Role Of Conductivity Spatial Structure In Determining The Locations Of Sprite Initiation

Thesis (Ph.D.) University of Alaska Fairbanks, 2003Sprites are transient optical signatures of mesospheric electrical breakdown in response to lightning discharges. Multiple sprites are often observed to occur simultaneously, laterally displaced from the underlying causative cloud-to-ground (CG) lightning discharge. The causes of this lateral displacement are presently not understood. This dissertation investigates the role of neutral density perturbations in determining the locations of sprite initiation. The work was performed in three interrelated studies. (1) A detailed statistical study of the temporal-spatial relationships between sprites and the associated CG was performed for July 22, 1996. The distribution of sprite offsets relative to the underlying lightning had a mean of ~40 km. The distribution of sprite onset delays following the parent lightning had a mean of ~20--30 ms, consistent with theoretical estimates for the electron avalanche-to-streamer transition in the mesosphere. (2) A follow-up study for the same observations was performed to investigate the relationship of the sprites to convective activity in the underlying thunderstorm, using GOES-8 infrared imagery of cloud-top temperatures. The sprite generating thunderstorm was a Mesoscale Convective System (MCS). The maximum sprite and -CG production of the system were simultaneously reached at the time of maximum contiguous cloud cover of the coldest region, corresponding to the period of greatest convective activity of the system. Thunderstorm convective activity is a potential source of gravity waves and mesospheric turbulence. (3) Computer simulations of the temporal-spatial evolution of lightning-induced electric fields in a turbulent upper atmosphere were performed. The modeled turbulence in the simulations spanned the amplitude range 10% to 40% of the ambient background neutral density, with characteristic scale sizes of 2 km and 5 km, respectively. The results indicate that neutral density spatial structure, similar to observed turbulence in the mesosphere, facilitates electrical breakdown in isolated regions of density depletions at sprite initiation altitudes. These spatially distributed breakdown regions provide the seed electrons necessary for sprite generation, and may account for the observed sprite offsets

Donor funding and crowding out of public spending: Evidence from low and middle-income countries

In many low-resource settings agricultural output and public spending on agriculture are in decline, raising questions about the effectiveness of agricultural aid. To understand why these trends are occurring, we examined factors that affect the share of government spending on agriculture. Using a sample of 66 low- and middle-income countries from 1996-2010 we use dynamic panel regression models to explore: (1) the impact of agricultural aid on public expenditure to agriculture, and (2) the impact of aid on domestic resource mobilisation, which indirectly affects public expenditures. Our results provide evidence of a strong substitution effect, especially in low-income countries, suggesting aid to agriculture is treated as fungible. We also found evidence that aid loans resulted in higher tax revenues, while aid grants decreased tax effort, which may account for decreasing public investment in agriculture. To improve aid effectiveness, donors need to work with recipients to understand country needs and the fiscal environment of the receiving government

Type-4 spinors: transmuting from Elko to single-helicity spinors

In this communication we briefly report an unexpected theoretical discovery which emerge from the mapping of Elko mass-dimension-one spinors into single helicity spinors. Such procedure unveils a class of spinor which is classified as type-4 spinor field within Lounesto classification. In this paper we explore the underlying physical and mathematical contents of the type-4 spinor.Comment: 9 pages, 0 figure

Analytical development of bird pecking force equation for a self-metering poultry feeder

The concept of a self-metering poultry feeder was developed.  The theoretical analysis of the forces involved in its operation was done and a generalized pecking force model was developed.  Mathematical expressions, logical assumptions, graphical relations and models as well as statistical analyses were adopted in the pecking force analysis. This pecking force relates to some design parameters like feed flow rate, hopper aperture, etc. The generalized equation was tested using a fabricated model of the equipment.  Experimental results show that the equation can be used to predict the performance of the machine reasonably and also the level of satiety and bird vigor determine the amount of pecking force which was described by a polynomial regression relationship (of the 4th order with R2 > 0.9) which increases with increasing aperture opening with time of feeding by different ages of birds. The pecking force reached 10N for <8 weeks birds after about 40 minutes for the highest aperture opening. For the three sample categories of birds, the pecking force was consistently lower with the smallest aperture Ca1 and highest with aperture Ca3. Quantity of feed consumed decreased with feeding time in a power regression relationship and the birds, irrespective of the ages had a feel of satiety after 50 minutes of feeding with feed consumed being less than 0.1g. The general performance of each category of bird is a function of their age and number, vigor and pecking action

Inventorying of herbal remedies used to control small ruminant’s parasites in Southern Benin

A botanical survey was undertaken in two agro-ecological zones of southern Benin, aiming inventorying the plants used by farmers as antiparasitic remedies in small ruminants. In total, 253 smallholders of livestock have been sampled throughout 90 villages and underwent a structured interview. The result revealed that 20% of interviewed people use indigenous knowledge based on plants. Twenty two plants of 18 families have been cited as effective remedies to parasitic diseases of small ruminants. Xanthoxylum zanthoxyloides (Rutaceae) and Carica papaya (Caricaceae) were the most frequently cited(75% of plants users) followed by Spondias mombin (Anacardiaceae) and Moringa oleifera (Moringaceae). Leaves were the most frequently plant organ generally used in infusion (100%). Farmers think this medication is effective. Though widely reported, the effectiveness of these recipes still belongs to empirical knowledge awaiting proof

Dosimetric differences between cesium-131 and iodine-125 brachytherapy for the treatment of resected brain metastases

Purpose: To compare treatment plans and evaluate dosimetric characteristics of permanent cesium-131 (131Cs) vs. iodine-125 (125I) implants used in brain brachytherapy. Material and methods: Twenty-four patients with 131Cs implants from a prospective phase I/II trial were re-planned with 125I implants. In order to evaluate the volume of brain tissue exposed to radiation therapy (RT), the dose volume histogram was generated for both radioisotopes. To evaluate the dosimetric differences of the two radioisotopes we compared homogeneity (HI) and conformity indices (CI), and dose covering 100% (D100), 90% (D90), 80% (D80), and 50% (D50) of the clinical target volume (CTV). Results: At the 100%, 90%, 80%, and 50% isodose lines, the 131Cs plans exposed less mean volume of brain tissue than the 125I plans (p \u3c 0.001). The D100, D90, D80, and D50 were smaller for 131Cs (p \u3c 0.001). The HI and CI for 131Cs vs. 125I were 19.71 vs. 29.04 and 1.31 vs. 1.92, respectively (p \u3c 0.001). Conclusions: Compared to 125I, 131Cs exposed smaller volumes of brain tissue to equivalent doses of radiation and delivered lower radiation doses to equivalent volumes of the CTV. 131Cs exhibited a higher HI, indicating increased uniformity of doses within the CTV. Lastly, 131Cs presented a CI closer to 1, indicating that the total volume receiving the prescription dose was closer to the desired CTV volume. These results suggest that 131Cs is dosimetrically superior to 125I and may explain the reason for the 0% incidence of radiation necrosis (RN) in our previously published prospective study using 131Cs

Stomach fluke infection in sahelian and West African dwarf small ruminants in Benin

A cross-sectional study was carried out between December 2010 and November 2011 in order to determine the prevalence and the variation factors of the stomach fluke infection in small ruminants of Benin. The paunch and the honeycomb (rumen-reticulum) of 366 sheep and 390 goats of West African Dwarf (WAD) or Sahelian breeds were selected from the two major agro-climatic areas of the country (Northern area and Southern area) and examined.  The results showed an overall prevalence of 14.3% (108 infected subjects out of 756 examined) with 9 to 315 flukes per infected animal. Frequency and intensity of infections have been significantly (p <0.001) higher in wet seasons (27.35%) than in dries (3.61%). Three other associated factors (species, breed and origin) influenced notably (p<0.01) the infection rates. Then, the highest rate (26.06%) was recorded with Sahelian sheep followed by Sahelian goats (16.29%), WAD sheep (9.09%) and WAD goats (6.54%). Northern areas appeared as a favourable environment for the infection

Simultaneous observations of equatorial F-region plasma depletions over Brazil during the Spread-F Experiment (SpreadFEx)

From September to November 2005, the NASA Living with a Star program supported the Spread-F Experiment campaign (SpreadFEx) in Brazil to study the effects of convectively generated gravity waves on the ionosphere and their role in seeding Rayleigh-Taylor instabilities, and associated equatorial plasma bubbles. Several US and Brazilian institutes deployed a broad range of instruments (all-sky imagers, digisondes, photometers, meteor/VHF radars, GPS receivers) covering a large area of Brazil. The campaign was divided in two observational phases centered on the September and October new moon periods. During these periods, an Utah State University (USU) all-sky CCD imager operated at São João d'Aliança (14.8° S, 47.6° W), near Brasilia, and a Brazilian all-sky CCD imager located at Cariri (7.4° S, 36° W), observed simultaneously the evolution of the ionospheric bubbles in the OI (630 nm) emission and the mesospheric gravity wave field. The two sites had approximately the same magnetic latitude (9–10° S) but were separated in longitude by ~1500 km. <br><br> Plasma bubbles were observed on every clear night (17 from Brasilia and 19 from Cariri, with 8 coincident nights). These joint datasets provided important information for characterizing the ionospheric depletions during the campaign and to perform a novel longitudinal investigation of their variability. Measurements of the drift velocities at both sites are in good agreement with previous studies, however, the overlapping fields of view revealed significant differences in the occurrence and structure of the plasma bubbles, providing new evidence for localized generation. This paper summarizes the observed bubble characteristics important for related investigations of their seeding mechanisms associated with gravity wave activity

Observations of the relationship between sprite morphology and in-cloud lightning processes

[1] During a thunderstorm on 23 July 2003, 15 sprites were captured by a LLTV camera mounted at the observatory on Pic du Midi in the French Pyrénées. Simultaneous observations of cloud-to-ground (CG) and intracloud (IC) lightning activity from two independent lightning detection systems and a broadband ELF/VLF receiver allow a detailed study of the relationship between electrical activity in a thunderstorm and the sprites generated in the mesosphere above. Results suggest that positive CG and IC lightning differ for the two types of sprites most frequently observed, the carrot- and column-shaped sprites. Column sprites occur after a short delay (<30 ms) from the causative +CG and are associated with little VHF activity, suggesting no direct IC action on the charge transfer process. On the other hand, carrot sprites are delayed up to about 200 ms relative to their causative +CG stroke and are accompanied by a burst of VHF activity starting 25–75 ms before the CG stroke. While column sprites associate with short-lasting (less than 30 ms) ELF/VLF sferics, carrot sprites associate with bursts of sferics initiating at the time of the causative +CG discharge and persisting for 50 to 250 ms, indicating extensive in-cloud activity. One carrot event was found to be preceded by vigorous IC activity and a strong, long-lived cluster of ELF/VLF sferics but lacking a +CG. The observations of ELF/VLF sferic clusters associated with lightning and sprites form the basis for a discussion of the reliability of lightning detection systems based on VHF interferometry.Peer ReviewedPostprint (published version