Evaluating the Applicability of the Fokker-Planck Equation in Polymer Translocation: A Brownian Dynamics Study

Brownian dynamics (BD) simulations are used to study the translocation dynamics of a coarse-grained polymer through a cylindrical nanopore. We consider the case of short polymers, with a polymer length, N, in the range N=21-61. The rate of translocation is controlled by a tunable friction coefficient, gamma_{0p}, for monomers inside the nanopore. In the case of unforced translocation, the mean translocation time scales with polymer length N as ~ (N-N_p)^alpha, where N_p is the average number of monomers in the nanopore. The exponent approaches the value alpha=2 when the pore friction is sufficiently high, in accord with the prediction for the case of the quasi-static regime where pore friction dominates. In the case of forced translocation, the polymer chain is stretched and compressed on the cis and trans sides, respectively, for low gamma_{0p}. However, the chain approaches conformational quasi-equilibrium for sufficiently large gamma_{0p}. In this limit the observed scaling of with driving force and chain length supports the FP prediction that is proportional to N/f_d for sufficiently strong driving force. Monte Carlo simulations are used to calculate translocation free energy functions for the system. The free energies are used with the Fokker-Planck equation to calculate translocation time distributions. At sufficiently high gamma_{0p}, the predicted distributions are in excellent agreement with those calculated from the BD simulations. Thus, the FP equation provides a valid description of translocation dynamics for sufficiently high pore friction for the range of polymer lengths considered here. Increasing N will require a corresponding increase in pore friction to maintain the validity of the FP approach. Outside the regime of low N and high pore friction, the polymer is out of equilibrium, and the FP approach is not valid.Comment: 13 pages, 11 figure

AGN-Induced Cavities in NGC 1399 and NGC 4649

We present an analysis of archival Chandra and VLA observations of the E0 galaxy NGC 1399 and the E2 galaxy NGC 4649 in which we investigate cavities in the surrounding X-ray emitting medium caused by the central AGN. We calculate the jet power required for the AGN to evacuate these cavities and find values of ~8x10^{41} erg/s and ~14x10^{41} erg/s for the lobes of NGC 1399 and ~7x10^{41} erg/s and ~6x10^{41} erg/s for those of NGC 4649. We also calculate the k/f values for each cavity, where k is the ratio of the total particle energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f is the volume filling factor of the plasma in the cavity. We find that the values of k/f for the lobes of NGC 1399 are ~93 and ~190, and those of the lobes of NGC 4649 are ~15000 and ~12000. We conclude that the assumed spectrum describes the electron distribution in the lobes of NGC 1399 reasonably well, and that there are few entrained particles. For NGC 4649, either there are many entrained particles or the model spectrum does not accurately describe the population of electrons.Comment: 8 pages, 2 figures, accepted for publication in MNRA

Jobseekers Regime and Flexible New Deal, the Six Month Offer and Support for the Newly Unemployed evaluations: An early process study

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On viscosity, conduction and sound waves in the intracluster medium

Recent X-ray and optical observations of the Perseus cluster indicate that the viscous and conductive dissipation of sound waves is the mechanism responsible for heating the intracluster medium and thus balancing radiative cooling of cluster cores. We discuss this mechanism more generally and show how the specific heating and cooling rates vary with temperature and radius. It appears that the heating mechanism is most effective above 10^7K, which allows for radiative cooling to proceed within normal galaxy formation but will stifle the growth of very massive galaxies. The scaling of the wavelength of sound waves with cluster temperature and feedback in the system are investigated.Comment: 5 pages, 4 figures, MNRAS accepte

Fossil AGN jets as ultra high energy particle accelerators

Remnants of AGN jets and their surrounding cocoons leave colossal magnetohydrodynamic (MHD) fossil structures storing total energies ~10^{60} erg. The original active galacic nucleus (AGN) may be dead but the fossil will retain its stable configuration resembling the reversed-field pinch (RFP) encountered in laboratory MHD experiments. In an RFP the longitudinal magnetic field changes direction at a critical distance from the axis, leading to magnetic re-connection there, and to slow decay of the large-scale RFP field. We show that this field decay induces large-scale electric fields which can accelerate cosmic rays with an E^{-2} power-law up to ultra-high energies with a cut-off depending on the fossil parameters. The cut-off is expected to be rigidity dependent, implying the observed composition would change from light to heavy close to the cut-off if one or two nearby AGN fossils dominate. Given that several percent of the universe's volume may house such slowly decaying structures, these fossils may even re-energize ultra-high energy cosmic rays from distant/old sources, offsetting the ``GZK-losses'' due to interactions with photons of the cosmic microwave background radiation and giving evidence of otherwise undetectable fossils. In this case the composition would remain light to the highest energies if distant sources or fossils dominated, but otherwise would be mixed. It is hoped the new generation of cosmic ray experiments such as the Pierre Auger Observatory and ultra-high energy neutrino telescopes such as ANITA and lunar Cherenkov experiments will clarify this.Comment: 11 pages, 6 figures, additional references and explanations. Accepted for publication in MNRA

The prevalence and causes of vision loss in Indigenous Australians: the National Indigenous Eye Health Survey

Aim: To determine the prevalence and causes of vision loss in Indigenous Australians. Design, setting and participants: A national, stratified, random cluster sample was drawn from 30 communities across Australia that each included about 300 Indigenous people of all ages. A sample of non-Indigenous adults aged 40 years was also tested at several remote sites for comparison. Participants were examined using a standardised protocol that included a questionnaire (self-administered or completed with the help of field staff), visual acuity (VA) testing on presentation and after correction, visual field testing, trachoma grading, and fundus and lens photography. The data were collected in 2008. Main outcome measures: VA; prevalence of low vision and blindness; causes of vision loss; rates of vision loss in Indigenous compared with non-Indigenous adults. Results: 1694Indigenouschildrenand1189Indigenousadultswereexamined, representing recruitment rates of 84% for children aged 5–15 years and 72% for adults aged 40 years. Rates of low vision (VA \u3c 6/12 to 6/60) were 1.5% (95% CI, 0.9%–2.1%) in children and 9.4% (95% CI, 7.8%–11.1%) in adults. Rates of blindness (VA \u3c 6/60) were 0.2% (95% CI, 0.04%–0.5%) in children and 1.9% (95% CI, 1.1%–2.6%) in adults. The principal cause of low vision in both adults and children was refractive error. The principal causes of blindness in adults were cataract, refractive error and optic atrophy. Relative risks (RRs) of vision loss and blindness in Indigenous adults compared with adults in the mainstream Australian population were 2.8 and 6.2, respectively. By contrast, RRs of vision loss and blindness in Indigenous children compared with mainstream children were 0.2 and 0.6, respectively. Conclusion: Many causes of vision loss in our sample were readily avoidable. Better allocation of services and resources is required to give all Australians equal access to eye health services

Radio Bubbles in Clusters

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with Ghz radio emission, to our sample, and also investigating ``ghost bubbles,'' i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 < k/f < 1000. In the assumption that there is pressure equilibrium between the radio-emitting plasma and the surrounding thermal X-ray gas, none of the radio lobes has equipartition between the relativistic particles and the magnetic field. A Monte-Carlo simulation of the data led to the conclusion that there are not enough bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared to those in the same cluster. A study of the Brightest 55 cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, t_cool < 3 Gyr, and a large central temperature drop, T_centre/T_outer< 1/2. Of these between 12 (70 per cent) and 15 (75 per cent), contain bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.Comment: 12 pages, Accepted for publication in MNRA

Particle Energies and Filling Fractions of Radio Bubbles in Cluster Cores

Using Chandra images of cluster cores with clear radio bubbles, we have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Radiative and dynamical constraints on the bubbles indicate that the ratio of the energy factor, k, to the volume filling factor, f, lies within the range 1 < k/f < 1000. Assuming pressure equilibrium between the radio-emitting plasma and the surrounding X-ray gas, none of the lobes have equipartition between relativistic particles and magnetic field. There is no evidence for any dependence of the upper limit of the k/f ratio on any physical parameter of the cluster or the radio source. The distribution of the upper limit on k/f appears to be bimodal, the value for some clusters being ~3 and for the others ~300. We show that this is may due to the composition of the jet which forms the bubbles, the variation in the volume filling fraction or variation in the amount of re-acceleration occurring in the bubble.Comment: 12 pages, 9 figures; accepted for publication in MNRA

The radio properties of a complete, X-ray selected sample of nearby, massive elliptical galaxies

We investigate the radio properties of a complete sample of nearby, massive, X-ray bright elliptical and S0 galaxies. Our sample contains 18 galaxies with ROSAT All-Sky Survey X-ray fluxes Fx_(0.1-2.4 keV) > 3 x 10^(-12) erg/s/cm^2, within a distance of 100 Mpc. For these galaxies, we have complete (18/18) VLA radio and Chandra X-ray coverage. Nuclear radio emission is detected from 17/18 of the galaxies. Ten of the galaxies exhibit extended radio emission; of these ten, all but one also exhibit clear evidence of interaction of the radio source with the surrounding, X-ray emitting gas. Among the seven galaxies with unresolved radio sources, one has clear, and one has small, cavity-like features in the Chandra X-ray images; a third has a disturbed X-ray morphology. Using a radio luminosity limit equivalent to L_(1.4 Ghz) > 10^(23) W/Hz to calculate the radio-loud fraction, we find that this misses the majority of the radio detected galaxies in the sample. We determine integrated radio-to-X-ray flux ratios for the galaxies, GRx, which are shown to span a large range (factor of 100). We calculate the mass-weighted cooling times within 1 kpc, and find hints for an anticorrelation with the radio luminosity. We also calculate limits on k/f, where k is the ratio of the total particle energy to that of relativistic electrons radiating in the range 10 MHz-10 GHz and f is the volume filling factor of the plasma in the cavity. The k/f distribution is also broad, reflecting previous results for larger galaxy clusters. Lowering the X-ray flux limit, at the expense of less complete VLA and Chandra coverage, increases the size of our sample to 42 galaxies. Nuclear radio activity is detected in at least 34/42 of this extended sample.Comment: Accepted for publication in MNRAS, 19 pages, 11 Figures and 7 Table