Active Metamaterials with Negative Static Electric Susceptibility

Although well‐established textbook arguments suggest that static electric susceptibility χ(0) must be positive in “all bodies,” it has been pointed out that materials that are not in thermodynamic equilibrium are not necessarily subject to this restriction. Media with inverted populations of atomic and molecular energy levels have been predicted theoretically to exhibit a χ(0) < 0 state, however the systems envisioned require reduced temperature, reduced pressure, and an external pump laser to maintain the population inversion. Further, the existence of χ(0) < 0 has never been confirmed experimentally. Here, a completely different approach is taken to the question of χ(0) < 0 and a design concept to achieve “true” χ(0) < 0 is proposed based on active metamaterials with internal power sources. Two active metamaterial structures are fabricated that, despite still having their power sources implemented externally for reasons of practical convenience, provide evidence in support of the general concept. Effective values are readily achieved at room temperature and pressure and are tunable throughout the range of stability −1 < χ(0) < 0, resulting in experimentally‐determined magnitudes that are over one thousand times greater than those predicted previously. Since χ(0) < 0 is the missing electric analog of diamagnetism, this work opens the door to new technological capabilities such as stable electrostatic levitation

Accretions of Various Types of Dark Energies onto Morris-Thorne Wormhole

In this work, we have studied accretion of the dark energies onto Morris-Thorne wormhole. For quintessence like dark energy, the mass of the wormhole decreases and phantom like dark energy, the mass of wormhole increases. We have assumed two types of dark energy like variable modified Chaplygin gas (VMCG) and generalized cosmic Chaplygin gas (GCCG). We have found the expression of wormhole mass in both cases. We have found the mass of the wormhole at late universe and this is finite. For our choices the parameters and the function $B(a)$, these models generate only quintessence dark energy (not phantom) and so wormhole mass decreases during evolution of the universe. Next we have assumed 5 kinds of parametrizations of well known dark energy models. These models generate both quintessence and phantom scenarios. So if these dark energies accrete onto the wormhole, then for quintessence stage, wormhole mass decreases upto a certain value (finite value) and then again increases to infinite value for phantom stage during whole evolution of the universe. We also shown these results graphically.Comment: 9 pages, 7 figures. arXiv admin note: text overlap with arXiv:1112.615

Invasive Lionfish Drive Atlantic Coral Reef Fish Declines

Indo-Pacific lionfish (Pterois volitans and P. miles) have spread swiftly across the Western Atlantic, producing a marine predator invasion of unparalleled speed and magnitude. There is growing concern that lionfish will affect the structure and function of invaded marine ecosystems, however detrimental impacts on natural communities have yet to be measured. Here we document the response of native fish communities to predation by lionfish populations on nine coral reefs off New Providence Island, Bahamas. We assessed lionfish diet through stomach contents analysis, and quantified changes in fish biomass through visual surveys of lionfish and native fishes at the sites over time. Lionfish abundance increased rapidly between 2004 and 2010, by which time lionfish comprised nearly 40% of the total predator biomass in the system. The increase in lionfish abundance coincided with a 65% decline in the biomass of the lionfish's 42 Atlantic prey fishes in just two years. Without prompt action to control increasing lionfish populations, similar effects across the region may have long-term negative implications for the structure of Atlantic marine communities, as well as the societies and economies that depend on them

The bashful and the boastful : prestigious leaders and social change in Mesolithic Societies

The creation and maintenance of influential leaders and authorities is one of the key themes of archaeological and historical enquiry. However the social dynamics of authorities and leaders in the Mesolithic remains a largely unexplored area of study. The role and influence of authorities can be remarkably different in different situations yet they exist in all societies and in almost all social contexts from playgrounds to parliaments. Here we explore the literature on the dynamics of authority creation, maintenance and contestation in egalitarian societies, and discuss the implications for our interpretation and understanding of the formation of authorities and leaders and changing social relationships within the Mesolithic

Genetics reveal the identity and origin of the lionfish invasion in the Mediterranean Sea

Following aquarium releases, invasive lionfishes have colonized large areas of the Caribbean and western Atlantic, resulting in an immense ecological damage. The early stages of that invasion are poorly known. Indeed, a lag of time between the introduction and detection often preclude genetic characterization of that crucial phase. With elevated awareness, the recent invasion of Pterois miles was quickly detected in the Mediterranean Sea. We hereby show that the very first individuals establishing populations in the Mediterranean Sea display haplotypes that nest within the large genetic diversity of Red Sea individuals, thus indicating an invasion via the Suez Canal. We also show that only two haplotypes are detected in the Mediterranean Sea, suggesting that few individuals may have been involved in the invasion. Thus, we conclude that the Mediterranean invasion is the result of a movement of individuals from the Red Sea, rather than from other means, and that low genetic diversity does not seem to have a negative effect on the success and spread of lionfish into the Mediterranean Sea

Wavelength tuning of the photonic band gap of an achiral nematic liquid crystal filled into a chiral polymer scaffold

In this paper, we demonstrate electric field-induced wavelength tuning of the entire photonic band-gap of an achiral nematic liquid crystal (LC) filled into a chiral polymer scaffold. This chiral polymer scaffold has been formed by creating a template of a chiral nematic LC phase, which remarkably does not compromise the optical finesse of the band-gap when compared to that of a conventional, polymer-stabilized chiral nematic LC. We present results on the spectral shift and temporal evolution of the photonic band-gap in the presence of an external a.c. electric field. It is shown that, initially, there is a rapid (τ ≈ 1 ms) blue-shift of the longwavelength band-edge followed by a considerably slower blue-shift (τ ≈ 6.5 s) of the entire band-gap. We compare the results with those obtained for a polymer-stabilized chiral nematic LC where only a blue-shift of the long-wavelength band-edge is observed. Consequently, we find that, for the templated sample, the tuning range is more than a factor of two greater than that observed for the polymer-stabilized chiral nematic LC for the same range of electric field amplitudes. It is also found that there is little in the way of hysteresis upon increasing and decreasing the applied electric field magnitude. Finally, we present experimental evidence that suggests that the blue-shift of the entire band-gap is due to an additional tuning mechanism present only for the case of the templated samples. This is believed to be caused by a contraction of the pitch that results from a translational motion of the polymer network. The greater tuning range observed in these templated samples are potentially important for the development of tunable 1-dimensional photonic band-gaps and LC lasers. Furthermore, it avoids the use of d.c. electric fields that can lead to long-term issues regarding stability

Wavelength tuning of the photonic band gap of an achiral nematic liquid crystal filled into a chiral polymer scaffold

In this paper, we demonstrate electric field-induced wavelength tuning of the entire photonic band-gap of an achiral nematic liquid crystal (LC) filled into a chiral polymer scaffold. This chiral polymer scaffold has been formed by creating a template of a chiral nematic LC phase, which remarkably does not compromise the optical finesse of the band-gap when compared to that of a conventional, polymer-stabilized chiral nematic LC. We present results on the spectral shift and temporal evolution of the photonic band-gap in the presence of an external a.c. electric field. It is shown that, initially, there is a rapid (τ ≈ 1 ms) blue-shift of the longwavelength band-edge followed by a considerably slower blue-shift (τ ≈ 6.5 s) of the entire band-gap. We compare the results with those obtained for a polymer-stabilized chiral nematic LC where only a blue-shift of the long-wavelength band-edge is observed. Consequently, we find that, for the templated sample, the tuning range is more than a factor of two greater than that observed for the polymer-stabilized chiral nematic LC for the same range of electric field amplitudes. It is also found that there is little in the way of hysteresis upon increasing and decreasing the applied electric field magnitude. Finally, we present experimental evidence that suggests that the blue-shift of the entire band-gap is due to an additional tuning mechanism present only for the case of the templated samples. This is believed to be caused by a contraction of the pitch that results from a translational motion of the polymer network. The greater tuning range observed in these templated samples are potentially important for the development of tunable 1-dimensional photonic band-gaps and LC lasers. Furthermore, it avoids the use of d.c. electric fields that can lead to long-term issues regarding stability

Speckle contrast reduction of laser light using a chiral nematic liquid crystal diffuser

High coherence in laser light causes spatially distributed interference called speckle. In applications such as holographic projection, this undesirable side effect degrades image clarity. The current methods of speckle reduction, such as a rotating ground-glass diffuser, require additional bulky moving parts. Here, we present an alternative technology based upon a compact, electrohydrodynamic chiral nematic liquid crystal device. A spatially random phase modulation of the incident light is achieved through the electrohydrodynamic instabilities that are induced by an alternating electric field. Using a chiral nematic liquid crystal device that is doped with an ionic compound, we find that the speckle contrast can be reduced by as much as 80%

Speckle contrast reduction of laser light using a chiral nematic liquid crystal diffuser

High coherence in laser light causes spatially distributed interference called speckle. In applications such as holographic projection, this undesirable side effect degrades image clarity. The current methods of speckle reduction, such as a rotating ground-glass diffuser, require additional bulky moving parts. Here, we present an alternative technology based upon a compact, electrohydrodynamic chiral nematic liquid crystal device. A spatially random phase modulation of the incident light is achieved through the electrohydrodynamic instabilities that are induced by an alternating electric field. Using a chiral nematic liquid crystal device that is doped with an ionic compound, we find that the speckle contrast can be reduced by as much as 80%

Femtosecond fiber Bragg grating fabrication with adaptive optics aberration compensation

We present fiber Bragg gratings (FBGs) fabricated using adaptive optics aberration compensation for the first time to the best of our knowledge. The FBGs are fabricated with a femtosecond laser by the point-by-point method using an air-based objective lens, removing the requirement for immersion oil or ferrules. We demonstrate a general phase correction strategy that can be used for accurate fabrication at any point in the fiber cross-section. We also demonstrate a beam-shaping approach that nullifies the aberration when focused inside a central fiber core. Both strategies give results which are in excellent agreement with coupled-mode theory. An extremely low wavelength polarization sensitivity of 4 pm is reported