3,493 research outputs found
Controlling the commoners
The making of rules by institutions of collective action, such as commons, has been and still is an instrument to promote desired behaviour and to prevent free-riding and other individual actions that might affect the collective interest negatively. In this article, we use the historical markeboeken of four Dutch commons (marken) to study the way in which commoners sought to guarantee the resilience and longevity of the common, by analysing the design of regulations against unauthorized use, the interaction of those rules with internal and external developments, and the effects that various forms of penalty may have had on the behaviour of commoners
Edge local complementation for logical cluster states
A method is presented for the implementation of edge local complementation in
graph states, based on the application of two Hadamard operations and a single
controlled-phase (CZ) gate. As an application, we demonstrate an efficient
scheme to construct a one-dimensional logical cluster state based on the
five-qubit quantum error-correcting code, using a sequence of edge local
complementations. A single physical CZ operation, together with local
operations, is sufficient to create a logical CZ operation between two logical
qubits. The same construction can be used to generate any encoded graph state.
This approach in concatenation may allow one to create a hierarchical quantum
network for quantum information tasks.Comment: 15 pages, two figures, IOP styl
Constraints on the nature of dust particles by infrared observations
The far-infrared (FIR) emissivity of dust is an important parameter
characterizing the physical properties of the grains. With the availability of
stellar databases and far-infrared data from Infrared Space Observatory (ISO)
it is possible to compare the optical and infrared properties of dust, and
derive the far-infrared emissivity with respect to the optical extinction.
In this paper we present the results of a systematic analysis of the FIR
emissivity of interstellar clouds observed with ISOPHOT (the photometer onboard
ISO) at least at two infrared wavelengths, one close to ~100um and one at
200um. We constructed FIR emission maps, determined dust temperatures, created
extinction maps using 2MASS survey data, and calculated far-infrared emissivity
for each of these clouds. We present the largest homogeneously reduced database
constructed so far for this purpose. During the data analysis special care was
taken on possible systematic errors. We find that far-infrared emissivity has a
clear dependence on temperature.
The emissivity is enhanced by a factor of usually less than 2 in the low dust
temperature regime of 12K<=T_d<=14K. This result suggests larger grain sizes in
those regions. However, the emissivity increase of typically below 2 restricts
the possible grain growth processes to ice-mantle formation and coagulation of
silicate grains, and excludes the coagulation of carbonaceous particles on the
scales of the regions we investigated.
In the temperature range 14K<=T_d<=16K a systematic decrease of emissivity is
observed with respect to the values of the diffuse interstellar matter.
Possible scenarios for this behaviour are discussed in the paper.Comment: Accepted for publication in MNRA
Maximally entangled mixed states of two qubits
We consider mixed states of two qubits and show under which global unitary
operations their entanglement is maximized. This leads to a class of states
that is a generalization of the Bell states. Three measures of entanglement are
considered: entanglement of formation, negativity and relative entropy of
entanglement. Surprisingly all states that maximize one measure also maximize
the others. We will give a complete characterization of these generalized Bell
states and prove that these states for fixed eigenvalues are all equivalent
under local unitary transformations. We will furthermore characterize all
nearly entangled states closest to the maximally mixed state and derive a new
lower bound on the volume of separable mixed states
Competition and Facilitation: Contrasting Effects of Artemisia Tridentata on Desert vs Montane Pines
Circumstantial evidence suggests that Artemisia tridentata may out-compete Pinus ponderosa and P. jefferyi for water at ecotones between shrub steppe and montane forest vegetation in the Great Basin. Other studies indicate that within the shrub steppe Artemisia may act as a nurse plant for a third species of pine, P. monophylla. We used field experiments to study these contrasting effects of Artemisia on P, ponderosa and P. monophylla within the contest of the distributional patterns in western Nevada of all three species on andesite, and on sites where hydrothermal activity has altered the andesite. At intermediate elevations in the Great Basin Artemisia and P. monophylla are restricted to unaltered desert soils, whereas P. ponderosa is restricted to acidic, nutrient-poor altered andesite. Although mature P. monophylla were virtually absent in our study plots on altered andesite, first- and second-year seedlings were common. On adjacent unaltered andesite, all size classes of P. monophylla occurred, and P. monophylla seedlings were associated with Artemisia shrubs. Pinus ponderosa and P. jefferyi adults and seedlings were rare on unaltered andesite, but a wide range of size classes was found on altered andesite. In experiments, all P. ponderosa seedlings on unaltered andesite were consumed by predators regardless of positive or negative spatial association with shrubs. Of the P, monophylla seedlings that germinated on unaltered andesite, all that were under shrubs survived, but only 6% of those that germinated in the intershrub spaces survived, On the open altered andesite the mortality of P. monophylla seedlings due to abiotic stress was high, with a final survival of only 3%, whereas 25% of P, ponderosa seedlings survived the iir-st growing season on altered andesite. On unaltered andesite, survival and conductance of P. ponderosa saplings was enhanced by shrub removal, but P. monophylla survival was significantly higher under shrubs than in shrub-removal plots or in intershrub spaces, In Artemisia-removal experiments, we found that Artemisia competed with P. ponderosa seedlings and saplings for water. Removal of Artemisia decreased water use efficiency (WUE) of P. monophylla seedlings. The absence of Artemisia may restrict Pinus monophylla from out-crops of altered andesite in the Great Basin, but provide refuges for P. ponderosa
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