无粘性颗粒堆底的应力分布

从弹性理论出发 ,推导出了变系数弹性模型。利用此模型 ,计算了二维沙堆式样里的应力分布 ,得到了试样底面应力分布曲线有低陷的结论 ,并用不同方法验证了模型的稳定性与准确性。

Charge-balanced codoping enables exceeding doping limit and ultralow thermal conductivity

Materials with low thermal conductivity are applied extensively in energy management,and breaking the amorphous limits of thermal conductivity to solids has attracted widespread attention from scientists.Doping is a common strategy for achieving low thermal conductivity that can offer abundant scattering centers in which heavier dopants always result in lower phonon group velocities and lower thermal conductivities.However,the amount of equivalent heavyatom single dopant available is limited.Unfortunately,nonequivalent heavy dopants have finite solubility because of charge imbalance.Here,we propose a charge balance strategy for SnS by substituting Sn2+with Ag^(+)and heavy Bi^(3+),improving the doping limit of Ag from 2%to 3%.Ag and Bi codoping increases the point defect concentration and introduces abundant boundaries simultaneously,scattering the phonons at both the atomic scale and nanoscale.The thermal conductivity of Ag0.03Bi0.03Sn0.94S decreased to 0.535 W·m^(−1)·K^(−1)at room temperature and 0.388 W·m^(−1)·K^(−1)at 275°C,which is below the amorphous limit of 0.450 W·m^(−1)·K^(−1)for SnS.This strategy offers a simple way to enhance the doping limit and achieve ultralow thermal conductivity in solids below the amorphous limit without precise structural modification.

Hyperhomocysteinemia independently causes and promotes atherosclerosis in LDL receptor-deficient mice

Background Hyperhomocysteine is an independent risk factor of coronary heart disease （CHD）. However, whether hyperhomocys teine affects the progression of atherosclerosis is unclear. In the present study, we examined the effect of hyperhomocysteine on the forma tion of atherosclerosis in low-density lipoprotein receptor-deficient （LDLr ） mice. Methods Forty-eight 7-week-old LDLr/ mice were assigned to the following groups： mice fed a standard rodent diet （control group）, mice fed a high-methionine diet （high-methionine group）, mice fed a high-fat diet （high-fat group）, and mice fed a diet high in both methionine and fat （high-methionine and high-fat group）. At the age of 19, 23, and 27 weeks, four mice at each interval in every group were sacrificed. Results At the end of the study, mice did not show atherosclerotic lesions in the aortic sinus and aortic surface until 27 weeks old in the control group. However, atherosclerotic lesions developed in the other three groups at 19 weeks. The amount of atherosclerotic lesions on the aortic surface was lower in the high-methionine group than in the high-fat group （P 〈 0.001）. Atherosclerotic lesions on the aortic surface in the high-methionine and high-fat group were the most severe. The mean area of atherosclerotic lesions in the aortic sinus compared with atherosclerotic lesions on the aortic surface was lower in the high-methionine group than in the high-fat group （P 〈 0.001）. Atherosclerotic lesions in the aortic sinus in the high-methionine and high-fat group were the most severe. Conclusions Homocysteinemia accelerates atherosclerotic lesions and induces early atherosclerosis independently in LDLrmice. Reducing the level of homocysteinemia may be beneficial for prevention and treatment of CHD.

Building surface defects by doping with transition metal on ultrafine TiO_2 to enhance the photocatalytic H_2 production activity

Inefficient charge separation and limited light absorption are two critical issues associated with high‐efficiency photocatalytic H2production using TiO2.Surface defects within a certain concentration range in photocatalyst materials are beneficial for photocatalytic activity.In this study,surface defects(oxygen vacancies and metal cation replacement defects)were induced with a facile and effective approach by surface doping with low‐cost transition metals(Co,Ni,Cu,and Mn)on ultrafine TiO2.The obtained surface‐defective TiO2exhibited a3–4‐fold improved activity compared to that of the original ultrafine TiO2.In addition,a H2production rate of3.4μmol/h was obtained using visible light(λ>420nm)irradiation.The apparent quantum yield(AQY)at365nm reached36.9%over TiO2‐Cu,significantly more than the commercial P25TiO2.The enhancement of photocatalytic H2production activity can be attributed to improved rapid charge separation efficiency andexpanded light absorption window.This hydrothermal treatment with transition metal was proven to be a very facile and effective method for obtaining surface defects.

Characteristics and mechanism of low permeability beach-bar sandstone reservoir of Es4 in Dongying sag

Core and cast sections observation and description,and logging,scanning electron microscope and core lab analysis data etc. were applied to the present research of the characteristics and mechanism of low permeability beach-bar sandstone reservoir of Es4 in Dongying sag. The results indicated the reservoir has the characteristics of middle-low pores,low-permeability,low compositional and structural maturity,and thin throat. The low-permeability is mainly due to sedimentation (fine particles and argillaceous inter beds) and diagenesis (compaction,cementation,and dissolution). The cementation reduced the physical property of the reservoir mainly by carbonate cementation,quartz autogeny and enragement,and autogeny clay. Clay minerals usually jam the pores by filling holes,close-fitting the wall of hole,bridging,wrapping grains,and separate attaching the pores and so on. The dissolution is insufficient so as not to improve the porosity and permeability of the reservoir obviously. So it is also an important factor of forming low-permeability reservoir.

Effect of coating material and lubricant on forming force and surface defects in wire drawing process

A pilot wire drawing machine as well as wire end-pointing roller was developed. Using these machines, a wire drawing test for four different coating materials and two different lubricants was performed as the reduction ratio increased from 10% to 30%. Materials used for a substrate in this study are plain carbon steel （AIS11045） and ultra low carbon bainite steel. To compute the friction coefficient between the coating layer of wire and the surface of die lbr a specific lubricant, a series of finite element analyses were carried out. SEM observations were also conducted to investigate the surface defects of wire deformed. Results show that the behavior of drawing force varies with the lubricant-type at the initial stage of drawing. The powder-typed lubricant with a large particle causes the retardation of lull lubrication on the entire contact surface and the local delamination of coating layer on the wire surface. As the flow stress of a substrate increases, the delamination becomes severe.

Design of UWB Band-pass Filters with GPS Band Rejection

This paper presents a compact Ultra-Wideband （UWB） band-pass filter using a high-pass filter and a low-pass one, and the resonator with lumped elements. The structure of our proposed bandpass filter is very simple and the Defected Ground Structure（DGS） structure is used to get the low-pass filter characteristics. This proposed band-pass filter can be much smaller than a cascaded type filter. As a result of simulation, the insertion loss is less than 0.3 dB throughout the pass-band of 2.2 GHz- 10.6 GHz, while the return loss is more than 18 dB. And it has rejection level of 36 dB at GPS band.

Squamous cell carcinoma of the anus-an opportunistic cancer in HIV-positive male homosexuals

Squamous cell carcinoma of the anus （SCCA） is a com- mon cancer in the human immunodeficiency virus （HIV）- infected population, and its incidence continues to in- crease in male homosexuals. Combined chemoradiation with mitomycin C and 5-fiuorouracil was poorly tolerated by severely immunocompromised patients in the early 1990s. In the era of highly active antiretroviral therapy （HAART）, however, recent data indicate that： （1） most HIV patients with anal cancer can tolerate standard chemotherapy regimens; and （2） this approach is associ- ated with survival rates similar to those of HIV-negative patients. However, HIV-positive patients with SCCA are much younger, more likely to develop local tumor recur- rence, and ultimately die from anal cancer than immune competent patients. Taken together, these findings suggest that anal cancer is an often fatal neoplasia in mid- dle-aged HIV-positive male homosexuals. In this popula- tion, SCCA is an opportunistic disease resulting in patients with suboptimal immune function from persistent infection and prolonged exposition to oncogenic human papillomaviruses （HPVs）. Large-scale cancer-prevention strategies （routine anuscopy and anal papanicolaou test- ing） should be implemented in this population. In addi- tion, definitive eradication of oncogenic HPVs within the anogenital mucosa of high-risk individuals might require a proactive approach with repeated vaccination.

Photoluminescence and defect evolution of nano-ZnO thin films at low temperature annealing

Nano-ZnO thin films composed of nanoparticles with sizes of 10-16 nm on silicon substrates at low temperature were prepared by sol-gel method.By placing the nano-ZnO thin films at room temperature or annealing at 100°C in air for 10 h intermittently,within a total 70 h annealing time,the evolution of PL spectra of the nano-ZnO thin films were studied in detail.As the annealing time increases,the PL peaks shift from violet to blue and green bands.The PL peaks at violet and blue bands decrease with the annealing time,but the PL peaks at green band are opposite.The PL spectra are related to the defects in the nano-ZnO thin films.The PL peaks positioned at 430 nm are mainly related to defects of zinc interstatials(Zni),oxygen vacancies and(Vo);the ones at 420 nm to oxygen interstitials(Oi),Zinc vacancies(Vzn),Zni ;and the ones at 468 nm to Vzn,Zni,and charged oxygen interstatials(Vo+).The green luminescence is related to Oi,Vo and Zni.The evolutions of PL spectra and the defects are also related to the concentrations of Zn in the thin films,the thicknesses of the films and the annealing time.For the films with 0.5 M and 1.0 M Zn concentrations,after 20 h and 30 h annealing in air at 100°C,respectively,either placing them in air at room temperature or continuing anneal in air at 100°C,the PL spectra are stable.Under the low temperature annealing,Zni decreases with the annealing time,and Oi increases.Sufficient Oi favors to keep the nano-ZnO thin films stable.This result is important to nano-ZnO thin films as electron transport layers in inverted or tandem organic solar cells.

Effect of Cu on the boron segregation at grain boundaries and vacancy-type defects in ultra-low carbon micro-alloy steels

By thermal neutron irradiation particle tracking autoradiography(PTA)technique,the development of boron segregation at grain boundaries in ultra-low carbon micro-alloy steels was investigated during cooling from 1150°C to 850°C,and the effect of Cu on boron segregation at grain boundaries was discussed.By positron annihilation lifetime(PAL)technique,the changes of vacancy-type defects with temperatures and the effect of Cu on vacancy-type defects in the cooling process were discussed.Results show that,the concentration of boron at grain boundaries increases rapidly at the beginning of the cooling;after that,it begins to decrease;and then,it increases gradually again.The addition of Cu not only increases the concentration of boron at grain boundaries but also speeds up the development process of boron segregation at grain boundaries.During the continuous cooling process,the addition of Cu significantly affects the change of vacancy-type defects with temperatures in ultra-low carbon micro-alloy steels.