244,331 research outputs found
Quantum photonic networks in diamond
Advances in nanotechnology have enabled the opportunity to fabricate nanoscale optical devices
and chip-scale systems in diamond that can generate, manipulate, and store optical signals
at the single-photon level. In particular, nanophotonics has emerged as a powerful interface
between optical elements such as optical fibers and lenses, and solid-state quantum objects
such as luminescent color centers in diamond that can be used effectively to manipulate
quantum information. While quantum science and technology has been the main driving
force behind recent interest in diamond nanophotonics, such a platform would have many
applications that go well beyond the quantum realm. For example, diamond’s transparency
over a wide wavelength range, large third-order nonlinearity, and excellent thermal properties
are of great interest for the implementation of frequency combs and integrated Raman lasers.
Diamond is also an inert material that makes it well suited for biological applications and for
devices that must operate in harsh environments
Studies of cationic amphiphilic drug catalysed membrane degradation
Imperial Users onl
Roadmap on semiconductor-cell biointerfaces.
This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world
Programmable interactions with biomimetic DNA linkers at fluid membranes and interfaces
At the heart of the structured architecture and complex dynamics of
biological systems are specific and timely interactions operated by
biomolecules. In many instances, biomolecular agents are spatially confined to
flexible lipid membranes where, among other functions, they control cell
adhesion, motility and tissue formation. Besides being central to several
biological processes, \emph{multivalent interactions} mediated by reactive
linkers confined to deformable substrates underpin the design of
synthetic-biological platforms and advanced biomimetic materials. Here we
review recent advances on the experimental study and theoretical modelling of a
heterogeneous class of biomimetic systems in which synthetic linkers mediate
multivalent interactions between fluid and deformable colloidal units,
including lipid vesicles and emulsion droplets. Linkers are often prepared from
synthetic DNA nanostructures, enabling full programmability of the
thermodynamic and kinetic properties of their mutual interactions. The coupling
of the statistical effects of multivalent interactions with substrate fluidity
and deformability gives rise to a rich emerging phenomenology that, in the
context of self-assembled soft materials, has been shown to produce exotic
phase behaviour, stimuli-responsiveness, and kinetic programmability of the
self-assembly process. Applications to (synthetic) biology will also be
reviewed.Comment: 63 pages, revie
Computational Models of Material Interfaces for the Study of Extracorporeal Shock Wave Therapy
Extracorporeal Shock Wave Therapy (ESWT) is a noninvasive treatment for a
variety of musculoskeletal ailments. A shock wave is generated in water and
then focused using an acoustic lens or reflector so the energy of the wave is
concentrated in a small treatment region where mechanical stimulation enhances
healing. In this work we have computationally investigated shock wave
propagation in ESWT by solving a Lagrangian form of the isentropic Euler
equations in the fluid and linear elasticity in the bone using high-resolution
finite volume methods. We solve a full three-dimensional system of equations
and use adaptive mesh refinement to concentrate grid cells near the propagating
shock. We can model complex bone geometries, the reflection and mode conversion
at interfaces, and the the propagation of the resulting shear stresses
generated within the bone. We discuss the validity of our simplified model and
present results validating this approach
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
The mechanism of porosity formation during solvent-mediated phase transformations
Solvent-mediated solid-solid phase transformations often result in the
formation of a porous medium, which may be stable on long time scales or
undergo ripening and consolidation. We have studied replace- ment processes in
the KBr-KCl-H2O system using both in situ and ex situ experiments. The
replacement of a KBr crystal by a K(Br,Cl) solid solution in the presence of an
aqueous solution is facilitated by the gen- eration of a surprisingly stable,
highly anisotropic and connected pore structure that pervades the product
phase. This pore structure ensures efficient solute transport from the bulk
solution to the reacting KBr and K(Br,Cl) surfaces. The compositional profile
of the K(Br,Cl) solid solu- tion exhibits striking discontinuities across
disc-like cavities in the product phase. Similar transformation mechanisms are
probably important in con- trolling phase transformation processes and rates in
a variety of natural and man-made systems.Comment: 22 pages, 7 figure
Tuning ubiquinone position in biomimetic monolayer membranes
Artificial lipid bilayers have been extensively studied as models that mimic natural membranes (biomimetic membranes). Several attempts of biomimetic membranes inserting ubiquinone (UQ) have been performed to enlighten which the position of UQ in the lipid layer is, although obtaining contradictory results. In this work, pure components (DPPC and UQ) and DPPC:UQ mixtures have been studied using surface pressure-area isotherms and Langmuir-Blodgett (LB) films of the same compounds have been transferred onto solid substrates being topographically characterized on mica using atomic force microscopy and electrochemically on indium tin oxide slides. DPPC:UQ mixtures present less solid-like physical state than pure DPPC indicating a higher-order degree for the latter. UQ influences considerably DPPC during the fluid state, but it is mainly expelled after the phase transition at ˜˜ 26 mN·m^-1 for the 5:1 ratio and at ˜˜ 21 mN·m^-1 for lower UQ content. The thermodynamic studies confirm the stability of the DPPC:UQ mixtures before that event, although presenting a non-ideal behaviour. The results indicate that UQ position can be tuned by means of the surface pressure applied to obtain LB films and the UQ initial content. The UQ positions in the biomimetic membrane are distinguished by their formal potential: UQ located in “diving” position with the UQ placed in the DPPC matrix in direct contact with the electrode surface ( -0.04±0.02 V), inserted between lipid chains without contact to the substrate ( 0.00±0.01 V) and parallel to the substrate, above the lipid chains ( 0.09±0.02 V).Peer ReviewedPostprint (author's final draft
Similarities between action potentials and acoustic pulses in a van der Waals fluid
An action potential is typically described as a purely electrical change that
propagates along the membrane of excitable cells. However, recent experiments
have demonstrated that non-linear acoustic pulses that propagate along lipid
interfaces and traverse the melting transition, share many similar properties
with action potentials. Despite the striking experimental similarities, a
comprehensive theoretical study of acoustic pulses in lipid systems is still
lacking. Here we demonstrate that an idealized description of an interface near
phase transition captures many properties of acoustic pulses in lipid
monolayers, as well as action potentials in living cells. The possibility that
action potentials may better be described as acoustic pulses in soft interfaces
near phase transition is illustrated by the following similar properties:
correspondence of time and velocity scales, qualitative pulse shape, sigmoidal
response to stimulation amplitude (an `all-or-none' behavior), appearance in
multiple observables (particularly, an adiabatic change of temperature),
excitation by many types of stimulations, as well as annihilation upon
collision. An implication of this work is that crucial functional information
of the cell may be overlooked by focusing only on electrical measurements.Comment: 8 pages, 5 figure
Photodegradation of nimodipine and felodipine in microheterogeneous systems
IndexaciĂłn: Web of Science; ScieloThe photochemical behavior of nimodipine (NIMO) and felodipine (FELO), photolabile drugs widely used as antihypertensive calcium channel blockers, is studied in constrained media. Specifically, we are interested in the kinetic analysis of 4-aryl-1,4-dihydropyridine photodegradation processes when they are incorporated in biological-mimicking systems like micelles or liposomes. In order to establish if the nature of the head of surfactant (ionic or nonionic) could be important modulating the photo-reactivity of these drugs, we studied the photodegradation of NIMO and FELO incorporated in micelles formed with sodium dodecyl sulfate (SDS, anionic), dodecyl-pyridinium chloride (DPC, cationic) and mono lauryl sucrose ester (MLS, nonionic) as surfactants. Additionally, the results of the photodegradation of these compounds in liposomes were also included. The results clearly indicate that both dihydropyridines studied, NIMO and FELO, are located near to the interface, but the surface charge of micelles does not affect neither, the photodegradation rate constant nor the photodegradation products profile. The absence of singlet oxygen generation in micellar media is consistent with the proposition of these 4-aryl-1,4-dihidropyridines located near to the interface of the micelle, where a polar environment is sensed. In addition, the ethanol preferential location on membranes and dihydropyridine enhanced photodegradation by alcohol presence are interesting results to consider in future research.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072012000300025&nrm=is
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