胶束中的若丹明6G荧光增强和激光行为

使用阴离子表面活性剂十二烷基硫酸钠 (SDS)有效的增强了若丹明 6G染料水溶液的荧光 ,在若丹明 6G浓度分别为 5 47× 10 -7和 5 47× 10 -4 mol·L-1时 ,最大增强比率分别为 1 95和 9 7。在后一浓度下SDS的加入使若丹明 6G染料激光阈值降低 ,能量转化效率提高。不加SDS时的激光阈值功率密度约为 6 5MW·cm-2 ,加入 4 1× 10 -2 mol·L-1的SDS后 ,激光阈值功率密度降为 0 8MW·cm-2 。泵浦光功率密度为 6 5MW·cm-2 时 ,能量转化效率达到 2 5 %。同时还观察到SDS的加入使溶液吸收谱、荧光谱和染料激光发生了红移。对以上现象的物理机制进行了讨论。

悬浮染料液滴显现激光行为

来自丹麦科技大学、瑞典Lund大学和Astra Zeneca’s研发中心的研究者宣布，他们首次观察到了悬浮液滴中能重复实现的激光。该实验开创了利用激光作用探测液滴中微生物或化学变化的新途径。

低温剥蚀LA-ICP-MS准确测定硫化物矿物多元素分析研究

硫化物矿物中元素含量及其分布可示踪硫化物成矿过程、辨别金属来源和沉积过程的物理化学条件,在地质学、矿床学等领域具有重要的应用价值。激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)已成功应用于硫化物矿物元素微区分析研究,但激光与物质作用产生的热效应严重制约分析结果的可靠性。本文建立了一种高精密度、高准确度的低温剥蚀LA-ICP-MS测定硫化物矿物多元素方法。采用自行研制的Peltier低温剥蚀池可有效抑制硫化物矿物LA-ICP-MS分析中的热效应,提高分析结果的精密度和准确度。扫描电子显微镜(SEM)表明:在低温(-30℃)条件下可在一定程度地抑制激光剥蚀引起的热效应,减少样品熔化和气溶胶气相再沉积;而通过气溶胶颗粒分析发现低温剥蚀可以减小样品气溶胶颗粒的平均尺寸,得到的颗粒粒径分布范围也较小。不同元素信号强度的精密度(RSD)从常温下的20.1%~34.4%改善到11.5%~15.8%,元素的检出限为0.054~0.077μg/g。将该低温LA-ICP-MS系统应用于实验室内部标样黄铜矿Ccp-1分析,测定值与参考值之间的标准偏差在7%以内。

Microstructure and properties of laser micro welded joint of TiNi shape memory alloy

Butt welding of 0.2 mm-thick TiNi shape memory alloy sheet （SMA） was carried out using impulse laser, and tensile strength, fracture morphology, microstructure and phase change behaviour of welded joint were studied. The results show that using impulse laser can realize good butt welding of TiNi SMA sheet, tensile strength of welded joint is 683 MPa, which achieves 97% of that of cold rolled base metal, and the fracture mode of welded joint is ductile type as well as base metal. The welded joint can be divided into four zones according to grain size and microstructure. The microstructures of welded seam center zone are fine equiaxed crystals and the microstructures of both lower surface and upper surface edge zones are columnar crystals. When welded joint is vacuum annealed after welding, the phase transformation process is basically similar to the annealed base metal.

Effects of TiC addition on properties of laser particle deposited WC-Co-Cr and WC-Ni coatings

The mechanisms by which titanium carbide （TiC） improves the properties of tungsten carbide （WC） coatings deposited on duplex stainless steels using laser particle injection technique were investigated. The relationships between laser process parameters and the synthesized composite were studied. The morphologies and microstructures of the feedstock powders and composite coatings were characterized using scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDX） techniques. Surface hardness of the composite layers was determined using the Vickers microhardness tester while its corrosion behaviour in 3.5%NaCl solution was investigated by potentiodynamic polarization curve measurement method. As a result of the laser treatment, microstructures characterized by hard ceramic particles with strong bonding to substrate were formed on the surface layer of the steels. The addition of TiC to WC resulted in microstructures free from cracks, pores and intermetallics which could be detrimental to the properties of the composites. High microhardness was observed and most of the coatings shifted the corrosion potential to more noble values with the pseudo-passive curve.

Structural characteristics and high-temperature tribological behaviors of laser cladded NiCoCrAlY−B_(4)C composite coatings on Ti6Al4V alloy

In order to improve the hardness and tribological performance of Ti6Al4V alloy,NiCoCrAlY-B_(4)C composite coatings with B_(4)C of 5%,10%and 15%(mass fraction)were fabricated on its surface by laser cladding(LC).The morphologies,chemical compositions and phases of obtained coatings were analyzed using scanning electronic microscope(SEM),energy dispersive spectrometer(EDS),and X-ray diffraction(XRD),respectively.The effects of B_(4)C mass fraction on the coefficient of friction(COF)and wear rate of NiCoCrAlY-B_(4)C coatings were investigated using a ball-on-disc wear tester.The results show that the NiCoCrAlY-B_(4)C coatings with different B_(4)C mass fractions are mainly composed of NiTi,NiTi_(2),α-Ti,CoO,AlB_(2),TiC,TiB and TiB_(2)phases.The COFs and wear rates of NiCoCrAlY-B_(4)C coatings decrease with the increase of B_(4)C content,which are contributed to the improvement of coating hardness by the B_(4)C addition.The wear mechanisms of NiCoCrAlY-B_(4)C coatings are changed from adhesive wear and oxidation wear to fatigue wear with the increase of B_(4)C content.

In situ laser deposition of NiTi intermetallics for corrosion improvement of Ti-6Al-4V alloy

NiTi intermetallic coatings were fabricated on the surface of Ti-6Al-4V alloy by melting Ni and Ti powders using laser metal deposition（LMD） process.The effects of NiTi reinforcement content on the microstructure,hardness and corrosion properties of the coatings were examined.The results show that the deposited coatings are characterized by NiTi,NiTi2 and NiTi3 intermetallic phases.An appreciable increase in corrosion resistance is obtained for all the coatings,and Ti55Ni45 coating shows the highest corrosion resistance;while coatings Ti50Ni50 and Ti45Ni55 follow in that succession.The reinforcement materials are proven to be corrosion resistant in the tested environment,and the effect of Ti is more dominant.

Improved Behaviour Control on Laser Cruise of Autonomous Mobile Robot

The software of behaviour-based algorithm~ was parted to several functional modules which represented different behaviours with different priorities. A basic algorithm with S-type arbiter and an improved algorithm with I-type arbiter were compared. The improved algorithm can reduce judging time and avoid some mistakes of the basic one. In mapping obstacles, the robot adjusted the spread angle according to different distances to obstacles in scaled vector field histogram （SVFH） algorithm, and then the robot turned more sharply in near obstacles than in far obstacles, which made the robot move more safely and smoothly in a cluttered room.

A review of particulate-reinforced aluminum matrix composites fabricated by selective laser melting

Selective laser melting(SLM)is an emerging layer-wise additive manufacturing technique that can generate complex components with high performance.Particulate-reinforced aluminum matrix composites(PAMCs)are important materials for various applications due to the combined properties of Al matrix and reinforcements.Considering the advantages of SLM technology and PAMCs,the novel SLM PAMCs have been developed and researched in recent years.Therefore,the current research progress about the SLM PAMCs is reviewed.Firstly,special attention is paid to the solidification behavior of SLM PAMCs.Secondly,the important issues about the design and fabrication of high-performance SLM PAMCs,including the selection of reinforcement,the influence of parameters on the processing and microstructure,the defect evolution and phase control,are highlighted and discussed comprehensively.Thirdly,the performance and strengthening mechanism of SLM PAMCs are systematically figured out.Finally,future directions are pointed out on the advancement of high-performance SLM PAMCs.

Microstructure and abrasion wear behavior of Ni-based laser cladding alloy layer at high temperature

Ni-based alloy coating on 21-4-N heat-resistant steel was prepared using CO2 laser, and the high-temperature abrasion wear was tested. The microstructure of this cladding layer and its abrasion wear behavior at high temperature by changing compositions and temperatures were investigated by means of optical microscope and scanning electron microscope. Among the three compositions of cladding layer, i.e. Ni21+20%WC+0.5%CeO2, Ni25+20%WC+0.5%CeO2 and Ni60+20%WC+0.5%CeO2, the experimental results show that Ni21+20%WC+ 0.5%CeO2 cladding layer is made up of finer grains, and presents the best abrasion wear behavior at high temperature. The wear pattern of laser cladding layer is mainly grain abrasion at lower temperature, and it would be changed to adhesive abrasion and oxide abrasion at higher temperature.

Effect of Biodiesel Soot on Tribological Behavior of Liquid Paraffin

Biodiesel soot （BDS） was collected from the combustion of biodiesel using a self-made soot trap. The effect of BDS on the txibological behavior of liquid paraffin （LP） was investigated using a four-ball txibometer. A rotating viscometer was used to investigate the effect of BDS on the viscosity of LE The morphology, composition, and tribological mechanism of BDS were studied by means of FETEM, XRD, XPS, SEM/EDS, and the 3D laser scanning microscopy. Test results showed that the BDS aggregates were chain-like, and the average diameter of BDS was 35 nm. The BDS existed in the form of graphitic layers and amorphous carbon. The oxygen-containing functional groups in BDS consisted of the （C-O-C） and （C-O-H）. With an increasing BDS content, the dynamic viscosity of LP increased and the maximum non-seizure load increased initially and became stable later. In addition, the average wear scar diameter （AWSD） of LP increased and the average friction coefficient of LP decreased at first and then increased later. The tribological mechanisms could be ascribed to the variation in content of BDS： BDS could act as a friction modifier for a lower friction coefficient in case of low BDS content. However, the BDS aggregates could lead to increase of abrasive wear to influence the lubricating oil film at higher content of BDS, which would reduce the friction reduction ability and wear resistance of LP.

Dynamics of Two-Photon Lasers with A Atomic Level Configuration

We derive the dimensionless dynamic equations of two-photon lasers with A atomic level configuration by using the quantum Langevin equation method with the considerations of atomic coherence and injected classical fields. Then we analyze the stability and the chaotic dynamics of the two-photon laser by calculating the bifurcation diagram and the maximum Lyapunov exponent （MLE）. Our results show that the Lorenz strange attractors and one-focus strange attractors can exist in this system, and the chaos can be induced or inhibited by the injected classical fields via Hopfbifurcations or crises, while the atomic coherence induces chaos via crises, and inhibit chaos via Hopf bifurcation or crises.

Fe-Zn supersaturated solid solution prepared by mechanical alloying and laser sintering to accelerate degradation

The slow degration of iron limits its bone implant application.The solid solution of Zn in Fe is expected to accelerate the degradation.In this work,mechanical alloying(MA)was used to prepare Fe-Zn powder with supersaturated solid solution.MA significantly decreased the lamellar spacing between particles,thus reducing the diffusion distance of solution atoms.Moreover,it caused a number of crystalline defects,which further promoted the solution diffusion.Subsequently,the MA-processed powder was consolidated into Fe-Zn part by laser sintering,which involved a partial melting/rapid solidification mechanism and retained the original supersaturated solid solution.Results proved that the Fe-Zn alloy became more susceptible with a lowered corrosion potential,and thereby an accelerated corrosion rate of(0.112±0.013)mm/year.Furthermore,it also exhibited favorable cell behavior.This work highlighted the advantage of MA combined with laser sintering for the preparation of Fe-Zn implant with improved degradation performance.

Wear behavior of Ti6Al4V biomedical alloys processed by selective laser melting, hot pressing and conventional casting

The aim of this work was to study the influence of the processing route on the microstructural constituents,hardness andtribological(wear and friction)behavior of Ti6Al4V biomedical alloy.In this sense,three different processing routes were studied:conventional casting,hot pressing and selective laser melting.A comprehensive metallurgical,mechanical and tribologicalcharacterization was performed by X-ray diffraction analysis,Vickers hardness tests and reciprocating ball-on-plate wear tests ofTi6Al4V/Al2O3sliding pairs.The results showed a great influence of the processing route on the microstructural constituents andconsequent differences on hardness and wear performance.The highest hardness and wear resistance were obtained for Ti6Al4Valloy produced by selective laser melting,due to a markedly different cooling rate that leads to significantly different microstructurewhen compared to hot pressing and casting.This study assesses and confirms that selective laser melting is potential to producecustomized Ti6Al4V implants with improved wear performance.

Electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V controlled by elements segregation and phases distribution

The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the solution treatment−aging(STA)process aggravates the element micro-segregation compared to the annealing process,leading to varied Al and V contents of the phases from different samples.It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation.The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution,especially the difficult-to-dissolve phase.And then,the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced.Compared to the annealed sample,the higher dissolution rate of the STA sample is beneficial to the electrochemical machining(ECM)of Ti6Al4V.

Influence of Yttrium Implantation on Oxidation Behavior of Pure Nickel at 1000℃

Isothermal and cyclic oxidation behaviors of pure and yttrium-implanted nickel were studied at 1 000℃ in air. The oxide scales formed on nickel substrates were performed using SEM and TEM. It was found that Y-implantation greatly improved the anti-oxidation ability of nickel both in isothermal and cyclic oxidizing experiments. Laser Raman microscopy was also used to study the stress status of oxide scales formed on nickel with and without yttrium. The main reason for the improvement in anti-oxidation and adhesion of oxide scale was Y-implantation greatly reduced the grain size of NiO and lowered the compressive stress within the scale. Yttrium implantation enhanced the adhesion of protective NiO oxide scale formed on nickel substrate.

Assessment of negative phototaxis in long-term fasted Glyptocidaris crenularis:a new insight into measuring stress responses of sea urchins in aquaculture

A cost-effective method was designed to measure the behavioral response of negative phototaxis to high-intensity illumination in the sea urchin Glyptocidaris crenularis. Ninety sea urchins were randomly and equally divided into two aquaculture environment groups： a fasted group, which was starved during the experiment, and a fed group. After 10 months, the total mortality of each group was recorded. Then, 15 sea urchins were randomly selected from each group and behavioral responses to high-intensity illumination were investigated for each sea urchin. After the behavioral experiment, body measurements of the trial sea urchins were taken. The results reveal that food deprivation significantly affected test diameter （P〈0.01）, body weight （P〈0.01）, gonad weight （P〈0.0I）, and gut weight （P〈0.01）. Furthermore, food deprivation also affected negative phototaxis behaviors of time to rapid spine movement （P〈0.01）, time to the 1 cm position （P〈0.05）, and walking distance in 300 s （P〈0.01）, but not time to body reaction （P〉0.05）. The mortality rates of fasted and fed urchins were 6.7% and 0%, respectively. The present study provides evidence that food deprivation has a significant effect on phenotypic traits and behavioral responses to high-intensity illumination in the sea urchin G. crenularis. With this method, environmental stressors can be easily detected by measuring proper optional indicators. This study provides a new insight into measuring stress responses of sea urchins in aquaculture. However, further studies should be carried out to understand more environmental factors and to compare this potential behavioral method with immune, physiological, and epidemiological approaches.

Navigation of Robot Using VFH＋ Algorithm

This paper describes a reactive navigation proposed for a differentially driven robot. The aim of the reactive navigation is to prescribe behavior to the robot based on actual sensor values that is collision-free. Analysis of reactive navigation methods shows that there is no reliable reactive collision-free method. However, method VFH＋ is suboptimal reactive navigation method for static environment. Original method was proposed for ultrasonic rangefinders. Nowadays, much more sophisticated sensors are available. That is why our modification is proposed for a laser rangefinder attached to indoor mobile robot. Results are presented as simulation in Matlab and also as experiments with real robot. Based on these experiments, it can be claimed that VFH＋ is very effective reactive navigation method for various sensors and environments and it can be modified for different requirements on robot behavior.

Thermal-induced transformation of wetting behaviors on laser-textured SiC surfaces

Thermal-induced transformation of wetting behaviors on laser-textured silicon carbide （SIC） surfaces was discussed in this work. To investigate the transformation, a quenching experiment was conducted and an X-ray diffractometer was used to measure the residual stress. The experimental results demonstrate that the significantly enhanced hydrophilicity was induced by the increasing thermal residual stress of SiC materials after the aqueous quenching. It was found that the decrease in the contact angle increased with the increasing quenching temperature. Quenching at 350℃ led to the change of contact angle from 89.28° to 70.88° for the smooth surface, while from 72.25° to 33.75° for the laser-textured surface with depth 8 μm. Further, the surface hydrophobicity was enhanced by the release of thermal residual stress after quenching, thereby leading to an increase in the contact angle over time. The transformation of wetting behaviors on laser textured SiC surfaces can be achieved mutually by the aqueous quenching method.