56016 research outputs found
Sort by
?????? ????????? ?????? ?????? ?????? ??? ?????? ????????? ????????? ????????? ????????????
No full textDepartment of Mechanical Engineeringclos
A Structural Study of Protein Intermediate States Using Photolysis-Induced pH-Jump Method
No full textDepartment of Physicsclos
A study on atmospheric CO2 concentration using a global chemical transport model
No full textDepartment of Urban and Environmental Engineering (Disaster Management Engineering)clos
A STUDY ON PROCESS PARAMETERS AND MANUFACTURING SUSTAINABILITY OF ADDITIVELY MANUFACTURED LATTICE STRUCTURE UNDER THE UNIAXIAL COMPRESSION
Get PDFDepartment of Mechanical EngineeringAdditive manufacturing (AM), also called 3D printing, is a new process that can improve the inefficiency of existing manufacturing processes and has been applied to various industries, such as vehicles and space. In order to replace the existing process, the newly proposed method must be verified in terms of sustainability as well as quality and efficiency of production. This research presents verification of the newly introduced AM process through one case study about cushion manufacturing. In the conventional cushion manufacturing process, there are inefficient processes, such as a requirement of too many types of foam and a dependency on a manual assembly process that relies on the skill of the individual worker.
In this study, a selective laser sintering (SLS) process for improving the cushioning process is suggested. Through orthogonal and regression analysis, the relationship between the three SLS process parameters (laser power, scan speed, and hatching distance) and cushion comfort factors (compression load, sag factor, and hysteresis loss rate) was derived by polynomial fitting to replace the conventional cushion foam with the additively manufactured lattice structure. In addition, the results of the comparison between AM process and the conventional manufacturing (CM) process in two aspects of energy use and environmental impact were derived through the life cycle assessment (LCA) of the cushion manufacturing process.
The results show that AM has clear advantages in both energy use and environmental impact in less than 75 production volumes, and the derived regression equation shows that desirable cushion properties can be implemented through only one process and one material. The presented parametric design and sustainable assessment framework will contribute as a decision-making tool for researchers and market stakeholders who want to improve the inefficiency of existing processes in all industries.ope
Coverage Path Planning Fused Multi-UAV Source Term Estimation
No full textDepartment of Mechanical EngineeringWhen a gas leak occurs from an industrial complex, the leakage point, or source term location must be determined. The presented algorithm suggests a strategy that allows multiple unmanned aerial vehicles (UAV) to estimate a source term location with high accuracy within a grid-based area. The strategy consists of three main algorithmic steps: cellular decomposition, optimal coverage path planning, and information theory-based movement policy. Suggested cellular decomposition method divides the area to designate a conflict-free sub-search-space to individual UAV, while accounting the assigned individual flight velocity, and take-off position. The path planning strategy forms paths based on every point located in end of each grid row. The first waypoint is chosen as the closest point from the take-off position, and it recursively updates the nearest end point set to generate the shortest path. Then, the path planning strategy forms paths based on every point located in end of each grid row. The first waypoint is chosen as the closest point from the vehicle-starting position, and it recursively updates the nearest end point set to generate the shortest path. The path planning policy produces four path candidates by alternating the starting point (left or right edge), and the travel direction (vertical or horizontal). The optimal-selection policy is enforced to maximize the search efficiency, which is time dependentthe policy imposes the total path-length and turning number criteria per candidate. Vehicles send measurements and position data to a single particle filter for source term estimation while pursuing the coverage paths. As particle filter converges to a certain level, the vehicles are attracted toward arbitrary radius from the particle filter mean. UAVs compare the measurement data to confirm whether the actual source position is nearby the particle filter mean. The presented method demonstrates that UAVs estimate the source term location with high accuracy in numerical simulation and field experiment.ope
????????? ?????? ?????? ????????? ????????? ??????
No full textDepartment of Mechanical Engineeringclos
Development of Prismatic Cells for Rechargeable Seawater Batteries and its Stabilization
No full textSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))clos
Double-Floating-Gate van der Waals Transistor for High-Precision Synaptic Operations
Get PDFDepartment of Materials Science and EngineeringTwo-dimensional materials and their heterostructures have thus far been identified as leading candidates for nanoelectronics owing to the near-atom thickness, superior electrostatic control, and adjustable device architecture. These characteristics are indeed advantageous for neuro-inspired computing hardware where the precise programming is strongly required. However, its successful demonstration fully utilizing all of the given benefits remains to be further developed. Herein, we present van der Waals (vdW) integrated synaptic transistors with multi-stacked floating gates, which are reconfigured upon surface oxidation. When compared with a conventional device structure with a single floating gate, our double-floating-gate (DFG) device exhibits better non-volatile memory performance, including a large memory window (100 V), high on???off current ratio (107), relatively long retention time (5000 s), and satisfactory cyclic endurance (500 cycles), all of which can be attributed to its increased chargestorage capacity and spatial redistribution. This facilitates highly effective modulation of trapped charge density with a large dynamic range. Consequently, the DFG transistor exhibits an improved weight update profile in long-term potentiation/depression synaptic behavior for nearly ideal classification accuracies of up to 96.12% (MNIST) and 81.68% (Fashion-MNIST). Our work adds a powerful option to vdW-bonded device structures for highly efficient neuromorphic computing.ope
Effect of Residual Stress on Stress Corrosion Cracking Behavior of Stainless Steel 304L in Secondary Water Environment of Nuclear Power Plant
No full textDepartment of Nuclear Engineeringclos
????????? ????????? ????????? ?????????????????? ?????? ??????????????? ????????? ??????: ??????, ???????????? ??? ????????????
No full textDepartment of ChemistryHyperbranched polyhydrocarbons (PHCs) synthesized by electrochemical polymerization are
attractive polymeric materials in the context of synthetic methods, mechanism analyses, and structural
analyses. We note that (i) large-scale continuous production of PHC by electrochemical polymerization,
(ii) mechanism analysis in the aspects of initiation, propagation, and termination, (iii) structural analysis
method for hyperbranched PHC. The continuous production system controlled the monomer loading
and product transfer by changing flow direction in a home-built continuous flow system that facilitates
preparation, work-up, and scale-up of the electrochemical polymerization. The polymerization can be
tuned by adjusting reaction time, cell configuration, molar ratio of input chemicals, and the solvent
types. Through the above parametric studies, sufficient amounts of product are generated by continuous
production that characterization of the PHCs by a wide variety of methods is possible. Dichloromethane
(CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4) were used to synthesize PHCs as a
monomer. The oxidation/reduction behaviors of these monomers and acetonitrile (CH3CN) as a solvent
were investigated by cyclic voltammetry (CV) and chronoamperometry: with the aim to investigate
overall synthetic pathway using isotope-labeled chemicals. The CV analysis performed to distinguish
functions of anode and cathode when stainless steel electrodes were used, and to investigate the
mechanism of polymerization processes. The mechanism of initiation and propagation was analyzed by
CV combined with nuclear magnetic resonance (NMR) and fourier transform infrared (FT-IR),
furthermore, we accurately identified the termination where the hydrogen atoms in PHCs came from
using NMR analyses with deuterated acetonitrile (CD3CN) and chloroform (CDCl3). A signal-to-noise
ratio in 13C-NMR spectra according to quantitative relation of 12C/13C produced a participation ratio of
each chemical in the electrochemical polymerization. NMR techniques including 1H-NMR, quantitative
13C-NMR, distortionless enhancement by polarization transfer (DEPT) 13C-NMR, and heteronuclear
single quantum coherence (HSQC) 1H-13C 2D NMR along with elemental analysis and FT-IR were used
to experimentally assess the likely structure of this complex polymer with random branching. The
polymer structure was modelled based on the NMR results. Room temperature density, refractive index,
melting temperature, and IR spectrum were good matches to the values, and spectrum, calculated using
the simulated structure. Calculated Hildebrand solubility parameters for the simulated structure
rationalize the room temperature solubility measured in a range of solvents. The experimental and
modeling methods are likely to be applicable to any type of highly random branched polymers.
Particularly, structural analysis by various NMR techniques is the first comprehensive elucidation of
the structure of an unknown and randomly hyperbranched polymer by combining experimental results
and theoretical simulation, and the methods described should find broad use in the future.clos