791 research outputs found
Chaperone-assisted translocation of flexible polymers in three dimensions
Polymer translocation through a nanometer-scale pore assisted by chaperones
binding to the polymer is a process encountered in vivo for proteins. Studying
the relevant models by computer simulations is computationally demanding.
Accordingly, previous studies are either for stiff polymers in three dimensions
or flexible polymers in two dimensions. Here, we study chaperone-assisted
translocation of flexible polymers in three dimensions using Langevin dynamics.
We show that differences in binding mechanisms, more specifically, whether a
chaperone can bind to a single or multiple sites on the polymer, lead to
substantial differences in translocation dynamics in three dimensions. We show
that the single-binding mode leads to dynamics that is very much like that in
the constant-force driven translocation and accordingly mainly determined by
tension propagation on the cis side. We obtain for the
exponent for the scaling of the translocation time with polymer length. This
fairly low value can be explained by the additional friction due to binding
particles. The multiple-site binding leads to translocation whose dynamics is
mainly determined by the trans side. For this process we obtain . This value can be explained by our derivation of for
constant-bias translocation, where translocated polymer segments form a globule
on the trans side. Our results pave the way for understanding and utilizing
chaperone-assisted translocation where variations in microscopic details lead
to rich variations in the emerging dynamics.Comment: 10 pages, 12 figure
Dynamics of polymer ejection from capsid
Polymer ejection from a capsid through a nanoscale pore is an important
biological process with relevance to modern biotechnology. Here, we study
generic capsid ejection using Langevin dynamics. We show that even when the
ejection takes place within the drift-dominated region there is a very high
probability for the ejection process not to be completed. Introducing a small
aligning force at the pore entrance enhances ejection dramatically. Such a pore
asymmetry is a candidate for a mechanism by which a viral ejection is
completed. By detailed high-resolution simulations we show that such capsid
ejection is an out-of-equilibrium process that shares many common features with
the much studied driven polymer translocation through a pore in a wall or a
membrane. We find that the escape times scale with polymer length, . We show that for the pore without the asymmetry the previous
predictions corroborated by Monte Carlo simulations do not hold. For the pore
with the asymmetry the scaling exponent varies with the initial monomer density
(monomers per capsid volume) inside the capsid. For very low densities
the polymer is only weakly confined by the capsid, and we
measure , which is close to obtained for polymer
translocation. At intermediate densities the scaling exponents
and for and , respectively. These scalings are in
accord with a crude derivation for the lower limit . For the
asymmetrical pore precise scaling breaks down, when the density exceeds the
value for complete confinement by the capsid, . The
high-resolution data show that the capsid ejection for both pores, analogously
to polymer translocation, can be characterized as a multiplicative stochastic
process that is dominated by small-scale transitions.Comment: 10 pages, 6 figure
Magnetic excitations in nuclei with neutron excess
The excitation of the , and modes in O, O,
O, O, Ca, Ca, Ca and Ca nuclei is
studied with self-consistent random phase approximation calculations.
Finite-range interactions of Gogny type, containing also tensor-isospin terms,
are used. We analyze the evolution of the magnetic resonances with the
increasing number of neutrons, the relevance of collective effects, the need of
a correct treatment of the continuum and the role of the tensor force.Comment: 18 pages, 12 figures, 2 tables, accepted for publication in Physical
Review
Two neutrino positron double beta decay of Cd for transition
The two neutrino positron double beta decay of Cd for 0
0 transition has been studied in the Hartree-Fock-Bogoliubov model in
conjunction with the summation method. In the first step, the reliability of
the intrinsic wave functions of Cd and Pd nuclei has been
tested by comparing the theoretically calculated results for yrast spectra,
reduced : transition probabilities, quadrupole moments
and gyromagnetic factors with the available experimental
data. In the second step, the nuclear transition matrix element and
the half-life for 0 0 transition have been
calculated with these wave functions. Moreover, we have studied the effect of
deformation on nuclear transition matrix element MComment: 20 page
Nuclear and particle physics aspects of the 2nbb-decay of 150Nd
A discussion is given on possible realization of the Single State Dominance
(SSD) hypothesis in the case of the two-neutrino double beta decay(2nbb-decay)
of 150Nd with 1^- ground state of the intermediate nucleus. We conclude that
the SSD hypothesis is expected to be ruled out by precision measurement of
differential characteristics of this process in running NEMO 3 or planed
SuperNEMO experiments unlike some unknown low-lying 1^+ state of 150Pm does
exist. This problem can be solved via (d,2He) charge-exchange experiment on
150Sm. Further, we address the question about possible violation of the Pauli
exclusion principle for neutrinos and its consequences for the energy
distributions of the 2nbb-decay of 150Nd. This phenomenon might be a subject of
interest of NEMO 3 and SuperNEMO experiments as well.Comment: Revtex, 4 pages, 2 figures, Contributed to MEDEX'07, Prague, Czech
Rep., June 11-14, 200
In-Medium Similarity Renormalization Group with Chiral Two- Plus Three-Nucleon Interactions
We use the recently proposed In-Medium Similarity Renormalization Group
(IM-SRG) to carry out a systematic study of closed-shell nuclei up to
\nuc{Ni}{56}, based on chiral two- plus three-nucleon interactions. We
analyze the capabilities of the IM-SRG by comparing our results for the
ground-state energy to Coupled Cluster calculations, as well as to quasi-exact
results from the Importance-Truncated No-Core Shell Model. Using chiral two-
plus three-nucleon Hamiltonians whose resolution scales are lowered by
free-space SRG evolution, we obtain good agreement with experimental binding
energies in \nuc{He}{4} and the closed-shell oxygen isotopes, while the
calcium and nickel isotopes are somewhat overbound.Comment: 11 pages, 7 figures, submitted to Phys. Rev.
Ethical issues related to the use of gerontechnology in older people care: A scoping review
Background:Demographic trends indicate growth of population aged 65 and older in Western countries. One of the greatest challenges is to provide high-quality care for all. Technological solutions designed for older people, gerontechnology, can somewhat balance the gap between resources and the increasing demand of healthcare services. However, there are also ethical issues in the use of gerontechnology that need to be pointed out.Purpose:To describe what ethical issues are related to the use of gerontechnology in the care of community-dwelling older people.Methods:A scoping review was performed to identify and analyse studies concerning ethical issues when using gerontechnology in the home care of older people. The literature search was limited to studies published after 1990 and addressed to the electronic databases CINAHL, PubMed, Cochrane, Medic, IEEE Explore and Web of Science. The search was performed in July−August 2018. Data from empirical studies were analysed using thematic analysis.Ethical considerations:This scoping review was conducted in accordance with good scientific practice. The work of other researchers was respected and cited appropriately.Results:A total of 17 studies were identified. Two main themes were found. ‘Balancing between the benefits of using gerontechnology and the basic rights of older people’, consisted of the subthemes safety, privacy and autonomy. The other main theme, ‘Gerontechnology as a risk of insecurity for older people’, included the subthemes fear of losing human contact and concern and fear. Surveillance and monitoring technologies were mainly studied.Conclusion:These results suggest that there may be ethical issues related to the use of gerontechnology and they must therefore be taken into consideration when implementing technology in the care of community-dwelling older people.</div
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