Biophysical Characterization of Interactions Involving Importin-α during Nuclear Import

Proteins containing the classical nuclear localization sequences (NLSs) are imported into the nucleus by the importin-α/β heterodimer. Importin-α contains the NLS binding site, whereas importin-β mediates the translocation through the nuclear pore. We characterized the interactions involving importin-α during nuclear import using a combination of biophysical techniques (biosensor, crystallography, sedimentation equilibrium, electrophoresis, and circular dichroism). Importin-α is shown to exist in a monomeric autoinhibited state (association with NLSs undetectable by biosensor). Association with importin-β (stoichiometry, 1:1; K D = 1.1 × 10 -8 M) increases the affinity for NLSs; the importin-α/β complex binds representative monopartite NLS (simian virus 40 large T-antigen) and bipartite NLS (nucleoplasmin) with affinities (K D = 3.5 × 10 -8 M and 4.8 × 10 -8 M, respectively) comparable with those of a truncated importin-α lacking the autoinhibitory domain (T-antigen NLS, K D = 1.7 × 10 -8 M; nucleoplasmin NLS, K D = 1.4 × 10 -8 M). The autoinhibitory domain (as a separate peptide) binds the truncated importin-α, and the crystal structure of the complex resembles the structure of full-length importin-α. Our results support the model of regulation of nuclear import mediated by the intrasteric autoregulatory sequence of importin-α and provide a quantitative description of the binding and regulatory steps during nuclear import.

The nuclear matter effects in π0 photoproduction at high energies

The in-medium influence on π0 photoproduction from spin zero nuclei is carefully studied in the GeV range using a straightforward Monte Carlo analysis. The calculation takes into account the relativistic nuclear recoil for coherent mechanisms (electromagnetic and nuclear amplitudes) plus a time dependent multi-collisional intranuclear cascade approach (MCMC) to describe the transport properties of mesons produced in the surroundings of the nucleon. A detailed analysis of the meson energy spectra for the photoproduction on 12C at 5.5 GeV indicates that both the Coulomb and nuclear coherent events are associated with a small energy transfer to the nucleus (≲ 5 MeV), while the contribution of the nuclear incoherent mechanism is vanishing small within this kinematical range. The angular distributions are dominated by the Primakoff peak at extreme forward angles, with the nuclear incoherent process being the most important contribution above θπ0 ≲ 20. Such consistent Monte Carlo approach provides a suitable method to clean up nuclear backgrounds in some recent high precision experiments, such as the PrimEx experiment at the Jefferson Laboratory Facility.

Nuclear mitochondrial-like sequences in ants: Evidence from Atta cephalotes (Formicidae: Attini)

Nuclear mitochondrial-like sequences (numts) are copies of mitochondrial DNA that have migrated to the genomic DNA. We present the first characterization of numts in ants, these numts being homologues to a mitochondrial DNA fragment containing loci the 3′ portion of the cytochrome oxidase I gene, an intergenic spacer, the tRNA leucine gene and the 5′ portion of the cytochrome oxidase II gene. All 67 specimens of Atta cephalotes (Hymenoptera: Formicidae: Attini) investigated had these homologues, which are within two monophyletic groups that we called numt1 and numt2. Numt1 and numt2 sequences are less variable than mitochondrial sequences and released from the severe purifying selection constraining the evolution of mitochondrial genes. Their formation probably involved bottlenecks related to two distinct transfer events of ancient and fast evolving mitochondrial DNA fragments to comparative slowly evolving nuclear DNA regions. © 2007 The Authors.

Estudos estruturais com a importina-α de mamíferos e peptídeos de sequências de localização nuclear (NLS)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Inibição da maturação nuclear pela butirolactona I durante o transporte de oócitos bovinos destinados à produção in vitro de embrões (PIV)

Pós-graduação em Medicina Veterinária - FCAV

Estudo teórico da contribuição do espalhamento nuclear não elástico na trajetória de prótons de energias entre 50 e 250 MeV em materiais de interesse em radiologia: aplicação em tomografia com prótons

The goal of this work is to study the process of interaction of protons with matter through Monte Carlo simulation. For this purpose, it was employed the SRIM program (Stopping and Range of Ions in Matter ) and MCNPX (Monte Carlo N-Particle eXtended) v2.50. This work is going to support the development of a tomography system with protons. It was studied the interaction of proton with the follow materials: Polimethyl Mehacralate (PMMA), MS20 Tissue Substitute and water. This work employed energies in range of 50 MeV and 250 MeV, that is the range of clinical interest. The energy loss of proton after cross a material layer, the decreasing of its intensity, the angular and lateral de ection of incident beam, including and excluding nuclear interactions. This work is related with Medical Physics and Material Physics, like interaction of radiation with matter, particle transport phenomena, and the experimental methods in Nuclear Physics like simulation and computational by Monte Carlo method

Shearless transport barriers in magnetically confined plasmas

Shearless transport barriers appear in confined plasmas due to non-monotonic radial profiles and cause localized reduction of transport even after they have been broken. In this paper we summarize our recent theoretical and experimental research on shearless transport barriers in plasmas confined in toroidal devices. In particular, we discuss shearless barriers in Lagrangian magnetic field line transport caused by non-monotonic safety factor profiles. We also discuss evidence of particle transport barriers found in the TCABR Tokamak (University of Sao Paulo) and the Texas Helimak (University of Texas at Austin) in biased discharges with non-monotonic plasma flows.

Neutronics analyses for fast spectrum nuclear systems and scenario studies for advanced nuclear fuel cycles

The present PhD thesis summarizes the three-years study about the neutronic investigation of a new concept nuclear reactor aiming at the optimization and the sustainable management of nuclear fuel in a possible European scenario. A new generation nuclear reactor for the nuclear reinassance is indeed desired by the actual industrialized world, both for the solution of the energetic question arising from the continuously growing energy demand together with the corresponding reduction of oil availability, and the environment question for a sustainable energy source free from Long Lived Radioisotopes and therefore geological repositories. Among the Generation IV candidate typologies, the Lead Fast Reactor concept has been pursued, being the one top rated in sustainability. The European Lead-cooled SYstem (ELSY) has been at first investigated. The neutronic analysis of the ELSY core has been performed via deterministic analysis by means of the ERANOS code, in order to retrieve a stable configuration for the overall design of the reactor. Further analyses have been carried out by means of the Monte Carlo general purpose transport code MCNP, in order to check the former one and to define an exact model of the system. An innovative system of absorbers has been conceptualized and designed for both the reactivity compensation and regulation of the core due to cycle swing, as well as for safety in order to guarantee the cold shutdown of the system in case of accident. Aiming at the sustainability of nuclear energy, the steady-state nuclear equilibrium has been investigated and generalized into the definition of the ``extended'' equilibrium state. According to this, the Adiabatic Reactor Theory has been developed, together with a New Paradigm for Nuclear Power: in order to design a reactor that does not exchange with the environment anything valuable (thus the term ``adiabatic''), in the sense of both Plutonium and Minor Actinides, it is required indeed to revert the logical design scheme of nuclear cores, starting from the definition of the equilibrium composition of the fuel and submitting to the latter the whole core design. The New Paradigm has been applied then to the core design of an Adiabatic Lead Fast Reactor complying with the ELSY overall system layout. A complete core characterization has been done in order to asses criticality and power flattening; a preliminary evaluation of the main safety parameters has been also done to verify the viability of the system. Burn up calculations have been then performed in order to investigate the operating cycle for the Adiabatic Lead Fast Reactor; the fuel performances have been therefore extracted and inserted in a more general analysis for an European scenario. The present nuclear reactors fleet has been modeled and its evolution simulated by means of the COSI code in order to investigate the materials fluxes to be managed in the European region. Different plausible scenarios have been identified to forecast the evolution of the European nuclear energy production, including the one involving the introduction of Adiabatic Lead Fast Reactors, and compared to better analyze the advantages introduced by the adoption of new concept reactors. At last, since both ELSY and the ALFR represent new concept systems based upon innovative solutions, the neutronic design of a demonstrator reactor has been carried out: such a system is intended to prove the viability of technology to be implemented in the First-of-a-Kind industrial power plant, with the aim at attesting the general strategy to use, to the largest extent. It was chosen then to base the DEMO design upon a compromise between demonstration of developed technology and testing of emerging technology in order to significantly subserve the purpose of reducing uncertainties about construction and licensing, both validating ELSY/ALFR main features and performances, and to qualify numerical codes and tools.

LRP1 modulates APP trafficking and APP metabolism within compartments of the secretory pathway. Increased AICD generation is ineffective in nuclear translocation and transcriptional activation

LRP1 modulates APP trafficking and metabolism within compartments of the secretory pathway The amyloid precursor protein (APP) is the parent protein to the amyloid beta peptide (Abeta) and is a central player in Alzheimer’s disease (AD) pathology. Abeta liberation depends on APP cleavage by beta- and gamma-secretases. To date, only a unilateral view of APP processing exists, excluding other proteins, which might be transported together and/or processed dependent on each other by the secretases described above. The low density lipoprotein receptor related protein 1 (LRP1) was shown to function as such a mediator of APP processing at multiple steps. Newly synthesized LRP1 can interact with APP, implying an interaction between these two proteins early in the secretory pathway. Therefore, we wanted to investigate whether LRP1 can mediate APP trafficking along the secretory pathway, and, if so, whether it affects APP processing. Indeed, we demonstrate that APP trafficking is strongly influenced by LRP1 transport through the endoplasmic reticulum (ER) and Golgi compartments. LRP1-constructs with ER- and Golgi-retention motifs (LRP-CT KKAA, LRP-CT KKFF) had the capacity to retard APP trafficking at the respective steps in the secretory pathway. Here, we provide evidence that APP metabolism occurs in close conjunction with LRP1 trafficking, highlighting a new role of lipoprotein receptors in neurodegenerative diseases. Increased AICD generation is ineffective in nuclear translocation and transcriptional activity A sequence of amyloid precursor protein (APP) cleavages gives rise to the APP intracellular domain (AICD) together with amyloid beta peptide (Abeta) and/or p3 fragment. One of the environmental factors identified favouring the accumulation of AICD appears to be a rise in intracellular pH. This accumulation is a result of an abrogated cleavage event and does not extend to other secretase substrates. AICD can activate the transcription of artificially expressed constructs and many downstream gene targets have been discussed. Here we further identified the metabolism and subcellular localization of the constructs used in this well documented gene reporter assay. We also co-examined the mechanistic lead up to the AICD accumulation and explored possible significances for its increased expression. We found that most of the AICD generated under pH neutralized conditions is likely that cleaved from C83. Furthermore, the AICD surplus is not transcriptionally active but rather remains membrane tethered and free in the cytosol where it interacts with Fe65. However, Fe65 is still essential in AICD mediated transcriptional transactivation although its exact role in this set of events is unclear.

Nuclear charge radius determination of 7,10 Be and the one-neutron halo nucleus 11 Be

The only nuclear model independent method for the determination of nuclear charge radii of short-lived radioactive isotopes is the measurement of the isotope shift. For light elements (Z < 10) extremely high accuracy in experiment and theory is required and was only reached for He and Li so far. The nuclear charge radii of the lightest elements are of great interest because they have isotopes which exhibit so-called halo nuclei. Those nuclei are characterized by a a very exotic nuclear structure: They have a compact core and an area of less dense nuclear matter that extends far from this core. Examples for halo nuclei are 6^He, 8^He, 11^Li and 11^Be that is investigated in this thesis. Furthermore these isotopes are of interest because up to now only for such systems with a few nucleons the nuclear structure can be calculated ab-initio. In the Institut für Kernchemie at the Johannes Gutenberg-Universität Mainz two approaches with different accuracy were developed. The goal of these approaches was the measurement of the isotope shifts between (7,10,11)^Be^+ and 9^Be^+ in the D1 line. The …first approach is laser spectroscopy on laser cooled Be^+ ions that are trapped in a linear Paul trap. The accessible accuracy should be in the order of some 100 kHz. In this thesis two types of linear Paul traps were developed for this purpose. Moreover, the peripheral experimental setup was simulated and constructed. It allows the efficient deceleration of fast ions with an initial energy of 60 keV down to some eV and an effcient transport into the ion trap. For one of the Paul traps the ion trapping could already be demonstrated, while the optical detection of captured 9^Be^+ ions could not be completed, because the development work was delayed by the second approach. The second approach uses the technique of collinear laser spectroscopy that was already applied in the last 30 years for measuring isotope shifts of plenty of heavier isotopes. For light elements (Z < 10), it was so far not possible to reach the accuracy that is required to extract information about nuclear charge radii. The combination of collinear laser spectroscopy with the most modern methods of frequency metrology …finally permitted the …first-time determination of the nuclear charge radii of (7,10)^Be and the one neutron halo nucleus 11^Be at the COLLAPS experiment at ISOLDE/ CERN. In the course of the work reported in this thesis it was possible to measure the absolute transition frequencies and the isotope shifts in the D1 line for the Be isotopes mentioned above with an accuracy of better than 2 MHz. Combination with the most recent calculations of the mass effect allowed the extraction of the nuclear charge radii of (7,10,11)^Be with an relative accuracy better than 1%. The nuclear charge radius decreases from 7^Be continuously to 10^Be and increases again for 11^Be. This result is compared with predictions of ab-initio nuclear models which reproduce the observed trend. Particularly the "Greens Function Monte Carlo" and the "Fermionic Molecular Dynamic" model show very good agreement.

Fast and accurate numerical solutions in some problems of particle and radiation transport: synthetic acceleration for the method of short characteristics, Doppler-broadened scattering kernel, remote sensing of the cryosphere

The aim of this work is to present various aspects of numerical simulation of particle and radiation transport for industrial and environmental protection applications, to enable the analysis of complex physical processes in a fast, reliable, and efficient way. In the first part we deal with speed-up of numerical simulation of neutron transport for nuclear reactor core analysis. The convergence properties of the source iteration scheme of the Method of Characteristics applied to be heterogeneous structured geometries has been enhanced by means of Boundary Projection Acceleration, enabling the study of 2D and 3D geometries with transport theory without spatial homogenization. The computational performances have been verified with the C5G7 2D and 3D benchmarks, showing a sensible reduction of iterations and CPU time. The second part is devoted to the study of temperature-dependent elastic scattering of neutrons for heavy isotopes near to the thermal zone. A numerical computation of the Doppler convolution of the elastic scattering kernel based on the gas model is presented, for a general energy dependent cross section and scattering law in the center of mass system. The range of integration has been optimized employing a numerical cutoff, allowing a faster numerical evaluation of the convolution integral. Legendre moments of the transfer kernel are subsequently obtained by direct quadrature and a numerical analysis of the convergence is presented. In the third part we focus our attention to remote sensing applications of radiative transfer employed to investigate the Earth's cryosphere. The photon transport equation is applied to simulate reflectivity of glaciers varying the age of the layer of snow or ice, its thickness, the presence or not other underlying layers, the degree of dust included in the snow, creating a framework able to decipher spectral signals collected by orbiting detectors.

Valorisation of organic waste: new developments from proton nuclear magnetic resonance characterization

The last half-century has seen a continuing population and consumption growth, increasing the competition for land, water and energy. The solution can be found in the new sustainability theories, such as the industrial symbiosis and the zero waste objective. Reducing, reusing and recycling are challenges that the whole world have to consider. This is especially important for organic waste, whose reusing gives interesting results in terms of energy release. Before reusing, organic waste needs a deeper characterization. The non-destructive and non-invasive features of both Nuclear Magnetic Resonance (NMR) relaxometry and imaging (MRI) make them optimal candidates to reach such characterization. In this research, NMR techniques demonstrated to be innovative technologies, but an important work on the hardware and software of the NMR LAGIRN laboratory was initially done, creating new experimental procedures to analyse organic waste samples. The first results came from soil-organic matter interactions. Remediated soils properties were described in function of the organic carbon content, proving the importance of limiting the addition of further organic matter to not inhibit soil processes as nutrients transport. Moreover NMR relaxation times and the signal amplitude of a compost sample, over time, showed that the organic matter degradation of compost is a complex process that involves a number of degradation kinetics, as a function of the mix of waste. Local degradation processes were studied with enhanced quantitative relaxation technique that combines NMR and MRI. The development of this research has finally led to the study of waste before it becomes waste. Since a lot of food is lost when it is still edible, new NMR experiments studied the efficiency of conservation and valorisation processes: apple dehydration, meat preservation and bio-oils production. All these results proved the readiness of NMR for quality controls on a huge kind of organic residues and waste.

Global modeling of pollutant transport and deposition from anthropogenic emission hot spots on global scale

Urban centers significantly contribute to anthropogenic air pollution, although they cover only a minor fraction of the Earth's land surface. Since the worldwide degree of urbanization is steadily increasing, the anthropogenic contribution to air pollution from urban centers is expected to become more substantial in future air quality assessments. The main objective of this thesis was to obtain a more profound insight in the dispersion and the deposition of aerosol particles from 46 individual major population centers (MPCs) as well as the regional and global influence on the atmospheric distribution of several aerosol types. For the first time, this was assessed in one model framework, for which the global model EMAC was applied with different representations of aerosol particles. First, in an approach with passive tracers and a setup in which the results depend only on the source location and the size and the solubility of the tracers, several metrics and a regional climate classification were used to quantify the major outflow pathways, both vertically and horizontally, and to compare the balance between pollution export away from and pollution build-up around the source points. Then in a more comprehensive approach, the anthropogenic emissions of key trace species were changed at the MPC locations to determine the cumulative impact of the MPC emissions on the atmospheric aerosol burdens of black carbon, particulate organic matter, sulfate, and nitrate. Ten different mono-modal passive aerosol tracers were continuously released at the same constant rate at each emission point. The results clearly showed that on average about five times more mass is advected quasi-horizontally at low levels than exported into the upper troposphere. The strength of the low-level export is mainly determined by the location of the source, while the vertical transport is mainly governed by the lifting potential and the solubility of the tracers. Similar to insoluble gas phase tracers, the low-level export of aerosol tracers is strongest at middle and high latitudes, while the regions of strongest vertical export differ between aerosol (temperate winter dry) and gas phase (tropics) tracers. The emitted mass fraction that is kept around MPCs is largest in regions where aerosol tracers have short lifetimes; this mass is also critical for assessing the impact on humans. However, the number of people who live in a strongly polluted region around urban centers depends more on the population density than on the size of the area which is affected by strong air pollution. Another major result was that fine aerosol particles (diameters smaller than 2.5 micrometer) from MPCs undergo substantial long-range transport, with about half of the emitted mass being deposited beyond 1000 km away from the source. In contrast to this diluted remote deposition, there are areas around the MPCs which experience high deposition rates, especially in regions which are frequently affected by heavy precipitation or are situated in poorly ventilated locations. Moreover, most MPC aerosol emissions are removed over land surfaces. In particular, forests experience more deposition from MPC pollutants than other land ecosystems. In addition, it was found that the generic treatment of aerosols has no substantial influence on the major conclusions drawn in this thesis. Moreover, in the more comprehensive approach, it was found that emissions of black carbon, particulate organic matter, sulfur dioxide, and nitrogen oxides from MPCs influence the atmospheric burden of various aerosol types very differently, with impacts generally being larger for secondary species, sulfate and nitrate, than for primary species, black carbon and particulate organic matter. While the changes in the burdens of sulfate, black carbon, and particulate organic matter show an almost linear response for changes in the emission strength, the formation of nitrate was found to be contingent upon many more factors, e.g., the abundance of sulfuric acid, than only upon the strength of the nitrogen oxide emissions. The generic tracer experiments were further extended to conduct the first risk assessment to obtain the cumulative risk of contamination from multiple nuclear reactor accidents on the global scale. For this, many factors had to be taken into account: the probability of major accidents, the cumulative deposition field of the radionuclide cesium-137, and a threshold value that defines contamination. By collecting the necessary data and after accounting for uncertainties, it was found that the risk is highest in western Europe, the eastern US, and in Japan, where on average contamination by major accidents is expected about every 50 years.

Molecular plating of thin lanthanide layers with improved material properties for nuclear applications

In der vorliegenden Arbeit werden Experimente beschrieben, die zu einem vertieften Verständnis fundamentaler Prozesse bei der elektrochemischen Herstellung von Dünnschichten, sog. Targets, für kernphysikalische und -chemische Studien führten. Targets wurden mittels 'Molecular Plating' (MP) hergestellt, indem eine Elektrodeposition aus organischem Medium in der Regel bei konstantem Strom in Zwei-Elektroden-Zellen. Die Resultate erlaubten, optimierte Herstellungs-bedingungen zu ermitteln, welche die Produktion deutlich verbesserter Targets erlaubten. MP bei konstantem Strom ist ein massentransportkontrollierter Prozess. Der angelegte Strom wird durch einen konstanten Fluss elektroaktiver Spezies zur Kathode – auf der die Schicht wächst – und Anode aufrechterhalten. Die Untersuchungen zeigten, dass das Zellenpotential des Elektrodepositionsystems immer durch den Ohm'schen Spannungsabfall auf Grund des Widerstandes der verwendeten Lösung dominiert wurde. Dies erlaubte die Herleitung einer Beziehung zwischen dem Zellenpotential und der Konzentration der elektroaktiven Spezies. Die Beziehung erlaubt die Erklärung des gemessenen zeitlichen Verlaufs des Zellenpotentials während der Abscheidung als Funktion der Elektrolytkonzentration. Dies dient als Basis, auf der nun ein umfassenderes Bild der Prozesse, die für die charakteristischen Minima im Potentialverlauf einer Abscheidung verantwortlich sind, gewonnen werden kann. Es konnte gezeigt werden, dass die Minima mit der fast vollständigen Entfernung (durch Abscheidung) der aus einem gelösten Salz erzeugten Nd-Ionen korrespondieren. Die abgeschiedene Spezies wurde als Nd3+ identifiziert, vermutlich als Carboxylat, Oxid oder Hydroxid, was auf Grund der hohen negative Werte des Standardredoxpotentials der Lanthanide verständlich erscheint. Von den vorliegenden elektroaktiven Spezies tragen die Nd3+ Ionen nur zu knapp 20% zum Gesamtstrom bei. Durch Elektrolyse tragen auch die Lösungsmittelkomponenten zu diese Strom bei. Die Gegenwart von elektrolysiertem Lösungsmittel wurde in Analysen der Dünnschichten bestätigt. Diese waren immer mit chemi- und physisorbierten Lösungsmittelmolekülen bedeckt. Die Analyse der Dünnschichten zeigte, dass die Oberflächen von einem furchenartiges Netz durchzogen waren, und dass diese während des Trocknen der Schichten nach dem MP entstanden. Ob die Schichten an Luft oder in inerter Atmosphäre trockneten, hatte keinen Einfluss. Es wurden Experimente mit mehreren Lösungsmitteln durchgeführt, die sich deutlich in ihren physikalischen Eigenschaften, v.a. dem Siedepunkt, unterschieden. Furchenfreie Dünnschichten konnten insbesondere bei MP in N,N-dimethylformamide (DMF) erzeugt werden. Die Verwendung von DMF in Kombination mit einer Abscheidung auf sehr glatten Substraten erlaubte die Produktion von sehr homogenen, glatten und defektfreien Schichten. Diese waren vermutlich geringeren inneren Spannungen während des Trocknens ausgesetzt, als Schichten auf raueren Substraten oder solche, die aus flüchtigeren Lösungsmitteln hergestellt wurden. Die Oberflächenrauigkeit des Substrats und das gewählte Lösungsmittel wurden so als Schlüsselfaktoren für die Produktion hochqualitativer Schichten identifiziert. Es konnte gezeigt werden, dass mit MP eine sehr effiziente Methode zur Herstellung homogener Schichten mit exzellenter Ausbeute ist. In weiteren Experimenten mit dem primordialen Alpha-Emitter 147Sm als Modellisotop wurde die Eignung solcher Schichten als Alpha-Quelle untersucht. Sowohl die Energieauflösung als auch der Anteil der Alpha-Teilchen, die den Detektor erreichten, waren von den Quelleneigenschaften abhängig. Die Effekte wurden verschiedenen Variablen der Dünnschicht zugeordnet, welche die Alpha-Spektren beeinflussten. Dominant war die Wahl des Lösungsmittels und die Rauigkeit des Substrats. Dies beeinflusste Schichtdicke und -morphologie sowie die Art des Schichtwachstums und veränderte die Detektionseffizienz in Alpha-Messungen bis zu 15%. Nur homogene, ebene Schichten, die aus DMF auf glatten Substraten abgeschieden wurden, eignen sich optimal als Alpha-Quelle. Die gewonnenen Ergebnisse erlauben die optimierte Herstellung nuklearer Targets durch MP. Künftige Anwendungen beinhalten insbesondere die Herstellung von Targets für neutroneninduzierte Spaltexperimente und untergrundarmeAlpha-Messungen sehr kleiner Aktivitäten.