Cellular automata modelling of hantarvirus infection

Hantaviruses are a group of viruses which have been identified as being responsible for the outbreak of diseases such as the hantavirus pulmonary syndrome. In an effort to understand the characteristics and dynamics of hantavirus infection, mathematical models based on differential equations have been developed and widely studied. However, such models neglect the local characteristics of the spreading process and do not include variable susceptibility of individuals. In this paper, we develop an alternative approach based on cellular automata to analyze and study the spatiotemporal patterns of hantavirus infection.     

Decomposability for division algebras of exponent two and associated forms

This article investigates the structure of quadratic forms and of division algebras of exponent two over fields of characteristic different from two with the property that the third power of the fundamental ideal in the associated Witt ring is torsion free.      

Sums of squares in function fields of hyperelliptic curves

We study sums of squares, quadratic forms, and related field invariants in a quadratic extension of the rational function field in one variable over a hereditarily pythagorean base field.     

Rheological properties of carboxymethyl cellulose (CMC) solutions

In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure–properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.     

Circularly Symmetric Static Metric in Three Dimensions and Its Killing Symmetry

In this note we consider a general three-dimensional circularly symmetric static metric and investigate possible Killing symmetries it possesses.We then summarize the work by addressing Einstein equations and briefly discuss their implications on the energy momentum content of some of the metrics that arise in the process.     

Generation of an ultrabroadband supercontinuum in the mid-infrared region using dispersion-engineered GeAsSe photonic crystal fiber

An ultrabroadband mid-infrared (MIR) region supercontinuum (SC) is demonstrated numerically through dispersion-engineered traditional chalcogenide (ChG) photonic crystal fiber (PCF). By varying structural parameters pitch (hole to hole spacing) and air-hole diameter to pitch ratio, a number of 10-mm-long hexagonal PCFs made employing GeAsSe ChG glass as a core and air-holes of hexagonal lattice running through their lengths as a cladding are optimized to predict an efficient mid-infrared region SC spectral emission by pumping them using a tunable pump source between 2.9 and 3.3 µm. Simulations are carried out using an ultrashort pump pulse of 100-fs duration with a low pulse peak powers of between 3 and 4 kW into the optimized designs. It is found through numerical analysis that efficient SC spectral broadening with flattened output can be obtained by increasing the PCF pitch rather than increasing the PCF cladding containing air-hole diameter although a larger nonlinear coefficient could be obtained through increasing air-hole diameter of an optimized design. Simulation results show that the SC spectra can be broadened up to 12.2 µm for a certain design with a peak power of 3 kW. Using a peak power of 4 kW, it is possible to obtain SC spectral broadening beyond 14 µm with an optimized design spanning the wavelength range from 1.8 to 14 µm which covers the electromagnetic spectrum required for MIR molecular fingerprint region applications such as sensing and biological imaging.     

Synthesis and magnetic characterization of nickel ferrite nanoparticles prepared by co-precipitation route

Magnetic nanoparticles of nickel ferrite (NiFe₂O₄) have been synthesized by co-precipitation route using stable ferric and nickel salts with sodium hydroxide as the precipitating agent and oleic acid as the surfactant. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses confirmed the formation of single-phase nickel ferrite nanoparticles in the range 8-28 nm depending upon the annealing temperature of the samples during the synthesis. The size of the particles (d) was observed to be increasing linearly with annealing temperature of the sample while the coercivity with particle size goes through a maximum, peaking at ∼11 nm and then decreases for larger particles. Typical blocking effects were observed below ∼225 K for all the prepared samples. The superparamagnetic blocking temperature (T_B) was found to be increasing with increasing particle size that has been attributed to the increased effective anisotropy energy of the nanoparticles. The saturation moment of all the samples was found much below the bulk value of nickel ferrite that has been attributed to the disordered surface spins or dead/inert layer in these nanoparticles.     

Cross Psi(B)-energy operator-based signal detection

In this paper, two methods for signal detection and time-delay estimation based on the cross Psi(B)-energy operator are proposed. These methods are well suited for mono-component AM-FM signals. The Psi(B) energy operator measures how much one signal is present in another one. The peak of the Psi(B) operator corresponds to the maximum of interaction between the two signals. Compared to the cross-correlation function, the Psi(B) operator includes temporal information and relative changes of the signal which are reflected in its first and second derivatives. The discrete version of the continuous-time form of the Psi(B) operator, which is used in its implementation, is presented. The methods are illustrated on synthetic and real signals and the results compared to those of the matched filter and the cross correlation. The real signals correspond to impulse responses of buried objects obtained by active sonar in iso-speed single path environments.     

Measurement of the fundamental thermal noise limit in a cryogenic sapphire frequency standard using bimodal maser oscillations

We report observations of the Schawlow-Townes noise limit in a cryogenic sapphire secondary frequency standard. The effect causes a fundamental limit to the frequency stability, and was measured through the novel excitation of a bimodal maser oscillation of a Whispering Gallery doublet at 12.04 GHz. The beat frequency of 10 kHz between the oscillations enabled a sensitive probe for this measurement of fractional frequency instability of 10(-14) tau(-1/2) with only 0.5 pW of output power.