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1. Physiological responses to light explain competition and facilitation in a tree diversity experiment

   https://doi.org/10.1111/1365-2745.13637  

   Kothari, Shan ; Montgomery, Rebecca A. ; Cavender‐Bares, Jeannine ; Wright, ed., Alexandra ( March 2021 , Journal of Ecology)

   Ecologists often invoke interspecific facilitation to help explain positive biodiversity–ecosystem function relationships in plant communities, but seldom test how it occurs. One mechanism through which one species may facilitate another is by ameliorating abiotic stress. Physiological experiments show that a chronic excess of light can cause stress that depresses carbon assimilation. If shading by a plant's neighbours reduces light stress enough, it may facilitate that plant's growth. If light is instead most often a limiting factor for photosynthesis, shading may have an adverse, competitive effect.

   In a temperate tree diversity experiment, we measured stem growth rates and photosynthetic physiology in broadleaf trees across a gradient of light availability imposed by their neighbours. At the extremes, trees experienced nearly full sun (monoculture), or were shaded by nearby fast‐growing conifers (shaded biculture).

   Most species had slower growth rates with larger neighbours, implying a net competitive effect. On the other hand, the two most shade‐tolerant species (Tilia americanaandAcer negundo) and the most shade‐intolerant one (Betula papyrifera) had faster stem growth rates with larger neighbours. The two shade‐tolerant species had the greatest increases in photoinhibition (reduced dark‐acclimatedF_v/F_m) across the gradient of increasing light availability, which suggests they are more vulnerable to chronic light stress. While most species had lower carbon assimilation rates in the shaded biculture treatment,T. americanahad rates up to 25% higher.T. americanaalso dropped its leaves 3–4 weeks earlier in monocultures, curtailing its growing season.

   We conclude that although large neighbours can cause light limitation in shade‐intolerant species, they can also increase growth through abiotic stress amelioration in shade‐tolerant species. Finally, in shade‐intolerantB. papyrifera, we find a pattern of stem elongation in trees with larger neighbours, which suggests that a shade avoidance response may account for the apparent positive trend in stem volume.

   Synthesis. Both positive and negative species interactions in our experiment can be explained in large part by the photosynthetic responses of trees to the light environment created by their neighbours. We show that photosynthetic physiology can help explain the species interactions that underlie biodiversity–ecosystem function relationships. The insights that ecologists gain by searching for such physiological mechanisms may help us forecast species interactions under environmental change.

    

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2. Friction factor for turbulent open channel flow covered by vegetation

   https://doi.org/10.1038/s41598-019-41477-7  

   Wang, Wei-Jie ; Peng, Wen-Qi ; Huai, Wen-Xin ; Katul, Gabriel G. ; Liu, Xiao-Bo ; Qu, Xiao-Dong ; Dong, Fei ( March 2019 , Scientific Reports)

   The need for operational models describing the friction factorfin streams remains undisputed given its utility across a plethora of hydrological and hydraulic applications concerned with shallow inertial flows. For small-scale roughness elements uniformly covering the wetted parameter of a wide channel, the Darcy-Weisbachf = 8(u_*/U_b)²is widely used at very high Reynolds numbers, whereu_*is friction velocity related to the surface kinematic stress,U_b = Q/Ais bulk velocity,Qis flow rate, andAis cross-sectional area orthogonal to the flow direction. In natural streams, the presence of vegetation introduces additional complications to quantifyingf, the subject of the present work. Turbulent flow through vegetation are characterized by a number of coherent vortical structures: (i) von Karman vortex streets in the lower layers of vegetated canopies, (ii) Kelvin-Helmholtz as well as attached eddies near the vegetation top, and (iii) attached eddies well above the vegetated layer. These vortical structures govern the canonical mixing lengths for momentum transfer and their influence onfis to be derived. The main novelty is that the friction factor of vegetated flow can be expressed asf_v = 4C_d(U_v/U_b)²whereU_vis the spatially averaged velocity within the canopy volume, andC_dis a local drag coefficient per unit frontal area derived to include the aforemontioned layer-wise effects of vortical structures within and above the canopy along with key vegetation properties. The proposed expression is compared with a number of empirical relations derived for vegetation under emergent and submerged conditions as well as numerous data sets covering a wide range of canopy morphology, densities, and rigidity. It is envisaged that the proposed formulation be imminently employed in eco-hydraulics where the interaction between flow and vegetation is being sought.

    

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3. On the perturbation effect and LET dependence of beam quality correction factors in carbon ion beams

   https://doi.org/10.1002/mp.16089  

   Khan, Ahtesham Ullah ; Nelson, Nicholas P. ; Culberson, Wesley S. ; DeWerd, Larry A. ( December 2022 , Medical Physics)

   In a recent study, we reported beam quality correction factors,f_Q, in carbon ion beams using Monte Carlo (MC) methods for a cylindrical and a parallel‐plate ionization chamber (IC). A non‐negligible perturbation effect was observed; however, the magnitude of the perturbation correction due to the specific IC subcomponents was not included. Furthermore, the stopping power data presented in the International Commission on Radiation Units and Measurements (ICRU) report 73 were used, whereas the latest stopping power data have been reported in the ICRU report 90.

   The aim of this study was to extend our previous work by computingf_Qcorrection factors using the ICRU 90 stopping power data and by reporting IC‐specific perturbation correction factors. Possible energy or linear energy transfer (LET) dependence of thef_Qcorrection factor was investigated by simulating both pristine beams and spread‐out Bragg peaks (SOBPs).

   The TOol for PArticle Simulation (TOPAS)/GEANT4 MC code was used in this study. A 30 × 30 × 50 cm³water phantom was simulated with a uniform 10 × 10 cm²parallel beam incident on the surface. A Farmer‐type cylindrical IC (Exradin A12) and two parallel‐plate ICs (Exradin P11 and A11) were simulated in TOPAS using the manufacturer‐provided geometrical drawings. Thef_Qcorrection factor was calculated in pristine carbon ion beams in the 150–450 MeV/u energy range at 2 cm depth and in the middle of the flat region of four SOBPs. Thek_Qcorrection factor was calculated by simulating thef_Qocorrection factor in a⁶⁰Co beam at 5 cm depth. The perturbation correction factors due to the presence of the individual IC subcomponents, such as the displacement effect in the air cavity, collecting electrode, chamber wall, and chamber stem, were calculated at 2 cm depth for monoenergetic beams only. Additionally, the mean dose‐averaged and track‐averaged LET was calculated at the depths at which thef_Qwas calculated.

   The ICRU 90f_Qcorrection factors were reported. Thep_discorrection factor was found to be significant for the cylindrical IC with magnitudes up to 1.70%. The individual perturbation corrections for the parallel‐plate ICs were <1.0% except for the A11p_celcorrection at the lowest energy. Thef_Qcorrection for the P11 IC exhibited an energy dependence of >1.00% and displayed differences up to 0.87% between pristine beams and SOBPs. Conversely, thef_Qfor A11 and A12 displayed a minimal energy dependence of <0.50%. The energy dependence was found to manifest in the LET dependence for the P11 IC. A statistically significant LET dependence was found only for the P11 IC in pristine beams only with a magnitude of <1.10%.

   The perturbation andk_Qcorrection factor should be calculated for the specific IC to be used in carbon ion beam reference dosimetry as a function of beam quality.

    

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4. Distinct features of calcium handling and β‐adrenergic sensitivity in heart failure with preserved versus reduced ejection fraction

   https://doi.org/10.1113/JP280425  

   Kilfoil, Peter J. ; Lotteau, Sabine ; Zhang, Rui ; Yue, Xin ; Aynaszyan, Stephan ; Solymani, Ryan E. ; Cingolani, Eugenio ; Marbán, Eduardo ; Goldhaber, Joshua I. ( September 2020 , The Journal of Physiology)

   Heart failure (HF), the leading cause of death in developed countries, occurs in the setting of reduced (HFrEF) or preserved (HFpEF) ejection fraction. Unlike HFrEF, there are no effective treatments for HFpEF, which accounts for ∼50% of heart failure.

   Abnormal intracellular calcium dynamics in cardiomyocytes have major implications for contractility and rhythm, but compared to HFrEF, very little is known about calcium cycling in HFpEF.

   We used rat models of HFpEF and HFrEF to reveal distinct differences in intracellular calcium regulation and excitation‐contraction (EC) coupling.

   While HFrEF is characterized by defective EC coupling at baseline, HFpEF exhibits enhanced coupling fidelity, further aggravated by a reduction in β‐adrenergic sensitivity.

   These differences in EC coupling and β‐adrenergic sensitivity may help explain why therapies that work in HFrEF are ineffective in HFpEF.

   Heart failure with reduced or preserved ejection fraction (respectively, HFrEF and HFpEF) is the leading cause of death in developed countries. Although numerous therapies improve outcomes in HFrEF, there are no effective treatments for HFpEF. We studied phenotypically verified rat models of HFrEF and HFpEF to compare excitation‐contraction (EC) coupling and protein expression in these two forms of heart failure. Dahl salt‐sensitive rats were fed a high‐salt diet (8% NaCl) from 7 weeks of age to induce HFpEF. Impaired diastolic relaxation and preserved ejection fraction were confirmed in each animal echocardiographically, and clinical signs of heart failure were documented. To generate HFrEF, Sprague‐Dawley (SD) rats underwent permanent left anterior descending coronary artery ligation which, 8–10 weeks later, led to systolic dysfunction (verified echocardiographically) and clinical signs of heart failure. Calcium (Ca²⁺) transients were measured in isolated cardiomyocytes under field stimulation or patch clamp. Ultra‐high‐speed laser scanning confocal imaging captured Ca²⁺sparks evoked by voltage steps. Western blotting and PCR were used to assay changes in EC coupling protein and RNA expression. Cardiomyocytes from rats with HFrEF exhibited impaired EC coupling, including decreased Ca²⁺transient (CaT) amplitude and defective couplon recruitment, associated with transverse (t)‐tubule disruption. In stark contrast, HFpEF cardiomyocytes showed saturated EC coupling (increasedI_Ca, high probability of couplon recruitment with greater Ca²⁺release synchrony, increased CaT) and preserved t‐tubule integrity. β‐Adrenergic stimulation of HFpEF myocytes with isoprenaline (isoproterenol) failed to elicit robust increases inI_Caor CaT and relaxation kinetics. Fundamental differences in EC coupling distinguish HFrEF from HFpEF.

    

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5. Hybrid dielectric slot-plasmonic ring resonator for Purcell enhancement

   https://doi.org/10.1088/1402-4896/acff45  

   Mirzaei-Ghormish, S. ; Smalley, D. E. ; Shahabadi, M. ; Mohammad-Taheri, M. ; Camacho, Ryan M. ( October 2023 , Physica Scripta)

   We present a computational study of Purcell factor enhancement for a novel hybrid-plasmonic ring resonator using a novel implementation of the body-of-revolution (BOR) finite-difference time-domain (FDTD) method. In this hybrid structure, a dielectric slot ring is surrounded by a metallic ring such that a hybrid plasmonic mode is generated within two thin low-index gaps. The surrounding metallic ring decreases the binding loss for small ring radii, leading to high-quality factors and mode-field confinement. The hybrid resonator shows high quality-factor values above 10³and small mode volumes down to${10}^{-3}{\left(\frac{\lambda }{n}\right)}^3$simultaneously, thus providing large Purcell factors (F_p> 10⁴). The distributed strong confinement within two gaps renders the proposed resonator useful for multi-emitter applications.

    

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