Hopping Transport in the Presence of Site Energy Disorder: Temperature and Concentration Scaling of Conductivity Spectra

Recent measurements on ion conducting glasses have revealed that conductivity spectra for various temperatures and ionic concentrations can be superimposed onto a common master curve by an appropriate rescaling of the conductivity and frequency. In order to understand the origin of the observed scaling behavior, we investigate by Monte Carlo simulations the diffusion of particles in a lattice with site energy disorder for a wide range of both temperatures and concentrations. While the model can account for the changes in ionic activation energies upon changing the concentration, it in general yields conductivity spectra that exhibit no scaling behavior. However, for typical concentrations and sufficiently low temperatures, a fairly good data collapse is obtained analogous to that found in experiment.Comment: 6 pages, 4 figure

The role of citizen science in addressing grand challenges in food and agriculture research

The power of citizen science to contribute to both science and society is gaining increased recognition, particularly in physics and biology. Although there is a long history of public engagement in agriculture and food science, the term ‘citizen science’ has rarely been applied to these efforts. Similarly, in the emerging field of citizen science, most new citizen science projects do not focus on food or agriculture. Here, we convened thought leaders from a broad range of fields related to citizen science, agriculture, and food science to highlight key opportunities for bridging these overlapping yet disconnected communities/fields and identify ways to leverage their respective strengths. Specifically, we show that (i) citizen science projects are addressing many grand challenges facing our food systems, as outlined by the United States National Institute of Food and Agriculture, as well as broader Sustainable Development Goals set by the United Nations Development Programme, (ii) there exist emerging opportunities and unique challenges for citizen science in agriculture/food research, and (iii) the greatest opportunities for the development of citizen science projects in agriculture and food science will be gained by using the existing infrastructure and tools of Extension programmes and through the engagement of urban communities. Further, we argue there is no better time to foster greater collaboration between these fields given the trend of shrinking Extension programmes, the increasing need to apply innovative solutions to address rising demands on agricultural systems, and the exponential growth of the field of citizen science.This working group was partially funded from the NCSU Plant Sciences Initiative, College of Agriculture and Life Sciences ‘Big Ideas’ grant, National Science Foundation grant to R.R.D. (NSF no. 1319293), and a United States Department of Food and Agriculture-National Institute of Food and Agriculture grant to S.F.R., USDA-NIFA Post Doctoral Fellowships grant no. 2017-67012-26999.http://rspb.royalsocietypublishing.orghj2018Forestry and Agricultural Biotechnology Institute (FABI

SIMPLE MODELS FOR THE IONIC CONDUCTION MECHANISM IN GLASSES

De nombreux verres montrent une conductivité relativement élevée due aux ions lithium à cause de faibles énergies d'activation. Suivant Anderson et Stuart l'énergie d'activation résulte (i) de la distorsion élastique des "passages", (ii) à la séparation des charges cathioniques des charges anioniques. Des calculs simples pour un réseau rigide montrent que l'effet (i) à l'énergie d'activation est le plus faible dans le cas de Li+, comparé aux autres ions alcalins, alors que la contribution (ii) est maximum. La valeur calculée pour Li+ est plus élevée que l'énergie d'activation observée. On propose que les verres conducteurs au lithium sont ioniques avec la faculté pour les groupements anioniques de tourner et de "relayer" le passage des ions Li+ d'un groupe à un autre. Les ions Li+ peuvent contourner les anions. L'effet de relaxation diélectrique peut aussi abaisser l'énergie d'activation.Many glasses show relatively high lithium ion conductivities which result from low activation energies. Following Anderson and Stuart, the activation energy is attributed to (i) the elastic distortion of "doorways" and (ii) the separation of cationic from anionic charges. Simple calculations for a rigid network show that the contribution of (i) to the activation energy is least for Li+ compared with the other alkali metal ions, while the contribution of (ii) is the greatest for this ion. The calculated value for Li+ is larger than the observed activation energy. It is suggested that the Li-conducting glasses are ionic with anionic groups having freedom to rotate and "hand-on" Li+ ions from one group to another, and the Li+ ions can "roll around" the anions. The effect of dielectric relaxation may also lower the activation energy