bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient evolution regimes in a multiscale dynamo model: Timescales of the reversal mechanism
Authors: Narteau C. , Le Mouël J. L.
Published: January 2005

In order to better understand the origin and nature of reversals of the Earth's magnetic field, we examine the reversal mechanism of a multiscale dynamo model. This model can be described as a cellular automaton with long‐range interaction. Different states correspond to different types of helical motions, and a hierarchical structure of length scales is used to mimic helicity transfers in fully developed turbulence. These multiscale helical motions and a differential rotation are the ingredients of a schematic αω dynamo. The model exhibits rich behavior, including long periods of stable magnetic polarity (i.e., chrons), sudden reversals, excursions, and secular variation. Three transient regimes of evolution emerge: (1) Chrons are initiated by an amplification mechanism, which involves spontaneous reorientation of large length scale circulation and an α‐quenching mechanism reinforcing the asymmetry of flow during runaway growth in magnetic field intensity. (2) During the chrons the injection of turbulence at small length scale slowly restores the symmetry of the system and leads to reversal. (3) During reversals the magnetic field does not remember its previous polarity, its intensity collapses, and spontaneous reorientation of large length scale circulation is more likely to occur (see regime 1). Reversal duration therefore corresponds to an upper value of the time constants for underlying turbulence in the absence of a magnetic field. We observe a constant excursion rate during chrons and a power law relationship between the reversal rate and the magnitude of helical forcing until a limit for dynamo action is reached. Extrapolated to the Earth's dipole field, this model predicts the duration of both chrons and reversals and sheds light on physical processes that may be responsible for their systematic occurrence.
Tropospheric ozone changes at unpolluted and semipolluted regions induced by stratospheric ozone changes
Authors: Isaksen I. S. A. , Zerefos C. , Kourtidis K. , Meleti C. , Dalsøren Stig B. , Sundet J. K. , Grini A. , Zanis P. , Balis D.
Published: January 2005

Model studies show that changes in photodissociation rates resulting from changes in ozone column densities induce changes in lower tropospheric ozone, which vary significantly with location and time of the year. The validity of the model results is tested against daily total ozone and ground level ozone at three selected stations (Samoa, Mauna Loa, and Hohenpeissenberg). Observational data for a period of more than 1 decade have been analyzed. Comparisons are made of model‐simulated distribution of ozone and its precursors (NOx and CO) at the three stations. Further comparisons are made of observed and model‐calculated sensitivity in surface ozone to reduction in ozone column densities. Calculations performed with a global‐scale chemical transport model (CTM) with extensive ozone chemistry reproduce well the observed levels and seasonal distribution of NOx, CO, and ozone at remote background stations (Samoa and Mauna Loa) and at stations in more polluted regions (Hohenpeissenberg). A chemical box model is used to demonstrate the chemical link between surface ozone changes and changes in total ozone for different NOx levels. Model studies and analysis of the observational data show that ground level ozone at the remote, low‐NOx stations of Mauna Loa and Samoa is correlated positively with total ozone, with an exception at Mauna Loa during winter months. A reduction in ozone column densities, which leads to enhanced photochemical activity, reduces ozone levels at ground level. The sensitivity of surface ozone to changes in total ozone is particularly large in the low‐NOx regime at Samoa. An anticorrelation between ground level ozone and total ozone is found at the Hohenpeissenberg station both in the observational data and in the model results during wintertime with high NOx levels. Enhanced photochemical activity leads to enhanced ozone production. There is, however, a disagreement between the observed and CTM‐modeled sensitivity in surface ozone to ozone column density during the summer months at Hohenpeissenberg. The strong anticorrelation found in the observations, giving increases in surface ozone at low ozone column densities, is not present in the CTM model studies. It is suggested that a correlation between low ozone column densities and stagnant high‐pressure systems is an important cause for the observed anticorrelation.
Changes in Cerebral Blood Flow and Cerebral Oxygen Metabolism during Neural Activation Measured by Positron Emission Tomography: Comparison with Blood Oxygenation Level-Dependent Contrast Measured by Functional Magnetic Resonance Imaging
Authors: Ito Hiroshi , Ibaraki Masanobu , Kanno Iwao , Fukuda Hiroshi , Miura Shuichi
Published: January 2005

The discrepancy between the increases in cerebral blood flow (CBF) and CMRO2 during neural activation causes an increase in venous blood oxygenation and, therefore, a decrease in paramagnetic deoxyhemoglobin concentration in venous blood. This can be detected by functional magnetic resonance imaging (fMRI) as blood oxygenation level-dependent (BOLD) contrast. In the present study, changes in the cerebral oxygen extraction fraction (OEF) that corresponds to the ratio of CMRO2 to CBF, and in the BOLD signal during neural activation, were measured by both positron emission tomography (PET) and fMRI in the same human subjects. C15O, 15O2, and H215O PET studies were performed in each subject at rest (baseline) and during performance of a right-hand motor task. Functional magnetic resonance imaging studies were then performed to measure the BOLD signal under the two conditions. During performance of the motor task, a significant increase in CBF and a significant decrease in OEF were observed in the left precentral gyrus, left superior frontal gyrus, right precentral gyrus, right cingulate gyrus, and right cerebellum. A significant positive correlation was observed between changes in the CBF and the BOLD signal, and a significant negative correlation was observed between changes in the OEF and the BOLD signal. This supports the assumption on which BOLD contrast studies during neural activation are based.
Multiconfiguration self-consistent-field theory based upon the fragment molecular orbital method
Authors: Fedorov Dmitri G. , Kitaura Kazuo
Published: January 2005

The fragment molecular orbital (FMO) method was combined with the multiconfiguration self-consistent-field (MCSCF) theory. One- and two-layer approaches were developed, the former involving all dimer MCSCF calculations and the latter limiting MCSCF calculations to a small part of the system. The accuracy of the two methods was tested using the six electrons in six orbitals complete active space type of MCSCF and singlet spin state for phenol+(H2O)n, n=16,32,64 (6-31G* and 6-311G* basis sets); α helices and β strands of phenylalanine-(alanine)n, n=4,8,16 (6-31G*). Both double-ζ and triple-ζ quality basis sets with polarization were found to have very similar accuracy. The error in the correlation energy was at most 0.000 88 a.u., the error in the gradient of the correlation energy was at most 6.×10−5 a.u./bohr and the error in the correlation correction to the dipole moment was at most 0.018 D. In addition, vertical singlet-triplet electron excitation energies were computed for phenol+(H2O)n, (n=16,32,64), 6-31G*, and the errors were found to be at most 0.02 eV. Approximately linear scaling was observed for the FMO-based MCSCF methods. As an example, an FMO-based MCSCF calculation with 1262 basis functions took 98 min on one 3.0 GHz Pentium4 node with 1 Gbyte RAM.
Determining the geometry of strongly hydrogen-bonded silanols in a layered hydrous silicate by solid-state nuclear magnetic resonance
Authors: Gardiennet Carole , Marica Florea , Fyfe Colin A. , Tekely Piotr
Published: January 2005

High-resolution solid-state NMR spectroscopy is exploited to obtain structural constraints involving strongly hydrogen-bonded silanols in octosilicate, a prominent member of the layered hydrous sodium silicates. Proton-silicon cross-polarization dynamics reveals that octosilicate contains two types of Q3 silicons present in hydrogen-bonded –Si–O–H⋯O–Si– and –Si–O−–type sites which can only be distinguished by their different abilities to cross polarize and the different mobilities of neighboring hydrous species. The theoretical analysis of the oscillating components of the polarization transfer buildup curves suggests that the model of heteronuclear pairs is an adequate description of the quantum spin system within hydrogen-bonded –Si–O–H⋯O–Si– fragments. We also show that dipolar modulated, slow speed magic-angle Si29 NMR spectrum provides unique geometric information on strongly hydrogen-bonded silanols. The dipolar modulated spinning sidebands contain all the information necessary to determine the internuclear Si⋯H distances as well as the magnitude and orientation of the principal elements of the Si29 chemical shielding tensor in the molecular frame. The data provide definite proof of the intralayer character of strongly hydrogen-bonded silanol groups in a bridging, albeit not symmetric, position between neighboring tetrahedra. The approach developed in this work may be useful to obtain structural information on related layered alkali metal silicates, silica gels as well as on other classes of microporous materials.
Photoelectron spectroscopy and ab initio study of the doubly antiaromatic B62− dianion in the LiB6− cluster
Authors: Alexandrova Anastassia N. , Boldyrev Alexander I. , Zhai Hua-Jin , Wang Lai-Sheng
Published: January 2005

A metal-boron mixed cluster LiB6− was produced and characterized by photoelectron spectroscopy and ab initio calculations. A number of electronic transitions were observed and used to compare with theoretical calculations. An extensive search for the global minimum of LiB6− was carried out via an ab initio genetic algorithm technique. The pyramidal C2v (1A1) molecule was found to be the most stable at all levels of theory. The nearest low-lying isomer was found to be a triplet C2 (3B) structure, 9.2 kcal/mol higher in energy. Comparison of calculated detachment transitions from LiB6− and the experimental photoelectron spectra confirmed the C2v pyramidal global minimum structure. Natural population calculation revealed that LiB6− is a charge-transfer complex, Li+B62−, in which Li+ and B62− interact in a primarily ionic manner. Analyses of the molecular orbitals and chemical bonding of B62− showed that the planar cluster is twofold (π- and σ-) antiaromatic, which can be viewed as the fusion of two aromatic B3− units.
Photoluminescence of mechanically polished ZnO
Authors: Hamby D. W. , Lucca D. A. , Klopfstein M. J.
Published: January 2005

The effects of mechanical polishing on the photoluminescence (PL) from each polar face of wurtzite-structure ZnO are presented. Differences observed for the 4.2K PL of a mechanically polished surface when compared to that of a chemomechanically polished surface include broadened bound-exciton peaks, hot-exciton luminescence, and a donor-acceptor pair peak at 3.2108eV. Analysis of this donor-acceptor pair peak results in estimated donor and acceptor ionization energies of 52±10 and 230±10meV, respectively, with a mean separation distance between pairs of approximately 3–4nm. The donors and acceptors are attributed to point defects introduced by dislocation motion during the polishing process and identified as octahedral Zn interstitials and Zn vacancies, respectively.
Cell parameter determination of a twisted-nematic liquid crystal display by single-wavelength polarimetry
Authors: Durán Vicente , Lancis Jesús , Tajahuerce Enrique , Jaroszewicz Zbigniew
Published: January 2005

Optical transmittance of a 90-twisted nematic liquid crystal cell inserted between crossed or parallel polarizers is neither sensitive to the molecular twist sense nor to the exchange between the extraordinary and the ordinary birefringence axis at the input face of the cell. In this article, the equivalence between a twisted-nematic liquid crystal cell and the combination of a retardation wave plate and a polarization rotator is fully exploited to understand the physical origin of these ambiguities. We determine, in a simple way, cell parameters by means of standard cell transmittance measurements when both crossed and parallel polarizers are rotated simultaneously. We show that this procedure, which is subjected to the aforementioned ambiguities, can be completed by additional polarimetric measurements. In particular, we demonstrate that the twist angle, twist sense, retardation, and the rubbing direction can be univocally determined by experimental measurement of the Stokes parameters of the light transmitted through the cell at one wavelength. Laboratory results corresponding to a commercial liquid crystal display panel are carried out.
Impurity doping effect on thermal stability of InGaN∕GaN multiple quantum-well structures
Authors: Kusakabe Kazuhide , Hara Tomoaki , Ohkawa Kazuhiro
Published: January 2005

Thermal stability of InGaN∕GaN multiple quantum-well (MQW) structures grown by metalorganic vapor phase epitaxy on (0001) sapphire substrates was investigated. Samples were annealed under atmospheric nitrogen ambient at 1000°C after growth. The thermal stability of MQW structures was estimated by high-resolution x-ray diffraction. It was found that thermal annealing degraded MQW periodicity in an undoped sample. This was due to the thermal diffusion of indium atoms via Ga vacancies in the GaN barrier region. It was also found that both Si doping and Mg doping improved the thermal stability of MQW structures. This mechanism was considered that Si and Mg, which were incorporated into column-III sites, prevented formation of the Ga vacancies. Thus, the thermal diffusion of indium atoms was suppressed. Room temperature photoluminescence (PL) from the Si-doped MQWs retained intense emission after annealing, while the undoped and Mg-doped MQWs showed degradation of PL intensities after annealing. It was, therefore, found that Si was a desirable dopant to promote the thermal stability of InGaN∕GaN MQWs.
Electron transport in In-rich InxGa1−xN films
Authors: Lin Shih-Kai , Wu Kun-Ta , Huang Chao-Ping , Liang C.-T. , Chang Y. H. , Chen Y. F. , Chang P. H. , Chen N. C. , Chang C. A. , Peng H. C. , Shih C. F. , Liu K. S. , Lin T. Y.
Published: January 2005

We have performed electrical transport measurements on metal-organic vapor phase epitaxy grown In-rich InxGa1−xN (x=1, 0.98, and 0.92) films. Within the experimental error, the electron density in InGaN films is temperature independent over a wide temperature range (4K⩽T⩽285K). Therefore, InxGa1−xN (0.92⩽x⩽1) films can be regarded as degenerate semiconductor systems. The experimental results demonstrate that electron transport in In-rich InxGa1−xN (x=1, 0.98, and 0.92) films is metalliclike. This is supported by the temperature dependence of the density, resistivity, and mobility which is similar to that of a metal. We suggest that over the whole measuring temperature range residue imperfection scattering limits the electron mobility in In-rich InxGa1−xN (x=1, 0.98, and 0.92) films.
Characteristics of moderate current vacuum discharge triggered by multipicosecond and nanosecond duration laser pulses
Authors: Moorti A. , Kumbhare S. R. , Naik P. A. , Gupta P. D. , Romanov I. V. , Korobkin Yu. V. , Rupasov A. A. , Shikanov A. S.
Published: January 2005

A comparative study of the characteristics of moderate-current (∼10kA), low-energy (⩽20J) vacuum discharge triggered by multipicosecond and nanosecond duration laser pulses is performed. Temporal profiles of the x-ray emission, discharge current, and anode voltage measured in vacuum discharge created between a planar titanium cathode and a conical point-tip anode are observed to be quite different for the two regimes of the laser pulse duration. While cathode plasma jet pinching is clearly observed in the discharge created by low-energy (∼5mJ), 27 ps full width at half-maximum (FWHM) laser pulses, a feeble pinching occurred for 4 ns (FWHM) laser pulses only above a threshold energy of ∼250mJ. In addition to the multiple K-shell x-ray pulses emitted from the titanium anode up to 100 ns, evidence of a much harder x-ray component (hν>100keV) is also seen in the discharge triggered by picosecond laser pulses.
Spectroscopic imaging diagnostics for burning plasma experiments
Authors: Stutman D. , Finkenthal M. , Suliman G. , Tritz K. , Delgado-Aparicio L. , Kaita R. , Johnson D. , Soukhanovskii V. , May M. J.
Published: January 2005

Spectroscopic imaging of plasma emission profiles from a few electron volts to tens of kilo-electron volts enables basic diagnostics in present day tokamaks. For the more difficult burning plasma conditions, light extraction and detection techniques, as well as instrument designs need to be investigated. As an alternative to light extraction with reflective optics, we discuss normal incidence, transmissive-diffractive optics (e.g., transmission gratings), which might withstand plasma exposure with less degradation of optical properties. Metallic multilayer reflectors are also of interest for light extraction. Although a shift of the diffraction peak might occur, instrument designs that accommodate such shifts are possible. As imaging detectors we consider “optical” arrays based on conversion of the short-wavelength light into visible light followed by transport of the visible signal with hollow lightguides. The proposed approaches to light extraction and detection could enable radiation resistant diagnostics.
Rotating cavity for high-field angle-dependent microwave spectroscopy of low-dimensional conductors and magnets
Authors: Takahashi Susumu , Hill Stephen
Published: January 2005

The cavity perturbation technique is an extremely powerful method for measuring the electrodynamic response of a material in the millimeter- and submillimeter spectral range (10GHz–1THz), particularly in the case of high-field/frequency magnetic resonance spectroscopy. However, the application of such techniques within the limited space of a high-field magnet presents significant technical challenges. We describe a 7.62mm×7.62mm (diameter×length) rotating cylindrical cavity which overcomes these problems. The cylinder is mounted transverse to the bore of the magnet, coupling is achieved through the sidewalls of the cavity, and the end plate is then rotated (by means of an external drive) instead of the body of the cavity itself. Therefore, rotation does not affect the cylindrical geometry, or the mechanical connections to the incoming waveguides. The TE011 mode frequency of the cavity is 51.863GHz, with the possibility to work on higher-order modes to frequencies of order 350GHz. Neither the quality factor (∼22000 for the fundamental mode) or the coupling to the cavity are significantly affected for full 360° of rotation. The rotation mechanism provides excellent angle resolution (<0.1°), and is compact enough to enable measurements in the high-field (up to 45T) magnets at the National High Magnetic Field Laboratory. Two-axis rotation capabilities are also possible in conjunction with split-pair magnet configurations. We present examples of angle-dependent measurements which illustrate the unique capabilities of this rotating cavity, including: high-field angle-dependent measurements of an unusual form of cyclotron resonance in anisotropic organic conductors; and angle-dependent high-frequency single-crystal electron paramagnetic resonance measurements in single-molecule magnets.
All-in-one static and dynamic nanostencil atomic force microscopy/scanning tunneling microscopy system
Authors: Zahl Percy , Bammerlin Martin , Meyer Gerhard , Schlittler Reto R.
Published: January 2005

The nanostencil is a tool for resistless lithography. It allows the direct patterning of complex nanometer-sized structures composed of a wide range of materials in an ultrahigh vacuum environment. This is combined with state-of-the-art scanning probe microscopy techniques (atomic force microscopy, scanning tunneling microscopy) and an electronic four-point probe. Moreover, all these capabilities are in situ and autoaligned in the field of view. The direct patterning is based on the shadow-mask technique and allows multimask processes in a static and dynamic manner.
A low-cost, high-performance, digital signal processor-based lock-in amplifier capable of measuring multiple frequency sweeps simultaneously
Authors: Sonnaillon Maximiliano Osvaldo , Bonetto Fabián Jose
Published: January 2005

A high-performance digital lock-in amplifier implemented in a low-cost digital signal processor (DSP) board is described. This lock in is capable of measuring simultaneously multiple frequencies that change in time as frequency sweeps (chirps). The used 32-bit DSP has enough computing power to generate N=3 simultaneous reference signals and accurately measure the N=3 responses, operating as three lock ins connected in parallel to a linear system. The lock in stores the measured values in memory until they are downloaded to the a personal computer (PC). The lock in works in stand-alone mode and can be programmed and configured through the PC serial port. Downsampling and multiple filter stages were used in order to obtain a sharp roll off and a long time constant in the filters. This makes measurements possible in presence of high-noise levels. Before each measurement, the lock in performs an autocalibration that measures the frequency response of analog output and input circuitry in order to compensate for the departure from ideal operation. Improvements from previous lock-in implementations allow measuring the frequency response of a system in a short time. Furthermore, the proposed implementation can measure how the frequency response changes with time, a characteristic that is very important in our biotechnological application. The number of simultaneous components that the lock in can generate and measure can be extended, without reprogramming, by only using other DSPs of the same family that are code compatible and work at higher clock frequencies.
Novel and Disparate Hydrogen-Bonding Associations in 13-Amino-6-hydroxy-13-methyl-1,4,8,11-tetraazacyclotetradecane Tetrahydrochloride Monohydrate
Authors: Harrowfield Jack M. , Kim Yang , Lee Young Hoon , Nealon Gareth L. , Skelton Brian W. , White Allan H.
Published: January 2005

The title compound crystallizes in the monoclinic space group Pn with two independent [LH4]Cl4·H2O formula units (L = 13-amino-6-hydroxy-13-methyl-1,4,8,11-tetraazacyclotetradecane) in the asymmetric unit. Despite pseudo-symmetry, these two units exhibit subtle and interesting differences in their hydrogen-bonded association by the interchange of the water molecule site with one of the chloride anions. Although a pentamine, L crystallizes as a tetrahydrochloride in which the tetracation has a conformation similar to that of tetraprotonated cyclam (1,4,8,11-tetraazacyclotetradecane), despite a different pattern of protonation sites. Difficulties in purification are perpetuated in the crystal, the minor isomeric component co-crystallizing in one of the cation sites.
5-Nitrosalicylic Acid and its Proton-Transfer Compounds with Aliphatic Lewis Bases
Authors: Smith Graham , Hartono Andy W. , Wermuth Urs D. , Healy Peter C. , White Jonathan M. , Rae A. David
Published: January 2005

The crystal structures of the proton-transfer compounds of 5-nitrosalicylic acid (5-nsa) with morpholine (morph), hexamethylenetetramine (hmt), and ethylenediamine (en) have been determined and their solid-state packing structures described. The compounds are [(morph)+(5-nsa)–] 1, [(hmt)+(5-nsa)–·H2O] 2, and [(en)2+2(5-nsa)–·H2O] 3. In all compounds, protonation of the hetero-nitrogen of the Lewis base occurs. With 1, the 5-nsa anions and the morpholine cations lie, respectively, in or across crystallographic mirror planes and are linked within the planes by hydrogen-bonding interactions through the aminium group and the carboxylic and phenolic oxygens of the anionic 5-nsa species giving a two-dimensional sheet polymer. Compound 2 is an unusual structure with the planar 5-nsa anions lying within pseudo mirror planes and cyclically linked by duplex water bridges through a single carboxylate oxygen into centrosymmetric dimers. The hmt cation molecules are disordered across the pseudo mirror and are strongly linked by N+–H···O hydrogen bonds only to the water molecules with peripheral weak hmt C–H···O hydrogen bonds extending the dimer within and between the dimer planes. Compound 3 is a network polymer comprised of the 5-nsa anions, the en dianions, and the water molecule in an extensive hydrogen-bonded structure.
Olefin Metathesis: Catalyst Development, Microwave Catalysis, and Domino Applications
Authors: Aitken Steven G. , Abell Andrew D.
Published: January 2005

Olefin metathesis, a process by which alkylidene groups on alkenes are exchanged, is reviewed with reference to the historical development of functional catalysts and microwave catalysis. The advent of new catalysts and improved reaction conditions has paved the way for the development of new and versatile domino processes that combine either different metathesis events or a key metathesis reaction with another reaction in a particularly atom economic and ‘green’ sense. We review this area as a convenient route to some otherwise difficult to prepare systems.
Secondary Metabolites from the Marine Alga Caulerpa brownii (Chlorophyta)
Authors: Handley Jackie T. , Blackman Adrian J.
Published: January 2005

The green seaweed Caulerpa brownii (Chlorophyta, Caulerpaceae) occurs in Tasmania in two morphological forms (branched and unbranched) and each form has a different profile of diterpenoid secondary metabolites. Unbranched specimens gave rise to the novel secondary metabolites 11, 13, 14, 17, and 18, the secondary metabolite 8 that has been isolated for the first time as a natural product, as well as the known compounds 1 and 3–7. Branched specimens of C. brownii yielded the novel terpenoid esters 21 and the known compounds 1 and 2.
Whole-Cell Biotransformation of m-Ethyltoluene into 1S,6R-5-Ethyl-1,6-dihydroxycyclohexa-2,4-diene-1-carboxylic Acid as an Approach to the C-Ring of the Binary Indole - Indoline Alkaloid Vinblastine
Authors: Banwell Martin G. , Edwards Alison J. , Lupton David W. , Whited Gregg
Published: January 2005

The title compound 3, a potential building block for the construction of analogues of the clinically important anti-cancer agent vinblastine (1), has been prepared in an efficient manner through a whole-cell biotransformation of m-ethyltoluene (4) using the microorganism Pseudomonas putida BGXM1 which expresses the enzyme toluate dioxygenase (TADO). Metabolite 3 was readily converted into derivatives 5–8 using conventional chemical techniques and the structure, including absolute stereochemistry, of the last of these was established by single-crystal X-ray analysis.
Recent biological invasion may hasten invasional meltdown by accelerating historical introductions
Authors: Grosholz Edwin D.
Published: January 2005

Biological invasions are rapidly producing planet-wide changes in biodiversity and ecosystem function. In coastal waters of the U.S., >500 invaders have become established, and new introductions continue at an increasing rate. Although most species have little impact on native communities, some initially benign introductions may occasionally turn into damaging invasions, although such introductions are rarely documented. Here, I demonstrate that a recently introduced crab has resulted in the rapid spread and increase of an introduced bivalve that had been rare in the system for nearly 50 yr. This increase has occurred through the positive indirect effects of predation by the introduced crab on native bivalves. I used field and laboratory experiments to show that the mechanism is size-specific predation interacting with the different reproductive life histories of the native (protandrous hermaphrodite) and the introduced (dioecious) bivalves. These results suggest that positive interactions among the hundreds of introduced species that are accumulating in coastal systems could result in the rapid transformation of previously benign introductions into aggressively expanding invasions. Even if future management efforts reduce the number of new introductions, given the large number of species already present, there is a high potential for positive interactions to produce many future management problems. Given that invasional meltdown is now being documented in natural systems, I suggest that coastal systems may be closer to this threshold than currently believed.
Drosophila
peptidoglycan recognition protein LC (PGRP-LC) acts as a signal-transducing innate immune receptor
Authors: Choe Kwang-Min , Lee Hyangkyu , Anderson Kathryn V.
Published: January 2005

Drosophila
peptidoglycan recognition protein LC (PGRP-LC), a transmembrane protein required for the response to bacterial infection, acts at the top of a cytoplasmic signaling cascade that requires the death-domain protein Imd and an IκB kinase to activate Relish, an NF-κB family member. It is not clear how binding of peptidoglycan to the extracellular domain of PGRP-LC activates intracellular signaling because its cytoplasmic domain has no homology to characterized proteins. Here, we demonstrate that PGRP-LC binds Imd and that its cytoplasmic domain is critical for its activity, suggesting that PGRP-LC acts as a signal-transducing receptor. The PGRP-LC cytoplasmic domain is also essential for the formation of dimers, and results suggest that dimerization may be required for receptor activation. The PGRP-LC cytoplasmic domain can mediate formation of heterodimers between different PGRP-LC isoforms, thereby potentially expanding the diversity of ligands that can be recognized by the receptor.
A form of DISC1 enriched in nucleus: Altered subcellular distribution in orbitofrontal cortex in psychosis and substance/alcohol abuse
Authors: Sawamura Naoya , Sawamura-Yamamoto Takako , Ozeki Yuji , Ross Christopher A. , Sawa Akira
Published: January 2005

Disrupted-In-Schizophrenia 1(DISC1) was identified as the sole gene whose ORF is truncated and cosegregates with major mental illnesses in a Scottish family.DISC1has also been suggested, by association and linkage studies, to be a susceptibility gene for schizophrenia (SZ) in independent populations. However, no analysis of DISC1 protein in human brains, especially those of patients with SZ, has yet been conducted. Here we performed a biochemical analysis of DISC1 protein in a well characterized set of autopsied brains, including brains of patients with SZ, bipolar disorder, and major depression (MD), as well as normal control brains. We identified an isoform of DISC1 by using MS and demonstrated that it is enriched in the nucleus of HeLa cells. In the orbitofrontal cortex, the subcellular distribution of this DISC1 isoform, assessed by the nuclear to cytoplasmic ratio in the immunoreactivity of the isoform, is significantly changed in brains from patients with SZ and MD. This altered distribution is also observed in those subjects with substance and alcohol abuse. The changes in MD brains are significantly influenced by substance/alcohol abuse as well as postmortem interval; however, the alteration in SZ brains is free from brain-associated confounding factors, although an interaction with substance/alcohol abuse cannot be completely ruled out. These results suggest that DISC1 may be implicated in psychiatric conditions in other populations than the unique Scottish family.
Expression of a viral polymerase-bound host factor turns human cell lines permissive to a plant- and insect-infecting virus
Authors: de Medeiros Ricardo B. , Figueiredo Juliana , Resende Renato de O. , De Avila Antonio C.
Published: January 2005

Tospoviruses are the only plant-infecting members of the
Bunyaviridae
family of ambisense ssRNA viruses. Tomato spotted wilt tospovirus (TSWV), the type-member, also causes mild infection on its main insect vector,
Frankliniella occidentalis
. Herein, we identified an
F. occidentalis
putative transcription factor (FoTF) that binds to the TSWV RNA-dependent RNA polymerase and to viral RNA. Using
in vitro
RNA synthesis assays, we show that addition of purified FoTF improves viral replication, but not transcription. Expression of FoTF deletion mutants, unable to bind the RNA-dependent RNA polymerase or viral RNA, blocks TSWV replication in
F. occidentalis
cells. Finally, expression of FoTF wild-type turns human cell lines permissive to TSWV replication. These data indicate that FoTF is a host factor required for TSWV replication
in vitro
and
in vivo
, provide an experimental system that could be used to compare molecular defense mechanisms in plant, insect, and human cells against the same pathogen (TSWV), and could lead to a better understanding of evolutionary processes of ambisense RNA viruses.
Pathogenic hantaviruses bind plexin–semaphorin–integrin domains present at the apex of inactive, bent αvβ3 integrin conformers
Authors: Raymond Tracy , Gorbunova Elena , Gavrilovskaya Irina N. , Mackow Erich R.
Published: January 2005

The αvβ3 integrins are linked to human bleeding disorders, and pathogenic hantaviruses regulate the function of αvβ3 integrins and cause acute vascular diseases. αvβ3 integrins are present in either extended (active) or dramatically bent (inactive) structures, and interconversion of αvβ3 conformers dynamically regulates integrin functions. Here, we show that hantaviruses bind human αvβ3 integrins and that binding maps to the plexin–semaphorin–integrin (PSI) domain present at the apex of inactive, bent, αvβ3-integrin structures. Pathogenic hantaviruses [New York-1 virus (NY-1V) and Hantaan virus (HTNV)] bind immobilized β3 polypeptides containing the PSI domain, and human (but not murine) β3 polypeptides inhibit hantavirus infectivity. Substitution of human β3 residues 1–39 for murine β3 residues directed pathogenic hantavirus infection of nonpermissive CHO cells expressing chimeric αvβ3 receptors. Mutation of murine β3 Asn-39 to Asp-39 present in human β3 homologues (N39D) permitted hantavirus infection of cells and specified PSI domain residue interactions with pathogenic hantaviruses. In addition, cell-surface expression of αvβ3 locked in an inactive bent conformation conferred hantavirus infectivity of CHO cells. Our findings indicate that hantaviruses bind to a unique domain exposed on inactive integrins and, together with prior findings, suggest that this interaction restricts αvβ3 functions that regulate vascular permeability. Our findings suggest mechanisms for viruses to direct hemorrhagic or vascular diseases and provide a distinct target for modulating αvβ3-integrin functions.
Gene delivery of human apolipoprotein E alters brain Aβ burden in a mouse model of Alzheimer's disease
Authors: Dodart Jean-Cosme , Marr Robert A. , Koistinaho Milla , Gregersen Beth M. , Malkani Seema , Verma Inder M. , Paul Steven M.
Published: January 2005

Apolipoprotein E (apoE) alleles are important genetic risk factors for Alzheimer's disease (AD), with the ε4 allele increasing and the ε2 allele decreasing risk for developing AD. ApoE has been shown to influence brain amyloid-β peptide (Aβ) and amyloid burden, both in humans and in transgenic mice. Here we show that direct intracerebral administration of lentiviral vectors expressing the three common human apoE isoforms differentially alters hippocampal Aβ and amyloid burden in the PDAPP mouse model of AD. Expression of apoE4 in the absence of mouse apoE increases hippocampal Aβ1–42levels and amyloid burden. By contrast, expression of apoE2, even in the presence of mouse apoE, markedly reduces hippocampal Aβ burden. Our data demonstrate rapid apoE isoform-dependent effects on brain Aβ burden in a mouse model of AD. Gene delivery of apoE2 may prevent or reduce brain Aβ burden and the subsequent development of neuritic plaques.
The N-terminal to C-terminal motif in protein folding and function
Authors: Krishna Mallela M. G. , Englander S. Walter
Published: January 2005

Essentially all proteins known to fold kinetically in a two-state manner have their N- and C-terminal secondary structural elements in contact, and the terminal elements often dock as part of the experimentally measurable initial folding step. Conversely, all N–C no-contact proteins studied so far fold by non-two-state kinetics. By comparison, about half of the single domain proteins in the Protein Data Bank have their N- and C-terminal elements in contact, more than expected on a random probability basis but not nearly enough to account for the bias in protein folding. Possible reasons for this bias relate to the mechanisms for initial protein folding, native state stability, and final turnover.
Glutamate regulation of DARPP-32 phosphorylation in neostriatal neurons involves activation of multiple signaling cascades
Authors: Nishi Akinori , Watanabe Yasuo , Higashi Hideho , Tanaka Masatoshi , Nairn Angus C. , Greengard Paul
Published: January 2005

Dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) plays a central role in medium spiny neurons in the neostriatum in the integration of various neurotransmitter signaling pathways. In its Thr-34-phosphorylated form, it acts as a potent protein phosphatase-1 inhibitor, and, in its Thr-75-phosphorylated form, it acts as a cAMP-dependent kinase inhibitor. Here, we investigated glutamate-dependent signaling cascades in mouse neostriatal slices by analyzing the phosphorylation of DARPP-32 at Thr-34 and Thr-75. Treatment with glutamate (5 mM) caused a complex change in DARPP-32 Thr-34 phosphorylation. An initial rapid increase in Thr-34 phosphorylation was NMDA/α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/metabotropic glutamate-5 receptor-dependent and was mediated through activation of a neuronal nitric oxide synthase/nitric oxide/cGMP/cGMP-dependent kinase signaling cascade. A subsequent decrease in phosphorylation was attributable to activation of an NMDA/AMPA receptor/Ca
2+
/protein phosphatase-2B signaling cascade. This decrease was followed by rephosphorylation via a pathway involving metabotropic glutamate-5 receptor/phospholipase C and extracellular receptor kinase signaling cascade. Treatment with glutamate initially decreased Thr-75 phosphorylation through activation of NMDA/AMPA receptor/Ca
2+
/protein phosphatase-2A signaling. Thereafter, glutamate slowly increased Thr-75 phosphorylation through activation of metabotropic glutamate-1 receptor/phospholipase C signaling. Our analysis of DARPP-32 phosphorylation in the neostriatum revealed that glutamate activates at least five different signaling cascades with different time dependencies, resulting in complex regulation of protein kinase and protein phosphatase activities.
Mesoscopic self-organization of a self-assembled supramolecular rectangle on highly oriented pyrolytic graphite and Au(111) surfaces
Authors: Gong Jian-Ru , Wan Li-Jun , Yuan Qun-Hui , Bai Chun-Li , Jude Hershel , Stang Peter J.
Published: January 2005

A self-assembled supramolecular metallacyclic rectangle was investigated with scanning tunneling microscopy on highly oriented pyrolytic graphite and Au(111) surfaces. The rectangles spontaneously adsorb on both surfaces and self-organize into well ordered adlayers. On highly oriented pyrolytic graphite, the long edge of the rectangle stands on the surface, forming a 2D molecular network. In contrast, the face of the rectangle lays flat on the Au(111) surface, forming linear chains. The structures and intramolecular features obtained through high-resolution scanning tunneling microscopy imaging are discussed.
Anticipating the three-dimensional consequences of eye movements
Authors: Wexler Mark
Published: January 2005

Rapid eye movements called saccades give rise to sudden, enormous changes in optic information arriving at the eye; how the world nonetheless appears stable is known as the problem of spatial constancy. One consequence of saccades is that the directions of all visible points shift uniformly; directional or 2D constancy, the fact that we do not perceive this change, has received extensive study for over a century. The problems raised by 3D consequences of saccades, on the other hand, have been neglected. When the eye rotates in space, the 3D orientation of all stationary surfaces undergoes an equal-and-opposite rotation with respect to the eye. When presented with a an optic simulation of a saccade but with the eyes still, observers readily perceive this depth rotation of surfaces; when simultaneously performing the corresponding saccade, the 3D orientations of surfaces are perceived as stable, a phenomenon I propose calling 3D spatial constancy. In experiments presented here, observers viewed ambiguous 3D rotations immediately before, during, or after a saccade. The results show that before the eyes begin to move the brain anticipates the 3D consequences of saccades, preferring to perceive the rotation opposite to the impending eye movement. Further, the anticipation is absent when observers fixate while experiencing optically simulated saccades, and therefore must be evoked by extraretinal signals. Such anticipation could provide a mechanism for 3D spatial constancy and transsaccadic integration of depth information.
α-Lytic protease can exist in two separately stable conformations with different His
57
mobilities and catalytic activities
Authors: Haddad Kristin Coffman , Sudmeier James L. , Bachovchin Daniel A. , Bachovchin William W.
Published: January 2005

α-Lytic protease is a bacterial serine protease widely studied as a model system of enzyme catalysis. Here we report that lyophilization induces a structural change in the enzyme that is not reversed by redissolution in water. The structural change reduces the mobility of the active-site histidine residue and the catalytic activity of the enzyme. The application of mild pressure to solutions of the altered enzyme reverses the lyophilization-induced structural change and restores the mobility of the histidine residue and the enzyme's catalytic activity. This effect of lyophilization permits a unique opportunity for investigating the relationship between histidine ring dynamics and catalytic activity. The results demonstrate that His
57
in resting enzymes is more mobile than previously thought, especially when protonated. The histidine motion and its correlation to enzyme activity lend support to the reaction-driven ring flip hypothesis.
Loss of perivascular aquaporin 4 may underlie deficient water and K
+
homeostasis in the human epileptogenic hippocampus
Authors: Eid Tore , Lee Tih-Shih W. , Thomas Marion J. , Amiry-Moghaddam Mahmood , Bjørnsen Lars P. , Spencer Dennis D. , Agre Peter , Ottersen Ole P. , de Lanerolle Nihal C.
Published: January 2005

An abnormal accumulation of extracellular K
+
in the brain has been implicated in the generation of seizures in patients with mesial temporal lobe epilepsy (MTLE) and hippocampal sclerosis. Experimental studies have shown that clearance of extracellular K
+
is compromised by removal of the perivascular pool of the water channel aquaporin 4 (AQP4), suggesting that an efficient clearance of K
+
depends on a concomitant water flux through astrocyte membranes. Therefore, we hypothesized that loss of perivascular AQP4 might be involved in the pathogenesis of MTLE. Whereas Western blot analysis showed an overall increase in AQP4 levels in MTLE compared with non-MTLE hippocampi, quantitative ImmunoGold electron microscopy revealed that the density of AQP4 along the perivascular membrane domain of astrocytes was reduced by 44% in area CA1 of MTLE vs. non-MTLE hippocampi. There was no difference in the density of AQP4 on the astrocyte membrane facing the neuropil. Because anchoring of AQP4 to the perivascular astrocyte endfoot membrane depends on the dystrophin complex, the localization of the 71-kDa brain-specific isoform of dystrophin was assessed by immunohistochemistry. In non-MTLE hippocampus, dystrophin was preferentially localized near blood vessels. However, in the MTLE hippocampus, the perivascular dystrophin was absent in sclerotic areas, suggesting that the loss of perivascular AQP4 is secondary to a disruption of the dystrophin complex. We postulate that the loss of perivascular AQP4 in MTLE is likely to result in a perturbed flux of water through astrocytes leading to an impaired buffering of extracellular K
+
and an increased propensity for seizures.
Natural-scene geometry predicts the perception of angles and line orientation
Authors: Howe Catherine Q. , Purves Dale
Published: January 2005

Visual stimuli that entail the intersection of two or more straight lines elicit a variety of well known perceptual anomalies. Preeminent among these anomalies are the systematic overestimation of acute angles, the underestimation of obtuse angles, and the misperceptions of line orientation exemplified in the classical tilt, Zöllner, and Hering illusions. Here we show that the probability distributions of the possible real-world sources of projected lines and angles derived from a range-image database of natural scenes accurately predict each of these perceptual peculiarities. These findings imply that the perception of angles and oriented lines is determined by the statistical relationship between geometrical stimuli and their physical sources in typical visual environments.
Clonal expansion of hepatocytes during chronic woodchuck hepatitis virus infection
Authors: Mason William S. , Jilbert Allison R. , Summers Jesse
Published: January 2005

Chronic hepadnavirus infections cause liver damage with ongoing death and regeneration of hepatocytes. In the present study we set out to quantify the extent of liver turnover by measuring the clonal proliferation of hepatocytes by using integrated viral DNA as a genetic marker for individual hepatocyte lineages. Liver tissue from woodchucks with chronic woodchuck hepatitis virus (WHV) infection was assayed for randomly integrated viral DNA by using inverse PCR. Serial endpoint dilution of viral–cell junction fragments into 96-well plates, followed by nested PCR and DNA sequencing, was used to determine the copy number of specific viral cell junctions as a measure of the clonal distribution of infected cell subpopulations. The results indicated that the livers contained a minimum of 100,000 clones of >1,000 cells containing integrated DNA, representing at least 0.2% of the hepatocyte population of the liver. Because cells with integrated WHV DNA comprised only 1–2% of total liver cells, it is likely that the total number of clones far exceeds this estimate, with as much as one-half of the liver derived from high copy clones of >1,000 cells. It may be inferred that these clones have a strong selective growth or survival advantage. The results provide evidence for a large amount of hepatocyte proliferation and selection having occurred during the period of chronic WHV infection (≈1.5 years) in these animals.