Dominant Root Research Articles

Increases in voltage may produce false-negatives when using transcranial motor evoked potentials to detect an isolated nerve root injury

Transcranial Motor Evoked Potentials (TcMEPs) are sometimes used during lumbar spine surgery in order to detect and prevent an intraoperative nerve root injury. Typically, a fixed stimulus is applied, and one monitors for changes in response amplitude from several myotomes. Increased stimulating voltage may or may not alter the response after an acute injury. We suture ligated the dominant root innervating the tibialis anterior (TA) muscle in 7 experiments in swine monitored with TcMEPs. Injury to the root was confirmed by an increase in threshold current needed to evoke an EMG response in the TA (from 0.32 ± 0.10 to 2.3 ± 0.9 mA, P < 0.01). We recorded TcMEPs at baseline, after injury, and with incremental 25 V increases in stimulation up to 100 V. After ligation, mean TcMEP amplitude in the TA decreased by 56% from baseline (P < 0.01). Adding voltage progressively restored mean amplitude to within 17% of baseline, but with wide variability in the response. In 1 experiment, there was no augmentation; 3 studies showed partial improvement toward baseline; and in 3 studies, the amplitude was augmented to levels above baseline. An acute nerve root injury may be detected by TcMEP monitoring. However, if the stimulating voltage is increased after injury, the response may or may not be affected. In complex spine procedures, adjustments to TcMEP stimulating parameters are often needed to maintain reproducible responses. However, if these changes are made during a period where injury might occur, this could mask the changes and lead to a false-negative interpretation.

Bias Reduction in Dynamic Panel Data Models by Common Recursive Mean Adjustment*

The within-group estimator (same as the least squares dummy variable estimator) of the dominant root in dynamic panel regression is known to be biased downwards. This article studies recursive mean adjustment (RMA) as a strategy to reduce this bias for AR(p) processes that may exhibit cross-sectional dependence. Asymptotic properties for N,T→∞ jointly are developed. When ( log 2T)(N/T)→ζ, where ζ is a non-zero constant, the estimator exhibits nearly negligible inconsistency. Simulation experiments demonstrate that the RMA estimator performs well in terms of reducing bias, variance and mean square error both when error terms are cross-sectionally independent and when they are not. RMA dominates comparable estimators when T is small and/or when the underlying process is persistent.

Characterization of the mating type ( MAT) locus in the Phialocephala fortinii s.l. – Acephala applanata species complex

Members of the Phialocephala fortinii sensu lato – Acephala applanata species complex (PAC) are the dominant root endophytes of woody plants in temperate and boreal forests. In the present study, the mating type ( MAT) idiomorphs of eight species belonging to the PAC were cloned. Because direct cloning of MAT idiomorphs was not possible, species phylogenetically placed between the PAC and other helotialean species with characterized MAT locus were used for an intermediate cloning step. Whereas A. applanata showed a homothallic organization structure of the MAT locus, all other species either contained the MAT1-1 or MAT1-2 idiomorph indicative of heterothallism. A Tc1-like transposable element was found within the MAT locus of A. applanata. Analysis of A. applanata strains collected over a broad geographical range showed that the transposable element was present in all A. applanata strains, suggesting an ancient transposition event. Moreover, a partial MAT1-1-1 gene was identified within MAT1-2 idiomorphs, a common phenomenon in the order Helotiales. However, this partial gene was not fixed in all populations of the species. The evolution of the MAT locus with regard to different mating systems is discussed for the species complex.

Generalised Kostka–Foulkes polynomials and cohomology of line bundles on homogeneous vector bundles

Let G be a simple algebraic group and B a Borel subgroup. We consider generalisations of Lusztig’s q-analogues of weight multiplicity, where the set of positive roots is replaced with the multiset of weights of a B-submodule N of an arbitrary finite-dimensional G-module V. The corresponding polynomials in q are called generalised Kostka–Foulkes polynomials (gKF). We prove vanishing theorems for the cohomology of line bundles on G × B N and derive from this a sufficient condition for the non-negativity of the coefficients of gKF. We also consider in detail the case in which V is the simple G-module whose highest weight is the short dominant root and N is the B-submodule whose weights are all short positive roots.

Characterization of graphs using domination polynomials

Let G be a simple graph of order n . The domination polynomial of G is the polynomial D ( G , x ) = ∑ i = 1 n d ( G , i ) x i , where d ( G , i ) is the number of dominating sets of G of size i . A root of D ( G , x ) is called a domination root of G . We denote the set of distinct domination roots by Z ( D ( G , x ) ) . Two graphs G and H are said to be D -equivalent, written as G ∼ H , if D ( G , x ) = D ( H , x ) . The D -equivalence class of G is [ G ] = { H : H ∼ G } . A graph G is said to be D -unique if [ G ] = { G } . In this paper, we show that if a graph G has two distinct domination roots, then Z ( D ( G , x ) ) = { − 2 , 0 } . Also, if G is a graph with no pendant vertex and has three distinct domination roots, then Z ( D ( G , x ) ) ⊆ { 0 , − 2 ± 2 i , − 3 ± 3 i 2 } . Also, we study the D -equivalence classes of some certain graphs. It is shown that if n ≡ 0 , 2 ( mod 3 ) , then C n is D -unique, and if n ≡ 0 ( mod 3 ) , then [ P n ] consists of exactly two graphs.

Tuning the leading roots of a second order DC servomotor with proportional retarded control

The stabilization of a second order system through a proportional delay controller insuring a specified closed loop exponential decay s is studied. The analysis in the frequency domain allows the determination of the s-stabilizability regions of the controller. The locus of the dominant roots is analyzed in detail and the characterization of some key loci, including the maximum achievable decay is obtained. The tuning of a DC servomotor experimental setup illustrates the results.

Mixed-muscle electrode placement (“jumping” muscles) may produce false-negative results when using transcranial motor evoked potentials to detect an isolated nerve root injury in a porcine model

Placing EMG electrode pairs that span several muscles is sometimes used to enhance the efficacy of electromyographic recordings. This technique, often referred to as "jumping," has not been studied when using Motor Evoked Potentials (TcMEP) for detecting isolated spinal nerve root injury during spine surgery. TcMEPs were obtained in seven pigs under general anesthesia. One pair of recording electrodes was placed entirely within the tibialis anterior (TA) muscle; a second pair had one lead in the TA and the other in the gastrocnemius muscle (TA-GAS). The dominant root innervating the TA was determined using evoked EMG. MEP amplitudes recorded by the TA and TA-GAS electrodes were compared before and after suture ligation of this root in 12 separate experiments. Mean baseline TcMEP amplitude was not significantly different for the TA vs. TA-GAS. After root ligation, mean amplitude dropped from baseline by 72 +/- 13% in the TA vs. 50 +/- 29% in the TA-GAS (p < 0.01). All amplitudes decreased by >50% in the TA group; half of the TA-GAS group had <50% decrease in amplitude. Mixed-myotomal recording electrodes did not consistently increase baseline TcMEP amplitude. The decrease in amplitude after ligation was both smaller and more variable in the "jumped" TA-GAS electrodes. Thus, this technique may allow someone relying on TcMEP monitoring to miss an otherwise detectable isolated nerve root injury (i.e., have a false-negative result).

Relative Efficacy of Transcranial Motor Evoked Potentials, Mechanically-Elicited Electromyography, and Evoked EMG to Assess Nerve Root Function During Sustained Retraction in a Porcine Model

This is an animal experiment using transcranial motor evoked potentials (TcMEP), mechanically elicited electromyography (EMG), and evoked EMG during spinal nerve root retraction in a pig model. To compare the sensitivity of these 3 electrophysiological measures for a constant retraction force applied to an isolated lumbar nerve root for a specific duration of time. The incidence of nerve root injury during lumbar spine surgery ranges from 0.2% to 31%. Direct retraction of spinal nerve roots may cause these injuries, but the amount and duration of force that may safely be applied is not clear. Using an established porcine model, we examined the changes occurring to multimyotomal TcMEPs, mechanically elicited EMGs, and evoked EMGs during continuous retraction of a nerve root at a constant force applied over 10 minutes. TcMEP, mechanically elicited EMG, and evoked EMG responses were recorded from the tibialis anterior (TA) muscle in 10 experiments. The dominant root innervating the TA was determined with evoked EMG; preretraction TcMEP and nerve root stimulation threshold (NRT) was obtained. The dominant root was retracted at 2 Newton (N) for 10 minutes. TcMEP trials were elicited every minute during retraction. NRT was measured immediately after retraction. TcMEP and NRT were measured after 10 minutes of recovery. RESULTS.: During the 10 minutes of retraction at 2 N, the amplitude of the TA muscle progressively decreased in all trials in a highly significant curvilinear fashion. The mean TcMEP amplitude decreased 59% +/- 14% from baseline values. The mean NRT after 10 minutes of retraction at 2 N rose to 1.8 +/- 0.7 mA (P < 0.01 vs. baseline). The NRT increase after retraction strongly correlated with the decrease in motor evoked potentials amplitude in the TA (R = 0.90, P < 0.001). EMG activity was variable; tonic EMG was observed in only 2 nerve roots (20%). Three electrophysiologic methods were used intraoperatively to assess neural function during retraction of a single nerve root. Retraction produced consistent changes in TcMEPs and evoked EMG. These 2 methods show promise for assessing the limits on the force and duration of nerve root retraction during spine surgery. Mechanically elicited EMG was not sensitive to the amount and duration of nerve root retraction.

Bias Reduction in Dynamic Panel Data Models by Common Recursive Mean Adjustment

The within-group estimator (same as the least squares dummy variable estimator) of the dominant root in dynamic panel regression is known to be biased downwards. This paper studies recursive mean adjustment (RMA) as a strategy to reduce this bias for AR(p) processes that may exhibit cross-sectional dependence. Asymptotic properties for N, T → ∞ jointly are developed. When (log2 T)(N/T ) → ζ where ζ is a non-zero constant, the estimator exhibits nearly negligible inconsistency. Simulation experiments demonstrate that the RMA estimator performs well in terms of reducing bias, variance and mean square error both when error terms are cross-sectionally independent and when they are not. RMA dominates comparable estimators when T is small and/or when the underlying process is persistent.

Dark septate endophytes (DSE) of the Phialocephala fortinii s.l. – Acephala applanata species complex in tree roots: classification, population biology, and ecology

Dark septate endophytes (DSE), a diverse group of ascomycetes, are dominant root colonizers in many ecosystems. The most frequent DSE in natural forest ecosystems in the Northern hemisphere belong to the Phialocephala fortinii s.l. – Acephala applanata species complex (PAC). Recently, species rank was assigned to seven cryptic species (CSP) of P. fortinii s.l.: Phialocephala fortinii s. str. C.J.K. Wang &amp; H.E. Wilcox, Phialocephala europaea C.R. Grünig et T.N. Sieber, Phialocephala helvetica C.R. Grünig et T.N. Sieber, Phialocephala letzii C.R. Grünig et T.N. Sieber, Phialocephala subalpina C.R. Grünig et T.N. Sieber, Phialocephala turiciensis C.R. Grünig et T.N. Sieber, and Phialocephala uotolensis C.R. Grünig et T.N. Sieber. PAC species occur on all parts of the root system of trees, from mycorrhizal root tips to the stem base. Up to 80% of fine roots in forest stands can be colonized by them, and up to eight species occur sympatrically. The present work is a mixture of review and reconsideration of published work in the light of the subdivision of P. fortinii s.l. into several species. We review the current knowledge related to taxonomy, geographical distribution, population biology, and ecology of PAC species. We identified strains of P. fortinii s.l. from previously published studies to species level. The reassessment of earlier studies indicates that PAC species behave in a versatile manner along the mutualism-parasitism continuum and lifestyle designation is complicated by the use of different experimental systems. Finally we define the most promising research areas, which will contribute to elucidate the ecological role of root endophytes in general and PAC species in particular.

Computation of dominant real roots of polynomials

The computation of the dominant positive roots of univariate polynomials is a key step for real root isolation algorithms. We propose a new device for computing dominant real roots and compare it with other methods. For roots surpassing unity, we obtain better results than the classical estimates of Lagrange and Long-champ. We also discuss a new refined result on bounds for positive roots that can be used for all polynomials with sign changes.

Non-Markovian diffusion over a parabolic potential barrier: Influence of the friction-memory function

The over-passing probability across an inverted parabolic potential barrier is investigated according to the classical and quantal generalized Langevin equations. It is shown that, in the classical case, the asymptotic value of the over-passing probability is determined by a single dominant root of the "characteristic function," and it is given by a simple expression. The expression for the over-passing probability is quite general, and details of dissipation mechanism and memory effects enter into the expression only through the dominant root of the characteristic equation.

The Entrepreneurship-Philanthropy Nexus: Nonmarket Source of American Entrepreneurial Capitalism

What differentiates American capitalism from all other forms of industrial capitalism is a historical focus on both the creation of wealth (entrepreneurship) and the reconstitution of wealth (philanthropy). Philanthropy has been part of the implicit American social contract that continuously nurtures and revitalizes economic prosperity. Much of the new wealth created historically has been given back to the community to build many of the great social institutions that have paved the way for future economic growth. This entrepreneurship-philanthropy nexus has not been fully explored by either economists or the general public. The purpose of this paper is to suggest that American philanthropists-particularly those who have made their own fortunes-create foundations that, in turn, contribute to greater and more widespread economic prosperity through knowledge creation. Analyzing philanthropy sheds light on our current understanding of how economic development has occurred, as well as the roots of American economic dominance.

Power Classes Of Recurrence Sequences

In this note, we improve upon a result from [4] concerning q-power classes of linearly recurrent sequences with a dominant root.

Persistence change tests and shifting stable autoregressions

In this paper we investigate the behaviour of persistence change tests when applied to series whose dominant autoregressive root displays a single structural shift, but is less than unity in each regime, and draw comparison with the persistence change case.

A new method for screening the contingencies before dynamic security assessment of a multimachine power system

AbstractThis paper proposes a novel method for identifying the faults that would impact the transient stability of a multimachine power system. In this method each synchronous machine's swing equation is formulated in the form of a closed loop transfer function in Laplace domain (s‐plane). The duration of a fault under consideration, and the changes of maximum electrical power output of the machine during and after the fault are included in the same transfer function. Then the narrowest possible range containing the real part of the ‘dominant’ root of each machine's characteristic equation is identified on the real axis of s‐plane. This is because it is the real part that decides whether the transient response would sustain or subside. If the average of the lower limits of the real parts of dominant roots for all the machines is in the left half but very close to the imaginary axis (poorly damped) or in the right half of the s‐plane (absence of damping), the system as a whole is unstable under the considered fault. The proposed method is extremely fast. An extensive digital simulation test and comparison of the proposed method with a conventional step‐by‐step (SBS) numerical integration method has been done on a 25‐machine practical system belonging to Bangladesh Power Development Board (BPDB), and good agreements observed for an array of fault scenarios. The faults for which the aforesaid average lower limit is in the left half plane but its distance from imaginary axis is marginally above or below an established minimum value, can be further investigated by a detailed time domain simulation (TDS) transient stability analysis technique. Thus the proposed method is useful for real‐time screening of the contingencies (e.g., faults) before being subjected to a full‐scale dynamic security analysis in a power system of any size with any number of machines. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador

Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50� ). Three tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m, 48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased significantly from 6.1 � 10 )3 m 2 m )1 at 1900 m to 3.2 � 10 )3 m 2 m )1 at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently. Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide anchorage in soils with low bulk density and in environments with high wind speeds. Abbreviations: AR – aspect ratio; CSA – cross sectional area; DBH – diameter at breast height; ZRT – zone of rapid taper

Observation and Simulation of Root Reinforcement on Abandoned Mediterranean Slopes

The mechanics of root reinforcement have been described satisfactorily for a single root or several roots passing a potential slip plane and verified by field experiments. Yet, precious little attempts have been made to apply these models to the hillslope scale pertinent to landsliding at which variations in soil and vegetation become important. On natural slopes positive pore pressures occur often at the weathering depth of the soil profile. At this critical depth root reinforcement is crucial to avert slope instability. This is particularly relevant for the abandoned slopes in the European part of the Mediterranean basin where root development has to balance the increasing infiltration capacity during re-vegetation. Detailed investigations related to root reinforcement were made at two abandoned slopes susceptible to landsliding located in the Alcoy basin (SE Spain). On these slopes semi-natural vegetation, consisting of a patchy herbaceous cover and dispersed Aleppo pine trees, has established itself. Soil and vegetation conditions were mapped in detail and large-scale, in-situ direct shear tests on the topsoil and pull-out tests performed in order to quantify root reinforcement under different vegetation conditions. These tests showed that root reinforcement was present but limited. Under herbaceous cover, the typical reinforcement was in the order of 0.6 kPa while values up to 18 kPa were observed under dense pine cover. The tests indicate that fine root content and vegetation conditions are important factors that explain the root reinforcement of the topsoil. These findings were confirmed by the simulation of the direct shear tests by means of an advanced root reinforcement model developed in FLAC 2D. Inclusion of the root distribution for the observed vegetation cover mimics root failure realistically but returns over-optimistic estimates of the root reinforcement. When the root reinforcement is applied with this information at the hillslope scale under fully saturated and critical hydrological conditions, root pull-out becomes the dominant root failure mechanism and the slip plane is located at the weathering depth of the soil profile where root reinforcement is negligible. The safety factors increase only slightly when roots are present but the changes in the surface velocity at failure are more substantial. Root reinforcement on these natural slopes therefore appears to be limited to a small range of critical hydrological conditions and its mitigating effect occurs mainly after failure.

A new phase-lead design method using the root locus diagrams

A new phase-lead design method using the root locus diagrams is proposed. In the traditional phase-lead root locus design procedure, the designer has no direct control to the steady-state error constant of the resulting closed-loop system. In order to obtain a satisfactory steady-state error constant, the designer has to try different locations of the compensator's zero and the desired dominant roots. However, the procedure does not indicate to the designer how to alter the locations to obtain the desired steady-state error constant. With the new method presented in this note, the applicability of the phase lead compensation network is determined once the desired dominant roots are given, and the maximum steady-state error constant can be directly determined. If the desired steady-state error constant rely within the limit, the desired steady-state error constant together with the desired dominant roots are directly used to obtain the compensator. If the desired stead-state error constant exceeds the reachable limit, the note proposes a way to find out the proper locations of the desired dominant roots.

Intrinsically dynamic population models

Intrinsically dynamic models (IDMs) depict populations whose cumulative growth rate over a number of intervals equals the product of the long term growth rates (that is the dominant roots or dominant eigenvalues) associated with each of those intervals. Here the focus is on the birth trajectory produced by a sequence of population projection (Leslie) matrices. The elements of a Leslie matrix are represented as straightforward functions of the roots of the matrix, and new relationships are presented linking the roots of a matrix to its Net Reproduction Rate and stable mean age of childbearing. Incorporating mortality changes in the rates of reproduction yields an IDM when the subordinate roots are held constant over time. In IDMs, the birth trajectory generated by any specified sequence of Leslie matrices can be found analytically. In the Leslie model with 15 year age groups, the constant subordinate root assumption leads to reasonable changes in the age pattern of fertility, and equations (27) and (30) provide the population size and structure that result from changing levels of net reproduction. IDMs generalize the fixed rate stable population model. They can characterize any observed population, and can provide new insights into dynamic demographic behavior, including the momentum associated with gradual or irregular paths to zero growth.