230 research outputs found
A one-dimensional model for theoretical analysis of single molecule experiments
In this paper we compare two polymer stretching experiments. The outcome of
both experiments is a force-extension relation. We use a one-dimensional model
to show that in general the two quantities are not equal. In certain limits,
however, both force-extension relations coincide.Comment: 11 pages, 5 figure
A two-parameter random walk with approximate exponential probability distribution
We study a non-Markovian random walk in dimension 1. It depends on two
parameters eps_r and eps_l, the probabilities to go straight on when walking to
the right, respectively to the left. The position x of the walk after n steps
and the number of reversals of direction k are used to estimate eps_r and
eps_l. We calculate the joint probability distribution p_n(x,k) in closed form
and show that, approximately, it belongs to the exponential family.Comment: 12 pages, updated reference to companion paper cond-mat/060126
A generalized quantum microcanonical ensemble
We discuss a generalized quantum microcanonical ensemble. It describes
isolated systems that are not necessarily in an eigenstate of the Hamilton
operator. Statistical averages are obtained by a combination of a time average
and a maximum entropy argument to resolve the lack of knowledge about initial
conditions. As a result, statistical averages of linear observables coincide
with values obtained in the canonical ensemble. Non-canonical averages can be
obtained by taking into account conserved quantities which are non-linear
functions of the microstate.Comment: improved version, new titl
Grand canonical ensemble in generalized thermostatistics
We study the grand-canonical ensemble with a fluctuating number of degrees of
freedom in the context of generalized thermostatistics. Several choices of
grand-canonical entropy functional are considered. The ideal gas is taken as an
example.Comment: 14 pages, no figure
Superstatistical distributions from a maximum entropy principle
We deal with a generalized statistical description of nonequilibrium complex
systems based on least biased distributions given some prior information. A
maximum entropy principle is introduced that allows for the determination of
the distribution of the fluctuating intensive parameter of a
superstatistical system, given certain constraints on the complex system under
consideration. We apply the theory to three examples: The superstatistical
quantum mechanical harmonic oscillator, the superstatistical classical ideal
gas, and velocity time series as measured in a turbulent Taylor-Couette flow
Unravelling the functions of biogenic volatiles in boreal and temperate forest ecosystems
Living trees are the main source of biogenic volatile organic compounds (BVOCs) in forest ecosystems, but substantial emissions originate from leaf and wood litter, the rhizosphere and from microorganisms. This review focuses on temperate and boreal forest ecosystems and the roles of BVOCs in ecosystem function, from the leaf to the forest canopy and from the forest soil to the atmosphere level. Moreover, emphasis is given to the question of how BVOCs will help forests adapt to environmental stress, particularly biotic stress related to climate change. Trees use their vascular system and emissions of BVOCs in internal communication, but emitted BVOCs have extended the communication to tree population and whole community levels and beyond. Future forestry practices should consider the importance of BVOCs in attraction and repulsion of attacking bark beetles, but also take an advantage of herbivore-induced BVOCs to improve the efficiency of natural enemies of herbivores. BVOCs are extensively involved in ecosystem services provided by forests including the positive effects on human health. BVOCs have a key role in ozone formation but also in ozone quenching. Oxidation products form secondary organic aerosols that disperse sunlight deeper into the forest canopy, and affect cloud formation and ultimately the climate. We also discuss the technical side of reliable BVOC sampling of forest trees for future interdisciplinary studies that should bridge the gaps between the forest sciences, health sciences, chemical ecology, conservation biology, tree physiology and atmospheric science
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