bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic structure of SiO2: Charge redistribution contributions to the dynamic dipoles/effective charges of the infrared active normal modes
Authors: Whitten J. L. , Zhang Y. , Menon M. , Lucovsky G.
Published: October 2002

This article applies ab initio calculations at the (i) Hartree–Fock self-consistent field single determinant and (ii) configuration interaction multideterminant expansion levels to study the diagonal components of the dynamic dipoles, Δμi/Δqj with i=j, or equivalently infrared effective charges, ei*, associated with asymmetric bond stretching νy, symmetric bond stretching νz, and out-of-plane bond rocking νx, normal mode infrared active vibrations of noncrystalline SiO2. The normal mode dynamic dipoles (hereafter, Δμ/qi) are decomposed into equilibrium charge density (ionic) and orbital variation (charge redistribution) contributions. The calculations are based on small clusters in which Si–O–Si groups are connected through O atoms to embedding Si atom terminators Si* that emulate the connectivity of these Si–O–Si groups to the SiO2 continuous random network. Values of Δμ/Δqi have been determined as a function of the Si–O–Si bond angle α at the bridging O-atom sites, and agree with values obtained from analysis of infrared spectra. Finally, the ab initio calculations are extended to noncrystalline silicon–carbon alloys and silicon nitride, and values of Δμ/Δqi are determined for infrared active vibrations associated with N- and C-atom asymmetric stretching normal mode motions. The normalized equilibrium charge density or ionic contributions of the O, N, and C atoms follow trends expected on the basis of their relative Pauling electronegativities in bonds with Si.
Impact of the colloidal silica particle size on physical vapor deposition tungsten removal rate and surface roughness
Authors: Bouvet D. , Beaud P. , Fazan P. , Sanjines R. , Jacquinot E.
Published: October 2002

With the development of sub-0.25 μm technologies, interconnect integration is more sensitive to the surface quality and to the roughness of tungsten-polished layers. Consequently, alumina-based slurries are progressively replaced by silica-based slurries (fumed or colloidal), characterized by much smaller and softer particles. In contrast to the many investigators of alumina-based slurries, only a few investigations have been carried out on the effect of the particle size on the physical vapor deposition (PVD) tungsten, PVD titanium, and thermal oxide removal rates and on the surface roughness after polishing. In this article, we evaluate four different colloidal silica-based slurries having different particle sizes. We find that the most promising slurry is the one with the smallest particle size. We also show that the tungsten removal rate mechanism is probably neither a scratching/indentation nor a surface contact type mechanism, but most likely a mechanism controlled by the growth kinetics of the passivation layer.
Mechanism of anomalous current transport in n-type GaN Schottky contacts
Authors: Hasegawa Hideki , Oyama Susumu
Published: October 2002

Temperature T dependences of the current–voltage (I–V) characteristics of Ni and Pt/n-GaN Schottky contacts were measured in detail, and the results were analyzed from various viewpoints. Large deviations from the thermionic emission transport were observed in the I–V–T behavior with anomalously large reverse leakage currents. Forward characteristics could be fitted into the classical thermionic-field emission (TFE)/field emission (FE) model. However, an unusually high doping density had to be assumed, and the reverse characteristics were far away from measured data. A new thin surface barrier (TSB) model was proposed in which the width of the Schottky barrier is reduced due to the presence of unintentional surface donors. Analysis of TFE/TE process through the TSB region has led to sets of I–V–T curves that reproduce almost perfectly the observed forward and reverse I–V–T behavior with correct orders of magnitude of currents. Deep donors related to nitrogen vacancy are suggested to be the origin of surface donors producing TSBs.
Fabrication of single-electron tunneling transistors with an electrically formed Coulomb island in a silicon-on-insulator nanowire
Authors: Kim Dae Hwan , Sung Suk-Kang , Kim Kyung Rok , Lee Jong Duk , Park Byung-Gook
Published: October 2002

For the purpose of controllable characteristics, silicon single-electron tunneling transistors with an electrically formed Coulomb island are proposed and fabricated on the basis of the sidewall process technique. The fabricated devices are based on a silicon-on-insulator (SOI) metal–oxide–semiconductor (MOS) field effect transistor with the depletion gate. The key fabrication technique consists of two sidewall process techniques. One is the patterning of a uniform SOI nanowire, and the other is the formation of n-doped polysilicon sidewall depletion gates. While the width of a Coulomb island is determined by the width of a SOI nanowire, its length is defined by the separation between two sidewall depletion gates which are formed by a conventional lithographic process combined with the second sidewall process. These sidewall techniques combine the conventional lithography and process technology, and guarantee the compatibility with complementary MOS process technology. Moreover, critical dimension depends not on the lithographical limit but on the controllability of chemical vapor deposition and reactive-ion etching. Very uniform weakly p-doped SOI nanowire defined by the sidewall technique effectively suppresses unintentional tunnel junctions formed by the fluctuation of the geometry or dopant in SOI nanowire, and the Coulomb island size dependence of the device characteristics confirms the good controllability. A voltage gain larger than one and the controllability of Coulomb oscillation peak position are also successfully demonstrated, which are essential conditions for the integration of a single-electron tunneling transistor circuit. Further miniaturization and optimization of the proposed device will make room temperature designable single-electron tunneling transistors possible in the foreseeable future.
Morphological evolution of epitaxial cobalt–semiconductor compound layers during growth in a scanning tunneling microscope
Authors: Goldfarb I. , Briggs G. A. D.
Published: October 2002

We investigate the mechanisms of CoSi2 and CoGe2 growth by carefully controlled e-beam evaporation of Co onto Si(001) and Ge/Si(001) substrates from the very initial submonolayer stage, monitored in situ by scanning tunneling microscopy, aided by reflection high-energy electron diffraction. In order to grow different epilayer morphologies, we use flat and vicinal surfaces and two different methods of synthesis: reactive deposition (where Co is deposited onto a hot substrate), and solid-phase reaction (where Co is deposited at lower, or room, temperature). We attempt to account for the observed morphological differences in the epilayers by correlating them with parametric differences in the deposition and growth processes.
Simplified bond-hyperpolarizability model of second harmonic generation: Application to Si-dielectric interfaces
Authors: Wang J.-F. T. , Powell G. D. , Johnson R. S. , Lucovsky G. , Aspnes D. E.
Published: October 2002

We show that the anisotropies of second-harmonic-generation (SHG) intensities of singular and vicinal (111) and (001)Si–dielectric interfaces can be described accurately as dipole radiation originating from the anharmonic motion of bond charges parallel to the bond directions. This simplified bond-hyperpolarizability model not only provides a simpler and mathematically more efficient representation of SHG, but also allows a direct physical interpretation at the bond level, which was lacking in previous approaches. Application to oxidized and nitrided Si–SiO2 interfaces provides new insight into bonding that occurs at these interfaces as well as the origin of SHG.
Electronic structure of high-k transition metal oxides and their silicate and aluminate alloys
Authors: Lucovsky G. , Zhang Y. , Rayner G. B. , Appel G. , Ade H. , Whitten J. L.
Published: October 2002

This article addresses differences between the electronic structure of: (i) alternative high-k transition metal (TM) rare earth dielectrics and (ii) SiO2 and Si oxynitride alloys by presenting a systematic x-ray absorption spectroscopy study of transitions between TM n p-core states and TM metal n+1−d⋆ and n+2 s⋆ antibonding/conduction band states (n=2, 3, and 4) that is complemented by studies of O atom K1 edge absorption spectra. Ab initio calculations based on small clusters establish the localization of the n+1 d⋆ states on the TM metals. Ab initio electronic structure calculations are also used to interpret other aspects of the optical, ultraviolet, x-ray, and electron spectroscopies, and also provide a basis for interpretation of electrical results, thereby narrowing the field of possible replacement dielectrics for advanced semiconductor devices.
TiSiN films produced by chemical vapor deposition as diffusion barriers for Cu metallization
Authors: Joseph S. , Eizenberg M. , Marcadal C. , Chen L.
Published: October 2002

The decrease in microelectronic device dimensions and the continuous effort to increase the speed and performance of devices have led to the need to replace the current metallization of Al(Cu) with Cu. This metal must be isolated from the neighboring dielectrics by a thin diffusion barrier layer. The currently employed diffusion barrier materials are Ta and TaN produced by advanced physical vapor deposition methods. The need for conformality and for the use of extremely thin layers serves as a driving force to look for chemical vapor deposition as the future deposition method. TiSiN films produced by using a cyclic process of thermal decomposition of tetrakis-dimethylamino-titanium followed by H2/N2 plasma and a flash of SiH4 are attractive candidates as diffusion barriers for Cu metallization in future devices. In this research, we have extensively studied the barrier integrity using secondary ion mass spectroscopy (SIMS) depth profiling and SECCO etch-pitting test. The sample configuration used was Cu/barrier/Si. Cu diffusion was detected by SIMS after annealing at 500 °C. Etch pits were first found after annealing at 600 °C. It was found that the plasma treatment is the main factor improving the barriers ability to prevent Cu diffusion to the substrate, most probably due to the higher density of the treated film, while the addition of SiH4 only slightly improves the barriers integrity due to the formation of Si3N4. A correlation between the TiSiN microstructure and its barrier integrity is proposed.
Profile control of high aspect ratio trenches of silicon. I. Effect of process parameters on local bowing
Authors: Boufnichel M. , Aachboun S. , Grangeon F. , Lefaucheux P. , Ranson P.
Published: October 2002

A cryogenic etching method with SF6/O2 chemistry plasma in an Alcatel inductively coupled plasma reactor is used to achieve deep trenches with high aspect ratio (depth/width >10) and high anisotropy. The mean etch rate in 2 μm wide and 100 μm deep trenches is about 3.5 μm/min. The slope of the trenches can be adjusted from 88° to 90° by selecting appropriate process conditions and selectivity (silicon/SiO2 mask) is higher than 400:1. However, profiles still present a defect: they need to be improved, mainly by reducing the local bowing effect. Local bowing is lateral etching located on the sidewalls and resulting in profiles destruction. This article deals with the study of the local bowing and profile improvement by changing process parameters. We investigated the effect of the process parameters (pressure, bias voltage, temperature, gas flow rates, etc.), and the mechanisms responsible for local bowing are discussed and evaluated. The final aim is to find the cause of the appearance of local bowing and thus the means to reduce or eliminate it. We especially showed that local bowing depends on the efficiency of the trench passivation mechanism and on ion energy and density: ions seem to be responsible of the destruction of the passivation layer.
Real-time spectro-ellipsometric characterization of Si/Si1−xGex multiple quantum wells grown on Si(100) substrates
Authors: Akazawa Housei
Published: October 2002

In situ spectro-ellipsometric measurement was used to obtain the various structural parameters that characterize Si/Si1−xGex multiple quantum wells grown on Si(100) substrates. The primary feature of the evolution of the ellipsometric angles (Ψ, Δ) in the time domain is a short-period oscillation of their signal levels resulting from the change in optical contrast when the top layer is alternately exchanged between Si1−xGex and Si. The top layer material and the number of layer pairs at each moment of growth can be derived from this oscillation. At transparent energies, the long-period modulation structure resulting from the optical interference between the whole multiple quantum well (MQW) and the Si substrate superimposes itself as an envelope curve on the short-period oscillation. The overall growth rate of the MQW is derived from the modulation period. One can quickly discriminate two-dimensional (2D) planar growth and 3D island growth by examining the Ψ-Δ trajectories; 2D growth shows finite-size, closed-loop trajectories at 3.4 eV, whereas 3D growth shows drift motion of the oscillatory loops towards the region of lower Ψ and Δ angles.
Scanning spreading resistance microscopy current transport studies on doped III–V semiconductors
Authors: Lu R. P. , Kavanagh K. L. , Dixon-Warren St. J. , SpringThorpe A. J. , Streater R. , Calder I.
Published: October 2002

Two-dimensional (2D) carrier concentration profiling using scanning spreading resistance microscopy (SSRM) has been carried out on molecular beam epitaxy-grown GaAs and InP dopant calibration samples. The current transport mechanisms between the diamond-coated SSRM tip and the III–V semiconductor cleaved surface (110) was investigated as a function of semiconductor dopant concentration via current–voltage (I–V) measurement. A positive or negative tip bias was applied while scanning over each dopant concentration region (1016–1019 cm−3). The results were compared to simulated I–V curves based on thermionic emission theory. The best fits to the data obtained under forward bias indicated that the contact barrier heights, φb, were much lower than expected from conventional large area planar contacts to GaAs or InP. The effect increases with increasing doping concentration, as a result of a combination of barrier height lowering mechanisms such as image forces, thermionic field emission and minority carrier injection. Under reverse bias, the thermionic emission theory only holds for highly doped semiconductors while for low doping, surface and bulk generation currents determine the overall detectable SSRM current.
Numerical algorithms for spatial registration of line fiducials from cross‐sectional images
Authors: Lee Sangyoon , Fichtinger Gabor , Chirikjian Gregory S.
Published: October 2002

We present several numerical algorithms for six‐degree‐of‐freedom rigid‐body registration of line fiducial objects to their marks in cross‐sectional planar images, such as those obtained in CT and MRI, given the correspondence between the marks and line fiducials. The area of immediate application is frame‐based stereotactic procedures, such as radiosurgery and functional neurosurgery. The algorithms are also suitable to problems where the fiducial pattern moves inside the imager, as is the case in robot‐assisted image‐guided surgical applications. We demonstrate the numerical methods on clinical CT images and computer‐generated data and compare their performance in terms of robustness to missing data, robustness to noise, and speed. The methods show two unique strengths: (1) They provide reliable registration of incomplete fiducial patterns when up to two‐thirds of the total fiducials are missing from the image; and (2) they are applicable to an arbitrary combination of line fiducials without algorithmic modification. The average speed of the fastest algorithm is 0.3236 s for six fiducial lines in real CT data in a Matlab implementation.
Dose characterization in the near‐source region for two high dose rate brachytherapy sources
Authors: Wang Ruqing , Allen Li X.
Published: October 2002

High dose rate (HDR) sources are currently used in intravascular brachytherapy (IVB) for the peripheral arterial system. This poses a demand on evaluating accurate dose parameters in the near‐source region for such sources. The purpose of this work is to calculate the dose parameters for the old VariSource HDR source and the new microSelectron HDR source, using Monte Carlo electron and photon transport simulation. The two‐dimensional (2D) dose rate distributions and the air kerma strengths for the two HDR sources were calculated by EGSnrc and EGS4 Monte Carlo codes. Based on these data, the dose parameters proposed in the AAPM TG‐60 protocol were derived. The dose rate constants obtained are for the old VariSource source, and for the new microSelectron source at the reference point The 2D dose rate distributions, the radial dose functions, and the anisotropy functions presented for the two sources cover radial distances ranging from 0.5 to 10 mm. In the near‐source region on the transverse plane, the dose effects of the charged particle nonequilibrium and the beta‐particle dose contribution were studied. It is found that at radial distances ranging from 0.5 to 2 mm, these effects increase the calculated dose rates by up to 29% for the old VariSource source, and by up to 12% for the new microSelectron source, which, in turn, change values of the radial dose function and the anisotropy function. The present dose parameters, which account for the charged particle nonequilibrium and the beta particle contribution, may be used for accurate IVB dose calculation.
Dosimetric characteristics of Novalis shaped beam surgery unit
Authors: Yin Fang‐Fang , Zhu Jingeng , Yan Hui , Gaun Haiqun , Hammoud Rabih , Ryu Samuel , Kim Jae H.
Published: October 2002

The dosimetric characteristics of a new dedicated radiosurgical treatment unit are systematically measured in terms of its percent depth dose, beam profile, and relative scatter factor. High‐resolution diode detector, mini‐ion‐chamber detector, and conventional Kodak XV films are used to measure dosimetric data for a range of field sizes from 6×6 mm to 100×100 mm. The effects of collimator size, micro‐multileaf collimator shape, and detector type on the dosimetric data are investigated. Results indicate that, with careful design, accurate dosimetric data could be acquired using either a dedicated diode detector or a mini‐ion‐chamber detector, and film detector. Special attention is required when measuring dosimetric data for small field sizes such as 6×6 mm.
Interinstitutional variations of sensitometric curves of radiographic dosimetric films
Authors: Bos Luc J. , Danciu Claudia , Cheng Chee‐Wai , Brugmans Marco J. P. , van der Horst Astrid , Minken André , Mijnheer Ben J.
Published: October 2002

Depth and field size dependence of the sensitometric curves of radiographic films have been studied by various groups. Limited information is, however, available on the magnitude of the variations in sensitometric curves applied in clinical practice in different institutions. In this study we assessed in a systematic way the effect of the various parameters influencing the shape of the sensitometric curve: batch composition, irradiation conditions, film processing, and film scanning. Two types of film, Kodak X‐Omat V and CEA TVS, were irradiated, processed, and analyzed in three different institutions. The interinstitutional variation of the sensitometric curves, expressed as the OD variation at 50 cGy, can be up to 32% and is mainly caused by differences in film processing and to a lesser degree to differences in batch composition, film scanning, and irradiation conditions. For the Kodak films, the average OD difference at 50 cGy between the three institutions is 17% as a result of differences in batch composition and 25% due to differences in processing conditions. For the CEA films these data are 6% and 24%, respectively. The long‐term variation of the sensitometric curves of KODAK films in one institution was smaller than the differences in batch composition between the three institutions. The sensitometric curves of CEA films showed in one institution a large variation with time; the shape gradually varied from sigmoidal to quasilinear. By using relative OD values rather than absolute OD values, variations in sensitometric curves of KODAK films can be reduced to 2%. Consequently, one sensitometric curve is sufficient to derive relative dose values. If processing conditions are well controlled, it might therefore be advantageous to determine the absolute OD only at one or two dose values, in combination with a “universal” relative sensitometric curve.
Heisenberg and the critical mass
Authors: Bernstein Jeremy
Published: October 2002

An elementary treatment of the critical mass used in nuclear weapons is presented and applied to an analysis of the wartime activities of the German nuclear program. In particular, the work of Werner Heisenberg based on both wartime and postwar documents is discussed.
Entangled photon apparatus for the undergraduate laboratory
Authors: Dehlinger Dietrich , Mitchell M. W.
Published: October 2002

We present detailed instructions for constructing and operating an apparatus to produce and detect polarization-entangled photons. The source operates by type I spontaneous parametric downconversion in a two-crystal geometry. Photons are detected in coincidence by single-photon counting modules and show strong angular and polarization correlations. We observe more than 100 entangled photon pairs per second. A test of a Bell inequality can be performed in an afternoon.
The effects of spatial separation in distance on the informational and energetic masking of a nearby speech signal
Authors: Brungart Douglas S. , Simpson Brian D.
Published: October 2002

Although many studies have shown that intelligibility improves when a speech signal and an interfering sound source are spatially separated in azimuth, little is known about the effect that spatial separation in distance has on the perception of competing sound sources near the head. In this experiment, head-related transfer functions (HRTFs) were used to process stimuli in order to simulate a target talker and a masking sound located at different distances along the listener’s interaural axis. One of the signals was always presented at a distance of 1 m, and the other signal was presented 1 m, 25 cm, or 12 cm from the center of the listener’s head. The results show that distance separation has very different effects on speech segregation for different types of maskers. When speech-shaped noise was used as the masker, most of the intelligibility advantages of spatial separation could be accounted for by spectral differences in the target and masking signals at the ear with the higher signal-to-noise ratio (SNR). When a same-sex talker was used as the masker, the intelligibility advantages of spatial separation in distance were dominated by binaural effects that produced the same performance improvements as a 4–5-dB increase in the SNR of a diotic stimulus. These results suggest that distance-dependent changes in the interaural difference cues of nearby sources play a much larger role in the reduction of the informational masking produced by an interfering speech signal than in the reduction of the energetic masking produced by an interfering noise source.
A multiple regression model for urban traffic noise in Hong Kong
Authors: To W. M. , Ip Rodney C. W. , Lam Gabriel C. K. , Yau Chris T. H.
Published: October 2002

This article describes the roadside traffic noise surveys conducted in heavily built-up urban areas in Hong Kong. Noise measurements were carried out along 18 major roads in 1999. The measurement data included L10, L50, L90, Leq, Lmax, the number of light vehicles, the number of heavy vehicles, the total traffic flow, and the average speed of vehicles. Statistical analysis using the analysis of variance (ANOVA) and Tukey test (p<0.05) reveals that the total traffic flow and the number of heavy vehicles are the most significant factors of urban traffic noise. Multiple regression was used to derive a set of empirical formulas for predicting L10 noise level due to road traffic. The accuracy of these empirical formulas is quantified and compared to that of another widely used prediction model in Hong Kong—the Calculation of Road Traffic Noise. The applicability of the selected multiple regression model is validated by the noise measurements performed in the winter of 2000.
Carbon Nanotubes--the Route Toward Applications
Authors: Baughman Ray H. , Zakhidov Anvar A. , de Heer Walt A.
Published: October 2002

Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.
A Thymic Precursor to the NK T Cell Lineage
Authors: Benlagha Kamel , Kyin Tim , Beavis Andrew , Teyton Luc , Bendelac Albert
Published: October 2002

CD1d-restricted autoreactive natural killer (NK1.1
+
) T cells function as regulatory cells in various disease conditions. Using improved tetramer tracking methodology, we identified a NK1.1
–
thymic precursor and followed its differentiation and emigration to tissues by direct cell transfer and in situ cell labeling studies. A major lineage expansion occurred within the thymus after positive selection and before NK receptor expression. Surprisingly, cytokine analysis of the developmental intermediates between NK
−
and NK
+
stages showed a T helper cell T
H
2 to T
H
1 conversion, suggesting that the regulatory functions of NK T cells may be developmentally controlled. These findings characterize novel thymic and postthymic developmental pathways that expand autoreactive cells and differentiate them into regulatory cells.
Proterozoic Ocean Chemistry and Evolution: A Bioinorganic Bridge?
Authors: Anbar A. D. , Knoll A. H.
Published: October 2002

Recent data imply that for much of the Proterozoic Eon (2500 to 543 million years ago), Earth's oceans were moderately oxic at the surface and sulfidic at depth. Under these conditions, biologically important trace metals would have been scarce in most marine environments, potentially restricting the nitrogen cycle, affecting primary productivity, and limiting the ecological distribution of eukaryotic algae. Oceanic redox conditions and their bioinorganic consequences may thus help to explain observed patterns of Proterozoic evolution.
Current Rectification by Pauli Exclusion in a Weakly Coupled Double Quantum Dot System
Authors: Ono K. , Austing D. G. , Tokura Y. , Tarucha S.
Published: October 2002

We observe spin blockade due to Pauli exclusion in the tunneling characteristics of a coupled quantum dot system when two same-spin electrons occupy the lowest energy state in each dot. Spin blockade only occurs in one bias direction when there is asymmetry in the electron population of the two dots, leading to current rectification. We induce the collapse of the spin blockade by applying a magnetic field to open up a new spin-triplet current-carrying channel.
Cytomegalovirus Recruitment of Cellular Kinases to Dissolve the Nuclear Lamina
Authors: Muranyi Walter , Haas Jürgen , Wagner Markus , Krohne Georg , Koszinowski Ulrich H.
Published: October 2002

The passage of large-sized herpesviral capsids through the nuclear lamina and the inner nuclear membrane to leave the nucleus requires a dissolution of the nuclear lamina. Here, we report on the functions of M50/p35, a β-herpesviral protein of murine cytomegalovirus. M50/p35 inserts into the inner nuclear membrane and is aggregated by a second viral protein, M53/p38, to form the capsid docking site. M50/p35 recruits the cellular protein kinase C for phosphorylation and dissolution of the nuclear lamina, suggesting that herpesviruses target a critical element of nuclear architecture.
Networks for Seeing
Authors: Martin Kevan A. C.
Published: October 2002

Computational Neuroscience of Vision
. Edmund T. Rolls and Gustavo Deco. Oxford University Press, Oxford, 2002. 587 pp. $90, £50. ISBN 0-19-852489-7. Paper, $45, £24.95. ISBN 0-19-852488-9.

The authors combine a neural network framework with evidence from neurophysiology, neuroimaging, and neuropsychology to consider how the human brain implements visual perception.
Chemical Synthesis of Poliovirus cDNA: Generation of Infectious Virus in the Absence of Natural Template
Authors: Cello Jeronimo , Paul Aniko V. , Wimmer Eckard
Published: October 2002

Full-length poliovirus complementary DNA (cDNA) was synthesized by assembling oligonucleotides of plus and minus strand polarity. The synthetic poliovirus cDNA was transcribed by RNA polymerase into viral RNA, which translated and replicated in a cell-free extract, resulting in the de novo synthesis of infectious poliovirus. Experiments in tissue culture using neutralizing antibodies and CD155 receptor–specific antibodies and neurovirulence tests in
CD155
transgenic mice confirmed that the synthetic virus had biochemical and pathogenic characteristics of poliovirus. Our results show that it is possible to synthesize an infectious agent by in vitro chemical-biochemical means solely by following instructions from a written sequence.
hamlet
, a Binary Genetic Switch Between Single- and Multiple- Dendrite Neuron Morphology
Authors: Moore Adrian W. , Jan Lily Yeh , Jan Yuh Nung
Published: October 2002

The dendritic morphology of neurons determines the number and type of inputs they receive. In the
Drosophila
peripheral nervous system (PNS), the external sensory (ES) neurons have a single nonbranched dendrite, whereas the lineally related multidendritic (MD) neurons have extensively branched dendritic arbors. We report that
hamlet
is a binary genetic switch between these contrasting morphological types. In
hamlet
mutants, ES neurons are converted to an MD fate, whereas ectopic
hamlet
expression in MD precursors results in transformation of MD neurons into ES neurons. Moreover,
hamlet
expression induced in MD neurons undergoing dendrite outgrowth drastically reduces arbor branching.
Public Information and Breeding Habitat Selection in a Wild Bird Population
Authors: Doligez Blandine , Danchin Etienne , Clobert Jean
Published: October 2002

According to the “public information” hypothesis, some animal species may monitor the current reproductive success of conspecifics to assess local habitat quality and to choose their own subsequent breeding site. To test this hypothesis experimentally, we manipulated two components of public information, the mean number of offspring raised locally (“quantity”) and their condition (“quality”), in the collared flycatcher
Ficedula albicollis
. Immigration rate decreased with local offspring quantity but did not depend on local offspring quality, suggesting that immigrants are deprived of information regarding local quality. Conversely, emigration rate increased both when local offspring quantity or quality decreased, suggesting that residents can use both components of public information.
Myelin-Associated Glycoprotein as a Functional Ligand for the Nogo-66 Receptor
Authors: Liu Betty P. , Fournier Alyson , GrandPré Tadzia , Strittmatter Stephen M.
Published: October 2002

Axonal regeneration in the adult central nervous system (CNS) is limited by two proteins in myelin, Nogo and myelin-associated glycoprotein (MAG). The receptor for Nogo (NgR) has been identified as an axonal glycosyl-phosphatidyl-inositol (GPI)–anchored protein, whereas the MAG receptor has remained elusive. Here, we show that MAG binds directly, with high affinity, to NgR. Cleavage of GPI-linked proteins from axons protects growth cones from MAG-induced collapse, and dominant-negative NgR eliminates MAG inhibition of neurite outgrowth. MAG-resistant embryonic neurons are rendered MAG-sensitive by expression of NgR. MAG and Nogo-66 activate NgR independently and serve as redundant NgR ligands that may limit axonal regeneration after CNS injury.
Focusing on Truth and Beauty
Authors: Miller Jake
Published: October 2002

Envisioning Science
The Design and Craft of the Science Image. Felice Frankel. MIT Press, Cambridge, MA, 2002. 336 pp. $55, £37.95. ISBN 0-262-06225-9.

In this how-to manual, Frankel provides researchers and students with a guide to using the aesthetic powers of photography to better communicate the results of their science.
Analytic and Algorithmic Solution of Random Satisfiability Problems
Authors: Mézard M. , Parisi G. , Zecchina R.
Published: October 2002

We study the satisfiability of random Boolean expressions built from many clauses withKvariables per clause (K-satisfiability). Expressions with a ratio α of clauses to variables less than a threshold αcare almost always satisfiable, whereas those with a ratio above this threshold are almost always unsatisfiable. We show the existence of an intermediate phase below αc, where the proliferation of metastable states is responsible for the onset of complexity in search algorithms. We introduce a class of optimization algorithms that can deal with these metastable states; one such algorithm has been tested successfully on the largest existing benchmark of K-satisfiability.
White Collar-1, a Circadian Blue Light Photoreceptor, Binding to the
frequency
Promoter
Authors: Froehlich Allan C. , Liu Yi , Loros Jennifer J. , Dunlap Jay C.
Published: October 2002

In the fungus
Neurospora crassa
, the blue light photoreceptor(s) and signaling pathway(s) have not been identified. We examined light signaling by exploiting the light sensitivity of the
Neurospora
biological clock, specifically the rapid induction by light of the clock component
frequency
(
frq
). Light induction of
frq
is transcriptionally controlled and requires two cis-acting elements (LREs) in the
frq
promoter. Both LREs are bound by a White Collar–1 (WC-1)/White Collar–2 (WC-2)–containing complex (WCC), and light causes decreased mobility of the WCC bound to the LREs. The use of in vitro–translated WC-1 and WC-2 confirmed that WC-1, with flavin adenine dinucleotide as a cofactor, is the blue light photoreceptor that mediates light input to the circadian system through direct binding (with WC-2) to the
frq
promoter.
Photothermal Imaging of Nanometer-Sized Metal Particles Among Scatterers
Authors: Boyer David , Tamarat Philippe , Maali Abdelhamid , Lounis Brahim , Orrit Michel
Published: October 2002

Ambient optical detection of labeled molecules is limited for fluorescent dyes by photobleaching and for semiconducting nanoparticles by “blinking” effects. Because nanometer-sized metal particles do not optically bleach, they may be useful optical labels if suitable detection signals can be found. We demonstrate far-field optical detection of gold colloids down to diameters of 2.5 nanometers with a photothermal method that combines high-frequency modulation and polarization interference contrast. The photothermal image is immune to the effects of scattering background, which limits particle imaging through Rayleigh scattering to diameters larger than 40 nanometers.
Fusion Pore Dynamics and Insulin Granule Exocytosis in the Pancreatic Islet
Authors: Takahashi Noriko , Kishimoto Takuya , Nemoto Tomomi , Kadowaki Takashi , Kasai Haruo
Published: October 2002

Insulin secretion from intact mouse pancreatic islets was investigated with two-photon excitation imaging. Insulin granule exocytosis occurred mainly toward the interstitial space, away from blood vessels. The fusion pore was unusually stable with a lifetime of 1.8 seconds. Opening of the 1.4-nanometer-diameter pore was preceded by unrestricted lateral diffusion of lipids along the inner wall of the pore, supporting the idea that this structure is composed of membrane lipids. When the pore dilated to 12 nanometers, the granules rapidly flattened and discharged their contents. Thus, our methodology reveals fusion pore dynamics in intact tissues at nanometer resolution.
Direct Evidence for a Marine Source of C
1
and C
2
Alkyl Nitrates
Authors: Chuck Adele L. , Turner Suzanne M. , Liss Peter S.
Published: October 2002

Alkyl nitrates are a significant component of the “odd nitrogen” reservoir and play an important role in regulating tropospheric ozone levels in remote marine regions. Measurements of methyl and ethyl nitrate in seawater and air samples along two Atlantic Ocean transects provide the first direct evidence for an oceanic source of these compounds. Equatorial surface waters were highly supersaturated (up to 800%) in both species, with the waters in the temperate regions generally being closer to equilibrium. A simple box model calculation suggests that the equatorial source could be a major component of the local atmospheric alkyl nitrate budget.
Economic Reasons for Conserving Wild Nature
Authors: Balmford Andrew , Bruner Aaron , Cooper Philip , Costanza Robert , Farber Stephen , Green Rhys E. , Jenkins Martin , Jefferiss Paul , Jessamy Valma , Madden Joah , Munro Kat , Myers Norman , Naeem Shahid , Paavola Jouni , Rayment Matthew , Rosendo Sergio , Roughgarden Joan , Trumper Kate , Turner R. Kerry
Published: October 2002

On the eve of the World Summit on Sustainable Development, it is timely to assess progress over the 10 years since its predecessor in Rio de Janeiro. Loss and degradation of remaining natural habitats has continued largely unabated. However, evidence has been accumulating that such systems generate marked economic benefits, which the available data suggest exceed those obtained from continued habitat conversion. We estimate that the overall benefit:cost ratio of an effective global program for the conservation of remaining wild nature is at least 100:1.
Meiotic Arrest in the Mouse Follicle Maintained by a G
s
Protein in the Oocyte
Authors: Mehlmann Lisa M. , Jones Teresa L. Z. , Jaffe Laurinda A.
Published: October 2002

The mammalian ovarian follicle consists of a multilayered complex of somatic cells that surround the oocyte. A signal from the follicle cells keeps the oocyte cell cycle arrested at prophase of meiosis I until luteinizing hormone from the pituitary acts on the follicle cells to release the arrest, causing meiosis to continue. Here we show that meiotic arrest can be released in mice by microinjecting the oocyte within the follicle with an antibody that inhibits the stimulatory heterotrimeric GTP–binding protein G
s
. This indicates that G
s
activity in the oocyte is required to maintain meiotic arrest within the ovarian follicle and suggests that the follicle may keep the cell cycle arrested by activating G
s
.
Subduction and Recycling of Nitrogen Along the Central American Margin
Authors: Fischer Tobias P. , Hilton David R. , Zimmer Mindy M. , Shaw Alison M. , Sharp Zachary D. , Walker James A.
Published: October 2002

We report N and He isotopic and relative abundance characteristics of volatiles emitted from two segments of the Central American volcanic arc. In Guatemala, δ
15
N values are positive (i.e., greater than air) and N
2
/He ratios are high (up to 25,000). In contrast, Costa Rican N
2
/He ratios are low (maximum 1483) and δ
15
N values are negative (minimum –3.0 per mil). The results identify shallow hemipelagic sediments, subducted into the Guatemalan mantle, as the transport medium for the heavy N. Mass balance arguments indicate that the subducted N is efficiently cycled to the atmosphere by arc volcanism. Therefore, the subduction zone acts as a “barrier” to input of sedimentary N to the deeper mantle.
Segregating Sister Genomes: The Molecular Biology of Chromosome Separation
Authors: Nasmyth Kim
Published: October 2002

During cell division, each daughter cell inherits one copy of every chromosome. Accurate transmission of chromosomes requires that the sister DNA molecules created during DNA replication are disentangled and then pulled to opposite poles of the cell before division. Defects in chromosome segregation produce cells that are aneuploid (containing an abnormal number of chromosomes)—a situation that can have dire consequences. Aneuploidy is a leading cause of spontaneous miscarriages in humans and is also a hallmark of many human cancer cells. Recent work with yeast,
Xenopus
, and other model systems has provided new information about the proteins that control chromosome segregation during cell division and how the activities of these proteins are coordinated with the cell cycle.
Marketing Drugs to Mend Minds
Authors: Meltzer Herbert Y.
Published: October 2002

The Creation of Psychopharmacology
. David Healy. Harvard University Press, Cambridge, MA, 2002. 479 pp. $39.95, £27.50, € 39.95. ISBN 0-674-00619-4

In this follow-up to his earlier
The An-tidepressant Era
, Healy offers a history of the discovery and development of antipsy-chotic drugs. He argues that financial as well as clinical pressures led to ever more aggressively marketed medications.
Genetic and Biochemical Characterization of CGB-1, an Ambler Class B Carbapenem-Hydrolyzing β-Lactamase from
Chryseobacterium gleum
Authors: Bellais Samuel , Naas Thierry , Nordmann Patrice
Published: October 2002

Chryseobacterium gleum
(previously included in the
Flavobacterium
IIb species) is a gram-negative aerobe that is a source of nosocomial infections. An Ambler class B β-lactamase gene was cloned and expressed in
Escherichia coli
from reference strain
C. gleum
CIP 103039 that had reduced susceptibility to expanded-spectrum cephalosporins and carbapenems. The purified β-lactamase, CGB-1, with a pI value of 8.6 and a determined relative molecular mass of ca. 26 kDa, hydrolyzed penicillins; narrow- and expanded-spectrum cephalosporins; and carbapenems. CGB-1 was a novel member of the molecular subclass B1 of metallo-enzymes. It had 83 and 42% amino acid identity with IND-1 from
Chryseobacterium indologenes
and BlaB from
C. meningosepticum
, respectively. Thus, in addition to the previously characterized clavulanic acid-inhibited extended-spectrum β-lactamase CGA-1 of Ambler class A,
C. gleum
produces a very likely chromosome-borne class B β-lactamase.
Isoniazid-Induced Transient High-Level Resistance in
Mycobacterium tuberculosis
Authors: Viveiros Miguel , Portugal Isabel , Bettencourt Rosário , Victor Thomas C. , Jordaan Annemarie M. , Leandro Clara , Ordway Diane , Amaral Leonard
Published: October 2002

An American Type Culture Collection reference strain and eight clinical strains of
Mycobacterium tuberculosis
, all of which were susceptible to isoniazid (INH) (mean MIC, 0.06 mg/liter) and negative for the Ser315Thr
katG
mutation, were left in their BACTEC 12B vials (for use with the BACTEC 460-TB method) containing 0.1 mg of INH per liter for periods of up to 28 days after the completion of the antibiotic susceptibility test. Each eventually grew to levels compatible with those of INH-resistant strains. Successive passages in INH-containing BACTEC 12B vials and onto solid media showed that the resistance noted above was maintained. Successive passages of these
M. tuberculosis
strains in which INH resistance had been induced into BACTEC 12B vials or solid media containing stepwise increases in INH concentrations eventually yielded organisms resistant to 20 mg of INH per liter. Transfer of cells in which INH resistance had been induced to drug-free medium followed by repeated passages in that medium eventually yielded organisms whose susceptibility to INH was identical to that of the original parent strains. The cycle of induced INH resistance could be repeated with these now INH-susceptible cells. The use of
M. tuberculosis
identification probes and IS
6110
-based restriction fragment length polymorphism analyses of cultures throughout the induction of INH resistance and the reversal of resistance in drug-free medium eliminated the possibility that the culture was contaminated or that the initial specimen had a mixed type of infection. Induced high-level resistance to INH (20 mg/liter) could be reduced 100-fold with a subinhibitory concentration of reserpine but not with verapamil. These results collectively suggest that high-level resistance to INH can be induced in INH-susceptible
M. tuberculosis
strains by the induction of a reserpine-sensitive efflux mechanism.
Samarangenin B from
Limonium sinense
Suppresses Herpes Simplex Virus Type 1 Replication in Vero Cells by Regulation of Viral Macromolecular Synthesis
Authors: Kuo Yuh-Chi , Lin Lie-Chwen , Tsai Wei-Jern , Chou Cheng-Jen , Kung Szu-Hao , Ho Yen-Hui
Published: October 2002

Inhibitory effects of ethanolic extracts from 10 Chinese herbs on herpes simplex virus type 1 (HSV-1) replication were investigated. By a bioassay-guided fractionation procedure, samarangenin B (Sam B) was isolated from
Limonium sinense
; Sam B significantly suppressed HSV-1 multiplication in Vero cells without apparent cytotoxicity. Time-of-addition experiments suggested that the inhibitory action of Sam B on HSV-1 replication was not due to the blocking of virus adsorption. In an attempt to further localize the point in the HSV-1 replication cycle where arrest occurred, a set of key regulatory events leading to viral multiplication was examined, including viral immediate-early (α), early (β), and late (γ) gene expression and DNA replication. Results indicated that levels of glycoprotein B (gB), gC, gD, gG, and infected-cell protein 5 (ICP5) expression and gB mRNA expression in Vero cells were impeded by Sam B. Data from PCR showed that replication of HSV-1 DNA in Vero cells was arrested by Sam B. Furthermore, Sam B decreased DNA polymerase, ICP0, and ICP4 gene expression in Vero cells. Results of an electrophoretic mobility shift assay demonstrated that Sam B interrupted the formation of an α-
trans
-induction factor/C1/Oct-1/GARAT multiprotein complex. The mechanisms of antiviral action of Sam B seem to be mediated, at least in part, by inhibiting HSV-1 α gene expression, including expression of the ICP0 and ICP4 genes, by blocking β transcripts such as DNA polymerase mRNA, and by arresting HSV-1 DNA synthesis and structural protein expression in Vero cells. These results show that Sam B is an antiviral agent against HSV-1 replication.
In Vitro and In Vivo Synergy of Fosmidomycin, a Novel Antimalarial Drug, with Clindamycin
Authors: Wiesner Jochen , Henschker Dajana , Hutchinson David B. , Beck Ewald , Jomaa Hassan
Published: October 2002

Fosmidomycin acts through inhibition of 1-deoxy-
d
-xylulose 5-phosphate (DOXP) reductoisomerase, a key enzyme of the nonmevalonate pathway of isoprenoid biosynthesis. It possesses potent antimalarial activity in vitro and in murine malaria. In a recent clinical study, fosmidomycin was effective and well tolerated in the treatment of patients with acute uncomplicated
Plasmodium falciparum
malaria but resulted in an unacceptably high rate of recrudescence. In order to identify a potential combination partner, the interaction of fosmidomycin with a number of antimalarial drugs in current use was investigated in a series of in vitro experiments. Synergy was observed between fosmidomycin and the lincosamides, lincomycin and clindamycin. The efficacy of a combination of fosmidomycin and clindamycin was subsequently demonstrated in the
Plasmodium vinckei
mouse model.