39 research outputs found
Component-wise Power Estimation of Electrical Devices Using Thermal Imaging
This paper presents a novel method to estimate the power consumption of
distinct active components on an electronic carrier board by using thermal
imaging. The components and the board can be made of heterogeneous material
such as plastic, coated microchips, and metal bonds or wires, where a special
coating for high emissivity is not required. The thermal images are recorded
when the components on the board are dissipating power. In order to enable
reliable estimates, a segmentation of the thermal image must be available that
can be obtained by manual labeling, object detection methods, or exploiting
layout information. Evaluations show that with low-resolution consumer infrared
cameras and dissipated powers larger than 300mW, mean estimation errors of 10%
can be achieved.Comment: 10 pages, 8 figure
Path Integration and Separation of Variables in Spaces of Constant Curvature in Two and Three Dimensions
In this paper path integration in two- and three-dimensional spaces of
constant curvature is discussed: i.e.\ the flat spaces \bbbr^2 and \bbbr^3,
the two- and three-dimensional sphere and the two- and three dimensional
pseudosphere. The Laplace operator in these spaces admits separation of
variables in various coordinate systems. In all these coordinate systems the
path integral formulation will be stated, however in most of them an explicit
solution in terms of the spectral expansion can be given only on a formal
level. What can be stated in all cases, are the propagator and the
corresponding Green function, respectively, depending on the invariant distance
which is a coordinate independent quantity. This property gives rise to
numerous identities connecting the corresponding path integral representations
and propagators in various coordinate systems with each other.Comment: 70 pages, AmSTeX, DESY 93 - 141 (mailer corrupted file, and truncated
it
Towards polarization-based excitation tailoring for extended Raman spectroscopy
Undoubtedly, Raman spectroscopy is one of the most elaborate spectroscopy tools in materials science, chemistry, medicine and optics. However, when it comes to the analysis of nanostructured specimens or individual sub-wavelength-sized systems, the access to Raman spectra resulting from different excitation schemes is usually very limited. For instance, the excitation with an electric field component oriented perpendicularly to the substrate plane is a difficult task. Conventionally, this can only be achieved by mechanically tilting the sample or by sophisticated sample preparation. Here, we propose a novel experimental method based on the utilization of polarization tailored light for Raman spectroscopy of individual nanostructures. As a proof of principle, we create three-dimensional electromagnetic field distributions at the nanoscale using tightly focused cylindrical vector beams impinging normally onto the specimen, hence keeping the traditional beam-path of commercial Raman systems. In order to demonstrate the convenience of this excitation scheme, we use a sub-wavelength diameter gallium-nitride nanostructure as a test platform and show experimentally that its Raman spectra depend sensitively on its location relative to the focal vector field. The observed Raman spectra can be attributed to the interaction with transverse and pure longitudinal electric field components. This novel technique may pave the way towards a characterization of Raman active nanosystems, granting direct access to growth-related parameters such as strain or defects in the material by using the full information of all Raman modes
Vacuum orbit and spontaneous symmetry breaking in hyperbolic sigma models
We present a detailed study of quantized noncompact, nonlinear SO(1,N)
sigma-models in arbitrary space-time dimensions D \geq 2, with the focus on
issues of spontaneous symmetry breaking of boost and rotation elements of the
symmetry group. The models are defined on a lattice both in terms of a transfer
matrix and by an appropriately gauge-fixed Euclidean functional integral. The
main results in all dimensions \geq 2 are: (i) On a finite lattice the systems
have infinitely many nonnormalizable ground states transforming irreducibly
under a nontrivial representation of SO(1,N); (ii) the SO(1,N) symmetry is
spontaneously broken. For D =2 this shows that the systems evade the
Mermin-Wagner theorem. In this case in addition: (iii) Ward identities for the
Noether currents are derived to verify numerically the absence of explicit
symmetry breaking; (iv) numerical results are presented for the two-point
functions of the spin field and the Noether current as well as a new order
parameter; (v) in a large N saddle-point analysis the dynamically generated
squared mass is found to be negative and of order 1/(V \ln V) in the volume,
the 0-component of the spin field diverges as \sqrt{\ln V}, while SO(1,N)
invariant quantities remain finite.Comment: 60 pages, 12 Figures, AMS-Latex; v2: results on vacuum orbit and
spontaneous symmetry breaking extended to all dimension
Exact propagators for SUSY partners
Pairs of SUSY partner Hamiltonians are studied which are interrelated by
usual (linear) or polynomial supersymmetry. Assuming the model of one of the
Hamiltonians as exactly solvable with known propagator, expressions for
propagators of partner models are derived. The corresponding general results
are applied to "a particle in a box", the Harmonic oscillator and a free
particle (i.e. to transparent potentials).Comment: 31 page
High-Throughput Analysis of Calcium Signalling Kinetics in Astrocytes Stimulated with Different Neurotransmitters
Astrocytes express a wide range of receptors for neurotransmitters and hormones that are coupled to increases in intracellular Ca2+ concentration, enabling them to detect activity in both neuronal and vascular networks. There is increasing evidence that astrocytes are able to discriminate between different Ca2+-linked stimuli, as the efficiency of some Ca2+ dependent processes – notably release of gliotransmitters – depends on the stimulus that initiates the Ca2+ signal. The spatiotemporal complexity of Ca2+ signals is substantial, and we here tested the hypothesis that variation in the kinetics of Ca2+ responses could offer a means of selectively engaging downstream targets, if agonists exhibited a “signature shape” in evoked Ca2+ response. To test this, astrocytes were exposed to three different receptor agonists (ATP, glutamate and histamine) and the resultant Ca2+ signals were analysed for systematic differences in kinetics that depended on the initiating stimulus. We found substantial heterogeneity between cells in the time course of Ca2+ responses, but the variation did not correlate with the type or concentration of the stimulus. Using a simple metric to quantify the extent of difference between populations, it was found that the variation between agonists was insufficient to allow signal discrimination. We conclude that the time course of global intracellular Ca2+ signals does not offer the cells a means for distinguishing between different neurotransmitters