bluuebunny/crossref_metadata_2025 huggingface dataset:
Sub-0.1 μm gate etch processes: Towards some limitations of the plasma technology?
Authors: Desvoivres L. , Vallier L. , Joubert O.
Published: July 2002

Gate structures with dimensions smaller than 0.1 μm on gate oxides thinner than 2 nm have been patterned in a high density plasma helicon source. The chemistry which seems best adapted uses an HBr/O2 mixture ensuring high selectivity to the gate oxide and an etch anisotropy allowing the critical dimension control in the 0.1 μm regime to be acceptable. Kinetic ellipsometry has been used to measure silicon and SiO2 etch rates and carefully control the process in real time. X-ray photoelectron spectroscopy (XPS) studies have been performed to determine the chemical topography of SiO2 masked gate stacks with different aspect ratios. In particular, the chemical composition and thickness of the sidewall passivation layer have been determined. We have also observed an unsuspected behavior of thin gate oxides during the overetch step of the process. By combining XPS and spectroscopic ellipsometry, we have attributed this behavior to reactive species penetration through the thin gate oxide. This phenomenon could play an important role in the sub 0.1 μm complementary metal-oxide-semiconductors process optimization.
Sol-Gel and CVD Co3O4 Thin Films Characterized by XPS
Authors: Armelao Lidia , Barreca Davide , Gross Silvia , Tondello Eugenio
Published: July 2002

The present investigation is focused on x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XE-AES) analysis of the main core levels (O 1s, Co 2p, and Co LVV) of nanocrystalline Co3O4 coatings. The samples were obtained by CVD and sol-gel routes. Co(dpm)2 (Hdpm = 2,2-6,6-tetramethyl-3,5-heptanedione) was chosen as CVD precursor thanks to its appreciable volatility, the absence of direct Co–C bonds and the presence of thermally labile Co–O moieties. The preparation of the sol-gel films was accomplished starting from methanolic solutions of Co(OCOCH3)2⋅4H2O due to the clean conversion of cobalt acetate into cobalt oxides. The obtained Co3O4 films were bluish-brown, homogenous, crack-free, and adhered well to the substrates. The microstructural analyses revealed the formation of single-phase nanostructured layers with average crystallite dimensions ranging between 15 and 26 nm.
Structure of a Bag/Hsc70 Complex: Convergent Functional Evolution of Hsp70 Nucleotide Exchange Factors
Authors: Sondermann Holger , Scheufler Clemens , Schneider Christine , Höhfeld Jörg , Hartl F.-Ulrich , Moarefi Ismail
Published: July 2002

Bag (Bcl2-associated athanogene) domains occur in a class of cofactors of the eukaryotic chaperone 70-kilodalton heat shock protein (Hsp70) family. Binding of the Bag domain to the Hsp70 adenosine triphosphatase (ATPase) domain promotes adenosine 5′-triphosphate–dependent release of substrate from Hsp70 in vitro. In a 1.9 angstrom crystal structure of a complex with the ATPase of the 70-kilodalton heat shock cognate protein (Hsc70), the Bag domain forms a three-helix bundle, inducing a conformational switch in the ATPase that is incompatible with nucleotide binding. The same switch is observed in the bacterial Hsp70 homolog DnaK upon binding of the structurally unrelated nucleotide exchange factor GrpE. Thus, functional convergence has allowed proteins with different architectures to trigger a conserved conformational shift in Hsp70 that leads to nucleotide exchange.
Rising CO
2
Levels and the Fecundity of Forest Trees
Authors: LaDeau Shannon L. , Clark James S.
Published: July 2002

We determined the reproductive response of 19-year-old loblolly pine (
Pinus taeda
) to 4 years of carbon dioxide (CO
2
) enrichment (ambient concentration plus 200 microliters per liter) in an intact forest. After 3 years of CO
2
fumigation, trees were twice as likely to be reproductively mature and produced three times as many cones and seeds as trees at ambient CO
2
concentration. A disproportionate carbon allocation to reproduction under CO
2
enrichment results in trees reaching maturity sooner and at a smaller size. This reproductive response to future increases in atmospheric CO
2
concentration is expected to change loblolly dispersal and recruitment patterns.
Bacterial Recognition of Mineral Surfaces: Nanoscale Interactions Between
Shewanella
and α-FeOOH
Authors: Lower Steven K. , Hochella Michael F. , Beveridge Terry J.
Published: July 2002

Force microscopy has been used to quantitatively measure the infinitesimal forces that characterize interactions between
Shewanella oneidensis
(a dissimilatory metal-reducing bacterium) and goethite (α-FeOOH), both commonly found in Earth near-surface environments. Force measurements with subnanonewton resolution were made in real time with living cells under aerobic and anaerobic solutions as a function of the distance, in nanometers, between a cell and the mineral surface. Energy values [in attojoules (10
−18
joules)] derived from these measurements show that the affinity between
S. oneidensis
and goethite rapidly increases by two to five times under anaerobic conditions in which electron transfer from bacterium to mineral is expected. Specific signatures in the force curves suggest that a 150-kilodalton putative iron reductase is mobilized within the outer membrane of
S. oneidensis
and specifically interacts with the goethite surface to facilitate the electron transfer process.
African Origin of Modern Humans in East Asia: A Tale of 12,000 Y Chromosomes
Authors: Ke Yuehai , Su Bing , Song Xiufeng , Lu Daru , Chen Lifeng , Li Hongyu , Qi Chunjian , Marzuki Sangkot , Deka Ranjan , Underhill Peter , Xiao Chunjie , Shriver Mark , Lell Jeff , Wallace Douglas , Wells R Spencer , Seielstad Mark , Oefner Peter , Zhu Dingliang , Jin Jianzhong , Huang Wei , Chakraborty Ranajit , Chen Zhu , Jin Li
Published: July 2002

To test the hypotheses of modern human origin in East Asia, we sampled 12,127 male individuals from 163 populations and typed for three Y chromosome biallelic markers (YAP, M89, and M130). All the individuals carried a mutation at one of the three sites. These three mutations (YAP+, M89T, and M130T) coalesce to another mutation (M168T), which originated in Africa about 35,000 to 89,000 years ago. Therefore, the data do not support even a minimal in situ hominid contribution in the origin of anatomically modern humans in East Asia.
A Giant Sauropod Dinosaur from an Upper Cretaceous Mangrove Deposit in Egypt
Authors: Smith Joshua B. , Lamanna Matthew C. , Lacovara Kenneth J. , Dodson Peter , Smith Jennifer R. , Poole Jason C. , Giegengack Robert , Attia Yousry
Published: July 2002

We describe a giant titanosaurid sauropod dinosaur discovered in coastal deposits in the Upper Cretaceous Bahariya Formation of Egypt, a unit that has produced three
Tyrannosaurus
-sized theropods and numerous other vertebrate taxa.
Paralititan stromeri
is the first tetrapod reported from Bahariya since 1935. Its 1.69-meter-long humerus is longer than that of any known Cretaceous sauropod. The autochthonous scavenged skeleton was preserved in mangrove deposits, raising the possibility that titanosaurids and their predators habitually entered such environments.
Sorting of Mannose 6-Phosphate Receptors Mediated by the GGAs
Authors: Puertollano Rosa , Aguilar Rubén C. , Gorshkova Inna , Crouch Robert J. , Bonifacino Juan S.
Published: July 2002

The delivery of soluble hydrolases to lysosomes is mediated by the cation-independent and cation-dependent mannose 6-phosphate receptors. The cytosolic tails of both receptors contain acidic-cluster-dileucine signals that direct sorting from the trans-Golgi network to the endosomal-lysosomal system. We found that these signals bind to the VHS domain of the Golgi-localized, γ-ear–containing, ARF-binding proteins (GGAs). The receptors and the GGAs left the trans-Golgi network on the same tubulo-vesicular carriers. A dominant-negative GGA mutant blocked exit of the receptors from the trans-Golgi network. Thus, the GGAs appear to mediate sorting of the mannose 6-phosphate receptors at the trans-Golgi network.
Cell Cycle Regulation of Myosin-V by Calcium/Calmodulin-Dependent Protein Kinase II
Authors: Karcher Ryan L. , Roland Joseph T. , Zappacosta Francesca , Huddleston Michael J. , Annan Roland S. , Carr Steven A. , Gelfand Vladimir I.
Published: July 2002

Organelle transport by myosin-V is down-regulated during mitosis, presumably by myosin-V phosphorylation. We used mass spectrometry phosphopeptide mapping to show that the tail of myosin-V was phosphorylated in mitotic
Xenopus
egg extract on a single serine residue localized in the carboxyl-terminal organelle-binding domain. Phosphorylation resulted in the release of the motor from the organelle. The phosphorylation site matched the consensus sequence of calcium/calmodulin–dependent protein kinase II (CaMKII), and inhibitors of CaMKII prevented myosin-V release. The modulation of cargo binding by phosphorylation is likely to represent a general mechanism regulating organelle transport by myosin-V.
Telomere Position Effect in Human Cells
Authors: Baur Joseph A. , Zou Ying , Shay Jerry W. , Wright Woodring E.
Published: July 2002

In yeast, telomere position effect (TPE) results in the reversible silencing of genes near telomeres. Here we demonstrate the presence of TPE in human cells. HeLa clones containing a luciferase reporter adjacent to a newly formed telomere express 10 times less luciferase than do control clones generated by random integration. Luciferase expression is restored by trichostatin A, a histone deacetylase inhibitor. Overexpression of a human telomerase reverse transcriptase complementary DNA results in telomere elongation and an additional 2- to 10-fold decrease in expression in telomeric clones but not control clones. The dependence of TPE on telomere length provides a mechanism for the modification of gene expression throughout the replicative life-span of human cells.
Bt Toxin Resistance from Loss of a Putative Carbohydrate-Modifying Enzyme
Authors: Griffitts Joel S. , Whitacre Johanna L. , Stevens Daniel E. , Aroian Raffi V.
Published: July 2002

The development of resistance is the main threat to the long-term use of toxins from
Bacillus thuringiensis
(Bt) in transgenic plants. Here we report the cloning of a Bt toxin resistance gene,
Caenorhabditis elegans bre-5
, which encodes a putative β-1,3-galactosyltransferase. Lack of
bre-5
in the intestine led to resistance to the Bt toxin Cry5B. Wild-type but not
bre-5
mutant animals were found to uptake toxin into their gut cells, consistent with
bre-5
mutants lacking toxin-binding sites on their apical gut.
bre-5
mutants displayed resistance to Cry14A, a Bt toxin lethal to both nematodes and insects; this indicates that resistance by loss of carbohydrate modification is relevant to multiple Bt toxins.
The Kondo Effect in an Artificial Quantum Dot Molecule
Authors: Jeong H. , Chang A. M. , Melloch M. R.
Published: July 2002

Double quantum dots provide an ideal model system for studying interactions between localized impurity spins. We report on the transport properties of a series-coupled double quantum dot as electrons are added one by one onto the dots. When the many-body molecular states are formed, we observe a splitting of the Kondo resonance peak in the differential conductance. This splitting reflects the energy difference between the bonding and antibonding states formed by the coherent superposition of the Kondo states of each dot. The occurrence of the Kondo resonance and its magnetic field dependence agree with a simple interpretation of the spin status of a double quantum dot.
No Supermassive Black Hole in M33?
Authors: Merritt David , Ferrarese Laura , Joseph Charles L.
Published: July 2002

We observed the nucleus of M33, the third-brightest galaxy in the Local Group, with the Space Telescope Imaging Spectrograph at a resolution at least a factor of 10 higher than previously obtained. Rather than the steep rise expected within the radius of gravitational influence of a supermassive black hole, the random stellar velocities showed a decrease within a parsec of the center of the galaxy. The implied upper limit on the mass of the central black hole is only 3000 solar masses, about three orders of magnitude lower than the dynamically inferred mass of any other supermassive black hole. Detecting black holes of only a few thousand solar masses is observationally challenging, but it is critical to establish how supermassive black holes relate to their host galaxies, and which mechanisms influence the formation and evolution of both.
Inwardly Rotating Spiral Waves in a Reaction-Diffusion System
Authors: Vanag Vladimir K. , Epstein Irving R.
Published: July 2002

Almost 30 years have passed since the discovery of concentric (target) and spiral waves in the spatially extended Belousov-Zhabotinsky (BZ) reaction. Since then, rotating spirals and target waves have been observed in a variety of physical, chemical, and biological reaction-diffusion systems. All of these waves propagate out from the spiral center or pacemaker. We report observations of inwardly rotating spirals found in the BZ system dispersed in water droplets of a water-in-oil microemulsion. These “antispirals” were also generated in computer simulations.
Oscillations in Phanerozoic Seawater Chemistry: Evidence from Fluid Inclusions
Authors: Lowenstein Tim K. , Timofeeff Michael N. , Brennan Sean T. , Hardie Lawrence A. , Demicco Robert V.
Published: July 2002

Systematic changes in the chemistry of evaporated seawater contained in primary fluid inclusions in marine halites indicate that seawater chemistry has fluctuated during the Phanerozoic. The fluctuations are in phase with oscillations in seafloor spreading rates, volcanism, global sea level, and the primary mineralogies of marine limestones and evaporites. The data suggest that seawater had high Mg
2+
/Ca
2+
ratios (>2.5) and relatively high Na
+
concentrations during the Late Precambrian [544 to 543 million years ago (Ma)], Permian (258 to 251 Ma), and Tertiary through the present (40 to 0 Ma), when aragonite and MgSO
4
salts were the dominant marine precipitates. Conversely, seawater had low Mg
2+
/Ca
2+
ratios (<2.3) and relatively low Na
+
concentrations during the Cambrian (540 to 520 Ma), Silurian (440 to 418 Ma), and Cretaceous (124 to 94 Ma), when calcite was the dominant nonskeletal carbonate and K-, Mg-, and Ca-bearing chloride salts, were the only potash evaporites.
Identification of Ubiquitin Ligases Required for Skeletal Muscle Atrophy
Authors: Bodine Sue C. , Latres Esther , Baumhueter Susanne , Lai Venus K.-M. , Nunez Lorna , Clarke Brian A. , Poueymirou William T. , Panaro Frank J. , Na Erqian , Dharmarajan Kumar , Pan Zhen-Qiang , Valenzuela David M. , DeChiara Thomas M. , Stitt Trevor N. , Yancopoulos George D. , Glass David J.
Published: July 2002

Skeletal muscle adapts to decreases in activity and load by undergoing atrophy. To identify candidate molecular mediators of muscle atrophy, we performed transcript profiling. Although many genes were up-regulated in a single rat model of atrophy, only a small subset was universal in all atrophy models. Two of these genes encode ubiquitin ligases:
Muscle RING Finger 1
(
MuRF1
), and a gene we designate
Muscle Atrophy F-box
(
MAFbx
), the latter being a member of the SCF family of E3 ubiquitin ligases. Overexpression of
MAFbx
in myotubes produced atrophy, whereas mice deficient in either
MAFbx
or
MuRF1
were found to be resistant to atrophy. These proteins are potential drug targets for the treatment of muscle atrophy.
Application of the Marcus Cross Relation to Hydrogen Atom Transfer Reactions
Authors: Roth Justine P. , Yoder Jeffrey C. , Won Tae-Jin , Mayer James M.
Published: July 2002

The transfer of a hydrogen atom—a proton and an electron—is a fundamental process in chemistry and biology. A variety of hydrogen atom transfer reactions, involving iron complexes, phenols, hydroxylamines,
t
BuOOH, toluene, and related radicals, are shown to follow the Marcus cross relation. Thus, the Marcus theory formalism based on ground-state energetics and self-exchange rates, originally developed for electron transfer processes, is also valuable for hydrogen atom transfer. Compounds that undergo slow proton transfer (C–H bonds) or slow electron transfer (cobalt complexes) also undergo slow hydrogen atom transfer. Limitations of this approach are also discussed.
Dynamics of Depolarization and Hyperpolarization in the Frontal Cortex and Saccade Goal
Authors: Seidemann Eyal , Arieli Amos , Grinvald Amiram , Slovin Hamutal
Published: July 2002

The frontal eye field and neighboring area 8Ar of the primate cortex are involved in programming and execution of saccades. Electrical microstimulation in these regions elicits short-latency contralateral saccades. To determine how spatiotemporal dynamics of microstimulation-evoked activity are converted into saccade plans, we used a combination of real-time optical imaging and microstimulation in behaving monkeys. Short stimulation trains evoked a rapid and widespread wave of depolarization followed by unexpected large and prolonged hyperpolarization. During this hyperpolarization saccades are almost exclusively ipsilateral, suggesting an important role for hyperpolarization in determining saccade goal.
A Four Unit Cell Periodic Pattern of Quasi-Particle States Surrounding Vortex Cores in Bi
2
Sr
2
CaCu
2
O
8+δ
Authors: Hoffman J. E. , Hudson E. W. , Lang K. M. , Madhavan V. , Eisaki H. , Uchida S. , Davis J. C.
Published: July 2002

Scanning tunneling microscopy is used to image the additional quasi-particle states generated by quantized vortices in the high critical temperature superconductor Bi
2
Sr
2
CaCu
2
O
8+δ
. They exhibit a copper-oxygen bond–oriented “checkerboard” pattern, with four unit cell (4
a
0
) periodicity and a ∼30 angstrom decay length. These electronic modulations may be related to the magnetic field–induced, 8
a
0
periodic, spin density modulations with decay length of ∼70 angstroms recently discovered in La
1.84
Sr
0.16
CuO
4
. The proposed explanation is a spin density wave localized surrounding each vortex core. General theoretical principles predict that, in the cuprates, a localized spin modulation of wavelength λ should be associated with a corresponding electronic modulation of wavelength λ/2, in good agreement with our observations.
SHP-2 Tyrosine Phosphatase as an Intracellular Target of
Helicobacter pylori
CagA Protein
Authors: Higashi Hideaki , Tsutsumi Ryouhei , Muto Syuichi , Sugiyama Toshiro , Azuma Takeshi , Asaka Masahiro , Hatakeyama Masanori
Published: July 2002

Helicobacter pylori
CagA protein is associated with severe gastritis and gastric carcinoma. CagA is injected from the attached
Helicobacter pylori
into host cells and undergoes tyrosine phosphorylation. Wild-type but not phosphorylation-resistant CagA induced a growth factor–like response in gastric epithelial cells. Furthermore, CagA formed a physical complex with the SRC homology 2 domain (SH2)–containing tyrosine phosphatase SHP-2 in a phosphorylation-dependent manner and stimulated the phosphatase activity. Disruption of the CagA–SHP-2 complex abolished the CagA-dependent cellular response. Conversely, the CagA effect on cells was reproduced by constitutively active SHP-2. Thus, upon translocation, CagA perturbs cellular functions by deregulating SHP-2.
Requirement of the Activation-Induced Deaminase (
AID
) Gene for Immunoglobulin Gene Conversion
Authors: Arakawa Hiroshi , Hauschild Jessica , Buerstedde Jean-Marie
Published: July 2002

Three phenotypically distinct processes—somatic hypermutation, gene conversion, and switch recombination—remodel the functionally rearranged immunoglobulin (Ig) loci in B cells. Somatic hypermutation and switch recombination have recently been shown to depend on the activation-induced deaminase (
AID
) gene product. Here, we show that the disruption of the
AID
gene in the chicken B cell line DT40 completely blocks Ig gene conversion and that this block can be complemented by reintroduction of the
AID
complementary DNA. This demonstrates that the
AID
master gene controls all B cell–specific modifications of vertebrate Ig genes.
Mapping the One-Dimensional Electronic States of Nanotube Peapod Structures
Authors: Hornbaker D. J. , Kahng S.-J. , Misra S. , Smith B. W. , Johnson A. T. , Mele E. J. , Luzzi D. E. , Yazdani A.
Published: July 2002

Arrays of C
60
molecules nested inside single-walled nanotubes represent a class of nanoscale materials having tunable properties. We report electronic measurements of this system made with a scanning tunneling microscope and demonstrate that the encapsulated C
60
molecules modify the local electronic structure of the nanotube. Our measurements and calculations also show that a periodic array of C
60
molecules gives rise to a hybrid electronic band, which derives its character from both the nanotube states and the C
60
molecular orbitals.
Heterotopic Shift of Epithelial-Mesenchymal Interactions in Vertebrate Jaw Evolution
Authors: Shigetani Yasuyo , Sugahara Fumiaki , Kawakami Yayoi , Murakami Yasunori , Hirano Shigeki , Kuratani Shigeru
Published: July 2002

Genes involved in late specification of the mandibular arch, the source of the vertebrate jaw, are expressed with similar patterns in the oral regions of chick and lamprey embryos. However, morphological comparisons indicate that apparently orthologous homeobox genes were expressed in different subdivisions of the ectomesenchyme in the two species. Therefore, the homology and gene expression of the oral region are uncoupled during the transition from agnathan to gnathostome; we conclude that a heterotopic shift of tissue interaction was involved in the evolution of the jaw.
Role of Prostacyclin in the Cardiovascular Response to Thromboxane A
2
Authors: Cheng Yan , Austin Sandra C. , Rocca Bianca , Koller Beverly H. , Coffman Thomas M. , Grosser Tilo , Lawson John A. , FitzGerald Garret A.
Published: July 2002

Thromboxane (Tx) A
2
is a vasoconstrictor and platelet agonist. Aspirin affords cardioprotection through inhibition of TxA
2
formation by platelet cyclooxygenase (COX-1). Prostacyclin (PGI
2
) is a vasodilator that inhibits platelet function. Here we show that injury-induced vascular proliferation and platelet activation are enhanced in mice that are genetically deficient in the PGI
2
receptor (IP) but are depressed in mice genetically deficient in the TxA
2
receptor (TP) or treated with a TP antagonist. The augmented response to vascular injury was abolished in mice deficient in both receptors. Thus, PGI
2
modulates platelet-vascular interactions in vivo and specifically limits the response to TxA
2
. This interplay may help explain the adverse cardiovascular effects associated with selective COX-2 inhibitors, which, unlike aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), inhibit PGI
2
but not TxA
2
.
Thermochemistry and Aqueous Solubilities of Hydrotalcite-Like Solids
Authors: Allada Rama kumar , Navrotsky Alexandra , Berbeco Hillary Thompson , Casey William H.
Published: July 2002

Hydrotalcites are used in technology as catalysts and anion exchangers and are important sinks for environmental contaminants. Their compositional variability makes it important, but difficult, to estimate their aqueous solubility. We report calorimetric measurements of the heats of formation of cobalt-aluminum hydrotalcite phases. The heat and free energy of formation from the elements are equal to those of mechanical mixtures of binary compounds, namely hydroxides and carbonates. The interlayer anion is much more important than the cation in determining the solubility of the hydrotalcite phase and its ability to contain or release heavy metals to the environment. Because hydrotalcites do not have an unreactive polymer as a structural core, their aqueous stability will change dramatically with composition, particularly with anion content. This simple mechanical mixture model allows prediction of aqueous solubilities and trace metal retention in a variety of geochemical settings.
Responding to the Challenge of Communicable Disease in Europe
Authors: MacLehose Laura , McKee Martin , Weinberg Julius
Published: July 2002

In the 1960s and 1970s, communicable disease seemed a minor threat, but since then the emergence of new infections and the reemergence of old diseases has provoked a renewed focus on European communicable disease surveillance and control. A “network approach” among European countries has been successful in detecting some international outbreaks, but management and funding aspects remain unresolved. Surveillance outside the European Union has faced new challenges as a result of economic and political change following the collapse of communism. Subsequently, innovative international surveillance schemes are currently being implemented in the countries of Central and Eastern Europe and the former Soviet Union. The challenge for surveillance in Europe is to ensure that it has the capacity to meet both the needs of today and the diseases of the future.
Dynamics of Thymocyte-Stromal Cell Interactions Visualized by Two-Photon Microscopy
Authors: Bousso Philippe , Bhakta Nirav R. , Lewis Richard S. , Robey Ellen
Published: July 2002

Thymocytes are selected to mature according to their ability to interact with self major histocompatibility complex (MHC)–peptide complexes displayed on the thymic stroma. Using two-photon microscopy, we performed real-time analysis of the cellular contacts made by developing thymocytes undergoing positive selection in a three-dimensional thymic organ culture. A large fraction of thymocytes within these cultures were highly motile. MHC recognition was found to increase the duration of thymocyte–stromal cell interactions and occurred as both long-lived cellular associations displaying stable cell-cell contacts and as shorter, highly dynamic contacts. Our results identify the diversity and dynamics of thymocyte interactions during positive selection.
Lymphatic Metastasis in the Absence of Functional Intratumor Lymphatics
Authors: Padera Timothy P. , Kadambi Ananth , di Tomaso Emmanuelle , Carreira Carla Mouta , Brown Edward B. , Boucher Yves , Choi Noah C. , Mathisen Douglas , Wain John , Mark Eugene J. , Munn Lance L. , Jain Rakesh K.
Published: July 2002

Lymphatic metastasis contributes to mortality from solid tumors. Whether metastasizing cancer cells reach lymph nodes via intratumor lymphatic vessels is unknown. Here, we examine functional lymphatics associated with mouse tumors expressing normal or elevated levels of vascular endothelial growth factor–C (VEGF-C), a molecule that stimulates lymphangiogenesis. Although VEGF-C overexpression increased lymphatic surface area in the tumor margin and lymphatic metastasis, these tumors contained no functional lymphatics, as assessed by four independent functional assays and immunohistochemical staining. These findings suggest that the functional lymphatics in the tumor margin alone are sufficient for lymphatic metastasis and should be targeted therapeutically.
Microfluidic Control Using Colloidal Devices
Authors: Terray Alex , Oakey John , Marr David W. M.
Published: July 2002

By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.
Achievement of Thermal Stability by Varying Metabolic Heat Production in Flying Honeybees
Authors: Harrison Jon F. , Fewell Jennifer H. , Roberts Stephen P. , Hall H. Glenn
Published: July 2002

Thermoregulation of the thorax allows endothermic insects to achieve power outputs during flight that are among the highest in the animal kingdom. Flying endothermic insects, including the honeybee
Apis mellifera
, are believed to thermoregulate almost exclusively by varying heat loss. Here it is shown that a rise in air temperature from 20° to 40°C causes large decreases in metabolic heat production and wing-beat frequency in honeybees during hovering, agitated, or loaded flight. Thus, variation in heat production may be the primary mechanism for achieving thermal stability in flying honeybees, and this mechanism may occur commonly in endothermic insects.
Galileo Photopolarimeter-Radiometer Observations of Jupiter and the Galilean Satellites
Authors: Orton G. S. , Spencer J. R. , Travis L. D. , Martin T. Z. , Tamppari L. K.
Published: July 2002

Photopolarimeter-Radiometer (PPR) maps of daytime temperatures on Ganymede at a resolution of 220 kilometers show the expected anticorrelation with albedo, but morning temperatures were about 10 kelvin warmer than expected. Europa had a subsolar temperature of 128 kelvin and a lower effective thermal inertia than either Ganymede or Callisto, and Io's night side was cooler than predicted by recent models, perhaps requiring revision of heat-flow estimates. The lowest 250-millibar temperatures in the Great Red Spot (GRS) generally corresponded to the visually darkest regions. Temperatures remained cold north of the GRS, but they rose by as much as 6 kelvin to the south over the 2800-kilometer PPR resolution. A visually bright region northwest of the GRS was also relatively cold. It is likely that NH
3
clouds affected the determination of the 500-millibar temperature field, which appears qualitatively different.
Fennoscandian Earthquakes: Whole Crustal Rupturing Related to Postglacial Rebound
Authors: Arvidsson Ronald
Published: July 2002

Local and regional earthquake locations provide seismic evidence that large shield earthquakes have occurred in northern Fennoscandia. These paleoearthquakes, with fault lengths of up to 160 kilometers and average displacements of up to 15 meters, were triggered by nonisostatic compressive stresses caused by the removal of the ice at the end of the last deglaciation. The Fennoscandian faults were probably formed by single events that ruptured through most of the crust. The largest event, moment magnitude
M
W
≈ 8.2, was larger than other known stable continent earthquakes outside failed rifts or extended crust.
Signal Transduction by DR3, a Death Domain-Containing Receptor Related to TNFR-1 and CD95
Authors: Chinnaiyan Arul M. , O'Rourke Karen , Yu Guo-Liang , Lyons Robert H. , Garg Manish , Duan D. Roxanne , Xing Lily , Gentz Reiner , Ni Jian , Dixit Vishva M.
Published: July 2002

Tumor necrosis factor receptor-1 (TNFR-1) and CD95 (also called Fas or APO-1) are cytokine receptors that engage the apoptosis pathway through a region of intracellular homology, designated the “death domain.” Another death domain-containing member of the TNFR family, death receptor 3 (DR3), was identified and was shown to induce both apoptosis and activation of nuclear factor κB. Expression of DR3 appears to be restricted to tissues enriched in lymphocytes. DR3 signal transduction is mediated by a complex of intracellular signaling molecules including TRADD, TRAF2, FADD, and FLICE. Thus, DR3 likely plays a role in regulating lymphocyte homeostasis.
Direct Observation of Vortex Dynamics in Superconducting Films with Regular Arrays of Defects
Authors: Harada K. , Kamimura O. , Kasai H. , Matsuda T. , Tonomura A. , Moshchalkov V. V.
Published: July 2002

The microscopic mechanism of the matching effect in a superconductor, which manifested itself as the production of peaks or cusps in the critical current at specific values of the applied magnetic field, was investigated with Lorentz microscopy to allow direct observation of the behavior of vortices in a niobium thin film having a regular array of artificial defects. Vortices were observed to form regular and consequently rigid lattices at the matching magnetic field, at its multiples, and at its fractions. The dynamic observation furthermore revealed that vortices were most difficult to move at the matching field, whereas excess vortices moved easily.
Red-Emitting Semiconductor Quantum Dot Lasers
Authors: Fafard S. , Hinzer K. , Raymond S. , Dion M. , McCaffrey J. , Feng Y. , Charbonneau S.
Published: July 2002

Visible-stimulated emission in a semiconductor quantum dot (QD) laser structure has been demonstrated. Red-emitting, self-assembled QDs of highly strained InAlAs have been grown by molecular beam epitaxy on a GaAs substrate. Carriers injected electrically from the doped regions of a separate confinement heterostructure thermalized efficiently into the zero-dimensional QD states, and stimulated emission at ∼707 nanometers was observed at 77 kelvin with a threshold current of 175 milliamperes for a 60-micrometer by 400-micrometer broad area laser. An external efficiency of ∼8.5 percent at low temperature and a peak power greater than 200 milliwatts demonstrate the good size distribution and high gain in these high-quality QDs.
Chemiluminescence in the Agglomeration of Metal Clusters
Authors: König L. , Rabin I. , Schulze W. , Ertl G.
Published: July 2002

The agglomeration of copper or silver atoms in a matrix of noble gas atoms to form small clusters may be accompanied by the emission of visible light. Spectral analysis reveals the intermediate formation of electronically excited atoms and dimers as the source of the chemiluminescence. A mechanism is proposed, according to which the gain in binding energy upon cluster formation may even lead to the ejection of excited fragments as a result of unstable intermediate configurations. A similar concept was introduced in the field of nuclear reactions by Niels Bohr 60 years ago.
Tricorn Protease—The Core of a Modular Proteolytic System
Authors: Tamura Tomohiro , Tamura Noriko , Cejka Zdenka , Hegerl Reiner , Lottspeich Friedrich , Baumeister Wolfgang
Published: July 2002

Large macromolecular assemblies have evolved as a means of compartmentalizing reactions in organisms lacking membrane-bounded compartments. A tricorn-shaped protease was isolated from the archaeon
Thermoplasma
and was shown to form a multisubunit proteolytic complex. The 120-kilodalton monomer assembled to form a hexameric toroid that could assemble further into a capsid structure. Tricorn protease appeared to act as the core of a proteolytic system; when it interacted with several smaller proteins, it displayed multicatalytic activities.
Evidence for Life on Earth More Than 3850 Million Years Ago
Authors: Holland Heinrich D.
Published: July 2002

When did life first appear on Earth? Previous efforts to answer this fundamental question have found early life as far back as 3450 million years ago, in rock formations in Australia. In his Perspective, Holland discusses data recently published by Mojzsis
et al
. in the journal
Nature
that pushes the earliest life back to more than 3850 million years ago.
Compressibility, Phase Transitions, and Oxygen Migration in Zirconium Tungstate, ZrW
2
O
8
Authors: Evans J S. O. , Hu Z. , Jorgensen J. D. , Argyriou D. N. , Short S. , Sleight A. W.
Published: July 2002

In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW
2
O
8
) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data. This phase transition can be reversed by heating at 393 kelvin and 1 atmosphere and involves the migration of oxygen atoms in the lattice. The high-pressure phase shows negative thermal expansion from 20 to 300 kelvin. The relative thermal expansion and compressibilities of the cubic and orthorhombic forms can be explained in terms of the “cross-bracing” between polyhedra that occurs as a result of the phase transition.
Neptune's Deep Chemistry
Authors: Hubbard W. B.
Published: July 2002

Molecules such as C
2
H
2
and C
2
H
6
have been observed in the atmosphere of Neptune, one of the giant planets composed mostly of hydrogen and helium. Planetary scientists have puzzled over whether these hydrocarbons are formed as ultraviolet light from the sun induces photochemical reactions in atmospheric methane. In his Perspective, Hubbard discusses simulations reported in the same issue by Ancilotto
et al
. (p.
1288
) suggesting that C
2
H
6
may be produced by high-pressure chemical reactions deep within the planet.
Synergy Paper Questioned at Toxicology Meeting
Authors: Kaiser Jocelyn
Published: July 2002

CINCINNATI
—Last summer, a modest set of test-tube experiments made quite a splash. It was found that in cell cultures, pairs of pesticides were up to 1600 times more potent at triggering a hormonelike response than was either of the chemicals alone. The findings sent a chill through the U.S. Environmental Protection Agency, which suddenly faced the possibility that all their safety tests of single chemicals were suspect. In the months since, however, several teams of researchers have been unable to replicate the results. While some scientists think that the synergy results merit further study, others have written them off as unlikely to be of relevance to people.
Melting Temperature and Partial Melt Chemistry of H
2
O-Saturated Mantle Peridotite to 11 Gigapascals
Authors: Kawamoto Tatsuhiko , Holloway John R.
Published: July 2002

The H
2
O-saturated solidus of a model mantle composition (Kilborne Hole peridotite nodule, KLB-1) was determined to be just above 1000°C from 5 to 11 gigapascals. Given reasonable H
2
O abundances in Earth’s mantle, an H
2
O-rich fluid could exist only in a region defined by the wet solidus and thermal stability limits of hydrous minerals, at depths between 90 and 330 kilometers. The experimental partial melts monotonously became more mafic with increasing pressure from andesitic composition at 1 gigapascal to more mafic than the starting peridotite at 10 gigapascals. Because the chemistry of the experimental partial melts is similar to that of kimberlites, it is suggested that kimberlites may be derived by low-temperature melting of an H
2
O-rich mantle at depths of 150 to 300 kilometers.
Phylogenetic Analysis of Glycolytic Enzyme Expression
Authors: Pierce V. A. , Crawford D. L.
Published: July 2002

Although differences among species in enzyme maximal activity or concentration are often interpreted as adaptive and important for regulating metabolism, these differences may simply reflect phylogenetic divergence. Phylogenetic analysis of the expression of the glycolytic enzymes among 15 taxa of a North American fish genus (
Fundulus)
indicated that most variation in enzyme concentration is due to evolutionary distance and may be nonadaptive. However, three enzymes’ maximal activities covary with environmental temperature and have adaptive value. Additionally, two pairs of enzymes covary, indicating coevolution. Thus, metabolic flux may be modulated by many different enzymes rather than by a single rate-limiting enzyme.
Reverse Transcriptase Motifs in the Catalytic Subunit of Telomerase
Authors: Lingner Joachim , Hughes Timothy R. , Shevchenko Andrej , Mann Matthias , Lundblad Victoria , Cech Thomas R.
Published: July 2002

Telomerase is a ribonucleoprotein enzyme essential for the replication of chromosome termini in most eukaryotes. Telomerase RNA components have been identified from many organisms, but no protein component has been demonstrated to catalyze telomeric DNA extension. Telomerase was purified from
Euplotes aediculatus
, a ciliated protozoan, and one of its proteins was partially sequenced by nanoelectrospray tandem mass spectrometry. Cloning and sequence analysis of the corresponding gene revealed that this 123-kilodalton protein (p123) contains reverse transcriptase motifs. A yeast (
Saccharomyces cerevisiae
) homolog was found and subsequently identified as
EST2
(ever shorter telomeres), deletion of which had independently been shown to produce telomere defects. Introduction of single amino acid substitutions within the reverse transcriptase motifs of Est2 protein led to telomere shortening and senescence in yeast, indicating that these motifs are important for catalysis of telomere elongation in vivo. In vitro telomeric DNA extension occurred with extracts from wild-type yeast but not from
est2
mutants or mutants deficient in telomerase RNA. Thus, the reverse transcriptase protein fold, previously known to be involved in retroviral replication and retrotransposition, is essential for normal chromosome telomere replication in diverse eukaryotes.
Protactinium-231 Dating of Carbonates by Thermal Ionization Mass Spectrometry: Implications for Quaternary Climate Change
Authors: Edwards R. Lawrence , Cheng H. , Murrell M. T. , Goldstein S. J.
Published: July 2002

Measurement of protactinium-231 (
231
Pa) in carbonates by thermal ionization mass spectroscopy yields
231
Pa ages that are more than 10 times more precise than those determined by decay counting. Carbonates between 10 and 250,000 years old can now be dated with
231
Pa methods. Barbados corals that have identical
231
Pa and thorium-230 (
230
Th) ages indicate that the timing of sea level change over parts of the last glacial cycle is consistent with the predictions of the Astronomical Theory. Two Devils Hole calcite subsamples record identical
231
Pa and
230
Th ages, suggesting that the chronology of this climate record is accurate.
Crystal Structure of the Cytochrome bc
1
Complex from Bovine Heart Mitochondria
Authors: Xia Di , Yu Chang-An , Kim Hoeon , Xia Jia-Zhi , Kachurin Anatoly M. , Zhang Li , Yu Linda , Deisenhofer Johann
Published: July 2002

On the basis of x-ray diffraction data to a resolution of 2.9 angstroms, atomic models of most protein components of the bovine cytochrome bc
1
complex were built, including core 1, core 2, cytochrome b, subunit 6, subunit 7, a carboxyl-terminal fragment of cytochrome c
1
, and an amino-terminal fragment of the iron-sulfur protein. The positions of the four iron centers within the bc
1
complex and the binding sites of the two specific respiratory inhibitors antimycin A and myxothiazol were identified. The membrane-spanning region of each bc
1
complex monomer consists of 13 transmembrane helices, eight of which belong to cytochrome b. Closely interacting monomers are arranged as symmetric dimers and form cavities through which the inhibitor binding pockets can be accessed. The proteins core 1 and core 2 are structurally similar to each other and consist of two domains of roughly equal size and identical folding topology.
Induction of Cell Migration by Matrix Metalloprotease-2 Cleavage of Laminin-5
Authors: Giannelli Gianluigi , Falk-Marzillier Jutta , Schiraldi Oronzo , Stetler-Stevenson William G. , Quaranta Vito
Published: July 2002

Structural changes in the extracellular matrix are necessary for cell migration during tissue remodeling and tumor invasion. Specific cleavage of laminin-5 (Ln-5) by matrix metalloprotease–2 (MMP2) was shown to induce migration of breast epithelial cells. MMP2 cleaved the Ln-5 γ2 subunit at residue 587, exposing a putative cryptic promigratory site on Ln-5 that triggers cell motility. This altered form of Ln-5 is found in tumors and in tissues undergoing remodeling, but not in quiescent tissues. Cleavage of Ln-5 by MMP2 and the resulting activation of the Ln-5 cryptic site may provide new targets for modulation of tumor cell invasion and tissue remodeling.
Epidermal Cell Differentiation in
Arabidopsis
Determined by a
Myb
Homolog,
CPC
Authors: Wada Takuji , Tachibana Tatsuhiko , Shimura Yoshiro , Okada Kiyotaka
Published: July 2002

The roots of plants normally carry small hairs arranged in a regular pattern. Transfer DNA–tagged lines of
Arabidopsis thaliana
included a mutant with few, randomly distributed root hairs. The mutated gene
CAPRICE
(
CPC
) encoded a protein with a Myb-like DNA binding domain typical of transcription factors involved in animal and plant development. Analysis in combination with other root hair mutations showed that
CPC
may work together with the
TTG
gene and upstream of the
GL2
gene. Transgenic plants overexpressing
CPC
had more root hairs and fewer trichomes than normal. Thus, the
CPC
gene determines the fate of epidermal cell differentiation in
Arabidopsis
.
High-Pressure Transformation of Al
2
O
3
Authors: Funamori Nobumasa , Jeanloz Raymond
Published: July 2002

X-ray diffraction measurements indicate that ruby (Cr
3+
doped α-Al
2
O
3
) transforms to the Rh
2
O
3
(II) structure when heated to temperatures exceeding ∼1000 kelvin at pressures above ∼100 gigapascals, in agreement with predictions from ab initio quantum mechanical calculations. The high-pressure phase did not quench upon decompression to ambient pressure, and the occurrence of this phase transformation may affect interpretations of static (diamond-anvil cell) and dynamic (shock-wave) experiments at ultra-high pressures.
Multivariable Dependence of Fe-Mg Partitioning in the Lower Mantle
Authors: Mao Ho-kwang , Shen Guoyin , Hemley Russell J.
Published: July 2002

High-pressure diamond-cell experiments indicate that the iron-magnesium partitioning between (Fe,Mg)SiO
3
-perovskite and magnesiowüstite in Earth's lower mantle depends on the pressure, temperature, bulk iron/magnesium ratio, and ferric iron content. The perovskite stability field expands with increasing pressure and temperature. The ferric iron component preferentially dissolves in perovskite and raises the apparent total iron content but had little effect on the partitioning of the ferrous iron. The ferrous iron depletes in perovskite at the top of the lower mantle and gradually increases at greater depth. These changes in iron-magnesium composition should affect geochemical and geophysical properties of the deep interior.
Magnetic Properties of Hexagonal Closed-Packed Iron Deduced from Direct Observations in a Diamond Anvil Cell
Authors: Gilder Stuart , Glen Jonathan
Published: July 2002

The attraction of hexagonal closed packed (hcp) iron to a magnet at 16.9 gigapascals and 261 degrees centigrade suggests that hcp iron is either paramagnetic or ferromagnetic with susceptibilities from 0.15 to 0.001 and magnetizations from 1800 to 15 amperes per meter. If dominant in Earth's inner core, paramagnetic hcp iron could stabilize the geodynamo.
Engineering Broader Specificity into an Antibiotic-Producing Polyketide Synthase
Authors: Marsden Andrew F. A. , Wilkinson Barrie , Cortés Jesús , Dunster Nicholas J. , Staunton James , Leadlay Peter F.
Published: July 2002

The wide-specificity loading module for the avermectin-producing polyketide synthase was grafted onto the first multienzyme component (DEBS1) of the erythromycin-producing polyketide synthase in place of the normal loading module. Expression of this hybrid enzyme in the erythromycin producer
Saccharopolyspora erythraea
produced several novel antibiotic erythromycins derived from endogenous branched-chain acid starter units typical of natural avermectins. Because the avermectin polyketide synthase is known to accept more than 40 alternative carboxylic acids as starter units, this approach opens the way to facile production of novel analogs of antibiotic macrolides.
Dangling Bond Dynamics on the Silicon (100)-2×1 Surface: Dissociation, Diffusion, and Recombination
Authors: McEllistrem Marcus , Allgeier Matthew , Boland John J.
Published: July 2002

The dynamics of dangling bond (DB) diffusion was studied after deuterium desorption from the silicon (100)-2×1 surface. At elevated temperatures, paired DB sites produced after desorption unpaired as deuterium atoms hopped from adjacent dimers. Below 620 kelvin, the unpaired configuration most commonly observed corresponded to two DBs on adjacent silicon dimers. At higher temperatures, unpaired DBs executed one-dimensional walks along the dimer rows, and recombination was observed with the same partner after walks lasting many minutes. The frequency and extent of these excursions increased with temperature. Above 660 kelvin, complete dissociation was observed and was sometimes followed by recombination by means of partner exchange. The implications for low-temperature materials growth are discussed.