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  • 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.
71

Electric Field and Drift Characteristics Studies for the Multiwire Chambers of the Third Plane of HADES

Kanaki, Kalliopi 31 March 2010 (has links) (PDF)
Aim of this report is the investigation of suitable operational conditions for the drif{}t chambers MDC III installed in the HADES setup. The simulations performed showed that operating the drif{}t chambers in a mode with nearly constant electron drif{}t velocity in a predominant part of the cell allows a more precise and fast tracking. This is particularly important for electrons and positrons; here the invariant dilepton mass must be reconstructed with high precision to get a resolution of $\Delta M/M\approx 1\%$ for the $\omega$ and $\phi$ mass peaks and thus a chance to verify also small in-medium mass shif{}ts. This helps to realize the physics program at HADES which focuses on the search for such mass shif{}ts to get insight into the in-medium behaviour of hadrons in dense strongly interacting matter.
72

Electric Field and Drift Characteristics Studies for the Multiwire Chambers of the Third Plane of HADES

Kanaki, Kalliopi January 2003 (has links)
Aim of this report is the investigation of suitable operational conditions for the drif{}t chambers MDC III installed in the HADES setup. The simulations performed showed that operating the drif{}t chambers in a mode with nearly constant electron drif{}t velocity in a predominant part of the cell allows a more precise and fast tracking. This is particularly important for electrons and positrons; here the invariant dilepton mass must be reconstructed with high precision to get a resolution of $\Delta M/M\approx 1\%$ for the $\omega$ and $\phi$ mass peaks and thus a chance to verify also small in-medium mass shif{}ts. This helps to realize the physics program at HADES which focuses on the search for such mass shif{}ts to get insight into the in-medium behaviour of hadrons in dense strongly interacting matter.
73

Concept Drift in Surgery Prediction

Beyene, Ayne, Welemariam, Tewelle January 2012 (has links)
Context: In healthcare, the decision of patient referral evolves through time because of changes in scientific developments, and clinical practices. Existing decision support systems of patient referral are based on the expert systems approach. This usually requires manual updates when changes in clinical practices occur. Automatically updating the decision support system by identifying and handling so-called concept drift improves the efficiency of healthcare systems. In the stateof-the- art, there are only specific ways of handling concept drift; developing a more generic technique which works regardless of restrictions on how slow, fast, sudden, gradual, local, global, cyclical, noisy or otherwise changes in internal distribution, is still a challenge. Objectives: An algorithm that handles concept drift in surgery prediction is investigated. Concept drift detection techniques are evaluated to find out a suitable detection technique in the context of surgery prediction. Moreover, a plausible combination of detection and handling algorithms including the proposed algorithm, Trigger Based Ensemble (TBE)+, are evaluated on hospital data. Method: Experiments are conducted to investigates the impact of concept drift on prediction performance and to reduce concept drift impact. The experiments compare three existing methods (AWE, Active Classifier, Learn++) and the proposed algorithm, Trigger Based Ensemble(TBE). Real-world dataset from orthopedics department of Belkinge hospital and other domain dataset are used in the experiment. Results: The negative impact of concept drift in surgery prediction is investigated. The relationship between temporal changes in data distribution and surgery prediction concept drift is identified. Furthermore, the proposed algorithm is evaluated and compared with existing handling approaches. Conclusion: The proposed algorithm, Trigger Based Ensemble (TBE), is capable of detecting the occurrences of concept drifts and to adapt quickly to various changes. The Trigger Based Ensemble algorithm performed comparatively better or sometimes similar to the existing concept drift handling algorithms in the absence of noise. Moreover, the performance of Trigger Based Ensemble is consistent for small and large dataset. The research is of twofold contributions, in that it is improving surgery prediction performance as well as contributing one competitive concept drift handling algorithm to the area of computer science.
74

Second order wave excitation and damping forces on floating bodies

Tong, Koon Chung January 1988 (has links)
No description available.
75

A magnetic study of the west Iberia and conjugate rifted continental margins : constraints on rift-to-/drift processes

Russell, Simon Mark January 1999 (has links)
The analysis and modelling of magnetic anomalies at the conjugate rifted continental margins of the southern Iberia Abyssal Plain (TAP) and Newfoundland Basin have revealed that the sources of magnetic anomalies are distinctly different across both each margin and between the two margins. Analyses of synthetic anomalies and gridded sea surface magnetic anomaly charts west of Iberia and east of Newfoundland were accomplished by the methods of Euler deconvolution, forward and inverse modelling of the power spectrum, reduction-to-the-pole, and forward and inverse indirect methods. In addition, three near-bottom magnetometer profiles were analysed by the same methods in addition to the application of componental magnetometry. The results have revealed that oceanic crust, transitional basement and thinned continental crust are defined by magnetic sources with different characteristics. Over oceanic crust, magnetic sources are present as lava-flow-like bodies whose depths coincide with the top of acoustic basement seen on MCS profiles. Top-basement source depths are consistent with those determined in two other regions of oceanic crust. In the southern IAP, oceanic crust, ~4 km thick with magnetizations up to +1.5 A/m, generated by organized seafloor spreading was first accreted -126 Ma at the position of a N-S oriented segmented basement peridotite ridge. To the west, seafloor spreading anomalies can be modelled at spreading rates of 10 mm/yr or more. Immediately to the east, in a zone -10-20 km in width, I identify seafloor spreading anomahes which can only be modelled assuming variable spreading rates. In the OCT, sources of magnetic anomalies are present at the top of basement and up to -6 km beneath. I interpret the uppermost source as serpentinized peridotite, and the lowermost source as intruded gabbroic bodies which were impeded, whilst rising upwards, by the lower density serpentinized peridotites. Intrusion was accompanied by tectonism and a gradual change in conditions from rifting to seafloor spreading as the North Atlantic rift propagated northwards in Early Cretaceous times. Within thinned continental crust, sources are poorly lineated, and distributed in depth. Scaling relationships of susceptibility are consistent with the sources of magnetic anomalies within continental crust. OCT-type intrusions may be present in the mantle beneath continental crust. At the conjugate Newfoundland margin, seafloor spreading anomalies can be modelled at rates of 8 and 10 mm/yr suggesting an onset age consistent with that of the IAP. In the OCT there, I propose that magnetic anomalies are sourced in near top-basement serpentinized peridotites. An absence of magmatic material and the differences in basement character (with the IAP) suggest that conjugate margin evolution may have been asymmetric.
76

Do Trichoptera in running water fly upstream?

Larsson, Malin January 2015 (has links)
Drift moves aquatic insects downstream, risking depopulation of upstream reaches. However, the necessity and exist­ence of an upstream flight to compensate for drift has not been undisputed. I analysed a sample of approximately 70 000 Trichoptera from a stream in northern Sweden collected during one season in 1974. The overall flight direction was upstream. Females had a stronger upstream flight than males and species varied in both flight direction and strength of the preference. Flight direction was not affected by wind or trap type. Upstream flight varied during the season and with different larval behaviours. Upstream flight increased with the size of the imago and with the abun­dance in flight. A colonisation cycle might be in effect but even though upstream flight occurs, it might not be neces­sary to sustain populations in upstream reaches.
77

Revision inför företagskonkurser : En undersökning om förändringen i revisionsberättelsens anmärkningar

Hassel, Jakob, Zetterman, David January 2016 (has links)
Syftet med studien är att kunna förklara hur en oren revisionsberättelse ser ut och förändras inför en företagskonkurs. I teorin redogörs det för olika teoretiska begrepp som studien utgår från, vilka är: konkurs, revisionsberättelse, oren revisionsberättelse, Big 4 och byte av revisor. Teorier som studien grundar sig i presenteras i den teoretiska referensramen och de är: Försäkran, Förbättring, Försäkring samt Förväntningsgap. Studien utgår från ett kvantitativt angreppssätt. En innehållsanalys genomförs där anmärkningar i revisionsberättelser samlas in och granskas. Studien samlar in data genom en longitudinell undersökningsdesign. 555 företag ingår i empirin där totalt 3037 anmärkningar har observerats i revisionsberättelserna. Författarna har i studien kunnat fastställa att det föreligger en generell ökning av anmärkningar inför inledd konkurs. Det kan konstateras att ökningen inte enbart sker för antalet anmärkta företag utan författarna har även kommit fram till att antalet anmärkningar per företag ökar. Studien visar även att ökningen sker successivt inför varje revisionsberättelse.
78

Aspects of the glaciation and superficial deposits of Pembrokeshire

John, Brian Stephen January 1965 (has links)
"Since the publication of the work of Jehu and Charlesworth the distribution and significance of the glacial deposits of the Irish Sea have remained in a somewhat confused condition." So said Professor W.D. Evans in 1964. This thesis represents an attempt to remove the confusion from one small corner of the Irish Sea basin; it is concentrated largely in North Pembrokeshire, and aims to resolve some of the stratigraphic and chronological problems concerned with the Pleistocene deposits of the region. There is a long history of research into the glaciation of North Pembrokeshire. Most of the early work was undertaken in Dewisland (the St. David's Peninsula), but in the major contributions of Jehu (1904) ond Charlesworth (1929) something was revealed of the Pleistocene history of North Pembrokeshire as a whole. Subsequent work has been greatly influenced by these two authors, and there has been no detailed field study of the area since Charlesworth. As a result, many controversies have arisen in recent years; these range from the purely stratigraphic problems of the classic tripartite drift succession and the nature of the Upper Boulder-clay to the absolute age of the Pembrokeshire drifts. Again, there is doubt concerning the number of glaciations represented in North Pembrokeshire; about the existence of the South Wales End-moraine, the pro-glacial lakes, and the so-called overflow channels of Charlesworth; and about the age and origins of the coastal features of the county. These are among the problems that this thesis attempts to answer.
79

Drifts and their short-period perturbations in the lower ionosphere observed at Collm during 1983 - 1999

Gavrilov, Nikolaj M., Jacobi, Christoph, Kürschner, Dierk 02 December 2016 (has links) (PDF)
Estimations of the intensity of short-period perturbations of the horizontal drift velocity at 80 - 110 km altitude are made using data from the regular low-frequency D1 ionospheric reflection observations at Collm, Germany (52° N, 15° E) for the period 1983 - 1999. A simple half-hourly-difference numerical filter is used to extract perturbations with time scales between 0.7 and 3 hours. The results are compared with the mean drift analyses in order to study the interaction between short-period perturbations and the mean circulation. The average monthly variances of short-period perturbations of the zonal velocity near 80 km altitude show a main maximum in summer, a smaller maximum in winter, and minimum values at the equinoxes. At higher altitudes the summer maximum is shifted towards spring, and another maximum of perturbation variances in autumn appears at altitudes near and above 100 km. The seasonal changes of variances of the meridional velocity show maximum values in spring and summer, also some indications for an increase of the summer maximum at altitudes larger than 100 km are found. The observed altitude changes of the seasonal variations of drift perturbation variances are consistent with some numerical calculations of the height structure of a spectrum of internal gravity waves in the middle and upper atmosphere. / Die Intensität kurzperiodischer Störungen der horizontalen Driftgeschwindigkeit im Höhenbereich zwischen 80 und 110 km wurde anhand der regulären D1 Langwellenreflexionsmessungen in Collm (52° N, 15° E), bestimmt. Verwendet wurden Daten der Jahre 1983 - 1999. Ein einfache numerische Filter basierend auf den Unterschieden aufeinanderfolgender halbstündiger Windmittelwerte wurde verwendet, um Störungen im Zeitbereich von 0.7 - 3 Stunden zu ermitteln. Die Ergebnisse wurden mit Analysen der mittleren Drift verglichen, um die Wechselwirkungen zwischen kurzperiodischen Störungen und der mittleren Zirkulation zu untersuchen. Die mittlere monatliche Varianz der kurzperiodischen Störungen der Zonalgeschwindigkeit bei etwa 80 km zeigt ein Hauptmaximum im Sommer und ein schwächeres Maximum im Winter, wobei die Minima während der Aquinoktien auftreten. In grösseren Höhen verschiebt sich das Sommermaximum zum Frühjahr hin, und in Höhen über 100 km erscheint im Herbst ein weiteres Maximum. Der Jahresgang der meridionalen Windstörungen zeigt maximale Werte in Frühjahr/Sommer, und es sind auch Hinweise auf eine Verstärkung des Sommermaximums oberhalb von 100 km zu finden. Die gemessenen Höhenänderungen im Jahresgang der kurzperiodischen Driftschwankungen entsprechen numerischen Ergebnissen der Höhenabhängigkeit interner Schwerewellen in der mittleren und oberen Atmosphäre.
80

Do Investors Over-react to Patterns of Past Financial Performance Measures?

Alwathainani, Abdulaziz 01 January 2006 (has links)
The objectives of this thesis are threefold. First, this dissertation examines whether patterns (growth and consistency in growth) of firms' past financial performance influence investors' perceptions about stock values and future performance of these firms. Second, multiple estimation horizons of past performance variables (ranging from one to five years) are used to assess whether the interaction between growth patterns and measurement interval lengths of these variables influence investor expectations. Third, this thesis examines whether an intermediate price drifts (e.g. Jegadeesh and Titman [1993]) and subsequent long-horizon price reversal (e.g. DeBondt and Thaler (1985)] are manifestations of a market over-reaction as suggested in recent studies (e.g. Lee and Swaminathail [2000]).Annual data on sales, earnings, cash flow, and stock returns over various time periods from a sample of publicly traded firms listed on the NYSE, AMEX, and NASDAQ exchanges from 1983 to 1999 are used to address the research questions proposed in this thesis. The evidence provided in this study shows that low-growth firms outperform their high-growth firm counterparts across different performance variables, estimation intervals, and investment horizons except in the first post-formation year for firms ranked by their prior one-year financial growth rate (except for sales growth). These return differentials between low and high growth firms increase uniformly as more years of past financial performance added.Furthermore, when ranking firms based on the consistency of their prior financial growth rates over multiple estimation periods, this study finds that a firm consistently achieving low (high) growth rates that places it in the lowest (highest) growth 40 percent earns high (low) stock returns. The consistency in a firm's prior financial performance influences the behavior of its future stock returns, i.e. the longer the consistency of exceptionally strong (weak) performance of a firm, the greater (lower) its subsequent stock returns. However, the incremental impact of an additional year of growth consistency on future returns seems to dissipate after the third year of prior performance data, suggesting that it may not take investors longer than three years to assume that a firm's past growth will continue for many years to come. Thus, additional evidence confirming investors' prior beliefs will not lead to a significant price drift because their expectations are already reflected in market prices.First year returns for firms except SG exhibit a strong financial drift. The price drift seems to persist even with longer estimation horizons. Multiple regression analyses suggest that reported higher returns for low-growth firms is not due to risk as measured by market betas or book-to-market ratios, nor is it due to the disproportionate impact caused by relatively smaller firms. As well, the one-year-ahead size-adjusted abnormal returns are significantly and negatively related to the size-adjusted abnormal returns for years 2 through 5. This result indicates that the evidence of a price drift reported in the first post-formation year might be due to a market over-reaction, a finding consistent with results reported by Lee and Swaminathan (2000). In additional analysis, return performance for all growth portfolios for the month of January is compared to the remainder of the year. No evidence indicating that returns to these portfolios are driven by extraordinary performance of low-growth firms in the month of January.For all variables (except for past sales growth and to some degree past stock returns), the financial drift in year one return for portfolios based on prior-one year of past performance data, is significantly stronger than that reported in Chan et al. (2004). Results reported in this thesis indicate that the average abnormal return differential between low and high growth firms for the five-year estimation intervals (with exception of past sales growth) is greater than 10 percentage points. The evidence contradicts that documented in Chan et al. (2004). They find no discernable evidence of price reversals over the next 36-months after ranking firms by their five-year growth rates in sales, operating income, and net income. However, results of this study are consistent with the predictions of behavioral models (e.g. Daniel et al. [I998] and Lakonishok et al. [1994]) suggesting that investors put excessive weight on patterns of a firm's past financial performance when projecting its future prospects.

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