Characterization of cell lysis events on a microfluidic device for high-throughput single cell analysis

A microfluidic device capable of rapidly analyzing cells in a high-throughput manner using electrical cell lysis is further characterized. In the experiments performed, cell lysis events were studied using an electron multiplying charge coupled device camera with high frame rate (>100 fps) data collection. It was found that, with this microfluidic design, the path that a cell follows through the electric field affects the amount of lysate injected into the analysis channel. Elimination of variable flow paths through the electric field was achieved by coating the analysis channel with a polyamine compound to reverse the electroosmotic flow (EOF). EOF reversal forced the cells to take the same path through the electric field. The improved control of the cell trajectory will reduce device-imposed bias on the analysis and maximizes the amount of lysate injected into the analysis channel for each cell, resulting in improved analyte detection capabilities.     

Pre-nucleation dynamics of organic molecule self-assembly investigated by PEEM

Pre-nucleation dynamics, nucleation and templated self-assembly of a conjugated planar aromatic molecule are investigated by photoemission electron microscopy (PEEM). The high resolution of individual molecular layers in PEEM, in combination with a numerical simulation, reveals the dynamic behaviour of molecules during the pre-nucleation deposition period and their temperature dependence. The in situ deposition of p-sexiphenyl (6P) molecules on Cu(110) and Cu(110) 2 × 1-O surfaces in ultrahigh vacuum, when monitored by PEEM in real-time allows (a) layer densities, (b) meta-stable layer filling by 6P molecules, (c) dynamic surface redistributions during layer filling and (d) critical density spontaneous dewetting to be accurately measured. The comparison of 6P deposited on Cu(110) to Cu(110) 2 × 1-O enables temperature dependent 6P nucleation processes on Cu(110) to be elucidated from PEEM. The interplay between energetically stable molecular arrangements and kinetically stabilised arrangements is shown to dominate the pre- and post-nucleation processes. In combination with additional data obtained during post-nucleation deposition times, such as surface diffusion anisotropies and nucleation energies, it is concluded that the pre-requisite for 6P nucleation, in a lying down orientation, is the formation of a double tilted layer with at least one layer being meta-stable.     

The isomorphism problem for some universal operator algebras

This paper addresses the isomorphism problem for the universal (non-self-adjoint) operator algebras generated by a row contraction subject to homogeneous polynomial relations. We find that two such algebras are isometrically isomorphic if and only if the defining polynomial relations are the same up to a unitary change of variables, and that this happens if and only if the associated subproduct systems are isomorphic. The proof makes use of the complex analytic structure of the character space, together with some recent results on subproduct systems. Restricting attention to commutative operator algebras defined by a radical ideal of relations yields strong resemblances with classical algebraic geometry. These commutative operator algebras turn out to be algebras of analytic functions on algebraic varieties. We prove a projective Nullstellensatz connecting closed ideals and their zero sets. Under some technical assumptions, we find that two such algebras are isomorphic as algebras if and only if they are similar, and we obtain a clear geometrical picture of when this happens. This result is obtained with tools from algebraic geometry, reproducing kernel Hilbert spaces, and some new complex-geometric rigidity results of independent interest. The C^?-envelopes of these algebras are also determined. The Banach-algebraic and the algebraic classification results are shown to hold for the wot-closures of these algebras as well.     

An operator-valued Lyapunov theorem

We generalize Lyapunov's convexity theorem for classical (scalar-valued) measures to quantum (operator-valued) measures. In particular, we show that the range of a nonatomic quantum probability measure is a weak^?-closed convex set of quantum effects (positive operators bounded above by the identity operator) under a sufficient condition on the non-injectivity of integration. To prove the operator-valued version of Lyapunov's theorem, we must first define the notions of essentially bounded, essential support, and essential range for quantum random variables (Borel measurable functions from a set to the bounded linear operators acting on a Hilbert space).     

A model of a 2-player stopping game with priority and asynchronous observation

Various models of 2-player stopping games have been considered which assume that players simultaneously observe a sequence of objects. Nash equilibria for such games can be found by first solving the optimal stopping problems arising when one player remains and then defining by recursion the normal form of the game played at each stage when both players are still searching (a 2 × 2 matrix game). The model considered here assumes that Player 1 always observes an object before Player 2. If Player 1 accepts the object, then Player 2 does not see that object. If Player 1 rejects an object, then Player 2 observes it and may choose to accept or reject it. It is shown that such a game can be solved using recursion by solving appropriately defined subgames, which are played at each moment when both players are still searching. In these subgames Player 1 chooses a threshold, such that an object is accepted iff its value is above this threshold. The strategy of Player 2 in this subgame is a stopping rule to be used when Player 1 accepts this object, together with a threshold to be used when Player 1 rejects the object. Whenever the payoff of Player 1 does not depend on the value of the object taken by Player 2, such a game can be treated as two optimisation problems. Two examples are given to illustrate these approaches.     

Cyanogen on Ni(110): an experimental and theoretical study

Adsorption of cyanogen, C₂N₂, on a Ni(110) surface has been investigated by combining low energy electron diffraction, thermal desorption and angular resolved ultra-violet photoemission experiments as well as model cluster calculations using the linear combination of Gaussian-type orbitals local density functional method as well as a force field approach. Results of mirror plane photoemission experiments on the ordered c(2 × 2) monolayer could be rationalized by invoking adsorbates bonded to the surface via the π electrons, with their axis oriented along the [001] direction, across the grooves of the (110) surface, leading to an assignment of all six adsorbate-derived valence orbitals. However, unlike in a previous study on the analogous chemisorption system Pd(110)/C₂N₂, only one mirror plane was detected. A possible tilt of the adsorbates in the (1 0) plane was related to crowding on the closer spaced nickel surface by estimating the lateral interaction within the adsorption layer using force field models. Electronic structure calculations on various chemisorption model clusters confirmed the experimental orbital assignment and the orientation of the adsorbate axis essentially along the [001] direction. Best agreement with UPS data was found for the orbital splitting pattern of an adsorption geometry where the C-N groups bind sideways on-top of nickel atoms in the first crystal plane. On the other hand, bonding along in the troughs of the (110) surface leads to a distinctly different ordering of the valence orbitals, at variance with the experimental assignment.     

A cautionary tale of principal component analysis: an example from inductively-coupled plasma/atomic emission spectrometry

Principal component analysis (PCA) is a widely used chemometric technique, but there can be serious limitations on the validity of the conclusions. In the example given, PCA was applied to identify the causes of noise and drift in inductively-coupled plasma/atomic emission spectrometry (ICP/AES). The effects of ten possible instrumental variables on lines of 24 elements were measured independently to establish distinctive “fingerprints”. PCA showed that >90% of the variance in routine analysis was correlated between elements, rather than being random. However, the multi-element ‘fingerprints’ identified as the principal components did not correspond to any of those established as suspected causes. A model based on variation of two of the suspected causes of error was used to simulate analysis by ICP/AES. When subjected to PCA, the simulated data also gave erroneous fingerprints in the principal components that closely matched those found in the real data. The reason for the failure of PCA to identify the causes of the variation was found to be that the two apparently independent causes had correlated multi-element effects. Caution is therefore required in the identification of principal components in terms of recognisable features.     

A review of electronics design for auger electron spectroscopy

The technique of modulation phase-sensitive detection for Auger electron spectroscopy has changed little in principle since its inception in the late 1960's. However the 1970's have seen significant improvements with the introduction of highly-tuned preamplifiers, high performance oscillators, the use of integral rather than derivative spectra, and dynamical background substraction. These Improvements have largely been brought about by the availability of inexpensive integrated circuits (IC's) and by computer control. The authors have considered new modulation coupling approaches and the up-dating of high voltage ramp windowing circuits.