Bedeutung und Regulation von Apolipoprotein J in atherosklerotischen Läsionen

Apolipoprotein J (ApoJ) ist ein heterodimeres sekretiertes Glycoprotein, welchem sowohl antiapoptotische als auch antiinflammatorische Eigenschaften zugeschrieben werden. Es wird unter vielen pathophysiologischen Zuständen verstärkt exprimiert. Dazu zählen viele Krankheiten wie z.B. Krebs, M. Alzheimer, Creuzfeldt Jakob und Atherosklerose. Die vorliegende Arbeit befasst sich zum Einen mit der Funktion von ApoJ bei Atherosklerose und zum Anderen mit der Regulation von ApoJ durch in atherosklerotischen Läsionen vorkommende Bestandteile. Für die Untersuchungen der Funktion von ApoJ bei der Atherosklerose wurde die „Mainzer Hypothese“ zugrunde gelegt, die davon ausgeht, dass enzymatisch verdautes LDL (high density lipoprotein) (E-LDL) ursächlich für die Entstehung von atherosklerotischen Läsionen ist. In der vorliegenden Arbeit konnte gezeigt werden, dass ApoJ zwar an E-LDL bindet, nicht aber an natives LDL und dass durch diese Bindung die zytotoxische Wirkung von E-LDL auf glatte Muskelzellen der Ratte unterdrückt wird. Mittels Annexinfärbung und Caspase-Messung konnte gezeigt werden, dass ApoJ in diesem Fall eine antiapoptotische Funktion aufweist. Durch immunhistochemische Untersuchungen an humanen Gewebsschnitten aus frühen atherosklerotischen Läsionen konnte eine Kolokalisation von ApoJ und E-LDL nachgewiesen werden. Diese Ergebnisse unterstreichen die Mainzer Hypothese. Durch eine Behandlung von glatten Muskelzellen der Ratte mit den Lipoproteinen LDL/E-LDL und nekrotischen Zellen sollte die Regulation von ApoJ durch in atherosklerotischen Läsionen vorhandenen Stimuli untersucht werden. Frühere Arbeiten unserer Arbeitsgruppe konnten bereits zeigen, dass eine Behandlung mit nekrotischen Zellen zu einer vermehrten Expression der ApoJ-mRNA führt und dass diese Regulation in Korrelation mit der Expression von Toll-like Rezeptoren (TLR) der verschiedenen Zellen steht. In dieser Arbeit konnte RNA aus nekrotischen Zellen als ApoJ-induzierende Komponente identifiziert werden. Durch Inhibition der TLR3-Signalwege konnten erste Hinweise darüber gewonnen werden, über welche Signaltransduktionswege die ApoJ Regulation erfolgt. Eine Behandlung der Zellen mit E LDL und LDL hingegen führte zu einer Repression der ApoJ-Sekretion. Diese Ergebnisse deuten darauf hin, dass in atherosklerotischen Läsionen sowohl ApoJ induzierende wie auch repremierende Stimuli vorhanden sind.

Effect of mixing, particle interaction, and spatial dimension on the glass transition

In this thesis, the influence of composition changes on the glass transition behavior of binary liquids in two and three spatial dimensions (2D/3D) is studied in the framework of mode-coupling theory (MCT).The well-established MCT equations are generalized to isotropic and homogeneous multicomponent liquids in arbitrary spatial dimensions. Furthermore, a new method is introduced which allows a fast and precise determination of special properties of glass transition lines. The new equations are then applied to the following model systems: binary mixtures of hard disks/spheres in 2D/3D, binary mixtures of dipolar point particles in 2D, and binary mixtures of dipolar hard disks in 2D. Some general features of the glass transition lines are also discussed. The direct comparison of the binary hard disk/sphere models in 2D/3D shows similar qualitative behavior. Particularly, for binary mixtures of hard disks in 2D the same four so-called mixing effects are identified as have been found before by Götze and Voigtmann for binary hard spheres in 3D [Phys. Rev. E 67, 021502 (2003)]. For instance, depending on the size disparity, adding a second component to a one-component liquid may lead to a stabilization of either the liquid or the glassy state. The MCT results for the 2D system are on a qualitative level in agreement with available computer simulation data. Furthermore, the glass transition diagram found for binary hard disks in 2D strongly resembles the corresponding random close packing diagram. Concerning dipolar systems, it is demonstrated that the experimental system of König et al. [Eur. Phys. J. E 18, 287 (2005)] is well described by binary point dipoles in 2D through a comparison between the experimental partial structure factors and those from computer simulations. For such mixtures of point particles it is demonstrated that MCT predicts always a plasticization effect, i.e. a stabilization of the liquid state due to mixing, in contrast to binary hard disks in 2D or binary hard spheres in 3D. It is demonstrated that the predicted plasticization effect is in qualitative agreement with experimental results. Finally, a glass transition diagram for binary mixtures of dipolar hard disks in 2D is calculated. These results demonstrate that at higher packing fractions there is a competition between the mixing effects occurring for binary hard disks in 2D and those for binary point dipoles in 2D.

Optische Experimente zur Untersuchung der Nichtgleichgewichtsdynamik kolloidaler Suspensionen

In der vorliegenden Forschungsarbeit wird die Konkurrenz von Kristallisation und Verglasung in metastabilen kolloidalen Hart-Kugel(HK)-Modellsystemen mit dynamischer und zeitaufgelöster statischer Lichtstreuung untersucht. Durch gleichzeitige Messungen mit beiden Methoden an derselben Probe gelang es, mit hoher Genauigkeit und aussagekräftiger Statistik nachzuweisen, dass in beiden Systemklassen eine starke Korrelation der strukturellen und dynamischen Eigenschaften vorliegt und diese Korrelation zu quantifizieren. Ein zentraler Teil der Arbeit bestand in dem Aufbau einer geeigneten Lichtstreuanlage mit der erstmalig Messungen der Dynamik und der Struktur simultan an derselben nicht-ergodischen Probe durchgeführt werden konnten. Für die dynamische Lichtstreuung wurde ein Flächendetektor (CCD-Kamera) verwendet. In Kombination mit einer speziellen Detektionsoptik ermöglicht dies, die gleichzeitige Detektion von Streulicht aus unterschiedlichen Probenbereichen (Subensembles). Damit kann gleichzeitig die Dynamik in unterschiedlichen Subensembles mit einer Auflösung von 15,8x15,8µm2 untersucht werden. Die Lichtstreuanlage wurde ausführlich charakterisiert und ihre korrekte Funktionsweise mithilfe von Vergleichsmessungen an etablierten Lichtstreuanlagen bestätigt. Die zeitliche Entwicklung der Dynamik und der Struktur von metastabilen Proben wurde unterhalb, am und oberhalb des Glasübergangs quantifiziert. Dabei zeigte das untersuchte kolloidale HK-Modellsystem alle typischen Eigenschaften eines HK-Systems. Die kristallisierenden Proben zeigten das etablierte zweistufige Kristallisationsszenario mit entsprechender Kristallisationskinetik und die Glasproben zeigten das erwartete Alterungsverhalten. Bei dem zweistufigen Kristallisationsszenario kommt es zuerst zur Nukleation einer metastabilen Zwischenphase von sogenannten Precursorn. In einer zweiten Stufe bilden sich Kristallite innerhalb dieser Precursor. Durch Vergleich zwischen kristallisierenden und verglasenden Proben konnte auch während der Verglasung die Bildung von Precursorn beobachtet werden. Die Korrelation zwischen der Anzahl an Precursorn und der Partikeldynamik legt die Vermutung nahe, dass das immer noch unverstandene Phänomen der Alterung von Gläsern mit der Bildung von Precursorn zusammenhängt. Verhinderte Kristallisation führt zu einer starken Verlangsamung der Partikeldynamik. Die Partikeldynamik einer Probe am Glasübergang zeigt, dass die Probe vor Einsetzen der Kristallisation eine glasartige Dynamik aufwies. Dies legt die Vermutung nahe, dass einkomponentige kolloidale HK-Gläser den Gleichgewichtszustand (Kristall) auf langen Zeitskalen erreichen können. Durch die Untersuchung der Partikeldynamik von metastabilen Proben in einzelnen Subensembles konnte eine heterogene Verteilung der Partikeldynamik nachgewiesen werden. Es existieren Bereiche, in denen die Partikeldynamik schneller oder langsamer ist als in anderen Bereichen. Gleichzeitig zeigen die Messungen der strukturellen Eigenschaften, dass metastabile Proben auch heterogen bezüglich ihrer Struktur sind. Mithilfe dieser Messungen konnte die zeitliche Entwicklung des Anteils an langsamen Partikeln und des Anteils an Partikeln innerhalb von Objekten höherer Ordnung (Precursor/Kristallite) bestimmt werden. Es zeigte sich eine direkte Korrelation zwischen dem Anteil an langsamen Partikeln und dem Anteil an Partikeln in Objekten höherer Ordnung. Die Untersuchung der Dynamik und der Struktur in einzelnen Subensembles lieferte einen weiteren Hinweis darauf, dass Subensembles, in denen eine stärker ausgeprägte strukturelle Ordnung vorliegt, auch bevorzugt eine langsamere Partikeldynamik aufweisen.

Hearing in the mind's ear: A PET investigation of musical imagery and perception

Neuropsychological studies have suggested that imagery processes may be mediated by neuronal mechanisms similar to those used in perception. To test this hypothesis, and to explore the neural basis for song imagery, 12 normal subjects were scanned using the water bolus method to measure cerebral blood flow (CBF) during the performance of three tasks. In the control condition subjects saw pairs of words on each trial and judged which word was longer. In the perceptual condition subjects also viewed pairs of words, this time drawn from a familiar song; simultaneously they heard the corresponding song, and their task was to judge the change in pitch of the two cued words within the song. In the imagery condition, subjects performed precisely the same judgment as in the perceptual condition, but with no auditory input. Thus, to perform the imagery task correctly an internal auditory representation must be accessed. Paired-image subtraction of the resulting pattern of CBF, together with matched MRI for anatomical localization, revealed that both perceptual and imagery. tasks produced similar patterns of CBF changes, as compared to the control condition, in keeping with the hypothesis. More specifically, both perceiving and imagining songs are associated with bilateral neuronal activity in the secondary auditory cortices, suggesting that processes within these regions underlie the phenomenological impression of imagined sounds. Other CBF foci elicited in both tasks include areas in the left and right frontal lobes and in the left parietal lobe, as well as the supplementary motor area. This latter region implicates covert vocalization as one component of musical imagery. Direct comparison of imagery and perceptual tasks revealed CBF increases in the inferior frontal polar cortex and right thalamus. We speculate that this network of regions may be specifically associated with retrieval and/or generation of auditory information from memory.

Is restricted femoral navigation sufficient for accuracy of total knee arthroplasty?

A total knee arthroplasty performed with navigation results in more accurate component positioning with fewer outliers. It is not known whether image-based or image-free-systems are preferable and if navigation for only one component leads to equal accuracy in leg alignment than navigation of both components. We evaluated the results of total knee arthroplasties performed with femoral navigation. We studied 90 knees in 88 patients who had conventional total knee arthroplasties, image-based total knee arthroplasties, or total knee arthroplasties with image-free navigation. We compared patients' perioperative times, component alignment accuracy, and short-term outcomes. The total surgical time was longer in the image-based total knee arthroplasty group (109 +/- 7 minutes) compared with the image-free (101 +/- 17 minutes) and conventional total knee arthroplasty groups (87 +/- 20 minutes). The mechanical axis of the leg was within 3 degrees of neutral alignment, although the conventional total knee arthroplasty group showed more (10.6 degrees ) variance than the navigated groups (5.8 degrees and 6.4 degrees , respectively). We found a positive correlation between femoral component malalignment and the total mechanical axis in the conventional group. Our results suggest image-based navigation is not necessary, and image-free femoral navigation may be sufficient for accurate component alignment.

Quantifying the ecological benefits of lakeshore restoration in northern Wisconsin

Housing development has increased dramatically in the Midwest with a high concentration around lakes. This development plays an important role in the economy of Northwoods communities. However, poorly planned development has the potential to alter a lake’s ecological processes and integrity. Studies have documented the impacts of housing developments and reported dramatic, negative changes to the flora and fauna in Vilas County, Wisconsin. One component of my research included examining the previously unstudied effects of residential development on the abundance and diversity of medium to large-bodied mammals using lakeshore ecosystems. The results suggest that a higher diversity of mammals were detected on low-development lakes. Coyotes were the most numerous species detected with the majority encountered on low-development lakes. White-tailed deer and red fox were more abundant on high-development lakes as compared to low-development lakes. I concluded that high-development lakes are having a negative affect on the mammal community in this area. Recently, lakeshore restoration has occurred on privately owned property in Vilas County and elsewhere in the Northwoods, but little is known about the benefit, if any, from these restoration efforts. A partnership between government agencies and academia has launched a long-term research project investigating the ecological benefits of lakeshore restoration. I investigated the impacts of using down woody material (DWM) to increase the success of restoration projects. Specifically, I tested the hypothesis that down woody material would reduce the variation in soil temperature, retain soil moisture, and improve plant survival and growth rates. I randomly assigned three DWM coverage treatments (0%, 25%, and 50%) on 3 m × 3 m experimental plots (n = 10 per treatment). The mean maximum soil temperature, temperature variation, and change in soil moisture content were significantly lower in the 25% and 50% DWM plots. I found no difference in survival, but snowberry (Symphoricarpos albus) and Barren strawberry (Waldstenia fragaroides) growth was significant greater in the 25% and 50% DWM plots. DWM addition can be considered a useful technique to physically manipulate soil properties and improve plant growth. Finally, I provided baseline data on vegetation structure, bird and small mammal community diversity and abundance for three lakes targeted for restoration efforts and their paired reference lakes. This study is one of the first of it kind in the area and continuing to document the degree of change in subsequent years will provide insight into the way the local ecosystem functions and how ecological communities are structured.

Auswirkung des anisotropen Gefüges strahlgeschmolzener Bauteile auf mechanische Eigenschaftswerte

Die Strahlschmelztechnologie entwickelt sich in vielen Anwendungsbereichen zu einer echten Alternative zu den konventionellen Fertigungsverfahren. Dieser Trend wird gerade durch die Verarbeitung von serienidentischen, einkomponentigen Pulvern zur Herstellung metallischer Bauteile verstärkt, wodurch sich wiederum neue Entwicklungs- und Einsatzpotentiale ergeben. Allerdings weisen die Strahlschmelzbauteile keine vollkommen übereinstimmenden Werkstoffkennwerte im Vergleich zu herkömmlich hergestellten Bauteilen auf, wodurch die Akzeptanz durch Industrie und Forschung eingeschränkt wird. Eine exakte Beschreibung (Nachweis) der Materialeigenschaften von strahlgeschmolzenen Bauteilen wird in dem Maße wichtiger, mit dem diese Verfahren zur Fertigung von Endprodukten herangezogen werden. Weiterhin spielt die Anisotropie des Gefüges strahlgeschmolzener Bauteile eine große Rolle. Aus diesem Grund wurden im RTC Duisburg umfangreiche Festigkeitsuntersuchungen (statisch und dynamisch) in Abhängigkeit von der Baulage, des Oberflächenzustandes und verschiedener Belichtungsstrategien durchgeführt. In diesem Vortrag werden ausgewählte Ergebnisse zu den Untersuchungen vorgestellt.

Integrating Events Across Levels of Consciousness

Our knowledge grows as we integrate events experienced at different points in time. We may or may not become aware of events, their integration, and their impact on our knowledge and decisions. But can we mentally integrate two events, if they are experienced at different time points and at different levels of consciousness? In this study, an event consisted of the presentation of two unrelated words. In the stream of events, half of events shared one component ("tree desk" … "desk fish") to facilitate event integration. We manipulated the amount of time and trials that separated two corresponding events. The contents of one event were presented subliminally (invisible) and the contents of the corresponding overlapping event supraliminally (visible). Hence, event integration required the binding of contents between consciousness levels and between time points. At the final test of integration, participants judged whether two supraliminal test words ("tree fish") fit together semantically or not. Unbeknown to participants, half of test words were episodically related through an overlap ("desk"; experimental condition) and half were not (control condition). Participants judged episodically related test words to be closer semantically than unrelated test words. This subjective decrease in the semantic distance between test words was both independent of whether the invisible event was encoded first or second in order and independent of the number of trials and the time that separated two corresponding events. Hence, conscious and unconscious memories were mentally integrated into a linked mnemonic representation.

Sizing up your enemy: individual predation vulnerability predicts migratory probability

Partial migration, in which a fraction of a population migrate and the rest remain resident, occurs in an extensive range of species and can have powerful ecological consequences. The question of what drives differences in individual migratory tendency is a contentious one. It has been shown that the timing of partial migration is based upon a trade-off between seasonal fluctuations in predation risk and growth potential. Phenotypic variation in either individual predation risk or growth potential should thus mediate the strength of the trade-off and ultimately predict patterns of partial migration at the individual level (i.e. which individuals migrate and which remain resident). We provide cross-population empirical support for the importance of one component of this model—individual predation risk—in predicting partial migration in wild populations of bream Abramis brama, a freshwater fish. Smaller, high-risk individuals migrate with a higher probability than larger, low-risk individuals, and we suggest that predation risk maintains size-dependent partial migration in this system.

An 'Ideal' Decomposition of Industry Dynamics: An Application to the Nationwide and State Level U.S. Banking Industry

This paper considers the aggregate performance of the banking industry, applying a modified and extended dynamic decomposition of bank return on equity. The aggregate performance of any industry depends on the underlying microeconomic dynamics within that industry . adjustments within banks, reallocations between banks, entry of new banks, and exit of existing banks. Bailey, Hulten, and Campbell (1992) and Haltiwanger (1997) develop dynamic decompositions of industry performance. We extend those analyses to derive an ideal decomposition that includes their decomposition as one component. We also extend the decomposition, consider geography, and implement decomposition on a state-by-state basis, linking that geographic decomposition back to the national level. We then consider how deregulation of geographic restrictions on bank activity affects the components of the state-level dynamic decomposition, controlling for competition and the state of the economy within each state and employing fixed- and random-effects estimation for a panel database across the fifty states and the District of Columbia from 1976 to 2000.

An 'Ideal' Deconposition of Industry Dynamics: An Application to the Nationwide and State Level U.S. Banking Industry

This paper considers the aggregate performance of the banking industry, applying a modified and extended dynamic decomposition of bank return on equity. The aggregate performance of any industry depends on the underlying microeconomic dynamics within that industry --- adjustments within banks, reallocations between banks, entry of new banks, and exit of existing banks. Bailey, Hulten, and Campbell (1992) and Haltiwanger (1997) develop dynamic decompositions of industry performance. We extend those analyses to derive an ideal dynamic decomposition that includes their dynamic decomposition as one component. We also extend the decomposition, consider geography, and implement decomposition on a state-by-state basis, linking that geographic decomposition back to the national level. We then consider how deregulation of geographic restrictions on bank activity affects the components of the state-level dynamic decomposition, controlling for competition and the state of the economy within each state and employing fixed- and random-effects estimation for a panel database across the fifty states and the District of Columbia from 1976 to 2000.

Role of telomere dysfunction, DNA damage response and p53 mutations in tumorigenesis and aging

The ends of eukaryotic chromosomes are protected by specialized ribonucleoprotein structures termed telomeres. Telomeres protect chromosomes from end-to-end fusions, inappropriate repair and degradation. Disruption of this complex activates an ATM/ATR DNA damage response (DDR) pathway. One component of the complex is the Protection Of Telomeres 1 (POT1) protein, an evolutionarily conserved protein which binds single-stranded 3' overhang and is required for both chromosomal end protection and telomere length regulation. The mouse contains two POT1 orthologs, Pot1a and Pot1b. Here we show that both proteins colocalize with telomeres through interaction with the adapter protein TPP1. In addition, compared to Pot1a, the OB-folds of Pot1b possess less sequence specificity for telomeres. Disruption of POT1 proteins result in telomere dysfunction and activation of an ATR-dependent DDR at telomeres, suggesting that this response is normally suppressed by POT1 binding to the single-stranded G-overhang. ^ Telomeres are maintained by telomerase, and its absence in somatic cells results in telomere progressive loss that triggers the activation of p53. Telomere dysfunction initiates genomic instability and induces both p53-dependent replicative senescence and apoptosis to suppress tumorigenesis. In the absence of functional p53, this genomic instability promotes cancer. It was previously not known which aspect of the p53 dependent DNA damage response is important to suppress tumorigenesis initiated by dysfunctional telomeres. The p53R172P knock-in mouse, which is unable to induce apoptosis but retains intact cell cycle arrest/cellular senescence pathways, allowed us to examine whether p53-dependent apoptosis is a major tumor suppression pathway initiated in the setting of telomere dysfunction. Spontaneous tumorigenesis remains potently suppressed in late generation telomerase null mice possessing the p53P/P mutation. These results suggest that suppression of spontaneous tumorigenesis initiated by dysfunctional telomeres requires activation of a p53-dependent senescence pathway. In addition, we used another knock-in mouse model with a p53R172H (p53H) point mutation to test the hypothesis that telomere dysfunction promotes chromosomal instability and accelerates the onset of tumorigenesis in vivo in the setting of this most common gain-of-function mutation in the human Li Fraumeni cancer syndrome. We unexpectedly observed that telomerase null mice possessing dysfunctional telomeres in the setting of the p53H/+ mutation develop significantly fewer tumors, die prematurely and exhibit higher level of cellular senescence, apoptosis and elevated genomic instability compared to telomerase intact p53H/+ and telomerase null p53+/+ mice. These contrasting results thus link cancer and aging to the functional status of telomeres and the integrity of the p53 pathway. ^

A review of the Malaria Chemoprophylaxis Compliance Program at ExxonMobil Corporation

ExxonMobil, a Fortune 500 oil and gas corporation, has a global workforce with employees assigned to projects in areas at risk for infectious diseases, particularly malaria. As such, the corporation has put in place a program to protect the health of workers and ensure their safety in malaria endemic zones. This program is called the Malaria Control Program (MCP). One component of this program is the more specific Malaria Chemoprophylaxis Compliance Program (MCCP), in which employees enroll following consent to random drug testing for compliance with the company's chemoprophylaxis requirements. Each year, data is gathered on the number of employees working in these locations and are selected randomly and tested for chemoprophylaxis compliance. The selection strives to test each eligible worker once per year. Test results that come back positive for the chemoprophylaxis drug are considered "detects" and tests that are negative for the drug and therefore show the worker is non-compliant at risk for severe malaria infection are considered "non-detect". ^ The current practice report used aggregate data to calculate statistics on test results to reflect compliance among both employees and contractors in various malaria-endemic areas. This aggregate, non-individualized data has been compiled and reflects the effectiveness and reach of ExxonMobil's Malaria Chemoprophylaxis Compliance Program. In order to assess compliance, information on the number of non-detect test results was compared to the number of tests completed per year. The data shows that over time, non-detect results have declined in both employee and contractor populations, and vary somewhat by location due to size and scope of the MCCP implemented in-country. Although the data indicate a positive trend for the corporation, some recommendations have been made for future implementation of the program.^

Geochemistry and isotopic ratios of boninites and related rocks of the Izu-Bonin Forearc

Twenty-six samples representing the wide range of lithologies (low- and intermediate-Ca boninites and bronzite andesites, high-Ca boninites, basaltic andesites-rhyolites) drilled during Leg 125 at Sites 782 and 786 on the Izu-Bonin outer-arc high have been analyzed for Sr, Nd, and Pb isotopes. Nd-Sr isotope covariations show that most samples follow a trend parallel to a line from Pacific MORB mantle (PMM) to Pacific Volcanogenic sediment (PVS) but displaced slightly toward more radiogenic Sr. Pb isotope covariations show that all the Eocene-Oligocene samples plot along the Northern Hemisphere Reference Line, indicating little or no Pb derived from subducted pelagic sediment in their source. Two young basaltic andesite clasts within sediment do have a pelagic sediment signature but this may have been gained by alteration rather than subduction. In all isotopic projections, the samples form consistent groupings: the tholeiites from Site 782 and Hole 786A plot closest to PMM, the boninites and related rocks from Sites 786B plot closest to PVS, and the boninite lavas from Hole 786A and late boninitic dikes from Hole 786B occupy an intermediate position. Isotope-trace element covariations indicate that these isotopic variations can be explained by a three-component mixing model. One component (A) has the isotopic signature of PMM but is depleted in the more incompatible elements. It is interpreted as representing suboceanic mantle lithosphere. A second component (B) is relatively radiogenic (epsilon-Nd = ca 4-6; 206Pb/204Pb = ca 19.0-19.3; epsilon-Sr = ca -10 to -6)). Its trace element pattern has, among other characteristics, a high Zr/Sm ratio, which distinguishes it from the ìnormalî fluid components associated with subduction and hotspot activity. There are insufficient data at present to tie down its origin: probably it was either derived from subducted lithosphere or volcanogenic sediment fused in amphibolite facies; or it represents an asthenospheric melt component that has been fractionated by interaction with amphibole-bearing mantle. The third component (C) is characterized by high contents of Sr and high epsilon-Sr values and is interpreted as a subducted fluid component. The mixing line on a diagram of Zr/Sr against epsilon-Sr suggests that component C may have enriched the lithosphere (component A) before component B. These components may also be present on a regional basis but, if so, may not have had uniform compositions. Only the boninitic series from nearby Chichijima would require an additional, pelagic sediment component. In general, these results are consistent with models of subduction of ridges and young lithosphere during the change from a ridge-transform to subduction geometry at the initiation of subduction in the Western Pacific.

Predicting academic performance with learning analytics in virtual learning environments: A comparative study of three interaction classifications

Learning analytics is the analysis of static and dynamic data extracted from virtual learning environments, in order to understand and optimize the learning process. Generally, this dynamic data is generated by the interactions which take place in the virtual learning environment. At the present time, many implementations for grouping of data have been proposed, but there is no consensus yet on which interactions and groups must be measured and analyzed. There is also no agreement on what is the influence of these interactions, if any, on learning outcomes, academic performance or student success. This study presents three different extant interaction typologies in e-learning and analyzes the relation of their components with students? academic performance. The three different classifications are based on the agents involved in the learning process, the frequency of use and the participation mode, respectively. The main findings from the research are: a) that agent-based classifications offer a better explanation of student academic performance; b) that at least one component in each typology predicts academic performance; and c) that student-teacher and student-student, evaluating students, and active interactions, respectively, have a significant impact on academic performance, while the other interaction types are not significantly related to academic performance.