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251.
Sandra S. Donato Virginia Chu Duarte M. F. Prazeres Joao P. Conde 《Electrophoresis》2013,34(4):575-582
The spatial and temporal control of biological species is essential in complex microfluidic biosystems. In addition, if the biological species is a cell, microfluidic handling must ensure that the cell's metabolic viability is maintained. The use of DEP for cell manipulation in microfluidics has many advantages because it is remote and fast, and the voltages required for cell trapping scale well with miniaturization. In this paper, the conditions for bacterial cell (Escherichia coli) trapping using a quadrupole electrode configuration in a PDMS microfluidic channel were developed both for stagnant and for in‐flow fluidic situations. The effect of the electrical conductivity of the fluid, the applied electric field and frequency, and the fluid‐flow velocity were studied. A dynamic exchange between captured and free‐flowing cells during DEP trapping was demonstrated. The metabolic activity of trapped cells was confirmed by using E. coli cells genetically engineered to express green fluorescent protein under the control of an inducible promoter. Noninduced cells trapped by negative DEP and positive DEP were able to express green fluorescent protein minutes after the inducer was inserted in the microchannel system immediately after DEP trapping. Longer times of trapping prior to exposure to the inducer indicated first a degradation of the cell metabolic activity and finally cell death. 相似文献
252.
R Montero A Peralta Conde V Ovejas M Fernández-Fernández F Castaño JR Vázquez de Aldana A Longarte 《The Journal of chemical physics》2012,137(6):064317
The evolution of the isolated pyrrole molecule has been followed after excitation in the 265-217 nm range by using femtosecond time delayed ionization. The transients collected in the whole excitation range show the vanishing of the ionization signal in the femtosecond time scale, caused by the relaxation along a πσ(?) type state (3s a(1)←π 1a(2)), which is the lowest excited electronic state of the molecule. This surface is dissociative along the NH bond, yielding a 15 ± 3 fs lifetime that reflects the loss of the ionization cross-section induced by the ultrafast wavepacket motion. Although a weak πσ(?) absorption is detected, the state is mainly reached through internal conversion of the higher bright ππ(?) transitions, which occurs with a 19 ± 3 fs lifetime. In addition to its resonant excitation, the intense ππ(?) absorption extending in the 220-190 nm interval is also out-of-resonance populated at energies far to the red from its absorption onset. This coherent adiabatic excitation of the ππ(?) transition should follow the excitation pulse (coherent population return effect), but instead the system relaxes toward the lower πσ(?) surface through a conical intersection during the interaction time, leading to the population of πσ(?) state at wavelengths as long as 265 nm. According to the observed behavior, the time evolution of the system in the full excitation range studied is modeled by a coherent treatment that provides key insights on the photophysical properties of the molecule. 相似文献
253.
N Nogueira O Conde M Miñones JM Trillo J Miñones 《Journal of colloid and interface science》2012,385(1):202-210
The behavior of poly(2-hydroxyethyl methacrylate) (PHEMA) polymer monolayer spread on water was studied under various experimental conditions. The influence of subphase pH and temperature, compression speed, elapsed time from the deposit of the monolayer and the recording of the surface pressure-area (π-A) isotherms, as well as the number of polymer molecules deposited at the air/water surface (surface concentration) was studied. The obtained results show that PHEMA exhibits a very stable monolayer given that it is unaffected by modifications in the majority of these variables. Only the elapsed time between the spreading of the monolayer and the beginning of compression causes a small change in the π-A isotherms that consists in an increase in the area occupied by the film. This is attributed to the greater unfolding with time of the polymer's monomers at the air/water interface. The plateau that appears on π-A curves of the PHEMA monolayer is attributed to the reorientation of their hydroxyethyl polar groups through their C-O-C bonds, as well as to the reorientation of the ethylene (CH(2)) groups that link the monomers, which provokes a folding of the polymer's chains causing an accordion configuration. The existence of this structure is confirmed by the presence of numerous noise peaks in the relative thickness versus time curve corresponding to this region. In the same fashion, the images observed from Brewster angle microscopy (BAM) reveal the existence of light-dark "bands" relative to the different regions of this particular structure. 相似文献
254.
Cristian Conde 《Journal of Mathematical Analysis and Applications》2009,356(2):664-673
We study the geometry of the set Δp, with 1<p<∞, which consists of perturbations of the identity operator by p-Schatten class operators, which are positive and invertible as elements of B(H). These manifolds have natural and invariant Finsler structures. In [C. Conde, Geometric interpolation in p-Schatten class, J. Math. Anal. Appl. 340 (2008) 920-931], we introduced the metric dp and exposed several results about this metric space. The aim of this work is to prove that the space (Δp,dp) behaves in many senses like a nonpositive curvature metric space. 相似文献
255.
Conde L. Leon L. Ibanez L.F. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(4):548-552
The electron transport properties of plasma clouds generated by a hollow cathode discharge are investigated. The voltage-current characteristic curves indicate that the electron-emitted electron current depends on both bias voltage and discharge current. The spatial dependence of the electronic density, plasma potential, and electronic temperature is measured. The energy loss rate of a high energy group of electrons with the radial distance is also presented. These experimental results are compared with a nonisothermal transport model which reproduces the spatial dependence of plasma properties 相似文献
256.
Eliana?M.?F.?Vieira Sergey?LevichevEmail author Carlos?J.?Dias Rui?Igreja Maja?Buljan Sigrid?Bernstorff Olinda?Conde Adil?Chahboun Anabela?G.?Rolo Maria?J.?M.?Gomes 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(7):336
The charge storage behavior of nanostructures based on Si1?x Ge x (0 ≤ x ≤ 1) nanocrystals (NCs) in an Al2O3 matrix was investigated. The structures have been grown by RF magnetron sputtering and subsequently annealed at temperatures ranging from 700 °C to 1000 °C for 30 min in nitrogen ambient. The stoichiometry of the SiGe NCs and the alumina crystalline structure were found to be significantly dependent on the RF power and the annealing temperature. The sizes of the SiGe NCs and their distribution were investigated by grazing incidence small angle X-ray scattering (GISAXS). The capacitance-voltage (C-V) and conductance-voltage (G-V) measurements were performed to investigate the charge trapping characteristics of the memory structures. The C-V hysteresis width depends on variations in the crystalline structure resulting from different annealing temperatures. It is also shown that charge injection is governed by the Fowler-Nordheim tunnel mechanism for higher electric fields. 相似文献