Biharmonic Split Ring Resonator Metamaterial: Artificially dispersive effective density in thin periodically perforated plates

We present in this paper a theoretical and numerical analysis of bending waves localized on the boundary of a platonic crystal whose building blocks are split ring resonators (SRR). We first derive the homogenized parameters of the structured plate using a three-scale asymptotic expansion in the linearized biharmonic equation. In the limit when the wavelength of the bending wave is much larger than the typical heterogeneity size of the platonic crystal, we show that it behaves as an artificial plate with an anisotropic effective Young modulus and a dispersive effective mass density. We then analyze dispersion diagrams associated with bending waves propagating within an infinite array of SRR, for which eigen-solutions are sought in the form of Floquet-Bloch waves. We finally demonstrate that this structure displays the hallmarks of All-Angle-Negative-Refraction(AANR) and it leads to superlensing and ultrarefraction effects, interpreted thanks to our homogenization model as a consequence of negative and vanishing effective density, respectively.Comment: 17 pages, 6 figure

The Gas Temperature of Starless Cores in Perseus

In this paper we study the determinants of starless core temperatures in the Perseus molecular cloud. We use NH3 (1,1) and (2,2) observations to derive core temperatures (T_kin) and data from the COMPLETE Survey of Star Forming Regions and the c2d Spitzer Legacy Survey for observations of the other core and molecular cloud properties. The kinetic temperature distribution probed by NH3 is in the fairly narrow range of 9 - 15 K. We find that cores within the clusters IC348 and NGC1333 are significantly warmer than "field" starless cores, and T_kin is higher within regions of larger extinction-derived column density. Starless cores in the field are warmer when they are closer to class O/I protostars, but this effect is not seen for those cores in clusters. For field starless cores, T_kin is higher in regions in which the 13CO linewidth and the 1.1mm flux from the core are larger, and T_kin is lower when the the peak column density within the core and average volume density of the core are larger. There is no correlation between T_kin and 13CO linewidth, 1.1mm flux, density or peak column density for those cores in clusters. The temperature of the cloud material along the line of sight to the core, as measured by CO or far-infrared emission from dust, is positively correlated with core temperature when considering the collection of cores in the field and in clusters, but this effect is not apparent when the two subsamples of cores are considered separately.Comment: Accepted to ApJ; 13 pages, including 3 tables and three figure

Practical lessons for winning support for radical transport projects

This paper proposes that while many plans and solutions to the transport problems of the 21st Century have been mooted, very few have succeeded in significantly improving the situation within Europe. It is suggested that many schemes face problems at the project implementation stage due to adverse public and/or political reaction. This paper incorporates a series of vignettes, several of which are based on indepth interviews with practitioners directly involved in the implementation of 'radical'transport schemes from around the world in an attempt to draw lessons as to how they overcame this, not least in terms of how the implementation of alternative strategies by European policy-makers could be shaped and adopted world-wide

Seasonal prevalence and distribution of ticks on the Accra Plains of Ghana and their association with dermatophilosis

The professional and scientific literature on the epidemiology, treatment and economic importance of dermatophilosis has been reviewed. Particular attention being paid to the role of ticks, especially Amblyomma variegatum in causing overt disease and tick associated losses. In addition chemical and alternate methods of tick control including the use of resistant breeds of cattle, modification of vegetation and the microclimate, the introduction of tick-resistant grasses and host vaccination against ticks are discussed.An experiment herd of 26 animals and five local herds containing 605 animals on the Coastal Plains of Ghana were studied.The seasonal abundance of ticks, their association with dermatophilosis and the systemic effects of the ticks on their hosts were investigated. Four genera, Amblyomma, Boophilus, Rhipicephalus and Hyalomma were identified on cattle, A. variegatum being the predominant tick species occurring throughout the year with peak infestations in the two rainy seasons. A highly significant positive correlation was revealed between A. variegatum and dermatophilosis in four of five local herds. Unexpectedly, a significant correlation was found between Hyalomma rufipes and dermatophilosis twice and between Rhipicephalus senegalensis and dermatophilosis once in the local herds.Clinical dermatophilosis developed two months after severe tick infestation. The immune responsiveness of tick-infested cattle was suppressed as assessed by the lymphocyte transformation test (LTT) and confirmed by [3H]-thymidine incorporation assays. Decreased lymphocyte responsiveness in the Friesian cattle coincided with peak tick levels and clinical dermatophilosis. In vitro lymphocyte responsiveness to Concanavalin A in culture medium containing foetal calf serum was suppressed by serum from cattle infested with ticks. Similarly, serum from cattle infested with ticks and infected with dermatophilosis suppressed lymphocytes derived from "clean" animals i.e. control animals treated with acaricides.Repeated experimental infections in cattle healed spontaneously in spite of the fact that the immune responses of the animals were suppressed. Resolution occurred fast after the second and third infections but not after the fourth infection which healed at the same time as the first.Cross-reaction was observed between D. congolensis and PPD. The practical significance of the observed association in relation to tuberculosis skin test is discussed.It is suggested that indigenous breeds of cattle which are more resistant to ticks and dermatophilosis be kept on the Coastal Plains of Ghana. It is also recommended that acaricides with long residual activity backed-up with long-acting oxytetracycline injectables be used during periods of high tick activity to keep tick levels at low numbers. Selective hand-dressing may then be used to treat any individual animals with large tick burdens in the dry seasons

Strong Modification of the Nonlinear Optical Response of Metallic Subwavelength Hole Arrays

The influence of hole shape on the nonlinear optical properties of metallic subwavelength hole arrays is investigated. It is found that the amount of second harmonics generated can be enhanced by changing the hole shape. In part this increase is a direct result of the effect of hole shape on the linear transmission properties. Remarkably, in addition to enhancements that follow directly from the linear properties of the array, we find a hot hole shape. For rectangular holes the effective nonlinear response is enhanced by more than 1 order of magnitude for one particular aspect ratio. This enhancement can be attributed to slow propagation of the fundamental wavelength through the holes which occurs close to the hole cutoff