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This numerical study focuses on the coherent structures and bypass transition mechanism of the Stokes boundary layer in the intermittently turbulent regime. In particular, the initial disturbance is produced by a temporary roughness element that is removed immediately after triggering a two-dimensional vortex tube under an inflection-point instability. The present study reveals a complete scenario of self-induced motion of a vortex tube after rollup from the boundary layer. The trajectory of the vortex tube is reasonably described based on the Helmholtz point-vortex equation. The three-dimensional transition of the vortex tube is attributed to the Crow instability, which leads to a sinusoidal disturbance that eventually evolves into a ring-like structure, especially for the weaker vortex. Further investigation demonstrates that three-dimensional or quasi-three-dimensional vortex perturbations in the free stream play a critical role in the boundary layer transition through a bypass mechanism, which is featured by the non-modal and explosive transient growth of the subsequent boundary layer instabilities. This transition scenario is found to be analogous to the oblique transition in the steady boundary layer, both of which are characterised by the formation of streaks, rollup of hairpin-like vortices and burst into turbulent spots. In addition, the streamwise propagation of turbulent spots is discussed in detail. To shed more light on the nature of the intermittently turbulent Stokes boundary layer, a conceptual model is proposed for the periodically self-sustaining mechanism of the turbulent spots based on the present numerical results and experimental evidence reported in the literature.
We develop a stakeholder framework that examines how firms respond to the conflicting demands that arise from governments and investors in the context of corporate philanthropic giving. We argue that firms that experience such conflict exhibit a decoupling response in philanthropic giving. Furthermore, we identify the boundary conditions of the relationship between the conflicting pressures and the decoupling response. Drawing on stakeholder salience literature, we argue that this relationship will be weakened when CEOs perceive government demands as more salient (such as those with a communist ideology) and when CEOs are less sensitive to investor claims (such as those with fewer career concerns). We find empirical support for our arguments using a sample of 8,857 Chinese listed firms from 2006 to 2015. Our study contributes to the literature on stakeholder theory, decoupling, and corporate philanthropy.
Oscillatory flow around a cluster of four circular cylinders in a diamond arrangement is investigated using two-dimensional direct numerical simulation over Keulegan–Carpenter numbers (KC) ranging from 4 to 12 and Reynolds numbers (Re) from 40 to 230 at four gap-to-diameter ratios (G) of 0.5, 1, 2 and 4. Three types of flows, namely synchronous, quasi-periodic and desynchronized flows (along with 14 flow regimes) are mapped out in the (G, KC, Re)-parameter space. The observed flow characteristics around four cylinders in a diamond arrangement show a few unique features that are absent in the flow around four cylinders in a square arrangement reported by Tong et al. (J. Fluid Mech., vol. 769, 2015, pp. 298–336). These include (i) the dominance of flow around the cluster-scale structure at
and 1, (ii) a substantial reduction of regime D flows in the regime maps, (iii) new quasi-periodic (phase trapping)
and 1) and period-doubling
) and most noteworthily (iv) abnormal behaviours at (
) (referred to as holes hereafter) such as the appearance of spatio-temporal synchronized flows in an area surrounded by a single type of synchronized flow in the regime map (
). The mode competition between the cluster-scale and cylinder-scale flows is identified as the key flow mechanism responsible for those unique flow features, with the support of evidence derived from quantitative analysis. Phase dynamics is introduced for the first time in bluff-body flows, to the best knowledge of the authors, to quantitatively interpret the flow response (e.g. quasi-periodic flow features) around the cluster. It is instrumental in revealing the nature of regime
flows where the cluster-scale flow features are largely synchronized with the forcing of incoming oscillatory flow (phase trapping) but are modulated by localized flow features.
Propofol is a intravenous anaesthetic most commonly used in ultrasound oocyte retrieval. We studied if the use of propofol had an effect on mouse oocyte maturation, pregnancy, childbirth and progeny and investigated the correlation between propofol side effects and reproductive performance in mice. There was no statistical difference in mating, pregnancy, childbirth, litter size, the number of stillbirths and survival between each group (P>0.05). Propofol also had no effect on polar body extrusion in oocyte maturation as well as on pronucleus formation and, subsequently, early embryo development (P>0.05). An increased concentration of propofol had no effect on this result, although propofol at more than 0.01 mg/ml reduced polar body extrusion. Different concentrations of propofol had no effect on oocyte culture in vitro, pronucleus formation and early embryo development.
In the theory of spontaneous combustion, identifying the critical value of the Frank-Kamenetskii parameter corresponds to solving a bifurcation point problem. There are two different numerical methods used to solve this problem—the direct and indirect numerical methods. The latter finds the bifurcation point by solving a partial differential equation (PDE) problem. This is a better method to find the bifurcation point for complex geometries. This paper improves the indirect numerical method by combining the grid-domain extension method with the matrix equation computation method. We calculate the critical parameters of the Frank-Kamenetskii equation for some complex geometries using the indirect numerical method. Our results show that both the curve of the outer boundary and the height of the geometries have an effect on the values of the critical Frank-Kamenetskii parameter, however, they have little effect on the critical dimensionless temperature.
The hyperbolic quadratic eigenvalue problem (HQEP) was shown to admit Courant–Fischer type min–max principles in 1955 by Duffin and Cauchy type interlacing inequalities in 2010 by Veselić. It can be regarded as the closest analog (among all kinds of quadratic eigenvalue problem) to the standard Hermitian eigenvalue problem (among all kinds of standard eigenvalue problem). In this paper, we conduct a systematic study on the HQEP both theoretically and numerically. On the theoretical front, we generalize Wielandt–Lidskii type min–max principles and, as a special case, Fan type trace min/max principles and establish Weyl type and Wielandt–Lidskii–Mirsky type perturbation results when an HQEP is perturbed to another HQEP. On the numerical front, we justify the natural generalization of the Rayleigh–Ritz procedure with existing principles and our new optimization principles, and, as consequences of these principles, we extend various current optimization approaches—steepest descent/ascent and nonlinear conjugate gradient type methods for the Hermitian eigenvalue problem—to calculate a few extreme eigenvalues (of both positive and negative type). A detailed convergence analysis is given for the steepest descent/ascent methods. The analysis reveals the intrinsic quantities that control convergence rates and consequently yields ways of constructing effective preconditioners. Numerical examples are presented to demonstrate the proposed theory and algorithms.
The Mn-steel matrix composite locally reinforced with in situ TiC–TiB2 ceramic particulate was successfully fabricated using a thermal explosion-casting route in a Cu–Ti–B4C system with various B4C particle sizes. With the increase of B4C particle size, the ignition temperature increased, the combustion temperature decreased, and the size of the TiC and TiB2 ceramic particulates became smaller. The hardness, friction coefficient, and wear resistance of the composite were higher than those of the Mn-steel matrix. With the increase of B4C particle size, the size of the TiC and TiB2 ceramic particulates fabricated in the local reinforcing region decreased, the interface bonding between reinforcing region and matrix became poor, and the number of pores in the local reinforcing region increased. Moreover, the composite with ∼3.5 μm B4C showed the best antiwear property. At a low load of 20 N, the dominant wear mechanisms of the Mn-steel matrix composite were microcutting and abrasive wear. While, at a high load of 80 N, the dominant wear mechanisms were microcutting and adhesion wear associated with the formation of delamination layer.
The association of 24 h urinary Na and potassium excretion with the risk of the metabolic syndrome (MetS) has not been studied in China. The aim of the present study was to examine this association by analysing the data from 1906 study participants living in north China. To this end, 24 h urine samples were collected. Of the 1906 participants, 471 (24·7 %) had the MetS. The mean urinary Na and K excretion was 228·7 and 40·8 mmol/d, respectively. After multivariate adjustment, the odds of the MetS significantly increased across the increasing tertiles of urinary Na excretion (1·00, 1·40 and 1·54, respectively). For the components of the MetS, the odds of central obesity, elevated blood pressure and elevated TAG, but not the odds of low HDL-cholesterol and elevated fasting glucose, significantly increased with the successive tertiles of urinary Na excretion. Furthermore, for every 100 mmol/d increase in urinary Na excretion, the odds of the MetS, central obesity, elevated blood pressure and elevated TAG was significantly increased by 29, 63, 22 and 21 %, respectively. However, urinary K excretion was not significantly associated with the risk of the MetS. These findings suggest that high Na intake might be an important risk factor for the MetS in Chinese adults.
X-ray emission from Kr13+ ions in the energy range 1.2–3.6 MeV in steps of 0.6 MeV impacting on an Au target was investigated on electron cyclotron resonance ion source at the Heavy Ion Research Facility in Lanzhou. It was found that a shift of the X-ray lines to the higher energy side occurred. We measured the relationship between the characteristic of X-ray yield of Au M X-rays and Kr L X-rays as a function of incident energy. Furthermore, M-shell X-ray production cross-section of Au induced by Kr13+ was measured. The measured cross-section of target is compared to the classical binary-encounter approximation and plane-wave-born approximation theoretical model, which is a significant different between experimental and theoretical model.
LA-ICP-MS U–Pb dating of Lower Devonian detrital zircon samples from three representative sections in the South China block yields dominant Grenvillian and Pan-African populations, similar to the age distribution of early Palaeozoic samples from Gondwana, the Tethyan Himalaya and West Australia, in particular. Hf isotopic compositions indicate the contributions of juvenile crust at 1.6 Ga and 2.5 Ga, and bear a resemblance to their counterparts from SE Australia and West Antarctica, revealing the mixed origin of the Pan-African and Grenvillian grains from juvenile magmas and melting of pre-existing crustal rocks. These results suggest that the South China block should be considered an integral part of East Gondwana in early Palaeozoic time, rather than a discrete continental block in the Palaeo-Pacific or a fragment of Laurentia.
The aim of the present study was to investigate the effects of Bifidobacterium adolescentis (Bif) supplementation on visceral fat accumulation and insulin sensitivity of the metabolic syndrome in HF-diet-fed rats. Adult male Wistar rats (n 10 per group) were fed four different experimental diets for 12 weeks as follows: standard diet; high-fat (HF) diet; a mix of HF diet and Bif; a mix of standard diet and Bif. Liver, mesenteric fat, epididymal fat, retroperitoneal fat, and inguinal fat, pancreas and triceps surae in all four groups of the rats were weighed, while liver steatosis and insulin sensitivity were evaluated at the end point of the study. As the number of intestinal Bifidobacterium species decreased obviously, fat pad weight and body weight increased significantly in the HF group compared with in the other three groups (P <0·05). Addition of Bif led to a reduction in body weight and fat pad weight (P <0·05). With an increase in liver weight, more severe steatosis of hepatocytes was observed in the HF group compared with in the other three groups. A significant decrease of the glucose infusion rate and pancreas weight was found in the HF group (P <0·05). This deleterious effect was alleviated when Bif was added to the diets. Bifidobacterium supplementation ameliorated visceral fat accumulation and insulin sensitivity of the metabolic syndrome in HF-diet-fed rats.
Transgenes integrated into mammalian cells are silenced rapidly. This phenomenon correlates with repressed chromatin structure marked by histone hypoacetylation. This study investigated the effect of trichostatin A (TSA; a histone-deacetylase inhibitor) on EGFP expression in transfected cells and embryonic development after somatic cell nuclear transfer (SCNT). Porcine adult fibroblasts were transfected with a pEGFP-C1 vector. Then transfected cells, donor cells for SCNT, were pretreated with TSA, with the untreated cells being used as the control. Expression of EGFP in donor cells and reconstructed embryos was detected when exposed to blue light. Results showed that the percentage of EGFP-positive cells significantly increased when the transfected cells were treated with TSA and the increased expression of EGFP was sustained to at least the morula stage. In addition, the cytotoxic effect of TSA on the transfected cells was dose dependent. In conclusion, TSA can rescue the silenced EGFP gene. Even after transferring the TSA-treated cells to enucleated recipient oocytes, TSA retained the ability to rescue a silenced EGFP gene. In addition, TSA had an impact on cell proliferation.
We report the terahertz (THz) emission from the wurzite indium nitride (InN) films grown by molecular beam epitaxy (MBE). More than two orders of magnitude of THz power enhancement has been achieved from the InN film grown along the a-axis and magnesium (Mg) doped InN with a critical carrier concentration. The primary radiation mechanism of the a-plane InN film is found to be due to the acceleration of photoexcited carriers under the polarization-induced in-plane electric field perpendicular to the a-axis. Apparent azimuthal angle dependences of THz wave amplitude and the second harmonic generation are observed from a-plane InN. In the Mg-doped films, Mg as the acceptors compensate the native donors in the InN films and large band bending over a wider space-charge region causes the enhancement of THz emission power compared to the undoped InN.
Ultrathin (∼10 nm) InN ion selective field effect transistors (ISFETs) show a current variation ratio of 3.5 % per pH decade with a response time of less than 10 s. When the ISFET is employed as an electrolyte FET, the current variation of 18 % was measured as the gate bias changes from zero to 0.3 V given a drain-source voltage of 0.1 V. The high current (resistance) variation ratio is attributed to the ultrathin epilayer and an unusual phenomenon of intrinsic strong electron accumulation on InN surface, which enables a chemical/biological sensor with high sensitivity and resolution and permits detection of a slight concentration variation of the electrolyte. The pH response measurement of 10-nm-thick InN ISFETs investigated was performed in an aqueous solution titrated with diluted NaOH and HCl. The Helmholtz potential built at the electrolyte-InN interface is governed by direct adsorption of H+ ions at the surface metal oxides, modulating the channel current of the InN ISFETs. The channel current monotonically decreases as the pH value of an aqueous solution increases from 2 to 10. The sensitivity and resolution were found to be 58.3 mV per decade and 0.02 pH change, respectively. Besides, the detection of DNA hybridization was further performed after the InN surface was modified with MPTMS and probe DNA. A complementary target DNA solution of 100 nM led to a current decrease of approximate 6 uA, corresponding to the current variation of 0.74 %. The hybridization between negatively charged complementary DNA and the immobilized probe DNA caused the depletion of carriers at the InN surface, suppressing the channel current. The functionalized InN ISFETs are suitable for genetic analysis in clinical diagnostics without any labeling reagent. Such an InN-based sensor is appealing in the regime of chemical and biological sensing applications.
The elements for the Semliki forest virus (SFV) RNA replicon were obtained from the Alphavirus genome. It was designed to overcome the poor efficacy of some current plasmid vectors. Genes coding for viral replicases are preserved while genes coding for structural proteins are replaced by foreign genes in the RNA replicon. High levels of RNA replication and expression of foreign genes in the cytoplasm are regulated by the replicases. To evaluate the effects of the SFV RNA replicon on the improvement of gene expression, a LacZ gene was inserted into pIRES-neo digested by BamHI and dephosphorylated by alkaline phosphatase to construct pIRES-neo-LacZ. The RNA replicon vector pCMV-rep-LacZ and two conventional cytomegalovirus (CMV) promoter-based vectors (pLNCX-LacZ and pIRES-neo-LacZ) were transfected, using Lipofectin, to prepared 293 cells. Growth hormone releasing hormone (GHRH) expression vectors (pCMV-Rep-GHRH, pCDNA3.1(+)-GHRH and pIRES-neo-GHRH) were also tested using the same procedure. Target gene expression was detected with radioimmunoassay (RIA) and reverse transcription-polymerase chain reaction (RT-PCR). Results showed that the expression level of the RNA replicon vector was 2–3 times higher than with normal plasmid vectors. This result will help to improve the efficiency of gene expression in eukaryotic cells.
A prevailing belief is that opioids tend not to impair cognitive performance in opioid-dependent users. However, the impact of heroin abuse on verbal memory, especially on working memory, is not well studied and the results available are inconsistent.
This study was carried out to test the hypothesis that abstinent heroin abusers have intact working memory capacity.
N-back task and backward digit span task were used to measure the verbal working memory capacity in 28 abstinent heroin abusers and 25 controls matched for age, education level and gender. Forward digit span task was used as a control task to measure short-term memory capacity.
Compared with the control subjects, heroin abusers showed normal backward/forward digit spans but significant performance impairment in the n-back task.
Abstinent heroin abusers have intact short-term memory capacity but impaired verbal working memory capacity.
Intergeneric transfer of plasmid vectors pSET152 and pHL212 from donor Escherichia coli ET12567/pUZ8002 and S17-1 to Streptomyces cinnamonensis was demonstrated and optimized. Assisted by this conjugation system, nsdA gene disruption was achieved through PCR-targeted gene replacement. One AprRKanS exconjugant BIB309 was then isolated and confirmed to be the nsdA null mutant. Compared with the starting strain, monensin production by the nsdA− mutant BIB309 increased 270% in vitro.