PubMed Health⌕ Search

Biomedical subjects

P Gori

Publications and source records attributed to P Gori.

At least 19 recordsLinked to original sources
PubMed2005

Ultrastructure of mature spermatozoids in the fern Asplenium onopteris L.

Asplenium onopteris L. spermatozoids are 8-8.5 microm long in the form of spirals with 4.5 turns. They have about 50 flagella. The nucleus occupies the last three posterior turns. Chromatin is partly honeycomb-shaped and partly highly condensed. An electron transparent space crossed by dense fibers delimits the condensed chromatin. Here, the nuclear membranes are closely apposed without any space between them and the plasmalemma often invaginates among elements of the microtubular ribbon, connecting with the outer nuclear membrane. An electron opaque body apparently links and anchors all anterior spermatozoid components. The cytoplasm contains plastids with starch grains, (lipid) bodies and different membrane systems, which are presumably plasmalemma derivatives involved in a process of cytoplasmic reduction.

Microscopy, Electron↗
PubMed2002

Propagation-independent fields.

Nondiffracting beams are solutions of the wave equation which keep their shape during free propagation. Because of this property, they are widely studied, both as mechanical and electromagnetic waves. Another scheme, however, can be devised in order to find beams that, even if do not maintain their shape upon propagation, are independent on the propagation distance, apart from a phase factor. In this sense it can be said that these beams are also nondiffracting. In this work, the scheme leading to this different kind of nondiffracting fields, which we term propagation-independent beams, is presented. Closed-form expressions for a few of these fields, for 1-D sources, are found. A method, which in principle is able to produce beams of this type, is given. This also clarifies some of their properties. Finally, the item of finite realizations of these beams, which in principle require infinite-dimension sources, is analyzed through numerical simulations. It is also shown that the practical feasibility of these fields poses some limitations on the bandwidth they can present.

Journal Article↗
PubMed2001

Optimization of wide-band linear arrays.

An optimization method is proposed for linear arrays to be used in ultrasound systems under wide-band operation. A fast algorithm, the threshold accepting, has been utilized to determine the element positions and weight coefficients of a linear array that generates a desired beam pattern. To reduce the computational burden in the optimization procedure, an efficient numerical routine for the beam pattern evaluation has been implemented. We address the optimization problem of both dense and sparse wide-band arrays. In the first case, the goal is to minimize the side-lobe energy by varying the element weights; we compare the optimized beam pattern with that obtained with classical shading functions, showing that better results can be achieved with a wide-band optimization. We also consider the optimization of the layout (positions and weights) of a sparse linear array to achieve a desired beam pattern with a fixed or minimum number of array elements. The comparison of the proposed method with a narrow-band optimization algorithm is presented, showing that better performances (about -7 dB further reduction of the side-lobe level) can be achieved with a wide-band sparse array optimization. Further numerical simulations are given, showing that the proposed method yields better results than wide-band sparse random arrays and periodic arrays with the same aperture width.

Journal Article↗
PubMed2000

A novel approach to the aperture windowing in medical imaging.

A new technique is proposed to improve the lateral resolution in the conventional B-mode imaging systems, which enables a simple array aperture windowing in the transmitting mode. Amplitude shaping is performed without modifying the transmitting voltage of the array elements, but only varying the excitation pulse length from one element to another. This method presents some attractive practical advantages, and the reduction of the sidelobe energy is comparable to that attainable with a conventional aperture windowing. Parametric plots are given, which transform an amplitude apodization into a 'time apodization' for any type of transducer array.

Ultrasonography↗
PubMed2000

A new beamforming technique for ultrasonic imaging systems

We propose a simple, versatile and inexpensive beamforming method that performs the aperture windowing of an ultrasonic transducer array in the transmit mode, without modifying the driver voltage, but simply controlling the length of the electric pulse driving the array elements. A conversion formula has been determined that permits us to compute, for a desired emitted pulse amplitude, the corresponding driving pulse length to be applied. Any shading function can be implemented over any type of transducer array, using very low-cost hardware. Computer simulations and experimental measurements, with a 3.8 MHz convex array, confirm the effectiveness of this approach in enhancing the contrast resolution, since the off-axis intensity in the radiated beam pattern is largely reduced.

Journal Article↗
PubMed1997

Effects of simulated acid rain on pollen physiology and ultrastructure in the apple.

Viability, germination and tube length were investigated in pollen grains of field-grown 'Summerred' apple trees (Malus domestica Borkh) exposed to deionized water, rainfall or simulated acid rain at pH 5.6, 4.0 and 3.0. Pollen viability and germination significantly decreased with lower values of pH and with increasing number of treatments. The effects of pH 5.6 and natural rainfall were not significant. Electron microscope investigation of vegetative pollen cells of plants exposed to acid rain at pH 4.0 and 3.0 showed modified features in mitochondria, plastids and endoplasmic reticulum.

Journal Article↗
PubMed1990

[Magnesium and potassium aspartate during the third pregnancy trimester].

Following a critical review of published reports on the use of magnesium during the third quarter of pregnancy, the paper examines the value of blood magnesium tests during pregnancy as well as the validity of administrating kalium aspartate and magnesium aspartate to treat the risk of premature birth.

Adult↗
PubMed1987

Mechanism of action and efficacy of verapamil and beta-blockers in exercise-induced ventricular tachycardia.

To determine the antiarrhythmic efficacy of beta-blockers (beta-B) and verapamil (V) in exercise-induced ventricular tachycardia (Ex-VT), nine patients with reproducible Ex-VT (in two consecutive exercise tests) were studied by means of electrophysiologic study (EPS) in basal conditions and serial exercise testing after beta-B (metoprolol 25 mg tid to 100 mg qid; oxprenolol 40 mg tid) and/or V (80-160 mg tid). Ejection fraction was normal in four cases and depressed in five. Of these nine patients, four developed Ex-VT during chronic amiodarone treatment, which was continued. During EPS, VT was induced at a critical atrial pacing rate in one case, and with the extrastimulus technique in four. Ventricular tachycardia was not inducible with either technique in four patients. Five of the six patients on beta-B and none of the seven on V developed Ex-VT, although they achieved the same or higher work-loads as compared to the basal exercise tests. In the case with rate-dependent VT, beta-B and V prevented VT at work-loads, sinus rates and double products significantly higher than those obtained in basal conditions. In the others, maximal heart rate and double product were lower on beta-B and showed a wide variability on V. V and beta-B appeared to be highly effective in preventing Ex-VT, in patients with normal heart as well as in those with greatly depressed ejection fraction. Both of the drugs appeared to suppress re-entry or triggered activity in the patient with rate-dependent Ex-VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1985

May early exercise testing after myocardial infarction predict the extent of coronary artery disease?

To determine whether exercise testing performed soon after myocardial infarction may predict the degree of coronary artery disease, 78 patients performed stress testing and coronary angiography 15 +/- 5 and 64 +/- 35 days, respectively, after myocardial infarction. Out of 34 patients with a positive test, 22 (65%) demonstrated a multivessel disease, and 37 (84%) out of 44 patients with a negative test had normal coronary angiograms or single vessel disease (p = .0006). In addition to stress testing, no clinical parameter considered (infarct location, heart failure and cardiomegaly) was predictive of the extent of coronary artery disease.

Coronary Angiography↗
PubMed1984

Compliance with cardiac rehabilitation in the elderly.

To evaluate the compliance of the elderly with cardiac rehabilitation (CR) after myocardial infarction, 370 consecutive patients greater than or equal to 65 years of age, admitted to our Coronary Care Unit over a period of 2 years, were examined: 48 died in the hospital, 34 were transferred to other wards and 29 were unable to perform a submaximal exercise test before discharge. Out of the remaining 259 patients, 43 began the CR and 32 completed it with a good outcome. Eleven patients interrupted the CR because of associated diseases. A social investigation was carried out on 83 of the 259 patients discharged from our ward. In addition to associated diseases and an extremely low exercise tolerance (41% of cases), the lack of participation was due to socioeconomic problems (9.5%), to lack of motivation (52.3%) and to inadequate information (38.1%). Nevertheless, 76% of patients indicated that they attained their previous way of life in a relatively short period of time. It is concluded that: CR is useful in patients who complete it; low compliance is due mainly to medical problems and lack of motivation; better information might slightly increase the compliance in our Center; most patients can, in any case, reach their previous way of life. It is debatable whether CR is advisable in old age, or should be directed towards selected groups of patients.

Aged↗
PubMed1983

[Early exercise test after myocardial infarct: prognostic stratification].

Exercise testing in myocardial infarction before discharge has been used for treatment and exercise prescription in the post-hospital phase. Aim of this study was to investigate the prognostic significance, within one year after the infarction, of submaximal exercise testing before discharge. 428 patients performed the test 14.5 days after the acute episode and were followed for 12 months. The following variables were examined: heart rate, blood pressure, rate-pressure product at maximum exercise, total work and reasons for stopping the test (fatigue, submaximal HR, BP greater than or equal to 200/110, hypotension, ischemic or arrhythmic response). Two events were considered: 1) non fatal reinfarction; 2) cardiac death. Two methods of multivariate analysis (Cox's model regression analysis and discriminant analysis) were used. None of the considered variables was found to be predictive of non fatal reinfarction. According to Cox's model total performed work and hypertensive response were found to be predictive of cardiac death, while using discriminant analysis only total work had a predictive value (discriminant function: L = 0.00094 X total work performed + 1.48643; p less than 0.01). In detail, the higher the total work, the better the probabilities of survival, while in patients who stopped the test because of hypertension, the probabilities of cardiac death were lower. Exercise testing performed in uncomplicated myocardial infarction before hospital discharge provides, the basis for a more rational management of patients in the post-infarction phase, and contributes to identify a subset of high-risk patients.

Aged↗
PubMed1979

[Early exercise testing after myocardial infarction (author's transl)].

203 patients suffering from acute myocardial infarction performed a cycloergometric submaximal exercise test before leaving hospital. The causes for stopping the test were fatigue or submaximal heart rate (24,1%), angina (14,2%), ischaemic S-T changes (28,08%), arrhythmias (4,9%) and changes of blood pressure (17,2%). No important complications were observed. The test proved useful for the definition of more objective criteria in order to prescribe an individualized rehabilitation programme. Above all it was possible to prescribe treatment which would not have otherwise been prescribed at the time of discharge. The short term prognostic value is not, however quite clear as yet.

Angina Pectoris↗