146 research outputs found
Gravity gradient effect on a LEO satellite with an elliptic orbit and unsymmetrical mass properties
No full textCorresponding Author:
Mechanical Engineering Department, College of Engineering, King Saud University, P.O. Box 800
Riyadh-11421, Saudi Arabia
Telehone: +966-1-4676659
Email: [email protected] study presented in this paper investigates the dynamic behavior of a low earth orbit (LEO) satellite due to gravity gradient disturbances when the product of inertia terms of the spacecraft and the orbit eccentricity are considered. It is shown that the classical stable solution for the gravity gradient disturbance becomes unstable if at least one product of inertia term exceeds a critical value. Dimensional analysis technique is used to develop the significant dimensionless groups which were used to correlate the data generated from the response of the coupled roll, pitch and yaw dynamics. Based on the findings of these groups, stability maps are developed to predict the influence of the product of inertia terms on the long-term behavior of the spacecraft attitude dynamics. The developed stability maps are verified numerically and successful prediction of a spacecraft stability condition due to gravity gradient disturbance is achieved
WIDE-BANDWIDTH COMB-ASSISTED SPECTROSCOPY IN THE FINGERPRINT REGION AND APPLICATION TO THE ν1 FUNDAMENTAL BAND OF 14N216O
No full textMost spectroscopic data available in databases such as HITRAN are retrieved from FTIR measurements and suffer from uncertainties at the MHz level. Much more accurate data, by up to four orders of magnitude, can be achieved using an optical frequency comb to calibrate the frequency axis of a cw laser source. Actually, in the mid-infrared region, at least beyond 5 m, the only available commercial solution for a widely tunable cw laser is represented by extended cavity quantum cascade lasers (EC-QCLs), whose locking to an optical frequency comb has been so far inhibited by a large amount of frequency noise, leading to linewidths of about 20 MHz \footnote{Knabe K., Williams P. A., Giorgetta F., Armacost C. M., Crivello S., Radunsky M., and Newbury N., Opt. Express 20, 12432-12442 (2012)}.
In this work we overcome this limitation and describe a spectrometer that relies on the frequency locking of an EC-QCL tunable in the 7.55-8.2 m range to a 1.9 m Tm fiber comb \footnote{Lamperti M., Alsaif B., Gatti D., Fermann M., Farooq A., and Marangoni M., Sci. Rep. 8,1292 (2018)}. It is applied to the first comb-calibrated direct characterisation of the \nub{1} fundamental band of \chem{N_2O}, specifically of nearly 70 lines in the 1240 – 1310 \wn range, from P(40) to R(31). The spectroscopic constants of the upper state are derived from a fit of the line centers with an average rms uncertainty of 4.8x10 \wn(144 kHz). The coupling of the spectrometer to a high-finesse optical cavity to the purpose of enhancing its sensitivity and addressing weaker absorbers, is also discussed
Melioidosis: Spectrum of radiological manifestations
No full textMelioidosis, a bacterial infection caused by Burkholderia pseudomallei is expanding in its endemicity around the world. Melioidosis most commonly infects adults with an underlying predisposing condition, mainly diabetes mellitus. Primary skin and soft tissue involvement is more common in younger patients. Almost every organ can be affected, but the most commonly affected organ is the lung followed by the spleen. Melioidosis has a wide range of radiological manifestations making it a mimicker. Diagnosis requires a high index of clinical suspicion in patients with septicemia or a fever of unknown origin living in or with a travel history to endemic areas. We present a pictorial review of the radiological manifestations of melioidosis, which is a useful knowledge for radiologists to help arrive at an early diagnosis. In this pictorial review, we present the radiological manifestations chosen from 139 patients with culture proven melioidosis. Illustrated examples are chosen from our clinical experience of the past 15 years at the National University Hospital in Singapore
Hybrid technique for image compression based on five modulus method and K-L-Transform
No full textCompression is one of the important field in digital image processing , due to that a lot of technique were adopted in this field.
In this research a five modulus was applied on image compression then try to hybrid it with K-L-Transform ,then studying the efficiency of each of them individually in addition to the hybrid technique .
The hybrid technique give very efficient compression ratio and also the original and retrieved image are very closed to each of them Measuring the correlation factor ,PSNR and MSE shows approach high recommended for approach
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Diabetes and obesity in adult Saudi population
No full textIn this series of studies, three issues were addressed. First, the prevalence of undiagnosed diabetes (high fasting blood glucose with no prior diagnosis of diabetes) and how different they are from the diagnosed diabetes in risk factors. Second, the prevalence and risk factors of overweight and obesity were described in the general population. Finally, an evaluation of the relationship between obesity and type 2 diabetes were made in Saudi adult men and women. Our study population came from a national cross sectional survey which included 3271 males and females, age 30-70 years old. All participants completed a specifically designed questionnaire, and a comprehensive physical examination which included blood pressure and anthropometric measurements. Fasting serum samples were analyzed for glucose and blood lipids. A number of compelling findings have resulted from this research. First, the prevalence of diabetes is high with 30% of men and 25% of women diabetics. Undiagnosed diabetes presents a substantial problem; they constitute 41% of the total diabetic population and 11% of the total population. Undiagnosed diabetics are however, similar to diagnosed diabetes with uncontrolled fasting blood glucose level and many of the associated risk factors. Second, the prevalence of obesity is also high with 49.15% in women and 29.94% in men identified as obese and an additional 31.55% of females and 41.91% of males identified as overweight. Third, in this study population, 12% are obese diabetics and in the diabetic population 43% are obese diabetics. Diabetes appears to have a harmful effect on blood lipids, which seem to worsen when diabetes is combined with obesity. Based on these findings, obesity and diabetes appear to have created very serious complications and prevalent health problems in adult Saudi population between the age of 30-70 years old. Because about half of the population are under 18 years old, there is a very good chance for the government to successfully implement education and health programs to prevent and control these two conditions from becoming an epidemic in future generations
Comprehensive collection of uniaxial stress-strain data for rubberized concreteMendeley Data
No full textThis dataset article encompasses a thorough compilation of 80 uniaxial stress-strain datasets obtained from cylindrical rubberized concrete specimens subjected to compression testing. Data collection was meticulously conducted through a systematic review and extraction of stress-strain datasets from 68 rubberized concrete mixtures sourced from diverse literature references, incorporating rubber of different origins, sizes, volumes and characteristics. Additionally, stress-strain data for 48 cylindrical specimens, representing 12 different mixes with various rubber sizes and contents, were obtained from laboratory experiments performed by the author. The datasets provide valuable insights for researchers interested in the compressive behavior of rubberized concrete and offers valuable resources for further analysis and modeling studies
Fault Identification and Classification of Asynchronous Motor Drive Using Optimization Approach with Improved Reliability
No full textThis article aims to provide a technique for identifying and categorizing interturn insulation problems in variable-speed motor drives by combining Salp Swarm Optimization (SSO) with Recurrent Neural Network (RNN). The goal of the proposed technique is to detect and classify Asynchronous Motor faults at their early stages, under both normal and abnormal operating conditions. The proposed technique uses a recurrent neural network in two phases to identify and label interturn insulation concerns, with the first phase being utilised to establish whether or not the motors are healthy. In the second step, it discovers and categorises potentially dangerous interturn errors. The SSO approach is used in the second phase of the recurrent neural network learning procedure, with the goal function of minimizing error in mind. The proposed CSSRN technique simplifies the system for detecting and categorizing the interturn insulation issue, resulting in increased system precision. In addition, the proposed model is implemented in the MATLAB/Simulink, where metrics such as accuracy, precision, recall, and specificity may be analysed. Similarly, existing methods such as Adaptive Neuro-Fuzzy Inference System (ANFIS), Recurrent Neural Network (RNN), and Salp Swarm Algorithm Artificial Neural Network (SSAANN) are utilised to evaluate metrics such as Root mean squared error (RMSE), Mean bias error (MBE), Mean absolute percentage error (MAPE), consumption, and execution time for comparative analysis
Medical students’ perception of the learning environment at King Saud University Medical College, Saudi Arabia, using DREEM Inventory
No full textMona M Soliman,1,2 Kamran Sattar,2 Sami Alnassar,3 Faisal Alsaif,4 Khalid Alswat,5 Mohamed Alghonaim,6 Maysoon Alhaizan,7 Nawaf Al-furaih7 1Department of Physiology, 2Department of Medical Education, 3Department of Surgery, College of Medicine, King Saud University, 4Department of Surgery, King Saud University Medical City, 5Department of Internal Medicine, 6Department of Medicine, 7College of Medicine, King Saud University, Riyadh, Saudi Arabia Background: The students’ perception of the learning environment is an important aspect for evaluation and improvement of the educational program. The College of Medicine at King Saud University (KSU) reformed its curriculum in 2009 from a traditional to a system-oriented hybrid curriculum.Objective: The objective of the present study was to determine the perception of the second batch (reformed curriculum) of medical graduates about the educational environment at the College of Medicine, KSU, using the Dundee Ready Education Environment Measure (DREEM) scale.Methods: The fifth year medical students were asked to evaluate the educational program after graduation in May 2014. The questionnaire was distributed to the graduate students electronically. The DREEM questionnaire consisted of 50 items based on Likert’s scale; and five domains, namely, students’ perceptions of learning, perceptions of teachers, academic self-perceptions, perceptions of atmosphere, and social self-perceptions. Data were analyzed using SPSS.Results: A total of 62 students participated in the study. The score for students’ perception of learning among medical students ranged from 2.93 to 3.64 (overall mean score: 40.17). The score for students’ perception of teachers ranged from 2.85 to 4.01 (overall mean score: 33.35). The score for students’ academic self-perceptions ranged from 3.15 to 4.06 (overall mean score: 28.4). The score for students’ perception of atmosphere ranged from 2.27 to 3.91 (overall mean score: 41.32). The score for students’ social self-perceptions ranged from 2.85 to 4.33 (overall mean score: 24.33). The general perceptions of the students in all five sub-scales were positive.Conclusion: The overall student’s perception about the educational environment was satisfactory. This study was important to evaluate the students’ perception of the learning environment among medical graduates of the reformed curriculum and provided guidance on areas of improvement in the curriculum. Keywords: medical students, perception, learning environment, DREEM inventory, Saudi Arabi
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