Correlation effects in sequential energy branching: an exact model of the Fano statistics

Correlation effects in in the fluctuation of the number of particles in the process of energy branching by sequential impact ionizations are studied using an exactly soluble model of random parking on a line. The Fano factor F calculated in an uncorrelated final-state "shot-glass" model does not give an accurate answer even with the exact gap-distribution statistics. Allowing for the nearest-neighbor correlation effects gives a correction to F that brings F very close to its exact value. We discuss the implications of our results for energy resolution of semiconductor gamma detectors, where the value of F is of the essence. We argue that F is controlled by correlations in the cascade energy branching process and hence the widely used final-state model estimates are not reliable -- especially in the practically relevant cases when the energy branching is terminated by competition between impact ionization and phonon emission.Comment: 11 pages, 4 figures. Submitted to Physical Review

Evaluation of game templates to support programming activities in schools

Game creation challenges in schools potentially provide engaging, goal-oriented, and interactive experiences in classes; thereby supporting the transfer of knowledge for learning in a fun and pedagogic manner. A key element of the ongoing European project No One Left Behind (NOLB) is to integrate a game-making teaching framework (GMTF) into the educational app Pocket Code. Pocket Code allows learners to create programs in a visual Lego®-style way to facilitate learning how to code at secondary high schools. The concept of the NOLB GMTF is based on principles of the Universal Design for Learning (UDL) model. Its focus lies on three pillars of learning: the what, how, and why. Thereby, the NOLB GMTF is a common set of concepts, practices, pedagogy, and methods. This framework provides a coherent approach to learning and teaching by integrating leisure oriented gaming methods into multi-discipline curricula. One output of this framework is the integration of game-based methods via game templates that refer to didactical scenarios that include a refined set of genres, assets, rules, challenges, and strategies. These templates allows: 1) teachers to start with a well-structured program, and 2) pupils to add content and adjust the code to integrate their own ideas. During the project game genres such as adventure, action, and quiz, as well as rewards or victory point mechanisms, have been embedded into different subjects, e.g., science, mathematics, and arts. The insights gained during the class hours were used to generate 13 game templates, which are integrated in Create@School (a new version of the Pocket Code app which targets schools). To test the efficiency of these templates, user experience (UX) tests were conducted during classes to compare games created by pupils who used templates and those who started to create a game from scratch. Preliminary results showed that these templates allow learners to focus on subject-relevant problem solving activities rather than on understanding the functionality of the app. This directly leads to more time to express their creativity in different levels and more time for extra tasks

The EBEX Experiment

EBEX is a balloon-borne polarimeter designed to measure the intensity and polarization of the cosmic microwave background radiation. The measurements would probe the inflationary epoch that took place shortly after the big bang and would significantly improve constraints on the values of several cosmological parameters. EBEX is unique in its broad frequency coverage and in its ability to provide critical information about the level of polarized Galactic foregrounds which will be necessary for all future CMB polarization experiments. EBEX consists of a 1.5 m Dragone-type telescope that provides a resolution of less than 8 arcminutes over four focal planes each of 4 degree diffraction limited field of view at frequencies up to 450 GHz. The experiment is designed to accommodate 330 transition edge bolometric detectors per focal plane, for a total of up to 1320 detectors. EBEX will operate with frequency bands centered at 150, 250, 350, and 450 GHz. Polarimetry is achieved with a rotating achromatic half-wave plate. EBEX is currently in the design and construction phase, and first light is scheduled for 2008.Comment: 13 pages, 10 figures. Figure 1 is changed from the one which appeared in the Proceedings of the SPI

Temperature dependence of Al0.2Ga0.8As X-ray photodiodes for X-ray spectroscopy

Two custom-made Al0.2Ga0.8As p+-i-n+ mesa X-ray photodiodes (200 μm diameter, 3 μm i layer) have been electrically characterised across the temperature range −20 °C to 60 °C. The devices were connected to a custom-made charge sensitive preamplifier to produce an AlGaAs photon-counting X-ray spectrometer. The devices' responses to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV) were investigated across the temperature range −20 °C to 20 °C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 °C was 1.06 keV (with the detector at 10 V reverse bias). Improved FWHM was observed with the devices at temperatures of 0 °C (0.86 keV) and −20 °C (0.83 keV) with the photodiode reverse biased at 30 V. The average electron hole pair creation energy was experimentally measured and determined to be 4.43 eV ± 0.09 eV at 20 °C, 4.44 eV ± 0.10 eV at 0 °C, and 4.56 eV ± 0.10 eV at −20 °C

Searching for interstellar C60+ using a new method for high signal-to-noise HST/STIS spectroscopy

Due to recent advances in laboratory spectroscopy, the first optical detection of a very large molecule has been claimed in the diffuse interstellar medium (ISM): ${{\rm{C}}}_{60}^{+}$ (ionized Buckminsterfullerene). Confirming the presence of this molecule would have significant implications regarding the carbon budget and chemical complexity of the ISM. Here we present results from a new method for ultra-high signal-to-noise ratio (S/N) spectroscopy of background stars in the near-infrared (at wavelengths of 0.9–1 μm), using the Hubble Space Telescope (HST) Imaging Spectrograph (STIS) in a previously untested "STIS scan" mode. The use of HST provides the crucial benefit of eliminating the need for error-prone telluric-correction methods in the part of the spectrum where the ${{\rm{C}}}_{60}^{+}$ bands lie and where the terrestrial water vapor contamination is severe. Our STIS spectrum of the heavily reddened B0 supergiant star BD+63 1964 reaches an unprecedented S/N for this instrument (~600–800), allowing the detection of the diffuse interstellar band (DIB) at 9577 Å attributed to ${{\rm{C}}}_{60}^{+}$, as well as new DIBs in the near-IR. Unfortunately, the presence of overlapping stellar lines, and the unexpected weakness of the ${{\rm{C}}}_{60}^{+}$ bands in this sightline, prevents conclusive detection of the weaker ${{\rm{C}}}_{60}^{+}$ bands. A probable correlation between the 9577 Å DIB strength and interstellar radiation field is identified, which suggests that more strongly irradiated interstellar sightlines will provide the optimal targets for future ${{\rm{C}}}_{60}^{+}$ searches

Ultra High Energy Cosmology with POLARBEAR

Observations of the temperature anisotropy of the Cosmic Microwave Background (CMB) lend support to an inflationary origin of the universe, yet no direct evidence verifying inflation exists. Many current experiments are focussing on the CMB's polarization anisotropy, specifically its curl component (called "B-mode" polarization), which remains undetected. The inflationary paradigm predicts the existence of a primordial gravitational wave background that imprints a unique B-mode signature on the CMB's polarization at large angular scales. The CMB B-mode signal also encodes gravitational lensing information at smaller angular scales, bearing the imprint of cosmological large scale structures (LSS) which in turn may elucidate the properties of cosmological neutrinos. The quest for detection of these signals; each of which is orders of magnitude smaller than the CMB temperature anisotropy signal, has motivated the development of background-limited detectors with precise control of systematic effects. The POLARBEAR experiment is designed to perform a deep search for the signature of gravitational waves from inflation and to characterize lensing of the CMB by LSS. POLARBEAR is a 3.5 meter ground-based telescope with 3.8 arcminute angular resolution at 150 GHz. At the heart of the POLARBEAR receiver is an array featuring 1274 antenna-coupled superconducting transition edge sensor (TES) bolometers cooled to 0.25 Kelvin. POLARBEAR is designed to reach a tensor-to-scalar ratio of 0.025 after two years of observation -- more than an order of magnitude improvement over the current best results, which would test physics at energies near the GUT scale. POLARBEAR had an engineering run in the Inyo Mountains of Eastern California in 2010 and will begin observations in the Atacama Desert in Chile in 2011.Comment: 8 pages, 6 figures, DPF 2011 conference proceeding

The new generation CMB B-mode polarization experiment: POLARBEAR

We describe the Cosmic Microwave Background (CMB) polarization experiment called Polarbear. This experiment will use the dedicated Huan Tran Telescope equipped with a powerful 1,200-bolometer array receiver to map the CMB polarization with unprecedented accuracy. We summarize the experiment, its goals, and current status

The bolometric focal plane array of the Polarbear CMB experiment

The Polarbear Cosmic Microwave Background (CMB) polarization experiment is currently observing from the Atacama Desert in Northern Chile. It will characterize the expected B-mode polarization due to gravitational lensing of the CMB, and search for the possible B-mode signature of inflationary gravitational waves. Its 250 mK focal plane detector array consists of 1,274 polarization-sensitive antenna-coupled bolometers, each with an associated lithographed band-defining filter. Each detector's planar antenna structure is coupled to the telescope's optical system through a contacting dielectric lenslet, an architecture unique in current CMB experiments. We present the initial characterization of this focal plane