Randomized trial in malignant biliary obstruction:Plastic vs partially covered metal stents

AIM:To compare efficacy and complications of par-tially covered self-expandable metal stent(pcSEMS)to plastic stent(PS)in patients treated for malignant,infrahilar biliary obstruction.METHODS:Multicenter prospective randomized clinical trial with treatment allocation to a pcWallstent(SEMS)or a 10 French PS.Palliative patients aged≥18,for infrahilar malignant biliary obstruction and a Karnofsky performance scale index>60%from 6 participating North American university centers.Primary endpoint was time to stent failure,with secondary outcomes of death,adverse events,Karnofsky performance score and short-form-36 scale administered on a three-monthly basis for up to 2 years.Survival analyses were performed for stent failure and death,with Cox proportional hazards regression models to determine significant predictive characteristics.RESULTS:Eighty-five patients were accrued over 37mo,42 were randomized to the SEMS group and 83patients were available for analyses.Time to stent failure was 385.3±52.5 d in the SEMS and 153.3±19.8 d in the PS group,P=0.006.Time to death did not differ between groups(192.3±23.4 d for SEMS vs211.5±28.0 d for PS,P=0.70).The only significant predictor was treatment allocation,relating to the time to stent failure(P=0.01).Amongst other measured outcomes,only cholangitis differed,being more common in the PS group(4.9%vs 24.5%,P=0.029).The small number of patients in follow-up limits longitudinal assessments of performance and quality of life.From an initially planned 120 patients,only 85 patients were recruited.CONCLUSION:Partially covered SEMS result in a longer duration till stent failure without increased complication rates,yet without accompanying measurable benefits in survival,performance,or quality of life.

Impact Wear Properties of Metal-Plastic Multilayer Composites Filled with Glass Fiber Treated with Rare Earth Element Surface Modifier

The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.

Effect of Rare Earths-Treated Glass Fiber on Impact Wear-Resistance of Metal-Plastic Multilayer Composites

The friction and wear properties under impact load and dry friction conditions of metal-plastic multilayer composites filled with glass fiber, treated with rare earth elements, were investigated. The worn surfaces were observed and analyzed by scanning electron microscopy (SEM). It shows that applying rare earth elements surface modifier to treat the glass fiber surface can enhance the interfacial adhesion between the glass fiber and polytetrafluoroethylene (PTFE), as well as promote the interface properties of the composites. This helps to form a uniformly distributed and high adhesive transfer film on the counterface and abate the friction between the composite and the counterface. As a result, the wear of composite is greatly reduced. The composite exhibits excellent friction properties and impact wear-resistance.

Simulation of bulk metal forming processes using one-step finite element approach based on deformation theory of plasticity

The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The one-step forward simulations of compression and rolling processes were presented as examples,and the results were compared with those obtained by classical incremental FE simulation to verify the feasibility and validity of the proposed method.

Effects of Metal Absorber Thermal Conductivity on Clear Plastic Laser Transmission Welding

In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.

Determination of Different Trace Heavy Metals in Children’s Plastic Toys Imported to the West Bank/Palestine by ICP/MS-Environmental and Health Aspects

The main aim of this study is to assess the quality of inexpensive plastic toys imported to Palestinian Markets. The content of heavy metals (Pb, Cd, Cr, Hg, As, Se, Ba, and Zn) was analyzed in 50 plastic toys purchased from local markets in Palestine and 17 plastic toys purchased from Israeli markets for comparison. After the digestion of samples with concentrated nitric acids and hydrogen peroxide using a microwave digester, the concentrations of the selected heavy metals were determined by ICP-MS Agilent 7500 in Al-Quds University. Results revealed that 40% of the Palestinian toy samples had high concentration (above international limits) of Pb, 30% of Cd, 34% of Cr, 6% of Hg, 42% of As, 32% of Se, 20% of Ba, and 40% of Zn. On the other hand, 95% of the Israeli samples were safe, and their concentrations were less than the maximum internationally allowable limits. In the same context, ten toy samples (2.5 gm each) had been crushed and dipped for 8 hours in a solution of artificial saliva. The solution was acidified and tested for heavy metal concentrations, but none of the migration concentrations exceeded the international maximum allowable limit. High levels of heavy metal concentrations, found in the plastic toys from the Palestinian markets could form a health hazard to children and put their lives at risk. It could be also an indirect source for environmental pollution.

On the homogenization of metal matrix composites using strain gradient plasticity

The homogenized response of metal matrix composites（MMC） is studied using strain gradient plasticity.The material model employed is a rate independent formulation of energetic strain gradient plasticity at the micro scale and conventional rate independent plasticity at the macro scale. Free energy inside the micro structure is included due to the elastic strains and plastic strain gradients. A unit cell containing a circular elastic fiber is analyzed under macroscopic simple shear in addition to transverse and longitudinal loading. The analyses are carried out under generalized plane strain condition. Micro-macro homogenization is performed observing the Hill-Mandel energy condition,and overall loading is considered such that the homogenized higher order terms vanish. The results highlight the intrinsic size-effects as well as the effect of fiber volume fraction on the overall response curves, plastic strain distributions and homogenized yield surfaces under different loading conditions. It is concluded that composites with smaller reinforcement size have larger initial yield surfaces and furthermore,they exhibit more kinematic hardening.

Analysis of localized shear deformation of ductile metal based on gradient-dependent plasticity

Shear localization in linear strain softening heterogeneous material under simple shear was investigated analytically. The closed-form solutions obtained based on gradient plasticity theory considering interactions and interplaying among microstructures due to heterogeneity of metal material show that in the normal direction of shear band, elastic shear displacement is linear; while plastic and total shear displacement are non-linear. Elastic shear strain in the band is uniform and the non-uniformity of total shear displacement stems from localized plastic shear displacement. In the center of the band, plastic and total shear displacement all reach their maximum values. In strain-softening process, elastic displacement decreases as flow shear stress decreases. Contrarily, plastic and total shear displacement increase and manifest shear localization occurs progressively. Under the same shear stress level, plastic and total shear displacement increase as strain softening modulus and elastic shear modulus decrease. The present analytical solutions were compared with many experimental results and the agreement is good.

Should a fully covered self-expandable biliary metal stent be anchored with a double-pigtail plastic stent? A retrospective study

BACKGROUND The migration rate of fully covered self-expandable metal stents(FCSEMSs) has been reported to be between 14% to 37%. Anchoring of FCSEMSs using a doublepigtail plastic stent(DPS) may decrease migration.AIM To compare stent migration rates between patients who received FCSEMS alone and those who received both an FCSEMS and anchoring DPS.METHODS We conducted a retrospective analysis of endoscopy reporting system and medical records of 1366 patients who underwent endoscopic retrograde cholangiopancreatography(ERCP) with FCSEMS placement at the University of Kentucky health care. Between July 2015 and April 2017,203 patients with FCSEMS insertion for the treatment of malignant biliary stricture,benign biliary stricture,post-sphincterotomy bleeding,bile leak,and cholangitis drainage were identified. The review and analysis were conducted through our endoscopy reporting system(ProVation~? MD) and medical records. Categorical data were analyzed using Chi-Square and Fischer exact test and continuous data using nonparametric tests. A regression analysis was performed to identify factors independently associated with increased risk of stent migration. We determinedan FCSEMS migration endoscopically if the stent was no longer visible in the major papilla.RESULTS1366 patients had undergone ERCP by three advanced endoscopists over 21-mo period; among these,203 patients had FCSEMSs placed. 65 patients had FCSEMSs with DPS,and 138 had FCSEMSs alone. 65 patients had FCSEMSs with DPS,and 138 had FCSEMSs alone. 95 patients had a malignant stricture,82 patients had a benign stricture,12 patients had bile leak,12 patients had cholangitis,and nine patients had post-sphincterotomy bleeding. The migration rate in patients with anchored FCSEMSs with DPS was 6%,and those without anchoring DPS was 10%(P = 0.35). Overall,migration was reported in 18 patients with FCSEMSs placement out of 203 patients with an overall migration rate of 9.7%. There was no significant association between anchoring the FCSEMSs with DPS and the risk of stent migration. Only patients with the previous sphincterotomy and begin biliary stricture were found to have a statistically significant difference in the migration rate between patients who had FCSEMS with DPS and FCSEMS alone(P = 0.01).CONCLUSION The risk of migration of biliary FCSEMS was 9.7 %. Anchoring an FCSEMS with DPS does not decrease the risk of stent migration.

Aluminum ion beam surface modification of elastic metallic-plastic pads for improving tribological properties

Elastic metallic-plastic pads（EMP） were irradiated by low energy aluminum ion in a metal vapor vacuum arc（MEVVA） 80-10 implantation system. The samples were irradiated with 20keV Al ion with the influx from 1×1015 to 1×1016 Al/cm2. Then the as-irradiated samples were measured by ESCA, XRD, AFM/FFM and a nano-probe. It is found that the hardness of as-irradiated samples is 5-6 times as that of the pristine ones. The worn depth of sample implanted at ion influx of 1×1016 Al/cm2 is about one eighth of that of the pristine sample at the same load. The XRD results show that there are some Al2O3 and AlF3 intermingled with the phase of polytetrafluoroethylene（PTFE）. The experimental results reveal that the tribological properties of EMP can be significantly improved by the ion beam surface modification.

Room temperature plastic deformation behavior of ZrCuNiAl bulk metallic glasses

The Zr62.55Cu17.55Ni9.9Al10 bulk metallic glass （BMG） was prepared by using copper-mold suction-casting. X-ray diffraction and differential scanning calorimetry were utilized to determine its structure and thermal stability. Uniaxial compression and Rockwell indenta- tion tests were adopted to study the plastic deformation behavior at room temperature. The results show that the glass transition temperature and the onset temperature of exothermic reaction of the BMG are 651.5 and 748 K, respectively. During the compression test, the BMGs undergo an engineering strain of about 2.5%, i.e., true strain of 2.8%, and then fracture. The BMGs deform via the formation and propagation of shear bands. Under indentation loading, the BMGs deform through the formation of radiation-like and circular shear bands. The circular shear bands form earlier than the radiation-like ones, The formation mechanism of shear bands in the BMGs was analyzed and discussed.

Determination of Content of Eight Elements in Metal Coating Smeared on Waste Plastics by X-ray Fluorescence Spectrometry

X-ray fluorescence spectrometry was used to detect the content of eight elements in metal coating smeared on waste plastics,and effects of sample cups,elements in plastic substrate,and interaction of elements in metal coating on detection results were analyzed. The results show that the RSD of the method used to detect element content in the metal coating smeared on the waste plastics ranged from 0.008% to 0.044%; the determination range of the eight elements was 0.002%-52.0%,and their detection limit ranged from 0.0002% to 0.0008%. The determination results of X-ray fluorescence spectrometry were consistent with that of ICP-AES. The method can provide technical support for the determination of damage and pollution caused by metal coating smeared on waste plastics.

Mg-Cu-Zn-Y-Zr bulk metallic glassy composite with high strength and plasticity

Mg65Cu20Zn5Y9Zr1 bulk metallic glass matrix composite with a diameter of 2 mm was produced by copper mold casting. Upon cooling the Mg65Cu20Zn5Y9Zr1 melt, Mg2Cu acicular crystalline phase precipitates uniformly with a size of about 20 μm long and 1 μm thick while the remaining melt undergoes glass transition. Room temperature compression tests revealed that the high fracture strength up to 830 MPa and the plastic strain of 2.4% before failure are obtained for the Mg-based bulk metallic glass matrix composite. The formation of the Mg2Cu phase was proposed to contribute to high strength and plastic deformation of the material.

Analysis of FCC sheet metal forming with rate-independent polycrystalline plasticity FEM

A rate-independent polycrystalline plasticity constitutive model considering self and latent hardening was developed. Next, a new orientation probability assignment method was proposed and the crystal orientations were assigned to FE integration points, which represent crystals and can rotate individually. Then cup drawing of FCC aluminum sheet was studied using crystalline plasticity finite element analysis. The results show that the validity of proposed model is proved through comparison between numerical results and experimental ones. {001}<110> texture can lead to earing at 45° direction, while {124}<211> texture at 0° and 90° directions. For the rolled aluminum sheet, which contains strong {001}<110> texture, earing is formed at 45° direction after cup drawing. For the annealing aluminum sheet, due to the balance between two main textures, the flange earing tendency is not obvious.

EFFECTS OF MICROSTRUCTURE ON THE MACROSCOPIC ELASTO-PLASTIC PROPERTIES OF METAL MATRIX COMPOSITES

The generalized self-consistent finite-element iterative averaging method was adopted to analyze the elasto-plastic tensile properties of SiC whiskers reinforced aluminum matrix composites. The effects of varying fiber's aspect ratio and volume fraction on the macroscopic elasto-plastic deformation of the composites were studied. By the analysis of microscopic stress fields, the relation between the propagation of the elasto-plastic region in the matrix and the macroscopic elasto-plastic deformation of composites was discussed. It was found that the propagation of the plastic region in the matrix between the fiber's ends would affect prominently the elasto-plastic tensile behaviour of the composites. It was shown that the characterization of the stress-strain response in terms of the 0.2% offset yield strength is incomplete.

Contrast-free air cholangiography-assisted unilateral plastic stenting in malignant hilar biliary obstruction

BACKGROUND:Endoscopic palliation in malignant hilar biliary obstruction requires endoscopic retrograde cholangiopancreatography (ERCP),whereas contrast injection leads to cholangitis.Contrast-free metal stenting with or without magnetic resonance cholangiopancreatography (MRCP) has shown encouraging results,but MRCP and metal stents are costly.There have been no reports on the use of air cholangiography.METHODS:We prospectively evaluated the role of air cholangiography-assisted unilateral plastic stenting in 10 patients with type Ⅱ malignant hilar biliary obstruction.A retrospectively analysed group of 10 patients treated with contrast-free unilateral metal stenting served as historical controls.RESULTS:Ten patients with unresectable type Ⅱ malignant hilar biliary obstruction were studied.Air cholangiography detected type Ⅱ obstruction in all patients,similar to MRCP.The patients underwent unilateral stenting.Successful endoscopic drainage was achieved in all patients.The mean patency of the stent was 95.8±17.5 days in the study group and 143.9±115.1 days in the control group (P=0.20).The mean survival was 121.8±41.6 days in the study group and 154.9±122.5 days in the control group (P=0.42).KaplanMeier analysis showed an estimated median survival of 100:95% CI (65.9,134.1) days in the study group and 98:95% CI (84.1,111.9) days in the control group (P=0.62).Cholangitis occurred in none of the patients and there were no 30-day deaths nor major complications.Air cholangiographyassisted unilateral plastic stenting was cheaper than contrastfree unilateral metal stenting.CONCLUSION:Air cholangiography-assisted unilateral plastic stenting is as safe and effective as contrast-free unilateral metal stenting in type Ⅱ malignant hilar biliary obstruction for palliating patients,but it is cheaper.

Mechanics and forming theory of liquid metal forging

On the basis of steel liquid forging and aluminium alloy liquid forging, liquid metal forging was investigated, such as the assembly model, metal plastic flowing, the force displacement curves, the harmonious equation, calculation of value of altitude deformation and determination of specific pressure of liquid metal forging. On the basis of the theory of metal plastic forming and the characteristics of liquid metal forging, the achievements on the mechanics and forming theory of liquid metal forging were given out by combining the theory and experiments systematically, and an important preparation for establishing liquid metal forging theory was suggested.

PARTICULATE SIZE EFFECTS IN THE PARTICLE-REINFORCED METAL-MATRIX COMPOSITES

The influences of I,article size on the mechanical properties of the particulate metal matrix composite;are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly using the conventional elastic-plastic theory. It is because that no length scale parameters are involved in the conventional theory. In the present research, using the strain gradient plasticity theory, a systematic research of the particle size effect in the particulate metal matrix composite is carried out. The roles of many composite factors, such as: the particle size, the Young's modulus of the particle, the particle aspect ratio and volume fraction, as well as the plastic strain hardening exponent of the matrix material, are studied in detail. In order to obtain a general understanding for the composite behavior, two kinds of particle shapes, ellipsoid and cylinder, are considered to check the strength dependence of the smooth or non-smooth particle surface. Finally, the prediction results will be applied to the several experiments about the ceramic particle-reinforced metal-matrix composites. The material length scale parameter is predicted.