bluuebunny/crossref_metadata_2025 huggingface dataset:
A survey of modal logics characterising behavioural equivalences for non-deterministic and stochastic systems
Authors: BERNARDO MARCO , BOTTA STEFANIA
Published: March 2008

Behavioural equivalences are a means of establishing whether computing systems possess the same properties. The specific set of properties that are preserved by a specific behavioural equivalence clearly depends on how the system behaviour is observed and can usually be characterised by means of a modal logic. In this paper we consider three different approaches to the definition of behavioural equivalences – bisimulation, testing and trace – applied to three different classes of systems – non-deterministic, probabilistic and Markovian – and we survey the nine resulting modal logic characterisations, each of which stems from the Hennessy–Milner logic. We then compare the nine characterisations with respect to the logical operators, in order to emphasise the differences between the three approaches in the definition of behavioural equivalences and the regularities within each of them. In the probabilistic and Markovian cases we also address the issue of whether the probabilistic and temporal aspects should be treated in a local or global way and consequently whether the modal logic interpretation should be qualitative or quantitative.
Towards an algorithmic construction of cut-elimination procedures
Authors: CIABATTONI AGATA , LEITSCH ALEXANDER
Published: March 2008

We investigate cut elimination in propositional substructural logics. The problem is to decide whether a given calculus admits (reductive) cut elimination. We show that for commutative single-conclusion sequent calculi containing generalised knotted structural rules and arbitrary logical rules the problem can be decided by resolution-based methods. A general cut-elimination proof for these calculi is also provided.
Combinatorial laplacians and positivity under partial transpose
Authors: HILDEBRAND ROLAND , MANCINI STEFANO , SEVERINI SIMONE
Published: March 2008

The density matrices of graphs are combinatorial laplacians normalised to have trace one (Braunsteinet al. 2006b). If the vertices of a graph are arranged as an array, its density matrix carries a block structure with respect to which properties such as separability can be considered. We prove that the so-called degree-criterion, which was conjectured to be necessary and sufficient for the separability of density matrices of graphs, is equivalent to the PPT-criterion. As such, it is not sufficient for testing the separability of density matrices of graphs (we provide an explicit example). Nonetheless, we prove the sufficiency when one of the array dimensions has length two (see Wu (2006) for an alternative proof). Finally, we derive a rational upper bound on the concurrence of density matrices of graphs and show that this bound is exact for graphs on four vertices.
Orbiting Carbon Observatory: Inverse method and prospective error analysis
Authors: Connor Brian J. , Boesch Hartmut , Toon Geoffrey , Sen Bhaswar , Miller Charles , Crisp David
Published: March 2008

The objective, design, and implementation of the OCO inverse method are presented. The inverse method is the algorithm which finds the profile‐weighted mean mixing ratio, XCO2, which best fits the measured spectrum, given a “forward model” which calculates the spectrum for a given atmospheric state, surface, and instrument properties. Minimizing bias among comparative values of XCO2 is a critical objective. The algorithm uses an “optimal,” maximum a posteriori inverse method, with weak a priori constraint, and employs a state vector containing atmospheric and surface properties expected to vary significantly between soundings. An extensive operational characterization and error analysis will be employed, producing quantities designed to aid atmospheric modelers in use of the OCO data. In particular, comparison to inverse models of surface CO2 flux will require use of the OCO column averaging kernel and a priori state vector. An off‐line error analysis has also been developed for more detailed error studies, and its use is illustrated by prospective application to case studies of nadir observations in summer and winter at three sites. Uncertainties due to noise, geophysical variability, and spectroscopic parameters are considered in detail. At low and midlatitudes, the single‐sounding errors due to these sources are expected to be ∼0.7–0.8 ppm for high‐sun conditions and ∼1.5–2.5 ppm for low sun (winter). Errors from the same sources in semimonthly regional averages are predicted to be <1 ppm for all conditions.
Directional median filtering for regional‐residual separation of bathymetry
Authors: Kim Seung‐Sep , Wessel Paul
Published: March 2008

We present a new spatial filter designed to separate short‐length‐scale bathymetric features from regional bathymetry. The directional median (DiM) filter divides a given filter circle into N “bow tie” sectors, allocates data points inside the filter circle to each sector based on their relative position within the circle, estimates a median for each sector, and returns the lowest of these N medians. This approach prevents DiM filtering from choosing the biased medians near the features on a sloping regional trend, which is a serious artifact of standard median filtering. As the bathymetry comprises diverse length‐scale features, the separated results vary with the choice of filter width. Such variations are spatially distributed. Using a finite range of filter widths, we evaluate the spatial distribution of variations in the DiM‐based separation by estimating their median absolute deviation (MAD) at each data point. The distribution of MAD values is indicative of uncertainties inherent in the separation. We demonstrate the effectiveness of DiM filtering with both synthetic and actual bathymetric data.
Skeletal P/Ca tracks upwelling in Gulf of Panamá coral: Evidence for a new seawater phosphate proxy
Authors: LaVigne Michèle , Field M. Paul , Anagnostou Eleni , Grottoli Andréa G. , Wellington Gerard M. , Sherrell Robert M.
Published: March 2008

The supply of limiting nutrients to the low latitude ocean is controlled by physical processes linked to climate variations, but methods for reconstructing past nutrient concentrations in the surface ocean are few and indirect. Here, we present laser ablation mass spectrometry results that reveal annual cycles of P/Ca in a 4‐year record from the scleractinian coral Pavona gigantea (mean P/Ca = 118 μmol mol−1). The P/Ca cycles track variations in past seawater phosphate concentration synchronously with skeletal Sr/Ca‐derived temperature variations associated with seasonal upwelling in the Gulf of Panamá. Skeletal P/Ca varies seasonally by 2–3 fold, reflecting the timing and magnitude of dissolved phosphate variations. Solution cleaning experiments on drilled coral powders show that over 60% of skeletal P occurs in intracrystalline organic phases. Coral skeleton P/Ca holds promise as a proxy record of nutrient availability on time scales of decades to millennia.
Temporary vegetation disturbance as an explanation for permanent loss of tidal wetlands
Authors: Kirwan Matthew L. , Murray A. Brad , Boyd W. Sean
Published: March 2008

Coastal ecosystems respond to sea level and sediment supply change according to complex, three‐way interactions between vegetation, hydrology, and sediment transport. While biogeomorphic feedbacks preserve the morphology of intertidal surfaces covered by marshland, we demonstrate with numerical model and field experimentation that temporary disturbance to vegetation facilitates rapid and widespread degradation. Vertical accretion slows in disturbed areas, allowing localized submergence of the marsh platform, tidal prism enlargement, and permanent channel network expansion. Vegetated portions of an episodically disturbed platform accrete more rapidly than rates of relative sea level rise, giving submerging marshland the appearance of maintaining elevation. This feedback between vegetation disturbance and channel erosion, and its effect on platform accretion, may explain peculiar patterns of wetland loss in Europe and North America.
Influence of the internally induced magnetic field on the plasma interaction of Europa
Authors: Schilling N. , Neubauer F. M. , Saur J.
Published: March 2008

In this paper, we study the influence of electromagnetic induction in Europa's interior on the plasma interaction in the vicinity of Europa. We describe the temporally periodic interaction between Europa and the Jovian magnetosphere with a three‐dimensional time‐dependent model. Our model describes simultaneously the three‐dimensional plasma interaction of Europa's atmosphere with Jupiter's magnetosphere and the electromagnetic induction in a subsurface conducting layer due to time‐varying magnetic fields and plasmas including their mutual feedbacks. We find that the induced magnetic fields cause time varying asymmetries in the current density and the plasma density outside Europa. We show that the Alfvén current system is deformed and displaced because of the induced magnetic fields. Furthermore, the plasma wake of Europa is deformed because of the induction. Remarkably, therefore the influence of the induced fields on the Alfvén wings and the plasma wake may be seen at distances where the induced fields are already negligible. The effects of induction on the wake structure are most clearly visible in the E4 flyby magnetic field and plasma observations, which are in good agreement with our simulation. The resulting structure of Europa's plasma wake could explain why Galileo measurements did not detect high plasma densities along the E4 trajectory.
Energetics of Madden Julian Oscillations in the NCAR CAM3: A Composite View
Authors: Mu Mingquan , Zhang Guang J.
Published: March 2008

This study further examines the simulation of the tropical Madden‐Julian oscillation (MJO) using the modified Zhang‐McFarlane convection scheme in the National Center for Atmospheric Research Community Atmospheric Model version 3 (CAM3). The results demonstrate that modifications to the Zhang‐McFarlane scheme lead to significantly enhanced MJO and much improvement of the MJO structures. However, the propagation speed is too fast compared to observations. The westward tilting structures of moisture flux convergence over the western Pacific warm pool are simulated very well by the modified CAM3 (CAM3m). The modified Zhang‐McFarlane convection scheme also improves the energetic structures of the MJOs. With the climatological mean of the energetics from the composite MJO removed, the energy budget terms show clear eastward propagation following MJO movement in the CAM3m and ECMWF reanalysis (ERA40). The results further support that the interaction between convection and large‐scale circulation is important in the maintenance and growth of the MJO through perturbation kinetic energy (PKE) conversion from perturbation available potential energy (PAPE) generated by the correlation of specific volume (α) and large‐scale heating (Q1). Too weak Q1 and PAPE generated through (α, Q1) is responsible for the weak MJO and intraseasonal variability simulated by the standard CAM3. Too strong climatology mean of the energetics in the CAM3m may be caused by too strong stationary intraseasonal variability. Moisture flux convergence is responsible for the changes of specific humidity in the CAM3m and CAM3 during the cycle of the MJO over the Indian and western Pacific Oceans. These results indicate that interaction between convection, moisture and convergence in the lower troposphere may be responsible for the MJO development over the Indian and western Pacific Ocean in both observations and simulations. The weak intraseasonal variability and MJO simulated by the original Zhang‐McFarlane deep convection scheme is attributed to the lack of coherent shallow convection ahead of deep convection in the MJO cycle.
Neuroprotective Effects of Tempol, a Catalytic Scavenger of Peroxynitrite-Derived Free Radicals, in a Mouse Traumatic Brain Injury Model
Authors: Deng-Bryant Ying , Singh Indrapal N , Carrico Kimberly M , Hall Edward D
Published: March 2008

We examined the ability of tempol, a catalytic scavenger of peroxynitrite (PN)-derived free radicals, to reduce cortical oxidative damage, mitochondrial dysfunction, calpain-mediated cytoskeletal (α-spectrin) degradation, and neurodegeneration, and to improve behavioral recovery after a severe (depth 1.0 mm), unilateral controlled cortical impact traumatic brain injury (CCI-TBI) in male CF-1 mice. Administration of a single 300 mg/kg intraperitoneal dose of tempol 15 mins after TBI produced a complete suppression of PN-mediated oxidative damage (3-nitrotyrosine, 3NT) in injured cortical tissue at 1 h after injury. Identical tempol dosing maintained respiratory function and attenuated 3NT in isolated cortical mitochondria at 12 h after injury, the peak of mitochondrial dysfunction. Multiple dosing with tempol (300 mg/kg intraperitoneally at 15 mins, 3, 6, 9, and 12 h) also suppressed α-spectrin degradation by 45% at its 24 h post-injury peak. The same dosing regimen improved 48 h motor function and produced a significant, but limited (17.4%, P<0.05), decrease in hemispheric neurodegeneration at 7 days. These results are consistent with a mechanistic link between PN-mediated oxidative damage to brain mitochondria, calpain-mediated proteolytic damage, and neurodegeneration. However, the modest neuroprotective effect of tempol suggests that multitarget combination strategies may be needed to interfere with posttraumatic secondary injury to a degree worthy of clinical translation.
Detection of Phosphorylated NF-H in the Cerebrospinal Fluid and Blood of Aneurysmal Subarachnoid Hemorrhage Patients
Authors: Lewis Stephen B , Wolper Regina A , Miralia Lynn , Yang Cui , Shaw Gerry
Published: March 2008

Blood and cerebrospinal fluid (CSF) of 30 Fisher grade 3 aneurysmal subarachnoid hemorrhage (ASAH) patients were analyzed for the presence of the phosphorylated axonal form of the major neurofilament subunit NF-H (pNF-H), a promising biomarker of axonal injury. Patient demographic data including development of vasospasm and outcome scores at 6 months after aneurysmal rupture (AR) were evaluated. Higher pNF-H blood levels in the first few days after AR were strongly predictive of a negative outcome. Blood pNF-H levels in most recovering patients showed a steady increase into the second week after AR, presumably reflecting axonal degeneration secondary to the original insult. Almost half of the patients studied showed sudden dramatic peaks of pNF-H protein release into CSF in the 3- to 14-day time period after AR, which must reflect profound, coordinated, and secondary loss of axons. Patients in whom vasospasm was detected had significantly more pNF-H in both blood and CSF compared with those in whom vasospasm was not detected. We conclude that the analysis of pNF-H levels in blood and CSF differentiates between patients with poor and favorable outcomes and also reveals several novel features of ASAH progression and recovery.
Aspirin Resistance is More Common in Lacunar Strokes than Embolic Strokes and is Related to Stroke Severity
Authors: Englyst Nicola A , Horsfield Gill , Kwan Joseph , Byrne Christopher D
Published: March 2008

The aim of this study was to investigate the relationship between aspirin resistance, ischaemic stroke subtype, stroke severity, and inflammatory cytokines. Aspirin resistance was assessed by thrombelastography in 45 people with ischaemic stroke and 25 controls. Plasma interleukin (IL)-6 was measured. Stroke severity was assessed using the modified Rankin scale and National Institute of Health Stroke Score within 72 h of stroke. Aspirin resistance was more common in the stroke than the control group (67% versus 40%, P=0.028), and within the stroke group the aspirin-resistant group had a higher Rankin score (4.0 versus 2.0, P=0.013). Aspirin resistance was greater in lacunar than embolic strokes (platelet activation 79% versus 59%, P=0.020). The stroke aspirin-resistant group had higher levels of IL-6 than the stroke aspirin-sensitive group (2.4±1 versus 1.8±0.9 ng/mL, P=0.037). Using multivariate analysis, we examined the interrelationships between aspirin resistance, IL-6, and stroke severity. These analyses showed that IL-6 was independently associated with stroke severity as the outcome ( B=3.738, P=0.036), and aspirin resistance was independently associated with IL-6 ( B=0.765, P=0.005) as the outcome. In conclusion, aspirin resistance is related to stroke severity and aspirin resistance is more common in lacunar strokes than embolic strokes.
Large-amplitude quantum mechanics in polyatomic hydrides. II. A particle-on-a-sphere model for XHn (n=4,5)
Authors: Deskevich Michael P. , McCoy Anne B. , Hutson Jeremy M. , Nesbitt David J.
Published: March 2008

This paper describes the application of a relatively simple, but computationally tractable, “particle-on-a-sphere” (POS) model for quantum-mechanical calculation of large-amplitude, H atom dynamics in polyatomic hydrides (XHn), based on radially relaxed, two-dimensional angular motion of H atoms on the surface of a sphere. This work focuses on systems with many degrees of freedom, i.e., XH4 (eight dimensional) and XH5 (ten dimensional), with corresponding molecular analogs of CH4 and CH5+ and is applicable to rovibrationally excited states with J⩾0. A pairwise-additive potential fit for CH5+, which yields remarkable agreement with geometries, energies, and barrier heights on the full-dimensional surface of Brown et al. [J. Chem. Phys. 121, 4105 (2004)] is presented. Comparisons with experimental data and diffusion quantum Monte Carlo (DMC) methods test convergence for the POS model and provide insight into multidimensional quantum rovibrational dynamics. In particular, POS energy-level patterns for a series of scaled CH5+ potentials indicate an absence of strong tunneling behavior, consistent with the highly delocalized wave functions, large zero-point energies, and small interconversion barriers noted in previous DMC studies of Brown et al.
Formulation and implementation of direct algorithm for the symmetry-adapted cluster and symmetry-adapted cluster–configuration interaction method
Authors: Fukuda Ryoichi , Nakatsuji Hiroshi
Published: March 2008

We present a new computational algorithm, called direct algorithm, for the symmetry-adapted cluster (SAC) and SAC–configuration interaction (SAC-CI) methodology for the ground, excited, ionized, and electron-attached states. The perturbation-selection technique and the molecular orbital index based direct sigma-vector algorithm were combined efficiently with the use of the sparse nature of the matrices involved. The formal computational cost was reduced to O(N2×M) for a system with N-active orbitals and M-selected excitation operators. The new direct SAC-CI program has been applied to several small molecules and free-base porphin and has been shown to be more efficient than the conventional nondirect SAC-CI program for almost all cases. Particularly, the acceleration was significant for large dimensional computations. The direct SAC-CI algorithm has achieved an improvement in both accuracy and efficiency. It would open a new possibility in the SAC/SAC-CI methodology for studying various kinds of ground, excited, and ionized states of molecules.
Complex polarization propagator calculations of magnetic circular dichroism spectra
Authors: Solheim Harald , Ruud Kenneth , Coriani Sonia , Norman Patrick
Published: March 2008

It is demonstrated that the employment of the nonlinear complex polarization propagator enables the calculation of the complete magnetic circular dichroism spectra of closed-shell molecules, including at the same time both the so-called Faraday A and B terms. In this approach, the differential absorption of right and left circularly polarized light in the presence of a static magnetic field is determined from the real part of the magnetic field-perturbed electric dipole polarizability. The introduction of the finite lifetimes of the electronically excited states into the theory results in response functions that are well behaved in the entire spectral region, i.e., the divergencies that are found in conventional response theory approaches at the transition energies of the system are not present. The applicability of the approach is demonstrated by calculations of the ultraviolet magnetic circular dichroism spectra of para-benzoquinone, tetrachloro-para-benzoquinone, and cyclopropane. The present results are obtained with the complex polarization propagator approach in conjunction with Kohn–Sham density functional theory and the standard adiabatic density functionals B3LYP, CAM-B3LYP, and BHLYP.
Identification of the optically active vibrational modes in the photoluminescence of MEH-PPV films
Authors: da Silva M. A. T. , Dias I. F. L. , Duarte J. L. , Laureto E. , Silvestre I. , Cury L. A. , Guimarães P. S. S.
Published: March 2008

The temperature dependence of the photoluminescence properties of a thin film of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene-vinylene], MEH-PPV, fabricated by spin coating, is analyzed. The evolution with temperature of the peak energy of the purely electronic transition, of the first vibronic band, of the effective conjugation length, and of the Huang–Rhys factors are discussed. The asymmetric character of the pure electronic transition peak and the contribution of the individual vibrational modes to the first vibronic band line shape are considered by a model developed by Cury et al. [J. Chem. Phys. 121, 3836 (2004)]. The temperature dependence of the Huang–Rhys factors of the main vibrational modes pertaining to the first vibronic band allows us to identify two competing vibrational modes. These results show that the electron coupling to different vibrational modes depends on temperature via reduction of thermal disorder.
Magnetohydrodynamic simulations of massive gas injection into Alcator C-Mod and DIII-D plasmas
Authors: Izzo V. A. , Whyte D. G. , Granetz R. S. , Parks P. B. , Hollmann E. M. , Lao L. L. , Wesley J. C.
Published: March 2008

Disruption mitigation experiments using massive gas injection (MGI) on Alcator C-Mod [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] and DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] have shown that magnetohydrodynamics (MHD) plays an important role. The three-dimensional MHD code NIMROD [Sovinec et al., J. Comput. Phys. 195, 355 (2004)] has been extended to include atomic physics taken from the KPRAD code to perform simulations of MGI. Considerable benchmarking of the code has been done against Alcator C-Mod for neon and helium gas jet experiments. The code successfully captures the qualitative sequence of events observed in MGI experiments up to the end of the thermal quench. Neon jet simulations also show quantitative agreement with the experimental thermal quench onset time. For helium gas jets, we show that a small percent boron density can significantly alter the results even in the presence of a helium jet with three orders of magnitude higher density. The thermal quench onset time is considerably overpredicted unless boron radiation is included. A DIII-D helium jet simulation shows a faster rise time for total radiated power than the experiment, but comparable amplitude. Similar to the important role of boron in C-Mod, carbon radiation is a significant factor in DIII-D helium jet simulations and experiments.
Bed friction effects on the stability of a stationary hydraulic jump in a rectangular upward sloping channel
Authors: Defina Andrea , Susin Francesca Maria , Viero Daniele Pietro
Published: March 2008

The issue of the bed friction effect on the stability of a stationary hydraulic jump in a rectangular upward sloping channel is investigated through a combined theoretical and experimental approach. The theoretical stability criterion proposed by Defina and Susin [Phys. Fluids 15, 3883 (2003)] is generalized to include rough wall flows. The results of an extensive series of experiments are then presented. The adopted experimental procedure is detailed, and results are compared with theoretical predictions. It is shown that the proposed stability criterion successfully predicts both the stable and unstable behavior of the jump for smooth and rough wall flow, at least in the range of small upward bottom slopes.
Monte Carlo simulation of cross-plane thermal conductivity of nanostructured porous silicon films
Authors: Randrianalisoa Jaona , Baillis Dominique
Published: March 2008

This paper presents a Monte Carlo (MC) modeling of heat conduction in heavily doped (p+ and n+) porous silicon (PS) films known as mesoporous silicon (meso-PS). A three-dimensional pore network generator is developed to better reproduce the structure of low porosity (fv<50%) meso-PS. The submicron scale heat conduction modeled by the Boltzman transport equation is simulated using the MC method in which the nonlinear phonon dispersion curves of bulk silicon and the phonon lifetime dependent on temperature, frequency, and polarization are taken into account. The proposed method has been applied to predict the effect of the porosity (10%–47%), pore sizes (10–20nm), pore arrangement (p+- and n+-type), temperature (50–500K), and film thickness (50nm–1μm) on the cross-plane thermal conductivity of meso-PS films. Moreover, the simulation results enable to deduce the scattering mean free path (MFP) of phonons in the PS and the scattering MFP due to phonon-pore wall interaction. At room temperature, the thermal conductivity of meso-PS is shown one to two orders of magnitude smaller than that of bulk silicon. A drastic simplification of the phonon dispersion curves and phonon MFP, such as in the Debey approximation, results in an overestimation (by about three times) of the thermal conductivity of meso-PS. The thermal conductivity decreases when the pore size decreases or the porosity increases. For a given porosity and pore size, the thermal conductivity of doped p+-type PS is much smaller than that of doped n+-type PS. Finally, the simulations of thermal conductivity of doped p+-type PS are shown in good agreement with available experimental data which confirms the validity of the current modeling.
Plasmon turbulence spectra with the filamentation patterns in a laser plasma
Authors: Liu X. L. , Liu S. Q. , Yang X. S.
Published: March 2008

The instantaneous spectra of the transverse, Langmuir, and ion-sound plasmons near the critical surface in a laser-plasma are numerically obtained from the complete Zakharov equations under the condition of the nonstatic limit. They are used to discuss the filamentation process in the strong Langmuir turbulence. From the turbulence spectra, the energy flux flow from small k space to large k space can be identified. The higher incident laser intensity associated with a quicker filamentation process can also be identified.
Mini-conference on helicon plasma sources
Authors: Scime E. E. , Keesee A. M. , Boswell R. W.
Published: March 2008

The first two sessions of this mini-conference focused attention on two areas of helicon source research: The conditions for optimal helicon source performance and the origins of energetic electrons and ions in helicon source plasmas. The final mini-conference session reviewed novel applications of helicon sources, such as mixed plasma source systems and toroidal helicon sources. The session format was designed to stimulate debate and discussion, with considerable time available for extended discussion.
Phase-perturbation-free measurement of electro-optic effect based on Mach–Zehnder interferometer
Authors: Iwamura Tomo , Liu Xin Yi , Suka Shota , Umegaki Shinsuke
Published: March 2008

A novel method of evaluating the electro-optic (EO) effect is proposed based on a Mach–Zehnder interferometer, where the interference fringes are perturbed by air turbulence and/or other mechanical vibrations of an optical bench. The method enables the practical and industrial measurement of the EO coefficient in any environment. It also provides the continuous or repetitive measurement, leading to evaluation of temporal change of an EO coefficient or orientation relaxation of an EO-chromophore containing polymer poled by an electric field.
Highly sensitive detection of near-field Raman scattered light from strained Si∕SiGe heterostructures by scanning near-field optical Raman microscope using ultraviolet resonant Raman scattering
Authors: Yoshikawa M. , Murakami M. , Ishida H.
Published: March 2008

We have developed a scanning near-field Raman microscope (SNORM) with a hollow pyramidal probe that uses ultraviolet resonant Raman scattering and measured changes in the near-field and far-field Raman intensities of strained Si∕SiGe heterostructures as a function of a probe-sample distance R. We observed that the near-field Raman intensity of a strained Si film dramatically decreased with an increase in the probe-sample distance. The decay curve of the near-field Raman intensity was approximately expressed by the R−3 plot calculated from a simple model based on dipole-dipole interaction. This confirms that our SNORM detects the near-field light from the sample.
Magnetic reconnection with electron viscosity in electron magnetohydrodynamics
Authors: Cai Huishan , Li Ding
Published: March 2008

The general dispersion relation of collisionless reconnection instability due to electron viscosity μe in the whistler frequency is derived. In the framework of electron magnetohydrodynamics (EMHD), the evolution of magnetic reconnection instability is studied, and the linear growth rates are obtained. The scaling laws of the reconnection instability growth rate with respect to the electron viscosity in constant-ψ (used in the tearing mode) and low-k regimes are obtained, respectively, and compare with those obtained in standard magnetohydrodynamic theory. In the constant-ψ regime for “tearing-mode-like” instability, the growth rate is proportional to μe1∕4, while in the low-k regime, it is proportional to μe1∕8.
Relation between growth dynamics and the spatial distribution of intrinsic defects in self-assembled colloidal crystal films
Authors: Lozano G. , Míguez H.
Published: March 2008

Herein we establish a clear relation between the parameters that govern the growth dynamics and the structural quality of colloidal crystal films. We report an optical analysis of the spatial distribution of intrinsic defects in colloidal crystal films and correlate our results with a theoretical model describing the growth dynamics of such lattices. We find that the amount of defects fluctuates periodically and decreases along the growth direction of the lattice. We demonstrate that these spatial variations are a direct consequence of the temporal oscillations of the crystal film formation velocity, which are inherent to the colloidal particle deposition process.
A new sample holder for laser-excited pump-probe magnetic measurements on a Focus photoelectron emission microscope
Authors: Miguel Jorge , Bernien Matthias , Bayer Daniela , Sánchez-Barriga Jaime , Kronast Florian , Aeschlimann Martin , Dürr Hermann A. , Kuch Wolfgang
Published: March 2008

A custom-made Omicron-compatible sample holder for time-resolved photoelectron emission microscopy experiments is presented. It comprises a sample plate with four contacts that hosts a chip carrier where the semiconductor substrate is mounted. Covering the sample holder, a 6mm diameter mask protects electrostatically the sample from the extractor lens voltage while keeping the imaging quality unperturbed. The improvements are a greater sample lifetime and the ability to withstand much higher currents in the stripline that provides the magnetic pulse to the magnetic microstructure.
Interface modification for highly efficient organic photovoltaics
Authors: Steim Roland , Choulis Stelios A. , Schilinsky Pavel , Brabec Christoph J.
Published: March 2008

We present highly efficient inverted polymer:fullerene bulk-heterojunction solar cells by incorporation of a nanoscale organic interfacial layer between the indium tin oxide (ITO) and the metal oxide electron-conducting layer. We demonstrate that stacking of solution-processed organic and metal oxide interfacial layers gives highly charged selective low ohmic cathodes. The incorporation of a polyoxyethylene tridecyl ether interfacial layer between ITO and solution-processed titanium oxide (TiOx) raised the power conversion efficiency of inverted organic photovoltaics to 3.6%, an improvement of around 15% in their performance over comparable devices without the organic interfacial layer.
Diffusive to drift-diffusion crossover of spin transport in the low-field regime
Authors: Miah M. Idrish
Published: March 2008

Electric field-dependent electron spin diffusion in GaAs is investigated experimentally. We consider the three spin transport regimes, namely diffusive, drift-diffusion crossover, and drift. Of them, spin transport in the diffusive and drift-diffusion crossover regimes is studied in more detail. We also estimate the drift-diffusion crossover field (Ex) and the intrinsic spin diffusion length (δs) in the nondegenerate regime. The estimated value of δs is found to be 1.74μm, a factor of 0.87 lower than that reported in the literature. The technique, however, demonstrates it as a convenient and useful tool to measure Ex and δs in semiconductors.
Photoconductivity in BiFeO3 thin films
Authors: Basu S. R. , Martin L. W. , Chu Y. H. , Gajek M. , Ramesh R. , Rai R. C. , Xu X. , Musfeldt J. L.
Published: March 2008

The optical properties of epitaxial BiFeO3 thin films have been characterized in the visible range. Variable temperature spectra show an absorption onset near 2.17eV, a direct gap (2.667±0.005eV at 300K), and charge transfer excitations at higher energy. Additionally, we report photoconductivity in BiFeO3 films under illumination from a 100mW∕cm2 white light source. A direct correlation is observed between the magnitude of the photoconductivity and postgrowth cooling pressure. Dark conductivities increased by an order of magnitude when comparing films cooled in 760 and 0.1Torr. Large increases in photoconductivity are observed in light.
Effect of image charges in the drain delay of AlGaN∕GaN high electron mobility transistors
Authors: Chung J. W. , Zhao X. , Wu Y.-R. , Singh J. , Palacios T.
Published: March 2008

The drain delay in AlGaN∕GaN submicron high electron mobility transistors (HEMTs) accounts for almost 25% of the total electron delay. This long delay significantly limits the maximum frequency performance and linearity of these devices. This paper studies the origin of this important delay assuming that it is inversely proportional to α, a parameter related to how injected channel electrons image at different contacts in the HEMT. Through analysis and two-dimensional simulations, we have found that α equals 3 in a standard HEMT. This value has been confirmed experimentally through the coupling of Monte Carlo simulations and drain delay measurements.
Theoretical study on the transport property of p-Si∕n-SrTiO3−δ
Authors: Hu Chun-lian , Han Peng , Jin Kui-juan , Lu Hui-bin , Yang Guo-Zhen
Published: March 2008

The transport property of p-Si∕n-SrTiO3−δ heterojunction has been obtained self-consistently with the drift-diffusion model at the temperature range from 200to300K by applying Richardson current at the interface. The band structures, electric field intensities, and carrier distributions at various bias voltages or temperatures are obtained from our calculation. Furthermore, the evolution of the I-V behavior with the temperature is also obtained theoretically. From the good agreement between our calculated results and the experimental data, we can conclude that the rectification property in the perovskite-silicon p-n junction is owing to the drift-diffusion mechanism and the transport property of Si substrate significantly contributes to the almost linear characteristic of the I-V curves.
Si-doped high Al-content AlGaN epilayers with improved quality and conductivity using indium as a surfactant
Authors: Al tahtamouni T. M. , Sedhain A. , Lin J. Y. , Jiang H. X.
Published: March 2008

Effects of indium as a surfactant for the growth of Si-doped Al0.75Ga0.25N epilayers by metal organic chemical vapor deposition have been studied. It was found that the use of indium as a surfactant improved the overall material quality of these epilayers, as evidenced by decreasing the (a) density of surface pits, (b) screw dislocation density, and (c) intensity of the deep level impurity transition with increasing indium flow rate. Hall effect measurements also yielded increased conductivity and electron concentration with increasing indium flow rate. The results suggested that indium as a surfactant counteracts the incorporation of defects responsible for self-compensation for n-type doping, namely, cation vacancies, in high Al-content AlGaN epilayers. A correlation between the intensity of the deep level impurity transition and screw dislocation density was also established.
Spatially direct charged exciton photoluminescence in undoped ZnSe∕BeTe type-II quantum wells
Authors: Ji Z. W. , Takeyama S. , Mino H. , Oto K. , Muro K. , Akimoto R.
Published: March 2008

Photoluminescence (PL) spectra occurred as a spatially direct optical transition inside of the ZnSe layer in undoped ZnSe∕BeTe∕ZnSe type-II quantum structures have been studied. We have found that the charged exciton transition was observed at the lower energy side of the exciton transition in the spatially direct PL. The formation of the charged exciton was attributed to the accumulated electrons in the ZnSe layer after the photoexcitation accompanied by the holes being escaped from this well and injected into the BeTe layer.
Very low turn-on voltage and high brightness tris-(8-hydroxyquinoline) aluminum-based organic light-emitting diodes with a MoOx p-doping layer
Authors: Xie Guohua , Meng Yanlong , Wu Fengmin , Tao Chen , Zhang Dandan , Liu Mingjun , Xue Qin , Chen Wen , Zhao Yi
Published: March 2008

We have demonstrated an organic light-emitting diode based on molybdenum oxide (MoOx) doped 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA) as a p-type doping hole injection layer. The tris-(8-hydroxyquinoline) aluminum (Alq3)-based organic light-emitting diodes show high brightness at very low operating voltage, 100cd∕m2 at 3.2V and 1000cd∕m2 at 4.4V, corresponding to a low turn-on voltage of 2.4V. Such improved properties are attributed to the formation of the charge transfer complex produced by doping MoOx into m-MTDATA, which provides much more free hole carriers, and the introduction of an efficient electron-injecting layer to improve the performance.
Phosphor-free white light-emitting diode with laterally distributed multiple quantum wells
Authors: Park Il-Kyu , Kim Ja-Yeon , Kwon Min-Ki , Cho Chu-Young , Lim Jae-Hong , Park Seong-Ju
Published: March 2008

A phosphor-free white light-emitting diode (LED) was fabricated with laterally distributed blue and green InGaN∕GaN multiple quantum wells (MQWs) grown by a selective area growth method. Photoluminescence and electroluminescence (EL) spectra of the LED showed emission peaks corresponding to the individual blue and green MQWs. The integrated EL intensity ratio of green to blue emission varied from 2.5 to 6.5 with the injection current below 300mA, but remained constant at high injection currents above 300mA. The stability of the emission color at high currents is attributed to parallel carrier injection into both MQWs.
High crystalline-quality III-V layer transfer onto Si substrate
Authors: Chen Peng , Jing Yi , Lau S. S. , Xu Dapeng , Mawst Luke , Alford T. L. , Paulson Charles , Kuech T. F.
Published: March 2008

In this study, an approach combining ion cutting and selective chemical etch for the transfer of high crystalline-quality III-V layers on SiO2∕Si substrate has been investigated. This layer transfer scheme takes advantage of the ion-cutting process by conserving III-V substrates for reuse and simultaneously improving the transferred layer quality and surface condition without using chemical and mechanical polishing. The relocation of the ion-implantation damage maximum enables the transfer of relatively defect-free InP-based layers onto a Si substrate coated with an oxide layer and results in structures ready for further optoelectronic device fabrication or epitaxial growth.
Terahertz Raman laser based on silicon doped with phosphorus
Authors: Pavlov S. G. , Hübers H.-W. , Böttger U. , Zhukavin R. Kh. , Shastin V. N. , Hovenier J. N. , Redlich B. , Abrosimov N. V. , Riemann H.
Published: March 2008

Raman-type stimulated emission at frequencies between 5.0 and 5.2THz as well as between 6.1 and 6.4THz has been realized in silicon crystals doped by phosphorus donors. The Raman laser operates at around 5K under optical excitation by a pulsed, frequency-tunable infrared free electron laser. The frequencies of the observed laser emission are close to the frequencies of the intracenter laser lines which originate from the 2p0 and 2p± phosphorus states. The Stokes shift of 3.16THz is equal to the difference between the energies of the phosphorus ground state, 1s(A1), and the 1s(E) excited state.
Depolarization field mitigated domain engineering in nickel diffused lithium tentalate
Authors: Peng L.-H. , Tseng Y.-P. , Lin K.-L. , Huang Z.-X. , Huang C.-T. , Kung A.-H.
Published: March 2008

We demonstrated a domain reversal mechanism on Z-cut congruent-grown lithium tentalate (LiTaO3) composed of nickel (Ni) diffusion followed by pulse field poling. Domain nucleation and forward growth were found confined to the nondiffused regions, where the commonly observed serrated domain fronts in poled LiTaO3 were absent in this work. These observations are ascribed to the formation of domain nucleation barrier by the depolarization field and reveal the divergence effect in the ferroelectric spontaneous polarization at the domain boundary due to Ni diffusion. This mechanism simplifies the fabrication of periodically poled LiTaO3 for second-harmonic generation in the blue spectral regime.
Electron paramagnetic resonance of Co2+ compounds (abstract)
Authors: Wan Ke-Lin , Zhao Min-Guang , Xiong Quan , Bai Gui-Ru
Published: March 2008

In cubic crystal field, the ground state of d7 configuration is 4T1 which is an orbital degenerate state. Even though it is in low symmetric crystal field, the orbital degeneracy of 4T1 is not completely quenched. So it makes it difficult to study its ground-state properties, such as the electron spin resonance g factors and the splitting of ground state. Usually, the method of ‘‘T-P’’ equivalence which is not convenient to investigate the physical processes was used in the previous works. In the present work, the formulae of d-d transition, the splitting of ground state, and the electron paramagnetic resonance parameter, which relate these quantities to the crystal structure as the d orbit of Co2+ is employed, are derived. The present theory shows that g∥>g⊥ and g∥<g⊥ are due to the different distortion of ligands along C3 axis. On the basis of ab initio, the formulae obtained are applied to deal with the magnetic properties of some Co2+ compounds. The agreement of theory with the experiment shows that the present theory is reasonable.
Analyses of Mlc–IIB
Glc
interaction and a plausible molecular mechanism of Mlc inactivation by membrane sequestration
Authors: Nam Tae-Wook , Jung Ha Il , An Young Jun , Park Young-Ha , Lee Sang Hee , Seok Yeong-Jae , Cha Sun-Shin
Published: March 2008

In
Escherichia coli
, glucose-dependent transcriptional induction of genes encoding a variety of sugar-metabolizing enzymes and transport systems is mediated by the phosphorylation state-dependent interaction of membrane-bound enzyme IICB
Glc
(EIICB
Glc
) with the global repressor Mlc. Here we report the crystal structure of a tetrameric Mlc in a complex with four molecules of enzyme IIB
Glc
(EIIB), the cytoplasmic domain of EIICB
Glc
. Each monomer of Mlc has one bound EIIB molecule, indicating the 1:1 stoichiometry. The detailed view of the interface, along with the high-resolution structure of EIIB containing a sulfate ion at the phosphorylation site, suggests that the phosphorylation-induced steric hindrance and disturbance of polar intermolecular interactions impede complex formation. Furthermore, we reveal that Mlc possesses a built-in flexibility for the structural adaptation to its target DNA and that interaction of Mlc with EIIB fused only to dimeric proteins resulted in the loss of its DNA binding ability, suggesting that flexibility of the Mlc structure is indispensable for its DNA binding.
A nanostructure-initiator mass spectrometry-based enzyme activity assay
Authors: Northen Trent R. , Lee Jinq-Chyi , Hoang Linh , Raymond Jason , Hwang Der-Ren , Yannone Steven M. , Wong Chi-Huey , Siuzdak Gary
Published: March 2008

We describe a Nanostructure-Initiator Mass Spectrometry (NIMS) enzymatic (Nimzyme) assay in which enzyme substrates are immobilized on the mass spectrometry surface by using fluorous-phase interactions. This “soft” immobilization allows efficient desorption/ionization while also enabling the use of surface-washing steps to reduce signal suppression from complex biological samples, which results from the preferential retention of the tagged products and reactants. The Nimzyme assay is sensitive to subpicogram levels of enzyme, detects both addition and cleavage reactions (sialyltransferase and galactosidase), is applicable over a wide range of pHs and temperatures, and can measure activity directly from crude cell lysates. The ability of the Nimzyme assay to analyze complex mixtures is illustrated by identifying and directly characterizing β-1,4-galactosidase activity from a thermophilic microbial community lysate. The optimal enzyme temperature and pH were found to be 65°C and 5.5, respectively, and the activity was inhibited by both phenylethyl-β-
d
-thiogalactopyranoside and deoxygalactonojirimycin. Metagenomic analysis of the community suggests that the activity is from an uncultured, unsequenced γ-proteobacterium. In general, this assay provides an efficient method for detection and characterization of enzymatic activities in complex biological mixtures prior to sequencing or cloning efforts. More generally, this approach may have important applications for screening both enzymatic and inhibitor libraries, constructing and screening glycan microarrays, and complementing fluorous-phase organic synthesis.
Unmodified self antigen triggers human CD8 T cells with stronger tumor reactivity than altered antigen
Authors: Speiser Daniel E. , Baumgaertner Petra , Voelter Verena , Devevre Estelle , Barbey Catherine , Rufer Nathalie , Romero Pedro
Published: March 2008

Human cancer vaccines are often prepared with altered “analog” or “heteroclitic” antigens that have been optimized for HLA class I binding, resulting in enhanced immunogenicity. Here, we take advantage of CpG oligodeoxynucleotides as powerful vaccine adjuvants and demonstrate the induction of high T cell frequencies in melanoma patients, despite the use of natural (unmodified) tumor antigenic peptide. Compared with vaccination with analog peptide, natural peptide induced T cell frequencies that were approximately twofold lower. However, T cells showed superior tumor reactivity because of (i) increased functional avidity for natural antigen and (ii) enhancement of T cell activation and effector function. Thus, novel vaccine formulations comprising potent immune stimulators may allow to circumvent the need for modified antigens and can induce highly functional T cells with precise antigen specificity.