Tunneling through two resonant levels: fixed points and conductances

We study point contact tunneling between two leads of a Tomonaga-Luttinger liquid through two degenerate resonant levels in parallel. This is one of the simplest cases of a quantum junction problem where the Fermi statistics of the electrons plays a non-trivial role through the Klein factors appearing in bosonization. Using a mapping to a `generalized Coulomb model' studied in the context of the dissipative Hofstadter model, we find that any asymmetry in the tunneling amplitudes from the two leads grows at low temperatures, so that ultimately there is no conductance across the system. For the symmetric case, we identify a non-trivial fixed point of this model; the conductance at that point is generally different from the conductance through a single resonant level.Comment: 6 pages, 3 figure

Diffuse Neutron Scattering Study of Magnetic Correlations in half-doped La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) Manganites

The short range ordered magnetic correlations have been studied in half doped La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) compounds by polarized neutron scattering technique. On doping Sr2+ for Ca2+ ion, these compounds with x = 0.1, 0.3, and 0.4 exhibit CE-type, mixture of CE-type and A-type, and A-type antiferromagnetic ordering, respectively. Magnetic diffuse scattering is observed in all the compounds above and below their respective magnetic ordering temperatures and is attributed to magnetic polarons. The correlations are primarily ferromagnetic in nature above T\_N, although a small antiferromagnetic contribution is also evident. Additionally, in samples x = 0.1 and 0.3 with CE-type antiferromagnetic ordering, superlattice diffuse reflections are observed indicating correlations between magnetic polarons. On lowering temperature below T\_N the diffuse scattering corresponding to ferromagnetic correlations is suppressed and the long range ordered antiferromagnetic state is established. However, the short range ordered correlations indicated by enhanced spin flip scattering at low Q coexist with long range ordered state down to 3K. In x = 0.4 sample with A-type antiferromagnetic ordering, superlattice diffuse reflections are absent. Additionally, in comparison to x = 0.1 and 0.3 sample, the enhanced spin flip scattering at low Q is reduced at 310K, and as temperature is reduced below 200K, it becomes negligibly low. The variation of radial correlation function, g(r) with temperature indicates rapid suppression of ferromagnetic correlations at the first nearest neighbor on approaching TN. Sample x = 0.4 exhibits growth of ferromagnetic phase at intermediate temperatures (~ 200K). This has been further explored using SANS and neutron depolarization techniques.Comment: 13 pages, 12 figures, To appear in Physical Review

Interplay of 4f-3d Magnetism and Ferroelectricity in DyFeO3

DyFeO3 exhibits a weak ferromagnetism (TNFe ~ 645 K) that disappears below a spin-reorientation (Morin) transition at TSRFe ~ 50 K. It is also known that applied magnetic field induces ferroelectricity at the magnetic ordering temperature of Dy-ions (TNDy ~ 4.5 K). Here, we show that the ferroelectricity exists in the weak ferromagnetic state (TSRFe < T < TN,C) without applying magnetic field, indicating the crucial role of weak ferromagnetism in inducing ferroelectricity. 57Fe M\"ossbauer studies show that hyperfine field (Bhf) deviates from mean field-like behaviour that is observed in the weak ferromagnetic state and decreases below the onset of spin-reorientation transition (80 K), implying that the Bhf above TSR had additional contribution from Dy-ions due to induced magnetization by the weak ferromagnetic moment of Fe-sublattice and below TSR, this contribution decreases due to collinear ordering of Fe-sublattice. These results clearly demonstrate the presence of magnetic interactions between Dy(4f) and Fe(3d) and their correlation with ferroelectricity in the weak ferromagnetic state of DyFeO3.Comment: 5 pages, 6 figures, published in EP

Heterogeneity of monosomy 3 in fine needle aspiration biopsy of choroidal melanoma.

PurposeTo report on the heterogeneity of monosomy 3 in a fine needle aspiration biopsy obtained transsclerally from choroidal melanoma for prognosis.MethodsAll clinical records for patients who had been diagnosed with choroidal melanoma and underwent iodine-125 plaque brachytherapy with intraoperative transscleral fine needle aspiration biopsy from January 2005 to August 20, 2011, and who had a positive result for monosomy 3 according to fluorescence in situ hybridization as reported by clinical cytogenetics testing were collected. Patient age and sex, total number of cells evaluated and number of cells positive for monosomy 3, tumor size, and metastatic outcome were recorded for each patient.ResultsA positive result for monosomy 3 was reported in 93 patients who underwent transscleral fine needle aspiration biopsy. Two patients were lost to follow-up immediately post-operatively, and the remaining 91 patients were included in this study. The mean number of cells evaluated in the biopsy was 273 (range 28 to 520). The mean percentage of cells positive for monosomy 3 was 62.9% (range 4.7%-100%). The mean tumor height was 5.91 mm (range 1.99 to 10.85 mm). Larger tumors were associated with a higher percentage of cells positive for monosomy 3. During the average follow-up interval of 28.9 months (range 3-76 months), choroidal melanoma metastasis developed in 18 (20%) patients. Patients whose tumors had 1%-33% of cells positive for monosomy 3 had a significantly lower risk of metastasis-related death compared to patients whose tumors harbored a higher percentage of monosomy 3 (p = 0.04).ConclusionsCytogenetic heterogeneity of fluorescent in situ hybridization for monosomy 3 exists in a biopsy sample. Larger tumors were more likely to have a higher percentage of monosomy 3 positive cells in the sample. Furthermore, patients whose tumors had more than 33% of cells positive for monosomy 3 had a poorer prognosis than patients whose tumors had lower percentages of monosomy 3

A theoretical review of the operation of vibratory stress relief with particular reference to the stabilization of large-scale fabrications

Vibratory stress relief (VSR) is widely used on large welded fabrications to stabilize the structures so that they do not distort during further machining or during operational duty. The level of applied stress achieved during VSR on such structures is only 5–10 per cent of the yield stress. It is, therefore, not obvious how these applied loads come to modify the level of residual stress. It is suggested here that the reason for the success of VSR applied to large fabrications lies (a) in the origin of the residual stresses and (b) in the partial relief of these residual stresses by the initiation of the transformation of retained austenite particles (in the size range from 1 to 25 µm) by the movement of dislocations into positions that are favourable for the nucleation of martensite embryos. The shear deformation associated with the transformation of retained austenite into martensite will reduce the residual stress field to the point where the stability of the structure may be assured

Magnetic Field resulting from non-linear electrical transport in single crystals of charge-ordered Pr0.63_{0.63} Ca0.37_{0.37} MnO3_{3}}

In this letter we report that the current induced destabilization of the charge ordered (CO) state in a rare-earth manganite gives rise to regions with ferromagnetic correlation. We did this experiment by measurement of the I-V curves in single crystal of the CO system Pr$_{0.63}$Ca$_{0.37}$MnO$_{3}$ and simultanously measuring the magnetization of the current carrying conductor using a high T$_c$ SQUID working at T = 77K. We have found that the current induced destabilization of the CO state leads to a regime of negative differential resistance which leads to a small enhancement of the magnetization of the sample, indicating ferromagnetically aligned moments.Comment: 4 pages LateX, 4 eps figure

Critical exponents and the correlation length in the charge exchange manganite spin glass Eu_{0.5}Ba_{0.5}MnO_{3}

The critical regime of the charge exchange (CE) manganite spin glass Eu_{0.5}Ba_{0.5}MnO_{3} is investigated using linear and non linear magnetic susceptibility and the divergence of the third ordered susceptibility (chi{_3}) signifying the onset of a conventional freezing transition is experimentally demonstrated. The divergence in chi{_3}, dynamical scaling of the linear susceptibility and relevant scaling equations are used to determine the critical exponents associated with this freezing transition, the values of which match well with the 3D Ising universality class. Magnetic field dependence of the spin glass response function is used to estimate the spin correlation length which is seen to be larger than the charge/orbital correlation length reported in this system.Comment: 4 pages, 4 Figure