In this work the synthesis, characterization, and gas transport properties of hydrogen selective silica membranes were studied along with the catalytic reforming of CH₄ with CO₂ (CH₄ + CO z 2 CO + 2 H₂) in a hydrogen separation membrane reactor. The silica membranes were prepared by chemical vapor deposition (CVD) of a thin SiO₂ layer on porous supports (Vycor glass and alumina) using thermal decomposition of tetraethylorthosilicate (TEOS) in an inert atmosphere. These membranes displayed high hydrogen permeances (10⁻⁸ - 10⁷ mol m⁻² s⁻¹ Pa⁻¹) and excellent H₂ selectivities (above 99.9 %) over other gases (CH₄, CO, and CO₂). The membranes were characterized using Scanning Electron Microscopy and Atomic Force Microscopy, and the mechanism of gas transport was studied applying existing theories with a newly developed treatment. The catalytic reforming of CH₄ with CO₂ was carried out in a membrane reactor installed with a hydrogen separation ceramic membrane. The reaction was conducted at various pressures (1 - 20 atm) and temperatures (873 K and 923 K) at non-equilibrium conditions, and the results were compared with those obtained in a packed bed reactor in order to evaluate performance of the membrane reactor for the reaction. It was found that concurrent and selective removal of hydrogen from the reaction in the membrane reactor resulted in considerable enhancements in the yields of the reaction products, H₂ and CO. The enhancements in the product yields in the membrane reactor increased with pressure showing a maximum at 5 atm, and then decreased at higher pressures. This was due to a trade-off between a thermodynamic quantity (hydrogen production by the reaction) and transport property (hydrogen separation through the membrane). It was also found that the reverse water-gas shift (RWGS) reaction occurred simultaneously with the reforming reaction giving the detrimental effect on the reaction system by reducing the amount of hydrogen production in favor of water. This was particularly significant at high pressures. / Ph. D.

Previous research on grazing behavior has shown that ruminants will select a mixed diet. The use of adjacent monocultures is an essential tool for determining dietary preference of forages. Much of the work to date has been conducted with white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). Partial preference for white clover over ryegrass has been reported consistently and partial preference for legumes is thought to occur regardless of the legume and grass species being evaluated. Two forage species, tall fescue (Festuca arundinacea Schreb. or Lolium arundinaceum (Schreb.) S.J. Darbyshire) and alfalfa (Medicago sativa subsp. sativa L.), which had not been evaluated together previously as adjacent monocultures were grazed by beef steers in the present set of experiments. Steers exhibited a partial preference for alfalfa of 61 to 65% when given a choice of grazing alfalfa or tall fescue as adjacent monocultures, regardless of the ground area proportion of the two forages offered. Steers grazing tall fescue monocultures spent more time ruminating (P = 0.02) and tended to graze less time (P = 0.06) than steers in adjacent monoculture treatments. Time spent idling, number of prehensions and mastications, and bite rate were similar (P > 0.05) among treatments. Steers grazing tall fescue monocultures spent less time standing, more time lying, were less active and took fewer steps (P ≤ 0.05) than steers in adjacent monoculture treatments. Grazing behavior was examined when alfalfa had not been in the previous diet of the steers. Cattle without previous experience grazing alfalfa spent 78% of the time grazing alfalfa, whereas after having experience grazing it they spent a lower (P = 0.04) proportion of their time grazing alfalfa (72%). Overall proportion of the day spent grazing both forages was lower (P = 0.0001) when alfalfa was novel (40%), compared to when steers were experienced grazing both forages (46%). Proportion of the day spent idling was greater (P < 0.0001) when alfalfa was novel (35%), compared to when both forages were familiar to the steers (26%). Previous research has reported that ruminants exhibit a diurnal pattern of preference by decreasing the proportion of white clover consumed from morning to late afternoon while increasing the proportion of perennial ryegrass in the diet. This is thought to be a strategy to increase fiber intake before nightfall or as a response to higher carbohydrate levels in grass in the afternoon. In the present study, proportion of grazing time in alfalfa was higher (P = 0.02) in the afternoon (76.8 %) than in the morning (72.1 %). While fiber concentration was higher in the tall fescue, carbohydrate concentrations were similar. Steers were not attempting to increase fiber intake in the afternoon in the present study. Dry matter intake of steers grazing adjacent monocultures of alfalfa and tall fescue was estimated with n-alkanes. Diet composition was estimated using n-alkanes and long chain alcohols (LCOH) in several different combinations. The use of LCOH added additional characterization of the forages, but diet composition estimates were not different (P ≥ 0.22) than when estimated using four different n-alkanes. Laboratory analysis costs may be reduced if n-alkanes alone can adequately characterize the forages being consumed, depending on the forage species in question. Meteorological conditions impacted DMI with intake being less in hotter conditions. Steers had similar partial preferences for alfalfa over tall fescue (P = 0.13, 79% and 70% alfalfa in yr 1 and 2, respectively) even though total DMI differed between years (P = 0.002, 9.4 kg d-1 and 4.5 kg d-1 in yr 1 and 2, respectively). Lower DMI in yr 2 was attributed to hotter air temperatures. When animals are consuming two different forages as adjacent monocultures such as in the current experiments, it is important to determine the proportion of each forage in the diet before calculating DMI using odd chain n-alkanes of the forage along with a dose even chained n-alkane. Dry matter intake can be overestimated if the proportion of the forages consumed is not estimated and accounted for in the equation. This would apply to other studies utilizing mixed swards or any diet containing multiple components that differ in concentration of the n-alkane being used for DMI estimation. Analysis of n-alkane concentration should be performed on each item in the diet and the proportion of each item in the diet estimated so that the right value can be used in the calculation. Differences in marker concentrations between years also indicate the importance of analyzing those concentrations in the feed or forage at the time of fecal collection and not using values reported from previous research. / Ph. D.

Our knowledge of whether hurricanes cause lasting changes in forest composition and the patterns and role of fire in Caribbean dry forests are lacking. This project combines paleoecological and paleotempestological methods to document the disturbance and environmental history of the last 1000 yrs at Laguna Alejandro, situated in the lowland dry forests of arid SW Dominican Republic. I analyzed multiple proxy data sources of a 160 cm coastal lagoon sediment profile. High-resolution (1 cm) sampling for loss-on-ignition and magnetic susceptibility indicated multiple erosion and hurricane events, including a hurricane ~996 cal YBP, and several erosion events and hurricanes between ~321 cal YBP and present day. Pollen analysis documented 32 plant families with most levels dominated by pollen of Fabaceae (legumes), the Urticales order, and Cyperaceae (sedges), though families of upland and montane vegetation are also present ~510-996 cal YBP. All pollen slides contained microscopic charcoal indicating the occurrence of regional or extra-local fires over the last ~1000 yrs. Local fires, as indicated by macroscopic charcoal, occurred before ~434 cal YBP and may be tied to hurricanes, increased moisture in the region (thereby increased fuel and ignition chances), or prehistoric human activities. Pollen spectra representing periods before and after disturbance events were similar and may support the idea of forest resilience, but more samples are needed. Multiple erosion events between ~294 cal YBP and present may be tied to hurricanes or tropical storms and increasing late-Holocene aridity in the region as documented by several studies from the Caribbean. / Master of Science

Microbial community composition plays a vital role in soil biogeochemical cycling. Information that explains the biogeography of microorganisms is consequently necessary for predicting the timing and magnitude of important ecosystem services mediated by soil biota, such as decomposition and nutrient cycling. Theory developed to explain patterns in plant and animal distributions such as the prevalent relationship between ecosystem productivity and diversity may be successfully extended to microbial systems and accelerate an emerging ecological understanding of the "unseen majority." These considerations suggest a need to define the important mechanisms which affect microbial biogeography as well as the sensitivity of community structure/function to changing climatic or environmental conditions. To this end, my dissertation covers three data chapters in which I have 1) examined patterns in bacterial biogeography using gradients of environmental severity and productivity to identify changes in community diversity (e.g. taxonomic richness) and structure (e.g. similarity); 2) detected potential bacterial ecotypes associated with distinct soil habitats such as those of high alkalinity or electrical conductivity and; 3) measured environmental controls over the function (e.g. primary production, exoenzyme activity) of soil organisms in an environment of severe environmental limitations. Sampling was performed in the polar desert of Antarctica's McMurdo Dry Valleys, a model ecosystem which hosts microbially-dominated soil foodwebs and displays heterogeneously distributed soil properties across the landscape. Results for Chapter 2 indicate differential effects of resource availability and geochemical severity on bacterial communities, with a significant productivity-diversity relationship that plateaus near the highest observed concentrations of the limiting resource organic carbon (0.30mg C/g soil). Geochemical severity (e.g. pH, electrical conductivity) primarily affected bacterial community similarity and successfully explained the divergent structure of a subset of samples. 16S rRNA amplicon pyrosequencing further revealed in Chapter 3 the identity of specific phyla that preferentially exist within certain habitats (i.e. Acidobacteria in alkaline soils, Nitrospira in mesic soils) suggesting the presence of niche specialists and spatial heterogeneity of taxa-specific functions (i.e. nitrite oxidation). Additionally, environmental parameters had different explanatory power towards predicting bacterial richness at varying taxonomic scales, from 57% of phylum-level richness with pH to 91% of order- and genus-level richness with moisture. Finally, Chapter 4 details a simultaneous sampling of soil communities and their associated ecosystem functions (primary productivity, enzymatic decomposition) and indicates that the overall organic substrate diversity may be greater in mesic soils where bacterial diversity is also highest, thus a potentially unforeseen driver of community dynamics. I also quantified annual rates of soil production which range between 0.7 - 18.1g C/m2/yr from the more arid to productive soils, respectively. In conclusion, the extension of biogeographical theory for macroorganisms has proven successful and both environmental severity and resource availability have obvious (although different) effects on the diversity and composition of soil microbial communities. / Ph. D.

Modern Dry Low Emissions (DLE) combustors are characterized by highly swirling and expanding flows that makes the convective heat load on the combustor liner gas side difficult to predict and estimate. A coupled experimental-numerical study of swirling flow and its effects on combustor liner heat transfer inside a DLE annular combustor model is presented. A simulated scaled up annular combustor shell was designed with a generic fuel nozzle provided by Solar Turbines to create the swirl in the flow. The experiment was simulated with a cold flow and heated walls. An infrared camera was used to obtain the temperature distribution along the liner wall. Experimentally measured pressure distributions were compared with the heat transfer results. The experiment was conducted at various Reynolds Numbers to investigate the effect on the heat transfer peak locations and pressure distributions. A CFD study was performed using Fluent and turbulence models and used to corroborate and verify the experimental results. Results show that the heat transfer enhancement in the annulus has slightly different characteristics for the concave and convex walls. Results also show a much slower drop in heat transfer coefficient enhancement with increasing Reynolds number compared to can combustors from a previous study. An introductory study of the effect of a soft wall on the heat transfer on the combustor liner is also presented. / Master of Science

The most ubiquitous mode of frost formation on substrates is condensation frosting, where dew drops condense on a supercooled surface and subsequently freeze, and has been known since the time of Aristotle. The physics of frost incipience at a microscopic scale has, nevertheless, eluded researchers because of an unjustified ansatz regarding the primary mechanism of condensation frosting. It was widely assumed that during condensation frosting each supercooled droplet in the condensate population freezes in isolation by heterogeneous nucleation at the solid-liquid interface, quite analogous to the mechanism of icing. This assumption has very recently been invalidated with strong experimental evidence which shows that only a single droplet has to freeze by heterogeneous nucleation (typically by edge effects) in order to initiate condensation frosting in a supercooled condensate population. Once a droplet has frozen, it subsequently grows an ice bridge towards its nearest neighboring liquid droplet, freezing it in the process. Thus ensues a chain reaction of ice bridging where the newly frozen droplets grow ice bridges toward their nearest neighbor liquid droplets forming a percolating network of interconnected frozen droplets. Not always are these ice bridges successful in connecting to their adjacent liquid droplets. Sometimes the liquid droplet can completely evaporate before the ice bridges can connect, thus forming a local dry region in the vicinity of the ice bridge. In this work, we first formulate a thermodynamic framework in order to understand the localized vapor pressure gradients that emerge in mixed-mode phase-change systems and govern condensation and frost phenomena. Following this, we study droplet pair interactions between a frozen droplet and a liquid droplet to understand the physics behind the local ice bridge connections. We discuss the emergent scaling laws in ice bridging dynamics, their relative size dependencies, and growth rates. Thereafter, we show how with spatial control of interdroplet distances in a supercooled condensate and temporal control of the first freezing event, we can tune global frost propagation on a substrate and even cause a global failure of all ice bridges to create a dry zone. Subsequently, we perform a systematic study of dry zones and derive a scaling law for dry zones that collapses all of our experimental data spanning a wide parameter space. We then show that almost always the underlying mechanism behind the formation of dry zones around any hygroscopic droplet is inhibition of growth and not inhibition of nucleation. We end with a discussion and preliminary results of our proposed anti-frosting surface that uses ice itself to prevent frost. / Master of Science / In the movie Iron Man, during the very final battle sequence between our eponymous hero and Iron Monger, there is a moment when Tony Stark realizes that Iron Monger can fly. Immediately Iron Man shoots up into the sky. He tries to reach as high as he can. Iron Monger chases after him. Eventually, high up in the sky amidst the clouds, Iron Monger catches up. He grabs Iron Man in his enormous grip and punches him. It seems like there is no escape for Iron Man. But right then, writhing in Iron Monger’s grip, Tony Stark asks Iron Monger, ‘How’d you solve the icing problem?’ It is then revealed that Iron Monger’s suit has completely frozen over, whereas Iron Man’s suit has no ice whatsoever. Iron Monger shuts down and starts falling from the sky. The icing problem, which Tony Stark mentions, occurs when supercooled liquid water droplets impact on a chilled substrate and subsequently freeze. Another way of accretion of ice constitutes the frosting problem. The most common mode of frost formation on a surface is called condensation frosting, where the ambient water vapor first condenses on the chilled surface as dew drops, and these liquid droplets subsequently freeze. Until very recently, it was widely assumed that during condensation frosting all the dew droplets freeze in isolation at the solid-liquid interface, without interacting with each other. This assumption, however, is not true. It has recently been shown that in order to initiate condensate frosting, only a single droplet has to freeze by itself, at the solid-liquid interface. Thereafter, frost propagates by the formation of an inter-droplet ice bridge network, where the frozen droplets grow ice bridges toward their nearest neighbor liquid droplets. Interestingly, these ice bridges are not always successful in connecting to their adjacent liquid droplets. If the inter-droplet distance is too large, the liquid droplet can completely evaporate before the ice bridges can connect, thus forming a local dry region in the vicinity of the ice bridge. In this work, we do extensive experiments to investigate the underlying physics of frost incipience on a microscopic scale. We then derive scaling laws for successful ice connections, their growth rates and for dry zone formations, and end by discussing possible anti-frosting strategies. It appears that Tony Stark in his universe has solved the icing problem, and most probably also the frosting problem. In reality, however, on earth, we have not. Though anti-icing has received a lot of attention, the same cannot be said about the frosting problem. This work tries to take the first steps towards that. Quite ironically, it looks like ice itself might be the solution to the frosting problem, because of its ability to create dry zones.

Determining intake of feeds in horses is an important factor in incorporating supplements in their diets. Fecal recoveries (R), fecal output (FO), dry matter digestibility (DMD) and dry matter intake (DMI) were estimated using alkanes as markers in 8 thoroughbred geldings. The experiment compared two diets in a 2 X 2 latin square experiment. The diets were mixed grass hay only (H) and the same hay plus a cereal by-product (H + CBP). The cereal by-product (CBP) was the high fat component added to feeds at Virginia Tech's Middleburg Agricultural Research and Extension Center. The apparent digestibility of ether extract (EE) and other nutrients in the H and H + CBP, as well as the partial digestibility of CBP were also determined. The periods were 21 d each with a dietary accommodation period followed by eight days of dosing the even chain alkanes dotriacontaine (C32) and hexatriacontane (C36) as external markers. Total collection (TC) was performed the last 4 d of dosing. The results show that mean recoveries of alkanes were close to 100%, but the range for individual alkanes was wide, and the pattern of recoveries for alkanes of different chain length was inconsistent from feed to feed. The results also indicate that mean estimates of the DMI, DMD and FO of a feed, such as H or H + CBP, are determined with reasonable accuracy by means of alkane markers. In contrast, alkane estimates of DMI and DMD in an individual horse fail to predict corresponding TC estimates. The alkane estimate of FO in an individual horse predicts a TC value with error of 16.4%. The CBP was found to be an excellent source of EE, CP and fiber but a poor source of Ca. / Master of Science

There are more than three thousand landfills in the United States, in which approximately 55% (1998, U. S. EPA 1999) of the MSW generated in the US is buried. The majority of the landfills are conventional, but in the last two decades new types of landfills, called leachate recycle and bioreactor landfills, have been designed and tested as an enhanced environment for biochemical degradation of municipal solid waste. All the landfills are regulated under Subtitle D of the Resource Conservation and Recovery Act (RCRA). The shortage of time and money has limited the amount of research done on waste stability analysis. The purpose of this study was to evaluate the importance of lignocelluloses in biodegradation and the secondary settlement based on dry density and typical landfill evaluating parameters. Both parts of the study samples were collected and analyzed from eleven landfills. In the first part of the study, bioreactor landfills were found more effective, faster in the degradation of VS and cellulose as compared to conventional landfills. The time required for stabilization is reduced to about 1/3 that of conventional landfills. The lignocelluloses degradation that occurs in these landfills is happening in two phases. In the initial, rapid degradation phase, the primary degradation substrate is cellulose. In the second phase, after cellulose degraded to 15-20% of the waste, degradation of the remaining cellulose along with lignin and the hemicelluloses takes place. The start of lignin and hemicellulose degradation results in an increase in the biochemical methane potential (BMP). In the second part of the study, the addition of moisture to the landfills presented a contentious issue. Moisture is encouraged for MSW refuse degradation, but for settlement it reduces compressibility. In leachate recycle landfills, the dry density is higher than in conventional landfills; therefore there is more available room for further MSW load. The increase can reach up to 40 percent in total volume. / Master of Science

Yes / In the current practice, at the end of life of a reinforced concrete struc-ture, it is destructively demolished, and the demolition waste is limited to downcycling and low-tech applications, while the remaining is being landfilled. A recent report showed that construction and demolition waste (CDW) is the big-gest waste stream in the EU by weight, accounting for over 800 million tons in 2018, i.e. around 32% of the total waste generated. This approach is clearly wasteful of energy, jeopardizing the health of individuals and environments and at high cost. However, design for deconstruction (DfD) of reinforced concrete structures would facilitate the future reuse of structural elements at the end of their life, potentially achieving a significant reduction in embodied energy of structures and CO2 emission as well as giving the owners the benefit of retaining the value of their assets. In this paper, recent research developments and practical applications of DfD of reinforced concrete structures are reviewed and key technical issues are dis-cussed. The focus is on connections that should be designed in such a way to al-low demounting of precast reinforced concrete structural elements, including beam/column, wall/wall, column/column and segmental slab connections. The main achievements and progress to date are outlined for each type of dry connec-tions, along with the aspects that still need to be developed. The paper concludes with an outline of challenges in the application of DfD in concrete structures. / This project was supported by the Newton Prize 2020, UK-Turkey award, grant ref number NP2020PB\100026, funded by the Department for Business, Energy & Industrial Strategy. It has also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100. / This paper is from the fib Symposium 2023, Building for the future: Durable, Sustainable, Resilient. 5-7 Jun, Istanbul, Turkey.

Yes / This paper presents an experimental investigation of a new dry connection for reinforced concrete slab elements. Seven full-scale slabs were tested; one slab was monolithic as control specimens, while the other six were assembled using top and bottom steel plates joined by high tensile steel bolts. Two scenarios were proposed for the connection, a simple bolted connection, and a connection with a shear key. The parameters studied were the use of stirrups at the connection section, the step size of the shear key as well as the bolt diameter and number. The test results showed that using a shear key at the assembled section in demountable slabs is more efficient than the simple bolted connection, providing higher flexural stiffness, load capacity, and less deflection. However, increasing the shear key step size improved the flexural performance of the demountable slabs. In addition, adding stirrups to the assembled section enhanced the flexural stiffness and the total load capacity of the demountable slabs. Furthermore, the predictions for the moment capacity and deflection demountable slabs have reasonably good agreement with the experimental results but require additional calibrated data from experiments to be generalized. / Department for Business, Energy and Industrial Strategy (BEIS)