Structural Anomalies at the Magnetic and Ferroelectric Transitions in RMn2O5RMn_2O_5 (R=Tb, Dy, Ho)

Strong anomalies of the thermal expansion coefficients at the magnetic and ferroelectric transitions have been detected in multiferroic $RMn_2O_5$. Their correlation with anomalies of the specific heat and the dielectric constant is discussed. The results provide evidence for the magnetic origin of the ferroelectricity mediated by strong spin-lattice coupling in the compounds. Neutron scattering data for $HoMn_2O_5$ indicate a spin reorientation at the two low-temperature phase transitions

Wormholes in String Theory

A wormhole is constructed by cutting and joining two spacetimes satisfying the low energy string equations with a dilaton field. In spacetimes described by the "string metric" the dilaton energy-momentum tensor need not satisfy the weak or dominant energy conditions. In the cases considered here the dilaton field violates these energy conditions and is the source of the exotic matter required to maintain the wormhole. There is also a surface stress-energy, that must be produced by additional matter, where the spacetimes are joined. It is shown that wormholes can be constructed for which this additional matter satisfies the weak and dominant energy conditions, so that it could be a form of "normal" matter. Charged dilaton wormholes with a coupling between the dilaton and the electromagnetic field that is more general than in string theory are also briefly discussed.Comment: 9 pages, LaTex, submitted to Phys. Rev.

The Brightest Cluster Galaxy in Abell 85: The Largest Core Known so far

We have found that the brightest cluster galaxy (BCG) in Abell~85, Holm 15A, displays the largest core so far known. Its cusp radius, $r_{\gamma} = 4.57 \pm 0.06$ kpc ($4.26^{\prime\prime}\pm 0.06^{\prime\prime}$), is more than 18 times larger than the mean for BCGs, and $\geq1$ kpc larger than A2261-BCG, hitherto the largest-cored BCG (Postman, Lauer, Donahue, et al. 2012) Holm 15A hosts the luminous amorphous radio source 0039-095B and has the optical signature of a LINER. Scaling laws indicate that this core could host a supermassive black hole (SMBH) of mass $M_{\bullet}\thicksim (10^{9}-10^{11})\,M_{\odot}$. We suggest that cores this large represent a relatively short phase in the evolution of BCGs, whereas the masses of their associated SBMH might be set by initial conditions.Comment: 14 pages, 3 figure, 2 tables, accepted for publication in ApJ Letters on October 6th, 2014, replacement of previous manuscript submitted on May 30th, 2014 to astro-p

Densidade populacional de Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) nas fases de ovo, larva e adulto em milho.

Estudou-se a flutuacao populacional de ovos, lagartas e adultos de Helicoverpa zea (Boddie) na cultura do milho (Zea mays), durante a fase de liberacao de estilos-estigma, no inverno, na primavera e outono, em Sete Lagoas, MG. Foi obtida uma grande quantidade de ovos, com tendencia a diminuicao juntamente com o secamento dos estilos-estigma. Essa quantidade nao correlacionou com o pequeno numero de lagartas amostradas, nem com o valor constante de machos adultos capturados. Fatores de mortalidade especialmente associados a ovos e a lagartas de primeiros instares exerceram papel importante na diminuicao da populacao do inseto. Portanto, nas condicoes onde os experimentos foram conduzidos, as decisoes a respeito de epocas de aplicacoes de inseticidas, embasadas somente no numero de machos capturados em armadilhas de feromonios ou no numero de ovos amostrados nos estilos-estigma, nao traduzem a real necessidade de medidas de controle. Para estimar a populacao de H. zea nas espigas de milho, o melhor indice foi portanto o numero de lagartas/estigma. A disponibilidade constante de alimento e as condicoes favoraveis de clima na regiao mantem uma populacao constante de adultos de modo a nao ser possivel detectar picos de ocorrencia em armadilhas

Critical energy flux and mass in solvable theories of 2d dilaton gravity

In this paper we address the issue of determining the semiclassical threshold for black hole formation in the context of a one-parameter family of theories which continuously interpolates between the RST and BPP models. We find that the results depend significantly on the initial static configuration of the spacetime geometry before the influx of matter is turned on. In some cases there is a critical energy density, given by the Hawking rate of evaporation, as well as a critical mass $m_{cr}$ (eventually vanishing). In others there is neither $m_{cr}$ nor a critical flux.Comment: LaTeX file, 12 pages, 4 figure