High Quality Micro Research Articles

Electrochemical microsurface texturing with reusable masked patterned tool

A unique and innovative concept of maskless electrochemical micromachining (EMM) method is used to generate the microsurface textures with low cost and short time. Maskless EMM setup consisting of EMM cell, electrode fixtures, electrode connections and constricted vertical cross flow electrolyte guiding scheme has been developed indigenously to carry out the experimental investigations for the generation of micro circular patterns. In this method, one reusable patterned cathode tool has been utilized to fabricate many high quality micro circular patterns economically. The effect of major process parameters like applied voltage, duty ratio, inter electrode gap, flow rate, pulse frequency and machining time on textured characteristics i.e. overcut, depth and surface roughness (Ra) has been investigated. Arrays of 8000 micro circular impressions are generated by maskless electrochemical micromachining. An analysis has been done to find out the best parametric combination on the basis of micrographs and experimental results.

Development of a precision grinding machine system for the fabrication of micro V-grooves array

The microstructures arrays are widely used and have good prospects in different applications because of their special and unique engineering functions. Micro V-grooves array is one of the most common micro structures used for optical and biomedical functions. Precision grinding is one of the micro mechanical machining technologies for a wide range of hard non-ferrous materials to fabricate micro structures array. In this paper, a three-axis computer numerical control (CNC) grinding machine tool is designed for the grinding of micro V-grooves array on hard and brittle materials. Material removal and machining strategy are studied for the grinding of V-grooves array. A machining strategy design (MSD) system is established to generate NC program, simulate the tool paths and machining process as well as predict the total machining time for the grinding of V-grooves array in the developed machine tool. Experiments are designed to grind flat surface and micro V-grooves array on optical glass. The experimental results show that the grinding machine tool can produce high quality surface and micro V-grooves array with sub-micrometer form accuracy.

Size effects in micro rolling of metals

Size effects are a unique characteristic with miniaturisation, and may cause a number of unexpected problems in micro rolling of metals in the aspects of mechanical behaviour, tribology, and scatter of material behaviour. This paper has introduced three kinds of micro rolling technologies, including micro ultrathin strip rolling, micro flexible rolling and micro cross wedge rolling, and analysed the size effects appeared in each of the micro rolling process. This paper will be helpful for understanding the problem of size effects, and can contribute to the manufacturing of high quality micro metallic products by minimising the impact of size effects in micro rolling with optimised processing parameters.

Innovative Design and Implementation of the Flipped Classroom Teaching Mode Based on the Micro-courses

Aiming at the common phenomenon in higher vocational colleges such as the sources of students are complex, a greater basic knowledge’s difference between students, their poor autonomous learning ability and lacking of learning interest and so on, this essay analyzes the main problems existing in the traditional teaching mode in Higher Vocational Education and the characteristics of Higher Vocational College students, shares the techniques of making high-quality micro course, designs innovatively the integration of the theory and practice of the Flip class teaching model, and designs teacher’s teaching activities in the circle of before and middle and after the course in details. Additionally, this essay introduces application of Flip class on internet.

Lead the Production of Micro Courses and Promote College Teachers' Research on Deepening Teaching

College teachers' teaching is faced with huge challenges in the Internet plus era, however, high-quality micro teaching resources can provide guarantees to improve teaching effect under this circumstance. Schoolman Center for Teaching Development should communicate with the companies in related technology actively according to the problems of the shortage of micro class resources and no experience in equipment operation and no understanding of technology and so on. Measures for improving the use of micro teaching model and the teaching research and teaching effect such as recording the micro class, technical training and the study on the subject should be taken, which can form firm backing for the college teachers.

Hybrid process of fabricating high-quality micro wine-glass fused silica resonators

A new hybrid method, which combines improved glass-blown technology with wet etching, is reported to fabricate micro wine-glass resonators with high-quality fused silica. The optimum placement is compared to achieve the resonators with good shell shape. The typical shell diameter is about 4mm and its thickness covers from dozens to hundreds of micrometers. The etching rates in corrosion solutions with different ratios and at different thicknesses of hemispherical shells are studied. We also conclude how to precisely control the thickness. The corrosion solutions with different ratios of HF solution to NH4F solution make the spherical shells rougher in different degrees. The best roughness is 0.581 nm in the 1: 8 ratio corrosion solution while the original roughness is 0.537 nm. This fact shows that the resonator remains atomically smooth surface. Based on the glassblowing spherical fused silica structure, the thickness of the resonator is effectively controlled by buffered oxide etch (BOE) technology according to the measured etching rate. The measured resonant frequency of the hemispherical shell at ambient pressure and room temperature is 1.75 kHz of rocking mode which is close to the simulated frequency. Using such a low-cost hybrid approach, we can fabricate high-quality microscale resonators in batch.

Developing a Process Chain with WEDG Technology and Pulse ECM to Fabricate Ultra Micro Pins

Micro tools are widely used in some industry application, such as medical device, touching probe and micro electrode for EDM. Micro tools with diameter less than 50μm have been successful to fabricate since the development of WEDG technology. Recently, some reports point out that it is also possible to produce micro tools with diameter less than 5μm by WEDG technology. However the machining efficiency and tool will be bending when the diameter is less than 10μm by WEDG Technology. Due to the electro-discharge and fluid action force, it is a still critical problem to fabricate a straight and tiny micro tool with diameter less than 10μm. In order to fabricate micro tool with diameter less than 10μm, a combined process of WEDG technology and electro chemical machining was proposed in this study. After WEDG technology applying to fabricate a micro tool with diameter approximately 40μm. Pulse ECM was used on the same machine to re-shape micro tools with diameter below 10μm. The experimental results show that with charge-coupled device (CCD) assistance the hybrid process is possible to fabricate a length of 1mm and diameter 10μm micro tool. To fabricate high quality micro tools, the parameters of WEDG technology and ECM such as discharge voltage, processing time, concentration of electrolyte will be also investigated in this study. It is expected that micro tools could be fabricated more efficiency by this process.

Economics and the Modern Economic Historian

I reflect on the role of modern economic history in economics. I document a substantial increase in the percentage of papers devoted to economic history in the top-5 economic journals over the last few decades. I discuss how the study of the past has contributed to economics by providing ground to test economic theory, improve economic policy, understand economic mechanisms, and answer big economic questions. Recent graduates in economic history appear to have roughly similar prospects to those of other economists in the economics job market. I speculate how the increase in availability of high quality micro level historical data, the decline in costs of digitizing data, and the use of computationally intensive methods to convert large-scale qualitative information into quantitative data might transform economic history in the future.

Studies on Growth Mechanism of Annealed Graphite Powder and Gas-Sensor Applications

High quality micro sheet rhombohedral graphite crystals were synthesized by Hummer method using compounds of MWCNT, K2S2O8and P2O5. The growth mechanisms were discussed by finite element simulation. The synthetic sheet rhombohedral graphite crystals showed a higher growth rate in radial direction than that in axial direction. Raman spectrum and Fourier transform infrared spectrum indicated that synthesized sheet rhombohedral Graphite had fewer crystal lattice distortions with no impurities. Finite element simulations indicated that the solvent metal convection field in the radial direction was stronger than that in the axial direction. As prepared graphite powder was annealed at 1350 oC to obtain diamond nanoparticles. The as-prepared products were exposed to formaldehyde gas.

Femtosecond laser 3D fabrication of whispering-gallery-mode microcavities

Whispering-gallery-mode (WGM) microcavities with high-quality factors and small volumes have attracted intense interests in the past decades because of their potential applications in various research fields such as quantum information, sensing, and optoelectronics. This leads to rapid advance in a variety of processing technologies that can create high-quality WGM micro- cavities. Due to the unique characteristics of femtosecond laser pulses with high peak intensity and ultrashort pulse duration, femtosecond laser shows the ability to carry out ultrahigh precision micromachining of a variety of transparent materials through nonlinear multiphoton absorption and tunneling ionization. This review paper describes the basic principle of femtosecond laser direct writing, and presents an overview of recent progress concerning femtosecond laser three-dimensional (3D) fabrications of optical WGM microcavities, which include the advances in the fabrications of passive and active WGMs microcavities in a variety of materials such as polymer, glass and crystals, as well as in processing the integrated WGM-microcavity device. Lastly, a summary of this dynamic field with a future perspective is given.

High energy micro electron beam generation using chirped laser pulse in the presence of an axial magnetic field

In this paper, the generation of high-quality and high-energy micro electron beam in vacuum by a chirped Gaussian laser pulse in the presence of an axial magnetic field is numerically investigated. The features of energy and angular spectra, emittances, and position distribution of electron beam are compared in two cases, i.e., in the presence and absence of an external magnetic field. The electron beam is accelerated with higher energy and qualified in spatial distribution in the presence of the magnetic field. The presence of an axial magnetic field improves electron beam spatial quality as well as its gained energy through keeping the electron motion parallel to the direction of propagation for longer distances. It has been found that a 64 μm electron bunch with about MeV initial energy becomes a 20 μm electron beam with high energy of the order of GeV, after interacting with a laser pulse in the presence of an external magnetic field.

Farmed fish value chain analysis with emphasis on value addition and traceability: case of Kirinyaga County in Kenya

Fish farming contributes to the attainment of food and nutritional security by providing high-quality fish proteins and micro and macro nutrients thereby minimizing hidden hunger. Fish supply in Kenya is mostly from capture fisheries, particularly fresh water lakes that contribute more than 90 per cent of the total fish produced. Agri-food supply chains involve the flow of products and information, and activities from production through to processing and consumption. Through value addition, at each stage, the value is increased along the chain. Traceability enhances tracking and tracing of fish and fish products information in the supply chains. A situational assessment was conducted along the farmed fish value chain in Kirinyaga County in Kenya in June and July 2013. The objective of the study was to assess traceability along the farmed fish value chain. Data was collected using semi-structured questionnaires and data analysis was done using SPSS version 16 software. Most farmers stocked mixed sex tilapi...

Insights Into the Solution Crystallization of Oriented Alq3 and Znq2 Microprisms and Nanorods.

Optimized solution-based methods to grow high quality micro- and nanocrystals of organic semi-conductors with defined size, shape and orientation are important to a variety of optoelectronic applications. In this context, we report the growth of single crystal micro- and nanostructures of the organic semiconductors Tris(8-hydroxyquinoline)aluminum (Alq3) and bis(8-hydroxyquinoline)zinc (Znq2) terminating in flat crystal planes using a combination of evaporative and antisolvent crystallization. By controlling substrate-specific nucleation and optimizing the conditions of growth, we generate vertically-oriented hexagonal prism arrays of Alq3, and vertical half-disks and sharp-edged rectangular prisms of Znq2. The effect of process variables such as ambient vapour pressure, choice of anti-solvent and temperature on the morphology and crystal habit of the nanostructures were studied and the results of varying them catalogued to gain a better understanding of the mechanism of growth.

Probing deformed commutators with macroscopic harmonic oscillators.

A minimal observable length is a common feature of theories that aim to merge quantum physics and gravity. Quantum mechanically, this concept is associated with a nonzero minimal uncertainty in position measurements, which is encoded in deformed commutation relations. In spite of increasing theoretical interest, the subject suffers from the complete lack of dedicated experiments and bounds to the deformation parameters have just been extrapolated from indirect measurements. As recently proposed, low-energy mechanical oscillators could allow to reveal the effect of a modified commutator. Here we analyze the free evolution of high-quality factor micro- and nano-oscillators, spanning a wide range of masses around the Planck mass mP (≈22 μg). The direct check against a model of deformed dynamics substantially lowers the previous limits on the parameters quantifying the commutator deformation.

Melt-Blown and Electrospun Drug-Loaded Polymer Fiber Mats for Dissolution Enhancement: A Comparative Study

Melt blowing (MB) was investigated to prepare a fast dissolving fibrous drug-loaded solid dispersion and compared with solvent-based electrospinning (SES) and melt electrospinning (MES). As a conventional solvent-free technique coupled with melt extrusion and using a high-speed gas stream, MB can provide high-quality micro- and nanofibers at industrial throughput levels. Carvedilol, a weak-base model drug with poor water solubility, was processed using a common composition optimized for the fiber spinning and blowing methods based on a hydrophilic vinylpyrrolidone-vinyl acetate copolymer (PVPVA64) and PEG 3000 plasticizer. Scanning electron microscopy combined with fiber diameter analysis showed diameter distributions characteristic to each prepared fibrous fabrics (the mean value increased toward SES<MB<MES). Differential scanning calorimetry and X-ray diffraction studies revealed that the incorporated drug was in amorphous form regardless the preparation method. The HPLC studies demonstrated that all of the materials produced by the different techniques passed the regulatory purity requirements. The fibers exhibited ultrafast drug release tested under neutral pH conditions; the melt-blown sample dissolved within 2 min owing to its large specific surface area. The presented results confirm the applicability of MB as a novel formulation technique for polymer-based drug delivery systems.

Fabrication of Micro Single Chamber Solid Oxide Fuel Cell Using Photolithography and Pulsed Laser Deposition

This paper focuses on the fabrication of micro-coplanar interdigitated single chamber solid oxide fuel cell (μ-SC-SOFC) using a combination of micropatterning technique and thin-film deposition technology. Photolithography was used to generate the micro-interdigitated photoresist patterns on the substrates. Pulsed laser deposition (PLD) method was used to deposit thin films of microstructured electrolytes yttrium stabilized zirconia (YSZ) and electrodes (anode: YSZ + NiO and cathode: lanthanum strontium ferrous cobalt (LSCF)). Process parameters were optimized to obtain consistent functional microstructure and crystal morphology. This research shows good potential for combinatorial manufacturing methods to fabricate high quality and repeatable micro fuel cell components.

Eco-Friendly ECM in citric Acid electrolyte with microwire and microfoil Electrodes

In this research, eco-friendly electrochemical machining (ECM) characteristics for drilling and milling stainless steel using microwire and microfoil electrodes in citric acid electrolyte are investigated. According to cell configuration and applied pulse conditions, extraordinary phenomena such as tool electrode cut-off due to Joule heating followed by fractured tool welding to the work substrate, electrolyte capillary action around the tool electrode, and tool shaking by evolved bubbles are observed and their effects on micro ECM performances are discussed. Complex micro/nano textures were found on the inner wall of the drilled holes under strict pulse conditions and their generation mechanism is described. Metal structure formed on the bottom of the blind hole under weak electric conditions hinders further drilling. By adjusting electrochemical conditions, micro holes, 37 μm in diameter with 100 μm depth and 26 μm in diameter with 50 μm depth, are drilled using a 10 μm thick tungsten wire electrode. A complex micro hand pattern is fabricated by electrochemical milling on SS 304 substrate. Furthermore, high quality micro grooves with dimension of 34 μm wide and 17 μm deep are machined using 20 μm thick stainless steel foil electrode. Finally, micro electrochemical reverse drilling technique is newly suggested and its effectiveness on machining time reduction is validated.

Electro-Chemical Micro Drilling by Micro-Spherical Electrode

Manufacture of micro holes in difficult-to-machine material is very difficult, electro-chemical machining (ECM) is one of the more appropriate approach. However, micro holes fabricated using ECM can have different diameters at the entrances and exits and such tapering effect is not localized. In this work, a new ECM method named electro-chemical micro drilling (ECMD) for machining high quality straight micro holes in difficult-to-machine material was introduced, and the micro-spherical electrode fabricated by a hybrid technique combining micro-ECM with one pulse electro discharge (OPED) was used in ECMD process. Micro-spherical electrode and ultra short pulses (tens of nanosecond scale) were used to locally dissolve the area with the effect of voltage, pulse width and pulse frequency on the localization distance being studied. High quality micro holes with a diameter of 42 µm in a 70 µm thick nickel foil were drilled using micro-spherical electrode with a sphere diameter of 30 µm.

Preparing micro sections of entire (dry) conifer increment cores for wood anatomical time-series analyses

The type of samples most commonly used in dendro sciences are increment cores of conifers. These cores allow for an easy determination and measurement of ring-width variations over long time periods. For wood anatomical analyses, the cores have to be split into pieces to enable the preparation of high quality micro sections for detailed measurements of cell properties. A major drawback of this procedure is the fact that it is labor intensive and time consuming. We present a new technique enabling the preparation of micro sections of entire increment cores up to a length of 40cm. For that purpose we combined standard wood-anatomical techniques with the application of Mowiol glue and common Tesa tape. We tested the introduced method on increment cores of Larix decidua Mill. sampled years ago for ring-width analyses to reanalyze them on a microscopic level. The ability to cut these long sections will tremendously reduce the time needed to prepare micro sections. This is of special interest for wood anatomical image analyses of cores used before to create long ring-width chronologies for any kind of environmental reconstructions.

Laser-assisted machining process simulation for precision mould/die manufacturing

Laser-assisted machining (LAM) is a kind of thermally assisted manufacturing process which preheats workpiece material with a highly-localized laser beam and then is followed by a conventional machining operation. It could greatly improve the machinability and gives better machining quality, especially suitable for hard-to-cut materials such as superalloys, tool steels. For manufacturing the high-precision moulds/dies that could fabricate micro and precision components, the thermal assistance at the local cutting zone, will help to lower the cutting force and consequently improve the internal surface quality of the machined moulds/dies. In this paper, a numerical study of the laser-assisted cutting of plastic mould steel NAK80 is reported. The simulation of LAM of NAK80 is realized by combining two procedures: simulation of moving laser heat source applied on the local surface of workpiece which causes the corresponding temperature field arise and material soften, and simulation of the subsequent cutting processes. This research will offer the die/mould manufacturers a more efficient planning tool for the fabrication of the micro, precision dies/moulds of high surface quality, and hence, for forming the high-quality micro components as well as for longer die/mould life.