Revista Jurídica Digital UANDES
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A case study on 3D characterisation of pore structure in a tight sandstone gas reservoir:The Collyhurst Sandstone, East Irish Sea Basin, northern England
No full textPore systems of tight-gas reservoirs control important parameters such as flow capacity, producible pore volumes, hydrocarbon flow rates and storage which are complex to characterise and to quantify. Detailed understanding of 3D pore structure is vital in predicting tight-gas reservoir productivity. This study investigates the pore architecture of a sandstone sample from Collyhurst Sandstone Formation, northern England, a tight gas reservoir. X-ray Computed Tomography (XCT) was employed to quantify the pore system (pore size, shape, geometry, and connectivity). Three types of pores were identified: inter-grain pores which are at the boundary of detrital grains and/or authigenic minerals, intra-grains pores which are pores within the detrital mineral grains, and intra-cement pores which are pores within the cement phase (authigenic minerals). The first pore type is primary in origin, whereas the latter two are secondary pores. A centerline tree and a pore network model (PNM) algorithm were applied for pore network analysis and a porosity value was estimated. The image-based porosity value was validated with laboratory experimental measurement. 3D image estimates 3.1% volume porosity, while 4.6% was recorded from the laboratory experiment. Spatial quantification of pore types and analysis of pore connectivity of the studied sandstone improves understanding on gas flow behaviour and gas storage. Furthermore, the results are useful in predicting permeability and multi-flow phase properties in a tight gas reservoir
Environmental impacts of copper‑indium‑gallium-selenide (CIGS) photovoltaics and the elimination of cadmium through atomic layer deposition
No full textThin-film technologies have been part of the rapidly-expanding solar photovoltaics (PV) market for many years, led by cadmium-telluride (CdTe) and copper‑indium‑gallium-selenide (CIGS). However, their environmental impacts remain largely unknown, particularly considering state-of-the-art CIGS manufacturing techniques. This study estimates the life cycle environmental impacts of CIGS PV installations in the UK and Spain, including balance-of-system components, using real manufacturing data. It also analyses newly-developed CIGS, replacing the cadmium sulphide (CdS) buffer layer with zinc oxysulphide (Zn(O,S)) via atomic layer deposition (ALD). The results show that UK installations have 72% higher impacts than those in Spain, including climate change (25.1 vs 14.6 g CO2 eq./kWh). The inverter and electrical components are the main contributors (46% on average), followed by the PV modules (41%). In comparison to CdTe, mono-Si and multi-Si PV, CIGS has 6%–90% lower impacts in 16 out of 18 categories, including climate change (16%–50% lower). However, metal depletion is five times higher, and land use 12%–31% greater. The replacement of CdS has a small but positive effect, demonstrating that cadmium can be eliminated from the CIGS life cycle without environmental penalties. These results will be of interest to PV manufacturers and policy makers, indicating improvement opportunities and areas for policy intervention
Fabrication Cost Analysis for Contactless 3-D ICs
No full textThe manufacturing cost of contactless 3-D circuitswith inductive links is explored for the first time. The high-volumemanufacturing (HVM) cost of contactless 3-D ICs is modeledby considering the on-chip inductor area and other importantparameters, such as the coupling efficiency, which depend uponspecific steps of the fabrication process. Inductive links basedon current mode logic (CML) transceivers are simulated acrossa number of integration scenarios in a commercial 65 nmCMOS technology process, thereby evaluating the cost of thesemanufacturing options for performance and power objectives. Assuming a 10 Gbps data rate, the power and area of the inductive link are determined for wafer-to-wafer and die-to-wafer integration and communication distances in the range of 5 um (face-to-face) to 120 um (face-to-back). A HVM cost estimation for each investigated inductive link scheme is provided for these integration approaches. Additional processing steps attributed to 3-D integration increase the aggregate cost by 2.5% to 4.5% for a case study of a three-tier stack, compared to a conventional 2-D process. Moreover, the yield is explored for each integration approach considering the inductor area for contactless 3-D ICs
Institutionalised whiteness, racial microaggressions and Black bodies out of place in Higher Education
No full textOn the morning of Friday 3rd February 2017, Femi Nylander - a Black Oxford alumnus - walked through the grounds of Oxford University’s Harris Manchester College. Later that morning a CCTV image of Femi was circulated to staff and students who were urged to ‘maintain vigilance’. Whilst ‘post-racial’ ideology insists on framing such incidents as isolated aberrations bereft of wider structural and institutional context, in this article I draw upon the theoretical concepts of racial microaggressions and bodies out of place in order to disrupt this hegemonic interpretation. Adopting the Critical Race Theory (CRT) method of counter-narrative, I centralise the voices of student campaigns as sites of legitimate experiential knowledge. These campaigns reveal a web of whiteness that undergirds Higher Education. It is this web, I argue, that ensnares Femi on the day in question. Thus, Femi’s experience cannot be understood in abstraction from structural white supremacy and institutionalised whiteness.<br/
Semantic Frame Embeddings for Detecting Relations between Software Requirements
No full textThe early phases of requirements engineering (RE) deal with a vast amount of software requirements (i.e.,requirements that define characteristics of software systems), which are typically expressed in natural language. Analysing such unstructured requirements, usually obtained from stakeholders’ inputs, is considered a challenging task due to the inherent ambiguity and inconsistencyof natural language. To support such a task, methods based on natural language processing (NLP) can be employed. One of the more recent advances in NLP is the use of word embeddings for capturing contextual information, which can then be applied in word analogy tasks. In this paper, we describe a new resource, i.e., embedding-based representations of semantic frames in FrameNet, which was developed to support the detection of relations between software requirements. Our embeddings, which encapsulate contextual information at the semantic frame level, were trained on a large corpus of requirements (i.e., a collection of more than three million mobile application reviews). The similarity between these frame embeddings is then used as a basis for detecting semantic relatedness between software requirements. Compared with existing resources underpinned by frame embeddings built upon pre-trained vectors, our proposed frame embeddings obtained better performance against judgments of an RE expert. These encouraging results demonstrate the potential of the resource in supporting RE analysis tasks (e.g., traceability), which we plan to investigate as part of our immediate future work
Performance Evaluation of IEEE 1588 for Precision Timing in IEC 61850 Substations
No full textTime synchronisation with 1 ms accuracy is widely used in the power industry. However, more advanced power system applications such as Phasor Measurement Units (PMUs), travelling wave fault location detectors, and IEC 61850 process bus require sub-microsecond accuracy. Inadequate synchronisation deteriorates the protection, control and automation performance and may potentially cause catastrophic failures. Hence, a system that ensures a reliable and accurate time synchronisation becomes critical to the future of power system protection and control.The traditional way to disseminate time signals in transmission substations is achieved using dedicated timing methods based on the IRIG-B time code or one pulse per second (1-PPS) via copper cables or optic fibres [1]. The UK often synchronises a large number of IEDs in a substation by deploying multiple distributed GPS/GNSS receivers. The quality of GPS/GNSS receivers vary significantly which results in different performance characteristics. In addition, satellite signals are subject to radio frequency interference so it is vulnerable to jamming or spoofing attacks. With the aid of IEEE 1588-2008 Precision Time Protocol (PTP), the time information can be encapsulated in the Ethernet packets and communicated using the same communication network as IEC 61850 Sample Value (SV) and Generic Object Oriented Substation Events (GOOSE) messages. PTP can deliver 1 us precision in the Ethernet network, which saves the cost of using dedicated cables for timing and reduces the number of GPS/GNSS receivers. This paper recognises the global trend to apply PTP in future substations built in accordance with IEC 61850 standards.To reliably distribute time signals in an IEC 61850 substation, Rapid Spanning Tree Protocol (RSTP) is often used instead of a simple Star connection. In addition, Parallel Redundancy Protocol (PRP) and High-availability Seamless Redundancy (HSR) are two seamless redundancy protocols as per IEC 62439-3 and are designed to achieve zero failover time [2]. Although IEEE 1588-2008 does not consider synchronisation over redundant networks, the extension of the standard is included in IEC 62439-3 [2] and IEC 61850-9-3 [3]. For large scale transmission substations, a more complex architecture is required. IEC 61850-90-4 introduces topologies for connecting the station bus and the process bus, e.g. PRP over HSR (PRP-HSR), RSTP over HSR (RSTP-HSR) and HSR over HSR (HSR-HSR) [4]. Combining the station bus and process bus together allows the message exchange between station bus and process bus to be achieved more easily.2This paper presents a real-time assessment of time synchronisation performance for IEC 61850 substations with commercially-available PTP devices. The transient behaviours of various GPS/GNSS receivers are first investigated. After that, the paper focuses on the distribution of PTP messages in redundant process bus architectures such as RSTP, PRP and HSR. Finally, the timing accuracy in the complete substation architectures including PRP-HSR, RSTP-HSR and HSR-HSR topologies are investigated in the presence of SV and GOOSE traffic. The results in this paper provide the power industry with the knowledge of real-time synchronisation performance they can expect to obtain when using PTP in a substation
Impact of Time Synchronisation Errors on Transformer Differential Protection that uses the IEC 61850 Process Bus
No full textConventional transformer differential protection uses current transformers (CTs) to reduce each primary current to a suitable secondary value. If a fault occurs within the transformer, the protection initiates a trip command via a contact, opens the circuit breakers and clears the fault. With the development of the IEC 61850 process bus, the analogue measurement values can be digitised into Sampled Values (SVs) and transmitted across an Ethernet communication network. In addition, digital status information, such as indications, alarms and trip signals, can be distributed across the same network using Generic Object-Oriented Substation Event (GOOSE) messages. An IEC 61850 based transformer differential protection intelligent electronic device (IED) compares the SVs from either, standalone Merging Units (MUs) connected to conventional CTs, or directly using Non-Conventional Instrument Transformers (NCITs). Then it matches the SV steams from each set of CTs according to their Sample Counters (SmpCnt). The protection IED then calculates the differential current and issues a trip signal if it exceeds the bias operation threshold. The correct operation of differential protection relies on the accuracy of the time synchronisation process applied to MUs or NCITs. Inadequate synchronisation accuracy will cause an angle shift of the phasors and result in an increase in differential currents, which can lead to protection mal-operations. SVs are required to have a timing accuracy of better than 1µs, and this is traditionally achieved using 1-PPS or the IRIG-B time code implemented using dedicated cabling systems. In contemporary times, the power industry is moving towards using IEEE 1588 Precision Time Protocol (PTP) to achieve the same level of timing precision without the need for separate cables. The time information is encapsulated in Ethernet messages which share the same communication network as SV and GOOSE. This paper investigates the impact of time synchronisation errors on a transformer differential protection that uses SV process bus. The paper first uses mathematical derivations to illustrate how inadequate synchronisation affects the differential current calculations and indicates the consequences on the protection operating response during internal and external faults. A multi-vendor hardware testbed is then utilised to experimentally validate the theoretical results. The testbed simulates a real substation communication network with a redundant coupling of both station bus and process bus HSR (high-availability seamless redundancy) rings. Time deviations are created using a network impairment emulator that manipulates the PTP messages content to precisely “spoof” the MUs. The results have shown the protection scheme becomes more sensitive because of the introduced phase angle shift. The impact on the differential current is the most severe in the operating area related to the first slope of the restraint curve. <br/
Ageing significantly impacts the biomechanical function and structural composition of skin
No full textSkin ageing is a complex process involving the additive effects of skin’s interaction with its external environment, predominantly chronic sun exposure, upon a background of timedependent intrinsic ageing. Here, using non-invasive cutometry and ballistometry, we explore the consequences of ageing on the biomechanical function of skin in otherwise healthy white Northern European volunteers. Intrinsic skin ageing caused biomechanical decline; skin loses both resilience (P<0.01) and elasticity (P<0.001) which is characterised histologically by modest effacement of rete ridges (P<0.05) and disorganisation of papillary dermal elastic fibres. At photoexposed sites, biomechanical testing identified significant loss of biomechanical function - particularly in the aged cohort. Photoaged forearm displayed severe loss of resilience (P<0.001) and elasticity (P<0.001); furthermore with repetitive testing, fatigue (P<0.001), hysteresis (P<0.001) and viscous “creep” (P<0.001) were exacerbated. Histologically, both young and aged forearm displayed flattening of rete ridges and disruption to the arrangement of elastic fibres. We conclude that maintenance of skin architecture is inherently associated with optimal biomechanical properties. Modest perturbations to skin architecture – as exemplified by intrinsic ageing – result in moderate functional decline. Chronic sun-exposure causes fundamental changes to the clinical and histological appearance of skin and these are reflected by an extreme alteration in biomechanical function