Hot phonon decay in supported and suspended exfoliated graphene

Near infrared pump-probe spectroscopy has been used to measure the ultrafast dynamics of photoexcited charge carriers in monolayer and multilayer graphene. We observe two decay processes occurring on 100 fs and 2 ps timescales. The first is attributed to the rapid electron-phonon thermalisation in the system. The second timescale is found to be due to the slow decay of hot phonons. Using a simple theoretical model we calculate the hot phonon decay rate and show that it is significantly faster in monolayer flakes than in multilayer ones. In contrast to recent claims, we show that this enhanced decay rate is not due to the coupling to substrate phonons, since we have also seen the same effect in suspended flakes. Possible intrinsic decay mechanisms that could cause such an effect are discussed.Comment: 4 pages, 3 figure

A hierarchical frailty model applied to two-generation melanoma data

We present a hierarchical frailty model based on distributions derived from non-negative Lévy processes. The model may be applied to data with several levels of dependence, such as family data or other general clusters, and is an alternative to additive frailty models. We present several parametric examples of the model, and properties such as expected values, variance and covariance. The model is applied to a case-cohort sample of age at onset for melanoma from the Swedish Multi-Generation Register, organized in nuclear families of parents and one or two children. We compare the genetic component of the total frailty variance to the common environmental term, and estimate the effect of birth cohort and gender. © 2010 The Author(s).published_or_final_versionSpringer Open Choice, 21 Feb 201

In situ chemically specific mapping of agrochemical seed coatings using stimulated Raman scattering microscopy.

This is the author accepted manuscript. The final version is available from Wiley-VCH-Verlag via the DOI in this record.Providing sufficient, healthy food for the increasing global population is putting a great deal of pressure on the agrochemical industry to maximise crop yields without sustaining environmental damage. The growth and yield of every plant with sexual reproduction, depends on germination and emergence of sown seeds, which is affected greatly by seed disease. This can be most effectively controlled by treating seeds with pesticides before they are sown. An effective seed coating treatment requires a high surface coverage and adhesion of active ingredients onto the seed surface and the addition of adhesive agents in coating formulations plays a key role in achieving this. Although adhesive agents are known to enhance seed germination, little is understood about how they affect surface distribution of actives and how formulations can be manipulated to rationally engineer seed coating preparations with optimized coverage and efficacy. We show, for the first time, that stimulated Raman scattering (SRS) microscopy can be used to map the seed surface with microscopic spatial resolution and with chemical specificity to identify formulation components distributed on the seed surface. This represents a major advance in our capability to rationally engineer seed coating formulations with enhanced efficacy.We thank the funding from the Biotechnology and Biological Sciences Research Council (BBSRC, BB/M017915/1 and BB/K013602/1)

In vivo chemical and structural analysis of plant cuticular waxes using stimulated Raman scattering microscopy.

The cuticle is a ubiquitous, predominantly waxy layer on the aerial parts of higher plants that fulfils a number of essential physiological roles, including regulating evapotranspiration, light reflection, and heat tolerance, control of development, and providing an essential barrier between the organism and environmental agents such as chemicals or some pathogens. The structure and composition of the cuticle are closely associated but are typically investigated separately using a combination of structural imaging and biochemical analysis of extracted waxes. Recently, techniques that combine stain-free imaging and biochemical analysis, including Fourier transform infrared spectroscopy microscopy and coherent anti-Stokes Raman spectroscopy microscopy, have been used to investigate the cuticle, but the detection sensitivity is severely limited by the background signals from plant pigments. We present a new method for label-free, in vivo structural and biochemical analysis of plant cuticles based on stimulated Raman scattering (SRS) microscopy. As a proof of principle, we used SRS microscopy to analyze the cuticles from a variety of plants at different times in development. We demonstrate that the SRS virtually eliminates the background interference compared with coherent anti-Stokes Raman spectroscopy imaging and results in label-free, chemically specific confocal images of cuticle architecture with simultaneous characterization of cuticle composition. This innovative use of the SRS spectroscopy may find applications in agrochemical research and development or in studies of wax deposition during leaf development and, as such, represents an important step in the study of higher plant cuticles

Frailty modeling of bimodal age-incidence curves of nasopharyngeal carcinoma in low-risk populations

The incidence of nasopharyngeal carcinoma (NPC) varies widely according to age at diagnosis, geographic location, and ethnic background. On a global scale, NPC incidence is common among specific populations primarily living in southern and eastern Asia and northern Africa, but in most areas, including almost all western countries, it remains a relatively uncommon malignancy. Specific to these low-risk populations is a general observation of possible bimodality in the observed age-incidence curves. We have developed a multiplicative frailty model that allows for the demonstrated points of inflection at ages 15–24 and 65–74. The bimodal frailty model has 2 independent compound Poisson-distributed frailties and gives a significant improvement in fit over a unimodal frailty model. Applying the model to population-based cancer registry data worldwide, 2 biologically relevant estimates are derived, namely the proportion of susceptible individuals and the number of genetic and epigenetic events required for the tumor to develop. The results are critically compared and discussed in the context of existing knowledge of the epidemiology and pathogenesis of NPC

Differential expression of akirin gene in black tiger shrimp Penaeus monodon in response to immunostimulant administration and infections with Vibrio harveyi and white spot syndrome virus

The akirin gene, which is strictly localized in the nucleus, plays a critical role in regulating antimicrobial peptide transcription, and has parallel functions to NF-kappa B signaling pathway in both vertebrates and invertebrates. In shrimp, the akirin gene is expressed as innate immunity in response to microbial infection. In the present study, expression of akirin gene in Penaeus monodon with respect to Vibrio harveyi and white spot syndrome virus (WSSV) infections and immunostimulant (beta-glucan) administration were investigated by quantitative polymerase chain reaction. The gene was expressed in various tissue samples of healthy shrimp. Maximum level of expression was immediately after V. harveyi infection, suggesting that it may be an early response gene. Gene expression was remarkably upregulated in the lymphoid organ, gill, and hepatopancreas, whereas downregulation was observed in hemocytes compared with the control. In the case of WSSV-infected samples, the akirin gene was significantly downregulated in the lymphoid organ but there was no significant difference in expression pattern in hemocytes compared to the control. In gill tissue, maximum expression was observed after 2 hr of infection, the same in hepatopancreas. Experimental challenge of beta-glucan fed shrimp infected with V. harveyi and WSSV resulted in significant upregulation of akirin gene expression in lymphoid and gill tissue

Bioavailability of nanoscale metal oxides TiO(2), CeO(2), and ZnO to fish

addresses: The Hatherly Laboratories, University of Exeter, Prince of Wales Road, Exeter EX4 4PS, UK.types: Journal Article; Research Support, Non-U.S. Gov'tCopyright © 2010 American Chemical Society. Post print version of article deposited. The final published version is available from: http://dx.doi.org/10.1021/es901971aNanoparticles (NPs) are reported to be a potential environmental health hazard. For organisms living in the aquatic environment, there is uncertainty on exposure because of a lack of understanding and data regarding the fate, behavior, and bioavailability of the nanomaterials in the water column. This paper reports on a series of integrative biological and physicochemical studies on the uptake of unmodified commercial nanoscale metal oxides, zinc oxide (ZnO), cerium dioxide (CeO(2)), and titanium dioxide (TiO(2)), from the water and diet to determine their potential ecotoxicological impacts on fish as a function of concentration. Particle characterizations were performed and tissue concentrations were measured by a wide range of analytical methods. Definitive uptake from the water column and localization of TiO(2) NPs in gills was demonstrated for the first time by use of coherent anti-Stokes Raman scattering (CARS) microscopy. Significant uptake of nanomaterials was found only for cerium in the liver of zebrafish exposed via the water and ionic titanium in the gut of trout exposed via the diet. For the aqueous exposures undertaken, formation of large NP aggregates (up to 3 mum) occurred and it is likely that this resulted in limited bioavailability of the unmodified metal oxide NPs in fish

Label-free chemically specific imaging in planta with stimulated Raman scattering microscopy.

The growing world population puts ever-increasing demands on the agricultural and agrochemical industries to increase agricultural yields. This can only be achieved by investing in fundamental plant and agrochemical research and in the development of improved analytical tools to support research in these areas. There is currently a lack of analytical tools that provide noninvasive structural and chemical analysis of plant tissues at the cellular scale. Imaging techniques such as coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microscopy provide label-free chemically specific image contrast based on vibrational spectroscopy. Over the past decade, these techniques have been shown to offer clear advantages for a vast range of biomedical research applications. The intrinsic vibrational contrast provides label-free quantitative functional analysis, it does not suffer from photobleaching, and it allows near real-time imaging in 3D with submicrometer spatial resolution. However, due to the susceptibility of current detection schemes to optical absorption and fluorescence from pigments (such as chlorophyll), the plant science and agrochemical research communities have not been able to benefit from these techniques and their application in plant research has remained virtually unexplored. In this paper, we explore the effect of chlorophyll fluorescence and absorption in CARS and SRS microscopy. We show that with the latter it is possible to use phase-sensitive detection to separate the vibrational signal from the (electronic) absorption processes. Finally, we demonstrate the potential of SRS for a range of in planta applications by presenting in situ chemical analysis of plant cell wall components, epicuticular waxes, and the deposition of agrochemical formulations onto the leaf surface

Drug delivery into microneedle-porated nails from nanoparticle reservoirs

Copyright © 2015. Published by Elsevier B.V.Author's post-print version. The definitive version is available from the publisher via doi: 10.1016/j.jconrel.2015.10.026This study demonstrates the potential of polymeric nanoparticles as drug reservoirs for sustained topical drug delivery into microneedle-treated human nail. Laser scanning confocal microscopy was used to image the delivery of a fluorescent model compound from nanoparticles into the nail. A label-free imaging technique, stimulated Raman scattering microscopy, was applied, in conjunction with two-photon fluorescence imaging, to probe the disposition of nanoparticles and an associated lipophilic 'active' in a microneedle-porated nail. The results provide clear evidence that the nanoparticles function as immobile reservoirs, sequestered on the nail surface and in the microneedle-generated pores, from which the active payload can be released and diffuse laterally into the nail over an extended period of time