Is IRAS 03134 + 5958 a Herbig-Haro object?     

K. V. K. Iyengar  T. N. Rengarajan 《Journal of Astrophysics and Astronomy》1986,7(3):237-240

The source IRAS 03134 + 5958 identified by Iyengar & Verma (1984) on the Palomar Observatory Sky Survey (POSS) prints with a nonstellar optical object with [P – R]≃ 5.3 ± 1.5 is near the edge of Lynds dark cloud No. 1384 and is either embedded in or behind the cloud. The galactic latitude of this source (b ^II = 2‡.3), its positionvis-a-vis the Lynds dark cloud, its nonstellar appearance, high [P – R] colour and its far-infrared spectrum, all suggest the possibility of its being a Herbig-Haro (HH) object. To test this possibility we undertook measurements of its proper motion and variability (two of the characteristic properties of HH objects). These yield μ_a = (3.6 ± 2.3) arcsec/century and μ_δ= (−1.2 ± 2.0) arcsec/century for its proper motion. The source reveals large variation in brightness between 1950 and 1954. Optical line studies of the source are required to confirm its classification as an HH object.  相似文献   

A model for the constant-head pumping test conducted in vertically fractured media     

J. M. Markle  R. K. Rowe  K. S. Novakowski 《国际地质力学数值与分析法杂志》1995,19(7):457-473

An analytical model for the constant-head pumping test is developed for a partially penetrating well that has a finite thickness skin, and intersects a single vertical fracture. In the model, the fracture is fully confined and flow occurs only in the fracture. The model is developed using Laplace transform and finite Fourier transform methods. The model is to be used for analysing well test data from vertically fractured media and for verifying numerical models. Dimensionless curves are used to study the effects of a finite thickness skin and a partially penetrating wellbore. In the presence of a finite thickness skin, or a partially penetrating wellbore, a typical flow response for the constant-head pumping test has three distinct periods of flow corresponding to small-, intermediate- and large-time. Small- and large-time approximations are presented for the model. For tests where the wellbore is fully penetrating, or the partial penetration ratio is known, these approximations can be used to analyse field data.  相似文献   

Drumlin formation in Southern Anglesey and Arvon,Northwest Wales     

Jane K. Hart 《第四纪科学杂志》1995,10(1):3-14

This is a study of Late Devensian drumlins formed in southern Anglesey and Arvon, northwest Wales. This area was affected by ice sheet coalescence when the Welsh ice sheet met with the lrish Sea ice sheet, and drumlins were formed once the two had coalesced. It is suggested that the drumlins were the result of net subglacial soft-bed erosion, and that they represent more resistant cores within the subglacial deforming layer. The drumlins have either gravel or till cores, and where the core was deformable, large-scale compressive glaciotectonic structures were seen (e.g. Dinas Dinlle) with local subglacial compression of –59%. Where the cores were more resistant (e.g. Lleiniog) these were not deformed but remained as more competent masses within the deforming layer. It is suggested that the less competent material flowed around the cores, some remaining as a thin carapace, but most of the material being removed down glacier, leaving the drumlins as erosional remnants. In northwest Wales there is a multi-till sequence that traditionally has been interpreted as having been deposited as the result of separate ice-sheet advances and retreats. However, in this study, it is suggested that the different tills were deposited as the result of ice-sheet coalescence, and that sites such as Dinas Dinlle do not show evidence of a major readvance in the retreat of the Devensian ice, but are indicative of continuously changing conditions within the subglacial deforming bed.  相似文献   

The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections     

S. P. Plunkett  G. E. Brueckner  K. P. Dere  R. A. Howard  M. J. Koomen  C. M. Korendyke  D. J. Michels  J. D. Moses  N. E. Moulton  S. E. Paswaters  O. C. St. Cyr  D. G. Socker  D. Wang  G. M. Simnett  D. K. Bedford  D. A. Biesecker  C. J. Eyles  S. J. Tappin  R. Schwenn  P. L. Lamy  A. Llebaria 《Solar physics》1997,175(2):699-718

We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s^-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s^-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702  相似文献   

The lost world of the olenid trilobites   总被引：1，自引：0，他引：1  

EUAN N. K. CLARKSON &  CECILIA M. TAYLOR 《Geology Today》1995,11(4):147-154

Trilobites of the Family Olenidae (Upper Cambrian to Upper Ordovidan) were closely tied to an oxygen-poor environment. They show a remarkable range of adaptations, testifying to a singular evolutionary plasticity.  相似文献   

Age distribution of open clusters as a function of their linear diameter and age-dependence of cluster masses     

A. K. Pandey  B. C. Bhatt  H. S. Mahra 《Astrophysics and Space Science》1987,129(2):293-302

From the well-observed data of star clusters, the age distribution of galactic clusters is obtianed as a function of their linear diameter and it is concluded that the observed age distribution of clusters for different linear diameter intervals within 1500 pc, is not seriously affected by the selection effects. If we assume that the rate of formation of clusters is constant, the lifetimes _1/2 of the clusters for different linear diameter intervals have been obtained and it is found that the clusters with a linear diameter in the range 0–1.9 pc have longer lifetimes than the clusters having linear diameters larger than 2.0 pc.Total masses of 57 clusters have been obtained using the catalogues of Piskunov (1983) and Myakutinet al. (1984). A study of age-dependence of cluster masses, based on the total masses of the clusters obtained in the present study and the cluster masses given by Bruch and Sanders (1983) and Lynga (1983b), shows that there is a decreasing trend in the total mass with the age, however, there is an increasing trend after the age of about 10⁸ yr. It is also concluded that the initial rate of formation of rich clusters was relatively higher than the present rate of formation.  相似文献   

A new period and period changes in VZ Hydrae     

R. K. Srivastava 《Astrophysics and Space Science》1987,133(1):71-79

A new period (P=2 _. ^d 9042997) of the eclipsing binary system VZ Hydrae has been given, which is based on all the available times of minima. The period based on the photoelectric epochs has also been presented. The O?C diagram and detailed period study of VZ Hya have been presented for the first time, and the period changes have been estimated in different portions of the O?C diagram. Significant period changes do not appear to have occurred in VZ Hya, however, the O?C diagram suggests that the period of the system shows a slow tendency to increase. Period changes of 10^?5 d (?) to 10^?7 d have occurred around the years 1933, 1971, and 1975. All four period changes are noted in the time-interval 1918 to 1978. Upward treands appear stronger than the declining trends. Secondary minima show larger fluctuations than the primary minima. The fluctuations of the O?C values around the zero-line of VZ Hya demands notice for searching out the cause of period variations such as the presence of a third body.  相似文献   

Spectroscopy of CN Orionis     

K. H. Mantel  H. Barwig  R. Haefner  R. Schoembs 《Astrophysics and Space Science》1987,131(1-2):501-505

Two outbursts and a minimum phase of the dwarf nova CN Orionis have been observed spectroscopically. One outburst was covered almost completely. The outburst spectra show periodic variations of the absorption lines which are interpreted with the formation of an elliptic disc during outburst stage. During decline from outburst a narrow emission line appears in the core of the broad H absorption line. The balmer decrement in the outburst phase is much steeper than in the minimum phase. This implies that during the outburst the emission line region is located more outward in the disk. The semi amplitude of the radial velocity curve was determined to K1=152 km/s±10 km/s. Using the photometric orbital period and an assumption about the inclination angle the approximate system parameters could be derived.Based on observations colleted at the European Southern Observatory, La Silla, Chile and at Mount Stromlo Observatory, Canberra, Australia.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.  相似文献   

Outmigration patterns in development transition of rural areas     

Kaistha KC 《Population geography : a journal of the Association of Population Geographers of India》1987,9(1-2):25-36

Using a broadened concept of migration, which includes circulatory migration and commuting, this paper maintains that the patterns of outmigration vary a great deal when the level of development of a rural area is treated as an independent variable. This study uses a stratified conditional sample of 192 households selected from 3 areas: 53 households from a low developed (LDL) area, 56 from a medium (MDL), and 83 from a high (HDL). Data were collected by personal observation, interview, and genealogical methods at both the household and individual level. The households are divided into 3 main categories: 1) non-migrating, 2) commuting only, and 3) migrating (which is further divided into migrating within and migrating outside the boundaries of the district). Results show that 1) 37.51% of household members neither commute nor have migrated outside the village; 2) using the narrow definition of migration, only 10% of males over age 15 migrate, while including commuting in the definition increases the percentage to 40; 3) proportions of non-migrating households decrease from 58.4% for the LDL, to 35.7% for the MDL, to 25.3% for the HDL area; 4) the proportion of commuting only households increases from 26.4% for the LDL, to 35.7% to the MDL, and 55.4% for the HDL area; 5) 15.2% of households in the LDL, 28.6% in the MDL, and 19.3% in the HDL area experience a permanent change in residence; 6) as development accelerates, the overall volume of outmigration increases; 7) the flow of migration from rural to rural areas is mostly limited to the MDL area, while cityward migration increasingly occurs on both LDL and HDL areas; 8) the median age of commuters increases with rising levels of development; and 9) almost all migrants from the LDL area are employed in low prestige occupations, most from the HDL area have higher prestige jobs, and those from the MDL area have both high and low prestige jobs.  相似文献   

Multiple windbreaks: An aeolean ensemble   总被引：1，自引：0，他引：1  

K. J. McAneney  M. J. Judd 《Boundary-Layer Meteorology》1991,54(1-2):129-146

Near-neutral measurements of the turbulent wind field within and above a sequence of 15 parallel windbreaks on a flat pastoral site are presented. The windbreak fences each had a porosity of 60% and were equally-spaced at 6 times their height (h = 2 m). The following conclusions seem justified for wind directions within 10 ° of the normal to the array:

1. Above the windbreaks (2h), mean windspeeds first decreased and then increased asymptotically to a value in equilibrium with the new surface roughness. At 0.5h, windspeeds exhibited a slow increase down the entire array.
2. Reflecting differences in approach flows, the drag on the initial fence was almost twice that on barriers farther downstream. This reduction in momentum extraction per windbreak was associated with an elevation in the zero-plane displacement to a level equal to 0.8h.
3. At positions well-removed from the initial fences, mean windspeeds were reduced throughout the entire region below shelter height. In this region, the flow became increasingly dominated by downward moving air with velocities much greater than the local average. The zone of reduced turbulence was small, extending only 2h downstream of a barrier at a height of 0.25h. This corresponded with the region excluded from smoke trails released at the top of windbreaks.
4. An approximate TKE budget mid-way between windbreaks 7 and 8 suggests that shear and wake production peak near z = h and that production is balanced by dissipation and vertical transport components. Advective and inertial interaction terms are negligible at this midway position but are likely to be major sources of TKE closer to the windbreak. Local equilibrium is attained above z = 1.5h implying the existence of a constant-stress layer.

The measurements show the practical difficulty of simultaneously reducing both mean windspeeds and turbulence levels with repeated windbreaks at conventional spacings for horticultural applications.  相似文献