bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling impacts of carbon sequestration on net greenhouse gas emissions from agricultural soils in China
Authors: Qiu Jianjun , Li Changsheng , Wang Ligang , Tang Huajun , Li Hu , Van Ranst Eric
Published: February 2009

Soil organic carbon (SOC) contents in many farmlands have been depleted because of the long‐term history of intensive cultivation in China. Chinese farmers are encouraged to adopt alternative management practices on their farms to sequester SOC. On the basis of the availability of carbon (C) resources in the rural areas in China, the most promising practices are (1) incorporating more crop residue in the soils and (2) resuming traditional manure fertilizer. By implementing the alternative practices, increase in SOC content has been observed in some fields. This paper investigates how the C sequestration strategies could affect nitrous oxide (N2O) and methane (CH4) emissions from the agricultural soils in six selected sites across China. A process‐based model, denitrification‐decomposition or DNDC, which has been widely validated against data sets of SOC dynamics and N2O and CH4 fluxes observed in China, was adopted in the study to quantify the greenhouse gas impacts of enhanced crop residue incorporation and manure amendment under the diverse climate, soil, and crop rotation conditions across the six agroecosystems. Model results indicated that (1) when the alternative management practices were employed C sequestration rates increased, however, N2O or CH4 emissions were also increased for these practices; and (2) reducing the application rates of synthetic fertilizer in conjunction with the alternative practices could decrease N2O emissions while at the same time maintaining existing crop yields and C sequestration rates. The modeling approach could help with development of spatially differentiated best management practices at large regional scales.
Potential export of unattached benthic macroalgae to the deep sea through wind‐driven Langmuir circulation
Authors: Dierssen H. M. , Zimmerman R. C. , Drake L. A. , Burdige D. J.
Published: February 2009

Carbon export to the deep sea is conventionally attributed to the sinking of open ocean phytoplankton. Here, we report a Langmuir supercell event driven by high winds across the shallow Great Bahama Bank that organized benthic non‐attached macroalgae, Colpomenia sp., into visible windrows on the seafloor. Ocean color satellite imagery obtained before and after the windrows revealed a 588 km2 patch that rapidly shifted from highly productive macroalgae to bare sand. We assess a number of possible fates for this macroalgae and contend that this event potentially transported negatively buoyant macroalgae to the deep Tongue of the Ocean in a pulsed export of >7 × 1010 g of carbon. This is equivalent to the daily carbon flux of phytoplankton biomass in the pelagic tropical North Atlantic and 0.2–0.8% of daily carbon flux from the global ocean. Coastal banks and bays are highly productive ecosystems that may contribute substantially to carbon export to the deep sea.
Partial Derivative Fitted Taylor Expansion: An efficient method for calculating gas‐liquid equilibria in atmospheric aerosol particles: 1. Inorganic compounds
Authors: Topping David , Lowe Douglas , McFiggans Gordon
Published: February 2009

Parameterizations for calculating the equilibrium vapor pressure of the semivolatile inorganic gases, HNO3, HCl, and NH3, above an aqueous aerosol are presented. The hybrid Partial Derivative Fitted Taylor Expansion (PD‐FiTE) approach uses optimized model parameters describing the interaction between different inorganic ions, resulting in comparable computational performance with existing reduced methods while remaining accurate. Comparisons with the most accurate inorganic activity coefficient model available indicate that PD‐FiTE performs very well over the parameterization space of the system H+‐NH4+‐Na+‐SO42−‐HSO4−‐NO3−‐Cl− at 298.15 K. The linear additive framework allows the inclusion of further species. However, including the ability to describe the interaction between inorganic and organic components will be presented in a future publication. Coupling PD‐FiTE to a coupled box model of gaseous chemistry and aerosol microphysics in a test case investigating marine aerosol passing through a polluted environment demonstrates its robustness and ability to capture fine details of important phenomena such as the outgassing of HCl in response to HNO3 uptake by sea‐salt particles.
Vegetation‐atmosphere‐soil nutrient feedbacks in the Amazon for different deforestation scenarios
Authors: Senna Mônica Carneiro Alves , Costa Marcos Heil , Pires Gabrielle Ferreira
Published: February 2009

In recent decades, large areas of the Amazon forest have been deforested and the rainforest's future may be dependent on climate and soil nutrient feedbacks associated with deforestation. This is a two‐way biosphere‐atmosphere interaction problem: the response of the regional climate system to the land cover varies with the forest growth, which, in turn, depends on climate and nutrient stress. Nutrient stress also varies with forest age, being most severe for young forests and declining as forests mature. Here we use a coupled climate‐biosphere model to investigate how these feedbacks interact to control the secondary forest recovery after different deforestation scenarios, looking for a threshold of deforestation that could cause dangerous interference on the Amazon recovery. Results show that the reduction in rainfall is proportional to the amount of deforestation and is more drastic when the deforested area is higher than 40% of the original forest extent. In addition, this simulated precipitation reduction alone is not sufficient to prevent the rainforest regrowth. However, when the precipitation reduction is associated with a soil nutrient stress, a savannization process may start over southern Amazonia (northern Mato Grosso state), no matter how much is deforested. In this region, a large precipitation reduction in the transition from the dry to the rainy season and an increase in the dry season duration are favorable to the savanna maintenance on nutrient‐limited simulations. These results may be a valuable tool for prioritizing forest conservation in this region, which presently has the highest clearing rate in Amazonia.
Rising and setting GPS occultations by use of open‐loop tracking
Authors: Ao C. O. , Hajj G. A. , Meehan T. K. , Dong D. , Iijima B. A. , Mannucci A. J. , Kursinski E. R.
Published: February 2009

The success of GPS occultations has been demonstrated by several missions including GPS/MET, CHAMP, SAC‐C, GRACE, and COSMIC. However, tracking the GPS signal in the lower troposphere or obtaining accurate refractivity there has proven particularly challenging. The first receiver software with open‐loop (OL) tracking capability was recently tested and successfully implemented on SAC‐C. Besides improving the ability to probe deeper into the lower troposphere and planetary boundary layer, OL tracking also enables the acquisition of rising GPS signals for the first time, thereby doubling the number of occultations from the same instrument. In this paper, we describe the atmospheric Doppler and delay models used in the SAC‐C and COSMIC OL tracking software. We discuss the testing carried out on SAC‐C and present some examples of OL processing. We show that OL data give vast improvements in sampling the lowest part of the atmosphere. Over 80% of the SAC‐C OL profiles now reach below 2 km altitude in the tropics, compared to only 50% achieved under closed‐loop tracking.
Modeling the impact of ClNO2 on ozone formation in the Houston area
Authors: Simon H. , Kimura Y. , McGaughey G. , Allen D. T. , Brown S. S. , Osthoff H. D. , Roberts J. M. , Byun D. , Lee D.
Published: February 2009

During the summer of 2006, nitryl chloride (ClNO2) mixing ratios of over 1 ppb were measured in the Houston urban area. Nitryl chloride is potentially important to atmospheric chemistry in urban environments because its photolysis products include both NO2 and chlorine atoms. Chlorine atoms have previously been shown to significantly increase ozone formation in urban Houston. Photochemical modeling was performed using the Comprehensive Air quality Model with extensions (CAMx) to estimate the effects of observed nitryl chloride concentrations on local chemistry in southeast Texas. CAMx was modified to include a formation mechanism for nitryl chloride as well as its photolysis reaction. Comparisons between model predictions and ambient measurements showed that the model‐predicted ClNO2 concentrations were within the range of observed data. Model simulations predict that ClNO2 increases total reactive chlorine mass by 20–40% in the atmosphere of southeast Texas. Despite the high reactivity of chlorine, nitryl chloride caused only modest increases in ozone concentrations (up to 1.0–1.5 ppb when baseline 1‐h average ozone concentrations were between 60 and 85 ppb). The chemistry and physical processes which affect ozone formation were further investigated using box model simulations and a Lagrangian process analysis tool (LPA) within the gridded photochemical modeling simulations. These analyses showed that vertical dispersion and local atmospheric composition moderated the effect of nitryl chloride on ozone mixing ratios.
Changes in Experimental Stroke Outcome across the Life Span
Authors: Liu Fudong , Yuan Rongwen , Benashski Sharon E , McCullough Louise D
Published: February 2009

Acute ischemic stroke is a leading cause of mortality and disability in the elderly. Age is the most important nonmodifiable risk factor for stroke, yet many preclinical models continue to examine only young male animals. It remains unclear how experimental stroke outcomes change with aging and with biologic sex. If sex differences are present, it is not known whether these reflect an intrinsic differing sensitivity to stroke or are secondary to the loss of estrogen with aging. We subjected both young and aging mice of both sexes to middle cerebral artery occlusion (MCAO). Young female mice had smaller strokes compared with age-matched males, an effect that was reversed by ovariectomy. Stroke damage increased with aging in female mice, whereas male mice had decreased damage after MCAO. Blood–brain barrier (BBB) permeability changes are correlated with infarct size. However, aging mice had significantly less edema formation, an effect that was independent of sex and histologic damage. Differences in the cellular response to stroke occur across the life span in both male and female mice. These differences need to be considered when developing relevant therapies for stroke patients, the majority of whom are elderly.
Histone arginine methylations: their roles in chromatin dynamics and transcriptional regulation
Authors: Litt Michael , Qiu Yi , Huang Suming
Published: February 2009

PRMTs (protein arginine N-methyltransferases) specifically modify the arginine residues of key cellular and nuclear proteins as well as histone substrates. Like lysine methylation, transcriptional repression or activation is dependent upon the site and type of arginine methylation on histone tails. Recent discoveries imply that histone arginine methylation is an important modulator of dynamic chromatin regulation and transcriptional controls. However, under the shadow of lysine methylation, the roles of histone arginine methylation have been under-explored. The present review focuses on the roles of histone arginine methylation in the regulation of gene expression, and the interplays between histone arginine methylation, histone acetylation, lysine methylation and chromatin remodelling factors. In addition, we discuss the dynamic regulation of arginine methylation by arginine demethylases, and how dysregulation of PRMTs and their activities are linked to human diseases such as cancer.
A new method for annular jet control based on cross-flow injection
Authors: Vanierschot M. , Persoons T. , Van den Bulck E.
Published: February 2009

We propose a new method for controlling the outflow of a fully turbulent annular jet based on the cross-flow injection of secondary jets. Details are provided on an in-house designed nozzle with a specific geometry that causes an attachment of the annular jet to the nozzle cone when cross-flow injection is applied. When this cross injection is suddenly taken away, the nozzle attached jet evolves toward a stable wall jet. Time-resolved stereo particle image velocimetry measurements are used to characterize the three different flow patterns (annular, nozzle attached, and wall jet) and the aim of this investigation is to gain a deeper understanding into the physics of the transition from the nozzle attached jet to the wall jet.
Enhancement in sensitivity of copper sulfide thin film ammonia gas sensor: Effect of swift heavy ion irradiation
Authors: Sagade Abhay Abhimanyu , Sharma Ramphal , Sulaniya Indra
Published: February 2009

The studies are carried out on the effect of swift heavy ion (SHI) irradiation on surface morphology and electrical properties of copper sulfide (CuxS) thin films with three different chemical compositions (x values). The irradiation experiments have been carried out on CuxS films with x=1.4, 1.8, and 2 by 100 MeV gold heavy ions at room temperature. These as-deposited and irradiated thin films have been used to detect ammonia gas at room temperature (300 K). The SHI irradiation treatment on x=1.4 and 1.8 copper sulfide films enhances the sensitivity of the gas sensor. The results are discussed considering high electronic energy deposition by 100 MeV gold heavy ions in a matrix of copper sulfide.
The effects of carbon coating on nanoripples induced by focused ion beam
Authors: Ran Guang , Zhang Jiaming , Wei Qiangmin , Xi Shengqi , Zu Xiaotao , Wang Lumin
Published: February 2009

The morphology and topography of self-assembled nanoripple structures on LaAlO3 (100) surface with and without carbon coating were characterized using focused ion beam (FIB)/scanning electron microscope, as well as ex situ atomic force microscopy and transmission electron microscopy. When the surface was not covered by carbon coating and had low roughness, well-ordered and highly uniform nanoripples self-assembled on the surface bombarded by FIB. In contrast, disordered nanoripples formed after carbon coating. The deposited carbon significantly influences the morphology of surface nanoripples due to its effect on the surface roughness that affect the dynamic competition between the roughening and smoothing processes. This discovery suggests a means for fabricating well-ordered and highly uniform nanoripples for nanoscale devices application.
Effect of patterning on the saturation magnetization in MgO based nanopillars
Authors: Cornelissen S. , Bianchini L. , Helmer A. , Devolder T. , Kim Joo-Von , Op de Beeck M. , Van Roy W. , Lagae L. , Chappert C.
Published: February 2009

We have studied the effect of nanopillar patterning on the saturation magnetization of the CoFeB free layer in MgO magnetic tunnel junctions. Before patterning, the free layer magnetization is measured by ferromagnetic resonance and is found to be close to the bulk value, with no detectable interface anisotropy. After patterning, the shape anisotropy and the frequency of the main spin wave mode indicate that the free layer magnetization is substantially reduced. Current dependent measurements indicate that this is not due to Joule heating. Size dependent measurements indicate that the magnetization reduction most likely arises from process damage during the etching step.
Superconductivity in a strongly correlated electron system: A theoretical study
Authors: Caixeiro E. S. , Troper A.
Published: February 2009

In this work we study the superconductivity within an attractive two-dimensional one-band Hubbard model. We consider a d-wave superconducting gap and a Hubbard-I approximation to describe the strongly correlated superconducting regime. We use the Green’s function method to obtain the order parameter Δ and the superconducting critical temperature Tc. The results show that for fixed values of the superconducting attractive potential U(U<0), the gap increases for low temperatures but diminishes abruptly as the temperature increases. The effect of pressure is discussed, varying the next-nearest-neighbor hopping t2, yielding a change in Tc, and also in Δ0, and a tendency to suppress the superconductivity.
Optimal design of stator interior permanent magnet machine based on finite element analysis
Authors: Zhang Jianzhong , Cheng Ming , Hua Wei
Published: February 2009

This article investigates the optimal design of the stator interior permanent magnet (SIPM) machine for sinusoidal electromotive force (EMF) waveform. The key is to develop a design approach for the rotor pole arc and rotor skewing of the SIPM machine in such a way that total harmonic distortion of the EMF waveform is the minimum. The two-dimensional finite element analysis is employed to calculate the magnetic field distributions in terms of the different rotor pole arc and rotor skewing angle. A prototype of three-phase 12/10-pole SIPM machine is used for exemplification. Both the predicted and measured results are given to illustrate the proposed machine.
Microwave tunability in a GaAs-based multiferroic heterostructure: Co2MnAl/GaAs/PMN-PT
Authors: Chen Y. , Gao J. , Lou J. , Liu M. , Yoon S. D. , Geiler A. L. , Nedoroscik M. , Heiman D. , Sun N. X. , Vittoria C. , Harris V. G.
Published: February 2009

A strong magnetoelectric (ME) interaction is presented in a magnetostrictive-semiconductor-piezoelectric heterostructure that consists of the Huesler alloy, Co2MnAl, GaAs, and lead magnesium niobate-lead titanate (PMN-PT). The laminated Co2MnAl/GaAs/PMN-PT structure, having a thickness of 19 nm/180 μm/500 μm, demonstrates a ferromagnetic resonance (FMR) field shift of 28 Oe with an external electric field of 200 V across the PMN-PT substrate. This corresponds to a resonance frequency shift of ∼125 MHz at X-band. It yields a large ME coupling (7 Oe cm/kV) and microwave tunability (∼32 MHz/kV cm−1), compared to other trilayer multiferroic composite structures. In addition, static magnetization measurement indicates a reduction in the remanence magnetization while applying the electric field, which corroborates the ME interactions mediated by the translation of magnetoelastic forces in this structure. This work explores the potential of multiferroic heterostrucuture transducers for use in FMR microwave devices tuned by electric fields.
Enhancement in nanoscale electrical properties of lead zirconic titanate island fabricated by focused ion beam
Authors: Liang R. H. , Rémiens D. , Deresmes D. , Soyer C. , Troadec D. , Dong X. L. , Yang L. H. , Desfeux R. , Da Costa A. , Blach J. F.
Published: February 2009

Lead zirconic titanate (PZT) microscale island (1 μm–100 nm) was fabricated by focused ion beam before its crystallization, followed by the annealing treatment at the crystallization temperature. Local electrical properties were evaluated by piezoresponse force microscopy technique. Compared to the PZT island fabricated after crystallization, the result shows that there is noticeable enhancement in nanoscale electrical properties of PZT island fabricated before crystallization, especially when the island size decreases. Raman spectra and Kelvin force microscopy result both show that there are little degradations on the PZT surface after this amorphous etching process. The mechanism will be discussed in this paper. These results are very beneficial to the development of the ferroelectric film applications in the dynamic random access memory, ferroelectric random access memory, and micro-electro-mechanical system field.
Role of Co clusters in wurtzite Co:ZnO dilute magnetic semiconductor thin films
Authors: Wei He , Yao Tao , Pan Zhiyun , Mai Cong , Sun Zhihu , Wu Ziyu , Hu Fengchun , Jiang Yong , Yan Wensheng
Published: February 2009

The magnetic nature of Zn1−xCoxO dilute magnetic semiconductor (DMS) thin films grown by pulsed laser deposition is investigated by x-ray absorption fine structure spectroscopy and x-ray diffraction. We show that a single phase of the substitutional Co atoms occupied Zn sites in the ZnO matrix exists in the Zn0.98Co0.02O DMS thin film while a secondary phase of the Co clusters is formed in Zn0.95Co0.05O and Zn0.90Co0.10O thin films. Despite the formation of Co clusters, the average magnetic moment MS per Co atom is sharply decreased with increasing Co concentration, which suggests that the small Co clusters are superparamagnetic. For the Zn0.98Co0.02O DMS thin film, the local structural distortion around the substitutional Co atoms is interpreted as the origin of intrinsic weak room-temperature ferromagnetism.
Extended cyclic uniaxial loading of stretchable gold thin-films on elastomeric substrates
Authors: Graz Ingrid M. , Cotton Darryl P. J. , Lacour Stéphanie P.
Published: February 2009

Gold thin-films (50 nm thick) on silicone membranes are reversibly stretchable. They exhibit continuous electrical conduction when pulled and relaxed by tens of percent. Here, we show that gold thin-film conductors on elastomeric substrates can withstand extensive uniaxial stretch cycling without electrical failure. The gold film develops into an interconnected network of islands, which reversibly move on the surface of the elastomer with applied strain. The resulting electrical resistance of the conductor remains finite and reproducible over 250 000 cycles to 20% applied strain.
The photophysics of singlet, triplet, and degradation trap states in 4,4-N,N′-dicarbazolyl-1,1′-biphenyl
Authors: Jankus Vygintas , Winscom Chris , Monkman Andrew P.
Published: February 2009

In this paper we report the results of optical characterization of 4,4-N,N′-dicarbazolyl-1,1′-biphenyl (CBP), known as a host material for phosphorescent light emitting devices. Using absorption, steady state, and time-resolved spectroscopy, we explore the singlet and triplet states in solid and solution samples of CBP. In solutions we observe two distinct short-lived states with well-resolved emission originating from individual molecule singlet states (at 365 and 380 nm) and “quenching” low energy (LE) states (at 404 and 424 nm). The latter are seen only in saturated solutions and solid samples. Both of those species have different lifetimes. After UV exposure of very concentrated degassed solution the intensities of the LE bands starts to decrease. The longer the solution is exposed to UV, the less emission is seen at 404 and 424 nm, until it is totally gone. The spectrum of the highly concentrated solution is then the same as the spectrum of dilute solution, i.e., only emission at 365 and 380 nm is present. An increase in intensities of the singlet emission peaks correlates with an increase in UV exposure time. Similar behavior is observed in evaporated CBP film. We propose that this behavior is due to chemical instability of the weak N–C bonding of carbazolyl moiety—this creates new degradational species over time which dissociate after exposure to UV. We believe this to be the reason for variation in CBP fluorescence and delayed fluorescence spectra recorded by various research groups. Further, we detected two types of very long-lived states. One of these states (higher energy) is ascribed to molecular phosphorescence emission, the other to emission from low energy triplet trap states which we relate to degradational species. We propose that triplets are more easily caught by these latter sites when their hopping rate increases, and they emit inefficiently from these lower energy sites.
2
E
1
Ar17+ decay and conventional radioactive sources to determine efficiency of semiconductor detectors
Authors: Lamour Emily , Prigent Christophe , Eberhardt Benjamin , Rozet Jean Pierre , Vernhet Dominique
Published: February 2009

Although reliable models may predict the detection efficiency of semiconductor detectors, measurements are needed to check the parameters supplied by the manufacturers, namely, the thicknesses of dead layer, beryllium window, and crystal active area. The efficiency of three silicon detectors has been precisely investigated in their entire photon energy range of detection. In the zero to a few keV range, we developed a new method based on the detection of the 2E1 decay of the metastable Ar17+ 2s→1s transition. Very good theoretical knowledge of the energetic distribution of the 2E1 decay mode enables precise characterization of the absorbing layers in front of the detectors. In the high-energy range (>10 keV), the detector crystal thickness plays a major role in the detection efficiency and has been determined using a A241m source.
Van der Waals interactions at surfaces by density functional theory using Wannier functions
Authors: Silvestrelli Pier Luigi , Benyahia Karima , Grubisiĉ Sonja , Ancilotto Francesco , Toigo Flavio
Published: February 2009

The method, recently developed to include van der Waals interactions in the density functional theory by using the maximally localized Wannier functions, is extended to the case of atoms and fragments weakly bonded (physisorbed) to metal and semimetal surfaces, thus opening the way to realistic simulations of surface-physics processes, where van der Waals interactions play a key role. Successful applications to the case of Ar on graphite and of Ar, He, and H2 on the Al(100) surface are presented.
The Hartman effect in graphene
Authors: Wu Zhenhua , Chang Kai , Liu J. T. , Li X. J. , Chan K. S.
Published: February 2009

We investigate theoretically the Hartman effect in quantum tunneling through single and double barriers in a single graphene layer. The numerical results indicate that the Hartman effect in graphene depends heavily on the incident angle and the energy of the carrier in the tunneling process through single and double barriers. We find that the Hartman effect disappears for normal incidence and appears when the incident angle and energy are larger than some critical values.
Spin-dependent shot noise in fractal semiconductor multilayers with two ferromagnetic contacts
Authors: Liu De , Kong Xiao-Jun
Published: February 2009

We investigate the spin-dependent shot noise properties of electrons tunneling through fractal semiconductor multilayers (FSMs) sandwiched between two ferromagnets (Fs) with arbitrary relative magnetization direction in the presence of the Rashba spin-orbit interaction and an electric field. Within the framework of the Landauer–Büttiker scattering formalism, the current, shot noise, and Fano factor of the F/FSM/F heterostructures are numerically calculated and compared with those of periodic semiconductor multilayers (PSMs) again with ferromagnetic contacts. The results indicate that the shot noise becomes strongly spin dependent and can be greatly modulated not only by the external electric field and Rashba spin-orbit interaction but also by the structural configuration and length of the semiconductor multilayers. Interestingly, compared to the F/PSM/F heterostructures, the current, shot noise, and Fano factor of the F/FSM/F heterostructures can exhibit a more marked quantum size effect, along with typical low-frequency aperiodic oscillations as the bias voltage or the Rashba spin-orbit coupling strength increases. There is little Rashba spin-orbit coupling strength dependence with increasing angle between the two magnetic moments of the left and right ferromagnets.
High-frequency permeability spectra of FeCoSiN/Al2O3 laminated films: Tuning of damping by magnetic couplings dependent on the thickness of each ferromagnetic layer
Authors: Xu Feng , Zhang Xiaoyu , Phuoc Nguyen Nguyen , Ma Yungui , Ong C. K.
Published: February 2009

In this work, we investigate the high-frequency permeability spectra of as-sputtered FeCoSiN/Al2O3 laminated films, and discuss their dependence on the thickness of each FeCoSiN layer, based on the phenomenological Landau–Lifshitz–Gilbert equation. The damping factor and coercivity show their minima with lamination, deviating from the expectation based on the grain size confinement effect. Such dependences on the layer thickness indicate the influence of magnetic coupling. The decreases in the damping factor and the coercivities with lamination can be partially attributed to the decrease in the magnetostatic coupling induced by ripple structures. The enhanced damping and enlarged coercivity values obtained with further lamination are ascribed to the enhanced Néel couplings. The dependences show that the lamination can be effective in tuning the magnetization dynamics by changing the magnetic couplings.
A study of the vibrational and thermoelectric properties of silicon type I and II clathrates
Authors: Li J. C. , Wang C. L. , Wang M. X. , Peng H. , Zhang R. Z. , Zhao M. L. , Liu J. , Zhang J. L. , Mei L. M.
Published: February 2009

First principles calculations are employed to investigate both type I and II silicon clathrates. The phonon and infrared spectra of both types of clathrate are obtained. We find a localized vibrational mode of Si46 whose frequency is 375.0 cm−1, where the vibration in the mode localizes in the hexagonal chain. The heat capacity of both clathrates is the same as that of the diamond phase Si (d-Si). When the temperature is lower than 100 K, the Debye temperatures of the clathrates are higher than that of d-Si; however, the Debye temperatures of both clathrates at high temperature (>100 K) are lower than that of the d-Si. The mean free paths (λ) and thermal conductivities (κ) of the clathrates are larger than those of d-Si at low temperature. The Seebeck coefficients (S) of the clathrates are higher than that of d-Si in the temperature interval 300–1000 K; however, both clathrates exhibit a lower value of σ/τ when compared to the d-Si.
HfO
x
N
y
gate dielectric on p-GaAs
Authors: Dalapati G. K. , Sridhara A. , Wong A. S. W. , Chia C. K. , Chi D. Z.
Published: February 2009

Plasma nitridation method is used for nitrogen incorporation in HfO2 based gate dielectrics for future GaAs-based devices. The nitrided HfO2 (HfOxNy) films on p-GaAs improve metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, hysteresis, and leakage current. An equivalent oxide thickness of 3.6 nm and a leakage current density of 10−6 A cm−2 have been achieved at VFB−1 V for nitrided HfO2 films. A nitride interfacial layer (GaAsO:N) was observed at HfO2–GaAs interface, which can reduce the outdiffusion of elemental Ga and As during post-thermal annealing process. Such suppression of outdiffusion led to a substantial enhancement in the overall dielectric properties of the HfO2 film.
Ga-related photoluminescence lines in Ga-doped ZnO grown by plasma-assisted molecular-beam epitaxy
Authors: Yang Z. , Look D. C. , Liu J. L.
Published: February 2009

Low-temperature photoluminescence (PL) and temperature-dependent Hall-effect (T-Hall) measurements were carried out in undoped and Ga-doped ZnO thin films grown by molecular-beam epitaxy. As the carrier concentration increases from 1.8×1018 to 1.8×1020 cm−3, the dominant PL line at 9 K changes from I1 (3.368–3.371 eV) to IDA (3.317–3.321 eV), and finally to I8 (3.359 eV). The dominance of I1, due to ionized-donor bound excitons, is unexpected in n-type samples but is shown to be consistent with the T-Hall results. We also show that IDA has characteristics of a donor-acceptor-pair transition, and use a detailed, quantitative analysis to argue that it arises from GaZn donors paired with Zn-vacancy (VZn) acceptors. In this analysis, the GaZn0/+ energy is well-known from two-electron satellite transitions, and the VZn0/− energy is taken from a recent theoretical calculation.
Electronic cooling of a submicron-sized metallic beam
Authors: Muhonen J. T. , Niskanen A. O. , Meschke M. , Pashkin Yu. A. , Tsai J. S. , Sainiemi L. , Franssila S. , Pekola J. P.
Published: February 2009

We demonstrate electronic cooling of a suspended AuPd island using superconductor-insulator-normal metal tunnel junctions. This was achieved by developing a simple fabrication method for reliably releasing narrow submicron-sized metal beams. The process is based on reactive ion etching and uses a conducting substrate to avoid charge-up damage and is compatible with, e.g., conventional e-beam lithography, shadow-angle metal deposition, and oxide tunnel junctions. The devices function well and exhibit clear cooling, up to a factor of 2 at sub-Kelvin temperatures.
Thickness dependent electronic structure of La0.6Sr0.4MnO3 layer in SrTiO3/La0.6Sr0.4MnO3/SrTiO3 heterostructures studied by hard x-ray photoemission spectroscopy
Authors: Yoshimatsu K. , Horiba K. , Kumigashira H. , Ikenaga E. , Oshima M.
Published: February 2009

The authors have investigated changes in the electronic structures of digitally controlled La0.6Sr0.4MnO3 (LSMO) layers sandwiched between SrTiO3 as a function of LSMO layer thickness in terms of hard x-ray photoemission spectroscopy (HX-PES). The HX-PES spectra show the evolution of Mn 3d derived states near the Fermi level and the occurrence of metal-insulator transition at 8 ML. The detailed analysis for the thickness dependent HX-PES spectra reveals the existence of the less conducting and nonmagnetic transition layer with a film thickness of about 4 ML in the interface region owing to significant interaction through the interface.
Materializing a binary hyperlens design
Authors: Kildishev Alexander V. , Chettiar Uday K. , Jacob Zubin , Shalaev Vladimir M. , Narimanov Evgenii E.
Published: February 2009

We present a design of cylindrical hyperlens made of a layered binary material. The design approach uses an improved effective medium theory to take account of radius-dependent effects due to curvature of material interfaces resulting in nonperiodically distributed thicknesses of the lens layers. The performance of this lens is compared versus the designs with periodically thick layers, which we showed in earlier papers. Detailed quantitative results analyzed for the lenses with the same number and starting order of layers prove better functioning of the lens designed with this approach.
Response to “Comment on ‘Pinch current limitation effect in plasma focus’” [Appl. Phys. Lett. 94, 076101 (2009)]
Authors: Lee S. , Saw S. H.
Published: February 2009

The main point of the comment [Appl. Phys. Lett. 94, 076101 (2009)] is that Eq. (2) and consequentially Eq. (3) of the commented paper [Appl. Phys. Lett. 92, 021503 (2008)] require correction. The alternative equation suggested in the comment is derived using Kirchhoff’s voltage rule. The comment consider only the energy distribution in the inductive components and the resultant equation confirms a progressive lowering of the Ipinch/Ipeak ratio as the static inductance L0 is reduced, lowering from 0.87 to 0.31 as L0 is reduced from 100 to 5 nH according to the revised formula corresponding to Eq. (3), compared to 0.63–0.25 according to Eq. (3). This progressive lowering of the ratio Ipinch/Ipeak due to the inductive energy distribution is one of two factors responsible for the pinch current limitation. The other factor is the progressive reduction in the L-C interaction time compared to the current dip duration denoted by δcap in Eq. (2). The comment does not deal with δcap at all; hence, its conclusion based on inductive energy distribution only is not useful, since in the low L0 region when pinch current limitation begins to manifest, δcap becomes more and more the dominant factor. In any case, the results of the paper do not depend on Eqs. (2) and (3), which are used in the paper only for illustrative purposes.
Electronic transport properties in doped C60 molecular devices
Authors: Zhang Xiao-Jiao , Long Meng-Qiu , Chen Ke-Qiu , Shuai Z. , Wan Qing , Zou B. S. , Zhang Yan
Published: February 2009

By applying nonequilibrium Green’s functions in combination with the density-functional theory, we investigate the electronic transport properties of molecular junctions constructed by C60, C59N, and C59B. The results show that the electronic transport properties of molecular junctions can be modulated by doped atoms. Negative differential resistance behavior can be observed in a certain bias range for C60 molecular junction but cannot be observed in C59N and C59B molecular junctions. A mechanism is proposed for the doping effect and negative differential resistance behavior.
Magnetoelastic/piezoelectric laminated structures for tunable remote contactless magnetic sensing and energy harvesting
Authors: Finkel Peter , Lofland Samuel E. , Garrity Ed
Published: February 2009

In this letter, we report a method for a tunable magnetic field sensor based on the magnetoelastic coupling properties of a magnetoelastic/piezoelectric laminated composite structure. The magnetically and elastically tunable, flexural resonant mode in the bimorph FeNi36% (invar)/polyvinylidene fluoride clamped bilayer has been investigated by Doppler laser spectroscopy. Here we demonstrate that this bimorph structure can be used for low-frequency contactless detection of magnetic field fluctuation and magnetic field monitoring.
Why do antiferroelectrics show higher fatigue resistance than ferroelectrics under bipolar electrical cycling?
Authors: Lou X. J.
Published: February 2009

We show that our fatigue model developed recently for ferroelectrics could explain why antiferroelectrics show higher fatigue resistance than ferroelectrics under bipolar electrical cycling. The better fatigue endurance of antiferroelectrics in comparison with their ferroelectric counterparts originates from their lower depolarization field, their lower local injected power density, and consequently their lower local phase decomposition probability at the phase nucleation sites. The model, which could explain the fact that unipolar pulses will produce no or little fatigue in ferroelectrics, predicts that evident fatigue will occur in at least one of the two hysteretic branches of antiferroelectrics under unipolar electrical cycling.
Inverse square-root field dependence of conductivity in organic field-effect transistors
Authors: Wei J. H. , Gao Y. L. , Wang X. R.
Published: February 2009

Variable-range hopping is usually the main electron transport mechanism of an organic semiconductor at low temperature. For an organic field-effect transistor at low temperature and under both high source-drain bias and high gate voltage, it is argued that multistep tunneling (MUST) can dominate charge transport. The MUST occurs through the assistance of randomly distributed localized states. The conductivity depends exponentially on the inverse of the square-root of electric field. This result explains well the recent experimental observation [A. S. Dhoot et al., Phys. Rev. Lett. 96, 246403 (2006)].
Elucidation of the Mechanism for the S - N-type Smiles Rearrangement on Pyridine Rings
Authors: Li Jinghua , Wang Lushan
Published: February 2009

The Smiles rearrangement (SR) is an important strategy for synthesizing heterocyclic compounds. Many pyridine moiety-containing complexes are biologically active. Although the success has been archived in the development of the SR on the pyridine ring to obtain pyridine moiety-containing heterocyclic compounds, not much is known about the detailed SR mechanism. Here, we report a theoretical study on a typical S–N-type SR reaction involved in the synthesis of thiazinone-fused pyridines. We studied both the ipso-SR process and the direct nucleophilic substitution reactions on the ortho-positions to rationalize the experimentally observed ipso-SR product. The calculated results show the ipso-SR consists of two elementary steps, the intramolecular ipso-position substitution and subsequent ring closure, and the barrier for the rate-determining step is 65.98 kJ mol–1 and the overall reaction is exothermic by 116.94 kJ mol–1, confirming the reaction is kinetically feasible and thermodynamically favourable under mild experimental conditions (such as controlled microwave heating). The present results provide a clear picture for understanding the S–N-type SR on the pyridine ring to synthesize pyridine moiety-containing heterocycles.
Solvent-Induced Structural Changes in Complexes of 1,2-Bis(3-(3-pyridyl)pyrazolyl)ethane
Authors: Prananto Yuniar P. , Turner David R. , Lu Jinzhen , Batten Stuart R.
Published: February 2009

A series of complexes have been obtained using the flexible ditopic ligand 1,2-bis(3-(3-pyridyl)pyrazolyl)ethane (LEt) with M(SCN)2 (M = Co, Fe) and ZnCl2. The ligand is observed to exist in a variety of conformations with rotations around the ethane spacer and around the pyridyl/pyrazole bond. The bridging length of the ligand (i.e., distance between pyridyl nitrogen atoms) varies by 3.5 Å depending on its geometry. Three different cobalt(ii) complexes of the general form [Co(LEt)2(SCN)2]·Solv (where Solv is a variable number/type of non-coordinated solvent) have been structurally characterized and form a series of solvent dependant supramolecular isomers. When Solv = 2MeCN a (4,4)-sheet is formed (1), however, when Solv = H2O an alternate ‘collapsed’ (4,4)-sheet is observed (2). Changing the solvent to two molecules of N,N-dimethylformamide (DMF) leads to a radical change in structure with a one-dimensional (1D) polymer formed (3) that contains two bridging ligands between adjacent metal atoms (i.e., maintaining the same metal/ligand ratio as in the (4,4)-sheet structures). A monomeric thiocyanate complex [Fe(LEt)2(SCN)2(H2O)2] (4) is reported in which the bispyridyl ligands are terminal and partake in an extended hydrogen-bonded network. A 1D polymer [Zn(LEt)Cl2] (5) is also presented. The structures of the metal complexes are contrasted with that of the free ligand.
Wheat roots proliferate in response to nitrogen and phosphorus fertilisers in Sodosol and Vertosol soils of south-eastern Australia
Authors: Officer S. J. , Dunbabin V. M. , Armstrong R. D. , Norton R. M. , Kearney G. A.
Published: February 2009

Root growth responses to separately placed of bands of N and P fertiliser were examined at the 3-leaf (GS13) and stem extension growth stages (GS30) for wheat (Triticum aestivum L. cv. Yitpi) growing in 2 major alkaline soil types from the rainfed (375–420 mm) grain production regions of south-eastern Australia. Intact cores of a Sodosol and a Vertosol were destructively sampled and changes in root length density (RLD) and root diameter distribution within the soil profile were examined using restricted maximum likelihood analysis and principal component analysis, respectively. At GS13, RLD increased in the Vertosol when only P was applied, although there was no shoot growth response. The root response to P consisted of a spatially generalised increase in RLD, rather than a specific increase in the vicinity of the P fertiliser band. There was a substantially greater, but still generalised, increase in RLD in the Vertosol when both N and P fertiliser were applied, although there was no response to N fertiliser (without P). The distribution of root length in diameter classes changed with depth in the profile at GS13 but was otherwise similar, regardless of soil types and fertiliser treatment. The root responses to fertiliser at GS30 also consisted of a generalised proliferation of RLD in the topsoil, with no detectable fertiliser-specific changes in the location or structure of the root system. Shoot and root growth increased to a similar level at GS30 when plants were supplied with N, irrespective of P, and root diameter distributions were again insensitive to fertiliser treatment. Plants responded to N by increasing the RLD of relatively fine roots (100–250 μm), which was a P style of acquisition strategy that was possibly triggered by moisture limitations. Consequently, the root responses to fertiliser under realistic semi-arid conditions did not follow expectations based on nutrient acquisition studies. Instead, wheat plants responded to N or P fertiliser with a generalised proliferation of fine roots, apparently to better compete for finite water and nutrients.
Positive charge discovered across Western Australian wheatbelt soils challenges key soil and nitrogen management assumptions
Authors: Wong M. T. F. , Wittwer K.
Published: February 2009

Nitrogen management in Western Australia (WA) and in cropping areas elsewhere in Australia assumes that soil contains negligible or no positive charge and is therefore unable to retain nitrate against leaching. The amount of water needed to displace nitrate is thus assumed to be the drainable volume of water held by the soil (1 pore volume), and in sandy soils about 100 mm drainage is assumed to be required to displace nitrate by 1 m. The clay mineralogy of the highly weathered soils of the WA wheatbelt is dominated by kaolinite and iron and aluminium oxides. This mineralogy suggests likely occurrence of positive charge and anion exchange capacity (AEC), since these minerals can carry positive charge under normal acidic field situations. We measured AEC of soils sampled widely across the WA wheatbelt by independent leaching and batch equilibration methods of charge measurement. This showed widespread occurrence of positive charge and AEC in these soils. AEC ranged from 0 to 2.47 mmolc/kg and is linearly correlated with the potassium chloride or monocalcium phosphate extractable sulfate content of the soil. This correlation provides a rapid screening method to identify soils with positive charge. Application of ion-chromatographic theory showed that AEC has a large effect in delaying nitrate leaching by up to 12.5 pore volumes. The most highly charged soil (2.47 mmolc/kg) thus needed 12.5 times more water to displace nitrate than currently assumed. This potentially large delay in nitrate leaching affects the optimum amount and time of fertiliser application, rates of soil acidification attributed to nitrate leaching and the benefit of ameliorating subsoils to allow roots access to subsoil water and leached nitrate. It also calls into question the use of anions such as bromide to trace water flow and estimate recharge in these soils.
Quantifying the benefits of accounting for yield potential in spatially and seasonally responsive nutrient management in a Mediterranean climate
Authors: Oliver Y. M. , Robertson M. J.
Published: February 2009

Crop yield potential is a chief determinant of nutrient requirements, but there is little objective information available on the gains in profitability that can be made by accounting for the influences of soil type and season on yield potential when making fertiliser decisions. We conducted such an assessment using crop growth simulation coupled to nutrient response curves for wheat-growing at 4 locations in the low-medium rainfall zone of Western Australia. At each location, the yield potential was simulated on 10 soil types with plant-available water capacity (PAWC) ranging from 34 to 134 mm, which represent the major soils types in Western Australia. Soil survey maps were available to quantify soil type variability and the historical climate record (1974–2005) for seasonal variability.
The benefits possible for fertiliser (NPK) management that takes account of variation in crop yield potential due to season and soil type by having ‘perfect knowledge’ ranged from $2 to 40/ha. Seasonal variation was more important than soil type for the better soils (high PAWC), providing two-thirds of the benefit of perfect knowledge. On low PAWC soils, knowledge of soils and seasonal influences on yield potential were similar contributors to profit gains. An assessment of one yield forecasting system showed that about 50% of the maximum gains could be captured if seasons could be categorised as below, at, or above average at the time the fertiliser decision is made. In each catchment, 30–40% of fields showed scope for benefits in accounting for within-field variation in soil type due to large variation in PAWC, and therefore yield. Maximum profit gains and reductions in nutrient excess were greater in the low rainfall locations and also on the low PAWC soil types.