381 research outputs found
Optimal detection of homogeneous segment of observations in stochastic sequence
A Markov process is registered. At random moment the distribution of
observed sequence changes. Using probability maximizing approach the optimal
stopping rule for detecting the change is identified. Some explicit solution is
obtained.Comment: 13 page
Some Aspects of Classical and Quantum Phases
We study classical and quantum phases in the adiabatic Born-Oppenheimer
context. These include a classical astronomical case, the general dual
description of the phases, a new "Paradox" connected to scattering Berry phase
and its resolution and various elaboration of
topological/geometrical/non-abelian phases.Comment: 18 pages, 4 figure
Biogeochemical factors contributing to enhanced carbon storage following afforestation of a semi-arid shrubland
International audienceEcosystems in dry regions are generally low in productivity and carbon (C) storage. We report, however, large increases in C sequestration following afforestation of a semi-arid shrubland with Pinus halepensis trees. Using C and nitrogen (N) inventories, based in part on site-specific allometric equations, we measured an increase in the standing ecosystem C stock from 2380 g C m?2 in the shrubland to 5840 g C m?2 in the forest after 35 years, with no significant change in N stocks. The total amount of C produced by the forest was estimated as 6250 g C m?2. Carbon sequestration following afforestation was associated with increased N use efficiency as reflected by an overall increase in C/N ratio from 7.6 in the shrubland to 16.6 in the forest. The C accumulation rate in the forest was particularly high for soil organic C (SOC; increase of 1760 g C m?2 or 50 g C m?2 yr?1), which was associated with the following factors: 1) Analysis of a small 13C signal within this pure C3 system combined with size fractionation of soil organic matter indicated a significant addition of new SOC derived from forest vegetation (68% of total forest SOC) and a considerable portion of the old original shrubland SOC (53%) still remaining in the forest. 2) A large part of both new and old SOC appeared to be protected from decomposition as about 60% of SOC under both land-use types were in mineral-associated fractions. 3) A short-term decomposition study indicated decreased decomposition of lower-quality litter and SOC in the forest, based on reduced decay rates of up to 90% for forest compared to shrubland litter. 4) Forest soil included a significant component of live and dead roots. Our results showed the considerable potential for C sequestration, particularly in soils, following afforestation in semi-arid regions, which is particularly relevant in light of persistent predictions of drying trends in the Mediterranean and other regions
``Weighing'' a closed system and the time-energy uncertainty principle
A gedanken-experiment is proposed for `weighing'' the total mass of a closed
system from within the system. We prove that for an internal observer the time
, required to measure the total energy with accuracy , is
bounded according to . This time-energy uncertainty
principle for a closed system follows from the measurement back-reaction on the
system. We generally examine what other conserved observables are in principle
measurable within a closed system and what are the corresponding uncertainty
relations.Comment: 8 page
Model for Entangled States with Spin-Spin Interaction
A system consisting of two neutral spin 1/2 particles is analyzed for two
magnetic field perturbations: 1) an inhomogeneous magnetic field over all
space, and 2) external fields over a half space containing only one of the
particles. The field is chosen to point from one particle to the other, which
results in essentially a one-dimensional problem. A number of interesting
features are revealed for the first case: the singlet, which has zero potential
energy in the unperturbed case, remains unstable in the perturbing field. The
spin zero component of the triplet evolves into a bound state with a double
well potential, with the possibility of tunneling. Superposition states can be
constructed which oscillate between entangled and unentangled states. For the
second case, we show that changes in the magnetic field around one particle
affect measurements of the spin of the entangled particle not in the magnetic
field nonlocally. By using protective measurements, we show it is possible in
principle to establish a nonlocal interaction using the two particles, provided
the dipole-dipole potential energy does not vanish and is comparable to the
potential energy of the particle in the external field
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