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Wntless (WLS), an evolutionarily conserved multi-pass transmembrane protein, is essential for secretion of Wnt proteins. Wnt-triggered signaling pathways control many crucial life events, whereas aberrant Wnt signaling is tightly associated with many human diseases including cancers. Here, we report the cryo-EM structure of human WLS in complex with Wnt3a, the most widely studied Wnt, at 2.2 Å resolution. The transmembrane domain of WLS bears a GPCR fold, with a conserved core cavity and a lateral opening. Wnt3a interacts with WLS at multiple interfaces, with the lipid moiety on Wnt3a traversing a hydrophobic tunnel of WLS transmembrane domain and inserting into membrane. A β-hairpin of Wnt3a containing the conserved palmitoleoylation site interacts with WLS extensively, which is crucial for WLS-mediated Wnt secretion. The flexibility of the Wnt3a loop/hairpin regions involved in the multiple binding sites indicates induced fit might happen when Wnts are bound to different binding partners. Our findings provide important insights into the molecular mechanism of Wnt palmitoleoylation, secretion and signaling., The transmembrane protein Wntless (WLS) is essential for the secretion of Wnt proteins, which are signaling molecules of the Wnt signaling pathways. Here, the authors present the 2.2 Å cryo-EM structure of human WLS in complex with Wnt3a and discuss mechanistic implications for the palmitoleoylation of Wnt3a that is required for WLS mediated Wnt secretion.

This paper analyzes the facilities in cold areas to determine the factors that affect the location of charging stations. According to the operating characteristics of pure electric vehicles in cold areas and the service coverage of charging stations, a service model for charging stations based on the shortest possible mileage of remaining power is constructed. With the charging station service model based on the shortest mileage of the remaining power, and the greedy algorithm is used to solve the problem to determine the location of the charging station. Finally, based on the data related to the operation of pure electric vehicles in Urumqi and the service coverage radius of the charging station, the charging station in Urumqi was deployed.

We propose an innovative method of material classification based on the imaging model of pulsed time-of-flight (ToF) camera integrated with the unique signature that describes physical properties of each material named reflection point spread function (RPSF). First, the optimization method reduces the effect of material surface interreflection, which would affect RPSF and lead to decreased accuracy in classification, by alternating direction method of multipliers (ADMM). A method named feature vector normalization is proposed to extract material RPSF features. Second, according to the nonlinearity of the feature vectors, the structure of hidden layer neurons of radial basis function (RBF) neural network is optimized based on singular value decomposition (SVD) to improve generalization. Finally, the similar appearance of plastics and metals are classified on turntable-based measurement system by own design. The average classification accuracy reaches 93.3%, and the highest classification accuracy reaches 94.6%.

To solve the coordinate scheduling problem of satellite observations, a mathematical programming model was established. Considering that tasks have different deadlines and available resources, two algorithms time flexibility algorithm (TFA) and priority based algorithm (PBA) were proposed. Besides, a novel squeaky wheel optimization (SWO) optimization strategy was suggested to get better results. The experimental results indicate that TFA and PBA are suitable for different conditions of coordinate scheduling, and SWO can improve the results of PBA

Facial Expression Recognition (FER) for various low-resolution images is an important task and need in applications of analyzing crowd scenes (station, classroom, etc.). Due to the discriminative feature loss caused by reduced resolution, classifying various low-resolution facial images into the right category is still a challenging task. In this work, we proposed a novel generative adversarial network-based feature level super-resolution method for robust facial expression recognition (FSR-FER), which can reduce the chance of privacy leaking without restoring high-resolution facial images. In particular, a pre-trained FER model was employed as a feature extractor, and a generator network G and a discriminator network D are trained with features extracted from low-resolution and corresponding high-resolution images. Generator network G tries to transform features of low-resolution images to more discriminative ones by making them closer to the ones of corresponding high-resolution images. For better classification performance, we also proposed an effective classification-aware loss reweighting strategy based on the classification probability calculated by a fixed FER model to make our model focus more on samples that are prone to misclassification. Experimental results on the Real-World Affective Faces (RAF) Database and Static Facial Expressions in the Wild (SFEW) 2.0 dataset demonstrate that our method achieves satisfying results on various down-sample factors with a single model and has better performance on low-resolution images compared with methods using image super-resolution and expression recognition separately.

This study presents a method for material recognition using a pulsed time-of-flight (ToF) camera. The method measures the material bidirectional reflectance distribution function (BRDF) as a feature for material recognition by a pulsed ToF camera. We use the measurements of incident light at different angles to form the BRDF feature vectors. The feature vectors are used to build a training and test set to train and validate a classifier to perform the recognition. We choose the radial basis function (RBF) neural network as a classifier based on the nonlinear characteristics of material BRDF. Finally, we construct a turntable-based measurement system and use the material BRDF as the feature for classifying a variety of materials including metals and plastics. The optimized RBF neural network can achieve a recognition accuracy of 94.6%.

We extend the previously presented two-path interference compensation method for pulsed Time-of-Flight (ToF) cameras to three or more paths. By generalizing the model of multipath effect, we transform the measured vector consisting of multiple light periods to make it sparse and apply the L 1 norm regularization algorithm to estimate the depth of the main path component. In theory, the combination of any number of components can be separated. Due to the experimental conditions, we validate the proposed method in the three-path scene. Experiments show that the components are effectively separated.

To eliminate harmful localized corrosion, a new approach by constructing superhydrophobic WO3@TiO2 hierarchical nanoflake surface beyond FeW amorphous alloy formed on stainless steel was proposed. Facile dealloying and liquid deposition was employed at low temperature to form a nanostructured layer composing inner WO3 nanoflakes coated with TiO2 nanoparticles (NPs) layer. After further deposition of PFDS on nanoflakes, the contact angle reached 162° while the corrosion potential showed a negative shift of 230 mV under illumination, resulting in high corrosion resistance in 3.5 wt% NaCl solution. The tradeoff between superhydrophobic surface and photo-electro response was investigated. It was found that this surface feature makes 316 SS be immune to localized corrosion and a pronounced photo-induced process of electron storage/release as well as the stability of the functional layer were detected with or without illumination, and the mechanism behind this may be related to the increase of surface potential due to water repellence and the delayed cathodic protection of semiconducting coating derived mainly from the valence state changes of WO3. This study demonstrates a simple and low-cost electrochemical approach for protection of steel and novel means to produce superhydrophobic surface and cathodic protection with controllable electron storage/release on engineering scale.

Solar-powered water splitting with photoelectrochemical (PEC) devices is considered to be a promising method to simultaneously harvest and store solar energy at a large scale. Nanostructured semiconductors offer potential advantages in PEC application due to their large surface area and size-dependent properties, such as increased absorption coefficient, increased band-gap energy and reduced carrier-scattering rate. In this contribution, self-doped tungsten trioxide (WO 3−x ) nanoflake arrays were synthesized via a new route which involves the dealloying of Fe–W amorphous alloy, thermal treatment in air and properly cathodic polarization. The effects of different cathodic polarization current leading to different x value in WO 3−x on the morphology, phase, and photoelectrochemical performance of the resultant samples were investigated. It was found that WO 3−x with the appropriate x value presents a dramatic photoelectrochemical current density of 8.7 mA cm −2 in the presence of methanol as a hole scavenger, five folds larger than that of pristine WO 3 nanoflakes. UV–vis reflection spectra suggest that the light absorption spectrum range of WO 3−x extends from UV to visible light region. Electrochemical impedance spectroscopy disclosed that the unique nanoflake architecture and the surface defects offer improved light harvesting as well as efficient charge transportation.

Photo-receptors are widely present in both prokaryotic and eukaryotic cells, which serves as the foundation of tuning cell behaviors with light. While practices in eukaryotic cells have been relatively established, trials in bacterial cells have only been emerging in the past few years. A number of light sensors have been engineered in bacteria cells and most of them fall into the categories of two-component and one-component systems. Such a sensor toolbox has enabled practices in controlling synthetic circuits at the level of transcription and protein activity which is a major topic in synthetic biology, according to the central dogma. Additionally, engineered light sensors and practices of tuning synthetic circuits have served as a foundation for achieving light based real-time feedback control. Here, we review programming bacteria cells with light, introducing engineered light sensors in bacteria and their applications, including tuning synthetic circuits and achieving feedback controls over microbial cell culture.

This paper proposes a secure transmission scheme based on the twice channel estimation in a three- node MIMO system according to the malicious pilot contamination. Firstly, the pilot transmission length is divided into two segments during the reverse training stage and the legitimate receiver allocates all the power to one arbitrary segment for transmitting the pilot. Then, the transmitter obtains the approximate estimation of the eavesdropping channel and an erroneous CSI of the main channel based on the twice channel estimation. After eliminating the eavesdropping channel from the erroneous CSI, the transmitter transmits both the signal and the artificial noise based on the modified CSI to ensure the transmission. Finally, the simulation results show that the proposed scheme significantly improves the security performance.

This paper analyses the security performance based on the average rate over the Rayleigh fading channel. Firstly, we use the average decoding rate and the average eavesdropping rate to measure the security performance and derive the analytical expressions for them. Then, the purpose of maximizing the average decoding rate and minimizing the average eavesdropping rate is modeled as a double objective optimization problem. By using linear weighted method, the security problem is transferred into a single objective optimization problem. On the basis, an optimal transmission rate algorithm based on steepest descent method for the optimization problem is further proposed. Finally, the simulation results show the effects of the transmission rate, the eavesdropping position, the number of loop iterations and other factors on the security performance.

Variable geometry turbine (VGT) has been widely applied in internal combustion engines to improve the engine transient response and torque at low speed. One of the most popular variable geometry turbine is the variable nozzle turbine (VNT), in which the nozzle vanes can be rotated along the pivoting axis and thus the flow passage through the nozzle can be adjusted to match with different engine operating conditions. One disadvantage of the VNT is the turbine efficiency degradation due to the leakage flow in the nozzle endwall clearance, which is needed to allow the nozzle vanes to rotate without sticking. Especially at small nozzle open condition, there is large loading on the nozzle and high pressure gradient between the nozzle pressure and suction side. Strong leakage flow exists inside the nozzle endwall clearance from pressure side to suction side, leading to large flow loss and turbine stage efficiency degradation. In the present paper, a novel split sliding variable nozzle turbine (SSVNT) has been proposed to reduce the nozzle leakage flow and to improve turbine stage efficiency. The idea is to divide the nozzle into two parts: one part is fixed and the other part can slide along the partition surface. The mechanism of nozzle flow passage variation in SSVNT is different from that of the traditional pivoting VNT. The sliding vane and the fixed vane together form an integrated vane. The flow of the turbine is determined by the passage of the integrated vanes. When moving the sliding vane to large radius position, the nozzle flow passage opens up and the turbine has high flow capacity. When moving the sliding vane towards small radius position, the nozzle flow passage closes down and the turbine has low flow capacity. As the fixed vane doesn’t need endwall clearance, there is no leakage flow inside the fixed vane and the total leakage flow through the integrated vane can be reduced. Based on calibrated numerical modeling, the analysis results showed that there is up to 12% turbine stage efficiency improvement with the SSVNT design at small nozzle open condition while maintaining the same flow capacity and efficiency at large nozzle open condition, compared to the conventional VNT. The mechanism of efficiency improvement in the SSVNT design has also been discussed.

The superimposed influences of the blade rows in a multistage compressor are important because different matches of upstream and downstream blades can result in significant differences in the stator wake oscillation. Numerical investigation of the axial stator wake oscillation, which is affected upstream by the axial rotor and downstream by the radial rotor, was performed in an axial-radial combined compressor. Many configurations with different blade numbers and locations, which influence axial stator wake oscillation were investigated. When rotors have equal blade numbers, the axial stator wake oscillates periodically versus time within time T (moving blade passing 1/3 revolution). In contrast, stator wake oscillates irregularly within T when rotors have different blade numbers. A model-split subtraction method is presented in order to separate the influences of the individual blade rows on the wake oscillation of the axial stator. Analysis from the rotor-stator configuration showed that the unsteady flow angle fluctuation response is caused by the upstream rotor. For the rotor-stator-rotor configuration, the unsteady flow angle fluctuations are influenced by up- and downstream blade rows. With the model-split subtraction method, the up- and downstream influences on the flow angle fluctuation could be clearly separated and quantified. Low amplitudes could be observed when the influences from up- and downstream moving rows were superimposed with the “positive peak-negative peak” type wave. Clocking investigations were carried out to change the relative superimposed phase of influences from the surrounding blade rows in order to modulate the amplitudes of the axial stator wake oscillation. However, the amplitudes did not reach the maximum when they were superimposed with “positive peak-positive peak” type wave due to the impact of the interaction between the two moving blade rows.

Diabetic nephropathy, the most common cause of progressive chronic renal failure and end-stage renal disease, has now reached global proportions. The only means to rescue diabetic patients on dialysis is renal transplantation, a very effective therapy but severely limited by the availability of donor kidneys. Hence, we tested the role of intravenous renal cell transplantation (IRCT) on obese/diabetic Zucker/SHHF F1 hybrid (ZS) female rats with severe ischemic and diabetic nephropathy. Renal ischemia was produced by bilateral renal clamping of the renal arteries at 10 wk of age, and IRCT with genetically modified normal ZS male tubular cells was given intravenously at 15 and 20 wk of age. Rats were euthanized at 34 wk of age. IRCT with cells expressing serum amyloid A had strong and long-lasting beneficial effects on renal function and structure, including tubules and glomeruli. However, donor cells were found engrafted only in renal tubules 14 wk after the second infusion. The results indicate that IRCT with serum amyloid A-positive cells is effective in preventing the progression of chronic kidney disease in rats with diabetic and ischemic nephropathy.

Despite advances in the treatment of diabetic nephropathy (DN), currently available therapies have not prevented the epidemic of progressive chronic kidney disease (CKD). The morbidity of CKD, and the inexorable increase in the prevalence of end-stage renal disease, demands more effective approaches to prevent and treat progressive CKD. We undertook next-generation sequencing in a rat model of diabetic nephropathy to study in depth the pathogenic alterations involved in DN with progressive CKD. We employed the obese, diabetic ZS rat, a model that develops diabetic nephropathy, characterized by progressive CKD, inflammation, and fibrosis, the hallmarks of human disease. We then used RNA-seq to examine the combined effects of renal cells and infiltrating inflammatory cells acting as a pathophysiological unit. The comprehensive systems biology analysis of progressive CKD revealed multiple interactions of altered genes that were integrated into morbid networks. These pathological gene assemblies lead to renal inflammation and promote apoptosis and cell cycle arrest in progressive CKD. Moreover, in what is clearly a major therapeutic challenge, multiple and redundant pathways were found to be linked to renal fibrosis, a major cause of kidney loss. We conclude that systems biology applied to progressive CKD in DN can be used to develop novel therapeutic strategies directed to restore critical anomalies in affected gene networks.

In this paper, the mathematical model of the flow filed in centrifugal compressor of turbocharger was studied. Based on the theory of computational fluid dynamics (CFD), performance curves and parameter distributions of the compressor were obtained from the 3-D numerical simulation by using CFX. Meanwhile, the influences of grid number and distribution on compressor performance were investigated, and numerical calculation method was analyzed and validated, through combining with test data. The results obtained show the increase of the grid number has little influence on compressor performance while the grid number of single-passage is above 300,000. The results also show that the numerical calculation mass flow rate of compressor choke situation has a good consistent with test results, and the maximum difference of the diffuser exit pressure between simulation and experiment decrease to 3.5% with the assumption of 6 kPa additional total pressure loss at compressor inlet. The numerical simulation method in this paper can be used to predict compressor performance, and the difference of total pressure ratio between calculation and test is less than 7%, and the total-to-total efficiency also have a good consistent with test.

A turbocharger compressor with a wide flow range and a high efficiency is important to the application of advanced clean combustion technologies, such as homogeneous charge compression ignition and low-temperature combustion, in diesel engines. Self-recirculation casing treatment is one of the techniques that can extend the compressor surge margin without much efficiency penalty. The underlying physics of the self-recirculation casing treatment technology were investigated with computational fluid dyamics modeling and bench testing in this study. It is identified that, if the bleed slot of the self-recirculation casing treatment is located upstream of the impeller passage’s throat area, self-recirculation casing treatment improves the surge margin but the throat still limits the maximum flow capacity of the compressor. On the other hand, if the bleed slot of the self-recirculation casing treatment is located at the impeller passage’s throat area, the self-recirculation casing treatment improves the maximum flow capacity but results in a significant compressor efficiency penalty in the low-flow range. An active self-recirculation casing treatment design was proposed. The active self-recirculation casing treatment design extends the compressor flow capacity and improves the surge margin without an efficiency penalty through dual bleed slots with one upstream and the other downstream of the leading edge of the splitter blades. In the choke condition, the upstream bleed slot will be closed; near the surge condition, the downstream bleed slot will be closed. In the middle flow range, both bleed slots are closed. Both the numerical data and the bench testing results show that the maximum flow rate could be extended by about 15% and the surge margin by about 20% without an efficiency penalty. The mechanism of the performance improvement is also numerically studied.

Acute kidney injury (AKI) and chronic renal failure (CKD) are the most challenging problems in nephrology. Multiple therapies have been attempted but these interventions have minimal effects on the eventual outcomes, and all too often the result is end-stage renal disease (ESRD). The only effective therapy for ESRD is renal transplantation but only a small fraction of patients receive transplants. In this work we introduce a novel approach to transplantation designed to regenerate kidneys afflicted by severe AKI or CKD: intravenous renal cell transplantation (IRCT) with adult rat primary renal cells reprogrammed to express the SAA gene localized and engrafted in kidneys of rat recipients that had severe AKI or CKD. IRCT significantly resolved renal dysfunction and limited kidney damage, inflammation, and fibrosis. Severe CKD was successfully improved by IRCT using kidney cells from donor rats or by renal cell self-donation in a form of autotransplantation. We propose that IRCT with adult primary renal cells reprogrammed to express the SAA gene can be used to effectively treat AKI and CKD.

Assembling an axial rotor and a stator at centrifugal compressor upstream to build an axial-radial combined compressor could achieve high pressure ratio and efficiency by appropriate size augment. Then upstream potential flow and wake effect appear at centrifugal impeller inlet. In this paper, the axial-radial compressor is unsteadily simulated by three-dimensional Reynolds averaged Navier-Stokes equations with uniform and circumferential distorted total pressure inlet condition to investigate upstream effect on radial rotor. The results show that span-wise nonuniform total pressure distribution is generated and radial and circumferential combined distortion is formed at centrifugal rotor inlet. The upstream stator wake deflects to rotor rotation direction and decreases with blade span increases. Circumferential distortion causes different separated flow formations at different pitch positions. The tip leakage vortex is suppressed in centrifugal blade passages. Under distorted inlet condition, flow direction of centrifugal impeller leading edge upstream varies evidently near hub and shroud but varies slightly at mid-span. In addition, compressor stage inlet distortion produces remarkable effect on blade loading of centrifugal blade both along chordwise and pitchwise.

Four kinds of aggregation patterns of CdO grains were formed on the surface of N silicon substrate heated at 580 degrees C for 1 h in an evaporation-deposition device. They were ellipse-shaped or quasi-circular-shaped aggregate, long ribbon-shaped aggregate, long chain-shaped or long double-chain-shaped aggregate, and long ellipse-chain-shaped aggregate. These aggregates consisted of numerous grains or tiny crystals, and deposited on top of the CdO bush-like long crystal clusters grown earlier. They exhibited clearly spontaneous self-organization aggregation performance. Surface defects of the virgin N silicon crystal were analyzed, and mechanism of the self-organization aggregation was discussed with a defect induced aggregation (DIA) model. (C) 2010 Elsevier B.V. All rights reserved.

Cu film and Ti/Cu film on polyimide substrate were prepared by ion implantation and ion beam assisted deposition (IBAD) techniques. Three-dimension white-light interfering profilometer was used to measure thickness of each film. The thickness of the Cu film and Ti/Cu film ranged between 490 nm and 640 nm. The depth profile, surface morphology, roughness, adhesion, nanohardness, and modulus of the Cu and Ti/Cu films were measured by scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindenter, respectively. The polyimide substrates irradiated with argon ions were analyzed by scanning electron microscopy (SEM) and AFM. The results suggested that both the Cu film and Ti/Cu film were of good adhesion with polyimide substrate, and ion beam techniques were suitable to prepare thin metal film on polyimide.

Serum amyloid A protein (SAA), a prominent component of the acute-phase response, is strongly expressed in developing and repairing kidneys and promotes tubulogenesis. Accordingly, we reprogrammed relatively undifferentiated NRK52E cells with the mouse SAA1.1 gene and transplanted SAA-positive and -negative cells into rats with acute renal failure. We found that SAA-positive cells accelerated renal recovery in three models of acute renal failure: gentamicin nephrotoxicity, cisplatin-mediated renal injury, and ischemia-reperfusion renal injury. The dramatic improvement of renal failure was demonstrable within 2 days, consistent with an early paracrine effect. However, abundant donor cells were also found integrated in the healing tubular architecture after 7 days. We conclude that infusions of SAA-positive cells promote renal recovery after acute renal failure and offer a potentially powerful and novel therapy of renal failure.

Micro-aftershocks with magnitude range of 1.5–4 around the Wenchuan earthquake epicenter, the southern part of the Longmenshan fault zone, exhibit good frequency-magnitude linear relationships, thus enabling b-value analysis. The average b-value for micro-aftershocks of M1.5–4 from July to December of 2008 in our local study region is about 0.88, similar to the b-value for all aftershocks of M3.0–5.5 from May, 2008 to May, 2009 along the whole Longmenshan fault zone. The similarity between the local and regional b-values possibly indicates that the southern part of the Longmenshan fault zone has similar seismogenic environment to the whole Longmenshan fault zone. Alternatively, it may also imply that b-values derived from all events without consideration of structural variation can not discriminate local-scale tectonic information. The present study shows that the b-value for the Wenchuan earthquake micro-aftershocks varies with different regions. The b-value in southwest of the Yingxiu town is higher than that in the northeast of the Yingxiu town. The high b-value in the southwest part where the Wenchuan earthquake main shock hypocenter located indicates that the current stress around the hypocenter region is much lower than its surrounding area. The b-values are also dependent on depth. At shallow depths of

A three-dimensional local-scale P-velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network. Checkerboard tests show that our tomographic model has lateral and vertical resolution of ∼2 km. The high-resolution P-velocity model revealed interesting structures in the seismogenic layer: (1) The Guanxian-Anxian fault, Yingxiu-Beichuan fault and Wenchuan-Maoxian fault of the Longmen Shan fault zone are well delineated by sharp upper crustal velocity changes; (2) The Pengguan massif has generally higher velocity than its surrounding areas, and may extend down to at least ∼10 km from the surface; (3) A sharp lateral velocity variation beneath the Wenchuan-Maoxian fault may indicate that the Pengguan massif's western boundary and/or the Wenchuan-Maoxian fault is vertical, and the hypocenter of the Wenchuan earthquake possibly located at the conjunction point of the NW dipping Yingxiu-Beichuan and Guanxian-Anxian faults, and vertical Wenchuan-Maoxian fault; (4) Vicinity along the Yingxiu-Beichuan fault is characterized by very low velocity and low seismicity at shallow depths, possibly due to high content of porosity and fractures; (5) Two blocks of low-velocity anomaly are respectively imaged in the hanging wall and foot wall of the Guanxian-Anxian fault with a ∼7 km offset with ∼5 km vertical component.

Ti films with a thickness of 1.6 mu m (group A) and 4.6 mu m (group B) were prepared on surface of silicon crystal by metal vapor vacuum arc (MEVVA) ion implantation combined with ion beam assisted deposition (IBAD). Different anneal temperatures ranging from 100 to 500 degrees C were used to investigate effect of temperature on residual stress and mechanical properties of the Ti films. X-ray diffraction (XRD) was used to measure residual stress of the Ti films. The morphology, depth pro. le, roughness, nanohardness, and modulus of the Ti films were measured by scanning electron microscopy (SEM), scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindentation, respectively. The experimental results suggest that residual stress was sensitive to film thickness and anneal temperature. The critical temperatures of the sample groups A and B that residual stress changed from compressive to tensile were 404 and 428 degrees C, respectively. The mean surface roughness and grain size of the annealed Ti films increased with increasing anneal temperature. The values of nanohardness and modulus of the Ti films reached their maximum values near the surface, then, reached corresponding values with increasing depth of the indentation. The mechanism of stress relaxation of the Ti films is discussed in terms of re-crystallization and difference of coefficient of thermal expansion between Ti film and Si substrate. (C) 2008 Elsevier B. V. All rights reserved.

Polylacticacid (PLA) was submitted to high-flux carbon ion implantation with energy of 40 keV. It was investigated to the effect of ion fluence (1 × 1012–1 × 1015 ions/cm2) on the properties of the polymer. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), wettability, and roughness were employed to study change of structure and properties of the as-implanted PLA samples. Six carbon bonds, that is, C, C H, C O C, C O, O C O, and 〉C O, were observed on surfaces of the as-implanted PLA samples. The intensities of various chemical bonds changed with increasing ion fluence. AFM images displayed that there was irradiation damage and that it was related closely with ion fluence. At fluence as high as 1 × 1015 ions/cm2 surface-restructuring phenomenum took place on the surface of the PLA. Wettability was also affected by the variation on the fluence. With increasing ion fluence, the water contact angle of the as-implanted PLA samples changed gradually reaching a maximum of 76.5° with 1 × 1013 ions/cm2. The experimental results revealed that carbon ion fluence strongly affected surface chemical bond, morphology, wettability, and roughness of the PLA samples.

Two groups of Mo/Si films were deposited on surface of Si( 1 0 0) crystal. The first group of the samples was prepared by both ion beam assisted deposition (IBAD) and metal vapor vacuum arc (MEVVA) ion implantation technologies under temperatures from 200 to 400 degrees C. The deposited species of IBAD were Mo and Si, and different sputtering Ar ion densities were selected. The mixed Mo/Si films were implanted by Mo ion with energy of 94 keV, and fluence of Mo ion was 5 x 10(16) ions/cm(2). The second group of the samples was prepared only by IBAD under the same test temperature range. The Mo/ Si samples were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), sheet resistance, nanohardness, and modulus of the Mo/ Si films were also measured. For the Mo/ Si films implanted with Mo ion, XRD results indicate that phase of the Mo/Si films prepared at 400 and 300 degrees C was pure MoSi2. Sheet resistance of the Mo/ Si films implanted with Mo ion was less than that of the Mo/Si films prepared without ion implantation. Nanohardness and modulus of the Mo/ Si films were obviously affected by test parameters. (C) 2007 Elsevier B. V. All rights reserved.

Silicon carbide (SiC) films were synthesized by combined metal vapor vacuum are (MEVVA) ion implantation with ion beam assisted deposition (IBAD) techniques. Carbon ions with 40 keV energy were implanted into Si(1 0 0) substrates at ion fluence of 5 x 10(16) ions/cm(2). Then silicon and carbon atoms were co-sputtered on the Si(1 0 0) substrate surface, at the same time the samples underwent assistant Ar-ion irradiation at 20 keV energy. A group of samples with substrate temperatures ranging from 400 to 600 degrees C were used to analyze the effect of temperature on formation of the SiC film. Influence of the assistant Ar-ion irradiation was also investigated. The structure, morphology and mechanical properties of the deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation, respectively. The bond configurations were obtained from IR absorption and Raman spectroscopy. The experimental results indicate that microcrystalline SiC films were synthesized at 600 degrees C. The substrate temperature and assistant Ar-ion irradiation played a key role in the process. The assistant Ar-ion irradiation also helps increasing the nanohardness and bulk modulus of the SiC films. The best values of nanohardness and bulk modulus were 24.1 and 282.6 GPa, respectively. (c) 2007 Elsevier B.V. All rights reserved.

Poly(propylene carbonate) (PPC) was implanted by oxygen ion with energy of 40 keV. The influence of experimental parameters was investigated by varying ion fluence from 1 × 1012 to 1 × 1015 ions/cm2. XPS, SEM, surface roughness, wettability, hardness, and modulus were employed to investigate structure and properties of the as-implanted PPC samples. Eight chemical groups, i.e., carbon, C H, C O C, C O, O C O, C O, , and groups were observed on surfaces of the as-implanted samples. The species and relative intensities of the chemical groups changed with increasing ion fluence. SEM images displayed that irradiation damage was related strongly with ion fluence. Both surface-recovering and shrunken behavior were observed on surface of the PPC sample implanted with fluence of 1 × 1015 ions/cm2. As increasing ion fluence, the surface roughness of the as-implanted PPC samples increased firstly, reached the maximum value of 159 nm, and finally decreased down the minimum value. The water droplet contact angle of the as-implanted PPC samples changed gradually with fluence, and reached the minimum value of 70° with fluence of 1 × 1015 ions/cm2. The hardness and modulus of the as-implanted PPC samples increased with increasing ion fluence, and reached their corresponding maximum values with fluence of 1 × 1015 ions/cm2. The experimental results revealed that oxygen ion fluence closely affected surface chemical group, morphology, surface roughness, wettability, and mechanical properties of the as-implanted PPC samples.

Two groups of Cr/Cu multilayer films were deposited on surfaces of Si (1 0 0) crystal and Al2O3 ceramic, respectively. One group was prepared by both metal vapor vacuum-arc (MEVVA) ion implantation and ion beam assistant deposition (IBAD) technologies with different sputtering ion densities and deposition times. The other group was prepared only by IBAD. The morphologies of the Cr/Cu films and cross-section micrographs were observed by scanning electron microscopy (SEM). Nanohardness, modulus, and adhesive strength of the Cr/Cu films were measured by a nano-indenter. Continuous stiffness measurement (CSM) was used while measuring nanohardness and modulus of the samples. The experimental data indicate that the adhesive strength of the samples prepared with MEVVA ion implantation was about 3-3.5 times higher than one of the corresponding samples prepared without MEVVA ion implantation. The nanohardness and modulus of the Cr/Cu films were obviously affected by the test parameters and substrate kind. (c) 2006 Elsevier B.V. All rights reserved.

Three groups of copper films were deposited on the surfaces of the Si (100) crystal by both metal vapor vacuum arc (MEVVA) ion implantation and ion beam assistant deposition (IBAD) technologies. Before coating Cu film by IBAD two groups of the samples were implanted by 68keV Cu ion with fluence of 3 x 10(17) ion s/cm(2). Different sputtering ion densities and deposition times of IBAD were selected for three groups of the samples. The internal stresses in the copper films were analyzed by X-ray diffraction (XRD). The morphologies of the copper films and cross-section micrographs were observed by scanning electron microscopy (SEM). The adhesive strength of the Cu films was measured by a nano indenter. The experimental data indicate that all the copper films possessed compressive stress, which was increased as the film thickness increased. The internal stresses of the samples prepared without Cu ion implantation were minimum among three groups of the samples. The adhesive strength of the samples prepared with MEVVA ion implantation was much higher than one of the samples prepared without MEVVA ion implantation. (c) 2006 Elsevier B.V. All rights reserved.

Plasma-enhanced chemical vapor deposition (PECVD) was used to grow Fe-catalyzed carbon nanotubes (CNTs). The coiled CNTs were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanotubes were about 10–50 nm in diameter and well beyond 2 μm in length. Field emission properties showed that the turn-on emission threshold field was about 2.5 V/μm with a current density of 0.1 μA/cm 2 and the maximal current density reached about 15 μA/cm 2 at the electric field of 6.75 V/μm. The FN plots revealed that the field emission of the CNTs followed Fowler–Nordheim behavior. For the work function of CNTs to be 5.0 eV, the field enhancement factor calculated from the slopes of the FN plots was about 7600.

Plasma-enhanced chemical vapor deposition (PECVD) method was employed to grow the Fe-catalyzed carbon nanotubes (CNTs). The grown CNTs with a uniform diameter in the range of about 10–20 nm and the typical lengths beyond 1 μm resulted in a very high aspect ratio. The Raman and TEM results showed that the grown CNTs contained a large amount of carbonaceous particles and crystal defects, such as pentagon–heptagon pair defects. XPS measurement indicated that the CNTs had C H covalent bonds. Field emission characteristics exhibited the low turn-on threshold field of 2.75 V/μm and the maximum emission current density of 7.75 mA/cm 2 at 6.5 V/μm. The growth mechanism of CNTs and the effects of hydrogen plasma on their structure were discussed.