113 research outputs found
Indirect measurement of the magnetocaloric effect using a novel differential scanning calorimeter with magnetic field
Curli
are bacterial appendages involved in the adhesion of cells
to surfaces; their synthesis is regulated by many genes such as <i>csgD</i> and <i>ompR</i>. The expression of the two
curli subunits (CsgA and CsgB) in <i>Escherichia coli</i> (<i>E. coli</i>) is regulated by CsgD; at the same time, <i>csgD</i> transcription is under the control of OmpR. Therefore,
both genes are involved in the control of curli production. In this
work, we elucidated the role of these genes in the nanomechanical
and adhesive properties of <i>E. coli</i> MG1655 (a laboratory
strain not expressing significant amount of curli) and its curli-producing
mutants overexpressing OmpR and CsgD, employing atomic force microscopy
(AFM). Nanomechanical analysis revealed that the expression of these
genes gave origin to cells with a lower Young’s modulus (<i>E</i>) and turgidity (<i>P</i><sub>0</sub>), whereas
the adhesion forces were unaffected when genes involved in curli formation
were expressed. AFM was also employed to study the primary structure
of the curli expressed through the freely jointed chain (FJC) model
for polymers. CsgD increased the number of curli on the surface more
than OmpR did, and the overexpression of both genes did not result
in a greater number of curli. Neither of the genes had an impact on
the structure (total length of the polymer and number and length of
Kuhn segments) of the curli. Our results further suggest that, despite
the widely assumed role of curli in cell adhesion, cell adhesion force
is also dictated by surface properties because no relation between
the number of curli expressed on the surface and cell adhesion was
found
Three Dimensional Polarimetric Neutron Tomography of Magnetic Fields
Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron
Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a
technique capable of measuring and reconstructing three dimensional magnetic
field strengths and directions unobtrusively and non-destructively with the
potential to probe the interior of bulk samples which is not amenable
otherwise.
Using a pioneering polarimetric set-up for ToF neutron instrumentation in
combination with a newly developed tailored reconstruction algorithm, the
magnetic field generated by a current carrying solenoid has been measured and
reconstructed, thereby providing the proof-of-principle of a technique able to
reveal hitherto unobtainable information on the magnetic fields in the bulk of
materials and devices, due to a high degree of penetration into many materials,
including metals, and the sensitivity of neutron polarisation to magnetic
fields. The technique puts the potential of the ToF time structure of pulsed
neutron sources to full use in order to optimise the recorded information
quality and reduce measurement time.Comment: 12 pages, 4 figure
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