bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal sensing interval in cognitive radio networks with imperfect spectrum sensing
Authors: Liu Boyang , Li Zan , Si Jiangbo , Zhou Fuhui
Published: January 2016

Spectrum sensing is performed at the beginning of each time slot in traditional cognitive radio networks, which is unreasonable and needless since the presence or the absence of a primary user (PU) always lasts several time slots. A hidden Markov model is used to describe the imperfect spectrum sensing process over Rayleigh fading channels. On the basis of the sensing results, a hybrid interweave/underlay mode is exploited by the secondary user (SU) to achieve a higher throughput. To solve the tradeoff problem among the average energy consumption for spectrum sensing, the average throughput of SU and the average interference to the PU, an optimisation problem is proposed. The optimal sensing interval to determine when the next spectrum sensing should be performed is obtained by solving the optimisation problem. Numerical results are given to verify the authors’ analysis.
Supplementary automatic generation control using controllable energy storage in electric vehicle battery swapping stations
Authors: Xie Pingping , Li Yinhong , Zhu Lin , Shi Dongyuan , Duan Xianzhong
Published: January 2016

One of the significant impacts of the growing penetration of intermittent renewable energy sources is upon the frequency response of power system. Compared with the dispersive electric vehicle energy storage, electric vehicle battery swapping station (BSS), as an emerging form of storage, can provide a more reliable supplementary regulation service for frequency control. This study has proposed a new supplementary automatic generation control (AGC) strategy using controllable energy storage in BSSs, referred to as station‐to‐grid (S2G). A Monte–Carlo stochastic simulation method is utilised to estimate the equivalent controllable capacity (CC) of BSSs, and then the lumped S2G equivalent model subject to SOC limits and CC constrains is presented. A filter‐based AGC coordinated strategy is used to allocate the regulation power between generators and BSSs. The proposed AGC strategy is validated in a two‐area interconnected power system with significant load and wind power fluctuations. Comparison analysis demonstrates the availability of the proposed models and control methods.
Subsynchronous oscillation and its practical mitigation project at the Hulun Buir power plant generating for a Chinese extra‐high‐voltage AC and DC hybrid transmission network
Authors: Wenhui Qu , Jianguo Jiang , Qian Zhao , Yu Zuo
Published: January 2016

In China, subsynchronous oscillation (SSO) appears continually at the Hulun Buir (HB) power plant, which is part of the extra‐high‐voltage (EHV) AC and DC hybrid transmission networks from the HB League power base to the Northeast. Related closely to the power delivered by the EHVDC link, these oscillations lead to fatigue accumulation, life‐time reductions and even failures in the turbogenerators at the HB power plant. After a study of the oscillations, an inverse energy injection method is proposed to suppress the SSO phenomenon. According to the method, a bulk power electronic device is developed that is based on a multilevel voltage source converter to generate inverse energy. The mitigation device is implemented at the HB power plant. Field tests are conducted, and the results demonstrate that the device can depress SSO to levels that exceed the requirements, proving the effectiveness of the mitigation device.
Synchrophasor based thermal overhead line monitoring considering line spans and thermal transients
Authors: Kubis Andreas , Rehtanz Christian
Published: January 2016

A synchrophasor‐based thermal line monitoring scheme enabling the measurement of line spans and therewith temperature profiles is presented. Further, the measurement of thermal transients with synchrophasors has become feasible by incorporating non‐steady state heat equations and local weather data. The proof of concept is executed with an electro‐thermal line modelling approach in combination with sensitivity analyses of various power flow scenarios, data processing time steps and weather updating rates. It has been shown, that the relative measurement error of this method is ±0.2% at ideal thermal static and ±2.0% at ideal thermal transient conditions for various load currents with reference to the original temperature. Finally, the accuracy at highly volatile weather conditions as well as the suitability for practical implementation is discussed.
Federated ultra‐tightly coupled GPS/INS integrated navigation system based on vector tracking for severe jamming environment
Authors: Li Kui , Zhao Jiaxing , Wang Xueyun , Wang Lei
Published: January 2016

Considering all integration methods currently available for global positioning system (GPS) and inertial navigation system (INS) integrated navigation system, ultra‐tightly coupled (UTC) GPS/INS system is the best choice for accurate and robust navigation. However the performance of UTC GPS/INS system based on scalar tracking (ST) degrades in severe jamming environments. To solve this problem an innovative federated UTC GPS/INS system based on vector tracking (VT) is proposed. On the basis of UTC integration, three Kalman filters are developed to accomplish the goals of signal amplitude estimation, VT and integration navigation. By replacing the traditional ST loops with VT filter, the tracking ability is remarkably reinforced. More importantly, a new mathematical model of VT is proposed and the key innovation of this model is that it can provide adaptation ability to integration Kalman filter, so that the navigation performance can be improved under various jamming conditions. A simulation platform covering all procedures of GPS/INS integrated navigation is employed to verify the effectiveness of the proposed architecture. Tracking and navigation results show that the federated UTC GPS/INS integrated system based on VT improves both the tracking and navigation performance significantly under severe jamming environments compared with that of ST system.
Energy transfer in structured and unstructured environments: Master equations beyond the Born-Markov approximations
Authors: Iles-Smith Jake , Dijkstra Arend G. , Lambert Neill , Nazir Ahsan
Published: January 2016

We explore excitonic energy transfer dynamics in a molecular dimer system coupled to both structured and unstructured oscillator environments. By extending the reaction coordinate master equation technique developed by Iles-Smith et al. [Phys. Rev. A 90, 032114 (2014)], we go beyond the commonly used Born-Markov approximations to incorporate system-environment correlations and the resultant non-Markovian dynamical effects. We obtain energy transfer dynamics for both underdamped and overdamped oscillator environments that are in perfect agreement with the numerical hierarchical equations of motion over a wide range of parameters. Furthermore, we show that the Zusman equations, which may be obtained in a semiclassical limit of the reaction coordinate model, are often incapable of describing the correct dynamical behaviour. This demonstrates the necessity of properly accounting for quantum correlations generated between the system and its environment when the Born-Markov approximations no longer hold. Finally, we apply the reaction coordinate formalism to the case of a structured environment comprising of both underdamped (i.e., sharply peaked) and overdamped (broad) components simultaneously. We find that though an enhancement of the dimer energy transfer rate can be obtained when compared to an unstructured environment, its magnitude is rather sensitive to both the dimer-peak resonance conditions and the relative strengths of the underdamped and overdamped contributions.
CO oxidation on Pt(111) at near ambient pressures
Authors: Krick Calderón S. , Grabau M. , Óvári L. , Kress B. , Steinrück H.-P. , Papp C.
Published: January 2016

The oxidation of CO on Pt(111) was investigated simultaneously by near ambient pressure X-ray photoelectron spectroscopy and online gas analysis. Different CO:O2 reaction mixtures at total pressures of up to 1 mbar were used in continuous flow mode to obtain an understanding of the surface chemistry. By temperature-programmed and by isothermal measurements, the onset temperature of the reaction was determined for the different reactant mixtures. Highest turnover frequencies were found for the stoichiometric mixture. At elevated temperatures, the reaction becomes diffusion-limited in both temperature-programmed and isothermal measurements. In the highly active regime, no adsorbates were detected on the surface; it is therefore concluded that the catalyst surface is in a metallic state, within the detection limits of the experiment, under the applied conditions. Minor bulk impurities such as silicon were observed to influence the reaction up to total inhibition by formation of non-platinum oxides.
Temperature dependence of hydrogenated amorphous silicon solar cell performances
Authors: Riesen Y. , Stuckelberger M. , Haug F.-J. , Ballif C. , Wyrsch N.
Published: January 2016

Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer (i-layer), and the thicknesses of the a-Si:H i-layer and p-type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the Voc generally varies linearly with the Voc value. The Jsc increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 °C and 80 °C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p-layer and to a recombination decrease with temperature. Due to the FF(T) behavior, the Pmpp (T) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the Pmpp (T) curves of two cells with different i-layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchâtel (Switzerland) the best cell at STC also has the best energy yield. However, for a different climate or cell configuration, this may not be true.
Collisionless expansion of pulsed radio frequency plasmas. I. Front formation
Authors: Schröder T. , Grulke O. , Klinger T. , Boswell R. W. , Charles C.
Published: January 2016

The dynamics during plasma expansion are studied with the use of a versatile particle-in-cell simulation with a variable neutral gas density profile. The simulation is tailored to a radio frequency plasma expansion experiment [Schröder et al., J. Phys. D: Appl. Phys. 47(5), 055207 (2014)]. The experiment has shown the existence of a propagating ion front. The ion front features a strong electric field and features a sharp plasma potential drop similar to a double layer. However, the presented results of a first principle simulation show that, in general, the ion front does not have to be entangled with an electric field. The propagating electric field reflects the downstream ions, which stream with velocities up to twice as high as that of the ion front propagation. The observed ion density peak forms due to the accumulation of the reflected ions. The simulation shows that the ion front formation strongly depends on the initial ion density profile and is subject to a wave-breaking phenomenon. Virtual diagnostics in the code allow for a direct comparison with experimental results. Using this technique, the plateau forming in the wake of the plasma front could be indirectly verified in the expansion experiment. Although the simulation considers profiles only in one spatial dimensional, its results are qualitatively in a very good agreement with the laboratory experiment. It can successfully reproduce findings obtained by independent numerical models and simulations. This indicates that the effects of magnetic field structures and tangential inhomogeneities are not essential for the general expansion dynamic. The presented simulation will be used for a detailed parameter study dealt with in Paper II [Schröder et al., Phys. Plasma 23, 013512 (2016)] of this series.
Collisionless expansion of pulsed radio frequency plasmas. II. Parameter study
Authors: Schröder T. , Grulke O. , Klinger T. , Boswell R. W. , Charles C.
Published: January 2016

The plasma parameter dependencies of the dynamics during the expansion of plasma are studied with the use of a versatile particle-in-cell simulation tailored to a plasma expansion experiment [Schröder et al., J. Phys. D: Appl. Phys. 47, 055207 (2014); Schröder et al., Phys. Plasmas 23, 013511 (2016)]. The plasma expansion into a low-density ambient plasma features a propagating ion front that is preceding a density plateau. It has been shown that the front formation is entangled with a wave-breaking mechanism, i.e., an ion collapse [Sack and Schamel, Plasma Phys. Controlled Fusion 27, 717 (1985); Sack and Schamel, Phys. Lett. A 110, 206 (1985)], and the launch of an ion burst [Schröder et al., Phys. Plasmas 23, 013511 (2016)]. The systematic parameter study presented in this paper focuses on the influence on this mechanism its effect on the maximum velocity of the ion front and burst. It is shown that, apart from the well known dependency of the front propagation on the ion sound velocity, it also depends sensitively on the density ratio between main and ambient plasma density. The maximum ion velocity depends further on the initial potential gradient, being mostly influenced by the plasma density ratio in the source and expansion regions. The results of the study are compared with independent numerical studies.
CO adsorption on small Aun (n = 1–4) structures supported on hematite. I. Adsorption on iron terminated α-Fe2O3 (0001) surface
Authors: Pabisiak Tomasz , Winiarski Maciej J. , Kiejna Adam
Published: January 2016

This is the first of two papers dealing with the adsorption of Au and formation of Aun nanostructures (n = 1–4) on hematite (0001) surface and adsorption of CO thereon. The stoichiometric Fe-terminated (0001) surface of hematite was investigated using density functional theory in the generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) form with Hubbard correction U, accounting for strong electron correlations (PBE+U). The structural, energetic, and electronic properties of the systems studied were examined for vertical and flattened configurations of Aun nanostructures adsorbed on the hematite surfaces. The flattened ones, which can be viewed as bilayer-like structures, were found energetically more favored than vertical ones. For both classes of structures the adsorption binding energy increases with the number of Au atoms in a structure. The adsorption of Aun induces charge rearrangement at the Aun/oxide contact which is reflected in work function changes. In most considered cases Aun adsorption increases the work function. A detailed analysis of the bonding electron charge is presented and the corresponding electron charge rearrangements at the contacts were quantified by a Bader charge analyses. The interaction of a CO molecule with the Aun nanostructures supported on α-Fe2O3 (0001) and the oxide support was studied. It is found that the CO adsorption binding to the hematite supported Aun structures is more than twice as strong as to the bare hematite surface. Analysis of the Bader charges on the atoms showed that in each case CO binds to the most positively charged (cationic) atom of the Aun structure. Changes in the electronic structure of the Aun species and of the oxide support, and their consequences for the interactions with CO, are discussed.
Monolayer MoS2 self-switching diodes
Authors: Al-Dirini Feras , Hossain Faruque M. , Mohammed Mahmood A. , Hossain Md Sharafat , Nirmalathas Ampalavanapillai , Skafidas Efstratios
Published: January 2016

This paper presents a new molybdenum disulphide (MoS2) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS2 monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS2 results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70.
Superior endurance performance of nonvolatile memory devices based on discrete storage in surface-nitrided Si nanocrystals
Authors: Yu Jie , Chen Kunji , Ma Zhongyuan , Zhang Xinxin , Jiang Xiaofan , Huang Xinfan , Zhang Yongxing , Wang Lingling
Published: January 2016

The surface-nitrided silicon nanocrystals (Si-NCs) floating gate nonvolatile memory (NVM) devices were fabricated by 0.13 μm node CMOS technology. The surface-nitrided Si-NCs were formed in-situ by low-pressure chemical vapor deposition and followed by nitridation treatment in NH3 ambient. It is found that the nitridation treatment not only enhances the control effect of gate voltage on channel carriers by passivation of the Si-NCs surface defects but also suppresses releasing of the stored carriers among the neighboring Si-NCs and leakage from Si-NCs to channel through the tunneling oxide by a silicon nitride cover layer acted as potential barrier. Consequently, the storage carriers are fully discrete in the Si-NCs, which are different from that in the conventional poly-crystal Si or SONOS floating gate NVM devices. The surface-nitrided Si-NCs NVM devices show lower subthreshold swing value of 0.13 V/decade, faster P/E speed characteristics of 1 μs at ±7 V, and good retention characteristics at room temperature. Furthermore, due to the improvement of the tunneling oxide quality by nitridation treatment, the stable memory window of 1.7 V has been kept after 107 P/E cycles, showing superior endurance characteristics with the good retention characteristics. Our fabrication of surface-nitrided Si-NCs floating gate NVM is compatible with the standard CMOS technology, which may be employed in the 3-D NAND technology to further improve the device performance.
Transient thermal imaging of a vertical cavity surface-emitting laser using thermoreflectance microscopy
Authors: Garcia V. G. , Farzaneh M.
Published: January 2016

Thermal transient response at the surface of a Vertical Cavity Surface-emitting Laser (VCSEL) is measured under operating conditions using a thermoreflectance imaging technique. From the transient curve, a thermal time constant of (9.7 ± 0.5) μs is obtained for the device surface in response to a 40 μs heating pulse. A cross-plane thermal diffusivity of the order of 2 × 10−6 m2/s has been deduced from both the experimental data and heat transfer modeling. This reduced thermal diffusivity compared to the bulk is attributed to the enhanced phonon scattering at the boundaries of the VCSEL's multi-layered structure.
Magnetic-field dependence of Brownian and Néel relaxation times
Authors: Dieckhoff Jan , Eberbeck Dietmar , Schilling Meinhard , Ludwig Frank
Published: January 2016

The investigation of the rotational dynamics of magnetic nanoparticles in magnetic fields is of academic interest but also important for applications such as magnetic particle imaging where the particles are exposed to magnetic fields with amplitudes of up to 25 mT. We have experimentally studied the dependence of Brownian and Néel relaxation times on ac and dc magnetic field amplitude using ac susceptibility measurements in the frequency range between 2 Hz and 9 kHz for field amplitudes up to 9 mT. As samples, single-core iron oxide nanoparticles with core diameters between 20 nm and 30 nm were used either suspended in water-glycerol mixtures or immobilized by freeze-drying. The experimentally determined relaxation times are compared with theoretical models. It was found that the Néel relaxation time decays much faster with increasing field amplitude than the Brownian one. Whereas the dependence of the Brownian relaxation time on the ac and dc field amplitude can be well explained with existing theoretical models, a proper model for the dependence of the Néel relaxation time on ac field amplitude for particles with random distribution of easy axes is still lacking. The extrapolation of the measured relaxation times of the 25 nm core diameter particles to a 25 mT ac field with an empirical model predicts that the Brownian mechanism clearly co-determines the dynamics of magnetic nanoparticles in magnetic particle imaging applications, in agreement with magnetic particle spectroscopy data.
Responsivity enhancement of ZnO/Pt/MgZnO/SiO2 and MgZnO/Pt/ZnO/SiO2 structured ultraviolet detectors by surface plasmons in Pt nanoparticles
Authors: Sun Long , Jiang Dayong , Zhang Guoyu , Liu Rusheng , Duan Qian , Qin Jieming , Liang Qingcheng , Gao Shang , Hou Janhua , Zhao Jianxun , Liu Wanqiang , Shen Xiande
Published: January 2016

The structured (ZnO/Pt/MgZnO/SiO2) ultraviolet detector was fabricated and demonstrated to investigate how metallic nanoparticles localized surface plasmons contribute when the two different dielectrics surrounded simultaneously. After sandwiching the Pt nanoparticles between the double layers of MgZnO and ZnO, the extinction was increased largely. Meanwhile, by examining the dependence of MgZnO and ZnO peak responsivity enhancement ratio, we found that MgZnO was significantly larger than ZnO. The interpretation by considering is that the localized surface plasmons of energy match with MgZnO which is superior to ZnO. In order to validate this conclusion and make it more accurate, we also fabricated the MgZnO/Pt/ZnO/SiO2 structure. Our work suggests that rational integration of double-layer and metal nanoparticles is a viable approach to perceive localized surface plasmons with double-layer ultraviolet detectors, which may help to advance optoelectronic devices.
Hot carrier and hot phonon coupling during ultrafast relaxation of photoexcited electrons in graphene
Authors: Iglesias J. M. , Martín M. J. , Pascual E. , Rengel R.
Published: January 2016

We study, by means of a Monte Carlo simulator, the hot phonon effect on the relaxation dynamics in photoexcited graphene and its quantitative impact as compared with considering an equilibrium phonon distribution. Our multi-particle approach indicates that neglecting the hot phonon effect significantly underestimates the relaxation times in photoexcited graphene. The hot phonon effect is more important for a higher energy of the excitation pulse and photocarrier densities between 1 and 3 × 1012 cm−2. Acoustic intervalley phonons play a non-negligible role, and emitted phonons with wavelengths limited up by a maximum (determined by the carrier concentration) induce a slower carrier cooling rate. Intrinsic phonon heating is damped in graphene on a substrate due to the additional cooling pathways, with the hot phonon effect showing a strong inverse dependence with the carrier density.
An experimentally supported model for the origin of charge transport barrier in Zn(O,S)/CIGSSe solar cells
Authors: Chua Rou Hua , Li Xianglin , Walter Thomas , Teh Lay Kuan , Hahn Thomas , Hergert Frank , Mhaisalkar Subodh , Wong Lydia Helena
Published: January 2016

Zinc oxysulfide buffer layers with [O]:[S] of 1:0, 6:1, 4:1, 2:1, and 1:1 ratios were deposited by atomic layer deposition on Cu(In,Ga)(S,Se)2 absorbers and made into finished solar cells. We demonstrate using Time-Resolved Photoluminescence that the minority carrier lifetime of Zn(O,S) buffered solar cells is dependent on the sulfur content of the buffer layer. τ1 for devices with [O]:[S] of 1:0–4:1 are <10 ns, indicating efficient charge separation in devices with low sulfur content. An additional τ2 is observed for relaxed devices with [O]:[S] of 2:1 and both relaxed and light soaked devices with [O]:[S] of 1:1. Corroborated with one-dimensional electronic band structure simulation results, we attribute this additional decay lifetime to radiative recombination in the absorber due to excessive acceptor-type defects in sulfur-rich Zn(O,S) buffer layer that causes a buildup in interface-barrier for charge transport. A light soaking step shortens the carrier lifetime for the moderately sulfur-rich 2:1 device when excess acceptors are passivated in the buffer, reducing the crossover in the dark and illuminated I-V curves. However, when a high concentration of excess acceptors exist in the buffer and cannot be passivated by light soaking, as with the sulfur-rich 1:1 device, then cell efficiency of the device will remain low.
Spin dynamics, electronic, and thermal transport properties of two-dimensional CrPS4 single crystal
Authors: Pei Q. L. , Luo X. , Lin G. T. , Song J. Y. , Hu L. , Zou Y. M. , Yu L. , Tong W. , Song W. H. , Lu W. J. , Sun Y. P.
Published: January 2016

2-Dimensional (2D) CrPS4 single crystals have been grown by the chemical vapor transport method. The crystallographic, magnetic, electronic, and thermal transport properties of the single crystals were investigated by the room-temperature X-ray diffraction, electrical resistivity ρ(T), specific heat CP(T), and the electronic spin response (ESR) measurements. CrPS4 crystals crystallize into a monoclinic structure. The electrical resistivity ρ(T) shows a semiconducting behavior with an energy gap Ea = 0.166 eV. The antiferromagnetic transition temperature is about TN = 36 K. The spin flipping induced by the applied magnetic field is observed along the c axis. The magnetic phase diagram of CrPS4 single crystal has been discussed. The extracted magnetic entropy at TN is about 10.8 J/mol K, which is consistent with the theoretical value R ln(2S + 1) for S = 3/2 of the Cr3+ ion. Based on the mean-field theory, the magnetic exchange constants J1 and Jc corresponding to the interactions of the intralayer and between layers are about 0.143 meV and −0.955 meV are obtained based on the fitting of the susceptibility above TN, which agree with the results obtained from the ESR measurements. With the help of the strain for tuning the magnetic properties, monolayer CrPS4 may be a promising candidate to explore 2D magnetic semiconductors.
Frequency response of curved bilayer microcantilevers with applications to surface stress measurement
Authors: Najafi Sohi Ali , Nieva Patricia M.
Published: January 2016

Bilayer microcantilevers are normally curved because of fabrication-induced stresses. When used in biological/chemical sensing applications, the absorption of target agents onto the functionalized surface of the microcantilever creates a surface stress that shifts its resonance frequency. Despite numerous efforts, the mechanisms of surface stress-induced shift in the resonance frequency of microcantilevers remain elusive. To address this problem, this work presents a detailed analysis of the frequency response of microcantilevers, with different width-to-thickness ratios and curvature levels, using classical lamination theory and the Rayleigh–Ritz method. Based on the results of this analysis, a new relationship between resonance frequency shift and curvature variation due to differential surface stress loading is established. By comparing the strain energies associated with the in-plane and out-of-plane displacements of the microcantilever at different curvature levels, a new implicit model for surface stress-induced resonance frequency shift in microcantilevers is presented. Verified against the results of experiments carried out on gold/polysilicon microcantilevers, the new model is expected to provide a better understanding of surface stress-microcantilever resonator interaction, which is critical to systematic optimization of resonance-based micro sensors.
Effect of sputtering pressure on microstructure and bolometric properties of Nb:TiO2−x films for infrared image sensor applications
Authors: Reddy Y. Ashok Kumar , Shin Young Bong , Kang In-Ku , Lee Hee Chul
Published: January 2016

This study aims to investigate the influence of the sputtering pressure (PS) on Nb:TiO2−x films to enhance the bolometric properties. A decrease in the growth rate with the sputtering pressure was perceived in amorphous Nb:TiO2−x films. The incorporation of oxygen with PS was confirmed in an X-ray photo electron spectroscopy analysis. The electrical resistivity was increased with an increase in PS due to a decrease in the number of oxygen vacancies. The linear I-V characteristics confirmed the ohmic contact behavior between the Nb:TiO2−x layer and the electrode material. The present investigation finds that the sample with lower resistivity has good bolometric properties with low noise and high universal bolometric parameters. Finally, the Nb:TiO2−x sample deposited at a sputtering pressure of 2 mTorr shows better bolometric properties than other materials for infrared image sensor applications.
Influence of piezoelectric strain on the Raman spectra of BiFeO3 films deposited on PMN-PT substrates
Authors: Himcinschi Cameliu , Guo Er-Jia , Talkenberger Andreas , Dörr Kathrin , Kortus Jens
Published: January 2016

BiFeO3 epitaxial thin films were deposited on piezoelectric 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-PT) substrates with a conductive buffer layer (La0.7Sr0.3MnO3 or SrRuO3) using pulsed laser deposition. The calibration of the strain values induced by the electric field applied on the piezoelectric PMN-PT substrates was realised using X-Ray diffraction measurements. The method of piezoelectrically induced strain allows one to directly obtain a quantitative correlation between the strain and the shift of the Raman-active phonons. This is a prerequisite for making Raman scattering a strong tool to probe the strain coupling in multiferroic nanostructures. Using the Poisson's number for BiFeO3, one can determine the volume change induced by strain, and therefore the Grüneisen parameters for specific phonon modes.
A controllable IC-compatible thin-film fuse realized using electro-explosion
Authors: Ding Xuran , Lou Wenzhong , Feng Yue
Published: January 2016

A controllable IC-compatible thin-film fuse was developed that had Al/SiO2 thin-film stacks on a silicon substrate. The micro fuse has both a traditional mode and a controllable mode when applied as a fuse. It blows at 800 mA and 913.8 mV in the traditional mode. In the controllable mode, it blows within 400 ns at 10 V. It can be used for small electronic elements as well as electropyrotechnic initiators to improve the no-firing current.
A bioeconomic analysis of conserving freshwater values in an agricultural landscape
Authors: Warfe D. M. , Tisdell J. G.
Published: January 2016

Water is a finite resource that must be shared among multiple users and economic and conservation objectives can often be seen as being in conflict. We explored this perception by conducting an integrated bioeconomic analysis of irrigated agriculture and the conservation of freshwater attributes in an agricultural landscape, the Tasmanian Midlands. We constructed a simple bioeconomic model based on current hydrology, water allocation, land use and freshwater ecosystem values, and quantified the economic returns from irrigation under a range of future climate, agricultural development and conservation scenarios. We found that projected climate conditions and conserving freshwater values in good condition had small effects on economic returns to irrigators, and that enterprise diversity and the area irrigated were major drivers of economic returns in this landscape. The availability of land suitable for irrigation rather than irrigation water itself appeared most likely to limit the economic returns from irrigation in the future. We provide a multi-criteria analysis for comparing development and conservation scenarios at a regional scale to inform planning and decision making in conservation and natural resource management. Our approach brings irrigation and conservation concerns into the same context and demonstrates that conservation need not necessarily limit agricultural development.
Barrett’s Esophagus
Authors: Naini Bita V. , Souza Rhonda F. , Odze Robert D.
Published: January 2016

This review provides a summary of our current understanding of, and the controversies surrounding, the diagnosis, pathogenesis, histopathology, and molecular biology of Barrett’s esophagus (BE) and associated neoplasia. BE is defined as columnar metaplasia of the esophagus. There is worldwide controversy regarding the diagnostic criteria of BE, mainly with regard to the requirement to histologically identify goblet cells in biopsies. Patients with BE are at increased risk for adenocarcinoma, which develops in a metaplasia-dysplasia-carcinoma sequence. Surveillance of patients with BE relies heavily on the presence and grade of dysplasia. However, there are significant pathologic limitations and diagnostic variability in evaluating dysplasia, particularly with regard to the more recently recognized unconventional variants. Identification of non–morphology-based biomarkers may help risk stratification of BE patients, and this is a subject of ongoing research. Because of recent achievements in endoscopic therapy, there has been a major shift in the treatment of BE patients with dysplasia or intramucosal cancer away from esophagectomy and toward endoscopic mucosal resection and ablation. The pathologic issues related to treatment and its complications are also discussed in this review article.
Blood transcriptomes reveal novel parasitic zoonoses circulating in Madagascar's lemurs
Authors: Larsen Peter A. , Hayes Corinne E. , Williams Cathy V. , Junge Randall E. , Razafindramanana Josia , Mass Vanessa , Rakotondrainibe Hajanirina , Yoder Anne D.
Published: January 2016

Zoonotic diseases are a looming threat to global populations, and nearly 75% of emerging infectious diseases can spread among wildlife, domestic animals and humans. A ‘One World, One Health’ perspective offers us an ideal framework for understanding and potentially mitigating the spread of zoonoses, and the island of Madagascar serves as a natural laboratory for conducting these studies. Rapid habitat degradation and climate change on the island are contributing to more frequent contact among humans, livestock and wildlife, increasing the potential for pathogen spillover events. Given Madagascar's long geographical isolation, coupled with recent and repeated introduction of agricultural and invasive species, it is likely that a number of circulating pathogens remain uncharacterized in lemur populations. Thus, it is imperative that new approaches be implemented for de novo pathogen discovery. To this end, we used non-targeted deep sequencing of blood transcriptomes from two species of critically endangered wild lemurs (
Indri indri
and
Propithecus diadema
) to characterize blood-borne pathogens. Our results show several undescribed vector-borne parasites circulating within lemurs, some of which may cause disease in wildlife, livestock and humans. We anticipate that advanced methods for de novo identification of unknown pathogens will have broad utility for characterizing other complex disease transmission systems.
Queen pheromones modulate DNA methyltransferase activity in bee and ant workers
Authors: Holman Luke , Trontti Kalevi , Helanterä Heikki
Published: January 2016

DNA methylation is emerging as an important regulator of polyphenism in the social insects. Research has concentrated on differences in methylation between queens and workers, though we hypothesized that methylation is involved in mediating other flexible phenotypes, including pheromone-dependent changes in worker behaviour and physiology. Here, we find that exposure to queen pheromone affects the expression of two DNA methyltransferase genes in
Apis mellifera
honeybees and in two species of
Lasius
ants, but not in
Bombus terrestris
bumblebees. These results suggest that queen pheromones influence the worker methylome, pointing to a novel proximate mechanism for these key social signals.
Stretch-induced network reconfiguration of collagen fibres in the human facet capsular ligament
Authors: Zhang Sijia , Bassett Danielle S. , Winkelstein Beth A.
Published: January 2016

Biomaterials can display complex spatial patterns of cellular responses to external forces. Revealing and predicting the role of these patterns in material failure require an understanding of the statistical dependencies between spatially distributed changes in a cell's local biomechanical environment, including altered collagen fibre kinematics in the extracellular matrix. Here, we develop and apply a novel extension of network science methods to investigate how excessive tensile stretch of the human cervical facet capsular ligament (FCL), a common source of chronic neck pain, affects the local reorganization of collagen fibres. We define collagen alignment networks based on similarity in fibre alignment angles measured by quantitative polarized light imaging. We quantify the reorganization of these networks following macroscopic loading by describing the dynamic reconfiguration of network communities, regions of the material that display similar fibre alignment angles. Alterations in community structure occur smoothly over time, indicating coordinated adaptation of fibres to loading. Moreover, flexibility, a measure of network reconfiguration, tracks the loss of FCL's mechanical integrity at the onset of anomalous realignment (AR) and regions of AR display altered community structure. These findings use novel network-based techniques to explain abnormal collagen fibre reorganization, a dynamic and coordinated multivariate process underlying tissue failure.
Non-dimensional physics of pulsatile cardiovascular networks and energy efficiency
Authors: Yigit Berk , Pekkan Kerem
Published: January 2016

In Nature, there exist a variety of cardiovascular circulation networks in which the energetic ventricular load has bothsteadyandpulsatilecomponents. Steady load is related to the mean cardiac output (CO) and the haemodynamic resistance of the peripheral vascular system. On the other hand, the pulsatile load is determined by the simultaneous pressure and flow waveforms at the ventricular outlet, which in turn are governed through arterial wave dynamics (transmission) and pulse decay characteristics (windkessel effect). Both the steady and pulsatile contributions of the haemodynamic power load are critical for characterizing/comparing disease states and for predicting the performance of cardiovascular devices. However, haemodynamic performance parameters vary significantly from subject to subject because of body size, heart rate and subject-specific CO. Therefore, a ‘normalized’ energy dissipation index, as a function of the ‘non-dimensional’ physical parameters that govern the circulation networks, is needed for comparative/integrative biological studies and clinical decision-making. In this paper, a complete network-independent non-dimensional formulation that incorporates pulsatile flow regimes is developed. Mechanical design variables of cardiovascular flow systems are identified and the Buckingham Pi theorem is formally applied to obtain the corresponding non-dimensional scaling parameter sets. Two scaling approaches are considered to address both the lumped parameter networks and the distributed circulation components. The validity of these non-dimensional number sets is tested extensively through the existing empirical allometric scaling laws of circulation systems. Additional validation studies are performed using a parametric numerical arterial model that represents the transmission and windkessel characteristics, which are adjusted to represent different body sizes and non-dimensional haemodynamic states. Simulations demonstrate that the proposed non-dimensional indices are independent of body size for healthy conditions, but are sensitive to deviations caused by off-design disease states that alter the energetic load. Sensitivity simulations are used to identify the relationship between pulsatile power loss and non-dimensional characteristics, and optimal operational states are computed.
Large-scale signatures of unconsciousness are consistent with a departure from critical dynamics
Authors: Tagliazucchi Enzo , Chialvo Dante R. , Siniatchkin Michael , Amico Enrico , Brichant Jean-Francois , Bonhomme Vincent , Noirhomme Quentin , Laufs Helmut , Laureys Steven
Published: January 2016

Loss of cortical integration and changes in the dynamics of electrophysiological brain signals characterize the transition from wakefulness towards unconsciousness. In this study, we arrive at a basic model explaining these observations based on the theory of phase transitions in complex systems. We studied the link between spatial and temporal correlations of large-scale brain activity recorded with functional magnetic resonance imaging during wakefulness, propofol-induced sedation and loss of consciousness and during the subsequent recovery. We observed that during unconsciousness activity in frontothalamic regions exhibited a reduction of long-range temporal correlations and a departure of functional connectivity from anatomical constraints. A model of a system exhibiting a phase transition reproduced our findings, as well as the diminished sensitivity of the cortex to external perturbations during unconsciousness. This framework unifies different observations about brain activity during unconsciousness and predicts that the principles we identified are universal and independent from its causes.
‘Dirty work’, but someone has to do it: Howard P. Robertson and the refereeing practices of
Physical Review
in the 1930s
Authors: Lalli Roberto
Published: January 2016

In the 1930s the mathematical physicist Howard P. Robertson was the main referee of the journal
Physical Review
for papers concerning general relativity and related subjects. The rich correspondence between Robertson and the editors of the journal enables a historical investigation of the refereeing process of
Physical Review
at the time that it was becoming one of the most influential physics periodicals in the world. By focusing on this case study, the paper investigates two complementary aspects of the evolution of the refereeing process: first, the historical evolution of the refereeing practices in connection with broader contextual changes, and second, the attempts to define the activity of the referee, including the epistemic virtues required and the journal's functions according to the participants' categories. By exploring the tension between Robertson's idealized picture about how the referee should behave and the desire to promote his intellectual agenda, I show that the evaluation criteria that Robertson employed were contextually dependent and I argue that, in the 1930s, through his reports the referee had an enormous power in defining what direction future research should take.
Leaf processing behaviour in
Atta
leafcutter ants: 90% of leaf cutting takes place inside the nest, and ants select pieces that require less cutting
Authors: Garrett Ryan W. , Carlson Katherine A. , Goggans Matthew Scott , Nesson Michael H. , Shepard Christopher A. , Schofield Robert M. S.
Published: January 2016

Leafcutter ants cut trimmings from plants, carry them to their underground nests and cut them into smaller pieces before inoculating them with a fungus that serves as a primary food source for the colony. Cutting is energetically costly, so the amount of cutting is important in understanding foraging energetics. Estimates of the cutting density, metres of cutting per square metre of leaf, were made from samples of transported leaf cuttings and of fungal substrate from field colonies of
Atta cephalotes
and
Atta colombica
. To investigate cutting inside the nest, we made leaf-processing observations of our laboratory colony,
A. cephalotes
. We did not observe the commonly reported reduction of the leaf fragments into a pulp, which would greatly increase the energy cost of processing. Video clips of processing behaviours, including behaviours that have not previously been described, are linked. An estimated 2.9 (±0.3) km of cutting with mandibles was required to reduce a square metre of leaf to fungal substrate. Only about 12% (±1%) of this cutting took place outside of the nest. The cutting density and energy cost is lower for leaf material with higher ratios of perimeter to area, so we tested for, and found that the laboratory ants had a preference for leaves that were pre-cut into smaller pieces. Estimates suggest that the energy required to transport and cut up the leaf material is comparable to the metabolic energy available from the fungus grown on the leaves, and so conservation of energy is likely to be a particularly strong selective pressure for leafcutter ants.
An anisotropic, viscoplastic power law for face-centred cubic crystals: comparative evaluations in the Goss and Brass orientations of channel die compression
Authors: Havner Kerry S.
Published: January 2016

An anisotropic, viscoplastic power law is introduced and applied to analysis of the Goss and Brass orientations, and compared with predictions from rate-independent theory and experiment. The structure of the new power law is so chosen that it has the capability of approaching rate-independent results for lattice rotation and crystal shearing, after finite rotation about the load axis, in the range of unstable lattice orientations in (110) channel die compression. (Rate-independent predictions of shear and lattice rotation are in good to very good agreement with experiments on aluminium and copper in that range, whereas classicisotropicpower-law results are not.) It is established that, for sufficiently large power-law exponentn, the new anisotropic, elasto-viscoplastic theory predicts: (i) lattice stability in each of the Goss and Brass orientations, consistent with both experiment and rate-independent theory; (ii) zero crystal shear in the Goss orientation, also consistent with both; (iii) finite shear in the Brass orientation, in very good agreement with experiment and rate-independent theory; and (iv) a lateral-constraint stress that remains essentially elastic in both orientations, as predicted by rate-independent theory and close to experimental measurements for aluminium and copper in the Brass orientation.