Wedge immersed thermistor bolometers

An immersed thermistor bolometer for the detection of ultraviolet, visible, and infrared radiation is described. Two types of immersed bolometers are discussed. The immersion of thermistor flakes in a lens, or half immersed by optical contact on a lens, is examined. Lens materials are evaluated for optimum immersion including fused aluminum oxide, beryllium oxide, and germanium. The application of the bolometer to instruments in which the entrance pupil of the immersion optics has a high aspect ratio is considered

Wedge immersed thermistor bolometer measures infrared radiation

Wedge immersed-thermistor bolometer measures infrared radiation in the atmosphere. The thermistor flakes are immersed by optical contact on a wedge-shaped germanium lens whose narrow dimension is clamped between two complementary wedge-shaped germanium blocks bonded with a suitable adhesive

Translation-Rotation Coupling in Transient Grating Experiments : Theoretical and Experimental Evidences

The results of a Transient Grating experiment in a supercooled molecular liquid of anisotropic molecules and its theoretical interpretation are presented. These results show the existence of two distinct dynamical contributions in the response function of this experiment, density and orientation dynamics. These dynamics can be experimentally disentangled by varying the polarisation of the probe and diffracted beams and they have been identified and measured in a Heterodyne Detected experiment performed on m-toluidine. The results of the theory show a good qualitative agreement with the measurements at all temperatures.Comment: PDF format, 14 pages including 4 figures, accepted for publication in EPL. minor modification

Morphology of rain water channelization in systematically varied model sandy soils

We visualize the formation of fingered flow in dry model sandy soils under different raining conditions using a quasi-2d experimental set-up, and systematically determine the impact of soil grain diameter and surface wetting property on water channelization phenomenon. The model sandy soils we use are random closely-packed glass beads with varied diameters and surface treatments. For hydrophilic sandy soils, our experiments show that rain water infiltrates into a shallow top layer of soil and creates a horizontal water wetting front that grows downward homogeneously until instabilities occur to form fingered flows. For hydrophobic sandy soils, in contrast, we observe that rain water ponds on the top of soil surface until the hydraulic pressure is strong enough to overcome the capillary repellency of soil and create narrow water channels that penetrate the soil packing. Varying the raindrop impinging speed has little influence on water channel formation. However, varying the rain rate causes significant changes in water infiltration depth, water channel width, and water channel separation. At a fixed raining condition, we combine the effects of grain diameter and surface hydrophobicity into a single parameter and determine its influence on water infiltration depth, water channel width, and water channel separation. We also demonstrate the efficiency of several soil water improvement methods that relate to rain water channelization phenomenon, including pre-wetting sandy soils at different level before rainfall, modifying soil surface flatness, and applying superabsorbent hydrogel particles as soil modifiers

A Simple Analytical Model of Evaporation in the Presence of Roots

Root systems can influence the dynamics of evapotranspiration of water out of a porous medium. The coupling of evapotranspiration remains a key aspect affecting overall root behavior. Predicting the evapotranspiration curve in the presence of roots helps keep track of the amount of water that remains in the porous medium. Using a controlled visual set-up of a 2D model soil system consisting of monodisperse glass beads, we first perform experiments on actual roots grown in partially saturated systems under different relative humidity conditions. We record parameters such as the total mass loss in the medium and the resulting position of the receding fronts and use these experimental results to develop a simple analytical model that predicts the position of the evaporating front as a function of time as well as the total amount of water that is lost from the medium due to the combined effects of evaporation and transpiration. The model is based on fundamental principles of evaporation flux and includes empirical assumptions on the quantity of stoma in the leaves and the transition time between regime 1 and regime 2. The model also underscores the importance of a much prolonged root life as long as the root is exposed to a partially saturated zone composed of a mixture of air and water. Comparison between the model and experimental results shows good prediction of the position of the evaporating front as well as the total mass loss from evapotranspiration in the presence of real root systems. These results provide additional understanding of both complex evaporation phenomenon and its influence on root mechanisms.Comment: 10 pages, 6 figure

Observation of a nanophase segregation in LiCl aqueous solutions from Transient Grating Experiments

Transient Grating experiments performed on supercooled LiCl, RH2O solutions with R>6 reveal the existence of a strong, short time, extra signal which superposes to the normal signal observed for the R=6 solution and other glass forming systems. This extra signal shows up below 190 K, its shape and the associated timescale depend only on temperature, while its intensity increases with R. We show that the origin of this signal is a phase separation between clusters with a low solute concentration and the remaining, more concentrated, solution. Our analysis demonstrates that these clusters have a nanometer size and a composition which are rather temperature independent, while increasing R simply increases the number of these clusters.Comment: 19 pages+ 8 figures+ 2 table

Kinetics of Gravity-Driven Water Channels Under Steady Rainfall

We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-2D experimental set-up composed of a random close packing of mono-disperse glass beads. Using controlled experiments, we analyze the finger instabilities that develop from the wetting front as a function of fundamental granular (particle size) and fluid properties (rainfall, viscosity).These finger instabilities act as precursors for water channels, which serve as outlets for water drainage. We look into the characteristics of the homogeneous wetting front and channel size as well as estimate relevant time scales involved in the instability formation and the velocity of the channel finger tip. We compare our experimental results with that of the well-known prediction developed by Parlange and Hill [1976]. This model is based on linear stability analysis of the growth of perturbations arising at the interface between two immiscible fluids. Results show that in terms of morphology, experiments agree with the proposed model. However, in terms of kinetics we nevertheless account for another term that describes the homogenization of the wetting front. This result shows that the manner we introduce the fluid to a porous medium can also influence the formation of finger instabilities.Comment: 13 pages, 7 figure