Increase Of Relaxation Frequency Research Articles

Essence - A New Electrochemical Platform

There is a great demand for a fast, on-site screening test, especially during the COVID-19 pandemic. However, most point-of-care (POC) sensors usually suffer from insufficient sensitivity and selectivity. Often these devices have a very high rate of false positives and false negatives. The incorrect data could result in low customer usage (both the patient and the doctor) due to decreased confidence in the results. Portable ELISA-based kits can have low rates of false-positive and false negatives. However, ELISA is inherently complicated and often requires a specialist on-site to ensure the success of each sample's high costs and time.Here we show a new electrochemical platform called ESSENCE. ESSENCE is an Electrochemical Sensor that uses a Shear-Enhanced, flow-through Nanoporous Capacitive Electrode. ESSENCE can overcome current electrochemical sensors' selectivity and sensitivity limitations. The ESSENCE sensor architecture is a microfluidic channel sandwiched between two gold micro-electrode glass slides, formed a non-planar interdigitated porous electrode that improved electric field penetration compared with the traditional planar interdigitated electrode. The porous electrode structure used in this research has a high Zeta potential compared to the bare glass surface. This results in a significantly smaller Debye double-layer (EDL) length than in a clear channel. Due to a smaller EDL length, the relaxation frequency increases, which shifts the EIS signal to a higher frequency range (1kHz to 100MHz) and results in a fast response with a higher signal-to-noise ratio in Electrochemical Impedance Spectroscopy(EIS) measurements.Further, the modular fabrication of the ESSENCE chip allows ESSENCE to target different biomolecules from DNAs to protein cancer biomarkers by simply changing the packed transducer material. However, the packing material’s conductivity represents a significant challenge to the electrochemical response of ESSENCE. The high conductivity of the transducer material shorts the system leading to a pure resistive response. Impedance spectroscopy (EIS) response of ESSENCE cannot be distinguished enough to determine if the sensor is working. ESSENCE has a switchable electrode system for usage in multiple configurations like a material electrode, clear electrode, and working electrode to overcome these limitations. For carbon nanotube (CNT) transducers with functionalized oligos on the CNT, a 20-fold jump in the signal is noticed from the working electrode configuration compared to the other configurations. It is worthwhile to note that depending on the biomolecule (DNA or Protein), the surface charge transfer resistance (Rct) in the EIS signal of ESSENCE can either show a decrease (DNA) or increase (protein) on the binding of the target bio-molecule (target DNA to DNA or target protein to protein). The change in the Rct depends on the charge of the molecule. It has been seen that on the binding of a target protein, the active area of the electrode surface decreased, leading to a reduction in current and a concomitant increase in Rct. On binding of the target DNA, the capture-target DNA pair essentially becomes a part of the electrode due to its charge. This increase in charge is more significant than any reduction in the surface area due to the DNA's binding. This leads to an increase in current to the packed electrode, leading to a concomitant decrease in Rct.The fluid flow through the porous electrode increases mixing, minimizes diffusion, and generates a significantly enhanced fluidic shear force. This force e can unbind most of the false-positive signals generated by non-specific binding, such as physical adhesive or biofouling. The porous electrode also provides a high surface area to volume ratio to capture the target analyte leading to increased sensitivity. We have an automatic fluidic control system in ESSENCE that minimized any errors in the operation of ESSENCE. Our system has high selectivity and sensitivity for DNA (fM sensitivity, selective against non-target DNA), breast cancer biomarker proteins (p53, pg/L sensitivity, selective against non-target HER2). Figure 1

Cole Relaxation Frequency as a Prognostic Parameter for Breast Cancer.

We previously reported successful classification of breast cancer versus benign tissue using the Cole relaxation frequency measured on tissue excised during breast surgery as part of a study at two urban hospitals in the U.S. Midwest. Using that health system's cancer registry, we have discovered retrospectively that outcomes for patients who participated in the initial study can be classified correctly in 3 well-differentiated categories: nonrecurrent (NR); recurrent with no metastasis (RNM); and recurrent with metastasis (RM). As Cole relaxation frequency increases, the classification moves from NR to RNM and finally to RM. Multivariate analysis showed a significant association of "time-cancer-free" for all patients in these recurrent categories, with P-values ranging between 0.0001 to 0.0047. Thus, this follow-up report shows the potential feasibility of using Cole relaxation frequency as a prognostic parameter in a larger prospective study.

Dielectric Study of Multiwall Carbon Nanotube Dispersed Nematic Liquid Crystal Mixture

In the present work, multiwall carbon nanotube dispersed/doped nematic liquid crystal mixture have been synthesized by ultrasonication technique and studied using dielectric spectroscopy tools in the frequency range of 10 kHz-40 MHz. We have observed that the dielectric permittivity, loss and relaxation frequency of a nematic liquid crystal (MBBA) are influenced by the presence of multiwall carbon nanotube as a function of frequency and temperature. The value of dielectric permittivity increases with the dispersion of multiwall carbon nanotube due to π-π interaction of MWCNT and LC molecules. However, an increase in relaxation frequency is also found in dispersed samples. The MWCNT with almost identical size within themselves are dispersed at 0.5% concentration into nematic LC. The MWCNT-nematic LC composites are not only of fundamental importance, but also useful materials for device applications such as liquid crystal displays.

Electro-optic, dielectric and optical studies of NiFe2O4-ferroelectric liquid crystal: a soft magnetoelectric material

ABSTRACTIn the present study, magnetic nanoparticles (NP, nickel ferrite) in different concentrations into ferroelectric liquid crystal (FLC) mixture have been prepared and studied. The effect of nickel ferrite concentration on the electro-optic, dielectric and optical properties of FLC mixture has been studied and discussed. An improvement in spontaneous polarization, response time in nickel ferrite-FLC-doped samples compared to FLC is observed and explained on the basis of dipole moment and anchoring phenomena. The Goldstone mode (GM) is detected in all samples and follows a Debye-type relaxation behaviour. A twofold increase in relaxation frequency for the doped sample rather than the pure sample has been observed. The band gap was found more or less independent of doping concentration. The activation energy (Ea) also decreases on increasing the doping amount.

Effect of Martensitic Transformation on the Optical Spectra of Cu-Mn-Al Alloy

The effect of martensitic transformation on the transport and optical properties of Cu-4.9Mn-23.4Al (at.%) alloy is reported. The resistivity measurements revealed the transformation temperatures Ms =284K and Af=303K. The optical properties of Cu-4.9Mn-23.4Al (at.%) alloy have been investigated at several temperatures near the region of austenite-martensite transformation. It was shown that intraband absorption is dominates in alloy for ħω < 2.5 eV energy range. Plasma Ωp and relaxation γ frequencies of free charge carriers for Cu-4.9Mn-23.4Al (at.%) alloy were evaluated at several temperatures on the basis of Drude analysis of the alloy optical properties in the intraband absorption region. The growth of electrical resistance induced by martensitic transformation upon alloy cooling obtained directly from the resistivity measurements correlates nicely with the results derived from the optical measurements and can be explained by the reduction of the plasma frequency Ωp as well as increase in relaxation frequency γ of free charge carriers.

Wavenumber-Domain Theory of Terahertz Single-Walled Carbon Nanotube Antenna

A theoretical study is presented on the characteristics of terahertz antennas formed by metallic single-walled carbon nanotube (SWCNT) dipoles. The Boltzmann transport equation and Maxwell's equations are combined with boundary conditions of the electron distribution function, in order to formulate a wavenumber-domain integral equation for the current, which considers the spatial dispersion and provides higher level of accuracy and generality than existing approaches. Through proper approximations of that equation, the same spatial integral equations from several other studies can be drawn. The radiation properties of the SWCNT antenna are derived from the wavenumber-domain current. Numerical results are given for short dipole antennas and those with length close to the half wavelength in free space. They are compared to the results calculated by other methods. We also investigate the frequency dependence of conductance under different values of relaxation frequency and find the increase of relaxation frequency leads to strong attenuation of surface-wave resonances.

Dielectric spectroscopy of Polymer Stabilised Ferroelectric Liquid Crystals

Dielectric measurements were carried out in the frequency range from 20 Hz to 500 kHz on Polymer Stabilised Ferroelectric Liquid Crystals (PSFLCs). Polymerisation in the Smectic A* (Sm A*) and the Smectic C* (Sm C*) phase at equal polymer concentration results in a dielectric strength which is nearly twice the value in the latter case. An increase of the polymer concentration results in a decrease of the dielectric strength and an increase in relaxation frequency. The textural morphology and transmission intensity due to the residual birefringence of the polymer network in the isotropic phase, revealed a correlation between the interactions of the liquid crystal molecules with the polymer network. Results for polymerizing in the tilted Sm C* phase with a large bias field are also reported which show that the structure of the phase in which the system was polymerised affects the dielectric properties. The observed differences in dielectric behaviour can be explained by the polymer network morphology formed due to the interplay of phase and temperature on the stabilised ferroelectric liquid crystal materials.

Twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals

We report our studies on the refractive indices and twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals. Dynamic light scattering (DLS) was employed to measure the twist viscoelastic coefficient as a function of temperature and the length of alkoxy chain. Our studies show that the twist viscoelastic coefficient is about three times smaller than that of the ordinary alkoxy-cyanobiphenyl nematic liquid crystals. DLS experiments carried out on this system with applied electric field show that the director relaxation frequency increases. These measurements yield the ratio of dielectric anisotropy to twist viscosity. We have also estimated the activation energy corresponding to twist viscosity.

The effect of thermal treatment on the magnetic properties of Ge-doped FeNbB alloys

The effects of Ge doping on the magnetic properties of nanocrystalline FeNbB ribbons are investigated. For amorphous Fe80Nb10Ge3B7 alloy, three crystallization processes are observed when heated from room temperature to 1173 K. At 973 K, a harder magnetic phase is formed, which brings about a constricted hysteresis loop. A large increase of relaxation frequency and a dramatic drop of permeability of 973 K-annealed Fe80Nb10Ge3B7 alloy are observed. The presence of Nb is essential for the nanocrystallization of α-Fe grains. If Nb is replaced by Ge completely, the thermal treatment will lead to the formation of coarse-grained Fe3Ge phase rather than nanosized α-Fe grains. The coarse-grained Fe3Ge results in a remarkable drop in magnetic softness.

The change of magnetic relaxation in neutron irradiated Ni–Cr–Mo steel

AbstractThe change of the hysteresis loop and the permeability spectra due to neutron irradiation was investigated on broken Charpy specimens of A508 Class 2 pressure vessel steel weldments which were exposed to irradiation levels of 1.23 × 1019 n/cm2 and 3.94 × 1019 n/cm2. The saturation magnetization slightly decreased, but the coercivity increased by 16% in the 3.94 × 1019 n/cm2 irradiated sample. The permeability decreases with neutron dose, while the relaxation frequency increases. The behavior of permeability spectra due to neutron irradiation was explained by the equation of the damped harmonic motions. These results can be interpreted on the basis of a variation of the extent of domain wall pinning, as manifested in changes in the spring constant α, increasing with neutron dose. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical Properties of Liquid Aluminum and Al–Ce Alloy

The Beattie ellipsometric method is used to investigate the index of refraction and the absorption coefficient of liquid aluminum and Al–3 at. % Ce alloy in the wavelength range from 0.44 to 2.3 μm at a temperature of 1173 K. The experimental results are used to calculate the dispersion dependences of light conductance, reflectivity, and functions of characteristic loss of electron energy. The results of measurements in the infrared (IR) spectrum are used to determine the concentration of conduction electrons, plasma frequency, relaxation frequency, and the limiting light conductance. It turns out that an addition of 3 at. % Ce to aluminum causes almost no change in the concentration of charge carriers, whereas the relaxation frequency increases, which leads to a decrease in the electrical conductivity of the liquid alloy.

Soft magnetic behaviour and permeability spectra in amorphous and nanocrystalline Fe 80.5Nb 7B 12.5 alloys

The magnetic behaviour and the frequency dependencies of the complex magnetic permeability are studied in a series of heat-treated amorphous and nanocrystalline Fe 80.5Nb 7B 12.5 samples with different volume fractions of the crystalline phase. The magnetic behaviour has been studied by vibrating sample magnetometry (VSM) and by room-temperature hysteresis loop measurements. The spectra of real and imaginary parts of the complex permeability, μ( f)= μ′( f)−j μ′′( f) , were measured using an impedance analyzer in the frequency range from 0.01 to 10 MHz. The obtained permeability spectra for the investigated nanocrystalline alloys show typical features of a domain wall relaxation dispersion. A marked deterioration of the soft magnetic behaviour takes place in the partially crystallized samples after annealing for 1 h at 803 K. This is reflected by a drastic reduction of permeability and a strong increase of relaxation frequency. An improvement of soft magnetic behaviour characterized by low values of coercivity and relaxation frequency as well as by high permeability is observed after annealing for 1 h at 883 K which resulted in an advanced degree of nanocrystallization in the samples.

Effect of proton irradiation on magnetic relaxation in amorphous material

The frequency spectra of the susceptibility in the amorphous Fe 81B 13.5Si 3.5C 2 of as-quenched and proton-irradiated samples show a typical Debye-type relaxation of domain walls. The susceptibility decreases with proton dose, while the relaxation frequency increases. The results are discussed in terms of the domain size and internal stress at the induced defects after proton irradiation.

The dielectric response of polystyrene latexes: Effects of alterations in the structure of the particle surface

The presence of a “hairy” layer has been hypothesized to explain discrepancies between the electrokinetic theory and experiments with polystyrene latexes by Van der Put and Bijsterbosch ( J. Colloid Interface Sci. 92, 499 (1983)]. We tested the hypothesis by making electrokinetic measurements on latexes before and after they had been heated above the polystyrene glass transition temperature. This sort of treatment may smooth the particle surface by collapsing or removing the charged polymer filaments which comprise the layer. Low-frequency dielectric measurements reveal that heat treatment improves the agreement between experiment and theory. For an amphoteric latex, the dielectric constant and conductivity decrease with heat-treatment time, and the characteristic relaxation frequency increases. This is consistent with the hairy surface hypothesis, suggesting that heat treatment smooths the surface, creating particles which more closely conform to the assumptions of the classical theory. Experiments with an anionic latex further suggest the presence of surface structure, but discrepancies between experiment and theory persist; it appears that factors other than hairiness contribute to these discrepancies. The suspension's dielectric properties are evidently very sensitive to the state of the particle surface, and thus dielectric spectroscopy offers a promising means of studying the structure of colloidal interfaces.

Ultrasonic Studies of Intermolecular Vibrational-Vibrational Energy Transfer in Liquid Mixtures

Vibrational relaxation studies of liquid furan-cyclohexane and dichloromethane-cyclohexane mixtures were made with three ultrasonic techniques, high-resolution Bragg reflection, Brillouin scattering and pulse-echo-overlap. The velocity and absorption were measured in the frequency range from 3 MHz to 5 GHz. The relaxation frequencies were obtained as a function of concentration of cyclohexane. The increase in relaxation frequency was found to be caused by the fast process of intermolecular vibrational-vibrational energy transfer. The results were analyzed with the binary collision theory. The rate constants of the energy transfer from the 605 cm -1 mode of furan to the 522 cm -1 mode of cyclohexane, and from the 717 cm -1 mode of dichloromethane to the 522 cm -1 mode of cyclohexane were estimated to be 3×10 10 s -1 for both V–V transfers.

Critical fluctuations in the weakly anharmonic crystal model of a structural phase transition

The criteria for the existence of a central peak in the spectral density of the soft optical mode, in a weakly anharmonic crystal model of a piezoelectric-ferroelectric are examined. We investigate the effects of the critical fluctuations of the optic mode on the internal relaxation process believed responsible for the appearance of a central peak, the relaxation to local equilibrium of the acoustic phonons. The critical fluctuations induce a diffusion in momentum space of the acoustic phonons, leading to an increase in the effective relaxation frequency of the acoustic-phonon distribution function, and a critical increase in the acoustic-phonon linewidth. The increase in relaxation frequency is not sufficient to eliminate the distinct central peak, however, and we conclude that the model will always exhibit a central peak if the anharmonic coupling coefficients are sufficiently small.

Temperature Dependence of Low-Frequency Sound Attenuation in Fresh and Sea Water

Low-frequency sound-absorption measurements in both fresh and sea water show anomalous behavior that is consistent with a relaxation process near 1 kHz. Furthermore, comparison of the 4°C measurements in the Atlantic Ocean and Lake Superior with the 13° Mediterranean Sea values indicate an increase in relaxation frequency with temperature corresponding to an activation energy of almost 10 kcal/mole. Further experiments are planned in Lake Tanganyika and the Red Sea (23°C) to test the hypothesis.