Numerical investigation of the effect of seasonal variations of depthof-closure on shoreline evolution

The current study presents the effects of seasonal variations in the depth-of-closure(Dc)on shoreline evolution using a numerical,one-line shoreline model.Beach erosion of the southern beach of the Nha Trang Coast,which is located in south central of Vietnam,is selected as the study area.This study area is immensely influenced by the tropical monsoon climate that has a clear pattern of large waves in the northeast monsoon season and calm waves in the non-monsoon season.The analysis of the long-term measured shoreline variations from a video-camera system has found a strong correlation of these variations to the monsoon-dominated wave characteristics in the Nha Trang Bay.Therefore,a new approach for determining the depth-of-closure with consideration of the seasonal wave climate changes is purposed in the current study.By implementing this new approach into a numerical,one-line shoreline model,it is found that the seasonal variations of Dc appear to better describe the periodical shoreline evolution due to the monsoon-dominated wave characteristics for the Nha Trang Coast.Such important findings are considered to commonly apply for monsoon-dominated coastal regions in general.These findings are useful information not only for scientific readers but also for the coastal authorities and managers in order to make better countermeasure plans against this kind of erosion mechanism in the future.     

Granitoids in the Dalat zone,southern Vietnam: age constraints on magmatism and regional geological implications

The Dalat zone in southern Vietnam comprises a Cretaceous Andean-type magmatic arc with voluminous granitoids and contemporary volcanic rocks. On the basis of petrographical and mineralogical studies, the granitoids were subdivided into three suites: Dinhquan, Deoca and Cana. Rocks of the Dinhquan suite are hornblende–biotite diorites, granodiorites and minor granites. The Cana suite encompasses mainly leucocratic biotite-bearing granites with scarce hornblende. The Deoca suite is made up of granodiorites, monzogranites and granites. Geochemically, the granitoids are of subalkaline affinity, belong to the high-K, calc-alkaline series, and most of them display typical features of I-type granites. This paper presents the new Rb–Sr mineral and U–Pb zircon and titanite age data for the granitoids, which establish the ages of the plutonic suites as: the Dinhquan at ~112–100 Ma, Cana at ~96–93 Ma and Deoca at ~92–88 Ma. These ages are significantly different from earlier publications, and indicate that the earliest magmatism in the Dalat zone began at ~112 Ma ago, that is ~30–50 Ma later than previously thought. Our geochronological data are also support the continuation of an Andean-type arc running from SE China via southern Vietnam to SW Borneo.     

Late Devonian-Early Carboniferous peak sulphide mineralization in the Western Hercynides

The Late Devonian-Early Carboniferous (Dinantian) within the Western Hercynides is marked by the formation of volcanic-hosted massive sulphide deposits: Chessy and Chizeuil in the Brévenne and Somme successions of the French Massif Central; Bodennec and La Porte-aux-Moines in the Châteaulin Basin of the French Armorican Massif; Rio Tinto, Neves-Corvo, Tharsis, etc., in the Volcano-Sedimentary formation of the Iberian Pyrite Belt; and Ketara, Draa Sfar and Hajar in the Jebilet-Guemassa district of the Moroccan Southern Meseta. Although these deposits show a slightly diachronous emplacement in response to a progressive migration of the metalliferous event from Late Devonian in France to Dinantian in Morocco, it is nevertheless possible to define an overall metalliferous ‘‘peak” around 350 Ma. The mineralization of the Armorican, Iberian and Moroccan sectors took place in epicontinental domains of the outer zone of the Hercynian belt, whereas that of the northeastern Massif Central occurred within the inner zone of the belt. This difference is registered by variations both in the geochemical characteristics of the ores (Sn in the outer zone and Mo-Ni in the inner zone) and in their lead isotopic signatures (clear mantle participation exclusively in the inner zone). In many cases the ores appear to be closely related to the felsic member of a bimodal magmatic association, although the massive sulphide deposits in the outer zone are more commonly associated with sedimentary rocks whereas those in the inner zone are hosted by felsic volcanic rocks. Another feature that should be noted is that the host sequences of the massive sulphide deposits commonly seem to be underlain by chaotic formations (notably with olistoliths) reflecting the beginning of Hercynian orogenic activity in the outer zone. It can be concluded that the peak mineralization took place within tensional domains developed during a period of plate convergence, and that it occurred around 350 Ma after a major period of Devonian compression but before the Carboniferous continental closure.     

Hydrogeological investigation in the Mekong Delta around Ho-Chi-Minh City (South Vietnam) by electric tomographyInvestigation hydrogéologique dans le delta du Mékong,autour de la ville de Ho-Chi-Minh (Sud-Vietnam), par tomographie électrique

In the Mekong Delta (South Vietnam), the agglomeration of Ho-Chi-Minh (HCM) City, with more than 5 million inhabitants, is confronted with a dramatic shortage of fresh water supply because of the pollution of several aquifers at different depths. The electric tomography, obtained by concurrent inversion of two complementary geoelectrical methods, the Vertical Electrical Sounding (VES) and the Magneto-Telluric Sounding (MTS), turned out to be very efficient to provide a complete electrical image of the underground from the surface until about 800 m depth. This methodology constitutes a very cheap guide for the evaluation of the quality of the groundwater resources in the vast alluvial plain of the Mekong Delta. To cite this article: V.N. Pham et al., C. R. Geoscience 334 (2002) 733–740.     

The fiberless multislit spectrograph SFM

We describe the multislit spectrograph SFM. It is designed to obtain simultaneously spectrograms of faint objects over a field of 10 arcminutes for an entrance aperture ratio f/10, or of 15 arcmin for f/8. The SFM makes the dispersed image of the entrance slits directly, without any fiber optics. The number of entrance slits can be as large as a few hundreds, depending on the distribution of the sources on the sky and on the wavelength range. The present reciprocal dispersion is 79Åmm^–1 in the wavelength range 3600 – 6400Å. The SFM is expected to reachm _v22 with a signal to noise ratio of 10 for a spectral resolution of 3.3Å and an integration time of 5 hours, when used with the photon counting detector CP40.Radial velocities can be measured either by using calibration spectrograms or by the objective prism technique.The mask of entrance slits is made photochemically from a plate previously recorded of the field to be observed, taken during the same observing run. The auxiliary equipment Mascograph, specially designed for this purpose, is described.First spectrograms in the field of M15 obtained with the SFM using the Calar-Alto 3.50m telescope are presented.Based on observations collected at the Calar-Alto 3.5m telescope, operated by the German MPIfA (Heidelberg), and at the 3.60m CFHT, operated jointly by the Canadian SRC, the French CNRS and the University of Hawaii     

Extended (15 × 6 AU) Hα Emission Around T Tau N

We present an image of T Tauri N reconstructed from speckle interferometry observations made at the 3.6 m Canada-France-Hawaii telescope (CFHT). Two spectral windows, at Hα [6540-6580 Å] and red continuum [6580-6840 Å] were used. The star is unresolved in the continuum (θ ≤ 0″038), setting an upper limit for its size of ≤ 5.3 AU (assuming a 140 pc distance). At Hα (continuum subtracted) two components are observed, an unresolved one with 70% of the Hα flux and a resolved 0″106 × 0″043 (15 × 6 AU) with 30 %. The extended component is elongated in the North-South direction. The extended Hα component scale, it's non-detection in the continuum, and TTau Hα profile shape suggest that the extension is a disk corona.     

Assessment of the impacts of climate change and brackish irrigation water on rice productivity and evaluation of adaptation measures in Ca Mau province,Vietnam

This paper presents applications of the peaks-over-threshold methodology for both the univariate and the recently introduced bivariate case, combined with a novel bootstrap approach. We compare the proposed bootstrap methods to the more traditional profile likelihood. We have investigated 63 years of the European Climate Assessment daily precipitation data for five Hungarian grid points, first separately for the summer and winter months, then aiming at the detection of possible changes by investigating 20 years moving windows. We show that significant changes can be observed both in the univariate and the bivariate cases, the most recent period being the most dangerous in several cases, as some return values have increased substantially. We illustrate these effects by bivariate coverage regions.     

Propagation of Pc 1 pulsations in off-meridian directions

Experimental investigations on the horizontal propagation of Pc 1 pulsations in directions out of the geomagnetic meridian have been carried out using data recorded over a three-year period at four widely-separated middle and low latitude stations. The results obtained show that Pc 1 signals propagate in off-meridian directions, and that horizontal propagation characteristics in the early morning hours have small directional changes.     

Ionospheric dispersion and Pc 1 pulsations

Dispersion measurements were performed on geomagnetic pulsation data recorded over an Australasian network in a search for evidence of ionospheric dispersion of Pc 1 signals. A method of analysis was adopted in which the slope of emission elements of a selected Pc 1 event are examined individually. It has been found that there are no significant ionospheric dispersion effects for propagation between middle and low latitudes. Magnetospheric propagation paths calculated from dispersion measurements show large variations and are not considered generally reliable.     

Groundwater resources management under environmental constraints in Shiroishi of Saga plain, Japan

A sinking of the land surface due to the pumping of groundwater has long been recognized as an environmental issue in the Shiroishi plain of Saga, Japan. Land subsidence can have several negative economic and social implications such as changes in groundwater and surface water flow patterns, restrictions on pumping in land subsidence prone areas, localized flooding, failure of well casings as well as shearing of structures. To minimize such an environmental effect, groundwater management should be considered in this area. In this study, a new integrated numerical model that integrates a three-dimensional numerical groundwater flow model coupled with a one-dimensional soil consolidation model and a groundwater optimization model was developed to simulate groundwater movement, to predict ground settlement and to search for optimal safe yield of groundwater without violating physical, environmental and socio-economic constraints. It is found that groundwater levels in the aquifers greatly vary from season to season in response to the varying climatic and pumping conditions. Consequently, land subsidence has occurred rapidly throughout the area with the Shiroishi plain being the most prone. The predicted optimal safe yield of the pumping amount is about 5 million m³. The study also suggests that pumping with this optimal amount will minimize the rate of land subsidence over the entire area. An erratum to this article can be found at