bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic diversity and structure ofindicarice varieties from two heterotic pools of southern China and IRRI
Authors: Xie Fangming , Guo Longbiao , Ren Guangjun , Hu Peisong , Wang Feng , Xu Jianlong , Li Xinqi , Qiu Fulin , dela Paz Madonna Angelita
Published: October 2012

Investigation of genetic diversity and the relationships among varieties and breeding lines is of great importance to facilitate parental selection in the development of inbred and hybrid rice varieties and in the construction of heterotic groups. The technology of single nucleotide polymorphism (SNP) is being advanced for the assessment of population diversity and genetic structures. We characterized 215 widely cultivatedindicarice varieties developed in southern China and at the International Rice Research Institute (IRRI) using IRRI-developed SNP oligonucleotide pooled assay (OPA) to provide grouping information of rice mega-varieties for further heterotic pool study. The results revealed that the Chinese varieties were more divergent than the IRRI varieties. Two major subpopulations were clustered for the varieties using a model-based grouping method. The IRRI varieties were closely grouped and separated clearly from the majority of the Chinese varieties. The Chinese varieties were subclustered into three subgroups, but there was no clear evidence to separate the Chinese varieties into subgroups geographically, indicating a great degree of genetic integration of alleles and shared ancestries among those high-yielding modern varieties.
Public vs private administration of rural health insurance schemes: a comparative study in Zhejiang of China
Authors: Zhou Xiaoyuan , Mao Zhengzhong , Rechel Bernd , Liu Chaojie , Jiang Jialin , Zhang Yinying
Published: October 2012

Since 2003, China has experimented in some of the country's counties with the private administration of the New Cooperative Medical Scheme (NCMS), a publicly subsidized health insurance scheme for rural populations. Our study compared the effectiveness and efficiency of private vs public administration in four counties in one of China's most affluent provinces in the initial stage of the NCMS's implementation. The study was undertaken in Ningbo city of Zhejiang province. Out of 10 counties in Ningbo, two counties with private administration for the NCMS (Beilun and Ninghai) were compared with two others counties with public administration (Zhenhai and Fenghua), using the following indicators: (1) proportion of enrollees who were compensated for inpatient care; (2) average reimbursement–expense ratio per episode of inpatient care; (3) overall administration cost; (4) enrollee satisfaction. Data from 2004 to 2006 were collected from the local health authorities, hospitals and the contracted insurance companies, supplemented by a randomized household questionnaire survey covering 176 households and 479 household members. In our sample counties, private administration of the NCMS neither reduced transaction costs, nor improved the benefits of enrollees. Enrollees covered by the publicly administered NCMS were more likely to be satisfied with the insurance scheme than those covered by the privately administered NCMS. Experience in the selected counties suggests that private administration of the NCMS did not deliver the hoped-for results. We conclude that caution needs to be exercised in extending private administration of the NCMS.
Analysis of large‐amplitude stratospheric mountain wave event observed from the AIRS and MLS sounders over the western Himalayan region
Authors: Niranjan Kumar K. , Ramkumar T. K. , Krishnaiah M.
Published: October 2012

Mountain waves in the stratosphere have been observed over elevated topographies using both nadir‐looking and limb‐viewing satellites. However, the characteristics of mountain waves generated over the Himalayan Mountain range and the adjacent Tibetan Plateau are relatively less explored. The present study reports on three‐dimensional (3‐D) properties of a mountain wave event that occurred over the western Himalayan region on 9 December 2008. Observations made by the Atmospheric Infrared Sounder on board the Aqua and Microwave Limb Sounder on board the Aura satellites are used to delineate the wave properties. The observed wave properties such as horizontal (λx, λy) and vertical (λz) wavelengths are 276 km (zonal), 289 km (meridional), and 25 km, respectively. A good agreement is found between the observed and modeled/analyzed vertical wavelength for a stationary gravity wave determined using the Modern Era Retrospective Analysis for Research and Applications (MERRA) reanalysis winds. The analysis of both the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis and MERRA winds shows that the waves are primarily forced by strong flow across the topography. Using the 3‐D properties of waves and the corrected temperature amplitudes, we estimated wave momentum fluxes of the order of ∼0.05 Pa, which is in agreement with large‐amplitude mountain wave events reported elsewhere. In this regard, the present study is considered to be very much informative to the gravity wave drag schemes employed in current general circulation models for this region.
Tracing hydrologic model simulation error as a function of satellite rainfall estimation bias components and land use and land cover conditions
Authors: Gebregiorgis Abebe S. , Tian Yudong , Peters‐Lidard Christa D. , Hossain Faisal
Published: October 2012

The key question that is asked in this study is “how are the three independent bias components of satellite rainfall estimation, comprising hit bias, missed, and false precipitation, physically related to the estimation uncertainty of soil moisture and runoff for a physically based hydrologic model?” The study also investigated the performance of different satellite rainfall products as a function of land use and land cover (LULC) type. Using the entire Mississippi river basin as the study region and the variable infiltration capacity (VIC)‐3L as the distributed hydrologic model, the study of the satellite products (CMORPH, 3B42RT, and PERSIANN‐CCS) yielded two key findings. First, during the winter season, more than 40% of the rainfall total bias is dominated by missed precipitation in forest and woodland regions (southeast of Mississippi). During the summer season, 51% of the total bias is governed by the hit bias, and about 42% by the false precipitation in grassland‐savanna region (western part of Mississippi basin). Second, a strong dependence is observed between hit bias and runoff error, and missed precipitation and soil moisture error. High correlation with runoff error is observed with hit bias (∼0.85), indicating the need for improving the satellite rainfall product's ability to detect rainfall more consistently for flood prediction. For soil moisture error, it is the total bias that correlated significantly (∼0.78), indicating that a satellite product needed to be minimized of total bias for long‐term monitoring of watershed conditions for drought through continuous simulation.
Lateral entrainment rate in shallow cumuli: Dependence on dry air sources and probability density functions
Authors: Lu Chunsong , Liu Yangang , Niu Shengjie , Vogelmann Andrew M.
Published: October 2012

Entrainment processes in convective clouds often occur stochastically and entrainment rate estimates depend on the distance from the cloud from which the dry air is entrained. However, no observational studies exist on either the distance dependence or probability density function of entrainment rate, hindering understanding and the parameterization of convection. Here entrainment rate in cloud cores is estimated using a recently developed mixing fraction approach that is applied to in situ aircraft measurements of cumuli from the RACORO field program. The results are used to examine, for the first time, probability density functions of entrainment rate and their dependence on the distance from the edge of the cloud core from which the dry air is entrained. The estimated entrainment rate decreases when the dry air is entrained from increasing distance from the edge of the cloud core; this is because the air farther from the edge of the cloud core is drier than the neighboring air that is within the humid shell around the cumulus cloud core. Probability density functions of entrainment rate vary with the distance and height above the cloud‐base, and all are well fitted by lognormal distributions. The implications of the results for convection parameterizations are discussed.
Structure and dynamics of the nightside poleward boundary: Sounding rocket and ground‐based observations of auroral electron precipitation in a rayed curtain
Authors: Lynch K. A. , Hampton D. , Mella M. , Zhang Binzheng , Dahlgren H. , Disbrow M. , Kintner P. M. , Lessard M. , Lundberg E. , Stenbaek‐Nielsen H. C.
Published: October 2012

The Cascades2 auroral sounding rocket provides a case study for comparing multipoint in situ ionospheric observations of a nightside auroral poleward boundary intensification with ground‐based optical observations of the same event. Cascades2 was launched northward from Poker Flat Alaska on 20 March 2009 at 11:04 UT. The 13 min flight reached an apogee of 564 km over the northern coast of Alaska. The experiment included a five‐payload array of in situ instrumentation, ground cameras at three different points under the trajectory, multiple ground magnetometers, the Poker Flat Incoherent Scatter Radar (PFISR) radar, and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft in the magnetotail. The rays of the poleward boundary intensification (PBI) curtain have along‐arc motions of 8.5 km/s and along‐arc spacings of 16 km. Modulated maximum energy envelopes and energy fluxes of the associated electron precipitation correspond to this spatial structure of the visible rays. The electron precipitation is additionally modulated at a higher frequency, and velocity dispersion analysis of these 8 Hz signatures implies Alfvénic wave‐particle acceleration of an ambient ionospheric electron source occurring a few hundred km above the observation point. These observations parameterize the curtain of Alfvénic activity above the PBI event, both in the dispersive ionosphere and in the magnetotail reconnection region. The along‐arc variations in brightness correspond to variations in precipitating electron energy flux interpreted as an along‐arc modulation of the maximum energy of the Alfvénic wave‐particle acceleration process; this is a new interpretation of the formation of rayed structures in auroral curtains. We consider the various possible magnetospheric and ionospheric drivers for the control of the observed along‐arc structuring and motions.
Tropical Indo‐Pacific Ocean chlorophyll response to MJO forcing
Authors: Jin Daeho , Murtugudde Raghu , Waliser Duane E.
Published: October 2012

Previous studies that analyzed ocean color satellite data have suggested that the primary mechanism of surface chlorophyll (Chl) response to the MJO is wind‐induced turbulent mixing and the corresponding mixed layer entrainment. In this study, this notion is examined with an ocean biophysical model in an ensemble framework, focusing on upper ocean processes (z < 200 m). As a whole, the model's mean Chl state is lower than observations except in the tropical Pacific basin, but its seasonal variation is acceptable, particularly in the tropical Indian Ocean. In this basin, the model can simulate surface Chl responses to the MJO consistent with the observations in terms of the phase‐by‐phase anomaly evolution patterns. These Chl responses are mostly induced by surface wind forcing, which is consistent with previous studies. Further investigation of subsurface variations is performed at select grid points, and it is revealed that (1) entrained nutrients are the primary source of enhancement for surface Chl concentration and detrainment blooms are relatively less common; (2) in limited regions, Ekman pumping can effectively reduce Chl concentration; and (3) both entrainment/detrainment and Ekman pumping mechanisms rely on background states of nutrient availability, so the same forcing can result in completely different Chl responses depending on the background state.
Characteristics of acoustic emissions induced by fluid front displacement in porous media
Authors: Moebius Franziska , Canone Davide , Or Dani
Published: October 2012

The dynamics of fluid displacement in porous media often affect phase entrapment and shape macroscopic transport properties and thus are of considerable interest for a range of natural and engineering applications. The macroscopic motion of a displacement front is composed of numerous abrupt pore‐scale invasion events that involve rapid interfacial jumps and reconfigurations with associated mechanical and interfacial energy release detectable as acoustic emissions (AE). We conducted systematic experiments of fluid displacement and measured associated AE during passage of fluid fronts (primarily drainage) within assemblies of glass beads of different sizes. Results indicated distinct acoustic signatures associated with different displacement processes, reflecting dependency on porous media pore size, displacement flow rate, and liquid properties. The rich AE signals associated with front dynamics exhibited power law relationships between the number of AE events and their amplitudes, reminiscent of avalanche‐like invasion processes. In addition to AE signals emanating from rapid emptying or filling of pores (Haines jumps), other processes such as redistribution and interfacial reconfigurations behind a drainage front and grain rearrangement may generate AE. Characteristic AE signatures generated by displacement processes in different media and under various boundary conditions offer a promise for remote detection of pore‐scale fluid interfacial dynamics in porous media that may shape macroscopic transport properties (e.g., linked with phase entrapment).
Viruses in the desert: a metagenomic survey of viral communities in four perennial ponds of the Mauritanian Sahara
Authors: Fancello Laura , Trape Sébatien , Robert Catherine , Boyer Mickaël , Popgeorgiev Nikolay , Raoult Didier , Desnues Christelle
Published: October 2012

Here, we present the first metagenomic study of viral communities from four perennial ponds (gueltas) located in the central Sahara (Mauritania). Three of the four gueltas (Ilij, Molomhar and Hamdoun) are located at the source of three different wadis belonging to the same hydrologic basin, whereas the fourth (El Berbera) belongs to a different basin. Overall, sequences belonging to tailed bacteriophages were the most abundant in all four metagenomes although electron microscopy and sequencing confirmed the presence of other viral groups, such as large DNA viruses. We observed a decrease in the local viral biodiversity in El Berbera, a guelta with sustained human activities, compared with the pristine Ilij and Molomhar, and sequences related to viruses infecting crop pests were also detected as a probable consequence of the agricultural use of the soil. However, the structure of the El Berbera viral community shared the common global characteristics of the pristine gueltas, that is, it was dominated by Myoviridae and, more particularly, by virulent phages infecting photosynthetic cyanobacteria, such as Prochlorococcus and Synechococcus spp. In contrast, the Hamdoun viral community was characterized by a larger proportion of phages with the potential for a temperate lifestyle and by dominant species related to phages infecting heterotrophic bacteria commonly found in terrestrial environments. We hypothesized that the differences observed in the structural and functional composition of the Hamdoun viral community resulted from the critically low water level experienced by the guelta.
Iron-reducing bacteria accumulate ferric oxyhydroxide nanoparticle aggregates that may support planktonic growth
Authors: Luef Birgit , Fakra Sirine C , Csencsits Roseann , Wrighton Kelly C , Williams Kenneth H , Wilkins Michael J , Downing Kenneth H , Long Philip E , Comolli Luis R , Banfield Jillian F
Published: October 2012

Iron-reducing bacteria (FeRB) play key roles in anaerobic metal and carbon cycling and carry out biogeochemical transformations that can be harnessed for environmental bioremediation. A subset of FeRB require direct contact with Fe(III)-bearing minerals for dissimilatory growth, yet these bacteria must move between mineral particles. Furthermore, they proliferate in planktonic consortia during biostimulation experiments. Thus, a key question is how such organisms can sustain growth under these conditions. Here we characterized planktonic microbial communities sampled from an aquifer in Rifle, Colorado, USA, close to the peak of iron reduction following in situ acetate amendment. Samples were cryo-plunged on site and subsequently examined using correlated two- and three-dimensional cryogenic transmission electron microscopy (cryo-TEM) and scanning transmission X-ray microscopy (STXM). The outer membranes of most cells were decorated with aggregates up to 150 nm in diameter composed of ∼3 nm wide amorphous, Fe-rich nanoparticles. Fluorescent in situ hybridization of lineage-specific probes applied to rRNA of cells subsequently imaged via cryo-TEM identified Geobacter spp., a well-studied group of FeRB. STXM results at the Fe L2,3 absorption edges indicate that nanoparticle aggregates contain a variable mixture of Fe(II)–Fe(III), and are generally enriched in Fe(III). Geobacter bemidjiensis cultivated anaerobically in the laboratory on acetate and hydrous ferric oxyhydroxides also accumulated mixed-valence nanoparticle aggregates. In field-collected samples, FeRB with a wide variety of morphologies were associated with nano-aggregates, indicating that cell surface Fe(III) accumulation may be a general mechanism by which FeRB can grow while in planktonic suspension.
Accuracy of protist diversity assessments: morphology compared with cloning and direct pyrosequencing of 18S rRNA genes and ITS regions using the conspicuous tintinnid ciliates as a case study
Authors: Bachy Charles , Dolan John R , López-García Purificación , Deschamps Philippe , Moreira David
Published: October 2012

Deep-sequencing technologies are becoming nearly routine to describe microbial community composition in environmental samples. The 18S ribosomal DNA (rDNA) pyrosequencing has revealed a vast diversity of infrequent sequences, leading to the proposition of the existence of an extremely diverse microbial ‘rare biosphere’. Although rare microbes no doubt exist, critical views suggest that many rare sequences may actually be artifacts. However, information about how diversity revealed by molecular methods relates to that revealed by classical morphology approaches is practically nonexistent. To address this issue, we used different approaches to assess the diversity of tintinnid ciliates, a species-rich group in which species can be easily distinguished morphologically. We studied two Mediterranean marine samples with different patterns of tintinnid diversity. We estimated tintinnid diversity in these samples employing morphological observations and both classical cloning and sequencing and pyrosequencing of two different markers, the 18S rDNA and the internal transcribed spacer (ITS) regions, applying a variety of computational approaches currently used to analyze pyrosequence reads. We found that both molecular approaches were efficient in detecting the tintinnid species observed by microscopy and revealed similar phylogenetic structures of the tintinnid community at the species level. However, depending on the method used to analyze the pyrosequencing results, we observed discrepancies with the morphology-based assessments up to several orders of magnitude. In several cases, the inferred number of operational taxonomic units (OTUs) largely exceeded the total number of tintinnid cells in the samples. Such inflation of the OTU numbers corresponded to ‘rare biosphere’ taxa, composed largely of artifacts. Our results suggest that a careful and rigorous analysis of pyrosequencing data sets, including data denoising and sequence clustering with well-adjusted parameters, is necessary to accurately describe microbial biodiversity using this molecular approach.
Metabolic inflexibility and protein lysine acetylation in heart mitochondria of a chronic model of Type 1 diabetes
Authors: Vadvalkar Shraddha S. , Baily C. Nathan , Matsuzaki Satoshi , West Melinda , Tesiram Yasvir A. , Humphries Kenneth M.
Published: October 2012

Diabetic cardiomyopathy refers to the changes in contractility that occur to the diabetic heart that can arise in the absence of vascular disease. Mitochondrial bioenergetic deficits and increased free radical production are pathological hallmarks of diabetic cardiomyopathy, but the mechanisms and causal relationships between mitochondrial deficits and the progression of disease are not understood. We evaluated cardiac mitochondrial function in a rodent model of chronic Type 1 diabetes (OVE26 mice) before the onset of contractility deficits. We found that the most pronounced change in OVE26 heart mitochondria is severe metabolic inflexibility. This inflexibility is characterized by large deficits in mitochondrial respiration measured in the presence of non-fatty acid substrates. Metabolic inflexibility occurred concomitantly with decreased activities of PDH (pyruvate dehydrogenase) and complex II. Hyper-acetylation of protein lysine was also observed. Treatment of control heart mitochondria with acetic anhydride (Ac2O), an acetylating agent, preferentially inhibited respiration by non-fatty acid substrates and increased superoxide production. We have concluded that metabolic inflexibility, induced by discrete enzymatic and molecular changes, including hyper-acetylation of protein lysine residues, precedes mitochondrial defects in a chronic rodent model of Type 1 diabetes.
Akt is efficiently activated by PIF-pocket- and PtdIns(3,4,5)P3-dependent mechanisms leading to resistance to PDK1 inhibitors
Authors: Najafov Ayaz , Shpiro Natalia , Alessi Dario R.
Published: October 2012

Mutations leading to inappropriate activation of Akt isoforms contribute to proliferation and survival of a significant proportion of human cancers. Akt is activated by phosphorylation of its T-loop residue (Thr308) by PDK1 (3-phosphoinositide-dependent kinase-1) and its C-terminal hydrophobic motif (Ser473) by mTORC2 [mTOR (mammalian target of rapamycin) complex 2]. Potent PDK1 inhibitors such as GSK2334470 have recently been elaborated as potential anti-cancer agents. However, these compounds were surprisingly ineffective at suppressing Akt activation. In the present study we demonstrate that resistance to PDK1 inhibitors results from Akt being efficiently recruited to PDK1 via two alternative mechanisms. The first involves ability of Akt and PDK1 to mutually interact with the PI3K (phosphoinositide 3-kinase) second messenger PtdIns(3,4,5)P3. The second entails recruitment of PDK1 to Akt after its phosphorylation at Ser473 by mTORC2, via a substrate-docking motif termed the PIF-pocket. We find that disruption of either the PtdIns(3,4,5)P3 or the Ser473 phosphorylation/PIF-pocket mechanism only moderately impacts on Akt activation, but induces marked sensitization to PDK1 inhibitors. These findings suggest that suppression of Ser473 phosphorylation by using mTOR inhibitors would disrupt the PIF-pocket mechanism and thereby sensitize Akt to PDK1 inhibitors. Consistent with this, we find combing PDK1 and mTOR inhibitors reduced Akt activation to below basal levels and markedly inhibited proliferation of all of the cell lines tested. Our results suggest further work is warranted to explore the utility of combining PDK1 and mTOR inhibitors as a therapeutic strategy for treatment of cancers that harbour mutations elevating Akt activity.
Pulsed laser operated high rate charging of Fe-doped LiNbO3 crystal for electron emission
Authors: Louchev Oleg A. , Wada Satoshi , Saito Norihito , Hatano Hideki , Kitamura Kenji
Published: October 2012

High rate 600 ppm Fe-doped LiNbO3 crystal charging for electron emission by pulsed laser radiation is studied theoretically for 532 nm ≈10 ns laser pulse fluence 0.01-6 J/cm2. The previous experimental results are used as a reference point for developing analytical and computational estimates which show that high charging rate under pulsed laser radiation is due to roughly equal contributions from: (i) photogalvanic current, (ii) pyroelectric current, and (iii) electron drift by laser induced electric field. The computational photo-refractive model, verified against experimental data, additionally includes recombination rate non-linearity giving very significant feedback effect for charge density, electric field, and electron energy under laser fluence above 0.5 J/cm2. Theoretical study is finalized by the expressions linking the laser fluence with resulting surface charge density and repulsive energy for emitted electrons. The model gives also the estimate of the laser damage threshold fluence at ≈6 J/cm2 above which the laser induced electric field accelerates the electrons to an energy sufficient for electron impact ionization from the valence band. In operation below this threshold single laser pulse is shown to provide surface charge densities above 10−7 C/cm2 with the repulsive energy close to 106 eV. A high frequency pulsed laser with single pulse fluence below the damage threshold is suggested to achieve the repulsive energies above 106 eV.
The study and performance of a modified ENIEM conventional refrigerator to serve as a photovoltaic powered one under Algerian climate conditions
Authors: Laidi M. , Hanini S. , Abbad B. , Bedja M. , Ouali M. , Ferhat Y. , Guers S.
Published: October 2012

This paper describes the design and development stages followed to convert a conventional vapour compression refrigerator to a solar powered one. A conventional refrigerator ENIEM 160 l was chosen and some changes were introduced on it to reduce the cooling load and consequently the power it required. Three prototypes were designed and tested; AC (alternative current) electrical power drives the first one using a converter, the Danfoss compressor that works with DC (direct current) was set up in the second, and BDF35 with Eutectic evaporator AC15 were used in the third refrigerator. The hermetic compressor was switched on and off to maintain an average inside air temperature between a maximum and minimum air temperature established by the thermostat. Many tests were carried out over 1 yr to study the performance of each of the refrigerator's components and especially the compressor, the eutectic evaporator, as well as the system as a whole. These prototypes were installed and tested in Algeria, in two different climate types: mild, along the Mediterranean coast, and arid, in the Sahara. The data gathered as well as the analysis processes enabled our team to evaluate pertinent system components and optimize the equipment to specific environments and load requirements. It can be concluded that the performance of the eutectic refrigerator is very stable and it can serve for perishable food storage, vaccine, and drug depositing at low temperatures in remote areas using half energy and a low number of battery.
The fate of the Wilson-Fisher fixed point in non-commutative ϕ4
Authors: Ydri Badis , Bouchareb Adel
Published: October 2012

In this article we study non-commutative vector sigma model with the most general ϕ4 interaction on Moyal-Weyl spaces. We compute the 2- and 4-point functions to all orders in the large N limit and then apply the approximate Wilson renormalization group recursion formula to study the renormalized coupling constants of the theory. The non-commutative Wilson-Fisher fixed point interpolates between the commutative Wilson-Fisher fixed point of the Ising universality class which is found to lie at zero value of the critical coupling constant a* of the zero dimensional reduction of the theory, and a novel strongly interacting fixed point which lies at infinite value of a* corresponding to maximal non-commutativity beyond which the two-sheeted structure of a* as a function of the dilation parameter disappears.
Real analytic quasi-periodic solutions for the derivative nonlinear Schrödinger equations
Authors: Geng Jiansheng , Wu Jian
Published: October 2012

In this paper, we show that one dimension derivative nonlinear Schrödinger equation admits a whitney smooth family of small amplitude, real analytic quasi-periodic solutions with two Diophantine frequencies. The proof is based on a partial Birkhoff normal form reduction and an abstract infinite dimensional Kolmogorov-Arnold-Moser (KAM) theorem.
Extended states for polyharmonic operators with quasi-periodic potentials in dimension two
Authors: Karpeshina Yulia , Shterenberg Roman
Published: October 2012

We consider a polyharmonic operator H = ( − Δ)l + V(x) in dimension two with l ⩾ 2, l being an integer, and a quasi-periodic potential V(x). We prove that the absolutely continuous spectrum of H contains a semiaxis and there is a family of generalized eigenfunctions at every point of this semiaxis with the following properties. First, the eigenfunctions are close to plane waves ei⟨k, x⟩ at the high energy region. Second, the isoenergetic curves in the space of momenta k corresponding to these eigenfunctions have a form of slightly distorted circles with holes (Cantor type structure). A new method of multiscale analysis in the momentum space is developed to prove these results.
Robustness of random graphs based on graph spectra
Authors: Wu Jun , Barahona Mauricio , Tan Yue-jin , Deng Hong-zhong
Published: October 2012

It has been recently proposed that the robustness of complex networks can be efficiently characterized through the natural connectivity, a spectral property of the graph which corresponds to the average Estrada index. The natural connectivity corresponds to an average eigenvalue calculated from the graph spectrum and can also be interpreted as the Helmholtz free energy of the network. In this article, we explore the use of this index to characterize the robustness of Erdős-Rényi (ER) random graphs, random regular graphs, and regular ring lattices. We show both analytically and numerically that the natural connectivity of ER random graphs increases linearly with the average degree. It is also shown that ER random graphs are more robust than the corresponding random regular graphs with the same number of vertices and edges. However, the relative robustness of ER random graphs and regular ring lattices depends on the average degree and graph size: there is a critical graph size above which regular ring lattices are more robust than random graphs. We use our analytical results to derive this critical graph size as a function of the average degree.
Development of knife-edge ridges on ion-bombarded surfaces
Authors: Holmes-Cerfon Miranda , Zhou Wei , Bertozzi Andrea L. , Brenner Michael P. , Aziz Michael J.
Published: October 2012

We demonstrate in both laboratory and numerical experiments that ion bombardment of a modestly sloped surface can create knife-edge like ridges with extremely high slopes. Small pre-fabricated pits expand under ion bombardment, and the collision of two such pits creates knife-edge ridges. Both laboratory and numerical experiments show that the pit propagation speed and the precise shape of the knife edge ridges are universal, independent of initial conditions, as has been predicted theoretically. These observations suggest a method of fabrication in which a surface is pre-patterned so that it dynamically evolves to a desired target pattern made of knife-edge ridges.
Defect characterisation based on heat diffusion using induction thermography testing
Authors: He Yunze , Pan Mengchun , Luo Feilu
Published: October 2012

Pulsed eddy current (PEC) thermography (a.k.a. induction thermography) has been successfully applied to detect defects (corrosion, cracks, impact, and delamination) in metal alloy and carbon fiber reinforced plastic. During these applications, the defect detection mechanism is mainly investigated based on the eddy current interaction with defect. In this paper, defect characterisation for wall thinning defect and inner defect in steel is investigated based on heat diffusion. The paper presents the PEC thermography testing, which integrates the reflection mode and transmission mode by means of configuring two cameras on both sides of sample. The defect characterisation methods under transmission mode and reflection mode are investigated and compared through 1D analytical analysis, 3D numerical studies, and experimental studies. The suitable detection mode for wall thinning and inner defects quantification is concluded.
Implication of exotic topography depths of surface nanopits in scanning tunneling microscopy of HgCdTe
Authors: Zha F. X. , Li M. S. , Shao J. , Wang Q. Y. , Ren X. R. , An K. , Zhao X. L. , Shen X. C.
Published: October 2012

The vacancy doped p-type narrow band semiconductor of Hg0.73Cd0.27Te was characterized by ultra-high vacuum scanning tunneling microscopy (STM) and spectroscopy. The imaging displays surprisingly different topographies for positive and negative imaging biases, between which the observed surface pits with the negative bias are few tens nanometers shallower than their counterparts with the positive bias. The effect is subjected to two different local tunneling mechanisms which are not solely dictated by surface electronic properties. The observation contrasts with the conventional geometric view of the nanometer-scale corrugation of STM topography.
Influence of catalytic gold and silver metal nanoparticles on structural, optical, and vibrational properties of silicon nanowires synthesized by metal-assisted chemical etching
Authors: Dawood M. K. , Tripathy S. , Dolmanan S. B. , Ng T. H. , Tan H. , Lam J.
Published: October 2012

We report on the structural and vibrational characterization of silicon (Si) nanowire arrays synthesized by metal-assisted chemical etching (MACE) of Si deposited with metal nanoparticles. Gold (Au) and silver (Ag) metal nanoparticles were synthesized by glancing angle deposition, and MACE was performed in a mixture of H2O2 and HF solution. We studied the structural differences between Au and Ag-etched Si nanowires. The morphology of the synthesized nanowires was characterized by scanning electron microscopy and transmission electron microscopy. The optical and vibrational properties of the Si nanostructures were studied by photoluminescence and Raman spectroscopy using three different excitation sources (UV, visible, and near-infrared) and are correlated to their microstructures. The structural differences between Au-etched and Ag-etched nanowires are due to the higher degree of hole injection by the Au nanoparticle and diffusion into the Si nanowires, causing enhanced Si etching by HF on the nanowire surface. Au-etched nanowires were observed to be mesoporous throughout the nanowire while Ag-etched nanowires consisted of a thin porous layer around the crystalline core. In addition, the surface-enhanced resonant Raman scattering observed is attributed to the presence of the sunken metal nanoparticles. Such Si nanostructures may be useful for a wide range of applications such as photovoltaic and biological and chemical sensing.
Characteristics of ion-acoustic solitary wave in a laboratory dusty plasma under the influence of ion-beam
Authors: Deka M. K. , Adhikary N. C. , Misra A. P. , Bailung H. , Nakamura Y.
Published: October 2012

We study the influence of ion beam and charged dust impurity on the propagation of dust ion-acoustic solitary wave in an unmagnetized plasma consisting of Boltzmann distributed electrons, positive ions, positive ion beam, and negatively charged immobile dusts in a double plasma device. On interacting with an ion beam, the solitary wave is bifurcated into a compressive fast and a rarefactive slow beam mode, and appears along with the primary wave. However, there exists a critical velocity of the beam beyond which the amplitude of the fast solitary wave starts diminishing and rarefactive slow beam mode propagates with growing amplitude. Whereas, the presence of charged dust impurity in the plasma reduces this critical beam velocity and a substantial modification in the phase velocity of the slow beam mode is observed with increasing dust density. Furthermore, the nonlinear wave velocity (Mach number) as well as the width of the compressive solitons are measured for different beam velocity and dust density, and are compared with those obtained from the K-dV equation. The experimental results are found in a well agreement with the theoretical predictions.
First principles calculations of the band offset at SrTiO3−TiO2 interfaces
Authors: D'Amico Nunzio Roberto , Cantele Giovanni , Ninno Domenico
Published: October 2012

We report on first principles calculations of the properties of the epitaxial SrTiO3−TiO2 (anatase) heterojunction, with an emphasis on the electronic band profile and lineup at the interface. The valence and conduction band offsets are calculated as a function of the number of anatase layers deposited onto the SrTiO3, as well as of the position of an oxygen vacancy with respect to the interface. It is shown that the presence of oxygen vacancies in the SrTiO3 is a way to effectively lower the barrier heights at the interface. Our results are in agreement with recent experiments reporting nearly zero band offset.
Preparation and investigation of the A-site and B-site terminated SrTiO3(001) surface: A combined experimental and theoretical x-ray photoelectron diffraction study
Authors: Raisch C. , Chassé T. , Langheinrich Ch. , Chassé A.
Published: October 2012

We have investigated surface composition, structure, and termination of SrTiO3(001) samples (STO) following typical steps of standard ex situ and in situ preparation procedures by performing x-ray photoelectron spectroscopy (XPS) and x-ray photoelectron diffraction (XPD) experiments, and multiple scattering cluster (MSC) calculations. XPS has confirmed the presence of Sr2+, Ti4+, and O2-related to STO. Well-developed diffraction features have been observed in all XPD polar scans demonstrating the good structural ordering of the investigated surfaces. In order to permit a detailed comparison of XPD experiment and theory, we have especially taken care of effects due to the angular dependent instrument function by applying a new ratio procedure. Thus, we achieved a very good agreement between results of MSC calculations and experimental angular distributions. A fingerprint region has been identified in Sr3d polar scans, which has exhibited both evident dependencies on surface preparation steps in the experiments and clear sensitivity to surface termination in the theoretical modeling. In this manner, we have been able to describe as-received samples and in situ-treated samples as being TiO2- and SrO-terminated, respectively. Standard buffered hydrofluoric acid-treated samples turned out to be mostly TiO2-terminated but with a non-negligible admixture of different, likely SrO-type termination.
Optimizing diode thickness for thin-film solid state thermal neutron detectors
Authors: Murphy John W. , Kunnen George R. , Mejia Israel , Quevedo-Lopez Manuel A. , Allee David , Gnade Bruce
Published: October 2012

In this work, we investigate the optimal thickness of a semiconductor diode for thin-film solid state thermal neutron detectors. We evaluate several diode materials, Si, CdTe, GaAs, C (diamond), and ZnO, and two neutron converter materials, 10B and 6LiF. Investigating a coplanar diode/converter geometry, we determine the minimum semiconductor thickness needed to achieve maximum neutron detection efficiency. By keeping the semiconductor thickness to a minimum, gamma rejection is kept as high as possible. In this way, we optimize detector performance for different thin-film semiconductor materials.
Infrared absorption coefficients of vertically aligned carbon nanotube films
Authors: Ye H. , Wang X. J. , Lin W. , Wong C. P. , Zhang Z. M.
Published: October 2012

Vertically aligned carbon nanotube (VACNT) films have promising applications in solar cells, radiometers, and photonic devices. We have fabricated VACNT films with thicknesses of 10, 36, 45, and 120 μm on silicon substrates. The absorption coefficient of each film is obtained from the measured regular transmittance from 1 to 19 μm wavelengths, using a ratio method. The degree of alignment of the VACNT films is estimated by comparison of experiments with an analysis based on the effective medium theory. The effect of thickness on the absorption coefficient of the VACNT films is elucidated according to their morphologies.
Magnetodielectric effect of CuO grown within highly ordered two dimensional mesoporous silica template SBA 15
Authors: Mandal Amrita , Banerjee Shilpi , Banerjee Sourish , Chakravorty Dipankar
Published: October 2012

A two component, inhomogeneous medium can produce magnetodielectric (MD) effect without any magnetoelectric coupling. Here, we have prepared an inhomogeneous material by growing CuO within two dimensional mesostructures of silica template SBA-15 by a single step method. The (CuO)x-(SBA-15)1−x nanocomposites with different weight percentages (x = 0.2, 0.35, and 0.5) were characterized by small angle x-ray diffraction study and transmission electron microscopy. Both studies confirmed the highly ordered hexagonal mesostructure for CuO(20) where 20 is the weight percentage of CuO in nanocomposite (i.e., x = 0.2). The mesostructure was destroyed on increasing the percentage of CuO incorporated. The nanocomposites exhibited magnetodielectric effect with dielectric constant change of 4.4% and 3% for CuO(20) and CuO(35), respectively, at 1.8 T magnetic field. This effect was explained on the basis of a two dimensional inhomogeneous two component composite model. No such effect occurs in CuO(50) due to total disappearance of the ordered mesostructure.
Compositionally graded relaxed AlGaN buffers on semipolar GaN for mid-ultraviolet emission
Authors: Young Erin C. , Wu Feng , Romanov Alexey E. , Haeger Daniel A. , Nakamura Shuji , Denbaars Steven P. , Cohen Daniel A. , Speck James S.
Published: October 2012

In this Letter, we report on the growth and properties of relaxed, compositionally graded AlxGa1 − xN buffer layers on freestanding semipolar (202¯1) GaN substrates. Continuous and step compositional grades with Al concentrations up to x = 0.61 have been achieved, with emission wavelengths in the mid-ultraviolet region as low as 265 nm. Coherency stresses were relaxed progressively throughout the grades by misfit dislocation generation via primary (basal) slip and secondary (non-basal) slip systems. Threading dislocation densities in the final layers of the grades were less than 106/cm2 as confirmed by plan-view transmission electron microscopy and cathodoluminescence studies.
Spreading and atomization of droplets on a vibrating surface in a standing pressure field
Authors: Deepu P. , Basu Saptarshi , Saha Abhishek , Kumar Ranganathan
Published: October 2012

We report the first observation and analytical model of deformation and spreading of droplets on a vibrating surface under the influence of an ultrasonic standing pressure field. The standing wave allows the droplet to spread, and the spreading rate varies inversely with viscosity. In low viscosity droplets, the synergistic effect of radial acoustic force and the transducer surface acceleration also leads to capillary waves. These unstable capillary modes grow to cause ultimate disintegration into daughter droplets. We find that using nanosuspensions, spreading and disintegration can be prevented by suppressing the development of capillary modes and subsequent break-up.
Interdependence of reversal asymmetry and training effect in Ir22Mn78/Ni81Fe19 bilayers probed with magnetoresistance
Authors: Fulara Himanshu , Chaudhary Sujeet , Kashyap Subhash C.
Published: October 2012

Using magnetoresistance as a probe we demonstrate the correlation between reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. During the training procedure, both exchange bias field and the degree of asymmetry decrease monotonically following a very similar trend. The analysis of the magnetoresistance behaviour establishes that the two distinct training mechanisms are operative. The first one is exhibited by an abrupt single cycle training effect and an accompanying pronounced reversal asymmetry, attributed to the presence of biaxial anisotropy in the IrMn layer. The second one displays a gradual cycling dependence due to thermal depinning of uncompensated antiferromagnetic spins.
All-optical on-chip dynamic frequency conversion
Authors: Castellanos Muñoz M. , Petrov A. Yu. , Eich M.
Published: October 2012

Dynamic processes allow controlling light through a fast modification of the optical properties of the confining structure while the light is present in it. Here, we demonstrate the on-chip dynamic frequency conversion of a light signal by performing this modification through a short optical switching pulse co-propagating on-chip with the signal. A frequency-dependent propagation velocity allows the switching pulse to overtake a co-propagating signal pulse running ahead while on its way driving the dynamic process. We show a dynamic frequency shift of up to 70 GHz with a conversion efficiency of up to 25%.
Structural change in polar nanoregion in alkali niobate added Pb(Zn1/3Nb2/3)0.95Ti0.05O3 single crystal and its effect on ferroelectric properties
Authors: Park Jong-Sung , Jung Youngsoo , Lee Jung-Kun
Published: October 2012

Pb(Zn1/3Nb2/3)0.95Ti0.05O3 (PZNT) single crystals with 5 mol. % alkali niobate such as LiNbO3 (LN), NaNbO3 (NN), and KNbO3 (KN) were fabricated by using a flux method to investigate the effect of A-site cation radius on the structure and ferroelectric properties of PZNT under electric field (E-field). Their structure and properties showed different electric field dependence. Polarization versus electric field and strain versus electric field curves of PZNT-0.05LN showed E-field induced phase transition from a relaxor state to a normal ferroelectric state. However, only relaxor behavior was observed in PZNT-0.05NN and PZNT-0.05KN. The effect of A-site ion doping is attributed to the change in local lattice distortion and polar nano-region. When smaller cation such as Li ion substitutes Pb ion, the off-center displacement of Nb ion stabilizes rhombohedral lattice distortion. They, in turn, facilitate the development of macro-domains under electric field (E-field) in PZNT-0.05LN. In contrast, the substitution of Pb with larger cations such as Ni and K decreases the rhombohedral distortion of PZNT, which leads to the disappearance of unique E-field induced phase transition from rhombohedral to tetragonal phase in PZNT. Therefore, non-linear electrostrictive behavior of relaxor ferroelectrics is found in PZNT-0.05NN and PZNT-0.05KN.