RESUMO
AIM: To examine in a laboratory setting the efficacy of moderate to high strength magnetic fields, as a potential bacteriostatic stimulus, against Enterococcus faecalis, one of the causative agents for infection during root canal treatments. METHODOLOGY: Four different strengths (1, 2, 3 and 4 T) of the pulsed magnetic field (PMF) were applied in thirty repetitions to bacterial suspension. A pickup coil setup was used to measure the electromotive force induced inside the bacterial suspensions. The optical density (OD) was monitored over time (for 16 h 40 min) during the post-treatment period to assess bacterial growth. Along with the change in OD values, live/dead assay, membrane depolarization study, atomic force microscopy (AFM), scanning electron microscopy (SEM) and reactive oxygen species (ROS) assay on selected samples were studied to evaluate the effect of PMFs. All results were analysed using one-way ANOVA followed by post hoc Tukey test and considered significant at p < .05. Regression analysis (at a confidence of 95%, α = 0.05) was performed on the bacterial growth and membrane depolarization studies to determine progressive changes of the outcomes. RESULTS: The peak value of the induced electromotive force was recorded as 0.25 V, for the 4 T magnetic field pulse with a pulse width of 16 ms. There was a significant arrest of bacterial cell growth after an exposure to PMFs of 1 T, 3 T and 4 T (ANOVA score: F (4, 495) =395.180 at p = .05). The image-based qualitative results of the live/dead assay using fluorescence microscopy techniques indicated that an exposure to higher PMFs (3 T/ 4 T) induced a bacteriostatic effect in a longer post-exposure timescale. Evidence of altered membrane potential within the 2 h of exposure to 4 T PMF was supported by the incidence of elevated ROS. For the ROS assay, a significant difference occurred for 4 T exposed samples (ANOVA score: calculated F (1, 3) =20.2749 at p = .05). SEM and AFM observations corroborated with the outcomes, by portraying significant membrane damage. CONCLUSION: In a laboratory setting, PMFs with higher magnitudes (3 T and 4 T) were capable of inducing bacteriostatic effects on E. faecalis.
Assuntos
Biofilmes , Enterococcus faecalis , Campos Magnéticos , Microscopia Eletrônica de VarreduraRESUMO
The hexatic fluid refers to a phase in between a solid and a liquid that has short-range positional order but quasi-long-range orientational order. In the celebrated theory of Berezinskii, Kosterlitz, and Thouless and subsequently refined by Halperin, Nelson, and Young, it was predicted that a two-dimensional hexagonal solid can melt in two steps: first, through a transformation from a solid to a hexatic fluid, which retains quasi-long-range orientational order; and then from a hexatic fluid to an isotropic liquid. In this Letter, using a combination of real space imaging and transport measurements, we show that the two-dimensional vortex lattice in an a-MoGe thin film follows this sequence of melting as the magnetic field is increased. Identifying the signatures of various transitions on the bulk transport properties of the superconductor, we construct a vortex phase diagram for a two-dimensional superconductor.
RESUMO
Controlled waveform magnets (CWMs) are a class of pulsed magnets whose pulse shape with time can be programmed by the user. With a CWM, the user gains control not only over the magnitude of the field but also over its rate of change. In this work we present a table-top CWM, driven by a capacitor bank, capable of producing virtually any user-shaped magnetic field waveform up to 10 tesla. Insulated gate bipolar transistor chips have been paralleled to form the high current switch and paralleled chips of SiC Schottky diodes form the crowbar diode module. Sample controlled waveforms including flat-tops up to 10 tesla and some triangular magnetic field pulses have been successfully generated for 10-20 ms with a ripple <1%.
