331 research outputs found
Long-term P weathering and recent N deposition control contemporary plant-soil C, N, and P
Models are needed to understand how plant-soil nutrient stores and fluxes have responded to the last two centuries of widespread anthropogenic nutrient pollution and predict future change. These models need to integrate across carbon, nitrogen, and phosphorus (C, N, and P) cycles and simulate changes over suitable timescales using available driving data. It is also vital that they are constrainable against observed data to provide confidence in their outputs. To date, no models address all of these requirements. To meet this need, a new model, N14CP, is introduced, which is initially applied to Northern Hemisphere temperate and boreal ecosystems over the Holocene. N14CP is parameterized and tested using 88 northern Europe plot-scale studies, providing the most robust test of such a model to date. The model simulates long-term P weathering, based on the assumption of a starting pool of weatherable P (Pweath0, gâmâ2), which is gradually transformed into organic and sorbed pools. Nitrogen fixation (and consequently primary production) is made dependent on available P. In the absence of knowledge about the spatial variability of Pweath0, N14CP produces good average soil and plant variables but cannot simulate variations among sites. Allowing Pweath0 to vary between sites improves soil C, N, and P results greatly, suggesting that contemporary soil C, N, and P are sensitive to long-term P weathering. Most sites were found to be N limited. Anthropogenic N deposition since 1800 was calculated to have increased plant biomass substantially, in agreement with observations and consequently increased soil carbon pools
Qubits from Number States and Bell Inequalities for Number Measurements
Bell inequalities for number measurements are derived via the observation
that the bits of the number indexing a number state are proper qubits.
Violations of these inequalities are obtained from the output state of the
nondegenerate optical parametric amplifier.Comment: revtex4, 7 pages, v2: results identical but extended presentation,
v3: published versio
Two qubits of a W state violate Bell's inequality beyond Cirel'son's bound
It is shown that the correlations between two qubits selected from a trio
prepared in a W state violate the Clauser-Horne-Shimony-Holt inequality more
than the correlations between two qubits in any quantum state. Such a violation
beyond Cirel'son's bound is smaller than the one achieved by two qubits
selected from a trio in a Greenberger-Horne-Zeilinger state [A. Cabello, Phys.
Rev. Lett. 88, 060403 (2002)]. However, it has the advantage that all local
observers can know from their own measurements whether their qubits belongs or
not to the selected pair.Comment: REVTeX4, 5 page
Maximal Violation of Bell Inequalities using Continuous Variables Measurements
We propose a whole family of physical states that yield a violation of the
Bell CHSH inequality arbitrarily close to its maximum value, when using
quadrature phase homodyne detection. This result is based on a new binning
process called root binning, that is used to transform the continuous variables
measurements into binary results needed for the tests of quantum mechanics
versus local realistic theories. A physical process in order to produce such
states is also suggested. The use of high-efficiency spacelike separated
homodyne detections with these states and this binning process would result in
a conclusive loophole-free test of quantum mechanics.Comment: 7 pages, 5 figures, to appear in PRA in a slightly different versio
A Zoology of Bell inequalities resistant to detector inefficiency
We derive both numerically and analytically Bell inequalities and quantum
measurements that present enhanced resistance to detector inefficiency. In
particular we describe several Bell inequalities which appear to be optimal
with respect to inefficient detectors for small dimensionality d=2,3,4 and 2 or
more measurement settings at each side. We also generalize the family of Bell
inequalities described in Collins et all (Phys. Rev. Lett. 88, 040404) to take
into account the inefficiency of detectors. In addition we consider the
possibility for pairs of entangled particles to be produced with probability
less than one. We show that when the pair production probability is small, one
must in general use different Bell inequalities than when the pair production
probability is high.Comment: 12 pages, revtex. Appendix completed, minor revision
Dissipation-assisted quantum gates with cold trapped ions
It is shown that a two-qubit phase gate and SWAP operation between ground
states of cold trapped ions can be realised in one step by simultaneously
applying two laser fields. Cooling during gate operations is possible without
perturbing the computation and the scheme does not require a second ion species
for sympathetic cooling. On the contrary, the cooling lasers even stabilise the
desired time evolution of the system. This affords gate operation times of
nearly the same order of magnitude as the inverse coupling constant of the ions
to a common vibrational mode.Comment: 4 pages, 5 figures, substantially revised versio
Revealing Bell's Nonlocality for Unstable Systems in High Energy Physics
Entanglement and its consequences - in particular the violation of Bell
inequalities, which defies our concepts of realism and locality - have been
proven to play key roles in Nature by many experiments for various quantum
systems. Entanglement can also be found in systems not consisting of ordinary
matter and light, i.e. in massive meson--antimeson systems. Bell inequalities
have been discussed for these systems, but up to date no direct experimental
test to conclusively exclude local realism was found. This mainly stems from
the fact that one only has access to a restricted class of observables and that
these systems are also decaying. In this Letter we put forward a Bell
inequality for unstable systems which can be tested at accelerator facilities
with current technology. Herewith, the long awaited proof that such systems at
different energy scales can reveal the sophisticated "dynamical" nonlocal
feature of Nature in a direct experiment gets feasible. Moreover, the role of
entanglement and CP violation, an asymmetry between matter and antimatter, is
explored, a special feature offered only by these meson-antimeson systems.Comment: 6 pages, 3 figure
Reversed Frontotemporal Connectivity During Emotional Face Processing in Remitted Depression
BackgroundVulnerability to relapse persists after remission of an acute episode of major depressive disorder. This has been attributed to abnormal biases in the processing of emotional stimuli in limbic circuits. However, neuroimaging studies have not so far revealed consistent evidence of abnormal responses to emotional stimuli in limbic structures, such as the amygdala, in remitted depression. This suggests the problem might lie in the integrated functioning of emotion processing circuits.MethodsWe recruited 22 unmedicated patients in remission from major depressive disorder (rMDD) and 21 age-matched healthy control subjects. Functional magnetic resonance imaging was performed during a face emotion processing task. Dynamic causal modeling was used with Bayesian model selection to determine the most likely brain networks and valence-specific modulation of connectivity in healthy control subjects and rMDD.ResultsIn healthy volunteers, sad faces modulated bi-directional connections between amygdala and orbitofrontal cortex and between fusiform gyrus and orbitofrontal cortex. Happy faces modulated unidirectional connections from fusiform gyrus to orbitofrontal cortex. In rMDD, the opposite pattern was observed, with evidence of happy faces modulating bidirectional frontotemporal connections and sad faces modulating unidirectional fusiformâorbitofrontal connections.ConclusionsParticipants with rMDD have abnormal modulation of frontotemporal effective connectivity in response to happy and sad face emotions, despite normal activations within each region. Specifically, processing of mood incongruent happy information was associated with a more richly modulated frontotemporal brain network, whereas mood congruent sad information was associated with less network modulation. This supports a hypothesis of dysfunction within corticoâlimbic connections in individuals vulnerable to depression
Bell inequalities and entanglement in solid state devices
Bell-inequality checks constitute a probe of entanglement -- given a source
of entangled particles, their violation are a signature of the non-local nature
of quantum mechanics. Here, we study a solid state device producing pairs of
entangled electrons, a superconductor emitting Cooper pairs properly split into
the two arms of a normal-metallic fork with the help of appropriate filters. We
formulate Bell-type inequalities in terms of current-current cross-correlators,
the natural quantities measured in mesoscopic physics; their violation provides
evidence that this device indeed is a source of entangled electrons.Comment: 4 pages, 1 figur
Thinking about growth : a cognitive mapping approach to understanding small business development
School of Managemen
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