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991.
Nanohole arrays in metal films allow extraordinary optical transmission (EOT); the phenomenon is highly advantageous for biosensing applications. In this article, we theoretically investigate the performance of refractive index sensors, utilizing square and hexagonal arrays of nanoholes, that can monitor the spectral position of EOT signals. We present near- and far-field characteristics of the aperture arrays and investigate the influence of geometrical device parameters in detail. We numerically compare the refractive index sensitivities of the two lattice geometries and show that the hexagonal array supports larger figure-of-merit values due to its sharper EOT response. Furthermore, the presence of a thin dielectric film that covers the gold surface and mimics a biomolecular layer causes larger spectral shifts within the EOT resonance for the hexagonal array. We also investigate the dependence of the transmission responses on hole radius and demonstrate that hexagonal lattice is highly promising for applications demanding strong light transmission. 相似文献
992.
A log-periodic toothed nanoantenna based on graphene is proposed, and its multi-resonance properties with respect to the variations of the chemical potential are investigated. The field enhancement and radar cross-section of the antenna for different chemical potentials are calculated, and the effect of the chemical potential on the resonance frequency is analyzed. In addition, the dependence of the resonance frequency on the substrate is also discussed. It is shown that large modulation of resonance intensity in log-periodic toothed nanoantenna can be achieved via turning the chemical potential of graphene. The tunability of the resonant frequencies of the antenna can be used to broad tuning of spectral features. The property of tunable multi-resonant field enhancement has great prospect in the field of graphene-based broadband nanoantenna, which can be applied in non-linear spectroscopy, optical sensor, and near-field optical microscopy. 相似文献
993.
Zidong Zhang Shuhui Chen Xiujie Ji Chen Qin Huimin Wang Peitao Xie Runhua Fan 《Plasmonics (Norwell, Mass.)》2016,11(2):373-379
Metamaterials are artificial periodic structures with negative permittivity and permeability. Several interesting properties can be obtained in metamaterials, such as negative index behavior, which can be used for building perfect lenses, cloaking, antennas, etc. As the metamaterial’s properties are determined by its structure, the key challenge is to reduce the fabrication cost of the periodic structure on the micrometer or nanometer scale for realistic applications. In this paper, we experimentally demonstrate a new one-step method for the fabrication of a large-area infrared metamaterial at extremely low cost. A metallic mesh is used as a shadow mask during the pulsed laser deposition (PLD) process to fabricate a FeNi/SiC/FeNi multilayer sandwich structure on Si substrate (cm2 level). The sample shows a strong absorption peak in the infrared frequency range, and the absorption intensity changes with the sample’s geometry. 相似文献
994.
Sangita Roopak Nilesh Kumar Pathak Alok Ji R. P. Sharma 《Plasmonics (Norwell, Mass.)》2016,11(2):425-432
We suggest numerical method to study the optical response of metal nanostructures. The analysis of optical properties such as scattering and absorption by coated and noncoated nanogeometry has been done using discrete dipole approximation (DDA) method. The core-shell nanogeometry supports surface plasmon resonances, which are highly tunable from 400 to 1100 nm. The tunability of surface plasmon resonance (SPR) highly depends on the structural anisotropy and chosen core-shell material. Further, we have observed that aspect ratio is one of the key parameter to decide the nature and position of the plasmonic peaks and magnitude of optical cross section. We have also shown that coated nanospheroid is a more appropriate geometry as compared to coated nanosphere and noncoated nanospheroid in terms of wide tunability of surface plasmon resonance. The wide tunability in SPR is observed for the effective radii 90 nm core-shell (Au@SiO2) nanospheroid with aspect ratio 0.1. 相似文献
995.
We present a broadband plasmonic metamaterial absorber in the infrared region based on localized surface plasmon polaritons (LSPPs). The unit cell of the proposed metamaterial absorber consists of a multi-cavity structure, in which absorption resonances can be tuned independently through the modification of the width and shift of metallic walls. In order to avoid the degeneration between two contiguous resonances, which dramatically reduces the bandwidth, we introduce a zigzag design rule to arrange the cavities within a compact unit. Thus, the possible number of resonances is greatly increased, enabling an ultrabroadband absorption. A broadband absorber is demonstrated with only a few-layer structure and it also has an incident-angle-insensitive feature. Our results have potential applications in photovoltaic devices, emitters, sensors, and camouflage systems. 相似文献
996.
Ken Fukami Kiyoshi Kawai Sayaka Takeuchi Yoshito Harada Yoshio Hagura 《Food biophysics》2016,11(4):410-416
To understand the fundamental physical properties of calcium maltobionate (MBCa), its water sorption isotherm, glass transition temperature (T g), and viscosity (η) were investigated and compared with those of maltobionic acid (MBH) and maltose. Although amorphous maltose crystalized at water activity (a w) higher than 0.43, MBCa and MBH maintained an amorphous state over the whole a w range. In addition, MBCa had a higher T g and greater resistance to water plasticizing than MBH and maltose. These properties of MBCa likely originate from the strong interaction between MBCa and water induced by electrostatic interactions. Moreover, the effects of temperature and water content on η of an aqueous MBCa solution were evaluated, and its behavior was described using a semi-empirical approach based on a combination of T g extrapolated by the Gordon-Taylor equation and a non-Arrhenius formula known as the Vogel–Fulcher–Tammann equation. This result will be useful for understating the effect of MBCa addition on the solution’s properties. 相似文献
997.
Serena E. Dool Colin F. J. O’Donnell Joanne M. Monks Sebastien J. Puechmaille Gerald Kerth 《Conservation Genetics》2016,17(5):1067-1079
The New Zealand long-tailed bat (Chalinolobus tuberculatus) is an endemic species threatened with extinction. Since the arrival of humans, massive deforestation has occurred and invasive mammalian predators were introduced. As a result, C. tuberculatus’ distribution shrank dramatically and became fragmented. To aid the management of the remaining populations, two Evolutionary Significant Units (ESUs) were designated: one on each of New Zealand’s main islands. We utilised mitochondrial sequence data (cytb, 703 bp) and 10 nuclear DNA microsatellite loci to reconstruct the demographic history of this species, to characterise the level of genetic diversity in remaining populations, and to assess the current connectivity between them. Our results indicate that the North Island, with the highest genetic diversity, served as a glacial refuge, with a loss of diversity following the path recolonization to the south of the South Island. However, our data are also consistent with continued, or at least very recent, genetic exchange between colonies across the species distribution. The only exception is the Hanging Rock colony on the east coast of the South Island, which appears to be isolated. Thus, there was no support for the previously designated ESUs. Signatures of past population declines were found in three colonies, the most extreme of which was found in Hanging Rock. Consequently, we recommend that it be genetically rescued via translocation from a donor population. In general, future management priorities should treat Chalinolobus tuberculatus as a single unit, focusing on maintaining connectivity between remaining populations, together with continued roost protection and pest control. 相似文献
998.
Theresa L. Cole Michael P. Hammer Peter J. Unmack Peter R. Teske Chris J. Brauer Mark Adams Luciano B. Beheregaray 《Conservation Genetics》2016,17(6):1377-1391
Distinguishing the relative influence of historic (i.e. natural) versus anthropogenic factors in metapopulation structure is an important but often overlooked step in management programs of threatened species. Biotas in freshwater wetlands and floodplains, such as those in the Murray–Darling Basin (MDB)—one of Australia’s most impacted ecosystems, are particularly susceptible to anthropogenic fragmentation. Here we present a comprehensive multilocus assessment of genetic variation in the threatened southern pygmy perch Nannoperca australis (578 individuals; 45 localities; microsatellite, allozyme and mitochondrial DNA datasets), an ecological specialist with low dispersal potential. We assess patterns of spatial structure and genetic diversity in populations spanning the highly fragmented MDB and test whether recent anthropogenic modification has disrupted range-wide connectivity. We detected strong and hierarchical population structure, very low genetic diversity and lack of contemporary gene flow across the MDB. In contrast, the apparent absence of pronounced or long-term phylogeographic structure suggests that observed population divergences generally do not reflect deeply historic natural fragmentation. Coalescent-based analyses supported this inference, revealing that divergence times between populations from the upper and lower MDB fall into the period of European settlement. It appears that the observed contemporary isolation of populations is partly explained by the severe modification of the MDB post-dating the onset of European settlement. Our integrated approach substantially improves the interpretation of how fragmentation impacts present-day biodiversity. It also provides novel contributions for risk-assessing management actions in the context of captive breeding and translocations of small freshwater fishes, a group of increasing global conservation concern. 相似文献
999.
Jeremy Larroque Jean-Michel Vandel Guillaume Queney Sébastien Devillard 《Conservation Genetics》2016,17(6):1293-1306
Maintenance of genetic variation is of critical importance for wild populations since low levels limit the species’ ability to respond to different threats (diseases, predators, environmental changes) in both the long and the short term. Human activities could impact the genetic variation of wild species in multiple ways, including via fragmentation and harvesting. We used an individual-based landscape genetics approach to describe the impact of landscape elements and trapping pressure on the spatial genetic structure of a large sample (n = 370) of the stone marten (Martes foina) in central-eastern France (Bresse). An analysis of isolation-by-resistance using a causal modeling approach showed an influence of landscape cover and/or trapping pressure on gene flow according to age and sex class. Overall, the connectivity in the study area is provided mainly by vegetation cover, while roads and open areas partially impede it. Unexpectedly for this “urban adapter” species, buildings could reduce gene flow. We also emphasized the sex-dependent effect of trapping on gene flow. Genetic differentiation in males was influenced by trapping pressure and landscape structure while only the latter influenced genetic differentiation in females. A stronger isolation by distance in males than in females suggested that at the scale of the study area, males are more exposed to trapping pressure, which reduces effective dispersal. Overall, the combination of both landscape and trapping costs might create an ‘ecological trap’ that could disrupt gene flow, leading to a north–south division in the study area. 相似文献
1000.
Karina Martins Renato Kenji Kimura Ana Flávia Francisconi Salvador Gezan Karen Kainer Alexander V. Christianini 《Conservation Genetics》2016,17(3):509-520
In hyper fragmented biomes, conservation of extant biota relies on preservation and proper management of remnants. The maintenance of genetic diversity and functional connectivity in a landscape context is probably key to long-term conservation of remnant populations. We measured the genetic diversity in seedlings and adults of tree Copaifera langsdorffii and evaluated whether edge and density-dependent effects drive natural regeneration in a set of very small and degraded Brazilian Atlantic forest fragments. We evaluated the role of small remnants in the conservation of genetic diversity in a hyper fragmented landscape and discuss the challenge of long-term population sustainability of such altered habitats. High genetic diversity in adults indicated these fragments are valuable targets for C. langsdorffii in situ conservation, but both genetic diversity and divergence among patches decreased in seedlings. In our landscape, regeneration increased as it neared edges and adults; suggesting this population is resilient to fragmentation. However, at a broader scale, current levels of gene flow have not been sufficient to prevent the loss of genetic diversity across generations. Restoration plans, even at a small scale, are necessary to promote fragment connectivity and spatially expand opportunities for the fairly restricted gene flow observed in this severely fragmented Brazilian Atlantic forest region. 相似文献