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In order to ascertain the distribution characteristics of soil heavy metal pollution and main pollution sources in a small watershed in the southern mountainous area of Ningxia and to ensure the quality of the soil environment, the contents of heavy metals Pb, Ni, Zn, Mn, Cu, Cr, and Cd in 260 surface soil samples (0-20 cm) were collected and determined. Based on the soil background value in Ningxia, the soil heavy metal pollution status and potential ecological risk were evaluated through the single factor index, Nemera composite index, and potential ecological risk index, and the method of combining positive definite matrix factor analysis (PMF) and Kriging interpolation was used to analyze the soil heavy metal spatial distribution and source. The results showed that the average contents of

A composite deck system composed of ultrahigh performance concrete (UHPC) and an orthotropic steel deck has been proposed to solve fatigue cracking and corrosion problems in traditional orthotropic steel deck systems. In a prefabricated steel-UHPC composite deck system, a wet joint is usually formed between two adjacent prefabricated UHPC layers. The interface between the prefabricated UHPC layer and cast-in situ UHPC is defined as a wet joint. To investigate the tensile behaviours of the wet joint, a novel tensile specimen configuration simulating the wet joint was initially proposed. The effects of reinforcement diameter and embedment length were experimentally investigated. The test results revealed that increasing the embedment length could enhance the crack resistance at the wet joint, but the influence could be neglected when the embedment length is greater than 10 db (db = diameter of reinforcement). Based on tensile tests, three-dimensional FE models were developed to simulate the tensile behaviours of the wet joint, and their accuracy was confirmed by the test results. With the validated FE model, the effect of UHPC thickness on the tensile behaviours of wet joints was investigated. Finally, specific design parameters were recommended according to the test and numerical results.

A hybrid joint with the Nb interlayer consisting of two metallurgical joining interfaces was obtained by the laser welding induced brazing method. The fusion zone comprising the Ti-based and Nb-based solid solutions formed at the Ti6Al4V/Nb interface, while the diffusion bonding layer comprising the Cu-based and Nb-based solid solutions formed at the Nb/Cu interface. The use of niobium interlayer successfully prevented the mixing of Ti and Cu in the molten pool to avoid the formation of TixCuy brittle phases. The tensile strength of the Ti6Al4V/Cu joints with the Nb interlayer increased to 225 MPa, and the joints exhibited the ductile fracture. The fracture region formed at the Cu side near the Nb/Cu interface.

A novel reinforced concrete (RC) vertical bent frame structure system consisting of a RC frame structure and RC bent structure has been proposed for the development of large-scale thermal power plants. To better understand the seismic performance of RC bent columns in vertical bent frame structures, a 1/5-scale representative component selected from a common vertical bent frame structure was tested by quasi-static testing (QST). The failure mode hysteretic characteristics, ductility, energy dissipation capacities of RC bent columns were investigated. Based on the experimental results, finite element models for the bent frame columns and vertical bent frame structures were developed and the nonlinear dynamic analyses were carried out. The results of finite element analysis indicate that the axial pressure ratio has significant effects on the seismic behaviour of RC bent columns. The relationship of drift angle for bent frame column under frequent earthquake and infrequent earthquake are investigated. The limitation values of axial compression ratios and the inter-storey drift angle for RC bent columns in vertical bent frame structures are suggested.

Back-streaming neutrons from the spallation target of the China Spallation Neutron Source (CSNS) that emit through the incoming proton channel were exploited to build a white neutron beam facility (the so-called Back-n white neutron source), which was completed in March 2018. The Back-n neutron beam is very intense, at approximately 2*10^7 n/cm^2/s at 55 m from the target, and has a nominal proton beam with a power of 100 kW in the CSNS-I phase and a kinetic energy of 1.6 GeV and a thick tungsten target in multiple slices with modest moderation from the cooling water through the slices. In addition, the excellent energy spectrum spanning from 0.5 eV to 200 MeV, and a good time resolution related to the time-of-flight measurements make it a typical white neutron source for nuclear data measurements; its overall performance is among that of the best white neutron sources in the world. Equipped with advanced spectrometers, detectors, and application utilities, the Back-n facility can serve wide applications, with a focus on neutron-induced cross-section measurements. This article presents an overview of the neutron beam characteristics, the experimental setups, and the ongoing applications at Back-n., Comment: 11 pages, 9 figures

Ultra-lightweight cement composite (ULCC) has attracted extensive research interests in both civil and offshore engineering constructions due to its high specific strengths. In order to satisfy different engineering construction demands, four types novel steel fiber reinforced ultra-lightweight cement composite (ULCC) with different densities ranging from 1250 kg/m3 to 1550 kg/m3 were proposed. Extensive standard compressive and tensile tests were performed to obtain the mechanical properties of these ULCCs with different densities, which will offer useful information for the developments of design on engineering constructions with such types of ULCC. Based on these test results, constitutive laws were established to describe the compressive and tensile stress–strain behaviors of ULCC with varying densities. Regarding the applications of the ULCC in engineering constructions, a ULCC flat slab with density of 1550 kg/m3 under concentrated loading was tested. The failure mechanisms and ultimate strength behaviors of this ULCC flat slab were reported. 3D FE model was also developed to simulate the structural behaviors of the novel ULCC flat slab, and its accuracy was confirmed by the reported test results. With the validated FE model and reported mechanical properties of ULCC with different densities, structural behaviors of ULCC flat slabs with these ULCCs were investigated. Analytical model based on the method of bending resistance in MCS-EPFL was proposed to predict the ultimate resistance of ULCC flat slab.

The joining of Ti6Al4V and Inconel 718 constitutes a great challenge, due to the TixNiy, Ti-Cr, and Ti-Fe brittle phases’ formation. For the solution of this problem, niobium was selected as an interlayer and the pulsed laser welding-induced eutectic reaction technology was proposed. Two metallurgical bonding zones based on two different bonding mechanisms were identified for the Ti6Al4V/Inconel718 dissimilar joint. When the laser beam was positioned at the Ti6Al4V/Nb interface, the Ti6Al4V and the Nb sheet were partially melted, for the Ti6Al4V and niobium to be joined through fusion welding, while the atomic interdiffusion and the eutectic reaction were responsible for the joining at the Nb/Inconel 718 interface. No TixNiy, Ti-Cr, or Ti-Fe intermetallics were detected in the weld, demonstrating that the unmelted Nb interlayer acted as a diffusion barrier between the Ti6Al4V and the Inconel 718. The eutectic reaction layer formed at the Nb/Inconel 718 interface with the main microstructure of the Ni-Nb system intermetallics. The welded joints fractured at the reaction layer at the maximum tensile strength of 145 MPa and the fracture mode was cleavage fracture.

The effect of Ni interlayer thickness on chemical composition, microstructure and mechanical properties of laser welding of Mo and stainless steel was analyzed systematically. Experimental results indicated that with the increase in thickness of Ni interlayer, the number of Mo Fe IMCs, the hardness at the Mo-FZ interface, the width and grain size in the heat affected zone of Mo side and the thickness of Mo Fe IMCs layer decreased significantly. The maximum tensile strength attained 351 MPa for joints with 0.1 mm thick Ni interlayer. With excessive (>0.1 mm) Ni addition in the welded joint, the mechanical properties deteriorated due to the formation incomplete fusion, void and crack defects. The tensile investigation showed that the weakest area of the joint was Mo Fe IMCs layer. When an appropriate thickness of Ni interlayer is used, the Mo Fe IMCs layer can be strengthened by increasing diffusion ability of Mo to FZ and Ni concentration in the Mo Fe IMCs and restraining of Mo Fe IMCs, consequently producing high-quality welded joints.

Pulsed laser welding was used to weld dissimilar joints in Ti6Al4V/Nb alloys. The effect of heat input on the microstructural characterizations and mechanical properties of the joints was investigated. The experimental results show that underfill defects disappeared in the fusion zone (FZ) as the heat input increased. No intermetallic compounds were formed in the FZ, but a dendritic zone of Ti-rich phases and an island zone of Nb-rich phases were present for all welded joints, indicating that composition segregation occurred in the Ti6Al4V/Nb dissimilar joint. Moreover, the microstructure and mechanical heterogeneity in the FZ of the welded joint increased with increasing heat input. The microhardness of the island area was lower than that of the dendritic zone in the FZ, because it possessed higher levels of Nb. The results of the tensile tests show that the joints fractured at the Nb base metal side, suggesting that the strength of the FZ is higher than that of the Nb base metal.

In this paper, a novel laser welding method with Nb/Cu multi-interlayer was developed for improving the mechanical properties of NiTi/301SS joint. A hybrid joint consisting three metallurgical joining zones was obtained based on different welding mechanisms through a single pass welding. The self-fusion welding was formed on the Nb interlayer, and the fusion zone was composed of Nb-based solution. NiTi and Nb were well bonded by eutectic reaction, and the NiTi/Nb interface contained Nb-based solution, NiTi phase and Nb-NiTi eutectic structure. Nb and 301SS were joined by brazing because of the melting of Cu, and the Nb/Cu/301SS interface consisted of Nb-, Cu-, and Fe-based solutions and a little Fe7Nb6 intermetallic. The strength and ductility of the joints with interlayer were 126% and 188% higher than the joints without interlayer, respectively. The use of Nb/Cu multi-interlayer completely prevented the formation of Ti-Fe and TixNiy IMCs, which can improve significantly mechanical properties of joints.

Direct welding of Mo and stainless steel is exceptionally difficult due to intrinsic brittleness of Mo and the formation of brittle Fe-Mo phases. To explore the feasibility of welding of Mo and stainless steel, the laser offset method was used in this study. Experimental results show that the offset of the laser beam toward stainless steel has a positive effect for the quality of Mo/Fe dissimilar joint. As the laser beam shifts from the Mo side to the stainless steel side, the formation of welding defects and Fe-Mo intermetallic compounds (IMCs) are effectively restricted because of the decrease amount of molten Mo. The decrease of Fe-Mo IMCs contributes to the reduction of hardness in the joints. With an increase of laser offset, the thickness of Fe-Mo IMCs layer decreased, consequently the tensile strength of joints increased first and then decreased in the laser offset range of 0.2–0.5 mm. The highest tensile strength of the joints is 290 MPa at the laser offset of 0.3 mm. All joints failed in the Fe-Mo IMCs layer with brittle fracture mode during tensile tests, indicating the weakest zone of the joint was Fe-Mo IMCs layer. A sound weld of Mo and stainless steel can be obtained if an appropriate thickness of Fe-Mo IMCs layer is produced by adjusting the laser offset.

To improve the quality of the joints between Ti6Al4V and Inconel 718, fiber laser welding with Nb/Cu multi-interlayer was attempted by laser welding induced brazing-welding method. The hybrid joint comprising different metallurgical areas was created based on fusion welding and brazing welding mechanisms through one welding. Ti6Al4V and Nb well bonded by the fusion welding, and the fusion zone was characterized by the formation of (α + β Ti, Nb) solid solutions. Nb and Inconel 718 were joined by brazing because of the melting of Cu foil, and the Nb/Cu/Inconel 718 interface mainly consisted of the Nb-based, Cu-based, and Ni-based solid solutions. The joint failed in the Nb/Cu/Inconel 718 interface with the maximum strength of 260 MPa, exhibiting brittle-like failure behavior due to the formation of voids and microcracks at the Nb/Cu/Inconel 718 interface. The addition of Nb/Cu multi-interlayer can help prevent the formation of IMCs and improves the mechanical properties of the joint.

The aim of this investigation was to evaluate the effect of microstructure heterogeneity on the tensile and low cycle fatigue properties of electron beam welded (EBW) Ti6Al4V sheets. To achieve this goal, the tensile and low cycle fatigue property in the EBW joints and base metal (BM) specimens is compared. During the tensile testing, digital image correlation technology was used to measure the plastic strain field evolution within the specimens. The experimental results showed that the tensile ductility and low cycle fatigue strength of EBW joints are lower than that of BM specimens, mainly because of the effect of microstructure heterogeneity of the welded joint. Moreover, the EBW joints exhibit the cyclic hardening behavior during low fatigue process, while BM specimens exhibit the cyclic softening behavior. Compared with the BM specimens with uniform microstructure, the heterogeneity of microstructure in the EBW joint is found to decrease the mechanical properties of welded joint.

Gangmin Wang,1,* XiaoLong Gao,2,* GuoJun Gu,2 ZhiHong Shao,2 MingHua Li,2 PeiJun Wang,2 JianRong Yang,3 XiaoJun Cai,4 YongYong Li4 1Department of Urology, Huashan Hospital, Fudan University, 2Department of Radiology, Tongji Hospital, School of Medicine, Tongji University, Shanghai, 3Department of Hepatobiliary Surgery, Third People’s Hospital of Guangxi Zhuang Autonomous Region, Nanning, 4Institute for Advanced Materials and Nano Biomedicine, School of Material Science and Engineering, Tongji University, Shanghai, People’s Republic of China *These authors contributed equally to this work Abstract: A polyethylene glycol–poly(ε-benzyloxycarbonyl-l-lysine) (PEG-SS-PLL) block copolymer based on a disulfide-linked, novel biodegradable catiomer bearing a PEG-sheddable shell was developed to avoid “PEG dilemma” in nanoparticle intracellular tracking of PEG-PLL where PEG was nondegradable. However, PEG-SS-PLL catiomers have not been used to deliver small interfering VEGF RNA (siVEGF) in antiangiogenesis gene therapy. In this study, we aimed to investigate whether this novel biodegradable catiomer can deliver siVEGF into cancer cells and at the same time have an antitumor effect in a xenograft mouse model. It was found that PEG-SS-PLL efficiently delivered siVEGF with negligible cytotoxicity, and significantly decreased the expression of VEGF at both the messenger-RNA and protein levels both in vitro and in vivo, and thus tumor growth was inhibited. Our findings demonstrated that PEG-SS-PLL/siVEGF could potentially be applied to antiangiogenesis gene therapy for hepatocellular carcinoma. Keywords: polyethylene glycol, poly lysine, disulfide, VEGF, antiangiogenesis, hepatocellular carcinoma, siRNA

The present paper studied the evolution of tensile damage in joints welded using laser beam welding (LBW) and gas tungsten arc welding (TIG) under a uniaxial tensile load. The damage evolution in the LBW joints and TIG-welded joints was studied by using digital image correlation (DIC) technology and monitoring changes in Young’s modulus during tensile testing. To study the mechanism of void nucleation and growth in the LBW joints and TIG-welded joints, test specimens with various amounts of plastic deformation were analyzed using a scanning electron microscope (SEM). Compared with TIG-welded joints, LBW-welded joints have a finer microstructure and higher microhardness in the fusion zone. The SEM analysis and DIC test results indicated that the critical strain of void nucleation was greater in the LBW-welded joints than in the TIG-welded joints, while the growth rate of voids was lower in the LBW-welded joints than in the TIG-welded joints. Thus, the damage ratio in the LBW joints was lower than that in the TIG-welded joints during tensile testing. This can be due to the coarser martensitic α′ and the application of TC-1 welding rods in the TIG-welded joint.

In this study, four welding methods, pulsed laser welding, defocused pulsed laser welding, laser–arc tandem welding, and laser–arc hybrid welding, were tested on 304 stainless steel sheets, and the differences between the weld cross-section outlines, especially the weld depth, were compared under different welding conditions. The author suggests that during the hybrid welding process, the upper part of the keyhole was surrounded by a large amount of melt such that the evaporation recoil pressure caused the gas–liquid interface to move towards the solid–liquid interface near weld pool surface. This flow behavior promoted both heat transfer from the central region of the weld pool to the solid–liquid interface near the weld pool surface, which resulted in an increased weld width, and increased the diameter of the upper part of the keyhole, which reduced the number of times the laser beam is reflected inside the keyhole and the coupling efficiency of laser energy. During pulse Nd:YAG laser–TIG arc tandem welding, there was a smaller amount of melt around the keyhole, which made it easier to form a U-shaped keyhole, which benefited the multiple reflection of laser beam in the keyhole and promoted the coupling of laser energy. The weld depths obtained from tandem welding and laser–arc hybrid welding were similar, which may be related to the difference in the keyhole shapes produced from the two welding processes.

The overlapping factor of pulsed laser welding is used to help understand the correlation between welding parameters and the quality of Ti6Al4V welded joints. The number of porosity decreases with the increase in overlapping factor, and the welded joints are almost completely free of porosity when overlapping factor is greater than 75%. This can be attributed to the fact that the remelted volume of the spot region increases with the increase of overlapping factor, which assists porosity formed in the previous pulse wave in escaping from molten pool formed by the subsequent pulse. With the increase of overlapping factor, the weld microstructure becomes much coarser and the width of the fully transformed region of heat affected zone increases, which reduces the microstructure gradient and microhardness gradient from the fusion zone to heat affected zone. A method to evaluate the porosity susceptibility of a specific welding condition prior to actual welding process is presented.

The effect of the overlapping factor on the microstructures and mechanical properties of pulsed Nd:YAG laser welded Ti6Al4V alloy sheets was investigated by microstructural observations, microhardness tests, tensile tests and fatigue tests. A microstructural examination shows that by increasing the overlapping factor, the grains in the fusion zone become coarser, and the width of the heat affected zone increases. As overlapping factor increases, the width of region composed completely of martensite α′ and the secondary α phase in the heat affected zone increases, consequently the gradient of microstructure along the direction from the fusion zone to base metal decreases, so does the gradient of microhardness. The results of tensile and fatigue tests reveal that the joints made using medium overlapping factor exhibit better mechanical properties than those welded with low and high overlapping factors. Based on the experimental results, it can be stated that a sound weld of Ti6Al4V alloy can be obtained if an appropriate overlapping factor is used.

The present work is aimed at comparatively studying fatigue damage evolution of a pulsed Nd:YAG laser beam-welded (LBW) joint and the base metal (BM) of Ti6Al4V alloy subjected to cyclic loading. To reveal crack nucleation and propagation during the fatigue process, in situ fatigue was generated using infrared measurement methods. The results indicate that the rate of damage accumulated in the LBW joint was higher than in the BM specimens during a fatigue test, which decreased the fatigue life of the LBW joint. This observation is attributable to the LBW joint fusion zone microstructure, which has a higher void nucleation and growth rate compared with the BM microstructure.

In this study, the influence of weld cross-sectional profiles and microstructure, under different welding conditions, was investigated on the mechanical properties of pulsed Nd:YAG laser-welded joint of Ti6A14V alloy. The V- and H-shaped weld cross-section profiles were obtained under low and high heat input, respectively. The microstructure in the fusion zone (FZ) of V- and H-shaped welded joint consisted of a fine acicular martensitic α′ solidification structure within the prior-β grains, responsible for the maximum hardness in the FZ. Tensile tests revealed that the V-shaped welded joint fractured at the near heat-affected zone (HAZ)/base metal (BM) interface, but the H-shaped welded joint fractured in the BM. Furthermore, the tensile strength of the V-shaped welded joint was lower than that of the H-shaped welded joint. This was attributed to the fact that the heterogeneity of strain distribution at the interface of HAZ and BM of the V-shaped welded joint was greater than that of the H-shaped welded joint during tensile process.

The influence of the large microstructure gradient the fatigue damage behaviour of laser beam welded Ti6Al4V was investigated. The experimental results showed that the damage evolution of fatigue residual strength in the LBW joint was higher than that in the base metal (BM) sample, and the fatigue crack growth resistance of the fusion zone (FZ) in the LBW joint was greater than that of the BM. Compared with BM specimens, the heterogeneous micro-plastic deformation was easier to obtain in the LBW joint under fatigue load due to high large microstructure gradient, which promotes crack initiation in the LBW welded joint.

This paper reports on a study aiming at comparing properties of the Ti6Al4V titanium alloy joints between pulsed Nd:YAG laser welding and traditional fusion welding. To achieve the research purpose, Ti6Al4V titanium alloy plates with a thickness of 0.8 mm were welded using pulsed Nd:YAG laser beam welding (LBW) and gas tungsten arc welding (TIG), respectively. Residual distortions, weld geometry, microstructure and mechanical properties of the joints produced with LBW and TIG welding were compared. During the tensile test, with the aid of a high speed infrared camera, evolution of the plastic strain within tensile specimens corresponding to LBW and TIG welding were recorded and analyzed. Compared with the TIG, the welded joint by LBW has the characters of small overall residual distortion, fine microstructure, narrow heat-affected zone (HAZ), high Vickers hardness. LBW welding method can produce joints with higher strength and ductility. It can be concluded that Pulsed Nd:YAG laser welding is much more suitable for welding the thin Ti6Al4V titanium alloy plate than TIG welding.

A bioreducible polyethylenimine (SS-PEI) was successfully applied as a nonviral carrier for the delivery of plasmid DNA and VEGF-siRNAin vitroandin vivo. The SS-PEI could strongly condense DNA or siRNA into nanosized complexes (below 200 nm) with positive surface charges.In vitrotransfection experiments using GFP plasmid as gene reporter showed that the complexes of SS-PEI/DNA were able to efficiently transfect HepG2 cells, with efficiency comparable to that of polyethylenimine, a gold standard for nonviral gene delivery. Moreover, the complexes of SS-PEI/VEGF-siRNA could lead to reduced levels of VEGF protein in HepG2 cellsin vitro. Treatment with the complexes of SS-PEI/VEGF-siRNA efficiently inhibited HepG2 tumor growth in an xenograft mouse model. The data of this study imply that the SS-PEI is a potent nucleic acid carrier applicable for liver cancer gene therapy.

The title compound, 2-hydroxyand-4-methylthioxanthone（C14H10O2S）has been prepared from 2,2'-dithiosalicylic acid and 3-methylphenonl and characterized by IR and 1H NMR spectra. The yield was higher in the presence of P2O5.Its crystal structure was determined by single-crystal X-ray diffraction. Crystal data for the title compound: the triclinic system, space group P-1, with a = 7.4699(11)Å, b = 7.4839(11) (13)Å,c = 19.659(3) (11)Å,α=87.981(3) º,β= 85.678(3) º , γ= 82.618(3) º，Z=2，V= 1086.5(3) Å 3，Dc= 1.481mg.m-3,F（000）=504,µ= 0.281mm-1,R=0.0588 and wR= 0.1333.The results of crystal structure determination show that there exist intra-molecular hydrogen bonds, resulting in a framework of dimmers. C(1), C(2), C(3), C(4), C(5), C(6), C(7), C(8), C(9), C(10), C(11), C(12), C(13) and S(1) is coplanar in one molecular of the dimmer, and C(15), C(16), C(17), C(18), C(19), C(20), C(21), C(22), C(23), C(24), C(25), C(26),C(27) and S(2) is coplanar in the other molecular of the dimmer. The dihedral angle between the two molecular plans is 28.10（0.08）, which shows that two molecular plans is not parallel in the framework of dimmers.

Theranostic nano-polyplexes containing gene and imaging agents hold a great promise for tumor diagnosis and therapy. In this work, we develop a group of new gadolinium (Gd)-chelated cationic poly(urethane amide)s for gene delivery and T1-weighted magnetic resonance (MR) imaging. Cationic poly(urethane amide)s (denoted as CPUAs) having multiple disulfide bonds, urethane and amide linkages were synthesized by stepwise polycondensation reaction between 1,4-bis(3-aminopropyl)piperazine and a mixture of di(4-nitrophenyl)-2, 2'-dithiodiethanocarbonate (DTDE-PNC) and diethylenetriaminepentaacetic acid (DTPA) dianhydride at varied molar ratios. Then, Gd-chelated CPUAs (denoted as GdCPUAs) were produced by chelating Gd(III) ions with DTPA residues of CPUAs. These GdCPUAs could condense gene into nanosized and positively-charged polyplexes in a physiological condition and, however, liberated gene in an intracellular reductive environment. In vitro transfection experiments revealed that the GdCPUA at a DTDE-PNC/DTPA residue molar ratio of 85/15 induced the highest transfection efficiency in different cancer cells. This efficiency was higher than that yielded with 25kDa branched polyethylenimine as a positive control. GdCPUAs and their polyplexes exhibited low cytotoxicity when an optimal transfection activity was detected. Moreover, GdCPUAs may serve as contrast agents for T1-weighted magnetic resonance imaging. The results of this work indicate that biodegradable Gd-chelated cationic poly(urethane amide) copolymers have high potential for tumor theranostics.

One new siRNA sequence was found efficient for human telomerase reverse transcriptase (hTERT) gene silencing in vitro in five types of human cancer cells. Then, a biodegradable polyethylenimine containing multiple disulfide bonds (SS-PEI) was successfully applied as a potent non-viral carrier for intracellular delivery of the hTERT siRNA in vitro and in vivo. The SS-PEI could strongly bind siRNA to form nano-sized and positively-charged complexes, but which were readily destabilized to sufficiently release siRNA in a reducing environment. Transfection experiments showed that the complexes of SS-PEI/hTERT siRNA were able to transfect HepG2 cells in vitro, inducing reduced levels of hTERT mRNA and hTERT protein, decreased telomerase activity, cell growth inhibition and significant cell apoptosis. Besides, treatment with the complexes of SS-PEI/hTERT siRNA could inhibit HepG2 tumor growth in a xenograft mouse model. Importantly, the SS-PEI revealed relatively low cytotoxicity in vitro and at an appropriate dose had no adverse effect on liver and kidney functions in vivo. The results of this study indicate that SS-PEI/siRNA-induced hTERT gene silencing provides a promising method for human cancer gene therapy.

To explore the effects on Aβ plaques of neural stem cells transplanted into an Alzheimer disease mouse model.A total of twenty 12-months-old APP+PS1 double transgenic AD mice were randomly divided into two groups.One group received neural stem cells transplantation, that was NSC group, another mice received an equal quantity 0.01 mol/L PBS, as positive control group. After 5 weeks transplantation, the total number of Aβ plaques examined by immunohistochemistry, the ratio of compact of Aβ plaques by TS staining, and whether NSCs migrate into Aβ plaques by immunofluorescence monitoring.There was no difference in total number of Aβ plaques between NSC group (181 ± 12) and PBS (179 ± 14) group after transplantation (P0.05). There was no difference in the number of TS+ plaques between NSC group (54.9%) and PBS (55.7%) group after eight weeks NSCs transplantation (P0.05). (2) However, engrafted NSCs showed partial chemotaxis toward Aβ plaques.NSCs transplantation did not have a significant impact on Aβ plaques of AD mice, but the tropism of engrafted NSCs may be capable of replacing lost or damaged cells and reverse the course of AD mice in some extent.

To explore the feasibility of in vivo labeling of adult rat neural progenitor cells (NPCs) in subventricular zone (SVZ) with superparamagnetic iron oxide particles (SPIOs) for tracking of magnetic resonance imaging (MRI).A total of 7 SD rats were stereotactically injected with 3 µl SPIOs (7 mg Fe/ml) into anterior horn of right lateral ventricle and then 5-bromo-2'-deoxyuridine (BrdU) was injected intraperitoneally once daily for 1 week. MRI was performed at 1, 3, 7 and 14 days post-injection. After the final MRI scan, all rats were transcardially perfused and their brains removed and fixed. The sections were processed for Prussian blue iron staining and Prussian blue plus BrdU immunohistochemical staining.In all experimental animals, SPIOs were predominantly located in the anterior horn of right lateral ventricle and partial SPIOs entered the ventricular system. A needle path and a distribution of SPIOs along rostral migratory stream (RMS) towards olfactory bulb (OB) were depicted at the sagittal view of T2(*)WI, moderate MR artifact was visible and SPIOs tracking NPCs were successful (success rate of 100%). The result of staining showed SPIOs labeling NPCs were effective. And the labeling rates were 75.5%, 42.3%, 23.6% in SVZ, RMS and OB respectively.Effective in vivo labeling of adult rat NPCs in SVZ with SPIOs is feasible. And dynamical migration of labeling NPCs along RMS towards OB may be visualized on MRI.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by extracellular accumulation of amyloid deposits. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor whose levels have been shown to be decreased in AD brains. BDNF supplementation can offer improvement in the course of AD. However, the means of assessment are still relatively limited. In the present study, 1H-MRS was used to evaluate the therapeutic effects of bilateral intraventricular BDNF infusion into Alzheimer's disease APP/PS1 double transgenic mice. For comparison to the 1H-MRS observations, Fluoro-Jade B staining and immunofluorescence for beta amyloid peptides (Aβ), glial fibrillary acidic protein, and tropomyosin-related kinase B (TrkB) were also performed. Our results showed that N-acetylaspartate (NAA) levels increased and myoinositol levels decreased in the BDNF group compared with the PBS group. However, the BDNF group NAA level was still lower than the control group at 6 weeks after infusion. These changes correlated with increased immunoreactivity for TrkB, decreased compact Aβ peptide containing plaques, and decreased Fluoro-Jade B-positive cells in the BDNF-infused mice compared to vehicle controls. These findings demonstrate that 1H-MRS may be a promising means of evaluating the therapeutic effects of BDNF on AD.

To explore the effects of a continuous low-dose of X-ray upon neuronal morphology and expression of microtubule associated protein-2 (MAP-2) in hippocampus of young rats.A total of 18 Sprague-Dawley rats aged 35 days were randomly divided into two irradiated groups and one control group (n = 6 each). The irradiated groups received different doses of 0.2 mGy/d, 1.0 mGy/d for 7 consecutive days while the control group sham radiation. The hippocampal pyramidal cell was observed by HE staining, the expression of MAP-2 by immunohistochemistry and Western blot, and the morphologies of microtubule and synapse in CA1 by electron microscopy.(1) The phenomenon of neurodegeneration was observed in the 1.0 mGy group while the control and 0.2 mGy groups were normal; (2) the average optical density of positive MAP-2 protein significantly decreased in the 1.0 mGy group (0.242 ± 0.017) in the region of CA1 versus the control group (0.282 ± 0.016) (F = 14.419, P = 0.005). And the average optical density of positive MAP-2 significantly increased in the 0.2 mGy group (0.331 ± 0.017) compared with the control group (F = 21.700, P = 0.002). The expression of total MAP-2 significantly decreased in the 1.0 mGy group (0.332 ± 0.001) versus the control group (0.370 ± 0.012) (F = 28.055, P = 0.000). And the expression of total MAP-2 significantly increased in the 0.2 mGy group (0.455 ± 0.018) versus the control group (F = 61.974, P = 0.002); (3) there were the reduction of microtubule and the damage of postsynaptic density (PSD) in the 1.0 mGy group in hippocampal CA1. Increased microtubule and normal synapses were found in the 0.2 mGy group in hippocampal CA1.The expression of MAP-2 is strongly associated with the integrity of hippocampal neurons in young rats. The 0.2 mGy group may promote the proliferation of hippocampal microtubule in hippocampus and further promote the expression of MAP-2. And the damage of microtubule and PSD on neuron could reduce the expression of MAP-2 in the 1.0 mGy group.

To observe and investigate the neuroimaging characters in early progression of transgenic Alzheimer's disease (AD) mice model, and make sure the diagnosis value of 7.0 T high field magnetic resonance microimaging (MRMI).APP/PS-1 transgenic mice aged 3, 6, 9 months and the same aged wild type mice were each divided into 6 groups (6 mice in every groups) based on age. The mice brains were scaned with 7.0T high magnetic field MR. Then the mice were killed. The Aβ immunohistochemistry examination was analyzed in the mice brains specimens, and pathological changes were in comparison with the T(2) weighted imaging in the mice brains.There were a few Aβ plaques in the brains of 6 months APP/PS-1 transgenic mice, while Aβ plaques were increased both in number and volume in the cerebral cortex and hippocampus of 9 months AD mice. The brains of APP/PS-1 double transgenic mice of 3, 6 months and the control group mice were not showed intensity loss on T(2) weighted MR images, while the signal intensity loss was visualized in the cerebral cortex and hippocampus of 9 months AD mice.7.0T high magnetic field MR could display Aβ plaques in the brains of APP/PS-1 double transgenic mice of 9 months and it is helpful to diagnosis early AD.