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In a memory hierarchy, there are various classes of memory systems depending on the access latency. A typical memory hierarchy consists of a CPU cache, DRAM, and an SSD or HDD. The DRAM has an access latency of 100ns, while flash memory has a latency of about 50μs [1]. Recently, new non-volatile memories with latencies of less than 10μs, including PRAM, MRAM, and ReRAM [2], are getting attention for business-critical systems such as big-data analysis and storage caches. To meet the low latency requirements, a new type of NAND flash, Z-NAND, with a read time (t R ) of 3μs has also been introduced [3]. Figure 20.2.1 shows a feature comparison between Z-NAND and conventional 3D NAND [4,5]. The Z-NAND achieves a read time of 3μs, which is 15–20 times faster than conventional NAND. Write throughput reaches up to 160MB/s with a 100μs program time. To further minimize read latency, I/O circuit support a DDR interface for both x8 and x16 mode. To take full advantage of such low-latency memory devices, reduction of memory access overhead is necessary. In this paper, we introduce an NVMe SSD controller which leverages the advantages of the low-latency NAND and enables the reduction of total memory access time, thereby minimizing overall system latency.

Although Compton camera may has a great potential as next generation imaging modality comparing to SPECT and PET, its fully three-dimensional image reconstruction requires the considerable computational burden and the spatial resolution is suffered from the various physical phenomena arising during detection process. In this study, we investigated the accelerated statistical image reconstruction in which system matrix included a resolution recovery (RR) technique. We considered 3D Gaussian resolution model for the integrated angular and geometric uncertainties. The angular uncertainty is closely related to the limited energy resolution of the Compton camera and Doppler broadening and the geometric uncertainty is due to the segmented detectors. For RR, the 3D Gaussian resolution model is incorporated into listmode OSEM (LMOSEM) using image-space convolution operation. We investigated two different RR approaches: one (denoted by LMOSEM-RRF) is when the convolution is only performed in forward projection step, and the other (denoted by LMOSEM-RRFB) is when it is performed in both forward and backward projection steps. The simulation results showed that both RR approaches gave an improvement on spatial resolution for the resolution-degraded data due to both angular and geometric uncertainties. Although LMOSEM-RRF provided better resolution than LMOSEM-RRFB, LMOSEM-RRFB could still useful for low counting statistics in measurement.

This paper presents a novel approach to rectify a low mechanical frequency to a higher resonant frequency mode, i.e. frequency up conversion. The device consists of a sharp probe, micro superelastic NiTi ridges, a micro slider, and a piezoelectric bimorph cantilever. A probe tip attached on the edge of a piezoelectric cantilever travels along the ridges attached onto a micro slider mechanism. Experimental results show that power output per unit area is substantially larger than conventional resonance approaches.