Modeling pion physics in the ϵ\epsilon-regime of two-flavor QCD using strong coupling lattice QED

In order to model pions of two-flavor QCD we consider a lattice field theory involving two flavors of staggered quarks interacting strongly with U(1) gauge fields. For massless quarks, this theory has an $SU_L(2)\times SU_R(2) \times U_A(1)$ symmetry. By adding a four-fermion term we can break the U_A(1) symmetry and thus incorporate the physics of the QCD anomaly. We can also tune the pion decay constant F, to be small compared to the lattice cutoff by starting with an extra fictitious dimension, thus allowing us to model low energy pion physics in a setting similar to lattice QCD from first principles. However, unlike lattice QCD, a major advantage of our model is that we can easily design efficient algorithms to compute a variety of quantities in the chiral limit. Here we show that the model reproduces the predictions of chiral perturbation theory in the $\epsilon$-regime.Comment: 24 pages, 7 figure

Absence of vortex condensation in a two dimensional fermionic XY model

Motivated by a puzzle in the study of two dimensional lattice Quantum Electrodynamics with staggered fermions, we construct a two dimensional fermionic model with a global U(1) symmetry. Our model can be mapped into a model of closed packed dimers and plaquettes. Although the model has the same symmetries as the XY model, we show numerically that the model lacks the well known Kosterlitz-Thouless phase transition. The model is always in the gapless phase showing the absence of a phase with vortex condensation. In other words the low energy physics is described by a non-compact U(1) field theory. We show that by introducing an even number of layers one can introduce vortex condensation within the model and thus also induce a KT transition.Comment: 5 pages, 5 figure

Mitoparans: mitochondriotoxic cell penetrating peptides and novel inducers of apoptosis.

Acknowledgments The authors would like to thank Keith Holding at the University of Wolverhampton for his outstanding technical support. This work was supported in part by Samantha Dickson Brain Tumour Trust.Introduction: The amphipathic helical peptide mastoparan (MP; H-INLKALAALAKKIL-NH2) inserts into biological membranes to modulate the activity of heterotrimeric G proteins and other targets. Moreover, whilst cell free models of apoptosis demonstrate MP to facilitate mitochondrial permeability transition and release of apoptogenic cytochrome c, MP-induced death of intact cells has been attributed to its non-specific membrane destabilising properties (necrotic mechanisms). However, MP and related peptides are known to activate other signalling systems, including p42/p44 MAP kinases and could therefore, also modulate cell fate and specific apoptotic events. The ability of MP to facilitate mitochondrial permeability in cell free systems has lead to proposals that MP could be of utility in tumour therapeutics provided that it conferred features of cellular penetration and mitochondrial localization. We have recently reported that our highly potent amphipathic MP analogue mitoparan (mitP; [Lys5,8Aib10]MP; Aib = -aminoisobutyric acid) specifically promotes apoptosis of human cancer cells, as was confirmed by in situ TUNEL staining and activation of caspase-3. Moreover, we have also demonstrated that mitP penetrates plasma membranes and redistributes to co-localize with mitochondria. Complementary studies, using isolated mitochondria, further demonstrated that mitP, through co-operation with a protein of the permeability transition pore complex voltage-dependent anion channel (VDAC), induced swelling and permeabilization of mitochondria, leading to the release of the apoptogenic factor cytochrome c. An expanding field of peptide and cell penetrating peptide (CPP) research has focussed on the selective targeting of tumours by engineering constructs that incorporate cell-specific or tissue–specific address motifs. Peptidyl address motifs could enhance the selectivity of drug delivery whilst the improved cellular uptake offered by CPP enhances bioavailability. Thus and as a potential therapeutic strategy, we extended our findings to design target-specific mitP analogues. The integrin-specific address motif RGD and a Fas ligand mimetic WEWT were incorporated by N-terminal acylation of mitP to produce novel tandem-linked chimeric peptides

Emergent particle-hole symmetry in spinful bosonic quantum Hall systems

When a fermionic quantum Hall system is projected into the lowest Landau level, there is an exact particle-hole symmetry between filling fractions $\nu$ and $1-\nu$. We investigate whether a similar symmetry can emerge in bosonic quantum Hall states, where it would connect states at filling fractions $\nu$ and $2-\nu$. We begin by showing that the particle-hole conjugate to a composite fermion `Jain state' is another Jain state, obtained by reverse flux attachment. We show how information such as the shift and the edge theory can be obtained for states which are particle-hole conjugates. Using the techniques of exact diagonalization and infinite density matrix renormalization group, we study a system of two-component (i.e., spinful) bosons, interacting via a $\delta$-function potential. We first obtain real-space entanglement spectra for the bosonic integer quantum Hall effect at $\nu=2$, which plays the role of a filled Landau level for the bosonic system. We then show that at $\nu=4/3$ the system is described by a Jain state which is the particle-hole conjugate of the Halperin (221) state at $\nu=2/3$. We show a similar relationship between non-singlet states at $\nu=1/2$ and $\nu=3/2$. We also study the case of $\nu=1$, providing unambiguous evidence that the ground state is a composite Fermi liquid. Taken together our results demonstrate that there is indeed an emergent particle-hole symmetry in bosonic quantum Hall systems.Comment: 10 pages, 8 figures, 4 appendice

The Effects of Chlorophyll Assimilation on Carbon Fluxes in a Global Biogeochemical Model

In this paper, we investigated whether the assimilation of remotely-sensed chlorophyll data can improve the estimates of air-sea carbon dioxide fluxes (FCO2). Using a global, established biogeochemical model (NASA Ocean Biogeochemical Model, NOBM) for the period 2003-2010, we found that the global FCO2 values produced in the free-run and after assimilation were within -0.6 mol C m(sup -2) y(sup -1) of the observations. The effect of satellite chlorophyll assimilation was assessed in 12 major oceanographic regions. The region with the highest bias was the North Atlantic. Here the model underestimated the fluxes by 1.4 mol C m(sup -2) y(sup -1) whereas all the other regions were within 1 mol C m(sup -2) y(sup -1) of the data. The FCO2 values were not strongly impacted by the assimilation, and the uncertainty in FCO2 was not decreased, despite the decrease in the uncertainty in chlorophyll concentration. Chlorophyll concentrations were within approximately 25% of the database in 7 out of the 12 regions, and the assimilation improved the chlorophyll concentration in the regions with the highest bias by 10-20%. These results suggest that the assimilation of chlorophyll data does not considerably improve FCO2 estimates and that other components of the carbon cycle play a role that could further improve our FCO2 estimates

Role of the σ\sigma-resonance in determining the convergence of chiral perturbation theory

The dimensionless parameter $\xi = M_\pi^2/(16 \pi^2 F_\pi^2)$, where $F_\pi$ is the pion decay constant and $M_\pi$ is the pion mass, is expected to control the convergence of chiral perturbation theory applicable to QCD. Here we demonstrate that a strongly coupled lattice gauge theory model with the same symmetries as two-flavor QCD but with a much lighter $\sigma$-resonance is different. Our model allows us to study efficiently the convergence of chiral perturbation theory as a function of $\xi$. We first confirm that the leading low energy constants appearing in the chiral Lagrangian are the same when calculated from the $p$-regime and the $\epsilon$-regime as expected. However, $\xi \lesssim 0.002$ is necessary before 1-loop chiral perturbation theory predicts the data within 1%. For $\xi > 0.0035$ the data begin to deviate dramatically from 1-loop chiral perturbation theory predictions. We argue that this qualitative change is due to the presence of a light $\sigma$-resonance in our model. Our findings may be useful for lattice QCD studies.Comment: 5 pages, 6 figures, revtex forma

IRAS04496-6958: A luminous carbon star with silicate dust in the Large Magellanic Cloud

We describe ISO observations of the obscured Asymptotic Giant Branch (AGB) star IRAS04496-6958 in the Large Magellanic Cloud (LMC). This star has been classified as a carbon star. Our new ISOCAM CVF spectra show that it is the first carbon star with silicate dust known outside of the Milky Way. The existence of this object, and the fact that it is one of the highest luminosity AGB stars in the LMC, provide important information for theoretical models of AGB evolution and understanding the origin of silicate carbon stars.Comment: 4 pages, 3 figures, accepted for publication in A&A Letter

Alanine scanning mutagenesis of a high-affinity nitrate transporter highlights the requirement for glycine and asparagine residues in the two nitrate signature motifs

Common to all of the nitrate nitrite porter family are two conserved motifs in transmembrane helices 5 and 11 termed NS (nitrate signature) 1 and NS2. Although perfectly conserved substrate-interacting arginine residues have been described in transmembrane helices 2 and 8, the role of NSs has not been investigated. In the present study, a combination of structural modelling of NrtA (nitrate transporter from Aspergillus nidulans) with alanine scanning mutagenesis of residues within and around the NSs has been used to shed light on the probable role of conserved residues in the NSs. Models show that Asn 168 in NS1 and Asn 459 in NS2 are positioned approximately midway within the protein at the central pivot point in close proximity to the substrate-binding residues Arg 368 and Arg 87 respectively, which lie offset from the pivot point towards the cytoplasmic face. The Asn 168 /Arg 368 and Asn 459 /Arg 87 residue pairs are relatively widely separated on opposite sides of the probable substrate translocation pore. The results of the present study demonstrate the critical structural contribution of several glycine residues in each NS at sites of close helix packing. Given the relative locations of Asn 168 /Arg 368 and Asn 459 /Arg 87 pairs, the validity of the models and possible role of the NSs together with the substrate-binding arginine residues are discusse