1,917 research outputs found
A weather related causal analysis on consolidated delay at Newark Liberty International Airport
No full textThe closure of the European airspace due to the eruption of the Icelandic volcano Eyjafjallajokull in 2010 proved a major challenge for airlines and aviation authorities on a global scale. In contrast, more seasonal adverse meteorological conditions afflict many airports in the northern eastern seaboard of the United States. Newark Liberty International Airport (KEWR) is a representative airport that endures severe weather based delays. This dissertation explores the utilisation of Bayesian Networks (BN) and heuristic analyses to investigate weather based delays at Newark Liberty International airport (KEWR). In particular, it aims to understand which weather variables (namely, precipitation, visibility and wind) have the most impact on weather based delays at KEWR in contrast to past studies that have studied more generic weather phenomena (e.g. thunderstorms) at the same airport. An analysis using temporal functionality with Bayesian Networks (BN) software and heuristic analyses was conducted. Data extracted from weather and aviation based websites was extracted using software. The quality of the information was cross referenced with official data sources and validated using BN tools. The results revealed a causal correlation chain between crosswinds above a certain threshold and high delays at KEWR at various points in the experimentation. Though other meteorological elements examined had an impact on delays, airport authorities and airlines can mitigate these factors to a certain scale using Federal Aviation Authority (FAA) approved technology and training. Consequently, the implications could be significant on existing FAA and regional policy with Ground Delay Program (GDP) and Noise Abatement Procedures (NAP). These policies can be profound and far reaching for airlines, in terms of operating procedures and fuel cost implications. These findings can further alter the balance between efficiency, public safety and airline costing affecting all major stakeholders as this dissertation will investigate
High thermal conductance across c-BN/diamond interface
No full textHigh thermal conductivity electronic components with low interfacial thermal resistance are of technological importance and fundamental interest of research. Diamond, a superhard material with ultrahigh thermal conductivity at room temperature, is desirable for microelectronics thermal management. Cubic polymorph of boron nitride (c-BN) is a promising material due to wide bandgap and diamond like structure and properties. To understand the nature in thermal transport of diamond, c-BN and the most commonly used silicon (Si) semiconductor, ab initio phonon Boltzmann transport equations are employed to investigate lattice vibrational properties of these three materials. At 300 K, the predicted thermal conductivity of Si, diamond and c-BN reached 142, 2112, and 736 W/(m·K), respectively. What's more, heat transport phenomena across the interfaces of Si/diamond, c-BN/diamond and Si/c-BN are unfolded. In comparison, the interfacial thermal conductance of c-BN/diamond is ten-fold of Si/diamond; besides, the thermal conductance across Si/c-BN interface is 20.2% larger than that of Si/diamond at 300 K and 18.9% larger at 340 K. These findings provide us new vision and potential solution to heat dissipation of high-local-power density devices, shedding light on future thermal management of c-BN and diamond related electronics.Peer reviewe
A data-based comparison of BN-HRA models in assessing human error probability: An offshore evacuation case study
No full textBayesian Network (BN) has been increasingly exploited to improve different aspects of Human Reliability Analysis (HRA), resulting in a new generation of HRA techniques, known as BN-HRA models. However, validating and evaluating the accuracy of BN-HRA models is still a challenging task. In this study, we have assessed and compared the performance of some of well-known BN-HRA techniques using human performance data obtained from an offshore evacuation simulation. Based on the role of data in quantifying the BN-HRA models, three categories of BN-HRA models have been considered: (i) BN-CREAM and BN-SPARH, which are based on predefined rules (rule-based methods), (ii) Bayesian Parameter Learning (BPL), which is entirely based on the available data (data-based method), and (iii) BN-SLIM model which is based on both the available data and the predefined rules (hybrid method). The results of the present study show that the data-based methods, i.e., BN-SLIM and BPL, in general outperform the rule-based methods. Cross-validation analysis further demonstrates the superiority of BN-SLIM over BPL, particularly in case of data scarcity.Safety and Security Scienc
3D flow simulation of dual thrust solid rocket motors during starting transient
No full textNumerical studies have been carried out to examine the pre-ignition chamber dynamics of dual-thrust solid rocket motors. Using a three-dimensional unsteady, second-orderimplicit, shear-stress transport k–ω turbulence model, detailed parametric studies have been carried out to examine conclusively aerodynamic choking and the existence of a fluid throat at the transition region during the startup transient of dual-thrust motors. In the numerical study, a fully implicit finite volume scheme of the compressible, pressure based Navier– Stokes equations is employed. It is confirmed that, at the subsonic inflow conditions, there is a possibility of the occurrence of internal flow choking in dual-thrust motors with large length-to-diameter ratio (L/d > 44) due to the formation of a fluid throat at the beginning of the transition region induced by area blockage caused by boundarylayer-displacement thickness. The internal flow choking results in the formation of shock waves inside the dualthrust motor. The shock waves and the new turbulence level altered the location of the reattachment point and also enhanced the heat flux to the propellant surface, which obviously will lead to undesirable startup transient due to erosive/transient burn rate enhancement. More numerical results of inert simulators of dual-thrust motors with horizontal and flip-horizontal positions are presented with tangible explanations in this paper for establishing the internal flow choking in dual-thrust solid rocket motors with narrow upstream port
Pilihan Raya Kecil (PRK) Cameron Highlands: kemenangan BN atau kekalahan PH?
No full textArtikel ini bertujuan membincangkan Pilihan Raya Kecil di Cameron Highlands dan pergelutan kerusi Parlimen antara Barisan Nasional (BN) dan Pakatan Harapan (PH). Dalam PRK ini, calon BN telah memenangi dan mengekalkan kerusi tradisi Parlimen Cameron Highlands dengan mengalahkan calon PH. Sehubungan itu, artikel ini menerangkan beberapa faktor yang mendorong pengundi untuk mengundi BNantaranya adalah faktor kesesuaian calon, faktor kesetiaan rakyat, kerjasama UMNO-PAS, politik perkauman dan faktor bangsa. Selain itu, artikel ini juga menerangkan beberapa faktor yang menghalang sokongan undi terhadap PH seperti kegagalan PH menunaikan janji dalam Manifesto PH dalam PRU 14, strategi kempen, kesesuaian calon, isu integriti dan penerimaan terhadap calon oleh pengundi. Berdasarkan faktor tarikan sokongan pengundi kepada BN dan faktor tolakan sokongan pengundi terhadap PH, beberapa pengajaran yang dapat dijadikan sebagai panduan daripada PRK Cameron Highlands turut dikemukakan
BN nanospheres as CpG ODN carriers for activation of toll-like receptor 9
No full textFor the first time, we demonstrated BN nanospheres (BNNSs) can interact with biomolecules and deliver unmethylated cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) into cells to activate toll-like receptor 9 (TLR9), which is a very important process for therapy of cancers and allergy diseases
Pilihan Raya Kecil (PRK) rantau 2019: isyarat peralihan sokongan rakyat kepada BN?
No full textArtikel ini bertujuan membincangkan Pilihan Raya Kecil (PRK) Dewan Undangan Negeri (DUN) di Rantau, Negeri Sembilan yang diadakan pada 13 April 2019. Pilihan Raya Kecil Rantau menyaksikan kemenangan calon Barisan Nasional (BN) mengalahkan calon Pakatan Harapan (PH) dengan undi majoriti yang besar. Sehubungan itu, artikel ini menjelaskan beberapa faktor yang telah memangkin kemenangan BN di Rantauantaranya adalah kredibiliti calon, sentimen Melayu-Islam, sokongan pengundi bukan Melayu, janji-janji Manifesto PH PRU 14 dan sokongan pengundi muda. Selain itu, artikel ini juga membincangkan beberapa faktor yang menjadi kekangan kepada PH untuk merampas kerusi DUN dalam PRK Rantau seperti kekecewaan rakyat terhadap PH, kerjasama UMNO-PAS, sentimen Melayu-Islam oleh UMNO, budaya politik berkempen, kerjasama dalam kalangan parti komponen PH dan kebebasan media
Dislocation assisted crack healing in h-BN nanosheets
No full textInteraction between dislocations and crack tip stress-fields drives the fracture toughness enhancement mechanisms in h-BN.</p
Adsorption and Catalytic Activation of the Molecular Oxygen on the Metal Supported h-BN
No full textAdsorption and catalytic activation of the molecular oxygen on the hexagonal boron nitride (h-BN) monolayer supported on Ni(111) and Cu(111) surfaces have been studied theoretically using density functional theory. It is demonstrated that an inert h-BN monolayer can be functionalized and become catalytically active on the transition metal support as a result of mixing of the metal d and h-BN pi bands
BN-SLIM: A Bayesian network methodology for human reliability assessment based on Success Likelihood Index Method (SLIM)
No full textSuccess Likelihood Index Model (SLIM) is one of the widely-used deterministic techniques in human reliability assessment especially when data is insufficient. However, this method suffers from epistemic uncertainty as it extremely relies on expert judgment for determining the model parameters such as the rates and weights of the performance shaping factors (PSFs). Besides, given an operation consisting of several tasks, SLIM calculates the human error probability (HEP) by ignoring possible dependencies among the tasks.The present study is aimed at using Bayesian Network (BN) for improving the performance of SLIM in handling uncertainty arising from experts opinion and lack of data. To this end, SLIM is combined with BN to form the so-called BN-SLIM technique. We demonstrate how BN-SLIM can consider uncertainty associated with the rates of PSFs by using probability distributions. BN-SLIM is also able to provide a better estimation of human error probability by considering conditional dependencies resulting from common PSFs. The probability updating feature of BN-SLIM can be used to identify the PSFs contributing the most to human failure event. The outperformance of BN-SLIM over SLIM is demonstrated via an illustrative example.Safety and Security Scienc
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