A simulation-optimization model for selecting the location of fuel-breaks to minimize expected losses from forest fires

Fuel-breaks function to restrict the spread of wildfire through a forest and thereby reduce the damage to values lost when fires escape. The challenge of selecting optimal locations of fuel-breaks arises from the uncertainty over how future fires might originate and spread spatially in the future. In this research, we evaluate a new approach to addressing this uncertainty through the formulation and application of a decision support model using simulation-optimization. The problem is formulated as a combinatorial simulation-optimization problem with the objective of minimizing fire-risk subject to a limit on the total area to be used as fuel-breaks. A stochastic simulation model of fire-spread was designed to estimate the fire-risk of each candidate solution produced by a metaheuristic search algorithm. The model was tested on a forest of 220,000 ha in north-western Ontario. The objective function (total fire-risk) of the solution found using the simulation-optimization model was significantly lower than the objective function of a solution found using a greedy heuristic—a spatially blind approach, by which the highest risk stands were iteratively removed until the allowable limit on fuel-breaks was reached. This significant difference indicates that the spatial relationships between selected fuel-breaks is an important factor in reducing a forest's total fire-risk. Hence, the spatial layouts of the best solutions were visually analyzed using GIS-software to illustrate patterns that result in reduced fire-risk at the landscape-scale. We conclude that this modeling approach, while computationally intensive, can be used to support improved spatial decisions on the location of fuel-breaks.     

Follicle Wave Growth in Cattle

Ovarian follicle growth in cattle culminates in the selection of a single dominant follicle which attains the ability for final maturation and ovulation once or twice during the luteal phase and at the end of the oestrous cycle, as well as during other reproductive states. This review will describe in detail the first follicle wave of the cycle leading to selection of the first wave dominant follicle, indicating the specific gonadotrophin dependencies of cohort and dominant follicles, and relating follicle fate to steroidogenesis. As a differential gonadotrophin response of growing antral follicles during the follies‐stimulating hormone (FSH) decline may determine which follicle becomes selected, first wave follicles are also characterized in relation to intrafollicular growth factors, which may modify the gonadotrophin response, such as inhibins and members of the insulin‐like growth factor (IGF) family. Subsequently, the follicular control of the transient FSH rise and decline so crucial to dominant follicle selection will be discussed. It is concluded that successful hormonal manipulation of follicle wave growth and dominant follicle selection will depend on our detailed understanding of the gonadotrophin requirements of differentiating wave follicles.     

The structure of the upper atmosphere of mars: In situ accelerometer measurements from mars global surveyor

The Mars Global Surveyor (MGS) z-axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near 90 degreesE and 90 degreesW, in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere.     

Patterns of Follicular Growth in Superovulated Sheep and Influence on Endocrine and Ovarian Response

Objectives of this study were to characterize patterns of follicular development in sheep superovulated with purified follicle stimulating hormone (FSH) (OVAGEN^TM, ICP, Auckland, New Zealand) and to determine its influence on preovulatory events (onset of the oestrus behaviour and timing of the preovulatory luteinizing hormone surge) and ovarian response (ovulation rate and embryo yield). Number and size of all ≥ 23 mm follicles from the first FSH injection to withdrawal of progestagen sponges was determined by transrectal ultrasonography just prior to every FSH injection in nine Manchega ewes superovulated with eight decreasing doses (ml) (1.5 × 3, 1.25 × 2 and 1 × 3) of OVAGEN injected twice daily from 60 h before to 24 h after the withdrawal of 40 mg fluorogestone acetate sponges. Oestrous detection and jugular blood sampling for LH radioimmunoassay were performed every 3 h from 14 to 53 h after sponge removal and ovulation rate and number of embryos were determined 4 days after progestagen withdrawal. Administration of OVAGEN induced a significant rise (p < 0.0005) in the number of follicles ≥ 4 mm in size because of an increased growth in size of follicles from the first FSH injection to sponge removal, an increase in the number of newly detected follicles from 12 to 36 h of the first FSH dose (p < 0.005) and a decrease in regression rate from 24 h (p < 0.001). The number of follicles 2–3 mm in size at first FSH dose (10.4 ± 1.5) was positively correlated with the number of ≥ 4 mm follicles at 0 h (19.0 ± 2.7, p < 0.01). A higher number of ≥ 4 mm follicles at 0 h was related with an earlier appearance of oestrus (31.5 ± 1.5 h, p = 0.08) and LH surge (45.0 ± 2.3 h, p < 0.005), and a higher ovulation rate (18.2 ± 3.8, p < 0.005). On the other hand, the rate of embryo recovery was decreased in ewes with earlier preovulatory LH peaks (p < 0.005), with a shorter interval between oestrus and LH peak (p < 0.05).     

Regional chemical characteristics of lakes in North America Part II: Eastern United States

A survey of 1592 lakes ( >4 ha and ≤ 2,000 ha) was conducted in Fall, 1984. The study area was three regions of the eastern United States (Northeast, Upper Midwest, and Southeast) expected to contain the most lakes with acid neutralizing capacity (ANC) ≤400 μeq/L. The design of the survey provides statistically reliable estimates of the number, location and chemical characteristics of lakes in the study area. Frequency distribution statistics are presented for pH, ANC, sulfate and organic anion. The highest percentages and numbers of acidic lakes occurred in Florida, the Adirondaks, and the Upper Peninsula of Michigan. The highest percentages and numbers of lakes with high sulfate concentrations occurred in the Poconos/Catskills, Southern New England and Florida. The highest percentages and numbers of lakes with high organic anion concentrations occurred in Northeastern Minnesota, the Upper Great Lakes Area and Florida. The percentage of acidic lakes by sulfate concentration class revealed no discernable pattern across subregions. In contrast, the acidic lakes occur with the highest frequency in the lowest organic anion concentration class. The complex distribution of low ANC lakes cannot be explained simply by sulfate concentrations or organic acids.     

Molecular Basis of Gene-for-Gene Specificity in Bacterial Speck Disease of Tomato

Transient expression of the Pseudomonas syringae avirulence gene avrPto in plant cells resulted in a Pto-dependent necrosis. The AvrPto avirulence protein was observed to interact directly with the Pto resistance protein in the yeast two-hybrid system. Mutations in the Pto and avrPto genes which reduce in vivo activity had parallel effects on association in the two-hybrid assay. These data suggest that during infection the pathogen delivers AvrPto into the plant host cell and that resistance is specified by direct interaction of Pto with AvrPto.