bluuebunny/crossref_metadata_2025 huggingface dataset:
Holmboe modes revisited
Authors: Umurhan O. M. , Heifetz E.
Published: June 2007

A scaling analysis is presented better identifying the conditions in which the Boussinesq approximation may be used to study shear disturbances like that of Holmboe modes. The classic Holmboe normal mode instability is then reanalyzed by including baroclinic effects whose introduction alters the onset of Holmboe’s traveling-wave instability depending on the direction of the propagating modes. Since the introduction of baroclinicity is tantamount to relaxing the Boussinesq assumption, it means that in the presence of shear there is now a vertical variation of the horizontal momentum flux that alters the phase speed and structure of the classic Holmboe modes; the physical source of their broken right-left propagatory symmetry is associated with this physical effect. Furthermore, the regions of parameter space in which Holmboe’s classic analysis predicts there to be nonpropagating double instabilities now supports propagating Holmboe modes when baroclinic effects are included. We also find that a globally constant shear profile behaves as a stabilizing agent, in contradiction to the destabilizing role that shear normally plays in the classic Kelvin-Helmholtz problem of a shear-density interface. The general relationship between the normal modes of this type of system to that of the continuous spectrum is also noted. We also find that the baroclinic effects explored here probably do not manifest in terrestrial oceanographic and laboratory conditions, although they may do so in atmospheres.
Aluminum as a pressure-transmitting medium cum pressure standard for x-ray diffraction experiments to 200 GPa with diamond anvil cells
Authors: Singh Anil K. , Liermann Hanns-Peter , Akahama Yuichi , Kawamura Haruki
Published: June 2007

The compressive strength of 99.999% pure aluminum as a function of pressure to 215 GPa has been determined from the linewidth analysis of high-pressure x-ray diffraction patterns recorded with beveled-diamond anvil cell. The strength is found to increase linearly from 0.3(1) GPa at zero pressure to 5.0(2) GPa at 200 GPa. The data to 55 GPa with flat anvil diamond cell suggest that the strength of 99.999% pure aluminum increases from 0.21(8) GPa at zero pressure to 1.1(1) GPa at 55 GPa and the extrapolated strength at 200 GPa is 3.3(4). Significantly larger strength obtained with beveled-diamond anvil cell most likely arises due to larger radial stress gradients than in the case of flat anvils. The strength of aluminum is compared with those of argon to 50 GPa and of helium to 70 GPa. The use of face-centered cubic phase of aluminum in the dual role of a pressure standard and solid pressure-transmitting medium to 200 GPa is discussed.
Optimization in gradient networks
Authors: Gulbahce Natali
Published: June 2007

Gradient networks can be used to model the dominant structure of complex networks. Previous work has focused on random gradient networks. Here we study gradient networks that minimize jamming on substrate networks with scale-free and Erdős-Rényi structure. We introduce structural correlations and strongly reduce congestion occurring on the network by using a Monte Carlo optimization scheme. This optimization alters the degree distribution and other structural properties of the resulting gradient networks. These results are expected to be relevant for transport and other dynamical processes in real network systems.
Optimal flux patterns in cellular metabolic networks
Authors: Almaas Eivind
Published: June 2007

The availability of whole-cell-level metabolic networks of high quality has made it possible to develop a predictive understanding of bacterial metabolism. Using the optimization framework of flux balance analysis, I investigate the metabolic response and activity patterns to variations in the availability of nutrient and chemical factors such as oxygen and ammonia by simulating 30 000 random cellular environments. The distribution of reaction fluxes is heavy tailed for the bacteria H. pylori and E. coli, and the eukaryote S. cerevisiae. While the majority of flux balance investigations has relied on implementations of the simplex method, it is necessary to use interior-point optimization algorithms to adequately characterize the full range of activity patterns on metabolic networks. The interior-point activity pattern is bimodal for E. coli and S. cerevisiae, suggesting that most metabolic reactions are either in frequent use or are rarely active. The trimodal activity pattern of H. pylori indicates that a group of its metabolic reactions (20%) are active in approximately half of the simulated environments. Constructing the high-flux backbone of the network for every environment, there is a clear trend that the more frequently a reaction is active, the more likely it is a part of the backbone. Finally, I briefly discuss the predicted activity patterns of the central carbon metabolic pathways for the sample of random environments.
Nature-inspired interconnects for self-assembled large-scale network-on-chip designs
Authors: Teuscher Christof
Published: June 2007

Future nanoscale electronics built up from an Avogadro number of components need efficient, highly scalable, and robust means of communication in order to be competitive with traditional silicon approaches. In recent years, the networks-on-chip (NoC) paradigm emerged as a promising solution to interconnect challenges in silicon-based electronics. Current NoC architectures are either highly regular or fully customized, both of which represent implausible assumptions for emerging bottom-up self-assembled molecular electronics that are generally assumed to have a high degree of irregularity and imperfection. Here, we pragmatically and experimentally investigate important design tradeoffs and properties of an irregular, abstract, yet physically plausible three–dimensional (3D) small-world interconnect fabric that is inspired by modern network-on-chip paradigms. We vary the framework’s key parameters, such as the connectivity, number of switch nodes, and distribution of long- versus short-range connections, and measure the network’s relevant communication characteristics. We further explore the robustness against link failures and the ability and efficiency to solve a simple toy problem, the synchronization task. The results confirm that (1) computation in irregular assemblies is a promising and disruptive computing paradigm for self-assembled nanoscale electronics and (2) that 3D small-world interconnect fabrics with a power-law decaying distribution of shortcut lengths are physically plausible and have major advantages over local two–dimensional and 3D regular topologies.
Effect of electron thermal motion on plasma heating in a magnetized inductively coupled plasma
Authors: Aman-ur-Rehman  , Pu Yi-Kang
Published: June 2007

Power absorbed inside the magnetized inductively coupled plasma (MICP) is calculated using three different warm MICP models and is then compared with the result of the cold MICP model. The comparison shows that in the propagating region (ω<∣Ωe∣), under the cavity resonance conditions, warm plasma heating Swarm is significantly less than the cold plasma heating Scold, unless the distance traveled by the electrons due to their thermal motion, during the effective wave period, becomes significantly less than the wavelength of the cavity wave. Furthermore, in the propagating region, when ω≈∣Ωe∣, there appears a valley on the plot of η(ω)=Swarm∕Scold versus ω showing the negative effect of electron thermal motion on plasma heating. This valley widens and gets smoother with an increase in the plasma length. In the nonpropagating region (ω>∣Ωe∣), the maximum value of η(ω) exists when ω−∣Ωe∣≈vth∕δ, showing that, in the presence of the external magnetic field, the thermal motion of the electrons leads to a Doppler shift of the frequencies, at which collisionless heating is the dominant mode of electron heating. Furthermore, in the nonpropagating region, when ω≈∣Ωe∣, the skin depth of the right circularly polarized electric field decreases with magnetic field. This decrease in the skin depth results in an increase of collisionless heating under the Doppler-shifted wave particle resonant condition of ω−∣Ωe∣≈vth∕δ. It is also observed that, for large plasma length, the results of all the three warm MICP models are consistent with each other.
One- and two-dimensional modeling of argon K-shell emission from gas-puff Z-pinch plasmas
Authors: Thornhill J. W. , Chong Y. K. , Apruzese J. P. , Davis J. , Clark R. W. , Giuliani J. L. , Terry R. E. , Velikovich A. L. , Commisso R. J. , Whitney K. G. , Frese M. H. , Frese S. D. , Levine J. S. , Qi N. , Sze H. , Failor B. H. , Banister J. W. , Coleman P. L. , Coverdale C. A. , Jones B. , Deeney C.
Published: June 2007

In this paper, a theoretical model is described and demonstrated that serves as a useful tool for understanding K-shell radiating Z-pinch plasma behavior. Such understanding requires a self-consistent solution to the complete nonlocal thermodynamic equilibrium kinetics and radiation transport in order to realistically model opacity effects and the high-temperature state of the plasma. For this purpose, we have incorporated into the MACH2 two-dimensional magnetohydrodynamic (MHD) code [R. E. Peterkin et al., J. Comput. Phys. 140, 148 (1998)] an equation of state, called the tabular collisional radiative equilibrium (TCRE) model [J. W. Thornhill et al., Phys. Plasmas 8, 3480 (2001)], that provides reasonable approximations to the plasma’s opacity state. MACH2 with TCRE is applied toward analyzing the multidimensional implosion behavior that occurred in Decade Quad (DQ) [D. Price et al., Proceedings of the 12th IEEE Pulsed Power Conference, Monterey, CA, edited by C. Stallings and H. Kirbie (IEEE, New York, 1999), p. 489] argon gas puff experiments that employed a 12cm diameter nozzle with and without a central gas jet on axis. Typical peak drive currents and implosion times in these experiments were ∼6MA and ∼230ns. By using Planar Laser Induced Fluorescence measured initial density profiles as input to the calculations, the effect these profiles have on the ability of the pinch to efficiently produce K-shell emission can be analyzed with this combined radiation-MHD model. The calculated results are in agreement with the experimental result that the DQ central-jet configuration is superior to the no-central-jet experiment in terms of producing more K-shell emission. These theoretical results support the contention that the improved operation of the central-jet nozzle is due to the better suppression of instabilities and the higher-density K-shell radiating conditions that the central-jet configuration promotes. When we applied the model toward projecting argon K-shell yield behavior for Sandia National Laboratories’ ZR machine (∼25MA peak drive currents, ∼100ns implosion times) [D. McDaniel et al., Proceedings of the 5th International Conference on Dense Z-Pinches, Albuquerque, NM, 2002, edited by J. Davis, C. Deeney, and N. R. Pereira (American Institute of Physics, New York, 2002), Vol. 651, p. 23] for experiments that utilize the 12cm diameter central-jet nozzle configuration, it predicts over 1MJ of K-shell emission is attainable.
Dynamics and stability of dispersions of polyelectrolyte-filled multilayer microcapsules
Authors: Kim Byoung-Suhk , Lobaskin Vladimir , Tsekov Roumen , Vinogradova Olga I.
Published: June 2007

The authors report dynamic and coagulation properties of a dispersion of polyelectrolyte multilayer microcapsules filled with solutions of a strong polyelectrolyte. Microcapsules are shown to take a charge of the sign of encapsulated polyions and are characterized by a nonuniform distribution of inner polyions, which indicates a semipermeability of the shell and a leakage of counterions. The capsule self-diffusion coefficient in the vicinity of the similarly charged wall is measured using a particle tracking procedure from confocal images of the dispersion. The diffusion of capsules in the force field suggests that the effective interaction potential contains an electrostatic barrier, so that we deal with the same types of interaction forces as for solid particles. The theoretical estimates of the authors show that when microcapsules are in close proximity, their interaction should even be quantitatively the same as that of colloids with the same surface potential. However, due to the mobility of inner polyions they might repel stronger at large distances. The authors thus conclude that the encapsulation of charged polymers is an important factor in determining the adhesion and interaction properties of multilayer microcapsules.
Optimal internal coordinates, vibrational spectrum, and effective Hamiltonian for ozone
Authors: Zúñiga José , Picón José Antonio G. , Bastida Adolfo , Requena Alberto
Published: June 2007

In this paper the authors use the optimal internal vibrational coordinates previously determined for the electronic ground state of the ozone molecule to study the vibrational spectrum of the molecule employing the second empirical potential energy surface calculated by Tyuterev et al. [Chem. Phys. Lett. 316, 271 (2000)]. First, the authors compute variationally all the bound vibrational energy levels of the molecule up to the dissociation limit and state the usefulness of the optimal coordinates in this respect, which allows us to converge all the bound levels using relatively small anharmonic basis sets. By analyzing the expansion coefficients of the wave functions, they show then that a large portion of the vibrational spectrum of O3 can be structured in nearly separable polyadic groups characterized by the polyad quantum number N=n1+n2+nθ corresponding to the optimal internal coordinates. Accordingly, they determine an internal effective vibrational Hamiltonian for O3 by fitting the effective Hamiltonian parameters to the experimental vibrational frequencies, using as input parameters in the fit those extracted from an analytical second-order Van Vleck perturbation theory calculation. It is finally shown that the internal effective Hamiltonian thus obtained accurately describes the vibrational spectrum of ozone in the low and medium energy regimes.
Multiple attractors, long chaotic transients, and failure in small-world networks of excitable neurons
Authors: Riecke Hermann , Roxin Alex , Madruga Santiago , Solla Sara A.
Published: June 2007

We study the dynamical states of a small-world network of recurrently coupled excitable neurons, through both numerical and analytical methods. The dynamics of this system depend mostly on both the number of long-range connections or “shortcuts”, and the delay associated with neuronal interactions. We find that persistent activity emerges at low density of shortcuts, and that the system undergoes a transition to failure as their density reaches a critical value. The state of persistent activity below this transition consists of multiple stable periodic attractors, whose number increases at least as fast as the number of neurons in the network. At large shortcut density and for long enough delays the network dynamics exhibit exceedingly long chaotic transients, whose failure times follow a stretched exponential distribution. We show that this functional form arises for the ensemble-averaged activity if the failure time for each individual network realization is exponentially distributed.
Coulomb contribution to the direct current electrical conductivity of dense partially ionized plasmas
Authors: Adams J. R. , Shilkin N. S. , Fortov V. E. , Gryaznov V. K. , Mintsev V. B. , Redmer R. , Reinholz H. , Röpke G.
Published: June 2007

The Coulomb contribution to the electrical conductivity of partially ionized plasmas is discussed and its general behavior is investigated. Recent experiments on the direct current conductivity in shock wave induced argon and xenon plasmas are analyzed in this context. Within the relaxation time approach, the Coulomb contribution is extracted by eliminating the contribution of scattering from neutrals. Alternatively, the Coulomb contribution can be calculated directly within linear-response theory. In particular, from the latter approach a generalized Spitzer factor is derived for taking into account electron-electron interactions within the relaxation time approximation. Experimental results for the Coulomb contribution to the electrical conductivity are in reasonable agreement with an interpolation formula derived from linear-response theory.
Influence of unit cell rotated on the focusing in a two-dimensional photonic-crystal-based flat lens
Authors: Feng Zhifang , Wang Xiuguo , Li Zhiyuan , Zhang DaoZhong
Published: June 2007

Focusing in photonic crystal (PC) slab has been studied theoretically and experimentally. PCs are composed of a unit cell repeated periodically. In this article, we investigate in detail the influence of the continuous rotation of the unit cell on the focus in a two-dimensional photonic-crystal-based flat lens by the finite-difference time-domain method and experimental measurement. It is found that the focusing can appear within a large range of rotated angle of the unit cell. When the rotation exceeds a certain angle, the focusing disappears. However, it is interesting that the focusing does not depart from the symmetric center because of rotation of the unit cell.
High thermoelectric properties of p-type pseudobinary (Cu4Te3)x–(Bi0.5Sb1.5Te3)1−x alloys prepared by spark plasma sintering
Authors: Cui Jiaolin , Xiu Weijie , Xue Haifeng
Published: June 2007

Cu 4 Te 3 substituted (Cu4Te3)x–(Bi0.5Sb1.5Te3)1−x (x=0–0.2) alloys were prepared using spark plasma sintering technique and their thermoelectric properties were evaluated. Measurements show that the alloy with x=0.025 reveals very high electrical conductivity and low lattice thermal conductivity, the Seebeck coefficient that increases linearly with temperature is dependent on Cu4Te3 concentration. The maximum ZT value of 1.26 for the alloy with x=0.025 is achieved at 474K, whereas that of the state-of-the-art thermoelectric material Bi0.5Sb1.5Te3 is only 0.58 at 318K, thus indicating that the currently prepared pseudobinary alloy is very encouraging.
Spectrometer for lanthanides’ K x-ray fluorescence
Authors: Sakurai Kenji , Mizusawa Mari , Terada Yasuko
Published: June 2007

X-ray fluorescence analysis is a highly useful technique for determining the chemical composition of matter. The present article describes the successful development of a wavelength-dispersive x-ray fluorescence spectrometer for a fairly high-energy range, 30–60keV, that can contribute to studying lanthanides’ Kβ spectra with high-energy resolution. By combining a new high-energy synchrotron light source and the present spectrometer, it has been demonstrated that the full width at half maximum for lanthanum’s Kβ1 is 32eV and that all the peaks in the spectra are fully resolved. This corresponds to an energy resolution E∕ΔE of 1180, which is ten times better than a conventional system based on a Ge detector, which can detect only two peaks, Kβ1 and Kβ2, in seven peaks. The present spectrometer can open up a new field in x-ray spectrometry.
Sterilization of bacterial endospores by an atmospheric-pressure argon plasma jet
Authors: Uhm Han S. , Lim Jin P. , Li Shou Z.
Published: June 2007

Argon plasma jets penetrate deep into ambient air and create a path for oxygen radicals to sterilize microbes. A sterilization experiment with bacterial endospores indicates that an argon-oxygen plasma jet very effectively kills endospores of Bacillus atrophaeus (ATCC 9372), thereby demonstrating its capability to clean surfaces and its usefulness for reinstating contaminated equipment as free from toxic biological warfare agents. However, the spore-killing efficiency of the atmospheric-pressure argon-oxygen jet depends very sensitively on the oxygen concentration in the argon gas.
Time-resolved photoelectron imaging of large anionic methanol clusters: (Methanol)n−(n∼145–535)
Authors: Kammrath Aster , Griffin Graham B. , Verlet Jan R. R. , Young Ryan M. , Neumark Daniel M.
Published: June 2007

The dynamics of an excess electron in size-selected methanol clusters is studied via pump-probe spectroscopy with resolution of ∼120fs. Following excitation, the excess electron undergoes internal conversion back to the ground state with lifetimes of 260–175fs in (CH3OH)n−(n=145–535) and 280–230fs in (CD3OD)n−(n=210–390), decreasing with increasing cluster size. The clusters then undergo vibrational relaxation on the ground state on a time scale of 760±250fs. The excited state lifetimes for (CH3OH)n− clusters extrapolate to a value of 157±25fs in the limit of infinite cluster size.
Interaction of scrape-off layer currents with magnetohydrodynamical instabilities in tokamak plasmas
Authors: Fitzpatrick Richard
Published: June 2007

A simple theoretical model is developed which describes how current eddies are excited in the scrape-off layer (SOL) of a large-aspect-ratio, low-β, circular cross-section tokamak by time-varying magnetohydrodynamical instabilities originating from within the plasma. This model is used to study the interaction of SOL currents with tearing modes and resistive wall modes in a typical tokamak plasma. SOL currents are found to be fairly effective at braking the rotation of tearing modes, and to have a significant destabilizing effect on resistive wall modes.
Polymer functionalized piezoelectric-FET as humidity/chemical nanosensors
Authors: Lao Chang Shi , Kuang Qin , Wang Zhong L. , Park Myung-Chul , Deng Yulin
Published: June 2007

By coating one side of the surface of a ZnO nanobelt (NB) with multilayer polymers using an electrostatic self-assembling process, a humidity/chemical nanosensor based on piezoelectric field effect transistor (PE-FET) is demonstrated. The working principle of the PE-FET relies on the self-contraction/expansion of the polymer, which builds up a strain in the piezoelectric NB and induces a potential drop across the NB that serves as the gate voltage for controlling the current flowing through the NB. The response of PE-FET to the phase transition of the coating polymer was also demonstrated. The device is a component for nanopiezotronics.
Resonator combined with a piezoelectric actuator for chemical analysis by force microscopy
Authors: Kawai Yusuke , Ono Takahito , Esashi Masayoshi , Meyer Ernst , Gerber Christoph
Published: June 2007

A high frequency silicon resonator for dynamic scanning force microscopy is combined with an integrated piezoelectric actuation element for large displacements. A high resonance frequency is required for imaging on the nanometer scale, and a large displacement is needed for the chemical analysis of the material at the end of the probe. The small piezoelectric resonator is formed at the end of a long piezoelectric actuator using a silicon micromachining technology. The resonator can be oscillated at 96.4kHz, and the actuator generates a maximum displacement of 15μm at the end of the probe. The dynamic-mode scanning force microscopy capability, using the integrated piezoelectric resonator, is demonstrated on a 2μm pitch Au grating.
Reduction of magnetization in Zn0.9Fe0.1O diluted magnetic semiconducting nanoparticles by doping of Co or Mn ions
Authors: Mandal S. K. , Nath T. K. , Das A.
Published: June 2007

We have investigated structural, magnetic, optical, and electrical transport properties of Zn0.9−xFe0.1(Co∕Mn)xO (x=0.05,0.1 for Co and x=0.1 for Mn) diluted magnetic semiconducting nanoparticles synthesized through low temperature chemical “pyrophoric reaction process.” From transmission electron micrograph, particle sizes are found to be in the nanometric regime (∼7nm) and single crystalline in nature. The magnetization measurements reveal that doping of Co or Mn ions in ZnFeO nanometric matrix decreases the values of coercive field and average magnetization, not due to just increasing the total dopant concentration. It has been attributed to the formation of antiferromagnetic or paramagnetic states in ferromagnetic infinite cluster (spanning of magnetic polarons) by doping of Co or Mn ions. The strong irreversibility has been observed to persist at and above room temperature in magnetization versus temperature curve. The semiconducting band gap of those nanoparticles has been estimated using recorded absorbance spectra. The electrical behaviors of those samples have been investigated over the wide temperature and frequency range using ac complex impedance spectroscopy.
Periodic orbit analysis at the onset of the unstable dimension variability and at the blowout bifurcation
Authors: Pereira R. F. , de S. Pinto S. E. , Viana R. L. , Lopes S. R. , Grebogi C.
Published: June 2007

Many chaotic dynamical systems of physical interest present a strong form of nonhyperbolicity called unstable dimension variability (UDV), for which the chaotic invariant set contains periodic orbits possessing different numbers of unstable eigendirections. The onset of UDV is usually related to the loss of transversal stability of an unstable fixed point embedded in the chaotic set. In this paper, we present a new mechanism for the onset of UDV, whereby the period of the unstable orbits losing transversal stability tends to infinity as we approach the onset of UDV. This mechanism is unveiled by means of a periodic orbit analysis of the invariant chaotic attractor for two model dynamical systems with phase spaces of low dimensionality, and seems to depend heavily on the chaotic dynamics in the invariant set. We also described, for these systems, the blowout bifurcation (for which the chaotic set as a whole loses transversal stability) and its relation with the situation where the effects of UDV are the most intense. For the latter point, we found that chaotic trajectories off, but very close to, the invariant set exhibit the same scaling characteristic of the so-called on-off intermittency.
Bifunctional carbon nanotube networks for supercapacitors
Authors: Kaempgen M. , Ma J. , Gruner G. , Wee G. , Mhaisalkar S. G.
Published: June 2007

Highly conducting and porous carbon nanotube (CNT) networks are used as the sole electron conducting material in supercapacitors. The high conductivity of CNT networks and the high surface area allow the replacement of both the metallic current collector and the active material that forms one side of the electrochemical double layer. The combination of both functions in one single layer leads to lightweight charge storage devices that can be manufactured using simple and cheap room temperature methods. The authors have demonstrated that the specific capacitance of such CNT electrodes is comparable to that of other carbon electrodes.
Evolution with the annealing treatments of the photoluminescence mechanisms in a-SiNx:H alloys prepared by reactive evaporation
Authors: Molinari M. , Rinnert H. , Vergnat M.
Published: June 2007

A wide range of amorphous hydrogenated silicon nitride thin films with an excess of silicon was prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions. A strong visible photoluminescence at room temperature was observed for the as-deposited films as well as for films annealed up to 1100°C. The chemical composition and the structure of the films were investigated using x-ray photoelectron, thermal desorption, and Raman spectroscopies, infrared absorption measurements, grazing incidence x-ray diffraction experiments, and transmission electron microscopy. Two luminescence mechanisms were identified for the films depending on the annealing temperature. For annealing temperatures below 650°C, the films are made of amorphous silicon-rich phases mixed with nitrogen-rich phases. These inhomogeneities in the chemical composition, coupled with the evolution of the photoluminescence energies and intensities with the hydrogen content, suggest that the emission is due to the recombination process of the photogenerated carriers within the band-tail states. For temperatures higher than 800°C, a phase separation occurs and the films could be described as silicon nanoclusters embedded in an insulating amorphous silicon nitride matrix. The clusters are amorphous, and then crystallized when the annealing temperature is high enough. The correlation between the clusters sizes and the photoluminescence results suggests that the emission observed after annealing treatments at temperature higher than 900°C is due to the quantum confinement of the carriers inside the silicon clusters. By carefully choosing the preparation and the annealing conditions, it is possible to tune the photoluminescence energy in the visible range.
Excited state dynamics of the Ho3+ ions in holmium singly doped and holmium, praseodymium-codoped fluoride glasses
Authors: Librantz André Felipe Henriques , Jackson Stuart D. , Jagosich Fabio Henrique , Gomes Laércio , Poirier Gaël , Ribeiro Sidney José Lima , Messaddeq Younes
Published: June 2007

The deactivation of the two lowest excited states of Ho3+ was investigated in Ho3+ singly doped and Ho3+, Pr3+-codoped fluoride (ZBLAN) glasses. We establish that 0.1–0.3mol% Pr3+ can efficiently deactivate the first excited (I75) state of Ho3+ while causing a small reduction of ∼40% of the initial population of the second excited (I65) state. The net effect introduced by the Pr3+ ion deactivation of the Ho3+ ion is the fast recovery of the ground state of Ho3+. The Burshstein model parameters relevant to the Ho3+→Pr3+ energy transfer processes were determined using a least squares fit to the measured luminescence decay. The energy transfer upconversion and cross relaxation parameters for 1948, 1151, and 532nm excitations of singly Ho3+-doped ZBLAN were determined. Using the energy transfer rate parameters we determine from the measured luminescence, a rate equation model for 650nm excitation of Ho3+-doped and Ho3+, Pr3+-doped ZBLAN glasses was developed. The rate equations were solved numerically and the population inversion between the I65 and the I75 excited states of Ho3+ was calculated to examine the beneficial effects on the gain associated with Pr3+ codoping.
Development of a magnetic quartz crystal microbalance
Authors: Yu George Y. , Hunt William D. , Josowicz Mira , Janata Jiri
Published: June 2007

A new technique for measurement of magnetic properties of materials is demonstrated. It can be used for the measurement of thin magnetic films during their chemical modification. The resonance frequency of a quartz crystal microbalance (QCM) with conducting polymer (polyaniline) suspension in poly(ethylene glycol) was observed to increase with increasing the externally applied uniform dc magnetic field. Slowly sweeping the magnetic field between 0 and 3.1T results in a frequency-field response curve. Chemical doping was done by exposing the polyaniline-emeraldine base film to HCl vapor. The change in population of free spins is reflected in increased frequency-field curve magnitude after HCl doping. Two working hypotheses explaining this observation are offered to explain how frequency of QCM with deposited magnetic film shifts with increasing intensity of the magnetic field.
Determining interfacial properties of submicron low-k films on Si substrate by using wedge indentation technique
Authors: Yeap Kong Boon , Zeng Kaiyang , Jiang Haiyan , Shen Lu , Chi Dongzhi
Published: June 2007

This article presents studies on using a wedge indentation technique to determine interfacial adhesion properties of low-k dielectric films, namely, methyl-silsesquioxane (MSQ) and black diamond (BD™)films, both on a Si substrate. Interfacial crack initiation and propagation processes in the MSQ/Si system are studied by using focused-ion-beam sectioning of the indentation impressions created by wedge tips with 90° and 120° of inclusion angles, respectively. Furthermore, the indentation induced stress is found to be proportional to the ratio of the indentation volume and the interface delamination crack volume for both plane strain and nonplane strain cases. With this analysis, the interface toughness of the MSQ/Si and BD/Si system, in terms of the strain energy release rate, is determined. The interface toughness for the MSQ/Si system is found to be a value of 1.89±0.28J∕m2 for the 90° wedge tip indentation and 1.92±0.08J∕m2 for the 120° wedge tip indentation. In addition, using the 120° wedge tip, the interface toughnesses of the BD films on the Si substrate with 200 and 500nm thicknesses are found to be the values of 6.62±1.52 and 6.35±2.27J∕m2, respectively.
Defect generation at the Si–SiO2 interface following corona charging
Authors: Jin Hao , Weber K. J. , Dang N. C. , Jellett W. E.
Published: June 2007

A combination of capacitance-voltage and lifetime decay measurements is used to show that corona biasing of silicon oxidized samples results in the generation of additional interface defects and an increase in surface recombination. The onset of interface degradation occurs at relatively low electric fields, estimated to be less than ∼+∕−1.2MV∕cm. The majority of the defects generated by corona biasing can be removed by a short annealing at 400°C. The results are consistent with the hypothesis that atomic hydrogen is chiefly responsible for the observed degradation. Corona biasing, even at low electric fields, cannot be relied on as a noninvasive characterization tool.
Stabilization of the liquid crystal director in the patterned vertical alignment mode through formation of pretilt angle by reactive mesogen
Authors: Kim Sang Gyun , Kim Sung Min , Kim Youn Sik , Lee Hee Kyu , Lee Seung Hee , Lee Gi-Dong , Lyu Jae-Jin , Kim Kyeong Hyeon
Published: June 2007

In the patterned vertical alignment (PVA) cell in which multidomains are formed from the perfect vertical alignment through an oblique field only, the formation of disclinations between liquid crystal (LC) molecules is inevitable in the presence of an electric field, which lowers transmittance and the response time. In the proposed PVA device, the pretilt angle is formed in four different directions through the polymerization of an UV curable reactive mesogen monomer at the surface. In this way, the reorientation of LC responding to an electric field is well defined, and thus the device shows reduced threshold voltage and much improved response time in all gray scales.
Upconversion injection in rubrene/perylene-diimide-heterostructure electroluminescent diodes
Authors: Pandey Ajay K. , Nunzi Jean-Michel
Published: June 2007

The authors implement and demonstrate in this letter a scheme that permits to drive electroluminescence with an extremely low turn-on voltage. The device behaves like compound semiconductors, in which the electroluminescence turn-on voltage is about the same as the open circuit voltage for the photovoltaic effect. However, the electroluminescence turn-on voltage is about half of the band gap of the emitting material that cannot be explained using current models of charge injection in organic semiconductors. The authors hereby propose explanation through an Auger-type two-step injection mechanism.
Biosensor utilizing resist-derived carbon nanostructures
Authors: Lee Jung A , Lee Seung S. , Lee Kwang-Cheol , Park Se Il , Woo Byung-Chill , Lee Jeong-O
Published: June 2007

The authors present a biosensor using pyrolyzed electron beam resist nanostructures as an active conducting channel. Versatile, arbitrarily shaped nanostructures such as nanowires, nanodots, and suspended nanobridges are fabricated by a facile electron beam resist thermal decomposition method. The nanostructures typically show 15–21nm thickness, 100–200nm width, 0.6nm roughness, and p-type majority conduction with tailored resistivity of 5.2–0.75Ωcm. Streptavidin-biotin binding and pH dependent conductance modulation are demonstrated using pyrolyzed resist based devices.
Control of microfabricated structures powered by flagellated bacteria using phototaxis
Authors: Steager Edward , Kim Chang-Beom , Patel Jigarkumar , Bith Socheth , Naik Chandan , Reber Lindsay , Kim Min Jun
Published: June 2007

Flagellated bacteria have been employed as microactuators in low Reynolds number fluidic environments. SU-8 microstructures have been fabricated and released on the surface of swarming Serratia marcescens, and the flagella propel the structures along the swarm surface. Phototactic control of these structures is demonstrated by exposing the localized regions of the swarm to ultraviolet light. The authors additionally discuss the control of microstructures in an open channel powered by bacteria which have been docked through a blotting technique. A tracking algorithm has been developed to analyze swarming patterns of the bacteria as well as the kinematics of the microstructures.
Vibration energy harvesting device based on air-spaced piezoelectric cantilevers
Authors: Wang Zhuo , Xu Yong
Published: June 2007

This letter reports a piezoelectric device based on air-spaced composite cantilevers for vibration energy harvesting. With air-spaced piezoelectric cantilevers, the voltage generated due to vibrations is larger since the distance between the piezoelectric layer and the neutral plane is increased. In addition, the energy conversion efficiency is also increased. A simplified analytical model was developed to explain the advantages and facilitate the selection of design parameters. Finite element simulation was also carried out to verify the analytical results. A prototype was successfully assembled and tested.
How to create and detect N-dimensional entangled photons with an active phase hologram
Authors: Stütz Martin , Gröblacher Simon , Jennewein Thomas , Zeilinger Anton
Published: June 2007

The experimental realization of multidimensional quantum states may lead to unexplored and interesting physics, as well as advanced quantum communication protocols. The orbital angular momentum of photons is a well suitable discrete degree of freedom for implementing high-dimensional quantum systems. The standard method to generate and manipulate such photon modes is to use bulk and fixed optics. Here the authors demonstrate the utilization of a spatial light modulator to manipulate the orbital angular momentum of entangled photons generated in spontaneous parametric downconversion. They show that their setup allows them to realize photonic entanglement of up to 21 dimensions, which in principle can be extended to even larger dimensions.
Photoluminescent behavior of SrBi2Nb2O9 powders explained by means of β-Bi2O3 phase
Authors: Volanti D. P. , Cavalcante L. S. , Paris E. C. , Simões A. Z. , Keyson D. , Longo V. M. , de Figueiredo A. T. , Longo E. , Varela J. A. , De Vicente F. S. , Hernandes A. C.
Published: June 2007

Photoluminescence (PL) behavior of SrBi2Nb2O9 (SBN) powders was explained by means of β-Bi2O3 phase on the SBN lattice. Oxygen vacancies and recombination of electrons holes in the valence band lead to the formation of [NbO5∙VOx], [NbO5∙VO•] and [NbO5∙VO••] complex clusters which are the main reason for the PL at room temperature. X-ray diffraction and Fourier transform Raman spectroscopy were used as tools to investigate the structural changes in SBN lattice allowing to correlate [NbO5∙VO•]∕[NbO6]′ ratio with the evolution of the visible PL emission in the SBN powders.
Rehabilitation of field tunnel erosion using techniques developed for construction with dispersive soils
Authors: Hardie M. A. , Cotching W. E. , Zund P. R.
Published: June 2007

Past repairs of field tunnel erosion using mechanical treatments (deep ripping, contour furrowing, contour ripping, etc.) and reestablishment of perennial vegetation have often failed, resulting in further tunnelling. Techniques to prevent ‘piping’ (tunnel erosion) in earth dams constructed using sodic clays have not been used in the repair of field tunnel erosion; however, these techniques have the potential to reduce recurrent failure. Installation of an optical fibre cable in a Grey Sodosol and Grey Dermosol at a site near Dunalley, Tasmania, in November 2001, resulted in the formation of a 380-m-long tunnel erosion system. Detailed site investigations and soil analysis in 2004 indicated that the tunnel erosion resulted from the consequences of inadequate compaction during the installation of the optical fibre cable, and secondary processes such as capture of surface and subsurface flow, dispersion of sodic clays, and translocation of dispersed clay platelets through the poorly compacted fill. Repair works consisted of excavating the entire length of the tunnel system, chemical amelioration with gypsum, compaction of repacked fill to reduce internal porosity, and installation of sand blocks to capture and remove water moving along the reinstalled cable. Inspections conducted 2 years after completion of the repair works indicated the site to be stable; however, it is acknowledged that this is too short an interval to adequately assess the long-term stability of repair works and techniques employed at the site. Due to the costs associated with the application of dam construction techniques, their use for the repair of field tunnel erosion is likely to only be justified where continued erosion poses a risk of damage to high value infrastructure.
Modelling DCD effect on nitrate leaching under controlled conditions
Authors: Vogeler Iris , Blard Adeline , Bolan Nanthi
Published: June 2007

Effects of nitrogen losses through nitrate leaching are one of the major environmental issues worldwide. To determine the potential effect of dicyandiamide (DCD), a nitrification inhibitor, on the transformation of urea nitrogen and subsequent nitrate leaching, incubation and column leaching experiments were performed. Tokomaru silt loam soil was treated with urea, DCD, or urea plus DCD. A control was also used.
In the laboratory incubation experiment, the conversion of urea to ammonium (i.e. ammonification process or urea hydrolysis) occurred within a day, thereby increasing the soil pH from 5.8 to 6.9. DCD did not affect the ammonification process. However, DCD did slow down the subsequent oxidation of ammonium to nitrate (i.e. nitrification process). The half-life time of ammonium in this soil was increased from 9 days for the urea treatment to 31 days for the urea + DCD treatment. The production of nitrate was 5 times slower when DCD was added.
In the leaching experiments, half the columns were leached after 1 day of incubation (Day 1), the other half 7 days later (Day 7). For Day 1, no significant differences in nitrate leaching could be seen between the treatments, as the nitrification had not yet taken place. For Day 7, DCD decreased nitrate leaching by 71% with a corresponding decrease in nitrate-induced cation leaching, including ammonium. Thus, DCD seems to be effective in decreasing both ammonium and nitrate leaching, but its high solubility and thus mobility could be a limitation to its use.
The convection–dispersion equation, including source–sink terms for nitrogen transformations, ammonification, and nitrification rate constants, and a factor for nitrification inhibition by DCD, accounting for degradation and efficiency of DCD, could be used reasonably well to simulate nitrate leaching from the column leaching experiments. However, model parameter values for nitrification rate, and efficiency and decay rate for DCD, were different from those obtained from the incubation experiments, which was probably because of the difference in water content of soil between the incubation and leaching experiments.
Effectiveness of hydrated lime and artificial zeolite amendments and sedum (Sedum sediforme) plant cover in controlling soil erosion from an acid soil
Authors: Andry Henintsoa , Yamamoto Tahei , Inoue Mitsuhiro
Published: June 2007

There are over 350 different species of sedum (Sedum spp.) and most of them can tolerate harsh conditions including very cold to hot temperatures, drought, and poor and stony soil. Sedum plants are used in rock gardens and edging flower beds, and for greening the tops of buildings, cottages, and thatched roofs. However, little is known about the effectiveness of sedum as vegetation cover in protecting soil erosion from a road embankment made of acid soil. Acid soil is believed to be vulnerable to soil erosion and is not suitable for plant growth. Liming treatment is required first before revegetation to alleviate the soil acidity; however, lime incorporation may affect the soil physical properties and, consequently, runoff and sediment generation. A rainfall simulation study was conducted to test the effectiveness of hydrated lime and artificial zeolite as amendments and Sedum sediforme (Rupestria group) as vegetation cover in controlling soil erosion from an acid soil taken from mountain cuts in Yamaguchi prefecture, Japan, where it is used for road embankment. The soil was treated with 0.5% lime and 10% zeolite. Two rainfall intensities of 30 and 60 mm/h were tested for 2 and 1 h, respectively, on sedum-growing soil plots measuring 0.50 by 0.30 by 0.05 m. Three levels of vegetation cover (bare soil, 25%, 75%) of sedum plant of 5-month growth under 2-day irrigation intervals were tested.
The incorporation of hydrated lime and artificial zeolite amendments improved wet aggregate stability, which contributed to significant decrease in surface runoff, sediment concentration, and total soil loss by rain splash from the bare soil. Zeolite was more effective in promoting plant growth than the lime treatment; as a result the decrease in sediment generation and soil loss by rain splash, compared with the control, was larger with zeolite than with lime. Under both intensities of simulated rain, the sediment concentration and total soil loss by rain splash decreased significantly (P < 0.05) with increasing surface cover. The correlation between cumulative soil loss (CSL) and cumulative surface runoff was linear and significant (P < 0.001) and the slope coefficient decreased with increasing surface cover. This suggests that the sediment carrying capacity or the erosivity of the surface runoff was constant and it decreased with increasing surface cover. The sedum cover reduced the CSL up to 72 and 79% under 30 and 60 mm/h rainfall intensities, respectively. The mean weight diameter of the soil sediment transported by runoff and soil loss by rain splash were significantly increased, and therefore, the silt and clay proportion of the crust material formed on the soil surface decreased up to 6 and 16% under 25 and 75% vegetation cover, respectively. These results demonstrate that hydrated lime and artificial zeolite could be used as amendments and sedum plant as vegetation covers in controlling soil erosion from an acid soil.
The Size of the Nucleus Increases as Yeast Cells Grow
Authors: Jorgensen Paul , Edgington Nicholas P. , Schneider Brandt L. , Rupeš Ivan , Tyers Mike , Futcher Bruce
Published: June 2007

It is not known how the volume of the cell nucleus is set, nor how the ratio of nuclear volume to cell volume (N/C) is determined. Here, we have measured the size of the nucleus in growing cells of the budding yeast Saccharomyces cerevisiae. Analysis of mutant yeast strains spanning a range of cell sizes revealed that the ratio of average nuclear volume to average cell volume was quite consistent, with nuclear volume being ∼7% that of cell volume. At the single cell level, nuclear and cell size were strongly correlated in growing wild-type cells, as determined by three different microscopic approaches. Even in G1-phase, nuclear volume grew, although it did not grow quite as fast as overall cell volume. DNA content did not appear to have any immediate, direct influence on nuclear size, in that nuclear size did not increase sharply during S-phase. The maintenance of nuclear size did not require continuous growth or ribosome biogenesis, as starvation and rapamycin treatment had little immediate impact on nuclear size. Blocking the nuclear export of new ribosomal subunits, among other proteins and RNAs, with leptomycin B also had no obvious effect on nuclear size. Nuclear expansion must now be factored into conceptual and mathematical models of budding yeast growth and division. These results raise questions as to the unknown force(s) that expand the nucleus as yeast cells grow.