111 research outputs found
Diffusion of electrons in random magnetic fields,
Diffusion of electrons in a two-dimensional system in static random magnetic
fields is studied by solving the time-dependent Schr\"{o}dinger equation
numerically. The asymptotic behaviors of the second moment of the wave packets
and the temporal auto-correlation function in such systems are investigated. It
is shown that, in the region away from the band edge, the growth of the
variance of the wave packets turns out to be diffusive, whereas the exponents
for the power-law decay of the temporal auto- correlation function suggest a
kind of fractal structure in the energy spectrum and in the wave functions. The
present results are consistent with the interpretation that the states away
from the band edge region are critical.Comment: 22 pages (8 figures will be mailed if requested), LaTeX, to appear in
Phys. Rev.
A narrative analysis of career transition themes and outcomes using chaos theory as a guiding metaphor
In a rapidly changing world of work little research exists on mid-career transitions. We investigated these using the open-systems approach of chaos theory as a guiding metaphor and conducted interviews with seven mid-career individuals chosen for their experience of a significant mid-career transition. Four common themes were identified through narrative analysis, where âfalse startsâ to a career were a common experience prior to finding a career âfitâ. Career transitions, precipitated by a trigger state and/or event such as a period of disillusionment, were an important part of this âfinding a fitâ process. Overall, career success outcomes were shaped by a combination of chaos elements: chance, unplanned events, and non-linearity of resultant outcomes. We discuss implications for future research and for practice
Solar parameters for modeling interplanetary background
The goal of the Fully Online Datacenter of Ultraviolet Emissions (FONDUE)
Working Team of the International Space Science Institute in Bern, Switzerland,
was to establish a common calibration of various UV and EUV heliospheric
observations, both spectroscopic and photometric. Realization of this goal
required an up-to-date model of spatial distribution of neutral interstellar
hydrogen in the heliosphere, and to that end, a credible model of the radiation
pressure and ionization processes was needed. This chapter describes the solar
factors shaping the distribution of neutral interstellar H in the heliosphere.
Presented are the solar Lyman-alpha flux and the solar Lyman-alpha resonant
radiation pressure force acting on neutral H atoms in the heliosphere, solar
EUV radiation and the photoionization of heliospheric hydrogen, and their
evolution in time and the still hypothetical variation with heliolatitude.
Further, solar wind and its evolution with solar activity is presented in the
context of the charge exchange ionization of heliospheric hydrogen, and in the
context of dynamic pressure variations. Also the electron ionization and its
variation with time, heliolatitude, and solar distance is presented. After a
review of all of those topics, we present an interim model of solar wind and
the other solar factors based on up-to-date in situ and remote sensing
observations of solar wind. Results of this effort will further be utilised to
improve on the model of solar wind evolution, which will be an invaluable asset
in all heliospheric measurements, including, among others, the observations of
Energetic Neutral Atoms by the Interstellar Boundary Explorer (IBEX).Comment: Chapter 2 in the planned "Cross-Calibration of Past and Present Far
UV Spectra of Solar System Objects and the Heliosphere", ISSI Scientific
Report No 12, ed. R.M. Bonnet, E. Quemerais, M. Snow, Springe
Splenectomy for splenomegaly and secondary hypersplenism
Splenomegaly and secondary hypersplenism may be associated with acute and chronic infections, autoimmune states, portal hypertension or splenic vein thrombosis, and a number of infiltrative and neoplastic conditions involving the spleen. Our experience and that of others with these various conditions demonstrates that the decision to perform splenectomy should be based on well-defined and often strictly limited indications. Except for idiopathic splenomegaly, the presence and severity of secondary hypersplenism or severely symptomatic splenomegaly should be well documented. In each case, the potential for palliation and known mean duration of expected response must be weighed against the increased morbidity and mortality of splenectomy (as compared to operation for âprimaryâ hypersplenism) . La splĂ©nomĂ©galie avec hypersplĂ©nisme secondaire relĂšve de multiples causes: infection aigue ou chronique, Ă©tats autoimmunologiques, hypertension portale, thrombose de la veine splĂ©nique, lĂ©sions tumorales splĂ©niques. L'expĂ©rience de l'auteur qui rejoint celle de nombreux collĂšgues lui permet d'affirmer que les indications de la splĂ©nectomie doivent ĂȘtre bien dĂ©finies et sont strictement limitĂ©es. A l'exception de la splĂ©nomĂ©galie idiopathique, l'existence et l'intensitĂ© de l'hypersplĂ©nisme, l'importance des symptomes provoquĂ©s par la splĂ©nomĂ©galie doivent ĂȘtre aprrĂ©ciĂ©es avec prĂ©cision. Dans chaque cas le potentiel de la rĂ©mission de l'affection et la durĂ©e de la rĂ©mission doivent ĂȘtre pris en considĂ©ration en fonction de l'Ă©ventuelle morbiditĂ© et de l'Ă©ventuelle mortalitĂ© de la splĂ©nectomie (par comparaison avec la splĂ©nectomie pour hypersplĂ©nisme primaire). Eplenomegalia e hiperesplenismo secundario pueden estar asociados con infecciones agudas y crĂłnicas, estados autoinmunes (sĂndrome de Felty, lupus eritematoso sistĂ©mico), âesplenomegalia congestivaâ por hipertensiĂłn portal o trombosis de la vena esplĂ©nica y con una variedad de entidades de tipo infiltrativo y neoplĂĄsico que afectan al bazo (sarcoidosis, enfermedad de Gaucher, varios desĂłrdenes mieloproliferativos y linfomas). Nuestra experiencia, y aquella de otros autores, con tales condiciones demuestra que la decisiĂłn de realizar esplenectomĂa debe estar fundamentada en indicaciones bien definidas y estrictamente limitadas. Excepto en casos de esplenomegalia idiopĂĄtica, la presencia y severidad del hiperesplenismo secundario o de esplenomegalia severamente sintomĂĄtica debe ser bien documentada. En cada caso debe determinarse el potencial de paliaciĂłn y la duraciĂłn de la respuesta que se espera obtener frente a la incrementada morbilidad y mortalidad de la esplenectomĂa (en comparaciĂłn con la operaciĂłn que se realiza por hiperesplenismo âprimarioâ).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41318/1/268_2005_Article_BF01655279.pd
The origins and spread of domestic horses from the Western Eurasian steppes
Analysis of 273 ancient horse genomes reveals that modern domestic horses originated in the Western Eurasian steppes, especially the lower Volga-Don region.Domestication of horses fundamentally transformed long-range mobility and warfare(1). However, modern domesticated breeds do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling(2-4) at Botai, Central Asia around 3500 bc(3). Other longstanding candidate regions for horse domestication, such as Iberia(5) and Anatolia(6), have also recently been challenged. Thus, the genetic, geographic and temporal origins of modern domestic horses have remained unknown. Here we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they expanded rapidly across Eurasia from about 2000 bc, synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioural adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association(7) between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe around 3000 bc(8,9) driving the spread of Indo-European languages(10). This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium bc Sintashta culture(11,12).Descriptive and Comparative Linguistic
The origins and spread of domestic horses from the Western Eurasian steppes
Domestication of horses fundamentally transformed long-range mobility and warfare. However, modern domesticated breeds do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling at Botai, Central Asia around 3500 bc. Other longstanding candidate regions for horse domestication, such as Iberia and Anatolia, have also recently been challenged. Thus, the genetic, geographic and temporal origins of modern domestic horses have remained unknown. Here we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they expanded rapidly across Eurasia from about 2000 bc, synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioural adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe around 3000 bc driving the spread of Indo-European languages. This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium bc Sintashta culture
Auroral Processes at the Giant Planets: Energy Deposition, Emission Mechanisms, Morphology and Spectra
Observation of higher confined exciton states in serpentine superlattices by linear polarized excitation spectroscopy
(Al,Ga)As serpentine superlattice (SSL) quantum-wire arrays with a paraboliccrescent cross section have been grown on vicinal GaAs substrates by molecular beam epitaxy. The quantum wires have dimensions on the order of 5 nm and 1D confined valence band states have been reported previously. Here we report on subsequent SSL samples having photoluminescence (PL) linewidths of 5 meV and displaying well-resolved excitation spectra. The data were obtained at 1.4 K and include linearly-polarized PL and PL excitation spectra (PLE) taken normal to the vicinal (100) surface. These data were fitted with effective-mass calculations that include the SSL geometry, valence band mixing, and imperfect lateral composition modulation. In linear polarized PLE (polarized parallel and perpendicular to the quantum wires), we have been able to resolve a SSL-induced heavy-light hole splitting of the ground state exciton. The observed heavy-light hole splitting is of the order of 5 meV with an electron-heavy hole subband separation of 15-20 meV. We extract a lateral composition modulation between the barrier and the wire to be 15 % from the observed heavy-light hole splitting corresponding to a lateral potential-energy difference in the conduction band of about 120 meV
Internationalisation of Counseling Psychology: Constructing Cross-National Consensus and Collaboration
Increased Prevalence of Developmental Venous Anomalies in Children with Intracranial Neoplasms
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