79 search hits
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The classification of isotrivially fibred surfaces with p_g=q=2, and topics on Beauville surfaces
(2010)
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Matteo Penegini
- In our thesis we treat mainly two topics: the classification of isotrivially fibred surfaces with p_g=q=2, and the construction of new Beauville surfaces. An isotrivially fibred surface is a smooth projective surface endowed with a morphism onto a smooth curve such that all the smooth fibres are isomorphic to each other. The first goal of this thesis is to classify the isotrivially fibred surfaces with p_g=q=2 completing and extending a result by Zucconi. As an important byproduct, we provide new examples of minimal surfaces of general type with p_g=q=2 and K^2=4,5 and the first example with K^2=6. We say that a surface S is isogenous to a product of curves if S = (C times F )/G, for C and F smooth curves and G a finite group acting freely on C times F. Beauville surfaces are a special case of surfaces isogenous to a product. In this thesis we include part of a joint work with Shelly Garion, in which we construct new Beauville surfaces with group G either PSL(2,p^e), or A_n, or S_n, proving a conjecture of Bauer, Catanese and Grunewald. The proofs rely on probabilistic group theoretical results of Liebeck and Shalev, and on classical results of Macbeath. The thesis is divided into three chapters, which are subdivided in several sections. In the first chapter we treat the problem of the classification of isotrivially fibred surfaces with p_g=q=2. We start by recalling some basic facts and theorems about fibred surfaces and surfaces isogenous to a higher product of curves. Then we solve the classification problem using techniques coming from both geometry and combinatorial group theory. In the second chapter we deal with Beauville surfaces. First we give a group theoretical characterization of them. Then we enunciate a theorem of Liebeck and Shalev that we use for the construction of Beauville surfaces with group A_n or S_n. Afterwards we also study Beauville surfaces with group PSL(2,p^e). In the third chapter we give a description of the locus, in the moduli space of surfaces of general type, corresponding to the surfaces isogenous to a product with p_g=q=2 described in the first chapter. Indeed, by the results proven by Catanese, this locus is a union of connected components, whose number can be computed using a theorem of Bauer and Catanese. In the same way we are able to provide an asymptotic result about the number of connected components of the moduli space corresponding to certain families of Beauville surfaces with group either PSL(2,p^e), or A_n, or (mathbb{Z}/nmathbb{Z})^2 as p and n go to infinity.
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Molecular Characterization of Sugarcane Yellow Leaf Virus (SCYLV) and its Effect on Sucrose Transporters in Sugarcane Saccharum spp. hybrids
(2010)
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Abdelaleim Ismail Ibrahim ElSayed
- Sugarcane is an important crop plant and has served as a source of sugar for hundreds of years, recently it is used to produce bioethanol, a renewable bio-fuel energy source. Sugarcane yellow leaf virus (SCYLV) was detected in the late 1990s first in Hawaii as a causal agent of a sugarcane disease which leads to sugarcane yellow leaf syndrome and reduced sugar yield. The presence of Sugarcane yellow leaf virus was determined by RT-PCR in several sugarcane cultivars, mostly from Hawaii. Interesting was the comparison of so-called susceptible versus resistant cultivars. As expected, the susceptible Hawaiian cultivars H73-6110 and H87-4094 showed strong PCR amplification products of SCYLV, while the virus-free line H87-4094, produced by tissue culture, showed no PCR product. The three resistant cultivars H87-4319, H78-4153 and H78-7750 showed quite different amplification patterns. While H78-4153 and H78-7750 expressed a weak but specific band of the correct size, unexpectedly H87-4319 showed strong amplification product. Three Cuban cultivars (C1051-73, JA-605 and CP52-43) showed low titer of SCYLV. No PCR amplificate was obtained with the moderately susceptible cultivar H65-7052. Aphids feeding on cv. H87-4094 contained sufficient virus to yield a SCYLV-signal similar in strength as from preparations from resistant cultivars. Northern blot analysis supported the results obtained from RT-PCR. The presence of SCYLV in the cultivars with low amount of virus titer (H87-4319, H78-7750 and H78-4153) indicated that they should better be called tolerant for the virus in the sense that they allow a low replication rate for SCYLV. Virus preparations from 3 Hawaiian cultivars (two susceptible and one resistant) were fully sequenced. Quantitative analysis for four different genome regions of SCYLV covering the 6 ORFs has been performed for these 3 cultivars using the GeXP analysis system. The transcript levels of the different regions of SCYLV in these cultivars were present at very different quantities, for example ORF0-1 transcripts were up to 10 times more frequent than transcripts of ORF3-4. The SCYLV-sequences from the 3 Hawaiian cultivars were aligned to published full and partial sequences. The phylograms corroborated previous findings that the so-called YLS-segment coding for the coat protein shows the least genetic diversity, whereas the other sequence fragments A-D, representing the ORFs 0-5, expressed a twofold higher diversity. The phylograms of partial sequences and of the whole genome placed the Hawaiian SCYLV-strains next to the Peru strain, apart from the BRA-strains and well apart from the REU-strains. It is proposed that the Hawaiian SCYLV is considered as own group together with the Peru strain as HAW-PER. The sequences from the two susceptible cultivars had a deletion of 48 to 54 nt in ORF1, which codes for the gene silencing suppressor/RNA-dependent RNA-polymerase complex. It is speculated that this deletion is important for the proliferation rate of the virus in the plant. Sucrose is the main product of sugarcane, which accumulates in the stalk internodes in excess of 50 % of the dry weight. To gain an overview of the physiological status of SCYLV-infected sugarcane compared to virus-free plants, gene expression. Sucrose increased rapidly between internodes 3 and 7, reaching a maximum in internodes 7. Sugars content in leaves, seedling and internodes were increased as effect of the SCYLV-infection. Sucrose phosphate synthase (SPSII) transcript levels were approximately the same in sink, source and internodes with a trend to be higher in the mature internodes. A sucrose transporter of Hawaiian cultivar was isolated and sequenced and classified as ShSUT1A. There is high variability among the SUT1 subfamily with identities of 70-97%. The identity between ShSUT1A and ShSUT1 was 97.4%. It is expressed in sink, source and storage tissues. The ShSUT1A was expressed at approximately similar extent in SCYLV-infected and virus-free sugarcane. In addition a partial sequence of a sucrose transporter belonging to the SUT4 family was first obtained in sugarcane and its transcript levels in plant organs were measured. Quantitative analysis for sucrose transporters (ShSUT1 and ShSUT4) using the GeXP analysis system showed that sucrose transporter ShSUT1 was at a higher transcript expression than ShSUT4 in sink and source leaves, but not in mature internodes. In conclusion, - SCYLV from Hawaiian cultivars was characterized as belonging to an own subgroup (HAW- PER), - A deletion of 48-54 nt was detected in the SCYLV-sequence from susceptible cultivars, which may be correlated to virus proliferation, and - large differences in transcript levels of the viral ORFs were found. - Sucrose transporter transcripts and SPSII transcripts were not strictly correlated to SCYLV- infection and do not explain the pathological effect of SCYLV on sugarcane.
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Soil moisture fluctuations recorded in Saharan dust deposits on Lanzarote (CanaryIslands) over the last 180 ka
(2010)
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Hans von Suchodoletz
Hedi Oberhänsli
Ulrich Hambach
Ludwig Zöller
Markus Fuchs
Dominik Faust
- Aeolian sediments trapped in volcanically dammed valleys on Lanzarote, Canary Islands, were investigated in order to reveal environmental changes over the last 180 ka. Clay content and frequency dependent magnetic susceptibility were used as proxies for pedogenesis and palaeo-soil moisture. During the last 180 ka, these proxies showed a general pattern of enhanced soil moisture during glacials and stadials and more arid conditions during interglacials and interstadials. Comparisons of these results with proxies from regional palaeoclimate studies identified a positive correlation with proxies of trade wind strength off northwest Africa and inverse correlations with both sea surface temperatures in the northeast Atlantic and the extent of Mediterranean vegetation. Possible causes for the observed pattern include a glacial enhancement of precipitation from westerly cyclones, a change in relative humidity due to fluctuating air temperatures and an occasional influence of the African summer monsoon. Although it is not yet possible to clearly differentiate among these factors, it is clear that the first two factors must have been primarily dominant. These results represent the first quasi-continuous terrestrial data testifying to environmental changes in the northwest African coastal area for the last 180 ka and complement the abundant data derived from marine cores of the region. High latitude dynamics had a major influence in this area and were intermediated by North Atlantic sea surface temperatures. A possible negative correlation can also be observed with the orbital obliquity cycle with a 10 ka time lag, which is similar to the lag recorded from North Atlantic sea surface temperatures.
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Parallel Low-Storage Runge-Kutta Solvers for ODE Systems with Limited Access Distance
(2010)
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Matthias Korch
Thomas Rauber
- We consider the solution of initial value problems (IVPs) of large systems of ordinary differential equations (ODEs) for which memory space requirements determine the choice of the integration method. In particular, we discuss the space-efficient sequential and parallel implementation of embedded Runge-Kutta (RK) methods. We focus on the exploitation of a special structure of commonly appearing ODE systems, referred to as "limited access distance", to improve scalability and memory usage. Such systems may arise, for example, from the semi-discretization of partial differential equations (PDEs). The storage space required by classical RK methods is directly proportional to the dimension n of the ODE system and the number of stages s of the method. We propose an implementation strategy based on a pipelined processing of the stages of the RK method and show how the memory usage of this computation scheme can be reduced to less than three storage registers by an overlapping of vectors without compromising the choice of method coefficients or the potential for efficient stepsize control. We analyze and compare the scalability of different parallel implementation strategies in detailed runtime experiments on different parallel architectures.
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Optimal Control Problems Governed by Nonlinear Partial Differential Equations and Inclusions
(2010)
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Julia Fischer
- The focus of this thesis lies on examining the solvability of optimal control problems constrained by nonlinear partial differential equations (PDE) and inclusions (PDI). There exist statements on the existence of solutions for optimal control problems with linear and semi-linear PDEs with monotone parts. The theory for non-monotone PDEs resp. the related optimal control problems is, to the author’s knowledge, incomplete regarding important issues. This concerns particularly the case of PDEs containing mappings, which only satisfy boundedness conditions on restricted sets. At first an optimal control problem is considered, which is characterized by a Laplace equation with Dirichlet boundary conditions and a nonlinear non-monotone Nemytskii operator. Under the decisive assumption of the existence of so called sub- and supersolutions for this differential equation and by introducing a truncation operator we can define an auxiliary problem which is characterized by a pseudomonotone operator. Thereby the solution theory for pseudomonotone operators of Brézis (1968) is applicable. Moreover, starting with the definitions of sub- und supersolution it can be shown, that every solution of the auxiliary problem is a solution of the original problem. The choice of a new optimal control problem which substitutes the original optimal control problem is again governed by the properties of the auxiliary operator. The equivalence of the auxiliary problem to the original problem and the existence of at least one solution can be shown. The technique of applying the Theorem of Lax-Milgram on a linearized problem can be adapted to the semi-linear non-monotone case. This procedure is already known from the theory of semi-linear monotone problems. For optimal control problems with quasi-linear differential equations, different methods are required. As in the semi-linear case, the property of pseudomonotonicity plays a key role in proving the existence of a solution of the quasi-linear PDE. In the proof of the existence of a solution for the optimal control problem other properties of the auxiliary operator are exploited. In the elliptic case operators which satisfy the S+ -property are important. In order to utilize this property, a transformation of the operator to some coercive auxiliary operator is necessary. For this reason a term is added, which penalizes the deviation from the admissible set of states. This term is characterized by a factor, which is derived explicitly in this work. The proof of the existence of a solution of the optimal control problem with parabolic equations is based on the definition of an auxiliary operator, coercivity and the S+ -property of operators. The set of solutions of the considered PDE is compact, but the number of solutions and the situation to each other is unknown. This leads to difficulties in deriving necessary optimality conditions. For this reason a direct approach to solve the optimal control problem with semi-linear PDEs is introduced. It is assumed, that the state constraints coincide with the sub- and the supersolution of the PDE with the upper and lower boundary of the control variable. Using an auxiliary operator, this assumption allows the formulation of an equivalent optimal control problem without pointwise state constraints. Through semi-discretization we can define a family of optimal control problems on a finite dimensional state-space. Existence of a subsequence of solutions of these optimal control problems which converges to a solution of the original problem is shown. Another important class of optimal control problems include differential inclusions which are described by multivalued operators. Quasi-linear elliptic inclusions are examined under global as well as local boundedness conditions. Under the assumption of global boundedness the properties of pseudomonotonicity and coercivity for a multivalued auxiliary operator are proven. The existence of at least one solution for the original inclusion follows from the application of a result from Hu and Papageorgiou (1997) on the auxiliary problem. The existence of at least one solution of the optimal control problem is proven by exploiting the coercivity of the multivalued auxiliary operator and the S+ -property of the non-multivalued part of this mapping. In the case of multivalued mappings of Clarke’s gradient type, the existence of at least one solution of the optimal control problem can be shown under local boundedness conditions. Elliptic as well as parabolic quasi-linear inclusions are considered. The proof is again based on coercivity and the S+ -property of the related auxiliary operators and the embedding properties of the spaces.
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Improved Intermittent Clutter Filtering For Wind Profiler Radar
(2010)
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Volker Lehmann
- Ground-based remote measurements of the vertical profile of the horizontal wind vector in the atmosphere by radar wind profiler (RWP) is a technique that has been significantly developed since the first demonstration with the Jicamarca radar by Woodman and Guillen in the early 1970s. Currently, there exist several operational networks of those instruments in the USA, Europe and Japan which provide continuous wind measurements in real-time and most of the data are successfully assimilated in numerical weather prediction models. Although this is an obvious indication of maturity, practical experience has shown that further improvements are both possible and necessary. While the high sensitivity of these clear-air radars is required for receiving the weak atmospheric echoes, it makes them also particularly vulnerable to unwanted radar returns and in-band radio frequency interference. Signal processing must therefore especially deal with the problem of filtering of these unwanted contributions, to avoid associated measurement errors. A specific difficulty are clutter echoes from various airborne objects, such as aircraft or birds, which generate strong, intermittent contributions to the received signal. The standard RWP signal processing is not able to deal with these signals in an efficient way, because the model assumption on which the processing is based is violated. With the development of sophisticated mathematical tools for the analysis of non-stationary signals in the last two decades and a better understanding of the practically relevant RWP clutter issues, a number of efforts have been made to tackle especially the challenging problem of intermittent clutter returns from migrating birds. In this dissertation it is shown that the signal structure of RWP raw data contaminated by intermittent clutter is much clearer revealed by a joint time-frequency analysis based on the windowed Fourier transform than by other possible signal descriptions, in particular pure time or frequency representations. An effective intermittent clutter reduction algorithm, called the Gabor filter, is obtained by a combination of a numerically feasible discrete Gabor frame expansion with the statistical test for a stationary Gaussian random signal. This approach is optimized by using near-tight frames and selecting a time-frequency resolution that provides a jointly sparse representation of both atmospheric and clutter signal components. A first evaluation of this approach has shown a superior performance in comparison with hitherto existing methods, but it was also found that additional quality-control of the derived Doppler spectra is still required during extreme bird migration events. The latter is in all likelihood indicative of a principal limit of radar wind profiling during such conditions. However, an effective quality control of the measurement is possible through a combination of a stationarity estimate provided by the Gabor algorithm with a-priori information about typical atmospheric echoes.
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Investigation of the properties of iron-bearing alloys and silicates and their implications for the Earth’s lower mantle and core
(2010)
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Olga Narygina
- (1) (Mg,Fe)(Si,Al)O3 perovskite comprises about 80% of the Earth’s lower mantle by volume, leaving ~ 15% to (Mg,Fe)O ferropericlase and ~ 5% to CaSiO3 perovskite. Therefore characteristics of the lower mantle would be determined mostly by the properties of the silicate perovskite and ferropericlase. While high-spin – low-spin crossover in (Mg,Fe)O is nicely described in literature, the electronic state of iron in silicate perovskite at high pressures and temperatures remains controversial. Conclusions derived from the results of X-ray emission (XES) and nuclear forward scattering (NFS) spectroscopic studies of Fe-bearing silicate perovskite are not in agreement on the pressure and temperature conditions of the transition and on whether Fe2+ or Fe3+ or both iron cations are involved. We undertook an alternative study of (Mg,Fe)(Si,Al)O3 perovskite at a wide pressure and temperature range using a number of different spectroscopic techniques (conventional Mössbauer, X-ray absorption near edge structure (XANES), NFS and X-ray diffraction (XRD) spectroscopies), in order to get a rather complete picture regarding the spin state of iron in this compound. Desirable pressures relevant to those in the Earth’s lower mantle were achieved by means of diamond anvil cells, equipped with miniature external resistive heaters, providing homogeneous heating up to 1000 K, which enables us to estimate the effect of temperature as well. Our Mössbauer and XANES data, collected at pressures to 110 GPa and temperatures to 1000 K for silicate perovskite, revealed a gradual transition involving Fe2+, which at room temperature occurs over a rather wide pressure range, 35-70 GPa, but becomes narrow at high temperatures. This observation coincides with the previously reported drop in spin number revealed by XES. Taking this into account and based on the fact that our XRD measurements, performed at the corresponding pressure-temperature conditions, do not suggest any appreciable structural change in perovskite, we conclude that the origin of the observed transition is fully electronic. Considering the simplified energy diagram of ferrous iron, sitting in 8-12 fold coordinated polyhedra in the perovskite structure, and by analysing the effect of pressure on the distribution of valence electrons over the energy levels, we propose stabilization of intermediate spin Fe2+ in magnesium silicate perovskite at pressures over 35 GPa. The gradual character of high-spin – intermediate-spin crossover in silicate perovskite does not assume any abrupt changes of the lower mantle properties. However due to the negative Clapeyron slope of the transition in some areas in the uppermost lower mantle, located in the vicinity of subducting slabs or hot mantle upwellings, they would have slightly different properties (namely electrical and thermal conductivity, element partitioning) with respect to the surrounding mantle. (2) Although the effect of spin transitions in lower mantle silicate perovskite and ferropericlase on the iron partitioning between these two phases has been widely discussed in the literature, the question remains open, mainly due to the lack of in situ experiments under the relevant pressure and temperature conditions. We approach this problem using combined in situ synchrotron XRD and XANES spectroscopic measurements with laser-heated diamond anvil cell (LH-DAC) technique. The assemblages of perovskite and ferropericlase were synthesized via the breakdown reaction of ringwoodite or a natural San Carlos olivine. Our data, collected from 22 GPa to 115 GPa, after laser heating to 1950 K and 2300 K, confirmed previously reported preferred partitioning of iron in low-spin ferropericlase with respect to high or intermediate spin perovskite. Increase of temperature was shown to slightly increase the amount of Fe in perovskite. (3) The phase diagram of Fe-enriched FeNi alloy at elevated pressures and temperatures comparable to those in the Earth’s core as well as the effect of the potential light element in the core on the system remains under debate. The reason is very simple: the necessary pressure-temperature range (300-350 GPa and 5,000-7,000 K) is hardly achieved in the laboratory. Conditions close to those in the core can be created in LH-DAC experiments; however the main disadvantage of the technique is a lack of control on the system under study. In contrast, the large-volume press (LVP) provides rather equilibrated and controllable experimental conditions, although at significantly lower pressures. Therefore we carried out a “cross-checking” study of phase relations in Fe1-xNix (0.10 < x < 0.22) and Fe0.90Ni(0.10-x)Cx (0.01 < x < 0.05) systems at pressures to 52 GPa and temperatures to 2600 K, using LH-DAC and LVP high pressure techniques. In situ and ex situ sample analyses were done by means of XRD, Mössbauer spectroscopy, and scanning and transmission electron microscopies. We showed that laser heating in the DAC can promote undesired reactions between the sample (FeNi alloy in our case) and carbon, which upon laser heating diffuses from the diamond anvils through the pressure-transmitting layers. We investigated the mechanism of carbon incorporation into the structure of FeNi alloy at high pressures and temperatures, and showed that rapid cooling of fcc-structured carbon-bearing FeNi alloy to room temperature (either in the case of LH-DAC or LVP quenched experiments) results in the formation of the metastable solid solution of bcc-FeNi, bct-Fe-Ni-C (known in metallurgy as martensite) and a certain amount of preserved fcc Fe-Ni-C.
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The effect of iron on the stability, water content and compressibility of mantle silicates – Implications for a hydrous Martian interior
(2010)
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Geertje Ganskow
- Summary This thesis addresses three different effects of Fe on the properties of nominally anhydrous transition minerals and dense hydrous Mg-silicates. Furthermore, the potential presence of dense hydrous Mg-Fe silicates (DHMS) in the Martian interior and the water storage potential of a hydrous Martian mantle are evaluated. 1. The effect of iron on the water content of ringwoodite The results show that the water contents of Fe-rich ringwoodites of about 0.4-0.7 wt% H2O are considerably reduced compared to pure Mg-ringwoodite. Thus, the ringwoodite samples show an inverse correlation of Fe- and water content. The Mg-site octahedra represent the favored protonation site in ferroan ringwoodites corresponding to the Mg2+=2H+ water substitution mechanism. In addition, Fe3+ diminishes the water content of ringwoodites due to the reduction of potential protonation sites. This is caused by the creation of Mg-site vacancies by the oxidation of Fe and the occupation of octahedral sites by Fe-atoms, which are probably not involved in water substitution mechanism. These results indicate that less water can be stored in nominally anhydrous mantle silicates of Fe-rich planetary mantles. 2. The effect of iron on the compressibility of hydrous ferroan ringwoodite The effect of Fe on the compressibility of ringwoodite is particularly important for the interpretation of the structure of Fe-rich planetary interiors such as the Martian mantle. Measurements at ambient conditions yield to unit-cell lattice parameters of a=8.1597(6) Å and V=543.28(13) ų (run 3854) and a=8.1384(3) Å and V=539.03(7) ų (run 4218). The P-V data were fitted with a second-order Birch-Murnaghan equation of state. The first pressure derivative of the bulk modulus, K´, was fixed to the value of 4 yielding to the following refined equation of state parameters: V0=543.32(7) ų and KT0=186.5(9) GPa (run 3854) and V0=539.01(5) ų and KT0=184.1(7) GPa (run 4218). Structural refinements indicate significant octahedral vacancies in sample 4218 due to the presence of 0.1 Fe3+ a.p.f.u. and the substitution of ~0.37 wt% H2O. The values of bulk modulus of (Mg,Fe)2SiO4-ringwoodites found in this study are very similar to that of the Fe-endmember ringwoodite, which suggests that the Fe substitution has little effect on the compressibility of ringwoodite. This also indicates that the close-packing of oxygens of the spinel structure is the major factor in determining its compressibility. This cannot be affected by the presence of up to 0.1 a.p.f.u. of vacancies. 3. The effect of iron on the stability of hydrous mantle silicates The transformation pressure of olivine to wadsleyite (simple Martian mantle composition) is lowered by 2 GPa. The shifts of stability fields toward lower pressures are possibly caused by the presence of Fe3+ and H2O. The shift of the olivine-wadsleyite transition would result in an extended upper mantle transition zone, compared to the anhydrous mantle, and consequently yield an increased water storage potential of the Martian mantle. The DHMS, phase D and superhydrous B (SHyB) show stabilities up to 1300°C at 23 GPa (phase D, MgFeSiO4+9.5 wt% H2O bulk composition) and for the simple Martian mantle composition up to 1450°C at 20.5 GPa (phase D and SHyB), which represents a higher stability of DHMS than previously reported. This suggests that phase D and SHyB are relevant DHMS in Fe-rich mantles of planetary systems. 4. The potential presence of dense hydrous Mg-Fe silicates in the Martian interior and the water storage potential of a hydrous Martian mantle This experimental study of mantle silicates indicates that the Martian mantle consists basically of upper mantle with olivine, garnet and pyroxene, as well as upper and lower transition zone build up by wadsleyite and ringwoodite together with pyroxene and majoritic-garnet, respectively. The water contents of wadsleyite with 0.6 wt% H2O and ringwoodite with 1.1 wt% H2O are reduced compared to the Mg-endmembers. The Martian transition zone, however, shows the largest water storage capacity since the upper mantle mineral olivine accommodates up to 0.3 wt% H2O. Pressure and temperature conditions at the core-mantle boundary are insufficient to reach the perovskite stability field, i.e. a lower Martian mantle cannot be expected based on the results of this study. These results imply that significant amounts of water can be stored in the Martian transition zone as well as the upper mantle. In addition, DHMS would be stable up to 1450°C at 20.5 GPa in a hydrous Martian mantle model. On the basis of thermal evolution models of the Martian mantle, and Fe partitioning data between mineral phases and melt it is discussed that DHMS may form in the Martian interior at P-T conditions corresponding to the lower Martian transition zone.
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Control of the release of digestive enzymes in the cricket Gryllus bimaculatus and the fall armyworm, Spodoptera frugiperda
(2010)
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Digali Lwalaba
- This thesis investigates control of the release of digestive enzymes in the cricket Gryllus bimaculatus and the fall armyworm, Spodoptera frugiperda. 1. Control of enzyme release in the cricket G. bimaculatus. Using flat-sheet preparations of the caecum, digestive enzyme release was investigated. More trypsin, aminopeptidase and amylase are secreted in the caecum of fed crickets than in unfed crickets, but basal levels of certain enzymes are released continuously even in unfed animals. A variable ratio of nutrients in ingested food leads to a different ratio of digestive enzyme release, but a high nutrient component in the food does not necessarily induce a high digestive enzyme release for that component. Maltose and glucose elevate amylase release from the tissues into the incubation medium, but starch does not. Bovine serum albumin (BSA), peptone and a mixture of amino acids have almost no effect on the release of aminopeptidase, and only low concentrations of peptone increase trypsin release. In crickets, the continuous release of proteases is sufficient to meet the needs for growth, and only moderate stimulation of trypsin results from feeding. Carbohydrates are used for energy, and the release of amylase is adjusted to the amount of food ingested. The neuropeptide allatostatin Grybi-AS 5 elevates the release of amylase in fed females, but not of trypsin or aminopeptidase, however, both amylase and trypsin release are stimulated by AS 5 in unfed crickets. Fed crickets have sufficient trypsin to obtain needed amino acids, but unfed do not, therefore the AS stimulation of trypsin release in unfed crickets makes sense. 2. Control of enzyme release in the larvae of S. frugiperda. A flat-sheet preparation of the ventriculus was used to test the release of amylase, trypsin and aminopeptidase in response to specific nutrients in the food and to specific neuropeptides. The epithelial secretion rate of amylase and trypsin was about 20% of the amount of enzyme present in the ventricular lumen, which, considering the efficient counter-current recycling of enzymes, suggests that the secretion rate is adequate to replace egested enzymes. Dietary carbohydrates are used for energy, and larvae adjust amylase activity to carbohydrate ingestion. Amylase activity is 5-times higher in fed compared to unfed larvae, and sugars in the incubation medium induces more than a 300 % increase in amylase release. Plants contain a low level of protein, but larvae need proteins for growth, thus the larvae can not afford to lose proteins by egestion. Therefore, trypsin activity remains high even in unfed larvae. As a result, proteins and amino acids have little or no effect on trypsin or aminopeptidase release in incubated tissues. The control of enzymes release in response to food is most likely mediated through neurohormones. Indeed, an allatostatin (Spofr-AS A5) inhibits amylase and trypsin release, and allatotropin (Manse- AT) stimulates amylase and trypsin release. Spofr-AS A5 also inhibits ileum myoactivity and Manse- AT stimulates myoactivity. 3. Inhibition of enzyme release in the larvae of S. frugiperda. Exogenous inhibitors are produced by plants, and are ingested by the insect. Endogenous inhibitors are produced by the gut epithelial cells themselves. A dose-dependent inhibition of endogenous enzymes occur in the lumen after feeding L6 larvae with the exogenous serine protease inhibitor from soybean (SBTI), the specific trypsin inhibitor TLCK, an aminopeptidase inhibitor (bestatin), and an amylase inhibitor from wheat. Inhibition in tissue extracts is seen only with higher doses of SBTI and TLCK. Inhibition of enzyme release into the incubation medium is apparent only with very high doses of SBTI. Inhibition in the tissues and inhibition of release indicate a direct cellular response to an inhibitor present in the lumen. The elevation of aminopeptidase activity in response to ingested trypsin inhibitors indicates a cellular synthesis in response to the product of a digestive enzyme. The enzymes investigated are irreversibly inactivated by 10 min at 90°C, but the corresponding inhibitors are not, therefore endogenous inhibitors could be identified. Endogenous inhibitors are present in the ventricular cells and in the lumen. We suggest that the endogenous protease inhibitors may protect the epithelium by inactivation of the trypsin in underfed larvae. This is the first explanation of how insects are able to secrete an active trypsin.
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Der Einfluss der Ketten- und der Persistenzlänge auf den Soret-Effekt in verdünnten Polymerlösungen
(2010)
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Dominik Stadelmaier
- In dieser Arbeit wurde der Einfluss der Kettenlänge und -steifheit auf den Soret-Effekt in verdünnten Polymerlösungen untersucht. Dazu wurden die Transportkoeffizienten Soret-Koeffizient, Thermodiffusionskoeffizient und Diffusionskoeffizient D an Polymerlösungen im Grenzfall unendlicher Verdünnung bei einer Temperatur von 22 °C bestimmt. Bei den untersuchten Polymeren handelt es sich um Polystyrol (PS), Polydimethylsiloxan (PDMS), Polymethylmethacrylat (PMMA) und Poly-t-butylmethacrylat (PtBMA). Zudem wurden die linearen Alkane Hexan, Oktan, Dekan, Dodekan, Pentadekan, Hexadekan und Eicosan gemessen, die alle als Oligomere des Polymers Polyethylen (PE) betrachtet werden können. Als Lösungsmittel wurden Chloroform, Cyclohexan, Cyclohexanon, Cyclooktan, Ethylacetat, Ethylbenzol, Methyl-Ethyl-Keton (MEK), Tetrahydrofuran (THF) und Toluol verwendet. Zur Untersuchung des Einflusses der Kettenlänge auf den Soret-Effekt wurden Experimente an PS-Oligomeren in einem Molmassenbereich von 10 kg/mol bis hin zum effektiven Monomer Ethylbenzol sowie an den genannten linearen Alkanen durchgeführt. Der Einfluss der Persistenzlänge wurde durch Messungen an hochpolymeren Lösungen der Polymere PDMS, PMMA und PtBMA untersucht, wobei zusätzlich die auf unendlich große Molmassen extrapolierten Werte der n-Alkane herangezogen wurden. Bei den Untersuchungen der PS-Oligomere wurde in dieser Arbeit festgestellt, dass bei großen Polymermassen die Lösungsmittelviskosität der dominierende und einzig signifikante Parameter des Lösungsmittels für Thermodiffusion wird und dass das Produkt eta D_T einen gemeinsamen Plateau-Wert erreicht. Bei kürzeren Ketten nehmen die Thermodiffusionskoeffizienten ab, zudem liegen die Datenpunkte für verschiedene Lösungsmittel nicht mehr auf einer gemeinsamen Kurve. In einigen Fällen wird sogar ein Vorzeichenwechsel des Soret-Koeffizienten beobachtet. Ein Vergleich der Ergebnisse zweier effektiver Monomere, die sich nur bezüglich ihrer Endgruppe unterscheiden, zeigt, dass die Abnahme des Thermodiffusionskoeffizienten bei Verkürzung der Kettenlänge nicht auf einen Endgruppeneffekt zurückzuführen ist. Auch die früher in der Literatur zu findende Annahme, dass die Molmassenunabhängigkeit bei großen Massen eine Monomereigenschaft des Polymers ist, wird durch diese Beobachtung nicht gestützt. Die für Thermodiffusion relevanten Einheiten sind stattdessen korrelierte Segmente mit einer dem Kuhnschen Segment vergleichbaren Größe. Der Soret-Koeffizient steigt bei kurzen Ketten mit zunehmender Masse monoton an. Ein Wechsel des Lösungsmittels führt zu einer nahezu konstanten Verschiebung, unabhängig von der Molmasse. Für lange Polymerketten wird der hydrodynamische Radius die dominierende Eigenschaft für den Soret-Koeffizienten. Die Messungen der linearen Alkane ergänzen die für PS entwickelte Beschreibung durch Hinzunahme eines Polymers mit signifikant kürzerem korrelierten Segment. Auch für das Polymer PE verhalten sich sehr kurze Oligomere wie kleine Moleküle, d.h. es existieren keine einfachen Regeln zur Vorhersage des thermophoretischen Verhaltens. Anders als bei PS besitzen alle gemessenen Alkanlösungen negative Thermodiffusionskoeffizienten. Der molmassenunabhängige Bereich ist messtechnisch nicht zugänglich, da längere PE-Ketten bei Raumtemperatur in praktisch allen Lösungsmitteln unlöslich sind. Eine Extrapolation der Messdaten auf unendlich große Molmassen ergibt, anders als bei PS, molmassenabhängige Plateaus für das Produkt eta D_T. Die Untersuchungen der hochpolymeren Polymerlösungen von PDMS, PMMA und PtBMA erweitern das empirische Modell um den Einfluss unterschiedlicher Persistenzlängen auf den Soret-Effekt. Bei hinreichend großen Einheiten, die der Thermodiffusion unterliegen, ergeben sich lösungsmittelunabhängige Plateau-Werte für eta D_T. Darüber hinaus wird der Thermodiffusionskoeffizient unabhängig von der chemischen Natur der Polymere. Voraussetzung dafür ist offenbar, dass die Masse der korrelierten Segmente um mindestens eine Größenordnung über der Masse des Lösungsmittels liegt. Für sehr flexible Polymere hingegen werden niedrigere Werte für eta D_T erreicht und die Plateau-Werte bleiben lösungsmittelabhängig. Auch negative Thermodiffusionskoeffizienten treten auf. Eine Extrapolation der konzentrationsabhängig gemessenen Thermodiffusionskoeffizienten von Literaturdaten zeigt, dass die meisten kleineren Moleküle den für Polymere typischen Plateau-Wert nicht erreichen. Eine mögliche Schlussfolgerung daraus ist, dass die hier formulierte empirische Beschreibung nicht nur für korrelierte Segmente innerhalb einer Polymerkette, sondern auch für Einzelmoleküle gültig ist. Allerdings existieren auch Systeme, bei denen Abweichungen von den genannten Gesetzmäßigkeiten auftreten.
