Evaluation of Air-Kerma and Absorbed Dose to Water for External Radiotherapy Beam Using Ionization Chamber

Radiotherapy is the most widely applied oncologic treatment modality utilizing ionizing radiation. A high degree of accuracy, reliability and reproducibility is required for a successful treatment outcome. Measurement using ionization chamber is a prerequisite for absorbed dose determination for external beam radiotherapy. Calibration coefficient is expressed in terms of air kerma and absorbed dose to water traceable to Secondary Standards Dosimetry Laboratory. The objective of this work was to evaluate the level of accuracy of ionization chamber used for clinical radiotherapy beam determination. Measurement and accuracy determination were carried out according to IAEA TRS 398 protocol. Clinical farmers type ionization chamber measurement and National Reference standard from Secondary Standards Dosimetry Laboratory were both exposed to cobalt-60 beam and measurement results compared under the same environmental conditions. The accuracy level between National Reference Standard and clinical radiotherapy standard was found to be −1.92% and −2.02% for air kerma and absorbed dose to water respectively. To minimize the effect of error and maximize therapeutic dose during treatment in order to achieve required clinical outcome, calibration factor was determined for air kerma (Nk) as 49.7 mGy/nC and absorbed dose to water ND, as 52.9 mGy/nC. The study established that radiotherapy beam measurement chain is prone to errors. Hence there is a need to independently verify the accuracy of radiation dose to ensure precision of dose delivery. The errors must be accounted for during clinical planning by factoring in calibration factor to minimize the systematic errors during treatment, and thereby providing enough room to achieve ±5% dose delivery to tumor target as recommended by ICRU.

Measurement of air kerma rate and ambient dose equivalent rate using the G(E) function with hemispherical CdZnTe detector

Since the room-temperature detector CdZnTe(CZT) has advantages in terms of detection efficiency,energy resolution, and size, it has been extensively used to detect X-rays and gamma-rays. So far, nuclear radiation detectors such as cerium chloride doped with lanthanum bromide(LaBr_3(Ce)), thallium doped with cesium iodide(sI(Tl)), thallium doped with sodium iodide(NaI(Tl)),and high-purity germanium(HPGe) primarily use the spectroscopy-dose rate function(G(E)) to achieve the accurate measurement of air kerma rate(K_a) and ambient dose equivalent rate(H*(10)). However, the spectroscopy-dose rate function has been rarely measured for a CZT detector. In this study, we performed spectrum measurement using a hemispherical CZT detector in a radiation protection standards laboratory. The spectroscopy-dose rate function G(E) of the CZT detector was calculated using the least-squares method combined with the standard dose rate at the measurement position. The results showed that the hemispherical CZT detector could complete the measurement of air kerma rate(K_a) and ambient dose equivalent rate(H*(10)) by using the G(E) function at energies between 48 keV and 1.25 MeV, and the relative intrinsic errors were, respectively, controlled within ± 2. 3 and ± 2. 1%.

The Comparison of Measurement Methods for Air-Kerma Rate in Narrow-Spectrum Series

The air-kerma is one of the most important physical quantities in ionizing radiation dosimetry. The measurement of airkerma rate in narrow-spectrum series is the basis to determine the radiation dose at protection level. In this article, the absolute measurement method is used to derive the standard air-kerma rate of the ISO 4037 narrow-spectrum series that ranges from 60 kV to 150 kV by a primary standard ionization chamber,it is used in direct comparison for air kerma. The indirect method is used to obtain the air-kerma rate by a secondary standard transfer ionization chamber named A5 chamber with calibration factors of the corresponding reference qualities. The results are very similar comparing between absolute and indirect methods for air-kerma rate, all the differences are within ±3.3%.

Feasibility study on determining the conventional true value of gamma-ray air kerma in a minitype reference radiation

A minitype reference radiation(MRR) with dimensions of only 1 m × 1 m × 1 m has been developed for the in situ calibration of photon dosimeters.The present work conducts a feasibility study on determining the conventional true value of gamma-ray air kerma at the point of test in the MRR.Owing to its smaller dimensions,the scattered gamma-rays in the MRR are expected to induce a non-negligible interference with the radiation field compared with conditions in the standard reference radiation stipulated by ISO4037-1 or GB/T12162.1.A gamma-ray spectrometer was employed to obtain the spectra of scattered gamma-rays within the MRR,and the feature components of the spectra were extracted by principal component analysis to characterize the interference of a dosimeter probe in the radiation field.A prediction model of the CAK at the point of test was built by least squares support vector machine based on the feature component data obtained from nine sample dosimeters under five different dose rates.The mean prediction error of the CAK prediction model was within ±4.5%,and the maximum prediction error was about ±10%.

Relationship between Formation Water Rate,Equivalent Penetration Rate and Volume Flow Rate of Air in Air Drilling

Formation water invasion is the most troublesome problem associated with air drilling. However, it is not economical to apply mist drilling when only a small amount of water flows into wellbore from formation during air drilling. Formation water could be circulated out of the wellbore through increasing the gas injection rate. In this paper, the Angel model was modified by introducing Nikurade friction factor for the flow in coarse open holes and translating formation water rate into equivalent penetration rate. Thus the distribution of annular pressure and the relationship between minimum air injection rate and formation water rate were obtained. Real data verification indicated that the modified model is more accurate than the Angel model and can provide useful information for air drilling.

Study on the Relationship between the Oceanic Nino Index and Surface Air Temperature and Precipitation Rate over the Kingdom of Saudi Arabia

Abnormal weather conditions and extreme weather existed over the Kingdom Saudi Arabia (KSA) through the last decades. The present paper investigates the relationship between the Oceanic Nino Index (ONI) and variability of surface air temperature and precipitation rate over KSA through the period from 1950 to 2015 year. The NCEP/NCAR Reanalysis of monthly data sets of the mean surface air temperature and precipitation rate for the domain of the KSA is used. In addition, El Nino3.4 monthly data through the period (1950-2015) are used. For that period, the data set of the three months moving average of Nino3.4 anomaly, Oceanic Nino index (ONI), is used and analyzed. The time series, anomaly and correlation coefficient techniques are used to analyze the data sets through the present study. The results revealed that the KSA climate parameters, temperature and precipitation rates are controlled by ONI mainly in the autumn and winter seasons.

Improvement of uniformity in cultivation environment and crop growth rate by hybrid control of air flow devices

A complete control type plant factory has high efficiency in terms of cultivation area by constructing vertical multiple layered cultivation beds.However,it has a problem of irregular crop growth due to temperature deviation at upper and lower beds and increases in energy consumption by a prolonged cultivation period.In this work,air flow rate inside a facility was improved by a hybrid control of air flow devices like air conditioning and air circulation fan with an established wireless sensor network to minimize temperature deviations between upper and lower beds and to promote crop growth.The performance of proposed system was verified with an experimental environment or Case A wherein air conditioning device was operated without a control algorithm and Case B wherein air conditioning and circulation fans were alternatively operated based on the hybrid control algorithm.After planting leafy vegetables under each experimental condition,crops were cultivated for 21 days.As a result,Case B wherein AC(air conditioning) and ACF(air-circulation fan) were alternatively operated based on the hybrid control algorithm showed that fresh mass,number of leaves,and leaf length for the crops grown were increased by 40.6%,41.1%,and 11.1%,respectively,compared to Case A.

Influence of Air Flow Rate on Functional Evaluation of Semicircular Canals

Objective To study the influence of unilateral air flow rate change on the result of caloric test.Materials and Methods The unilateral weakness(UW) index was calculated when the air flow rate was set at 6 L /min in both ears(called symmetric stimulation) and again when it was set at 6 L /min in left ear and 3 L /min in the right ear(called asymmetric stimulation).Each individual subject was tested with both symmetrical and asymmetrical stimulations.Paired t test was used to examine the differences between results from symmetrical and asymmetrical stimulations.Result UW index decreased in response to asymmetrical stimulation.Conclusion Unilaterally decreased air flow rate can produce indices suggesting ipsilateral UW,which can be misleading.

Measurements of Air-kerma in Mammography X-Ray Standard Using Free-air Chamber

Mammography x-rays standard is required to improve the quality of mammary machine and reduce the dose for w omen and staff. The molybdenum target x-rays machine is used as the radiation source and free-air cylindrical chamber is designed for detecting photon. Four standard radiation qualities are established w ith international standard documents as references. The Correction factors including air attenuation,scattered radiation,fluorescence,w all transmission,electron loss are studied in the four radiation quality. The uncertainty in absolute measurement of air-kerma includes air volume measurement of ionization chambers,current measurement,measurement of temperature and pressure,measurement of correction factors,physical constants and orientation of the reference distance. The relative combined standard uncertainty is 0.24%.

Study on the Relationship of Spray Rate to Air Pressure and Gravity Drop of Siphonic Nozzle

In order to further clarify the spraying performance of siphonic nozzle, the spray rate of siponic cone nozzle with aperture of 1.0 mm was determined at 15 different air pressure levels and 12 gravity drop levels, and DPS and SPSS were used to make the difference analysis and modeling, which clarified the relationship between the spray rate of the siphonic cone nozzle with aperture of 1.0 mm and air pressure and gravity drop, getting the regression equation of Y=406.854P＋ 1.904G＋77.524. The study could provide a theoretical basis for the optimization and improvement of plant protection spraying equipment.

Air pressure law of a reservoir constructed in karst sinkholes

Karst sinkholes with natural negative landform provide favorable conditions for the pumped storage reservoir construction for less excavation work.However,the construction of the reservoir would plug the natural karst channels for water and air,which would cause remarkable air pressure in karst channels when the groundwater level fluctuates.A large laboratory simulation test was carried out to study the air pressure variation of a reservoir built on the karst sinkhole.The air pressure in the karst channel and inside the model was monitored during the groundwater rising and falling process.Result showed that the variation of air pressure in the karst channel and the surrounding rock exhibited a high degree of similarity.The air pressure increased rapidly at the initial stage of water level rising,followed by a slight decrease,then the air pressure increased sharply when the water level approached the top of the karst cave.The initial peak of air pressure and the final peak of air pressure were defined,and both air pressure peaks were linearly increasing with the water level rising rate.The negative air pressure was also analyzed during the drainage process,which was linearly correlated with the water level falling rate.The causes of air pressure variation in karst channels of a pumped storage reservoir built on the karst sinkhole were discussed.The initial rapid increase,then slight decrease and final sudden increase of air pressure were controlled by the combined effects of air compression in karst channel and air seepage into the surrounding rock.For the drainage process,the instant negative air pressure and gradual recovering of air pressure were controlled by the combined effects of negative air pressure induced by water level falling and air supply from surrounding rock.This work could provide valuable reference for the reservoir construction in karst area.

NUMERICAL RESEARCH ON IMPACT OF AIR SYSTEM BLEEDING ON COMPRESSOR PERFORMANCE

Bled air from the high pressure compressor takes up 3%—5% in the air system.However,there are not many studies on the compressor performance after bleeding.By analyzing the low-speed single-stage compressors,six bleeding structures are presented according to their influence mechanism on the compressor performance,and five kinds of bleeding rate are applied to one of the structures.A numerical simulation is performed to study the influence of bleeding rates and structures on the compressor performance.The results show that for the stators with the large flow separation in the corner,bleeding a small amount of air from the end-wall region can improve the total pressure increase and the stability margin.Moreover there is an optimum value of the bleeding rate in the stator casing.

Influence of environmental conditions on airborne infection risk in ward

In order to study the influence of parameters on airborne transmitted diseases in a hospital ward,a pollutant decay equation and a Wells-Riley model are adopted to study the relationship between the airborne infection risk and the parameters such as the ventilation rate,the number of susceptible persons and the volume of the ward.The results show that the airborne infection risk can be reduced by increasing the ventilation rate.For two wards with the same air change per hour（ACH）but different volumes,the ventilation rate in a large room is higher than that in a small one.The number of the infected persons in the ward increases with the increase in the susceptible persons when the ACH is a constant.Therefore,the ventilation rate in the ward is not only estimated by the ACH but also related to the volume of the ward and the number of the susceptible persons.

Effect of Air Injector on the Performance of an Air-lift for Conveying River Sand

An air-lift has been more recently applied in the dredging, deep-seated beach placer mining and underground mining engineering. However, the influence and mechanism of various parameters on the air-lift performance are not quite clear, especially the influence of flow pattern on lifting efficiency. Focusing on the problems mentioned above, the key part of the air-lift （namely, the air injector） was proposed aimed to reduce friction loss in the inner pipe according to improving flow field performance, thus increase the lifting efficiency. The study of relative factors of the performance of an air-lift is performed and the river sand is used as simulation of underground ore bed. The total lifting height of the experimental system is 3 m, the water flux, mass flow of solid particles, concentration of particles and lifting efficiency are measured under the same submergence ratios by changing the air injector, which is divided into nine specifications of air injection in this research. The experimental results indicate that the optimal air flow rate corresponding to excellent performance of the air-lift can be obtained in the range of 35-40 m3/h. The air injection method has a great effect on the performance of the air-lift, the air injector with three nozzles is better than that in the case of one or two nozzles. Further more, the air injection angle and arrangement of air injection pipes also have great effect on the performance of an air-lift. The proposed research results have guiding significance for engineering application.

Study on NOx Formation in CH4/Air Jet Combustion

With the development of reaction kinetics and transfer science, the modeling of NOx formation plays more and more important roles in the protection of environment and the design of combustion reactors; in this case,turbulence-chemistry model and NOx formation model are the two most important aspects. For thermal NOx mechanism, this article studied the CH4/air system and applied a set of latest NO formation rate constants published at the Leed University which replaced the original model code in FLUENT to increase its precision on prediction of NO concentration. The realizable k-ε model, Reynold Stress model and standard k-ε model were also investigated to predict the turbulent combustion reaction, which indicated that the simulation results of velocities, temperatures and concentrations of combustion productions by the standard k-ε model were in good accordance with the experimental data. With the application of the simulation results to the experimental data to fit some important kinetic parameters in the equation of O atom model and revision of the equation later, this article obtained a new NO formation rate model. It has been proved that the prediction of the developed model coincides well with the measurements.

Effects of Photosynthetically Active Radiation and Air Temperature on CO_2 Uptake of Pterocarpus macrocarpus in the Open Field

Since trees and plants can absorb CO2, forests are widely regarded as a carbon sink that may control the amount of CO2 in the atmosphere. The CO2 uptake rate of plants is affected by the plant species and environmental conditions such as photosynthetically active radiation (PAR), temperature, water and nutrient contents. PAR is the most immediate environmental control on photosynthesis while air temperature affects both photorespiration and dark respiration. In the natural condition, PAR and temperature play an important role in net CO2 uptake. The effects of PAR and air temperature on the CO2 uptake of Pterocarpus macrocarpus grown in a natural habitat were studied in the present work. Due to many uncontrollable factors, a simple rectangular hyperbola could not represent the measured data. The data were divided into groups of 2oC intervals; CO2 uptake in each group may then be related to PAR by a rectangular hyperbola function. Using the obtained functions, the effect of PAR was removed from the original data. The PAR-independent CO2 uptake was then related to air temperature. Finally, the effects of PAR (I) and air temperature (Ta) on the CO2 uptake rate (A) were combined as: (-0.0575Ta2+2.6691Ta-23.264)I A= ——————————————— (-0.00766Ta2+0.40666Ta-3.99924) (-4.8794Ta2+227.13Ta-2456.9)+I

Microbiological assessment of indoor air of a teaching hospital in Nigeria

Objective:To investigate the quality of indoor air of different wards and units of Olabisi Onabanjo University Teaching Hospital, Sagamu, to ascertain their contribution to infection rate in the hospital.Methods:The microbial quality of indoor air of nine wards/units of Olabisi Onabanjo University Teaching Hospital, Sagamu, Nigeria was conducted. Sedimentation technique using open Petri-dishes containing different culture media was employed and samplings were done twice daily, one in the morning shortly after cleaning and before influx of people/patients into the wards/units and the other in the evening when a lot of activities would have taken place in these wards. Isolates were identified according to standard methods.Results:Results showed that there was a statistically significant difference(氈2= 6.0167) in the bacteria population of the different sampling time whereas it was not so for fungi population(氈2= 0.2857). Male medical ward(MMW) and male surgical general(MSG) recorded the highest bacterial and fungal growth while the operating theatre(OT) was almost free of microbial burden. The bacteria isolates were Staphylococcus aureus, Klebsiellasp., Bacillus cereus, Bacillus subtilis, Streptococcus pyogenes andSerratia marscenceswhile the fungi isolates includedAspergillus flavus, Penicilliumsp.,Fusariumsp.,Candida albicansandAlternariasp.Staphylococcus aureuswas the predominantly isolated bacterium whilePenicilliumsp. was the most isolated fungus.Conclusions:Though most of the microbial isolates were potential and or opportunistic pathogens, there was no correlation between the isolates in this study and the surveillance report of nosocomial infection during the period of study, hence the contribution of the indoor air cannot be established. From the reduction noticed in the morning samples, stringent measures such as proper disinfection and regular cleaning, restriction of patient relatives' movement in and out of the wards/units need to be enforced so as to improve the quality of indoor air of our hospital wards/units.

Adaptive Wall-Based Attachment Ventilation:A Comparative Study on Its Effectiveness in Airborne Infection Isolation Rooms with Negative Pressure

The transmission of coronavirus disease 2019(COVID-19)has presented challenges for the control of the indoor environment of isolation wards.Scientific air distribution design and operation management are crucial to ensure the environmental safety of medical staff.This paper proposes the application of adaptive wall-based attachment ventilation and evaluates this air supply mode based on contaminants dispersion,removal efficiency,thermal comfort,and operating expense.Adaptive wall-based attachment ventilation provides a direct supply of fresh air to the occupied zone.In comparison with a ceiling air supply or upper sidewall air supply,adaptive wall-based attachment ventilation results in a 15%–47%lower average concentration of contaminants,for a continual release of contaminants at the same air changes per hour(ACH;10 h^(-1)).The contaminant removal efficiency of complete mixing ventilation cannot exceed 1.For adaptive wall-based attachment ventilation,the contaminant removal efficiency is an exponential function of the ACH.Compared with the ceiling air supply mode or upper sidewall air supply mode,adaptive wall-based attachment ventilation achieves a similar thermal comfort level(predicted mean vote(PMV)of0.1–0.4;draught rate of 2.5%–6.7%)and a similar performance in removing contaminants,but has a lower ACH and uses less energy.

Surface warming patterns dominate the uncertainty in global water vapor plus lapse rate feedback

Climate feedbacks have been usually estimated using changes in radiative effects associated with increased global-mean surface temperature. Feedback uncertainties, however, are not only functions of global-mean surface temperature increase. In projections by global climate models, it has been demonstrated that the geographical variation of sea surface temperature change brings significant uncertainties into atmospheric circulation and precipitation responses at regional scales. Here we show that the spatial pattern of surface warming is a major contributor to uncertainty in the combined water vapour-lapse rate feedback. This is demonstrated by computing the global-mean radiative effects of changes in air temperature and relative humidity simulated by 31 climate models using a methodology based on radiative kernels. Our results highlight the important contribution of regional climate change to the uncertainty in climate feedbacks, and identify the regions of the world where constraining surface warming patterns would be most effective for higher skill of climate projections.

Recent changes in ground surface thermal regimes in the context of air temperature warming over the Heihe River Basin, China

Changes in ground surface thermal regimes play a vital role in surface and subsurface hydrology, ecosystem diversity and productivity, and global thermal, water and carbon budgets as well as climate change. Estimating spring, summer, autumn and winter air temperatures and mean annual air temperature（MAAT） from 1960 through 2008 over the Heihe River Basin reveals a statistically significant trend of 0.31 °C/decade, 0.28 °C/decade, 0.37 °C/decade, 0.50 °C/decade, and 0.37 °C /decade, respectively. The averaged time series of mean annual ground surface temperature（MAGST） and maximum annual ground surface temperature（MaxAGST） for 1972–2006 over the basin indicates a statistically significant trend of 0.58 °C/decade and 1.27 °C/decade, respectively. The minimum annual ground surface temperature（MinAGST） in the same period remains unchanged as a whole. Estimating surface freezing/thawing index as well as the ratio of freezing index to thawing index（RFT） in the period between 1959 and 2006 over the basin indicates a statistically significant trend of-42.5 °C-day/decade, 85.4 °C-day/decade and-0.018/decade, respectively.