Static and dynamic magnetic properties of densely packed magnetic nanowire arrays

PublishedJournal ArticleThe static and dynamic magnetic properties of magnetic nanowire arrays with high packing density (>0.4) and wire diameter much greater than the exchange length have been studied by static and time-resolved magneto-optical Kerr effect measurements and micromagnetic simulations. The nanowires were formed by electrodeposition within a nanoporous template such that their symmetry axes lay normal to the plane of the substrate. A quantitative and systematic investigation has been made of the static and dynamic properties of the array, which lie between the limiting cases of a single wire and a continuous ferromagnetic thin film. In particular, the competition between anisotropies associated with the shape of the individual nanowires and that of the array as a whole has been studied. Measured and simulated hysteresis loops are largely anhysteretic with zero remanence, and the micromagnetic configuration is such that the net magnetization vanishes in directions orthogonal to the applied field. Simulations of the remanent state reveal antiferromagnetic alignment of the magnetization in adjacent nanowires and the formation of vortex flux closure structures at the ends of each nanowire. The excitation spectra obtained from experiment and micromagnetic simulations are in qualitative agreement for magnetic fields applied both parallel and perpendicular to the axes of the nanowires. For the field parallel to the nanowire axes, there is also good quantitative agreement between experiment and simulation. The resonant frequencies are initially found to decrease as the applied field is increased from remanence. This is the result of a change of mode profile within the plane of the array from nonuniform to uniform as the ground state evolves with increasing applied field. Quantitative differences between experimental and simulated spectra are observed when the field is applied perpendicular to the nanowire axes. The dependence of the magnetic excitation spectra upon the array packing density is explored, and dispersion curves for spin waves propagating within the array parallel to the nanowire axis are presented. Finally, a tunneling of end modes through the middle region of the nanowires was observed. The tunneling is more efficient for wires forming densely packed arrays, as a result of the extended penetration of the dynamic demagnetizing fields into the middle of the wires and due to the lowering of the tunneling barrier by the static demagnetizing field of the array. © 2013 American Physical Society.The authors gratefully acknowledge the assistance of V.-A. Antohe and S. Tuilard with sample fabrication and M. Dvornik, M. Franchin, and H. Fangohr with micromagnetic simulations. The financial support from the European Community’s Seventh Framework Programme (FP7/2007-2013) under Grant Agreements No. 212257 MASTER (fabrication and experiment) and No. 233552 DYNAMAG (simulations) is gratefully acknowledged. We also gratefully acknowledge financial support from a UKIERI-DST standard research award (Grants No. SA 07-021 and No. DST/INT/UKIERI/SA/P- 2/2008) for travel between S. N. B. N. C. B. S., India, and the University of Exeter, United Kingdom. Finally, V.V.K. gratefully acknowledges funding received from the U.K. Engineering and Physical Sciences Research Council Project No. EP/E055087/1

GENERA KARANG KERAS DI PULAU BARRANG LOMPO DAN BONE BATANG BERDASARKAN METODE IDENTIFIKASI CORAL FINDER

Penelitian tentang “Genera Karang Keras Di Pulau Barranglompo Dan Bonebatang Berdasarkan Metode Identifikasi Coral Finder” telah dilakukan pada bulan Januari hingga April 2016. Penelitian ini bertujuan mengetahui variasi genera karang keras yang ada di Pulau Barranglompo dan Pulau Bonebatang. Pengambilan data dilakukan dengan metode “Line Intercept Transect (LIT)”, di sisi selatan, barat dan utara masing – masing pada kedalaman 3 dan 10 m. Penentuan genera karang dilakukan berdasarkan metode identifikasi Coral Finder. Hasil penelitian menunjukkan bahwa pada kedalaman 3 m genera karang yang ditemukan di Pulau Bonebatang (31 genera) lebih banyak dibandingkan dengan Pulau Barranglompo (24 genera). Kondisi sebaliknya ditemukan pada pada kedalaman 10 m jumlah genera karang di Pulau Barranglompo (29 genera) lebih tinggi dibandingkan dengan Pulau Bonebatang (27 genera). Genera yang paling umum ditemukan pada kedalaman 3 m di Barranglompo yaitu Acropora, Fungia,dan Porites. Sedangkan di Pulau Bonebatang ditemukan pada genera Ctenactis, Fungia, Pachyseris danPorites. Pada kedalaman 10 m, genera karang yang paling dominan di Pulau Barranglompo adalah Acropora dan Fungia. Sedangkan di Pulau Bonebatang didominasi olehAcropora, Fungia, dan Seriatopora. Dampak antropogenik di Pulau Barranglompo didominasi oleh pembuangan sampah sedangkan Pulau Bonebatang dipengaruhi oleh aktifitas pengeboman ikan. Kata Kunci: Genera Karang, Coral Finder Pulau Barranglompo, Pulau Bonebatang, Spermonde

Thermally induced magnetization dynamics of optically excited YIG/Cu/Ni81Fe19 trilayers

This is the final version of the article. Available from American Physical Society via the DOI in this record.The response of Y3Fe5O12/Cu/Ni81Fe19 trilayer structures to excitation by a femtosecond laser pulse has been studied in optical pump-probe experiments and compared with the response of Y3Fe5O12 (YIG) and Ni81Fe19 reference samples. The optical pump induces a partial demagnetization of the Ni81Fe19, a large thermal gradient within the YIG, and temperature differences across the interfaces within the sample stack. When a moderate magnetic field is applied close to normal to the sample plane, so as to quasialign the YIG magnetization with the field and cant the Ni81Fe19 magnetization from the plane, ultrafast demagnetization initiates precession of the Ni81Fe19 magnetization. The transient temperature profile within the samples has been modeled using a one-dimensional finite-element computational model of heat conduction, while the magnetization dynamics are well described by a macrospin solution of the Landau-Lifshitz-Gilbert equation. The precessional response of the Ni81Fe19 layers within the trilayers and the Ni81Fe19 reference sample are very similar for pump fluences of up to 1.5 mJ/cm2, beyond which irreversible changes to the magnetic properties of the films are observed. These results suggest that the spin Seebeck effect is ineffective in modifying the precessional dynamics of the present YIG/Cu/Ni81Fe19 samples when subject to ultrafast optical excitation.The authors gratefully acknowledge financial support from Engineering and Physical Sciences Research Council Grant No. EP/J018767/1 and an EPSRC CASE award with Dr. D. Williams of Hitachi Cambridge. H.J.M. acknowledges financial support in the form of a scholarship from “The Establishment of Martyrs of Iraq.

Performance Testing of Aero-Naut CAMFolding Propellers

The increase in popularity of unmanned aerial vehicles (UAVs) has been driven by their use in civilian, education, government, and military applications. However, limited on-board energy storage significantly limits flight time and ultimately usability. The propulsion system plays a critical part in the overall energy consumption of the UAV; therefore, it is necessary to determine the most optimal combination of possible propulsion system components for a given mission profile, i.e. propellers, motors, and electronic speed controllers (ESC). Hundreds of options are available for the different components with little performance specifications available for most of them. By examining a variety of existing long-endurance aircraft, Aero-Naut CAM carbon folding propellers were identified as the most commonly used type of commercial-off-the-shelf propeller. However, no performance data exist in the open literature for the Aero-Naut CAM carbon folding propellers. This paper describes the performance testing of 40 Aero-Naut CAM carbon propellers in 2-blade configuration with diameters of 9 to 16 in with various pitch values. The propellers were tested at rotation rates of 3,000 to 7,000 RPM and advancing flows of 8 to 80 ft/s, depending on the propeller and testing equipment limitations. Results are presented for the 40 propellers tested under static and advancing flow conditions with several key observations being discussed. The data produced will be available for download on the UIUC Propeller Data Site and on the Unmanned Aerial Vehicle Database

Iterative Distribution-Aware Sampling for Probabilistic Symbolic Execution

Probabilistic symbolic execution aims at quantifying the probability of reaching program events of interest assuming that program inputs follow given probabilistic distributions. The technique collects constraints on the inputs that lead to the target events and analyzes them to quantify how likely it is for an input to satisfy the constraints. Current techniques either handle only linear constraints or only support continuous distributions using a “discretization” of the input domain, leading to imprecise and costly results. We propose an iterative distribution-aware sampling approach to support probabilistic symbolic execution for arbitrarily complex mathematical constraints and continuous input distributions. We follow a compositional approach, where the symbolic constraints are decomposed into sub-problems whose solution can be solved independently. At each iteration the convergence rate of the com- putation is increased by automatically refocusing the analysis on estimating the sub-problems that mostly affect the accuracy of the results, as guided by three different ranking strategies. Experiments on publicly available benchmarks show that the proposed technique improves on previous approaches in terms of scalability and accuracy of the results