8 research outputs found
Non-Ideal Program-Time Conservation in Charge Trap Flash for Deep Learning
Training deep neural networks (DNNs) is computationally intensive but arrays
of non-volatile memories like Charge Trap Flash (CTF) can accelerate DNN
operations using in-memory computing. Specifically, the Resistive Processing
Unit (RPU) architecture uses the voltage-threshold program by stochastic
encoded pulse trains and analog memory features to accelerate vector-vector
outer product and weight update for the gradient descent algorithms. Although
CTF, offering high precision, has been regarded as an excellent choice for
implementing RPU, the accumulation of charge due to the applied stochastic
pulse trains is ultimately of critical significance in determining the final
weight update. In this paper, we report the non-ideal program-time conservation
in CTF through pulsing input measurements. We experimentally measure the effect
of pulse width and pulse gap, keeping the total ON-time of the input pulse
train constant, and report three non-idealities: (1) Cumulative V_T shift
reduces when total ON-time is fragmented into a larger number of shorter
pulses, (2) Cumulative V_T shift drops abruptly for pulse widths < 2 {\mu}s,
(3) Cumulative V_T shift depends on the gap between consecutive pulses and the
V_T shift reduction gets recovered for smaller gaps. We present an explanation
based on a transient tunneling field enhancement due to blocking oxide
trap-charge dynamics to explain these non-idealities. Identifying and modeling
the responsible mechanisms and predicting their system-level effects during
learning is critical. This non-ideal accumulation is expected to affect
algorithms and architectures relying on devices for implementing mathematically
equivalent functions for in-memory computing-based acceleration
Autofluorescence of Model Polyethylene Terephthalate Nanoplastics for Cell Interaction Studies
This work contributes to fill one of the gaps regarding nanoplastic interactions with
biological systems by producing polyethylene terephthalate (PET) model nanoplastics, similar to
those found in the marine environment, by means of a fast top-down approach based on mechanical
fragmentation. Their size distribution and morphology were characterized by laser diffraction and
atomic force microscopy (AFM). Their autofluorescence was studied by spectrofluorimetry and
fluorescence imaging, being a key property for the evaluation of their interaction with biota. The
emission spectra of label-free nanoplastics were comparable with those of PET nanoplastics labeled
with Nile red. Finally, the suitability of label-free nanoplastics for biological studies was assessed
by in vitro exposure with Mytilus galloprovincialis hemolymphatic cells in a time interval up to 6 h.
The nanoplastic internalization into these cells, known to be provided with phagocytic activity, was
assessed by fluorescence microscopy. The obtained results underlined that the autofluorescence of
the model PET nanoplastics produced in the laboratory was adequate for biological studies having
the potential to overcome the disadvantages commonly associated with several fluorescent dyes,
such as the tendency to also stain other organic materials different from plastics, to form aggregates
due to intermolecular interactions at high concentrations with a consequent decrease in fluorescence
intensity, and to dye desorption from nanoparticles. The results of the autofluorescence study
provide an innovative approach for plastic risk assessment
Scaffolds for bone regeneration made of hydroxyapatite microspheres in a collagen matrix
Biomimetic scaffolds with a structural and chemical composition similar to native bone tissue may be promising for bone tissue regeneration. In the present work hydroxyapatite mesoporous microspheres (mHA) were incorporated into collagen scaffolds containing an ordered interconnected macroporosity. The mHA were obtained by spray drying of a nano hydroxyapatite slurry prepared by the precipitation technique. X-ray diffraction (XRD) analysis revealed that the microspheres were composed only of hydroxyapatite (HA) phase, and energy-dispersive x-ray spectroscopy (EDS) analysis revealed the Ca/P ratio to be 1.69 which is near the value for pure HA. The obtained microspheres had an average diameter of 6 μm, a specific surface area of 40 m(2)/g as measured by Brunauer-Emmett-Teller (BET) analysis, and Barrett-Joyner-Halenda (BJH) analysis showed a mesoporous structure with an average pore diameter of 16 nm. Collagen/HA-microsphere (Col/mHA) composite scaffolds were prepared by freeze-drying followed by dehydrothermal crosslinking. SEM observations of Col/mHA scaffolds revealed HA microspheres embedded within a porous collagen matrix with a pore size ranging from a few microns up to 200 μm, which was also confirmed by histological staining of sections of paraffin embedded scaffolds. The compressive modulus of the composite scaffold at low and high strain values was 1.7 and 2.8 times, respectively, that of pure collagen scaffolds. Cell proliferation measured by the MTT assay showed more than a 3-fold increase in cell number within the scaffolds after 15 days of culture for both pure collagen scaffolds and Col/mHA composite scaffolds. Attractive properties of this composite scaffold include the potential to load the microspheres for drug delivery and the controllability of the pore structure at various length scales
Apoptotic volume decrease (AVD) in A549 cells exposed to water-soluble fraction of particulate matter (PM10)
Exposure to atmospheric particulate matter (PM) is recognized as a human health risk factor of great concern. The present work aimed to study the cellular mechanisms underlying cytotoxic effects of airborne particulate matter <10 mu m in size (PM10), sampled in an urban background site from January to May 2020, on A549 cells. In particular, the study addressed if PM10 exposure can be a main factor in the induction of the Apoptotic Volume Decrease (AVD), which is one of the first events of apoptosis, and if the generation of intracellular oxidative stress can be involved in the PM10 induction of apoptosis in A549 cells. The cytotoxicity of PM10 samples was measured by MTT test on cells exposed for 24 h to the PM10 aqueous extracts, cell volume changes were monitored by morphometric analysis of the cells, apoptosis appearance was detected by annexin V and the induction of intracellular oxidative stress was evaluated by the ROS sensitive CM-H2DCFDA fluorescent probe. The results showed cytotoxic effects ascribable to apoptotic death in A549 cells exposed for 24 h to aqueous extracts of airborne winter PM10 samples characterized by high PM10 value and organic carbon content. The detected reduced cell viability in winter samples ranged from 55% to 100%. Normotonic cell volume reduction (ranging from about 60% to 30% cell volume decrease) after PM10 exposure was already detectable after the first 30 min clearly indicating the ability of PM10, mainly arising from biomass burning, to induce Apoptotic Volume Decrease (AVD) in A549 cells. AVD was prevented by the pre-treatment with 0.5 mM SITS indicating the activation of Clefflux presumably through the activation of VRAC channels. The exposure of A549 cells to PM10 aqueous extracts was able to induce intracellular oxidative stress detected by using the ROS-sensitive probe CM-H2DCFDA. The PM10induced oxidative stress was statistically significantly correlated with cell viability inhibition and with apoptotic cell shrinkage. It was already evident after 15 min exposure representing one of the first cellular effects caused by PM exposure. This result suggests the role of oxidative stress in the PM10 induction of AVD as one of the first steps in cytotoxicity
Intracellular Antioxidant Activity of Biocompatible Citrate-Capped Palladium Nanozymes
A method for the aqueous synthesis of stable and biocompatible citrate-coated palladium nanoparticles (PdNPs) in the size range comparable to natural enzymes (4–8 nm) has been developed. The toxicological profile of PdNPs was assessed by different assays on several cell lines demonstrating their safety in vitro also at high particle concentrations. To elucidate their cellular fate upon uptake, the localization of PdNPs was analyzed by Transmission Electron Microscopy (TEM). Moreover, crucial information about their intracellular stability and oxidation state was obtained by Sputtering-Enabled Intracellular X-ray Photoelectron Spectroscopy (SEI-XPS). TEM/XPS results showed significant stability of PdNPs in the cellular environment, an important feature for their biocompatibility and potential for biomedical applications. On the catalytic side, these PdNPs exhibited strong and broad antioxidant activities, being able to mimic the three main antioxidant cellular enzymes, i.e., peroxidase, catalase, and superoxide dismutase. Remarkably, using an experimental model of a human oxidative stress-related disease, we demonstrated the effectiveness of PdNPs as antioxidant nanozymes within the cellular environment, showing that they are able to completely re-establish the physiological Reactive Oxygen Species (ROS) levels in highly compromised intracellular redox conditions