Gamow-Teller strength distribution in proton-rich nucleus 57Zn and its implications in astrophysics

Gamow-Teller (GT) transitions play a preeminent role in the collapse of stellar core in the stages leading to a Type-II supernova. The microscopically calculated GT strength distributions from ground and excited states are used for the calculation of weak decay rates for the core-collapse supernova dynamics and for probing the concomitant nucleosynthesis problem. The B(GT) strength for ⁵⁷Zn is calculated in the domain of proton-neutron Quasiparticle Random Phase Approximation (pn-QRPA) theory. No experimental insertions were made (as usually made in other pn-QRPA calculations of B(GT) strength function) to check the performance of the model for proton-rich nuclei. The calculated B(GT) strength distribution is in good agreement with measurements and shows differences with the earlier reported shell model calculation. The pn-QRPA model reproduced the measured low-lying strength for ⁵⁷Zn better in comparison to the KB3G interaction used in the large-scale shell model calculation. The stellar weak rates are sensitive to the location and structure of these low-lying states in daughter ⁵⁷Cu. The structure of ⁵⁷Cu plays a sumptuous role in the nucleosynthesis of proton-rich nuclei. The primary mechanism for producing such nuclei is the rp-process and is believed to be important in the dynamics of the collapsing supermassive stars. Small changes in the binding and excitation energies can lead to significant modifications of the predictions for the synthesis of proton rich isotopes. The ?? ⁺-decay and electron capture (EC) rates on ⁵⁷Zn are compared to the seminal work of Fuller, Fowler and Newman (FFN). The pn-QRPA calculated ?? ⁺-decay rates are generally in good agreement with the FFN calculation. However at high stellar temperatures the calculated ?? ⁺-decay rates are almost half of FFN rates. On the other hand, for rp-process conditions, the calculated electron capture (?? ⁺-decay) rates are bigger than FFN rates by more than a factor 2 (1.5) and may have interesting astrophysical consequences.     

From clergymen to computers—the advent of virtual palaeontology

Palaeontology was established as a science in the Victorian era, yet has roots that stretch deeper into the recesses of history. More than 2000 years ago, the Greek philosopher Aristotle deduced that fossil sea shells were once living organisms, and around 500 ad Xenophanes used fossils to argue that many areas of land must have previously been submarine. In 1027, the Persian scholar Avicenna suggested that organisms were fossilized by petrifying fluids; this theory was accepted by most natural philosophers up until the eighteenth century Enlightenment, and even beyond. The late 1700s were notable for the work of Georges Cuvier who established the reality of extinction. This, coupled with advances in the recognition of faunal successions made by the canal engineer William Smith, laid the framework for the discipline that would become known as palaeontology. As the nineteenth century progressed, the scientific community became increasingly well organized. Most fossil workers were gentleman scientists and members of the clergy, who self‐funded their studies in a new and exciting field. Many of the techniques used to study fossils today were developed during this ‘classical’ period. Perhaps the most fundamental of these is to expose a fossil by splitting the rock housing it, and then conduct investigations based upon the exposed surface ( Fig. 1 ). This approach has served the science well in the last two centuries, having been pivotal to innumerable advances in our understanding of the history of life. Nevertheless, there are many cases where splitting a rock in this way results in incomplete data recovery; those where the fossils are not flattened, but are preserved in three‐dimensions. Even the ephemeral soft‐tissues of organisms are occasionally preserved in a three‐dimensional state, for example in the Herefordshire, La Voulte Sûr Rhone and Orsten ‘Fossil Lagerstätten’ (sites of exceptional fossil preservation). These rare and precious deposits provide a wealth of information about the history of life on Earth, and are perhaps our most important resource in the quest to understand the palaeobiology of extinct organisms. With the aid of twenty‐first century technology, we can now make the most of these opportunities through the field of ‘virtual palaeontology’—computer‐aided visualization of fossils.

Figure 1 Open in figure viewer PowerPoint A split nodule showing the fossil within, in this case a cockroachoid insect. Fossil 4 cm long (From Garwood & Sutton, in press ).     

Transport properties and model-based dynamical properties of Omani crude oils

We have measured the density and viscosity of five crude oil samples, collected from various hydrocarbon reservoirs in Oman, as functions of temperature. The measured quantities are expressed in terms of fitted formulae allowing their easy usage for different computational and simulation works. As an application, these thermo-physical data have been utilized to investigate the flow dynamics of hydrocarbon films under gravity at various temperatures. We have modeled the flow of these crude oils to study the dynamics of falling films in an open-top rectangular pipe set at various angular alignments under the assumption of Newtonian fluid describing a laminar flow. The adopted model of the investigation is not entirely novel, but the calculations aim to apply the model to various Omani crude oil samples with various American Petroleum Institute (API) values; the calculated results shed light on the dynamics of these crude oil films, which might be correlated to crude oil purification mechanism and open-top transportation.     

Timeline analysis and wavelet multiscale analysis of the AKARI All-Sky Survey at 90 μm

We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio  (S/N) > 5  for a single detector row is  1.1 ± 0.1 Jy  which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds.     

Analysis of Pore Pressure and Stress Distribution around a Wellbore Drilled in Chemically Active Elastoplastic Formations

Drilling in low-permeable reactive shale formations with water-based drilling mud presents significant challenges, particularly in high-pressure and high-temperature environments. In previous studies, several models were proposed to describe the thermodynamic behaviour of shale. Most shale formations under high pressure are expected to undergo plastic deformation. An innovative algorithm including work hardening is proposed in the framework of thermo-chemo-poroelasticity to investigate the effect of plasticity on stresses around the wellbore. For this purpose a finite-element model of coupled thermo-chemo-poro-elastoplasticity is developed. The governing equations are based on the concept of thermodynamics of irreversible processes in discontinuous systems. In order to solve the plastic problem, a single-step backward Euler algorithm containing a yield surface-correction scheme is used to integrate the plastic stress–strain relation. An initial stress method is employed to solve the non-linearity of the plastic equation. In addition, super convergent patch recovery is used to accurately evaluate the time-dependent stress tensor from nodal displacement. The results of this study reveal that thermal and chemical osmosis can significantly affect the fluid flow in low-permeable shale formations. When the salinity of drilling mud is higher than that of pore fluid, fluid is pulled out of the formation by chemical osmotic back flow. Similar results are observed when the temperature of drilling mud is lower than that of the formation fluid. It is found that linear elastic approaches to wellbore stability analysis appear to overestimate the tangential stress around the wellbore and produce more conservative stresses compared to the results of field observation. Therefore, the drilling mud properties obtained from the elastoplastic wellbore stability in shales provide a safer mud weight window and reduce drilling cost.     

The interrelationship between travel behavior and life choices in adapting to flood disasters

Disasters resulting from climate change are shown to be important determinants of people’s life choice decisions. In the literature, travel behavior choice and life choices are usually addressed separately under disasters such as flood and cyclone. However, travel behavior may be interdependent with other life choices, jointly shaping people’s adaptation decisions. To this end, the paper advances the literature by exploring the interrelationship between changes in travel behavior and job and residential location under flood disasters, while separating coastal and inland observations. For this purpose, a stated preference survey was conducted in 14 cities of Bangladesh in early 2013. An analysis approach based on structural equation modeling was developed to investigate the correlations between travel behavior change and job and residential location changes. Model estimation results suggest that flood impacts have significant influences on inland people’s life choices, while coastal people’s life choices are mainly affected by flood adaptation responses and attitudes. Significant correlations between travel behavior change and job and residential location changes are found for both observations. Moreover, both coastal and inland people tend not to change residential locations if changes in job location and travel behavior are made. Inland people may not change travel behavior if their job and/or residential locations are changed, but coastal people’s job and residential location changes are associated with changes in travel behavior. Travel behavior change is found to have more of an effect on residential location change than job location change in both regions. These findings conclude that the two-way relationship between travel behavior and life choices should be taken into account in future analyses, and thus adaptation policies to climate change disasters could be better linked with people’s behavioral responses.