Teaching-Communication Methodologies in the Medical Profession

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66477/2/10.1177_108056997603900103.pd

Methods matter: Different biodiversity survey methodologies identify contrasting biodiversity patterns in a human modified rainforest — A case study with amphibians

Understanding how well tropical forest biodiversity can recover following habitat change is often difficult due to conflicting assessments arising from different studies. One often overlooked potentially confounding factor that may influence assessments of biodiversity response to habitat change, is the possibility that different survey methodologies, targeting the same indicator taxon, may identify different patterns and so lead to different conclusions. Here we investigated whether two different but commonly used survey methodologies used to assess amphibian communities, pitfall trapping and nocturnal transects, indicate the same or different responses of amphibian biodiversity to historic human induced habitat change. We did so in a regenerating rainforest study site located in one of the world's most biodiverse and important conservation areas: the Manu Biosphere Reserve. We show that the two survey methodologies tested identified contrasting biodiversity patterns in a human modified rainforest. Nocturnal transect surveys indicated biodiversity differences between forest with different human disturbance histories, whereas pitfall trap surveys suggested no differences between forest disturbance types, except for community composition. This pattern was true for species richness, diversity, overall abundance and community evenness and structure. For some fine scale metrics, such as species specific responses and abundances of family groups, both methods detected differences between disturbance types. However, the direction of differences was inconsistent between methods. We highlight that for assessments of rainforest recovery following disturbance, survey methods do matter and that different biodiversity survey methods can identify contrasting patterns in response to different types of historic disturbance. Our results contribute to a growing body of evidence that arboreal species might be more sensitive indicators than terrestrial communities. © 2016 Elsevier Lt

Effect of Morphology and Manganese Valence on the Voltage Fade and Capacity Retention of Li[Li_2/12Ni_3/12Mn_7/12]O₂

We have determined the electrochemical characteristics of the high voltage, high capacity Li-ion battery cathode material Li­[Li_2/12Ni_3/12Mn_7/12]­O₂ prepared using three different synthesis routes: sol–gel, hydroxide coprecipitation, and carbonate coprecipitation. Each route leads to distinct morphologies and surface areas while maintaining the same crystal structures. X-ray photoelectron spectroscopy (XPS) measurements reveal differences in their surface chemistries upon cycling, which correlate with voltage fading. Indeed, we observe the valence state of Mn on the surface to decrease upon lithiation, and this reduction is specifically correlated to discharging below 3.6 V. Furthermore, the data shows a correlation of the formation of Li₂CO₃ with the Mn oxidation state from the decomposition of electrolyte. These phenomena are related to each material’s electrochemistry in order to expand upon the reaction mechanisms taking place–specifically in terms of the particle morphology produced by each synthetic approach

Elucidating the Phase Transformation of Li₄Ti₅O₁₂ Lithiation at the Nanoscale

This work provides insight regarding the fundamental lithiation and delithiation mechanism of the popular lithium ion battery anode material, Li₄Ti₅O₁₂ (LTO). Our results quantify the extent of reaction between Li₄Ti₅O₁₂ and Li₇Ti₅O₁₂ at the nanoscale, during the first cycle. Lithium titanate’s discharge (lithiation) and charge (delithiation) reactions are notoriously difficult to characterize due to the <i>zero-strain</i> transition occurring between the end members Li₄Ti₅O₁₂ and Li₇Ti₅O₁₂. Interestingly, however, the latter compound is electronically conductive, while the former is an insulator. We take advantage of this critical property difference by using conductive atomic force microscopy (c-AFM) to locally monitor the phase transition between the two structures at various states of charge. To do so, we perform <i>ex situ</i> characterization on electrochemically cycled LTO thin-films that are never exposed to air. We provide direct confirmation of the manner in which the reaction occurs, which proceeds <i>via</i> percolation channels within single grains. We complement scanning probe analyses with an X-ray photoelectron spectroscopy (XPS) study that identifies and explains changes in the LTO surface structure and composition. In addition, we provide a computational analysis to describe the unique electronic differences between LTO and its lithiated form

Probing the Mechanism of Sodium Ion Insertion into Copper Antimony Cu₂Sb Anodes

We report experimental studies to understand the reaction mechanism of the intermetallic anode Cu₂Sb with Na and demonstrate that it is capable of retaining about 250 mAh g^–1 over 200 cycles when using fluoroethylene carbonate additive. X-ray diffraction data indicate during the first discharge the reaction leads to the formation of crystalline Na₃Sb via an intermediate amorphous phase. Upon desodiation the Na₃Sb reverts to an amorphous phase, which then recrystallizes into Cu₂Sb at full charge, indicating a high degree of structural reversibility. The structure after charging to 1 V is different from that of Cu₂Sb, as indicated by X-ray absorption spectroscopy and ¹²¹Sb Mössbauer spectroscopy, and is due to the formation of an amorphous Na–Cu–Sb phase. At full discharge, an isomer shift of −8.10 mm s^–1 is measured, which is close to that of a Na₃Sb reference powder (−7.95 mm s^–1) and in agreement with the formation of Na₃Sb domains. During charge, the isomer shift at 1 V (−9.29 mm s^–1) is closer to that of the pristine material (−9.67 mm s^–1), but the lower value is consistent with the lack of full desodiation, as expected from the potential profile and the XAS data

Understanding the Role of NH₄F and Al₂O₃ Surface Co-modification on Lithium-Excess Layered Oxide Li_1.2Ni_0.2Mn_0.6O₂

In this work we prepared Li_1.2Ni_0.2Mn_0.6O₂ (LNMO) using a hydroxide co-precipitation method and investigated the effect of co-modification with NH₄F and Al₂O₃. After surface co-modification, the first cycle Coulombic efficiency of Li_1.2Ni_0.2Mn_0.6O₂ improved from 82.7% to 87.5%, and the reversible discharge capacity improved from 253 to 287 mAh g^–1 at C/20. Moreover, the rate capability also increased significantly. A combination of neutron diffraction (ND), high-resolution transmission electron microscopy (HRTEM), aberration-corrected scanning transmission electron microscopy (a-STEM)/electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS) revealed the changes of surface structure and chemistry after NH₄F and Al₂O₃ surface co-modification while the bulk properties showed relatively no changes. These complex changes on the material’s surface include the formation of an amorphous Al₂O₃ coating, the transformation of layered material to a spinel-like phase on the surface, the formation of nanoislands of active material, and the partial chemical reduction of surface Mn⁴⁺. Such enhanced discharge capacity of the modified material can be primarily assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material facilitated with preactivated Mn³⁺ on the surface, and stabilization of the Ni-redox pair. These insights will provide guidance for the surface modification in high-voltage-cathode battery materials of the future