skip to main content

Search for: All records

Creators/Authors contains: "Zhang, Q."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Free, publicly-accessible full text available October 1, 2024
  2. Free, publicly-accessible full text available October 1, 2024
  3. We propose a novel Learned Alternating Minimization Algorithm (LAMA) for dual-domain sparse-view CT image reconstruction. LAMA is naturally induced by a variational model for CT reconstruction with learnable nonsmooth nonconvex regularizers, which are parameterized as composite functions of deep networks in both image and sinogram domains. To minimize the objective of the model, we incorporate the smoothing technique and residual learning architecture into the design of LAMA. We show that LAMA substantially reduces network complexity, improves memory efficiency and reconstruction accuracy, and is provably convergent for reliable reconstructions. Extensive numerical experiments demonstrate that LAMA outperforms existing methods by a wide margin on multiple benchmark CT datasets. 
    more » « less
    Free, publicly-accessible full text available October 1, 2024
  4. Ferroelectric materials are currently some of the most widely applied material systems and are constantly generating improved functions with higher efficiencies. Advancements in poly(vinylidene fluoride) (PVDF)–based polymer ferroelectrics provide flexural, coupling-efficient, and multifunctional material platforms for applications that demand portable, lightweight, wearable, and durable features. We highlight the recent advances in fluoropolymer ferroelectrics, their energetic cross-coupling effects, and emerging technologies, including wearable, highly efficient electromechanical actuators and sensors, electrocaloric refrigeration, and dielectric devices. These developments reveal that the molecular and nanostructure manipulations of the polarization-field interactions, through facile defect biasing, could introduce enhancements in the physical effects that would enable the realization of multisensory and multifunctional wearables for the emerging immersive virtual world and smart systems for a sustainable future.

    more » « less
  5. Compared with the Fe40Mn20Cr20Ni20 high-entropy alloy in an homogenized state, it has higher incipient plastic strength after high-temperature aging, which is attributed to the generation of short-range orderings (SROs) caused by the local composition fluctuations. Based on nanoindentation results at different loading rates, the evolution trends of homogeneous and heterogeneous dislocation-nucleation modes under the effect of SROs are revealed for the first time. Under the action of the high-solution friction stress, which is caused by the high loading rate, and coherency-strain field, which is caused by SROs, the critical shear stress of the dislocation nucleation increases. Furthermore, with the increase of the loading rate, the probability of heterogeneous nucleation in homogenized samples increases, while that in aged samples is the opposite. From the perspective of the distribution of dislocation-nucleation sites, this opposite trend can be well explained by assuming the spreading resistance of an activatable region. In short, the present work reveals the pivotal role of SROs on dislocation-nucleation modes and paves the way for the quantitative study concerning SROs and their strengthening effects. 
    more » « less
  6. We use Kremser and Blagoev’s [1] role-routine ecology to theorize about the effects of concurrency in complex service organizations, such as outpatient medical clinics. In a typical clinic, teams of specialized individuals serve multiple clients at the same time. There can be concurrency within a patient visit (a technician may be preparing for a procedure while the doctor talks to the patient) and concurrency between patient visits (multiple patients being treated in the clinic). Using data from electronic health records, we estimate the effects of concurrency within and between patient visits on the duration of patient visits in a set of dermatology clinics. As expected, we find that concurrency within patient visits is associated with reduced duration, while concurrency between visits is associated with increased duration. We discuss the implication of these findings for process mining and discovery of process models in organizations where process instances are not independent. 
    more » « less
  7. null (Ed.)
    Functional electrical stimulation (FES) is a potential technique for reanimating paralyzed muscles post neurological injury/disease. Several technical challenges including difficulty in measuring and compensating for delayed muscle activation levels inhibit its satisfactory control performance. In this paper, an ultrasound (US) imaging approach is proposed to measure delayed muscle activation levels under the implementation of FES. Due to low sampling rates of US imaging, a sampled data observer (SDO) is designed to estimate the muscle activation in a continuous manner. The SDO is combined with continuous-time dynamic surface control (DSC) approach that compensates for the electromechanical delay (EMD) in the tibialis anterior (TA) activation dynamics. The stability analysis based on the Lyapunov-Krasovskii function proves that the SDO-based DSC plus delay compensation (SDO-DSC-DC) approach achieves semi-global uniformly ultimately bounded (SGUUB) tracking performance. Simulation results on an ankle dorsiflexion neuromusculoskeletal system show the root mean square error (RMSE) of desired trajectory tracking is reduced by 19.77 % by using the proposed SDO-DSC-DC compared to the DSC-DC without the SDO. The findings provide potentials for rehabilitative devices, like powered exoskeleton and FES, to assist or enhance human limb movement based on the corresponding muscle activities in real-time. 
    more » « less

    The evolutionary sequence for high-mass star formation starts with massive starless clumps that go on to form protostellar, young stellar objects and then compact H ii regions. While there are many examples of the three later stages, the very early stages have proved to be elusive. We follow-up a sample of 110 mid-infrared dark clumps selected from the ATLASGAL catalogue with the IRAM telescope in an effort to identify a robust sample of massive starless clumps. We have used the HCO+ and HNC (1-0) transitions to identify clumps associated with infall motion and the SiO (2-1) transition to identity outflow candidates. We have found blue asymmetric line profile in 65 per cent of the sample, and have measured the infall velocities and mass infall rates (0.6–36 × 10−3 M⊙ yr−1) for 33 of these clumps. We find a trend for the mass infall rate decreasing with an increase of bolometric luminosity to clump mass, i.e. star formation within the clumps evolves. Using the SiO 2-1 line, we have identified good outflow candidates. Combining the infall and outflow tracers reveals that 67 per cent of quiescent clumps are already undergoing gravitational collapse or are associated with star formation; these clumps provide us with our best opportunity to determine the initial conditions and study the earliest stages of massive star formation. Finally, we provide an overview of a systematic high-resolution ALMA study of quiescent clumps selected that allows us to develop a detailed understanding of earliest stages and their subsequent evolution.

    more » « less