Las “moscas de las flores” (Diptera: Syrphidae) en Lules, Tucumán

La familia Syrphidae es un grupo de insectos que se caracteriza por ser moscas grandes y vistosas capaces de adoptar la apariencia de abejas o avispas para defenderse de los depredadores. Los adultos generalmente se encuentran sobre las flores o en vuelo suspendido en lugares soleados, de ahí que sean llamados comúnmente “moscas de las flores” o “flower flies”. Su tamaño fluctúa de 4 a 25 mm, el cuerpo puede ser delgado o robusto y presentar coloración metálica u opaca. El abdomen es variable en forma, de ancho a muy delgado (Sarmiento Cordero et al., 2010).Fil: Maza, Noelia. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sopena, Y. N.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; ArgentinaFil: Assaf, M. J. T.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; ArgentinaFil: Paz, Miriam Rosana. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Jaime, Adriana Patricia. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentin

Experimental Study of Parametric Autoresonance in Faraday Waves

The excitation of large amplitude nonlinear waves is achieved via parametric autoresonance of Faraday waves. We experimentally demonstrate that phase locking to low amplitude driving can generate persistent high-amplitude growth of nonlinear waves in a dissipative system. The experiments presented are in excellent agreement with theory.Comment: 4 pages, 4 eps figures, to appear in Phys. Rev. Let

Soft Robotics: Cerebellar Inspired Control of Artificial Muscles

Soft robots have the potential to greatly improve human-robot interaction via intrinsically safe, compliant designs. However, new compliant materials used in soft robotics – artificial muscles – are fabricated with poor tolerances and have time-varying dynamics. Therefore, a key technical challenge is to develop adaptive control algorithms for these materials. Here, we take a novel bio-inspired approach to artificial muscle control using the adaptive filter model of the cerebellum. The cerebellum is a brain structure essential for fine-tuning human performance in a diverse range of sensory and motor tasks. Its ability to automatically calibrate and adapt to changes in a wide variety of systems using a homogenous, repeating structure suggests that cerebellar-inspired models are highly suited to controlling artificial muscles in a range of tasks. We investigate the performance of the cerebellar adaptive filter algorithm in the displacement control of a soft actuator. Experimental results demonstrate that the cerebellar algorithm is successful and learns to accurately control the time-varying dynamics of the soft actuator in real-time

The Conformal Limit of the 0A Matrix Model and String Theory on AdS(2)

We analyze the conformal limit of the matrix model describing flux backgrounds of two dimensional type 0A string theory. This limit is believed to be dual to an AdS(2) background of type 0A string theory. We show that the spectrum of this limit is identical to that of a free fermion on AdS(2), suggesting that there are no closed string excitations in this background.Comment: 17 pages, 1 figur

The Moduli Space and M(atrix) Theory of 9d N=1 Backgrounds of M/String Theory

We discuss the moduli space of nine dimensional N=1 supersymmetric compactifications of M theory / string theory with reduced rank (rank 10 or rank 2), exhibiting how all the different theories (including M theory compactified on a Klein bottle and on a Mobius strip, the Dabholkar-Park background, CHL strings and asymmetric orbifolds of type II strings on a circle) fit together, and what are the weakly coupled descriptions in different regions of the moduli space. We argue that there are two disconnected components in the moduli space of theories with rank 2. We analyze in detail the limits of the M theory compactifications on a Klein bottle and on a Mobius strip which naively give type IIA string theory with an uncharged orientifold 8-plane carrying discrete RR flux. In order to consistently describe these limits we conjecture that this orientifold non-perturbatively splits into a D8-brane and an orientifold plane of charge (-1) which sits at infinite coupling. We construct the M(atrix) theory for M theory on a Klein bottle (and the theories related to it), which is given by a 2+1 dimensional gauge theory with a varying gauge coupling compactified on a cylinder with specific boundary conditions. We also clarify the construction of the M(atrix) theory for backgrounds of rank 18, including the heterotic string on a circle.Comment: 43 pages, 7 figures, JHEP format. v3: typos correcte

Weak localization in disordered systems at the ballistic limit

The weak localization (WL) contribution to the two-level correlation function is calculated for two-dimensional disordered conductors. Our analysis extends to the nondiffusive (ballistic) regime, where the elastic mean path is of order of the size of the system. In this regime the structure factor (the Fourier transform of the two-point correlator) exhibits a singular behavior consisting of dips superimposed on a smooth positive background. The strongest dips appear at periods of the periodic orbits of the underlying clean system. Somewhat weaker singularities appear at times which are sums of periods of two such orbits. The results elucidate various aspects of the weak localization physics of ballistic chaotic systems.Comment: 13 pages, 13 figure

Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare?

We report the discovery by the Swift hard X-ray monitor of the transient source Swift J2058.4+0516 (Sw J2058+05). Our multi-wavelength follow-up campaign uncovered a long-lived (duration >~ months), luminous X-ray (L_X,iso ~ 3 x 10^47 erg s^-1) and radio (nu L_nu,iso ~ 10^42 erg s^-1) counterpart. The associated optical emission, however, from which we measure a redshift of 1.1853, is relatively faint, and this is not due to a large amount of dust extinction in the host galaxy. Based on numerous similarities with the recently discovered GRB 110328A / Swift J164449.3+573451 (Sw J1644+57), we suggest that Sw J2058+05 may be the second member of a new class of relativistic outbursts resulting from the tidal disruption of a star by a supermassive black hole. If so, the relative rarity of these sources (compared with the expected rate of tidal disruptions) implies that either these outflows are extremely narrowly collimated (theta < 1 degree), or only a small fraction of tidal disruptions generate relativistic ejecta. Analogous to the case of long-duration gamma-ray bursts and core-collapse supernovae, we speculate that rapid spin of the black hole may be a necessary condition to generate the relativistic component. Alternatively, if powered by gas accretion (i.e., an active galactic nucleus [AGN]), Sw J2058+05 would seem to represent a new mode of variability in these sources, as the observed properties appear largely inconsistent with known classes of AGNs capable of generating relativistic jets (blazars, narrow-line Seyfert 1 galaxies).Comment: Minor typos correcte

Commitment versus persuasion in the three-party constrained voter model

In the framework of the three-party constrained voter model, where voters of two radical parties (A and B) interact with "centrists" (C and Cz), we study the competition between a persuasive majority and a committed minority. In this model, A's and B's are incompatible voters that can convince centrists or be swayed by them. Here, radical voters are more persuasive than centrists, whose sub-population consists of susceptible agents C and a fraction zeta of centrist zealots Cz. Whereas C's may adopt the opinions A and B with respective rates 1+delta_A and 1+delta_B (with delta_A>=delta_B>0), Cz's are committed individuals that always remain centrists. Furthermore, A and B voters can become (susceptible) centrists C with a rate 1. The resulting competition between commitment and persuasion is studied in the mean field limit and for a finite population on a complete graph. At mean field level, there is a continuous transition from a coexistence phase when zeta= Delta_c. In a finite population of size N, demographic fluctuations lead to centrism consensus and the dynamics is characterized by the mean consensus time tau. Because of the competition between commitment and persuasion, here consensus is reached much slower (zeta=Delta_c) than in the absence of zealots (when tau\simN). In fact, when zeta<Delta_c and there is an initial minority of centrists, the mean consensus time asymptotically grows as tau\simN^{-1/2} e^{N gamma}, where gamma is determined. The dynamics is thus characterized by a metastable state where the most persuasive voters and centrists coexist when delta_A>delta_B, whereas all species coexist when delta_A=delta_B. When zeta>=Delta_c and the initial density of centrists is low, one finds tau\simln N (when N>>1). Our analytical findings are corroborated by stochastic simulations.Comment: 25 pages, 6 figures. Final version for the Journal of Statistical Physics (special issue on the "applications of statistical mechanics to social phenomena"

PTF11eon/SN2011dh: Discovery of a Type IIb Supernova From a Compact Progenitor in the Nearby Galaxy M51

On May 31, 2011 UT a supernova (SN) exploded in the nearby galaxy M51 (the Whirlpool Galaxy). We discovered this event using small telescopes equipped with CCD cameras, as well as by the Palomar Transient Factory (PTF) survey, and rapidly confirmed it to be a Type II supernova. Our early light curve and spectroscopy indicates that PTF11eon resulted from the explosion of a relatively compact progenitor star as evidenced by the rapid shock-breakout cooling seen in the light curve, the relatively low temperature in early-time spectra and the prompt appearance of low-ionization spectral features. The spectra of PTF11eon are dominated by H lines out to day 10 after explosion, but initial signs of He appear to be present. Assuming that He lines continue to develop in the near future, this SN is likely a member of the cIIb (compact IIb; Chevalier and Soderberg 2010) class, with progenitor radius larger than that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor. Our data imply that the object identified in pre-explosion Hubble Space Telescope images at the SN location is possibly a companion to the progenitor or a blended source, and not the progenitor star itself, as its radius (~10^13 cm) would be highly inconsistent with constraints from our post-explosion photometric and spectroscopic data