931 research outputs found
The Shorter Poems of Anthony Hecht
A critical discussion of Hecht's achievement in the short poem form. This article was later developed into a chapter in the author's book Sparring with the Sun
Non-Markovian data-driven modeling of single-cell motility
Trajectories of human breast cancer cells moving on one-dimensional circular tracks are modeled by thenon-Markovian version of the Langevin equation that includes an arbitrary memory function. When averagedover cells, the velocity distribution exhibits spurious non-Gaussian behavior, while single cells are characterizedby Gaussian velocity distributions. Accordingly, the data are described by a linear memory model whichincludes different random walk models that were previously used to account for various aspects of cell motilitysuch as migratory persistence, non-Markovian effects, colored noise, and anomalous diffusion. The memoryfunction is extracted from the trajectory data without restrictions or assumptions, thus making our approachtruly data driven, and is used for unbiased single-cell comparison. The cell memory displays time-delayedsingle-exponential negative friction, which clearly distinguishes cell motion from the simple persistent randomwalk model and suggests a regulatory feedback mechanism that controls cell migration. Based on the extractedmemory function we formulate a generalized exactly solvable cell migration model which indicates thatnegative friction generates cell persistence over long timescales. The nonequilibrium character of cell motionis investigated by mapping the non-Markovian Langevin equation with memory onto a Markovian model thatinvolves a hidden degree of freedom and is equivalent to the underdamped active Ornstein-Uhlenbeck process
Development of bacteria-based bioassays for arsenic detection in natural waters
Arsenic contamination of natural waters is a worldwide concern, as the drinking water supplies for large populations can have high concentrations of arsenic. Traditional techniques to detect arsenic in natural water samples can be costly and time-consuming; therefore, robust and inexpensive methods to detect arsenic in water are highly desirable. Additionally, methods for detecting arsenic in the field have been greatly sought after. This article focuses on the use of bacteria-based assays as an emerging method that is both robust and inexpensive for the detection of arsenic in groundwater both in the field and in the laboratory. The arsenic detection elements in bacteria-based bioassays are biosensor-reporter strains; genetically modified strains of, e.g., Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Rhodopseudomonas palustris. In response to the presence of arsenic, such bacteria produce a reporter protein, the amount or activity of which is measured in the bioassay. Some of these bacterial biosensor-reporters have been successfully utilized for comparative in-field analyses through the use of simple solution-based assays, but future methods may concentrate on miniaturization using fiberoptics or microfluidics platforms. Additionally, there are other potential emerging bioassays for the detection of arsenic in natural waters including nematodes and clam
Period bouncers as detached magnetic cataclysmic variables
The general prediction that more than half of all CVs have evolved past the
period minimum is in strong disagreement with observational surveys, which show
that the relative number of these objects is just a few per cent. Here, we
investigate whether a large number of post-period minimum CVs could detach
because of the appearance of a strong white dwarf magnetic field potentially
generated by a rotation- and crystallization-driven dynamo. We used the MESA
code to calculate evolutionary tracks of CVs incorporating the spin evolution
and cooling as well as compressional heating of the white dwarf. If the
conditions for the dynamo were met, we assumed that the emerging magnetic field
of the white dwarf connects to that of the companion star and incorporated the
corresponding synchronization torque, which transfers spin angular momentum to
the orbit. We find that for CVs with donor masses exceeding 0.04 Msun, magnetic
fields are generated mostly if the white dwarfs start to crystallize before the
onset of mass transfer. It is possible that a few white dwarf magnetic fields
are generated in the period gap. For the remaining CVs, the conditions for the
dynamo to work are met beyond the period minimum, when the accretion rate
decreased significantly. Synchronization torques cause these systems to detach
for several Gyrs even if the magnetic field strength of the white dwarf is just
one MG. If the rotation- and crystallization-driven dynamo - which is currently
the only mechanism that can explain several observational facts related to
magnetism in CVs and their progenitors - or a similar temperature-dependent
mechanism is responsible for the generation of magnetic field in white dwarfs,
most CVs that have evolved beyond the period minimum must detach for several
Gyrs at some point. This reduces the predicted number of semi-detached period
bouncers by up to 60-80 per cent.Comment: A&A letters, in pres
Process Optimization for Recombinant Protein Expression in Insect Cells
Insect cells can be used for the efficient production of heterologous proteins. The baculovirus expression vector system (BEVS) in Spodoptera frugiperda cells and the stable transformation of Drosophila melanogaster S2 cells are widely used for this purpose. Whereas BEVS is a transient expression system for rapid protein production, stable D. melanogaster cell lines are compatible with more complex processes modes. This chapter describes the setup of both systems, including steps for the generation of expression vectors and comprehensive optimization approaches. The genetic elements available in each system are described, as well as the use of different cloning and transfection methods and advanced process monitoring to achieve robust protein expression in larger-scale bioreactors
Teoria de carreiras e percepção de âncoras de carreiras pela nova geração de trabalhadores
O presente trabalho aborda o tema de carreiras profissionais e a importância da teoria
de âncoras de carreira de Edgar Schein. Com Objetivo principal de fazer uma comparação
entre a percepção direta dos entrevistados com o resultado do inventário de âncoras de
carreira de Schein, foi possÃvel mostrar que há um grande nÃvel de consistência quando
comparados os dois resultados. Porem o principal resultado pode ser evidenciado nos pontos
em que não houve tal consistência, mostrando que há um certo nÃvel de dissonância cognitiva
que deve ser explorado em maior profundidade. O trabalho é constituÃdo por uma revisão
bibliográfica sobre as quatro principais teorias clássicas que visam a descrever o
desenvolvimento de carreiras empresarias. Posteriormente é apresentada a teoria de âncoras
de carreira e esta é utilizada para a pesquisa de campo que foi aplicada em um departamento
financeiro de uma multinacional do ramo de tecnologia da informação
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