Small-scale universality in fluid turbulence

Turbulent flows in nature and technology possess a range of scales. The largest scales carry the memory of the physical system in which a flow is embedded. One challenge is to unravel the universal statistical properties that all turbulent flows share despite their different large-scale driving mechanisms or their particular flow geometries. In the present work, we study three turbulent flows of systematically increasing complexity. These are homogeneous and isotropic turbulence in a periodic box, turbulent shear flow between two parallel walls, and thermal convection in a closed cylindrical container. They are computed by highly resolved direct numerical simulations of the governing dynamical equations. We use these simulation data to establish two fundamental results: (i) at Reynolds numbers Re ∼ 10² the fluctuations of the velocity derivatives pass through a transition from nearly Gaussian (or slightly sub-Gaussian) to intermittent behavior that is characteristic of fully developed high Reynolds number turbulence, and (ii) beyond the transition point, the statistics of the rate of energy dissipation in all three flows obey the same Reynolds number power laws derived for homogeneous turbulence. These results allow us to claim universality of small scales even at low Reynolds numbers. Our results shed new light on the notion of when the turbulence is fully developed at the small scales without relying on the existence of an extended inertial range.An enduring notion in the phenomenology of turbulence is the universality of small scales. It has been taken for granted in theoretical approaches (e.g., refs. 1–8) and analyzed in numerical simulations (9–11) as well as various laboratory experiments (e.g., refs. 5 and 12). The standard paradigm is that whereas the large scales are nonuniversal, reflecting the circumstances of their generation, an increasingly weaker degree of nonuniversality is imparted to small scales with increasing separation between the large and small scales. This scale separation is thought to increase with the flow Reynolds number, so a proper test of universality has been thought to require very high Reynolds numbers. Consequently, many substantial efforts have been made to produce such high-Reynolds-number flows (e.g., ref. 12).Here, we show evidence for an alternative point of view: If one resolves small scales accurately, one observes, even at low Reynolds numbers, universal scaling of velocity gradients that manifest primarily at small scales. We stress that small-scale dynamics are strongly nonlinear even in low-Reynolds-number flows driven by large-scale forcing. There is thus considerable merit in measuring or simulating low-Reynolds-number flows much more accurately than has been the practice and exploring the evidence for universality (or lack thereof), instead of advancing as inevitable the notion that useful lessons about universality are possible only at very high Reynolds numbers. Indeed, another result of this paper is that there exists a threshold Reynolds number above which Gaussian-like fluctuations tend to assume intermittent characteristics of fully developed flows and that these features can be extracted by accessing increasingly smaller scales even if the Reynolds numbers are quite moderate. The latter result is especially important for purposes of identifying a fixed point in certain renormalization group expansion procedures (8).     

Double deletion of orexigenic neuropeptide Y and dynorphin results in paradoxical obesity in mice

Objective

Orexigenic neuropeptide Y (NPY) and dynorphin (DYN) regulate energy homeostasis. Single NPY or dynorphin deletion reduces food intake or increases fat loss. Future developments of obesity therapeutics involve targeting multiple pathways. We hypothesised that NPY and dynorphin regulate energy homeostasis independently, thus double NPY and dynorphin ablation would result in greater weight and/or fat loss than the absence of NPY or dynorphin alone.

Design and methods

We generated single and double NPY and dynorphin knockout mice (NPYΔ, DYNΔ, NPYDYNΔ) and compared body weight, adiposity, feeding behaviour, glucose homeostasis and brown adipose tissue uncoupling protein-1 (UCP-1) expression to wildtype counterparts.

Results

Body weight and adiposity were significantly increased in NPYDYNΔ, but not in NPYΔ or DYNΔ. This was not due to increased food intake or altered UCP-1 expression, which were not significantly altered in double knockouts. NPYDYNΔ mice demonstrated increased body weight loss after a 24-h fast, with no effect on serum glucose levels after glucose injection.

Conclusions

Contrary to the predicted phenotype delineated from single knockouts, double NPY and dynorphin deletion resulted in heavier mice, with increased adiposity, despite no significant changes in food intake or UCP-1 activity. This indicates that combining long-term opioid antagonism with blockade of NPY-ergic systems may not produce anti-obesity effects.     

Controlled release from a mechanically-stimulated thermosensitive self-heating composite hydrogel

Temperature has been extensively explored as a trigger to control the delivery of a payload from environment-sensitive polymers. The need for an external heat source only allows limited spatiotemporal control over the delivery process. We propose a new approach by using the dissipative properties of a hydrogel matrix as an internal heat source when the material is mechanically loaded. The system is comprised of a highly dissipative hydrogel matrix and thermo-sensitive nanoparticles that shrink upon an increase in temperature. Exposing the hydrogel to a cyclic mechanical loading for a period of 5 min leads to an increase of temperature of the nanoparticles. The concomitant decrease in the volume of the nanoparticles increases the permeability of the hydrogel network facilitating the release of its payload. As a proof-of-concept, we showed that the payload of the hydrogel is released after 5–8 min following the initiation of the mechanical loading. This delivery method would be particularly suited for the release of growth factor as it has been shown that cell receptor to growth factor is activated 5–20 min following a mechanical loading.     

探讨太阳伤寒证是新型冠状病毒(2019-nCoV)肺炎的初始阶段—微汗解表严防疫毒内陷

在防控新型冠状病毒(2019-nCoV)肺炎的过程中,中医药可以发挥更大的作用。以生命定义核心,结合维持人体能量代谢过程和干细胞分裂过程五个基本因素就能构建人体内新型代谢模型。这个模型中,水液和热能的排泄是人体内代谢过程的最后步骤,也是太阳经的生理学基础。太阳经受到寒气后可以出现以热能排泄障碍为主的临床表现如发热,也可以出现以水液潴留为主要临床表现,如水肿等。根据新型冠状病毒(2019-nCoV)在感染人体后早期出现的上呼吸道症状和发热等辨证为太阳伤寒经证,出现肺部感染后辨证为太阳脏证。太阳经证治疗以温经散寒为主,而太阳脏证则需要采用急下、峻下及清热开窍为主的治法。太阳表证、经证未解,忌用寒凉药物和食物,这样才能将防治关口前移,避免邪毒内陷而致病情加重。     

大鼠肝再生启动阶段能量代谢物靶向定量分析

目的 探讨大鼠肝再生(LR)启动阶段能量代谢物的变化对LR的调控作用.方法 大鼠随机分为3组,每组5只,包括两个部分肝切除组(PH)和1个正常对照组.运用质谱选择反应检测扫描/多反应检测扫描(SRM/MRM)对29种能量代谢物的含量进行靶向代谢组学鉴定.运用Ingenuity Pathway Analysis(IPA)...     

Energetics of active sodium-potassium transport following stimulation with insulin,adrenaline or salbutamol in rat soleus muscle

The total metabolic energy expenditure associated with active Na–K-transport over the first 20 min of stimulation with insulin, adrenaline or salbutamol (H_mNa–K) was determined from direct calorimetric and tracer ion flux measurements in isolated muscles at rest. The reversible work performed by the Na–K-pump during the same interval of time (W_revNa–K) was calculated as the product of the ouabain-suppressible Na–K transfers and the mean free energy increase imparted to the two ions as they are transported against their electrochemical gradients across the plasma membrane. Comparison of membrane potential and intracellular Na and K concentrations before and after the stimulations indicated that part of W_revNa–K had contributed to increase the ion electrochemical gradients in the preparation (i.e. had not been lost as heat) during the 20 min period. Accordingly, the maximum value of H_mNa–K was taken as the sum of the ouabain-suppressible heat production and W_revNa–K. Following stimulation with insulin, adrenaline or salbutamol this maximum corresponded to 10, 10 and 12% respectively, of basal metabolism. Under the same three conditions, the minimum energetic efficiency of the active Na–K-transport process, defined as the ratio between W_revNa–K and maximum H_mNa–K, was 35, 41 and 38%, respectively.     

Noninvasive assessment of the viscoelasticity of peripheral arteries

Currently used methods of examining the mechanical properties of blood vessel walls are either indirect or invasive, or measure vessel diameter and pressure waveforms at different sites. We developed a noninvasive technique to assess the mechanical properties and viscoelasticity of peripheral arteries. The pressure-strain elastic modulus (Ep) and the viscoelastic properties (energy dissipation ratio, EDR) of the common carotid artery (CCA), brachial artery (BA), radial artery (RA) and dorsalis pedis artery (DPA) were determined by means of palpating pressure and diameter distension waveforms extracted from high-resolution ultrasonography. The methodology was validated in vitro using an elastic tube phantom, as well as in vivo. In vivo study in 10 healthy volunteers (mean age 22 y) showed that the pressure-diameter curves were nonlinear, with an inflection at about 85–90 mmHg, and routed clockwise with slight hysteresis. The CCA (n = 5) had a mean diameter of 6.74 mm and the pulsatile diameter distension was 12.2%. The Ep calculated at the CCA was 0.44 × 10⁶ dyne/cm² with an EDR of 7.18%. The BA, RA and DPA (n = 10) had mean diameters of 3.91 mm, 2.21 mm and 2.12 mm; arterial strains of 4.60%, 4.25% and 8.91%; mean Ep of 1.39, 1.45, 0.90 × 10⁶ dyne/cm²; and mean EDRs of 6.34%, 6.15% and 5.60%, respectively. The method presented is relatively simple to implement clinically and has potential as a new diagnostic tool for detecting local vascular changes.