Search

The implementation of a new method to control line-commutated converters in discontinuous conduction mode is presented. The method is based on the modification of the thyristor's firing angle [alpha] using a linear approximation, yielding nearly the same dynamic performance as in continuous conduction mode. The firing angle is corrected by adding a supplementary angle [DELTA][alpha], calculated by estimating the average output current. The proposed technique significantly reduces computational burden, thus being suitable for online calculation. Both simulations and experimental results are presented on a 1-kW laboratory prototype. Index Terms--Estimation, nonlinear control, power supplies, thyristors.

Ventricular arrhythmias are frequently observed in the elderly population secondary to alterations of electrophysiological properties that occur with the normal aging process of the heart. However, the underlying mechanisms remain poorly understood. The aim of the present study was to determine specific age-related changes in electrophysiological properties and myocardial structure in the ventricles that can be related to a structural-functional arrhythmogenic substrate. Multiple unipolar electrograms were recorded in vivo on the anterior ventricular surface of four control and seven aged rats during normal sinus rhythm and ventricular pacing. Electrical data were related to morphometric and immunohistochemical parameters of the underlying ventricular myocardium. In aged hearts total ventricular activation time was significantly delayed (QRS duration: +69%), while ventricular conduction velocity did not change significantly compared with control hearts. Moreover, ventricular activation patterns displayed variable numbers of epicardial breakthrough points whose appearance could change with time. Morphological analysis in aged rats revealed that heart weight and myocyte transverse diameter increased significantly, scattered microfoci of interstitial fibrosis were mostly present in the ventricular subendocardium, and gap junction connexin expression decreased significantly in ventricular myocardium compared with control rats. Our results show that in aged hearts delayed total ventricular activation time and abnormal activation patterns are not due to delayed myocardial conduction and suggest the occurrence of impaired impulse propagation through the conduction system leading to uncoordinated myocardial excitation. Impaired interaction between the conduction system and ventricular myocardium might create a potential reentry substrate, contributing to a higher incidence of ventricular arrhythmias in the elderly population. epicardial mapping; breakthrough point; aged heart

The international experiment called the European Aqua Thermodynamic Experiment (EAQUATE) was held in September 2004 in Italy and the United Kingdom to validate Aqua satellite Atmospheric Infrared Sounder (AIRS) radiance measurements and derived products with certain ground-based and airborne systems use ful for validating hyperspectral satellite sounding observations. A range of flights over land and marine surfaces were conducted to coincide with overpasses of the AIRS instrument on the Earth Observing System Aqua platform. Direct radiance evaluation of AIRS using National Polar-Orbiting Operational Environmental Satellite System (NPOESS) Airborne Sounder Testbed-Interferometer (NAST-I) and the Scanning High-Resolution Infrared Sounder has shown excellent agreement. Comparisons of level-2 retrievals of temperature and water vapor from AIRS and NAST-I validated against high-quality lidar and dropsonde data show that the 1-K/1-km and 10%/1-km requirements for temperature and water vapor (respectively) are generally being met. The EAQUATE campaign has proven the need for synergistic measurements from a range of observing systems for satellite calibration/validation and has paved the way for future calibration/validation activities in support of the Infrared Atmospheric Sounding Interferometer on the European Meteorological Operational platform and Cross-Track Infrared Sounder on the U.S. NPOESS Prepatory Project platform.

Whether human capital increases or decreases earnings uncertainty is an open question from an empirical standpoint. Yet, most policy prescriptions regarding human capital formation are based on models that impose riskiness on this human capital investment. In this paper we extend the dynamic Mirrlees taxation framework to include investments in human capital and derive prescriptions that are robust to the risk characteristics of human capital. Savings should be discouraged, human capital investments encouraged and both types of investment driven to an efficient level from an aggregate perspective. These prescriptions are also robust to whether investments are individually observed or not. JEL classification: H21; H24 Keywords: Education; Optimal taxation; Endogenous policy instruments

Paced breathing (PB) around 0.25 Hz has been advocated as a means to avoid confounding and to standardize measurements in short-term investigations of autonomic cardiovascular regulation. Controversy remains, however, as to whether it causes any alteration in autonomic control. We addressed this issue in 40 supine, middle-aged, healthy volunteers by assessing the changes induced by PB (0.25 Hz for 8 min) on 1) ventilatory parameters, 2) the indexes of autonomic control of cardiovascular function, and 3) the spectral indexes of cardiovascular variability. Subjects were grouped into group 1 (n = 31), if spontaneous breathing was regular and within the high-frequency (HF) band (0.15-0.45 Hz), or group 2 (n = 9), if it was irregular or slow ( heart rate variability; controlled breathing; baroreflex sensitivity; spectral analysis

Animal studies have demonstrated that visceral afferent stimulation alters autonomic cardiovascular reflexes. This mechanism might play an important role in the pathophysiology of conditions associated with visceral hypersensitivity, such as irritable bowel syndrome (IBS). As such, studies in humans are lacking, we measured viscerosensory-cardiovascular reflex interactions in IBS patients and healthy controls. Systolic blood pressure (SBP), heart rate (HR), and arterial baroreflex sensitivity (BRS) were studied in 87 IBS patients and 36 healthy controls under baseline conditions and during mild (15 mmHg) and intense (35 mmHg) visceral stimulation by rectal balloon distension. BRS was computed from continuous ECG and arterial blood pressure signals (Finapres-method) during 5-min periods of 15-min metronome respiration. Baseline SBP and HR were not different between patients and controls. In both groups, SBP increased similarly during rectal stimulation, whereas HR decreased during mild and increased intense stimulation. BRS was significantly higher in patients compared with controls at baseline (7.9 [+ or -] 5.4 vs. 5.7 [+ or -] 3.7 ms/mmHg, P = 0.03) and increased significantly in both groups during mild stimulation. This increase persisted in controls during intense stimulation, but BRS returned to baseline in patients. BRS was not significantly different between groups during rectal distension. This study demonstrates the presence of a viscerosensory-cardiovascular reflex in healthy individuals and in IBS patients. The increased BRS in IBS patients at baseline may either be a training-effect (frequent challenging of the reflex) or reflects altered viscerosensory processing at the nucleus tractus solitarii. autonomic nervous system; colonic diseases; functional; blood pressure; heart rate; baroreflex

In preparation for a possible space mission, a breadboard version named REFIR-BB of the Radiation Explorer in the Far Infrared (REFIR) instrument has been built. The REFIR is a Fourier-transform spectrometer with a new optical layout operating in the spectral range 100-1100 [cm.sup.-1] with a resolution of 0.5 [cm.sup.-1], a 7-s acquisition time, and a signal-to-noise ratio of better than 100. Its mission is the spectral measurement in the far infrared of the Earth's outgoing emission, with particular attention to the long-wavelength spectral region, which is not covered by either current or planned space missions. This measurement is of great importance for deriving an accurate estimate of the radiation budget in both clear and cloudy conditions. The REFIR-BB permits the trade-off among all instrument parameters to be studied, the optical layout to be tested, and the data-acquisition strategy to be optimized. The breadboard could be used for high-altitude ground-based campaigns or could be flown for test flights on aircraft or balloon stratospheric platforms. The breadboard's design and the experimental results are described, with particular attention to the acquisition strategy and characterization of the interferometer. Tests were performed both in laboratory conditions and in vacuum. Notwithstanding a loss of efficiency above 700 [cm.sup.1] caused by the poor performance of the photolithographic polarizers used as beam splitters, the results demonstrate the feasibility of using the spectrometer for space applications. OCIS codes: 300.6300, 300.6270, 120.3180, 010.0010.

The synthesis of Aryloxytitanatranes are described. The Aryloxytitanatranes adopt monomeric, trigonal bipyramidal structures, as confirmed by X-ray crystallography.

In cardiovascular variability analysis, the significance of the coupling between two time series is commonly assessed by setting a threshold level in the coherence function. While traditionally used statistical tests consider only the parameters of the adopted estimator, the required zero-coherence level may be affected by some features of the observed series. In this study, three procedures, based on the generation of surrogate series sharing given properties with the original but being structurally uncoupled, were considered: independent identically distributed (IID), Fourier transform (FT), and autoregressive (AR). IID surrogates maintained the distribution of the original series, while FT and AR surrogates preserved the power spectrum. The ability of the three methods to define the threshold for zero coherence was validated and compared by computer simulations reproducing typical cardiovascular interactions. While the IID threshold depended only on record length and design parameters of the coherence estimator, FT and AR thresholds were frequency-dependent with peaks corresponding to the local maxima of the estimated coherence. FT and AR surrogates were able to compensate spurious coherence peaks due to equal-frequency but independent oscillations in the two series. The benefit of frequency-dependent thresholds was evident for short series with narrow-band oscillations. Thus, surrogates preserving the power spectrum of the original series are recommended to avoid false coupling detections in the presence of oscillations occurring at nearby frequencies but produced by different mechanisms, as may frequently happen in cardiovascular and cardiorespiratory regulation. Index Terms--Cardiovascular variability, coherence function, coupling significance, spectral analysis, surrogate data.

The synthesis and photophysical properties of novel luminescence ruthenium(II) bipyridyl complexes containing one, two or six lower rim acid-amide-modified calix[4]arene moities covalently linked to the bipyridine groups are reported, which are designed to coordinate and sense luminescent lanthanide ions.

The effect of occupational exposure to styrene on frequencies of chromosomal aberrations and binucleated cells with micronuclei and on single-strand break levels in peripheral blood lymphocytes was studied in 86 [...]

Byline: M. Canesi (1), L. Perbellini (2), L. Maestri (3), A. Silvani (1), L. Zecca (4), L. Bet (5), G. Pezzoli (1) Keywords: Key words Parkinson's disease; aging; hydrocarbons; n-hexane; 2,5-hexanedione; metabolism Abstract: Although genomic screening studies have identified several genes associated with Parkinson's disease (PD), there is evidence that environmental factors are also involved in the pathogenesis of the disease and that hydrocarbon-solvents may be one of them. The genetic component is less evident in late-onset PD. To assess whether age and PD may affect the catabolism of the hydrocarbon n-hexane, a two-part study was performed. In the first part the urinary levels of its main metabolites, 2,5-hexanedione and 2,5-dimethylpyrroles, were measured in 108 patients and 108 healthy controls, matched by age and sex. Metabolite urinary excretion was significantly reduced in PD patients as compared with controls and was inversely related to age in both groups. In the second part the same comparison was made between 24 non-smoking and 10 smoking patients, matched to controls, after smoking of a hydrocarbon-rich cigarette. In these subjects also n-hexane and 2,5-hexanedione blood levels were measured. There was no appreciable difference in n-hexane blood levels between patients and controls in non-smokers, whereas there was a significant increase in patients over controls in smokers (p &lt 0.01). 2,5-hexanedione blood levels were significantly lower in patients than in healthy controls, both in non-smokers and in smokers, but the reduction was more pronounced in smokers (-46.3 % versus -10.7 %). The same was true for 2,5-hexanedione and 2,5-dimethylpyrrole urinary levels. This study suggests that aging and PD may be associated with a reduction in the capacity to eliminate the hydrocarbon n-hexane. This metabolic alteration may play a role in the pathogenesis of PD. Author Affiliation: (1) Department of Neuroscience, Parkinson Institute, Istituti Clinici di Perfezionamento, Via Bignami 1, 20126 Milano, Italy. pezzoli@parkinson.it, IT (2) Dept. Medicine and Public Health, University of Verona, Verona, Italy, IT (3) Fondazione S. Maugeri, Pavia, Italy, IT (4) Institute of Advanced Biomedical Technologies, National Research Council, Milan, Italy, IT (5) Institute of Clinical Neurology, University of Milan, Milan, Italy, IT Article note: Received: 18 March 2002, Received in revised form: 9 October 2002, Accepted: 29 November 2002 Funding: Fondazione Grigioni per il Morbo di Parkinson Associazione Italiana Parkinsoniani. Correspondence to Gianni Pezzoli

The 4'-dimethylaminoflavylium ion in the liquid solution goes through a significant network of chemical reactions restricted by pH and light excitation. However, the multistate/multifunctional features of 4'- dimethylaminoflavylium are further analyzed in the framework of write-lock-read-unlock-erase phases.

The complexation of the luminescent lanthanide ions by a polylysin dendrimer that contains 21 amide groups in the interior and 24 dansyl units in the periphery are analysed. Result revealed that the formation of the metal complexes is accompanied by a quenching of the fluorescent excited state of the dansyl units and sensitized near-infrared emission of the lanthanide ion in fluid solution at 298 K.

Several novel redox-active and photoactive ruthenium(II) and osmium(II) bipyridyl-, ferrocene-, and cobaltocenium-containing macrocyclic receptors, with the ability to selectively sense anionic guest species through electrochemical and optical methodologies, have been prepared. Hydrogen bonding and respective macrocyclic cavity size to anion recognition is important. The receptors were found to form strong and selective complexes with C1-, Hsub2POsub4- and OAc- anions.

A photochromic system using synthetic flavylium salt in aqueous solution is used to create a write-lock-read-unlock-erase molecular switching system. The system, which can be switched on and off using temperature and pH controls, can be used as an optical memory device with multiple storage and non-destructive readout capacity. The photochromic systems are illustrated and their spectral analysis described.

The reliability of an isokinetic hand grip endurance test was investigated. The subjects performed six maximal endurance tests in two different positions with a hand grip toll attached to an isokinetic dynamometer. The proposed isokinetic endurance test was recommended as a useful tool for quantifying work-related functional capacity of the upper limbs and in vocational rehabilitation.

The energy- and electron-transfer quenching mechanisms of the lowest triplet excited state of biacetyl (2,3-butanedione) incarcerated in a hemicarcerand were systematically studied in CH2Cl2 solution at room temperature. Findings indicated that the walls of the hemicarcerand permit only very weak electronic interaction between imprisoned triplet biacetyl and external quenchers.

Treating girls with ornithine transcarbamylase deficiency with sodium phenylbutyrate appears to prevent the long-term neurologic damage characteristic of this disease. Ornithine transcarbamylase converts dietary nitrogen to urea, which is excreted in the urine. People with the enzyme deficiency cannot produce urea, so ammonia builds up in their blood, which can damage the brain. Thirty-two girls with the deficiency were treated with sodium phenylbutyrate, which safely excretes dietary nitrogen. The treatment reduced the risk of neurologic complications and stabilized many of the girls' intellectual function.

To evaluate the effects of record length selection on the accuracy of spectral estimates of heart rate variability (HRV), a simulation study was carried out using a set of 58 signals obtained by autoregressive (AR) fitting a representative sample of real HRV signals. Four record lengths of 180, 300, 420, and 540 s were considered. Spectral estimation was performed by both the Blackman-Tukey (B-T) and AR methods. Accuracy was assessed for: 1) point spectral estimates, by computing the normalized averaged bias (NAB) and variance (NAV); and 2) the most commonly used spectral parameters [total power (TP) and the powers in the bands: very low frequency (VLF) (0 / 0.04 Hz), low frequency (LF) (0.04 / 0.15 Hz), and high frequency (HF) (0.15 / 0.45 Hz)], by computing the normalized bias (NB) and variance (NV). The results are: whatever the record length considered, the 90th percentiles (90P) of the NAB were [less than]10%, whereas those of the NB were [less than]9% for TP, LF, and HF powers, and [less than]14% for the VLF power, in both methods. The NAV was proportional to the reciprocal of record length, showing high 90P values for the shortest record length (26.4% for B-T and 44.2% for AR). The NV showed the same trend but 90P values were much lower ([less than]8% for TP, LF, and HF powers and [less than]19% for VLF power, in both methods). In the final part of the paper a procedure for the computation of approximate upper bounds of the relative absolute error of spectral measures at each record length, based on the knowledge of the NB and NV, is presented.

The luminescent behavior of 14 (Ru tpy-X tpy-Y) (sup 2+) complexes was studied. The investigation, which was conducted when tpy = 2,2':6',2-terpyridine and X = Y = electronic donor or acceptor substituents, demonstrated the complexes' strong luminescence at 77 K and the red-shifted energy of the emission maximum of the electron-accepting and electron-donating substituents. In addition, it revealed the increase in luminescence quantum yield and excited state lifetime of the electron-accepting substituents at room temperature.

The synthesis and characterization of the complexes of Eu3+, Tb3+ and Gd3+ with a branched hexaazacyclooctadecane ligand containing six 2,2'-bipyridine (bpy) pendant units were reported. The FAB+ mass spectrometry of the complexes were carried out in CH3OH, CH3CN, H2O and alcohol solutions. Coordination of the bpy units was studied by absorption, emission and excitation spectroscopy. The luminescence spectra and lifetimes of the complexes were compared with that for mononuclear complexes of a branched triazacyclononane ligand containing three bpy pendant units.

It is possible to use an easy and inexpensive flash spectroscopy experiment to teach students about concepts of transient decay kinetics and time-resolved spectra in an inexpensive and easy way. A chemical system in which a polychromatic light flash forms the transient species with lifetimes of subseconds to seconds is used. A relatively simple computer-interface spectrophotometer capable of acquiring 1- or 5 points/sec can follow kinetics. As time resolution goes up in a flash spec system, cost goes up. Usually flash spec is not in university curricula.