Biomedical subjects
Publications and source records attributed to A Picozzi.
We demonstrate theoretically and experimentally in an optical fiber system that partially temporally incoherent light exhibits modulational instability during its propagation in an instantaneous response nonlinear medium. We show that the modulation frequency and gain are substantially increased with respect to the corresponding values of coherent modulational instability.
In optical second-harmonic generation with normal dispersion, the virtually infinite bandwidth of the unbounded, hyperbolic, modulational instability leads to quenching of spatial multisoliton formation and to the occurrence of a catastrophic spatiotemporal breakup when an extended beam is left to interact with an extremely weak external noise with a coherence time much shorter than that of the pump.
We show that the parametric process in quadratic nonlinear media supports three-dimensional (3D) hybrid solitary wave solution in which a transverse vortex solitons embedded in an infinite plane-wave background is sustained by a longitudinal parametric solitary wave. The structure of the parametric solitary wave results from the interplay of the quadratic nonlinearity and the temporal walk off (i.e., the velocity mismatch) between the interacting waves. The 3D hybrid solitary wave proved to be robust with respect to modulational instability, a feature that contrasts with previous studies on quadratic vortex solitons that revealed them to be always modulationally unstable. We show that the mechanism of stabilization of the vortex background lies on the temporal walkoff between the interacting waves that is able to drift the modulational instability out of the temporally localized structure that constitutes the 3D hybrid solitary wave.
We consider the basic problem of spontaneous parametric generation from quantum noise fluctuations in the presence of a continuous plane-wave pump. We show, both numerically and analytically, that the walk-off between the down-converted fields is the key ingredient that leads to the generation of coherent fields in the parametric process. Along these lines, our theory reveals that, in the absence of walk-off, diffraction and chromatic dispersion in usual quadratically nonlinear materials only lead to incoherent erratic dynamics. Moreover, a two-dimensional study shows that, when the walk-off is exclusively temporal (or spatial), the parametric process is not able to yield the generation of spatially (or temporally) coherent fields. This study sheds light on the problem of coherence in parametric fluorescence and, in particular, allows us to explain various recent experimental observations.
We show analytically and numerically that, under certain conditions, coherent localized structures can be generated and sustained from an incoherent source in quadratic nonlinear media. This phenomenon, which relies on the convection between the waves interacting in the medium, leads to the formation of a novel type of three-wave parametric soliton composed of both coherent and incoherent fields.
We investigate the influence of dispersion on parametric solitary waves. We show that dispersion is responsible for a transition towards a new type of dynamical solitary wave characterized by the presence of traveling phase defect arrays within their envelopes. The transition is described analytically through an original extension of the Kolmogorov-Petrovskii-Piskunov approach to front propagation into unstable states.
BACKGROUND: Color kinesis (CK) is a new echocardiographic technique for the assessment of left ventricular (LV) wall motion based on acoustic quantification. Using integrated backscatter data, this technique identifies the pixel value transitions from blood to myocardial tissue throughout systole and tracks endocardial motion in real time. The color-encoded images, built on a frame-by-frame basis by adding one color at a time, provide an integrated display of the timing and amplitude of endocardial motion in a single end-systolic frame. Recent studies have shown that CK is a promising clinical tool for quantitative assessment of regional LV function. OBJECTIVES: The aim of this study was to evaluate the feasibility and accuracy of CK in identifying the regional wall-motion abnormalities diagnosed by conventional two-dimensional (2-D) echocardiography in patients after acute myocardial infarction (AMI). METHODS: The end-systolic color overlays were analyzed using a method to quantify the regional timing and amplitude of endocardial systolic excursion (ESE) based on the count of the numbers of colors. At this point, the total duration (ESE timing) and distance (ESE amplitude) of endocardial excursion from end-diastolic to end-systolic color-frame was calculated in each segment. In 54 patients after AMI, we compared the feasibility and ability of CK superimposed on 2-D superimposed on 2-D superimposed on 2-D echocardiographic images and visual 2-D echo analysis to evaluate the endocardial border excursion in parasternal short-axis (SAX) and apical four-(AP4CH) and two-(AP2CH) chamber views. In 20 normal subjects, the end-systolic color overlays were used to evaluate the variability of the measurements of ESE timing (msec) and amplitude (cm) and to define the reference values. Image quality was considered adequate if at least 12 of 16 segments could be evaluated for systolic function by conventional visual 2-D echo. Among 54 patients, 35 with adequate studies were selected to determine the accuracy of quantitative analysis of CK images in identifying regional wall-motion abnormalities. RESULTS: The SAX view was obtained in 36 of 54 patients; of the possible 216 segments, 210 (97%) were adequately visualized by 2-D echocardiography and 207 (96%) by CK. Apical views were obtained in 50 patients (93%); of the possible 300 segments, 93% were visualized by 2-D echocardiography and 90% by CK in the AP4CH view and 94% and 92%, respectively, were visualized by the two methods in the AP2CH view. In normal subjects, measurements of ESE timing and amplitude were found to be consistent and the mean values were 346 msec (range 280-360) and 0.99 cm (range 0.72-1.26) respectively. In the 35 selected patients, 2-D echocardiography identified 355 normokinetic segments in which ESE timing and amplitude were similar to the reference values. In 83 hypokinetic segments and 108 akinetic segments, ESE timing and amplitude were significantly inferior to values of normokinetic segments (p < 0.001). An ESE timing below the reference values of 280 msec identified all of the 191 asynergic segments (sensitivity and specificity = 100%) and an ESE amplitude of less than 0.70 cm identified 188 asynergic segments (sensitivity = 98% and specificity = 99%). CONCLUSIONS: CK showed good feasibility and diagnostic accuracy in identifying regional wall motion abnormalities in patients with acute myocardial infarction. The model used in our study for the quantitative analysis of color kinesis images, which provided easy and feasible indices of timing and amplitude of endocardial excursion, enabled fast and objective evaluation of LV regional wall motion.
The drug prescribing practices of dentists should be of interest to the dental profession, drug manufacturers, the medical profession and dental educators. This article presents an update on an earlier similar survey reported by the authors as well as information on current infection control procedures, the treatment of hepatitis and AIDS patients, and generic drug substitution. The classes of drugs that are important to the practitioner and the level of prescribing activity have not changed appreciably since the earlier study. There has been, however, a significant change in nonopioid analgesic drug preference with ibuprofen overtaking aspirin and acetaminophen by a wide margin. That age affects the character of practice was confirmed: far fewer older practitioners report prescribing drugs than do their younger counterparts. A very gratifying finding was the high level of compliance with ADA recommendations regarding infectious diseases although fears over treating AIDS patients remain high.
The information presented in this article suggests that the drug responses of the elderly may be greater than those in the young or essentially the same. We have presented evidence that the pharmacokinetics in the elderly would probably tend toward prolonging the half-life and delaying the clearance of many drugs. Pharmacodynamic changes are more ambiguous, increasing sensitivity to some drugs and decreasing sensitivity to others. Compliance errors, from whatever cause, lead to unpredictable intake of drugs. Psychosocioeconomic factors contribute to compliance errors and no doubt also lead to increased intake of combination of drugs. Multiple diseases are common among the elderly, but it is not clear how disease states, per se, affect drug responses unless the specifically diseased organ is focally important in the handling of drugs. Alterations in perception of pain and in reflex and immune competence will produce changes in all directions. Use of multiple drugs almost certainly will create an environment favorable to drug interactions and adverse reactions. What is the dentist to do with these conflicting effects of aging in drug therapy? There are a few, and only a few, rules that can be said to have a solid basis in fact. Elderly patients seem to be more sensitive to the depressant effects of drugs. It is wise, therefore, to reduce the dosage of such drugs as the benzodiazepines, general anesthetics, analgesics, and sedative-hypnotics in the elderly. Old people are apparently more sensitive to certain drugs, for example, the neuromuscular blocking drugs. It would be wise to reduce the dosage of these for the older patient. The geriatric person appears to be less sensitive to pain; it would be wise to prescribe analgesics for such patients in lower doses. Elderly patients are known to have lost some of their reflex ability to maintain homeostasis. This should be taken into consideration when drugs that affect blood pressure, heart rate, and smooth muscle tone are used. Elderly patients are almost certain to be taking multiple medications. Drug interactions, as well as adverse drug reactions (which are exaggerated in the elderly), are likely to occur in this polypharmaceutical setting. It is critical that the dentist be continually informed of the pharmacologic status of each patient and be aware of the likelihood of interactions between drugs prescribed by the dentist, drugs-prescribed by the physician, and drugs that are self-administered.
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A recent study reported that regular use of commercial mouthwashes produced a significant incidence of oral reactions, including epithelial peeling, inflammation, ulceration and geographic tongue-like lesions. In view of the widespread use of these preparations, without apparent deleterious effects, an investigation of two commercial preparations (Scope, Listerine) and an experimental mouthwash containing cetyl pyridinium chloride was undertaken to assess the possible irritant effects on the oral soft tissue under stringent test conditions. A double blind design was used and soft tissue effects were measured over a two week period. Rinses were used full strength, 20 cc 3 times daily. Examinations were conducted by an oral pathologist at the start and conclusion of the test period, and a record was made of the occurrence of erythema, hyperemia/prominent vasculature, inflammation, petechia, keratosis, tongue coating, and ulceration. These observations did not reveal any soft tissue conditions beyond those which would be expected in the normal population.
A total of 246 physicians who either had graduated from or had matriculated without graduating from dental school prior to entering a medical school were identified, and a combination multiple-choice, open-ended questionnaire was mailed to the group. Completed questionnaires were recived from 194 subjects for a 79 percent response rate. The questionnaire was designed to elicit information about the decision to study dentistry and the subsequent decision to study medicine. The authors were also interested in the process of admission to medical school, in academic performance in both schools, in choice of medical specialty, and in attitudes toward dentistry and medicine.
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The end point methodology did not indicate a difference between the agents. The prophylaxis effect was only demonstrable through 8 weeks, although the analysis of variance indicated a prophylaxis effect on gingival index throughout the study. An agent effect was not demonstrable in the study. The "positive control," chlorhexidine, did not give the same results in this brushing study as in previous no-brushing studies reported by Loe and by our group. One might conclude that the effectiveness of brushing in reducing gingivitis is greater than the effect of chlorhexidine. Decreasing plaque and gingivitis scores are seen with increasing time, probably reflecting increased subject interest and involvement in the study. Mere involvement in the study apparently produced a beneficial effect on gingival health. This "placebo effect" also has been noted in an earlier study. A similar decrease in plaque scores in a placebo group attributable to a general improvement of oral hygiene was reported by Gjermo and Rolla. The subjects who began the study with no calculus (prophylaxis group) had consistently lower calculus scores than those not given a prophylaxis. This difference became less distinct at later exams, as the treated group developed calculus. The agents, although ineffective under the test regimen produced no adverse effects.