The dynamics of the mesosphere and lower thermosphere: a brief review

The dynamics of the mesosphere-lower thermosphere (MLT) (60 to 110 km) is dominated by waves and their effects. The basic structure of the MLT is determined by momentum deposition by small-scale gravity waves, which drives a summer-to-winter pole circulation at the mesopause. Atmospheric tides are also an important component of the dynamics of the MLT. Observations from extended ground-based networks, satellites as well as numerical modelling show that non-migrating tidal modes in the MLT are more important than previously thought, with evidence for directly coupling into the thermosphere/ionosphere. Major disturbances lower in the atmosphere, such as wintertime sudden stratospheric warmings, temporarily disrupt the circulation pattern and thermal structure of the MLT. In the equatorial mesosphere, gravity wave driving leads to oscillations in the zonal wind on semiannual time scales, although variability on quasi-biennial time scales is also apparent. Planetary-scale waves such as the quasi-two-day wave temporarily dominate the dynamics of the summertime MLT, especially in the southern hemisphere. Impacts may include short-term changes to the thermal structure and physics of the high-latitude MLT. Here, we briefly review the dynamics of the MLT, with a particular emphasis on developments in the past decade.Robert A Vincen

Ab initio derivation of multi-orbital extended Hubbard model for molecular crystals

From configuration interaction (CI) ab initio calculations, we derive an effective two-orbital extended Hubbard model based on the gerade (g) and ungerade (u) molecular orbitals (MOs) of the charge-transfer molecular conductor (TTM-TTP)I_3 and the single-component molecular conductor [Au(tmdt)_2]. First, by focusing on the isolated molecule, we determine the parameters for the model Hamiltonian so as to reproduce the CI Hamiltonian matrix. Next, we extend the analysis to two neighboring molecule pairs in the crystal and we perform similar calculations to evaluate the inter-molecular interactions. From the resulting tight-binding parameters, we analyze the band structure to confirm that two bands overlap and mix in together, supporting the multi-band feature. Furthermore, using a fragment decomposition, we derive the effective model based on the fragment MOs and show that the staking TTM-TTP molecules can be described by the zig-zag two-leg ladder with the inter-molecular transfer integral being larger than the intra-fragment transfer integral within the molecule. The inter-site interactions between the fragments follow a Coulomb law, supporting the fragment decomposition strategy.Comment: 16 pages, 8 figures, published versio

Scholarly Productivity In Developing Countries: An Analysis Of Levels And Patterns Among Doctoral Holders In Uganda

Doctoral holders are considered to be key actors in the creation of innovation and knowledge. However, this generalization may not hold true for doctoral holders in all countries. This study sought to assess the scholarly productivity of these highly qualified individuals in Uganda. The investigation is based on data sourced from the 2012 Careers and Productivity of Doctoral Holders (CDH) Survey conducted in the country. The data adopted comprise a total of 534 records of doctoral holders who were 70 years or younger by 2010 and living permanently or domiciled in Uganda. Journal Article(s) and book(s) (co)authored were adopted in this study as measures of productivity of a doctoral holder. The status and pattern of (co)authored journal article(s) and/or book(s) were assessed by doctoral holder characteristics using the Pearson Chi-square Test and Complementary Log-log regression. The number of (co)authored journal articles and books (including book chapters and monographs) was assessed by doctoral holder characteristics using the Kruskal-Wallis test and Poisson regression. In the results, the proportion of doctoral holders (29.2%) who had (co)authored journal article(s) and/or book(s) by the time of the study points to low scholarly productivity of these highly qualified individuals in the country. Though doctoral graduates of other African universities and those from international universities were more likely to have (co)authored article(s) and/or book(s), the number of (co)authored articles was significantly higher among graduates of Ugandan institutions. Further, the number of (co)authored articles was significantly higher among the males and doctoral holders who graduated before 2000. However, no significant variations in the number of (co)authored books were noted among doctoral holder characteristics. Nevertheless, the low scholarly productivity of doctoral holders in Uganda is certainly a mirror reflection of the situation in many developing countries

Nondestructive Evaluation (NDE) for Thermal-Spray Coatings

Thermal spray is the process of depositing metal, alloy, and ceramic coatings on properly prepared substrate materials so that they solidify on and bond mechanically, chemically, and metallurgically to the substrate materials. Thermal-spray coatings are applied to improve surface-wear characteristics, to provide resistance to heat, oxidation, and chemical environments; to restore dimension to the original equipment manufacturer\u27s (OEM) specifications; to reduce erosion wear; and to improve corrosion control

The Employability Status of Makerere University Graduates

The study applied the pathways approach, Survey Monkey and Snowballing techniques to ascertain the employability status of the 2012 graduates of Makerere University. The majority of the graduates were employed in the public sector on full time basis. The young graduates, however, favorably competed for entry job opportunities with the mature graduates. A reasonable number of the 2012 Makerere University graduates were engaged in self-employment as an avenue for addressing the problem of graduate unemployment in Uganda. Key words: Graduate unemployment, Makerere University, Tracer studies, Pathways DOI: 10.7176/JEP/10-6-1

A comparison of mean winds and gravity wave activity in the northern and southern polar MLT

Mean winds and waves observed in the mesosphere and lower thermosphere with MF radars located at Davis (69°S, 78°E) and Poker Flat (65°N, 147°W) are compared. Measurements covering the period from 1999 to mid 2000 show differences in the strength of the horizontal wind fields. In the southern hemisphere the zonal and meridional winds reach their maximum values near the summer solstice, but are delayed by 2–3 weeks in the northern hemisphere. Gravity wave variances also show significant differences, as do the strength of vertical velocities.Andrew Dowdy and Robert A. Vincent, Kiyoshi Igarashi and Yasuhiro Murayama, Damian J. Murph

On the tear resistance of skin.

Tear resistance is of vital importance in the various functions of skin, especially protection from predatorial attack. Here, we mechanistically quantify the extreme tear resistance of skin and identify the underlying structural features, which lead to its sophisticated failure mechanisms. We explain why it is virtually impossible to propagate a tear in rabbit skin, chosen as a model material for the dermis of vertebrates. We express the deformation in terms of four mechanisms of collagen fibril activity in skin under tensile loading that virtually eliminate the possibility of tearing in pre-notched samples: fibril straightening, fibril reorientation towards the tensile direction, elastic stretching and interfibrillar sliding, all of which contribute to the redistribution of the stresses at the notch tip