Nonlinear modeling of the dynamic effects of arterial pressure and CO2 variations on cerebral blood flow in healthy humans

The effect of spontaneous beat-to-beat mean arterial blood pressure fluctuations and breath-to-breath end-tidal CO2 fluctuations on beat-to-beat cerebral blood flow velocity variations is studied using the Laguerre-Volterra network methodology for multiple-input nonlinear systems. The observations made from experimental measurements from ten healthy human subjects reveal that, whereas pressure fluctuations explain most of the high-frequency blood flow velocity variations (above 0.04 Hz), end-tidal CO2 fluctuations as well as nonlinear interactions between pressure and CO2 have a considerable effect in the lower frequencies (below 0.04 Hz). They also indicate that cerebral autoregulation is strongly nonlinear and dynamic (frequency-dependent). Nonlinearities are mainly active in the low-frequency range (below 0.04 Hz) and are more prominent in the dynamics of the end-tidal CO2-blood flow velocity relationship. Significant nonstationarities are also revealed by the obtained models, with greater variability evident for the effects of CO2 on blood flow velocity dynamics.     

Detection of skin cancer by classification of Raman spectra

Skin lesion classification based on in vitro Raman spectroscopy is approached using a nonlinear neural network classifier. The classification framework is probabilistic and highly automated. The framework includes a feature extraction for Raman spectra and a fully adaptive and robust feedforward neural network classifier. Moreover, classification rules learned by the neural network may be extracted and evaluated for reproducibility, making it possible to explain the class assignment. The classification performance for the present data set, involving 222 cases and five lesion types, was 80.5%+/-5.3% correct classification of malignant melanoma, which is similar to that of trained dermatologists based on visual inspection. The skin cancer basal cell carcinoma has a classification rate of 95.8%+/-2.7%, which is excellent. The overall classification rate of skin lesions is 94.8%+/-3.0%. Spectral regions, which are important for network classification, are demonstrated to reproduce. Small distinctive bands in the spectrum, corresponding to specific lipids and proteins, are shown to hold the discriminating information which the network uses to diagnose skin lesions.     

High-power deuterium Raman laser at 632 nm

We demonstrate a continuous-wave deuterium Raman laser that generates more than 160 mW of Stokes output power despite severe thermal effects. This output power represents nearly an order-of-magnitude increase over any previously reported continuous-wave Raman laser and is the first such system to our knowledge that uses deuterium gas as the Raman medium. The high output power is achieved through careful consideration of the electronic feedback design, frequency actuators, and pump-laser intensity noise.     

Determination of uronic acids in isolated hemicelluloses from kenaf using diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and the curve-fitting deconvolution method

Hemicellulose samples were isolated from kenaf (Hibiscus cannabinus L.). Hemicellulosic fractions usually contain a variable percentage of uronic acids. The uronic acid content (expressed in polygalacturonic acid) of the isolated hemicelluloses was determined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and the curve-fitting deconvolution method. A linear relationship between uronic acids content and the sum of the peak areas at 1745, 1715, and 1600 cm(-1) was established with a high correlation coefficient (0.98). The deconvolution analysis using the curve-fitting method allowed the elimination of spectral interferences from other cell wall components. The above method was compared with an established spectrophotometric method and was found equivalent for accuracy and repeatability (t-test, F-test). This method is applicable in analysis of natural or synthetic mixtures and/or crude substances. The proposed method is simple, rapid, and nondestructive for the samples.     

Quantitative analysis of the in situ Fourier transform infrared absorption and emission spectrum of gas-phase SiO (Deltav = 1 and 2) produced in Si-N-O fiber growth

The in situ Fourier transform infrared (FT-IR) spectrum of gasphase SiO produced in silicon oxynitride fiber growth has been quantitatively analyzed. Both absorption and emission FT-IR spectra at a spectral resolution of 0.5 cm(-1) were produced from the reaction zone at 1450 degrees C. The fundamental and hot bands were observed with vibrational levels up to v = 7. For the purposes of quantitative analysis the individual vibration-rotation integrated line strengths for the three main isotopes,( 28)SiO,( 29)SiO, and( 30)SiO, were calculated based on ab initio quantum chemical calculations of the electric dipole moment function and the transition moment. Vibrational anharmonicity and Hermann-Wallis correction factors were also incorporated. From the line strengths at specific temperatures and the known Dunham coefficients, the absorbance spectrum was simulated with best fits giving the averaged SiO concentration in the 400 mm reaction zone of 1.0 x 10(17) molecules/cm(3). Such quantitative measurements demonstrate the power of in situ infrared (IR) spectroscopy combined with quantum chemical calculations. The rapid determination of synthetic calibration datasets for chemometric analysis can thus lead to correlation of gas-phase species concentrations with fiber growth properties and subsequently to real-time process control.     

Use of infrared spectroscopy for the determination of electronegativity of rare earth elements

Infrared spectroscopy has been used to study a series of synthetic agardite minerals. Four OH stretching bands are observed at around 3568, 3482, 3362, and 3296 cm(-1). The first band is assigned to zeolitic, non-hydrogen-bonded water. The band at 3296 cm(-1) is assigned to strongly hydrogen-bonded water with an H bond distance of 2.72 A. The water in agardites is better described as structured water and not as zeolitic water. Two bands at around 999 and 975 cm(-1) are assigned to OH deformation modes. Two sets of AsO symmetric stretching vibrations were found and assigned to the vibrational modes of AsO(4) and HAsO(4) units. Linear relationships between positions of infrared bands associated with bonding to the OH units and the electronegativity of the rare earth elements were derived, with correlation coefficients >0.92. These linear functions were then used to calculate the electronegativity of Eu, for which a value of 1.1808 on the Pauling scale was found.     

Criticality accident dosimetry by chromosomal analysis

The technique of measuring the frequency of dicentric chromosomal aberrations in blood lymphocytes was used to estimate doses in a simulated criticality accident. The simulation consisted of three exposures; approximately 5 Gy with a bare source and 1 and 2 Gy with a lead-shielded source. Three laboratories made separate estimates of the doses. These were made by the iterative method of apportioning the observed dicentric frequencies between the gamma and neutron components, taking account of a given gamma/neutron dose ratio, and referring the separated dicentric frequencies to dose-response calibration curves. An alternative method, based on Bayesian ideas, was employed. This was developed for interpreting dicentric frequencies in situations where the gamma/neutron ratio is uncertain. Both methods gave very similar results. One laboratory produced dose estimates close to the eventual exercise reference doses and the other laboratories estimated slightly higher values. The main reason for the higher values was the calibration relationships for fission neutrons.     

Response of a lithium gadolinium borate scintillator in monoenergetic neutron fields

Accurate estimation of neutron dose requires knowledge of the neutron energy distribution in the working environment. Existing neutron spectrometry systems, Bonner spheres for example, are large and bulky, and require long data acquisition times. A portable system that could indicate the approximate neutron energy spectrum in a short time would be extremely useful in radiation protection. A composite scintillator, consisting of lithium gadolinium borate crystals in a plastic scintillator matrix, produced by Photogenics is being tested for this purpose. A prototype device based on this scintillator and digital pulse processing electronics has been calibrated using quasi-monoenergetic neutron fields at the low-scatter facility of the UK National Physical Laboratory (NPL). Energies selected were 144, 250, 565, 1400, 2500 and 5000 keV, with correction for scattered neutrons being made using the shadow cone technique. Measurements were also made in the NPL thermal neutron field. Pulse distributions collected with the digitiser in capture-gated mode are presented, and detection efficiency and energy resolution derived. For comparison, neutron spectra were also collected using the commercially available Microspec N-Probe from Bubble Technology Industries, which consists of an NE213 scintillator and a 3He proportional counter.     

A CoMFA study of COX-2 inhibitors with receptor based alignment

A diverse set of 53 cyclooxygenase-2 (COX-2) inhibitors which were aligned in two different ways were subjected to CoMFA analysis. The first method of alignment of the molecules was based on the binding information sourced from the crystallographic study, from which CoMFA Model 1 was derived. The second mode of alignment was generated by docking the inhibitors in the binding pocket using the DOCK and AFFINITY suite of programs; this gave a second model. The CoMFA Model 2 was slightly better than Model 1 in terms of the statistical parameters r(2) and q(2). The two models could predict very well the activity of a test set of diverse molecules, with a predictive r(2) of 0.593 and 0.768, respectively. Besides the QSAR results, the docking studies give a deep insight into the H-bonding interactions between the inhibitors and residues in the active site of the enzyme, which can be exploited in designing better inhibitors. Useful ideas on activity improvement could be gleaned from these models.