentary lifestyle ,Orthodontics ,business.industry ,Tendon stiffness ,030229 sport sciences ,Bicep brachii muscle ,Distal bicep tendon ,Elasticity ,Tendon ,medicine.anatomical_structure ,lcsh:R855-855.5 ,Elasticity Imaging Techniques ,Sedentary Behavior ,Underweight ,medicine.symptom ,business ,Elastography ,030217 neurology & neurosurgery ,Research Article - Abstract
Background This study aimed to investigate the relationship between stiffness of the bicep brachii muscle (BBM) and distal bicep tendon (DBT) and effects of weight lifting (pre- to post-workout changes) among groups with different body mass indexes (BMI). Methods Participants were divided into four groups according to BMI: A, underweight (2); B, normal (18.5–24.9 kg/m2); C, overweight (25.0–29.9 kg/m2); and D, obese (> 30.0 kg/m2). All participants were males who were untrained and had sedentary lifestyle without involvement in sports activities for the past 12 months. Ultrasonographic measurements to determine muscle and tendon stiffness was performed on the dominant side (i.e., right side) of the upper extremities in all participants. Results Twenty-one healthy and untrained males volunteered to participate in this study; 14 were nonsmokers and 7 were smokers. The mean age and BMI were 22.5 ± 1.5 years and 23.8 ± 6.3 kg/m2, respectively. Groups A, B, C, and D had four, ten, four, and three participants, respectively. The BBM thickness did not increase with increase in BMI and was not significantly different (P > .05) between groups. The BBM stiffness was significantly different (all P Conclusions Our study revealed that the BBM thickness is independent of BMI. After weight lifting, BBM stiffness in groups A and B increased for BBM compared to those in groups C and D. A similar trend was also recorded for DBT. Weight lifting in concentric and eccentric motions affects the stiffness of the BBM and DBT, thus weight lifting plays a role in adjusting the stiffness of the BBM and DBT. Trial registration The study was approved by ethics committee of the College of Applied Medical Sciences (CAMS 080-3839; March 14, 2018).
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- 2020
9. Elastographic Measurement of Strain Ratio in Finger Tendons of Weight Lifters and Non-Weight Lifters
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Eraj Humayun Mirza, Alwaleed Aldawsari, Ravish Javed, Mahdi Alqahtani, and Abdulmajeed Almutrafi
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body regions ,Materials science ,medicine ,Health Informatics ,Radiology, Nuclear Medicine and imaging ,Strain (injury) ,Weight lifters ,musculoskeletal system ,medicine.disease ,Biomedical engineering - Abstract
This study aimed to determine the difference in stiffness and thickness of finger tendons between individuals who performed weight lifting (trained subjects) and those who did not perform weightlifting (untrained subjects) as well as provide real-time diagnosis of tendon stiffness. The study was divided into two groups according to their physical activity level. Individuals who performed training for their upper body for a minimum of 30 minutes, 5 days a week for at least 6 months were categorized as trained individuals, whereas those who did not train were categorized as untrained individuals. Tendon strain ratio and thickness of the index and middle fingers and body mass index (BMI) of trained and untrained adult males were measured. A total of 20 healthy individuals were enrolled for the study. Untrained individuals tended to have higher strain ratios than trained individuals. Tendon thickness between the groups was slightly different. Increased BMI was found in untrained individuals. Trained individuals had stiffer finger tendons than untrained individuals. Different activities, sedentary lifestyles or lifting weight can substantially affect the properties and size of the tendon, which can lead to strengthening or weakening of the finger tendon.
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- 2020
10. Enhanced Photocatalytic and Antibacterial Ability of Cu-Doped Anatase TiO2 Thin Films: Theory and Experiment
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John Buckeridge, Andreas Kafizas, Benjamin A. D. Williamson, Abdullah M. Alotaibi, Sean P. Nair, Carlos Sotelo-Vazquez, Sanjayan Sathasivam, Ivan P. Parkin, Mahdi Alqahtani, David O. Scanlon, Jiang Wu, and The Royal Society
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Anatase ,Staphylococcus aureus ,Materials science ,Photoluminescence ,Ultraviolet Rays ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,01 natural sciences ,09 Engineering ,Catalysis ,Escherichia coli ,TiO2 ,General Materials Science ,Nanoscience & Nanotechnology ,Thin film ,Nanoscopic scale ,Titanium ,Photoelectron Spectroscopy ,Doping ,Models, Theoretical ,021001 nanoscience & nanotechnology ,CVD ,hybrid-DFT ,0104 chemical sciences ,Anti-Bacterial Agents ,antibacterial ,Chemical engineering ,thin films ,Photocatalysis ,Thermodynamics ,03 Chemical Sciences ,0210 nano-technology ,Antibacterial activity ,photocatalysis ,Copper ,Research Article - Abstract
Multifunctional thin films which can display both photocatalytic and antibacterial activity are of great interest industrially. Here, for the first time, we have used aerosol assisted chemical vapour deposition (AACVD) to deposit highly photoactive thin films of Cu-doped anatase TiO2 on glass substrates. The films displayed much enhanced photocatalytic activity relative to pure anatase, and showed excellent antibacterial (vs S.Aureus and E.Coli) ability. Using a combination of transient absorption spectroscopy (TAS), photoluminescence (PL) measurements and hybrid density functional theory calculations, we have gained nanoscopic insights into the improved properties of the Cu-doped TiO2 films. Our analysis has highlighted that the interactions between substitutional and interstitial Cu in the anatase lattice can explain the extended exciton lifetimes observed in the doped samples, and the enhanced UV/visible light photoactivities observed.
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- 2020
11. Heteroepitaxy of GaP on silicon for efficient and cost-effective photoelectrochemical water splitting
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Sanjayan Sathasivam, Eunsoo Kim, Yuriy I. Mazur, Christopher S. Blackman, Gregory J. Salamo, Xueming Xia, Ivan P. Parkin, Ludmilla Steier, Mourad Benamara, Huiyun Liu, Hyunjung Shin, Fan Cui, Jiang Wu, and Mahdi Alqahtani
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Technology ,Materials science ,Energy & Fuels ,Silicon ,Hydrogen ,PHOTOCATHODE ,Materials Science ,chemistry.chemical_element ,Materials Science, Multidisciplinary ,02 engineering and technology ,Photocathode ,Atomic layer deposition ,General Materials Science ,Hydrogen production ,Photocurrent ,Science & Technology ,Chemistry, Physical ,Renewable Energy, Sustainability and the Environment ,business.industry ,PHOTOANODES ,0303 Macromolecular and Materials Chemistry ,General Chemistry ,021001 nanoscience & nanotechnology ,Chemistry ,chemistry ,LAYER ,Physical Sciences ,TIO2 ,Optoelectronics ,Reversible hydrogen electrode ,Water splitting ,0210 nano-technology ,business - Abstract
Photoelectrochemical production of hydrogen by using sunlight to split water offers a sustainable approach for clean energy generation. III-V semiconductors have shown the highest efficiencies for photoelectrochemical water splitting but the prohibitive cost of commercial single-crystalline GaP wafers limit practical use and large-scale application. Here, we report a high-quality GaP photocathode directly grown on a silicon substrate by solid-source molecular beam epitaxy. The photocathode can be stabilized under acidic electrolyte 1 M HClO 4 (pH 0) by combining an amorphous TiO 2 layer coated with a molybdenum sulphide MoS 2 hydrogen evolution catalyst by atomic layer deposition (ALD). Under simulated AM 1.5G solar illumination, the Si/GaP photocathode yielded a maximum photocurrent density of 0.95 (mA cm -2 ) with a proton reduction onset potential of 467 mV versus the reversible hydrogen electrode. The average faradaic efficiency of the Si/GaP photocathode was measured to be over 73.4 ± 20.2% for over 100 minutes. The photoelectrochemical studies for the Si/GaP photocathode show the potential for widespread deployment of cost-effective photoelectrodes for hydrogen generation.
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- 2019
12. Body Mass Index and Segmental Mass Correlation With Elastographic Strain Ratios of the Quadriceps Tendon
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Saleh S Altayyar, Mahdi Alqahtani, Ahmed Al‐Suwayyid, Abdulrhman Al‐Musallam, Eraj Humayun Mirza, and Ravish Javed
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Adult ,Male ,Strain (injury) ,Body Mass Index ,Quadriceps Muscle ,030218 nuclear medicine & medical imaging ,Tendons ,Correlation ,Young Adult ,03 medical and health sciences ,0302 clinical medicine ,medicine ,Humans ,Radiology, Nuclear Medicine and imaging ,Mass index ,Prospective Studies ,Sedentary lifestyle ,Orthodontics ,030219 obstetrics & reproductive medicine ,Radiological and Ultrasound Technology ,business.industry ,Ultrasound ,medicine.disease ,Tendon ,medicine.anatomical_structure ,Elasticity Imaging Techniques ,Quadriceps tendon ,business ,Body mass index - Abstract
OBJECTIVES The aim of this study was to establish a relationship between quadriceps tendon stiffness and its properties and variations in the body mass index (BMI) and segmental mass. METHODS This study was conducted in 3 groups according to their BMI (A, low [ 25.0 kg/m2 ]). All of the participants included had a sedentary lifestyle and did not do any weightlifting or any kind of sports activity in the previous 6 months. Ultrasound measurements were performed on the participants' lower right extremities, since it was the dominant side for all of the participants. RESULTS A total of 40 healthy untrained men participated in the study. The mean age of the participants ± SD was 22.1 ± 1.3 years; the age ranges for groups A (n = 6), B (n = 18), and C (n = 16) were 19-23, 19-25, and 20-25 years, respectively; 28 of the participants were nonsmokers, and 12 of were smokers. A strong statistical difference (all P
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- 2018
13. Using a Deep Learning Method and Data from Two-Dimensional (2D) Marker-Less Video-Based Images for Walking Speed Classification
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Kamarul Hawari Ghazali, Mohammad Fazle Rabbi, Saleh S Altayyar, Omar Altwijri, Mahdi Alqahtani, Mohammed Almijalli, Nizam Uddin Ahamed, and Tasriva Sikandar
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2d images ,Computer science ,Movement ,TP1-1185 ,02 engineering and technology ,Walking ,Biochemistry ,Article ,Analytical Chemistry ,rehabilitation ,03 medical and health sciences ,0302 clinical medicine ,gait impairment ,0202 electrical engineering, electronic engineering, information engineering ,Humans ,Computer vision ,human mobility ,Aged care ,Electrical and Electronic Engineering ,Instrumentation ,Video based ,Gait ,Functional movement ,Aged ,business.industry ,Chemical technology ,Deep learning ,quasi-periodic pattern ,deep learning ,Atomic and Molecular Physics, and Optics ,walking speed pattern ,Walking Speed ,Preferred walking speed ,Gait impairment ,marker-less video ,020201 artificial intelligence & image processing ,Artificial intelligence ,business ,LSTM ,walking speed classification ,030217 neurology & neurosurgery ,2D image - Abstract
Human body measurement data related to walking can characterize functional movement and thereby become an important tool for health assessment. Single-camera-captured two-dimensional (2D) image sequences of marker-less walking individuals might be a simple approach for estimating human body measurement data which could be used in walking speed-related health assessment. Conventional body measurement data of 2D images are dependent on body-worn garments (used as segmental markers) and are susceptible to changes in the distance between the participant and camera in indoor and outdoor settings. In this study, we propose five ratio-based body measurement data that can be extracted from 2D images and can be used to classify three walking speeds (i.e., slow, normal, and fast) using a deep learning-based bidirectional long short-term memory classification model. The results showed that average classification accuracies of 88.08% and 79.18% could be achieved in indoor and outdoor environments, respectively. Additionally, the proposed ratio-based body measurement data are independent of body-worn garments and not susceptible to changes in the distance between the walking individual and camera. As a simple but efficient technique, the proposed walking speed classification has great potential to be employed in clinics and aged care homes.
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- 2021
14. Assessment of GaPSb/Si tandem material association properties for photoelectrochemical cells
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Lipin Chen, Rozenn Bernard, Charles Cornet, Soline Boyer-Richard, Yoan Léger, Tony Rohel, Christophe Levallois, Jean-Marc Jancu, Nicolas Bertru, Jiang Wu, Julie Stervinou, Antoine Létoublon, Mahdi Alqahtani, Ivan P. Parkin, Rozenn Piron, Institut des Fonctions Optiques pour les Technologies de l'informatiON (Institut FOTON), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-École Nationale Supérieure des Sciences Appliquées et de Technologie (ENSSAT)-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT), University College of London [London] (UCL), King Abdulaziz City for Science and Technology [Riyadh], Région Bretagne and King Abdulaziz City for Science and Technology (KACST), Riyadh, Saudi Arabia. China Scholarship Council (CSC) for Ph.D financial support (No. 2017-6254). RENATECH (French Network of Major Technology Centers) within Nanorennes for technological support., ANR-14-CE26-0014,ANTIPODE,Analyse approfondie de la nucléation III-V/Si pour les composants photoniques hautement intégrés(2014), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-École Nationale Supérieure des Sciences Appliquées et de Technologie (ENSSAT)-Centre National de la Recherche Scientifique (CNRS), and King Abdulaziz City for Science and Technology [Riyadh] (KACST)
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Materials science ,1.7/1.1eV bandgap combination ,Band gap ,FOS: Physical sciences ,02 engineering and technology ,Applied Physics (physics.app-ph) ,III-V/Si photoelectrode ,tandem material ,010402 general chemistry ,solar water splitting ,01 natural sciences ,7. Clean energy ,[SPI.MAT]Engineering Sciences [physics]/Materials ,Tight binding ,band alignment ,Absorption (electromagnetic radiation) ,Condensed Matter - Materials Science ,Tandem ,Renewable Energy, Sustainability and the Environment ,business.industry ,Oxygen evolution ,Materials Science (cond-mat.mtrl-sci) ,Physics - Applied Physics ,Photoelectrochemical cell ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Optoelectronics ,Direct and indirect band gaps ,0210 nano-technology ,business ,Molecular beam epitaxy - Abstract
International audience; Here, the structural, electronic and optical properties of the GaP 1-x Sb x /Si tandem materials association are determined in view of its use for solar water splitting applications. The GaPSb crystalline layer is grown on Si by Molecular Beam Epitaxy with different Sb contents. The bandgap value and bandgap type of GaPSb alloy are determined on the whole Sb range, by combining experimental absorption measurements with tight binding (TB) theoretical calculations. The indirect (X-band) to direct (Γ-band) cross-over is found to occur at 30% Sb content. Especially, at a Sb content of 32%, the GaP 1-x Sb x alloy reaches the desired 1.7eV direct bandgap, enabling efficient sunlight absorption, that can be ideally combined with the Si 1.1 eV bandgap. Moreover, the band alignment of GaP 1-x Sb x alloys and Si with respect to water redox potential levels has been analyzed, which shows the GaPSb/Si association is an interesting combination both for the hydrogen evolution and oxygen evolution reactions. These results open new routes for the development of III-V/Si low-cost high-efficiency photoelectrochemical cells.
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- 2021
15. A hierarchical 3D TiO2 /Ni nanostructure as an efficient hole-extraction and protection layer for GaAs photoanodes
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Sanjayan Sathasivam, Michael Grätzel, Fan Cui, Ivan P. Parkin, Mohamed Ebaid, Andreas Kafizas, Mahdi Alqahtani, Tung-Chun Lee, Ahmed Y. Alyamani, Hyeon-Ho Jeong, Peer Fischer, Jiang Wu, and The Royal Society
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Nanostructure ,Materials science ,Passivation ,General Chemical Engineering ,0904 Chemical Engineering ,gap ,p-n heterojunction ,02 engineering and technology ,010402 general chemistry ,water splitting ,01 natural sciences ,photoanodes ,solar-energy ,0399 Other Chemical Sciences ,surface ,Environmental Chemistry ,General Materials Science ,Thin film ,business.industry ,GaAs ,Organic Chemistry ,Oxygen evolution ,General Chemistry ,021001 nanoscience & nanotechnology ,recombination ,transient absorption-spectroscopy ,0104 chemical sciences ,Amorphous solid ,General Energy ,water oxidation ,charge-transfer ,Optoelectronics ,Water splitting ,Nanorod ,photogenerated holes ,0210 nano-technology ,business ,nanorods ,transient-absorption spectroscopy ,hematite photoanodes ,Layer (electronics) ,0301 Analytical Chemistry - Abstract
Photoelectrochemical (PEC) water splitting is a promising clean route to hydrogen fuel. The best-performing materials (III/V semiconductors) require surface passivation, as they are liable to corrosion, and a surface co-catalyst to facilitate water splitting. At present, optimal design combining photoelectrodes with oxygen evolution catalysts remains a significant materials challenge. Here, we demonstrate that nickel-coated amorphous three-dimensional (3D) TiO(2)core-shell nanorods on a TiO(2)thin film function as an efficient hole-extraction layer and serve as a protection layer for the GaAs photoanode. Transient-absorption spectroscopy (TAS) demonstrated the role of nickel-coated (3D) TiO(2)core-shell nanorods in prolonging photogenerated charge lifetimes in GaAs, resulting in a higher catalytic activity. This strategy may open the potential of utilizing this low-cost (3D) nanostructured catalyst for decorating narrow-band-gap semiconductor photoanodes for PEC water splitting devices.
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- 2020
16. A Hierarchical 3D TiO
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Mahdi, Alqahtani, Andreas, Kafizas, Sanjayan, Sathasivam, Mohamed, Ebaid, Fan, Cui, Ahmed, Alyamani, Hyeon-Ho, Jeong, Tung, Chun Lee, Peer, Fischer, Ivan, Parkin, Michael, Grätzel, and Jiang, Wu
- Abstract
Photoelectrochemical (PEC) water splitting is a promising clean route to hydrogen fuel. The best-performing materials (III/V semiconductors) require surface passivation, as they are liable to corrosion, and a surface co-catalyst to facilitate water splitting. At present, optimal design combining photoelectrodes with oxygen evolution catalysts remains a significant materials challenge. Here, we demonstrate that nickel-coated amorphous three-dimensional (3D) TiO
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- 2020
17. EMG-Based Classification of Forearm Muscles in Prehension Movements: Performance Comparison of Machine Learning Algorithms
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Sam Matiur Rahman, Omar Altwijri, Mahdi Alqahtani, and Md. Asraf Ali
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Flexor Carpi Ulnaris ,medicine.diagnostic_test ,Computer science ,business.industry ,Electromyography ,Machine learning ,computer.software_genre ,Random forest ,medicine.anatomical_structure ,Forearm ,Margin (machine learning) ,Feature (machine learning) ,medicine ,AdaBoost ,Extensor Carpi Radialis Longus ,Artificial intelligence ,business ,computer ,Algorithm - Abstract
This paper aimed to classify two forearm muscles known as Flexor Carpi Ulnaris (FCU) and Extensor Carpi Radialis Longus (ECRL) using surface Electromyography (sEMG) signal during different hand prehension tasks, such as cylindrical, tip, spherical, palmar, lateral and hook while grasping any object. Thirteen Machine Learning (ML) algorithms were analyzed to compare their performance using a single EMG time domain feature called integrated EMG (IEMG). The tree-based methods have the top performance to classify the forearm muscles than other ML methods among all those 13 ML algorithms. Results showed that 4 out of 5 tree-based classifiers achieved more than 75% accuracies, where the random forest method showed maximum classification accuracy (85.07%). Additionally, these tree-based ML methods computed the variable importance in classification margin. The results showed that the lateral grasping was the most important moving variable for all those algorithms except AdaBoost where tipping was the most significant movement variable for this method. We hope, this ML- and EMG-based classification results presented in the paper may alleviate some of the problems in implementing advanced forearm prosthetics, rehabilitation devices and assistive biomedical robots.
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- 2020
18. Investigation of the EMG activity of erector spinae and trapezius muscles during Islamic prayer (Salat)
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Mahdi Alqahtani, Mohammad Fazle Rabbi, Nizam Uddin Ahamed, Omar Altwijri, Kamarul Hawari Ghazali, and Izzeldin I. Mohd
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Adult ,Male ,musculoskeletal diseases ,Dorsum ,030506 rehabilitation ,medicine.medical_specialty ,Posture ,Paraspinal Muscles ,Physical Therapy, Sports Therapy and Rehabilitation ,02 engineering and technology ,Electromyography ,Sitting ,Islam ,Back muscles ,03 medical and health sciences ,Physical medicine and rehabilitation ,0202 electrical engineering, electronic engineering, information engineering ,medicine ,Erector spinae muscles ,Humans ,Orthopedics and Sports Medicine ,medicine.diagnostic_test ,business.industry ,Rehabilitation ,musculoskeletal system ,Sitting Positions ,body regions ,Superficial Back Muscles ,Female ,020201 artificial intelligence & image processing ,Prostration ,0305 other medical science ,business ,Trapezius muscle - Abstract
This study aimed to investigate the electrical activity of two muscles located at the dorsal surface during Islamic prayer (Salat). Specifically, the electromyography (EMG) activity of the erector spinae and trapezius muscles during four positions observed while performing Salat, namely standing, bowing, sitting and prostration, were investigated. Seven adult subjects with an average age of 28.1 (± 3.8) years were included in the study. EMG data were obtained from their trapezius and erector spinae muscles while the subjects maintained the specific positions of Salat. The EMG signal was analysed using time and frequency domain features. The results indicate that the trapezius muscle remains relaxed during the standing and sitting positions while the erector spinae muscle remains contracted during these two positions. Additionally, during the bowing and prostration positions of Salat, these two muscles exhibit the opposite activities: the trapezius muscle remains contracted while the erector spinae muscle remains relaxed. Overall, both muscles maintain a balance in terms of contraction and relaxation during bowing and prostration position. The irregularity of the neuro-muscular signal might cause pain and prevent Muslims from performing their obligatory prayer. This study will aid the accurate understanding of how the back muscles respond in specific postures during Salat.
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- 2018
19. InGaN/GaN Multiple Quantum Well Photoanode Modified with Cobalt Oxide for Water Oxidation
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Sanjayan Sathasivam, Sultan Ben-Jaber, Abdullah I. Alhassan, Mahdi Alqahtani, Huiyun Liu, Yong Qin, Bin Zhang, Fan Cui, Christopher S. Blackman, Jiang Wu, Shuji Nakamura, and Ivan P. Parkin
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Photocurrent ,Materials science ,Oxygen evolution ,Energy Engineering and Power Technology ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Indium gallium nitride ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Materials Chemistry ,Electrochemistry ,Chemical Engineering (miscellaneous) ,Reversible hydrogen electrode ,Water splitting ,Electrical and Electronic Engineering ,0210 nano-technology ,Cobalt oxide ,Quantum well - Abstract
Indium gallium nitride (InGaN) is an attractive semiconductor, with a tunable direct bandgap for photoelectrochemical water splitting, but it corrodes in aqueous electrolytes. Cobalt oxide (CoOx) is a promising cocatalyst to protect photoelectrodes and accelerate the charge transfer. CoOx is earth-abundant and stable in extremely alkaline conditions and shows high activity for the oxygen evolution reaction (OER). In this work, we demonstrate that CoOx directly deposited onto InGaN/GaN multiple quantum well photoanodes exhibits excellent activity and stability in a strong alkaline electrolyte, 1 M NaOH (pH = 13.7), for water oxidation up to 28 h, while a reference sample without the catalyst degraded rapidly in the alkaline electrolyte. Under simulated solar illumination, the CoOx-modified InGaN/GaN quantum well photoanode showed a high photocurrent density of 1.26 mA cm–2 at 1.23 V and an onset potential of −0.03 V versus a reversible hydrogen electrode.
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- 2018
20. Photoelectrochemical water oxidation of GaP 1−x Sb x with a direct band gap of 1.65 eV for full spectrum solar energy harvesting
- Author
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Charles Cornet, Ivan P. Parkin, Antoine Létoublon, Nicolas Bertru, Rozenn Piron, Sanjayan Sathasivam, Soline Boyer-Richard, Lipin Chen, Yoan Léger, Mahdi Alqahtani, Christophe Levallois, Pamela Jurczak, Jiang Wu, Jean-Marc Jancu, University College of London [London] (UCL), Institut des Fonctions Optiques pour les Technologies de l'informatiON (Institut FOTON), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-École Nationale Supérieure des Sciences Appliquées et de Technologie (ENSSAT)-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT), 14-CE26-0014-01, Agence Nationale de la Recherche, King Abdulaziz City for Science and Technology, Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-École Nationale Supérieure des Sciences Appliquées et de Technologie (ENSSAT)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Photocurrent ,Silicon ,Renewable Energy, Sustainability and the Environment ,business.industry ,Band gap ,Energy Engineering and Power Technology ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Solar energy ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,Artificial photosynthesis ,[SPI.MAT]Engineering Sciences [physics]/Materials ,Monocrystalline silicon ,Fuel Technology ,chemistry ,[SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic ,Optoelectronics ,Reversible hydrogen electrode ,Direct and indirect band gaps ,0210 nano-technology ,business - Abstract
International audience; Hydrogen produced using artificial photosynthesis, i.e. solar splitting of water, is a promising energy alternative to fossil fuels. Efficient solar water splitting demands a suitable band gap to absorb near full spectrum solar energy and a photoelectrode that is stable in strongly alkaline or acidic electrolytes. In this work, we demonstrate for the first time, a perfectly relaxed GaP0.67Sb0.33 monocrystalline alloy grown on a silicon substrate with a direct band gap of 1.65 eV by molecular beam epitaxy (MBE) without any evidence of chemical disorder. Under one Sun illumination, the GaP0.67Sb0.33 photoanode with a 20 nm TiO2 protective layer and 8 nm Ni co-catalyst layer shows a photocurrent density of 4.82 mA cm−2 at 1.23 V and an onset potential of 0.35 V versus the reversible hydrogen electrode (RHE) in 1.0 M KOH (pH = 14) aqueous solution. The photoanode yields an incident-photon-to-current efficiency (IPCE) of 67.1% over the visible range between wavelengths 400 nm to 650 nm. Moreover, the GaP0.67Sb0.33 photoanode was stable over 5 h without degradation of the photocurrent under strong alkaline conditions under continuous illumination at 1 V versus RHE. Importantly, the direct integration of the 1.65 eV GaP0.67 Sb0.33 on 1.1 eV silicon may pave the way for an ideal tandem photoelectrochemical system with a theoretical solar to hydrogen efficiency of 27%.
- Published
- 2019
21. Ensemble-Based Machine Learning Algorithms for Classifying Breast Tissue Based on Electrical Impedance Spectroscopy
- Author
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Nasim Ahmed, Mahdi Alqahtani, Omar Altwijri, Nizam Uddin Ahamed, Sam Matiur Rahman, and Asraf Ali
- Subjects
Boosting (machine learning) ,business.industry ,Computer science ,Deep learning ,Decision tree ,Machine learning ,computer.software_genre ,Ensemble learning ,Random forest ,Tree (data structure) ,Artificial intelligence ,AdaBoost ,Gradient boosting ,business ,Algorithm ,computer - Abstract
The initial identification of breast cancer and the prediction of its category have become a requirement in cancer research because they can simplify the subsequent clinical management of patients. The application of artificial intelligence techniques (e.g., machine learning and deep learning) in medical science is becoming increasingly important for intelligently transforming all available information into valuable knowledge. Therefore, we aimed to classify six classes of freshly excised tissues from a set of electrical impedance measurement variables using five ensemble-based machine learning (ML) algorithms, namely, the random forest (RF), extremely randomized trees (ERT), decision tree (DT), gradient boosting tree (GBT) and AdaBoost (Adaptive Boosting) (ADB) algorithms, which can be subcategorized as bagging and boosting methods. In addition, the ranked order of the variables based on their importance differed across the ML algorithms. The results demonstrated that the three bagging ensemble ML algorithms, namely, RF ERT and DT, yielded better classification accuracies (78–86%) compared with the two boosting algorithms, GBT and ADB (60–75%). We hope that these our results would help improve the classification of breast tissue to allow the early prediction of cancer susceptibility.
- Published
- 2019
22. Patellar Tendon Segmental Strain Ratios using Ultrasound Elastography Technique
- Author
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Wissal Mesfar, Mohamed Zoubir A. Bendjaballah, Mahdi Alqahtani, Eraj Humayun Mirza, and Ravish Javed
- Subjects
musculoskeletal diseases ,Orthodontics ,medicine.diagnostic_test ,business.industry ,Strain (injury) ,musculoskeletal system ,medicine.disease ,Fat pad ,Tendon ,medicine.anatomical_structure ,Medicine ,Elastography ,Tendinopathy ,business ,Body mass index ,Volunteer ,Patellar tendon rupture - Abstract
The purpose of this study is to analyze the values of the stiffness of different segments (proximal, distal and medial) of patellar tendon with respect to Hoffa Fat Pad, which will postulate to the framework in understanding the area bearing more force (stress) for the patellar tendon. It can help in understanding and avoiding the patellar tendon rupture or tendinopathy. Three volunteers were selected for the current study and were classified into three arrangements (weak, normal and obese) according to their Body Mass Index. The first volunteer (A; weak) was having BMI of 16 kg/m2, the second volunteer (B; normal) was having BMI of 22 kg/m2 and the third volunteer (C; obese) was having BMI of 27 kg/m2. All participants were reported to be non-smokers with mean BMI ± SD and mean age ± SD, $21.61 \pm 5.508$ Kg/m2 and $26 \pm 3$ years, respectively. Patellar tendon length and strain ratios reading were performed on the dominant side of each volunteer. All the three segments (proximal, medial and distal) of patellar tendon showed presence of significant difference for most of the readings between the three volunteers, however, a significant difference in length is present for every volunteer. Our findings suggest that strain value at a particular region of a tendon are independent values irrespective of weight, body mass index and physical activity. Though, more research and further studies are required to validate the independence of strain value at a particular region of the patellar tendon.
- Published
- 2019
23. Strain Elastography & Tissue Characterisation as a Tool to Differentiate Tumor from Healthy Tissue
- Author
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Omar Altuwaijri, Mahdi Alqahtani, and Ravish Javed
- Subjects
Strain elastography ,Ultrasound probe ,Pixel ,medicine.diagnostic_test ,Region of interest ,Feature (computer vision) ,medicine ,Healthy tissue ,Elastography ,Imaging phantom ,Mathematics ,Biomedical engineering - Abstract
The purpose of this study was to compare diagnostic values of normal and effected tissues with two techniques using strain elastography and tissues characterization. This study was carried out on a breast phantom containing all human body parameters. Analysis was performed using a lone phantom to correlate a relation between the values of Strain Elastography (SE) and first order texture parameters results. For SE SonixTouch Q+ (Ultrasonix Medical Corporation, 130-4311 Viking Way, Richmond, Canada) device using a linear-array ultrasound probe at a frequency of 10MHz with a gain of 40%. Elastography breast phantom was purchased from CAE healthcare USA, 3600 Edgelake Drive Sarasota FL, USA. For tissue characterization a Region of Interest (ROI) that encompasses both (normal and stiffer) areas were selected. MAZDA software was used to carry out the image analysis (mean and variance) of the tumour and healthy tissue, ROI of 1600 pixels at both regions was selected. An affirmative and resilient outcome was observed between the numerals of normal and tumor tissues, both for SE and first order texture parameters values. After our study we suggest that SE and tissue characterisation via first order texture parameter is a reliable technique to highlight normal and tumor tissue (with respect to same reference, for SE technique only). SE and first order texture parameters (mean and variance) paved way in highlighting the breast tumors fully. It is suggested that SE being more reliable approach in determining the stiffness for breast lesion, as it produces the results with real time imaging. However texture parameter gives an objective assessment of the image with a discriminating feature of the tissue.
- Published
- 2018
24. Influence of gain settings on strain ratios of elastographic image and texture parameters of B-mode image on thyroid tissue
- Author
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Ravish Javed, Eraj Humayun Mirza, Mahdi Alqahtani, and Ramsha Urooj Baig
- Subjects
Pulmonary and Respiratory Medicine ,Thyroid nodules ,medicine.diagnostic_test ,Strain (chemistry) ,business.industry ,Thyroid ,Ultrasound ,medicine.disease ,Imaging phantom ,medicine.anatomical_structure ,Pediatrics, Perinatology and Child Health ,medicine ,Elastography ,Texture (crystalline) ,Gain setting ,business ,Biomedical engineering ,Mathematics - Abstract
Thyroid nodules are benign though suspicious. Examination through elastography technique is beneficial as it provides real time and first hand evidence about the tissue stiffness by providing a strain value on comparing suspected and normal tissue. Until now, there is no established method that allows to categorise strain ratios whether tumour or normal. Changes in gain settings can significantly alter measurement and ultimately the clinical findings. The objectives of this study are to assess the effect of gain settings on strain ratios of isoechoic stiff lesions in a thyroid gland phantom, and the difference in strain ratios with first order texture parameters at different gain settings. In this study we have reported the effect of gain setting parameter on strain ratios of the thyroid tumour. Furthermore, first order texture parameters (mean and variance) were discussed with respect to increase in gain settings. Higher strain ratios were observed as gain increased. Significant differences in first order texture parameters can be observed for mean of tumour when compared with normal thyroid tissue. Variance did not demonstrate any significant difference. It was concluded that gain parameter effect the strain ratios and texture parameters. This may affect the interpretation of results. It is advised to use elastography in combination with B-mode ultrasound, and sonographers must use a balanced approach when changing equipment parameters.
- Published
- 2018
25. In Vitro Characterization of Thermal Behaviour and Bone Marrow Stromal Cell Attachment on Chitosan/Polycaprolactone (CS/PCL) Nanofibrous Scaffolds
- Author
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Mohammed Fayez Al Rez, H. Fouad, Ezzedine Laourine, Martin Hild, Dilbar Aibibu, Chokri Cherif, Amer Mahmood, Sarah Abuelreich, Muthurangan Manikandan, S. W. Gosavi, Mohamed Hashem, S. G. Ansari, Fahad S. Al-Mubaddel, Y. A. Elnakady, and Mahdi Alqahtani
- Subjects
General Materials Science - Published
- 2015
26. SIGNIFICANCE OF ELECTROMYOGRAPHY IN THE ASSESSMENT OF DIABETIC NEUROPATHY
- Author
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Kamarul Hawari Ghazali, Md. Asraf Ali, Nizam Uddin Ahamed, Sam Matiur Rahman, Zahari Taha, Mahdi Alqahtani, Kenneth Sundaraj, Mohammad Fazle Rabbi, and Omar Altwijri
- Subjects
medicine.medical_specialty ,Rehabilitation ,Diabetic neuropathy ,medicine.diagnostic_test ,Diabetes mellitus ,medicine.medical_treatment ,Biomedical Engineering ,medicine ,Physical therapy ,Nerve conduction study ,Electromyography ,medicine.disease - Abstract
Diabetic neuropathy is one of the physical complications of diabetes mellitus (DM) patients with a long history of diabetes. An electromyography (EMG)-based assessment may be very useful for the management of diabetic neuropathy. In the present study, we aimed to summarize all of the findings and recommendations obtained from previous studies that investigated the application of EMG to the assessment of diabetic neuropathy. An extensive search of the prominent electronic databases PubMed, Google Scholar and Scopus was performed to evaluate the following areas: (i) what are the muscles to be evaluated by EMG for neuropathy assessment, (ii) what type of EMG methodologies have been used and (iii) what recommendation can be made for neuropathy detection. The major findings are summarized as follows: (i) very few studies have analyzed the correlation of the EMG signals acquired from peripheral muscles affected in neuropathy with those obtained with non-neuropathic complications, such as ankle sprain; (ii) EMG has been applied for the detection of diabetic neuropathy more than diabetes treatment; and (iii) neuropathy detection using an EMG-based assessment were mainly performed for type 2 DM patients aged at least 50 years.
- Published
- 2019
27. Influence of BMI on Elastographic Strain Ratios of Achilles Tendon
- Author
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Mahdi Alqahtani, Eraj Humayun Mirza, Abdullah Alzahrani, and AbdulAziz Al-Mujalli
- Subjects
musculoskeletal diseases ,Achilles tendon ,medicine.medical_specialty ,business.industry ,nutritional and metabolic diseases ,030209 endocrinology & metabolism ,Strain (injury) ,030229 sport sciences ,Overweight ,musculoskeletal system ,medicine.disease ,Surgery ,03 medical and health sciences ,0302 clinical medicine ,medicine.anatomical_structure ,Achilles tendon injury ,medicine ,Achilles tendon rupture ,medicine.symptom ,Tendinopathy ,Underweight ,business ,Body mass index - Abstract
The Achilles tendon have two major problems due to injury; one being a chronic injury called Achilles tendinopathy and the second being acute injury which are more commonly known as Achilles tendon rupture. Changes in stiffness of Achilles tendon is alarming and can cause deleterious effects on quality of life in an individual. Achilles tendon is reported to be affected significantly due to the weight of an individual. The effect of Body Mass Index (BMI) on stiffness of Achilles tendon was evaluated in the current study. Elastography was performed on individuals ranging from 19 to 23 years for detecting the stiffness of the Achilles tendon. Individuals were grouped according to their BMI in 3 categories (underweight, normal and overweight) and their strain ratios were measured. The strain ratio results for all volunteers were ranging from 1.03 to 6 (1.03 for underweight and 6 for overweight). Difference in weight of individuals effect the Achilles tendon stiffness. The overweight individuals had the highest stiffness while the underweight individuals had the lowest. It is concluded that higher stiffness may likely lead to Achilles tendon injury.
- Published
- 2016
28. Relationship Between EMG Activity and Endurance Time of the Biceps Brachii During Isokinetic Contraction
- Author
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Omar Altwijri, Nizam Uddin Ahamed, Kenneth Sundaraj, Mahdi Alqahtani, Nasir Ahmed, and S. A. M. Matiur Rahman
- Subjects
Root mean square ,Motor unit ,medicine.medical_specialty ,Contraction (grammar) ,medicine.anatomical_structure ,Physical medicine and rehabilitation ,Biomechanics ,medicine ,Upper limb ,Physical strength ,Biceps ,Mathematics ,Rehabilitation engineering - Abstract
Studies of the surface electromyographic or EMG signal on the skeletal muscles have provided valuable information on the physiology to understand the motor unit activity strategy during contraction. This paper investigated the relationship between EMG and time during isokinetic contraction (a type of exercises or movement to increase muscular strength) from the upper limb’s biceps brachii (BB) muscle. Five right-hand-dominated male subjects (age 23.2 ± 1.6 years) participated in the study. The muscle activation during load lifting (using a standard 6-kg dumbbell) was determined as the root mean square (RMS) electromyographic signal normalized to the peak RMS EMG signal of a maximal contraction for 10 s. For the statistical analysis, the slope of the regression relationship was used to test the relationships between EMG and time from the maximal voluntary isokinetic contraction (MVC). The measurement duration (10 s) was divided into four phases for analyzing the relationship. The results of the study showed a linear but poor relationship between EMG and time during such contraction, where r 2 = 0.11 and F = 3.74. Also, no significant difference exits from the analysis where, P = 0.062. These results provided insight toward applications of biomedical engineering methods in the analysis and control of the neuromuscular system, ergonomics field of research, rehabilitation engineering, and movement biomechanics during such type of dynamic contraction.
- Published
- 2016
29. High Speed and Stable Solution-Processed Triple Cation Perovskite Photodetectors
- Author
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Shibin Li, Ting Zhang, Waseem Ahmad, Mahdi Alqahtani, Jiang Wu, Chunming Gao, Zhi David Chen, Peng Zhang, Hao Chen, Zhiming Wang, and Yafei Wang
- Subjects
Materials science ,business.industry ,Schottky barrier ,Bandwidth (signal processing) ,Optical communication ,Photodetector ,02 engineering and technology ,Photodetection ,Specific detectivity ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Optoelectronics ,0210 nano-technology ,business ,Low voltage ,Dark current - Abstract
Photodetectors, which can convert light signals into electrical signals, are important opto‐electronic devices in imaging, optical communication, biomedical/biological sensing, and so on. Here a solution‐processed photodetector based on the triple cation perovskite is demonstrated. The perovskite photodetectors show a high detectivity, high speed, as well as excellent environmental stability. Operating at a low voltage bias of 2 V, the photodetectors exhibit a large on/off ratio of 105, high specific detectivity of ≈1013 Jones, and a fast photoresponse with 3 dB bandwidth up to 0.82 MHz. Further analysis demonstrates that such performance originates from the modulated Schottky barrier height by illumination. The barrier suppresses dark current without any illumination, but it can be effectively lowered under illumination, thus resulting in a more efficient charge extraction and collection. The results demonstrate a great potential of triple cation perovskite in photodetection and provide a route to achieve high performance devices.
- Published
- 2018
30. Relation between EMG signal activation and time lags using feature analysis during dynamic contraction
- Author
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Nasim Ahmed, Omar Altwijri, S. A. M. Matiur Rahaman, Kenneth Sundaraj, Nizam Uddin Ahamed, and Mahdi Alqahtani
- Subjects
Correlation ,Root mean square ,Coefficient of determination ,Amplitude ,Coefficient of variation ,Speech recognition ,Statistics ,Regression analysis ,Analysis of variance ,Biceps ,Mathematics - Abstract
This study examined the effects of electromyographic (EMG) signals from Biceps Brachii (BB) muscle on the root mean square (RMS)-time relationships during dynamic contraction. Ten healthy and right hand dominated male subjects were volunteered for the experiments. The RMS features were extracted from the corresponding EMG signals (amplitude of the full wave EMG) for 10 seconds in 5 minutes intervals between each trial. Ten seconds (or 10000 ms) were divided into 4 time lags to identify the muscle activity and relationship between EMG and time using different statistical analysing techniques, such as mean, regression analysis, correlation, ANOVA, and coefficient of variation (CoV) for muscle activity variation. The results shows that large positive linear association between EMG and endurance time where the points are close to the linear trend line (R squared = 0.93 and F-ratio = 453.1). Signal steadiness is better during last time lags (1.66% during 7501–10000 ms) compared to initial time duration (10.35% during 0–2500 ms).
- Published
- 2015
31. A Comparative Study of Shear-Wave Elastography and Strain Elastography on a Breast Phantom for Diagnosis of Tumor and Cyst
- Author
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Mubarak Dhafer Al-Qahtani, Mahdi Alqahtani, Eraj Humayun Mirza, and Mohammed Fahad Al-Muqati
- Subjects
medicine.medical_specialty ,Strain elastography ,medicine.diagnostic_test ,business.industry ,Ultrasound ,medicine.disease ,Imaging phantom ,Breast phantom ,body regions ,Breast cancer ,Medicine ,Mammography ,Cyst ,Radiology ,Elastography ,skin and connective tissue diseases ,business - Abstract
A lump in breast may suggest a possible development of breast cancer. As the tumor develops, it changes the physical property of the tissue by changing its stiffness. To detect the tumor generally mammography is performed. The findings of mammography are often inaccurate as it does not take into account the stiffness of tissue. Elastography is an imaging technique to measure the stiffness of tissues. In the current study, we have used a breast phantom to analyze differences between a tumor and a cyst via comparing shear-wave elastography and strain elastography techniques. Both the techniques performed equally for the diagnosis of tumour. However, it is suggested that strain elastography must be used in the diagnosis of a cyst as it provides enhanced details of the surrounding tissues.
- Published
- 2015
32. EMG-force relationship during static contraction: Effects on sensor placement locations on biceps brachii muscle
- Author
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Asraf Ali, Kenneth Sundaraj, Mahdi Alqahtani, Omar Altwijri, Anamul Islam, and Nizam Uddin Ahamed
- Subjects
Adult ,Male ,Coefficient of variation ,Biomedical Engineering ,Biophysics ,Health Informatics ,Bioengineering ,Muscle Strength Dynamometer ,Isometric exercise ,Electromyography ,Biceps ,Biomaterials ,Root mean square ,Linear regression ,medicine ,Humans ,Muscle, Skeletal ,Mathematics ,Analysis of Variance ,medicine.diagnostic_test ,Repeated measures design ,Muscle belly ,Anatomy ,Arm ,Linear Models ,Muscle Contraction ,Information Systems ,Biomedical engineering - Abstract
The relationship between surface electromyography (EMG) and force have been the subject of ongoing investigations and remain a subject of controversy. Even under static conditions, the relationships at different sensor placement locations in the biceps brachii (BB) muscle are complex.The aim of this study was to compare the activity and relationship between surface EMG and static force from the BB muscle in terms of three sensor placement locations.Twenty-one right hand dominant male subjects (age 25.3 ± 1.2 years) participated in the study. Surface EMG signals were detected from the subject's right BB muscle. The muscle activation during force was determined as the root mean square (RMS) electromyographic signal normalized to the peak RMS EMG signal of isometric contraction for 10 s. The statistical analysis included linear regression to examine the relationship between EMG amplitude and force of contraction [40-100% of maximal voluntary contraction (MVC)], repeated measures ANOVA to assess differences among the sensor placement locations, and coefficient of variation (CoV) for muscle activity variation.The results demonstrated that when the sensor was placed on the muscle belly, the linear slope coefficient was significantly greater for EMG versus force testing (formular^{2}/formula= 0.61, P0.05) than when placed on the lower part (formular^{2}/formula=0.31, P0.05) and upper part of the muscle belly (formular^{2}/formula=0.29, P0.05). In addition, the EMG signal activity on the muscle belly had less variability than the upper and lower parts (8.55% vs. 15.12% and 12.86%, respectively).These findings indicate the importance of applying the surface EMG sensor at the appropriate locations that follow muscle fiber orientation of the BB muscle during static contraction. As a result, EMG signals of three different placements may help to understand the difference in the amplitude of the signals due to placement.
- Published
- 2014
33. Investigation of the EMG-time relationship of the biceps Brachii muscle during contractions
- Author
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Nizam Uddin Ahamed, Omar Altwijri, R. Badlishah Ahmad, Mahdi Alqahtani, Nasim Ahmed, and Kenneth Sundaraj
- Subjects
Contraction ,Contraction (grammar) ,Biceps brachii muscle ,business.industry ,Time lag ,Physical Therapy, Sports Therapy and Rehabilitation ,Muscle belly ,Anatomy ,Isometric exercise ,Concentric ,Biceps ,EMG ,Medicine ,Eccentric ,Original Article ,business ,Simulation - Abstract
[Purpose] This study investigated the changes in the slope of EMG-time curves (relationship) at the maximal and different levels of dynamic (eccentric and concentric) and static (isometric) contractions. [Subjects and Methods] The subject was a 17 year-old male adolescent. The surface EMG signal of the dominant arm's biceps brachii (BB) was recorded through electrodes placed on the muscle belly. [Results] The results obtained during the contractions show that the regression slope was very close to 1.00 during concentric contraction, whereas those of eccentric and isometric contractions were lower. Significant differences were found for the EMG amplitude and time lags among the contractions. [Conclusion] The results show that the EMG signal of the BB varies among the three modes of contraction and the relationship of the EMG amplitude with a time lag gives the best fit during concentric contraction.
- Published
- 2015
34. Age Related Differences in the Surface EMG Signals on Adolescent's Muscle during Contraction
- Author
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Omar Altwijri, Mahdi Alqahtani, Nizam Uddin Ahamed, Matiur Rahman, Zahari Taha, and Abdelhakim Deboucha
- Subjects
medicine.medical_specialty ,Contraction (grammar) ,business.industry ,Coefficient of variation ,Biomechanics ,Repeated measures design ,030229 sport sciences ,Biceps ,Correlation ,03 medical and health sciences ,0302 clinical medicine ,Physical medicine and rehabilitation ,Age related ,Linear regression ,Physical therapy ,Medicine ,business ,030217 neurology & neurosurgery - Abstract
The aim of this study was to investigate whether there are differences in the amplitude of the EMG signal among five different age groups of adolescent's muscle. Fifteen healthy adolescents participated in this study and they were divided into five age groups (13, 14, 15, 16 and 17 years). Subjects were performed dynamic contraction during lifting a standard weight (3-kg dumbbell) and EMG signals were recorded from their Biceps Brachii (BB) muscle. Two common EMG analysis techniques namely root mean square (RMS) and mean absolute values (MAV) were used to find the differences. The statistical analysis was included: linear regression to examine the relationships between EMG amplitude and age, repeated measures ANOVA to assess differences among the variables, and finally Coefficient of Variation (CoV) for signal steadiness among the groups of subjects during contraction. The result from RMS and MAV analysis shows that the 17-years age groups exhibited higher activity (0.28 and 0.19 mV respectively) compare to other groups (13-Years: 0.26 and 0.17 mV, 14-years: 0.25 and 0.23 mV, 15-Years: 0.23 and 0.16 mV, 16-years: 0.23 and 0.16 mV respectively). Also, this study shows modest correlation between age and signal activities among all age group's muscle. The experiential results can play a pivotal role for developing EMG prosthetic hand controller, neuromuscular system, EMG based rehabilitation aid and movement biomechanics, which may help to separate age groups among the adolescents.
- Published
- 2016
35. Gender Effects in Surface Electromyographic Activity of the Biceps Brachii Muscle During Prolonged Isometric Contraction
- Author
-
Mahdi Alqahtani, Zulkifli bin md yusof, Nizam Uddin Ahamed, S. A. M. Matiur Rahman, Kenneth Sundaraj, and Omar Altwijri
- Subjects
medicine.medical_specialty ,Contraction ,Biceps brachii muscle ,medicine.diagnostic_test ,Computer science ,Electromyography ,Biomechanics ,Gender ,Isometric exercise ,RMS ,musculoskeletal system ,Biceps ,Rehabilitation engineering ,body regions ,Physical medicine and rehabilitation ,EMG ,Biceps Brachii ,medicine ,General Earth and Planetary Sciences ,Muscle activity ,General Environmental Science - Abstract
The muscle activity, electromyographic (EMG) signal steadiness and relationships between the EMG signal and endurance time among males and females have long been investigated and continue to be a subject of controversy. The aim of this study was to explore the electromyographic effects on the biceps brachii (BB) muscle of male and female subjects during prolonged isometric contraction (for 90 s). Twenty right-handed (10 male and 10 female) subjects participated in this study. The EMG analysis was accomplished in the time domain by calculating the amplitude content of the signals as the root mean square (EMG-RMS). The statistical analysis included linear regression to examine the relationships between the EMG amplitude (%MVC) and the endurance time, repeated-measures ANOVA to assess differences among the variables, and calculation of the coefficient of variation (CoV) to assess the steadiness of the signal. The results revealed that the linear slope coefficient of the EMG as a function of time (r2 = 0.56, p < 0.05) obtained for male subjects during contraction was significantly greater than that obtained for females (r2 = 0.11, p > 0.05). Additionally, the EMG signal activity generated by the male BB muscle (10.25%) exhibits less variability than that generated by the female BB muscle (12.11%). The experimental results indicate the suitability of developing an EMG prosthetic hand controller and the use of EMG analysis in the fields of neuromuscular system research, rehabilitation engineering and movement biomechanics, which may help separate male and female subjects.
- Full Text
- View/download PDF
36. Fuzzy logic-based improved ventilation system for the pharmaceutical industry
- Author
-
Kenneth Sundaraj, Mohammad Fazle Rabbi, Omar Altwijri, Tasriva Sikandar, Mahdi Alqahtani, Izzeldin Ibrahim Abdelaziz, Md. Asraf Ali, and Sam Matiur Rahman
- Subjects
Environmental Engineering ,Computer science ,business.industry ,020209 energy ,General Chemical Engineering ,General Engineering ,ComputerApplications_COMPUTERSINOTHERSYSTEMS ,02 engineering and technology ,010501 environmental sciences ,01 natural sciences ,Fuzzy logic ,Manufacturing engineering ,law.invention ,Hardware and Architecture ,law ,Ventilation (architecture) ,0202 electrical engineering, electronic engineering, information engineering ,Computer Science (miscellaneous) ,business ,0105 earth and related environmental sciences ,Biotechnology ,Pharmaceutical industry - Abstract
Indoor air quality in pharmaceutical industry plays a vital role in the production and storing of medicine. Stable indoor environment including favorable temperature, humidity, air flow and number of microorganisms requires consistent monitoring. This paper aimed to develop a fuzzy logic-based intelligent ventilation system to control the indoor air quality in pharmaceutical sites. Specifically, in the proposed fuzzy inference system, the ventilation system can control the air flow and quality in accordance with the indoor temperature, humidity, air flow and microorganisms in the air. The MATLAB® fuzzy logic toolbox was used to simulate the performance of the fuzzy inference system. The results show that the efficiency of the system can be improved by manipulating the input-output parameters according to the user’s demands. Compared with conventional heating, ventilation and air-conditioning (HVAC) systems, the proposed ventilation system has the additional feature of the existence of microorganisms, which is a crucial criterion of indoor air quality in pharmaceutical laboratories.
37. Age Related Differences in the Surface EMG Signals on Adolescent's Muscle during Contraction.
- Author
-
Nizam Uddin Ahamed, Zahari Taha, Mahdi Alqahtani, Omar Altwijri, Matiur Rahman, and Abdelhakim Deboucha
- Published
- 2016
- Full Text
- View/download PDF
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