bluuebunny/crossref_metadata_2025 huggingface dataset:
Femtosecond Resolution of Soft Mode Dynamics in Structural Phase Transitions
Authors: Dougherty Thomas P. , Wiederrecht Gary P. , Nelson Keith A. , Garrett Mark H. , Jensen Hans P. , Warde Cardinal
Published: October 2006

The microscopic pathway along which ions or molecules in a crystal move during a structural phase transition can often be described in terms of a collective vibrational mode of the lattice. In many cases, this mode, called a "soft" phonon mode because of its characteristically low frequency near the phase transition temperature, is difficult to characterize through conventional frequency-domain spectroscopies such as light or neutron scattering. A femtosecond time-domain analog of light-scattering spectroscopy called impulsive stimulated Raman scattering (ISRS) has been used to examine the soft modes of two perovskite ferroelectric crystals. The low-frequency lattice dynamics of KNbO
3
and BaTiO
3
are clarified in a manner that permits critical evaluation of microscopic models for their ferroelectric transitions. The results illustrate the advantages of ISRS over conventional Raman spectroscopy of low-frequency, heavily damped soft modes.
Nanochannel Array Glass
Authors: Tonucci R. J. , Justus B. L. , Campillo A. J. , Ford C. E.
Published: October 2006

The fabrication and characterization of a glass containing a regular parallel array of submicrometer channels or capillaries are described. The capillaries are arranged in a two-dimensional hexagonal close packing configuration with channel diameters as small as 33 nanometers and packing densities as high as 3 × 10
10
channels per square centimeter. The high-temperature stability of the nanochannel glass array is well suited as a host or template for the formation of quantum confined semiconductor structures or as a mask for massively parallel patterned lithographic applications.
A Prediction of Mars Seismicity from Surface Faulting
Authors: Golombek Matthew P. , Banerdt W. Bruce , Tanaka Kenneth L. , Tralli David M.
Published: October 2006

The shallow seismicity of Mars has been estimated by measurement of the total slip on faults visible on the surface of the planet throughout geologic time. Seismicity was calibrated with estimates based on surface structures on the moon and measured lunar seismicity that includes the entire seismogenic lithosphere. Results indicate that Mars is seismically active today, with a sufficient number of detectable marsquakes to allow seismic investigations of its interior.
Predator-Induced Phenotypical Change in Body Morphology in Crucian Carp
Authors: Brönmark Christer , Miner Jeffrey G.
Published: October 2006

In a field experiment where the presence or absence of piscivorous pike (
Esox lucius
) in ponds was manipulated, the morphology of crucian carp (
Carassius carassius
) diverged, such that individuals became deeper bodied in pond sections with pike. A laboratory experiment confirmed that the presence of this predator induced a change in body morphology in the carp. Estimation of prey vulnerability to predation by pike, a gape-limited predator, revealed that this increase in body depth resulted in crucian carp reaching a size that provided refuge from predation. However, this change in morphology incurs a cost through an increase in drag when the carp are swimming. Because crucian carp are limited by resources in the absence of piscivores and by the substantial cost of the defensive morph in their presence, phenotypic plasticity should be the optimal strategy for this species.
EMF
, an
Arabidopsis
Gene Required for Vegetative Shoot Development
Authors: Sung Z. R. , Belachew A. , Shunong Bai , Bertrand-Garcia R.
Published: October 2006

In higher plants, the transition from the vegetative to the reproductive state in the shoot meristem initiates flowering. To study this floral transition, a constitutively flowering mutant of
Arabidopsis thaliana
ecotype
columbia, embryonic flower
(
emf
), was characterized. No vegetative shoots were produced from
emf
embryos or calli; the shoot apical meristems (SAMs) in the
emf
embryos were altered compared to wild-type SAMs. The mutant SAMs enlarged precociously and produced inflorescence meristems upon germination. These results suggest that the dominant, wild-type allele
EMF
is required for the vegetative state of the SAM. In the absence of
EMF
function, the mutant embryo assumes the reproductive state.
Paleohydrology of Late Pleistocene Superflooding, Altay Mountains, Siberia
Authors: Baker Victor R. , Benito Gerardo , Rudoy Alexey N.
Published: October 2006

Cataclysmic flooding is a geomorphological process of planetary significance. Landforms of flood origin resulted from late Pleistocene ice-dammed lake failures in the Altay Mountains of south-central Siberia. Peak paleoflows, which exceeded 18 × 10
6
cubic meters per second, are comparable to the largest known terrestrial discharges of freshwater and show a hydrological scaling relation to floods generated by catastrophic dam failures. These seem to have been Earth's greatest floods, based on a variety of reconstructed paleohydraulic parameters.
Late Cenozoic Uplift of Denali and Its Relation to Relative Plate Motion and Fault Morphology
Authors: Fitzgerald Paul G. , Stump Edmund , Redfield Thomas F.
Published: October 2006

Apatite fission-track analysis of samples that cover a 4-kilometer vertical section from the western flank of Denali (Mount McKinley), North America's highest mountain, suggests that the mountain massif was formed by rapid uplift (> 1 kilometer per million years) beginning ∼6 million years ago (Ma). Uplift was a result of the morphology of the Denali fault and a change in motion of the Pacific plate with respect to North America at ∼5 Ma, which created opposing tangential vectors of relative movement along the fault and forced the intervening crustal blocks upward.
Organorhenium Chemistry
Authors: Casey Charles P.
Published: October 2006

As organometallic chemists have delved into the chemistry of rhenium, an amazing variety of unusual stable organorhenium compounds have been synthesized and novel reaction pathways have been uncovered. The broad range of stable organorhenium compounds can be traced to the availability of oxidation states from -III to VII and to the high strength of bonds to rhenium. New types of reaction mechanism are seen in response to the reluctance of rhenium to form coordinatively unsaturated complexes.
Regional Ground-Water Mixing and the Origin of Saline Fluids: Midcontinent, United States
Authors: Musgrove MaryLynn , Banner Jay L.
Published: October 2006

Ground waters in three adjacent regional flow systems in the midcontinent exhibit extreme chemical and isotopic variations that delineate large-scale fluid flow and mixing processes and two distinct mechanisms for the generation of saline fluids. Systematic spatial variations of major ion concentrations, H, O, and Sr isotopic compositions, and ground-water migration pathways indicate that each flow system contains water of markedly different origin. Mixing of the three separate ground waters exerts a fundamental control on ground-water composition. The three ground waters are: (i) dilute meteoric water recharged in southern Missouri; (ii) saline Na-Ca-Cl water in southeastern Kansas of far-traveled meteoric origin that acquired its salinity by halite dissolution; and (iii) Na-Ca-Cl brines in north-central Oklahoma that may have originated as Paleozoic seawater.
South Asian Summer Monsoon Variability in a Model with Doubled Atmospheric Carbon Dioxide Concentration
Authors: Meehl Gerald A. , Washington Warren M.
Published: October 2006

Doubled atmospheric carbon dioxide concentration in a global coupled ocean-atmosphere climate model produced increased surface temperatures and evaporation and greater mean precipitation in the south Asian summer monsoon region. As a partial consequence, interannual variability of area-averaged monsoon rainfall was enhanced. Consistent with the climate sensitivity results from the model, observations showed a trend of increased interannual variability of Indian monsoon precipitation associated with warmer land and ocean temperatures in the monsoon region.
True Atomic Resolution by Atomic Force Microscopy Through Repulsive and Attractive Forces
Authors: Ohnesorge F. , Binnig G.
Published: October 2006

The (10
1
4) cleavage plane of calcite has been investigated by atomic force microscopy in water at room temperature. True lateral atomic-scale resolution was achieved; the atomic-scale periodicities as well as the expected relative positions of the atoms within each unit cell were obtained. Along monoatomic step lines, atomic-scale kinks, representing point-like defects, were resolved. Attractive forces on the order of 10
-11
newton acting between single atomic sites on the sample and the front atoms of the tip were directly measured and provided the highest, most reliable resolution on a flat, well-ordered surface.
Catastrophic Volcanic Collapse: Relation to Hydrothermal Processes
Authors: López Dina L. , Williams Stanley N.
Published: October 2006

Catastrophic volcanic collapse, without precursory magmatic activity, is characteristic of many volcanic disasters. The extent and locations of hydrothermal discharges at Nevado del Ruiz volcano, Colombia, suggest that at many volcanoes collapse may result from the interactions between hydrothermal fluids and the volcanic edifice. Rock dissolution and hydrothermal mineral alteration, combined with physical triggers such as earthquakes, can produce volcanic collapse. Hot spring water compositions, residence times, and flow paths through faults were used to model potential collapse at Ruiz. Caldera dimensions, deposits, and alteration mineral volumes are consistent with parameters observed at other volcanoes.
Optically Active Carbon: Kinetic Resolution of C
76
by Asymmetric Osmylation
Authors: Hawkins Joel M. , Meyer Axel
Published: October 2006

The chiral fullerene C
76
was kinetically resolved by asymmetric osmylation providing an example of an optically active allotrope of a pure element. C
76
recovered from the treatment of racemic C
76
with OsO
4
and a chiral alkaloid ligand, showed a specific rotation [α]
D
of -4000° (> 97 percent enantiomeric excess) and a circular dichroism spectrum corresponding to the ultraviolet spectrum. Regenerated C
76
formed by reducing the asymmetrically osmylated C
76
with SnCl
2
was enriched in the opposite enantiomer. Analysis of the local curvature of the C
76
molecule indicated that OsO
4
should selectively add to 2 of the 30 types of bonds in C
76
. This regioselectivity was supported chromatographically and interpreted in terms of the kinetic resolution.
Hydrodynamic Stability Without Eigenvalues
Authors: Trefethen Lloyd N. , Trefethen Anne E. , Reddy Satish C. , Driscoll Tobin A.
Published: October 2006

Fluid flows that are smooth at low speeds become unstable and then turbulent at higher speeds. This phenomenon has traditionally been investigated by linearizing the equations of flow and testing for unstable eigenvalues of the linearized problem, but the results of such investigations agree poorly in many cases with experiments. Nevertheless, linear effects play a central role in hydrodynamic instability. A reconciliation of these findings with the traditional analysis is presented based on the "pseudospectra" of the linearized problem, which imply that small perturbations to the smooth flow may be amplified by factors on the order of 10
5
by a linear mechanism even though all the eigenmodes decay monotonically. The methods suggested here apply also to other problems in the mathematical sciences that involve nonorthogonal eigenfunctions.
Ices on the Surface of Triton
Authors: Cruikshank Dale P. , Roush Ted L. , Owen Tobias C. , Geballe Thomas R. , de Bergh Catherine , Schmitt Bernard , Brown Robert H. , Bartholomew Mary Jane
Published: October 2006

The near-infrared spectrum of Triton reveals ices of nitrogen, methane, carbon monoxide, and carbon dioxide, of which nitrogen is the dominant component. Carbon dioxide ice may be spatially segregated from the other more volatile ices, covering about 10 percent of Triton's surface. The absence of ices of other hydrocarbons and nitriles challenges existing models of methane and nitrogen photochemistry on Triton.
Surface Ices and the Atmospheric Composition of Pluto
Authors: Owen Tobias C. , Roush Ted L. , Cruikshank Dale P. , Elliot James L. , Young Leslie A. , de Bergh Catherine , Schmitt Bernard , Geballe Thomas R. , Brown Robert H. , Bartholomew Mary Jane
Published: October 2006

Observations of the 1.4- to 2.4-micrometer spectrum of Pluto reveal absorptions of carbon monoxide and nitrogen ices and confirm the presence of solid methane. Frozen nitrogen is more abundant than the other two ices by a factor of about 50; gaseous nitrogen must therefore be the major atmospheric constituent. The absence of carbon dioxide absorptions is one of several differences between the spectra of Pluto and Triton in this region. Both worlds carry information about the composition of the solar nebula and the processes by which icy planetesimals formed.
Micromachining a Miniaturized Capillary Electrophoresis-Based Chemical Analysis System on a Chip
Authors: Harrison D. Jed , Fluri Karl , Seiler Kurt , Fan Zhonghui , Effenhauser Carlo S. , Manz Andreas
Published: October 2006

Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.
Seismic Determination of Elastic Anisotropy and Mantle Flow
Authors: Park Jeffrey , Yu Yang
Published: October 2006

When deformed, many rocks develop anisotropic elastic properties. On many seismic records, a long-period (100 to 250 seconds), "quasi-Love" wave with elliptical polarization arrives slightly after the Love wave but before the Rayleigh wave. Mantle anisotropy is sufficient to explain these observations qualitatively as long as the "fast" axis of symmetry is approximately horizontal. Quasi-Love observations for several propagation paths near Pacific Ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the Pacific plate.
Cooperative Formation of Inorganic-Organic Interfaces in the Synthesis of Silicate Mesostructures
Authors: Monnier A. , Schüth F. , Huo Q. , Kumar D. , Margolese D. , Maxwell R. S. , Stucky G. D. , Krishnamurty M. , Petroff P. , Firouzi A. , Janicke M. , Chmelka B. F.
Published: October 2006

A model is presented to explain the formation and morphologies of surfactant-silicate mesostructures. Three processes are identified: multidentate binding of silicate oligomers to the cationic surfactant, preferential silicate polymerization in the interface region, and charge density matching between the surfactant and the silicate. The model explains present experimental data, including the transformation between lamellar and hexagonal mesophases, and provides a guide for predicting conditions that favor the formation of lamellar, hexagonal, or cubic mesostructures. Model Q
230
proposed by Mariani and his co-workers satisfactorily fits the x-ray data collected on the cubic mesostructure material. This model suggests that the silicate polymer forms a unique infinite silicate sheet sitting on the gyroid minimal surface and separating the surfactant molecules into two disconnected volumes.
Laser
40
Ar/
39
Ar Evaluation of Slow Cooling and Episodic Loss of
40
Ar from a Sample of Polymetamorphic Muscovite
Authors: Hames W. E. , Hodges K. V.
Published: October 2006

Volume diffusion models predict that crystals with large diffusion dimensions can record a wide range of thermal conditions in the Earth's crust. Direct measurements of the zoning of radiogenic argon-40 in single muscovite porphyroblasts, from a complex terrain in the Vermont Appalachians, record multiple crustal events that span 150 million years. The crystal radius was the effective dimension for argon diffusion (approximately 1000 micrometers). Late deformation features inside the crystals locally decreased the diffusion dimension and promoted loss of argon-40. Zoning patterns of radiogenic isotopes, as observed in this study, are an increasingly important diagnostic tool for studying the thermal record of tectonic processes.
A Direct Measurement of the Terrestrial Mass Accretion Rate of Cosmic Dust
Authors: Love S. G. , Brownlee D. E.
Published: October 2006

The mass of extraterrestrial material accreted by the Earth as submillimeter particles has not previously been measured with a single direct and precise technique that samples the particle sizes representing most of that mass. The flux of meteoroids in the mass range 10
–9
to 10
–4
grams has now been determined from an examination of hypervelocity impact craters on the space-facing end of the Long Duration Exposure Facility satellite. The meteoroid mass distribution peaks near 1.5 × 10
–5
grams (200 micrometers in diameter), and the small particle mass accretion rate is (40 ± 20) × 10
6
kilograms per year, higher than previous estimates but in good agreement with total terrestrial mass accretion rates found by geochemical methods. This mass input is comparable with or greater than the average contribution from extraterrestrial bodies in the 1-centimeter to 10-kilometer size range.
Crustal Thickness on the Mid-Atlantic Ridge: Bull's-Eye Gravity Anomalies and Focused Accretion
Authors: Tolstoy Maya , Harding Alistair J. , Orcutt John A.
Published: October 2006

Spreading segments of the Mid-Atlantic Ridge show negative bull's-eye anomalies in the mantle Bouguer gravity field. Seismic refraction results from 33°S indicate that these anomalies can be accounted for by variations in crustal thickness along a segment. The crust is thicker in the center and thinner at the end of the spreading segment, and these changes are attributable to variations in the thickness of layer 3. The results show that accretion is focused at a slow-spreading ridge, that axial valley depth reflects the thickness of the underlying crust, and that along-axis density variations should be considered in the interpretation of gravity data.
Single Molecules Observed by Near-Field Scanning Optical Microscopy
Authors: Betzig Eric , Chichester Robert J.
Published: October 2006

Individual carbocyanine dye molecules in a sub-monolayer spread have been imaged with near-field scanning optical microscopy. Molecules can be repeatedly detected and spatially localized (to ∼λ/50 where λ is the wavelength of light) with a sensitivity of at least 0.005 molecules/(Hz)
1/2
and the orientation of each molecular dipole can be determined. This information is exploited to map the electric field distribution in the near-field aperture with molecular spatial resolution.
A Specialization for Speech Perception
Authors: Liberman Alvin M. , Mattingly Ignatius G.
Published: October 2006

The processes that underlie perception of consonants and vowels are specifically phonetic, distinct from those that localize sources and assign auditory qualities to the sound from each source. This specialization, or module, increases the rate of information flow, establishes the parity between sender and receiver that every communication system must have, and provides for the natural development of phonetic structures in the species and in the individual. The phonetic module has certain properties in common with modules that are "closed" (for example, sound localization or echo ranging in bats) and, like other members of this class, is so placed in the architecture of the auditory system as to preempt information that is relevant to its special function. Accordingly, this information is not available to such "open" modules as those for pitch, loudness, and timbre.
Polymer Synthesis and Organotransition Metal Chemistry
Authors: Grubbs Robert H. , Tumas William
Published: October 2006

Mechanistic and synthetic studies in organometallic chemistry have provided considerable insight into olefin metathesis and Ziegler-Natta polymerization. New homogeneous olefin metathesis catalysts based on high oxidation state transition metals have opened new opportunities in polymer synthesis by providing unprecedented control in ring-opening polymerization of cyclic alkenes. The recent development of living coordinative polymerization systems has led to the preparation of a number of new, interesting materials, including block copolymers, conducting polymers or precursors, and ionophoric polymeric substrates.
Mouse Lymph Node Homing Receptor cDNA Clone Encodes a Glycoprotein Revealing Tandem Interaction Domains
Authors: Siegelman Mark H. , van de Rijn Matthijs , Weissman Irving L.
Published: October 2006

Isolation of a clone encoding the mouse lymph node homing receptor reveals a deduced protein with an unusual protein mosaic architecture, containing a separate carbohydrate-binding (lectin) domain, an epidermal growth factor-like (EGF) domain, and an extracellular precisely duplicated repeat unit, which preserves the motif seen in the homologous repeat structure of complement regulatory proteins and other proteins. The receptor molecule is potentially highly glycosylated, and contains an apparent transmembrane region. Analysis of messenger RNA transcripts reveals a predominantly lymphoid distribution in direct relation to the cell surface expression of the MEL-14 determinant, and the cDNA clone is shown to confer the MEL-14 epitope in heterologous cells. The many novel features, including ubiquitination, embodied in this single receptor molecule form the basis for numerous approaches to the study of cell-cell interactions.
Recording and Interpretation of Cerebral Magnetic Fields
Authors: Hari Riitta , Lounasmaa Olli V.
Published: October 2006

Contemporary brain research progresses along two main lines: the microlevel approach explores single neurons and subcellular elements, while macrolevel studies focus on more complex cerebral functions, including behavior. This review presents results obtained mainly in our laboratory by means of an intermediate method, magnetoencephalography (MEG), which reflects cortical activity of neuronal populations at the level of cytoarchitectonic areas. Because it is completely noninvasive, MEG can be used to study brain functions that are characteristically human.
Developmental Biology of T Cell Receptors
Authors: Strominger Jack L.
Published: October 2006

T cell receptors are the antigen-recognizing elements found on the effector cells of the immune system. Two isotypes have been discovered, TCR-γδ and TCR-αβ, which appear in that order during ontogeny. The maturation of prothymocytes that colonize the thymic rudiment at defined gestational stages occurs principally within the thymus, although some evidence for extrathymic maturation also exists. The maturation process includes the rearrangement and expression of the T cell receptor genes. Determination of these mechanisms, the lineages of the cells, and the subsequent thymic selection that results in self-tolerance is the central problem in developmental immunology and is important for the understanding of autoimmune diseases.
Amplification of a Gene Related to Mammalian mdr Genes in Drug-Resistant
Plasmodium falciparum
Authors: Wilson Craig M. , Serrano Adelfa E. , Wasley Annemarie , Bogenschutz Michael P. , Shankar Anuraj H. , Wirth Dyann F.
Published: October 2006

The malaria parasite
Plasmodium falciparum
contains at least two genes related to the mammalian multiple drug resistance genes, and at least one of the
P. falciparum
genes is expressed at a higher level and is present in higher copy number in a strain that is resistant to multiple drugs than in a strain that is sensitive to the drugs.
Morphogenesis of the Polarized Epithelial Cell Phenotype
Authors: Rodriguez-Boulan Enrique , Nelson W. James
Published: October 2006

Polarized epithelial cells play fundamental roles in the ontogeny and function of a variety of tissues and organs in mammals. The morphogenesis of a sheet of polarized epithelial cells (the trophectoderm) is the first overt sign of cellular differentiation in early embryonic development. In the adult, polarized epithelial cells line all body cavities and occur in tissues that carry out specialized vectorial transport functions of absorption and secretion. The generation of this phenotype is a multistage process requiring extracellular cues and the reorganization of proteins in the cytoplasm and on the plasma membrane; once established, the phenotype is maintained by the segregation and retention of specific proteins and lipids in distinct apical and basal-lateral plasma membrane domains.
Circumsporozoite Protein Heterogeneity in the Human Malaria Parasite
Plasmodium vivax
Authors: Rosenberg Ronald , Wirtz Robert A. , Lanar David E. , Sattabongkot Jetsumon , Hall Ted , Waters Andrew P. , Prasittisuk Chusak
Published: October 2006

Phenotypic heterogeneity in the repetitive portion of a human malaria circumsporozoite (CS) protein, a major target of candidate vaccines, has been found. Over 14% of clinical cases of uncomplicated
Plasmodium vivax
malaria at two sites in western Thailand produced sporozoites immunologically distinct from previously characterized examples of the species. Monoclonal antibodies to the CS protein of other
P. vivax
isolates and to other species of human and simian malarias did not bind to these nonreactive sporozoites, nor did antibodies from monkeys immunized with a candidate vaccine made from the repeat portion of a New World CS protein. The section of the CS protein gene between the conserved regions I and II of a nonreactive isolate contained a nonapeptide repeat, Ala-Asn-Gly-Ala-Gly-Asn-Gln-Pro-Gly, identical at only three amino acid positions with published nonapeptide sequences. This heterogeneity implies that a
P. vivax
vaccine based on the CS protein repeat of one isolate will not be universally protective.
Dictyostelium discoideum
: a Model System for Cell-Cell Interactions in Development
Authors: Devreotes Peter
Published: October 2006

The cellular slime mold
Dictyostelium discoideum
undergoes a transition from single-celled amoebae to a multicellular organism as a natural part of its life cycle. A method of cell-cell signaling that controls chemotaxis, morphogenesis, and gene expression has developed in this organism, and a detailed understanding of this signaling system provides clues to mechanisms of intercellular communication in the development of metazoans.
G
1
Events and Regulation of Cell Proliferation
Authors: Pardee Arthur B.
Published: October 2006

Cells prepare for S phase during the G
1
phase of the cell cycle. Cell biological methods have provided knowledge of cycle kinetics and of substages of G
1
that are determined by extracellular signals. Through the use of biochemical and molecular biological techniques to study effects of growth factors, oncogenes, and inhibitors, intracellular events during G
1
that lead to DNA synthesis are rapidly being discovered. Many cells in vivo are in a quiescent state (G
0
), with unduplicated DNA. Cells can be activated to reenter the cycle during G
1
. Similarly, cells in culture can be shifted between G
0
and G
1
. These switches in and out of G
1
are the main determinants of post-embryonic cell proliferation rate and are defectively controlled in cancer cells.
Checkpoints: Controls That Ensure the Order of Cell Cycle Events
Authors: Hartwell Leland H. , Weinert Ted A.
Published: October 2006

The events of the cell cycle of most organisms are ordered into dependent pathways in which the initiation of late events is dependent on the completion of early events. In eukaryotes, for example, mitosis is dependent on the completion of DNA synthesis. Some dependencies can be relieved by mutation (mitosis may then occur before completion of DNA synthesis), suggesting that the dependency is due to a control mechanism and not an intrinsic feature of the events themselves. Control mechanisms enforcing dependency in the cell cycle are here called checkpoints. Elimination of checkpoints may result in cell death, infidelity in the distribution of chromosomes or other organelles, or increased susceptibility to environmental perturbations such as DNA damaging agents. It appears that some checkpoints are eliminated during the early embryonic development of some organisms; this fact may pose special problems for the fidelity of embryonic cell division.
The Cycle of Violence
Authors: Widom Cathy Spatz
Published: October 2006

Despite widespread belief that violence begets violence, methodological problems substantially restrict knowledge of the long-term consequences of childhood victimization. Empirical evidence for this cycle of violence has been examined. Findings from a cohort study show that being abused or neglected as a child increases one's risk for delinquency, adult criminal behavior, and violent criminal behavior. However, the majority of abused and neglected children do not become delinquent, criminal, or violent. Caveats in interpreting these findings and their implications are discussed in this article.
Implantation of Vascular Grafts Lined with Genetically Modified Endothelial Cells
Authors: Wilson James M. , Birinyi Louis K. , Salomon Robert N. , Libby Peter , Callow Allan D. , Mulligan Richard C.
Published: October 2006

The possibility of using the vascular endothelial cell as a target for gene replacement therapy was explored. Recombinant retroviruses were used to transduce the
lacZ
gene into endothelial cells harvested from mongrel dogs. Prosthetic vascular grafts seeded with the genetically modified cells were implanted as carotid interposition grafts into the dogs from which the original cells were harvested. Analysis of the graft 5 weeks after implantation revealed genetically modified endothelial cells lining the luminal surface of the graft. This technology could be used in the treatment of atherosclerosis disease and the design of new drug delivery systems.
Freeze Avoidance in a Mammal: Body Temperatures Below 0°C in an Arctic Hibernator
Authors: Barnes Brian M.
Published: October 2006

Hibernating arctic ground squirrels,
Spermophilus parryii
, were able to adopt and spontaneously arouse from core body temperatures as low as -2.9°C without freezing. Abdominal body temperatures of ground squirrels hibernating in outdoor burrows were recorded with temperature-sensitive radiotransmitter implants. Body temperatures and soil temperatures at hibernaculum depth reached average minima during February of -1.9° and -6°C, respectively. Laboratory-housed ground squirrels hibernating in ambient temperatures of -4.3°C maintained above 0°C thoracic temperatures but decreased colonic temperatures to as low as -1.3°C. Plasma sampled from animals with below 0°C body temperatures had normal solute concentrations and showed no evidence of containing antifreeze molecules.
Science Education in the United States: What the Scientific Community Can Do
Authors: Massey Walter E.
Published: October 2006

It is argued that the need to improve science education should be a national priority. Ways are suggested by which the federal government and the scientific community, working together, can address this issue. It is recommended that scientists, engineers, and educators make a significant personal and institutional commitment to participate in science education activities, and that the President of the United States provide the personal leadership to generate a national commitment to the improvement of education at all levels.
Identification of the Cystic Fibrosis Gene: Chromosome Walking and Jumping
Authors: Rommens Johanna M. , Iannuzzi Michael C. , Kerem Bat-Sheva , Drumm Mitchell L. , Melmer Georg , Dean Michael , Rozmahel Richard , Cole Jeffery L. , Kennedy Dara , Hidaka Noriko , Zsiga Martha , Buchwald Manuel , Tsui Lap-Chee , Riordan John R. , Collins Francis S.
Published: October 2006

An understanding of the basic defect in the inherited disorder cystic fibrosis requires cloning of the cystic fibrosis gene and definition of its protein product. In the absence of direct functional information, chromosomal map position is a guide for locating the gene. Chromosome walking and jumping and complementary DNA hybridization were used to isolate DNA sequences, encompassing more than 500,000 base pairs, from the cystic fibrosis region on the long arm of human chromosome 7. Several transcribed sequences and conserved segments were identified in this cloned region. One of these corresponds to the cystic fibrosis gene and spans approximately 250,000 base pairs of genomic DNA.
Neuroanatomical Correlates of Anticipatory Anxiety
Authors: Reiman Eric M. , Fusselman Maureen J. , Fox Peter T. , Raichle Marcus E.
Published: October 2006

Positron emission tomographic measurements of regional blood flow, a marker of local neuronal activity, were used to investigate the neuroanatomical correlates of a normal emotion. Healthy volunteers were studied before, during, and after anticipation of a painful electric shock. During anticipatory anxiety, there were significant blood flow increases in bilateral temporal poles, the same regions recently implicated in a lactate-induced anxiety attack in patients with panic disorder. Thus, the temporal poles seem to be involved in normal and pathological forms of human anxiety.
Metastatic Hibernomas in Transgenic Mice Expressing an α-Amylase-SV40 T Antigen Hybrid Gene
Authors: Fox Niles , Crooke Rosanne , Hwang Lih-Hwa S> , Schibler Ueli , Knowles Barbara B. , Solter Davor
Published: October 2006

Mice transgenic for a hybrid gene containing the liver promoter of the mouse α-amylase gene (
Amy-1
a
) fused to the SV40 tumor antigen coding region unexpectedly developed malignant brown adipose tissue tumors (malignant hibernomas). Expression of the α-amylase gene had previously been thought to be confined to the liver parotid, and pancreas; however, analysis of white and brown adipose tissue from nontransgenic mice revealed expression of the endogenous
Amy-1
a
gene in these tissues. Gene constructs driven by the
Amy-1
a
liver promoter thus provide a means of targeting gene expression to the adipocyte cell lineage in transgenic mice. Moreover, the high frequency of metastases in the liver, lungs, spleen, heart, and adrenals of these mice provides an experimental system in which to study the development of disseminated malignancy.
A Role for a 70-Kilodalton Heat Shock Protein in Lysosomal Degradation of Intracellular Proteins
Authors: Chiang Hui-Ling , Terlecky Stanley R. , Plant Charles P. , Dice J. Fred
Published: October 2006

A 73-kilodalton (kD) intracellular protein was found to bind to peptide regions that target intracellular proteins for lysosomal degradation in response to serum withdrawal. This protein cross-reacted with a monoclonal antibody raised to a member of the 70-kD heat shock protein (hsp70) family, and sequences of two internal peptides of the 73-kD protein confirm that it is a member of this family. In response to serum withdrawal, the intracellular concentration of the 73-kD protein increased severalfold. In the presence of adenosine 5′-triphosphate (ATP) and MgCl
2
, the 73-kD protein enhanced protein degradation in two different cell-free assays for lysosomal proteolysis.
Proton Motive Force Involved in Protein Transport Across the Outer Membrane of
Aeromonas salmonicida
Authors: Wong Kevin R. , Buckley J. Thomas
Published: October 2006

Many Gram-negative bacteria export proteins to the exterior. Some of these proteins are first secreted into the periplasm and then cross the outer membrane in a separate step. The source of energy required for the translocation is unknown. Export of the extracellular protein proaerolysin from the periplasm through the outer membrane of
Aeromonas salmonicida
is inhibited by a proton ionophore and by low extracellular
p
H. One possible explanation of these results is that a proton gradient across the outer membrane is required for export.
Vaccination Against Experimental Allergic Encephalomyelitis with T Cell Receptor Peptides
Authors: Howell Mark D. , Winters Steven T. , Olee Tsaiwei , Powell Henry C. , Carlo Dennis J. , Brostoff Steven W.
Published: October 2006

Experimental allergic encephalomyelitis (EAE) is an autoimmune disease of the central nervous system mediated by CD4
+
T cells reactive with myelin basic protein (MBP). Rats were rendered resistant to the induction of EAE by vaccination with synthetic peptides corresponding to idiotypic determinants of the β chain VDJ region and Jα regions of the T cell receptor (TCR) that are conserved among encephalitogenic T cells. These findings demonstrate the utility of TCR peptide vaccination for modulating the activity of autoreactive T cells and represent a general therapeutic approach for T cell-mediated pathogenesis.
In Vivo Footprinting of a Muscle Specific Enhancer by Ligation Mediated PCR
Authors: Mueller Paul R. , Wold Barbara
Published: October 2006

In vivo protein-DNA interactions at the developmentally regulated enhancer of the mouse muscle creatine kinase (MCK) gene were examined by a newly developed polymerase chain reaction (PCR) footprinting procedure. This ligation mediated, single-sided PCR technique permits the exponential amplification of an entire sequence ladder. Several footprints were detected in terminally differentiated muscle cells where the MCK gene is actively transcribed. None were observed in myogenic cells prior to differentiation or in nonmuscle cells. Two footprints appear to correspond to sites that can bind the myogenic regulator MyoD1 in vitro, whereas two others represent muscle specific use of apparently general factors. Because MyoD1 is synthesized by undifferentiated myoblasts, these data imply that additional regulatory mechanisms must restrict the interaction between this protein and its target site prior to differentiation.
Genomic Sequencing and Methylation Analysis by Ligation Mediated PCR
Authors: Pfeifer Gerd P. , Steigerwald Sabine D. , Mueller Paul R. , Wold Barbara , Riggs Arthur D.
Published: October 2006

Genomic sequencing permits studies of in vivo DNA methylation and protein-DNA interactions, but its use has been limited because of the complexity of the mammalian genome. A newly developed genomic sequencing procedure in which a ligation mediated polymerase chain reaction (PCR) is used generates high quality, reproducible sequence ladders starting with only 1 microgram of uncloned mammalian DNA per reaction. Different sequence ladders can be created simultaneously by inclusion of multiple primers and visualized separately by rehybridization. Relatively little radioactivity is needed for hybridization and exposure times are short. Methylation patterns in genomic DNA are readily detectable; for example, 17 CpG dinucleotides in the 5′ region of human X-linked PGK-1 (phosphoglycerate kinase 1) were found to be methylated on an inactive human X chromosome, but unmethylated on an active X chromosome.
Leukotrienes and Lipoxins: Structures, Biosynthesis, and Biological Effects
Authors: Samuelsson Bengt , Dahlén Sven-Erik , Lindgren Jan Åke , Rouzer Carol A. , Serhan Charles N.
Published: October 2006

Arachidonic acid is released from membrane phospholipids upon cell stimulation (for example, by immune complexes and calcium ionophores) and converted to leukotrienes by a 5-lipoxygenase that also has leukotriene A4synthetase activity. Leukotriene A4, an unstable epoxide, is hydrolyzed to leukotriene B4or conjugated with glutathione to yield leukotriene C4and its metabolites, leukotriene D4and leukotriene E4. The leukotrienes participate in host defense reactions and pathophysiological conditions such as immediate hypersensitivity and inflammation. Recent studies also suggest a neuroendocrine role for leukotriene C4in luteinizing hormone secretion. Lipoxins are formed by the action of 5- and 15-lipoxygenases on arachidonic acid. Lipoxin A causes contraction of guinea pig lung strips and dilation of the microvasculature. Both lipoxin A and B inhibit natural killer cell cytotoxicity. Thus, the multiple interaction of lipoxygenases generates compounds that can regulate specific cellular responses of importance in inflammation and immunity.
A Cytoplasmic Protein Stimulates Normal N-
ras
p21 GTPase, But Does Not Affect Oncogenic Mutants
Authors: Trahey Meg , McCormick Frank
Published: October 2006

The role of guanine nucleotides in
ras
p21 function was determined by using the ability of p21 protein to induce maturation of
Xenopus
oocytes as a quantitative assay for biological activity. Two oncogenic mutant human N-
ras
p21 proteins, Asp12 and Val12, actively induced maturation, whereas normal Gly12 p21 was relatively inactive in this assay. Both mutant proteins were found to be associated with guanosine triphosphate (GTP) in vivo. In contrast, Gly12 p21 was predominantly guanosine diphosphate (GDP)-bound because of a dramatic stimulation of Gly12 p21-associated guanosine triphosphatase (GTPase) activity. A cytoplasmic protein was shown to be responsible for this increase in activity. This protein stimulated GTP hydrolysis by purified Gly12 p21 more than 200-fold in vitro, but had no effect on Asp12 or Val12 mutants. A similar factor could be detected in extracts from mammalian cells. It thus appears that, in
Xenopus
oocytes, this protein maintains normal p21 in a biologically inactive, GDP-bound state through its effect on GTPase activity. Furthermore, it appears that the major effect of position 12 mutations is to prevent this protein from stimulating p21 GTPase activity, thereby allowing these mutants to remain in the active GTP-bound state.
An M2 Muscarinic Receptor Subtype Coupled to Both Adenylyl Cyclase and Phosphoinositide Turnover
Authors: Ashkenazi Avi , Winslow John W. , Peralta Ernest G. , Peterson Gary L. , Schimerlik Michael I. , Capon Daniel J. , Ramachandran Janakiraman
Published: October 2006

To investigate whether a particular receptor subtype can be coupled to multiple effector systems, recombinant M2 muscarinic receptors were expressed in cells lacking endogenous receptor. The muscarinic agonist carbachol both inhibited adenylyl cyclase and stimulated phosphoinositide hydrolysis. The stimulation of phosphoinositide hydrolysis was significantly less efficient and more dependent on receptor levels than the inhibition of adenylyl cyclase. Both responses were mediated by guanine nucleotide binding proteins, as evidenced by their inhibition by pertussis toxin; the more efficiently coupled adenylyl cyclase response was significantly more sensitive. Thus, individual subtypes of a given receptor are capable of regulating multiple effector pathways.
Alternative Mechanisms for Activation of Human Immunodeficiency Virus Enhancer in T Cells
Authors: Nabel Gary J. , Rice Stephen A. , Knipe David M. , Baltimore David
Published: October 2006

The expression of human immunodeficiency virus (HIV) after T cell activation is regulated by NF-κB, an inducible DNA-binding protein that stimulates transcription. Proteins encoded by a variety of DNA viruses are also able to activate expression from the HIV enhancer. To determine how this activation occurs, specific genes from herpes simplex virus type 1 and adenovirus that activate HIV in T lymphoma cells have been identified. The cis-acting regulatory sequences in the HIV enhancer that mediate their effect have also been characterized. The relevant genes are those for ICP0—an immediate-early product of herpes simplex virus type 1—and the form of E1A encoded by the 13
S
messenger RNA of adenovirus. Activation of HIV by adenovirus E1A was found to depend on the TATA box, whereas herpesvirus ICP0 did not work through a single defined cis-acting element. These findings suggest multiple pathways that can be used to bypass normal cellular activation of HIV, and they raise the possibility that infection by herpes simplex virus or adenovirus may directly contribute to the activation of HIV in acquired immunodeficiency syndrome by mechanisms independent of antigenic stimulation in T cells.
Cleaving DNA at Any Predetermined Site with Adapter-Primers and Class-IIS Restriction Enzymes
Authors: Kim Sun C. , Podhajska Anna J. , Szybalski Waclaw
Published: October 2006

A four-component system has been designed that makes it possible to prepare a double-stranded (ds) DNA fragment; one fragment end is predesigned (by the use of a class-IIS restriction enzyme and adapter-primer), and the other end corresponds to any normal restriction cut. The system is composed of the phage M13mp7 single-stranded (ss) target DNA; the Fok I restriction enzyme; an oligodeoxynucleotide adapter-primer, which permits one to introduce Fok I cuts at any specified site in the target DNA; and DNA polymerase, which converts the ss target into a ds form ready for cloning. In this system, the oligodeoxynucleotide adapter-primer serves several purposes. The 5′ hairpin ds domain of the adapter-primer contains the Fok I recognition site. Its 3′ ss domain selects a complementary site on the target ss DNA, hybridizes with it to form the ds cleavage site, and serves as a primer to convert the ss M13mp7 target to ds DNA.
HIV-1 Production from Infected Peripheral Blood T Cells After HTLV-I Induced Mitogenic Stimulation
Authors: Zack Jerome A. , Cann Alan J. , Lugo James P. , Chen Irvin S. Y.
Published: October 2006

The human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus type I (HTLV-I) are two distinct human retroviruses that infect T cells. Recent epidemiologic studies have identified a cohort of individuals that are coinfected with both viruses. It is reported here that human peripheral blood leukocytes infected with HIV-1 in vitro can be induced to produce large quantities of HIV-1 after mitogenic stimulation by noninfectious HTLV-I virions. It is also shown that HTLV-I virions may exert this effect prior to, immediately following, or well after the cells are infected with HIV-1. These results provide further impetus for epidemiologic studies of dually infected individuals to determine whether HTLV-I may act as a cofactor for acquired immunodeficiency syndrome (AIDS).
Mitochondrial Transformation in Yeast by Bombardment with Microprojectiles
Authors: Johnston Stephen A. , Anziano Paul Q. , Shark Kathy , Sanford John C. , Butow Ronald A.
Published: October 2006

The genetic transformation of mitochondria and chloroplasts has been an intractable problem. The newly developed "biolistic" (biological ballistic) process was used to deliver DNA into yeast cells to stably transform their mitochondria. A nonreverting strain, which is respiratory deficient because of a deletion in the mitochondrial
oxi3
gene, was bombarded with tungsten microprojectiles coated with DNA bearing sequences that could correct the
oxi3
deletion. Respiratory-competent transformants were obtained in which the introduced
oxi3
DNA is integrated at the homologous site in the mitochondrial genome. Organelle genomes can now be manipulated by molecular genetic techniques in the same way as nuclear genomes.