Smooth Side Research Articles

One-pot preparation of thin nanoporous copper foils with enhanced light absorption and SERS properties

A facile hydrothermal method has been presented to prepare free-standing nanoporous Cu foils (NPCFs) having a thickness of ~1.4 μm and an area of up to ~10 cm2, which were grown on the inwall of a Teflon-lined autoclave by assembling and reducing CuxO nanoparticle intermediates and then peeling themselves off in the cooling period of the reaction. The pore sizes of NPCFs can be adjusted by varying the reaction time. It is observed that the NPCFs with water absorbed inside their nanopores show excellent flexibility while dried ones exhibit a highly hydrophobic nature. Compared with commercially available Cu foils, the as-synthesized NPCFs show enhanced ability to absorb light over a wide range of wavelengths from 200 to 1000 nm because of their nanoporosity. The highest absorbance and the biggest enhancement can reach 86% at 300 nm and 43% at 575 nm, respectively. The smooth side of NPCFs with a hemisphere-like surface demonstrates outstanding surface-enhanced Raman scattering performance by employing Rhodamine 6G as the probe molecule, which agrees well with the results of finite-difference time-domain simulation.

Microfabrication of high aspect ratio BST pillar arrays by epoxy gel casting from aqueous suspensions with added water soluble epoxy resin

The present paper reports on the successful fabrication of micro-sized pillar arrays of Ba0.6Sr0.4TiO3 (BST) electroceramics via cost effective epoxy gel casting (EGC) consolidation method based on the in situ polymerization of aqueous suspensions with added water soluble epoxy resin. The synthesized BST solid solution powder was fine milled and surface protected against hydrolysis to avoid its degradation in the aqueous environment. The micro patterning process was divided in the following steps: (i) production of high quality SU-8 master moulds by photolithography and of the respective negative replicas in PDMS (soft mould); (ii) casting of stable high solid loading BST suspensions in the soft moulds with added setting agents followed by de-moulding, drying and sintering. Patterned array of hexagonal shaped pillars with 320μm of height and side length ∼40μm were obtained with smooth side wall features along height. Various structural, mechanical and electrical properties of BST material after sintering were also measured to demonstrate the feasibility of the proposed aqueous processing route.

Heat transfer and friction factor characteristics of turbulent flow through a circular tube fitted with vortex generator inserts

Abstract Local heat transfer coefficients and average pressure drop measurements for turbulent flow in a circular tube fitted with a nonconventional insert are presented here. The insert was fabricated with a central rod on which curved delta wing vortex generators were attached on opposite sides at specific axial locations. The influence of pitch to projected length ratio (p/pl), height to tube inner diameter ratio (e/d) and angle of attack (α) on the heat transfer performance are reported here. Air was used as the working fluid and local heat transfer measurements for both smooth and rough surface sides of the tube are reported for fully developed turbulent flow with Reynolds number (Re) varying between 10,000 and 45,000. The average Nusselt number ratio with and without the insert (Nua/Nus), at constant Reynolds number (Re) is found to be in the range of 1.3–5.0. The Nusselt number ratio (Nua/Nuc), based on equal pumping power is found to be in the range of 1.0–1.8. Empirical correlations are developed for Nusselt Number and friction factor in terms of Reynolds number (Re), pitch to projected length ratio (p/pl), height to tube inner diameter ratio (e/d) and angle of attack (α).

Electrochemistry of Inorganic Precipitates Formed in Self-Organizing Chemical Systems

The interfacing of two solutions, each containing a reactive ion (e.g. Fe+2 / HS-), produces a self-assembling mineral film or membrane at the solution interface. When one solution is injected into the other, the membrane forms as a self-organizing “chemical garden” structure that grows vertically upward according to buoyancy and internal fluid pressure. When the solutions are instead interfaced across a porous template, such as parchment paper or dialysis tubing, the precipitate forms as a mineral film on the template. In either case, the formation of self-assembling precipitates in steep chemical/pH gradients at solution interfaces produces inorganic membranes that exhibit organized structure at both macro and micro scales. Chemical garden membranes can grow as bulbs, tubes, or gelatinous ‘chimney’-like structures, and the membranes themselves are permeable to some ions, and exhibit morphological gradients from interior to exterior (e.g. a crystalline side and a smoother side). Inorganic membranes often exhibit compositional gradients from interior to exterior as well, reflecting the chemical gradients in which they precipitated. These are dynamic chemical systems and in recent work we have studied the ability of mineral membranes to generate and maintain electrical potentials (Barge et al. 2012). Inorganic membranes of iron sulfides produced on dialysis tubing templates between contrasting solutions were also found to be partially bipolar and capable of preferential ion exchange, as well as electrically conductive (Barge et al. 2014). In some ways, the self-assembling inorganic precipitates formed in solution interface experiments are similar to the ion-exchange membranes and gas diffusion layers in commercial as well as experimental fuel cells. This has led to some preliminary work in using commercially available electrode / GDL material as a template to precipitate chemical membranes that can then be used in fuel cell experiments (Barge et al. 2014) to determine if these are capable of acting as redox catalysts. Interfacial precipitates can be grown in many different reactant systems and depending on the chemistry can be useful for various materials / electrochemical applications. Natural analogs to these self-assembling membranes include the growth of chimneys at hydrothermal vents, which are formed as minerals precipitate in the chemical / pH gradient where subsurface hydrothermal fluid feeds into the chemically contrasting seawater. Hydrothermal chimneys are natural chemical gardens, and it has even been proposed that life on Earth emerged in such a system, so we can also use electrochemical studies of out-of-equilibrium chemical precipitates to understand the mechanisms that might operate in geological settings.L. M. Barge, T. P. Kee, I. J. Doloboff, J. M. P. Hampton, M. Ismail, M. Pourkashanian, J. Zeytounian, M. M. Baum, J. Moss, C.-K. Lin, R. D. Kidd, I. Kanik (2014) The Fuel Cell Model of Abiogenesis: A New Approach to Origin-of-Life Simulations. Astrobiology, 14(3):254-70.L.M. Barge, I. J. Doloboff, L. M. White, G. D. Stucky, M. J. Russell, I. Kanik. (2012) Characterization of Iron-Phosphate-Silicate Chemical Garden Structures. Langmuir, 28 (8), pp 3714-3721.

Mechanical quality factor enhancement in a silicon micromechanical resonator by low-damage process using neutral beam etching technology

The fabrication and evaluation of silicon micromechanical resonators using neutral beam etching (NBE) technology is presented. An etching technique based on a low energy neutral beam of Cl2/F2/O2 is introduced for making nano-trench patterns on 5 µm-thick silicon. The NBE technology has been investigated to form a highly-anisotropic etching shape. A 5 μm-deep trench pattern having smooth side walls with a gap width of 230 nm is achieved by using NBE. Additionally, a fabrication method for silicon resonators using NBE technology is proposed. The resonant frequency of the fabricated devices with a length of 500 μm, width of 440 μm and thickness of 5 μm is 9.66 MHz, and the average quality factor (Q) value is around 78 000. The devices fabricated by both deep reactive ion etching (DRIE) and NBE are evaluated and compared. The devices fabricated by NBE show that the motional resistances are reduced by almost 11 times from 645 kΩ to 59 kΩ and their output signals (insertion loss) are increased by approximately 15 dB in comparison with those fabricated by DRIE. Especially, devices fabricated by NBE provide the higher Q factors (average Q factor value of around 78 000) than those (average Q factor value of around 61 000) fabricated by DRIE in the same resonator parameters and measurement conditions.

3D Geometric Modeling of Francis Turbine Blades Based on Wooden Patterns and UG Software

To quickly and easily get a smooth and accurate 3D model of blades, This paper was based on the two-dimensional wooden patterns of the existing francis turbine blades in "AutoCAD", by importing UG software platform, directly translating two-dimensional lines to get three-dimensional wooden patterns, without calculating the spatial coordinates of distribution points on the blade section lines, obtaining the optimized smooth pressure sides and suction sides of the blades by characteristic surface intersecting lines, after partial rounding and sewing the sheets, the process of three-dimensional modeling of blades was finally completed. This takes a solid foundation for hydraulic performance prediction and CFD numerical simulation analysis of the francis turbine. The blade modeling method described in this article has some reference value.

NO, via its target Cx37, modulates calcium signal propagation selectively at myoendothelial gap junctions.

BackgroundGap junctional calcium signal propagation (transfer of calcium or a calcium releasing messenger via gap junctions) between vascular cells has been shown to be involved in the control of vascular tone. We have shown before that nitric oxide (NO) inhibits gap junctional communication in HeLa cells exclusively expressing connexin 37 (HeLa-Cx37) but not in HeLa-Cx40 or HeLa-Cx43. Here we studied the effect of NO on the gap junctional calcium signal propagation in endothelial cells which, in addition to Cx37, also express Cx40 and Cx43. Furthermore, we analyzed the impact of NO on intermuscle and on myoendothelial gap junction-dependent calcium signal propagation. Since specific effects of NO at one of these three junctional areas (interendothelial/ myoendothelial/ intermuscle) may depend on a differential membrane localization of the connexins, we also studied the distribution of the vascular connexins in small resistance arteries.ResultsIn endothelial (HUVEC) or smooth muscle cells (HUVSMC) alone, NO did not affect gap junctional Ca2+ signal propagation as assessed by analyzing the spread of Ca2+ signals after mechanical stimulation of a single cell. In contrast, at myoendothelial junctions, it decreased Ca2+ signal propagation in both directions by about 60% (co-cultures of HUVEC and HUVSMC). This resulted in a longer maintenance of calcium elevation at the endothelial side and a faster calcium signal propagation at the smooth muscle side, respectively. Immunohistochemical stainings (confocal and two-photon-microscopy) of cells in co-cultures or of small arteries revealed that Cx37 expression was relatively higher in endothelial cells adjoining smooth muscle (culture) or in potential areas of myoendothelial junctions (arteries). Accordingly, Cx37 - in contrast to Cx40 - was not only expressed on the endothelial surface of small arteries but also in deeper layers (corresponding to the internal elastic lamina IEL). Holes of the IEL where myoendothelial contacts can only occur, stained significantly more frequently for Cx37 and Cx43 than for Cx40 (endothelium) or Cx45 (smooth muscle).ConclusionNO modulates the calcium signal propagation specifically between endothelial and smooth muscle cells. The effect is due to an augmented distribution of Cx37 towards myoendothelial contact areas and potentially counteracts endothelial Ca2+ signal loss from endothelial to smooth muscle cells. This targeted effect of NO may optimize calcium dependent endothelial vasomotor function.

Convective heat transfer of molten salt in circular tube with nonuniform heat flux

Convective heat transfer performances of molten salt in circular tube with nonuniform heat flux were experimentally investigated using unilateral copper coating tubes. Various experiments were carried out within the range of Reynolds number 10,000–67,000, Prandtl number 4.5–8, and the heat flux ratio of 1.0, 2.0 and 5.7. The results showed that there existed large wall temperature difference in the tube section with nonuniform heat flux, and associated Nusselt number of molten salt flow increased with Reynolds number and Prantal number. Compared with Sieder–Tate correlation, Nusselt number on the smooth side with lower heat flux was mostly larger, while Nusselt number on coating side with higher heat flux was mostly lower. Experimental heat transfer correlation for molten salt flow in circular tube with nonuniform heat flux was developed by least-squares method, and it very well fit with experimental data and classical correlations. In general, average Nusselt number of molten salt flow in circular tube had little relation with nonuniform heat flux, but Nusselt number difference on different sides increased with the heat flux ratio.

Interaction Between “Safe Sites” and “Safe Sides” for Germination of Neurada procumbens (Neuradaceae) in the Middle East

The seed bank of Neurada procumbens, a prostrate annual common in sandy desert habitats, is vulnerable to surface disturbances. Moreover, its seeds are highly heteromorphic, having both spinose and non-spinose sides, which affects both the vertical distribution of seeds and diaspores, and the precise position in which they lie in the soil. Here we explore the ecological implications of two factors, “safe sites” within habitats and seed orientation or “safe sides”, on seedling establishment and the seed bank. In three natural populations, the vertical distribution of buried, germinable diaspores decreased with soil depth. Most diaspores occurred at the surface (0–1 cm below the surface), while none were observed below 10 cm. Seedling emergence decreased with depth and reached zero in diaspores below 5 cm. Seedling emergence also proved highly sensitive to the orientation of diaspores in soil. Diaspores lying on their smooth side with the spinose upper side directed upwards reached the highest seedling emergence of 61 %. Root length ranged from 10 to 16 cm, and the root to shoot ratio varied between 22.8 and 30.3 cm, depending on diaspore size. Diaspores near the surface may constitute a more transient component of the seed bank, as few of these remained viable for more than a year. Persistence of Neurada seed banks seems to depend not only on vertical movement of diaspores among habitat “safe sites” but also on different seed position alternatives.

Flash-lamp annealing of ZnO-layers on copper–indium–gallium–sulphide layers: A spectroscopic ellipsometry study

Polycrystalline copper–indium–(gallium)–sulphide (CI(G)Su) absorbers were analysed by spectroscopic ellipsometry (SE) with special emphasis on the optical band gap energy. Rough CI(G)Su absorber films grown by reactive magnetron sputtering were peeled off from molybdenum coated glass substrates. The smooth back side of CI(G)Su absorbers was suited for the SE analysis. Furthermore, these samples were covered with a thin zinc oxide (ZnO) layer and heat-treated with a commercial xenon flash lamp annealing system (FLA) as well as by thermal annealing in an argon atmosphere. The effect of zinc on CI(G)Su absorber films was studied by secondary ion mass spectrometry depth profiling as well as by SE analysis. The optical modelling of spectral Stokes parameters was performed by using a multilayer approach over a spectral range from 1.5 to 4.3eV. Spectral absorption coefficients were calculated in every process stage, i.e. (i) peeled samples, (ii) ZnO deposition, (iii) FLA treatment and (iv) etching of the ZnO. Special emphasis was given to the shift of the optical band gap due to the various treatments. While the SE analysis was quite sensitive to the change of optical band gaps due to a varying gallium content in the CI(G)Su absorber layers, a significant shift of the optical band gap due to increasing zinc content was not detectable.

Resist evaluation for proton beam writing, Ni mold fabrication and nano-replication

Proton beam writing (PBW) is a new direct-write technique which has shown great potential to fabricate structures down to 20 nm level in resist material. Protons can be accelerated up to a high energy (3.5 MeV) at Centre for Ion Beam Applications. Because the mass of a proton is much larger than the mass of an electron (mp:me = 1,800:1), the energy of the secondary electrons is very small compared with secondary electrons generated by electron beam lithography. Therefore, a proton will travel along a straight path into resist and secondary electrons will only expose the resist within several nanometers around the path of the proton. PBW is capable of fabricating structures with very straight, vertical and smooth sidewalls without proximity effect. This is very important when combining PBW with Ni electroplating and nanoimprinting as well as injection molding. High quality Ni molds with smooth and vertical side walls are critical in nanoimprint lithography and injection molding. In our experiments, several new resists including AR-P 3250, a mixture of AR-P 3250 and AR 300-12, and ma-N 2401 are tested with PBW for the production of high aspect ratio Ni molds and thermoplastic replication with these molds. High aspect ratio structures (up to 7) are fabricated at a width of 500 nm in Ni molds. The structures are transferred to plastic via nanoimprinting and injection molding.

On Solvability of the Neumann Boundary Value Problem for Non-homogeneous Biharmonic Equation

In this work we investigate the Neumann boundary value problem in the unit ball for a nonhomogeneous biharmonic equation. It is well known, that even for the Poisson equation this problem does not have a solution for an arbitrary smooth right hand side and boundary functions; it follows from the Green formula, that these given functions should satisfy a condition called the solvability condition. In the present paper these solvability conditions are found in an explicit form for the natural generalization of the Neumann problem for the non-homogeneous biharmonic equation. The method used is new for these type of problems. We first reduce this problem to the Dirichlet problem, then use the Green function of the Dirichlet problem recently found by T. Sh. Kal’menov and D. Suragan

Accuracy Performance Parameters of Seam Bowling, Measured with a Smart Cricket Ball

In seam bowling, the spin vector precesses rapidly into the torque vector, thereby crossing from one hemisphere to the other once torque is imparted onto the ball. However, the spin axis reaches the torque vector only at large times. If the spin axis does not coincide with the pole of the ball, the seam wobbles and introduces another roughness element. Thus, if the seam is angled toward the smooth side (for half a period per spin revolution) then the flow is turbulent on both sides of the ball and the aerodynamic side force decreases and vanishes, thereby disturbing the swing. The aim of this study was to investigate how accurate is the placement of the spin axis at release of the ball. A smart cricket ball instrumented with three high-speed MEMS gyroscopes was used for this purpose and the data of four spin bowlers were analysed. It was found that the spin axis can under- and overshoot the optimal position of the ball as well as deviate off the pole. The spin rates recorded were 15-20 rps produced by peak torques of 0.29-0.39 Nm. The deviation of the spin axis correlated with the torque, indicating that too much torque imparted onto the ball worsens the accuracy of bowling. Undershooting the optimal position is due to equal torques imparted by index and middle fingers. The optimal position of the spin axis can be achieved if the middle finger is closer to the seam than the index. This causes an overshooting torque vector and allows the spin axis to be placed at the pole of the ball at release.

Semi-Fredholm Solvability in the Framework of Singular Solutions for the (3+1)-D Protter-Morawetz Problem

For the four-dimensional nonhomogeneous wave equation boundary value problems that are multidimensional analogues of Darboux problems in the plane are studied. It is known that for smooth right-hand side functions the unique generalized solution may have a strong power-type singularity at only one point. This singularity is isolated at the vertexOof the boundary light characteristic cone and does not propagate along the bicharacteristics. The present paper describes asymptotic expansions of the generalized solutions in negative powers of the distance toO. Some necessary and sufficient conditions for existence of bounded solutions are proven and additionally a priori estimates for the singular solutions are obtained.

Optimized Development of Sebaceous Fingermarks on Nonporous Substrates with Conformal Columnar Thin Films

A form of physical vapor deposition, called the conformal-evaporated-film-by-rotation (CEFR) method, was optimized for the conformal deposition of columnar thin films (CTFs) on sebaceous fingermarks. Relying on the surface topology of the fingermark, the CTF development technique is different from traditional development techniques. After the optimization of the development conditions, the CTF development technique was found to be superior to traditional development methods on several nonporous substrates: the smooth side of Scotch(®) Multitask, Gorilla(®) , and Scotch(®) Duct tapes; clear and black soft plastics; stained and sealed walnut and cherry woods; partial bloody fingermarks on stainless steel; and discharged cartridge casings. It was equally as good as other development techniques on other substrates, but worse on a few. The optimization study is expected to assist in designing a mobile CEFR apparatus capable of on-scene development of fingermarks.

Singular solutions with exponential growth to Protter’s problems

Four-dimensional boundary value problems which were formulated by Proter for the nonhomogeneous wave equation are studied. They can be considered as multidimensional versions of the Darboux problems in ℝ2. Protter’s problem is not well posed in the frame of classical solvability. On the other hand, it is known that the unique generalized solution may have a strong power-type singularity at one boundary point. This singularity is isolated at the vertex of the characteristic cone and does not propagate along the cone. Some known results suggest that the solution may have at most exponential growth. We construct an infinitely smooth right-hand side function such that the corresponding generalized solution to Protter’s problem has an exponential singularity.

Design, Optimization, and Evaluation of Al–2139 Compression Panel with Integral T-Stiffeners

A T-stiffened panel was designed and optimized for minimum mass subjected to constraints on buckling load, yielding, and crippling or local stiffener failure using a new analysis and design tool named EBF3PanelOpt. The panel was designed for a compression loading configuration, a realistic load case for a typical aircraft skin-stiffened panel. The panel was integrally machined from a 2139 aluminum alloy plate and was tested in compression. The panel was loaded beyond buckling and strains, and out-of-plane displacements were extracted from 36 strain gages and one linear variable displacement transducer. A digital photogrammetric system was used to obtain full-field displacements and strains on the smooth (unstiffened) side of the panel. The experimental data were compared with the strains and out-of-plane deflections from a high-fidelity nonlinear finite element analysis. The test data indicated that the panel buckled at the linear elastic buckling eigenvalue predicted for the panel. The out-of-plane displacement measured by the digital photogrammetric system compared well both qualitatively and quantitatively with the nonlinear finite element solution in the postbuckling regime. Furthermore, the experimental strains compared well with both the linear and nonlinear finite element models before buckling. The weight of the optimized panel was 20% less than that of a T-stiffened panel optimized using conventional design techniques.

Effect of Silicon Doping on GaN Nanorods during Vapor–Liquid–Solid Growth

High optical quality and reproducible Si-doped GaN nanorods (NRs) were grown by low pressure metal–organic chemical vapor deposition. Different fluxes of SiH4 were introduced and at 2.7×10-9 mol/min the optimized morphology was obtained. Clear improvement of GaN NRs morphology characterized by smooth side walls and straightness was achieved after Si-doping. Near-band edge (NBE) emission at 356.88 nm (3.474 eV) and small full width at half maximum (FWHM) of 27.3 meV, measured by room temperature photoluminescence, confirmed the high optical and crystalline qualities. For Si-doped GaN NRs, a small blue-shift of NBE emission peak was observed, which was attributed to the band-filling effects.

All Zinc-Blende GaAs/(Ga,Mn)As Core–Shell Nanowires with Ferromagnetic Ordering

Combining self-catalyzed vapor-liquid-solid growth of GaAs nanowires and low-temperature molecular-beam epitaxy of (Ga,Mn)As, we successfully synthesized all zinc-blende (ZB) GaAs/(Ga,Mn)As core-shell nanowires on Si(111) substrates. The ZB GaAs nanowire cores are first fabricated at high temperature by utilizing the Ga droplets as the catalyst and controlling the triple phase line nucleation, then the (Ga,Mn)As shells are epitaxially grown on the side facets of the GaAs core at low temperature. The growth window for the pure phase GaAs/(Ga,Mn)As core-shell nanowires is found to be very narrow. Both high-resolution transmission electron microscopy and scanning electron microscopy observations confirm that all-ZB GaAs/(Ga,Mn)As core-shell nanowires with smooth side surface are obtained when the Mn concentration is not more than 2% and the growth temperature is 245 °C or below. Magnetic measurements with different applied field directions provide strong evidence for ferromagnetic ordering in the all-ZB GaAs/(Ga,Mn)As nanowires. The hybrid nanowires offer an attractive platform to explore spin transport and device concepts in fully epitaxial all-semiconductor nanospintronic structures.

Ordered silicon nanowires prepared by template-assisted morphological design and metal-assisted chemical etching

We reported a metal-assisted chemical etching approach to manufacture well-aligned silicon nanowires (SiNWs). Highly ordered gold (Au) mesh was achieved via vacuum evaporation on anodized aluminum oxide (AAO). It was revealed that the diameter and length of SiNWs could be controlled by adjusting the size of holes in Au mesh and etching duration, respectively. We found that the SiNWs fabricated by etching for 5min were vertically oriented to form an array, while longer etching duration led to bunched SiNWs. The resulting SiNWs, which exhibited smooth side walls, uniform diameter, and high aspect ratio, were proved to grow along the [100] crystal direction of silicon.