bluuebunny/crossref_metadata_2025 huggingface dataset:
Topographic Instability: Tests
Authors: Egger Joseph , Hoinka Klaus-Peter
Published: February 2008

Theories of topographic instability predict growth of perturbations of mean flow and wave modes due to their interaction with mountains under favorable conditions. Mountain torques form an important part of this interaction. It has been suggested that topographic instabilities contribute significantly to the subseasonal variability of the atmosphere but observational tests of topographic instability mechanisms have not yet been performed. Greenland is selected as a test bed because of its isolation, simple shape, and appropriate size. The observed flow development during mountain torque events is investigated in terms of a regression analysis. Changes of axial angular momentum and zonal mean wind with respect to the torques are monitored for domains covering Greenland since the acceleration (deceleration) of the regional zonal flow in response to a positive (negative) torque is a key feature of topographic instability. In particular, southern and northern analysis domains are considered separately in order to test “dipole” instability theories in addition to “monopole” situations where the meridional extent of the pressure perturbations is similar to that of Greenland. Moreover, zonal bands are used as analysis domains. It is found that the response of the zonal wind to the torques is quite small and not systematic. There is no evidence of monopole or dipole topographic instability. A less detailed analysis for the Tibetan Plateau leads to the same result. Reasons for these negative outcomes are discussed as are shortcomings of the tests.
A New Rossby Wave–Breaking Interpretation of the North Atlantic Oscillation
Authors: Woollings Tim , Hoskins Brian , Blackburn Mike , Berrisford Paul
Published: February 2008

This paper proposes the hypothesis that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wave–breaking events over the North Atlantic. These events lead to synoptic situations similar to midlatitude blocking that are referred to as high-latitude blocking episodes. A positive NAO is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic, unblocked situation. A negative NAO is a description of periods in which episodes occur frequently. A similar, but weaker, relationship exists between wave breaking over the Pacific and the west Pacific pattern.

Evidence is given to support this hypothesis by using a two-dimensional potential-vorticity-based index to identify wave breaking at various latitudes. This is applied to Northern Hemisphere winter data from the 40-yr ECMWF Re-Analysis (ERA-40), and the events identified are then related to the NAO.

Certain dynamical precursors are identified that appear to increase the likelihood of wave breaking. These suggest mechanisms by which variability in the tropical Pacific, and in the stratosphere, could affect the NAO.
Uniform Asymptotics for the Linear Kelvin Wave in Spherical Geometry
Authors: Boyd John P. , Zhou Cheng
Published: February 2008

The Kelvin wave is the gravest eigenmode of Laplace’s tidal equation. It is widely observed in both the ocean and the atmosphere. In the absence of mean currents, the Kelvin wave depends on two parameters: the zonal wavenumber s (always an integer) and Lamb’s parameter ε. An asymptotic approximation valid in the limit s2 + ε ≫ 1 is derived that generalizes the usual “equatorial wave” limit that ε → ∞ for fixed s. Just as shown for Rossby waves two decades ago, the width of the Kelvin wave is (ε + s2)−1/4 rather than ε−1/4 as in the classical equatorial beta-plane approximation.
Collisions of Cloud Droplets in a Turbulent Flow. Part V: Application of Detailed Tables of Turbulent Collision Rate Enhancement to Simulation of Droplet Spectra Evolution
Authors: Pinsky M. , Khain A. , Krugliak H.
Published: February 2008

The present study is a continuation of the series of studies dedicated to the investigation of cloud droplet collisions in turbulent flow with characteristics that are typical of real clouds. Detailed tables of collision kernels and collision efficiencies calculated in the presence of hydrodynamic interaction of droplets are presented. These tables were calculated for a wide range of turbulent parameters. To illustrate the sensitivity of droplet size distribution (DSD) evolution to the turbulence-induced increase in the collision rate, simulations of DSD evolution are preformed by solving the stochastic kinetic equation for collisions. The results can be applied to cloud modeling. The tables of collision efficiencies and collision kernels are available upon request. Some unsolved problems related to collisions of droplets and ice hydrometeors in turbulent clouds are discussed in the conclusion.
Impact of the Atmospheric Boundary Layer on Mountain Waves
Authors: Jiang Qingfang , Smith Ronald B. , Doyle James D.
Published: February 2008

Interaction between mountain waves and the atmospheric boundary layer (BL) has been investigated using a mesoscale model with BL parameterizations and analytical BL models. The impact of the BL diagnosed from the mesoscale model simulations is in qualitative agreement with the analytical BL models. In general, for stratified flow over a mesoscale ridge, the influence of the BL tends to shift wave patterns upstream, decrease the wave drag by up to 60% and the momentum flux above the BL top by up to 80%, and significantly delay the onset of wave breaking.

It has been demonstrated that the BL effect is governed by four nondimensional parameters, namely, the nondimensional BL depth, BL shape factor, nonhydrostatic parameter, and frictional adjustment parameter. The BL effect is stronger over a rougher surface, which creates a deeper BL with a smaller shape factor (i.e., slower BL flow). The scale dependence of the BL effect is governed by the nonhydrostatic and frictional adjustment parameters. For narrow terrain, the BL reduces mountain drag through rapid inertial adjustment and behaves like an inviscid shear layer, and the momentum reduction across the BL is negligible. The attenuation of the momentum flux across the BL is more substantial over a wider ridge because of the increasing importance of frictional adjustment. The BL effect decreases with increasing ridge height and for 3D terrain.
Growth of Cloud Droplets by Turbulent Collision–Coalescence
Authors: Xue Yan , Wang Lian-Ping , Grabowski Wojciech W.
Published: February 2008

An open question in cloud physics is how rain forms in warm cumulus as rapidly as it is sometimes observed. In particular, the growth of cloud droplets across the size gap from 10 to 50 μm in radius has not been fully explained. In this paper, the authors investigate the growth of cloud droplets by collision–coalescence, taking into account both the gravitational mechanism and several enhancements of the collision–coalescence rate due to air turbulence. The kinetic collection equation (KCE) is solved with an accurate bin integral method and a newly developed parameterization of turbulent collection kernel derived from direct numerical simulation of droplet-laden turbulent flows. Three other formulations of the turbulent collection kernel are also considered so as to assess the dependence of the rain initiation time on the nature of the collection kernel. The results are compared to the base case using the Hall hydrodynamical–gravitational collection kernel. Under liquid water content and eddy dissipation rate values typical of small cumulus clouds, it is found that air turbulence has a significant impact on the collection kernel and thus on the time required to form drizzle drops. With the most realistic turbulent kernel, the air turbulence can shorten the time for the formation of drizzle drops by about 40% relative to the base case, applying measures based on either the radar reflectivity or the mass-weighted drop size. A methodology is also developed to unambiguously identify the three phases of droplet growth, namely, the autoconversion phase, the accretion phase, and the larger hydrometeor self-collection phase. The important observation is that even a moderate enhancement of collection kernel by turbulence can have a significant impact on the autoconversion phase of the growth.
Aerosol Effects on Clouds, Precipitation, and the Organization of Shallow Cumulus Convection
Authors: Xue Huiwen , Feingold Graham , Stevens Bjorn
Published: February 2008

This study investigates the effects of aerosol on clouds, precipitation, and the organization of trade wind cumuli using large eddy simulations (LES). Results show that for this shallow-cumulus-under-stratocumulus case, cloud fraction increases with increasing aerosol as the aerosol number mixing ratio increases from 25 (domain-averaged surface precipitation rate ∼0.65 mm day−1) to 100 mg−1 (negligible surface precipitation). Further increases in aerosol result in a reduction in cloud fraction. It is suggested that opposing influences of aerosol-induced suppression of precipitation and aerosol-induced enhancement of evaporation are responsible for this nonmonotonic behavior.

Under clean conditions (25 mg−1), drizzle is shown to initiate and maintain mesoscale organization of cumulus convection. Precipitation induces downdrafts and cold pool outflow as the cumulus cell develops. At the surface, the center of the cell is characterized by a divergence field, while the edges of the cell are zones of convergence. Convergence drives the formation and development of new cloud cells, leading to a mesoscale open cellular structure. These zones of new cloud formation generate new precipitation zones that continue to reinforce the cellular structure. For simulations with an aerosol concentration of 100 mg−1 the cloud fields do not show any cellular organization. On average, no evidence is found for aerosol effects on the lifetime of these clouds, suggesting that cloud fraction response to changes in aerosol is tied to the frequency of convection and/or cloud size.
Gravity Currents in a Deep Anelastic Atmosphere
Authors: Bryan George H. , Rotunno Richard
Published: February 2008

This study presents analytic results for steady gravity currents in a channel using the deep anelastic equations. Results are cast in terms of a nondimensional parameter H/H0 that relates the channel depth H to a scale depth H0 (the depth at which density goes to zero in an isentropic atmosphere). The classic results based on the incompressible equations correspond to H/H0 = 0. For cold gravity currents (at the bottom of a channel), assuming energy-conserving flow, the nondimensional current depth h/H is much smaller, and nondimensional propagation speed C/(gH)1/2 is slightly smaller as H/H0 increases. For flows with energy dissipation, C/(gH)1/2 decreases as H/H0 increases, even for fixed h/H. The authors conclude that as H/H0 increases the normalized hydrostatic pressure rise in the cold pool increases near the bottom of the channel, whereas drag decreases near the top of the channel; these changes require gravity currents to propagate slower for steady flow to be maintained. From these results, the authors find that steady cold pools have a likely maximum depth of 4 km in the atmosphere (in the absence of shear). For warm gravity currents (at the top of a channel), h/H is slightly larger and C/(gH)1/2 is much larger as H/H0 increases. The authors also conduct two-dimensional numerical simulations of “lock-exchange flow” to provide an independent evaluation of the analytic results. For cold gravity currents the simulations support the analytic results. However, for warm gravity currents the simulations show unsteady behavior that cannot be captured by the analytic theory and which appears to have no analog in incompressible flow.
Toward Elimination of the Warm Bias in Historic Radiosonde Temperature Records—Some New Results from a Comprehensive Intercomparison of Upper-Air Data
Authors: Haimberger Leopold , Tavolato Christina , Sperka Stefan
Published: February 2008

The apparent cooling trend in observed global mean temperature series from radiosonde records relative to Microwave Sounding Unit (MSU) radiances has been a long-standing problem in upper-air climatology. It is very likely caused by a warm bias of radiosonde temperatures in the 1980s, which has been reduced over time with better instrumentation and correction software. The warm bias in the MSU-equivalent lower stratospheric (LS) layer is estimated as 0.6 ± 0.3 K in the global mean and as 1.0 ± 0.3 K in the tropical (20°S–20°N) mean. These estimates are based on comparisons of unadjusted radiosonde data, not only with MSU data but also with background forecast (BG) temperature time series from the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and with two new homogenized radiosonde datasets. One of the radiosonde datasets [Radiosonde Observation Correction using Reanalyses (RAOBCORE) version 1.4] employs the BG as reference for homogenization, which is not strictly independent of MSU data. The second radiosonde dataset uses the dates of the breakpoints detected by RAOBCORE as metadata for homogenization. However, it relies only on homogeneous segments of neighboring radiosonde data for break-size estimation. Therefore, adjustments are independent of satellite data.

Both of the new adjusted radiosonde time series are in better agreement with satellite data than comparable published radiosonde datasets, not only for zonal means but also at most single stations. A robust warming maximum of 0.2–0.3K (10 yr)−1 for the 1979–2006 period in the tropical upper troposphere could be found in both homogenized radiosonde datasets. The maximum is consistent with mean temperatures of a thick layer in the upper troposphere and upper stratosphere (TS), derived from M3U3 radiances. Inferred from these results is that it is possible to detect and remove most of the mean warm bias from the radiosonde records, and thus most of the trend discrepancy compared to MSU LS and TS temperature products.

The comprehensive intercomparison also suggests that the BG is temporally quite homogeneous after 1986. Only in the early 1980s could some inhomogeneities in the BG be detected and quantified.
Variability of the Meridional Overturning in the North Atlantic from the 50-Year GECCO State Estimation
Authors: Köhl Armin , Stammer Detlef
Published: February 2008

The German partner of the consortium for Estimating the Circulation and Climate of the Ocean (GECCO) provided a dynamically consistent estimate of the time-varying ocean circulation over the 50-yr period 1952–2001. The GECCO synthesis combines most of the data available during the entire estimation period with the ECCO–Massachusetts Institute of Technology (MIT) ocean circulation model using its adjoint. This GECCO estimate is analyzed here for the period 1962–2001 with respect to decadal and longer-term changes of the meridional overturning circulation (MOC) of the North Atlantic. A special focus is on the maximum MOC values at 25°N. Over this period, the dynamically self-consistent synthesis stays within the error bars of H. L. Bryden et al., but reveals a general increase of the MOC strength. The variability on decadal and longer time scales is decomposed into contributions from different processes. Changes in the model’s MOC strength are strongly influenced by the southward communication of density anomalies along the western boundary originating from the subpolar North Atlantic, which are related to changes in the Denmark Strait overflow but are only marginally influenced by water mass formation in the Labrador Sea. The influence of density anomalies propagating along the southern edge of the subtropical gyre associated with baroclinically unstable Rossby waves is found to be equally important. Wind-driven processes such as local Ekman transport explain a smaller fraction of the variability on those long time scales.
A Method for Processing Acoustic Doppler Current Profiler Velocity Data from Towed, Undulating Vehicles
Authors: Pan Jiayi , Jay David A.
Published: February 2008

The utility of the acoustic Doppler current profiler (ADCP) for sampling small time and space scales of coastal environments can be enhanced by mounting a high-frequency (1200 kHz) ADCP on an oscillating towed body. This approach requires both an external reference to convert the measured shears to velocities in the earth coordinates and a method to determine the towed body velocities. During the River Influence on the Shelf Ecosystems (RISE) project cruise, a high-frequency (1200 kHz) and narrowbeam ADCP with mode 12 sampling was mounted on a TRIAXUS oscillating towfish, which steers a 3D path behind the ship. This deployment approach extended the vertical range of the ADCP and allowed it to sample near-surface waters outside the ship’s wake. The measurements from a ship-mounted 1200-kHz narrowbeam ADCP are used as references for TRIAXUS ADCP data, and a method of overlapping bins is employed to recover the entire vertical range of the TRIAXUS ADCP. The TRIAXUS vehicle horizontal velocities are obtained by removing the derived ocean current velocity from the TRIAXUS ADCP measurements. The results show that the method is practical.
A Simulation Study Using a Local Ensemble Transform Kalman Filter for Data Assimilation in New York Harbor
Authors: Hoffman Ross N. , Ponte Rui M. , Kostelich Eric J. , Blumberg Alan , Szunyogh Istvan , Vinogradov Sergey V. , Henderson John M.
Published: February 2008

Data assimilation approaches that use ensembles to approximate a Kalman filter have many potential advantages for oceanographic applications. To explore the extent to which this holds, the Estuarine and Coastal Ocean Model (ECOM) is coupled with a modern data assimilation method based on the local ensemble transform Kalman filter (LETKF), and a series of simulation experiments is conducted. In these experiments, a long ECOM “nature” run is taken to be the “truth.” Observations are generated at analysis times by perturbing the nature run at randomly chosen model grid points with errors of known statistics. A diverse collection of model states is used for the initial ensemble. All experiments use the same lateral boundary conditions and external forcing fields as in the nature run. In the data assimilation, the analysis step combines the observations and the ECOM forecasts using the Kalman filter equations. As a control, a free-running forecast (FRF) is made from the initial ensemble mean to check the relative importance of external forcing versus data assimilation on the analysis skill. Results of the assimilation cycle and the FRF are compared to truth to quantify the skill of each.

The LETKF performs well for the cases studied here. After just a few assimilation cycles, the analysis errors are smaller than the observation errors and are much smaller than the errors in the FRF. The assimilation quickly eliminates the domain-averaged bias of the initial ensemble. The filter accurately tracks the truth at all data densities examined, from observations at 50% of the model grid points down to 2% of the model grid points. As the data density increases, the ensemble spread, bias, and error standard deviation decrease. As the ensemble size increases, the ensemble spread increases and the error standard deviation decreases. Increases in the size of the observation error lead to a larger ensemble spread but have a small impact on the analysis accuracy.
De-Aliasing of Large-Scale High-Frequency Barotropic Signals from Satellite Altimetry in the Japan/East Sea
Authors: Xu Yongsheng , Watts D. Randolph , Park Jae-Hun
Published: February 2008

In the Japan/East Sea, energetic high-frequency large-scale barotropic motions are shown to lead to large aliasing errors in satellite altimetry observations. The combined aliasing from several neighboring and crossing tracks produces artificial mesoscale signals in altimeter-mapped products, significantly changing the map interpretation. The alias can be well suppressed by subtracting the large-scale barotropic motions observed by bottom pressure sensors. By using coastal tide gauge data in the Japan/East Sea, about 78% of the alias source variance can be removed, which offers an alternative way to suppress the alias for other time intervals without bottom pressure measurements.
Some Remarks on the Reliability of Categorical Probability Forecasts
Authors: Bröcker Jochen
Published: February 2008

Studies on forecast evaluation often rely on estimating limiting observed frequencies conditioned on specific forecast probabilities (the reliability diagram or calibration function). Obviously, statistical estimates of the calibration function are based on only limited amounts of data and therefore contain residual errors. Although errors and variations of calibration function estimates have been studied previously, either they are often assumed to be small or unimportant, or they are ignored altogether. It is demonstrated how these errors can be described in terms of bias and variance, two concepts well known in the statistics literature. Bias and variance adversely affect estimates of the reliability and sharpness terms of the Brier score, recalibration of forecasts, and the assessment of forecast reliability through reliability diagram plots. Ways to communicate and appreciate these errors are presented. It is argued that these errors can become quite substantial if individual sample points have too large influence on the estimate, which can be avoided by using regularization techniques. As an illustration, it is discussed how to choose an appropriate bin size in the binning and counting method, and an appropriate bandwidth parameter for kernel estimates.
An Observational Study of Environmental Dynamical Control of Tropical Cyclone Intensity in the Atlantic
Authors: Zeng Zhihua , Chen Lianshou , Wang Yuqing
Published: February 2008

An attempt has been made to extend the analysis of environmental dynamical control of tropical cyclone (TC) intensity recently performed for the western North Pacific to the North Atlantic. The results show that both the vertical shear and translational speed have negative effects on TC intensity, which is consistent with previous findings for other basins. It shows that few TCs intensified when they moved faster than 15 m s−1. The threshold vertical shear of 20 m s−1—defined as the difference of total winds between 200 and 850 hPa averaged within 5° latitude around the TC center—is found above which few TCs intensified and below which most TCs could reach their lifetime peak intensity. The average intensity of total TCs in the Atlantic is a bit smaller than that in the western North Pacific. The SST-determined empirical maximum potential intensity (EMPI) for a TC for 1981–2003 in this study is slightly higher than that found for 1962–92 by DeMaria and Kaplan in the Atlantic, however.

To be consistent with the theoretical TC MPI, a new EMPI has been constructed, which includes the effect of thermodynamic efficiency. This new EMPI marginally improves the estimation of real TC maximum intensity because the thermodynamic efficiency is largely determined by SST. To include the environmental dynamical control of TC intensity, a dynamical efficiency has been introduced, which is inversely proportional to the combined amplitude of the vertical shear and translational speed. With this dynamical efficiency, an empirical maximum intensity (EMI) for Atlantic TCs has been constructed. This EMI includes not only the positive contribution by SST but also the effects of both thermodynamic and dynamical efficiencies, and it provides more accurate estimations of TC maximum intensity. Furthermore, the formulation of the new EMI explains the observed behavior of TC maximum intensity by thermodynamic and dynamical controls in a transparent and easy-to-interpret manner.
Reproducible and Irreproducible Components in Ensemble Simulations with a Regional Climate Model
Authors: Separovic Leo , de Elía Ramon , Laprise René
Published: February 2008

High-resolution limited-area models (LAMs) have been widely employed to downscale coarse-resolution climate simulations or objective analyses. The growing evidence that LAM climate statistics can be sensitive to initial conditions suggests that a deterministic verification of LAM solutions in terms of finescale atmospheric features might be misguided. In this study a 20-member ensemble of LAM integrations with perturbed initial conditions, driven by NCEP–NCAR reanalyses, is conducted for a summer season over a midlatitude domain. Ensemble simulations allow for the separation of the downscaled information in two parts: a unique, reproducible component associated with lateral-boundary and surface forcing, and an irreproducible component associated with internal variability. The partition in the reproducible and irreproducible components and their seasonal statistics is examined as a function of horizontal length scale, geographical position within the domain, height, and weather episodes during the season. The scale analysis of time-dependent model variables shows that, at scales smaller than a few hundred kilometers, the irreproducible component dominates, on average, the model solution, implying that the downscaled information at these scales is mainly in stochastic form. The constraint exerted by the surface forcing on the internal variability is weak. For seasonal averages, the reproducible component dominates at all scales, although for precipitation the reproducible and irreproducible components are of the same order of magnitude at scales smaller than 150 km. These results imply a need for a probabilistic approach to LAM climate simulations and their verification, especially for shorter integration times, from months to seasons.
Mesoscale Moisture Transport by the Low-Level Jet during the IHOP Field Experiment
Authors: Tollerud Edward I. , Caracena Fernando , Koch Steven E. , Jamison Brian D. , Hardesty R. Michael , McCarty Brandi J. , Kiemle Christoph , Collander Randall S. , Bartels Diana L. , Albers Steven , Shaw Brent , Birkenheuer Daniel L. , Brewer W. Alan
Published: February 2008

Previous studies of the low-level jet (LLJ) over the central Great Plains of the United States have been unable to determine the role that mesoscale and smaller circulations play in the transport of moisture. To address this issue, two aircraft missions during the International H2O Project (IHOP_2002) were designed to observe closely a well-developed LLJ over the Great Plains (primarily Oklahoma and Kansas) with multiple observation platforms. In addition to standard operational platforms (most important, radiosondes and profilers) to provide the large-scale setting, dropsondes released from the aircraft at 55-km intervals and a pair of onboard lidar instruments—High Resolution Doppler Lidar (HRDL) for wind and differential absorption lidar (DIAL) for moisture—observed the moisture transport in the LLJ at greater resolution. Using these observations, the authors describe the multiscalar structure of the LLJ and then focus attention on the bulk properties and effects of scales of motion by computing moisture fluxes through cross sections that bracket the LLJ. From these computations, the Reynolds averages within the cross sections can be computed. This allow an estimate to be made of the bulk effect of integrated estimates of the contribution of small-scale (mesoscale to convective scale) circulations to the overall transport. The performance of the Weather Research and Forecasting (WRF) Model in forecasting the intensity and evolution of the LLJ for this case is briefly examined.
Rapid Sampling of Severe Storms by the National Weather Radar Testbed Phased Array Radar
Authors: Heinselman Pamela L. , Priegnitz David L. , Manross Kevin L. , Smith Travis M. , Adams Richard W.
Published: February 2008

A key advantage of the National Weather Radar Testbed Phased Array Radar (PAR) is the capability to adaptively scan storms at higher temporal resolution than is possible with the Weather Surveillance Radar-1988 Doppler (WSR-88D): 1 min or less versus 4.1 min, respectively. High temporal resolution volumetric radar data are a necessity for rapid identification and confirmation of weather phenomena that can develop within minutes. The purpose of this paper is to demonstrate the PAR’s ability to collect rapid-scan volumetric data that provide more detailed depictions of quickly evolving storm structures than the WSR-88D. Scientific advantages of higher temporal resolution PAR data are examined for three convective storms that occurred during the spring and summer of 2006, including a reintensifying supercell, a microburst, and a hailstorm. The analysis of the reintensifying supercell (58-s updates) illustrates the capability to diagnose the detailed evolution of developing and/or intensifying areas of 1) low-altitude divergence and rotation and 2) rotation through the depth of the storm. The fuller sampling of the microburst’s storm life cycle (34-s updates) depicts precursors to the strong surface outflow that are essentially indiscernible in the WSR-88D data. Furthermore, the 34-s scans provide a more precise sampling of peak outflow. The more frequent sampling of the hailstorm (26-s updates) illustrates the opportunity to analyze storm structures indicative of rapid intensification, the development of hail aloft, and the onset of the downdraft near the surface.
Characterization of Failure Modes in CFRP Composites — An ANN Approach
Authors: Bhat Chandrashekhar , Bhat M.R. , Murthy C.R.L.
Published: February 2008

Carbon fiber reinforced polymer (CFRP) composite specimens with different thickness, geometry, and stacking sequences were subjected to fatigue spectrum loading in stages. Another set of specimens was subjected to static compression load. On-line acoustic Emission (AE) monitoring was carried out during these tests. Two artificial neural networks, Kohonen-self organizing feature map (KSOM), and multi-layer perceptron (MLP) have been developed for AE signal analysis. AE signals from specimens were clustered using the unsupervised learning KSOM. These clusters were correlated to the failure modes using available a priori information such as AE signal amplitude distributions, time of occurrence of signals, ultrasonic imaging, design of the laminates (stacking sequences, orientation of fibers), and AE parametric plots. Thereafter, AE signals generated from the rest of the specimens were classified by supervised learning MLP. The network developed is made suitable for on-line monitoring of AE signals in the presence of noise, which can be used for detection and identification of failure modes and their growth. The results indicate that the characteristics of AE signals from different failure modes in CFRP remain largely unaffected by the type of load, fiber orientation, and stacking sequences, they being representatives of the type of failure phenomena. The type of loading can have effect only on the extent of damage allowed before the specimens fail and hence on the number of AE signals during the test. The artificial neural networks (ANN) developed and the methods and procedures adopted show significant success in AE signal characterization under noisy environment (detection and identification of failure modes and their growth).
Progressive Failure of Marine GFRP Laminated Plates Under Impulsive Water Pressure
Authors: Chung Cheng-Hsien , Lee Ya-Jung
Published: February 2008

When fiber-reinforced plastic (FRP) crafts sail at high speed, very large slamming forces impact the bottom structures of crafts. Therefore, the capacity to resist these forces is an important factor when designing crafts. In the past, the instability and complexity of material properties in failure analysis, in addition to the difficulties in conducting the laminate failure experiments due to water impact, resulted in few studies investigating the failure progress of FRP laminates subjected to water impact. This study presents a novel impulsive water-pressure failure experimental system that combines a hydraulic system with a water-pressure failure experimental fixture used in previous work, to generate impulsive water pressure. Using this system, the FRP laminates are deformed and damaged under water impact. In numerical analysis, the finite element software ABAQUS and user subroutine user-defined field (USDFLD) are utilized to calculate the strain field of laminates as a basis of failure evaluation and stiffness degradation of a structure after specifying failure criteria and stiffness modification curve obtained from material tests for different materials. By comparison with experimental data, the numerical model can be validated, regardless of whether the impulsive water loads are sufficiently small or large to cause structure failure. Consequently, based on the results of this study, the abilities of analyzing the dynamic failure progress under out-of-plane impulsive water pressure and the corresponding experimental systems can be well established. Furthermore, the capacity of FRP laminates in resisting water pressure can also be elucidated.
Elastic Properties of Short-fiber Polymer Composites, Derivation and Demonstration of Analytical Forms for Expectation and Variance from Orientation Tensors
Authors: Jack David A. , Smith Douglas E.
Published: February 2008

Existing methods for predicting elastic properties of short-fiber polymer composites from fiber orientation tensors are based on the orientation average of a transversely isotropic stiffness tensor. These evaluations focus solely on average properties and have yet to include a quantitative measure of property variation. Recognizing the statistical nature of fiber orientations within the composite commonly defined through the fiber orientation distribution function, analytical expressions are developed here to predict both expectation and variance of the material stiffness tensor from a fiber orientation distribution function. The fiber orientation distribution function is expanded through the Laplace series of complex spherical harmonics and results demonstrate that material stiffness tensor expectation is a function of orientation tensors up through fourth-order and the corresponding variance requires orientation tensors up through eighth-order. Numerical simulations obtained with the method of Monte-Carlo for sample sets generated from statistically independent unidirectional samples belonging to the fiber orientation distribution function from the accept—reject generation algorithm are shown to agree with the analytic expressions for material expectation and variance.
Plant Fiber — Industrial Waste Reinforced Polymer Composites as a Potential Wood Substitute Material
Authors: Saxena Mohini , Morchhale R.K. , Asokan P. , Prasad B.K.
Published: February 2008

This investigation deals with the property characterization and utilization of abundantly available and renewable resources of plant fibers such as jute and sisal. These plant fibers along with industrial wastes (fly ash and red mud) have been used for synthesizing value added composite materials. Relevant engineering properties such as physical and mechanical, resistance to abrasive wear, weathering and fire, etc., of the plant fiber reinforced polymer matrix composites so synthesized were characterized. The characteristics of conventional wood and other commercially available potential candidate building materials were also compared to assess the application potential of the newly developed materials vis-a-vis their conventional counterparts. The study reveals that the developed polymer—natural fiber—industrial (inorganic) waste composites attain far superior mechanical properties and resistance to abrasive wear, fire, water absorption, weathering, and chemical attack, as compared to their conventional counterparts such as wood, medium density fibre (MDF) boards, particle board, etc. The versatile material system so developed has potential for wood substitute applications like door shutters, flooring tiles, roofing sheets, partitions, etc., and is envisaged to significantly contribute towards forest conservation and environmental protection. The study strongly suggests that the newly developed plant fiber and/or industrial waste reinforced polymer composite materials are quite capable to serve as a potential cost and energy effective, technologically viable, and attractive substitute to the conventionally used wood and other identical materials. The study gains significance from the fact that earlier investigators have focussed their attention mainly towards exploring the use of chopped (sisal), and textile (jute) composites for different engineering applications including building while the present study examines the suitability of abundantly available natural fibers such as sisal and jute in the presence of otherwise harmful industrial wastes like red mud and fly ash for synthesizing polymer-based composites. This is followed by assessing the potential of the developed composite materials as a cost and energy effective wood substitute for building applications.
Impact Damage Resistance and Tolerance of Honeycomb Core Sandwich Panels
Authors: Raju K.S. , Smith B.L. , Tomblin J.S. , Liew K.H. , Guarddon J.C.
Published: February 2008

The damage resistance and tolerance of flat [(0/45),/core/(45/0), ] sandwich plates with honeycomb core subjected to low-velocity impacts using hemispherical steel impactors has been investigated experimentally. The effects of impactor diameter on the impact behavior, resulting impact damage states, and residual strength under in-plane compressive loading was of particular interest. The impact responses characterized in terms of peak impact force was observed to be dependent on the facesheet type, core thickness, and impactor size, but was found to be independent of the boundary support conditions. The smaller impactor produced damage states characterized by residual dent depths that were comparable to the core thickness, accompanied by visible facesheet fractures. The larger diameter impactor produced damage states with large core damage regions but with dent depths less than the facesheet thickness. Under in-plane compressive loading, depending on the impact damage state, contrasting failure mechanisms involving net-section fracture and buckling failure were observed. A reduction in compressive strength up to 60% of the undamaged strength has been observed.
Effects of Small-Group Reading Instruction and Curriculum Differences for Students Most at Risk in Kindergarten
Authors: Kamps Debra , Abbott Mary , Greenwood Charles , Wills Howard , Veerkamp Mary , Kaufman Jorun
Published: February 2008

This article describes the implementation of small-group reading instruction as secondary- and tertiary-level components of a three-tier model of prevention and intervention. The study consisted of 83 students who were targeted in the winter of kindergarten as being at high risk for reading failure. Intervention consisted of evidence-based curriculum delivered in groups of one to six students during 30- to 40-min sessions a minimum of three times per week over a 2-year period. Outcome data were collected for early literacy skills, using the Dynamic Indicators of Basic Early Literacy Skills and Woodcock Reading Mastery Test, with comparisons across the different curricula. Results indicated that students in the more directed, explicit intervention groups generally out-performed students in the comparison group. Implications for future research and practice implementing schoolwide three-tier prevention models are discussed.
Response to Varying Amounts of Time in Reading Intervention for Students With Low Response to Intervention
Authors: Wanzek Jeanne , Vaughn Sharon
Published: February 2008

Two studies examined response to varying amounts of time in reading intervention for two cohorts of first-grade students demonstrating low levels of reading after previous intervention. Students were assigned to one of three groups that received (a) a single dose of intervention, (b) a double dose of intervention, or (c) no intervention. Examination of individual student response to intervention indicated that more students in the treatment groups demonstrated accelerated learning over time than students in the comparison condition. Students' responses to the single-dose and double-dose interventions were similar over time. Students in all conditions demonstrated particular difficulties with gains in reading fluency. Implications for future research and practice within response to intervention models are provided.
Measuring the Dimensions of Alphabetic Principle on the Reading Development of First Graders
Authors: Harn Beth A. , Stoolmiller Mike , Chard David J.
Published: February 2008

This article presents critical issues related to word reading development within Ehri's theoretical context by focusing primarily on the relation of decoding skill (of nonwords) to word reading and the development of unitization. Within this context, issues and considerations related to research, measurement, and reading development are presented from research and field-based perspectives. Analyses examining the relation between a measure of alphabetic principle, Nonsense Word Fluency (NWF), and fluency with connected text, Oral Reading Fluency (ORF), across first grade demonstrated a linear relation between the measures, which was attenuated for students initially above criterion on the NWF measure. A new scoring approach to the NWF measure is presented to capture initial unitization development and was found to account for unique variance in initial status and growth on ORF and provide instructionally relevant information on the nature of developing alphabetic principle skills. Considerations for future research and school-based applications are provided.
Predicting Reading Success in a Multilevel Schoolwide Reading Model
Authors: Chard David J. , Stoolmiller Mike , Harn Beth A. , Wanzek Jeanne , Vaughn Sharon , Linan-Thompson Sylvia , Kame'enui Edward J.
Published: February 2008

Despite recent research findings that implicate a long list of student variables that predict reading success or failure, these predictor variables have not been considered in the context of contemporary models of multitiered schoolwide reading intervention. This longitudinal, retrospective study follows 668 kindergarten and first-grade students identified as at risk for later reading difficulties through third grade. Key predictor variables were examined to determine their validity for predicting initial status and growth on oral reading fluency, third-grade oral reading fluency, and third-grade performance on a standardized test of reading. Results are provided in light of the instructional model provided. Implications for instruction and assessment are discussed.
When Local Models Fail
Authors: Epstein Brian
Published: February 2008

Models treating the simple properties of social groups have a common shortcoming. Typically, they focus on the local properties of group members and the features of the world with which group members interact. I consider economic models of bureaucratic corruption, to show that (a) simple properties of groups are often constituted by the properties of the wider population, and (b) even sophisticated models are commonly inadequate to account for many simple social properties. Adequate models and social policies must treat certain factors that are not local to individual members of the group, even if those factors are not causally connected to those individuals.
Weighted Explanations in History
Authors: Northcott Robert
Published: February 2008

Weighted explanations , whereby some causes are deemed more important than others, are ubiquitous in historical studies. Drawing from influential recent work on causation, I develop a definition of causal-explanatory strength. This makes clear exactly which aspects of explanatory weighting are subjective and which objective. It also sheds new light on several traditional issues, showing for instance that: underlying causes need not be more important than proximate ones; several different causes can each be responsible for most of an effect; small causes need not be less important than big ones; and non-additive interactive effects between causes present no particular difficulty.
Objectivity, Value Spheres, and “Inherent Laws”
Authors: Bruun Hans Henrik
Published: February 2008

I give an account of Max Weber's views concerning the basis of the objectivity of the cultural sciences. In this connection, I offer a critical discussion of his distinction between different “value spheres,” each with its own “intrinsic logic.” I then consider parallels between Weber's “value spheres” and central elements of Bourdieu's field theory and Luhmann's systems theory, and try to show to what extent Bourdieu's and Luhmann's problems, and the solutions they suggest, can be seen as similar to Weber's. I conclude by a general consideration of Weber's, Bourdieu's, and Luhmann's approach to the problem of objectivity.
Essay: Punitiveness as “Behavior Management”
Authors: Toch Hans
Published: February 2008

Behavior management plans (BMPs) are temporary deprivation experiences that have been advertised as promoting the discontinuance of habitual misbehavior in institutions. In practice, these interventions are often invoked in retaliation or as punishment when individual inmates are uncooperative or troublesome. In settings that already offer a rock-bottom quality of life—such as segregation units in prisons—BMPs reliably call for intolerably stressful conditions that tend to compromise the mental health of persons who are subjected to these conditions. The cycle is predictably exacerbated when the behavior that is targeted is symptomatic of mental illness in the first place, as is frequently the case.
Adolescent Psychopathy
Authors: Amato Julie M. , Cornell Dewey G. , Xitao Fan
Published: February 2008

This study compared five proposed factor models of psychopathy in a sample of 227 adolescent incarcerated offenders and psychiatric inpatients. Results of confirmatory factor analysis indicated that both Cooke and Michie's three-factor model and a four-factor parceled solution using Hare's four factors provided excellent fit. The original two-factor model and the three- and four-factor models from the Psychopathy Checklist: Youth Version manual provided inadequate fit. Correlational analyses revealed a meaningful pattern of statistically significant relationships between psychopathy factor scores and several factor scores on the Millon Adolescent Clinical Inventory (MACI). Regression analyses indicated that Hare's antisocial factor (Factor 4) provided incremental validity beyond other psychopathy factors in predicting scores on the MACI antisocial-delinquent factor.
Not in My Neighborhood
Authors: Burchfield Keri B. , Mingus William
Published: February 2008

Community registration laws requiring sex offenders to register with local law enforcement have become increasingly popular and increasingly restrictive in recent years. Although these laws were passed under the auspices of protecting communities from dangerous and violent sexual predators, little research has addressed their efficacy or their consequences. Building on a social capital framework that emphasizes the resources provided by local ties to family, friends, and the community, data from semistructured interviews with 23 sex offenders were analyzed to explore their experiences with local social capital while being registered and on and off of parole. Sex offenders discuss problems accessing and participating in networks of local social capital, incidents of community residential mobilization against them, and their experiences with formal barriers to social capital, including parole restrictions.