Capillary Barrier Effect from Underlying Coarser Soil Layer

Infiltration tests were conducted on soil columns of silty sand over pea gravel, concrete sand over pea gravel, and silty sand over concrete sand to investigate the capillary barrier effect of an underlying coarser soil layer. Water movement across the interface occurred when the suction head at the interface reached the breakthrough head of the coarser lower soil layer, defined as the suction head at which the coarser layer first became conductive, regardless of infiltration rate or the properties of the overlying finer soil layer. Thus, the coarser lower soil layer controlled breakthrough in this study. After infiltration was terminated, the suction head near the interface increased above the breakthrough head and the barrier was restored. The breakthrough head did not change substantially after eight test cycles of breakthrough and restoration for a capillary barrier with a pea gravel as the coarser lower soil layer. The barrier formed with the concrete sand as the coarser layer permitted breakthrough at a greater suction head than did the barrier with the pea gravel, indicating that the more uniform and coarse the lower soil layer is, the more effective the capillary barrier.     

Extended-cavity surface-emitting diode laser as active mirror controlling modelocked Ti:sapphire laser

Directly controlled, stable modelocking of a Ti:sapphire oscillator is demonstrated using a commercially available electrically pumped vertical extended-cavity surface-emitting laser as an active saturable absorber mirror. Modelocking is controlled by applying a pulsed current to the saturable absorber. Pulse durations of /spl sim/330 ps are observed.     

Supporting children's mental health in schools: Teacher perceptions of needs, roles, and barriers.

There is a significant research to practice gap in the area of mental health practices and interventions in schools. Understanding the teacher perspective can provide important information about contextual influences that can be used to bridge the research to practice gap in school-based mental health practices. The purpose of this study was to examine teachers' perceptions of current mental health needs in their schools; their knowledge, skills, training experiences and training needs; their roles for supporting children's mental health; and barriers to supporting mental health needs in their school settings. Participants included 292 teachers from 5 school districts. Teachers reported viewing school psychologists as having a primary role in most aspects of mental health service delivery in the school including conducting screening and behavioral assessments, monitoring student progress, and referring children to school-based or community services. Teachers perceived themselves as having primary responsibility for implementing classroom-based behavioral interventions but believed school psychologists had a greater role in teaching social emotional lessons. Teachers also reported a global lack of experience and training for supporting children's mental health needs. Implications of the findings are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Parametric Study of Unsaturated Drainage Layers in a Capillary Barrier

Unsaturated drainage layers (UDLs) have been demonstrated to greatly increase the lateral diversion capacity of capillary barriers. The inclusion of a UDL allows native soils suitable for vegetation growth to be used as the finer soil as lateral drainage properties of the layer no longer need to be considered. A comprehensive numerical study was conducted to investigate the influence of the interface slope and the UDL material on the system's ability to laterally divert downward moving moisture. A capillary barrier system with and without a UDL was simulated for 10 years using daily varying climatic data for three locations in the United States. Three different sands were simulated as the UDL and were modeled at slopes of 5, 10, and 20%. The numerical results confirm that the inclusion of an unsaturated drainage layer at the fine∕coarse interface of a capillary barrier can provide significant improvements in the performance of the cover system by laterally draining water. This improvement in performance may allow the system to be successfully implemented in climates wetter than previously were thought suitable. The diversion length (the distance water is diverted laterally with no downward flow through the fine∕coarse interface) of a capillary barrier with a UDL was found to be proportional to the slope of the fine∕coarse interface. In addition, a relationship between lateral diversion lengths in a capillary barrier and the UDL material was developed and found to be dependent on the unsaturated flow characteristics of the UDL. These relationships allow the performance of a variety capillary barrier UDL designs to be calculated knowing the behavior of one system for a given location.     

Gigahertz repetition-rate from directly diode-pumped femtosecondCr:LiSAF laser

Gigahertz repetition-rate, fundamental modelocking of a directly diode-pumped femtosecond laser is demonstrated for the first time. Transform-limited pulses of 146 fs duration are produced from a compact Cr:LiSAF laser incorporating a semiconductor saturable absorber mirror and pumped by inexpensive, narrow-stripe red laser diodes     

In situ gas permeability measurements to delineate damage in rock salt

In situ gas permeability measurements can be used to distinguish regions within rock salt formations which have experienced disturbance or damage. High-resolution hydrologic testing reveals rock salt well removed from an excavation (i.e. undisturbed) is a low permeability, low porosity, porous medium with a significant pore (brine) pressure. In this region, rock salt is effectively impermeable to gas due to threshold capillary pressures which preclude gas from displacing the resident brine. In a region confined to a depth of less than about one effective radius of an excavation, rock salt is typically permeable to gas. The measured gas permeabilities are consistent with a partially saturated, dilated zone developing adjacent to the excavation. The extent and nature of the damaged region interpreted from gas permeability measurements is consistent with other measurements and analyses. Thus, gas permeability measurements serve as effective means for detecting and delineating the damaged region.