In order to realize better understanding of influential order sequences of surrounding atmospheres on break arc durations of electrical contacts in DC load conditions, a quantitative mathematical model, which aims to indicate dependences of break arc durations on several gas parameters such as molecular mass, viscosity, specific heat capacity, thermal conductivity, electro-negativity, and ionization potential, was analyzed. Break arc durations of AgCdO contact pairs were measured in several kinds of surrounding atmospheres (N2, Ar, He, air, O2 and CO2) under different DC voltage and current conditions, and data fitting processes were conducted. As a result, a candidate mathematical model was established, which could indicate possible influential order sequences of surrounding atmospheres on break arc durations in the range of the tested conditions.
Microwave mammography is a promising alternative to X-ray based imaging modalities, because of its small size, low cost, and cell-friendly exposure. More importantly, this modality enables the suppression of surface reflection clutter, which can be enhanced by introducing accurate surface shape estimations. However, near-field measurements can reduce the shape estimation accuracy, due to a mismatch between the reference and observed waveforms. To mitigate this problem, this study incorporates envelope-based shape estimation and finite-difference time-domain(FDTD)-based waveform correction with a fractional derivative adjustment. Numerical simulations based on realistic breast phantoms derived from magnetic resonance imaging (MRI) show that the proposed method significantly enhances the accuracy of breast surface imaging and the performance of surface clutter rejection.
The performance of a network router/switch has improved significantly over past decades with explosively increasing internet and data center traffic. The performance of a router heavily depends on the memory system, e.g. DRAM based packet buffers, which often limits the scalability of a router. However, a widening gap between memory I/O bus and memory cell array speed and decreasing row buffer locality from increasing channels and banks severely reduce the performance gain from state-of-the-art memory technology such as DDR4 or HBM2 DRAM. Priorworks improved memory bandwidth by maintaining SRAM-based per-queue or per-bank input/output buffers in the memory controller to support a DRAM-based packet buffer. The buffers temporarily store packets when bank conflicts occur but are unable to prevent interference-inducing traffic from thrashing DRAM's row buffers. In this study, we directly integrate SRAM into the DRAM-based packet buffer and map those packets degrading row buffer locality of DRAM into SRAM. This maximizes locality and parallelism of DRAM accesses. The proposed scheme can benefit any existing schemes. Experimental results show 22.41% improvement over the best existing scheme for a single channel in terms of the memory bandwidth utilization under harsh congested scenarios.
A one-dimensional lattice of tunnel-diode oscillators is investigated for potential high-speed frequency divider. In the evolution of the investigated lattice, the high-frequency oscillation dominates over the low-frequency oscillation. When a base oscillator is connected at the end, and generates oscillatory signals with a frequency higher than that of the synchronous lattice oscillation, the oscillator output begins to move in the lattice. This one-way property guarantees that the oscillation dynamics of the lattice have only slight influence on the oscillator motion. Moreover, counter-moving pulses in the lattice exhibit pair annihilation through head-on collisions. These lattice properties enable an efficient frequency division method. Herein, the operating principles of the frequency divider are described, along with a numerical validation.
Phase-sensitive amplification (PSA) has unique properties, such as the quantum-limited noise figure of 0 dB and the phase clamping effect. This study investigates PSA characteristics when a chirped pulse is incident. The signal gain, the output waveform, and the noise figure for an optical pulse having been chirped through chromatic dispersion or self-phase modulation before amplification are analyzed. The results indicate that the amplification properties for a chirped pulse are different from those of a non-chirped pulse, such that the signal gain is small, the waveform is distorted, and the noise figure is degraded
In this paper, an improved charge pump (CP) and a modified nonlinear phase frequency detector (PFD) are designed and fabricated in a 90-nm CMOS process. The CP is optimized with a combination of circuit techniques such as pedestal error cancel scheme to eliminate the charge injection and the other non-ideal characteristics. The nonlinear PFD is based on a modified circuit topology to enhance the acquisition capability of the PLL. The optimized CP and nonlinear PFD are integrated into a Ka-band PLL. The measured output current mismatch ratio of the improved CP is less than 1% when the output voltage Vout fluctuates between 0.2 to 1.1V from a 1.2V power supply. The measured phase error detection range of the modified nonlinear PFD is between -2π and 2π. Owing to the modified CP and PFD, the measured reference spur of the Ka-band PLL frequency synthesizer containing the optimized CP and PFD is only -56.409dBc at 30GHz at the locked state.