Satellite power system: Concept development and evaluation program. Volume 3: Power transmission and reception. Technical summary and assessment

Efforts in the DOE/NASA concept development and evaluation program are discussed for the solar power satellite power transmission and reception system. A technical summary is provided together with a summary of system assessment activities. System options and system definition drivers are described. Major system assessment activities were in support of the reference system definition, solid state system studies, critical technology supporting investigations, and various system and subsystem tradeoffs. These activities are described together with reference system updates and alternative concepts for each of the subsystem areas. Conclusions reached as a result of the numerous analytical and experimental evaluations are presented. Remaining issues for a possible follow-on program are identified

Excitation of Small Quantum Systems by High-Frequency Fields

The excitation by a high frequency field of multi--level quantum systems with a slowly varying density of states is investigated. A general approach to study such systems is presented. The Floquet eigenstates are characterized on several energy scales. On a small scale, sharp universal quasi--resonances are found, whose shape is independent of the field parameters and the details of the system. On a larger scale an effective tight--binding equation is constructed for the amplitudes of these quasi--resonances. This equation is non--universal; two classes of examples are discussed in detail.Comment: 4 pages, revtex, no figure

Plant roots steer resilience to perturbation of river floodplains

Freshwater ecosystems along river floodplains host among the greatest biodiversity on Earth and are known to respond to anthropic pressure. For water impounded systems, resilience to changes in the natural flow regime is believed to be bi-directional. Whether such resilience prevents the system from returning to pristine conditions after the flow regime changes reverse is as yet unclear, though widely documented. In this work we show that temporal irreversibility of river floodplains to recover their status may be explained by the dynamics of riparian water-tolerant plant roots. Our model is a quantitative tool that will benefit scientists and practitioners in predicting the impact of changing flow regimes on long-term river floodplain dynamics

Diffusive Ionization of Relativistic Hydrogen-Like Atom

Stochastic ionization of highly excited relativistic hydrogenlike atom in the monochromatic field is investigated. A theoretical analisis of chaotic dynamics of the relativistic electron based on Chirikov criterion is given for the cases of one- and three-dimensional atoms. Critical value of the external field is evaluated analitically. The diffusion coefficient and ionization time are calculated.Comment: 13 pages, latex, no figures, submitted to PR

Reducing multiphoton ionization in a linearly polarized microwave field by local control

We present a control procedure to reduce the stochastic ionization of hydrogen atom in a strong microwave field by adding to the original Hamiltonian a comparatively small control term which might consist of an additional set of microwave fields. This modification restores select invariant tori in the dynamics and prevents ionization. We demonstrate the procedure on the one-dimensional model of microwave ionization.Comment: 8 page

Folding, Design and Determination of Interaction Potentials Using Off-Lattice Dynamics of Model Heteropolymers

We present the results of a self-consistent, unified molecular dynamics study of simple model heteropolymers in the continuum with emphasis on folding, sequence design and the determination of the interaction parameters of the effective potential between the amino acids from the knowledge of the native states of the designed sequences.Comment: 8 pages, 3 Postscript figures, uses RevTeX. Submitted to Physical Review Letter

Frailty in perioperative patients in three South African academic hospitals

Background. Frailty is a state characterised by diminished physiological reserve that leaves an individual vulnerable to external stressors and delays recovery. Frailty assessments are proving to be more valuable in predicting poor perioperative outcomes than other well-known perioperative risk assessment tools. Very few studies using validated frailty assessment tools have been done to assess the prevalence of frailty in South Africa (SA), and none have assessed the intraoperative implications of frailty in a surgical population.Objectives. To determine the demographics and frailty levels of patients presenting for surgery at three academic hospitals in Johannesburg, compare intraoperative complications between the frail and non-frail patients, and compare the association between frailty scores and American Society of Anesthesiologists Physical Status (ASA-PS) scores.Methods. We prospectively enrolled 299 patients aged 18 - 90 years undergoing various types of elective surgery between mid-November 2016 and mid-March 2017 in three SA academic hospitals. Frailty was assessed using the nine-point Clinical Frailty Scale (CFS) and defined as a score of ≥5. The CFS and demographic and clinical data were documented by the anaesthetists assigned to the respective elective lists. The primary outcome measure was intraoperative complications (hypotension, desaturation, and need for vasopressors and blood transfusion). We also compared associations between the patients’ comorbidities and frailty and those between the CFS and ASA-PS scores.Results. Of a total of 299 patients included in the study (mean age (standard deviation) 50.6 (15.8) years), 156 (52%) were women and 67 (22%) were classified as frail. Compared with patients who were not classified as frail, the frail group had significantly higher incidences of hypotension (odds ratio (OR) 1.87, 95% confidence interval (CI) 1.083 - 3.259; p=0.02) and desaturation (OR 3.79, 95% CI 1.367 - 10.54; p=0.01), and were more likely to need vasopressors (OR 2.81, 95% CI 1.607 - 4.912; p=0.00) and blood transfusion (OR 3.26, 95% CI 1.138 - 9.368; p=0.02). On multivariable logistic regression analysis, adjusting for factors related to frailty such as age, gender and comorbidities, desaturation was significantly associated with frailty (adjusted OR (aOR) 4.21, 95% CI 1.31 - 13.53; p=0.01), and the frail were more likely to require blood transfusion (aOR 5.36, 95% CI 1.50 - 19.16; p=0.01) and were older and had more comorbidities. Higher ASA-PS scores were also strongly associated with frailty.Conclusions. The prevalence of frailty was high among surgical patients. Consistent with other studies, frailty was associated with older age and multiple comorbidities. The association between frailty and intraoperative complications found in this study may indicate and help inform areas of further research

Role of Secondary Motifs in Fast Folding Polymers: A Dynamical Variational Principle

A fascinating and open question challenging biochemistry, physics and even geometry is the presence of highly regular motifs such as alpha-helices in the folded state of biopolymers and proteins. Stimulating explanations ranging from chemical propensity to simple geometrical reasoning have been invoked to rationalize the existence of such secondary structures. We formulate a dynamical variational principle for selection in conformation space based on the requirement that the backbone of the native state of biologically viable polymers be rapidly accessible from the denatured state. The variational principle is shown to result in the emergence of helical order in compact structures.Comment: 4 pages, RevTex, 4 eps figure

The Dynamics of a Meandering River

We present a statistical model of a meandering river on an alluvial plane which is motivated by the physical non-linear dynamics of the river channel migration and by describing heterogeneity of the terrain by noise. We study the dynamics analytically and numerically. The motion of the river channel is unstable and we show that by inclusion of the formation of ox-bow lakes, the system may be stabilised. We then calculate the steady state and show that it is in agreement with simulations and measurements of field data.Comment: Revtex, 12 pages, 2 postscript figure