Context. The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, Rω, where the local plasma frequency equals the observing ...frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10–90 MHz) solar radio emission originating from the middle and upper corona. Aims. We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer Rω, and a scale height temperature, T. These results can be combined into coronal density and temperature profiles. Methods. We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with Rω and T as fitting parameters. Results. In the low corona, Rω < 1.5 solar radii, we find high scale height temperatures up to 2.2 × 106 K, much more than the brightness temperatures usually found there. But if all Rω values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. Conclusions. These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or extreme ultraviolet (EUV) data. Future observations will provide continuous frequency coverage. This continuous coverage eliminates the need for local hydrostatic density models in the data analysis and enables the analysis of more complex coronal structures such as those with closed magnetic fields.
The Ugi four-component reaction was investigated as a tool for the functionalization of peptide arrays via post-synthetic side-chain modification, mimicking post-translational processes. ...Additionally, as a proof of concept for the synthesis of peptidomimetics on arrays, the integration of an Ugi unit into a growing peptide chain was demonstrated.
We report the discovery of very-high-energy (VHE) g-ray emission of the binary system PSR B 1259-63/SS 2883 of a radio pulsar orbiting a massive, luminous Be star in a highly eccentric orbit. The ...observations around the 2004 periastron passage of the pulsar were performed with the four 13 m Cherenkov telescopes of the HESS experiment, recently installed in Namibia and in full operation since December 2003. Between February and June 2004, a g-ray signal from the binary system was detected with a total significance above 13s. The flux was found to vary significantly on timescales of days which makes PSR B 1259-63 the first variable galactic source of VHE g-rays observed so far. Strong emission signals were observed in pre- and post-periastron phases with a flux minimum around periastron, followed by a gradual flux decrease in the months after. The measured time-averaged energy spectrum above a mean threshold energy of 380 GeV can be fitted by a simple power law F0(E/1 TeV)G with a photon index G = 2.7 c 0.2stat c 0.2sys and flux normalisation F0 = (1.3 c 0.1stat c 0.3sys) x 10-12 TeV-1 cm-2 s-1. This detection of VHE g-rays provides unambiguous evidence for particle acceleration to multi-TeV energies in the binary system. In combination with coeval observations of the X-ray synchrotron emission by the RXTE and INTEGRAL instruments, and assuming the VHE g-ray emission to be produced by the inverse Compton mechanism, the magnetic field strength can be directly estimated to be of the order of 1 G.
Spatially selective deposition of electrically charged microparticles onto integrated circuits that generate electrical fields in programmable patterns using electrodes on their surface was ...previously limited to a pixel pitch of 100
μm. Now, we demonstrate spatially selective deposition onto pixels of 45
μm pitch in experiments on a test chip allowing arbitrary patterns, but being of limited size and of fixed characteristics, complemented by COMSOL simulations. Experiments on a prototype high voltage CMOS chip demonstrate the feasibility of miniaturisation in the first place, imply simulations of interest that cannot be tested experimentally and, conversely, complement the simplified simulation models by reality checks. Using COMSOL for the optimisation of the setup parameters, particles of decreasing average diameter in a number of aerosol and electrical field geometries are simulated with particular attention to minimising contamination (deposition of particles on undesirable locations). Combining these results, the average particle diameter is decreased from 10
μm to less than 3
μm and the deposition voltage is reduced from 100
V to 30
V, when using pixels with a pitch of 45
μm. Optimising these parameters allows for more than quadrupling the spot density compared to the previous chip, on which combinatorial particle deposition with minimal contamination is achieved. Peptide arrays, having been previously shown to be a major application for this method, benefit in particular, as the increase in density from 10,000
pixels/cm
2 to approximately 50,000
pixels/cm
2 promises a significant decrease in cost-per-peptide and amount of test specimens required.
We built high voltage complementary metal oxide semiconductor (CMOS) chips that generate electrical fields on their surface, such that electrically charged microparticles (diameter 10–20
μm on ...average) can be addressed on distinct pixel electrodes according to arbitrary field patterns. Each pixel contains a memory cell in canonical low-voltage CMOS-technology controlling a high voltage (30–100
V) potential area on the top metal layer. Particle transfer with minimal contaminations in less than 10
s for a complete chip was observed for pixels of 100
μm
×
100
μm down to 65
μm
×
65
μm. This allows a new way to create surface modifications on top of CMOS chips without need for additional masks or stamps. Using suitable particles, a chemically modified chip surface, and compatible chemistry, this method can be utilized for self-aligned high-density biopolymer arrays, e.g., peptide arrays. Transfer of microparticles loaded with amino acids for combinatorial peptide synthesis is demonstrated. Successful synthesis of different peptides (octamers) was proven by immunostaining. Based on results obtained by a chip containing pixel areas of different characteristics, a chip for biological applications with 16,384
pixels (10,000
pixel/cm
2) was built. Good homogeneity of peptide synthesis over the chip area was verified by immunostaining.
The behavior of charged bio polymer micro particles when deposited onto a CMOS chip can be analytically modeled in form of the incompressible Navier-Stokes equation and the electrostatic Poisson ...equation, as we describe in this article. Based on these models, numerical simulations of depositions can be implemented in COMSOL that lead to improvements in the experimental setup, optimizing the size and charge distribution of the micro particles. Adapting the experiments according to the simulation results, we will show the powerful gain in deposition precision, which is essential for a contamination-free deposition and hence high quality combinatorial deposition.
A device for the measurement of q/m-values and charge degradation of triboelectrically charged particles deposited on a surface was developed. The setup is based on the integration of currents, which ...are induced in a Faraday cage by insertion of a solid support covered with charged particles. The conductivity of different particle supports was taken into account. The 'blow-off' method, in which the particles are first deposited, and then blown off using an air stream, can be used for characterization of triboelectric properties of particles relative to different surfaces.
Image processing and pattern analysis can evaluate the deposition quality of triboelectrically charged microparticles on charged surfaces. The image processing method presented in this paper aims at ...controlling the quality of peptide arrays generated by particle based solid phase Merrifield combinatorial peptide synthesis. Incorrectly deposited particles are detected before the amino acids therein are coupled to the growing peptide. The calibration of the image acquisition is performed in a supervised training step in which all parameters of the quality analyzing algorithm are learnt given one representative image. Then, the correct deposition pattern is determined by a linear support vector machine. Knowing the pattern, contaminated areas can be detected by comparing the pattern with the actual deposition. Taking into account the resolution of the image acquisition system and its magnification factor, the number and size of contaminating particles can be calculated out of the number of connected foreground pixels.
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