We report results from high Prandtl number turbulent thermal convection experiments. The viscous boundary layer and the Reynolds number are measured in four different fluids over wide ranges of the Prandtl number Pr and the Rayleigh number Ra, all in a single convection cell of unity aspect ratio. We find that the normalized viscous layer thickness may be represented as delta(v)/L=0.65Pr(0.24)Ra(-0.16). The Reynolds number based on the oscillation frequency of the large-scale flow is found as Re(o)(Ra,Pr)=1.1Ra(0.43)Pr(-0.76) and that based on the rms velocity Re(rms)(Ra,Pr)=0.84Ra(0.40)Pr-0.86. Both the Ra and the Pr exponents of Re(V(m))(Ra,Pr) based on the maximum velocity of the circulating wind appear to vary across the range of Pr covered, changing from 0.5 to 0.68 and -0.88 to -0.95, respectively, as Pr is increased from 6 to 1027.

Local convective heat flux in turbulent thermal convection is obtained from simultaneous velocity and temperature measurements in an aspect-ratio-one convection cell filled with water. It is found that fluctuations of the vertical heat flux are highly intermittent and are determined primarily by the thermal plumes in the system. The experiment reveals a unique mechanism for the heat transport in turbulent convection. DOI: 10.1103/PhysRevLett.90.074501 PACS numbers: 47.27.Te, 44.25.+f An important issue in the study of turbulent RayleighBénard convection is to understand how heat is transported vertically through a convection cell [1][2][3]. A large number of global heat transport measurements have been carried out in various convecting fluids and under different experimental conditions. Some of the measurements were conducted with wide parameter range and great precession [4 -9]. These measurements have stimulated considerable theoretical efforts, aimed at explaining the functional form of the measured Nusselt number (normalized heat flux), Nu(Ra,Pr), as a function of the two experimental control parameters: the Rayleigh number Ra and the Prandtl number Pr. Like many transport phenomena in condensed matter physics, the measured macroscopic transport properties can often be explained by theories with different microscopic mechanisms [1][2][3][4]. A main issue of an unresolved theoretical debate is whether the heat transport in turbulent convection is determined primarily by thermal plumes, which erupt from the upper and lower thermal boundary layers, or by the large-scale circulation (LSC) that spans the height of the convection cell. Direct measurements of the local convective heat flux, therefore, become essential to the understanding of the heat transport mechanism in turbulent convection.In this Letter, we report direct measurements of the normalized local convective heat flux, Jr hvr; tTr; ti t H=T, over varying Rayleigh numbers and spatial positions r across the entire cell. Here is the thermal diffusivity of the convecting fluid, T is the temperature difference across the cell height H ( 20:5 cm), and h. . .i t represents an average over time t. In the experiment, the local temperature fluctuation Tr;t Tr;t ÿ T 0 and the flow velocity vr;t are measured simultaneously. The mean temperature T 0 of the bulk fluid is kept at 30 C and the corresponding Prandtl number, Pr =, is 5:4. The convection cell is an upright cylindrical cell of aspect ratio one and is filled with water. Details about the apparatus have been described elsewhere [10]. The upper and lower plates are made of brass and the sidewall is a transparent Plexiglas ring with a narrow and long rectangular flat window for velocity measurement. Two silicon rubber film heaters connected in parallel are sandwiched on the backside of the lower plate to provide constant and uniform heating. The upper plate is in contact with a cooling chamber, whose temperature is maintained constant by circulating cold water from a temperature bath.Local velocity meas...

A systematic study of velocity oscillations in turbulent thermal convection is carried out in small aspect-ratio cells filled with water. Local velocity fluctuations and temperature-velocity cross-correlation functions are measured over varying Rayleigh numbers and spatial positions across the entire convection cell. These structural measurements reveal how the thermal plumes interact with the bulk fluid in a closed cell and provide an interesting physical picture for the dynamics of the temperature and velocity oscillations in turbulent convection.

High-throughput Illumina RNA-seq was used for deep sequencing analysis of the transcriptome of poly(A)+ RNA from mycelium grown under three different conditions: 30 days darkness (sample 118), 80 days darkness (313W), and 30 days darkness followed by 50 days in the light (313C), in order to gain insight into the molecular mechanisms underlying the process of light-induced brown film (BF) formation in the edible mushroom, Lentinula edodes. Of the three growth conditions, BF formation occurred in 313C samples only. Approximately 159.23 million reads were obtained, trimmed, and de novo assembled into 31,511 contigs with an average length of 1,746 bp and an N 50 of 2,480 bp. Based on sequence orientations determined by a BLASTX search against the NR, Swiss-Prot, COG, and KEGG databases, 24,246 (76.9 %) contigs were assigned putative descriptions. Comparison of 313C/118 and 313C/313W expression profiles revealed 3,958 and 5,651 significantly differentially expressed contigs (DECs), respectively. Annotation using the COG database revealed that candidate genes for light-induced BF formation encoded proteins linked to light reception (e.g., WC-1, WC-2, phytochrome), light signal transduction pathways (e.g., two-component phosphorelay system, mitogen-activated protein kinase pathway), and pigment formation (e.g., polyketide synthase, O-methyltransferase, laccase, P450 monooxygenase, oxidoreductase). Several DECs were validated using quantitative real-time polymerase chain reaction. Our report is the first to identify genes associated with light-induced BF formation in L. edodes and represents a valuable resource for future genomic studies on this commercially important mushroom.

A systematic study of the local convective heat transport in turbulent thermal convection is carried out in small-aspect-ratio cells filled with water. The local convective heat flux is obtained from the simultaneous velocity and temperature measurements over varying Rayleigh numbers and spatial positions across the entire convection cell. Large fluctuations of the local convective heat flux are found mainly in the vertical direction and they are determined primarily by the thermal plumes in the system. The experiment reveals the spatial distribution of the local convective heat flux in a closed cell and thus settles a long-debated issue on how heat is transported in small-aspect-ratio cells.