The nascent coffee ring with arbitrary droplet contact set: an asymptotic analysis

We consider the effect of droplet geometry on the early-stages of coffee ring formation during the evaporation of a thin droplet with an arbitrary simple, smooth, pinned contact line. We perform a systematic matched asymptotic analysis of the small-capillary number, large-solutal Péclet number limit for two different evaporative models: a kinetic model, in which the evaporative flux is effectively constant across the droplet, and a diffusive model, in which the flux is singular at the contact line. For both evaporative models, solute is transported to the contact line by a capillary flow in the droplet bulk while, local to the contact line, solute diffusion counters advection. The resulting interplay leads to the formation of the nascent coffee-ring profile. By exploiting a coordinate system embedded in the contact line, we solve explicitly the local leading-order problem, deriving a similarity profile (in the form of a gamma distribution) that describes the nascent coffee-ring. Notably, for an arbitrary contact-line geometry, the ring characteristics change due to the concomitant asymmetry in the shape of the droplet free surface, the evaporative flux (for diffusive evaporation) and the mass flux into the contact line. We utilize the asymptotic model to determine the effects of contact-line geometry on the growth of the coffee ring for a droplet with an elliptical contact set. Our results offer mechanistic insight into the effect of contact-line curvature on the development of the coffee-ring from deposition up to jamming of the solute; moreover our model predicts when finite concentration effects become relevant

Molten Metal Loop Driven by Electromagnetic Pump

The first challenge of this proposed study was the gauges for the loop, which were not functioning properly and giving off inaccurate data due to a loop flow issue. Therefore a new loop design, including gauges, was created to gather accurate data for the electromagnetic pump. The electromagnetic pump used in this experiment differs from the standard electromagnetic motors by using rare earth magnets set into opposing steel plates that rotate simultaneously. Accurate data from the velocity and pressure gauges is necessary so the correlation between the EM pump’s speed and the flow velocity could be calculated. This technology could be advantageous to industries using metal transportation, by saving both money and time for industries. A loop for molten metal must be created so that differential pressure and flow rate can be tracked accurately. This can be found through the use of research, model development, and previous design work. To accomplish this task, SolidWorks was used to create models of the molten metal loop to be built. Based on this data, the design was manufactured and tested to ensure it can accurately gather data. The important outcomes for this project were to develop correlations between the flux generated by the electromagnetic pump and the RPMs. If this was achieved, then the possible incorporation of a Laser Induced Breakdown Spectroscopy (LIBS) system will be incorporated to analyze the different compositions (contaminations) of the molten metal in the loop. Multiple ports were be added to the loop for implementation of the quartz window in anticipation of future use of the LIBS system, as well as other measurement apparatuses. In the meantime, the LIBS system will not be addressed at this stage in the project.https://scholarscompass.vcu.edu/capstone/1049/thumbnail.jp

The nascent coffee ring with arbitrary droplet contact set: an asymptotic analysis

We consider the effect of droplet geometry on the early-stages of coffee ring formation during the evaporation of a thin droplet with an arbitrary simple, smooth, pinned contact line. We perform a systematic matched asymptotic analysis of the small-capillary number, large-solutal Peclet number limit for two evaporative models: a kinetic model, in which the evaporative flux is constant across the droplet, and a diffusive model, in which the evaporative flux is singular at the contact line. For both evaporative models, solute is transported to the contact line by a capillary flow while, local to the contact line, solute diffusion counters advection. The resulting interplay leads to the formation of the nascent coffee ring. By exploiting a coordinate system embedded in the contact line, we solve explicitly the local leading-order problem, deriving a similarity profile (in the form of a gamma distribution) that describes the coffee ring profile in its early stages. Notably, the ring characteristics change due to the concomitant asymmetry in the shape of the droplet free surface, the evaporative flux (in the diffusive evaporative regime) and the mass flux into the contact line. We utilize the asymptotic model to determine the effects of geometry on the growth of the coffee ring for a droplet with an elliptical contact set. Our results offer mechanistic insight into the effect of contact-line curvature on the development of the coffee-ring from deposition up to jamming of the solute; moreover our model predicts when finite concentration effects become relevant

Magnetic Untwisting in Most Solar X-Ray Jets

From 54 Xray jets observed in the polar coronal holes by Hinode's XRay Telescope (XRT) during coverage in movies from Solar Dynamic Observatory's Atmospheric Imaging Assembly (AIA) taken in its He II 304 band at a cadence of 12 s, we have established a basic characteristic of solar Xray jets: untwisting motion in the spire. In this presentation, we show the progression of few of these Xray jets in XRT images and track their untwisting in AIA He II images. From their structure displayed in their XRT movies, 19 jets were evidently standard jets made by interchange reconnection of the magneticarcade base with ambient open field, 32 were evidently blowout jets made by blowout eruption of the base arcade, and 3 were of ambiguous form. As was anticipated from the >10,000 km span of the base arcade in most polar Xray jets and from the disparity of standard jets and blowout jets in their magnetic production, few of the standard Xray jets (3 of 19) but nearly all of the blowout Xray jets (29 of 32) carried enough cool (T is approximately 105 K) plasma to be seen in their He II movies. In the 32 Xray jets that showed a cool component, the He II movies show 10100 km/s untwisting motions about the axis of the spire in all 3 standard jets and in 26 of the 29 blowout jets. Evidently, the open magnetic field in nearly all blowout Xray jets and probably in most standard Xray jets carries transient twist. This twist apparently relaxes by propagating out along the open field as a torsional wave. Highresolution spectrograms and Dopplergrams have shown that most TypeII spicules have torsional motions of 1030 km/s. Our observation of similar torsional motion in Xray jets strengthens the case for TypeII spicules being made in the same way as Xray jets, by blowout eruption of a twisted magnetic arcade in the spicule base and/or by interchange reconnection of the twisted base arcade with the ambient open field. This work was funded by NASA's Heliophysics Division through its LWS TRT Program and its Hinode Project, and by NSF through its Research Experience for Undergraduates Program

Magnetic Untwisting in Most Solar X-Ray Jets

If TypeII spicules are made like Xray jets by granulesize emerging bipoles, then they plausibly power the quiet corona and solar wind

Developing an On-Line Interactive Health Psychology Module.

On-line teaching material in health psychology was developed which ensured a range of students could access appropriate material for their course and level of study. This material has been developed around the concept of smaller 'content chunks' which can be combined into whole units of learning (topics), and ultimately, a module. On the basis of the underlying philosophy that the medium is part of the message, we considered interactivity to be a key element in engaging the student with the material. Consequently, the key aim of this development was to stimulate and engage students, promoting better involvement with the academic material, and hence better learning. It was hoped that this was achieved through the development of material including linked programmes and supporting material, small Java Scripts and basic email, forms and HTML additions. This material is outlined as are some of the interactive activities introduced, and the preliminary student and tutor experience described

Exploring Expressions of Possible Selves with High School and College Students with Learning Disabilities

In this article, we explore a program designed to engage high school and college students with learning disabilities (LD) in conversations about their hopes, expectations, and fears for the future. We explore the mindset of students by focusing on their self-identified passions for life and sense of strengths and limitations. We found that males and females differed in goals related to Academics, Work Ethic, Degree Specific Statements, and Money and Finances. For example, females emphasized “Academic Goals” more frequently than males and focused on topics such as GPA and work ethic in school. However, males made more “Degree Specific Statements” than females, more often emphasizing the desire to be financially stable or have a career with a large income. These differences suggest that college transition staff may want to focus on goals identified by male and female students with LD as a way to be more responsive to student self-identified goals

Sensory nerve transfers in the upper limb after peripheral nerve injury:a scoping review

Nerve transfer for motor nerve paralysis is an established technique for treating complex nerve injuries. However, nerve transfer for sensory reconstruction has not been widely used, and published research on this topic is limited compared to motor nerve transfer. The indications and outcomes of nerve transfer for the restoration of sensory function remain unproven. This scoping review examines the indications, outcomes and complications of sensory nerve transfer. In total, 22 studies were included; the major finding is that distal sensory nerve transfers are more successful than proximal ones in succeeding protective sensation. Although the risk of extension of the sensory deficit with donor site loss and morbidity from neuromas remain a barrier to wider adoption, these complications were not reported in the review. Further, the scarcity of studies and small patient series limit the ability to determine sensory nerve transfer success. However, sensory restoration remains an opportunity for surgeons to pursue.</p

Sensory nerve transfers in the upper limb after peripheral nerve injury:a scoping review

Nerve transfer for motor nerve paralysis is an established technique for treating complex nerve injuries. However, nerve transfer for sensory reconstruction has not been widely used, and published research on this topic is limited compared to motor nerve transfer. The indications and outcomes of nerve transfer for the restoration of sensory function remain unproven. This scoping review examines the indications, outcomes and complications of sensory nerve transfer. In total, 22 studies were included; the major finding is that distal sensory nerve transfers are more successful than proximal ones in succeeding protective sensation. Although the risk of extension of the sensory deficit with donor site loss and morbidity from neuromas remain a barrier to wider adoption, these complications were not reported in the review. Further, the scarcity of studies and small patient series limit the ability to determine sensory nerve transfer success. However, sensory restoration remains an opportunity for surgeons to pursue.</p