90 research outputs found
Synthesis, Characterization, and Thermoelectric Properties of Radical Siloxanes
More than half of the annual energy consumption in the United States is lost as waste heat. Polymer-based thermoelectric devices have the potential to utilize this waste heat both sustainably and cost-effectively. Although conjugated polymers currently dominate research in organic thermoelectrics, the potential of using polymers with radical pendant groups have yet to be realized. These polymers have been found to be as conductive as pristine (i.e., not doped) poly(3-hexylthiophene) (P3HT), a commonly-used charge-transporting conjugated polymer. This could yield promising avenues for thermoelectric material design as radical polymers are more synthetically tunable and are hypothesized to have a high Seebeck coefficient. In this report, the compound 4,4,5,5-tetramethyl-2-(3-vinylphenyl)imidazolidine-1,3-diol was synthesized and then used to produce a polymer with a radical pendant group. A polysiloxane backbone was synthetically targeted to produce a material with a low glass transition temperature. The polymer is then characterized for its material and thermoelectric properties
Infrared conductivity of hole accumulation and depletion layers in (Ga,Mn)As- and (Ga,Be)As-based electric field-effect devices
We have fabricated electric double-layer field-effect devices to
electrostatically dope our active materials, either =0.015
GaMnAs or =3.2 GaBeAs. The devices
are tailored for interrogation of electric field induced changes to the
frequency dependent conductivity in the accumulation or depletions layers of
the active material via infrared (IR) spectroscopy. The spectra of the
(Ga,Be)As-based device reveal electric field induced changes to the IR
conductivity consistent with an enhancement or reduction of the Drude response
in the accumulation and depletion polarities, respectively. The spectroscopic
features of this device are all indicative of metallic conduction within the
GaAs host valence band (VB). For the (Ga,Mn)As-based device, the spectra show
enhancement of the far-IR itinerant carrier response and broad mid-IR resonance
upon hole accumulation, with a decrease of these features in the depletion
polarity. These later spectral features demonstrate that conduction in
ferromagnetic (FM) GaMnAs is distinct from genuine metallic
behavior due to extended states in the host VB. Furthermore, these data support
the notion that a Mn-induced impurity band plays a vital role in the electron
dynamics of FM GaMnAs. We add, a sum-rule analysis of the spectra
of our devices suggests that the Mn or Be doping does not lead to a substantial
renormalization of the GaAs host VB
Measurement of HCFC-22 and HFC-152a Sorption by Polymers Using a Quartz Crystal Microbalance
Interactive effects of forest die-off and drying-rewetting cycles on C and N mineralization
Mediterranean forests will experience more frequent and intense drought periods and extreme rainfall events in the coming decades. Concomitantly, drought-induced forest die-off is likely to increase. Changes in rainfall patterns and forest die-off directly influence soil microbial communities and activity and, consequently, carbon (C) and nitrogen (N) turnover, but their interactive effects have not yet been explored. We investigated the short-, and the long-term interactive effects of forest die-off and drying-rewetting cycles on soil C and N mineralization rates of a Mediterranean woodland. Soil samples collected under and out of the influence of holm oak (Quercus ilex) trees with different defoliation degrees (six healthy, six affected and six dead) were incubated under two contrasting water regimes (i.e. drying-rewetting cycles vs. constant soil moisture). Potential soil C and N mineralization responded differently to water regimes, with an overall 55% increase in C mineralization and a 22% decrease in N mineralization in the drying-rewetting cycle treatment compared to the constant moisture treatment. Holm oak decline decreased the response of C mineralization while increased the response of N mineralization to the drying-rewetting cycles at both the short- and the long-term. Moreover, N turnover showed a higher sensitivity to these environmental changes than that of C during most of the year. Our study provides solid evidence that an intensification of the drying-rewetting regimes can result in a decoupling of soil C and N cycles in Mediterranean forests and that forest die-off might enhance this decoupling at both the short- and the long-term, with important implications for the ecosystem functioning.This study was supported by the International Laboratory of Global Change (LINCGlobal, CSIC4540), the Spanish Ministry of Economy and Competitiveness grant VERONICA (CGL2013-42271-P), the Community of Madrid grant REMEDINAL3-CM (S2013/MAE-2719) and the FCT/MEC through national funds and the co-funding by the FEDER (PT2020 Partnership Agreement and COMPETE 2020, UID/BIA/04004/2013). The authors are especially grateful to David López-Quiroga and Ana Prado Comesaña for their excellent help in the field and laboratory and to Aldo Barreiro for his assistance with data and statistical analysis. AR was supported by the Spanish National Research Council (CSIC) in the JAE-doc modality co-financed by the European Social Fund (ESF) and by a Postdoctoral Grant of the Portuguese Science and Technology Foundation (SFRH/BDP/108913/2015)
Tuning the Thermoelectric Properties of a Conducting Polymer through Blending with Open-Shell Molecular Dopants
Analysis of the dispersion and absorption curves of non-linear relaxation-reorientation for the molecules of water and fibrinogen
Methadone treatment in medical private practice: outcome according to the number of courses followed
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