2,488 research outputs found
Automatic Differentiation for Inverse Problems in X-ray Imaging and Microscopy
Computational techniques allow breaking the limits of traditional imaging methods, such as time restrictions, resolution, and optics flaws. While simple computational methods can be enough for highly controlled microscope setups or just for previews, an increased level of complexity is instead required for advanced setups, acquisition modalities or where uncertainty is high; the need for complex computational methods clashes with rapid design and execution. In all these cases, Automatic Differentiation, one of the subtopics of Artificial Intelligence, may offer a functional solution, but only if a GPU implementation is available. In this paper, we show how a framework built to solve just one optimisation problem can be employed for many different X-ray imaging inverse problems
Echo-detected electron paramagnetic resonance spectra of spin-labeled lipids in membrane model systems
Optical spin injection and spin lifetime in Ge heterostructures
We demonstrate optical orientation in Ge/SiGe quantum wells and study their
spin properties. The ultrafast electron transfer from the center of the
Brillouin zone to its edge allows us to achieve high spin-polarization
efficiencies and to resolve the spin dynamics of holes and electrons. The
circular polarization degree of the direct-gap photoluminescence exceeds the
theoretical bulk limit, yielding ~37% and ~85% for transitions with heavy and
light holes states, respectively. The spin lifetime of holes at the top of the
valence band is found to be ~0.5 ps and it is governed by transitions between
heavy and light hole states. Electrons at the bottom of the conduction band, on
the other hand, have a spin lifetime that exceeds 5 ns below 150 K. Theoretical
analysis of the electrons spin relaxation indicates that phonon-induced
intervalley scattering dictates the spin lifetime.Comment: 5 pages, 3 figure
NNLO Logarithmic Expansions and Precise Determinations of the Neutral Currents near the Z Resonance at the LHC: The Drell-Yan case
We present a comparative study of the invariant mass and rapidity
distributions in Drell-Yan lepton pair production, with particular emphasis on
the role played by the QCD evolution. We focus our study around the Z resonance
( GeV) and perform a general analysis of the
factorization/renormalization scale dependence of the cross sections, with the
two scales included both in the evolution and in the hard scatterings. We also
present the variations of the cross sections due to the errors on the parton
distributions (pdf's) and an analysis of the corresponding -factors.
Predictions from several sets of pdf's, evolved by MRST and Alekhin are
compared with those generated using \textsc{Candia}, a NNLO evolution program
that implements the theory of the logarithmic expansions, developed in a
previous work. These expansions allow to select truncated solutions of varying
accuracy using the method of the -space iterates. The evolved parton
distributions are in good agreement with other approaches. The study can be
generalized for high precision searches of extra neutral gauge interactions at
the LHC.Comment: 75 pages,30 figures, 30 table
Composition profiling of inhomogeneous SiGe nanostructures by Raman spectroscopy
In this work, we present an experimental procedure to measure the composition distribution within inhomogeneous SiGe nanostructures. The method is based on the Raman spectra of the nanostructures, quantitatively analyzed through the knowledge of the scattering efficiency of SiGe as a function of composition and excitation wavelength. The accuracy of the method and its limitations are evidenced through the analysis of a multilayer and of self-assembled islands
The Planck-LFI flight model composite waveguides
The Low Frequency Instrument on board the PLANCK satellite is designed to
give the most accurate map ever of the CMB anisotropy of the whole sky over a
broad frequency band spanning 27 to 77 GHz. It is made of an array of 22
pseudo-correlation radiometers, composed of 11 actively cooled (20 K) Front End
Modules (FEMs), and 11 Back End Modules (BEMs) at 300K. The connection between
the two parts is made with rectangular Wave Guides. Considerations of different
nature (thermal, electromagnetic and mechanical), imposed stringent
requirements on the WGs characteristics and drove their design. From the
thermal point of view, the WG should guarantee good insulation between the FEM
and the BEM sections to avoid overloading the cryocooler. On the other hand it
is essential that the signals do not undergo excessive attenuation through the
WG. Finally, given the different positions of the FEM modules behind the focal
surface and the mechanical constraints given by the surrounding structures,
different mechanical designs were necessary. A composite configuration of
Stainless Steel and Copper was selected to satisfy all the requirements. Given
the complex shape and the considerable length (about 1.5-2 m), manufacturing
and testing the WGs was a challenge. This work deals with the development of
the LFI WGs, including the choice of the final configuration and of the
fabrication process. It also describes the testing procedure adopted to fully
characterize these components from the electromagnetic point of view and the
space qualification process they underwent. Results obtained during the test
campaign are reported and compared with the stringent requirements. The
performance of the LFI WGs is in line with requirements, and the WGs were
successfully space qualified.Comment: this paper is part of the Prelaunch status LFI papers published on
JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/jins
The LuGRE project: a scientific opportunity to study GNSS signals at the Moon
The Lunar GNSS Receiver Experiment (LuGRE) is a joint NASA-Italian Space Agency (ASI) payload on the Firefly Blue Ghost Mission 1 with the goal to demonstrate GNSS-based positioning, navigation, and timing at the Moon. When launched, LuGRE will collect GPS and Galileo measurements in transit between Earth and the Moon, in lunar orbit, and on the lunar surface, and will conduct onboard and ground-based navigation experiments using the collected data. These investigations will be based on the observation of the data collected by a custom development performed by the company Qascom, based on the Qascom QN400-Space GNSS receiver. The receiver is able to provide, PVT solutions, the GNSS raw observables obtained by the real time operation, as well as snapshots of IF digital samples collected by the RF front-end at frequencies L1/E1 and L5/E5. These data will be the input for the different science investigations, that require then the development of proper analysis tools that will be the core of the ground segment during the mission. The current work done by the science team of NASA and ASI, which is supported by a research team at Politecnico di Torino, is planning the data acquisitions during the time windows dedicated to the LuGRE payload in the checkout, transit and surface mission phases
Inventory completeness and accuracy of taxonomic determination: outcomes of a large scale barcoding effort of echinoderms in Terra Nova Bay (Antarctica, Ross Sea)
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