Plane-symmetric inhomogeneous magnetized viscous fluid universe with a variable Λ\Lambda

The behavior of magnetic field in plane symmetric inhomogeneous cosmological models for bulk viscous distribution is investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density $(\xi =\xi_{0}\rho^{n})$. The values of cosmological constant for these models are found to be small and positive which are supported by the results from recent supernovae Ia observations. Some physical and geometric aspects of the models are also discussed.Comment: 18 pages, LaTex, no figur

Atmospheric trends and radiative forcings of CF4 and C2F6 inferred from firn air.

The atmospheric histories of two potent greenhouse gases, tetrafluoromethane (CF4) and hexafluoroethane (C2F6), have been reconstructed for the 20th century based on firn air measurements from both hemispheres. The reconstructed atmospheric trends show that the mixing ratios of both CF4 and C2F6 have increased during the 20th century by factors of similar to 2 and similar to 10, respectively. Initially, the increasing mixing ratios coincided with the rise in primary aluminum production. However, a slower atmospheric growth rate for CF4 appears to be evident during the 1990s, which supports recent aluminum industry reports of reduced CF4 emissions. This work illustrates the changing relationship between CF4 and C2F6 that is likely to be largely the result of both reduced emissions from the aluminum industry and faster growing emissions of C2F6 from the semiconductor industry. Measurements of C2F6 in the older firn air indicate a natural background mixing ratio of < 0.3 parts per trillion (ppt), demonstrating that natural sources of this gas are negligible. However, CF4 was deduced to have a preindustrial mixing ratio of 34 +/- 1 ppt (similar to 50% of contemporary levels). This is in good agreement with the previous work of Harnisch et al. (18) and provides independent confirmation of their results. As a result of the large global warming potentials of CF4 and C2F6, these results have important implications for radiative forcing calculations. The radiative forcings of CF4 and C2F6 are shown to have increased over the past 50 years to values in 2001 of 4.1 x 10(-3) Wm(-2) and 7.5 x 10(-4) Wm(-2), respectively, relative to preindustrial concentra tions. These forcings are small compared to present day forcings due to the major greenhouse gases but, if the current trends continue, they will continue to increase since both gases have essentially infinite lifetimes. There is, therefore, a large incentive to reduce perfluorocarbon emissions such that, through the implementation of the Kyoto Protocol, the atmospheric growth rates may decline in the future

A two-component regulatory system playing a critical role in plant pathogens and endosymbionts is present in Brucella abortus and controls cell invasion and virulence

Two mutants showing increased sensitivity to polycations and surfactants were obtained by transposon mutagenesis of virulent Brucella abortus 2308 Nal(r). These mutants showed no obvious in vitro growth defects and produced smooth-type lipopolysaccharides. However, they hardly multiplied or persisted in mouse spleens, displayed reduced invasiveness in macrophages and HeLa cells, lost the ability to inhibit lysosome fusion and were unable to replicate intracellularly. Subsequent DNA analyses identified a two-component regulatory system [Brucella virulence related (Bvr)] with a regulatory (BvrR) and sensory (BvrS) protein. Cloning on bvrR in the BvrR-deficient mutant restored the resistance to polycations and, in part, the invasiveness to polycations and, in part, the invasiveness and the ability to multiply intracellularly. BvrR and BvrS were highly similar (87-89% and 70-80% respectively) to the regulatory and sensory proteins of the chromosomally encoded Rhizobium meliloti Chvl-ExoS and Agrobacterium tumefaciens Chvl-ChvG systems previously shown to be critical for endosymbiosis and pathogenicity in plants. Divergence among the three sensory proteins was located mostly within a periplasmic domain probably involved in stimulus sensing. As B. abortus, R. meliloti and A. tumefaciens are phylogenetically related, these observations suggest that these systems have a common ancestor that has evolved to sense stimuli in plant and animal microbial environments.Dos mutantes que muestran una mayor sensibilidad a los policationes y a los tensioactivos se obtuvieron por mutagénesis de transposones de la Brucella abortus 2308 Nal(r) virulenta. Estos mutantes no mostraron defectos evidentes de crecimiento in vitro y produjeron lipopolisacáridos de tipo suave. Sin embargo, apenas se multiplicaron o persistieron en el bazo de los ratones, mostraron una menor capacidad de invasión en macrófagos y células HeLa, perdieron la capacidad de inhibir la fusión de lisosomas y fueron incapaces de replicarse intracelularmente. Los análisis posteriores del ADN identificaron un sistema regulador de dos componentes [Brucella virulence related (Bvr)] con una proteína reguladora (BvrR) y otra sensorial (BvrS). La clonación en bvrR en el mutante deficiente en BvrR restauró la resistencia a los policationes y, en parte, la capacidad de invasión a los policationes y, en parte, la capacidad de invasión y de multiplicación intracelular. BvrR y BvrS eran muy similares (87-89% y 70-80% respectivamente) a las proteínas reguladoras y sensoriales de los sistemas Rhizobium meliloti Chvl-ExoS y Agrobacterium tumefaciens Chvl-ChvG codificados cromosómicamente, que habían demostrado ser críticos para la endosimbiosis y la patogenicidad en las plantas. La divergencia entre las tres proteínas sensoriales se localizó sobre todo en un dominio periplásmico probablemente implicado en la detección de estímulos. Dado que B. abortus, R. meliloti y A. tumefaciens están filogenéticamente relacionados, estas observaciones sugieren que estos sistemas tienen un ancestro común que ha evolucionado para percibir estímulos en entornos microbianos vegetales y animales.Universidad Nacional, Costa RicaEscuela de Medicina Veterinari