Dust Devil Tracks

Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earth’s surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between ∼1 m and ∼1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of ≥500 μm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550–850 nm on Mars and around 0.5 % in the wavelength range from 300–1100 nm on Earth. The removal of an equivalent layer thickness around 1 μm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand-sized material that is eroded from the outer vortex area of a dust devil is redeposited in annular patterns in the central vortex region. This type of DDT can also be found in on Mars in orbital image data, and although in situ studies are lacking, terrestrial analog studies, laboratory work, and numerical modeling suggest they have the same formation mechanism as those on Earth. Finally, bright DDTs are characterized by their continuous track pattern and high albedo compared to their undisturbed surroundings. They are found on both planets, but to date they have only been analyzed in situ on Earth. Here, the destruction of aggregates of dust, silt and sand by dust devils leads to smooth surfaces in contrast to the undisturbed rough surfaces surrounding the track. The resulting change in photometric properties occurs because the smoother surfaces have a higher reflectance compared to the surrounding rough surface, leading to bright DDTs. On Mars, the destruction of surficial dust-aggregates may also lead to bright DDTs. However, higher reflective surfaces may be produced by other formation mechanisms, such as dust compaction by passing dust devils, as this may also cause changes in photometric properties. On Mars, DDTs in general are found at all elevations and on a global scale, except on the permanent polar caps. DDT maximum areal densities occur during spring and summer in both hemispheres produced by an increase in dust devil activity caused by maximum insolation. Regionally, dust devil densities vary spatially likely controlled by changes in dust cover thicknesses and substrate materials. This variability makes it difficult to infer dust devil activity from DDT frequencies. Furthermore, only a fraction of dust devils leave tracks. However, DDTs can be used as proxies for dust devil lifetimes and wind directions and speeds, and they can also be used to predict lander or rover solar panel clearing events. Overall, the high DDT frequency in many areas on Mars leads to drastic albedo changes that affect large-scale weather patterns

Current assessment of the Red Rectangle band problem

In this paper we discuss our insights into several key problems in the identification of the Red Rectangle Bands (RRBs). We have combined three independent sets of observations in order to try to define the constraints guiding the bands. We provide a summary of the general behavior of the bands and review the evidence for a molecular origin of the bands. The extent, composition, and possible absorption effects of the bands are discussed. Comparison spectra of the strongest band obtained at three different spectral resolutions suggests that an intrinsic line width of individual rotational lines can be deduced. Spectroscopic models of several relatively simple molecules were examined in order to investigate where the current data are weak. Suggestions are made for future studies to enhance our understanding of these enigmatic bands

Particle technology education in the 21st century – Outcomes from the IFPRI sponsored workshop in Sheffield, April 2017

In April 2017, IFPRI sponsored a workshop at the University of Sheffield to assess the current state of global particle technology education and chart a course forward. There is a clearly demonstrated need for trained graduates at all levels across a broad spectrum of industries. Workshop participants recommended a top down approach for curriculum renewal and developed key high-level learning attributes for undergraduate education in particle science and engineering. Participants further identified a variety of barriers to integrating particle technology into undergraduate engineering curricula such as the crowded engineering curriculum, a perception that particle technology is more an art than a science, and that it is an orphan subject that fits uncomfortably in standard engineering disciplines. Nevertheless, change is possible with better underlying science, new textbooks and software tools, examples of excellent programs and courses, and increasing demand from employers for skills in the area, as compared to 25 years ago. Suggestions for how to do this are reported. It will take persistence and cooperation between both academia and industry to achieve a significantly higher percentage of engineers trained in particle science and engineering. This education will benefit society in solving the world's current and future technological grand challenges

Preservation for future use of the autologous saphenous vein during femoro-popliteal bypass surgery is inexpedient.

Contains fulltext : 71390.pdf (publisher's version ) (Closed access)PURPOSE: To investigate the usefulness of greater saphenous vein preservation for future vascular reconstructions during femoro-popliteal bypass surgery. DESIGN: Post-hoc analysis of data acquired in a randomized multi-centre clinical trial comparing two different vascular prostheses (ClinicalTrials.gov ID: NCT 00523263). PATIENTS AND METHODS: The true frequency of ipsilateral saphenous vein use in subsequent femoro-popliteal and coronary bypass surgery was investigated through case-record analysis with a median follow-up of 60 months in 100 consecutive patients, that received a prosthetic femoro-popliteal bypass between 1996 and 2001. RESULTS: An ipsilateral secondary femoro-popliteal bypass was performed in 11 patients (11%) at a mean interval of 34 months (range 1-96). The ipsilateral saphenous vein was applied for these procedures in 8 cases (8%). The cumulative probability of receiving a subsequent bypass was 8% at 3 years and 10% at 5 years follow-up respectively. One patient (1%) underwent CABG at 8 years follow-up with the use of ipsilateral lower leg saphenous vein segments only. CONCLUSION: Preservation of the greater saphenous vein in supragenicular femoro-popliteal bypass surgery is not a valid argument for application of prosthetic material