121 research outputs found
Winking filaments due to cyclic evaporation-condensation
Observations have shown that some filaments appear and disappear in the
H line wing images periodically. There have been no attempts to model
these "winking filaments" thus far. The evaporation--condensation mechanism is
widely used to explain the formation of solar filaments. Here, we demonstrate,
for the first time, how multi-dimensional evaporation--condensation in an
arcade setup invariably causes a stretching of the magnetic topology. We aim to
check whether this magnetic stretching during cyclic evaporation--condensation
could reproduce a winking filament. We used our open-source code MPI-AMRVAC to
carry out 2D magnetohydrodynamic simulations based on a quadrupolar
configuration. A periodic localized heating, which modulates the
evaporation--condensation process, was imposed before, during, and after the
formation of the filament. Synthetic H and 304 \r{A}, images were
produced to compare the results with observations. For the first time, we
noticed the winking filament phenomenon in a simulation of the formation of
on-disk solar filaments, which was in good agreement with observations.
Typically, the period of the winking is different from the period of the
impulsive heating. A forced oscillator model explains this difference and fits
the results well. A parameter survey is also done to look into details of the
magnetic stretching phenomenon. We found that the stronger the heating or the
higher the layer where the heating occurs, the more significant the winking
effect appears.Comment: 14 pages, 6 figures. Accepted by A&
How should this patient with repeated aspiration pneumonia be managed and treated?—a proposal of the Percutaneous ENdoscopIc Gastrostomy and Tracheostomy (PENlIGhT) procedure
Cerebrovascular accident (CVA) is commonly seen among the elderly with a substantial proportion of patients suffering from long-term dysphagia and/or an inability to protect their airway. This potentially imposes on them an increased risk of malnutrition and aspiration pneumonia. In this article, we present a patient with malnutrition and dysphagia secondary to CVA. We propose a procedure for which we will name the Percutaneous ENdoscopIc Gastrostomy and Tracheostomy (PENlIGhT) procedure for placement of percutaneous endoscopic gastrostomy (PEG) and tracheostomy tube (TT) at the same time. The medical literature was systematically reviewed for both PEG and tracheostomy, aiming to provide the state-of-the-art evidence for clinical use of the PENlIGhT procedure. In clinical practice, the PENlIGhT procedure is indicated for patients who are expected to have prolonged swallowing disturbance and mechanical ventilation. Some prediction tools and scores can be helpful to identify such groups of patients. Patients with poor neurological outcomes who require prolonged maintenance of life are also good candidates for the PENlIGhT procedure
Chaotic Phase-Coded Waveforms with Space-Time Complementary Coding for MIMO Radar Applications
A framework for designing orthogonal chaotic phase-coded waveforms with space-time complementary coding (STCC) is proposed for multiple-input multiple-output (MIMO) radar applications. The phase-coded waveform set to be transmitted is generated with an arbitrary family size and an arbitrary code length by using chaotic sequences. Due to the properties of chaos, this chaotic waveform set has many advantages in performance, such as anti-interference and low probability of intercept. However, it cannot be directly exploited due to the high range sidelobes, mutual interferences, and Doppler intolerance. In order to widely implement it in practice, we optimize the chaotic phase-coded waveform set from two aspects. Firstly, the autocorrelation property of the waveform is improved by transmitting complementary chaotic phase-coded waveforms, and an adaptive clonal selection algorithm is utilized to optimize a pair of complementary chaotic phase-coded pulses. Secondly, the crosscorrelation among different waveforms is eliminated by implementing space-time coding into the complementary pulses. Moreover, to enhance the detection ability for moving targets in MIMO radars, a method of weighting different pulses by a null space vector is utilized at the receiver to compensate the interpulse Doppler phase shift and accumulate different pulses coherently. Simulation results demonstrate the efficiency of our proposed method
Chaotic Phase-Coded Waveforms with Space-Time Complementary Coding for MIMO Radar Applications
A framework for designing orthogonal chaotic phase-coded waveforms with space-time complementary coding (STCC) is proposed for multiple-input multiple-output (MIMO) radar applications. The phase-coded waveform set to be transmitted is generated with an arbitrary family size and an arbitrary code length by using chaotic sequences. Due to the properties of chaos, this chaotic waveform set has many advantages in performance, such as anti-interference and low probability of intercept. However, it cannot be directly exploited due to the high range sidelobes, mutual interferences, and Doppler intolerance. In order to widely implement it in practice, we optimize the chaotic phase-coded waveform set from two aspects. Firstly, the autocorrelation property of the waveform is improved by transmitting complementary chaotic phase-coded waveforms, and an adaptive clonal selection algorithm is utilized to optimize a pair of complementary chaotic phase-coded pulses. Secondly, the crosscorrelation among different waveforms is eliminated by implementing space-time coding into the complementary pulses. Moreover, to enhance the detection ability for moving targets in MIMO radars, a method of weighting different pulses by a null space vector is utilized at the receiver to compensate the interpulse Doppler phase shift and accumulate different pulses coherently. Simulation results demonstrate the efficiency of our proposed method
Neural Dysfunction Underlying Working Memory Processing at Different Stages of the Illness Course in Schizophrenia:A Comparative Meta-analysis
Schizophrenia (SCZ), as a chronic and persistent disorder, exhibits working
memory deficits across various stages of the disorder, yet the neural
mechanisms underlying these deficits remain elusive with inconsistent
neuroimaging findings. We aimed to compare the brain functional changes of
working memory in patients at different stages: clinical high risk (CHR),
first-episode psychosis (FEP), and long-term SCZ, using meta-analyses of
functional magnetic resonance imaging (fMRI) studies. Following a systematic
literature search, fifty-six whole-brain task-based fMRI studies (15 for CHR,
16 for FEP, 25 for long-term SCZ) were included. The separate and pooled
neurofunctional mechanisms among CHR, FEP and long-term SCZ were generated by
Seed-based d Mapping toolbox. The CHR and FEP groups exhibited overlapping
hypoactivation in the right inferior parietal lobule, right middle frontal
gyrus, and left superior parietal lobule, indicating key lesion sites in the
early phase of SCZ. Individuals with FEP showed lower activation in left
inferior parietal lobule than those with long-term SCZ, reflecting a possible
recovery process or more neural inefficiency. We concluded that SCZ represent
as a continuum in the early stage of illness progression, while the neural
bases are inversely changed with the development of illness course to long-term
course
Engineering ferroelectricity in monoclinic hafnia
Ferroelectricity in the complementary metal-oxide semiconductor
(CMOS)-compatible hafnia (HfO) is crucial for the fabrication of
high-integration nonvolatile memory devices. However, the capture of
ferroelectricity in HfO requires the stabilization of
thermodynamically-metastable orthorhombic or rhombohedral phases, which entails
the introduction of defects (e.g., dopants and vacancies) and pays the price of
crystal imperfections, causing unpleasant wake-up and fatigue effects. Here, we
report a theoretical strategy on the realization of robust ferroelectricity in
HfO-based ferroelectrics by designing a series of epitaxial
(HfO)/(CeO) superlattices. The advantages of the designated
ferroelectric superlattices are defects free, and most importantly, on the base
of the thermodynamically stable monoclinic phase of HfO. Consequently, this
allows the creation of superior ferroelectric properties with an electric
polarization 25 C/cm and an ultralow polarization-switching energy
barrier at 2.5 meV/atom. Our work may open an entirely new route towards
the fabrication of high-performance HfO based ferroelectric devices
Direct Imaging of Kinetic Pathways of Atomic Diffusion in Monolayer Molybdenum Disulfide
Direct observation of atomic migration both on and below surfaces is a long-standing but important challenge in materials science as diffusion is one of the most elementary processes essential to many vital material behaviors. Probing the kinetic pathways, including metastable or even transition states involved down to atomic scale, holds the key to the underlying physical mechanisms. Here, we applied aberration-corrected transmission electron microscopy (TEM) to demonstrate direct atomic-scale imaging and quasi-real-time tracking of diffusion of Mo adatoms and vacancies in monolayer MoS 2, an important two-dimensional transition metal dichalcogenide (TMD) system. Preferred kinetic pathways and the migration potential-energy landscape are determined experimentally and confirmed theoretically. The resulting three-dimensional knowledge of the atomic configuration evolution reveals the different microscopic mechanisms responsible for the contrasting intrinsic diffusion rates for Mo adatoms and vacancies. The new insight will benefit our understanding of material processes such as phase transformation and heterogeneous catalysis
Adaptive Radio Frequency Interference Mitigation for Passive Bistatic Radar Using OFDM Waveform
High frequency passive bistatic radar (HFPBR) is a novel and promising technique in development. DRM broadcast exploiting orthogonal frequency division multiplexing (OFDM) technique supplies a good choice for the illuminator of HFPBR. HFPBR works in crowded short wave band. It faces severe radio frequency interference (RFI) problem. In this paper, a theoretical analysis of the range-domain correlation of RFI in OFDM-based HF radar is presented. A RFI mitigation method in the range domain is introduced. After the direct-path wave rejection, the interference subspace is constructed using the echo signals at the reserved range bins. Then RFI in the effective range bins is mitigated by the subspace projection, using the correlation among different range bins. The introduced algorithm is easy to perform in practice and the RFI mitigation performance is evaluated using the experimental data of DRM-based HFPBR
Advances in cultivation, wastewater treatment application, bioactive components of Caulerpa lentillifera and their biotechnological applications
The edible seaweed Caulerpa lentillifera, a powerful natural food source that is rich in protein, minerals, dietary fibers, vitamins, saturated fatty acids and unsaturated fatty acids, has been mass cultured in some Asian countries and has been the focus of researchers in recent years. Here, the operational conditions of its culture, application in wastewater treatment, and bioactive components are summarized and comparatively analyzed. Based on previous studies, salinity, nutrient concentrations, irradiance and temperature are stress factors for algal growth. Moreover, dried Caulerpa lentillifera seaweed is efficient in the biosorption of heavy metals and cationic dyes in wastewater, and fresh seaweed can be introduced as a biofilter in aquaculture system treatment. In addition, among the rich bioactive compounds in Caulerpa lentillifera, the phenolic compounds show the potential ability for regulating glucose metabolism in vivo. Polysaccharides and oligosaccharides exhibit anticoagulant, immunomodulatory effects and cancer-preventing activity. Siphonaxanthin is a compound with attractive novel functions in cancer-preventing activity and lipogenesis-inhibiting effects. Furthermore, the antioxidant activity of siphonaxanthin extracted from Caulerpa lentillifera could be stronger than that of astaxanthin. This review offers an overview of studies of Caulerpa lentillifera addressing various aspects including cultivation, wastewater treatment and biological active components which may provide valuable information for the cultivation and utilization of this green alga
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