bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid atomic force/scanning tunneling lithography
Authors: Wilder Kathryn , Soh Hyongsok T. , Atalar Abdullah , Quate Calvin F.
Published: July 2002

We present a new technique for performing lithography with scanning probes that has several advantages over standard methods. This hybrid lithography system combines the key features of the atomic force microscope (AFM) and the scanning tunneling microscope (STM) by incorporating two independent feedback loops, one to control current and one to control force. We demonstrate a minimum resolution of 41 nm and nanometer alignment capabilities. This lithography system is capable of writing continuous features over sample topography. Topography is often present in real patterning applications and poses problems for AFM and STM lithography. We report 100 nm resist features patterned over 180 nm of topography created by local oxidation of silicon. The hybrid AFM/STM system is designed as a robust scanning probe lithography tool, capable of high-speed patterning and suited for integrated circuit lithography applications.
Etching of 3C-SiC using CHF3/O2 and CHF3/O2/He plasmas at 1.75 Torr
Authors: Fleischman Aaron J. , Zorman Christian A. , Mehregany Mehran
Published: July 2002

This article discusses the etching and selectivity of 3C-SiC films grown on Si substrates using CHF3/O2 and CHF3/O2/He plasmas at a pressure of 1.75 Torr. The addition of helium increases the etch rates of SiC and Si for most CHF3 and O2 concentrations. For both CHF3/O2 and CHF3/O2/He plasmas with O2 concentrations up to 85%, the SiC etch rate increases monotonically and the Si etch rate decreases monotonically with increased percentages of O2. At an O2 concentration of 80%, the addition of helium to the CHF3/O2 plasma results in an etch rate of 1267 Å/min, which is the highest reported for etching 3C-SiC using a CHF3-based plasma in a conventional, parallel plate plasma reactor. The addition of helium also increases the etch anisotropy. This study also investigated aluminum micromasking of SiC etch fields and finds the primary source to be sputtered aluminum from the etch mask.
New insights on SiGe growth instabilities
Authors: Berbezier I. , Gallas B. , Lapena L. , Fernandez J. , Derrien J. , Joyce B.
Published: July 2002

In this work we investigate the influence of the Si substrate orientation on the growth instability of strained Si1−xGex heterostructures. The work mainly consists in atomic force microscopy and grazing incidence x-ray diffraction analyses of the Si1−xGex layers deposited by gas source molecular beam epitaxy on vicinal Si substrates tilted from (001) to (111) surfaces. The major result is that the two- to three-dimensional growth transition is dramatically affected by the orientation of the substrate but also by the equilibrium shape of silicon. For instance, we evidence the layer by layer growth of Si1−xGex on Si (111) in contrast to the nucleation of three-dimensional islands on 2° off Si (111) in the same experimental conditions. We systematically verify that the homoepitaxial growth of unstressed Si on vicinal Si (111) consists in a regular array of single steps. Therefore, we propose that the stress induced by the heteroepitaxial growth destabilizes the regular step train by reducing the repulsive elastic interaction between steps, and induces step-bunching. The presence of close-spaced steps and the metastability of the vicinal surfaces increase the tendency towards instable growth and result to earlier development of bunching. Despite the accompanying increase of surface area, the development of low-energy facets balances the surface free energy excess. In all cases, step-bunching instability is a kinetic pathway towards the faceted equilibrium state. Long annealing treatment of the strained metastable Si1−xGex layers confirms this last point.
Roughness of thermal oxide layers grown on ion implanted silicon wafers
Authors: Iacona Fabio , Raineri Vito , La Via Francesco , Rimini Emanuele
Published: July 2002

We have studied by atomic force microscopy (AFM) the surface morphology of SiO2 layers grown by thermal oxidation of silicon wafers implanted with As, B, Ge, or Si ions. In order to grow oxides having comparable thickness at different temperatures, we have employed both dry and wet processes. Roughness values up to 0.4 nm have been measured on the surface of these oxides. Surface morphology is not influenced by the oxidation ambient, while temperature-related effects are predominant. For low temperature oxidation (920 °C), the predominating effects are due to the behavior of the implanted species, and mainly consist in segregation phenomena, that are the result of a complex competition among different factors, including the segregation coefficient, the relative diffusion rates in the oxide and silicon, and the oxidation rate. At higher temperature (1100 °C), impurity segregation is inhibited or considerably reduced by the increased diffusivity, and defects formation, due to the evolution of the radiation damage, becomes the main effect. Finally, the comparison among AFM, Rutherford backscattering spectrometry, and transmission electron microscopy data has allowed to demonstrate that the morphologies of the SiO2 surfaces are tightly related to the corresponding SiO2/Si interfaces.
Resist processes for hybrid (electron-beam/deep ultraviolet) lithography
Authors: Tedesco S. , Mourier T. , Dal’zotto B. , McDougall A. , Blanc-Coquant S. , Quéré Y. , Paniez P. J. , Mortini B.
Published: July 2002

This article describes the different mix and match writing strategies using both an optical deep ultraviolet (DUV) stepper (ASML/90) and an electron-beam (e-beam) system (LEICA VB6HR) with both positive and negative tone chemically amplified resists. These resists, mainly developed for DUV applications, have shown very good performance under e-beam exposure. Negative tone resists such as the Shipley XP90166 and UVN2, and positive tone resists such as the Shipley UVIII and UV5 have been optimized in terms of soft bake temperatures, postexposure bake temperatures, and development process. Resolutions in the range of 40–50 nm have been obtained using a 50 keV accelerating voltage. Delay time effect has been quantified and different behaviors under vacuum and in air have been pointed out.
Molecular beam epitaxy growth of Ge1−yCy alloys on Si (100) with high carbon contents
Authors: Roe K. J. , Dashiell M. W. , Kolodzey J. , Boucaud P. , Lourtioz J.-M.
Published: July 2002

Group IV alloys are attracting strong interest for Si-based optoelectronics. The effects of C on the electrical and optical properties, however, are still not well understood, especially for high Ge content. In this report, we describe optical, structural, and compositional measurements of a series of thick, relaxed p-type Ge1−yCy layers on n-type Si (100) substrates. The alloy layers were 0.5 μm thick and were grown by solid source molecular beam epitaxy at a substrate temperature of 300 °C and p-type doped with different B concentrations. X-ray diffraction indicated that the layers were single crystalline and nearly fully relaxed. The optical absorption was measured using a waveguide structure using Fourier transform infrared spectroscopy. The absorption data versus photon energy data fit indicated an indirect band gap, and one sample had a band gap of 774 meV compared to 660 meV for pure Ge. For single-crystalline, relaxed layers, the effect of C was to increase the band gap energy. These measurements show that alloying Ge with C provides a way to vary the optical absorption, which may be useful for device applications.
Characterization of Al, Cu, and TiN surface cleaning following a low-K dielectric etch
Authors: Matsuo P. J. , Standaert T. E. F. M. , Allen S. D. , Oehrlein G. S. , Dalton T. J.
Published: July 2002

The cleaning of Al, TiN, and Cu blanket samples was investigated in a high density inductively coupled plasma reactor, and compared with results for silicon. After simulating the dielectric overetch exposure of these substrates to a CHF3 discharge, an in situ O2 plasma clean and subsequent Ar+ premetal sputter clean were performed and evaluated using ellipsometry and x-ray photoelectron spectroscopy. Following the fluorocarbon exposure, significant C and F residues were observed. Exposure to a O2 plasma clean greatly reduced this contamination. Subsequent treatment with an Ar+ sputter further reduced the thickness of the modified surface layer. Comparisons of the cleaning results with silicon suggest an efficient cleaning procedure, especially in the cases of copper and titanium nitride. The response of several blanket, oxide-like low-K dielectrics to the O2 plasma treatment were also studied and compared to SiO2. While a fluorinated SiO2(SiOF) exhibited SiO2-like stability, deep modifications were observed in both hydrogen silsesquioxane and methyl silsesquioxane, consistent with the removal of hydrogen and carbon from these films. These results were compared to a dedicated chamber design, where no fluorocarbons contaminate the reactor. The dedicated chamber methodology offered no significant advantage.
Time-of-flight high-mass spectrometer observation of large size Nb clusters toward assembling of size controlled clusters
Authors: Hihara Takehiko , Sumiyama Kenji
Published: July 2002

Using a plasma-gas-condensation-type cluster source, we could obtain nano-scale clusters with the average diameter between 2 and 13 nm. In order to detect such large free clusters containing 1–105 atoms, we have constructed a time-of-flight high-mass spectrometer (TOF-HMS). The size distribution of the Nbn clusters observed by the TOF-HMS is in good agreement with the result of the transmission electron microscope observation. The mass spectra have been measured with varying the operational parameters of the cluster source. They are shifted to the smaller size direction and the mass distribution becomes narrower with increasing the He gas flow rate, VHe, and keeping the Ar gas flow rate, VAr, constant. These features are attributable to the decrease in the residence times of gaseous species in the cluster source. The cluster size increases with increasing the Ar gas pressure and lowering the temperature of the cluster source.
Effects of H2 plasma treatment on low dielectric constant methylsilsesquioxane
Authors: Chang Ting-Chang , Liu Po-Tsun , Mei Yu-Jen , Mor Yi-Shian , Perng Tsu-Hsiu , Yang Ya-Liang , Sze Simon M.
Published: July 2002

The quality of organic low-k methylsilsesquioxane (MSQ) film is degraded by the damage of oxygen plasma and hygroscopic behavior during photoresist stripping. In addition, the interaction between MSQ and copper is worth investigating. In this work, we have studied the H2 plasma treatment to improve the quality and enhance the copper penetration resistance of MSQ. Experimental results show the leakage current of MSQ decreases as the H2 plasma treatment time is increased. The dielectric constant of treated samples also remains constant (∼2.7). In addition, the copper diffusion resistance of MSQ film is significantly promoted. The H2 plasma treatment can provide additional hydrogen to passivate the inner structure of porous MSQ film as well as reduce the probability of moisture uptake and interaction with Cu atoms. Therefore, the low-k dielectric properties of MSQ are significantly enhanced by H2 plasma treatment.
Nanometric aperture arrays fabricated by wet and dry etching of silicon for near-field optical storage application
Authors: Lee M. B. , Atoda N. , Tsutsui K. , Ohtsu M.
Published: July 2002

We fabricated nanometric aperture arrays in order to apply to an optical probe in high-density near-field optical storage for increase of data-transmission rate. The aperture arrays were fabricated by forming concave pyramidal grooves on a silicon-on-insulator wafer with electron beam lithography and wet anisotropic etching. Modification of the apex shape of the grooves by re-oxidation and subsequent reactive ion dry etching was able to increase the uniformity of the aperture size remarkably. The light transmission efficiency of the fabricated apertures was measured to be ∼10−3 when the aperture size was 100 nm, which was higher than that of a conventional optical fiber probe by several orders of magnitude.
Orientation control in PZT/Pt/TiN multilayers with various Si and SiO2 underlayers for high performance ferroelectric memories
Authors: Kushida-Abdelghafar Keiko , Torii Kazuyoshi , Mine Toshiyuki , Kachi Tsuyoshi , Fujisaki Yoshihisa
Published: July 2002

To suppress fluctuation in capacitor characteristics, highly oriented lead zirconate titanate (or PbZrxTi1−xO3 (PZT) films are required in ultralarge scale ferroelectric memories whose capacitor size is comparable to PZT grain size. The (111) orientation, which is closely related to spontaneous polarization, is achieved when PZT film is grown on highly (111) oriented platinum film. The degree of Pt(111) orientation is dependent on the crystallinity of the underlying TiN barrier metal. Furthermore, the crystallinity of the TiN is strongly dependent on the type of underlying material. The crystallinity of the TiN film grown on amorphous Si is much better than the crystallinity achieved on thermally oxidized Si. The surface energy difference between the TiN and underlayer may affect the growth mode of the TiN films. The crystallinity of the TiN film on rougher Si surfaces, such as in situ crystallized poly-Si, is inferior to the crystallinity observed on amorphous Si. Therefore, a smooth Si buffer layer is required underneath the capacitor to improve performance of the PZT/Pt/TiN capacitor. The modified planarized stacked structure presented in this article uses a postannealed crystalline Si as a buffer layer underneath the capacitor.
Search of optimum bias voltage for oxide patterning on Si using scanning tunneling microscopy in air
Authors: Tseng Kuen-Syh , Hsieh T. E. , Lo Shih-Che , Lin Hsi-Fu
Published: July 2002

Nanometer-scale oxide patterns were fabricated on H-passivated Si using a scanning tunneling microscopy (STM) in air. We found that the optimum bias voltage to generate clean and uniform oxide patterns depends on the composition of the tip material rather than on the tip head sharpness. For tungsten tips, oxide patterns with the desired geometrical features can be obtained at bias voltages ranging from −0.8 to −1.2 V, while for platinum–iridium tips, the bias voltages lie between −1.5 and −2.5 V at a fixed tunneling current of 2.0 nA. These biases correspond to the working voltage generating the oxide pattern with the lowest apparent depth. Beyond these voltage ranges, tip scratching on the sample surface or field-induced mass transfer from the tip might occur, as evidenced by tip wearing and the contamination of debris of tip material in the vicinity of the patterns. On the other hand, the tip head sharpness affects the width and the height of line patterns. When extremely fine oxide lines were desired, a sharp tip has to be used for STM patterning.
Effect of oxygen plasma exposure of porous spin-on-glass films
Authors: Kondoh E. , Asano T. , Nakashima A. , Komatu M.
Published: July 2002

Hydrogen-methyl-siloxane-based porous spin-on-glass films were exposed to an oxidative plasma. The plasma exposure resulted in the loss of hydrophobic groups such as Si–H and Si–CH3. The formation of silanole groups, the decrease in film thickness, and moisture uptake were also observed. When the substrate was biased during exposure, these tendencies were found to be suppressed.
Divergent Thinking About Self-Defense
Authors: Howard Jonathan
Published: July 2002

Tending Adam's Garden
Evolving the Cognitive Immune Self. Irun R. Cohen. Academic Press, San Diego, 2000. 286 pp. $49.95, £32.95. ISBN 0-12-178355-3.

The War Within Us
Everyman's Guide to Infection and Immunity. by Cedric Mims. Academic Press, San Diego, 2000. 288 pp. $39.95, $25.95. ISBN 0-12-498251-4.

These two books offer lay audiences two very different perspectives on the immune system. Cohen's holistic concepts on how the system functions are far from the views of most researchers in the field; Mims's account of how the body responds to microbial invaders falls much closer to the mainstream.
Things Fall Apart
Authors: Shope Robert E.
Published: July 2002

Betrayal of Trust
The Collapse of Global Public Health. Laurie Garrett. Hyperion, New York, 2000. 768 pp. $30, C$42.95, £22.95. ISBN 0-7868-6522-9.

Through meticulously researched and engagingly written accounts of public health crises in India, the Congo, the former Soviet Union, and three sites in the United States, Garrett documents the frightening deterioration of the world's infrastructure for preventive medicine.
Life from Smut
Authors: Margulis Lynn
Published: July 2002

Sparks of Life
Darwinism and the Victorian Debates over Spontaneous Generation. James E. Strick. Harvard University Press, Cambridge, MA, 2000. 298 pp. $45, £30.95. ISBN 0-674-00292-X.

Centering his account on Henry Bastian (the last great supporter of the idea that organisms can suddenly arise from nonliving materials), Strick examines the disputes among early Darwinians that helped prepare the foundations of microbiology and speed the acceptance of the germ theory of disease.
The Republican Temple of Nature
Authors: Duris Pascal
Published: July 2002

Utopia's Garden
French Natural History from Old Regime to Revolution. E. C. Spary. University of Chicago Press, Chicago, 2000. 337 pp. $70, £44.50. ISBN 0-226-76862-7. Paper, $25, £16. ISBN 0-226-76863-5.

Spary examines the transformation of the Jardin du Roi into the Muséum National d'Histoire Naturelle. She finds the institution's survival through the tumult of the French Revolution was aided by its claims that it could help educate the citizens while increasing national prosperity and individual virtue.
Evidence for a Solar System-Size Accretion Disk Around the Massive Protostar G192.16-3.82
Authors: Shepherd D. S. , Claussen M. J. , Kurtz S. E.
Published: July 2002

Seven-millimeter continuum observations of a massive bipolar outflow source, G192.16–3.82, were made at a milli–arc-second resolution with a capability that links the National Radio Astronomy Observatory's Very Large Array radio interferometer with the Very Long Baseline Array antenna, located in Pie Town, New Mexico. The observations provide evidence for a true accretion disk that is about the size of our solar system and located around a massive star. A model of the radio emission suggests the presence of a binary protostellar system. The primary protostar, G192 S1, at the center of the outflow, with a protostar mass of about 8 to 10 times the solar mass, is surrounded by an accretion disk with a diameter of 130 astronomical units (AU). The mass of the disk is on the order of the protostar mass. The outflow is poorly collimated with a full opening angle of about 40 degrees; there is no indication of a more highly collimated jetlike component. The companion source, G192 S2, is located 80 AU north of the primary source.
Boltzmann's Science, Irony and Achievement
Authors: Kadanoff Leo P.
Published: July 2002

Boltzmann's Atom
The Great Debate That Launched a Revolution in Physics. David Lindley. Free Press, New York, 2001. 272 pp. $24, C$35.50. ISBN 0-684-85186-5.

Lindley's scientific biography offers nonspecialists the story of the late 19th-century debates over existence of atoms and the validity of statistical approaches to mechanics.
Fatally Flawed Iconoclasm
Authors: Scott Eugenie C.
Published: July 2002

Icons of Evolution
Science or Myth? Why Much of What We Teach About Evolution is Wrong. Jonathan Wells. Regnery, Washington, DC, 2000. 352 pp. $27.95. ISBN 0-89526-276-2.

Addressing the non-specialist, Wells argues that because textbooks sometimes present examples of evolution in incorrect or misleading ways, evolution itself is a fiction. His book is currently being favorably cited by proponents of creation science and "intelligent design" theories.
Is God All in the Mind?
Authors: Shermer Michael
Published: July 2002

Why God Won't Go Away
Brain Science and the Biology of Belief. Andrew Newberg, Eugene D'Aquili, and Vince Rause. Ballantine, New York, 2001. 234 pp. $24.95, C$37.95. ISBN: 0-345-44033-1.

Emphasizing their interpretation of the neurophysiology of mystic experiences, the authors argue that the religious impulse is rooted in the biology of the brain.
Formative Effects of Federal Funding
Authors: Strick James E.
Published: July 2002

Shaping Biology
The National Science Foundation and American Biological Research, 1945-1975. Toby Appel. Johns Hopkins University Press, Baltimore, 2000. 408 pp. $42.50. ISBN 0-8018-6321-X.

Making extensive use of NSF archives and her own interviews, Appel presents a ground-breaking examination of the influence of the NSF on U.S. biological research during its first three decades. Many of the topics she examines--such as basic versus applied science, supporting individuals versus institutions, elitism versus distributive funding, red tape and account-ability--remain relevant and contentious.
Controversial Crusader Against Cancer
Authors: Löwy Ilana
Published: July 2002

Dr. Folkman's War
Angiogenesis and the Struggle to Defeat Cancer. Robert Cooke. Random House, New York, 2001. 383 pp. $25.95, C$37.95. ISBN 0-375-50244-0.

This account, written by a medical journalist, highlights Folkman's perspective on his research into the possibilities of treating cancer by controlling the supply of blood to tumor.
Wallace at Center Stage
Authors: Nelson Gareth
Published: July 2002

Alfred Russel Wallace
A Life. Peter Raby. Chatto and Windus (Random House), London, and Princeton University Press, Princeton, NJ, 2001. 352 pp. £20. ISBN 0-7011-6838-2. $29.95. ISBN 0-691-00695-4.

Raby offers the general reader an account of the life, interests, and major activities of the co-discoverer of the theory of evolution by natural selection.
Repeating Deep Earthquakes: Evidence for Fault Reactivation at Great Depth
Authors: Wiens Douglas A. , Snider Nathaniel O.
Published: July 2002

We have identified three groups of deep earthquakes showing nearly identical waveforms in the Tonga slab. Relocation with a cross-correlation method shows that each cluster is composed of 10 to 30 earthquakes along a plane 10 to 30 kilometers in length. Some of the earthquakes are colocated, demonstrating repeated rupture of the same fault, and one pair of events shows identical rupture complexity, suggesting that the temporal and spatial rupture pattern was repeated. Recurrence intervals show an inverse time distribution, indicating a strong temporal control over fault reactivation. Runaway thermal shear instabilities may explain temporally clustered earthquakes with similar waveforms located along slip zones weakened by shear heating. Earthquake doublets that occur within a few hours are consistent with events recurring before the thermal energy of the initial rupture can diffuse away.
The Story of Strata-Smith
Authors: Oldroyd David
Published: July 2002

The Map That Changed the World
William Smith and the Birth of Modern Geology. Simon Winchester. Viking, London, and HarperCollins, New York, 2001. 352 pp. £12.99. ISBN 0-67-088407-3. $26, C$39.50. ISBN 0-06-019361-1.

Winchester sketches the life and accomplishments of the engineer and surveyor who recognized that strata can be ordered according to their fossil contents and used principle to prepare the first geological map of England and Wales
Making Sense of Deformed Rocks
Authors: Wojtal Steven
Published: July 2002

The Techniques of Modern Structural Geology
Vol. 3: Applications of Continuum Mechanics in Structural Geology. John G. Ramsay and Richard J. Lisle. Academic Press, San Diego, 2000. 372 pp. Paper, $65, £43.95. ISBN 0-12-576923-7.

In this long-awaited concluding volume of what has become a classic text, the authors describe mathematical methods for interpreting geometric aspects of naturally deformed rocks.
Course Changes for the Research University
Authors: Rosenzweig Robert M.
Published: July 2002

The Creation of the Future
The Role of the American University. Frank H. T. Rhodes. Cornell University Press, Ithaca, NY, 2001. 286 pp. $29.95, £19.95. ISBN 0-8014-3937-X.

Rhodes, emeritus president of Cornell University, examines the historical development, current circumstances, and future prospects of research universities in the United States. He discusses the changes he believes are necessary to meet present-day and forthcoming challenges, the greatest of which he identifies as the loss of community.
Despised Source of Whining and Worse
Authors: Farley John
Published: July 2002

Mosquito
A Natural History of Man's Most Persistent and Deadly Foe. Andrew Spielman and Michael D'Antonio. Hyperion, New York, 2001. 267 pp. $22.95, C$32.95. ISBN 0-7868-6781-7. Faber and Faber, London. £10.99. ISBN 0-571-20980-7.

Spielman, an authority on mosquito-borne diseases, and D'Antonio, a science journalist, have collaborated to provide a popular account of mosquitoes, their roles as disease vectors, and the efforts of humans to combat them. The book includes numerous stories and anecdotes that Spielman has gathered over the course of his career.
Song for an Ocean Planet
Authors: McNutt Marcia K.
Published: July 2002

Great Waters
An Atlantic Passage. Deborah Cramer. Norton, New York, 2001. 442 pp. $27.95, C$39.99. ISBN 0-393-02019-3.

Cramer uses an ocean voyage as the framework for a natural history of the Atlantic that incorporates findings by oceanographers, geologists, biologists, and chemists. Her account highlights current threats to the sea's environment and productivity.
Politics Is Hell
Authors: Sarewitz Daniel
Published: July 2002

Science, Money, and Politics
Political Triumph and Ethical Erosion. Daniel S. Greenberg. University of Chicago Press, Chicago, 2001. 540 pp. $35, £22.50.ISBN 0-226-30634-8.

Our review notes that this exploration of the interface between science and the U.S. federal government reveals "a scientific community that behaves remarkably, amusingly, and, at times, terrifyingly like the population at large."
Toward the Invisible Computer
Authors: Greenberger Martin
Published: July 2002

The Unfinished Revolution
Human-Centered Computers and What They Can Do For Us. Michael Dertouzos. HarperCollins, New York, 2001. 240 pp. $26, C$39.50, £10.99. ISBN 0-06-662067-8.

In his final book, the late director of MIT's Laboratory for Computer Science outlines a future in which simplified and improved relations between humans and information technology will complete the computer revolution.
Surface Stress and Thermodynamic Nanoscale Size Selection
Authors: Hannon J. B. , Tersoff J. , Tromp R. M.
Published: July 2002

Using the Si(111) surface as an example, we show how temperature can be used to tune the size of domains during a surface phase transition. From analysis of the measured stable domain sizes, we determine key material parameters and clarify the close relationship between nucleation and thermodynamic size selection. More generally, the model we developed describes nanoscale self-assembly processes in contact with a reservoir (for example, liquid- or vapor-phase epitaxy).
The Promise and Perils of Wnt Signaling Through β-Catenin
Authors: Moon Randall T. , Bowerman Bruce , Boutros Michael , Perrimon Norbert
Published: July 2002

Wnt pathways are involved in the control of gene expression, cell behavior, cell adhesion, and cell polarity. In addition, they often operate in combination with other signaling pathways. The Wnt/β-catenin pathway is the best studied of the Wnt pathways and is highly conserved through evolution. In this pathway, Wnt signaling inhibits the degradation of β-catenin, which can regulate transcription of a number of genes. Some of the genes regulated are those associated with cancer and other diseases (for example, colorectal cancer and melanomas). As a result, components of the Wnt/β-catenin pathway are promising targets in the search for therapeutic agents. Information about Wnt pathways is available both in canonical terms and at the species level. In addition to the canonical Wnt/β-catenin pathway, information is now available for
Drosophila
,
Caenorhabditis elegans
, and
Xenopus
. The STKE Connections Maps for these pathways provide an important tool in accessing this large body of complex information.
New Research Strategy Draws Criticism
Authors: Balter Michael
Published: July 2002

Paris--On 3 October, an interministerial committee chaired by Prime Minister Alain Juppé unveiled a sweeping panoply of measures designed to harness French science to serve the needs of France's ailing economy. The government will shift research funds into priority areas and push scientists to reorient their own priorities, for example by including patent records as part of the evaluation of publicly funded researchers. The announcement has prompted anxiety among researchers that it will tip the balance away from basic science.
New 'Alzheimer's Mouse' Produced
Authors: Marx Jean
Published: July 2002

Alzheimer's researchers have long wanted a realistic animal model of the disease, and last week's announcement in

Science

of a new, genetically engineered strain of mice that suffers both brain degeneration and memory deficits brought them a big step closer to that goal. The new mouse strain develops the same brain deposits of a protein called amyloid that are seen in human sufferers, and it should allow researchers to test the controversial idea that the amyloid deposition actually causes the brain changes that lead to memory loss. Already the mouse's developers have found that the animals have a biochemical abnormality that may be crucial to amyloid deposition--an increase in a particular “sticky” amyloid fragment.
A Warped View of Time Travel
Authors: Parsons Paul
Published: July 2002

The curved space and time of Einstein's theory of general relativity permits both time travel and travel at speeds faster than that of light. In his Perspective, Parsons describes recent theoretical studies that show how, in principle, a spacecraft in a bubble of warped space-time could travel faster than light. One consequence of this result is that such a spacecraft could also travel back in time.
Small Refugees Suffer the Effects of Early Neglect
Authors: Holden Constance
Published: July 2002

Under the regime of Romanian dictator Nicolae Ceausescu, thousands of orphans languished for months or years in huge, state-run orphanages. Scientists are now studying the children to try to understand how early deprivation alters brain chemistry and behavior
The Case of the Missing Migrants
Authors: Tangley Laura
Published: July 2002

Are new methods for cultivating coffee harmful to migratory songbirds? Some studies suggest that the shift from shade to sun plantations all across Latin America may be contributing to the decline of the birds
RAC Regulation of Actin Polymerization and Proliferation by a Pathway Distinct from Jun Kinase
Authors: Joneson Tom , McDonough Michele , Bar-Sagi Dafna , Van Aelst Linda
Published: July 2002

The RAC guanine nucleotide binding proteins regulate multiple biological activities, including actin polymerization, activation of the Jun kinase (JNK) cascade, and cell proliferation. RAC effector loop mutants were identified that separate the ability of RAC to interact with different downstream effectors. One mutant of activated human RAC protein, RAC
V12H40
(with valine and histidine substituted at position 12 and 40, respectively), was defective in binding to PAK3, a Ste20-related p21-activated kinase (PAK), but bound to POR1, a RAC-binding protein. This mutant failed to stimulate PAK and JNK activity but still induced membrane ruffling and mediated transformation. A second mutant, RAC
V12L37
(with leucine substituted at position 37), which bound PAK but not POR1, induced JNK activation but was defective in inducing membrane ruffling and transformation. These results indicate that the effects of RAC on the JNK cascade and on actin polymerization and cell proliferation are mediated by distinct effector pathways that diverge at the level of RAC itself.
Repeated Bursts Puzzle Astronomers
Authors: Watson Andrew
Published: July 2002

Last week, a U.S.-Russian team announced that four space-based detectors have picked up what might be a vital clue in one of the biggest mysteries of modern astronomy. The detectors picked up signals of four gamma-ray bursts from the same patch of sky in the space of 2 days. This is the first time that gamma-ray bursts, whose origin is still a mystery, have been seen to repeat.
Does Europa's Ice Hide an Ocean?
Authors: Kerr Richard A.
Published: July 2002

An image sent down late last week from the Galileo spacecraft orbiting Jupiter offers the sharpest view yet of the Jovian moon Europa, adding new hints that there may be a water ocean sealed beneath the moon's icy surface—which raises the possibility, however faint, of life on this distant world.
Opening the Way to Gene Activity
Authors: Pennisi Elizabeth
Published: July 2002

For decades, molecular biologists have suspected that a chemical modification called acetylation plays an important role in regulating gene activity, but they have had trouble proving it. Now researchers in several labs have identified several acetylating and deacetylating enzymes, and they have linked the reaction directly to the machinery that reads the genes: The acetylating enzymes have turned out to be proteins already known to associate with the transcription factors that turn genes on and off. What's more, the new work indicates that acetylation is important for cell growth control, and that when it becomes misdirected, cancer may develop.
Clouds Gather Over Deuterium Sighting
Authors: Glanz James
Published: July 2002

CHICAGO
—Astronomers have withdrawn a dramatic claim made last year: that the early universe had 10 times more deuterium than other evidence suggested. Because the amount of this scarce hydrogen isotope created in the big bang is inversely related to the universe's total density of matter, the high levels, measured in a distant gas cloud, implied a surprisingly rarefied universe. But it now appears that the researchers may have misinterpreted the cloud's spectrum.
More Than Just Frequency Detectors?
Authors: Thomson Alex M.
Published: July 2002

Connection from neuron to neuron in the cortex of the brain becomes less effective with each successive action potential but eventually recovers after the end of the action potential burst. Two new reports, one in this issue (
p. 220
), present many-neuron models with these properties and show that these neurons respond to large changes in the frequency of individual inputs (they act as frequency detectors) or to simultaneous changes in many inputs (they act as coincidence detectors). In her Perspective, Thomson explains the origin of the modeled properties and discusses the accuracy with which these models mimic the behavior of real cortical cells. Such modeling of many neurons with real properties reveals computational characteristics of the circuit not apparent from analyses of individual cells.
African Malaria Studies Draw Attention
Authors: Marshall Eliot
Published: July 2002

About 100 scientists and public health experts from around the world gathered in Dakar, Senegal, last week to kick off what could become a new, coordinated program to attack the disease in Africa. Much of the impetus for the initiative came from Harold Varmus, director of the U.S. National Institutes of Health, and Maxime Schwartz, director of France's Institut Pasteur, who both attended the meeting. Varmus said the focus of the new initiative would be on building up research capabilities in Africa. A smaller session is expected to be held later this year to nail down funding commitments.
Making Single Electrons Compute
Authors: Service Robert F.
Published: July 2002

As chipmakers shrink features on computer chips to ever smaller dimensions, electrons begin to spill over the barriers meant to confine them. Now researchers are designing a new class of devices that overcomes this problem by manipulating electrons one at a time. These new devices could give rise to computers that are far more powerful—and less power-hungry—than today's computers.
Designing Therapies That Target Tumor Blood Vessels
Authors: Barinaga Marcia
Published: July 2002

Traditional cancer treatments seek to attack cancer cells directly, with surgery, radiation, or chemotherapy. But a new wave of therapies is attempting an indirect strike: shutting off the blood vessels through which tumors get the oxygen and nutrients they need to live and grow. Recent work suggests that this might be done with drugs, some naturally occurring, that can prevent tumors from forming the new blood vessels they need. Alternately, as a report appearing on
page 547
suggests, it might be possible to shrink or even eliminate tumors by administering agents that trigger clot formation in tumor-feeding vessels.
Biologists Mobilize Against Anti-Genetics Referendum
Authors: Koenig Robert
Published: July 2002

In about a year, the people of Switzerland will vote on a constitutional amendment that, if approved, would ban basic research involving the genetic manipulation of animals and would forbid the release of any genetically altered organism into the environment. Prominent Swiss scientists and drug companies warn that research would have to move abroad if the amendment is passed.
Space Scientists Find Fiscal Relief
Authors: Lawler Andrew
Published: July 2002

Space science advocates say a summit between Administration and congressional leaders is no longer necessary because of a brighter long-term budgetary picture for NASA.
What Makes Us Tick?
Authors: Guarente Leonard
Published: July 2002

A mutant
Caenorhabditis elegans
worm, defective in the gene
clk-1
, lives an extraordinarily long time. In this issue, Ewbank
et al
. (p.
980
) report the sequence of
clk-1
and find that it is homologous to the yeast gene
CAT5/COQ7
, whose product regulates the transcription of genes that control yeast metabolism. In his Perspective, Guarente describes how these findings fit into a model of aging in which life-span is determined by the accumulation of damage to the organism, perhaps at a rate proportional to metabolism, and the counteracting repair of such damage.
Direct Measurement of Single-Molecule Diffusion and Photodecomposition in Free Solution
Authors: Xu Xiao-Hong , Yeung Edward S.
Published: July 2002

Continuous monitoring of submillisecond free-solution dynamics of individual rhodamine-6G molecules and 30-base single-stranded DNA tagged with rhodamine was achieved. Fluorescence images were recorded from the same set of isolated molecules excited either through the evanescent field at the quartz-liquid interface or as a thin layer of solution defined by micron-sized wires, giving diffraction-limited resolution of interconnected attoliter volume elements. The single-molecule diffusion coefficients were smaller and the unimolecular photodecomposition lifetimes were longer for the dye-DNA covalent complex as compared with those of the dye molecule itself. Unlike bulk studies, stochastic behavior was found for individual molecules of each type, and smaller diffusion coefficients were observed.
Death and Transfiguration of a Triple Junction in the South Atlantic
Authors: Ligi M. , Bonatti E. , Bortoluzzi G. , Carrara G. , Fabretti P. , Penitenti D. , Gilod D. , Peyve A. A. , Skolotnev S. , Turko N.
Published: July 2002

Three major lithospheric plates—Antarctic, South American, and African—meet in the South Atlantic near Bouvet Island where the Mid-Atlantic Ridge (MAR), the Southwest Indian Ridge (SWIR), and the American Antarctic Ridge converge toward a fast evolving triple junction. A major magmatic pulse has recently built a new, swollen segment of the SWIR (Spiess Ridge) that is propagating toward the MAR at a rate of 4 to 5 centimeters per year, disrupting a former ridge-ridge-ridge (RRR) triple junction. A new triple junction will be established about 70 kilometers to the north when the propagating SWIR/Spiess segment will impact with the MAR, probably within the next 1 million years. The American Antarctic Ridge will take advantage of the MAR/SWIR duel by capturing an approximately 70-kilometer stretch of MAR, whereas the Antarctic plate will increase its size.
Famous Felids
Authors: Adams Dawn A.
Published: July 2002

The Big Cats and Their Fossil Relatives.
An Illustrated Guide to Their Evolution and Natural History. ALAN TURNER. Illustrations by Mauricio Anton. Columbia University Press, New York, 1997. xx, 233 pp., illus., + plates. $39.95. ISBN 0-231-10228-3.
Nonhuman Kindness
Authors: Charles Snowdon T.
Published: July 2002

Good Natured.
The Origins of Right and Wrong in Humans and Other Animals. FRANS DE WAAL. Harvard University Press, Cambridge, MA, 1996. viii, 296 pp., illus., + plates. $24.95 or £16.50. ISBN 0-674-35660-8.
A Rise to Distinction
Authors: Doel Ronald E.
Published: July 2002

American Astronomy.
Community, Careers, and Power, 1859-1940. JOHN LANKFORD, with Ricky L. Slavings. University of Chicago Press, Chicago, 1997. xxvi, 447 pp., illus. $65 or £51.95. ISBN 0-226-46886-0.
Speedbumps for Adaptationism
Authors: Feder Martin E.
Published: July 2002

Adaptation.
MICHAEL R. ROSE and GEORGE V. LAUDER, Eds. Academic Press, San Diego, 1996. xiv, 511 pp., illus. $69.95 or £52, ISBN 0-12-596420-x; paper, $34.95 or £24.95, ISBN 0-12-596421-8.
Aging: Questions and Prospects
Authors: Charlesworth Brian
Published: July 2002

Why We Age.
What Science Is Discovering About the Body's Journey Through Life. STEVEN N. AUSTAD. Wiley, New York, 1997. xii, 244 pp., illus. $24.95, C$34.95, or £19.99. ISBN 0-471-14803-2.

Between Zeus and the Salmon.
The Biodemography of Longevity. KENNETH W. WACHTER and CALEB E. FINCH, Eds. National Academy Press, Washington, DC, 1997. viii, 312 pp., illus. $44 or £35.95. ISBN 0-309-05787-6. To be published 3 November.
Adatom Pairing Structures for Ge on Si(100): The Initial Stage of Island Formation
Authors: Qin X. R. , Lagally M. G.
Published: July 2002

With the use of scanning tunneling microscopy, it is shown that germanium atoms adsorbed on the (100) surface of silicon near room temperature form chainlike structures that are tilted from the substrate dimer bond direction and that consist of two-atom units arranged in adjoining substrate troughs. These units are distinctly different from surface dimers. They may provide the link missing in our understanding of the elementary processes in epitaxial film growth: the step between monomer adsorption and the initial formation of two-dimensional growth islands.
An Inverse Compton Process for the Excess Diffuse EUV Emission from the Virgo and Coma Galaxy Clusters
Authors: Hwang Chorng-Yuan
Published: July 2002

The excess extreme-ultraviolet (EUV) emission detected in the Virgo and Coma clusters is explained by inverse Compton scattering of cosmic microwave background photons, which are scattered by the relativistic electrons that account for the extended radio synchrotron emission of these clusters. The lower limits of the average magnetic fields of these clusters estimated from the EUV excess are close to the equipartition magnetic fields derived from radio observations, indicating that the electron energies and magnetic field energies might be close to equipartition. The excess emission suggests energy reservoirs of ∼10
61
and ∼10
60
ergs for the Coma and Virgo clusters, respectively.
Water in Betelgeuse and Antares
Authors: Jennings Donald E. , Sada Pedro V.
Published: July 2002

Absorption lines of hot water have been identified in the infrared spectra of Betelgeuse (α Orionis) and Antares (α Scorpii) near 12.3 micrometers (811 to 819 wavenumbers). The water lines originate in the atmospheres of the stars, not in their circumstellar material. The spectra are similar in structure to umbral sunspot spectra. Pure rotation water lines of this type will occur throughout the spectra of cool stars at wavelengths greater than 10 micrometers. From the water spectra, the upper limit for the temperature in the line formation region in both stars is 2800 kelvin. The water column density in both stars is (3 ± 2) × 10
18
molecules per square centimeter, yielding an abundance relative to atomic hydrogen of
n
(H
2
O)/
n
(H) ≈ 10
−
7
.
Materials with Negative Compressibilities in One or More Dimensions
Authors: Baughman Ray H. , Stafström Sven , Cui Changxing , Dantas Socrates O.
Published: July 2002

Rare crystal phases that expand in one or more dimensions when hydrostatically compressed are identified and shown to have negative Poisson's ratios. Some of these crystals (i) decrease volume and expand in two dimensions when stretched in a particular direction and (ii) increase surface area when hydrostatically compressed. Possible mechanisms for achieving such negative linear and area compressibilities are described for single crystals and composites, and sensor applications are proposed. Materials with these properties may be used to fabricate porous solids that either expand in all directions when hydrostatically compressed with a penetrating fluid or behave as if they are incompressible.
No Longer Alone
Authors: Kolter Roberto
Published: July 2002

Bacteria as Multicellular Organisms.
JAMES A. SHAPIRO and MARTIN DWORKIN, Eds. Oxford University Press, New York, 1997. xiv, 466 pp., illus. $95 or £69.50, ISBN 0-19-509159-0.
Images of an Inventor Hero
Authors: Friedel Robert
Published: July 2002

Alexander Graham Bell. The Life and Times of the Man Who Invented the Telephone.
EDWIN S. GROSVENOR and MORGAN WESSON. Abrams, New York, 1997. 304 pp., illus. $45 or C$60. ISBN 0-8109-4005-1.
Structure of the Upper Mantle Under the EPR from Waveform Inversion of Regional Events
Authors: Webb Spahr C. , Forsyth Donald W.
Published: July 2002

Waveform inversions of seismograms recorded at the Mantle Electromagnetic and Tomography (MELT) Experiment ocean bottom seismometer array from regional events with paths following the East Pacific Rise (EPR) require that low shear velocities (<3.7 km/s) extend to depths of more than 100 km below the rise axis. Velocities increase with average crustal age along ray paths. The reconciliation of Love and Rayleigh wave data requires that shear flow has aligned melt pockets or olivine crystals, creating an anisotropic uppermost mantle.
Synchronous Climate Changes in Antarctica and the North Atlantic
Authors: Steig E. J. , Brook E. J. , White J. W. C. , Sucher C. M. , Bender M. L. , Lehman S. J. , Morse D. L. , Waddington E. D. , Clow G. D.
Published: July 2002

Central Greenland ice cores provide evidence of abrupt changes in climate over the past 100,000 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic, confirming the link between millennial-scale climate variability and ocean thermohaline circulation. It is shown here that two of the most prominent North Atlantic events—the rapid warming that marks the end of the last glacial period and the Bølling/Allerød–Younger Dryas oscillation—are also recorded in an ice core from Taylor Dome, in the western Ross Sea sector of Antarctica. This result contrasts with evidence from ice cores in other regions of Antarctica, which show an asynchronous response between the Northern and Southern Hemispheres.
Simulating Nerves and Networks
Authors: Hasselmo Michael E.
Published: July 2002

Methods in Neuronal Modeling
From Ions to Networks (2nd ed.). Christof Koch and Idan Segev, Eds. MIT Press, Cambridge, MA, 1998. 687 pp. $60. ISBN 0-262-11231-0.

The seven new and seven extensively revised chapters in this summary of computational neuroscience techniques provide a firm foundation for simulating the function of neurons and neural circuits. The authors have made important progress towards effectively constraining models with biological detail at a cellular level.
Edison--The View from Menlo Park
Authors: Kevles Bettyann Holtzmann
Published: July 2002

Edison
A Life of Invention. Paul Israel. Wiley, New York, 1998. 552 pp. $30, C$42.50. ISBN 0-471-52942-7.

This biography utilizes the extensive documentary record left by Edison and his research and business associates to explain his legendary success as an inventor.