Improving stability margins in discrete-time LQG controllers

Some of the problems are discussed which are encountered in the design of discrete-time stochastic controllers for problems that may adequately be described by the Linear Quadratic Gaussian (LQG) assumptions; namely, the problems of obtaining acceptable relative stability, robustness, and disturbance rejection properties. A dynamic compensator is proposed to replace the optimal full state feedback regulator gains at steady state, provided that all states are measurable. The compensator increases the stability margins at the plant input, which may possibly be inadequate in practical applications. Though the optimal regulator has desirable properties the observer based controller as implemented with a Kalman filter, in a noisy environment, has inadequate stability margins. The proposed compensator is designed to match the return difference matrix at the plant input to that of the optimal regulator while maintaining the optimality of the state estimates as directed by the measurement noise characteristics

Absence of Luttinger's Theorem due to Zeros in the Single-Particle Green Function

We show exactly with an SU(N) interacting model that even if the ambiguity associated with the placement of the chemical potential, $\mu$, for a T=0 gapped system is removed by using the unique value $\mu(T\rightarrow 0)$, Luttinger's sum rule is violated even if the ground-state degeneracy is lifted by an infinitesimal hopping. The failure stems from the non-existence of the Luttinger-Ward functional for a system in which the self-energy diverges. Since it is the existence of the Luttinger-Ward functional that is the basis for Luttinger's theorem which relates the charge density to sign changes of the single-particle Green function, no such theorem exists. Experimental data on the cuprates are presented which show a systematic deviation from the Luttinger count, implying a breakdown of the electron quasiparticle picture in strongly correlated electron matter.Comment: Published version with supplemental material rebutting the recent criticism that our theorem fails if the ground-state degeneracy is lifte

Imaging the phase of an evolving Bose-Einstein condensate wavefunction

We demonstrate a spatially resolved autocorrelation measurement with a Bose-Einstein condensate (BEC) and measure the evolution of the spatial profile of its quantum mechanical phase. Upon release of the BEC from the magnetic trap, its phase develops a form that we measure to be quadratic in the spatial coordinate. Our experiments also reveal the effects of the repulsive interaction between two overlapping BEC wavepackets and we measure the small momentum they impart to each other

Phase fluctuations in anisotropic Bose condensates: from cigars to rings

We study the phase-fluctuating condensate regime of ultra-cold atoms trapped in a ring-shaped trap geometry, which has been realized in recent experiments. We first consider a simplified box geometry, in which we identify the conditions to create a state that is dominated by thermal phase-fluctuations, and then explore the experimental ring geometry. In both cases we demonstrate that the requirement for strong phase fluctuations can be expressed in terms of the total number of atoms and the geometric length scales of the trap only. For the ring-shaped trap we discuss the zero temperature limit in which a condensate is realized where the phase is fluctuating due to interactions and quantum fluctuations. We also address possible ways of detecting the phase fluctuating regime in ring condensates.Comment: 10 pages, 5 figures, minor edit

Gravitational wave detectors based on matter wave interferometers (MIGO) are no better than laser interferometers (LIGO)

We show that a recent claim that matter wave interferometers have a much higher sensitivity than laser interferometers for a comparable physical setup is unfounded. We point out where the mistake in the earlier analysis is made. We also disprove the claim that only a description based on the geodesic deviation equation can produce the correct physical result. The equations for the quantum dynamics of non-relativistic massive particles in a linearly perturbed spacetime derived here are useful for treating a wider class of related physical problems. A general discussion on the use of atom interferometers for the detection of gravitational waves is also provided.Comment: 16 pages, REVTeX4; minor changes, one figure and a few references were added, an additional appendix was included where we explain why, contrary to the claims in gr-qc/0409099, the effects due to the reflection off the mirrors cancel out in the final result for the phase shif

FIMO: scanning for occurrences of a given motif

Summary: A motif is a short DNA or protein sequence that contributes to the biological function of the sequence in which it resides. Over the past several decades, many computational methods have been described for identifying, characterizing and searching with sequence motifs. Critical to nearly any motif-based sequence analysis pipeline is the ability to scan a sequence database for occurrences of a given motif described by a position-specific frequency matrix

Cortical cells are altered by factors including bone morphogenetic protein released from a placental barrier model under altered oxygenation

Episodes of hypoxia and hypoxia/reoxygenation during foetal development have been associated with increased risk of neurodevelopmental conditions presenting in later life. The mechanism for this is not understood; however, several authors have suggested that the placenta plays an important role. Previously we found both placentas from a maternal hypoxia model and pre-eclamptic placentas from patients release factors lead to a loss of dendrite complexity in rodent neurons. Here to further explore the nature and origin of these secretions we exposed a simple in vitro model of the placental barrier, consisting of a barrier of human cytotrophoblasts, to hypoxia or hypoxia/reoxygenation. We then exposed cortical cultures from embryonic rat brains to the conditioned media (CM) from below these exposed barriers and examined changes in cell morphology, number, and receptor presentation. The barriers released factors that reduced dendrite and astrocyte process lengths, decreased GABAB1 staining, and increased astrocyte number. The changes in astrocytes required the presence of neurons and were prevented by inhibition of the SMAD pathway and by neutralising Bone Morphogenetic Proteins (BMPs) 2/4. Barriers exposed to hypoxia/reoxygenation also released factors that reduced dendrite lengths but increased GABAB1 staining. Both oxygen changes caused barriers to release factors that decreased GluN1, GABAAα1 staining and increased GluN3a staining. We find that hypoxia in particular will elicit the release of factors that increase astrocyte number and decrease process length as well as causing changes in the intensity of glutamate and GABA receptor staining. There is some evidence that BMPs are released and contribute to these changes

Crystalline Silicate Emission in the Protostellar Binary Serpens--SVS20

We present spatially resolved mid-infrared spectroscopy of the class I/flat-spectrum protostellar binary system SVS20 in the Serpens cloud core. The spectra were obtained with the mid-infrared instrument T-ReCS on Gemini-South. SVS20-South, the more luminous of the two sources, exhibits a mid-infrared emission spectrum peaking near 11.3 \micron, while SVS20-North exhibits a shallow amorphous silicate absorption spectrum with a peak optical depth of $\tau \sim 0.3$. After removal of the the line-of-sight extinction by the molecular common envelope, the ``protostar-only'' spectra are found to be dominated by strong amorphous olivine emission peaking near 10 \micron. We also find evidence for emission from crystalline forsterite and enstatite associated with both SVS20-S and SVS20-N. The presence of crystalline silicate in such a young binary system indicates that the grain processing found in more evolved HAeBe and T Tauri pre-main sequence stars likely begins at a relatively young evolutionary stage, while mass accretion is still ongoing.Comment: Accepted for publication by The Astrophysical Journa

Economic development, human development, and the pursuit of happiness, April 1, 2, and 3, 2004

This repository item contains a single issue of the Pardee Conference Series, a publication series that began publishing in 2006 by the Boston University Frederick S. Pardee Center for the Study of the Longer-Range Future. This was the Center's spring conference, which took place during April 1, 2, and 3, 2004.The conference asks the questions, how can we make sure that the benefits of economic growth flow into health, education, welfare, and other aspects of human development; and what is the relationship between human development and economic development? Speakers and participants discuss the role that culture, legal and political institutions, the UN Developmental Goals, the level of decision-making, and ethics, play in development

High healthcare utilization near the onset of medically unexplained symptoms

Objective: Patients with medically unexplained syndromes (MUS) often do not receive appropriate healthcare. A critical time for effective healthcare is the inception of MUS. The current study examined data from a prospective longitudinal study of Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) soldiers to understand the relationship of increasing physical symptom burden to healthcare utilization. Methods: Data was examined from a prospective study of OEF/OIF soldiers assessed before and one year after deployment (n = 336). Physical symptom burden was measured with the Patient Health Questionnaire (PHQ-15). Analyses were conducted with polynomial regression and response surface analysis (RSA). Results: Increases in physical symptom burden predicted greater healthcare utilization one year after deployment: primary care practitioner (slope = − 0.26, F = 4.07, p = 0.04), specialist (slope = − 0.43, F = 8.67, p = 0.003), allied health therapy (e.g., physical therapy) (slope = − 0.41, F = 5.71, p = 0.02) and mental health (slope = − 0.32, F = 4.04, p = 0.05). There were no significant difference in utilization between those with consistently high levels and those with increases in physical symptom burden. Conclusion: This is the first prospective study to examine, and show, a relationship between onset of clinically significant physical symptoms and greater healthcare utilization. Our data suggest that patients with increasing physical symptom burden have the same level of healthcare as patients with chronic physical symptom burden. Needed next steps are to better understand the quality of care at inception and determine how to intervene so that recommended approaches to care are provided from the onset