8,332 research outputs found
High-resolution methods for fluorescence retrieval from space
The retrieval from space of a very weak fluorescence signal was studied in the O2A and O2B oxygen atmospheric absorption bands. The accuracy of the method was tested for the retrieval of the chlorophyll fluorescence and reflectance terms contributing to the sensor signal. The radiance at the top of the atmosphere was simulated by means of a commercial radiative-transfer program at a high resolution (0.1 cm-1). A test data set was generated in order to simulate sun-induced chlorophyll fluorescence at the top of the canopy. Reflectance terms were spectrally modeled using cubic splines and fluorescence by means of the sum of two Voigt functions. Sensor radiance residual minimization was performed in the presence of a multiplicative noise, thus ensuring that the sensor simulations were realistic. The study, which focused on the possibility of retrieving fluorescence with an accuracy better than 10%, was performed for instrument resolutions ranging from about 0.4 cm-1 to 2 cm-1 in order to test the algorithm for the characteristics of existing and planned hyper-spectral sensors. The algorithm was also used to retrieve fluorescence in the single O2A band at the OCO and TANSO-FTS instrument spectral resolution
Inducing false memories by manipulating memory self-efficacy
The aim of this paper is to investigate the relationship between self-efficacy and false memories using the Deese/Roediger–McDermott (DRM) paradigm, whereby people falsely remember words not presented in lists. In two studies participants were presented with DRM lists and asked to recall and recognize presented items. In the first study, we found a significant relationship between memory self-efficacy (MSE) and susceptibility to associative memory illusions, both in recall and recognition. They also received the Memory Self-Efficacy Questionnaire (MSEQ), the Big Five Questionnaire (BFQ) and the backward digit span (BDS) test. In the second study, MSE was manipulated in order to assess whether changes influenced the sensitivity parameter in DRM tasks. Results showed that the manipulation was effective in decreasing self-efficacy, which in turn affected the probability of reporting critical lures as well as sensitivity. Possible explanations for the effect are discussed
Bistability, softening, and quenching of magnetic moments in Ni-filled carbon nanotubes
The authors apply first-principles calculations to investigate the interplay
between structural, electronic, and magnetic properties of nanostructures
composed of narrow nanotubes filled with metallic nanowires. The focus is on
the structural and magnetic responses of Ni-filled nanotubes upon radial
compression. Interestingly, metastable flattened structures are identified, in
which radially deformed nanotubes are stabilized by the interactions with the
encapsulated wire. Moreover, our results indicate a quenching of the magnetic
moment of the wire upon compression, as a result of the transfer of charge from
the to the orbitals of the atoms in the wire.Comment: 4 pages, 4 figure
Test of Einstein Equivalence Principle for 0-spin and half-integer-spin atoms: Search for spin-gravity coupling effects
We report on a conceptually new test of the equivalence principle performed
by measuring the acceleration in Earth's gravity field of two isotopes of
strontium atoms, namely, the bosonic Sr isotope which has no spin vs the
fermionic Sr isotope which has a half-integer spin. The effect of
gravity upon the two atomic species has been probed by means of a precision
differential measurement of the Bloch frequency for the two atomic matter waves
in a vertical optical lattice. We obtain the values for the E\"otv\"os parameter and
for the coupling between nuclear spin and gravity.
This is the first reported experimental test of the equivalence principle for
bosonic and fermionic particles and opens a new way to the search for the
predicted spin-gravity coupling effects.Comment: 5 pages, 4 figures. New spin-gravtity coupling analysis on the data
added to the manuscrip
Towards a plug&play solution for real-time precise positioning on mass-market devices
Despite pedestrian and vehicle navigation are the key applications enabled by the development of GNSS technology, the best approach to obtain accurate, reliable, continuous and robust PVT (Position-Velocity-Timing) solutions for this purpose has yet to be identified. The real limiting factor is the environment in which the users usually navigate: e.g. multipath effects and cycle slips in harsh urban environments strongly affect, respectively, pseudorange measurements and the continuity of carrier-phase observations. Therefore, positioning services relying on code-based algorithms cannot always meet the required accuracy - which varies depending on the targeted use case -; on the other hand, phase-based approaches as Real-Time Kinematic (RTK) and Precise Point Positioning (PPP) require strong effort to deal with the ambiguity term and its reinitialization when cycle slips occur. These problems are amplified when GNSS measurements from Android smartphone are considered due to the low-cost, linearly polarized and multi-purpose antenna which inevitably impacts on the quality of GNSS observables. This paper focuses on the performance analysis of GNSS POWER - an algorithm based on the loosely coupling between Single Point Positioning (SPP) solutions and variometric velocity - combined with IGS SSR corrections to increase the accuracy achievable in a real-time stand-alone solution. The integration of SSR corrections within GNSS POWER algorithm is validated in both static and kinematic scenarios using high-end GNSS receivers and Andorid smartphones. The results demonstrated the advantages of using SSR corrections on SPP and GNSS POWER solutions also on Android devices opening to new applications of real-time stand-alone positioning approaches on mass-market devices
Bragg gravity-gradiometer using the S-P intercombination transition of Sr
We present a gradiometer based on matter-wave interference of
alkaline-earth-metal atoms, namely Sr. The coherent manipulation of the
atomic external degrees of freedom is obtained by large-momentum-transfer Bragg
diffraction, driven by laser fields detuned away from the narrow
S-P intercombination transition. We use a well-controlled
artificial gradient, realized by changing the relative frequencies of the Bragg
pulses during the interferometer sequence, in order to characterize the
sensitivity of the gradiometer. The sensitivity reaches
s for an interferometer time of 20 ms, limited only by geometrical
constraints. We observed extremely low sensitivity of the gradiometric phase to
magnetic field gradients, approaching a value 10 times lower than the
sensitivity of alkali-atom based gradiometers. An efficient double-launch
technique employing accelerated red vertical lattices from a single
magneto-optical trap cloud is also demonstrated. These results highlight
strontium as an ideal candidate for precision measurements of gravity
gradients, with potential application in future precision tests of fundamental
physics.Comment: 10 pages, 7 figure
Group theory analysis of electrons and phonons in N-layer graphene systems
In this work we study the symmetry properties of electrons and phonons in
graphene systems as function of the number of layers. We derive the selection
rules for the electron-radiation and for the electron-phonon interactions at
all points in the Brillouin zone. By considering these selection rules, we
address the double resonance Raman scattering process. The monolayer and
bilayer graphene in the presence of an applied electric field are also
discussed.Comment: 8 pages, 6 figure
Indirect Self-Modulation Instability Measurement Concept for the AWAKE Proton Beam
AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment,
is a proof-of-principle R&D experiment at CERN using a 400 GeV/c proton beam
from the CERN SPS (longitudinal beam size sigma_z = 12 cm) which will be sent
into a 10 m long plasma section with a nominal density of approx. 7x10^14
atoms/cm3 (plasma wavelength lambda_p = 1.2mm). In this paper we show that by
measuring the time integrated transverse profile of the proton bunch at two
locations downstream of the AWAKE plasma, information about the occurrence of
the self-modulation instability (SMI) can be inferred. In particular we show
that measuring defocused protons with an angle of 1 mrad corresponds to having
electric fields in the order of GV/m and fully developed self-modulation of the
proton bunch. Additionally, by measuring the defocused beam edge of the
self-modulated bunch, information about the growth rate of the instability can
be extracted. If hosing instability occurs, it could be detected by measuring a
non-uniform defocused beam shape with changing radius. Using a 1 mm thick
Chromox scintillation screen for imaging of the self-modulated proton bunch, an
edge resolution of 0.6 mm and hence a SMI saturation point resolution of 1.2 m
can be achieved.Comment: 4 pages, 4 figures, EAAC conference proceeding
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