RESUMEN
We discuss 4D Lagrangian descriptions, across dimensions IR duals, of compactifications of the 6D (D, D) minimal conformal matter theory on a sphere with arbitrary number of punctures and a particular value of flux as a gauge theory with a simple gauge group. The Lagrangian has the form of a "star shaped quiver" with the rank of the central node depending on the 6D theory and the number and type of punctures. Using this Lagrangian one can construct across dimensions duals for arbitrary compactifications (any, genus, any number and type of USp punctures, and any flux) of the (D, D) minimal conformal matter gauging only symmetries which are manifest in the ultraviolet.
RESUMEN
We discuss certain structural analogies between supersymmetric quiver gauge theories and lattice models leading to fracton phases of matter. In particular, classes of quiver models can be viewed as lattice models having subsystem symmetries, dimensions of moduli spaces growing linearly with the size of the lattice, and having excitations with limited mobility (with "excitations" and "mobility" properly defined).
RESUMEN
We study two cases of interrelations between the enhancement of symmetries in the infrared (IR) and duality properties of supersymmetric quantum field theories in four dimensions. First, we discuss an SU(2) N=1 model with four flavors, singlet fields, and a superpotential. We show that this model flows to a conformal field theory with E_{6}×U(1) global symmetry. The enhancement of the flavor symmetry follows from Seiberg duality. The second example is concerned with an SU(4) gauge theory with matter in the fundamental and antisymmetric representations. We argue that this model has enhanced SO(12) symmetry in the IR, and, guided by this enhancement, we deduce a new IR duality.
RESUMEN
We suggest that at least some of the strongly coupled N=2 quantum field theories in 4D can have a nonconformal N=1 Lagrangian description flowing to them at low energies. In particular, we construct such a description for the N=2 rank one superconformal field theory with E(6) flavor symmetry, for which a Lagrangian description was previously unavailable. We utilize this description to compute several supersymmetric partition functions.
RESUMEN
We describe a fast activity-dependent homeostatic regulation of intrinsic excitability of identified neurons in mouse dorsal striatum, the striatal output neurons. It can be induced by brief bursts of activity, is expressed on a time scale of seconds, limits repetitive firing, and can convert regular firing patterns to irregular ones. We show it is due to progressive recruitment of the KCNQ2/3 channels that generate the M current. This homeostatic mechanism is significantly reduced in striatal output neurons of the R6/2 transgenic mouse model of Huntington's disease, at an age when the neurons are hyperactive in vivo and the mice begin to exhibit locomotor impairment. Furthermore, it can be rescued by bath perfusion with retigabine, a KCNQ channel activator, and chronic treatment improves locomotor performance. Thus, M-current dysfunction may contribute to the hyperactivity and network dysregulation characteristic of this neurodegenerative disease, and KCNQ2/3 channel regulation may be a target for therapeutic intervention.
Asunto(s)
Cuerpo Estriado/fisiopatología , Modelos Animales de Enfermedad , Homeostasis , Enfermedad de Huntington/fisiopatología , Locomoción , Animales , RatonesRESUMEN
Rat P2X2 receptors open at an undetectably low rate in the absence of ATP. Furthermore, two allosteric modulators, zinc and acidic pH, cannot by themselves open these channels. We describe here the properties of a mutant receptor, K69C, before and after treatment with the thiol-reactive fluorophore Alexa Fluor 546 C(5)-maleimide (AM546). Xenopus oocytes expressing unmodified K69C were not activated under basal conditions nor by 1,000 µM ATP. AM546 treatment caused a small increase in the inward holding current which persisted on washout and control experiments demonstrated this current was due to ATP independent opening of the channels. Following AM546 treatment, zinc (100 µM) or acidic external solution (pH 6.5) elicited inward currents when applied without any exogenous ATP. In the double mutant K69C/H319K, zinc elicited much larger inward currents, while acidic pH generated outward currents. Suramin, which is an antagonist of wild type receptors, behaved as an agonist at AM546-treated K69C receptors. Several other cysteine-reactive fluorophores tested on K69C did not cause these changes. These modified receptors show promise as a tool for studying the mechanisms of P2X receptor activation.
Asunto(s)
Adenosina Trifosfato/metabolismo , Compuestos de Quinolinio/química , Receptores Purinérgicos P2X2/química , Receptores Purinérgicos P2X2/metabolismo , Zinc/metabolismo , Animales , Expresión Génica , Concentración de Iones de Hidrógeno , Maleimidas/química , Modelos Moleculares , Mutagénesis Sitio-Dirigida , Oocitos/metabolismo , Ratas , Receptores Purinérgicos P2X2/genética , Suramina/farmacología , Xenopus laevisRESUMEN
Photochemical switches represent a powerful method for improving pharmacological therapies and controlling cellular physiology. Here we report the photoregulation of GABA(A) receptors (GABA(A)Rs) by a derivative of propofol (2,6-diisopropylphenol), a GABA(A)R allosteric modulator, which we have modified to contain photoisomerizable azobenzene. Using α(1)ß(2)γ(2) GABA(A)Rs expressed in Xenopus laevis oocytes and native GABA(A)Rs of isolated retinal ganglion cells, we show that the trans-azobenzene isomer of the new compound (trans-MPC088), generated by visible light (wavelengths ~440 nm), potentiates the γ-aminobutyric acid-elicited response and, at higher concentrations, directly activates the receptors. cis-MPC088, generated from trans-MPC088 by ultraviolet light (~365 nm), produces little, if any, receptor potentiation/activation. In cerebellar slices, MPC088 co-applied with γ-aminobutyric acid affords bidirectional photomodulation of Purkinje cell membrane current and spike-firing rate. The findings demonstrate photocontrol of GABA(A)Rs by an allosteric ligand, and open new avenues for fundamental and clinically oriented research on GABA(A)Rs, a major class of neurotransmitter receptors in the central nervous system.
Asunto(s)
Regulación Alostérica/efectos de la radiación , Luz , Receptores de GABA-A/metabolismo , Receptores de GABA-A/efectos de la radiación , Animales , Compuestos Azo/química , Electrofisiología , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Propofol/química , Propofol/farmacología , Células de Purkinje/efectos de los fármacos , Células de Purkinje/metabolismo , Células de Purkinje/efectos de la radiación , Ratas , Ratas Sprague-Dawley , Receptores de GABA-A/efectos de los fármacos , Xenopus laevis , Ácido gamma-AminobutíricoRESUMEN
Clustering in low density nuclear matter has been investigated using the NIMROD multidetector at Texas A&M University. Thermal coalescence modes were employed to extract densities, ρ, and temperatures, T, for evolving systems formed in collisions of 47A MeV (40)Ar+(112)Sn, (124)Sn and (64)Zn+(112)Sn, (124)Sn. The yields of d, t, (3)He, and (4)He have been determined at ρ=0.002 to 0.03 nucleons/fm(3) and T=5 to 11 MeV. The experimentally derived equilibrium constants for α particle production are compared with those predicted by a number of astrophysical equations of state. The data provide important new constraints on the model calculations.
RESUMEN
In the adult mammalian brain, GABA(A) receptors (GABA(A)Rs) are responsible for the predominant forms of synaptic inhibition, but these receptors can excite neurons when the chloride equilibrium potential (E(Cl)) is depolarized. In many mature neurons, GABA(A)Rs are found on presynaptic terminals where they exert depolarizing effects. To understand whether excitatory GABA action affects axonal function, we used transverse cerebellar slices to measure the effects of photolysis of caged GABA on the initiation and propagation of compound parallel fiber (PF) action potentials (APs). Photolysis of caged GABA increased the amplitude and conduction velocity of PF APs; GABA reuptake blockers and a positive modulator of GABA(A)Rs enhanced these effects. In contrast, a modulator selective for δ-subunit-containing GABA(A)Rs did not enhance these effects and responsiveness remained in δ(-/-) mice, arguing that δ-subunit-containing GABA(A)Rs are not required. Synaptically released GABA also increased PF excitability, indicating that the mechanism is engaged by physiological signals. A Hodgkin-Huxley-style compartmental model of the PF axon and granule cell body was constructed, and this model recapitulated the GABA-dependent decrease in AP threshold and the increase in conduction velocity, features that were sensitive to E(Cl) and to the voltage dependence of sodium channel inactivation. The model also predicts that axonal GABA(A)Rs could affect orthodromic spike initiation. We conclude that GABA acting on cerebellar PFs facilitates both spike generation and propagation, allowing axons of granule cells to passively integrate signals from inhibitory interneurons and influence information flow in the input layer to the cerebellar cortex.
Asunto(s)
Potenciales de Acción/fisiología , Axones/fisiología , Fibras Nerviosas Mielínicas/fisiología , Receptores de GABA-A/fisiología , Potenciales de Acción/efectos de los fármacos , Animales , Axones/efectos de los fármacos , Estimulación Eléctrica/métodos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Fibras Nerviosas Mielínicas/efectos de los fármacos , Técnicas de Cultivo de Órganos , Fotólisis , Ácido gamma-Aminobutírico/metabolismo , Ácido gamma-Aminobutírico/farmacologíaRESUMEN
In-medium binding energies and Mott points for d, t, 3He and α clusters in low-density nuclear matter have been determined at specific combinations of temperature and density in low-density nuclear matter produced in collisions of 47A MeV 40Ar and 64Zn projectiles with 112Sn and 124Sn target nuclei. The experimentally derived values of the in-medium modified binding energies are in good agreement with recent theoretical predictions based upon the implementation of Pauli blocking effects in a quantum statistical approach.
RESUMEN
We show that the superconformal index (the partition function on the three-sphere times a circle) of a certain class of 4D supersymmetric field theories is exactly equal to a partition function of q-deformed nonsupersymmetric 2D Yang-Mills theory.
RESUMEN
The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions, and astrophysical phenomena. New data from heavy-ion collisions can be used to extract the free symmetry energy and the internal symmetry energy at subsaturation densities and temperatures below 10 MeV. Conventional theoretical calculations of the symmetry energy based on mean-field approaches fail to give the correct low-temperature, low-density limit that is governed by correlations, in particular, by the appearance of bound states. A recently developed quantum-statistical approach that takes the formation of clusters into account predicts symmetry energies that are in very good agreement with the experimental data. A consistent description of the symmetry energy is given that joins the correct low-density limit with quasiparticle approaches valid near the saturation density.
RESUMEN
Experiments at the Relativistic Heavy Ion Collider (RHIC) suggest that the state of matter produced in the experiments has a low shear-viscosity to entropy-density ratio eta/s. We ask here the following question: what is this ratio in the usual finite nuclei at low temperature? We use the experimental and theoretical results for the widths of giant vibrational states in nuclei in order to calculate the above ratio. We find that the values of eta/s are not very different from the ones found in the RHIC experiments.
RESUMEN
P2X receptors are ATP-gated ion channels made up of three similar or identical subunits. It is unknown whether ligand binding is intersubunit or intrasubunit, either for agonists or for allosteric modulators. Zinc binds to rat P2X2 receptors and acts as an allosteric modulator, potentiating channel opening. To probe the location of this zinc binding site, P2X2 receptors bearing mutations of the histidines at positions 120 and 213 were expressed in Xenopus oocytes. Studies of H120C and H213C mutants produced five lines of evidence consistent with the hypothesis that the residues in these positions bind zinc. Mixing of subunits containing the H120A or H213A mutation generated receptors that showed zinc potentiation, even though neither of these mutant receptors showed zinc potentiation on its own. Furthermore, expression of trimeric concatamers with His --> Ala mutations at some but not all six positions showed that zinc potentiation correlated with the number of intersubunit histidine pairs. These results indicate that zinc potentiation requires an interaction across a subunit interface. Expression of the H120C/H213C double mutant resulted in the formation of ectopic disulfide bonds that could be detected by changes in the physiological properties of the receptors after treatment with reducing and oxidizing agents. Immunoblot analysis of H120C/H213C protein separated under nonreducing conditions demonstrated that the ectopic bonds were between adjacent subunits. Taken together, these data indicate that His120 and His213 sit close to each other across the interface between subunits and are likely to be key components of the zinc binding site in P2X2 receptors.