جستجوی مقالات مرتبط با کلیدواژه « relative humidity » در نشریات گروه « فیزیک »

In present work, zinc oxide (ZnO) nanorods were synthesized by a simple hydrothermal method and its methane gas sensing features was studied under different gas concentrations and various relative humidity at room temperature. ZnO nanorods characterization investigated by X-ray diffraction (XRD) and Field effect scanning electron microscopy (FE-SEM). The results were showed the wurtzite phase of the crystallized hexagonal structure with porous architecture. A high response of 77.1% was obtained under 0.15 vol% methane gas concentration at 30% relative humidity, while a low response of 32.2% was achieved toward 0.037 vol% methane gas level at 90% relative humidity. Moreover, the low response/recovery time of 95.4/45.9 s was obtained under 0.15 vol% gas concentration. The solid state sensor of the ZnO nanorods displayed high response and good selectivity to methane gas than that other air components at environmental conditions. Finally, the methane gas sensing mechanism of the ZnO nanorods sensor was discussed as well.

Atmospheric visibility is a key factor in everyday life mainly in aviation, industry and surface traffic. It has been defined as the greatest distance at which an observer can just see a black object viewed against the horizon sky which is known as the visual range. Furthermore, light extinction which is mostly due to absorption and scattering effects of aerosols in the atmosphere, can be calculated from visual range using Koschmieder formula. Visibility and extinction have similar units. In a non-polluted atmosphere, visibility ranges from 145 to 225 km, and in normal atmospheric condition it ranges from 10 to 100 km; yet in polluted areas it can be remarkably low down. Visibility is regularly measured at synoptic meteorological stations all over the world as a standard meteorological parameter. Skilled observers have been measuring the visual range using individual markers at known distance from the meteorological location against the horizon sky.
In this paper, airport visibility data for the period of 1970 to 2010 are examined in the four busiest airports in Iran including Tehran-Mehrabad, Mashhad, Shiraz and Isfahan. All data from the four airport stations have been used for analyzing the temporal variations. The analyses are based on daily average measurements, i.e. the average of 9, 12 and 15 UTC data. Midday values are usually used in studies of this kind as they are more representative of regional visibility levels, because early morning radiation fogs and high relative humidity which may reflect only the local environment would regularly have dispersed by midday. The historical trends of extinction coefficient based on visual range for the four aforementioned airports are computed. Trend is determined by a least square regression analysis of midday average extinction. In general, an upward atmospheric extinction trend is seen for all stations. Tehran-Mehrabad airport has the most increasing trend. The extinction was around 0.3 km-1 in early 70’s but it increases in the present and reaches up to around 0.4 km-1.
Airport visibility data that inherently undervalue the true visibility are most appropriately summarized by cumulative percentiles. The Nth cumulative percentile is the visibility that is equal or exceeds N percent of the time. Visibility data lends itself well to the treatment in this manner. Daily visibility observations are investigated during the last four decades at 10th and 90th cumulative percentiles to show the threshold visibility in each airport. The 10th and 90th cumulative percentiles of visibility are used to identify the frequency of ‘good’ and ‘poor’ visibilities, respectively. Results show that there is not a distinctive difference between the 40-year poor or good visibilities among all stations. However, Tehran airport has the least quantity in visual range than the other airports. The good visibility has the largest threshold value of around 20 km in Shiraz and Mashhad airports.
Monthly comparison of extinction for 40 years, shows that there is an about 2-km difference between winter months and the rest of the year. It can be due to the effect of weather or concentration of pollutants in different months. The results of correlation analysis indicate that the difference may be due to the variation in relative humidity value in different months. To minimize the effect of humidity, the days with relative humidity value of above 70 percent and cloudiness of above 4/8 of sky are removed from the visibility trend analysis. Detailed analyses show that the trends of the screened days are nearly parallel to the trends of raw data, but with a slight difference in each airport. Increase in extinction is also observed since 1970 when absolute values of extinction change. The extinction trend is not significantly changed in Tehran and Isfahan airport which may emphasis on the role of air pollution on atmospheric extinction.

Solar radiation, a renewable energy, is the most effective, economical and the safest source of energy which has the potential to be the major source of energy in near future. As a result optimum use of solar energy needs precise siting of solar site. The most accurate way of measuring solar radiation is using pyranometer which is not so popular around the world because of its high charge and lack of facilities. Therefore, nowadays the researchers use climatic and environmental parameters to estimate solar radiation (Belcher and DeGaetano, 2007: 10). Although meteorological parameters, namely relative humidity, cloudiness percentage, temperature and hours of sunshine affect the amount of earth received radiation, research has proved that hours of sunshine is the most effective factor on receiving radiation; it has been proved in the model of linear regression of Angstrom in the way of FAO- penman-Monteith method. Approximately 1445"> of Iran area, having 240-250 sunny days yearly is capable of producing a lot of solar energy. Angstrom model (1924) was made based on the relationship between received radiation and sunshine hours (Angstrom, 1924: 122). It was revised in 1940 (Prescott, 1940: 115). Sabziparvar (2008: 1002) believed that out of various studies, aiming at presenting a simple equation to estimate solar radiation in central arid region of Iran, Sabagh method has the least number of errors. This study aimed at finding the effect of climatic parameters, especially relative humidity on the amount of total received radiation between Minab and Bandarabas stations. In the present research daily data of synoptic meteorology stations of Minab and Bandarabas during the temporal period of 2006-2009 were studied in order to estimate not only the amount of received radiation but also the effect of relative humidity on radiation decrease in real standard mode. The aforesaid stations were chosen due to their similar features like the height difference less than 20m altitude, 4◦ latitude while different distance from the source of moist; Oman sea and Persian gulf. The amounts of solar radiation was estimated, using Bird and Hulstrom model, by considering both locative features (altitude, latitude and longitude) and climatic features (relative humidity, temperature, pressure, sunshine hours, sun height, atmosphere albedo, particle absorbing, earth albedo, atmosphere mass, ozone absorption and Rayleigh distribution). Moreover in order to estimate the effect of relative humidity on total received radiation decrease the values of climatic variables were supposed stable in standard mode. Finally daily and monthly values were presented as tables and graphs. Discussion and The findings of this study showed that the maximum amount of total received radiation of Minab station was in June, 14.48 MJ/m-2/ d-1, while for Bandarabas station was in May, 13.97 MJ/m-2/ d-1. In fact this difference during a month is due to the difference in the amount of relative humidity. In other words, high radiation of Bandarabas station in May is the result of both its less relative humidity than warm months and high solar height. As summer comes radiation decreases, for the amount of moist in atmosphere increases. The lowest amount of total received radiation of Bandarabas is in cold months in which slight angle of sun are the major reason for low received radiation. Besides total received radiation of Minab during winter is less than Bandarabas which is the result of more moist in June. Minab station received maximum amount of solar radiation coinciding with highest height of sun. In addition, sunshine hour decrease leads to minimum total received radiation during cold month. The most considerable point is total received radiation of Minab which is less than Bandarabas, for relative humidity of Minab is more than Bandarabas. Studying the effect of relative humidity on standard atmosphere showed that the amounts of total received radiation of the stations are not stable: it varies both in January form maximum amount, 6.4 MJ/ m-2/ d-1, with relative humidity of 10% to minimum amount, 5.6 MJ/ m-2/ d-1 with relative humidity of 90%, and in June from maximum amount, 18.4 MJ/m-2/ d-1 with relative humidity of 10% to minimum amount, 15.8 MJ/ m-2/ d-1, with relative humidity of 90%. As a matter of fact the amount of relative humidity in average mode has more effect on total received radiation compared with its low or high mode. Moreover it is necessary to say that the amount of total received radiation in different hours is 4 MJ/ m-2/ d-1, minimum, and 16 MJ/m-2/ d-1, maximum, considering the effect of relative humidity. Totally, it seems that Minab than BandarAbas station has more potential for energy production to Set Solar Sites because Minab station recive more radiation.

Ice can form on aircraft surface at 0° C or colder temperatures when liquid water is present. This can happen both on the ground and at the flight levels of the aircraft. Aircraft icing has not only an impact on flight safety but has also an economic impact. According to the report of research department of the FAA (Federal Aviation Administration)‎, from 1982 to 2001, 13% of accidents due to aircraft icing resulted in loss of human life, about 30 cases in 20 years. This research refers to case studies in Mehrabad airport during winter in order to determine the threshold values of some important indices in aircraft icing forecast. In the first case study, aircraft engine failed and emergency landing occurred due to aircraft icing. Second case study is considered because of domination of a very cold outbreak in northern parts of Iran and all Mehrabad flights were cancelled. In addition to study the synoptic and thermodynamic weather patterns, the relevant MM5 outputs including vertical velocity, liquid water content (LWC)‎ and relative humidity are surveyed and their thresholds are compared with other studies in this area including Ellrod and Bailey in 2007 and Henderson in 2006. Synoptic conditions are analyzed using GFS data with 1° resolutions in latitude and longitude directions (http://nomads.ncdc.noaa.gov/data.php)‎. The initial and boundary conditions come from the operational 12Z runs of global forecasting system (GFS)‎ of NCEP (National Center for Environmental Prediction)‎ for MM5 (Meso scale Model version 5) model(Dudhia 1993; Grell et al. 1994) to survey the NWP model outputs. Satellite images as the other reference in this study, are taken from METEOSAT-7 which provides one image every 30minutes over Iran. Thermodynamic charts are drawn by RAOB software using Mehrabad station upper air sounding data to determine the threshold values of instability indices such as LI, KI, SI, and SWEAT. The most important results of this research show that large scale patterns are not a suitable factor to determine the type and severity of icing. Relative humidity and vertical velocity as the outputs of the MM5 regional numerical weather prediction model does have a rather good consistence with the observations and their thresholds are quite similar with other thresholds gained from the other parts of the world and the small differences can be due to topographical and boundary conditions in the regional model. The liquid water content values do not match the available thresholds and require more research. Thermodynamic charts show temperature and dew point deficits values can show the aircraft icing conditions but the thermodynamic indices such as LI, KI, SI, and SWEAT are not suitable and did not satisfy icing conditions. It can be said that due to shallow stratiform clouds which are reported in Mehrabad station observations provides threshold values so that the dew point deficit is less than 3°C, temperature between zero and -10°C, vertical velocity -0.2 hPa/s, relative humidity more than 75% in 700 hPa level are good diagnosis in the first guess in aircraft icing and they make easy icing forecast for the Mehrabad airport area.