• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 44
  • 18
  • 15
  • 9
  • 8
  • 8
  • 4
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 138
  • 20
  • 15
  • 14
  • 13
  • 12
  • 11
  • 11
  • 10
  • 10
  • 10
  • 9
  • 9
  • 9
  • 9
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Latitudinal Gradients in Body Size in Marine Tardigrades

Bartels, Paul J., Fontaneto, Diego, Roszkowska, Milena, Nelson, Diane R., Kaczmarek, Łukasz 16 March 2020 (has links)
Homeotherms and many poikilotherms display a positive relationship between body size and latitude, but this has rarely been investigated in microscopic animals. We analysed all published records of marine Tardigrada to address whether microscopic marine invertebrates have similar ecogeographical patterns to macroscopic animals. The data were analysed using spatially explicit generalized least squares models and linear models. We looked for latitudinal patterns in body size and species richness, testing for sampling bias and phylogenetic constraints. No latitudinal pattern was detected for species richness, and sampling bias was the strongest correlate of species richness. A hump-shaped increase in median body size with latitude was found, and the effect remained significant for the Northern Hemisphere but not for the Southern. The most significant effect supporting the latitudinal gradient was on minimum body size, with smaller species disappearing at higher latitudes. Our results suggest that biogeographical signals were observed for body size, albeit difficult to detect in poorly studied groups because of swamping from biased sampling effort and from low sample size. We did not find a significant correlation with the latitudinal pattern of body size and ecologically relevant net primary productivity.
92

HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds

Malhotra, Garima 15 June 2016 (has links)
The equatorial Quasi Biennial Oscillation (QBO) is known to be an important source of inter-annual variability at mid and high latitudes in both hemispheres. Coupling between QBO and the polar vortex has been extensively studied over the past few decades, however, less is known about QBO influences in the mid-latitude mesosphere. One reason for this is the relative lack of instrumentation available to study mesospheric dynamics at mid-latitudes. In this study, we have used the mid-latitude SuperDARN HF radar at Saskatoon (52.16 N, -106.53 E) to study inter-annual variation in mesospheric winds. The specific aim was to determine whether or not a Quasi Biennial signature could be identified in the Saskatoon mesosphere, and if so, to understand its relationship with the equatorial stratospheric QBO. To achieve this goal, a technique has been developed which extracts meteor echoes from SuperDARN near-range gates and then applies least-squares fitting across all radar beam directions to calculate hourly averages of the zonal and meridional components of the mesospheric neutral wind. Subsequent analysis of 13 years (2002-2014) of zonal wind data produced using this technique indicates that there is indeed a significant QBO signature present in Saskatoon mesospheric winds during late winter (Jan-Feb). This mesospheric QBO signature is in opposite phase with the equatorial stratospheric QBO, such that when QBO (at 50 hPa) is in its easterly (westerly) phase, the late winter winds in Saskatoon mesosphere become more (less) westerly. To further examine the source of the signature, we also analyzed winds in the Saskatoon stratosphere between 5 hPa and 70 hPa using the ECMWF ERA-Interim reanalysis data set, and found that the late winter stratospheric winds become less (more) westerly when QBO is easterly (westerly). This QBO signature in the mid-latitude stratospheric winds is essentially the same as that observed for the polar vortex in previous studies but it is opposite in phase to the mid-latitude mesospheric QBO. We therefore conclude that filtering of gravity waves through QBO-modulated stratospheric winds plays a major role in generating the mesospheric QBO signature we have identified in the Saskatoon HF radar data. When the Saskatoon stratospheric winds are anomalously westward during easterly QBO, the gravity waves having westward momentum might be filtered out, depositing a net eastward momentum in the mesosphere as they propagate upwards. This would result in increased westerly mesospheric winds at Saskatoon. The opposite would happen when the equatorial QBO is westerly. / Master of Science
93

High-latitude sedimentation in response to climate variability during the Cenozoic

Varela Valenzuela, Natalia Ines 03 January 2024 (has links)
Here we investigate sedimentological responses to past climate change in shallow to deep marine depositional environments. Our primary study spans from the Late Pliocene to the Pleistocene (3.3 to 0.7 Ma), and features results from two International Ocean Discovery Program (IODP) Sites U1525 and U1524. Each of these sites is discussed in separate chapters here (Chapters 1 and 2). This interval experienced the change from the warming of the Late Pliocene, known as the Mid-Piacenzian Warming Period, to the Pleistocene cooling. This shift significantly impacted the expansion of the West Antarctic Ice Sheet, sea ice/polynya formation, and, notably, the genesis of Antarctic Bottom Water (AABW), a crucial component of the global thermohaline circulation. In Chapter 1, we propose that turbidite currents, arising from the formation of dense shelf water (DSW) in the Ross Sea (a precursor to AABW), leave a distinct record in the levees of Hillary Canyon. This canyon acts as a conduit, channeling DSW into the deep ocean and contributing to AABW production. By analyzing turbidite beds based on their frequency, thickness, and grain size, we gain insights into the historical occurrence and magnitude of these currents. Furthermore, we explore the influence of factors such as shelf availability and sea ice/polynya formation within the broader climate context of AABW formation. Chapter 2 shifts its focus to the sedimentological variability from shelf-to-slope along Hillary Canyon. This chapter examines the turbidite record associated with AABW formation within the shared timeframe (2.1 to 0.7 million years ago) between IODP Sites U1524 and U1525, and the impact of along slope currents and other processes in the sedimentary deposition and transport. The second study interval (Chapter 3), focuses on the regional sedimentological response proximal to a hydrothermal vent complex associated with the Paleocene-Eocene Thermal Maximum (PETM; ca. 56 Ma), a global warming event during which thousands of Gt C was released into the ocean-atmosphere on Kyr timescales. IODP Site U1568, strategically located near the hydrothermal vent complex and part of a broader drilling transect in the Modgunn Arch, North Atlantic, is the main study subject. This site's proximity to the vent complex offers a distinctive environment for refining our understanding of stratigraphy and sedimentology within the PETM. We achieve this through a comprehensive analysis of grain size and composition, coupled with a comparison to XRF data. Our findings show that the timing between the onset of the PETM and the response of the sedimentary system to the warming, reflected in the grain size coarsening after the start of the PETM, is not synchronous. Notably, the transition from a marine to a more terrestrial composition predates this shift in grain size, aligning with the PETM onset instead. / Doctor of Philosophy / Deep-marine core records are invaluable sources of sedimentological information that provide insights into the ocean's response to past climates. These cores, extracted from the deep-ocean floor, contain layers of sediment that accumulate over time because of the different processes that occur in the ocean. Analyzing these sediments, by looking at their physical characteristics like how frequently are they deposited, the thickness of the layers, their grain size, and their composition helps to reconstruct past environmental conditions and understand how the oceans have responded to climatic changes. This dissertation focuses on studying the record of two main processes. The first one is the sedimentary record left behind by the formation of Antarctic Bottom Water (AABW), one of the coldest (-1°C), deepest (> 2000 meters below sea level), and densest water masses in the ocean. AABW is a key component of the global ocean circulation system, often referred to as the "global conveyor belt" or the thermohaline circulation. This circulation pattern plays a crucial role in redistributing heat, salt, and nutrients around the world's oceans. AABW is formed near Antarctica through a process that begins with the cooling and sinking of surface waters near the continent. As these waters sink, they become denser and eventually form AABW, filling the deep ocean basins around Antarctica. The dense water flows from the surface to the bottom of the ocean forming turbidity currents. These turbidity currents, dense plumes of water and sediments, flow down submarine conduits, such as Hillary Canyon in the Ross Sea, Antarctica, leaving a sedimentary record in the levees or flanks, called turbidites. The turbidite sequences in sediment cores can reveal information about the frequency and magnitude of these currents, providing insights into the sediment transport processes in deep-marine settings, and for this work, the history of the AABW formation over the last 3.3 Ma. This study will help to understand what are the main controls for AABW formation across different climates in the past, and how we project this into the future climate scenarios. In the second part of the study (Chapter 3), we look at the sedimentary record of a warming event that happened around 56 million years ago. This event, known as the Paleocene-Eocene Thermal Maximum (PETM), involved a significant amount of carbon being released into the air and oceans over thousands of years (150,000 to 200,000). Our focus is IODP Site U1568, located near a submarine hydrothermal vent, and part of a larger drilling transect in the North Atlantic's Modgunn Arch. The vent's unique location provides a crucial perspective for understanding how the system responded to the warming during the Paleocene-Eocene Thermal Maximum (PETM). This warming event was triggered by the release of carbon into the atmosphere, with the vent serving as one of the conduits for this release. To understand this, we studied the grain size and content of the sediment, and compared that with XRF data. Changes in grain size serve as indicators of shifts in the energy of the environment – coarser grains signify a more energetic system. Warmer weather, for instance, can increase precipitation, leading to more erosion and sediment influx into the basin. This influx also brings in more materials from the land, as evidenced by the presence of microfossils and plant fragments. Our discoveries indicate that the sedimentary system responded gradually to the PETM, as reflected in the coarsening of grain size after the PETM's onset. Notably, the transition from a marine to a more terrestrial composition occurred before the change in grain size, aligning more closely with the initiation of the PETM itself.
94

Effect of computer assisted instruction on students' achievement and attitude towards latitude and longitude in Ogun State, Nigeria

Akintade, Caleb Ayodele 02 1900 (has links)
For the past few years, the West African Examination Council (WAEC) Chief Examiners’ reports on students’ performance in mathematics have indicated that some topics (e.g. concepts of latitude and longitude) have posed a major problem for students at the senior secondary school level. This poor achievement of students in understanding the topic may be associated with the traditional “chalk and talk” method that teachers use in teaching the concept. Education reforms in recent years, have advocated for a student-centred method of teaching; a method that allows individualstudent towork at his own pace or in groups. Various researchers have encouraged the use of different forms of ICT, such as computer-assisted instruction (CAI), in the teaching of mathematics to improve students’ learning of topics in mathematics perceived to be difficult. With all the efforts concentrated on improving students’ performance in mathematics, no research studies have been conducted on the effectiveness of CAI on students’ achievement and attitude towards the learning of the concepts of latitude and longitude in Nigerian secondary schools. The study employed pre-test, post-test non-equivalent control group, quasi-experimental design involving two groups: experimental group (162) and control group (158) research design to investigate the effect of the CAI method of teaching on 2nd year senior secondary school students’ achievement and attitude to latitude and longitude.Instruments for the research study were Achievement test in latitude and longitude (ATLL); questionnaire on students’ attitude to latitude and longitude (QSALL); semi-structured interview and class observations protocol. The instruments were validated, and found reliable via a pilot study before they were employed for the main study. Datacollectedwere analysed using both the descriptive and inferential statistics to answer the research questions and to test the stated null hypotheses. Results showed a statistically significant difference in the post-test mean scores of the experimental and the control groups, whereas there was no statistally significant difference in the pre-test mean scores of these two groups. In addition, the results revealed non- significant difference between the mean scores of girls and boys in the post-test. Furthermore, there was no significant difference between science students’ post-test mean scores and their counterparts in the arts and commercial classes, and there was no interactive effect related to treatment, gender and students’ subject area in the post-test. Specifically, the knowledge in this study has added another dimension to everyday experiences of students in mathematics when the software was used to teach the perceived difficult topics, and they were actively involved in the learning process through the use of CAI techniques. The study concludes with recommendations for future research, because even though it is limited to Ogun State, it has potential for future research to be undertaken by expanding its scope to cover many other states in Nigeria. This study also recommends that efforts be made to integrate the philosophy of CAI to the teaching curriculum in Nigeiran secondary schools. Furthermore, applications of the recommendations would be appropriate for the improvement to the teaching methodology of mathematics and other science-related subjects in Nigerian secondary schools / Mathematics Education / Ph. D. (MSTE)
95

Det handlar om anknytning : En kvalitativ studie om socialsekreterares resonemang om anknytningens betydelse för en gynnsam utveckling

Enochsson Pålebo, Mariah, Österberg, Hanna January 2016 (has links)
The aim of this study was to receive a rapt understanding of how child-welfare officer’s reasons about the meaning of attachment theory, from the child´s best, in placements of a child. The aim was also to examine the possibilities child-welfare officer´s feel they have to work with the child´s best and attachment in focus. The study has a qualitative approach and the empirical material is collected thru semi-structured interviews. The theoretical framework used is attachment theory, the child´s best and street-level bureaucracy. The result of the study shows that child-welfare officers have equivalent knowledge, experiences and thoughts about the meaning of attachment theory for a favorable development in foster children. The study concludes is that more knowledge about attachment theory is necessary and child-welfare officers demands methods to better assess attachment patterns in children. The child-welfare officers express frustration when they talk about matters in the "grey area" and situations where different perspectives clashes and the child´s best end up in the background. / Studiens syfte var att erhålla en fördjupad förståelse för hur socialsekreterare i den sociala barnavården resonerar om anknytningens betydelse, utifrån barnets bästa, vid familjehemsplacering av ett barn. Syftet var också att ta reda på vilka möjligheter socialsekreterare upplever sig ha att arbeta med barnets bästa och anknytning i fokus. Studien har en kvalitativ ansats och materialet är insamlat genom semistrukturerade intervjuer. Den teoretiska tolkningsram som används är anknytningsteori, barnets bästa samt gräsrotsbyråkrati. Studiens resultat visar att socialsekreterare har likvärdiga kunskaper, erfarenheter och tankar om anknytningens betydelse för en gynnsam utveckling hos familjehemsplacerade barn. Studiens slutsats är att mer kunskap om anknytningsteori är nödvändig och socialsekreterare efterfrågar metoder för att bättre kunna bedöma anknytningsmönster hos barn. Socialsekreterarna ger uttryck för frustration när de berättar om så kallade gråzonsärenden och situationer där olika perspektiv är i konflikt och barnets bästa hamnar i skymundan.
96

Geometric Model for Tracker-Target Look Angles and Line of Sight Distance

Laird, Daniel T. 10 1900 (has links)
ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NV / To determine the tracking abilities of a Telemetry (TM) antenna control unit (ACU) requires 'truth data' to analyze the accuracy of measured, or observed tracking angles. This requires we know the actual angle, i.e., that we know where the target is above the earth. The positional truth is generated from target time-space position information (TSPI), which implicitly places the target's global positioning system (GPS) as the source of observational accuracy. In this paper we present a model to generate local look-angles (LA) and line-of-sight (LoS) distance with respect to (w.r.t.) target global GPS. We ignore inertial navigation system (INS) data in generating relative position at time T; thus we model the target as a global point in time relative to the local tracker's global fixed position in time. This is the first of three companion papers on tracking This is the first of three companion papers on tracking analyses employing Statistically Defensible Test & Evaluation (SDT&E) methods.
97

Adaptation of Drosophila melanogaster to altitudinal and latitudinal climatic gradients : the role of the heat-shock RNA gene hsr-omega

Collinge, Janelle Elyse January 2004 (has links)
Abstract not available
98

Essays in regulatory focus and price acceptance

Patil, Ashutosh R. 06 July 2009 (has links)
Part one of the thesis studies differential diagnosticity towards substantive extrinsic information available in the environment. This research tests the interaction between regulatory focus and availability of extrinsic-substantive information such as consensus information, on the range of acceptable price. Prior research on regulatory focus led us to two divergent predictions. Our findings lend support to the asymmetric-elaboration account. Under this account, only prevention-oriented consumers are likely to change their acceptable price range if combinations of favorable-and-unfavorable consensus information are available in the environment, while promotion-oriented consumers disregard such information. We find that this difference is due to the differences in the level of difficulty experienced in specifying acceptable price range across the two regulatory foci. Further, we also undertake random-parameters regression models that provide unique general findings. For example, we find that for promotion-oriented consumers it is their high-level product construal, while for prevention-oriented consumers it is their low-level product construal that influences their respective acceptable price ranges, irrespective of level of external information available. Theoretical and managerial implications are discussed.
99

Trembling aspen site index in relation to site quality in northern British Columbia

Klinka, Karel, Chen, Han Y. H., Chourmouzis, Christine January 1998 (has links)
Accurate and reliable predictions of site index (height of dominant trees at a reference age, usually 50 years at breast-height) for timber crop species is essential for silvicultural site-specific decision making. Site index can be predicted from site quality once the relationship between site index and site quality has been quantified. Site quality is defined as the sum of all environmental factors affecting the biotic community, such as the factors directly influencing the growth of vascular plants (light, heat, soil moisture, soil nutrients, and soil aeration). Since these factors vary greatly in time, indirect estimates of site quality have widely been used as predictors for site index in various multiple regression models. Trembling aspen (Populus tremuloides Michx.) is the most widely distributed broadleaf species in British Columbia, especially in the Boreal White and Black Spruce (BWBS) biogeoclimatic zone. Growing this species for sustainable timber production requires a good understanding of its productivity attributes and accurate predictions of its growth. This extension note presents (1) relationships between trembling aspen site index and some indirect measures of site quality, and (2) site index prediction models using the indirect measures of site quality as predictors.
100

Burnout, work, stress of conscience and coping among female and male patrolling police officers / Utbrändhet, arbete, samvetsstress och coping hos kvinnliga och manliga poliser

Backteman-Erlanson, Susann January 2013 (has links)
Background. Police work is a stressful occupation with frequent exposure to traumatic events and psychological strain from work might increase the risk of burnout. This thesis focuses on patrolling police officers (PPO), who work most of their time in the community and have daily contact with the public. Since police work traditionally is a male coded occupation we assume that there are differences between women and men in burnout as well as experiences from psychosocial work environment. Aim. The overall aim of this thesis is to explore burnout, psychosocial and physical work environment, coping strategies, and stress of conscience when taking gender into consideration among patrolling police officers. Methods. This thesis employs both qualitative and quantitative methods. In Paper I a qualitative approach with narrative interviews was used where male PPO described experiences of traumatic situations when caring for victims of traffic accidents. A convenience sample of nine male PPO from a mid-sized police authority was recruited. Interviews were analyzed using qualitative content analysis. Papers II, III, and IV were based on a cross-sectional survey from a randomly selected sample stratified for gender from all 21 local police authorities in Sweden. In the final sample, 1554 PPOs were invited (778 women, 776 men), response rate was 55% (n=856) in total, 56% for women (n=437) and 53% for men (n=419). The survey included a self-administered questionnaire based on instruments measuring burnout, stress of conscience, psychosocial and physical work environment, and coping. Results. Findings from Paper I were presented in three themes; “being secure with the support system,” “being confident about prior successful actions,” and “being burdened with uncertainty.” Results from Paper II showed high levels of emotional exhaustion (EE), 30% for female PPOs and 26% for male PPOs. High levels of depersonalization (DP) were reported for 52 % of female PPO, corresponding proportions for male were 60%. Multiple logistic regression showed that stress of conscience (SCQ-A), high demand, and organizational climate increased the risk of EE for female PPO. For male PPO stress of conscience (SCQ-A), low control and high demand increased the risk of EE. Independent of gender, stress of conscience (SCQ-A) increased the risk of DP. Psychometric properties of the WOCQ were investigated with exploratory factor analysis and confirmatory factor analysis, a six-factor solution was confirmed. DIF analysis was detected for a third of the items in relation to gender. In Paper IV a block wise hierarchical multiple regression analysis was performed investigating the predictive impact of psychological demand, decision latitude, social support, coping strategies, and stress of conscience on EE as well as DP. Findings revealed that, regardless of gender, risk of EE and DP increased with a troubled conscience amongst the PPO. Conclusion. “Being burdened with uncertainty” in this male-dominated context indicate that the PPO did not feel confident talking about traumatic situations, which might influence their coping strategies when arriving to a similar situation. This finding can be related to Paper II and IV showing that stress of conscience increased the risk of both EE and DP. The associations between troubled conscience and the risk of experiencing both emotional exhaustion and depersonalization indicate that stress of conscience should be considered when studying the influence of the psychosocial work environment on burnout. Results from this study show that the psychosocial work environment is not satisfying and needs improvement for patrolling police officers in Sweden. Further studies including both qualitative and quantitative (longitudinal) methods should be used to improve knowledge in this area to increase conditions for preventive and rehabilitative actions.

Page generated in 0.0629 seconds