AFM characterization of bovine enamel and dentine after acid-etching

Teeth are constituted mainly of hydroxyapatite molecules (Ca₁₀(PO₄)₆(OH)₂), grouped in different microstructural arrangements, depending on the dental layer considered (enamel or dentine). In the present work, these dental microstructural arrangements were characterized by atomic force microscopy. Enamel and dentine samples were cut from freshly extracted bovine incisor teeth. After metallographic polishing, the dental surfaces were etched with lactic acid (113.8 mmol/L, pH 3.3). Three etching times were tested: 1, 3 and 5 min. Atomic force micrographs showed that 1 min of etching time was effective to remove the smear layer, polishing debris and scratches, and display the characteristics of interest for both enamel and dentine. Although the bovine dental enamel rod cross-section presented keyhole-like shape, its measured dimensions (8.8 μm of major axis and 3.7 μm of minor axis) exhibited an insignificant discrepancy from human prisms diameters. Bovine dentinal tubules displayed larger mean diameters (4.0 μm) and a lower density (～17,100 tubules/mm²) than human dentine, suggesting that the use of bovine dentine as a substitute for human dentine in resin adhesion investigations should be reconsidered. Apatite nanoparticles presented a mean radius (22–23 nm) considerably smaller than that of human teeth.     

Effective laser ablation of enamel and dentine without thermal side effects

We present a feasibility study into laser treating dental materials by using femtosecond pulses generated by a titanium:sapphire laser system which consisted of an oscillator and a regenerative amplifier. The pulse duration was varied between 200 fs and 2 ps. The observed energy thresholds for the ablation process of dentine and enamel were clearly smaller than those observed when longer pulse durations were used. The consequence of this observation is a lower thermal load within the vicinity of the radiated area. Thus no thermal damage or mechanical damage, such as cracks, were produced during the laser treatment. Commercially available femtosecond laser systems can produce ablation rates in healthy and in-vitro demineralized dental material 2 mm3 per min and 6-16 mm3 per min, respectively. These values are an order of magnitude larger than those produced by picosecond laser systems at the same time pulse energy and pulse repetition rate. The brightness of the plasma spark generated by the laser treatment depended on the dimineralization of the teeth. This may allow online control of the laser treatment.     

Influence of thermal treatment on the microstructure and electrical and optical properties of SnS thin films

The influence of thermal treatment on the microstructure and electrical and optical properties of SnS films obtained by the “hot-wall” method has been investigated. It has been established that the thermal treatment does not lead to the formation of foreign phases in the film composition. The average film roughness after the thermal treatment increases from 10 to 20 nm. Resistivity after the thermal treatment decreases from 230 to 100 Ωcm (T = 300 K), while the temperature coefficient of thermopower increases from 40 to 330 μV K^?1. The band gap is 1.46 eV. The adsorption edge is not displaced after the thermal treatment.     

A contactless method for investigating the thermal properties of thin films

The photothermal deflection technique has been extended as a contactless method to investigate thermal transport in thin films. A theoretical model is developed which quantitatively describes the transport behavior, and is shown to be in excellent agreement with experimental results. This approach yields the thermal diffusivity directly and in a spatially-resolved manner.     

A new microstructure for pool boiling

Combining electrocoating and etching processes, we have developed a new type of microstructure for nucleate boiling. The basic elements of the structure are cylindrically shaped; their density ranges up to 10⁷ cm⁻².To test the efficiency of the structure, the outer surface of a tube has been provided with such a structure and used in pool boiling experiments with the refrigerant R141b at atmospheric pressure. The results obtained show the heat flux to remain independent of the wall superheat in the fully developed boiling region. The behavior is novel. It is most probably associated with the density of active bubble nucleation sites. Activated at a certain wall superheat, the density of the sites generating bubbles remains apparently unaffected by raising the heat flux. Given that these preliminary results should be confirmed by further experiments, the microstructure developed will be suitable for nucleate boiling in general, but for keeping the heating surface largely isothermal, despite the variation of the heat flux, in particular.     

高铁酸钾制备新方法与光谱表征

以次氯酸钙为原料制备了高纯度高铁酸钾,研究内容包括:高铁酸钾的性质反应温度对产率的影响,重结晶温度对产率的影响,反应时间对产率的影响,次氯酸钙用量对产率的影响。确定了反应温度为25℃,重结晶温度为0℃,反应时间为40 min,反应所需的次氯酸钙用量为理论用量的1.2倍,产率为75%以上。利用直接分光光度法对产物纯度进行了分析,测得产物纯度达到92%以上。论文以红外光谱法、紫外分光光度法、X衍射法对产物进行表征,证明以次氯酸钙为原料制得的产物为高铁酸钾。     

A colloidal crystal microstructure fiber: fabrication and characterization

A method of fabricating colloidal crystal microstructured fiber is presented. The proposed structure relies on partial etching of the cladding layer of a single-mode fiber and growth of colloidal photonic crystals inside eroded area. The photonic crystal cylindrical annulus embedded in fiber is characterized by optical and scanning electron microscopy. The optical characterization was analyzed by optical transmission spectroscopy. The measurement results show a about 1550-nm band gap. The results also reveal the possibility of cladding cylindrical fibers with three-dimensional photonic crystals.     

Laser interference metallurgy: A new method for periodic surface microstructure design on multilayered metallic thin films

Methods for micro- and nanostructuring are essential for functionalization of materials surfaces. In particular, photon-assisted methods for synthesis of functional surfaces have been intensively investigated in the last years. In this study, a new method for surface modification and production of long-range order periodical structures called “laser interference metallurgy” is explored. A metallic thin film sample consisting of three layers composed of Fe, Cu and Al (from top to bottom) on a glass substrate was irradiated with an interference pattern using a Nd:YAG laser (wavelength of 355 nm, 10 ns of pulse duration). For the interference pattern, a configuration producing a line-type energy distribution was chosen. The laser fluence was high enough to melt the aluminium and copper layers at the interference maxima but the iron layer remained in the solid state. Thus, diffusive and convective exchange occurred between aluminium and copper at the energy maxima positions leading to periodical alloy formation with a long-range order. Because it remained in solid state, the iron layer at the top acted as a protective layer effectively preventing removal of the molten layers. The interaction of the different layers was characterized using FIB, TEM and EDX in STEM mode.     

Influence of misch metal content on microstructure and magnetic properties of R–Fe–B magnets sintered by dual alloy method

MM_(14)Fe_(79.9)B_(6.1)/Nd_(13.5)Fe_(80.5)B_6 magnets were fabricated by dual alloy method(MM, misch metal). Some magnets have two Curie temperatures. Curie temperatures T_(c1)corresponds to the main phase which contains more La Ce, and T_(c1) decreases from 276.5?C to 256.6?C with the content of MM increasing from 30.3 at.% to 50.6 at.%. The variation of Br with the increase of MM indicates the existence of inter-grain exchange coupling in the magnets. When MM/R ≤ 30.3 at.%,the magnetic properties can reach the level of the intrinsic coercivity Hcj≥ 7.11 kOe and the maximum energy product(BH)max≥ 41 MGOe. Compared with Nd, La and Ce are easier to diffuse to the grain boundaries in the sintering process,and this will cause the decrease of H_(cj) Due to the diffusion between the grains, the atomic ratio of La, Ce, Pr, and Nd in each grain is different and the percentage of Nd in all grains is higher than that in misch metal.     

Elemental and chemical compounds study of enamel and dentine of porcine primary molar teeth

For the enamel and dentin of porcine primary molar teeth, the spatial variability of the elements and chemical groups was studied with the aim of identifying the chemistry of porcine teeth, and it was then compared with results for human primary teeth. Porcine teeth were taken from specially bred animals. An electron microprobe was applied for the elemental analyses and a Raman microscope for the determination of chemical groups. The distribution of the main elements (Ca, P) was similar for both porcine and human teeth, whereas major differences were found in the distributions of minor elements (Mg, Sr, Cl, C). Carbonates were present in porcine dentin mainly as A-substituted species, whereas the B-substituted ones prevailed in enamel. The mechanism of asymmetric enrichment of Ca and P was quantitatively calculated as a consequence of Mg release. The layer close to the surface of the enamel with air had a unique composition. Cl involvement in enamel close to the boundary with air is a complex process, coupled with the involvement of Sr and release of Mg. The discoveries shed light on the role of elements in apatites, especially the role of carbonates and magnesium in porcine teeth, and put in doubt the potential use of pig apatite as a substitute for human apatite in filling materials.     

Composite coatings of polyamide/graphene: microstructure,mechanical, thermal,and barrier properties

This effort reports on novel fluorinated polyamide (FPA) and polyamide 1010 (PA1010)-based blends and graphene reinforced nanocomposite. PA1010/FPA (80:20) blend was opted as matrix material on the basis of molecular weight, thermal, and shear stress performance. Graphene was obtained through in situ chemical method of graphene oxide reduction. PA1010/FPA/Graphene nanocomposites was developed using various graphene loadings (up to 5 wt.%). Thin film coatings were prepared on glass substrate. Consequently, the PA1010/FPA/Graphene attained regular spongy morphological pattern. PA1010/FPA/Graphene 3 also showed improved T₀ and T_max of 534 and 591 °C relative to the neat blend (T₁₀ 423 °C; T_max 551 °C). Limiting oxygen index measurement indicated better non-flammability of PA1010/FPA/Graphene 1–3 nanocomposite series (57–60%) relative to the blend series (28–31%). UL94 tests also showed V-0 rating for nanocomposites. Furthermore, PA1010/FPA/Graphene 3 nanocomposite revealed significantly high tensile strength (62 MPa), flexural modulus (1690 MPa), and adhesive properties to be utilized as coating materials. The nanocomposite coatings also displayed outstanding barrier properties against O₂ and H₂O compared with neat blends.     

The impulse photopyroelectric method for thermal characterization of electrically conducting polymers

For electrically conducting polypyrole films, the thermal diffusivity and thermal conductivity were obtained by modeling the signals from the photopyroelectric flash technique with a one-dimensional four-layer system. This method has a number of advantages over the sinusoidal excitation: wide thickness range, fast acquisition, simple and cheap setup. This first thermal characterization of polypyrole films shows an increasing thermal conductivity with dopant ion concentration.     

Influence of HF catalyst on the microstructure properties of ultra low-k thin films prepared by sol-gel method

This paper reports that by using the hydrofluoric acid （HF） as the acid catalyst, F doped nanoporous low-k SiO2 thin films have been prepared by means of sol-gel method. The characterization of atomic force microscopy and Fourier transform infrared spectroscopy demonstrates that the HF catalyzed films are more hydrophobic. The N2 adsorption/desorption experiments show that the suited introduction of HF increases the porosity and decreases the pore size distribution （about 10 nm） in the films. The above results indicate that the hydrofluoric acid is the more suitable acid catalyst than the hydrochloric one for preparing nanoporous ultra low-k SiO2 thin films.     

A new multi-spectral feature level image fusion method for human interpretation

Various different methods to perform multi-spectral image fusion have been suggested, mostly on the pixel level. However, the jury is still out on the benefits of a fused image compared to its source images. We present here a new multi-spectral image fusion method, multi-spectral segmentation fusion (MSSF), which uses a feature level processing paradigm. To test our method, we compared human observer performance in a three-task experiment using MSSF against two established methods: averaging and principle components analysis (PCA), and against its two source bands, visible and infrared. The three tasks that we studied were: (1) simple target detection, (2) spatial orientation, and (3) camouflaged target detection. MSSF proved superior to the other fusion methods in all three tests; MSSF also outperformed the source images in the spatial orientation and camouflaged target detection tasks. Based on these findings, current speculation about the circumstances in which multi-spectral image fusion in general and specific fusion methods in particular would be superior to using the original image sources can be further addressed.     

A new method for orbit determination: Unit vector method

In this paper, a method of orbit determination is presented according to the principle of unit vector method (UVM). The model and arithmetic are improved and it not only suits initial orbit determination with short arc data, it also suits orbit improvement with data longer. It is also suitable for orbit of any eccentricity and any inclination. It omits most partial derivatives of all the elements which must be calculated in classical differential orbit improvement (DOI), so, it is more efficient than DOI, and the accuracy of orbit determination and convergence of algorithm are also improved appreciably.     

A new thermal conductivity model for nanofluids

In a quiescent suspension, nanoparticles move randomly and thereby carry relatively large volumes of surrounding liquid with them. This micro-scale interaction may occur between hot and cold regions, resulting in a lower local temperature gradient for a given heat flux compared with the pure liquid case. Thus, as a result of Brownian motion, the effective thermal conductivity, k_eff, which is composed of the particles conventional static part and the Brownian motion part, increases to result in a lower temperature gradient for a given heat flux. To capture these transport phenomena, a new thermal conductivity model for nanofluids has been developed, which takes the effects of particle size, particle volume fraction and temperature dependence as well as properties of base liquid and particle phase into consideration by considering surrounding liquid traveling with randomly moving nanoparticles.The strong dependence of the effective thermal conductivity on temperature and material properties of both particle and carrier fluid was attributed to the long impact range of the interparticle potential, which influences the particle motion. In the new model, the impact of Brownian motion is more effective at higher temperatures, as also observed experimentally. Specifically, the new model was tested with simple thermal conduction cases, and demonstrated that for a given heat flux, the temperature gradient changes significantly due to a variable thermal conductivity which mainly depends on particle volume fraction, particle size, particle material and temperature. To improve the accuracy and versatility of the k_effmodel, more experimental data sets are needed.     

Photoacoustic characterization of optical and thermal properties of CdSe quantum dots

We report on the optical absorption properties of as prepared CdSe quantum dots (QDs) measured by the photoacoustic (PA) method. CdSe QDs were fabricated by the chemical solution deposition (CD) technique. With increasing growing time, the redshift of the PA spectra can be clearly observed and optical absorption in the visible region due to CdSe Q-dots is demonstrated. The average diameters of the CdSe QDs for each growth time interval is estimated using the effective mass approximation giving diameters ranging from 2.6 nm to 3.4 nm. These values are comparable to those obtained by scanning tunnelling microscope (STM). Thus, PA spectroscopy is useful to obtain the QDs sizes as grown and with no further preparation. In addition, PA measurements provide also the thermal diffusivity of samples of different sizes which in this case show an increase by at least an order of magnitude than the bulk value.     

Near-eutectic Zn-Mg alloys: Interrelations of solidification thermal parameters,microstructure length scale and tensile/corrosion properties

Zn-Mg alloys are considered to have potential application in bone implants, since both metals are biocompatible and have biodegradable characteristics. Adding Mg to Zn can boost mechanical and corrosion resistances. However, the literature is very limited on quantifying the interrelation of solidification parameters, microstructural features and mechanical/corrosion properties of Zn-Mg alloys. The present study examines the interrelations of alloy Mg content, macrosegregation effects, morphology and scale of the matrix and eutectic phases, nature of intermetallics and tensile and corrosion properties of near-eutectic Zn-Mg alloys. The alloys samples are obtained by unsteady-state directional solidification resulting in a wide range of solidification thermal parameters and microstructures. We examine microstructural features of both dendritic and complex regular eutectic phases. It is shown that the eutectic exhibits a bimodal pattern with neighboring areas of coarse and fine lamellae. Experimental growth laws relating the primary, secondary and eutectic spacings to the solidification cooling rate and growth rate are proposed. Hall-Petch type equations are derived expressing tensile strength and elongation to dendritic and eutectic spacings. Electrochemical parameters determined by polarization curves during corrosion tests and SEM analyses of corroded areas have shown that the alloy having an essentially eutectic microstructure is associated with better corrosion resistance.