Calibration of dosemeters used in mammography with different X ray qualities: Euromet Project No. 526

The effect of different X ray radiation qualities on the calibration of mammographic dosemeters was investigated within the framework of a EUROMET (European Collaboration in Measurement Standards) project. The calibration coefficients for two ionization chambers and two semiconductor detectors were established in 13 dosimetry calibration laboratories for radiation qualities used in mammography. They were compared with coefficients for other radiation qualities, including those defined in ISO 4037-1, with first half value layers in the mammographic range. The results indicate that the choice of the radiation quality is not crucial for instruments with a small energy dependence of the response. However, the radiation quality has to be chosen carefully if instruments with a marked dependence of their response to the radiation energy are calibrate

Deterministic and stochastic descriptions of gene expression dynamics

A key goal of systems biology is the predictive mathematical description of gene regulatory circuits. Different approaches are used such as deterministic and stochastic models, models that describe cell growth and division explicitly or implicitly etc. Here we consider simple systems of unregulated (constitutive) gene expression and compare different mathematical descriptions systematically to obtain insight into the errors that are introduced by various common approximations such as describing cell growth and division by an effective protein degradation term. In particular, we show that the population average of protein content of a cell exhibits a subtle dependence on the dynamics of growth and division, the specific model for volume growth and the age structure of the population. Nevertheless, the error made by models with implicit cell growth and division is quite small. Furthermore, we compare various models that are partially stochastic to investigate the impact of different sources of (intrinsic) noise. This comparison indicates that different sources of noise (protein synthesis, partitioning in cell division) contribute comparable amounts of noise if protein synthesis is not or only weakly bursty. If protein synthesis is very bursty, the burstiness is the dominant noise source, independent of other details of the model. Finally, we discuss two sources of extrinsic noise: cell-to-cell variations in protein content due to cells being at different stages in the division cycles, which we show to be small (for the protein concentration and, surprisingly, also for the protein copy number per cell) and fluctuations in the growth rate, which can have a significant impact.Comment: 23 pages, 5 figures; Journal of Statistical physics (2012

Detection and isolation of cell-derived microparticles are compromised by protein complexes due to shared biophysical parameters

Numerous diseases, recently reported to associate with elevated microvesicle/microparticle (MP) counts, have also long been known to be characterized by accelerated immune complex (IC) formation. The goal of this study was to investigate the potential overlap between parameters of protein complexes (e.g. ICs or avidin-biotin complexes) and MPs, which might perturb detection and/or isolation of MPs. In this work, after comprehensive characterization of MPs by electron microscopy, atomic force microscopy, dynamic light scattering analysis and flow cytometry, for the first time we drive attention to the fact that protein complexes, especially insoluble ICs, overlap in biophysical properties (size, light scattering, sedimentation) with MPs. This, in turn, affects MP quantification by flow cytometry and purification by differential centrifugation, especially in diseases in which IC formation is common, including not only autoimmune diseases, but also hematological disorders, infections and cancer. These data may necessitate reevaluation of certain published data on patient-derived MPs, and contribute to correct the clinical laboratory assessment of the presence and biological functions of MPs in health and disease

New method to detect size, timespan and flow in nanoplasmonic fusion

The differential Hanbury-Brown and Twiss analysis is widely used in astrophysics and in relativistic heavy ion physics to determine the size and timespan of emitted particles. Here we propose to adopt theis method for laser induced nanoplasmonic inertial confinement fusion. The aim is to determine the parameters of emitted Deuterium and Helium$^4$ nuclei at the ignition of the fusion target. In addition of spatial volume and timespan the method is able to detect specific space-time correlation patterns, which are connected to collective flow at ignition

Drought rewires the cores of food webs

Droughts are intensifying across the globe, with potentially devastating implications for freshwater ecosystems. We used new network science approaches to investigate drought impacts on stream food webs and explored potential consequences for web robustness to future perturbations. The substructure of the webs was characterized by a core of richly connected species surrounded by poorly connected peripheral species. Although drought caused the partial collapse of the food webs, the loss of the most extinction-prone peripheral species triggered a substantial rewiring of interactions within the networks’ cores. These shifts in species interactions in the core conserved the underlying core/periphery substructure and stability of the drought-impacted webs. When we subsequently perturbed the webs by simulating species loss in silico, the rewired drought webs were as robust as the larger, undisturbed webs. Our research unearths previously unknown compensatory dynamics arising from within the core that could underpin food web stability in the face of environmental perturbations

Efficient derivation of NPCs, spinal motor neurons and midbrain dopaminergic neurons from hESCs at 3% oxygen

This protocol has been designed to generate neural precursor cells (NPCs) from human embryonic stem cells (hESCs) using a physiological oxygen (O(2)) level of 3% and chemically defined conditions. The first stage involves suspension culture of hESC colonies at 3% O(2), where they acquire a neuroepithelial identity over two weeks. This timescale is comparable to that at 20% O(2), but survival is enhanced. Sequential application of retinoic acid (RA) and purmorphamine (PM), from day 14 to 28, directs differentiation towards spinal motor neurons. Alternatively, addition of FGF-8 and PM generates midbrain dopaminergic neurons. OLIG2 induction in motor neuron precursors is 2-fold greater than at 20% O(2), whereas EN1 is 5-fold enhanced. 3% NPCs can be differentiated into all three neural lineages, and such cultures can be maintained long-term in the absence of neurotrophins. The ability to generate defined cell types at 3% O(2) should represent a significant advance for in vitro disease modelling and potentially cell-based therapies

Comparative study on the uniform energy deposition achievable via optimized plasmonic nanoresonator distributions

Plasmonic nanoresonators of core-shell composition and nanorod shape were optimized to tune their absorption cross-section maximum to the central wavelength of a short pulse. Their distribution along a pulse-length scaled target was optimized to maximize the absorptance with the criterion of minimal absorption difference in between neighbouring layers. Successive approximation of layer distributions made it possible to ensure almost uniform deposited energy distribution up until the maximal overlap of two counter-propagating pulses. Based on the larger absorptance and smaller uncertainty in absorptance and energy distribution core-shell nanoresonators override the nanorods. However, optimization of both nanoresonator distributions has potential applications, where efficient and uniform energy deposition is crucial, including phase transitions and even fusion

Crater Formation and Deuterium Production in Laser Irradiation of Polymers with Implanted Nano-antennas

Recent validation experiments on laser irradiation of polymer foils with and without implanted golden nano-particles are discussed. First we analyze characteristics of craters, formed in the target after its interaction with laser beam. Preliminary experimental results show significant production of deuterons when both the energy of laser pulse and concentration of nano-particles are high enough. We consider the deuteron production via the nuclear transmutation reactions $p+C\rightarrow d+X$ where protons are accelerated by Coulomb field, generated in the target plasma. We argue that maximal proton energy can be above threshold values for these reactions and the deuteron yield may noticeably increase due to presence of nano-particles.Comment: 9 pages, 4 figure