Thorough investigation on the high-temperature polymorphism of dipentyl-perylenediimide: thermal expansion vs. polymorphic transition

N,N′-Dipentyl-3,4,9,10-perylendiimide (PDI-C5) is an organic semiconducting material which has been extensively investigated as model compound for its optoelectronic properties. It is known to be highly thermally stable, that it exhibits solid-state transitions with temperature and that thermal treatments lead to an improvement in its performance in devices. Here we report a full thermal characterization of PDI-C5 by combination of differential scanning calorimetry, variable temperature X-ray diffraction, hot stage microscopy, and variable temperature Raman spectroscopy. We identified two high temperature polymorphs, form II and form III, which form respectively at 112 °C and at 221 °C and we determined their crystal structure from powder data. Form II is completely reversible upon cooling with low hysteresis, while form III revealed a different thermal behaviour upon cooling depending on the technique and crystal size. The crystal structure features of the different polymorphs are discussed and compared, and we looked into the role of the perylene core and alkyl chains during solid-state transitions. The thermal expansion principal axis of PDI-C5 crystal forms is reported showing that all the reported forms possess negative thermal expansion (X1) and large positive thermal expansion (X3) which are correlated to thermal behaviour observed

Debye screening in strongly coupled N=4 supersymmetric Yang-Mills plasma

Using the AdS/CFT correspondence, we examine the behavior of correlators of Polyakov loops and other operators in N=4 supersymmetric Yang-Mills theory at non-zero temperature. The implications for Debye screening in this strongly coupled non-Abelian plasma, and comparisons with available results for thermal QCD, are discussed.Comment: 21 pages, 5 figures, significantly expanded discussion of Polyakov loop correlator and static quark-antiquark potentia

Effective lattice theories for Polyakov loops

We derive effective actions for SU(2) Polyakov loops using inverse Monte Carlo techniques. In a first approach, we determine the effective couplings by requiring that the effective ensemble reproduces the single-site distribution of the Polyakov loops. The latter is flat below the critical temperature implying that the (untraced) Polyakov loop is distributed uniformly over its target space, the SU(2) group manifold. This allows for an analytic determination of the Binder cumulant and the distribution of the mean-field, which turns out to be approximately Gaussian. In a second approach, we employ novel lattice Schwinger-Dyson equations which reflect the SU(2) x SU(2) invariance of the functional Haar measure. Expanding the effective action in terms of SU(2) group characters makes the numerics sufficiently stable so that we are able to extract a total number of 14 couplings. The resulting action is short-ranged and reproduces the Yang-Mills correlators very well.Comment: 27 pages, 8 figures, v2: method refined, chapter and references adde

On three dimensional coupled bosons

This is a new version of the paper, which uses the same methods as in the previous version, but the model is now different. We study two complex scalar fields coupled through a quadratic interaction in 2+1 dimensions. We use the method of bilinears as suggested by Rajeev. The resulting classical theory is studied within the linear approximation and we show that there is a possible bound state for the composite type particles for a range of coupling constant strengths.Comment: 12 pages, to appear in JM

Widespread Receptivity to Neuropeptide PDF throughout the Neuronal Circadian Clock Network of Drosophila Revealed by Real-Time Cyclic AMP Imaging

SummaryThe neuropeptide PDF is released by sixteen clock neurons in Drosophila and helps maintain circadian activity rhythms by coordinating a network of ∼150 neuronal clocks. Whether PDF acts directly on elements of this neural network remains unknown. We address this question by adapting Epac1-camps, a genetically encoded cAMP FRET sensor, for use in the living brain. We find that a subset of the PDF-expressing neurons respond to PDF with long-lasting cAMP increases and confirm that such responses require the PDF receptor. In contrast, an unrelated Drosophila neuropeptide, DH31, stimulates large cAMP increases in all PDF-expressing clock neurons. Thus, the network of ∼150 clock neurons displays widespread, though not uniform, PDF receptivity. This work introduces a sensitive means of measuring cAMP changes in a living brain with subcellular resolution. Specifically, it experimentally confirms the longstanding hypothesis that PDF is a direct modulator of most neurons in the Drosophila clock network

Domain Walls and Metastable Vacua in Hot Orientifold Field Theories

We consider "Orientifold field theories", namely SU(N) gauge theories with Dirac fermions in the two-index representation at high temperature. When N is even these theories exhibit a spontaneously broken Z2 centre symmetry. We study aspects of the domain wall that interpolates between the two vacua of the theory. In particular we calculate its tension to two-loop order. We compare its tension to the corresponding domain wall in a SU(N) gauge theory with adjoint fermions and find an agreement at large-N, as expected from planar equivalence between the two theories. Moreover, we provide a non-perturbative proof for the coincidence of the tensions at large-N. We also discuss the vacuum structure of the theory when the fermion is given a large mass and argue that there exist N-2 metastable vacua. We calculate the lifetime of those vacua in the thin wall approximation.Comment: 29 pages, 4 figures. v2: minor changes in the introduction section. to appear in JHE

Wigner--Dyson statistics for a class of integrable models

We construct an ensemble of second--quantized Hamiltonians with two bosonic degrees of freedom, whose members display with probability one GOE or GUE statistics. Nevertheless, these Hamiltonians have a second integral of motion, namely the boson number, and thus are integrable. To construct this ensemble we use some ``reverse engineering'' starting from the fact that $n$--bosons in a two--level system with random interactions have an integrable classical limit by the old Heisenberg association of boson operators to actions and angles. By choosing an $n$--body random interaction and degenerate levels we end up with GOE or GUE Hamiltonians. Ergodicity of these ensembles completes the example.Comment: 3 pages, 1 figur

The phosphoinositide-binding protein p40phox activates the NADPH oxidase during FcγIIA receptor–induced phagocytosis

Superoxide produced by the phagocyte reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is essential for host defense. Enzyme activation requires translocation of p67phox, p47phox, and Rac-GTP to flavocytochrome b558 in phagocyte membranes. To examine the regulation of phagocytosis-induced superoxide production, flavocytochrome b558, p47phox, p67phox, and the FcγIIA receptor were expressed from stable transgenes in COS7 cells. The resulting COSphoxFcγR cells produce high levels of superoxide when stimulated with phorbol ester and efficiently ingest immunoglobulin (Ig)G-coated erythrocytes, but phagocytosis did not activate the NADPH oxidase. COS7 cells lack p40phox, whose role in the NADPH oxidase is poorly understood. p40phox contains SH3 and phagocyte oxidase and Bem1p (PB1) domains that can mediate binding to p47phox and p67phox, respectively, along with a PX domain that binds to phosphatidylinositol-3-phosphate (PI(3)P), which is generated in phagosomal membranes. Expression of p40phox was sufficient to activate superoxide production in COSphoxFcγR phagosomes. FcγIIA-stimulated NADPH oxidase activity was abrogated by point mutations in p40phox that disrupt PI(3)P binding, or by simultaneous mutations in the SH3 and PB1 domains. Consistent with an essential role for PI(3)P in regulating the oxidase complex, phagosome NADPH oxidase activation in primary macrophages ingesting IgG-coated beads was inhibited by phosphatidylinositol 3 kinase inhibitors to a much greater extent than phagocytosis itself. Hence, this study identifies a role for p40phox and PI(3)P in coupling FcγR-mediated phagocytosis to activation of the NADPH oxidase

Body Fixed Frame, Rigid Gauge Rotations and Large N Random Fields in QCD

The "body fixed frame" with respect to local gauge transformations is introduced. Rigid gauge "rotations" in QCD and their \Sch equation are studied for static and dynamic quarks. Possible choices of the rigid gauge field configuration corresponding to a nonvanishing static colormagnetic field in the "body fixed" frame are discussed. A gauge invariant variational equation is derived in this frame. For large number N of colors the rigid gauge field configuration is regarded as random with maximally random probability distribution under constraints on macroscopic--like quantities. For the uniform magnetic field the joint probability distribution of the field components is determined by maximizing the appropriate entropy under the area law constraint for the Wilson loop. In the quark sector the gauge invariance requires the rigid gauge field configuration to appear not only as a background but also as inducing an instantaneous quark-quark interaction. Both are random in the large N limit.Comment: 29 pages LATEX, Weizmann Institute preprint WIS-93/40/Apr -P

Phenomenological Equations of State for the Quark-Gluon Plasma

Two phenomenological models describing an SU(N) quark-gluon plasma are presented. The first is obtained from high temperature expansions of the free energy of a massive gluon, while the second is derived by demanding color neutrality over a certain length scale. Each model has a single free parameter, exhibits behavior similar to lattice simulations over the range T_d - 5T_d, and has the correct blackbody behavior for large temperatures. The N = 2 deconfinement transition is second order in both models, while N = 3,4, and 5 are first order. Both models appear to have a smooth large-N limit. For N >= 4, it is shown that the trace of the Polyakov loop is insufficient to characterize the phase structure; the free energy is best described using the eigenvalues of the Polyakov loop. In both models, the confined phase is characterized by a mutual repulsion of Polyakov loop eigenvalues that makes the Polyakov loop expectation value zero. In the deconfined phase, the rotation of the eigenvalues in the complex plane towards 1 is responsible for the approach to the blackbody limit over the range T_d - 5T_d. The addition of massless quarks in SU(3) breaks Z(3) symmetry weakly and eliminates the deconfining phase transition. In contrast, a first-order phase transition persists with sufficiently heavy quarks.Comment: 22 pages, RevTeX, 9 eps file