88 research outputs found
Static and dynamic analysis of shear deformable composite shells of revolution by semi-analytical approach
No full textIn the present study, multi-segment numerical integration technique is applied for the static and dynamic analysis of macroscopically anisotropic shells of revolution including transverse shear deformation. Application of the multi-segment numerical integration technique is achieved through the use of finite exponential Fourier transform of the fundamental shell of revolution equations governing the static loading and free vibration of the shell of revolution. For the non-axisymmetrically loaded shells of revolution, the paper presents the numerical integration based solution process of the transformed shell variables and back transformation to obtain the physical shell variables. As a follow-up study, multi-segment numerical integration technique is extended to the solution of free vibration problem of anisotropic composite shells of revolutionwhich are wound along the semi-geodesic fiber paths counting on the preset friction used during the winding process. Sample results are obtained for truncated conical and spherical shells of revolution for which the winding angle and the thickness vary along the shell axis, and the effect of preset friction on the vibration characteristics of filament wound shells of revolution is particularly analyzed
PENTACARBONYL(1,4-DIISOPROPYL-1,4-DIAZABUTADIENE)CHROMIUM - ISOLATION AND REACTIVITY OF THE MONODENTATE INTERMEDIATE EN-ROUTE TO CR(CO)4(IPROP-DAB) CHELATE RING-CLOSURE
No full textExchange of the olefin ligand in Cr(CO)5(eta2-(Z)-cyclooctene) by 1,4-diisopropyl-1,4-diazabutadiene (iprop-DAB) yields Cr(CO)5(iprop-DAB) (1), where the potentially bidentate DAB ligand coordinates in a monodentate fashion. Complex 1 is isolated as red crystals and fully characterized (elemental analysis, IR, UV-vis, H-1 NMR and C-13 NMR spectra). In hydrocarbon solution at ambient temperature it decays via two competitive routes involving (a) chelate ring closure with CO extrusion to form Cr(CO)4(iprop-DAB) (2) and (b) loss of the iprop-DAB ligand and takeup of CO to form Cr(CO)6, as monitored by means of NMR, UV-vis, and IR spectroscopy. Favorable conditions for the chelate ring closure leading to 2 are the high concentration of 1, the presence of added iprop-DAB, and the absence of CO, while the opposite is true for the formation of Cr(CO)6. The decay of 1 is retarded in the presence of increasing amounts of added iprop-DAB. It essentially follows pseudo-first-order kinetics with k(obs) approaching a lower limiting value of 2.7 x 10(-5) s-1 under Ar at 23-degrees-C, whereby Cr(CO)4(iprop-DAB) (2) and Cr(CO)6 are formed in a ca. 20:1 ratio. Experiments at variable temperature yield DELTAH(double dagger) = 48 +/- 6 kJ mol-1 and DELTAS(double dagger) = -170 +/- 18 J K-1 mol-1. In the presence of added CO or (E)-cyclooctene (ECO) the decay of 1 is accelerated, whereby additional Cr(CO)6 or Cr(CO)5(eta2-ECO) are formed at the expense of Cr(CO)4(iprop-DAB) (2) production. Complementary studies involving continuous irradiation of Cr(CO)6 and iprop-DAB indicate that photogenerated 1 subsequently undergoes photolytic CO dissociation with formation of 2 in addition to the thermal chelate ring closure
Activation parameters in flash photolysis studies of Mo(CO)6
No full textReported is a combined time-resolved optical (TRO) and infrared (TRIR) spectroscopic investigation of the flash photolysis of MO(CO)6 in cyclohexane solution. TRIR studies using 308 nm excitation led to transient bleaching of the strong v(CO) band at 1987 cm(-1) of Mo(CO)(6) and appearance of new bands at 1931 and 1964 cm(-1) attributed to Mo(CO)(5)(SOl). Using a high pressure/variable temperature flow cell, the kinetics of back reaction with CO (k(CO)) to regenerate the hexacarbonyl was studied over the P-CO range 1-20 atm and at five temperatures. These data gave k(CO) = 4.6 +/- 0.2 x 10(6) M-1 s(-1) (298 K) and the activation parameters DeltaH(CO)(double dagger) = 32.6 +/- 13 kJ/mol and AS -7.3 +/- 11 J mol(-1) K-1 from which an interchange mechanism was proposed. The analogous species seen in the TRO experiment displayed a transient absorbance at 420 nm and analogous kinetics properties although at lower P-CO self-trapping with Mo(CO())6 (to give Mo-2(CO)(11)) is a competitive process. The Mo(CO)(5)(SOl) transient could also be trapped by "PrBr (k(RBr) = 5.3 +/- 0.7 x 10(7) M-1 s(-1)). (C) 2003 Elsevier B.V. All rights reserved
Preparation and characterization of polystyrene-b-poly(2-vinylpyridine) coordinated to metal ion nanoparticles
No full textIn this study, Co, Cr or Au3+ functional polystyrene-block- poly(2-vinylpyridine), PS-b-P2VP complexes were prepared and characterized. Coordination of metal atom or ion to nitrogen atom of pyridine rings was confirmed by FTIR analyses. The strength and efficiency of coordination of P2VP blocks to Co, Cr or Au3+ mainly depends on charge and stability of the complex formed that is mainly related to the energy of d orbitals. The results reveal that the thermal stability of the polymer composite formed increases with the increase in strength of the coordination. Changes in thermal decomposition mechanism and product distribution were recorded. Degradation of P2VP units coordinated to Cr, Co or Au3+ was started by loss of pyridine units leaving an unsaturated and/or crosslinked polymer backbone that degraded at relatively high temperatures. © 2014 Elsevier B.V
Thermal decomposition of polystyrene-b-poly(2-vinylpyridine) coordinated to co nanoparticles
No full textDirect pyrolysis mass spectrometry analyses of polystyrene-block-poly(2-vinylpyridne), PS-b-P2VP, indicated that the thermal degradation of each component occurred independently through the decomposition pathways proposed for the corresponding homopolymers; depolymerization for PS and depolymerization and loss of protonated oligomers for P2VP by a more complex degradation mechanism. On the other hand, upon coordination to cobalt nanoparticles, thermal decomposition of the P2VP blocks was initiated by loss of pyridine units, leaving an unsaturated and/or crosslinked polymer backbone that degraded at relatively high temperatures. © 2009 Elsevier Ltd. All rights reserved
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The machine protection system for the R&D energy recovery LINAC
No full textThe Machine Protection System (MPS) is a device-safety system that is designed to prevent damage to hardware by generating interlocks, based upon the state of input signals generated by selected sub-systems. It protects all the key machinery in the R&D Project called the Energy Recovery LINAC (ERL) against the high beam current. The MPS is capable of responding to a fault with an interlock signal within several microseconds. The ERL MPS is based on a National Instruments CompactRIO platform, and is programmed by utilizing National Instruments' development environment for a visual programming language. The system also transfers data (interlock status, time of fault, etc.) to the main server. Transferred data is integrated into the pre-existing software architecture which is accessible by the operators. This paper will provide an overview of the hardware used, its configuration and operation, as well as the software written both on the device and the server side
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SRF photoinjector for proof-of-principle experiment of coherent electron cooling at RHIC
No full textCoherent Electron Cooling (CEC) based on Free Electron Laser (FEL) amplifier promises to be a very good way to cool protons and ions at high energies. A proof of principle experiment to demonstrate cooling at 40 GeV/u is under construction at BNL. One of possible sources to provide sufficient quality electron beam for this experiment is a SRF photoinjector. In this paper we discuss design and simulated performance of the photoinjector based on existing 112 MHz SRF gun and newly designed single-cavity SRF linac operating at 704 MHz
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Lattice design for the future ERL-based electron hadron colliders eRHIC and LHeC
No full textWe present a lattice design of a CW Electron Recovery Linacs (ERL) for future electron hadron colliders eRHIC and LHeC. In eRHIC, an six-pass ERL installed in the existing Relativistic Heavy Ion Collider (RHIC) tunnel will collide 5-30 GeV polarized electrons with RHIC's 50-250 (325) GeV polarized protons or 20-100 (130) GeV/u heavy ions. In LHeC a stand-along, 3-pass 60 GeV CW ERL will collide polarized electrons with 7 TeV protons. After collision, electron beam energy is recovered and electrons are dumped at low energy. Two superconducting linacs are located in the two straight sections in both ERLs. The multiple arcs are made of Flexible Momentum Compaction lattice (FMC) allowing adjustable momentum compaction for electrons with different energies. The multiple arcs, placed above each other, are matched to the two linac's straight sections with splitters and combiners
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