Photon scattering cross sections of H2 and He measured with synchrotron radiation

Total (elastic + inelastic) differential photon scattering cross sections have been measured for H2 gas and He, using an X-ray beam. Absolute measured cross sections agree with theory within the probable errors. Relative cross sections (normalized to theory at large S) agree to better than one percent with theoretical values calculated from wave functions that include the effect of electron-electron Coulomb correlation, but the data deviate significantly from theoretical independent-particle (e.g., Hartree-Fock) results. The ratios of measured absolute He cross sections to those of H2, at any given S, also agree to better than one percent with theoretical He-to-H2 cross-section ratios computed from correlated wave functions. It appears that photon scattering constitutes a very promising tool for probing electron correlation in light atoms and molecules

Deposition of aerially applied spray to a stream within a vegetative barrier

Drift of aerially applied forest herbicides can result in chemical deposition to streams. Riparian vegetation is expected to attenuate drift, but there is little corresponding data. A field study was conducted in the Coast Range west of Corvallis, Oregon, to evaluate the effectiveness of forested riparian buffers. The buffers studied are typical of those used for small and medium fish-bearing streams in western Oregon as mandated by the Oregon Forest Practices Act. A helicopter sprayed two tracers over four transects. Twenty trials were conducted, resulting in over 1400 tracer samples. Results confirm that these vegetative barriers are effective at reducing deposition into streams. Reduction of deposition on artificial foliage samplers placed immediately above the stream surface ranged from 37% to 99% and averaged 92%. Reductions were less clear in stable atmospheric conditions due to low wind speed and highly variable wind directions. Low wind speed conditions are not generally high-drift scenarios, but there is evidence that drift of suspended droplets beyond the barrier, comprising a small fraction of the total mass, increases in stable conditions

Fuels treatment and wildfire effects on runoff from Sierra Nevada mixed-conifer forests

We applied an eco-hydrologic model (Regional Hydro-Ecologic Simulation System [RHESSys]), constrained with spatially distributed field measurements, to assess the impacts of forest-fuel treatments and wildfire on hydrologic fluxes in two Sierra Nevada firesheds. Strategically placed fuels treatments were implemented during 2011–2012 in the upper American River in the central Sierra Nevada (43 km2) and in the upper Fresno River in the southern Sierra Nevada (24 km2). This study used the measured vegetation changes from mechanical treatments and modelled vegetation change from wildfire to determine impacts on the water balance. The well-constrained headwater model was transferred to larger catchments based on geologic and hydrologic similarities. Fuels treatments covered 18% of the American and 29% of the Lewis catchment. Averaged over the entire catchment, treatments in the wetter central Sierra Nevada resulted in a relatively light vegetation decrease (8%), leading to a 12% runoff increase, averaged over wet and dry years. Wildfire with and without forest treatments reduced vegetation by 38% and 50% and increased runoff by 55% and 67%, respectively. Treatments in the drier southern Sierra Nevada also reduced the spatially averaged vegetation by 8%, but the runoff response was limited to an increase of less than 3% compared with no treatment. Wildfire following treatments reduced vegetation by 40%, increasing runoff by 13%. Changes to catchment-scale water-balance simulations were more sensitive to canopy cover than to leaf area index, indicating that the pattern as well as amount of vegetation treatment is important to hydrologic response

Reaeration in a turbulent stream system

The oxygen concentration in a stream is an important parameter of water quality. Changes in oxygen concentrations can affect various stream organisms including fish. Foresters have become concerned with predicting the impacts of forest activities on oxygen levels in streams. Slash, which accumulates in streams as a result of harvesting activities, is a food source for stream organisms. During aerobic respiration, oxygen is utilized. Under some conditions the oxygen concentration can be depleted below acceptable levels. Large, fish bearing streams are generally well protected by forest practice regulations. For smaller streams without fish populations, the issue is one of downstream impairment of water quality as deoxygenated water enters fish-bearing reaches. A natural process counteracting oxygen depletion is reaeration. Reaeration is the exchange of gases between the atmosphere and water. This process operates to maintain oxygen near the saturation concentration. The change in the oxygen deficit in a stream is a function of the existing deficit and the reaeration rate coefficient. The objective of this study was to develop a predictive equation for the reaeration rate coefficient based on the hydraulic characteristics of stream channels. This is a a first step in developing guidelines to regulate harvesting residues in streams. Seven natural stream sites were selected in Oregon. These sites represented a wide range of hydraulic conditions. The stream reaches were segregated into segments of uniform hydraulic characteristics. Sodium sulfite was injected into the stream to artificially deplete the oxygen concentration. The recovery of the oxygen concentration was used to determine the reaeration rate coefficient. Several models for the reaeration process were tested using regression techniques. Some were models proposed by other investigators and some were developed independently. The predictive equation which fit the data best is a function of the maximum unit energy dissipation rate (ED) and a depth parameter (HD): [equation-see PDF] This equation is consistent with theoretical descriptions of gas exchange phenomena. As the rate of energy dissipation increases in a segment, the turbulence in the segment also increases. Turbulence promotes an increase in the liquid-atmosphere interface area and in the exchange rate of volume elements in the interface. Reaeration is stimulated when deaerated water from the bulk flow of the stream replaces the oxygen saturated water in the surface film. As the area of liquid-atmosphere contact increases, the total flux of oxygen molecules into the depleted fluid volume increases. As the fluid volume increases, the change in concentration for a specific flux of molecules decreases. The depth term (HD) can be used to describe the ratio of the surface area to the volume of fluid in the segment. In this study, the depth term used was the discharge divided by the mean width and maximum velocity. This approach adjusts for dead zones that do not actively mix with the bulk flow. For field applications, predicting the reaeration coefficient for any temperature (T) requires that the slope (s), active width (WD), maximum velocity (UD), and discharge (Q), be measured for uniform stream segments. These variables are combined in the following equation: [equation- see PDF] Using the predicted reaeration rates, estimates of mean segment velocities, biochemical oxygen demand loading, and rates of oxygen demand decay, it is possible to predict the oxygen concentration of a stream moving through and downstream from a harvesting site. The reaeration rate influences the maximum deficit and time required for recovery and can be used to evaluate the risks that debris accumulations pose to water quality

Computerized microtomography for new applications

The advent of high brilliance synchrotron sources has stimulated the development of advanced x-ray microtomography. However, materials research problems challenge existing tomographic techniques. High spatial resolution is required to identify and characterize microstructure in real materials. Good elemental sensitivity is required to study the effects of microalloying. Three-dimensional crystal texture, strain and phase information is required to understand advanced materials. Materials samples can include a wide range of elements, can come in unfavorable geometries, and sometimes require dynamic measurements of their three-dimensional structure. One challenge for x-ray microtomography is the measurement of low concentrations with good spatial resolution and high elemental sensitivity. Another challenge to standard x-ray microtomography is the study of elemental distributions in planar structures where elemental sensitivity is required in one or two dimensions, but the spatial sensitivity in all three dimensions is not required. For a large class of materials, crystalline structure, strain and texture are critical to the materials properties. Recent work has now demonstrated the possibility of extending X-ray microdiffraction to the study of three dimensional crystallographic distributions. Efforts are now underway at the APS, ALS, SSRL and NSLS to further develop x-ray microdiffraction and x-ray microdiffraction tomography. The measurement of strain and texture in three dimensions will have important applications to the study of high J{sub c} high {Tc} superconductors, the study of second phase distributions and texture in composite materials, and the study of crack and void evolution in structural and electronic materials. Another frontier for x-ray tomography is the development of dynamic, real-time measurements

An Analysis of Students' Writing Skill Taught by Project-Based Learning Model at the Tenth Grade of SMK Negeri 1 Dharma Caraka Gunungsitoli Selatan in 2022/2023

The researcher conducted a study entitled An Analysis of Students' Writing Skill Taught by Project-Based Learning Model at the Tenth Grade of SMK Negeri 1 Dharma Caraka Gunungsitoli Selatan in 2022/2023, with the aim to find and describe students' writing skill and the problems faced by students in writing taught by project-based learning model at the Tenth Grade of SMK Negeri 1 Dharma Caraka Gunungsitoli Selatan in 2022/2023. This research had conducted using descriptive qualitative research method. The data was collected and analyzed using the Miles and Huberman (1984) data analysis model. The results of the study showed that there were 12% or 4 students got the excellent category, there were 58% or 19 students got the good category, there were 15% or 5 students got the average category, there were 15% or 5 students got the fair category. Meanwhile, the average writing skill of students of class X Askep 2 SMK Negeri 1 Dharma Caraka Gunungsitoli Selatan who were taught using a project-based learning model were good with an average of 65.27, which meant that students had written descriptive text according to the form but still incomplete, less organized but the main idea is already visible, the choice of words and expressions is sometimes less precise but does not interfere with the meaning, and there are some mistakes in spelling but the meaning is not blurred. Meanwhile, the problems that students often encountered when writing English texts were cognitive problems consisting of generic structure, grammar, and spelling problems

Twenty Years of Drilling the Deepest Hole in Ice

No abstract available. doi:10.2204/iodp.sd.11.05.2011</a