Hydrogen bonding in cubic (H_2O)_8 and OH∙(H_2O)_7 clusters

A systematic study is presented for OH∙(H_2O)_7 clusters derived from the cubic (H_2O)_8 octamer by replacing one water with a hydroxyl radical. The system is a prototype for atmospheric water clusters containing the environmentally important OH species, and for OH adsorbed at the surface of ice. The full set of 39 symmetry-distinct cubic OH∙(H_2O)_7 clusters is enumerated, and the structures are determined using ab initio quantum chemical methods. Graph invariants are employed to obtain a unified analysis of the stability and structure of cubic (H_2O)_8 and OH∙(H_2O)_7, relating these physical properties to the various hydrogen-bond topologies present in these clusters. To accomplish this the graph invariant formalism is extended to treat a hydrogen bonding impurity within a pure water network

Synchronization of coupled stochastic limit cycle oscillators

For a class of coupled limit cycle oscillators, we give a condition on a linear coupling operator that is necessary and sufficient for exponential stability of the synchronous solution. We show that with certain modifications our method of analysis applies to networks with partial, time-dependent, and nonlinear coupling schemes, as well as to ensembles of local systems with nonperiodic attractors. We also study robustness of synchrony to noise. To this end, we analytically estimate the degree of coherence of the network oscillations in the presence of noise. Our estimate of coherence highlights the main ingredients of stochastic stability of the synchronous regime. In particular, it quantifies the contribution of the network topology. The estimate of coherence for the randomly perturbed network can be used as means for analytic inference of degree of stability of the synchronous solution of the unperturbed deterministic network. Furthermore, we show that in large networks, the effects of noise on the dynamics of each oscillator can be effectively controlled by varying the strength of coupling, which provides a powerful mechanism of denoising. This suggests that the organization of oscillators in a coupled network may play an important role in maintaining robust oscillations in random environment. The analysis is complemented with the results of numerical simulations of a neuronal network. PACS: 05.45.Xt, 05.40.Ca Keywords: synchronization, coupled oscillators, denoising, robustness to noise, compartmental modelComment: major revisions; two new section

Can child injury prevention include healthy risk promotion?

To reflect on the role of risk-taking and risky play in child development and consider recommendations for the injury prevention field, a symposium was held prior to the November 2013 Canadian Injury Prevention and Safety Promotion Conference. Delegates heard from Canadian and international researchers, practitioners and play safety experts on child development, play space design and playground safety, provision of recreation, and legal and societal perceptions of risk and hazard. The presenters provided multidisciplinary evidence and perspectives indicating the potential negative effect on children’s development of approaches to injury prevention that prioritise safety and limit children’s opportunities for risky play. Delegates considered the state of the field of injury prevention and whether alternative approaches were warranted. Each presenter prepared a discussion paper to provide the opportunity for dialogue beyond attendees at the symposium. The resulting discussion papers provide a unique opportunity to consider and learn from multiple perspectives in order to develop a path forward

Essais de régénération artificielle par semis de la subéraie de Numidie orientale.

La régénération naturelle du chêne-liège par semis, se heurte à de nombreux problèmes aussi bien biotiques qu'abiotiques. Des essais de semis «in situ» ont été effectués pour tester l'efficacité de certaines techniques, s'inspirant de travaux sur le changement de la morphologie du système racinaire de certaines essences forestières à enracinement pivotant. Les résultats obtenus sont concluants, à savoir : le crochetage du sol est primordial pour la réussite du semis direct de chêne-liège et qu'en son absence, la pré-germination des glands et, à un moindre titre, la décapitation du pivot, avant la mise en terre, peuvent s'avérer assez bénéfiques

Soil Moisture Active Passive (SMAP) Calibration and Validation Plan and Current Activities

The primary objective of the SMAP calibration and validation (Cal/Val) program is demonstrating that the science requirements (product accuracy and bias) have been met over the mission life. This begins during pre-launch with activities that contribute to high quality products and establishing post-launch validation infrastructure and continues through the mission life. However, the major focus is on a relatively short Cal/Val period following launch. The general approach and elements of the SMAP Cal/Val plan will be described and along with details on several ongoing or recent field experiments designed to address both near- and long-term Cal/Val

Effect of vessel wettability on the foamability of "ideal" surfactants and "real-world" beer heads

The ability to tailor the foaming properties of a solution by controlling its chemical composition is highly desirable and has been the subject of extensive research driven by a range of applications. However, the control of foams by varying the wettability of the foaming vessel has been less widely reported. This work investigates the effect of the wettability of the side walls of vessels used for the in situ generation of foam by shaking aqueous solutions of three different types of model surfactant systems (non-ionic, anionic and cationic surfactants) along with four different beers (Guinness Original, Banks’s Bitter, Bass No 1 and Harvest Pale). We found that hydrophilic vials increased the foamability only for the three model systems but increased foam stability for all foams except the model cationic system. We then compared stability of beer foams produced by shaking and pouring and demonstrated weak qualitative agreement between both foam methods. We also showed how wettability of the glass controls bubble nucleation for beers and champagne and used this effect to control exactly where bubbles form using simple wettability patterns

Salvage decision-making based on carbon following an eastern spruce budworm outbreak

Forest disturbances, such as an eastern spruce budworm (Choristoneura fumiferana) outbreak, impact the strength and persistence of forest carbon sinks. Salvage harvests are a typical management response to widespread tree mortality, but the decision to salvage mortality has large implications for the fate of carbon stocks (including forest carbon and harvested wood products) in the near and long terms. In this study, we created decision-support models for salvage harvesting based on carbon after an eastern spruce budworm outbreak. We used lasso regression to determine which stand characteristics (e.g., basal area) are the best predictors of carbon 40 years after an outbreak in both salvage and no salvage scenarios. We modeled carbon at year 40 for different treatment scenarios and discount rates. Treatment scenarios represent residual stand conditions that may be present when an outbreak occurs. Economic discount rates were applied to 40-year carbon values to account for near and long-term carbon storage aspects. We found that the volume and size of eastern spruce budworm host species are significant predictors of salvage preference based on carbon. We found overall that salvaging less volume is recommended to avoid major swings in carbon budgets and that discounting carbon values to apply weight to near or long-term sequestration greatly affects whether salvaging is preferred. Lasso models are constructed for the northeastern US, however, similar concepts may be applied beyond our study area and potentially for other insect outbreaks similar to spruce budworm, such as mountain pine beetle (Dendroctonus ponderosae) or hemlock woolly adelgid (Adelges tsugae). From a policy standpoint widespread salvaging could create a large carbon emissions deficit with the risk of not being fully replenished within a desired timeframe. Since salvaging is often financially driven, especially for private landowners, carbon market payments or incentives for not salvaging is a consideration for future policy

Canadian Experiment for Soil Moisture in 2010 (CanEX-SM10): Overview and Preliminary Results

The Canadian Experiment for Soil Moisture in 2010 (CanEx-SM10) was carried out in Saskatchewan, Canada from 31 May to 16 June, 2010. Its main objective was to contribute to Soil Moisture and Ocean salinity (SMOS) mission validation and the pre-launch assessment of Soil Moisture and Active and Passive (SMAP) mission. During CanEx-SM10, SMOS data as well as other passive and active microwave measurements were collected by both airborne and satellite platforms. Ground-based measurements of soil (moisture, temperature, roughness, bulk density) and vegetation characteristics (Leaf Area Index, biomass, vegetation height) were conducted close in time to the airborne and satellite acquisitions. Besides, two ground-based in situ networks provided continuous measurements of meteorological conditions and soil moisture and soil temperature profiles. Two sites, each covering 33 km x 71 km (about two SMOS pixels) were selected in agricultural and boreal forested areas in order to provide contrasting soil and vegetation conditions. This paper describes the measurement strategy, provides an overview of the data sets and presents preliminary results. Over the agricultural area, the airborne L-band brightness temperatures matched up well with the SMOS data. The Radio frequency interference (RFI) observed in both SMOS and the airborne L-band radiometer data exhibited spatial and temporal variability and polarization dependency. The temporal evolution of SMOS soil moisture product matched that observed with the ground data, but the absolute soil moisture estimates did not meet the accuracy requirements (0.04 m3/m3) of the SMOS mission. AMSR-E soil moisture estimates are more closely correlated with measured soil moisture

Size limits the formation of liquid jets during bubble bursting

A bubble reaching an air–liquid interface usually bursts and forms a liquid jet. Jetting is relevant to climate and health as it is a source of aerosol droplets from breaking waves. Jetting has been observed for large bubbles with radii of R≫100 μm. However, few studies have been devoted to small bubbles (R<100 μm) despite the entrainment of a large number of such bubbles in sea water. Here we show that jet formation is inhibited by bubble size; a jet is not formed during bursting for bubbles smaller than a critical size. Using ultrafast X-ray and optical imaging methods, we build a phase diagram for jetting and the absence of jetting. Our results demonstrate that jetting in bubble bursting is analogous to pinching-off in liquid coalescence. The coalescence mechanism for bubble bursting may be useful in preventing jet formation in industry and improving climate models concerning aerosol production

The ties that bind: How the dominance of WeChat combines with guanxi to inhibit and constrain China’s contentious politics

Despite the market dominance of the 'WeChat' app in today's China, we currently know little about its significance for contentious politics. This paper argues that MIMAs facilitate communication within relatively strong tie networks (compared to conventional Social Network Sites) which prior research indicates is potentially consequential for patterns of contentious political engagement. Drawing on evidence from a series of Chinese WeChat-user focus groups, we reveal that these ‘chat apps’ create spaces where, although users are often connected through strong ties offline, contentious politics rarely manifests. This trend is driven by a range of dynamics, which we elaborate in a theoretically-informed thematic analysis. When contentious politics does emerge, it is reported by our focus group participants to be largely confined to matters of ‘pragmatic’ and/or ‘safe’ politics that concern defending the interests of individuals or discrete groups, but do not challenge the wider political system