We report on a physics-based suite of machine-learning algorithms which performs online, real-tim... more We report on a physics-based suite of machine-learning algorithms which performs online, real-time photovoltaic-array incipient hot-spot diagnostics and prognostics, using as input panel-string electrical sensor data. These data consist of module-string currents and voltages and their instantaneous (filtered) rates of change, acquired via a combination of analog and digital sensors. Our diagnostics algorithms comprise thermal and electrical System ID stages, augmented by a Bayesian MAP (Maximum A posteriori Probability) inference engine utilizing a simplified stochastic, spline-based integrated plant model in the optical, electrical and thermal domains. Our (path-integral, physics-based) MAP inference engine detects incipient hot-spots; attributes them to the most likely proximate- and underlying causes (such as shading or dust-deposition patterns, direct heating, inherent mismatches or circuit failures); and renders quantitative estimates of the most likely culpable environmental factor (e.g. a time-varying shading pattern). The same simplified plant model is periodically used to prognosticate the likely future evolution of the incipient hot spot. Our diagnostics and prognostics algorithms can be applied to simulated and/or empirical data (the latter from our roof-top PV lab at Carnegie Mellon). The algorithms leverage changes in estimated conductances in different regions of the electrical state-space, and at different granularities (cells, panels, strings and full array). It take into account temperature coefficients, ohmic- and optical heating, and (optionally) inherent electrical mismatches. Our algorithm suite requires as input neither temperature sensors, nor sub-panel electrical data, nor load sweeps; even pyranometer data is optional. The only necessary sensor data are string electrical data at the actual instantaneous in-operation external load (either with or without a perturb-and-observe MPPT control procedure). Digitized measurements of the low-pass-filtered time derivatives of these currents are useful, but if not available they can be replaced with numerical differentiation. However, occasional voltage sweeps - augmented with pyranometer, thermal and intra-panel (bypass diode voltage) data from our heavily instrumented PV array - along with online astronomical and meteorological data and artificially induced shading patterns - are used to validate our algorithms and to improve the baseline System ID parameters estimation.
The development of advanced signal processing algorithms specifically for Micro/Nano Electro Mech... more The development of advanced signal processing algorithms specifically for Micro/Nano Electro Mechanical Systems (MEMS/NEMS) based sensors has been largely unexplored and can be regarded as the single most important area for improving the performance of these devices. In this paper we present three classes of algorithms that were created to extract weak signals from devices operating in different sensing modalities.
The motion of a physical system acted upon by external torqueless forces causes the relativistic ... more The motion of a physical system acted upon by external torqueless forces causes the relativistic Thomas precession of the system’s spin vector, relative to an inertial frame. A time-dependent force that returns the system to its initial velocity is considered. The precession accumulates to become a finite rotation of the final spin vector, relative to its initial value. This rotation is commonly explained as the Wigner rotation due to the sequence of pure boosts caused by the force. An alternative interpretation is presented here: The rotation is due to the change of the spin vector as it is parallel-transported around the closed trajectory described by the system in hyperbolic three-velocity space. As an application, the angle of precession for a planar motion is shown to be equal to the area enclosed by the trajectory in velocity space.
Properties of the diocotron instability in a relativistic sheet electron beam propagating through... more Properties of the diocotron instability in a relativistic sheet electron beam propagating through a rectangular conducting wall are investigated within the framework of a macroscopic cold fluid model. The electron beam is assumed to be partially neutralized by the positive immobile ions with the fractional charge neutralization f. The eigenvalue equation is obtained for low-frequency perturbations in standing waves. The dispersion relation of the diocotron instability is derived and used to investigate stability properties for a broad range of system parameters including the ratio a/d of the beam thickness (2a) to the conductor gap (2d) and the charge neutralization f. The dispersion relation indicates that the system is stabilized by increasing the neutralization f to 1/γ2b, where γb is the characteristic value of the beam relativistic factor. It is also shown that the diocotron perturbations are completely stabilized by increasing the beam thickness to more than one-half the conductor gap (i.e., a/d≳0.5) for f=0. The growth rate of instability is a substantial fraction of the diocotron frequency if the system is unstable.
We address the problem of choosing an initial state and final measurement that enable maximal ret... more We address the problem of choosing an initial state and final measurement that enable maximal retrodiction of the result of an unknown intermediate spin measurement of a spin-(1/2 particle, along any one of a given set of directions. Details are given of the derivation of the most general possible solution of the problem, which we reported recently. The maximal retrodiction is shown to be the determination of the result of the intermediate spin measurement, along any of four different directions that span three-dimensional space and satisfy a specific linear relation.
We present a family of classical spacetimes in 2 + 1 dimensions. Such a spacetime is produced by ... more We present a family of classical spacetimes in 2 + 1 dimensions. Such a spacetime is produced by a Nambu-Goto self-gravitating string. Due to the special properties of three-dimensional gravity, the metric is completely described as a Minkowski space with two identified worldsheets. In the flat limit, the standard string is recovered. The formalism is developed for an open string with massive endpoints, but applies to other boundary conditions as well. We consider another limit, where the string tension vanishes in geometrical units but the end-masses produce finite deficit angles. In this limit, our open string reduces to the free-masses solution of Gott, which possesses closed timelike curves when the relative motion of the two masses is sufficiently rapid. We discuss the possible causal structures of our spacetimes in other regimes. It is shown that the induced worldsheet Liouville mode obeys (classically) a differential equation, similar to the Liouville equation and reducing to...
A new adiabatic method for improving iterative blocking-truncation approximations in lattice mode... more A new adiabatic method for improving iterative blocking-truncation approximations in lattice models is presented, and applied to a test model. In this approach, the high-frequency (fast) modes are frozen into wave functions that change with the slow modes. (Submitted to Physical Review D) Work supported by the Department of Energy, contract DE-AC03-76SF00515.-2-
Alice strings are cosmic strings that turn matter into antimatter. Although they arise naturally ... more Alice strings are cosmic strings that turn matter into antimatter. Although they arise naturally in many GUT’s, it has long been believed that because of the monopole problem they can have no cosmological effects. We show this conclusion to be false; by using the Langacker-Pi mechanism, monopoles can in fact be annihilated while Alice strings are left intact. This opens up the possibility that they can after all contribute to cosmology, and we mention some particularly important examples.
There exists a class of cosmic strings that turn matter into antimatter (Alice strings). In a GUT... more There exists a class of cosmic strings that turn matter into antimatter (Alice strings). In a GUT where the unbroken gauge group contains charge conjugation (C), such strings form when a phase transition renders C a discrete symmetry. They become boundaries of domain walls at a later, C-breaking transition. These ‘Alice walls ’ are cosmologically harmless, but can play an important role in baryogenesis. We present a three-generation toy model with scalar baryons, where a quasi-static Alice wall (or a gas of such walls) temporarily gives rise to net baryogenesis of uniform sign everywhere in space. This becomes a permanent baryon excess if the wall shrinks away early enough. We comment on the possible relevance of a similar mechanism to baryogenesis in a realistic SO(10) unification model, where Alice walls would form at the scale of left-right symmetry breaking.
We present a family of classical spacetimes in 2+1 dimensions. Such a spacetime is produced by a ... more We present a family of classical spacetimes in 2+1 dimensions. Such a spacetime is produced by a Nambu-Goto self-gravitating string. Due to the special properties of three-dimensional gravity, the metric is completely described as a Minkowski space with two identified worldsheets. In the flat limit, the standard string is recovered. The formalism is developed for an open string with massive endpoints, but applies to other boundary conditions as well. We consider another limit, where the string tension vanishes in geometrical units but the end-masses produce finite deficit angles. In this limit, our open string reduces to the free-masses solution of Gott, which possesses closed timelike curves when the relative motion of the two masses is sufficiently rapid. We discuss the possible causal structures of our spacetimes in other regimes. It is shown that the induced worldsheet Liouville mode obeys ( classically) a differential equation, similar to the Liouville equation and reducing to ...
We report on a physics-based suite of machine-learning algorithms which performs online, real-tim... more We report on a physics-based suite of machine-learning algorithms which performs online, real-time photovoltaic-array incipient hot-spot diagnostics and prognostics, using as input panel-string electrical sensor data. These data consist of module-string currents and voltages and their instantaneous (filtered) rates of change, acquired via a combination of analog and digital sensors. Our diagnostics algorithms comprise thermal and electrical System ID stages, augmented by a Bayesian MAP (Maximum A posteriori Probability) inference engine utilizing a simplified stochastic, spline-based integrated plant model in the optical, electrical and thermal domains. Our (path-integral, physics-based) MAP inference engine detects incipient hot-spots; attributes them to the most likely proximate- and underlying causes (such as shading or dust-deposition patterns, direct heating, inherent mismatches or circuit failures); and renders quantitative estimates of the most likely culpable environmental factor (e.g. a time-varying shading pattern). The same simplified plant model is periodically used to prognosticate the likely future evolution of the incipient hot spot. Our diagnostics and prognostics algorithms can be applied to simulated and/or empirical data (the latter from our roof-top PV lab at Carnegie Mellon). The algorithms leverage changes in estimated conductances in different regions of the electrical state-space, and at different granularities (cells, panels, strings and full array). It take into account temperature coefficients, ohmic- and optical heating, and (optionally) inherent electrical mismatches. Our algorithm suite requires as input neither temperature sensors, nor sub-panel electrical data, nor load sweeps; even pyranometer data is optional. The only necessary sensor data are string electrical data at the actual instantaneous in-operation external load (either with or without a perturb-and-observe MPPT control procedure). Digitized measurements of the low-pass-filtered time derivatives of these currents are useful, but if not available they can be replaced with numerical differentiation. However, occasional voltage sweeps - augmented with pyranometer, thermal and intra-panel (bypass diode voltage) data from our heavily instrumented PV array - along with online astronomical and meteorological data and artificially induced shading patterns - are used to validate our algorithms and to improve the baseline System ID parameters estimation.
The development of advanced signal processing algorithms specifically for Micro/Nano Electro Mech... more The development of advanced signal processing algorithms specifically for Micro/Nano Electro Mechanical Systems (MEMS/NEMS) based sensors has been largely unexplored and can be regarded as the single most important area for improving the performance of these devices. In this paper we present three classes of algorithms that were created to extract weak signals from devices operating in different sensing modalities.
The motion of a physical system acted upon by external torqueless forces causes the relativistic ... more The motion of a physical system acted upon by external torqueless forces causes the relativistic Thomas precession of the system’s spin vector, relative to an inertial frame. A time-dependent force that returns the system to its initial velocity is considered. The precession accumulates to become a finite rotation of the final spin vector, relative to its initial value. This rotation is commonly explained as the Wigner rotation due to the sequence of pure boosts caused by the force. An alternative interpretation is presented here: The rotation is due to the change of the spin vector as it is parallel-transported around the closed trajectory described by the system in hyperbolic three-velocity space. As an application, the angle of precession for a planar motion is shown to be equal to the area enclosed by the trajectory in velocity space.
Properties of the diocotron instability in a relativistic sheet electron beam propagating through... more Properties of the diocotron instability in a relativistic sheet electron beam propagating through a rectangular conducting wall are investigated within the framework of a macroscopic cold fluid model. The electron beam is assumed to be partially neutralized by the positive immobile ions with the fractional charge neutralization f. The eigenvalue equation is obtained for low-frequency perturbations in standing waves. The dispersion relation of the diocotron instability is derived and used to investigate stability properties for a broad range of system parameters including the ratio a/d of the beam thickness (2a) to the conductor gap (2d) and the charge neutralization f. The dispersion relation indicates that the system is stabilized by increasing the neutralization f to 1/γ2b, where γb is the characteristic value of the beam relativistic factor. It is also shown that the diocotron perturbations are completely stabilized by increasing the beam thickness to more than one-half the conductor gap (i.e., a/d≳0.5) for f=0. The growth rate of instability is a substantial fraction of the diocotron frequency if the system is unstable.
We address the problem of choosing an initial state and final measurement that enable maximal ret... more We address the problem of choosing an initial state and final measurement that enable maximal retrodiction of the result of an unknown intermediate spin measurement of a spin-(1/2 particle, along any one of a given set of directions. Details are given of the derivation of the most general possible solution of the problem, which we reported recently. The maximal retrodiction is shown to be the determination of the result of the intermediate spin measurement, along any of four different directions that span three-dimensional space and satisfy a specific linear relation.
We present a family of classical spacetimes in 2 + 1 dimensions. Such a spacetime is produced by ... more We present a family of classical spacetimes in 2 + 1 dimensions. Such a spacetime is produced by a Nambu-Goto self-gravitating string. Due to the special properties of three-dimensional gravity, the metric is completely described as a Minkowski space with two identified worldsheets. In the flat limit, the standard string is recovered. The formalism is developed for an open string with massive endpoints, but applies to other boundary conditions as well. We consider another limit, where the string tension vanishes in geometrical units but the end-masses produce finite deficit angles. In this limit, our open string reduces to the free-masses solution of Gott, which possesses closed timelike curves when the relative motion of the two masses is sufficiently rapid. We discuss the possible causal structures of our spacetimes in other regimes. It is shown that the induced worldsheet Liouville mode obeys (classically) a differential equation, similar to the Liouville equation and reducing to...
A new adiabatic method for improving iterative blocking-truncation approximations in lattice mode... more A new adiabatic method for improving iterative blocking-truncation approximations in lattice models is presented, and applied to a test model. In this approach, the high-frequency (fast) modes are frozen into wave functions that change with the slow modes. (Submitted to Physical Review D) Work supported by the Department of Energy, contract DE-AC03-76SF00515.-2-
Alice strings are cosmic strings that turn matter into antimatter. Although they arise naturally ... more Alice strings are cosmic strings that turn matter into antimatter. Although they arise naturally in many GUT’s, it has long been believed that because of the monopole problem they can have no cosmological effects. We show this conclusion to be false; by using the Langacker-Pi mechanism, monopoles can in fact be annihilated while Alice strings are left intact. This opens up the possibility that they can after all contribute to cosmology, and we mention some particularly important examples.
There exists a class of cosmic strings that turn matter into antimatter (Alice strings). In a GUT... more There exists a class of cosmic strings that turn matter into antimatter (Alice strings). In a GUT where the unbroken gauge group contains charge conjugation (C), such strings form when a phase transition renders C a discrete symmetry. They become boundaries of domain walls at a later, C-breaking transition. These ‘Alice walls ’ are cosmologically harmless, but can play an important role in baryogenesis. We present a three-generation toy model with scalar baryons, where a quasi-static Alice wall (or a gas of such walls) temporarily gives rise to net baryogenesis of uniform sign everywhere in space. This becomes a permanent baryon excess if the wall shrinks away early enough. We comment on the possible relevance of a similar mechanism to baryogenesis in a realistic SO(10) unification model, where Alice walls would form at the scale of left-right symmetry breaking.
We present a family of classical spacetimes in 2+1 dimensions. Such a spacetime is produced by a ... more We present a family of classical spacetimes in 2+1 dimensions. Such a spacetime is produced by a Nambu-Goto self-gravitating string. Due to the special properties of three-dimensional gravity, the metric is completely described as a Minkowski space with two identified worldsheets. In the flat limit, the standard string is recovered. The formalism is developed for an open string with massive endpoints, but applies to other boundary conditions as well. We consider another limit, where the string tension vanishes in geometrical units but the end-masses produce finite deficit angles. In this limit, our open string reduces to the free-masses solution of Gott, which possesses closed timelike curves when the relative motion of the two masses is sufficiently rapid. We discuss the possible causal structures of our spacetimes in other regimes. It is shown that the induced worldsheet Liouville mode obeys ( classically) a differential equation, similar to the Liouville equation and reducing to ...
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Papers by Shahar Ben-Menahem