Fracture Toughness Measurements and Acoustic Emission Activity in Brittle Rocks

Fracture toughness measurements under static loading conditions have been carried out in Barre and Lac du Bonnet granites. An advanced AE technique has been adopted to monitor real-time crack initiation and propagation around the principal crack in these tests to understand the processes of brittle failure under tension and related characteristics of the resulting fracture process zone. The anisotropy of Mode I fracture toughness has been investigated along specific directions. Microcrack density and orientation analysis from thin section studies have shown these characteristics to be the primary cause of the observed variation in fracture toughness, which is seen to vary between 1.14 MPa.(m)^1/2 and 1.89 MPa.(m)^1/2 in Barre granite. The latter value represents the case in which the crack is propagated at right angles to the main set of microcracks. The creation of a significant fracture process zone surrounding the propagating main crack has been confirmed. Real-time imaging of the fracture process and formation of fracture process zone by AE techniques yielded results in very good agreement with those obtained by direct optical analysis.     

一种有效提高DEM建模速度的方法设计及实现

文中利用动态数据链表的技术 ,为等高线数据重新设计了一种数据结构和检索方法 ,从而实现了内存中有效地操作等高线数据 ,使基于矢量等高线数据的 DEM建模速度得到了显著的提高     

HNO3 and PSC Measurements from the Transall: Sequestering of HNO3 in the Winter of 1994/95

In the winter of 1994/95 the TRANSALL research aircraft performed several flights in the region of the Arctic vortex during the period of low stratospheric temperatures. The results of simultaneous measurements of HNO3 column amounts by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and of aerosol backscatter profiles by the Ozone Lidar EXperiment (OLEX) are presented for two typical flight scenarios across the polar vortex boundary on December 17, 1994 and January 11/12, 1995. On December 17 and January 12, the column amounts of gaseous HNO3 decreased significantly in regions with low stratospheric temperatures. This decrease was correlated with the extent of the polar stratospheric clouds. Depolarisation measurements showed that type Ib PSCs were observed primarily, but equilibrium calculations for H2SO4/HNO3/H2O aerosols seem to underestimate the observed HNO3 sequestering.     

等离子体发射光谱法测定重晶石中钡铁和硅

重晶石经Ｎａ２ＣＯ３熔融,水浸取,过滤。沉淀经ＨＣｌ溶解后,用电感耦合等离子体发射光谱法同时测定主成分ＢａＳＯ４和次量成分Ｆｅ２Ｏ３以及滤液中的ＳｉＯ２,结果与部颁标准方法符合。方法精密度好,主量组分ＢａＳＯ４测定的ＲＳＤ（ｎ＝６）为０．２４％,次量组分Ｆｅ２Ｏ３和ＳｉＯ２的ＲＳＤ（ｎ＝６）分别是３．６９％和１．４５％。     

Extragalactic source counts and contributions to the anisotropies of the cosmic microwave background: predictions for the Planck Surveyor mission

We present predictions for the counts of extragalactic sources, the contributions to fluctuations and their angular power spectrum in each channel foreseen for the Planck Surveyor (formerly COBRAS/SAMBA ) mission. The contribution to fluctuations owing to clustering of both radio and far-IR sources is found to be generally small in comparison with the Poisson term; however the relative importance of the clustering contribution increases and may eventually become dominant if sources are identified and subtracted down to faint flux limits. The central Planck frequency bands are expected to be 'clean': at high galactic latitude (| b | > 20°), where the reduced galactic noise does not prevent the detection of the extragalactic signal, only a tiny fraction of pixels is found to be contaminated by discrete extragalactic sources. Moreover, the 'flat' angular power spectrum of fluctuations resulting from extragalactic sources substantially differs from that of primordial fluctuations; therefore, the removal of contaminating signals is eased even at frequencies where point sources give a sizeable contribution to the foreground noise.     

The high-velocity molecular stream in W51B: a ring structure with compact H ii regions

We present ¹³ CO J  = 1 − 0 line observations of the H  ii region complex W51B located in the high-velocity (HV) stream. These observations reveal a filamentary and clumpy structure in the molecular gas. The mean local standard of rest (LSR) velocity ∼ + 65 km s⁻¹ of the molecular gas in this region is greater than the maximum velocities allowed by kinematic Galactic rotation curves. The size and mass of the molecular clouds are ∼ 48 × 17 pc² and ∼ 2.4 × 10⁵ M⊙ respectively. In a position–velocity diagram, molecular gas in the southern part comprises a redshifted ring structure with v _LSR=+ 60 to +73 km s⁻¹. The velocity gradient of this ring is ∼ 0.5 km s⁻¹ pc⁻¹, and the mass is ∼ 6.2 × 10⁴ M⊙. If we assume that the ring is expanding with a uniform velocity, the expansion velocity, radius and kinetic energy are ∼ 7 km s⁻¹, ∼ 13 pc and ∼ 3.0 × 10 ⁴⁹ erg respectively. The kinetic energy and mass spectrum of the ring could be explained by an expanding cylindrical cloud with a centrally condensed mass distribution. The locations of two compact H  ii regions, G49.0−0.3 and G48.9−0.3, coincide with the two molecular clumps in this ring. We discuss star formation, and the mechanism that produced the ring structure.     

The 10-μm profile of molecular-cloud and diffuse ISM silicate dust

High signal-to-noise ratio spectra are presented of the 10-μm silicate absorption feature in lines of sight towards Elias 16 and 18 in the Taurus dark cloud, and towards the heavily reddened supergiant Cyg OB2 no. 12. The observations are fitted with laboratory and astronomical spectra to produce intrinsic absorption profiles. These features, which represent molecular-cloud and diffuse ISM dust respectively, are better fitted with emissivity spectra of the Trapezium and μ Cephei than they are with those of laboratory, terrestrial, or other observations of circumstellar silicates. The difference in width between the silicate band in the two environments can be almost entirely ascribed to a broad excess absorption in the long-wavelength wing of the profiles, which is much stronger in the molecular-cloud lines of sight, and possibly reflects grain growth in the denser environment. Limits are placed on the strength of fine spectral structure; if there is a crystalline silicate component in these spectra, it is most likely to be serpentine. Column-density upper limits for methanol and the photolysis product hexamethylenetetramine (HMT) are less than a few per cent of those of water ice and silicates.     

ISO observations of molecular hydrogen in the DR 21 bipolar outflow

We demonstrate that a wide range of molecular hydrogen excitation can be observed in protostellar outflows at wavelengths in excess of 5 μm. Cold H₂ in DR 21 is detected through the pure rotational transitions in the ground vibrational level (0–0). Hot H₂ is detected in pure rotational transitions within higher vibrational levels (1–1, 1–2, etc.). Although this emission is relatively weak, we have detected two 1–1 lines in the DR 21 outflow with the ISO SWS instrument. We thus investigate molecular excitation over energy levels corresponding to the temperature range 1015–15 722 K, without the uncertainty introduced by differential extinction when employing near-infrared data.
This gas is thermally excited. We uncover a rather low H₂ excitation in the DR 21 West Peak. The line emission cannot be produced from single C-shocks or J-shocks; a range of shock strengths is required. This suggests that bow shocks and/or bow-generated supersonic turbulence is responsible. We are able to distinguish this shock-excited gas from the fluoresced gas detected in the K band, providing support for the dual-excitation model of Fernandes, Brand & Burton.     

A textbook case of bow shock entrainment in a YSO outflow

Near-infrared images in H₂ line emission and submillimetre maps in CO J  = 3–2 emission illustrate the remarkable association between a molecular bow shock and the redshifted molecular outflow lobe in W75N. The flow lobe fits perfectly into the wake of the bow, as one would expect if the lobe represented swept-up gas. Indeed, these observations strongly support the 'bow shock' entrainment scenario for molecular outflows driven by young stars.   The characteristics of the bow shock and CO outflow lobe are compared with those of numerical simulations of jet-driven flows. These models successfully reproduce the bulge and limb-brightening in the CO outflow, although the model H₂ bow exhibits more structure extending back along the flow axis. We also find that the size of the flow, the high mass fraction in the flow at low outflow velocities (low γ values) and the high CO/H₂ luminosity ratio indicate that the system is evolved. We also predict a correlation, in evolved systems, between outflow age and the CO/H₂ luminosity ratio.