Community, Population, and Growth dynamics of Alnus tenuifolia: Implications for nutrient cycling on an Interior Alaskan floodplain

Thesis (M.S.) University of Alaska Fairbanks, 2008This study describes the community, population, and growth dynamics of Alnus tenuifolia (thinleaf alder) and implications for nutrient cycling on the Tanana River floodplains. Through symbiotic N-fixation inputs, alder contributed to soil N accumulation with time. N-fixation itself was likely limited by soil P. Soil N was positively related to alder stem density in early successional stands. Community structure varied along a temporal gradient of changing environmental characteristics, but variations in successional patterns were found. Landscape scale alder recruitment varied temporally and was apparently linked to interactions between geofluvial processes, seed production and dispersal, and herbivory. A widespread stem canker outbreak has resulted in high alder mortality and likely reductions in N-fixation inputs. Disease incidence and mortality were positively related to stem density. Alder radial growth was sensitive to drought during June and August. Alder growth was positively related to river level, suggesting that fluctuation in hyporheic flow is important to alder water balance, especially on lower terraces. The sensitivity of alder growth to meteorological drought was heightened with increasing terrace elevation. Long-term climatic trends suggest that drought will become more common and severe, resulting in reductions in alder-mediated ecosystem N inputs

Climate-induced changes in ecological dynamics of the Alaskan boreal forest: a study of fire-permafrost interactions

Thesis (Ph.D.) University of Alaska Fairbanks, 2016A warming climate is expected to cause widespread thawing of discontinuous permafrost, and the co-occurrence of wildfire may function to exacerbate this process. Here, I examined the vulnerability of permafrost to degradation from fire disturbance as it varies across different landscapes of the Interior Alaskan boreal forest using a combination of observational, modeling, and remote sensing approaches. Across all landscapes, the severity of burning strongly influenced both post-fire vegetation and permafrost degradation. The thickness of the remaining surface organic layer was a key control on permafrost degradation because its low thermal conductivity limits ground heat flux. Thus, variation in burn severity controlled the local distribution of near-surface permafrost. Mineral soil texture and permafrost ice content interacted with climate to influence the response of permafrost to fire. Permafrost was vulnerable to deep thawing after fire in coarse-textured or rocky soils throughout the region; low ice content likely enabled this rapid thawing. After thawing, increased drainage in coarse-textured soils caused reductions in surface soil moisture, which contributed to warmer soil temperatures. By contrast, permafrost in fine-textured soils was resilient to fire disturbance in the silty uplands of the Yukon Flats ecoregion, but was highly vulnerable to thawing in the silty lowlands of the Tanana Flats. The resilience of silty upland permafrost was attributed to higher water content of the active layer and the associated high latent heat content of the ice-rich permafrost, coupled with a relatively cold continental climate and sloping topography that removes surface water. In the Tanana Flats, permafrost in silty lowlands thawed after fire despite high water and ice content of soils. This thawing was associated with significant ground surface subsidence, which resulted in water impoundment on the flat terrain, generating a positive feedback to permafrost degradation and wetland expansion. The response of permafrost to fire, and its ecological effects, thus varied spatially due to complex interactions between climate, topography, vegetation, burn severity, soil properties, and hydrology. The sensitivity of permafrost to fire disturbance has also changed over time due to variation in weather at multi-year to multi-decadal time scales. Simulations of soil thermal dynamics showed that increased air temperature, increased snow accumulation, and their interactive effects, have since the 1970s caused permafrost to become more vulnerable to talik formation and deep thawing from fire disturbance. Wildfire coupled with climate change has become an important driver of permafrost loss and ecological change in the northern boreal forest. With continued climate warming, we expect fire disturbance to accelerate permafrost thawing and reduce the likelihood of permafrost recovery. This regime shift is likely to have strong effects on a suite of ecological characteristics of the boreal forest, including surface energy balance, soil moisture, nutrient cycling, vegetation composition, and ecosystem productivity.Introduction -- Chapter 1: Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests -- Chapter 2: Edaphic and microclimatic controls over permafrost response to fire in interior Alaska -- Chapter 3: Landscape effects of wildfire on permafrost distribution in interior Alaska derived from remote sensing -- Conclusions

Defensive Walls of Tobolsk Kremlin: a Historical and Architectural Sketch

The article was prepared in connection with the announcement of the year of Semyon Ulyanovich Remezov in the city of Tobolsk in 2021. Information has been collected on the history of the construction and rebuilding of the fortress walls and towers of the Tobolsk Kremlin, which rarely attracted the attention of researchers. A review of the history of the fence construction in the Sofia courtyard is carried out. Particular attention is paid to the stages of the construction of the Kremlin stone walls, the surviving elements of defensive architecture in them. The authors clarify some provisions from the classical works of V. I. Kochedamov, draw on new sources, including photographs from restoration work in the middle of the 20th century from the funds of the Tobolsk Historical and Architectural Museum-Reserve. The results of a comparative architectural analysis of the Kremlin walls of Tobolsk with synchronous and previous monuments of Russian military architecture are presented in the article. It has been established that the walls of the Tobolsk Kremlin were more of a symbolic-decorative than a military char-acter. It was determined that they represented a symbiosis of the Moscow Kremlin architecture of the late 15th century with the architecture of the Smolensk fortress wall, 17th century monastery fences and, possibly, the fence of the Bishops' court in Rostov

Observation of micropores in hard-carbon using Xe-129 NMR porosimetry

The existence of micropores and the change of surface structure in pitch-based hard-carbon in xenon atmosphere were demonstrated using Xe-129 NMR. For high-pressure (4.0 MPa) Xe-129 NMR measurements, the hard-carbon samples in Xe gas showed three peaks at 27, 34 and 210 ppm. The last was attributed to the xenon in micropores (<1 nm) in hard-carbon particles. The NMR spectrum of a sample evacuated at 773 K and exposed to 0.1 MPa Xe gas at 773 K for 24 h showed two peaks at 29 and 128 ppm, which were attributed, respectively, to the xenon atoms adsorbed in the large pores (probably mesopores) and micropores of hard-carbon. With increasing annealing time in Xe gas at 773 K, both peaks shifted and merged into one peak at 50 ppm. The diffusion of adsorbed xenon atoms is very slow, probably because the transfer of molecules or atoms among micropores in hard-carbon does not occur readily. Many micropores are isolated from the outer surface. For that reason, xenon atoms are thought to be adsorbed only by micropores near the surface, which are easily accessible from the surrounding space.</p

Overview of neurosurgical capacity in St. Lucia

When we talk about the most scenic Caribbean islands, St. Lucia is one of those islands that certainly come into our mind. It is a beautiful tourist destination and the place of post-volcanic paradise on earth. However, just like many remote Caribbean islands, St. Lucians (name for local population) used to have its own difficulties of obtaining on demand basic neurosurgical services in their homeland. This beautiful Caribbean island, socioeconomically falls in the same category as most low-and middle-income countries (LMICs) and unfortunately echoes the same unmet surgical and anaesthesia needs as the rest of them

3D study of morphology and dynamics of zeolite nucleation

The principle aspects and constrains of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na-rich aluminosilicate system. A detailed time-series EMT-type zeolite crystallization study in the model hydrogel system is performed in order to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods is employed to analyze the gel evolution complementing the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core-shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels

Study of Xenon Mobility in the Two Forms of MIL-53(Al) Using Solid-State NMR Spectroscopy

The Al-based metal–organic framework (MOF) MIL-53­(Al) exhibits a structural transition between a large-pore (<i>lp</i>) form and a narrow-pore (<i>np</i>) one. Such change is induced by temperature, external pressure, or the adsorption of guest molecules. ¹²⁹Xe solid-state NMR experiments under static and magic-angle spinning (MAS) conditions have been used to study the <i>lp</i>–<i>np</i> transition in MIL-53­(Al) initially loaded with xenon gas under a pressure of 5 × 10⁴ Pa (at room temperature). The conversion of the <i>lp</i> form into the <i>np</i> one when the temperature decreases from 327 to 237 K and the reopening of the pores below 230 K are then observed. Furthermore, ¹H → ¹²⁹Xe cross-polarization under MAS (CPMAS) experiments demonstrate the possibility to observe the <i>np</i> phase at <i>T</i> ≤ 230 K, while the <i>lp</i> one is unseen because the xenon residence time is too short for successful cross-polarization transfer. Moreover, even for the <i>np</i> phase at 199 K, the xenon atoms still exhibit significant motion on time scale faster than a few milliseconds. We prove the exchange of Xe atoms between the <i>lp</i> and <i>np</i> forms at room temperature with the two-dimensional (2D) ¹²⁹Xe EXchange SpectroscopY (EXSY) NMR method. Using ¹²⁹Xe selective inversion recovery (SIR) experiments, the rate for this exchange has been measured at 43 ± 6 s^–1

Comparative study of in situ N2 rotational Raman spectroscopy methods for probing energy thermalisation processes during spin-exchange optical pumping

Spin-exchange optical pumping (SEOP) has been widely used to produce enhancements in nuclear spin polarisation for hyperpolarised noble gases. However, some key fundamental physical processes underlying SEOP remain poorly understood, particularly in regards to how pump laser energy absorbed during SEOP is thermalised, distributed and dissipated. This study uses in situ ultra-low frequency Raman spectroscopy to probe rotational temperatures of nitrogen buffer gas during optical pumping under conditions of high resonant laser flux and binary Xe/N2 gas mixtures. We compare two methods of collecting the Raman scattering signal from the SEOP cell: a conventional orthogonal arrangement combining intrinsic spatial filtering with the utilisation of the internal baffles of the Raman spectrometer, eliminating probe laser light and Rayleigh scattering, versus a new in-line modular design that uses ultra-narrowband notch filters to remove such unwanted contributions. We report a ~23-fold improvement in detection sensitivity using the in-line module, which leads to faster data acquisition and more accurate real-time monitoring of energy transport processes during optical pumping. The utility of this approach is demonstrated via measurements of the local internal gas temperature (which can greatly exceed the externally measured temperature) as a function of incident laser power and position within the cell

NMR hyperpolarization techniques of gases

Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4–8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can often be readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This Minireview covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science