Coupling and decoupling processes in monsoonal surface layer using MONTBLEX-90 tower data

ABSTRACT. MONI'BLEX-90 data of Varanasi and Jodhpur have been used to study the physical processes in the surface layer. The results show that turbulent transfer of heat, momentum and moisture commence at an average eddy viscosity of an order of magnitude 5.13 × 10-1 J -s kg-1 during rainy day. In absolutely stable case, eddy viscosity may be equal to 4.94 × 10-4 J-s kg-1 or less to decouple surface layer from rest of the planetary boundary layer for extinction of the turbulent transfer of fluxes. These results were based on 8m and 15m meteorological tower observations and surface soil temperature using analytical solution of Byun (1990) and K theory. It was found that the surface layer is decoupled only in case of stability of Class - A because bulk Richardson number is greater than zero and corresponding stability parameter is positive.

Micrometeorological Aspects of Spraying within a Surface Inversion.

Pesticide applications during surface inversions can lead to spray drift causing severe damage up to several kilometers off-target. Current regulations in Australia prohibit spray application of certain agricultural chemicals when hazardous surface inversions exist. This severely limits spray opportunities.Surface inversions can be classified as weakly or strongly stable. In the weakly stable case, moderate to strong turbulent mixing is not supportive of long-distance concentrated drift. In the very stable case, weak turbulent mixing can support the transport of high concentrations of fine material over long distances. A review of the literature and our analyses indicate that if the turbulence, as measured by the standard deviation of the vertical wind speed σw, is greater than about 0.2 m/s then turbulence-driven mixing and dispersion is moderate to strong and conversely if σw is less than about 0.2 m/s then turbulence-driven mixing and dispersion is weaker (an order of magnitude). The concept of maximum downward heat flux as a natural division between the regimes is applied within Monin-Obukhov Stability Theory and it is shown that the observed mean σw of 0.2 m/s aligns with the ridge line of maximum heat flux in stable conditions. The level of turbulence in the weakly stable regime is comparable to the turbulence typically observed in near-neutral conditions which are recommended under current guidelines as suitable for spraying and is therefore seen as an acceptable prerequisite to avoid non-dispersive spraying conditions.

SARS-Cov-2 Viral Load as an Indicator for COVID-19 Patients' Hospital Stay

Background/objective: The novel coronavirus disease 2019 (COVID-19) pandemic has posed a global threat to public health. An objective strategy is quintessential to handle resources prudently. This study assessed the utility of the quantitative polymerase chain reaction (qPCR) cycle of threshold (Ct) to evaluate the severity of the COVID-19 infection. The study also assessed the duration of the hospital and the management of healthcare resources. Methods: This cross-sectional study was carried out among 306 patients admitted to COVID-19 care centers in the Kingdom of Bahrain from 20th March 2020 to 5th April 2020. Standard qPCR was used to estimate the viral load, and data was analyzed to investigate the relationship between Ct values and various variables. Results: Out of 306 patients, two fatalities, one active stable case, and 303 recovered cases were reported. Ct value was negatively associated (P value <0.001) with the length of hospital stay. Viral clearance was also inversely associated with the Ct values. Conclusion: Ct value was inversely associated with the duration of hospital stay (and time to viral clearance); the higher Ct value was indicative of a faster time to viral clearance. This association could aid in the management of both the infection and resources. Keywords: Bahrain; COVID-19; Length of Stay; Public Health; Resource Allocation; Viral Load

Meso- to micro-scale modeling of atmospheric stability effects on wind turbine wake behavior in complex terrain

Most detailed modeling and simulation studies of wind turbine wakes have considered flat terrain scenarios. Wind turbines, however, are commonly sited in mountainous or hilly terrain to take advantage of accelerating flow over ridgelines. In addition to topographic acceleration, other turbulent flow phenomena commonly occur in complex terrain, and often depend upon the thermal stratification of the atmospheric boundary layer. Enhanced understanding of wind turbine wake interaction with these terrain-induced flow phenomena can significantly improve wind farm siting, optimization, and control. In this study, we simulate conditions observed during the Perdigão field campaign in 2017, consisting of flow over two parallel ridges with a wind turbine located on top of one of the ridges. We use the Weather Research and Forecasting model (WRF) nested down to micro-scale large-eddy simulation (LES) at 10 m resolution, with a generalized actuator disk (GAD) wind turbine parameterization to simulate turbine wakes. Two case studies are selected, a stable case where a mountain wave occurs and a convective case where a recirculation zone forms in the lee of the ridge with the turbine. The WRF-LES-GAD model is validated against data from meteorological towers, soundings, and a tethered lifting system, showing good agreement for both cases. Comparisons with scanning Doppler lidar data for the stable case show that the overall characteristics of the mountain wave are well-captured, although the wind speed is underestimated. For the convective case, the size of the recirculation zone within the valley shows good agreement. The wind turbine wake behavior shows dependence on atmospheric stability, with different amounts of vertical deflection from the terrain and persistence downstream for the stable and convective conditions. For the stable case, the wake follows the terrain along with the mountain wave and deflects downwards by nearly 100 m below hub-height at four rotor diameters downstream. For the convective case, the wake deflects above the recirculation zone over 50 m above hub-height at the same downstream distance. This study demonstrates the ability of the WRF-LES-GAD model to capture the expected behavior of wind turbine wakes in regions of complex terrain, and thereby to potentially improve wind turbine siting and operation in hilly landscapes.

Influence of the initial orbital period and accretion efficiency on the low-mass binary evolution

This paper presents detailed evolutionary models of low-mass binary systems (1.25 + 1 M?) with initial orbital periods of 10, 50 and 100 days and accretion efficiency of 10%, 20%, 50%, and a conservative assumption. All models are calculated with the MESA (Modules for Experiments in Stellar Astrophysics) evolutionary code. We show that such binary systems can evolve via a stable Case B mass transfer into long period helium white dwarf systems.

SARS-Cov-2 Viral Load as an Indicator for COVID-19 Patients’ Hospital Stay

Background/objectiveThe novel coronavirus disease 2019 (COVID-19) pandemic poses a global threat to the public health. There is a challenge in measuring the patient’s length of hospital stay and managing the healthcare resources to handle the situation successfully. Our objective is to use the qPCR cycle of threshold (Ct) as a tool in evaluating the severity of the infection and hence the length of hospital stay to better utilize and manage the healthcare resources.MethodsThis cross sectional study was carried out on 306 patients who admitted to COVID-19 care centers in Kingdom of Bahrain from 20th March 2020 to 5th April 2020. Standard qPCR was used to estimate the viral load and data were analyzed to investigate the relationship between Ct values and various variables.ResultsOut of 306 patients, 2 deaths, 1 active stable case and 303 recovered cases were reported. Ct value was significantly and negatively associated (P value <0.001) with length of hospital stay. The viral clearance was also inversely associated with the Ct values.ConclusionCt value was inversely associated with hospital stay duration (and time to viral clearance), higher the Ct value is indicative of faster time to viral clearance. This association could help to better manage the infection and resources allocation.

Prognosticating the spread of covid-19 pandemic based on optimal arima estimators

Background: COVID-19 cases have been reported as a global threat and several studies are being conducted using various modelling techniques to evaluate patterns of disease dispersion in the upcoming weeks. Here we propose a simple statistical model that could be used to predict the epidemiological extent of community spread of COVID-19from the explicit data based on optimal ARIMA model estimators. Methods: Raw data was retrieved on confirmed cases of COVID-19 from Johns Hopkins University (https://github.com/CSSEGISandData/COVID-19) and Auto-Regressive Integrated Moving Average (ARIMA) model was fitted based on cumulative daily figures of confirmed cases aggregated globally for ten major countries to predict their incidence trend. Statistical analysis was completed by using R 3.5.3 software. Results: The optimal ARIMA model having the lowest Akaike information criterion (AIC) value for US (0,2,0); Spain (1,2,0); France (0,2,1); Germany (3,2,2); Iran (1,2,1); China (0,2,1); Russia (3,2,1); India (2,2,2); Australia (1,2,0) and South Africa (0,2,2) imparted the nowcasting of trends for the upcoming weeks. These parameters are (p, d, q) where p refers to number of autoregressive terms, d refers to number of times the series has to be differenced before it becomes stationary, and q refers to number of moving average terms. Results obtained from ARIMA model showed significant decrease cases in Australia; stable case for China and rising cases has been observed in other countries. Conclusion: This study tried their best at predicting the possible proliferate of COVID-19, although spreading significantly depends upon the various control and measurement policy taken by each country.

Tempered relaxation equation and related generalized stable processes

Fractional relaxation equations, as well as relaxation functions time-changed by independent stochastic processes have been widely studied (see, for example, [21], [33] and [11]). We start here by proving that the upper-incomplete Gamma function satisfies the tempered-relaxation equation (of index ρ ∈ (0, 1)); thanks to this explicit form of the solution, we can then derive its spectral distribution, which extends the stable law. Accordingly, we define a new class of selfsimilar processes (by means of the n-times Laplace transform of its density) which is indexed by the parameter ρ: in the special case where ρ = 1, it reduces to the stable subordinator. Therefore the parameter ρ can be seen as a measure of the local deviation from the temporal dependence structure displayed in the standard stable case.