Supersolidity, entropy and frustration

We study the properties of t-t'-V model of hard-core bosons on the triangular lattice that can be realized in optical lattices. By mapping to the spin-1/2 XXZ model in a field, we determine the phase diagram of the t-V model where the supersolid characterized by the ordering pattern (x,x,-2x') ("ferrimagnetic" or SS A) is a ground state for chemical potential \mu >3V. By turning on either temperature or t' at half-filling \mu =3V, we find a first order transition from SS A to the elusive supersolid characterized by the (x,-x,0) ordering pattern ("antiferromagnetic" or SS C). In addition, we find a large region where a superfluid phase becomes a solid upon raising temperature at fixed chemical potential. This is an analog of the Pomeranchuk effect driven by the large entropic effects associated with geometric frustration on the triangular lattice.Comment: 4 pages, igures, LaTe

Is the energy status influencing dispersion in American glass eel?

International audienceThe American eel has a facultative catadromous life cycle. Spawning occurs in Sargasso Sea and growth occurs into freshwater or saltwater habitats over a wide geographical range. The selection of suitable habitat for growth begins at the glass eel stage. Based on the hypothesis of conditional dispersion strategy, energetic status would determine whether glass eels would express freshwater or saltwater preference. Glass eels were captured from two rivers from Nova Scotia and two rivers from Québec in 2011 and 2012. Following salinity preference experiments, glass eels were classified as “inactive” or as “active with preference for fresh water” and “active with preference for salt water”. They were anaesthetized in MS 222, weighed, measured and frozen in carbonic ice. Results indicate that glass eels expressing preference for freshwater had the highest condition factor. Total content of glycogen and lipids were measured in order to test whether or not the three groups of glass eels could be differentiated based on their energy status whatever the river and the year of fishing and results will be presented

Controllable pulse parameter TMS and TMS-EEG as novel approaches to improve neural targeting with rTMS in human cerebral cortex

Repetitive transcranial magnetic stimulation (rTMS) can produce after-effects on the excitability and function of the stimulated cortical site that outlasts the period of stimulation for several minutes or hours (Hamada et al., 2008; Huang et al., 2005; Ridding and Ziemann, 2010; Sommer et al., 2013). These are thought to involve early phases of long term potentiation/depression at cortical synapses. Depending on the area stimulated, the after-effects can influence performance of a variety of cognitive and motor tasks, as well as learning (Parkin et al., 2015; Censor and Cohen, 2011). Reports of beneficial effects on behaviour in healthy populations have led to widespread interest in applying rTMS therapeutically, for example in patients with neuropsychiatric and neurological disorders (George et al., 2013; Lefaucheur et al., 2014; Ridding and Rothwell, 2007). A major issue with rTMS protocols is that the effects vary considerably within and between individuals (Hamada et al., 2013; Lopez-Alonso et al., 2014; Simeoni et al., 2016; Hinder et al., 2014; Vallence et al., 2015; Vernet et al., 2013; Goldsworthy et al., 2014; Maeda et al., 2000), which causes problems in replication of results in a research setting (Heroux et al., 2015), and is an obstacle to using rTMS in a therapeutic setting. A separate, but related, issue is that rTMS over a given cortical area is often assumed to affect all neuronal populations equally and thus affect all behaviours involving that area similarly, but this may not be true. Here we argue that advanced technologies and methodologies, such as controllable pulse parameter TMS (cTMS; (Peterchev et al., 2014)) and combining TMS with electroencephalography (EEG) (Ilmoniemi and Kicic, 2010; Peterchev et al., 2014), might facilitate the development of more selective forms of stimulation targeting particular neuronal populations or brain states, and ultimately improve the reliability and behavioural specificity of rTMS protocols

Field Theory And Second Renormalization Group For Multifractals In Percolation

The field-theory for multifractals in percolation is reformulated in such a way that multifractal exponents clearly appear as eigenvalues of a second renormalization group. The first renormalization group describes geometrical properties of percolation clusters, while the second-one describes electrical properties, including noise cumulants. In this context, multifractal exponents are associated with symmetry-breaking fields in replica space. This provides an explanation for their observability. It is suggested that multifractal exponents are ''dominant'' instead of ''relevant'' since there exists an arbitrary scale factor which can change their sign from positive to negative without changing the Physics of the problem.Comment: RevTex, 10 page

Invariants of Triangular Lie Algebras

Triangular Lie algebras are the Lie algebras which can be faithfully represented by triangular matrices of any finite size over the real/complex number field. In the paper invariants ('generalized Casimir operators') are found for three classes of Lie algebras, namely those which are either strictly or non-strictly triangular, and for so-called special upper triangular Lie algebras. Algebraic algorithm of [J. Phys. A: Math. Gen., 2006, V.39, 5749; math-ph/0602046], developed further in [J. Phys. A: Math. Theor., 2007, V.40, 113; math-ph/0606045], is used to determine the invariants. A conjecture of [J. Phys. A: Math. Gen., 2001, V.34, 9085], concerning the number of independent invariants and their form, is corroborated.Comment: LaTeX2e, 16 pages; misprints are corrected, some proofs are extende

Conditions for magnetically induced singlet d-wave superconductivity on the square lattice

It is expected that at weak to intermediate coupling, d-wave superconductivity can be induced by antiferromagnetic fluctuations. However, one needs to clarify the role of Fermi surface topology, density of states, pseudogap, and wave vector of the magnetic fluctuations on the nature and strength of the induced d-wave state. To this end, we study the generalized phase diagram of the two-dimensional half-filled Hubbard model as a function of interaction strength $U/t$, frustration induced by second-order hopping $t^{\prime}/t$, and temperature $T/t$. In experiment, $U/t$ and $t^{\prime}/t$ can be controlled by pressure. We use the two-particle self-consistent approach (TPSC), valid from weak to intermediate coupling. We first calculate as a function of $t^{\prime}/t$ and $U/t$ the temperature and wave vector at which the spin response function begins to grow exponentially.D-wave superconductivity in a half-filled band can be induced by such magnetic fluctuations at weak to intermediate coupling, but only if they are near commensurate wave vectors and not too close to perfect nesting conditions where the pseudogap becomes detrimental to superconductivity. For given $U/t$ there is thus an optimal value of frustration $t^{\prime}/t$ where the superconducting $T_c$ is maximum. The non-interacting density of states plays little role. The symmetry d$_{x^{2}-y^{2}}$ vs d$_{xy}$ of the superconducting order parameter depends on the wave vector of the underlying magnetic fluctuations in a way that can be understood qualitatively from simple arguments

Stormy weather in 3C 196.1: nuclear outbursts and merger events shape the environment of the hybrid radio galaxy 3C 196.1

We present a multi-wavelength analysis based on archival radio, optical and X-ray data of the complex radio source 3C 196.1, whose host is the brightest cluster galaxy of a $z=0.198$ cluster. HST data show H$\alpha$+[N II] emission aligned with the jet 8.4 GHz radio emission. An H$\alpha$+[N II] filament coincides with the brightest X-ray emission, the northern hotspot. Analysis of the X-ray and radio images reveals cavities located at galactic- and cluster- scales. The galactic-scale cavity is almost devoid of 8.4 GHz radio emission and the south-western H$\alpha$+[N II] emission is bounded (in projection) by this cavity. The outer cavity is co-spatial with the peak of 147 MHz radio emission, and hence we interpret this depression in X-ray surface brightness as being caused by a buoyantly rising bubble originating from an AGN outburst $\sim$280 Myrs ago. A \textit{Chandra} snapshot observation allowed us to constrain the physical parameters of the cluster, which has a cool core with a low central temperature $\sim$2.8 keV, low central entropy index $\sim$13 keV cm$^2$ and a short cooling time of $\sim$500 Myr, which is $<0.05$ of the age of the Universe at this redshift. By fitting jumps in the X-ray density we found Mach numbers between 1.4 and 1.6, consistent with a shock origin. We also found compelling evidence of a past merger, indicated by a morphology reminiscent of gas sloshing in the X-ray residual image. Finally, we computed the pressures, enthalpies $E_{cav}$ and jet powers $P_{jet}$ associated with the cavities: $E_{cav}\sim7\times10^{58}$ erg, $P_{jet}\sim1.9\times10^{44}$ erg s$^{-1}$ for the inner cavity and $E_{cav}\sim3\times10^{60}$ erg, $P_{jet}\sim3.4\times10^{44}$ erg s$^{-1}$ for the outer cavity.Comment: 14 pages, 4 figures, ApJ accepte