Ultra-large bandwidth hollow-core guiding in all-silica Bragg fibers with nano-supports

We demonstrate a new class of hollow-core Bragg fibers that are composed of concentric cylindrical silica rings separated by nanoscale support bridges. We theoretically predict and experimentally observe hollow-core confinement over an octave frequency range. The bandwidth of bandgap guiding in this new class of Bragg fibers exceeds that of other hollow-core fibers reported in the literature. With only three rings of silica cladding layers, these Bragg fibers achieve propagation loss of the order of 1 dB/m.Comment: 9 pages including 5 figure

Lack of consensus in social systems

We propose an exactly solvable model for the dynamics of voters in a two-party system. The opinion formation process is modeled on a random network of agents. The dynamical nature of interpersonal relations is also reflected in the model, as the connections in the network evolve with the dynamics of the voters. In the infinite time limit, an exact solution predicts the emergence of consensus, for arbitrary initial conditions. However, before consensus is reached, two different metastable states can persist for exponentially long times. One state reflects a perfect balancing of opinions, the other reflects a completely static situation. An estimate of the associated lifetimes suggests that lack of consensus is typical for large systems.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let

Food habits of wintering double-crested cormorants in the Mississippi Delta

Given its ubiquity, it is not surprising that agriculture, including fin fish aquaculture, contributes to food webs worldwide and is used by numerous wildlife for foraging and meeting other needs. Double-crested Cormorants (Phalacrocorax auritus) impact United States commercial aquaculture and are considered the primary avian predator in catfish (Ictalurus spp.) aquaculture facilities in the Mississippi Delta. Recent changes in aquaculture practices, regulatory policies, and decreased overall hectares in production prompted this study that assessed cormorant consumption of catfish in relation to their night roosts through surveys and diet analysis. Cormorants were collected from night roosts from October through April 2016–2018 (n=69 collections). On average, catfish constituted 33% of a cormorant\u27s overall diet, which is less than reported in previous studies. There was no statistical difference between consumption of channel (I. punctatus) and hybrid catfish (I. punctatus x I. furcatus) based on biomass estimates, and the greatest consumption of catfish occurred in the months of February and March. The best fit model for predicting catfish consumption was the cubic polynomial function of the area of catfish aquaculture within a 30.6 km forage buffer of a night roost. Our findings will inform wildlife managers about relationships between cormorant night roost locations and consumption of catfish and aid decision making with respect to cormorant management. Despite cormorants having shifted consumption to naturally occurring fish species associated with changes to aquaculture, aquaculture remains an important part of regional food webs

Predicting consistent foraging ecologies of migrating waterbirds: Using stable isotope and parasite measurements as indicators of landscape use

The emergence of novel human pathogens is frequently linked with zoonotic events and human-wildlife interactions that promote disease transmission. Consequently, surveillance of wildlife populations for candidate diseases that could spread to humans is beneficial, but requires widespread collections of numerous samples. A legitimate means to acquire large sample sizes of waterfowl is through cooperation between researchers and hunters, who also work in concert with natural resource managers, landowners, and agricultural entities -e.g., aquaculture facilities. In addition to understanding the occurrence and spread of parasites and pathogens by birds, these samples can be used to answer questions about the ecology of various waterbird species. Body mass and morphometric data on hunter-donated specimen are useful for understanding bird condition and other dynamics of birds; however, when breast meat is removed prior to the acquisition of specimen weight, samples might not be as desirable. Here, we evaluate the utility of data obtained from a bird species that might be targeted by hunters and subsequently used to learn about their disease dynamics. Lesser Scaup (Aythya affinis) collected at aquaculture facilities were assessed for their stable isotope concentrations and parasites communities to learn about the birds’ foraging ecology. Discriminant analyses designed to classify birds by the aquaculture pond type from which they were collected included isotope data, Principal Components derived from parasite community data of 7 types, and birds’ body mass. We compared these to Double-crested Cormorants (Nannopterum auritum) feeding on catfish and found the two waterbird species exhibited different infracommunities of parasites Furthermore, some scaup demonstrated fish aquaculture pond type fidelity. Bird body mass was an important metric to include in analytical models when all parasite datatypes were not available. However, the combination of stable isotope concentrations and parasite infracommunity data (that includes prevalence, abundance, volume, and energy use) in models resulted in host ecology differentiation equal or better than models where bird body mass was included. Hunter-derived samples should be encouraged as a means for sample acquisition and be considered as an approach for aquaculture-wildlife conflict management as the information that can be obtained through these samples is multifaceted

Depredation Impact of Double-Crested Cormorants (Phalacrocorax auritus) on Commercial Catfish Production in the Mississippi Delta

Double-crested Cormorants (Phalacrocorax auritus) impact United States commercial aquaculture and are considered the greatest avian predators on catfish (Ictalurus spp.) aquaculture facilities. Cormorants are especially problematic in the Delta region in western Mississippi, where catfish production is concentrated providing ideal wintering and foraging areas. Although cormorant/aquaculture dynamics have been studied, recent changes in aquaculture practices, regulatory policies, and decreased overall hectares in production merit contemporary research. Therefore, we estimated abundance and distribution of cormorants at their night roosts and assessed diet related to catfish consumption. Aerial surveys of cormorant night roosts were flown from October through April, 2016-2018. Following each survey, three active night roosts were randomly selected for harvesting cormorants for later necropsy and stomach contents assessment. We completed 25 total surveys and counted an average of 23,379 cormorants (range 5,026 to 40,535) pooled over years (corrected for observer and method bias). A total of 728 cormorants from 27 different night roosts were collected across years. Survey count models estimated 4.2 and 5 million cormorant forage days in the Delta during winters 2016-2017 and 2017-2018, respectively. Throughout the study, catfish comprised 33% of the prey biomass detected; shad (Dorosoma spp.) also were dominant (58%) prey. Evidence suggests that the area of catfish aquaculture surrounding a night roost within a 30.6-km forage buffer is an important predictor for a bird’s relative amount of catfish consumption. These results will inform wildlife managers regarding relationships between cormorant night roost locations in the Delta and disproportionate consumption of catfish, enhancing techniques to reduce fish losses on aquaculture facilities

Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures

The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures

Inferring introduction routes of invasive species using approximate Bayesian computation on microsatellite data

Determining the routes of introduction provides not only information about the history of an invasion process, but also information about the origin and construction of the genetic composition of the invading population. It remains difficult, however, to infer introduction routes from molecular data because of a lack of appropriate methods. We evaluate here the use of an approximate Bayesian computation (ABC) method for estimating the probabilities of introduction routes of invasive populations based on microsatellite data. We considered the crucial case of a single source population from which two invasive populations originated either serially from a single introduction event or from two independent introduction events. Using simulated datasets, we found that the method gave correct inferences and was robust to many erroneous beliefs. The method was also more efficient than traditional methods based on raw values of statistics such as assignment likelihood or pairwise F(ST). We illustrate some of the features of our ABC method, using real microsatellite datasets obtained for invasive populations of the western corn rootworm, Diabrotica virgifera virgifera. Most computations were performed with the DIYABC program (http://www1.montpellier.inra.fr/CBGP/diyabc/)

Moisture sensitivity examination of asphalt mixtures using thermodynamic, direct adhesion peel and compacted mixture mechanical tests

Moisture damage in asphalt mixtures is a complicated mode of pavement distress that results in the loss of stiffness and structural strength of the asphalt pavement layers. This paper evaluated the moisture sensitivity of different aggregate–bitumen combinations through three different approaches: surface energy, peel adhesion and the Saturation Ageing Tensile Stiffness (SATS) tests. In addition, the results obtained from these three tests were compared so as to characterise the relationship between the thermodynamic and the mechanical tests. The surface energy tests showed that the work of adhesion in dry conditions was bitumen type dependent, which is in agreement with the peel test. After moisture damage, all of these three tests found that the moisture sensitivity of aggregate–bitumen combinations were mainly aggregate type dependent. Based on the peel test, the moisture absorption and mineralogical compositions of aggregate were considered as two important factors to moisture sensitivity. This phenomenon suggests that in a susceptible asphalt mixture, the effect of aggregate may be more influential than the effect of bitumen. The SATS test and the peel test showed similar moisture sensitivity results demonstrating the good correlation between these two mechanical tests. However, the surface energy tests and the mechanical tests cannot correlate in terms of moisture sensitivity evaluation