The coming and going of a marl lake: multi-indicator palaeolimnology reveals abrupt ecological change and alternative views of reference conditions

Eutrophication is the most pressing threat to highly calcareous (marl) lakes in Europe. Despite their unique chemistry and biology, comprehensive studies into their unimpacted conditions and eutrophication responses are underrepresented in conservation literature. A multi-indicator palaeolimnological study spanning ca. 1260–2009 was undertaken at Cunswick Tarn (UK), a small, presently eutrophic marl lake, in order to capture centennial timescales of impact. Specific aims were to (1) establish temporal patterns of change (gradual/abrupt) across biological groups, thereby testing theories of resistance of marl lake benthic communities to enrichment, and (2) compare the core record of reference condition with prevailing descriptions of high ecological status. Analyses of sediment calcium (Ca), phosphorus (P), pigments, diatoms, testate amoebae, cladocerans, and macrofossils, revealed three abrupt changes in ecosystem structure. The first (1900s), with biomass increases in charophytes and other benthic nutrient-poor indicators, supported ideas of resistance to eutrophication in Chara lakes. The second transition (1930s), from charophyte to angiosperm dominance, occurred alongside reductions in macrophyte cover, increases in eutrophic indicators, and a breakdown in marling, in support of ideas of threshold responses to enrichment. Core P increased consistently into the 1990s when rapid transitions into pelagic shallow lake ecology occurred and Cunswick Tarn became biologically unidentifiable as a marl lake. The moderate total P at which these changes occurred suggests high sensitivity of marl lakes to eutrophication. Further, the early record challenges ideas of correlation between ecological condition, charophyte biomass and sediment Ca. Instead, low benthic production, macrophyte cover, and Ca sedimentation, was inferred. Management measures must focus on reducing external nutrient and sediment loads at early stages of impact in order to preserve marl lakes

On The Potential of Minimal Flavour Violation

Assuming the Minimal Flavour Violation hypothesis, we derive the general scalar potential for fields whose background values are the Yukawa couplings. We analyze the minimum of the potential and discuss the fine-tuning required to dynamically generate the mass hierarchies and the mixings between different quark generations. Two main cases are considered, corresponding to Yukawa interactions being effective operators of dimension five or six (or, equivalently, resulting from bi-fundamental and fundamental scalar fields, respectively). At the renormalizable and classical level, no mixing is naturally induced from dimension five Yukawa operators. On the contrary, from dimension six Yukawa operators one mixing angle and a strong mass hierarchy among the generations result.Comment: 33 pages, 6 figures; Note added in proof on the stability of the minima of the scalar potential; results unchanged; references adde

Consequences of fish kills for long-term trophic structure in shallow lakes: implications for theory and restoration

Fish kills are a common occurrence in shallow, eutrophic lakes, but their ecological consequences, especially in the long-term, are poorly understood. We studied the decadal-scale response of two UK shallow lakes to fish kills using a palaeolimnological approach. Eutrophic and turbid Barningham Lake experienced two fish kills in the early 1950s and late 1970s with fish recovering after both events, whereas less eutrophic, macrophyte-dominated Wolterton Lake experienced one kill event in the early 1970s from which fish failed to recover. Our palaeo-data show fish-driven trophic cascade effects across all trophic levels (covering benthic and pelagic species) in both lakes regardless of pre-kill macrophyte coverage and trophic status. In turbid Barningham Lake, similar to long-term studies of biomanipulations in other eutrophic lakes, effects at the macrophyte-level are shown to be temporary after the first kill (c.20 years) and non-existent after the second kill. In plant-dominated Wolterton Lake permanent fish disappearance failed to halt a long-term pattern of macrophyte community change (e.g. loss of charophytes and over-wintering macrophyte species) symptomatic of eutrophication. Important implications for theory and restoration ecology arise from our study. Firstly, our data support ideas of slow eutrophication-driven change in shallow lakes where perturbations are not necessary prerequisites for macrophyte loss. Secondly, the study emphasises a key need for lake managers to reduce external nutrient-loading if sustainable and long-term lake restoration is to be achieved. Our research highlights the enormous potential of multi-indicator palaeolimnology and alludes to an important need to consider potential fish kill signatures when interpreting results

The flavor puzzle in multi-Higgs models

We reconsider the flavor problem in the models with two Higgs doublets. By studying two generation toy models, we look for flavor basis independent constraints on Yukawa couplings that will give us the mass hierarchy while keeping all Yukawa couplings of the same order. We then generalize our findings to the full three generation Standard Model. We find that we need two constraints on the Yukawa couplings to generate the observed mass hierarchy, and a slight tuning of Yukawa couplings of order 10%, much less than the Standard Model. We briefly study how these constraints can be realized, and show how flavor changing currents are under control for $K-\bar{K}$ mixing in the near-decoupling limit.Comment: 26 pages, typos are corrected, references are added, the final versio

Predictive feedback control and Fitts' law

Fitts’ law is a well established empirical formula, known for encapsulating the “speed-accuracy trade-off”. For discrete, manual movements from a starting location to a target, Fitts’ law relates movement duration to the distance moved and target size. The widespread empirical success of the formula is suggestive of underlying principles of human movement control. There have been previous attempts to relate Fitts’ law to engineering-type control hypotheses and it has been shown that the law is exactly consistent with the closed-loop step-response of a time-delayed, first-order system. Assuming only the operation of closed-loop feedback, either continuous or intermittent, this paper asks whether such feedback should be predictive or not predictive to be consistent with Fitts law. Since Fitts’ law is equivalent to a time delay separated from a first-order system, known control theory implies that the controller must be predictive. A predictive controller moves the time-delay outside the feedback loop such that the closed-loop response can be separated into a time delay and rational function whereas a non- predictive controller retains a state delay within feedback loop which is not consistent with Fitts’ law. Using sufficient parameters, a high-order non-predictive controller could approximately reproduce Fitts’ law. However, such high-order, “non-parametric” controllers are essentially empirical in nature, without physical meaning, and therefore are conceptually inferior to the predictive controller. It is a new insight that using closed-loop feedback, prediction is required to physically explain Fitts’ law. The implication is that prediction is an inherent part of the “speed-accuracy trade-off”

The Impact of Flavour Changing Neutral Gauge Bosons on B->X_s gamma

The branching ratio of the rare decay B->X_s gamma provides potentially strong constraints on models beyond the Standard Model. Considering a general scenario with new heavy neutral gauge bosons, present in particular in Z' and gauge flavour models, we point out two new contributions to the B->X_s gamma decay. The first one originates from one-loop diagrams mediated by gauge bosons and heavy exotic quarks with electric charge -1/3. The second contribution stems from the QCD mixing of neutral current-current operators generated by heavy neutral gauge bosons and the dipole operators responsible for the B->X_s gamma decay. The latter mixing is calculated here for the first time. We discuss general sum rules which have to be satisfied in any model of this type. We emphasise that the neutral gauge bosons in question could also significantly affect other fermion radiative decays as well as non-leptonic two-body B decays, epsilon'/epsilon, anomalous (g-2)_mu and electric dipole moments.Comment: 31 pages, 5 figures; version published on JHEP; added magic QCD numbers for flavour-violating Z gauge boson contribution to B -> X_s gamm

Flavourful Production at Hadron Colliders

We ask what new states may lie at or below the TeV scale, with sizable flavour-dependent couplings to light quarks, putting them within reach of hadron colliders via resonant production, or in association with Standard Model states. In particular, we focus on the compatibility of such states with stringent flavour-changing neutral current and electric-dipole moment constraints. We argue that the broadest and most theoretically plausible flavour structure of the new couplings is that they are hierarchical, as are Standard Model Yukawa couplings, although the hierarchical pattern may well be different. We point out that, without the need for any more elaborate or restrictive structure, new scalars with "diquark" couplings to standard quarks are particularly immune to existing constraints, and that such scalars may arise within a variety of theoretical paradigms. In particular, there can be substantial couplings to a pair of light quarks or to one light and one heavy quark. For example, the latter possibility may provide a flavour-safe interpretation of the asymmetry in top quark production observed at the Tevatron. We thereby motivate searches for diquark scalars at the Tevatron and LHC, and argue that their discovery represents one of our best chances for new insight into the Flavour Puzzle of the Standard Model.Comment: 18 pp., 8 figures, references adde

Purpose in life predicts better emotional recovery from negative stimuli

Purpose in life predicts both health and longevity suggesting that the ability to find meaning from life’s experiences, especially when confronting life’s challenges, may be a mechanism underlying resilience. Having purpose in life may motivate reframing stressful situations to deal with them more productively, thereby facilitating recovery from stress and trauma. In turn, enhanced ability to recover from negative events may allow a person to achieve or maintain a feeling of greater purpose in life over time. In a large sample of adults (aged 36-84 years) from the MIDUS study (Midlife in the U.S., http://www.midus.wisc.edu/), we tested whether purpose in life was associated with better emotional recovery following exposure to negative picture stimuli indexed by the magnitude of the eyeblink startle reflex (EBR), a measure sensitive to emotional state. We differentiated between initial emotional reactivity (during stimulus presentation) and emotional recovery (occurring after stimulus offset). Greater purpose in life, assessed over two years prior, predicted better recovery from negative stimuli indexed by a smaller eyeblink after negative pictures offset, even after controlling for initial reactivity to the stimuli during the picture presentation, gender, age, trait affect, and other well-being dimensions. These data suggest a proximal mechanism by which purpose in life may afford protection from negative events and confer resilience is through enhanced automatic emotion regulation after negative emotional provocation

Flavour in supersymmetry: horizontal symmetries or wave function renormalisation

We compare theoretical and experimental predictions of two main classes of models addressing fermion mass hierarchies and flavour changing neutral currents (FCNC) effects in supersymmetry: Froggatt-Nielsen (FN) U(1) gauged flavour models and Nelson-Strassler/extra dimensional models with hierarchical wave functions for the families. We show that whereas the two lead to identical predictions in the fermion mass matrices, the second class generates a stronger suppression of FCNC effects. We prove that, whereas at first sight the FN setup is more constrained due to anomaly cancelation conditions, imposing unification of gauge couplings in the second setup generates conditions which precisely match the mixed anomaly constraints in the FN setup. Finally, we provide an economical extra dimensional realisation of the hierarchical wave functions scenario in which the leptonic FCNC can be efficiently suppressed due to the strong coupling (CFT) origin of the electron mass.Comment: 23 page

The influence of soil communities on the temperature sensitivity of soil respiration

Soil respiration represents a major carbon flux between terrestrial ecosystems and the atmosphere, and is expected to accelerate under climate warming. Despite its importance in climate change forecasts, however, our understanding of the effects of temperature on soil respiration (RS) is incomplete. Using a metabolic ecology approach we link soil biota metabolism, community composition and heterotrophic activity, to predict RS rates across five biomes. We find that accounting for the ecological mechanisms underpinning decomposition processes predicts climatological RS variations observed in an independent dataset (n = 312). The importance of community composition is evident because without it RS is substantially underestimated. With increasing temperature, we predict a latitudinal increase in RS temperature sensitivity, with Q10 values ranging between 2.33 ±0.01 in tropical forests to 2.72 ±0.03 in tundra. This global trend has been widely observed, but has not previously been linked to soil communities