2,780 research outputs found
Observation of Wannier-Stark localization at the surface of BaTiO films by photoemission
Observation of Bloch oscillations and Wannier-Stark localization of charge
carriers is typically impossible in single-crystals, because an electric field
higher than the breakdown voltage is required. In BaTiO however, high
intrinsic electric fields are present due to its ferroelectric properties. With
angle-resolved photoemission we directly probe the Wannier-Stark localized
surface states of the BaTiO film-vacuum interface and show that this effect
extends to thin SrTiO overlayers. The electrons are found to be localized
along the in-plane polarization direction of the BaTiO film
Polar catastrophe and electronic reconstructions at the LaAlO3/SrTiO3 interface: evidence from optical second harmonic generation
The so-called "polar catastrophe", a sudden electronic reconstruction taking
place to compensate for the interfacial ionic polar discontinuity, is currently
considered as a likely factor to explain the surprising conductivity of the
interface between the insulators LaAlO3 and SrTiO3. We applied optical second
harmonic generation, a technique that a priori can detect both mobile and
localized interfacial electrons, to investigating the electronic polar
reconstructions taking place at the interface. As the LaAlO3 film thickness is
increased, we identify two abrupt electronic rearrangements: the first takes
place at a thickness of 3 unit cells, in the insulating state; the second
occurs at a thickness of 4-6 unit cells, i.e., just above the threshold for
which the samples become conducting. Two possible physical scenarios behind
these observations are proposed. The first is based on an electronic transfer
into localized electronic states at the interface that acts as a precursor of
the conductivity onset. In the second scenario, the signal variations are
attributed to the strong ionic relaxations taking place in the LaAlO3 layer
A bank of unscented Kalman filters for multimodal human perception with mobile service robots
A new generation of mobile service robots could be ready soon to operate in human environments if they can robustly estimate position and identity of surrounding people. Researchers in this field face a number of challenging problems, among which sensor uncertainties and real-time constraints.
In this paper, we propose a novel and efficient solution for simultaneous tracking and recognition of people within the observation range of a mobile robot. Multisensor techniques for legs and face detection are fused in a robust probabilistic framework to height, clothes and face recognition algorithms. The system is based on an efficient bank of Unscented Kalman Filters that keeps a multi-hypothesis estimate of the person being tracked, including the case where the latter is unknown to the robot.
Several experiments with real mobile robots are presented to validate the proposed approach. They show that our solutions can improve the robot's perception and recognition of humans, providing a useful contribution for the future application of service robotics
Standing out from the crowd: Both cue numerosity and social information affect attention in multi-agent contexts
Groups of people offer abundant opportunities for social interactions. We used a two-phase task to investigate how social cue numerosity and social information about an individual affected attentional allocation in such multi-agent settings. The learning phase was a standard gaze-cuing procedure in which a stimulus face could be either uninformative or informative about the upcoming target. The test phase was a group-cuing procedure in which the stimulus faces from the learning phase were presented in groups of three. The target could either be cued by the group minority (i.e., one face) or majority (i.e., two faces) or by uninformative or informative stimulus faces. Results showed an effect of cue numerosity, whereby responses were faster to targets cued by the group majority than the group minority. However, responses to targets cued by informative identities included in the group minority were as fast as responses to targets cued by the group majority. Thus, previously learned social information about an individual was able to offset the general enhancement of cue numerosity, revealing a complex interplay between cue numerosity and social information in guiding attention in multi-agent settings
Detection of UWB ranging measurement quality for collaborative indoor positioning
Wireless communication signals have become popular alternatives for indoor positioning and navigation due to lack of navigation satellite signals in such environments. The signal characteristics determine the method used for positioning as well as the positioning accuracy. Ultra-wideband (UWB) signals, with a typical bandwidth of over 1 GHz, overcome multipath problems in complicated environments. Hence, potentially achieves centimetre-level ranging accuracy in open areas. However, signals can be disrupted when placed in environments with obstructions and cause large ranging errors. This paper proposes a ranging measurement quality indicator (RQI) which detects the UWB measurement quality based on the received signal strength pattern. With a detection validity of more than 83%, the RQI is then implemented in a ranging-based collaborative positioning system. The relative constraint of the collaborative network is adjusted adaptively according to the detected RQI. The proposed detection and positioning algorithm improves positioning accuracy by 80% compared to non-adaptive collaborative positioning
Characterization of irradiated RD53A pixel modules with passive CMOS sensors
We are investigating the feasibility of using CMOS foundries to fabricate
silicon detectors, both for pixels and for large-area strip sensors. The
availability of multi-layer routing will provide the freedom to optimize the
sensor geometry and the performance, with biasing structures in poly-silicon
layers and MIM-capacitors allowing for AC coupling. A prototyping production of
strip test-structures and RD53A compatible pixel sensors was recently completed
at LFoundry in a 150nm CMOS process. This paper will focus on the
characterization of irradiated and non-irradiated pixel modules, composed by a
CMOS passive sensor interconnected to a RD53A chip. The sensors are designed
with a pixel cell of in case of DC coupled
devices and for the AC coupled ones. Their
performance in terms of charge collection, position resolution, and hit
efficiency was studied with measurements performed in the laboratory and with
beam tests. The RD53A modules with LFoundry silicon sensors were irradiated to
fluences up to
Observation of phase noise reduction in photonically synthesized sub-THz signals using a passively mode-locked laser diode and highly selective optical filtering
A Continuous Wave (CW) sub-THz photonic synthesis setup based on a single Passively Mode-Locked Laser Diode (PMLLD) acting as a monolithic Optical Frequency Comb Generator (OFCG) and highly selective optical filtering has been implemented to evaluate the phase noise performance of the generated sub-THz signals. The analysis of the synthesized sub-THz signals up to 120 GHz gives as a result an effective reduction of the electrical linewidth when compared to direct harmonic generation that begins at 50 GHz and becomes greater as the frequency increases. The phase noise reduction offered by the setup, along with its integration potential, cost and bandwidth, make it a promising candidate to the development of an integrated and high performance low phase noise local oscillator in the sub-THz range.Work supported by the Spanish Ministry of Science and Technology through the project TEC2009-14525-C02-02 and by the European Commission FP7 iPHOS Project. The work by A.R. Criado has been supported by the Spanish Ministry of Science and Technology under the FPI Program, Grant# BES2010-030290.Publicad
HV/HR-CMOS sensors for the ATLAS upgrade—concepts and test chip results
In order to extend its discovery potential, the Large Hadron Collider (LHC) will have a major upgrade (Phase II Upgrade) scheduled for 2022. The LHC after the upgrade, called High-Luminosity LHC (HL-LHC), will operate at a nominal leveled instantaneous luminosity of 5× 1034 cm−2 s−1, more than twice the expected Phase I . The new Inner Tracker needs to cope with this extremely high luminosity. Therefore it requires higher granularity, reduced material budget and increased radiation hardness of all components. A new pixel detector based on High Voltage CMOS (HVCMOS) technology targeting the upgraded ATLAS pixel detector is under study. The main advantages of the HVCMOS technology are its potential for low material budget, use of possible cheaper interconnection technologies, reduced pixel size and lower cost with respect to traditional hybrid pixel detector. Several first prototypes were produced and characterized within ATLAS upgrade R&D effort, to explore the performance and radiation hardness of this technology.
In this paper, an overview of the HVCMOS sensor concepts is given. Laboratory tests and irradiation tests of two technologies, HVCMOS AMS and HVCMOS GF, are also given
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