One-Dimensional Directed Sandpile Models and the Area under a Brownian Curve

We derive the steady state properties of a general directed ``sandpile'' model in one dimension. Using a central limit theorem for dependent random variables we find the precise conditions for the model to belong to the universality class of the Totally Asymmetric Oslo model, thereby identifying a large universality class of directed sandpiles. We map the avalanche size to the area under a Brownian curve with an absorbing boundary at the origin, motivating us to solve this Brownian curve problem. Thus, we are able to determine the moment generating function for the avalanche-size probability in this universality class, explicitly calculating amplitudes of the leading order terms.Comment: 24 pages, 5 figure

The Herbarium And Type Specimens Of Thomas Henry Kearney, Jr. From 1890‐1901

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149754/1/tax02826.pd

Adapting to the digital age: a narrative approach

The article adopts a narrative inquiry approach to foreground informal learning and exposes a collection of stories from tutors about how they adapted comfortably to the digital age. We were concerned that despite substantial evidence that bringing about changes in pedagogic practices can be difficult, there is a gap in convincing approaches to help in this respect. In this context, this project takes a “bottom-up” approach and synthesises several life-stories into a single persuasive narrative to support the process of adapting to digital change. The project foregrounds the small, every-day motivating moments, cultural features and environmental factors in people's diverse lives which may have contributed to their positive dispositions towards change in relation to technology enhanced learning. We expect that such narrative approaches could serve to support colleagues in other institutions to warm up to ever-changing technological advances

Direct evidence for a piezoelectriclike effect in coherently strained SiGe/Si heterostructures

A hybrid acoustic spectroscopy technique has been used to demonstrate the (reversible) conversion of high frequency electric fields into longitudinal acoustic waves within a modulation-doped pseudomorphic Si/Si0.88Ge0.12/Si heterostructure. This provides compelling evidence for the existence of a piezoelectriclike coupling within such structures

Molecular Characterization and Tissue-Specific Gene Expression of Dermacentor variabilis α-catenin in Response to Rickettsial Infection

Alpha catenin is a cytoskeleton protein that acts as a regulator of actin rearrangement by forming an E-cadherin adhesion complex. In Dermacentor variabilis, a putative α-catenin (Dvα-catenin) was previously identified as differentially regulated in ovaries of ticks chronically infected with Rickettsia montanensis. To begin characterizing the role(s) of Dvα-catenin during rickettsial infection, the full-length Dvα-catenin cDNA was cloned and analysed. Comparative sequence analysis demonstrates a 3069-bp cDNA with a 2718-bp open reading frame with a sequence similar to Ixodes scapularis α-catenin. A portion of Dvα-catenin is homologous to the vinculin-conserved domain containing a putative actin-binding region and β-catenin-binding and -dimerization regions. Quantitative reverse-transcription PCR analysis demonstrated that Dvα-catenin is predominantly expressed in tick ovaries and is responsive to tick feeding. The tissue-specific gene expression analysis of ticks exposed to Rickettsia demonstrates that Dvα-catenin expression was significantly downregulated 12 h after exposure to R. montanensis, but not in Rickettsia amblyommii-exposed ovaries, compared with Rickettsia-unexposed ticks. Studying tick-derived molecules associated with rickettsial infection will provide a better understanding of the transmission dynamics of tick-borne rickettsial diseases

Area distribution and the average shape of a L\'evy bridge

We consider a one dimensional L\'evy bridge x_B of length n and index 0 < \alpha < 2, i.e. a L\'evy random walk constrained to start and end at the origin after n time steps, x_B(0) = x_B(n)=0. We compute the distribution P_B(A,n) of the area A = \sum_{m=1}^n x_B(m) under such a L\'evy bridge and show that, for large n, it has the scaling form P_B(A,n) \sim n^{-1-1/\alpha} F_\alpha(A/n^{1+1/\alpha}), with the asymptotic behavior F_\alpha(Y) \sim Y^{-2(1+\alpha)} for large Y. For \alpha=1, we obtain an explicit expression of F_1(Y) in terms of elementary functions. We also compute the average profile < \tilde x_B (m) > at time m of a L\'evy bridge with fixed area A. For large n and large m and A, one finds the scaling form = n^{1/\alpha} H_\alpha({m}/{n},{A}/{n^{1+1/\alpha}}), where at variance with Brownian bridge, H_\alpha(X,Y) is a non trivial function of the rescaled time m/n and rescaled area Y = A/n^{1+1/\alpha}. Our analytical results are verified by numerical simulations.Comment: 21 pages, 4 Figure

Maximum relative height of one-dimensional interfaces : from Rayleigh to Airy distribution

We introduce an alternative definition of the relative height h^\kappa(x) of a one-dimensional fluctuating interface indexed by a continuously varying real paramater 0 \leq \kappa \leq 1. It interpolates between the height relative to the initial value (i.e. in x=0) when \kappa = 0 and the height relative to the spatially averaged height for \kappa = 1. We compute exactly the distribution P^\kappa(h_m,L) of the maximum h_m of these relative heights for systems of finite size L and periodic boundary conditions. One finds that it takes the scaling form P^\kappa(h_m,L) = L^{-1/2} f^\kappa (h_m L^{-1/2}) where the scaling function f^\kappa(x) interpolates between the Rayleigh distribution for \kappa=0 and the Airy distribution for \kappa=1, the latter being the probability distribution of the area under a Brownian excursion over the unit interval. For arbitrary \kappa, one finds that it is related to, albeit different from, the distribution of the area restricted to the interval [0, \kappa] under a Brownian excursion over the unit interval.Comment: 25 pages, 4 figure

Increased gravitational force reveals the mechanical, resonant nature of physiological tremor

Human physiological hand tremor has a resonant component. Proof of this is that its frequency can be modified by adding mass. However, adding mass also increases the load which must be supported. The necessary force requires muscular contraction which will change motor output and is likely to increase limb stiffness. The increased stiffness will partly offset the effect of the increased mass and this can lead to the erroneous conclusion that factors other than resonance are involved in determining tremor frequency. Using a human centrifuge to increase head-to-foot gravitational field strength, we were able to control for the increased effort by increasing force without changing mass. This revealed that the peak frequency of human hand tremor is 99% predictable on the basis of a resonant mechanism. We ask what, if anything, the peak frequency of physiological tremor can reveal about the operation of the nervous system.This work was funded by a BBSRC Industry Interchange Award to J.P.R.S. and R.F.R. C.J.O. was funded by BBSRC grant BB/I00579X/1. C.A.V. was funded by A∗Midex (Aix-Marseille Initiative of Excellence

Decellularization of human donor aortic and pulmonary valved conduits using low concentration sodium dodecyl sulfate

The clinical use of decellularised cardiac valve allografts is increasing. Long term data will be required to determine whether they outperform conventional cryopreserved allografts. Valves decellularised using different processes may show varied long-term outcomes. It is therefore important to understand the effects of specific decellularisation technologies on the characteristics of donor heart valves. Human cryopreserved aortic and pulmonary valved conduits were decellularised using hypotonic buffer, 0.1% (w/v) SDS and nuclease digestion. The decellularised tissues were compared to cellular cryopreserved valve tissues using histology, immunohistochemistry, quantitation of total DNA, collagen and glycosaminoglycan content, in vitro cytotoxicity assays, uniaxial tensile testing and subcutaneous implantation in mice. The decellularised tissues showed no histological evidence of cells or cell remnants and over 97% DNA removal in all regions (arterial wall, muscle, leaflet and junction). The decellularised tissues retained collagen IV and von Willebrand factor staining with some loss of fibronectin, laminin and chondroitin sulphate staining. There was an absence of MHC Class I staining in decellularised pulmonary valve tissues, with only residual staining in isolated areas of decellularised aortic valve tissues. The collagen content of the tissues was not decreased following decellularisation however the glycosaminoglycan content was reduced. Only moderate changes in the maximum load to failure of the tissues were recorded post-decellularisation. The decellularised tissues were non-cytotoxic in vitro, and were biocompatible in vivo in a mouse subcutaneous implant model. The decellularisation process will now be translated into a GMP compatible process for donor cryopreserved valves with a view to future clinical use

Effect of different scintillator choices on the x-ray imaging performance of CMOS sensors

The ability of wafer scale Complementary Metal Oxide Semiconductor (CMOS) imagers to integrate sensing with analogue to digital conversion at the pixel level has led to their widespread appeal in a variety of imaging applications. This has led to significant improvement in speed and reduction in read-out noise in these imagers when compared to charge-coupled devices (CCDs) and amorphous silicon/selenium based flat panel imagers (FPIs). This paper compares the performance characteristics of CMOS X-ray detectors in various configurations by varying certain parameters of a typical X-ray detector such as fibre optic face plate (FOP), scintillator substrate coating, sensor pixel pitch and scintillator thickness. The evaluations were carried out using RQA5 (70 kV) radiation beam quality aimed at general radiography applications. At comparable Air Kerma values, detectors with a fibre optic plate showed an overall better DQE performance at most spatial frequencies, starting slightly lower at low frequencies then overtaking the “no-FOP” case at mid and high frequencies. The analysis of detectors with different substrate coatings for the scintillators showed comparatively higher DQE for the white-coated aluminium substrate scintillator compared to the black-coated one. The DQE comparison of detectors with and pixel pitch resulted in a higher DQE for the pixel pitch one, with the caveat that the scintillator was thick enough as to render differences in pMTF negligible. Finally, the comparison of scintillators with varying thicknesses showed that the thickest scintillator yielded the highest DQE. These characterisation studies helped in understanding the suitability of these different configurations in various general radiography application scenarios and could be of help to prospective users to determine the overall configuration that best fits their specific imaging needs