The Effect of Tube Wall Stiffness on the Speed of Waves in Tubes

The heart creates pulsatile flow in the arterial and pulmonary circulations. The vessels that make up these systems are distensible, so part of each pulse of blood fills the increasing volume of these vessels, while the remaining blood continues to flow down the vessel. Once the pulse has passed, and the valves from the heart are closed, the vessels contract under their own elasticity, pushing the “stored” blood further down the system. Thus the flow at the beginning of the aorta varies differently over time to flow further down that vessel. Different vessels in each circulatory system appear to have different wall thicknesses and stiffnesses. Further, some organs like the kidney and the brain would appear to function better under continuous blood flow rather than pulsatile flow. Thus we are interested in how wall stiffness of the vessels affects how much blood is “stored” from each pulse and then pushed on down the system, and how the velocity of the wave is affected by wall stiffness. We wish to understand how the body does supply more uniform flow to some organs than to other parts of the circulation. The distensibility of seven tubes with different wall stiffness and thickness was measured. Meter lengths of the three tubes most sensitive to pressure change were attached to a pump that delivered a pulsatile waveform resembling aortic flow. The flowrate and pressure changes were measured in the proximal and distal part of each tube. The distensibility of each tube was calculated again and found to be slightly larger than in the first experiment, possibly due to the non-steady state situation. As expected, the more stiff the tube the less the volume that can be stored. Of interest are the rate of reduction in storage with wall stiffness, and the rate of change in wave speed

Simulated recovery of LEO objects using sCMOS blind stacking

We present the methodology and results of a simulation to determine the recoverability of LEO objects using a blind stacking technique. The method utilises sCMOS and GPU technology to inject and recover LEO objects in real observed data. We explore the target recovery fraction and pipeline run-time as a function of three optimisation parameters; number of frames per data-set, exposure time, and binning factor. Results are presented as a function of magnitude and velocity. We find that target recovery using blind stacking is significantly more complete, and can reach fainter magnitudes, than using individual frames alone. We present results showing that, depending on the combination of optimisation parameters, recovery fraction is up to 90% of detectable targets for magnitudes up to 13.5, and then falls off steadily up to a magnitude limit around 14.5. Run-time is shown to be a few multiples of the observing time for the best combinations of optimisation parameters, approaching real-time processing.Comment: 14 pages, 14 figures. Accepted for publication in Advances in Space Research (ASR

Dealing with missing data in a multi-question depression scale: a comparison of imputation methods

BACKGROUND: Missing data present a challenge to many research projects. The problem is often pronounced in studies utilizing self-report scales, and literature addressing different strategies for dealing with missing data in such circumstances is scarce. The objective of this study was to compare six different imputation techniques for dealing with missing data in the Zung Self-reported Depression scale (SDS). METHODS: 1580 participants from a surgical outcomes study completed the SDS. The SDS is a 20 question scale that respondents complete by circling a value of 1 to 4 for each question. The sum of the responses is calculated and respondents are classified as exhibiting depressive symptoms when their total score is over 40. Missing values were simulated by randomly selecting questions whose values were then deleted (a missing completely at random simulation). Additionally, a missing at random and missing not at random simulation were completed. Six imputation methods were then considered; 1) multiple imputation, 2) single regression, 3) individual mean, 4) overall mean, 5) participant's preceding response, and 6) random selection of a value from 1 to 4. For each method, the imputed mean SDS score and standard deviation were compared to the population statistics. The Spearman correlation coefficient, percent misclassified and the Kappa statistic were also calculated. RESULTS: When 10% of values are missing, all the imputation methods except random selection produce Kappa statistics greater than 0.80 indicating 'near perfect' agreement. MI produces the most valid imputed values with a high Kappa statistic (0.89), although both single regression and individual mean imputation also produced favorable results. As the percent of missing information increased to 30%, or when unbalanced missing data were introduced, MI maintained a high Kappa statistic. The individual mean and single regression method produced Kappas in the 'substantial agreement' range (0.76 and 0.74 respectively). CONCLUSION: Multiple imputation is the most accurate method for dealing with missing data in most of the missind data scenarios we assessed for the SDS. Imputing the individual's mean is also an appropriate and simple method for dealing with missing data that may be more interpretable to the majority of medical readers. Researchers should consider conducting methodological assessments such as this one when confronted with missing data. The optimal method should balance validity, ease of interpretability for readers, and analysis expertise of the research team

Caracterização mecânica das argamassas de assentamento para alvenaria estrutural – previsão e modo de ruptura

Este trabalho pretende avaliar o comportamento mecânico das argamassas de assentamento para o uso estrutural, por meio das propriedades de resistência à compressão, tração na flexão e módulo de elasticidade, sob estados de tensões uniaxial e multiaxial. Portanto, estabelecer correlações entre os resultados mecânicos de diferentes traços de argamassas, relações água/cimento e geometria da amostra associada ao modo de ruptura. As principais conclusões obtidas, entre outras, são: existe uma relação potencial entre a resistência a compressão da amostra de geometria cúbica, cilíndrica e a resistência à flexão (amostra de geometria prismática) em função da relação água/cimento; a função linear é a que melhor ajusta os valores médios do módulo de elasticidade em função da resistência à compressão; a envoltória de ruptura da argamassa confinada lateralmente pode ser representada como uma relação linear de Mohr-Coulomb; observou-se, por meio de ensaios de microscopia eletrônica de varredura a existência de fissuras de retração na interface pasta-agregado e poros isolados, devido ao fluxo ascendente de água causado pela exsudação

Simulated recovery of LEO objects using sCMOS blind stacking

We present the methodology and results of a simulation to determine the recoverability of LEO objects using a blind stacking technique. The method utilises sCMOS and GPU technology to inject and recover LEO objects in real observed data. We explore the target recovery fraction and pipeline run-time as a function of three optimisation parameters; number of frames per data-set, exposure time, and binning factor. Results are presented as a function of magnitude and velocity. We find that target recovery using blind stacking is significantly more complete, and can reach fainter magnitudes, than using individual frames alone. We present results showing that, depending on the combination of optimisation parameters, recovery fraction is up to 90% of detectable targets for magnitudes up to 13.5, and then falls off steadily up to a magnitude limit around 14.5. Run-time is shown to be a few multiples of the observing time for the best combinations of optimisation parameters, approaching real-time processing

Surfactant protein D inhibits HIV-1 infection of target cells via interference with gp120-CD4 interaction and modulates pro-inflammatory cytokine production

© 2014 Pandit et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Surfactant Protein SP-D, a member of the collectin family, is a pattern recognition protein, secreted by mucosal epithelial cells and has an important role in innate immunity against various pathogens. In this study, we confirm that native human SP-D and a recombinant fragment of human SP-D (rhSP-D) bind to gp120 of HIV-1 and significantly inhibit viral replication in vitro in a calcium and dose-dependent manner. We show, for the first time, that SP-D and rhSP-D act as potent inhibitors of HIV-1 entry in to target cells and block the interaction between CD4 and gp120 in a dose-dependent manner. The rhSP-D-mediated inhibition of viral replication was examined using three clinical isolates of HIV-1 and three target cells: Jurkat T cells, U937 monocytic cells and PBMCs. HIV-1 induced cytokine storm in the three target cells was significantly suppressed by rhSP-D. Phosphorylation of key kinases p38, Erk1/2 and AKT, which contribute to HIV-1 induced immune activation, was significantly reduced in vitro in the presence of rhSP-D. Notably, anti-HIV-1 activity of rhSP-D was retained in the presence of biological fluids such as cervico-vaginal lavage and seminal plasma. Our study illustrates the multi-faceted role of human SPD against HIV-1 and potential of rhSP-D for immunotherapy to inhibit viral entry and immune activation in acute HIV infection. © 2014 Pandit et al.The work (Project no. 2011-16850) was supported by Medical Innovation Fund of Indian Council of Medical Research, New Delhi, India (www.icmr.nic.in/)

Exploring SDA sensor architectures for the surveillance of geosynchronous spacecraft

Significant changes have taken place in the space domain over the past decade, with a growing number of emerging space-faring nations and commercial actors gaining access to the operational environment. The consequential diversification of space activities has brought about a need for a reassessment of space domain awareness (SDA) capabilities. Numerous states are developing their operational capability to undertake space-based activities, with potentially widespread ramifications for the safety of spacecraft. Rendezvous and proximity operations are becoming more prevalent in the geosynchronous (GSO) region for mission lifetime extension, active removal of debris, and satellite inspection, in all cases giving rise to novel challenges for SDA systems. What's more, there remains a largely uncharacterised population of small debris in the vicinity of the GSO region, uncovered by bespoke surveys with large aperture telescopes, and posing a significant risk to active satellites. In 2022, the UK Space Agency commissioned a study into the requirements and opportunities for SDA in the UK, carried out by CGI with support from the Global Network On Sustainability In Space (GNOSIS) and UKspace. The study highlighted research and development of sovereign sensors as one of its key recommendations, both to improve the UK's sensing capability and to contribute to closing gaps in global SDA capability. To this end, we explore the key requirements for future SDA sensor architectures, with a focus on ground-based electro-optical systems for the surveillance of spacecraft in the GSO region. Archival two-line element sets are used to simulate catalogued resident space objects (RSOs) passing through a grid of surveillance regions, tasked with monitoring the neighbourhoods of high-value assets in the vicinity of the geostationary belt, while the derived population from ESA's Meteoroid and Space Debris Terrestrial Environment Reference (MASTER) model is used as a basis for simulating the GSO debris field. We assess the observability of transiting RSOs from the vantage point of La Palma, Canary Islands, taking a variety of observational constraints into account, including the Earth's shadow, lunation, and the galactic plane. We examine the performance of the simulated surveillance regions in the context of comprehensive, yet cost-effective SDA provision. Estimated costs are weighed against important metrics for essential SDA tasks (e.g., catalogue maintenance , change detection, and conjunction analysis), such as the total traffic observed per night, the cadence of the observations, and the temporal coverage of registered RSOs. The results of the simulation are used to inform a discussion of key sensor architecture requirements for effective SDA of GSO assets, taking into consideration a combination of sensor characteristics (e.g., sensitivity, resolution, and wavelength band) and other factors (e.g., geographical placement, site quality, and observational strategy) influencing SDA capabilities. We provide a commentary on the advantages and limitations of the different architectures considered and conclude with a list of recommendations for the designs of future SDA systems for the protection of GSO spacecraft

Serum brain-derived neurotrophic factor: Determinants and relationship with depressive symptoms in a community population of middle-aged and elderly people

OBJECTIVES: Brain-derived neurotrophic factor (BDNF) is involved in major depressive disorder and neurodegenerative diseases. Clinical studies, showing decreased serum BDNF levels, are difficult to interpret due to limited knowledge of potential confounders and mixed results for age and sex effects. We explored potential determinants of serum BDNF levels in a community sample of 1230 subjects. METHODS: Multiple linear regression analyses with serum BDNF level as the dependent variable were conducted to explore the effect of four categories of potential BDNF determinants (sampling characteristics, sociodemographic variables, lifestyle factors and somatic diseases) and of self-reported depressive symptoms (Beck's Depression Inventory (BDI). RESULTS: Our results show that BDNF levels decline with age in women, whereas in men levels remain stable. Moreover, after controlling for age and gender, the assays still showed lower serum BDNF levels with higher BDI sum scores. Effects remained significant after correction for two main confounders (time of sampling and smoking), suggesting that they serve as molecular trait factors independent of lifestyle factors. CONCLUSIONS: Given the age-sex interaction on serum BDNF levels and the known association between BDNF and gonadal hormones, research is warranted to delineate the effects of the latter interaction on the risk of psychiatric and neurodegenerative diseases