bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences between Archean and Proterozoic lithospheres: Assessment of the possible major role of thermal conductivity
Authors: Petitjean S. , Rabinowicz M. , Grégoire M. , Chevrot S.
Published: March 2006

We study heat transfer through the conductive lithosphere and convective mantle on the basis of a 2‐D convection model in order to better understand the differences between Archean and Proterozoic lithospheres. The original improvement in the modeling consists of a precise track of the cutoff temperature between conduction and convection. The conductive lithosphere is undeformable, and the convective mantle has a constant viscosity. The conductive lithosphere in Archean cratons is assumed to have a lower radiogenic heat production in the crust and/or the conductive mantle, and/or a higher cutoff temperature (attributed to a stiffening of the more depleted mantle) relative to Proterozoic terrains. We also investigate the effect of a fourth factor never considered before: an enhancement of the vertical thermal conductivity in the conductive Archean mantle due to a vertical lineation. Our model successfully predicts the observations on the Canadian and South African shields. A high vertical thermal conductivity in the Archean lithospheric mantle possibly associated to a radiogenic crust depletion explains many observations: i.e., (1) the development of a thick Archean cold root, (2) a dipping cold convective plume beneath Archean cratons, (3) a uniform mantle heat flux along Archean and Proterozoic terrains, and (4) strong high seismic velocity anomalies over Archean cratons. In addition, a lower radiogenic heat production of the lithospheric mantle or a larger cutoff temperature in Archean cratons is not favored by our models. Finally, we investigate how a cold root and a sub‐Archean cold mantle plume react to the shear induced by large‐scale mantle flow and to the collision with a hot mantle plume. Models show that shear removes the cold plume from below the Archean craton, but cold dipping instabilities are periodically generated inside the convective boundary layer below the Archean cratonic lid. However, the thick Archean lithospheric root may survive several orogeneses. In addition, the models show that it takes at least 200 Myr for a hot mantle plume to erode the thick lithospheric root. This suggests that an Archean root may only disappear if the plate remains above a hot plume for a very long time.
Impact of ULF oscillations in solar wind dynamic pressure on the outer radiation belt electrons
Authors: Ukhorskiy A. Y. , Anderson B. J. , Takahashi K. , Tsyganenko N. A.
Published: March 2006

This work addresses radial transport of outer radiation belt electrons due to ULF disturbances of geomagnetic field. A new approach to calculating inductive electric field is developed and implemented using a dynamical model of the storm‐time geomagnetic field. The approach is used to analyze the effects associated with solar wind dynamic pressure (Pdyn). It is found that Pdyn produces large‐scale electric fields with maximum intensity at noon and midnight local time. Derived fields are used in test particle calculations of relativistic electron dynamics. The results show that even moderate oscillations of Pdyn typical for quiet‐time magnetosphere can result in rapid electron scattering across the drift shells, which identifies Pdyn as one of the primary mechanisms of radial transport in the belt. Calculations show that electron motion is inconsistent with radial diffusion, and hence a more detailed description is required for accurate predictions of electron fluxes in the belt.
Influence of the tropics on the climate of the South Atlantic
Authors: Grodsky Semyon A. , Carton James A.
Published: March 2006

The climate of the tropical Atlantic is shown to undergo slow basinwide changes with time‐scales of five years that include changes in surface winds, SST, and sea level. Further south in the Agulhas eddy corridor 35°S–25°S there are sea level fluctuations (superimposed on the dominant mesoscale eddies) on a similar timescale with amplitudes of 10 cm and with westward phase propagation of 4 cm s−1, giving rise to phase variations between the western and eastern sides of the basin. In the eastern basin sea level anomalies are accompanied by 0.5°C SST variations, while in the west the relationship is more complex. Here we explore the possibility that these subtropical sea level fluctuations are produced by the poleward propagation of the tropical sea level anomalies.
Nanosize effect on the hygroscopic growth factor of aerosol particles
Authors: Biskos G. , Russell L. M. , Buseck P. R. , Martin S. T.
Published: April 2006

The hygroscopic growth factors of NaCl particles having dry mobility diameters of 6 to 60 nm were measured using a tandem nano‐Differential Mobility Analyzer. The growth factors steadily decreased within detection limit for dry sizes below 40 nm. The decrease is quantitatively predicted by a model that includes the Kelvin effect and a size‐dependent shape factor. This factor is not tuned to the data but rather is grounded in theoretical predictions from literature. Agreement in growth factors for particles generated by two independent methods (namely, vaporization‐condensation and electrospray), as well as observations of prompt deliquescence, indicates the absence of significant chemical impurities.
Identifying the roles of the ocean and atmosphere in creating a rapid equatorial response to a Southern Ocean anomaly
Authors: Blaker A. T. , Sinha B. , Ivchenko V. O. , Wells N. C. , Zalesny V. B.
Published: March 2006

Recent research has identified a rapid ocean response mechanism to salinity anomalies in the Southern Ocean using an idealised ocean model. Here we examine the relative importance of the ocean and atmosphere in creating an equatorial response to a Southern Ocean anomaly. Using a coupled climate model with realistic bottom topography and land relief, two rapid teleconnections are produced from a high latitude anomaly. An equatorial ocean response can be seen after 30 days. The mechanism producing this response is shown to rely on barotropic and baroclinic oceanic wave propagation. A second, atmospheric, response is seen in the Northern Hemisphere (NH) high latitudes, driven by atmospheric Rossby waves. The ocean quickly responds to the atmospheric signal above it, resulting in sea surface temperature anomalies at NH high latitudes.
Asymmetric vertical internal wave propagation
Authors: van Haren Hans
Published: March 2006

Yearlong data from a single ADCP above the northern extension of the Mid‐Atlantic Ridge are used to investigate vertical internal wave propagation in the open ocean (395–1025 m). Whilst 80% of incoherent semidiurnal tidal (D2) phase propagates downward, 90% of near‐inertial (f) phase propagates upward. Most upward propagating f‐phase is found at sub‐f frequencies σmin(N = f) ≈ 0.74f < σ ≤ 0.99f, N the buoyancy frequency and σmin the lower bound of the inertio‐gravity (IG) wave band following the ‘non‐traditional approach’, which includes the horizontal component of the Earth's rotation in momentum equations. The upper bound of mostly downward propagating D2‐phase coincides with the upper IG‐bound σmax(N = f) ≈ 1.35f. The limited band [σmin, σmax] demonstrates that f and D2 contain special internal waves concerning vertical propagation. It is suggested that this is partially attributable to small‐scale step layering in N, with N = f separating ‘trapping’ from ‘classic propagating’ wave regimes, rendering the mean large‐scale N ≈ 18f less important.
Long‐term persistence in climate and the detection problem
Authors: Rybski Diego , Bunde Armin , Havlin Shlomo , von Storch Hans
Published: March 2006

We have analyzed six recently reconstructed records (Jones et al., 1998; Mann et al., 1999; Briffa, 2000; Esper et al., 2002; McIntyre and McKitrick, 2003; and Moberg et al., 2005) of the Northern Hemisphere temperatures and found that all are governed by long‐term persistence. Due to the long‐term persistence, the mean temperature variations σ(m, L) between L years, obtained from moving averages over m years, are considerably larger than for uncorrelated or short‐term correlated records. We compare the values for σ(m, L) with the most recent temperature changes ΔTi(m, L) in the corresponding instrumental record and determine the year ic where ΔTi(m, L)/σ(m, L) exceeds a certain threshold and the first year id when this could be detected. We find, for example, that for the climatologically relevant parameters m = 30, L = 100, and the threshold 2.5, the values (ic, id) range, for all records, between (1976, 1990) for Mann et al. (1999) and (1988, 2002) for Jones et al. (1998). Accordingly, the hypothesis that at least part of the recent warming cannot be solely related to natural factors, may be accepted with a very low risk, independently of the database used.
Characteristic ion distributions in the dynamic auroral transition region
Authors: Zeng W. , Horwitz J. L. , Tu J.‐N.
Published: April 2006

A Dynamic Fluid Kinetic (DyFK) simulation is conducted to study the H+/O+ flows and distribution functions in the high‐latitude dynamic transition region, specifically from 1000 km to about 4000 km altitude. Here, the collisional‐to‐collisionless transition region is that region where Coulomb collisions have significant but not dominant effects on the ion distributions. In this study, a simulation flux tube, which extends from 120 km to 3 RE altitude, is assumed to experience a pulse of auroral effects for approximately 20 minutes, including both soft electron precipitation and transverse wave heating, and then according to different geophysical circumstances, either to relax following the cessation of such auroral effects or to be heated further continuously by waves with power at higher frequencies. Our principal purpose in this investigation is to elicit the characteristic ion distribution functions in the auroral transition region, where both collisions and kinetic processes play significant roles. The characteristics of the simulated O+ and H+ velocity distributions, such as kidney bean shaped H+ distributions, and O+ distributions having cold cores with upward folded conic wings, resemble those observed by satellites at similar altitudes and geographic conditions. From the simulated distribution function results under different geophysical conditions, we find that O+‐O+ and O+‐H+ collisions, in conjunction with the kinetic and auroral processes, are key factors in the velocity distributions up to 4000 km altitude, especially for the low speed portions, for both O+ and H+ ions.
Drag coefficient reduction at very high wind speeds
Authors: Bye John A. T. , Jenkins Alastair D.
Published: March 2006

The correct representation of the 10‐m drag coefficient for momentum (K10) at extreme wind speeds is very important for modeling the development of tropical depressions and may also be relevant to the understanding of other intense marine meteorological phenomena. We present a unified boundary layer model for (K10), which takes account of both the wave field and spray production, and asymptotes to the growing wind wave state in the absence of spray. The theoretical development is based on an air‐sea system with shear layers in both fluids and contains three constants that must be determined empirically. This is done using data from observations, and the resulting behavior is interpreted in terms of spray. A feature of the results is the prediction of a broad maximum in K10. For a spray velocity of 9 m s−1, it is found that a maximum of K10 ∼ 2.0 × 10−3 occurs for a 10‐m wind speed, u10 ∼ 40 m s−1, in agreement with recent GPS sonde data in tropical cyclones. Thus K10 is “capped” at its maximum value for all higher wind speeds expected. A physically based model, where spray droplets are injected horizontally into the airflow and maintained in suspension by air turbulence, gives qualitatively similar results. The effect of spray is also shown to flatten the sea surface by transferring energy to longer wavelengths.
L band wind profiler observations of convective boundary layer over Gadanki, India (13.5°N, 79.2°E)
Authors: Kumar Karanam Kishore , Jain A. R.
Published: March 2006

Results from a convection campaign, which was carried out during May–August 1999 using VHF/L band wind profiler, optical rain gauge, and radiosonde flights at National MST Radar Facility, Gadanki (13.5°N, 79.2°E), are discussed. During this period, L band wind profiler observations have been made for a total of 110 days, and radiosonde observations have been made during 19 July to 14 August 1999. L band wind profiler–derived refractive index structure constant profiles have been used to estimate the convective boundary layer (CBL) height and are compared with radiosonde observations. Comparison has shown a good agreement with a regression coefficient of 0.84 between these two independent measurements. Radiosonde observations are also used to estimate the level of free convection, which are used for studying the triggering of convection. An attempt has been made to study the evolution of the CBL in dry convection (nonprecipitating) and precipitation days. Precipitation days comprise both premonsoon and monsoon seasons. In the present study, premonsoon days are defined as the dry to wet transition period and monsoon days as the early monsoon period. The intriguing result from these studies is the distinguishable CBL evolution observed in the preconvective environments of premonsoon and monsoon periods. These observations provide evidence for the use of wind profilers to closely monitor the onset of convective instability. Furthermore, observations of the boundary layer at various geographical locations using multiplatform instruments are sought to strengthen the results depicted here. However, the results discussed here nevertheless prove the potential of the L band wind profiler as an important tool for operational meteorology and provide new insights on the usage of wind profiler observations.
Hydrothermal regimes of the dry active layer
Authors: Ishikawa Mamoru , Zhang Yinsheng , Kadota Tsutomu , Ohata Tetsuo
Published: April 2006

Evaporation and condensation in the soil column clearly influence year‐round nonconductive heat transfer dynamics in the dry active layer underlying semiarid permafrost regions. We deduced this from heat flux components quantified using state‐of‐the‐art micrometeorological data sets obtained in dry and moist summers and in winters with various snow cover depths. Vapor moves easily through large pores, some of which connect to the atmosphere, allowing (1) considerable active layer warming driven by pipe‐like snowmelt infiltration, and (2) direct vapor linkage between atmosphere and deeper soils. Because of strong adhesive forces, water in the dry active layer evaporates with great difficulty. The fraction of latent heat to total soil heat storage ranged from 26 to 45% in dry and moist summers, respectively. These values are not negligible, despite being smaller than those of arctic wet active layer, in which only freezing and thawing were considered.
Wiskott–Aldrich syndrome protein is involved in αIIbβ3‐mediated cell adhesion
Authors: Tsuboi Shigeru , Nonoyama Shigeaki , Ochs Hans D
Published: March 2006

The Wiskott–Aldrich syndrome (WAS) is an X‐chromosome‐linked immunodeficiency disorder. The most common symptom seen in WAS patients is bleeding. One of the main causes of bleeding is defective platelet aggregation. The causative gene of WAS encodes WAS protein (WASP). Here, we show that WASP binds to the calcium‐ and integrin‐binding protein (CIB) in platelets. CIB was originally identified as a protein binding to the αIIb cytoplasmic tail of platelet integrin αIIbβ3, which has a primary role in platelet aggregation. We also show that the WASP–CIB complex is important in αIIbβ3‐mediated cell adhesion, and that in patients mutant forms of WASP are expressed at reduced levels or show lower affinities for CIB than wild‐type WASP. Our results indicate that impaired complex formation between mutant WASPs and CIB reduces αIIbβ3‐mediated cell adhesion and causes defective platelet aggregation, resulting in bleeding.
Increased p53 activity does not accelerate telomere‐driven ageing
Authors: García‐Cao Isabel , García‐Cao Marta , Tomás‐Loba Antonia , Martin‐Caballero Juan , Flores Juana M , Klatt Peter , Blasco María A , Serrano Manuel
Published: March 2006

There is a great interest in determining the impact of p53 on ageing and, for this, it is important to discriminate among the known causes of ageing. Telomere loss is a well‐established source of age‐associated damage, which by itself can recapitulate ageing in mouse models. Here, we have used a genetic approach to interrogate whether p53 contributes to the elimination of telomere‐damaged cells and its impact on telomere‐driven ageing. We have generated compound mice carrying three functional copies of the p53 gene (super‐p53) in a telomerase‐deficient background and we have measured the presence of chromosomal abnormalities and DNA damage in several tissues. We have found that the in vivo load of telomere‐derived chromosomal damage is significantly decreased in super‐p53/telomerase‐null mice compared with normal‐p53/telomerase‐null mice. Interestingly, the presence of extra p53 activity neither accelerates nor delays telomere‐driven ageing. From these observations, we conclude that p53 has an active role in eliminating telomere‐damaged cells, and we exclude the possibility of an age‐promoting effect of p53 on telomere‐driven ageing.
Charge breeding of isotope on-line-created radioactive ions using an electron cyclotron resonance ion trap
Authors: Geller R. , Lamy T. , Sortais P.
Published: March 2006

In the coming years huge ion-beam projects are foreseen. They deal with specific isotope on-line (ISOL) beams such as ISOL-created radioactive ions. The beam intensities are exceptionally high (>1012ions∕s), the radioactive lifetimes are short (⩽1s), and the ion energy is very high (⩾150GeV∕u). In general in order to minimize the size of the accelerator one needs highly charged ISOL ions and therefore charge breeders are a must. In contrast with the CERN system, utilizing a Penning trap and an electron-beam ion source charge breeder (where the maximum ion beam cannot exceed 106ions∕s) the Grenoble group launched in 1995 an electron cyclotron resonance (ECR) system capable of storing 1012ions∕s and delivering highly charged ISOL ions. In this article we show that this storage is possible for low-ion-energy ISOL ions following classical slowing down theory. In this case the injected ISOL ions are slowed down by ion-ion collisions which yield ion storage inside the ECR plasma, but also charge breeding by the energetic ECR electrons bombarding the slowed down ions.
High-current vacuum-arc ion and plasma source “Raduga-5” application to intermetallic phase formation
Authors: Stepanov Igor B. , Ryabchikov Alexander I. , Kozlov Eduard V. , Sharkeev Yurii P. , Shulepov Ivan A. , Kurzina Irina A. , Sivin Denis O.
Published: March 2006

Phase composition, structural state, and mechanical properties of the ion-doped surface layers of Ni, Ti, and Fe targets with Al and Ti ions implanted into using the metal ion beam and plasma source Raduga 5 have been investigated. The high-intensity mode of implantation allowed us to obtain the ion-doped layers with the thickness exceeding the ion projected range by several orders of magnitude. By the transmission electron microscopy, it has been found that the fine-dispersed equilibrium intermetallic phases (Me3Al, MeAl) and the solid solution of aluminum were formed in the doped Ni, Ti, and Fe surface layers at the depth of up to 2600nm. The maximum dopant concentration reached 75%. It has been shown that the average size of the formed phases was of 70nm. The microhardness of the different target surface layers increased by 1.5–3 times. The wear resistance of the samples did not change within the temperature range of 300–700K.
Plasma immersion ion charge state and mass spectrometer
Authors: Ryabchikov Alexander I. , Ryabchikov Igor A. , Stepanov Igor B. , Sinebryukhov Andrei A.
Published: March 2006

This work is devoted to the development and investigation of a new spectrometer for the measurement of ion charge state and mass composition of a plasma based on the combination of two methods—plasma immersion ion acceleration and time-of-flight ion separation. Ion acceleration in the spectrometer is carried out in the short-pulse mode by applying a negative bias potential to the plasma-immersed drift tube. The measurement of the ion current at the end of the tube using time-of-flight ion separation must be done after the bias potential pulse termination. The investigations of the ion charge state were carried out using a dc vacuum-arc Ti metal plasma. It is experimentally shown that the application of a negative bias potential with a pulse amplitude of more than 1.5 kV and duration in the range from 50 to 1000 ns allows measuring the spectra with good charge state and mass resolution for various plasma concentrations and drift tube lengths from 0.5 to 0.9 m. The spectrometer is noted for the design simplicity and compactness. It can be used for ion charge state and mass composition investigation in the wide range of concentration of most Periodic Table metal element plasmas.
Aggregation of polyalanine in a hydrophobic environment
Authors: Soto Patricia , Baumketner Andrij , Shea Joan-Emma
Published: March 2006

The dimerization of polyalanine peptides in a hydrophobic environment was explored using replica exchange molecular dynamics simulations. A nonpolar solvent (cyclohexane) was used to mimic, among other hydrophobic environments, the hydrophobic interior of a membrane in which the peptides are fully embedded. Our simulations reveal that while the polyalanine monomer preferentially adopts a β-hairpin conformation, dimeric phases exist in an equilibrium between random coil, α-helical, β-sheet, and β-hairpin states. A thermodynamic characterization of the dimeric phases reveals that electric dipole-dipole interactions and optimal side-chain packing stabilize α-helical conformations, while hydrogen bond interactions favor β-sheet conformations. Possible pathways leading to the formation of α-helical and β-sheet dimers are discussed.
Nonadiabatic reactant-product decoupling calculation for the F(P1∕22)+H2 reaction
Authors: Zhang Yan , Xie Ting-Xian , Han Ke-Li , Zhang John Z. H.
Published: March 2006

In this paper we present a theoretical study using time-dependent nonadiabatic reactant-product decoupling method for the state-to-state reactive scattering calculation of F(P1∕22)+H2 (ν=j=0) reaction on the Alexander-Stark-Werner potential energy surface. In this nonadiabatic state-to-state calculation, the full wave function is partitioned into reactant component and a sum of all product components. The reactant and product components of the wave function are solved independently. For the excited state reaction, the state-to-state reaction probabilities for J=0.5 are calculated. Comparing the state-to-state reaction probabilities, it is found that the vibrational population of the HF product is dominated by vibrational levels ν=2 and 3. The rotation specific reaction probabilities of HF product in j=1 and 2 are larger than those in other rotational levels. As the rotation quantum number j increases, the positions of the peak in the rotational reaction probability of HF product in ν=3 shift to higher collision energy.
Room temperature demonstration of GaN∕AlN quantum dot intraband infrared photodetector at fiber-optics communication wavelength
Authors: Vardi A. , Akopian N. , Bahir G. , Doyennette L. , Tchernycheva M. , Nevou L. , Julien F. H. , Guillot F. , Monroy E.
Published: March 2006

We fabricated a communication wavelength photodetector based on intraband transition in GaN∕AlN self-assembled quantum dot heterostructures. The quantum dot photodetector is based on in-plane transport and has a room temperature spectral peak responsivity of 8mA∕W at wavelength of 1.41μm. We use multipass waveguide geometry to show that the polarization sensitive optical absorption spectrum of the heterostructure is nearly the same as its photocurrent spectral response. This establishes that the detector’s response is due to the presence of quantum dots in its active layer. We use photoluminescence, transmission, and intraband photocurrent spectroscopy to consistently describe the alignment between the energy levels of the quantum dots and that of the wetting layer.
Study of blue phases transition kinetics by thermal lens spectroscopy in cholesteryl nonanoate
Authors: Mayén-Mondragón R. , Yáñez-Limón J. M.
Published: March 2006

The thermal lens signal distortion recorded on the BPI supercooled blue phase of a cholesteryl nonanoate thin sample was studied. Results showed that the distortion develops as the induced thermal gradient generated by the excitation beam incidence promotes local transitions to the BPII and BPIII blue phases and to the isotropic liquid. BPII Bragg scattering of the excitation beam wavelength along with a thermo-optic coefficient change produces a thermal lens effect decay. As this phase disappears the signal recovers strength and reaches a steady state. On lowering the sample temperature, the peak value of the distortion shifts to longer times. Considering Johnson-Mehl-Avrami-Kolmogorov-type kinetics, the effective rate constants, the preexponential factor, and the overall effective activation energy for the transformations BPI to BPII and BPII to isotropic liquid were determined. A mathematical model was developed to represent the thermal lens signal variation produced during each transformation. This article shows an interesting application of thermal lens spectroscopy to the determination of phase transition kinetic parameters of cholesteric liquid crystals.
Eigenmode analysis of photoacoustic sensors via finite element method
Authors: Baumann Bernd , Kost Bernd , Groninga Hinrich , Wolff Marcus
Published: March 2006

In the field of photoacoustic sensors, research has mainly been concentrating on the investigation of cylinder shaped cells. For cylinder cells, important acoustical properties can be obtained by analytical methods. In recent years, cells with other shapes have come into focus. In these cases, the sound spectrum and other quantities of interest cannot be obtained by analytical means. Finite element tools, however, are well suited to deal with unconventional geometries. In this article we present results concerning the eigenmodes of T-shaped photoacoustic cells.
Simple Hartmann test data interpretation for ophthalmic lenses
Authors: Salas-Peimbert Didia Patricia , Trujillo-Schiaffino Gerardo , González-Silva Jorge Alberto , Almazán-Cuellar Saúl , Malacara-Doblado Daniel
Published: March 2006

This article describes a simple Hartmann test data interpretation that can be used to evaluate the performance of ophthalmic lenses. Considering each spot of the Hartmann pattern such as a single test ray, using simple ray tracing analysis, it is possible to calculate the power values from the lens under test at the point corresponding with each spot. The values obtained by this procedure are used to plot the power distribution map of the entire lens. We present the results obtained applying this method with single vision, bifocal, and progressive lenses.
In situ microtensile stage for electromechanical characterization of nanoscale freestanding films
Authors: Han Jong H. , Saif M. Taher A.
Published: March 2006

This article presents the second generation of a microtensile stage that allows mechanical and electrical characterizations of nanoscale freestanding material samples in situ in analytical chambers such as scanning electron microscopy and transmission electron microscopy. The first generation [M. A. Haque and M. T. A. Saif, Proc. Natl. Acad. Sci. U.S.A. 101, 6335 (2004)] had the limitation of mechanical characterization only. Furthermore, it had a high probability of sample failure during fabrication and the force sensor could only be calibrated by cleaving the stage after sample testing. The new stage prevents sample failure (100% yield) and allows (1) calibration prior to testing without cleaving and (2) resistivity measurement of the sample at different temperatures, in addition to stress-strain measurements under uniaxial tension. A new fabrication process is also presented, which involves only two lithographic steps and a single Si etching step to fabricate the testing stage and the sample together with necessary electrical isolations for resistivity measurement. Testing stages are fabricated using the new process and are applied to test a 100-nm-thick freestanding Al sample with 65nm grain size. The stress-strain response of the sample shows an elastic modulus of 61GPa. The room temperature resistivity of this nanograined specimen is almost 20 times higher than the bulk value. The resistivity decreases irreversibly with increasing temperature (tested up to 98°C) and time without any significant grain growth. Upon cooling from 98°C, the resistivity increases with the decreasing temperature, contrary to bulk metallic behavior.
Fast determination method of cell thickness and time-dependent twist angle in twisted-nematic liquid-crystal cells
Authors: Honma Michinori , Nose Toshiaki , Sato Susumu
Published: March 2006

We propose a determination method of a cell thickness d and a time-dependent twist angle Φt in a twisted-nematic liquid-crystal (TN-LC) cell using circularly and homogeneously aligned LC cells and multiple wavelengths of incident light. Influences of a spectrum distribution on determining Φt and d are theoretically discussed, compared with a monochromatic laser light source. It is found that the influence of the spectrum distribution becomes stronger with an increase in the thickness of TN-LC cells. We propose a compensation method of the influence of the spectrum width in order to accurately determine Φt and d of TN-LC cells. Results of the determination of Φt and d of two TN-LC cells are presented, and the availability of the proposed determination method using three interference filters is confirmed experimentally.
Littrow-type external-cavity diode laser with a triangular prism for suppression of the lateral shift of output beam
Authors: Takamizawa Akifumi , Yonezawa Gen , Kosaka Hideo , Edamatsu Keiichi
Published: March 2006

We demonstrate a Littrow-type external-cavity diode laser with an additional triangular prism united to a diffraction grating. In this configuration, while the laser wavelength can be tuned by rotating the grating that constitutes an external cavity, the prism outside the cavity compensates for the lateral shift of the output beam. It is estimated that the lateral shift of the output beam is only 2μm over the tuning range of 12.91nm. In fact, the output beam was coupled into a single-mode fiber with constant efficiency over the wavelength range without any adjustment of the coupling optics.
Efficient loading of a He* magneto-optic trap using a liquid He cooled source
Authors: Swansson J. A. , Dall R. G. , Truscott A. G.
Published: March 2006

We report loading large numbers (up to 3×109) of metastable triplet helium atoms into a magneto-optical trap using an atomic beam derived from a liquid He (LHe) cooled dc discharge source. Moreover, we compare the effect of liquid N2 cooling to LHe cooling the source and demonstrate that LHe cooling offers a significant increase in performance.
Two-dimensional array of coupled nanomechanical resonators
Authors: Zalalutdinov Maxim K. , Baldwin Jeffrey W. , Marcus Martin H. , Reichenbach Robert B. , Parpia Jeevak M. , Houston Brian H.
Published: March 2006

Two-dimensional arrays of coupled nanomechanical plate-type resonators were fabricated in single crystal silicon using e-beam lithography. Collective modes were studied using a double laser setup with independent positioning of the point laser drive and interferometric motion detector. The formation of a wide acoustic band has been demonstrated. Localization due to disorder (mistune) was identified as a parameter that limits the propagation of the elastic waves. We show that all 400 resonators in our 20×20 array participate in the extended modes and estimate group velocity and density of states. Applications utilizing the resonator arrays for radio frequency signal processing are discussed.
Vortex-flow electromagnetic emission in stacked intrinsic Josephson junctions
Authors: Bae Myung-Ho , Lee Hu-Jong
Published: March 2006

We confirmed the existence of the collective transverse plasma modes excited by the motion of the Josephson vortex lattice in stacked intrinsic Josephson junctions of Bi2Sr2CaCu2O8+x by observing the multiple subbranches in the Josephson-vortex-flow current-voltage characteristics. We also observed the symptom of the microwave emission from the resonance between the Josephson vortex lattice and the collective transverse plasma modes, which provides the possibility of developing Josephson-vortex-flow electromagnetic oscillators.
Magnesium oxide as a candidate high-κ gate dielectric
Authors: Yan L. , Lopez C. M. , Shrestha R. P. , Irene E. A. , Suvorova A. A. , Saunders M.
Published: March 2006

Magnesium oxide (MgO) thin films with sharp interfaces were deposited by sputtering of a Mg target on Si. The film stack was characterized using spectroscopic ellipsometry and transmission electron microscopy and the film static dielectric constant (κ) and interface traps were determined. An amorphous SiO2 layer was found at the MgO∕Si interface as a result of subcutaneous Si oxidation. κ for the MgO films was found to be about twice that of SiO2, and the interface trap densities of MgO∕Si were found to be comparable with SiO2∕Si, rendering MgO competitive with all presently considered high-κ dielectrics.
Mechanics of a process to assemble microspheres on a patterned electrode
Authors: Zhu Ting , Suo Zhigang , Winkleman Adam , Whitesides George M.
Published: March 2006

A process has been demonstrated recently to assemble microspheres on a patterned electrode under the influence of an applied voltage. Here we examine the mechanics of this process, and describe both the conditions under which excess microspheres jump off the electrode when the voltage is applied, and the forces that attract the remaining microspheres to the desired positions. A quantitative mechanistic understanding of this process rationalizes experimental observations, provides scaling relations, and suggests modifications of the process.
Single-crystalline trumpetlike zinc phosphide nanostructures
Authors: Shen G. Z. , Bando Y. , Hu J. Q. , Golberg D.
Published: March 2006

Single-crystalline trumpetlike Zn3P2 nanostructures composed of hollow cones supported by nanowires have been prepared via a simple thermochemical method, which utilized ZnS and GaP as the source materials. The as-synthesized nanostructures are composed of single-crystalline Zn3P2 nanowires with diameters of ∼50nm and large diameter hollow cones with diameters increasing from 50nm at the bottom to 600nm at the top. Photoluminescence study of the trumpetlike Zn3P2 nanostructures shows a broad emission centered at ∼585nm at room temperature.
Complexity Theory in the Study of Space and Place
Authors: Manson Steven , O'Sullivan David
Published: March 2006

Researchers across disciplines apply complexity theory to issues ranging from economic development to earthquake prediction. The breadth of applications speaks to the promise of complexity theory, but there remain a number of challenges to be met, particularly those related to its ontological and epistemological dimensions. We identify a number of key issues by asking three questions. Does complexity theory operate at too general a level to enhance understanding? What are the ontological and epistemological implications of complexity? What are the challenges in modeling complexity? In answering these questions, we argue that, although complexity offers much to the study of place and space, research in these areas has a number of strengths that enhance complexity research.
Ecological and Urban Systems Models: Some Explorations of Similarities in the Context of Complexity Theory
Authors: Wilson Alan G
Published: March 2006

There are similarities of form between urban system models and models of ecosystems. These are systematically explored and a general model formulation which embraces both kinds of model is presented. Some insights are gained by using ideas from ecosystem modelling in urban modelling. The biggest gains, however, are for ecosystem modelling. It is demonstrated that urban techniques can be used for incorporating spatial competition effects into such models in novel ways, and that the complex dynamics can then be effectively interpreted. Urban systems have contributed significantly to complexity theory in the past—because they are complicated enough to be interesting but simple enough to be solvable. These insights can now be transferred to complex (spatial) ecosystems. The possibility of joint eco-urban models is explored.
Complexity Theory as a Link between Space and Place
Authors: Portugali Juval
Published: March 2006

Since the early 1970s, the notions of space and place have been located on the two sides of a barricade that divides what has been described as science's two great cultures. Space is located among the ‘hard’ sciences as a central term in the attempt of geography to transform the discipline from a descriptive into a quantitative, analytic, and thus scientific, enterprise. Place, on the other hand, is located among the ‘soft’ humanities and social philosophy oriented social sciences as an important notion in the post-1970 attempt to transform geography from a positivistic into a humanistic, structuralist, hermeneutic, critical science. More recently, the place-oriented geographies have adopted postmodern, poststructuralist, and deconstruction approaches, while the quantitative spatial geographies have been strongly influenced by theories of self-organization and complexity. In this paper I first point to, and then explore, structural similarities between complexity theories and theories oriented toward social philosophy. I then elaborate the thesis that, in consequence, complexity theories have the potential to bridge the geographies of space and place and, by implication, the two cultures of science. Finally, discuss in some detail conceptual and methodological implications.
Is it Easier to Escape from Low Pay in Urban Areas? Evidence from the United Kingdom
Authors: Phimister Euan , Theodossiou Ioannis , Upward Richard
Published: March 2006

In this paper we compare periods of low-paid employment between urban and rural areas in the United Kingdom. Using the British household panel survey, we estimate the probability that a period of low-paid employment will end, followed by a number of possible outcomes, namely a higher-paid job, self-employment, unemployment, and leaving the labour force. The results show that there are statistically significant differences in the dynamics of low pay across urban and rural labour markets, particularly in terms of exits to higher pay and out of the labour force. After controlling for different personal and job characteristics across markets, urban low-pay durations are somewhat shorter on average, with a higher probability of movement to a higher-paid job. The results suggest that any urban–rural differences in the typical low-pay experience are concentrated among certain types of individuals, such as young workers and women without qualifications.
Representing Complex Places: A Narrative Approach
Authors: Uprichard Emma , Byrne David
Published: March 2006

The authors argue that narratives—the plural being very important—are crucial for the representation of complex urban spaces. They do this by drawing on first-hand empirical examples from a previous examination of people's understanding of ‘postindustrial transformation’ from the past through the present to the future, and earlier work on children's understanding of their own places in the present and the future. In so doing, they propose that the use of narratives must be part of the repertoire of approaches used to represent complex urban systems. This does not imply an abandonment of interest in or search for causal generative mechanisms in system change. Rather, it is a recognition that narratives enable human actors to express the meaning that underlies their own agency as part of their account of the trajectories of places.
Complexity at Advancing Ecotones and Frontiers
Authors: Malanson George P , Zeng Yu , Walsh Stephen J
Published: March 2006

Ecotones, such as advancing treelines, have been examined as complex self-organizing systems. Frontiers of human settlement may share some of their spatial characteristics, because they too include feedbacks between spatial pattern and process. Advancing frontiers of three study areas in the Amazonian region of Ecuador are analyzed with the aid of Landsat imagery to detect change. Power-law distributions of advancing deforestation are found, which are indicative of possible complexity. Alternative approaches in self-organized complexity, including self-organized percolation and the inverse-cascade model, and an approach to complexity involving optimization—highly optimized tolerance—are considered. Some combination of these, based on their common ancestry in percolation theory, might provide insights into population–environment interaction at settlement frontiers.
Predicting the impact of perennial phases on average leakage from farming systems in south-western Australia
Authors: Ward P. R.
Published: March 2006

Rising watertables and dryland salinity in southern Australia are due to excess groundwater recharge after the replacement of native vegetation by annual crops and pastures. The inclusion of perennial plants into agricultural systems has been proposed as a possible method of recharge reduction, through the creation of a buffer (extra water storage capacity generated by the perennial in comparison with an annual crop or pasture). However, the role of perennial phases under conditions of highly episodic leakage is not well understood. In this paper, a simple Leakage/Buffer Model (LeBuM) was developed to determine the effect of perennial phases on long-term average annual leakage, incorporating episodic events. Mechanistic modelling studies on contrasting soil types were used to demonstrate that leakage for any given May–December period was directly related to soil water storage at 1 May. From this finding, it follows that leakage from a phase rotation can be calculated if the size of the buffer, and the leakage quantity in the absence of a buffer, are known for each stage of the rotation. LeBuM uses a long-term sequence of leakage values in the absence of a buffer as input, and the maximum buffer size, its rate of development, and the length of perennial and annual phases are specified as parameters. LeBuM was applied to leakage data modelled for 5 contrasting soil types over 100 years at 24 sites in the Western Australian wheatbelt. Phase rotations on duplex, waterlogging duplex, or loamy sand soils reduced leakage by >90% for regions with <380 mm annual rainfall, but were less effective in wetter regions and on deep sands or acid loamy sands. Nevertheless, phase rotations if adopted widely could delay the onset of salinity by as much as several decades.
Growth hormone is produced within the hippocampus where it responds to age, sex, and stress
Authors: Donahue Christine P. , Kosik Kenneth S. , Shors Tracey J.
Published: March 2006

Recent studies by our group and others have demonstrated that growth hormone (GH) is produced endogenously within the hippocampal formation, a brain structure associated with learning and aspects of emotional experience. Here, we demonstrate that this endogenously produced GH is modulated by age and sex differences and the presence of estrogen. GH mRNA levels were higher in females than males, especially during proestrus, a stage of estrus when estrogen levels are elevated. Moreover, GH expression was increased in ovariectomized females that were treated with estradiol. This increase in GH mRNA in response to estrogen was followed by the appearance of GH protein and was negatively correlated with the expression levels of insulin-like growth factor-I mRNA, suggesting a feedback relationship between insulin-like growth factor-I and GH in the brain. GH mRNA levels were also elevated in primary neuronal cultures exposed to 17-β-estradiol
in vitro
, further confirming the direct influence of estrogen on GH expression. Finally, exposure to an acute stressful event increased the expression and production of GH in both males and females. However, the stress-induced increase of GH in females depended on the stage of the estrous cycle in which they were exposed to the stressful event. Together, these data further demonstrate that GH is endogenously produced in the adult hippocampal formation, where it is regulated by age, estrogen, and exposure to environmental stimuli. These results suggest that GH may be involved in functions ascribed to the hippocampus, such as learning and the response to stressful experience.
Protein stability promotes evolvability
Authors: Bloom Jesse D. , Labthavikul Sy T. , Otey Christopher R. , Arnold Frances H.
Published: April 2006

The biophysical properties that enable proteins to so readily evolve to perform diverse biochemical tasks are largely unknown. Here, we show that a protein’s capacity to evolve is enhanced by the mutational robustness conferred by extra stability. We use simulations with model lattice proteins to demonstrate how extra stability increases evolvability by allowing a protein to accept a wider range of beneficial mutations while still folding to its native structure. We confirm this view experimentally by mutating marginally stable and thermostable variants of cytochrome P450 BM3. Mutants of the stabilized parent were more likely to exhibit new or improved functions. Only the stabilized P450 parent could tolerate the highly destabilizing mutations needed to confer novel activities such as hydroxylating the antiinflammatory drug naproxen. Our work establishes a crucial link between protein stability and evolution. We show that we can exploit this link to discover protein functions, and we suggest how natural evolution might do the same.
Transcriptional and posttranscriptional regulation of transcription factor expression in
Arabidopsis
roots
Authors: Lee Ji-Young , Colinas Juliette , Wang Jean Y. , Mace Daniel , Ohler Uwe , Benfey Philip N.
Published: April 2006

Understanding how the expression of transcription factor (TF) genes is modulated is essential for reconstructing gene regulatory networks. There is increasing evidence that sequences other than upstream noncoding can contribute to modulating gene expression, but how frequently they do so remains unclear. Here, we investigated the regulation of TFs expressed in a tissue-enriched manner in

Arabidopsis

roots. For 61 TFs, we created GFP reporter constructs driven by each TF’s upstream noncoding sequence (including the 5′UTR) fused to the GFP reporter gene alone or together with the TF’s coding sequence. We compared the visually detectable GFP patterns with endogenous mRNA expression patterns, as defined by a genome-wide microarray root expression map. An automated image analysis method for quantifying GFP signals in different tissues was developed and used to validate our visual comparison method. From these combined analyses, we found that (
i
) the upstream noncoding sequence was sufficient to recapitulate the mRNA expression pattern for 80% (35/44) of the TFs, and (
ii
) 25% of the TFs undergo posttranscriptional regulation via microRNA-mediated mRNA degradation (2/24) or via intercellular protein movement (6/24). The results suggest that, for

Arabidopsis

TFs, upstream noncoding sequences are major contributors to mRNA expression pattern establishment, but modulation of transcription factor protein expression pattern after transcription is relatively frequent. This study provides a systematic overview of regulation of TF expression at a cellular level.