14,061 research outputs found
Collective spin waves in arrays of Permalloy nanowires with single-side periodically modulated width
We have experimentally and numerically investigated the dispersion of
collective spin waves prop-agating through arrays of longitudinally magnetized
nanowires with periodically modulated width. Two nanowire arrays with
single-side modulation and different periodicity of modulation were studied and
compared to the nanowires with homogeneous width. The spin-wave dispersion,
meas-ured up to the third Brillouin zone of the reciprocal space, revealed the
presence of two dispersive modes for the width-modulated NWs, whose amplitude
of magnonic band depends on the modula-tion periodicity, and a set of
nondispersive modes at higher frequency. These findings are different from
those observed in homogeneous width NWs where only the lowest mode exhibits
sizeable dis-persion. The measured spin-wave dispersion has been satisfactorily
reproduced by means of dynam-ical matrix method. Results presented in this work
are important in view of the possible realization of frequency tunable magnonic
device
Heterogeneous feature space based task selection machine for unsupervised transfer learning
Ā© 2015 IEEE. Transfer learning techniques try to transfer knowledge from previous tasks to a new target task with either fewer training data or less training than traditional machine learning techniques. Since transfer learning cares more about relatedness between tasks and their domains, it is useful for handling massive data, which are not labeled, to overcome distribution and feature space gaps, respectively. In this paper, we propose a new task selection algorithm in an unsupervised transfer learning domain, called as Task Selection Machine (TSM). It goes with a key technical problem, i.e., feature mapping for heterogeneous feature spaces. An extended feature method is applied to feature mapping algorithm. Also, TSM training algorithm, which is main contribution for this paper, relies on feature mapping. Meanwhile, the proposed TSM finally meets the unsupervised transfer learning requirements and solves the unsupervised multi-task transfer learning issues conversely
Bypassing the structural bottleneck in the ultrafast melting of electronic order
The emergent properties of quantum materials, such as symmetry-broken phases
and associated spectral gaps, can be effectively manipulated by ultrashort
photon pulses. Impulsive optical excitation generally results in a complex
non-equilibrium electron and lattice dynamics that involves multiple processes
on distinct timescales, and a common conception is that for times shorter than
about 100 fs the gap in the electronic spectrum is not seriously affected by
lattice vibrations. Here, we directly monitor the photo-induced collapse of the
spectral gap in a canonical charge-density-wave material, blue bronze
Rb0.3MoO3. We find that ultra-fast (about 60 fs) vibrational disordering due to
efficient hot-electron energy dissipation quenches the gap significantly faster
than the typical structural bottleneck time corresponding to one half-cycle
oscillation (about 315 fs) of the coherent charge-density-wave amplitude mode.
This result not only demonstrates the importance of incoherent lattice motion
in the photo-induced quenching of electronic order, but also resolves the
perennial debate about the nature of the spectral gap in a coupled
electron-lattice system
Mapping repetitive structural tunnel environments for a biologically-inspired climbing robot
Ā© 2015, World Scientific Publishing Co. Pte Ltd. All rights reserved. This paper presents an approach to using noisy and incomplete depth-camera datasets to detect reliable surface features for use in map construction for a caterpillar-inspired climbing robot. The approach uses a combination of plane extraction, clustering and template matching techniques to infer from the restricted dataset a usable map. This approach has been tested in both laboratory and real-world steel bridge tunnel datasets generated by a climbing robot, with the results showing that the generated maps are accurate enough for use in localisation and step trajectory planning
Mystery of Excess Low Energy States in a Disordered Superconductor in a Zeeman Field
Tunneling density of states measurements of disordered superconducting (SC)
Al films in high Zeeman fields reveal a significant population of subgap states
which cannot be explained by standard BCS theory. We provide a natural
explanation of these excess states in terms of a novel disordered
Larkin-Ovchinnikov (dLO) phase that occurs near the spin-paramagnetic
transition at the Chandrasekhar-Clogston critical field. The dLO superconductor
is characterized by a pairing amplitude that changes sign at domain walls.
These domain walls carry magnetization and support Andreev bound states, which
lead to distinct spectral signatures at low energy.Comment: 5 pages, 4 figures, plus supplementary section describing methods (2
pages
Tuning and Locking the Localized Surface Plasmon Resonances of CuS (Covellite) Nanocrystals by an Amorphous CuPdxS Shell
[Image: see text] We demonstrate the stabilization of the localized surface plasmon resonance (LSPR) in a semiconductor-based coreāshell heterostructure made of a plasmonic CuS core embedded in an amorphous-like alloyed CuPd(x)S shell. This heterostructure is prepared by reacting the as-synthesized CuS nanocrystals (NCs) with Pd(2+) cations at room temperature in the presence of an electron donor (ascorbic acid). The reaction starts from the surface of the CuS NCs and proceeds toward the center, causing reorganization of the initial lattice and amorphization of the covellite structure. According to density functional calculations, Pd atoms are preferentially accommodated between the bilayer formed by the SāS covalent bonds, which are therefore broken, and this can be understood as the first step leading to amorphization of the particles upon insertion of the Pd(2+) ions. The position and intensity in near-infrared LSPRs can be tuned by altering the thickness of the shell and are in agreement with the theoretical optical simulation based on the MieāGans theory and Drude model. Compared to the starting CuS NCs, the amorphous CuPd(x)S shell in the coreāshell nanoparticles makes their plasmonic response less sensitive to a harsh oxidation environment (generated, for example, by the presence of I(2))
Pillared two-dimensional metal-organic frameworks based on a lower-rim acid appended calix[4]arene
Solvothermal reactions of the lower-rim functionalized diacid calix[4]arene 25,27-bis(methoxycarboxylic acid)-26,28-dihydroxy-4-tert-butylcalix[4]arene (LHā) with Zn(NOā)āā¢6HāO and the dipyridyl ligands 4,4/-bipyridyl (4,4/-bipy), 1,2-di(4-pyridyl)ethylene (DPE) or 4,4/-azopyridyl (4,4/-azopy) afforded a series of 2-D structures of the formulae {[Zn(4,4/-bipy)(L)]ā¢2Ā¼DEF}n (1), {[Znā(L)(DPE)]ā¢DEF}n (2) and {[Zn(OHā)ā(L)(4,4/-azopy)]ā¢DEF}n (3) (DEF = diethylformamide)
In-situ marginalisation : social impact of Chinese mega-projects
This study offers a detailed analysis of an underāresearched social problem of ināsitu marginalisation and its causes by drawing on the concept of state entrepreneurialism. Our empirical data stem from the Lingang mega project in Shanghai and one of its neighbourhoods named Neighbourhood No.57 where we find that the residents have not been relocated but are instead suffering from declining public services and environmental quality from surrounding industrial developments. The root cause of this problem is the municipal governmentās prioritisation of its strategic objectives of economic development over the livelihood of local residents. The strategic vision of the municipality has led to mass relocation in its early phases of development but in its later stages leaves many residents waiting for relocation whilst being gradually surrounded by industrial developments. Despite continued residential complaints and petitions, ināsitu marginalisation is not resolved due to the institutional arrangement of Lingang, which has centralised planning and financing powers to newly created projectāoriented state organisation. Social responsibilities have been relegated to lowerātiered governments in Lingang which have neither planning power nor the financial resources to resolve the problems of residents. By examining the case of Lingang, this paper provides a different analytical framework for explaining the social problems emerging from Chinaās mega urban developments
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