Small Parameter Variations Research Articles

Probability density of field and intensity fluctuations of structured light in a turbulent atmosphere

Distributions of the probability density of fluctuations of the intensity and real and imaginary parts of the complex field amplitude of the Laguerre–Gaussian laser beam propagating through a turbulent atmosphere, provided that the beam scintillation index takes values larger than unity, are studied. The calculations are performed through numerical simulation and with application of an analytical approach based on the expansion of the probability distribution density of the wave field into the Edgeworth series. The comparison of the results of numerical and analytical calculations has demonstrated that the probability density distribution of intensity fluctuations of the laser beam is resistant to small variations in parameters of the probability density distribution of fluctuations of the real and imaginary parts of the wave field. In addition, the earlier formulated statement that the normalized probability density of intensity fluctuations of a laser beam at any point of the space occupied by this beam is determined by the value of the scintillation index and does not depend directly on the turbulent propagation conditions is confirmed. It is shown that the probability density of intensity fluctuations constructed with the Edgeworth approximation of the probability density of field fluctuations is in good agreement with the results of numerical simulation and the fractional exponential distribution for the values of the scintillation index ranging from 1.0 to 1.6.

Improved Energy Absorption in 3D Woven Composites by Weave Parameter Manipulation

3D woven composites show significantly improved out-of-plane properties over traditional 2D laminates. This high through-thickness reinforcement is desirable in crashworthiness applications where crushing energy can be increased by composites’ improved interlaminar toughness. However, their use in practical applications is stunted by the poor understanding of how small variations in weave parameters, whether intended or not, affect the performance of these materials. Here, we demonstrate that small changes in textile properties, in this case pick density and float length have a knock-on effect that can greatly improve or diminish the crush performance of a 3D woven layer-to-layer structural fabric. Quasi-static and dynamic energy absorption values up to approximately 95J/g and 92J/g respectively are achieved. Crush performance is investigated on omega-shaped coupons, under both quasi-static and dynamic loading conditions with crush rates between 2mm/min and 8.5m/s. The failure mechanisms present during progressive crush under quasi-static loading transitions between more expected brittle dominated failure and ductile dominated failure, which is more typical of metals under similar loading conditions. Whereas when dynamic loading is considered, the materials present a more typical splaying failure event. As a result, additional exploration of the three-point bending response of these varied architectures is presented as a means of further explaining the interplay between lamina bending and progressive folding/micro-buckling in these materials. The effect of the weave’s architectural alterations on physical composite properties such as weight, density and conformability to shape is also investigated.

Combination of pulsed laser ablation and inert gas condensation for the synthesis of nanostructured nanocrystalline, amorphous and composite materials.

A new instrument combining pulsed laser ablation and inert gas condensation for the production of nanopowders is presented. It is shown that various nanostructured materials, such as regular metallic, semiconducting, insulating materials, complex high entropy alloys, amorphous alloys, composites and oxides can be synthesized. The unique variability of the experimental set-up is possible due to the reproducible control of laser power (pulse energy and repetition rate), laser ablation pattern on the target, and experimental conditions during the inert gas condensation, all of which can be controlled and optimized independently. Microstructure analysis of the as-prepared composite and amorphous Ni60Nb40 nanopowders establishes the instrument's ability for the synthesis of materials with unique compositions and atomic structure. It is further shown that small variations of the synthesis parameters can influence materials properties of the final product, in terms of particle size, composition and properties. As an example, the laser power has been used to control the magnetic properties of amorphous Ni60Nb40 nanopowders. A few selected examples of the manifold possibilities of the new synthesis apparatus are presented in this report together with detailed structural characterization of the produced nanopowders.

A mathematical model for the robust blood glucose tracking.

In this paper, we study the problem of the robust blood glucose tracking. Tracking here means that the error between a state variable of a system under control and its desired time-varying reference converges to zero over time. Robustness here means that a controller designed for a system can tolerate a small variation of the system parameters. Since the parameters in the blood glucose regulation system differ in people, such a robust controller is useful in the insulin pump technology: an insulin pump equipped with such a robust controller could be used in a group of people. Thus, in our study, parameter uncertainties are introduced into a mathematical model of the blood glucose regulation system. Using an actual blood glucose level as feedback and an exogenous glucose input and a desired glucose reference as feedforward, we design a robust feedback and feedforward controller, which drives the blood glucose to track the desired time-varying glucose reference for any small uncertainties. Numerical simulations with published experimental blood glucose data are conducted to further confirm our theoretical results.

Weierstrass Approach to Asymptotic Behavior Characterization of Critical Imaginary Roots for Retarded Differential Equations

This paper focuses on the analysis of the behavior of characteristic roots of time-delay systems, when the delay is subject to small parameter variations. The analysis is performed by means of the ...

Na3MnZr(PO4)3: A High-Voltage Cathode for Sodium Batteries

Sodium batteries have been regarded as promising candidates for large-scale energy storage application, provided cathode hosts with high energy density and long cycle life can be found. Herein, we report NASICON-structured Na3MnZr(PO4)3 as a cathode for sodium batteries that exhibits an electrochemical performance superior to those of other manganese phosphate cathodes reported in the literature. Both the Mn4+/Mn3+ and Mn3+/Mn2+ redox couples are reversibly accessed in Na3MnZr(PO4)3, providing high discharge voltage plateaus at 4.0 and 3.5 V, respectively. A high discharge capacity of 105 mAh g-1 was obtained from Na3MnZr(PO4)3 with a small variation of lattice parameters and a small volume change on extraction of two Na+ ions per formula unit. Moreover, Na3MnZr(PO4)3 exhibits an excellent cycling stability, retaining 91% of the initial capacity after 500 charge/discharge cycles at 0.5 C rate. On the basis of structural analysis and density functional theory calculations, we have proposed a detailed desodiation pathway from Na3MnZr(PO4)3 where Mn and Zr are disordered within the structure. We further show that the cooperative Jahn-Teller distortion of Mn3+ is suppressed in the cathode and that Na2MnZr(PO4)3 is a stable phase.

The swampland, quintessence and the vacuum energy

It has recently been conjectured that string theory does not admit de Sitter vacua, and that quintessence explains the current epoch of accelerated cosmic expansion. A proposed, key prediction of this scenario is time-varying couplings in the dark sector, induced by the evolving quintessence field. We note that cosmological models with varying couplings suffer from severe problems with quantum corrections, beyond those shared by all quintessence models. The vacuum energy depends on the masses and couplings of the theory, and even small variations of parameters can lead to overwhelmingly large corrections to the effective potential. We find that quintessence models with varying parameters can be realised in consistent quantum theories by either: 1) enforcing exceptional levels of fine-tuning; 2) realising some unknown mechanism that cancels all undesirable contributions to the effective potential with unprecedented accuracy; or 3) ensuring that the quintessence field couples exclusively to very light states, and does not backreact on heavy fields.

Uncertainty analysis and estimation of robust AIREBO parameters for graphene

AIREBO is one of the commonly utilized interatomic potential (IP) for performing molecular dynamics (MD) simulations of graphene and carbon nanostructures. With its parameters fitted to a limited dataset, property prediction outside of the original training set can be challenging and can lead to uncertainty in the predicted values. This is especially important for 2D materials such as graphene which have limited experimental data and have widely varying predicted properties in the literature. In this study, we conducted a comprehensive Uncertainty Quantification (UQ) analysis of AIREBO potential parameters and their corresponding effect on the predicted properties of graphene. We found that computed output properties were highly sensitive to small variations in IP parameters. For instance, a 0.5% change in IP parameters led to a 66% change in the predicted elastic constants. Based on our UQ analysis, we developed a new robust IP parameter set for the AIREBO potential with significantly reduced sensitivity towards output properties. The robust parameters were derived using a Markov Chain Monte Carlo scheme, considering gaussian noise in available DFT data. We were also able to obtain realistic error bars on MD predictions by using posterior probability distributions and propagating the underlying variance to the final properties.

Study on the Impact of Machine Parameter Variations on Performance of Modular Pulsed Alternator Power System

As the muzzle energy in the electromagnetic launch increases, it becomes necessary to use a modular pulsed alternator power system composed of multiple pairs of machines connected in parallel. In practical situations, however, parameter variations between two machines are inevitable, and it has uncertain effects on the system performance. Furthermore, due to pulsed alternators driving railgun through a rectifier, the system connection scheme has two options: 1) two machines are connected in parallel before connecting them to the rectifier and 2) two machines are connected in parallel after connecting them to the rectifier. The sensitivity of two topologies to the parameter variations is also uncertain. To make sense of this uncertainty, the impact of machine parameter variations on the system performance is investigated. This paper is performed on the simulation of a pair of pulsed alternators driving a railgun, using one-factor-at-a-time method to observe the system performance in the parameter variations. The sensitivity of two topologies is analyzed taking into account small variations in machine manufacturing parameters—rotor inertia, field winding, and armature winding and in machine control parameters—rotor speed and rotor angle. The results reveal that the system performance is more sensitive to the machine control parameters compared with the machine manufacturing parameters, especially the initial offset in the rotor angle. Furthermore, the connection scheme in which two machines connected in parallel before connecting them to the rectifier is the more robust and is less sensitivity to parameter variations compared with the other topology. This paper is aimed at the identification of the most sensitive parameter and the more robust topology to provide support for the further application.

The Iron State in Spleen and Liver Tissues from Patients with Hematological Malignancies Studied Using Magnetization Measurements and Mössbauer Spectroscopy

In this overview, we present the results of the study of spleen and liver tissues taken from healthy donors in comparison with those from patients with (i) non-Hodgkin B-cell lymphomas, namely, mantle cell lymphoma and marginal zone B-cell lymphoma, (ii) acute myeloid leukemia, and (iii) primary myelofibrosis. The study was carried out using Mössbauer spectroscopy and magnetization measurements for the analysis of ferritin-like iron in spleen and liver tissues. Magnetization measurements demonstrated small differences in the saturation magnetic moments and revealed additional paramagnetic components. Two liver samples demonstrated unusual behavior of the magnetic moment when the zero-field-cooled curve was over the field-cooled curve in the temperature range between ~40 and ~70 K. Relative iron content variations in the tissue cells as well as small variations in the 57Fe hyperfine parameters were demonstrated for healthy and patients' spleen and liver tissues on the base of measured Mössbauer spectra. The results obtained permit us to suggest small differences in the ferritin iron core structure in spleen and liver tissues from healthy donors and patients with hematological malignancies.

Recombination Waves in Dusty Plasma of a Non-Self-Sustained Discharge

The steady-state, spatially periodic, structures generated by the evolution of the nonlinear stage of recombination instability in dusty plasma of a non-self-sustained discharge are studied. The research has revealed two types of structures typical for this kind of discharge; they differ in the rates of the increment of recombination instability. The features of each type of structure are described, and the mechanism of their formation is presented. It is shown that the calculation results qualitatively and, with a small variation of discharge parameters, quantitatively agree with the experimental data.

Modelling Transition From Normal To Epileptic Eeg Signals: A Neuron-Astrocyte Mass Action Approach

Epileptic seizures occur intermittently as a result of complex dynamical interactions among many regions of the brain. The sudden and apparently unpredictable nature of refractory seizures is one of the most disabling aspects of the disease. Therefore, there is need for interdisciplinary research efforts directed at better understanding of the mechanisms involved in the emergence of epileptic seizures. Our research objective in this field is the use of applied methods from deterministic and nondeterministic dynamical systems modeling to study epilepsy. Dynamical systems refer to systems whose state variables evolve in time. By the assumption of deterministic system,the physiological system (the brain) can be treated as low dimensional without any random components. Nondeterministic assumption on the other hand allows randomness in some input components. We developed at the macroscopic level physiologically based mathematical models of parts of the brain believed to be eliciting the abnormal signals observed during Generalized Absence Epilepsy (GAE) and Temporal Lobe Epilepsy (TLE). In developing our models, we considered the activities of nerve cells, the surrounding astrocyte cells and the dynamics of extracellular neurotransmitters and conducted parameter sensitivity studies on our models. The models were then validated using Electroencephalogram (EEG) data of epileptic patients. The important conclusion from our findings is that the transition from normal to epileptic brain activity is critically dependent on small variations in few system parameters and/or the balance between a small number of system parameters, be it neural or astrocytes activity dependent

Fast and sensitive method for the determination of trace 1,2,4-triazole and 4-amino-1,2,4-triazole by hydrophilic interaction liquid chromatography (HILIC) in antifungal drug substance

An HILIC method was developed to quantitatively determine trace amounts of 1,2,4-triazole and 4-amino-1,2,4-triazole in fluconazole drug substance. Separation was achieved on HILIC column using isocratic elution with mixture of water, acetonitrile and phosphoric acid mobile phase and UV detection at 205 nm. The method was validated according to ICH guideline requirements and was determined to be linear in the range of 0.6–22.0 μg/mL. Method accuracy and precision were assessed by spiking 1,2,4-triazole and 4-amino-1,2,4-triazole at three levels over the range of 2.5–15 μg/mL, the recoveries ranged from 78.6% to 95.7% for 1,2,4-triazole and 94.6% to 103.4% for 4-amino-1,2,4-triazole. The intermediate precision was represented by the overall %RSD of 6.9% (n = 9) for 1,2,4-triazole and 3.6% (n = 9) for 4-amino-1,2,4-triazole. The method was also shown to be repeatable at concentration levels of 2.5, 12.5 and 15 μg/mL with n = 3 %RSD values of 3.7%, 1.0% and 1.3% for 1,2,4-triazole, and 0.3%, 1.2% and 0.6% for 4-amino-1,2,4-triazole. The method was found to be specific, stability-indicating and has a detection limit of 0.8 μg/mL and a quantitation limit of 2.5 μg/mL. Finally, the method was demonstrated to be robust to small variations of key chromatographic parameters.

Independent caudal fin actuation enables high energy extraction and control in two-dimensional fish-like group swimming

We study through numerical simulation the optimal hydrodynamic interactions and basic vorticity control mechanisms for two fish-like bodies swimming in tandem. We show that for a fish swimming in the wake of an upstream fish, using independent pitch control of its caudal fin, in addition to optimized body motion, results in reduction of the energy needed for self-propulsion by more than 50 %, providing a quasi-propulsive efficiency of 90 %, up from 60 % without independent caudal fin control. Such high efficiency is found over a narrow parametric range and is possible only when the caudal fin is allowed to pitch independently from the motion of the main body. We identify the vorticity control mechanisms employed by the body and tail to achieve this remarkable performance through thrust augmentation and destructive interference with the upstream fish-generated vortices. A high sensitivity of the propulsive performance to small variations in caudal fin parameters is found, underlying the importance of accurate flow sensing and feedback control. We further demonstrate that using lateral line-like flow measurements to drive an unscented Kalman filter, the near-field vortices can be localized within 1 % of the body length, and be used with a phase-lock controller to drive the body and tail undulation of a self-propelled fish, moving within the wake of an upstream fish, to stably reach the optimal gait and fully achieve maximum energy extraction.

Tuning the antimicrobial behaviour of Cu85Zr15 thin films in “wet” and “dry” conditions through structural modifications

The antimicrobial behaviour of Cu85Zr15 at.% thin films prepared by magnetron sputtering was studied in both wet and dry conditions. Small variations in key deposition processing parameters (pressure and substrate temperature) enabled the growth of thin films with similar nanostructures but different degrees of compactness, according to the Thornton's structural zone model. This model has proven its effectiveness in providing sensitive structural information to explain significant differences in antimicrobial behaviour of the CuZr thin films, even when processing conditions lie within the same structural zone. The antimicrobial behaviour has been studied for E. coli and S. aureus for up to 4 h of “dry” contact. Structures of lower compactness, grown at higher deposition pressure, are shown to provide higher antimicrobial activity for “dry” conditions than for “wet” conditions. For thin films of CuZr deposited at 0.5 Pa, the reduction percentage of bacteria is 99.47%, which is much higher than the results of 70–80% obtained for the films deposited at 0.1 and 0.3 Pa. Microscopy studies indicate that for 4 h of contact time, bacteria exhibit inner damage and even lysis, however, no morphological changes are detected because of the short timeframes used.

The long-period massive binary HD 54662 revisited

Context.HD 54662is an O-type binary star belonging to the CMa OB1 association. Because of its long-period orbit, this system is an interesting target to test the adiabatic wind shock model.Aims. The goal of this study is to improve our knowledge of the orbital and stellar parameters ofHD 54662and to analyze its X-ray emission to test the theoretical scaling of X-ray emission with orbital separation for adiabatic wind shocks.Methods. We applied a spectral disentangling code to a set of optical spectra to determine the radial velocities and the individual spectra of the primary and secondary stars. The orbital solution of the system was established and the reconstructed individual spectra were analyzed by means of the CMFGEN model atmosphere code. We fitted two X-ray spectra using a Markov chain Monte Carlo algorithm and compared these spectra to the emission expected from adiabatic shocks.Results. We determine an orbital period of 2103.4 days, a surprisingly low orbital eccentricity of 0.11, and a mass ratiom2/m1of 0.84. Combined with the orbital inclination inferred in a previous astrometric study, we obtain surprisingly low masses of 9.7 and 8.2M⊙. From the disentangled primary and secondary spectra, we infer O6.5 spectral types for both stars, of which the primary is about two times brighter than the secondary. The softness of the X-ray spectra for the two observations, the very small variation of best-fitting spectral parameters, and the comparison of the X-ray-to-bolometric luminosity ratio with the canonical value for O-type stars allow us to conclude that X-ray emission from the wind interaction region is quite low and that the observed emission is rather dominated by the intrinsic emission from the stars. We cannot confirm the runaway status previously attributed toHD 54662by computing the peculiar radial and tangential velocities. We find no X-ray emission associated with the bow shock detected in the infrared.Conclusions. The lack of hard X-ray emission from the wind-shock region suggests that the mass-loss rates are lower than expected and/or that the pre-shock wind velocities are much lower than the terminal wind velocities. The bow shock associated withHD 54662possibly corresponds to a wind-blown arc created by the interaction of the stellar winds with the ionized gas of the CMa OB1 association rather than by a large differential velocity between the binary and the surrounding interstellar medium.

Energy transfer driven tunable emission of Tb/Eu co-doped lanthanum molybdate nanophosphors

Tb3+/Eu3+ co-doped lanthanum molybdate nanophosphors were synthesized by conventional co-precipitation method. The Powder X-ray diffractogram revealed the formation of highly crystalline tetragonal nanocrystals with space group I41/a and the detailed analysis of the small variation of lattice parameters with Tb/Eu co-doping on the host lattice were carried out based on the ionic radii of the dopants. The FTIR spectra is employed to identify the fundamental vibrational modes in La2-x-y (MoO4)3:xTb, yEu nanocrystals. The formation of nanocrystals by oriented attachment was recognized from the HR TEM images and the d-spacing calculated was in accordance with that corresponding to highest intensity diffraction peak in the XRD patterns. The constituent elements present in the samples were identified with the aid of EDAX and elemental mapping analysis. The broad Mo6+- O2− CTB and the sharp excitation peaks of Tb and Eu identified from the UV–Vis absorption spectra facilitates the suitability of exciting the phosphors effectively over NUV and visible region of the spectra. The possibility of energy transfer from host to Tb3+/Eu3+ ions and from Tb3+ to Eu3+ ions were confirmed from the PL excitation spectra monitoring 5D0→7F2 transition of Eu3+ ions around 615 nm. The correlated analysis of PL emission spectra, life time measurements and CIE diagram, upon different excitation channels elucidate the excellent luminescent properties of La2-x-y (MoO4)3:xTb, yEu nanophosphors with tunable emission colours in a wide range varying from yellow green region to reddish orange region and the efficient energy transfer from Tb3+ to Eu3+ ions in lanthanum molybdate host lattice. The Tb→Eu energy transfer efficiency and probability were calculated from the decay measurements and the values were found to be satisfactory for exploiting the prepared nanophosphors for the development of multifunctional luminescent nanophosphors.

Shape Optimization of Devices Taking Into Account Production Tolerances

This paper presents a new technique of shape optimization of devices taking into account acceptable tolerances of their dimensions. The technique is based on a combination of classic optimization procedures and a sensitivity analysis carried out in several steps in the course of the optimization process. This analysis is able to decide whether the given variant is worth further optimizing or the changes in the objective functions are unacceptably high even with small variations of parameters (such a variant is immediately rejected). The power of the methodology is illustrated on an example of induction brazing, whose results are discussed.

Observation of Stable Sound Field Components in Lake Ladoga

The paper presents the results of processing measurement data on the spatiotemporal structures of sound fields in Lake Ladoga. Measurements were taken with an extended vertical receiver array. The aim of processing was to isolate the field components that were stable with respect to small variations in the waveguide parameters. Since a model of the medium is inevitably inaccurate, such components can be predicted with greater accuracy than the total field. In terms of the ray approach, a stable component is generated by a beam of rays propagating over close trajectories. The discussed experiment analyzed sound fields excited by a point source that emitted wideband pulses, as well as the fields of wave beams excited by the emitting vertical array at fixed frequencies. In both cases, the processing results showed that the isolated stable components, as expected, coincide substantially better with the prediction of theoretical calculation (by the wide angle parabolic equation method) than with the total wave field.

Floristic composition, structure and soil-vegetation relations in three white-sand soil patches in central Amazonia

ABSTRACT The Amazonian white-sand vegetation presents a set of unique features, such as the dominance of a few species, high endemism and low species richness, which differentiate it from other Amazonian forests. Soil parameters have long been recognized as the main drivers of white-sand vegetation (WSV) characteristics. However, how they influence the composition, richness and structure of this vegetation type is still poorly understood. In this study we investigated the variation in floristic composition between patches and the soil-vegetation relations in three central Amazonian WSV patches. We tested whether slight differences in soil properties are linked with differences in floristic composition, species richness and forest structure in adjacent patches. In each patch three plots of 50 x 50 m were sampled (a total of 2.25 ha). Soil samples were collected for each plot. The sampling cutoff for arboreal individuals was DBH ≥ 5 cm. We sampled a total of 3956 individuals belonging to 40 families and 140 species. In each patch only a few species were dominant, but the dominant species varied among patches. Differences among patches were significant, but plots in the same patch tended to have similar species composition. The variable sum of bases (SB) was directly related to species composition, however, species richness and forest structure were not related to soil parameters. Even small variations in soil parameters can change species composition in WSV, although these variations do not necessarily influence the richness and other structural parameters.