4,465 research outputs found
A low cost adaptive digital predistorter for linearization of power amplifiers in MIMO transmitters
No full textAn adaptive digital predistortion (PD) technique is proposed for linearization of power amplifiers (PAs) in multiple-input multiple-output (MIMO) transmitters. We consider a PD structure equipped with only one combined feedback path while conventional systems have multiple feedback paths. Hence, the proposed structure is much simpler than that of multiple feedback paths. Based on the structure, a new PD algorithm is derived. The simulation results show that linearization performance of the proposed method is almost the same as the conventional multiple feedback technique while the former is much simpler to implement than the latter
Use of Training Subcarriers for Synchronization in Low Latency Uplink Communication with GFDM
No full textDigital predistortion for power amplifiers in hybrid MIMO systems with antenna subarrays
No full textImprovement in thermal stability of MOCVD and characterization of low- temperature stress hump of nickel silicide
No full text학위논문(박사) - 한국과학기술원 : 신소재공학과, 2005.2, [ iv, 114 p. ]TiN 및 a-Si interlayer에 의한 reactive MOCVD 의 열안정성 향상과 Ni/Si 고상반응에서 나타나는 저온 응력증가(low-temperature stress hump) 현상에 대하여 연구하였다.
형성을 위하여 MOCVD precursor는 Cyclopentadienyl dicarbonyl cobalt, 를 사용하였으며, 기판은 gate용 poly-Si blanket wafer를 이용하였다. Sputtered TiN 박막을 poly-Si과 MOCVD 의 중간층으로 이용할 경우 열안정성을 1000℃ 까지 향상시킬 수 있었다. Interlayer가 없는 경우 900℃에서부터 grain boundry grooving에 의한 agglomeration이 발생되어 면저항이 증가하는 것에 비하여 크게 개선되는데, 이는 TiN 박막이 N2 stuffing에 상관없이 Co와 Si의 상호확산을 고온까지 효과적으로 방지하기 때문이다. TiN interlayer를 사용한 MOCVD 의 열화과정을 1000℃ 60분간의 가혹한 열처리후 분석한 결과 columnar 구조를 가지는 TiN 박막의 diffusion pipe와 같은 빈 공간을 통하여 Co와 Si이 확산되어 TiN 박막 밑에서도 가 생성되고 TiN 박막 내부에도 일부 가 형성되며, 원래의 층도 grooving이 상당히 진행된 형태로 나타났다. 그러나 여전히 연속적인 막을 형성하고 있었고 interlayer가 없는 시편 대비 월등히 낮은 면저항을 유지하였다. A-Si을 interlayer로 이용할 경우 TiN interlayer 보다는 효과가 떨어지나 의 열안정성이 역시 크게 개선되었다. 이는 poly-Si과 a-Si간 계면에 존재하는 불연속 자연산화막이 TiN과 같은 확산방지막 역할을 했기 때문으로 밝혀졌다.
Ni/Si의 in-situ stress-temperature 측정 시 100℃ ~ 140℃의 온도구간에서 나타나는 니켈 실리사이드 특유의 저온 인장응력 증가(stress hump) 현상 규명을 위한 실험결과, 이는 실리사이드 반응과는 무관하며 as-dep 상태부터 Ni과 Si의 계면에 존재하는 비정질 Ni-Si 층을 통한 Ni 원자의 Si 기판으로의 확산에 의한 것임을 밝혔으며, 이를 모델로서 제시하였다. Ni 박막과 Si 기판의 고상반응에 의한 Ni silicidation 시 나타나는 상 생성 순서는 온도에 따라 140℃ 부근에서 가 첫 번째 상으로 생성되며, 이후 약 210℃에서 로부터 NiSi 로의 상전이가 일어나기 시작하여 240℃에서 완료된다. 여러 연구자들에 의해 보고된 바와 같은 피라미드 형태의 epitaxial 는 500℃까지의 온도구간에서는 발견되지 않았으며, 이는 본 실험에서 사용한 undoped (001)Si 기판과 더불어 계면에 어떠한 산화막과 같은 확산방지막이 없었기 때문으로 판단된다. Ni/Si 고상반응에 의한 Ni silicide 형성 시 안정하고 균일한 NiSi 막을 얻기 위해서 RTP 온도는 400℃ 이상이어야 하며 500℃, 30초 조건에서 capping layer에 상관없는 가장 안정한 NiSi를 얻을 수 있었다. TiN capping을 한 경우 열안정성이 가장 우수하였으며, 600℃ ~800℃까지 면저항이 증가하지 않는 특성을 확보할 수 있었다.한국과학기술원 : 신소재공학과
A 915 MHz, 499 μW, –99 dBm, and 100 kbps BFSK Direct Conversion Receiver
No full textThis paper presents an ultra-low power (ULP) high sensitivity binary frequency-shift keying (BFSK) direct conversion receiver (RX) for the internet of things (IoT). By employing a combination of a 2-stage ring voltage-controlled oscillator (VCO) and a 50 %-to-25 % duty conversion passive mixer, the power consumption is dramatically reduced. The prototype of the proposed RX which is implemented in a 55 nm CMOS technology shows −99 dBm sensitivity for 915 MHz 100 kbps BFSK signal while dissipating 499 µW from 0.9 V supply
Metabolic Engineering of Pichia pastoris for Hyaluronic Acid Production with High Molecular Weight
No full textCombined multiple transcriptional repression mechanisms generate ultrasensitivity and oscillations
No full text© 2022 The Author(s) Published by the Royal Society. All rights reserved.Transcriptional repression can occur via various mechanisms, such as blocking, sequestration and displacement. For instance, the repressors can hold the activators to prevent binding with DNA or can bind to the DNA-bound activators to block their transcriptional activity. Although the transcription can be completely suppressed with a single mechanism, multiple repression mechanisms are used together to inhibit transcriptional activators in many systems, such as circadian clocks and NF-κB oscillators. This raises the question of what advantages arise if seemingly redundant repression mechanisms are combined. Here, by deriving equations describing the multiple repression mechanisms, we find that their combination can synergistically generate a sharply ultrasensitive transcription response and thus strong oscillations. This rationalizes why the multiple repression mechanisms are used together in various biological oscillators. The critical role of such combined transcriptional repression for strong oscillations is further supported by our analysis of formerly identified mutations disrupting the transcriptional repression of the mammalian circadian clock. The hitherto unrecognized source of the ultrasensitivity, the combined transcriptional repressions, can lead to robust synthetic oscillators with a previously unachievable simple design.11Nsciescopu
Distinct trajectory of post-fire GPP across forest types in Siberia
No full textWildfire is one of the dominant disturbances in the Siberian boreal forest, affecting the capacity of forests to uptake carbon. Impacts of wildfires on forest carbon uptake are substantially varied by tree compositions, however, the loss of carbon uptake capability across different forest types remains uncertain. Here, we tracked post-fire changes in gross primary production (GPP) across five forest types in Siberia, namely, evergreen needleleaf forests (ENF), deciduous needleleaf forests (DNF), deciduous broadleaf forests (DBF), mixed forests (MF), and woody savannas (WSVN), using satellite-based observation data from 2001 to 2023. Results revealed substantial reductions in GPP after wildfire followed by gradual recovery except DBF. The GPP changes one year after wildfire (Delta GPP1yr) and recovery rates of GPP notably differed by forest types. In ENF, Delta GPP1yr reached -63.4 g C m-2yr-1, which is larger than that in MF, DNF, and WSVN by -20.6, -31.3, and -42.7 g C m-2 yr-1, respectively. Consistently, the GPP recovery rate is the lowest in ENF, at 63.7%. Furthermore, significant decreasing trends in 5-year mean of Delta GPP1 yr in DNF, MF, and WSVN exceed -1.0 g C m-2yr-1 yr-1, indicating intensified impacts of increased wildfire intensity and/or extent on forest carbon. Our findings highlight the urgent need for establishing fire management and forest recovery strategies adapted to different forest types to enhance ecosystem resilience.
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