Uncorrelated System Research Articles

The role of the local structure on the thermal transport within dissociated and complexed Molten salt mixtures

Contrary to the solid state, the understanding of thermal transport within molten salts remains limited. This study aims at establishing a robust theoretical framework for describing and predicting thermal transport in complex and dissociated multicomponent molten salt mixtures, considering both the composition and temperature variables. The proposed approach, based on kinetic theory, considers the local perturbation of kinetic energy through mass fluctuation, weighted by a function dependent on the thermal conductivity of the uncorrelated system and the local structure. The local structure is described in terms of the concentration of free and complex ions, determined either experimentally (using NMR) or through equilibrium atomistic simulations. The thermal transport within several molten salt systems, including KCl, Al2O3, LiF-KF, LiF-NaF-KF (FLiNaK), KCl-MgCl2, NaCl-KCl-MgCl2, and the NaF-AlF3 system, are presented as case studies using the proposed approach. Furthermore, a molecular-level perspective of thermal conduction within molten salts is discussed.

Intrinsic decoherence dynamics and dense coding in dipolar spin system

The quantum decoherence is an ineluctable process when a quantum system interacts with its surrounding environment. Milburn’s dynamical master equation, as a modified shape of the Schrödinger equation, is typically used to study the effects decoherence even without intervention of environment. We studied the temporal evolution of non-local correlations in a dipolar-coupled spin system under the influence of intrinsic decoherence. Primarily, the generation in correlations of Einstein–Podolsky–Rosen steering, measurement-induced non-locality and entanglement in an uncorrelated initial system state were studied. Also, the effect of the intrinsic decoherence on the quality of the dense coding capacity dynamics for the dipolar-coupled spin system was examined. Our results highlight that the initial system’s role in defining the quantum correlations’ robustness, and we also brought out the impacts of system’s parameters on the non-local correlations and the efficiency of dense coding process.

Hallmarks of Majorana mode leaking into a hybrid double quantum dot

We investigate the spectral and transport properties of a double quantum dot laterally attached to a topological superconducting nanowire, hosting the Majorana zero-energy modes. Specifically, we consider a geometry, in which the outer quantum dot is embedded between the external normal and superconducting leads, forming a circuit. First, we derive analytical expressions for the bound states in the case of an uncorrelated system and discuss their signatures in the tunneling spectroscopy. Then, we explore the case of strongly correlated quantum dots by performing the numerical renormalization group calculations, focusing on the interplay and relationship between the leaking Majorana mode and the Kondo states on both quantum dots. Finally, we discuss feasible means to experimentally probe the in-gap quasiparticles by using the Andreev spectroscopy based on the particle-to-hole scattering mechanism.

Mott versus Hybridization Gap in the Low-Temperature Phase of 1T-TaS_{2}.

We address the long-standing problem of the ground state of 1T-TaS_{2} by computing the correlated electronic structure of stacked bilayers using the GW+EDMFT method. Depending on the surface termination, the semi-infinite uncorrelated system is either band insulating or exhibits a metallic surface state. For realistic values of the on-site and inter-site interactions, a Mott gap opens in the surface state, but it is smaller than the gap originating from the bilayer structure. Our results are consistent with recent scanning tunneling spectroscopy measurements for different terminating layers, and with our own photoemission measurements, which indicate the coexistence of spatial regions with different gaps in the electronic spectrum. By comparison to exact diagonalization data, we clarify the interplay between Mott insulating and band insulating behavior in this archetypal layered system.

A general continuous time Markov chain approximation for multi-asset option pricing with systems of correlated diffusions

Continuous time Markov Chain (CTMC) approximation techniques have received increasing attention in the option pricing literature, due to their ability to solve complex pricing problems, although existing approaches are mostly limited to one or two dimensions. This paper develops a general methodology for modeling and pricing financial derivatives which depend on systems of stochastic diffusion processes. This is accomplished with a general decorrelation procedure, which reduces the system of correlated diffusions to an uncorrelated system. This enables simple and efficient approximation of the driving processes by univariate CTMC approximations. Weak convergence of the approximation is demonstrated, with second order convergence in space. Numerical experiments demonstrate the accuracy and efficiency of the method for various European and early-exercise options in two and three dimensions.

A General Continuous Time Markov Chain Approximation for Multi-Asset Option Pricing With Systems of Correlated Diffusions

Continuous time Markov Chain (CTMC) approximation techniques have received increasing attention in the option pricing literature, due to their ability to solve complex pricing problems, although existing approaches are mostly limited to one or two dimensions. This paper develops a general methodology for modeling and pricing financial derivatives which depend on systems of stochastic diffusion processes. This is accomplished with a general de-correlation procedure, which reduces the system of correlated diffusions to an uncorrelated system. This enables simple and efficient approximation of the driving processes by uni-variate CTMC approximations. Weak convergence of the approximation is demonstrated, with second order convergence in space. Numerical experiments demonstrate the accuracy and efficiency of the method for various European and early-exercise options in two and three dimensions.

Performance analysis of beamforming aided uncorrelated mm-Wave MIMO system for IEEE 802.15.3c standard

Millimeter wave (mm-wave) at 60 GHz is a revolutionary technology for ultra-high data rate indoor communications. Unfortunately, due to unfavorable channel characteristics, communication at 60 GHz suffers from poor link budget, high penetration loss and severe signal attenuation. To improve the link budget and the quality of the received signal, the beamforming techniques must be incorporated. In this paper, we derive analytically tractable bit error rate (BER) for the analog beamforming aided mm-wave communication system over the modified IEEE 802.15.3c channel model. It also takes into account the impact of the Rake receivers, which are used to capture the signal energy carried by the multipath components. Monte Carlo simulations have also been carried out to validate the accuracy of the analytical framework. In addition, the impact of Rake’s fingers, power decay factors and arrival times on the BER of the 60 GHz system is also highlighted.

Size dependence of dynamic fluctuations in liquid and supercooled water.

We study the evolution of dynamic fluctuations averaged over different space lengths and time scales to characterize spatially and temporally heterogeneous behavior of TIP4P/2005 water in liquid and supercooled states. Analyzing a 250 000 molecules simulated system, we provide evidence of the existence, upon supercooling, of a significant enhancement of spatially localized dynamic fluctuations stemming from regions of correlated mobile molecules. We show that both the magnitude of the departure from the value expected for the system-size dependence of an uncorrelated system and the system size at which such a trivial regime is finally recovered clearly increase upon supercooling. This provides a means to estimate an upper limit to the maximum length scale of influence of the regions of correlated mobile molecules. Notably, such an upper limit grows two orders of magnitude on cooling, reaching a value corresponding to a few thousand molecules at the lowest investigated temperature.

Measure of positive and not completely positive single-qubit Pauli maps

The time evolution of an initially uncorrelated system is governed by a completely positive (CP) map. More generally, the system may contain initial (quantum) correlations with an environment, in which case the system evolves according to a not-completely positive (NCP) map. It is an interesting question what the relative measure is for these two types of maps within the set of positive maps. After indicating the scope of the full problem of computing the true volume for generic maps acting on a qubit, we study the case of Pauli channels in an abstract space whose elements represent an equivalence class of maps that are identical up to a non-Pauli unitary. In this space, we show that the volume of NCP maps is twice that of CP maps.

Electronic Excited States from the Adiabatic-Connection Formalism with Complete Active Space Wave Functions.

It is demonstrated how the recently proposed multireference adiabatic-connection (AC) approximation for electron correlation energy ( Pernal , K. Electron Correlation from the Adiabatic Connection for Multireference Wave Functions . Phys. Rev. Lett. 2018 , 120 , 013001 ) can be extended to predicting correlation energy in excited states of molecules. It is the first successful application of the AC approach to computing excited-states energies of molecules using a complete active space (CAS) wave function as a reference. The unique feature of the AC-CAS approach with respect to popular methods such as CASPT2 and NEVPT2 is that it requires only one- and two-particle reduced density matrices, making it possible to efficiently treat large spaces of active electrons. Application of the simpler variant of AC, the AC0, which is based on the first-order expansion of the AC integrand at the uncorrelated system limit, to excited states yields excitation energies with accuracy rivaling that of the NEVPT2 method but at greatly reduced computational cost.

Percolation thresholds and fractal dimensions for square and cubic lattices with long-range correlated defects.

We study long-range power-law correlated disorder on square and cubic lattices. In particular, we present high-precision results for the percolation thresholds and the fractal dimension of the largest clusters as a function of the correlation strength. The correlations are generated using a discrete version of the Fourier filtering method. We consider two different metrics to set the length scales over which the correlations decay, showing that the percolation thresholds are highly sensitive to such system details. By contrast, we verify that the fractal dimension d_{f} is a universal quantity and unaffected by the choice of metric. We also show that for weak correlations, its value coincides with that for the uncorrelated system. In two dimensions we observe a clear increase of the fractal dimension with increasing correlation strength, approaching d_{f}→2. The onset of this change does not seem to be determined by the extended Harris criterion.

Novel Expressions and Applications for the Level Crossing Rate of Maximal Ratio Combining in the Presence of Cochannel Interferers

The level crossing rate (LCR) is an important second-order statistical quantity that characterizes the rate of occurrence of fading time intervals. In this paper, we investigate the LCR of multiantenna flat-fading channels in the presence of additive white Gaussian noise and cochannel interferers with unequal received powers and Doppler shifts. We first present a unified approach to derive the exact LCR of the signal-to-interference-noise ratio at a receiver, where maximum ratio combining is deployed over spatially correlated or uncorrelated systems. Through the exact LCR derivation, we identify an accurate approach to obtain a simplified approximate LCR expression in the spatially uncorrelated system case. Benefits of the LCR expressions derived in the paper are demonstrated in two important applications: 1) the packet error rate is evaluated through the finite-state Markov channel model; and 2) the optimum packet length to maximize the throughput of the system with the stop-and-wait automatic repeat request protocol is derived. The analytical results are validated by simulations.

Multiple Staggered Mesh Ewald: Boosting the Accuracy of the Smooth Particle Mesh Ewald Method.

The smooth particle mesh Ewald (SPME) method is the standard method for computing the electrostatic interactions in the molecular simulations. In this work, we develop the multiple staggered mesh Ewald (MSME) method, which averages the SPME forces computed on, for example, M, staggered meshes. We prove, from a theoretical perspective, that the MSME is as accurate as the SPME, but uses M2 times less mesh points in a certain parameter range. In the complementary parameter range, the MSME is as accurate as the SPME with twice the interpolation order. The theoretical conclusions are numerically validated both by a uniform and uncorrelated charge system, and by a three-point-charge water system that is widely used as solvent for the biomacromolecules.

On Small Terminal MIMO Antennas, Harmonizing Characteristic Modes With Ground Plane Geometry

multiple input–multiple output (MIMO) antenna systems are defined by fundamental figure of merits (FoM), such as branch imbalance, total efficiency, mean effective gain (MEG), and the correlation coefficient. Those FoM requirements are challenging, specially when applied to electrically small mobile devices, i.e., smart-phones, due to the form factor-reduced dimensions and multiplicity of adjacent frequency bands of operation. Uncorrelated antennas are especially important for MIMO antenna systems; other than few exceptional cases, the reduction of magnitude of complex correlation coefficient will increase the system capacity and data throughput. This work proposes an MIMO antenna system for mobile terminals, based on a realistic form factor and packaging implementation, with a very low magnitude of the complex correlation coefficient and an impressive isolation. An isolation better than 20 dB has been achieved using a folded monopole and a commonly adopted planar inverted F antenna (PIFA) on a platform with a very small form factor ( ${\bf{100}}\times {\bf{50}}\times {\bf{10}}\;\bf{mm}$ ). The proposed implementation is based on the synergy of two known techniques that consists in the: 1) reference ground plane geometry manipulation and 2) in the application of the characteristic mode theory to obtain orthogonal radiation modes. Since MIMO antenna systems at frequencies higher than 1.7 GHz are naturally proper isolated and decorreleated, this work demonstrates the proposed antenna topology enabling higher isolation and uncorrelated antenna system at 750 MHz, which is more difficult to achieve in form factors smaller than ${\bf{1}}\boldsymbol{\lambda}$ , while maintaining high total efficiency and adequate gain imbalance. In this paper, a simulation model and prototype ( ${\bf{1/4}}\boldsymbol{\lambda}$ long) measurement results are presented, demonstrating the implementation feasibility of such antenna system in realistic mobile device embodiment.

Effects of ursolic acid on the structural and morphological behaviours of dipalmitoyl lecithin vesicles

Effects of ursolic acid on the structural and morphological characteristics of dipalmitoyl lecithin(DPPC)-water system was studied by using differential scanning calorimetry (DSC), small- and wide-angle X-ray scattering (SWAXS), freeze-fracture method combined with transmission electron-microscopy (FF-TEM) and infrared spectroscopy (FT-IR). The surface of the uncorrelated lipid system is rippled or grained and a huge number of small, presumably unilamellar vesicles are present if the UA/DPPC molar ratio is 0.1mol/mol or higher. Besides the destroyed layer packing of regular multilamellar vesicles, non-bilayer (e.g. cubic or hexagonal) local structures are evidenced by SAXS and FF-TEM methods. The ability of UA to induce non-bilayer structures in hydrated DPPC system originates from the actual geometry form of associated lipid and UA molecules as concluded from the FT-IR measurements and theoretical calculations. Beside numerous beneficial e.g. chemopreventive and chemotherapeutic effect of ursolic acid against cancer, their impact to modify the lipid bilayers can be utilized in liposomal formulations.

Compact and closely spaced tunable printed F‐slot multiple‐input–multiple‐output antenna system for portable wireless applications with efficient diversity

In this work, miniaturised tunable two-antenna multiple-input–multiple-output (MIMO) systems composed of printed F-slot shaped are developed to operate in the global positioning system (GPS), personal communication system (PCS), distributed control system and Universal Mobile Telecommunications System bands. The two-element MIMO antenna occupies a volume of 50 × 37.5 × 1.6 mm3, and is printed on an FR4 substrate. Initially, the frequency tunability of the MIMO antennas was verified by lumped capacitors with values between 0.75 to 2.75 pF to achieve a tuning range from 1.55 to 2.07 GHz while the low mutual coupling between the radiators was accomplished by adding an I-shaped branch to a cut-away ground plane. The two antennas are then loaded with varactors to simultaneously achieve miniaturisation and tunability. Simulation and measurement results demonstrate the successful implementation of a tunable MIMO with coupling reduction mechanism for a portable handheld wireless transceiver. The channel capacity of the proposed antenna is investigated and found to be close to that of a un-correlated system with efficient diversity in which the mutual coupling across the full bandwidth was better than −13 dB. Owing to the compact size and ease of manufacture, the proposed antennas can be a promising solution for adaptive MIMO systems in handheld devices.

Quantum discord from system–environment correlations

In an initially uncorrelated mixed separable bi-partite system, quantum correlations can emerge under the action of a local measurement or local noise []. We analyse this counter-intuitive phenomenon using quantum discord as a quantifier. We then relate changes in quantum discord to system–environment correlations between the system in a mixed state and some purifying environmental mode using the Koashi–Winter inequality. On this basis, we suggest an interpretation of discord as a byproduct of transferring entanglement and correlations around the different subsystems of a global pure state.

Compact Multi-Band PIFAs on a Semi-Populated Mobile Handset With Tunable Isolation

In this communication, miniaturized tunable two-antenna systems composed of printed inverted-F antennas (PIFAs) are developed for a semi-populated mobile phone handset. The PIFAs are loaded with a series combination of an inductor and a varactor to simultaneously achieve miniaturization and tunability. The compact 32 mm-long PIFAs demonstrate tuning range of more than 240 MHz covering personal telecommunication bands from LTE-band13 to GSM900 MHz. As well a miniaturized tunable parasitic element is integrated in the handset to efficiently suppress coupling between the PIFAs to below <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$-$</tex></formula> 28 dB across the entire operational bandwidth of the antennas. Simulation and measurement results demonstrate the successful implementation of a tunable MIMO system with passive adjustable coupling reduction mechanism for mobile handsets and achievement of a channel capacity profile close to that of an un-correlated system.

Generation of quantum correlations for two qubits through a common reservoir

Recently, besides entanglement, an entropy-based measurement called quantum discord has been used to describe the quantum correlations in separable and non-separable states. Here we compare the dynamics of entanglement with that of quantum discord, in the case of two qubits in a common thermal or squeezed reservoir. We focus on the generation of quantum correlations, starting from an uncorrelated system.

Alternative parameterizations of the multiple-trait random regression model for milk yield and somatic cell score via recursive links between phenotypes

Multiple-trait random regression models with recursive phenotypic link from somatic cell score (SCS) to milk yield on the same test day and with different restrictions on co-variances between these traits were fitted to the first-lactation Canadian Holstein data. Bayesian methods with Gibbs sampling were used to derive inferences about parameters for all models. Bayes factor indicated that the recursive model with uncorrelated environmental effects between traits was the most plausible specification in describing the data. Goodness of fit in terms of a within-trait weighted mean square error and correlation between observed and predicted data was the same for all parameterizations. All recursive models estimated similar negative causal effects from SCS to milk yield (up to -0.4 in 46-115 days in milk in lactation). Estimates of heritabilities, genetic and environmental correlations for the first two regression coefficients (overall level of a trait and lactation persistency) within both traits were similar among models. Genetic correlations between milk and SCS were dependent on the restrictions on genetic co-variances for these traits. Recursive model with uncorrelated system genetic effects between milk and SCS gave estimates of genetic correlations of the opposite sign compared with a regular multiple-trait model. Phenotypic recursion between milk and SCS seemed, however, to be the only source of environmental correlations between these two traits. Rankings of sires for total milk yield in lactation, average daily SCS and persistency for both traits were similar among models. Multiple-trait model with recursive links between milk and SCS and uncorrelated random environmental effects could be an attractive alternative for a regular multiple-trait model in terms of model parsimony and accuracy.