ALBERT

Description: Convective heat transfer characteristics of microencapsulated phase change material slurries (MPCSs) flowing in a circular tube under constant heat flux are studied and a feasible heat transfer model is presented. The heat transfer coefficient of MPCS and the wall temperature of the circular tube are simulated. The simulation results agree qualitatively with the experimental results. The effects of Stefan (Ste) number, mass concentration, phase change temperature range, and Reynolds (Re) number on heat transfer characteristics are discussed. The results indicate that the Ste-number and mass fraction are the most important parameters influencing heat transfer properties compared to the phase change temperature range and Re-number which less affect these characteristics. The heat transfer characteristics of microencapsulated phase change slurries are analyzed and the effects of Stefan number, mass concentration, and Reynolds number are discussed. The phase change process, Stefan number, and mass fraction influence these heat transfer characteristics significantly. The heat transfer coefficient increases with higher Reynolds numbers.

Description: Convective heat transfer characteristics of microencapsulated phase change material slurries (MPCSs) flowing in a circular tube under constant heat flux are studied and a feasible heat transfer model is presented. The heat transfer coefficient of MPCS and the wall temperature of the circular tube are simulated. The simulation results agree qualitatively with the experimental results. The effects of Stefan (Ste) number, mass concentration, phase change temperature range, and Reynolds (Re) number on heat transfer characteristics are discussed. The results indicate that the Ste-number and mass fraction are the most important parameters influencing heat transfer properties compared to the phase change temperature range and Re-number which less affect these characteristics. The heat transfer characteristics of microencapsulated phase change slurries are analyzed and the effects of Stefan number, mass concentration, and Reynolds number are discussed. The phase change process, Stefan number, and mass fraction influence these heat transfer characteristics significantly. The heat transfer coefficient increases with higher Reynolds numbers.

Description: The AGILE satellite detects Terrestrial Gamma-ray Flashes (TGFs) in the 0.35–100 MeV energy range using its Mini-Calorimeter (MCAL) instrument with an average detection rate of 10 TGFs/month. Thanks to its Low Earth Orbit with only 2.5 degree of inclination, AGILE guarantees an unprecedented exposure above the equator, where both lightning activity and TGF detection peak. Here we report the comparison between the AGILE TGFs detected between March 2009 and February 2010 and full climatology lightning worldwide distribution based on satellite optical observations from LIS (Lightning Imaging Sensor) and OTD (Optical Transient Detector) instruments. This approach is complementary to the one-to-one TGF/lightning correlations by ground-based sferics measurements. Based on mono and bi-dimensional Kolmogorov-Smirnov tests, we show that the AGILE TGFs and time-averaged global lightning in the equatorial area are not drawn from the same distribution. However, we find significant regional differences in the degree of correlation as well as in the TGF/lightning ratio. In the case of south east Asia we find a 87% probability for the TGF and lightning being samples of the same distribution. This result supports the idea that the physical conditions at play in TGF generation can have strong geographical and climatological modulation. Based on the assumption that the observed range of TGF/flash ratio holds at all latitudes we can estimate a global rate of $\dot{N}$ $\simeq$ 220 ÷ 570 TGFs per day. The observed TGF/flash geographical modulation as well as the TGF global rate estimate are in agreement with previous observations.

Description: The ecological situation of the Tarim River basin in China seriously declined since the early 1950's, mainly due to a strong increase in water abstraction for irrigation purposes. In order to restore the ecological system and support sustainable development of the Tarim River basin region in China, more hydrological studies are demanded to properly understand the processes of the watershed and efficiently manage the water resources. Such studies are, however, complicated due to the limited data availability, especially in the mountainous headwater regions of the Tarim River basin. This study investigated the usefulness of remote sensing (RS) data in order to overcome that lack of data in the spatially distributed hydrological modelling of the basin. Complementary to the conventional station based (SB) data, the RS products that are directly used in this study include precipitation, evapotranspiration and leaf area index (LAI). They are derived from raw image data of the Chinese Fengyun meteorological satellite and from the Moderate Resolution Imaging Spectroradiometer (MODIS). The MODIS land surface temperature was used to calculate the atmospheric temperature lapse rate to describe the temperature dependency on topographical variations. Moreover, MODIS based snow cover images were used to obtain model initial conditions and as validation reference for the snow model component. Comparison of model results based on RS input versus conventional SB input exhibited similar results in terms of high and low river runoff extremes, cumulative runoff volumes in both runoff and snow melting seasons, and spatial and temporal variability of snow cover. During summer time, when the snow cover shrinks in the permanent glacier region, it was found that the model resolution influences the model results dramatically; hence showing the importance of detailed (RS based) spatially distributed input data. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Three-dimensional simulations of bubble formation in Newtonian and non-Newtonian fluids through a microchannel T-junction are conducted by the volume-of-fluid method. For Newtonian fluids, the critical capillary number Ca for the transition of the bubble breakup mechanism is dependent on the velocity ratio between the two phases and the microchannel dimension. For the power law fluid, the bubble diameter decreases and the generation frequency increases with higher viscosity parameter K and power law index n . For a Bingham fluid, the viscous force plays a more important role in microbubble formation. Due to the yield stress τ y , a high-viscous region is developed in the central area of the channel and bubbles deform to a flat ellipsoid shape in this region. The bubble diameter and generation frequency are almost independent of K . Microbubbles are an important part of chemical and biomedical engineering. Three-dimensional simulations of bubble generation in both Newtonian and non-Newtonian fluids were performed in a microchannel T-junction by the volume-of-fluid model. The influences of viscosity parameter K , power law index n , and yield stress τ y on the bubble breakup mechanism, shape, size, and generation frequency were investigated.

Description: Natural ecosystems in the region of the lower Tarim river in northwestern China, strongly deteriorated since the 1950s due to an expanding desertification. As a result, the downstream Tarim river reaches became permanently dry land. This historical evolution in land-use change is typically the result of the anthropogenic impact on natural ecosystems. Based on a spatially distributed hydrological catchment model bi-directionally linked with a fully hydrodynamic MIKE11 river model, land-use changes characterized by historical changes in leaf area index (LAI) of vegetation as well as the evolution of irrigated surface areas, can be causally related to changes in water resources (groundwater storage and surface water resources). An increased surface area of irrigated (agricultural) land together with a majority of inefficient irrigation methods, did lead to a strong increase of water resources consumption of the farmlands located in the upper Tarim river area. Evidently, this evolution influenced available water resources downstream in the Tarim basin. As a result, farmland has been gradually relocated to the upstream regions. This has led to reduced flows from the upper Tarim stream, which subsequently accelerated the dropping of the groundwater level downstream in the basin. This study moreover demonstrates that land surface biomass changes (cumulative LAI) along the lower Tarim river are strongly related to the changes in groundwater storage. Copyright © 2012 John Wiley & Sons, Ltd.

Description: [1]  For solar minimum, the spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly (EIA) are simultaneously analyzed to investigate F-region irregularities for the first time. The data were observed by the Chungli ionosonde, YMSM GPS receiver, and DMSP satellites during 1996. It is found that in the observed ionograms, the frequency spread F (FSF) usually comes after the range spread F (RSF) in a series of nighttime spread F events. This results in that the maximum occurrence of RSF appears before that of FSF in the nighttime variations in occurrence probabilities. Moreover, the seasonal variation for RSF is close to that for FSF. Both have a board maximum in the J-months and a secondary maximum in December. These indicate that RSF and FSF should be regarded as one type of spread F, which is the all spread F (ASF) in this study. Because the equatorial plasma bubbles occur infrequently during solar minimum, the F-region irregularities forming ASF are not related to the equatorial spread F. On the other hand, the similarity in seasonal occurrence between ASF and medium-scale traveling ionospheric disturbances (MSTIDs) demonstrates that the F-region irregularities near the EIA crest are mainly generated by the gradient drift instability driven by MSTIDs. The irregularities, generated by MSTIDs, mostly occur in the bottomside of F-region. Consequently, the events of significant GPS phase fluctuations and plasma bubble near the EIA crest are rare during 1996.

Description: Whistler waves that can produce anomalous resistivity by affecting electrons’ motion have been suggested as one of the mechanisms responsible for magnetic reconnection in the electron diffusion region (EDR). Such type of waves, however, has rarely been observed inside the EDR so far. In this study, we report such an observation by Magnetospheric Multiscale (MMS) mission. We find large-amplitude whistler waves propagating away from the X line with a very small wave-normal angle. These waves are probably generated by the perpendicular temperature anisotropy of the ~300 eV electrons inside the EDR, according to our analysis of dispersion relation and cyclotron-resonance condition; they significantly affect the electron-scale dynamics of magnetic reconnection, and thus support previous simulations.

Description: Knowledge of the rock types and pressure-temperature conditions at crustal depths in an active orogeny is key to understanding the mechanism of mountain building and its associated modern deformation, erosion and earthquakes. Seismic-wave velocities by themselves generally do not have the sensitivity to discriminate one rock type from another or to decipher the P-T conditions at which they exist. But laboratory-measured ratios of velocities of P to S waves (Vp/Vs) have been shown to be effective. Results of 3-D Vp and Vp/Vs tomographic imaging based on dense seismic arrays in the highly seismic environment of Taiwan provides the first detailed Vp/Vs structures of the orogen. The sharp reduction in the observed Vp/Vs ratio in the felsic core of the mountain belts implies that the α-β quartz transition temperature is reached at a mean depth of 24 ± 3 km. The transition temperature is estimated to be 750 ± 25°C at this depth, yielding an average thermal gradient of 30 ± 3°C/km.