38,281 research outputs found
Topological jamming of spontaneously knotted polyelectrolyte chains driven through a nanopore
The advent of solid state nanodevices allows for interrogating the
physico-chemical properties of a polyelectrolyte chain by electrophoretically
driving it through a nanopore. Salient dynamical aspects of the translocation
process have been recently characterized by theoretical and computational
studies of model polymer chains free from self-entanglement. However,
sufficiently long equilibrated chains are necessarily knotted. The impact of
such topological "defects" on the translocation process is largely unexplored,
and is addressed in this study. By using Brownian dynamics simulations on a
coarse-grained polyelectrolyte model we show that knots, despite being trapped
at the pore entrance, do not "per se" cause the translocation process to jam.
Rather, knots introduce an effective friction that increases with the applied
force, and practically halts the translocation above a threshold force. The
predicted dynamical crossover, which is experimentally verifiable, is of
relevance in applicative contexts, such as DNA nanopore sequencing.Comment: 6 pages; 7 figure
The Transition to College Process in PR-CETP Scholars
This article describes a study about the experiences of a group of students during the transition from high school to college. The students are future teachers who evidenced a high level of academic achievement in high school and received merit scholarships from the Puerto Rico Collaborative for Excellence in Teacher Preparation (PR-CETP). Two groups of students were compared: those who sustained a high GPA during their freshman year, and those who did not and, therefore, no longer qualified for the scholarship. The study was carried out through focused interviews with eight students, from three universities, four of whom maintained the scholarship and four who did not. Findings indicate that the main problems encountered were academic and social, and that the students received support from their families during the entire process. Regarding formal support, they pointed out that they felt highly satisfied with the services provided by PR-CETP and the universities, but they also pointed out (particularly those who lost the scholarship) that they needed additional services from the universities. They suggested, for example, better tutoring, and social activities among the scholars. The interviewed students, in general, consider that they faced the transition successfully since most of them described their academic, emotional, and social status as satisfactory at the time of the interviews
CVD of CrO2 Thin Films: Influence of the Deposition Parameters on their Structural and Magnetic Properties
This work reports on the synthesis of CrO2 thin films by atmospheric pressure
CVD using chromium trioxide (CrO3) and oxygen. Highly oriented (100) CrO2 films
containing highly oriented (0001) Cr2O3 were grown onto Al2O3(0001) substrates.
Films display a sharp magnetic transition at 375 K and a saturation
magnetization of 1.92 Bohr magnetons per f.u., close to the bulk value of 2
Bohr magnetons per f.u. for the CrO2.
Keywords: Chromium dioxide (CrO2), Atmospheric pressure CVD, Spintronics.Comment: 5 pages, 6 figure
Broadband X-ray spectrum of the newly discovered broad line radio galaxy IGR J21247+5058
In this paper we present radio and high energy observations of the INTEGRAL
source IGR J21247+5058, a broad line emitting galaxy obscured by the Galactic
plane. Archival VLA radio data indicate that IGR J21247+5058 can be classified
as an FRII Broad Line Radio Galaxy. The spectrum between 610 MHz and 15 GHz is
typical of synchrotron self-absorbed radiation with a peak at 8 GHz and a low
energy turnover; the core fraction is 0.1 suggestive of a moderate Doppler
boosting of the base of the jet. The high energy broad-band spectrum was
obtained by combining XMM-Newton and Swift/XRT observation with INTEGRAL/IBIS
data. The 0.4-100 keV spectrum is well described by a power law, with slope
=1.5, characterised by complex absorption due to two layers of material
partially covering the source and a high energy cut-off around 70-80 keV.
Features such as a narrow iron line and a Compton reflection component, if
present, are weak, suggesting that reprocessing of the power law photons in the
accretion disk plays a negligible role in the source.Comment: 7 pages, 7 figures, 3 tables, accepted for pubblication on MNRA
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