bluuebunny/crossref_metadata_2025 huggingface dataset:
A Golden Age? Unemployment and the American Labor Market, 1880–1910
Authors: JAMES JOHN A. , THOMAS MARK
Published: March 2004

We calculate the natural rate of unemployment in 1909 by first estimating equations for the incidence and time lost in unemployment on a pooled dataset integrating the manuscript sample of the 1910 census and state BLS surveys and then simulating a counterfactual unemployment rate as if the economy had been on trend that year with business-cycle effects neutralized. Following a similar procedure for the 1960s, we find the natural rate in the earlier period to have been substantially higher. The demise of casual unskilled labor, or floaters, seems to have been an important contributory factor.
Why Isn't the Whole of Spain Industrialized? New Economic Geography and Early Industrialization, 1797–1910
Authors: ROSÉS JOAN R.
Published: March 2004

Spain provides an opportunity to study the causes of regional differences in industrial development over the nineteenth century. As transportation costs decreased and barriers to domestic trade were eliminated, Spanish manufacturing became increasingly concentrated in a few regions. This article combines Heckscher-Ohlin and economic-geography frameworks and finds that comparative-advantage and increasing-return effects were economically very significant and practically explained all differences in industrialization levels across regions. The deficits of some regions in terms of industrialization appear to have been largely attributable to their factor endowments and the absence of home-market effects for modern industries.
Why Schumpeter was Right: Innovation, Market Power, and Creative Destruction in 1920s America
Authors: NICHOLAS TOM
Published: March 2004

Are firms with strong market positions powerful engines of technological progress? Joseph Schumpeter thought so, but his hypothesis has proved difficult to verify empirically. This article highlights Schumpeterian market-power and creative-destruction effects in a sample of early-twentieth-century U.S. industrial firms; his contention that an efficiently functioning capital market has a positive effect on the rate of innovation is also confirmed. Despite market power abuses by incumbents, the extent of innovation stands out: 21 percent of patents assigned to the firms sampled between 1920 and 1928 are cited in patents granted between 1976 and 2002.
Peeking Backward: Regional Aspects of Industrial Growth in Post-Unification Italy
Authors: FENOALTEA STEFANO
Published: March 2004

The new sectoral estimates of industrial production in 1871, 1881, 1901, and 1911 are regionally allocated using census labor-force data. The regional aggregates suggest that the “industrial triangle” emerged over these decades out of a traditional surplus-recycling economy. The concomitant change in the industrial rankings argues against attributing the regions' different paths to their different initial conditions; surprisingly, too, overall growth does not seem closely tied to industrial development. The disaggregated estimates suggest in turn that the industrial structure of the various regions remained relatively similar, as if comparative advantages were generically industrial rather than sector-specific.
Wage and Industry Effects in U.S. Regional Incomes, 1840 to 1987: A CES Wage Index Method
Authors: COOKE STEPHEN C.
Published: March 2004

The Solow growth and the Heckscher-Ohlin trade models describe two competing processes through which regional incomes converge over time. Solow's model attributes rising productivity of labor to additional regional capital investments. Heckscher-Ohlin's trade model ascribes the relocation of high value industries to regions with low wage rates. On the other hand Paul Krugman expects incomes to diverge over time as regions with an initial advantage maintain it through ever increasing external economies of scale. The Solow and Heckscher-Ohlin models imply that incomes converge through the movement of high quality labor and capital and high value goods and services into low income regions respectively.
Identity and violence: the politics of youth in Ijebu-Remo, Nigeria
Authors: Nolte Insa
Published: March 2004

This article examines the politics of youth in Ijebu-Remo (henceforth Remo) from the 1950s to the present. The emergence of the politics of youth in the 1950s and 1960s drew on precolonial discourse and was closely associated with the emergence of Remo's anti-federal postcolonial political identity. Since Nigeria's political and economic decline in the mid-1980s, strong feelings of exclusion – strengthened further by the political sidelining of Yoruba-speaking politicians in national politics between 1993 and 1999 – have contributed to an increase of nationalist sentiment in Remo youth politics. This is enacted through secrecy, a reinvention and utilisation of ‘traditional’ cultural practice, and the growing definition of local identity through ethnic discourse. Traditionally, Remo youth and elite politics have legitimised and supported each other, but the cohesion between these groups has declined since the return to democracy in 1999. Rivalry and conflict over local and national resources have led to bitter intergroup fighting, and young men's strategies to combat social exclusion remain mostly individual.
Understanding policy processes in Ethiopia: a response
Authors: Keeley James , Scoones Ian
Published: March 2004

We appreciate the opportunity to engage with Nyssen et al.'s (2004, this issue) response to our earlier JMAS paper (Keeley & Scoones 2000). While they make a number of important points – many of which we agree with – we feel, however, that they fundamentally misrepresent our paper, and miss the central argument. This may be due to lack of clarity on our part, so, to kick off our response, it is perhaps worth reiterating the key points of the original piece.
One step forward, two steps back? Paradoxes of natural resources management decentralisation in Cameroon
Authors: Oyono Phil René
Published: March 2004

Theory informs us that decentralisation, a process through which powers, responsibilities and resources are devolved by the central state to lower territorial entities and regionally/locally elected bodies, increases efficiency, participation, equity, and environmental sustainability. Many types and forms of decentralisation have been implemented in Africa since the colonial period, with varying degrees of success. This paper explores the process of forest management decentralisation conducted in Cameroon since the mid-1990s, highlighting its foundations and characterising its initial assets. Through the transfer of powers to peripheral actors for the management of forestry fees, Council Forests and Community [or Village] Forests, this policy innovation could be empowering and productive. However, careful observation and analysis of relationships between the central state and regional/local-level decentralised bodies, on the one hand, and of the circulation of powers, on the other, show – after a decade of implementation – that the experiment is increasingly governed by strong tendencies towards ‘re-centralisation’, dictated by the practices of bureaucrats and state representatives. The paper also confirms recent empirical studies of ‘the capture of decentralised actors’. It finally shows how bureaucrats and state authorities are haunted by the Frankenstein's monster syndrome, concerning state–local relationships in decentralised forest management.
Leading from behind: democratic consolidation and the chieftaincy in South Africa
Authors: Williams J. Michael
Published: March 2004

Despite the dramatic changes that have occurred in South Africa over the last fifteen years, the chieftaincy remains an important political institution that continues to exercise authority. It has not only been given official recognition and protection in the constitution, but has attempted to become more involved in activities such as development, local government, and elections. How this institution might affect the process of democratic consolidation, however, has failed to generate much research. This article explores the ways in which the chieftaincy has responded to the introduction of democratic electoral practices at the local level. While the chieftaincy has not been immune from the social and political changes that have swept through the country since the transition, it has nonetheless sought to direct, or redirect, these changes in ways that bolster its own authority. Many local communities expect the chieftaincy not only to assist with the formal electoral process, but also to allow for more participation within local level chieftaincy institutions. A close examination of chieftaincy–societal relations demonstrates that while the chieftaincy has been affected by new democratic rules and practices, it has also influenced how local communities practice and understand these same rules and practices. This mutually transformative process illustrates the complexity of democratic consolidation, as well as the ability of the chieftaincy to adapt to changing political and social environments without sacrificing its unique claims to authority.
Environmental policy in Ethiopia: a rejoinder to Keeley and Scoones
Authors: Nyssen Jan , Haile Mitiku , Moeyersons Jan , Poesen Jean , Deckers Jozef
Published: March 2004

Ongoing land degradation in Ethiopia requires urgent action, and has been addressed at different levels of society, including widespread soil and water conservation activities, and the introduction of technologies which integrate local knowledge and farmer's initiatives. This comment, drawing on extensive research on soil erosion processes in Ethiopia since 1994, in intense cooperation with farmers and local authorities, challenges the conclusions of a paper published in this journal on environmental rehabilitation and rapid agricultural intensification for food self-sufficiency in Ethiopia (Keeley & Scoones 2000). In our view, this paper firstly underestimates the importance of environmental degradation and apparently rejects current conservation techniques and policy, and secondly makes an artificial contradiction between environmental rehabilitation policy and a participatory approach. In our experience, and in line with studies reviewed elsewhere, natural resources conservation in Ethiopia is directed towards an integration of food self-sufficiency with conservation/restoration of the environment, and frequently follows a participatory approach.
Revision of the lichen genus Menegazzia in Japan, including two new species
Authors: BJERKE Jarle W.
Published: March 2004

Five Japanese species of the lichen genus Menegazzia are recorded. Menegazzia caviisidia Bjerke & P. James sp. nov. is characterized by numerous globose to dactyliform to narrowly obovate, hollow isidia, small conical perforations, and thamnolic acid as the major medullary constituent. It appears to be a rare species, so far known only from three localities on Honshu. The status of the primary species M. asahinae is elucidated. Menegazzia pedicellata Bjerke sp. nov. is a rare caperatic acid-containing species previously included in M. asahinae s. lat. Menegazzia asahinae s. str. has perforated margins of apothecia and contains the stictic acid complex. Menegazzia asahinae f. subimpertusa and M. pseudocyphellata are reduced to synonymy with M. asahinae s. str. Two sorediate species are known, viz. M. subsimilis and M. terebrata.
Phylogenetic relationships and species concepts in Parmelia s. str. (Parmeliaceae) inferred from nuclear ITS rDNA and β-tubulin sequences
Authors: MOLINA María del Carmen , CRESPO Ana , BLANCO Oscar , LUMBSCH H. Thorsten , HAWKSWORTH David L.
Published: March 2004

The phylogenetic relationships of 16 species of Parmelia s. str. are presented based on sequences of nuITS rDNA from 56 specimens, and β-tubulin gene sequences from 29 collections. Parmelia serrana sp. nov. a Mediterranean species morphologically very close to P. saxatilis is described. Parmelia ernstiae is the sister-group to P. saxatilis s. str., and a further undescribed North American species of the P. saxatilis complex may require recognition. The isidiate P. squarrosa is closely allied to the sorediate P. sulcata, which is paraphyletic. Japanese samples of P. cochleata form a monophyletic group but too few collections of these were studied to reach firm conclusions regarding their relationships. An epitype is selected for the lectotype of Lichen saxatilis to unequivocally fix the application of that epithet.
Phoma fuliginosa sp. nov., from Caloplaca trachyphylla in Nebraska, with a key to the known lichenicolous species
Authors: HAWKSWORTH David L. , COLE Mariette S.
Published: March 2004

Phoma fuliginosa sp. nov. is described and illustrated from apothecia of Caloplaca trachyphylla (Teloschistaceae) collected in Nebraska, USA. The species is distinguished from other lichenicolous fungi referred to the genus in the shape and size of the conidia. It is considered pragmatic to continue to use the generic name Phoma for this group of lichenicolous coelomycetes until cultural and molecular information is available, although these fungi may later prove not to be congeneric amongst themselves nor with the species occurring on plants. A key to the 14 lichenicolous species now accepted in Phoma is provided, and notes on reports of some additional collections referred to the genus are included.
Guest Editor's Preface: The Eighth International Workshop on
the Physics of Compressible Turbulent Mixing
Authors: Schilling Oleg
Published: March 2004

This issue of Laser and Particle Beams contains 27
contributed articles based on presentations given at the eighth
International Workshop on the Physics of Compressible Turbulent Mixing
(IWPCTM) (see http://www.llnl.gov/IWPCTM), held at the
California Institute of Technology, Pasadena, California from December
9 to 14, 2001, and organized jointly by the Lawrence Livermore National
Laboratory (LLNL) and the California Institute of Technology. This
conference is the eighth in a biennial series of conferences on the
general subject of experimental, numerical, and theoretical studies of
compressible turbulent mixing, initiated by LLNL in the late 1980s.
Previous conferences were held in Princeton, New Jersey (1988),
Pleasanton, California (1989), Royaumont, France (1991), Cambridge,
United Kingdom (1993), Stony Brook, New York (1995), Marseille, France
(1997), and St. Petersburg, Russia (1999). The ninth IWPCTM is to be
held at the University of Cambridge in 2004.
A new turbulent two-field concept for modeling Rayleigh–Taylor, Richtmyer–Meshkov, and Kelvin–Helmholtz mixing layers
Authors: LLOR ANTOINE , BAILLY PASCAL
Published: March 2004

An accurate turbulent mixing model for gravitationally induced instabilities with arbitrarily variable accelerations has been developed to capture the following physical aspects: (1) directed transport, (2) correct buoyancy forces, (3) turbulence diffusion, and (4) geometrical aspects. We present the two-structure two-fluid two-turbulence concept (2SFK), which consistently answers these requirements by identifying the large-scale transport structures in a statistical approach. An example of a 2SFK-based model is given and applied to the Rayleigh–Taylor case.
Efficient perturbation methods for Richtmyer–Meshkov and Rayleigh–Taylor instabilities: Weakly nonlinear stage and beyond
Authors: VANDENBOOMGAERDE M. , CHERFILS C. , GALMICHE D. , GAUTHIER S. , RAVIART P.A.
Published: March 2004

The simplified perturbation method of Vandenboomgaerdeet al.(2002) is applied to both the Richtmyer–Meshkov and the Rayleigh–Taylor instabilities. This theory is devoted to the calculus of the growth rate of the perturbation of the interface in the weakly nonlinear stage. In the standard approach, expansions appear to be series in time. We build accurate approximations by retaining only the terms with the highest power in time. This simplifies and accelerates the solution. High order expressions are then easily reachable. For the Richtmyer–Meshkov instability, multimode configurations become tractable and the selection mode process can be studied. Inferences for the intermediate nonlinear regime are also proposed. In particular, a class of homothetic configurations is inferred; its validity is verified with numerical simulations even as vortex structures appear at the interface. This kind of method can also be used for the Rayleigh–Taylor instability. Some examples are presented.
Three-dimensional multimode Rayleigh–Taylor and Richtmyer–Meshkov instabilities at all density ratios
Authors: KARTOON D. , ORON D. , ARAZI L. , SHVARTS D.
Published: March 2004

The three-dimensional (3D) turbulent mixing zone (TMZ) evolution under Rayleigh–Taylor and Richtmyer–Meshkov conditions was studied using two approaches. First, an extensive numerical study was made, investigating the growth of a random 3D perturbation in a wide range of density ratios. Following that, a new 3D statistical model was developed, similar to the previously developed two-dimensional (2D) statistical model, assuming binary interactions between bubbles that are growing at a 3D asymptotic velocity. Confirmation of the theoretical model was gained by detailed comparison of the bubble size distribution to the numerical simulations, enabled by a new analysis scheme that was applied to the 3D simulations. In addition, the results for the growth rate of the 3D bubble front obtained from the theoretical model show very good agreement with both the experimental and the 3D simulation results. A simple 3D drag–buoyancy model is also presented and compared with the results of the simulations and the experiments with good agreement. Its extension to the spike-front evolution, made by assuming the spikes' motion is governed by the single-mode evolution determined by the dominant bubbles, is in good agreement with the experiments and the 3D simulations. The good agreement between the 3D theoretical models, the 3D numerical simulations, and the experimental results, together with the clear differences between the 2D and the 3D results, suggest that the discrepancies between the experiments and the previously developed models are due to geometrical effects.
Scaling in the shock–bubble interaction
Authors: LEVY K. , SADOT O. , RIKANATI A. , KARTOON D. , SREBRO Y. , YOSEF-HAI A. , BEN-DOR G. , SHVARTS D.
Published: March 2004

The passage of a shock wave through a spherical bubble results in the formation of a vortex ring. In the present study, simple dimensional analysis is used to show that the circulation is linearly dependent on the surrounding material speed of soundcsand the initial bubble radiusR. In addition, it is shown that the velocities characterizing the flow field are linearly dependent on the speed of sound, and are independent of the initial bubble radius. The dependence of the circulation on the shock wave Mach numberMis derived by Samtaney and Zabusky (1994) as (1 + 1/M+ 2/M2) (M− 1). Experiments were performed for slow/fast (air-helium) and fast/slow (air-SF6) interactions. Full numerical simulations were conducted resulting in good agreement. From the results, it is seen that in both cases, according to the proposed scaling, the vortex ring velocity is bubble radius independent. The numerical results for the slow/fast interaction show that the proposed Mach scaling is valid forM< 2. AboveM≅ 2, the topology of the bubble changes due to a competition between the upstream surface of the bubble and the undisturbed shock wave.
An experimental study of the high Mach number and high initial-amplitude effects on the evolution of the single-mode Richtmyer–Meshkov instability
Authors: SADOT O. , RIKANATI A. , ORON D. , BEN-DOR G. , SHVARTS D.
Published: March 2004

The present article describes an experimental study that is a part of an integrated theoretical (Rikanatiet al.2003) and experiential investigation of the Richtmyer–Meshkov (RM) hydrodynamic instability that develops on a perturbed contact surface by a shock wave. The Mach number and the high initial-amplitude effects on the evolution of the single-mode shock-wave-induced instability were studied. To distinguish between the above-mentioned effects, two sets of shock-tube experiments were conducted: high initial amplitudes with a low-Mach incident shock and small amplitude initial conditions with a moderate-Mach incident shock. In the high-amplitude experiments a reduction of the initial velocity with respect to the linear prediction was measured. The results were compared to those predicted by a vorticity deposition model and to previous experiments with moderate and high Mach numbers done by others and good agreement was found. The result suggested that the high initial-amplitude effect is the dominant one rather than the high Mach number effect as suggested by others. In the small amplitude–moderate Mach numbers experiments, a reduction from the impulsive theory was noted at late stages. It is concluded that while high Mach number effect can dramatically change the behavior of the flow at all stages, the high initial-amplitude effect is of minor importance at the late stages. That result is supported by a two-dimensional numerical simulation.
A general buoyancy–drag model for the evolution of the Rayleigh–Taylor and Richtmyer–Meshkov instabilities
Authors: SREBRO YAIR , ELBAZ YONI , SADOT OREN , ARAZI LIOR , SHVARTS DOV
Published: March 2004

The growth of a single-mode perturbation is described by a buoyancy–drag equation, which describes all instability stages (linear, nonlinear and asymptotic) at time-dependent Atwood number and acceleration profile. The evolution of a multimode spectrum of perturbations from a short wavelength random noise is described using a single characteristic wavelength. The temporal evolution of this wavelength allows the description of both the linear stage and the late time self-similar behavior. Model results are compared to full two-dimensional numerical simulations and shock-tube experiments of random perturbations, studying the various stages of the evolution. Extensions to the model for more complicated flows are suggested.
Late-time growth of the Richtmyer–Meshkov instability for different Atwood numbers and different dimensionalities
Authors: YOSEF-HAI A. , SADOT O. , KARTOON D. , ORON D. , LEVIN L.A. , SARID E. , ELBAZ Y. , BEN-DOR G. , SHVARTS D.
Published: March 2004

The late-time growth rate of the Richtmyer–Meshkov instability was experimentally studied at different Atwood numbers with two-dimensional (2D) and three-dimensional (3D) single-mode initial perturbations. The results of these experiments were found to be in good agreement with the results of the theoretical model and numerical simulations. In another set of experiments a bubble-competition phenomenon, which was observed in previous work for 2D initial perturbation (Sadotet al., 1998), was shown to exist also when the initial perturbation is of a 3D nature.
Experimental study into the Rayleigh–Taylor turbulent mixing
zone heterogeneous structure
Authors: KUCHERENKO Yu.A. , PYLAEV A.P. , MURZAKOV V.D. , BELOMESTNIH A.V. , POPOV V.N. , TYAKTEV A.A.
Published: March 2004

Experiments conducted on the SOM facility at the Russian Federal
Nuclear Center–VNIITF, concerning the turbulent mixing induced by
the Rayleigh–Taylor instability in a three-layer system of
immiscible liquids are described. The fluids are contained in a small
tank 6.4 cm × 5.4 cm × 12 cm, which is accelerated
vertically downward by a gas gun. The mixing layer evolution was imaged
by seeding one of the fluids with particles and using a bidirectional
light sheet method (refractive index matching was used to minimize
measurement errors). Experiments were performed for two different
accelerations (g = 350 g0 and g =
100 g0, where g0 = 980
cm/s2, and the acceleration decreases with distance
traveled), and with aqueous solutions of glycerin and benzene (with
density ratio 1.6). The lower, middle, and upper layers were a sodium
hyposulfite–glycerin solution, a water–glycerin solution,
and benzene, respectively. The glycerin solution was seeded with
particles. The principal objective of the experiments was to obtain the
distribution of fluid particle sizes arising from the mixing of the
immiscible fluids.
RFNC–VNIITF multifunctional shock tube for investigating the evolution of instabilities in nonstationary gas dynamic flows
Authors: KUCHERENKO Yu.A. , SHESTACHENKO O.E. , BALABIN S.I. , PYLAEV A.P.
Published: March 2004

The design, operation, and functionality of the multifunctional shock tube (MST) facility at the Russian Federal Nuclear Center–VNIITF are described. When complete, the versatile MST consists of three different driver sections that permit the execution of three different classes of experiments on the compressible turbulent mixing of gases induced by the (1) Richtmyer–Meshkov instability (generated by a stationary shock wave with shock Mach numbers <5), (2) Rayleigh–Taylor instability (generated by compression wave such that acceleration of the interface is <105g0, whereg0= 9.8 m/s2), and (3) combined Richtmyer–Meshkov and Rayleigh–Taylor instability (generated by a nonstationary shock wave with initial pressure at the front 5 × 106Pa and acceleration of ≤106g0of the interface). For each of these types of experiments, the density ratio of the gases is ρ2/ρ1≤ 34. Perturbations are imposed on a thin membrane, embedded in a thin wire array of microconductors that is destroyed by an electric current. In addition, various limitations of experimental techniques used in the study of interfacial instability generated turbulent mixing are also briefly discussed.
Mix experiments using a two-dimensional convergent shock-tube
Authors: HOLDER D.A. , SMITH A.V. , BARTON C.J. , YOUNGS D.L.
Published: March 2004

This article reports the first Richtmyer–Meshkov instability
experiments using an improved version of the Atomic Weapons
Establishment convergent shock tube. These investigate the
shock-induced turbulent mixing across the interfaces of an
air/dense gas/air region. Multipoint ignition of a detonatable
gas mixture produces a cylindrically convergent shock that travels into
a test cell containing the dense gas region. The mixing process is
imaged with shadowgraphy. Sample results are presented from an
unperturbed experiment and one with a notch perturbation imposed on one
of the dense gas interfaces. The unperturbed experiment shows the
mixing across the dense gas boundaries and the motion of the bulk dense
gas region. Imposition of the notch perturbation produces a
mushroom-shaped air void penetrating the dense gas region.
Three-dimensional simulations performed using the AWE TURMOIL3D code
are presented and compared with the sample experimental results. A very
good agreement is demonstrated. Conducting these first turbulent mixing
experiments has highlighted a number of areas for future development of
the convergent shock-tube facility; these are also presented.
Rayleigh–Taylor instability at a tilted interface in laboratory experiments and numerical simulations
Authors: HOLFORD JOANNE M. , DALZIEL STUART B. , YOUNGS DAVID
Published: March 2004

This article investigates the molecular mixing caused by Rayleigh–Taylor (RT) instability of a gravitationally unstable density interface tilted at a small angle to the horizontal. The mixing is measured by the increase in background potential energy, and the mixing efficiency, or fraction of energy irreversibly lost to fluid motion doing work against gravity, is calculated. Laboratory experiments are carried out using saline and fresh water, and modeled with compressible numerical simulations, with a suitable choice of parameters and initial conditions. The experiments show that the high cumulative efficiency of mixing in RT instability at a horizontal interface is only slightly reduced by an interface tilt of up to 10°, despite the strong overturning that occurs. Instantaneous mixing efficiencies as high as 0.5–0.6 are measured, when RT instability is active, with lower values of about 0.35 during the subsequent overturning. The numerical simulations capture the most unstable scales and the overturning motion well, but generate more mixing than the experiments, with the instantaneous mixing efficiency remaining at 0.5 for most of the run. The difference may be due to restratification at small scales in the high Prandtl number experiments.
Dynamics of the bubble front in the Richtmyer–Meshkov instability
Authors: ABARZHI S.I.
Published: March 2004

We describe the evolution of the large-scale coherent structure of bubbles and spikes in the Richtmyer–Meshkov instability. Our multiple harmonic analysis accounts for a non-local character of the nonlinear dynamics. A new type of the evolution of the bubble front is found. A comparison to so-called “Layzer-type” local models is performed.
Theoretical methods for the determination of mixing
Authors: CHENG BAOLIAN , GLIMM JAMES , JIN HYEONSEONG , SHARP DAVID
Published: March 2004

Acceleration-driven fluid mixing is studied here from a theoretical point of view. Considerable progress has been achieved in the understanding of mix. Theories of the authors are reviewed that allow prediction of the edge of the mixing zone, in agreement with experimental data. Theories that describe the distribution of masses within the mixing region are also reviewed. The theory we present describes a chunk mix regime, in which two phases are mixed at a chunk level, but for which there is no atomic mixing. Thus the two phases are segregated into disjoint regions of space.
Numerical methods for the determination of mixing
Authors: GEORGE E. , GLIMM J. , LI X.L. , MARCHESE A. , XU Z.-L. , GROVE J.W. , SHARP DAVID H.
Published: March 2004

We present a Rayleigh–Taylor mixing rate simulation with an acceleration rate falling within the range of experiments. The simulation uses front tracking to prevent interfacial mass diffusion. We present evidence to support the assertion that the lower acceleration rate found in untracked simulations is caused, at least to a large extent, by a reduced buoyancy force due to numerical interfacial mass diffusion. Quantitative evidence includes results from a time-dependent Atwood number analysis of the diffusive simulation, which yields a renormalized mixing rate coefficient for the diffusive simulation in agreement with experiment. We also present the study of Richtmyer–Meshkov mixing in cylindrical geometry using the front tracking method and compare it with the experimental results.
Shock interaction with a heavy gas cylinder: Emergence of vortex bilayers and vortex-accelerated baroclinic circulation generation
Authors: GUPTA SANDEEP , ZHANG SHUANG , ZABUSKY NORMAN J.
Published: March 2004

We present a numerical study to late times of a Richtmyer–Meshkov environment: a weak shock (M= 1.095) interacting with a heavy cylindrical bubble. The bubble interface is modeled as a diffuse interfacial transition layer (ITL) with finite thickness. Our simulation with the piecewise parabolic method (PPM) yields very good agreement in large- and intermediate-scale features with Jacobs' experiment (Jacobs, 1993). We note the primary circulation enhancement deposited baroclinically upon the incident shock wave, and significant secondary baroclinic circulation enhancement, first observed in Zabusky and Zhang (2002). We propose that this vortex-accelerated circulation deposition is universal. These baroclinic processes are mediated by a strong gradient intensification and stretching of the ITL and result in close-lying vortex bilayers (VBLs) and the emergence of vortex projectiles (VPs). These account for the elongated, kidney-shaped morphology of the rolled up bubble domain at late times.
Jet and vortex flows in a shock/ hemispherical-bubble-on-wall
configuration
Authors: PENG GAOZHU , ZABUSKY NORMAN J. , ZHANG SHUANG
Published: March 2004

We suggest an easily obtained laboratory configuration to observe jet
and vortex flows for the Richtmyer–Meshkov (accelerated
inhomogeneous flow) environment. A hemispherical bubble in air
with density ratio of 5 is placed against an ideally reflecting wall
and struck by a planar shock. This also models a spherical bubble
struck symmetrically by two identical approaching shocks, that is, a
“reshock” configuration. For all Mach numbers
(M = 1.2, 1.5, and 2.0), our axisymmetric simulations show
that the heavy hemispherical bubble expands axially away from the wall
as a jet, and a weaker vortex ring moves radially along the wall. In
addition, when M = 1.5, a ringlike vortex projectile (VP) of
small diameter follows closely behind the reflected shock and is
associated with its moving triple point. This VP contains an entrained
shocklet and quadrupole structure of dilatation. Various methods are
applied to quantify the emerging coherent structures.
Arbitrary Lagrange–Eulerian code simulations of turbulent Rayleigh–Taylor instability in two and three dimensions
Authors: WEBER S.V. , DIMONTE G. , MARINAK M.M.
Published: March 2004

We have performed simulations of the evolution of the turbulent Rayleigh–Taylor instability with an arbitrary Lagrange–Eulerian code. The problem specification was defined by Dimonteet al.(2003) for the “alpha group” code intercomparison project. Perfect γ = 5/3 gases of densities 1 and 3 g/cm3are accelerated by constant gravity. The nominal problem uses a 2562× 512 mesh with initial random multiwavelength interface perturbations. We have also run three-dimensional problems with smaller meshes and two-dimensional (2D) problems of several mesh sizes. Under-resolution lowered linear growth rates of the seed modes to 5-60% of the analytic values, depending on wavelength and orientation to the mesh. However, the mix extent in the 2D simulations changed little with grid refinement. Simulations without interface reconstruction gave penetration only slightly reduced from the case with interface reconstruction. Energy dissipation differs little between the two cases. The slope of the penetration distance versus time squared, corresponding to the α parameter inh= αAgt2, decreases with increasing time in these simulations. The slope, α, is consistent with the linear electric motor data of Dimonte and Schneider (2000), but the growth is delayed in time.
Shock–planar curtain interactions: Strong secondary
baroclinic deposition and emergence of vortex projectiles and late-time
inhomogeneous turbulence
Authors: ZHANG SHUANG , ZABUSKY NORMAN J.
Published: March 2004

We continue our previous investigations (Yang, Zabusky,
& Chern, 1990; Zabusky & Zhang,
2002) of the interaction of a shock with a planar, inclined curtain
(slow/fast/slow) to a wider Mach number range (M =
1.5, 2.0, and 5.0) and longer times. In all cases, the generic features
may be explained in terms of the opposite-signed vortex layers
(deposited by the shock wave), which approach and collide to form a
complex vortex bilayer (VBL). At M ≤ 2.0, the VBL
traverses the shock tube and eventually collides with the opposite
horizontal boundary and evolves into upstream and downstream moving
inhomogeneous vortex projectiles (VPs) (Zabusky & Zeng, 1998). This is manifested as
early-time “breakthrough” (Yang, Zabusky,
& Chern, 1990). During the traversal, we observe and scale a
strong secondary baroclinic circulation enhancement. We track and quantify
the VPs and show that their velocities compare well to that from a simple
vortex model. We also display turbulent domains and a new rapid early time
turbulization at M = 5, when the VBL is narrower.
Vortex structures and turbulence emerging in a supernova 1987a configuration: Interactions of “complex” blast waves and cylindrical/spherical bubbles
Authors: ZHANG SHUANG , ZABUSKY NORMAN J. , NISHIHARA KATSUNOBU
Published: March 2004

We examine the interaction of both cylindrical and spherical bubbles (2D) and acomplexblast wave, which consists of an approaching shock/contact discontinuity/shock (Kanget al., 2001a, 2001b). Such configurations may arise following a supernova explosion, for example, SN 1987A, where a complex blast wave is presently approaching a high density “circumstellar ring” (CR) (Borkowskiet al., 1997). Using simulations with the piecewise parabolic method algorithm (Colella & Woodward, 1984), we emphasize the appearance of vortex bilayers, vortex projectiles, and turbulent domains on the downstream and upstream sides of the bubble. We believe that the interfacial deformation of the CR is associated with astrong blast-wave driven accelerated inhomogeneous flow instabilityin ahigh densitymedium and thus will have a different character than the more common planar shock-driven Richtmyer–Meshkov instability.
WMS–III performance in epilepsy patients following temporal lobectomy
Authors: DOSS ROBERT C. , CHELUNE GORDON J. , NAUGLE RICHARD I.
Published: March 2004

We examined performances on the Wechsler Memory Scale–3rd Edition (WMS–III) among patients who underwent temporal lobectomy for the control of medically intractable epilepsy. There were 51 right (RTL) and 56 left (LTL) temporal lobectomy patients. All patients were left hemisphere speech-dominant. The LTL and RTL patients were comparable in terms of general demographic, epilepsy, and intellectual/attention factors. Multivariate analyses revealed a significant crossover interaction (p< .001), with the RTL group scoring significantly lower on the visual than auditory indexes while the LTL group scored significantly lower on the auditory than visual memory indexes. Within-group pairwise analyses revealed statistically significant auditoryversusvisual index score comparisons (allp< .001) for both surgical groups. Discriminant analysis (p< .001) identified Verbal Paired Associates I, Faces I, and Family Pictures II to significantly discriminate RTL and LTL patients, with an overall correct classification rate of 81.3%. Our findings suggest that the WMS–III is sensitive to modality-specific memory performance associated with unilateral temporal lobectomy. (JINS, 2004,10, 173–179.)
Longitudinal outcomes of very low birth weight: Neuropsychological findings
Authors: TAYLOR H. GERRY , MINICH NORI M. , KLEIN NANCY , HACK MAUREEN
Published: March 2004

To investigate the effects of very low birth weight (VLBW, <1500 g) on the development of neuropsychological skills, we assessed 67 children with birth weight <750 g, 64 with birth weight 750–1499 g, and 67 term-born controls. Growth modeling of raw scores from mean ages 7–14 years revealed persistent VLBW sequelae. Even when adjusting for IQ, the <750 g group scored more poorly than the term-born group on measures of language processing, verbal list learning, and perceptual–motor and organizational abilities. This group also made slower age-related progress than the control group on tests of perceptual-motor and executive functions. Environmental factors moderated group differences in change on other cognitive measures. These results revealed further evidence for slower skill development in both VLBW groups relative to controls, as well as“catch-up” growth in the 750–1499 g group on some measures. The findings suggest age-related changes in the cognitive sequelae of VLBW that depend on the skill assessed, the degree of VLBW, and environmental factors. (JINS, 2004,10, 149–163.)
Attentional functioning and white matter integrity among survivors
of malignant brain tumors of childhood
Authors: MULHERN RAYMOND K. , WHITE HOLLY A. , GLASS JOHN O. , KUN LARRY E. , LEIGH LAURIE , THOMPSON STEPHEN J. , REDDICK WILBURN E.
Published: March 2004

Children surviving treatment for malignant brain tumors commonly have
problems maintaining their premorbid levels of intellectual development
and academic achievement. Our group has been especially interested in
the effects of treatment on normal appearing white matter (NAWM) on MRI
and the influence of NAWM volumes on neurocognitive functioning. The
present study assessed NAWM and attentional abilities among 37
long-term survivors of malignant brain tumors, ranging in age from 1.7
to 14.8 (Mdn = 6.5) years at diagnosis, who had been treated
with cranial radiation therapy with or without chemotherapy 2.6 to 15.3
(Mdn = 5.7) years earlier. On the Conners' Continuous
Performance Test, the Overall Index and 7 of the other 10 indices were
significantly deficient compared to age- and gender-corrected normative
values. After statistically controlling for the effects of age at
diagnosis and time elapsed from treatment, 5 of the 8 indices were
significantly associated with cerebral white matter volumes and/or
specific regional white matter volumes of the prefrontal/frontal
lobe and cingulate gyrus. No gender effects were observed. The results
of the present study further support the contention that NAWM is an
important substrate for treatment-induced neurocognitive problems among
survivors of malignant brain tumors of childhood. (JINS, 2004,
10, 180–189.)
Functional and anatomical memory indices in patients with or at
risk for Alzheimer's disease
Authors: PHILLIPS NATALIE A. , CHERTKOW HOWARD , LEBLANC MANON M. , PIM HEATHER , MURTHA SUSAN
Published: March 2004

We investigated the sensitivity of the P300 event-related brain
potential (ERP) recorded during a memory-demanding task to memory
function in subjects with dementia of the Alzheimer's type (DAT),
those with mild cognitive impairment (MCI), and normal elderly
controls. We also explored the ability of neuropsychological (delayed
verbal memory), neuroanatomical (MRI-based hippocampal volume), and
electrophysiological (memory search P300 amplitude) memory measures to
distinguish between the three subject groups using discriminant
function analyses. Fourteen patients with DAT, 16 with MCI, and 15 age-
and education-matched controls were tested. P300 amplitude was reduced
in DAT subjects at all levels of memory load; however, it did not
differ between MCI and control subjects. Delayed verbal memory
performance best discriminated DAT from MCI and control subjects, while
delayed verbal memory and hippocampal volume best discriminated MCI
subjects from controls. These results support the utility of
neuropsychological and neuroanatomical measures in diagnosing dementia
and do not support the notion that P300 amplitude is sensitive to
mild memory dysfunction when measured using the current task.
(JINS, 2004, 10, 200–210.)
Visual attention in long-term survivors of leukemia receiving cranial radiation therapy
Authors: SCHATZ JEFFREY , KRAMER JOEL H. , ABLIN ARTHUR R. , MATTHAY KATHERINE K.
Published: March 2004

The effect of cranial radiation therapy (CRT) on visual attention was examined in long-term survivors of childhood acute lymphoblastic leukemia (ALL) compared to peers with no history of ALL (n= 24) using a cued orienting task and a global–local task. ALL participants treated with CRT (n= 13) demonstrated an increased cost in response time with invalid spatial orienting cues and inefficient shifts of attention across hierarchical levels. ALL participants treated only with chemotherapy (n= 8) showed performance similar to the non-ALL comparison group. Participants with exposure to CRT early in life appeared to largely account for the attention deficits, and showed particular difficulties with shifting attention from the local level of stimuli to the global level. The data are consistent with prior reports emphasizing attention deficits following CRT, and suggest that attention shifting may be particularly affected by CRT early in life. (JINS, 2004,10, 211–220.)
Retrograde amnesia in patients with rupture and surgical repair of
anterior communicating artery aneurysms
Authors: O'CONNOR MARGARET G. , LAFLECHE GINETTE M.C.
Published: March 2004

The retrograde amnesia of patients with memory loss related to
rupture and surgical repair of anterior communicating artery (ACoA)
aneurysms is compared with the retrograde amnesia of temporal amnesic
patients and nonamnesic control participants. Two tests which focus on
popular culture but which differ according to extent of news exposure
and the cognitive processes necessary for task performance were used to
measure retrograde memory. ACoA patients demonstrated more significant
retrograde memory problems than did nonamnesic controls; however, the
severity and pattern of their memory loss was less severe than that
seen in association with temporal amnesia. Different factors influenced
the remote memory loss of respective groups: ACoA patients'
problems were related to impaired lexical retrieval whereas temporal
amnesic patients had problems secondary to both retrieval and storage
deficits. (JINS, 2004, 10, 221–229.)
The sensitivity of dual-task performance to cognitive status in
aging
Authors: HOLTZER ROEE , BURRIGHT RICHARD G. , DONOVICK PETER J.
Published: March 2004

The present study examined dual-task performance in elders with
cognitive impairments and normal controls. The participants (N
= 60; M age = 84.6) were recruited from residential facilities
and the community. They were assigned to one of three groups: (1)
cognitive impairment; (2) residential facility control; (3) community
control. Two different dual-task conditions were comprised of simple
tests that are presumably processed via separate perceptual
modalities: 1 visual–manual and 1 auditory–verbal. The
first condition consisted of a visual cancellation test and an auditory
digit span. The second condition was comprised of an alternate form of
the visual cancellation test and letter fluency. MANOVA examined the
effect of cognitive status (3-level independent variable) on 3 indices
of dual-task performance (letter fluency, digit span, visual
cancellation). Analyses controlled for age, education and performance
on each test when performed alone. The results revealed that the
cognitive impairment group incurred significantly greater dual-task
costs compared to both control groups. Furthermore, as was evident from
discriminant function analyses, the dual-task measures were very
accurate and better than the traditional neuropsychological measures at
discriminating elders with cognitive impairments from normal controls.
(JINS, 2004, 10, 230–238.)
Neuropsychological and information processing deficits following
mild traumatic brain injury
Authors: MATHIAS JANE L. , BEALL JACQUI A. , BIGLER ERIN D.
Published: March 2004

Neuroradiological and neuropathological investigations have found
evidence of diffuse brain damage in the frontal and temporal lobes,
corpus callosum, and fornices in patients who have sustained a mild
traumatic brain injury (TBI). However, neuropsychological assessments
of these patients do not typically target many of the subtle
information processing deficits that may arise from diffuse damage
involving the frontotemporal regions of the brain as well as white
matter pathology, including the corpus callosum. Consequently, we have
a limited understanding of the deficits that may be attributable to
temporary or permanent disruptions to these functional pathways. This
study assessed a group of mild TBI patients (N = 40) and a
matched control group (N = 40) on a number of standard
neuropsychological tests of selective and sustained attention, verbal
and non-verbal fluency, and verbal memory. In addition, reaction time
(RT) tasks, requiring both the inter- and intra-hemispheric processing
of visual and tactile information, were used to assess the functional
integrity of the tracts that are likely to be affected by diffuse
damage. In the 1st month after sustaining their injury, the mild TBI
group demonstrated deficits in attention, non-verbal fluency, and
verbal memory. They also demonstrated slower visual and tactile RTs,
with the visual RTs of mild TBI patients being more affected by
increased task difficulty and the need to transfer information across
the corpus callosum, than did their matched controls. (JINS,
2004, 10, 286–297.)