Publications

ABSTRACT The scaling of CO 2 and water vapour transfer from leaf to canopy dimensions was achieved by integrating mechanistic models for physiological (photosynthesis, stomatal conductance and soil/root and bole respiration) and micrometeorological (radiative transfer, turbulent transfer and surface energy exchanges) processes. The main objectives of this paper are to describe a canopy photosynthesis and evaporation model for a temperate broadleaf forest and to test it against field measurements. The other goal of this paper is to use the validated model to address some contemporary ecological and physiological questions concerning the transfer of carbon and water between forest canopies and the atmosphere. In particular, we examine the role of simple versus complex radiative transfer models and the effect of environmental (solar radiation and CO 2 ) and ecophysiological (photo‐synthetic capacity) variables on canopy‐scale carbon and water vapour fluxes.

The binary nature of Northern California's ecohydrology, in which water is either abundantly available or scarce, should be reflected in the root architecture of the native blue oak. Our objective was to quantify carbon storage and understand how the form of the root system facilitates ecosystem functioning despite the asynchrony between winter water availability, spring leaf growth, and dry‐summer canopy maintenance. To do this, we surveyed coarse root distribution with a ground penetrating radar (GPR), due to its advantages in covering large areas rapidly and non‐destructively. We calibrated root biomass detected by GPR against roots excavated from a number of small pits. Based on a survey of six tree configurations (varying in age, size, and clumping), we found that coarse roots occupy the full soil profile and that coarse root biomass of old large trees reached a peak directly above the bedrock. As opposed to other semi‐arid regions, where trees often develop extensive shallow lateral coarse roots to exploit the entire wet‐soil medium, we found that root density decreased with distance from the bole, and dropped sharply beyond a distance of 2 m. We upscaled tree root biomass to stand scale (2.8 ± 0.4 kg m −2 ) based on lidar analysis of the relative abundance of each tree configuration. We argue that this deep and narrow root structure reflects the ecohydrology of oaks in this ecosystem. An extensive lateral root system would not be beneficial during the growing season, when water is sufficiently abundant, nor during summer, when soil water is highly limited.

A relationship is derived between differences in electric polarization between bands and the "shift vector" that controls part of a material's bulk photocurrent, then demonstrated in several models. Electric polarization has a quantized gauge ambiguity and is normally observed at surfaces via the surface charge density, while shift current is a bulk property and is described by shift vector gauge invariant at each point in momentum space. They are connected because the same optical transitions that are described in shift currents pick out a relative gauge between valence and conduction bands. We also discuss subtleties arising when there are points at the Brillouin zone where optical transitions are absent. We conclude that two-dimensional materials with significant interband polarization differences should have high bulk photocurrent, meaning that the modern theory of polarization can be used as a straightforward way to search for bulk photovoltaic material candidates.

Both compensation incentives and managed care market pressures were significantly associated with the use of evidence-based care management practices. The lack of association for culture may be due to the relatively amorphous nature of most physician organizations at this point.

I review the use of Type Ia supernovae (SNe Ia) in the 1998 discovery of the accelerating expansion of the Universe, as well as the subsequent use of SNe Ia to study the expansion history in more detail, determine the equation-of-state parameter w, and measure the current value of the Hubble constant. This is the lightly edited transcript of a lecture given at the Standard Model at 50 Symposium held at Case Western University, June 1-4, 2018, and thus corresponds to the state of the field in mid-2018; however, a few post-symposium updates were included in 2019. Also, this version includes at the end a brief update (December 2023) on the early-time vs. late-time Hubble tension, which has now reached a level of 5 sigma based on SNe Ia alone and is supported by several other low-redshift determinations of the Hubble constant.

Multielectron redox in Li 2 FeS 2 is achieved through both cation and anion redox. 1,2 While the redox mechanism has been investigated experimentally, questions remain regarding the transition from Fe to S redox, persulfide formation, and the inability to reach the large theoretical capacity. Here, we revisit the charging process by analyzing atomic and electronic structures using density functional theory (DFT) calculations. The initial redox stage is found to proceed by Fe oxidation with increased Fe–S covalency driven by a ligand-to-metal charge transfer. The observed Fe redox limit (60–75%) 2 arises from phase separation as further oxidation is calculated to result in decomposition into Li-rich and S-rich phases. This phase separation induces a shift from Fe to S redox with charge compensation transitioning from oxidation of nonbonding Fe states to oxidation of nonbonding S states. Li vacancies at high states of charge create space for FeS 4 tetrahedra to tilt, facilitating S–S bond formation. Subsequent delithiation beyond ~1.5 e – would require unstable S hole formation in the layered structure or a conversion to pyrite FeS 2 , hence the inability to completely delithiate Li 2 FeS 2 . This work provides fundamental insights into the nature of cation and anion redox in Li 2 FeS 2 , informing the development of other high-capacity sulfide cathodes for Li-ion batteries. [1] Hansen, C. J.; Zak, J. J.; Martinolich, A. J.; Ko, J. S.; Bashian, N. H.; Kaboudvand, F.; Van der Ven, A.; Melot, B. C.; Nelson Weker, J.; See, K. A. Multielectron, J. Am. Chem. Soc. 2020 , 142 (14), 6737–6749. [2] Patheria, E. S.; Guzman, P.; Soldner, L. S.; Qian, M. D.; Morrell, C. T.; Kim, S. S.; Hunady, K.; Priesen Reis, E. R.; Dulock, N. V.; Neilson, J. R.; Nelson Weker, J.; Fultz, B.; See, K. A., J. Am. Chem. Soc. 2025 . https://doi.org/10.1021/jacs.4c18440. Figure 1