4 ◦C and beyond: what did this mean for biodiversity in the past?

How do the predicted climatic changes (IPCC, 2007) for the next century compare in magnitude and rate to those that Earth has previously encountered? Are there comparable intervals of rapid rates of temperature change, sea-level rise and levels of atmospheric CO2 that can be used as analogues to assess possible biotic responses to future change? Or are we stepping into the great unknown? This perspective article focuses on intervals in time in the fossil record when atmospheric CO2 concentrations increased up to 1200 ppmv, temperatures in mid- to high-latitudes increased by greater than 4 ?C within 60 years, and sea levels rose by up to 3 m higher than present. For these intervals in time, case studies of past biotic responses are presented to demonstrate the scale and impact of the magnitude and rate of such climate changes on biodiversity. We argue that although the underlying mechanisms responsible for these past changes in climate were very different (i.e. natural processes rather than anthropogenic), the rates and magnitude of climate change are similar to those predicted for the future and therefore potentially relevant to understanding future biotic response. What emerges from these past records is evidence for rapid community turnover, migrations, development of novel ecosystems and thresholds from one stable ecosystem state to another, but there is very little evidence for broad-scale extinctions due to a warming world. Based on this evidence from the fossil record, we make four recommendations for future climate-change integrated conservation strategies.

Optical transmission through single subwavelength apertures using prism coupled input of laser light of annular intensity profile

Light transmission through a single subwavelength aperture in a silver film is examined with a novel input configuration comprising an annular laser beam of variable diameter that is prism-coupled to the back face of the silver. Transmission peaks driven by excitation of the back-face surface plasmon mode or by the aperture resonance itself are separately observed. For both cases, comparison of films with and without a front-face, circular grating implies significantly more efficient coupling from the aperture fields to the front-face surface plasmon than directly to free radiation. (c) 2007 Optical Society of America.

Effect of signal intensity normalization on the multivariate analysis of spectral data in complex 'real-world' datasets

Spectral signal intensities, especially in 'real-world' applications with nonstandardized sample presentation due to uncontrolled variables/factors, commonly require additional spectral processing to normalize signal intensity in an effective way. In this study, we have demonstrated the complexity of choosing a normalization routine in the presence of multiple spectrally distinct constituents by probing a dataset of Raman spectra. Variation in absolute signal intensity (90.1% of total variance) of the Raman spectra of these complex biological samples swamps the variation in useful signals (9.4% of total variance), degrading its diagnostic and evaluative potential.

Relativistically correct hole-boring and ion acceleration by circularly polarized laser pulses

The problem of the 'hole-boring' (HB)-type of radiation pressure acceleration of ions by circularly polarized laser pulses interacting with overdense plasmas is considered in the regime where the dimensionless scaling parameter I/rho c(3) becomes large. In this regime a non-relativistic treatment of the 'HB' problem is no longer adequate. A new set of fully relativistic formulae for the mean ion energy and 'HB' velocity is derived and validated against one-dimensional particle-in-cell simulations. It is also found that the finite acceleration time of the ions results in large energy spreads in the accelerated ion beam even under the highly idealized conditions of constant laser intensity and uniform mass density.

Customs-Related Transaction Costs, Firm Size and International Trade Intensity

Customs are generally perceived as a time-consuming impediment to international trade. However, few studies have empirically examined the determinants and the impact of this type of government-imposed transaction costs. This paper analyses the role of firm size as a determinant of customs-related transaction costs, as well as the effect of firm size on the relationship between these costs and the international trade intensity of firms. The results of this study indicate that customs-related transaction costs repress international trade activities of firms, even at low levels of these costs. The paper identifies transaction-related economies of scale, simplified customs procedures and advanced information and communication technology as main determinants of customs-related transaction costs. It is shown that when these factors are taken into account, firm size has no effect on customs-related transaction costs. Policy implications are considered for firm strategy and public policy.

Firm Size and Export Intensity: Solving an Empirical Puzzle.

This paper presents a transaction costs analysis of the firm size and export intensity relationship. We submit that relation-specific investments and the costs of safeguarding these investments play a significant role in export relationships. Firm size related differences with respect to these factors are used to explain the different relationships between firm size and export intensity that have been found in previous studies. The theoretical framework is tested empirically, and support is found for different industries.

Out-of-field cell survival following exposure to intensity-modulated radiation fields

PURPOSE:
To determine the in-field and out-of-field cell survival of cells irradiated with either primary field or scattered radiation in the presence and absence of intercellular communication.
METHODS AND MATERIALS:
Cell survival was determined by clonogenic assay in human prostate cancer (DU145) and primary fibroblast (AGO1552) cells following exposure to different field configurations delivered using a 6-MV photon beam produced with a Varian linear accelerator.
RESULTS:
Nonuniform dose distributions were delivered using a multileaf collimator (MLC) in which half of the cell population was shielded. Clonogenic survival in the shielded region was significantly lower than that predicted from the linear quadratic model. In both cell lines, the out-of-field responses appeared to saturate at 40%-50% survival at a scattered dose of 0.70 Gy in DU-145 cells and 0.24 Gy in AGO1522 cells. There was an approximately eightfold difference in the initial slopes of the out-of-field response compared with the a-component of the uniform field response. In contrast, cells in the exposed part of the field showed increased survival. These observations were abrogated by direct physical inhibition of cellular communication and by the addition of the inducible nitric oxide synthase inhibitor aminoguanidine known to inhibit intercellular bystander effects. Additional studies showed the proportion of cells irradiated and dose delivered to the shielded and exposed regions of the field to impact on response.
CONCLUSIONS:
These data demonstrate out-of-field effects as important determinants of cell survival following exposure to modulated irradiation fields with cellular communication between differentially irradiated cell populations playing an important role. Validation of these observations in additional cell models may facilitate the refinement of existing radiobiological models and the observations considered important determinants of cell survival.

Temporal characterization and in vitro comparison of cell survival following the delivery of 3D-conformal, intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT)

A phantom was designed and implemented for the delivery of treatment plans to cells in vitro. Single beam, 3D-conformal radiotherapy (3D-CRT) plans, inverse planned five-field intensity-modulated radiation therapy (IMRT), nine-field IMRT, single-arc volumetric modulated arc therapy (VMAT) and dual-arc VMAT plans were created on a CT scan of the phantom to deliver 3 Gy to the cell layer and verified using a Farmer chamber, 2D ionization chamber array and gafchromic film. Each plan was delivered to a 2D ionization chamber array to assess the temporal characteristics of the plan including delivery time and 'cell's eye view' for the central ionization chamber. The effective fraction time, defined as the percentage of the fraction time where any dose is delivered to each point examined, was also assessed across 120 ionization chambers. Each plan was delivered to human prostate cancer DU-145 cells and normal primary AGO-1522b fibroblast cells. Uniform beams were delivered to each cell line with the delivery time varying from 0.5 to 20.54 min. Effective fraction time was found to increase with a decreasing number of beams or arcs. For a uniform beam delivery, AGO-1552b cells exhibited a statistically significant trend towards increased survival with increased delivery time. This trend was not repeated when the different modulated clinical delivery methods were used. Less sensitive DU-145 cells did not exhibit a significant trend towards increased survival with increased delivery time for either the uniform or clinical deliveries. These results confirm that dose rate effects are most prevalent in more radiosensitive cells. Cell survival data generated from uniform beam deliveries over a range of dose rates and delivery times may not always be accurate in predicting response to more complex delivery techniques, such as IMRT and VMAT.

Assessing software upgrades, plan properties and patient geometry using intensity modulated radiation therapy (IMRT) complexity metrics

Purpose: The aim of this study is to compare the sensitivity of different metrics to detect differences in complexity of intensity modulated radiation therapy (IMRT) plans following upgrades, changes to planning parameters, and patient geometry. Correlations between complexity metrics are also assessed.