Discovery of highly excited long-lived isomers in neutron-rich hafnium and tantalum isotopes through direct mass measurements

A study of cooled 1??Au projectile-fragmentation products has been performed with a storage ring. This has enabled metastable nuclear excitations with energies up to 3 MeV, and half-lives extending to minutes or longer, to be identified in the neutron-rich nuclides 1?3(,)1??(,)1??Hf and 1??(,)1??Ta. The results support the prediction of a strongly favored isomer region near neutron number 116.     

Temperature dependence of the optical transition energies of carbon nanotubes: the role of electron-phonon coupling and thermal expansion

Tunable Raman spectroscopy is used to measure the optical transition energies Eii of individual single wall carbon nanotubes. Eii is observed to shift down in energy by as much as 50 meV, from -160 to 300 degrees C, in contrast with previous measurements performed on nanotubes in alternate environments, which show upshifts and downshifts in Eii with temperature. We determine that electron-phonon coupling explains our experimental observations of nanotubes suspended in air, neglecting thermal expansion. In contrast, for nanotubes in surfactant or in bundles, thermal expansion of the nanotubes' environment exerts a nonisotropic pressure on the nanotube that dominates over the effect of electron-phonon coupling.     

Imaging and sizing of diamond nanoparticles

Typical disturbances of biological environment such as background scatter and refractive index variations have little effect on the size-dependent scattering property of highly refractive nanocrystals, which are potentially attractive optical labels. We report on what is to our knowledge the first investigation of these scattering optical labels, and their sizing, in particular, by imaging at subvideo frame rates and analyzing samples of diamond nanocrystals deposited on a glass substrate in air and in a matrix of weakly scattering polymer. The brightness of a diffraction-limited spot appears to serve as a reliable measure of the particle size in the Rayleigh scattering limit.     

Electron correlation effects on the femtosecond dephasing dynamics of E22 excitons in (6,5) carbon nanotubes

Highly nonlinear pump fluence dependence was observed in the ultrafast one-color pump-probe responses excited by 38 fs pulses resonant with the E(22) transition in a room-temperature solution of (6,5) carbon nanotubes. The differential probe transmission (ΔT/T) at the peak of the pump-probe response (τ = 20 fs) was measured for pump fluences from ～10(13) to 10(17) photons/pulse cm(2). The onset of saturation is observed at ～2 × 10(15) photons/pulse cm(2) (～8 × 10(5) excitons/cm). At pump fluences >4 × 10(16) photons/pulse cm(2) (～1.6 × 10(6) excitons/cm), ΔT/T decreases as the pump fluence increases. Analogous signal saturation behavior was observed for all measured probe delays. Despite the high exciton density at saturation, no change in the E(22) population decay rate was observed at short times (<300 fs). The pump probe signal was modeled by a third-order perturbation theory treatment that includes the effects of inhomogeneous broadening. The observed ΔT/T signal is well-fit by a pump-fluence-dependent dephasing rate linearly dependent on the number of excitons created by the pump pulse. Therefore, the observed nonlinear pump intensity dependence is attributed to the effects of quasi-elastic exciton-exciton interactions on the dephasing rates of single carbon nanotubes. The low fluence total dephasing time is 36 fs, corresponding to a homogeneous width of 36 meV (290 cm(-1)), and the derived E(22) inhomogeneous width is 68 meV (545 cm(-1)). These results are contrasted with photon-echo-derived parameters for the E(11) transition.     

Metabolomics profiling of extracellular metabolites in recombinant Chinese Hamster Ovary fed‐batch culture

A metabolomics‐based approach was used to time profile extracellular metabolites in duplicate fed‐batch bioreactor cultures of recombinant Chinese Hamster Ovary (CHO) cells producing monoclonal IgG antibody. Culture medium was collected and analysed using a high‐performance liquid chromatography (HPLC) system in tandem with an LTQ‐Orbitrap mass spectrometer. An in‐house software was developed to pre‐process the LC/MS data in terms of filtering and peak detection. This was followed by principal component analysis (PCA) to assess variance amongst the samples, and hierarchical clustering to categorize mass peaks by their time profiles. Finally, LC/MS² experiments using the LTQ‐Orbitrap (where standard was available) and SYNAPT? HDMS (where standard was unavailable) were performed to confirm the identities of the metabolites. Two groups of identified metabolites were of particular interest; the first consisted of metabolites that began to accumulate when the culture entered stationary phase. The majority of them were amino acid derivatives and they were likely to be derived from the amino acids in the feed media. Examples included acetylphenylalanine and dimethylarginine which are known to be detrimental to cell growth. The second group of metabolites showed a downward trend as the culture progressed. Two of them were medium components – tryptophan and choline, and these became depleted midway into the culture despite the addition of feed media. The findings demonstrated the potential of utilizing metabolomics to guide medium design for fed‐batch culture to potentially improve cell growth and product titer. Copyright © 2009 John Wiley & Sons, Ltd.     

An Alternative Synthesis of 2-Chloro-5-Hydroxypyridine: A Key Component of the Non-Opioid Analgesic Agent ABT-594

The synthesis of the biologically useful synthon 2-chloro-5-hydroxypyridine from 3-iodo-6-chloropyridine is described.     

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

Non-resonant microwave absorption (NRMA) studies of superconducting MgB₂ and a sample containing ∼10% by weight of MgO in MgB₂ are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB₂ sample. A linear temperature dependence of the lower critical field H _c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB₂ + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB₂ sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below T _c while in the MgB₂ + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.