Tires, Tracks, and Tethering: Idaho Steep Slope Harvesting

Steep slope timber harvesting often falls under scrutiny of labor, safety, and operational challenges, but is beginning to advance past these barriers through substantial technological progression. Across previous decades, large advancements of technology have occurred in ground-based timber harvesting systems, giving mechanized options to every phase of timber harvesting. These progressions have created outcomes including, but not limited to, improved worker safety and reduced risk, increased productivity and reduced harvest cost, while also increasing consistent harvest output through seasonal conditions. Timber harvesting methods on steep slopes historically involved motor-manual tree felling and labor-intensive extraction, but are now giving way to mechanization in steep slope harvesting. Tether-assist technology is now bringing the decades of progression from groundbased harvesting systems onto steep slopes. With the ability of ground-based harvesting systems to now traverse slopes steeper than previously possible, there is much to learn of their impacts and relationships with the landscape. Previously developed state and federal government policies in the Pacific Northwest (PNW), within the United States of America (USA), limit ground-based harvesting equipment on steep slopes. Different levels of regulation come into application by means of restriction for traditional ground based harvesting equipment above specified slope thresholds, in addition to extra requirements and some restrictions for tether-assist technology. This research is a case study showcasing soil impacts of traditional steep slope cable harvesting systems alongside developing tether-assist ground-based harvesting systems in similar terrain and timber conditions. Felling methods vary from motor-manual to mechanized directional felling head, while extraction methods incorporate grapple skidder, shovel, and cable logging, each exhibiting a different interaction with the site. Pre-harvest and post-harvest observations were collected of bulk density and penetrometer resistance for impact characterization and comparison. Bulk density measures work to capture differences in top-soil disturbance, while penetrometer resistance captures soil profile differences at increased depths. Sampling consisted of pre-operation and post-operation measurements taken at repeated locations on an established grid, allowing for paired testing of observations. The results from this study have shown differences in harvest system and operational area impacts, with each configuration contributing a unique distribution of soil impact to the harvest area. Through a variety of cable, tracked, and rubber tire equipment, this is to be expected due to the differing contact relationships and payload interactions with the soils in the harvest area. Machine passes and spatial distribution of machine activity was also found to be variable between harvest system configurations. These differing outcomes led to support traditional trends found in ground-based harvesting soil disturbance studies, with grapple skidding exhibiting the greatest impacts followed by shovel, and cable logging. Although trends in the data led to this comparative conclusion, significant differences were not found between either of the tether-assisted skidder or shovel systems. Further development of tethered logging system research is necessary, as trends may be similar to flat ground, yet additional forces via tether tension and extra payload may be entering new magnitudes

Propensity score matching with clustered data. An application to the estimation of the impact of caesarean section on the Apgar score

This article focuses on the implementation of propensity score matching for clustered data. Different approaches to reduce bias due to cluster-level confounders are considered and compared using Monte Carlo simulations. We investigated methods that exploit the clustered structure of the data in two ways: in the estimation of the propensity score model (through the inclusion of fixed or random effects) or in the implementation of the matching algorithm. In addition to a pure within-cluster matching, we also assessed the performance of a new approach, 'preferential' within-cluster matching. This approach first searches for control units to be matched to treated units within the same cluster. If matching is not possible within-cluster, then the algorithm searches in other clusters. All considered approaches successfully reduced the bias due to the omission of a cluster-level confounder. The preferential within-cluster matching approach, combining the advantages of within-cluster and between-cluster matching, showed a relatively good performance both in the presence of big and small clusters, and it was often the best method. An important advantage of this approach is that it reduces the number of unmatched units as compared with a pure within-cluster matching. We applied these methods to the estimation of the effect of caesarean section on the Apgar score using birth register data

Ecophysiology and application of acidophilic sulfur-reducing microorganisms

Sulfur-reducing prokaryotes play an important role in the sulfur biogeochemical cycle, especially in deep-sea vents, hot springs and other extreme environments. The reduction of elemental sulfur is not very favorable thermodynamically, but still provides enough energy for growth of microorganisms. Currently known sulfur reducers are spread over about 69 genera within 9 phyla in the Bacteria domain and 37 genera within 2 phyla in the Archaea domain. Elemental sulfur reduction can occur with polysulfide as an intermediate or via direct cell attachment to the solid substrate. At least four different enzymes are involved in those pathways, and these enzymes are also detected in several microorganisms that are potential sulfur reducers, but not reported as such in literature so far. The ecological distribution of sulfur respiration seems to be more widespread at high temperatures with neutral pH. However, some sulfur reducers can grow at pH as low as 1. The sulfide produced from sulfur reduction can selectively precipitate metals by varying the pH values from 2 to 7, depending on the target metal. Therefore, acidophilic sulfur reducers are of particular interest for application in selective precipitation and recovery of heavy metals from metalliferous waste streams. This chapter explores the ecology and physiology of elemental sulfur reducers, and discusses technologies that can be set up to exploit acidophilic sulfur reducers.The doctoral study program of A.P. Florentino is supported by the organization of the Brazilian Government for the development of Science and Technology CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico). Research of I. Sánchez-Andrea and A.J.M. Stams is financed by ERC grant project 323009 and by Gravitation grant project 024.002.002 from the Netherlands Ministry of Education, Culture and Science