Phase In Such Systems Research Articles

Manifestation of the hexatic phase in confined two-dimensional systems with circular symmetry

Quasi-two-dimensional systems play an important role in the manufacture of various devices for the needs of nanoelectronics. Obviously, the functional efficiency of such systems depends on their structure, which can change during phase transitions under the influence of external conditions (for example, temperature). Until now, the main attention has been focused on the search for signals of phase transitions in continuous two-dimensional systems. One of the central issues is the analysis of the conditions for the nucleation of the hexatic phase in such systems, which is accompanied by the appearance of defects in the Wigner crystalline phase at a certain temperature. However, both practical and fundamental questions arise about the critical number of electrons at which the symmetry of the crystal lattice in the system under consideration will begin to break and, consequently, the nucleation of defects will start. The dependences of the orientational order parameter and the correlation function, which characterize topological phase transitions, as functions of the number of particles at zero temperature have been studied. The calculation results allows us to establish the precursors of the phase transition from the hexagonal phase to the hexatic one for N = 92, 136, 187, considered as an example.

Thermal and dissipative effects on the heating transition in a driven critical system

We study the dissipative dynamics of a periodically driven inhomogeneous critical lattice model in one dimension. The closed system dynamics starting from pure initial states is well-described by a driven Conformal Field Theory (CFT), which predicts the existence of both heating and non-heating phases in such systems. Heating is inhomogeneous and is manifested via the emergence of black-hole like horizons in the system. The robustness of this CFT phenomenology when considering thermal initial states and open systems remains elusive. First, we present analytical results for the Floquet CFT time evolution for thermal initial states. Moreover, using exact calculations of the time evolution of the lattice density matrix, we demonstrate that for short and intermediate times, the closed system phase diagram comprising heating and non-heating phases, persists for thermal initial states on the lattice. Secondly, in the fully open system with boundary dissipators, we show that the nontrivial spatial structure of the heating phase survives particle-conserving and non-conserving dissipations through clear signatures in mutual information and energy density evolution.

Dynamic characterization of wall temperature in LOX/CH[formula omitted] rocket engine operating conditions using phosphor thermometry

Accurate surface temperature prediction is essential for the lifetime and efficiency of a rocket engine. The new ambition of future reusable engines requires perfect knowledge of the thermal environment encountered. In the design phase of such systems and to improve numerical simulations, more resolved experimental data are needed. Experiments are thus conducted by Lab. EM2C, ONERA, CNES, and ArianeGroup on the cryotechnic test bench MASCOTTE operated by ONERA. Conditions representative of those encountered in the gas generator of a rocket engine are investigated. Among them is the cryogenic injection of transcritical methane and oxygen at a very low mixture ratio (0.3) and high pressure (up to 60 bar) through a single coaxial injection element. The present work aims at characterizing the temperature of several surfaces of the combustion chamber in a series of hot fire tests performed in the transient thermal regime and in a short period of time (∼30 s). For this purpose, dynamic Laser Induced Phosphorescence (LIP) is implemented with the Full Spectrum Fitting method (FSF method), a dedicated approach developed by Lab. EM2C. Single-shot measurements are performed to simultaneously track the temperature of five surfaces at 10 Hz located near and downstream of the flame with a 30 K uncertainty. Data indicate that the temperature peak at ignition can be recorded with LIP measurements in contrast to conventional sensors. The analysis of gas and surface temperatures shows that convection is the predominant heat transfer mode and drives the surface temperature. Thanks to LIP thermometry on the internal and external faces of one of the silica windows, a 1D semi-infinite medium model is applied, showing excellent agreement with the measurements. Fitting this model on the measurements allows the estimation of the local convection coefficient and the prediction of the temperature at any depth inside the walls.

Evolved interactions stabilize many coexisting phases in multicomponent liquids

Phase separation has emerged as an essential concept for the spatial organization inside biological cells. However, despite the clear relevance to virtually all physiological functions, we understand surprisingly little about what phases form in a system of many interacting components, like in cells. Here we introduce a numerical method based on physical relaxation dynamics to study the coexisting phases in such systems. We use our approach to optimize interactions between components, similar to how evolution might have optimized the interactions of proteins. These evolved interactions robustly lead to a defined number of phases, despite substantial uncertainties in the initial composition, while random or designed interactions perform much worse. Moreover, the optimized interactions are robust to perturbations, and they allow fast adaption to new target phase counts. We thus show that genetically encoded interactions of proteins provide versatile control of phase behavior. The phases forming in our system are also a concrete example of a robust emergent property that does not rely on fine-tuning the parameters of individual constituents.

Fault tolerance and noise immunity in freespace diffractive optical neural networks

Free-space diffractive optical networks are a class of trainable optical media that are currently being explored as a novel hardware platform for neural engines. The training phase of such systems is usually performed in a computer and the learned weights are then transferred onto optical hardware (‘ex-situ training’). Although this process of weight transfer has many practical advantages, it is often accompanied by performance degrading faults in the fabricated hardware. Being analog systems, these engines are also subject to performance degradation due to noises in the inputs and during optoelectronic conversion. Considering diffractive optical networks trained for image classification tasks on standard datasets, we numerically study the performance degradation arising out of weight faults and injected noises and methods to ameliorate these effects. Training regimens based on intentional fault and noise injection during the training phase are only found marginally successful at imparting fault tolerance or noise immunity. We propose an alternative training regimen using gradient based regularization terms in the training objective that are found to impart some degree of fault tolerance and noise immunity in comparison to injection based training regimen.

Symmetry-protected topological phases in spinful bosons with a flat band

We theoretically demonstrate that interacting symmetry-protected topological (SPT) phases can be realized with ultracold spinful bosonic atoms loaded on the lattices which have a flat band at the bottom of the band structure. Ground states of such systems are not conventional Mott insulators in the sense that the ground states possess not only spin fluctuations but also non-negligible charge fluctuations. The SPT phases in such systems are determined by both spin and charge fluctuations at zero temperature. We find that the many-body ground states of such systems can be exactly obtained in some special cases, and these exact ground states turn out to serve as representative states of the SPT phases. As a concrete example, we demonstrate that spin-1 bosons on a sawtooth chain can be in an SPT phase protected by $\mathbb{Z}_2 \times \mathbb{Z}_2$ spin rotation symmetry or time-reversal symmetry, and this SPT phase is a result of spin fluctuations. We also show that spin-3 bosons on a kagome lattice can be in an SPT phase protected by $D_2$ point group symmetry, but this SPT phase is, however, a result of charge fluctuations.

A Sizing Method for PV–Battery–Generator Systems for Off-Grid Applications Based on the LCOE

Electricity supply in nonelectrified areas can be covered by distributed renewable energy systems. The main disadvantage of these systems is the intermittent and often unpredictable nature of renewable energy sources. Moreover, the temporal distribution of renewable energy may not match that of energy demand. Systems that combine photovoltaic modules with electrical energy storage (EES) can eliminate the above disadvantages. However, the adoption of such solutions is often financially prohibitive. Therefore, all parameters that lead to a functionally reliable and self-sufficient power generation system should be carefully considered during the design phase of such systems. This study proposes a sizing method for off-grid electrification systems consisting of photovoltaics (PV), batteries, and a diesel generator set. The method is based on the optimal number of PV panels and battery energy capacity whilst minimizing the levelized cost of electricity (LCOE) for a period of 25 years. Validations against a synthesized load profile produced grid-independent systems backed by different accumulator technologies, with LCOEs ranging from 0.34 EUR/kWh to 0.46 EUR/kWh. The applied algorithm emphasizes a parameter of useful energy as a key output parameter for which the solar harvest is maximized in parallel with the minimization of the LCOE.

The Improvement of a Brain Computer Interface Based on EEG Signals

Purpose: Brain Computer Interface (BCI) has provided a novel way of communication that can significantly revolutionize life of people suffering from disabilities. Motor Imagery (MI) EEG BCI is one of the most promising solutions to address. The main phases of such systems include signal acquisition, pre-processing, feature extraction, classification and the intended interface. The challenging obstacles in such systems are to detect and extract efficient features that present reliability and robustness alongside promising classification accuracy. In this paper it is endeavored to present a robust method for a two-class MI BCI that results in high accuracy. Materials and Methods: For this purpose, the dataset 2b from BCI competition 2008, consisting of three channels (C3, C and Cz), was utilized. Firstly, the signals were bandpass filtered. Secondly, Common Spatial Pattern (CSP) was employed and then a number of features, including non-linear chaotic features were extracted from channels C3 and C4. After feature selection phase the number of features were reduced to 38 and 47. Finally, these features were fed into two classifiers, namely Support Vector Machine classifier (SVM) and Bagging to evaluate the performance of the system. Results: Classification accuracy and Cohen’s Kappa coefficient of the proposed method for two MI EEG channels are 96.40% and 0.92, respectively. Conclusion: These results indicate the high accuracy and stability of our method in comparison with similar studies. Therefore, it can be a promising approach in two-class MI BCI systems.

Mineralogy and genesis of pyrochlore apatitite from The Good Hope Carbonatite, Ontario: A potential niobium deposit

AbstractThe Good Hope carbonatite is located adjacent to the Prairie Lake alkaline rock and carbonatite complex in northwestern Ontario. The occurrence is a heterolithic breccia consisting of diverse calcite, dolomite and ferrodolomite carbonatites containing clasts of magnesio-arfvedsonite + potassium feldspar, phlogopite + potassium feldspar together with pyrochlore-bearing apatitite clasts. The apatitite occurs as angular, boudinaged and schlieren clasts up to 5 cm in maximum dimensions. In these pyrochlore occurs principally as euhedral single crystals (0.1–1.5 cm) and can comprise up to 25 vol.% of the clasts. Individual clasts contain compositionally- and texturally-distinct suites of pyrochlore. The pyrochlores are hosted by small prismatic crystals of apatite (~100–500 μm × 10–25 μm) that are commonly flow-aligned and in some instances occur as folds. Allotriogranular cumulate textures are not evident in the apatitites. The fluorapatite does not exhibit compositional zonation under back-scattered electron spectroscopy, although ultraviolet and cathodoluminescence imagery shows distinct cores with thin (<50 μm) overgrowths. Apatite lacks fluid or solid inclusions of other minerals. The apatite is rich in Sr (7030–13,000 ppm) and rare earth elements and exhibits depletions in La, Ce, Pr and Nd (La/NdCN ratios (0.73–1.14) relative to apatite in cumulate apatitites (La/NdCN > 1.5) in the adjacent Prairie Lake complex. The pyrochlore are primarily Na–Ca pyrochlore of relatively uniform composition and minor Sr contents (<2 wt.% SrO). Irregular resorbed cores of some pyrochlores are A-site deficient (>50%) and enriched in Sr (6–10 wt.% SrO), BaO (0.5–3.5 wt.%), Ta2O5 (1–2 wt.%) and UO2 (0.5–2 wt.%). Many of the pyrochlores exhibit oscillatory zoning. Experimental data on the phase relationships of haplocarbonatite melts predicts the formation of apatite and pyrochlore as the initial liquidus phases in such systems. However, the texture of the clasts indicates that pyrochlore and apatite did not crystallise together and it is concluded that pyrochlores formed in one magma have been mechanically mixed with a different apatite-rich magma. Segregation of the apatite–pyrochlore assemblage followed by lithification resulted in the apatitites, which were disrupted and fragmented by subsequent batches of diverse carbonatites. The genesis of the pyrochlore apatitites is considered to be a process of magma mixing and not simple in situ crystallisation.

Probing the nature of central objects in extreme-mass-ratio inspirals with gravitational waves

We extend the work of Ryan on mapping the spacetime of the central object of an extreme mass-ratio inspiral (EMRI) by using gravitational waves (GWs) emitted by the system, which may be observed in future missions such as LISA. Whether the central object is a black hole or not can be probed by observing the phasing of these waves, which carry information about its mass and spin multipole moments. We go beyond the phase terms found by Ryan, which were obtained in the quadrupolar approximation of the point-particle limit, and derive terms up to the fifth post-Newtonian (PN) order. Since corrections due to horizon absorption (i.e., if the central object is a black hole) and tidal heating appear by that order, at 2.5PN and 5PN, respectively, we include them here. Corrections due to the motion of the central object, which was addressed only partially by Ryan, are included as well. Additionally, we obtain the contribution of the higher order radiative multipole moments. For the tidal interaction, our results have been derived in the approximation of the Newtonian tidal field. Therefore, in the potential for tidal field only the contribution due to the mass of the central object has been included as well. Using these results we argue that it might be possible for LISA to probe if the central object in an EMRI has a horizon or not. We also discuss how our results can be used to test the No-hair theorem from the inspiral phase of such systems.

Fermionic Lieb-Schultz-Mattis theorems and weak symmetry-protected phases

The Lieb-Schultz-Mattis (LSM) theorem and its higher-dimensional generalizations by Oshikawa and Hastings establish that a translation-invariant lattice model of spin-$1/2$'s can not have a non-degenerate ground state preserving both spin and translation symmetries. Recently it was shown that LSM theorems can be interpreted in terms of bulk-boundary correspondence of certain weak symmetry-protected topological (SPT) phases. In this work we discuss LSM-type theorems for two-dimensional fermionic systems, which have no bosonic analogs. They follow from a general classification of weak SPT phases of fermions in three dimensions. We further derive constraints on possible gapped symmetry-enriched topological phases in such systems. In particular, we show that lattice translations must permute anyons, thus leading to "symmetry-enforced" non-Abelian dislocations, or "genons". We also discuss surface states of other weak SPT phases of fermions.

Fermionic matrix product states and one-dimensional short-range entangled phases with antiunitary symmetries

We extend the formalism of Matrix Product States (MPS) to describe one-dimensional gapped systems of fermions with both unitary and anti-unitary symmetries. Additionally, systems with orientation-reversing spatial symmetries are considered. The short-ranged entangled phases of such systems are classified by three invariants, which characterize the projective action of the symmetry on edge states. We give interpretations of these invariants as properties of states on the closed chain. The relationship between fermionic MPS systems at an RG fixed point and equivariant algebras is exploited to derive a group law for the stacking of fermionic phases. The result generalizes known classifications to symmetry groups that are non-trivial extensions of fermion parity and time-reversal.

A New Technology Applied to Power System Stability Control: Phase Sequence Exchange Technology

AC transmission systems are often affected by stability issues. During the design phase of such systems, their ability to cope with the various kinds of disturbance is taken into consideration, however, sudden large disturbances may still result in power angle instability, which can greatly increase the risk of an overarching power system break down. Therefore, the development of a safety protection system is a priority in the field of power system construction. In response to this problem, we propose a new exploratory solution strategy - Phase Sequence Exchange Technology (PSET). The PSET can be summarized as follows: when the power angle of an equivalent dual power supply system swings to a suitable angle between 90° and 180°, disconnect the primary side phase of the communication line by power electronic equipment and causing the swift misalignment of the connection. The A, B, C three-phase sequence then, connects to the three-phase C, A, B sequence. The PSET instantaneously realizes this change and reduces the power angle by 120°, pulling the formerly increasing power angle back to a smaller angle and preventing the system from becoming imbalanced. In this paper, the mechanism which improves the stability of the PSET is explained by using the equal area rule. The threshold of the PSET work angle is determined by the energy function and the unbalanced potential energy in the system that can be effectively reduced by the PSET. Based on these findings, the phase trajectory method is used to determine the evaluation criteria for the PSET. This allows us to establish whether the PSET is effective by examining the state of the system after the fault is removed. Finally, an example is given in order to verify the effectiveness of the PSET and to prove that PSET is able to prevent the system from becoming imbalanced while still maintaining its structural integrity.

Towards Fully Synthetic Transition Metal-Nitrogen-Carbon Electrocatalysts for Oxygen Reduction Reaction

Electrocatalytic reduction of oxygen as a type of heterogeneous catalysis employs a solid state catalytic phase immobilized on a highly conducting electrode to reduce oxygen dissolved in aqueous electrolytes. Due to the presence of two or more phases in such systems, the role of the solid-liquid (catalyst surface-electrolyte) interface becomes very critical in governing the catalytic activity and rate of reaction. Oxygen reduction reaction (ORR) mostly follows an inner-sphere electron transfer pathway, i.e., bond formation/bond breaking process between the active redox species and the catalyst surface during electron transfer. As the nature of the catalytic surface has a significant effect on these processes, understanding of the catalyst surface and molecular structure is of paramount importance. Extensive research using spectroscopic and electrochemical tools has previously established detailed structure-property relationships of M-N-C catalysts in ORR.1 However, because of the structural disorder introduced by typically used high-temperature synthesis methods for Fe-N-C catalysts, control on the nature and distribution of the catalytically active sites in these materials is a critical challenge. In this work, we establish the use of fully synthetic, non-pyrolysis routes based on total organic/inorganic synthesis towards generating M-N-C catalysts that incorporate specific active sites and closely resemble the microstructure of their pyrolyzed counterparts. This molecular synthesis route affords a very precise understanding of the catalyst structure and a much greater control on it. The model M-N-C catalysts synthesized are termed as arylated arenes. Arylated arenes are a separate class of molecules that can be synthesized by multi-arylation strategies.2 Since metal coordinated to nitrogen atoms (MN4) is an established active site for the direct 4-electron reduction of O2, our approach aimed to incorporate this moiety in the pyridinic arylated arene designed specifically for this work. A three-step reaction scheme was used for the synthesis of a pyridinic nitrogen-containing arene which was then complexed with Fe2+ ion. Non-aqueous media were used for different steps and techniques like recrystallization and column chromatography employed for purification of the products. The complexed arene was heterogenized on a 3D graphene support. The materials were studied by NMR spectroscopy and X-ray photoelectron spectroscopy (XPS). The catalysts with and without support were then tested for electrocatalytic properties using a rotating ring-disk electrode along with the control samples. The results observed show remarkable promise as the Fe-coordinated pyridinic arene supported on 3D graphene (Fe-Ar GNS) exhibits better oxygen reduction catalysis as compared to the pyrolyzed Fe-coordinated pyridinic arene (Fe-Ar pyrolyzed) proved by linear sweep voltammetry. This result offers new prospects for non-pyrolytic synthesis routes for M-N-C catalysts in the future. Specific active sites can be incorporated into the catalysts by this method and their density can also be controlled. In this way, a fundamentally novel approach can be used to impact activity of M-N-C catalysts for electrocatalytic applications.

Hybrid geometric-random template-placement algorithm for gravitational wave searches from compact binary coalescences

Astrophysical compact binary systems consisting of neutron stars and blackholes are an important class of gravitational wave (GW) sources for advanced LIGO detectors. Accurate theoretical waveform models from the inspiral, merger and ringdown phases of such systems, are used to filter detector data under the template based matched filtering paradigm. An efficient grid over the parameter space at a fixed minimal match has a direct impact on the overall time taken by these searches. We present a new hybrid geometric-random template placement algorithm for signals described by two masses and one spin magnitude parameters. Such template banks could potentially be used in GW searches from binary neutron stars and neutron star-blackhole systems. The template placement is robust and is able to automatically accommodate curvature and boundary effects with no fine tuning. We also compare these banks against vanilla-stochastic template banks and show that while both are equally efficient in the fitting-factor sense, the bank sizes are $\sim 25 \%$ larger in the stochastic method. Further, we show that the generation of the proposed hybrid banks can be sped-up by nearly an order of magnitude over the stochastic bank. Generic issues related to optimal implementation are discussed in detail. These improvements are expected to directly reduce the computational cost of gravitational wave searches.

Band gap and broken chirality in single‐layer and bilayer graphene

magnified imageChirality is one of the key features governing the electronic properties of single‐ and bilayer graphene: the basics of this concept and its consequences on transport are presented in this review. By breaking the inversion symmetry, a band gap can be opened in the band structures of both systems at the K‐point. This leads to interesting consequences for the pseu‐dospin and, therefore, for the chirality. These consequences can be accessed by investigating the evolution of the Berry phase in such systems. Experimental observations of Fabry–Pérot interference in a dual‐gated bilayer graphene device are finally presented and are used to illustrate the role played by the band gap on the evolution of the pseudospin. The presented results can be attributed to the breaking of the chirality in the energy range close to the gap. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Structural feedback analysis of a hearing aid using finite element and lumped parameters methods

Hearing aids are designed to overcome hearing losses suffered by some individuals and operated by measuring and amplifying the acoustic field at certain frequency depending on the user hearing loss. In many cases, its transducers (microphone and loudspeaker) are near located, and a feedback signal phenomenon may occur, either through structural or airborne transmission. The structural feedback is characterized by a vibrational response at the microphone position produced by the loudspeaker, also called receiver, that result in a unwanted signal due to the microphone vibration sensitivity. If not properly controlled, the feedback signal builds up, resulting in a loud whistle at the user ear causing great discomfort. The objective of this work is to analyse the structural feedback mechanism at a behind-the-ear hearing aid, and proposed a numerical approach that allows the consideration of the phenomena during the design phase of such systems. A numerical model, based on the finite element method (FEM) and the lumped parameters method, was used to analyse and quantify the problem. While the hearing aid case was modelled using FEM, the receiver and its suspensions were represented by means of a single degree-of-freedom or a multiple degree-of-freedom systems. The procedures used to define material properties and dynamic parameters are presented and discussed. Experimental tests are used to validate the models separately and to determine vibration levels imposed at the microphone location during the hearing aid operation, which are used to verify the overall accuracy of the numerical model. Finally, a sensitivity analysis is performed, indicating some design options that can be used to minimize the structural feedback problem in hearing aids.

Hole statistics and superfluid phases in quantum dimer models

Quantum dimer models (QDMs) arise as low-energy effective models for frustrated magnets. Some of these models have proven successful in generating a scenario for exotic spin liquid phases with deconfined spinons. Doping, i.e., the introduction of mobile holes, has been considered within the QDM framework and partially studied. A fundamental issue is the possible existence of a superconducting phase in such systems and its properties. For this purpose, the question of the statistics of the mobile holes (or ``holons'') shall be addressed first. Such issues are studied in detail in this paper for generic doped QDMs defined on the most common two-dimensional lattices (square, triangular, honeycomb, kagome, \dots{}) and involving general resonant loops. We prove a general ``statistical transmutation'' symmetry of such doped QDMs by using composite operators of dimers and holes. This exact transformation enables us to define duality equivalence classes (or families) of doped QDMs, and provides the analytic framework to analyze dynamical statistical transmutations. We discuss various possible superconducting phases of the system. In particular, the possibility of an exotic superconducting phase originating from the condensation of (bosonic) charge-$e$ holons is examined. A numerical evidence of such a superconducting phase is presented in the case of the triangular lattice, by introducing a gauge-invariant holon Green's function. We also make the connection with a Bose-Hubbard model on the kagome lattice which gives rise, as an effective model in the limit of strong interactions, to a doped QDM on the triangular lattice.

Product vacua with boundary states

We introduce a family of quantum spin chains with nearest-neighbor interactions that can serve to clarify and refine the classification of gapped quantum phases of such systems. The gapped ground states of these models can be described as a product vacuum with a finite number of particles bound to the edges. The numbers of particles, ${n}_{L}$ and ${n}_{R}$, that can bind to the left and right edges of the finite chains serve as indices of the particular phase a model belongs to. All these ground states, which we call product vacua with boundary states (PVBS), can be described as matrix product states (MPS). We present a curve of gapped Hamiltonians connecting the Affleck-Kennedy-Lieb-Tasaki (AKLT) model to its representative PVBS model, which has indices ${n}_{L}={n}_{R}=1$. We also present examples with ${n}_{L}={n}_{R}=J$, for any integer $J\ensuremath{\ge}1$, that are related to a recently introduced class of $\text{SO}(2J+1)$-invariant quantum spin chains.

Designing a meta-model for a generic robotic agent system using Gaia methodology

The emergence of multi-agent systems in the past years has led to the development of new methodologies to assist in the requirements and architectural analysis, as well as in the design phases of such systems. Consequently, several Agent Oriented Software Engineering (AOSE) methodologies have been proposed. In this paper, we analyze some AOSE methodologies, including Gaia, which supports the architectural design stage, and some proposed extensions. We then use an adapted version of this methodology to design an abstract generic system meta-model for a multi-robot application, which can be used as a basis for the design of these systems, avoiding or shortening repetitive tasks common to most systems. Based on the proposed Generic Robotic Agent Meta-Model (GRAMM), two distinct models for two different applications are derived, demonstrating the versatility and adaptability of the meta-model. By adapting the Gaia methodology to the design of open systems, this work makes the designers’ job faster and easier, decreasing the time needed to complete several tasks, while at the same time maintaining a high-level overview of the system.