Midrapidity neutral-pion production in proton-proton collisions at square root s = 200 GeV

The invariant differential cross section for inclusive neutral-pion production in p+p collisions at sqrt[s]=200 GeV has been measured at midrapidity (|eta|<0.35) over the range 1相似文献   

Elliptic flow of identified hadrons in Au+Au collisions at sqrt sNN =200 GeV

The anisotropy parameter (v(2)), the second harmonic of the azimuthal particle distribution, has been measured with the PHENIX detector in Au+Au collisions at sqrt[s(NN)]=200 GeV for identified and inclusive charged particle production at central rapidities (|eta|<0.35) with respect to the reaction plane defined at high rapidities (|eta|=3-4 ). We observe that the v(2) of mesons falls below that of (anti)baryons for p(T)>2 GeV/c, in marked contrast to the predictions of a hydrodynamical model. A quark-coalescence model is also investigated.     

Scaling properties of proton and antiproton production in sqrt[s(NN)]=200 GeV Au+Au collisions

We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in Au+Au collisions at sqrt[s(NN)]=200 GeV measured at midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta (1.5相似文献   

Diels-Alder reactions of 5-vinyl-1-acyl-2-aryl-2,3-dihydro-4-pyridones: regio- and stereoselective synthesis of octahydroquinolines

[reaction: see text] Readily available 5-vinyldihydropyridones 2 undergo Diels-Alder cyclization with various dienophiles to afford novel octahdroquinolines. The process is highly stereoselective and provides heterocyclic products containing synthetically useful functionality.     

Crystals from concentrated glyme mixtures. The single-crystal structure of LiClO4

A procedure for the preparation of high-quality single crystals from concentrated glyme mixtures is presented. Anhydrous single crystals of LiNO(3) and LiClO(4) were prepared in this manner, and the single-crystal structure of LiClO(4) (orthorhombic, Pnma, a = 8.6447(12) A, b = 6.8512(10) A, c = 4.8254(7) A, Z = 4) was determined as an example. This procedure is expected to be widely applicable for not only salts but also a wide range of other materials solvated by glymes.     

The ep -->e'p eta reaction at and above the S11(1535) baryon resonance

New cross sections for the reaction e p-->e p eta are reported for total center of mass energy W = 1.5--1.86 GeV and invariant momentum transfer Q2 = 0.25--1.5 (GeV/c)(2). This large kinematic range allows extraction of important new information about response functions, photocouplings, and eta N coupling strengths of baryon resonances. Newly observed structure at W approximately 1.65 GeV is shown to come from interference between S and P waves and can be interpreted with known resonances. Improved values are derived for the photon coupling amplitude for the S11(1535) resonance.     

High peak power operation and harmonic generation of a single-polarization, Yb-doped photonic crystal fiber amplifier

We report on the use of a single-polarization, 41 μm core-diameter, intrinsically single-mode photonic crystal fiber (PCF) to obtain high peak power (up to 800 kW), 1 ns-duration pulses in a 100:1 linearly polarized, intrinsically single-mode (M²  1.2) output. By transmitting the PCF output through nonlinear crystals, we also obtained efficient second, third, and fourth harmonic generation resulting in peak power >400 kW in the visible (green, 531 nm) and 200 kW in the UV (265.5 nm). To our knowledge these results represent the highest peak power obtained in a linearly polarized output from a fiber and the highest peak power in the visible and UV obtained through harmonic generation of the direct fiber output.     

A multifrequency-resonator-based system for high-sensitivity high-field EPR investigations of small single crystals

In this paper, we describe a multifrequency spectroscopic system which is ideally suited to EPR investigations of very small single crystals. Our method utilizes oversized resonant cavities and a continuously tunable vector network analyzer. This system provides excellent sensitivity over a broad frequency range from about 30 GHz up to about 120 GHz, and in magnetic fields up to 33 T.     

A method for the study of surface corrosion beneath protective layers

This work is concerned with the development of a technique to observe the onset of corrosion as it occurs beneath a temporary protective layer. Such temporary protectives include paints, varnishes, greases and oils that are applied to metal surfaces to give short-term protection from corrosion. The objective of this project was to develop a technique that could be used to evaluate the effectiveness of various temporary protectives in different environments, without the need to remove the protective layer, thus eliminating the possibility of any chemical changes or loss of corrosion products occurring as a result of removal. The temporary protective layers are typically 25Μm for paints and 15Μm per layer for varnishes. The 6.3 keV fluorescence X-ray is able to penetrate such layers, but the large escape depth (∼10Μm) of the X-rays means that for a thin protective layer a large proportion of the X-rays detected will originate from deep within the substrate and the resultant spectrum will be representative of the bulk rather than the surface. To enhance the surface sensitivity of the CXMS technique, the near surface region must be enriched in the isotope Fe-57. To achieve this, Fe-57 was vacuum evaporated onto the surface of mild steel substrates and subsequently diffused into the near surface region. An approximate 20 nm Fe-57 layer was deposited onto mild steel samples. The surface enriched samples were then annealed to allow the Fe-57 to diffuse into the near surface region of the mild steel substrate, and also to allow back diffusion of the substrate. A diffusion model was developed to predict the surface distribution of Fe-57 as a function of annealing parameters. The computer diffusion model allowed the ideal annealing conditions to be estimated to obtain a required near surface environment. It was essential that the annealing conditions did not result in any surface oxidation, and did result in a surface that was characteristic of mild steel. CEMS and CXMS spectra were recorded of samples before and after annealing, and also dynamic Secondary Ion Mass Spectrometry (SIMS) was used to monitor the enrichment and diffusion process. Energy Dispersive X-ray Analysis (EDXA) was also used to characterize the surface. A number of enriched samples were prepared and treated with a variety of surface temporary protectives. The CXMS spectra were recorded before and after exposure of the coated samples to various aggressive environments.