Resonant TMR inversion in LiF/EuS based spin-filter tunnel junctions

Resonant tunneling can lead to inverse tunnel magnetoresistance when impurity levels rather than direct tunneling dominate the transport process. We fabricated hybrid magnetic tunnel junctions of CoFe/LiF/EuS/Ti, with an epitaxial LiF energy barrier joined with a polycrystalline EuS spin-filter bar-rier. Due to the water solubility of LiF, the devices were fully packaged in situ. The devices showed sizeable positive TMR up to 16% at low bias voltages but clearly inverted TMR at higher bias voltages. The TMR inversion depends sensitively on the thickness of LiF, and the tendency of inversion disap-pears when LiF gets thick enough and recovers its intrinsic properties

Anomalous stopping of laser-accelerated intense proton beam in dense ionized matter

Ultrahigh-intensity lasers (10$^{18}$-10$^{22}$W/cm$^{2}$) have opened up new perspectives in many fields of research and application [1-5]. By irradiating a thin foil, an ultrahigh accelerating field (10$^{12}$ V/m) can be formed and multi-MeV ions with unprecedentedly high intensity (10$^{10}$A/cm$^2$) in short time scale ($\sim$ps) are produced [6-14]. Such beams provide new options in radiography [15], high-yield neutron sources [16], high-energy-density-matter generation [17], and ion fast ignition [18,19]. An accurate understanding of the nonlinear behavior of beam transport in matter is crucial for all these applications. We report here the first experimental evidence of anomalous stopping of a laser-generated high-current proton beam in well-characterized dense ionized matter. The observed stopping power is one order of magnitude higher than single-particle slowing-down theory predictions. We attribute this phenomenon to collective effects where the intense beam drives an decelerating electric field approaching 1GV/m in the dense ionized matter. This finding will have considerable impact on the future path to inertial fusion energy.Comment: 8 pages, 4 figure

Energy loss enhancement of very intense proton beams in dense matter due to the beam-density effect

Thoroughly understanding the transport and energy loss of intense ion beams in dense matter is essential for high-energy-density physics and inertial confinement fusion. Here, we report a stopping power experiment with a high-intensity laser-driven proton beam in cold, dense matter. The measured energy loss is one order of magnitude higher than the expectation of individual particle stopping models. We attribute this finding to the proximity of beam ions to each other, which is usually insignificant for relatively-low-current beams from classical accelerators. The ionization of the cold target by the intense ion beam is important for the stopping power calculation and has been considered using proper ionization cross section data. Final theoretical values agree well with the experimental results. Additionally, we extend the stopping power calculation for intense ion beams to plasma scenario based on Ohm's law. Both the proximity- and the Ohmic effect can enhance the energy loss of intense beams in dense matter, which are also summarized as the beam-density effect. This finding is useful for the stopping power estimation of intense beams and significant to fast ignition fusion driven by intense ion beams

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Experimental Study on Cumulative Plastic Deformation of Coarse-Grained Soil High-Grade Roadbed under Long-Term Vehicle Load

According to the change characteristics of the subgrade moisture content and the mechanical calculation of several typical highways, the test scheme of the permanent deformation of coarse soil was formulated. The relationship between the permanent deformation of coarse-grained soil and the stress level, compaction degree, moisture content, and loading frequency was studied by cyclic loading triaxle testing. The results show that the permanent deformation of coarse-grained soil increases with the increase in partial stress and moisture content and decreases with the increase in compaction degree. The experimental data were fitted by the Tseng-Lytton model, and the correlation coefficients were 92%, which indicated that the model could be used to predict the permanent deformation of coarse soil. The relationships between the model coefficient and the moisture content and spring back modulus were obtained by the multiple regression method. Finally, the permanent deformation of the subgrade soil was calculated by using the layered summation method and a typical subgrade pavement structure

Progress of Placement Optimization for Accelerating VLSI Physical Design

Placement is essential in very large-scale integration (VLSI) physical design, as it directly affects the design cycle. Despite extensive prior research on placement, achieving fast and efficient placement remains challenging because of the increasing design complexity. In this paper, we comprehensively review the progress of placement optimization from the perspective of accelerating VLSI physical design. It can help researchers systematically understand the VLSI placement problem and the corresponding optimization means, thereby advancing modern placement optimization research. We highlight emerging trends in modern placement-centric VLSI physical design flows, including placement optimizers and learning-based predictors. We first define the placement problem and review the classical placement algorithms, then discuss the application bottleneck of the classical placement algorithms in advanced technology nodes and give corresponding solutions. After that, we introduce the development of placement optimizers, including algorithm improvements and computational acceleration, pointing out that these two aspects will jointly promote accelerating VLSI physical design. We also present research working on learning-based predictors from various angles. Finally, we discuss the common and individual challenges encountered by placement optimizers and learning-based predictors

A Self-Assembled Copper-Selenocysteine Nanoparticle for Enhanced Chemodynamic Therapy via Oxidative Stress Amplification

Chemodynamic therapy (CDT) as a catalytic anticancer strategy utilizes transition metal ions to initiate the Fenton reaction to produce high levels of cytotoxic hydroxyl radicals(·OH) in situ. Nevertheless, current existing CDTs are normally restricted by the high levels of existing antioxidant molecules and/or enzymes, such as glutathione (GSH) and thioredoxin reductase (TrxR), in a tumor internal environment, which could suppress CDT via ·OH depletion. Herein, to enhance ·OH-induced cellular damage by CDT, a self-assembled copper-selenocysteine nanoparticles (Cu-SeC NPs) was fabricated through a one-pot process. In our design, once Cu-SeC NPs were endocytosed by tumor cells, Cu2+ was reduced to Cu+ by cellular GSH, promoting in situ Fenton-like reactions to trigger ·OH rapid production in cells as well as the depletion of GSH. Furthermore, the gradually released selenocysteine can inhibit TrxR activity to weaken the protection of antioxidant systems and provide a favorable microenvironment for CDT. As a result, both paths synergistically resulted in massive reactive oxygen species (ROS) accumulation and amplified oxidative stress in tumor sites for enhanced CDT. As a new intelligent anticancer nanoplatform, Cu-SeC NPs exhibit synergistic antitumor effects with negligible systemic toxicity. Thus, the proposed strategy provides a new avenue for further development of progressive therapeutic systems

Photochemical Charge Separation at Particle Interfaces: The n‑BiVO₄–p-Silicon System

The charge transfer properties of interfaces are central to the function of photovoltaic and photoelectrochemical cells and photocatalysts. Here we employ surface photovoltage spectroscopy (SPS) to study photochemical charge transfer at a p-silicon/n-BiVO₄ particle interface. Particle films of BiVO₄ on an aluminum-doped p-silicon wafer were obtained by drop-coating particle suspensions followed by thermal annealing at 353 K. Photochemical charge separation of the films was probed as a function of layer thickness and illumination intensity, and in the presence of methanol as a sacrificial electron donor. Electron injection from the BiVO₄ into the p-silicon is clearly observed to occur and to result in a maximum photovoltage of 150 mV for a 1650 nm thick film under 0.3 mW cm^–2 illumination at 3.5 eV. This establishes the BiVO₄–p-Si interface as a tandem-like junction. Charge separation in the BiVO₄ film is limited by light absorption and by slow electron transport to the Si interface, based on time-dependent SPS measurements. These problems need to be overcome in functional tandem devices for photoelectrochemical water oxidation