An Improved Approach for Measurement of Coupled Heat and Water Transfer in Soil Cells

Laboratory experiments on coupled heat and water transfer in soil have been limited in their measurement approaches. Inadequate temperature control creates undesired two-dimensional distributions of both temperature and moisture. Destructive sampling to determine soil volumetric water content (θ) prevents measurement of transient θ distributions and provides no direct information on soil thermal properties. The objectives of this work were to: (i) develop an instrumented closed soil cell that provides one-dimensional conditions and permits in situ measurement of temperature, θ, and thermal conductivity (λ) under transient boundary conditions, and (ii) test this cell in a series of experiments using four soil type–initial θ combinations and 10 transient boundary conditions. Experiments were conducted using soil-insulated cells instrumented with thermo-time domain reflectometry (T-TDR) sensors. Temperature distributions measured in the experiments show nonlinearity, which is consistent with nonuniform thermal properties provided by thermal moisture distribution but differs from previous studies lacking one-dimensional temperature control. The T-TDR measurements of θ based on dielectric permittivity, volumetric heat capacity, and change in volumetric heat capacity agreed well with post-experiment sampling, providing r 2 values of 0.87, 0.93, and 0.95, respectively. Measurements of θ and λ were also consistent with the shapes of the observed temperature distributions. Techniques implemented in these experiments allowed observation of transient temperature, θ, and λ distributions on the same soil sample for 10 sequentially imposed boundary conditions, including periods of rapid redistribution. This work demonstrates that, through improved measurement techniques, the study of heat and water transfer processes can be expanded in ways previously unavailable

Testing a nitrogen fertilizer applicator designed to reduce leaching losses

Conventional practices for nitrogen fertilization of corn produce soil conditions that are conducive to preferential water flow and nitrate leaching. A new fertilizer applicator is proposed that will more effectively protect the fertilizer from infiltrating water and thus reduce the potential for leaching. The device forms a small compacted layer of soil above the subsurface fertilizer band and then mounds soil into a surface dome directly above the fertilizer band. This new localized compaction and doming (LCD) method is evaluated by measuring soil physical properties around the fertilizer band and comparing them with measurements made within the conventional knifing system. The LCD applicator increased penetration resistance from 0.50 to 0.75 MPa at the fertilizer band. As the knife slit above the fertilizer band was closed by the LCD applicator, soil bulk density was increased from 1.2 to 1.4 g/cm3 in the region. The ponded infiltration rate through the fertilizer band was reduced from 19.7 cm/h at the conventional knife slit to 10.1 cm/h at the LCD surface. Reduced water flow through the fertilizer band will result in reduced NO3-N movement. Nitrate movement was measured during a growing season in a corn field, and NO3-N applied by the LCD applicator moved approximately 60% as deep as NO3-N applied by a conventional knife applicator. The ability to restrict NO3-N movement by modifying the surface soil at N application represents a simple yet effective strategy to reduce NO3-N leaching losses and possible impacts on groundwater quality

Physiological response to groundwater depth varies among species and with river flow regulation

We investigated the physiological response of two native riparian tree species (Populus fremontii and Salix gooddingii) and one exotic species (Tamarix chinensis) to groundwater availability along gradients of depth to groundwater at two rivers in Arizona. Depth to groundwater (DGW) at the dam-regulated Bill Williams River (BWR) was relatively constant and shallow (,4 m). Populus fremontii at BWR did not experience reduced water availability at deeper groundwater depths, as evidenced by high predawn water potential. However, leaf gas exchange of P. fremontii was sensitive to high vapor pressure deficit where surface flow was ephemeral at BWR. Lower predawn water potentials of S. gooddingii at BWR suggested reduced water availability at deeper groundwater depths, but these reductions did not adversely affect net photosynthetic rate. Along the range of depth to groundwater at BWR, all three species suffered little canopy dieback, and dieback was not related to depth to groundwater. Depth to groundwater at the free-flowing Hassayampa River (HRP) was much greater and declined more rapidly in the ephemeral reaches than at BWR. Both P. fremontii and S. gooddingii experienced reduced water availability at deeper groundwater depths at HRP, as evidenced by lower predawn water potential. Both species also experienced reduced leaf gas exchange at deeper groundwater depths. Canopy dieback of all species was higher at HRP than at BWR and increased with increasing DGW, especially when DGW fell below 3 m. There was evidence to support branch sacrifice in these three riparian tree species as a means of improving water status in the surviving shoot. However, branch sacrifice was insufficient to prevent mortality in some of the native trees where DGW fell below 3 m at HRP. In contrast to the native species, T. chinensis showed no change in water availability, leaf gas exchange, or canopy dieback with increasing DGW at either river. Leaf gas exchange was lower and dieback was greater for T. chinensis at HRP where depth to groundwater was greater than at BWR, but there was no mortality at either river. Our results show that deep groundwater is more detrimental to the physiological condition of P. fremontii and S. gooddingii than it is to T. chinensis. Also, the pronounced differences in DGW and tree physiological performance between BWR and HRP suggest that dam regulation can increase water availability to mature trees in some desert riparian ecosystems. Finally, our study also provides estimates of the range of DGW that can maintain healthy, mature P. fremontii and S. gooddingii trees

Neurogenin2 Expression in Ventral and Dorsal Spinal Neural Tube Progenitor Cells Is Regulated by Distinct Enhancers

AbstractThe basic helix-loop-helix transcription factor Neurogenin2 (NGN2) is expressed in distinct populations of neural progenitor cells within the developing central and peripheral nervous systems. Transgenic mice containing ngn2/lacZ reporter constructs were used to study the regulation of ngn2 in the developing spinal cord. ngn2/lacZ transgenic embryos containing sequence found 5′ or 3′ to the ngn2 coding region express lacZ in domains that reflect the spatial and temporal expression profile of endogenous ngn2. A 4.4-kb fragment 5′ of ngn2 was sufficient to drive lacZ expression in the ventral neural tube, whereas a 1.0-kb fragment located 3′ of ngn2 directed expression to both dorsal and ventral domains. Persistent β-gal activity revealed that the NGN2 progenitor cells in the dorsal domain give rise to a subset of interneurons that send their axons to the floor plate, and the NGN2 progenitors in the ventral domain give rise to a subset of motor neurons. We identified a discrete element that is required for the activity of the ngn2 enhancer specifically in the ventral neural tube. Thus, separable regulatory elements that direct ngn2 expression to distinct neural progenitor populations have been defined

Method for Maintaining One-Dimensional Temperature Gradients in Unsaturated, Closed Soil Cells

One-dimensional temperature gradients are difficult to achieve in nonisothermal laboratory studies because, in addition to desired axial temperature gradients, ambient temperature interference (ATI) creates a radial temperature distribution. Our objective was to develop a closed soil cell with limited ATI. The cell consists of a smaller soil column, the control volume, surrounded by a larger soil column, which provides radial insulation. End boundary temperatures are controlled by a new spiral-circulation heat exchanger. Four cell size configurations were tested for ATI under varying ambient temperatures. Results indicate that cells with a 9-cm inner column diameter, 5-cm concentric soil buffer, and either 10- or 20-cm length effectively achieved one-dimensional temperature conditions. At 30°C ambient temperature, and with axial temperature gradients as large as 1°C cm−1, average steady-state radial temperature gradients in the inner soil columns were−1 Thus, these cell configurations meet the goal of maintaining a one-dimensional temperature distribution. These cells provide new opportunities for improving the study of coupled heat and water movement in soil

The effect of display rules on illusion of transparency in children

The illusion of transparency, the tendency for people to overestimate how obvious their internal states appear to outside observers, was examined in 25 school-age children. While previous researchers studied undergraduate participants, we aimed to expand the developmental literature by investigating whether children exhibit the illusion of transparency in the same manner as undergraduates. We presented each child with three pleasant-tasting drinks and two unpleasant-tasting drinks. Two undergraduate observers and the children rated facial expressions after each sip. Our results supported our hypothesis with no illusion of transparency for the unpleasant drinks; however, an illusion was found for the pleasant drinks. The children\u27s inability to follow display rules may explain the absence of the illusion of transparency for the unpleasant condition