526 research outputs found
Dynamic structural response of Core-Loc
No full textThe Core-Loc, invented and developed at the Waterways Experiment Station (WES), is a new-generation, optimized breakwater concrete armor unit for protecting shoreline and navigation structures.Because of the very difficult construction, in-service, and repair conditions associated with high-energy wave environments, a need was identified to characterize the dynamic impact structural response of the Core-Loc. The most common method of accomplishing this goal is the drop test. Drop tests are used to evaluate the structural performance of a given armor unit when it is exposed to impact loads. During the test, the armor unit is dropped from incrementally increasing heights onto a rigid concrete base until the unit breaks apart. In this case, the drop heights were increased in 25-mm increments until the units totally failed
Probabilistic design of Core-loc armoured breakwaters
No full textDeterministic design methods are commonly used to determine preliminary breakwater designs. Partial safety factors take into account previous experiences and provide a robust preliminary design. However, local circumstances can prove to differ considerably compared to average design conditions and stochastic variations in breakwater strength parameters are commonly neglected. With new armouring techniques, such as Core-loc armouring, the uncertainties about the armour strength are relatively large. Design guidelines include a safety factor, but often an additional safety margin is applied in the final design of the armouring to ensure stability. This can result in structure strengths more, or less, than locally required. The economic optimum geometry with the lowest costs is possibly not achieved. These costs consist of the initial construction cost, the collapse damage cost and the economic damage cost due to downtime. To include the damage cost or risk (= failure probability x economic consequence) of breakwater collapse and functional failure, a probabilistic approach can be used to determine the failure probabilities. In Veracruz, Mexico, the port authority of the Port of Veracruz investigates the feasibility of a large port extension next to the existing port of Veracruz. In the preliminary layout a Core-loc armoured breakwater is anticipated to provide shelter at a container terminal and quay location. Deterministic design methods result in an element weight of 18.7t (8.5m3). Two construction methods are evaluated: a water-based and a land-based construction method, with crest heights of 3m +SWL and 11m +SWL respectively. In this deterministic evaluation the economic consequences of functional failure are not taken into account, but both alternatives fulfilled the harbour tranquillity restrictions by the port authority: a maximum downtime of 5%. The water-based construction method is elected as the best construction method, due to lower construction costs of 110.7 million. A crest height of 7m +SWL complies with an allowable downtime of approximately 0.2%. The downtime costs are of considerable more influence than estimated by the port authority. Also the consequences of a breakwater collapse result in a 65% heavier element weight. The discounted total costs over the lifetime of the breakwater are 219 million for the deterministic design. The collapse costs and downtime costs have a significant influence on the total costs over the lifetime and therefore on the economic optimal geometry of the breakwater. A more robust design than deterministically derived can reduce the total cost over the lifetime by almost 50%.Civil Engineering and Geoscience
Merging SoC and LOC Together
No full textA promising combination of the semiconductor integrated System-on-a-Chip (SoC) with the Lab-on-a-Chip (LOC) is brought in this paper. In this paper, we propose a new technology which enables monolithic integration of the self-assembled biological system, the MEMS structure, the microfluidic system, and CMOS electronic circuits together. Utilizing this approach, more functionality is introduced into the SoC, while the LOC becomes more intelligent and controllable. A Post-CMOS fabrication approach that meets the requirements is demonstrated to validate the idea.Engineering, Electrical & ElectronicPhysics, AppliedEICPCI-S(ISTP)
Gate modulation of the long-range magnetic order in a vanadium-doped WSe2 semiconductor
No full text© Author(s) 2020 Generation of spin-charge coupling by doping semiconductors with magnetic dopants is a promising approach for gate-tunable spintronic devices without applying an external magnetic field. Here, we demonstrate that the magnetic orders in V-doped WSe2 can be modulated by tuning carrier densities using ab initio calculations. We found that at a low V-doping concentration limit, the long-range ferromagnetic order is enhanced by increasing the hole density. In contrast, this long-range ferromagnetic order is suppressed at high electron density by compensating the p-type V dopant, originating from the strong localized antiferromagnetic coupling between V and W atoms and between V and Se atoms. The hole-mediated long-range magnetic exchange is similar to 70 meV, thus strongly suggesting the ferromagnetism in V-doped WSe2 at room temperature. Our findings on strong coupling between charge and spin order in V-doped WSe2 provide plenty of room for multifunctional gate-tunable spintronics11Nsciescopu
Teacher’s Perception: Designing Step-by-Step LOC-R (Literacy, Orientation, Collaboration, Reflection) in Sociocultural Literacy Teaching
No full textSociocultural literacy is required in Indonesia to sustain the nation’s integrity. As a result, the Ministry of Religious included it in the AKMI component. It is essential in developing creative learning in the future post-AKMI learning environment in 2021. This article exposes the step-by-step LOC-R paradigm, which became an alternative to study sociocultural literacy following the adoption of AKMI. During the process of designing learning activities from this set of LOC-R stages, there is also a teacher’s perspective to consider. Literacy, orientation, collaboration, and reflection are all highly important steps in building sociocultural literacy competences, since they steadily develop students’ cognitive processes. The author of the module, which includes eight learning activities using LOC-R syntax, claims that development will be simple provided teachers understand the flow, principles, and basics of sociocultural literacy acquisition
Application-oriented microfluidic LOC devices for the detection of microorganisms, toxic chemicals and serological biomarkers
No full textLab-on-a-chip (LOC) technology has advanced over the past several decades. As miniaturized multiphase multistep reactors, LOCs are suitable for the implementation of complex liquid phase reactions in the field of biomedical detection. This doctoral thesis focused on the development of new LOC devices and relevant functionalities for various application cases, including microbe detection, water-safety testing, while also presenting preliminary studies on the measurement of signal molecules in blood.
The application-oriented R&D (research and development) strategy was employed in the studies on a series of biomedical LOC devices. Technological challenges, e.g. optimization of on-chip quantification NASBA (nucleic acid sequence-based amplification) protocols, system design etc. were resolved in individual cases. Based on a low-cost R&D strategy, most LOCs in this doctoral work were developed for bench-top equipment as disposable components. It is worth noting that a methodological concept is also developed and summarized in this thesis, i.e., the selection of decision support mechanisms (DSMs) for biomedical LOC devices.
The DSM is the supporting mechanism generating measurable signals in the LOC, and translating them into a meaningful conclusion, which can help users to make decisions in the real application field. Namely, DSMs can enable LOC-based testing and are thus a distinguished feature of application-oriented LOC devices. The author categorized the research achievements presented in this thesis into three distinctive classes, as follows:
1) Conventional DSMs commonly employed in current biomedical experimental approaches.
Articles I, II and III focus on this category of DSMs. The series of LOCs in these reports were modelled on standard microtiter plates, and thus these chips are completely compatible with the microplate readers commonly utilized in biological laboratories. Article I reported the design, fabrication and validation of a disposable 43-chamber LOC device for quantitative detection of waterborne pathogens. Its principle was similar to conventional ELISA(enzyme-linked immunosorbent assay) tests for microbes, entitled X. Zhao: Application-oriented microfluidic LOC devices for the detection of microorganisms, toxic chemicals and serological biomarkers immuno-NASBA assay. A synthetic peptide and two common waterborne pathogens (Escherichia coli and rotavirus) in artificial samples were used to validate the LOC functions, which indicated that the LOC device has the potential to quantify traces of waterborne pathogens with high specificity.
Article II described the development of a LOC platform for environmental investigations into aquatic microorganisms, on the basis of quantitative NASBA (Q-NASBA). The LOC system was composed of a membrane-based sampling module, a sample preparation cassette, and a 24-channel Q-NASBA chip. The DSM of the LOC was derived from the polyurethane-foam-unit (PFU) method, which has been widely used to evaluate environmental pollution in fresh water. The multifunctional system could simplify and standardize the complicated processes of microbial detection.
Article III addressed the implementation of a 384-chamber microfluidic simulator with the incorporated functions of pathogen identification and antimicrobial susceptibility testing (AST) for personalizing the antibiotic treatment of urinary tract infections (UTIs). Its DSM adopted the diagnosis principle of conventional ATP bioluminescence assay (ATP-BLA) for living microbial cells.
2) Unconventional DSMs for contrived LOC systems. The second class of biomedical LOCs employs tailored DSMs, which are still derived from known working principles. However, the concrete mechanisms and diagnostic criteria are arbitrary in contrived functional LOCs.
Article IV investigated a bioluminescent-cell-based continuous-flow device, termed a ‘living-cell chip’, with a self defining DSM to implement real-time broad-spectrum online monitoring of water quality. The prototype integrated a T-junction droplet generator, counter-flow micro-mixers, and time-delay channels. The LOC device can mix the water sample and Vibrio fischeri cell sensors into a droplet flow, and incubate the droplets in the time-delay channels before optical detection. Its DSM relies upon the relationship between the toxicant concentration in the water sample and the relative luminescence units of the bioluminescent cells in the running droplets, which is obviously different from the conventional intermittent method of ISO11384. The proposed LOC system shows great promise for an early warning system against potential toxicant chemicals in drinking water.
3) Developing prognostic/diagnosis DSMs for biomedical-database-dependent LOC systems with the aid of computational modelling. The third category relies on computational modelling within a large-scale medical/healthcare database, which is currently emerging and is not yet completely developed.
Article V reported a pilot study on the design and fabrication of the LOC device for signal molecule profiling in blood.
Articles VI proposed the potential roadmap and preliminary experimental approach for the construction of a human signal-molecule-profiling database (HSMPD) by the use of the former LOC device, leading to prognostic/diagnosis DSMs in the future
NMR shieldings from sum-over-states density-functional-perturbation theory: Further testing of the ‘‘Loc.3’’ approximation
No full textThe development and implementation of sum-over-states density-functional-perturbation theory (SOS-DFPT) [V.G. Malkin, O.L. Malkina, M.E. Casida, and D.R. Salahub, J. Am. Chem. Soc. 116, 5898 (1994)] has allowed a significant improvement in the accuracy of nuclear magnetic resonance (NMR) chemical shift values over the Hartree–Fock approximation. Furthermore, due to its computational efficiency, SOS-DFPT has opened the way to the study of systems of increased size compared to those that may be approached by more sophisticated but also computationally more intensive methods, such as Møller–Plesset perturbation theory or coupled-cluster theory. The success of SOS-DFPT relies on the introduction of an ad hoc correction to the excitation energy that improves the calculation of the paramagnetic component of the NMR shielding tensor. The lack of a clear physical basis for this approximation has left the SOS-DFPT open to some criticism. We have shown in a previous article [E. Fadda, M.E. Casida, and D.R. Salahub, Int. J. Quantum Chem. 91, 67 (2003)] that the electric field and magnetic field responses are given by equivalent expressions within the Tamm–Dancoff approximation of time-dependent density-functional theory (TD-DFT). This provides an SOS-DFPT expression which, upon restriction to diagonal contributions, yields a new rigorous “Loc.3” approximation. In this article, we more than double our original test set of 10 molecules for 13C, 15N, and 17O chemical shifts to a set of 25 molecules. In addition, we compare the results of “Loc.3” SOS-DFPT with the results of promising recent functionals for DFT calculations of chemical shifts. The results show not only that the “Loc.3” approximation represents the rigorous physical connection between SOS-DFPT and TD-DFT, but also that it has very good potential for the prediction of NMR shielding constants, opening the way to further developments in DFT-based NMR parameter calculations
Long-range ferromagnetic ordering in vanadium-doped WSe2 semiconductor
No full text© 2019 Author(s).We report long-range ferromagnetic ordering in a vanadium-doped monolayer WSe2 semiconductor using spin-polarized density functional calculations. We found that the vanadium dopant is located in the fully occupied state inside the valence band, inherent from spin-orbit coupling, leading to the presence of free holes in the valence band. As a consequence, the spin-polarized hole carriers are delocalized not only in the vanadium site but also persistently in the tungsten sites distant from vanadium to facilitate the long-range ferromagnetic ordering in the vanadium-doped monolayer WSe2. Our findings of this study pave the way for the future exploration of carrier-mediated room-temperature two-dimensional ferromagnetic semiconductors via magnetic dopants11sciescopu
Revealing antiferromagnetic transition of van der Waals MnPS3 via vertical tunneling electrical resistance measurement
No full textUnderstanding the correlation between the electronic and magnetic properties of materials is a crucial step to functionalize or modulate their properties. However, it is not straightforward to electrically characterize magnetic insulators, especially large-bandgap materials, due to their high resistivity. Here, we successfully performed electrical measurements of a two-dimensional (2D) antiferromagnetic insulator, van der Waals-layered MnPS3, by accounting for the vertical graphene/MnPS3/graphene heterostructure. Antiferromagnetic transition is observed by the variance in electrical resistance from the paramagnetic to antiferromagnetic transition near similar to 78 K in the vertically stacked heterostructure devices, which is consistent with the magnetic moment measurement. This opens an opportunity for modulating the magnetic transition of 2D van der Waals materials via an electrical gate or surface functionalization. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)11sciescopu
Greedy layerwise training of convolutional neural networks
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 61-63).Layerwise training presents an alternative approach to end-to-end back-propagation for training deep convolutional neural networks. Although previous work was unsuccessful in demonstrating the viability of layerwise training, especially on large-scale datasets such as ImageNet, recent work has shown that layerwise training on specific architectures can yield highly competitive performances. On ImageNet, the layerwise trained networks can perform comparably to many state-of-the-art end-to-end trained networks. In this thesis, we compare the performance gap between the two training procedures across a wide range of network architectures and further analyze the possible limitations of layerwise training. Our results show that layerwise training quickly saturates after a certain critical layer, due to the overfitting of early layers within the networks. We discuss several approaches we took to address this issue and help layerwise training improve across multiple architectures. From a fundamental standpoint, this study emphasizes the need to open the blackbox that is modern deep neural networks and investigate the layerwise interactions between intermediate hidden layers within deep networks, all through the lens of layerwise training.by Loc Quang Trinh.M. Eng.M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Scienc
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