The evolution of massive stars to explosion

We review the possible evolutionary paths from massive stars to explosive endpoints as various types of supernovae associated with Population I and hence with massive stars: Type II-P, Type II-L, Type Ib, Type Ic, and the hybrid events SN 1987K and SN 1993J. We identify SN 1954A as another hybrid event from the evidence for both H and He in its spectrum with velocities nearly the same as SN 1983J. Evidence for ejected⁵⁶Ni mass of 0.07 M suggests that SN II-P underwent standard iron core collapse, not collapse of an O–Ne–Mg core nor thermonuclear explosion of a C–O core. Most SN II-P presumably arise in single stars or wide binaries of 10–20 M. There may be indirect evidence for duplicity in some cases in the form of strong Ba II lines, such as characterized SN 1987A. SN II-L are recognizably distinct from typical SN II-P and must undergo a significantly different evolution. Despite indications that SN II-L have small envelopes that may be helium enriched, they are also distinct from events like SN 1993J that must have yet again a different evolution. The SN II-L that share a common Luminosity seem to have ejected a small nickel mass and hence may come from stars with O–Ne–Mg cores. The amount of nickel ejected by the exceptionally bright events, SN 1980K and SN 1979C, remains controversial. SN Ib require the complete loss of the H envelope, either to a binary companion or to a wind. The few identified have relatively large ejecta masses. It is not clear what evolutionary processes distinguish SN Ib's evolving in binary systems from hybrid events that retain some H in the envelope. SN Ic events are both H and He deficient. Binary models that can account for transfer of an extended helium envelope from low mass helium cores, 2 to 4 M, imply C–O core masses that are roughly consistent with that deduced from the ejecta mass plus a neutron star, 2 to 3 M. It is possible that the hybrid events are the result of Roche lobe overflow and that the pure events, SN Ib or SN Ic, result from common envelope evolution.     

Mg/Al合金粉末热压烧结中相变扩散过程研究

利用OLYMPUS GX71金相显微镜及EDS对Al-15％Mg热压烧结样品进行金相显微组织观察与成分分析,探讨烧结过程中组织演变过程。实验结果表明：热压烧结过程中两种粉体发生互扩散,首先在Mg颗粒边缘形成γ（Al12Mg17）相,而后随扩散的进行γ相转变为β（Al3Mg2）相,Mg颗粒由外向内不断的形成γ相,而后不断的转变为β相,直到全部生成β相。随温度的降低,β相会以极其细小的颗粒形式析出;利用真空热压烧结方法在420℃,150Mpa下保压3—4h进行固相烧结获得密度低于2．5g／cm^3致密度达98％以上的Al—15％Mg合金。     

超高分子量聚乙烯纤维/碳纤维混杂复合材料研究

研究了在层内和层间两种混杂方式下,T300与表面处理前后的超高分子量聚乙烯（UHMWPE）纤维混杂复合材料的弯曲强度和ILSS的变化,结果表明层间混杂复合材料的黏结性比层内混杂好。在相同的混杂方式下,采用未处理的DC88纤维、合成的VE树脂,混杂复合材料的ILSS比E 51体系提高25%以上。采用VE树脂和处理后DC88/T300层间混杂,控制含胶质量在40%时,ILSS达到42.5MPa,是未处理的DC88/E 51体系的ILSS的5倍。混杂复合材料密度在1.12～1.24g/cm³之间,在航空航天结构材料减重上有良好的应用前景。     

Effects of Hybrid Voltages on Oxide Formation on 6061 Al-alloys During Plasma Electrolytic Oxidation

Plasma electrolytic oxidation (PEO) is carried out on 6061 Al-alloys in a weak alkaline electrolyte containing NaOH, Na₂SiO₃ and NaCl. Centered on the correlation of composition and structure, analyses by means of X-ray diffration (XRD), scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) are conducted on the specimens, which have been PEO-treated under hybrid voltages of different direct current (DC) values (140-280 V) with constant alternate current (AC) amplitude (200 V). Attention is paid to the composition, properties and growth mechanism of oxide layers formed with hybrid voltages. Moreover, the main effects of DC value are discussed. Ceramic layers with a double-layer structure which combines hard outer and soft inner layers are found to be consist of α-Al₂O₃, γ-Al₂O₃ and mullite. With the DC values increasing, the growth of the ceramic layers tends to have increasingly obvious three-stage feature.     

Ion Temperatures as Observed in a Solar Coronal Hole

From the widths of the extreme ultraviolet (EUV) lines measured by the SUMER instrument on SOHO, it was found previously (Tu et al. 1998) that the average temperature of Ne⁺⁷, at heights (relative to h₀) above the southern solar limb from 17″ to 64″, ranges between 1.3 and 5 × 10⁶ K and of Ne⁺⁶ between 1 and 4 × 10⁶ K. For mass-per-charge numbers greater than 4 the temperatures of the ions increase slightly with increasing mass-per-charge, while the thermal speed reveals no clear trend. We present a new data set with exposure times much longer than the ones in the previous study. The results obtained from line width analysis of Fe XII (1242 Å), Mg X (1249 Å), Mg VIII (772 Å) Ne VIII (770 Å), and Si VIII (1445 Å) support our previous study. In this case, the trend of increasing temperature begins at a mass-per-charge number of 3. A qualitative explanation based on ion-cyclotron-resonance heating within linear kinetic theory is suggested.     

结构参数对两相冲压发动机喷管性能影响分析

为了分析气液两相冲压发动机的喷管参数对推力及效率的影响,分别针对不同参数条件下喷管中泡状气液两相流场,基于双流体模型,采用变步长的Runge-Kutta法进行数值模拟。并对喷管中临界泡状流进行分析,重点研究了喷管喉部与入口面积比、半扩张角和半收缩角在各种气液质量流率比条件下对喷管推力及推进效率的影响,计算结果表明,推力随着喷管喉部与入口面积比增大而减小,气液质量流率比较大时,效率随其增大而增大;半扩张角增大时,推力和效率同时减小;半收缩角对喷管推力及效率影响均不大。在给定的喷管参数下,气液质量流率比在一定程度上增大时,喷管推力及效率同时增大。     

金属间化合物Ho_2Co_(17-x)Si_x的磁性能机制研究

研究了非磁性原子Si替代Co对Ho2 Co17金属间化合物结构和磁性的影响。X射线衍射表明 ,所有Ho2 Co17 xSix(x =0 .5 ,1.0 ,1.5 ,2 .0 ,2 .5 ,3.0 )化合物都为Th2 Ni17型六角结构 ;化合物的晶格常数和单胞体积都随Si含量的增加而呈线性下降。磁性测量表明 ,Ho2 Co17 xSix 化合物的居里温度和饱和磁化强度均随Si含量的增加而呈线性下降。从热磁曲线测量观察到 ,当 0 .5≤x≤ 3.0时Ho2 Co17 xSix 化合物出现由易面到易轴的自旋重取向 ,自旋重取向温度Tsr随Si原子含量的增加先下降 ,而后又上升 ,在x =2 .5处出现最低点。     

Thermoelectric Properties of Mg_2Si_(1-x)Sn_x Synthesized by Bulk Mechanical Alloying

Bulk mechanical alloying (BMA) has been successfully applied to solid-state synthesis of p-type and n-type thermoelectric mate-rials Mg2Si1–xSnx (x = 0, 0.2, 0.4, 0.6, 0.8, 1) from element-powders at the room temperature in a relatively short time. The electrical conductivity, the Seebeck coefficient and the thermal conductivity of the Mg2Si1–xSnx are quite sensitive to the x-content. With the x-content rising, the electrical conductivity increases. When x = 0.6, it reaches the lowest and Mg2Si shows an n-type of semi-conducting. However, when x = 0.2 and T >525 K, the Seebeck coefficient of the samples will change the opposite way. While x≥0.4, the samples present a p-type of semi-conducting. The figure of merit, Z of Mg2Si1–xSnx will be obtained in the range from 300 K to 700 K. When x = 0.6, Z proves to be higher than that of other samples at 300 K≤T≤650 K.     

工艺参数对2A12铝合金微弧氧化陶瓷层生长的影响

研究了正／负向电流密度、频率和正／负向占空比对铝合金微弧氧化陶瓷层生长的影响,采用扫描电子显微镜（SEM）和X射线衍射仪（XRD）,分析了不同氧化时间陶瓷层表面和截面形貌、成分和相组成,讨论了陶瓷层的生长过程。研究表明,正／负向电流密度相同时,随电流密度的增加膜层厚度增大;而当正向电流密度相同时,负向电流密度增加有利于膜层的生长;成膜速率随脉冲频率和负向占空比增加,均呈现先增大后减小的趋势;陶瓷层总厚度随氧化时间接近于线性增长,致密层占总膜层的比例先快速增加,其后略微下降。SEM结果显示,随氧化时间延长,样品表面膜厚度趋于均匀,界面处氧化膜变得比较平坦。陶瓷层主要由α—Al2O3和γ-Al2O3相组成,随氧化时间的延长,γ-Al2O3相在陶瓷层中的相对含量逐渐减少。而α-Al2O3相的含量逐渐提高。     

The Engineering Radiation Monitor for the Radiation Belt Storm Probes Mission

An Engineering Radiation Monitor (ERM) has been developed as a supplementary spacecraft subsystem for NASA’s Radiation Belt Storm Probes (RBSP) mission. The ERM will monitor total dose and deep dielectric charging at each RBSP spacecraft in real time. Configured to take the place of spacecraft balance mass, the ERM contains an array of eight dosimeters and two buried conductive plates. The dosimeters are mounted under covers of varying shielding thickness to obtain a dose-depth curve and characterize the electron and proton contributions to total dose. A 3-min readout cadence coupled with an initial sensitivity of ～0.01 krad should enable dynamic measurements of dose rate throughout the 9-hr RBSP orbit. The dosimeters are Radiation-sensing Field Effect Transistors (RadFETs) and operate at zero bias to preserve their response even when powered off. The range of the RadFETs extends above 1000 krad to avoid saturation over the expected duration of the mission. Two large-area (～10 cm²) charge monitor plates set behind different thickness covers will measure the dynamic currents of weakly-penetrating electrons that can be potentially hazardous to sensitive electronic components within the spacecraft. The charge monitors can handle large events without saturating (～3000 fA/cm²) and provide sufficient sensitivity (～0.1 fA/cm²) to gauge quiescent conditions. High time-resolution (5 s) monitoring allows detection of rapid changes in flux and enables correlation of spacecraft anomalies with local space weather conditions. Although primarily intended as an engineering subsystem to monitor spacecraft radiation levels, real-time data from the ERM may also prove useful or interesting to a larger community.     

Solar EUV and UV Emission Line Observations Above a Polar Coronal Hole

The roll manoeuvre of SOHO on September 3, 1997 provided the opportunity to study the northern coronal hole with SUMER slits in east-west orientation, so that polar plumes and inter-plume lanes could be observed simultaneously. A preliminary analysis of the observations shows that lines emitted by ions with the lowest formation temperatures (with the exceptions of Ne⁷⁺ and Ar⁷⁺) have the largest ratios of plume to lane radiances at heights between 35 000 km and 70 000 km above the photosphere. All lines have narrower widths inside plumes than outside. Electron densities have been deduced in plumes and lanes from Si VIII and Mg VIII line radiance ratios. The Mg IX pair was used to determine the corresponding electron temperatures. Neon (with a high first-ionization potential) is found to be less abundant relative to magnesium (with low FIP) in a plume compared to an inter-plume lane, but the variation is smaller than previously determined Ne/Mg abundance ratios in a plume relative to the photosphere. This revised version was published online in June 2006 with corrections to the Cover Date.     

碳化硅反射镜材料性能预测

预测了反应烧结SiC（RBSiC）的物理及部分力学性能与游离Si含量的变化关系，并对预测值与测量值进行比较以验证其符合程度。经预测，随Si含量的增加，RBSiC的密度呈线性下降，尤其是气孔对材料密度的影响非常明显;线膨胀系数和热导率均应呈加速上升趋势，比热容稍有下降；各模量均有下降趋势。随着气孔的增加，RBSiC的膨胀量变化不明显，比热容和热导率均呈减速下降趋势。RBSiC测量值与预测值产生偏差是因为材料中Si含量的增加导致缺陷增多以及计算性能用数据有偏差所致，但预测仍能较符合RBSiC性能随Si含量变化趋势，因此认为预测值较为合理可作为性能参考值使用。     

FeCoVSiB非晶合金磁性能的研究

研究了Fe78Co5V2 Si6 B9非晶合金有效磁导率 μ′、损耗P随频率、磁场强度的变化 ;根据材料使用温度的不同 ,同时研究了在 0 .6 4A m磁场下 ,磁导率随温度的变化。研究表明 ,磁场强度一定时 ,Fe78Co5V2Si6 B9非晶合金的有效磁导率随频率增加而降低 ;频率一定时 ,有效磁导率随磁场强度的增加而增加 ;铁芯损耗均随频率、磁场强度的增加而增加 ;非晶态合金Fe78Co5V2 Si6 B9经不同温度、不同保温时间热处理后 ,磁导率随使用温度的变化 ,自室温始先略有增大 ,而后 ,随温度升高而降低     

空间电离辐射对镧系光学玻璃透射率的影响

利用60Coγ射线对镧火石玻璃和镧冕玻璃进行辐照,研究不同辐照剂量对光学透射率的影响及其在空间光学系统中使用的适应性,辐照总剂量最大达到10 kGy。结果表明:所有玻璃在辐照后可见光透射率都下降了,而在近红外波段仍然保持较高的透射率。尽管镧火石玻璃LaF10平均透射率在辐照前最小,但是辐照后LaF10透射率衰减是所有玻璃中最小的。模拟了8个不同轨道高度地球辐射环境10年累积的总剂量以及经过10 mm铝屏蔽后的累积总剂量。发现对于10年任务期,在3 000、6 000和10 000 km轨道需要增加屏蔽层厚度,而在其他5个轨道,10 mm厚的铝屏蔽可以保证镧系玻璃满足系统对透射率的要求。     

RP-3航空煤油层流燃烧特性的影响因素

为了获得RP 3航空煤油燃烧特性的主要影响因素,在定容燃烧弹中试验测量了初始温度范围为390~450K、初始压力范围为01~07MPa、当量比范围为06~15条件下RP 3航空煤油的火焰发展特性,并分析了RP 3航空煤油火焰稳定性与层流燃烧速率的主要影响因素。结果表明:无拉伸火焰传播速率与层流燃烧速率随初始压力的升高或初始温度的降低而逐渐降低,但燃烧压力峰值却逐渐升高;随当量比的升高,无拉伸火焰传播速率、层流燃烧速率与燃烧压力峰值呈现先增加后降低的趋势,无拉伸火焰传播速率与层流燃烧速率在当量比为12时达到最大,燃烧压力峰值在当量比为10达到最大;马克斯坦长度随当量比的增加或初始压力的升高而逐渐变小,火焰前锋面稳定性变差,但是,初始温度对马克斯坦长度的影响不确定。      

碳纤维表面CVD硅涂层对其性能的影响

 分析了碳纤维表面化学气相沉积Ｓｉ涂层的相结构,研究了Ｓｉ涂层对碳纤维抗氧化性能及强度的影响。结果表明：涂层中Ｓｉ元素呈非晶态分布；Ｓｉ涂层可提高碳纤维的抗氧化性能；氧化温度不同,Ｓｉ涂层碳纤维的氧化失重或增重规律也不相同。同时,Ｓｉ涂层降低了碳纤维拉伸强度,而适度空气氧化又可使Ｓｉ涂层碳纤维强度得到大幅度提高；Ｓｉ涂层碳纤维的强度随氧化温度、氧化时间的变化而改变。     

超声速湍流导管烧蚀流场稳定性研究

对超声速湍流导管烧蚀流场进行理论计算,选取了初始面积比为2.0和3.0的超声速导管,得到了在绝热指数为1.1、1.2和1.3三个典型状态下总焓、马赫数、导管内压力、静焓及恢复焓随导管截面积加大的计算结果。研究表明:试验过程中总焓不变,但由于试验材料烧蚀导致导管的截面积加大将引起其余流场参数的变化,马赫数随导管的截面积加大而加大,其余参数随导管的截面积加大而降低,在导管截面积增大20%时,马赫数增幅在9%以内,导管内压力降幅在20%以上,静焓降幅在8%以内,恢复焓降幅在1%以内,绝热指数的上升将引起导管参数增幅或降幅加大,初始面积比加大,将引起导管参数增幅或降幅减小。     

原子氧环境对硅凝胶材料的侵蚀效应研究

简述了DC93-500和GN511硅凝胶材料原子氧环境试验过程,分析和考察了DC93-500和GN511硅凝胶材料在原子氧环境作用下的侵蚀效应,探索了原子氧环境对硅凝胶材料的作用机理.结果表明在原子氧环境作用下,DC93-500和GN511硅凝胶材料样品的可见光透射率明显下降;样品表面被氧化并出现龟裂裂纹和凸起的小岛;随着原子氧作用累积通量的进一步增加,样品表面会由于小岛被剥落而发生质损现象;相对于GN511而言,DC93-500硅凝胶材料在原子氧环境下的结构和性质较为稳定.     

Si3N4-TiN-SiC复相陶瓷的燃烧合成

利用高压气－固燃烧合成法,以ＴｉＳｉ２和ＳｉＣ为原料制备了Ｓｉ３Ｎ４－ＴｉＮ－ＳｉＣ复相陶瓷,实验中发现反应过程中出现的液相降低了产物的转子率;分析了稀释剂对产物的转化率与燃烧温度的影响及氮气压力在燃烧中的作用;解决了液相,稀剂和燃烧温度之间的矛盾,即通过提高氮气压力来完成。     

脉冲激光辐射下VO_2薄膜的光限幅性能

采用反应溅射和后续退火工艺,在石英衬底上制备具有热致相变特性的VO_2薄膜,并对薄膜的光学性能进行表征。研究发现:在弱光辐射下,随着温度的改变,薄膜的透射率在可见及近红外光区会发生显著变化,具有良好的相变光开关特性;在强光辐射下,制备的VO_2薄膜同样具有良好的红外光调制深度;当脉冲激光波长为1064 nm时,随着脉冲能量的逐渐增强,薄膜的表面反射率逐渐降低,光限幅性能呈现出先升高再降低的趋势,其透射率最低可降至7%,薄膜的脉冲激光损伤阈值约为50 mJ/cm~2。