Surface Roughness Enhancement of Indirect-SLS Metal Parts by Laser Surface Polishing

Laser polishing by means of shallow surface melting of indirect-SLS metal parts was achieved using high power CO2 and Nd:YAG lasers raster scanned at high speed. This was an effective technique for reducing surface roughness. The fast moving laser beam provides just enough heat energy to cause melting of the surface peaks. The molten mass then flows into the surface valleys by surface tension, gravity and laser pressure, thus diminishing the roughness. Surface roughness Ra data were obtained by profilometry measurements of the polished samples. An analytical model was developed based on the assumption that the surface of an SLS part consists of semi-spherical caps. The model was used to predict the Ra values as a function of laser power, scan speed and precursor powder particle size. The modeled results fit the empirical data within a 15% error.The Laboratory of Freeform Fabrication gratefully acknowledges the support of the Office of Naval Research for funding the project “Surface Engineering for SFF Processes”, Grant Nº: N00014-00-1-0334Mechanical Engineerin

Viral antibody dynamics in a chiropteran host

1. Bats host many viruses that are significant for human and domestic animal health, but the dynamics of these infections in their natural reservoir hosts remain poorly elucidated.<p></p> 2. In these, and other, systems, there is evidence that seasonal life-cycle events drive infection dynamics, directly impacting the risk of exposure to spillover hosts. Understanding these dynamics improves our ability to predict zoonotic spillover from the reservoir hosts.<p></p> 3. To this end, we followed henipavirus antibody levels of >100 individual E. helvum in a closed, captive, breeding population over a 30-month period, using a powerful novel antibody quantitation method.<p></p> 4. We demonstrate the presence of maternal antibodies in this system and accurately determine their longevity. We also present evidence of population-level persistence of viral infection and demonstrate periods of increased horizontal virus transmission associated with the pregnancy/lactation period.<p></p> 5.The novel findings of infection persistence and the effect of pregnancy on viral transmission, as well as an accurate quantitation of chiropteran maternal antiviral antibody half-life, provide fundamental baseline data for the continued study of viral infections in these important reservoir hosts

Defining the need for surgical intervention following a snakebite still relies heavily on clinical assessment: The experience in Pietermaritzburg, South Africa

Background. This audit of snakebites was undertaken to document our experience with snakebite in the western part of KwaZulu-Natal (KZN) Province, South Africa (SA).Objective. To document our experience with snakebite in the western part of KZN, and to interrogate the data on patients who required some form of surgical intervention.Methods. A retrospective study was undertaken at the Pietermaritzburg Metropolitan Trauma Service, Pietermaritzburg, SA. The Hybrid Electronic Medical Registry was reviewed for the 5-year period January 2012 - December 2016. All patients admitted to the service for management of snakebite were included.Results. The offending snake is rarely identified, and the syndromic approach is now the mainstay of management. Most envenomations seen during the study period were cytotoxic, presenting with painful progressive swelling (PPS). We did not see any purely neurotoxic or haemotoxic envenomations. Antivenom is required for a subset of patients. The indications are essentially PPS that increases by >15 cm over an hour, PPS up to the elbow or knee after 4 hours, PPS of the whole limb after 8 hours, threatened airway, shortness of breath, associated clotting abnormalities and compartment syndrome. If no symptoms have manifested within 1 hour of a snakebite, clinically significant envenomation is unlikely to have occurred. Antivenom is associated with a high rate of anaphylaxis and should only be administered when absolutely indicated, preferably in a high-care setting under continuous monitoring. The need for surgery is less well defined. Urgent surgery is indicated for compartment syndrome of the limb, which is a potentially life- and limb-threatening condition. Its diagnosis is usually made clinically, but this is difficult in snakebites. Morbidity and cost increase dramatically once fasciotomy is required, as evidenced by much longer hospital stay. There is frequently a degree of cross-over between cytotoxicity and haemotoxicity in envenomations that require fasciotomy, which means that fasciotomy may result in catastrophic bleeding and should be preceded by the administration of antivenom, especially in patients with a low platelet count or a high international normalised ratio. Physiological and biochemical markers are unhelpful in assessing the need for fasciotomy. Objective methods include measurement of compartment pressures and ultrasound.Conclusion. The syndromic management of snakebite is effective and safe. There is a high incidence of anaphylactic reactions to antivenom, and its administration must be closely supervised. In our area we overwhelmingly see cytotoxic snakebites with PPS. Surgery is often needed, and we need to refine our algorithms in terms of deciding on surgery

Entrainment of the Melatonin Rhythms in Early Postnatal Lambs and Their Mothers

Although the developing sheep can produce an appropriately timed melatonin rhythm as early as 1 week after birth, it is not known whether the lamb is able to adjust its melatonin rhythm to a change in daylength. The ability of the young lamb to entrain its pattern of melatonin secretion to a new photoperiod was determined in the present study. Eight female lambs and their mothers were raised in long days (LD 16:8) beginning 2 weeks post partum. At 7 weeks of age, the time of lights-off was advanced 8 hr, the short-day photoperiod then being LD 8:16; the time of lights-on remained unchanged. Concentrations of melatonin were measured in blood samples collected hourly on days - 1, 0, 2, 4, 6, and 13 relative to the light change. On day 0, all mothers and daughters had advanced the onset of melatonin secretion by at least 1 hr, and by day 13, 12 of 16 had completely entrained to the new photoperiod. The rate of entrainment among individuals varied; the mean rate for lambs and mothers did not differ. This study provides evidence that the melatonin-rhythm-generating system matures shortly after birth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68290/2/10.1177_074873048900400405.pd

Performance evaluation of a mechanically ventilated heat recovery (MVHR) system as part of a series of UK residential energy retrofit measures

This study involves a detailed analysis of a mechanically ventilated heat recovery (MVHR) system installed as a case study retrofit project in a UK test dwelling. Comparisons of predicted and in situ performance are made through the calculation of a theoretical and practical heat loss coefficient value (HLC). Analysis revealed underperformance in the installed MVHR system, as compared to predicted data. Issues were identified in the installation and function of the control unit and ductwork. Improvement work enabled the system to function more closely to optimum performance levels. However, discrepancies still existed between the predicted and actual HLC values, which were largely accounted for through theoretical heat loss calculations attributable to slight imbalances within the system supply and extract rates. When normalised, the data still showed an unaccounted heat loss of approximately 6 W/K in both MVHR tests. The study reinforces the need for high quality MVHR installation and commissioning work, which is critical to ensure that a system can perform to the optimum levels specified in manufacturer literature. Education and training throughout the supply chain is essential in achieving this, as system inefficiencies can lead to unnecessary heat losses resulting from increased levels of air infiltration or leakage

Improving the airtightness in an existing UK dwelling: the challenges, the measures and their effectiveness

Air infiltration, occurring through gaps in the building envelope, can contribute up to one third of total heat losses associated with older UK dwellings [1]. Therefore, reducing the rate of air leakage (i.e. improving air ‘tightness’) can have a positive effect in terms of decreasing space heating requirements. This study presents an investigation of the effectiveness of airtightness measures applied in a retrofit context to a UK dwelling. A phased programme of refurbishment work was undertaken to a test dwelling at the University of Nottingham campus, UK. Evaluation techniques, including building energy modelling (SAP 2009), air pressurisation tests and thermal imaging, were performed. The study demonstrates that the use of conventional draught-proofing measures can achieve a reduction in air permeability of over 30% when compared with the house base case value of 15.57 m3/(h.m2) @ 50 Pa. This reduction was only achievable with close attention to installation detail. Further measures of service penetration and floor sealing enabled the air permeability to be reduced to as low as 4.74 m3/(h m2) @ 50 Pa. Modelling of the test dwelling predicted an initial space heating supply energy requirement of 32,373 kWh, which was reduced to 23,197 kWh by a combination of the air tightness measures, insulation, and system (boiler and ventilation) improvements. Air tightness measures alone contributed to approximately 9% of the predicted total reduction, half of which was due to relatively straight-forward draught-proofing. Other more advanced air tightness measures were considerably more expensive, though cheaper approaches to their application could help reduce payback times

Radiative Corrections to One-Photon Decays of Hydrogenic Ions

Radiative corrections to the decay rate of n=2 states of hydrogenic ions are calculated. The transitions considered are the M1 decay of the 2s state to the ground state and the E1(M2) decays of the $2p_{1/2}$ and $2p_{3/2}$ states to the ground state. The radiative corrections start in order $\alpha (Z \alpha)^2$, but the method used sums all orders of $Z\alpha$. The leading $\alpha (Z\alpha)^2$ correction for the E1 decays is calculated and compared with the exact result. The extension of the calculational method to parity nonconserving transitions in neutral atoms is discussed.Comment: 22 pages, 2 figure

The Approach to Ergodicity in Monte Carlo Simulations

The approach to the ergodic limit in Monte Carlo simulations is studied using both analytic and numerical methods. With the help of a stochastic model, a metric is defined that enables the examination of a simulation in both the ergodic and non-ergodic regimes. In the non-ergodic regime, the model implies how the simulation is expected to approach ergodic behavior analytically, and the analytically inferred decay law of the metric allows the monitoring of the onset of ergodic behavior. The metric is related to previously defined measures developed for molecular dynamics simulations, and the metric enables the comparison of the relative efficiencies of different Monte Carlo schemes. Applications to Lennard-Jones 13-particle clusters are shown to match the model for Metropolis, J-walking and parallel tempering based approaches. The relative efficiencies of these three Monte Carlo approaches are compared, and the decay law is shown to be useful in determining needed high temperature parameters in parallel tempering and J-walking studies of atomic clusters.Comment: 17 Pages, 7 Figure

Particle interactions with single or multiple 3D solar reconnecting current sheets

The acceleration of charged particles (electrons and protons) in flaring solar active regions is analyzed by numerical experiments. The acceleration is modelled as a stochastic process taking place by the interaction of the particles with local magnetic reconnection sites via multiple steps. Two types of local reconnecting topologies are studied: the Harris-type and the X-point. A formula for the maximum kinetic energy gain in a Harris-type current sheet, found in a previous work of ours, fits well the numerical data for a single step of the process. A generalization is then given approximating the kinetic energy gain through an X-point. In the case of the multiple step process, in both topologies the particles' kinetic energy distribution is found to acquire a practically invariant form after a small number of steps. This tendency is interpreted theoretically. Other characteristics of the acceleration process are given, such as the mean acceleration time and the pitch angle distributions of the particles.Comment: 18 pages, 9 figures, Solar Physics, in pres