242 research outputs found
Chemically driven switches for online detection of pH changes in microfluidic devices
The internal walls of microfabricated fluidic channels were functionalized with a selfassembled monolayer of Rhodamine B lactam. This molecule has the capability to interconvert between its open fluorescent amide form and the closed non-fluorescent lactam form upon changes of the pH conditions. The interconversion (switch) between the two reversible forms is achieved by addition of an acid or a base and is consistent with a reaction mechanism of the first order. This paper describes the online observation of such fluorescent switch covalently anchored to the channel and proposes this method as a possible sensor for the monitoring of pH changes in microreactors
Stochastic Domination in Space-Time for the Contact Process
Liggett and Steif (2006) proved that, for the supercritical contact process
\non certain graphs, the upper invariant measure stochastically dominates an
\ni.i.d.\\ Bernoulli product measure. In particular, they proved this for
\n and (for infection rate sufficiently large) -ary homogeneous
\ntrees .
\n In this paper we prove some space-time versions of their results. We do this
\nby combining their methods with specific properties of the contact process and
\ngeneral correlation inequalities.
\n One of our main results concerns the contact process on with .
\nWe show that, for large infection rate, there exists a subset of the
\nvertices of , containing a "positive fraction" of all the vertices of
\n, such that the following holds: The contact process on observed on
\n stochastically dominates an independent spin-flip process. (This is
\nknown to be false for the contact process on graphs having subexponential
\ngrowth.)
\n We further prove that the supercritical contact process on
\nobserved on certain -dimensional space-time slabs stochastically dominates
\nan i.i.d.\\ Bernoulli product measure, from which we conclude strong mixing
\nproperties important in the study of certain random walks in random
\nenvironment
Intercorrelation study of dietary and biochemical data from schoolchildren in the Pretoria area
No Abstrac
On the minimization of Dirichlet eigenvalues of the Laplace operator
We study the variational problem \inf \{\lambda_k(\Omega): \Omega\
\textup{open in}\ \R^m,\ |\Omega| < \infty, \ \h(\partial \Omega) \le 1 \},
where is the 'th eigenvalue of the Dirichlet Laplacian
acting in , \h(\partial \Omega) is the - dimensional
Hausdorff measure of the boundary of , and is the Lebesgue
measure of . If , and , then there exists a convex
minimiser . If , and if is a minimiser,
then is also a
minimiser, and is connected. Upper bounds are
obtained for the number of components of . It is shown that if
, and then has at most components.
Furthermore is connected in the following cases : (i) (ii) and (iii) and (iv) and
. Finally, upper bounds on the number of components are obtained for
minimisers for other constraints such as the Lebesgue measure and the torsional
rigidity.Comment: 16 page
Polarization cross-coupling in a polymer microlaser upon double-pulse excitation
Quantum Matter and Optic
Biophysical and enzymatic properties of aminoglycoside adenylyltransferase AadA6 from Pseudomonas aeruginosa
AbstractThe gene coding for the aminoglycoside adenylyltransferase (aadA6) from a clinical isolate of Pseudomonas aeruginosa was cloned and expressed in Escherichia coli strain BL21(DE3)pLysS. The overexpressed enzyme (AadA6, 281 amino-acid residues) and a carboxy-terminal truncated variant molecule ([1-264]AadA6) were purified to near homogeneity and characterized. Light scattering experiments conducted under low ionic strength supported equilibrium between monomeric and homodimeric arrangements of the enzyme subunits. Circular Dichroism spectropolarimetry indicated a close structural relation to adenylate kinases. Both forms modified covalently the aminoglycosides streptomycin and spectinomycin. The enzyme required at least 5mM MgCl2 for normal Michaelis–Menten kinetics. Streptomycin exhibited a strong substrate inhibition effect at 1mM MgCl2. The truncated 17 residues at the C-terminus have little influence on protein folding, whereas they have a positive effect on the enzymic activity and stabilize dimers at high protein concentrations (>100μM). Homology modelling and docking based on known crystal structures yielded models of the central ternary complex of monomeric AadA6 with ATP and streptomycin or spectinomycin
Femtosecond frequency comb based distance measurement in air
Interferometric measurement of distance using a femtosecond frequency comb is demonstrated and compared with a counting interferometer displacement measurement. A numerical model of pulse propagation in air is developed and the results are compared with experimental data for short distances. The relative agreement for distance measurement in known laboratory conditions is better than 1
Nieuwe verwaarding algenbiomassa : literatuurstudie en praktische screening van enkele ontsluitingsmethoden
Om de eiwitten, oliën, koolhydraten, carotenoïden en andere nuttige stoffen aanwezig in algencellen los van elkaar te kunnen benutten, is het nodig om de celwanden van de algen open te breken, ofwel om de algen te ontsluiten. Uiteraard is het van belang om dit te doen op een manier die de te winnen componenten zo min mogelijk beschadigt. Dit rapport bestaat uit twee delen. Het eerste is een literatuurstudie waarin een aantal algensoorten wordt omschreven, met waar mogelijk nadruk op de celwandstructuur. Verder wordt een aantal methoden beschreven om de celwanden te openen of te verzwakken. In het tweede deel van het rapport worden een aantal uitgevoerde proeven beschreven waarbij algen zijn behandeld met enzymen, schoonmaakazijn, of ethanol
Experimental demonstration of distance measurement with a femtosecond frequency comb laser
We experimentally demonstrate that a stabilized femtosecond frequency comb can be applied as a tool for distance measurement in an interferometric scheme. A proof of principle of this method, as proposed by Ye [5], is provided by measuring a displacement of about 15 cm in air and comparing it to a reference value from a calibrated laser interferometer. The experiment shows that the new scheme easily achieves an accuracy better than one optical fringe. [DOI: 10.2971/jeos.2008.08003
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