The role of radiative losses in self-extinguishing and self-wrinkling flames

We have developed a general theory of non-adiabatic premixed flames that is valid for flames of arbitrary shape that fully accounts for the hydrodynamic and diffusive-thermal processes, and incorporates the effects of volumetric heat losses. The model is used to describe aspects of experimentally observed phenomena of self-extinguishing (SEFs) and self-wrinkling flames (SWFs), in which radiative heat losses play an important role. SEFs are spherical flames that propagate considerable distances in sub-limit conditions before suddenly extinguishing. Our results capture many aspects of this phenomenon including an explicit determination of flame size and propagation speed at quenching. SWFs are hydrodynamically unstable flames in which cells spontaneously appear on the flame surface once the flame reaches a critical size. Our results yield expressions of the critical flame size at the onset of wrinkling and expected cell size beyond the stability threshold. The various possible burning regimes are mapped out in parameter space.     

Quantum chemical studies of non-covalent interactions between the ethyl cation and rare gases

By taking into consideration the facts that rare gases (Ar, He, Kr, and Ne) are practically inert and that the structure of the ethyl cation (C₂H₅⁺) is stabilized through the hyperconjugation effect, a theoretical study at the B3LYP/6-311 + +G(d,p) level of calculation was carried out here in order to investigate the formation of the C₂H₅⁺···Ar, C₂H₅⁺···He, C₂H₅⁺···Kr, and C₂H₅⁺···Ne complexes. The charge transfers among H and Ar, He, Kr or Ne prove that the loss of electronic density on the rare gases are clearly noticeable. Additionally, the synergism between the structural changes and the vibration shifts have been demonstrated and justified on the basis of the Bent rule and QTAIM calculations. In complement, the interaction strength in H⁺···Ar, H⁺···He, H⁺···Kr, and H⁺···Ne was examined, although the covalent character is completely null because these contacts are very weak.     

The combinatorics of τ-covers

We solve four out of the six open problems concerning critical cardinalities of topological diagonalization properties involving τ-covers, show that the remaining two cardinals are equal, and give a consistency result concerning this remaining cardinal. Consequently, 21 open problems concerning potential implications between these properties are settled. We also give structural results based on the combinatorial techniques.     

Visibility preserving terrain simplification— an experimental study

The terrain surface simplification problem has been studied extensively, as it has important applications in geographic information systems and computer graphics. The goal is to obtain a new surface that is combinatorially as simple as possible, while maintaining a prescribed degree of similarity with the original input surface. Generally, the approximation error is measured with respect to distance (e.g., Hausdorff) from the original or with respect to visual similarity. In this paper, we propose a new method of simplifying terrain surfaces, designed specifically to maximize a new measure of quality based on preserving inter-point visibility relationships. Our work is motivated by various problems of terrain analysis that rely on inter-point visibility relationships, such as optimal antenna placement.

We have implemented our new method and give experimental evidence of its effectiveness in simplifying terrains according to our quality measure. We experimentally compare its performance with that of other leading simplification methods.     

Acoustic centering of sources measured by surrounding spherical microphone arrays

The radiation patterns of acoustic sources have great significance in a wide range of applications, such as measuring the directivity of loudspeakers and investigating the radiation of musical instruments for auralization. Recently, surrounding spherical microphone arrays have been studied for sound field analysis, facilitating measurement of the pressure around a sphere and the computation of the spherical harmonics spectrum of the sound source. However, the sound radiation pattern may be affected by the location of the source inside the microphone array, which is an undesirable property when aiming to characterize source radiation in a unique manner. This paper presents a theoretical analysis of the spherical harmonics spectrum of spatially translated sources and defines four measures for the misalignment of the acoustic center of a radiating source. Optimization is used to promote optimal alignment based on the proposed measures and the errors caused by numerical and array-order limitations are investigated. This methodology is examined using both simulated and experimental data in order to investigate the performance and limitations of the different alignment methods.     

Investigation of spherical loudspeaker arrays for local active control of sound

Active control of sound can be employed globally to reduce noise levels in an entire enclosure, or locally around a listener's head. Recently, spherical loudspeaker arrays have been studied as multiple-channel sources for local active control of sound, presenting the fundamental theory and several active control configurations. In this paper, important aspects of using a spherical loudspeaker array for local active control of sound are further investigated. First, the feasibility of creating sphere-shaped quiet zones away from the source is studied both theoretically and numerically, showing that these quiet zones are associated with sound amplification and poor system robustness. To mitigate the latter, the design of shell-shaped quiet zones around the source is investigated. A combination of two spherical sources is then studied with the aim of enlarging the quiet zone. The two sources are employed to generate quiet zones that surround a rigid sphere, investigating the application of active control around a listener's head. A significant improvement in performance is demonstrated in this case over a conventional headrest-type system that uses two monopole secondary sources. Finally, several simulations are presented to support the theoretical work and to demonstrate the performance and limitations of the system.     

Voltage-controlled metal binding on polyelectrolyte-functionalized nanopores

Most of the research in the field of nanopore-based platforms is focused on monitoring ion currents and forces as individual molecules translocate through the nanopore. Molecular gating, however, can occur when target analytes interact with receptors appended to the nanopore surface. Here we show that a solid state nanopore functionalized with polyelectrolytes can reversibly bind metal ions, resulting in a reversible, real-time signal that is concentration dependent. Functionalization of the sensor is based on electrostatic interactions, requires no covalent bond formation, and can be monitored in real time. Furthermore, we demonstrate how the applied voltage can be employed to tune the binding properties of the sensor. The sensor has wide-ranging applications and, its simplest incarnation can be used to study binding thermodynamics using purely electrical measurements with no need for labeling.     

Growth and characterization of a novel organic nonlinear optical material: l-alanine 2-furoic acid

l-alanine 2-furoic acid (LA2FA), a novel organic third order nonlinear optical material was grown by slow solvent evaporation technique at room temperature. The grown single crystals were characterized by XRD, spectral, thermal, optical, dielectric and third order nonlinear properties. LA2FA crystallizes into triclinic system with the space group P1. The cell parameters are found to be a = 3.97 Å, b = 7.09 Å, c = 10.69 Å, α = 73.61°, β = 83.57°, γ = 84.21° and V = 286 Å3. The modes of vibrations of different molecular groups present in LA2FA were identified by FTIR studies. The optical transparency of the grown crystals was investigated by UV–visible spectrum. The absorption spectrum reveals that the crystal has a high UV cut off of 245 nm and photonic band gap of 2.5 eV. The scanning electron microscope (SEM) study has been carried out to determine the surface morphology of the grown crystal. The thermal behavior of the crystal investigated using thermo gravimetric (TG) and differential thermal analysis (DTA) indicates that the material does not decompose before melting. The third order NLO property was studied in detail by z-scan technique.     

Short expressions of permutations as products and cryptanalysis of the Algebraic Eraser

On March 2004, Anshel, Anshel, Goldfeld, and Lemieux introduced the Algebraic Eraser scheme for key agreement over an insecure channel, using a novel hybrid of infinite and finite noncommutative groups. They also introduced the Colored Burau Key Agreement Protocol (CBKAP), a concrete realization of this scheme.