Peatlands and the carbon cycle: from local processes to global implications - a synthesis

Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15-30% of the world's soil carbon ( C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change. The main drivers controlling most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange ( NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors. Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO2 and CH4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales

Zero delay synchronization of chaos in coupled map lattices

We show that two coupled map lattices that are mutually coupled to one another with a delay can display zero delay synchronization if they are driven by a third coupled map lattice. We analytically estimate the parametric regimes that lead to synchronization and show that the presence of mutual delays enhances synchronization to some extent. The zero delay or isochronal synchronization is reasonably robust against mismatches in the internal parameters of the coupled map lattices and we analytically estimate the synchronization error bounds.Comment: 9 pages, 9 figures ; To appear in Phys. Rev.

Deep electronic states in ion-implanted Si

In this paper we present an overview of the deep states present after ion-implantation by various species into n-type silicon, measured by Deep Level Transient Spectroscopy (DLTS) and high resolution Laplace DLTS (LDLTS). Both point and small extended defects are found, prior to any anneal, which can therefore be the precursors to more detrimental defects such as end of range loops. We show that the ion mass is linked to the concentrations of defects that are observed, and the presence of small interstitial clusters directly after ion implantation is established by comparing their behaviour with that of electrically active stacking faults. Finally, future applications of the LDLTS technique to ion-implanted regions in Si-based devices are outlined.</p

Convergence Characteristics of the Cumulant Expansion for Fourier Path Integrals

The cumulant representation of the Fourier path integral method is examined to determine the asymptotic convergence characteristics of the imaginary-time density matrix with respect to the number of path variables $N$ included. It is proved that when the cumulant expansion is truncated at order $p$, the asymptotic convergence rate of the density matrix behaves like $N^{-(2p+1)}$. The complex algebra associated with the proof is simplified by introducing a diagrammatic representation of the contributing terms along with an associated linked-cluster theorem. The cumulant terms at each order are expanded in a series such that the the asymptotic convergence rate is maintained without the need to calculate the full cumulant at order $p$. Using this truncated expansion of each cumulant at order $p$, the numerical cost in developing Fourier path integral expressions having convergence order $N^{-(2p+1)}$ is shown to be approximately linear in the number of required potential energy evaluations making the method promising for actual numerical implementation.Comment: 47 pages, 2 figures, submitted to PR

Electronic structure and light-induced conductivity in a transparent refractory oxide

Combined first-principles and experimental investigations reveal the underlying mechanism responsible for a drastic change of the conductivity (by 10 orders of magnitude) following hydrogen annealing and UV-irradiation in a transparent oxide, 12CaO.7Al2O3, found by Hayashi et al. The charge transport associated with photo-excitation of an electron from H, occurs by electron hopping. We identify the atoms participating in the hops, determine the exact paths for the carrier migration, estimate the temperature behavior of the hopping transport and predict a way to enhance the conductivity by specific doping.Comment: 4 pages including 4 figure

The HI and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics

We present observations of the distribution and kinematics of neutral and ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system. Ionized gas is present over a huge spread in velocity (1100 km/s) in the disk of NGC 1144, but HI emission is detected over only 1/3 of this velocity range, in an area that corresponds to the NW half of the disk. In the nuclear region of NGC 1144, a jump in velocity in the ionized gas component of 600 km/s is observed. Faint, narrow HI absorption lines are also detected against radio sources in the SE part of the disk of NGC 1144, which includes regions of massive star formation and a Seyfert nucleus. The peculiar HI distribution, which is concentrated in the NW disk, seems to be the inverse of the molecular distribution which is concentrated in the SE disk. Although this may partly be the result of the destruction of HI clouds in the SE disk, there is circumstantial evidence that the entire HI emission spectrum of NGC 1144 is affected by a deep nuclear absorption line covering a range of 600 km/s, and is likely blueshifted with respect to the nucleus. In this picture, a high column-density HI stream is associated with the nuclear ionized gas velocity discontinuity, and the absorption effectively masks any HI emission that would be present in the SE disk of NGC 1144.Comment: manuscript, arp118.ps: 28 pages; 1 Table: arp118.tab1.ps; 16 Figures: arp118.fig1-16.ps; Accepted to Ap

Short-term genome stability of serial Clostridium difficile ribotype 027 isolates in an experimental gut model and recurrent human disease

Copyright: © 2013 Eyre et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedClostridium difficile whole genome sequencing has the potential to identify related isolates, even among otherwise indistinguishable strains, but interpretation depends on understanding genomic variation within isolates and individuals.Serial isolates from two scenarios were whole genome sequenced. Firstly, 62 isolates from 29 timepoints from three in vitro gut models, inoculated with a NAP1/027 strain. Secondly, 122 isolates from 44 patients (2–8 samples/patient) with mostly recurrent/on-going symptomatic NAP-1/027 C. difficile infection. Reference-based mapping was used to identify single nucleotide variants (SNVs).Across three gut model inductions, two with antibiotic treatment, total 137 days, only two new SNVs became established. Pre-existing minority SNVs became dominant in two models. Several SNVs were detected, only present in the minority of colonies at one/two timepoints. The median (inter-quartile range) [range] time between patients’ first and last samples was 60 (29.5–118.5) [0–561] days. Within-patient C. difficile evolution was 0.45 SNVs/called genome/year (95%CI 0.00–1.28) and within-host diversity was 0.28 SNVs/called genome (0.05–0.53). 26/28 gut model and patient SNVs were non-synonymous, affecting a range of gene targets.The consistency of whole genome sequencing data from gut model C. difficile isolates, and the high stability of genomic sequences in isolates from patients, supports the use of whole genome sequencing in detailed transmission investigations.Peer reviewe

In vitro assessment of Clostridium difficile PCR ribotype 002: the most prevalent C. difficile ribotype in the United Kingdom.

Simon Baines, Iye Ameh, Jane Freeman, W.N. Fawley, M.H. Wilcox, ‘In vitro assessment of Clostridium difficile PCR ribotype 002: the most prevalent C. difficile ribotype in the United Kingdom’, poster presented at the 25th European Congress on Clinical Microbiology and Infectious Diseases, Copenhagen, Denmark, 25-28 August, 2015.Background: Clostridium difficile infection (CDI) causes substantial morbidity and healthcare expenditure across Europe. UK prevalence of C. difficile PCR ribotype 027 (NAP1) has declined dramatically recently and other ribotypes have emerged, including ribotype 002 (CD002); now the most prevalent UK ribotype. CD002 is also responsible for CDI in many countries across Europe, including: France, Germany, Ireland, and The Netherlands. We assessed the in vitro phenotypic characteristics of CD002 from across Europe to determine traits that may contribute to its increasing clinical prevalence. Material/methods: Sixty CD002 were studied: UK isolates from 2007-2008 (geographically distinct, N=15), UK isolates from 2011-2013 (19 locations, N=22), and non-UK European isolates from 2012-2014 (N=23, 20 locations). Antimicrobial susceptibilities (13 antimicrobials) were evaluated using an agar incorporation method. Maximum specific growth rates (μmax) were calculated and cytotoxin titres (log10-relative units, RU) determined using Vero cell cytotoxicity assays. Biofilm formation was quantified using 96-well microtitre plate assays and sporulation capacities assessed in liquid culture by quantifying spore-formation over 120 h (CFU/mL). Results: All isolates were susceptible metronidazole, vancomycin, tetracycline and linezolid (MICs ≤2 mg/L). Clindamycin resistance (MIC ≥8 mg/L) was more common in non-UK CD002 (30%) than UK strains (5-13%). Resistance to erythromycin, clarithromycin, nitrofurantoin, chloramphenicol, and moxifloxacin was uncommon (5-7%). MICs for penicillin’s remained below resistance breakpoints, regardless of origin, in all but one isolate (ampicillin MIC 2 mg/L). All CD002 were resistant to trimethoprim (MICs >128 mg/L) and ciprofloxacin (MICs ≥8 mg/L). One MDR strain (UK, 2007) was observed that was macrolide, fluoroquinolone, ampicillin, and nitrofurantoin resistant. Significantly faster μmax was seen in non-UK CD002 (0.92 ±0.058 h-1) than recent/older UK strains (0.76 ±0.063/0.69 ±0.028 h-1 respectively) (P<0.001). Cytotoxin production did not differ significantly (median titres 2-3 RU) between CD002 groups. Recent UK/non-UK CD002 formed significantly greater biofilms by 3 days than asynchronous UK CD002 (P<0.001). Sporulation studies demonstrated that recent UK/non-UK CD002 sporulated more at 24 h than older UK CD002; 18.6-fold/31.2-fold respectively (P<0.05), but by 120 h sporulation did not differ. Conclusions: Recent CD002 from diverse European locations were assessed for traits that may help to explain emergence of CD002 in the UK and compared to asynchronous CD002. Previous studies demonstrated elevated CD002 μmax compared to hypervirulent ribotypes 027/078; and the present study demonstrated that recent non-UK CD002 μmax were significantly further elevated vs. UK isolates. Non-UK CD002 were more clindamycin resistant, but other antimicrobial susceptibilities were similar between CD002 groups. Recent CD002 demonstrated significantly increased sporulation capacities at 24 h and more extensive 3 day biofilm formation compared to asynchronous UK CD002, which could enhance their survival and transmission early in an episode CDI. Further phenotypic and genetic studies are required to evaluate further characteristics of CD002 that may be associated with its emergence in the UK.Peer reviewedFinal Published versio

Intracluster stars in the Virgo cluster core

We have investigated the properties of the diffuse light in the Virgo cluster core region, based on the detection of intracluster planetary nebulae (PNe) in four fields. We eliminate the bias from misclassified faint continuum objects, using improved Monte Carlo simulations, and the contaminations by high redshift Ly$\alpha$ galaxies, using the Ly$\alpha$ luminosity function in blank fields. Recent spectroscopic observations confirm that our photometric PN samples are well-understood. We find that the diffuse stellar population in the Virgo core region is inhomogeneous on scales of 30'-90': there exist significant field-to-field variations in the number density of PNe and the inferred amount of intracluster light, with some empty fields, some fields dominated by extended Virgo galaxy halos, and some fields dominated by the true intracluster component. There is no clear trend with distance from M87. The mean surface luminosity density, its rms variation, and the mean surface brightness of diffuse light in our 4 fields are $\Sigma_B = 2.7 x 10^{6}$ L$_{B\odot}$ arcmin$^{-2}$, ${rms} = 2.1 \times 10^{6}$ L$_{B\odot}$ arcmin$^{-2}$, and $\bar{\mu}_{B}=29.0$ mag arcsec$^{-2}$ respectively. Our results indicate that the Virgo cluster is a dynamically young environment, and that the intracluster component is associated at least partially with local physical processes like galaxy interactions or harassment. We also argue, based on kinematic evidence, that the so-called 'over-luminous' PNe in the halo of M84 are dynamically associated with this galaxy, and must thus be brighter than and part of a different stellar population from the normal PN population in elliptical galaxies.Comment: 31 pages, 6 figure. In press on the Astronomical Journa