Rectangular subsonic jet flow field measurements

Flow field measurements of three subsonic rectangular cold air jets are presented. The three cases had aspect ratios of 1x2, 1x4 at a Mach number of 0.09 and an aspect ratio of 1x2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemometer system. The data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data are presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made

Sphingosine 1-phosphate : regulation of receptor signalling and cross-talk with chemokines

PhD ThesisThe generation and execution of adaptive immune responses require fine control of the migration of lymphocytes in homeostasis and inflammation. Recently it has been shown that certain chemokines and the lipid sphingosine 1-phosphate interact to regulate egress of resting T cells from lymph nodes. As T cells are exposed simultaneously to many chemokines and S1P at other points in their life-cycle, other instances of cross-talk are likely. How S1P receptor signalling changes following T cell activation, and how S1P may modulate cellular responses to chemokines before and after this transition, are important questions. S1P pre-treatment enhanced the chemotaxis of Jurkat T cells towards CXCL12. This was a specific effect as S1P did not affect the amount of cell surface CXCR4 or certain signalling responses downstream of chemokine stimulation. Unexpectedly, this effect was opposite to that observed with primary resting cells, where S1P treatment suppressed migration towards CXCL12. The chemokine-induced phosphorylation of Akt was unaffected, suggesting a PI3Kindependent effect. In contrast, S1P enhanced the migration of activated T cells towards the inflammatory chemokine CXCL10. Using an S1P receptor 1-selective agonist it was shown that receptor signalling in T cells was lost transiently after activation. This was demonstrated, using siRNA, to be partly dependent on the initial upregulation of CD69. The relevance of modulation of S1PR1 signalling was explored further in vivo. The S1P receptor super-agonist FTY720 sequestered activated alloreactive cells in a peripheral lymph node, suggesting that their egress was dependent on S1P receptor signalling. These results show that S1P is a key regulator of T cell migration at three different stages of their life-cycle: before activation, in their response to homeostatic chemokines; following activation, in their ability to egress lymphatic tissue; and finally in the responses of differentiated effector cells to inflammatory chemokines.British Heart Foundatio

Monitoring the low doping regime in graphene using Raman 2D peak-splits: Comparison of gated Raman and transport measurements

Avoiding charge density fluctuations and impurities in graphene is vital for high-quality graphene-based devices. Traditional characterization methods require device fabrication and electrical transport measurements, which are labor-intensive and time-consuming. Existing optical methods using Raman spectroscopy only work for doping levels higher than ~10^12 cm^-2. Here, we propose an optical method using Raman 2D peak-splitting (split between the Raman 2D1 and 2D2 peaks at low doping levels). Electrostatically gated Raman measurements combined with transport measurements were used to correlate the 2D peak-split with the charge density on graphene with high precision (2x10^10 cm^-2 per 2D peak-split wavenumber). We found that the Raman 2D peak-split has a strong correlation with the charge density at low doping levels, and that a lower charge density results in a larger 2D peak-split. Our work provides a simple and non-invasive optical method to quantify the doping level of graphene from 10^10 cm^-2 to 10^12 cm^-2, two orders of magnitude higher precision than previously reported optical methods. This method provides a platform for estimating the doping level and quality of graphene before fabricating graphene deviceshttps://arxiv.org/abs/1908.10961First author draf

Nest Predation by brown-headed cowbirds (Molothrus ater)

The reproductive success of parasites is entirely dependent on their ability to encounter suitable hosts. Obligate brood parasitic birds may increase host encounter rate, and consequently their reproductive output, if they cause unsuitable late-stage host nests to fail thereby stimulating the host to create another nest that they can parasitize. I tested key predictions of this ‘farming’ hypothesis for the brown-headed cowbird (Molothrus ater). I found evidence that cowbird attacks are not uncommon, a basic requirement of the hypothesis. Furthermore, I found multiple lines of evidence that cowbird attacks are not indiscriminate, but directed at non-parasitized nests and at those at a developmental stage too late to be suitable for parasitism. I experimentally demonstrate that cowbirds determine the age of a nest by directly puncturing a portion of the clutch or indirectly by attending to the absolute number of eggs. Cowbirds also parasitized a high proportion of the re-nesting attempts following their attacks suggesting that they take advantage of the reproductive opportunities they create. A Monte Carlo model comparing simulated farming and non-farming cowbirds also shows that a farming strategy may lead to higher reproductive output likely by enhancing individual nest discovery as opposed to increasing the number of nests. How cowbirds occupy space may also provide insight into how they encounter potential hosts. Utilization distributions (UDs) are among the most applicable methods of quantifying space use. In one of the first practical applications of a multidimentional UD that includes time as a dimension, I show that cowbirds were significantly more likely to be found around nesting sites when a nest was active suggesting that cowbirds optimize their nest searching. I did not, however, find a difference in probability of occurrence depending on the developmental stage of a nest. I also found evidence that cowbirds become less territorial later in the day. Comparisons to strictly spatial UDs suggest that including a time dimension may provide a more realistic model of how cowbirds find host nests and interact with one another. Thus, cowbirds can discriminate appropriate vs inappropriate nests and adjust their predatory and spatial behaviour accordingly to improve their encounters with hosts

Victory, torcs and iconology in Rome and Britain

This article takes an iconological approach to the interpretation of coin imagery, highlighting the multiple, changing meanings of images as they travel from person to person and culture to culture. Two contrasting case studies are presented. The first discusses the movement of classical images to Iron Age Britain, focusing on the figure of Nike/Victory. The selective nature of image-adoption by British kings is demonstrated, as well as the different meanings Mediterranean classical images communicated in their new context. The second case study discusses the adoption of the torc as both an image and object in Roman culture, tracing how the torc transformed from a ‘barbarian’ attribute to a demonstration of Roman military valour and skill. Both case studies demonstrate the multiple meanings a coin image may have, dependant on viewer and context

The Impact of 8(a) Small Business Graduation

The 8(a) small business set-aside program is designed to support small business participation in the federal market and to foster small business growth. However, 8(a) graduates do not fare well over time, with more than 60% no longer receiving federal prime contract obligations less than 10 years after graduation from set-aside eligibility. Those who were still federal prime contractors gained very little additional government business, with the average contract obligation up only 3.3% to $6.25 million, from$6.05 million (showing a decline when adjusting for inflation). Additionally, 8(a) graduates still depended on set-asides for more than half of their federal prime contract dollars. Overall, they are not rewarded for graduation.Naval Postgraduate School Acquisition Research Progra

Monolayer MoS2 strained to 1.3% with a microelectromechanical system

We report on a modified transfer technique for atomically thin materials integrated onto microelectromechanical systems (MEMS) for studying strain physics and creating strain-based devices. Our method tolerates the non-planar structures and fragility of MEMS, while still providing precise positioning and crack free transfer of flakes. Further, our method used the transfer polymer to anchor the 2D crystal to the MEMS, which reduces the fabrication time, increases the yield, and allowed us to exploit the strong mechanical coupling between 2D crystal and polymer to strain the atomically thin system. We successfully strained single atomic layers of molybdenum disulfide (MoS2) with MEMS devices for the first time and achieved greater than 1.3% strain, marking a major milestone for incorporating 2D materials with MEMS We used the established strain response of MoS2 Raman and Photoluminescence spectra to deduce the strain in our crystals and provide a consistency check. We found good comparison between our experiment and literature.Published versio