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Papers by Robert Sims

Conference Record of the 2004 IEEE Industry Applications Conference, 2004. 39th IAS Annual Meeting., 2000

An electrodynamic screen was designed, built, and tested for the removal of particles from its su... more An electrodynamic screen was designed, built, and tested for the removal of particles from its surface. The technology has a large number of applications ranging from space exploration to biotechnology. An AC signal was applied to the shield and it was studied the effect of its amplitude, shape, and frequency to the shield's particle removal properties. The best working conditions

The Sherrington-Kirkpatrick spin glass model has been studied as a source of insight into the sta... more The Sherrington-Kirkpatrick spin glass model has been studied as a source of insight into the statistical mechanics of systems with highly diversified collections of competing low energy states. The goal of this summary is to present some of the ideas which have emerged in the mathematical study of its free energy. In particular, we highlight the perspective of the cavity dynamics, and the related variational principle. These are expressed in terms of Random Overlap Structures (ROSt), which are used to describe the possible states of the reservoir in the cavity step. The Parisi solution is presented as reflecting the ansatz that it suffices to restrict the variation to hierarchal structures which are discussed here in some detail. While the Parisi solution was proven to be correct, through recent works of F. Guerra and M. Talagrand, the reasons for the effectiveness of the Parisi ansatz still remain to be elucidated. We question whether this could be related to the quasi-stationarity of the special subclass of ROSts given by Ruelle's hierarchal `random probability cascades' (also known as GREM).

Probab Theory Relat Field, 2006

The subject of this work are random Schroedinger operators on regular rooted tree graphs T\TT wit... more The subject of this work are random Schroedinger operators on regular rooted tree graphs T\TT with stochastically homogeneous disorder. The operators are of the form Hlambda(omega)=T+U+lambdaV(omega)H_\lambda(\omega) = T + U + \lambda V(\omega)Hlambda(omega)=T+U+lambdaV(omega) acting in ell2(T)\ell^2(\T)ell2(T), with TT T the adjacency matrix, UUU a radially periodic potential, and V(omega)V(\omega)V(omega) a random potential. This includes the only class of homogeneously random operators for which it was proven that the spectrum of Hlambda(omega)H_\lambda(\omega)Hlambda(omega) exhibits an absolutely continuous (ac) component; a results established by A. Klein for weak disorder, in case U=0 and V(omega)V(\omega)V(omega) given by iid random variables on T\TT. Our main contribution is a new method for establishing the persistence of ac spectrum under weak disorder. The method yields the continuity in the disorder parameter of the ac spectral density of Hlambda(omega)H_\lambda(\omega)Hlambda(omega) at lambda=0\lambda = 0lambda=0. The latter is shown to converge in the L1L^1L1 sense over closed intervals in which H_0H_0H_0 has no singular spectrum. The analysis extends to random potentials whose values at different sites need not be independent, assuming only that their joint distribution is weakly correlated across different tree branches.

Some recent developments in the theory of quantum spin systems are reviewed.

The simulation ofphysical parameters provides a virtual environment for the design and optimizati... more The simulation ofphysical parameters provides a virtual environment for the design and optimization ofinstrumentation. pplyingphysical laws and theorems to natural phenomena defines the behavior ofanalytical processes. Simulation provides means for the adjustment of specific ...

Eprint Arxiv 0712 2323, Dec 1, 2007

We consider standard subordinacy theory for general Sturm--Liouville operators and give criteria ... more We consider standard subordinacy theory for general Sturm--Liouville operators and give criteria when boundedness of solutions implies that no subordinate solutions exist. As applications, we prove a Weidmann-type result for general Sturm--Liouville operators and investigate the absolutely continuous spectrum of radially symmetric quantum trees.

We study one-dimensional, continuum Bernoulli-Anderson models with general single-site potentials... more We study one-dimensional, continuum Bernoulli-Anderson models with general single-site potentials and prove positivity of the Lyapunov exponent away from a discrete set of critical energies. The proof is based on F\"urstenberg's Theorem. The set of critical energies is described explicitly in terms of the transmission and reflection coefficients for scattering at the single-site potential. In examples we discuss the asymptotic behavior of generalized eigenfunctions at critical energies.

The methods used to prove the main result must be incorrect, as they can be used to arrive at a c... more The methods used to prove the main result must be incorrect, as they can be used to arrive at a contradiction with previously known results. Thus the paper was withdrawn.

We summarize recent works on the stability under disorder of the absolutely continuous spectra of... more We summarize recent works on the stability under disorder of the absolutely continuous spectra of random operators on tree graphs. The cases covered include: Schr\"odinger operators with random potential, quantum graph operators for trees with randomized edge lengths, and radial quasi-periodic operators perturbed by random potentials.

Contemporary Mathematics, 2006

We summarize recent works on the stability under disorder of the absolutely continuous spectra of... more We summarize recent works on the stability under disorder of the absolutely continuous spectra of random operators on tree graphs. The cases covered include: Schrödinger operators with random potential, quantum graph operators for trees with randomized edge lengths, and radial quasi-periodic operators perturbed by random potentials.

Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344), 2002

In order to find the conditions that would provide the best Faraday cage penetration, two powders... more In order to find the conditions that would provide the best Faraday cage penetration, two powders (acrylic and epoxy) corona and tribo charged, were sprayed inside aluminum panels bent at varying angles (15, 30, 45, 60, and 90 degrees) in the direction of flow. The electrical field lines were simulated using Lorentz 2D software and the electrical field intensities generated

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009

... Robert A. Sims1, Zachary Roth2, Timothy McComb1, Lawrence Shah1, Vikas Sudesh1, Poutous Menel... more ... Robert A. Sims1, Zachary Roth2, Timothy McComb1, Lawrence Shah1, Vikas Sudesh1, Poutous Menelaos2, Eric Johnson2, Martin C. Richardson1 1.Townes ... elements which stabilize and spectrally narrow the output are desired for methods of scaling to higher powers, such as ...

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009

Abstract A system for multi-kilometer atmospheric propagation experiments including a master osci... more Abstract A system for multi-kilometer atmospheric propagation experiments including a master oscillator with~ 108 nm tunability and a power amplifier tested as an oscillator with~ 58% slope efficiency and stable 200 W output power is discussed.

Laser Technology for Defense and Security V, 2009

We have designed and developed a grating based thulium (Tm) doped fiber laser with ~150 nm tuning... more We have designed and developed a grating based thulium (Tm) doped fiber laser with ~150 nm tuning range which is used as the master oscillator in a master oscillator power amplifier (MOPA) thulium fiber laser system. Due to thermal instability in the grating used for tuning, the MO could produce a power up to 4.5 W, beyond which the oscillator

Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344), 2002

The corrosion resistance of electrostatic powder coatings depends upon obtaining a smooth, nonpor... more The corrosion resistance of electrostatic powder coatings depends upon obtaining a smooth, nonporous film deposited uniformly over the surface of the entire substrate. The film must be free of voids, pinholes, and other surface defects. Two common defects on powder coated film arise from: (1) Faraday Cage effect causing uneven film thickness of recessed surface and (2) back corona that

Advanced Solid-State Photonics, 2009

ABSTRACT Single-mode laser action, up to 4-times the threshold power, in a diode-pumped Nd-doped ... more ABSTRACT Single-mode laser action, up to 4-times the threshold power, in a diode-pumped Nd-doped phosphate glass fiber having a 300-μm core is demonstrated. Subtle differences associated with the effectiveness of diode-pumping gain-guided, index-antiguided fibers are discussed.

Solid State Lasers XVIII: Technology and Devices, 2009

Eye-safe, high power tunable narrow linewidth lasers are important for various applications such ... more Eye-safe, high power tunable narrow linewidth lasers are important for various applications such as atmospheric propagation measurements. We have investigated two techniques of generating narrow linewidth thulium 2-μm fiber lasers, utilizing a reflective volume Bragg grating (VBG), and a guided mode resonance filter (GMRF) as a cavity end mirror. A stable narrow linewidth (50 pm), tunable (from 2004 nm to 2054 nm) thulium doped fiber laser using a reflective VBGg was demonstrated. A CW power of 17 W was achieved. Using a GMRF as an end mirror we showed a narrow linewidth (~30 pm) laser with an output power of 5.8W, and at a slope efficiency of 44%.

There are strong indications that dust is of great importance on Mars. Dust appears to have both ... more There are strong indications that dust is of great importance on Mars. Dust appears to have both long-term effects on the surface geologic evo- lution as well as on the aeolian processes in the present climate conditions. Early spacecraft missions (1) confirmed hypotheses from telescopic work that changes observed in the planet's surface markings are caused by wind-driven redistribu- tion

Conference Record of the 2004 IEEE Industry Applications Conference, 2004. 39th IAS Annual Meeting., 2000

An electrodynamic screen was designed, built, and tested for the removal of particles from its su... more An electrodynamic screen was designed, built, and tested for the removal of particles from its surface. The technology has a large number of applications ranging from space exploration to biotechnology. An AC signal was applied to the shield and it was studied the effect of its amplitude, shape, and frequency to the shield's particle removal properties. The best working conditions

The Sherrington-Kirkpatrick spin glass model has been studied as a source of insight into the sta... more The Sherrington-Kirkpatrick spin glass model has been studied as a source of insight into the statistical mechanics of systems with highly diversified collections of competing low energy states. The goal of this summary is to present some of the ideas which have emerged in the mathematical study of its free energy. In particular, we highlight the perspective of the cavity dynamics, and the related variational principle. These are expressed in terms of Random Overlap Structures (ROSt), which are used to describe the possible states of the reservoir in the cavity step. The Parisi solution is presented as reflecting the ansatz that it suffices to restrict the variation to hierarchal structures which are discussed here in some detail. While the Parisi solution was proven to be correct, through recent works of F. Guerra and M. Talagrand, the reasons for the effectiveness of the Parisi ansatz still remain to be elucidated. We question whether this could be related to the quasi-stationarity of the special subclass of ROSts given by Ruelle's hierarchal `random probability cascades' (also known as GREM).

Probab Theory Relat Field, 2006

The subject of this work are random Schroedinger operators on regular rooted tree graphs T\TT wit... more The subject of this work are random Schroedinger operators on regular rooted tree graphs T\TT with stochastically homogeneous disorder. The operators are of the form Hlambda(omega)=T+U+lambdaV(omega)H_\lambda(\omega) = T + U + \lambda V(\omega)Hlambda(omega)=T+U+lambdaV(omega) acting in ell2(T)\ell^2(\T)ell2(T), with TT T the adjacency matrix, UUU a radially periodic potential, and V(omega)V(\omega)V(omega) a random potential. This includes the only class of homogeneously random operators for which it was proven that the spectrum of Hlambda(omega)H_\lambda(\omega)Hlambda(omega) exhibits an absolutely continuous (ac) component; a results established by A. Klein for weak disorder, in case U=0 and V(omega)V(\omega)V(omega) given by iid random variables on T\TT. Our main contribution is a new method for establishing the persistence of ac spectrum under weak disorder. The method yields the continuity in the disorder parameter of the ac spectral density of Hlambda(omega)H_\lambda(\omega)Hlambda(omega) at lambda=0\lambda = 0lambda=0. The latter is shown to converge in the L1L^1L1 sense over closed intervals in which H_0H_0H_0 has no singular spectrum. The analysis extends to random potentials whose values at different sites need not be independent, assuming only that their joint distribution is weakly correlated across different tree branches.

Some recent developments in the theory of quantum spin systems are reviewed.

The simulation ofphysical parameters provides a virtual environment for the design and optimizati... more The simulation ofphysical parameters provides a virtual environment for the design and optimization ofinstrumentation. pplyingphysical laws and theorems to natural phenomena defines the behavior ofanalytical processes. Simulation provides means for the adjustment of specific ...

Eprint Arxiv 0712 2323, Dec 1, 2007

We consider standard subordinacy theory for general Sturm--Liouville operators and give criteria ... more We consider standard subordinacy theory for general Sturm--Liouville operators and give criteria when boundedness of solutions implies that no subordinate solutions exist. As applications, we prove a Weidmann-type result for general Sturm--Liouville operators and investigate the absolutely continuous spectrum of radially symmetric quantum trees.

We study one-dimensional, continuum Bernoulli-Anderson models with general single-site potentials... more We study one-dimensional, continuum Bernoulli-Anderson models with general single-site potentials and prove positivity of the Lyapunov exponent away from a discrete set of critical energies. The proof is based on F\"urstenberg's Theorem. The set of critical energies is described explicitly in terms of the transmission and reflection coefficients for scattering at the single-site potential. In examples we discuss the asymptotic behavior of generalized eigenfunctions at critical energies.

The methods used to prove the main result must be incorrect, as they can be used to arrive at a c... more The methods used to prove the main result must be incorrect, as they can be used to arrive at a contradiction with previously known results. Thus the paper was withdrawn.

We summarize recent works on the stability under disorder of the absolutely continuous spectra of... more We summarize recent works on the stability under disorder of the absolutely continuous spectra of random operators on tree graphs. The cases covered include: Schr\"odinger operators with random potential, quantum graph operators for trees with randomized edge lengths, and radial quasi-periodic operators perturbed by random potentials.

Contemporary Mathematics, 2006

We summarize recent works on the stability under disorder of the absolutely continuous spectra of... more We summarize recent works on the stability under disorder of the absolutely continuous spectra of random operators on tree graphs. The cases covered include: Schrödinger operators with random potential, quantum graph operators for trees with randomized edge lengths, and radial quasi-periodic operators perturbed by random potentials.

Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344), 2002

In order to find the conditions that would provide the best Faraday cage penetration, two powders... more In order to find the conditions that would provide the best Faraday cage penetration, two powders (acrylic and epoxy) corona and tribo charged, were sprayed inside aluminum panels bent at varying angles (15, 30, 45, 60, and 90 degrees) in the direction of flow. The electrical field lines were simulated using Lorentz 2D software and the electrical field intensities generated

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009

... Robert A. Sims1, Zachary Roth2, Timothy McComb1, Lawrence Shah1, Vikas Sudesh1, Poutous Menel... more ... Robert A. Sims1, Zachary Roth2, Timothy McComb1, Lawrence Shah1, Vikas Sudesh1, Poutous Menelaos2, Eric Johnson2, Martin C. Richardson1 1.Townes ... elements which stabilize and spectrally narrow the output are desired for methods of scaling to higher powers, such as ...

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009

Abstract A system for multi-kilometer atmospheric propagation experiments including a master osci... more Abstract A system for multi-kilometer atmospheric propagation experiments including a master oscillator with~ 108 nm tunability and a power amplifier tested as an oscillator with~ 58% slope efficiency and stable 200 W output power is discussed.

Laser Technology for Defense and Security V, 2009

We have designed and developed a grating based thulium (Tm) doped fiber laser with ~150 nm tuning... more We have designed and developed a grating based thulium (Tm) doped fiber laser with ~150 nm tuning range which is used as the master oscillator in a master oscillator power amplifier (MOPA) thulium fiber laser system. Due to thermal instability in the grating used for tuning, the MO could produce a power up to 4.5 W, beyond which the oscillator

Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344), 2002

The corrosion resistance of electrostatic powder coatings depends upon obtaining a smooth, nonpor... more The corrosion resistance of electrostatic powder coatings depends upon obtaining a smooth, nonporous film deposited uniformly over the surface of the entire substrate. The film must be free of voids, pinholes, and other surface defects. Two common defects on powder coated film arise from: (1) Faraday Cage effect causing uneven film thickness of recessed surface and (2) back corona that

Advanced Solid-State Photonics, 2009

ABSTRACT Single-mode laser action, up to 4-times the threshold power, in a diode-pumped Nd-doped ... more ABSTRACT Single-mode laser action, up to 4-times the threshold power, in a diode-pumped Nd-doped phosphate glass fiber having a 300-μm core is demonstrated. Subtle differences associated with the effectiveness of diode-pumping gain-guided, index-antiguided fibers are discussed.

Solid State Lasers XVIII: Technology and Devices, 2009

Eye-safe, high power tunable narrow linewidth lasers are important for various applications such ... more Eye-safe, high power tunable narrow linewidth lasers are important for various applications such as atmospheric propagation measurements. We have investigated two techniques of generating narrow linewidth thulium 2-μm fiber lasers, utilizing a reflective volume Bragg grating (VBG), and a guided mode resonance filter (GMRF) as a cavity end mirror. A stable narrow linewidth (50 pm), tunable (from 2004 nm to 2054 nm) thulium doped fiber laser using a reflective VBGg was demonstrated. A CW power of 17 W was achieved. Using a GMRF as an end mirror we showed a narrow linewidth (~30 pm) laser with an output power of 5.8W, and at a slope efficiency of 44%.

There are strong indications that dust is of great importance on Mars. Dust appears to have both ... more There are strong indications that dust is of great importance on Mars. Dust appears to have both long-term effects on the surface geologic evo- lution as well as on the aeolian processes in the present climate conditions. Early spacecraft missions (1) confirmed hypotheses from telescopic work that changes observed in the planet's surface markings are caused by wind-driven redistribu- tion