Volatility spillovers,structural breaks and uncertainty in technology sector markets

This study uses the dynamic conditional correlation to investigate how technology subsector stocks interact with financial assets in the face of economic and financial uncertainty.Our results suggest that structural breaks have diverse effects on financial asset connectedness and that the level of bond linkage increases when the trend breaks.We see a growing co-movement between the technology sector and major financial assets when uncertainty is considered.Overall,our findings indicate that the connectedness response varies depending on the type of uncertainty shock.

Exact Geometric Relationships, Symmetry Breaking and Structural Stability for Single-Walled Carbon Nanotubes

We pioneered a study about how the geometric relationship of single-walled carbon nanotubes(SWCNT) is influenced by curvature factor and non-planar geometry factor in cylindrical coordinate system based on the assumption of complete symmetry. The bond length and angle of every carbon-carbon bonds are determined by using the principle of the minimum energy. The results of the paper include(1) From the calculation result, the symmetry breaking appears for chiral carbon nanotubes, while the part symmetry appears for achiral carbon nanotubes with increasing curvature.(2) The synergistic effect of bond lengths and bond angles is first found.(3) We conclude that the influence of non-planar geometry factor can be completely ignored on bond lengths and bond angles when the curvature parameter has been included in the model.(4)The two fractal dimensions are given from the nanoscale to the macroscale for zigzag topology and armchair topology respectively. Fractal dimensions of SWCNT show special characteristics, varying with the length of SWCNT until the lengths approach infinity. The close and inevitable correlations among curvature, symmetry breaking and stability of SWCNTs can be summed up as: the increase of curvature causes symmetry breaking,and such symmetry breaking will further reduce the structural stability.

Factor Vector Autoregressive Estimation of Heteroskedastic Persistent and Non Persistent Processes Subject to Structural Breaks

In the paper, a general framework for large scale modeling of macroeconomic and financial time series is introduced. The proposed approach is characterized by simplicity of implementation, performing well independently of persistence and heteroskedasticity properties, accounting for common deterministic and stochastic factors. Monte Carlo results strongly support the proposed methodology, validating its use also for relatively small cross-sectional and temporal samples.

The role of structural inheritance in continental break-up and exhumation of Alpine Tethyan mantle(Canavese Zone,Western Alps)

The Canavese Zone(CZ)in the Western Alps represents the remnant of the distal passive margin of the Adria microplate,which was stretched and thinned during the Jurassic opening of the Alpine Tethys.Through detailed geological mapping,stratigraphic and structural analyses,we document that the continental break-up of Pangea and tectonic dismemberment of the Adria distal margin,up to mantle rocks exhumation and oceanization,did not simply result from the syn-rift Jurassic extension but was strongly favored by older structu ral inheritances(the Proto-Canavese Shear Zone),which controlled earlier lithospheric weakness.Our findings allowed to redefine in detail(i)the tectono-stratigraphic setting of the Variscan metamorphic basement and the Late Carbonife rous to Early Cretaceous CZ succession,(ii)the role played by inherited Late Carboniferous to Early Triassic structures and(iii)the significance of the CZ in the geodynamic evolution of the Alpine Tethys.The large amount of extensional displacement and crustal thinning occurred during different pulses of Late Carbonife rous-Early Triassic strike-slip tectonics is wellconsistent with the role played by long-lived regional-scale wrench faults(e.g.,the East-Variscan Shear Zone),suggesting a re-discussion of models of mantle exhumation driven by low-angle detachment faults as unique efficient mechanism in stretching and thinning continental crust.

On-Line Structural Breaks Estimation for Non-stationary Time Series Models

Non-stationary time series could be divided into piecewise stationary stochastic signal. However, the number and locations of breakpoints, as well as the approximation function of the respective segment signal are unknown. To solve this problem, a novel on-line structural breaks estimation algorithm based on piecewise autoregressive processes is proposed. In order to find the "best" combination of the number, lengths, and orders of the piecewise autoregressive (AR) processes, the Akaikes Information Criterion (AIC) and Yule-Walker equations are applied to estimate an AR model fit to the data. Numerical results demonstrate that the proposed estimation algorithm is suitable for different data series. Furthermore, the algorithm is used in a clinical study of electroencephalogram (EEG) with satisfactory results, and the ability to deal with real-time data is the most outstanding characteristic of on-line structural breaks estimation algorithm proposed.

Is There Hysteresis in Unemployment in OECD Countries？ Evidence From Panel Unit Root Test With Structural Breaks

This study tests the hysteresis hypothesis of unemployment in fifteen OECD countries by using panel unit root tests which allow for structural breaks. We apply annual unemployment rates covering 1985-2008 periods. We test whether unemployment rates are stationary by using second generation tests which allow cross section dependency among series and panel unit root test based on structural break advanced by Carrion-i-Silvestre, Barrio-Castro and Lopez-Bazo （2005）. We find series as a stationary process with structural breaks according to Carrion-i Silvestre et al. （2005） test, while we find series as unit root process with second generation panel unit root test. According to the Carrion-i Silvestre et al. （2005） test, we find the evidence of absence of hysteresis in analyzed countries. As a result, temporary shocks have temporary effects on unemployment instead of permanent effect. Structural factors can affect the natural rate of unemployment and, therefore, unemployment would be stationary around a process that is subject to structural breaks. So, there still exists a unique natural rate of unemployment to which the economy eventually will converge.

Asymmetric Price Transmission and Structural Breaks in the Relationship between Costa Rican Markets of Livestock Cattle, Beef and Milk

The vertical price transmission is generally considered as the relationship between two markets of the same production chain However, we can expand this concept to another relation which has not been deeply investigated： the joint products. They are the products which are produced in a single production process, but not correspond to the same chain. An especial case is the beef and milk markets in Costa Rica. Even if these products usually correspond to disconnect chains, in Costa Rica farms make use of cattle to produce both meat and milk. The cointegration framework is applied in order to indentify the price transmission among these markets. In addition, the asymmetric behavior and structural breaks are taken into account. Price transmission between each market pair was found. First, the cattle prices adjust in the milk-cattle relationship, second, beef meat prices adjust in the cattle-beef meat and in the milk - beef meat relationship. Finally, the equations allowing for structural breaks affect the estimates in the following three ways： after the break the elasticities became higher than 1, there is more evidence of cointegration, and the adjustment coefficients are significant only when a change in the long run is allowed.

Covariate-Assisted Matrix Completion with Multiple Structural Breaks

In matrix completion,additional covariates often provide valuable information for completing the unobserved entries of a high-dimensional low-rank matrix A.In this paper,the authors consider the matrix recovery problem when there are multiple structural breaks in the coefficient matrix β under the column-space-decomposition model A=Xβ+B.A cumulative sum(CUSUM)statistic is constructed based on the penalized estimation of β.Then the CUSUM is incorporated into the Wild Binary Segmentation(WBS)algorithm to consistently estimate the location of breaks.Consequently,a nearly-optimal recovery of A is fulfilled.Theoretical findings are further corroborated via numerical experiments and a real-data application.

Upper trophic structure in the Atlantic Patagonian shelf break as inferred from stable isotope analysis

The Patagonian Shelf is a very productive region with dif ferent ecosystem structures. A long history of fishing in the Southwestern Atlantic Ocean combined with a complex hydrographic structure, with a permanent front over the shelf-break and dif ferent coastal frontal regions, and a wide non-frontal area in between have made the food web in this area more complex and have resulted in changes to the spatialtemporal scale. Stable isotopes of carbon and nitrogen were used to determine the trophic structure of the Patagonian shelf break which was previously poorly understood. The results indicated that the average δ^(15)N value of pelagic guild(I llex argentinus) was remarkable lower than those of the other guilds. The δ^(13)C values of almost all species ranged from-17‰ to-18‰, but S tromateus brasiliensis had a significant lower δ^(13)C value. Compared with the southern Patagonian shelf, short food chain length also occurred. The impact of complex oceanographic structures has resulted in food web structure change to the temporal-spatial scale on the Patagonian shelf. The Patagonian shelf break can be considered as a separated ecosystem structure with lower δ^(15)N values.

破壁前后灵芝孢子粗多糖含量、结构及单糖组成对比分析

为明确破壁对灵芝孢子粗多糖含量、结构及单糖组成的影响,以灵芝粗多糖提取含量为指标,对灵芝粗多糖的提取工艺进行优化,获得灵芝孢子粗多糖超声辅助水提取的最佳工艺参数为超声温度55℃、超声时间8 h,此工艺条件下从破壁灵芝孢子粉中提取的粗多糖含量为(15.873±0.746)mg/g。采用最佳提取工艺条件提取破壁前后灵芝孢子粗多糖,对比其灵芝孢子粗多糖含量、纯度、DPPH自由基清除率以及单糖组成和多糖结构,结果显示破壁处理后灵芝孢子粗多糖含量提高233.396%,但其纯度下降了19.898%;破壁后灵芝孢子多糖DPPH自由基清除率也有较大提升;破壁处理对灵芝孢子多糖的单糖组成种类没有明显改变,但在单糖含量上存在显著性差异,特别是岩藻糖、半乳糖和甘露糖;红外光谱结果显示破壁前后灵芝孢子粉提取的灵芝孢子粗多糖在结构、组成上无明显差异,均是含有D⁃吡喃葡萄糖环的多糖。

复合材料薄膜盖结构与功能一体化设计

目的解决传统硬质泡沫塑料易碎盖存在的承压能力不足、冲破性能不稳定、不能有效防潮控湿、电磁兼容性差等缺陷。方法以某型导弹武器系统发射筒密封盖为主要应用对象开展薄膜盖设计,主要包括总体结构设计、零部件设计、功能设计及仿真验证。结果薄膜盖经密封、承压、冲破、电磁兼容等性能考核,均满足装备贮存使用要求,冲破盖体所受的最大峰值冲击力可稳定保持在1200~1600 N。结论建立了薄膜盖结构与功能一体化设计方法,可满足在研型号对新型密封盖的设计需求,并为新型号弹箭发射筒大尺寸密封盖的顺利研制提供技术储备。

一种新型四孔异形蜂窝包装夹层结构力学性能研究

目的随着新材料和新结构的发展,包装材料结构要求在包装运输过程中对产品具有更高的保护能力。为了丰富包装材料结构并在保证力学性能条件下设计新型蜂窝结构。方法以传统正六边形蜂窝结构为基础构建新型四孔异形蜂窝结构,通过对可降解树脂材料的试件进行理论分析、仿真分析和实验验证研究其力学特性。结果新型四孔异形蜂窝包装夹层结构横向和纵向的力学性能,相较于传统的正六边形和正八边形蜂窝结构提升了17%,具有更好的外载荷承载能力。结论本研究对包装材料结构给出了新的思路,对包装行业的发展起到支持作用。

基于CEL方法的带结构物溃坝流数值模拟

随着全球气温的不断升高,极端天气现象增多,溃坝现象成为水工结构方向需要重点防范的自然灾害。溃坝流的发展会对下游结构物产生巨大的破坏作用,因此深入探究溃坝流现象的水动力学特性以及溃坝流下游结构物所受到的冲击力影响势在必行。本文针对带有结构物的溃坝流动问题现象,采用CEL方法(Coupled Eulerian-Lagrangian analysis,耦合欧拉-拉格朗日方法),对于溃坝流的发展、演化进行了数值模拟。研究结果表明,模拟结果中溃坝流自由表面及流体尖端时程变化与文献试验结果拟合较好,CEL方法可应用在溃坝流现象的模拟,并且具有较好的准确性和精度。结构物材料性能、高度及与结构物与溃坝流间的位置,均会影响溃坝流的运动状态以及结构物的受力变形状态,在不考虑结构物破坏的情况下,提高结构物弹性模量,增加结构物高度,以及减小结构物与溃坝流间的距离均可提高结构物对于溃坝流的阻挡作用。

玄武岩复合纱线的制备及强伸性能分析

为探究玄武岩复合纱线的强伸性能,分别制备了芯纱为单股、双股的玄武岩包覆纱,分析了玄武岩单股无捻结构芯纱包覆纱、玄武岩双股加捻结构芯纱、玄武岩双股无捻及加捻结构芯纱包覆纱在不同条件下的强伸性能变化规律。研究表明:以单股玄武岩为芯纱,外包不同种类材料如芳纶、超高分子量聚乙烯、锦纶及其复合纱时,纱线的强伸性能变化规律不同;以双股玄武岩为芯纱,复捻锭速在750 r/min且捻度为50捻/m时,芯纱强伸性能稳定,是合适的加捻参数;玄武岩双股加捻结构芯纱包覆纱强力较高,且随着包覆捻度的增大,其断裂强力变化明显小于双股无捻结构芯纱包覆纱。

基于定向挤压的核桃破壳有限元分析及破壳装置设计

针对目前核桃破壳机构适应性不强、破壳率不高、整仁率低的问题,从核桃破壳前定向预处理的视角,探索核桃在破壳加工前果体姿态定向处理对挤压破壳受力的影响因素。同时,以云南漾濞核桃为研究对象,通过3D扫描获取核桃三维实体模型,进行多组过静态压力有限元仿真试验,结果表明:在核桃果体上最佳受力区为核桃中线位置的横径方向,该位置受力最均匀、裂纹扩展效果最佳、最易破壳。基于有限元分析结果,设计出一次破壳与二次破壳相继进行的核桃定向破壳机构,并对核桃的破壳过程进行了力学分析,结果表明:破壳机构中弹簧的刚度系数及锤头旋转角度为影响核桃破壳的关键因素。研究结果可为核桃破壳设备的设计提供有创新意义的理论支撑。

碎冰与圆柱结构相互作用实验技术研究

针对难以开展冰载荷测量的实验难题,设计一套碎冰与圆柱结构相互作用的力学实验方案。制备非冻结模型冰,以微小力传感器为数据采集工具,利用波流水槽开展碎冰与圆柱结构相互作用的力学实验。实验测试不同冰速下的碎冰载荷,对冰载荷实验的现象,冰力特性以及数值精度进行分析。通过与文献结果对比,该实验方案测试所得冰载荷幅值吻合良好,呈现载荷分布的离散现象,展现碎冰与结构的翻转、旋转、堆积现象,为碎冰载荷的技术研究及分析预报奠定基础。

低压直流固态断路器分断特性优化方法研究

为提高在直流系统发生短路故障时固态断路器(SSCB)的分断能力,提出一种考虑分断特性的低压直流固态断路器参数多目标优化方法。首先对短路故障时SSCB的分断流程进行详细分析,通过理论与仿真确定了限流电感LB和金属氧化物压敏电阻的限电压能力系数γ对分断特性的影响。以分断特性为基础,建立了SSCB的分断冲击性能指标、分断时间指标、能量吸收指标三个优化目标函数,通过多目标粒子群算法对目标函数进行优化,采用结合决策者偏好的逼近于理想解的排序方法对优化方案进行决策。优化结果表明,在各种决策者偏好下的优化方案,其优化设计后的元件参数LB和γ均能显著提高SSCB的分断性能。

视电阻率法在隐伏岩溶灾害调查中的应用

隐伏岩溶发育引起的地面塌陷和地裂缝等地质灾害频繁发生,提高勘查方法和解译精度在隐伏岩溶区灾害调查中尤为重要。视电阻率法数据处理、反演算法以及综合解译方法的进步为地质灾害调查提供了有力手段。本文引入视电阻率三维模型,结合二维剖面分析,对采集的视电阻率数据进行综合整理,丰富了数据处理方法,提高了数据模块关联性,有效提高了解译精度和地质模型契合度。结合钻探验证情况对泰安市桥沟地区隐伏岩溶塌陷区进行分析研究,通过隐伏岩溶发育区的视电阻率特征,分析岩溶发育范围和成因,为隐伏岩溶区灾害调查提供了良好的地球物理应用和参考价值。

基于多目标遗传算法的PDC复合片交界结构优化设计

为改善PDC复合片界面处的结合能力,提升其整体的抗冲击性和稳定性,提出了一种新型交界结构。采用有限元方法,对比了外界载荷影响下所设计交界结构和常规界面结构复合片的应力分布状态,并基于提出的交界结构,考虑其结构参数的影响,使用最优填充空间法进行采样,结合最小二乘法构建了结构场的二阶响应面近似模型;以交界结构参数为设计变量,结构场等效应力、最大剪应力和最大主应力的最大值为设计目标,采用多目标遗传算法对响应面近似模型进行优化。研究结果表明,相同模拟条件下,相比常规交界结构,新型交界结构的等效应力最大值降低了50.7%,剪应力最大值降低了52.0%,最大主应力最大值降低了22.4%。优化后的PDC复合片在相同条件下,等效应力、最大剪应力及最大主应力均降低14%以上,且具有更好的破岩稳定性,能有效避免应力集中,同时热稳定性增强。研究结果为PDC复合片优化设计提供了理论依据,同时提供了新的优化方法,有助于降低研发成本。

高压电脉冲刺激对于热处理花岗岩影响的实验研究

高压电脉冲技术作为一种环保、可控、高效的破碎坚硬岩石的方法,其潜在应用场景值得进一步深入发掘。本文研究了高压电脉冲诱导干热岩产生预损伤和劣化方法的效果。对热处理后花岗岩薄片试样施加了不同峰值电压的高压电脉冲刺激,探讨了高压电脉冲对于热处理花岗岩的影响。此外,还研究了初始温度对高压电脉冲刺激花岗岩的影响。结果表明:当外加峰值电压超过96 kV时,热处理花岗岩试样发生贯穿性的破裂,峰值电压越高,贯穿裂纹网络越复杂。当电压从96 kV增加到144kV时,花岗岩试样的微裂纹密度从8.63 mm/mm^(2)增加到13.26 mm/mm^(2)。随着热处理温度的升高,花岗岩发生电击穿的难度逐渐降低。在120 kV电脉冲放电刺激3次后,所有热处理温度高于400℃的花岗岩试样均能发生贯穿破裂。高压电脉冲刺激造成花岗岩产生的最大损伤发生在300~400℃的温度区间内。通过扫描电子显微镜观察到,随着试样处理温度的升高,内部孔隙和裂缝的发育情况逐渐加剧,孔隙大小、裂缝宽度和深度也随之增加。这项研究有望为建造干热岩人工储层提供新的见解。