Photoreceptor types and distributions in the retinae of insectivores.

The retinae of insectivores have been rarely studied, and their photoreceptor arrangements and expression patterns of visual pigments are largely unknown. We have determined the presence and distribution of cones in three species of shrews (common shrew Sorex araneus, greater white-toothed shrew Crocidura russula, dark forest shrew Crocidura poensis; Soricidae) and in the lesser hedgehog tenrec Echinops telfairi (Tenrecidae). Special cone types were identified and quantified in flattened whole retinae by antisera/antibodies recognizing the middle-to-long-wavelength-sensitive (M/L-)cone opsin and the short-wavelength-sensitive (S-)cone opsin, respectively. A combination of immunocytochemistry with conventional histology was used to assess rod densities and cone/rod ratios. In all four species the rods dominate at densities of about 230,000-260,000/mm2. M/L- and S-cones are present, comprising between 2% of the photoreceptors in the nocturnal Echinops telfairi and 13% in Sorex araneus that has equal diurnal and nocturnal activity phases. This suggests dichromatic color vision like in many other mammals. A striking feature in all four species are dramatically higher S-cone proportions in ventral than in dorsal retina (0.5% vs. 2.5-12% in Sorex, 5-15% vs. 30-45% in Crocidura poensis, 3-12% vs. 20-50% in Crocidura russula, 10-30% vs. 40-70% in Echinops). The functional and comparative aspects of these structural findings are discussed.

Generation and nonlinear evolution of shore-oblique/transverse sand bars

The coupling between topography, waves and currents in the surf zone may selforganize to produce the formation of shore-transverse or shore-oblique sand bars on an otherwise alongshore uniform beach. In the absence of shore-parallel bars, this has been shown by previous studies of linear stability analysis, but is now extended to the finite-amplitude regime. To this end, a nonlinear model coupling wave transformation and breaking, a shallow-water equations solver, sediment transport and bed updating is developed. The sediment flux consists of a stirring factor multiplied by the depthaveraged current plus a downslope correction. It is found that the cross-shore profile of the ratio of stirring factor to water depth together with the wave incidence angle primarily determine the shape and the type of bars, either transverse or oblique to the shore. In the latter case, they can open an acute angle against the current (upcurrent oriented) or with the current (down-current oriented). At the initial stages of development, both the intensity of the instability which is responsible for the formation of the bars and the damping due to downslope transport grow at a similar rate with bar amplitude, the former being somewhat stronger. As bars keep on growing, their finite-amplitude shape either enhances downslope transport or weakens the instability mechanism so that an equilibrium between both opposing tendencies occurs, leading to a final saturated amplitude. The overall shape of the saturated bars in plan view is similar to that of the small-amplitude ones. However, the final spacings may be up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller or larger. In the case of alongshore migrating bars, the asymmetry of the longshore sections, the lee being steeper than the stoss, is well reproduced. Complex dynamics with merging and splitting of individual bars sometimes occur. Finally, in the case of shore-normal incidence the rip currents in the troughs between the bars are jet-like while the onshore return flow is wider and weaker as is observed in nature.

Self-organization mechanisms for the formation on nearshore crescentic and transverse sand bars

The formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow-water equations and on a simpli ed sediment transport parameterization. By assuming normally approaching waves and a saturated surf zone, rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed. Two types of bedforms appear: one is a crescentic bar pattern centred around the breakpoint and the other, herein modelled for the rst time, is a transverse bar pattern. The feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations. Basically, the waves stir up the sediment and keep it in suspension with a certain cross-shore distribution of depth-averaged concentration. Then, a current flowing with (against) the gradient of sediment concentration produces erosion (deposition). It is shown that inside the surf zone, these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms. Numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro-morphodynamic input conditions to which of the patterns develops. It is suggested that crescentic bar growth would be favoured by high-energy conditions and ne sediment while transverse bars would grow for milder waves and coarser sediment. In intermediate conditions mixed patterns may occur.

Transverse Joint Sealing with Various Sealants, HR-203, 1983

Iowa's first portland cement concrete pavement was constructed in 1904 in the City of LeMars. A portion of that pavement served traffic until 1974 at which time it was resurfaced. The first rural Iowa pee pavement (16' wide, 6" to 7" thick) was constructed under the direction of the Iowa State Highway Commission in 1913. Some of Iowa's early pavements had transverse joints at 25-foot spacings. At that time, joint spacings across the nation ranged from 24 to 100 ft. There have been many changes in joint design over the years with some pavements being constructed without transverse joints. Joint spacing on Iowa primary pavements has generally remained around 20 feet with this spacing having been adopted as an Iowa standard in 1954. Until 1978 it was common to specify a 40-foot joint spacing on secondary pavements. The performance of the pavements with joint spacings greater than 20 feet, and in some cases no contraction joints, generated a 1955 research project on joint spacing. This project was 16 miles long containing sections without contraction joints and sections with joints sawed at intervals of 20, 50 and 80 feet. Approximately half of the sawed joints were left unsealed. The results of this research supported the 20-foot spacing, but were inconclusive regarding the benefits of sealing. One of the desired characteristics of joint sealing material is that it should act as a moisture barrier and prevent the intrusion of surface water. It was generally accepted from past experience that the hot poured type joint seals did not provide this effective moisture barrier.

Transverse Joint Sealing with Improved Sealers, HR-276, 1991

Concern about premature joint sealant failures occurring in portland cement concrete (PCC) pavements gave impetus to initiating this research project. Eight sealants, including three silicone sealants, were evaluated and tested in the lab as well as incorporated in approximately 700 joints in the field and evaluated over a six-year period. The preliminary data show that among the silicone sealants, Dow Corning 888 rated the highest. However, this was rated third overall behind the W. R. Meadows cold-applied Sof Seal and Crafco #231 hot pour sealants. The W. R. Meadows and Crafco sealants cost approximately 30 percent and 50 percent less to furnish and place than the Dow Corning product. All joint sealants will continue to be evaluated.

Transverse Cracking Study of Asphalt Pavement, HR-1020, 1981

At a pavement management study meeting in Omaha, Nebraska, September 12 and 13, 1979, the states of Iowa, Kansas and Nebraska agreed on the need for an in-depth engineering study of thermal cracking of bituminous pavement. In addition, the states of Oklahoma and North Dakota agreed to participate in the study. The scope of the study was to analyze all functions relating to the thermal cracking problem to determine how different uses of preventative materials, mix design measures, maintenance repairs, and design of bituminous pavements and overlays might be contributing to the problem and to determine what improvements might be made in these procedures to reduce the problem of thermal cracking. This publication describes the study and its conclusions. One of the conclusions is that the study did not address what the authors believe to be the major contributor to transverse cracking - the subgrade and subbase.

Transverse Cracking of Asphalt Pavements, HR-1040, Summary Report, 1982

This report summarizes the analysis of transverse cracking in asphalt pavement by a five state study team from Iowa, Kansas, Nebraska, North Dakota, and Oklahoma. The study was initiated under the sponsorship of the Federal Highway Administration and four evaluation conferences were held during the course of the study. Each state conducted a crack inventory on their asphalt pavement. An effort was made to correlate this inventory with numerous factors that were considered to be pertinent to the cracking problem. One state did indicate that there was a correlation between transverse cracking severity and the subsurface geology. The other states were unable to identify any significant factors as being the primary contributors. The analysis of the problem was divided into, (1) mix design, (2) maintenance, and (3) 3R rehabilitation. Many potential factors to be considered were identified under each of these three study divisions. There were many conclusions as to good and bad practices. One major conclusions was that a more effective crack maintenance program with early sealing was essential. Some new practices were suggested as potentially more cost effective in design, construction and maintenance. The interchange of methods and procedures by individual states yielded benefits in that other states selected practices that would be an improvement to their program.

Evaluation of Transverse Joint Forming Methods for PCC Pavement, TR-532, 2006

The members of the Iowa Concrete Paving Association, the National Concrete Pavement Technology Center Research Committee, and the Iowa Highway Research Board commissioned a study to examine alternative ways of developing transverse joints in portland cement concrete pavements. The present study investigated six separate variations of vertical metal strips placed above and below the dowels in conventional baskets. In addition, the study investigated existing patented assemblies and a new assembly developed in Spain and used in Australia. The metal assemblies were placed in a new pavement and allowed to stay in place for 30 days before the Iowa Department of Transportation staff terminated the test by directing the contractor to saw and seal the joints. This report describes the design, construction, testing, and conclusions of the project.

Degree of previous cutting in explaining the differences in diameter distributions between mature managed and natural Norway spruce forests

Abstract

A critical evaluation of secondary cancer risk models applied to Monte Carlo dose distributions of 2-dimensional, 3-dimensional conformal and hybrid intensity-modulated radiation therapy for breast cancer.

The comparison of radiotherapy techniques regarding secondary cancer risk has yielded contradictory results possibly stemming from the many different approaches used to estimate risk. The purpose of this study was to make a comprehensive evaluation of different available risk models applied to detailed whole-body dose distributions computed by Monte Carlo for various breast radiotherapy techniques including conventional open tangents, 3D conformal wedged tangents and hybrid intensity modulated radiation therapy (IMRT). First, organ-specific linear risk models developed by the International Commission on Radiological Protection (ICRP) and the Biological Effects of Ionizing Radiation (BEIR) VII committee were applied to mean doses for remote organs only and all solid organs. Then, different general non-linear risk models were applied to the whole body dose distribution. Finally, organ-specific non-linear risk models for the lung and breast were used to assess the secondary cancer risk for these two specific organs. A total of 32 different calculated absolute risks resulted in a broad range of values (between 0.1% and 48.5%) underlying the large uncertainties in absolute risk calculation. The ratio of risk between two techniques has often been proposed as a more robust assessment of risk than the absolute risk. We found that the ratio of risk between two techniques could also vary substantially considering the different approaches to risk estimation. Sometimes the ratio of risk between two techniques would range between values smaller and larger than one, which then translates into inconsistent results on the potential higher risk of one technique compared to another. We found however that the hybrid IMRT technique resulted in a systematic reduction of risk compared to the other techniques investigated even though the magnitude of this reduction varied substantially with the different approaches investigated. Based on the epidemiological data available, a reasonable approach to risk estimation would be to use organ-specific non-linear risk models applied to the dose distributions of organs within or near the treatment fields (lungs and contralateral breast in the case of breast radiotherapy) as the majority of radiation-induced secondary cancers are found in the beam-bordering regions.

Height distributions of Scots pine sapling stands affected by retained tree and edge stand competition

Abstract

Finite mixture analysis of beauty-contest data using generalised beta distributions

This paper introduces a mixture model based on the beta distribution, without preestablishedmeans and variances, to analyze a large set of Beauty-Contest data obtainedfrom diverse groups of experiments (Bosch-Domenech et al. 2002). This model gives a bettert of the experimental data, and more precision to the hypothesis that a large proportionof individuals follow a common pattern of reasoning, described as iterated best reply (degenerate),than mixture models based on the normal distribution. The analysis shows thatthe means of the distributions across the groups of experiments are pretty stable, while theproportions of choices at dierent levels of reasoning vary across groups.

What matters for predicting spatial distributions of trees: techniques, data, or species' characteristics?

Data characteristics and species traits are expected to influence the accuracy with which species' distributions can be modeled and predicted. We compare 10 modeling techniques in terms of predictive power and sensitivity to location error, change in map resolution, and sample size, and assess whether some species traits can explain variation in model performance. We focused on 30 native tree species in Switzerland and used presence-only data to model current distribution, which we evaluated against independent presence-absence data. While there are important differences between the predictive performance of modeling methods, the variance in model performance is greater among species than among techniques. Within the range of data perturbations in this study, some extrinsic parameters of data affect model performance more than others: location error and sample size reduced performance of many techniques, whereas grain had little effect on most techniques. No technique can rescue species that are difficult to predict. The predictive power of species-distribution models can partly be predicted from a series of species characteristics and traits based on growth rate, elevational distribution range, and maximum elevation. Slow-growing species or species with narrow and specialized niches tend to be better modeled. The Swiss presence-only tree data produce models that are reliable enough to be useful in planning and management applications.

Calibrating predicted tree diameter distributions in Catalonia, Spain

Abstract