Modification of the Penman method for computing bare soil evaporation

The Penman equation, which calculates potential evaporation, was modified by Staple (1974, Soil Science Society of America Proceedings 38 : 837) to include in it the relative vapour pressure h_s of an unsaturated soil to predict actual evaporation from a soil surface. This improved the prediction when the difference between the temperature of the soil surface and ambient air is relatively small. The objectives of this study were (i) to revise it further using the actual temperature of the soil surface and air to provide the upper boundary condition in computing evaporative flux from the soil surface and (ii) to determine the range of water content for which the modified form of the Penman equation is applicable. The method adopted was tested by a series of outdoor experiments with a clay soil. The method of Staple (1974) overestimated the rate of evaporation above the water content 0·14 m³ m^?3 (up to 30% deviation), whereas the new method agreed well with the measured rates (maximum 7% deviation). Below 0·14 m³ m^?3 water content, both methods underestimated, but the Staple (1974) method deviated more from the measured values: the deviations were above 70% and around 30% for the Staple (1974) and the new methods respectively. Although the new method provided accurate solutions for a wider range of water content from saturation to the lower limit of the liquid phase of a particular soil, the modification did not respond to the vapour phase of the soil moisture. Therefore, in the dry range (i.e. in the vapour phase in which the flow was entirely as vapour), either resistance models or a Fickian equation should be used. Although the effect of salinity on the measured rates was significant, the model erroneously calculated the same rates for both saline and non‐saline conditions. The effect of soil texture can easily be accounted by defining appropriate matric potential water content ψ_m(θ) and soil relative humidity water content h_s(θ) relationships. Copyright © 2007 John Wiley & Sons, Ltd.     

The deepest Hubble Space Telescope far-ultraviolet observations in the Large Magellanic Cloud

We present a new analysis of the deepest pure-ultraviolet (UV) observations with the highest angular resolution ever performed. A set of 12 exposures with the Hubble Space Telescope ( HST ) WFPC2 and F160BW filter obtained in parallel observing mode, which cover ∼12 arcmin² in the Large Magellanic Cloud (LMC), north of the bar and in the 'general field' region of the LMC, contain stars with far-UV monochromatic magnitudes as faint as 22 mag. The 198 detected UV sources represent an accumulated exposure of  ≥ 2 × 10⁴ s  and reveal stars as faint as   m _UV≃ 20 mag  . We combine these observations with deep UBVI charge-coupled device (CCD) imaging of the same region reaching as faint as   V ≃ 26 mag  , and reselect probable optical counterparts for the UV sources. After a two-stage search-and-analysis process, we detect robust counterparts for 129 stars. These are mostly upper main-sequence stars, from early B to early A spectral classes, with several F stars. We point out the lack of blue supergiants, which could have been easily detected in our survey. We measure a foreground extinction   E ( B − V ) ≃ 0.08 mag  by Galactic dust and a surface density of star formation rate twice the average Galactic value. These observations indicate that relatively recent star formation took place even off the bar of the LMC.     

3种塘鳢含肉率及肌肉营养成分分析与比较

对褐塘鳢(Oxyeleotris marmoratusBleeker)、尖头塘鳢(Eleotris oxycephalaTemminck et Schlegel)和线纹尖塘鳢(Oxyeleotris lineolatus)含肉率和肌肉营养成分进行了分析与比较。结果表明,含肉率以褐塘鳢为最高(51.26%),其次是尖头塘鳢(47.08%)和线纹尖塘鳢(42.53%)。3种圹鳢的蛋白质、灰分和水分含量基本一致,但粗脂肪的含量差异较大,最高为尖头塘鳢(0.33%),其次是褐塘鳢(0.23%)和线纹尖塘鳢(0.13%)。必需氨基酸含量大小依次是褐塘鳢(8.92%)>尖头塘鳢(8.83%)>线纹尖塘鳢(8.53%)。呈味氨基酸含量大小顺序是尖头塘鳢(7.72%)>褐塘鳢(7.65%)>线纹尖塘鳢(7.45%)。可见,三种塘鳢肉味鲜美、脂肪含量低、营养丰富,经济性状较好,值得推广养殖。     

Snow water content estimation from measured snow temperature

The vertical temperature profiles of snow and sea ice have been measured in the Arctic during the 2nd Chinese National Arctic Research Expedition in 2003(CHINARE2003).The high-resolution temperature profile in snow is solved by one-dimensional heat transfer equation.The effective heat diffusivity,internal heat sources are identified.The internal heat source refers to the penetrated solar radiation which usually warms the lower part of the snow layer in summer.By temperature gradient analysis,the zero level can be clarified quantitatively as the boundary of the dry and wet snow.According to the in situ time series of vertical temperature profile,the time series of water content in snow is obtained based on an evaluation method of snow water content associated with the snow and ice physical parameters.The relationship of snow water content and snow temperature and temporal-spatial distribution of snow water content are presented     

Study of the HII regions in the spiral galaxy NGC6384

The galaxy NGC6384 has been observed with an IPCS through Hα and [NII] narrow-band interference filters for direct imagery with the 2.6-m Byurakan telescope. We studied the main physical parameters of the identified 98 HII regions, their diameter and luminosity functions, as well the [NII]/Hα ratio distribution. The integrated distribution function of the HII region diameters can be well fitted by the exponential function. The characteristic diameter has the value (Do = 217 pc) predicted for a galaxy of its measured luminosity. The luminosity function of HII regions has a double power law profile with relatively shallow slope at low luminosities (α = −0.4), an abrupt turnover at logL(Hα) ≈ 38.75, and sharper slope at higher luminosities (α = −2.3). The correlation between the luminosity and diameter of HII regions confirms that in general they are constant density, radiation-bound systems. [NII]/Hα ratio data for the HII regions show that there is a negative radial gradient of [NII]/Hα. In the central region of the galaxy, nitrogen abundance is higher than in the periphery. The properties of the HII region population of this AGN galaxy do not differ significantly from the properties of the HII region population of the “normal” galaxies. Reexamining the location of the type Ia SN 1971L in the galaxy, we confirm that it lies on the spiral arm at about 8″.6 far from the closest HII region N 53 (F81). Such a location can be taken as proof that the progenitor of this SN does not belong to an old, evolved stellar population. Published in Astrofizika, Vol. 50, No. 4, pp. 519–533 (November 2007).     

The field of NGC 6397 as a test for Galactic models

Taking advantage of recent Hubble Space Telescope ( HST ) data for field stars in the region of the Galactic globular cluster NGC 6397, we tested the predictions of several Galactic models with star counts reaching a largely unexplored range of magnitudes, down to V ∼26.5. After updating the input stellar ( V − I ) colours, we found that the two-component Bahcall–Soneira (B&S) model can be put into satisfactory agreement with observations for suitable choices of disc/spheroid luminosity functions (LFs). However, if one assumes the disc LF of Gould, Bahcall and Flynn together with the spheroid LF of Gould, Flynn and Bahcall, there is no way to reconcile the predicted and observed V -magnitude distribution. We also analysed the agreement between observed and predicted magnitude and colour distributions for two selected models with a thick disc component. Even in this case there are suitable combinations of model parameters and faint-magnitude LFs that can give a reasonable agreement with observational star counts in both magnitude and colour. However, the above-quoted combination of Gould et al. LFs again gives predictions in clear disagreement with observations.