bluuebunny/crossref_metadata_2025 huggingface dataset:
Measures and Models of Budgetary Policy
Authors: Wlezien Christopher , Soroka Stuart N.
Published: May 2003

This manuscript considers the theoretical and empirical differences between appropriations and outlays and the implications of these differences for analyses of public budgeting in the United States. The research focuses on two questions: (1) What is the relationship between appropriations and outlays over time in different budgetary functions? and (2) What is the consequence of using appropriations or outlays in analyses of budgetary change? Results indicate that the relationship between appropriations and outlays varies quite considerably (and surprisingly) across functions and that the differences matter quite a lot, at least in certain areas. Indeed, whether one uses appropriations or outlays may lead one to draw very different conclusions about the politics of public budgeting. Budgetary measures, it appears, really matter.
Shopping for Schools: How Do Marginal Consumers Gather Information About Schools?
Authors: Buckley Jack , Schneider Mark
Published: May 2003

The theory of the marginal consumer holds that a subset of better informed consumers can create a globally more efficient market through their purchase decisions. In the market for education created by recent school choice initiatives, these “market mavens” are essential to the successful functioning of the choice system given the empirically documented low quantity and quality of information possessed by the average consumer. Little is known, however, about the differences between how marginal consumers and average consumers of education search for information and make decisions about their children's schooling.
The Impact of Police Officer Diversity on Police‐Caused Homicides
Authors: Smith Brad W.
Published: May 2003

Macrolevel studies of police killings generally focus on testing the conflict and community violence hypotheses. This research generally supports both the conflict proposition that minority threat is related to police violence and the community violence proposition that locations with higher levels of violence have a greater number of police‐caused homicides. However, some of the most common proposals to reduce police‐citizen violence, namely changing police personnel, are largely overlooked in existing research. The majority of studies that have examined police homicides do not acknowledge the possibility that the personnel composition of police agencies may affect levels of police violence. The current article extends previous lines of research on police‐caused homicides by including measures of the personnel composition of police agencies as predictors of police‐caused homicides. More specifically, this study examined the influence of minority and female representation within large municipal police agencies on police‐caused homicides. The findings show that more diversified departments do not have significantly lower levels of police‐caused homicides. The results do, however, support both the conflict and community violence propositions. Furthermore, the pattern of findings suggests the existence of a generalized threat in the nation's largest cities.
ALGEBRAIC K-THEORY IN LOW DEGREE AND THE NOVIKOV ASSEMBLY MAP
Authors: MATTHEY MICHEL , OYONO-OYONO HERVÉ
Published: May 2003

We prove that the Novikov assembly map for a group $\Gamma$ factorizes, in ‘low homological degree’, through the algebraic K-theory of its integral group ring. In homological degree 2, this answers a question posed by N. Higson and P. Julg. As a direct application, we prove that if $\Gamma$ is torsion-free and satisfies the Baum-Connes conjecture, then the homology group $H_{1}(\Gamma;\,\mathbb{Z})$ injects in $K_{1}(C^{*}_{r}\Gamma)$ and in $K_{1}^{\rm alg}(A)$, for any ring $A$ such that $\mathbb{Z}\Gamma\subseteq A\subseteq C^{*}_{r}\Gamma$. If moreover $B\Gamma$ is of dimension less than or equal to 4, then we show that $H_{2}(\Gamma;\,\mathbb{Z})$ injects in $K_{0}(C^{*}_{r}\Gamma)$ and in $K_{2}^{\rm alg}(A)/\Delta_{2}$, where $A$ is as before, and $\Delta_{2}$ is generated by the Steinberg symbols $\{\gamma,\,\gamma\}$, for $\gamma\in\Gamma$.

2000 Mathematical Subject Classification: primary 19D55, 19Kxx, 58J22; secondary: 19Cxx, 19D45, 43A20, 46L85.
RULED SPECIAL LAGRANGIAN 3-FOLDS IN [Copf ]3
Authors: JOYCE DOMINIC
Published: May 2003

This is the fifth in a series of papers constructing explicit examples of special Lagrangian submanifolds in ${\mathbb C}^m$. A submanifold of ${\mathbb C}^m$ is ruled if it is fibred by a family of real straight lines in ${\mathbb C}^m$. This paper studies ruled special Lagrangian 3-folds in ${\mathbb C}^3$, giving both general theory and families of examples. Our results are related to previous work of Harvey and Lawson, Borisenko, and Bryant.
Special Lagrangian cones in ${\mathbb C}^3$ are automatically ruled, and each ruled special Lagrangian 3-fold is asymptotic to a unique special Lagrangian cone. We study the family of ruled special Lagrangian 3-folds N asymptotic to a fixed special Lagrangian cone N0. We find that this depends on solving a linear equation, so that the family of such N has the structure of a vector space. We also show that the intersection $\Sigma$ of N0 with the unit sphere ${\mathcal S}^5$ in ${\mathbb C}^3$ is a Riemann surface, and construct a ruled special Lagrangian 3-fold N asymptotic to N0 for each holomorphic vector field w on $\Sigma$.
As corollaries of this we write down two large families of explicit special Lagrangian 3-folds in ${\mathbb C}^3$ depending on a holomorphic function on $\mathbb C$, which include many new examples of singularities of special Lagrangian 3-folds. We also show that each special Lagrangian T2-cone N0 can be extended to a 2-parameter family of ruled special Lagrangian 3-folds asymptotic to N0, and diffeomorphic to $T^2\times{\mathbb R}$.

2000 Mathematical Subject Classification: 53C38, 53D12.
THE INTERSECTION OF OPPOSED BIG CELLS IN THE REAL FLAG VARIETY OF TYPE G2
Authors: MARSH R. J. , RIETSCH K.
Published: May 2003

We compute the Euler characteristics of the individual connected
components of the intersection of two opposed big cells in the real flag variety of type G2, verifying a conjecture of Rietsch [6].

2000 Mathematical Subject Classification: primary 14M15; secondary 20G20.
AN EXTENSION OF THE CLASSICAL RIBAUCOUR TRANSFORMATION
Authors: DAJCZER MARCOS , TOJEIRO RUY
Published: May 2003

We extend the notion of Ribaucour transformation from classical surface theory to the theory of holonomic submanifolds of pseudo-Riemannian space forms with arbitrary dimension and codimension, that is, submanifolds with flat normal bundle admitting a global system of principal coordinates. Bianchi gave a positive answer to the question of whether among the Ribaucour transforms of a surface with constant mean or Gaussian curvature there exist other surfaces with the same property. Our main achievement is to solve the same problem for the class of holonomic submanifolds with constant sectional curvature.

2000 Mathematical Subject Classification: 53B25, 58J72.
POLYNOMIAL DEHN FUNCTIONS AND THE LENGTH OF ASYNCHRONOUSLY AUTOMATIC STRUCTURES
Authors: BRIDSON MARTIN R.
Published: May 2003

We extend the range of observed behaviour among length functions of optimal asynchronously automatic structures. We do so by means of a construction that yields asynchronously automatic groups with finite aspherical presentations where the Dehn function of the group is polynomial of arbitrary degree. Many of these groups can be embedded in the automorphism group of a free group. Moreover, the fact that the groups have aspherical presentations makes them useful tools in the search to determine the spectrum of exponents for second order Dehn functions. We contribute to this search by giving the first exact calculations of groups with quadratic and superquadratic exponents.

2000 Mathematical Subject Classification:20F06, 20F65, 20F69.
MODEL THEORY OF DIFFERENCE FIELDS, II: PERIODIC IDEALS AND THE TRICHOTOMY IN ALL CHARACTERISTICS
Authors: CHATZIDAKIS ZOÉ , HRUSHOVSKI EHUD , PETERZIL YA'ACOV
Published: May 2003

We classify all possible combinatorial geometries associated with
one-dimensional difference equations, in any characteristic.
The theory of difference fields admits a proper interpretation of itself, namely the reduct
replacing the automorphism by its nth power. We show that these reducts admit a successively
smoother theory as n becomes large; and we succeed in defining a limit structure to these reducts,
or rather to the structure they induce on one-dimensional sets. This limit structure is shown to be
a Zariski geometry in (roughly) the sense of Hrushovski and Zil'ber. The trichotomy is thus obtained
for the limit structure as a consequence of a general theorem, and then shown to be inherited by the
original theory.

2000 Mathematical Subject Classification: 03C60; (primary) 03C45,
03C98, 08A35, 12H10 (secondary)
ON THE CLASSIFICATION OF NUCLEAR C*-ALGEBRAS
Authors: DADARLAT MARIUS , EILERS SØREN
Published: May 2003

We employ results from KK-theory, along with quasidiagonality techniques, to obtain wide-ranging classification results for nuclear C*-algebras. Using a new realization of the Cuntz picture of the Kasparov groups we show that two morphisms inducing equal KK-elements are approximately stably unitarily equivalent. Using K-theory with coefficients to associate a partial KK-element to an approximate morphism, our result is generalized to cover such maps. Conversely, we study the problem of lifting a (positive) partial KK-element to an approximate morphism.
These results are employed to obtain classification results for certain classes of quasidiagonal C*-algebras introduced by H. Lin, and to reprove the classification of purely infinite simple nuclear C*-algebras of Kirchberg and Phillips. It is our hope that this work can be the starting point of a unified approach to the classification of nuclear C*-algebras.

2000 Mathematical Subject Classification: primary 46L35; secondary 19K14, 19K35, 46L80.
ON BOHR'S INEQUALITY
Authors: PAULSEN VERN I. , POPESCU GELU , SINGH DINESH
Published: May 2003

Bohr's inequality says that if $f(z) = \sum^{\infty}_{n = 0} a_n z^n$ is a bounded analytic function on the closed unit disc, then $\sum^{\infty}_{n = 0} \lvert a_n\rvert r^n \leq \Vert f\Vert_{\infty}$ for $0 \leq r \leq 1/3$ and that $1/3$ is sharp. In this paper we give an operator-theoretic proof of Bohr's inequality that is based on von Neumann's inequality. Since our proof is operator-theoretic, our methods extend to several complex variables and to non-commutative situations.

We obtain Bohr type inequalities for the algebras of bounded analytic functions and the multiplier algebras of reproducing kernel Hilbert spaces on various higher-dimensional domains, for the non-commutative disc algebra ${\mathcal A}_n$, and for the reduced (respectively full) group C*-algebra of the free group on $n$ generators.

We also include an application to Banach algebras. We prove that every Banach algebra has an equivalent norm in which it satisfies a non-unital version of von Neumann's inequality.

2000 Mathematical Subject Classification: 47A20, 47A56.
Using a Concentrating Solar Reactor to Produce Hydrogen and Carbon Black via Thermal Decomposition of Natural Gas: Feasibility and Economics
Authors: Spath Pamela L. , Amos Wade A.
Published: May 2003

Producing hydrogen in a cost-effective manner while minimizing environmental impacts is a big challenge. Hydrogen can be generated with carbon as a by-product from thermal decomposition of natural gas. A system using a solar reactor to produce hydrogen on-site for fueling stations was examined for its technical and economic feasibility. Integrated energy and material balance calculations were made to determine the amount of hydrogen that could be produced from a given reactor size and heliostat field area. Hourly solar data were applied to the model to properly estimate real storage requirements. This paper gives the results of the study including the greenhouse gas emissions and energy balance.
Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field
Authors: Kearney D. , Herrmann U. , Nava P. , Kelly B. , Mahoney R. , Pacheco J. , Cable R. , Potrovitza N. , Blake D. , Price H.
Published: May 2003

An evaluation was carried out to investigate the feasibility of utilizing a molten salt as the heat transfer fluid (HTF) and for thermal storage in a parabolic trough solar field to improve system performance and to reduce the levelized electricity cost. The operating SEGS (Solar Electric Generating Systems located in Mojave Desert, California) plants currently use a high temperature synthetic oil consisting of a eutectic mixture of biphenyl/diphenyl oxide. The scope of this investigation included examination of known critical issues, postulating solutions or possible approaches where potential problems exist, and the quantification of performance and electricity cost using preliminary cost inputs. The two leading candidates were the so-called solar salt (a binary salt consisting of 60% NaNO3 and 40% KNO3) and a salt sold commercially as HitecXL (a ternary salt consisting of 48% CaNO32, 7% NaNO3, and 45% KNO3). Assuming a two-tank storage system and a maximum operation temperature of 450°C, the evaluation showed that the levelized electricity cost can be reduced by 14.2% compared to a state-of-the-art parabolic trough plant such as the SEGS plants. If higher temperatures are possible, the improvement may be as high as 17.6%. Thermocline salt storage systems offer even greater benefits.
Ray travel times at long ranges in acoustic waveguides
Authors: Virovlyansky A. L.
Published: May 2003

The Hamiltonian formalism in terms of the action-angle variables is applied to study ray travel times in a waveguide with a smooth sound speed profile perturbed by a weak range-dependent inhomogeneity. A simple approximate formula relating the differences in ray travel times to range variations of action variables is derived. This relation is applied to study range variations of the timefront (representing ray arrivals in the time-depth plane). Widening and bias of timefront segments in the presence of perturbations are considered. Qualitative and quantitative explanations are given to surprising stability of early portions of timefronts observed in both numerical simulations and field experiments. This phenomenon is interpreted from the viewpoint of Fermat’s principle. By ray tracing in a realistic deep water environment with an internal-wave-induced perturbation it has been demonstrated that our approach can be used at ranges up to, at least, 3000 km.
Evoked potential recording during echolocation in a false killer whale Pseudorca crassidens (L)
Authors: Supin Alexander Ya. , Nachtigall Paul E. , Pawloski Jeffrey , Au Whitlow W. L.
Published: May 2003

Auditory brainstem responses (ABRs) were recorded in a false killer whale while the animal echolocated a target. The ABR collection was triggered by echolocation clicks of the animal. In these conditions, the recorded ABR pattern contained a duplicate set of waves. A comparison of ABR wave delays recorded during echolocation with those recorded during regular external stimulation with experimenter generated clicks showed that the first set of waves may be a response to the emitted click whereas the second one may be a response to the echo. Both responses, to the emitted click and to the echo, were of comparable amplitude in spite of the intensity difference of these two sounds that may differ by more than 40 dB near the animal’s head. This finding indicates the presence of some mechanism of releasing responses to echoes from masking by loud emitted clicks. The evoked-potential method may be productive to investigate these mechanisms.
Ray dynamics in long-range deep ocean sound propagation
Authors: Brown Michael G. , Colosi John A. , Tomsovic Steven , Virovlyansky Anatoly L. , Wolfson Michael A. , Zaslavsky George M.
Published: May 2003

Recent results relating to ray dynamics in ocean acoustics are reviewed. Attention is focused on long-range propagation in deep ocean environments. For this class of problems, the ray equations may be simplified by making use of a one-way formulation in which the range variable appears as the independent (timelike) variable. Topics discussed include integrable and nonintegrable ray systems, action-angle variables, nonlinear resonances and the KAM theorem, ray chaos, Lyapunov exponents, predictability, nondegeneracy violation, ray intensity statistics, semiclassical breakdown, wave chaos, and the connection between ray chaos and mode coupling. The Hamiltonian structure of the ray equations plays an important role in all of these topics.
Measurements of human middle ear forward and reverse acoustics: Implications for otoacoustic emissions
Authors: Puria Sunil
Published: May 2003

Middle and inner ears from human cadaver temporal bones were stimulated in the forward direction by an ear-canal sound source, and in the reverse direction by an inner-ear sound source. For each stimulus type, three variables were measured: (a) Pec—ear-canal pressure with a probe-tube microphone within 3 mm of the eardrum, (b) Vst—stapes velocity with a laser interferometer, and (c) Pv—vestibule pressure with a hydrophone. From these variables, the forward middle-ear pressure gain (M1), the cochlear input impedance (Zc), the reverse middle-ear pressure gain (M2), and the reverse middle-ear impedance (M3) are directly obtained for the first time from the same preparation. These measurements can be used to fully characterize the middle ear as a two-port system. Presently, the effect of the middle ear on otoacoustic emissions (OAEs) is quantified by calculating the roundtrip middle-ear pressure gain GmeRT as the product of M1 and M2. In the 2–6.8 kHz region, |GmeRT| decreases with a slope of −22 dB/oct, while OAEs (both click evoked and distortion products) tend to be independent of frequency; this suggests a steep slope in vestibule pressure from 2 kHz to at least 4 kHz for click evoked OAEs and to at least 6.8 kHz for distortion product OAEs. Contrary to common assumptions, measurements indicate that the emission generator mechanism is frequency dependent. Measurements are also used to estimate the reflectance of basally traveling waves at the stapes, and apically generated nonlinear reflections within the vestibule.
Power dissipation and time-averaged pressure in oscillating flow through a sudden area change
Authors: Smith Barton L. , Swift G. W.
Published: May 2003

Experiments on oscillating flow at the abrupt transition between a two-dimensional channel and essentially infinite space are presented. It is shown that phenomena associated with the transition are functions of three independent dimensionless parameters including the dimensionless radius rounding the edge of the end of the channel. The effect of each of these three parameters on the time-averaged pressure difference across the transition and the acoustic power dissipation is explored by holding two parameters fixed while varying the third. Evidence is presented that the losses due to oscillatory flow in this geometry are smaller than would be expected from commonly accepted values for steady flow in similar geometry.
Modeling the frequency dependence (5–120 MHz) of ultrasound backscattering by red cell aggregates in shear flow at a normal hematocrit
Authors: Fontaine Isabelle , Cloutier Guy
Published: May 2003

The frequency dependence of the ultrasound signal backscattered by blood in shear flow was studied using a simulation model. The ultrasound backscattered signal was computed with a linear model that considers the characteristics of the ultrasound system and tissue acoustic properties. The tissue scattering properties were related to the position and shape of the red blood cells (RBCs). A 2D microrheological model simulated the RBC dynamics in a Couette shear flow system. This iterative model, described earlier [Biophys. J. 82, 1696–1710 (2002)], integrates the hydrodynamic effect of the flow, as well as adhesive and repulsive forces between RBCs. RBC aggregation was simulated at 40% hematocrit and shear rates of 0.05–2 s−1. The RBC aggregate sizes ranged, on average, from 3.3 RBCs at 2 s−1 to 33.5 cells at 0.05 s−1. The ultrasound backscattered power was studied at frequencies between 5–120 MHz and insonification angles between 0–180°. At frequencies below approximately 30 MHz, the ultrasound backscattered power increased as the shear rate was decreased and the size of the aggregates was raised. A totally different scattering behavior was noted above 30 MHz. Typical spectral slopes of the backscattered power (log–log scale) between 5–25 MHz equaled 3.8, whereas slopes down to 0.6 were measured at 0.05 s−1, between 40–60 MHz. The ultrasound backscattered power was shown to be angle dependent at low frequencies (5–25 MHz). The anisotropy persisted at high frequencies (>25 MHz) for small aggregates (at 2 s−1). In conclusion, this study sheds some light on the blood backscattering behavior with an emphasis on the non-Rayleigh regime. Additional experimental studies may be necessary to validate the simulation results, and to fully understand the relation between the ultrasound backscattered power, level of RBC aggregation, shear rate, frequency, and insonification angle.
Erratum: “A perturbation method for the modes of cylindrical acoustic waveguides in the presence of temperature gradients” [J. Acoust. Soc. Am. 102, 160–163 (1997)]
Authors: McCartin Brian J.
Published: May 2003

This note concerns itself with the correction of an algebraic mistake as well as its consequences for the results and conclusions of J. Acoust. Soc. Am. 102(1), 160–163 (1997). An addendum is attached which outlines the modifications necessary for the correct treatment of degenerate modes.
Prediction of the interior pressure oscillations included by flow over a cavity
Authors: Hong Jin-Seok , Park Jong Beom , Mongeau Luc
Published: May 2003

The flow-excited resonance of an open cavity exposed to a grazing flow was investigated experimentally. Flow visualization provided information about the position and the strength of the vortices formed over the orifice. A model based on vortex sound theory was used to predict the frequency and the relative magnitude of the self-sustained interior pressure oscillations. Values for the vortex circulation strength and the convection speed were estimated using a least mean square method. The analytical predictions were compared with experimental values and are in reasonably good agreement with the experimental data. The influence of spoilers and other control devices on the excitation mechanism was investigated.
Eye-Specific Retinogeniculate Segregation Independent of Normal Neuronal Activity
Authors: Huberman Andrew D. , Wang Guo-Yong , Liets Lauren C. , Collins Odell A. , Chapman Barbara , Chalupa Leo M.
Published: May 2003

The segregation of initially intermingled left and right eye inputs to the dorsal lateral geniculate nucleus (DLGN) during development is thought to be in response to precise spatial and temporal patterns of spontaneous ganglion cell activity. To test this hypothesis, we disrupted the correlated activity of neighboring ganglion cells in the developing ferret retina through immunotoxin depletion of starburst amacrine cells. Despite the absence of this type of correlated activity, left and right eye inputs segregated normally in the DLGN. By contrast, when all spontaneous activity was blocked, the projections from the two eyes remained intermingled. Thus, certain features of normal neural activity patterns are not required for the formation of eye-specific projections to the DLGN.
Unmasking the S-Phase-Promoting Potential of Cyclin B1
Authors: Moore Jonathan D. , Kirk Jane A. , Hunt Tim
Published: May 2003

In higher eukaryotes, the S phase and M phase of the cell cycle are triggered by different cyclin-dependent kinases (CDKs). For example, in frog egg extracts, Cdk1–cyclin B catalyzes entry into mitosis but cannot trigger DNA replication. Two hypotheses can explain this observation: Either Cdk1–cyclin B fails to recognize the key substrates of its S-phase–promoting counterparts, or its activity is somehow regulated to prevent it from activating DNA synthesis. Here, we show that Cdk1–cyclin B1 has cryptic S-phase–promoting abilities that can be unmasked by relocating it from the cytoplasm to the nucleus and moderately stimulating its activity. Subcellular localization of vertebrate CDKs and the control of their activity are thus critical factors for determining their specificity.
The Ecology of Arsenic
Authors: Oremland Ronald S. , Stolz John F.
Published: May 2003

Arsenic is a metalloid whose name conjures up images of murder. Nonetheless, certain prokaryotes use arsenic oxyanions for energy generation, either by oxidizing arsenite or by respiring arsenate. These microbes are phylogenetically diverse and occur in a wide range of habitats. Arsenic cycling may take place in the absence of oxygen and can contribute to organic matter oxidation. In aquifers, these microbial reactions may mobilize arsenic from the solid to the aqueous phase, resulting in contaminated drinking water. Here we review what is known about arsenic-metabolizing bacteria and their potential impact on speciation and mobilization of arsenic in nature.
A Mesoscale Iron Enrichment in the Western Subarctic Pacific Induces a Large Centric Diatom Bloom
Authors: Tsuda Atsushi , Takeda Shigenobu , Saito Hiroaki , Nishioka Jun , Nojiri Yukihiro , Kudo Isao , Kiyosawa Hiroshi , Shiomoto Akihiro , Imai Keiri , Ono Tsuneo , Shimamoto Akifumi , Tsumune Daisuke , Yoshimura Takeshi , Aono Tatsuo , Hinuma Akira , Kinugasa Masatoshi , Suzuki Koji , Sohrin Yoshiki , Noiri Yoshifumi , Tani Heihachiro , Deguchi Yuji , Tsurushima Nobuo , Ogawa Hiroshi , Fukami Kimio , Kuma Kenshi , Saino Toshiro
Published: May 2003

We have performed an in situ test of the iron limitation hypothesis in the subarctic North Pacific Ocean. A single enrichment of dissolved iron caused a large increase in phytoplankton standing stock and decreases in macronutrients and dissolved carbon dioxide. The dominant phytoplankton species shifted after the iron addition from pennate diatoms to a centric diatom,
Chaetoceros debilis
, that showed a very high growth rate, 2.6 doublings per day. We conclude that the bioavailability of iron regulates the magnitude of the phytoplankton biomass and the key phytoplankton species that determine the biogeochemical sensitivity to iron supply of high-nitrate, low-chlorophyll waters.
Explaining the Abundance of Ants in Lowland Tropical Rainforest Canopies
Authors: Davidson Diane W. , Cook Steven C. , Snelling Roy R. , Chua Tock H.
Published: May 2003

The extraordinary abundance of ants in tropical rainforest canopies has led to speculation that numerous arboreal ant taxa feed principally as “herbivores” of plant and insect exudates. Based on nitrogen (N) isotope ratios of plants, known herbivores, arthropod predators, and ants from Amazonia and Borneo, we find that many arboreal ant species obtain little N through predation and scavenging. Microsymbionts of ants and their hemipteran trophobionts might play key roles in the nutrition of taxa specializing on N-poor exudates. For plants, the combined costs of biotic defenses and herbivory by ants and tended Hemiptera are substantial, and forest losses to insect herbivores vastly exceed current estimates.
Sediment-Dispersed Extraterrestrial Chromite Traces a Major Asteroid Disruption Event
Authors: Schmitz Birger , Häggström Therese , Tassinari Mario
Published: May 2003

Abundant extraterrestrial chromite grains from decomposed meteorites occur in middle Ordovician (480 million years ago) marine limestone over an area of ∼250,000 square kilometers in southern Sweden. The chromite anomaly gives support for an increase of two orders of magnitude in the influx of meteorites to Earth during the mid-Ordovician, as previously indicated by fossil meteorites. Extraterrestrial chromite grains in mid-Ordovician limestone can be used to constrain in detail the temporal variations in flux of extraterrestrial matter after one of the largest asteroid disruption events in the asteroid belt in late solar-system history.
Asymmetrical Allocation of NMDA Receptor ε2 Subunits in Hippocampal Circuitry
Authors: Kawakami Ryosuke , Shinohara Yoshiaki , Kato Yuichiro , Sugiyama Hiroyuki , Shigemoto Ryuichi , Ito Isao
Published: May 2003

Despite its implications for higher order functions of the brain, little is currently known about the molecular basis of left-right asymmetry of the brain. Here we report that synaptic distribution of
N
-methyl-D-aspartate (NMDA) receptor GluRϵ2 (NR2B) subunits in the adult mouse hippocampus is asymmetrical between the left and right and between the apical and basal dendrites of single neurons. These asymmetrical allocations of ϵ2 subunits differentiate the properties of NMDA receptors and synaptic plasticity between the left and right hippocampus. These results provide a molecular basis for the structural and functional asymmetry of the mature brain.
Long-Term Effects of Wildfire on Ecosystem Properties Across an Island Area Gradient
Authors: Wardle David A. , Hörnberg Greger , Zackrisson Olle , Kalela-Brundin Maarit , Coomes David A.
Published: May 2003

Boreal forest soils play an important role in the global carbon cycle by functioning as a large terrestrial carbon sink or source, and the alteration of fire regime through global change phenomena may influence this role. We studied a system of forested lake islands in the boreal zone of Sweden for which fire frequency increases with increasing island size. Large islands supported higher plant productivity and litter decomposition rates than did smaller ones, and, with increasing time since fire, litter decomposition rates were suppressed sooner than was ecosystem productivity. This contributes to greater carbon storage with increasing time since fire; for every century without a major fire, an additional 0.5 kilograms per square meter of carbon becomes stored in the humus.
Boon and Bane of Metal Ions in Medicine
Authors: Thompson Katherine H. , Orvig Chris
Published: May 2003

In biological systems metal ions promote responses that range from deficiency to toxicity. Some, such as iron and zinc, have a known optimal intake range for normal, healthy individuals. Metal ions contained within well-designed molecules already constitute a great boon for the medicinal pharmacopoeia. However, whether essential or not, the threshold for toxicity can be very low. One of the challenges of designing metal-based drugs is to balance the potential toxicity of an active formulation with the substantial positive impact of these increasingly common therapeutic and diagnostic aids.
The Interface Between the Biological and Inorganic Worlds: Iron-Sulfur Metalloclusters
Authors: Rees Douglas C. , Howard James B.
Published: May 2003

Complex iron-sulfur metalloclusters form the active sites of the enzymes that catalyze redox transformations of N
2
, CO, and H
2
, which are likely components of Earth's primordial atmosphere. Although these centers reflect the organizational principles of simpler iron-sulfur clusters, they exhibit extensive elaborations that confer specific ligand-binding and catalytic properties. These changes were probably achieved through evolutionary processes, including the fusion of small clusters, the addition of new metals, and the development of cluster assembly pathways, driven by selective pressures resulting from changes in the chemical composition of the biosphere.
Structural Basis of Multiple Drug-Binding Capacity of the AcrB Multidrug Efflux Pump
Authors: Yu Edward W. , McDermott Gerry , Zgurskaya Helen I. , Nikaido Hiroshi , Koshland Daniel E.
Published: May 2003

Multidrug efflux pumps cause serious problems in cancer chemotherapy and treatment of bacterial infections. Yet high-resolution structures of ligandtransporter complexes have previously been unavailable. We obtained x-ray crystallographic structures of the trimeric AcrB pump from
Escherichia coli
with four structurally diverse ligands. The structures show that three molecules of ligands bind simultaneously to the extremely large central cavity of 5000 cubic angstroms, primarily by hydrophobic, aromatic stacking and van der Waals interactions. Each ligand uses a slightly different subset of AcrB residues for binding. The bound ligand molecules often interact with each other, stabilizing the binding.
The Ratios of Life
Authors: Michaels Anthony F.
Published: May 2003

Ecological Stoichiometry
The Biology of Elements from Molecules to the Biosphere. Robert W. Sterner and James J. Elser. Princeton University Press, Princeton, NJ, 2002. 463 pp., illus. $75, £52. ISBN 0-691-07490-9. Paper, $29.95, £19.95. ISBN 0-691-07491-7.

Sterner and Elser build a case for the important role that understanding the distribution of elements in organisms will play in making sense of ecosystems, both terrestrial and aquatic.
Efficient Epoxidation of Olefins with ≥99% Selectivity and Use of Hydrogen Peroxide
Authors: Kamata Keigo , Yonehara Koji , Sumida Yasutaka , Yamaguchi Kazuya , Hikichi Shiro , Mizuno Noritaka
Published: May 2003

Epoxides are an important class of industrial chemicals that have been used as chemical intermediates. Catalytic epoxidation of olefins affords an interesting production technology. We found a widely usable green route to the production of epoxides: A silicotungstate compound, [γ-SiW10O34(H2O)2]4–, is synthesized by protonation of a divacant, lacunary, Keggin-type polyoxometalate of [γ-SiW10O36]8–and exhibits high catalytic performance for the epoxidation of various olefins, including propylene, with a hydrogen peroxide (H2O2) oxidant at 305 kelvin. The effectiveness of this catalyst is evidenced by ≥99% selectivity to epoxide, ≥99% efficiency of H2O2utilization, high stereospecificity, and easy recovery of the catalyst from the homogeneous reaction mixture.
Calculated Phonon Spectra of Plutonium at High Temperatures
Authors: Dai X. , Savrasov S. Y. , Kotliar G. , Migliori A. , Ledbetter H. , Abrahams E.
Published: May 2003

We constructed computer-based simulations of the lattice dynamical properties of plutonium using an electronic structure method, which incorporates correlation effects among the f-shell electrons and calculates phonon spectra at arbitrary wavelengths. Our predicted spectrum for the face-centered cubic δ phase agrees well with experiments in the elastic limit and explains unusually large shear anisotropy of this material. The spectrum of the body-centered cubic phase shows an instability at zero temperature over a broad region of the wave vectors, indicating that this phase is highly anharmonic and can be stabilized at high temperatures by its phonon entropy.
The Biogeochemical Cycles of Trace Metals in the Oceans
Authors: Morel F. M. M. , Price N. M.
Published: May 2003

Planktonic uptake of some essential metals results in extraordinarily low concentrations in surface seawater. To sequester or take up these micronutrients, various microorganisms apparently release strong complexing agents and catalyze redox reactions that modify the bioavailability of trace metals and promote their rapid cycling in the upper water column. In turn, the low availability of some metals controls the rate of photosynthesis in parts of the oceans and the transformation and uptake of major nutrients such as nitrogen. The extremely low concentrations of several essential metals are both the cause and the result of ultraefficient uptake systems in the plankton and of widespread replacement of metals by one another for various biochemical functions.
State-Specific Correlation of Coincident Product Pairs in the F + CD
4
Reaction
Authors: Lin Jim J. , Zhou Jingang , Shiu Weicheng , Liu Kopin
Published: May 2003

When a chemical reaction forms two molecular products, even if the state-resolved differential cross section (DCS) for each product is obtained individually, the coincident attributes of the coproducts are still lacking. We exploit a method that provides coincidence information by measuring the state-resolved, pair-correlated DCS. Exemplified by the reaction F + CD
4
→ DF + CD
3
, a time-sliced ion velocity imaging technique was used to measure the velocity distribution of a state-selected CD
3
product and to reveal the information of the coincident DF in a state-correlated manner. The correlation of different product state pairs shows a striking difference, which opens up a new way to unravel the complexity of a polyatomic reaction.
Microfluidic Memory and Control Devices
Authors: Groisman Alex , Enzelberger Markus , Quake Stephen R.
Published: May 2003

We demonstrate microscopic fluidic control and memory elements through the use of an aqueous viscoelastic polymer solution as a working fluid. By exploiting the fluid's non-Newtonian rheological properties, we were able to demonstrate both a flux stabilizer and a bistable flip-flop memory. These circuit elements are analogous to their solid-state electronic counterparts and could be used as components of control systems for integrated microfluidic devices. Such miniaturized fluidic circuits are insensitive to electromagnetic interference and may also find medical applications for implanted drug-delivery devices.
Recombinant Antibodies to the Small GTPase Rab6 as Conformation Sensors
Authors: Nizak Clément , Monier Solange , del Nery Elaine , Moutel Sandrine , Goud Bruno , Perez Franck
Published: May 2003

Here we report an approach, based on antibody phage display, to generate molecular conformation sensors. Recombinant antibodies specific to the guanosine triphosphate (GTP)–bound conformation of the small guanosine triphosphatase (GTPase) Rab6, a regulator of membrane traffic, were generated and used to locate Rab6·GTP in fixed cells, and, after green fluorescent protein (GFP) tagging and intracellular expression, to follow Rab6·GTP in vivo. Rab6 was in its GTP-bound conformation on the Golgi apparatus and transport intermediates, and the geometry of transport intermediates was modulated by Rab6 activity. More generally, the same approach could be applied to other molecules that can be locked in a particular conformation in vitro.
People and the Trees
Authors: Donahue Brian
Published: May 2003

Deforesting the Earth
From Prehistory to Global Crisis. Michael Williams. University of Chicago Press, Chicago, 2003. 715 pp. $70, £49. ISBN 0-226-89926-8.

Williams provides an abundantly documented, scholarly account of the impact of humans on forests over the past 6000 years.
Molecular Architecture of the Multiprotein Splicing Factor SF3b
Authors: Golas Monika M. , Sander Bjoern , Will Cindy L. , Lührmann Reinhard , Stark Holger
Published: May 2003

The splicing factor SF3b is a multiprotein complex essential for the accurate excision of introns from pre-messenger RNA. As an integral component of the U2 small nuclear ribonucleoprotein (snRNP) and the U11/U12 di-snRNP, SF3b is involved in the recognition of the pre-messenger RNA's branch site within the major and minor spliceosomes. We have determined the three-dimensional structure of the human SF3b complex by single-particle electron cryomicroscopy at a resolution of less than 10 angstroms, allowing identification of protein domains with known structural folds. The best fit of a modeled RNA-recognition motif indicates that the protein p14 is located in the central cavity of the complex. The 22 tandem helical repeats of the protein SF3b155 are located in the outer shell of the complex enclosing p14.
Transition Metal Speciation in the Cell: Insights from the Chemistry of Metal Ion Receptors
Authors: Finney Lydia A. , O'Halloran Thomas V.
Published: May 2003

The essential transition metal ions are avidly accumulated by cells, yet they have two faces: They are put to use as required cofactors, but they also can catalyze cytotoxic reactions. Several families of proteins are emerging that control the activity of intracellular metal ions and help confine them to vital roles. These include integral transmembrane transporters, metalloregulatory sensors, and diffusible cytoplasmic metallochaperone proteins that protect and guide metal ions to targets. It is becoming clear that many of these proteins use atypical coordination chemistry to accomplish their unique goals. The different coordination numbers, types of coordinating residues, and solvent accessibilities of these sites are providing insight into the inorganic chemistry of the cytoplasm.
Production of Genetically Engineered Biotinylated Interleukin-2 and Its Application in a Rapid Nonradioactive Assay for T-Cell Activation
Authors: Jordan Robert A. , Preissler Mark T. , Banas Jeffrey A. , Gosselin Edmund J.
Published: May 2003

The development of reliable assay systems that can measure lymphocyte activation in vitro has been a major goal of immunodiagnostics. Traditionally, tritiated thymidine incorporation has been used to monitor T-cell activation. Other methods include enzyme-linked immunosorbent assay (ELISA), enzyme-linked immunospot assay, and colorimetric assays. We have established a lymphocyte activation assay that utilizes fluorescein isothiocyanate (FITC)-streptavidin bound to recombinant biotinylated human interleukin-2 (IL-2). Utilizing recombinant DNA technology, a unique monobiotinylated human IL-2 has been created and isolated using the Promega PinPoint vector system. ELISA has been used to demonstrate streptavidin binding and recognition by a human IL-2-specific antibody. IL-2 function has been demonstrated using a murine IL-2-dependent T-cell line, CTLL-2, responsive to human IL-2. Recombinant biotinylated human IL-2 conjugated to streptavidin-FITC or streptavidin-horseradish peroxidase has been used to monitor T-cell activation in the presence of antigen as well as mitogen. The sensitivity and convenience of this method make this lymphocyte activation assay an attractive alternative to tritiated thymidine incorporation as a method for monitoring T-cell activation. In addition, the availability of a recombinant biotinylated human IL-2 will permit the production of a uniform product suitable for diagnostic and clinical application.
Immunoglobulin G Subisotype Responses of Pneumonic and Healthy, Exposed Foals and Adult Horses toRhodococcus equiVirulence-Associated Proteins
Authors: Hooper-McGrevy Kathleen E. , Wilkie Bruce N. , Prescott John F.
Published: May 2003

Rhodococcus equicauses severe pyogranulomatous pneumonia in foals and in immunocompromised humans. Replication of virulent isolates within macrophages correlates with the presence of a large plasmid which encodes a family of seven virulence-associated proteins (VapA and VapC to VapH), whose functions are unknown. Although cell-mediated immunity is thought to be crucial in eliminatingR. equiinfection, antibody partially protects foals. The antibody response to both VapA and VapC was similar in six adult horses and six naturally exposed but healthy foals, as well as in eight foals withR. equipneumonia. The immunoglobulin G (IgG) subisotype response of pneumonic foals to Vap proteins was significantly IgGb biased and also had a trend toward higher IgGT association compared to the isotype association of antibody in adult horses and healthy exposed foals. This suggests that in horses, IgGb and IgGT are Th2 isotypes and IgGa is a Th1 isotype. Furthermore, it suggests that foals which developR. equipneumonia have a Th2-biased, ineffective immune response whereas foals which become immune develop a Th1-biased immune response. Pneumonic foals had significantly more antibody to VapD and VapE than did healthy exposed foals. This may indicate a difference in the expression of these two Vap proteins during persistent infection. Alternatively, in pneumonic foals the deviation of the immune response toward VapD and VapE may reflect a bias unfavorable toR. equiresistance. These data indicate possible age-related differences in the equine immune response affecting Th1-Th2 bias as well as antibody specificity bias, which together favor the susceptibility of foals toR. equipneumonia.
Respiratory Disease in Kennelled Dogs: Serological Responses toBordetella bronchisepticaLipopolysaccharide Do Not Correlate with Bacterial Isolation or Clinical Respiratory Symptoms
Authors: Chalker Victoria J. , Toomey Crista , Opperman Shaun , Brooks Harriet W. , Ibuoye Michael A. , Brownlie Joe , Rycroft Andrew N.
Published: May 2003

The role ofBordetella bronchisepticain a natural outbreak of canine infectious respiratory disease was investigated both by culture and serological analysis.B. bronchisepticawas found in the lungs of a large proportion of clinically healthy dogs and in a greater proportion of dogs with respiratory disease. Using a lipopolysaccharide (LPS) antigen-based enzyme-linked immunosorbent assay, we analyzed the serological responses of a large number of dogs. Dogs with high antibody levels showed no protection from disease, and there was no correlation between the development of disease and rising antibody titer. Similarly, there was no difference in antibody levels in dogs with and withoutB. bronchisepticain the lungs. Antibodies to LPS have no predictive value in determining which animals will contract respiratory disease, how severe the disease will be, or which dogs will haveB. bronchisepticacolonizing the lungs.
Effects of Sample Collection and Storage Methods on Antipneumococcal Immunoglobulin A in Saliva
Authors: Nurkka A. , Obiero J. , Käyhty H. , Scott J. A. G.
Published: May 2003

Saliva contains components of both the mucosal and systemic immune systems. Variable flow rates, immunoglobulin proteases, and variation in collection and storage methods all introduce differences in the estimated concentrations of antibodies. We evaluated the effect of four collection methods and three storage protocols on the concentrations of immunoglobulin A (IgA) antibodies to pneumococcal capsular antigens 1, 5, 6B, and 14 and to pneumococcal surface adhesin A (PsaA) in saliva. Specimens were collected from 30 healthy Kenyan adults by collecting drool, by pipette suction, and with two commercial kits, OraSure and Oracol. Aliquots from each specimen were snap-frozen with glycerol in liquid nitrogen or stored for 4 to 8 h at +4°C either with or without the addition of protease enzyme inhibitors prior to storage at −70°C. Anticapsular IgA concentrations were not significantly different with different collection methods, but snap-freezing the specimens in liquid nitrogen led to concentrations 41 to 47% higher than those of specimens stored by the other methods (
P
< 0.0005).
Relationship between Plasma Interleukin-12 (IL-12) and IL-18 Levels and Severe Malarial Anemia in an Area of Holoendemicity in Western Kenya
Authors: Chaisavaneeyakorn Sujittra , Othoro Caroline , Shi Ya Ping , Otieno Juliana , Chaiyaroj Sansanee C. , Lal Altaf A. , Udhayakumar Venkatachalam
Published: May 2003

In this study, we investigated whether levels of interleukin-12 (IL-12) and IL-18 in plasma are associated with severe malarial anemia outcomes in an area of holoendemicity in western Kenya. We compared plasma IL-12 and IL-18 levels in six groups of children grouped into the categories aparasitemic, asymptomatic, mild malaria, high-density uncomplicated malaria (UC), moderate malarial anemia (MMA), or severe malarial anemia (SMA). IL-12 levels were significantly reduced in children with SMA (P< 0.05) but not in other groups compared to children in the aparasitemic control group. IL-18, a cytokine known to be critical for the induction of gamma interferon along with IL-12, was produced more frequently (70%) in children with UC (P= 0.06) than in children in the aparasitemic control group (32%). However, in the SMA group the IL-18 response rate declined to 30%, which was similar to that in the aparasitemic control group, which showed a 32% response rate. This finding suggests that the IL-18 response may be impaired in children with SMA. In summary, the results from this study support the hypothesis that impairment of IL-12 and/or IL-18 response may contribute to the development of severe malarial anemia in areas of holoendemicity for malaria.