Minimal size of a barchan dune

Barchans are dunes of high mobility which have a crescent shape and propagate under conditions of unidirectional wind. However, sand dunes only appear above a critical size, which scales with the saturation distance of the sand flux [P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002); B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B {\bf{28,}} 321 (2002); G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E {\bf{64,}} 31305 (2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. {\bf{89,}} 264301 (2002) that this flux fetch distance is itself constant. Indeed, this could not explain the proto size of barchan dunes, which often occur in coastal areas of high litoral drift, and the scale of dunes on Mars. In the present work, we show from three dimensional calculations of sand transport that the size and the shape of the minimal barchan dune depend on the wind friction speed and the sand flux on the area between dunes in a field. Our results explain the common appearance of barchans a few tens of centimeter high which are observed along coasts. Furthermore, we find that the rate at which grains enter saltation on Mars is one order of magnitude higher than on Earth, and is relevant to correctly obtain the minimal dune size on Mars.Comment: 11 pages, 10 figure

Clinical investigation of the novel iron-chelating agent, CP94, to enhance topical photodynamic therapy of nodular basal cell carcinoma.

Clinical TrialMulticenter StudyThis is the peer reviewed version of the article which has been published in final form at DOI: 10.1111/j.1365-2133.2008.08668.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.© 2008 The AuthorsJournal Compilation © 2008 British Association of DermatologistsBACKGROUND: Photodynamic therapy (PDT) involves the activation of a photosensitizer by visible light to produce activated oxygen species within target cells, resulting in their destruction. Evidence-based guidelines support the efficacy of PDT using topical 5-aminolaevulinic acid (ALA-PDT) in actinic keratoses, Bowen disease and basal cell carcinoma (BCC). Efficacy for nodular BCC appears inferior to that for superficial BCC unless prior debulking or repeat treatments are performed. Objectives The aim of this study was to assess the safety and efficacy of adding a novel iron-chelating agent, CP94 (1,2-diethyl-3-hydroxypyridin-4-one hydrochloride), to topical ALA, to temporarily increase the accumulation of the photosensitizer in the tumour. METHODS: A mixed topical formulation of ALA + increasing concentrations of CP94 was used to carry out PDT on previously biopsied nodular BCC with no prior lesion preparation using standard light delivery. The area was assessed clinically and surgically excised 6 weeks later for histological examination. RESULTS: Enhanced PDT using 40% CP94 resulted in significantly greater clearance rates in nodular BCC than with ALA-PDT alone, in our protocol of single-treatment PDT with no lesion preparation. CONCLUSIONS: The results of this study demonstrate the safe and effective use of an enhanced ALA-PDT protocol for nodular BCC using CP94, with no adverse reactions to this modification. This is the first time this formulation has been used in patients. This formulation is now the focus of further study

A two-species continuum model for aeolian sand ripples

We formulate a continuum model for aeolian sand ripples consisting of two species of grains: a lower layer of relatively immobile clusters, with an upper layer of highly mobile grains moving on top. We predict analytically the ripple wavelength, initial ripple growth rate and threshold saltation flux for ripple formation. Numerical simulations show the evolution of realistic ripple profiles from initial surface roughness via ripple growth and merger.Comment: 9 pages, 3 figure

Islet autoantibody status in a multi-ethnic UK clinic cohort of children presenting with diabetes.

OBJECTIVE: We prospectively determined islet autoantibody status in children presenting with diabetes to a single UK region in relation to ethnicity. DESIGN: 316 (68.0% non-white) children presenting with diabetes between 2006 and 2013 were tested centrally for islet cell autoantibodies (ICA) and glutamic acid decarboxylase autoantibodies (GAD-65) at diagnosis, and if negative for both, tested for insulin autoantibodies (IAA). The assay used to measure GAD-65 autoantibodies changed from an in-house to a standardised ELISA method during the study. RESULTS: Even with use of the standardised ELISA method, 25.8% of children assigned a diagnosis of type 1 diabetes still tested negative for all three autoantibodies. 30% of children assigned a diagnosis of type 2 diabetes were autoantibody positive, and these had the highest glycated haemoglobin (HbA1c) levels at 12 months follow-up compared with other groups (p value for analysis of variance <0.001), although the sample size was small. Autoantibody positivity was similar between non-white and white children regardless of assay used (60.0% (n=129) vs 56.4% (n=57), χ2=0.9, p=0.35), as was mean GAD-65 autoantibody levels, but fewer non-white children had two or more autoantibodies detectable (13% (n=28) vs 27.7% (n=28), χ2=12.1, p=0.001). CONCLUSION: Islet autoantibody positivity was associated with a more severe phenotype, as demonstrated by poorer glycaemic control, regardless of assigned diabetes subtype. Positivity did not differ by ethnic group

Dune formation on the present Mars

We apply a model for sand dunes to calculate formation of dunes on Mars under the present Martian atmospheric conditions. We find that different dune shapes as those imaged by Mars Global Surveyor could have been formed by the action of sand-moving winds occuring on today's Mars. Our calculations show, however, that Martian dunes could be only formed due to the higher efficiency of Martian winds in carrying grains into saltation. The model equations are solved to study saltation transport under different atmospheric conditions valid for Mars. We obtain an estimate for the wind speed and migration velocity of barchan dunes at different places on Mars. From comparison with the shape of bimodal sand dunes, we find an estimate for the timescale of the changes in Martian wind regimes.Comment: 16 pages, 12 figure

Particle dynamics of a cartoon dune

The spatio-temporal evolution of a downsized model for a desert dune is observed experimentally in a narrow water flow channel. A particle tracking method reveals that the migration speed of the model dune is one order of magnitude smaller than that of individual grains. In particular, the erosion rate consists of comparable contributions from creeping (low energy) and saltating (high energy) particles. The saltation flow rate is slightly larger, whereas the number of saltating particles is one order of magnitude lower than that of the creeping ones. The velocity field of the saltating particles is comparable to the velocity field of the driving fluid. It can be observed that the spatial profile of the shear stress reaches its maximum value upstream of the crest, while its minimum lies at the downstream foot of the dune. The particle tracking method reveals that the deposition of entrained particles occurs primarily in the region between these two extrema of the shear stress. Moreover, it is demonstrated that the initial triangular heap evolves to a steady state with constant mass, shape, velocity, and packing fraction after one turnover time has elapsed. Within that time the mean distance between particles initially in contact reaches a value of approximately one quarter of the dune basis length

Unequal relationships in high and low power distance societies: a comparative study of tutor - student role relations in Britain and China

This study investigated people's conceptions of an unequal role relationship in two different types of society: a high power distance society and a low power distance society. The study focuses on the role relationship of tutor and student. British and Chinese tutors and postgraduate students completed a questionnaire that probed their conceptions of degrees of power differential and social distance/closeness in this role relationship. ANOVA results yielded a significant nationality effect for both aspects. Chinese respondents judged the relationship to be closer and to have a greater power differential than did British respondents. Written comments on the questionnaire and interviews with 9 Chinese academics who had experienced both British and Chinese academic environments supported the statistical findings and indicated that there are fundamental ideological differences associated with the differing conceptions. The results are discussed in relation to Western and Asian concepts of leadership and differing perspectives on the compatibility/incompatibility of power and distance/closeness

Spatially-resolved Thermal Continuum Absorption against the Supernova Remnant W49B

We present sub-arcminute resolution imaging of the Galactic supernova remnant W49B at 74 MHz (25") and 327 MHz (6"), the former being the lowest frequency at which the source has been resolved. While the 327 MHz image shows a shell-like morphology similar to that seen at higher frequencies, the 74 MHz image is considerably different, with the southwest region of the remnant almost completely attenuated. The implied 74 MHz optical depth (~ 1.6) is much higher than the intrinsic absorption levels seen inside two other relatively young remnants, Cas A and the Crab Nebula, nor are natural variations in the relativistic electron energy spectra expected at such levels. The geometry of the absorption is also inconsistent with intrinsic absorption. We attribute the absorption to extrinsic free-free absorption by a intervening cloud of thermal electrons. Its presence has already been inferred from the low-frequency turnover in the integrated continuum spectrum and from the detection of radio recombination lines toward the remnant. Our observations confirm the basic conclusions of those measurements, and our observations have resolved the absorber into a complex of classical HII regions surrounded either partially or fully by low-density HII gas. We identify this low-density gas as an extended HII region envelope (EHE), whose statistical properties were inferred from low resolution meter- and centimeter-wavelength recombination line observations. Comparison of our radio images with HI and H_2CO observations show that the intervening thermal gas is likely associated with neutral and molecular material as well.Comment: 18 pages, LaTeX with AASTeX-5, 5 figures in 7 PostScript files; accepted for publication in the Ap