Presence Of Variations Research Articles

Is lymph node count an ideal quality indicator for cancer care?

Although lymph node count has substantial appeal as a quality indicator because of the ease of measurement, the presence of variation in the population, the association with survival for many cancers, and the previous success of quality intervention programs, improvements in patient outcome by increasing lymph node counts have not yet been demonstrated. This article discusses potential pitfalls in the use of lymph node count as a quality indicator.

Techniques to Extend Canary-Based Standby $V_{DD}$ Scaling for SRAMs to 45 nm and Beyond

<i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VDD</i> scaling is an efficient technique to reduce SRAM leakage power during standby mode. The data retention voltage (DRV) defines the minimum <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VDD</i> that can be applied to an SRAM cell without losing data. The conventional worst-case guard-banding approach selects a fixed standby supply voltage at design time to accommodate the variability of DRV, which sacrifices potential power savings for non-worst-case scenarios. We have proposed a canary-based feedback to achieve aggressive power savings by tracking PVT variations through canary cell failures. In this paper, we show new measured silicon results that confirm the ability of the canary scheme to track PVT changes. We thoroughly analyze the adaptiveness of the canary cells for tracking changes in the SRAM array, including the ability to track PVT fluctuations. We present circuits for robustly building the control logic that implements the feedback mechanism at subthreshold supply voltages, and we derive a new analytical model to help tune the canary cells in the presence of variations. To realistically quantify the potential savings achievable by the canary scheme, we assess the impact of various sources of overhead. Finally, we investigate the performance of the canary based scheme in nanometer technologies, and we show that it promises to provide substantial standby power savings down to the 22 nm node.

Commentary: Heterogeneity in meta-analysis should be expected and appropriately quantified

It is generally accepted that meta-analyses should assess heterogeneity, which may be defined as the presence of variation in true effect sizes underlying the different studies. This assessment might be achieved by performing a statistical test for heterogeneity, by quantifying its magnitude, by quantifying its impact or by a combination of these. Patsopoulos, Evangelou and Ioannidis propose methods for examining the effect of excluding studies (or groups of studies) on an assessment of heterogeneity. 1 Their methods offer benefits over the sometimes practiced ‘leave one out’ approach to sensitivity analysis, by recognizing that the overall effect (against which heterogeneity is measured) changes each time an influential study is excluded. The authors offer a sequential approach (in which the overall effect and heterogeneity measure are re-estimated after the most influential study is removed at each iteration), and a combinatorial approach (in which groups of studies are removed). I suspect the sequential approach may often be performed informally in practice, whereby an obvious outlier is excluded, but another study then appears to be an outlier compared with the remaining studies and is in turn excluded. Of course, if heterogeneity permeates the entire set of studies, one might be tempted continue excluding studies to reduce heterogeneity until a single study remains. A predefined stopping rule (a ‘desired heterogeneity threshold’, in the authors’ terminology) may therefore appear to offer a useful way forward. Sensitivity analyses are important components of meta-analyses and should be widely encouraged. But is it helpful to assess sensitivity of heterogeneity measures to exclusion of studies, and is it sensible in particular to define a ‘desired threshold’ in terms of

Analytical model-based technique for efficient evaluation of noise robustness considering parameter variations

In this paper, we present an accurate method for analytical derivation of noise rejection curves (NRCs) and the associated noise susceptibility metric in the presence of variations in process and environmental parameters. The method involves modeling of the pull-up and pull-down resistances of combinational gates using approximated BSIM4 model-based device equations. Comparisons of the analytical model with circuit simulations show that the impact of parameter variations on the noise susceptibility is accurately captured by our model. The average (maximum) error associated with the noise susceptibility is found to be as low as 2.6% (6.7%). Our model can predict the noise susceptibility under parameter variations more than five orders of magnitude faster than circuit simulations, which makes it suitable for design optimization for noise robustness.

Online Estimation of Implement Dynamics for Adaptive Steering Control of Farm Tractors

This paper presents a method to utilize a cascaded extended Kalman filter to estimate the slope of the dc gain Mdc of the steer angle to yaw rate transfer function with respect to the velocity of the tractor. The online estimate of the dc gain for different implements is used to compensate for changes in the yaw dynamics of the tractor implement cause by variations in the hitch loading. This is accomplished by using the online estimate of Mdc to modify the tractor controller gains based on a lookup table of predetermined values that are calculated from system identification tests for different implements. An online analysis of the data is used to determine if enough excitation in the yaw dynamics is available for estimation of the dc gain. The sensitivity of the controller to model simplifications, incorrect velocities, and Mdc estimate errors as well as the accuracy and rate of convergence of the estimated Mdc are also investigated. Experimental and simulation results are provided that show the validity of the Mdc estimate. Finally, experimental results show that the control performance is maintained in the presence of variation in hitch loading and tractor velocity using the adaptive control strategy based on the dc gain estimate for a given implementcondition.

Seed dispersal kernel estimation without fecundities

Seed dispersal kernel estimation without fecundities

Credit Frictions and Optimal Monetary Policy

We extend the basic (representative-household) New Keynesian [NK] model of the monetary transmission mechanism to allow for a spread between the interest rate available to savers and borrowers, that can vary for either exogenous or endogenous reasons. We find that the mere existence of a positive average spread makes little quantitative difference for the predicted effects of particular policies. Variation in spreads over time is of greater significance, with consequences both for the equilibrium relation between the policy rate and aggregate expenditure and for the relation between real activity and inflation. Nonetheless, we find that the target criterion - a linear relation that should be maintained between the inflation rate and changes in the output gap - that characterises optimal policy in the basic NK model continues to provide a good approximation to optimal policy, even in the presence of variations in credit spreads. We also consider a spread-adjusted Taylor in which the intercept of the Taylor rule is adjusted in proportion to changes in credit spreads. We show that while such an adjustment can improve upon an unadjusted Taylor rule, the optimal degree of adjustment is less than 100 percent; and even with the correct size of adjustment, such a rule of thumb remains inferior to the targeting rule. This is part of a series of BIS Working Papers (273 to 278) collecting papers presented at the BIS's Seventh Annual Conference on Whither monetary policy? Monetary policy challenges in the decade ahead in Luzern, Switzerland, on 26-27 June 2008. The event brought together senior representatives of central banks and academic institutions to exchange views on this topic. BIS Paper 45 contains the opening address of William R White (BIS), the contributions of the policy panel on Beyond price stability - the challenges ahead and speeches by Edmund Phelps (Columbia University) and Martin Wolf (Financial Times). The participants in the policy panel discussion chaired by Malcolm D Knight (BIS) were Martin Feldstein (Harvard University), Stanley Fischer (Bank of Israel), Mark Carney (Bank of Canada) and Jean-Pierre Landau (Banque de France). This Working Paper includes comments by Olivier Blanchard and Charles Goodhart.

Assessing pitcher and catcher influences on base stealing in Major League Baseball

A formal statistical analysis is performed to determine the extent to which pitchers and catchers can influence stolen-base attempts and successes. Two response proportions, attempt/opportunity and success/attempt, are modelled separately using mixed-effects logistic regression models applied to situations with a runner on first and other bases empty. Data include the first innings of all Major League Baseball games played between 1978 and 1990, which encompasses over 48,000 opportunities and 9000 attempts. Pitchers and catchers are entered as random effects and various other factors thought to influence stolen-base attempts and successes are entered as fixed effects. Variance components are estimated and hypotheses tests indicate that the population variance components for both pitchers and catchers are significant for both response proportions. The presence of variation among players at the respective positions is interpreted as evidence that stolen-base defence is a real skill exhibited to varying extents by different players. Furthermore, the variance component for pitchers is greater than that for catchers for both response proportions, indicating that pitchers have greater potential to affect stolen-base attempts and successes. Under usual conditions, it is estimated that 95% of pitchers have first-inning stolen-base success/attempt probabilities between 0.50 and 0.84, while 95% of catchers have probabilities between 0.59 and 0.79.

Embryology of Swertia (Gentianaceae) relative to taxonomy

The embryological features of three species of Swertia (s.l.) - S. erythrosticta, S. franchetiana, and S. tetraptera were characterized, and the observations were used, together with previously gathered data on other species, to evaluate a recently proposed polyphyly, based on molecular data, of Swertia s.l. Comparisons of species within the genus showed that they have diversified embryologically, and there are significant between-species differences. Notable features that vary between species include the number of cell layers that form the anther locule wall, the construction of the wall of the mature anther, tapetum origin, the cell number in mature pollen grains, the structure of the fused margins of the two carpels, the ovule numbers in placental cross-sections, the shape of the mature embryo sac, the degree of ovule curvature, antipodal variation and the presence of a hypostase, and seed appendages. They share characters that are widely distributed in the tribe Gentianeae, such as a dicotyledonous type of anther wall formation, a glandular tapetum with uninucleate cells, simultaneous cytokinesis following the meiosis of the microsporocytes, tetrahedral microspore tetrads, superior, bicarpellary and unilocular ovaries, unitegmic and tenuinucellar ovules, Polygonum-type megagametophytes, progamous fertilization, nuclear endosperm, and Solanad-type embryogeny. The presence of variation in embryological characters amongst the species of Swertia s.l. strongly supports the view that Swertia s.l. is not a monophyletic group. Frasera is better separated from Swertia s.l. as an independent genus, and is only distantly related to Swertia s. s. judging from the numerous differences in embryology. Swertia tetraptera is very closely related to Halenia, as they show identical embryology. (C) 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 383-400.

Aging affects the predictive control of grip force during object manipulation

We examined the effects of aging on the predictive control of grip force during object manipulation under various external force fields. Participants rhythmically moved a hand-held object (m = 0.4 kg) in the horizontal plane under three experimental conditions: (1) with an elastic cord attached to the upper arm (ARM), (2) with the elastic cord attached to the object (OBJECT), and (3) without any elastic cord (NO ELAST). Performance was evaluated in terms of both metric and spectral characteristics of the grip force (GF) profile, in relation to the movement-induced variations in load at the object-finger interface (LFO). The performance of a group of 12 older adults (mean age = 66.3 years) was compared to the performance of a group of 12 young adults (mean age = 25.0 years), whose metric characteristics were reported earlier (Exp. Brain Res. 172:331, 2006). Although elderly participants exerted a larger mean GF, a tight linear coupling between GF and LFO was found for both groups in OBJECT. In ARM and NO ELAST, coefficients of cross-correlations were markedly lower, the more so for the elderly participants. Adjustments in GF occurred slightly in advance of variations in LFO in young adults (+7 ms) and somewhat delayed in the elderly (-26 ms). Spectral analyses revealed that in OBJECT, LFO and GF varied primarily at the frequency of movement. In ARM and NO ELAST, where LFO varied at twice this frequency, GF modulations contained a substantial frequency component at the frequency of movement, with this effect being more pronounced for the elderly participants. We conclude that both young and older adults demonstrate a predictive control of GF, capable of separating external force fields acting on the arm or on object-finger interface. However, in the presence of variations in LFO occurring at twice the frequency of movement, the spectral profile of GF exhibits a non-functional component of variation at the frequency of movement. Aging amplifies this latter effect, thereby affecting the efficiency of the predictive control of grip force.

Observables and prediction modeling in the presence of ultra-wideband heterogeneity

Underlying virtually all propagation and scattering models is an intuitive understanding; the acoustic field is observable using a device of a sufficiently small size to obtain a sufficiently dense set of discrete measurements. This assumes the field variation cuts off at an inner length scale larger than the device size, assuring that no information is lost to the inherent spatial averaging in any measurement. This understanding is faulty in the presence of environment heterogeneity observed on an extreme range of length scales. The reason is that all physical devices have finite accuracy, which limits their ability to capture variation on scales significantly larger than their size, in the presence of variation on intermediate scales. A more refined understanding of the ability to observe a field requires multiple devices, an unbounded hierarchy in the limit, to obtain multiple dense sets of discrete ‘‘observables.’’ This, then, suggests a different class of prediction models for environments with ultra-wideband heterogeneity, expressed in multiple sets of discrete variables, each set describing field variation in a limited subband. A framework for formulating these prediction models and their application to a scenario for which environment heterogeneity has no inner scale cutoff is presented.

First-Principles, Data-Based, and Hybrid Modeling and Optimization of an Industrial Hydrocracking Unit

The first-principles, data-based, and hybrid modeling strategies are employed to simulate an industrial hydrocracking unit, to make a comparative performance assessment of these strategies, and to do optimization. A first-principles model (FPM) based on the pseudocomponent approach (Bhutani, N.; Ray, A. K.; Rangaiah, G. P. Ind. Eng. Chem. Res. 2006, 45, 1354) is coupled with neural network(s) in different hybrid architectures. Data-based and hybrid models are promising for important predictions in the presence of variations in operating conditions, feed quality, and catalyst deactivation. Data-based models are purely empirical and are developed using neural networks, whereas the neural-network component of a hybrid model is used to obtain either updated model parameters in the FPM connected in series or to correct predictions of the FPM. This article presents data-based models and three hybrid models, their implementation and evaluation on an industrial hydrocracking unit for predicting steady-state perfo...

Networking with multi‐service GEO satellites: cross‐layer approaches for bandwidth allocation

AbstractCross‐layer Radio Resource Management (CL‐RRM) has been recently investigated by quite a few research groups in wireless communications. In the specific satellite‐networking environment, the paper presents an overview of different CL‐RRM techniques devoted to dynamic bandwidth allocation, whose interactions span the physical, data link, network and transport layers, in various combinations. A multi‐service setting is considered, in the presence of variations in both traffic and channel conditions. Regarding the latter, bit and coding rate adaptation are adopted as fade countermeasure, and their effect on the higher layers is modelled as a bandwidth reduction. Traffic models and methodologies for dynamic bandwidth allocation and performance optimization are discussed. Numerical examples are presented to highlight throughput/fairness trade‐offs for long‐lived TCP connections that share multiple channels with different fading depth. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Variation for Tipburn Resistance in Lettuce

Tipburn (TB) is a physiological disorder that results in necrosis along the margins of lettuce leaves. The disorder is objectionable to consumers and reduces the shelf life of whole and minimally processed lettuce. The objectives were to 1) determine the variation for tipburn resistance in iceberg, romaine, green leaf, and red leaf cultivars; and 2) determine the genotype × location interaction for tipburn resistance. Tipburn incidence was recorded on 10 plants in each of three repetitions in Salinas, Calif., and Yuma, Ariz., trials with 20 iceberg, 21 romaine, 11 green leaf, and six red leaf cultivars. Data were analyzed using analysis of variance type statistics of ranked data. Variation for TB resistance was found in all lettuce types at both locations, although iceberg cultivars (average percentage of TB = 31% Salinas; 77% Yuma) had significantly (P &lt; 0.01) higher levels of resistance at both location than romaine (58% Salinas, 81% Yuma), green leaf (52% Salinas; 88% Yuma), and red leaf (43% Salinas, 89% Yuma). The Yuma, Ariz., trial was more conducive for TB, and had less variation (range of percentage of TB = 33% to 100% Yuma, 0% to 100% Salinas). Four iceberg, one green leaf, and one red leaf genotype with industry acceptable levels of TB (&lt;5%) were identified in the Salinas environment. Genotype × location interaction was present (P &lt; 0.01), and included rank order changes within all lettuce types. The correlation between the locations was low, 0.26, but significant (P = 0.045). A need exists for romaine, green leaf, and red leaf germplasm with improved TB resistance, particularly in the Yuma environment. The presence of variation within each lettuce type and genotype × location indicates that genetic improvement should be possible using within type crosses followed by selection in the Yuma or Salinas target environment.

SATURATED FLOW PROPERTIES OF DIFFERENT SOIL-SAND SYSTEMS AS RELATED TO THEIR PARTICLE- AND MICROPORE-SIZE DISTRIBUTIONS

It is known that soil's hydraulic conductivity or permeability is strictly related to many physical properties fundamental for the use and management of the soil. However, limited information is available on the relations between microporosity and hydraulic properties of the soil. An investigation has been carried out on different soil-sand systems to evaluate and correlate their flow properties (i.e., saturated hydraulic conductivity, and permeability), to the particle- and micropore-size distributions of the soils. Both saturated hydraulic conductivity, K sat , and permeability, k sat , were calculated applying a model which characterizes the process of either steady-state or nonsteady-state saturated flow through the soil- or clay-sand systems when in the presence of variations in the intrinsic permeability of the solid matrix during percolation (Aringhieri and Capurro, 1994; Aringhieri and Giachetti, 2001). Particle-and micropore-size distributions and the specific surface area of the soils were then related to the parameters characterizing the saturated flow. Under these conditions, the results showed an exponential decrease in the hydraulic conductivity or permeability of the system by increasing the percentage of the finest size-grade particles present in the soil. The reduction in the permeability of the system, k sat , was also exponentially related to an increase of either specific surface area or the maximum contribution to the total microporosity of the soil, (Δv p /Δr p ) max , which is largely due to pores of about 20 A effective pore radius, rp.

Karyological and allozyme variability of Far Eastern voles Microtus fortis Büchner, 1889 (Cricetidae, Rodentia) from the Russian Far East

Karyological (G-, C-, and NOR-banding) and allozyme analyses were carried out for island and continental populations of the vole Microtus fortis from the Far East of Russia. Variability of the autosome pair 7 was found. The presence of variation in the number of telomere heterochromatin blocks in the populations of Far Eastern voles was confirmed. NOR-staining of the Far Eastern vole chromosomes was carried out, showing stability of the number and the positions of the nucleolus organizer regions. Ten enzyme systems and three non-enzyme proteins (controlled in total by 25 interpretable loci) were examined in the Far Eastern vole from the island and continental populations. All of the loci were shown to be monomorphic, except for one esterase locus, which exhibited polymorphism at the intrapopulation and interpopulation levels. The issue of distribution of the Far Eastern vole subspecies is discussed. It is suggested that M. fortis pelliceus occurs not only in the Russian Far East, but also in Northern Transbaikalia.

Analysis of QCM gas sensor transient response by visualizing gas concentration

AbstractGas‐source localization systems are required to quickly detect gas concentrations at various locations while moving. It is therefore necessary to design the system by taking account of the delay in the response and recovery of the gas sensor in the presence of variations in gas concentration. Also, in order to model the dynamic characteristics of the gas sensor in open air, it is essential to understand the delay in response and recovery of the gas sensor. To carry out a transient response analysis of such a gas sensor, it is necessary to know the gas concentration (changing in time) at the gas sensor. In the present study, in order to analyze the transient response of a QCM (quartz crystal microbalance) gas sensor, the gas concentration is visualized. A photodiode is placed close to the gas sensor and the intensity of scattered laser light is measured optically in order to know the concentration of the gas passing over the sensor. The sensor response and the intensity of scattered light are measured simultaneously and the sensor response is estimated from the visualized gas concentration by means of the models of a second‐order system and a neural network. When the measured results and the estimated results are compared, the model based on the neural network is found to estimate more accurately. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(6): 14–21, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10062

Maximum - Ultra-low voltage circuit design in the presence of variations

Maximum - Ultra-low voltage circuit design in the presence of variations

Curves vs. skeletons in object recognition

The type of representation used in describing shape can have a significant impact on the effectiveness and efficiency of a recognition strategy. Shape has been represented by a point set, outline curve and shock-graph (medial axis). The curve-based representation can be viewed as point-based representation with additional organization, namely, order along a contour; shock-based representation, in turn, can be viewed as curve-based representation with additional organization, namely, pairing of contours. This additional complexity in organization leads to greater computational effort in deriving and matching these representations. However, it leads to an increase in robustness in the presence of variations. In this paper, we examine the tradeoff between robustness and computational complexity for curve- and shock-based representations. Our results indicate that the additional computational effort required in shock-graph matching is worthwhile in the presence of large amount variations, in particular those involving the presence of articulation or rearrangement of parts. However, when the space of variations is smaller, curve matching is a better strategy due to its lower complexity and roughly equivalent recognition rate.

Estimating the Rate of Gene Conversion on Human Chromosome 21

There is a growing recognition that gene conversion can be an important factor in shaping fine-scale patterns of linkage disequilibrium in the human genome. We devised simple multilocus summary statistics for estimating gene-conversion rates from genomewide polymorphism data sets. In addition to being computationally feasible for very large data sets, these summaries were designed to yield robust estimates of gene-conversion rates in the presence of variation in crossing-over rates. Using our summaries, we analyzed 21,840 biallelic single-nucleotide polymorphisms (SNPs) on human chromosome 21. Our results indicate that models including both crossing over and gene conversion fit the overall short-range data (0-5 kb) of chromosome 21 much better than do models including crossing over alone. The estimated ratio of gene-conversion rate to crossing-over rate has a range of 1.6-9.4, depending on the assumed conversion tract length (in the range of 500-50 bp). Removal of the 5,696 SNPs that occur in known mutational hotspots (CpG sites) did not significantly change our conclusions, suggesting that recurrent mutations alone cannot explain our data.