Acoustic signatures of the seafloor: Tools for predicting grouper habitat

Groupers are important components of commercial and recreational fisheries. Current methods of diver-based grouper census surveys could potentially benefit from development of remotely sensed methods of seabed classification. The goal of the present study was to determine if areas of high grouper abundance have characteristic acoustic signatures. A commercial acoustic seabed mapping system, QTC View Series V, was used to survey an area near Carysfort Reef, Florida Keys. Acoustic data were clustered using QTC IMPACT software, resulting in three main acoustic classes covering 94% of the area surveyed. Diver-based data indicate that one of the acoustic classes corresponded to hard substrate and the other two represented sediment. A new measurement of seabed heterogeneity, designated acoustic variability, was also computed from the acoustic survey data in order to more fully characterize the acoustic response (i.e., the signature) of the seafloor. When compared with diver-based grouper census data, both acoustic classification and acoustic variability were significantly different at sites with and without groupers. Sites with groupers were characterized by hard bottom substrate and high acoustic variability. Thus, the acoustic signature of a site, as measured by acoustic classification or acoustic variability, is a potentially useful tool for stratifying diver sampling effort for grouper census.

Signatures of Topological Superconductors

Topological superconductors are particularly interesting in light of the active ongoing experimental efforts for realizing exotic physics such as Majorana zero modes. These systems have excitations with non-Abelian exchange statistics, which provides a path towards topological quantum information processing. Intrinsic topological superconductors are quite rare in nature. However, one can engineer topological superconductivity by inducing effective p-wave pairing in materials which can be grown in the laboratory. One possibility is to induce the proximity effect in topological insulators; another is to use hybrid structures of superconductors and semiconductors.

The proposal of interfacing s-wave superconductors with quantum spin Hall systems provides a promising route to engineered topological superconductivity. Given the exciting recent progress on the fabrication side, identifying experiments that definitively expose the topological superconducting phase (and clearly distinguish it from a trivial state) raises an increasingly important problem. With this goal in mind, we proposed a detection scheme to get an unambiguous signature of topological superconductivity, even in the presence of ordinarily detrimental effects such as thermal fluctuations and quasiparticle poisoning. We considered a Josephson junction built on top of a quantum spin Hall material. This system allows the proximity effect to turn edge states in effective topological superconductors. Such a setup is promising because experimentalists have demonstrated that supercurrents indeed flow through quantum spin Hall edges. To demonstrate the topological nature of the superconducting quantum spin Hall edges, theorists have proposed examining the periodicity of Josephson currents respect to the phase across a Josephson junction. The periodicity of tunneling currents of ground states in a topological superconductor Josephson junction is double that of a conventional Josephson junction. In practice, this modification of periodicity is extremely difficult to observe because noise sources, such as quasiparticle poisoning, wash out the signature of topological superconductors. For this reason, We propose a new, relatively simple DC measurement that can compellingly reveal topological superconductivity in such quantum spin Hall/superconductor heterostructures. More specifically, We develop a general framework for capturing the junction's current-voltage characteristics as a function of applied magnetic flux. Our analysis reveals sharp signatures of topological superconductivity in the field-dependent critical current. These signatures include the presence of multiple critical currents and a non-vanishing critical current for all magnetic field strengths as a reliable identification scheme for topological superconductivity.

This system becomes more interesting as interactions between electrons are involved. By modeling edge states as a Luttinger liquid, we find conductance provides universal signatures to distinguish between normal and topological superconductors. More specifically, we use renormalization group methods to extract universal transport characteristics of superconductor/quantum spin Hall heterostructures where the native edge states serve as a lead. Interestingly, arbitrarily weak interactions induce qualitative changes in the behavior relative to the free-fermion limit, leading to a sharp dichotomy in conductance for the trivial (narrow superconductor) and topological (wide superconductor) cases. Furthermore, we find that strong interactions can in principle induce parafermion excitations at a superconductor/quantum spin Hall junction.

As we identify the existence of topological superconductor, we can take a step further. One can use topological superconductor for realizing Majorana modes by breaking time reversal symmetry. An advantage of 2D topological insulator is that networks required for braiding Majoranas along the edge channels can be obtained by adjoining 2D topological insulator to form corner junctions. Physically cutting quantum wells for this purpose, however, presents technical challenges. For this reason, I propose a more accessible means of forming networks that rely on dynamically manipulating the location of edge states inside of a single 2D topological insulator sheet. In particular, I show that edge states can effectively be dragged into the system's interior by gating a region near the edge into a metallic regime and then removing the resulting gapless carriers via proximity-induced superconductivity. This method allows one to construct rather general quasi-1D networks along which Majorana modes can be exchanged by electrostatic means.

Apart from 2D topological insulators, Majorana fermions can also be generated in other more accessible materials such as semiconductors. Following up on a suggestion by experimentalist Charlie Marcus, I proposed a novel geometry to create Majorana fermions by placing a 2D electron gas in proximity to an interdigitated superconductor-ferromagnet structure. This architecture evades several manufacturing challenges by allowing single-side fabrication and widening the class of 2D electron gas that may be used, such as the surface states of bulk semiconductors. Furthermore, it naturally allows one to trap and manipulate Majorana fermions through the application of currents. Thus, this structure may lead to the development of a circuit that enables fully electrical manipulation of topologically-protected quantum memory. To reveal these exotic Majorana zero modes, I also proposed an interference scheme to detect Majorana fermions that is broadly applicable to any 2D topological superconductor platform.

Birth Weight, Working Memory and Epigenetic Signatures in IGF2 and Related Genes: A MZ Twin Study

Neurodevelopmental disruptions caused by obstetric complications play a role in the etiology of several phenotypes associated with neuropsychiatric diseases and cognitive dysfunctions. Importantly, it has been noticed that epigenetic processes occurring early in life may mediate these associations. Here, DNA methylation signatures at IGF2 (insulin-like growth factor 2) and IGF2BP1-3 (IGF2-binding proteins 1-3) were examined in a sample consisting of 34 adult monozygotic (MZ) twins informative for obstetric complications and cognitive performance. Multivariate linear regression analysis of twin data was implemented to test for associations between methylation levels and both birth weight (BW) and adult working memory (WM) performance. Familial and unique environmental factors underlying these potential relationships were evaluated. A link was detected between DNA methylation levels of two CpG sites in the IGF2BP1 gene and both BW and adult WM performance. The BW-IGF2BP1 methylation association seemed due to non-shared environmental factors influencing BW, whereas the WM-IGF2BP1 methylation relationship seemed mediated by both genes and environment. Our data is in agreement with previous evidence indicating that DNA methylation status may be related to prenatal stress and later neurocognitive phenotypes. While former reports independently detected associations between DNA methylation and either BW or WM, current results suggest that these relationships are not confounded by each other.

Variation in the isotopic signatures of juvenile gray snapper (Lutjanus griseus) from five southern Florida region

Measurements of 18O/16O and 13C/12C ratios in the carbonate of juvenile gray snapper (Lutjanus griseus) sagittal otoliths collected during 2001–2005 from different southern Florida regions indicated significant variations in the ratios between Florida Bay and surrounding areas. Annual differences in isotopic composition were also observed. Classification accuracy of individual otoliths to a region averaged 80% (63% to 96%), thereby enabling the probability of assigning an unknown individual to the appropriate juvenile nursery habitat. Identification of isotopic signatures in the otoliths of gray snapper from Florida Bay and adjacent ecosystems may be important for distinguishing specific portions of the bay that are crucial nursery grounds for juveniles. Separation of gray snapper between geographic regions and nursery sites is possible and has the potential to establish a link between adult gray snapper present on offshore reefs and larvae and juveniles at nursery habitats in Florida Bay or adjacent areas.

New insights into the diets of harbor seals (Phoca vitulina) in the Salish Sea revealed by analysis of fatty acid signatures

Harbor seals (Phoca fvitulina) are an abundant predator along the west coast of North America, and there is considerable interest in their diet composition, especially in regard to predation on valued fish stocks. Available informationon harbor seal diets, primarily derived from scat analysis, suggests that adult salmon (Oncorhynchus spp.), Pacific Herring (Clupea pallasii), and gadids predominate. Because diet assessments based on scat analysis may be biased, we investigated diet composition through quantitative analysis of fatty acid signatures. Blubber samples from 49 harbor seals captured in western North America from haul-outs within the area of the San Juan Islands and southern Strait of Georgia in the Salish Sea were analyzed for fatty acid composition, along with 269 fish and squid specimens representing 27 potential prey classes. Diet estimates varied spatially, demographically, and among individual harbor seals. Findings confirmed the prevalence of previously identified prey species in harbor seal diets, but other species also contributed significantly. In particular, Black (Sebastes melanops) and Yellowtail (S. flavidus) Rockfish were estimated to compose up to 50% of some individual seal diets. Specialization and high predation rates on Black and Yellowtail Rockfish by a subset of harbor seals may play a role in the population dynamics of these regional rockfish stocks that is greater than previously realized.

Elemental signatures in otoliths of larval walleye pollock (Theragra chalcogramma) from the northeast Pacific Ocean

The population structure of walleye pollock (Theragra chalcogramma) in the northeastern Pacific Ocean remains unknown. We examined elemental signatures in the otoliths of larval and juvenile pollock from locations in the Bering Sea and Gulf of Alaska to determine if there were significant geographic variations in otolith composition that may be used as natural tags of population affinities. Otoliths were assayed by using both electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Elements measured at the nucleus of otoliths by EPMA and laser ablation ICP-MS differed significantly among locations. However, geographic groupings identified by a multivariate statistical approach from EPMA and ICP-MS were dissimilar, indicating that the elements assayed by each technique were controlled by separate depositional processes within the endolymph. Elemental profiles across the pollock otoliths were generally consistent at distances up to 100 μm from the nucleus. At distances beyond 100 μm, profiles varied significantly but were remarkably consistent among individuals collected at each location. These data may indicate that larvae from various spawning locations are encountering water masses with differing physicochemical properties through their larval lives, and at approximately the same time. Although our results are promising, we require a better understanding of the mechanisms controlling otolith chemistry before it will be possible to reconstruct dispersal pathways of larval pollock based on probe-based analyses of otolith geochemistry. Elemental signatures in otoliths of pollock may allow for the delineation of fine-scale population structure in pollock that has yet to be consistently revealed by using population genetic approaches.

Cross-species chromosome painting unveils cytogenetic signatures for the Eulipotyphla and evidence for the polyphyly of Insectivora

Insectivore-like animals are traditionally believed among the first eutherian mammals that have appeared on the earth. The modern insectivores are thus crucial for understanding the systematics and phylogeny of eutherian mammals as a whole. Here cross-spe

Intrinsic terahertz plasmon signatures in chemical vapour deposited graphene

Plasmonic resonance at terahertz (THz) frequencies can be achieved by gating graphene grown via chemical vapour deposition (CVD) to a high carrier concentration. THz time domain spectroscopy of such gated monolayer graphene shows resonance features around 1.6 THz, which appear as absorption peaks when the graphene is electrostatically p-doped and change to enhanced transmission when the graphene is n-doped. Superimposed on the Drude-like frequency response of graphene, these resonance features are related to the inherent poly-crystallinity of CVD graphene. An understanding of these features is necessary for the development of future THz optical elements based on CVD graphene. © 2013 AIP Publishing LLC.

Excitation energy dependent raman signatures of ABA- and ABC-stacked few-layer graphene

The dependence of the Raman spectrum on the excitation energy has been investigated for ABA-and ABC- stacked few-layer graphene in order to establish the fingerprint of the stacking order and the number of layers, which affect the transport and optical properties of few-layer graphene. Five different excitation sources with energies of 1.96, 2.33, 2.41, 2.54 and 2.81â €...eV were used. The position and the line shape of the Raman 2D, G*, N, M, and other combination modes show dependence on the excitation energy as well as the stacking order and the thickness. One can unambiguously determine the stacking order and the thickness by comparing the 2D band spectra measured with 2 different excitation energies or by carefully comparing weaker combination Raman modes such as N, M, or LOLA modes. The criteria for unambiguous determination of the stacking order and the number of layers up to 5 layers are established.

Variation in stable isotope signatures of seston and a zooplanktivorous fish in a eutrophic Chinese lake

Temporal and spatial changes in delta(13)C and delta(15)N of seston (mainly phytoplankton) and isotopic relationship between seston and the lake anchovy (Coilia ectenes) were studied in the large eutrophic freshwater Lake Chaohu in China. Much of the spatial and temporal variation in delta(13)C of lake anchovies was explained by variation in seston, indicating a strong link between pelagic primary production and higher order consumers. Because the lake is shallow, there were no significant differences in delta(13)C and delta(15)N of seston between surface and overlying waters. Spatially, the relatively high delta(13)C and delta(15)N of seston in the western part of the lake might be due to high levels of anthropogenically derived N and C introduced from the surrounding cities through sewage drainage systems. The trophic position of the lake anchovy in the food web of Lake Chaohu was estimated to be 2.9-4.1 (3.5 +/- 0.4), which agrees well with the previous stomach content analysis suggesting that the lake anchovy fed both on zooplankton and small planktivorous fishes.

Fatty-acids and their C-13 signatures in seep carbonates from hydrocarbon seeps on the upper (GC 185) and lower (AC 645) continental slope of the Gulf of Mexico

Here we reported the fatty-acids and their δ 13C values in seep carbonates collected from Green Canyon lease block 185 (GC 185; Sample GC-F) at upper continental slope (water depth: ∼540 m), and Alaminos Canyon lease block 645 (GC 645; Sample AC-E) at lower continental slope (water depth: ∼2200 m) of the Gulf of Mexico. More than thirty kinds of fatty acids were detected in both samples. These fatty acids are maximized at C16. There is a clear even-over-odd carbon number predominance in carbon number range. The fatty acids are mainly composed of n-fatty acids, iso-/anteiso-fatty acids and terminally branched odd-numbered fatty acids (iso/anteiso). The low δ 13C values (−39.99‰ to.32.36‰) of n-C12:0, n-C13:0, i-C14:0and n-C14:0 suggest that they may relate to the chemosynthetic communities at seep sites. The unsaturated fatty acids n-C18:2 and C18:1Δ9 have the same δ 13C values, they may originate from theBeggiatoa/Thioploca. Unlike other fatty acids, the terminally branched fatty acids (iso/anteiso) show lowerδ 13C values (as low as −63.95‰) suggesting a possible relationship to sulfate reducing bacteria, which is common during anaerobic oxidation of methane at seep sites.

Did an extensive forest ever develop on the Chinese Loess Plateau during the past 130 ka?: a test using soil carbon isotopic signatures

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