Robust D-wave pairing correlations in a hole-doped spin-fermion model

Pairing correlations are studied numerically in a hole-doped spin-fermion model. Simulations performed on up to 12 x 12 clusters provide indications of D-wave superconductivity away from half-filling comparable to those of the 2D t-J model. The pairing correlations are the strongest in the direction perpendicular to the dynamic stripes that appear in the ground state at some densities. An optimal doping, where correlations are maximized, was observed at approximately 25% doping with an estimated T(c) approximately 100-200 K, in qualitative agreement with high-T(c) cuprates' phenomenology, while pairing correlations are suppressed by static stripe inhomogeneities.     

Analysis of electroweak precision data and prospects for future improvements

We update our previous work on an analysis of the electroweak data by including new and partly preliminary data available up to the 1996 summer conferences. The new results on the partial decay widths into and hadrons now offer a consistent interpretation of all data in the minimal standard model. The value extracted for the strong interaction coupling constant agrees well with determinations in other areas. New constraints on the universal parameters , and are obtained from the updated measurements. No signal of new physics is found in the , , analysis once the SM contributions with GeV and those of not a too heavy Higgs boson are accounted for. The naive QCD-like technicolor model is now ruled out at the 99% CL even for the minimal model with . In the absence of a significant new physics effect in the electroweak observables, constraints on masses of the top quark, , and Higgs boson, , are derived as a function of and the QED effective coupling . The preferred range of depends rather strongly on the actual value of : for , while for at 95% CL. Prospects due to forthcoming improved measurements of asymmetries, the mass of the weak boson , and are discussed. Anticipating uncertainties of 0.00020 for , 20 MeV for , and 2 GeV for , the new physics contributions to the , , parameters will be constrained more severely, and, within the SM, the logarithm of the Higgs mass can be constrained to about . The better constraints on , , and on within the minimal SM should be accompanied with matching precision in . Received: 18 June 1997     

Experimental evaluation of the ξ-function for an atmospheric argon plasma near 104 K

The ξ-functions for an atmospheric argon plasma have been evaluated within an accuracy of ±9% over the visible region (400–800 nm) at several temperatures in the 10⁴ K region. The plasma has been produced by a low-voltage, high-current arc jet and its parameters have been determined by using a recently published value for the atomic transition probability.     

Crystal growth of Co ferrite on fine acicular γ-Fe2O3 particles

Highly coercive magnetic powder was obtained by growing cobalt ferrite on the surface of γ-Fe₂O₃ particles in highly alkaline suspensions containing cobalt and ferrous ions in a Co/Fe molar ratio = $\text{1}\text{2}$. The mechanism of the growth and the structure of cobalt ferrite on γ-Fe₂O₃ were studied by X-ray diffraction and electron diffraction techniques. Results show that crystals of cobalt ferrite CoFe₂O₄ with a spinel type crystal structure of lattice constant 8.415 Å grew epitaxially on γ-Fe₂O₃. The acicular direction of the epitaxially grown Co-γ-Fe₂O₃ as well as γ-Fe₂O₃ was in the [$\text{1}$01] direction. It was found that from the lattice constant value and the half width of X-ray diffraction peaks, the lattice constant epitaxially grown Co γ-Fe₂O₃ may be attributed to two kinds of crystals, viz., seed γ-Fe₂O₃ ($\text{a = 8.35 ～ 8.37}\text{A}\text{?}$) which was partly reduced to Fe₃O₄, and surface layer CoFe₂O₄ ($\text{a = 8.415}\text{A}\text{?}$). The crystal growth in the interface between the seed crystals and the growth layer was affected by the crystal structure of the seed crystals. The lattice constant of CoFe₂O₄ which was located in the vicinity of the interface was almost equal to that of the seed crystals.     

Vector meson pole dominance in Jψ decays into mesons

The validity of the assumption that $\text{J}\text{ψ}$ decays into mesons proceed via ω, φ and ?⁰ poles followed by cascade decays is examined. $\text{Λ(}\text{J}\text{ψ}\text{→}\text{B}\text{π)}$ is well reproduced by using $\text{Λ(}\text{J}\text{ψ}\text{→ ?π), Λ(ω → ?π), Λ(}\text{B}\text{→ ωπ)}$ and the B → ωπ helicity structure. The structure of OZI-violating $\text{J}\text{ψ}\text{?}\text{V}{}^0$ transitions including the electromagnetic contribution is examined, and compared with the data on inclusive $\text{J}\text{ψ}$ decay.     

Intramolecular participation in alkoxycarbenium ion pools

[reaction: see text] Alkoxycarbenium ions having no substituents on the cationic carbon have been accumulated as "cation pools" by the introduction of an ether group in an appropriate position. Intramolecular participation of the ether oxygen is suggested to be responsible for stabilization of the alkoxycarbenium ions.     

Highly selective Friedel-Crafts monoalkylation using micromixing

Highly selective Friedel-Crafts monoalkylation of aromatic compounds with N-acyliminium ions has been achieved by efficient 1:1 mixing using a multilamination-type micromixer.     

Proton-sensitive fluorescent organogels

A 1,10-phenanthroline-appended cholesterol-based gelator (1) and its nongelling reference compound (2) were synthesized. Among 19 solvents tested herein, gelator 1 could gelate 11 solvents including alcohols, dipolar aprotic solvents, organic acids and a base (triethylamine), indicating that 1 acts as a versatile gelator. The TEM observation gave a visual image showing that fibrillar aggregates are entangled in the three-dimensional network structure. In the fluorescence measurements, most gels afforded an emission maximum at 394 nm (purple emission), whereas only the acetic acid gel afforded an emission maximum at 522 nm (yellow emission). Thus, the influence of protonation of the 1,10-phenanthroline nitrogens (by trifluoroacetic acid) on the fluorescence properties in the gel phase was investigated in detail. The results have established that the fluorescence intensity of 1 x H+ becomes particularly strong in the gel phase, presumably because of the energy transfer from neutral 1* to protonated 1 x H+ and the restriction of the 1 x H+ molecular motion. The finding suggests the possibility that the gel system would be useful not only as a new proton-sensitive fluorescence system but also as a new medium for designing efficient energy transfer systems.     

Three-dimensional elastic wave scattering by a layer containing vertical periodic fractures

Elastic wave scattering off a layer containing a single set of vertical periodic fractures is examined using a numerical technique based on the work of Hennion et al. [J. Acoust. Soc. Am. 87, 1861-1870 (1990)]. This technique combines the finite element method and plane wave method to simulate three-dimensional scattering off a two-dimensional fractured layer structure. Each fracture is modeled explicitly, so that the model can simulate both discrete arrivals of scattered waves from individual fractures and multiply scattered waves between the fractures. Using this technique, we examine changes in scattering characteristics of plane elastic waves as a function of wave frequency, angle of incidence, and fracture properties such as fracture stiffness, height, and regular and irregular spacing.