Facilitated Asymmetric Exclusion

We introduce a class of facilitated asymmetric exclusion processes in which particles are pushed by neighbors from behind. For the simplest version in which a particle can hop to its vacant right neighbor only if its left neighbor is occupied, we determine the steady state current and the distribution of cluster sizes on a ring. We show that an initial density downstep develops into a rarefaction wave that can have a jump discontinuity at the leading edge, while an upstep results in a shock wave. This unexpected rarefaction wave discontinuity occurs generally for facilitated exclusion processes.Comment: 4 pages, 5 figures, revtex4 format. Version 2 contains various minor changes in response to referee comments. For publication in PR

Survival of the Scarcer

We investigate extinction dynamics in the paradigmatic model of two competing species A and B that reproduce (A-->2A, B-->2B), self-regulate by annihilation (2A-->0, 2B-->0), and compete (A+B-->A, A+B-->B). For a finite system that is in the well-mixed limit, a quasi-stationary state arises which describes coexistence of the two species. Because of discrete noise, both species eventually become extinct in time that is exponentially long in the quasi-stationary population size. For a sizable range of asymmetries in the growth and competition rates, the paradoxical situation arises in which the numerically disadvantaged species according to the deterministic rate equations survives much longer.Comment: 5 pages, 2-column revtex4-1 format; current revision has stylistic changes in response to referees, for publication in PRE Rapid Communication

Highly Dispersed Networks Generated by Enhanced Redirection

We analyze growing networks that are built by enhanced redirection. Nodes are sequentially added and each incoming node attaches to a randomly chosen 'target' node with probability 1-r, or to the parent of the target node with probability r. When the redirection probability r is an increasing function of the degree of the parent node, with r-->1 as the parent degree diverges, networks grown via this enhanced redirection mechanism exhibit unusual properties, including: (i) multiple macrohubs---nodes with degrees proportional to the number of network nodes N; (ii) non-extensivity of the degree distribution in which the number of nodes of degree k, N_k, scales as N^{nu-1}/k^{nu}, with 1<nu<2; (iii) lack of self-averaging, with large fluctuations between individual network realizations. These features are robust and continue to hold when the incoming node has out-degree greater than 1 so that networks contain closed loops. The latter networks are strongly clustered; for the specific case of the double attachment, the average local clustering coefficient is =4(ln2)-2=0.77258...Comment: 26 pages, 12 figures, IOP format. This manuscript is a comprehensive account of work reported briefly in arXiv:1307.3768. Version 2: two minor typos fixed and one other small change in response to referee report. Version 3: minor typos fixed. Final version of publication in JSTA

Can a Lamb Reach a Haven Before Being Eaten by Diffusing Lions?

We study the survival of a single diffusing lamb on the positive half line in the presence of N diffusing lions that all start at the same position L to the right of the lamb and a haven at x=0. If the lamb reaches this haven before meeting any lion, the lamb survives. We investigate the survival probability of the lamb, S_N(x,L), as a function of N and the respective initial positions of the lamb and the lions, x and L. We determine S_N(x,L) analytically for the special cases of N=1 and N--->oo. For large but finite N, we determine the unusual asymptotic form whose leading behavior is S_N(z)\simN^{-z^2}, with z=x/L. Simulations of the capture process very slowly converge to this asymptotic prediction as N reaches 10^{500}.Comment: 13 pages, 6 figures, IOP format; v2: small changes in response to referee and editor comment

Elemental Abundances in NGC 3516

We present RGS data from an XMM-Newton observation of the Seyfert 1 galaxy NGC 3516, taken while the continuum source was in an extreme low state. The spectrum shows numerous emission lines including the H-like lines of C, N and O and the He-like lines of N, O and Ne. These data show that the N lines are far stronger than would be expected from gas of solar abundances. Based on our photoionization models, we find that N is overabundant compared to C, O and Ne by at least a factor of 2.5. We suggest this is the result of secondary production of N in intermediate mass stars, and indicative of the history of star formation in NGC 3516.Comment: 19 pages, 3 color figures. ApJ in pres

Reduction of cytotoxicity of benzalkonium chloride and octenidine by Brilliant Blue G

The irritative effects of preservatives found in ophthalmologic solution, or of antiseptics used for skin disinfection is a consistent problem for the patients. The reduction of the toxic effects of these compounds is desired. Brilliant Blue G (BBG) has shown to meet the expected effect in presence of benzalkonium chloride (BAK), a well known preservative in ophthalmic solutions, and octenidine dihydrochloride (Oct), used as antiseptic in skin and wound disinfection. BBG shows a significant protective effect on human corneal epithelial (HCE) cells against BAK and Oct toxicity, increasing the cell survival up to 51 % at the highest BAK or Oct concentration tested, which is 0.01 %, both at 30 min incubation. Although BBG is described as a P2x7 receptor antagonist, other selective P2x7 receptor antagonists, OxATP (adenosine 5’-triphosphate-2’,3’-dialdehyde) and DPPH (N’-(3,5-dichloropyridin-4-yl)-3-phenylpropanehydrazide), did not reduce the cytotoxicity of neither BAK nor Oct. Therefore we assume that the protective effect of BBG is not due to its action on the P2x7 receptor. Brilliant Blue R (BBR), a dye similar to BBG, was also tested for protective effect on BAK and Oct toxicity. In presence of BAK no significant protective effect was observed. Instead, with Oct a comparable protective effect was seen with that of BBG. To assure that the bacteriostatic effect is not affected by the combinations of BAK/BBG, Oct/BBG and Oct/BBR, bacterial growth inhibition was analyzed on different Gram-negative and Gram-positive bacteria. All combinations of BAK or Oct with BBG hinder growth of Gram-positive bacteria. The combinations of 0.001 % Oct and BBR above 0.025 % do not hinder the growth of B. subtilis. For Gram-negative bacteria, BBG and BBR reduce, but do not abolish, the antimicrobial effect of BAK nor of Oct. In conclusion, the addition of BBG at bacterial inhibitory concentrations is suggested in the ready-to-use ophthalmic preparations and antiseptic solutions

Simultaneous UV and X-ray Spectroscopy of the Seyfert 1 Galaxy NGC 5548. I. Physical Conditions in the UV Absorbers

We present new UV spectra of the nucleus of the Seyfert 1 galaxy NGC 5548, which we obtained with the Space Telescope Imaging Spectrograph at high spectral resolution, in conjunction with simultaneous Chandra X-ray Observatory spectra. Taking advantage of the low UV continuum and broad emission-line fluxes, we have determined that the deepest UV absorption component covers at least a portion of the inner, high-ionization narrow-line region (NLR). We find nonunity covering factors in the cores of several kinematic components, which increase the column density measurements of N V and C IV by factors of 1.2 to 1.9 over the full-covering case; however, the revised columns have only a minor effect on the parameters derived from our photoionization models. For the first time, we have simultaneous N V and C IV columns for component 1 (at -1040 km/s), and find that this component cannot be an X-ray warm absorber, contrary to our previous claim based on nonsimultaneous observations. We find that models of the absorbers based on solar abundances severely overpredict the O VI columns previously obtained with the Far Ultraviolet Spectrograph, and present arguments that this is not likely due to variability. However, models that include either enhanced nitrogen (twice solar) or dust, with strong depletion of carbon in either case, are successful in matching all of the observed ionic columns. These models result in substantially lower ionization parameters and total column densities compared to dust-free solar-abundance models, and produce little O VII or O VIII, indicating that none of the UV absorbers are X-ray warm absorbers.Comment: 33 pages, 5 figures (Figures 3 and 4 are in color), Accepted for publication in the Astrophysical Journa