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Second Moment (second + moment)
Selected AbstractsThe Impact of Uncertainty ShocksECONOMETRICA, Issue 3 2009Nicholas Bloom Uncertainty appears to jump up after major shocks like the Cuban Missile crisis, the assassination of JFK, the OPEC I oil-price shock, and the 9/11 terrorist attacks. This paper offers a structural framework to analyze the impact of these uncertainty shocks. I build a model with a time-varying second moment, which is numerically solved and estimated using firm-level data. The parameterized model is then used to simulate a macro uncertainty shock, which produces a rapid drop and rebound in aggregate output and employment. This occurs because higher uncertainty causes firms to temporarily pause their investment and hiring. Productivity growth also falls because this pause in activity freezes reallocation across units. In the medium term the increased volatility from the shock induces an overshoot in output, employment, and productivity. Thus, uncertainty shocks generate short sharp recessions and recoveries. This simulated impact of an uncertainty shock is compared to vector autoregression estimations on actual data, showing a good match in both magnitude and timing. The paper also jointly estimates labor and capital adjustment costs (both convex and nonconvex). Ignoring capital adjustment costs is shown to lead to substantial bias, while ignoring labor adjustment costs does not. [source] MODFLOW 2000 Head Uncertainty, a First-Order Second Moment MethodGROUND WATER, Issue 3 2003Harry S. Glasgow A computationally efficient method to estimate the variance and covariance in piezometric head results computed through MODFLOW 2000 using a first-order second moment (FOSM) approach is presented. This methodology employs a first-order Taylor series expansion to combine model sensitivity with uncertainty in geologic data. MOD-FLOW 2000 is used to calculate both the ground water head and the sensitivity of head to changes in input data. From a limited number of samples, geologic data are extrapolated and their associated uncertainties are computed through a conditional probability calculation. Combining the spatially related sensitivity and input uncertainty produces the variance-covariance matrix, the diagonal of which is used to yield the standard deviation in MODFLOW 2000 head. The variance in piezometric head can be used for calibrating the model, estimating confidence intervals, directing exploration, and evaluating the reliability of a design. A case study illustrates the approach, where aquifer transmis-sivity is the spatially related uncertain geologic input data. The FOSM methodology is shown to be applicable for calculating output uncertainty for (1) spatially related input and output data, and (2) multiple input parameters (trans-missivity and recharge). [source] Electron localization and the second moment of the exchange hole,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2009J. G. ÁngyánArticle first published online: 16 APR 200 Abstract The localization tensor, which is a global measure of the itinerant character of the electrons, has been defined by Resta as the second cumulant moment of the position operator per electron. It seems to be a meaningful parameter not only for solids but also for finite molecular systems. In the independent-particle limit, this quantity can be interpreted as the density-weighted average of the second moment of the exchange hole. After examining several possible local measures based on the moment analysis of the exchange hole, it turns out that the density weighted squared exchange hole dipole moment might be a useful local indicator of electron localization. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Modelling Overdispersion for Complex Survey DataINTERNATIONAL STATISTICAL REVIEW, Issue 3 2001E.A. Molina Summary The population characteristics observed by selecting a complex sample from a finite identified population are the result of at least two processes: the process which generates the values attached to the units in the finite population, and the process of selecting the sample of units from the population. In this paper we propose that the resulting observations by viewed as the joint realization of both processes. We overcome the inherent difflculty in modelling the joint processes of generation and selection by exploring second moment and other simplifying assumptions. We obtain general expressions for the mean and covariance function of the joint processes and show that several overdispersion models discussed in the literature for the analysis of complex surveys are a direct consequence of our formulation, undere particular sampling schemes and population structures. Résumé Les caracté d'une population sont observées grâce à un échantillon complexe sélectionnéâ partir d'une poplation finie. Ces caractéristiques sont le résultat de l'échantillon des unités de ette population. Dans cet article, nous considérons que l'observation globale peut être vue comme une réalisation simultanée de ces deux processus. Nous tentons de surmonter la difficulté intrinsèque liée à la modélisation du double processus de génération et de sélection par une étude du moment d'ordre deux et en considérant d'autres hypothèses simplificatrices. Nous obtenons une expression générale pour la moyenne et la covariance liée au sondage complexes, sont une conséquence directe de notre formulation, losque l'on considère un plan de sondage particulier et une population ayant une structure spécifique. [source] Exercise When Young Provides Lifelong Benefits to Bone Structure and Strength,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2007Stuart J Warden PT Abstract Short-term exercise in growing rodents provided lifelong benefits to bone structure, strength, and fatigue resistance. Consequently, exercise when young may reduce the risk for fractures later in life, and the old exercise adage of "use it or lose it" may not be entirely applicable to the skeleton. Introduction: The growing skeleton is most responsive to exercise, but low-trauma fractures predominantly occur in adults. This disparity has raised the question of whether exercised-induced skeletal changes during growth persist into adulthood where they may have antifracture benefits. This study investigated whether brief exercise during growth results in lifelong changes in bone quantity, structure, quality, and mechanical properties. Materials and Methods: Right forearms of 5-week-old Sprague-Dawley rats were exercised 3 days/week for 7 weeks using the forearm axial compression loading model. Left forearms were internal controls and not exercised. Bone quantity (mineral content and areal density) and structure (cortical area and minimum second moment of area [IMIN]) were assessed before and after exercise and during detraining (restriction to home cage activity). Ulnas were removed after 92 weeks of detraining (at 2 years of age) and assessed for bone quality (mineralization) and mechanical properties (ultimate force and fatigue life). Results: Exercise induced consistent bone quantity and structural adaptation. The largest effect was on IMIN, which was 25.4% (95% CI, 15.6,35.3%) greater in exercised ulnas compared with nonexercised ulnas. Bone quantity differences did not persist with detraining, whereas all of the absolute difference in bone structure between exercised and nonexercised ulnas was maintained. After detraining, exercised ulnas had 23.7% (95% CI, 13.0,34.3%) greater ultimate force, indicating enhanced bone strength. However, exercised ulnas also had lower postyield displacement (,26.4%; 95% CI, ,43.6% to ,9.1%), indicating increased brittleness. This resulted from greater mineralization (0.56%; 95% CI, 0.12,1.00%), but did not influence fatigue life, which was 10-fold greater in exercised ulnas. Conclusions: These data indicate that exercise when young can have lifelong benefits on bone structure and strength, and potentially, fracture risk. They suggest that the old exercise adage of "use it or lose it" may not be entirely applicable to the skeleton and that individuals undergoing skeletal growth should be encouraged to perform impact exercise. [source] Spatial distributions of mean age and higher moments in steady continuous flowsAICHE JOURNAL, Issue 10 2010M. Liu Abstract Transport equations and boundary conditions for spatial distribution of age moments in steady continuous flows are derived. Mean age is the first moment. The coefficient of variation is obtained from the second moment. Mixing-cup averaged mean age and higher moments across the exit plane are identical to the corresponding moments of the residence-time distribution. Numerical solutions for a 2-D (two-dimensional) reactor are studied and compared with those from a transient tracer equation. Agreement is excellent. Local tracer distribution function curves reveal that mean age is located on the long tail for both convection dominated short circuiting paths and diffusion dominated dead zones. Computing cost for the mean age and higher moment equations is orders of magnitude lower than that for the transient tracer concentration equation, making this mean age method an efficient tool to study mixing in steady continuous flow systems. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] NMR search for polymorphic phase transformations in chlorpropamide form-A at high pressuresJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2009sicki Abstract The high-pressure effects on chlorpropamide (C10H13ClN2O3S) form-A have been studied by 1H NMR spectroscopy at high pressures up to 800 MPa in the temperature range 90,300 K. A study of the NMR second moment and spin-lattice relaxation time has been completed by a calculation of the steric hindrances for molecular reorientations and simulations of the second moment of the NMR line by the Monte,Carlo method, which enabled a precise description of molecular dynamics in the compound studied. Reorientations of the methyl group, oscillations and reorientations of the chlorophenyl ring and reorientations of the propyl group have been revealed and respective activation parameters extracted. No phase transformation of the compound form-A has been detected. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1426,1437, 2009 [source] NMR spectroscopy of citrate in solids: cross-polarization kinetics in weakly coupled systemsMAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2008Jian Feng Abstract Solid-state NMR spectroscopy is a potentially powerful method for obtaining molecular level structural information crucial for understanding the specific relationship between calcite crystals and occluded organic molecules that are important in biomineralization and biomimetic materials. In this work, a method is developed based on cross-polarization/magic angle spinning (CP/MAS) NMR to measure the heteronuclear distances and obtain structural information for large intracrystalline citrate defects in a synthetic calcite/citrate composite. Using compounds with well-characterized crystal structures, Mg(II) citrate and Sr(II) citrate, a correlation is established between TIS, the CP time, and M2IS, the van Vleck heteronuclear dipolar second moment, which contains distance and structural information. This correlation is supported by peak assignments obtained from calculations of the 13C chemical shifts for crystalline Mg(II) citrate. On the basis of TIS,1versusM2IS correlation, measurement of TIS for carbonate ions associated with citrate defects in a calcite(13C-enriched)/citrate coprecipitate yields an estimate for the distance between citrate and the nearest carbonate carbon that indicates close spatial proximity and provides useful constraints for future computational study. The applicability of TIS,1versusM2IS correlations to other weakly coupled spin-1/2 systems is discussed in terms of the effects of 1H homonuclear dipolar coupling, using the CP kinetics of Zn(II) dihydroxybenzoate and kaolinite for comparison. The results suggest a limited range of correlation constants and indicate that quantitative information can be obtained from CP/MAS kinetics obtained under similar experimental conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] 1H NMR study of internal motions and quantum rotational tunneling in (CH3)4NGeCl3MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2008K. J. Mallikarjunaiah Abstract (CH3)4NGeCl3 is prepared, characterized and studied using 1H NMR spin lattice relaxation time and second moment to understand the internal motions and quantum rotational tunneling. Proton second moment is measured at 7 MHz as function of temperature in the range 300,77 K and spin lattice relaxation time (T1) is measured at two Larmor frequencies, as a function of temperature in the range 270,17 K employing a homemade wide-line/pulsed NMR spectrometers. T1 data are analyzed in two temperature regions using relevant theoretical models. The relaxation in the higher temperatures (270,115 K) is attributed to the hindered reorientations of symmetric groups (CH3 and (CH3)4N). Broad asymmetric T1 minima observed below 115 K down to 17 K are attributed to quantum rotational tunneling of the inequivalent methyl groups. Copyright © 2007 John Wiley & Sons, Ltd. [source] The SAURON project , IV.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006The mass-to-light ratio, lenticular galaxies, the Fundamental Plane of elliptical, the virial mass estimator ABSTRACT We investigate the well-known correlations between the dynamical mass-to-light ratio (M/L) and other global observables of elliptical (E) and lenticular (S0) galaxies. We construct two-integral Jeans and three-integral Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field stellar kinematics to about one effective (half-light) radius Re. They have well-calibrated I -band Hubble Space Telescope WFPC2 and large-field ground-based photometry, accurate surface brightness fluctuation distances, and their observed kinematics is consistent with an axisymmetric intrinsic shape. All these factors result in an unprecedented accuracy in the M/L measurements. We find a tight correlation of the form (M/L) = (3.80 ± 0.14) × (,e/200 km s,1)0.84±0.07 between the M/L (in the I band) measured from the dynamical models and the luminosity-weighted second moment ,e of the LOSVD within Re. The observed rms scatter in M/L for our sample is 18 per cent, while the inferred intrinsic scatter is ,13 per cent. The (M/L),,e relation can be included in the remarkable series of tight correlations between ,e and other galaxy global observables. The comparison of the observed correlations with the predictions of the Fundamental Plane (FP), and with simple virial estimates, shows that the ,tilt' of the FP of early-type galaxies, describing the deviation of the FP from the virial relation, is almost exclusively due to a real M/L variation, while structural and orbital non-homology have a negligible effect. When the photometric parameters are determined in the ,classic' way, using growth curves, and the ,e is measured in a large aperture, the virial mass appears to be a reliable estimator of the mass in the central regions of galaxies, and can be safely used where more ,expensive' models are not feasible (e.g. in high-redshift studies). In this case the best-fitting virial relation has the form (M/L)vir= (5.0 ± 0.1) ×Re,2e/(LG), in reasonable agreement with simple theoretical predictions. We find no difference between the M/L of the galaxies in clusters and in the field. The comparison of the dynamical M/L with the (M/L)pop inferred from the analysis of the stellar population, indicates a median dark matter fraction in early-type galaxies of ,30 per cent of the total mass inside one Re, in broad agreement with previous studies, and it also shows that the stellar initial mass function varies little among different galaxies. Our results suggest a variation in M/L at constant (M/L)pop, which seems to be linked to the galaxy dynamics. We speculate that fast-rotating galaxies have lower dark matter fractions than the slow-rotating and generally more-massive ones. If correct, this would suggest a connection between the galaxy assembly history and the dark matter halo structure. The tightness of our correlation provides some evidence against cuspy nuclear dark matter profiles in galaxies. [source] A queuing model for due date control in a multiserver repair shopNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2001Joris Keizers This paper deals with a repair shop with multiple parallel servers, which has to carry out planned overhauls. Each overhaul consists of a large number of maintenance jobs. The overhaul process is interrupted by randomly arriving emergency jobs. To control the delivery performance of the overhauls, knowledge about the overhaul makespan distribution should be available. Using a 2-dimensional Markov model, we derive the first and second moment of the overhaul makespan analytically for the case that the repair times of all overhaul jobs are identically and exponentially distributed. For the case of nonidentical repair time distributions, an approximation is presented. Simulation shows that the makespan distribution fitted on these moments gives an excellent approximation. © John Wiley & Sons, Inc. Naval Research Logistics 48: 281,282, 2001 [source] Variation mode and effect analysis: an application to fatigue life predictionQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 2 2009Pär Johannesson Abstract We present an application of the probabilistic branch of variation mode and effect analysis (VMEA) implemented as a first-order, second-moment reliability method. First order means that the failure function is approximated to be linear around the nominal values with respect to the main influencing variables, while second moment means that only means and variances are taken into account in the statistical procedure. We study the fatigue life of a jet engine component and aim at a safety margin that takes all sources of prediction uncertainties into account. Scatter is defined as random variation due to natural causes, such as non-homogeneous material, geometry variation within tolerances, load variation in usage, and other uncontrolled variations. Other uncertainties are unknown systematic errors, such as model errors in the numerical calculation of fatigue life, statistical errors in estimates of parameters, and unknown usage profile. By treating also systematic errors as random variables, the whole safety margin problem is put into a common framework of second-order statistics. The final estimated prediction variance of the logarithmic life is obtained by summing the variance contributions of all sources of scatter and other uncertainties, and it represents the total uncertainty in the life prediction. Motivated by the central limit theorem, this logarithmic life random variable may be regarded as normally distributed, which gives possibilities to calculate relevant safety margins. Copyright © 2008 John Wiley & Sons, Ltd. [source] Some bounds on the coupon collector problemRANDOM STRUCTURES AND ALGORITHMS, Issue 2 2004Servet Martinez Abstract This work addresses on the coupon collector problem and its generalization introduced by Flajolet, Gardy, and Thimonier. In our main results, we show a ratio limit theorem for the random time of the generalized coupon collector problem, and, further, we give the leading term and the geometric rate for the distribution of this random time, when the number of throws is large. For the classical coupon collector problem, we give a bound on the conditional second moment for the number of visits to the coupons, relying strongly on a result of Holst on extremal distributions. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004 [source] A Measure of Fundamental Volatility in the Commercial Property MarketREAL ESTATE ECONOMICS, Issue 4 2003Shaun A. Bond The low level of volatility observed in appraisal-based commercial property indices relative to other asset classes has been frequently noted and extensively commented on in the real estate finance literature. However, the volatility of such commercial property indices is only one source of information on the second moment of commercial property returns. The volatility of securitized property returns forms another potential source of information, though there is some uncertainty about how closely the volatility of securitized returns may match the volatility of the underlying asset. Each measure of volatility has a potential source of noise associated with it. This paper proposes a fundamental measure of volatility for the commercial property market by using a stochastic volatility model to filter out the signal in the different sources of volatility information. This allows for different measures of volatility to be decomposed into transitory noise and unobserved fundamental volatility. The suitability of such an approach and the properties of the underlying fundamental volatility series are analyzed using data from the U.K. property market. [source] Variance scaling in shallow-cumulus-topped mixed layersTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 628 2007R. A. J. Neggers Abstract Scaling of thermodynamic variance in shallow-cumulus-topped mixed layers is studied using large-eddy simulation (LES). First, the performance of the top-down scaling (the turbulent flux at mixed-layer top divided by w*) is evaluated for transient shallow-cumulus convection over land. The results indicate that this scaling fails to capture all the variance in the top half of the mixed layer when shallow cumulus clouds are present. A variance-budget analysis is then performed, to derive a new scaling for the variance at mixed-layer top, which differs from the standard top-down scaling by a factor of one Richardson number. The essential new features of the proposed scaling are that the local vertical gradient is retained and that a balance is assumed between gradient production of variance and removal by transport and dissipation, using an adjustment time-scale given by w*/h. Evaluation against LES for a range of different cases, including a dry convective boundary layer as well as steady-state marine and transient continental shallow cumulus, reveals a data-collapse of the newly-scaled variance, for all hours and all cases in the top half of the mixed layer. The corresponding vertical structure is shown to resemble a power-law function. The results suggest that the structure of variance in the dry convective boundary layer is similar to that in the sub-cloud mixed layer. In transient situations, the scaling reproduces the time-development of variance at sub-cloud mixed-layer top. The new cloud-base variance scale is then further interpreted in the context of statistical cloud schemes, which depend on the variance as the second moment of the associated probability density function. The results suggest that the area fraction of the moist convective thermals uniquely depends on the ratio of cloud-base transition-layer depth to sub-cloud mixed-layer depth. This puts ,valve'- or ventilation-type closures for the cloud-base mass flux in the context of the variance budget for the sub-cloud layer. Copyright © 2007 Royal Meteorological Society [source] Subexponential Distributions , Large Deviations with Applications to Insurance and Queueing ModelsAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 1 2004Aleksandras Baltr Summary This paper presents a fine large-deviations theory for heavy-tailed distributions whose tails are heavier than exp(,,t and have finite second moment. Asymptotics for first passage times are derived. The results are applied to estimate the finite time ruin probabilities in insurance as well as the busy period in a GI/G/1 queueing model. [source] Progress in the Understanding of Drug,Receptor Interactions, Part,2: Experimental and Theoretical Electrostatic Moments and Interaction Energies of an Angiotensin II Receptor Antagonist (C30H30N6O3S)CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2007Raffaella Soave Dr. Abstract A combined experimental and theoretical charge density study of an angiotensin II receptor antagonist (1) is presented focusing on electrostatic properties such as atomic charges, molecular electric moments up to the fourth rank and energies of the intermolecular interactions, to gain an insight into the physical nature of the drug,receptor interaction. Electrostatic properties were derived from both the experimental electron density (multipole refinement of X-ray data collected at T=17,K) and the ab initio wavefunction (single molecule and fully periodic calculations at the DFT level). The relevance of S,,,O and S,,,N intramolecular interactions on the activity of 1 is highlighted by using both the crystal and gas-phase geometries and their electrostatic nature is documented by means of QTAIM atomic charges. The derived electrostatic properties are consistent with a nearly spherical electron density distribution, characterised by an intermingling of electropositive and -negative zones rather than by a unique electrophilic region opposed to a nucleophilic area. This makes the first molecular moment scarcely significant and ill-determined, whereas the second moment is large, significant and highly reliable. A comparison between experimental and theoretical components of the third electric moment shows a few discrepancies, whereas the agreement for the fourth electric moment is excellent. The most favourable intermolecular bond is show to be an NH,,,N hydrogen bond with an energy of about 50,kJ,mol,1. Key pharmacophoric features responsible for attractive electrostatic interactions include CH,,,X hydrogen bonds. It is shown that methyl and methylene groups, known to be essential for the biological activity of the drug, provide a significant energetic contribution to the total binding energy. Dispersive interactions are important at the thiophene and at both the phenyl fragments. The experimental estimates of the electrostatic contribution to the intermolecular interaction energies of six molecular pairs, obtained by a new model proposed by Spackman, predict the correct relative electrostatic energies with no exceptions. [source] Infinite time aggregation for the critical Patlak-Keller-Segel model in ,2COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 10 2008Adrien Blanchet We analyze the two-dimensional parabolic-elliptic Patlak-Keller-Segel model in the whole Euclidean space ,2. Under the hypotheses of integrable initial data with finite second moment and entropy, we first show local-in-time existence for any mass of "free-energy solutions," namely weak solutions with some free-energy estimates. We also prove that the solution exists as long as the entropy is controlled from above. The main result of the paper is to show the global existence of free-energy solutions with initial data as before for the critical mass 8,/,. Actually, we prove that solutions blow up as a delta Dirac at the center of mass when t , , when their second moment is kept constant at any time. Furthermore, all moments larger than 2 blowup as t , , if initially bounded. © 2007 Wiley Periodicals, Inc. [source] The Boys from Bothaville, or the Rise and Fall of King Maize: A South African StoryJOURNAL OF AGRARIAN CHANGE, Issue 4 2004HENRY BERNSTEIN This paper tells the story, for the first time, of a maverick maize farmers' association in South Africa during the period of apartheid. NAMPO (National Maize Producers' Organization), that grew out of SAMPI (South African Maize Producers' Institute), ultimately achieved a unique, if short-lived, breach in the normal operations of ,organized agriculture': a set of relations and practices that bound together white farmers, the National Party and the state. The paper provides an account of SAMPI/NAMPO's project of ,King Maize' and an explanation of its fall after a brief period of victory from 1981 to 1985. This explanation draws on broader patterns of agrarian change in contemporary capitalism combined with the fracturing of the original agrarian bloc of apartheid in the 1980s, marking the end of a ,second moment' of South Africa's version of a Prussian path of capitalist development. [source] Time series analysis of wind speed with time-varying turbulenceENVIRONMETRICS, Issue 2 2006Bradley T. Ewing Abstract The characterization of the time series properties of wind speed, in terms of the mean and variance, is important and relevant to both engineers and businesses. This research investigates the first and second moments of the Texas Tech WERFL wind speed data utilizing the ARMA-GARCH-in-mean framework. The methodology allows the conditional variance to depend on the size of past shocks (i.e. gusts) in the series. Results have important implications for wind energy production as well as for the operational and financial hedging strategies of companies exposed to wind-related risk. The findings can be summarized as follows: (i) mean wind speeds measured at different heights above ground exhibit persistence and are highly dependent on immediate past wind speed values; (ii) regardless of the height at which the data were collected, wind speed exhibits time-varying variance; (iii) persistence in conditional variance increases with height at which the data were collected; (iv) there is strong evidence that conditional volatility is positively correlated with mean wind speed while the magnitude of this relationship declines with height. Copyright © 2005 John Wiley & Sons, Ltd. [source] A test of two methods of radiographically deriving long bone cross-sectional properties compared to direct sectioning of the diaphysisINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 5 2002Jay T. Stock Abstract Numerous studies have made use of cross-sectional geometry to describe the distribution of cortical bone in long bone diaphyses. Several methods can be used to measure or estimate cross-sectional contours. Direct sectioning (DSM) of the diaphysis is not appropriate in most curatorial contexts, and is commonly substituted with methods based upon bi-planar radiography: a latex cast method (LCM) or an eccentric elliptical method (EEM). Previous studies have demonstrated that the EEM provides accurate estimates of area measurements, while providing less accurate estimates of second moments of area (Biknevicius & Ruff, 1992; Runestad et al., 1993; Lazenby, 1997). The LCM has been commonly employed, as a way to estimate section contours more accurately, yet the validity of this method has not been adequately documented. This study measures the agreement of these methods against DSM of long bone diaphyses using 21 sections of canine tibiae derived from a study of total hip arthroplasty. The accuracy and agreement of these methods is evaluated using reduced major axis regression, paired sample t-tests and tests for agreement (Bland & Altman, 1986). The results illustrate that the LCM provides a reasonable estimate of cross-sectional dimensions, producing cross-sectional properties that are on average within 5% of properties derived from the DSM. The EEM is found to provide adequate estimates of true cross-sectional areas, but poor estimates of second moments of area. The use of the LCM is supported for all cross-sectional properties, but the EEM is only accurate in total area, cortical area and percent cortical area estimates. Copyright © 2002 John Wiley & Sons, Ltd. [source] Warranty reserves for nonstationary sales processesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2002Shau-Shiang Ja Estimation of warranty costs, in the event of product failure within the warranty period, is of importance to the manufacturer. Costs associated with replacement or repair of the product are usually drawn from a warranty reserve fund created by the manufacturer. Considering a stochastic sales process, first and second moments (and thereby the variance) are derived for the manufacturer's total discounted warranty cost of a single sale for single-component items under four different warranty policies from a manufacturer's point of view. These servicing strategies represent a renewable free-replacement, nonrenewable free-replacement, renewable pro-rata, and a nonrenewable minimal-repair warranty plans. The results are extended to determine the mean and variance of total discounted warranty costs for the total sales over the life cycle of the product. Furthermore, using a normal approximation, warranty reserves necessary for a certain protection level, so that reserves are not completely depleted, are found. Results and their managerial implications are studied through an extensive example. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 499,513, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10023 [source] Estimating body mass in subadult human skeletonsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Gwen Robbins Abstract Methods for estimating body mass from the human skeleton are often required for research in biological or forensic anthropology. There are currently only two methods for estimating body mass in subadults: the width of the distal femur metaphysis is useful for individuals 1,12 years of age and the femoral head is useful for older subadults. This article provides age-structured formulas for estimating subadult body mass using midshaft femur cross-sectional geometry (polar second moments of area). The formulas were developed using data from the Denver Growth Study and their accuracy was examined using an independent sample from Franklin County, Ohio. Body mass estimates from the midshaft were compared with estimates from the width of the distal metaphysis of the femur. Results indicate that accuracy and bias of estimates from the midshaft and the distal end of the femur are similar for this contemporary cadaver sample. While clinical research has demonstrated that body mass is one principle factor shaping cross-sectional geometry of the subadult midshaft femur, clearly other biomechanical forces, such as activity level, also play a role. Thus formulas for estimating body mass from femoral measurements should be tested on subadult populations from diverse ecological and cultural circumstances to better understand the relationship between body mass, activity, diet, and morphology during ontogeny. Am J Phys Anthropol 143:146,150, 2010. © 2010 Wiley-Liss, Inc. [source] Technical note: The effect of midshaft location on the error ranges of femoral and tibial cross-sectional parametersAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010Vladimír Sládek Abstract In comparing long-bone cross-sectional geometric properties between individuals, percentages of bone length are often used to identify equivalent locations along the diaphysis. In fragmentary specimens where bone lengths cannot be measured, however, these locations must be estimated more indirectly. In this study, we examine the effect of inaccurately located femoral and tibial midshafts on estimation of geometric properties. The error ranges were compared on 30 femora and tibiae from the Eneolithic and Bronze Age. Cross-sections were obtained at each 1% interval from 60 to 40% of length using CT scans. Five percent of deviation from midshaft properties was used as the maximum acceptable error. Reliability was expressed by mean percentage differences, standard deviation of percentage differences, mean percentage absolute differences, limits of agreement, and mean accuracy range (MAR) (range within which mean deviation from true midshaft values was less than 5%). On average, tibial cortical area and femoral second moments of area are the least sensitive to positioning error, with mean accuracy ranges wide enough for practical application in fragmentary specimens (MAR = 40,130 mm). In contrast, tibial second moments of area are the most sensitive to error in midshaft location (MAR = 14,20 mm). Individuals present significant variation in morphology and thus in error ranges for different properties. For highly damaged fossil femora and tibiae we recommend carrying out additional tests to better establish specific errors associated with uncertain length estimates. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source] TIME VARIABILITY IN MARKET RISK AVERSIONTHE JOURNAL OF FINANCIAL RESEARCH, Issue 3 2009Dave Berger Abstract We adopt realized covariances to estimate the coefficient of risk aversion across portfolios and through time. Our approach yields second moments that are free from measurement error and not influenced by a specified model for expected returns. Supporting the permanent income hypothesis, we find risk aversion responds to consumption-smoothing behavior. As income increases, or as the consumption-to-income ratio falls, relative risk aversion decreases. We also document variation in risk aversion across portfolios: risk aversion is highest for small and value portfolios. [source] Price discovery in the hang seng index markets: Index, futures, and the tracker fundTHE JOURNAL OF FUTURES MARKETS, Issue 9 2004Raymond W. So In this paper, price discovery among the Hang Seng Index markets is investigated using the Hasbrouck and Gonzalo and Granger common-factor models and the multivariate generalized autoregressive conditional heteroskedasticity (M-GARCH) model. Minute-by-minute data from the Hang Seng Index, Hang Seng Index futures, and the tracker fund show that the movements of the three markets are interrelated. The futures markets contain the most information, followed by the spot market. The tracker fund does not contribute to the price discovery process. The three markets exhibit spillover effects, indicating that their second moments are linked, even though the flow of information from the tracker fund to the other markets is minimal. Overall results suggest that the three markets have different degrees of information processing abilities, although they are governed by the same set of macroeconomic fundamentals. © 2004 Wiley Periodicals, Inc. Jrl Fut Mark 24:887,907, 2004 [source] Multiperiod hedging with futures contractsTHE JOURNAL OF FUTURES MARKETS, Issue 12 2002Aaron Low The hedging problem is examined where futures prices obey the cost-of-carry model. The resultant hedging model explicitly incorporates maturity effects in the futures basis. Formulas for the optimal static and dynamic hedges are derived. Although these formulas are developed for the case of direct hedging, the framework used is sufficiently flexible so that these formulas can be applied to many cross-hedging situations. The performance of the model is compared with that of several other models for two hedging scenarios: one involving a financial asset and the other involving a commodity. In both cases, significant maturity effects were found in the first and second moments of the futures basis. Our hedging formulas outperformed other hedging strategies on an ex-ante basis. © 2002 Wiley Periodicals, Inc. Jrl Fut Mark 22:1179,1203, 2002 [source] Return and Volatility Dynamics in the Spot and Futures Markets in Australia: An Intervention Analysis in a Bivariate EGARCH-X FrameworkTHE JOURNAL OF FUTURES MARKETS, Issue 9 2001Ramaprasad Bhar This article provides evidence of linkages between the equity market and the index futures market in Australia, where the futures market has experienced a major structural event due to the futures contract respecification. A bivariate Exponential Generalized Autoregressive Conditional Heteroskedasticity (EGARCH) model is developed that includes a cointegrating residual as an explanatory variable for both the conditional mean and the conditional variance. The conditional mean returns from both markets are influenced by the long-run equilibrium relationship, and these markets are informationally linked through the second moments. The crossmarket spillovers exhibit asymmetric behavior in that the volatility responses to past standardized innovations are different for market advances and market retreats. An intervention analysis shows that some of the parameters describing the return-generating process have shifted after the contract respecification by the futures exchange. © 2001 John Wiley & Sons, Inc. Jrl Fut Mark 21:833,850, 2001 [source] TIME-VARYING UNCERTAINTY AND THE CREDIT CHANNELBULLETIN OF ECONOMIC RESEARCH, Issue 4 2008Victor Dorofeenko E4; E5; E2 ABSTRACT We extend the Carlstrom and Fuerst (American Economic Review, 1997, 87, pp. 893,910) agency cost model of business cycles by including time-varying uncertainty in the technology shocks that affect capital production. We first demonstrate that standard linearization methods can be used to solve the model yet second moments enter the economy's equilibrium policy functions. We then demonstrate that an increase in uncertainty causes, ceteris paribus, a fall in investment supply. We also show that persistence of uncertainty affects both quantitatively and qualitatively the behaviour of the economy. [source] | |||||||||||||||||||||||||