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Quantitative computed tomography has identified a cluster of women (33%) cooking with biomass fuels (wood) with image-based markers of functional small airways disease and associated alterations in regional lung mechanics. Texture and image registration-based metrics of lung function may allow for early detection of potential inflammatory processes that may arise in response to inhaled biomass smoke, and help identify phenotypes of chronic lung disease prevalent in nonsmoking women in the developing world.

We introduce the concept of angular correlation for estimating the instantaneous correlation matrix with a single multivariate realization. The proposed estimator is generally a positive definite correlation matrix and robust in that for bivariate normal data, the sample angular correlation is equally likely to be above or below the population correlation coefficient. We then generalize the dynamic conditional correlation (DCC) model to the dynamic conditional angular correlation (DCAC) model. We demonstrate the efficacy and robustness of the proposed methods against leptokurticity, with some numerical experiments. In particular, a real application illustrates the better performance of the DCAC model than the DCC model in portfolio construction.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressively enlarging cysts. Here we elucidate the interplay between oxidative stress, mitochondrial dysfunction, and metabolic derangement using two mouse models of PKD1 mutation, PKD1RC/null and PKD1RC/RC. Mouse kidneys with PKD1 mutation have decreased mitochondrial complexes activity. Targeted proteomics analysis shows a significant decrease in proteins involved in the TCA cycle, fatty acid oxidation (FAO), respiratory complexes, and endogenous antioxidants. Overexpressing mitochondrial-targeted catalase (mCAT) using adeno-associated virus reduces mitochondrial ROS, oxidative damage, ameliorates the progression of PKD and partially restores expression of proteins involved in FAO and the TCA cycle. In human ADPKD cells, inducing mitochondrial ROS increased ERK1/2 phosphorylation and decreased AMPK phosphorylation, whereas the converse was observed with increased scavenging of ROS in the mitochondria. Treatment with the mitochondrial protective peptide, SS31, recapitulates the beneficial effects of mCAT, supporting its potential application as a novel therapeutic for ADPKD., Daneshgar et al. investigated the role of mitochondrial dysfunction in ADPKD and mitochondria protective agents as potential therapeutics. The authors reported decreased mitochondrial complex activity and downregulation of mitochondrial and metabolic proteins in ADPKD, and proposed mCAT overexpression or SS31 treatment to slow cystogenesis.

Due to the efficient photocarrier separation and collection coming from their distinctive band structures, superlattice nanowires (NWs) have great potential as active materials for high-performance optoelectronic devices. In this work, InGaZnO NWs with superlattice structure and controllable stoichiometry are obtained by ambient-pressure chemical vapor deposition. Along the NW axial direction, perfect alternately stacking of InGaO(ZnO)

Despite the recent advances in electrochemical water splitting, developing cost-effective and highly efficient electrocatalysts for oxygen evolution reaction (OER) still remains a substantial chall...

We studied the valley dependent transport properties of bilayer-monolayer graphene junctions consisting of a device region of bilayer zigzag ribbon connected to monolayer zigzag ribbon leads. We determined numerically using the python package Kwant the valley dependent conductance through the junctions in an energy range in which each valley has at most two subbands in a single layer ribbon. There is a Fermi energy in this range in which the K to K conductance drops significantly to below 0.2 e 2 / h (spin degree of freedom is included), while the K to K′ conductance remains high. This means a high percentage of the incident K electrons are transferred to the K′ valley in the outgoing lead. A number of junctions can be designed with K to K′ conductance larger than 1.2 e 2 / h , which have a conversion efficiency higher than 84% and there are also junctions with K to K′ conductance between 1.2 e 2 / h and 0.6 e 2 / h (the conversion efficiency > 66%). Changing the transverse dimension, the conductance features are shifted in energy without significant change to the qualitative behavior. When the longitudinal dimension of the junction is changed, the qualitative features are changed in a way, which resembles the relation between the band structure of armchair ribbons and the dimer numbers along the ribbon's transverse direction. For some junctions, this interesting intervalley scattering property can be explained by Fano resonance. Our results show that these bilayer-monolayer junctions can be used as efficient intervalley converters in valleytronic devices.

We study the spin transport in bilayer graphene nanoribbons (BGNs) in the presence of Rashba spin-orbit interaction (SOI) and external gate voltages. It is found that the spin polarization can be significantly enhanced by the interlayer asymmetry or longitudinal mirror asymmetry produced by external gate voltages. Rashba SOI alone in BGNs can only generate current with spin polarization along the in-plane y direction, but the polarization components can be found along the x, y and z directions when a gate voltage is applied. High spin polarization with flexible orientation is obtained in the proposed device. Our findings shed new light on the generation of highly spin-polarized current in BGNs without external magnetic fields, which could have useful applications in spintronics device design.

We studied the valley dependent transport in a T junction consisting of an armchair lead and two zigzag leads. Electrons transmitted from the armchair lead to the two outgoing zigzag leads can be valley polarized. When the two outgoing leads have different widths, electrons are pushed into the wider lead and as a result, the valley polarization of the current in the narrow lead is enhanced with an oscillatory dependence on energy. The oscillation pattern is determined by the widths of the two zigzag leads. We analyzed the total local density of states of the device region of the junction and cannot find features that attribute this enhancement to quasi-bound state formation.

Multivariate time-series (MTS) data are prevalent in diverse domains and often high dimensional. We propose new random projection ensemble classifiers with high-dimensional MTS. The method first applies dimension reduction in the time domain via randomly projecting the time-series variables into some low-dimensional space, followed by measuring the disparity via some novel base classifier between the data and the candidate generating processes in the projected space. Our contributions are twofold: (i) We derive optimal weighted majority voting schemes for pooling information from the base classifiers for multiclass classification and (ii) we introduce new base frequency-domain classifiers based on Whittle likelihood (WL), Kullback-Leibler (KL) divergence, eigen-distance (ED), and Chernoff (CH) divergence. Both simulations for binary and multiclass problems, and an Electroencephalogram (EEG) application demonstrate the efficacy of the proposed methods in constructing accurate classifiers with high-dimensional MTS.

This study investigated the direct roles of hydrogen peroxide (H2 O2 ) in kidney aging using transgenic mice overexpressing glutathione peroxidase-1 (GPX1 TG). We demonstrated that kidneys in old mice recapitulated kidneys in elderly humans and were characterized by glomerulosclerosis, tubular atrophy, interstitial fibrosis, and loss of cortical mass. Scavenging H2 O2 by GPX1 TG significantly reduced mitochondrial and total cellular reactive oxygen species (ROS) and mitigated oxidative damage, thus improving these pathologies. The potential mechanisms by which ROS are increased in the aged kidney include a decreased abundance of an anti-aging hormone, Klotho, in kidney tissue, and decreased expression of nuclear respiratory factor 2 (Nrf2), a master regulator of the stress response. Decreased Klotho or Nrf2 was not improved in the kidneys of old GPX1 TG mice, even though mitochondrial morphology was better preserved. Using laser capture microdissection followed by label-free shotgun proteomics analysis, we show that the glomerular proteome in old mice was characterized by decreased abundance of cytoskeletal proteins (critical for maintaining normal glomerular function) and heat shock proteins, leading to increased accumulation of apolipoprotein E and inflammatory molecules. Targeted proteomic analysis of kidney tubules from old mice showed decreased abundance of fatty acid oxidation enzymes and antioxidant proteins, as well as increased abundance of glycolytic enzymes and molecular chaperones. GPX1 TG partially attenuated the remodeling of glomerular and tubule proteomes in aged kidneys. In summary, mitochondria from GPX1 TG mice are protected and kidney aging is ameliorated via its antioxidant activities, independent and downstream of Nrf2 or Klotho signaling.

One-way edge states are emerging as a robust way to control light in $t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ $p\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}s$, in which a high gap Chern number is essential for generating multiple one-way edge states for multiplexing and demultiplexing circuits. Contrary to approaches using gyrotropic photonic crystals, this study shows how reciprocal continuous media with a gauge field and chirality can be used to generate a gap Chern number greater than 1, and to support a maximum of 4 one-way edge states. Such media can be further used to construct one-way signal combiners and splitters, in which branching and transmission efficiencies can be accurately controlled.

Purpose Quantitative computed tomography (QCT)-derived measures of lung density are valued methods for objectively characterizing lung parenchymal and peripheral airways disease and are being used in a growing number of lung disease focused trials. Detector and reconstruction improvements in CT technology have allowed for significant radiation dose reduction in image acquisition with comparable qualitative image quality. We report the impact of detector type and reconstruction type on QCT lung density measures in relation to decreasing dose indices. Methods Two sets of studies were completed in an in vivo pig model with a SOMATOM Definition Flash CT system: (a) prior to system upgrade with conventional detectors (UFC) and filtered back projection (FBP), and (b) post system upgrade with integrated electronic detectors (STELLAR) and iterative reconstruction (SAFIRE). CT data were acquired across estimated CT volume dose indices (CTDIvol ) ranging from 0.75 to 15 mGy at both inspiratory and expiratory breath holds. Semiautomated lung segmentations allowed calculation of histogram median, kurtosis, and 15th percentile. Percentage of voxels below -910 HU and -950 HU (inspiratory), and -856 HU (expiratory) were also examined. The changes in these QCT metrics from dose reduction (15 mGy down to 0.75 mGy) were calculated relative to paired reference values (15 mGy). Results were compared based on detector and reconstruction type. Results In this study, STELLAR detectors improved concordance with 15 mGy values down to 3 mGy for inspiratory scans and 6 mGy for expiratory scans. The addition of SAFIRE reconstruction in all acquired measurements resulted in minimal deviation from reference values at 0.75 mGy. Conclusion The use of STELLAR integrated electronic detectors and SAFIRE iterative reconstruction may allow for comparable lung density measures with CT dose indices down to 0.75 mGy.

Maximum likelihood estimation of a censored autoregressive model with exogenous variables (CARX) requires computing the conditional likelihood of blocks of data of variable dimensions. As the random block dimension generally increases with the censoring rate, maximum likelihood estimation becomes quickly numerically intractable with increasing censoring. We introduce a new estimation approach using the complete-incomplete data framework with the complete data comprising the observations were there no censoring. We introduce a system of unbiased estimating equations motivated by the complete-data score vector, for estimating a CARX model. The proposed quasi-likelihood method reduces to maximum likelihood estimation when there is no censoring, and it is computationally efficient. We derive the consistency and asymptotic normality of the quasi-likelihood estimator, under mild regularity conditions. We illustrate the efficacy of the proposed method by simulations and a real application on phosphorus concentration in river water.

We studied the valley dependent transport in graphene L junctions connecting an armchair lead and a zigzag lead. The junction can be used in valleytronic devices and circuits. Electrons injected from the armchair lead into the junction is not valley polarized, but they can become valley polarized in the zigzag lead. There are Fermi energies, where the current in the zigzag lead is highly valley polarized and the junction is an efficient generator of valley polarized current. The features of the valley polarized current depend sensitively on the widths of the two leads, as well as the number of dimers in the armchair lead, because this number has a sensitive effect on the band structure of the armchair lead. When an external potential is applied to the junction, the energy range with high valley polarization is enlarged enhancing its function as a generator of highly valley polarized current. The scaling behavior found in other graphene devices is also found in L junctions, which means that the results presented here can be extended to junctions with larger dimensions after appropriate scaling of the energy.

There are two valleys in the band structure of graphene zigzag ribbons, which can be used to construct valleytronic devices. We studied the use of a T junction formed by an armchair ribbon and a zigzag ribbon to detect the valley-dependent currents in a zigzag graphene ribbon. A current flowing in a zigzag ribbon is divided by the T junction into the zigzag and armchair leads and this separation process is valley dependent. By measuring the currents in the two outgoing leads, the valley-dependent currents in the incoming lead can be determined. The method does not require superconducting or magnetic elements as in other approaches and thus will be useful in the development of valleytronic devices.

Agricultural landscapes often leak inorganic nitrogen to the stream network, usually in the form of nitrate-nitrite (NO x -N), degrading downstream water quality on both the local and regional scales. While the spatial distribution of nitrate sources has been delineated in many watersheds, less is known about the complicated temporal dynamics that drive stream NO x -N because traditional methods of stream grab sampling are often conducted at a low frequency. Deployment of accurate real-time, continuous measurement devices that have been developed in recent years enables high-frequency sampling that provides detailed information on the concentration-discharge relation and the timing of NO x -N delivery to streams. We aggregated 15-min interval NO x -N and discharge data over a nine-year period into daily averages and then used robust statistical methods to identify how the discharge regime within an artificially-drained agricultural watershed reflected catchment hydrology and NO x -N delivery pathways. We then quantified how transport and supply limitations varied from year-to-year and how dependence of these limitations varied with climate, especially drought. Our results show NO x -N concentrations increased linearly with discharge up to an average “turning point” of 1.42 mm of area-normalized discharge, after which concentrations decline with increasing discharge. We estimate transport and supply limitations to govern 57 and 43 percent, respectively, of the NO x -N flux over the nine-year period. Drought effects on the NO x -N flux linger for multiple years and this is reflected in a greater tendency toward supply limitations in the three years following drought. How the turning point varies with climate may aid in prediction of NO x -N loading in future climate regimes.

The threshold diffusion model assumes a piecewise linear drift term and a piecewise smooth diffusion term, which constitutes a rich model for analyzing nonlinear continuous-time processes. We consider the problem of testing for threshold nonlinearity in the drift term. We do this by developing a quasi-likelihood test derived under the working assumption of a constant diffusion term, which circumvents the problem of generally unknown functional form for the diffusion term. The test is first developed for testing for one threshold at which the drift term breaks into two linear functions. We show that under some mild regularity conditions, the asymptotic null distribution of the proposed test statistic is given by the distribution of certain functional of some centered Gaussian process. We develop a computationally efficient method for calibrating the p-value of the test statistic by bootstrapping its asymptotic null distribution. The local power function is also derived, which establishes the consistency of...

We study the spin-dependent transport properties of graphene nanoribbons with Rashba spin-orbit interaction (SOI). It is found that highly spin polarized electrical currents can be produced in asymmetrically-notched graphene nanoribbons, and the polarization components are found to be along the x, y and z directions. The spin polarization is largely enhanced by breaking the spatial symmetries of ideal graphene nanoribbons with Rashba SOI, and the spin polarized electrical currents with higher flexibility in the orientation of the polarization can be generated. This offers new possibilities for the generation of high spin polarization in graphene nanoribbons without external magnetic fields.

We introduce a certain Markovian representation for the threshold autoregressive moving‐average (TARMA) process with which we solve the long‐standing problem regarding the irreducibility condition of a first‐order TARMA model. Under some mild regularity conditions, we obtain a complete classification of the parameter space of an invertible first‐order TARMA model into parametric regions over which the model is either transient or recurrent, and the recurrence region is further subdivided into regions of null recurrence or positive recurrence, or even geometric recurrence. We derive a set of necessary and sufficient conditions for the ergodicity of invertible first‐order TARMA processes.

We propose a dual-gate field-effect transistor in graphene under the irradiation of off-resonant circularly polarized light. Graphene heterojunction is created by tuning the carrier densities in graphene through a top gate and back gate. The conductance of the graphene heterojunction oscillates periodically with the top and back gate voltages due to the Fabry-Perot resonances. It is found that the proposed device can act as a promising field-effect transistor, and the “on” and “off” states are controlled by the gate voltages and the off-resonant circularly polarized light. Comparing our simulation results with the experimental results, we find that our theoretical calculations agree well with the reported experiments. Our theoretical simulation enables new possibilities for the design of a photon controllable field-effect transistor in graphene, and it can also work as an optical sensor.

We proposed a new method to generate pure valley current in a three-terminal graphene junction using intrinsic asymmetry in graphene nanostructures. The three-terminal junction consists of one zigzag lead and two armchair leads. We found that a pure valley current can be obtained in the zigzag lead by applying a positive bias to one of the armchair leads and a negative bias to the other armchair lead. Our theoretical results provide us with deeper understanding of the generation mechanism of pure valley current and may stimulate further experimental studies of pure valley current in graphene and graphene-like materials.

Cluster ensemble has become an important extension to traditional clustering algorithms, yet the cluster ensemble problem is very challenging due to the inherent difficulty in resolving the label correspondence problem. We adapted the integrated K-means - Laplacian clustering approach to solve the cluster ensemble problem by exploiting both the attribute information embedded in the cluster labels and the pairwise relations among the objects. The optimal solution of the proposed approach requires computing the pseudo inverse of the normalized Laplacian matrix and the eigenvalue decomposition of a large matrix, which can be computationally burdensome for large scale document datasets. We devised an effective algebraic transformation method for efficiently carrying out the aforementioned computations and proposed an integrated K-means - Laplacian cluster ensemble approach (IKLCEA). Experimental results with benchmark document datasets demonstrate that IKLCEA outperforms other cluster ensemble techniques on most cases. In addition, IKLCEA is computationally efficient and can be readily employed in large scale document applications.

Purpose: A test object (phantom) is an important tool to evaluate comparability and stability of CTscanners used in multicenter and longitudinal studies. However, there are many sources of error that can interfere with the test object-derived quantitative measurements. Here the authors investigated three major possible sources of operator error in the use of a test object employed to assess pulmonary density-related as well as airway-related metrics. Methods: Two kinds of experiments were carried out to assess measurement variability caused by imperfect scanning status. The first one consisted of three experiments. A COPDGene test object was scanned using a dual source multidetector computed tomographic scanner (Siemens Somatom Flash) with the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) inspiration protocol (120 kV, 110 mAs, pitch = 1, slice thickness = 0.75 mm, slice spacing = 0.5 mm) to evaluate the effects of tilt angle, water bottle offset, and air bubble size. After analysis of these results, a guideline was reached in order to achieve more reliable results for this test object. Next the authors applied the above findings to 2272 test object scans collected over 4 years as part of the SPIROMICS study. The authors compared changes of the data consistency before and after excluding the scans that failed to pass the guideline. Results: This study established the following limits for the test object: tilt index ≤0.3, water bottle offset limits of [−6.6 mm, 7.4 mm], and no air bubble within the water bottle, where tilt index is a measure incorporating two tilt angles around x- and y-axis. With 95% confidence, the density measurement variation for all five interested materials in the test object (acrylic, water,lung, inside air, and outside air) resulting from all three error sources can be limited to ±0.9 HU (summed in quadrature), when all the requirements are satisfied. The authors applied these criteria to 2272 SPIROMICS scans and demonstrated a significant reduction in measurement variation associated with the test object. Conclusions: Three operator errors were identified which significantly affected the usability of the acquired scan images of the test object used for monitoring scanner stability in a multicenter study. The authors’ results demonstrated that at the time of test object scan receipt at a radiology core laboratory, quality control procedures should include an assessment of tilt index, water bottle offset, and air bubble size within the water bottle. Application of this methodology to 2272 SPIROMICS scans indicated that their findings were not limited to the scanner make and model used for the initial test but was generalizable to both Siemens and GE scanners which comprise the scanner types used within the SPIROMICS study.

Rationale and Objectives We evaluated the role of automated quantitative computed tomography (CT) scan interpretation algorithm in detecting interstitial lung disease (ILD) and/or emphysema in a sample of elderly subjects with mild lung disease. We hypothesized that the quantification and distributions of CT attenuation values on lung CT, over a subset of Hounsfield units (HUs) range (−1000 HU, 0 HU), can differentiate early or mild disease from normal lung. Materials and Methods We compared the results of quantitative spiral rapid end-exhalation (functional residual capacity, FRC) and end-inhalation (total lung capacity, TLC) CT scan analyses of 52 subjects with radiographic evidence of mild fibrotic lung disease to the results of 17 normal subjects. Several CT value distributions were explored, including (1) that from the peripheral lung taken at TLC (with peels at 15 or 65 mm), (2) the ratio of (1) to that from the core of lung, and (3) the ratio of (2) to its FRC counterpart. We developed a fused-lasso logistic regression model that can automatically identify sub-intervals of −1000 HU and 0 HU over which a CT value distribution provides optimal discrimination between abnormal and normal scans. Results The fused-lasso logistic regression model based on (2) with 15-mm peel identified the relative frequency of CT values of over −1000 HU and −900 and those over −450 HU and −200 HU as a means of discriminating abnormal versus normal lung, resulting in a zero out-sample false-positive rate, and 15% false-negative rate of that was lowered to 12% by pooling information. Conclusions We demonstrated the potential usefulness of this novel quantitative imaging analysis method in discriminating ILD and/or emphysema from normal lungs.

The properties of one dimensional Kronig–Penney type of periodic electric and vector potential on ABC-trilayer graphene superlattices are investigated. The energy spectra obtained with periodic vector potentials shows the emergence of extra Dirac points in the energy spectrum with finite energies. For identical barrier and well widths, the original as well as the extra Dirac points are located in the ky=0 plane. An asymmetry between the barrier and well widths causes a shift in the extra Dirac points away from the ky=0 plane. Extra Dirac points having same electron hole crossing energy as that of the original Dirac point as well as finite energy Dirac points are generated in the energy spectrum when periodic electric potential is applied to the system. By applying electric and vector potential together, the symmetry of the energy spectrum about the Fermi level is broken. A tunable band gap is induced in the energy spectrum by applying both electric and vector potential simultaneously with different barrier and well widths.

The threshold diffusion (TD) model assumes a piecewise linear drift term and piecewise smooth diffusion term, which can capture many nonlinear features and volatility clustering often observed in financial time series data. We solve the problem of option pricing with a TD asset pricing process by deriving the minimum entropy martingale measure, which is the risk-neutral measure closest to the underlying TD probability measure in terms of Kullback-Leibler divergence, given the historical regime-switching pattern. The proposed valuation model is illustrated with a numerical example.

The threshold diffusion process, first introduced by Tong (1990), is a continuous-time process satisfying a stochastic differential equation with a piecewise linear drift term and a piecewise smooth diffusion term, e.g., a piecewise constant function or a piecewise power function. We consider the problem of estimating the (drift) parameters indexing the drift term of a threshold diffusion process with continuous-time observations. Maximum likelihood estimation of the drift parameters requires prior knowledge of the functional form of the diffusion term, which is, however, often unavailable. We propose a quasi-likelihood approach for estimating the drift parameters of a two-regime threshold diffusion process that does not require prior knowledge about the functional form of the diffusion term. We show that, under mild regularity conditions, the quasi-likelihood estimators of the drift parameters are consistent. Moreover, the estimator of the threshold parameter is super consistent and weakly converges to some non-Gaussian continuous distribution. Also, the estimators of the autoregressive parameters in the drift term are jointly asymptotically normal with distribution the same as that when the threshold parameter is known. The empirical properties of the quasi-likelihood estimator are studied by simulation. We apply the threshold model to estimate the term structure of a long time series of US interest rates. The proposed approach and asymptotic results can be readily lifted to the case of a multi-regime threshold diffusion process.

Valley polarized transport was studied in graphene cross junctions consisting of a bilayer graphene device region connected to 4 monolayer graphene leads. Electrons injected from the armchair leads to the zigzag leads can be valley polarized in a range of Fermi energies. The valley polarization is produced by quantum interference and the Fano resonance effect in the device region. We also studied the dependence of the valley polarization on the dimensions of the junction and a vertical electric field applied to the device region. The valley polarization depends sensitively on the electric field, which enables us to control the valley polarization electrically.

We investigate the tunnel magnetoresistance (TMR) in an armchair phosphorene nanoribbon modulated by two ferromagnetic stripes. It is shown that large TMR can be achieved by applying a perpendicularly electric field to the phosphorene plane. We find that the TMR can be adjusted by an external gate voltage, and the TMR oscillates periodically from positive to negative by a slight change of the gate voltage. This characteristic can be observed in a wide region of exchange splitting values. Our findings open the way to design phosphorene-based spintronics nanodevices, and it may contribute to the future low power spintronic applications.

We investigate the spin-dependent transport properties in normal/ferromagnetic/normal phosphorene nanoribbon (PNR) junctions where an external gate electrode is attached to the ferromagnetic region. The exchange splitting in ferromagnetic phosphorene is induced by ferromagnetic proximity effect. We found that the current through this junction is spin polarized due to the exchange field induced in phosphorene. The spin polarization oscillates with the external gate voltage, and the spin polarization can be reversed from 100% to −100% by a slight change of the gate voltage. The controllable spin transport in phosphorene nanoribbons can have useful applications in the development of spintronic devices.

We studied the spin-transfer torque (STT) in graphene based normal-metal/topological-insulator/ferromagnet heterostructures (N/TI/F), which is induced by the helical spin-polarized current in the quantum spin Hall insulator. We found that the STT is comparable in magnitude to the STT in ferromagnetic-normal- ferromagnetic graphene junction, while not requiring additional ferromagnetic layer with fixed magnetization, which makes it advantageous for the manipulation of magnetic devices in spintronics. More interestingly, the STT is very robust in our proposed nanostructure, as it is immune to changes in the geometry due to an asymmetrically notch or the presence of random nanopores in the quantum spin Hall insulator. Our theoretical prediction suggests that graphene based quantum spin Hall insulator could be used for very efficient magnetization manipulation for magnetic materials.

We study the autocorrelation structure of aggregates from a bivariate continuous-time process. The underlying model is assumed to be a stationary bivariate Continuous-time Auto-Regressive Fractionally Integrated MovingAverage (CARFIMA) process driven by two independent standard fractional Brownian motions with two Hurst parameters. The limiting model of the aggregates, as the extent of aggregation increases to infinity, is shown to be an instantaneous linear transformation of two independent fractional Gaussian noises with the same Hurst parameters of the continuous-time process from which the aggregates arederived. We derive the likelihood ratio test for testing the equality of the two Hurst parameters, within the framework of Whittle likelihood. The limiting properties of the proposed test statistic and Whittle likelihood estimation are derived, and their finite sample properties are studied by simulation. The efficacy of the proposed approach is demonstrated with a data analysis.

Nitrogen (N) removal within reservoirs can be substantial, but few studies have reported the relative importance of various N-retention pathways. Assessing N-removal processes in reservoirs is important for quantifying the impacts of reservoirs on downstream water quality. In this study, we used a time-series approach to quantify the relative importance of various N-removal processes in the Saylorville Reservoir in Iowa. Dynamic regression modeling of upstream–downstream changes in key water-quality surrogates (pH, hardness, alkalinity, and suspended solids) and their relation to N concentration changes were used to estimate the relative importances of denitrification, N assimilation by algal uptake, and sedimentation of N on N retention in the reservoir. Assuming that decreasing N concentrations in the reservoir are the sum of these three processes, we estimate that denitrification is the dominant N removal process (60.9 %) followed by algal assimilation (37.9 %) and sedimentation (1.2 %). Our approach represents a new method of establishing the relative importance of N-removal processes in reservoirs and quantifying the impacts of reservoirs on downstream water quality.

We have investigated the electronic structure and carrier mobility of monolayer black phosphorus nanoribbons (BPNRs) using density functional theory combined with Boltzmann transport method with relaxation time approximation. It is shown that the calculated ultrahigh electron mobility can even reach the order of 10(3) to 10(7) cm(2) V(-1) s(-1) at room temperature. Owing to the electron mobility being higher than the hole mobility, armchair and diagonal BPNRs behave like n-type semiconductors. Comparing with the bare BPNRs, the difference between the hole and electronic mobilities can be enhanced in ribbons with the edges terminated by H atoms. Moreover, because the hole mobility is about two orders of magnitude larger than the electron mobility, zigzag BPNRs with H termination behave like p-type semiconductors. Our results indicate that BPNRs can be considered as a new kind of nanomaterial for applications in optoelectronics, nanoelectronic devices owing to the intrinsic band gap and ultrahigh charge mobility.

The new third-generation dual-source computed tomographic (CT) scanners and third-generation iterative reconstruction software enable substantial reductions in radiation dose to the patient.1 This is of great importance to the medical imaging community because the recent increase in the use of x-ray CT has greatly increased the amount of ionizing radiation received by populations in the United States and other countries around the world.2,3 The recently published National Lung Cancer Screening Trial study showed a 20% decrease in mortality from lung cancer with the use of screening CT scans of the thorax in patients at high risk for lung cancer.4–7 The use of CT for lung cancer screening will further increase the number of x-ray CT studies performed on the thorax. Reducing the CT radiation dose to the thorax would be of great benefit to patients enrolled in lung cancer screening programs. Computed tomography is also increasingly being used to establish quantitative phenotypes to subtype lung diseases such as COPD and asthma,8–15 and reducing the CT dose in these CT studies would also be beneficial. The medical imaging community has been trying to reduce the amount of ionizing radiation to the general population using a number of approaches. These include using medical imaging studies only when they are known to be beneficial to the patient, substituting nonionizing radiation studies such as ultrasound and magnetic resonance imaging for x-ray CT studies whenever possible, lowering the radiation dose of both radiographic and x-ray CT studies as much as possible while still maintaining adequate image quality and image noise levels, and, finally, encouraging CT manufacturers to pursue advanced technological solutions for reducing the radiation exposures necessary to provide diagnostic images of the thorax and other body parts. It is very important for quantitative CT scanning of the lung to maintain the accuracy of the CT attenuation values with acceptable levels of image noise. This is accomplished using carefully designed CT protocols.16 It is also important to monitor the performance of CT scanners that are used for obtaining quantitative measurements over time. This is typically achieved using CT test objects (CT phantoms) that are made up of nonbiologic materials that simulate different in vivo tissue CT densities such as soft tissue, water, lung tissue, and air. The COPDGene 1 test object in the COPDGene phase 1 multicenter National Institutes of Health study is one of the commonly used CT test objects that is used for CT quality control.17 This CT test object has been used in a number of National Institutes of Health and privately sponsored multicenter lung research studies that use quantitative CT to phenotype lung disease including COPDGene, multi-ethnic study of atherosclerosis, severe asthma research program, and subpopulations and intermediate outcome measures in COPD study. We have recently described18 the effects of reducing dose on CT attenuation values in the COPDGene 2 test object using a second-generation dual-source CT scanner, SOMATOM Definition FLASH, and second-generation iterative reconstruction software, SAFIRE.19 In that study, we showed that the COPDGene 2 test object can be used to assess the effects of decreasing dose on the mean attenuation values of the 8 materials in the COPDGene 2 test object using weighted filtered back projection (WFBP) and using the SAFIRE iterative reconstruction method. In this study, we have sought to evaluate the quantitative stability of measures derived from the COPDGene 2 test object while lowering imaging to ultralow doses, taking advantage of advances in third-generation dual-source CT technologies including third-generation iterative reconstruction methods.

We propose an electrically controllable valley beam splitter of massive Dirac electrons through the valley dependent Goos–Hanchen effect. The device consists of a monolayer graphene grown on a substrate and two ferromagnetic stripes with magnetizations directed along the current direction (the x axis). We found that the transmitted K and K′ valley electron beams exit at different longitudinal positions, and they can be separated spatially. The lateral displacements for the K and K′ valley electron beams, as well as their separations, can be enhanced by the transmission resonances formed between the two ferromagnetic stripes. The spatial separation between the K and K′ valley electron beams can reach values up to several thousands of wavelengths, which indicates that we can collect the two beams at different positions in the experiment. Our results can stimulate further experimental investigation of valley beam splitter in gapped graphene.

This special issue of the Journal of Business & Economic Statistics on “Regime Switching and Threshold Models” is motivated by the mounting empirical evidence of important nonlinearities in regress...

Dengue, a viral infection transmitted between people by mosquitoes, is today one of the most rapidly spreading diseases in the world. Here, we report the analyses covering 11 years (2005–2015) from the city of Guangzhou in southern China. Using the first eight years of data to develop an ecological-based model for the dengue system, we reliably predict the following three years of dengue dynamics – years with exceptionally extensive dengue outbreaks. We demonstrate that climate conditions, through the effects of rainfall and temperature on mosquito abundance and dengue transmission rate, play key roles in explaining the temporal dynamics of dengue incidence in the human population. Our study thus contributes to a better understanding of dengue dynamics and provides a predictive tool for preventive dengue-reduction strategies.

Methacholine challenge tests are used to measure changes in pulmonary function that indicate symptoms of asthma. In addition to pulmonary function tests, which measure global changes in pulmonary function, computed tomography images taken at full inspiration before and after administration of methacholine provide local air volume changes (hyper-inflation post methacholine) at individual acinar units, indicating local airway hyperresponsiveness. Some of the acini may have extreme air volume changes relative to the global average, indicating hyperresponsiveness, and those extreme values may occur in clusters. We propose a Gaussian mixture model with a spatial smoothness penalty to improve prediction of hyperresponsive locations that occur in spatial clusters. A simulation study provides evidence that the spatial smoothness penalty improves prediction under different data-generating mechanisms. We apply this method to computed tomography data from Seoul National University Hospital on five healthy and ten asthmatic subjects. Copyright © 2017 John Wiley & Sons, Ltd.

The human lung airway is a complex inverted tree-like structure. Detailed airway measurements can be extracted from MDCT-scanned lung images, such as segmental wall thickness, airway diameter, parent-child branch angles, etc. The wealth of lung airway data provides a unique opportunity for advancing our understanding of the fundamental structure-function relationships within the lung. An important problem is to construct and identify important lung airway features in normal subjects and connect these to standardized pulmonary function test results such as FEV1%. Among other things, the problem is complicated by the fact that a particular airway feature may be an important (relevant) predictor only when it pertains to segments of certain generations. Thus, the key is an efficient, consistent method for simultaneously conducting group selection (lung airway feature types) and within-group variable selection (airway generations), i.e., bi-level selection. Here we streamline a comprehensive procedure to process the lung airway data via imputation, normalization, transformation and groupwise principal component analysis, and then adopt a new composite penalized regression approach for conducting bi-level feature selection. As a prototype of composite penalization, the proposed composite bridge regression method is shown to admit an efficient algorithm, enjoy bi-level oracle properties, and outperform several existing methods. We analyze the MDCT lung image data from a cohort of 132 subjects with normal lung function. Our results show that, lung function in terms of FEV1% is promoted by having a less dense and more homogeneous lung comprising an airway whose segments enjoy more heterogeneity in wall thicknesses, larger mean diameters, lumen areas and branch angles. These data hold the potential of defining more accurately the “normal” subject population with borderline atypical lung functions that are clearly influenced by many genetic and environmental factors.

We study the spin and valley dependent transport in a silicene superlattice under the influence of a magnetic exchange field, a perpendicular electric field and a voltage potential. It is found that a gate-voltage-controllable fully spin and valley polarized current can be obtained in the proposed device and the spin and valley polarizations are sensitive oscillatory functions of the voltage potential. In properly designed superlattice structure, the spin and valley polarizations can be reversed from −100% to 100% by a slight change in the external voltage potential. The energy dispersion relations of the superlattice structure are also investigated, which helps us to understand the effects of the superlattice structure. The switching of the spin direction and the valley of the tunneling electrons by a gate voltage enables new possibilities for spin or valley control in silicene-based spintronics and valleytronics.

Excessive phosphorus (P) in rivers is prompting states to develop strategies to reduce P concentrations and export. The goal of this study was to assess the current condition by analyzing trends in total P (TP) concentrations at 40 river monitoring sites in Iowa for the period 1998 to 2013. We used monthly river monitoring data collected by the State of Iowa at ambient sites located beyond the influence of point sources or cities. Study objectives were to assess the presence of any linear trends in the TP concentration data using a time-series method that accounted for temporal correlation in the data and discharge and to combine the trend information from individual sites into an assessment of the statewide rate of change in river TP concentrations. Results indicated that annual TP concentrations were significantly decreasing at 12 sites (0.05), with concentrations ranging from 7.5% (Maple River) to 2.6% (Boyer River) and averaging 4.1% for the 12 sites. No statistically significant change was measured at 28 sites (0.05), although all but four of these sites had decreasing concentrations. As a population of sampled rivers across Iowa, TP concentrations were declining at an annual rate of approximately 2.6%. The decreasing trends are consistent with reported reductions in sediment concentrations measured in the Raccoon River and with decreasing trends detected in other midwestern rivers. We attribute the decreasing TP trends primarily to improvements in conservation and land management. Although reducing nonpoint source TP concentrations in Iowa rivers will be a tremendous challenge for the agricultural community, progress is being made toward meeting this goal with existing programs.

We study highly valley- and spin-polarized current in single-layer gapped graphene without spin-orbit coupling. The structure considered is a three-barrier structure with one spin-splitting barrier and two electrical potential barriers with vector potentials. The electrons in the two valleys transmit differently because of the valley-dependent reflection between two adjacent barriers, while the spin-up and spin-down electrons transmit differently because of the spin splitting. The structure is different from other structures in which spin-orbit coupling plays an important role in the observation of valley- and spin-polarized current. We can control the spin and valley polarization by changing the width of the barrier or the strength of the spin splitting. The structure proposed in this paper can be used to make valley and spin devices.