Two-level Case Research Articles

A deep neural network-based model for OSA severity classification using unsegmented peripheral oxygen saturation signals

Obstructive sleep apnea (OSA) is a common type of sleep-related breathing disorder, and polysomnography (PSG) remains the gold standard for its diagnosis. However, it takes a significant amount of time to perform PSG in a well-equipped laboratory, and patients typically have to wait a long time for a PSG test. In view of this, over recent years portable and even wearable tools for OSA classification have been developed as a low-cost and easy-to-use alternative to PSG. In this paper, a deep neural network (DNN)-based model was developed to classify OSA severity using peripheral oxygen saturation (SpO2) signals; it showed the following advantages. First, the presented model takes unsegmented SpO2 signals recorded overnight as its input, and OSA severity is then classified as one of four levels as the output. Consequently, there is obviously no need to label segmented signals, and the tremendous amount of effort spent on signal segmentation and then annotation can be completely saved. Second, a high generalization ability is provided since the largest amount of data were used to test the model. This feature gives the model an improved reliability for clinical use. Notably, the outperformance of this work is highlighted in a two-level classification case (with a cutoff apnea–hypopnea index of 5), where the accuracy and the sensitivity increased to above 91% and 95%, respectively.

Kinetic theory of collisionless relaxation for systems with long-range interactions

We develop the kinetic theory of collisionless relaxation for systems with long-range interactions in relation to the statistical theory of Lynden-Bell. We treat the multi-level case. We make the connection between the kinetic equation obtained from the quasilinear theory of the Vlasov equation and the relaxation equation obtained from a maximum entropy production principle. We propose a method to close the infinite hierarchy of kinetic equations for the phase level moments and obtain a kinetic equation for the coarse-grained distribution function in the form of a generalized Landau, Lenard–Balescu or Kramers equation associated with a generalized form of entropy (Chavanis, 2004). This allows us to go beyond the two-level case associated with a Fermi–Dirac-type entropy. We discuss the numerous analogies with two-dimensional turbulence. We also mention possible applications of the present formalism to fermionic and bosonic dark matter halos.

Spin-Mapping Methods for Simulating Ultrafast Nonadiabatic Dynamics

Many chemical reactions exhibit nonadiabatic effects as a consequence of coupling between electronic states and/or interaction with light. While a fully quantum description of nonadiabatic reactions is unfeasible for most realistic molecules, a more computationally tractable approach is to combine a classical description of the nuclei with a quantum description of the electronic states. Combining the formalisms of quantum and classical dynamics is however a difficult problem for which standard methods (such as Ehrenfest dynamics and surface hopping) may be insufficient. In this article, we review a new trajectory-based approach developed in our group that is able to describe nonadiabatic dynamics with a higher accuracy than previous approaches but for a similar level of computational effort. This method treats the electronic states with a phase-space representation for discrete-level systems, which in the two-level case is analogous to a spin-½. We point out the key features of the method and demonstrate its use in a variety of applications, including ultrafast transfer through conical intersections, damped coherent excitation under coupling to a strong light field, and nonlinear spectroscopy of light-harvesting complexes.

Hybrid quantum–classical chaotic NEMS

We present an exactly solvable model of a hybrid quantum–classical system of a Nitrogen-Vacancy (NV) center spin (quantum spin) coupled to a nanocantilever (classical) and analyze the enforcement of the regular or chaotic classical dynamics onto the quantum spin dynamics. The main problem we focus in this paper is whether the classical dynamical chaos may induce chaotic effects in the quantum spin dynamics or not. We explore several characteristic criteria of the quantum chaos, such as quantum Poincaré recurrences, generation of coherence and energy level distribution and observe interesting chaotic effects in the spin dynamics. Dynamical chaos imposed in the cantilever dynamics through the kicking pulses induces the stochastic dynamics on the quantum subsystem. We consider a quantum system of two and three levels and show that in a two-level case, type of stochasticity is not conforming all the characteristic features of the quantum chaos and is distinct from it. We also explore the effect of quantum feedback on dynamics of the cantilever and the entire system.

Nested-sphere description of the N -level Chern number and the generalized Bloch hypersphere

The geometric interpretation of (pseudo)spin 1/2 systems on the Bloch sphere has been appreciated across different areas ranging from condensed matter to quantum information and high energy physics. Although similar notions for larger Hilbert spaces are established in mathematics, they have been so far less explored beyond the two-level case for practical usage in condensed matter settings, or have involved restrictions to sub manifolds within the full Hilbert space. We here employ a coherence vector description to theoretically characterize a general N-level system on the higher dimensional generalized Bloch (hyper)sphere by respecting the structure of the underlying SU(N) algebra and construct physically intuitive geometric pictures for topological concepts. Focusing on two spatial dimensions, we reveal a geometric interpretation for the Chern number in larger Hilbert spaces in terms of a nested structure comprising N-1 two-spheres. We demonstrate that for the N-level case, there is an exterior two-sphere that provides a useful characterization of the system, notably by playing a primary role in determining the Chern number. The external sphere can be directly measured in ultracold atoms via well-established band mapping techniques, thereby imparting knowledge of the topological nature of state. We also investigate how the time evolution of the coherence vector defined on the generalized Bloch hypersphere can be utilized to extract the full state vector in experiments, allowing us to develop a tomography scheme involving quenches for three-level systems. Our geometric description opens up a new avenue for the interpretation of the topological classification and the dynamical illustration of multi-level systems, which in turn is anticipated to help in the design of new experimental probes.

Inverse design approach to x-ray quantum optics with Mössbauer nuclei in thin-film cavities

Thin-film cavities containing layers of M\"ossbauer nuclei have been demonstrated to be a rich platform for x-ray quantum optics. At low excitation, these systems can be described by effective few-level schemes, thereby providing tunable artificial quantum systems at hard x-ray energies. With the recent advent of an ab initio theory, a numerically efficient description of these systems is now possible. On this basis, we introduce the inverse design and develop a comprehensive optimization for an archetypal system with a single resonant layer, corresponding to an artificial two-level scheme. We discover a number of qualitative insights into x-ray photonic environments for nuclei that will likely impact the design of future x-ray cavities and thereby improve their performance. The methods presented readily generalize beyond the two-level case and thus provide a clear perspective towards the inverse design of more advanced tunable x-ray quantum optical level schemes.

Randomness and Irreversiblity in Quantum Mechanics: A Worked Example for a Statistical Theory.

The randomness of some irreversible quantum phenomena is a central question because irreversible phenomena break quantum coherence and thus yield an irreversible loss of information. The case of quantum jumps observed in the fluorescence of a single two-level atom illuminated by a quasi-resonant laser beam is a worked example where statistical interpretations of quantum mechanics still meet some difficulties because the basic equations are fully deterministic and unitary. In such a problem with two different time scales, the atom makes coherent optical Rabi oscillations between the two states, interrupted by random emissions (quasi-instantaneous) of photons where coherence is lost. To describe this system, we already proposed a novel approach, which is completed here. It amounts to putting a probability on the density matrix of the atom and deducing a general “kinetic Kolmogorov-like” equation for the evolution of the probability. In the simple case considered here, the probability only depends on a single variable describing the state of the atom, and yields the statistical properties of the atom under the joint effects of coherent pumping and random emission of photons. We emphasize that allows the description of all possible histories of the atom, as in Everett’s many-worlds interpretation of quantum mechanics. This yields solvable equations in the two-level atom case.

Optimal Denial-of-Service Attack Strategy on State Estimation Over Infinite-Time Horizon

Security issues of cyber-physical systems have become a timely and hot topic in recent years. In this brief, we investigate the power-constrained optimal denial-of-service (DoS) attack strategy with multiple power levels on state estimation over infinite-time horizon. We start from the two-level case and explicitly derive out the basic form of optimal attack strategy. In order to handle the intractability brought about by the larger number of levels, we develop an equivalent property for general multi-level cases that the multi-level scheduling can be viewed as a feasible combination of several sub-schedules with a designed stochastic-triggered manner, which provides a necessary condition of optimal solution. Moreover, based on the practical communication model, we give the condition under which the optimal schedule can be uniquely and explicitly determined for the two-pick strategy. Numerical simulations are accomplished to verify the effectiveness of our proposed methods.

A hierarchical mean field model of interacting spins

We consider a system of hierarchical interacting spins under dynamics of spin-flip type with a ferromagnetic mean field interaction, scaling with the hierarchical distance, coupled with a system of linearly interacting hierarchical diffusions of Ornstein–Uhlenbeck type. In particular, the diffusive variables enter in the spin-flip rates, effectively acting as dynamical magnetic fields. In absence of the diffusions, the spin-flip dynamics can be thought of as a modification of the Curie–Weiss model. We study the mean field and the two-level hierarchical model, in the latter case restricting to a subcritical regime, corresponding to high temperatures, obtaining macroscopic limits at different spatio-temporal scales and studying the phase transitions in the system. We also formulate a generalization of our results to the kth level hierarchical case, for any k finite, in the subcritical regime. We finally address the supercritical regime, in the zero-temperature limit, for the two-level hierarchical case, proceeding heuristically with the support of numerics.

A closed-form solution to multi-level image thresholding

This paper proposes an analytical formulation relying on the least square error. Similar results were also found for the cross correlation, within-class, and between-class variance. At first, a continuous distribution is hypothesized (for derivation purposes only) to produced a modified form of the well-known OTSU method. This hypothesis is “identical” to Otsu in terms of output performance and the need for an exhaustive search. However, apart from being derived from the continuous form, the proposed scheme requires less computational power. It turns out that the optimum threshold equals the average of the adjacent regions’ means. For some images, the scheme can result in multi-level thresholdeds. A direct form was then suggested to obtain a non-exhaustive solution. The idea is simply to approximate the non-continuous error function (used by the least square formulation and OTSU) with a forth order polynomial defined in the normalized gray intensity range [0,1]. The optimum threshold can then be found as a function of the roots of a second order polynomial whose coefficients are the solution of a 2x2 linear system. The performance of the proposed non-exhaustive solution is slightly inferior to OTSU in general, however; some images produced improved performance. Nevertheless, The proposed scheme can be easily generalized to the multi-level case without the need for an exhaustive search. For n+1 levels (i.e. n thresholds), the output is obtained by solving an nxn linear system followed by finding the roots of a n-order polynomial. The computational cost is clearly superior to the exhaustive search. In addition, as validated with some images, the performance is encouraging. Extension to the general clustering case is highly envolved with the exception of the two-level case (for any dimension) that has been successfully derived in this work.

On computation of optimal strategies in oligopolistic markets respecting the cost of change

The paper deals with a class of parameterized equilibrium problems, where the objectives of the players do possess nonsmooth terms. The respective Nash equilibria can be characterized via a parameter-dependent variational inequality of the second kind, whose Lipschitzian stability, under appropriate conditions, is established. This theory is then applied to evolution of an oligopolistic market in which the firms adapt their production strategies to changing input costs, while each change of the production is associated with some “costs of change”. We examine both the Cournot-Nash equilibria as well as the two-level case, when one firm decides to take over the role of the Leader (Stackelberg equilibrium). The impact of costs of change is illustrated by academic examples.

Modulation and Capacitor Voltage Balancing Control of Multilevel NPC Dual Active Bridge DC–DC Converters

The present paper provides a solution to operate multilevel dual active bridge (ML-DAB) converters built upon neutral point clamped switching legs in a full-bridge disposition and with any number of levels on either side of the converter. The main issue of such converters is addressing the inherent unbalance of the dc-link capacitor voltages, which hinders the proper operation and optimum utilization of the converter. The proposed solution comprises a generalized to N levels modulation and control scheme that allows operating these converters, while guaranteeing the proper balance of the dc-link capacitor voltages. The suitability of the proposed solution is verified through simulation and experimental tests performed in five different converter configurations, three of them with an asymmetric number of voltage levels, proving that capacitor voltage balance is achievable in a wide range of operation conditions. Moreover, the efficiency of the ML-DAB converters is demonstrated to be superior to the conventional two-level DAB case.

Student model initialization using domain knowledge ontology representative subset

In intelligent e-learning systems that adapt a learning and teaching process to student knowledge, it is important to adapt the system as quickly as possible. However, adaptation is not possible until the student model is initialized. In this paper, a new approach to student model initialization using domain knowledge representative subset is described. The approach defines which concepts from domain knowledge should be included in the initial test so the system can make conclusions about what students truly know about domain knowledge. This representative subset of domain knowledge is defined using non-semantic mathematical approach based on graph theory. The initial test, created over a domain knowledge representative subset, guarantees encompassing all concepts that are relevant to domain knowledge. A two-level case study is conducted on what would be the representative subset of one selected domain knowledge. It compares semantically selected domain knowledge representative subsets (semantical analysis was done by domain area experts) to a non-semantical, mathematically selected domain knowledge representative subset. The results of the case study show that problems of inequality of semantically selected domain knowledge representative subsets are easily overcome using the presented approach.

Valuing humane lives in two-level utilitarianism

AbstractI examine the two-level utilitarian case for humane animal agriculture (by R. M. Hare and Gary Varner) and argue that it fails on its own terms. The case states that, at the ‘intuitive level’ of moral thinking, we can justify raising and killing animals for food, regarding them as replaceable, while treating them with respect. I show that two-level utilitarianism supports, instead, alternatives to animal agriculture. First, the case for humane animal agriculture does not follow from a commitment to two-level utilitarianism combined with a commitment to respecting animal lives. Second, the two-level utilitarian case falls prey to a compartmentalization problem and cannot uphold both respect and replaceability. What I call ‘humane lives’ are not appropriately valued by the lights of two-level utilitarianism itself.

Two-level uncapacitated lot-sizing problem considering the financing cost of working capital requirement

During financial crisis, companies constantly need free cash flows to efficiently react to any uncertainty, thus ensuring solvency. Working capital requirement (WCR) has been recognized as a key factor for releasing tied up cash in companies. However, in literatures related to lot-sizing problem, WCR has only been studied in the single-level supply chain context. In this paper, we initially adopt WCR model for a multi-level case. A two-level (supplier-customer) model is established on the basis of the classic multi-level lot-sizing model integrated with WCR financing cost. To tackle this problem, we propose sequential and centralized approaches to solve the two-level case with a serial chain structure. The ZIO (Zero Inventory Ordering) property is further confirmed valid in both cases. This property allows us to establish a dynamic programming-based algorithm, which solves the problem in O(T4). Finally, numerical tests show differences in optimal plans obtained by both approaches and the influence of varying delays in payment on the WCR of both actors.

Cervical disk arthroplasty

Anterior cervical discectomy and fusion (ACDF) is a well-established surgical intervention for degenerative cervical spine pathology. Concerns over pseudarthrosis and adjacent segment degeneration (ASD), however, have led to an increased interest in motion-preserving alternatives. Cervical disc arthroplasty (CDA) may reduce ASD through preservation of cervical biomechanics and has demonstrated non-inferiority when compared to ACDF in medium-term studies with indications for single- and two-level cervical disease. This chapter describes the indications, biomechanical properties of common designs, and complications of CDA. Additionally, we describe a two-level CDA case study and highlight some pearls and pitfalls associated with CDA implantation as it is more technically demanding than ACDF. While CDA may represent a viable alternative to ACDF with fewer complications, studies are needed to establish its long-term safety.

Efficient Predictive Torque Control for Induction Motor Drive

Finite control set model predictive control is an emerging technique for the control of power electronic converters. This paper introduces a simple and efficient predictive torque control (PTC) algorithm for induction motor drive. The proposed technique eliminates the need for flux-weighting factor for the conventional PTC. As a result, tedious offline tuning is no longer required. At the same time, the proposed technique ensures that the relative importance between torque and flux ripples is determined in an online fashion. Moreover, unlike the conventional method that needs to evaluate the cost function seven times (for two-level three-phase inverter case), the proposed method needs only to test four voltage vectors at each control sample which leads to a significant reduction in the computation time and switching frequency without sacrificing the performance. The effectiveness of the proposed method is demonstrated by both simulation and experimental results with comprehensive comparisons with the reported literature.

Exact solution to a kind of multi-level Rosen-Zener models

Exact solution to the driven quantum system with an explicitly time-dependent Hamiltonian is not only an issue of fundamental importance to quantum mechanics itself, but also a ubiquitous problem in the design for quantum control. In particular, the nonadiabatic transition induced by the time-dependent external field is often involved in order to target the quantum state for the atomic and molecular systems. In this paper we investigate the exact dynamics and the associated nonadiabatic transition in a typical driven model, the Rosen-Zener model and its multi-level extension, by virtue of the algebraic dynamical method. Previously, this kind of driven models, especially of the two-level case, were solved by converting the corresponding Schrödinger equation to a hypergeometric equation. The property of the dynamical transition of the system was then achieved by the asymptotic behavior of the yielded hypergeometric function. A critical drawback related to such methods is that they are very hard to be developed so as to treat the multi-level extension of the driven model. Differing from the above mentioned method, we demonstrate that the particular kind of the Rosen-Zener model introduced here could be solved analytically via a canonical transformation or a gauge transformation approach. In comparison, we show that the present method at least has two aspects of advantages. Firstly, the method enables one to describe the evolution of the wavefunction of the system analytically over any time interval of the pulse duration. Moreover, we show that the method could be exploited to deal with the multi-level extensions of the model. The explicit expression of the dynamical basis states, including the three-level system and the four-level system, is presented and the transition probabilities induced by the nonadiabatic evolution among different levels are then characterized for the model during the time evolution. In addition, our study reveals further that the dual model of the driven system can be constructed. Since the dynamical invariant of a solvable system can always be obtained within the framework of the algebraic dynamical method, the general connection between the dual model and the original one, including the solvability and their dynamical invariants, are established and characterized distinctly.

Dynamical transitions in a modulated Landau–Zener model with finite driving fields

We investigate a special time-dependent quantum model which assumes the Landau–Zener driving form but with an overall modulation of the intensity of the pulsing field. We demonstrate that the dynamics of the system, including the two-level case as well as its multi-level extension, is exactly solvable analytically. Differing from the original Landau–Zener model, the nonadiabatic effect of the evolution in the present driving process does not destroy the desired population transfer. As the sweep protocol employs only the finite driving fields which tend to zero asymptotically, the cutoff error due to the truncation of the driving pulse to the finite time interval turns out to be negligibly small. Furthermore, we investigate the noise effect on the driving protocol due to the dissipation of the surrounding environment. The losses of the fidelity in the protocol caused by both the phase damping process and the random spin flip noise are estimated by solving numerically the corresponding master equations within the Markovian regime.

Urban innovation through policy integration: Critical perspectives from 100 smart cities mission in India

Abstract Smart cities commentary often highlights the technological and entrepreneurial aspects of the city. But, the dimensions of local policy and politics is surprisingly little debated. Mega cities in the rapidly urbanising economies develop a plethora of urban policies and plans cultivated by various state and local agencies. These are often overlapping or conflicting and as a result do not produce desired outcomes. Prospective smart cities tend to add a new layer of plan and devise extra institutional instrument in to this already complex environment. We challenge this idea of smart cities being another stand-alone initiative and explore how integration of plans and unification of smart city visions with the overarching city development goals can better support effective urban transformation and local innovation. This research addresses the complex planning and governance mechanisms in the world's fastest growing economy – India - which has initiated an ambitious mission to transform 100 urban areas across the country into “smart cities”. The federal program involves the provision of centrally devised guidelines for smart city development. These combined with local level policy and institutional initiatives in designated smart cities in India shape a multiplicity of policies and programs. A two-level case study is presented in this paper as a critical polemic on this policy landscape. Investigation along these lines provide opportunities for identification of underlying patterns and challenges of smart city developments in India. The paper concludes with a series of recommendations for building sound smart city policy frameworks in emerging economies.