Constraining the formation conditions of the ancient martian ALH 84001 carbonates

The martian meteorite ALH 84001 contains carbonates that provide information about the past aqueous conditions on Mars 3.9 Ga, and have been suggested to display signatures of martian organics. Determining the conditions under which the carbonates formed is crucial for addressing whether there was once life on Mars and the history of martian hydrosphere and atmosphere. This study has combined new sample preparation techniques with fresh isotopic analyses of ALH 84001 carbonates and analogue materials, geochemical modelling and the testing of future equipment (WatSen) suitable for carbonate detection on Mars. The results from these lnvestigations have provided quantitative constraints on the formation environment for the ALH 84001 carbonates and an instrument capable of detecting carbonates on Mars. The microscale carbon and oxygen analyses of ALH 84001 carbonates provide the first combined transient study across the carbonates with δ13C and δ18O values correlated ,with chemical compositions. The δ13C values range from -18.6% to +23.2% extending and lowering the previous ion microprobe δ13C range found and suggests that reduced carbon is present in the carbonates. This component exists as either macromolecular carbon introduced through subsequent alteration, terrestrial contamination or martian organics. The δ18O range -0.1% +27.1% is consistent with previous authors and displays a clear correlation with δ18O enrichment with distance from the carbonates core to edge. An 18.6% range in δ18O values was measured across analogue carbonates similar in size, shape and chemical variation which formed in a hydrothermal environmen

Towards population estimates for birds of central Africa’s Albertine Rift

Globally, biodiversity faces severe pressures, which are likely to increase with ongoing climate change and a growing human population. Despite birds being one of the world’s best-monitored taxa, data on population sizes, distributions and demography remain patchy, rendering threat evaluation and mitigation planning difficult. Few studies comparing impacts of data collection methods on population estimation exist. Accurate population data are fundamental for conservation applications. In this thesis, I first use distance sampling, a method of density estimation accounting for individuals’ detectability, to compare the efficacy of two widely-used data collection methods, line transects and point counts. I demonstrate point counts obtain systematically higher density estimates, and show there are marked differences in estimates between methods related to species behavioural and morphological traits. The results demonstrate that survey method should be evaluated case-by-case, considering issues such as target species and landscape characteristics. Following this, I apply distance sampling to estimate population sizes of birds across regions of central Africa’s Albertine Rift, a global biodiversity hotspot lacking baseline data. This region harbours the continent’s highest levels of vertebrate species richness and endemism but faces major threats from climate and land-use change. This work reveals non-uniform patterns of species richness and densities, helping identify priority regions and habitats to protect individual endemic and threatened species. Finally, I investigate the effects of competitor abundance and habitat on abundance of the endemic and threatened bird species in the region. These analyses indicate little effect of competitor abundance, with habitat being a more important determinant of population sizes. In fact, species identified as competitors largely occur at higher abundances when co-occurring, something possibly attributable to habitat quality effects dominating over competitive interactions in driving density patterns. These findings suggest that translocation of species between mountain peaks in the Albertine Rift, a possible solution to extinction risk in this region where many populations occur on isolated high elevation sites, is unlikely to be detrimental to potential competitor species already present at recipient sites

Strong Evidence that the Galactic Bulge is Shining in Gamma Rays

There is growing evidence that the Galactic Center Excess identified in the $\textit{Fermi}$-LAT gamma-ray data arises from a population of faint astrophysical sources. We provide compelling supporting evidence by showing that the morphology of the excess traces the stellar over-density of the Galactic bulge. By adopting a template of the bulge stars obtained from a triaxial 3D fit to the diffuse near-infrared emission, we show that it is detected at high significance. The significance deteriorates when either the position or the orientation of the template is artificially shifted, supporting the correlation of the gamma-ray data with the Galactic bulge. In deriving these results, we have used more sophisticated templates at low-latitudes for the $\textit{Fermi}$ bubbles compared to previous work and the three-dimensional Inverse Compton (IC) maps recently released by the ${\tt GALPROP}$ team. Our results provide strong constraints on Millisecond Pulsar (MSP) formation scenarios proposed to explain the excess. We find that an $\textit{admixture formation}$ scenario, in which some of the relevant binaries are $\textit{primordial}$ and the rest are formed $\textit{dynamically}$, is preferred over a primordial-only formation scenario at $7.6\sigma$ confidence level. Our detailed morphological analysis also disfavors models of the disrupted globular clusters scenario that predict a spherically symmetric distribution of MSPs in the Galactic bulge. For the first time, we report evidence of a high energy tail in the nuclear bulge spectrum that could be the result of IC emission from electrons and positrons injected by a population of MSPs and star formation activity from the same site.Comment: 21 pages, 13 figures, V2: Minor changes to match submitted version, V3: matches JCAP published versio

Comparing the Galactic Bulge and Galactic Disk Millisecond Pulsars

The Galactic Center Excess (GCE) is an extended gamma-ray source in the central region of the Galaxy found in Fermi Large Area Telescope (Fermi-LAT) data. One of the leading explanations for the GCE is an unresolved population of millisecond pulsars (MSPs) in the Galactic bulge. Due to differing star formation histories it is expected that the MSPs in the Galactic bulge are older and therefore dimmer than those in the Galactic disk. Additionally, correlations between the spectral parameters of the MSPs and the spin-down rate of the corresponding neutron stars have been observed. This implies that the bulge MSPs may be spectrally different from the disk MSPs. We perform detailed modelling of the MSPs from formation until observation. Although we confirm the correlations, we do not find they are sufficiently large to significantly differentiate the spectra of the bulge MSPs and disk MSPs when the uncertainties are accounted for. Our results demonstrate that the population of MSPs that can explain the gamma-ray signal from the resolved MSPs in the Galactic disk and the unresolved MSPs in the boxy bulge and nuclear bulge can consistently be described as arising from a common evolutionary trajectory for some subset of astrophysical sources common to all these different environments. We do not require that there is anything unusual about inner Galaxy MSPs to explain the GCE. Additionally, we use a more accurate geometry for the distribution of bulge MSPs and incorporate dispersion measure estimates of the MSPs' distances. We find that the elongated boxy bulge morphology means that some the bulge MSPs are closer to us and so easier to resolve. We identify three resolved MSPs that have significant probabilities of belonging to the bulge population.Comment: 37 pages, 20 figures, V3: Minor grammatical corrections/clarifications. Reflects version to appear in JCAP. V4: Minor typos correcte

Engineering Dehydrated Amino Acid Residues in the Antimicrobial Peptide Nisin

The small antimicrobial peptide nisin, produced by Lactococcus lactis, contains the uncommon amino acid residues dehydroalanine and dehydrobutyrine and five thio ether bridges. Since these structures are posttranslationally formed from Ser, Thr, and Cys residues, it is feasible to study their role in nisin function and biosynthesis by protein engineering. Here we report the development of an expression system for mutated nisin Z (nisZ) genes, using nisin A producing L. lactis as a host. Replacement by site-directed mutagenesis of the Ser-5 codon in nisZ by a Thr codon, led to a mutant with a dehydrobutyrine instead of a dehydroalanine residue at position 5, as shown by NMR. Its antimicrobial activity was 2-10-fold lower relative to wild-type nisin Z, depending on the indicator strain used. In another mutagenesis study a double mutation was introduced in the nisZ gene by replacing the codons for Met-17 and Gly-18 by codons for Gln and Thr, respectively, as in the third lanthionine ring of the related antimicrobial peptide subtilin from Bacillus subtilis. This resulted in the simultaneous production of two mutant species, one containing a Thr residue and the other containing a dehydrobutyrine residue at position 18, both having different bacteriocidal properties.

Public preferences for the Swiss electricity system after the nuclear phase-out : a choice experiment

Energy transition towards a sustainable system comprising various energy sources is a major challenge. We conducted a representative survey in the German-speaking part of Switzerland to elicit the population's preferences for electricity from solar, wind or natural gas under different institutional and site-specific conditions. Based on a choice experiment we found a consistent preference for electricity based on solar energy and - to a lesser degree - wind energy, built in existing industrial and commercial areas. We identified five distinct population groups, three of which have a very pronounced profile concerning energy attributes: ‘Pro Renewables', ‘Pro Switzerland’, and ‘Pro Landscape’. The largest two groups, 'Moderates' and ‘Contra Status Quo’ value attributes fairly equally. All groups except Pro Landscape prefer electricity from Switzerland, and all groups except Pro Switzerland accept imports of renewable electricity, preferably from plants operated by Swiss firms. We suggest that unfamiliarity rather than nationalism is at the root of opposition to imports of renewables. An energy mix focusing on renewables and including border-crossing electricity infrastructure could pave the way for a cost-efficient energy transition towards a sustainable and resilient electricity system. Our results show that it would also be publicly acceptable by the majority of the Swiss population

Maturation pathway of nisin and other lantibiotics:post-translationally modified antimicrobial peptides exported by Gram-positive bacteria

Lantibiotics form a family of highly modified peptides which are secreted by several Gram-positive bacteria. They exhibit antimicrobial activity, mainly against other Gram-positive bacteria, by forming pores in the cellular membrane. These antimicrobial peptides are ribosomally synthesized and contain leader peptides which do not show the characteristics of signal sequences. Several amino acid residues of the precursor lantibiotic are enzymatically modified, whereafter secretion and processing of the leader peptide takes place, yielding the active antimicrobial substance. For several lantibiotics the gene clusters encoding biosynthetic enzymes, translocator proteins, self-protection proteins, processing enzymes and regulatory proteins have been identified. This MicroReview describes the current knowledge about the biosynthetic, immunity and regulatory processes leading to lantibiotic production. Most of the attention is focused on the lantibiotic nisin, which is produced by the food-grade bacterium Lactococcus lactis and is widely used as a preservative in the food industry

The Andromeda Gamma-Ray Excess: Background Systematics of the Millisecond Pulsars and Dark Matter Interpretations

Since the discovery of an excess in gamma rays in the direction of M31, its cause has been unclear. Published interpretations focus on a dark matter or stellar related origin. Studies of a similar excess in the Milky Way center motivate a correlation of the spatial morphology of the signal with the distribution of stellar mass in M31. However, a robust determination of the best theory for the observed excess emission is very challenging due to large uncertainties in the astrophysical gamma-ray foreground model. Here we perform a spectro-morphological analysis of the M31 gamma-ray excess using state-of-the-art templates for the distribution of stellar mass in M31 and novel astrophysical foreground models for its sky region. We construct maps for the old stellar populations of M31 based on observational data from the PAndAS survey and carefully remove the foreground stars. We also produce improved astrophysical foreground models by using novel image inpainting techniques based on machine learning methods. We find that our stellar maps, taken as a proxy for the location of a putative population of millisecond pulsars in the bulge of M31, reach a statistical significance of $5.4\sigma$, making them as strongly favoured as the simple phenomenological models usually considered in the literature, e.g., a disk-like template with uniform brightness. Our detection of the stellar templates is robust to generous variations of the astrophysical foreground model. Once the stellar templates are included in the astrophysical model, we show that the dark matter annihilation interpretation of the signal is unwarranted. Using the results of a binary population synthesis model we demonstrate that a population of about one million unresolved MSPs could naturally explain the observed gamma-ray luminosity per stellar mass, energy spectrum, and stellar bulge-to-disk flux ratio.Comment: 15 pages, 11 figures, comments are welcom