bluuebunny/crossref_metadata_2025 huggingface dataset:
Rutherford Backscattering to Study the Near-Surface Region of Volatile Liquids and Solids
Authors: Krieger Ulrich K. , Huthwelker Thomas , Daniel Christian , Weers Uwe , Peter Thomas , Lanford William A.
Published: July 2002

Here we describe the use of Rutherford backscattering spectrometry (RBS) to measure quantitative in situ elemental profiles with high depth resolution, online and nondestructively, in volatile substances (liquid and frozen acids, ice). Samples for analysis are held in a chamber with controlled temperature and partial pressures designed to match conditions for aerosols in Earth's atmosphere. This technique is demonstrated in studies of water solubility in sulfuric acid, hydrochloric acid (HCl) on ice surfaces, the formation of a HCl-hexahydrate surface layer on evaporating HCl-doped ice, and the diffusion of water through this layer.
Existence of an
16
O-Rich Gaseous Reservoir in the Solar Nebula
Authors: Krot Alexander N. , McKeegan Kevin D. , Leshin Laurie A. , MacPherson Glenn J. , Scott Edward R. D.
Published: July 2002

Carbonaceous chondrite condensate olivine grains from two distinct petrographic settings, calcium-aluminum–rich inclusion (CAI) accretionary rims and amoeboid olivine aggregates (AOAs), are oxygen-16 (
16
O) enriched at the level previously observed inside CAIs. This requires that the gas in the nebular region where these grains condensed was
16
O-rich. This contrasts with an
16
O-poor gas present during the formation of chondrules, suggesting that CAIs and AOAs formed in a spatially restricted region of the solar nebula containing
16
O-rich gas. The
16
O-rich gas composition may have resulted either from mass-independent isotopic chemistry or from evaporation of regions with enhanced dust/gas ratios, possibly in an X-wind environment near the young Sun.
Early Warming of Tropical South America at the Last Glacial-Interglacial Transition
Authors: Seltzer G. O. , Rodbell D. T. , Baker P. A. , Fritz S. C. , Tapia P. M. , Rowe H. D. , Dunbar R. B.
Published: July 2002

Glaciation in the humid tropical Andes is a sensitive indicator of mean annual temperature. Here, we present sedimentological data from lakes beyond the glacial limit in the tropical Andes indicating that deglaciation from the Last Glacial Maximum led substantial warming at high northern latitudes. Deglaciation from glacial maximum positions at Lake Titicaca, Peru/Bolivia (16°S), and Lake Junin, Peru (11°S), occurred 22,000 to 19,500 calendar years before the present, several thousand years before the Bølling-Allerød warming of the Northern Hemisphere and deglaciation of the Sierra Nevada, United States (36.5° to 38°N). The tropical Andes deglaciated while climatic conditions remained regionally wet, which reflects the dominant control of mean annual temperature on tropical glaciation.
An R&D Victory, But for How Long?
Authors: Lawler Andrew
Published: July 2002

The drastic cuts in spending on federal R&D proposed by House Republicans in 1995 failed to materialize, and last month the 104th Congress went home after approving a 1997 budget that will boost federal spending on science by 4%, including a whopping 7% increase for the National Institutes of Health. But long-term funding prospects remain uneven regardless of who wins in November.
New Attacks Breach Computer Codes
Authors: Seife Charles
Published: July 2002

The computer security systems that lock up messages in supposedly unreadable code are taking hit after hit. In the past year, a security consultant found a sneaky way to read “secure” public-key messages, and a team of researchers showed how to unravel entire public-key encryption systems. In the latest attack, a cryptographer has cracked tough secret-key systems including the Data Encryption Standard, widely used in credit card verification and automated teller machines.
Panel Finds EMFs Pose No Threat
Authors: Kaiser Jocelyn
Published: July 2002

A National Research Council report concludes that ordinary exposure to electromagnetic fields from power lines and household appliances does not cause cancer, neurobehavioral disorders, or reproductive and developmental problems. But the debate over EMFs is unlikely to be put to rest.
Mouse Model for Pregnancy Problem?
Authors: Gura Trisha
Published: July 2002

By mating two genetically engineered strains of mice, a Japanese research team reports in this issue ((
p.995
) that it may have produced a mouse model for pregnancy-induced hypertension, a serious condition that develops late in pregnancy and threatens the life of both the mother and the child she is carrying.
Origins Researchers Win Gore's Ear, Not Pocketbook
Authors: Lawler Andrew
Published: July 2002

Last week, the scientific buzz about the possibility of fossil life on Mars and the significance of planets circling other stars earned the rapt attention of Vice President Al Gore. But it's too early to know whether that high-level political attention will translate into a stable budget for NASA's space science program.
Biologists Put on Mathematical Glasses
Authors: Fagerström Torbjörn , Jagers Peter , Schuster Peter , Szathmary Eörs
Published: July 2002

Fagerström, Jagers, Schuster, and Szathmary outline the state of a new field—theoretical biology—as discussed at a recent meeting in Sweden.
Europa's Differentiated Internal Structure: Inferences from Two Galileo Encounters
Authors: Anderson J. D. , Lau E. L. , Sjogren W. L. , Schubert G. , Moore W. B.
Published: July 2002

Doppler data generated with the Galileo spacecraft’s radio carrier wave during two Europa encounters on 19 December 1996 (E4) and 20 February 1997 (E6) were used to measure Europa’s external gravitational field. The measurements indicate that Europa has a predominantly water ice-liquid outer shell about 100 to 200 kilometers thick and a deep interior with a density in excess of about 4000 kilograms per cubic meter. The deep interior could be a mixture of metal and rock or it could consist of a metal core with a radius about 40 percent of Europa’s radius surrounded by a rock mantle with a density of 3000 to 3500 kilograms per cubic meter. The metallic core is favored if Europa has a magnetic field.
Surface Stress in the Self-Assembly of Alkanethiols on Gold
Authors: Berger Rüdiger , Delamarche Emmanuel , Lang Hans Peter , Gerber Christoph , Gimzewski James K. , Meyer Ernst , Güntherodt Hans-Joachim
Published: July 2002

Surface stress changes and kinetics were measured in situ during the self-assembly of alkanethiols on gold by means of a micromechanical sensor. Self-assembly caused compressive surface stress that closely followed Langmuir-type adsorption kinetics up to monolayer coverage. The surface stress at monolayer coverage increased linearly with the length of the alkyl chain of the molecule. These observations were interpreted in terms of differences in surface potential. This highly sensitive sensor technique has a broad range of applicability to specific chemical and biological interactions.
Observations of
PKKP
Precursors Used to Estimate Small-Scale Topography on the Core-Mantle Boundary
Authors: Earle Paul S. , Shearer Peter M.
Published: July 2002

Stacks of global seismic data reveal the time and distance dependence of high-frequency (1-hertz) precursors to the seismic phase
PKKP
. Synthetic seismogram modeling shows that scattering from random small-scale topography at the
PKKP
core-mantle
–
boundary reflection point generates precursory arrivals similar to those seen in the data. Models with a root mean square core-mantle–boundary topography of 250 to 350 meters and correlation length of 7 to 10 kilometers explain the main features of the data. However, a systematic range-dependent misfit between observed and predicted precursor power suggests that inner core scattering may contribute to the precursors.
Electronic Coherence and Collective Optical Excitations of Conjugated Molecules
Authors: Mukamel Shaul , Tretiak Sergei , Wagersreiter Thomas , Chernyak Vladimir
Published: July 2002

Optical spectroscopy of conjugated molecules is described by using collective electronic coordinates, which represent the joint dynamics of electron-hole pairs. The approach relates the optical signals directly to the dynamics of charges and bond orders (electronic coherences) induced by the radiation field and uses only ground-state information, thus avoiding the explicit calculation of excited molecular states. The resulting real-space picture is reminiscent of the normal-mode analysis of molecular vibrations and offers a unified framework for the treatment of other types of systems including semiconductor nanostructures and biological complexes. Spatial coherence displayed in two-dimensional plots of the five electronic normal modes that dominate the optical response of poly(
p
-phenylene vinylene) oligomers with up to 50 repeat units (398 carbon atoms) in the 1.5- to 8-electronvolt frequency range suggests a saturation to bulk behavior at about five repeat units.
CD4-Independent Binding of SIV gp120 to Rhesus CCR5
Authors: Martin Kathleen A. , Wyatt Richard , Farzan Michael , Choe Hyeryun , Marcon Luisa , Desjardins Elizabeth , Robinson James , Sodroski Joseph , Gerard Craig , Gerard Norma P.
Published: July 2002

CCR5 and CD4 are coreceptors for immunodeficiency virus entry into target cells. The gp120 envelope glycoprotein from human immunodeficiency virus strain HIV-1(YU2) bound human CCR5 (CCR5
hu
) or rhesus macaque CCR5 (CCR5
rh
) only in the presence of CD4. The gp120 from simian immunodeficiency virus strain SIVmac239 bound CCR5
rh
without CD4, but CCR5
hu
remained CD4-dependent. The CD4-independent binding of SIVmac239 gp120 depended on a single amino acid, Asp
13
, in the CCR5
rh
amino-terminus. Thus, CCR5-binding moieties on the immunodeficiency virus envelope glycoprotein can be generated by interaction with CD4 or by direct interaction with the CCR5 amino-terminus. These results may have implications for the evolution of receptor use among lentiviruses as well as utility in the development of effective intervention.
A View from the Other Side
Authors: Adelman Richard C.
Published: July 2002

Toward the End of Time.
JOHN UPDIKE. Knopf, New York, 1997. x, 337 pp. $25 or C$35. ISBN 0-375-40006-0.
How to Teach Science
Authors: Arch Stephen
Published: July 2002

Student-Active Science
. Models of Innovation in College Science Teaching. ANN P. McNEAL and CHARLENE D'AVANZO, Eds. Saunders College (Harcourt Brace), Fort Worth, TX, 1997. xxvi, 490 pp., illus. Paper, $47, ISBN 0-03-024307-6. From a conference, June 1996.
Energy Transduction on the Nanosecond Time Scale: Early Structural Events in a Xanthopsin Photocycle
Authors: Perman Benjamin , Šrajer Vukica , Ren Zhong , Teng Tsu-yi , Pradervand Claude , Ursby Thomas , Bourgeois Dominique , Schotte Friederich , Wulff Michael , Kort Remco , Hellingwerf Klaas , Moffat Keith
Published: July 2002

Photoactive yellow protein (PYP) is a member of the xanthopsin family of eubacterial blue-light photoreceptors. On absorption of light, PYP enters a photocycle that ultimately transduces the energy contained in a light signal into an altered biological response. Nanosecond time-resolved x-ray crystallography was used to determine the structure of the short-lived, red-shifted, intermediate state denoted [pR], which develops within 1 nanosecond after photoelectronic excitation of the chromophore of PYP by absorption of light. The resulting structural model demonstrates that the [pR] state possesses the
cis
conformation of the 4-hydroxyl cinnamic thioester chromophore, and that the process of
trans
to
cis
isomerization is accompanied by the specific formation of new hydrogen bonds that replace those broken upon excitation of the chromophore. Regions of flexibility that compose the chromophore-binding pocket serve to lower the activation energy barrier between the dark state, denoted pG, and [pR], and help initiate entrance into the photocycle. Direct structural evidence is provided for the initial processes of transduction of light energy, which ultimately translate into a physiological signal.
Conservation of Substrate Recognition Mechanisms by tRNA Splicing Endonucleases
Authors: Fabbri Stefania , Fruscoloni Paolo , Bufardeci Emanuela , Negri Elisa Di Nicola , Baldi Maria I. , Attardi Domenica Gandini , Mattoccia Emilio , Tocchini-Valentini Glauco P.
Published: July 2002

Accuracy in transfer RNA (tRNA) splicing is essential for the formation of functional tRNAs, and hence for gene expression, in both Eukaryotes and Archaea. The specificity for recognition of the tRNA precursor (pre-tRNA) resides in the endonuclease, which removes the intron by making two independent endonucleolytic cleavages. Although the eukaryal and archaeal enzymes appear to use different features of pre-tRNAs to determine the sites of cleavage, analysis of hybrid pre-tRNA substrates containing eukaryal and archaeal sequences, described here, reveals that the eukaryal enzyme retains the ability to use the archaeal recognition signals. This result indicates that there may be a common ancestral mechanism for recognition of pre-tRNA by proteins.
Toward HIV Eradication or Remission: The Tasks Ahead
Authors: Ho David D.
Published: July 2002

Recent advances in the understanding of viral kinetics and drug therapies have led to the real possibility that HIV can be kept under tight control or that an infected person can be rendered totally free of virus. There are major hurdles in the way of these goals, and David Ho discusses some of the strategies being considered.
A Small, Nonpeptidyl Mimic of Granulocyte-Colony- Stimulating Factor
Authors: Tian Shin-Shay , Lamb Peter , King Andrew G. , Miller Stephen G. , Kessler Linda , Luengo Juan I. , Averill Laurie , Johnson Randall K. , Gleason John G. , Pelus Louis M. , Dillon Susan B. , Rosen Jonathan
Published: July 2002

A nonpeptidyl small molecule SB 247464, capable of activating granulocyte–colony-stimulating factor (G-CSF) signal transduction pathways, was identified in a high-throughput assay in cultured cells. Like G-CSF, SB 247464 induced tyrosine phosphorylation of multiple signaling proteins and stimulated primary murine bone marrow cells to form granulocytic colonies in vitro. It also elevated peripheral blood neutrophil counts in mice. The extracellular domain of the murine G-CSF receptor was required for the activity of SB 247464, suggesting that the compound acts by oligomerizing receptor chains. The results indicate that a small molecule can activate a receptor that normally binds a relatively large protein ligand.
Innovative History of the Chemical Industry
Authors: Freeman Christopher
Published: July 2002

Chemicals and Long-Term Economic Growth
Insights from the Chemical Industry. Ashish Arora, Ralph Landau and Nathan Rosenberg, Eds. Wiley-Interscience, New York, and Chemical Heritage Foundation, 1998. 576 pp. $69.95. ISBN 0-471-18247-8.

The editors have assembled a thorough, insightful examination of the history and economics of the chemical industry in Britain, Germany, Japan, and the United States. Contributors consider the roles of science, innovation, technology, organization, and government and financial policies in creating economic growth, and in determining why "certain industries excel in certain areas."
The Density of Hydrous Magmatic Liquids
Authors: Ochs Frederick A. , Lange Rebecca A.
Published: July 2002

Density measurements on several hydrous (≤19 mole percent of H
2
O) silicate melts demonstrate that dissolved water has a partial molar volume (
V̄

H
2

O
) that is independent of the silicate melt composition, the total water concentration, and the speciation of water. The derived value for
V̄

H
2

O
is 22.9 ± 0.6 cubic centimeters per mole at 1000°C and 1 bar of pressure, whereas the partial molar thermal expansivity (∂
V̄

H
2

O
/∂
T
) and compressibility (∂
V̄

H
2

O
/∂
P
) are 9.5 ± 0.8 × 10
−3
cubic centimeters per mole per kelvin and −3.2 ± 0.6 × 10
−4
cubic centimeters per mole per bar, respectively. The effect of 1 weight percent dissolved H
2
O on the density of a basaltic melt is equivalent to increasing the temperature of the melt by ∼400°C or decreasing the pressure of the melt by ∼500 megapascals. These measurements are used to illustrate the viability of plagioclase sinking in iron-rich basaltic liquids and the dominance of compositional convection in hydrous magma chambers.
Decay of the GRB 990123 Optical Afterglow: Implications for the Fireball Model
Authors: Castro-Tirado Alberto J. , Zapatero-Osorio Marı́a Rosa , Caon Nicola , Cairós Luz Marina , Hjorth Jens , Pedersen Holger , Andersen Michael I. , Gorosabel Javier , Bartolini Corrado , Guarnieri Adriano , Piccioni Adalberto , Frontera Filippo , Masetti Nicola , Palazzi Eliana , Pian Elena , Greiner Jochen , Hudec Renè , Sagar Ram , Pandey Anil K. , Mohan Vinay , Yadav Ramakant K. S. , Nilakshi  , Björnsson Gunnlaugur , Jakobsson Páll , Burud Ingunn , Courbin Frederic , Valentini Gaetano , Piersimoni Anna , Aceituno Jesús , Montoya Luz Marı́a , Pedraz Santos , Gredel Roland , Claver Charles F. , Rector Travis A. , Rhoads James E. , Walter Fabian , Ott Jürgen , Hippelein Hans , Sánchez-Béjar Victor , Gutiérrez Carlos , Oscoz Alejandro , Zhu Jin , Chen Jiansheng , Zhang Haotong , Wei Jianyan , Zhou Aiying , Guziy Sergei , Shlyapnikov Aleksei , Heise John , Costa Enrico , Feroci Marco , Piro Luigi
Published: July 2002

Broad-band (ultraviolet to near-infrared) observations of the intense gamma ray burst GRB 990123 started ∼8.5 hours after the event and continued until 18 February 1999. When combined with other data, in particular from the Robotic Telescope and Transient Source Experiment (ROTSE) and the Hubble Space Telescope (HST), evidence emerges for a smoothly declining light curve, suggesting some color dependence that could be related to a cooling break passing the ultraviolet-optical band at about 1 day after the high-energy event. The steeper decline rate seen after 1.5 to 2 days may be evidence for a collimated jet pointing toward the observer.
The Benefits of Selective Thinking
Authors: Pagel Mark
Published: July 2002

Evolution in Health and Disease
. Stephen C. Stearns, Ed. Oxford University Press, Oxford, 1999. 344 pp. $95, £55. ISBN 0-19-850110-2. Paper, $45, £23.50. ISBN 0-19-850445-4.

Stearns and the more than 60 participants at a 1997 conference on evolutionary medicine have produced a surprisingly broad yet readable volume, which demonstrates the applicability of evolutionary biology to problems of disease and suffering.
Self-Similarity in the Distribution and Abundance of Species
Authors: Harte John , Kinzig Ann , Green Jessica
Published: July 2002

If the fraction of species in area
A
that are also found in one-half of that area is independent of
A
, the distribution of species is self-similar and a number of observed patterns in ecology, including the widely cited species-area relationship connecting species richness to censused area, follow. Self-similarity also leads to a species-abundance distribution, which deviates considerably from the commonly assumed lognormal distribution and predicts considerably more rare species than the latter. Because the abundance distribution is derived under the condition of self-similarity, it may be widely applicable beyond ecology.
Single-Crystal-Like Diffraction Data from Polycrystalline Materials
Authors: Wessels Thomas , Baerlocher Christian , McCusker Lynne B.
Published: July 2002

A method for solving structures from powder diffraction data was developed, and its validity was demonstrated on three complex structures. The method uses a textured sample and exploits the high intensity and parallel nature of synchrotron radiation. In principle, crystal structures as complex as those routinely solved by single-crystal methods can be determined with this approach. For example, the as-synthesized form of the zeolite UTD-1, with 69 nonhydrogen atoms in the asymmetric unit, could be solved directly. With this method, a larger range of structural complexity becomes accessible to scientists interested in the structures of polycrystalline materials that cannot be grown as single crystals.
An Evolutionary Dead End?
Authors: Orr H. Allen
Published: July 2002

Phenotypic Evolution
A Reaction Norm Perspective. Carl D. Schlichting and Massimo Pigliucci. Sinauer Associates, Sunderland, MA, 1998. 400 pp. Paper, $38.95. ISBN 0-87893-799-4.

Schlichting and Pigliucci argue for the evolutionary importance of the "developmental reaction norm," a concept that combines adaptive plasticity, development, and allometry.
Unraveling the Electronic Structure of Individual Photosynthetic Pigment-Protein Complexes
Authors: van Oijen Antoine M. , Ketelaars Martijn , Köhler Jürgen , Aartsma Thijs J. , Schmidt Jan
Published: July 2002

Low-temperature single-molecule spectroscopic techniques were applied to a light-harvesting pigment-protein complex (LH2) from purple photosynthetic bacteria. The properties of the electronically excited states of the two circular assemblies (B800 and B850) of bacteriochlorophyll a (BChl a) pigment molecules in the individual complexes were revealed, without ensemble averaging. The results show that the excited states of the B800 ring of pigments are mainly localized on individual BChl a molecules. In contrast, the absorption of a photon by the B850 ring can be consistently described in terms of an excitation that is completely delocalized over the ring. This property may contribute to the high efficiency of energy transfer in these photosynthetic complexes.
Superradiant Rayleigh Scattering from a Bose-Einstein Condensate
Authors: Inouye S. , Chikkatur A. P. , Stamper-Kurn D. M. , Stenger J. , Pritchard D. E. , Ketterle W.
Published: July 2002

Rayleigh scattering off a Bose-Einstein condensate was studied. Exposing an elongated condensate to a single off-resonant laser beam resulted in the observation of highly directional scattering of light and atoms. This collective light scattering is caused by the coherent center-of-mass motion of the atoms in the condensate. A directional beam of recoiling atoms was built up by matter wave amplification.
Coordinate Regulation of
RAG1
and
RAG2
by Cell Type-Specific DNA Elements 5' of
RAG2
Authors: Yu Wong , Misulovin Ziva , Suh Heikyung , Hardy Richard R. , Jankovic Mila , Yannoutsos Nikos , Nussenzweig Michel C.
Published: July 2002

RAG1
and
RAG2
are essential for V(D)J recombination and lymphocyte development. These genes are thought to encode a transposase derived from a mobile genetic element that was inserted into the vertebrate genome 450 million years ago. The regulation of
RAG1
and
RAG2
was investigated in vivo with bacterial artificial chromosome (BAC) transgenes containing a fluorescent indicator. Coordinate expression of
RAG1
and
RAG2
in B and T cells was found to be regulated by distinct genetic elements found on the 5′ side of the
RAG2
gene. This observation suggests a mechanism by which asymmetrically disposed cis DNA elements could influence the expression of the primordial transposon and thereby capture RAGs for vertebrate evolution.
Structure for Theories of Biology
Authors: Mayr Ernst
Published: July 2002

Sex and Death
An Introduction to Philosophy of Biology. Kim Sterelny and Paul E. Griffiths. University of Chicago Press, Chicago, 1999. 456 pp. $60, £47.95. ISBN 0-226-77303-5. Paper, $22, £17.50. ISBN 0-226-77304-3.

Sterelny and Griffiths provide broad ranging and clearly written survey of contemporary issues in the philosophy of biology ranging from the nature of genes, organisms, and species to macroevolution, human nature, and what constitutes life.
Formation of Cycloidal Features on Europa
Authors: Hoppa Gregory V. , Tufts B. Randall , Greenberg Richard , Geissler Paul E.
Published: July 2002

Cycloidal patterns are widely distributed on the surface of Jupiter's moon Europa. Tensile cracks may have developed such a pattern in response to diurnal variations in tidal stress in Europa's outer ice shell. When the tensile strength of the ice is reached, a crack may occur. Propagating cracks would move across an ever-changing stress field, following a curving path to a place and time where the tensile stress was insufficient to continue the propagation. A few hours later, when the stress at the end of the crack again exceeded the strength, propagation would continue in a new direction. Thus, one arcuate segment of the cycloidal chain would be produced during each day on Europa. For this model to work, the tensile strength of Europa's ice crust must be less than 40 kilopascals, and there must be a thick fluid layer below the ice to allow sufficient tidal amplitude.
A New Primate from the Middle Eocene of Myanmar and the Asian Early Origin of Anthropoids
Authors: Jaeger J.-J. , Thein Tin , Benammi M. , Chaimanee Y. , Soe Aung Naing , Lwin Thit , Tun Than , Wai San , Ducrocq S.
Published: July 2002

A new genus and species of anthropoid primate,
Bahinia pondaungensis
gen. et sp. nov., is described from the Yashe Kyitchaung locality in the Late Middle Eocene Pondaung Formation (Myanmar). It is related to
Eosimias
, but it is represented by more complete remains, including upper dentition with associated lower jaw fragment. It is interpreted as a new representative of the family Eosimiidae, which corresponds to the sister group of the Amphipithecidae and of all other anthropoids. Eosimiidae are now recorded from three distinct Middle Eocene localities in Asia, giving support to the hypothesis of an Asian origin of anthropoids.
Tales of Cooling
Authors: Goodstein David
Published: July 2002

Absolute Zero and the Conquest of Cold
. Tom Shachtman. Houghton Mifflin, Boston, 1999. 271 pp. $25. ISBN 0-395-93888-0.

In his first book on science, writer Shachtman provides a fresh perspective on the scientific and commercial histories of cold. His account suffers from numerous factual errors that could have been easily corrected.
Density of Phonon States in Iron at High Pressure
Authors: Lübbers R. , Grünsteudel H. F. , Chumakov A. I. , Wortmann G.
Published: July 2002

The lattice dynamics of the hexagonal close-packed (hcp) phase of iron was studied with nuclear inelastic absorption of synchrotron radiation at pressures from 20 to 42 gigapascals. A variety of thermodynamic parameters were derived from the measured density of phonon states for hcp iron, such as Debye temperatures, Grüneisen parameter, mean sound velocities, and the lattice contribution to entropy and specific heat. The results are of geophysical interest, because hcp iron is considered to be a major component of Earth's inner core.
Chain Mobility in the Amorphous Region of Nylon 6 Observed under Active Uniaxial Deformation
Authors: Loo Leslie S. , Cohen Robert E. , Gleason Karen K.
Published: July 2002

A specially designed solid-state deuterium nuclear magnetic resonance probe was used to examine the effect of uniaxial elongation on the chain mobility in the amorphous region of semicrystalline nylon 6. In measurements conducted near the glass transition temperature, there was measurable deformation-induced enhancement of the mobility of the amorphous chains up to the yield point. This enhanced mobility decayed once deformation was stopped. Enhanced mobility was not observed in deformation at room temperature. The mechanics of deformation can be explained by the Robertson model for glassy polymers near the glass transition temperature, which states that applied stress induces liquid-like behavior in the polymer chains.
If You Build It, Will It Know?
Authors: Markman Arthur B.
Published: July 2002

Understanding Intelligence
. Rolf Pfeifer and Christian Scheier. MIT Press, Cambridge, MA, 1999. 717 pp. $60. ISBN 0-262-16181-8.

Pfeifer and Scheier provide a comprehensive introduction to embodied cognitive science that will be particularly helpful for people interested in building robots as part of their research into the processes of intelligence.
Quantifying Denitrification and Its Effect on Ozone Recovery
Authors: Tabazadeh A. , Santee M. L. , Danilin M. Y. , Pumphrey H. C. , Newman P. A. , Hamill P. J. , Mergenthaler J. L.
Published: July 2002

Upper Atmosphere Research Satellite observations indicate that extensive denitrification without significant dehydration currently occurs only in the Antarctic during mid to late June. The fact that denitrification occurs in a relatively warm month in the Antarctic raises concern about the likelihood of its occurrence and associated effects on ozone recovery in a colder and possibly more humid future Arctic lower stratosphere. Polar stratospheric cloud lifetimes required for Arctic denitrification to occur in the future are presented and contrasted against the current Antarctic cloud lifetimes. Model calculations show that widespread severe denitrification could enhance future Arctic ozone loss by up to 30%.
Holes in a Quantum Spin Liquid
Authors: Xu Guangyong , Aeppli G. , Bisher M. E. , Broholm C. , DiTusa J. F. , Frost C. D. , Ito T. , Oka K. , Paul R. L. , Takagi H. , Treacy M. M. J.
Published: July 2002

Magnetic neutron scattering provides evidence for nucleation of antiferromagnetic droplets around impurities in a doped nickel oxide–based quantum magnet. The undoped parent compound contains a spin liquid with a cooperative singlet ground state and a gap in the magnetic excitation spectrum. Calcium doping creates excitations below the gap with an incommensurate structure factor. We show that weakly interacting antiferromagnetic droplets with a central phase shift of π and a size controlled by the correlation length of the quantum liquid can account for the data. The experiment provides a quantitative impression of the magnetic polarization cloud associated with holes in a doped transition metal oxide.
Molecular Analysis of Plant Migration and Refugia in the Arctic
Authors: Abbott Richard J. , Smith Lisa C. , Milne Richard I. , Crawford Robert M. M. , Wolff Kirsten , Balfour Jean
Published: July 2002

The arctic flora is thought to have originated during the late Tertiary, approximately 3 million years ago. Plant migration routes during colonization of the Arctic are currently unknown, and uncertainty remains over where arctic plants survived Pleistocene glaciations. A phylogenetic analysis of chloroplast DNA variation in the purple saxifrage (
Saxifraga oppositifolia
) indicates that this plant first occurred in the Arctic in western Beringia before it migrated east and west to achieve a circumpolar distribution. The geographical distribution of chloroplast DNA variation in the species supports the hypothesis that, during Pleistocene glaciations, some plant refugia were located in the Arctic as well as at more southern latitudes.
Xenon as a Complex Ligand: The Tetra Xenono Gold(II) Cation in AuXe
4
2+
(Sb
2
F
11
−
)
2
Authors: Seidel Stefan , Seppelt Konrad
Published: July 2002

The first metal-xenon compound with direct gold-xenon bonds is achieved by reduction of AuF
3
with elemental xenon. The square planar AuXe
4
2+
cation is established by a single-crystal structure determination, with a gold-xenon bond length of approximately 274 picometers. The bonding between gold and xenon is of the σ donor type, resulting in a charge of approximately 0.4 per xenon atom.
Modulated Chemical Doping of Individual Carbon Nanotubes
Authors: Zhou Chongwu , Kong Jing , Yenilmez Erhan , Dai Hongjie
Published: July 2002

Modulation doping of a semiconducting single-walled carbon nanotube along its length leads to an intramolecular wire electronic device. The nanotube is doped
n
-type for half of its length and
p
-type for the other half. Electrostatic gating can tune the system into
p
-
n
junctions, causing it to exhibit rectifying characteristics or negative differential conductance. The system can also be tuned into
n
-type, exhibiting single-electron charging and negative differential conductance at low temperatures. The low-temperature behavior is manifested by a quantum dot formed by chemical inhomogeneity along the tube.
Toward Separation and Purification of Olefins Using Dithiolene Complexes: An Electrochemical Approach
Authors: Wang Kun , Stiefel Edward I.
Published: July 2002

The complex Ni[S
2
C
2
(CF
3
)
2
]
2
reacts with light olefins, including ethylene and propylene, selectively and reversibly. The reaction is not poisoned by hydrogen gas, carbon monoxide, acetylene, or hydrogen sulfide, which are commonly present in olefin streams, presumably because olefin binding occurs through the sulfur ligand rather than the metal center. The reversible reaction of olefins with Ni[S
2
C
2
(CN)
2
]
2

n

(
n
= 0, −1, −2) can be controlled electrochemically, where the oxidation state–dependent binding and release of olefins are fast on the electrochemical time scale. The observed tolerance to poisons and controllable electrochemical reactivity present an alternative approach to the separation of olefins from complex streams.
Bactericidal Activity of Quinupristin-Dalfopristin against
Staphylococcus aureus
: Clindamycin Susceptibility as a Surrogate Indicator
Authors: Fuchs Peter C. , Barry Arthur L. , Brown Steven D.
Published: July 2002

Of 516
Staphylococcus aureus
strains tested, 97.1% were susceptible to quinupristin-dalfopristin, which was bactericidal for 22 (56%) of the 39 strains tested, comparable to vancomycin. All 17 clindamycin and macrolide-resistant strains were inhibited but not killed by quinupristin-dalfopristin, whereas all 22 clindamycin-susceptible strains (5 were macrolide resistant) were killed.
Intravitreal, Retinal, and Central Nervous System Foscarnet Concentrations after Rapid Intravenous Administration to Rabbits
Authors: López-Cortés Luis F. , Ruiz-Valderas R. , Lucero-Muñoz M. J. , Cordero E. , Pastor-Ramos M. T. , Marquez J.
Published: July 2002

Retinal, vitreous humor, brain, and cerebrospinal fluid (CSF) foscarnet levels were measured by high-performance liquid chromatography after administration of an intravenous dose of 120 mg/kg of body weight to 32 pigmented rabbits. A pharmacokinetic analysis was done using a two-compartment model. The penetration ratios, defined as ratios of retinal, vitreous humor, brain, and CSF areas under the concentration-time curve from 0 to 2 h were 110% ± 1%, 12.3% ± 0.7%, 118% ± 1%, and 20.2% ± 2.2%, respectively. These results suggest a good penetration of foscarnet into the retinal and brain tissues, reaching higher concentrations than those estimated from vitreous humor and CSF levels.
Selective Interaction of the Human Immunodeficiency Virus Type 1 Reverse Transcriptase Nonnucleoside Inhibitor Efavirenz and Its Thio-Substituted Analog with Different Enzyme-Substrate Complexes
Authors: Maga Giovanni , Ubiali Daniela , Salvetti Raul , Pregnolato Massimo , Spadari Silvio
Published: July 2002

Accumulating data have brought the nonnucleoside reverse transcriptase (RT) inhibitors (NNRTIs) into the forefront of antiretroviral therapy. Among the emerging compounds in this class, a particularly attractive one is efavirenz (Sustiva), recently approved for clinical use by the U.S. Food and Drug Administration. In the present study, the equilibrium dissociation constants for efavirenz binding to the different catalytic forms of human immunodeficiency virus type 1 RT as well as the association and dissociation rates have been determined using a steady-state kinetic approach. In addition, the same enzymological analysis has been extended to the thio-substituted analog, sefavirenz, which showed comparable activity in vitro against RT. Both compounds have been found to act as purely uncompetitive inhibitors at low drug concentrations (5 to 50 nM) and as mixed noncompetitive inhibitors at higher doses (50 to 500 nM). This behavior can be interpreted in terms of the relative affinities for the different catalytic forms of the enzyme. Both efavirenz and sefavirenz showed increasing affinities for the different forms of RT in the following order: free enzyme < (i.e., bound with lower affinity) binary RT–template-primer (TP) complex < ternary RT-TP-deoxynucleoside triphosphate (dNTP) complex. The rate of binding of the two inhibitors to the different enzyme-substrate complexes was well below the diffusion limit (on the order of 10
4
M
−1
s
−1
); however, both inhibitors, when bound to the ternary RT-TP-dNTP complex, showed very low dissociation rates, on the order of 10
−4
s
−1
for both compounds, typical of tightly binding inhibitors. Thus, efavirenz and its thio-substituted derivative sefavirenz appear to be peculiar in their mechanism of action, being selective tightly binding inhibitors of the ternary RT-TP-dNTP complex. Efavirenz is the first clinically approved NNRTI to show this property.
Antimicrobial Susceptibility and Clinical Sources of
Dolosigranulum pigrum
Cultures
Authors: Laclaire L. , Facklam R.
Published: July 2002

Antimicrobial susceptibilities of 27 clinical isolates of
Dolosigranulum pigrum
were determined. All were susceptible to amoxicillin, cefotaxime, cefuroxime, clindamycin, levofloxacin, meropenem, penicillin, quinupristin-dalfopristin, rifampin, tetracycline, and vancomycin. Fifteen of the isolates were intermediate to chloramphenicol. One isolate was resistant to trimethoprim-sulfamethoxazole. Two isolates were susceptible, 10 were intermediate, and 15 were resistant to erythromycin.
Identification and Characterization of
vanB2
Glycopeptide Resistance Elements in Enterococci Isolated in Scotland
Authors: McGregor K. F. , Young H.-K.
Published: July 2002

Thirty-two
vanB
glycopeptide-resistant enterococci (28
Enterococcus faecium
and 4
Enterococcus faecalis
) were collected from hospitalized patients in Glasgow, Edinburgh, Dundee, and Aberdeen, Scotland, and the
vanB
element in each was compared to
vanB1
of
E. faecalis
strain ATCC 51299.
Hha
I digestion of PCR fragments of the
vanB
ligase gene was used to identify
vanB
subtypes. All
E. faecium
isolates were
vanB2
, and all
E. faecalis
isolates were
vanB1
. Restriction fragment length polymorphism analysis of a 5,180-bp

vanS
B
-vanX
B

long-PCR fragment of the
vanB
cluster showed the loss of
Hae
II restriction sites in

vanS
B

,
vanW
, and

vanX
B

in strains containing a
vanB2
ligase gene. Partial sequences of genes in the
vanB2
cluster for two genomically distinct Scottish isolates were >99.8% identical to each other.

vanS
B2

,

vanX
B2

, and
vanB2
sequences differed at the nucleotide level from those of

vanS
B

,

vanX
B

, and
vanB
by 4.2, 4.6, and 4.8%, respectively. The
vanB2
resistance element appears to be widespread among VanB glycopeptide-resistant
E. faecium
strains isolated in Scottish hospitals.
Comparative In Vitro Activities of Ertapenem (MK-0826) against 1,001 Anaerobes Isolated from Human Intra-Abdominal Infections
Authors: Goldstein Ellie J. C. , Citron Diane M. , Vreni Merriam C. , Warren Yumi , Tyrrell Kerin L.
Published: July 2002

By using an agar dilution method, the comparative in vitro activities of ertapenem (MK-0826) were studied against 1,001 anaerobes isolated from human intra-abdominal infections in 17 countries worldwide. MK-0826 was uniformly active against all isolates, including all
Bacteroides fragilis
group species isolates, with the exception of 12 of 61 (20%) strains of
Bilophila wadsworthia
, 3 strains of lactobacilli, and 1 isolate of
Acidaminococcus fermentans
. Geographical variation in activity was not observed.
Antimalarial Activities of Aminooxy Compounds
Authors: Berger Bradley J.
Published: July 2002

Twenty-three aminooxy compounds have been examined for their ability to inhibit the growth of the malaria parasite
Plasmodium falciparum
in vitro. Eight of these compounds were found to have 50% inhibitory concentrations less than 10 μM, with the best drugs being canaline (the aminooxy analogue of ornithine) and CGP51905A at 297 ± 23.6 nM and 242 ± 18.8 nM, respectively. Canaline was also assayed in combination with the ornithine decarboxylase inhibitor difluoromethylornithine, and the two drugs were found to be synergistic in antimalarial activity.
Evaluation of Current Activities of Fluoroquinolones against Gram-Negative Bacilli Using Centralized In Vitro Testing and Electronic Surveillance
Authors: Sahm Daniel F. , Critchley Ian A. , Kelly Laurie J. , Karlowsky James A. , Mayfield David C. , Thornsberry Clyde , Mauriz Yolanda R. , Kahn James
Published: July 2002

Given the propensity for
Enterobacteriaceae
and clinically significant nonfermentative gram-negative bacilli to acquire antimicrobial resistance, consistent surveillance of the activities of agents commonly prescribed to treat infections arising from these organisms is imperative. This study determined the activities of two fluoroquinolones, levofloxacin and ciprofloxacin, and seven comparative agents against recent clinical isolates of
Enterobacteriaceae
,
Pseudomonas aeruginosa
,
Acinetobacter baumannii
, and
Stenotrophomonas maltophilia
using two surveillance strategies: 1) centralized in vitro susceptibility testing of isolates collected from 27 hospital laboratories across the United States and 2) analysis of data from The Surveillance Network Database-USA, an electronic surveillance network comprising more than 200 laboratories nationwide. Regardless of the surveillance method,
Enterobacteriaceae
,
P. aeruginosa
, and
A. baumannii
demonstrated similar rates of susceptibility to levofloxacin and ciprofloxacin. Susceptibilities to the fluoroquinolones approached or exceeded 90% for all
Enterobacteriaceae
except
Providencia
spp. (≤65%). Approximately 70% of
P. aeruginosa
and 50% of
A. baumanii
isolates were susceptible to both fluoroquinolones. Among
S. maltophilia
isolates, 50% more isolates were susceptible to levofloxacin than to ciprofloxacin. Overall, the rate of ceftazidime nonsusceptibility among
Enterobacteriaceae
was 8.7%, with fluoroquinolone resistance rates notably higher among ceftazidime-nonsusceptible isolates than ceftazidime-susceptible ones. Multidrug-resistant isolates were present among all species tested but were most prevalent for
Klebsiella pneumoniae
and
Enterobacter cloacae
. No gram-negative isolates resistant only to a fluoroquinolone were encountered, regardless of species. Thus, while levofloxacin and ciprofloxacin have maintained potent activity against
Enterobacteriaceae
, the potential for fluoroquinolone resistance, the apparent association between fluoroquinolone and cephalosporin resistance, and the presence of multidrug resistance in every species examined emphasize the need to maintain active surveillance of resistance patterns among gram-negative bacilli.
Sequencing of Cytomegalovirus UL97 Gene for Genotypic Antiviral Resistance Testing
Authors: Lurain Nell S. , Weinberg Adriana , Crumpacker Clyde S. , Chou Sunwen
Published: July 2002

The widespread use of ganciclovir (GCV) to treat cytomegalovirus (CMV) infections in immunosuppressed patients has led to the development of drug resistance. Phenotypic assays for CMV drug resistance are presently too time-consuming to be therapeutically useful. To support the development of genotypic assays for GCV resistance, the complete sequences of the UL97 phosphotransferase genes in 28 phenotypically GCV-sensitive CMV clinical isolates were determined. The gene was found to be highly conserved, with nucleotide sequence identity among strains ranging from 98.6 to 100% and amino acid sequence identity of >99%. Primers for a genotypic assay were designed to amplify codons 400 to 707, because all known UL97 mutations conferring drug resistance occur at three sites within this region. This part of the UL97 gene was amplified from over 50 clinical isolates, and two sequencing reactions for the coding strand were successfully used to identify GCV resistance mutations. This genotypic assay can be performed in 48 h using genomic DNA extracted from cell monolayers at very low levels of virus infectivity, thus rapidly providing therapeutically useful results.
Measurement of Effects of Antibiotics in Bioluminescent
Staphylococcus aureus
RN4220
Authors: Tenhami Mervi , Hakkila Kaisa , Karp Matti
Published: July 2002

The spread of antibiotic resistance among pathogenic bacteria is a serious threat to humans and animals. Therefore, unnecessary use should be minimized, and new antimicrobial agents with novel mechanisms of action are needed. We have developed an efficient method for measuring the action of antibiotics which is applied to a gram-positive strain,
Staphylococcus aureus
RN4220. The method utilizes the firefly luciferase reporter gene coupled to the metal-inducible
cadA
promoter in a plasmid, pTOO24. Correctly timed induction by micromolar concentrations of antimonite rapidly triggers the luciferase gene transcription and translation. This sensitizes the detection system to the action of antibiotics, and especially for transcriptional and translational inhibitors. We show the results for 11 model antibiotics with the present approach and compare them to an analytical setup with a strain where luciferase expression is under the regulation of a constitutive promoter giving only a report of metabolic inhibition. The measurement of light emission from intact living cells is shown to correlate extremely well (
r
= 0.99) with the conventional overnight growth inhibition measurement. Four of the antibiotics were within a 20% concentration range and four were within a 60% concentration range of the drugs tested. This approach shortens the assay time needed, and it can be performed in 1 to 4 h, depending on the sensitivity needed. Furthermore, the assay can be automatized for high-throughput screening by the pharmaceutical industry.
Carbapenem Resistance Mechanisms in
Pseudomonas aeruginosa
Clinical Isolates
Authors: Pai Hyunjoo , Kim Jong-Won , Kim Jungmin , Lee Ji Hyang , Choe Kang Won , Gotoh Naomasa
Published: July 2002

In order to define the contributions of the mechanisms for carbapenem resistance in clinical strains of
Pseudomonas aeruginosa
, we investigated the presence of OprD, the expressions of the MexAB-OprM and MexEF-OprN systems, and the production of the β-lactamases for 44 clinical strains. All of the carbapenem-resistant isolates showed the loss of or decreased levels of OprD. Three strains overexpressed the MexAB-OprM efflux system by carrying mutations in
mexR
. These three strains had the amino acid substitution in MexR protein, Arg (CGG) → Gln (CAG), at the position of amino acid 70. None of the isolates, however, expressed the MexEF-OprN efflux system. For the characterization of β-lactamases, at least 13 isolates were the depressed mutants, and 12 strains produced secondary β-lactamases. Based on the above resistance mechanisms, the MICs of carbapenem for the isolates were analyzed. The MICs of carbapenem were mostly determined by the expression of OprD. The MICs of meropenem were two- to four-fold increased for the isolates which overexpressed MexAB-OprM in the background of OprD loss. However, the elevated MICs of meropenem for some individual isolates could not be explained. These findings suggested that other resistance mechanisms would play a role in meropenem resistance in clinical isolates of
P. aeruginosa
.
Characterization of Class 1 Integrons from
Pseudomonas aeruginosa
That Contain the
bla
VIM-2
Carbapenem-Hydrolyzing β-Lactamase Gene and of Two Novel Aminoglycoside Resistance Gene Cassettes
Authors: Poirel Laurent , Lambert Thierry , Türkoglü Salih , Ronco Esthel , Gaillard Jean-Louis , Nordmann Patrice
Published: July 2002

Two clonally unrelated
Pseudomonas aeruginosa
clinical strains, RON-1 and RON-2, were isolated in 1997 and 1998 from patients hospitalized in a suburb of Paris, France. Both isolates expressed the class B carbapenem-hydrolyzing β-lactamase VIM-2 previously identified in Marseilles in the French Riviera. In both isolates, the
bla
VIM-2
cassette was part of a class 1 integron that also encoded aminoglycoside-modifying enzymes. In one case, two novel aminoglycoside resistance gene cassettes,
aacA29a
and
aacA29b
, were located at the 5′ and 3′ end of the
bla
VIM-2
gene cassette, respectively. The
aacA29a
and
aacA29b
gene cassettes were fused upstream with a 101-bp part of the 5′ end of the
qacE
cassette. The deduced amino acid sequence AAC(6′)-29a protein shared 96% identity with AAC(6′)-29b but only 34% identity with the
aacA7
-encoded AAC(6′)-I1, the closest relative of the AAC(6′)-I family enzymes. These aminoglycoside acetyltransferases had amino acid sequences much shorter (131 amino acids) than the other AAC(6′)-I enzymes (144 to 153 amino acids). They conferred resistance to amikacin, isepamicin, kanamycin, and tobramycin but not to gentamicin, netilmicin, and sisomicin.