Confinement in a Double Barrier Structure in the Presence of an Electric Field

The effect of electric field on the electron resonant tunnelling into a double barrier structure is studied. We show for particular field strengths an increase of the tunnelling time which leads us to explain the Stark-ladder localization and Bloch oscillations in superlattices and to discuss the quenching of luminescence in multiple quantum wells.Comment: Latex 7 pages with 4 figures. The figures are included in this version and the figure caption is slightly modifie

Wind Preview-Based Model Predictive Control of Multi-Rotor UAVs Using LiDAR

Autonomous outdoor operations of Unmanned Aerial Vehicles (UAVs), such as quadrotors, expose the aircraft to wind gusts causing a significant reduction in their position-holding performance. This vulnerability becomes more critical during the automated docking of these vehicles to outdoor charging stations. Utilising real-time wind preview information for the gust rejection control of UAVs has become more feasible due to the advancement of remote wind sensing technology such as LiDAR. This work proposes the use of a wind-preview-based Model Predictive Controller (MPC) to utilise remote wind measurements from a LiDAR for disturbance rejection. Here a ground-based LiDAR unit is used to predict the incoming wind disturbance at the takeoff and landing site of an autonomous quadrotor UAV. This preview information is then utilised by an MPC to provide the optimal compensation over the defined horizon. Simulations were conducted with LiDAR data gathered from field tests to verify the efficacy of the proposed system and to test the robustness of the wind-preview-based control. The results show a favourable improvement in the aircraft response to wind gusts with the addition of wind preview to the MPC; An 80% improvement in its position-holding performance combined with reduced rotational rates and peak rotational angles signifying a less aggressive approach to increased performance when compared with only feedback based MPC disturbance rejection. System robustness tests demonstrated a 1.75 s or 120% margin in the gust preview’s timing or strength respectively before adverse performance impact. The addition of wind-preview to an MPC has been shown to increase the gust rejection of UAVs over standard feedback-based MPC thus enabling their precision landing onto docking stations in the presence of wind gusts

PRIMUS: The relationship between Star formation and AGN accretion

We study the evidence for a connection between active galactic nuclei (AGN) fueling and star formation by investigating the relationship between the X-ray luminosities of AGN and the star formation rates (SFRs) of their host galaxies. We identify a sample of 309 AGN with $10^{41}<L_\mathrm{X}<10^{44}$ erg s$^{-1}$ at $0.2 < z < 1.2$ in the PRIMUS redshift survey. We find AGN in galaxies with a wide range of SFR at a given $L_X$. We do not find a significant correlation between SFR and the observed instantaneous $L_X$ for star forming AGN host galaxies. However, there is a weak but significant correlation between the mean $L_\mathrm{X}$ and SFR of detected AGN in star forming galaxies, which likely reflects that $L_\mathrm{X}$ varies on shorter timescales than SFR. We find no correlation between stellar mass and $L_\mathrm{X}$ within the AGN population. Within both populations of star forming and quiescent galaxies, we find a similar power-law distribution in the probability of hosting an AGN as a function of specific accretion rate. Furthermore, at a given stellar mass, we find a star forming galaxy $\sim2-3$ more likely than a quiescent galaxy to host an AGN of a given specific accretion rate. The probability of a galaxy hosting an AGN is constant across the main sequence of star formation. These results indicate that there is an underlying connection between star formation and the presence of AGN, but AGN are often hosted by quiescent galaxies

The flux of iron and iron isotopes from San Pedro Basin sediments

Iron is an important nutrient in the ocean, but the different sources and sinks of iron are not well constrained. Here, we use measurements of Fe concentration and Fe stable isotope ratios to evaluate the importance of reducing continental margins as a source of Fe to the open ocean. Dissolved iron concentration ([Fe]) and iron stable isotope ratios (δ^(56)Fe) were measured in the San Pedro and Santa Barbara basins. Dissolved δ^(56)Fe ranges from −1.82‰ to 0.00‰ in the San Pedro Basin and from −3.45‰ to −0.29‰ in the Santa Barbara Basin, and in both basins the lowest δ^(56)Fe values and highest Fe concentrations are found at the bottom of the basin reflecting the input of isotopically light Fe from reducing sediment porewaters. In the San Pedro Basin, we are also able to fingerprint an advective source of Fe from shallow continental shelves next to the basin and the atmospheric deposition of Fe into surface waters. A one-dimensional model of the Fe isotope cycle has been constructed for the deep silled San Pedro Basin. By fitting model output to data, values of several important iron cycle parameters are predicted including a flux of Fe from sediment porewaters into the water column of 0.32–1.14 μmol m^(−2) d^(−1), a first-order dissolved Fe precipitation rate constant of 0.0018–0.0053 d^(−1), a flux δ56Fe of −2.4‰, and an isotope effect for Fe precipitation of Δδ^(56)Fe_(particulate-dissolved) = −0.8‰. Applying our model-predicted Fe cycle parameters to the global ocean suggests that continental margins contribute 4–12% of world ocean dissolved Fe and make the ocean’s Fe lighter by −0.08‰ to −0.26‰. The dramatically negative δ^(56)Fe signature seen in the water column of the San Pedro and Santa Barbara basins demonstrate the utility of Fe isotopes as a tracer for continental margin Fe input from reducing sediments to the oceans, while the isotopic fractionation observed during loss of Fe from the dissolved phase suggests that this signature will be modified by subsequent reactions. Our modeling provides an initial framework for testing how these signals are transmitted into the open ocean

Influence of Duration of Homograft on Humoral Responses in Man

Elevated titers of natural antibodies have been demonstrated in the sera of patients following transplantation. These humoral responses were thought to be associated with rejection. This concept was challenged by investigators whose studies associated these responses with infection or with injection of heterologous serum. Nevertheless, the possible prognostic significance of these relatively simple tests has continued to evoke interest. This study was undertaken to compare the humoral responses in three different groups of patients with organ transplants in order to evaluate the influence of duration of the homograft and the attendant immunosuppression

Endorsement and Constructive Criticism of an Innovative Online Reflexive Self-Talk Intervention

This study prospectively followed the experiences of skilled athletes who were involved in an innovative reflexive self-talk online intervention targeting goal-directed self-talk. Four experienced female athletes between the ages of 20 and 40 years were invited to an initial interview, a 4-week intervention, and two post-intervention interviews. Two applied sport psychologists used an online Socratic questioning approach to encourage their athletes to describe challenging scenarios, think about their use of self-talk and its effectiveness, and explore alternative self-statements that could be used in future situations. Data were multi-sourced stemming from the psychologists, athletes, and third parties (e.g., coach). Three athletes completed the intervention, whereas one athlete withdrew prematurely, mainly because the Socratic questioning approach and the online mode of delivery did not meet her preferences. From the three athlete who had completed the intervention, there was endorsement and constructive criticism of the intervention and its online delivery mode. The intervention, largely due to the accompanying raised awareness of self-talk use and refined content, seemingly benefited a range of variables including emotions, motivation, and confidence, both inside and outside of the athletes' sports life domain. Accordingly, this new type of online intervention warrants further consideration in the literature

von Willebrand Factor unfolding mediates platelet deposition in a model of high-shear thrombosis

Thrombosis under high-shear conditions is mediated by the mechanosensitive blood glycoprotein von Willebrand Factor (vWF). vWF unfolds in response to strong flow gradients and facilitates rapid recruitment of platelets in flowing blood. While the thrombogenic effect of vWF is well recognized, its conformational response in complex flows has largely been omitted from numerical models of thrombosis. We recently presented a continuum model for the unfolding of vWF, where we represented vWF transport and its flow-induced conformational change using convection-diffusion-reaction equations. Here, we incorporate the vWF component into our multi-constituent model of thrombosis, where the local concentration of stretched vWF amplifies the deposition rate of free-flowing platelets and reduces the shear cleaning of deposited platelets. We validate the model using three benchmarks: in vitro model of atherothrombosis, a stagnation point flow, and the PFA-100, a clinical blood test commonly used for screening for von Willebrand Disease (vWD). The simulations reproduced the key aspects of vWF-mediated thrombosis observed in these experiments, such as the thrombus location, thrombus growth dynamics, and the effect of blocking platelet-vWF interactions. The PFA-100 simulations closely matched the reported occlusion times for normal blood and several hemostatic deficiencies, namely, thrombocytopenia, vWD Type 1, and vWD Type 3. Overall, the multi-constituent model of thrombosis presented in this work enables macro-scale 3-D simulations of thrombus formation in complex geometries over a wide range of shear rates and accounts for qualitative and quantitative hemostatic deficiencies in patient blood. The results also demonstrate the utility of the continuum model of vWF unfolding that could be adapted to other numerical models of thrombosis

Investigation of the strength of thermally conditioned basalt and e-glass fibres

It is projected that the total global production of composite materials will significantly exceed 10 million tons by 2015 of which over 90% will contain glass fibre reinforcement. Traditionally most of this composite material would be directed to landfill at end of life. Thus, recycling composites has started to gain great importance due to environmental and commercial aspects. The development of an efficient process to enable cost-effective regeneration of the mechanical properties of fibre for recycling, could result in a huge decrease of landfill disposal as well as the attenuation in CO2 emissions. There are several processes available for recycling composites but the most technologically advanced is thermal recycling. However, during the recycling process glass fibres that are treated at temperatures in a range between 300 up to 600 °C exhibit a huge drop in strength and as a result sometimes are considered as not reusable or unsuitable for reprocessing [1]. Although basalt fibre has been available for some time, recent development in the processing and production of basalt has resulted in the availability of continuous basalt fibre in similar form to traditional glass fibre. It is often stated that basalt has better high temperature resistance compared to E-glass fibre [2,3]. If this were true then basalt fibre may show better prospects to survive an end-of-life composite thermal recycling process as a useful reinforcement. The present work investigates and compares the changes in the mechanical properties of basalt fibres and E-Glass fibres when heat-treated to between 300 – 600 °C. Since the fibre surface plays an important role in the retained strength of brittle fibres, the investigation used fibre with similar epoxy compatible sizings in order to maximise the quality of the comparison. Results of single fibre testing of tensile strength and modulus are presented and discussed