| 1. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Guo, Xin, et al.
(författare)
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Machinability study on dry machining of white cast iron by polycrystalline cubic boron nitride inserts
- 2022
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Ingår i: Machining Science and Technology. - : Informa UK Limited. - 1091-0344 .- 1532-2483. ; 26:2, s. 137-159
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Tidskriftsartikel (refereegranskat)abstract
- The polycrystalline cubic boron nitride (PCBN) insert has been widely used in machining high chromium white cast iron (HCCI), which has the high hardness and abrasiveness. The aim of this article is to reveal that micro-mechanical properties play an essential role in assessing the machinability of high chromium cast iron. Grid nanoindentation is applied to measure the micro-hardness distribution. Based on grid nanoindentation results, the micro-hardness distribution is proposed to study the machinability. After the machining test of HCCI by the PCBN insert, the cutting force, tool wear, surface roughness, and chip formation showed that the micro-hardness distribution of materials has the better results than macro-hardness in machinability evaluation, and abrasive wear occurred on the rake and flank face of the cutting tool. The abrasiveness index that is related with the micro-hardness distribution and the abrasive wear effect in machining, for the most of high abrasion materials, has the possible to evaluate the dynamic cutting process and tool life in dry machining by using the PCBN insert. The micro-hardness distribution imported into the machinability model may propose a new way to improve the data exchange capability in the modern manufacturing process.
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| 3. |
- Hu, Cheng, et al.
(författare)
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On the steady-state workpiece flow mechanism and force prediction considering piled-up effect and dead metal zone formation
- 2021
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Ingår i: Journal of Manufacturing Science and Engineering. - : ASME International. - 1087-1357 .- 1528-8935. ; 143:4
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Tidskriftsartikel (refereegranskat)abstract
- The manufacturing of miniaturized components is indispensable in modern industries, where the uncut chip thickness (UCT) inevitably falls into a comparable magnitude with the tool edge radius. Under such circumstances, the ploughing phenomenon between workpiece and tool becomes predominant, followed by the notable formation of dead metal zone (DMZ) and piled-up chip. Although extensive models have been developed, the critical material flow status in such microscale is still confusing and controversial. In this study, a novel material separation model is proposed for the demonstration of workpiece flow mechanism around the tool edge radius. First, four critical positions of workpiece material separation are determined, including three points characterizing the DMZ pattern and one inside considered as stagnation point. The normal and shear stresses as well as friction factors along the entire contact region are clarified based on slip-line theory. It is found that the friction coefficient varies symmetrically about the stagnation point inside DMZ and remains constant for the rest. Then, an analytical force prediction model is developed with Johnson-Cook constitutive model, involving calibrated functions of chip-tool contact length and cutting temperature. The assumed tribology condition and morphologies of material separation including DMZ are clearly observed and verified through various finite element (FE) simulations. Finally, comparisons of cutting forces from cutting experiments and predicted results are adopted for the validation of the predictive model.
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| 4. |
- Jia, Pan, et al.
(författare)
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The combination of 2d layered graphene oxide and 3d porous cellulose heterogeneous membranes for nanofluidic osmotic power generation
- 2021
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Ingår i: Molecules. - : MDPI AG. - 1420-3049 .- 1420-3049 .- 1431-5157. ; 26:17
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Tidskriftsartikel (refereegranskat)abstract
- Salinity gradient energy, as a type of blue energy, is a promising sustainable energy source. Its energy conversion efficiency is significantly determined by the selective membranes. Recently, nanofluidic membrane made by two-dimensional (2D) nanomaterials (e.g., graphene) with densely packed nanochannels has been considered as a high-efficient membrane in the osmotic power generation research field. Herein, the graphene oxide-cellulose acetate (GO–CA) heterogeneous membrane was assembled by combining a porous CA membrane and a layered GO membrane; the combination of 2D nanochannels and 3D porous structures make it show high surface-charge-governed property and excellent ion transport stability, resulting in an efficient osmotic power harvesting. A power density of about 0.13 W/m2 is achieved for the sea–river mimicking system and up to 0.55 W/m2 at a 500-fold salinity gradient. With different functions, the CA and GO membranes served as ion storage layer and ion selection layer, respectively. The GO–CA heterogeneous membrane open a promising avenue for fabrication of porous and layered platform for wide potential applications, such as sustainable power generation, water purification, and seawater desalination.
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| 5. |
- Liu, Yang, et al.
(författare)
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Evolution of residual stress when turning a fillet radius in stainless steel
- 2023
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Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 85, s. 216-226
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Tidskriftsartikel (refereegranskat)abstract
- Most studies have been carried out to investigate the surface integrity induced by metal cutting process. However, the previous studies are limited to a longitudinal turning or orthogonal cutting operations and the residual stresses generated in a fillet radius have been ignored. This study uses a combination of experiments and numerical simulations to study the evolution of cutting forces, temperature, chip morphology, and residual stress distributions while turning a fillet radius in AISI 304. Finite Element (FE) models were developed with a Coupled Eulerian and Lagrangian (CEL) method, where the geometric model of the workpiece was established taking into account the previous machined surface profile at the four specific cutting faces. The model was validated by experimental cutting forces, chip morphology, and residual stress profiles. The changing trend of shape and area of uncut chip cross-section during fillet turning were analyzed to explain the evolution of cutting forces and temperatures. The results show that the cutting force components in cutting speed and tangential directions increase during the early stage of the fillet turning process and decrease after that, while the force in the radial direction shows an increasing trend during this process. The maximum temperature at the machined surface is increased along the tool path. In addition, magnitude and depth of residual stress are slightly changed during the fillet radius turning process, but a reduction of the residual stress profile can still be noticed.
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| 6. |
- Liu, Yang, et al.
(författare)
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FE analysis on the association between tool edge radius and thermal-mechanical load in machining Inconel 718
- 2021
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Ingår i: 18th CIRP Conference on Modeling of Machining Operations (CMMO), Ljubljana, Slovenia, June 15-17, 2021. - : Elsevier BV. - 2212-8271. ; 102, s. 91-96
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Konferensbidrag (refereegranskat)abstract
- The cutting edge geometry has a significant influence on thermal-mechanical loads and the quality of machined surface in machining operations. In this study, a joint numerical and experimental investigation was conducted to study the effects of tool edge radius on process variables (tool temperatures, force components, stresses) and process dynamics in orthogonal machining Inconel 718. The numerical model was implemented based on Coupled Eulerian-Lagrangian (CEL) formulation, in which the tool is regarded as elastic, making it possible to realise the fluctuation of the tool tip. The results show that the temperature at the tool tip is more sensitive to the change of edge radius than the maximum temperature at the tool-chip interface. The force components acting on rake face and flank face increase with increasing edge radius due to more negative effective rake angle and increasing ploughing depth respectively. Besides, the generated chip tends to be more segmented with increase of edge radius, causing severer fluctuation of forces and tool tip displacement. It was also found that a larger edge radius leads to a smaller uncut chip thickness and a poor surface roughness.
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| 7. |
- Liu, Yang, et al.
(författare)
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Investigation on residual stress evolution in nickel-based alloy affected by multiple cutting operations
- 2021
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Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 68, s. 818-833
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Tidskriftsartikel (refereegranskat)abstract
- Machining-induced residual stresses in a part can significantly influence its performance and service time. It is common that the final surface of the part is produced after multiple cuts in the machining process. In multiple cuts, the previous cuts could often generate accumulated strain/stress and temperature on the part surface. These accumulated strain/stress and temperature will be brought to the subsequent cut or final cut and continuously affect the cutting forces, process temperatures, deformation zones, etc. in subsequent cut, and eventually affect the final residual stresses on the part. This paper reports on a joint experimental and numerical investigation to explore the influence of previous cuts on surface residual stresses with consideration of cutting parameters, cutting procedure, and tool geometries in multiple cut of Inconel 718 alloy. Coupled Eulerian and Lagrangian (CEL) formulation is used in a two/three-cuts numerical model. The loading cycles of the selected material nodes are characterised based on isotropic constitutive model (Johnson-Cook model) to analyse the underlying mechanism of residual stress evolution during cutting sequences. The results show that accumulated stress/strain induced by previous cuts lead to a more curled chip morphology, a slight decrease in cutting force and a slight increase in feed force in the subsequent cut. An increased magnitude and depth of compressive residual stresses in the finished workpiece are generated owing to the influence of previous cuts, and this is more obvious when the previous cut is implemented at a larger uncut chip thickness, using a more negative rake angle or a larger edge radius tool. The residual stress level might be controlled by optimizing the previous cuts to get the desired surface integrity.
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| 8. |
- Liu, Yang, et al.
(författare)
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Numerical and experimental investigation of tool geometry effect on residual stresses in orthogonal machining of Inconel 718
- 2021
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Ingår i: Simulation Modelling Practice and Theory. - : Elsevier BV. - 1569-190X. ; 106
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Tidskriftsartikel (refereegranskat)abstract
- Residual stress has become more important than ever with the increasing performance requirement of components especially for those applied in safety-critical areas. As the machining process is fundamentally correlated with the acquired component properties, it is essential to fully understand the formation mechanism of residual stresses in the cutting process and its influence on the performance of the component. This paper presents results based on numerical and experimental analysis on the effect of tool geometry on thermal-mechanical load and residual stresses in orthogonal machining Inconel718 alloy. The Coupled Eulerian-Lagrangian (CEL) method is used to simulate the effect of tool geometry on temperatures, forces, equivalent plastic strains, and residual stresses. The local normal/tangential stress is introduced to determine the degree of the tensile plastic deformation induced by the tool. It is observed that a negative rake angle and a sharp edge radius tool tend to generate more compressive stress on the machined surface than the ones generated with positive rake angle tools and/or lager edge radius. Besides, an increase in flank wear produces less magnitude of compressive stress in subsurface due to a decreased local normal stress caused by increased flank contact length.
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| 9. |
- Liu, Yang, et al.
(författare)
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Numerical contribution to segmented chip effect on residual stress distribution in orthogonal cutting of Inconel718
- 2020
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Ingår i: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 109, s. 993-1005
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Tidskriftsartikel (refereegranskat)abstract
- Segmented chip morphology has a significant influence on distribution of residual stress and surface topography on machined surface in machining difficult-to-cut materials. In this paper, Coupled Eulerian and Lagrangian (CEL) model is employed to investigate the effect of segmented chip on surface integrity (residual stress distribution and surface topography) in orthogonal machining of Inconel718 with uncoated carbide inserts. A mesh sensitivity study of chip morphology and residual stress distribution is performed by developing the following three different grid resolutions: coarse (mesh size 35 μm), medium (10 μm) and fine (5 μm). Comparing with the experimental results, it is clear that the numerical model presents reasonable results, including the chip morphology, temperature distribution, cutting forces, residual stress profile and surface fluctuation period. As for the generated surface integrity, a waved surface and cyclic residual stress distribution are found with the segmented chip due to the periodical mechanical and thermal loadings acting on the machined surface. Furthermore, the formation of single chip segment is investigated in-depth to explain the residual stress distribution generation.
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| 10. |
- Nariyangadu, Sesha Bamini, et al.
(författare)
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New nonlinear optical crystal of rhodamine 590 acid phthalate
- 2020
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:33, s. 20863-20873
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and crystal structure of rhodamine 590 acid phthalate (RhAP) have been reported. This novel solid-state rhodamine derivative not only has a longer fluorescence lifetime compared to rhodamine solid-state matrixes where emission is quenched but also possesses strong nonlinear optical characteristics. The static and dynamic first- and second-order hyperpolarizabilities were calculated using the time-dependent density functional theory at the B3LYP/6-31+G∗ level. The computed static values of β and γof RhAP by the X-ray diffraction (XRD) structure were 31.9 × 10-30 and 199.0 × 10-36 esu, respectively. These values were about 62 times larger than the corresponding values in urea, an already well-known nonlinear optical material. The second-order hyperpolarizability of the compound was determined experimentally by measuring the two-photon absorption cross section using intensity-modulated light fields. The reported compound, excitable at near-infrared, exhibited frequency upconversion with the two-photon absorption coefficient enhanced by two orders of magnitude compared to that of the dye solution. Hosting the dye in the solid, at high concentrations, exploits the nonlinearity of the dye itself as well as results in significant excitonic effects including formation of broad exciton band and superradiance.
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