Deep-Tissue Anatomical Imaging of Mice Using Carbon Nanotube Fluorophores in the Second Near Infrared Window

Fluorescent imaging in the second near infrared window (NIR II, 1-1.4 {\mu}m) holds much promise due to minimal autofluorescence and tissue scattering. Here, using well functionalized biocompatible single-walled carbon nanotubes (SWNTs) as NIR II fluorescent imaging agents, we performed high frame rate video imaging of mice during intravenous injection of SWNTs and investigated the path of SWNTs through the mouse anatomy. We observed in real-time SWNT circulation through the lungs and kidneys several seconds post-injection, and spleen and liver at slightly later time points. Dynamic contrast enhanced imaging through principal component analysis (PCA) was performed and found to greatly increase the anatomical resolution of organs as a function of time post-injection. Importantly, PCA was able to discriminate organs such as the pancreas which could not be resolved from real-time raw images. Tissue phantom studies were performed to compare imaging in the NIR II region to the traditional NIR I biological transparency window (700- 900 nm). Examination of the feature sizes of a common NIR I dye (indocyanine green, ICG) showed a more rapid loss of feature contrast and integrity with increasing feature depth as compared to SWNTs in the NIR II region. The effects of increased scattering in the NIR I versus NIR II region were confirmed by Monte Carlo simulation. In vivo fluorescence imaging in the NIR II region combined with PCA analysis may represent a powerful approach to high resolution optical imaging through deep tissues, useful for a wide range of applications from biomedical research to disease diagnostics.Comment: Proceedings of the National Academy of Sciences (PNAS), 201

Facile Synthesis of Amine-Functionalized Eu3+-Doped La(OH)3 Nanophosphors for Bioimaging

Here, we report a straightforward synthesis process to produce colloidal Eu3+-activated nanophosphors (NPs) for use as bioimaging probes. In this procedure, poly(ethylene glycol) serves as a high-boiling point solvent allowing for nanoscale particle formation as well as a convenient medium for solvent exchange and subsequent surface modification. The La(OH)3:Eu3+ NPs produced by this process were ~3.5 nm in diameter as determined by transmission electron microscopy. The NP surface was coated with aminopropyltriethoxysilane to provide chemical functionality for attachment of biological ligands, improve chemical stability and prevent surface quenching of luminescent centers. Photoluminescence spectroscopy of the NPs displayed emission peaks at 597 and 615 nm (λex = 280 nm). The red emission, due to 5D0 → 7F1 and 5D0 → 7F2 transitions, was linear with concentration as observed by imaging with a conventional bioimaging system. To demonstrate the feasibility of these NPs to serve as optical probes in biological applications, an in vitro experiment was performed with HeLa cells. NP emission was observed in the cells by fluorescence microscopy. In addition, the NPs displayed no cytotoxicity over the course of a 48-h MTT cell viability assay. These results suggest that La(OH)3:Eu3+ NPs possess the potential to serve as a luminescent bioimaging probe

Real-time imaging using a 4.3-THz quantum cascade laser and a 320×240 microbolometer focal-plane array

Abstract: We report on the development of a compact, easy-to-use terahertz radiation source, which combines a quantum-cascade laser (QCL) operating at 3.1 THz with a compact, low-input-power Stirling cooler. The QCL, which is based on a two-miniband design, has been developed for high output and low electrical pump power. The amount of generated heat complies with the nominal cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power. Special care has been taken to achieve a good thermal coupling between the QCL and the cold finger of the cooler. The whole system weighs less than 15 kg including the cooler and power supplies. The maximum output power is 8 mW at 3.1 THz. With an appropriate optical beam shaping, the emission profile of the laser is fundamental Gaussian. The applicability of the system is demonstrated by imaging and molecular-spectroscopy experiments. Hübers, "Sub-megahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line," Appl. Phys. Lett. 96(7), 071112 (2010). ©2010 Optical Society of Americ

Parallel and Distributed Computing in Education (Invited Talk)

The natural world is certainly not organised through a central thread of control. Things happen as the result of the actions and interactions of unimaginably large numbers of independent agents, operating at all levels of scale from nuclear to astronomic. Computer systems aiming to be of real use in this real world need to model, at the appropriate level of abstraction, that part of it for which it is to be of service. If that modelling can reflect the natural concurrency in the system, it ought to be much simpler Yet, traditionally, concurrent programming is considered to be an advanced and difficult topic - certainly much harder than serial computing which, therefore, needs to be mastered first. But this tradition is wrong. This talk presents an intuitive, sound and practical model of parallel computing that can be mastered by undergraduate students in the first year of a computing (major) degree. It is based upon Hoare's mathematical theory of Communicating Sequential Processes (CSP), but does not require mathematical maturity from the students - that maturity is pre-engineered in the model. Fluency can be quickly developed in both message-passing and shared-memory concurrency, whilst learning to cope with key issues such as race hazards, deadlock, livelock, process starvation and the efficient use of resources. Practical work can be hosted on commodity PCs or UNIX workstations using either Java or the Occam multiprocessing language. Armed with this maturity, students are well-prepared for coping with real problems on real parallel architectures that have, possibly, less robust mathematical foundations

Weakly Forced Thunderstorms in the Southeast US Are Stronger Near Urban Areas

Abstract While cities are well documented to enhance precipitation through the urban rainfall effect (URE), the distinguishing characteristics of urban‐influenced storms that help establish the URE are poorly understood. The purpose of this study is to examine the morphological traits (i.e., size, duration, intensity, etc.) and near‐storm environmental conditions of weakly forced thunderstorms (WFTs) occurring near urban areas in the Southeast US relative to storms forming in surrounding rural areas. Urban WFTs are found to have higher reflectivities, are more likely to contain hail, and produce more lightning than nearby non‐urban storms, but their sizes and shapes are statistically indistinguishable. When disaggregated across individual urban areas, the increase in maximum composite reflectivity among urban storms is the most pervasive morphological difference, with 24 of the 31 cities displaying elevated reflectivities. Urban WFTs also benefit from near‐storm environments with greater instability and higher precipitation efficiency, which may further contribute to the URE

The visual perception of human locomotion

To function adeptly within our environment, we must perceive and interpret the movements of others. What mechanisms underlie our exquisite visual sensitivity to human m ovement? To address this question, a set of psychophysical studies was conducted to ascertain the temporal characteristics of the visual perception of human locomotion. Subjects viewed a computer-generated point-light walker presented within a mask under conditions of apparent motion. The temporal delay between the display frames as well as the motion characteristics of the mask were varied. With sufficiently long trial durations, performance in a direction discrimination task remained fairly constant across inter-stimulus interval (ISI) when the walker was presented within a random motion mask but increased with ISI when the mask motion duplicated the motion of the walker. This pattern of results suggests that both low-level and high-level visual analyses are involved in the visual perception of human locomotion. These findings are discussed in relation to recent neurophysiological data suggesting that the visual perception of human movement may involve a functional linkage between the visual and motor systems