Causes of exotic bird establishment across oceanic islands

The probability that exotic species will successfully establish viable populations varies between regions, for reasons that are currently unknown. Here, we use data for exotic bird introductions to 41 oceanic islands and archipelagos around the globe to test five hypotheses for this variation: the effects of introduction effort, competition, predation, human disturbance and habitat diversity (island biogeography). Our analyses demonstrate the primary importance of introduction effort for avian establishment success across regions, in concordance with previous analyses within regions. However, they also reveal a strong negative interaction across regions between establishment success and predation; exotic birds are more likely to fail on islands with species-rich mammalian predator assemblages

Distinct high-T transitions in underdoped Ba1−x_{1-x}Kx_{x}Fe2_{2}As2_{2}

In contrast to the simultaneous structural and magnetic first order phase transition $T_{0}$ previously reported, our detailed investigation on an underdoped Ba$_{0.84}$K$_{0.16}$Fe$_{2}$As$_{2}$ single crystal unambiguously revealed that the transitions are not concomitant. The tetragonal ($\tau$: I4/mmm) - orthorhombic ($\vartheta$: Fmmm) structural transition occurs at $T_{S}\simeq$ 110 K, followed by an adjacent antiferromagnetic (AFM) transition at $T_{N}\simeq$ 102 K. Hysteresis and coexistence of the $\tau$ and $\vartheta$ phases over a finite temperature range observed in our NMR experiments confirm the first order character of the structural transition and provide evidence that both $T_{S}$ and $T_{N}$ are strongly correlated. Our data also show that superconductivity (SC) develops in the $\vartheta$ phase below $T_{c}$ = 20 K and coexists with long range AFM. This new observation, $T_{S}\neq T_{N}$, firmly establishes another similarity between the hole-doped BaFe$_{2}$As$_{2}$ via K substitution and the electron-doped iron-arsenide superconductors.Comment: 4 pages, 3 figure

Elastic cavitation, tube hollowing, and differential growth in plants and biological tissues

Elastic cavitation is a well-known physical process by which elastic materials under stress can open cavities. Usually, cavitation is induced by applied loads on the elastic body. However, growing materials may generate stresses in the absence of applied loads and could induce cavity opening. Here, we demonstrate the possibility of spontaneous growth-induced cavitation in elastic materials and consider the implications of this phenomenon to biological tissues and in particular to the problem of schizogenous aerenchyma formation

Injective split systems

A split system $\mathcal S$ on a finite set $X$, $|X|\ge3$, is a set of bipartitions or splits of $X$ which contains all splits of the form $\{x,X-\{x\}\}$, $x \in X$. To any such split system $\mathcal S$ we can associate the Buneman graph $\mathcal B(\mathcal S)$ which is essentially a median graph with leaf-set $X$ that displays the splits in $\mathcal S$. In this paper, we consider properties of injective split systems, that is, split systems $\mathcal S$ with the property that $\mathrm{med}_{\mathcal B(\mathcal S)}(Y) \neq \mathrm{med}_{\mathrm B(\mathcal S)}(Y')$ for any 3-subsets $Y,Y'$ in $X$, where $\mathrm {med}_{\mathcal B(\mathcal S)}(Y)$ denotes the median in $\mathcal B(\mathcal S)$ of the three elements in $Y$ considered as leaves in $\mathcal B(\mathcal S)$. In particular, we show that for any set $X$ there always exists an injective split system on $X$, and we also give a characterization for when a split system is injective. We also consider how complex the Buneman graph $\mathcal B(\mathcal S)$ needs to become in order for a split system $\mathcal S$ on $X$ to be injective. We do this by introducing a quantity for $|X|$ which we call the injective dimension for $|X|$, as well as two related quantities, called the injective 2-split and the rooted-injective dimension. We derive some upper and lower bounds for all three of these dimensions and also prove that some of these bounds are tight. An underlying motivation for studying injective split systems is that they can be used to obtain a natural generalization of symbolic tree maps. An important consequence of our results is that any three-way symbolic map on $X$ can be represented using Buneman graphs.Comment: 22 pages, 3 figure

Association between psychological distress trajectories from adolescence to midlife and mental health during the pandemic: evidence from two British birth cohorts

BACKGROUND: This paper examined whether distinct life-course trajectories of psychological distress from adolescence to midlife were associated with poorer mental health outcomes during the pandemic. METHODS: We present a secondary analysis of two nationally representative British birth cohorts, the 1958 National Child Development Study (NCDS) and 1970 British Cohort Study (BCS70). We used latent variable mixture models to identify pre-pandemic longitudinal trajectories of psychological distress and a modified Poisson model with robust standard errors to estimate associations with psychological distress, life satisfaction and loneliness at different points during the pandemic. RESULTS: Our analysis identified five distinct pre-pandemic trajectories of psychological distress in both cohorts. All trajectories with prior symptoms of psychological distress irrespective of age of onset, severity and chronicity were associated with a greater relative risk of poorer mental health outcomes during the pandemic and the probability of poorer mental health associated with psychological distress trajectories remained fairly constant. The relationship was not fully attenuated when most recent pre-pandemic psychological distress and other midlife factors were controlled for. CONCLUSIONS: Whilst life-course trajectories with any prior symptoms of psychological distress put individuals at greater risk of poor mental health outcomes during the pandemic, those with chronic and more recent occurrences were at highest risk. In addition, prior poor mental health during the adult life-course may mean individuals are less resilient to shocks, such as pandemics. Our findings show the importance of considering heterogeneous mental health trajectories across the life-course in the general population in addition to population average trends

An ordinary differential equation model for full thickness wounds and the effects of diabetes

Wound healing is a complex process in which a sequence of interrelated phases contributes to a reduction in wound size. For diabetic patients, many of these processes are compromised, so that wound healing slows down. In this paper we present a simple ordinary differential equation model for wound healing in which attention focusses on the dominant processes that contribute to closure of a full thickness wound. Asymptotic analysis of the resulting model reveals that normal healing occurs in stages: the initial and rapid elastic recoil of the wound is followed by a longer proliferative phase during which growth in the dermis dominates healing. At longer times, fibroblasts exert contractile forces on the dermal tissue, the resulting tension stimulating further dermal tissue growth and enhancing wound closure. By fitting the model to experimental data we find that the major difference between normal and diabetic healing is a marked reduction in the rate of dermal tissue growth for diabetic patients. The model is used to estimate the breakdown of dermal healing into two processes: tissue growth and contraction, the proportions of which provide information about the quality of the healed wound. We show further that increasing dermal tissue growth in the diabetic wound produces closure times similar to those associated with normal healing and we discuss the clinical implications of this hypothesised treatment

Folding and unfolding phylogenetic trees and networks

Phylogenetic networks are rooted, labelled directed acyclic graphs which are commonly used to represent reticulate evolution. There is a close relationship between phylogenetic networks and multi-labelled trees (MUL-trees). Indeed, any phylogenetic network $N$ can be "unfolded" to obtain a MUL-tree $U(N)$ and, conversely, a MUL-tree $T$ can in certain circumstances be "folded" to obtain a phylogenetic network $F(T)$ that exhibits $T$. In this paper, we study properties of the operations $U$ and $F$ in more detail. In particular, we introduce the class of stable networks, phylogenetic networks $N$ for which $F(U(N))$ is isomorphic to $N$, characterise such networks, and show that they are related to the well-known class of tree-sibling networks.We also explore how the concept of displaying a tree in a network $N$ can be related to displaying the tree in the MUL-tree $U(N)$. To do this, we develop a phylogenetic analogue of graph fibrations. This allows us to view $U(N)$ as the analogue of the universal cover of a digraph, and to establish a close connection between displaying trees in $U(N)$ and reconcilingphylogenetic trees with networks

Dynamical derivation of Bode's law

In a planetary or satellite system, idealized as n small bodies in initially coplanar, concentric orbits around a large central body, obeying Newtonian point-particle mechanics, resonant perturbations will cause dynamical evolution of the orbital radii except under highly specific mutual relationships, here derived analytically apparently for the first time. In particular, the most stable situation is achieved (in this idealized model) only when each planetary orbit is roughly twice as far from the Sun as the preceding one, as observed empirically already by Titius (1766) and Bode (1778) and used in both the discoveries of Uranus (1781) and the Asteroid Belt (1801). ETC.Comment: 27 page

High Magnetic Field NMR Studies of LiVGe2_2O6_6, a quasi 1-D Spin S=1S = 1 System

We report $^{7}$Li pulsed NMR measurements in polycrystalline and single crystal samples of the quasi one-dimensional S=1 antiferromagnet LiVGe$_2$O$_6$, whose AF transition temperature is $T_{\text{N}}\simeq 24.5$ K. The field ($B_0$) and temperature ($T$) ranges covered were 9-44.5 T and 1.7-300 K respectively. The measurements included NMR spectra, the spin-lattice relaxation rate ($T_1^{-1}$), and the spin-phase relaxation rate ($T_2^{-1}$), often as a function of the orientation of the field relative to the crystal axes. The spectra indicate an AF magnetic structure consistent with that obtained from neutron diffraction measurements, but with the moments aligned parallel to the c-axis. The spectra also provide the $T$-dependence of the AF order parameter and show that the transition is either second order or weakly first order. Both the spectra and the $T_1^{-1}$ data show that $B_0$ has at most a small effect on the alignment of the AF moment. There is no spin-flop transition up to 44.5 T. These features indicate a very large magnetic anisotropy energy in LiVGe$_2$O$_6$ with orbital degrees of freedom playing an important role. Below 8 K, $T_1^{-1}$ varies substantially with the orientation of $B_0$ in the plane perpendicular to the c-axis, suggesting a small energy gap for magnetic fluctuations that is very anisotropic.Comment: submitted to Phys. Rev.