1,722,427 research outputs found
Reliability Analysis of LASER ULTRASONICS as an NDT method for surface defect detection in High Speed Hollow Train Axles using Experimental and Numerical Methods
No full textThe objective of the research is to find a methodology to test the train axle for possible surface defects using non-contact laser ultrasonic technique and then studying the reliability of this non-destructive test (NDT) method by considering a large set of defects with varying sizes to build Probability of Detection (POD) curve. Generally, this NDT technique has three parts: laser beam generation and impingement on a point over the test object surface, ultrasound propagation within the material of the test object and reception of the ultrasound wave propagated at a certain distance from the laser source position. The wave propagation will be influenced by the path where it propagates through and specifically it will be modified in presence of a defect. The part of methodology covered in this research is more concentrated on the laser beam incidence and ultrasound generation within the material and its behavior as it moves through the train axle under study. Laser ultrasonics is being considered a replacement of conventional ultrasonic testing method as it eliminates many limitations of conventional method and has advantages of its own. In case of train axles preventive maintenance is a challenge using conventional method as once mounted it is very difficult to reach all areas of axle and dismounting is never a good idea with respect to time and economy. Though rotating probe method needs only small elements to be removed to reach the central bore in case of hollow axles but there was still an urge to use a non-contact method which is feasible for hard to reach areas and does not require dismounting of the axle completely. Laser ultrasonics if found feasible in future not only kills this issue but it is also quicker and if used properly can detect wider range of surface defects. As a starting point it is necessary to know the behavior of ultrasonic waves in the material which is steel in our case. The steel axle under research is being used in high speed train ETR 460. It becomes harder to see the behavior of the waves when there is a hollow axle with various abrupt variations in cross section along the length. Surface acoustic waves (SAW) which are precisely Rayleigh surface waves in our case are the most important for detecting surface defects. These waves are almost half in speed to longitudinal waves and so are with smaller wavelengths for a given frequency to become more sensitive to any hurdles in their way. It also leads to many reflections in the detected signals due to central hole and fillets present on each variation of the cross section. A section of the axle with two fillets is selected initially to study all of the above behavior. 2D model of this section is numerically analyzed using COMSOL multi-physics code. A series of experiments is also carried on selected section using the lab equipment available to produce Nd: YAG (neodymium-doped yttrium aluminum garnet) laser in the infrared region with a short pulse of about 16 Megawatt (maximum power) for 12 nanoseconds duration. It theoretically causes about 5 nanometer of penetration in the steel to cause thermo-elastic regime. This value also varies on the basis of surface quality and frequency of laser beam used. Due to this phenomenon, a transient increase in temperature in a small volume of material causes a thermal stress which in turn propagates three types of waves: longitudinal waves, transverse waves and Rayleigh surface waves. The reception signal was read by using Laser Doppler Vibrometer (LDV). Another option may also be considered by using air-coupled ultrasonic transducer making the method a hybrid Laser Ultrasonic system. Behavior of the stated waves studied numerically and experimentally by measuring vertical displacement of a point at different locations by simulating defect of varying size and position is what can help in finalizing the objective. Along with this sensitivity and efficiency of the NDT method against different range of defect sizes is also important. It can be achieved by measuring POD curve of the system. This curve tells us about the largest probable size of defect which can be missed by the technique under consideration. Parametric studies run for different defect sizes give a curve against RMS of the signal and the amplitude of the Rayleigh wave. For example to study change in RMS of the vertical displacement of a point when measured after defect of a constant width and varying depth from no crack to a maximum crack depth showing a variable behavior with a small incremental step each time gives a probability measure of the detection of the defect. The Rayleigh Surface wave attenuation was one of the main changing factors considered due to the inclusion of the defects. The important information is extracted using POD Curve to look for the minimum size of defect to be seen by the method with required level of probability. It also helps to define the inspection interval of a train axle under service. First of all a range of crack sizes is to be defined in which the inspection system under question cannot determine if the object is defected or not. Then a large number of specimen are required in this range of defects to do further analysis. Linear regression analysis of these results is used to get the conventional POD curve. This type of POD curve built with inputs from numerical models is termed as Model Assisted POD curve or MAPOD curve. MAPOD curve avoids the expensive real building of test specimen for different defect sizes. A large number of trial experiments were done on the real axle without defect to incorporate natural noise of the inspection method in the numerical readings. The model to be used was refined multiple times to get a fully qualified model fulfilling all the real requirements and avoiding as much as possible the stochastic behavior of numerical methods involved. A generalized alpha time stepping algorithm was used in the time domain study of all the experiments. Direct Solver used was the famous MUMPS solver and Newton method was used for the iterative non-linear solution. At the end MAPOD curve for the specific settings used showed that the Laser-Ultrasonics is fairly suitable to detect the typical crack sizes and if a suitable configuration is found it is quite efficient to serve the purpose of in service inspection of train axles without using any conventional contact techniques
Correction to: Strategic crossing of biomass and harvest index—source and sink—achieves genetic gains in wheat
No full textAbstractThe original article was corrected. Author Muhammad Kundi should instead read: Muhammad Sohail.</jats:p
Correction to: Strategic crossing of biomass and harvest index—source and sink—achieves genetic gains in wheat (Euphytica, (2017), 213, 257, 10.1007/s10681-017-2040-z)
No full textThe original article was corrected. Author Muhammad Kundi should instead read: Muhammad Sohail
sj-docx-1-onc-10.1177_11795549221084832 – Supplemental material for Body Mass Index and Diabetes Mellitus May Predict Poorer Overall Survival of Oral Squamous Cell Carcinoma Patients: A Retrospective Cohort From a Tertiary-Care Centre of a Resource-Limited Country
No full textSupplemental material, sj-docx-1-onc-10.1177_11795549221084832 for Body Mass Index and Diabetes Mellitus May Predict Poorer Overall Survival of Oral Squamous Cell Carcinoma Patients: A Retrospective Cohort From a Tertiary-Care Centre of a Resource-Limited Country by Yumna Adnan, Syed Muhammad Adnan Ali, Muhammad Sohail Awan, Nida Zahid, Muhammad Ozair Awan, Hammad Afzal Kayani and Hasnain Ahmed Farooqui in Clinical Medicine Insights: Oncology</p
A PROSPECTIVE COHORT STUDY OF TETANUS; ITS MANAGEMENT AND ASSOCIATED RISK FACTORS
No full text*Hafiz Muhammad Asad Shakeel, Muhammad Sohail and Muhammad Umer Ali Ayu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Study on the role of recondensation flux in high power laser welding by computational fluid dynamics simulations
No full textPartial penetration welding with fiber laser on 20mm thick plates was carried out in horizontal position to study the role of secondary heating in modeling of high power fiber laser welding. Experiments were carried out using 18.8kW laser with 1.5 m/min welding speed at Ar assist gas flow rates of 0, 17, 29, and 40 l/min, all four cases show similar bead shape with bright emission of vapor plume. Numerical simulations were performed using volume of fluid method by considering three different models as models A–C. Model A considers only Fresnel reflection inside the keyhole using real time tracking of free surface. Model B considers vapor recondensation flux inside keyhole along with model A. Finally, model C is used, which considers vapor plume heating at 4100K temperature along with models A B. Secondary heating by recondensation and vapor plume is vital in modeling of high power fiber laser welding; especially, the upper part of the bead is more influenced due to secondary heating. Tungsten particles are also used to visualize the flow pattern of melt pool
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