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- Irshad, Hafiz Musammil, et al.
(författare)
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Effect of Ni content and Al2O3 particle size on the thermal and mechanical properties of Al2O3/Ni composites prepared by spark plasma sintering
- 2018
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Ingår i: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 76, s. 25-32
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Tidskriftsartikel (refereegranskat)abstract
- Alumina-nickel composites were prepared by carrying out spark plasma sintering (SPS) of nano-sized and micro-sized Al2O3particles with 15–45 wt% Ni powders. The powder materials were sintered at a temperature of1400 °C under a constant uniaxial pressure of 50 MPa. FESEM micrographs of the products showed uniformlydispersed nickel inclusions in both matrices at intergranular positions. Presence of Al2O3as the major phasealong with Ni as the minor phase was confirmed using XRD analysis. Thermal and mechanical properties of thenano- and micro-sized Al2O3/Ni composites were investigated. The thermal conductivity of nano-sized aluminacomposites was seen to increase with the increase in nickel content, however, an opposite trend was observed formicro-sized alumina-based composites. Moreover, thermal conductivities of all the composites decreased withincrease in temperature. The composites also showed high hardness and fracture toughness values of up to19.6 GPa and 4.71 MPa ∗ m1/2, respectively, and relative density values, between 79 and 99%, that decreasedwith increasing Ni content. Furthermore, the nano-sized Al2O3/Ni composites showed thermal and mechanicalproperties superior to those of the micro-sized Al2O3/Ni composite.
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| 5. |
- Irshad, Muneeb, et al.
(författare)
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A Brief Description of High Temperature Solid Oxide Fuel Cell's Operation, Materials, Design, Fabrication Technologies and Performance
- 2016
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 6:3
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Forskningsöversikt (refereegranskat)abstract
- Today's world needs highly efficient systems that can fulfill the growing demand for energy. One of the promising solutions is the fuel cell. Solid oxide fuel cell (SOFC) is considered by many developed countries as an alternative solution of energy in near future. A lot of efforts have been made during last decade to make it commercial by reducing its cost and increasing its durability. Different materials, designs and fabrication technologies have been developed and tested to make it more cost effective and stable. This article is focused on the advancements made in the field of high temperature SOFC. High temperature SOFC does not need any precious catalyst for its operation, unlike in other types of fuel cell. Different conventional and innovative materials have been discussed along with properties and effects on the performance of SOFC's components (electrolyte anode, cathode, interconnect and sealing materials). Advancements made in the field of cell and stack design are also explored along with hurdles coming in their fabrication and performance. This article also gives an overview of methods required for the fabrication of different components of SOFC. The flexibility of SOFC in terms fuel has also been discussed. Performance of the SOFC with varying combination of electrolyte, anode, cathode and fuel is also described in this article.
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| 6. |
- Irshad, Mohsin, 1984-
(författare)
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Realizing the systematic reuse of automated acceptance tests in practice
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Context: Automated acceptance testing has become a relevant practice of agile software development (e.g., Extreme Programming). Automated acceptance tests (AATs) are closely tied to requirements and provide a mechanism for continuous validation of requirements as system-level tests. Studies have shown that these tests are costly to develop, maintain, and reuse.Objectives: This thesis examines and supports the systematic reuse of automated acceptance tests by providing approaches to search, identity, adapt reusable test cases while considering the reuse costs. Additionally, the maintainability and usage of automated acceptance tests in largescale software projects are studied.Method: We used various research methods to investigate development, reuse, and maintaining the automated acceptance tests. Workshops and interviews of practitioners were used to identify the benefits and challenges of automated acceptance tests. Next, method engineering was used to construct a systematic reuse process for automated acceptance tests. Qualitative feedback collected using a survey, and industrial demonstration examined the reuse process’s performance expectancy, effort expectancy, and necessary facilitating conditions. Two systematic literature reviews are used to identify techniques to adapt tests for future reuse opportunities and calculate the reuse costs of automated acceptance tests. Later, we developed and evaluated an approach for refactoring behavior-driven development-based automated acceptance tests using action research.Results: A cost-aware systematic reuse process was constructed to support the reuse of automated acceptance tests containing eleven activities. For each activity, guidelines on expected input, expected output, the actors performing the activity, and techniques (automated using scripts) are suggested and evaluated. The techniques involve approaches to support development for reuse and methods to calculate the costs of reusing automated acceptance tests. The industrial evaluation of the reuse process and the techniques showed its usefulness and relevance for the industry. Furthermore, seven challenges (i.e., the scale of the software projects, ownership, lack of competence, cost benefits, specification of behaviors in large-scale projects, difficulty writing system-level test-cases, and versioning control of behaviors) and five benefits (i.e., understanding of a business aspect of requirements, improved quality of requirements, a guide to system-level use-cases, reuse of artifacts in large-scale projects, and help for test organization.) of using automated acceptance tests in large-scale projects are identified with software practitioners’ help. Later, we proposed a semiautomated four-step approach for pre-processing, measuring, ranking, and identifying refactoring candidates. The approach and the two proposed measures were successfully evaluated using two industrial projects. It was noted that similarity measures could support the maintenance of the specification base using refactoring.Conclusions: The studies show that automated acceptance tests are reusable and can be refactored using our proposed approach. The evaluation shows that the results apply to the software industry in the evaluated context. However, further work is required to evaluate the reuse process in different contexts.
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| 7. |
- Janko, Matthew, et al.
(författare)
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Contemporary Outcomes After Partial Resection of Infected Aortic Grafts
- 2021
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Ingår i: Annals of Vascular Surgery. - : Elsevier. - 0890-5096 .- 1615-5947. ; 76, s. 202-210
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Aortic graft infection remains a considerable clinical challenge, and it is unclear which variables are associated with adverse outcomes among patients undergoing partial resection.METHODS: A retrospective, multi-institutional study of patients who underwent partial resection of infected aortic grafts from 2002 to 2014 was performed using a standard database. Baseline demographics, comorbidities, operative, and postoperative variables were recorded. The primary outcome was mortality. Descriptive statistics, Kaplan-Meier (KM) survival analysis, and Cox regression analysis were performed.RESULTS: One hundred fourteen patients at 22 medical centers in 6 countries underwent partial resection of an infected aortic graft. Seventy percent were men with median age 70 years. Ninety-seven percent had a history of open aortic bypass graft: 88 (77%) patients had infected aortobifemoral bypass, 18 (16%) had infected aortobiiliac bypass, and 1 (0.8%) had an infected thoracic graft. Infection was diagnosed at a median 4.3 years post-implant. All patients underwent partial resection followed by either extra-anatomic (47%) or in situ (53%) vascular reconstruction. Median follow-up period was 17 months (IQR 1, 50 months). Thirty-day mortality was 17.5%. The KM-estimated median survival from time of partial resection was 3.6 years. There was no significant survival difference between those undergoing in situ reconstruction or extra-anatomic bypass (P = 0.6). During follow up, 72% of repairs remained patent and 11% of patients underwent major amputation. On univariate Cox regression analysis, Candida infection was associated with increased risk of mortality (HR 2.4; P = 0.01) as well as aortoenteric fistula (HR 1.9, P = 0.03). Resection of a single graft limb only to resection of abdominal (graft main body) infection was associated with decreased risk of mortality (HR 0.57, P = 0.04), as well as those with American Society of Anesthesiologists classification less than 3 (HR 0.35, P = 0.04). Multivariate analysis did not reveal any factors significantly associated with mortality. Persistent early infection was noted in 26% of patients within 30 days postoperatively, and 39% of patients were found to have any post-repair infection during the follow-up period. Two patients (1.8%) were found to have a late reinfection without early persistent postoperative infection. Patients with any post-repair infection were older (67 vs. 60 years, P = 0.01) and less likely to have patent repairs during follow up (59% vs. 32%, P = 0.01). Patients with aortoenteric fistula had a higher rate of any post-repair infection (63% vs. 29%, P < 0.01)CONCLUSION: This large multi-center study suggests that patients who have undergone partial resection of infected aortic grafts may be at high risk of death or post-repair infection, especially older patients with abdominal infection not isolated to a single graft limb, or with Candida infection or aortoenteric fistula. Late reinfection correlated strongly with early persistent postoperative infection, raising concern for occult retained infected graft material.
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| 8. |
- Janko, Matthew R., et al.
(författare)
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In-situ bypass is associated with superior infection-free survival compared with extra-anatomic bypass for the management of secondary aortic graft infections without enteric involvement
- 2022
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Ingår i: Journal of Vascular Surgery. - : Elsevier. - 0741-5214 .- 1097-6809. ; 76:2, s. 546-
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The optimal revascularization modality following complete resection of aortic graft infection (AGI) without enteric involvement remains unclear. The purpose of this investigation is to determine the revascularization approach associated with the lowest morbidity and mortality using real-world data in patients undergoing complete excision of AGI. Methods: A retrospective, multi-institutional study of AGI from 2002 to 2014 was performed using a standardized database. Baseline demographics, comorbidities, and perioperative variables were recorded. The primary outcome was infection-free survival. Descriptive statistics, Kaplan-Meier survival analysis, and univariate and multivariable analyses were performed. Results: A total of 241 patients at 34 institutions from seven countries presented with AGI during the study period (median age, 68 years; 75% male). The initial aortic procedures that resulted in AGI were 172 surgical grafts (71%), 66 endografts (27%), and three unknown (2%). Of the patients, 172 (71%) underwent complete excision of infected aortic graft material followed by in situ (in-line) bypass (ISB), including antibiotic-treated prosthetic graft (35%), autogenous femoral vein (neo-aortoiliac surgery) (24%), and cryopreserved allograft (41%). Sixty-nine patients (29%) underwent extra-anatomic bypass (EAB). Overall median Kaplan-Meier estimated survival was 5.8 years. Perioperative mortality was 16%. When stratified by ISB vs EAB, there was a significant difference in Kaplan-Meier estimated infection-free survival (2910 days; interquartile range, 391-3771 days vs 180 days; interquartile range, 27-3750 days; P <.001). There were otherwise no significant differences in presentation, comorbidities, or perioperative variables. Multivariable Cox regression showed lower infection-free survival among patients with EAB (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.6-3.6; P <.001), polymicrobial infection (HR, 2.2; 95% CI, 1.4-3.5; P = .001), methicillin-resistant Staphylococcus aureus infection (HR, 1.7; 95% CI, 1.1-2.7; P = .02), as well as the protective effect of omental/muscle flap coverage (HR, 0.59; 95% CI, 0.37-0.92; P = .02). Conclusions: After complete resection of AGI, perioperative mortality is 16% and median overall survival is 5.8 years. EAB is associated with nearly a two and one-half-fold higher reinfection/mortality compared with ISB. Omental and/or muscle flap coverage of the repair appear protective.
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| 9. |
- Khattak, Muhammad Irfan, et al.
(författare)
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A Planar UWB Antenna with Tripple Notched Bands
- 2017
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Ingår i: 2017 9th International Confernce on Computational Intelligence and Communication Networks (CICN). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509050017 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- This paper presents a rectangular planar monopole antenna with triple stop bands for ultra-wide band Applications. The antenna is compact size (24mm x 24mm x 1.6mm) and is covering the entire UWB band with VSWR < 2 except the band of WiMAX range from 3.07 - 4.73 GHz, the WLAN band range from 5.14 - 5.97 GHz and the ITU frequency band range from of 7.92 - 8.61 GHz. The three slots are added to this antenna to stop various bands. Different shaped slots i.e. inverted Z, C and U are introduced in radiating element to stop WiMAX, WLAN and ITU respectively. The antenna is simulated using High Frequency Structure Simulator (HFSS) using FR4 as a substrate.
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| 10. |
- Rafique, Asia, et al.
(författare)
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Significance enhancement in the conductivity of core shell nanocomposite electrolytes
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 5:105, s. 86322-86329
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Tidskriftsartikel (refereegranskat)abstract
- Today, there is great demand of electrolytes with high ionic conductivities at low operating temperatures for solid-oxide fuel cells. Therefore, a co-doped technique was used to synthesize a highly ionically conductive two phase nanocomposite electrolyte Sr/Sm-ceria-carbonate by a co-precipitation method. A significant increase in conductivity was measured in this co-doped Sr/Sm-ceria-carbonate electrolyte at 550 degrees C as compared to the more commonly studied samarium doped ceria. The fuel cell power density was 900 mW cm(-2) at low temperature (400-580 degrees C). The composite electrolyte was found to have homogenous morphology with a core-shell structure using SEM and TEM. The two phase core-shell structure was confirmed using XRD analysis. The crystallite size was found to be 30-60 nm and is in good agreement with the SEM analysis. The thermal analysis was determined with DSC. The enhancement in conductivity is due to two effects; co-doping of Sr in samarium doped ceria and it's composite with carbonate which is responsible for the core-shell structure. This co-doped approach with the second phase gives promise in addressing the challenge to lower the operating temperature of solid oxide fuel cells (SOFC).
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