Replica symmetry breaking in trajectories of a driven Brownian particle

We study a Brownian particle passively driven by a field obeying the noisy Burgers equation. We demonstrate that the system exhibits replica symmetry breaking in the path ensemble with the initial position of the particle being fixed. The key step of the proof is that the path ensemble with a modified boundary condition can be exactly mapped to the canonical ensemble of directed polymers.Comment: 12 pages, 16 figure

Calculation of 1RSB transition temperature of spin glass models on regular random graphs under the replica symmetric ansatz

We study $p$-spin glass models on regular random graphs. By analyzing the Franz-Parisi potential with a two-body cavity field approximation under the replica symmetric ansatz, we obtain a good approximation of the 1RSB transition temperature for $p=3$. Our calculation method is much easier than the 1RSB cavity method because the result is obtained by solving self-consistent equations with Newton's method.Comment: 21 pages, 1 figur

Chandra Observations and Optical Identification of Hard X-ray Sources Discovered with ASCA

We present the first results of the Chandra and optical follow-up observations of hard X-ray sources detected in the ASCA Medium Sensitivity Survey (AMSS). Optical identifications are made for five objects. Three of them show either weak or absent optical narrow emission lines and are at low redshift ~0.06. One of them is a broad line object at z=0.910 and one is a z=0.460 object with only narrow lines. All the narrow line objects show strong evidence for absorption in their X-ray spectra. Their line ratios are consistent with a Seyfert II/LINER identification as are the line widths. The three low redshift objects have the colors of normal galaxies and apparently the light is dominated by stars. This could be due to the extinction of the underlying nuclear continuum by the same matter that absorbs X-rays and/or due to the dilution of the central source by starlight. These results suggest that X-ray sources that appear as ``normal'' galaxies in optical and near-IR bands significantly contribute to the hard X-ray background. This population of objects has a high space density and probably dominates the entire population of active galaxies.Comment: 23 pages, 7 figures and 7 tables; accepted for publication in PAS

NOTE ON LOWER BOUNDS OF ENERGY GROWTH FOR SOLUTIONS TO WAVE EQUATIONS

In this note we study lower bounds of energy growth for solutions to wave equations which are compact in space perturbations of the wave equation ∂^2_tu−Δu=0. Assuming that there exists a null bicharacteristic (x(t),ξ(t)), parametrized by the time t, such that x(t) remains inside a ball and ξ(t) outside a ball for t≥0 we prove that the solution operator R(t) is bounded from below by constant times √ in the operator norm. We apply this result to examples constructed by the same idea as in Colombini and Rauch [1] and show that there exist compact in space perturbations which cause exp(ct^α) growth of the energy for any given 0≤α≤1

A class of Heisenberg models with the orthogonal dimer ground states

Extensions of the Shastry-Sutherland model are possible in various ways. In particular, it is possible to construct a natural model in three dimensions which has the exact dimer ground state. Recently found spin gap system SrCu_2(BO_3)_2 has this structure. The exchange constants between the layers is expected to be smaller than the intra-layer couplings. However, the exactness of the dimer state for the three dimensional structure is important to understand why magnetic properties of SrCu_2(BO_3)_2 are described well by the two dimensional model.Comment: 3 pages, 5 figures, to appear in Journal of Physics: Condensed Matte

Determination of etoposide serum concentrations in small pediatric samples by an improved method of reversed-phase high-performance liquid chromatography.

Several specific assays have been developed for the measurement of etoposide in biological fluids. As large samples are required for high sensitivity, these systems are not appropriate for a pediatric practice. In the present study, however, an improved method for the determination of serum levels of the anticancer drug etoposide was developed, using high-performance liquid chromatography with fixed-wavelength ultraviolet detection. Etoposide was extracted from serum using dichloromethane. The efficiency of extraction from serum was 85.7 +/- 7.7% for etoposide and 81.1 +/- 8.4% for diphenylhydantoin, the internal standard. The serum concentrations of etoposide were measured in 0.2-ml serum samples. The lower limit of detection was 50 ng/ml. Each measurement was completed within 5 min. The linear quantitation range for etoposide was 0.05-50 microg/ml. This assay presents an alternative method for routine measurement of serum levels of etoposide in the pediatric oncology setting.</p

Iron-Based Heavy Quasiparticles in SrFe4_{4}Sb12_{12}: An Infrared Spectroscopic Study

Temperature-dependent infrared reflectivity spectra of SrFe$_{4}$Sb$_{12}$ has been measured. A renormalized Drude peak with a heavy effective mass and a pronounced pseudogap of 10 meV develops in the optical conductivity spectra at low temperatures. As the temperature decreases below 100 K, the effective mass ($m^{*}$) rapidly increases, and the scattering rate ($1/\tau$) is quenched. The temperature dependence of $m^{*}$ and $1/\tau$ indicates that the hybridization between the Fe 3d spins and the charge carriers plays an important role in determining the physical properties of SrFe$_{4}$Sb$_{12}$ at low temperatures. This result is the clear evidence of the iron-based heavy quasiparticles.Comment: 5 pages, 5 figure

Temperature-Dependence of Magnetically-Active Charge Excitations in Magnetite across the Verwey Transition

We have studied the electronic structure of bulk single crystals and epitaxial films of magnetite Fe$_3$O$_4$. Fe $2p$ core-level spectra show clear differences between hard x-ray (HAX-) and soft x-ray (SX-) photoemission spectroscopy (PES), indicative of surface effects. The bulk-sensitive spectra exhibit temperature ($T$)-dependent charge excitations across the Verwey transition at $T_V$=122 K, which is missing in the surface-sensitive spectra. An extended impurity Anderson model full-multiplet analysis reveals roles of the three distinct Fe-species (A-Fe$^{3+}$, B-Fe$^{2+}$, B-Fe$^{3+}$) below $T_V$ for the Fe $2p$ spectra, and its $T-$dependent evolution. The Fe $2p$ HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the magnetically distinct sites associated with the charge excitations. Valence band HAXPES shows finite density of states at $E_F$ for the polaronic metal with remnant order above $T_V$, and a clear gap formation below $T_V$. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B-Fe$^{2+}$ and B-Fe$^{3+}$ electronic states, consistent with resistivity and bulk-sensitive optical spectra.Comment: 5 pages, 4 figures Accepted in Physical Review Letter