基于机器学习算法的盾构掘进地表沉降预测方法

针对有限元、地层损失率等方法难以考虑多参数耦合作用情况下的地表沉降预测的问题,基于BP神经网络(BPNN)和随机森林算法(RF)两种机器学习算法的多参数、非线性拟合能力,提出了预测盾构掘进过程中地表最大沉降以及纵向沉降曲线的预测方法.通过粒子群算法(PSO)确定机器学习算法的最优超参数,通过k折交叉验证方法提高预测方法的鲁棒性.结果表明BP神经网络的预测结果误差较大,难以预测到较大的地表沉降,随机森林算法能够准确预测地表最大沉降和纵向沉降曲线.     

Oxygen-rich carbon-nitrogen quantum dots as cocatalysts for enhanced photocatalytic H2 production activity of TiO2 nanofibers

We developed an one-step hydrothermal method to synthesize carbon-nitrogen quantum dots(CNQDs) with oxygen-rich functional groups.The sample was characterized by TEM,AFM,FT-IR,XPS,UV-vis absorption and PL spectra.The 0/C and N/C atomic ratio of typical CNQDs with diameters of 3-6 nm are ca.0.4 and 0.2,respectively.Without noble metal cocatalyst,the photocatalytic H_2 production rate of CNQDs/TiO_2 nanofibers(NFs)(112.4 μmol h~(-1) g~(-1)) is 1.8 times higher than that of TiO_2 NFs.The good absorption of light contributes to the enhanced photocatalytic H_2 performance.The CNQDs could be promising in biomedical imaging,optical data recording storage and photo/electrocatalysis,etc.     

点网成金——来自上网企业的报告

面对互联网时代全球经济一体化的挑战,企业上网的重要性和紧迫性似乎无需多言。关键在于,我国的传统企业到底该如何上网?上网后做些什么?电子商务大势所趋,尽管还远未成熟,但传统企业应该如何投身电子商务?是非常值得探讨的问题。     

基于民族数学背景下的新疆少数民族数学教育——以维吾尔族数学文化为例

少数民族地区数学教育质量不高与教学情境脱离学生的实际生活有关,与学生原有认知结构不产生联系的背景知识会使学习者学习新知识的效率下降。少数民族的数学教育要充分考虑到学生的文化背景,重视少数民族地区民族数学文化课程开发,民族数学教学案例的编写,结合学生实际按照"情景——问题"模式进行课堂教学,进而提高少数民族数学教育质量,促进民族地区的教育发展和人才培养。     

Microstructure and mechanical properties of the micrograined hypoeutectic Zn–Mg alloy

A biodegradable Zn alloy, Zn–1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures: gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples’ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness (Hv = 122 MPa), compressive yield strength (382 MPa), tensile yield strength (332 MPa), ultimate tensile strength (370 MPa), and elongation (9%). This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall–Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.     

基于STM32的煤矿井下传感器软件安全升级系统

为了探讨纵截面异形桩的受扭性状,考虑桩身纵向变截面特性,将桩-土体系沿深度方向划分为有限个微元段,建立均质地基中纵截面异形桩受扭弹塑性分析理论模型;基于传统圆形桩桩顶T-φ曲线与桩身扭矩、转角关系曲线,推导获得纵截面异形桩的桩身扭矩和扭转角近似解答,并基于MATLAB编制了相应的计算程序.继而,初步探讨了纵截面异形桩与等截面圆形桩受扭性能的异同点,并开展楔形桩受扭性能影响因素分析.研究结果表明:上端桩身直径对抗扭承载性能影响显著;等体积混凝土用量下,纵截面异形桩的抗扭性能相对优于等截面圆形桩,且楔形桩抗扭性能最优;相同桩顶扭矩荷载下,楔形桩抗扭承载力随桩身剪切模量、桩径、楔角的增加而增大,桩径提高1倍,桩顶抗扭承载力提高3～5倍.     

钢纤维间距对UHPC双丝拉拔性能的影响

通过双根钢纤维拉拔试验,研究超高性能混凝土（UHPC）中钢纤维间距（2?mm、 4?mm、6?mm、8?mm、10?mm和12?mm）对钢纤维在UHPC中拉拔性能的影响,采用0.2?mm的镀铜直圆形钢纤维,制作6组双丝试件和1组单丝试件进行拉拔试验. 通过拉拔荷载-滑移曲线、平均黏结强度、钢纤维最大拉拔应力等参数,并结合扫描电子显微镜（SEM）,观察了拔出后钢纤维的微观外貌、UHPC基体的隧洞微观形态和破坏部位的微观形态,全面分析了钢纤维的间距对UHPC基体-钢纤维拉拔性能的影响. 试验结果表明：钢纤维拉拔结果具有一定的离散性;双丝拉拔试验的最大拉拔荷载小于相应单丝结果的两倍;钢纤维和UHPC基体隧洞有着不同程度的损伤,双丝试件中的钢纤维表面划痕和基体隧洞的孔洞破坏较单丝严重,单丝试件的隧洞内壁则相对完整.     

新疆和田地区城镇化与土地生态系统服务价值耦合关系研究

了解城镇化与生态系统服务价值之间的耦合关系对生态管理和政策制定具有重要意义.基于城镇化与生态系统服务综合指标体系,采用价值系数法、熵值法与耦合协调度模型分别估算了和田地区各县市的生态系统服务价值、城镇化水平、城镇化与生态系统服务价值以及各子系统之间的互动胁迫关系.研究表明:和田地区各县市城镇化综合水平显著上升,生态系统...     

Rediscovery of the Neotoma population on Datil [Turner] Island, Sonora, México

On Datil [Turner] Island in the Gulf of California, we rediscovered a population of Neotoma varia, previously thought to be extinct. We captured 5 specimens: 1 was kept as a voucher, and 4 were examined and released. Analysis of previous surveys indicates that N. varia is not common on the island and occupies a very restricted range. Recolectamos especímenes de Neotoma varia de la Isla Dátil en el Golfo de California, una población anteriormente considerada ya extinta. De los cinco especímenes que recolectamos, cuatro se pusieron en libertad. El análisis de muestreos previos indica que N. varia no es común en la isla y que tiene una distribución muy limitada.     

Action mechanisms of a new erythrocyte-derived depressing factor

To investigate the action mechanisms of a new erythrocyte-derived depressing factor (EDDF), the focus is placed on the effect of EDDF on both cytosolic and nuclear free calcium (Ca²⁺) transportation in vascular smooth muscle cell (VSMC), as well as the apoptosis and cell cycle of VSMC of rats. EDDF has been extracted from human erythrocytes. The changes of Ca²⁺ levels in cytoplasm ([Ca²⁺]_i) and nucleus ([Ca²⁺]_n) have been observed using a laser scanning confocal microscope together with fluo-3/AM as a calcium indicator. Flow cytometric technique was used to study the effect of EDDF on cell cycle and apoptosis of VSMC. [Ca²⁺], and [Ca²⁺]_n were significantly decreased through several different pathways: ( i ) it reduced the Ca²⁺ influx by blocking L-type voltage-dependent calcium channel (L-VDC) and R-type voltage-dependent calcium channel (R-VDC); (ii) it inhibited the Ca²⁺ release from inositol 1, 4, 5-trisphosphate (IP₃) sensitive calcium store; and (iii) activated Ca²⁺-ATPase of sarcoplasmic reticulum (SR) and promoted the transportation of Ca²⁺ from cytoplasm to SR. However, EDDF seemed to have little inhibitory effect on the Ca²⁺ release from ryonodine sensitive calcium pool. It was also found that EDDF (10⁻⁴ g/mL) significantly decreased the proportion of S phase of human umbilical vein (HUV) and inhibited the proliferation of VSMC induced by angiotensin II (Angll, 10⁻⁵ mol/L). The apopotosis did not occur when VSMC was cultured under normal condition. While VSMC apoptosis was induced by Angll (10⁻⁵ mol/L) and EDDF (10⁻⁴ g/mL) seemed to have little effect on it. The inhibitory effect of EDDF on the elevation of [Ca²⁺]_i and [Ca²⁺]_n of VSMC might play an essential role in its action mechanisms and the ways it affects the Ca²⁺ handling of VSMC demonstrate that EDDF was different from other endogenous blood pressure regulators and some known antihypertensive drugs. EDDF could inhibit the proliferation of VSMC, which indicated that it might be beneficial to the prevention and treatment of hypertension and arteriosclerosis.