Dynamics of Stripes in Doped Antiferromagnets

We study the dynamics of the striped phase, which has previously been suggested to be the ground state of a doped antiferromagnet. Starting from the t-J model, we derive the classical equation governing the motion of the charged wall by using a ficticious spin model as an intermediate step. A wave-like equation of motion is obtained and the wall elasticity and mass density constants are derived in terms of the t and J parameters. The wall is then regarded as an elastic string which will be trapped by the pinning potential produced by randomly distributed impurities. We evaluate the pinning potential and estimate the threshold electric field which has to be applied to the system in order to release the walls. Besides, the dynamics of the stripe in the presence of a bias field below the threshold is considered and the high- and low-temperature relaxation rates are derived.Comment: 22 pages, RevTeX, 3 PS-figure

Combined intervention with pioglitazone and n-3 fatty acids in metformin-treated type 2 diabetic patients: improvement of lipid metabolism

Background: The marine n-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) exert numerous beneficial effects on health, but their potency to improve treatment of type 2 diabetic (T2D) patients remains poorly characterized. We aimed to evaluate the effect of a combination intervention using EPA?+?DHA and the insulin-sensitizing drug pioglitazone in overweight/obese T2D patients already treated with metformin.Methods: In a parallel-group, four-arm, randomized trial, 69 patients (66 % men) were assigned to 24-week-intervention using: (i) corn oil (5 g/day; Placebo), (ii) pioglitazone (15 mg/day; Pio), (iii) EPA?+?DHA concentrate (5 g/day, containing ~2.8 g EPA?+?DHA; Omega-3), or (iv) pioglitazone and EPA?+?DHA concentrate (Pio&amp; Omega-3). Data from 60 patients were used for the final evaluation. At baseline and after intervention, various metabolic markers, adiponectin and cytokines were evaluated in serum using standard procedures, EPA?+?DHA content in serum phospholipids was evaluated using shotgun lipidomics and mass spectrometry, and hyperinsulinemic-euglycemic clamp and meal test were also performed. Indirect calorimetry was conducted after the intervention. Primary endpoints were changes from baseline in insulin sensitivity evaluated using hyperinsulinemic-euglycemic clamp and in serum triacylglycerol concentrations in fasting state. Secondary endpoints included changes in fasting glycemia and glycated hemoglobin (HbA1c), changes in postprandial glucose, free fatty acid and triacylglycerol concentrations, metabolic flexibility assessed by indirect calorimetry, and inflammatory markers.Results: Omega-3 and Pio&amp; Omega-3 increased EPA?+?DHA content in serum phospholipids. Pio and Pio&amp; Omega-3 increased body weight and adiponectin levels. Both fasting glycemia and HbA1c were increased by Omega-3, but were unchanged by Pio&amp; Omega-3. Insulin sensitivity was not affected by Omega-3, while it was improved by Pio&amp; Omega-3. Fasting triacylglycerol concentrations and inflammatory markers were not significantly affected by any of the interventions. Lipid metabolism in the meal test and metabolic flexibility were additively improved by Pio&amp; Omega-3.Conclusion: Besides preventing a modest negative effect of n-3 fatty acids on glycemic control, the combination of pioglitazone and EPA?+?DHA can be used to improve lipid metabolism in T2D patients on stable metformin therapy.Trial registration: EudraCT number 2009-011106-42.<br/

Positivity, entanglement entropy, and minimal surfaces

The path integral representation for the Renyi entanglement entropies of integer index n implies these information measures define operator correlation functions in QFT. We analyze whether the limit $n\rightarrow 1$, corresponding to the entanglement entropy, can also be represented in terms of a path integral with insertions on the region's boundary, at first order in $n-1$. This conjecture has been used in the literature in several occasions, and specially in an attempt to prove the Ryu-Takayanagi holographic entanglement entropy formula. We show it leads to conditional positivity of the entropy correlation matrices, which is equivalent to an infinite series of polynomial inequalities for the entropies in QFT or the areas of minimal surfaces representing the entanglement entropy in the AdS-CFT context. We check these inequalities in several examples. No counterexample is found in the few known exact results for the entanglement entropy in QFT. The inequalities are also remarkable satisfied for several classes of minimal surfaces but we find counterexamples corresponding to more complicated geometries. We develop some analytic tools to test the inequalities, and as a byproduct, we show that positivity for the correlation functions is a local property when supplemented with analyticity. We also review general aspects of positivity for large N theories and Wilson loops in AdS-CFT.Comment: 36 pages, 10 figures. Changes in presentation and discussion of Wilson loops. Conclusions regarding entanglement entropy unchange

Klein tunneling in graphene: optics with massless electrons

This article provides a pedagogical review on Klein tunneling in graphene, i.e. the peculiar tunneling properties of two-dimensional massless Dirac electrons. We consider two simple situations in detail: a massless Dirac electron incident either on a potential step or on a potential barrier and use elementary quantum wave mechanics to obtain the transmission probability. We emphasize the connection to related phenomena in optics, such as the Snell-Descartes law of refraction, total internal reflection, Fabry-P\'erot resonances, negative refraction index materials (the so called meta-materials), etc. We also stress that Klein tunneling is not a genuine quantum tunneling effect as it does not necessarily involve passing through a classically forbidden region via evanescent waves. A crucial role in Klein tunneling is played by the conservation of (sublattice) pseudo-spin, which is discussed in detail. A major consequence is the absence of backscattering at normal incidence, of which we give a new shorten proof. The current experimental status is also thoroughly reviewed. The appendix contains the discussion of a one-dimensional toy model that clearly illustrates the difference in Klein tunneling between mono- and bi-layer graphene.Comment: short review article, 18 pages, 14 figures; v3: references added, several figures slightly modifie

Gauge theory in deformed N=(1,1) superspace

We review the non-anticommutative Q-deformations of N=(1,1) supersymmetric theories in four-dimensional Euclidean harmonic superspace. These deformations preserve chirality and harmonic Grassmann analyticity. The associated field theories arise as a low-energy limit of string theory in specific backgrounds and generalize the Moyal-deformed supersymmetric field theories. A characteristic feature of the Q-deformed theories is the half-breaking of supersymmetry in the chiral sector of the Euclidean superspace. Our main focus is on the chiral singlet Q-deformation, which is distinguished by preserving the SO(4) Spin(4) ``Lorentz'' symmetry and the SU(2) R-symmetry. We present the superfield and component structures of the deformed N=(1,0) supersymmetric gauge theory as well as of hypermultiplets coupled to a gauge superfield: invariant actions, deformed transformation rules, and so on. We discuss quantum aspects of these models and prove their renormalizability in the abelian case. For the charged hypermultiplet in an abelian gauge superfield background we construct the deformed holomorphic effective action.Comment: 1+60 pages, typos corrected, references adde

Limits of minimal models and continuous orbifolds

The lambda=0 't Hooft limit of the 2d W_N minimal models is shown to be equivalent to the singlet sector of a free boson theory, thus paralleling exactly the structure of the free theory in the Klebanov-Polyakov proposal. In 2d, the singlet sector does not describe a consistent theory by itself since the corresponding partition function is not modular invariant. However, it can be interpreted as the untwisted sector of a continuous orbifold, and this point of view suggests that it can be made consistent by adding in the appropriate twisted sectors. We show that these twisted sectors account for the `light states' that were not included in the original 't Hooft limit. We also show that, for the Virasoro minimal models (N=2), the twisted sector of our orbifold agrees precisely with the limit theory of Runkel & Watts. In particular, this implies that our construction satisfies crossing symmetry.Comment: 33 pages; v2: minor improvements and references added, published versio

Exploring Three-dimensional Higher-Spin Supergravity based on sl(N |N - 1) Chern-Simons theories

We investigate various aspects of higher-spin anti-de Sitter supergravity in three dimensions as described by Chern-Simons theory based on the finite-dimensional superalgebra sl(N |N - 1), with the particular case of N = 3 as our prime example. This class of theories serves as a natural supersymmetrization of the higher-spin gravity theory based on sl(N) Chern-Simons theories. We demonstrate explicitly that the asymptotic symmetry algebra contains the N = 2 superconformal algebra in each sector. The appropriate Killing spinor equations are derived and used to classify existing and new classical solutions. We also discuss holonomy conditions, higher-spin black holes and conical defect spacetimes in this class of theories.Comment: 41 pages, a few typos in v4 correcte

3D Gasdynamic Modelling of the Changes in the Flow Structure During Transition From Quiescent to Active State in Symbiotic Stars

The results of 3D modelling of the flow structure in the classical symbiotic system Z~Andromedae are presented. Outbursts in systems of this type occur when the accretion rate exceeds the upper limit of the steady burning range. Therefore, in order to realize the transition from a quiescent to an active state it is necessary to find a mechanism able to sufficiently increase the accretion rate on a time scale typical to the duration of outburst development. Our calculations have confirmed the transition mechanism from quiescence to outburst in classic symbiotic systems suggested earlier on the basis of 2D calculations (Bisikalo et al, 2002). The analysis of our results have shown that for wind velocity of 20 km/s an accretion disc forms in the system. The accretion rate for the solution with the disc is ~22.5-25% of the mass loss rate of the donor, that is, ~4.5-5*10^(-8)Msun/yr for Z And. This value is in agreement with the steady burning range for white dwarf masses typically accepted for this system. When the wind velocity increases from 20 to 30 km/s the accretion disc is destroyed and the matter of the disc falls onto the accretor's surface. This process is followed by an approximately twofold accretion rate jump. The resulting accretion rate growth is sufficient for passing the upper limit of the steady burning range, thereby bringing the system into an active state. The time during which the accretion rate is above the steady burning value is in a very good agreement with observations. The analysis of the results presented here allows us to conclude that small variations in the donor's wind velocity can lead to the transition from the disc accretion to the wind accretion and, as a consequence, to the transition from quiescent to active state in classic symbiotic stars.Comment: 21 pages, 7 figure

Prediction of HIV-1 virus-host protein interactions using virus and host sequence motifs

<p>Abstract</p> <p>Background</p> <p>Host protein-protein interaction networks are altered by invading virus proteins, which create new interactions, and modify or destroy others. The resulting network topology favors excessive amounts of virus production in a stressed host cell network. Short linear peptide motifs common to both virus and host provide the basis for host network modification.</p> <p>Methods</p> <p>We focused our host-pathogen study on the binding and competing interactions of HIV-1 and human proteins. We showed that peptide motifs conserved across 70% of HIV-1 subtype B and C samples occurred in similar positions on HIV-1 proteins, and we documented protein domains that interact with these conserved motifs. We predicted which human proteins may be targeted by HIV-1 by taking pairs of human proteins that may interact via a motif conserved in HIV-1 and the corresponding interacting protein domain.</p> <p>Results</p> <p>Our predictions were enriched with host proteins known to interact with HIV-1 proteins ENV, NEF, and TAT (p-value < 4.26E-21). Cellular pathways statistically enriched for our predictions include the T cell receptor signaling, natural killer cell mediated cytotoxicity, cell cycle, and apoptosis pathways. Gene Ontology molecular function level 5 categories enriched with both predicted and confirmed HIV-1 targeted proteins included categories associated with phosphorylation events and adenyl ribonucleotide binding.</p> <p>Conclusion</p> <p>A list of host proteins highly enriched with those targeted by HIV-1 proteins can be obtained by searching for host protein motifs along virus protein sequences. The resulting set of host proteins predicted to be targeted by virus proteins will become more accurate with better annotations of motifs and domains. Nevertheless, our study validates the role of linear binding motifs shared by virus and host proteins as an important part of the crosstalk between virus and host.</p

Photon and neutral pion production in Au+Au collisions at sqrt(s_{NN}) = 130 GeV

We report the first inclusive photon measurements about mid-rapidity (|y|<0.5) from Au+Au collisions at sqrt(s_{NN}) = 130 GeV at RHIC. Photon pair conversions were reconstructed from electron and positron tracks measured with the Time Projection Chamber (TPC) of the STAR experiment. With this method, an energy resolution of Delta(E)/E = 2% at 0.5 GeV has been achieved. Reconstructed photons have also been used to measure the transverse momentum (pt) spectra of pi0 mesons about mid-rapidity (|y| photon photon decay channel. The fractional contribution of the pi0 -> photon photon decay to the inclusive photon spectrum decreases by 20% +/- 5% between pt = 1.65 GeV/c and pt = 2.4 GeV/c in the most central events, indicating that relative to pi0 -> photon photon decay the contribution of other photon sources is substantially increasing.Comment: 13 pages, 14 figures, submitted to Phys. Rev.