1,556 research outputs found
Preliminary studies developing methods for the control of Chrysomya putoria, the African latrine fly, in pit latrines in The Gambia.
No full textOBJECTIVE: To explore ways of controlling Chrysomya putoria, the African latrine fly, in pit latrines. As pit latrines are a major source of these flies, eliminating these important breeding sites is likely to reduce village fly populations, and may reduce the spread of diarrhoeal pathogens. METHODS: We treated 24 latrines in a Gambian village: six each with (i) pyriproxyfen, an insect juvenile hormone mimic formulated as Sumilarv(®) 0.5 G, a 0.5% pyriproxyfen granule, (ii) expanded polystyrene beads (EPB), (iii) local soap or (iv) no treatment as controls. Flies were collected using exit traps placed over the drop holes, weekly for five weeks. In a separate study, we tested whether latrines also function as efficient flytraps using the faecal odours as attractants. We constructed six pit latrines each with a built-in flytrap and tested their catching efficiency compared to six fish-baited box traps positioned 10 m from the latrine. Focus group discussions conducted afterwards assessed the acceptability of the flytrap latrines. RESULTS: Numbers of emerging C. putoria were reduced by 96.0% (95% CIs: 94.5-97.2%) 4-5 weeks after treatment with pyriproxyfen; by 64.2% (95% CIs: 51.8-73.5%) after treatment with local soap; by 41.3% (95% CIs = 24.0-54.7%) after treatment with EPB 3-5 weeks after treatment. Flytraps placed on latrines collected C. putoria and were deemed acceptable to local communities. CONCLUSIONS: Sumilarv 0.5 G shows promise as a chemical control agent, whilst odour-baited latrine traps may prove a useful method of non-chemical fly control. Both methods warrant further development to reduce fly production from pit latrines. A combination of interventions may prove effective for the control of latrine flies and the diseases they transmit
Undrained stability of pit-in-pit braced excavations under hydraulic uplift
No full textPit-in-pit (PIP) excavations in an aquifer–aquitard system likely undergo catastrophic failures under the hydraulic uplift, the associated undrained stability problem, however, has not been well analyzed in the past. To this end, a hypothetical model of PIP braced excavation in typical soil layers of Shanghai, China is developed using the finite element limit analysis (FELA) tool. The FELA solutions of safety factors (FSs) against hydraulic uplift are verified with the results from the finite element analysis with strength reduction technique (SRFEA) and existing design approaches. Subsequently, FELA is employed to identify the triggering and failure mechanisms of PIP braced excavations subjected to hydraulic uplift. A series of parametric studies considering the various geometric configurations of the PIP excavation, undrained shear strengths of aquitard, and artesian pressures are carried out. The sensitivities of relevant design parameters are further assessed using a multivariate adaptive regression splines (MARS) model that is capable of accurately capturing the nonlinear relationships between a set of input variables and output variables in multi-dimensions. A MARS-based design equation used for predicting FS is finally presented using the artificial dataset from FELA for practical design uses.Geo-engineerin
Algorithms for Efficient Top-Down Join Enumeration
No full textFor a DBMS that provides support for a declarative query language like SQL, the query optimizer is a crucial piece of software. The declarative nature of a query allows it to be translated into many equivalent evaluation plans. The process of choosing a suitable plan from all alternatives is known as query optimization. The basis of this choice are a cost model and statistics over the data. Essential for the costs of a plan is the execution order of join operations in its operator tree, since the runtime of plans with different join orders can vary by several orders of magnitude. An exhaustive search for an optimal solution over all possible operator trees is computationally infeasible. To decrease complexity, the search space must be restricted. Therefore, a well-accepted heuristic is applied: All possible bushy join trees are considered, while cross products are excluded from the search.
There are two efficient approaches to identify the best plan: bottom-up and top-down join enumeration. But only the top-down approach allows for branch-and-bound pruning, which can improve compile time by several orders of magnitude, while still preserving optimality.
Hence, this thesis focuses on the top-down join enumeration. In the first part, we present two efficient graph-partitioning algorithms suitable for top-down join enumeration. However, as we will see, there are two severe limitations: The proposed algorithms can handle only (1) simple (binary) join predicates and (2) inner joins. Therefore, the second part adopts one of the proposed partitioning strategies to overcome those limitations. Furthermore, we propose a more generic partitioning framework that enables every graph-partitioning algorithm to handle join predicates involving more than two relations, and outer joins as well as other non-inner joins. As we will see, our framework is more efficient than the adopted graph-partitioning algorithm. The third part of this thesis discusses the two branch-and-bound pruning strategies that can be found in the literature. We present seven advancements to the combined strategy that improve pruning (1) in terms of effectiveness, (2) in terms of robustness and (3), most importantly, avoid the worst-case behavior otherwise observed.
Different experiments evaluate the performance improvements of our proposed methods. We use the TPC-H, TPC-DS and SQLite test suite benchmarks to evaluate our joined contributions
Modelling the Effects of Gate Pit-Stops on Apron Congestion
No full textDemand for air traffic is growing worldwide. In order to accommodate this growth, existing infrastructure such as gates should be used more efficiently. One technique to increase gate utilization is by introducing gate pit-stops. Introducing gate pit-stops leads to additional towing movements which can potentially interfere with other traffic on the apron. This in turn will lead to delays, which is undesirable. Currently, gate pit-stops are only performed for flights with a turnaround time of three hours or more. In order to investigate whether pit-stops can be effectively introduced on a broader scale, a model has been created that simulates gate assignments and apron movements. This model provides insight in the effect of gate pit-stops on gate utilization and apron congestion for different airport scenarios. Results show that introducing pit-stops for flights with a turnaround time of less than 180 minutes leads to an increase in flights that can be handled at a gate instead of a remote stand, at a small delay penalty. Airlines and airports can benefit from these findings as they will be able to handle more flights at a gate using existing infrastructure.Aerospace Engineerin
Homoplastic occurrence of perforated pit membranes and torus-bearing pit membranes in ancestral angiosperms as observed by field-emission scanning electron microscopy
No full textRecent studies demonstrated that perforated pit membranes (i.e., pit membranes with a large opening in their central portion) are commonly present between wood fibers in core eudicots. It is unclear whether this type of pit membranes might also occur in ancestral angiosperms. Therefore, structure of interfiber pit membranes was examined by field-emission scanning electron microscopy in nine species representing seven families that are located at more ancestral position than core eudicots. We found perforated pit membranes in three of the nine species. Our observations indicate that perforated pit membranes are relatively common even in ancestral groups of angiosperms. In the non-perforated pit membranes of the other six species, we found a range of structural variations. Thin-walled pit membranes without apparent intercellular layers were always found in three of the six species and the porosity of sheet-like pit membranes differed among the three species. Unlike the thin-walled pit membranes, interfiber pit membranes of Buxus microphylla var. japonica were thick-walled with obvious intercellular layers, and in Schisandra chinensis, we often observed torus-bearing pit membranes. Such variations in layered structure of pit membranes and homoplastic occurrence of torus-bearing pit membranes have not yet been reported for ancestral angiosperms. Our observations indicate that the structure of interfiber pit membranes might be more complicated than previous studies might suggest
Water and chemical budgets of gravel pit lakes: Case studies of fluvial gravel pit lakes along the Meuse River (The Netherlands) and coastal gravel pit lakes along the Adriatic Sea (Ravenna, Italy)
No full textGravel pit lakes form when gravel is excavated from below the water table of a phreatic or shallow confined aquifer. Typically many of these lakes are concentrated along naturally occurring sedimentary gravel deposits in areas where gravel is needed for construction. Most gravel pit lakes are relatively young features: most are less than 50 years old. The subject of this PhD thesis is to determine how gravel pit lakes change the hydrology and hydrochemistry of an aquifer, a watershed or a drainage basin. Hereto I studied gravel pit lakes in a fluvial freshwater setting of the Meuse Valley (the Netherlands) and gravel pit lakes excavated in ancient beach deposits, filled with brackish water along in the Adriatic coastal zone near Ravenna (Italy). One of the Dutch lakes is used for artificial recharge and drinking water production (DLV Lake) while some other gravel pit lakes are used for recreational purposes (swimming, sailing, scuba diving). The surface water of the lakes and other surface waters (wetlands, rivers) as well as groundwater up and downstream of the lakes was sampled and analyzed for major ion chemistry, trace elements and stable water isotopes. Chemical and water budgets were calculated. The excavation of many gravel pit lakes adds a large surface water area to a watershed. In the Dutch study site 71 lakes between the towns of Maastricht and Asselt add 20 km2 of surface water which is 0.26 % percent of the Dutch part of the Meuse watershed. In the Italian drainage basin thirteen lakes with a total surface of 684 hectares cover 6.6% % of the drainage basin. This increase causes a loss of freshwater since surface water evaporation rates in temperate and Mediterranean climates are usually higher than evapotranspiration rates of the pre-existing grassland and forest. The drainage pattern of a watershed changes in presence of gravel pit lakes causing fluctuations of the water table over a large area. In a low lying coastal zone, as the Italian study area, these fluctuations and the fact that the lakes form a constant head surface below sea level enhance salt water intrusion into the aquifer. Gravel pit lakes can be flow-through lakes where groundwater moves through the lake downstream towards a river or other draining feature (for instance a well field) or, alternatively, they may be in direct connection with a river. The gravel pit lakes that I studied in detail have in common that the water budget of the lakes is strongly determined by artificial drainage. In the Dutch DLV Lake, the artificial drainage is caused by pumping wells that extract water for drinking water production downstream of the lake. In the Italian case, the artificial drainage is induced by the land reclamation works that protect the low-lying land from flooding. Watersheds with multiple gravel pit lakes are more sensitive to changes in climate than watersheds without gravel pit lakes because surface water evaporation rates are more sensitive to changes in climate than evapotranspiration. Especially in groundwater fed gravel pit lakes, evaporated water is replaced by groundwater. Instead evapotranspiration of soil moisture in a watershed without gravel pit lakes, can increase only to certain extend as soil moisture is only fed by precipitation and not by groundwater flow. Water budget and conservative tracer modeling showed that because artificial drainage plays such a large role that changes in pumping rates needed to prevent flooding due to higher sea levels (The Italian study site) will affect evapo-concentration more than changes in surface water evaporation caused by climate change. Precipitation on the Italian gravel pit lakes is immediately mixed with brackish gravel pit lake water and can no longer recharge the fresh-brackish rainwater lenses in the upper part of the aquifer. Both the Dutch and the Italian gravel pit lake water has a high alkalinity, a high pH, and metal and trace element concentrations that differ from the groundwater in their respective watersheds. Differences do exist among the specific trace element concentrations, and their budgets in the lakes and the respective watersheds. This stems from the influence of sea water in the Italian case study and the specific soil chemistry of both settings. As and Ba, for example, show up in high concentrations in groundwater and gravel pit lake water in Italy but not in the Netherlands, where Ni, Zn and Al are more important. Differences in chemistry (Fe, SO4, HCO3, Ni etc. and pH) between gravel pit lake water and groundwater and variations along flow lines show that redox reactions in the soil near the gravel pit lakes occurred in both study sites. These reactions, enhanced by fluctuating water tables and/or denitrification of fertilized soils, have mobilized metals including Fe, Zn, and Ni and other elements such as Al and As. In part, these elements have been adsorbed again by the soil, as is the case for As in the Dutch site, in part they reach the gravel pit lakes where they precipitate on the lake bottom (for example, Fe, Zn, Ni, Al) and some elements remain (partly) in solution in the gravel pit lake water (e.g. As in the Italian lakes). The gravel pit lakes are strongly influenced by the land use and climate of their watershed. If circumstances change that would lead to less available oxygen either as DO or in NO3 or that would lead to a lower pH of the lake water, then the reactions that initially caused the deposition of the metals and trace elements on the lake bottom may be reversed. Metals and trace elements could go again into solution, possibly creating a toxic environment for plants, animals, and humans. These changes may be brought about by a change in land use, for example a reduction in the use of fertilizers, or a change in climate (less recharge of the aquifer), or slow leaching processes such as decalcification of the soil. On the other hand, an increasing eutrophication and primary production stimulated by high temperatures or less lake water circulation, would cause an increase in organic and fine grained material deposition to the lake bottom, which would help to fix the metals and trace elements in the lake bottom sediments. The rate of these processes may change over time since gravel pit lakes have formed only recently while land use and climate change play a role in their current and future evolution. The fixation of metals, C, nutrients and other elements in gravel pit lakes changes also the hydrochemistry of the estuary downstream of the lakes by preventing discharge of dissolved chemical elements into rivers and the sea. In order to assess and evaluate a watershed with gravel pit lakes for its safe use, it is necessary to monitor not only the lake water but also the groundwater, the water budget and the evolution of hydrochemical processes as climate and land use change.Department of Geoscience and EngineeringCivil Engineering and Geoscience
Development and Field Analysis of a Novel Servo Concrete Bracing System for Deep Foundation Pit Excavation
No full textThis study demonstrates the design and field implementation of an innovative servo concrete bracing system in foundation pit excavation. The bracing system comprises concrete struts, revised purlins, and hydraulic jacks, and its field performance is evaluated in a deep foundation pit project in Shanghai, China. The field measurements demonstrate that the servo bracing system effectively reduces the maximum lateral displacement of the retaining wall by up to 31%. Moreover, the servo jacks modify the wall’s flexural behavior by introducing local inflection points at certain depths and driving the displacement peak upward. Furthermore, the system’s performance varies with strut configuration, and servo forces influence not only the corresponding acting strut but also the adjacent struts’ behavior, implying that the monitoring scope should be expanded when applying the servo bracing system in actual engineering. This study provides a meaningful technical reference for future servo concrete bracing system applications in foundation pit engineering.Geo-engineerin
Perception of American Pit Bull Terriers
No full textabstract: Behavior traits were examined in an observed experiment with the presentation of an American Pit Bull Terrier. The experiment was conducted at two locations (Wal Mart, Pet Smart) with searching for behavior traits (positive, negative) with an American Pit Bull Terrier present. In contrast to the hypothesis, there was more positive behavior traits than negative behavior traits. Together, these findings suggest that the presentation of an American Pit Bull Terrier has a more positive outlook on the breed rather than negative. Similar studies should be conducted to change the legislation in regard of "Pit Bulls" that cause discrimination against the breed
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