The structure of water films on mica was locally
modified by contact with the tip of an atomic force
microscope
(AFM) in a humid environment. The subsequent evolution of the film
was studied by noncontact scanning
polarization force microscopy. At high relative humidity (>20%),
capillary condensation caused water to
form droplets and two-dimensional islands around the contact point.
The droplets evaporated in a short
period of time, but the islands remained for much longer periods
(hours). At low relative humidity (<20%),
the tip contact produced a circular depression in the local
polarizability. None of these structures could be
observed in contact AFM images which revealed only the usual atomically
flat mica surface.
Potassium mica was treated with different ionic solutions to replace the naturally occurring K+ on the
surface by Ca2+, Mg2+, and H+ ions. The extent of the exchange was monitored by variable emergence
angle X-ray photoelectron spectroscopy (XPS). Scanning polarization force microscopy (SPFM) was used
to measure the mobility of the surface ions as a result of water adsorption when the mica is exposed to
different humidity levels.
Low
cost, safety, and environmental benignity make rechargeable
aqueous Zn/MnO2 batteries promising candidates for large-scale
energy storage. However, the synthesis of MnO2 with excellent
electrochemical performance is limited to the traditional hydrothermal
method, which is difficult to scale up for mass production. Herein,
a ball-milling approach is developed to rapidly obtain Mn3O4 nanoparticles in large quantity. As the cathode material
of aqueous zinc ion battery, Mn3O4 gradually
transforms to ε-MnO2 in 1 M ZnSO4 + 1
M MnSO4 aqueous electrolyte with increasing cycles. Benefiting
from the unexpected phase transition from Mn3O4 to ε-MnO2, the cathode delivers a specific capacity
of 221 mAh g–1 at a current density of 100 mA g–1 and a good long-term cyclic stability over 500 cycles
with 92% capacity retention at a high rate of 500 mA g–1. The excellent battery performance combined with the cost-effective
preparation procedure, the good safety of aqueous mild electrolyte,
and the easy cell assembly are believed to promote the practical use
of the Zn/MnO2 battery in large-scale energy storage.
Key Points• Fev is required for endothelium-based HSC emergence.• Fev directly regulates ERK signaling to regulate HSC development cellautonomously.Reprogramming of somatic cells to desired cell types holds great promise in regenerative medicine. However, production of transplantable hematopoietic stem cells (HSCs) in vitro by defined factors has not yet been achieved. Therefore, it is critical to fully understand the molecular mechanisms of HSC development in vivo. Here, we show that Fev, an ETS transcription factor, is a pivotal regulator of HSC development in vertebrates. In fevdeficient zebrafish embryos, the first definitive HSC population was compromised and fewer T cells were found in the thymus. Genetic and chemical analyses support a mechanism whereby Fev regulates HSC through direct regulation of ERK signaling. Blastula transplant assay demonstrates that Fev regulation of HSC development is cell autonomous. Experiments performed with purified cord blood show that fev is expressed and functions in primitive HSCs in humans, indicating its conserved role in higher vertebrates. Our data indicate that Fev-ERK signaling is essential for hemogenic endothelium-based HSC development. (Blood. 2013;122(3):367-375)
Friction Force Microscopy studies on ion-exchanged mica
surfaces at different humidity levels were
performed. Ion exchange was achieved by treating the potassium
mica (muscovite) in different solutions
to replace K+ surface ions by Ca2+,
Mg2+, and H+. It is found that these
different surface ions can significantly
modify the tribological properties of mica.
The wetting properties of 8CB ( 4(')-n-octyl-4-cyanobiphenyl) on silicon wafers have been studied with scanning polarization force microscopy (SPFM). Layer-by-layer spreading of 8CB droplets is observed. With the help of the surface potential mapping capability of SPFM, we found that the molecular dipole of the first monolayer of 8CB is parallel to the surface. A layer of nearly vertical molecular dimers on top of the monolayer has an associated surface potential of 40 mV, which is attributed to a distortion of the dimer. The dimer distortion propagates to the subsequent smectic bilayers, producing an additional 7 mV potential increase in the second layer, 2 mV on the third, and approximately 1 mV on the fourth.
The condensation of glycerol on mica surfaces in ambient air was studied with scanning polarization force microscopy (SPFM). Two different wetting regimes were found that depend on the state of the surface. On freshly cleaved mica, glycerol condenses, forming flat films. The films expand until a uniform layer is formed. The first molecular layer of glycerol was found to be more strongly bound to the surface than were subsequent layers. On contaminated mica (after 2 h of exposure to air) droplets in the shape of spherical caps form that partially wet the substrate. The droplets grow indefinitely in the saturated vapor. The contact angle of droplets with heights <20 nm was found to deviate from the macroscopic value found in large drops. The results are discussed in the context of the long-range forces in the liquid film.
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