Directed recurrence networks for the analysis of nonlinear and complex dynamical systems.

Complex network approaches have been emerging as an analysis tool for dynamical systems. Different reconstruction methods from time series have been shown to reveal complicated behaviors that can be quantified from the network's topology. Directed recurrence networks have recently been suggested as one such method, complementing the already successful recurrence networks and expanding the applications of recurrence analysis.

A bottom-up approach for recurrence detection based on sampling distance.

One of the major problems faced in the recurrence analysis of dynamical systems is the tangential motion effect affecting the structures in recurrence plots and their quantification. This issue roots to the choice of a threshold for recurrence, making it a crucial parameter for such analyses. It has been shown that a variable threshold following the dynamical changes of the system is more suited to the analysis of non-stationary data as it mitigates this effect.

Directed recurrence networks.

Complex network approaches have attracted a growing interest in the analysis of nonlinear time series. Among other reconstruction methods, it has been shown that the recurrence plot can be used as the adjacency matrix for recurrence networks, expanding the applications of the already successful recurrence analysis. We study here the potential benefits of a directed formulation of recurrence networks through a simple modification of the recurrence plot.

A variable threshold for recurrence based on local attractor density.

Recurrence plots along with their quantification measures have demonstrated their usefulness for the study of dynamical systems in many fields. The distance threshold for recurrence is a crucial parameter influencing the observed recurrence structures, thus, the related quantification measures, and have been the object of several studies to find its optimal value. We suggest here a definition of recurrence based on the local attractor density to obtain more qualitative recurrence plots capturing the dynamics at different scales without suffering from variations in the tangential motion effect.

Nanometer-precise optical length measurement using near-field scanning optical microscopy with sharpened single carbon nanotube probe.

We have developed and characterized a plasmon-excitation scattering-type near-field scanning optical microscope with sharpened single carbon nanotube probe. The developed microscope can optically capture differences in the refractive index of single-nanometer surface structures. Statistical analysis enabled us to estimate the precision of the optical length measurement to 1.

Refilling of carbon nanotube cartridges for 3D nanomanufacturing.

Metal-filled carbon nanotubes (CNTs) are known to be used as pen-tip injectors for 3D manufacturing on the nanoscale. However, the CNT interior cannot accumulate enough material to fabricate complex metallic nanostructures. Therefore a method for refilling the CNT cartridge needs to be developed.

Three-dimensional evaluation of an independent multi-walled carbon nanotube probe by tomography with high-resolution transmission electron microscope.

We evaluated an independent multi-walled carbon nanotube (MWNT) probe by using tomography with a high-resolution transmission electron microscope to verify the three-dimensional structure of the probe tip. The new method of probe evaluation revealed the following features: (i) cutting the end of the MWNT probe caused the wall structure to disintegrate and encapsulated the graphene sheets fragmented by the discharged pulse; (ii) the cap of the MWNT probe was an open cylinder covered by walls similar in shape to a rectangular slit; (iii) the grooves of the inner walls of the MWNT probe, which were created by the discharge cutting method, maintained a cylindrical shape that was different from the peeling-off mechanism.

Ultracompact and highly sensitive common-path phase-shifting interferometer using photonic crystal polarizers as a reference mirror and a phase shifter.

We present a common-path phase-shifting interferometer in which photonic crystal polarizers (PCPs) are utilized as a reference mirror and a phase shifter, allowing ultracompact and highly sensitive optics. When a laser beam polarized at 45 degrees relative to the optical axis of the PCp-based reference mirror is incident, the polarization component parallel to the optical axis (s-polarized beam) is reflected and used as a reference beam. The perpendicular component (p-polarized beam) passes through the PCP coupled with a quarter-wave plate (QWP) and serves as a probe beam.

Simulation of photoacoustic imaging of microcracks in silicon wafers using a structure-changeable multilayered thermal diffusion model.

The detection characteristics for photoacoustic imaging of microcracks in silicon wafers were theoretically and quantitatively investigated using a numerical simulation. The simulation is based on a one-dimensional multilayered thermal diffusion model coupled with the thermal-wave impedance of each layer, the layer structures of which are constructed along the wafer surface and are variable according to the scanning position of the point heat source. As the modulation frequency was reduced, the spatial resolution of the temperature amplitude profile at the cracks decreased, showing good agreement with the experimentally obtained photoacoustic amplitude images.

General solution of undersampling frequency conversion and its optimization for parallel photodisplacement imaging.

A general solution of undersampling frequency conversion and its optimization for parallel photodisplacement imaging is presented. Phase-modulated heterodyne interference light generated by a linear region of periodic displacement is captured by a charge-coupled device image sensor, in which the interference light is sampled at a sampling rate lower than the Nyquist frequency. The frequencies of the components of the light, such as the sideband and carrier (which include photodisplacement and topography information, respectively), are downconverted and sampled simultaneously based on the integration and sampling effects of the sensor.

Real-time photodisplacement microscope for high-sensitivity simultaneous surface and subsurface inspection.

We have developed a new photodisplacement microscope system for practical use that achieves high-sensitivity simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram. In this system a linear region of photothermal displacement is excited on the sample surface for subsurface imaging by a line-focused intensity-modulated laser beam. Surface information such as reflectivity and topography along with the displacement is detected with a charge-coupled device sensor-based parallel heterodyne interferometer.

Simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed photodisplacement interferogram.

A new parallel photodisplacement technique has been developed that achieves simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram, which greatly simplifies the system and the optical alignment. A linear region of photodisplacement is excited on the sample for subsurface imaging by use of a line-focused intensity-modulated laser beam, and the displacement and surface information on reflectivity and topography are detected by a parallel heterodyne interferometer with a charge-coupled device linear image sensor used as a detector. The frequencies of three control signals for excitation and detection, that is, the heterodyne beat signal, modulation signal, and sensor gate pulse, are optimized such that surface and subsurface information components are space-frequency multiplexed into the sensor signal as orthogonal functions, allowing each to be discretely reproduced from Fourier coefficients.

Practical realization of high-speed photodisplacement imaging by use of parallel excitation and parallel heterodyne detection: a numerical study.

A new parallel photodisplacement technique that achieves extremely high-throughput imaging is proposed, and its practical realization is studied numerically. In this technique, a linear region of photothermal displacement is excited by use of a line-focusing intensity-modulated laser beam and detected with a parallel heterodyne interferometer in which a charge-coupled device linear image sensor is used. Because of the integration and sampling effects of the sensor, the interference light is spatiotemporally multiplexed.