新时代执法警察常规警情处置中的强制能力缺位研究

新时代执法警察在常规警情处置中的强制能力要达到专业化、职业化要求,能体现出公平正义、规范有效执法。当前仍有大量数据显示执法警察在常规警情处置中受伤甚至牺牲,这说明执法警察的强制能力与新时代要求有差距,因此要重视执法警察常规警情处置中的强制能力提升建设。执法警察在常规警情处置中的强制能力缺位主要体现在强制手段与法规条例要求,以及与极端违法犯罪手段不对等等方面。通过分析发现警察个体自身执法条件和警察组织环境会对执法警察强制手段实施带来影响。一方面,要以维护公安法治权力为导向,加强警察队伍自身执法条件建设;另一方面,要以保障警察执法权益为导向,加强公安机关组织环境建设。

警务改革与国家强制能力建设

近年来,随着社会的多元化和复杂化,原有的社会控制体系越来越不适应社会发展的需求。在这种背景下,中央和地方不断开展警务改革,试图藉此推进国家的强制能力建设。各地的警务改革实践主要有七种模式,这些警务改革模式体现了当前国家强制能力建设的两大核心特征:一方面通过警力下沉强化警察对社会进行控制的'渗透性权力',另一方面则通过执法规范化强调国家对警察进行规训的'抑制性权力'。'渗透性权力'是'抑制性权力'得以发生的前提,而'抑制性权力'是'渗透性权力'得以有效的保障。处理好这两者的辩证关系,是确保新时期国家强制能力建设顺利进行的关键。

新时代外勤警察强制执法能力的缺位

外勤警察强制执法能力要符合新时代的要求。新时代外勤警察强制执法能力存在一些缺位现象,主要体现在应急强制手段与法规条例的不对等、强制执法行为与人民生活需要的不对等、遇袭防卫措施与暴力犯罪环境的不对等、强制执法行动与社会效应的不对等方面。社会环境中存在的制度不完善、警察个体工作胜任条件差、公安机关组织不力、舆情导向偏颇等情况对外勤警察强制执法能力缺位会产生影响,应针对性地加强外勤警察强制执法能力的改善建设。

Effect of thermo-mechanical treatment on microstructure and mechanical properties of wire-arc additively manufactured Al-Cu alloy

Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.

Experiments and modeling of double-peak precipitation hardening and strengthening mechanisms in Al-Zn-Mg alloy

The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing）, was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing） were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.

Aging behavior and mechanical properties of 6013 aluminum alloy processed by severe plastic deformation

Structural features, aging behavior, precipitation kinetics and mechanical properties of a 6013 Al–Mg–Si aluminum alloy subjected to equal channel angular pressing （ECAP） at different temperatures were comparatively investigated with that in conventional static aging by quantitative X-ray diffraction （XRD） measurements, differential scanning calorimetry （DSC） and tensile tests. Average grain sizes measured by XRD are in the range of 66-112 nm while the average dislocation density is in the range of 1.20×10^14-1.70×10^14 m^-2 in the deformed alloy. The DSC analysis reveals that the precipitation kinetics in the deformed alloy is much faster as compared with the peak-aged sample due to the smaller grains and higher dislocation density developed after ECAP. Both the yield strength （YS） and ultimate tensile strength （UTS） are dramatically increased in all the ECAP samples as compared with the undeformed counterparts. The maximum strength appears in the samples ECAP treated at room temperature and the maximum YS is about 1.6 times that of the statically peak-aged sample. The very high strength in the ECAP alloy is suggested to be related to the grain size strengthening and dislocation strengthening, as well as the precipitation strengthening contributing from the dynamic precipitation during ECAP.

Effects of minor Sc and Zr additions on mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys

The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al Zn Mg Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al Zn Mg Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al3(Sc,Zr) and Al3Zr dispersoids. The volume of Al3Zr particles is less than that of Al3(Sc,Zr) particles, but the distribution of Al3(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.

Microstructure evolution and mechanical properties of Al−3.6Cu−1Li alloy via cryorolling and aging

An Al−3.6Cu−1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties.The microstructure and aging characteristics of the room temperature-rolled and the cryorolled alloys with 70%and 90%of thickness reductions were studied by microstructure analysis and mechanical tests.The samples subjected to cryorolling with 90%of thickness reduction have high strength and good toughness.This is mainly due to the inhibition of dynamic recovery and the accumulation of high-density dislocations in cryorolled samples.In addition,the artificial aging reveals that the temperature at which peak hardness is attained is inversely proportional to the deformation amount and directly proportional to the rolling temperature.Moreover,bright field images of cryorolled samples after aging indicate the existence of T1(Al2CuLi)precipitates.This suggests that the high stored strain energy enhances the aging kinetics of the alloy,which further promotes the nucleation of T1 phases.

Effect of double ageing on performance and establishment of prediction model for 6005 aluminum alloy

In the present investigation, the relation of pre-ageing temperature and pre-ageing time to mechanical properties was studied, and a model was established to predict the mechanical properties of AA6005 Al alloy. Compared with the experimental results, the deviation of the proposed model was limited to 8.1%, which showed reasonable accuracy of forecasting. It was found that the performance of AA6005 alloy was better at higher pre-ageing temperature with shorter pre-ageing time than that at T6 temper. The microstructure of the alloy was observed by transmission electron microscopy, and the results showed that high dislocation density and precipitate density existed at 160 ℃ and 200 ℃ pre-ageing, which were in good agreement with the model.

Combined effects of Bi and Sb elements on microstructure,thermal and mechanical properties of Sn−0.7Ag−0.5Cu solder alloys

This research investigated the combined effects of addition of Bi and Sb elements on the microstructure,thermal properties,ultimate tensile strength,ductility,and hardness of Sn−0.7Ag−0.5Cu(SAC0705)solder alloys.The results indicated that the addition of Bi and Sb significantly reduced the undercooling of solders,refined theβ-Sn phase and extended the eutectic areas of the solders.Moreover,the formation of SbSn and Bi phases in the solder matrix affected the mechanical properties of the solder.With the addition of 3 wt.%Bi and 3 wt.%Sb,the ultimate tensile strength and hardness of the SAC0705 base alloy increased from 31.26 MPa and 15.07 HV to 63.15 MPa and 23.68 HV,respectively.Ductility decreased due to grain boundary strengthening,solid solution strengthening,and precipitation strengthening effects,and the change in the fracture mechanism of the solder alloys.

Effect of Ti−6Al−4V particle reinforcements on mechanical properties of Mg−9Al−1Zn alloy

Mg−9Al−1Zn(AZ91)magnesium matrix composites reinforced by Ti−6Al−4V(TC4)particles were successfully prepared via powder metallurgical method.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)showed a mountain-like tendency with the increase of the TC4 content.The mechanical properties of AZ91 magnesium matrix composites reached the optimal point with TC4 content of 10 wt.%,realizing YS,UTS,and EL of 335 MPa,370 MPa,and 6.4%,respectively.The improvement of mechanical properties can be attributed to the effective load transfer from the magnesium matrix to the TC4 particles,dislocations associated with the difference in the coefficient of thermal expansion,good interfacial bonding between the Mg matrix and TC4 particles,and grain refinement strengthening.

霸权的“獠牙”:美国经济制裁制度的生成与进化

在大国之间发动现代战争成本愈发高昂的背景下,经济制裁成为美国在国际舞台上实施霸权强制力的最主要手段。美国之所以能够频繁且大规模地发起经济制裁,除了基于傲视同侪的总体国家实力,还得益于其国内一整套制定并执行经济制裁政策的复杂而完备的制度体系。这一制度体系以商务部工业和安全局以及财政部外国资产控制办公室为双核心,其他行政机构居中相互配合。这些机构在美国发起经济制裁的过程中发挥了主导作用,享有高度的政策自主性和话语权。这些机构在二战后先后受到美国遏制苏联“扩张”、护卫自由秩序和应对大国竞争的霸权战略目标的塑造,在打造和提升霸权强制能力需求的驱动下,历经了早期成长、成熟完善和进化升级三个演进阶段,逐步发展为如今高效运转的职能机构,并构成了美国发起兼具破坏力和威慑性的经济制裁的坚实国内制度基础。以商务部工业和安全局以及财政部外国资产控制办公室为核心的美国经济制裁制度,犹如美国霸权“巨兽”的狰狞“獠牙”,彰显出美国强大的霸权强制能力。