55 research outputs found
A Genealogical History of STS and Its Multiple Constructions: To Weave an Extensive Network for Gazing upon the Modern Sciences
No full textLinear instability of a supersonic boundary layer over a rotating cone
No full textIn this paper, we conduct a systematic study of the instability of a boundary layer over a rotating cone that is inserting into a supersonic stream with zero angle of attack. The base flow is obtained by solving the compressible boundary-layer equations using a marching scheme, whose accuracy is confirmed by comparing with the full Navier-Stokes solution. Setting the oncoming Mach number and the semi-apex angle to be 3 and 7 degrees, respectively, the instability characteristics for different rotating rates ((Omega) over bar, defined as the ratio of the rotating speed of the cone to the axial velocity) and Reynolds numbers (R) are revealed. For a rather weak rotation, (Omega) over bar << 1, only the modified Mack mode (MMM) exists, which is an extension of the supersonic Mack mode in a quasi-two-dimensional boundary layer to a rotation configuration. Further increase of (Omega) over bar leads to the appearance of a cross-flow mode (CFM), coexisting with the MMM but in the quasi-zero frequency band. The unstable zones of the MMM and CFM merge together, and so they are referred to as the type-I instability. When (Omega) over bar is increased to an O(1) level, an additional unstable zone emerges, which is referred to as the type-II instability to be distinguished from the aforementioned type-I instability. The type-II instability appears as a centrifugal mode (CM) when R is less than a certain value, but appears as a new CFM for higher Reynolds numbers. The unstable zone of the type-II CM enlarges as (Omega) over bar increases. The vortex structures of these types of instability modes are compared, and their large-R behaviours are also discussed
Effect of cone rotation on the nonlinear evolution of Mack modes in supersonic boundary layers
No full textIn this paper, we present a systematic study of the nonlinear evolution of the travelling Mack modes in a Mach 3 supersonic boundary layer over a rotating cone with a 7 degrees half-apex angle using the nonlinear parabolic stability equation (NPSE). To quantify the effect of cone rotation, six cases with different rotation rates are considered, and from the same streamwise position, a pair of oblique Mack modes with the same frequency but opposite circumferential wavenumbers are introduced as the initial perturbations for NPSE calculations. As the angular rotation rate Omega increases such that Omega($) over bar (defined as the ratio of the rotation speed of the cone to the streamwise velocity at the boundary-layer edge) varies from 0 to O(1), three distinguished nonlinear regimes appear, namely the oblique-mode breakdown, the generalised fundamental resonance and the centrifugal-instability-induced transition. For each regime, the mechanisms for the amplifications of the streak mode and the harmonic travelling waves are explained in detail, and the dominant role of the streak mode in triggering the breakdown of the laminar flow is particularly highlighted. Additionally, from the linear stability theory, the dominant travelling mode undergoes the greatest amplification for a moderate Omega, which, according to the e(N) transition-prediction method, indicates premature transition to turbulence. However, this is in contrast to the NPSE results, in which a delay of the transition onset is observed for a moderate Omega. Such a disagreement is attributed to the different nonlinear regimes appearing for different rotation rates. Therefore, the traditional transition-prediction method based on the linear instability should be carefully employed if multiple nonlinear regimes may appear
Secondary instability of stationary Görtler vortices originating from first/second Mack mode
No full textPrinciple of fundamental resonance in hypersonic boundary layers: an asymptotic viewpoint
No full textThe fundamental resonance (FR) in the nonlinear phase of the boundary-layer transition to turbulence appears when a dominant planar instability mode reaches a finite amplitude and the low-amplitude oblique travelling modes with the same frequency as the dominant mode, together with the stationary streak modes, undergo the strongest amplification among all the Fourier components. This regime may be the most efficient means to trigger the natural transition in hypersonic boundary layers. In this paper, we aim to reveal the intrinsic mechanism of the FR in the weakly nonlinear framework based on the large-Reynolds-number asymptotic technique. It is found that the FR is, in principle, a triad resonance among a dominant planar fundamental mode, a streak mode and an oblique mode. In the major part of the boundary layer, the nonlinear interaction of the fundamental mode and the streak mode seeds the growth of the oblique mode, whereas the interaction of the oblique mode and the fundamental mode drives the roll components (transverse and lateral velocity) of the streak mode, which leads to a stronger amplification of the streamwise component of the streak mode due to the lift-up mechanism. This asymptotic analysis clearly shows that the dimensionless growth rates of the streak and oblique modes are the same order of magnitude as the dimensionless amplitude of the fundamental mode ((is an element of) over bar (10)), and the amplitude of the streak mode is O((is an element of) over bar (-1)(10)) greater than that of the oblique mode. The main-layer solution of the streamwise velocity, spanwise velocity and temperature of both the streak and the oblique modes become singular as the wall is approached, and so a viscous wall layer appears underneath. The wall layer produces an outflux velocity to the main-layer solution, inclusion of which leads to an improved asymptotic theory whose accuracy is confirmed by comparing with the calculations of the nonlinear parabolised stability equations (NPSEs) at moderate Reynolds numbers and the secondary instability analysis (SIA) at sufficiently high Reynolds numbers
Receptivity of Mack modes to localized unsteady blowing and suction in a chemical non-equilibrium hypersonic boundary layer
No full textThis paper studies the local receptivity of the Mack-mode instability to localized unsteady blowing and suction (UBS) in a chemical non-equilibrium (CNE) hypersonic boundary layer. The five-species CNE model is employed, and the receptivity efficiency is formulated by use of the residual theorem. Compared with the results for the calorically perfect gas (CPG) model, we find that the real-gas effect enhances the receptivity efficiency remarkably in the majority of the second-mode frequency band, and the enhancement is mainly attributed to the modification of the base flow due to the CNE effect, which is akin to the cold-wall effect in hypersonic boundary layers. Combined with the destabilizing role of the CNE effect on the Mack second mode, it is concluded that the CNE effect would lead to a greater linearly accumulated perturbation amplitude, implying premature of transition to turbulence in a high-enthalpy hypersonic boundary layer subject to localized perturbations
Revisit of the oblique-breakdown regime in supersonic boundary layers and mechanism of the extra amplification of streak modes
No full textIn the low-Mach-number supersonic boundary layers, the oblique-breakdown regime may be the most efficient route to trigger the laminar-turbulent transition, because the most unstable Mack first mode always appears as an oblique wave. In this paper, we revisit this issue by use of the nonlinear parabolized stability equation (NPSE) approach and particularly focus on the extra amplification of the streak mode generated by the direct interaction of the introduced oblique modes. This mechanism is then well explained based on the weakly nonlinear analysis, and its predictions on the evolution of the streak mode and the two-dimensional traveling-wave mode are quantitatively confirmed by the NPSE calculations. Additionally, the important role of the streak mode, leading to the secondary instability, on triggering the transition onset is identified. Published under an exclusive license by AIP Publishing
Correlation analysis of bile acid spectrum and thyroid function in patients with autoimmune liver disease
No full text"Objective To explore the correlation between bile acid metabolic components and thyroid function indicators in patients with autoimmune liver disease（AILD）. Methods A total of 219 AILD patients admitted to the Second Hospital of Nanjing from January 2020 to March 2024 were included，including 98 patients with autoimmune hepatitis（AIH）and 121 patients with primary biliary cholangitis（PBC）. In addition，according to the principle of gender and age matching，90 healthy individuals who underwent physical examinations during the same period were selected as the control group. The differences in levels of serum biochemical data，thyroid hormone，and bile acid components among three groups were compared，and the correlation between the indexes was analyzed. Results Among the 15 detected bile acid metabolites，except for cholic acid（CA），chenodeoxycholic acid（CDCA），and deoxycholic acid（DCA），the concentrations of the other 12 bile acid components in AIH group and PBC group were significantly
increased（P<0.05），and the concentrations of ursodeoxycholic acid（UDCA），glycocholic acid（GCA），glycoursodeoxycholic
acid（GUDCA），taurocholic acid（TCA），and tauroursodeoxycholic acid（TUDCA）in PBC group were significantly higher than those in AIH group（P0.05）. Spearman correlation analysis showed that in PBC group，FT4 was negatively correlated with CA（r=- 0.810，P=0.008），and TPOAb was positively correlated with CDCA （r=0.373，P=0.003） and UDCA（r=0.412，P=0.001）. In AIH group，T3 was negatively correlated with taurodeoxycholic acid（TDCA）（r=-0.234，P=0.043），T4 was negatively correlated with taurochenodeoxycholic acid（TCDCA）（r=-0.251，P = 0.029）and CDCA（r=-0.232，P = 0.043），FT3 was negatively correlated with glycochenodeoxycholic acid（GCDCA）（r=- 0.247，P = 0.026）and TCDCA（r=- 0.229，P=0.040），while positively correlated with taurolithocholic acid（TLCA）（r=0.232，P=0.037），TPOAb was positively correlated with DCA（r=0.311，P=0.028）. Conclusion AILD can cause serum bile acid metabolism disorders and thyroid function abnormalities in patients，and thyroid function indicators are associated with the concentrations of some bile acids.
Changes of the Macrobenthos Community with Non-native Mangrove Rehabilitation (Kandelia obovata) and Salt Marsh Invasion (Spartina alterniflora) in Ximen Island, Zhejiang, China
No full textMacrobenthos organisms are vital ecological components of intertidal wetlands. This work studied effects of non-native mangrove rehabilitation (Kandelia obovata) and salt marsh invasion (Spartina alterniflora) on macrobenthos communities in Ximen Island (Zhejiang, China). The macrobenthos communities were compared between rehabilitated K. obovata forests of five different stand ages (2-, 8-, 11-, 16-, and 60-year-old) and adjacent S. alterniflora marsh and non-vegetated mudflat. Compared to the mudflat, S. alterniflora increased the abundance, Shannon–Wiener diversity index (H’), and Margalef's richness index (d’) of macrobenthos. Gastropoda abundance was high in the S. alterniflora marsh, whereas, malacostraca biomass was low. Within mangrove forests, macrobenthos abundance was positively correlated with the stand age of mangroves (Spearman Correlation, P < 0.05), but the corresponding H’, d’ and Pielou's evenness index (J’) showed negative correlations. Gastropoda dominated over macrobenthos in the younger stands (2–11 years in age), whereas, phascolosomatidea and bivalvia were more abundant in the older stands (16 and 60 years in age). Noticeably, the highest biomass for malacostraca was recorded from the 11-year-old stand. Macrobenthos communities differed among habitats, with the divergence in community structure between the S. alterniflora marsh and mangrove stands increasing with mangrove stand age, to be significantly different for stands planted over 16 years ago. Since the 16-year-old stand exhibited similar macrobenthos features to the 60-year-old stand, we speculated that, in the case of macrobenthos, a rehabilitated K. obovata forest can reach its maturity level at a time period of about 15 years in Ximen Island.We are grateful to Runjie Jin, Hengwei Wang, Dan Li, Hein Zar Htwe and Nuttiga Hempattarasuwan for assistance with field work. We also thank for doctor Yibo Liao and researcher Hangjun Wang for species identification of macrobenthos
Landscape and research trends of sarcopenic obesity research: A bibliometric analysis
No full textBackground: Sarcopenic obesity (SO) is a condition characterized by the coexistence of sarcopenia (loss of muscle mass and function) and obesity. This condition has emerged as a public health concern, particularly with the aging population. Despite an approximately 30-year history of SO research, detailed quantitative analysis of existing research was never undertaken. We aimed to depict the landscape of SO research using bibliometric analysis of literature. Methods: We searched the Web of Science Core Collection on January 15, 2023. The following bibliometric indicators were included: publication trend, the most influential country, the most active discipline, productive institutions, productive journals, prolific and highly cited authors, and highly cited publications. We constructed co-authorship network to explore individual-level, institutional-level, and international-level collaborative patterns in the VOSviewer or Sci2 software. Furthermore, keywords co-occurrence network was extracted by the VOSviewer software, and the burst-detection analysis of keywords was performed using the CiteSpace software. Results: A total of 2023 original articles were retrieved for data analysis. The publications increased dramatically in the last decade. The United States had the highest number of publications on SO (n = 904). The Seoul National University Hospital was the most prolific institution (n = 54) among the 2675 institutions analyzed. As for journals, Clinical Nutrition had the highest number of publications on SO (n = 75). Kim JH was the most prolific author (n = 25), while Cederholm T authored the most cited publication (9381 citations). More than 80 disciplines were involved in SO research, of which, “Geriatrics and Gerontology” was the most activated discipline. The European Working Group on Sarcopenia in Older People (EWGSOP) consensus was the most cited publication (7209 citations). Moreover, the hotspots of SO have been shifting from its biology, prevalence, and risk factors to its outcomes, prognostic factors, complications, and quality of life. Its relationships also evolved from being between SO and aging to being between SO and other diseases. Conclusions: Our study provided a comprehensive landscape of SO research, which may help researchers better identify key information and research trends in this field
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