Study of the centrally produced ωρ0 and ωω systems inpp interactions at 300 GeV/c

We have performed a search for vector-vector final states centrally produced in proton proton interactions at 300 GeV/c using the CERN Ω spectrometer. Evidence is found for ωρ⁰ production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s and for ωω production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s . However no evidence is found for ωø production in the reactionpp→p _f (K ⁺ K ^?π⁺π^?π⁰)p _s .     

Manganese‐Catalyzed Hydrofunctionalization of Alkenes

The manganese‐catalyzed hydrosilylation and hydroboration of alkenes has been developed using a single manganese(II) precatalyst and reaction protocol. Both reactions proceed with excellent control of regioselectivity and in high yields across a variety of sterically and electronically differentiated substrates (25 examples). Alkoxide activation, using NaO^tBu, was key to precatalyst activation and reactivity. Catalysis was achieved across various functional groups and on gram‐scale for both the developed methodologies with catalysts loadings as low as 0.5 mol %.     

Impact of an external radiation field on handheld XRF measurements for nuclear forensics applications

X-ray fluorescence (XRF) is an attractive technique for nuclear forensics applications. We evaluated a handheld XRF device by applying an external radiation field (10 mR/h–17 R/h) using two types of radiography sources: a ⁶⁰Co radiography camera for high-energy gamma emissions and an ¹⁹²Ir radiography camera for several low-energy gamma (0.604, 0.468, and 0.317 MeV) and decay daughter X-ray emissions. External radiation tests proved that radiation, in general, has a significant effect on the dead time or background at dose rates over 1 R/h for both the ¹⁹²Ir and ⁶⁰Co sources.     

Alternatives to pyridinediimine ligands: syntheses and structures of metal complexes supported by donor-modified alpha-diimine ligands

This report describes the synthesis and characterization of metal halide complexes (M = Mn, Fe, Co) supported by a new family of pendant donor-modified alpha-diimine ligands. The donor (N, O, P, S) substituent is linked to the alpha-diimine by a short hydrocarbon spacer forming a tridentate, mer-coordinating ligand structure. The tridentate ligands are assembled from monoimine precursors, the latter being synthesized by selective reaction with one carbonyl group of the alpha-dione. While attempts to separately isolate tridentate ligands in pure form were unsuccessful, metal complexes supported by the tridentate ligand are readily synthesized in-situ, by forming the ligand in the presence of the metal halide, resulting in a metal complex which subsequently crystallizes out of the reaction mixture. Metal complexes with NNN, NNO, NNP and NNS donor sets have been prepared and examples supported by NNN, NNP and NNS ligands have been structurally characterized. In the solid state, NNN and NNP ligands coordinate in a mer fashion and the metal complexes possess distorted square pyramidal structures and high spin (S = 2) electronic configurations. Compounds with NNS coordination environments display a variety of solid state structures, ranging from those with unbound sulfur atoms, including chloride bridged and solvent ligated species, to those with sulfur weakly bound to the metal center. The extent of sulfur ligation depends on the donor ability of the crystallization solvent and the substitution pattern of the arylthioether substituent.     

Comparison of level discrimination, increment detection, and comodulation masking release in the audio- and envelope-frequency domains

In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level discrimination performance and (2) lower tone-in-noise detection thresholds using a modulated masker compared to those using an unmodulated masker. In the current study, translations of these two experiments were carried out to test the hypothesis that analogous cues might be used in the envelope-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (ms = 0.25) and a range of AM frequencies (4-64 Hz). In a second experiment, masked sinusoidal AM detection thresholds were compared in conditions with and without slow and regular fluctuations imposed on the instantaneous masker AM depth. Release from masking was obtained only for very slow masker fluctuations (less than 2 Hz). A physiologically motivated model that effectively acts as a first-order envelope change detector accounted for several, but not all, of the key aspects of the data.     

Characterization of sealed radioactive sources: uncertainty analysis to improve detection methods

A radioactive ¹³⁷Cs source has been analyzed for the radioactive parent ¹³⁷Cs and stable decay daughter ¹³⁷Ba. The ratio of the daughter to parent atoms is used to estimate the date when Cs was purified prior to source encapsulation (an “age” since purification). The isotopes were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical separation. In addition, Ba was analyzed by isotope dilution ICP-MS (ID-ICP-MS). A detailed error analysis of the mass spectrometric work has been undertaken to identify areas of improvement, as well as quantifying the effect the errors have on the “age” determined. This paper reports an uncertainty analysis to identifying areas of improvement and alternative techniques that may reduce the uncertainties. In particular, work on isotope dilution using ICP-MS for the “age” determination of sealed sources is presented. The results will be compared to the original work done using external standards to calibrate the ICP-MS instrument.     

Activating hybrid modular interfaces in synthetic polyketide synthases by cassette replacement of ketosynthase domains

Unnatural combinations of polyketide synthase modules often fail to make a polyketide product. The causes of these failures are likely complex and are not yet amenable to rational correction. One possible explanation is the inability of the ketosynthase (KS) domain to extend the ketide donated to it by the upstream module. We therefore addressed the problem by exchanging KS domains of the acceptor module in a combinatorial fashion and coexpressing these chimeric modules with ketide-donor modules that naturally interact with the transplanted KS. This approach was remarkably successful in activating previously unproductive bimodular combinations, and the results augur well for the ongoing development of molecular tools to design and produce novel polyketides.     

781 Mbit/s photon-counting optical communications using a superconducting nanowire detector

We demonstrate 1550 nm photon-counting optical communications with a NbN-nanowire superconducting single-photon detector. Source data are encoded with a rate-1/2 forward-error correcting code and transmitted by use of 32-ary pulse-position modulation at 5 and 10 GHz slot rates. Error-free performance is obtained with -0.5 detected photon per source bit at a source data rate of 781 Mbits/s. To the best of our knowledge, this is the highest reported data rate for a photon-counting receiver.     

基于箭形累积损伤的裂纹尖端力学:奇异性分级和多尺度分段

在适度的空间和时间尺度组合下,裂纹既可在几个月中蠕变几个纳米,也能在几秒钟内扩展10km.虽然裂纹的尖端没有实际的质量,但是它能通过激活周围的物质而处于高能量状态.依赖于材料的损伤方向,激活质量的减少和增加可发生在尺度转变之前或之后.每个尺度区的分段阈值被假定为与裂纹尖端速度的平方a~2和激活质量密度M的乘积有关:W=M_(↓↑)a_(↑↓)~2和D=M~(↓↑)a_(↑↓)~2.W和D分别被称为直接吸收和自耗散能量密度.正如下标/上标符号所示,激活的质量密度M_(↓↑)和M~(↓↑)与裂纹尖端速度a变化趋势相反,既可增加也可减少.a~2和M的互补效应隐含着常用于宇宙物理学建模的膨胀和/或收缩的物理过程.在用于尺度敏感的裂纹尖端的行为时,激活的质量密度有相同的解释.分段时的多尺度可以由…皮观、纳观、微观和宏观…组成.因此,形象地说,材料损伤过程可以通过裂纹扩展过程中非均匀的总体和局部能量的传递来模拟.疲劳裂纹扩展引起的材料损伤被用来阐释由大到小和由慢到快的尺度/时间序,热力学中的冷→热和有序→无序转换.这一过程正巧与宇宙演化的箭形方向相反,宇宙演化遵循小→大和快→慢,而热力学相反,遵循热→冷和无序→有序.为了表示由损伤萌生所造成的类裂缝型缺陷的不均匀性,提出了一个被称为裂纹尖端力学(crack tip mechanics,CTM)的新模式.涉及的范围是模拟原子列之间的界面裂纹或连续体中分叉的切口.假如需要的话,尺寸和时间的范围可以复盖从皮观到宏观甚至更大.虽然采用疲劳裂纹来说明CTM的基本原理,在宇宙物理学背景中与直接吸收和自耗散相关的膨胀和收缩的情况可以描述裂纹周围激活质量的行为,它们可看为能量的汇或源.奇异性被用来捕获能量的源或汇的特性,物理上,两者作为界面的一部分,从数学上看则是不连续的线的一部分.能量从一种形式变为另一种形式取决于能量吸收或耗散的箭形损伤时间,这之中牵涉到尺度分段和奇异性强度的联合应用.材料组分随时间的劣化是根据指定的设计寿命导出的,从而使材料的响应与加载率的时间历史匹配.2024-T3铝板的皮观/纳观/微观/宏观开裂模型用来说明什么地方可以增加结构的寿命部分.皮观/纳观/微观/宏观/结构系统的性能随时间劣化可以用9个尺度转变物理参数来描述:纳观/微观区有3个(μ_(na/mi)~*,σ_(na/mi)~*,d_(na/mi)~*),微观/宏观区有3个(μ_(mi/ma)~*,σ_(mi/ma)~*,d_(mi/ma)~*),皮观/纳观区有3个(μ_(pi/na)~*,σ_(pi/na)~*,d_(pi/na)~*).下标pi,na,mi,ma和struc分别表示皮观、纳观、微观、宏观和结构.只要知道两个相连的尺度敏感参数,在较低尺度的时间相关的局部物理参数就完成了分析连续体的形式论,虽然它们并不需要用实验来知道.更具体地说,根据皮观→纳观→微观→宏观分别有1.25/1.00/0.75/0.50的λ奇异性强度,皮观裂纹、纳观裂纹、微观裂纹和宏观裂纹的转变特征是从时间箭形的指定的寿命预期来确定的.附加的0.25强度的奇异性可用于结构元件.回想起来,λ=0.5相应于断裂力学中的应力分量与r~(0.5)成反比,r是与宏观裂纹尖端的距离.微观裂纹、纳观裂纹和皮观裂纹分别赋予r~(-0.75),r~(-1.0),r~(-1.25)的奇异性.箭形时间(以年为单位)取决于问题的定义.设备的关键部件可用1.5~±/2.5~±/3.5~±/5.5~±寿命分布和总寿命为13~±年(a)的皮观/纳观/微观/宏观尺度来设计运行.上标±表示多于或少于实际运行的时间.累进损伤被假定为发生在皮观→纳观→微观→宏观方向.同样的方案用于20年总寿命的2024-T3铝板的疲劳损伤,按照1.5~±/2.5~±/3.5~±/5.5~±/7.0~±的方式将它的寿命分布在皮观、纳观、微观、宏观和结构的尺度上,这样的指定只是满足在每个尺度范围内损伤内部材料结构所用的能量匹配,因此可以强制执行在总寿命的跨度内精确的时间相关的材料性能劣化过程.     

Existence of near-zero minima in elastic photon–atom scattering

We consider near-zero minima in the photon–atom elastic scattering cross section, possible signatures of the presence of a particular element in a target, using the S-matrix approach. However, the usual formulation of this approach performs an averaging over magnetic substates at the level of the scattering amplitude that is approximate (except for the case of fully filled subshells). We consider whether the predicted near-zero minima persist in a more proper treatment. We find that near-zero minima seen below thresholds in scattering from ground-state atoms generally persist, but near-zero minima seen above thresholds in scattering from excited states may be spurious.