Simultaneous calculation of the helical pitch and the twist elastic constant in chiral liquid crystals from intermolecular torques

We present a molecular simulation method that yields simultaneously the equilibrium pitch wave number q and the twist elastic constant K2 of a chiral nematic liquid crystal by sampling the torque density. A simulation of an untwisted system in periodic boundary conditions gives the product K2q; a further simulation with a uniform twist applied provides enough information to separately determine the two factors. We test our new method for a model potential, comparing the results with K2q from a thermodynamic integration route, and with K2 from an order fluctuation analysis. We also present a thermodynamic perturbation theory analysis valid in the limit of weak chirality

Re-evaluating the Preferences of Recreational Gulf of Maine Cod and Haddock Anglers

Since 2013, fisheries managers have used a bioeconomic model to simulate the effect of proposed regulations on angler participation and subsequent fishing mortality for Gulf of Maine Atlantic cod and haddock using data from a choice experiment survey. In the year following the last choice experiment survey, however, Gulf of Maine cod fishery experienced unprecedented regulatory changes that, to this day, considerably limit recreational harvest. Given the potential influence of these regulatory changes on angler targeting behavior and preferences, we administered a new choice experiment survey in 2019. The new survey instrument and the sampling method were updated relative to the previous data collection effort to incorporate contemporary best-practice recommendations. In this paper, we estimate a panel mixed logit model using the new survey data to re-evaluate angler preferences for fishing trip attributes, results of which will parameterize the bioeconomic simulation model. We find that anglers value keeping cod more highly than keeping haddock, which is in contrast to the preference rankings elicited from the previously collected choice experiment data. These findings highlight the importance of collecting and analyzing updated data for policy analysis. We also test for attribute non-attendance, one type of behavioral anomaly that can occur in choice experiments and lead to biased preference parameter estimation. While many respondents indicated having not attended to one or more attributes, the econometric results suggest that some ignored attributes significantly affected choice behavior, which indicates a need to collect more informative non-attendance information in future data collection efforts

Minimum requirements for feedback enhanced force sensing

The problem of estimating an unknown force driving a linear oscillator is revisited. When using linear measurement, feedback is often cited as a mechanism to enhance bandwidth or sensitivity. We show that as long as the oscillator dynamics are known, there exists a real-time estimation strategy that reproduces the same measurement record as any arbitrary feedback protocol. Consequently some form of nonlinearity is required to gain any advantage beyond estimation alone. This result holds true in both quantum and classical systems, with non-stationary forces and feedback, and in the general case of non-Gaussian and correlated noise. Recently, feedback enhanced incoherent force sensing has been demonstrated [Nat. Nano. \textbf{7}, 509 (2012)], with the enhancement attributed to a feedback induced modification of the mechanical susceptibility. As a proof-of-principle we experimentally reproduce this result through straightforward filtering.Comment: 5 pages + 2 pages of Supplementary Informatio

Interpreting the seasonal cycles of atmospheric oxygen and carbon dioxide concentrations at American Samoa Observatory

We present seven years of atmospheric O2/N2 ratio and CO2 concentration data measured from flask samples collected at American Samoa. These data are unusual, exhibiting higher short-term variability, and seasonal cycles not in phase with other sampling stations. The unique nature of atmospheric data from Samoa has been noted previously from measurements of CO2, methyl chloroform, and ozone. With our O2 data, we observe greater magnitude in the short-term variability, but, in contrast, no clear seasonal pattern to this variability. This we attribute to significant regional sources and sinks existing for O2 in both hemispheres, and a dependence on both the latitudinal and altitudinal origins of air masses. We also hypothesize that some samples exhibit a component of "older" air, demonstrating recirculation of air within the tropics. Our findings could be used to help constrain atmospheric transport models which are not well characterized in tropical regions

Exploring Household Food Insecurity and Inter-generational Self-help Club Involvement Among Grandparents Raising Grandchildren Due to HIV/AIDS in Vietnam

Intergenerational Self-help Clubs (ISHCs), also known as “Empathy Clubs” in Vietnam may aid in improving quality of life and well-being for grandparent-headed households impacted by HIV/AIDS. However, less is known about how club membership impacts household food security. This cross-sectional, mixed methods study examines the differences in household food security and coping responses to food insecurity among 30 grandparents who are raising grandchildren due to HIV/AIDS, 15 who were involved in ISHC groups and 15 who were not involved in ISHC groups, in Hai Phong, Vietnam. In addition to qualitative interviews, all grandparents completed the Household Food Security Insecurity Access Scale (HFIAS) to assess the prevalence of food insecurity. Chi-square and t-tests were employed to detect differences between ISHC members and nonmembers. The food security domain of anxiety and uncertainty related to having enough food was statistically significant (t [28] = 2.27, p \u3c 0.03), with ISHC participants reporting less anxiety and uncertainty. Close to half (46%) of ISHC members reported mild food insecurity. By comparison, about the same percentage (47%) of nonmembers reported moderate food insecurity. Qualitative interviews revealed that food insecurity arose from barriers to accessing food, which led to three primary coping responses: 1) reconfiguring understandings of age-related nutritional needs, 2) erosive coping, and 3) engaging networks for nutritional support. Differences between members of the ISHCs and those without club involvement suggest that a strong community connection, perhaps bonding social capital, may play a role in reducing anxiety related to having enough food. Findings suggest that ISHCs may build social capital, provide psychosocial support, and increase food security among grandparent-headed households who face vulnerability

Vertebrate Hosts as Islands: Dynamics of Selection, Immigration, Loss, Persistence, and Potential Function of Bacteria on Salamander Skin.

Skin bacterial communities can protect amphibians from a fungal pathogen; however, little is known about how these communities are maintained. We used a neutral model of community ecology to identify bacteria that are maintained on salamanders by selection or by dispersal from a bacterial reservoir (soil) and ecological drift. We found that 75% (9/12) of bacteria that were consistent with positive selection, <1% of bacteria that were consistent with random dispersal and none of the bacteria that were consistent under negative selection had a 97% or greater match to antifungal isolates. Additionally we performed an experiment where salamanders were either provided or denied a bacterial reservoir and estimated immigration and loss (emigration and local extinction) rates of bacteria on salamanders in both treatments. Loss was strongly related to bacterial richness, suggesting competition is important for structuring the community. Bacteria closely related to antifungal isolates were more likely to persist on salamanders with or without a bacterial reservoir, suggesting they had a competitive advantage. Furthermore, over-represented and under-represented operational taxonomic units (OTUs) had similar persistence on salamanders when a bacterial reservoir was present. However, under-represented OTUs were less likely to persist in the absence of a bacterial reservoir, suggesting that the over-represented and under-represented bacteria were selected against or for on salamanders through time. Our findings from the neutral model, migration and persistence analyses show that bacteria that exhibit a high similarity to antifungal isolates persist on salamanders, which likely protect hosts against pathogens and improve fitness. This research is one of the first to apply ecological theory to investigate assembly of host associated-bacterial communities, which can provide insights for probiotic bioaugmentation as a conservation strategy against disease

Spatial variation of the physical conditions of molecular gas in galaxies

Multi-line studies of CO-12, CO-13, C-18O, HCN, and HCO(+) at 3 mm, 1.3 mm, and 0.8 mm using the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope, with the IRAM superconductor insulator superconductor (SIS) receivers and the Max Planck Institute for External Physics (MPE) 350 GHz SIS receiver, show that the densities and temperatures of molecular gas in external galaxies change significantly with position. CO-12 measures the densities and temperature of diffuse interclump molecular gas, but not the bulk of the molecular gas. Simple one-component models, with or without external heating, cannot account for the weakness of the CO-12 J = 3 to 2 line relative to J = 2 to 1 and J = 1 to 0. CO-12 does not trace the bulk of the molecular gas, and optical depth effects obviate a straightforward interpretation of CO-12 data. Instead, researchers turned to the optically thin CO isotopes and other molecular species. Isotopic CO lines measure the bulk of the molecular gas, and HCN and HCO(+) pick out denser regions. Researchers find a warm ridge of gas in IC 342 (Eckart et al. 1989), denser gas in the starburst nucleus of IC 342, and a possible hot-spot in NGC 2903. In IC 342, NGC 2146, and NGC 6764, the CO-13 J = 2 to 1 line is subthermally populated, implying gas densities less than or equal to 10(exp 4) cm(-3)