993 research outputs found
Effective Constraints for Relativistic Quantum Systems
Determining the physical Hilbert space is often considered the most difficult
but crucial part of completing the quantization of a constrained system. In
such a situation it can be more economical to use effective constraint methods,
which are extended here to relativistic systems as they arise for instance in
quantum cosmology. By side-stepping explicit constructions of states, such
tools allow one to arrive much more feasibly at results for physical
observables at least in semiclassical regimes. Several questions discussed
recently regarding effective equations and state properties in quantum
cosmology, including the spreading of states and quantum back-reaction, are
addressed by the examples studied here.Comment: 27 pages, 2 figures; v2: new appendix comparing effective constraints
and physical coherent states by an exampl
Particle Weights and their Disintegration I
The notion of Wigner particles is attached to irreducible unitary
representations of the Poincare group, characterized by parameters m and s of
mass and spin, respectively. However, the Lorentz symmetry is broken in
theories with long-range interactions, rendering this approach inapplicable
(infraparticle problem). A unified treatment of both particles and
infraparticles via the concept of particle weights can be given within the
framework of Local Quantum Physics. They arise as temporal limits of physical
states in the vacuum sector and describe the asymptotic particle content. In
this paper their definition and characteristic properties are worked out in
detail. The existence of the temporal limits is established by use of suitably
defined seminorms which are also essential in proving the characteristic
features of particle weights.Comment: 33 pages, amslatex, mathptm, minor corrections including numbering
schem
Lab School Paris. An educational living lab
In this chapter, the authors introduce Lab School Paris, the first lab school in France. After a general presentation of the university school context in France, they present the history of the foundation of Lab School Paris, the main theoretical principles upon which their pedagogical approach is grounded, and the wider network of research that aims at contributing to strengthen the links between scientific research in education and actual practices in the classrooms. (DIPF/Orig.
Automated Ground Truth Estimation For Automotive Radar Tracking Applications With Portable GNSS And IMU Devices
Baseline generation for tracking applications is a difficult task when
working with real world radar data. Data sparsity usually only allows an
indirect way of estimating the original tracks as most objects' centers are not
represented in the data. This article proposes an automated way of acquiring
reference trajectories by using a highly accurate hand-held global navigation
satellite system (GNSS). An embedded inertial measurement unit (IMU) is used
for estimating orientation and motion behavior. This article contains two major
contributions. A method for associating radar data to vulnerable road user
(VRU) tracks is described. It is evaluated how accurate the system performs
under different GNSS reception conditions and how carrying a reference system
alters radar measurements. Second, the system is used to track pedestrians and
cyclists over many measurement cycles in order to generate object centered
occupancy grid maps. The reference system allows to much more precisely
generate real world radar data distributions of VRUs than compared to
conventional methods. Hereby, an important step towards radar-based VRU
tracking is accomplished.Comment: 10 pages, 9 figures, accepted paper for 2019 20th International Radar
Symposium (IRS), Ulm, Germany, June 2019. arXiv admin note: text overlap with
arXiv:1905.1121
Low Cost Propulsion Development for Small Satellites at the Surrey Space Centre
The Surrey Space Centre (SSC) has led the way in demonstrating the utility of microsatellite size spacecraft for research, humanitarian, commercial, and military applications. SSC recognises that cost effective propulsion technology for small spacecraft is an enabling technology for expanding the utility of these assets and has been actively researching this field since 1993. This paper provides an overview of propulsion research and development at the Surrey Space Centre. The paper will summarise SSC goals for small spacecraft propulsion technology and link them to areas of propulsion research past, present and future. A review of Surrey\u27s propulsion history to include hybrid, monopropellant, cold gas and resistojet technology is presented. Design and integration of SSC cold gas and resistojet technologies on flight spacecraft will also be covered with an emphasis on the SSC low cost approach to qualification, integration and operation of these systems. These topics will be followed by a discussion of areas that are currently being investigated for near term research, specifically, H202 long term storage, expulsion, catalysis, Green monopropellant and hybrid technology utilising both N20 and H202. One topic covered in detail is a novel alternative geometry hybrid rocket motor. This motor is currently under development to provide a low-cost, intrinsically-safe and easy to integrate orbital upper-stage for small spacecraft. A prototype motor has been constructed and test results are presented
Effective Constraints and Physical Coherent States in Quantum Cosmology: A Numerical Comparison
A cosmological model with a cyclic interpretation is introduced, which is
subject to quantum back-reaction and yet can be treated rather completely by
physical coherent state as well as effective constraint techniques. By this
comparison, the role of quantum back-reaction in quantum cosmology is
unambiguously demonstrated. Also the complementary nature of strengths and
weaknesses of the two procedures is illustrated. Finally, effective constraint
techniques are applied to a more realistic model filled with radiation, where
physical coherent states are not available.Comment: 32 pages, 25 figure
On The KMS Condition for the critical Ising model
Using the KMS condition and exchange algebras we discuss the monodromy and
modular properties of two-point KMS states of the critical Ising model.Comment: 8 pages, TcilaTe
Modification of Pb quantum well states by the adsorption of organic molecules
The successful implementation of nanoscale materials in next generation optoelectronic devices crucially depends on our ability to functionalize and design low dimensional materials according to the desired field of application. Recently, organic adsorbates have revealed an enormous potential to alter the occupied surface band structure of tunable materials by the formation of tailored molecule-surface bonds. Here, we extend this concept of adsorption-induced surface band structure engineering to the unoccupied part of the surface band structure. This is achieved by our comprehensive investigation of the unoccupied band structure of a lead (Pb) monolayer film on the Ag(1 1 1) surface prior and after the adsorption of one monolayer of the aromatic molecule 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA). Using two-photon momentum microscopy, we show that the unoccupied states of the Pb/Ag(1 1 1) bilayer system are dominated by a parabolic quantum well state (QWS) in the center of the surface Brillouin zone with Pb p orbital character and a side band with almost linear dispersion showing Pb p orbital character. After the adsorption of PTCDA, the Pb side band remains completely unaffected while the signal of the Pb QWS is fully suppressed. This adsorption induced change in the unoccupied Pb band structure coincides with an interfacial charge transfer from the Pb layer into the PTCDA molecule. We propose that this charge transfer and the correspondingly vertical (partially chemical) interaction across the PTCDA/Pb interface suppresses the existence of the QWS in the Pb layer. Our results hence unveil a new possibility to orbital selectively tune and control the entire surface band structure of low dimensional systems by the adsorption of organic molecules
Modification of Pb quantum well states by the adsorption of organic molecules
he successful implementation of nanoscale materials in next generation optoelectronic devices crucially depends on our ability to functionalize and design low dimensional materials according to the desired field of application. Recently, organic adsorbates have revealed an enormous potential to alter the occupied surface band structure of tunable materials by the formation of tailored molecule-surface bonds. Here, we extend this concept of adsorption-induced surface band structure engineering to the unoccupied part of the surface band structure. This is achieved by our comprehensive investigation of the unoccupied band structure of a lead (Pb) monolayer film on the Ag(1 1 1) surface prior and after the adsorption of one monolayer of the aromatic molecule 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA). Using two-photon momentum microscopy, we show that the unoccupied states of the Pb/Ag(1 1 1) bilayer system are dominated by a parabolic quantum well state (QWS) in the center of the surface Brillouin zone with Pb p orbital character and a side band with almost linear dispersion showing Pb p orbital character. After the adsorption of PTCDA, the Pb side band remains completely unaffected while the signal of the Pb QWS is fully suppressed. This adsorption induced change in the unoccupied Pb band structure coincides with an interfacial charge transfer from the Pb layer into the PTCDA molecule. We propose that this charge transfer and the correspondingly vertical (partially chemical) interaction across the PTCDA/Pb interface suppresses the existence of the QWS in the Pb layer. Our results hence unveil a new possibility to orbital selectively tune and control the entire surface band structure of low dimensional systems by the adsorption of organic molecules
Fast and Mobile Cataract Detection by Applying Line Laser Eye Illumination
Cataract is observed when the eye lens becomes opaque. This condition causes blurred vision and is the main cause of blindness worldwide. Cataract diagnosis is usually performed during ophthalmologist examination using a slit lamp, which requires expertise, is expensive and bulky. In this study, we present a small handheld illumination setup for cataract detection. Ex-vivo porcine eyes are investigated to determine whether colored line lasers, 450 nm (blue), 520 nm (green) and 650 nm (red), which shine obliquely into the eye, are principally suited for detection of the Y shaped suture cataract and of cold cataract, respecting exposure limits of EU guideline 2006/25/EC. Camera images of the cataract exhibited good results under illumination with all line lasers. Observations with the physician’s eye led to an even better diagnosis of cataract. Generally, green laser light illumination was the best choice for cataract detection. With red laser light illumination it was also possible, but least suitable for this purpose. With this method, line lasers are a good choice for cataract identification, as cataract can be detected quickly and without much effort. This type of line laser illumination of the eye is safe and both types of cataract are detectable with all wavelengths. For the human eye, a further development of this system is conceivable
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