13,190 research outputs found
Earth's Energy Imbalance and Implications
Improving observations of ocean heat content show that Earth is absorbing
more energy from the sun than it is radiating to space as heat, even during the
recent solar minimum. The inferred planetary energy imbalance, 0.59 \pm 0.15
W/m2 during the 6-year period 2005-2010, confirms the dominant role of the
human-made greenhouse effect in driving global climate change. Observed surface
temperature change and ocean heat gain together constrain the net climate
forcing and ocean mixing rates. We conclude that most climate models mix heat
too efficiently into the deep ocean and as a result underestimate the negative
forcing by human-made aerosols. Aerosol climate forcing today is inferred to be
1.6 \pm 0.3 W/m2, implying substantial aerosol indirect climate forcing via
cloud changes. Continued failure to quantify the specific origins of this large
forcing is untenable, as knowledge of changing aerosol effects is needed to
understand future climate change. We conclude that recent slowdown of ocean
heat uptake was caused by a delayed rebound effect from Mount Pinatubo aerosols
and a deep prolonged solar minimum. Observed sea level rise during the Argo
float era is readily accounted for by ice melt and ocean thermal expansion, but
the ascendency of ice melt leads us to anticipate acceleration of the rate of
sea level rise this decade.Comment: 39 pages, 18 figures; revised version submitted to Atmos. Chem. Phy
An Introduction to Interactive Music for Percussion and Computers
Composers began combining acoustic performers with electronically produced sounds in the early twentieth century. As computer-processing power increased the potential for significant musical communication was developed. Despite the body of research concerning electronic music, performing a composition with a computer partner remains intimidating for performers. The purpose of this paper is to provide an introductory method for interacting with a computer. This document will first follow the parallel evolution of percussion and electronics in order to reveal how each medium was influenced by the other. The following section will define interaction and explain how this is applied to musical communication between humans and computers. The next section introduces specific techniques used to cultivate human-computer interaction. The roles of performer, instrument, composer and conductor will then be defined as they apply to the human performer and the computer. If performers are aware of these roles they will develop richer communication that can enhance the performer's and audience member's recognition of human-computer interaction. In the final section, works for percussion and computer will be analyzed to reveal varying levels of interaction and the shifting roles of the performer. Three compositions will illustrate this point, 120bpm from neither Anvil nor Pulley by Dan Trueman, It's Like the Nothing Never Was by Von Hansen, and Music for Snare Drum and Computer by Cort Lippe. These three pieces develop a continuum of increasing interaction, moving from interaction within a fully defined score, to improvisation with digital synthesis, to the manipulation of computerized compositional algorithms using performer input. The unique ways each composer creates interaction will expose the vast possibilities for performing with interactive music systems
DNA-Protein Binding Rates: Bending Fluctuation and Hydrodynamic Coupling Effects
We investigate diffusion-limited reactions between a diffusing particle and a
target site on a semiflexible polymer, a key factor determining the kinetics of
DNA-protein binding and polymerization of cytoskeletal filaments. Our theory
focuses on two competing effects: polymer shape fluctuations, which speed up
association, and the hydrodynamic coupling between the diffusing particle and
the chain, which slows down association. Polymer bending fluctuations are
described using a mean field dynamical theory, while the hydrodynamic coupling
between polymer and particle is incorporated through a simple heuristic
approximation. Both of these we validate through comparison with Brownian
dynamics simulations. Neither of the effects has been fully considered before
in the biophysical context, and we show they are necessary to form accurate
estimates of reaction processes. The association rate depends on the stiffness
of the polymer and the particle size, exhibiting a maximum for intermediate
persistence length and a minimum for intermediate particle radius. In the
parameter range relevant to DNA-protein binding, the rate increase is up to
100% compared to the Smoluchowski result for simple center-of-mass motion. The
quantitative predictions made by the theory can be tested experimentally.Comment: 21 pages, 11 figures, 1 tabl
Broken Time Translation Symmetry as a model for Quantum State Reduction
The symmetries that govern the laws of nature can be spontaneously broken,
enabling the occurrence of ordered states. Crystals arise from the breaking of
translation symmetry, magnets from broken spin rotation symmetry and massive
particles break a phase rotation symmetry. Time translation symmetry can be
spontaneously broken in exactly the same way. The order associated with this
form of spontaneous symmetry breaking is characterised by the emergence of
quantum state reduction: systems which spontaneously break time translation
symmetry act as ideal measurement machines. In this review the breaking of time
translation symmetry is first compared to that of other symmetries such as
spatial translations and rotations. It is then discussed how broken time
translation symmetry gives rise to the process of quantum state reduction and
how it generates a pointer basis, Born's rule, etc. After a comparison between
this model and alternative approaches to the problem of quantum state
reduction, the experimental implications and possible tests of broken time
translation symmetry in realistic experimental settings are discussed.Comment: 15 pages, 5 figure
To swim or not to swim: an interpretation of farmed mink's motivation for a water bath
How an animalâs behavioural (ethological) needs can be met is a pivotal issue in the assessment of welfare for captive animals. The value of swimming water for farmed mink is an example how scientific and societal questions relating to animal welfare can be answered. A number of studies have addressed the issue of the indispensability of swimming water for mink; however, so far with inconclusive evidence. In this paper, the results of these studies and related literature are reviewed.
First, the biological definition of need is discussed. Subsequently, attention is paid to the effects of the presence, absence and the removal of swimming water on behavioural and physiological correlates of well-being including stereotypic and anticipatory behaviour and urinary cortisol. Thereafter we discuss individual differences in the use of swimming water, the price animals pay for access to a water bath, and the effect of access to swimming water on juvenile play.
The main conclusions of the literature review are that 1) the use of a water bath for mink is most likely related to foraging behaviour (foraging areas: land and water); 2) absence of swimming water, without prior experience, does not lead to consistent changes in level of stereotypic behaviour, or anticipatory responses; 3) removal of a previously experienced water bath may induce short-term stress as indicated by behavioural parameters and elevated cortisol responses; 4) mink work hard for access to a swimming bath and running wheel in consumer demand studies. Other cage modifications such as tunnels and biting objects, may also provide environmental enrichment, if they are added to otherwise impoverished conditions; 5) There are individual differences in the use of swimming water: these are related in part to variation in prior experience of aquatic resources.; 6) As prior experience is important both with respect to individual use of swimming water and the response to deprivation, swimming water can not be described as biological need in the sense of a fixed requirement for survival. As swimming water appears to act as an incentive that induces its own motivation a more accurate term may be an âincentive induced or environmentally facilitated needâ. Given the available evidence, it is not possible to conclude whether mink that have never experienced swimming water, suffer as a consequence of its absence. However, it is possible to predict that mink with access to water have improved quality of life, due to increased behavioural opportunities, in comparison to farmed mink without access to swimming water. In practical terms, it is still open to debate whether mink should be provided with swimming water, or if alternative, less valued, but easier to install and maintain forms of environmental enrichment, should be provided in mink housing.
To clarify these issues a number of future studies would be valuable. These include; 1) whether specific environmental cues affect motivation to swim, such as the form of drinking water delivery systems ; 2) whether prior experience of swimming water affects its incentive value; in other words âcan you miss what you never experienced?â; 3) do behavioural parameters such as stereotypic behaviour; rebound effects and vacuum activity have any general utility in assessing the value of absent resources; 4) what are preferences for and the value of alternative resources which may act as substitutes for swimming water. In addition we would recommend further work investigating: relationship between access to swimming water and positive indicators of welfare such as play and/or anticipatory behaviour; the effects of preventing the performance of rewarding behaviours and deprivation of a previous experienced resource; and health and hygeine issues related to provision of a water bath. In future work, it would be desirable to present be the actual percentages of animals using a water bath during the experiment and the use of power analyses, to aid their interpretation
Effects on semiflexible polymer dynamics
The influence of hydrodynamic screening near a surface on the dynamics of a
single semiflexible polymer is studied by means of Brownian dynamics
simulations and hydrodynamicmean field theory. The polymer motion is
characterized in terms of the mean squared displacements of the end-monomers,
the end-to-end vector, and the scalar end-to-end distance. In order to control
hydrodynamic screening effects, the polymer is confined to a plane at a fixed
separation from the wall. When gradually decreasing this separation, a
crossover from Zimm-type towards Rouse (free-draining) polymerdynamics is
induced. However, this crossover is rather slow and the free-draining limit is
not completely reachedâsubstantial deviations from Rouse-like dynamics are
registered in both simulations and theoryâeven at distances of the polymer
from the wall on the order of the monomer size. Remarkably, the effect of
surface-induced screening of hydrodynamic interactions sensitively depends on
the type of dynamic observable considered. For vectorial quantities such as
the end-to-end vector, hydrodynamic interactions are important and therefore
surface screening effects are sizeable. For a scalar quantity such as the end-
to-end distance, on the other hand, hydrodynamic interactions are less
important, but a pronounced dependence of dynamic scaling exponents on the
persistence length to contour length ratio becomes noticeable. Our findings
are discussed against the background of single-molecule experiments on f-actin
[L. Le Goff et al., Phys. Rev. Lett.89, 258101
(2002)]10.1103/PhysRevLett.89.258101
Anomalous Anisotropic Diffusion Dynamics of Hydration Water at Lipid Membranes
The diffusional water dynamics in the hydration layer of a
dipalmitoylphosphatidylcholine bilayer is studied using molecular dynamics
simulations. By mapping the perpendicular water motion on the ordinary
diffusion equation, we disentangle free energetic and friction effects and
show that perpendicular diffusion is strongly reduced. The lateral water
motion exhibits anomalous diffusion up to several nanoseconds and is
characterized by even further decreased diffusion coefïŹcients, which by
comparison with coarse grained simulations are explained by the transient
corrugated effective free energy landscape imposed by the lipids. This is in
contrast to homogenous surfaces, where boundary hydrodynamic theory
quantitatively predicts the anisotropy of water diffusion
Machine Learning of Molecular Electronic Properties in Chemical Compound Space
The combination of modern scientific computing with electronic structure
theory can lead to an unprecedented amount of data amenable to intelligent data
analysis for the identification of meaningful, novel, and predictive
structure-property relationships. Such relationships enable high-throughput
screening for relevant properties in an exponentially growing pool of virtual
compounds that are synthetically accessible. Here, we present a machine
learning (ML) model, trained on a data base of \textit{ab initio} calculation
results for thousands of organic molecules, that simultaneously predicts
multiple electronic ground- and excited-state properties. The properties
include atomization energy, polarizability, frontier orbital eigenvalues,
ionization potential, electron affinity, and excitation energies. The ML model
is based on a deep multi-task artificial neural network, exploiting underlying
correlations between various molecular properties. The input is identical to
\emph{ab initio} methods, \emph{i.e.} nuclear charges and Cartesian coordinates
of all atoms. For small organic molecules the accuracy of such a "Quantum
Machine" is similar, and sometimes superior, to modern quantum-chemical
methods---at negligible computational cost
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