Performance Characterization of the Low-Power Halo Electric Propulsion System

Performance measurements have been obtained of a novel propulsion concept called the Halo thruster under development within the University of Surrey. The Halo thruster, a type of cusped-field thruster with close similarity to the cylindrical Hall thruster, is motivated by the need for low-power and low-cost electric propulsion for the small satellite sector. Two versions of the device are investigated in this study: a design using permanent magnets at high magnetic-field strength and a design using electromagnets with moderate field strength. While operating at 200 W discharge power, which is of particular interest to power-limited small satellite platforms, the permanent-magnet design achieved a maximum thrust efficiency of 8% at a specific impulse of approximately 900 s using a krypton propellant. By comparison, the electromagnet design achieved a maximum thrust efficiency of 28% at a specific impulse of approximately 1500 s at 200 W using a xenon propellant. For higher levels of power (tested up to 800 W), the performance of the electromagnetic design saturated at approximately 25% thrust efficiency using krypton and 30% using xenon. The thrust efficiency of the permanent-magnet design appeared to increase monotonically up to 600 W reaching a maximum value of 14%

The effects of tides on the water mass mixing and sea ice in the Arctic Ocean

In this study, we use a novel pan-Arctic sea ice-ocean coupled model to examine the effects of tides on sea ice and the mixing of water masses. Two 30 year simulations were performed: one with explicitly resolved tides and the other without any tidal dynamics. We find that the tides are responsible for a ∼15% reduction in the volume of sea ice during the last decade and a redistribution of salinity, with surface salinity in the case with tides being on average ∼1.0–1.8 practical salinity units (PSU) higher than without tides. The ice volume trend in the two simulations also differs: −2.09 × 103 km3/decade without tides and −2.49 × 103 km3/decade with tides, the latter being closer to the trend of −2.58 × 103 km3/decade in the PIOMAS model, which assimilates SST and ice concentration. The three following mechanisms of tidal interaction appear to be significant: (a) strong shear stresses generated by the baroclinic clockwise rotating component of tidal currents in the interior waters; (b) thicker subsurface ice-ocean and bottom boundary layers; and (c) intensification of quasi-steady vertical motions of isopycnals (by ∼50%) through enhanced bottom Ekman pumping and stretching of relative vorticity over rough bottom topography. The combination of these effects leads to entrainment of warm Atlantic Waters into the colder and fresher surface waters, supporting the melting of the overlying ice

Balancing patient-centered and safe pain care for non-surgical inpatients: clinical and managerial perspectives

Background: Hospitals and clinicians aim to deliver care that is safe. Simultaneously, they are ensuring that care is patient-centered, meaning that it is respectful of patients’ values, preferences, and experiences. However, little is known about delivering care in cases where these goals may not align. For example, hospitals and clinicians are facing the daunting challenge of balancing safe and patient-centered pain care for nonsurgical patients, due to lack of comprehensive care guidelines and complexity of this patient population. Methods: To gather clinical and managerial perspectives on the importance, feasibility, and strategies used to balance patient-centered care (PCC) and safe pain care for nonsurgical inpatients, we conducted in-depth, semi-structured interviews with hospitalists (n=10), registered nurses (n=10), and health care managers (n=10) from one healthcare system in the Midwestern United States. We systematically examined transcribed interviews and identified major themes using a thematic analysis approach. Results: Participants acknowledged the importance of balancing PCC and safe pain care. They envisioned this balance as a continuum, with certain patients for whom it is easier (e.g., opioid-naïve patient with a fracture), versus more difficult (e.g., patient with opioid use disorder). Participants also reported several strategies they use to balance PCC and safe pain care, including offering alternatives to opioids, setting realistic pain goals and expectations, and using a team approach. Conclusions: Clinicians and health care managers use various strategies to balance PCC and safe pain care for nonsurgical patients. Future studies should examine the effectiveness of these strategies on patient outcomes

Clinical perspectives on hospitals’ role in the opioid epidemic

Policymakers, legislators, and clinicians have raised concerns that hospital-based clinicians may be incentivized to inappropriately prescribe and administer opioids when addressing pain care needs of their patients, thus potentially contributing to the ongoing opioid epidemic in the United States. Given the need to involve all healthcare settings, including hospitals, in joint efforts to curb the opioid epidemic, it is essential to understand if clinicians perceive hospitals as contributors to the problem. Therefore, we examined clinical perspectives on the role of hospitals in the opioid epidemic

Hotspots of dense water cascading in the Arctic Ocean: Implications for the Pacific water pathways

We explore dense water cascading (DWC), a type of bottom‐trapped gravity current, on multidecadal time scales using a pan‐Arctic regional ocean‐ice model. DWC is particularly important in the Arctic Ocean as the main mechanism of ventilation of interior waters when open ocean convection is blocked by strong density stratification. We identify the locations where the most intense DWC events occur and evaluate the associated cross‐shelf mass, heat, and salt fluxes. We find that the modeled locations of cascading agree well with the sparse historical observations and that cascading is the dominant process responsible for cross‐shelf exchange in the boundary layers. Simulated DWC fluxes of 1.3 Sv (1 Sv = 106 m3/s) in the Central Arctic are comparable to Bering Strait inflow, with associated surface and benthic Ekman fluxes of 0.85 and 0.58 Sv. With ice decline, both surface Ekman flux and DWC fluxes are increasing at a rate of 0.023 and 0.0175 Sv/year, respectively. A detailed analysis of specific cascading sites around the Beaufort Gyre and adjacent regions shows that autumn upwelling of warm and saltier Atlantic waters on the shelf and subsequent cooling and mixing of uplifted waters trigger the cascading on the West Chukchi Sea shelf break. Lagrangian particle tracking of low salinity Pacific waters originating at the surface in the Bering Strait shows that these waters are modified by brine rejection and cooling, and through subsequent mixing become dense enough to reach depths of 160–200 m

Direct thrust measurement of a permanent magnet helicon double layer thruster

Direct thrust measurements of a permanent magnet helicon double layer thruster have been made using a pendulum thrust balance and a high sensitivity laser displacement sensor. At the low pressures used (0.08 Pa) an ion beam is detected downstream of the thruster exit, and a maximum thrust force of about 3 mN is measured for argon with an rf input power of about 700 W. The measured thrust is proportional to the upstream plasma density and is in good agreement with the theoretical thrust based on the maximum upstream electron pressure

Honesty mediates the relationship between serotonin and reaction to unfairness

How does one deal with unfair behaviors? This subject has long been investigated by various disciplines including philosophy, psychology, economics, and biology. However, our reactions to unfairness differ from one individual to another. Experimental economics studies using the ultimatum game (UG), in which players must decide whether to accept or reject fair or unfair offers, have also shown that there are substantial individual differences in reaction to unfairness. However, little is known about psychological as well as neurobiological mechanisms of this observation. We combined a molecular imaging technique, an economics game, and a personality inventory to elucidate the neurobiological mechanism of heterogeneous reactions to unfairness. Contrary to the common belief that aggressive personalities (impulsivity or hostility) are related to the high rejection rate of unfair offers in UG, we found that individuals with apparently peaceful personalities (straightforwardness and trust) rejected more often and were engaged in personally costly forms of retaliation. Furthermore, individuals with a low level of serotonin transporters in the dorsal raphe nucleus (DRN) are honest and trustful, and thus cannot tolerate unfairness, being candid in expressing their frustrations. In other words, higher central serotonin transmission might allow us to behave adroitly and opportunistically, being good at playing games while pursuing self-interest. We provide unique neurobiological evidence to account for individual differences of reaction to unfairness

An Analysis of Primary Care Clinician Communication About Risk, Benefits, and Goals Related to Chronic Opioid Therapy

Background. Safe opioid prescribing and effective pain care are particularly important issues in the United States, where decades of widespread opioid prescribing have contributed to high rates of opioid use disorder. Because of the importance of clinician-patient communication in effective pain care and recent initiatives to curb rising opioid overdose deaths, this study sought to understand how clinicians and patients communicate about the risks, benefits, and goals of opioid therapy during primary care visits. Methods. We recruited clinicians and patients from six primary care clinics across three health systems in the Midwest United States. We audio-recorded 30 unique patients currently receiving opioids for chronic noncancer pain from 12 clinicians. We systematically analyzed transcribed, clinic visits to identify emergent themes. Results. Twenty of the 30 patient participants were females. Several patients had multiple pain diagnoses, with the most common diagnoses being osteoarthritis (n = 10), spondylosis (n = 6), and low back pain (n = 5). We identified five themes: 1) communication about individual-level and population-level risks, 2) communication about policies or clinical guidelines related to opioids, 3) communication about the limited effectiveness of opioids for chronic pain conditions, 4) communication about nonopioid therapies for chronic pain, and 5) communication about the goal of the opioid tapering. Conclusions. Clinicians discuss opioid-related risks in varying ways during patient visits, which may differentially affect patient experiences. Our findings may inform the development and use of more standardized approaches to discussing opioids during primary care visits

Projected sea level rise and changes in extreme storm surge and wave events during the 21st century in the region of Singapore

Singapore is an island state with considerable population, industries, commerce and transport located in coastal areas at elevations less than 2 m making it vulnerable to sea-level rise. Mitigation against future inundation events requires a quantitative assessment of risk. To address this need, regional projections of changes in (i) long-term mean sea level and (ii) the frequency of extreme storm surge and wave events have been combined to explore potential changes to coastal flood risk over the 21st century. Local changes in time mean sea level were evaluated using the process-based climate model data and methods presented in the IPCC AR5. Regional surge and wave solutions extending from 1980 to 2100 were generated using ~ 12 km resolution surge (Nucleus for European Modelling of the Ocean – NEMO) and wave (WaveWatchIII) models. Ocean simulations were forced by output from a selection of four downscaled (~ 12 km resolution) atmospheric models, forced at the lateral boundaries by global climate model simulations generated for the IPCC AR5. Long-term trends in skew surge and significant wave height were then assessed using a generalised extreme value model, fit to the largest modelled events each year. An additional atmospheric solution downscaled from the ERA-Interim global reanalysis was used to force historical ocean model simulations extending from 1980–2010, enabling a quantitative assessment of model skill. Simulated historical sea surface height and significant wave height time series were compared to tide gauge data and satellite altimetry data respectively. Central estimates of the long-term mean sea level rise at Singapore by 2100 were projected to be 0.52 m (0.74 m) under the RCP 4.5 (8.5) scenarios respectively. Trends in surge and significant wave height 2 year return levels were found to be statistically insignificant and/or physically very small under the more severe RCP8.5 scenario. We conclude that changes to long-term mean sea level constitute the dominant signal of change to the projected inundation risk for Singapore during the 21st century. We note that the largest recorded surge residual in the Singapore Strait of ~ 84 cm lies between the central and upper estimates of sea level rise by 2100, highlighting the vulnerability of the region