533 research outputs found

    Where Working Memory Meets Long-Term Memory: The Interplay of List Length and Distractors on Memory Performance

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    Previous work regarding a counterintuitive benefit of increasing distractors on episodic long-term memory (LTM) has suggested that retrieval of memoranda in working memory (WM) after attention has been distracted may confer benefits to episodic LTM. The current study investigated two conceptions of how this may occur: either as an attentional refreshing of active memoranda within the focus of attention or as retrieval of a cohesive chunk of memoranda from outside the central component of WM. Given the literature suggesting that increasing the number of items to maintain in WM, or list length, incurs an attentional cost, the current study investigated whether increasing list length may reduce the beneficial impact of distractors on episodic LTM. In a series of three experiments we manipulated list length and the number of distractors following the memoranda in a Brown-Peterson-like-span task. Despite profound negative effects of list length and distractors on initial recall, the results indicated that list length did not interact with the beneficial effect of distractors on final free recall of the items. Furthermore, final free recall was consistent across serial position, in line with the view that all of the memoranda are retrieved as a chunk after each distractor. These findings emphasize the notion that recovering inactive information from outside of the central component of WM may impact its long-term retention. The theoretical implications regarding how retrieval may be a means by which LTM processes influence WM are discussed

    The place of lucerne in Western Australian agriculture

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    Lucerne, the world\u27s most important fodder legume, has never won largescale acceptance in West Australian farming, largely because of our success with productive subterranean clover pastures. But recent disease problems on sub. clover stands have led to greater interest in alternative species, especially lucerne, for higher rainfall areas. This article summarises our knowledge of lucerne establishment and management in W.A. and reviews current research aimed at achieving better results from lucerne

    Direct observation of hierarchical protein dynamics

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    One of the fundamental challenges of physical biology is to understand the relationship between protein dynamics and function. At physiological temperatures, functional motions arise from the complex interplay of thermal motions of proteins and their environments. Here, we determine the hierarchy in the protein conformational energy landscape that underlies these motions, based on a series of temperature-dependent magic-angle spinning multinuclear nuclear-magnetic-resonance relaxation measurements in a hydrated nanocrystalline protein. The results support strong coupling between protein and solvent dynamics above 160 kelvin, with fast solvent motions, slow protein side-chain motions, and fast protein backbone motions being activated consecutively. Low activation energy, small-amplitude local motions dominate at low temperatures, with larger-amplitude, anisotropic, and functionally relevant motions involving entire peptide units becoming dominant at temperatures above 220 kelvin

    ac Losses in a Finite Z Stack Using an Anisotropic Homogeneous-Medium Approximation

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    A finite stack of thin superconducting tapes, all carrying a fixed current I, can be approximated by an anisotropic superconducting bar with critical current density Jc=Ic/2aD, where Ic is the critical current of each tape, 2a is the tape width, and D is the tape-to-tape periodicity. The current density J must obey the constraint \int J dx = I/D, where the tapes lie parallel to the x axis and are stacked along the z axis. We suppose that Jc is independent of field (Bean approximation) and look for a solution to the critical state for arbitrary height 2b of the stack. For c<|x|<a we have J=Jc, and for |x|<c the critical state requires that Bz=0. We show that this implies \partial J/\partial x=0 in the central region. Setting c as a constant (independent of z) results in field profiles remarkably close to the desired one (Bz=0 for |x|<c) as long as the aspect ratio b/a is not too small. We evaluate various criteria for choosing c, and we show that the calculated hysteretic losses depend only weakly on how c is chosen. We argue that for small D/a the anisotropic homogeneous-medium approximation gives a reasonably accurate estimate of the ac losses in a finite Z stack. The results for a Z stack can be used to calculate the transport losses in a pancake coil wound with superconducting tape.Comment: 21 pages, 17 figures, accepted by Supercond. Sci. Techno

    Fundamental Oscillation Periods of the Interlayer Exchange Coupling beyond the RKKY Approximation

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    A general method for obtaining the oscillation periods of the interlayer exchange coupling is presented. It is shown that it is possible for the coupling to oscillate with additional periods beyond the ones predicted by the RKKY theory. The relation between the oscillation periods and the spacer Fermi surface is clarified, showing that non-RKKY periods do not bear a direct correspondence with the Fermi surface. The interesting case of a FCC(110) structure is investigated, unmistakably proving the existence and relevance of non-RKKY oscillations. The general conditions for the occurrence of non-RKKY oscillations are also presented.Comment: 34 pages, 10 figures ; to appear in J. Phys.: Condens. Mat

    Subterranean clover in W.A. 2. Characteristics required for agronomic success

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    Development of subterranean clover varieties is a rapidly changing scene, particularly in terms of farmer acceptance, disease and persistency problems. This is only to be expected, because this is an agricultural plant of only some 50 to 70 years standing, whereas many other pasture plants have been in common use for thousands of years

    Photochemical Pump and NMR Probe to monitor the formation and kinetics of hyperpolarized metal dihydrides

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    On reaction of IrI(CO)(PPh 3) 21with para-hydrogen(p-H 2),Ir(H) 2I(CO)(PPh 3) 22 is formed which exhibits strongly enhanced 1H NMR signals for its hydride resonances. Complex 2 also shows similar enhancement of its NMR spectra when it is irradiated under p-H 2. We report the use of this photochemical reactivity to measure the kinetics of H 2 addition by laser-synchronized reactions in conjunction with NMR. The single laser pulse promotes the reductive elimination of H 2 from Ir(H) 2I(CO)(PPh 3) 22 in C 6D 6 solution to form the 16-electron precursor 1, back reaction with p-H 2 then reforms 2 in a well-defined nuclear spin-state. The build up of this product can be followed by incrementing a precisely controlled delay (τ), in millisecond steps, between the laser and the NMR pulse. The resulting signal vs. time profile shows a dependence on p-H 2 pressure. The plot of k obs against p-H 2 pressure is linear and yields the second order rate constant, k 2, for H 2 addition to 1 of (3.26 ± 0.42) × 10 2 M −1 s −1. Validation was achieved by transient-UV-vis absorption spectroscopy which gives k 2 of (3.06 ± 0.40) × 10 2 M −1 s −1. Furthermore, irradiation of a C 6D 6 solution of 2 with multiple laser shots, in conjunction with p-H 2 derived hyperpolarization, allows the detection and characterisation of two minor reaction products, 2a and 3, which are produced in such low yields that they are not detected without hyperpolarization. Complex 2a is a configurational isomer of 2, while 3 is formed by substitution of CO by PPh
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