Magnitude Of ΔT Research Articles

A Closer Look at the Evolution of Supercooled Cloud Droplet Temperature and Lifetime in Different Environmental Conditions with Implications for Ice Nucleation in the Evaporating Regions of Clouds

Abstract This study investigates the evolution of temperature and lifetime of evaporating, supercooled cloud droplets considering initial droplet radius (r0) and temperature (), and environmental relative humidity (RH), temperature (T∞), and pressure (P). The time (tss) required by droplets to reach a lower steady-state temperature (Tss) after sudden introduction into a new subsaturated environment, the magnitude of ΔT = T∞ − Tss, and droplet survival time (tst) at Tss are calculated. The temperature difference (ΔT) is found to increase with T∞, and decrease with RH and P. ΔT was typically 1–5 K lower than T∞, with highest values (∼10.3 K) for very low RH, low P, and T∞ closer to 0°C. Results show that tss is <0.5 s over the range of initial droplet and environmental conditions considered. Larger droplets (r0 = 30–50 μm) can survive at Tss for about 5 s to over 10 min, depending on the subsaturation of the environment. For higher RH and larger droplets, droplet lifetimes can increase by more than 100 s compared to those with droplet cooling ignored. Tss of the evaporating droplets can be approximated by the environmental thermodynamic wet-bulb temperature. Radiation was found to play a minor role in influencing droplet temperatures, except for larger droplets in environments close to saturation. The implications for ice nucleation in cloud-top generating cells and near cloud edges are discussed. Using Tss instead of T∞ in widely used parameterization schemes could lead to enhanced number concentrations of activated ice-nucleating particles (INPs), by a typical factor of 2–30, with the greatest increases (≥100) coincident with low RH, low P, and T∞ closer to 0°C. Significance Statement Cloud droplet temperature plays an important role in fundamental cloud processes like droplet growth and decay, activation of ice-nucleating particles, and determination of radiative parameters like refractive indices of water droplets. Near cloud boundaries such as cloud tops, dry air mixes with cloudy air exposing droplets to environments with low relative humidities. This study examines how the temperature of a cloud droplet that is supercooled (i.e., has an initial temperature < 0°C) evolves in these subsaturated environments. Results show that when supercooled cloud droplets evaporate near cloud boundaries, their temperatures can be several degrees Celsius lower than the surrounding drier environment. The implications of this additional cooling of droplets near cloud edges on ice particle formation are discussed.

The Anisotropy and Polarization of Stress-Induced Microwave Radiation Changes in Granite and Their Significance for Seismic Remote Sensing

Incidence angles ( θ) and polarization modes ( p) are the essential factors for detecting earthquake (EQ)-related microwave radiation anomalies. However, their influences are still not well studied. In this article, research was carried out to simulate the observation of satellite on EQ under different θ and p. The microwave observation experiments were performed on granite samples pressed with θ from 0° to 30°, as well as vertical (v) to horizontal (h) polarizations under weak radiation environment. It was found that the stress-induced changes ( ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) in the samples' microwave brightness temperature ( T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) are anisotropic and polarized. It was observed that the trends of ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> may be reversed under different θ ( p), with a probability of 57.14% (14.29%). The magnitude of ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> at h is also prone to greater changes than that at v, with a probability of 67.86%. Theoretical analysis was performed based on crystal optics, Fresnel formulas, and dielectric physics. This phenomenon may relate to the combined action of piezoelectric effect, extension and contraction of ionic bonds, and turning-direction polarization. The sensitivity of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> to the change in permittivity was analyzed by theoretical simulation in order to reveal the effects of modification in θ and p on the T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> change in stress of rock. For rocks with permittivity ε = 7 - i0.3, the most and least sensitive θ are near 52° at h polarization and 69° at v polarization, respectively. Finally, the significance of these results was discussed.

A novel method to prioritize RNAseq data for post-hoc analysis based on absolute changes in transcript abundance.

The use of fold-change (FC) to prioritize differentially expressed genes (DEGs) for post-hoc characterization is a common technique in the analysis of RNA sequencing datasets. However, the use of FC can overlook certain population of DEGs, such as high copy number transcripts which undergo metabolically expensive changes in expression yet fail to exceed the ratiometric FC cut-off, thereby missing potential important biological information. Here we evaluate an alternative approach to prioritizing RNAseq data based on absolute changes in normalized transcript counts (ΔT) between control and treatment conditions. In five pairwise comparisons with a wide range of effect sizes, rank-ordering of DEGs based on the magnitude of ΔT produced a power curve-like distribution, in which 4.7-5.0% of transcripts were responsible for 36-50% of the cumulative change. Thus, differential gene expression is characterized by the high production-cost expression of a small number of genes (large ΔT genes), while the differential expression of the majority of genes involves a much smaller metabolic investment by the cell. To determine whether the large ΔT datasets are representative of coordinated changes in the transcriptional program, we evaluated large ΔT genes for enrichment of gene ontologies (GOs) and predicted protein interactions. In comparison to randomly selected DEGs, the large ΔT transcripts were significantly enriched for both GOs and predicted protein interactions. Furthermore, enrichments were were consistent with the biological context of each comparison yet distinct from those produced using equal-sized populations of large FC genes, indicating that the large ΔT genes represent an orthagonal transcriptional response. Finally, the composition of the large ΔT gene sets were unique to each pairwise comparison, indicating that they represent coherent and context-specific responses to biological conditions rather than the non-specific upregulation of a family of genes. These findings suggest that the large ΔT genes are not a product of random or stochastic phenomenon, but rather represent biologically meaningful changes in the transcriptional program. They furthermore imply that high abundance transcripts are associated with particularly cellular states, and as cells change in response to internal or external conditions, the relative distribution of the abundant transcripts changes accordingly. Thus, prioritization of DEGs based on the concept of metabolic cost is a simple yet powerful method to identify biologically important transcriptional changes and provide novel insights into cellular behaviors.

Evaluation and Regional Calibration of Solar Radiation Prediction Models in Southern Spain

AbstractSolar radiation (Rs) is a very important variable in agricultural meteorology, but it is measured at a very limited number of weather stations. In addition, Rs data are usually low quality because of to sensor failure or lack of calibration. Rs can be predicted from other meteorological measurements (e.g., air temperature), but the accuracy of these methods needs to be tested. In this work, the mechanistic model of Hargreaves-Samani, three modified versions of this model, a modified Bristow-Campbell equation, and the Mahmood-Hubbard model were evaluated at 56 sites in the Andalusian region in southern Spain. All of these methods use the daily temperature range of the air (ΔT=Tmax-Tmin) to estimate Rs. The estimated values of Rs were compared with measurements of Rs to check their suitability. The accuracy of the methods was primarily affected by the magnitude of ΔT, with larger ΔT resulting in a greater accuracy. Finally, the parameter of the Hargreaves-Samani equation (Kr) was adjusted to regiona...

Magnetothermal cooling with a phase separated manganite

We show that temperature of a current (I=20 mA) carrying manganite (Nd0.5Ca0.5Mn0.93Ni0.07O3) in presence of a magnetic field (H) decreases abruptly as much as ΔT=45 K (7 K) accompanied by a steplike decrease in magnetoresistance at a critical value of H when the base temperature is 40 K (100 K). The magnitude of ΔT and the position of magnetoresistance step decrease toward lower H with decreasing amplitude of the current. We discuss possible origins of the current and magnetic-field driven temperature change which may find applications in magnetothermal refrigeration besides magnetocaloric effect.

Nucleation energetics during homogeneous solidification in elemental metallic liquids

The solidification of a liquid by nucleation is an important first order phase transition process. It is known that in order for elemental liquids to solidify homogeneously, it is necessary to supercool the liquid to a characteristic temperature (TUC) below the thermodynamic melting point (TMP). Approximately 60 years ago Turnbull [J. Appl. Phys. 21, 1022 (1950)] established the empirical rule that ΔT∗=|TUC−TMP| is approximately given by 0.18 TMP for several elemental metallic liquids. We show here that the magnitude of ΔT∗ and TUC for the metals can be accurately predicted from classical nucleation theory (CNT) provided the excess volume resulting from the density difference between liquid and solid be accounted for. Specifically, the density change accompanying the formation of a microscopic nucleus of the solid from the liquid results in a volume change in the surrounding liquid. When this is included in the free energy calculations within CNT, the resulting predictions for ΔT∗ and TUC for several metals with TMP ranging from ∼200 to 2900 K are in very good agreement with experimental measurements. This theory also shows that there is a universal character in the minimum nucleation barrier energy and the critical radius. The minimum barrier energy occurs at temperature TN∼0.27 TMP for all the elemental liquids investigated, while the temperature dependencies of the barrier energy and the critical radius appear identical when expressed as a function of the scaled temperature TUC/TMP.

Implications of the oceanic thermal skin temperature deviation at high wind speed

Extensive oceanographic and atmospheric observations obtained during three independent experiments in the Atlantic Ocean are used to demonstrate the relationship between wind speed and the temperature deviation ΔT, which is defined as the sea surface skin temperature (SSST) minus the subsurface bulk sea surface temperature (BSST). At wind speeds &lt;6 m s−1, the variability of ΔT increases because thermal stratification complicates the measurement and interpretation of ΔT: extreme ΔT magnitudes of &gt;1.5 K are common during periods of high insolation. The variability of ΔT at night is reduced and extreme cool skin temperatures of &lt; −0.5 K are recorded. In all cases, at wind speeds &gt;6 m s−1, the variability of ΔT is diminished and the mean value of ΔT approximates a cool bias of −0.14 K±0.1 K. We conclude that BSST measurements obtained at wind speeds &gt;6 m s−1, when corrected for a small ( −0.14 K) cool bias, are representative of the SSST and can be used with confidence to validate satellite derived SSST. When the wind speed is &lt;6 m s−1 and the magnitude of ΔT is high, in situ radio metric SSST measurements are mandatory to validate satellite derived SSST.

Light transmittance as an index of cell volume in hippocampal slices: optical differences of interfaced and submerged positions

Light transmittance (T) in the CA1 region of hippocampal slices was measured during exposure to media of various osmolarities to determine the utility of optical measurements as an index of changes in cell volume. In slices positioned at the gas-liquid interface, hypo-osmotic medium consistently produced a decrease in T and hyperosmotic medium produced an increase in T. The magnitude of ΔT was graded as a function of the strength of osmotic change. All changes in T were reversible upon return to isosmotic medium. In contrast, osmotically induced changes in T in submerged slices were consistently opposite in direction to those observed in slices at the interface. The magnitude and direction of ΔT could be altered by systematic variation of the level of the bathing medium within the same chamber, indicating that both extrinsic optical properties of various interfaces, such as refraction and reflection, and intrinsic optical properties of the tissue contribute to the observed T. Spectral measurements eliminated the possibility that osmotically induced ΔT was the result of changes in light absorbance by intrinsic chromophores such as cytochromes or hemoglobin. The results show that measurements of ΔT can be a useful index of changes in cell volume in brain slices, provided that the level of the bath remains constant.

The glass transition of organic liquids confined to small pores

The glass-transition temperatures, T g, of organic liquids confined to small pores were studied by differential scanning calorimetry (DSC). The T g was measured as a function of pore size in controlled pore glasses (CPG) having pore diameters in the range of 40–730 Å. The surface of the glass was treated with hexamethyldisilazane to promote wetting by the organic liquids studied ( o-terphenyl and benzyl alcohol). Glasses formed in the pores had a lower T g than in the bulk and the reduction in T g increased as the pore size decreased. For example, the depression of the glass transition temperature, ΔT g, of benzyl alcohol in 40 Å and 85 Å pores was 7.2 K and 3.1 K, respectively. The magnitude of ΔT g also depends on the material; e.g. for o-terphenyl in the 85 Å pores, ΔT g was 8.8 K versus 3.1 K for benzyl alcohol. In general, it was noted that ΔT g was considerably less than for the depression of the crystalline melting point, ΔT m, studied in related work. For example, for benzyl alcohol in the 85 Å pores, ΔT m was ∼ 25 K and ΔT g was ∼ 3 K.

Fine Bubble Aeration. Mathematical Modeling of Time-Dependent Operation

Abstract The operation of fine bubble aeration columns in the time-dependent mode is modeled. The kinetics of mass transfer between the solution and the rising bubbles is included by means of a time-constant approach. The magnitude of Δt is limited by the requirement that uw · Δt/Δx be less than 1 (uw is the linear velocity of the aqueous phase); the magnitudes of the mass transfer time constant and the rise velocity of the bubbles do not affect the maximum value of Δt which can be used. The time constant for mass transfer is the reciprocal of the least positive eigenvalue of a suitably chosen diffusion problem. The effects of influent flow rate, number of compartments into which the column is partitioned, bubble boundary layer thickness, and Henry's constant for the volatile solute are examined. Transient effects associated with startup and with concentration pulses in the influent are studied.