Methods of efficient Monte-Carlo simulation when rare events are involved have been studied for several decades. Rare events are very important in the context of evaluating high quality computer/communication systems. Meanwhile, the efficient simulation of systems involving rare events poses great challenges. A simulation method is said to be efficient if the number of replicas required to get accurate estimates grows slowly, compared to the rate at which the probability of the rare event approaches zero. Despite the great success of the two mainstream methods, importance sampling (IS) and importance splitting, either of them can become inefficient under certain conditions, as reported in some recent studies. The purpose of this study is to look for possible enhancement of fast simulation methods. I focus on the ``level/phase process', a Markov process in which the level and the phase are two state variables. Furthermore, changes of level and phase are induced by events, which have rates that are independent of the level except at a boundary. For such a system, the event of reaching a high level occurs rarely, provided the system typically stays at lower levels. The states at those high levels constitute the rare event set. Though simple, this models a variety of applications involving rare events. In this setting, I have studied two efficient simulation methods, the rate tilting method and the adaptive splitting method, concerning their efficiencies. I have compared the efficiency of rate tilting with several previously used similar methods. The experiments are done by using queues in tandem, an often used test bench for the rare event simulation. The schema of adaptive splitting has not been described in literature. For this method, I have analyzed its efficiency to show its superiority over the (conventional) splitting method. The way that a system approaches a designated rare event set is called the system's large deviation behavior. Toward the end of gaining insight about the relation of system behavior and the efficiency of IS simulation, I quantify the large deviation behavior and its complexity. This work indicates that the system's large deviation behavior has a significant impact on the efficiency of a simulation method.

Retinoic acid (RA) has been recognized as a chemotherapeutic agent for various malignances such as lung, skin as well as cervical cancers. It binds to retinoid receptors heterodimers and consequently activates several RA-responsive genes which are involved in many biological processes including vertebrate development, bone growth, vision, haematopoiesis, cell growth, differentiation and apoptosis. These genes are under the control of numerous regulators to ensure their timely ordered activities. Among these regulators, we focused here on the 26S proteasome and ubiquitination. It has been reported that the activity of the ubiquitin/proteasome system (UPS) plays a fundamental role in retinoic acid receptor (RAR)-regulated transactivation. The mechanisms underlying this role, however, remain to be established. Chromatin immunoprecipitation (ChIP) assays in our study demonstrated that the 26S proteasome activity is important for preserving the occupancy of a TATA box-containing RA-responsive promoters by liganded retinoid receptors and thus by their coactivators. Additionally, by using coimmunoprecipitation assays and by measuring the half-life of retinoid receptors, we found that the non-proteolytic function of the proteasome is required for ligand-dependent association between DNA-free RAR-α and both DNA-free RXR-α and coactivators. Moreover, using immunofluorescent staining and in vivo ubiquitination assays, a proteasome inhibition-dependent cytoplasmic localization of RAR-α as well as ligand-enhanced ubiquitination and stabilization of RAR-α were shown. Our findings therefore, define novel mechanisms by which the UPS controls RAR-regulated genes. Furthermore, we shed new light on the regulators of retinoid receptors ubiquitination and subcellular localization.

No description available.

L'étude des gaz rares dans les eaux porales est fondamentale à la compréhension des échanges des espèces chimiques entre le sédiment et la colonne d'eau. Les gaz rares, inertes chimiquement, peuvent être utilisés pour quantifier les flux des espèces chimiques entrantes/sortantes du sédiment ou les processus de consommation/production de ces espèces telles que le carbone et l'azote. Cela permet de mieux visualiser les cycles biogéochimiques de ces éléments dans l'océan et les sédiments océaniques ou estuariens. Ainsi, lors d'une mission océanographique sur l'Estuaire du Saint-Laurent à bord du N.S. Coriolis II, en mai 2007, nous avons procédé à l'échantillonnage d'eaux porales et de sédiments. Cette mission s'est faite en collaboration avec des équipes de l'Université McGill, l'Université Concordia, l'Université de Montréal et de l'Université du Québec à Montréal. Ce groupe comprenait plusieurs membres du GEOTOP. Une nouvelle méthode d'échantillonnage et d'extraction a été mise au point empruntant plusieurs caractéristiques aux systèmes déjà existants. Les échantillons ont été analysés au laboratoire Gaz Rares à Montréal (GRAM). Nous avons découvert, dans plusieurs échantillons, que les concentrations des gaz rares Ne, Ar, Kr et Xe étaient plus élevées que celles attendues par dissolution des gaz atmosphériques dans l'eau de mer. Ces enrichissements semblent être dû à l'adsorption des gaz sur de la matière organique et son relargage dans l'eau porale pendant la décompression de l'échantillon lors de sa remonté à bord du navire. La présence de ces excès a des conséquences importantes dans le calcul des flux de toutes les espèces chimiques entrantes/sortantes du sédiment et une sous-estimation des processus de consommation/production des ces espèces dans les sédiments. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Gaz rares, Géochimie, Isotopes, Eau porale, Estuaire du Saint-Laurent, Sédiment.

The planting of native species is a common strategy for the conservation of biodiversity; it not only allows for the restoration of degraded habitat both within conservation reserves and the matrix lands between reserves, it supplements the populations of the floral species which are planted. These supplemental populations may play an important role in providing demographic security for rare species. However, the conservation of rare species depends on more than simply maintaining adequate numbers of the species: the diversity within the species must also be conserved. Although maintaining genetic diversity is increasingly a concern for formal species recovery efforts, there has been very little research done about the diversity within plantings by non-state actors. This research was undertaken to address this knowledge gap by studying the provenances of planted rare species and the activities of those who collect and grow these plants. This research was undertaken in the Carolinian zone of southern Ontario, a region with a large number of rare plant species and a large human population. Part of this study utilized semi-structured interviews with commercial seed collectors, commercial native plant growers, and non-commercial, hobbyist growers. A variety of factors limited the diversity with the seeds collected by commercial collectors. Due to difficulty in accessing information about the natural occurrences of rare species, collectors typically collected from the same, limited number of source plants. Trespassing on private property or protected lands was common to access these seed sources, although their preference for easily accessible, reliably fecund source plants on flat, mowed sites also meant that horticultural specimens were also desired. Many of these biases were passed on to commercial growers when the seed was sold by the commercial collectors. Commercial growers shared many collection practices with commercial collectors, creating similar restrictions on the diversity within their collections. However, further limitations in diversity were also created by the growers’ establishment of small populations of seed plants and by the trading of seeds and plants between growers. One boutique grower was a dominant source of seeds and plants in these trades. The limitations in the diversity within these rare species were passed onto those who purchased and planted them. This study also focused on enthusiastic native plant hobbyists and found that they not only purchased plants but collected and grew their own plants. They also traded with other hobbyists. Much of the information about where to collect seed or plants, as well as much of the seed or plants traded between hobbyists, originated with a key individual. Thus, this champion hobbyist plays a significant role in the character of planted examples of rare plant species and the genetics of the champion’s plants are heavily represented with other planted occurrences. The practices of commercial seed collectors, growers and native plant hobbyists create biases which limit the diversity within plantings of rare species. Although these plantings provide demographic security for these species, they do not represent the diversity within their remnant “wild” populations. Thus, important questions must be raised about the conservation value of these plantings. Since many of the practices of seed collectors and growers are also used when growing more common species, the diversity within plantings of these species should also be suspect. Although the lack of diversity within common species may not threaten the regional survival of the species in the short term, it may impact the ultimate success of restoration projects.

Rare earth ferrosilicon alloy is an important additive for ferrous metallurgy. It is mainly used to control the detrimental effects of sulfur in steel and to modify graphite structures in cast iron. The aim of this study was to optimize the conditions for the production of rare earth ferrosilicon alloy by metallothermic reduction process using a preconcentrate prepared from a bastnasite type of ore present in the Beylikahir-EskiSehir region of Turkey. In this study, the rare earth preconcentrate was reduced by aluminum together with ferrosilicon and rare earth ferrosilicon alloys were produced. The optimum conditions of reduction, which are time, temperature, reducer amounts and the basicity of the slag phase, were investigated by smelting in an induction furnace. At the end of the study, a rare earth ferrosilicon alloy containing 39.3 % rare earths, 37.5 % silicon, 19.3 % iron and 3.9 % aluminum was produced under the optimum conditions determined with 57.7 % rare earth metal recovery.

First published online: November 1, 2010 / 名古屋大学博士学位論文 学位の種類 : 博士(医学)(課程) 学位授与年月日:平成23年3月25日 久島周氏の博士論文として提出された

One of the fundamental properties of bulk metals is the cancellation of electric fields. The free charges inside of a metal will move until they find an arrangement where the internal electric field is zero. This implies that the electric dipole moment of a metal particle should be exactly zero, because an electric dipole moment requires a net separation of charge and thus a nonzero internal electric field. This thesis is an experimental study to see if this property continues to hold for tiny sub- nanometer metal particles called clusters (2 - 200 atom, R < 1 nm). We have measured the electric dipole moments of metal clusters made from 15 pure elements using a molecular beam electric deflection technique. We find that the observed dipole moments vary a great deal across the periodic table. Alkali metals have zero dipole moments, while transition metals and lanthanides all have dipole moments which are highly size dependent. In most cases, the measured dipole moments are independent of temperature (T = 20 - 50 K), and when there is a strong temperature dependence this suggests that there is a new state of matter present. Our interpretation of these results are that those clusters which have a non- zero dipole moment are non-metallic, in the sense that their electrons must be localized and prevented from moving to screen the internal field associated with a permanent dipole moment. This interpretation gives insight to several related phenomena and applications. We briefly discuss an example cluster system RhN where the measured electric dipole moments appear to be correlated with a the N2O reactivity. Finally, we discuss a series of magnetic deflection experiments on lanthanide clusters (Pr, Ho, Tb, and Tm). The magnetic response of these clusters is very complex and highly sensitive to size and temperature. We find that PrN (which is non-magnetic in the bulk) becomes magnetic in clusters and TmN clusters have magnetic moments lower than the atomic value as well as the bulk saturation value implying that the magnetic order in the cluster involves non-collinear or antiferromagnetic order. HoN and TbN show very similar size dependent trends suggesting that these clusters have similar structures.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 80-86). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 80-86). Also available on the Internet.