bluuebunny/crossref_metadata_2025 huggingface dataset:
Contact-Dependent Demyelination by
Mycobacterium leprae
in the Absence of Immune Cells
Authors: Rambukkana Anura , Zanazzi George , Tapinos Nikos , Salzer James L.
Published: July 2002

Demyelination results in severe disability in many neurodegenerative diseases and nervous system infections, and it is typically mediated by inflammatory responses.
Mycobacterium leprae
, the causative organism of leprosy, induced rapid demyelination by a contact-dependent mechanism in the absence of immune cells in an in vitro nerve tissue culture model and in
Rag1
-knockout (
Rag1
−/−
) mice, which lack mature B and T lymphocytes. Myelinated Schwann cells were resistant to
M. leprae
invasion but undergo demyelination upon bacterial attachment, whereas nonmyelinated Schwann cells harbor intracellular
M. leprae
in large numbers. During
M. leprae
–induced demyelination, Schwann cells proliferate significantly both in vitro and in vivo and generate a more nonmyelinated phenotype, thereby securing the intracellular niche for
M. leprae
.
Local Actin Polymerization and Dynamin Recruitment in SV40-Induced Internalization of Caveolae
Authors: Pelkmans Lucas , Püntener Daniel , Helenius Ari
Published: July 2002

Simian virus 40 (SV40) utilizes endocytosis through caveolae for infectious entry into host cells. We found that after binding to caveolae, virus particles induced transient breakdown of actin stress fibers. Actin was then recruited to virus-loaded caveolae as actin patches that served as sites for actin “tail” formation. Dynamin II was also transiently recruited. These events depended on the presence of cholesterol and on the activation of tyrosine kinases that phosphorylated proteins in caveolae. They were necessary for formation of caveolae-derived endocytic vesicles and for infection of the cell. Thus, caveolar endocytosis is ligand-triggered and involves extensive rearrangement of the actin cytoskeleton.
Direct Patterning of Modified Oligonucleotides on Metals and Insulators by Dip-Pen Nanolithography
Authors: Demers L. M. , Ginger D. S. , Park S.-J. , Li Z. , Chung S.-W. , Mirkin C. A.
Published: July 2002

The use of direct-write dip-pen nanolithography (DPN) to generate covalently anchored, nanoscale patterns of oligonucleotides on both metallic and insulating substrates is described. Modification of DNA with hexanethiol groups allowed patterning on gold, and oligonucleotides bearing 5′-terminal acrylamide groups could be patterned on derivatized silica. Feature sizes ranging from many micrometers to less than 100 nanometers were achieved, and the resulting patterns exhibited the sequence-specific binding properties of the DNA from which they were composed. The patterns can be used to direct the assembly of individual oligonucleotide-modified particles on a surface, and the deposition of multiple DNA sequences in a single array is demonstrated.
The Edge of Time: Dating Young Volcanic Ash Layers with the
40
Ar-
39
Ar Laser Probe
Authors: Chen Yanshao , Smith Patrick E. , Evensen Norman M. , York Derek , Lajoie Kenneth R.
Published: July 2002

Argon-40-argon-39 single-crystal dating of young (5000 to 30,000 years ago) volcanic ash layers erupted from the Mono Craters, California, shows that the method can yield meaningful ages in Holocene tephra. Because of ubiquitous xenocrystic contamination, the data do not form isochrons but plot in wedge-shaped regions on an argon isotopic diagram. The upper boundary of the region is an isochron matching the
14
C-derived age of the eruption. Such contamination-related patterns may be common in dating young materials by the single-crystal method. Argon dating by this method can help refine the time scale of physical and biological evolution over the past 100,000 years.
Stratospheric Mean Ages and Transport Rates from Observations of Carbon Dioxide and Nitrous Oxide
Authors: Boering K. A. , Wofsy S. C. , Daube B. C. , Schneider H. R. , Loewenstein M. , Podolske J. R. , Conway T. J.
Published: July 2002

Measurements of stratospheric carbon dioxide (CO
2
) and nitrous oxide (N
2
O) concentrations were analyzed to investigate stratospheric transport rates. Temporal variations in tropospheric CO
2
were observed to propagate into the stratosphere, showing that tropospheric air enters the lower tropical stratosphere continuously, ascends, and is transported rapidly (in less than 1 month) to both hemispheres. The mean age
A
of stratospheric air determined from CO
2
data is approximately 5 years in the mid-stratosphere. The mean age is mathematically equivalent to a conserved tracer analogous to exhaust from stratospheric aircraft. Comparison of values for
A
from models and observations indicates that current model simulations likely underestimate pollutant concentrations from proposed stratospheric aircraft by 25 to 100 percent.
The Clementine Bistatic Radar Experiment
Authors: Nozette S. , Lichtenberg C. L. , Spudis P. , Bonner R. , Ort W. , Malaret E. , Robinson M. , Shoemaker E. M.
Published: July 2002

During the Clementine 1 mission, a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle, β, for selected lunar areas. Observations of the lunar south pole yield a same-sense polarization enhancement around β = 0. Analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole. Radar observations of periodically solar-illuminated lunar surfaces, including the north pole, yielded no such enhancement. A probable explanation for these differences is the presence of low-loss volume scatterers, such as water ice, in the permanently shadowed region at the south pole.
Reduction of Voltage-Dependent Mg
2+
Blockade of NMDA Current in Mechanically Injured Neurons
Authors: Zhang Lei , Rzigalinski Beverly A. , Ellis Earl F. , Satin Leslie S.
Published: July 2002

Activation of the
N
-methyl-D-aspartate (NMDA) subtype of glutamate receptors is implicated in the pathophysiology of traumatic brain injury. Here, the effects of mechanical injury on the voltage-dependent magnesium (Mg
2+
) block of NMDA currents in cultured rat cortical neurons were examined. Stretch-induced injury was found to reduce the Mg
2+
blockade, resulting in significantly larger ionic currents and increases in intracellular free calcium (Ca
2+
) concentration after NMDA stimulation of injured neurons. The Mg
2+
blockade was partially restored by increased extracellular Mg
2+
concentration or by pretreatment with the protein kinase C inhibitor calphostin C. These findings could account for the secondary pathological changes associated with traumatic brain injury.
Intestinal Secretory Defects and Dwarfism in Mice Lacking cGMP-Dependent Protein Kinase II
Authors: Pfeifer Alexander , Aszódi Attila , Seidler Ursula , Ruth Peter , Hofmann Franz , Fässler Reinhard
Published: July 2002

Cyclic guanosine 3′,5′-monophosphate (cGMP)-dependent protein kinases (cGKs) mediate cellular signaling induced by nitric oxide and cGMP. Mice deficient in the type II cGK were resistant to
Escherichia coli
STa, an enterotoxin that stimulates cGMP accumulation and intestinal fluid secretion. The cGKII-deficient mice also developed dwarfism that was caused by a severe defect in endochondral ossification at the growth plates. These results indicate that cGKII plays a central role in diverse physiological processes.
Chaotic Beetles
Authors: Godfray Charles , Hassell Michael
Published: July 2002

Chaotic behavior of populations can be described mathematically but has not been observed often in real populations. In a report in this week's issue, Costantino
et al
. (
p. 389
) demonstrate chaotic behavior of a population of flour beetles, both in a predictive model and a real population. In their Perspective, Godfray and Hassell discuss the developments in the field that led to these findings and assess the importance of this first demonstration of chaos in an experimental setting.
Bulk Spin-Resonance Quantum Computation
Authors: Gershenfeld Neil A. , Chuang Isaac L.
Published: July 2002

Quantum computation remains an enormously appealing but elusive goal. It is appealing because of its potential to perform superfast algorithms, such as finding prime factors in polynomial time, but also elusive because of the difficulty of simultaneously manipulating quantum degrees of freedom while preventing environmentally induced decoherence. A new approach to quantum computing is introduced based on the use of multiple-pulse resonance techniques to manipulate the small deviation from equilibrium of the density matrix of a macroscopic ensemble so that it appears to be the density matrix of a much lower dimensional pure state. A complete prescription for quantum computing is given for such a system.
Kinetic Measurement of the Step Size of DNA Unwinding by
Escherichia coli
UvrD Helicase
Authors: Ali Janid A. , Lohman Timothy M.
Published: July 2002

The kinetic mechanism by which the DNA repair helicase UvrD of
Escherichia coli
unwinds duplex DNA was examined with the use of a series of oligodeoxynucleotides with duplex regions ranging from 10 to 40 base pairs. Single-turnover unwinding experiments showed distinct lag phases that increased with duplex length because partially unwound DNA intermediate states are highly populated during unwinding. Analysis of these kinetics indicates that UvrD unwinds duplex DNA in discrete steps, with an average “step size” of 4 to 5 base pairs (approximately one-half turn of the DNA helix). This suggests an unwinding mechanism in which alternating subunits of the dimeric helicase interact directly with duplex DNA.
Earth-Based Radio Tracking of the Galileo Probe for Jupiter Wind Estimation
Authors: Folkner W. M. , Preston R. A. , Border J. S. , Navarro J. , Wilson W. E. , Oestreich M.
Published: July 2002

Although the Galileo probe was designed to communicate only to the orbiter, the probe radio signal was detected at two Earth-based radio observatories where the signal was a billion times weaker. The measured signal frequency was used to derive a vertical profile of the jovian zonal wind speed. Due to the mission geometry, the Earth-based wind estimates are less sensitive to descent trajectory errors than estimates based on probe-orbiter Doppler measurements. The two estimates of wind profiles agree qualitatively; both show high wind speeds at all depths sampled.
Linking Mind and Brain in the Study of Mental Illnesses: A Project for a Scientific Psychopathology
Authors: Andreasen Nancy C.
Published: July 2002

Brain research on mental illnesses has made substantial advances in recent years, supported by conceptual and technological developments in cognitive neuroscience. Brain-based cognitive models of illnesses such as schizophrenia and depression have been tested with a variety of techniques, including the lesion method, tract tracing, neuroimaging, animal modeling, single-cell recording, electrophysiology, neuropsychology, and experimental cognitive psychology. A relatively sophisticated picture is emerging that conceptualizes mental illnesses as disorders of mind arising in the brain. Convergent data using multiple neuroscience techniques indicate that the neural mechanisms of mental illnesses can be understood as dysfunctions in specific neural circuits and that their functions and dysfunctions can be influenced or altered by a variety of cognitive and pharmacological factors.
Scanning Single-Electron Transistor Microscopy: Imaging Individual Charges
Authors: Yoo M. J. , Fulton T. A. , Hess H. F. , Willett R. L. , Dunkleberger L. N. , Chichester R. J. , Pfeiffer L. N. , West K. W.
Published: July 2002

A single-electron transistor scanning electrometer (SETSE)—a scanned probe microscope capable of mapping static electric fields and charges with 100-nanometer spatial resolution and a charge sensitivity of a small fraction of an electron—has been developed. The active sensing element of the SETSE, a single-electron transistor fabricated at the end of a sharp glass tip, is scanned in close proximity across the sample surface. Images of the surface electric fields of a GaAs/Al

x

Ga
1−

x

As heterostructure sample show individual photo-ionized charge sites and fluctuations in the dopant and surface-charge distribution on a length scale of 100 nanometers. The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample.
t-SNARE Activation Through Transient Interaction with a Rab-Like Guanosine Triphosphatase
Authors: Lupashin Vladimir V. , Waters M. Gerard
Published: July 2002

Intracellular vesicle targeting involves the interaction of vesicle proteins, termed v-SNAREs, with target membrane proteins, termed t-SNAREs. Assembly of v-SNARE–t-SNARE targeting complexes is modulated by members of the Sec1-Sly1 protein family, and by small guanosine triphosphatases termed Rabs. The interactions of these proteins during assembly of the endoplasmic reticulum–to-Golgi targeting complex in
Saccharomyces cerevisiae
were studied. The data suggest that the Rab protein Ypt1p transiently interacts with the t-SNARE Sed5p and results in displacement of the negative regulator Sly1p, allowing subsequent formation of the v-SNARE–t-SNARE targeting complex.
Adenosine: A Mediator of the Sleep-Inducing Effects of Prolonged Wakefulness
Authors: Porkka-Heiskanen Tarja , Strecker Robert E. , Thakkar Mahesh , Bjørkum Alvhild A. , Greene Robert W. , McCarley Robert W.
Published: July 2002

Both subjective and electroencephalographic arousal diminish as a function of the duration of prior wakefulness. Data reported here suggest that the major criteria for a neural sleep factor mediating the somnogenic effects of prolonged wakefulness are satisfied by adenosine, a neuromodulator whose extracellular concentration increases with brain metabolism and which, in vitro, inhibits basal forebrain cholinergic neurons. In vivo microdialysis measurements in freely behaving cats showed that adenosine extracellular concentrations in the basal forebrain cholinergic region increased during spontaneous wakefulness as contrasted with slow wave sleep; exhibited progressive increases during sustained, prolonged wakefulness; and declined slowly during recovery sleep. Furthermore, the sleep-wakefulness profile occurring after prolonged wakefulness was mimicked by increased extracellular adenosine induced by microdialysis perfusion of an adenosine transport inhibitor in the cholinergic basal forebrain but not by perfusion in a control noncholinergic region.
White Phosphors from a Silicate-Carboxylate Sol-Gel Precursor That Lack Metal Activator Ions
Authors: Green Will H. , Le Khoa P. , Grey Jonathan , Au Tiffany T. , Sailor Michael J.
Published: July 2002

Highly emissive (with an external quantum yield exceeding 35 percent at a 365-nanometer excitation wavelength) broadband phosphors can be synthesized from a tetraalkoxysilane sol-gel precursor and a variety of organic carboxylic acids. The air-stable phosphors were synthesized at low temperatures (less than 300°C) and displayed broad visible photoluminescence spectra that appeared white to the eye. Water-soluble phosphors can be prepared by the substitution of 3-aminopropyltriethoxysilane for tetraalkoxysilane in the synthesis. These materials are the most efficient extrinsic phosphors that do not contain activator metal ions.
Control of Filament Formation in
Candida albicans
by the Transcriptional Repressor TUP1
Authors: Braun Burkhard R. , Johnson Alexander D.
Published: July 2002

The pathogenic yeast
Candida albicans
regulates its cellular morphology in response to environmental conditions. Ellipsoidal, single cells (blastospores) predominate in rich media, whereas filaments composed of elongated cells that are attached end-to-end form in response to starvation, serum, and other conditions. The
TUP1
gene, which encodes a general transcriptional repressor in
Saccharomyces cerevisiae
, was isolated from
C. albicans
and disrupted. The resulting
tup1
mutant strain of
C. albicans
grew exclusively as filaments under all conditions tested.
TUP1
was epistatic to the transcriptional activator
CPH1
, previously found to promote filamentous growth. The results suggest a model where
TUP1
represses genes responsible for initiating filamentous growth and this repression is lifted under inducing environmental conditions.
The Stereodynamics of a Gas-Surface Reaction
Authors: Hou H. , Gulding S. J. , Rettner C. T. , Wodtke A. M. , Auerbach D. J.
Published: July 2002

Measurements of the influence of reactant alignment on the rates of chemical reactions provide direct information concerning the atomic motions necessary for chemical transformation. Data presented here show that at low collision energy, the dissociative adsorption of deuterium (D
2
) on the (111) surface of copper has a much higher probability for broadside than for end-on collisions. Furthermore, this steric preference is sensitive to the kinetic energy of the incident molecule, almost disappearing as the energy increases to 0.8 electron volt. This study shows that the dynamic conditions of a surface chemical reaction can profoundly influence the associated steric requirements.
Control of TRAIL-Induced Apoptosis by a Family of Signaling and Decoy Receptors
Authors: Sheridan James P. , Marsters Scot A. , Pitti Robert M. , Gurney Austin , Skubatch Maya , Baldwin Daryl , Ramakrishnan Lakshmi , Gray Christa L. , Baker Kevin , Wood William I. , Goddard Audrey D. , Godowski Paul , Ashkenazi Avi
Published: July 2002

TRAIL (also called Apo2L) belongs to the tumor necrosis factor family, activates rapid apoptosis in tumor cells, and binds to the death-signaling receptor DR4. Two additional TRAIL receptors were identified. The receptor designated death receptor 5 (DR5) contained a cytoplasmic death domain and induced apoptosis much like DR4. The receptor designated decoy receptor 1 (DcR1) displayed properties of a glycophospholipid-anchored cell surface protein. DcR1 acted as a decoy receptor that inhibited TRAIL signaling. Thus, a cell surface mechanism exists for the regulation of cellular responsiveness to pro-apoptotic stimuli.
Structural Basis for Cyclic Terpene Biosynthesis by Tobacco 5-Epi-Aristolochene Synthase
Authors: Starks Courtney M. , Back Kyoungwhan , Chappell Joseph , Noel Joseph P.
Published: July 2002

Terpene cyclases catalyze the synthesis of cyclic terpenes with 10-, 15-, and 20-carbon acyclic isoprenoid diphosphates as substrates. Plants have been a source of these natural products by providing a homologous set of terpene synthases. The crystal structures of 5-epi-aristolochene synthase, a sesquiterpene cyclase from tobacco, alone and complexed separately with two farnesyl diphosphate analogs were analyzed. These structures reveal an unexpected enzymatic mechanism for the synthesis of the bicyclic product, 5-epi-aristolochene, and provide a basis for understanding the stereochemical selectivity displayed by other cyclases in the biosynthesis of pharmacologically important cyclic terpenes. As such, these structures provide templates for the engineering of novel terpene cyclases.
Interpreting Dutch Cannabis Policy: Reasoning by Analogy in the Legalization Debate
Authors: MacCoun Robert , Reuter Peter
Published: July 2002

The Dutch depenalization and subsequent de facto legalization of cannabis since 1976 is used here to highlight the strengths and limitations of reasoning by analogy as a guide for projecting the effects of relaxing drug prohibitions. While the Dutch case and other analogies have flaws, they appear to converge in suggesting that reductions in criminal penalties have limited effects on drug use—at least for marijuana—but that commercial access is associated with growth in the drug-using population.
Structural Requirements for Glycolipid Antigen Recognition by CD1b-Restricted T Cells
Authors: Moody D. Branch , Reinhold Bruce B. , Guy Mark R. , Beckman Evan M. , Frederique Daphney E. , Furlong Stephen T. , Ye Song , Reinhold Vernon N. , Sieling Peter A. , Modlin Robert L. , Besra Gurdyal S. , Porcelli Steven A.
Published: July 2002

The human CD1b protein presents lipid antigens to T cells, but the molecular mechanism is unknown. Identification of mycobacterial glucose monomycolate (GMM) as a CD1b-presented glycolipid allowed determination of the structural requirements for its recognition by T cells. Presentation of GMM to CD1b-restricted T cells was not affected by substantial variations in its lipid tails, but was extremely sensitive to chemical alterations in its carbohydrate or other polar substituents. These findings support the view that the recently demonstrated hydrophobic CD1 groove binds the acyl chains of lipid antigens relatively nonspecifically, thereby positioning the hydrophilic components for highly specific interactions with T cell antigen receptors.
Arctic Environmental Change of the Last Four Centuries
Authors: Overpeck J. , Hughen K. , Hardy D. , Bradley R. , Case R. , Douglas M. , Finney B. , Gajewski K. , Jacoby G. , Jennings A. , Lamoureux S. , Lasca A. , MacDonald G. , Moore J. , Retelle M. , Smith S. , Wolfe A. , Zielinski G.
Published: July 2002

A compilation of paleoclimate records from lake sediments, trees, glaciers, and marine sediments provides a view of circum-Arctic environmental variability over the last 400 years. From 1840 to the mid-20th century, the Arctic warmed to the highest temperatures in four centuries. This warming ended the Little Ice Age in the Arctic and has caused retreats of glaciers, melting of permafrost and sea ice, and alteration of terrestrial and lake ecosystems. Although warming, particularly after 1920, was likely caused by increases in atmospheric trace gases, the initiation of the warming in the mid-19th century suggests that increased solar irradiance, decreased volcanic activity, and feedbacks internal to the climate system played roles.
Late Pliocene Faunal Turnover in the Turkana Basin, Kenya and Ethiopia
Authors: Behrensmeyer Anna K. , Todd Nancy E. , Potts Richard , McBrinn Geraldine E.
Published: July 2002

Analysis of a large sample of well-dated fossil mammals from localities in the Turkana Basin of Kenya and Ethiopia revealed sampling biases that affect patterns of faunal turnover during the late Pliocene. When these biases were accounted for, results indicated that 58 to 77 percent of the mammal species were replaced between 3.0 and 1.8 million years ago (Ma). Overall diversity increased from 3.0 to 2.0 Ma but then declined. No distinct turnover pulse is seen between 2.8 and 2.5 Ma; instead, the most significant period of faunal change began after 2.5 Ma and continued through 1.8 Ma.
Infrared Photorefractive Polymers and Their Applications for Imaging
Authors: Kippelen B. , Marder S. R. , Hendrickx E. , Maldonado J. L. , Guillemet G. , Volodin B. L. , Steele D. D. , Enami Y. , Sandalphon  , Yao Y. J. , Wang J. F. , Röckel H. , Erskine L. , Peyghambarian N.
Published: July 2002

Photorefractive polymers with high diffraction efficiency in the visible and near-infrared regions of the electromagnetic spectrum have been developed. These polymers, which have a large dynamic range because of their high orientational birefringence, incorporate a dye designed to have a large dipole moment and a high linear polarizability anisotropy. Such polymers have enabled demonstrations of imaging through scattering media, using a holographic time-gating technique at a wavelength that is compatible with the transparency of biological tissues and with the emission of low-cost semiconductor laser diodes.
Crystal Structures of Human Topoisomerase I in Covalent and Noncovalent Complexes with DNA
Authors: Redinbo Matthew R. , Stewart Lance , Kuhn Peter , Champoux James J. , Hol Wim G. J.
Published: July 2002

Topoisomerases I promote the relaxation of DNA superhelical tension by introducing a transient single-stranded break in duplex DNA and are vital for the processes of replication, transcription, and recombination. The crystal structures at 2.1 and 2.5 angstrom resolution of reconstituted human topoisomerase I comprising the core and carboxyl-terminal domains in covalent and noncovalent complexes with 22–base pair DNA duplexes reveal an enzyme that “clamps” around essentially B-form DNA. The core domain and the first eight residues of the carboxyl-terminal domain of the enzyme, including the active-site nucleophile tyrosine-723, share significant structural similarity with the bacteriophage family of DNA integrases. A binding mode for the anticancer drug camptothecin is proposed on the basis of chemical and biochemical information combined with these three-dimensional structures of topoisomerase I–DNA complexes.
Homeostasis and Self-Tolerance in the Immune System: Turning Lymphocytes off
Authors: Parijs Luk Van , Abbas Abul K.
Published: July 2002

The immune system responds in a regulated fashion to microbes and eliminates them, but it does not respond to self-antigens. Several regulatory mechanisms function to terminate responses to foreign antigens, returning the immune system to a basal state after the antigen has been cleared, and to maintain unresponsiveness, or tolerance, to self-antigens. Here, recent advances in understanding of the molecular bases and physiologic roles of the mechanisms of immune homeostasis are examined.
Friction Anisotropy and Asymmetry of a Compliant Monolayer Induced by a Small Molecular Tilt
Authors: Liley M. , Gourdon D. , Stamou D. , Meseth U. , Fischer T. M. , Lautz C. , Stahlberg H. , Vogel H. , Burnham N. A. , Duschl C.
Published: July 2002

Lateral force microscopy in the wearless regime was used to study the friction behavior of a lipid monolayer on mica. In the monolayer, condensed domains with long-range orientational order of the lipid molecules were present. The domains revealed unexpectedly strong friction anisotropies and non-negligible friction asymmetries. The angular dependency of these effects correlated well with the tilt direction of the alkyl chains of the monolayer, as determined by electron diffraction and Brewster angle microscopy. The molecular tilt causing these frictional effects was less than 15 degrees, demonstrating that even small molecular tilts can make a major contribution to friction.
Carbon Nanotube Quantum Resistors
Authors: Frank Stefan , Poncharal Philippe , Wang Z. L. , Heer Walt A. de
Published: July 2002

The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized. The experimental method involved measuring the conductance of nanotubes by replacing the tip of a scanning probe microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber. The conductance of arc-produced MWNTs is one unit of the conductance quantum
G
0
= 2
e
2
/
h
= (12.9 kilohms)
–1
. The nanotubes conduct current ballistically and do not dissipate heat. The nanotubes, which are typically 15 nanometers wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors. Extremely high stable current densities,
J
> 10
7
amperes per square centimeter, have been attained.
(Mg,Fe)SiO
3
-Perovskite Stability Under Lower Mantle Conditions
Authors: Serghiou G. , Zerr A. , Boehler R.
Published: July 2002

In three different experiments up to 100 gigapascals and 3000 kelvin, (Mg,Fe)SiO
3
-perovskite, the major component of the lower mantle, remained stable and did not decompose to its component oxides (Mg,Fe)O and SiO
2
. Perovskite was formed from these oxides when heated in a diamond anvil cell at pressures up to 100 gigapascals. Both MgSiO
3
crystals and glasses heated to 3000 kelvin at 75 gigapascals also formed perovskite as a single phase, as evident from Raman spectra. Moreover, fluorescence measurements on chromium-doped samples synthesized at these conditions gave no indication of the presence of MgO.
Ultrasonic Shear Wave Velocities of MgSiO
3
Perovskite at 8 GPa and 800 K and Lower Mantle Composition
Authors: Sinelnikov Yegor D. , Chen Ganglin , Neuville Daniel R. , Vaughan Michael T. , Liebermann Robert C.
Published: July 2002

Ultrasonic interferometric measurements of the shear elastic properties of MgSiO
3
perovskite were conducted on three polycrystalline specimens at conditions up to pressures of 8 gigapascals and temperatures of 800 kelvin. The acoustic measurements produced the pressure (
P
) and temperature (
T
) derivatives of the shear modulus (
G
), namely (∂
G/∂P
)
T
= 1.8 ± 0.4 and (∂
G/∂T
)
P
= −2.9 ± 0.3 × 10
−2
gigapascals per kelvin. Combining these derivatives with the derivatives that were measured for the bulk modulus and thermal expansion of MgSiO
3
perovskite provided data that suggest lower mantle compositions between pyrolite and C1 carbonaceous chondrite and a lower mantle potential temperature of 1500 ± 200 kelvin.
Ages of Prehistoric Earthquakes Revealed by Cosmogenic Chlorine-36 in a Bedrock Fault Scarp at Hebgen Lake
Authors: Zreda Marek , Noller Jay S.
Published: July 2002

Cosmogenic chlorine-36 reveals dates of the multiple prehistoric earthquakes that have produced a scarp on the Hebgen Lake fault. Apparent chlorine-36 ages are stratigraphically correct, follow a predicted theoretical pattern, and produce geologically reasonable model ages of 24, 20, 7.0, 2.6, 1.7, and 0.4 thousand years ago. This result demonstrates the feasibility of using cosmogenic chlorine-36 to extract paleoearthquake records from bedrock fault scarps.
Nanoengineering of Inorganic and Hybrid Hollow Spheres by Colloidal Templating
Authors: Caruso Frank , Caruso Rachel A. , Möhwald Helmuth
Published: July 2002

Hollow silica and silica-polymer spheres with diameters between 720 and 1000 nanometers were fabricated by consecutively assembling silica nanoparticles and polymer onto colloids and subsequently removing the templated colloid either by calcination or decomposition upon exposure to solvents. Scanning and transmission electron microscopy images demonstrate that the wall thickness of the hollow spheres can be readily controlled by varying the number of nanoparticle-polymer deposition cycles, and the size and shape are determined by the morphology of the templating colloid. The hollow spheres produced are envisioned to have applications in areas ranging from medicine to pharmaceutics to materials science.
Dual Requirement for Gephyrin in Glycine Receptor Clustering and Molybdoenzyme Activity
Authors: Feng Guoping , Tintrup Hartmut , Kirsch Joachim , Nichol Mia C. , Kuhse Jochen , Betz Heinrich , Sanes Joshua R.
Published: July 2002

Glycine receptors are anchored at inhibitory chemical synapses by a cytoplasmic protein, gephyrin. Molecular cloning revealed the similarity of gephyrin to prokaryotic and invertebrate proteins essential for synthesizing a cofactor required for activity of molybdoenzymes. Gene targeting in mice showed that gephyrin is required both for synaptic clustering of glycine receptors in spinal cord and for molybdoenzyme activity in nonneural tissues. The mutant phenotype resembled that of humans with hereditary molybdenum cofactor deficiency and hyperekplexia (a failure of inhibitory neurotransmission), suggesting that gephyrin function may be impaired in both diseases.
Role of DNA 5-Methylcytosine Transferase in Cell Transformation by
fos
Authors: Bakin A. V. , Curran T.
Published: July 2002

The Fos and Jun oncoproteins form dimeric complexes that stimulate transcription of genes containing activator protein–1 regulatory elements. We found, by representational difference analysis, that expression of DNA 5-methylcytosine transferase (
dnmt1
) in
fos
-transformed cells is three times the expression in normal fibroblasts and that
fos
-transformed cells contain about 20 percent more 5-methylcytosine than normal fibroblasts. Transfection of the gene encoding Dnmt1 induced morphological transformation, whereas inhibition of
dnmt1
expression or activity resulted in reversion of
fos
transformation. Inhibition of histone deacetylase, which associates with methylated DNA, also caused reversion. These results suggest that
fos
may transform cells through alterations in DNA methylation and in histone deacetylation.
Adaptation of Bulk Constitutive Equations to Insoluble Monolayer Collapse at the Air-Water Interface
Authors: Kampf J. Patrick , Frank Curtis W. , Malmström Eva E. , Hawker Craig J.
Published: July 2002

A constitutive equation based on stress-strain models of bulk solids was adapted to relate the surface pressure, compression rate, and temperature of an insoluble monolayer of monodendrons during collapse at the air-water interface. A power law relation between compression rate and surface pressure and an Arrhenius temperature dependence of the steady-state creep rate were observed in data from compression rate and creep experiments in the collapse region. These relations were combined into a single constitutive equation to calculate the temperature dependence of the collapse pressure with a maximum error of 5 percent for temperatures ranging from 10° to 25°C.
Role of the
S. typhimurium
Actin-Binding Protein SipA in Bacterial Internalization
Authors: Zhou Daoguo , Mooseker Mark S. , Galán Jorge E.
Published: July 2002

Entry of the bacterium
Salmonella typhimurium
into host cells requires membrane ruffling and rearrangement of the actin cytoskeleton. Here, it is shown that the bacterial protein SipA plays a critical role in this process. SipA binds directly to actin, decreases its critical concentration, and inhibits depolymerization of actin filaments. These activities result in the spatial localization and more pronounced outward extension of the
Salmonella
-induced membrane ruffles, thereby facilitating bacterial uptake.
A Cytotoxic Ribonuclease Targeting Specific Transfer RNA Anticodons
Authors: Ogawa T. , Tomita K. , Ueda T. , Watanabe K. , Uozumi T. , Masaki H.
Published: July 2002

The carboxyl-terminal domain of colicin E5 was shown to inhibit protein synthesis of
Escherichia coli
. Its target, as revealed through in vivo and in vitro experiments, was not ribosomes as in the case of E3, but the transfer RNAs (tRNAs) for Tyr, His, Asn, and Asp, which contain a modified base, queuine, at the wobble position of each anticodon. The E5 carboxyl-terminal domain hydrolyzed these tRNAs just on the 3′ side of this nucleotide. Tight correlation was observed between the toxicity of E5 and the cleavage of intracellular tRNAs of this group, implying that these tRNAs are the primary targets of colicin E5.
Viral Clearance Without Destruction of Infected Cells During Acute HBV Infection
Authors: Guidotti Luca G. , Rochford Rosemary , Chung Josan , Shapiro Max , Purcell Robert , Chisari Francis V.
Published: July 2002

Viral clearance during hepatitis B virus (HBV) infection has been thought to reflect the destruction of infected hepatocytes by CD8
+
T lymphocytes. However, in this study, HBV DNA was shown to largely disappear from the liver and the blood of acutely infected chimpanzees long before the peak of T cell infiltration and most of the liver disease. These results demonstrate that noncytopathic antiviral mechanisms contribute to viral clearance during acute viral hepatitis by purging HBV replicative intermediates from the cytoplasm and covalently closed circular viral DNA from the nucleus of infected cells.
Response of Plant-Insect Associations to Paleocene-Eocene Warming
Authors: Wilf Peter , Labandeira Conrad C.
Published: July 2002

The diversity of modern herbivorous insects and their pressure on plant hosts generally increase with decreasing latitude. These observations imply that the diversity and intensity of herbivory should increase with rising temperatures at constant latitude. Insect damage on fossil leaves found in southwestern Wyoming, from the late Paleocene–early Eocene global warming interval, demonstrates this prediction. Early Eocene plants had more types of insect damage per host species and higher attack frequencies than late Paleocene plants. Herbivory was most elevated on the most abundant group, the birch family (Betulaceae). Change in the composition of the herbivore fauna during the Paleocene-Eocene interval is also indicated.
Galileo Imaging of Atmospheric Emissions from Io
Authors: Geissler P. E. , McEwen A. S. , Ip W. , Belton M. J. S. , Johnson T. V. , Smyth W. H. , Ingersoll A. P.
Published: July 2002

The Galileo spacecraft has detected diffuse optical emissions from Io in high-resolution images acquired while the satellite was eclipsed by Jupiter. Three distinct components make up Io's visible emissions. Bright blue glows of more than 300 kilorayleighs emanate from volcanic plumes, probably due to electron impact on molecular sulfur dioxide. Weaker red emissions, possibly due to atomic oxygen, are seen along the limbs, brighter on the pole closest to the plasma torus. A faint green glow appears concentrated on the night side of Io, possibly produced by atomic sodium. Io's disk-averaged emission diminishes with time after entering eclipse, whereas the localized blue glows brighten instead.
How Much Caution in the Fields?
Authors: Duvick Donald N.
Published: July 2002

Hazard Identification of Agricultural Biotechnology
Finding Relevant Questions. Ad van Dommelen. International Books, Utrecht, The Netherlands, 1999. 238 pp. $29.95, £19.95, Dfl 59.95. ISBN 90-5727-034-X.

Van Dommelen proposes a method for resolving scientific disputes over the safety of transgenic organisms by taking a precautionary approach to their possible impact. He focuses on the identification of relevant research questions.
Apoptosis of T Cells Mediated by Ca
2+
-Induced Release of the Transcription Factor MEF2
Authors: Youn Hong-Duk , Sun Luo , Prywes Ron , Liu Jun O.
Published: July 2002

T cell receptor (TCR)–induced apoptosis of thymocytes is mediated by calcium-dependent expression of the steroid receptors Nur77 and Nor1. Nur77 expression is controlled by the transcription factor myocyte enhancer factor 2 (MEF2), but how MEF2 is activated by calcium signaling is still obscure. Cabin1, a calcineurin inhibitor, was found to regulate MEF2. MEF2 was normally sequestered by Cabin1 in a transcriptionally inactive state. TCR engagement led to an increase in intracellular calcium concentration and the dissociation of MEF2 from Cabin1, as a result of competitive binding of activated calmodulin to Cabin1. The interplay between Cabin1, MEF2, and calmodulin defines a distinct signaling pathway from the TCR to the Nur77 promoter during T cell apoptosis.
16°C Rapid Temperature Variation in Central Greenland 70,000 Years Ago
Authors: Lang C. , Leuenberger M. , Schwander J. , Johnsen S.
Published: July 2002

Variations in the
29
N
2
/
28
N
2
ratio of air bubbles trapped in polar ice cores and their relation to variations of the
18
O/
16
O of the ice allow past surface temperature variations and ice age–gas age differences to be determined. High-resolution measurements of
29
N
2
/
28
N
2
in Dansgaard-Oeschger event 19 (around 70,000 years before the present) in ice from Central Greenland show that at the beginning of the event, the ice age–gas age difference was 1090 ± 100 years. With the use of a combined firn densification, temperature, and gas diffusion model, the δ
18
O
ice
-temperature coefficient α was determined to be 0.42 ± 0.05 per mil per kelvin. This coefficient implies a mean surface temperature change of 16.0 kelvin (between 14.3 and 18.1 kelvin), which differs substantially from values derived from borehole temperatures and modern spatial δ
18
O
ice
–surface temperature correlations.
Seismic Consequences of Warm Versus Cool Subduction Metamorphism: Examples from Southwest and Northeast Japan
Authors: Peacock Simon M. , Wang Kelin
Published: July 2002

Warm and cool subduction zones exhibit differences in seismicity, seismic structure, and arc magmatism, which reflect differences in metamorphic reactions occurring in subducting oceanic crust. In southwest Japan, arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth; in northeast Japan, arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth. Thermal-petrologic models predict that oceanic crust subducting beneath southwest Japan is 300° to 500°C warmer than beneath northeast Japan, resulting in shallower eclogite transformation and slab dehydration reactions, and possible slab melting.
Three-Dimensional Structures of the TAF
II
-Containing Complexes TFIID and TFTC
Authors: Brand Marjorie , Leurent Claire , Mallouh Véronique , Tora Làszlò , Schultz Patrick
Published: July 2002

TBP (TATA-binding protein)–associated factors (TAF
II
s) are components of large multiprotein complexes such as TFIID, TFTC, STAGA, PCAF/GCN5, and SAGA, which play a key role in the regulation of gene expression by RNA polymerase II. The structures of TFIID and TFTC have been determined at 3.5-nanometer resolution by electron microscopy and digital image analysis of single particles. Human TFIID resembles a macromolecular clamp that contains four globular domains organized around a solvent-accessible groove of a size suitable to bind DNA. TFTC is larger and contains five domains, four of which are similar to TFIID.
The Way Things Move: Looking Under the Hood of Molecular Motor Proteins
Authors: Vale Ronald D. , Milligan Ronald A.
Published: July 2002

The microtubule-based kinesin motors and actin-based myosin motors generate motions associated with intracellular trafficking, cell division, and muscle contraction. Early studies suggested that these molecular motors work by very different mechanisms. Recently, however, it has become clear that kinesin and myosin share a common core structure and convert energy from adenosine triphosphate into protein motion using a similar conformational change strategy. Many different types of mechanical amplifiers have evolved that operate in conjunction with the conserved core. This modular design has given rise to a remarkable diversity of kinesin and myosin motors whose motile properties are optimized for performing distinct biological functions.
Functional Role of Caspase-1 and Caspase-3 in an ALS Transgenic Mouse Model
Authors: Li Mingwei , Ona Victor O. , Guégan Christelle , Chen Minghua , Jackson-Lewis Vernice , Andrews L. John , Olszewski Adam J. , Stieg Philip E. , Lee Jean-Pyo. , Przedborski Serge , Friedlander Robert M.
Published: July 2002

Mutations in the copper/zinc superoxide dismutase (SOD1) gene produce an animal model of familial amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. To test a new therapeutic strategy for ALS, we examined the effect of caspase inhibition in transgenic mice expressing mutant human SOD1 with a substitution of glycine to alanine in position 93 (mSOD1
G93A
). Intracerebroventricular administration of zVAD-fmk, a broad caspase inhibitor, delays disease onset and mortality. Moreover, zVAD-fmk inhibits caspase-1 activity as well as caspase-1 and caspase-3 mRNA up-regulation, providing evidence for a non–cell-autonomous pathway regulating caspase expression. Caspases play an instrumental role in neurodegeneration in transgenic mSOD1
G93A
mice, which suggests that caspase inhibition may have a protective role in ALS.
On the Origin of Internal Structure of Word Forms
Authors: MacNeilage Peter F. , Davis Barbara L.
Published: July 2002

This study shows that a corpus of proto-word forms shares four sequential sound patterns with words of modern languages and the first words of infants. Three of the patterns involve intrasyllabic consonant-vowel (CV) co-occurrence: labial (lip) consonants with central vowels, coronal (tongue front) consonants with front vowels, and dorsal (tongue back) consonants with back vowels. The fourth pattern is an intersyllabic preference for initiating words with a labial consonant–vowel–coronal consonant sequence (LC). The CV effects may be primarily biomechanically motivated. The LC effect may be self-organizational, with multivariate causality. The findings support the hypothesis that these four patterns were basic to the origin of words.
Intracellular Parasitism by the Human Granulocytic Ehrlichiosis Bacterium Through the P-Selectin Ligand, PSGL-1
Authors: Herron Michael J. , Nelson Curtis M. , Larson Janet , Snapp Karen R. , Kansas Geoffrey S. , Goodman Jesse L.
Published: July 2002

Human granulocytic ehrlichiosis (HGE) is a febrile tick-borne illness caused by a recently discovered intracellular bacterium remarkable for its tropism for professionally phagocytic neutrophils. Monoclonal antibodies against the P-selectin binding domain of the leukocyte P-selectin glycoprotein ligand, PSGL-1, prevented HGE cell binding and infection, as did enzymatic digestion of PSGL-1. Furthermore, simultaneous neoexpression in nonsusceptible cells of complementary DNAs for both PSGL-1 and its modifying α-(1,3) fucosyltransferase, Fuc-TVII, allowed binding and infection by HGE. Thus, the HGE bacterium specifically bound to fucosylated leukocyte PSGL-1. Selectin mimicry is likely central to the organism's unique ability to target and infect neutrophils.
Mode-Specific Energy Disposal in the Four-Atom Reaction OH + D
2
→ HOD + D
Authors: Strazisar Brian R. , Lin Cheng , Floyd Davis H.
Published: July 2002

Experiments, employing crossed molecular beams, with vibrational state resolution have been performed on the simplest four-atom reaction, OH + D
2
→ HOD + D. In good agreement with the most recent quantum scattering predictions, mode-specific reaction dynamics is observed, with vibration in the newly formed oxygen-deuterium bond preferentially excited to
v
= 2. This demonstrates that quantum theoretical calculations, which in the past decade have achieved remarkable accuracy for three-atom reactions involving three dimensions, have progressed to the point where it is now possible to accurately predict energy disposal in four-atom reactions involving six dimensions.
Spherical Bilayer Vesicles of Fullerene-Based Surfactants in Water: A Laser Light Scattering Study
Authors: Zhou Shuiqin , Burger Christian , Chu Benjamin , Sawamura Masaya , Nagahama Noriaki , Toganoh Motoki , Hackler Ulrich E. , Isobe Hiroyuki , Nakamura Eiichi
Published: July 2002

The low solubility of fullerenes in aqueous solution limits their applications in biology. By appropriate substitution, the fullerenes can be transformed into stabilized anions that are water soluble and can form large aggregated structures. A laser light scattering study of the association behavior of the potassium salt of pentaphenyl fullerene (Ph
5
C
60
K) in water revealed that the hydrocarbon anions Ph
5
C
60
−
associate into bilayers, forming stable spherical vesicles with an average hydrodynamic radius and a radius of gyration of about 17 nanometers at a very low critical aggregation concentration of less than 10
−7
moles per liter. The average aggregation number of associated particles in these large spherical vesicles is about 1.2 × 10
4
.
Limits on Silicon Nanoelectronics for Terascale Integration
Authors: Meindl James D. , Chen Qiang , Davis Jeffrey A.
Published: July 2002

Throughout the past four decades, silicon semiconductor technology has advanced at exponential rates in both performance and productivity. Concerns have been raised, however, that the limits of silicon technology may soon be reached. Analysis of fundamental, material, device, circuit, and system limits reveals that silicon technology has an enormous remaining potential to achieve terascale integration (TSI) of more than 1 trillion transistors per chip. Such massive-scale integration is feasible assuming the development and economical mass production of double-gate metal-oxide-semiconductor field effect transistors with gate oxide thickness of about 1 nanometer, silicon channel thickness of about 3 nanometers, and channel length of about 10 nanometers. The development of interconnecting wires for these transistors presents a major challenge to the achievement of nanoelectronics for TSI.