Unity Maximum Research Articles

CMOS Platform for Everyday Applications Using Submillimeter Electromagnetic Waves

CMOS (Complementary Metal Oxide Silicon) integrated circuits (ICs) technology is emerging as a means for realization of capable and affordable systems that operate at frequencies near 300GHz and higher. This is lowering a key barrier for utilizing the sub-millimeter electromagnetic waves in everyday applications. Despite the fact that the unity maximum available gain frequency, fmax of NMOS transistors (with connections to the tope metal layer) has peaked at 320 GHz, signal generation up to 1.33 THz, coherent detection up to 1.2 THz and incoherent detection up to 10 THz have been demonstrated using CMOS integrated circuits. Furthermore, highly integrated rotational spectroscopy transceivers operating at frequencies up to near 300 GHz, 300-GHz and 400-GHz concurrent transceiver pixels and arrays for high resolution radar imaging, and 300-GHz and 390-GHz transmitters, and 300-GHz receivers for high data-rate communication have been demonstrated in CMOS. The performances of these CMOS circuits are sufficient or close to being sufficient to support electronic smelling using rotational spectroscopy that can detect and quantify concentrations of a wide variety of gases; imaging that can enable operation in a wide range of visually impaired conditions; and high-bandwidth communication. Lastly, techniques for affordable packaging and testing sub-millimeter wave systems are suggested based on experimental demonstrations.

Compilation of Smart Cities Attributes and Quantitative Identification of Mismatch in Rankings

One practical way to define a “smart city” is to look at the specific qualities listed in a ranking study about smart cities. Such method gives de facto guidelines for classifying a city as being smart or not. Building upon this rationale, the current work in its first objective presents features adopted in evaluating the “smartness” of cities in seven evaluations and in its second objective arranges them in a suggested structure of six scopes with forty-three keywords. With these two objectives, the current study serves as a summary of various ranking studies in terms of being a collection place of many evaluation criteria. Four of the considered studies are the 2018 and 2019 annual editions from two sources, and comparing these criteria shows some changes over one year, and these updates are highlighted. A third objective of this study considers analyzing assigned ranks and utilizing a normalized score (limited to a maximum of unity) derived from the raw scores given in six ranking studies (out of the seven considered, with one ranking study excluded as it does not give raw numerical scores) to the six cities that commonly appear in all of them. This part shows with details the existence of mismatch not just in a one-time ranking, but also in a year-to-year trend, where a city appears to be improving according to one evaluator while appears to be degrading according to another evaluator. As a fourth objective, statistical analysis of the evaluation results was conducted, with quantitative assessment of rankings mismatch.

Characterization of vertical unsaturated flow reveals why storm runoff responses can be simulated by simple runoff-storage relationship models

Numerical experiments on vertical unsaturated flow using the Richards equation were conducted to examine the physical basis of why storm runoff responses from mountainous watersheds in tectonically active regions could be simulated by simple runoff models with a runoff-storage power-law relationship. Pressure head propagation transmitted through vertical unsaturated flow could produce a rapid response of the outflow from bottom of the soil column, regardless of the inherent soil hydraulic properties, similar to storm runoff responses observed on a hillslope in a ‘constant allocation period’ when a large constant portion of rainfall is allocated to storm runoff. Additional experiments were conducted both for an increasing stage of downward flux in response to increasing rainfall intensity and for a recession stage without rainfall, to investigate the detailed characteristics of vertical unsaturated flow. The creation of a wetting front during the increasing stage delayed the increase of outflow, but this delay was small during a constant allocation period. An interdependent relationship between the outflow rate and the total storage of the soil column throughout the recession stage was approximated by a power-law equation derived from relationships between total storage and constant outflow under steady-state conditions. The exponent of the power-law equation approached a maximum of unity as the column length decreased, and it approached the minimum value obtained from the intrinsic relationship between soil hydraulic conductivity and volumetric water content as the column length increased. The interdependence of the outflow rate with the total storage generally detected only in the unsaturated zone might cause a low sensitivity of outflow responses to the heterogeneities of soil hydraulic properties, justifying the application of simple runoff models in heterogeneous mountain watersheds.

Enhanced Nonlinear Companding Scheme for Reducing PAPR of OFDM Systems

A new companding scheme for reducing the peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) systems is proposed in this study. It proceeds from speech signal processing similar to the earliest $\mu$ -law companding (MC) model. The proposed scheme compands (compresses and expands) the amplitudes of OFDM signals to a maximum of 1 V. Besides significantly reducing the PAPR, the proposed technique is also able to function as a limiter, thus reducing the system complexity and limiting the amplitudes of OFDM symbols to a unity maximum voltage, which does not exist in other companding PAPR techniques. Over frequency-selective fading channels with frequency domain equalization and using minimum mean square error (MMSE) to minimize the noise overhead, the proposed technique outperforms four other companding schemes over light and severe fading conditions. Finally, we demonstrate that PAPR reduction using companding can dispense with corresponding decompanding scheme at the receiver as it amplifies the distortion noise, thereby reducing the bit error ratio performance and increasing the receiver complexity. We investigate the out-of-band interference of the proposed scheme and also show that it outperforms the other existing techniques by up to 5 dB.

(Keynote) Devices in CMOS for Terahertz Circuits and Systems

CMOS (Complementary Metal Oxide Silicon) integrated circuits (IC’s) technology is emerging as a means for realization of capable and affordable systems that operate at 300GHz and higher. Despite the fact that the unity maximum available gain frequency, fmax of NMOS transistors has peaked at ~320GHz somewhere between 65 and 32-nm technology nodes, signal generation up to 1.3THz and coherent detection up to 410GHz and incoherent detection up to ~10THz have been demonstrated using CMOS integrated circuits. Furthermore, a highly integrated rotational spectroscopy transceiver operating up to near 300GHz and imaging array operating at 820GHz have been demonstrated in CMOS. The nonlinear devices and circuit techniques that enable the operation at these frequencies beyond fmax will be described. Lastly, emerging applications, electronic nose/smelling using rotational spectroscopy that can detect and quantify concentrations of a wide variety of gases, imaging that can enable operation of autonomous systems in a wide range of weather conditions (rain, dust, snow, fog .. ), high-bandwidth communication over 1-2m long dielectric waveguides that can rival the bandwidth of optical communication systems, and electronic detectors that can make thermal imaging/night vision affordable will be discussed.

Unity maximum transient energy growth of heat-driven acoustic oscillations

Transient energy growth of acoustic disturbances may trigger thermoacoustic instability in a non-normal thermoacoustic system. In this work, minimizing transient energy growth of heat-driven acoustic oscillations in an open-ended thermoacoustic system is considered. For this, a state-space thermoacoustic model with an acoustically compact heat source and distributed monopole-like actuators is developed. The heat source gives rise to the mean temperature jump, as experimentally measured. It is modeled with a modified King’s Law. Coupling the unsteady heat release model with a Galerkin series expansion of the acoustic waves present enables the time evolution of flow disturbances and acoustical energy to be calculated, thus providing a platform on which to gain insight on the system’s transient stability behaviors and the non-normal response of the system to the dynamic actuators. It is first shown that implementing a linear-quadratic regulator (LQR) leads to the system being asymptotically stabilized. However, the LQR optimization strategy fails in eliminating the transient growth. This finding is consistent with Pseudospectra analysis of the present system. In order to achieve unity maximum transient growth, a Lyapunov-based optimization strategy is systematically designed. It is found that this optimization strategy achieves both exponential decay of the acoustical energy and unity maximum transient growth. Furthermore, the sound pressure level is reduced by approximately 25dB. In addition, the number of the actuators K is shown to be related to the mode number N as K=N.

Tunable chirality and circular dichroism of a topological insulator with C2v symmetry as a function of Rashba and Dresselhaus parameters

Polarization-sensitive devices rely on meta-materials to exhibit varying degrees of absorption of light of a given handedness. The chiral surface states of a topological insulator selectively absorb right- and left-circularly polarized light in the vicinity of the Dirac cone reaching its maximum of unity at the Γ point. In this letter, we show that a band gap open topological insulator with C2v symmetry, which is represented through a combination of Rashba and Dresselhaus Hamiltonians, alters the preferential absorption of left- and right-circularly polarized light allowing a smooth variation of the circular dichroism. This variation in circular dichroism, in a range of positive and negative values, is shown to be a function of the Rashba and Dresselhaus coupling parameters.

Nonlinear feedback control of self-sustained thermoacoustic oscillations

Acoustic disturbances could undergo transient growth to trigger thermoacoustic instability in a combustion system with non-orthogonal eigenmodes, even with stable eigenvalues and in the presence of conventional linear controllers. In this work, nonlinear feedback control of thermoacoustic oscillations in a Rijke-type combustion system is considered. A thermoacoustic model with distributed monopole-like actuators is presented. To stabilize the thermoacoustic system, a nonlinear feedback controller is developed. It is shown that the feedback controller achieves both exponential decay of the flow disturbance energy and unity maximum transient growth. The performance of the controller is illustrated with two systems: one associated with one mode and one actuator, and the other with two modes and two actuators. The successful demonstration indicates that the developed nonlinear controller has the potential to be applied to combustion systems with multiple modes.

Minimizing transient energy growth of nonlinear thermoacoustic oscillations

Abstract Thermoacoustic oscillations triggered by transient energy growth of flow disturbances are wanted in thermoacoustic prime movers or cooling systems. However, they are undesirable in many combustion systems, such as aero-engines, gas turbines, boilers and furnaces. In this work, minimizing transient energy growth of flow disturbances in a thermoacoustic system with Dirichlet boundary conditions is considered. For this, a simplified thermoacoustic model of a premixed laminar flame with an actuator is developed. It is formulated in state-space by expanding acoustic disturbances via Galerkin series and linearizing flame model and recasting it into the classical time-lag N - τ for controllers implementation. As a linear-quadratic-regulator (LQR) is implemented, the thermoacoustic oscillations exponentially decay. However, it is associated with transient energy growth of flow disturbances. To minimize the transient energy growth, a strict dissipativity controller designed basing on LQR is then implemented. Comparison is then made between the performances of these controllers. It is found that the strict dissipativity controller achieves both exponential decay of the thermoacoustic oscillations and unity maximum transient energy growth.

Feedback control of thermoacoustic oscillation transient growth of a premixed Laminar flame

Transient growth of combustion-excited oscillations could trigger thermoacoustic instability in a combustion system with nonorthogonal eigenmodes. In this work, feedback control of transient growth of combustion-excited oscillation in a simplified thermoacoustic system with Dirichlet boundary conditions is considered. For this a thermoacoustic model of a premixed laminar flame with an actuator is developed. It is formulated in state-space by expanding acoustic disturbances via Galerkin series and linearizing flame model and recasting it into the classical time-lag N-τ for controllers implementation. As a linear-quadratic-regulator (LQR) controller is implemented, the system becomes asymptotically stable. However, it is associated with transient growth of thermoacoustic oscillations, which may potentially trigger combustion instability. To eliminate the oscillations transient growth, a strict dissipativity controller is then implemented. Comparison is then made between the performances of these controllers. It is found that the strict dissipativity controller achieves both exponential decay of the oscillations and unity maximum transient growth.

Enhanced charge efficiency and reduced energy use in capacitive deionization by increasing the discharge voltage

Capacitive deionization (CDI) is an electrochemical method for water desalination using porous carbon electrodes. A key parameter in CDI is the charge efficiency, Λ, which is the ratio of salt adsorption over charge in a CDI-cycle. Values for Λ in CDI are typically around 0.5–0.8, significantly less than the theoretical maximum of unity, due to the fact that not only counterions are adsorbed into the pores of the carbon electrodes, but at the same time coions are released. To enhance Λ, ion-exchange membranes (IEMs) can be implemented. With membranes, Λ can be close to unity because the membranes only allow passage for the counterions. Enhancing the value of Λ is advantageous as this implies a lower electrical current and (at a fixed charging voltage) a reduced energy use. We demonstrate how, without the need to include IEMs, the charge efficiency can be increased to values close to the theoretical maximum of unity, by increasing the cell voltage during discharge, with only a small loss of salt adsorption capacity per cycle. In separate constant-current CDI experiments, where after some time the effluent salt concentration reaches a stable value, this value is reached earlier with increased discharge voltage. We compare the experimental results with predictions of porous electrode theory which includes an equilibrium Donnan electrical double layer model for salt adsorption in carbon micropores. Our results highlight the potential of modified operational schemes in CDI to increase charge efficiency and reduce energy use of water desalination.

Feedback control of acoustic disturbance transient growth in triggering thermoacoustic instability

Transient growth of acoustic disturbances could trigger thermoacoustic instability in a combustion system with non-orthogonal eigenmodes, even with stable eigenvalues. In this work, feedback control of transient growth of flow perturbations in a Rijke-type combustion system is considered. For this, a generalized thermoacoustic model with distributed monopole-like actuators is developed. The model is formulated in state-space to gain insights on the interaction between various eigenmodes and the dynamic response of the system to the actuators. Three critical parameters are identified: (1) the mode number, (2) the number of actuators, and (3) the locations of the actuators. It is shown that in general the number of the actuators K is related to the mode number N as K = N 2 . For simplicity in illustrating the main results of the paper, two different thermoacoustic systems are considered: system (a) with one mode and system (b) that involves two modes. The actuator location effect is studied in system (a) and it is found that the actuator location plays an important role in determining the control effort. In addition, sensitivity analysis of pressure- and velocity-related control parameters is conducted. In system (b), when the actuators are turned off (i.e., open-loop configuration), it is observed that acoustic energy transfers from the high frequency mode to the lower frequency mode. After some time, the energy is transferred back. Moreover, the high frequency oscillation grows into nonlinear limit cycle with the low frequency oscillation amplified. As a linear-quadratic regulator (LQR) is implemented to tune the actuators, both systems become asymptotically stable. However, the LQR controller fails in eliminating the transient growth, which may potentially trigger thermoacoustic instability. In order to achieve strict dissipativity (i.e., unity maximum transient growth), a transient growth controller is systematically designed and tested in both systems. Comparison is then made between the performance of the LQR controller and that of the transient growth controller. It is found in both systems that the transient growth controller achieves both exponential decay of the flow disturbance energy and unity maximum transient growth.

Dispersive characteristics of surface plasmon polaritons on negative refractive index gratings

The dispersive characteristics of surface plasmon polaritons (SPPs) supported by a periodically corrugated boundary between vacuum and a negative refractive index, isotropic material were studied theoretically by numerical solution of a dispersion equation. SPP dispersion curves were correlated with the optical response of the corrugated boundary in frequency regions where SPPs can be excited by a normally incident plane wave. Abrupt reflectivity variations, characterized by the presence of a near unity maximum and an almost zero minimum, were found in regions where the boundary without corrugation exhibits low reflectivity and rather featureless reflectivity curves.

Effect of the Combination of Spray Pyrolysis and Flame Oxidation Synthesis of Carbon Modified (CM)-n-TiO2 Thin Film Electrodes on Solar to Hydrogen Production Efficiency From Water

Carbon modified n-type titanium oxide (CM-n-TiO2) photoelectrodes were synthesized by natural gas flame oxidation (sample 1) and also by spray pyrolytic deposition on Ti metal sheets (Alfa, 0.25 mm thick) followed by their thermal flame oxidation (Sample 2). Sample 1 and sample 2 generated photocurrent density of 9.17 mA cm-2 and 13.83 mA cm-2 for water splitting at the same measured potential of - 0.7 V/SCE. at illumination intensity of 100 mW cm-2 from a 150 Watt Xenon Lamp respectively. The total photocurrent density of 12.15 mA cm-2 obtained by integration of wavelength, λ dependent photocurrent densities for sample 2 generated a total photoconversion efficiency of 12.33 % under illumination intensity of 100 mW cm-2 from a solar simulator. Importantly, under global Air Mass of 1.5 sunlight (1 sun) illumination, total photoconversion efficiency of 10.48 % for water splitting was observed for sample 2. Light concentration by oxygen gas bubbles temporarily trapped on highly porous and thicker CM-n-TiO2 surface of sample 2 acting as tiny lens helped to have observed quantum efficiency or incident photon conversion efficiency (IPCE) higher by a factor of ten in the UV region compared to theoretical maximum of unity and consequently generated such high photoconversion efficiency under global sunlight illumination.

Inheritance of condensed tannins in birdsfoot trefoil

Neither the inheritance of condensed tannins (CT) in tannin-positive birdsfoot trefoil (Lotus corniculatus L.), nor the quantitative genetic analysis of CT concentration in a forage legume have been previously reported. The objective of this study was to determine the inheritance of CT concentration in tannin-positive birdsfoot trefoil. High-, medium-, and low-tannin parents were selected from NC-83 birdsfoot trefoil germplasm and intercrossed in two independent six-parent diallel sets to generate progenies for quantitative genetic analyses. Maturity, herbage yield, leaf fraction (LF) and CT concentration were analyzed for 1067 individual F1 plants from 30 progenies in both diallel sets. Mean CT concentrations of the 30 progenies ranged from 6.1 to 93.4 g catechin equivalent (CE) kg−1 DM. General combining ability (GCA):specific combining ability (SCA) ratios of 0.93 and 1.0 were observed for CT concentration in both diallel sets, at or near the theoretical maximum of unity, indicating a predominance of additive genetic effects for CT concentration. Specific combining ability effects were detected in one diallel set where 3 of 15 progenies exhibited significant SCA effects. The evidence from this study indicated that CT concentration in birdsfoot trefoil was controlled primarily by additive genetic effects. Key words: Birdsfoot trefoil, condensed tannins, forage legume, inheritance, Lotus corniculatus, quantitative genetics

The distribution of the intervals between neural impulses in the maintained discharges of retinal ganglion cells

Simulated neural impulse trains were generated by a digital realization of the integrate-and-fire model. The variability in these impulse trains had as its origin a random noise of specified distribution. Three different distributions were used: the normal (Gaussian) distribution (no skew, normokurtic), a first-order gamma distribution (positive skew, leptokurtic), and a uniform distribution (no skew, platykurtic). Despite these differences in the distribution of the variability, the distributions of the intervals between impulses were nearly indistinguishable. These inter-impulse distributions were better fit with a hyperbolic gamma distribution than a hyperbolic normal distribution, although one might expect a better approximation for normally distributed inverse intervals. Consideration of why the inter-impulse distribution is independent of the distribution of the causative noise suggests two putative interval distributions that do not depend on the assumed noise distribution: the log normal distribution, which is predicated on the assumption that long intervals occur with the joint probability of small input values, and the random walk equation, which is the diffusion equation applied to a random walk model of the impulse generating process. Either of these equations provides a more satisfactory fit to the simulated impulse trains than the hyperbolic normal or hyperbolic gamma distributions. These equations also provide better fits to impulse trains derived from the maintained discharges of ganglion cells in the retinae of cats or goldfish. It is noted that both equations are free from the constraint that the coefficient of variation (CV) have a maximum of unity.(ABSTRACT TRUNCATED AT 250 WORDS)

Directivity index of partially random sonobuoy arrays

The directivity index DI of the partially random sonobuoy array described in a previous paper [J. Acoust. Soc. Am. 64, S123(A) (1978)] is analyzed. The analysis is based on the definition of DI as the ratio in decibels of the power received by a single omnidirectional hydrophone of unity gain to the array power normalized to unity maximum gain. The array power is a random variable. Its expected value is used in the definition of DI to define the “nominal DI.” The variance of the array power provides a measure of the variability of the DI among the members of an ensemble. The type of partially random array analyzed consists of N elements arranged in vertical strings of M elements each. With N constant, the variance of the array power tends to increase as M is increased. The increase is the result of the increasingly large contribution to the array power of the side-lobes at the main lobe elevation, which have a relatively large variance. The effects of the number of elements per string on the nominal DI and on the variability of the DI are examined quantitatively.

Kinetics of Quasifree Electron Reactions in the Liquids Methane, Krypton, and Xenon

The encounter efficiency of e− + N2O → N2O in the liquids methane, krypton, and xenon at 183 °K is f ≈ 105. The parameter β, for the nonhomogeneous kinetics of reactions in γ radiolysis spurs in the liquids, has values similar to those (1013–1014 V/cm2) obtained earlier for liquids such as cyclohexane, methanol, and water at 298 °K, in which f is approximately unity. Previous results for nitrous oxide in neopentane at 296 °K have been reinterpreted to obtain f ≈ 10−2. For solvents in which the electron mobility is very high (~103 cm2/Vs) the value of f is low. As the electron mobility decreases f increases to a maximum of unity.

A study of transference and solvation phenomena—I: Uranyl chloride in water, ethanol and water-ethanol solvents

Transference and solvation phenomena involving uranyl chloride (UO 2Cl 2) have been studied at 25·00 ± 0·01°C in water, ethanol and water-ethanol solvents. Transference phenomena as a function of the concentration of UO 2Cl 2 have been studied at the same temperature in water and in 99·7 weight per cent ethanol in water. The transference number of the anion in both water and in 99·7 weight per cent ethanol extrapolates to 0·64 and the cation to 0·36 at infinite dilution of the UO 2Cl 2. The transference number of the anion as a function of concentration reaches a maximum of unity at about 19·5 weight per cent UO 2Cl 2 and then decreases sharply with further increase of salt concentration. The maximum in water is explained as possibly arising from [UO 2Cl 3·solvent] − and [UO 2Cl·solvent] + ions of equal mobility. The dependence of anion transference number on solvent composition is qualitatively in agreement with the dependence, with respect to uranium (VI) ion, of the order of the electron exchange reaction between uranium (VI) and uranium (IV) ions. The plot of the moles of water per faraday transported from anode to cathode gave a sine-like curve when plotted against weight per cent ethanol in the solvent. The shape of this curve was explained on the basis of the alternate removal of layers of water of hydration on the UO 2Cl 3 − and UO 2Cl + ions and the successive replacement of these hydration layers with ethanol.