Analytical approach to quantile estimation in regional frequency analysis based on fuzzy framework

Regional frequency analysis is widely used for estimating quantiles of hydrological extreme events at sparsely gauged/ungauged target sites in river basins. It involves identification of a region (group of watersheds) resembling watershed of the target site, and use of information pooled from the region to estimate quantile for the target site. In the analysis, watershed of the target site is assumed to completely resemble watersheds in the identified region in terms of mechanism underlying generation of extreme event. In reality, it is rare to find watersheds that completely resemble each other. Fuzzy clustering approach can account for partial resemblance of watersheds and yield region(s) for the target site. Formation of regions and quantile estimation requires discerning information from fuzzy-membership matrix obtained based on the approach. Practitioners often defuzzify the matrix to form disjoint clusters (regions) and use them as the basis for quantile estimation. The defuzzification approach (DFA) results in loss of information discerned on partial resemblance of watersheds. The lost information cannot be utilized in quantile estimation, owing to which the estimates could have significant error. To avert the loss of information, a threshold strategy (TS) was considered in some prior studies. In this study, it is analytically shown that the strategy results in under-prediction of quantiles. To address this, a mathematical approach is proposed in this study and its effectiveness in estimating flood quantiles relative to DFA and TS is demonstrated through Monte-Carlo simulation experiments and case study on Mid-Atlantic water resources region, USA. (C) 2015 Elsevier B.V. All rights reserved.

Decreasing intensity of monsoon low-frequency intraseasonal variability over India

Understanding the changing nature of the intraseasonal oscillatory (ISO) modes of Indian summer monsoon manifested by active and break phase, and their association with extreme rainfall events are necessary for probabilistic estimation of flood-related risks in a warming climate. Here, using ground-based observed rainfall, we define an index to measure the strength of monsoon ISOs and show that the relative strength of the northward-propagating low-frequency ISO (20-60 days) modes have had a significant decreasing trend during the past six decades, possibly attributed to the weakening of large-scale circulation in the region during monsoon season. This reduction is compensated by a gain in synoptic-scale (3-9 days) variability. The decrease in low-frequency ISO variability is associated with a significant decreasing trend in the percentage of extreme events during the active phase of the monsoon. However, this decrease is balanced by significant increasing trends in the percentage of extreme events in the break and transition phases. We also find a significant rise in the occurrence of extremes during early and late monsoon months, mainly over eastern coastal regions. Our study highlights the redistribution of rainfall intensity among periodic (low-frequency) and non-periodic (extreme) modes in a changing climate scenario.

Event-triggered sampling using signal extrema for instantaneous amplitude and instantaneous frequency estimation

Event-triggered sampling (ETS) is a new approach towards efficient signal analysis. The goal of ETS need not be only signal reconstruction, but also direct estimation of desired information in the signal by skillful design of event. We show a promise of ETS approach towards better analysis of oscillatory non-stationary signals modeled by a time-varying sinusoid, when compared to existing uniform Nyquist-rate sampling based signal processing. We examine samples drawn using ETS, with events as zero-crossing (ZC), level-crossing (LC), and extrema, for additive in-band noise and jitter in detection instant. We find that extrema samples are robust, and also facilitate instantaneous amplitude (IA), and instantaneous frequency (IF) estimation in a time-varying sinusoid. The estimation is proposed solely using extrema samples, and a local polynomial regression based least-squares fitting approach. The proposed approach shows improvement, for noisy signals, over widely used analytic signal, energy separation, and ZC based approaches (which are based on uniform Nyquist-rate sampling based data-acquisition and processing). Further, extrema based ETS in general gives a sub-sampled representation (relative to Nyquistrate) of a time-varying sinusoid. For the same data-set size captured with extrema based ETS, and uniform sampling, the former gives much better IA and IF estimation. (C) 2015 Elsevier B.V. All rights reserved.

Applications of frequency modulation interference cancellers to multiaccess communications systems

Cancellation of interfering frequency-modulated (FM) signals is investigated with emphasis towards applications on the cellular telephone channel as an important example of a multiple access communications system. In order to fairly evaluate analog FM multiaccess systems with respect to more complex digital multiaccess systems, a serious attempt to mitigate interference in the FM systems must be made. Information-theoretic results in the field of interference channels are shown to motivate the estimation and subtraction of undesired interfering signals. This thesis briefly examines the relative optimality of the current FM techniques in known interference channels, before pursuing the estimation and subtracting of interfering FM signals.

The capture-effect phenomenon of FM reception is exploited to produce simple interference-cancelling receivers with a cross-coupled topology. The use of phase-locked loop receivers cross-coupled with amplitude-tracking loops to estimate the FM signals is explored. The theory and function of these cross-coupled phase-locked loop (CCPLL) interference cancellers are examined. New interference cancellers inspired by optimal estimation and the CCPLL topology are developed, resulting in simpler receivers than those in prior art. Signal acquisition and capture effects in these complex dynamical systems are explained using the relationship of the dynamical systems to adaptive noise cancellers.

FM interference-cancelling receivers are considered for increasing the frequency reuse in a cellular telephone system. Interference mitigation in the cellular environment is seen to require tracking of the desired signal during time intervals when it is not the strongest signal present. Use of interference cancelling in conjunction with dynamic frequency-allocation algorithms is viewed as a way of improving spectrum efficiency. Performance of interference cancellers indicates possibilities for greatly increased frequency reuse. The economics of receiver improvements in the cellular system is considered, including both the mobile subscriber equipment and the provider's tower (base station) equipment.

The thesis is divided into four major parts and a summary: the introduction, motivations for the use of interference cancellation, examination of the CCPLL interference canceller, and applications to the cellular channel. The parts are dependent on each other and are meant to be read as a whole.

Biophysical and network mechanisms of high frequency extracellular potentials in the rat hippocampus

A fundamental question in neuroscience is how distributed networks of neurons communicate and coordinate dynamically and specifically. Several models propose that oscillating local networks can transiently couple to each other through phase-locked firing. Coherent local field potentials (LFP) between synaptically connected regions is often presented as evidence for such coupling. The physiological correlates of LFP signals depend on many anatomical and physiological factors, however, and how the underlying neural processes collectively generate features of different spatiotemporal scales is poorly understood. High frequency oscillations in the hippocampus, including gamma rhythms (30-100 Hz) that are organized by the theta oscillations (5-10 Hz) during active exploration and REM sleep, as well as sharp wave-ripples (SWRs, 140-200 Hz) during immobility or slow wave sleep, have each been associated with various aspects of learning and memory. Deciphering their physiology and functional consequences is crucial to understanding the operation of the hippocampal network.

We investigated the origins and coordination of high frequency LFPs in the hippocampo-entorhinal network using both biophysical models and analyses of large-scale recordings in behaving and sleeping rats. We found that the synchronization of pyramidal cell spikes substantially shapes, or even dominates, the electrical signature of SWRs in area CA1 of the hippocampus. The precise mechanisms coordinating this synchrony are still unresolved, but they appear to also affect CA1 activity during theta oscillations. The input to CA1, which often arrives in the form of gamma-frequency waves of activity from area CA3 and layer 3 of entorhinal cortex (EC3), did not strongly influence the timing of CA1 pyramidal cells. Rather, our data are more consistent with local network interactions governing pyramidal cells' spike timing during the integration of their inputs. Furthermore, the relative timing of input from EC3 and CA3 during the theta cycle matched that found in previous work to engage mechanisms for synapse modification and active dendritic processes. Our work demonstrates how local networks interact with upstream inputs to generate a coordinated hippocampal output during behavior and sleep, in the form of theta-gamma coupling and SWRs.

Response of linear, viscous damped systems to excitations having time-varying frequency

The response of linear, viscous damped systems to excitations having time-varying frequency is the subject of exact and approximate analyses, which are supplemented by an analog computer study of single degree of freedom system response to excitations having frequencies depending linearly and exponentially on time.

The technique of small perturbations and the methods of stationary phase and saddle-point integration, as well as a novel bounding procedure, are utilized to derive approximate expressions characterizing the system response envelope—particularly near resonances—for the general time-varying excitation frequency.

Descriptive measurements of system resonant behavior recorded during the course of the analog study—maximum response, excitation frequency at which maximum response occurs, and the width of the response peak at the half-power level—are investigated to determine dependence upon natural frequency, damping, and the functional form of the excitation frequency.

The laboratory problem of determining the properties of a physical system from records of its response to excitations of this class is considered, and the transient phenomenon known as “ringing” is treated briefly.

It is shown that system resonant behavior, as portrayed by the above measurements and expressions, is relatively insensitive to the specifics of the excitation frequency-time relation and may be described to good order in terms of parameters combining system properties with the time derivative of excitation frequency evaluated at resonance.

One of these parameters is shown useful for predicting whether or not a given excitation having a time-varying frequency will produce strong or subtle changes in the response envelope of a given system relative to the steady-state response envelope. The parameter is shown, additionally, to be useful for predicting whether or not a particular response record will exhibit the “ringing” phenomenon.

U.S. west coast relative sea levels from tide gauges [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Examining secular changes in relative sea level along the U.S. west coast, we have identified strong tectonic signals. Tectonism exists not only on a coherent plate-wide scale (assuming a rigid plate approximation), but also on a sub-plate scale. In fact, differential tectonism between exotic or suspect geological terrain explains much of the spatial patterns of west coast tide-gauge data. Peltier's isostatic model appears not to explain the spatial pattern, implying glacio-isostatic adjustment is not the dominant contribution to the low-frequency signals. Eustatic effects cannot be identified unambiguously. These studies suggest several major questions/observations with regard to relative sea-level studies ...

Inferences from tree rings on low frequency variations in runoff in the interior western United States

EXTRACT (SEE PDF FOR FULL ABSTRACT): Low frequency variations in runoff, AD 1700-1964, in the interior western United States are inferred from smoothed tree-ring series averaged over north, central, and south regions. ... Relative locations of peaks and troughs in streamflow, precipitation, temperature, and tree-ring series suggest that annual precipitation and warm season evapotranspiration variations may both be important to low frequency fluctuations in tree growth and in streamflow.

Control of meiotic recombination frequency in plant genomes.

Sexual eukaryotes reproduce via the meiotic cell division, where ploidy is halved and homologous chromosomes undergo reciprocal genetic exchange, termed crossover (CO). CO frequency has a profound effect on patterns of genetic variation and species evolution. Relative CO rates vary extensively both within and between plant genomes. Plant genome size varies by over 1000-fold, largely due to differential expansion of repetitive sequences, and increased genome size is associated with reduced CO frequency. Gene versus repeat sequences associate with distinct chromatin modifications, and evidence from plant genomes indicates that this epigenetic information influences CO patterns. This is consistent with data from diverse eukaryotes that demonstrate the importance of chromatin structure for control of meiotic recombination. In this review I will discuss CO frequency patterns in plant genomes and recent advances in understanding recombination distributions.

Observation of locked phase dynamics and enhanced frequency stability in synchronized micromechanical oscillators

Even though synchronization in autonomous systems has been observed for over three centuries, reports of systematic experimental studies on synchronized oscillators are limited. Here, we report on observations of internal synchronization in coupled silicon micromechanical oscillators associated with a reduction in the relative phase random walk that is modulated by the magnitude of the reactive coupling force between the oscillators. Additionally, for the first time, a significant improvement in the frequency stability of synchronized micromechanical oscillators is reported. The concept presented here is scalable and could be suitably engineered to establish the basis for a new class of highly precise miniaturized clocks and frequency references. © 2013 American Physical Society.

In vivo guidance and assessment of liver radio-frequency ablation with acoustic radiation force elastography.

The initial results from clinical trials investigating the utility of acoustic radiation force impulse (ARFI) imaging for use with radio-frequency ablation (RFA) procedures in the liver are presented. To date, data have been collected from 6 RFA procedures in 5 unique patients. Large displacement contrast was observed in ARFI images of both pre-ablation malignancies (mean 7.5 dB, range 5.7-11.9 dB) and post-ablation thermal lesions (mean 6.2 dB, range 5.1-7.5 dB). In general, ARFI images provided superior boundary definition of structures relative to the use of conventional sonography alone. Although further investigations are required, initial results are encouraging and demonstrate the clinical promise of the ARFI method for use in many stages of RFA procedures.

Geometrical dependence in photoionization of H-2(+) in high-intensity, high-frequency, ultrashort laser pulses

The ionization dynamics of H2 + exposed to high-intensity, high-frequency, ultrashort laser pulses is investigated with two theoretical approaches. The time-dependent Schrödinger equation is solved by a direct numerical method, and a simple two-center interference-diffraction model is studied. The energy and angular distributions of the photoelectron for various internuclear distances and relative orientations between the internuclear axis of the molecule and the polarization of the field are calculated. The main features of the photoelectron spectrum pattern are described well by the interference-diffraction model, and excellent quantitative agreement between the two methods is found. The effect of quantal vibration on the photoelectron spectrum is also calculated. We find that vibrational average produces some broadening of the main features, but that the patterns remain clearly distinguishable.

Bimanual coordination: constraints imposed by the relative timing of homologous muscle activation

It has often been supposed that patterns of rhythmic bimanual coordination in which homologous muscles are engaged simultaneously, are performed in a more stable manner than those in which the same muscles are activated in an alternating fashion. In order to assess the efficacy of this constraint, the present study investigated the effect of forearm posture (prone or supine) on bimanual abduction-adduction movements of the wrist in isodirectional and non-isodirectional modes of coordination. Irrespective of forearm posture, non-isodirectional coordination was observed to be more stable than isodirectional coordination. In the latter condition, there was a more severe deterioration of coordination accuracy/stability as a function of cycling frequency than in the former condition. With elevations in cycling frequency, the performers recruited extra mechanical degrees of freedom, principally via flexion-extension of the wrist, which gave rise to increasing motion in the vertical plane. The increases in movement amplitude in the vertical plane were accompanied by decreasing amplitude in the horizontal plane. In agreement with previous studies, the present findings confirm that the relative timing of homologous muscle activation acts as a principal constraint upon the stability of interlimb coordination. Furthermore, it is argued that the use of manipulations of limb posture to investigate the role of other classes of constraint (e.g. perceptual) should be approached with caution because such manipulations affect the mapping between muscle activation patterns, movement dynamics and kinematics.

The challenge of revealing and tailoring the dynamics of radio-frequency plasmas

The complex dynamics of ionization and excitation mechanisms in capacitively coupled radio-frequency plasmas is discussed for single- and dual-frequency operations in low-pressure and atmospheric pressure plasmas. Electrons are energized through the dynamics of electric fields in the vicinity of the plasma boundary sheaths. Distinctly different power dissipation mechanisms can either co-exist or initiate mode transitions exhibiting characteristic spatio-temporal ionization structures. Phase resolved optical emission spectroscopy, in combination with adequate modelling of the population dynamics of excited states, and numerical simulations reveal dissipation associated with sheath expansion, sheath collapse, transient electron avalanches and wave–particle interactions. In dual-frequency systems the relative phase between the two frequency components provides additional strategies to tailor the plasma dynamics.

The role of human demographic history in determining the distribution and frequency of transferase-deficient galactosaemia mutations

Classical or transferase-deficient galactosaemia is an inherited metabolic disorder caused by mutation in the human Galactose-1-phosphate uridyl transferase (GALT) gene. Of some 170 causative mutations reported, fewer than 10% are observed in more than one geographic region or ethnic group. To better understand the population history of the common GALT mutations, we have established a haplotyping system for the GALT locus incorporating eight single nucleotide polymorphisms and three short tandem repeat markers. We analysed haplotypes associated with the three most frequent GALT gene mutations, Q188R, K285N and Duarte-2 (D2), and estimated their age. Haplotype diversity, in conjunction with measures of genetic diversity and of linkage disequilibrium, indicated that Q188R and K285N are European mutations. The Q188R mutation arose in central Europe within the last 20 000 years, with its observed east-west cline of increasing relative allele frequency possibly being due to population expansion during the re-colonization of Europe by Homo sapiens in the Mesolithic age. K285N was found to be a younger mutation that originated in Eastern Europe and is probably more geographically restricted as it arose after all major European population expansions. The D2 variant was found to be an ancient mutation that originated before the expansion of Homo sapiens out of Africa. Heredity (2010) 104, 148-154; doi:10.1038/hdy.2009.84; published online 29 July 2009