Using a cognitive architecture to examine what develops

Different theories of development propose alternative mechanisms by which development occurs. Cognitive architectures can be used to examine the influence of each proposed mechanism of development while keeping all other mechanisms constant. An ACT-R computational model that matched adult behavior in solving a 21-block pyramid puzzle was created. The model was modified in three ways that corresponded to mechanisms of development proposed by developmental theories. The results showed that all the modifications (two of capacity and one of strategy choice) could approximate the behavior of 7-year-old children on the task. The strategy-choice modification provided the closest match on the two central measures of task behavior (time taken per layer, r = .99, and construction attempts per layer, r = .73). Modifying cognitive architectures is a fruitful way to compare and test potential developmental mechanisms, and can therefore help in specifying “what develops.

On the Representation Theory of an Algebra of Braids and Ties

We consider the algebra ${\cal E}_n(u)$ introduced by F. Aicardi and J. Juyumaya as an abstraction of the Yokonuma-Hecke algebra. We construct a tensor space representation for ${\cal E}_n(u)$ and show that this is faithful. We use it to give a basis for ${\cal E}_n(u)$ and to classify its irreducible representations.Comment: 24 pages. Final version. To appear in Journal of Algebraic Combinatorics

Nutrient (C, N and P) enrichment induces significant changes in the soil metabolite profile and microbial carbon partitioning

The cycling of soil organic matter (SOM) and carbon (C) within the soil is governed by the presence of key macronutrients, particularly nitrogen (N) and phosphorus (P). The relative ratio of these nutrients has a direct effect on the potential rates of microbial growth and nutrient processing in soil and thus is fundamental to ecosystem functioning. However, the effect of changing soil nutrient stoichiometry on the small organic molecule (i.e., metabolite) composition and cycling by the microbial community remains poorly understood. Here, we aimed to disentangle the effect of stoichiometrically balanced nutrient addition on the soil metabolomic profile and apparent microbial carbon use efficiency (CUE) by adding a labile C source (glucose) in combination with N and/or P. After incorporation of the added glucose into the microbial biomass (48 h), metabolite profiling was undertaken by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). 494 metabolites were identified across all treatments mainly consisting of lipids (n = 199), amino acids (n = 118) and carbohydrates (n = 43), >97% of which showed significant changes in concentration between at least one treatment. Overall, glucose-C addition generally increased the synthesis of other carbohydrates in soil, while addition of C and N together increased peptide synthesis, indicative of protein formation and turnover. The combination of C and P significantly increased the number of fatty acids synthesised. There was no significant change in the PLFA-derived microbial community structure or microbial biomass following C, N and P addition. Further, N addition led to an increase in glucose-C partitioning into anabolic processes (i.e., increased CUE), suggesting the microbial community was N, but not P limited. Based on the metabolomic profiles observed here, we conclude that inorganic nutrient enrichment causes substantial shifts in both primary and secondary metabolism within the microbial community, leading to changes in resource flow and thus soil functioning, however, the microbial community illustrated significant metabolic flexibility

Is manganese-doped diamond a ferromagnetic semiconductor?

We use density-functional theoretical methods to examine the recent prediction, based on a mean-field solution of the Zener model, that diamond doped by Mn (with spin S=5/2) would be a dilute magnetic semiconductor that remains ferromagnetic well above room temperature. Our findings suggest this to be unlikely, for four reasons: (1) substitutional Mn in diamond has a low-spin S=1/2 ground state; (2) the substitutional site is energetically unfavorable relative to the much larger "divacancy" site; 3) Mn in the divacancy site is an acceptor, but with only hyperdeep levels, and hence the holes are likely to remain localized; (4) the calculated Heisenberg couplings between Mn in nearby divacancy sites are two orders of magnitude smaller than for substitutional Mn in germanium.Comment: 5 pages, 5 figure

Lowest observed surface and weld losses in fused silica fibres for gravitational wave detectors

High purity fused silica has become the cornerstone choice for use in the final monolithic stage of the mirror suspensions in the gravitational wave observatories Advanced LIGO (aLIGO) and Advanced Virgo (AdV). The ultra-low thermal noise contributed by these suspensions is one of the key improvements that permitted the Nobel prize winning first direct measurement of gravitational waves in 2015. This paper outlines the first in situ study undertaken to analyse the thermal noise of the final monolithic stage of the aLIGO Hanford detector mirror suspensions. We analysed short operational periods of this detector, when high excitation of the transverse 'violin' modes of the silica suspension fibres occurred. This allowed detailed measurements of the Q-factor of violin modes up to order 8 of individual fibres on separate masses. We demonstrate the highest silica fibre violin mode Q-factors yet measured of up to 2 × 109. From finite element modelling, the dominant surface and weld losses have been calculated to be a factor of 3 to 4 better than previously accepted, and as a result, we demonstrate that the level of noise in the aLIGO final stage silica suspensions is around 30%–40% better than previously estimated between frequencies of 10–500 Hz. This leads to an increase in the estimated event rate by a factor of 2 for aLIGO, if suspension thermal noise became the main limitation to the sensitivity of the detector

Leaf water δ18O reflects water vapour exchange and uptake by C3 and CAM epiphytic bromeliads in Panama

The distributions of CAM and C3 epiphytic bromeliads across an altitudinal gradient in western Panama were identified from carbon isotope (δ13C) signals, and epiphyte water balance was investigated via oxygen isotopes (δ18O) across wet and dry seasons. There were significant seasonal differences in leaf water (δ18Olw), precipitation, stored 'tank' water and water vapour. Values of δ18Olw were evaporatively enriched at low altitude in the dry season for the C3 epiphytes, associated with low relative humidity (RH) during the day. Crassulacean acid metabolism (CAM) δ18Olw values were relatively depleted, consistent with water vapour uptake during gas exchange under high RH at night. At high altitude, cloudforest locations, C3 δ18Olw also reflected water vapour uptake by day. A mesocosm experiment with Tillandsia fasciculata (CAM) and Werauhia sanguinolenta (C3) was combined with simulations using a non-steady-state oxygen isotope leaf water model. For both C3 and CAM bromeliads, δ18Olw became progressively depleted under saturating water vapour by day and night, although evaporative enrichment was restored in the C3 W. sanguinolenta under low humidity by day. Source water in the overlapping leaf base 'tank' was also modified by evaporative δ18O exchanges. The results demonstrate how stable isotopes in leaf water provide insights for atmospheric water vapour exchanges for both C3 and CAM systems

Electromagnetic transitions of the helium atom in superstrong magnetic fields

We investigate the electromagnetic transition probabilities for the helium atom embedded in a superstrong magnetic field taking into account the finite nuclear mass. We address the regime \gamma=100-10000 a.u. studying several excited states for each symmetry, i.e. for the magnetic quantum numbers 0,-1,-2,-3, positive and negative z parity and singlet and triplet symmetry. The oscillator strengths as a function of the magnetic field, and in particular the influence of the finite nuclear mass on the oscillator strengths are shown and analyzed.Comment: 10 pages, 8 figure

Extragenic suppressor mutations in ΔripA disrupt stability and function of LpxA

Background: Francisella tularensis is a Gram-negative bacterium that infects hundreds of species including humans, and has evolved to grow efficiently within a plethora of cell types. RipA is a conserved membrane protein of F. tularensis, which is required for growth inside host cells. As a means to determine RipA function we isolated and mapped independent extragenic suppressor mutants in ΔripA that restored growth in host cells. Each suppressor mutation mapped to one of two essential genes, lpxA or glmU, which are involved in lipid A synthesis. We repaired the suppressor mutation in lpxA (S102, LpxA T36N) and the mutation in glmU (S103, GlmU E57D), and demonstrated that each mutation was responsible for the suppressor phenotype in their respective strains. We hypothesize that the mutation in S102 altered the stability of LpxA, which can provide a clue to RipA function. LpxA is an UDP-N-acetylglucosamine acyltransferase that catalyzes the transfer of an acyl chain from acyl carrier protein (ACP) to UDP-N-acetylglucosamine (UDP-GlcNAc) to begin lipid A synthesis. Results: LpxA was more abundant in the presence of RipA. Induced expression of lpxA in the ΔripA strain stopped bacterial division. The LpxA T36N S102 protein was less stable and therefore less abundant than wild type LpxA protein. Conclusion: These data suggest RipA functions to modulate lipid A synthesis in F. tularensis as a way to adapt to the host cell environment by interacting with LpxA

Handlers of Algebraic Effects

Abstract. We present an algebraic treatment of exception handlers and, more generally, introduce handlers for other computational effects representable by an algebraic theory. These include nondeterminism, interactive input/output, concurrency, state, time, and their combinations; in all cases the computation monad is the free-model monad of the theory. Each such handler corresponds to a model of the theory for the effects at hand. The handling construct, which applies a handler to a computation, is based on the one introduced by Benton and Kennedy, and is interpreted using the homomorphism induced by the universal property of the free model. This general construct can be used to describe previously unrelated concepts from both theory and practice.