失败的价值

我为我的讲话选择了这个题目：“失败的价值（The Virtues of Failure）”，你们可能会奇怪：怎么今天我竞希望谈论失败呢？首先，失败对我是司空见惯的。第二．我相信创新性的研究是无数次失败和极少几次成功的混合。对科学界以外的许多人或刚开始做研究的学生们来说．这一事实也许并不那么显而易见。我们在报纸上和科学杂志上重视或强调的总是所获得的成就．其中文章给人的印象是，成功的次数大大超过了失败次数。这一错误观念又常常被一些口头讲话所加强：演讲者往往把研究工作讲得让人听起来像是不费什么力气的事．那不过是一步接一步的逻辑步骤罢了。然而上述印象实在是一种误导，每个研究者都知道这一点。真正的研究乃是一部由错误组成的喜剧．其中错误的事情一件接着一件发生。不妨用丘吉尔（Winston Churchill）的话来说，研究进展其实是怀着永不衰减的热情．     

Vibrational excitation through tug-of-war inelastic collisions

Vibrationally inelastic scattering is a fundamental collision process that converts some of the kinetic energy of the colliding partners into vibrational excitation(,). The conventional wisdom is that collisions with high impact parameters (where the partners only 'graze' each other) are forward scattered and essentially elastic, whereas collisions with low impact parameters transfer a large amount of energy into vibrations and are mainly back scattered. Here we report experimental observations of exactly the opposite behaviour for the simplest and most studied of all neutral-neutral collisions: we find that the inelastic scattering process H + D(2)(v = 0, j = 0, 2) --> H + D(2)(v' = 3, j' = 0, 2, 4, 6, 8) leads dominantly to forward scattering (v and j respectively refer to the vibrational and rotational quantum numbers of the D(2) molecule). Quasi-classical trajectory calculations show that the vibrational excitation is caused by extension, not compression, of the D-D bond through interaction with the passing H atom. However, the H-D interaction never becomes strong enough for capture of the H atom before it departs with diminished kinetic energy; that is, the inelastic scattering process is essentially a frustrated reaction in which the collision typically excites the outward-going half of the H-D-D symmetric stretch before the H-D(2) complex dissociates. We suggest that this 'tug of war' between H and D(2) is a new mechanism for vibrational excitation that should play a role in all neutral-neutral collisions where strong attraction can develop between the collision partners.     

Influence of soaking time in deep cryogenic treatment on the microstructure and mechanical properties of low-alloy medium-carbon HY-TUF steel

The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.     

Observation and interpretation of a time-delayed mechanism in the hydrogen exchange reaction

Extensive theoretical and experimental studies have shown the hydrogen exchange reaction H+H2 --> H2+H to occur predominantly through a 'direct recoil' mechanism: the H--H bonds break and form concertedly while the system passes straight over a collinear transition state, with recoil from the collision causing the H2 product molecules to scatter backward. Theoretical predictions agree well with experimental observations of this scattering process. Indirect exchange mechanisms involving H3 intermediates have been suggested to occur as well, but these are difficult to test because bimolecular reactions cannot be studied by the femtosecond spectroscopies used to monitor unimolecular reactions. Moreover, full quantum simulations of the time evolution of bimolecular reactions have not been performed. For the isotopic variant of the hydrogen exchange reaction, H+D2 --> HD+D, forward scattering features observed in the product angular distribution have been attributed to possible scattering resonances associated with a quasibound collision complex. Here we extend these measurements to a wide range of collision energies and interpret the results using a full time-dependent quantum simulation of the reaction, thus showing that two different reaction mechanisms modulate the measured product angular distribution features. One of the mechanisms is direct and leads to backward scattering, the other is indirect and leads to forward scattering after a delay of about 25 femtoseconds.