Aspect Ratio Effects on the Aerodynamic Performance of a Biomimetic Hummingbird Wing in Flapping.

Hummingbirds are flapping winged creatures with unique flight mechanisms. Their flight pattern is more similar to insects than other birds. Because their flight pattern provides a large lift force at a very small scale, hummingbirds can remain hovering while flapping. This feature is of high research value. In order to understand the high-lift mechanism of hummingbirds' wings, in this study a kinematic model is established based on hummingbirds' hovering and flapping process, and wing models imitating the wing of a hummingbird are designed with different aspect ratios. Therefore, with the help of computational fluid dynamics methods, the effect of aspect ratio changes on the aerodynamic characteristics of hummingbirds' hovering and flapping are explored in this study. Through two different quantitative analysis methods, the results of lift coefficient and drag coefficient show completely opposite trends. Therefore, lift-drag ratio is introduced to better evaluate aerodynamic characteristics under different aspect ratios, and it is found that the lift-drag ratio reaches a higher value when AR = 4. A similar conclusion is also reached following research on the power factor, which shows that the biomimetic hummingbird wing with AR = 4 has better aerodynamic characteristics. Furthermore, the study of the pressure nephogram and vortices diagram in the flapping process are examined, leading to elucidation of the effect of aspect ratio on the flow field around hummingbirds' wings and how these effects ultimately lead to changes in the aerodynamic characteristics of the birds' wings.

Short-range repulsive force model for near-contact interactions of bubbles.

We introduce a short-range repulsive force model to tackle near-contact interactions when the collision occurs between bubbles. In contrast to the previous numerical method adopting the adaptive mesh refinement technique, such a mesoscale model can be applied to a relatively coarse mesh, which can prevent the nonphysical coalescence between bubbles without excessive mesh refinement. We assume that the repulsive force is inversely proportional to the third power of distance, as a reasonable approximation to the short-range phase interactions. The model is validated against two different experiments. In both experiments, two identical bubbles rising side by side were considered. First, the experiment performed in a water-glycerol mixture helps determine the model parameter K. Second, three typical combinations of bubble size and initial separation distance are simulated, presenting different types of interactions, i.e., coalescence, bouncing coalescence, and bouncing separation, agreeing well with the second experiment, which was performed in pure water. Owing to its simplicity, this model can be easily implemented into existing codes, and it can be extended to the case with multiple bubbles or droplets.

Circadian rhythm resynchronization improved isoflurane-induced cognitive dysfunction in aged mice.

Postoperative cognitive dysfunction (POCD) is a common clinical phenomenon characterized by cognitive deficits in patients after anesthesia and surgery. Advanced age is a significant independent risk factor for POCD. We previously reported that in young mice, sleep-wake rhythm is involved in the isoflurane-induced memory impairment. In present study, we sought to determine whether advanced age increased the risk of POCD through aggravated and prolonged post-anesthetic circadian disruption in the elderly. We constructed POCD model by submitting the mice to 5-h 1.3% isoflurane anesthesia from Zeitgeber Time (ZT) 14 to ZT19. Under novel object recognition assay (NOR) and Morris water maze (MWM) test, We found 5-h isoflurane anesthesia impaired the cognition of young mice for early 3 days after anesthesia but damaged the aged for at least 1 week. With Mini-Mitter continuously monitoring, a 3.22 ±â€¯0.75 h gross motor activity acrophase delay was manifested in young mice on D1, while in the aged mice, the gross motor activity phase shift lasted for 3 days, consistent with the body temperature rhythm trends of change. Melatonin has been considered as an effective remedy for circadian rhythm shift. In aged mice, melatonin was pretreated intragastrically at the dose of 10 mg/kg daily for 7 consecutive days before anesthesia. We found that melatonin prevented isoflurane-induced cognitive impairments by restoring the locomotor activity and temperature circadian rhythm via clock gene resynchronization. Overall, these results indicated that Long-term isoflurane anesthesia induced more aggravated and prolonged memory deficits and circadian rhythms disruption in aged mice. Melatonin could prevent isoflurane-induced cognitive impairments by circadian rhythm resynchronization.

Three-dimensional instabilities for the flow around a heaving foil.

This paper investigates the three-dimensional instabilities of the flow past a periodically heaving airfoil. By comparison with a pitching foil [Deng et al., Phys. Rev. E 92, 063013 (2015)PLEEE81539-375510.1103/PhysRevE.92.063013], here we present distinctive characteristics for the heaving foil, particulary regarding its Floquet modes. By increasing the frequency (Sr), or equivalently decreasing the amplitude (A_{D}) along the marginal stability curve in the (Sr,A_{D}) phase space, the critical Floquet mode emerges sequentially as A, quasiperiodic (QP), and B. It is interesting to note that both modes A and B are synchronous with the base flow, in contrast to the quasiperiodic mode QP. To further investigate the instability across the marginal curve, we fix the frequency at Sr=0.187, of which the critical Floquet mode is located in the synchronous regime, while varying A_{D} around the critical point. We find that the dominant mode switches from mode A to mode B, while mode QP never becomes critical as we increase A_{D}. We note that mode S, a subharmonic mode, can also be unstable, which, however, is not physically realizable, because the magnitude of its Floquet multiplier is always smaller than that of mode B. We have also studied the influence of various Reynolds numbers at the same critical point on the marginal stability curve, with the results resembling that by varying the amplitude A_{D}.

Misaligned Feeding May Aggravate Pain by Disruption of Sleep-Awake Rhythm.

BACKGROUND: Increasing evidence suggests that patients with eating disorders are more likely to develop chronic pain. A misaligned diet has been reported to disrupt the sleep-awake rhythms. Combined with our previous investigation on circadian pain, we aimed to investigate the role of misaligned diet in the pain sensitivity and the underlying mechanisms. METHODS: Two-month-old C57BL/6J male mice were administered chronic constriction injury (CCI) surgery to establish neuropathic pain models. CCI mice were randomized to scheduled food access throughout the whole day (CCI-free), during the daytime (CCI-misaligned), and at night (CCI-aligned), respectively. The paw withdrawal mechanical threshold, indicating pain behavior, was measured by Von Frey. The gross motor activity pattern indicating the sleep-awake rhythm was monitored by Mini-Mitter. Melatonin (Mel) was administered to ameliorate the sleep-awake rhythm (CCI-free + Mel and CCI-misaligned + Mel). The expressions of circadian pain-related proteins were detected by quantitative polymerase chain reaction and western blot. The primary outcome is the pain threshold and the secondary outcome is the sleep-awake rhythm. RESULTS: Misaligned diet during the peri-CCI surgery period significantly decreased the paw withdrawal mechanical threshold compared with the CCI-free mice (day 14: 0.40 ± 0.09 vs 0.64 ± 0.15; P = .03;) and altered the sleep-awake rhythm. Mel pretreatment alleviated the increased pain (day 14, CCI-misaligned + Mel versus CCI-misaligned: day 14: 0.60 ± 0.13 vs 0.35 ± 0.12; P = .022) and the disrupted sleep-awake rhythm caused by misaligned feeding. The mRNA levels of N-methyl-D-aspartate receptor subtype 2B (NR2B), Ca/calmodulin-dependent protein kinase II (CaMKII), and cyclic adenosine monophosphate-response element binding protein (CREB) in the spinal dorsal horn increased in CCI-misaligned mice compared with the CCI-free mice. The phosphor-NR2B, phosphor-CaMKII, and phosphor-CREB also increased in CCI-misaligned mice compared with the CCI-free mice. However, the expressions of NR2B, CaMKII, and CREB were decreased in CCI-misaligned + Mel mice compared to CCI-misaligned mice at both transcriptional and translational levels. CONCLUSIONS: Misaligned diet might aggravate pain sensitivity through the disruption of the sleep-awake cycle, which could be recovered by Mel. NR2B-CaMKII-CREB may participate in the disruption of sleep-awake rhythm-mediated pain aggravation.

Perturbing NR2B-PSD-95 interaction relieves neuropathic pain by inactivating CaMKII-CREB signaling.

Neuropathic pain is characterized by central sensitization. The interaction between N-methyl-D-aspartate receptors (NMDARs) and postsynaptic density protein-95 (PSD-95) plays a major role in central sensitization. Here, we aimed to investigate the analgesic effect of disruption of the interaction between NMDAR and PSD-95. Chronic dorsal root ganglia compression model rats were used to mimic sciatica. Thermal hyperalgesia and mechanical allodynia were evaluated. The expression of spinal phospho-NR2B, PSD-95, calcium/calmodulin-dependent protein kinase II (CaMKII), and cAMP response element binding protein (CREB) was measured using western blotting. A mimetic peptide Myr-NR2B9c was injected intrathecally to disrupt the interaction between PSD-95 and NR2B and detected by coimmunoprecipitation. Chronic dorsal root ganglia compression surgery induced thermal hyperalgesia and mechanical allodynia, and upregulated pain-related proteins such as phospho-NR2B, PSD-95, CaMKII, and CREB expressions in the spinal cord. Myr-NR2B9c disrupted the interaction between NR2B-containing NMDARs and PSD-95 in the spinal cord. Intrathecal administration of Myr-NR2B9c attenuated neuropathic pain behaviors and downregulated the expressions of phospho-NR2B, PSD-95, CaMKII, and CREB in the spinal cord. The present study indicates that dissociation of NR2B-containing NMDARs from PSD-95 inactivates CaMKII and CREB signaling and relieves pain.

Application of Berendsen barostat in dissipative particle dynamics for nonequilibrium dynamic simulation.

The Berendsen barostat from molecular dynamics simulation is applied in both standard dissipative particle dynamics (DPD) and many-body dissipative particle dynamics (MDPD) simulations. The original Berendsen barostat works well in (M)DPD simulation of a single-component system under constant pressure condition and in nonequilibrium dynamic processes. The partial Berendsen barostat is proposed for multi-component system simulation with (M)DPD. The displacement rescaling process of the Berendsen barostat is only applied on the particles outside the center region, acting as a pressure "boundary condition." The center part forms the free zone, in which the interface shape and nonequilibrium dynamic behavior between different phases can be captured properly. An immiscible bubble in the second fluid under constant pressure condition is studied, and the oscillation of the bubble radius and fluctuation of systempressure can be obtained by the current barostat. Preliminary models for bubble growing and collapsing under square pressure wave and bubble oscillation under harmonic pressure wave are also reported in the current simulation. It shows that the partial Berendsen barostat is suitable for the modeling of nonequilibrium process of single or few droplets/bubbles in multi-component systems.

The Role of NR2B-CREB-miR212/132-CRTC1-CREB Signal Network in Pain Regulation In Vitro and In Vivo.

BACKGROUND: Chronic pain is a debilitating threat to human health, and its molecular mechanism remains undefined. Previous studies have illustrated a key role of cAMP response element-binding protein (CREB) in pain regulation; CREB-regulated transcription coactivator 1 (CRTC1) and microRNA212/132 (miR212/132) are also vital in synaptic plasticity. However, little is known about the interaction among these factors in pain condition. We conducted this experiment mainly to determine the crosstalk between CREB, CRTC1, and miR212/132 in vitro. Moreover, we explored the changes in hyperalgesia on chronic constrictive injury (CCI) mouse in vivo when given CREB-related adenovirus vectors, CRTC1-related adenovirus vectors, and miR212/132-locked nucleic acid (LNA). METHODS: We cultured primary neurons in the spinal cord of mouse embryos. Exogenous glutamate was added to cultured neurons to simulate in vivo pain process. Real-time quantitative polymerase chain reaction was used to determine changes of NR2B, CRTC1, CREB, and miR212/132 at the mRNA level; Western blot was used to detect p-NR2B, p-CREB, and CRTC1 at protein level. Von Frey cilia were used to study mechanical hyperalgesia in a murine model of CCI. CREB-miR (adenovirus vector interfering CREB gene), CREB-AD (adenovirus vector overexpressing CREB gene); CRTC1-miR (adenovirus vector interfering CRTC1 gene), CRTC1-AD (adenovirus vector overexpressing CRTC1 gene), and miR212/132-LNA were injected intrathecally. RESULTS: In vitro, 100 µmol/L glutamate induced p-CREB and miR212/132-LNA. CRTC1 protein was downregulated by CREB-miR and miR212/132-LNA. CRTC1 mRNA was upregulated by CREB-AD and downregulated by CREB-miR and miR212-LNA. P-CREB was upregulated by CRTC1-AD and downregulated by miR212/132. CREB mRNA was upregulated by CRTC1-AD and downregulated by CRTC1-miR. MiR212/132 was upregulated by CRTC1-AD and CREB-AD; downregulated by CREB-miR. In vivo, CRTC1-miR, CREB-miR, and miR212/132-LNA increased paw withdrawal mechanical threshold in various degrees. CONCLUSIONS: The NR2B-CREB-miR212/132-CRTC1-CREB signal network plays an important role in the regulation of pain. Intervening with any molecule in this signal network would reduce pain perception.

Effects of particle-fluid density ratio on the interactions between the turbulent channel flow and finite-size particles.

A parallel direct-forcing fictitious domain method is employed to perform fully resolved numerical simulations of turbulent channel flow laden with finite-size particles. The effects of the particle-fluid density ratio on the turbulence modulation in the channel flow are investigated at the friction Reynolds number of 180, the particle volume fraction of 0.84%, and the particle-fluid density ratio ranging from 1 to 104.2. The results show that the variation of the flow drag with the particle-fluid density ratio is not monotonic, with a larger flow drag for the density ratio of 10.42, compared to those of unity and 104.2. A significant drag reduction by the particles is observed for large particle-fluid density ratios during the transient stage, but not at the statistically stationary stage. The intensity of particle velocity fluctuations generally decreases with increasing particle inertia, except that the particle streamwise root-mean-square velocity and streamwise-transverse velocity correlation in the near-wall region are largest at the density ratio of the order of 10. The averaged momentum equations are derived with the spatial averaging theorem and are used to analyze the mechanisms for the effects of the particles on the flow drag. The results indicate that the drag-reduction effect due to the decrease in the fluid Reynolds shear stress is counteracted by the drag-enhancement effect due to the increase in the total particle stress or the interphase drag force for the large particle-inertia case. The sum of the total Reynolds stress and particle inner stress contributions to the flow drag is largest at the density ratio of the order of 10, which is the reason for the largest flow drag at this density ratio. The interphase drag force obtained from the averaged momentum equation (the balance theory) is significantly smaller than (but agrees qualitatively with) that from the empirical drag formula based on the phase-averaged slip velocity for large density ratios. For the neutrally buoyant case, the balance theory predicts a positive interphase force on the particles arising from the negative gradient of the particle inner stress, which cannot be predicted by the drag formula based on the phase-averaged slip velocity. In addition, our results show that both particle collision and particle-turbulence interaction play roles in the formation of the inhomogeneous distribution of the particles at the density ratio of the order of 10.

Effects of Atomization Injection on Nanoparticle Processing in Suspension Plasma Spray.

Liquid atomization is applied in nanostructure dense coating technology to inject suspended nano-size powder materials into a suspension plasma spray (SPS) torch. This paper presents the effects of the atomization parameters on the nanoparticle processing. A numerical model was developed to simulate the dynamic behaviors of the suspension droplets, the solid nanoparticles or agglomerates, as well as the interactions between them and the plasma gas. The plasma gas was calculated as compressible, multi-component, turbulent jet flow in Eulerian scheme. The droplets and the solid particles were calculated as discrete Lagrangian entities, being tracked through the spray process. The motion and thermal histories of the particles were given in this paper and their release and melting status were observed. The key parameters of atomization, including droplet size, injection angle and velocity were also analyzed. The study revealed that the nanoparticle processing in SPS preferred small droplets with better atomization and less aggregation from suspension preparation. The injection angle and velocity influenced the nanoparticle release percentage. Small angle and low initial velocity might have more nanoparticles released. Besides, the melting percentage of nanoparticles and agglomerates were studied, and the critical droplet diameter to ensure solid melting was drawn. Results showed that most released nanoparticles were well melted, but the agglomerates might be totally melted, partially melted, or even not melted at all, mainly depending on the agglomerate size. For better coating quality, the suspension droplet size should be limited to a critical droplet diameter, which was inversely proportional to the cubic root of weight content, for given critical agglomerate diameter of being totally melted.

Dynamical features of the wake behind a pitching foil.

As an extension of the previous study on the three-dimensional transition of the wake behind a pitching foil [Deng and Caulfield, Phys. Rev. E 91, 043017 (2015)], this investigation draws a comprehensive map on the pitching frequency-amplitude phase space. First, by fixing the Reynolds number at Re=1700 and varying the pitching frequency and amplitude, we identify three key dynamical features of the wake: first, the transition from Bénard-von Kármán (BvK) vortex streets to reverse BvK vortex streets, and second, the symmetry breaking of this reverse BvK wake leading to a deflected wake, and a further transition from two-dimensional (2D) wakes to three-dimensional (3D) wakes. The transition boundary between the 2D and 3D wakes lies top right of the wake deflection boundary, implying a correlation between the wake deflection and the 2D to 3D wake transition, confirming that this transition occurs after the wake deflection. This paper supports the previous extensive numerical studies under two-dimensional assumption at low Reynolds number, since it is indeed two dimensional except for the cases at very high pitching frequencies or large amplitudes. Furthermore, by three-dimensional direct numerical simulations (DNSs), we confirm the previous statement about the physical realizability of the short wavelength mode at ß=30 (or λ(z)=0.21) for Re=1500. By comparing the three-dimensional vortical structures by DNSs with that from the reconstruction of Floquet modes, we find a good consistency between them, both exhibiting clear streamwise structures in the wake.

[Effects of flow diverter with low porosity on cerebral aneurysms: a numerical stimulative study].

OBJECTIVE: To examine the influence of flow diverter on the alterations of cerebral intra-aneurysmal hemodynamics. METHODS: One wide-necked and one narrow-necked sidewall aneurysm in curved vessels were virtually reconstructed. Pulsatile computational fluid simulations were performed on each model for hemodynamic analysis. And the flow diverters were virtually deployed to cover the aneurysmal neck with parent vessels. The hemodynamic changes in parent vessels and aneurysms after a deployment of flow diverter devices with low porosity were studied by the Fluent software. RESULTS: After a deployment of flow diverter, the hemodynamics in aneurysm sac changed significantly. The peak velocity and wall stress strength in impingement zone of narrow-necked aneurysms decreased after the placement of a flow diverter. And similar change also occurred in wide-necked aneurysms, but with a less decreased span. CONCLUSION: Numerical simulation confirms that a flow diverter with low porosity significantly may modify the hemodynamics in aneurysms. Which is important for prevention of bleeding or rebleeding of intracranial aneurysm.

Sedimentation of a single particle between two parallel walls.

The sedimentation of a single circular particle between two parallel walls was studied by means of direct numerical simulation (DNS) and experiment. The improved implementation of distributed Lagrange multiplier/fictitious domain method used in our DNS is a promising new way for simulation of particulate flows. The settling behaviors of the particle are presented ranging in Reynolds number from 0 to about 700, which showed that our results for low Reynolds numbers agreed well with that reported before. Nevertheless, for higher Reynolds numbers our results were different from theirs. The long-term mean equilibrium positions in our results were all on the centerline, but not at off-center position as reported before. In order to validate our simulation, experiments were also conducted. The results showed that the sedimenting behavior simulated in this paper agreed well with our experiment result.

Direct numerical simulation of the motion of circular pollutant particles in Newtonian fluid.

An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite-element triangulation for the velocity and a "twice-coarser" triangulation for the pressure with a rectangular discretization for the velocity and pressure. For code validation, the sedimentation of a single particle in a two-dimensional channel was simulated. The results showed that the simulation is independent of the mesh size as well as the time step. The comparison between experimental data and this simulation showed that our code can give a more accurate simulation on the motion of particles than previous DLM code. The code was then applied to simulate the sedimentation of 600 particles in a rectangular box. The falling course is presented and discussed. At the same time, this simulation also demonstrates that the method presented in this paper can be used for solving the initial problems involving a lager number of particles exactly with computing durations kept at acceptable levels.