Use of stochastic control theory to model a forest management system

A forest management problem due to Hellman has been modelled as a stochastic control problem with one state variable (inventory level) and one control variable (consumption rate of wood by the factories). The stochastic process governing the evolution of the inventory level is transformed into an Itô stoachastic differential equation by approximating the compound Poisson process of wood arrivals into the depot as a Wiener process. The resulting stochastic control problem is solved by using the Hamilton-Jacobi-Bellman equation of stochastic dynamic programming. Two numerical examples illustrate the results.     

林道网综合评价的有向图模型

林道网规划是林业可持续发展中的一个重要问题，文中给出一个林道网综合评价的有向图模型，为林道网评价提供一种较为系统的方法。     

Study of the influence of different forest species on the microbial activity in soils

Microcalorimetry was used to study the seasonal evolution over one year of the microbial activity in a humic-eutrophic Cambisol soil as a function of its forest cover. The study was carried out on three soils with identical origin but covered with different forest species: pine, eucalyptus, and a typical Atlantic-humid riverside forest. Some other physical, chemical and biological properties and environmental parameters, mainly humidity and environmental temperature, were considered to analyze their influence on soil microbial activity. The study was performed using a microcalorimeter Thermal Analysis Monitor 2277 in which the experiments were carried out with 1 g soil samples treated with 1.25 mg glucose g^–1 soil. From the measured results it follows that pine forest soil is the least productive of the three, as it generates an average heat of 2.7 vs. 5.9 J g^–1 generated by the eucalyptus forest soil and 3.1 J g^–1 generated by the riverside forest soil. These results are dependent on the remaining physical, chemical and biological features analysed and because of this, pine forest soil, with a pH value 3.3 in spring, shows a small capacity to maintain a stable microbial population which is the lowest of the three (0.079·10⁸ to 0.46·10⁸ microorganisms g^–1 soil) while riverside soil microbial population is in the range from 7.9·10⁸ to 17·10⁸ microorganisms g^–1 soil.     

Forest waste as a potential alternative energy source

Following a method based on the procedure given by Hubbardet al. [1] the calorific values of combustion in oxygen at 298.15 K were measured by static-bomb calorimetry for forest residues. This waste mainly coming from mount reforestation, construction of firebreaks, etc., constitutes an important risk to originate forest fire. From combustion experiments the mean calorific value of all species studied was found close to 19 000 kJ·kg^?1, similar to calorific values of Municipal Waste. It can be concluded that this forest residues can be used as an additional fuel to be added to Municipal Solid Waste in energy recovery plants. By doing this, energy, in this moment lost as abandoned residues, can be recovered. At the same time the elimination of this waste minimizes the risk of forest fires. Our results reasonably agree with literature values.     

Spanning Forests and the q-State Potts Model in the Limit q →0

We study the q-state Potts model with nearest-neighbor coupling v=e^βJ−1 in the limit q,v → 0 with the ratio w = v/q held fixed. Combinatorially, this limit gives rise to the generating polynomial of spanning forests; physically, it provides information about the Potts-model phase diagram in the neighborhood of (q,v) = (0,0). We have studied this model on the square and triangular lattices, using a transfer-matrix approach at both real and complex values of w. For both lattices, we have computed the symbolic transfer matrices for cylindrical strips of widths 2≤ L ≤ 10, as well as the limiting curves B of partition-function zeros in the complex w-plane. For real w, we find two distinct phases separated by a transition point w=w₀, where w₀ =−1/4 (resp. w₀=−0.1753 ± 0.0002) for the square (resp. triangular) lattice. For w>w₀ we find a non-critical disordered phase that is compatible with the predicted asymptotic freedom as w → +∞. For w0 our results are compatible with a massless Berker–Kadanoff phase with central charge c=−2 and leading thermal scaling dimension x_T,1 = 2 (marginally irrelevant operator). At w=w₀ we find a “first-order critical point”: the first derivative of the free energy is discontinuous at w₀, while the correlation length diverges as w↓ w₀ (and is infinite at w=w₀). The critical ehavior at w=w₀ seems to be the same for both lattices and it differs from that of the Berker–Kadanoff phase: our results suggest that the central charge is c=−1, the leading thermal scaling dimension is x_T,1=0, and the critical exponents are ν=1/d=1/2 and α=1.     

Long-range timber supply planning for a vertically integrated paper mill

We consider a vertically integrated papermaking operation composed of an integrated pulp and paper mill with its regional supply network. Considering land procurement and harvest rotation as strategic decision variables, we construct a model to establish a long-range timber supply plan that minimizes the total discounted cost of meeting annual virgin wood fiber demand over an infinite horizon. Under appropriate assumptions on costs and storage, the land procurement and harvest rotation decisions are separable with harvest rotation being determined via a forest economics-type equation and land procurement being determined by a newsvendor-type equation.     

A 3-approximation algorithm for the subtree distance between phylogenies

In this paper, we give a (polynomial-time) 3-approximation algorithm for the rooted subtree prune and regraft distance between two phylogenetic trees. This problem is known to be NP-complete and the best previously known approximation algorithm is a 5-approximation. We also give a faster fixed-parameter algorithm for the rooted subtree prune and regraft distance than was previously known.     

Analytical X-Ray Microscopy on Psaronius sp. – A Contribution to Permineralization Process Studies

 290 Million years old petrifactions from the Lower Permian Rotliegend of Chemnitz were examined by analytical X-ray microscopy to determine their chemical composition. Mappings show the inhomogeneous distribution of the involved elements, which may reflect the former plant anatomy, as well as some contemporaneous processes of permineralization (with silica and fluorite) and agate-formation. Most prominent advantages of the analytical X-ray microscopy are the low preparation expense of the museum samples, the analysis scanning range and the X-ray spot diameter suitable with the dimension of the fossil plants.