Superconductivity and magnetic order in CaLaBaCu3O z

X-ray diffraction, thermogravimetric analysis, magnetization and Mossbauer studies of a⁵⁷Fe probe, in CaLaBa(Cu_1−x Fe _x )₃O _z withz=7, 6.5 andx=0.00 to 0.05 have been performed. Forz=7,T _c drops from 74 K forx=0.00 to 35 K forx=0.05. In CaLaBa(Cu_1−x Fe _x )₃O _z withz=7, 10% of the iron is magnetically ordered withH _eff=530 K kOe andT _N=400 K, even though the sample is superconducting. In the oxygen poor, non-superconducting samples (z=6.5) 20% of the iron is magnetically ordered withH _eff=340 kOe andT _N=340 K. Since the iron reflects the magnetic order of the Cu(2) ions, this may show that perhaps two inequivalent Cu(2) sites exist in CaLaBa(Cu_1−x Fe _x )₃O₇, ones of which is magnetically ordered. The experimental observations may be interpreted in terms of the special crystal structure which can allow superconductivity and magnetism to coexist, probably in separate Cu(2) planes.     

Two-photon laser-induced fluorescence of H O and D O molecules at ambient pressure

We have carried out experiments of two-photon excitation of vapor phase H₂O and D₂O molecules at atmospheric pressure. A narrow-band tunable UV OPO laser is used in the experiments. Transient B ₁ → B ₁ emission from the excited predissociating state is seen in both cases. The complete B ₁ ← A ₁ fluorescence excitation spectrum in the spectral range of 245-250 nm is measured and compared with theory. It is shown that the predissociation rate increases with the rotational quantum number K' _a > 2 more strongly than with K ^′2 _a . No perturbation effects on the measured LIF spectra are observed at a laser power density below 2 GW/cm². Experimental results indicate a negligible contribution from both molecular association and collisions with atmospheric gases. Only an extremely weak vibrational progression belonging to the second positive system of N₂ has been observed, which appears to be due to energy and charge transfer in N ⁺ ₂ ^* + H ₂ O collisions. Received 25 January 2002 / Received in final form 27 May 2002 Published online 4 March 2003     

LETTER: Gauge Choice and Geodetic Deflection in Conformal Gravity

Conformal gravity has been proposed as an alternative theory of gravity which can account for flat galactic rotation curves without recourse to copious quantities of dark matter. However it was shown that for the usual choice of the metric, the result is catastrophic for null or highly relativistic geodesics, the effect is exactly the opposite yielding an effective repulsion and less deflection in this case. It is the point of this paper, that any result for massive geodesics depends on the choice of conformal gauge, in contradistinction to the case of null geodesics. We show how it is possible to choose the gauge so that the theory is attractive for all geodesics.     

The Effect of varying correlation lengths on Anomalous Transport

Conventional concepts for transport in porous media assume that the heterogeneous distribution of hydraulic conductivities is the source for the contaminant temporal and spatial heavy tail. This tailing, known as anomalous or non-Fickian transport, can be captured by the β parameter in the continuous-time random walk framework. This study shows that with the increase in spatial correlation length between these heterogeneous distributions of hydraulic conductivities, the transport’s anomaly reduces; yet, the β value is unchanged, suggesting a topological component of the conductivity field, captured by the β. This finding is verified by an analysis of the solute transport, showing that the changing conductivity values have a moderate effect on the transport shape.

     

Photoexcitation of rare-gas neon and argon clusters doped with <Emphasis Type="Bold">H</Emphasis><Subscript><Emphasis Type="Bold">2</Emphasis></Subscript><Emphasis Type="Bold">O</Emphasis>

We have studied the fluorescence of electronically excited OH^*, H^* and H₂O^+* dissociation fragments after VUV excitation ( h ν≥11.6 eV) of rare-gas clusters (Rg = Ne, Ar) doped with H₂O molecules. In contrast to a free molecule, where Balmer H-series dominate the UV-visible spectra, only the OH ^* ( A ² Σ ⁺ ↦ X ² Π) emission band is observed in neon clusters. No emission of excited water ions has been observed. We find that while higher excitation energies (Ne vs. Ar) induce higher vibrational excitation of the OH^* ( A ) fragment, the rotational temperature is lower. This effect is attributed to the difference in the geometric position of the H₂O molecule on the surface or inside the Rg-cluster. The rotational relaxation in neon clusters is rapid while the vibrational relaxation is slow because of the coupling with the low energy matrix phonons. Received 7 March 2002 / Received in final form 27 May 2002 Published online 19 July 2002     

Isotopic effect on the cage-induced quenching of OH(A)/OD(A) inside small argon clusters

In this paper we report on the isotopic effect on the cage-induced excited-state quenching inside small Ar(m) clusters (m<10(2)) solvated in large Ne(N) clusters (N approximately 7.5x10(3)). Excited OH(A)/OD(A) fragments are produced by photodissociation of H2O and D2O molecules and the quenching agents are correspondingly H or D atoms. The decrease of the fluorescence yield with the size of the cluster m>m0 is observed in both cases and it is attributed to the formation of the cage of argon atoms around the doped molecule. Interestingly, more atoms are needed to induce the fluorescence quenching of OD*(A) fragments, m0=21+/-3, compared to the electronically excited state quenching of OH*(A) molecules, 11+/-2. A diffusion model containing two free parameters, the quenching cross section sigmaq and the number of argon atoms forming the cage m0, explains the effect in terms of the residence time of the hydrogen atom inside the cage. We suggest that the melting of the doped rare gas clusters is responsible for the different predissociation dynamics. The quenching cross section obtained from the experimental data is in good agreement with former experiments.     

Second order Kerr deflection

We perform a full second order calculation of the deflection of light along the equatorial plane in the Kerr metric. Previous Kerr deflection calculations were interested in obtaining the correction due to rotation to the Einstein deflection. By expanding to first order in the rotational parameter a, they obtain the Einstein deflection of 4M/r _o and the second order deflection due to rotation of , (where r _o is the point of closest approach). In this paper, we are interested in going beyond the rotational contribution for the purpose of astrophysical applications. We therefore keep all terms up to second order in our final weak field expansion. Besides the rotational contribution, we also obtain an extra second order term of . Since M > a, this extra term is greater than the rotational contribution of in astrophysical applications. When a/M is close to unity the terms are of the same order of magnitude.