bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resolution force sensor based on morphology dependent optical resonances of polymeric spheres
Authors: Ioppolo T. , Ayaz U. K. , Ötügen M. V.
Published: January 2009

Performance characteristics of a force sensor concept based on the morphology dependent resonance (MDR) shifts of micro-optical resonators have been investigated. Previous experimental studies have indicated that microsphere sensors with diameters ranging between 30 and 950 μm may have force resolutions reaching 10−5 N [T. Ioppolo et al., Appl. Opt. 47, 3009 (2008)]. In the present, we carry out a systematic analysis and experiments to investigate the sensitivity, resolution, and bandwidth limits of MDR-based force sensors. Expressions for MDR shifts due to applied force in the polar direction are obtained for microspheres of various dielectric materials in the diameter range of 300–950 μm. The analyses are compared with experimental results for polymethylmethacrylate and polydimethylsyloxane (PDMS) microsphere sensors. The results show that the strain effect on MDR shifts is dominant over that of mechanical stress. It also indicates that force sensitivities of the order of a 1 pN are feasible using hollow PDMS spheres. The sensor bandwidths range between 1 kHz and 1 MHz, depending on the sphere material.
Direct evidence for mode-specific vibrational energy relaxation from quantum time-dependent perturbation theory. I. Five-coordinate ferrous iron porphyrin model
Authors: Zhang Yong , Fujisaki Hiroshi , Straub John E.
Published: January 2009

The time scales and mechanisms of mode-specific vibrational energy relaxation in imidazole ligated ferrous iron porphine were studied using a non-Markovian time-dependent perturbation theory and density functional theory calculation. Seven normal modes, including ν4, ν7, and five Fe out-of-plane modes (Fe-oop), were treated as the relaxing system mode coupled to all other modes forming the bath. The derived cooling time constants for the ν4 and ν7 modes agree well with the results of previous experimental studies. The pathways for energy transfer from each system mode were identified. The γ7 mode, associated with Fe-oop motion with frequency ∼350 cm−1, was observed to couple strongly through its overtone with the ν7 porphine in-plane vibration. This suggests a possible mechanism for the excitation of the ν7 mode, which is distinct from the direct excitation together with Fe-oop motion of the ν4 mode. Four other Fe-oop motions were observed to couple to low frequency modes including those involving significant imidazole ligand motions. Through these couplings, excitation following ligand photodissociation may be efficiently transferred from the heme doming mode to the protein backbone motions essential to conformational changes associated with the protein’s function.
Ab initio study of stoichiometric gallium phosphide clusters
Authors: Kamal C. , Ghanty Tapan K. , Banerjee Arup , Chakrabarti Aparna
Published: January 2009

We have studied the static dipole polarizability of stoichiometric gallium phosphide clusters (GanPn with n=2–5) by employing various ab initio wave function based methods as well as density functional theory/time dependent density functional theory (DFT/TDDFT). The calculation of polarizability within DFT/TDDFT has been carried out by employing different exchange-correlation functionals, ranging from simple local density approximation to an asymptotically correct model potential-statistical average of orbital potential (SAOP) in order to study their influences. The values obtained by using the model potential-SAOP are lower than those obtained by local density approximation and generalized gradient approximation. A systematic analysis of our results obtained using the DFT/TDDFT with several exchange-correlation functionals shows that the values of polarizability obtained within generalized gradient approximation by using Perdew-Burke-Ernzerhof exchange with Lee–Yang–Parr correlation functional and Perdew–Burke–Ernzerhof exchange-correlation functionals are the closest to the corresponding results from Møller–Plesset perturbation theory. We have found that the value of average static dipole polarizability per atom reaches the bulk limit from the above as the size of the clusters increases.
Obliquely propagating dust-acoustic waves in dense quantum magnetoplasmas
Authors: Khan S. A. , Masood W. , Siddiq M.
Published: January 2009

Two-dimensional, obliquely propagating nonlinear quantum dust-acoustic waves in dense magnetized plasmas are investigated on the basis of a quantum hydrodynamic model. In this regard, the Zakharov–Kuznetsov (ZK) equation is derived using the small amplitude approximation method. The extended hyperbolic tangent method is employed to obtain solitary and explosive solutions of the ZK equation. It is found that the quantum effects related to the Bohm potential, dust concentration, external magnetic field, and obliqueness significantly modify the amplitude and width of both solitary and explosive pulses. The relevance of the study to dense plasmas is also discussed.
On the ultraviolet photofragmentation of CH3Xe+
Authors: Alekseyev Aleksey B. , Liebermann Heinz-Peter , Buenker Robert J.
Published: January 2009

The multireference spin-orbit configuration interaction method is employed to calculate potential energy surfaces for the ground and low-lying excited states of the CH3Xe+ cation as functions of the Xe–C bond length and the Xe–C–H angle. It is shown that the X̃ A11 ground state of CH3Xe+ is well bound (De=1.78 eV) and dissociates to the CH3+(X̃ A11′)+Xe(S1) limit. In contrast, all lowest excited states of CH3Xe+ are repulsive in the Franck–Condon region and converge to the strongly spin-split CH3(X̃ A2″)+Xe+(P23/2,1/2) asymptotes. Transition dipole moments for the low-lying valence states are computed at the X̃ A11 equilibrium geometry. It is shown that the first absorption continuum (A band) of CH3Xe+ is dominated by the parallel Q30+(A1)←X̃ A11 transition, which leads to the CH3+Xe+(P23/2) dissociation products. The perpendicular transitions to the Q1(E), Q31(E), and A31(E) states are found to be significantly weaker. The CH3Xe+ photodissociation process in its A band is analyzed on the basis of the computed data and compared with the photodissociation of the isovalent RgH+ (Rg=Ar,Kr,Xe), HI, and CH3I systems.
Efficient sampling for ab initio Monte Carlo simulation of molecular clusters using an interpolated potential energy surface
Authors: Nakayama Akira , Seki Nanami , Taketsugu Tetsuya
Published: January 2009

An approach is developed to enhance sampling for ab initio Monte Carlo and ab initio path integral Monte Carlo calculations of molecular clusters by utilizing an approximate potential as a guide to move in the configuration space more efficiently. The interpolated potential energy obtained by the moving least-squares method is used as an approximate potential, and this scheme is applied to a water molecule and small protonated water clusters (H3O+,H5O2+). It is found that the statistical errors are reduced by almost a factor of 3 in most calculations, which translates into a reduction in the computational cost by an order of magnitude. We also provide an automatic scheme where the ab initio data obtained during the simulation is added to the reference data set of interpolation dynamically, which further speeds up the convergence.
A two-dimensional lattice ion trap for quantum simulation
Authors: Clark Robert J. , Lin Tongyan , Brown Kenneth R. , Chuang Isaac L.
Published: January 2009

Quantum simulations of spin systems could enable the solution of problems that otherwise require infeasible classical resources. Such a simulation may be implemented using a well-controlled system of effective spins, such as a two-dimensional lattice of locally interacting ions. We propose here a layered planar rf trap design that can be used to create arbitrary two-dimensional lattices of ions. The design also leads naturally to ease of microfabrication. As a first experimental demonstration, we confine S88r+ ions in a millimeter-scale lattice trap and verify numerical models of the trap by measuring the motional frequencies. We also confine 440 nm diameter charged microspheres and observe ion-ion repulsion between ions in neighboring lattice sites. Our design, when scaled to smaller ion-ion distances, is appropriate for quantum simulation schemes, e.g., that of Porras and Cirac [Phys. Rev. Lett. 92, 207901 (2004)]. We note, however, that in practical realizations of the trap, an increase in the secular frequency with decreasing ion spacing may make a coupling rate that is large relative to the decoherence rate in such a trap difficult to achieve.
Origin of reduced polarizations in short-period BaTiO3/SrTiO3 ferroelectric superlattices
Authors: Lee Jun Hee , Yu Jaejun , Waghmare U. V.
Published: January 2009

We present an analysis of the polarization properties of BaTiO3/SrTiO3 superlattices using an effective Hamiltonian derived from first-principles calculations based on density-functional theory. We show that the hardening and modification of local soft modes at the interface environment is responsible for (a) the deviation of the interface structure from the bulk one and (b) the suppression of polarization in the short-period superlattices. The effect of this interfacial coupling is shown to be enhanced as the epitaxial strain becomes tensile.
On the distribution of the nodal sets of random spherical harmonics
Authors: Wigman Igor
Published: January 2009

We study the volume of the nodal set of eigenfunctions of the Laplacian on the m-dimensional sphere. It is well known that the eigenspaces corresponding to En=n(n+m−1) are the spaces En of spherical harmonics of degree n of dimension N. We use the multiplicity of the eigenvalues to endow En with the Gaussian probability measure and study the distribution of the m-dimensional volume of the nodal sets of a randomly chosen function. The expected volume is proportional to En. One of our main results is bounding the variance of the volume to be O(En/N). In addition to the volume of the nodal set, we study its Leray measure. We find that its expected value is n independent. We are able to determine that the asymptotic form of the variance is (const)/N.
Macroscopic control parameter for avalanche models for bursty transport
Authors: Chapman S. C. , Rowlands G. , Watkins N. W.
Published: January 2009

Similarity analysis is used to identify the control parameter RA for the subset of avalanching systems that can exhibit self-organized criticality (SOC). This parameter expresses the ratio of driving to dissipation. The transition to SOC, when the number of excited degrees of freedom is maximal, is found to occur when RA→0. This is in the opposite sense to (Kolmogorov) turbulence, thus identifying a deep distinction between turbulence and SOC and suggesting an observable property that could distinguish them. A corollary of this similarity analysis is that SOC phenomenology, that is, power law scaling of avalanches, can persist for finite RA with the same RA→0 exponent if the system supports a sufficiently large range of lengthscales, necessary for SOC to be a candidate for physical (RA finite) systems.
Enhanced resonant acceleration of electrons from intense laser interaction with density-attenuating plasma
Authors: Niu H. Y. , He X. T. , Zhou C. T. , Qiao Bin
Published: January 2009

An enhanced resonant acceleration scheme for electrons by intense circularly polarized laser pulse in a plasma with slowly attenuating density is proposed. As it propagates, the phase velocity and Doppler-shifted frequency of the laser both gradually decrease, so that the electrons moving in the combined laser and spontaneous fields can retain betatron resonance for a rather long time and effectively acquire energy from the laser. The theoretical analysis is verified by test-particle numerical calculations. It is shown that well-collimated GeV electron beams with very low beam divergence can be produced.
Competition between interlayer exchange and Zeeman energies on the way to saturation of magnetization in Fe/Cr multilayers
Authors: Khatua P. , Majumdar A. K.
Published: January 2009

We have studied the field and temperature dependence of magnetization on ion-beam sputtered Fe/Cr multilayers. The samples were characterized by small angle x-ray reflectivity and grazing incidence x-ray diffraction techniques. The temperature dependence of the magnetization at the saturation field (Hsat) is interpreted in terms of the spin-wave theory with an additional paramagnetic contribution from the nanometer size Cr. At moderately high magnetic fields but below Hsat, an unusual increase in the magnetization with temperature, for samples of higher Cr thickness, was observed. The presence of an anomalous peak, especially for the highest Cr thickness sample at around room temperature and at magnetic fields as high as 2 T, is believed to appear as a result of an intricate competition between the Fe–Fe interlayer exchange coupling and the Zeeman energy of the outer Fe spins for the requirement of the minimum energy state.
Simultaneous measurement of substrate temperature and thin-film thickness on SiO2/Si wafer using optical-fiber-type low-coherence interferometry
Authors: Ohta Takayuki , Koshimizu Chishio , Kawasaki Kanta , Takeda Keigo , Ito Masafumi
Published: January 2009

This paper proposes a technique for simultaneously monitoring the thickness of a SiO2 thin film and the temperature of a Si substrate. This technique uses low-coherence interferometry and has the potential to be used for online monitoring of semiconductor manufacturing processes. In low-coherence interferometry, when the optical path length of a layer is shorter than the coherence length of the light source, the two interference at the top and bottom interfaces of the layer overlap each other. In this case the detected peak position of the interference is shifted from the actual interface, resulting in an error in the temperature measurement, since the temperature is derived from the optical path length of the layer. To improve the accuracy of the temperature measurement, the effect of the overlapping interference was compensated by measuring the SiO2 thickness. The thickness of the Si substrate was 750 μm and the thickness of the SiO2 film was varied between 0 and 2 μm. The SiO2 thickness, which is shorter than the coherence length of the light source, was measured from the ratio of interference intensities of two superluminescent diodes (wavelengths: 1.55 and 1.31 μm). The measured ratio corresponded well with the theoretical one for SiO2 film thicknesses between 0 and 2 μm, and the error was less than 25 nm. The Si temperature was measured from the optical path length. In order to compensate for the overlapping interference, the shift in the peak position of the interference at the SiO2/Si interface was estimated from the measurement results of the SiO2 thickness. This improved the accuracy of the temperature measurement from 5.3 to 3.5 °C.
A design for a subminiature, low energy scanning electron microscope with atomic resolution
Authors: Eastham D. A. , Edmondson P. , Greene S. , Donnelly S. , Olsson E. , Svensson K. , Bleloch A.
Published: January 2009

We describe a type of scanning electron microscope that works by directly imaging the electron field-emission sites on a nanotip. Electrons are extracted from the nanotip through a nanoscale aperture, accelerated in a high electric field, and focused to a spot using a microscale Einzel lens. If the whole microscope (accelerating section and lens) and the focal length are both restricted in size to below 10 μm, then computer simulations show that the effects of aberration are extremely small and it is possible to have a system with approximately unit magnification at electron energies as low as 300 eV. Thus a typical emission site of 1 nm diameter will produce an image of the same size, and an atomic emission site will give a resolution of 0.1–0.2 nm (1–2 Å). Also, because the beam is not allowed to expand beyond 100 nm in diameter, the depth of field is large and the contribution to the beam spot size from chromatic aberrations is less than 0.02 nm (0.2 Å) for 500 eV electrons. Since it is now entirely possible to make stable atomic sized emitters (nanopyramids), it is expected that this instrument will have atomic resolution. Furthermore the brightness of the beam is determined only by the field emission and can be up to 1×106 times larger than in a typical (high energy) electron microscope. The advantages of this low energy, bright-beam electron microscope with atomic resolution are described and include the possibility of it being used to rapidly sequence the human genome from a single strand of DNA as well as being able to identify atomic species directly from the elastic scattering of electrons.
Effective negative refraction in anisotropic layered composites
Authors: Huang Yanyan , Gao Lei
Published: January 2009

We investigate the characteristics of electromagnetic wave propagation in a two-component layered structure composed of alternating isotropic metal material and anisotropic magnetic material. Effective permittivity and permeability tensors of the composite system are derived with transfer matrix method, and the effective wave vector ke, the time-averaged Poynting vector ⟨Se⟩, and the scalar product ke⟨Se⟩ are studied for realizing the quasi-left-handed material with negative refractive index, i.e., the absolute quasi-left-handed material. For transverse-electric polarized wave, numerical results show that in a certain frequency region, the composite system behaves as an absolute quasi-left-handed material, and the transition from positive index to negative index takes place by the adjustment of the incident frequency. Moreover, there exists an optimal volume fraction, at which the absolute quasi-left-handed frequency region has a maximal width.
Interdependence of contact properties and field- and density-dependent mobility in organic field-effect transistors
Authors: Scheinert Susanne , Paasch Gernot
Published: January 2009

The current characteristics of organic field-effect transistors (OFET) often show a disadvantageous nonlinearity at low drain voltages. It has been shown recently [J. Appl. Phys. 102, 054509 (2007)] that in top contact (TOC) OFETs this effect can be caused by trap recharging if the contacts are of Schottky type. For bottom contact (BOC) OFETs, in spite of controversial discussions, Schottky contacts as origin of the nonlinearity are often stated. At first, it is shown here by a mixed mode simulation that for large ideality factors a Schottky contact only at drain leads to such a nonlinearity. However, with the same Schottky contacts at drain and source the effect is covered by the high resistance of the contact at source. Next, the different influences of Schottky contacts on BOC OFETs and TOC OFETs with varying overlap of the source/drain contacts with the gate are clarified. Further, it is demonstrated with detailed two-dimensional simulations that the combination of the presence of Schottky contacts with a field dependence of the mobility can cause the nonlinearity. For the mobility we use the field dependent Pool/Frenkel model, and the models of Limketai et al.[Phys. Rev. B 75, 113203 (2007)] and Pasveer/Coehoorn et al.[Phys. Rev. Lett. 94, 206601 (2005)], which depend in addition on the carrier concentration. Their influence on the device performance has been clarified by the simulations. Simulated profiles of concentrations and fields lead to the understanding of the mechanism causing the nonlinearity. This mechanism is especially effective for the Pasveer/Coehoorn model. The field dependence of the mobility is a consequence of the energetic distribution of the hopping states and can hardly be avoided in solution based deposition of the active polymer layer. A strategy to prevent the nonlinearity is therefore an optimization of the contact-polymer interface such that the contacts become Ohmic.
A governing parameter for the melting phenomenon at nanocontacts by Joule heating and its application to joining together two thin metallic wires
Authors: Tohmyoh Hironori
Published: January 2009

For cutting and joining extremely thin metallic wires, the issue of Joule heating in the wires is considered. The middle of a section of a thin Pt wire with a diameter of about 800 nm was melted locally by a direct current supply, and the wire was cut at a predetermined point by applying a force to shear the molten part of the wire. Furthermore, a constant current was applied to a system in which the free ends of two Pt wires were contacted, and the wires were joined together. A parameter, which governs the melting phenomenon at the point of contact of very thin wires, is proposed. It was verified that the conditions required for joining thin wires were able to be determined by the parameter that depends on the applied current, the length and cross sectional area of the wires, and a function of the geometrical quantities for calibrating the thermal conditions.
400-fold reduction in saturation field by interlayering
Authors: Egelhoff W. F. , Bonevich J. , Pong P. , Beauchamp C. R. , Stafford G. R. , Unguris J. , McMichael R. D.
Published: January 2009

The buildup of stress with increasing thickness of magnetic thin films is a common phenomenon that often induces undesirable anisotropies that can convert an otherwise magnetically soft film into a magnetically hard one. We found that by interlayering such a magnetic thin film with films that are either not lattice matched or have a different crystal structure, reductions in the saturation field as large as 400-fold can be achieved. Differences in grain size appear to be responsible.
Enhanced effect of electron-hole plasma emission in Dy, Li codoped ZnO nanostructures
Authors: Cheng Baochang , Yu Xiaoming , Liu Hongjuan , Fang Ming , Zhang Lide
Published: January 2009

Pink branched Dy3+ and Li+ codoped ZnO nanowires were synthesized by simply annealing the polymeric precursor. For the undoped sample, electrons at the bottom of the conductor band return to the ground state via a process of free exciton and defect intermediate level, and subsequently emit 3.2 and 2.4 eV photons. Furthermore, their intensities both increase while their positions are almost invariant with increasing excitation intensity. For the doped nanostructure, compositional inhomogeneity results in localization of nonequilibrium carriers and enhances the photoluminescence performance. The near-band edge emission shows higher emission efficiency and is dominated by the transition of free electrons to free holes. Moreover, it also exhibits a power-dependent redshift and a broader and more asymmetric line shape on its lower-energy side with increasing excitation intensity. For the green emission in codoping ZnO nanostructures, the formation of deeper traps from the complexes of defects and impurities results into a redshift to 523 nm. Additionally, its position remains invariant with increasing excitation intensity. It is proposed that the charge compensation, surface passivation, and carrier delocalization lead to the fully suppressed green emission at higher excitation intensity.
Transport through metallic nanogaps in an in-plane three-terminal geometry
Authors: Mangin A. , Anthore A. , Della Rocca M. L. , Boulat E. , Lafarge P.
Published: January 2009

Fabrication of three-terminal nanoscale devices is a key issue in molecular electronics to implement field-effect molecular transistor. We present in this paper two different electromigration procedures to realize metallic nanogaps at room and liquid helium temperature. A room temperature controlled electromigration process, consisting of a gradual thinning of a nanowire until the formation of a one channel contact, gives the best yield of bare nanogaps, i.e., gaps with a tunneling-like behavior. At low temperature and for a not fully controlled electromigration process, metallic clusters may remain inside the nanogap. An in-plane side gate electrode coupled to the nanogap allows transport measurements as a function of the gate voltage. Using this external tool we investigate the properties of the nanogaps, showing how clusters can mimic molecular behavior.
IR variable angle spectroscopic ellipsometry study of high dose ion-implanted and annealed silicon wafers
Authors: Liu Xianming , Li Bincheng
Published: January 2009

We employed Fourier transform variable angle infrared spectroscopic ellipsometry (IRSE) in wavelength range of 2–30 μm to investigate a group of silicon wafers, which are implanted with high doses and annealed in high temperature. The IRSE spectra for samples with different implantation doses were analyzed physically. When the semiconductor is heavily doped, it becomes degenerated and the doped impurities cannot ionize completely. For the analysis of the IRSE data, we quantitated the ionization probability as a function of impurity concentration in the optical model to describe the carrier concentration profile, by which the impurity concentration and carrier concentration profiles can be determined simultaneously.
Dimensional considerations in achieving large quality factors for resonant silicon cantilevers in air
Authors: Naeli Kianoush , Brand Oliver
Published: January 2009

This work aims to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental flexural resonance at atmospheric pressure. The methodology of this work is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the captured data. For this purpose, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11, and 17 μm and lengths and widths ranging from 70 to 1050 μm and 80 to 230 μm, respectively, have been fabricated and tested. Combining the three dominant damping mechanisms, i.e., the air damping, support loss, and thermoelastic damping, the variation in the measured Q-factors with the cantilever geometrical dimensions is predicted. Also to better describe the experimental data, modified models for air damping have been developed. These modified models can predict the optimum length and thickness of a resonant cantilever to achieve the maximum quality factor at the fundamental flexural resonance mode in air.
Off-axis electron holographic potential mapping across AlGaAs/AlAs/GaAs heterostructures
Authors: Chung Suk , Johnson Shane R. , Zhang Yong-Hang , Smith David J. , McCartney Martha R.
Published: January 2009

The electrostatic potential profile across AlGaAs/AlAs/GaAs heterostructures containing 1-μm-thick n-doped (or p-doped) AlGaAs layers is measured using off-axis electron holography. Simulations of the potential profiles assuming no unintentional impurities in the undoped regions of the samples show small discrepancies with experiment. Revised simulations reproduce the measurements accurately, when a p-layer with an 8.4×1011 cm−2 acceptor density is included at the buffer/substrate interface to simulate the presence of unintentional carbon impurities.
Time-resolved spectroscopy on GaN nanocolumns grown by plasma assisted molecular beam epitaxy on Si substrates
Authors: Corfdir P. , Lefebvre P. , Ristić J. , Valvin P. , Calleja E. , Trampert A. , Ganière J.-D. , Deveaud-Plédran B.
Published: January 2009

A detailed study of excitons in unstrained GaN nanocolumns grown by plasma assisted molecular beam epitaxy on silicon substrates is presented. The time-integrated and time-resolved photoluminescence spectra do not depend significantly on the (111) or (001) Si surface used. However, an unusually high relative intensity of the two-electron satellite peak of the dominant donor-bound exciton line is systematically observed. We correlate this observation with the nanocolumn morphology determined by scanning electron microscopy, and therefore propose an interpretation based on the alteration of wave functions of excitonic complexes and of donor states by the proximity of the semiconductor surface. This explanation is supported by a model that qualitatively accounts for both relative intensities and time decays of the photoluminescence lines.
Three dimensional metal pattern transfer for replica molded microstructures
Authors: Zhao Yanzhu , Yoon Yong-Kyu , Choi Seong-O , Wu Xiaosong , Liu Zhan , Allen Mark G.
Published: January 2009

We report a replica molding process for simultaneously forming a three dimensional metal pattern on the surface of molded polymer microstructures. This technique uses noncovalent surface forces to guide the transfer of thin metal films from the three dimensional features of high aspect ratio poly(dimethylsiloxane) micromolds to polymeric replicates. The utility of this technique has been demonstrated by the fabrication of organic coplanar waveguides integrated with vertical Ka-band monopole antenna radiators. These microwave systems show good performance with over 18% bandwidth and greater than 16 dB return loss, demonstrating the versatility of this process.
Photoluminescence and positron annihilation spectroscopy investigation of (Ge, Er) codoped Si oxides deposited by magnetron sputtering
Authors: Heng C. L. , Chelomentsev E. , Peng Z. L. , Mascher P. , Simpson P. J.
Published: January 2009

We have investigated the nature of violet-blue emission from (Ge, Er) codoped Si oxides (Ge+Er+SiO2) using photoluminescence (PL) and positron annihilation spectroscopy (PAS) measurements. The PL spectra and PAS analysis for a control Ge-doped SiO2 (Ge+SiO2) indicate that Ge-associated neutral oxygen vacancies (Ge-NOV) are likely responsible for the major emission in the violet-blue band. For Ge+Er+SiO2, both Ge-NOV and GeO color centers are believed to be responsible for the emission band. The addition of Er has a significant influence on the emission, which is discussed in terms of Er-concentration-related structural change in the Ge+Er+SiO2.
Graphical template software for accurate micromanipulation in a scanning electron microscope
Authors: Kasaya Takeshi , Miyazaki Hideki T.
Published: January 2009

Micromanipulation techniques in a scanning electron microscope (SEM) have been utilized for assembling micrometer-sized structures. The precision of the assembled microstructures has been limited by the poor accuracy of the SEM image. We have developed a software to assist the operator in the accurate assembly of microstructures in a SEM, in which computer-generated outlines of the target structure [graphical templates (GTs)] are superimposed on the monitor. The displayed GTs are distorted on the basis of the image properties of the SEM evaluated in advance. As a consequence, the operator can construct microstructures with a high precision only by maneuvering the manipulator so that the outline of each object perfectly overlaps the GT without any alteration of the electron optics or circuits for improving the image accuracy.
High temperature phases in the 0.98PbZrO3–0.02Pb(Ni1/3Nb2/3)O3 ceramic
Authors: Qu W. , Tan X. , Vittayakorn N. , Wirunchit S. , Besser M. F.
Published: January 2009

The phase evolution with temperature in the 0.98PbZrO3–0.02Pb(Ni1/3Nb2/3)O3 ceramic was investigated with dielectric permittivity and polarization measurements, hot stage transmission electron microscopy, and high temperature x-ray diffraction. Below 190 °C, the ceramic is in the antiferroelectric phase with characteristic 14{110}c superlattice diffractions. In this stage, typical antiferroelectric 180° domains were observed. Between 190 and 220 °C, an intermediate phase, which is characterized by 12{110}c-type superlattice diffractions, was detected. Evidences are found to suggest that this intermediate phase is ferroelectric. The 12{110}c-type superlattice diffraction persists even into the paraelectric phase above 220 °C. In addition, there exists an incommensurate phase between the low temperature antiferroelectric phase and the intermediate ferroelectric phase.
The effect of periodicity on the extraordinary optical transmission of annular aperture arrays
Authors: Kofke Matthew J. , Waldeck David H. , Fakhraai Zahra , Ip Shell , Walker Gilbert C.
Published: January 2009

This work systematically evaluates the effect of array periodicity on the near infrared transmission characteristics of annular aperture arrays (AAAs) in gold films. Both the experimental and theoretical transmission spectra of AAAs are shown to be sensitive to the period and the arrangement of the apertures within the array. The spectra of square arrays with periods ranging from 1400 to 600 nm show a strong correlation with surface plasmon polariton (SPP)-Bloch modes of the metal/dielectric interfaces. For rectangular AAAs the transmission spectra are significantly attenuated and reveal a polarization sensitivity that arises from the breaking of the symmetry and degeneracy of the SPP-Bloch modes.
Long wavelength emissions of periodic yard-glass shaped boron nitride nanotubes
Authors: Chen Zhi-Gang , Zou Jin , Liu Gang , Li Feng , Cheng Hui-Ming , Sekiguchi Takashi , Gu Min , Yao Xiang-Dong , Wang Lian-Zhou , Lu Gao Qing
Published: January 2009

Extraordinary and stable long wavelength emission (centered at ∼685 nm) from the yard-glass shaped boron nitride nanotubes (YG-BNNTs) was observed in their cathodoluminescence and photoluminescence spectroscopy. The mechanism for this near-red light emission at ∼685 nm is attributed to the periodical nature of the BNNT units with regular lattice defects. The visible-light emission from YG-BNNTs indicates that this material has great potential for applications as nano-optical and/or nano-optoelectronic devices in nanoscale surgery and spectroscopy.
Nonlocal Aharonov–Bohm conductance oscillations in an asymmetric quantum ring
Authors: Buchholz S. S. , Fischer S. F. , Kunze U. , Reuter D. , Wieck A. D.
Published: January 2009

We investigate ballistic transport and quantum interference in a nanoscale quantum wire loop fabricated as a GaAs/AlGaAs field-effect heterostructure. Four-terminal measurements of current and voltage characteristics as a function of top gate voltages show negative bend resistance as a clear signature of ballistic transport. In perpendicular magnetic fields, phase-coherent transport leads to Aharonov–Bohm conductance oscillations, which show equal amplitudes in the local and the nonlocal measurement at a temperature of 1.5 K and above. We attribute this observation to the symmetry of the orthogonal cross junctions connecting the four quantum wire leads with the asymmetric quantum wire ring.
Field-responsive ion transport in nanopores
Authors: Lu Weiyi , Han Aijie , Kim Taewan , Punyamurtula Venkata K. , Chen Xi , Qiao Yu
Published: January 2009

The transport behavior of solvated ions in nanopores of a zeolite Y is field responsive. As an external electric field is applied, the observed change in effective solid-liquid interfacial tension is contradictory to the prediction of classic electrochemistry theory; it considerably increases no matter whether the applied voltage is positive or negative. This may be attributed to the breakdown of solvated ion and double-layer structures in the nanoenvironment.
Effects of barium incorporation into HfO2 gate dielectrics on reduction in charged defects: First-principles study
Authors: Umezawa Naoto
Published: January 2009

Reducing the number of charged defects in the gate insulating oxides is an essential task to improve the electrical properties of field-effect transistors. Our comprehensive study using first-principles calculations revealed that incorporating Ba atoms into HfO2 can markedly decrease the number of positive charges associated with oxygen vacancies (VO). This is attributed to the strong coupling of a Ba atom substituted for Hf (BaHf) with VO, rendering the complex defect BaHfVO stable in the charge-neutral state.
Enhanced growth of high quality single crystal diamond by microwave plasma assisted chemical vapor deposition at high gas pressures
Authors: Liang Qi , Chin Cheng Yi , Lai Joseph , Yan Chih-shiue , Meng Yufei , Mao Ho-kwang , Hemley Russell J.
Published: January 2009

Single crystals of diamond up to 18 mm in thickness have been grown by microwave plasma assisted chemical vapor deposition at gas pressures of up to 350 torr. Growth rates of up to 165 μm/h at 300 torr at high power density have been achieved. The processes were evaluated by optical emission spectroscopy. The high-quality single-crystal diamond grown at optimized conditions was characterized by UV-visible absorption and photoluminescence spectroscopy. The measurements reveal a direct relationship between residual absorption and nitrogen content in the gas chemistry. Fabrication of high quality single-crystal diamond at higher growth rates should be possible with improved reactor design that allows still higher gas synthesis pressures.
Perceptual Memory for Highly Familiar People's Body Shape: Manipulation of Images of the Self and Friend
Authors: Daury Noémy , Brooks Kevin , Brédart Serge
Published: January 2009

Previous studies have shown that people's ability to detect, from memory, alterations in highly familiar faces is excellent. Indeed, just noticeable differences for the detection of small alterations in a recognition-memory task were not significantly different from the corresponding measures in a perceptual-discrimination task (Brédart and Devue, 2006 Perception35 101–106; Ge et al, 2003 Perception32 601–614). The object of the present study was to evaluate whether people's perceptual memory for body shapes of very familiar persons reaches the high level of precision that was reported for face memory. For one group of participants, the task was to detect body shape alterations (an increase or a decrease of 2% to 10% of the waist-to-hip ratio) on photographs depicting either themselves or a friend. For another group of participants who did not know the target persons, the task was to discriminate whether two photographs presented side by side were the same or not. Results showed that the detection of alterations was significantly better in the perceptual-discrimination task than in the recognition-memory tasks (for the participant's own body as well as for the friend's body). In conclusion, the high fidelity of perceptual memory for very familiar faces does not extend to familiar body shapes.
CUR matrix decompositions for improved data analysis
Authors: Mahoney Michael W. , Drineas Petros
Published: January 2009

Principal components analysis and, more generally, the Singular Value Decomposition are fundamental data analysis tools that express a data matrix in terms of a sequence of orthogonal or uncorrelated vectors of decreasing importance. Unfortunately, being linear combinations of up to all the data points, these vectors are notoriously difficult to interpret in terms of the data and processes generating the data. In this article, we develop CUR matrix decompositions for improved data analysis. CUR decompositions are low-rank matrix decompositions that are explicitly expressed in terms of a small number of actual columns and/or actual rows of the data matrix. Because they are constructed from actual data elements, CUR decompositions are interpretable by practitioners of the field from which the data are drawn (to the extent that the original data are). We present an algorithm that preferentially chooses columns and rows that exhibit high “statistical leverage” and, thus, in a very precise statistical sense, exert a disproportionately large “influence” on the best low-rank fit of the data matrix. By selecting columns and rows in this manner, we obtain improved relative-error and constant-factor approximation guarantees in worst-case analysis, as opposed to the much coarser additive-error guarantees of prior work. In addition, since the construction involves computing quantities with a natural and widely studied statistical interpretation, we can leverage ideas from diagnostic regression analysis to employ these matrix decompositions for exploratory data analysis.
Uptake of particulate vaccine adjuvants by dendritic cells activates the NALP3 inflammasome
Authors: Sharp Fiona A. , Ruane Darren , Claass Benjamin , Creagh Emma , Harris James , Malyala Padma , Singh Manomohan , O'Hagan Derek T. , Pétrilli Virginie , Tschopp Jurg , O'Neill Luke A. J. , Lavelle Ed C.
Published: January 2009

Many currently used and candidate vaccine adjuvants are particulate in nature, but their mechanism of action is not well understood. Here, we show that particulate adjuvants, including biodegradable poly(lactide-
co
-glycolide) (PLG) and polystyrene microparticles, dramatically enhance secretion of interleukin-1β (IL-1β) by dendritic cells (DCs). The ability of particulates to promote IL-1β secretion and caspase 1 activation required particle uptake by DCs and NALP3. Uptake of microparticles induced lysosomal damage, whereas particle-mediated enhancement of IL-1β secretion required phagosomal acidification and the lysosomal cysteine protease cathepsin B, suggesting a role for lysosomal damage in inflammasome activation. Although the presence of a Toll-like receptor (TLR) agonist was required to induce IL-1β production in vitro, injection of the adjuvants in the absence of TLR agonists induced IL-1β production at the injection site, indicating that endogenous factors can synergize with particulates to promote inflammasome activation. The enhancement of antigen-specific antibody production by PLG microparticles was independent of NALP3. However, the ability of PLG microparticles to promote antigen-specific IL-6 production by T cells and the recruitment and activation of a population of CD11b
+
Gr1
−
cells required NALP3. Our data demonstrate that uptake of microparticulate adjuvants by DCs activates the NALP3 inflammasome, and this contributes to their enhancing effects on innate and antigen-specific cellular immunity.
Distinct mechanisms act in concert to mediate cell cycle arrest
Authors: Toettcher Jared E. , Loewer Alexander , Ostheimer Gerard J. , Yaffe Michael B. , Tidor Bruce , Lahav Galit
Published: January 2009

In response to DNA damage, cells arrest at specific stages in the cell cycle. This arrest must fulfill at least 3 requirements: it must be activated promptly; it must be sustained as long as damage is present to prevent loss of genomic information; and after the arrest, cells must re-enter into the appropriate cell cycle phase to ensure proper ploidy. Multiple molecular mechanisms capable of arresting the cell cycle have been identified in mammalian cells; however, it is unknown whether each mechanism meets all 3 requirements or whether they act together to confer specific functions to the arrest. To address this question, we integrated mathematical models describing the cell cycle and the DNA damage signaling networks and tested the contributions of each mechanism to cell cycle arrest and re-entry. Predictions from this model were then tested with quantitative experiments to identify the combined action of arrest mechanisms in irradiated cells. We find that different arrest mechanisms serve indispensable roles in the proper cellular response to DNA damage over time: p53-independent cyclin inactivation confers immediate arrest, whereas p53-dependent cyclin downregulation allows this arrest to be sustained. Additionally, p21-mediated inhibition of cyclin-dependent kinase activity is indispensable for preventing improper cell cycle re-entry and endoreduplication. This work shows that in a complex signaling network, seemingly redundant mechanisms, acting in a concerted fashion, can achieve a specific cellular outcome.
Psychosocial stress reversibly disrupts prefrontal processing and attentional control
Authors: Liston C. , McEwen B. S. , Casey B. J.
Published: January 2009

Relatively little is known about the long-term neurobiological sequelae of chronic stress, which predisposes susceptible patients to neuropsychiatric conditions affecting the prefrontal cortex (PFC). Animal models and human neuroimaging experiments provide complementary insights, yet efforts to integrate the two are often complicated by limitations inherent in drawing comparisons between unrelated studies with disparate designs. Translating from a rodent model of chronic stress where we have shown reversible disruption of PFC function, we show that psychosocial stress induces long-lasting but reversible impairments in behavioral and functional magnetic resonance imaging (fMRI) measures of PFC function in humans. Twenty healthy adults, exposed to 1 month of psychosocial stress, confirmed by a validated rating scale, were scanned while performing a PFC-dependent attention-shifting task. One month later, they returned for a second scanning session after a period of reduced stress, and their performance was compared with a twice-scanned, matched group of low-stress controls. Psychosocial stress selectively impaired attentional control and disrupted functional connectivity within a frontoparietal network that mediates attention shifts. These effects were reversible: after one month of reduced stress, the same subjects showed no significant differences from controls. These results highlight the plasticity of PFC networks in healthy human subjects and suggest one mechanism by which disrupted plasticity may contribute to cognitive impairments characteristic of stress-related neuropsychiatric conditions in susceptible individuals.
The promoter spacer influences transcription initiation via σ
70
region 1.1 of
Escherichia coli
RNA polymerase
Authors: Hook-Barnard India G. , Hinton Deborah M.
Published: January 2009

Transcription initiation is a dynamic process in which RNA polymerase (RNAP) and promoter DNA act as partners, changing in response to one another, to produce a polymerase/promoter open complex (RPo) competent for transcription. In
Escherichia coli
RNAP, region 1.1, the N-terminal 100 residues of σ
70
, is thought to occupy the channel that will hold the DNA downstream of the transcription start site; thus, region 1.1 must move from this channel as RPo is formed. Previous work has also shown that region 1.1 can modulate RPo formation depending on the promoter. For some promoters region 1.1 stimulates the formation of open complexes; at the P
minor
promoter, region 1.1 inhibits this formation. We demonstrate here that the AT-rich P
minor
spacer sequence, rather than promoter recognition elements or downstream DNA, determines the effect of region 1.1 on promoter activity. Using a P
minor
derivative that contains good σ
70
-dependent DNA elements, we find that the presence of a more GC-rich spacer or a spacer with the complement of the P
minor
sequence results in a promoter that is no longer inhibited by region 1.1. Furthermore, the presence of the P
minor
spacer, the GC-rich spacer, or the complement spacer results in different mobilities of promoter DNA during gel electrophoresis, suggesting that the spacer regions impart differing conformations or curvatures to the DNA. We speculate that the spacer can influence the trajectory or flexibility of DNA as it enters the RNAP channel and that region 1.1 acts as a “gatekeeper” to monitor channel entry.
Subdivisions of primary motor cortex based on cortico-motoneuronal cells
Authors: Rathelot Jean-Alban , Strick Peter L.
Published: January 2009

We used retrograde transneuronal transport of rabies virus from single muscles of rhesus monkeys to identify cortico-motoneuronal (CM) cells in the primary motor cortex (M1) that make monosynaptic connections with motoneurons innervating shoulder, elbow, and finger muscles. We found that M1 has 2 subdivisions. A rostral region lacks CM cells and represents an “old” M1 that is the standard for many mammals. The descending commands mediated by corticospinal efferents from old M1 must use the integrative mechanisms of the spinal cord to generate motoneuron activity and motor output. In contrast, a caudal region of M1 contains shoulder, elbow, and finger CM cells. This region represents a “new” M1 that is present only in some higher primates and humans. The direct access to motoneurons afforded by CM cells enables the newly recognized M1 to bypass spinal cord mechanisms and sculpt novel patterns of motor output that are essential for highly skilled movements.