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Detail dielectric measurements were carried out on two different liquid crystalline (LC) samples formed by bent core (BC) molecules, showing B1 and B2 phases in the temperature range 100–150°C. The thermal variation of real part of dielectric permittivity (ϵ′) represents a tiny dip only in the saturated B1 phase which might arising from the dipole orientation disorder due to the inherent phase instability. The experimental data have been used to determine different relaxation parameters. Evidently only one relaxation mode has been detected in the dielectric relaxation spectrum for both phases, which is attributed to the long axis molecular rotation process. [ABSTRACT FROM AUTHOR]

The dielectric relaxation behavior of a bent-core liquid-crystalline (BC) material showing B2 phase and its 17% mixture with another rod-like material (R-BC) has been investigated. The appearance of a newly induced B1 phase has been detected in the R-BC system. We found comparatively lower value of dielectric permittivity of the R-BC system than that of BC material. Moreover, a lower value of relaxation frequency of the long axis rotation mode in BC material compared to that of the R-BC material has been observed. These results have been discussed on the basis of molecular origin for the formation of B phases in the materials. [ABSTRACT FROM AUTHOR]

Dielectric relaxation behavior of a dichiral mesogenic liquid crystal material, viz. (R,S)-FPPY, having anomalous phase sequence has been studied over a wide range of frequency. Measured dielectric spectra show a new relaxation process, in addition to the usual Goldstone mode, in the SmC* phase, which has been assigned to the relaxation process originating from the dichirality of the compound. The overlapping of two molecular modes has been observed in the dielectric spectrum of both isotropic and optically isotropic (IsoX) phases. The present detailed dielectric spectroscopic studies also establish an interesting ferroelectric-like ordering in the unknown SmX* phase. [ABSTRACT FROM AUTHOR]

The temperature- and electric field-dependent dielectric relaxation and polarisation of a new chiral swallow tailed antiferroelectric liquid crystal, i.e. 1-ethylpropyl (S)-2-{6-[4-(4'-decyloxyphenyl)benzoyloxy]-2-naphthyl}propionate (abbreviated as EP10PBNP), were investigated. The electric field-induced dielectric loss spectra of EP10PBNP revealed electroclinic and anomalous dielectric behaviour in the chiral smectic A (SmA*)-chiral antiferroelectric smectic C (SmCA*) pre-transitional regime. From an analysis of thermal hysteresis of the dielectric constant, electric field-induced polarisation and dielectric loss spectra, the appearance of a ferrielectric-like mesophase is observed followed by an unstable SmCA* phase in the SmA*-SmCA* pre-transitional regime. [ABSTRACT FROM AUTHOR]

We report the effects of the rotational motion of the director around the chiral smectic cone on the dielectric relaxation and polarization reversal process in a surface stabilized ferroelectric liquid crystal cell. Measurement was made at a fixed temperature (40°C), far below the SmA–SmC* transition temperature (62°C) of the ferroelectric liquid crystal material (CS‐1027). The amount of switchable polarization (ASP), during the polarization reversal, is found to decrease with increasing frequency of the applied signal until a typical value of frequency (fl) is reached. This behaviour is considered to be due to the time‐dependent rotational motion of the director. The ASP value was calculated by measuring polarization–voltage (P–V) and capacitance–voltage (C–V) hysteresis loops as a function of the applied signal frequency and then following the Preisach model for the ferroelectric capacitor. The peaks of the C–V hysteresis loop, which correspond to the reversal of polarization, are gradually converted into wells for frequencies greater than a critical value (fi). The hysteresis loops shows ‘frustrated’ behaviour for frequencies between fl and fi. The inversion of the C–V hysteresis loop at higher frequencies (>fi) is attributed to the inversion of the dielectric biaxiality and the corresponding ‘frustrated’ behaviour arising due to competition between the dielectric and ferroelectric torques. A suitable equivalent circuit can be designed to represent the frequency‐dependent C–V and magnitude of admittance (conductance) –voltage (G–V) hysteresis behavior. [ABSTRACT FROM AUTHOR]

In this paper a frequency plane analysis of both normal and diseased ECG signals is performed specifically for disease identification. Image processing techniques are used to develop an automated data acquisition package of 12 lead ECG signals from paper records. A regeneration domain is also developed to check the captured pattern with the original wave shape. A QRS complex detector with an accuracy level ∼⃒98.4% in up to 30% signal to noise level is developed. Discrete Fourier transform (DFT) is performed to obtain the frequency spectrum of every ECG signal. Some interesting amplitude and phase response properties of chest lead V2, V3, V4, V6 and limb lead I, II, III, AVL, AVF are seen. Both amplitude and phase properties are different for normal and diseased subjects and can serve an important role in disease identification. A statistical analysis of amplitude property is carried out to show that this property is significantly different for normal and diseased subjects. [ABSTRACT FROM AUTHOR]

The temperature (25–120°C) and frequency (10?Hz–1?MHz) dependent dielectric relaxation spectra of different ferroelectric liquid crystals are found to show interesting scaling behaviour. Considering relaxation frequency (?max) as the scaling frequency, the imaginary part of the dielectric constants (??) of the ferroelectric liquid crystals are found to follow the universal scaling formula, i.e. when (??/??max) is plotted as a function of (f/?max), the scaling behaviour of a ferroelectric liquid crystal can be represented by a single master curve irrespective of film thickness, bias field and temperature; ??max is the maximum value of ?? at the frequency ?max and m is a parameter ~1. [ABSTRACT FROM AUTHOR]

We report the dielectric relaxation behaviour in the antiferroelectric SmC A * and ferrielectric SmC γ * phases of the antiferroelectric liquid crystal 4-[5-(4-octloxyphenyl)-2-pyrimidinyl]phenyl 4,4,4-trifluoro-3-(methoxyphenyl)butanoate which shows an antiferroelectric transition at around 88±0.1°C. In the SmC A * phase, two dielectric relaxation modes have been found, namely the usual antiferroelectric Goldstone mode and another arising from molecular rotation around its short axis. In the SmC γ * phase, one dielectric relaxation mode has been observed due to the ferrielectric Goldstone mode. Dielectric increments and relaxation frequencies of the antiferroelectric and ferrielectric phases are estimated from the fits of the Cole-Cole function of the dielectric spectrum. The dependence of the bias field in the ferrielectric phase is also discussed. [ABSTRACT FROM AUTHOR]

Studies the transport and dielectric properties of V[sub2]O[sub5]-MnO-TeO[sub2] glasses containing two transition metal ions. Change in the conductivity on addition of MnO; Difference between behavior of Mn-free and Mn-added glasses; Variation in the imaginary part of the dielectric constant for different glasses at different frequencies.

Anomalous dielectric relaxation behaviour is observed in the ferroelectric liquid crystalline polymer (viz. ferroelectric copolysiloxane (R)-COPS 11-10) around the ferroelectric SmC* to paraelectric SmA phase transition. Measurements have been performed on sample of thickness ~10 mum in indium-tin-oxide coated cell in the frequency range 10 Hz to 13 MHz. With increase of temperature, a gradual shift of the soft mode frequency towards the higher frequency side was observed, while a decrease in the relaxation strength was seen with the corresponding increase in temperature. The shifts of the soft modes in the SmC* and SmA phase are considered to be due to change in the viscosity of the polymer, as an increase in viscosity increases fluctuations of the coupling between the dipoles in the network even far from the paraelectric-ferroelectric phase transition. Application of a bias field causes a shift of the critical frequency towards the higher frequency side, while the dielectric strength (Δε) decreases under the bias field. The Cole-Cole fitting parameters obtained from the best fit of the dielectric constant data are found to be consistent with other similar materials. Another relaxation mode (molecular mode) was also observed which comes into play in both the smectic phases (SmC* and SmA) and contributes to the dielectric permittivity. [ABSTRACT FROM AUTHOR]

Homogeneous thick films (0.3-0.35mm thick) of glassy (Bi3Pb1)Sr3Ca3Cu4-nTinOx precursors with low (n = 0-0.0075) concentrations of Ti have been prepared by a fast-quenching technique and characterized by X-ray diffraction and scanning electron microscopy studies. By annealing these as-quenched glasses above their respective glass transition temperatures Tg, mostly the Bi-2212-type superconducting phase is obtained. The effect of Ti doping is to decrease the glass melting temperature as well as the annealing temperature (for making the ceramic phase, hereafter termed glass-ceramic (GC) phase) by about 20oC. The addition of Ti also reduces the formation of the high-Tc 2223 phase. However, the superconducting transition temperature Tc decreases linearly with increasing Ti content. The Abrikosov-Gor'kov pairbreaking mechanism is found to be satisfied. All these GC samples (except the n = 0.00 sample) follow Mott's variable-range hopping conduction mechanism above the superconducting transition temperature (normal state). The thermoelectric power data of the GC superconductor measured between 10 and 300K exhibits a nonlinear variation, showing a negative peak just above Tc. Both positive and negative values of the Seebeck coefficients exhibited by the samples indicate the presence of two types of carrier. A two-band model can be used to explain the linear part of the Seebeck coefficient above the negative maximum. The observed low temperature negative peak in the Seebeck coefficient is considered to be associated with the phonon-drag effect. [ABSTRACT FROM AUTHOR]

Photosensitivity in ferroelectric liquid crystal (FLC) material has been developed by dispersing Cadmium Sulfide (CdS) nano-particles in FLC (CdS-FLC) host. The nematic (N*) – ferroelectric (SmC*) phase transition temperature for the CdS-FLC sample in absence and presence of white light excitation decreases by 6 and 14°C, respectively, compared to host material due to enhanced disorder. The anomalous behaviour in temperature dependent dielectric permittivity of CdS-FLC sample in presence of white light excitation in N* as well as SmC* phase has been explained on the basis of enhanced free charged density and self assembly of CdS-LC in the phases. [ABSTRACT FROM AUTHOR]