I review the observational challenges of finding post T Tauri stars (PTTS), defined here as low-mass, pre–main-sequence stars with ages of 107–108 yr. Such stars are difficult to find because they are less active than younger T Tauri stars, and they may not be associated with molecular gas. They are useful for studying the evolution of circumstellar disks and stellar activity between the 106-yr...

Physiological effect of six levels of water stress (0, -0.1, -.03, -0.6, -0.9 and -1.2 MP) was studied on seed germination and plumule as well as radicule growth length in three species namely: Agropyron elongatum, Agropyron desertourm and Secale montanum. Polyethylene glycol (PEG) was used to provide appropriate water potentials. A total of 100 seeds in four replications (Petri dishes) were so...

Agropyron Gaertn. is the most important genus in Triticeae (Poaceae), which includes many forage grasses with high economic value. The genetic diversity and relationships of 36 accessions from five crested wheatgrass species were analyzed by gliadin markers. A total of 54 product bands were detected after acid polyacrylamide gel electrophoresis (A-PAGE), of which 100% were polymorphic. The gene...

We consider the problem of the apparent lack of old T Tauri stars in low-mass star forming regions in the framework of the standard model of low-mass star formation. We argue that the similarity between molecular cloud lifetime and ambipolar diffusion timescale implies that star formation does not take place instantaneously, nor at a constant rate. We conclude that the probability of finding a ...

this study was conducted to investigate allelopathic effect of the essential oil of artemisia herba-alba asso., on seed germination characteristics of  agropyron desertorum and agropyron cristatum in a laboratory experiment. essential oil was extracted from the aerial parts of artemisia herba-alba using a clevenger-type apparatus. the volatile chemical compositions of artemesia herba-alba were ...

Magnesium Concentration in Agropyron desertorum Fertilized with Mg and 1st H. F. Mayland and D. L. Grunes2 of humid pastures with N and K often increases the i id of tetany 3 4 nc ence ( , 4). Grass tetany, a Mg deficiency in ruminants, is responsible for large economic losses throughout temperate regions. Significant livestock losses occur in the semiarid western United States primarily when l...

We compute the rotation profile of a T Tauri star from the balance between the different components of the Reynolds stress and the meridional circulation. We first use a simple model to study the influence of the meridional flow on the differential rotation and vice versa. A more realistic model is then presented, which includes the stratification of the turbulence derived from a stellar model....

Pre-main-sequence stars are observed to be surrounded by both accretion flows and some kind of wind or jet-like outflow. Recent work by Matt and Pudritz has suggested that if classical T Tauri stars exhibit stellar winds with mass loss rates about 0.1 times their accretion rates, the wind can carry away enough angular momentum to keep the stars from being spun up unrealistically by accretion. T...