A finite-strain hyperviscoplastic model and undrained triaxial tests of peat

This paper presents a finite-strain hyperviscoplastic constitutive model within a thermodynamically consistent framework for peat which was categorised as a material with both rate-dependent and thermodynamic equilibrium hysteresis based on the data reported in the literature. The model was implemented numerically using implicit time integration and verified against analytical solutions under simplified conditions. Experimental studies on the undrained relaxation and loading-unloading-reloading behaviour of an undisturbed fibrous peat were carried out to define the thermodynamic equilibrium state during deviatoric loading as a prerequisite for further modelling, to fit particularly those model parameters related to solid matrix properties, and to validate the proposed model under undrained conditions. This validation performed by comparison to experimental results showed that the hyperviscoplastic model could simulate undrained triaxial compression tests carried out at five different strain rates with loading/unloading relaxation steps.Comment: 30 pages, 16 figures, 4 tables. This is a pre-peer reviewed version of manuscript submitted to the International Journal of Numerical and Analytical Methods in Geomechanic

Coalescence in low-viscosity liquids

The expected universal dynamics associated with the initial stage of droplet coalescence are difficult to study visually due to the rapid motion of the liquid and the awkward viewing geometry. Here we employ an electrical method to study the coalescence of two inviscid droplets at early times. We measure the growth dynamics of the bridge connecting the two droplets and observe a new asymptotic regime inconsistent with previous theoretical predictions. The measurements are consistent with a model in which the two liquids coalesce with a slightly deformed interface.Comment: 4 pages and 4 figure

A Simplified Cellular Automaton Model for City Traffic

We systematically investigate the effect of blockage sites in a cellular automaton model for traffic flow. Different scheduling schemes for the blockage sites are considered. None of them returns a linear relationship between the fraction of ``green'' time and the throughput. We use this information for a fast implementation of traffic in Dallas.Comment: 12 pages, 18 figures. submitted to Phys Rev

Two candidate brown dwarf companions around core helium-burning stars

Hot subdwarf stars of spectral type B (sdBs) are evolved, core helium-burning objects. The formation of those objects is puzzling, because the progenitor star has to lose almost its entire hydrogen envelope in the red-giant phase. Binary interactions have been invoked, but single sdBs exist as well. We report the discovery of two close hot subdwarf binaries with small radial velocity amplitudes. Follow-up photometry revealed reflection effects originating from cool irradiated companions, but no eclipses. The lower mass limits for the companions of CPD-64$^{\circ}$481 ($0.048\,M_{\rm \odot}$) and PHL\,457 ($0.027\,M_{\rm \odot}$) are significantly below the stellar mass limit. Hence they could be brown dwarfs unless the inclination is unfavourable. Two very similar systems have already been reported. The probability that none of them is a brown dwarf is very small, 0.02%. Hence we provide further evidence that substellar companions with masses that low are able to eject a common envelope and form an sdB star. Furthermore, we find that the properties of the observed sample of hot subdwarfs in reflection effect binaries is consistent with a scenario where single sdBs can still be formed via common envelope events, but their low-mass substellar companions do not survive.Comment: accepted to A&

Tomato Leaf Spot Control

The most important plant disease affecting tomatoes during the past 10 years in South Dakota has been a fungus disease known as Septoria leaf spot (Septoria lycopersici). Other diseases have been of minor importance, namely late blight, Alternaria leaf spot, wilt and virus troubles. Septoria leaf spot frequently develops rapidly and may, under favorable conditions, completely defoliate the crop within a few weeks. When defoliation by the disease occurs, the yield may be markedly reduced. Fruit produced on such plants becomes flabby and the flavor is of low quality. The tomato is one of our most important vegetable crops. It is grown by virtually every home gardener and is high in certain vitamins which are important in the family diet, though it is not grown extensively on a commercial scale in the state at the present time. Septoria leaf spot may be recognized by the characteristic spots (see cover) on the leaves and stems which are approximately one-eighth inch in diameter. The margins of the spots usually become dark reddish- brown in color while the centers are light grey with a few scattered tiny black specks. When the spots become very numerous the affected leaves turn from light green to brown, die and drop from the plants. When the leaves are killed by the disease the fruits ripen prematurely and have an insipid flavor. These symptoms should distinguish Septoria leaf spot from other fungus diseases affecting the foliage. Early blight (Alternaria solani) forms larger irregular spots onefourth to one-half inch in diameter with numerous inconspicuous concentric rings within the diseased spot. Late blight (Phytophthora infestans) forms larger patches on the leaves which may, under certain weather conditions, involve entire leaves. The lesions appear water-soaked at first, but later become light brown to dark brown and in moist weather show a white mildew-like growth on the lower side of the leaves. This disease also causes a characteristic brown rot of the fruit which may result in heavy losses in yield of marketable fruit. Tomato plants can be protected from these fungus diseases by repeated applications with an effective fungicide. The first application should be made when the leaf spots first appear, and then repeated at 10-day intervals. It has been shown experimentally that sprays provide better coverage and protection than dusts. The lower as well as the upper surfaces of the leaves should be covered. In order to determine the most effective fungicide for the control of tomato foliage diseases in South Dakota a series of field experiments was started in 1944 at the State College Experiment Station

Fungicides for Potato Blight Control

South Dakota has an important potato- growing area in Clark, Codington, Hamlin and Deuel counties. Production of certified seed has become one of the important phases of the potato industry in South Dakota. In addition to the main commercial seed and table stock production areas indicated above, smaller producing areas are located in various sections of the state, not to mention the familiar potato patch in most home gardens. Likewise, with the coming of irrigation in the James River Valley of South Dakota, potato production will probably increase further. Losses in yield and quality of potatoes are severe in seasons favorable to the development of foliage diseases. While these diseases do not occur in serious amounts every season in South Dakota, the profits may be wiped out in those years when they are prevalent. When these diseases strike in epidemic proportions, one of the important effects which they have on the crop is the prevention of normal sizing of the tubers, thereby resulting in a reduction of U. S. No. 1 potatoes. For this reason, it is important to know what control measures are effective and can be easily and quickly applied when these diseases strike the crop. An effective fungicide, properly applied, can control these foliage diseases, and by removing another crop hazard can thereby add to the stability of commercial and certified seed potato production in South Dakota. Chemical fungicides, applied as sprays or dusts, differ in their effectiveness in controlling crop diseases. A particular fungicide might be highly effective in combating one type of disease, but may not be very effective against another. Consequently, it becomes necessary to test many chemicals over a period of several years to determine their effectiveness as well as the dosage rate and the proper time of the season to apply them. The most prevalent fungus diseases affecting potato foliage in the state are early blight, caused by Alternaria solcmi, and late blight, caused by Phytophthora infestans. Early blight is present to some extent every season in South Dakota, and causes losses through reduced grade and yield. The disease first appears as small oval or angular brown spots on the leaves with characteristic target-like markings. As the spots increase in size and number the affected leaves die. As a result of this defoliation the yield, especially of U. S. No. 1 grade potatoes, is reduced. During those seasons when conditions are favorable for the development of late blight, losses through reduced yields and tuber rot become costly to potato growers. Late blight is favored by cool temperatures and relatively good moisture conditions. This disease first appears on the leaves as pale green, water-soaked, irregular-shaped spots which may enlarge rapidly, turn brown or black, and show a white mildew-like appearance on the lower surface of diseased leaves. The stems can become infected and the entire plant may be killed in a few days. Under conditions favorable for the disease (moderate temperatures, with high humidity, heavy clews or frequent rains), it can spread rapidly throughout a field. Spores from diseased foliage washed down to the tubers by rain or brought in contact with them during digging operations can expose tubers to infection with late blight. Late blight-infected tubers develop what is known as late blight tuber rot, either in the field or in storage. To protect potato plants from these fungus diseases, it is necessary to keep the foliage coated with an effective fungicide. It has been shown experimentally that fungicides applied as sprays provide better coverage and disease control than those applied as dusts. A series of field experiments were initiated in 1945 at the Experiment Station at Brookings with the object of developing a potato spray program adapted to South Dakota conditions. In 1946, these tests formed a part of a regional potato fungicide trial in which six states in the upper Mississippi Valley participated. From 1947 to 1949 the tests were included in the national cooperative fungicide experiments sponsored by a Special Committee on the Coordination of Field Tests with New Fungicidal Sprays and Dusts, appointed by the American Phytopathological Society

Effects of thermal recycling temperatures on the reinforcement potential of glass fibers

In the present work the reinforcement potential of thermally recycled glass fibers in injection molded Polypropylene (PP) composites was investigated. Microbond tests showed that fiber sizing lost its compatibility to the PP matrix after exposure to temperatures of 250 °C in air. The drop of the adhesion between fibers and PP was mirrored by a large reduction of the tensile strength of the injection molded PP composites. In inert atmosphere the degradation of the fiber sizing and the reduction of the IFSS were less rapid than in air but no significant difference was observed above 400 °C. It was concluded that thermally recycled glass fibers will require a post-treatment to act as an effective reinforcement in injection molded PP composites even if the thermal recycling was performed in an inert atmosphere. The post-treatment will need to improve the compatibility of the fibers to the polymer matrix and the fiber strength

Do wildflower strips enhance pest control in organic cabbage?

Within this project we assess whether wildflower strips and companion plants increase the control of cabbage pests Plutella xylostella L. (Lepidoptera: Plutellidae), Mamestra brassicae L. (Lepidoptera: Noctuidae) and Pieris rapae L. (Lepidoptera: Pieridae) by (1) naturally occurring parasitoids and predators and (2) mass‐releasedn Trichogramma brassciae (Bezdenko) (Hymenoptera: Trichogrammatidae) parasitoids. Two organic cabbage fields were used for this study: adjacent to each field a wildflower strip was sown and companion plants (Centaurea cyanus L. (Asteraceae)) intermixed within the crop. Within each field ~15,000 M. brassicae eggs were placed out to determine the parasitism rates by mass‐released T. brassicae and to assess the levels of egg predation. Over 1,000 lepidopteran larvae were collected and screened for hymenopteran and tachinid parasitoid DNA using a multiplex PCR assay. Invertebrate generalist predators (n=1,063) were collected for DNA‐based gut content analysis. The wildflower strip had a significant positive effect on M. brassicae egg parasitism rates as rates increased 5‐fold in the vicinity to the strip. Moreover, companion plants enhanced invertebrate predation on M. brassicae eggs. Both, the release of T. brassicae and the use of companion plants, however, did not significantly increase egg parasitism rates. The infestation of plants by caterpillars increased with distance to the wildflower strip and there was a trend of decreasing larval parasitism rates with distance to the strip. Currently the invertebrate predators are being molecularly analysed to assess predation on unparasitized and parasitized lepidopteran pests

Performance of Different Atrial Conduction Velocity Estimation Algorithms Improves with Knowledge about the Depolarization Pattern

Quantifying the atrial conduction velocity (CV) reveals important information for targeting critical arrhythmia sites that initiate and sustain abnormal electrical pathways, e.g. during atrial flutter. The knowledge about the local CV distribution on the atrial surface thus enhances clinical catheter ablation procedures by localizing pathological propagation paths to be eliminated during the intervention. Several algorithms have been proposed for estimating the CV. All of them are solely based on the local activation times calculated from electroanatomical mapping data. They deliver false values for the CV if applied to regions near scars or wave collisions. We propose an extension to all approaches by including a distinct preprocessing step. Thereby, we first identify scars and wave front collisions and provide this information for the CV estimation algorithm. In addition, we provide reliable CV values even in the presence of noise. We compared the performance of the Triangulation, the Polynomial Fit and the Radial Basis Functions approach with and without the inclusion of the aforementioned preprocessing step. The evaluation was based on different activation patterns simulated on a 2D synthetic triangular mesh with different levels of noise added. The results of this study demonstrate that the accuracy of the estimated CV does improve when knowledge about the depolarization pattern is included. Over all investigated test cases, the reduction of the mean velocity error quantified to at least 25 mm/s for the Radial Basis Functions, 14 mm/s for the Polynomial Fit and 14 mm/s for the Triangulation approach compared to their respective implementations without the preprocessing step. Given the present results, this novel approach can contribute to a more accurate and reliable CV estimation in a clinical setting and thus improve the success of radio-frequency ablation to treat cardiac arrhythmias