Search results for "Drift"
showing 10 items of 321 documents
A novel experimental system for the KDK measurement of the 40K decay scheme relevant for rare event searches
2020
Potassium-40 ($^{40}$K) is a long-lived, naturally occurring radioactive isotope. The decay products are prominent backgrounds for many rare event searches, including those involving NaI-based scintillators. $^{40}$K also plays a role in geochronological dating techniques. The branching ratio of the electron capture directly to the ground state of argon-40 has never been measured, which can cause difficulty in interpreting certain results or can lead to lack of precision depending on the field and analysis technique. The KDK (Potassium (K) Decay (DK)) collaboration is measuring this decay. A composite method has a silicon drift detector with an enriched, thermally deposited $^{40}$K source …
Nonadiabatic spin-transfer torque of magnetic vortex structures in a permalloy square
2014
The stationary displacement of a magnetic vortex core in a permalloy square caused by an ultrahigh direct current has been measured utilizing scanning electron microscopy with polarization analysis. Data have been analyzed for three different generic states of the Landau structure and up to a current density of $3\ifmmode\times\else\texttimes\fi{}{10}^{11}\mathrm{A}/{\mathrm{m}}^{2}$. This procedure allows for separating the effects caused by the Oersted field, the nonadiabatic, and the adiabatic spin-transfer torque. In addition, the spin polarization of the driving current $P=(65\ifmmode\pm\else\textpm\fi{}4)%$ is independently determined from the spin drift velocity of ${v}_{j}=(4.79\ifm…
Electric conduction in semiconductors: a pedagogical model based on the Monte Carlo method
2008
We present a pedagogic approach aimed at modelling electric conduction in semiconductors in order to describe and explain some macroscopic properties, such as the characteristic behaviour of resistance as a function of temperature. A simple model of the band structure is adopted for the generation of electron–hole pairs as well as for the carrier transport in moderate electric fields. The semiconductor behaviour is described by substituting the traditional statistical approach (requiring a deep mathematical background) with microscopic models, based on the Monte Carlo method, in which simple rules applied to microscopic particles and quasi-particles determine the macroscopic properties. We …
Performance of tracking stations of the underground cosmic-ray detector array EMMA
2018
Abstract The new cosmic-ray experiment EMMA operates at the depth of 75 m (50 GeV cutoff energy for vertical muons; 210 m.w.e.) in the Pyhasalmi mine, Finland. The underground infrastructure consists of a network of eleven stations equipped with multi-layer, position-sensitive detectors. EMMA is designed for cosmic-ray composition studies around the energy range of the knee, i.e., for primary particles with energies between 1 and 10 PeV. In order to yield significant new results EMMA must be able to record data in the full configuration for about three years. The key to the success of the experiment is the performance of its tracking stations. In this paper we describe the layout of EMMA an…
Decomposing encoding and decisional components in visual-word recognition: a diffusion model analysis.
2014
In a diffusion model, performance as measured by latency and accuracy in two-choice tasks is decomposed into different parameters that can be linked to underlying cognitive processes. Although the diffusion model has been utilized to account for lexical decision data, the effects of stimulus manipulations in previous experiments originated from just one parameter: the quality of the evidence. Here we examined whether the diffusion model can be used to effectively decompose the underlying processes during visual-word recognition. We explore this issue in an experiment that features a lexical manipulation (word frequency) that we expected to affect mostly the quality of the evidence (the dri…
The multiple directions of evolutionary change.
2008
The theory of Punctuated Equilibria challenges the neo-Darwinian tenet that evolution is a uniform process. Recently, an article by Hunt1 has found that directional change during the evolution of a lineage is relatively small (occurring only in 5% of 250 analyzed traits). Of those traits that were shown to follow a trend, size was more likely to show gradual changes, whereas shape changes were more random. Here, we provide a short view of the nature of evolutionary trends, showing that directional change within lineages and among clades provides valuable evolutionary information about the processes involved in their generation. BioEssays 30:521–525, 2008. © 2008 Wiley Periodicals, Inc.
Evolution of fitness in experimental populations of vesicular stomatitis virus
1996
Abstract The evolution of fitness in experimental clonal populations of vesicular stomatitis virus (VSV) has been compared under different genetic (fitness of initial clone) and demographic (population dynamics) regimes. In spite of the high genetic heterogeneity among replicates within experiments, there is a clear effect of population dynamics on the evolution of fitness. Those populations that went through strong periodic bottlenecks showed a decreased fitness in competition experiments with wild type. Conversely, mutant populations that were transferred under the dynamics of continuous population expansions increased their fitness when compared with the same wild type. The magnitude of …
Fitness Trade-Offs Determine the Role of the Molecular Chaperonin GroEL in Buffering Mutations
2015
Molecular chaperones fold many proteins and their mutated versions in a cell and can sometimes buffer the phenotypic effect of mutations that affect protein folding. Unanswered questions about this buffering include the nature of its mechanism, its influence on the genetic variation of a population, the fitness trade-offs constraining this mechanism, and its role in expediting evolution. Answering these questions is fundamental to understand the contribution of buffering to increase genetic variation and ecological diversification. Here, we performed experimental evolution, genome resequencing, and computational analyses to determine the trade-offs and evolutionary trajectories of Escherich…
The population genetics and evolutionary epidemiology of RNA viruses.
2004
Key Points The authors discuss the main mechanisms of RNA virus evolution — mutation, recombination, natural selection, genetic drift and migration, and how these interact to shape the genetic structure of populations.The quasispecies model of RNA virus evolution is explained and the question of whether this model provides an accurate description of RNA virus evolution is discussed.Experiments that can be carried out to test the basic principles of evolutionary theory are briefly described. The authors review what such experiments have told us about virus evolution and, more widely, what these experiments have revealed in terms of general evolutionary principles.RNA viruses evolve quickly, …
GENETIC VARIABILITY AND DRIFT LOAD IN POPULATIONS OF AN AQUATIC SNAIL
2004
Population genetic theory predicts that in small populations, random genetic drift will fix and accumulate slightly deleterious mutations, resulting in reduced reproductive output. This genetic load due to random drift (i.e., drift load) can increase the extinction risk of small populations. We studied the relationship between genetic variability (indicator of past population size) and reproductive output in eight isolated, natural populations of the hermaphroditic snail Lymnaea stagnalis. In a common laboratory environment, snails from populations with the lowest genetic variability mature slower and have lower fecundity than snails from genetically more variable populations. This result s…