Ultrafast dynamics of femtosecond laser-induced high spatial frequency periodic structures on silicon surfaces

Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.

Passive activity enhances residual control ability in patients with complete spinal cord injury

Patients with complete spinal cord injury retain the potential for volitional muscle activity in muscles located below the spinal injury level.However,because of prolonged inactivity,initial attempts to activate these muscles may not effectively engage any of the remaining neurons in the descending pathway.A previous study unexpectedly found that a brief clinical round of passive activity significantly increased volitional muscle activation,as measured by surface electromyography.In this study,we further explored the effect of passive activity on surface electromyographic signals during volitional control tasks among individuals with complete spinal cord injury.Eleven patients with chronic complete thoracic spinal cord injury were recruited.Surface electromyography data from eight major leg muscles were acquired and compared before and after the passive activity protocol.The results indicated that the passive activity led to an increased number of activated volitional muscles and an increased frequency of activation.Although the cumulative root mean square of surface electromyography amplitude for volitional control of movement showed a slight increase after passive activity,the difference was not statistically significant.These findings suggest that brief passive activity may enhance the ability to initiate volitional muscle activity during surface electromyography tasks and underscore the potential of passive activity for improving residual motor control among patients with motor complete spinal cord injury.

ANALYSIS ON SURFACE INTEGRITY DURING HIGH SPEED MILLING FOR NEW DAMAGE-TOLERANT TITANIUM ALLOY

Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool wear status. Results show that good surface integrity of TC21 can be obtained in high speed milling. In addition, even in acutely worn stages, there is no so-called serious hardening layer （or white layer） according to the studies on microhardness and metallurgical structure.

Preparation and characterization of amorphous boron powder with high activity

The amorphous boron powders with high activity were prepared by the high-energy ball milling-combustion synthesis method. The effects of the milling rate and milling time on the crystallinity, microscopic morphology and reactivity of amorphous boron powder were studied. The results show that the crystallinity of amorphous nano-boron powder is only 22.5%, and its purity reaches 92.86%. The high-energy ball milling can significantly refine boron powder particle sizes, whose average particle sizes are smaller than 50 nm, and specific surface areas are of up to 70.03 m2/g. When the transmission electron beam irradiates the samples, they rapidly melt. It can be seen that the monomer amorphous boron size is less than 30 nm from the specimen melting traces, which indicates that the samples have high reactivity.

Surface modification of Cu-25Cr alloy induced by high current pulsed electron beam

A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu-25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu-25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.

Preparation of Silica Gels with High Adsorption Activity for Extraction of Zirconium

Silica gels with a high specific surface area and high adsorption activity ,which have high selectivity and high adsorption capacity for zirconium in acidic high level radioactive liquid waste (HLLW), have been prepared from water-glass and hydrochloric acid through adding surfactants. The surfactant modifies the surface of the primary sol particles, thus suppresses the growth of the primary particle,but accelerates their agglomeration. The action of the surfactant is similar to that of the organic structure-directing agent and makes the sol cluster cross-linkage ring-like network in short order. The specific surface area of the silica gel is 998 m 2/g; the static adsorption capacity and the adsorption distribution coefficient for zirconium in HLLW are 32.6 mg/g and 56.1 mL/g, respectively.

High activity of a Pt decorated Ni/C nanocatalyst for hydrogen oxidation

The Pt decorated Ni/C nanocatalysts were prepared for hydrogen oxidation reaction（HOR） in fuel cell.By regulating the contents of Pt and Ni in the catalyst,both the composition and the structure affected the electrochemical catalytic characteristics of the Pt-Ni/C catalysts.When the Pt mass content was 3.1% percent and that of Ni was 13.9% percent,the Pt-Ni/C-3 catalyst exhibited a larger electrochemically active surface area and a higher exchange current density toward HOR than those of pure supported platinum sample.Our study demonstrates a feasible approach for designing the more efficient catalysts with lower content of noble metal for HOR in fuel cell.

Impact of Surface Sensible Heating over the Tibetan Plateau on the Western Pacific Subtropical High: A Land–Air–Sea Interaction Perspective

The impact of surface sensible heating over the Tibetan Plateau （SHTP） on the western Pacific subtropical high （WPSH） with and without air-sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually fol- lowed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an en- hanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly （SSTA） in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the at- mospheric dipole anomalies over the western Pacific. Therefore, the air-sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land-air-sea interaction framework.

Optimization of High-Protein Glutinous Rice Flour Production Using Response Surface Method

A response surface method was employed to study the effect of α-amylase concentration, hydrolysis temperature and time on the production of high protein glutinous rice flour(HPGRF). The suspension of glutinous rice flour(15%) that contained 6.52% protein was gelatinized and subsequently hydrolyzed by thermostable α-amylase. The hydrolysis yielded 0.144–0.222 g/g HPGRF with 29.4%–45.4% protein content. Hydrolysis time exerted a significant effect, while enzyme concentration and hydrolysis temperature showed insignificant effect on the protein content and production yield of HPGRF. The result of response surface method showed that the optimum condition for the production of HPGRF that contained at least 36% protein was treating gelatinized 15% glutinous rice flour suspension with 0.90 Kilo Novo α-amylase Unit(KNU)/g α-amylase at 80 oC for 99 min. By carrying out the predicted hydrolysis condition, HPGRF with 35.9% protein and 61.8% carbohydrates was resulted. The process yielded 0.172 g/g HPGRF. HPGRF contained higher amount of essential amino acids compared to glutinous rice flour. HPGRF had higher solubility and lower swelling power, and also showed no pasting peak compared with glutinous rice flour.

Wave height measurement in the Taiwan Strait with a portable high frequency surface wave radar

As an important equipment for sea state remote sensing, high frequency surface wave radar （HFSWR） has received more and more attention. The conventional method for wave height inversion is based on the ratio of the integration of the second-order spectral continuum to that of the first-order region, where the strong external noise and the incorrect delineation of the first- and second-order Doppler spectral regions due to spectral aliasing are two major sources of errors in the wave height. To account for these factors, two more indices are introduced to the wave height estimation, i.e., the ratio of the maximum power of the second-or- der continuum to that of the Bragg spectral region （RSCB） and the ratio of the power of the second harmonic peak to that of the Bragg peak （RSHB）. Both indices also have a strong correlation with the underlying wave height. On the basis of all these indices an empirical model is proposed to estimate the wave height. This method has been used in a three-months long experiment of the ocean state measuring and analyzing ra- dar, type S （OSMAR-S）, which is a portable HFSWR with compact cross-loop/monopole receive antennas developed by Wuhan University since 2006. During the experiment in the Taiwan Strait, the significant wave height varied from 0 to 5 m. The significant wave heights estimated by the OSMAR-S correlate well with the data provided by the Oceanweather Inc. for comparison, with a correlation coefficient of 0.74 and a root mean square error （RMSE） of 0.77 m. The proposed method has made an effective improvement to the wave height estimation and thus a further step toward operational use of the OSMAR-S in the wave height extraction.

Highly reversible lead-carbon battery anode with lead grafting on thecarbon surface

A novel C/Pb composite has been successfully prepared by electmless plating to reduce the hydrogenevolution and achieve the high reversibility of the anode of lead-carbon battery （LCB）. The depositedlead on the surface of C/Pb composite was found to be uniform and adherent to carbon surface. Becauselead has been stuck on the surface of C/Pb composite, the embedded structure suppresses the hydrogenevolution of lead-carbon anode and strengthens the connection between carbon additive and sponge lead.Compared with the blank anode, the lead-carbon anode with C/Pb composite displays excellent charge-discharge reversibility, which is attributed to the good connection between carbon additives and leadthat has been stuck on the surface of C/Pb composite during the preparation process. The addition of CIPb composite maintains a solid anode structure with high specific surface area and power volume, andthereby, it plays a significant role in the highly reversible lead-carbon anode.

Investigation of Surface Damage in Forming of High Strength and Galvanized Steel Sheets

Powdering/exfoliating of coatings and scratching galvanized steels and high strength steels （HSS）, are the main forms of surface damage in the forming of which result in increased die maintenance cost and scrap rate. In this study, a special rectangular box was developed to investigate the behavior and characteristics of surface damage in sheet metal forming （SMF） processes. U-channel forming tests were conducted to study the effect of tool hardness on surface damage in the forming of high strength steels and galvanized steels （hot-dip galvanized and galvannealed steels）. Experimental results indicate that sheet deformation mode influences the severity of surface damage in SMF and surface damage occurs easily at the regions where sheet specimen deforms under the action of compressive stress. Die corner is the position where surface damage initiates. For HSS sheet, surface damage is of major interest due to high forming pressure. The HSS and hot-dip galvanized steels show improved ability of damage-resistance with increased hardness of the forming tool. However, for galvannealed steel it is not the forming tool with the highest hardness value that performs best.

Hierarchical microstructures with high spatial frequency laser induced periodic surface structures possessing different orientations created by femtosecond laser ablation of silicon in liquids

High spatial frequency laser induced periodic surface structures(HSFLs)on silicon substrates are often developed on flat surfaces at low fluences near ablation threshold of 0.1 J/cm2,seldom on microstructures or microgrooves at relatively higher fluences above 1 J/cm^2.This work aims to enrich the variety of HSFLs-containing hierarchical microstructures,by femtosecond laser(pulse duration:457 fs,wavelength:1045 nm,and repetition rate:100 kHz)in liquids(water and acetone)at laser fluence of 1.7 J/cm^2.The period of Si-HSFLs in the range of 110–200 nm is independent of the scanning speeds(0.1,0.5,1 and 2 mm/s),line intervals(5,15 and 20μm)of scanning lines and scanning directions(perpendicular or parallel to light polarization direction).It is interestingly found that besides normal HSFLs whose orientations are perpendicular to the direction of light polarization,both clockwise or anticlockwise randomly tilted HSFLs with a maximal deviation angle of 50°as compared to those of normal HSFLSs are found on the microstructures with height gradients.Raman spectra and SEM characterization jointly clarify that surface melting and nanocapillary waves play important roles in the formation of Si-HSFLs.The fact that no HSFLs are produced by laser ablation in air indicates that moderate melting facilitated with ultrafast liquid cooling is beneficial for the formation of HSFLs by LALs.On the basis of our findings and previous reports,a synergistic formation mechanism for HSFLs at high fluence was proposed and discussed,including thermal melting with the concomitance of ultrafast cooling in liquids,transformation of the molten layers into ripples and nanotips by surface plasmon polaritons(SPP)and second-harmonic generation(SHG),and modulation of Si-HSFLs direction by both nanocapillary waves and the localized electric field coming from the excited large Si particles.

Surface chemical properties and pore structure of the activated coke and their effects on the denitrification activity of selective catalytic reduction

In order to study the mechanism of selective catalytic reduction of activated coke to remove NO in low-temperature flue gas and provide some theoretical basis for the development of related technologies.The pore sizedistribution and BET specific surface area of AC were obtain by data analyzing of N2 adsorption/desorption isotherm at -196 ℃ and carbon matrix and surface chemistry of virgin activated coke samples were characterized by acid-base titration and XPS.The process of selective catalytic reduction of activated coke (AC) samples with NH3 as reducing agent was studied in a fixed bed reactor at 150 ℃.The result shows that pore size distribution or BET specific surface of activated cokes have not correlation with denitrification activity for SCR.The NO reduction activities of the activated cokes are apparent to increase with their surface oxygen element content and total amount of acidic sites.Obviously there is good linear relationship between the NH3 adsorption capacity and activity for SCR with linear correlation coefficient 0.943.It has been presented that adsorption of NH3 on acidic functional groups in the edge of large polycyclic aromatic ring of activated coke is key rate controlling step in the SCR heterogeneous catalytic reaction.

Optimization of Inactivation Conditions of High Hydrostatic Pressure Using Response Surface Methodology

Response surface methodology (RSM) was employed in the present work and a second orderquadratic equation for high hydrostatic pressure (HHP) inactivation was built. Theadequacy of the model equation for predicting the optimum response values was verifiedeffectively by the validation data. Effects of temperature, pressure, and pressureholding time on HHP inactivation of Escherichia coli ATCC 8739 were explored. Byanalyzing the response surface plots and their corresponding contour plots as well assolving the quadratic equation, the optimum process parameters for inactivation E. coliof six log cycles were obtained as: temperature 32.2℃, pressure 346.4 MPa, and pressureholding time 12.6min.

Response of the Intensity of Subtropical High in the Northern Hemisphere to Solar Activity

Using the intensity data of each northern subtropical high measured by monthly 500 hPa height charts for the recent 38 years (1954-1991), we calculate their correlations with the monthly sunspot number and monthly solar radio flux at 10.7 cm wave length, respectively. Through strict test, we further confirm a series of high correlations. Next, using a method called the non-integer (year) wave, the significant response of each subtropical high's intensity to solar activity at its main period of 10.9-year length is found. Special attention is paid to that of the eastern Pacific high, the possible mechanism of such sensible response is also analysed.

Preparation and Characterization of Porous Yttrium Oxide Powders with High Specific Surface Area

The porous cubic yttrium oxides with high specific surface area were prepared yttrium nitrate and its complex formed with methyl salicylate. The specific surface area by the explosive decomposition of and properties of powders synthesized at various temperatures were characterized using BET, X-ray diffraction （XRD）, infrared spectra （IR）, and scanning electron microscopy （SEM）. The results indicate that the highest specific surface area is found to be 65.37 m^2·g^-1 at the calcination temperature of 600 ℃, and then decreases to 20.33 m2· g^- 1 with the calcination temperature rising from 600 to 900 ℃. The powders show strong surface activity for adsorping water and carbon dioxide in air, which also decreases with the rising calcination temperature. The drop both on the surface area and surface activity of samples at higher temperatures may be due to pore-narrowing（sintering） effects.

Surface tidal currents in the open sea area to the east of the Zhoushan Islands measured with high frequency surface wave radar

Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of surface tidal currents in the open sea area to the east of the Zhoushan Islands of Zhejiang Province, China are studied. The following conclusions are drawn from the analysis： the tidal current pattern in the open sea area to the east of Zhoushan Islands is primarily regular semidiurnal, which is significantly affected by the shallow water constituents. The directions of the major axes of tidal current ellipses of M2 lie approx- imately in the NW-SE direction. With the increasing of distance away from the coast, the directions of the tidal current ellipses gradually shift toward the E-W direction. The tidal currents are mainly reversing cur- rents. The spatial distribution of probable maximum current velocities decreases gradually from northeast to southwest which is basically in accordance with the spatial distribution of measured maximum current velocities. The residual currents near the coast are larger than those far away from the coast. The directions of the residual currents are basically north by east, and the angle to the due north increases gradually with the increasing distance away from the coast. The topography shows a certain impact on the spatial distri- bution of shallow water constituents, the rotation of tidal currents, the probable maximum currents and the residual currents.

High surface area biocarbon monoliths for methane storage

New energy sources that reduce the volume of harmful gases such as SO_(x)and NO_(x)released into the atmosphere are in constant development.Natural gas,primarily made up of methane,is being widely used as one reliable energy source for heating and electricity generation due to its high combustion value.Currently,natural gas accounts for a large portion of electricity generation and chemical feedstock in manufacturing plastics and other commercially important organic chemicals.In the near future,natural gas will be widely used as a fuel for vehicles.Therefore,a practical storage device for its storage and transportation is very beneficial to the deployment of natural gas as an energy source for new technologies.In this tutorial review,biomaterials-based carbon monoliths(CMs),one kind of carbonaceous material,was reviewed as an adsorbent for natural gas(methane)adsorption and storage.

Brassinosteroids mediate the effect of high temperature during anthesis on the pistil activity of photo-thermosensitive genetic male-sterile rice lines

Brassinosteroids(BRs)play critical roles in a wide range of plant developmental processes.However,it is unknown whether and how BRs mediate the effect of high temperature(HT)stress during anthesis on the pistil activity of photo-thermosensitive genetic male-sterile(PTSGMS)rice(Oryza sativa L.)lines.This study investigated the question.Three pot-grown PTSGMS rice lines were subjected to HT stress during anthesis.The contents of 24-epibrassinolide(24-EBL)and 28-homobrassinolide(28-HBL),the major forms of BR in rice plants,and levels of reactive oxygen species(ROS)or antioxidants(AOS),hydrogen peroxide(H2O2),1-aminocylopropane-1-carboxylic acid(ACC),ascorbic acid(AsA),and catalase activity in pistils,were determined.HT stress significantly reduced the contents of both 24-EBL and 28-EBL relative to those under normal temperatures,but the reduction varied by PTSGMS line.A line with higher BR contents under HT stress showed lower contents of ACC and H2O2,higher catalase activity and AsA content in pistils,and higher fertilization rate,seed-setting rate,and seed yield when the line was crossed with a restorer line,indicating that higher levels of BRs increase HT stress resistance.Applying 24-EBL,28-HBL or an inhibitor of BR biosynthesis confirmed the roles of BRs in response to HT stress.The results suggest that BRs mediate the effect of HT stress on pistil activity during anthesis and alleviate the harm of HT stress by increasing AOS and suppressing ROS generation.