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 $\beta \approx 1.26$ 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 $\beta \approx 1.36$. This value can be explained by our derivation of $\beta = 4/3$ 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, $\tau \sim N^\alpha$. 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) $\rho$ inside the capsid. For very low densities $\rho \le 0.002$ the polymer is only weakly confined by the capsid, and we measure $\alpha = 1.33$, which is close to $\alpha = 1.4$ obtained for polymer translocation. At intermediate densities the scaling exponents $\alpha = 1.25$ and $1.21$ for $\rho = 0.01$ and $0.02$, respectively. These scalings are in accord with a crude derivation for the lower limit $\alpha = 1.2$. For the asymmetrical pore precise scaling breaks down, when the density exceeds the value for complete confinement by the capsid, $\rho \gtrapprox 0.25$. 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 $1^+$, $2^-$ and $3^+$ modes in $^{16}$O, $^{22}$O, $^{24}$O, $^{28}$O, $^{40}$Ca, $^{48}$Ca, $^{52}$Ca and $^{60}$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 106^{106}Cd for 0+→0+0^+ \to 0^+ transition

The two neutrino positron double beta decay of $^{106}$Cd for 0$^{+} \to$ 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 $^{106}$Cd and $^{106}$Pd nuclei has been tested by comparing the theoretically calculated results for yrast spectra, reduced $B(E2$:$0^{+}\to 2^{+})$ transition probabilities, quadrupole moments $Q(2^{+})$ and gyromagnetic factors $g(2^{+})$ with the available experimental data. In the second step, the nuclear transition matrix element $M_{2\nu}$ and the half-life $T_{1/2}^{2\nu}$ for 0$^{+}\to$ 0$^{+}$ transition have been calculated with these wave functions. Moreover, we have studied the effect of deformation on nuclear transition matrix element M$_{2\nu}.$Comment: 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