144 research outputs found
Azimuthal diffusion of the large-scale-circulation plane, and absence of significant non-Boussinesq effects, in turbulent convection near the ultimate-state transition
We present measurements of the orientation and temperature
amplitude of the large-scale circulation in a cylindrical sample of
turbulent Rayleigh-Benard convection (RBC) with aspect ratio ( and are the diameter and height respectively) and for the
Prandtl number . Results for revealed a preferred
orientation with upflow in the West, consistent with a broken azimuthal
invariance due to Earth's Coriolis force [see \cite{BA06b}]. They yielded the
azimuthal diffusivity and a corresponding Reynolds number
for Rayleigh numbers over the range . In the classical state () the results
were consistent with the measurements by \cite{BA06a} for and
which gave , and with the
Prandtl-number dependence as found previously
also for the velocity-fluctuation Reynolds number \cite[]{HGBA15b}. At
larger the data for revealed a transition to a new
state, known as the "ultimate" state, which was first seen in the Nusselt
number and in at and
. In the ultimate state we found .
Recently \cite{SU15} claimed that non-Oberbeck-Boussinesq effects on the
Nusselt and Reynolds numbers of turbulent RBC may have been interpreted
erroneously as a transition to a new state. We demonstrate that their reasoning
is incorrect and that the transition observed in the G\"ottingen experiments
and discussed in the present paper is indeed to a new state of RBC referred to
as "ultimate".Comment: 12 pages, 4 figures, to be pub. in JFM
Logarithmic temperature profiles of turbulent Rayleigh-B\'enard convection in the classical and ultimate state for a Prandtl number of 0.8
We report on experimental determinations of the temperature field in the
interior (bulk) of turbulent Rayleigh-Benard convection for a cylindrical
sample with aspect ratio (diameter over height) of 0.50, both in the classical
and in the ultimate state. The Prandtl number was close to 0.8. We find a
"logarithmic layer" in which the temperature varies as A*ln(z/L) + B with the
distance z from the bottom plate of the sample. The amplitude A varies with
radial position r. In the classical state these results are in good agreement
with direct numerical simulations (DNS); in the ultimate state there are as yet
no DNS. A close analogy between the temperature field in the classical state
and the "Law of the Wall" for the time-averaged down-stream velocity in shear
flow is discussed.Comment: 27 pages, 15 figure
Mean velocity and temperature profiles in turbulent Rayleigh-Bénard convection at low Prandtl numbers
We report a direct numerical simulation (DNS) study of the mean velocity and temperature profiles in turbulent Rayleigh-Bénard convection (RBC) at low Prandtl numbers (Pr). The numerical study is conducted in a vertical thin disk with Pr varied in the range 0.17 ≤ Pr ≤ 4.4 and the Rayleigh number (Ra) varied in the range 5 × 10^8 ≤ Ra ≤ 1 × 10^10. By varying Pr from 4.4 to 0.17, we find a sharp change of flow patterns for the large-scale circulation (LSC) from a rigid-body rotation to a near-wall turbulent jet. We numerically examine the mean velocity equation in the bulk region and find that the mean horizontal velocity profile u(z) can be determined by a balance equation between the mean convection and turbulent diffusion with a constant turbulent viscosity νt. This balance equation admits a self-similarity jet solution, which fits the DNS data well. In the boundary-layer region, we find that both the mean temperature profile T(z) and u(z) can be determined by a balance equation between the molecular diffusion and turbulent diffusion. Within the viscous boundary layer, both u(z) and T(z) can be solved analytically and the analytical results agree well with the DNS data. Our careful characterisation of the mean velocity and temperature profiles in low-Pr RBC provides a further understanding of the intricate interplay between the LSC, plume emission and boundary-layer dynamics, and pinpoints the physical mechanism for the emergence of a pronounced LSC in low-Pr RBC
Heat transport by turbulent Rayleigh-B\'enard convection for $\Pra\ \simeq 0.83\times 10^{12} \alt \Ra\ \alt 10^{15}\Gamma = 0.50$
We report experimental results for heat-transport measurements, in the form
of the Nusselt number \Nu, by turbulent Rayleigh-B\'enard convection in a
cylindrical sample of aspect ratio ( m is
the diameter and m the height). The measurements were made using
sulfur hexafluoride at pressures up to 19 bars as the fluid. They are for the
Rayleigh-number range 3\times 10^{12} \alt \Ra \alt 10^{15} and for Prandtl
numbers \Pra\ between 0.79 and 0.86. For \Ra < \Ra^*_1 \simeq 1.4\times
10^{13} we find \Nu = N_0 \Ra^{\gamma_{eff}} with , consistent with classical turbulent Rayleigh-B\'enard convection in a
system with laminar boundary layers below the top and above the bottom plate.
For \Ra^*_1 < \Ra < \Ra^*_2 (with \Ra^*_2 \simeq 5\times 10^{14})
gradually increases up to . We argue that above
\Ra^*_2 the system is in the ultimate state of convection where the boundary
layers, both thermal and kinetic, are also turbulent. Several previous
measurements for are re-examined and compared with the present
results.Comment: 44 pages, 18 figures, submitted to NJ
Current Perspectives on Role of MSC in Renal Pathophysiology
In the course of the development and worsening of kidney disease, the treatments available are expensive and may cause adverse effects such as immune rejection, inadequate renal resources, or post-operative complications. Therefore, there is an urgent to develop more effective treatments. The advent of mesenchymal stem cells (MSCs) represents a new direction in this context. The current use of MSCs for the treatment of kidney disease has mostly involved experimental studies on animals and only a few clinical trials have been conducted. This review focused on the mechanisms of MSC involvement from different sources in the improvement of renal pathophysiology in recent years. These mechanisms include homing to damaged kidney tissue, and differentiating into or fusing with the innate cells of the kidney. The paracrine or endocrine action through secreting protective cytokines and/or releasing microvesicle from MSCs also plays a critical role in amelioration of kidney disease. With modern engineering technology like microRNA delivery and a combinational therapy approach such as reduction of renal fibrosis in obstructive nephropathy with MSCs and serelaxin, MSC may make great contribution to the improvement of renal pathophysiology. However, the therapeutic effects of MSC are still controversial and several problems remain unsolved. While it is too early to state that MSCs are useful for the treatment of renal diseases in clinic, it is thought that solutions to the existing problems will enable effective modulation of the biological characteristics of MSCs, thereby providing new and effective approaches for the treatment of renal diseases
The Effects of Electrical Acupuncture and Essential Amino Acid Supplementation on Sarcopenic Obesity in Male Older Adults: A Randomized Control Study
Objective: Aging which is accompanied by loss of skeletal muscle and increase of body fat in some adults older than 60 years does not only result in remarkable influences on daily life function but also increases the risk of cardiovascular events. This study used electrical acupuncture together with essential amino acid supplementation to treat sarcopenic obesity (SO) in male older adults. Methods: A total of 48 male participants with SO (>60 years old) were randomized to electrical acupuncture with oral essential amino acids (EA + AA) or oral essential amino acids alone (AA). Acupuncture points on the limbs were punctured and stimulated electrically once every 3 days for 12 weeks. All participants received essential amino acids orally, twice per day for 28 weeks. Body fat percentage (BFP) and appendicular skeletal muscle index (ASM/H2) was determined by bioelectrical impedance analysis. Results: Both groups exhibited significant changes in BFP after 12, 20, and 28 weeks compared with baseline values; for ASM/H2, there were significant differences to baseline values after 12, 20, and 28 weeks in the EA + AA group, but only after 28 weeks in the AA group. Between the two groups, there were significant differences in BFP after 12, 20, and 28 weeks, and in ASM/H2 after 20 and 28 weeks. Conclusion: Both methods decrease BFP and increase ASM/H2. In male older adults, electrical acupuncture with oral essential amino acids is more effective and can increase muscle mass in a shorter time than oral essential amino acids alone
Vertical Federated Learning
Vertical Federated Learning (VFL) is a federated learning setting where
multiple parties with different features about the same set of users jointly
train machine learning models without exposing their raw data or model
parameters. Motivated by the rapid growth in VFL research and real-world
applications, we provide a comprehensive review of the concept and algorithms
of VFL, as well as current advances and challenges in various aspects,
including effectiveness, efficiency, and privacy. We provide an exhaustive
categorization for VFL settings and privacy-preserving protocols and
comprehensively analyze the privacy attacks and defense strategies for each
protocol. In the end, we propose a unified framework, termed VFLow, which
considers the VFL problem under communication, computation, privacy, and
effectiveness constraints. Finally, we review the most recent advances in
industrial applications, highlighting open challenges and future directions for
VFL
- …