Table of contents

Ambient temperature fluctuations are of importance in a wide variety of scientific and technological arenas. In a series of experiments carried out in our laboratory over an 18-month period, we discovered that these fluctuations exhibit 1/f³ spectral behavior over the frequency range 1.0 × 10⁻⁵ ≤ f ≤ 2.5 × 10⁻² Hz, corresponding to 40 s ≤ T_f ≤ 1.2 d, where T_f = 1/f. This result emerges over a broad range of conditions. For longer time periods, 1.2 < T_f ≤ 11.6 d, corresponding to the frequency range 1.0 × 10⁻⁶ ≤ f < 1.0 × 10⁻⁵ Hz, we observed 1/f² spectral behavior. This latter result is in agreement with that observed in data collected at European weather stations. Scalograms computed from our data are consistent with the periodograms.

Soliton molecules can be formed in some possible mechanisms both theoretically and experimentally. In this paper, we introduce a new mechanism, namely the velocity resonant, to find soliton molecules. Under the velocity resonance mechanism, two solitons can form a kink-antikink molecule, an asymmetric soliton, a two-peak soliton and/or a far away bounded molecule depended on the selections of the wave numbers and the distance between two solitons of a molecule. The results are exhibited via three well known fifth order integrable systems which serve as a general fluid model, as well as models many other physical fields.

Pulsed laser deposition (PLD) of CuIn_1−xGa_xSe₂ (CIGS) provides a low cost, single-step process via which stoichiometric, high quality thin films for light harvesting applications can be produced. Little is known about the optical properties of PLD-deposited CIGS and how they compare with the respected properties of the well-studied evaporated or sputtered CIGS films. We report herein a systematic spectroscopic investigation, probing the influence of PLD deposition temperature on the energetics and dynamics of emission from CuIn_0.7Ga_0.3Se₂ films. Variable-temperature steady-state and time-resolved photoluminescence in combination with Gaussian lineshape analysis allow us to unravel the contribution and nature of three main radiative channels, with the high energy one associated with electronic and two lower energy ones with defect levels. The analysis show that the band-edge luminescence grows at the expense of defect emission as PLD temperature increases in the 300 °C–500 °C range. This is further supported by: (i) The dramatic increase of the band-edge recombination lifetime from 30 to 180 ns, (ii) The quenching in the carrier trapping rate from 0.25 ns⁻¹ to 0.09 ns⁻¹ as growth temperature increases. The results correlate well with structural and electrical characterization studies reported previously on PLD-grown CIGS and rationally interpret the improvement in their optoelectronic properties as PLD deposition temperature increases .

A flexible and cost-effective electromechanical device for tactile sensing based on ZnO nanorods (ZnO NRs) grown on fabrics is developed. Sensing performance and the electromechanical properties of ethylcellulose/polyurethane-coated ZnO NRs on fabric substrates were tested by the LCR meter, force transducer, vibrator, and pulse analyzer. The peak-to-peak output voltage at an applied force of 21.5 N dropped considerably for the wool-, nylon-, and PP substrates and reached to the order of 3.84 mV, 1.8 mV and 4.1 mV, respectively. Furthermore, the frequency dependency of the dissipation factors revealed abrupt changes at low frequencies, while these changes were negligible at high frequencies.

This report demonstrates the systematic study of electronic, mechanical, and optical properties of Fe_1−xCo_x alloy (x = 0.00, 0.05, 0.10, 0.15, 0.20, and 0.25) using plane wave ultrasoft pseudopotential based on spin-polarized density functional theory. The upshots expose overlapped of valence and conductance states and confirms electronic bands polarization. The energy bands are significantly shifted with increasing Co atoms. The dispersion energies reveal anisotropic behavior of electronic energy levels. The density of states manifests strong electronic interaction between Co and Fe atoms. The spin polarization is mainly attributed from the exchange interactions among electronic spins, which confirms the strong electron-electron interactions. Subsequently, spin polarization induces spin magnetic moments. Minority spin states are dominant for Fe_1−xCo_x alloy, which significantly changed the electronic properties. Moreover, Elastic constants confirm that all the phases of Fe_1−xCo_x alloy are mechanically stable, and the higher elastic modulus manifests better performance of the resistance to shape change and against uniaxial tensions. The optical properties of FeCo alloy exhibit strong interrelation with atomic composition of Fe and Co. The loss spectra reveal high plasmonic resonance that can be chemically tuned through atomic composition. The spin magnetic moments and high plasmonic resonance make the Fe_1−xCo_x alloys as the prominent mechanically stable materials for magneto-optical applications.

Concurrent neutron Compton scattering (NCS) and neutron diffraction experiments at temperatures between 70 K and 300 K have been performed on proton-conducting hydrated BaZr_0.7Ce_0.2Y_0.1O_3−δ (BZCY72) fabricated by spark plasma sintering. A combined neutron data analysis, augmented with density functional theory modelling of lattice dynamics, has enabled, for the first time, a mass-selective appraisal of the combined thermal and nuclear quantum effect on nuclear dynamics and thermodynamic stability of this technologically important proton conducting perovskite oxide. The analysis suggests that the nuclear dynamics in hydrated BZCY72 is a result of a subtle interplay of harmonic, anharmonic and thermal effects, with the increased anharmonic character of the lattice dynamics above the orthorhombic to rhombohedral phase transition at 85 K. The anharmonic effect seems to be most pronounced in the case of oxygen and cerium. The analysis of the proton momentum distribution reveals that the concentration of the hydrogen in the BZCY72 lattice is constant across the orthorhombic to rhombohedral phase transition and further down to the room temperature. Moreover, the average hydrogen concentration obtained from our analysis of the mass-resolved neutron Compton scattering data seems to be commensurate with the total vacancy concentration in the BZCY72 framework. The calculation of the vibrational enthalpy of both phases allows obtaining the value of the enthalpy of the orthorhombic to the rhombohedral phase transition of −3.1 ± 1 kJ mol⁻¹. Finally, our analysis of the nuclear kinetic energy of the proton obtained from NCS and the oxygen-oxygen distance distributions obtained from ND allows to conclude that BZCY72 in both the orthorhombic and rhombohedral phase at 70 K and 100 K respectively falls into the category of the KDP-type crystals where proton is probably under the influence of a double-well potential and forms hydrogen bonds of moderate strength. The obtained results have important ramifications for this technological important material.

The aim of the Laser Interferometer Space Antenna (LISA) is to detect gravitational waves through a phase modulation in long (2.5 Mkm) laser light links between spacecraft. Among other noise sources to be addressed are the phase fluctuations caused by a possible angular jitter of the emitted beam. The present paper follows our preceding one (Vinet et al 2019 Class. Quant. Grav.36, 205 003) based on an analytical study of the far field phase. We address here a numerical treatment of the phase, to first order in the emitted wavefront aberrations, but without any assumptions on the static bias term. We verify that, in the phase change, the higher order terms in the static mispointing are consistent with the results found in our preceding paper.

We consider a non-conserving zero-range process with hopping rate proportional to the number of particles at each site. Particles are added to the system with a site-dependent creation rate, and vanish with a uniform annihilation rate. On a fully-connected lattice with a large number of sites, the mean-field geometry leads to a negative binomial law for the number of particles at each site, with parameters depending on the hopping, creation and annihilation rates. This model can be mapped to population dynamics (if the creation rates are reproductive fitnesses in a haploid population, and the hopping rate is the mutation rate). It can also be mapped to a Bianconi–Barabási model of a growing network with random rewiring of links (if creation rates are the rates of acquisition of links by nodes, and the hopping rate is the rewiring rate). The steady state has recently been worked out and gives rise to occupation numbers that reproduce Kingman's house-of-cards model of selection and mutation. In this paper we solve the master equation using a functional method, which yields integral equations satisfied by the occupation numbers. The occupation numbers are shown to forget initial conditions at an exponential rate that decreases linearly with the fitness level. Moreover, they can be computed exactly in the Laplace domain, which allows to obtain the steady state of the system under resetting. The result modifies the house-of-cards result by simply adding a skewed version of the initial conditions, and by adding the resetting rate to the hopping rate.

Open devices with homogeneous material parameters are proposed and designed based on multi-folded transformation optics, including open cloak device, open field concentrator and open field amplifying device. In comparison with the previous transformation devices, the proposed open devices possess open windows with compact and embedded structures, providing a flexible approach for remote control or upgrade. The open cloaking devices can hide arbitrarily shaped/sized object in the core region, making it disappeared in visually for the outside viewers, while the open field concentrator can enhance or store EM energy in the core region, and the open field amplifying device can magnify the scattering field of a small object, generating an bigger illusory image with differential material parameter and size. The effectiveness and correctness of the proposed devices are validated by the numerical results obtained based on the commercial finite element software COMSOL Multiphysics. Such scheme is believed to find potential applications in remote controlling with impressive new functions.

Despite the utility of the Hill numbers, measuring diversity within complex systems and complex datasets, particularly regarding parts of a distribution to the whole—that is, different portions of diversity types to the entire system or dataset—is a challenging issue. In this paper, we attempt to relate the diversity of a part (or parts) of a distribution to the diversity of the whole. We derive this relationship for the Hill numbers ${}^{q}D$, and use these results to further examine the effect of a freely varying type on the diversity of the whole distribution.

We propose a new scheme for the recovery of complex-valued objects in a single-pixel hybrid correlation holography. The idea is to generate an intensity correlation hologram from the correlation of intensity fluctuations obtained over two channels, namely an optical channel equipped with a single pixel detector and a digital channel. The scheme has a theoretical basis which is described to reconstruct the objects from a single pixel detector. An experimental arrangement is proposed and as a first step towards realizing/implementing the technique, simulation of the experimental model was carried to image three complex objects.

We demonstrate that thicker layers can be achieved in gallium nitride (GaN) epitaxy by using a patterned silicon (Si) substrate compared to a planar Si substrate. GaN films were grown by metalorganic vapour-phase epitaxy on 6-inch Si (111) substrates patterned with arrays of squares with various corner shapes, height and lateral dimensions. Stress spatial distributions in the GaN pattern units were mapped out using confocal Raman spectroscopy. It was found that the corner shapes have an effect on the uniformity of the stress distribution. Patterns with round corners were found to have more uniform stress distribution than those with sharp corners. The largest crack-free square size for a 1.5 μm thick GaN film is 500 × 500 μm².

This study addresses the dielectric performance of nonpolar hydrocarbon liquids and mineral oils under negative polarity stress. Stopping length for non-breakdown streamers, breakdown voltages and velocities for various pre-breakdown streamer modes have been studied for a selection of model liquids (cyclohexane and white oils), for a gas to liquid oil, and a refined naphthenic transformer oil. Studies of propagation modes were done using an 80 mm point to plane gap and a step voltage with 0.5 μs rise time. Light emission and pre-breakdown currents have been recorded and instantaneous velocities have been derived from images of propagating streamers. Compared to positive polarity, there are less differences in streamer behaviour in the oils examined under negative polarity. Breakdown voltages and acceleration voltages are higher for negative streamers than for positive ones, while their propagation velocities are lower. While propagation modes for positive voltages are quite distinct, the mode changes for negative ones are more gradual. The behaviour of both positive and negative streamers is in line with the hypothesis that the propagation is governed by electron avalanches and quantum chemical properties of liquid components.

This study addresses the dielectric performance of nonpolar hydrocarbon liquids and mineral oils under positive polarity stress. It is of interest to improve knowledge on how functional properties of dielectric liquids vary, as new brands arrive in the market, and existing standards are unsuited for documenting the dielectric functional parameters of these new liquids. Stopping length for non-breakdown streamers, breakdown voltages and velocities for various pre-breakdown streamer modes have been studied for a selection of model liquids (cyclohexane and white oils), for a gas to liquid oil, and a refined naphthenic transformer oil. Studies of propagation modes were done using an 80 mm point to plane gap and a step voltage with a 0.5 μs rise time. Light emission and pre-breakdown currents have been recorded and instantaneous velocities have been derived from images of propagating streamers. There are clear differences in streamer stopping lengths and mode occurrence and mode velocities between these liquids. The differences seem to be influenced by molecular sizes governing evaporation energy for streamer formation and by concentration of aromatics which can be coupled to electron avalanche processes in the streamer heads.

We study higher order KdV equations from the GL(2, ${\mathbb{R}}$) ≅ SO(2,1) Lie group point of view. We find elliptic solutions of higher order KdV equations up to the ninth order. We argue that the main structure of the trigonometric/hyperbolic/elliptic N-soliton solutions for higher order KdV equations is the same as that of the original KdV equation. Pointing out that the difference is only the time dependence, we find N-soliton solutions of higher order KdV equations can be constructed from those of the original KdV equation by properly replacing the time-dependence. We discuss that there always exist elliptic solutions for all higher order KdV equations.

This article presents a cost optimisation study of neutron scattering instrumentation at the European Spallation Source (ESS) in Lund, Sweden. This is done by focusing on the main cost drivers for almost half of the instrument hardware—optics and shielding —and trading detailed cost functions against beam transmission functions in a multi-dimensional, yet simple, parameter space. A cost saving of almost 30% is identified. The method is demonstrated in a worked example on a mature instrument design, and there are no reductions in performance. The proposed solution is shown to correspond to a Nash equilibrium of simultaneous shielding and optics strategies, versus the baseline which is trapped by working through sequential strategies. Finally, this cost analysis is bench-marked against, and found to be in agreement with, the costs of operational facilities of a similar class.

This paper scrutinizes the effect of viscous dissipation on unsteady two-dimensional boundary layer flow of Williamson nanofluid over a stretching/Shrinking wedge. To express the boundary condition in concentration problem the passive control concept used. The governing PDEs are converted to ODEs by means of a similarity transformation before being solved numerically by finite difference scheme called Keller-Box method. The equations were numerically solved by using Matlab software 2013a. The characteristics of parameters such as wedge angle, unsteadiness, Williamson, slip, Brownian motion, thermophoresis, chemical reaction parameters, Prandtl number, Biot-number, Eckert number and Lewis number on velocity, concentration and temperature profiles and skin friction coefficient, Nusselt number and Sherwood number are presented in graphs and tables. The result of the study designates that the velocity profiles increased with an upsurge of wedge angle, unsteady parameter and suction parameter while it is diminished with an increase of Williamson and injection parameter. The temperature profiles upsurges with the distended Williamson parameter, Biot number and injection parameter, while it is declined for large values of wedge angle, unsteady and suction parameter. With an increase of Williamson, unsteady and suction parameter the concentration profiles upsurges, while it is decreased with an increase of wedge angle and injection parameter. The numerical results are compared with available literature and obtained a good agreement.

Indium-rich environmentally-friendly quantum dots (QDs) have received widespread attention due to the absence of cadmium. In this paper, AgInS₂ (AIS) QDs are synthesized by hot injection method. By adjusting the ratio of indium/silver (In/Ag = 1, 2, 3, 4, 5), the AIS QDs exhibit a blue shift from 868 nm to 603 nm with the indium composition increases. Therein, the AIS QDs with the ratio of In/Ag = 4 show a highest photoluminescent (PL) quantum yields (QYs) up to 57%. AIS QDs are coated with ZnS shell to passivate the surface defects, and the PL QYs of obtained core/shell AIS/ZnS QDs is increased to 72%. By using these AIS/ZnS QDs as light emitters, light emitting diodes are assembled with a stacked multi-layer structure ITO/PEDOT:PSS/Poly-TPD/QDs/ZnO:Mg/Al. The resulted electroluminescent (EL) device exhibits a maximum external quantum efficiency (EQE) of 1.25% and an open circuit voltage of 4.6 V corresponding to a maximum brightness of 1120 cd m⁻². Although the performances of the as fabricated AIS/ZnS-based device lag much behind than those of the Cd-based ones, they are expected to be enhanced with much more studies on the synthesis of the QDs and the optimization of device structure.

A dynamical model that can exhibit both fractal percolation growth and compact circular growth is presented. At any given cluster size, the dimension of a cluster growing on a two-dimensional square lattice depends on the ratio between the rates of two probabilistic processes, namely (i) the aggregation of lattice sites into the growing cluster and (ii) the relaxation of lattice sites into those available for potential aggregation. The proposed model approaches the limit of two-dimensional invasion percolation if the aggregation process is much faster than the relaxation process, and it approaches Eden's model for compact circular growth if the relaxation process is much faster than the aggregation process. Experimental examples of the fractal-growth regime include the percolation-like growth of bent-core smectics and calamitic smectics, where such fractal growth is attributed to the slow relaxation of molecules in a viscous supercooled medium.