No abstract

No abstract

Direct numerical simulations of turbulent channel flow at Reτ = 205 and 932 have been carried out to examine Taylor’s “frozen turbulence” hypothesis. The terms in Taylor’s hypothesis appear in the transport equation for instantaneous momentum (Navier-Stokes) in this flow. The additional terms, i.e., the additional convective acceleration term and the pressure gradient and viscous force terms, act to diminish the validity of Taylor’s hypothesis when they are relatively large compared to the Taylor’s hypothesis terms and are not in balance. A similar analysis has been applied to the transport equation for instantaneous vorticity. The additional terms in this equation, namely, the additional convective rates of change of vorticity terms, the stretching/compression/rotation of vorticity terms, and the viscous diffusion of vorticity terms, similarly act to diminish the validity of Taylor’s hypothesis when they are relatively large compared to the terms in the hypothesis and are not in balance. Where in the channel flow this diminishment occurs, and to what degree, and which of the non-Taylor’s hypothesis terms in the momentum and vorticity equations contribute most to this diminishment are unraveled here.

The abnormality occurs at molecular, cellular as well as network levels in patients with Alzheimer’s disease (AD) prior to diagnosis. Most previous connectivity studies were conducted at 1 out of 3 (local, meso and global) scales in subjects covering only part of the entire AD spectrum (subjective cognitive decline, SCD; amnestic mild cognitive impairment, aMCI; and then fully manifest AD). Data interpretation within the framework of disease progression is therefore difficult. The current study included 3 age- and sex-matched cohorts: SCD ( n = 32), aMCI ( n = 37) and fully-established AD ( n = 30). A group of healthy elderly subjects ( n = 40) were included as a normal control (NC). Network connectivity was examined at the local (degree centrality), meso [subgraph centrality (SC)], and global (eigenvector and page-rank centralities) levels. As compared to NC, SCD subjects had isolated decrease of SC in primary (somatomotor and visual) networks. aMCI subjects had decreased centralities at all three scales in associative (frontoparietal control, dorsal attention, limbic and default) networks. AD subjects had increased centrality at the global scale in all seven networks. There was a positive association between Montreal Cognitive Assessment (MoCA) scores and DC in the frontoparietal control network in SCD, a negative relationship between Mini-Mental State Examination (MMSE) scores and EC in the somatomotor network in AD. These findings suggest that the primary network is impaired as early as in SCD. Impairment in the associative network also starts at the local level at this stage and may contribute to the cognitive decline. As associative network impairment extends from local to meso and global scales in aMCI, compensatory mechanisms in the primary network are activated.

The ongoing Chinese Color Nest Project (CCNP) was established to create normative charts for brain structure and function across the human lifespan, and link age-related changes in brain imaging measures to psychological assessments of behavior, cognition, and emotion using an accelerated longitudinal design. In the initial stage, CCNP aims to recruit 1520 healthy individuals (6–90 years), which comprises three phases: developing (devCCNP: 6–18 years, N = 480), maturing (matCCNP: 20–60 years, N = 560) and aging (ageCCNP: 60–84 years, N = 480). In this paper, we present an overview of the devCCNP, including study design, participants, data collection and preliminary findings. The devCCNP has acquired data with three repeated measurements from 2013 to 2017 in Southwest University, Chongqing, China (CCNP-SWU, N = 201). It has been accumulating baseline data since July 2018 and the second wave data since September 2020 in Chinese Academy of Sciences, Beijing, China (CCNP-CAS, N = 168). Each participant in devCCNP was followed up for 2.5 years at 1.25-year intervals. The devCCNP obtained longitudinal neuroimaging, biophysical, social, behavioral and cognitive data via MRI, parent- and self-reported questionnaires, behavioral assessments, and computer tasks. Additionally, data were collected on children’s learning, daily life and emotional states during the COVID-19 pandemic in 2020. We address data harmonization across the two sites and demonstrated its promise of characterizing the growth curves for the overall brain morphometry using multi-center longitudinal data. CCNP data will be shared via the National Science Data Bank and requests for further information on collaboration and data sharing are encouraged.

This paper presents the concept of a diesel methanol compound combustion (DMCC) system and some experimental results on the application of the system to two diesel engines. In the DMCC system, diesel fuel is used for engine starting and for low load operation. At medium to high load, a fixed amount of diesel fuel is maintained while extra energy is acquired by injecting methanol into the intake manifold to form a homogeneous methanol/air mixture. The system was tested on two 4-cylinder diesel engines:  one naturally aspirated and the other turbocharged. In both cases, the DMCC is found to reduce brake specific equivalent fuel consumption, reduce smoke emission, and reduce NOx emission but increase CO and HC emissions.

No abstract

No abstract