Bilayers are synthetically made cell membranes that are used to study cell membrane properties and make functional
devices that incorporate inherent properties of the cell membranes. Lipids and proteins are two of the main components
of a cell membrane. Lipids provide the structure of the membrane in the form of two leaflets or layers that are held
together by the amphiphilic interaction between the lipids and water. Proteins are made from a combination of amino
acids and the properties of these proteins are dependent on the amino acid sequence. Some proteins are antibiotics and
can easily self insert into the membrane of a cell or into a synthetically formed bilayer. The peptide alamethicin is one
such antibiotic that easily inserts into a bilayer and changes the conductance properties of the bilayer. Analytical
models of the conductance change with respect to the potential and other variables across the bilayer follows the
nonlinear conductance changes seen with the incorporation of the peptide in a bilayer. The individual channels formed
by the peptide have been studied and the peptide has several discrete conductance levels. These discrete levels have
been shown to be dependent on the potential across the bilayer and several other variables including the lipid variety.
The conductance level for a single channel can change with time in a probabilistic fashion. This paper will model these
discrete conductance levels of the peptide alamethicin and the model of the single channel conductance will be used to
model the cumulative effect of multiple channels within a bilayer.
Two of the main components of cell membranes are lipids and proteins. Lipids are the passive structure of the
membrane that acts as a barrier between the inner and outer portions of the cell. Proteins are the active structure of the
membrane that allows signaling, energy conversion, and open channels between the inner and outer portions of the cell.
Artificially made membranes, called bilayers, can be made from natural or artificial membrane components at the
interface of aqueous volumes. Some bilayer properties are measured by inducing an artificial potential gradient across
the bilayer to induce ion flow. This ion flow is measured by measuring the resulting current output of the device that
induced the potential gradient. The lipids of the membrane act electrically as a small conductor and capacitor in parallel
where the measured capacitance is related to the area of the bilayer. Some proteins act electrically as an additional
conductor in parallel to the lipids with varying conductance properties depending on the specific protein. Some proteins
are pores that allow ions to flow freely through the membrane and others are gated and allow ions to flow at different
levels depending on the size and polarity of the potential gradient. A large system with multiple aqueous volumes and
multiple bilayers made of just passive membrane components can be modeled as an electrical network of resistors and
capacitors. The addition of proteins to this network increases the complexity of the system model because the proteins
usually do not act as a linear conductance and numerical methods are used to approximate what is happening in the system. This paper shows how a system of multiple aqueous volumes and multiple bilayers can be modeled as a system of first order odes, numerically solved, and then compared to the published results of a similar system.
Phospholipid molecules are the fundamental building blocks of cell membranes in living organisms. These molecules
are amphipathic with two hydrophobic fatty acid chains (tails) linked to a phosphate containing hydrophilic group (head)
that can spontaneously form a bilayer lipid membrane (BLM) with a 6-10 nm thickness in water. BLMs have been
classified using some porous synthetic substrate for support. Droplet interface bilayers (DIB) have allowed researchers
to study BLMs formed without the use of a porous synthetic substrate. The DIBs are formed at the interface of water
droplets and a non-polar solvent. The phospholipids will form a monolayer around the water droplets and when two
droplets are brought into contact with each other, a single bilayer will form. DIBs have been used to form networks of
BLMs that can be used for multiple purposes. The exact size of the BLM between two droplets is inferred from
electrical measurements. The two droplets can be connected through a pore in a synthetic substrate of known
dimensions that can limit the area of the BLM. This paper will present the results of forming a BLM on a synthetic
substrate by using the DIB method of formation.
Recent results have demonstrated that lipid bilayers have the ability to "self-heal" after mechanical failure. In a previous
study the maximum pressure that could be withstood by a bilayer lipid membrane (BLM) formed over a porous substrate
was measured and reported. This paper expands on this subject by exploring the ability of a BLM to spontaneously "self-heal"
or reform after having been pressurized until failure. A 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine
(SOPC) BLM is reconstituted over a silicon substrate that contains a single square aperture (25 x 25 μm) and is
pressurized until failure. It is found that the BLM spontaneously reforms multiple times over the aperture after the initial
failure. For each experiment the BLM is subjected to several pressurization cycles with a 70 mV potential applied
across the BLM. The current is measured using an impedance analyzer and indicates the presence of a BLM formed
over the aperture. It is found that electrical current conducted across the BLM increases from approximately 100 pA to
650 nA during each BLM failure and returns to 100 pA after BLM reformation. These results demonstrate that the
bilayer is reforming because the electrical resistance across the aperture is increasing by several orders of magnitude.
KEYWORDS: Acoustics, Linear filtering, Control systems, Systems modeling, Absorption, Temperature metrology, Scanning probe lithography, Data modeling, Device simulation, Actuators
A method for adaptive energy absorption in the low frequency region of acoustic cavities is presented. The method
is based on an adaptive scheme consisting of a self-tuning regulator (STR) that has the ability to target multiple modes
with a single actuator. The inner control loop of the STR uses positive position feedback (PPF) in series with a high- and
low-pass Butterworth filters for each controlled mode. The outer loop consists of an algorithm that locates the zero
frequencies of the collocated signal and uses these values to update the resonance frequency of the PPF filter and the cut-off
and cut-on frequencies of the Butterworth filters. Experimental results of a duct are provided that show how less than
a 10 percent change in the frequencies of the acoustic modes of the duct will cause a non-adaptive controller to go
unstable, but the STR will maintain stability and continue absorbing energy through a 20 percent change in the
frequencies of the acoustic modes of the duct. Additional experimental results of a fairing replica are provided that show
internal temperature variations can change the frequencies of the acoustic modes of this larger cavity and that the STR
can adapt to these changes and absorb acoustic energy.
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