Multichannel fiber laser Doppler vibrometer studies of low momentum and hypervelocity impacts

A multichannel optical fiber laser Doppler vibrometer was demonstrated with the capability of making simultaneous non-contact measurements of impacts at 3 different locations. Two sets of measurements were performed, firstly using small ball bearings (1 mm–5.5 mm) falling under gravity and secondly using small projectiles (1 mm) fired from an extremely high velocity light gas gun (LGG) with speeds in the range 1 km/s–8 km/s. Determination of impact damage is important for industries such as aerospace, military and rail, where the effect of an impact on the structure can result in a major structural damage. To our knowledge the research reported here demonstrates the first trials of a multichannel fiber laser Doppler vibrometer being used to detect hypervelocity impacts.     

Robust control of novel pendulum-type vibration isolation system

A novel pendulum-type vibration isolation system is proposed consisting of three active cables with embedded piezoelectric actuators and a passive elastomer layer. The dynamic response of the isolation module in the vertical and horizontal directions is modeled using the Lagrangian approach. The validity of the dynamic model is confirmed by comparing the simulation results for the frequency response in the vertical and horizontal directions with the experimental results. An approximate model is proposed to take into account system uncertainties such as payload changes and hysteresis effects. A robust quantitative feedback theory (QFT)-based active controller is then designed to ensure that the active control can achieve a high level of disturbance rejection in the low-frequency range even under variable loading conditions. It is shown that the controller achieves average disturbance rejection of ?14 dB in the 2–60 Hz bandwidth range and ?35 dB at the resonance frequency. The experimental results confirm that the proposed system achieves a robust vibration isolation performance under the payload in the range of 40–60 kg.     

Dual-wavelength investigation of laser-induced damage in multilayer mirrors at 532 and 1064 nm

Thin film beam splitters with high reflectivity at 532 nm and high transmittance at 1064 nm were deposited via reactive electron-beam evaporation with optimized parameters. The damage performance of the samples was investigated under irradiations of 532 nm laser only, 1064 nm laser only, and various combined laser fluences. The damages induced by the 1064 nm laser were primarily attributed to the initiators at the interface between the coatings and substrate. Under 532 nm laser irradiation only, two distinctive damage pits initiated by the submicron absorptive defects located at different coating depths and correlated to interfaces were observed. The damage effect under simultaneous irradiation in multilayer films was also investigated. The respective sensitive defects of the two lasers remained the precursors for causing damage. However, the dominant damage factors in simultaneous irradiation changed with the 1064 nm laser fluence, which also determined the coupling effect between the two lasers in terms of causing damage. Finally, correlative analysis methods were used to discuss the different coupling effects.     

Study on the bias-dependent effects of proton-induced damage in CdZnTe radiation detectors using ion beam induced charge microscopy

The influence of damage induced by 2 MeV protons on CdZnTe radiation detectors is investigated using ion beam induced charge (IBIC) microscopy. Charge collection efficiency (CCE) in irradiated region is found to be degraded above a fluence of 3.3 × 10¹¹ p/cm² and the energy spectrum is severely deteriorated with increasing fluence. Moreover, CCE maps obtained under the applied biases from 50 V to 400 V suggests that local radiation damage results in significant degradation of CCE uniformity, especially under low bias, i. e., 50 V and 100 V. The CCE nonuniformity induced by local radiation damage, however, can be greatly improved by increasing the detector applied bias. This bias-dependent effect of 2 MeV proton-induced radiation damage in CdZnTe detectors is attributed to the interaction of electron cloud and radiation-induced displacement defects.     

Detection of nanoscale ESD effect on GMR head signal using the wavelet transform technique: HBM and CDM cases

An electrical signal anomaly is an undesired signal and is difficult to detect by a commercial instrument due to its short duration and unpredictable fault on a signal. Since a GMR recording head is a stack of nanometer thick multilayers, in particular, a magnetic layer and conductor layers, for magnetic insulating spacers, it is very sensitive to electron movements. Visible damage is understandable and protectable but latent failure cannot be measured. It is possibly observed by using frequency-domain apparatus but certainly it is not real-time detection. Therefore, in order to detect a latent failure head affected by ESD in the time domain, current conventional instruments are ineffective. In this study, the wavelet transform technique using the 4th order Daubechies is proposed to detect the glitches on a magnetic recording head signal in the time domain. It is found that the glitches occur when the ESD level of the charged device model (CDM) and human body model (HBM) on giant magnetoresistive (GMR) heads are in ranges of 6–15 V and 40–120 V, respectively. The electrical test parameters and scanning electron microscope (SEM) photo of the recording heads show no visible change in reader sensor. To ensure the results, the GMR damage is observed by SEM when the CDM-ESD and HBM-ESD are 10 V and 130 V, respectively. The glitches in the magnetic response signal of the GMR head are found to increase when the ESD level is increased. Thus, the Daubechies wavelet transform technique can be a novel approach to detect the pre-degradation of a GMR head due to an ESD effect.     

Study on the formation mechanism of isoniazid crystal defects and defect elimination strategy based on ultrasound

In crystallization, crystal growth defects may reduce the strength and purity of crystals, which are not welcomed in the industry. Herein, isoniazid (INH) crystals were chosen as an example to investigate the formation of crystal defects at the molecular scale by combining experiments and molecular dynamics simulations. It was found that the strong interaction between the solvent and the crystal surface, high temperature, small stirring rate, and low supersaturation can lead to more pronounced crystal defects. The bulk severity of INH crystal defects was reflected by N₂ adsorption–desorption measurement. Besides, the single-crystal growth experiments manifested the rough growth mechanism for the (1 1 0) surface in the axial direction and the stepwise growth mechanism for the (0 0 2) surface in the radial direction. For the (1 1 0) surface, cavities occurred under the condition where the growth rate of the crystal edges and corners was greater than that of the surface center due to the starvation phenomenon of diffusion. While for the (0 0 2) surface, when the solvent removal rate was lower than the solute insertion rate, liquid inclusions were formed, which was verified by Raman microscopy. Furthermore, the ultrasonic strategy was successfully proposed to eliminate INH crystal defects and prepare perfect INH crystals. Moreover, the mechanism of ultrasound to reduce the crystal defect was proposed. We believe this work can provide insights into the design and preparation of defect-free crystals in crystallization.     

Weak mode coupling measurement with EMD-based method in polarization-maintaining fibers

The intensity and position of coupling points in polarization-maintaining fibers (PMFs) caused by force and twist can be effectively detected by Polarization Coupling Measurement (PCM). The sensitivity of detection will decrease due to the movement of scanning Michelson interferometer. To detect the weak coupling point, an EMD-based method is proposed in this paper. The experimental results illustrate that the EMD-based method can suppress the noise and improve the SNR effectively. The DWT method is also performed for a comparative study. The results show that the EMD-based method is effective and applicable for PCM and the coupling point can still be detected when the intensity is as weak as ? 70 dB.     

Localized defects related to the 14N+ ion irradiation-induced magnetism in SiC

The role of localized defects as they pertain to ferromagnetism in SiC, which contains only s and p electrons, is important but unclear. Here, room temperature, macroscopic magnetization is induced and can be tuned in 6H-SiC using ¹⁴N⁺ ion implantation. First-principles density functional theory computation results confirm that ¹⁴N⁺ ion implantation can enhance the ferromagnetic ordering of the local magnetic moments caused by vacancy and substitution defects. The calculated magnetization values in the energetically favored ferromagnetic ordering (1.47–2.93 emu/g for several vacancy and substitution defects) are larger than our experimental values (0.25 emu/g at 5 K and 0.08 emu/g at 300 K), but the result is qualitatively in agreement.     

Nanosecond-pulsed erbium-doped fiber lasers with graphene saturable absorber

We demonstrate graphene mode-locked nanosecond erbium-doped fiber laser in an all-fiber ring cavity. The clean and robust pulse train was generated at 27 mW pump power. Resultant central wavelength, repetition rate and pulse width was 1560 nm, 388 kHz and 6 ns, respectively. With two stage fiber amplifier, the output power was 553 mW, corresponding to single pulse energy of 1.4 μJ. In addition, the pulse-width can be varied ranging from 3 ns to 20 ns at repetition rate between 200 kHz and 1.54 MHz by changing the length of the laser cavity.     

Early sinkhole detection using a drone-based thermal camera and image processing

Accurate advance detection of the sinkholes that are occurring more frequently now is an important way of preventing human fatalities and property damage. Unlike naturally occurring sinkholes, human-induced ones in urban areas are typically due to groundwater disturbances and leaks of water and sewage caused by large-scale construction. Although many sinkhole detection methods have been developed, it is still difficult to predict sinkholes that occur in depth areas. In addition, conventional methods are inappropriate for scanning a large area because of their high cost. Therefore, this paper uses a drone combined with a thermal far-infrared (FIR) camera to detect potential sinkholes over a large area based on computer vision and pattern classification techniques.To make a standard dataset, we dug eight holes of depths 0.5–2 m in increments of 0.5 m and with a maximum width of 1 m. We filmed these using the drone-based FIR camera at a height of 50 m. We first detect candidate regions by analysing cold spots in the thermal images based on the fact that a sinkhole typically has a lower thermal energy than its background. Then, these regions are classified into sinkhole and non-sinkhole classes using a pattern classifier. In this study, we ensemble the classification results based on a light convolutional neural network (CNN) and those based on a Boosted Random Forest (BRF) with handcrafted features. We apply the proposed ensemble method successfully to sinkhole data for various sizes and depths in different environments, and prove that the CNN ensemble and the BRF one with handcrafted features are better at detecting sinkholes than other classifiers or standalone CNN.     

An asymptotic-preserving method for highly anisotropic elliptic equations based on a Micro–Macro decomposition

The concern of the present work is the introduction of a very efficient asymptotic preserving scheme for the resolution of highly anisotropic diffusion equations. The characteristic features of this scheme are the uniform convergence with respect to the anisotropy parameter 0 < ε ? 1, the applicability (on cartesian grids) to cases of non-uniform and non-aligned anisotropy fields b and the simple extension to the case of a non-constant anisotropy intensity 1/ε. The mathematical approach and the numerical scheme are different from those presented in the previous work [P. Degond, F. Deluzet, A. Lozinski, J. Narski, C. Negulescu, Duality-based asymptotic-preserving method for highly anisotropic diffusion equations, Communications in Mathematical Sciences 10 (1) (2012) 1–31] and its considerable advantages are pointed out.     

Discrimination methods for biological contaminants in fresh-cut lettuce based on VNIR and NIR hyperspectral imaging

The rapid detection of biological contaminants such as worms in fresh-cut vegetables is necessary to improve the efficiency of visual inspections carried out by workers. Multispectral imaging algorithms were developed using visible-near-infrared (VNIR) and near-infrared (NIR) hyperspectral imaging (HSI) techniques to detect worms in fresh-cut lettuce. The optimal wavebands that can detect worms in fresh-cut lettuce were investigated for each type of HSI using one-way ANOVA. Worm-detection imaging algorithms for VNIR and NIR imaging exhibited prediction accuracies of 97.00% (RI_547/945) and 100.0% (RI_1064/1176, SI_1064-1176, RSI-I_{(1064-1173)/1064}, and RSI-II_{(1064-1176)/(1064+1176)})_, respectively. The two HSI techniques revealed that spectral images with a pixel size of 1 × 1 mm or 2 × 2 mm had the best classification accuracy for worms. The results demonstrate that hyperspectral reflectance imaging techniques have the potential to detect worms in fresh-cut lettuce. Future research relating to this work will focus on a real-time sorting system for lettuce that can simultaneously detect various defects such as browning, worms, and slugs.     

Free-volume defects investigation of GeS2-Ga2S3-CsI chalcogenide glasses by positron annihilation spectroscopy

The transformation behavior of free-volume defect in (80GeS₂-20Ga₂S₃)_100-x (CsI)_x (x = 0, 5, 10, 15 mol%) chalcogenide glasses was studied by employing positron annihilation spectroscopic technique, which could reveal valuable information for in-depth understanding of nano-structural defects in glassy matrix. The results indicate that the structural changes caused by CsI additives can be adequately described by positron trapping modes determined with two-state model. The initial addition of CsI (x = 5 mol%) led to a void contraction, whereas, the void agglomeration occurred with the increase of CsI and the free-volume defects of the glasses were obviously reduced. The atomic density ρ is inversely proportional to the number of these defects. Meanwhile, the UV cut-off edge shifts toward short-wavelength with increasing of CsI. This study provides the valuable information of defects evolution in GeS₂-Ga₂S₃-CsI glasses.     

Radioluminescence of synthetic quartz related to alkali ions

The radioluminescence (RL) of synthetic quartzes (GEMMA Quartz & Crystal Company) has been measured at room temperature. Some samples were treated by electrodiffusion (“sweeping”) in order to change the concentrations of alkali ions, mainly Li⁺ and Na⁺, which in quartz are known to be linked to Al ions, substitutional for Si ions.The RL emission spectra show evidence of a role of alkali ions in affecting some specific emissions. All the spectra could be analysed as composed of four bands in the blue and UV region. Specifically, the well known blue emission at around 470 nm was seen to be composed by two bands at 430 nm (2.86 eV) and at 485 nm (2.53 eV). Effects of irradiation, during the RL measurements, were clearly seen only in the “Li swept in” sample, namely an increase in the 485 nm band intensity and a decrease in the 430 nm band one. The previously reported UV emission was detected at 355 nm (3.44 eV) in all the samples, being the most intense band in the “swept out” sample. A further UV emission was detected at 315 nm (3.94 eV), more intense in untreated samples.Possible assignments of the detected emission bands are discussed in relation to the defects of quartz, specifically focusing on the Al centres that are most affected by sweeping procedures.     

Ultrastructural analysis of the low level laser therapy effects on the lesioned anterior tibial muscle in the Gerbil

Low level laser therapy (LLLT) is known for its positive results but studies on the biological and biomodulator characteristics of the effects produced in the skeletal muscle are still lacking. In this study the effects of two laser dosages, 5 or 10 J/cm², on the lesioned tibial muscle were compared. Gerbils previously lesioned by 100 g load impact were divided into three groups: GI (n = 5) controls, lesion non-irradiated; GII (n = 5), lesion irradiated with 5 J/cm² and GIII (n = 5), lesion irradiated with 10 J/cm², and treated for 7 consecutive days with a laser He–Ne (λ = 633 nm). After intracardiac perfusion, the muscles were dissected and reduced to small fragments, post-fixed in 1% osmium tetroxide, dehydrated in increasing alcohol concentrations, treated with propylene oxide and embedded in Spurr resin at 60 °C. Ultrafine cuts examined on a transmission electron microscope (Jeol 1010) revealed in the control GI group a large number of altered muscle fibers with degenerating mitochondria, intercellular substance containing degenerating cell fragments and budding blood capillaries with underdeveloped endothelial cells. However, groups GII and GIII showed muscle fibers with few altered myofibrils, regularly contoured mitochondria, ample intermembrane spaces and dilated mitochondrial crests. The clean intercellular substance showed numerous collagen fibers and capillaries with multiple abluminal processes, intraluminal protrusions and several pinocytic vesicles in endothelial cells. It was concluded that laser dosages of 5 or 10 J/cm² delivered by laser He–Ne (λ = 633 nm) during 7 consecutive days increase mitochondrial activity in muscular fibers, activate fibroblasts and macrophages and stimulate angiogenesis, thus suggesting effectivity of laser therapy under these experimental conditions.     

Membrane cleaning with ultrasonically driven bubbles

A laboratory filtration plant for drinking water treatment is constructed to study the conditions for purely mechanical in situ cleaning of fouled polymeric membranes by the application of ultrasound. The filtration is done by suction of water with defined constant contamination through a membrane module, a stack of five pairs of flat-sheet ultrafiltration membranes. The short cleaning cycle to remove the cake layer from the membranes includes backwashing, the application of ultrasound and air flushing. A special geometry for sound irradiation of the membranes parallel to their surfaces is chosen. Two frequencies, 35 kHz and 130 kHz, and different driving powers are tested for their cleaning effectiveness. No cleaning is found for 35 kHz, whereas good cleaning results are obtained for 130 kHz, with an optimum cleaning effectiveness at moderate driving powers. Acoustic and optic measurements in space and time as well as analytical considerations and numerical calculations reveal the reasons and confirm the experimental results. The sound field is measured in high resolution and bubble structures are high-speed imaged on their nucleation sites as well as during their cleaning work at the membrane surface. The microscopic inspection of the membrane surface after cleaning shows distinct cleaning types in the cake layer that are related to specific bubble behaviour on the membrane. The membrane integrity and permeate quality are checked on-line by particle counting and turbidity measurement of the permeate. No signs of membrane damage or irreversible membrane degradation in permeability are detected and an excellent water permeate quality is retained.     

Hydrogen chemisorption on Si(111)√ 3×√ 3R30∘-B passivated surface studied by thermal desorption and scanning tunneling microscopy

Atomic H chemisorption on the Si(111)√ 3×√ 3R30^°-B surface has been studied by thermal desorption spectroscopy (TDS) and scanning tunneling microscopy (STM). The B-modified Si surface is known to be inert towards adsorbates, since the surface dangling bonds of Si adatoms are passivated by B atoms sitting in sub-surface sites. However, it was found that even on a perfectly passivated surface, H is adsorbed on the surface by destroying the original √ 3 × √ 3 structure. STM observations revealed that H exposure led to the creation of defects at surface sites, and H was subsequently adsorbed as Si-monohydride at these sites. H exposure also caused cluster island formation at the top surface. The islands are composed of hydrogenated amorphous Si atoms or B-hydrogen complexes.     

Thermographic visualization of the superficial vein and extravasation using the temperature gradient produced by the injected materials

There are few effective methods to detect or prevent the extravasation of injected materials such as chemotherapeutic agents and radiographic contrast materials. To investigate whether a thermographic camera could visualize the superficial vein and extravasation using the temperature gradient produced by the injected materials, an infrared thermographic camera with a high resolution of 0.04 °C was used. At the room temperature of 26 °C, thermal images and the time course of the temperature changes of a paraffin phantom embedded with rubber tubes (diameter 3.2 mm, wall thickness 0.8 mm) were evaluated after the tubes were filled with water at 15 °C or 25 °C. The rubber tubes were embedded at depths of 0 mm, 1.5 mm, and 3.0 mm from the surface of the phantom. Temperature changes were visualized in the areas of the phantom where the tubes were embedded. In general, changes were more clearly detected when greater temperature differences between the phantom and the water and shallower tube locations were employed. The temperature changes of the surface of a volunteer’s arm were also examined after a bolus injection of physiological saline into the dorsal hand vein or the subcutaneous space. The injection of 5 ml room-temperature (26 °C) saline into the dorsal hand vein enabled the visualization of the vein. When 3 ml of room-temperature saline was injected through the vein into the subcutaneous space, extravasation was detected without any visualization of the vein. The subtraction image before and after the injection clearly showed the temperature changes induced by the saline. Thermography may thus be useful as a monitoring system to detect extravasation of the injected materials.     

The geometries of coadsorbate layers of O and H on Ru(0 0 1): How well can quantitative LEED see hydrogen atoms?

Using a CCD LEED system for the collection of IV data with low beam damage, and full dynamical as well as tensor LEED calculations, we have determined the geometries of the (2 × 2)-(O + 3H) and the (2 × 2)-(O + H) coadsorbate structures on Ru(0 0 1). We show that here quantitative LEED can locate the H atoms very well. Not only their sites (hcp in the first, fcc in the second case), but also the Ru–H spacings and changes in the first two substrate layers are clearly determined. We argue that this success is due to the relatively large data range and to the smaller H mobility compared to pure H layers caused by their repulsive lateral interactions with the oxygen atoms.     

Effects of surface mechanical attrition treatment (SMAT) on a rough surface of AISI 316L stainless steel

Surface mechanical attrition treatment (SMAT) improves mechanical properties of metallic materials through the formation of nanocrystallites at their surface layer. It also modifies the morphology and roughness of the work surface. Surface roughening by the SMAT has been reported previously in a smooth specimen, however in this study the starting point was a rough surface and a smoothening phenomenon is observed. In this paper, the mechanisms involved in the surface smoothening of AISI 316L stainless steel during the SMAT are elucidated. The SMAT was conducted on a specimen with a roughness of R_a = 3.98 μm for 0–20 min. The size of milling balls used in the SMAT was varied from 3.18 mm to 6.35 mm. The modification of subsurface microhardness, surface morphology, roughness and mass reduction of the specimen due to the SMAT were studied. The result shows the increasing microhardness of the surface and subsurface of the steel due to the SMAT. The impacts of milling balls deform the surface and produce a flat-like structure at this layer. Surface roughness decreases until its saturation is achieved in the SMAT. The mass reduction of the specimens is also detected and may indicate material removal or surface erosion by the SMAT. The size of milling ball is found to be the important feature determining the pattern of roughness evolution and material removal during the SMAT. From this study, two principal mechanisms in the evolution of surface morphology and roughness during the SMAT are proposed, i.e. indentation and surface erosion by the multiple impacts of milling balls. A comparative study with the results of the previous experiment indicates that the initial surface roughness has no influence in the work hardening by the SMAT but it does slightly on the saturated roughness value obtained by this treatment.