Radiofrequency heating of nanoclusters and nanoparticles for enzyme activation

2018 Summer.Includes bibliographical references.Radiofrequency (RF) fields heat magnetic nanoparticles. Applications include remote drug delivery and noninvasive cancer therapy. The underlying objective is to increase temperatures precisely where desired without heating the surroundings. Before our work, the replicable limit of this precision has been in the micrometer range. To investigate the lower limit of this concept of local heat, we explored the RF remote activation of a thermophilic enzyme, thermolysin, covalently attached to gold coated iron oxide nanoparticles (6.1 nm in core diameter). Thermolysin activity was a function of applied radiofrequency power, independent of bulk solution temperature. Besides iron oxides, many other inorganic nanomaterials have been investigated for RF heating. One of the more interesting and controversial material choices is gold nanoparticles, primarily investigated for cancer treatment. Early reports of gold nanoparticle heating conflated the heating of supporting electrolytes with the heating of nanoparticles. Multiple mechanisms were proposed to account for the observed heat of gold nanoparticle suspensions. There was no consensus among specialists on how gold nanoparticles heat, if they heat at all. To investigate this, a critical review of the RF heating of gold nanoparticles field was performed with new experimental results presented to elucidate the confounding results. Following this, Au25(SR)18 gold nanoclusters were used as a model system to investigate the controversial heating rates reported for gold nanoparticles. For the first time the observed rates were explained entirely with a single mechanism: electrophoretic heating. The success of this reconciliation of theory and experiment considered the screened charge of the particle in addition to the contribution of the counterions. To enable deconvolution of possible contributions to gold nanoparticle heating by cluster decomposition products, an investigation of the practical stability of gold nanoclusters was conducted. It was found that organo-soluble particles with large ligands possessed over one month long lifetime in air-free non-polar solvents

Aerosols from biomass burning over the tropical South Atlantic region: Distributions and impacts

The NASA Global Tropospheric Experiment (GTE) Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE A) expedition was conducted September 21 through October 26, 1992, to investigate factors responsible for creating the seasonal South Atlantic tropospheric ozone maximum. During these flights, fine aerosol (0.1-3.0 μm) number densities were observed to be enhanced roughly tenfold over remote regions of the tropical South Atlantic and greater over adjacent continental areas, relative to northern hemisphere observations and to measurements recorded in the same area during Ac wet season. Chemical and meteorological analyses as well as visual observations indicate that the primary source of these enhancements was biomass burning occurring within grassland regions of north central Brazil and southeastern Africa. These fires exhibited fine aerosol (N) emission ratios relative to CO (dN/dCO) of 22.5 ± 9.7 and 23.6 ± 15.1 cm-3 parts per billion by volume (ppbv)-1 over Brazil and Africa, respectively. Convection coupled with counterclockwise flow around the South Atlantic subtropical anticyclone subsequently distributed these aerosols throughout the remote South Atlantic troposphere. We calculate that dilute smoke from biomass burning produced an average tenfold enhancement in optical depth over the continental regions as well as a 50% increase in this parameter over the middle South Atlantic Ocean; these changes correspond to an estimated net cooling of up to 25 W m-2 and 2.4 W m-2 during clear-sky conditions over savannas and ocean respectively. Over the ocean our analyses suggest that modification of CCN concentrations within the persistent eastern Atlantic marine stratocumulus clouds by entrainment of subsiding haze layers could significantly increase cloud albedo resulting in an additional surface radiative cooling potentially greater in magnitude than that caused by direct extinction of solar radiation by the aerosol particles themselves

Airborne observations of the tropospheric CO2 distribution and its controlling factors over the South Pacific Basin

Highly precise measurements of CO2 mixing ratios were recorded aboard both the NASA DC-8 and P3-B aircraft during the Pacific Exploratory Mission-Tropics conducted in August-October 1996. Data were obtained at altitudes ranging from 0.1 to 12 km over a large portion of the South Pacific Basin representing the most geographically extensive CO2 data set recorded in this region. These data along with CO2 surface measurements from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) and the National Institute of Water and Atmospheric Research (NIWA) were examined to establish vertical and meridional gradients. The CO2 spatial distribution in the southern hemisphere appeared to be largely determined by interhemispheric transport as air masses with depleted CO2 levels characteristic of northern hemispheric air were frequently observed south of the Intertropical Convergence Zone. However, regional processes also played a role in modulating background concentrations. Comparisons of CO2 with other trace gases indicated that CO2 values were influenced by continental sources. Large scale plumes from biomass burning activities produced enhanced CO2 mixing ratios within the lower to midtroposphere over portions of the remote Pacific. An apparent CO2 source was observed in the NOAA/ CMDL surface data between 15° N and 15° S and in the lower altitude flight data between 8° N and 8.5° S with a zone of intensity from 6.5° N to 1° S. Inferred from these data is the presence of a Southern Ocean sink from south of 15° S having two distinct zones seasonally out of phase with one another. Copyright 1999 by the American Geophysical Union

And the Noise Played on: Stochastic Gene Expression and HIV-1 Infection

Stochastic gene expression has been implicated in a variety of cellular processes, including cell differentiation and disease. In this issue of Cell, Weinberger et al. (2005) take an integrated computational-experimental approach to study the Tat transactivation feedback loop of HIV-1. They show that fluctuations in a key regulator, Tat, in an isogenic population of infected cells result in two distinct expression states corresponding to latent and productive HIV-1 infection. These findings demonstrate the importance of stochastic gene expression in molecular “decision-making.

The challenge of supporting networked personal inquiry learning across contexts

Supporting learning across different contexts can be challenging. Defining formal, informal and nonformal learning is the subject of continuing debate as each can be difficult to describe. We report on a study that evaluated the effectiveness of a Personal Inquiry toolkit on supporting personal inquiries into the sustainability of the food cycle, carried out across the contexts of home and an after school club in a UK secondary school. The toolkit consisted of a web-based Sustainability Investigator that could be accessed from any location, together with a selection of data-gathering tools such as environmental sensors (e.g. temperature probes) and cameras. It was designed to support students through the process of carrying out inquiries within the club and between the club and their home. Our main focus here is on describing how the Sustainability Investigator supported students' inquiries that were conceived and designed within the club and conducted at home. The 30 students (aged 12-14 years) chose to investigate home food storage, packaging and preservation. Our focus is on exploring the nature of the semi-formal club context and how this mediated students' use of the Sustainability Investigator. Analysis of our field notes, log files of students' use of the Sustainability Investigator, together with video and audio recordings of club sessions and interviews with teachers and pupils, suggest that while the pupils' use of the toolkit across contexts was sporadic and varied between students, they successfully completed personally relevant inquiries and developed positive attitudes to the process. This was different to the predictable, sustained and consistent use of the toolkit identified in our previous studies when the students used it (again successfully) to support their inquiries in a formal classroom setting (see e.g. Scanlon et al. 2009). Three main features of the school club context that mediated the ways in which the Sustainability Investigator was used by the students across contexts were: 1) the students' aims and priorities, 2) affordances and constraints of the technology, and 3) institutional priorities. We use this example of a study of learning across contexts to suggest implications of the work for the potential of a Personal Inquiry toolkit to support learning across the life course