Publications

Wetlands are significant contributors to global methane (CH4) emissions, a critical driver of climate change. However, the spatial heterogeneity of CH4 fluxes and the underlying mechanisms within these wetland ecosystems remains largely unexplored. This study examines the heterogeneity of CH4 emissions from different types of wetlands in Estonia and California, USA. The studied wetlands include free surface water treatment wetlands, recently restored peatlands in Estonia and three different restored wetlands in California that differ from each other in salinity level, tidal influence, vegetation, and restoration year. All studied sites except the free surface treatment wetlands are equipped with eddy covariance stations for continuous CO2, H2O, and CH4 measurements (open path LI-7500 and LI-7700 analyzers, LICOR Biosciences). Spatial heterogeneity in methane flux was assessed through static chamber measurements using a LI-7810 trace gas analyzer (LICOR Biosciences). Chamber measurement surveys revealed significant variations among gas measurement points within the eddy tower footprint. Additional parameters such as LAI, water pH, electrical conductivity, dissolved oxygen concentration, temperature, turbidity, salinity, water level, and dissolved gas concentration (dCO2 and dCH4; analyzed in the lab with GC-2014, Shimadzu) were measured from each sampling spot. After measurements, we collected surface sediment samples for soil TN, TOC, TIC, DOC, DIC, and DN analyses. Our results indicate significant variation in CH4 fluxes and soil C and N content within different sampling points and in different ecosystems. In the constructed wetland in Estonia, biweekly measurements from twelve distinct points over two years revealed significant heterogeneity in CH4 fluxes, with peak emissions ranging from 144 mg m-2 d-1 to 254.4 mg m-2 d-1 observed from specific chamber measurement plots. In contrast, the restored peatland showed a lower range of CH4 emissions (0.096 mg m-2 d-1 to 34.6 mg m-2 d-1) observed from six measurement plots. The preliminary measurements conducted in California wetlands also showed a large variation within and between the sites. These findings highlight the complex nature of CH4 flux heterogeneity in wetlands and the critical need for site-specific management strategies. Accurately quantifying and understanding these variations is essential for refining CH4 budgets and developing effective mitigation strategies for greenhouse gas emissions from wetland ecosystems.

Abstract Diaryl difluoromethanes are valuable targets for medicinal chemistry because they are bioisosteres of diaryl ethers and can function as replacements for diaryl methane, ketone, and sulfone groups. However, methods to prepare diaryl difluoromethanes are scarce, especially methods starting from abundant aryl halides. We report the Pd‐catalyzed aryldifluoromethylation of aryl halides with aryldifluoromethyl trimethylsilanes (TMSCF 2 Ar). The reaction occurs when the catalyst contains a simple, but unusual, dialkylaryl phosphine ligand that promotes transmetallation of the silane. Computational studies show that reductive elimination following transmetallation occurs with a low barrier, despite the fluorine atoms on the α‐carbon, due to coordination of the difluorobenzyl π‐system to palladium. The co‐development of a cobalt‐catalyzed synthesis of the silanes broadened the scope of the process including several applications to the synthesis biologically relevant diaryl difluoromethanes.

Abstract Benzylic fluorides are obtained by a three‐component coupling of unactivated amino‐alkenes, arylboronic acids, and Selectflour through an oxidative Heck mechanism.

A novel non-contact method of forming groove servo patterns on optical disk substrates has been demonstrated. The servo forming layer consists of a copolymer of (p-t-butyloxycarbonyloxy)styrene and styrene formulated with an onium salt which photogenerates acidic species upon exposure to deep UV radiation. If the film is heated after exposure to light the photogenerated acid cleaves the p-t-butyloxycarbonyl ("t-BOC") group resulting in a thickness change in the regions exposed to radiation. Glass substrates coated with this formulation were exposed with an appropriate mask to deep CV light and the image developed by a post exposure bake of 2 minutes at 90°C. A magneto-optic trilayer consisting of 710 A Zr0₂/800 A TbFeCo/710 A Zr0₂ was deposited onto the polymer surface. The complete structure has sufficient track error signal level to be trackable on a precision optical disk test stand with the TES servo loop closed and has a CNR of 53 dB, comparable to the same MO composition deposited on injection molded grooved polycarbonate substrates.

High in-plane anisotropies arise in layered materials with large structural difference along different in-plane directions. We report an extreme case in layered TiS₃, which features tightly bonded atomic chains along the <i>b</i>-axis direction, held together by weaker, interchain bonding along the <i>a</i>-axis direction. Experiments show thermal conductivity along the chain twice as high as between the chain, an in-plane anisotropy higher than any other layered materials measured to date. We found that in contrast to most other materials, optical phonons in TiS₃ conduct an unusually high portion of heat (up to 66% along the <i>b</i>-axis direction). The large dispersiveness of optical phonons along the chains, contrasted to many fewer dispersive optical phonons perpendicular to the chains, is the primary reason for the observed high anisotropy in thermal conductivity. The finding discovers materials with unusual thermal conduction mechanism, as well as provides new material platforms for potential heat-routing or heat-managing devices.

Magnesium oxide and sulfide spinels have recently attracted interest as cathode and electrolyte materials for energy-dense Mg batteries, but their observed electrochemical performance depends strongly on synthesis conditions. In this study, using first-principles calculations and percolation theory, we explore the extent to which spinel inversion influences Mg&lt;sup&gt;2+&lt;/sup&gt; ionic mobility in MgMn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; as a prototypical cathode, and MgIn&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;4&lt;/sub&gt; as a potential solid electrolyte. We find that spinel inversion and the resulting changes of the local cation ordering give rise to both increased and decreased Mg&lt;sup&gt;2+&lt;/sup&gt; migration barriers, along specific migration pathways, in the oxide as well as the sulfide. To quantify the impact of spinel inversion on macroscopic Mg&lt;sup&gt;2+&lt;/sup&gt; transport, we determine the percolation thresholds in both MgMn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; and MgIn&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;4&lt;/sub&gt;. Furthermore, we analyze the impact of inversion on the electrochemical properties of the MgMn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; cathode via changes in the phase behavior, average Mg insertion voltages and extractable capacities, at varying degrees of inversion. In conclusion, our results confirm that inversion is a major performance limiting factor of Mg spinels and that synthesis techniques or compositions that stabilize the well-ordered spinel structure are crucial for the success of Mg spinels in multivalent batteries.