Single-mode plane-polarized ytterbium-doped large-core fiber laser with 633-W continuous-wave output power

We demonstrate a cladding-pumped single-mode plane-polarized ytterbium-doped fiber laser generating 633 W of continuous-wave output power at 1.1 microm with 67% slope efficiency and a polarization extinction ratio better than 16 dB. The laser is end pumped through both fiber ends and shows no evidence of roll-over, even at the highest output power, which is limited only by the available pump power.     

Single-frequency, single-mode, plane-polarized ytterbium-doped fiber master oscillator power amplifier source with 264 W of output power

We present a single-frequency, single-mode, plane-polarized ytterbium-doped all-fiber master oscillator power amplifier source at 1060 nm generating 264 W of continuous-wave output power. The final-stage amplifier operated with a high gain of 19 dB and a high conversion efficiency of 68%. There was no evidence of rollover from stimulated Brillouin scattering even at the highest output power, and the maximum output was limited only by the available pump power.     

Radiation-driven hydrodynamics of high- hohlraums on the national ignition facility

The first hohlraum experiments on the National Ignition Facility (NIF) using the initial four laser beams tested radiation temperature limits imposed by plasma filling. For a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with an analytical model that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits with full NIF (1.8 MJ), greater, and of longer duration than required for ignition hohlraums.     

Nonequilibrium raftlike membrane domains under continuous recycling

We present a model for the kinetics of spontaneous membrane domain (raft) assembly that includes the effect of membrane recycling ubiquitous in living cells. We show that domains can have a broad power-law distribution with an average radius that scales with the 1/4 power of the domain lifetime when the line tension at the domain edges is large. For biologically reasonable recycling and diffusion rates, the average domain radius is in the tens of nm range, consistent with observations. This represents one possible link between signaling (involving rafts) and traffic (recycling) in cells. Finally, we present evidence that suggests that the average raft size may be the same for all scale-free recycling schemes.     

Efficient palladium-catalyzed cross-coupling of beta-chloroalkylidene/arylidene malonates using microwave chemistry

A general method for the synthesis of beta-aryl/alkylarylidene malonates is reported. The key step involves the coupling of an arylboronic acid to a beta-chloroalkyl/arylidene malonate, in the presence of K2CO3 and 1 mol % of the air-stable palladium catalyst (POPd) under microwave irradiation, to afford beta-aryl/alkylarylidene malonates in good yields. The combination of mild reaction conditions, air stable catalyst, microwave-enhanced chemistry, and high levels of functional group compatibility make this an attractive synthetic approach to this class of compounds.     

Productive chloroarene C-cl bond activation: palladium/phosphine-catalyzed methods for oxidation of alcohols and hydrodechlorination of chloroarenes

The palladium/phosphine-catalyzed productive chloroarene C-Cl bond activation provides general, efficient, and functional group friendly methods for the selective oxidation of alcohols and the hydrodechlorination of chloroarenes.     

A versatile chemo-enzymatic route to enantiomerically pure beta-branched alpha-amino acids

A series of diastereoisomers of beta-methyl-beta-phenylalanine analogues 1a-f have been prepared in enantiomerically pure form using a combination of chemo- and biocatalysis. Starting from l-threonine methyl ester 2, a range of beta,beta-disubstituted didehydroamino acids were obtained as their (Z)-isomers 6a-f. Asymmetric hydrogenation of these alkenes, using either the [Rh(R,R)-Et-DuPhos(COD)]BF4 or [Rh(S,S)-Et-DuPhos(COD)]BF4 catalyst, followed by hydrolysis yielded two of the four possible sets of diastereoisomers of the beta-branched amino acid. Subsequent stereoinversion, using a stereoselective amino acid oxidase in combination with a nonselective reducing agent, furnished the remaining two sets of diastereomers.     

Studies on pyridazine azide cyclisation reactions

Reaction of sodium azide with 4-methyl-3,5,6-tribromopyridazine results in the formation of 3,5,6-triazide intermediate which could cyclise to give two possible bicyclic products while ab initio calculations show that the formation of a tricyclic compound is extremely energetically unfavourable. However, experimentally, only one major product is isolated. The structure of this unstable product has been conclusively established by X-ray crystallography as 3,5-diazido-4-methyl[1,5-b]tetrazolopyridazine confirming theoretical predictions.     

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Implosion of indirectly driven reentrant-cone shell target

We have examined the implosion of an indirectly driven reentrant-cone shell target to clarify the issues attendant on compressing fuel for a fast ignition target. The target design is the hydrodynamic equivalent of a NIF cryoignition target scaled to be driven by Omega. Implosions were imaged with backlit x radiographs and modeled with LASNEX. The simulations were generally in good agreement with the experiments with respect to the shell diameter, density, and symmetry, but did not show the prestagnation central absorption maximum. The existence of material between the original cone and the shell is sensitive to gold M-band radiation, which penetrates the shell and ablates gold from the cone. The simulated radiographs using recently measured M-band fractions showed absorption between the cone and shell similar to the experiment. This gold ablation might be a problem in a cryoignition target.