Characterization of a landslide-triggered debris flow at a rainforest-covered mountain region in Brazil

Natural Hazards - Debris flows represent great hazard to humans due to their high destructive power. Understanding their hydrogeomorphic dynamics is fundamental in hazard assessment studies,...     

A simple generalization of wisdom's perturbative method

A simple generalization of Wisdom's perturbative method, as originally proposed by Wisdom (1985), is obtained. Any number of resonant cosines can be handled and the method can also accommodate more involved disturbing functions. Averaged trajectories are easily obtained by drawing level curves of the action. Here, the method is first tested for simple models of 3:1 and 2:1 resonant problems. Comparisons with numerical integration and surface-section curves show very good agreements.     

Line width observation of Heii 4686 Å and Hei 4713 Å in the chromosphere

Line profiles of He ii 4686 Å and He i 4713 Å from active regions in the chromosphere were observed during the total solar eclipse of February 16, 1980, with a grazing incidence objective grating spectrograph. The Doppler width of the He i triplet line of 4713 Å increases with height and the average width is compatible with width of metallic and hydrogen lines, suggesting that the kinetic temperature of He i triplet emitting region is T 8000 K. This can only be explained by recombination after photo-ionization due to coronal UV radiation. The Doppler width of the Paschen line of He ii 4686 is, without any correction for the separation of subcomponents of the line nor non-thermal velocity, 18.4 km s^-1. This line width also shows a tendency to increase with height. After comparison with Doppler widths of He i 4713 and the EUV lines, and a necessary subtraction of non-thermal velocity, it is shown that this line is emitted in a 2 × 10⁴ K temperature region, which again supports the view that this line is emitted through the recombination process after photoionization due to coronal XUV radiation below 228 Å.     

Multicomponent observation of crustal activity in the DPRI 800 m borehole close to the Nojima Fault

Abstract An 800 m borehole was drilled near the Nojima Fault, on which a strike–slip larger then 1 m occurred during the 1995 Hyogo-ken Nanbu earthquake ( M = 7.2). Crustal activity near the fault has been observed since May 1996 using a multicomponent instrument installed at the bottom of the borehole. Data of three components of strain, two components of tilt and temperature observed from May 1996 to December 1998 were analyzed. Long-term changes of strain and tilt show a north-east–south-west extension and southwards subsidence. As for the Earth tides and atmospheric effect, orientation of the principal axis of strain was mainly east-west and orientation of the maximum subsidence was mainly north-south. The observational data of strain had variations corresponding to a change in temperature at a depth of 800 m. The thermal expansion coefficient of the crust was calculated to be approximately 2.0 × 10⁻⁶/°K.     

Precise wideband photometry of photospheric faculae with an emphasis on the disk center

The center-to-limb variation of the excess intensity in faculae was obtained for 266 active regions with an accuracy of 10^–3. For this observation full-disk images were obtained with a rotating one-dimensional diode array whose rotation axis was set at the disk center, at the wavelength of 5450 Å with a bandpass of 400 Å. From the center-to-limb variation of excess intensity of active regions the excess effective temperature was found to be 6.4 K on the average where the mean longitudinal magnetic field is 65 G as measured by 5233 Å line. In other words the ratio of the excess radiative flux to the total flux was 0.44% on the average for the present measurements of low spatial resolution of 20.The average excess intensity for 60 active regions near the disk center was found to be 4 × 10^–4 of the quiet Sun intensity. This very low excess brightness averaged over the whole active region, in contrast to the reported high excess brightness of facular points (diameter 0.2) of 0.4, leads to a hypothesis that the background in between facular points in the active region is darker than the true quiet photosphere by 1%. It is further surmised that the inferred darkness of intra facular points is due to partial compensation for excess total irradiance of facular points. This interpretation is also consistent with previous observations of the contrast of facular points near the limb.     

On the 3/1 planar and circular resonant problem

The simplest model of a resonant problem of second order is the planar and circular case. Simplification like this is very old and for 3/1 resonance, several authors have studied this problem with different purposes. In this work, we test this model for the available asteroids, by applying Hori's perturbation method. Explicit solutions of the intermediate orbit are obtained. In the plane of two constants of the problem, all types of motion are described. By testing the model, it is shown that, in general, one can confirm results of numerical integrations indicating libration for a few number of asteroids and circulation for most of them. However, agreement in numerical values for amplitude and period of librations seems to be not possible mainly if Jupiter's eccentricity is neglected. On the other hand, even though there might be some physical reasons determining that only asteroids with high eccentricity may librate, it is shown that, from mathematical point of view, libration may occur even in the case of small eccentricities provided that some relations are satisfied.     

A comparative study of the photosynthetic activity among three temperate seagrass species in Northern Japan

The photosynthetic activity of Zostera marina, Zostera asiatica and Phyllospadix iwatensis shoots from populations of Hokkaido (Northern Japan) was determined using the pulse amplitude modulated (PAM) fluorometer. Several fluorescence parameters were measured as a function of irradiance and leaf age: electron transport rate (ETR), quantum yield, photochemical quenching (qP) and non‐photochemical quenching (NPQ). The leaf age determined by the leaf position in the shoot bundle strongly influenced the photosynthetic activity of Z. marina, Z. asiatica and P. iwatensis. Young leaves had the maximum electron transport rate (Zm: Leaf 1 = 15.7, Leaf 2 = 16.3; Za: Leaf 1 = 13.0, Leaf 2 = 12.2; and Pi: Leaf 1 = 12.5, Leaf 2 = 11.7) and showed higher photoprotection (NPQ) than old leaves. Among the studied seagrass species, Z. marina had the highest photosynthetic activity (ETR_max = 15.3), in accordance with the highest production in the field in comparison with the other two seagrass species. The PAM fluorometry technique showed to be effective in determining intraspecific (among‐leaves) and interspecific (among‐species) variation in seagrass photosynthetic activity.     

Accretion disc evolution in cataclysmic variables (the 1988 international time project in La Palma

A summary of data collected during a sixty night international campaign devoted to cataclysmic variables is presented.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Facular structures derived from precise two-color contrast observations

A precise solar surface photometric observing system was developed and intensity observations of the whole Sun were carried out at a fairly quiet period from December 1987 to April 1988, attaining the photometric accuracy of 10^–3. Using 28 days observation of 4 hours duration each and 0.3 s time interval, we obtained the center-to-limb variation of the ratio of the facular intensity contrast (I _f÷I_o) between two colors of 545 nm (G) and 770 nm (R): (I _f÷I₀)_G÷(I_f÷I₀)_R = 2.20 – 1.16, where is the direction cosine between the line of sight and the surface normal. While this relationship was obtained mostly for active regions from the whole Sun data, we also found an almost identical relation for the quiet Sun network by excluding active regions. This suggests the similarity of faculae at both places.Using the above relation and the difference of optical depth, , in two colors, we found that the facular temperature gradient, dT/d _G, is smaller than that of the quiet photosphere if the gradient is measured more or less vertically (i.e., seen at > 0.7) in accord with Foukal and Duvall (1985), while it is larger than that of the quiet photosphere if the temperature gradient is measured more obliquely (i.e., seen at > 0.7). These findings are free from the low spatial resolution of the present observations because the contrast ratio was used, and also independent of a specific model of hot-wall or hillock. In particular, if the true contrast of facular bright points of 0'2 size is taken as 40% in the green from high-resolution observations, the facular point temperature may even be increasing towards higher geometrical levels ar _G 1. We found also that the area filling factor in active regions is on the order of a few percent or so in accordance with the previous studies.