A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments

Luminescence dating is used extensively to provide absolute chronologies for Late Pleistocene sediments. Nowadays, most optical dates are based on quartz optically stimulated luminescence (OSL). However, the application of this signal is usually limited to the last ～100 ka because of saturation of the quartz luminescence signal with dose. In contrast, the feldspar infrared stimulated luminescence (IRSL) dose–response curve grows to much higher doses; this has the potential to extend the datable age range by a factor of 4–5 compared with quartz OSL. However, it has been known for several decades that this IRSL signal is unstable, and this instability often gives rise to significant age underestimation. Here we test against independent age control the recently developed feldspar post‐IR IRSL approach to the dating of sediments, which appears to avoid signal instability. A physical model explaining our observations is discussed, and the method is shown to be accurate back to 600 ka. The post‐IR IRSL signal is reduced by exposure to daylight more slowly than that from quartz and low‐temperature IRSL, preventing its general application to young (e.g. Holocene) sediments. Nevertheless, this new approach is widely applicable (feldspar of appropriate luminescence behaviour is even more ubiquitous than quartz). These characteristics make this a method of great importance for the dating of Middle and Late Pleistocene deposits.     

Dynamic behavior of offshore spar platforms under regular sea waves

Many innovative floating offshore structures have been proposed for cost effectiveness of oil and gas exploration and production in water depths exceeding one thousand meters in recent years. One such type of platform is the offshore floating Spar platform. The Spar platform is modelled as a rigid body with six degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar platform at the fairleads. The response dependent stiffness matrix consists of two parts (a) the hydrostatics provide restoring force in heave, roll and pitch, (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal springs. A unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of the moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for sea state conditions with and without coupling of degrees-of-freedom.     

GPS scintillation studies in the arctic region during the first winter-phase 2008 Indian Arctic Expedition

We present the results of scintillation studies based on the data obtained during the first winter-phase Indian Arctic Expedition in March 2008 at the Indian Himadri Station, Ny-Ålesund (78.9°N, 11.9°E), in the vicinity of the daytime cusp and under the nightside polar cap. A global-positioning-system ionospheric scintillation and TEC monitor (GISTM) receiver (model GSV4004A) was used to record scintillations and the total electron content (TEC). The polar ionosphere is more sensitive to phase than to amplitude scintillations. Occurrence of amplitude scintillation is confined to well-defined regions, while phase scintillation shows a strong characterization both in magnetic latitude and magnetic local time. Occurrence of amplitude and phase scintillation increases during disturbed compared with quiet days. During disturbed days, the phase-scintillation region is displaced towards lower latitudes, following the auroral oval. The observed noon peak in scintillation occurrence may indicate that the irregularities that generate scintillation are caused by precipitation in the daytime cusp/cleft region. A significant enhancement of the TEC and the rate of change of the TEC index (ROTI) signified transits of polar-cap patches across different satellite trajectories during geomagnetic storms. We found that patches are most likely to occur when IMF Bz is southward and/or K_p > 4. Loss of signal lock was more for the L2 signal than for L1, and shows a maximum in the morning sector. Positional errors tend to increase during disturbed conditions.     

Microflares as possible sources for coronal heating

We present a preliminary study of 27 microflares observed by Solar X-ray Spectrometer (SOXS) mission during July 2003 to August 2006. We found that all 27 microflares show the Fe-line feature peaking around 6.7 keV, which is an indicator of the presence of coronal plasma temperature ≥ 9 MK. On the other hand, the spectra of microflares show hybrid model of thermal and non-thermal emission, which further supports them as possible sources of coronal heating. Our results based on the analysis show that the energy relapsed by the microflares is good enough for heating of the active corona. We discuss our results in the light of the hybrid model of microflares production.     

Detection of Hα Intensity Oscillations in Solar Flares

We report here the first direct evidence for detection of H intensity oscillations in two extended flares of 15 November 1989 and 20 April 1991. The relative intensity variations measured with time at 18 different flare and chromospheric locations were analysed to obtain the oscillation modes. The analysis shows prominent 5- and 3-min modes in flares in addition to their existence in the chromosphere. However, there exists a frequency difference between the flare and chromospheric modes. This frequency deviation of about 300 µHz is proposed as an influence of higher magnetic field, location of the measurements (height) in chromosphere, and high temperature in the flare.