Total Peak Amplitude Research Articles

Demonstration of magnetic resonance Z-spectral imaging for fatty acid characterization of bone marrow at 3 T.

Magnetic resonance Z-spectral imaging (ZSI) has emerged as a new approach to measure fat fraction (FF). However, its feasibility for fat spectral imaging remains to be elucidated. In this study, a single-slice ZSI sequence dedicated to fat spectral imaging was designed, and its capability for fatty acid characterization was investigated on peanut oil samples, a multiple-vial fat-water phantom with varied oil volumes, and vertebral body marrow in healthy volunteers and osteoporosis patients at 3 T. The peanut oil spectrum was also recorded with a 400-MHz NMR spectrometer. A Gaussian-Lorentzian sum model was used to resolve water and six fat signals of the pure oil sample or four fat signals of the fat-water phantom or vertebral bone marrow from Z spectra. Fat peak amplitudes were normalized to the total peak amplitude of water and all fat signals. Normalized fat peak amplitudes and FF were quantified and compared among vials of the fat-water phantom or between healthy volunteers and osteoporosis patients. An unpaired student's t-test and Pearson's correlation were conducted, with pless than 0.05 considered statistically significant. The results showed that the peanut oil spectra measured with the ZSI technique were in line with respective NMR spectra, with amplitudes of the six fat signal peaks significantly correlated between the two methods (y = x + 0.001, r = 0.996, p< 0.001 under a repetition time of 1.6 s; and y = 1.026x - 0.003, r = 0.996, p< 0.001 under a repetition time of 3.1 s). Moreover, ZSI-measured FF exhibited a significant correlation with prepared oil volumes (y = 0.876x + 1.290, r = 0.996, p< 0.001). The osteoporosis patients showed significantly higher normalized fat peak amplitudes and FF in the L4 vertebral body marrow than the healthy volunteers (all p< 0.01). In summary, the designed ZSI sequence is feasible for fatty acid characterization, and has the potential to facilitate the diagnosis and evaluation of diseases associated with fat alterations at 3 T.

Stability indicating spectrophotometric methods for quantitative determination of bromazepam and its degradation product.

Four simple, sensitive and selective stability indicating spectrophotometric methods are presented for quantitative determination of the benzodiazepine drug; bromazepam (BMZ) and one of its reported potential impurities and degradation product; 2-(2-amino-5-bromobenzoyl) pyridine (ABP) in methanol. Method A, is isoabsorptive point coupled with D0 method, where good linearity was obtained by measuring the absorbance of BMZ at 264nm (Aiso) in the concentration range of 2-25μgmL-1, and the absorbance of ABP at its λmax 396nm in concentration range of 0.5-24μgmL-1. Method B, is ratio subtraction; the absorbance was measured at 233nm for BMZ using 20μgmL-1 of ABP, while ABP was determined directly at its λmax 396nm using methanol as a solvent. Method C, was based on measuring the total peak amplitude of the first derivative of the ratio spectra (DD1) of BMZ from 301 to 326nm using 10μgmL-1 of ABP as a divisor and determination of ABP at peak amplitude of 293nm using 5μgmL-1 of BMZ as a divisor. In method D, ratio difference method, good linearity was achieved for determination of BMZ and ABP by measuring the differences between the amplitudes of ratio spectra at 312nm and 274nm and differences between the amplitudes of ratio spectra at 274nm and 312nm, respectively. The stability of BMZ was investigated under different ICH recommended forced degradation conditions. The suggested methods were then successfully applied for determination of BMZ in its pharmaceutical formulations.

Detection of water variation in rosebuds during hot-air drying by LF-NMR and MRI

This study investigated drying kinetics and changes in water in rosebuds during hot air drying at 40, 50, 60, and 70 °C, using NMR and MRI technology to evaluate transverse relaxation times (T2), water status and distribution. Drying rate increased with temperature, with the Midilli model predicting the drying process of rosebuds more accurately than other mathematical models. Three water fractions with different T2 values were identified: T21 (0.1–2 ms), T22 (5–50 ms), and T23 (50–600 ms). Water status and distribution in rosebuds differed with a higher moisture content in receptacles than in petals. During drying, the total peak amplitude and T2 values in rosebuds declined (LF-NMR), with changes in internal water distribution shown by MRI. Moisture content was significantly correlated with LF-NMR parameters, especially ATotal/g. Therefore, the Midilli model described the drying of rosebuds, and LF-NMR and MRI technology can monitor changes in water status and distribution during drying.

Development and validation of stability-indicating methods for determination of torsemide

Four sensitive and precise methods for determination of torsemide in presence of its degradation product and in pharmaceutical formulation were developed and validated. Method A is the second derivative spectrophotometry at 262.4 nm with mean percentage recoveries 100.06±0.75. Method B is first derivative of the ratio spectra spectrophotometry, at 232.4, 244.6 nm and at the total peak amplitude from the maximum at 232.4 nm to the minimum at 244.6 nm ( 1 DD 232.4+244.6nm ). Method C is a TLC-densitometric one, for torsemide separation using acetone : chloroform : ethyl acetate (4:4:2 v/v) as a developing system. Method D is HPLC one, it provides complete separation of torsemide from its degradation product on C8 column with UV detection at 287 nm and recovery 99.98±0.76. The proposed methods have been successfully applied to the analysis of torsemide in pharmaceutical formulations without interference from other additives and the results were statistically compared with the official method. KEY WORDS : HPLC, Stability-indicating, Spectrophotometry, TLC-densitometry, Torsemide Bull. Chem. Soc. Ethiop. 2016 , 30(1), 13-25. DOI: http://dx.doi.org/10.4314/bcse.v30i1.2

Stability-Indicating Determination of Rebamipide in the Presence of its Acid Degradation Products

Four sensitive and precise stability-indicating methods for the determination of rebamipide (REB) in the presence of its acid-degradation products and in a pharmaceutical formulation were developed and validated. Method A used the first derivative of the ratio spectra (1DD) spectrophotometric method by measuring the peak amplitude at 249.4 nm (maximum) and at 259 nm (minimum), and at the total peak amplitude (from 249.4 to 259 nm, 1DD(249.4 + 259 nm)) in the range of 2-14 microg/mL. This method yielded mean recoveries of 99.87 +/- 0.83, 100.04 +/- 0.75, and 100.28 +/- 1.11%, respectively. Method B is a dual wavelength method, which allows the determination of REB in presence of its acid-degradation products by measuring the absorbance difference between 254 and 269 nm within a linearity range of 5-65 microg/mL; it showed a mean recovery of 99.84 +/- 1.06. Method C is a TLC-densitometric procedure in which REB was separated from its degradation products using a developing solution of methanol-chloroform-ammonia (8.5 + 1.5 + 0.5, v/v/v). The quantitative evaluation of REB at 329 nm was linear over the concentration range of 0.50-4.5 microg/band, with a mean recovery of 99.49 +/- 0.99% even in the presence of up to 90% degradation products. Method D is an RP-HPLC procedure. It provided the complete separation of REB from its degradation products on an Xterra C18 column using phosphate buffer (pH 6, 0.01 M)-methanol (1 + 1, v/v) as the mobile phase (UV detection at 254 nm). Recovery was 99.28 +/- 0.78% within the range of 10-190 microg/mL. The selectivity of the proposed methods was checked using laboratory-prepared mixtures. The proposed methods have been successfully applied to the analysis of REB in pharmaceutical dosage forms without interference from other dosage form excipients.

Neurogliaform cells of amygdala: a source of slow phasic inhibition in the basolateral complex

Synaptic inhibition in the amygdala actively participates in processing emotional information. To improve the understanding of interneurons in amygdala networks it is necessary to characterize the GABAergic cell types, their connectivity and physiological roles. We used a mouse line expressing a green fluorescent protein (GFP) under the neuropeptide Y (NPY) promoter. Paired recordings between presynaptic NPY-GFP-expressing (+) cells and postsynaptic principal neurons (PNs) of the basolateral amygdala (BLA) were performed. The NPY-GFP+ neurons displayed small somata and short dendrites embedded in a cloud of highly arborized axon, suggesting a neurogliaform cell (NGFC) type. We discovered that a NPY-GFP+ cell evoked a GABA(A) receptor-mediated slow inhibitory postsynaptic current (IPSC) in a PN and an autaptic IPSC. The slow kinetics of these IPSCs was likely caused by the low concentration and spillover of extracellular GABA. We also report that NGFCs of the BLA fired action potentials phase-locked to hippocampal theta oscillations in anaesthetized rats. When this firing was re-played in NPY+-NGFCs in vitro, it evoked a transient depression of the IPSCs. Presynaptic GABA(B) receptors and functional depletion of synaptic vesicles determined this short-term plasticity. Synaptic contacts made by recorded NGFCs showed close appositions, and rarely identifiable classical synaptic structures. Thus, we report here a novel interneuron type of the amygdala that generates volume transmission of GABA. The peculiar functional mode of NGFCs makes them unique amongst all GABAergic cell types of the amygdala identified so far.

On-center donor impurity-related nonlinear corrections to optical absorption and refractive index in a two-dimensional quantum ring

The donor impurity-related linear and nonlinear optical absorption as well as the linear and nonlinear corrections to the refractive index in a disc-shaped quantum dot under the effect of an external magnetic field and parabolic and inverse square confining potentials are calculated making use of the exact solutions for the two-dimensional motion of a conduction band electron in the system. It has been previously shown that this kind of structure may work well as a model for a quantum ring. In general terms, for a fixed confining configuration and the basic parameters typical of GaAs, the influence of an on-center donor impurity reflects in a blueshift of the resonant peak positions, together with a reduction in the peak amplitudes, affecting more significantly the nonlinear contributions. The results also show that the influence of the normally oriented magnetic field induces a blueshift in both the first and third order peaks of the calculated optical quantities. In addition, total peak amplitudes are shown to be growing functions of the magnetic field strength. The increase in the strength of the inverse square potential function enhances significantly the contribution from the nonlinear third-order terms in both the absorption and the relative correction to the refractive index.

Quantum disc plus inverse square potential. An analytical model for two‐dimensional quantum rings: Study of nonlinear optical properties

AbstractThe exact solutions for the two‐dimensional motion of a conduction band electron in a disc shaped quantum dot under the effect of an external magnetic field and parabolic and inverse square confining potentials are used to calculate the linear and nonlinear optical absorption as well as the linear and nonlinear corrections to the refractive index in the system. It is shown that this kind of structure may work well as a model for a quantum ring. Using the basic parameters typical of the GaAs, the results show that the influence of the normally oriented magnetic field induces a blueshift in both the first and third order peaks of the calculated optical quantities. In addition, total peak amplitudes are shown to be growing functions of the magnetic field strength. The increase in the strength of the inverse square potential function enhances significantly the contribution from the nonlinear third‐order terms in both the absorption and the relative correction to the refractive index.

VIP and PACAP inhibit L-, N- and P/Q-type Ca2+ channels of parasympathetic neurons in a voltage independent manner.

In this study, we investigated the effects of vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide 1-38 (PACAP) on the voltage-gated calcium currents in hamster submandibular ganglion neurons. VIP and PACAP inhibited the high threshold voltage-gated calcium current in a voltage-independent and a concentration-dependent manner via the G protein-mediated pathway. L-, N- and P/Q-type components of the total maximum voltage-gated calcium current accounted for 48.0 +/- 3.1% (n = 4), 35.1 +/- 4.7% (n = 4), and 13.5 +/- 2.3% (n = 3) of the total peak amplitude, respectively. VIP at a concentration of 1 microM inhibited the L-type calcium current by 33.2% +/- 1.4% (n = 4), the N-type current by 31.0 +/- 3.6%, and the P/Q-type current by 3.2 +/- 1.1% (n = 3). PACAP at a concentration of 1 microM inhibited the L-type current by 35.6 +/- 5.7%, the N-type current by 34.4 +/- 3.1% (n = 4), and the P/Q-type current by 6.4 +/- 2.1% (n = 2). However, VIP and PACAP did not inhibit the low threshold voltage-gated (T-type) calcium current. The rank order of potency was PACAP > VIP. In experiments replacing GTP with GDP-beta-S, the inhibitory effects of VIP and PACAP were prevented. In experiments of double-pulse protocol, depolarizing conditioning pulses could not relieve the inhibition of total high threshold voltage-gated calcium currents produced by VIP and PACAP. Therefore, the inhibition of the high threshold voltage-gated calcium channels produced by VIP and PACAP in hamster parasympathetic neurons differed in its mechanisms from that of N-type calcium channels in rat sympathetic neurons.

Coupled Sliding and Rocking of Embedded Foundations

Wide ranges of soil properties, foundation dimensions, and depths of embedment are considered, and typical results are presented for the maximum amplitudes of the sliding and rocking oscillations and the frequencies at which these maximum amplitudes occur. The natural frequencies of the system with and without radiation damping are dependent on the shear wave velocity and Poisson's ratio of the half-space material, the geometric proportions of the foundation, and the depth of embedment, and they increase substantially as the depth of embedment increases. The total peak amplitude of vibration for the coupled motion is expressed in terms of a linear function whose coefficients are dependent on Poisson's ratio, the foundation dimensions, and the depth of embedment depth, and graphical relationships are presented to facilitate the determination of these coefficients. The results obtained clearly illustrate that embedment of the foundation significantly decreases its total peak amplitude for a given exciting force.