The generalized Kochen-Specker theorem

A proof of the generalized Kochen-Specker theorem in two dimensions due to Cabello and Nakamura is extended to all higher dimensions. A set of 18 states in four dimensions is used to give closely related proofs of the generalized Kochen-Specker, Kochen-Specker and Bell theorems that shed some light on the relationship between these three theorems.Comment: 5 pages, 1 Table. A new third paragraph and an additional reference have been adde

The Projective Line Over the Finite Quotient Ring GF(2)[xx]/<x3−x>< x^{3} - x> and Quantum Entanglement II. The Mermin "Magic" Square/Pentagram

In 1993, Mermin (Rev. Mod. Phys. 65, 803--815) gave lucid and strikingly simple proofs of the Bell-Kochen-Specker (BKS) theorem in Hilbert spaces of dimensions four and eight by making use of what has since been referred to as the Mermin(-Peres) "magic square" and the Mermin pentagram, respectively. The former is a $3 \times 3$ array of nine observables commuting pairwise in each row and column and arranged so that their product properties contradict those of the assigned eigenvalues. The latter is a set of ten observables arranged in five groups of four lying along five edges of the pentagram and characterized by similar contradiction. An interesting one-to-one correspondence between the operators of the Mermin-Peres square and the points of the projective line over the product ring ${\rm GF}(2) \otimes \rm{GF}(2)$ is established. Under this mapping, the concept "mutually commuting" translates into "mutually distant" and the distinguishing character of the third column's observables has its counterpart in the distinguished properties of the coordinates of the corresponding points, whose entries are both either zero-divisors, or units. The ten operators of the Mermin pentagram answer to a specific subset of points of the line over GF(2)[$x$]/$$. The situation here is, however, more intricate as there are two different configurations that seem to serve equally well our purpose. The first one comprises the three distinguished points of the (sub)line over GF(2), their three "Jacobson" counterparts and the four points whose both coordinates are zero-divisors; the other features the neighbourhood of the point ($1, 0$) (or, equivalently, that of ($0, 1$)). Some other ring lines that might be relevant for BKS proofs in higher dimensions are also mentioned.Comment: 6 pages, 5 figure

Decoherence of a Measure of Entanglement

We demonstrate by an explicit model calculation that the decay of entanglement of two two-state systems (two qubits) is governed by the product of the factors that measure the degree of decoherence of each of the qubits, subject to independent sources of quantum noise. This demonstrates an important physical property that separated open quantum systems can evolve quantum mechanically on time scales larger than the times for which they remain entangled.Comment: 4 pages, 1 figur

Effect of H₂S and HCl contaminants on nickel and ceria pattern anode solid oxide fuel cells

In this study, with the motivation of elucidating the effect of H2S and HCl on solid oxide fuel cell anodes, nickel and ceria pattern anodes are prepared on yttrium-stabilized zirconia electrolyte, and the effect of H2S and HCl on their performance is tested using electrochemical impedance spectroscopy. However, it has been found that while H2S adversely impacts both nickel and ceria, the poisoning caused is reversible for nickel and only partially reversible for ceria. Poisoning kinetics are similar and fast for both materials, while recovery kinetics are slower for ceria than nickel. High sulfur coverage is the rate-limiting factor inferred from the elementary kinetic modeling. Unlike H2S, the presence of HCl appeared to be favorable for electrochemical oxidation as the polarization resistance of both pattern electrode cells decreased upon feeding HCl contaminated hydrogen gas. Similar behavior has not been reported previously, and the conclusion regarding underlying mechanisms requires further investigation

Impact of the invasive plant, Lantana camara, on bird assemblages at Malé Mahadeshwara Reserve Forest, South India

Lantana camara is an invasive species that is widespread in India. Using birds as an indicator taxon, we investigated whether Lantana invasion was correlated with changes in ecosystem health of the moist and dry deciduous forests at the Malé Madeshwara Hills, Karnataka. We studied Lantana at four densities, low, medium, and high, and a no-Lantana control. Bird species diversity, species richness, and abundance were lower at high densities of Lantana in both forest types. Evenness increased with increase in Lantana density. To better understand the observed changes in bird community composition, we segregated birds into 2 guild types: microhabitat guilds and foraging guilds. An increase in Lantana density was correlated with a decline in canopy birds (of the canopy microhabitat guilds) and insectivores (of the insectivore foraging guilds). Our results suggest that Lantana affects the structure of the bird community by decreasing diversity, and that Lantana affects certain guilds more than others

Are red-listed species threatened? A comparative analysis of red-listed and non-red-listed plant species in the Western Ghats, India

Red lists of taxa are important documents guiding the prioritization of conservation efforts. However the actual process of arriving at red lists has been contentious, because of the paucity of hard ecological data. In this article, we examine the red listing of plant species at two geographical scales: regional and local in the Western Ghats, India. At the regional level, we compared the rarity (or abundance) of the red listed and the co-occurring non-red-listed species in fifteen sites across Western Ghats. For the local level analysis, we compared the distribution and demographic profile of red-listed medicinal plants with co-occurring non-redlisted species at two field sites in the Western Ghats. At both the regional and the local scales, our analyses showed that the red-listed species, as a group are not any more disadvantaged than the non-red-listed species. Our results lay caution on the process of inclusion of species in red-lists and urge the necessity of strong field data to make the red-listing process more robust

Mass Varying Neutrinos, Quintessence, and the Accelerating Expansion of the Universe

We analyze the Mass Varying Neutrino (MaVaN) scenario. We consider a minimal model of massless Dirac fermions coupled to a scalar field, mainly in the framework of finite temperature quantum field theory. We demonstrate that the mass equation we find has non-trivial solutions only for special classes of potentials, and only within certain temperature intervals. We give most of our results for the Ratra-Peebles Dark Energy (DE) potential. The thermal (temporal) evolution of the model is analyzed. Following the time arrow, the stable, metastable and unstable phases are predicted. The model predicts that the present Universe is below its critical temperature and accelerates. At the critical point the Universe undergoes a first-order phase transition from the (meta)stable oscillatory regime to the unstable rolling regime of the DE field. This conclusion agrees with the original idea of quintessence as a force making the Universe roll towards its true vacuum with zero \Lambda-term. The present MaVaN scenario is free from the coincidence problem, since both the DE density and the neutrino mass are determined by the scale M of the potential. Choosing M ~ 10^{-3} eV to match the present DE density, we can obtain the present neutrino mass in the range m ~ 10^{-2}-1 eV and consistent estimates for other parameters of the Universe.Comment: 29 pages, 7 figures. V. 3: Analysis of the dynamics of the Universe and some refs. added; extended version to be published in PR

Continuous input nonlocal games

We present a family of nonlocal games in which the inputs the players receive are continuous. We study three representative members of the family. For the first two a team sharing quantum correlations (entanglement) has an advantage over any team restricted to classical correlations. We conjecture that this is true for the third member of the family as well.Comment: Journal version, slight modification