Nowadays flash memory is one of the most frequently used nonvolatile memories in electronic devices. However, since flash memory is based on Si transistors with floating gates which can store electronic charges, it has basic limitations in its speed and density. It takes longer than 1 lsec for electronic charges to be stored in a floating gate in one cell of flash memory. In addition, we'll reach density limitation in flash memory in the near future by conventional scaling methods, such as decrease in gate length or increase in dielectric constant of the gate oxide, which are commonly applied to Sibased 2-dimensional devices. Thus, in order to overcome the limitations of flash memory, we require a new nonvolatile memory which is not based on Si devices with electronic charge storing phenomena. Here we introduce a next generation nonvolatile memory consisting of two oxide resistors, NiO and VO 2 , where the former is a memory element storing data by utilizing so called bi-stable resistance switching and the latter is a switch element controlling access using the related threshold switching. Since the memory only utilizes resistance switching behaviors of the two oxide resistors, writing and reading times are around several 10s of ns. In addition, it overcomes density limitations by its compatibility with 3-dimensional stack structures due to its low processing temperature lower than 300°C. High performance tests show the feasibility of a universal memory which has advantages of both flash and static random access memories.Si-based flash memory has become the standard for nonvolatile memory which does not lose information in the absence of an external bias. Nonetheless it faces several barriers as cell size is reduced beyond the sub-micrometer region (currently having realized a 40 nm pattern for 32 gigabit NAND flash memory) [1] due to charge leakage across the tunnel oxide. In addition, it needs a little longer time (> 1 ls) to write information by storing charges in a floating gate of flash memory. The efforts of the semiconductor industries have been focused not only on developing scaling methods or modifying device structures for Si-based flash memories [1] but on finding a next generation memory using materials which can circumvent the fundamental limits of Si. The goal of a next generation memory is both to surpass flash memory for nonvolatile memory applications and to realize a universal memory which combines the advantages of nonvolatile slow memory such as flash memory and volatile fast memory such as static random access memory. In order to accomplish this, a class of materials and structures which have easy scalability and rapid programming speed in addition to nonvolatility and low power consumption must be developed. In general, nonvolatile memory consists of a memory element with bi-stable states under zero bias and a switch element with resistance controlled by external bias. The memory element stores the information and the switch element controls access to a specific memory element. Several gro...
The effects of various metal electrodes on the resistive switching of NiO thin films were investigated. Contrary to the belief that Pt is used for its high work function, which enables Ohmic contact to p-type NiO, resistive switching was observed in films with Ta or Al electrodes with a low work function in the as-deposited state. The resistive switching of films with a Ag or Cu top electrode with a low work function and high free energy of oxidation shows the importance of the formation of an oxide layer at the metal/NiO interface.
DWI MR enterography was noninferior to CE MR enterography for the evaluation of inflammation in Crohn disease in generally well-distended small bowel, except for the diagnosis of penetration.
Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies to components of the cell nucleus. These autoantibodies are predominantly produced with the help of follicular helper T (Tfh) cells and form immune complexes that trigger widespread inflammatory damage, including nephritis. In recent studies, mesenchymal stem cells (MSCs) elicited diverse, even opposing, effects in experimental and clinical SLE. Here we investigated the effect of human bone marrow-derived MSCs (hBM-MSCs) in a murine model of SLE, the F1 hybrid between New Zealand Black and New Zealand White strains (NZB/W). We found that infusion of female NZB/W mice with hBM-MSCs attenuated glomerulonephritis; it also decreased levels of autoantibodies and the incidence of proteinuria and improved survival. These effects coincided with a decrease in Tfh cells and downstream components. Infiltration of long-lived plasma cells into the inflamed kidney was also reduced in the hBM-MSC-treated mice. Importantly, hBM-MSCs directly suppressed the in vitro differentiation of naive CD4(+) T cells toward Tfh cells in a contact-dependent manner. These results suggest that MSCs attenuate lupus nephritis by suppressing the development of Tfh cells and the subsequent activation of humoral immune components. They thus reveal a novel mechanism by which MSCs regulate humoral autoimmune diseases such as SLE.
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