Théorie du pendule de Zöllner et du pendule de Lettau

Summary The theory of a Zöllner's horizontal pendulum with perfect wires of suspension is made. We use the Euler's angles of the axes of a system fixed in the moving body relatively to fixed axes and a fourth angle caracterising the amplitude of a motion of translation. We give the conditions for the decoupling of the four types of motion (pure rotation, pitching, rolling, translation) and the equations of forced motions.A rigorous theory of Lettau's double pendulum is initiated. We suppose that the primary pendulum has only one degree of freedom. First the case of a secondary pendulum not disturbing the primary one is examined, and then the case of an indifferent primary pendulum, wich enables us to understand what happens in the normal case. The potential energy of the secondary pendulum is not always a minimum in the central position when the plane of symmetry is vertical and it is possible that parasitesolutions appear, stabler than the central one. This study is extended to the case of a non-vertical plane of symmetry and indications are given for the study of the free motions of the system.In conclusion we could say that this system is simple only at first sight. Its use would be necessary in the case of a real great drift of the underground of the station. But in the contrary case ordinary simple pendulums are sufficient and more easy to understand.

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Resumo La movoj de horizontala Zöllnera pendolo estas difinataj pere de la Euleraj anguloj de triaksa sistemo ligita al la pendolo, rilate al fiksa sistemo, kaj de kvara angulo rilata al translacia movado. Ni donas la kondiojn necesajn por la senkuplado de tiuj kvar movoj (pura rotacio, tangado, ruligado, translacio) kaj la ekvaciojn de la devigataj movoj.La teorio de Lettaùa duobla pendolo estas multe pli kompleksa. Supozente ke la primara pendolo havas nur unu gradon de libereco, ni studas unue la movojn de la sistemo kiam la sekundara pendolo ne perturbas la primaran aù kiam tiu-i estas en indiferenta ekvilibro. Tio permesas kompreni tion kio okazas en la normala kazo. ar la potenciala energio de la sekundara pendolo ne estas iam minimuma en la centra pozicio kiam la simetria ebeno estas vertikala, parazitaj pozicioj povas ekzisti kiuj estas pli stabilaj ol la centra. Ni ekzamenas ankaù la kazon de nevertikala ebeno de simetrio kaj indikas kiel studi la liberajn movojn de la sistemo.

     

Water balance components estimation under scenarios of land cover change in the Vea catchment,West Africa

ABSTRACT

The need for a detailed investigation of the Vea catchment water balance components cannot be overemphasized due to its accelerated land-cover dynamics and the associated impacts on the hydrological processes. This study assessed the possible consequences of land-use change scenarios (i.e. business as usual, BAU, and afforestation for the year 2025) compared to the 2016 baseline on the Vea catchment’s water balance components using the Soil and Water Assessment Tool (SWAT) model. The data used include daily climate and discharge, soil and land use/land cover maps. The results indicate that the mean annual water yield may increase by 9.1% under the BAU scenario but decrease by 2.7% under the afforestation scenario; actual evapotranspiration would decrease under BAU but increase under afforestation; and groundwater recharge may increase under both scenarios but would be more pronounced under the afforestation scenario. These outcomes highlight the significance of land-cover dynamics in water resource management and planning at the catchment.     

Spatiotemporal characteristics of white mold and impacts on yield in soybean fields in South Dakota

ABSTRACT

White mold of soybeans is one of the most important fungal diseases that affect soybean production in South Dakota. However, there is a lack of information on the spatial characteristics of the disease and relationship with soybean yield. This relationship can be explored with the Normalized Difference Vegetation Index (NDVI) derived from Landsat 8 and a fusion of Landsat 8 and the Moderate Resolution Imaging Spectroradiometer (MODIS) images. This study investigated the patterns of yield in two soybean fields infected with white mold between 2016 and 2017, and estimated yield loss caused by white mold. Results show evidence of clustering in the spatial distribution of yield (Moran’s I = 0.38; p < 0.05 in 2016 and Moran’s I = 0.45; p < 0.05 in 2017) that can be explained by the spatial distribution of white mold in the observed fields. Yield loss caused by white mold was estimated at 36% in 2016 and 56% in 2017 for the worse disease pixels, with the most accurate period for estimating this loss on 21 August and 8 September for 2016 field and 2017 field, respectively. This study shows the potential of free remotely sensed satellite data in estimating yield loss caused by white mold.     

Characteristics of electron and high-energy proton flares

High-energy proton (E _p > 55 MeV) and electron (E _e > 50 keV) events were observed by University of Iowa experiments on the satellites Explorer 33 and 35. The solar X-ray (2–12 Å) flares associated with the energetic proton events were found to have in general higher peak fluxes, considerably longer decay times (t) and smaller rise to decay time ratios (r) than the X-ray flares associated with the electron events. The most common decay times and rise to decay time ratios are: 80 t 100 min, 0.1 r 0.2 for the proton X-ray flares and t 20 min, 0.3 r 0.7 for the electron ones.     

Lateral migration and bank erosion in a saltmarsh tidal channel in San Francisco Bay, California

Saltmarsh tidal channels have often been recognized as being stable landscape features, despite highly sinous planforms, severely undercut banks, and high rates of bank erosion. In an effort to solve this paradox, a saltmarsh tidal channel in the San Francisco Bay was monitored from March 1995 to March 1996. The short-term rate of bank erosion was measured using erosion pins and found to be 57 ± 10 mm yr^?1 on the outside banks of meander bends. In addition, a long-term maximum lateral migration rate of 23 ± 23 mm yr^?1 was estimated from aerial photos, producing a dimensionless channel migration rate (defined as the rate of migration divided by channel with), of 0.5% yr^?1. The difference in the rates of lateral migration and bank erosion is attributed to the persistence of failed bank material (slump blocks) in the channel. The slump blocks induce sedimentation, protect the banks, and prevent further bank erosion. A published stability analysis method for undercut banks is applied to determine a maximum overhanging width. Using the measured compressive and tensile strengths of rooted bank material, 16.55 ± 1.16 kPa and 2.93 ± 0.71 kPa, respectively, the maximum width of an undercut bank is calculated to be 0.69 m. The average width of slump blocks measured in the field is 0.67 ± 0.25 m. A simple numerical model predicting the rate of lateral migration is derived using the results from the stability analysis and data from sedimentation and erosion pins inserted throughout the channel. This model accurately predicts a rate of 23 ± 3 mm yr^?1.     

From subduction to transform motion: a seabeam survey of the Hellenic trench system

Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch.     

Etude expérimentale du comportement de l'uranium dans les magmas: États d'oxydation et coordinance

Depending upon oxygen fugacity, uranium exists in three different oxidation states in magmatic silicate liquids. The hexavalent state, present as the uranyl group, UO²⁺₂, is stable under highly oxidizing conditions, but can still be detected in the presence of the NiNiO buffer. Under the same conditions the pentavalent state forms about 30–40% of total uranium and is also characteristic of relatively high oxygen fugacities. Optical absorption spectra obtained on granitic and basaltic glasses synthesized in the presence of the NiNiO buffer are very different: this is interpreted as being due to the presence of UO⁺₂ complexes in the former and 6-coordinated U(V) in the latter. The tetravalent state is the most stable under reducing conditions: at the FeFeO buffer, it is the only one present. An 8-coordinated U(IV) species seems the most probable, by comparison of the spectra with those of crystallized U(IV) compounds. The trivalent state was not detected, even under the most reducing conditions. Interpretation of the spectra obtained in the glasses in terms of coordination and bonding is however difficult, due to the lack of knowledge of 5f-systems in iono-covalent systems such as oxide glasses. The presence of the pentavalent state must be taken into account in discussing partition coefficients of uranium and trans-uranium compounds in natural and synthetic systems (because of the effect of oxygen fugacity and oxide ion activity on the U(IV) U(V) system). During postmagmatic hydrothermal processes U(V) is destroyed, resulting in the early precipitation of U(IV) containing minerals and possible migration of uranyl ions.     

Glacier mass balance of tropical Zongo glacier, Bolivia, comparing hydrological and glaciological methods

A glaciological program has been undertaken since 1991 on Zongo glacier in Bolivia (6000–4850 m asl, 2.4 km², 16°S). This program involves mass balance measurements, hydrological studies and energy balance investigations. On outer-tropical glaciers, melting and snow accumulation are both maximum in the wet season (austral summer), whereas the dry season (winter) is a period of low ablation. Errors on each term of the glaciological (stakes, snow-pits and integration method of the measurements) and hydrological (precipitation, discharge and runoff coefficient of free ice areas) methods are investigated to estimate the overall accuracy of the mass balance measurements. The hydrological budget is less than the glaciological one (mean difference: 60 cm w.e. per year), but both methods reproduce similar inter-annual variations. Errors in assessment of evaporation or water storage inside the glacier cannot explain the discrepancy. Errors using the glaciological method are large (around ± 40 cm w.e. per year), but no bias can explain the departure from the hydrological balance. Errors on discharge measurements are small and the uncertainty on the runoff coefficient has a minor effect on the mass balance. We concluded that hydrological budgets are too low due to the catch deficiency of rain gauges and absence of precipitation measurements at high altitudes, emphasizing the difficulty to assess snowfall distribution in high mountainous basins.     

Modelling observed and future runoff from a glacierized tropical catchment (Cordillera Blanca, Perú)

Monthly runoff from the 34.3% glacierized tropical catchment of Llanganuco in the tropical Cordillera Blanca, Perú, is successfully simulated and compared with a measured 44 year time series. In the investigation area, the climate is characterized by all-year round homogenous temperature conditions and a strong variability in air humidity and moisture content of the atmosphere. Thus, contrary to the mid latitudes, the seasonal variation in glacier melt strongly depends on moisture-related variables, rather than on air temperature. The here presented ITGG-2.0-R model aims for these requirements. The lack of moisture-related input data other than precipitation demands for an intermediate calibration step. Net shortwave radiation, the emissivity of the atmosphere and a sublimation/melt ratio are related to precipitation amounts. Runoff is well simulated and correlates with the measured record with r² = 0.76. Seasonally obtained r² are only slightly smaller. On a long-term, the cumulative deviation is minor, and the mean annual cycle of runoff is reproduced rather well (r² = 0.99). Based on four different IPCC climate change scenarios, future runoff is simulated. All runoff scenarios are modelled for the respective steady-state glacier extent. This leads to a reduction in the glacier size and a decreased amount of glacier melt. On the other hand, direct runoff increases due to larger glacier free areas. Consequently, mean annual runoff remains almost unchanged, but the seasonality intensifies considerably with more runoff during the wet and less runoff during the dry season.