bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of the electron field emission process in polycrystalline diamond and diamond-like carbon thin films
Authors: Silva S. R. P. , Amaratunga G. A. J. , Okano K.
Published: July 2002

Electron field emission has been observed from carbon thin films at relatively low electric fields. These films range from amorphous carbon to polycrystalline diamond films. There are many models that attempt to account for the electron field emission process observed in these films. The initial models that were based on the emission due purely to a negative electron affinity have now been modified. The emission from diamond like carbon (DLC) films, although following a Fowler–Nordheim type curve, do not give realistic values for the emission areas or barriers purely based on a tunneling mechanism. Therefore, a model based on space charge band bending at the back junction is proposed to account for the electron emission at low electric fields from DLC. In this “space charge interlayer” model the real cathode is the substrate, from which hot electrons are created due to the fully depleted DLC film the electrons encounter before reaching the front surface of the film. In this article we extend the model to incorporate the emission of electrons from polycrystalline diamond thin films.
Analysis of submicron Cu–Ta–SiO2 structures by highly charged ion secondary ion mass spectroscopy
Authors: Schenkel T. , Wu K. J. , Li H. , Newman N. , Barnes A. V. , McDonald J. W. , Hamza A. V.
Published: July 2002

We have analyzed wafers with submicron copper lines on Ta/SiO2/Si by time-of-flight secondary ion mass spectrometry with highly charged projectiles. The goal of the study was to diagnose the effectiveness of different cleaning solutions during brush scrubbing after chemical mechanical polishing. The advantage of projectiles like Xe44+ lies in the fact that they produce up to three orders of magnitude more secondary ions than singly charge projectiles. Detection of molecular ions (e.g., Cu oxide, Cu hydrocarbon, and alumina ions) enables a detailed assessment of surface conditions on wafers. Analysis of correlations in secondary ion emission from individual impacts gives insight into the chemical structure and homogeneity on a length scale of about 10 nm.
Dry etching with gas chopping without rippled sidewalls
Authors: Volland B. , Shi F. , Hudek P. , Heerlein H. , Rangelow Ivo. W.
Published: July 2002

In the last years, silicon micromachining techniques based on high aspect ratio reactive ion etching with gas chopping have been developed. There the gas flow of etching and deposition gas precursors is chopped which results in controllable sidewall passivation and high anisotropy. However, the rippled sidewalls are a serious limit for various applications. We report on the development of a novel gas chopping etching technique (GCET) process in order to achieve a smooth (rippled free) sidewall surface. As the direct etch mask, we used a 1 or 2-μm-thick resist layer, which was lithographically patterned. The novelty of the process consists in the replacing of the isotropic etching step by an anisotropic etching step. In this way we omit the main source for sidewall ripples. GCET combined with inductively coupled plasmas and fluorine chemistry provide very high etch rates and good control of the sidewall slope. These techniques also can be applied to conventional reactive ion etching equipment with Cl or F based plasma chemistry. However, the techniques used in this study have lower selectivity (in range of 30) than the conventional GCET. A SiON/Si selectivity as high as 50 has been achieved.
Surface-adsorbed polystyrene spheres as a template for nanosized metal particle formation: Optical properties of nanosized Au particle
Authors: Takei H.
Published: July 2002

The use of surface-adsorbed monodisperse polystyrene spheres as a template for forming nanosized particles is described. This simple, yet general method is applicable to virtually any material that can be evaporated or sputtered, and monodisperse particles in the size range from tens of nanometers up to tens of micrometers are readily formed. We will demonstrate its versatility principally through the formation of Au particles having various optical properties produced by modifying their size and shape. We will further show that by changing the density of adsorbed polystyrene spheres as well as adsorbing spheres of two different sizes onto the same substrate allows further modifications of optical properties. Particles formed by this method promise to find a wide range of applications to products such as optical filters, substrates for spectroscopy, sensors, etc.
Fabrication of a silicon based nanometric oscillator with a tip form mass for scanning force microcopy operating in the GHz range
Authors: Kawakatsu Hideki , Toshiyoshi Hiroshi , Saya Daisuke , Fukushima Kimitake , Fujita Hiroyuki
Published: July 2002

The detectable force resolution of a mechanical oscillator used in scanning force microscopy can be improved by increasing its natural frequency fo and quality factor Q, and by decreasing the spring constant k and the temperature of operation T. For an oscillator having a structure that can be modeled as a concentrated mass-spring model, decreasing the mass of the oscillator is desirable since high fo can then be obtained without increasing the spring constant k. We have developed a novel fabrication technique for fabricating a nanometric oscillator by selective etching of silicon on insulator (SOI) wafers. The oscillator has the form of a tip supported by an elastic neck, and the tip serves as the mass. The tip and the neck length measure approximately 100 nm when fabricated using a separation by implanted oxygen wafer, and are around 1000 nm when fabricated using a bonded SOI wafer. The tips were made of silicon and the necks were made of silicon dioxide. The oscillator could be tailored to have its natural frequency in the range of 0.01–1 GHz and a spring constant between 10−1 and 102 N/m. The thin neck, whose diameter is of the order of 10 nm is not brittle and can survive angular bending of around 30°.
Pulsed plasma polymerization of an aromatic perfluorocarbon monomer: Formation of low dielectric constant, high thermal stability films
Authors: Han Licheng M. , Timmons Richard B. , Lee Wei W.
Published: July 2002

The plasma polymerization of the perfluoroallyl benzene monomer [(C6F5)CF2CF=CF2] was carried out under pulsed discharge conditions. Progressive changes in the composition of the plasma generated polymers were observed with sequential changes in the duty cycle of the pulsed discharge, as other reaction variables remaining constant. In particular, an increased retention of the aromatic ring of the starting monomer in the polymers is obtained with decreasing plasma duty cycles during film formation, as shown by x-ray photoelectron spectroscopy and Fourier-transform infrared analyses of these films. Dielectric constants of these perfluorinated films are consistently below a value of 2.0, measured over a frequency range of 5×102–1×105 Hz. Although thermal gravimetric analysis of the plasma films revealed significant weight loss beginning at temperature below 300 °C, up to 70%, dramatic improvement in the thermal stability of these films was observed following their thermal annealing at temperature of 350–400 °C under N2. The resultant annealed films exhibit negligible weight loss during subsequent thermogravimetric analysis at temperature as high as 420 °C. Most importantly, this gain in thermal stability of the plasma polymers is achieved with only minor increases in the dielectric constants, along with relatively minor changes in film compositions, following the thermal annealing processes. The implications of this study with respect to low dielectric constant requirements for future smaller feature size integrated circuits are discussed in this work.
The Early Evolution of the Inner Solar System: A Meteoritic Perspective
Authors: O'D. Alexander C. M. , Boss A. P. , Carlson R. W.
Published: July 2002

Formation of the solar system may have been triggered by a stellar wind. From then on, the solar system would have followed a conventional evolutionary path, including the formation of a disk and bipolar jets. The now extinct short-lived radionuclides beryllium-10 and, possibly, manganese-53 that were present in meteorites probably resulted from energetic particle irradiation within the solar system. Calcium-aluminum–rich inclusions (the oldest known solar system solids) and chondrules could have been produced by the bipolar jets, but it is more likely that they formed during localized events in the asteroid belt. The chondritic meteorites formed within the temperature range (100 to 400 kelvin) inferred for the midplane of classical T Tauri disks at 2 to 3 astronomical units from their central stars. However, these meteorites may retain a chemical memory of earlier times when midplane temperatures were much higher. Dissipation of the solar nebula occurred within a few million years of solar system formation, whereas differentiation of asteroidal-sized bodies occurred within 5 to 15 million years. The terrestrial planets took ∼100 million years to form. Consequently, they would have accreted already differentiated bodies, and their final assembly was not completed until after the solar nebula had dispersed. This implies that water-bearing asteroids and/or icy planetesimals that formed near Jupiter are the likely sources of Earth's water.
Mechanism of Actin-Based Motility
Authors: Pantaloni Dominique , Clainche Christophe Le , Carlier Marie-France
Published: July 2002

Spatially controlled polymerization of actin is at the origin of cell motility and is responsible for the formation of cellular protrusions like lamellipodia. The pathogens
Listeria monocytogenes
and
Shigella flexneri
, which undergo actin-based propulsion, are acknowledged models of the leading edge of lamellipodia. Actin-based motility of the bacteria or of functionalized microspheres can be reconstituted in vitro from only five pure proteins. Movement results from the regulated site-directed treadmilling of actin filaments, consistent with observations of actin dynamics in living motile cells and with the biochemical properties of the components of the synthetic motility medium.
Dendrodendritic Inhibition Through Reversal of Dopamine Transport
Authors: Falkenburger Björn H. , Barstow Karen L. , Mintz Isabelle M.
Published: July 2002

Synapses in the central nervous system are usually defined by presynaptic exocytotic release sites and postsynaptic differentiations. We report here a demonstration of dendrodendritic inhibition that does not engage a conventional synapse. Using amperometric and patch-clamp recordings in rat brain slices of the substantia nigra, we found that blockade of the dopamine transporter abolished the dendritic release of dopamine and the resulting self-inhibition. These findings demonstrate that dendrodendritic autoinhibition entails the carrier-mediated release of dopamine rather than conventional exocytosis. This suggests that some widely used antidepressants that inhibit the dopamine transporter may benefit patients in the early stages of Parkinson's disease.
Linearly Polarized Emission from Colloidal Semiconductor Quantum Rods
Authors: Hu Jiangtao , Li Liang-shi , Yang Weidong , Manna Liberato , Wang Lin-wang , Alivisatos A. Paul
Published: July 2002

Colloidal quantum rods of cadmium selenide (CdSe) exhibit linearly polarized emission. Empirical pseudopotential calculations predict that slightly elongated CdSe nanocrystals have polarized emission along the long axis, unlike spherical dots, which emit plane-polarized light. Single-molecule luminescence spectroscopy measurements on CdSe quantum rods with an aspect ratio between 1 and 30 confirm a sharp transition from nonpolarized to purely linearly polarized emission at an aspect ratio of 2. Linearly polarized luminescent chromophores are highly desirable in a variety of applications.
Expectation and Dopamine Release: Mechanism of the Placebo Effect in Parkinson's Disease
Authors: de la Fuente-Fernández Raúl , Ruth Thomas J. , Sossi Vesna , Schulzer Michael , Calne Donald B. , Stoessl A. Jon
Published: July 2002

The power of placebos has long been recognized for improving numerous medical conditions such as Parkinson's disease (PD). Little is known, however, about the mechanism underlying the placebo effect. Using the ability of endogenous dopamine to compete for [
11
C]raclopride binding as measured by positron emission tomography, we provide in vivo evidence for substantial release of endogenous dopamine in the striatum of PD patients in response to placebo. Our findings indicate that the placebo effect in PD is powerful and is mediated through activation of the damaged nigrostriatal dopamine system.
Impact of Landscape Management on the Genetic Structure of Red Squirrel Populations
Authors: Hale Marie L. , Lurz Peter W. W. , Shirley Mark D. F. , Rushton Steven , Fuller Robin M. , Wolff Kirsten
Published: July 2002

Landscape management practices that alter the degree of habitat fragmentation can significantly affect the genetic structure of animal populations. British red squirrels use “stepping stone” patches of habitat to move considerable distances through a fragmented habitat. Over the past few decades, the planting of a large conifer forest has connected groups of forest fragments in the north of England with those in southern Scotland. This “defragmentation” of the landscape has resulted in substantial genetic mixing of Scottish and Cumbrian genes in squirrel populations up to 100 kilometers from the site of the new forest. These results have implications for the conservation management of animal and plant species in fragmented landscapes such as those found in Britain.
Signaling to the Nucleus by an L-type Calcium Channel-Calmodulin Complex Through the MAP Kinase Pathway
Authors: Dolmetsch Ricardo E. , Pajvani Urvi , Fife Katherine , Spotts James M. , Greenberg Michael E.
Published: July 2002

Increases in the intracellular concentration of calcium ([Ca
2+
]
i
) activate various signaling pathways that lead to the expression of genes that are essential for dendritic development, neuronal survival, and synaptic plasticity. The mode of Ca
2+
entry into a neuron plays a key role in determining which signaling pathways are activated and thus specifies the cellular response to Ca
2+
. Ca
2+
influx through L-type voltage-activated channels (LTCs) is particularly effective at activating transcription factors such as CREB and MEF-2. We developed a functional knock-in technique to investigate the features of LTCs that specifically couple them to the signaling pathways that regulate gene expression. We found that an isoleucine-glutamine (“IQ”) motif in the carboxyl terminus of the LTC that binds Ca
2+
-calmodulin (CaM) is critical for conveying the Ca
2+
signal to the nucleus. Ca
2+
-CaM binding to the LTC was necessary for activation of the Ras/mitogen-activated protein kinase (MAPK) pathway, which conveys local Ca
2+
signals from the mouth of the LTC to the nucleus. CaM functions as a local Ca
2+
sensor at the mouth of the LTC that activates the MAPK pathway and leads to the stimulation of genes that are essential for neuronal survival and plasticity.
An Ossified Meckel's Cartilage in Two Cretaceous Mammals and Origin of the Mammalian Middle Ear
Authors: Wang Yuanqing , Hu Yaoming , Meng Jin , Li Chuankui
Published: July 2002

An ossified Meckel's cartilage has been recovered from two early Cretaceous mammals from China. This element is similar to Meckel's cartilage in prenatal and some postnatal extant mammals and indicates the relationship of Meckel's cartilage with the middle ear in early mammals. The evidence shows that brain expansion may not be the initial factor that caused the separation of postdentary bones from the dentary as middle ear ossicles during mammalian evolution. The failure of the dentary to seize reduced postdentary elements during ontogeny of early mammals is postulated as an alternative mechanism for the separation. Modifications of both feeding and hearing apparatuses in early mammals may have led to the development of the definitive mammalian middle ear.
Dynamics and Constancy in Cortical Spatiotemporal Patterns of Orientation Processing
Authors: Sharon Dahlia , Grinvald Amiram
Published: July 2002

How does the high selectivity to stimulus orientation emerge in the visual cortex? Thalamic feedforward-dominated models of orientation selectivity predict constant selectivity during the visual response, whereas intracortical recurrent models predict dynamic improvement in selectivity. We imaged the cat visual cortex with voltage-sensitive dyes to measure orientation-tuning dynamics of a large neuronal population. Tuning-curve width did not narrow after response onset, whereas the difference between preferred and orthogonal responses (modulation depth) first increased, then declined. We identified a suppression of the evoked responses, referred to as the evoked deceleration-acceleration (DA) notch, which was larger for the orthogonal response. Furthermore, peak selectivity of the tuning curves was contemporaneous with the evoked DA notch. These findings suggest that in the cat brain, sustained visual cortical processing does not narrow orientation tuning; rather, intracortical interactions may amplify modulation depth and suppress the orthogonal response relatively more than the preferred. Thus, feedforward models and recurrent models of orientation selectivity must be combined.
Global Efforts in Structural Genomics
Authors: Stevens Raymond C. , Yokoyama Shigeyuki , Wilson Ian A.
Published: July 2002

A worldwide initiative in structural genomics aims to capitalize on the recent successes of the genome projects. Substantial new investments in structural genomics in the past 2 years indicate the high level of support for these international efforts. Already, enormous progress has been made on high-throughput methodologies and technologies that will speed up macromolecular structure determinations. Recent international meetings have resulted in the formation of an International Structural Genomics Organization to formulate policy and foster cooperation between the public and private efforts.
Structural Basis of Gating by the Outer Membrane Transporter FecA
Authors: Ferguson Andrew D. , Chakraborty Ranjan , Smith Barbara S. , Esser Lothar , van der Helm Dick , Deisenhofer Johann
Published: July 2002

Siderophore-mediated acquisition systems facilitate iron uptake. We present the crystallographic structure of the integral outer membrane receptor FecA from
Escherichia coli
with and without ferric citrate at 2.5 and 2.0 angstrom resolution. FecA is composed of three distinct domains: the barrel, plug, and NH
2
-terminal extension. Binding of ferric citrate triggers a conformational change of the extracellular loops that close the external pocket of FecA. Ligand-induced allosteric transitions are propagated through the outer membrane by the plug domain, signaling the occupancy of the receptor in the periplasm. These data establish the structural basis of gating for receptors dependent on the cytoplasmic membrane protein TonB. By compiling available data for this family of receptors, we propose a mechanism for the energy-dependent transport of siderophores.
Microbial Activity at Gigapascal Pressures
Authors: Sharma Anurag , Scott James H. , Cody George D. , Fogel Marilyn L. , Hazen Robert M. , Hemley Russell J. , Huntress Wesley T.
Published: July 2002

We observed physiological and metabolic activity of
Shewanella oneidensis
strain MR1 and
Escherichia coli
strain MG1655 at pressures of 68 to 1680 megapascals (MPa) in diamond anvil cells. We measured biological formate oxidation at high pressures (68 to 1060 MPa). At pressures of 1200 to 1600 MPa, living bacteria resided in fluid inclusions in ice-VI crystals and continued to be viable upon subsequent release to ambient pressures (0.1 MPa). Evidence of microbial viability and activity at these extreme pressures expands by an order of magnitude the range of conditions representing the habitable zone in the solar system.
Ordering in a Fluid Inert Gas Confined by Flat Surfaces
Authors: Donnelly Stephen E. , Birtcher Robert C. , Allen Charles W. , Morrison Ian , Furuya Kazuo , Song Minghui , Mitsuishi Kazutaka , Dahmen Ulrich
Published: July 2002

High-resolution transmission electron microscopy images of room-temperature fluid xenon in small faceted cavities in aluminum reveal the presence of three well-defined layers within the fluid at each facet. Such interfacial layering of simple liquids has been theoretically predicted, but observational evidence has been ambiguous. Molecular dynamics simulations indicate that the density variation induced by the layering will cause xenon, confined to an approximately cubic cavity of volume ≈ 8 cubic nanometers, to condense into the body-centered cubic phase, differing from the face-centered cubic phase of both bulk solid xenon and solid xenon confined in somewhat larger (≥20 cubic nanometer) tetradecahedral cavities in face-centered cubic metals. Layering at the liquid-solid interface plays an important role in determining physical properties as diverse as the rheological behavior of two-dimensionally confined liquids and the dynamics of crystal growth.
A Bioartificial Liver--State of the Art
Authors: Strain Alastair J. , Neuberger James M.
Published: July 2002

End-stage liver disease is treated by liver transplantation, but donor organ shortages remain a serious problem. This has prompted the design of bioartificial liver devices to “bridge” patients until they either recover or receive a liver transplant. In these devices, patient plasma is circulated extracorporeally through a bioreactor that houses liver cells (hepatocytes) sandwiched between artificial plates or capillaries.
Atom-Resolved Imaging of Dynamic Shape Changes in Supported Copper Nanocrystals
Authors: Hansen Poul L. , Wagner Jakob B. , Helveg Stig , Rostrup-Nielsen Jens R. , Clausen Bjerne S. , Topsøe Henrik
Published: July 2002

In situ transmission electron microscopy is used to obtain atom-resolved images of copper nanocrystals on different supports. These are catalysts for methanol synthesis and hydrocarbon conversion processes for fuel cells. The nanocrystals undergo dynamic reversible shape changes in response to changes in the gaseous environment. For zinc oxide–supported samples, the changes are caused both by adsorbate-induced changes in surface energies and by changes in the interfacial energy. For copper nanocrystals supported on silica, the support has negligible influence on the structure. Nanoparticle dynamics must be included in the description of catalytic and other properties of nanomaterials. In situ microscopy offers possibilities for obtaining the relevant atomic-scale insight.
B Cell Antigen Receptor Signaling: Roles in Cell Development and Disease
Authors: Gauld Stephen B. , Dal Porto Joseph M. , Cambier John C.
Published: July 2002

Signals propagated through the B cell antigen receptor (BCR) are vital for the development and survival of B lymphocytes in both the bone marrow and the periphery. These signals not only guide maturation and activation but also affect the removal of potentially self-reactive B lymphocytes. Interestingly, these signals are known to be either ligand-independent (“tonic” signals) or induced by ligand (antigen) binding to the BCR. We focus on the problems that occur in B cell development due to defects in signals emanating from the BCR. In addition, we present the B Cell Antigen Receptor Pathway, an STKE Connections Map that illustrates the events involved in B cell signaling.
A Cellular Homolog of Hepatitis Delta Antigen: Implications for Viral Replication and Evolution
Authors: Brazas Robert , Ganem Don
Published: July 2002

Hepatitis delta virus (HDV) is a pathogenic human virus whose RNA genome and replication cycle resemble those of plant viroids. However, viroid genomes contain no open reading frames, whereas HDV RNA encodes a single protein, hepatitis delta antigen (HDAg), which is required for viral replication. A cellular gene whose product interacts with HDAg has now been identified, and this interaction was found to affect viral genomic replication in intact cells. DNA sequence analysis revealed that this protein, termed delta-interacting protein A (DIPA), is a cellular homolog of HDAg. These observations demonstrate that a host gene product can modulate HDV replication and suggest that HDV may have evolved from a primitive viroidlike RNA through capture of a cellular transcript.
Association of Spindle Assembly Checkpoint Component XMAD2 with Unattached Kinetochores
Authors: Chen Rey-Huei , Waters Jennifer C. , Salmon E. D. , Murray Andrew W.
Published: July 2002

The spindle assembly checkpoint delays anaphase until all chromosomes are attached to a mitotic spindle. The
mad
(mitotic arrest-deficient) and
bub
(budding uninhibited by benzimidazole) mutants of budding yeast lack this checkpoint and fail to arrest the cell cycle when microtubules are depolymerized. A frog homolog of
MAD2
(
XMAD2
) was isolated and found to play an essential role in the spindle assembly checkpoint in frog egg extracts. XMAD2 protein associated with unattached kinetochores in prometaphase and in nocodazole-treated cells and disappeared from kinetochores at metaphase in untreated cells, suggesting that XMAD2 plays a role in the activation of the checkpoint by unattached kinetochores. This study furthers understanding of the mechanism of cell cycle checkpoints in metazoa and provides a marker for studying the role of the spindle assembly checkpoint in the genetic instability of tumors.
How the Brain Gets Rhythm
Authors: Schechter Bruce
Published: July 2002

How does the brain generate the rhythms that may link separate sets of neurons responding to the same object? Particular neurons seem to act as pacemakers for the rhythms, while networks of other cells spread and synchronize them. Results from one group were reported in the 4 October issue of
Science
.
Will a Twist of Viral Fate Lead to a New Cancer Treatment?
Authors: Pennisi Elizabeth
Published: July 2002

Research reported in this issue (
p.373
) indicates that a modified version of a virus best known as a cause of respiratory infections may provide an intriguing new way to kill cancer cells while leaving normal cells unharmed.
A Cold Elixir for Physics
Authors: Glanz James
Published: July 2002

Douglas Osheroff, David Lee, and Robert Richardson have won this year's Nobel Prize in physics for their 1971 discovery of the superfluid helium-3—a strange, frictionless, quantum-mechanical substance that has held physicists spellbound ever since. For more information on this prize, see the
Nobel Foundation Web site
To Send Data, Physicists Resort to Quantum Voodoo
Authors: Taubes Gary
Published: July 2002

In a pursuit that holds a vague resemblance to voodoo, physicists are exploiting a quantum-mechanical paradox in which two particles are created simultaneously with their internal quantum states—their spin, for instance, or polarization—irrevocably “entangled.” These particles, linked at birth even though they may be separated by vast distances, can be used to transmit data or even to teleport entire quantum states.
Out, Damned CLIP! Out, I Say!
Authors: Roche Paul A.
Published: July 2002

The major histocompatibility complex (MHC) class II molecule displays peptide fragments of foreign proteins to trigger a defensive reaction from the immune system. Before insertion of the foreign peptides into the class II binding groove, a place-holding peptide CLIP must be removed. This is accomplished by the molecule DM, which is shown to increase the dissociation rate of a small class II-associated Ii peptide (CLIP) from class II (see report by Weber
et al
.,
p. 618
). Roche explains how DM can tell the difference between the class II-CLIP and foreign peptide-CLIP complexes.
Evidence for Charge-Flux Duality near the Quantum Hall Liquid-to-Insulator Transition
Authors: Shahar D. , Tsui D. C. , Shayegan M. , Shimshoni E. , Sondhi S. L.
Published: July 2002

A remarkable symmetry has been observed between the diagonal, nonlinear, current-voltage (
I-V

xx

) characteristics taken in the fractional quantum Hall effect (FQHE) liquid state of the two-dimensional electron system and those taken in the bordering insulating phase. When properly selected, the

I-V
xx

traces in the FQHE regime are identical, within experimental errors, to

V
xx
-I

traces in the insulator, that is, with the roles of the currents and voltages exchanged. These results can be interpreted as evidence for the existence of charge-flux duality symmetry in the system.
Presynaptic Calcium Current Modulation by a Metabotropic Glutamate Receptor
Authors: Takahashi Tomoyuki , Forsythe Ian D. , Tsujimoto Tetsuhiro , Barnes-Davies Margaret , Onodera Kayoko
Published: July 2002

Metabotropic glutamate receptors (mGluRs) regulate transmitter release at mammalian central synapses. However, because of the difficulty of recording from mammalian presynaptic terminals, the mechanism underlying mGluR-mediated presynaptic inhibition is not known. Here, simultaneous recordings from a giant presynaptic terminal, the calyx of Held, and its postsynaptic target in the medial nucleus of the trapezoid body were obtained in rat brainstem slices. Agonists of mGluRs suppressed a high voltage-activated P/Q-type calcium conductance in the presynaptic terminal, thereby inhibiting transmitter release at this glutamatergic synapse. Because several forms of presynaptic modulation and plasticity are mediated by mGluRs, this identification of a target ion channel is a first step toward elucidation of their molecular mechanism.
New Feathered Fossil Brings Dinosaurs and Birds Closer
Authors: Gibbons Ann
Published: July 2002

New York—A fossil of a seemingly downy dinosaur, recently discovered in China, strengthens the theory that birds evolved from dinosaurs. Photographs of the fossil were the talk of the Society of Vertebrate Paleontology meeting here, where they were first displayed, but some paleontologists remain convinced that birds descended from reptiles that preceded dinosaurs.
Doubts Cast on Leukemia Papers
Authors: Marshall Eliot
Published: July 2002

The discovery that a graduate student had apparently faked some data in papers co-authored by Francis Collins, director of the National Center for Human Genome Research, has cast doubt on recent research concerned with a chromosomal aberration and leukemia.
Persistence Pays Off in Defining History of Diffusion
Authors: Watson Andrew
Published: July 2002

In a series of recent papers, two separate groups of researchers, one French and the other a U.S.-Anglo-French collaboration, have shown that there is more than meets the eye in the decades-old mathematical description of diffusion. The diffusion equation, they contend, can do more than simply provide concentrations at specific points and times: With a newly identified exponent, it also produces information about how the process progressed.
Filling In the Blanks in the p53 Protein Structure
Authors: Pennisi Elizabeth
Published: July 2002

Because the p53 protein plays a critical role in protecting cells against cancer, researchers want to understand all aspects of its structure and function. In work reported in this issue (
p.948
) , researchers have now solved the three-dimensional structure of one previously unvisualized section of the protein—a key regulatory region in association with its regulator, a protein called MDM2. In an accompanying paper (
p.1001
), they also take a look at p53's interaction with another protein that may be involved in controlling the tumor suppressor's activity.
Past and Present Subtropical Summer Monsoons
Authors: Sirocko Frank
Published: July 2002

Monsoons contribute to cycles of flood and drought in southern Asia. Better forecasting of these important events will require deeper understanding of the factors that control them. In his Perspective, Sirocko discusses results presented by Clemens
et al
. (
p. 943
), who reveal new information in this issue about how past and present monsoons come about.
Lipid A--Target for Antibacterial Drugs
Authors: Vaara Martti
Published: July 2002

Bacteria are rapidly developing resistance to drugs, rendering treatment of some diseases difficult or impossible. A report by Onishi
et al
. in this issue (
p. 980
) announces the discovery of a new drug directed at a never-before-assaulted part of the bacteria, the lipid A portion of the bacterial outer membrane. In his Perspective, Vaara discusses the worldwide problem of drug-resistant pathogenic bacteria and how this new agent exemplifies the tack we must now take to fight these diseases.
Exoskeletons out of the Closet
Authors: Seger Jon
Published: July 2002

Female ants are more closely related to their sisters than to their brothers. To maximize the contribution of their genes to the colony, the female workers seem to promote the survival of female over male siblings. A report by Sundström
et al
. in this week's issue (
p. 993
) provides data to this effect, and in his Perspective, Seger discusses the historical evolution and implications of these ideas.
A Postelection Vote for Consensus
Authors: Lawler Andrew
Published: July 2002

In the wake of an election that reaffirmed divided government in Washington, Democrats and Republicans are calling for a truce in the bruising ideological fights of the last 2 years. That respite could help rescue research programs from the wholesale cuts needed to balance the federal budget
Guiding Neurons to the Cortex
Authors: Barinaga Marcia
Published: July 2002

Both humans and mice are affected by mutations that apparently interfere with the migration of cortical neurons from their birthplace deep in the brain to their final destinations in the cortex. Recently, neuroscientists have begun cloning the genes at fault, and this should help them piece together the signaling pathways the neurons use in finding their way.
Dynamics of Oxidation of a Fe
2+
-Bearing Aluminosilicate (Basaltic) Melt
Authors: Cooper Reid F. , Fanselow John B. , Weber J. K. Richard , Merkley Dennis R. , Poker David B.
Published: July 2002

Rutherford backscattering spectroscopy (RBS) and microscopy demonstrate that the ∼1400°C oxidation of levitated droplets of a natural Fe
2+
-bearing aluminosilicate (basalt) melt occurs by chemical diffusion of Fe
2+
and Ca
2+
to the free surface of the droplet; internal oxidation of the melt results from the required counterflux of electron holes. Diffusion of an oxygen species is not required. Oxidation causes the droplets to go subsolidus; magnetite (Fe
3
O
4
) forms at the oxidation-solidification front with a morphology suggestive of a Liesegang-band nucleation process.
A Rare Glimpse of an Early Human Face
Authors: Gibbons Ann
Published: July 2002

A new jaw that may be the oldest fossil of our genus has been discovered in Hadar, Ethiopia. Dated at 2.3 million years old, the upper jaw gives paleoanthropologists a glimpse of a critical but mysterious time in human evolution.
Hedgehog's Patterning Call Is Patched Through, Smoothly
Authors: Roush Wade
Published: July 2002

The Hedgehog protein is a key signaling molecule in embryogenesis, sending a message that allows embryonic hands to tell thumb from little finger, for example. But researchers have long sought the molecular receiver for Hedgehog's message and gotten conflicting results. New studies offer a reason why: Two proteins, Patched and Smoothened, appear to work together to receive and relay the signal.
Microwave Spectroscopy at the Dissociation Limit
Authors: Carrington Alan
Published: July 2002

An ion beam technique has been developed that combines some of the methods of mass spectrometry and molecular spectroscopy and is designed for the study of molecular ions at energy levels lying very close to the lowest dissociation limit. Microwave radiation is used to drive spectroscopic transitions, and electric field dissociation of the weakly bound levels provides a high degree of state selection for sensitive detection of the spectra. The analysis of the spectra requires unconventional approaches to the description of the long-range levels and their spectroscopic study and provides stringent tests of ab initio theories.
Japan Hopes to Cash In On Industry-University Ties
Authors: Normile Dennis
Published: July 2002

Tokyo—Japan's new push to get its universities to contribute more directly to economic growth has meant gleaming new labs and the latest equipment. It's also changed the way that the government funds academic research.
UT Southwestern: From Army Shacks to Research Elites
Authors: Kling James
Published: July 2002

Dallas—A mix of oil funds, state money, and private philanthropy has turned the University of Texas Southwestern Medical School into a research power. Its scientific strength rests on a combination of homegrown talent and superstars lured from other institutions with promises of ample research resources and the prospect of interdisciplinary studies.
Astronomers Tame a Workhorse Laser
Authors: Watson Andrew
Published: July 2002

Techniques for controlling chaos—a hair-trigger sensitivity to initial conditions—have enabled a group of researchers to stabilize a tunable infrared laser. The feat, reported onp
page 1498
, may be the first example of chaos control to move to practical application, because the laser is widely used in laboratory studies of cold gases resembling the atmospheres of the outer planets.
Korean Institute Ponders Role in Global Eradication Efforts
Authors: Normile Dennis
Published: July 2002

Seoul—Progress in finding vaccines against the leading killers in the developing world will require greater attention to the needs of those countries, says a group of scientists who are helping to launch the International Vaccine Institute in Seoul
A New Embryo Zoo
Authors: Roush Wade
Published: July 2002

Seoul—Progress in finding vaccines against the leading killers in the developing world will require greater attention to the needs of those countries, says a group of scientists who are helping to launch the International Vaccine Institute in Seoul.
Can Chip Devices Keep Shrinking?
Authors: Service Robert F.
Published: July 2002

Investigators are working to devise silicon-patterning schemes to produce features far smaller than those etched with today's lithographic systems, as reported in this week's issue. In an upcoming issue,
Science
will explore the new types of devices made possible by these technologies.
Polymorphs of Alumina Predicted by First Principles: Putting Pressure on the Ruby Pressure Scale
Authors: Thomson Kendall T. , Wentzcovitch Renata M. , Bukowinski Mark S. T.
Published: July 2002

Fully optimized quantum mechanical calculations indicate that Al
2
O
3
transforms from the corundum structure to the as yet unobserved Rh
2
O
3
(II) structure at about 78 gigapascals, and it further transforms to
Pbnm
-perovskite structure at 223 gigapascals. The predicted x-ray spectrum of the Rh
2
O
3
(II) structure is similar to that of the corundum structure, suggesting that the Rh
2
O
3
(II) structure could go undetected in high-pressure x-ray measurements. It is therefore possible that the ruby (Cr
3+
-doped corundum) fluorescence pressure scale is sensitive to the thermal history of the ruby chips in a given experiment.
Quantal Duration of Auditory Memories
Authors: Chew Sek Jin , Vicario David S. , Nottebohm Fernando
Published: July 2002

Neuronal responses in the caudomedial neostriatum (NCM) of adult zebra finches (
Taeniopygia guttata
) decreased upon repeated, unreinforced presentations of conspecific song, calls, or other complex sounds. This “stimulus-specific habituation” is a form of learning, and its spontaneous loss, a form of “forgetting.” Spontaneous forgetting occurred only at narrowly defined times (2 to 3, 6 to 7, 14 to 15, 17 to 18.5, 46 to 48, or 85 to 89 hours after first exposure to a stimulus), determined by stimulus class, number of presentations, and interval between presentations. The first five forgetting times coincided with periods when gene expression and protein synthesis in NCM were required for maintenance of the longer lasting (85 to 89 hours) habituation. The number of successive episodes of gene expression induced by a stimulus, but occurring long after stimulus presentation, appears to determine the quantal duration of auditory memories.
Probing Collective Motions of Terminally Anchored Polymers
Authors: Fytas George , Anastasiadis Spiros H. , Seghrouchni Rachid , Vlassopoulos Dimitris , Li Junbai , Factor Bradford J. , Theobald Wolfgang , Toprakcioglu Chris
Published: July 2002

Polymer chains attached by one end to an impenetrable surface at high coverage exemplify a tethered layer of mesoscopic dimensions. At equilibrium, thermal fluctuations of the segment density profile of the brushlike layer reflect the tethered chain dynamics; the probing of these fluctuations by evanescent-wave dynamic light scattering is reported. By utilizing a set of terminally attached layers with thicknesses (L
0
) from 45 to 130 nanometers, it was found that there is a preferred wavelength of order L
0
of these fluctuations with a concurrent slowing down of their thermal decay rate. This technique could open the route for the investigation of the largely unexplored area of polymer surface dynamics.
Formation of Chiral Interdigitated Multilayers at the Air-Liquid Interface Through Acid-Base Interactions
Authors: Kuzmenko Ivan , Buller Ronith , Bouwman Wim G. , Kjær Kristian , Als-Nielsen Jens , Lahav Meir , Leiserowitz Leslie
Published: July 2002

Thin interdigitated films composed of a long-chain, water-insoluble chiral acid
(p
-pentadecylmandelic acid of absolute configuration
R
) and a water-soluble chiral base (phenylethylamine,
R′
) were constructed at the air-solution interface. The (
R, R′
) structure was characterized to near-atomic resolution by grazing-incidence x-ray diffraction (GIXD). The two diastereomeric systems, (
R, R′
) and (
R, S′
), demonstrate similar surface pressure-molecular area isotherms, but their structures are completely different on the molecular level, as monitored by GIXD. Complementary data on these two architectures were provided by atomic force microscopy.
Functional Analysis of the Genes of Yeast Chromosome V by Genetic Footprinting
Authors: Smith Victoria , Chou Karen N. , Lashkari Deval , Botstein David , Brown Patrick O.
Published: July 2002

Genetic footprinting was used to assess the phenotypic effects of Ty1 transposon insertions in 268 predicted genes of chromosome V of
Saccharomyces cerevisiae.
When seven selection protocols were used, Ty1 insertions in more than half the genes tested (157 of 268) were found to result in a detectable reduction in fitness. Results could not be obtained for fewer than 3 percent of the genes tested (7 of 268). Previously known mutant phenotypes were confirmed, and, for about 30 percent of the genes, new mutant phenotypes were identified.
Neoteny in Lymphocytes:
Rag1
and
Rag2
Expression in Germinal Center B Cells
Authors: Han Shuhua , Zheng Biao , Schatz David G. , Spanopoulou Eugenia , Kelsoe Garnett
Published: July 2002

The products of the
Rag1
and
Rag2
genes drive genomic V(D)J rearrangements that assemble functional immunoglobulin and T cell antigen receptor genes. Expression of the
Rag
genes has been thought to be limited to developmentally immature lymphocyte populations that in normal adult animals are primarily restricted to the bone marrow and thymus. Abundant RAG1 and RAG2 protein and messenger RNA was detected in the activated B cells that populate murine splenic and Peyer's patch germinal centers. Germinal center B cells thus share fundamental characteristics of immature lymphocytes, raising the possibility that antigen-dependent secondary V(D)J rearrangements modify the peripheral antibody repertoire.
Transformation of Coordinated Dinitrogen by Reaction with Dihydrogen and Primary Silanes
Authors: Fryzuk Michael D. , Love Jason B. , Rettig Steven J. , Young Victor G.
Published: July 2002

The reaction of dihydrogen with a side-on bound dinitrogen complex of zirconium was investigated. Instead of a displacement of the dinitrogen moiety, which is the common mode of reactivity, a complex containing both a bridging hydride and a bridging hydrazido unit with a nitrogen-hydrogen bond was observed. This reaction was extended to primary silanes to produce a species that contained a nitrogen-silicon bond. In addition, an intermediate in the dihydrogen addition has been structurally characterized as having a bridging dihydrogen unit.
Unusual Oligomerization Required for Activity of NtrC, a Bacterial Enhancer-Binding Protein
Authors: Wyman Claire , Rombel Irene , North Anne K. , Bustamante Carlos , Kustu Sydney
Published: July 2002

Nitrogen regulatory protein C (NtrC) contacts a bacterial RNA polymerase from distant enhancers by means of DNA loops and activates transcription by allowing polymerase to gain access to the template DNA strand. It was shown that NtrC from
Salmonella typhimurium
must build large oligomers to activate transcription. In contrast to eukaryotic enhancer-binding proteins, most of which must bind directly to DNA, some NtrC dimers were bound solely by protein-protein interactions. NtrC oligomers were visualized with scanning force microscopy. Evidence of their functional importance was provided by showing that some inactive non-DNA-binding and DNA-binding mutant forms of NtrC can cooperate to activate transcription.
A Tonic Hyperpolarization Underlying Contrast Adaptation in Cat Visual Cortex
Authors: Carandini Matteo , Ferster David
Published: July 2002

The firing rate responses of neurons in the primary visual cortex grow with stimulus contrast, the variation in the luminance of an image relative to the mean luminance. These responses, however, are reduced after a cell is exposed for prolonged periods to high-contrast visual stimuli. This phenomenon, known as contrast adaptation, occurs in the cortex and is not present at earlier stages of visual processing. To investigate the cellular mechanisms underlying cortical adaptation, intracellular recordings were performed in the visual cortex of cats, and the effects of prolonged visual stimulation were studied. Surprisingly, contrast adaptation barely affected the stimulus-driven modulations in the membrane potential of cortical cells. Moreover, it did not produce sizable changes in membrane resistance. The major effect of adaptation, evident both in the presence and in the absence of a visual stimulus, was a tonic hyperpolarization. Adaptation affects a class of synaptic inputs, most likely excitatory in nature, that exert a tonic influence on cortical cells.
Gene Expression Profiles in Normal and Cancer Cells
Authors: Zhang Lin , Zhou Wei , Velculescu Victor E. , Kern Scott E. , Hruban Ralph H. , Hamilton Stanley R. , Vogelstein Bert , Kinzler Kenneth W.
Published: July 2002

As a step toward understanding the complex differences between normal and cancer cells in humans, gene expression patterns were examined in gastrointestinal tumors. More than 300,000 transcripts derived from at least 45,000 different genes were analyzed. Although extensive similarity was noted between the expression profiles, more than 500 transcripts that were expressed at significantly different levels in normal and neoplastic cells were identified. These data provide insight into the extent of expression differences underlying malignancy and reveal genes that may prove useful as diagnostic or prognostic markers.
Paleobotanical Evidence for High Altitudes in Nevada During the Miocene
Authors: Wolfe Jack A. , Schorn Howard E. , Forest Chris E. , Molnar Peter
Published: July 2002

Leaf physiognomy provides estimates of environmental parameters, including mean annual enthalpy, which is a thermodynamic parameter of the atmosphere that varies with altitude. Analyses of 12 mid-Miocene floras from western Nevada indicate that this part of the Basin and Range Province stood ∼3 kilometers above sea level at 15 to 16 million years ago, which is 1 to 1.5 kilometers higher than its present altitude. Much, if not all, of the collapse to present-day altitudes seems to have been achieved by ∼13 million years ago. The crust in much of this area has been extended and thinned throughout the past 40 to 50 million years, and the isostatic balance of a thinning crust requires subsidence, not uplift as suggested by previous paleobotanical work.