Magmatic sill formation during dike opening

The origin of horizontal magma-filled sills is disputed, particularly for extensional settings where the opening of vertical dikes is the predicted mode of magma intrusion. We simulate long-term extension followed by short-term dike opening in a two-dimensional viscoelastic medium representing a plate spreading center. We show that dike opening in extensionally stressed lithosphere can reduce sublithospheric vertical stresses enough for sill opening given three conditions: (1) the Maxwell time of the asthenosphere is <5× the time interval between dike episodes; (2) the average density of the lithosphere is not much greater than the magma density; and (3) the depth of an axial valley is smaller than a few hundred meters. This mechanism explains the presence of sills along much of the axis of faster-spreading ridges and their absence along slower-spreading centers where thick dense lithosphere and/or sizeable axial valleys exist.

Seismicity trends and detachment fault structure at 13°N, Mid-Atlantic Ridge

At slow-spreading ridges, plate separation is commonly partly accommodated by slip on long-lived detachment faults, exposing upper mantle and lower crustal rocks on the seafloor. However, the mechanics of this process, the subsurface structure, and the interaction of these faults remain largely unknown. We report the results of a network of 56 ocean-bottom seismographs (OBSs), deployed in 2016 at the Mid-Atlantic Ridge near 13°N, that provided dense spatial coverage of two adjacent detachment faults and the intervening ridge axis. Although both detachments exhibited high levels of seismicity, they are separated by an ~8-km-wide aseismic zone, indicating that they are mechanically decoupled. A linear band of seismic activity, possibly indicating magmatism, crosscuts the 13°30′N domed detachment surface, confirming previous evidence for fault abandonment. Farther south, where the 2016 OBS network spatially overlapped with a similar survey done in 2014, significant changes in the patterns of seismicity between these surveys are observed. These changes suggest that oceanic detachments undergo previously unobserved cycles of stress accumulation and release as plate spreading is accommodated.

Campylobacter contamination level in houseflies after exposure to materials containing Campylobacter

Although houseflies have been found to carry Campylobacter jejuni, little is known about the quantitative campylobacter level in naturally contaminated houseflies and their ability to contaminate surfaces. This study aimed to elucidate how houseflies’ previous exposure to campylobacter-contaminated material (faeces or liquid) for 1 or 4 h affects the acquired campylobacter level in houseflies and their contamination potential. Cups of 250 ml were added 5 g of chicken faeces or 1 ml liquid and spiked with approximately 3, 4, 5 or 7 log10 cfu C. jejuni. Sixteen houseflies were added to each cup. After 1 h of exposure, four houseflies were removed from the cup for enumeration of campylobacter in each fly by plate spreading. Another four houseflies were transferred onto Abeyta-Hunt-Bark (AHB) agar plates (9 cm) to assess possible contamination of surfaces. After 1 h on the AHB plate, each fly was tested for level of campylobacter. This procedure was repeated after approx. 4 h of exposure for the remaining eight houseflies. The C. jejuni acquisition in houseflies increased with exposure dose and was higher after liquid exposure compared with faeces exposure, while there was no significant effect of exposure time (1 vs 4 h). For faeces, 90.0% (n=80), 48.4% (n=64), 6.3% (n=48) and 0% (n=16) of houseflies were campylobacter-positive when exposed to 7, 5, 4, and 3 log10 cfu with a mean (±SE) of 2.0±0.1, 0.8±0.1, 0.3±0.0 and 0 log10 cfu recovered per campylobacter-positive fly, respectively. For liquid, 95.7% (n=47), 91.4% (n=47), 20.8% (n=48) and 6.3% (n=16) of houseflies were campylobacter-positive with a mean of 3.3±0.2, 2.0±0.1, 0.8±0.2 and 0.3±0.0 log10 cfu. The surface of the AHB plates was only contaminated by houseflies previously exposed to >4 log10, but the C. jejuni number found on the AHB surface did not correlate with the number found in the corresponding fly.

Effects of green algae, Chlorella Vulgaris, extracts and its bioactive substances on the biofilm-producing microorganism

The current study aims at the in-vitro use of 2 types of extracts of Chlorella Vulgaris, one of the most widely known green algae species in the world, to evaluate their effects on biofilm-producing bacteria. In this study, 7 species of algae were isolated from different environments and then diagnosed according to the sources of green algae and greenish algae. Some of these isolates were proliferated under constant laboratory conditions at 25±2 ̊C, 200μm/m2/sec, and 8:16 hours of light: dark using fixed farms. Then, these species were subjected to 2 types of polycarbonate-based solvents (hexane and chloroform). These extracts were tested on E.Coli, Klebsiella, Acinetobacter, Serratia mesccens, St epidermis, S. aureus, Candida albicans, and Aspergills niger. Using different methods of measuring turbidity of the red agar, micrometer plate, spreading Balacar, the effects of these extracts were examined on these microorganisms. Then, the algae were subjected to vertical chromatography to separate active substances. The hexane-based extract was more effective against E. coli, Acinetobacter, St. aureus. On the other hand, the chloroform-based extract showed slight effects on Acinetobacter and C. albicans. The best inhibitory activities were 30mm for Staphylococcus aureus and Serratia and 25mm for E. coli. The lowest inhibition activity was 15mm for Klebsiella and C. albicans. For the chloroform-based extract, the highest rate of inhibition was 20mm for Klebsiella and S. aureus. The lowest inhibition was 10mm for Acinetobacter and C. albicans. Separation method targeted the hexane-based extraction yielded hxan, gasoline group III ethyl estate, gasoline, group IV ethyl ester, methanol group, and methanol. The hexane + 25 ml of benzene and the fourth group of ethyl ester 25 + methanol showed higher inhibition activities against microbes than that using the other three groups. The hexane-based extracts and the related hexane + 25 ml of benzene and the fourth group of ethyl ester 25 + methanol of C. vulgaris were better than the chloroform-based extracts in their effectiveness against the studied microbes using the turbidity measurement method. Keywords: Biofilm; Chlorella Vulgaris; Extract effects; Microorganisms