Light depolarization effects during the Fréedericksz transition in nematic liquid crystals

This work is aimed to the photopolarimetric characterization of the disorder evolution occurring in homeotropically aligned nematic liquid crystal films during the electrically induced Freedericksz transition. The molecular director dynamics and the transversal reorientation modes are investigated by the analysis of the depolarization of the light beam emerging from the sample. Our measurements reveal unexpected depolarization effects at the transition, which we interpret in terms of director field unhomogeneity and defects creation. (C) 2007 Optical Society of America

Is Diversity the Missing Link in Coastal Fisheries Management?

Fisheries management has historically focused on the population elasticity of target fish based primarily on demographic modeling, with the key assumptions of stability in environmental conditions and static trophic relationships. The predictive capacity of this fisheries framework is poor, especially in closed systems where the benthic diversity and boundary effects are important and the stock levels are low. Here, we present a probabilistic model that couples key fish populations with a complex suite of trophic, environmental, and geomorphological factors. Using 41 years of observations we model the changes in eastern Baltic cod (Gadus morhua), herring (Clupea harengus), and Baltic sprat (Sprattus sprattus balticus) for the Baltic Sea within a Bayesian network. The model predictions are spatially explicit and show the changes of the central Baltic Sea from cod-to sprat-dominated ecology over the 41 years. This also highlights how the years 2004 to 2014 deviate in terms of the typical cod–environment relationship, with environmental factors such as salinity being less influential on cod population abundance than in previous periods. The role of macrozoobenthos abundance, biotopic rugosity, and flatfish biomass showed an increased influence in predicting cod biomass in the last decade of the study. Fisheries management that is able to accommodate shifting ecological and environmental conditions relevant to biotopic information will be more effective and realistic. Non-stationary modelling for all of the homogeneous biotope regions, while acknowledging that each has a specific ecology relevant to understanding the fish population dynamics, is essential for fisheries science and sustainable management of fish stocks

Comparative Evaluation Of The Efficacy Of Three Commercially Available Toothpastes On Dentin Hypersensitivity Reduction: An Eight-Week Clinical Study

OBJECTIVE: The objective of this eight-week, single-center, three-cell, double-blind, and randomized clinical study was to evaluate the dentin hypersensitivity reduction efficacy of three commercially available toothpastes: 1) Colgate Sensitive Pro-Relief Toothpaste (also marketed as elmex Sensitive Professional); 2) Sensodyne Rapid Relief Toothpaste; and (3) Crest Cavity Protection Toothpaste. METHODS: 150 subjects, having two teeth with tactile and air blast hypersensitivity, were assigned to one of the three study groups (50/group). Subjects were then asked to brush their teeth for one minute, twice daily, with the given toothpaste. The dentin hypersensitivity and oral tissues were evaluated at baseline, two weeks, four weeks, and eight weeks. Comparison of the treatment groups with respect to gender was conducted using a chi-square analysis, and with respect to age and baseline hypersensitivity scores was performed using the analysis of variance (ANOVA). Within-treatment effects were analyzed using the paired t-test, while the analysis of covariance (ANCOVA) was used to examine between-treatment effects. The post hoc Tukey test was performed for pair-wise comparisons. All statistical tests were two-sided using a significance level of alpha = 0.05. RESULTS: After two, four, and eight weeks of daily use of the products, all three groups showed a statistically significant reduction from baseline in tactile and air blast dentin hypersensitivity (p < 0.05). Colgate Sensitive Pro-Relief toothpaste produced a significant improvement in mean tactile and air blast dentin hypersensitivity scores, and was more effective than Sensodyne Rapid Relief toothpaste and Crest Cavity Protection toothpastes (p < 0.05). CONCLUSION: Colgate Sensitive Pro-ReliefToothpaste, used twice daily, significantly reduces dentin hypersensitivity, and is significantly more effective in reducing dentin hypersensitivity than Sensodyne Rapid Relief Toothpaste and Crest Cavity Protection Toothpaste

Sidney Holt, a giant in the history of fisheries science who focused on the future: his legacy and challenges for present-day marine scientists

Sidney J. Holt (1926–2019) was more than a founding father of quantitative fisheries science, and the man who “helped save the great whales.” His accomplishments, over a career spanning seven decades, run deeper: he was a champion of reductionism (i.e. able to identify the factors essential for management) and a systemic thinker who inspired scientists to think critically about marine conservation and management. This article draws on first-hand experiences with Sidney over the last 15 years, when he regularly collaborated with scholars of the ICES Working Group on the History of Fish and Fisheries and the Oceans Past Initiative. Four main themes emerged from our reflections on Sidney’s life and legacy, which constitute ongoing scientific challenges: (1) the suitability of maximum sustainable yield as a target reference point for fisheries management; (2) the future of marine mammal conservation; (3) successful implementation of ecosystem-based marine management; and (4) the value of historical perspectives for conservation and management. We consider Sidney’s work across these themes, in which he readily collaborated, focused on evidence-based solutions, and, where evidence was lacking, he advocated for the “precautionary principle.” We posit there is much that we, and future generations of scientists, can learn from his example

Large-Scale Spatio-Temporal Patterns of Mediterranean Cephalopod Diversity

Species diversity is widely recognized as an important trait of ecosystems’ functioning and resilience. Understanding the causes of diversity patterns and their interaction with the environmental conditions is essential in order to effectively assess and preserve existing diversity. While diversity patterns of most recurrent groups such as fish are commonly studied, other important taxa such as cephalopods have received less attention. In this work we present spatio-temporal trends of cephalopod diversity across the entire Mediterranean Sea during the last 19 years, analysing data from the annual bottom trawl survey MEDITS conducted by 5 different Mediterranean countries using standardized gears and sampling protocols. The influence of local and regional environmental variability in different Mediterranean regions is analysed applying generalized additive models, using species richness and the Shannon Wiener index as diversity descriptors. While the western basin showed a high diversity, our analyses do not support a steady eastward decrease of diversity as proposed in some previous studies. Instead, high Shannon diversity was also found in the Adriatic and Aegean Seas, and high species richness in the eastern Ionian Sea. Overall diversity did not show any consistent trend over the last two decades. Except in the Adriatic Sea, diversity showed a hump-shaped trend with depth in all regions, being highest between 200–400 m depth. Our results indicate that high Chlorophyll a concentrations and warmer temperatures seem to enhance species diversity, and the influence of these parameters is stronger for richness than for Shannon diversityVersión del editor4,411

Fishery Discards: Factors Affecting Their Variability within a Demersal Trawl Fishery

Discards represent one of the most important issues within current commercial fishing. It occurs for a range of reasons and is influenced by an even more complex array of factors. We address this issue by examining the data collected within the Danish discard observer program and describe the factors that influence discarding within the Danish Kattegat demersal fleet over the period 1997 to 2008. Generalised additive models were used to assess how discards of the 3 main target species, Norway lobster, cod and plaice, and their subcomponents (under and over minimum landings size) are influenced by important factors and their potential relevance to management. Our results show that discards are influenced by a range of different factors that are different for each species and portion of discards. We argue that knowledge about the factors influential to discarding and their use in relation to potential mitigation measures are essential for future fisheries management strategies

Considerations for management strategy evaluation for small pelagic fishes

Management strategy evaluation (MSE) is the state-of-the-art approach for testing and comparing management strategies in a way that accounts for multiple sources of uncertainty (e.g. monitoring, estimation, and implementation). Management strategy evaluation can help identify management strategies that are robust to uncertainty about the life history of the target species and its relationship to other species in the food web. Small pelagic fish (e.g. anchovy, herring and sardine) fulfil an important ecological role in marine food webs and present challenges to the use of MSE and other simulation-based evaluation approaches. This is due to considerable stochastic variation in their ecology and life history, which leads to substantial observation and process uncertainty. Here, we summarize the current state of MSE for small pelagic fishes worldwide. We leverage expert input from ecologists and modellers to draw attention to sources of process and observation uncertainty for small pelagic species, providing examples from geographical regions where these species are ecologically, economically and culturally important. Temporal variation in recruitment and other life-history rates, spatial structure and movement, and species interactions are key considerations for small pelagic fishes. We discuss tools for building these into the MSE process, with examples from existing fisheries. We argue that model complexity should be informed by management priorities and whether ecosystem information will be used to generate dynamics or to inform reference points. We recommend that our list of considerations be used in the initial phases of the MSE process for small pelagic fishes or to build complexity on existing single-species models.publishedVersio

Numerical simulation of vertical ground-water flux of the Rio Grande from ground-water temperature profiles, central New Mexico

An important gap in the understanding of the hydrology of the Middle Rio Grande Basin, central New Mexico, is the rate at which water from the Rio Grande recharges the Santa Fe Group aquifer system. Several methodologies.including use of the Glover-Balmer equation, flood pulses, and channel permeameters.have been applied to this problem in the Middle Rio Grande Basin. In the work presented here, ground-water temperature profiles and ground-water levels beneath the Rio Grande were measured and numerically simulated at four sites. The direction and rate of vertical ground-water flux between the river and underlying aquifer was simulated and the effective vertical hydraulic conductivity of the sediments underlying the river was estimated through model calibration. Seven sets of nested piezometers were installed during July and August 1996 at four sites along the Rio Grande in the Albuquerque area, though only four of the piezometer nests were simulated. In downstream order, these four sites are (1) the Bernalillo site, upstream from the New Mexico State Highway 44 bridge in Bernalillo (piezometer nest BRN02); (2) the Corrales site, upstream from the Rio Rancho sewage treatment plant in Rio Rancho (COR01); (3) the Paseo del Norte site, upstream from the Paseo del Norte bridge in Albuquerque (PDN01); and (4) the Rio Bravo site, upstream from the Rio Bravo bridge in Albuquerque (RBR01). All piezometers were completed in the inner-valley alluvium of the Santa Fe Group aquifer system. Ground-water levels and temperatures were measured in the four piezometer nests a total of seven times in the 24-month period from September 1996 through August 1998. The flux between the surface- and ground-water systems at each of the field sites was quantified by one-dimensional numerical simulation of the water and heat exchange in the subsurface using the heat and water transport model VS2DH. Model calibration was aided by the use of PEST, a model-independent computer program that uses nonlinear parameter estimation. Mean vertical hydraulic conductivities were estimated by model calibration and range from 1.5×10-5 to 5.8×10-6 meters per second (m/s). Mean simulated vertical ground-water flux for the BRN02 piezometer nest is 3.30×10-7 m/s; for the COR01 piezometer nest is 3.58×10-7 m/s; for the PDN01 piezometer nest is 4.22×10-7 m/s; and for the RBR01 piezometer nest is 2.05×10-7 m/s. Comparison of the simulated vertical fluxes and vertical hydraulic conductivities derived from this study with values from other studies in the Middle Rio Grande Basin indicate agreement between 1 and 3.5 orders of magnitude for hydraulic conductivity and within 1 order of magnitude for vertical flux

Transition Metals Complexed to Ordered Mesophases. Synthesis and Mesomorphic Properties of a Homologous Series of N-(4-Dodecyloxysalicylidene)-4'-Alkylanilines Complexed to Palladium(II)

The new [N-(4-dodecyloxysalicylidene)4'-CnH2n+1-aniline] palladium (II) derivatives, (R(n)L)(2)Pd, (1-6: n = 1-4,6,8 respectively) have been synthetized and their mesomorphic properties investigated by optical microscopy, DSC and X-ray diffraction measurements. Complexes 1-6, but 4, display a monotropic (1,5) or enantiotropic (2,3,6) smectic A mesophase. In 1-6 the geometry of the metal coordination sphere is square planar and with reference to homologous (R(n)L)(2)M compounds the mesomorphism of 1-6 appears at temperatures higher than for (R(n)L)(2)VO (distorted square pyramidal) or (R(n)L)(2)Cu (distorted square planar)

Metallomesogens. Synthesis and Mesomorphic Properties of 2-Hydroxy-4-n-Alkoxy-4'-n-Alkylazobenzenes Palladium(II) Complexes

The synthesis and characterization of o-hydroxyazobenzene mesogens [HL(n)(m)] which form the two different homologous series HL(n)(12) (2-hydroxy-4-n-dodecyloxy-4'-n-C(n)H2n+1-azobenzenes, n = 1-4, 6, 8) and HL1(m) (2-hydroxy-4-n-C(n)H2n+1-O-4'-methylazobenzenes, m = 7, 9, 12, 14) are reported. They form N and/or S(C) mesophases at quite low temperatures. These ligands react with [Pd(PhCN)2Cl2] or Pd[(Azoxy-6)Pd(MeCN)2]BF4 giving rise to the corresponding [L(n)(m)]2Pd and {(Azoxy-6)Pd[L(n)(m)]} species [Azoxy-6 is the deprotonated form of 4,4'-bis(hexyloxy)azoxybenzene]. The [L(n)(m)]2Pd compounds are not mesogenic. On the contrary, the cyclopalladated mixed-ligand complexes, {(Azoxy-6)Pd[L(n)(m)]}, are prevalently nematogenic as optical, DSC, and X-ray analysis evidence. The {(Azoxy-6)Pd[L(n)(12)]} compounds show enantiotropic nematic (n = 1), monotropic nematic (n = 2-4, 6) and monotropic nematic and S(c) mesophases (n = 8). The {(Azoxy-6)Pd[L1(m)]} species from monotropic (m = 7, 9) and enantiotropic (m = 12, 14) nematic mesophases. A comparison between thermal behavior displayed by [L(n)(m)]2Pd and {(Azoxy-6)Pd[L(n)(m)]} complexes seems to explain the role played by the respective rigid molecular cores. The electronic and/or structural modifications induced by the azoxy group are discussed