Student Papers (FSCI)

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    Joint species distribution modelling of multiple taxonomic groups shows that water quality explains most of the variation in aquatic community composition along a lake trophic gradient
    (Aquatic Ecology, 2025-05-09) Smith, Erin; Kirkwood, Andrea E.
    A key component of conservation biology is understanding how community composition responds to environmental conditions, including stressors (e.g., eutrophication). However, this is complicated by the accompanying shifts in taxa co-occurrence due to taxa interactions (e.g., competition, predation). Thus, we need to consider both taxa co-occurrence and abiotic conditions simultaneously to understand the relative influence of these factors on community composition. In this study, we aimed to elucidate the relative role of water quality and taxa co-occurrence in determining phytoplankton, zooplankton, and macroinvertebrate communities in a set of lakes varying in trophic status from oligotrophic to meso-eutrophic. We built joint species distribution models (JSDMs) using a generalized linear latent variable modelling approach to isolate the influence of abiotic variables and taxa co-occurrence for each level of the food web. We found that water quality explained most of the variation in community composition for all groups, especially for zooplankton (78%) and macroinvertebrate (62%) communities. Additionally, total phosphorus was a significant driver of many taxa in these groups. These findings indicate a strong “bottom-up” control of the lower aquatic food web in these lakes and signify an important role of phosphorus across a distinct trophic gradient. Overall, we demonstrate the effectiveness of JSDMs for determining the relative impacts of abiotic variables on community composition which can provide key insights for lake management.
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    The quantum and electromagnetic process of photon emission by the hydrogen atom
    (Physics Essay, 2021-04-07) Kowalski, Marian
    Light emitted from atoms during transitions of electrons from higher to lower discrete states has the form of photons carrying energy and angular momentum. This paper considers the process of emission of a single photon from the hydrogen atom by using quantum theory and Maxwell’s equations [W. Gough, Eur. J. Phys. 17, 208, 1996; L. D. Landau and E. M. Lifshitz, Quantum Mechanics (Pergamon Press, Oxford, 1965); J. D. Jackson, Classical Electrodynamics (John Wiley & Son, New York, 1975, 1982); P. M. Morse and H. Feshbach, Methods of Theoretical Physics (McGraw-Hill Book Company, Inc., New York, 1953)]. The electric and magnetic fields of a photon arise from the time-dependent quantum probability densities of the orbit and the spin current. This paper is an extension of the semiclassical description of photon emission published by the author earlier in 1999 [M. Kowalski, Phys. Essays 12, 312 (1999)]. In the semiclassical approach, the Coulomb force and a radiation resistance force have been taken into account to get time-dependent emission of the photon. In both the quantum and semiclassical cases, the transition takes place within a time interval equal to one period of the photon’s wave. The creation of a one-wavelength-long photon is supported by the results of experiments using ultrafast (ultrashort) laser pulses to generate excited atoms, which emit light pulses shorter than two photon wavelengths [F. Krausz and M. Ivanov, Rev. Mod. Phys. 81, 163 (2009); H. Kapteyn and M. Murnane, Phys. World 12, 31 (1999)]. VC 2021 Physics Essays Publication. [http://dx.doi.org/10.4006/0836-1398-34.2.116]