Asymptotic analysis of the Gunn effect with realistic boundary conditions

A general asymptotic analysis of the Gunn effect in n-type GaAs under general boundary conditions for metal-semiconductor contacts is presented. Depending on the parameter values in the boundary condition of the injecting contact, different types of waves mediate the Gunn effect. The periodic current oscillation typical of the Gunn effect may be caused by moving charge-monopole accumulation or depletion layers, or by low- or high-field charge-dipole solitary waves. A new instability caused by multiple shedding of (low-field) dipole waves is found. In all cases the shape of the current oscillation is described in detail: we show the direct relationship between its major features (maxima, minima, plateaus, etc.) and several critical currents (which depend on the values of the contact parameters). Our results open the possibility of measuring contact parameters from the analysis of the shape of the current oscillation.

Stationary states and phase diagram for a model of the Gunn effect under realistic boundary conditions

A general formulation of boundary conditions for semiconductor-metal contacts follows from a phenomenological procedure sketched here. The resulting boundary conditions, which incorporate only physically well-defined parameters, are used to study the classical unipolar drift-diffusion model for the Gunn effect. The analysis of its stationary solutions reveals the presence of bistability and hysteresis for a certain range of contact parameters. Several types of Gunn effect are predicted to occur in the model, when no stable stationary solution exists, depending on the value of the parameters of the injecting contact appearing in the boundary condition. In this way, the critical role played by contacts in the Gunn effect is clearly established.

Relation for the nonequilibrium population of the interface states: effects on the bias dependence of the ideality factors

By an analysis of the exchange of carriers through a semiconductor junction, a general relationship for the nonequilibrium population of the interface states in Schottky barrier diodes has been derived. Based on this relationship, an analytical expression for the ideality factor valid in the whole range of applied bias has been given. This quantity exhibits two different behaviours depending on the value of the applied bias with respect to a critical voltage. This voltage, which depends on the properties of the interfacial layer, constitutes a new parameter to complete the characterization of these junctions. A simple interpretation of the different behaviours of the ideality factor has been given in terms of the nonequilibrium charging properties of interface states, which in turn explains why apparently different approaches have given rise to similar results. Finally, the relevance of our results has been considered on the determination of the density of interface states from nonideal current-voltage characteristics and in the evaluation of the effects of the interfacial layer thickness in metal-insulator-semiconductor tunnelling diodes.

Loss of serum response factor in keratinocytes results in hyperproliferative skin disease in mice.

The transcription factor serum response factor (SRF) plays a crucial role in the development of several organs. However, its role in the skin has not been explored. Here, we show that keratinocytes in normal human and mouse skin expressed high levels of SRF but that SRF expression was strongly downregulated in the hyperproliferative epidermis of wounded and psoriatic skin. Keratinocyte-specific deletion within the mouse SRF locus during embryonic development caused edema and skin blistering, and all animals died in utero. Postnatal loss of mouse SRF in keratinocytes resulted in the development of psoriasis-like skin lesions. These lesions were characterized by inflammation, hyperproliferation, and abnormal differentiation of keratinocytes as well as by disruption of the actin cytoskeleton. Ultrastructural analysis revealed markedly reduced cell-cell and cell-matrix contacts and loss of cell compaction in all epidermal layers. siRNA-mediated knockdown of SRF in primary human keratinocytes revealed that the cytoskeletal abnormalities and adhesion defects were a direct consequence of the loss of SRF. In contrast, the hyperproliferation observed in vivo was an indirect effect that was most likely a consequence of the inflammation. These results reveal that loss of SRF disrupts epidermal homeostasis and strongly suggest its involvement in the pathogenesis of hyperproliferative skin diseases, including psoriasis.

L'exploitation des traces dans les accidents de la circulation

Les investigations dans le milieu des accidents de la circulation sont très complexes. Elles nécessitent la mise en oeuvre d'un grand nombre de spécialités venant de domaines très différents. Si certains de ces domaines sont déjà bien exploités, d'autres demeurent encore incomplets et il arrive de nos jours d'observer des lacunes dans la pratique, auxquelles il est primordial de remédier.Ce travail de thèse, intitulé « l'exploitation des traces dans les accidents de la circulation », est issu d'une réflexion interdisciplinaire entre de multiples aspects des sciences forensiques. Il s'agit principalement d'une recherche ayant pour objectif de démontrer les avantages découlant d'une synergie entre les microtraces et l'étude de la dynamique d'un accident. Afin de donner une dimension très opérationnelle à ce travail, l'ensemble des démarches entreprises a été axé de manière à optimiser l'activité des premiers intervenants sur les lieux.Après une partie introductive et ayant trait au projet de recherche, traitant des aspects théoriques de la reconstruction d'une scène d'accident, le lecteur est invité à prendre connaissance de cinq chapitres pratiques, abordés selon la doctrine « du général au particulier ». La première étape de cette partie pratique concerne l'étude de la morphologie des traces. Des séquences d'examens sont proposées pour améliorer l'interprétation des contacts entre véhicules et obstacles impliqués dans un accident. Les mécanismes de transfert des traces de peinture sont ensuite étudiés et une série de tests en laboratoire est pratiquée sur des pièces de carrosseries automobiles. Différents paramètres sont ainsi testés afin de comprendre leur impact sur la fragilité d'un système de peinture. Par la suite, une liste de cas traités (crash-tests et cas réels), apportant des informations intéressantes sur le traitement d'une affaire et permettant de confirmer les résultats obtenus est effectuée. Il s'ensuit un recueil de traces, issu de l'expérience pratique acquise et ayant pour but d'aiguiller la recherche et le prélèvement sur les lieux. Finalement, la problématique d'une banque de données « accident », permettant une gestion optimale des traces récoltées est abordée.---The investigations of traffic accidents are very complex. They require the implementation of a large number of specialties coming from very different domains. If some of these domains are already well exploited, others remain still incomplete and it happens nowadays to observe gaps in the practice, which it is essential to remedy. This thesis, entitled "the exploitation of traces in traffic accidents", arises from a multidisciplinary reflection between the different aspects of forensic science. It is primarily a research aimed to demonstrate the benefits of synergy between microtrace evidence and accidents dynamics. To give a very operational dimension to this work, all the undertaken initiatives were centred so as to optimise the activity of the first participants on the crime scene.After an introductory part treating theoretical aspects of the reconstruction of an accident scene the reader is invited to get acquainted with five practical chapters, according to the doctrine "from general to particular". For the first stage of this practical part, the problem of the morphology of traces is approached and sequences of examinations are proposed to improve the interpretation of the contacts between vehicles and obstacles involved in an accident. Afterwards, the mechanisms of transfer of traces of paint are studied and a series of tests in laboratory is practised on pieces of automobile bodies. Various parameters are thus tested to understand their impact on the fragility of a system of paint. It follows that a list of treated cases (crash-tests and real cases) is created, allowing to bring interesting information on the treatment of a case and confirm the obtained results. Then, this work goes on with a collection of traces, stemming from the acquired experience that aims to steer the research and the taking of evidence on scenes. Finally, the practical part of this thesis ends with the problem of a database « accident », allowing an optimal management of the collected traces.

Myelination in rat brain aggregating cell cultures.

Aggregates of fetal rat brain were maintained in rotating culture for 30-40 days and were analyzed morphologically and biochemically. At 4 days in culture all cells were undifferentiated. At 26 days in vitro over 90% of all cells within the aggregates could be identified as neurons, astrocytes or oligodendrocytes. Myelinated axons and morphologically mature synapses were present at 26 days. Myelination started between 18 and 19 days in culture as determined biochemically. Myelin basic protein sulphatide synthesis and 2′,3′-cyclic nucleotide 3′-phosphohydrolase activity increased with in vitro age. The amount of myelin observed within the aggregates was much lower than observed at the corresponding age in vivo. Neurons and neuronal processes were undergoing severe degeneration in the 40-day aggregates and synaptic contacts were not maintained. There were no normal myelinated axons at 40 days although multilammellar membranes were found intra- and extracellularly. The ganglioside pattern of the aggregates were qualitatively similar to rat whole brain. Quantitatively the GM3ganglioside was elevated in comparison to whole rat brain. Our results indicate that aggregating rat brain cultures provide a useful in vitro system for the biochemical and morphological analysis of myelin formation.

2009-2010 Juvenile Court Services School Liaison Program Data, July 2010

Data are provided to CJJP through statistical summary forms completed by the JCSLs. Because forms are completed only when meaningful contact between a student and a liaison takes place, only a portion of the total population served is reported. Meaningful contact is defined as having at least five contacts within a 60-day period (at any point during the academic year) regarding at least one of the referral reasons supplied on the form. Data are entered into a web-based application by the liaisons and retrieved electronically by CJJP via the internet. Service information is submitted and uploaded only at the end of the academic year.

TrkB and TrkC signaling are required for maturation and synaptogenesis of hippocampal connections

Recent studies have suggested a role for neurotrophins in the growth and refinement of neural connections, in dendritic growth, and in activity-dependent adult plasticity. To unravel the role of endogenous neurotrophins in the development of neural connections in the CNS, we studied the ontogeny of hippocampal afferents intrkB (¿/¿) and trkC (¿/¿) mice. Injections of lipophilic tracers in the entorhinal cortex and hippocampus of newborn mutant mice showed that the ingrowth of entorhinal and commissural/associational afferents to the hippocampus was not affected by these mutations. Similarly, injections of biocytin in postnatal mutant mice (P10¿P16) did not reveal major differences in the topographic patterns of hippocampal connections. In contrast, quantification of biocytin-filled axons showed that commissural and entorhinal afferents have a reduced number of axon collaterals (21¿49%) and decreased densities of axonal varicosities (8¿17%) in both trkB (¿/¿) and trkC (¿/¿) mice. In addition, electron microscopic analyses showed thattrkB (¿/¿) and trkC (¿/¿) mice have lower densities of synaptic contacts and important structural alterations of presynaptic boutons, such as decreased density of synaptic vesicles. Finally, immunocytochemical studies revealed a reduced expression of the synaptic-associated proteins responsible for synaptic vesicle exocytosis and neurotransmitter release (v-SNAREs and t-SNAREs), especially in trkB (¿/¿) mice. We conclude that neither trkB nor trkC genes are essential for the ingrowth or layer-specific targeting of hippocampal connections, although the lack of these receptors results in reduced axonal arborization and synaptic density, which indicates a role for TrkB and TrkC receptors in the developmental regulation of synaptic inputs in the CNS in vivo. The data also suggest that the genes encoding for synaptic proteins may be targets of TrkB and TrkC signaling pathways.

Nanomechanical properties of molecular organic thin films

Using atomic force microscopy we have studied the nanomechanical response to nanoindentations of surfaces of highly oriented molecular organic thin films (thickness¿1000¿nm). The Young¿s modulus E can be estimated from the elastic deformation using Hertzian mechanics. For the quasi-one-dimensional metal tetrathiafulvalene tetracyanoquinodimethane E~20¿GPa and for the ¿ phase of the p-nitrophenyl nitronyl nitroxide radical E~2GPa. Above a few GPa, the surfaces deform plastically as evidenced by discrete discontinuities in the indentation curves associated to molecular layers being expelled by the penetrating tip.

High-Temperature magnetic ordering in a new organic magnet

Magnetization, heat capacity, and neutron diffraction experiments on the beta-phase of the dithiadiazolyl radical, p-NC.C6F4.CNSSN., provide conclusive evidence that this system exhibits noncollinear antiferromagnetism at 35.5 K, an unprecedented temperature for an organic radical. On the basis of magnetization and powder neutron diffraction results, coupled with theoretical calculations of the spin distribution within the molecule, a magnetic structure for this compound is proposed in which the interactions propagate through S . . .N contacts.

Sex-linked genetic markers in the shrews of the Sorex araneus group : from free gene flow to speciation

SUMMARY: The shrews of the Sorex araneus group are morphologically .very similar, but have undergone a spectacular chromosomal evolution. Altogether, the shrews of this group present a complete array of every possible level of chromosomal and genetic differentiation. In South-Western Europe, four species are recognised: S. antiriorii, S. araneus, S. coronatus and S. granarius, which differ essentially by the amount and the composition of Robertsonian metacentric chromosomés. Additionally, several chromosome races of S. araneus are also present in the same region (i.e. Bretolet, Carlit, Cordon, Jura and Vaud). The objective of this thesis was to examine the genetic relationships between populations, races and /or species of the Sorex araneus group with a special emphasis onsex-specific markers (mtDNA and Y chromosome). We first investigate the evolutionary history of the shrews of the Sorex araneus group distributed in the South-Western Europe. The results of. these analyses confirmed the difficulty to draw a single dichotomic tree within this group. Incongruent mtDNA and Y chromosome phylogenies suggest further that genetic and chromosomal evolution are in this group partially independent processes and that the evolutionary history of the south-western European populations of the S. araneus group can only be understood if we consider secondary contacts between taxa, after their divergence (with genetic exchanges by means of hybridization and / or introgression). Using one male-inherited, one female inherited and eight biparentally inherited markers, we investigate the population genetic structure of the Valais shrew (Sorex antinorii). Overall there results suggest that two already well-differentiated genetic lineages colonized the Swiss Alps after the last glacial period and came into contact in the Rhône Valley. After the Valais shrew (Sorex antinorii) reached the Swiss Alps, it came into contact with the common shrew (Sorex araneus). When two species come into contact and hybridize, endogenous counter-selection of hybrids is usually first expressed as a reduced fertility or viability in hybrids of the heterogametic sex, a mechanism know as Haldane's rule (Haldane 1922). We first evaluated the extent of introgression for Y chromosome, mtDNA and autosomal markers in a hybrid zone between S. antinoriii and S. araneus. The overall level of genetic and karyotypic differentiation between the two species must be strong .enough to allow the detection asymmetric introgression. Secondly, we compared the levels of gene flow between chromosome common to both species and chromosome differently rearranged in each of them. We detected a significantly stronger genetic structure in rearranged chromosomes. Over a 10-year period, we even observed a decrease of genetic structure for common chromosomes. These results strongly support the role of chromosomal rearrangements in the reproductive barrier between S. araneus and S. anfinorii. Overall, this thesis underlines the need to use different inherited (paternally, maternally and / or biparentally) and chromosomally located (on common vs. on rearranged chromosomes) markers to obtain more accurate pictures of genetic relationships between populations or species. RÉSUMÉ: Les musaraignes du groupe Sorex araneus sont morphologiquement très proches, mais ont connu une spectaculaire évolution chromosomique. Prises dans leur ensemble, les musaraignes de ce groupe présentent tous les nivaux possibles de différenciation génétique et chromosomique. Dans le sud-ouest de l'Europe, quatre espèces appartenant à ce groupe sont présentes : S. antinorii, S. araneus, S. coronatus et S. granarius. Celles-ci diffèrent essentiellement par leur caryotype dont la variabilité est principalement due à des fusions Robertsoniennes. De plus, plusieurs races chromosomiques appartenant à S. araneus sont aussi présentes dans la même région (i.e. les races Bretolet, Carlit, Cordon, Jura et Vaud). L'objectif de cette thèse était d'examiner les relations génétiques entre populations, races et/ou espèces du groupe S. araneus, en utilisant particulièrement des marqueurs liés aux sexes (ADN mitochondrial et Chromosome Y). Nous avons dans un premier temps retracé l'histoire évolutive des musaraignes de ce groupe dans le sud-ouest de l'Europe. Les résultats dé ces analyses confirment qu'il est difficile de tracer un simple arbre dichotomique au sein de ce groupe. Les arbres phylogénétiques obtenus sur l'ADN mitochondrial et le chromosome Y sont incongruents et suggèrent de plus que l'évolution génétique et chromosomique sont des processus indépendants. L'histoire évolutive -des populations de ce groupe ne peut. être comprise qu'en considérant des contacts secondaires entre taxa postérieure à leur divergence et induisant des échanges génétiques par hybridation et/ou introgression. Par la suite, nous avons examiné la structure génétique des populations de la musaraigne du Valais, S. antinorii, en utilisant un marqueur transmis par les mâles, un marqueur transmis par les femelles et huit marqueurs transmis par les 2 sexes. Nos résultats suggèrent que deux lignées génétiquement bien différenciées aient colonisé les Alpes Suisses, après les dernières glaciations et entrent en contact dans là Vallée du Rhône. Après avoir franchi les Alpes Suisses, la musaraigne du Valais est entrée en contact avec là musaraigne commune (S. araneus). Lorsque deux espèces entrent en contact et s'hybrident, la sélection contre les hybrides implique habituellement une baisse de fertilité ou de viabilité des hybrides du sexe hétérogamétique (i.e. les mâles XY chez les mammifères). Ce mécanisme est connu sous le nom de règle de Haldane (Haldane 1922) et implique une plus forte structuration génétique de marqueurs males - spécifiques que des marqueurs femelles spécifiques. Nous avons donc évalué le degré d'introgression des marqueurs situés sur le chromosome Y, sur l'ADN mitochondrial et sur des autosomes dans une zone hybride entre S. araneus et S. antinorii. Le niveau de différenciation chromosomique et génétique entre les 2 espèces doit être suffisamment fort pour ne pas permettre la détection d'une introgression asymétrique entre les sexes. Dans un second temps, nous avons comparé les niveaux de flux de gênes mesurés à l'échelle du chromosome, pour des chromosomes communs aux deux espèces et pour des chromosomes différemment arrangées dans chacune des deux espèces. Nous avons détecté une structure génétique significativement plus forte sur les chromosomes réarrangés et comme la zone hybride a été étudiée à dix années d'intervalle, nous observons même une diminution de la structure génétique pour les chromosomes communs au cours du temps.. Ces résultats soutiennent fortement l'hypothèse d'un rôle des réarrangements chromosomiques dans l'établissement d'une barrière reproductive entre S. araneus et S. antinorii. Ainsi cette thèse souligne l'utilité d'utiliser des marqueurs génétiques avec différents modes de transmission. (par les mâles, par les femelles et/ou par les 2 sexes) ou localisés au niveau du chromosome (chromosomes communs vs chromosomes réarrangés) afin d'obtenir une image plus juste ou du moins plus complète des relations génétiques entre populations ou espèces.

Iowa Byways: The Official Guide to Iowa Byways, 2013

Browse through this guide and you’ll find the distinct flavor of what is available along each byway. Discover recreational, historic, cultural and scenic attractions using the maps and lists provided in the guide. You’ll find numbered attractions for each byway in or near the town listed. For a comprehensive list of byway features, visit www.iowabyways.org. Friendly local contacts are provided to help you along the way. Iowa Transportation Maps clearly tracking all the Iowa byways with red dotted lines are available at Iowa’s official welcome centers. Traveling Iowa’s byways you will experience small town America, while enjoying diverse landscapes and unique landforms that have been shaped over thousands of years. Iowa’s cultural heritage also plays a major role across all 11 byways, boasting hundreds of historic sites, national landmarks and interpretive centers, each telling Iowa’s stories from the first Native Americans through European immigrants to modern times. Glaciers once covered much of Iowa, shaping the broad flat plains of the prairie. These massive sheets of ice missed the northeast corner of the state, leaving the land along the Driftless Area Byway rugged and hilly with rock outcroppings, springs and cold water trout streams. Rivers coursed their way through the land, carving deep furrows in some places and leaving gently rolling hills in others. In western Iowa, wind has shaped fine sand into the impressive Loess Hills, a rare land form found in only one other place on earth. Iowa’s two national scenic byways and nine state byways offer unique varieties of scenic features, and more for you to see and do. View three states from atop a Mississippi River bluff, stop at a modern art museum and then tour a working farm. Explore a historic mill, visit a national aquarium, take a boat ride in a cave, purchase locally crafted pottery and wares from local artisans or trace the footsteps of Lewis and Clark. Experience the actual wagon ruts of the Mormon Trail, ride your bike 13 stories high, canoe a water trail, star gaze under Iowa’s darkest sky, and marvel at mounds built by prehistoric cultures. Agriculture wraps Iowa’s byways with an abundance of farmland vistas and fills Iowa lands with ever-changing crops and activities for you to “harvest.” You’ll see croplands on the vast flat plains and farmsteads sprinkled across rolling hills reminiscent of a Grant Wood painting. Along the way, you might wander in a corn maze, rest at a bed and breakfast, study farming in museums, discover the Iowa barn quilt collection or visit a working Amish farm. When you are ready to step outside your vehicle, you’ll find much more to do and see. Prairie, forests, rivers and public lands are abundant along Iowa’s byways; providing opportunities for you to stop and play in the outdoors with hiking, biking, kayaking and trout fishing. Classic hometowns with pride for their unique lore and offerings are found all along the byways. They invite you to taste local food, enjoy their architecture, and immerse yourself in the rich history and culture that defines them. Why not plan your next journey off the beaten path? No matter how you choose to make the most of every moment, we know that time spent along Iowa’s byways is sure to grow your love for Iowa’s diverse, beautiful vistas and authentic communities. Happy driving!

EADock: docking of small molecules into protein active sites with a multiobjective evolutionary optimization.

In recent years, protein-ligand docking has become a powerful tool for drug development. Although several approaches suitable for high throughput screening are available, there is a need for methods able to identify binding modes with high accuracy. This accuracy is essential to reliably compute the binding free energy of the ligand. Such methods are needed when the binding mode of lead compounds is not determined experimentally but is needed for structure-based lead optimization. We present here a new docking software, called EADock, that aims at this goal. It uses an hybrid evolutionary algorithm with two fitness functions, in combination with a sophisticated management of the diversity. EADock is interfaced with the CHARMM package for energy calculations and coordinate handling. A validation was carried out on 37 crystallized protein-ligand complexes featuring 11 different proteins. The search space was defined as a sphere of 15 A around the center of mass of the ligand position in the crystal structure, and on the contrary to other benchmarks, our algorithm was fed with optimized ligand positions up to 10 A root mean square deviation (RMSD) from the crystal structure, excluding the latter. This validation illustrates the efficiency of our sampling strategy, as correct binding modes, defined by a RMSD to the crystal structure lower than 2 A, were identified and ranked first for 68% of the complexes. The success rate increases to 78% when considering the five best ranked clusters, and 92% when all clusters present in the last generation are taken into account. Most failures could be explained by the presence of crystal contacts in the experimental structure. Finally, the ability of EADock to accurately predict binding modes on a real application was illustrated by the successful docking of the RGD cyclic pentapeptide on the alphaVbeta3 integrin, starting far away from the binding pocket.

The anti-apoptotic role of PPARbeta contributes to efficient skin wound healing.

PPARalpha and PPARbeta are expressed in the mouse epidermis during fetal development, but their expression progressively disappears after birth. However, the expression of PPARbeta is reactivated in adult mice upon proliferative stimuli, such as cutaneous injury. We show here that PPARbeta protects keratinocytes from growth factor deprivation, anoikis and TNF-alpha-induced apoptosis, by modulating both early and late apoptotic events via the Akt1 signaling pathway and DNA fragmentation, respectively. The control mechanisms involve direct transcriptional upregulation of ILK, PDK1, and ICAD-L. In accordance with the anti-apoptotic role of PPARbeta observed in vitro, the balance between proliferation and apoptosis is altered in the epidermis of wounded PPARbeta mutant mice, with increased keratinocyte proliferation and apoptosis. In addition, primary keratinocytes deleted for PPARbeta show defects in both cell-matrix and cell-cell contacts, and impaired cell migration. Together, these results suggest that the delayed wound closure observed in PPARbeta mutant mice involves the alteration of several key processes. Finally, comparison of PPARbeta and Akt1 knock-out mice reveals many similarities, and suggests that the ability of PPARbeta to modulate the Akt1 pathway has significant impact during skin wound healing.