Monolithic porous polymers have been prepared by photoinitiated polymerization within the channels of a microfluidic device and used for on-chip solid-phase extraction and preconcentration. The preparation of the monolithic material with hydrophobic and ionizable surface chemistries is easily achieved by copolymerization of butyl methacrylate with ethylene dimethacrylate, or 2-hydroxyethyl methacrylate and [2-(methacryloyloxy)ethyl]trimethylammonium chloride with ethylene dimethacrylate, respectively. The porous properties, and consequently the flow resistance, of the monolithic device are controlled by the use of a mixture of hexane and methanol as a porogenic mixture. This mixture was designed to meet the specific requirements for pore formation within macroporous monoliths useful in the microfluidic formats. The low flow resistance enables high flow rates of up to 10 microL/min, which corresponds to a linear flow velocity of 50 mm/s and far exceeds the flow velocities typical of the common analytical microchips. The function of the monolithic concentration device was first demonstrated using very dilute solutions of Coumarin 519. The performance in a more realistic application was then demonstrated with the enrichment of a hydrophobic tetrapeptide and also of green fluorescent protein for which an increase in concentration by a factor as high as 10(3) was achieved.
The authors prove that the piecewise-linear Lorenz circuit is chaotic in the sense of Shilnikov. They first prove the existence of a heteroclinic orbit, and then prove an inequality among the eigenvalues. In addition to a detailed analysis of the piecewise linear dynamics, interval analysis is utilized to prove various inequalities. This novel approach can be applied to many other problems that require proving rigorously the existence of either a homoclinic or a heteroclinic orbit. With this proof, the piecewise-linear Lorenz circuit becomes one of the very few real physical systems where chaos has been observed by laboratory measurement, confirmed by simulation, and proved mathematically.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
It is shown by experiment and by computer simulation that two mutually coupled PLLs (phase-locked loops) can become chaotic when they are operating in a marginal out-of-lock condition. i.e. when they are out-of-lock but very close to lock-in. The system is described by a fourth-order nonlinear autonomous equation. The power spectrum of the out-of-lock solution (close to lock-in) is observed to be a continuous broadband similar to that of a random signal. Moreover, the largest Lyapunov exponent is found to be positive. This chaotic regime has been observed over a large area of typical damping coefficients used in practical coupled PLL systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper presents several new algorithms which are used to implement two recently published uniqueness theorems applicable to nonlinear resistive circuits containing independent sources, two-terminal resistors and linear controlled sources. These programs are novel in that they allow a computer to test directly for qualitative behavior. The algorithms and the two programs which use them are described and results are presented for some examples from the original papers.
To take advantage of the remarkable computational efficiency of the canonical piecewise-linear approach for dc nonlinear electronic circuit analysis, the devices must be modeled by a canonical piecewise-linear model. This paper presents a unified parameter optimization algorithm for constructing such models. This algorithm is then applied to derive prototype canonical piecewise-linear models of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-n</tex> junction diodes, bipolar transistors, MOSFET's, and GaAs FET's. The canonical piecewise-linear model can be regarded as a universal model since its form remains unchanged for all devices. Only the coefficients differ from one device to another. For large-scale circuits, the canonical piecewise-linear representation has a decisive advantage over other representations in regard to the number of memory locations needed to specify the equations.
Synthetic polymers and dendrimers have been widely used by the medical community to overcome biological barriers and enhance in vivo biomedical applications. Despite the widespread use of biomaterials it has been generally extremely difficult to monitor noninvasively their fate in vivo. Here we report multilayered nanoprobes, consisting of a near-infrared core, nanoencapsulated in a biodegradable dendrimer, and surrounded by a shell of polyethylene oxide. Covalent encapsulation of the near-infrared fluorophores in the dendritic scaffold conferred enhanced stability to the nanoprobe with added resistance to enzymatic oxidation and prolonged blood residence time. Insight into the time course of biodegradation of the dendritic aliphatic polyester nanoprobe was gained using noninvasive whole body in vivo fluorescence lifetime imaging. As the dendritic shell biodegrades the NIR probe becomes exposed, enabling monitoring of fluorescence lifetime changes in vivo.
A facile patterning method for the functionalization of vertically aligned carbon nanotubes is described. Modification of the surface of nanotube forests with hydrophilic, hydrophobic, or polymerizable small molecules was achieved via UV-triggered attachment of perfluoroarylazides. Multiple functionalizations of the tube surface can be achieved. Macro- and micropatterning of forest substrates were demonstrated. Superhydrophobic surfaces containing superhydrophilic regions were prepared.
Read moreThe synthesis of a variety of core functionalized PEGylated polyester dendrimers and their in vitro and in vivo properties are described in this report. These water-soluble dendrimers have been designed to carry eight functional groups on their dendritic core for a variety of biological applications such as drug delivery and in vivo imaging as well as eight solubilizing groups. Using a common symmetrical aliphatic ester dendritic core and trifunctional amino acid moieties, a library of dendrimers with phenols, alkyl alcohols, alkynes, ketones, and carboxylic acid functionalities has been synthesized without the need for column chromatography. The amines were PEGylated, leaving the other functionality of the amino acid available for further manipulation such as the attachment of drugs and/or labels. Radiolabeling experiments with the PEGylated dendrimers showed that they had a long circulation half-life in mice, confirming the potential of this class of dendrimers for therapeutic and/or diagnostic applications. A carboxylic acid functionalized dendrimer was elaborated to carry doxorubicin bound via a hydrazone bond. The drug-loaded carrier accumulated more in tumors and less in healthy organs than the clinically used PEGylated liposomal formulation Doxil. The efficient synthesis, high versatility, and favorable biological properties make these PEGylated polyester dendrimers promising structures for therapeutic and/or imaging applications.
Read moreA polarity-directed organocatalytic cascade reaction of two different aldehydes with nitromethane in biphasic systems is reported. Since the involved aliphatic aldehydes exhibit similar reactivities, the predominantly formed cross-products of the reaction can be explained by slight differences in polarity. Most likely the proline (1)-catalyzed condensation of the more polar aldehyde with nitromethane succeeds first in the aqueous phase, thus releasing a nitroalkene intermediate. This species enriches in the organic phase consisting of the neat aldehydes, where it undergoes conjugate addition preferred with the less polar aldehyde, accelerated by secondary amine catalyst 2, respectively.
Read moreExperimental confirmation has been made on a negativeresistance oscillator circuit which exhibits the new period-adding route to chaos recently reported by Kaneko on a discrete map. The nonlinear element in the circuit is a negative-resistance device synthesized by using two bipolar transistors and four positive linear resistors. This circuit exhibits a new route to chaos; namely, through period-adding where the periods of two successive periodic waveforms belonging to each periodadding sequence differ by one; i.e., from period <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n - 1</tex> or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n + 1</tex> . The transition to chaos (after one or more periodic states) resulted directly from a loss of stability of a periodic state at a bifurcation point. Several general features of the periodic-chaotic transition sequence have been observed and presented.
Read moreLaser targets, created by fast optical breakdown of shock fronts produced in an electrothermal shock tube filled with D2 or H2, have been used for studies of resonance absorption of CO2 laser light. In these targets, the critical-surface density-gradient vector always points along the shock-tube axis, leading to reproducible hot-electron emission by plasma wave breaking. The angular distribution and energy spectrum of this emission have been studied. For 200 psec risetime laser pulses, the measured scaling of hot-electron temperature with laser pulse energy agrees with predictions of models of profile steepening by the ponderomotive force of the laser light. For 20 psec risetime laser pulses, the results are consistent with a model in which the detected electron emission is dominated by a ’’chirped’’ monoenergetic burst lasting only 1 to 2 psec. In this model, the electron energy spectrum is due to the integrated temporal variation of the enery of the burst, and the hot-electron temperature is practically independent of laser pulse energy.
Read moreAbstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Read moreUsing the notion of fading memory we prove very strong versions of two folk theorems. The first is that any time-invariant (TI) continuous nonlinear operator can be approximated by a Volterra series operator, and the second is that the approximating operator can be realized as a finite-dimensional linear dynamical system with a nonlinear readout map. While previous approximation results are valid over finite time intervals and for signals in compact sets, the approximations presented here hold for all time and for signals in useful (noncompact) sets. The discretetime analog of the second theorem asserts that any TI operator with fading memory can be approximated (in our strong sense) by a nonlinear moving- average operator. Some further discussion of the notion of fading memory is given.
Read moreEvidence is reported for a nonrandom process by which laser-produced plasmas emit suprathermal electrons. Emission is dominated by a 1 to 2 psec monoenergetic burst, during which the electron energy decreases rapidly. The suprathermal tail on the energy distribution is due to the integrated temporal variation of the electron energy, not to statistical processes. The hot-electron temperature thus produced is practically independent of laser pulse energy.
Read moreDepartment of Electrical Engineering and Computer Science Nagasaki University 1-14, Bunkyo-machi, Nagasaki-shi, 852 Japan E-mail: itoh@itoh.ec.nagasaki-u.ac.jp Department of Electrical Engineering and Computer Sciences University of California, Berkeley CA 94720, USA The communication systems via chaos synchronization are experimentally demonstrated using Chua's circuit.
Read moreAbstract The inherent saturation non‐linearity of the op amp is used to design circuits having a wide variety of useful non‐linear v‐i characteristics. These circuits are made of one op amp and 3 or 4 linear resistors which are passive under a rather mild assumption derived from the 3‐port paramountcy condition. Explicit design formulae are given for each prototype circuit and numerous examples are given and validated by actual measurements.
Read moreThis paper is a sequel to an earlier paper under the same title. Here we use a more realistic model of the Josephson-junction and present a rigorous analysis of its nonlinear dynamics under various ranges of model parameters. In particular, we prove that the qualitative properties of our model and of the simplified one are similar. This rigorous proof thereby justifies the choice of a simpler Josephson-junction model, which was chosen in the past mainly for tractability. The peculiar constant voltage-step (devil's staircase) phenomenon widely reported in the literature is carefully analyzed further in this paper. For the first time, we can give a fairly complete explanation of the mechanism leading to this exotic phenomenon. In particular, the variations in the length of the constant voltage steps which have baffled many researchers in the past can now be given a rational explanation. An analysis of the mechanisms which give rise to chaotic dynamics in the Josephson-junction circuit is also presented.
Read more
.webp){kind=small}
.webp){kind=small}