H 187 - At the Onset of a New Eclipse

CCD photometry data of the T Tauri star H 187 are presented. They show that a new eclipse of this star began at the end of 2004. Since only one eclipse of this star has been observed previously with a duration of 3.5 years, our data indicate that the eclipses of this object are periodic with a period P=4.9 years between eclipses. Thus, in terms of the absolute duration of the eclipses and in terms of their relative length as a fraction of the period, H 187 is one of the most exotic objects in the sky. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 529–534 (November 2005).     

Magnetostratigraphy of the lower Triassic volcanics from deep drill SG6 in western Siberia: evidence for long-lasting Permo–Triassic volcanic activity

The deep drill hole SG6 in western Siberia (66°N, 78.5°E) penetrated 1.1  km of lower Triassic basalts, which are possibly an extension of the central Siberian Permo– Triassic flood basalt province. About 300 samples of these basalts were progressively demagnetized and measured. Principal component analysis often shows multiple magnetizations carried by haematite and magnetite. The corrected mean inclinations are +77° and −77° for the haematite component. A magnetostratigraphic scale was derived and showed a N–R–N–R–N succession. This is quite different from the Noril'sk and Taimyr typical polarity scale, R–N.
  The basalts found in the SG6 deep drill hole are slightly younger than those of central Siberia and Taimyr. They correspond to middle–upper Induan age, whereas the Noril'sk and Taimyr sections correspond to an uppermost Permian and lower Induan age. Altogether they indicate that, after a high output rate of volcanic material near the Permo–Triassic boundary, this activity slowed down drastically on the Siberian platform and Taimyr, but persisted for several million years in western Siberia.     

Response of circular bridge decks to moving vehicles

This paper discusses the dynamic response of a curved bridge deck to a moving vehicle. The bridge deck is idealized as a set of annular sector plates and circular rings rigidly jointed together. On the basis of classical plate and ring theories a method has been developed to obtain the response to a moving vehicle idealized as a spring mass system. After obtaining the normal modes and frequencies and establishing the orthogonality conditions, the problem of the forced motion of the deck is solved by the method of spectral representation. Numerical results have been presented to illustrate the effect of several vehicle and bridge parameters on the response.     

Estimation of sedimentary thickness in the Godavari basin

A major portion of the southern part of the Indian subcontinent is classified as a stable continental region. However, a few segments in this region are punctuated by rifts and shear zones that are seismically active. The Godavari rift that sutures the eastern Dharwar and the Bastar cratons is one such region, prone to seismic hazard. Estimation of the sedimentary thickness in these seismically active regions assumes importance since locales of thick and soft sediments are vulnerable to destruction due to surface waves generated by earthquakes. In the present study, data from five broadband seismological stations are utilized to estimate the average sedimentary thickness of the Godavari region using the difference in travel times of the direct S and converted Sp phases from local earthquakes. The thickness of sediments varies between 0.32 and 4.32 km. Also, the site-specific response in terms of the fundamental resonance frequency and the corresponding amplifications are estimated using the well-established Nakamura technique. The predominant frequencies are in the range of 1.3–4.61 Hz, and the amplifications are higher (>1.5) for the stations inside the Godavari basin. Both the thickness and amplification values clearly indicate that the sediments tend to get thicker toward the center of the basin, in good agreement with the geological distribution of the sedimentary units.     

Jovian electron jets in interplanetary space

The COSPIN/KET experiment onboard Ulysses has been monitoring the flux of 3–20 MeV electrons in interplanetary space since the launch of Ulysses in October 1990. The origin of these electrons has been known for a long time to be the Jovian magnetosphere. Propagation models assuming interplanetary diffusion of these electrons in the ideal Parker magnetic field were successfully developed in the past. The average electron flux measured by our experiment agrees with these models for most of the times before and after the Jovian flyby of February 1992, i.e. in and out of the ecliptic down to 28° S of heliographic latitude for the last data presented here (end of March 1993).However, in addition to this average flux level well accounted for by diffusion in an ideal Parker field, we have found very short duration electron events which we call “jets”, characterized by: (i) a sharp increase and decrease of flux; (ii) a spectrum identical to the electron spectrum in the Jovian magnetosphere; and (iii) a strong first-order anisotropy. These jets only occur when the magnetic field at Ulysses lies close to the direction of Jupiter, and most of the time (86% of the events) points outwards from Jupiter, i.e. has the same polarity after the flyby as the Jovian dipole (North to South). These events are interpreted as crossings by Ulysses of magnetic flux tubes or sheets directly connected to the location of the Jovian magnetosphere from which electrons escape into interplanetary space. The average thickness of these sheets is 10¹¹cm or 14 Jovian radii. These jets are clearly identified up to 0.4 a.u. before the Jupiter flyby in the ecliptic plane, and up to 0.9 a.u. out of the ecliptic.Moreover, the characteristic rocking of the electron spectrum in the Jovian magnetosphere with a 10 h periodicity is found to be present during the jets, and predominantly during them. In the past, this modulation has been reported to be present in interplanetary space as far as 1 a.u. upwind of Jupiter, a fact which cannot be accounted for by diffusion in the average Parker magnetic field. Our finding gives a simple explanation to this phenomenon, the 10 h modulation being carried by the “jet” electrons which travel with no appreciable diffusion along magnetic field lines with a direction far from the ideal Parker spiral.     

Intrusion and differentiation of granitic magma at a high level in the crust: the Puscao pluton, Lima Province, Peru

Regression surface techniques have been used on partial whole-rockchemical analyses from the Puscao pluton to establish the three-dimensionalnature of the chemical variations within this body, which wasemplaced at a depth of between 4 km and 8 km within the crust.Block diagrams produced by the computer program are consistentwith the hypothesis that during the period preceding the totalconsolidation of the magma, the pluton has undergone in situdifferentiation to give a layered structure. Statistical analysis confirms that there is a large scale variationwithin the pluton and that local variation, such as might beexpected to result from the contamination of the Puscao magmaby assimilated volcanic material, did not contribute significantlyto the overall variation. Evidence is presented which suggests that the layering withinthe Puscao pluton was disturbed as a result of the emplacementof the much later Cañhas pluton, and that this disturbancehas the form of a simple doming centred upon the site of thepresent Cañas intrusion.     

Experiments on scalar dispersion within a model plant canopy,part III: An elevated line source

An experiment is reported in which heat was released as a passive tracer from an elevated lateral line source within a model plant canopy, with h _s = 0.85 h _c (h _s and h _c being the source and canopy heights, respectively). A sensor assembly consisting of three coplanar hot wires and one cold wire was used to measure profiles of mean temperature % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikamaana% aabaGaeqiUdehaaiaacMcaaaa!390C!\[(\overline \theta )\], temperature variance (Σ_θ ²), vertical and streamwise turbulent heat fluxes, and third moments of wind and temperature fluctuations. Conclusions were:

1. Despite the very heterogeneous flow within the canopy, the observed dispersive heat flux (due to spatial correlation between time-averaged temperature and vertical velocity) was small. However, there is evidence from the plume centroid (which was lower than h _s at the source) of systematic recirculating motions within the canopy.
2. The ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS% baaSqaaiabeI7aXjaab2gacaqGHbGaaeiEaaqabaGccaGGVaWaa0aa% aeaacqaH4oqCaaWaaSbaaSqaaiaab2gacaqGHbGaaeiEaaqabaaaaa!41DF!\[\sigma _{\theta {\text{max}}} /\overline \theta _{{\text{max}}} \] (of maximum values on vertical profiles) decreased from 1 near the source to an asymptotic value of 0.4 far downstream, in good agreement with previous experimental and theoretical work for concentration fluctuations in the surface layer well above the canopy.
3. The eddy diffusivity for heat from the line source (K _HL ) increased, downstream of the source, to a nearly constant ‘far-field’ vertical profile. Within the canopy, the far-field K _HL was an order of magnitude larger than K _HP , the equivalent diffusivity for a plane source; well above the canopy, the two were equal. The time scale defined by (far-field K _HL )/(vertical velocity variance) was independent of height within the canopy.
4. Budgets for temperature variance, vertical heat flux and streamwise heat flux are remarkably similar to the equivalent budgets for an elevated line source in the surface layer well above the canopy, except in the lower part of the canopy in the far field, where vertical transport is much more important than in the surface layer.
5. A random flight simulation of the mean height and depth of the temperature plume was generally in good agreement with experiment. However, details of the temperature and streamwise turbulent heat flux profiles were not correct, suggesting that the model formulation needs to be improved.