Black hole lasers in Bose-Einstein condensates

We consider elongated condensates that cross twice the speed of sound. In the absence of periodic boundary conditions, the phonon spectrum possesses a discrete and finite set of complex frequency modes that induce a laser effect. This effect constitutes a dynamical instability and is due to the fact that the supersonic region acts as a resonant cavity. We numerically compute the complex frequencies and density-density correlation function. We obtain patterns with very specific signatures. In terms of the gravitational analogy, the flows we consider correspond to a pair of black hole and white hole horizons, and the laser effect can be conceived as a self-amplified Hawking radiation. This is verified by comparing the outgoing flux at early time with the standard black hole radiation.Comment: iopams, 37 pages, 14 figures, 1 table; for associated gif animations, see http://people.sissa.it/~finazzi/bec_bhlasers/movies/ or http://iopscience.iop.org/1367-2630/12/9/095015/media. Published on New. J. Phys. (http://iopscience.iop.org/1367-2630/12/9/095015/). V2: few new comments, modified figure

Impact of Crude Oil on Soil Nitrogen Dynamics and Up-take by Legumes Grown in Wetland Ultisol of the Niger Delta

Abstract The effects of crude oil on soil nitrogen dynamics and cycling in plant-soil ecosystems and its effect on the growth of legumes (Calopogonium mucunoides, Centrosema pubescens and Pueraria phaseolodes) grown in wetland ultisols were investigated. The test plants species were grown on wetland soil simulated with 0.35, 10.8, 20.5, and 50 g•kg −1 levels of crude oil contamination. The results showed time and species dependent variation in mineral N content of the treated soils. The variation is indicative of significant interaction between the hydrocarbon content and plant species. Variations in microbial N and microbial C were similar and correlation between the microbial N and the total C (Organic matter (C) + hydrocarbon content (C)) in soil was highly significant (r = 0.96, n = 12, P ≤ 0.01). The presence of hydrocarbon contaminant widens the C:N ratio in soil and leads to more available N being immobilized by soil microorganisms, which reduces available N for plant uptake. This result implies that crude oil contamination significantly reduces N uptake by plants but increases N accumulation in soil microbial biomass. The findings show that N dynamics, transformation and cycling in soil are influenced by hydrocarbons and that the interactions between hydrocarbon content and plant species in contaminated soil are remarkable. The use of plant Centrosema pubescens with poultry manure or NPK fertilizer for bioremediation is more effective than that of Calopogonium mucunoides and Pueraria phaseoloides. However, the selective attributes of the various treatment approaches adopted here may be exploited for enhanced remediation of contaminated wetlands in the Niger Delta region of Nigeria

Dynamics of fluctuations in an optical analog of the Laval nozzle

Using the analogy between the description of coherent light propagation in a medium with Kerr nonlinearity by means of nonlinear Schr\"odinger equation and that of a dissipationless liquid we propose an optical analogue of the Laval nozzle. The optical Laval nozzle will allow one to form a transonic flow in which one can observe and study a very unusual dynamics of classical and quantum fluctuations including analogue of the Hawking radiation of real black holes. Theoretical analysis of this dynamics is supported by numerical calculations and estimates for a possible experimental setup are presented.Comment: 7 pages, 4 figure

Crude Oil-Degradation and Plasmid Profile of Nitrifying Bacteria Isolated from Oil-Impacted Mangrove Sediment in the Niger Delta of Nigeria

The crude oil degradability and plasmid profile of autotrophic nitrifying bacteria, Nitrosomonas and Nitrobacter species, isolated from mangrove sediment in the Niger Delta of Nigeria were studied. The effects of temperature, pH and optical density on the utilization of different carbon sources by the bacteria were also investigated. Results showed that nitrifying bacteria could utilize kerosene, diesel oil, jet fuel and engine oil as carbon sources. None utilized hexane and xylene but moderate growth was observed in benzene, phenol and toluene. However, their ability to utilized crude oil varied both in rates of utilization and in growth profiles. Mixed culture of the isolates degrades 52 % of crude oil introduced into the medium followed by Nitrosomonas sp. with 40 % degradation. The least was Nitrobacter sp. with 20 % degradation. The ability of the autotrophs to degrade crude oil was found to be plasmid-mediated through curing experiment and electrophoresis. The size of the plasmid involved was estimated to be 23 kb. The high crude oil utilization of the mixed culture implies that nitrifying bacteria isolated from contaminated ecosystem are excellent crude oil degraders and can be harnessed for bioremediation purposes

Marine Tar Residues: a Review

Abstract Marine tar residues originate from natural and anthropogenic oil releases into the ocean environment and are formed after liquid petroleum is transformed by weathering, sedimentation, and other processes. Tar balls, tar mats, and tar patties are common examples of marine tar residues and can range in size from millimeters in diameter (tar balls) to several meters in length and width (tar mats). These residues can remain in the ocean envi-ronment indefinitely, decomposing or becoming buried in the sea floor. However, in many cases, they are transported ashore via currents and waves where they pose a concern to coastal recreation activities, the seafood industry and may have negative effects on wildlife. This review summarizes the current state of knowledge on marine tar residue formation, transport, degradation, and distribution. Methods of detection and removal of marine tar residues and their possible ecological effects are discussed, in addition to topics of marine tar research that warrant further investigation. Emphasis is placed on ben-thic tar residues, with a focus on the remnants of the Deepwater Horizon oil spill in particular, which are still affecting the northern Gulf of Mexico shores years after the leaking submarine well was capped

Influence of electrical conductivity on microorganisms and rate of crude oil mineralization in Niger Delta ultisol

The effect of salinity on the population density of hydrocarbonoclastic microorganisms and oil degradation in a tropical ultisol was determined. Soils were simulated with 50gkg-1 of Qua Iboe Light (QIL) crude oil. Salt treatments included NaCI amendments to adjust the soil solution electrical conductivities (EC) to 40, 120 and 200 dSm-1. Treated soils were incubated at 28OC. Oil degradation was estimated from the gravimetric determinations of remaining oil. The results showed that amending the ultisol with crude oil stimulated the growth of oil degrading microorganisms, while salt concentration inducing an EC of 200 dSm-1 in oil amended ultisol resulted in a decrease in the amount oil mineralized. A significant positive correlation was found between the number of hydrocarbonoclastic microorganisms and levels of oil mineralization at EC 40 dSm-1 (r = 0.980, P = 0.05) and EC 120 dSm-1 (r = 0.976. P = 0.05) except at EC 200 dSm-1 (r = 0.855, P = 0.05). This is an indication that desalting of soils contaminated with oil and salts is required for a speedy bioremediation of an ultisol. Key words: Electrical conductivity, crude oil, hydrocarbonoclastic microorganismineralization. (Global Journal of Pure and Applied Sciences: 2003 9(4): 475-480

Prevalence of enteropathogens and their association with diarrhea among children of food vendors in Uyo, Nigeria

A survey of enteropathogens (bacteria-parasite co-infections) was carried out among 370 children of food vendors in Uyo, Nigeria. Faecal samples (311 formed and 59 diarrhoeic stools) were screened for intestinal helminths using standard parasitological procedures. The prevalence of the parasites encountered was: Hookworm (49.5%); Ascaris lumbricoides (42.8%) Trichuris trichiura (24.9%); Strongyloides stercoralis (2.7%); Entamoeba histolytica (10.0%) and Giardia lamblia (7.8%). Bacteriological analyses of the diarrhoeic stolls revealed the following bacterial isolates: Campylobacter species, Shigella species, Escherichia coli, Salmonella typhi, Yersinia enterocolitica, Clostridium species, Aeromonas hydrophila and Vibrio species. A strong association between the bacterial isolates and protozoan parasites (Entamoeba histolytica and Giardian lamblia) in diarrhoeic stools was evident. There was no significant (X2 = 0.44; P > 0.05) difference between infection and sex. All infections declined gradually with age but it was not statistically significant (X2 = 6.17; P > 0.001). A significant relationship existed between infection and type of school attended by the children (X2 = 19.65; P < 0.05), source of water supply (X2 = 13.59; P < 0.05) and type of toilet facility used (X2 = 68.83; P < 0.01). Since children are veritable sources of food contamination, the enforcement of hygienic practices therefore becomes imperative. Keywords: parasites, bacteria, children, food vendors, diarrhea, Nigeria Mary Slessor Journal of Medicine Vol. 5(1), 2005: 11-2