Effect of sodium nitroprusside on compound action potential thresholds in the gerbil cochlea

OBJECTIVE: Trials that do not allow rejection of the null hypothesis of no treatment effect may have had an inappropriate design. Trials are virtually never assessed for correlation between responses to different treatment modalities. METHODS: Using a hypothetical example and several published studies we examine the influence of correlation levels between treatment modalities on the sensitivity of testing. RESULTS: The level of correlation between responses to different treatment modalities is a major determinant of the sensitivity both of crossover and parallel group clinical trials. CONCLUSIONS: It is very relevant to assess a priori correlation levels between responses to the different treatment modalities of a trial. If a negative correlation is anticipated, a crossover design is likely to lack sensitivity. If a positive correlation is anticipated a parallel-group design seems less appropriate, because it would lack the extra sensitivity of accounting for the positive correlation. Both designs would seem suitable for approximately zero correlations (e.g. comparison vs baseline or vs placebo under the assumption that the number of placebo responders is negligible.     

Detection and Quantification of Free Glycerol in Virgin Olive Oil by <Superscript>31</Superscript>P-NMR Spectroscopy

³¹P-Nuclear magnetic resonance (NMR) spectroscopy was employed to detect and quantify free glycerol in virgin olive oils originating from various regions of Greece. This analytical method was based on the derivatization of the hydroxyl groups of glycerol with the tagging reagent 2-chloro-4,4,5,5-tetramethyldioxaphospholane, and identification of the phosphitylated compound on the basis of ³¹P chemical shifts. Quantification of glycerol in olive oils was accomplished by integration of the appropriate signals in the ³¹P NMR spectrum and the use of the phosphitylated cyclohexanol as internal standard. A linear correlation was observed between the glycerol content and 1,3-diacylglycerols and free acidity indicating that glycerol is the final product of the partial hydrolysis of triacylglycerols.     

NMR measurement of free and esterified sterols

This short account describes a novel analytical technique for the determination of total, free and esterified sterols in olive oil developed in our laboratory. This methodology is based on ¹H and ³¹P NMR spectroscopy. The latter spectroscopic analysis requires first the derivatization of the sterolic hydroxyl groups with a phosphitylating reagent. This NMR method shows a number of advantages over conventional methods for sterols determination, amongst which speed and simplicity are the most beneficial ones. The possibility of applying the NMR spectroscopy to other food matrices is discussed.     

Use of GPC-UV to determine the location of functional groups in styrenic polymers

Gel permeation chromatography (GPC) is one of the most important characterization tools of the polymer chemist. The coupling of GPC with ultraviolet (UV) spectroscopy (GPC–UV) increases the power of the tool even further. This article describes the use of GPC–UV to determine the location of functional groups in polymers. This information is important for characterization of functionalized polymers being used as building blocks for making block and graft copolymers, and for the elucidation of polymer degradation mechanisms. The use of GPC–UV for quantitation of the level of functional groups is hampered by the inability to achieve complete conversion of some UV transparent functional groups (e.g., hydroxyl and carbonyl) to the uniquely absorbing derivative needed for the analysis. Attempts to quantitatively derivatize polymer-bound functional groups using conditions developed for model compounds failed. However, the use of GPC–UV to locate functional groups in polymers (pendant vs. chain-end) is clearly demonstrated.     

An investigation of 1H and 13C longitudinal relaxation and relaxation in the rotating frame in solid poly(N‐vinylcarbazole)

¹H and ¹³C longitudinal relaxation times (T₁) and relaxation times in the rotating frame (T_1ρ) have been measured for poly(N‐vinylcarbazole) in the solid state in air and nitrogen atmospheres in an attempt to elucidate molecular motions. In air, the T₁ relaxation of both ¹H and ¹³C was dominated by interaction with absorbed paramagnetic oxygen. In nitrogen, the ¹³C T₁ relaxation times were long (>300 s) and were averaged by ¹³C–¹³C spin diffusion. The ¹³C T_1ρ relaxation times showed an exponential dependence on the strength of the rotating ¹³C magnetic field and were thus controlled by spin–spin processes rather than spin–lattice processes. © 2001 Society of Chemical Industry     

Bayesian testing simple hypotheses on The drift of a wiener process With randomly relayed observations

We present a Byesian test of simple hypotheses on the drift of the observation process X_t = θt + W_twhere θis a bernouli random variable (w_t) is a standard Wiener process. sequential tests δ = (T, d) are used, where T is a (F^X _t)-stopping time, d is a (F^X _t+n)-measurable decision function, n is a postive random variable with a given distribution. The cost function V(π, T, d) of any sequential test θ = (T, d) is based on costs of wrong decisions and observation, respectively.     

An Exact Input Current Analysis of Ideal Static PWM Inverters

The precise knowledge of current harmonics generated at the input of static pulsewidth modulated (PWM) inverters is essential in designing the input filter and in determining the interaction between the inverter and supply voltage bus. Despite its importance, however, this topic has been given mostly qualitative treatment. A novel harmonic analysis approach is employed with ideal static voltage source inverters to specify the harmonic spectra of their respective input currents. This information is subsequently used to compute the harmonic distortion of the input current and the ripple current for the input filter capacitor.     

Major and trace elements in milk and Halloumi cheese as markers for authentication of goat feeding regimes and geographical origin

Sixty samples of milk, Halloumi cheese and local grazing plants (i.e. shrubs) were collected over a year from dairy farms located on three different locations of Cyprus. Major and trace elements were quantified using inductively coupled plasma–atomic emission spectroscopy (ICP‐AES). Milk and Halloumi cheese produced in different geographical locations presented significant differences in the concentration of some of the elements analysed. Principal component analysis showed grouping of samples according to the region of production for both milk and cheese samples. These findings show that the assay of elements can provide useful fingerprints for the characterisation of dairy products.     

Characterization of Polyglycerol Polyricinoleate Formulations Using NMR Spectroscopy, Mass Spectrometry and Dynamic Light Scattering

Three different analytical techniques, namely NMR spectroscopy, mass spectrometry and dynamic light scattering, were used to unravel the structure and morphology of polyglycerol polyricinoleate (PGPR). This material is used as an emulsifier in the preparation of chocolate and other confectionary products. The use of 1D and 2D NMR techniques led to the distinction of two separate entities in commercial ricinoleic acid (RA) and PGPR samples, namely the monomeric and oligomeric RA (estolides). ¹H and ¹³C spectra of PGPR confirmed the presence of polyglycerol moieties of various lengths being esterified by RA and estolides and to a lesser extent by oleic and linoleic acids. ¹³C-NMR DOSY experiments demonstrated the occurrence of several species in PGPR. Electrospray Ionization and tandem Mass Spectrometry succeeded in identifying the presence of over 30 glycerol/polyglycerol species containing n glycerol moieties with n = 1–6 esterified by monomeric and oligomeric RA molecules. Dynamic light scattering contributed to the characterization of PGPR morphology. The PGPR mixture contains relatively small-sized entities (monomers, dimmers, trimmers) and larger aggregates resulted from chain association. The percentage of larger aggregates is minimal compared to small-sized species.     

Cis and trans components of lipids: Analysis by 1H NMR and silver shift reagents

In this study, the methodology of shift reagents was exploited to distinguish cis and trans unsaturation in oils and fats. The differential binding of silver ions (in the form of AgFOD) to cis and trans double bonds allowed the separation of the allylic and olefinic proton signals in the ¹H NMR spectra of mixtures of cis and trans methyl esters of monoene aliphatic acids and unsaturated triacylglycerol mixtures at low frequency spectrometers (300 MHz). Careful integration of the appropriate proton resonances in the recorded quantitative ¹H NMR spectra afforded percentage concentrations in very good agreement with the actual values. This ¹H NMR methodology was validated by analyzing AOCS Laboratory Proficiency Program GC samples containing various percentages of saturated, cis‐mono unsaturated, and cis‐polyunsaturated fat as well as trans content. This fast and relatively low‐cost NMR methodology could be used on line for obtaining nutrition labeling compositional data (NLCD) required for fat‐containing food products. Attempts to differentiate lipid molecules with different degree of unsaturation and positional distribution of cis double bonds were unsuccessful.