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Search Results: 1 - 10 of 229149 matches for " Matthew C. Jenkins "
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Colloidal suspensions in modulated light fields
Matthew C. Jenkins,Stefan U. Egelhaaf
Physics , 2008, DOI: 10.1088/0953-8984/20/40/404220
Abstract: Periodically-modulated potentials in the form of light fields have previously been applied to induce reversible phase transitions in dilute colloidal systems with long-range interactions. Here we investigate whether similar transitions can be induced in very dense systems, where inter-particle contacts are important. Using microscopy we show that particles in such systems are indeed strongly affected by modulated potentials. We discuss technical aspects relevant to generating the light-induced potentials and to imaging simultaneously the particles. We also consider what happens when the particle size is comparable with the modulation wavelength. The effects of selected modulation wavelengths as well as pure radiation pressure are illustrated.
Confocal microscopy of colloidal particles: towards reliable, optimum coordinates
Matthew C. Jenkins,Stefan U. Egelhaaf
Physics , 2007, DOI: 10.1016/j.cis.2007.07.006
Abstract: Over the last decade, the light microscope has become increasingly useful as a quantitative tool for studying colloidal systems. The ability to obtain particle coordinates in bulk samples from micrographs is particularly appealing. In this paper we review and extend methods for optimal image formation of colloidal samples, which is vital for particle coordinates of the highest accuracy, and for extracting the most reliable coordinates from these images. We discuss in depth the accuracy of the coordinates, which is sensitive to the details of the colloidal system and the imaging system. Moreover, this accuracy can vary between particles, particularly in dense systems. We introduce a previously unreported error estimate and use it to develop an iterative method for finding particle coordinates. This individual-particle accuracy assessment also allows comparison between particle locations obtained from different experiments. Though aimed primarily at confocal microscopy studies of colloidal systems, the methods outlined here should transfer readily to many other feature extraction problems, especially where features may overlap one another.
Combined holographic-mechanical optical tweezers: Construction, optimisation and calibration
Richard D. L. Hanes,Matthew C. Jenkins,Stefan U. Egelhaaf
Physics , 2009,
Abstract: A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers set-up. This provides great flexibility as the SLM creates an array of traps which can be moved smoothly and quickly with the GMM. To optimise performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45 degrees, smaller angles give a full 2pi phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.
Finding bridges in packings of colloidal spheres
Matthew C. Jenkins,Mark D. Haw,Gary C. Barker,Wilson C. K. Poon,Stefan U. Egelhaaf
Physics , 2010,
Abstract: We identify putative load-bearing structures (bridges) in experimental colloidal systems studied by confocal microscopy. Bridges are co-operative structures that have been used to explain stability and inhomogeneous force transmission in simulated granular packings with a range of densities. We show that bridges similar to those found in granular simulations are present in real experimental colloidal packings. We describe critically the bridge-finding procedure for real experimental data and propose a new criterion-Lowest Mean Squared Separation (LSQS)-for selecting optimum stabilisations.
Malaria Mosquitoes Attracted by Fatal Fungus
Justin George, Nina E. Jenkins, Simon Blanford, Matthew B. Thomas, Thomas C. Baker
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0062632
Abstract: Insect-killing fungi such as Beauveria bassiana are being evaluated as possible active ingredients for use in novel biopesticides against mosquito vectors that transmit malaria. Fungal pathogens infect through contact and so applications of spores to surfaces such as walls, nets, or other resting sites provide possible routes to infect mosquitoes in and around domestic dwellings. However, some insects can detect and actively avoid fungal spores to reduce infection risk. If true for mosquitoes, such behavior could render the biopesticide approach ineffective. Here we find that the spores of B. bassiana are highly attractive to females of Anopheles stephensi, a major anopheline mosquito vector of human malaria in Asia. We further find that An. stephensi females are preferentially attracted to dead and dying caterpillars infected with B. bassiana, landing on them and subsequently becoming infected with the fungus. Females are also preferentially attracted to cloth sprayed with oil-formulated B. bassiana spores, with 95% of the attracted females becoming infected after a one-minute visit on the cloth. This is the first report of an insect being attracted to a lethal fungal pathogen. The exact mechanisms involved in this behavior remain unclear. Nonetheless, our results indicate that biopesticidal formulations comprising B. bassiana spores will be conducive to attraction and on-source visitation by malaria vectors.
Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor
Matthew Pelliccione,Alec Jenkins,Preeti Ovartchaiyapong,Christopher Reetz,Eve Emmanuelidu,Ni Ni,Ania C. Bleszynski Jayich
Physics , 2015,
Abstract: High spatial resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogen-vacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor based on its atomic size and quantum-limited sensing capabilities afforded by long spin coherence times. Although the NV center has been successfully implemented as a nanoscale scanning magnetic probe at room temperature, it has remained an outstanding challenge to extend this capability to cryogenic temperatures, where many solid-state systems exhibit non-trivial magnetic order. Here we present NV magnetic imaging down to 6 K with 6 nm spatial resolution and 3 {\mu}T/$\sqrt{\mbox{Hz}}$ field sensitivity, first benchmarking the technique with a magnetic hard disk sample, then utilizing the technique to image vortices in the iron pnictide superconductor BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$ with $T_c$ = 30 K. The expansion of NV-based magnetic imaging to cryogenic temperatures represents an important advance in state-of-the-art magnetometry, which will enable future studies of heretofore inaccessible nanoscale magnetism in condensed matter systems.
On some families of modules for the current algebra
Matthew Bennett,Rollo Jenkins
Mathematics , 2015,
Abstract: Given a finite-dimensional module, $V$, for a finite-dimensional, complex, semi-simple Lie algebra $\lie g$ and a positive integer $m$, we construct a family of graded modules for the current algebra $\lie g[t]$ indexed by simple $\CC\lie S_m$-modules. These modules have the additional structure of being free modules of finite rank for the ring of symmetric polynomials and so can be localized to give finite-dimensional graded $\lie g[t]$-modules. We determine the graded characters of these modules and show that if $\lie g$ is of type $A$ and $V$ the natural representation, these graded characters admit a curious duality.
Drag Coefficients of Golf Balls  [PDF]
Peter E. Jenkins, Joseph Arellano, Mark Ross, Matthew Snell
World Journal of Mechanics (WJM) , 2018, DOI: 10.4236/wjm.2018.86019
Abstract: Drag across a golf ball can affect distance traveled when hitting a ball. An average golf ball will have a drag coefficient of, 0.24 < CD < 0.7, in a Reynolds number range of 30,000 < ReD < 108,000. This paper investigates the effect of dimple patterns on the boundary layer around a ball. Changing the depth of the dimple will cause a change to the drag coefficient. A deeper dimple pattern will cause a larger drag coefficient at higher velocities, u > 35 m/s. This research found that a significantly deeper dimple pattern will greatly affect the boundary layer, thus changing the drag coefficient and boundary layer.
The effect of improved rural sanitation on diarrhoea and helminth infection: design of a cluster-randomized trial in Orissa, India
Thomas Clasen, Sophie Boisson, Parimita Routray, Oliver Cumming, Marion Jenkins, Jeroen H J Ensink, Melissa Bell, Matthew C Freeman, Soosai Peppin, Wolf-Peter Schmidt
Emerging Themes in Epidemiology , 2012, DOI: 10.1186/1742-7622-9-7
Abstract: Randomisation resulted in an acceptable balance between trial arms. The sample size requirements appear to be met for the main study outcomes. Delays in intervention roll-out caused logistical problems especially for the planning of health outcome follow-up surveys. Latrine coverage at the end of the construction period (55%) remained below the target of 70%, a result that may, however, be in line with many other TSC intervention areas in India.We discuss a number of methodological problems encountered thus far in this study that may be typical for sanitation trials. Nevertheless, it is expected that the trial procedures will allow measuring the effectiveness of a typical rural sanitation campaign, with sufficient accuracy and validity.Diseases associated with poor sanitation cause a large burden of disease worldwide. Diarrhoea alone causes an estimated 4 billion cases and 1.9 million deaths each year among children under 5 years, or 19% of all under-5 deaths in low income settings [1]. Other major diseases associated with poor sanitation are soil-transmitted worm infections, trachoma, lymphatic filariasis and schistosomiasis [2]. In contrast to other Millennium Development Goals, sanitation coverage remains low with 2.5 billion people still lacking access to sanitation. Only 6% of rural residents in India have access to improved sanitation, and about 69% practice open defecation [3].Systematic reviews have suggested that improved sanitation may reduce diarrhoeal diseases by 22% to 36% [2,4-8]. The studies included in these reviews were observational or small-scale before/after intervention studies that combined sanitation with water supplies or hygiene. The methodological quality of the studies was generally poor [2,5-8]. To date, there is no randomized controlled trial of sanitation interventions to prevent diarrhoeal diseases [2,4-8]. Large RCTs may have been deemed difficult due to logistical constraints, including the long time frame of sanitation campaigns bot
Giant plateau in the THz Faraday angle in gated Bi2Se3
Gregory S. Jenkins,Andrei B. Sushkov,Don C. Schmadel,M. -H. Kim,Matthew Brahlek,Namrata Bansal,Seongshik Oh,H. Dennis Drew
Physics , 2012, DOI: 10.1103/PhysRevB.86.235133
Abstract: We report gated terahertz Faraday angle measurements on epitaxial Bi2Se3 thin films capped with In2Se3. A plateau is observed in the real part of the Faraday angle at an onset gate voltage corresponding to no band bending at the surface which persists into accumulation. The plateau is two orders of magnitude flatter than the step size expected from a single Landau Level in the low frequency limit, quantized in units of the fine structure constant. At 8 T, the plateau extends over a range of gate voltage that spans an electron density greater than 14 times the quantum flux density. Both the imaginary part of the Faraday angle and transmission measurements indicate dissipative off-axis and longitudinal conductivity channels associated with the plateau.
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