Detecting and quantifying temporal correlations in stochastic resonance via information theory measures

We show that Information Theory quantifiers are suitable tools for detecting and for quantifying noise-induced temporal correlations in stochastic resonance phenomena. We use the Bandt & Pompe (BP) method [Phys. Rev. Lett. 88, 174102 (2002)] to define a probability distribution, P, that fully characterizes temporal correlations. The BP method is based on a comparison of neighboring values, and here is applied to the temporal sequence of residence-time intervals generated by the paradigmatic model of a Brownian particle in a sinusoidally modulated bistable potential. The probability distribution P generated via the BP method has associated a normalized Shannon entropy, H[P], and a statistical complexity measure, C[P], which is defined as proposed by Rosso et al. [Phys. Rev. Lett. 99, 154102 (2007)]. The statistical complexity quantifies not only randomness but also the presence of correlational structures, the two extreme circumstances of maximum knowledge (“perfect order") and maximum ignorance (“complete randomness") being regarded an “trivial", and in consequence, having complexity C = 0. We show that both, H and C, display resonant features as a function of the noise intensity, i.e., for an optimal level of noise the entropy displays a minimum and the complexity, a maximum. This resonant behavior indicates noise-enhanced temporal correlations in the sequence of residence-time intervals. The methodology proposed here has great potential for the precise detection of subtle signatures of noise-induced temporal correlations in real-world complex signals.     

Temporal superresolution based on spectral decomposition of light signals

It is shown that in studies of the temporal characteristics of light signals it is possible to go beyond the limitations due to the temporal resolution of the electron-optical apparatus employed. For this, it is first necessary to perform an optical transformation of the initial radiation, and the results of the measurements must be processed by a special mathematical procedure. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 924–927 (25 June 1996)     

Real-time cardiac magnetic resonance cine imaging with sparse sampling and iterative reconstruction for left-ventricular measures: Comparison with gold-standard segmented steady-state free precession

BackgroundSegmented cine imaging with a steady-state free-precession sequence (Cine-SSFP) is currently the gold standard technique for measuring ventricular volumes and mass, but due to multi breath-hold (BH) requirements, it is prone to misalignment of consecutive slices, time consuming and dependent on respiratory capacity. Real-time cine avoids those limitations, but poor spatial and temporal resolution of conventional sequences has prevented its routine application. We sought to examine the accuracy and feasibility of a newly developed real-time sequence with aggressive under-sampling of k-space using sparse sampling and iterative reconstruction (Cine-RT).MethodsStacks of short-axis cines were acquired covering both ventricles in a 1.5 T system using gold standard Cine-SSFP and Cine-RT. Acquisition parameters for Cine-SSFP were: acquisition matrix of 224 × 196, temporal resolution of 39 ms, retrospective gating, with an average of 8 heartbeats per slice and 1–2 slices/BH. For Cine-RT: acquisition matrix of 224 × 196, sparse sampling net acceleration factor of 11.3, temporal resolution of 41 ms, prospective gating, real-time acquisition of 1 heart-beat/slice and all slices in one BH. LV contours were drawn at end diastole and systole to derive LV volumes and mass.ResultsForty-one consecutive patients (15 male; 41 ± 17 years) in sinus rhythm were successfully included. All images from Cine-SSFP and Cine-RT were considered to have excellent quality. Cine-RT-derived LV volumes and mass were slightly underestimated but strongly correlated with gold standard Cine-SSFP. Inter- and intra-observer analysis presented similar results between both sequences.ConclusionsCine-RT featuring sparse sampling and iterative reconstruction can achieve spatial and temporal resolution equivalent to Cine-SSFP, providing excellent image quality, with similar precision measurements and highly correlated and only slightly underestimated volume and mass values.     

Relaxation of radiative defects in irradiated triglycine sulfate

Nonmonotonic temporal behavior of the temperature dependence of the conductivity of ferroelectric triglycine sulfate is observed after its irradiation by small doses of x radiation. Such behavior is associated primarily with the formation of two types of radiation defects having different lifetimes. Fiz. Tverd. Tela (St. Petersburg) 40, 116–117 (January 1998)     

Temporal Intracavity Absorbance Determination Using Pulsed Ti: Sapphire Laser

Abstract

A tunable pulsed Ti: Sapphire laser was used to determine low concentrations using intracavity absorption spectroscopy with temporal resolution. The dependence of the laser-pulse evolution time on the absorbance of a sample introduced in the cavity (solution of 3,3-diethylthiatricarbocyanine iodide in dimethylsulphoxide) was studied theoretically and experimentally. The minimal experimentally measured absorbance was 8×10^?4. The possibility was shown of using a Ti:S laser to detect absorbance of 10^?5 via a temporal technique.     

Nonlinear propagation of light in semiconductors in the presence of two-photon excitation of biexcitons

The steady-and nonsteady-state passage of light through a ring resonator in the presence of two-photon excitation of biexcitons from the ground state of the crystal is studied. The values of the parameters for which complicated nonlinear temporal formations are possible in the system are found. The possibility of observing the predicted effects experimentally is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1999–2002 (November 1998)     

Formation of a high-current discharge plasma in metal vapor

A method of converting the energy of a capacitive store into the energy of a high-current gas discharge in aluminum vapor is investigated. The spatial and temporal characteristics of the gas-discharge plasma are studied. The electron temperature, density of charged particles, and conductivity of the plasma are determined. Zh. Tekh. Fiz. 69, 134–137 (November 1999)     

Sources of acoustoelectric conversion in concretes

Acoustoelectric conversion in concretes is investigated by physical modeling methods. It is shown by means of equivalent circuit calculations of the electric field in the sample-detector system that the surface of the sample has no effect on the parameters of the signal. An investigation of the temporal and spectral characteristics of acoustoelectric conversion in model and real concretes confirms the calculations. Zh. Tekh. Fiz. 69, 51–55 (October 1999)     

Evaluation of abdominal hemodynamics through compressed sensing accelerated functional imaging

PurposeTo compare the imaging characteristics of the volumetric-interpolated breath-hold examination (VIBE) using compressed-sensing (CS) acceleration (CS-VIBE) with the conventional sequence relying on parallel imaging to assess the potential use of CS-VIBE as a functional imaging technique for upper abdominal haemodynamics.Materials and methodsPatients (30 men, 27 women) suspected of having a hepatic disease underwent magnetic resonance imaging (MRI) of the liver, including a dynamic contrast-enhanced study. Gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid was used as the contrast agent. MRI data of two multi-phase breath-hold exams were used for intra-individual comparisons. The VIBE and CS-VIBE were performed on different days. Image quality in both sequences was qualitatively assessed by three experienced radiologists. Moreover, the contrast ratio (CR) of the aorta, portal vein, liver and pancreas to muscle tissue were measured as a quantitative assessment. For the CS-VIBE, a five-phase time–intensity curve (TIC) was created to evaluate haemodynamics. The measurement area included the pancreas, common hepatic artery, portal vein and superior mesenteric vein. The ratio of that area to the muscle tissue in the same cross section was used to create the TICs.ResultsThe qualitative assessment showed that artefacts were significantly different between the VIBE and CS-VIBE sequences. This finding indicated that the conventional VIBE had fewer artefacts. The CR was significantly higher for the CS-VIBE than for the VIBE images in all phases (p < 0.001). An evaluation of haemodynamics compared with those obtained by CT angiography showed almost the same temporal characteristics in the common hepatic artery, portal vein and superior mesenteric vein signals as those in a previous study.ConclusionCompared with the conventional VIBE, the CS-VIBE had significantly higher temporal resolution and higher image contrast. The temporal resolution of the CS-VIBE was sufficient for viewing abdominal haemodynamics. If the remaining limitation of acquisition speed for dynamic MRI can be adequately addressed, we believe that CS-VIBE functional images with high-contrast haemodynamics will be very useful in clinical practise.     

Splitting of an electromagnetic pulse on resonant reflection from a plasma film

It is found theoretically that the temporal profile of a quasimonochromatic electromagnetic pulse is strongly distorted on reflection from a thin (on the wavelength scale) film of a plasma-like (semiconductor, metallic) medium under plasma-resonance conditions. It is shown that an incident Gaussian pulse splits with time (completely or partially) into two reflected pulses, whose amplitudes can be controlled by varying the relationships among the parameters of the incident pulse and the film. Zh. Tekh. Fiz. 67, 65–68 (June 1997)     

Electromagnetic waves in the nonlocal Josephson electrodynamics of a thin film of a magnetic superconductor

An integrodifferential equation describing the dynamics of the phase difference with spatial and temporal nonlocality is derived for a Josephson junction in a thin film of magnetic superconductor. It is shown that the magnetic subsystem renormalizes the spectrum of small-amplitude electromagnetic excitations and leads to their damping. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 132–138 (25 January 1999)     

Conserved dynamics and interface roughening in spontaneous imbibition: A phase field model

The propagation and roughening of a fluid-gas interface through a disordered medium in the case of capillary driven spontaneous imbibition is considered. The system is described by a conserved (model B) phase-field model, with the structure of the disordered medium appearing as a quenched random field . The flow of liquid into the medium is obtained by imposing a non-equilibrium boundary condition on the chemical potential, which reproduces Washburn's equation for the slowing down motion of the average interface position H. The interface is found to be superrough, with global roughness exponent , indicating anomalous scaling. The spatial extent of the roughness is determined by a length scale arising from the conservation law. The interface advances by avalanche motion, which causes temporal multiscaling and qualitatively reproduces the experimental results of Horv'ath and Stanley (Phys. Rev. E 52, 5166 (1995)) on the temporal scaling of the interface. Received 24 November 1999     

Anomalous magnetic behavior of superconducting thin films in small magnetic fields [4] close to the transition temperature

Using a specially designed SQUID magnetometer we measured the temperature dependence of the critical current density in a ring patterned thin film for magnetic fields parallel to the c-axis. In addition, the temporal relaxation of the remanent state as prepared by field cooling in an external field of 100 Oe at different temperatures is determined. The j c ( T ) data show a field-dependent anomalous kink close to T_c pointing to reduced dissipation with increasing temperature allowing to construct a corresponding H-T borderline. A similar behavior is observed for the normalized relaxation rate S ( T ) as extracted from the temporal behavior of the remanent state, which, at low temperatures, exhibits the expected increase for increasing T-values, while an anomalous decrease of S ( T ) is found for temperatures above 85 K. While the low-T regime is attributed to creep of 2D pinned single vortex lines, the high-T behavior is suggested to be dominated by collective motion with a more sluggish dynamics. This change in dynamics is also reflected by the activation barriers for flux creep U ( j ), which show a corresponding crossover in μ from 0.06 to 0.99. An additional scaling analysis of the E-j characteristics for according to vortex glass theory reveals quasi-2D collective creep behavior with . Received: 8 April 1998 / Revised: 15 July 1998 / Accepted: 2 September 1998     

The natural history of streptozotocin-stimulated non-alcoholic steatohepatitis mice followed by Gd-EOB-DTPA-enhanced MRI: Comparison with simple steatosis mice

PurposeTo clarify the development of HCC, temporal change of steatosis and Gd-EOB-DTPA enhancement of non-alcoholic steatohepatitis (NASH) model mice by magnetic resonance imaging (MRI).Materials and methodsAll animal experiments were approved by the institution's Animal Research Committee. MRI was performed on six NASH and six simple steatosis (SS) model mice every 2 weeks from the ages of 8 weeks to 16 weeks. The sequential changes in the number and size of the focal liver lesions detected on Gd-EOB-DTPA-enhanced MRI were evaluated. Additionally, the hepatic fat fraction (HFF), contrast-to-noise ratio (CNR) and relative enhancement (RE) were calculated at each time point. The temporal changes and correlations in these parameters were evaluated.ResultsAll alive NASH model mice demonstrated focal liver lesions from week 10, at the latest. Number of the lesions increased with time, and all the lesion enlarged with time. All the lesions larger than 1 mm were confirmed as hepatocellular carcinoma (HCC) pathologically. While the HFF remained constant in NASH model mice, HFF in SS model mice dramatically increased with time. CNR of the NASH model mice remained constant through the study period, while CNR in SS model mice decreased with time. Although no correlation was seen in NASH model mice, the HFF showed a negative correlation against CNR and RE in SS model mice.ConclusionDevelopment of HCC was observed using Gd-EOB-DTPA-enhanced MRI only in NASH model mice. Degree of steatosis and hepatic enhancement by Gd-EOB-DTPA was both constant in NASH model mice, while steatosis increased and hepatic enhancement decreased with time in SS model mice.     

Fabry-Perot cavity in the field of a gravitational wave

The structure of the electromagnetic field inside a laser cavity—a gravitational-wave detector—is studied. The properties of the spatial and temporal phases of the standing electromagnetic wave are discussed in detail and the corrections appearing in the electric field of the wave as a result of the action of gravitational radiation on the optical system are determined. Zh. éksp. Teor. Fiz. 113, 398–408 (February 1998)     

Real-time volumetric MR thermometry using 3D echo-shifted sequence under an open source reconstruction platform

PurposeThe aim of this work is to implement real-time 3D MR thermometry for high intensity focused ultrasound (HIFU) monitoring.MethodsVolumetric MR thermometry was implemented based on a 3D echo-shifted sequence with short TR to improve temperature sensitivity. The 3D acquisition was accelerated in two phase encoding directions with controlled aliasing in volumetric parallel imaging (CAIPIRINHA). Image reconstruction was run in an open source reconstruction platform (Gadgetron).ResultsPhantom experiments showed the proposed volumetric thermometry was comparable to the fiber optical thermometer. In-vivo animal experiments in rabbit thigh showed that the temperature error before and after 4× acceleration was less than 0.65 °C. Finally, real-time 3D thermometry with temporal resolution ~3 s and spatial resolution 2 × 2 × 5 mm³ (spatial coverage 192 × 192 × 80 mm³) was achieved with Gadgetron reconstruction.ConclusionReal-time temperature monitoring was achieved in-vivo by using parallel imaging accelerated 3D echo-shifted sequence with Gadgetron reconstruction.     

Dynamic magnetic susceptibility of a superconductor with a relaxing magnetic moment

Within the framework of the diffusion approximation for the dynamic magnetic flux, a model is constructed for the dynamic magnetic susceptibility of a superconductor with a nonuniform and time-dependent magnetic field distribution in the sample. The possibility of appearance of peaks in the temperature (or frequency) dependence of χ″ in a structurally homogeneous superconducting sample in the presence of a magnetic-field-induced nonuniformity of the diffusion parameter is demonstrated. The character of the temporal evolution of the magnetic susceptibility during relaxation of the magnetic moment of the sample is predicted and its properties are investigated. Fiz. Tverd. Tela (St. Petersburg) 39, 811–815 (May 1997)     

Coherent suppression of the EPR-nutation signal in quartz

Bloch equations are used to derive an analytic expression for the integral nutation-signal decay rate in a two-level quantum system. It is found that when inhomogeneous line broadening is taken into account, the temporal decay of the response is due not only to coherent suppression but also to additional decay whose rate depends on the ratio of the Rabi frequency to the inhomogeneous linewidth. The results are used to explain the anomalous (Rabi-frequency-dependent) EPR-nutation decay detected in quartz in the experiments of R. Boscaino, F. M. Gelardi, and J. P. Corb [Phys. Rev. B 48, 7077 (1993)]. Contrary to the statement made by these researchers that this decay is non-Bloch, it is found that the process can be described by Bloch equations without any modification. Zh. éksp. Teor. Fiz. 114, 484–491 (August 1998)     

CsI(Tl) layers spectroscopy - comparison with crystals

Abstract

Emission and excitation spectra at liquid helium and liquid nitrogen temperature of CsI(Tl) single crystals and evaporated thin layers have revealed the existence of new centers in such materials. In particular, an emission band is observed around 460nm excited near 325 nm correlates with the quality of the evaporated thin film in terms of light yield and temporal behavior. The results can be interpreted using a dopant ion-bound exciton model involving different kinds of perturbed and non-perturbed centers.     

Repeated gamma-ray bursts from the June 15, 1991 solar flare

The results of the detection of repeated bursts of gamma rays with energies exceeding 30 MeV from the June 15, 1991 solar flare, observed with the Gamma-1 telescope, are examined. It is shown that they occur on the declining part of the temporal profile of the gamma radiation and last for ∼10 min (they occur 27 min after the optical part of the flare starts). No appreciable radiation bursts were observed during the subsequent quasiconstant part (∼20 min). It is concluded that repeated events in which particles are accelerated occur in the active stage of the powerful June 15, 1991 solar flare. It is noted that while the June 15, 1991 and March 26, 1991 gamma-ray bursts share a common character, their spectral and temporal characteristics are substantially different. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 889–893 (25 June 1996)