During the past decade, there has been a dramatic increase by postsecondary institutions in providing academic programs and course offerings in a multitude of formats and venues (Biemiller, 2009; Kucsera & Zimmaro, 2010; Lang, 2009; Mangan, 2008). Strategies pertaining to reapportionment of course-delivery seat time have been a major facet of these institutional initiatives; most notably, within many open-door 2-year colleges. Often, these enrollment-management decisions are driven by the desire to increase market-share, optimize the usage of finite facility capacity, and contain costs, especially during these economically turbulent times. So, while enrollments have surged to the point where nearly one in three 18-to-24 year-old U.S. undergraduates are community college students (Pew Research Center, 2009), graduation rates, on average, still remain distressingly low (Complete College America, 2011). Among the learning-theory constructs related to seat-time reapportionment efforts is the cognitive phenomenon commonly referred to as the spacing effect, the degree to which learning is enhanced by a series of shorter, separated sessions as opposed to fewer, more massed episodes. This ex post facto study explored whether seat time in a postsecondary developmental-level algebra course is significantly related to: course success; course-enrollment persistence; and, longitudinally, the time to successfully complete a general-education-level mathematics course. Hierarchical logistic regression and discrete-time survival analysis were used to perform a multi-level, multivariable analysis of a student cohort (N = 3,284) enrolled at a large, multi-campus, urban community college. The subjects were retrospectively tracked over a 2-year longitudinal period. The study found that students in long seat-time classes tended to withdraw earlier and more often than did their peers in short seat-time classes (p < .05). Additionally, a model comprised of nine statistically significant covariates (all with p-values less than .01) was constructed. However, no longitudinal seat-time group differences were detected nor was there sufficient statistical evidence to conclude that seat time was predictive of developmental-level course success. A principal aim of this study was to demonstrate—to educational leaders, researchers, and institutional-research/business-intelligence professionals—the advantages and computational practicability of survival analysis, an underused but more powerful way to investigate changes in students over time.

Orientador: Carlos Antonio Gamero / Banca: Silvio José Bicudo / Banca: Dirceu Maximino Fernandes / Banca: Antonio Renan Berchol da Silva / Banca: Carlos Eduardo Amgeli Furlani / Resumo: Cada sistema de manejo do solo é trabalhado de maneira própria, alterando de forma diferenciada as propriedades químicas, físicas e biológicas do solo, podendo requerer modificações nas recomendações e no manejo da adubação. Com o objetivo de avaliar o efeito da antecipação da adubação de semeadura, de dois sistemas de manejo do solo e dois espaçamentos entrelinhas no desempenho da cultura do milho, foi realizado este estudo. O experimento foi instalado e conduzido na Fazenda Experimental Lageado, pertencente à Faculdade de Ciências Agronômicas (FCA) da Universidade Estadual Paulista (UNESP), Campus de Botucatu, nos anos agrícolas de 2005/2006 e 2006/2007, em Nitossolo Vermelho Distroférrico. O delineamento experimental utilizado foi de blocos ao acaso com parcelas subsubdivididas e quatro repetições. As parcelas foram constituídas pelos sistemas de manejo do solo (plantio direto e preparo reduzido, caracterizado pela escarificação do solo por meio de equipamento provido de disco de corte da palhada e rolo nivelador/destorroador, trabalhando na profundidade entre 25 e 30 cm), as subparcelas pelas formas de adubação (adubação de pré-semeadura realizada na superfície do solo em área total antes da semeadura do milho e adubação convencional) e as subsubparcelas pelos espaçamentos entrelinhas (90 e 45 cm), totalizando 8 tratamentos. Os resultados obtidos foram submetidos ao teste de Tukey a 5% de probabilidade para comparar as médias entre os sistemas de manejo do solo, as formas de adubação, os espaçamentos entrelinhas e os desdobramentos das interações entre esses três fatores. As análises estatísticas demonstraram que o sistema plantio direto apresentou maior densidade do solo e resistência mecânica do solo à penetração, quando comparado ao preparo reduzido. Na operação de adubação de pré-semeadura os sistemas de manejo do solo... (resumo completo, clicar acesso eletrônico abaixo) / Abstract: Each soil tillage system is worked in proper way, modifying of differentiated form the chemical, physical and biological soil properties, and may require adaptations of fertilization recommendations and management. This study was conducted to evaluate the effect of sowing fertilization anticipation, two soil tillage systems and two row spacing on performance of the corn crop. The experiment was carried out at the "Faculdade de Ciências Agronômicas" (FCA), "Universidade Estadual Paulista" (UNESP), Botucatu-SP campus, from October 2005 to May 2007, in a Dystric Nitosol (FAO, 1974). The experimental design was in randomized blocks with split-split-plots and four repetitions. The main plots consisted of two soil tillage systems (no-tillage and reduced tillage with chisel plow with cut disk and planning roll, working at 25 to 30 cm deep), the split-plots of fertilizer application methods (surface fertilizer application before corn sowing and fertilizer application conventional) and split-split-plots of row spacings (0.90 m and 0.45 m), totalizing 8 treatments. Obtained results were analyzed by Tukey test at 5% of probability for comparing averages. Statistical analysis showed that no-tillage system had higher density as well as mechanical soil resistance to penetration, when compared to reduced tillage. For fertilizer application before corn sowing the soil tillage systems did not influence the traction force, bar power demanded, effective field capacity, demanded time, energy specific consumption and hourly fuel consumption; the reduced tillage showed higher area fuel consumption. For corn sowing it was observed that no-tillage system showed lower traction force, bar power demanded, energy specific consumption, hourly and area consumption of fuel. The 0.45 m row spacing showed higher traction force, bar power demanded, energy specific consumption... (Complete abstract click electronic access below) / Doutor

No description available.

A series of field, rainshelter, growth cabinet and modelling studies were conducted to investigate hot pepper response to different irrigation regimes and row spacings; to generate crop-specific model parameters; and to calibrate and validate the Soil Water Balance (SWB) model. Soil, climate and management data of five hot pepper growing regions of Ethiopia were identified to develop irrigation calendars and estimate water requirements of hot pepper under different growing conditions. High irrigation regimes increased fresh and dry fruit yield, fruit number, harvest index and top dry matter production. Yield loss could be prevented by irrigating at 20-25% depletion of plant available water, confirming the sensitivity of the crop to mild soil water stress. High plant density markedly increased fresh and dry fruit yield, water-use efficiency and dry matter production. Average fruit mass, succulence and specific leaf area were neither affected by row spacing nor by irrigation regimes. There were marked differences among the cultivars in fruit yields despite comparable top dry mass production. Average dry fruit mass, fruit number per plant and succulence were significantly affected by cultivar differences. The absence of interaction effects among cultivar and irrigation regimes, cultivars and row spacing, and irrigation regimes and row spacing for most parameters suggest that appropriate irrigation regimes and row spacing that maximize productivity of hot pepper can be devised across cultivars. To facilitate irrigation scheduling, a simple canopy cover based procedure was used to determine FAO-type crop factors and growth periods for different growth stages of five hot pepper cultivars. Growth analysis was done to calculate crop-specific model parameters for the SWB model and the model was successfully calibrated and validated for five hot pepper cultivars under different irrigation regimes or row spacings. FAO basal crop coefficients (Kcb) and crop-specific model parameters for new hot pepper cultivars can now be estimated from the database, using canopy characteristics, day degrees to maturity and dry matter production. Growth cabinet studies were used to determine cardinal temperatures, namely the base, optimum and cut-off temperatures for various developmental stages. Hot pepper cultivars were observed to require different cardinal temperatures for various developmental stages. Data on thermal time requirement for flowering and maturity between plants in growth cabinet and open field experiments matched closely. Simulated water requirements for hot pepper cultivar Mareko Fana production ranged between 517 mm at Melkassa and 775 mm at Alemaya. The simulated irrigation interval ranged between 9 days at Alemaya and 6 days at Bako, and the average irrigation amount per irrigation ranged between 27.9 mm at Bako and 35.0 mm at Zeway. / Thesis (PhD)--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

Das Befahren mit schweren Maschinen verursacht Bodenstrukturveränderungen, weshalb im Rahmen des forstlichen Bodenschutzes eine Funktionalisierung des Waldbodens vorgenommen und das Fahren auf Rückegassen konzentriert wird, die in unterschiedlichen Abständen angelegt werden können. Die ökonomischen Auswirkungen der Rückegassen beziehungsweise deren Abstände zueinander sind bisher wenig untersucht. Der Erhalt der Befahrbarkeit steht im Mittelpunkt forsttechnischer Betrachtungen. So steht eine Vielzahl von verschiedenen Maßnahmen zur Verfügung, um einen drohenden Verlust abzuwehren. Ist die forsttechnische Befahrbarkeit erst einmal verloren, kann sie nur durch langwierige bodenbiologische und -physikalische Prozesse wiederhergestellt werden. Kurzfristig ist sie nur durch die Befestigung der Rückegasse mit Wegebaumaterial wiederherzustellen. Die vorliegende Arbeit ermöglicht die ökonomische Abbildung von verschiedenen Effekten der Befahrung: Neben Kosten, die im Zusammenhang mit dem Erhalt oder der Wiederherstellung der technischen Befahrbarkeit auftreten, sind auch die Wirkungen auf die ertragskundliche Leistung des Bestandes sowie auf die Qualität zukünftig zu erntender Bäume abbildbar. Hierzu dient das Faustmann-Modell als forstökonomisches Handlungskalkül. Mit Hilfe einer numerischen Simulation der ertragskundlichen Datenbasis zur Berechnung der Holzerlösströme sowie der Kalkulation der forsttechnischen System- und Verfahrenskosten können Rentabilitätsunterschiede durch die Anwendung unterschiedlicher Feinerschließungssysteme ermittelt werden. Ferner wird das Modell um weitere Effekte der Befahrung erweitert, um die Auswirkungen auf die Rentabilität mittels Sensitivitätsanalyse zu untersuchen. Monetär nur schwer zu quantifizierende Effekte werden durch die Darstellung der Opportunitätskosten in die Betrachtungen einbezogen. Um den Einfluss der Zinskosten darzustellen, werden drei verschiedene Zinssätze unterstellt. Der Rentabilitätsnachteil durch Vergrößerung des Rückegassenabstandes von 20 auf 40 m beträgt je nach unterstellten Kalkulationszinssatz zwischen 7 und 14% der Rentabilität des Standardverfahren mit 20 m-Gassen. Der Nachteil durch die Anwendung von Seilkranverfahren beträgt zwischen 36 und 79%. Der Nachteil alternativer Verfahren steigt mit zunehmenden Zinssatz umso stärker, je mehr Begründungskosten im Modell berücksichtigt werden müssen. Unterstellt man den Verlust der biologischen Produktionsfunktion im Umfang der Flächeninanspruchnahme durch die Rückegassen, kommt es zur Umkehr der Optimalität Gassen im Abstand von 40 m und die darauf zur Anwendung kommenden Verfahren sind dann überlegen. Die Holzentwertungen wirken stärker auf die Rentabilität als die Volumenminderung. Der beobachtete Effekt wirkt umso stärker, je ungünstiger das Kosten-Erlös-Verhältnis ist. So konnte für das numerische Beispiel errechnet werden, dass ein Volumenunterschied zwischen den verschiedenen Feinerschließungssystemen von 7 bis 10% (je nach Zinssatz) notwendig ist, um Rentabilitätsgleichheit herzustellen. Gleiche Wirkung ist durch den Unterschied des mittleren Holzpreises von 5 bis 6% erreichbar. Bei beiden Effekten führt ein geringer Zinssatz eher zu einer Umkehr des Optimums, wenngleich die Wirkung bei der Holzentwertung deutlich kleiner ist. Für die Effekte auf die Volumen- beziehungsweise Wertleistung der Waldbestände durch größere Gassenzwischenbereiche und dadurch gesteigerter waldbaulicher Handlungsfreiheit gelten gleiche Zusammenhänge. Schäden an der forsttechnischen Befahrbarkeit wirken ebenfalls auf die Rentabilität der Waldbewirtschaftung. Durch die Einführung der Schadensarten „streckenproportional“ und „massenproportional“ sowie der Größe des Schadausmaßes und der Unterscheidung nach Schadschwere können die Effekte der Befahrung auf die forsttechnische Befahrbarkeit in ihren Wirkungen differenziert und Schlussfolgerungen für die Praxis abgeleitet werden. So führt der Ausbau von 38-44% der Rückegasse (im 20 m-System) auf Grund schwerer streckenproportionaler Schäden beziehungsweise von 69-72% der Rückegasse (im 20 m-System) auf Grund schwerer massenproportionaler Schäden sowie eine vollständige mittelschwere Schädigung, die ein Einebnen der Fahrspuren notwendig macht, zur Optimalität der 40 m-Rückegassenerschließung. Grundsätzlich gilt, dass der Rentabilitätsnachteil des 40 m-Gassensystems umso geringer wird, je teurer die Maßnahme und je größer der Zinssatz ist. Hingegen sollten 40 m-Seiltrassen nur auf solchen Standorten zur Anwendung kommen, die keine Befahrung zulassen. Die Ergebnisse können für eine Sanierung, die aus waldästhetischen beziehungsweise aus sonstigen gesellschaftlichen Erwägungen vollzogen wird, entsprechend übertragen werden. Die ökonomischen Effekte auf Grund von Schäden am Erschließungssystem sind mit solchen, die auf die Qualität oder das Volumen des Holzes wirken, beliebig kombinierbar. Eine eigens entwickelte Optimalitätsregel hilft bei der Wahl des effizienteren Gassenabstandes. Die Opportunitätskosten für den Bodenschutz – durch Reduzierung der Fläche die primär der Befahrung dient – von 20 auf 10% beziehungsweise für die Erhöhung der waldbaulichen Handlungsfreiheit durch die Verbreiterung der „Behandlungsblöcke“ betragen je nach Zinssatz zwischen 31 und 17 Euro pro Jahr und Hektar. Eine Reduzierung der Flächeninanspruchnahme von 20 auf 0% – durch die Anwendung von Seilkranverfahren – verursacht Opportunitätskosten in Höhe von 95 bis 165 Euro pro Jahr und Hektar. Ein zusätzlicher Gewinn an waldbaulicher Handlungsfreiheit entsteht dadurch nicht. Somit sind Verfahren mit Rückegassen im Abstand von 40 m hinsichtlich des Bodenschutzes und der waldbaulichen Handlungsfreiheit effizienter als Seilkranverfahren. Der forstlichen Praxis kann abschließend empfohlen werden, folgende fünf Rahmenbedingungen stets im Blick zu haben, um optimale Holzernteverfahren bestimmen zu können: die Begründungskosten, die Holzerlöse und -erntekosten, die Sanierungskosten sowie den Zinssatz.

No description available.

The acoustic emissions from supersonic jets represent an area of significant research needs; not only in the field of aero-acoustics, but in industry as well where high pressure let down processes have been known to cause acoustically induced vibrations. A common method to reduce the acoustic emissions of such processes involves dividing the single larger supersonic flow into several smaller ones. Though this is common practice, there is not yet a current model which describes the reduction of acoustic emissions from an array of smaller supersonic jets. Current research which studies supersonic jet arrays are mainly focused on the effects of screech. Though screech is important, due to its high amplitude acoustic pressure, this research focuses on the overall acoustic emissions radiated from supersonic jet arrays which can cause severe acoustic loadings. This research investigated the acoustic emissions and shock formations from several eight by eight arrays of axisymmetric jet experimentally. The array nozzle diameters investigated ranged from 1/8 inch to 1/4 inch and the spacing over diameter ratio ranged from 1.44 to 3. The net pressure ratios investigated ranged from 2 to 24. Results revealed a strong correlation between the acoustic emissions and the shock formations of the flow. Up until a critical net pressure ratio, the overall sound pressure levels were comparable to that of a single jet within an array. At net pressure ratios beyond the critical the overall sound pressure levels transitioned to higher decibel levels; equivalent to a single jet with an equivalent exit area of an entire array. Also, the characteristic acoustic frequency emitted from a nozzle array remained ultrasonic (above 20 kHz) at lower net pressure ratios and then shifted to audible levels (between 20 Hz to 20 kHz) at net pressure ratios beyond the critical. Also, before the critical net pressure ratio the shock cells from the jets within the array remained unmerged, but at net pressure ratios beyond the critical the shock cells merged and formed lattices of weak oblique shocks at first and then strong oblique shocks as the net pressure ratio continued to increase. The critical net pressure ratio was investigated by non-dimensional analysis. The non-dimensional analysis revealed that the critical net pressure ratio was a strong linear function of the spacing over diameter ratio. A linear model was derived which is able to predict the critical net pressure ratio, and in turn, predict a critical shift in the acoustic emissions of a nozzle array.

This study examined winter habitat use and nesting ecology of greater sage grouse (Centrocercus urophasianus) in Strawberry Valley (SV), Utah located in the north-central part of the state. We monitored sage grouse with the aid of radio telemetry throughout the year, but specifically used information from the winter and nesting periods for this study. Our study provided evidence that sage grouse show fidelity to nesting areas in subsequent years regardless of nest success. We found only 57% of our nests located within the 3 km distance from an active lek typically used to delineate critical nesting habitat. We suggest a more conservative distance of 10 km for our study area. Whenever possible, we urge consideration of nest-area fidelity in conservation planning across the range of greater sage grouse. We also evaluated winter-habitat selection at multiple spatial scales. Sage grouse in our study area selected gradual slopes with high amounts of sagebrush exposed above the snow. We produced a map that identified suitable winter habitat for sage grouse in our study area. This map highlighted core areas that should be conserved and will provide a basis for management decisions affecting Strawberry Valley, Utah.

In wireless communications, employing pilot symbols enables to estimate the state of the wireless channel at the expense of decreasing the number of symbols available for transmitting data. Addressing this trade-off is particularly challenging when the channel changes rapidly over time, since channel estimates become obsolete over short transmission periods. This master thesis proposes an analytical model to characterize this trade-off and develops an algorithm to find the near-optimal pilot spacing in terms of the achieved over spectral efficiency. This algorithm is simulated in a cellular system that serves uncrewed aerial vehicles. Numerical results indicate that the altitude of the uncrewed aerial vehicle, the Rician factor, the Doppler frequency, and the number of receive antennas influence the overall spectral efficiency and consequently, pilot spacing should take into account these system parameters. / I trådlös kommunikation möjliggör användning av pilotsymboler att uppskatta tillståndet för den trådlösa kanalen på bekostnad av att minska antalet tillgängliga symboler för att överföra data. Att ta itu med denna avvägning är särskilt utmanande när kanalen ändras snabbt över tiden, eftersom kanaluppskattningar blir föråldrade under korta överföringsperioder. Denna masteruppsats föreslår en analytisk modell för att karakterisera denna avvägning och utvecklar en algoritm för att hitta det närmast optimala pilotavståndet i termer av uppnådd över spektral effektivitet. Denna algoritm simuleras i ett cellulärt system som betjänar obemannade flygfarkoster. Numeriska resultat indikerar att höjden för det obemannade luftfartyget, Rician-faktorn, Dopplerfrekvensen, antalet mottagarantenner påverkar den totala spektrala effektiviteten och följaktligen bör pilotavståndet ta hänsyn till dessa systemparametrar.

The present thesis evaluates numerically and experimentally if the axial capacity of Auger Cast Piles (ACPs) constructed in interbedded layers of granular soil and Limestone should be reduced as a function of pile spacing. The numerical component of this thesis includes a series of parametric studies that consider different sets of normalized spacings, stiffness ratios, relative densities, unconfined compressive strengths, and installation effects for multiple subsurface conditions. The experimental program designed herein involves the construction of multiple components for a laboratory testing program of small-scale physical models that will validate the results of the numerical models in terms of capacities, efficiency ratios and normalized spacings.