The stability of the Roman arch

An analysis is presented to determine the conditions obtaining when the classical semicircular Roman arch is on the verge of collapse. In general, the analysis is rather involved although surprisingly simple results are obtained in one limiting case.     

Critical flicker frequency for paretics and schizophrenics.

"The results of this experiment tend to verify the hypothesis that CFF is in part a function of organic pathology. It has been shown that lower CFF is associated with cerebral neural malfunctioning resulting from paresis." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigation of fill and batch periods of sequencing batch biological reactors

Early use of sequencing batch (fill and draw) biological reactors was abandoned in favor of conventional continuous flow constant volume treatment systems because of operational difficulties. Recent advances in process control and the need to provide more reliable and consistent treatment have called for the re-evaluation of present biological treatment practices. Fill and draw reactors provide for equalization of flow and concentration, treatment of organics and quiescent sedimentation in the same system. This system also benefits from the theoretical advantages of the volume reductions expected from a plug flow system. Laboratory studies were conducted on fill and draw reactors. A mathematical model was developed to describe, as a function of time, the waste and organism concentration and the oxygen uptake rate. Close agreement between the measured and predicted values was obtained. These results plus the obvious potential benefits of batch treatment suggest that sequencing batch systems may serve as a process alternative to conventional treatment schemes.     

Live Lymphocyte Arrays for Biosensing

Systems designed to sensitively and accurately detect whole pathogen particles, their components, or other proteins diagnostic of infection or disease are of interest as sensors for biodefense and clinical diagnostics. To this end, we examined the potential of a sensing strategy based on live T‐cell/B‐cell interactions in a biosensor chip format. An approach to fabricate patterned hydrogel microwells functionalized at their bases with antibodies to promote specific immobilization of lymphocytes was developed and used to array single T cells in a regular pattern on a substrate. A sensing platform was created by overlaying arrayed T cells with a confluent layer of antigen‐capturing B cells. In this system, a peptide analyte added to the chip was captured by B cells and physically presented to arrayed T cells by B‐cell‐surface major histocompatibility complex molecules, triggering T cells through their T‐cell receptors. T‐cell recognition of the target peptide was detected by fluorescence measurements of T‐cell intracellular calcium levels, a biochemical read‐out of T‐cell receptor triggering. We demonstrate that this approach allows rapid, sensitive detection of a model peptide analyte, and that T‐cell arrays allow for maximal T‐cell/B‐cell contacts while simultaneously optimizing single‐cell fluorescence detection for analysis of the sensor response. This approach could be of interest for the design of sensing platforms that can detect both peptide fragments and whole intact pathogens, irrespective of surface mutations that might be induced naturally or during “weaponization”.     

In situ reflectance monitoring in MOVPE of a multiwafer reactor

A new design is presented that combines an interferometer and rotation monitor for in situ monitoring of variations in the growth process in Aixtron planetary reactors. Particular attention was paid to the growth of GaAs and Vertical Cavity Surface Emitting Laser (VCSEL) structures with the aim of increasing the level of understanding of the growth process and enable improvements in control and batch to batch reproducibility. It is anticipated that the properties of the Bragg reflectors will be predicted during the growth of the VCSEL structure by monitoring variations in the growth and using a predictive model based on the virtual interface model. Results are presented on planetary rotation under different reactor conditions, while the use of time resolved software to monitor growth, is discussed.     

Achieving Microparticles with Cell‐Instructive Surface Chemistry by Using Tunable Co‐Polymer Surfactants

A flow‐focusing microfluidic device is used to produce functionalized monodisperse polymer particles with surface chemistries designed to control bacterial biofilm formation. This is achieved by using molecularly designed bespoke surfactants synthesized via catalytic chain transfer polymerization. This novel approach of using polymeric surfactants, often called surfmers, containing a biofunctional moiety contrasts with the more commonly employed emulsion methods. Typically, the surface chemistry of microparticles are dominated by unwanted surfactants that dilute/mask the desired surface response. Time of flight secondary ion mass spectrometry (ToF‐SIMS) analysis of particles demonstrates that the comb‐graft surfactant is located on the particle surface. Biofilm experiments show how specifically engineered surface chemistries, generated by the surfactants, successfully modulate bacterial attachment to both polymer films, and microparticles. Thus, this paper outlines how the use of designed polymeric surfactants and droplet microfluidics can exert control over both the surface chemistry and size distribution of microparticle materials, demonstrating their critical importance for controlling surface‐cell response.     

An automatic cryptanalysis of simple substitution ciphers using compression

Automatic recognition of correct solutions as a result of a ciphertext only attack of simple ciphers is not a trivial issue and still remains a taxing problem. A new compression based method for the automatic cryptanalysis of simple substitution ciphers is introduced in this paper. In particular, this paper presents how a Prediction by Partial Matching (PPM) text compression scheme, a method that shows a high level of performance when applied to different natural language processing tasks, can also be used for the automatic decryption of simple substitution ciphers. Experimental results showed that approximately 92% of the cryptograms were decrypted correctly without any errors and 100% with just three errors or less. Extensive investigations are described in this paper, in order to determine which is the most appropriate type of PPM scheme that can be applied to the problem of automatically breaking substitution ciphers. This paper shows how a new character-based PPM variant significantly outperforms other schemes including the standard Gzip and Bzip2 compression schemes. We also apply a word-based variant which when combined with the character-based method leads to further improved results.     

Stochastic Particle Barcoding for Single‐Cell Tracking and Multiparametric Analysis

This study presents stochastic particle barcoding (SPB), a method for tracking cell identity across bioanalytical platforms. In this approach, single cells or small collections of cells are co‐encapsulated within an enzymatically‐degradable hydrogel block along with a random collection of fluorescent beads, whose number, color, and position encode the identity of the cell, enabling samples to be transferred in bulk between single‐cell assay platforms without losing the identity of individual cells. The application of SPB is demonstrated for transferring cells from a subnanoliter protein secretion/phenotyping array platform into a microtiter plate, with re‐identification accuracies in the plate assay of 96±2%. Encapsulated cells are recovered by digesting the hydrogel, allowing subsequent genotyping and phenotyping of cell lysates. Finally, a model scaling is developed to illustrate how different parameters affect the accuracy of SPB and to motivate scaling of the method to thousands of unique blocks.