Particle multiplicities in the fission-like reactions of 340 MeV Si on Th

Pre-scission and post-scission multiplicities of neutrons and alpha particles have been simultaneously measured for the fission-like reactions of 340 MeV ²⁸Si on ²³²Th. Dynamical model calculations using HICOL code predict that about 90% of the observed events are of quasi-fission type while the remaining 10% are from compound nucleus fission decay. Moving source fits were carried out to the observed neutron and alpha particle spectra, measured at different angles with respect to the fragment directions. The pre-scission and post-scission neutron multiplicities are deduced to be 8.7±2.0 and 9.4±2.0, respectively. The corresponding multiplicity values for alpha particles are found to be 0.22±0.08 and 0.1±0.03. From the measured post-scission neutron multiplicity, it is inferred that about 65±20 MeV of the initial excitation energy remains at scission. This may be compared to the value of 85±30 MeV estimated from PACE2 statistical model calculations, adjusted to reproduce the measured pre-scission neutron multiplicity. From a comparison of the Statistical Model predictions with the measured pre-scission neutron multiplicity, the fission delay is estimated to be of 5⁺⁷₋₃×10⁻²⁰ s which overlaps with the average duration of fission-like process from the contact to the scission point (2×10⁻²⁰ s) as determined from HICOL-based dynamical calculations. For the delay time deduced as above, the pre-scission alpha particle multiplicity calculated by the PACE2 code is about a factor two larger than the experimental one, demonstrating the difficulties in modelling the alpha particle emission from highly elongated shapes that characterize the fissioning system from the contact point to scission.     

Synthesis of protected norcysteines for SPPS compatible with Fmoc strategy

We report the synthesis of racemic Alloc-Ncy(Tmob)-OH, the resolution of its methyl ester and demonstrate its application to form a norcystine bridge in octreotide-amide using the Fmoc strategy on solid phase. N-Alloc and S-Tmob protections of norcysteine (Ncy) were found to be a preferred choice for Fmoc strategy over three other protected norcysteines synthesized, that is, Fmoc-Ncy(tBu)-OH, Alloc-Ncy(tBu)-OH, and Alloc-Ncy(Trt)-OH.     

Investigation of Diels–Alder Reaction of 7‐Substituted 4‐Styrylcoumarins with Symmetrical Dienophiles Leading to 3,4‐Annulated Coumarins

The thermal [4 + 2] cycloaddition reaction of 7‐substituted 4‐styrylcoumarins with N‐phenylmaleimide and tetracyanoethylene in nitrobenzene under reflux conditions rapidly gives 3,4‐annulated coumarins as the Diels–Alder adducts. The position of the surviving double bond was determined on the basis of NMR and supported by energies of the possible structures. The effects of the 7‐substituent and the solvent on the reaction were studied.     

Facile intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins leading to highly fluorescent coumarin-containing polycyclic compounds

The 4-(o-propargyloxy)styrylcoumarins are prepared by the condensation of O-propargylated salicylaldehyde with substituted coumarin-4-acetic acids. The intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins, without any catalyst gives fused-ring coumarins. The reaction in boiling nitrobenzene leads to aromatization of the initial Diels–Alder adduct and these aromatized products are highly fluorescent.     

Metal-free oxidative aromatization of 2-aryloxycyclohex-2-en-1-ones to 2-aryloxyphenols using DDQ/Amberlyst-15

Efficient metal-free oxidative aromatization of 2-aryloxycyclohex-2-en-1-ones was achieved by a combination of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and Amberlyst-15. The conditions for oxidative aromatization are mild and applicable for a variety of substrates, and Amberlyst-15 can be successfully recovered and recycled.     

An integrated computational approach to single-dimensional laser machining of magnesia

Magnesia (MgO) ceramic was machined using a pulsed Nd:YAG laser. A mathematical model was developed to predict machined effects. The model took into account the physical phenomena taking place during machining of the ceramic such as multiple reflections influencing the absorbed laser energy, thermal effects in vaporizing the material, dissociation energy losses and effect of vapor pressure in producing a cavity through the ceramic. The laser fluence, machining time and number of pulses required for machining a certain depth of cavity and the efficiency of machining in terms of the specific machining depth were estimated and compared with the experimental data, thus making the model useful for advance energy predictions and enhancement of machining efficiency.     

Coherent and incoherent processes in resonant photoemission

3 threshold. At threshold, the emission feature changes character and after a rather narrow transition region it appears at constant emission energy instead. Clear signatures of interference between the direct photoemission and autoionization channels are identified. Received: 6 March 1997     

From NEXAFS spectroscopy to new flat panel displays: A story of basic science with technological impact

The Twentieth NSRRC Users' Meeting was held successfully at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan from September 10th to 12th, 2014. The three-day meeting was the first such event to be held at the newly furnished Activity Center on the NSRRC campus, celebrating 20 years since the first NSRRC Users' Meeting and highlighting the prospective scientific frontiers marked by the newly established Taiwan Photon Source (TPS) storage ring.