198 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
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
Admission Blood Pressure in Relation to Clinical Outcomes and Successful Reperfusion After Endovascular Stroke Treatment
BACKGROUND AND PURPOSE: Optimal blood pressure (BP) targets before endovascular treatment (EVT) for acute ischemic stroke are unknown. We aimed to assess the relation between admission BP and clinical outcomes and successful reperfusion after EVT. METHODS: We used data from the MR CLEAN (Multicenter Randomized Controlled Trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands) Registry, an observational, prospective, nationwide cohort study of patients with ischemic stroke treated with EVT in routine clinical practice in the Netherlands. Baseline systolic BP (SBP) and diastolic BP (DBP) were recorded on admission. The primary outcome was the score on the modified Rankin Scale at 90 days. Secondary outcomes included successful reperfusion (extended Thrombolysis in Cerebral Infarction score 2B-3), symptomatic intracranial hemorrhage, and 90-day mortality. Multivariable logistic and linear regression were used to assess the associations of SBP and DBP with outcomes. The relations between BPs and outcomes were tested for nonlinearity. Parameter estimates were calculated per 10 mm Hg increase or decrease in BP. RESULTS: We included 3180 patients treated with EVT between March 2014 and November 2017. The relations between admission SBP and DBP with 90-day modified Rankin Scale scores and mortality were J-shaped, with inflection points around 150 and 81 mm Hg, respectively. An increase in SBP above 150 mm Hg was associated with poor functional outcome (adjusted common odds ratio, 1.09 [95% CI, 1.04-1.15]) and mortality at 90 days (adjusted odds ratio, 1.09 [95% CI, 1.03-1.16]). Following linear relationships, higher SBP was associated with a lower probability of successful reperfusion (adjusted odds ratio, 0.97 [95% CI, 0.94-0.99]) and with the occurrence of symptomatic intracranial hemorrhage (adjusted odds ratio, 1.06 [95% CI, 0.99-1.13]). Results for DBP were largely similar. CONCLUSIONS: In patients with acute ischemic stroke treated with EVT, higher admission BP is associated with lower probability of successful reperfusion and with poor clinical outcomes. Further research is needed to investigate whether these patients benefit from BP reduction before EVT
Deceleration and trapping of heavy diatomic molecules using a ring-decelerator
We present an analysis of the deceleration and trapping of heavy diatomic
molecules in low-field seeking states by a moving electric potential. This
moving potential is created by a 'ring-decelerator', which consists of a series
of ring-shaped electrodes to which oscillating high voltages are applied.
Particle trajectory simulations have been used to analyze the deceleration and
trapping efficiency for a group of molecules that is of special interest for
precision measurements of fundamental discrete symmetries. For the typical case
of the SrF molecule in the (N,M) = (2, 0) state, the ring-decelerator is shown
to outperform traditional and alternate-gradient Stark decelerators by at least
an order of magnitude. If further cooled by a stage of laser cooling, the
decelerated molecules allow for a sensitivity gain in a parity violation
measurement, compared to a cryogenic molecular beam experiment, of almost two
orders of magnitude
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