Ising Spin Glasses on Wheatstone-Bridge Hierarchical Lattices

Nearest-neighbor-interaction Ising spin glasses are studied on three different hierarchical lattices, all of them belonging to the Wheatstone-Bridge family. It is shown that the spin-glass lower critical dimension in these lattices should be greater than 2.32. Finite-temperature spin-glass phases are found for a lattice of fractal dimension $D \approx 3.58$ (whose unit cell is obtained from a simple construction of a part of the cubic lattice), as well as for a lattice of fractal dimension close to five.Comment: Accepted for publication in Physics Letters

Iron phthalocyanine and MnOx composite catalysts for microbial fuel cell applications

AbstractA low cost iron phthalocyanine (FePc)-MnOx composite catalyst was prepared for the oxygen reduction reaction (ORR) in the cathode of microbial fuel cells (MFCs).The catalysts were characterised using rotating ring disc electrode technique. The n number of electrons transferred, and H2O2 production from ORR was investigated. The FePc–MnOx composite catalyst showed higher ORR reduction current than FePc and Pt in low overpotential region. MFC with composite catalysts on the cathode was tested and compared to Pt and FePc cathodes. The cell performance was evaluated in buffered primary clarifier influent from wastewater treatment plant. The membrane-less single chamber MFC generated more power with composite FePcMnOx/MON air cathodes (143mWm−2) than commercial platinum catalyst (140mWm−2) and unmodified FePc/MON (90mWm−2), which is consistent with the RRDE study.The improvement was due to two mechanisms which abate H2O2 release from the composite. H2O2 is the reactant in two processes: (i) chemical regeneration of MnOx after electro-reduction to Mn2+, and (ii) peroxide undergoing chemical disproportionation to O2 and H2O on an electrochemically aged manganese surface retained in the film. Process (i) has the potential to sustain electrochemical reduction of MnOx at cathode potentials as high as 1.0VRHE

Functional analysis of dsRNAs (L1, L3, L5, and M2) associated with isometric 34-nm virions of Agaricus bisporus (white button mushroom)

cDNA clones of dsRNAs associated with La France disease of Agaricus bisporus were isolated, Clones corresponding to L1 and L5 dsRNAs were sequenced. The deduced amino acid sequence of L1 dsRNA (1078 amino acids, M(r) 121K) showed significant homology with RNA-dependent RNA polymerases of other dsRNA viruses. The deduced amino acid sequence of L5 dsRNA (724 amino acids, M(r) 82K) showed no homology with known proteins. Amino acid sequences of tryptic digests of three virion-associated proteins were determined. The 34-nm virion-associated protein of M(r) 115K was encoded by the L1 dsRNA, thus identifying this protein as the RNA-dependent RNA polymerase. The virion-associated protein of M(r) 90K was encoded by the previously sequenced L3 dsRNA. A cDNA clone of the previously sequenced M2 dsRNA was expressed in Escherichia coli and antibodies raised against this protein reacted only with a protein present in the cytoplasm of diseased A. bisporus fruit bodies but not in the 34-nm virions. (C) 1996 Academic Press, Inc

Propagation inhibition and wave localization in a 2D random liquid medium

Acoustic propagation and scattering in water containing many parallel air-filled cylinders is studied. Two situations are considered and compared: (1) wave propagating through the array of cylinders, imitating a traditional experimental setup, and (2) wave transmitted from a source located inside the ensemble. We show that waves can be blocked from propagation by disorders in the first scenario, but the inhibition does not necessarily imply wave localization. Furthermore, the results reveal the phenomenon of wave localization in a range of frequencies.Comment: Typos in Fiures are correcte

Thalamocortical Inputs Show Post-Critical-Period Plasticity

SummaryExperience-dependent plasticity in the adult brain has clinical potential for functional rehabilitation following central and peripheral nerve injuries. Here, plasticity induced by unilateral infraorbital (IO) nerve resection in 4-week-old rats was mapped using MRI and synaptic mechanisms were elucidated by slice electrophysiology. Functional MRI demonstrates a cortical potentiation compared to thalamus 2 weeks after IO nerve resection. Tracing thalamocortical (TC) projections with manganese-enhanced MRI revealed circuit changes in the spared layer 4 (L4) barrel cortex. Brain slice electrophysiology revealed TC input strengthening onto L4 stellate cells due to an increase in postsynaptic strength and the number of functional synapses. This work shows that the TC input is a site for robust plasticity after the end of the previously defined critical period for this input. Thus, TC inputs may represent a major site for adult plasticity in contrast to the consensus that adult plasticity mainly occurs at cortico-cortical connections

mTORC2 signaling drives the development and progression of pancreatic cancer

mTOR signaling controls several critical cellular functions and is deregulated in many cancers, including pancreatic cancer. To date, most efforts have focused on inhibiting the mTORC1 complex. However, clinical trials of mTORC1 inhibitors in pancreatic cancer have failed, raising questions about this therapeutic approach. We employed a genetic approach to delete the obligate mTORC2 subunit Rictor and identified the critical times during which tumorigenesis requires mTORC2 signaling. Rictor deletion resulted in profoundly delayed tumorigenesis. Whereas previous studies showed most pancreatic tumors were insensitive to rapamycin, treatment with a dual mTORC1/2 inhibitor strongly suppressed tumorigenesis. In late-stage tumor-bearing mice, combined mTORC1/2 and PI3K inhibition significantly increased survival. Thus, targeting mTOR may be a potential therapeutic strategy in pancreatic cancer

Instability of a Bose-Einstein Condensate with Attractive Interaction

We study the stability of a Bose-Einstein condensate of harmonically trapped atoms with negative scattering length, specifically lithium 7. Our method is to solve the time-dependent nonlinear Schrodinger equation numerically. For an isolated condensate, with no gain or loss, we find that the system is stable (apart from quantum tunneling) if the particle number N is less than a critical number N_c. For N > N_c, the system collapses to high-density clumps in a region near the center of the trap. The time for the onset of collapse is on the order of 1 trap period. Within numerical uncertainty, the results are consistent with the formation of a "black hole" of infinite density fluctuations, as predicted by Ueda and Huang. We obtain numerically N_c approximately 1251. We then include gain-loss mechanisms, i.e., the gain of atoms from a surrounding "thermal cloud", and the loss due to two- and three-body collisions. The number N now oscillates in a steady state, with a period of about 145 trap periods. We obtain N_c approximately 1260 as the maximum value in the oscillations.Comment: Email correspondence to [email protected] ; 18 pages and 9 EPS figures, using REVTeX and BoxedEPS macro

An Introduction to Data Analysis in Asteroseismology

A practical guide is presented to some of the main data analysis concepts and techniques employed contemporarily in the asteroseismic study of stars exhibiting solar-like oscillations. The subjects of digital signal processing and spectral analysis are introduced first. These concern the acquisition of continuous physical signals to be subsequently digitally analyzed. A number of specific concepts and techniques relevant to asteroseismology are then presented as we follow the typical workflow of the data analysis process, namely, the extraction of global asteroseismic parameters and individual mode parameters (also known as peak-bagging) from the oscillation spectrum.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Structural Probe of a Glass Forming Liquid: Generalized Compressibility

We introduce a new quantity to probe the glass transition. This quantity is a linear generalized compressibility which depends solely on the positions of the particles. We have performed a molecular dynamics simulation on a glass forming liquid consisting of a two component mixture of soft spheres in three dimensions. As the temperature is lowered (or as the density is increased), the generalized compressibility drops sharply at the glass transition, with the drop becoming more and more abrupt as the measurement time increases. At our longest measurement times, the drop occurs approximately at the mode coupling temperature $T_C$. The drop in the linear generalized compressibility occurs at the same temperature as the peak in the specific heat. By examining the inherent structure energy as a function of temperature, we find that our results are consistent with the kinetic view of the glass transition in which the system falls out of equilibrium. We find no size dependence and no evidence for a second order phase transition though this does not exclude the possibility of a phase transition below the observed glass transition temperature. We discuss the relation between the linear generalized compressibility and the ordinary isothermal compressibility as well as the static structure factor.Comment: 18 pages, Latex, 26 encapsulated postscript figures, revised paper is shorter, to appear in Phys. Rev.

Influence of next-nearest-neighbor electron hopping on the static and dynamical properties of the 2D Hubbard model

Comparing experimental data for high temperature cuprate superconductors with numerical results for electronic models, it is becoming apparent that a hopping along the plaquette diagonals has to be included to obtain a quantitative agreement. According to recent estimations the value of the diagonal hopping $t'$ appears to be material dependent. However, the values for $t'$ discussed in the literature were obtained comparing theoretical results in the weak coupling limit with experimental photoemission data and band structure calculations. The goal of this paper is to study how $t'$ gets renormalized as the interaction between electrons, $U$, increases. For this purpose, the effect of adding a bare diagonal hopping $t'$ to the fully interacting two dimensional Hubbard model Hamiltonian is investigated using numerical techniques. Positive and negative values of $t'$ are analyzed. Spin-spin correlations, $n(\bf{k})$, $\langle n\rangle$ vs $\mu$, and local magnetic moments are studied for values of $U/t$ ranging from 0 to 6, and as a function of the electronic density. The influence of the diagonal hopping in the spectral function $A(\bf{k},\omega)$ is also discussed, and the changes in the gap present in the density of states at half-filling are studied. We introduce a new criterion to determine probable locations of Fermi surfaces at zero temperature from $n(\bf{k})$ data obtained at finite temperature. It appears that hole pockets at ${\bf{k}}=(\pi/2,\pi/2)$ may be induced for negative $t'$ while a positive $t'$ produces similar features at ${\bf{k}}=(\pi,0)$ and $(0,\pi)$. Comparisons with the standard 2D Hubbard ($t'=0$) model indicate that a negative $t'$ hopping amplitude appears to be dynamically generated. In general, we conclude that it is very dangerous to extract a bare parameter of the Hamiltonian $(t')$ from PES data whereComment: 9 pages (RevTex 3.0), 12 figures (postscript), files packed with uufile