bluuebunny/crossref_metadata_2025 huggingface dataset:
Synergies and complementarities of CloudSat‐CALIPSO snow observations
Authors: Battaglia A. , Delanoë J.
Published: December 2012

Four years (2007–2010) of colocated 94 GHz CloudSat radar reflectivities and 532 nm CALIPSO Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) backscattering coefficients are used to globally characterize snow‐precipitating clouds. CALIOP is particularly useful for the detection of mixed and supercooled liquid water (SLW) layers. Liquid layers are common in snow precipitating clouds: overall/over sea/over land 49%/57%/33% of the snowy profiles present SLW or mixed‐phase layers. The spatial and seasonal dependencies of our results—with snowing clouds more likely to be associated with mixed phase during summer periods—are related to snow layer top temperatures. SLW occurs within the majority (>80%) of snow‐precipitating clouds with cloud tops warmer than 250 K, and is present 50% of the time when the snow‐layer top temperature is about 240 K. There is a marked tendency for such layers to occur close to the top of the snow‐precipitating layer (75% of the times within 500 m). Both instruments can be synergetically used for profiling ice‐phase‐only snow, especially for light snow (Z<0 dBZ, S<0.16 mm/h) when CALIOP is capable of penetrating, on average, more than half of the snow layer depth. These results have profound impact for deepening our understanding of ice nucleation and snow growth processes, for improving active and passive snow remote sensing techniques, and for planning snow‐precipitation missions.
On the angular effect of residual clouds and aerosols in clear‐sky infrared window radiance observations 2. Satellite experimental analyses
Authors: Nalli Nicholas R. , Barnet Christopher D. , Gambacorta Antonia , Maddy Eric S. , Xie Hua , King Thomas S. , Joseph Everette , Morris Vernon R.
Published: December 2012

This paper continues an investigation into the zenith angular effect of cloud‐contamination within “clear‐sky” infrared (IR) radiance observations commonly used in the retrieval of environmental data records (EDRs), which include “cloud‐cleared radiances” (as is typical from hyper/ultra spectral IR sounders), as well as “cloud‐masked” data (as is typical from imagers). The simple probability of clear line of sight (PCLoS) models and sensitivity studies of Part 1 (Nalli et al., 2012a) are corroborated with experimental analyses of environmental satellite data products as functions of sensor zenith angle, including sounder cloud‐cleared radiances (CCRs) and retrieved effective cloud fraction, as well as narrowband imager cloud masking. Analyses of hyperspectral microwindow calc − obs are performed using MetOp‐A Infrared Atmospheric Sounding Interferometer (IASI) CCR observations matched to dedicated radiosonde observations (RAOBs) during intensive validation field campaigns. The IASI calc − obs are found to exhibit a systematic positive bias with a strong concave‐up variation with satellite zenith angle (i.e., an increasing positive bias symmetric over the scanning range) on the order of 1–3 K in magnitude, a signal associated with both residual clouds and dust aerosols. This is corroborated by analysis of the IASI retrieved effective cloud fraction product compared to the expected angular variations predicted by the PCLoS models, which show that the observed concave‐up calc − obs variation may be the result of contamination by mid‐to‐upper tropospheric clouds. Finally, a corollary global analysis of the MetOp‐A Advanced Very High Resolution Radiometer (AVHRR) cloud‐mask shows concave‐up variation that may be underestimating the angular variation for global ensembles containing clouds with vertical development (i.e., aspect ratios >0.5). The results presented in this work thus support the sensitivity studies of Part 1, indicating that contamination by residual clouds and/or aerosols within clear‐sky observations can have a measurable concave‐up impact on the angular agreement of observations with calculations.
Energy exchange and water budget partitioning in a boreal minerogenic mire
Authors: Peichl Matthias , Sagerfors Jörgen , Lindroth Anders , Buffam Ishi , Grelle Achim , Klemedtsson Leif , Laudon Hjalmar , Nilsson Mats B.
Published: December 2012

This study investigated patterns and controls of the seasonal and inter‐annual variations in energy fluxes (i.e., sensible heat, H, and latent heat, λE) and partitioning of the water budget (i.e., precipitation, P; evapotranspiration, ET; discharge, Q; and soil water storage, ∆S) over five years (2001–2005) in a boreal oligotrophic fen in northern Sweden based on continuous eddy covariance, water table level (WTL), and weir measurements. For the growing season (May 1 to September 31), the 5 year averages (± standard deviation) of the midday (10:00 to 14:00 h) Bowen ratio (β, i.e., H/λE) was 0.86 ± 0.08. Seasonal and inter‐annual variability of β was mainly driven by λE which itself was strongly controlled by both weather (i.e., vapor pressure deficit, D, and net radiation, Rn) and physiological parameters (i.e., surface resistance). During the growing season, surface resistance largely exceeded aerodynamic resistance, which together with low mean values of the actual ET to potential ET ratio (0.55 ± 0.05) and Priestley‐Taylor α (0.89) suggests significant physiological constrains on ET in this well‐watered fen. Among the water budget components, the inter‐annual variability of ET was lower (199 to 298 mm) compared to Q (225 to 752 mm), with each accounting on average for 34 and 65% of the ecosystem water loss, respectively. The fraction of P expended into ET was negatively correlated to P and positively to Rn. Although a decrease in WTL caused a reduction of the surface conductance, the overall effect of WTL on ET was limited. Non‐growing season (October 1 to April 30) fluxes of H, λE, and Q were significant representing on average −67%, 13%, and 61%, respectively, of their growing season sums (negative sign indicates opposite flux direction between the two seasons). Overall, our findings suggest that plant functional type composition, P and Rn dynamics (i.e., amount and timing) were the major controls on the partitioning of the mire energy and water budgets. This has important implications for the regional climate as well as for ecosystem development, nutrient, and carbon dynamics.
Warming of surface waters in the mid‐latitude North Atlantic during Heinrich events
Authors: Naafs B. D. A. , Hefter J. , Grützner J. , Stein R.
Published: December 2012

During the six Heinrich events of the last 70 kyr, episodic calving from the circum‐Atlantic ice sheets released large numbers of icebergs into the North Atlantic. These icebergs and associated meltwater flux are hypothesized to have led to a shutdown of Atlantic Meridional Overturning Circulation and severe cooling in large parts of the Northern Hemisphere. However, due to the limited availability of high‐resolution records, the magnitude of sea surface temperature (SST) changes related to the impact of Heinrich events on the midlatitude North Atlantic is poorly constrained. Here we present a record of ‐based SSTs derived from sediments of Integrated Ocean Drilling Project Site U1313, located at the southern end of the ice‐rafted debris (IRD) belt in the midlatitude North Atlantic (41°N). We demonstrate that all six Heinrich events are associated with a rapid warming of surface waters by 2–4°C in a few thousand years. The presence of IRD leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and Heinrich events. We argue that this warming in the midlatitude North Atlantic is related to a northward expansion of the subtropical gyre during Heinrich events. As a wide range of studies demonstrated that in the central IRD belt Heinrich events are associated with low SSTs, these results thus identify an antiphased (seesaw) pattern in SSTs during Heinrich events between the midlatitude (warm) and northern North Atlantic (cold). This highlights the complex response of surface water characteristics in the North Atlantic to Heinrich events that is poorly reproduced by freshwater hosing experiments and challenges the widely accepted view that, within the IRD belt of the North Atlantic, Heinrich events coincide with periods of low SSTs.
Dynamically downscaled winter precipitation over complex terrain of the Central Rockies of Western Montana, USA
Authors: Silverman N. L. , Maneta M. P. , Chen S.‐H. , Harper J. T.
Published: December 2012

Key Points

NCEP GFS‐WRF winter precipitation downscale is compared to PRISM

Largest differences seen at high elevations and west of continental divide

WRF predicts higher amounts of precipitation than PRISM at high elevations
Protecting society
Authors: Uhlenhaut Christine , Burger Reinhard , Schaade Lars
Published: December 2012

Concerns over biosecurity remain unresolved, as the debate around the recent publications on human transmissible H5N1 flu demonstrated. A range of measures and the involvement of all stakeholders are needed to better protect society from malicious abuse of biological research.
EBEC 2012—An energetic time in Freiburg
Authors: Bernardi Paolo , Giorgio Valentina
Published: December 2012

The seventeenth European Bioenergetics Conference (EBEC) took place in September 2012 at the Albert‐Ludwigs‐University in Freiburg, Germany, and was hosted by Thorsten Friedrich. The conference is a biannual event that brings together researchers from across the globe to discuss progress in this diverse and challenging field.
Design for controllability
Authors: Tsukaya Hirokazu
Published: December 2012

The safety of genetically modified crops remains a contested issue, given the potential risk for human health and the environment. To further reduce any risks and alleviate public concerns, terminator technology could be used both to tag and control genetically modified plants.
Children’s Speech Recognition and Loudness Perception With the Desired Sensation Level v5 Quiet and Noise Prescriptions
Authors: Crukley Jeffery , Scollie Susan D.
Published: December 2012

Purpose

To determine whether Desired Sensation Level (DSL) v5 Noise is a viable hearing instrument prescriptive algorithm for children, in comparison with DSL v5 Quiet. In particular, the authors compared children’s performance on measures of consonant recognition in quiet, sentence recognition in noise, and loudness perception when fitted with DSL v5 Quiet and Noise.

Method

Eleven children (ages 8 to 17 years) with stable, congenital sensorineural hearing losses participated in the study. Participants were fitted bilaterally to DSL v5 prescriptions with behind-the-ear hearing instruments. The order of prescription was counterbalanced across participants. Repeated measures analysis of variance was used to compare performance between prescriptions.

Results

Use of the Noise prescription resulted in a significant decrease in consonant perception in Quiet with low-level input, but no difference with average-level input. There was no significant difference in sentence-in-noise recognition between the two prescriptions. Loudness ratings for input levels above 72 dB SPL were significantly lower with the noise prescription.

Conclusions

Average-level consonant recognition in quiet was preserved and aversive loudness was alleviated by the Noise prescription relative to the quiet prescription, which suggests that the DSL v5 Noise prescription may be an effective approach to managing the nonquiet listening needs of children with hearing loss.
Early Intervention in Localized Wegener’s Granulomatosis With Sensorineural Hearing Loss Preserves Hearing
Authors: Sriskandarajah Vasuky , Bansal Rhea A. , Yeoh Robin , Bansal Amolak S.
Published: December 2012

Purpose

Wegener’s granulomatosis has been renamedgranulomatosis with polyangiitis(GPA). In this article, the authors refer to WG as “WG/GPA” to indicate the old and new names of this condition. WG/GPA is a systemic necrotizing granulomatous vasculitis that can affect, in particular, the lungs, sinuses, and kidneys. The authors report 2 cases with antineutrophil cytoplasmic antibodies (c-ANCA) positive WG/GPA whose initial presentations were in the form of both conductive and sensorineural hearing loss without systemic features. The authors contrast the reversal of hearing loss and prevention of disease progression with early recognition and treatment.

Method

The authors present 2 contrasting cases of WG/GPA. Changes in hearing were measured through use of a GSI 61 audiometer as well as guidelines from the British Society of Audiology. Serum ANCA were detected by indirect immunofluorescence and formalin fixed neutrophils. Proteinase 3 (PR3) and myeloperoxidase antibodies were measured through use of a fluoroenzyme immunoassay.

Results

Persistent deafness and systemic disease are more likely, and more aggressive therapy was required when the diagnosis of WG/GPA was delayed.

Conclusion

WG/GPA should be considered in acute or subacute deafness presenting over days to weeks and even in the absence of systemic symptoms. A negative or weak ANCA with absent antibodies to serine PR3 and myeloperoxidase should not exclude the possible diagnosis of WG/GPA, and a high index of suspicion should be maintained.
Sequential Bilateral Cochlear Implantation: Speech Perception and Localization Pre- and Post-Second Cochlear Implantation
Authors: Dunn Camille C. , Tyler Richard S. , Witt Shelley , Ji Haihong , Gantz Bruce J.
Published: December 2012

Purpose

In this study, the authors sought to compare speech perception and localization in subjects who wear 1 cochlear implant (unilateral CI) or 1 cochlear implant and hearing aid (CI+HA) and then receive a second cochlear implant (bilateral CI), and to evaluate the importance of the duration between implant surgeries and duration of deafness.

Method

Nine subjects were tested on speech perception in quiet, and 13 subjects were tested on speech perception and localization in noise using an array of 8 loudspeakers. All subjects were tested with unilateral CI prior to bilateral implantation and then again with bilateral CI after at least 3 months of bilateral experience.

Results

No significant difference was found between bilateral CI and unilateral CI on averaged speech perception in quiet performance. A significant benefit was found for bilateral CI on averaged speech perception in noise and on localization. Nonsignificant correlations were found for duration between surgeries, duration of deafness, and duration of bilateral use.

Conclusions

Improvements for speech perception and localization played in background noise were indicated for most subjects after they received their 2nd implant. The correlations should be reassessed with a larger number of subjects to appropriately evaluate the effects of duration between surgeries, duration of deafness, and duration of bilateral use.
Hearing Aid Instruction Booklets: Employing Usability Testing to Determine Effectiveness
Authors: Brooke Ruth E. , Isherwood Sarah , Herbert Nicholas C. , Raynor David K. , Knapp Peter
Published: December 2012

Purpose

This study implemented performance-based usability and literature testing to determine whether people could use 2 instruction booklets for hearing aids (HAs) to carry out basic maintenance tasks and find and understand key facts.

Method

Using a cross-sectional study design, researchers recruited 40 participants (25 women, 15 men, ages 46–72 years) with no experience of HAs or audiology services to test instruction booklets for a Danalogic and Unitron HA (20 participants each). Participants were asked to follow instructions provided within the booklets to complete common HA tasks (e.g., cleaning the HA and mold and changing the battery) and demonstrate understanding of information. Participants' views of the booklets were then obtained within a short individual interview.

Results

Participants experienced problems in completing all tasks while following instructions provided by the Danalogic and Unitron booklets. Individual interviews highlighted further issues regarding layout, diagrams, and content, including missing information.

Conclusions

Some HA instruction booklets contain information that some users may find difficult to find, understand, and follow. These limitations may negatively impact on HA satisfaction and use. It is recommended that written information for clients be evaluated prior to use. This study supports the premise that performance-based usability and literature testing are appropriate methods to use.
An Evidence-Based Systematic Review of Amplitude Compression in Hearing Aids for School-Age Children With Hearing Loss
Authors: McCreery Ryan W. , Venediktov Rebecca A. , Coleman Jaumeiko J. , Leech Hillary M.
Published: December 2012

Purpose

Two clinical questions were developed: one addressing the comparison of linear amplification with compression limiting to linear amplification with peak clipping, and the second comparing wide dynamic range compression with linear amplification for outcomes of audibility, speech recognition, speech and language, and self- or parent report in children with hearing loss.

Method

Twenty-six databases were systematically searched for studies addressing a clinical question and meeting all inclusion criteria. Studies were evaluated for methodological quality, and effect sizes were reported or calculated when possible.

Results

The literature search resulted in the inclusion of 8 studies. All 8 studies included comparisons of wide dynamic range compression to linear amplification, and 2 of the 8 studies provided comparisons of compression limiting versus peak clipping.

Conclusions

Moderate evidence from the included studies demonstrated that audibility was improved and speech recognition was either maintained or improved with wide dynamic range compression as compared with linear amplification. No significant differences were observed between compression limiting and peak clipping on outcomes (i.e., speech recognition and self-/parent report) reported across the 2 studies. Preference ratings appear to be influenced by participant characteristics and environmental factors. Further research is needed before conclusions can confidently be drawn.
Hearing Technology and Cognition
Authors: Kalluri Sridhar , Humes Larry E.
Published: December 2012

Purpose

To summarize existing data on the interactions of cognitive function and hearing technology in older adults.

Method

A narrative review was used to summarize previous data for the short-term interactions of cognition and hearing technology on measured outcomes. For long-term outcomes, typically for 3–24 months of hearing aid use, a computerized database search was conducted.

Results

There is accumulating evidence that cognitive function can impact outcomes following immediate or short-term use of hearing aids and that hearing aids can impact immediate cognitive function. There is limited evidence regarding the long-term impact of hearing aids on cognition, and the most rigorous studies in this area have not observed a positive effect.

Conclusions

Although interactions have been observed between cognition and use of hearing aids for measures obtained following immediate or short-term usage of hearing technology, limited evidence is available following long-term usage, and that evidence that is available does not support an effect of hearing aids on cognitive function. More research is needed, however, including rigorous studies of older adults following longer periods of hearing aid usage.
Study of second harmonic generation by high power laser beam in magneto plasma
Authors: Sharma Prerana , Sharma R. P.
Published: December 2012

This paper examines the problem of nonlinear generation of second harmonic of a high power laser pulse propagating in magnetized plasma. The propagation of strong laser beam is proposed in the direction perpendicular to a relatively weak static magnetic field. The laser pulse is taken to be linearly polarized, with the orientation of its electric field that corresponds to an ordinary electromagnetic wave. Besides the standard ponderomotive nonlinearity, the appropriate wave equation also contains the nonlinearity that arises from the relativistic electron jitter velocities. During its propagation, the laser beam gets filamented on account of relativistic and pondermotive nonlinearities present in the plasma. The generated plasma wave gets coupled into the filamentary structures of the pump beam. Due to the expected presence of the beam filamentation, the work has been carried out by considering modified paraxial approximation (i.e., beyond the standard paraxial approximation of a very broad beam). It is found that the power of the plasma wave is significantly affected by the magnetic field strength in the presence of both relativistic and pondermotive nonlinearities. It is investigated that the second harmonic generation is also considerably modified by altering the strength of magnetic field. To see the effect of static magnetic field on the harmonic generation, a key parameter, i.e., the ratio of the cyclotron frequency ωc=eB0/mc over the laser frequency ω0 has been used, where c is the velocity of light, m and e are the mass and charge of the electron and B0 is the externally applied magnetic field.
Invited Review Article: High-speed flexure-guided nanopositioning: Mechanical design and control issues
Authors: Yong Y. K. , Moheimani S. O. R. , Kenton B. J. , Leang K. K.
Published: December 2012

Recent interest in high-speed scanning probe microscopy for high-throughput applications including video-rate atomic force microscopy and probe-based nanofabrication has sparked attention on the development of high-bandwidth flexure-guided nanopositioning systems (nanopositioners). Such nanopositioners are designed to move samples with sub-nanometer resolution with positioning bandwidth in the kilohertz range. State-of-the-art designs incorporate uniquely designed flexure mechanisms driven by compact and stiff piezoelectric actuators. This paper surveys key advances in mechanical design and control of dynamic effects and nonlinearities, in the context of high-speed nanopositioning. Future challenges and research topics are also discussed.
Characterization of Ru thin-film conductivity upon atomic layer deposition on H-passivated Si(111)
Authors: Roodenko K. , Park S. K. , Kwon J. , Wielunski L. , Chabal Y. J.
Published: December 2012

The sheet resistance measured by a four-probe technique is compared to the resistivity data derived from the optical response of thin ruthenium films grown on hydrogen-passivated Si(111) surfaces by atomic-layer deposition using cyclopentadienyl ethylruthenium dicarbonyl, Ru(Cp)(CO)2Et and O2 as gas reactant. The Drude-Landauer theory is applied to evaluate the spectroscopic ellipsometry response and the DC resistivity evaluated by 4-point probe measurements. Results indicate that thin Ru films (below ∼5 nm) deposited on Si exhibit a higher sheet resistance than similarly grown Ru films on TiN. This is explained by an island-growth mechanism at the initial stages of Ru deposition that greatly diminishes the film conductivity before the formation of a continuous film.
The route to high accuracy in ab initio calculations of Cu quadrupole-coupling constants
Authors: Cheng Lan , Stopkowicz Stella , Stanton John F. , Gauss Jürgen
Published: December 2012

We report nonrelativistic and scalar-relativistic coupled-cluster calculations of the copper quadrupole-coupling constants for eleven small copper-containing compounds. It is shown to be necessary to treat both electron-correlation and scalar-relativistic effects on the same footing even for a qualitatively correct description, because both effects are significant and are strongly coupled in the case of Cu electric-field gradients. We show that the three scalar-relativistic schemes employed in the present study—the leading order of direct perturbation theory, the spin-free exact two-component theory in its one-electron variant, and the spin-free Dirac-Coulomb approach—provide accurate treatments of scalar-relativistic effects for the copper compounds under study. Furthermore, we demonstrate that results close to the basis-set limit can be obtained by augmenting large uncontracted standard basis sets for copper with additional steep functions. It is also shown that high-level correlation effects (those beyond the perturbative treatment of triple excitations) make important contributions in the present case.
The nature of Cr center in GaN: Magnetic anisotropy of GaN:Cr single crystals
Authors: Gosk J. B. , Boćkowski M. , Grzegory I. , Szczytko J. , Twardowski A.
Published: December 2012

Magnetization measurements of the strain-free bulk GaN:Cr single crystals of wurtzite structure are reported. Strong magnetic anisotropy at low temperatures (2–10 K) was observed. The data were analyzed assuming Cr2+(d4) configuration. The crystal field model taking into account cubic field of tetrahedral symmetry, trigonal field along the c-axis simulating hexagonal structure, tetragonal static Jahn-Teller distortion, and the spin-orbit interaction provide a good description of the experimental magnetization data.
Coherent femtosecond low-energy single-electron pulses for time-resolved diffraction and imaging: A numerical study
Authors: Paarmann A. , Gulde M. , Müller M. , Schäfer S. , Schweda S. , Maiti M. , Xu C. , Hohage T. , Schenk F. , Ropers C. , Ernstorfer R.
Published: December 2012

We numerically investigate the properties of coherent femtosecond single electron wave packets photoemitted from nanotips in view of their application in ultrafast electron diffraction and non-destructive imaging with low-energy electrons. For two different geometries, we analyze the temporal and spatial broadening during propagation from the needle emitter to an anode, identifying the experimental parameters and challenges for realizing femtosecond time resolution. The simple tip-anode geometry is most versatile and allows for electron pulses of several ten of femtosecond duration using a very compact experimental design, however, providing very limited control over the electron beam collimation. A more sophisticated geometry comprising a suppressor-extractor electrostatic unit and a lens, similar to typical field emission electron microscope optics, is also investigated, allowing full control over the beam parameters. Using such a design, we find ∼230 fs pulses feasible in a focused electron beam. The main limitation to achieve sub-hundred femtosecond time resolution is the typical size of such a device, and we suggest the implementation of more compact electron optics for optimal performance.
Quantitative description of interactions between linear organic chromophores
Authors: Denis Jean-Christophe , Schumacher Stefan , Galbraith Ian
Published: December 2012

To model intermolecular excitation transfer between organic chromophores in the framework of Förster theory, the interaction matrix element is needed for all relative orientations and separations of chromophores. Simulations of extended multi-chromophoric systems thus require a fast but reliable approximation scheme to calculate these dipole interactions. By means of a comparative study of the dipole approximation with quantum chemistry, we demonstrate that the usual line-dipole theory, while suitable for short molecules, breaks down for longer molecules with inter-molecular separations similar to or smaller than the length of the interacting chromophores; a limit that is typically found in conjugated polymer thin films. As a remedy, we propose an improved way of distributing the sub-dipole moments within a line which provides results in very good agreement with the quantum chemistry, and is still simple enough to be used in large scale simulations.
The influence of geometry on the flow rate sensitivity to applied voltage within cone-jet mode electrospray
Authors: Ryan C. N. , Smith K. L. , Stark J. P. W.
Published: December 2012

This work investigates in greater detail than in previous studies the effect of geometry on the relationship between emitted flow rate and applied potential difference in cone-jet mode electrospray systems. The magnitude of the flow rate to voltage relationship is demonstrated to be sensitive to numerous geometric parameters. An explanation of this variation is offered; it is demonstrated that in the cone-jet mode of operation the change of flow rate with the applied extraction voltage is due to the change in electric field at the tip of the emitter. By a finite element method simulation of the assumed electrostatic process the analysis is further extended to include all geometric parameters. The results outlined show the change of flow rate with applied voltage in cone-jet mode electrospray can be significant. This dependence will, under some conditions, have a considerable effect on the electrospray flow rate, and consequently current and droplet size. This has implications on electrospray applications involving the use of the applied voltage to extract the sprayed solution, including nano-electrospray mass spectrometry techniques and some forms of electrospinning.
Physical properties of CdTe:Cu films grown at low temperature by pulsed laser deposition
Authors: de Moure-Flores F. , Quiñones-Galván J. G. , Guillén-Cervantes A. , Arias-Cerón J. S. , Contreras-Puente G. , Hernández-Hernández A. , Santoyo-Salazar J. , de la L. Olvera M. , Santana-Aranda M. A. , Zapata-Torres M. , Mendoza-Álvarez J. G. , Meléndez-Lira M.
Published: December 2012

CdTe:Cu films were grown by pulsed laser deposition on Corning glass slides at a substrate temperature of 300 °C. The thin films were grown using CdTe and Cu2Te powders, varying the Cu2Te concentration from 3 to 10 wt. %. The structural, compositional, optical, and electrical properties were analyzed as a function of the nominal copper concentration. X-ray diffraction shows that films have CdTe cubic phase. The compositional analysis indicates that CdTe:Cu films grown with lower Cu content have Te excess, on the other hand, films with higher Cu content have Te deficiencies. The electrical measurements showed that CdTe:Cu films grown with low Cu content present lowest resistivity.
Optical absorption modulation by selective codoping of SiGe core-shell nanowires
Authors: Amato Michele , Palummo Maurizia , Rurali Riccardo , Ossicini Stefano
Published: December 2012

First-principles calculations on the structural, electronic, and optical properties of B-P codoped SiGe core-shell nanowires are discussed. We show that the simultaneous addition of B and P impurities into the wire can be energetically favored with respect to the single-doping. We demonstrate that impurities energetic levels in the band gap are dependent by the Si/Ge band offset, as well as by their location in the wire (i.e., core or shell region). This electronic tunability results in a significant optical modulation, as demonstrated by the red-shift of the first optical peak when B and P locations are switched in the wire.
Laser-silicon interaction for selective emitter formation in photovoltaics. I. Numerical model and validation
Authors: Blecher J. J. , Palmer T. A. , DebRoy T.
Published: December 2012

Laser doping to form selective emitters offers an attractive method to increase the performance of silicon wafer based photovoltaics. However, the effect of processing conditions, such as laser power and travel speed, on molten zone geometry and the phosphorus dopant profile is not well understood. A mathematical model is developed to quantitatively investigate and understand how processing parameters impact the heat and mass transfer and fluid flow during laser doping using continuous wave lasers. Calculated molten zone dimensions and dopant concentration profiles are in good agreement with independent experimental data reported in the literature. The mechanisms for heat (conduction) and mass (convection) transport are examined, which lays the foundation for quantitatively understanding the effect of processing conditions on molten zone geometry and dopant concentration distribution. The validated model and insight into heat and mass transport mechanisms also provide the bases for developing process maps, which are presented in part II. These maps illustrate the effects of output power and travel speed on molten zone geometry, average dopant concentration, dopant profile shape, and sheet resistance.
Laser-silicon interaction for selective emitter formation in photovoltaics. II. Model applications
Authors: Blecher J. J. , Palmer T. A. , Reutzel E. W. , DebRoy T.
Published: December 2012

Laser doping is an attractive way to manufacture a selective emitter in high efficiency solar cells, but the underlying phenomena, which determine performance, are not well understood. The mathematical model developed in Part I solves the equations of conservation of mass, momentum, and energy and is used here to investigate the effects of processing parameters on molten zone geometry, average phosphorus dopant concentration, dopant profile shape, and sheet resistance. The empirically calculated sheet resistance values are in good agreement with independently measured sheet resistance values reported in the literature. Process maps for output power and travel speed show that molten zone geometry and sheet resistance are more sensitive to output power than travel speed. The highest molten zone depth-to-width aspect ratios and lowest sheet resistances for 532 nm laser beams are obtained at higher laser powers (>13 W) and lower travel speeds (<2 m/s). Once the power level is set, the travel speed can be varied for further optimization of dopant concentration and geometry.
On the origin of basal stacking faults in nonpolar wurtzite films epitaxially grown on sapphire substrates
Authors: Vennéguès P. , Chauveau J. M. , Bougrioua Z. , Zhu T. , Martin D. , Grandjean N.
Published: December 2012

The microstructure of nonpolar heteroepitaxial wurtzite films (GaN and ZnO-based) is dominated by the presence of planar basal stacking faults (BSFs). In this paper, transmission electron microscopy studies of both GaN and ZnO nonpolar films oriented either (11–20) or (1–100) and grown on sapphire substrates, permit to propose and evaluate different mechanisms of BSFs formation. The main mechanism of formation of BSFs results from a Volmer Weber growth mode. The first stage of the growth is a 3D nucleation. The 3D nuclei are relaxed at least along one in-plane orientation. BSFs are created in the coalescence boundaries in order to compensate translations between neighbouring islands. BSFs are well adapted to compensate in-plane translations in the case of nonpolar films. In fact, their plane is perpendicular to the substrate surface and this orientation is similar to the orientation of the coalescence boundaries. Moreover, their displacement vector has a component parallel to the translation between islands and their formation energy is low. On the other hand, in the case of the polar growth, BSFs are not adapted to compensate in-plane translation as their plane is perpendicular to the coalescence boundaries.
Enhanced quality factors and force sensitivity by attaching magnetic beads to cantilevers for atomic force microscopy in liquid
Authors: Hoof Sebastian , Nand Gosvami Nitya , Hoogenboom Bart W.
Published: December 2012

Dynamic-mode atomic force microscopy (AFM) in liquid remains complicated due to the strong viscous damping of the cantilever resonance. Here, we show that a high-quality resonance (Q>20) can be achieved in aqueous solution by attaching a microgram-bead at the end of the nanogram-cantilever. The resulting increase in cantilever mass causes the resonance frequency to drop significantly. However, the force sensitivity—as expressed via the minimum detectable force gradient—is hardly affected, because of the enhanced quality factor. Through the enhancement of the quality factor, the attached bead also reduces the relative importance of noise in the deflection detector. It can thus yield an improved signal-to-noise ratio when this detector noise is significant. We describe and analyze these effects for a set-up that includes magnetic actuation of the cantilevers and that can be easily implemented in any AFM system that is compatible with an inverted optical microscope.
Identification of defect types in moderately Si-doped GaInNAsSb layer in p-GaAs/n- GaInNAsSb/n-GaAs solar cell structure using admittance spectroscopy
Authors: Monirul Islam Muhammad , Miyashita Naoya , Ahsan Nazmul , Sakurai Takeaki , Akimoto Katsuhiro , Okada Yoshitaka
Published: December 2012

Bias dependence of the admittance spectroscopy of GaInNAsSb based solar cell structure has been performed to identify and characterize the type of defects, for example interface and/or bulk type defects in a moderately Si doped GaInNAsSb (n-GaInNAsSb) layer in the structure. From the zero bias admittance spectrum, three peaks namely E1, E2, and E3 corresponding to the localized level at 0.03 eV, 0.07 eV, and 0.16 eV below the conduction band edge (EC) of n-GaInNAsSb material, respectively, were found. Constant position of E2 and E3 peak in the admittance spectra in response to the various applied DC reverse bias suggests that E2 and E3 are related to the bulk type defects being spatially homogeneous throughout the bulk of the n- GaInNAsSb film. However, bias dependence admittance of the E1 peak along with the capacitance - voltage (C-V) measurement as well as characteristic feature in the temperature dependent junction capacitance value strongly suggests that E1 peak might be originated due to the free carrier relaxation in the n- GaInNAsSb layer in lower temperature. Conduction mechanism in the freeze-out regime has been discussed. Analysis of the admittance peak, E1 together with the characteristic features in the frequency dependence of the conduction in freeze out regime suggest that conduction properties of the n-GaInNAsSb material in the freeze-out condition is governed by Mott's variable range hopping mechanism.
Statistically modified surfaces: Experimental solutions for controlled scattered light
Authors: Brissonneau Vincent , Flory François , Escoubas Ludovic , Berginc Gérard , Simon Jean-Jacques
Published: December 2012

An experimental process is proposed to fabricate random rough surfaces which statistical properties can be controlled and tuned. The theoretical approach is developed opening the way to simple, low cost and large surface patterning method. A photoresist is exposed to a speckle pattern created from an argon ion laser. The laser beam has previously been shaped using a digital micromirror device, allowing controlling the correlation function of the speckle. The patterned resist is then transfer by reactive ion etching onto silicon, allowing use for optoelectronics applications. Examples of surfaces, fabricated with Gaussian and non-Gaussian (modified) correlation functions are shown and demonstrate an agreement with theoretical predictions.
Suppression of multi-level bipolar resistive switching in Ag/Pr0.7Ca0.3MnO3 interfaces at low temperatures
Authors: Tsui S. , Salvo C. , Lopez M.
Published: December 2012

Resistive switching phenomena induced by electric pulsing have been investigated for several years as a result of interest in memory technology development. We investigate the viability of bipolar resistive switching at cryogenic temperatures by cooling a Ag/Pr0.7Ca0.3MnO3 interface and subjecting it to varying applied voltage amplitudes. Upon cooling, the switching phenomenon is suppressed until it is no longer observable below 175 K. Varying the applied voltage reveals the existence of several discrete resistance states, and the cooling trends across different samples and pulsing amplitudes are similar. Our results indicate that an alteration in space charge density is the origin of the switch, and the mechanism for this low temperature suppression is the reduced mobility of local oxygen defects in this active interface layer.
Phase transitions and electromechanical properties for barium titanate and lead titanate ferroelectric crystals under one-dimensional shock wave compression
Authors: Gao Junjie , Xu Zhuo , Li Fei , Jiang Dongdong , Zhang Chonghui , Liu Yi , Liu Gaomin , He Hongliang
Published: December 2012

Ferroelectric phase transitions and electromechanical properties of BaTiO3 (BT) and PbTiO3 (PT) crystals under one-dimensional shock wave compression were investigated using Landau-Ginzburg-Devonshire phenomenological approach. The results showed that the Curie temperature of both BT and PT increased with increasing pressure. Under highest shock wave compression, the orthorhombic phase was the stable state for BT, while no ferroelectric-ferroelectric phase transition was induced for PT. At room temperature, the electromechanical parameters for PT and BT were found to decrease with increasing one-dimensional compression, except for the dielectric susceptibility ε22 and piezoelectric coefficient e24 of tetragonal BT. The variations of dielectric and piezoelectric parameters were analyzed according to the elastic Gibbs free-energy.
Enhanced dielectric properties of Pb0.92La0.08 Zr0.52Ti0.48O3 films with compressive stress
Authors: Ma Beihai , Liu Shanshan , Tong Sheng , Narayanan Manoj , (Balu) Balachandran U.
Published: December 2012

We deposited ferroelectric (Pb0.92La0.08)(Zr0.52Ti0.48)O3 (PLZT 8/52/48) films on nickel foils and platinized silicon (PtSi) substrates by chemical solution deposition. Prior to the deposition of PLZT, a conductive oxide buffer layer of LaNiO3 (LNO) was deposited on the nickel foil. Residual stresses of the films were determined by x-ray diffraction. Compressive stress of ≈−370 MPa and tensile stress of ≈250 MPa were measured in ≈2-μm-thick PLZT grown on LNO-buffered Ni foil and PtSi substrate, respectively. We also measured the following electrical properties for the PLZT films grown on LNO-buffered Ni and PtSi substrates, respectively: remanent polarization, ≈23.5 μC/cm2 and ≈10.1 μC/cm2; coercive electric field, ≈23.8 kV/cm and ≈27.9 kV/cm; dielectric constant at room temperature, ≈1300 and ≈1350; and dielectric loss at room temperature, ≈0.06 and ≈0.05. Weibull analysis determined the mean breakdown strength to be 2.6 MV/cm and 1.5 MV/cm for PLZT films grown on LNO-buffered Ni and PtSi substrates, respectively. The difference in dielectric properties and breakdown strength can be attributed to the residual stress in the PLZT films. Our results suggest that compressive stress enhances the dielectric breakdown strength of the PLZT films.
On the alternatives for bath correlators and spectral densities from mixed quantum-classical simulations
Authors: Valleau Stéphanie , Eisfeld Alexander , Aspuru-Guzik Alán
Published: December 2012

We investigate on the procedure of extracting a “spectral density” from mixed QM/MM calculations and employing it in open quantum systems models. In particular, we study the connection between the energy gap correlation function extracted from ground state QM/MM and the bath spectral density used as input in open quantum system approaches. We introduce a simple model which can give intuition on when the ground state QM/MM propagation will give the correct energy gap. We also discuss the role of higher order correlators of the energy-gap fluctuations which can provide useful information on the bath. Further, various semiclassical corrections to the spectral density, are applied and investigated. Finally, we apply our considerations to the photosynthetic Fenna-Matthews-Olson complex. For this system, our results suggest the use of the Harmonic prefactor for the spectral density rather than the Standard one, which was employed in the simulations of the system carried out to date.
Strongly coupled modes in a weakly driven micromechanical resonator
Authors: Venstra Warner J. , van Leeuwen Ronald , van der Zant Herre S. J.
Published: December 2012

We demonstrate a strong coupling between the flexural vibration modes of a clamped-clamped micromechanical resonator vibrating at low amplitudes. This coupling enables the direct measurement of the frequency response via amplitude- and phase modulation schemes using the fundamental mode as a mechanical detector. In the linear regime, a frequency shift of 0.8 Hz is observed for a mode with a line width of 5.8 Hz in vacuum. The measured response is well-described by the analytical model based on the Euler-Bernoulli beam including tension. Calculations predict an upper limit for the room-temperature Q-factor of 4.5×105 for our top-down fabricated micromechanical beam resonators.
Thermodynamic properties of aqueous sodium sulfate solutions to 773 K and 3 GPa derived from acoustic velocity measurements in the diamond anvil cell
Authors: Mantegazzi Davide , Sanchez-Valle Carmen , Reusser Eric , Driesner Thomas
Published: December 2012

The thermodynamic properties of a 1 m Na2SO4 solution have been determined to 773 K and 3 GPa from acoustic velocity measurements in externally heated diamond anvil cell using Brillouin spectroscopy. The measured acoustic velocities were inverted to obtain the density of the aqueous electrolyte solution with an accuracy of 0.3%–0.5%, and an equation of state (EoS) valid in the 293–773 K and 0.4–3 GPa range is proposed. The new EoS reproduces the experimental acoustic velocity data with a maximal deviation of 1.5% and allows deriving all thermodynamic properties of the aqueous solution, including isobaric heat capacity (CP), thermal expansion (αP), and compressibility (β) with an accuracy better than 3%–8%. The addition of dissolved sulfate species decreases the compressibility of water, consistent with the structure-maker character of SO42− ions in solution that enhance the hydrogen-bond network of the solvent.
Pullback asymptotic behavior of solutions for a non-autonomous non-Newtonian fluid on two-dimensional unbounded domains
Authors: Zhao Caidi
Published: December 2012

This paper studies the pullback asymptotic behavior of solutions for a non-autonomous non-Newtonian fluid on \documentclass[12pt]{minimal}\begin{document}$\Omega = \mathbb {R}\times (-L, L)$\end{document}Ω=R×(−L,L) for some L > 0. We first use the technique of truncation functions together with the decomposition of spatial domain to prove the existence of a pullback attractor in Ω. Then we discuss the upper semicontinuity of the pullback attractors when the spatial domains vary from Ωm to Ω, where \documentclass[12pt]{minimal}\begin{document}$\lbrace \Omega _m\rbrace _{m=1}^\infty$\end{document}{Ωm}m=1∞ is an expanding sequence of simply connected, bounded, and smooth subdomains of Ω such that \documentclass[12pt]{minimal}\begin{document}$\cup _{m=1}^\infty \Omega _m=\Omega$\end{document}∪m=1∞Ωm=Ω. Let \documentclass[12pt]{minimal}\begin{document}$\hat{\mathcal {A}}=\lbrace \mathcal {A}(\tau )\rbrace _{\tau \in \mathbb {R}}$\end{document}Â={A(τ)}τ∈R and \documentclass[12pt]{minimal}\begin{document}$\hat{\mathcal {A}}_m=\lbrace \mathcal {A}_m(\tau )\rbrace _{\tau \in \mathbb {R}}$\end{document}Âm={Am(τ)}τ∈R be the pullback attractors corresponding to Ω and Ωm, respectively. We establish for each \documentclass[12pt]{minimal}\begin{document}$\tau \in \mathbb {R}$\end{document}τ∈R that for any neighborhood \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(\mathcal {A}(\tau ))$\end{document}O(A(τ)) of \documentclass[12pt]{minimal}\begin{document}$\mathcal {A}(\tau )$\end{document}A(τ), \documentclass[12pt]{minimal}\begin{document}$\mathcal {A}_m(\tau )$\end{document}Am(τ) enters \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(\mathcal {A}(\tau ))$\end{document}O(A(τ)) if m is large enough.
Scanning tunneling microscopy with InAs nanowire tips
Authors: Flöhr Kilian , Sladek Kamil , Yusuf Günel H. , Ion Lepsa Mihail , Hardtdegen Hilde , Liebmann Marcus , Schäpers Thomas , Morgenstern Markus
Published: December 2012

Indium arsenide nanowires grown by selective-area vapor phase epitaxy are used as tips for scanning tunneling microscopy (STM). The STM tips are realized by positioning the wires manually on the corner of a double cleaved gallium arsenide wafer with sub-μm precision and contacting them lithographically, which is fully compatible with further integrated circuitry on the GaAs wafer. STM images show a z noise of 2 pm and a lateral stability of, at least, 0.5 nm on a Au(111) surface. I(z) spectroscopy reveals an exponential decay indicating tunneling through vacuum. Subsequent electron microscopy images of the tip demonstrate that the wires are barely modified during the STM imaging.