bluuebunny/crossref_metadata_2025 huggingface dataset:
Indoor localization system in a multi-block workspace
Authors: Park JaeHyun , Choi MunGyu , Zu YunFei , Lee JangMyung
Published: May 2009

This paper proposes methodologies and techniques for multi-block navigation of an indoor localization system with active beacon sensors. As service robots and ubiquitous technology have evolved, there is an increasing need for autonomous indoor navigation of mobile robots. In a large number of indoor localization schemes, the absolute position estimation method, relying on navigation beacons or landmarks, has been widely used due to its low cost and high accuracy. However, few of these schemes have managed to expand the applications for use in complicated workspaces involving many rooms or blocks that cover a wide region, such as airports and stations. Since the precise and safe navigation of mobile robots in complicated workspaces is vital for the ubiquitous technology, it is necessary to develop a multi-block navigation scheme. This new design of an indoor localization system includes ultrasonic attenuation compensation, dilution of both the precision analysis and fault detection, and an isolation algorithm using redundant measurements. These ideas are implemented on actual mobile robot platforms and beacon sensors, and experimental results are presented to test and demonstrate the new methods.
A homotopy-theoretic universal property of Leinster's operad for weak ω-categories
Authors: GARNER RICHARD
Published: May 2009

We explain how any cofibrantly generated weak factorisation system on a category may be equipped with a universally and canonically determined choice of cofibrant replacement. We then apply this to the theory of weak ω-categories, showing that the universal and canonical cofibrant replacement of the operad for strict ω-categories is precisely Leinster's operad for weak ω-categories.
A coloring property for countable groups
Authors: GAO SU , JACKSON STEVE , SEWARD BRANDON
Published: May 2009

Motivated by research on hyperfinite equivalence relations we define a coloring property for countable groups. We prove that every countable group has the coloring property. This implies a compactness theorem for closed complete sections of the free part of the shift action ofGon 2G. Our theorems generalize known results about.
LABOR TURNOVER COSTS AND THE CYCLICAL BEHAVIOR OF VACANCIES AND UNEMPLOYMENT
Authors: Silva José Ignacio , Toledo Manuel
Published: May 2009

This paper extends the Diamond-Mortensen-Pissarides (DMP) matching model with endogenous job destruction by introducing postmatch labor turnover costs. We consider training and separation costs that create heterogeneity among workers. In particular, there are two types of employed workers: (i) new entrants who need training in order to become fully productive, and (ii) incumbents who are fully productive and whose departure from the firm imposes costs on it. We find that our calibrated model, relative to the standard DMP model, comes closer to the data regarding the volatility of vacancies and unemployment without introducing unrealistic sensitivity to policy changes. Moreover, our extended model nearly reproduces the downward-sloping Beveridge curve, which is unusual when endogenous job destruction exists in this type of model.
High-Angle Annular Dark Field Scanning Transmission Electron Microscopy on Carbon-Based Functional Polymer Systems
Authors: Sourty Erwan , van Bavel Svetlana , Lu Kangbo , Guerra Ralph , Bar Georg , Loos Joachim
Published: May 2009

Two purely carbon-based functional polymer systems were investigated by bright-field conventional transmission electron microscopy (CTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). For a carbon black (CB) filled polymer system, HAADF-STEM provides high contrast between the CB agglomerates and the polymer matrix so that details of the interface organization easily can be revealed and assignment of the CB phase is straightforward. For a second system, the functional polymer blend representing the photoactive layer of a polymer solar cell, details of its nanoscale organization could be observed that were not accessible with CTEM. By varying the camera length in HAADF-STEM imaging, the contrast can be enhanced between crystalline and amorphous compounds due to diffraction contrast so that nanoscale interconnections between domains are identified. In general, due to its incoherent imaging characteristics HAADF-STEM allows for reliable interpretation of the data obtained.
Three-Dimensional Measurement of Line Edge Roughness in Copper Wires Using Electron Tomography
Authors: Ercius Peter , Gignac Lynne M. , Hu C.-K. , Muller David A.
Published: May 2009

Electrical interconnects in integrated circuits have shrunk to sizes in the range of 20–100 nm. Accurate measurements of the dimensions of these nanowires are essential for identifying the dominant electron scattering mechanisms affecting wire resistivity as they continue to shrink. We report a systematic study of the effect of line edge roughness on the apparent cross-sectional area of 90 nm Cu wires with a TaN/Ta barrier measured by conventional two-dimensional projection imaging and three-dimensional electron tomography. Discrepancies in area measurements due to the overlap of defects along the wire's length lead to a 5% difference in the resistivities predicted by the two methods. Tomography of thick cross sections is shown to give a more accurate representation of the original structure and allows more efficient sampling of the wire's cross-sectional area. The effect of roughness on measurements from projection images is minimized for cross-section thicknesses less than 50 nm, or approximately half the spatial frequency of the roughness variations along the length of the investigated wires.
The Applications ofIn SituElectron Energy Loss Spectroscopy to the Study of Electron Beam Nanofabrication
Authors: Chen Shiahn J. , Howitt David G. , Gierhart Brian C. , Smith Rosemary L. , Collins Scott D.
Published: May 2009

Anin situelectron energy loss spectroscopy (EELS) technique has been developed to investigate the dynamic processes associated with electron-beam nanofabrication on thin membranes. In this article, practical applications germane to e-beam nanofabrication are illustrated with a case study of the drilling of nanometer-sized pores in silicon nitride membranes. This technique involves successive acquisitions of the plasmon-loss and the core-level ionization-loss spectra in real time, both of which provide the information regarding the hole-drilling kinetics, including two respective rates for total mass loss, individual nitrogen and silicon element depletion, and the change of the atomic bonding environment. In addition, thein situEELS also provides an alternative method for endpoint detection with a potentially higher time resolution than by imaging. On the basis of the time evolution ofin situEELS spectra, a qualitative working model combining knock-on sputtering, irradiation-induced mass transport, and phase separation can be proposed.
Optimizing Electron Backscatter Diffraction of Carbonate Biominerals—Resin Type and Carbon Coating
Authors: Pérez-Huerta Alberto , Cusack Maggie
Published: May 2009

Electron backscatter diffraction (EBSD) is becoming a widely used technique to determine crystallographic orientation in biogenic carbonates. Despite this use, there is little information available on preparation for the analysis of biogenic carbonates. EBSD data are compared for biogenic aragonite and calcite in the common blue mussel,Mytilus edulis, using different types of resin and thicknesses of carbon coating. Results indicate that carbonate biomineral samples provide better EBSD results if they are embedded in resin, particularly epoxy resin. A uniform layer of carbon of 2.5 nm thickness provides sufficient conductivity for EBSD analyses of such insulators to avoid charging without masking the diffracted signal. Diffraction intensity decreases with carbon coating thickness of 5 nm or more. This study demonstrates the importance of optimizing sample preparation for EBSD analyses of insulators such as carbonate biominerals.
Modeling Rectangular Cantilevers during Torsion and Deflection for Application to Frictional Force Microscopy
Authors: Hayden Victor C. , Beaulieu Luc Y.
Published: May 2009

A numerical and experimental analysis of the optical beam deflection system used to monitor microcantilevers subjected to simultaneous deflection and twisting such as in lateral or frictional force microscopy was performed. This study focused on two optical beam deflection orientations where in the first case the optical beam and the detector are at a right angle to the length of the cantilever and the second case, which is the more standard orientation, the optical beam is parallel to the length of the lever. This study finds that it is possible to model the twist and the deflection separately and treat each motion independently. Simulations have shown that the above-mentioned systems are equivalent in accuracy and sensitivity for monitoring the simultaneous twist and deflection of cantilevers.
Nanogold as a Specific Marker for Electron Cryotomography
Authors: He Yongning , Jensen Grant J. , Bjorkman Pamela J.
Published: May 2009

While electron cryotomography (ECT) provides “molecular” resolution, three-dimensional images of unique biological specimens, sample crowdedness, and/or resolution limitations can make it difficult to identify specific macromolecular components. Here we used a 1.4 nm Nanogold® cluster specifically attached to the Fc fragment of IgG to monitor its interaction with the neonatal Fc receptor (FcRn), a membrane-bound receptor that transports IgG across cells in acidic intracellular vesicles. ECT was used to image complexes formed by Nanogold-labeled Fc bound to FcRn attached to the outer surface of synthetic liposomes. In the resulting three-dimensional reconstructions, 1.4 nm Nanogold particles were distributed predominantly along the interfaces where 2:1 FcRn-Fc complexes bridged adjacent lipid bilayers. These results demonstrate that the 1.4 nm Nanogold cluster is visible in tomograms of typically thick samples (∼250 nm) recorded with defocuses appropriate for large macromolecules and is thus an effective marker.
Pesticide distribution and use in vegetable production in the Red River Delta of Vietnam
Authors: Van Hoi Pham , Mol Arthur P.J. , Oosterveer Peter , van den Brink Paul J.
Published: May 2009

For a long time pesticides attracted interest from the Vietnamese governments and farmers for their positive effects in protecting crop yield losses resulting from pests and other plant diseases. Recently, the negative effects of pesticides on human health, natural food chains and the environment are increasingly being taken into account by both state and non-state actors. Striking a balance between positive and negative effects is complicated as, most likely, pesticides will continue to maintain their vital role in an agriculture-based country such as Vietnam. However, recently a shift can be noticed in farmers' selection and application of pesticides, initiated mainly by farmers themselves and to a lesser extent also by other actors such as the government, pesticide companies and distributors. This article provides an empirical insight into this shift, based on the results from research in four provinces in the Red River Delta. Possible implications for policies toward greening pesticide handling practices in vegetable production are drawn, such as removing inexpensive pesticides (often associated with high toxicity) from the market, giving technical training on pesticide selection and use to farmers, and reconsidering the role different actors can play in future safe vegetable production programs.
Magnetohydrodynamic simulation of non–flux rope coronal mass ejections
Authors: Zhang T. X. , Wu S. T.
Published: May 2009

Observations at 1 AU indicate that only 1/3 of coronal mass ejections (CMEs) have a flux rope structure, while the other 2/3 of CMEs have a complex disordered magnetic field. The initiation of the flux rope CMEs has been extensively simulated with various magnetohydrodynamic (MHD) models. However, the initiation of the non–flux rope CMEs is rarely done in numerical modeling. In this paper, we numerically simulate the physical origin and characteristics of the non–flux rope CMEs by using a three‐dimensional, axisymmetric, time‐dependent, self‐consistent MHD model. The results show that the emergence of a counterclockwise flux rope from the lower coronal boundary at the open magnetic field region, near the closed magnetic field lines, can initiate a magnetic configuration, which causes the magnetic reconnection at the coronal base. Physically, the magnetic field of the emerged counterclockwise flux rope has antipolarity with the background open field, and the location of the magnetic flux emergence is at the edge of a coronal hole. This magnetic reconnection between closed and open field lines at the coronal base generates an Alfvénic jet‐like plasma outflow. It could further develop into a non–flux rope CME if enough magnetic energy is deposited. Solar energetic particle (SEP) events in association with the non–flux rope CMEs are usually impulsive because the magnetic topology obtained from this simulation of non–flux rope CMEs corresponds to that proposed by Reames (2002) to lead impulsive SEP events.
Structural results for La Palma island using 3‐D gravity inversion
Authors: Camacho A. G. , Fernández J. , González P. J. , Rundle J. B. , Prieto J. F. , Arjona A.
Published: May 2009

A recent gravity survey composed of 317 bench marks all over the island of La Palma (Canary Islands) is used, in combination with satellite data for regional aspects, to obtain results about structural properties of the island connected with the tectonic environment and local volcanism. To that end, a nonlinear three‐dimensional gravity inversion approach is considered. The inversion scheme provides, in a nonsubjective form, the geometry of the anomalous bodies constructed in a random growth process. Results from the inversion can be interpreted in the framework of the geologic evolution of this ocean island volcano as a complex composite volcano with a large central body with high‐density corresponding to the older intrusive part of the basalt complex. New unexpected features are enlightened, such as large thermal anomalies in the upper mantle southward of La Palma, as well as fracture en echelon zones associable to a slow active process of dislocation related to the recent volcanism in the southern half of the island. The results obtained for La Palma as a test site testify to the usefulness of the developed gravity inversion methodology for structural studies on islands in general.
A wind tunnel investigation of the distortion of polluted water drops in the horizontal electric fields
Authors: Bhalwankar Rohini V. , Kamra A. K.
Published: May 2009

Distortion of the water drops freely suspended in a vertical wind tunnel is investigated when these drops are polluted with sulphate/nitrate salt and are also subjected to the horizontal electric fields. Results show that although the drops' average shape is not significantly affected, the magnitudes of drop oscillations decrease when these are formed from the water polluted with sulphate/nitrate salt. However, when these polluted drops are placed in a horizontal electric field, their oblateness increases with respect to that of the distilled water drops, and this increase in oblateness is more in higher electric fields. Results can possibly be explained because of the increase in surface tension, viscosity and density, and a more dominant effect due to the increase in electrical conductivity of the polluted water. Significance of the results is discussed in view of the possible modification of lightning activity in clouds formed over big cities.
Sensitivity of photolysis frequencies and key tropospheric oxidants in a global model to cloud vertical distributions and optical properties
Authors: Liu Hongyu , Crawford James H. , Considine David B. , Platnick Steven , Norris Peter M. , Duncan Bryan N. , Pierce Robert B. , Chen Gao , Yantosca Robert M.
Published: May 2009

Clouds directly affect tropospheric photochemistry through modification of solar radiation that determines photolysis frequencies. As a follow‐up study to our recent assessment of these direct radiative effects of clouds on tropospheric chemistry, this paper presents an analysis of the sensitivity of such effects to cloud vertical distributions and optical properties (cloud optical depths (CODs) and cloud single scattering albedo), in a global three‐dimensional (3‐D) chemical transport model. The model was driven with a series of meteorological archives (GEOS‐1 in support of the Stratospheric Tracers of Atmospheric Transport mission, or GEOS1‐STRAT, GEOS‐3, and GEOS‐4) generated by the NASA Goddard Earth Observing System (GEOS) data assimilation system. Clouds in GEOS1‐STRAT and GEOS‐3 have more similar vertical distributions (with substantially smaller CODs in GEOS1‐STRAT) while those in GEOS‐4 are optically much thinner in the tropical upper troposphere. We find that the radiative impact of clouds on global photolysis frequencies and hydroxyl radical (OH) is more sensitive to the vertical distribution of clouds than to the magnitude of column CODs. With random vertical overlap for clouds, the model calculated changes in global mean OH (J(O1D), J(NO2)) due to the radiative effects of clouds in June are about 0.0% (0.4%, 0.9%), 0.8% (1.7%, 3.1%), and 7.3% (4.1%, 6.0%) for GEOS1‐STRAT, GEOS‐3, and GEOS‐4, respectively; the geographic distributions of these quantities show much larger changes, with maximum decrease in OH concentrations of ∼15–35% near the midlatitude surface. The much larger global impact of clouds in GEOS‐4 reflects the fact that more solar radiation is able to penetrate through the optically thin upper tropospheric clouds, increasing backscattering from low‐level clouds. Model simulations with each of the three cloud distributions all show that the change in the global burden of ozone due to clouds is less than 5%. Model perturbation experiments with GEOS‐3, where the magnitude of 3‐D CODs are progressively varied from −100% to 100%, predict only modest changes (<5%) in global mean OH concentrations. J(O1D), J(NO2), and OH concentrations show the strongest sensitivity for small CODs and become insensitive at large CODs owing to saturation effects. Caution should be exercised not to use in photochemical models a value for cloud single scattering albedo lower than about 0.999 in order to be consistent with the current knowledge of cloud absorption at the ultraviolet wavelengths.
Relationship between photochemical ozone production and NOx oxidation in Houston, Texas
Authors: Neuman J. A. , Nowak J. B. , Zheng W. , Flocke F. , Ryerson T. B. , Trainer M. , Holloway J. S. , Parrish D. D. , Frost G. J. , Peischl J. , Atlas E. L. , Bahreini R. , Wollny A. G. , Fehsenfeld F. C.
Published: May 2009

An instrumented aircraft was used to study anthropogenic emissions and subsequent ozone and reactive nitrogen photochemistry in the continental boundary layer downwind of Houston, Texas. Measurements of ozone, carbon monoxide, NOx, and NOx oxidation products were conducted from the NOAA WP‐3 aircraft during the 2006 Texas Air Quality Study under a variety of meteorological conditions. Sixty‐five crosswind transects of plumes from Houston urban and industrial areas performed on 10 daytime flights from 13 September to 6 October 2006 are examined. Coincident measurements of NOx and its oxidation products show that NOx was oxidized predominately to nitric acid and peroxy acyl nitrates on time scales of a few hours. The observed relationships between O3 and NOx oxidation products are affected by both photochemistry and mixing of different air masses. On four flights, background pollutant mixing ratios were constant and CO to NOy enhancement ratios in downwind plume transects remained at the emission ratio. The enhancement ratio of O3 to NOx oxidation products was also nearly constant and could be used to derive ozone production efficiency (OPE) in plumes downwind from the Houston area. On the other flights, variable mixing of regionally polluted background air with plumes caused CO to NOy and O3 to NOy − NOx enhancement ratios to increase as plumes were transported. In such cases, enhancement ratios do not solely reflect plume processing, and OPE could not be determined. The OPE averages 5.9 ± 1.2 in coalesced plumes from urban and petrochemical industrial sources in Houston, with higher values in isolated plumes downwind from petrochemical facilities located along the Houston ship channel.
Interactions between soil thermal and hydrological dynamics in the response of Alaska ecosystems to fire disturbance
Authors: Yi Shuhua , McGuire A. David , Harden Jennifer , Kasischke Eric , Manies Kristen , Hinzman Larry , Liljedahl Anna , Randerson Jim , Liu Heping , Romanovsky Vladimir , Marchenko Sergei , Kim Yongwon
Published: May 2009

Soil temperature and moisture are important factors that control many ecosystem processes. However, interactions between soil thermal and hydrological processes are not adequately understood in cold regions, where the frozen soil, fire disturbance, and soil drainage play important roles in controlling interactions among these processes. These interactions were investigated with a new ecosystem model framework, the dynamic organic soil version of the Terrestrial Ecosystem Model, that incorporates an efficient and stable numerical scheme for simulating soil thermal and hydrological dynamics within soil profiles that contain a live moss horizon, fibrous and amorphous organic horizons, and mineral soil horizons. The performance of the model was evaluated for a tundra burn site that had both preburn and postburn measurements, two black spruce fire chronosequences (representing space‐for‐time substitutions in well and intermediately drained conditions), and a poorly drained black spruce site. Although space‐for‐time substitutions present challenges in model‐data comparison, the model demonstrates substantial ability in simulating the dynamics of evapotranspiration, soil temperature, active layer depth, soil moisture, and water table depth in response to both climate variability and fire disturbance. Several differences between model simulations and field measurements identified key challenges for evaluating/improving model performance that include (1) proper representation of discrepancies between air temperature and ground surface temperature; (2) minimization of precipitation biases in the driving data sets; (3) improvement of the measurement accuracy of soil moisture in surface organic horizons; and (4) proper specification of organic horizon depth/properties, and soil thermal conductivity.
Model projected changes of extreme wind events in response to global warming
Authors: Gastineau G. , Soden B. J.
Published: May 2009

The changes in the frequency of occurrence of extreme wind storm events in response to anthropogenic global warming are explored using a multi‐model ensemble of coupled climate model simulations. These changes, diagnosed using several different metrics based on the daily wind fields, indicate that the frequency of the most extreme wind events decreases over the tropics in association with the model‐projected weakening of the large‐scale atmospheric circulation. At higher latitudes, the strongest near‐surface wind events are found to increase in frequency in association with the amplified baroclinicity and poleward shift of the midlatitude storm tracks. The frequency of the heaviest precipitation events increases in all models, despite a systematic reduction of extreme upward vertical velocities, due to the increased moisture content of the lower troposphere. All of these changes are shown to be robust projections of current climate models.
Intra‐annual variation of wave number 4 structure of vertical E × B drifts in the equatorial ionosphere seen from ROCSAT‐1
Authors: Ren Zhipeng , Wan Weixing , Liu Libo , Xiong Jiangang
Published: May 2009

This paper studies the intra‐annual variation of the wave number 4 structure in the equatorial vertical E × B drifts at high solar flux level based on of the ROCSAT‐1 observations during the interval from 1999 to 2004. It is found that the daytime longitudinal structure is significant in northern summer and early autumn but weak in northern winter. This is consistent with the intra‐annual variations of the tidal mode DE3. At night, the intra‐annual variation of the wave number 4 structure shows some differences from that in daytime, which may relate to different dynamo mechanisms operating in different local time. We also found that the wave number 4 structure mainly shifts eastward during daytime in most of months, which is coincident with the eastward propagation of the DE3 tide. However, it is largely disturbed near sunrise and sunset. We attribute this disturbance as the jumping of the main dynamo region between E and F layers, as well as the different dynamo mechanisms in different dynamo regions.
Circadian rhythms and memory: not so simple as cogs and gears
Authors: Eckel‐Mahan Kristin L , Storm Daniel R
Published: May 2009

The influence of circadian rhythms on memory has long been studied; however, the molecular prerequisites for their interaction remain elusive. The hippocampus, which is a region of the brain important for long‐term memory formation and temporary maintenance, shows circadian rhythmicity in pathways central to the memory‐consolidation process. As neuronal plasticity is the translation of numerous inputs, illuminating the direct molecular links between circadian rhythms and memory consolidation remains a daunting task. However, the elucidation of how clock genes contribute to synaptic plasticity could provide such a link. Furthermore, the idea that memory training could actually function as a zeitgeber for hippocampal neurons is worth consideration, based on our knowledge of the entrainment of the circadian clock system. The integration of many inputs in the hippocampus affects memory consolidation at both the cellular and the systems level, leaving the molecular connections between circadian rhythmicity and memory relatively obscure but ripe for investigation.
Treatment of Cognitive-Communicative Disorders Following Blast Injury
Authors: de Riesthal Michael
Published: May 2009

Purpose: Mild traumatic brain injury (mTBI) following exposure to a blast is the signature injury of Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF). The purposes of this article are to describe the characteristics of the service members who experience blast injuries, the cognitive-communicative deficits they present, and the role of the speech-language pathologist (SLP) in managing these deficits.

Method: Demographic data for the service members who have experienced blast injuries in OIF/OEF are reviewed and reported. The literature on treating cognitive-communicative disorders following mTBI is reviewed and is discussed in the context of managing the deficits reported by service members returning from Iraq and Afghanistan.

Results and conclusions: Information regarding the effects of blast exposure on the human body continues to emerge. Data regarding the most effective treatment for cognitive-communicative deficits following blast injury are needed. For now, SLPs must rely on the best evidence from the civilian mTBI literature, clinical expertise, and the personal values of the individual with TBI to develop effective treatment programs targeting the cognitive-communicative disorders experienced by these individuals.
Test charge potential in the presence of electron acoustic waves in multispecies dusty plasma
Authors: Ali S.
Published: May 2009

An expression for the test charge potential is obtained in a multispecies dusty plasma, whose constituents are the Boltzmann distributed hot electrons, mobile cold electrons, immobile cold ions, and charge fluctuating isolated dust grains. The plasma response function involving the electron-acoustic waves becomes modified due to the inclusion of the dust-charge perturbations. The analytical and numerical investigations reveal that the Debye–Hückel screening and wakefield potentials are significantly affected by the plasma parameters such as the equilibrium dust number density, the dust grain radius, and the hot electron temperature. The relevance of the results to laboratory plasma, where the two distinct groups of electrons exist besides the static ions and isolated dust grains, is discussed.
Ultralow dark current Ge/Si(100) photodiodes with low thermal budget
Authors: Osmond J. , Isella G. , Chrastina D. , Kaufmann R. , Acciarri M. , von Känel H.
Published: May 2009

Vertical incidence photodiodes were fabricated from Ge grown epitaxially on Si(100) by low-energy plasma-enhanced chemical vapor deposition. Consideration of the energy band profiles of n-i-p and p-i-n heterostructures, and optimization of growth processes and thermal budget, allowed the performance of Ge photodectors integrated on Si(100) substrates to be optimized. Record low dark current density of Js=4.1×10−5 A/cm2 and external quantum efficiency at 1550 nm of η=32% were measured.
Effects of rf power on electron density and temperature, neutral temperature, and Te fluctuations in an inductively coupled plasma
Authors: Camparo James , Fathi Gilda
Published: May 2009

Atomic clocks that fly on global-navigation satellites such as global positioning system (GPS) and Galileo employ light from low-temperature, inductively coupled plasmas (ICPs) for atomic signal generation and detection (i.e., alkali/noble-gas rf-discharge lamps). In this application, the performance of the atomic clock and the capabilities of the navigation system depend sensitively on the stability of the ICP’s optical emission. In order to better understand the mechanisms that might lead to instability in these rf-discharge lamps, and hence the satellite atomic clocks, we studied the optical emission from a Rb/Xe ICP as a function of the rf power driving the plasma. Surprisingly, we found that the electron density in the plasma was essentially independent of increases in rf power above its nominal value (i.e., “rf-power gain”) and that the electron temperature was only a slowly varying function of rf-power gain. The primary effect of rf power was to increase the temperature of the neutrals in the plasma, which was manifested by an increase in Rb vapor density. Interestingly, we also found evidence for electron temperature fluctuations (i.e., fluctuations in the plasma’s high-energy electron content). The variance of these fluctuations scaled inversely with the plasma’s mean electron temperature and was consistent with a simple model that assumed that the total electron density in the discharge was independent of rf power. Taken as a whole, our results indicate that the electrons in alkali/noble-gas ICPs are little affected by slight changes in rf power and that the primary effect of such changes is to heat the plasma’s neutral species.
Atomic scale study of boron interstitial clusters in ion-implanted silicon
Authors: Ngamo M. , Duguay S. , Cristiano F. , Daoud-Ketata K. , Pareige P.
Published: May 2009

Monocrystalline silicon was implanted with boron (32 keV, 1.3×1015 at. cm−2), post-annealed (740°, 10 min, N2) and further analyzed at the atomic scale by atom probe tomography. A comparison between the as-implanted and annealed samples demonstrated the presence of large B–Si clusters after annealing which were associated with the well-known boron interstitial clusters. The cluster density (up to 5×1017 cm−3) and the number of B atoms per cluster (up to 50) were found to vary with the boron concentration. Only 8% of the B atoms were found trapped in those clusters, suggesting the presence of a majority of very small B–Si aggregates in correlation with simulations.
Crystallization dynamics of nitrogen-doped Ge2Sb2Te5
Authors: Shelby Robert M. , Raoux Simone
Published: May 2009

The crystallization of amorphous Ge2Sb2Te5 (GST) doped with nitrogen is studied with pulsed laser heating. The crystallization time of sputter-deposited films is increased by doping by as much as 100× for nitrogen concentrations of the order of 12 at. % in as-deposited amorphous films. Suppression of the formation of critical crystal nuclei is found to be responsible. The crystallization of melt-quenched amorphous material is also slowed by doping but less dramatically.
X-ray magnetic circular dichroism of pulsed laser deposited Co2MnSn and Co2MnSb thin films grown on GaAs (001)
Authors: Paudel Moti R. , Wolfe Christopher S. , Ali Naushad , Stadler Shane , Christodoulides Joseph A. , Ederer David L. , Li Yinwan , Callcott Thomas A. , Freeland John W.
Published: May 2009

We present the structural and element specific magnetic properties of Co2MnSn and Co2MnSb thin films grown on GaAs (100) substrates using pulsed laser deposition. X-ray magnetic circular dichroism (XMCD) spectra were measured for 400Å thick films at the L2,3 edges of Co and Mn. Element specific moments for Co and Mn in Co2MnSn were calculated from the x-ray absorption and XMCD spectra using the XMCD sum rules. The ratios of orbital to spin magnetic moments for Co and Mn were calculated for Co2MnSn and Co2MnSb.
Ferromagnetism in the Mn-based Heusler alloy Mn2NiSb
Authors: Luo Hongzhi , Meng Fanbin , Feng Zhongqiu , Li Yangxian , Zhu Wei , Wu Guangheng , Zhu Xiaoxi , Jiang Chengbao , Xu Huibin
Published: May 2009

A Mn-based Heusler alloy Mn2NiSb has been synthesized. First-principles calculations and experimental measurements were employed to investigate its electronic structure and magnetism. Theoretical calculation indicates a ferromagnetic coupling in Mn2NiSb and a total spin moment of 4.21μB/f.u., which agrees quite well with the saturation moment at 5 K. This ferromagnetic coupling arises from the larger lattice constant and more valence electrons compared with other Mn-based Heusler alloys. The partial spin moments for Mn (A), Mn (B), and Ni are 0.6, 3.30, and 0.3μB, respectively. The Curie temperature of Mn2NiSb is 647 K, indicating a strong exchange interaction between Mn atoms.
Morphology alterations during postsynthesis oxidation of Zn nanowires
Authors: Schroeder P. , Kast M. , Halwax E. , Edtmaier C. , Bethge O. , Brückl H.
Published: May 2009

Zinc metal nanowires have been oxidized at temperatures of 200–500 °C in ambient air in order to obtain ZnO nanowires. X-ray diffraction investigations reveal a complete transformation from Zn to ZnO at a temperature of ≥300 °C within 30 min. Temperature-induced grain growth attains saturation at about 350 °C. Scanning electron microscopy studies show a pronounced morphology change from smooth, unidirectional to rough, bursted nanorods at a temperature of >250 °C. The corresponding transformation mechanism is discussed.
Thermal probing of energy dissipation in current-carrying carbon nanotubes
Authors: Shi Li , Zhou Jianhua , Kim Philip , Bachtold Adrian , Majumdar Arun , McEuen Paul L.
Published: May 2009

The temperature distributions in current-carrying carbon nanotubes have been measured with a scanning thermal microscope. The obtained temperature profiles reveal diffusive and dissipative electron transport in multiwalled nanotubes and in single-walled nanotubes when the voltage bias was higher than the 0.1–0.2 eV optical phonon energy. Over 90% of the Joule heat in a multiwalled nanotube was found to be conducted along the nanotube to the two metal contacts. In comparison, about 80% of the Joule heat was transferred directly across the nanotube-substrate interface for single-walled nanotubes. The average temperature rise in the nanotubes is determined to be in the range of 5–42 K per microwatt Joule heat dissipation in the nanotubes.
Narrow asymmetric waveguide semiconductor lasers for improved temperature wavelength stability
Authors: Ryvkin Boris , Avrutin Eugene
Published: May 2009

We show theoretically that Fabry–Pérot semiconductor lasers using narrow asymmetric waveguides can offer much higher temperature stability of the lasing wavelength compared to structures with standard symmetrical waveguides. The mechanism of the low thermal sensitivity is the uniquely strong wavelength dependence of the confinement factor near the waveguide cutoff, which increases the blueshift of the modal gain peak with carrier density and helps offset the bandgap shrinkage with temperature.
Neutron-irradiated Schottky diodes with self-assembled InAs quantum dots: Optical and electrical properties
Authors: Schramm A. , Tukiainen A. , Pessa M. , Konetzni C. , Heyn Ch. , Hansen W.
Published: May 2009

The effect of neutron irradiation on optical and electrical properties of self-assembled InAs/GaAs quantum dots (QDs) is studied for neutron doses up to ϕn=3×1014 cm−2. The QDs are embedded in n-type GaAs Schottky diodes grown by molecular beam epitaxy on GaAs(001). We observe an initial increase in QD photoluminescence followed by a decrease as a function of neutron irradiation. The increase in photoluminescence is attributed to a more effective carrier trapping and relaxation from the wetting layer into the QDs via radiation-induced defects. The losses of photoluminescence at higher neutron doses are caused by defects, which act as nonradiative recombination centers. The observed dependence of the photoluminescence on the laser excitation power can be explained with saturation effects. Deep level transient spectroscopy experiments reveal multiple overlapping electron traps. Furthermore, an enhanced introduction of defects in the QD layer is observed. Electrical characterization of the Schottky diodes via capacitance-voltage spectroscopy reveals that the doping condition in the diodes changes due to the introduction of defects. This fact has to be taken into account if QDs are used in electrical devices in radiation-harsh environments as it is shown by low-temperature deep level transient spectroscopy experiments on electron emission processes from QD levels.
Integration of (208) oriented epitaxial Hf-doped Bi4Ti3O12 with (0002) GaN using SrTiO3/TiO2 buffer layer
Authors: Luo W. B. , Zhu J. , Li Y. R. , Wang X. P. , Zhang Y.
Published: May 2009

Hf-doped Bi4Ti3O12 (BTH) ferroelectric films with excellent electrical properties were epitaxially integrated with GaN semiconductor using (111) SrTiO3 (STO)/rutile (200) TiO2 as buffer layer. The STO/TiO2 buffer layer was deposited by laser molecular beam epitaxy. The structural characteristics of the buffer layer were in situ and ex situ characterized by reflective high energy electron diffraction, x-ray diffraction (XRD), and high resolution transmission microscopy. The overlaying SrRuO3 (SRO) and BTH films were then deposited by pulsed laser deposition. XRD spectra, including θ-2θ and Φ scans, show that the (208) BTH films were epitaxially grown on GaN, and the BTH films inherit the in-plane twin-domain of STO buffer layer. Electrical measurements demonstrate that the non-c axis BTH films possess a large remnant polarization (2Pr=45 μC/cm2), excellent fatigue endurance (10.2% degradation after 1.1×1010 switching cycles), and a low leakage current density (1.94×10−7 A/cm2 at an electric field of 200 kV/cm). These results reveal that the (208) BTH films with favorable electrical performance could be epitaxially grown on GaN template using STO/TiO2 buffer layer.
Proton redistribution and pseudoantiferroelectricity in H+ implanted Pb(Zr,Ti)O3 thin films
Authors: Zhang X. , Jiang A. Q. , Tang T. A.
Published: May 2009

Hydrogen ions were implanted into 500-nm-thick Pb(Zr,Ti)O3 ferroelectric thin films with different doses and energies. An antiferroelectric behavior was confirmed in the implanted thin films with proper H+ injection energies from independent measurements of polarization-electric hysteresis loops and capacitance-voltage curves. With the increase in the H+ doping concentration and implanting energy up to 25 keV, the characteristic pseudoantiferroelectric behavior becomes more evident in the films along with the concomitant reduction in the remnant polarization. However, the above antiferroelectricity is weakened for the restoration of a preferred ferroelectric state, once the implanting energy is higher than 35 eV. The consequent “Trim94” simulation of the H+ distribution as well as the induced oxygen vacancies (VO⋅⋅) indicates the almost linear shift in the depth for the maximum charge density within the film with the enhanced implanting energy until the depth moves out of the film thickness above 40 keV. Beyond the antiferroelectric dependence on the implanting energy in thin films, the previous ferroelectric state can also be rejuvenated under a bipolar-field stressing through the redistribution of the H+ and VO⋅⋅ concentrations. The rejuvenation process is accelerated upon heating due to the increased charge mobility. The doping charges are immobile during short-time domain switching but movable under a long-time negative/positive field with the estimated activation energy of 0.23/0.29 eV. This study implies the potential application of high-density charge storage of the implanted ferroelectric capacitor with the property comparable to a genuine antiferroelectric capacitor.
A model for the J-V characteristics of P3HT:PCBM solar cells
Authors: Kumar Pankaj , Jain S. C. , Kumar Vikram , Chand Suresh , Tandon R. P.
Published: May 2009

Current-voltage (J-V) characteristics of an organic bulk heterojunction solar cell have been modeled and compared with the measured characteristics of solar cell based on the blend of poly(3-hexylethiophene) (P3HT) and phenyl [6,6] C61 butyric acid methyl ester (PCBM). In an undoped organic double Schottky junction diode, for V<Vbi the electric field remains constant and is given by (Vbi−V)/d, where Vbi is the built-in voltage, V is the applied voltage, and d is sample thickness. We considered the effect of this constant electric field on the charge carrier transport and solved the drift and diffusion equations to model the J-V characteristics. For V<Vbi the current is found to be dominated by diffusion. A comparison of the theoretical results with the experimental data measured in dark and under different illumination intensities shows good agreement.
Influence of organic semiconductor-metal interfaces on the photoresponse of functionalized anthradithiophene thin films
Authors: Day J. , Platt A. D. , Subramanian S. , Anthony J. E. , Ostroverkhova O.
Published: May 2009

We report on the contribution of effects at the organic semiconductor-metal interfaces to dark current and to transient and continuous wave (cw) photocurrent in high-performance functionalized anthradithiophene (ADT) films deposited from solution on glass substrates with gold (Au) and aluminum (Al) electrodes. In all samples, fast sub-30 ps charge carrier photogeneration was observed under photoexcitation with 100 fs, 400 nm laser pulses. Amplitudes of the transient photocurrent measured in samples with Au and Al electrodes were similar within a factor of 2–4, depending on the sample and on the applied voltage. Compared to transient photocurrents, dark currents, and cw photocurrents exhibited pronounced differences between ADT films on Au and Al electrodes, with considerably higher currents in samples with Au electrodes. Measurements of photoresponse under uniform illumination were complemented by scanning photocurrent microscopy performed on the same samples. Photocurrent profiles were obtained by scanning the gap between coplanar electrodes with a tightly focused beam, either pulsed or cw, and measuring photocurrent, either transient or steady-state at every point. While samples with Au and Al electrodes exhibited similar distributions of the transient photocurrent amplitudes in the gap, those of the cw photocurrents exhibited dramatic differences, in agreement with results obtained under uniform illumination.
Modeling of electromechanical behavior of chitosan-blended cellulose electroactive paper (EAPap)
Authors: Jang Sang-Dong , Kim Joo-Hyung , Kim Jaehwan
Published: May 2009

Electromechanical bending actuation of chitosan-blended cellulose (CBC) electroactive paper (EAPap) was studied using a theoretical model, followed by an experimental comparison. The bending displacement of the model was calculated based on an ion traveling phenomenon and multilayered cantilever beam. By comparing the bending model and experimental data, we found that the bending model could predict the electromechanical actuation behavior as well as redistribution of ions inside of CBC EAPap under different humidity levels and electric fields. The bending actuation model of EAPap can be useful to investigate the electromechanical actuation behavior of EAPap devices such as artificial muscles, microrobots, and other various actuators.
Infrared observation of linear GeC3 trapped in solid Ar
Authors: Gonzalez Eric , Rittby C. M. L. , Graham W. R. M.
Published: May 2009

Linear GeC3 has been synthesized and its vibrational spectrum observed for the first time. The cluster was detected by Fourier transform infrared spectroscopy when the products from the dual laser ablation of either a pair of carbon and germanium rods or a single, sintered germanium-carbon rod were trapped in solid Ar at ∼10 K. Comparison of C13 isotopic shift measurements with the predictions of density functional theory calculations at the B3LYP/cc-pVDZ level has resulted in the identification of the ν1(σ) and ν2(σ) modes of linear GeC3 at 1903.9 and 1279.6 cm−1, respectively. For the related group IV clusters, this result is in contrast to SiC3 for which two cyclic isomers have been observed but similar to C4 for which only the linear isomer has been observed spectroscopically.
Analysis of temperature dependence of dark current mechanisms for long-wavelength HgCdTe photovoltaic infrared detectors
Authors: Hu W. D. , Chen X. S. , Yin F. , Quan Z. J. , Ye Z. H. , Hu X. N. , Li Z. F. , Lu W.
Published: May 2009

Resistance-voltage curves of n-on-p Hg1−хCdxTe long-wavelength infrared photodiodes forming 128-element array are measured in the temperature range of 40–150 K. Experimentally obtained characteristics are fitted by the simultaneous-mode nonlinear fitting program. The dark current mechanisms induced by diffusion, generation recombination, trap-assisted tunneling, band-to-band tunneling, and series resistance effect are included in the physical model for R-V curve fitting. Six characteristic parameters as function of temperature are extracted from measured R-V curves. The characteristics of extracted current components at low temperatures indicate significant contributions from tunneling effects, which is the dominant leakage current mechanism for reverse bias greater than approximately 50 mV. The Hg-vacancy-induced acceptor trap tends to invert to donor type at higher temperature, typically larger than 120 K, while it can maintain stable at the temperature of 60–40 K. The stable temperature of ion-implantation-induced traps is about 90–60 K, which possibly tends to be ionized at high temperature. However, a low operation temperature can induce the frozen effects of the ion-implantation-induced donor traps. Fitting certainty analysis shows that the error of one parameter can be magnified when one of the other types of dark current mechanisms dominates the dark current and is even infinitely enlarged under large reverse bias. The different bias regions at which each fitting parameter has the largest influence to the R-V curve should be ascertained. The results of the present work demonstrate that modeling of the dynamic resistance in small voltage range or at just operation temperature are insufficient for determining the mechanism of carrier transport across the Hg1−хCdxTe junction and a detailed theoretical study of the current-voltage characteristics in wider voltage range or at various temperatures should be carried out.