bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of endogenous mRNA levels on co‐suppression in tomato
Authors: Han Yuanhuai , Griffiths Allen , Li Hongying , Grierson Don
Published: March 2004

Introduction of truncated polygalacturonase (PG) transgenes into tomato plants caused the production of small interfering RNAs (siRNAs) and co‐suppression of both the endogenous and PG transgenes in ripening fruits by post‐transcriptional gene silencing. In order to test the possible effect on co‐suppression of the endogenous PG mRNA level, we transferred the PG transgenes from a PG‐silenced line (wild type background) by crossing to two ripening regulatory mutants with reduced PG: Never‐ripe (Nr, ∼10% endogenous PG mRNA compared to wild type) and ripening‐inhibitor (rin, ∼1% endogenous PG mRNA) and to wild type (as a control). The PG transgenes caused strong co‐suppression of the transgenes and the endogenous PG gene in cells with high PG mRNA background (wild type) and silencing appeared to be linked with higher transgene copy number and/or a particular transgene locus. In cells with low endogenous PG mRNA accumulation (Nr), the endogenous PG gene was preferentially suppressed compared to the transgenes, whose expression was not reduced significantly. The expression of the transgenes was also not reduced in the very low PG background (rin), in which endogenous PG was barely detectable. In all the analysed lines with all three PG background levels, siRNAs accumulated in leaves and green fruits, in which the endogenous PG gene is not transcribed. The relatively abundant production of siRNAs in most of the lines was linked with a particular transgene insert. These results suggest that a certain threshold level of endogenous PG mRNA is required for the co‐suppression of the truncated PG transgenes and the endogenous PG gene or for extensive silencing of the transgenes.
Insights into the structure of human cytomegalovirus large terminase subunit pUL56
Authors: Savva Christos G.W , Holzenburg Andreas , Bogner Elke
Published: March 2004

Terminases are a class of proteins which catalyze the generation of unit‐length genomes during DNA packaging. These essential proteins are conserved throughout the herpesviruses and many double‐stranded DNA bacteriophages. We have determined the structure of the large terminase subunit pUL56 of human cytomegalovirus, a highly pathogenic virus, to 2.6 nm resolution. Image analysis of purified pUL56 suggests that the molecule exists as a dimer formed by the association of two ring‐like structures positioned on top of each other and connected by a pronounced density on one side. The 3D reconstruction of pUL56 provides first structural insights into the active protein.
Interaction of actin and its 11‐amino acid C‐terminal peptide as cofactors with the adenovirus proteinase
Authors: Brown Mark T , Mangel Walter F
Published: March 2004

Actin bound to the adenovirus proteinase (AVP) with a lower equilibrium dissociation constant, 4.2 nM, than those exhibited by two viral, nuclear cofactors for AVP, the 11‐amino acid peptide pVIc and the viral DNA. The k
cat/K
m ratio for substrate hydrolysis by AVP increased 150 000‐fold in the presence of actin. The 11‐amino acid residue peptide corresponding to the C‐terminus of actin, which is highly homologous to pVIc, bound to AVP and stimulated its activity in the presence of DNA. As a cellular cofactor for AVP, AVP(actin) complexes may facilitate the cleavage of cytoskeletal proteins, preparing the infected cell for lysis and release of nascent virions.
On climatological mass, heat, and salt transports through the Barents Sea and Fram Strait from a pan‐Arctic coupled ice‐ocean model simulation
Authors: Maslowski Wieslaw , Marble Douglas , Walczowski Waldemar , Schauer Ursula , Clement Jaclyn L. , Semtner Albert J.
Published: March 2004

The northward flow of Atlantic Water via the Barents Sea and Fram Strait is modeled, and climatological volume, heat, and salt fluxes into the Arctic Ocean are investigated. We argue that understanding of climate change in the region requires the knowledge of the mean circulation before its variability can be determined. Since estimates of long‐term mean fluxes in the region are not available from observations, we present a modeling approach to quantify the climatological circulation and northward transports from the Norwegian Sea into the Arctic Ocean. A coupled ice‐ocean model of the pan‐Arctic region is configured at a 1/12° and 45‐level grid and is integrated for 7 decades using a combination of daily‐averaged 1979–2001 European Centre for Medium‐Range Weather Forecasts data. Simulated water mass characteristics are compared with climatological atlas and selected observational data. The separation of the Norwegian Atlantic Current into Barents Sea and Fram Strait branches and their relative contributions to the total mass and property input into the Arctic Ocean are quantified. We emphasize the Barents Sea because fewer direct measurements of transports exist there and because water masses are significantly altered along this path by the seasonal ice melt/formation and the freshwater inputs. Under the given atmospheric forcing the Barents Sea outflow is shown to significantly contribute to the boundary flow continuing along the slopes of the Arctic Ocean. On the basis of model results, we argue that the contribution of the Barents Sea branch of Atlantic Water into the Arctic Ocean is equally, if not more, important than the Fram Strait branch.
Dust‐acoustic Mach cones in magnetized electron‐dust plasmas of Saturn
Authors: Mamun A. A. , Shukla P. K.
Published: March 2004

We discuss the possibility of the Mach cone formation involving the modified dust‐acoustic waves in a dusty magnetoplasma composed of electrons and positively charged dust grains. It is shown that the modified dust‐acoustic waves, whose wavelength is of the order of (or shorter than) the electron gyroradius, are one of the viable candidates for the formation of Mach cones in Saturn's dusty rings.
On the regulation of minimum mid‐tropospheric temperatures in the Arctic
Authors: Tsukernik M. , Chase T. N. , Serreze M. C. , Barry R. G. , Pielke R. , Herman B. , Zeng X.
Published: March 2004

Observations indicate a minimum mid‐tropospheric Arctic winter temperature of about −45°C at 500 hPa. This minimum temperature coincides with that predicted for moist adiabatic ascent over a sea surface near its salinity‐adjusted freezing point. NCAR/NCEP Reanalysis data show that convective heating maxima averaged over the 50–70°N latitude band coincide both in longitude and altitude with total horizontal energy flux maxima entering the Arctic, indicating the significance of convection over open water on the winter Arctic energy budget. NCAR CCM single column model experiments simulating convective warming of a cold airmass moving over open water and radiative cooling as it moves again over cold land/sea ice support the hypothesis that the −45°C threshold can be maintained for 10–14 days after convective warming occurs. We speculate on the implications of this regulatory mechanism on surface temperatures.
Explosion dynamics of pyroclastic eruptions at Santiaguito Volcano
Authors: Johnson Jeffrey B. , Harris Andrew J. L. , Sahetapy‐Engel Steve T. M. , Wolf Rudiger , Rose William I.
Published: March 2004

In Jan. 2003 we monitored explosions at Santiaguito Volcano (Guatemala) with thermal, infrasonic, and seismic sensors. Thermal data from 2 infrared thermometers allowed computation of plume rise speeds, which ranged from 8 to 20 m/s. Rise rates correlated with cumulative thermal radiance, indicating that faster rising plumes correspond to explosions with greater thermal flux. The relationship between rise speeds and elastic energy is less clear. Seismic radiation may not scale well with thermal output and/or rise speed because some of the thermal component may be associated with passive degassing, which does not induce significant seismicity. But non‐impulsive gas release is still able to produce a high thermal flux, which is the primary control on buoyant rise speed.
Development of slender transport pathways in unsaturated fractured rock: Simulation with modified invasion percolation
Authors: Glass Robert J. , Nicholl Michael J. , Rajaram Harihar , Andre Benjamin
Published: March 2004

Slender transport pathways have been found in laboratory and field experiments within unsaturated fractured rock. Here we consider the simulation of such structures with a Modified form of Invasion Percolation (MIP). Results show that slender pathways form in fracture networks for a wide range of expected conditions, can be maintained when subsequent matrix imbibition is imposed, and may arise even in the context of primarily matrix flow due to the action of fractures as barriers to inter‐matrix block transport.
Water in the mantle: Results from electrical conductivity beneath the French Alps
Authors: Tarits P. , Hautot S. , Perrier F.
Published: March 2004

A deep magnetotelluric sounding in the French Alps provided a vertical electrical conductivity profile between ∼200–1000 km. Two prominent features are observed. First, the conductivity in the depth range 400–800 km is smaller than the conductivity of a pyrolite mantle obtained from laboratory results for a normal geotherm. Second, the data do not require the conductivity to change throughout the transition zone (410–660 km). In this part of the mantle, a temperature of 350–450 C less than normal explains the magnetotelluric conductivity profile. At 200–400 km, our model favors a cold mantle with 1000–1500 ppm of water dissolved in olivine. If correct, this model suggests that the subducted slab is dehydrated before reaching the transition zone.
Analysis of permeability scaling within single boreholes
Authors: Illman Walter A.
Published: March 2004

A pronounced permeability (k) scale effect has been previously observed through the analyses of single‐and cross‐hole pneumatic injection tests in unsaturated fractured tuff at the Apache Leap Research Site (ALRS) [Illman and Neuman, 2001, 2003; Vesselinov et al., 2001a, 2001b]. Here, we investigate whether such an effect is seen at the ALRS when one examines k data collected at multiple measurement scales within a single borehole. Results from single‐hole tests in 3 of 4 boreholes show that k increases with scale. However, this increase is considerably smaller than what has been previously surmised at the site. Data analysis reveals that flow is predominantly two‐dimensional (2D) for the single‐hole tests examined, and upscaling can be accomplished best by calculating a weighted arithmetic mean of individual measurements. The suppression of k scale effect within a single borehole is due to limited fracture connectivity near the injection interval which manifests as 2D flow. In contrast, flow during a cross‐hole test takes place through a highly connective fracture network which manifests as three‐dimensional (3D) flow.
Dayside flow bursts in the Earth's outer magnetosphere
Authors: Chen S.‐H. , Moore T. E.
Published: March 2004

Observations from the Polar/Thermal Ion Dynamics Experiment indicate the presence of cold magnetospheric/ionospheric H+, He+, and a trace of O+ in the vicinity of the subsolar magnetopause during intervals of moderate geomagnetic activity (Kp ∼ 4). These cold ions were accelerated to a perpendicular speed (ΔV⊥B) of the order of 100 km s−1 or 0.3 MA outward, relative to the magnetopause boundary oscillations. The accelerated flows produced ∼4 mV m−1 in convection electric field and carried ∼1–100 ions cm−3 in number density or ∼0.1–5 × 108 ions cm−2 s−1 in particle flux or 4 × 1025–2 × 1027 ions s−1 in transfer rate (assuming sunward convecting flux tube with latitudinal cross‐section of 1 RE in width and 10 RE in length along magnetopause). This rate of plasma transfer from inside the magnetopause is comparable with that entering the LLBL with the same incident cross section on the magnetopause from the solar wind influx. The occurrence of these flow burst events is accompanied by changes in the local magnetic field orientation, departing from nominal magnetospheric magnetic field, and is sensitive to the variation in the IMF clock angle. We suggest that the magnetospheric/ionospheric ions contribute plasma of dynamical significance to physical processes such as magnetic reconnection, for the cases presented in this study at the subsolar magnetopause.
Numerical simulations of the mantle lithosphere delamination
Authors: Morency C. , Doin M.‐P.
Published: March 2004

Sudden uplift, extension, and increased igneous activity are often explained by rapid mechanical thinning of the lithospheric mantle. Two main thinning mechanisms have been proposed, convective removal of a thickened lithospheric root and delamination of the mantle lithosphere along the Moho. In the latter case, the whole mantle lithosphere peels away from the crust by the propagation of a localized shear zone and sinks into the mantle. To study this mechanism, we perform two‐dimensional (2‐D) numerical simulations of convection using a viscoplastic rheology with an effective viscosity depending strongly on temperature, depth, composition (crust/mantle), and stress. The simulations develop in four steps. (1) We first obtain “classical” sublithospheric convection for a long time period (∼300 Myr), yielding a slightly heterogeneous lithospheric temperature structure. (2) At some time, in some simulations, a strong thinning of the mantle occurs progressively in a small area (∼100 km wide). This process puts the asthenosphere in direct contact with the lower crust. (3) Large pieces of mantle lithosphere then quickly sink into the mantle by the horizontal propagation of a detachment level away from the “asthenospheric conduit” or by progressive erosion on the flanks of the delaminated area. (4) Delamination pauses or stops when the lithospheric mantle part detaches or when small‐scale convection on the flanks of the delaminated area is counterbalanced by heat diffusion. We determine the parameters (crustal thicknesses, activation energies, and friction coefficients) leading to delamination initiation (step 2). We find that delamination initiates where the Moho temperature is the highest, as soon as the crust and mantle viscosities are sufficiently low. Delamination should occur on Earth when the Moho temperature exceeds ∼800°C. This condition can be reached by thermal relaxation in a thickened crust in orogenic setting or by corner flow lithospheric erosion in the overriding lithosphere of subduction zones.
Estimation of drag coefficient in James River Estuary using tidal velocity data from a vessel‐towed ADCP
Authors: Li Chunyan , Valle‐Levinson Arnoldo , Atkinson Larry P. , Wong Kuo Chuin , Lwiza Kamazima M. M.
Published: March 2004

A phase‐matching method is introduced to calculate the bottom drag coefficient in tidal channels with significant lateral variation of depth. The method is based on the fact that the bottom friction in a tidal channel causes tidal velocity to have a phase difference across the channel. The calculation involves a few steps. First, the observed horizontal velocity components are analyzed to obtain the amplitude and phase of the velocity at the major tidal frequency. The phase of the longitudinal velocity is then fitted to a relationship derived from the linearized momentum balance. The drag coefficient is then calculated. This method is applicable to narrow (approximately a few kilometers wide) tidal channels without strong stratification and where the cross‐channel variation of surface elevation is negligible compared to tidal amplitude. This analytic approach is easy to implement when appropriate observational data are available. It allows a spatial variation of the drag coefficient, and the resolution is only limited by that of the observations. The method is validated by identical twin experiments and applied to tidal velocity data, obtained in the James River Estuary, using an acoustic Doppler current profiler during spring tides and neap tides in October–November 1996. The obtained bottom drag coefficient ranged from 1.2 × 10−3 to 6.9 × 10−3 at different positions along two cross‐channel transects each 4 km long and 2 to 14 m deep. The maximum drag coefficient is found in the shallowest water near the banks of the estuary, while the minimum values occur between 9 and 12 m in the center of the channel. The friction of the lateral boundary may have contributed to the apparent increase of the bottom friction on the banks. The transverse mean values of the drag coefficient ranges between 2.2 and 2.3 × 10−3 for the spring and neap tides, respectively.
A comparison of mixed‐layer dynamics between the Arabian Sea and Bay of Bengal: One‐dimensional model results
Authors: Prasad T. G.
Published: March 2004

Using a one‐dimensional turbulent closure model, we investigate the physical mechanisms governing the seasonal evolution of mixed‐layer depth (MLD) and sea surface temperature (SST) along two meridional sections; 64.5°E and 88.5°E, which are representative of the open‐ocean conditions of the Arabian Sea and the Bay of Bengal. Several perturbation experiments have been performed to isolate and judge exactly the relative importance of wind stress and buoyancy forcing to the evolution of MLD and SST. The wind stress forcing is found to be significant during the summer monsoon, while buoyancy flux plays a significant role during the winter monsoon. During the summer monsoon (June–September), the MLD in the Arabian Sea deepens to 80 m owing to strong wind‐driven vertical mixing, but the weaker winds over the Bay of Bengal restrict the turbulent mixing to a shallow depth of ∼30 m. As a result, SST in the Arabian Sea (Bay of Bengal) decreases to ∼27°C (remains high ∼29°C). It is thus the asymmetry in the wind field that is responsible for the difference in MLD and SST between the Arabian Sea and the Bay of Bengal. During the winter monsoon (November–February), the MLD in the Arabian Sea penetrates to deeper than 80 m by convective vertical mixing because of strong negative buoyancy flux (net heat loss), but it is restricted to 40–50 m in the Bay of Bengal owing to reduced net heat loss from the ocean. It is the asymmetry in the buoyancy forcing caused by the difference in latent heat flux that is responsible for the difference in MLD and SST between the Arabian Sea and the Bay of Bengal. The atmospheric parameter that controls this buoyancy difference is the difference in humidity between the two basins. Thus it is the differences in surface forcing, rather than differences in the vertical salinity stratification, that are key in explaining the observed and modeled differences between the Arabian Sea and Bay of Bengal.
Atmospheric circulation influences on seasonal precipitation patterns in Alaska during the latter 20th century
Authors: L'Heureux Michelle L. , Mann Michael E. , Cook Benjamin I. , Gleason Byron E. , Vose Russell S.
Published: March 2004

A set of long, nearly complete daily precipitation series for Alaska spanning the latter half of the 20th century has been analyzed for seasonal relationships between variations in mean, heavy, and extreme precipitation and large‐scale atmospheric circulation variations at interannual, decadal, and secular timescales. Relationships with four candidate predictors (the Pacific North American (PNA), Arctic Oscillation (AO), Pacific Decadal Oscillation (PDO), and Nino3 indices) are used for insights into possible large‐scale climate forcing. Winter precipitation (mean and extreme) variability and trends along the south coast and interior of Alaska appear to be closely related to variations in the PNA pattern over this timeframe, while El Nino/Southern Oscillation (ENSO) influences, through the Nino3 index, appear to be significant along the south coast alone. Along the south coast the PNA and ENSO exert opposing influences on extreme (and mean) precipitation. Within interior Alaska the positive PNA pattern tends to suppress precipitation owing to orographic factors. Summer variations appear more closely related to the influence of the AO and PDO. The north slope region of Alaska appears to be too far removed from the influences of any of the examined predictors for any clear relationship to be evident.
Evidence for stratigraphic distortion in the Greenland Ice Core Project (GRIP) ice core during Event 5e1 (120 kyr BP) from gas isotopes
Authors: Landais Amaelle , Steffensen Jørgen Peder , Caillon Nicolas , Jouzel Jean , Masson‐Delmotte Valérie , Schwander Jakob
Published: March 2004

The disturbed stratigraphy of the ice in the lowest 10% of the Greenland GRIP ice core has been previously demonstrated using gas measurements (δ18O of O2 and CH4) on a few meters depth scale. However, rapid ice isotopic variations (on the scale of 20 cm) are experienced in the bottom of the GRIP ice core with complex chemical signatures that make them difficult to reconcile with a disturbed stratigraphy of the ice. This is the case for event 5e1, first described as a dramatic cooling 120 kyr BP. We analyzed at a 5 cm resolution the isotopic composition of the air from 2 m of the GRIP bottom ice core covering event 5e1. The δ15N measurements, combined with a basic firn modeling, lead to the solid conclusion that the rapid event 5e1 is not a climatic event. Rapid variations of δ18O of O2 (δ18Oatm) are in agreement with a disturbed ice stratigraphy. However, the double peak shape of the δ18Oatm, recalling chemical data at the same depth, requires processes of diffusion after the mixing or even postcoring, placing limits to the interpretation of some classical paleoclimatic proxies in small scale mixed ice (<1 m).
Hydrothermal plume dynamics on Europa: Implications for chaos formation
Authors: Goodman Jason C. , Collins Geoffrey C. , Marshall John , Pierrehumbert Raymond T.
Published: March 2004

Hydrothermal plumes may be responsible for transmitting radiogenic or tidally generated heat from Europa's rocky interior through a liquid ocean to the base of its ice shell. This process has been implicated in the formation of chaos regions and lenticulae by melting or exciting convection in the ice layer. In contrast to earlier work, we argue that Europa's ocean should be treated as an unstratified fluid. We have adapted and expanded upon existing work describing buoyant plumes in a rotating, unstratified environment. We discuss the scaling laws governing the flow and geometry of plumes on Europa and perform a laboratory experiment to obtain scaling constants and to visualize plume behavior in a Europa‐like parameter regime. We predict that hydrothermal plumes on Europa are of a lateral scale (at least 25–50 km) comparable to large chaos regions; they are too broad to be responsible for the formation of individual lenticulae. Plume heat fluxes (0.1–10 W/m2) are too weak to allow complete melt‐through of the ice layer. Current speeds in the plume (3–8 mm/s) are much slower than indicated by previous studies. The observed movement of ice blocks in the Conamara Chaos region is unlikely to be driven by such weak flow.
Shielding effect of an open-type hybrid magnetic shield with high-Tc superconducting loops
Authors: Seki Yusuke , Suzuki Daisuke , Ogata Kuniomi , Tsukada Keiji
Published: March 2004

Double-D-shaped high-Tc superconducting loops were used to form an open-ended, cylindrical magnetic shield for biomagnetic measurements. The total magnetic flux through such a superconducting loop stays constant; thus, the loop can shield a cylindrical magnetic shield from an external magnetic field that penetrates into it from its open ends. The high-Tc superconducting loops are made of Bi2Sr2Ca2Cu3Ox tape wire, and the cylindrical magnetic shield is made of flexible magnetic sheets composed of Fe–Cu–Nb–Si–B nanocrystalline alloy. Both axial and transverse magnetic field noise in the shield were measured with high-Tc superconducting quantum interference devices. These measurements indicate that the double-D-shaped high-Tc superconducting loops at each open end of a cylindrical magnetic shield reduce not only axial but also transverse magnetic field noise in the magnetic shield.
Optimization of a low-energy, high brightness electron gun for inverse photoemission spectrometers
Authors: Raj S. , Sarma D. D.
Published: March 2004

Availability of a low-energy, high current electron gun delivering a well-focused spot on the sample is essential for the inverse photoelectron spectroscopy. We have optimized an electron gun to obtain the maximum beam current at all electron kinetic energies of relevance with a reasonably small focus spot. Here we present the design, the procedure for the optimization, as well as the resulting characteristics of the electron gun.
Zero interference effect and electroabsorption for amorphous silicon-based solar cells
Authors: Lyou Jong H. , Schiff E. A.
Published: March 2004

We suggest that the measurement of electroabsorption be improved by observations of electrotransmittance and electroreflectance for amorphous silicon-based solar cells. The measurement is based on a model in which electroabsorption depends on the internal reflection and transmission and reflection are ultimately entangled to each other. Thus the model indicates that the electroabsorption is completely obtained at the condition, so called “the zero interference effect,” in which the interference effect is nulled. The condition of the zero interference effect is directly observed with a simultaneous measurement of electrotransmittance and electroreflectance, and determines the built-in potential for a transparent back-surfaced solar cell, but it is inconclusive, because of the absence of electrotransmittance, for a reflecting back-surfaced solar cell. But the built-in potential for the solar cell would rather be estimated with the offset potential at the photon energy near the absorber layer band gap (i.e., the low energy limit).
Diagnostic methods for time-resolved optical spectroscopy of shocked liquid deuterium
Authors: Dunham Greg , Bailey J. E. , Carlson A. , Lake P. , Knudson M. D.
Published: March 2004

Sandia National Laboratories Z facility generates shocks in liquid deuterium with pressures up to 100 GPa. Temperature measurements using spectroscopy of the shocked D2 self-emission can help discriminate between different deuterium equation of state models. Time-resolved spectra are recorded using four diagnostic systems, each composed of a fiber optic probe that transmits light from the shocked D2 to a remote streaked spectrometer. Calibration of the entire system in the streaked mode is performed using a xenon arc lamp. The absolute xenon arc lamp spectrum is determined by comparison with National Institute of Standards and Technology (NIST) standards. Data analysis is performed by measuring the wavelength-dependent efficiency for each system and applying this to determine the shocked D2 self-emission spectrum. Temperature is deduced from either the wavelength dependence of the spectral radiance, ignoring the absolute intensity, or from both the wavelength dependence and the absolute intensity. The shocked D2 temperature uncertainties obtained with the methods described here are well below the differences between D2 equation of state (EOS) models and these measurements should therefore provide new insight into D2 EOS physics.
Large volume high-pressure cell with supported moissanite anvils
Authors: Xu Ji-an , Mao Ho-kwang , Hemley Russell J. , Hines Earl
Published: March 2004

The recently developed moissanite anvil cell (MAC) has become a useful device for achieving both high-pressure and large sample volume in an anvil cell. We describe two improvements in the basic design of the MAC. First, the loading environment has been optimized by centering the load. Second, a variety of supported systems have been examined to provide anvil stability at high loads with large anvils. Sample volumes that are nearly three orders magnitude greater than allowed by conventional diamond anvil cells can be pressurized and characterized at ∼50 GPa.
Dual-mode CO2-laser/microwave-sideband spectrometer with broadband and saturation dip detection for CH3OH
Authors: Sun Zhen-Dong , Liu Qiang , Lees R. M. , Xu Li-Hong , Tretyakov M. Yu. , Dorovskikh V. V.
Published: March 2004

This work reports dual-mode operation of a broadly tunable CO2-laser/microwave-sideband spectrometer employing a Cheo waveguide modulator and a CO2 laser that can operate on hot and sequence band lines as well as low- and high-J regular band lines. The spectrometer has a broadband scanning mode at Doppler-limited resolution for spectral searching and assignment, and a narrow-band sub-Doppler mode for precision measurements. In broadband mode, a 6.7–18.5 GHz (∼0.4 cm−1) window can be covered for each sideband in a single microwave sweep with a tracking Fabry–Perot etalon filter under computer control. In sub-Doppler mode, saturation-dip spectra are obtained at sub-MHz resolution with absolute frequency measurement accuracy of the order of ±200 kHz. The instrumental performance is demonstrated via spectra of the C–O stretching fundamental vibrational band of methanol. Doppler-limited broadband scans have been recorded with good signal-to-noise ratio in both the low- and high-J regions of the 9.6-μm-CO2 laser band, while narrow-band sub-Doppler scans have permitted clean separation of very close-lying lines in the CH3OH spectrum. The measurement precision is confirmed for several CH3OH transition systems through closure of combination loops. Our results illustrate the wide coverage and excellent resolution obtainable with CO2-sideband infrared laser radiation in a broadly tunable and convenient infrared source with high potential for spectroscopic applications.
Three-dimensional ferroelectric domain imaging of bulk Pb(Zr,Ti)O3 by atomic force microscopy
Authors: Hong Seungbum , Ecabart Bastien , Colla Enrico L. , Setter Nava
Published: March 2004

We report on the ferroelectric domain evolution as a function of the depth of the surface of 100 μm thick bulk Pb(Zr,Ti)O3 (PZT) doped with 2% Nb. Ferroelectric domain imaging (FDI) was performed by piezoelectric detection assisted by atomic force microscopy (AFM). The depth evolution of the polarization orientation was obtained by repeated surface chemical etching followed by FDI. It was observed that backswitching mainly occurred close to 90° domain and grain boundaries. The depth of these domains was estimated to be about 500 nm. This indicates that nonpenetrating domains of opposite polarity can retain their polarization vector near the surface region without the help of a top electrode interface. It also supports the idea that they act as preferential nucleation sites for polarization reversal. We suggest that AFM FDI combined with proper etching methods could be used to construct a three-dimensional image of the whole domain structure by stacking two-dimensional images layer by layer.
Measurement of Young’s modulus and Poisson’s ratio of thin coatings using impact excitation and depth-sensing indentation
Authors: Maxwell A. S. , Owen-Jones S. , Jennett N. M.
Published: March 2004

Poisson’s ratio is important for the characterization of coatings, as it is needed to determine the mechanical properties of coatings using techniques such as depth-sensing indentation and surface acoustic wave spectroscopy. However, until now it has been extremely difficult to measure the Poisson ratio of a coating and it is commonly assumed, often incorrectly, that it is the same as that of the bulk material. A new technique has therefore been developed following recent developments in impact excitation and depth-sensing indentation to measure the Poisson ratio of coatings. Impact excitation was first used to determine the Young modulus of the coatings. These results were then used in combination with the plane strain modulus obtained from depth-sensing indentation to determine the Poisson ratio of the coating. This technique has been successfully applied to determine the Poisson ratio of sputter deposited TiN coatings up to 2.66 μm thick. Consistent values of Young’s modulus (427±9 GPa) and Poisson’s ratio (0.23±0.03) were obtained for all the coatings, which agree with literature values for similar but thicker coatings obtained using acoustic microscopy.
Frequency-stabilized single-mode cavity ring-down apparatus for high-resolution absorption spectroscopy
Authors: Hodges Joseph T. , Layer Howard P. , Miller William W. , Scace Gregory E.
Published: March 2004

We present a cavity ring-down spectroscopy apparatus suitable for high-resolution absorption spectroscopy. The central feature of the spectrometer is a ring-down cavity whose comb of eigenfrequencies is actively stabilized with respect to a tuneable, frequency-stabilized reference laser. By using dichroic ring-down cavity mirrors that are designed to have relatively high losses and low losses at the respective wavelengths of the reference laser and probe laser, the cavity stabilization dynamics are decoupled from frequency jitter of the probe laser. We use the cavity eigenfrequencies as markers in spectral scans and achieve a frequency resolution of ≈1 MHz. Five rovibrational transitions in the (2,0,1) vibrational band of water vapor near 0.935 μm are probed with a continuous-wave external-cavity diode laser, and their line strengths are determined and compared to literature values. Collisional narrowing effects and pressure shifting are observed, illustrating the applicability of the method for quantitative line shape studies of weakly absorbing systems.
Development of a measurement system of peroxy radicals using a chemical amplification/laser-induced fluorescence technique
Authors: Sadanaga Yasuhiro , Matsumoto Jun , Sakurai Ken-ichi , Isozaki Ryoko , Kato Shungo , Nomaguchi Tomoki , Bandow Hiroshi , Kajii Yoshizumi
Published: March 2004

An instrument for measuring atmospheric peroxy radicals has been developed by chemical amplification/laser-induced fluorescence (PERCA/LIF) technique. The small concentration of peroxy radicals is converted to the large amount of NO2, which is measured by laser-induced fluorescence instead of luminol chemiluminescence. Several advantages, that is, high sensitivity, high selectively, and fast time response, are expected by use of LIF for the NO2 measurement, in comparison with luminol chemiluminescence. When using this system, simultaneous measurements of NO2 and peroxy radicals are available. The present optimum condition for the reaction tube (1/4 in. Teflon) was determined to be the reaction tube length of 3 m, the NO and CO concentrations of 3 ppmv and 10%, respectively. The calibration, including humidity dependence of the detection sensitivity of peroxy radicals, was conducted and the present detection limit of peroxy radicals was determined to be 2.7 and 3.6 pptv at the ambient relative humidity of 50 and 80%, respectively, for the integration time of 1 min (S/N=2). This detection limit was calculated assuming the ambient O3 and NO2 mixing ratios of 30 and 20 ppbv, respectively. The influence of the NO2 detection sensitivity by adding high concentrations of CO was investigated and the quenching of excited NO2 by CO can affect the ambient measurement significantly under the high NO2 and low peroxy radical concentrations. Exploratory ambient air measurements were made in suburban area of Osaka, Japan. These results demonstrated the performance of PERCA/LIF for ambient measurements.
Feedback-controlled ion beam sculpting apparatus
Authors: Stein Derek M. , McMullan Ciaran J. , Li Jiali , Golovchenko Jene A.
Published: March 2004

We report the design of an “ion sculpting” instrument that enables the controlled fabrication of nanometer-sized structures in solid-state materials. The instrument employs a beam of kilo-electron-volt argon ions that impinge on a solid-state membrane containing prefabricated structures such as holes, slits, or cavities whose properties are to be modified. By controlling both the ion beam parameters and sample temperature, the instrument can be adjusted to either deliver or remove material from these articulations, for example opening or closing holes of various shapes. The instrument is unique in its use of feedback control for the crafting of structures that define a hole through which a component of the incident ion beam is permitted to pass and be monitored. Electrostatic ion optics refocus ions transmitted unimpeded through the hole, onto a detector capable of registering single ions. The transmission rate is a direct, real-time measure of the transmitting area that is used as a feedback signal to trigger the termination of the ion irradiation process precisely when a desired dimension is obtained. The ions thus serve the dual role of modifying and measuring the size of the nanoscale structures. The sensitivity of the ion beam sculpting apparatus to atomic-scale material rearrangement at the perimeter of a hole also enables the study of ion beam induced material transport at solid-state surfaces. The utility of the instrument as a fabrication tool has been demonstrated by the fabrication of nanopores used for recent single-molecule biophysics studies.
Theoretical analysis of the gravity-driven capillary viscometers
Authors: Berli Claudio L. A. , Deiber Julio A.
Published: March 2004

Gravity-driven capillary viscometers (GDCVs) are used to obtain the viscosity function of non-Newtonian fluids from measurements of the instantaneous fluid height in the overhead reservoir. The reliability of this viscometry depends on two main aspects: the accomplishment of the required flow condition in the apparatus and the appropriate conversion of raw data into rheometric functions. This work presents a rigorous theoretical analysis of the GDCV, thus providing criteria to achieve accurate measurements. The equations describing the rheometric flow in a GDCV are deduced from the basic laws of momentum and mass conservation. From these equations, the flow dynamics of the apparatus is studied and the constraints required to attain a quasi-steady-state flow are established. Under these conditions, the rheometric functions are written in terms of the instantaneous fluid height. In addition, a method to process experimental data of non-Newtonian fluids is proposed, which can handle the ill-posed problem associated with the determination of the viscosity function in this viscometry.
Low-pressure source of slow metastable rare gas atoms
Authors: van der Velden M. H. L. , Batelaan H. , te Sligte E. , Beijerinck H. C. W. , Vredenbregt E. J. D.
Published: March 2004

We investigate the properties of a commercial inverted magnetron pressure gauge for use as a source of slow metastable rare gas atoms. We find that the velocity distribution of the atoms as well as the pressure dependence of the output flux agree with a simple model. This shows that the low-velocity output of the source is enhanced over the Maxwell–Boltzmann form due to a velocity-dependent excitation probability. For argon, the center-line intensity per unit area of the source is measured to be greater than 4.2×1015 Ar 1s5 atoms/(s sr m2) at a pressure of 23 mPa. When observing the entire source area, the center-line intensity is at least 2.6×1011 Ar 1s5 atoms/(s sr).
Measurement errors in the mean and fluctuation velocities of spherical grains from a computer analysis of digital images
Authors: Xu Haitao , Reeves Anthony P. , Louge Michel Y.
Published: March 2004

We outline an algorithm to extract the mean and fluctuation velocities of identical spheres colliding in microgravity from a sequence of digital images. We analyze four kinds of intrinsic errors. The first two artificially reduce the apparent fluctuation velocity. They derive from the inability of the algorithm to track indistinguishable spheres moving with excessive speed, and from invisible collisions occurring between consecutive frames. The third is due to the finite pixel size. The resulting uncertainty in the position of the spheres increases the measured fluctuation velocity. The last arises from the partitioning of the flow domain in strips to calculate velocity profiles. While this last kind of error can always be reduced by increasing the number of images acquired, the first three cannot be made arbitrarily small without improving pixel resolution. Using microgravity experiments and numerical simulations of a shear flow, we illustrate insidious distortions of the mean and fluctuation velocity profiles that originate with the unavoidable errors that we have discussed.
Demining with Nd:YAG laser
Authors: Rothacher Thomas , Lüthy Willy , Weber Heinz P.
Published: March 2004

Laser neutralization of antipersonnel (AP) mines offers the enormous advantage to work from a safe distance. In this article the interaction of Nd:YAG laser radiation and four different types of blast AP mines is investigated. For this purpose, a very compact laser system for mine neutralization is developed. The incident power on the mine surfaces is varied from 20 to 70 W. Neutralization of all mines is achieved from a safe distance up to 50 m. The mines burn and finally detonate after an irradiation time of a few minutes. Detonation of the irradiated burning mines is considerably weaker compared to fully functional mines. Therefore, expected damage in the surrounding area is significantly reduced.
An in situ method for observing wax crystallization under pipe flow
Authors: Guthrie Sarah E. , Mazzanti Gianfranco , Steer Tyrone N. , Stetzer MacKenzie R. , Kautsky Sacha P. , Merz Hugh , Idziak Stefan H. J. , Sirota Eric B.
Published: March 2004

We report on an x-ray diffraction investigation of the nucleation and growth of wax crystals and the evolution of the resulting wax-gel deposit in mixtures of paraffin wax and dodecane under pipe flow. This work is an in situ x-ray diffraction study of wax crystallization in oil-wax mixtures under flow and is completely noninvasive. This technique is shown to be consistent with other methods.
Construction of an innovative heating apparatus for ultrahigh vacuum platens used in high pressure reaction cells
Authors: Romano Esteban J. , Schulz Kirk H.
Published: March 2004

A robust heater for use with platen sample holders which are incorporated on commercial ultrahigh vacuum (UHV) reaction cells is described. The system is built with readily available commercial parts and requires minimal tooling for construction. The heater, as built in this publication, will provide heating for standard 1 in. sample platens manufactured by Physical Electronics and other UHV equipment suppliers. A small gauge thermocouple is included in the design for temperature measurement. The heater is capable of resistively heating the sample platen to 1000 K while under UHV and at variable pressures up to approximately 1000 Torr pressure levels. The electrical requirements are 20 A at 6.25 V to attain the temperature of 1000 K in 19 min. The use of this design, in conjunction with a reaction cell, bridges the gap between surface science and conventional catalytic studies by allowing realistic exposure temperatures and pressures while keeping the material from being exposed to atmospheric conditions.
X-ray powder diffractometer for in situ structural studies in magnetic fields from 0 to 35 kOe between 2.2 and 315 K
Authors: Holm Aaron Patrick , Pecharsky Vitalij K. , Gschneidner Karl A. , Rink Roger , Jirmanus Munir N.
Published: March 2004

A technique for studying magnetic field induced structural changes at the atomic resolution is described. The instrument involves the coupling of a high resolution laboratory x-ray powder diffractometer, a helium flow cryostat, and a split-coil superconducting magnet allowing for in situ structural studies in a magnetic field between 0 to 35 kOe, and a temperature between 2.2 to 315 K. The data collected from a copper sample, which is used as a standard, at temperatures down to 4.3 K and in fields up to 10 kOe are presented. The ability to image massive magnetic field induced structural transformations is demonstrated utilizing powder diffraction data of Gd5Ge4 collected under both isothermal and isofield conditions at various temperatures below 15 K and magnetic fields up to 35 kOe. These results show the utility of our approach to obtain high precision structural information in the presence of a strong magnetic field.
X-ray imaging microscopy using Fresnel zone plate objective and quasimonochromatic undulator radiation
Authors: Suzuki Yoshio , Takeuchi Akihisa , Takano Hidekazu , Uesugi Kentaro , Oka Toshihiko , Inoue Katsuaki
Published: March 2004

An imaging microscopy experiment in a hard x-ray region has been performed at the undulator beamline 40XU of SPring-8. The helical undulator at the BL40XU provides quasimonochromatic radiation with a bandwidth of 1.2% at 8.34 keV. A Fresnel zone plate with an outermost zone width of 0.25 μm and a Fresnel zone number of 100 is used as an objective. The natural bandwidth of the undulator radiation of BL40XU is nearly equal to the monochromaticity required for the zone plate objective. Therefore, compared with conventional beamlines with a crystal monochromator, the available photon flux is higher by two orders. Fine structure of test patterns with 0.25 μm line and space was clearly observed at an x-ray energy of 8.34 keV within an exposure time of 1.5 ms.
Angle resolved microwave spectrometer for metamaterial studies
Authors: Starr A. F. , Rye P. M. , Mock J. J. , Smith D. R.
Published: March 2004

We describe an angle resolved microwave spectrometer (ARMS) based on a planar waveguide scattering chamber, capable of acquiring the angular distribution of TE polarized microwaves scattered from samples centered within the chamber. The spacing between the upper and lower conducting circular plates is 0.4 in. (∼1 cm), which, with the associated X-band waveguide adapters, fixes the frequency of operation of the ARMS to be optimally within the X-band frequency range (8–12 GHz). Microwave energy can be injected either as an apertured beam via an extended arm connected to the chamber, or via an antenna located in the center of the chamber. Power is detected at a waveguide adapter located on the periphery of the chamber, attached to a rotating arm that has an angular range of 180°. A computer controlled stepper motor attached to the rotating arm facilitates angular scanning with the data acquired at every angle in an automated fashion. The ARMS has excellent reproducibility and signal-to-noise characteristics, making it ideal for characterizing the refraction properties of metamaterial samples, or as a probe of the interaction between antennas and metamaterial substrates.
Compact low-power high-sensitivity angle sensor
Authors: Lockerbie N. A. , McDonald N. J. , Weston R. G.
Published: March 2004

We present the design of a compact battery-powered optical angle sensor, together with the first results obtained using the prototype measuring system. The output of the sensor is proportional to cos 2θ over a full 360°, where θ is the (possibly static) angle of rotation from a designated zero orientation. Over the more limited range of approximately ±20° the measured angular sensitivity is in excess of 70 mV/°, corresponding to an angular resolution of ±0.01°. Although the cos 2θ dependency was created in order to meet the requirements of a dynamical quadrupole measuring instrument, this sensor could be useful in applications which require a highly sensitive, yet compact, contactless, measurement of rotation, over (say) ±20°.