Development of laser ablation assisted resonant ionization mass spectrometry for isotope analysis

Stable isotope analysis using Laser Ablation Assisted Resonant Ionization Mass Spectrometry (LA-RIMS) is discussed. For the case of the ⁸⁷Sr/⁸⁶Sr isotope ratio measurements with a single color two-photon excitation scheme, the mass discrimination effects, which occur in LA-RIMS, are analyzed and a precision of 0.6% was extracted. For preparation of LA-RIMS on Hf isotopes, a novel two-color resonant excitation scheme with subsequent non-resonant ionization has been established using a high repetition-rate Ti:Sapphire laser system.     

Carboxymethyl poly(L‐histidine) as a new pH‐sensitive polypeptide at endosomal/lysosomal pH

A carboxymethyl poly(L ‐histidine) has been synthesized as a new pH‐sensitive polypeptide at endosomal/lysosomal pH. Because of its poor water solubility at physiological pH, an application of poly(L ‐histidine) with a pK_a around 6.0 has been limited in spite of the native possession of the pH‐dependent property change at endosomal pH. Although the unmodified poly(L ‐histidine) suddenly precipitates out of the aqueous medium above pH 6.0 as the result of the deprotonation of the imidazole groups, the water solubility of the resulting carboxymethyl poly(L ‐histidine) has been improved at physiological pH. A solution turbidity measurement proved that no significant effect on a rapid aggregate formation or phase separation of serum proteins is induced by carboxymethyl poly(L ‐histidine). Hemolysis assay showed that the carboxymethyl poly(L ‐histidine) enhances membrane disruptive ability at endosomal/lysosomal pH. The cellular uptake of luciferase in the presence of the carboxymethyl poly(L ‐histidine) increases intracellular luciferase activity, which suggests that the carboxymethyl poly(L ‐histidine) makes the luciferase escape from lysosomal degradation. The carboxymethyl poly(L ‐histidine) would be the fundamental compound for designing various drug carriers with the pH sensitivity at endosomal/lysosomal pH. Copyright © 2007 John Wiley & Sons, Ltd.     

57Fe mössbauer study of high-T c Y−Ba−Cu oxide superconductors

⁵⁷Fe Mössbauer measurements have been performed for Fe-doped YBa₂ (Cu_1-x Fe_x)₃O_7-v (x=0.005–0.10) superconducting oxides. Fe atoms mainly substitute at Cul chain sites and the fraction of Fe at Cu2 plane sites is discussed thermodynamically. The spin direction of Fe at Cu2 was determined to be normal to thec-axis using an oxygen deficient specimen having a strong texture along thec-axis. A magnetically broadened spectrum at 4.2 K for Fe at Cul is compared with a simulated one which takes the distribution of hyperfine fields into account.     

Single-shot detection of electrons generated by individual photons in a tunable lateral quantum dot

We demonstrate single-shot detection of single electrons generated by single photons using an electrically tunable quantum dot and a quantum point contact charge detector. By tuning the quantum dot in a Coulomb blockade before the photoexcitation, we observe the trapping and subsequent resetting of single photogenerated electrons. The photogenerated electrons can be stored in the dot for a tunable time range from shorter to longer than the spin-flip time T1. We combine this trap-reset technique with spin-dependent tunneling under magnetic fields to observe the spin-dependent photon detection within the T1.     

NMR study of coexistence of ferro- and antiferromagnetism in (Zr1−xNbx)Fe2

The magnetic phase diagram has been investigated in the C14 type (Zr_1−xNb_x)Fe₂ with x0.7 from ⁹³Nb NMR and magnetization measurements. In the compound with x = 0.825 a first order-like transition has been found to occur around 25 K from a canted state with the ferromagnetic moment in the basal plane to a ferromagnetic state with decreasing temperature.     

NMR and NQR studies of spin dynamics and superconductivity in High-T c oxides

The magnetic and superconducting properties in the high-T _c cuprates have been investigated over a wide hole doping range by⁶³Cu,¹⁷O and²⁰⁵Tl NMR and NQR in the lightly-doped La_2?xSr_xCuO₄ (LSCO), the heavily-doped Tl₂Ba₂CuO_6+y (TBCO) and the Zn-doped YBa₂Cu₃O₇ (YBCO₇). In low doping region, the large antiferromagnetic (AF) spin correlation around the zone boundary (q=Q) causes the Curie-Weiss behavior of⁶³(1/T ₁ T) associated with that of the staggered susceptibility χ_O(T) in LSCO. In the vicinity of the hole content whereT _c has a peak, the AF spin correlation still survives, although the magnetic coherence length ξ_M is considerably short being presumably (ξ_M/a) ～ 1. The further doping destroys progressively the AF spin correlation, which is no longer present is non-superconducting TBCO compounds. These NMR evidences signify that there is an intimate relation between the presence of the AF spin correlation and the onset of the superconductivity. The local collapse of AF spin correlation is a primary cause for the unexpected strong reduction ofT _c in case of the substitution of Zn impurities into the CuO₂ plane. The superconducting properties clarified by NMR experiments cannot be accounted for by the conventional BCS model or other isotropic s-wave models. A d-wave model is applicable in interpreting consistently most of the NMR results, if the finite density of states at the Fermi level is taken into consideration and is associated with the pair breaking effect. There are increasing evidences that the magnetic mechanism for the superconductivity is promising in high-T _c cuprates.     

Dynamic and steady-shear melt rheology of and ethylene-methacrylic acid copolymer and its salts

Studies have been made on the dynamic and steady-shear melt rheology of an ethylene–methacrylic acid copolymer and two of its salts obtained by partial neutralization with sodium and with calcium bases. Measurements were made with a Weissenberg rheogoniometer over a broad range of shear rates and frequency in the temperature interval mainly from 100 to 160°C. The temperature coefficients of dynamic and steady shear viscosity are evaluated at both constant shear rate and constant stress. Likewise, complex dynamic viscosities and apparent high steady-flow viscosities and intercompared at equivalent frequencies and shear rates. The un-ionized acid copolymer shows good correlation between the frequency dependence of the complex viscosity and the shear rate dependence of the apparent viscosity. This is not true for either the sodium salt or the calcium salt. These results are consistent with the two-phase structural model for these materials, i.e., a matrix of hydrocarbon in which are embedded ionic domains.     

A comment on preparation of amorphous stage in vacuum-deposited film from study of its crystallization

This work gives a comment on density change in amorphous stage during growth of vacuum-deposited film, which is based on change in rate of increase in film thickness of crystallized stage with increasing vapour stream, and thickness-dependence of crystallization temperature. This may offer an idea for the formation of ideal amorphous stage with void-free.