182 research outputs found
Orbital-Energy Splitting in Anion Ordered Ruddlesden-Popper Halide Perovskites for Tunable Optoelectronic Applications
The electronic orbital characteristics at the band edges plays an important
role in determining the electrical, optical and defect properties of perovskite
photovoltaic materials. It is highly desirable to establish the relationship
between the underlying atomic orbitals and the optoelectronic properties as a
guide to maximize the photovoltaic performance. Here, using first-principles
calculations and taking anion ordered Ruddlesden-Popper (RP) phase halide
perovskites CsGeICl as an example, we demonstrate
how to rationally optimize the optoelectronic properties (e.g., band gap,
transition dipole matrix elements, carrier effective masses, band width)
through a simple band structure parameter. Our results show that reducing the
splitting energy of p orbitals of B-site atom can effectively
reduce the band gap and carrier effective masses while greatly improving the
optical absorption in the visible region. Thereby, the orbital-property
relationship with is well established through biaxial compressive
strain. Finally, it is shown that this approach can be reasonably extended to
several other non-cubic halide perovskites with similar p orbitals
characteristics at the conduction band edges. Therefore, we believe that our
proposed orbital engineering approach provides atomic-level guidance for
understanding and optimizing the device performance of layered perovskite solar
cells
Output Feedback Fractional-Order Nonsingular Terminal Sliding Mode Control of Underwater Remotely Operated Vehicles
For the 4-DOF (degrees of freedom) trajectory tracking control problem of underwater remotely operated vehicles (ROVs) in the presence of model uncertainties and external disturbances, a novel output feedback fractional-order nonsingular terminal sliding mode control (FO-NTSMC) technique is introduced in light of the equivalent output injection sliding mode observer (SMO) and TSMC principle and fractional calculus technology. The equivalent output injection SMO is applied to reconstruct the full states in finite time. Meanwhile, the FO-NTSMC algorithm, based on a new proposed fractional-order switching manifold, is designed to stabilize the tracking error to equilibrium points in finite time. The corresponding stability analysis of the closed-loop system is presented using the fractional-order version of the Lyapunov stability theory. Comparative numerical simulation results are presented and analyzed to demonstrate the effectiveness of the proposed method. Finally, it is noteworthy that the proposed output feedback FO-NTSMC technique can be used to control a broad range of nonlinear second-order dynamical systems in finite time
Melting process of frozen sessile droplets on superhydrophobic surfaces
Superhydrophobic surfaces can exhibit icephobicity in many ways due to their
large contact angles and small rolling angles. The melting process of frozen
droplets on superhydrophobic surfaces is still unclear, hindering the
understanding of surface icephobicity. In this experimental study of the
melting process of frozen sessile droplets on superhydrophobic surfaces, we
find two types of melting morphologies with opposite vortex directions on a
single-scale nano-structured (SN) superhydrophobic substrate and a
hierarchical-scale micro-nano-structured (HMN) superhydrophobic substrate.
Melting pattern visualizations and flow field measurements showwed Marangoni
convection and natural convection occuring in the melting sessile droplets. For
the HMN superhydrophobic substrate, the internal flow was found to be dominated
by Marangoni convection due to the temperature gradient along the surface of
the droplet. For the SN superhydrophobic substrate, Marangoni convection was
inhibited by the superhydrophobic particles at the surface of the droplet,
which were shed from the fragile superhydrophobic substrate during the
freezing--melting process, as confirmed by surface characterizations of the
substrate and flow measurements of a water pool. These results will help
researchers better understand the melting process of frozen droplets and in
designing novel icephobic surfaces for numerous applications.Comment: 31 pages, 12 figure
AuE-IPA: An AU Engagement Based Infant Pain Assessment Method
Recent studies have found that pain in infancy has a significant impact on
infant development, including psychological problems, possible brain injury,
and pain sensitivity in adulthood. However, due to the lack of specialists and
the fact that infants are unable to express verbally their experience of pain,
it is difficult to assess infant pain. Most existing infant pain assessment
systems directly apply adult methods to infants ignoring the differences
between infant expressions and adult expressions. Meanwhile, as the study of
facial action coding system continues to advance, the use of action units (AUs)
opens up new possibilities for expression recognition and pain assessment. In
this paper, a novel AuE-IPA method is proposed for assessing infant pain by
leveraging different engagement levels of AUs. First, different engagement
levels of AUs in infant pain are revealed, by analyzing the class activation
map of an end-to-end pain assessment model. The intensities of top-engaged AUs
are then used in a regression model for achieving automatic infant pain
assessment. The model proposed is trained and experimented on YouTube
Immunization dataset, YouTube Blood Test dataset, and iCOPEVid dataset. The
experimental results show that our AuE-IPA method is more applicable to infants
and possesses stronger generalization ability than end-to-end assessment model
and the classic PSPI metric
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