Characterization of laser-treated Opuntia using FT-IR spectroscopy and thermal analysis

This paper presents the characterization of Opuntia samples whose thorns were removed by laser pulses. The characterization was performed by Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). In this study we performed a comparative analysis of samples before and after treatment by using a Nd:YAG laser emitting at 1064 nm with an energy variable of up to 0.9 J. It was determined that no significant morphological or compositional changes had taken place in the cactus epidermis due to the laser treatment.     

Optical properties of femtosecond laser-treated diamond

Coupling effect in spiral-shaped metamaterials composed of four half rings at different sizes is investigated to achieve tunability in THz range. This novel spiral-shaped structure was fabricated on flexible substrate with laser micro-lens array (MLA) lithography and measured by THz time domain spectroscopy (THz-TDS). The experimental results suggest that mutual capacitance and inductance coupling in the spiral-shaped structure would result in frequency shifts of the four resonances. The observed shifting trends of the four resonant frequencies are in good agreement with simulation and are further explained by the electric field distribution. By varying the gap sizes among the half rings, four resonant frequencies can be tuned flexibly. Such a spiral-shaped design has potential applications in multi-band tunable THz MEMS devices.     

Characterization of mineral paper by air-coupled ultrasonic spectroscopy

A novel technology in the paper industry makes possible to produce paper by using a mineral powder and a polymer instead of cellulose fibers. This new product is called mineral paper, it presents some potential environmental advantages compared with conventional paper, while it exhibit a similar appearance and properties. The purpose of this work is to determine the possibilities of an air-coupled ultrasonic technique using wide band signals and spectral analysis to study this kind of materials. As no direct contact nor coupling fluids between the paper and the transducers is required, this technique is specially well suited to this problem. It also offers good perspectives for the development of a on-line quality control system. A through transmission technique (0.15-2.3 MHz) is employed and Fourier analysis is performed to obtain both magnitude and phase spectra of the transmission coefficient. Properties in the thickness direction as well as in the paper plane has been determined by the excitation and analysis of thickness and plate resonances at several incident angles and different directions within the paper plane. Different paper grades (from 140 to 480 g/m²) have been studied. Very high attenuation coefficients and very low propagation velocities (and hence elastic constant) have been obtained for most cases, this can be explained by considering the large porosity of this material (up to 50%) and the microstructure: a mixture of solid grains with a resin with a relatively large fraction of air-filled pores. Measurements show that unlike conventional cellulose machine made paper this material is transversely isotropic (isotropic in the paper plane) and that the degree of anisotropy (when in-plane directions are compared with the thickness direction) largely depends on the level of resin impregnation.     

Experimental studies on the microstructure and hardness of laser-treated steel specimens

An experimental investigation with 5 kW CW CO₂ laser system was carried out to study the effects of different laser and process parameters on the microstructure and hardness of carbon steel specimen with varying carbon percentage. The laser beam is allowed to scan on the surface of the work piece varying the power (1.1–2.5 kW) and traverse speed (6–15 mm/s) at two different spot sizes using TEM_01* mode laser beam. The most hardenable microstructure achieved in case of three grades of carbon steel and the most influencing parameter on the value of hardness are reported. Besides the above study, some multipass operations are also carried out to recommend an appropriate gap between consecutive passes.     

Stress corrosion cracking behavior of Nd:YAG laser-treated aluminum alloy 7075

Nd-YAG laser surface treatment was conducted on 7075-T651 aluminum alloy with the aim of improving the stress corrosion cracking resistance of the alloy. Laser surface treatment was performed under two different gas environments, air and nitrogen. After the laser treatment, coarse constituent particles were removed and fine cellular/dendritic structures had formed. In addition, for the N₂-treated specimen, an AlN phase was detected. The results of the stress corrosion test showed that after 30 days of immersion, the untreated specimen had been severely attacked by corrosion, with intergranular cracks having formed along the planar grain boundaries of the specimen. For the air-treated specimen, some relatively long stress corrosion cracks and a small number of relatively large corrosion pits were found. The cracks mainly followed the interdendritic boundaries; the fusion boundary was found to be acting as an arrestor to corrosion attacks. In contrast, only few short stress corrosion cracks appeared in the N₂-treated specimen, indicating an improvement in corrosion initiation resistance. The superior corrosion resistance was attributed to the formation of the AlN phase in the surface of the laser-melted layer, which is an electrical insulator. The electrochemical impedance measurements taken during the stress corrosion test showed that the film resistance of the laser-treated specimens was always higher than that of the untreated specimen, with the N₂-treated specimen showing the highest resistance.     

The effects of process gas type on the surface condition of high-power diode laser-treated ordinary Portland cement

This paper examines the effects of using O₂, Ar and He process gasses during the treatment of the ordinary Portland cement (OPC) surface of concrete with a high-power diode laser (HPDL). The study revealed that, depending on the shield gas used, distinct difference existed in the surface condition of the concrete after HPDL treatment. In particular, the use of O₂ as the shield gas was seen to result in glazes with far fewer microcracks and porosities than those generated with either Ar or He shield gases. Such differences were found to be due to the smaller O₂ gas molecules dissolving molecularly into the open structure of the HPDL-generated glaze on the OPC surface of concrete and react with the glass network to increase the fluidity of the melt. This in turn was also seen to affect the cooling rate and therefore the tendency to generate microcracks.     

Development and experimental validation of analytical thermal models for the evaluation of the depth of laser-treated zones

Received: 5 January 1998/Accepted: 27 March 1998     

Geometry of crumpled paper

We measure the geometry of a crumpled sheet of paper with laser-aided topography and discuss its statistical properties. The curvature of an elastoplastic fold scales linearly with applied force. The curvature distribution follows an exponential form with regions of high curvature localized along ridges. The measured ridge length distribution is consistent with a hierarchical model for ridge breaking during crumpling. A large fraction of the ridges are observed to terminate without bifurcating, and the ridge network connectedness is not as complete as anticipated. The self-affinity of the surface is characterized by a Hurst exponent of 0.71+/-0.01 in contrast with previous results.     

Statistics of crumpled paper

A statistical study of crumpled paper is allowed by a minimal 1D model: a self-avoiding line bent at sharp angles--in which the elastic energy resides--put in a confining potential. Many independent equilibrium configurations are generated numerically and their properties are investigated. At small confinement, the distribution of segment lengths is log-normal in agreement with previous predictions and experiments. At high confinement, the system approaches a jammed state with a critical behavior, whereas the length distribution follows a gamma law in which the parameter is predicted as a function of the number of layers in the system.     

Characterization of Ti6Al4V implant surface treated by Nd:YAG laser and emery paper for orthopaedic applications

A more noble and biocompatible Ti alloy was achieved at fluence of 140 J cm⁻² where the implant indicated a higher degree of hardness (825HV), higher corrosion resistance (−0.21 V) and highest hydrophilicity (i.e. θ_c = 37°) compared with 70° of the control sample. These values corresponded to 58 and 39 mN m⁻¹ of surface tension respectively. The laser treated samples at 140 J cm⁻² showed higher wettability characteristics than mechanically roughened surface. Cell growth and their spreading condition in a specific area were analyzed by SEM and Image J Program software. Clearly, more cells were attached (1.2 × 10⁵) to and spread (488 μm²) over the surface at 140 J cm⁻² than in any other condition. Pathologically, the treated samples indicated no sign of infection.     

超声纸杯焊接技术

本文介绍一种超声纸杯焊接设备及焊接工艺。     

Introduction to Jebsen's paper

Brief comment on a 1921 paper by Jebsen.This work provides the first published proof of “Birkhoff's” theorem. The author, who seems to have been an undergraduate at the time (tragically, he died shortly afterwards) understood (as did many others) that Einstein's equations reduced considerably in a “minimal,” namely two-component, metric in a simple gauge such as Schwarzschild's; a good part of the paper is devoted to deriving this interval form.The originality of his work lies instead in showing that time-independence of the exterior Schwarzschild solution need not be assumed, but is a consequence of Einstein's equations.From a modern perspective, it is a bit surprising that this result was not found earlier: for example, Einstein studied the spherical solution in the linearized theory, whose kinship to Maxwell's might have suggested the obvious parallel to charge conservation. In current language, the theorem states gauge theories forbid monopole radiation because they have no helicity zero modes.Editor's note: Further references to early derivations of “Birkhoff's” theorem can be found in [1] and [2] while [3] is one of the few papers that calls it “Jebsen-Birkhoff.” Since few's was written a more detailed biography of Jebsen has now appeared: gr-qc/0508163, by Johausen &; Ravulal. Work supported by NSF Grant PHY04-00609     

Sonication of pulp and paper effluent

Final effluent from a pulp and paper kraft mill was exposed to power ultrasound at 357 kHz with the aim of reducing color, turbidity, and chemical oxygen demand (COD). Absorbance measurements showed a bleaching of the effluent at wavelengths above 250 nm, indicating loss of aromatic chromophores. Effluent turbidity also decreased. Surprisingly, there was no observable decrease in COD, within experimental error. This is attributed to the presence of bicarbonate and sulfate ions in the final effluent, which react with hydroxyl radicals and effectively block the oxidation of organics in the effluent. This was demonstrated by sonicating solutions of potassium hydrogen phthalate (KHP) containing chloride, bicarbonate, or sulfate ions, which are the major inorganic ions in the final effluent studied. A solution containing only 2.3 mM KHP showed a 19% reduction in COD after 6 h of sonication. An identical solution with 200 ppm chloride also showed a 19% COD reduction. However, solutions with 700 ppm sulfate and 400 ppm bicarbonate showed COD reductions of 11% and 3%, respectively.     

Laser optoacoustic measurement of paper porosity

The propagation of broadband ultrasonic pulses in combined media that consist of printing paper of different porosity saturated with different liquids is studied. The experiments are performed with three types of paper, namely, Zoom Ultra (Stora Enso, Finland) with surface densities of 80 and 100 g/m² and Data Copy (Mo Do, Sweden) with a surface density of 160 g/cm², and with two types of saturating liquids: ethanol and transformer oil. To excite ultrasonic pulses and to detect them with a high time resolution, the laser optoacoustic spectroscopy method is used. For each type of liquid-saturated paper, the phase velocity of ultrasound is measured in the frequency range of 5–35 MHz. The absence of any noticeable frequency dispersion of the phase velocity is revealed. The possibility of measuring the porosity of printing paper on the basis of the theoretical model of a two-phase medium with the use of the corresponding experimental data is demonstrated.     

Electronics with and on paper

Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for electronic applications, driven mainly by low‐cost and disposable applications. Adding to this interest, we must recognise the importance of the dream of wireless auto‐sustained and low‐energy‐consumption electronics. This dream can be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major biopolymer and of tremendous global economic importance. Most of the paper used up to now is optimised in terms of the required mechanical and physical properties to be used as the support of inks of different origins. In the future, specific electronic heterogeneous paper sheets should be fabricated aiming to get paper fibers with required bulk and surface functionalities, proper water/vapour barrier, size and diameter/thickness of the fibrils and full paper thickness. This will be the function of components/devices to be incorporated/integrated such as thin‐film transistors, complementary metal oxide semiconductor devices, passive electronic components (resistances, inductors and capacitors), memory transistors, electrochromics and thin‐film paper batteries. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Acoustic emission from paper fracture

We report tensile failure experiments on paper sheets. The acoustic emission energy and the waiting times between acoustic events follow power-law distributions. This remains true while the strain rate is varied by more than 2 orders of magnitude. The energy statistics has the exponent beta approximately 1.25+/-0.10 and the waiting times the exponent tau approximately 1.0+/-0.1, in particular, for the energy roughly independent of the strain rate. These results do not compare well with fracture models, for (brittle) disordered media, which as such exhibit criticality. One reason may be residual stresses, neglected in most theories.