Research on the Formation Mechanism of Surface Morphology in Three-Excitation Ultrasonic Spatial Vibration-Assisted Turning

To improve the machining performance of different processing materials, a three-excitation ultrasonic spatial vibration-assisted turning system is proposed, which realizes the non-unity of the plane where the cutting trajectory of the tool is located. The influence and formation law of three-excitation ultrasonic spatial vibration-assisted turning on the surface roughness of the workpiece under different vibration parameters (amplitude) and machining parameters (cutting speed, cutting depth, and feed) were analyzed by response surface methodology. The results show that in terms of vibration parameters, the influence of ultrasonic vibration applied in the horizontal direction on surface roughness is significantly greater than that of ultrasonic vibration applied in the vertical direction, while the feed has the greatest influence on surface roughness, followed by cutting speed. The surface roughness of common turning, one-dimensional ultrasonic vibration-assisted turning, ultrasonic elliptical vibration-assisted turning, and three-excitation ultrasonic spatial vibration-assisted turning were theoretically analyzed and experimentally compared. The results show that compared with the other three turning methods, the three-excitation ultrasonic spatial vibration-assisted turning can obtain a lower surface roughness and have good machinability.

The Impact of Alumina Nanofluids on Pool Boiling Performance on Biphilic Surfaces for Cooling Applications

This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling and heat transfer. For this purpose, biphilic surfaces (hydrophilic surfaces with superhydrophobic spots) were used, which allow the individual analysis of bubbles. Surfaces with different configurations of superhydrophobic regions were used. The thermophysical properties of fluids only vary slightly with increasing nanoparticle concentration. The evolution of the dissipated heat flux and temperature profiles for a nucleation time frame is independent of the fluid and imposed heat flux. It can be concluded that the optimal concentration of nanoparticles is 3 wt%. Using this nanoparticle concentration leads to lower surface temperature values than those obtained with water, the reference fluid. This is due to the changes in the balance of forces in the triple line, induced by increased wettability as a consequence of the deposited particles. Wherefore, smaller and more frequent bubbles are formed, resulting in higher heat transfer coefficients. This effect, although relevant, is still of minor importance when compared to that of the use of biphilic surfaces.

Imaging the electrostatic landscape of unstrained self-assemble GaAs quantum dots

Unstrained GaAs quantum dots are promising candidates for quantum information devices due to their optical properties, but their electronic properties have remained relatively unexplored until now. In this work, we systematically investigate the electronic structure and natural charging of GaAs quantum dots at room temperature using Kelvin probe force microscopy (KPFM). We observe a clear electrical signal from structures demonstrating a lower surface potential in the middle of the dot. We ascribe this to charge accumulation and confinement inside these structures. Our systematical investigation reveals that the change in surface potential is larger for a nominal dot filling of 2 nm and then starts to decrease for thicker GaAs layers. Using k . p calculation, we show that the confinement comes from the band banding due to the surface Fermi level pinning. Our results indicate that these self-assembled structures could be used to study physical phenomena connected to charged quantum dots like Coulomb blockade or Kondo effect.

Characterizing the Chemical Structure of Ti3C2Tx MXene by Angle-Resolved XPS Combined with Argon Ion Etching

Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti3C2Tx MXene. Survey scanning obtained on the sample surface showed that the sample mainly contains C, O, Ti and F elements, and a little Al element. Analyzing the angle-resolved narrow scanning of these elements indicated that a layer of C and O atoms was adsorbed on the top surface of the sample, and there were many O or F related Ti bonds except Ti–C bond. XPS results obtained after argon ion etching indicated staggered distribution between C–Ti–C bond and O–Ti–C, F–Ti bond. It is confirmed that Ti atoms and C atoms were at the center layer of Ti3C2Tx MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti3C2 layer acting as surface functional groups. The surface functional groups on the Ti3C2 layer were determined to include O2−, OH−, F− and O−–F−, among which F atoms could also desorb from Ti3C2Tx MXene easily. The schematic atomic structure of Ti3C2Tx MXene was derived from the analysis of XPS results, being consistent with theoretical chemical structure and other experimental reports. The results showed that angle-resolved XPS combing with argon ion etching is a good way to analysis 2D thin layer materials.

The Effects of Different Gaps on the Weld Morphology, Microstructure and Residual Stress of AH36 Steel were Studied by Laser Arc Hybrid Welding

In this study, laser (TruDisk16002)-arc (MAG) hybrid welding was used to weld a 5mm thick sheet of AH36 steel with a gap of 0mm and 1mm. The results show that when the current of MAG is 205A, the voltage is 31.9V, and the laser power is 7.5KW, the welds of 0mm gap and 1mm gap are well formed, showing a typical nail shape, and the 0mm gap weld is better than 1mm. Under the same welding process parameters, the heat-affected zone of a 0mm gap weld is less than 1mm. Upper bainite is found in the 1mm weld gap structure. In the two gap cases, the residual stress on the lower surface is larger than that on the upper surface, and the residual stress in the 1mm weld gap is larger. The weldability of 0mm weld gap is better than 1mm.

Cryogenic thermal insulating and mechanical properties of rigid polyurethane foams blown with hydrofluoroolefin: Effect of perfluoroalkane

The effect of perfluoroalkane (PFA) on the morphology, thermal conductivity, mechanical properties and thermal stability of rigid polyurethane (PU) foams was investigated under ambient and cryogenic conditions. The PU foams were blown with hydrofluorolefin. Morphological results showed that the minimum cell size (153 μm) was observed when the PFA content was 1.0 part per hundred polyols by weight (php). This was due to the lower surface tension of the mixed polyol solution when the PFA content was 1.0 php. The thermal conductivity of PU foams measured under ambient (0.0215 W/mK) and cryogenic (0.0179 W/mK at −100°C) conditions reached a minimum when the PFA content was 1.0 php. The low value of thermal conductivity was a result of the small cell size of the foams. The above results suggest that PFA acted as a nucleating agent to enhanced the thermal insulation properties of PU foams. The compressive and shear strengths of the PU foams did not appreciably change with PFA content at either −170°C or 20°C. However, it shows that the mechanical strengths at −170°C and 20°C for the PU foams meet the specification. Coefficient of thermal expansion, and thermal shock tests of the PU foams showed enough thermal stability for the LNG carrier’s operation temperature. Therefore, it is suggested that the PU foams blown by HFO with the PFA addition can be used as a thermal insulation material for a conventional LNG carrier.

Comparative LM, SEM and EDAX study of chalk glands on leaf and stem of two species of Plumbago Linn.

Stem and leaves of two species of PlumbagoLinn.viz. P. zeylanica Linn.andP. auriculata Lam. were investigated for the structure and chemical composition of chalk glands. Light Microscopy (LM) and Scanning Electron Microscopy (SEM) revealed the presence of chalk glands on both lower as well as upper surface of leaf and stem of both species. Chalk glands are abundant on lower surface and sparse on upper surface of leaf. Chalk glands are approximately hemispherical glands with oval or almost circular outline. It is composed of 8 cells arranged in two circles – central circle of 4 secretory cells and outer circle of 4 adjoining cells. Each secretory cell has depression which corresponds to pore. Each gland is surrounded by 4 subsidiary cells. No significant difference in the structure of chalk glands in both species was noticed. Chalk glands occupy three different positions with regard to epidermal cells –at the same level of the epidermis, slightly sunken in the epidermis and slightly raised above the epidermis. Common elements found in EDAX analysis of all chalk glands are carbon, oxygen, magnesium, sulphur, potassium and calcium. Differences in the presence of elements silicon, chlorine, aluminium, sodium, phosphorus were observed. The presence of significant amount of calcium in chalk glands and their dried deposits and absence of sodium and chlorine from dried deposits and even in some chalk glands appealed to use the term ‘Chalk gland’ instead of ‘Salt gland’ in Plumbago.

Morphometry and Stiffness of Red Blood Cells—Signatures of Neurodegenerative Diseases and Aging

Human red blood cells (RBCs) are unique cells with the remarkable ability to deform, which is crucial for their oxygen transport function, and which can be significantly altered under pathophysiological conditions. Here we performed ultrastructural analysis of RBCs as a peripheral cell model, looking for specific signatures of the neurodegenerative pathologies (NDDs)—Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD), utilizing atomic force (AFM) and conventional optical (OM) microscopy. We found significant differences in the morphology and stiffness of RBCs isolated from patients with the selected NDDs and those from healthy individuals. Neurodegenerative pathologies' RBCs are characterized by a reduced abundance of biconcave discoid shape, lower surface roughness and a higher Young’s modulus, compared to healthy cells. Although reduced, the biconcave is still the predominant shape in ALS and AD cells, while the morphology of PD is dominated by crenate cells. The features of RBCs underwent a marked aging-induced transformation, which followed different aging pathways for NDDs and normal healthy states. It was found that the diameter, height and volume of the different cell shape types have different values for NDDs and healthy cells. Common and specific morphological signatures of the NDDs were identified.

Experimental and Numerical Study of Surface Roughness of Thin Brass Wire Processed by Different Dieless Drawing Processes

This paper examines the surface roughness of a thin brass wire (140–200 microns in diameter) after two dieless drawing (DD) processes, i.e., conventional dieless drawing (CDD) and incremental dieless drawing (IDD). In incremental dieless drawing, small increments in deformation were applied in several passes. It has been proven that the IDD process not only has a greater efficiency but also enables obtaining a wire with significantly lower surface roughness. The explanation for these effects is based on the results of the numerical modeling of both compared processes. The developed numerical model takes into consideration the initial roughness of the wire surface, shape and dimensions of grains, and their diversified mechanical properties. Nanoindentation measurements, microstructure, and plastometric studies allowed us to find the effective flow stress distribution in the grains. The IDD process was found to be much more stable and develop a much more uniform distribution of grain strain than the CDD process. More homogeneous deformation results in surface roughness reduction. Approximately 25–30% reduction in surface roughness of the wire produced by the IDD process was predicted by simulations and confirmed experimentally.