PubMed Health⌕ Search

Biomedical subjects

G Gioia

Publications and source records attributed to G Gioia.

At least 19 recordsLinked to original sources

Fluctuating velocity and momentum transfer in dense granular flows.

We show experimentally that in a free-surface granular flow the fluctuating velocity brings about momentum transfer at a considerable rate only very close to the free surface. Away from the free surface, where the flow is dense and stratified (or laminar), the fluctuating velocity plays no prominent dynamic role and stems passively from a kinematic constraint: The strata of particles must shake laterally as they slip past one another in the direction of the mean flow. Based on this insight, we formulate a simple model for the fluctuating velocity of dense granular flows. The predictions of the model agree well with our experimental measurements.

Journal Article↗

Turbulent friction in rough pipes and the energy spectrum of the phenomenological theory.

The classical experiments on turbulent friction in rough pipes were performed by Nikuradse in the 1930s. Seventy years later, they continue to defy theory. Here we model Nikuradse's experiments using the phenomenological theory of Kolmogórov, a theory that is widely thought to be applicable only to highly idealized flows. Our results include both the empirical scalings of Blasius and Strickler and are otherwise in minute qualitative agreement with the experiments; they suggest that the phenomenological theory may be relevant to other flows of practical interest; and they unveil the existence of close ties between two milestones of experimental and theoretical turbulence.

Journal Article↗

Localized turbulent flows on scouring granular beds.

In many applications a sustained, localized turbulent flow scours a cohesionless granular bed to form a pothole. Here we use similarity methods to derive a theoretical formula for the equilibrium depth of the pothole. Whereas the empirical formulas customarily used in applications contain numerous free exponents, the theoretical formula contains a single one, which we show can be determined via the phenomenological theory of turbulence. Our derivation affords insight into how a state of dynamic equilibrium is attained between a granular bed and a localized turbulent flow.

Journal Article↗

Radial segregation patterns in rotating granular mixtures: waviness selection.

We model the radial segregation patterns that form in a thin rotating drum partially filled with beads of two sizes. We predict that the waviness (or amplitude-to-wavelength ratio, denoted w) of a pattern should be subjected to low-pass filtering with a cutoff waviness w(c) that depends strongly on the fill level of the drum. Then we perform experiments and find that w</=w(c) for all patterns, in accord with our prediction. We also find that w=w(c) for (and only for) steady patterns, and conclude that the waviness of a steady pattern is selected by the low-pass filtering.

Journal Article↗

Structure and kinematics in dense free-surface granular flow.

We show that the structure of a dense, free-surface boundary layer granular flow is similar to the structure of a laminar liquid flow: There is a strong component of order (stratification parallel to the mean flow) superposed with a mild component of disorder (self-diffusion perpendicular to the mean flow). We also show that the self-diffusion coefficient scales with the mean velocity and propose a model that relates this scaling to the ordered structure of the flow. Last, we show that the structure of the flow imprints an oscillatory signature (similar to that found in confined granular flow) on the mean velocity profile.

Journal Article↗

Two-phase densification of cohesive granular aggregates.

When poured into a container, cohesive granular materials form low-density, open granular aggregates. If pressure is applied to these aggregates, they densify by particle rearrangement. Here we introduce experimental and computational results suggesting that densification by particle rearrangement occurs in the form of a phase transition between two configurational phases of the aggregate. Then we show that the energy landscape associated with particle rearrangement is nonconvex and therefore consistent with our interpretation of the experimental and computational results. Our conclusions are relevant to many technological processes and natural phenomena.

Journal Article↗

Scaling and similarity in rough channel flows.

We show that Manning's empirical formula for the mean velocity of turbulent flows in channels represents the power-law asymptotic behavior of a flow of incomplete similarity in the relative roughness. We then derive the formula based on the phenomenological theory of turbulence. Our derivation yields the correct similarity exponent; it justifies Manning's use of a single parameter, the hydraulic radius, to characterize the geometry of the cross section; and it affords insight into the mechanism of momentum transfer.

Journal Article↗

Coronary rotational atherectomy via transradial approach: a study using radial artery intravascular ultrasound.

The use of coronary rotational atherectomy via radial artery (RA) has been limited because of the large diameter of guiding catheters. We studied the feasibility of this approach by sizing the RA by intravascular ultrasound (IVUS) and using 7 Fr (2.31 mm) guiding catheters. Seventeen transradial percutaneous transluminal coronary rotational atherectomy (PTCRA) procedures were performed in 16 patients, mean age 62 +/- 12 years, for a total of 19 vessels treated. The mean RA diameter was 2.9 +/- 0.36 mm and the mean reference diameter of the treated coronary vessels was 2.7 +/- 0.45 mm. The mean coronary percent stenosis was 74% +/- 10%, the mean minimum lumen diameter was 0.76 +/- 0.35 mm, and the mean lesion length was 16 +/- 19 mm. Ten vessels were treated with rotational atherectomy alone, or with adjunctive high pressure balloon angioplasty, achieving an acute lumen gain of 0.8 +/- 0.4 mm (P = 0. 001). Nine arteries had stent implantation in addition to rotational atherectomy, resulting in an acute lumen gain of 2.4 +/- 0.5 mm (P = 0.001). The success rate was 94%. There were no vascular complications. Two patients had a non-Q myocardial infarction. In conclusion, transradial PTCRA when used in conjunction with IVUS of the RA is a safe and feasible procedure in selected cases. This may be an alternative approach of revascularization technique especially for patients with limited vascular access and for those who require early ambulation or early discharge from the hospital.

Aged↗

Surgical treatment of far lateral lumbar disc herniation. Identification of compressed root and discectomy by lateral approach.

STUDY DESIGN: A new method is described of compressed root identification and discectomy for extraforaminal disc herniation, by a lateral intertransversalis approach. OBJECTIVES: To describe a safe surgical approach that does not require resection of adjacent bone structures during extraforaminal discectomy. SUMMARY OF BACKGROUND DATA: Most earlier series have reported approaches that damaged bordering bone structures with wide laminoarthrectomy. This is an attempt at a safer, simpler surgical approach. METHODS: Thirteen patients with lateral hernia have undergone this surgical procedure since 1995. Herniectomy was performed after identification of the compressed root within the iliopsoas muscle. RESULTS: All the patients resumed the upright position with the aid of semirigid brace 24 hours after surgery. Upon awakening from the anesthesia, no patient reported peripheral pain. Motor deficits resolved after physical rehabilitation in all but one patient. At a mean follow-up of 14 months, there was no report of back pain. CONCLUSION: The procedure described in this article offers a simple alternative to the valid procedures presently at hand. It offers the advantage of no bone resection and of minimizing nerve structures manipulation.

Adult↗

Postlaminectomy cervical dislocation in von Recklinghausen's disease. A case report.

STUDY DESIGN: A case of a 9-year-old girl with von Recklinghausen's disease who has acute tetraparesis caused by a complete dislocation of C6-C7 after a cervical laminectomy performed at another hospital. OBJECTIVES: To demonstrate the treatment difficulties of cervical spine abnormality associated with neurofibromatosis. SUMMARY OF BACKGROUND DATA: Craig and Govender have reported cases of neurofibromatosis of the cervical spine (1992). METHODS: The patient underwent emergency surgery starting with a posterior release of the articular facets and with the positioning of two Roy-Camille plates. The dislocation of C6-C7 was reduced by an anterior approach. Finally the Roy-Camille plates were removed, a plate was implanted posteriorly at the C6 and C7 joints, and a posterior cable was positioned around the C2-C3 posterior arches. RESULTS: More than 4.5 years after surgery, the patient's neurologic condition remains satisfactory. She can walk and run and has no sphincter disorders. CONCLUSIONS: The results underline the importance of simultaneous anterior and posterior surgical approaches in this disease.

Bone Plates↗

Prediction of outcome of patients with life-threatening ventricular arrhythmias treated with automatic implantable cardioverter-defibrillators using SPECT perfusion imaging.

BACKGROUND: In the present study, we examined the predictors of outcome of 103 patients with coronary artery disease and left ventricular dysfunction who had life-threatening ventricular arrhythmias and were treated with implantable cardioverter-defibrillators with the use of single-photon emission computed tomography (SPECT). METHODS AND RESULTS: During a mean follow-up of 29 months, there were 29 cardiac deaths. In comparison with patients who died, survivors had less diabetes mellitus (45% versus 19%, P < .007), higher left ventricular ejection fraction (23 +/- 9% versus 27 +/- 11%, P = .04), and fewer perfusion defects as determined with stress SPECT (15 +/- 5 versus 12 +/- 5, P < .004). Most of the perfusion defects were fixed, indicative of scarring; the extent of reversible defects did not differ (2 +/- 3 in survivors and 3 +/- 4 in nonsurvivors). Multivariate Cox survival analysis identified the number of fixed defects as the only independent predictor of death (chi 2 = 10, P = .002). There were six deaths among 42 patients (14%) with < 8 fixed defects compared with 23 deaths among 61 patients (38%) with > or = 8 defects (P = .005). The 4-year survival was better in patients with < 8 segmental fixed defects than in those with > or = 8 fixed defects (80% versus 36%) (chi 2 = 8, P = .005). CONCLUSIONS: The myocardial perfusion pattern is an important determinant of outcome in patients with life-threatening ventricular arrhythmias who are treated with a implantable cardioverter-defibrillator. The extent of scarring separates patients into high- and low-risk groups with a 2.7-fold difference in death rate.

Aged↗

Prognostic value of rest-redistribution tomographic thallium-201 imaging in ischemic cardiomyopathy.

The relation between the presence of viable myocardium by rest-redistribution thallium imaging and prognosis is not well defined. This study examined the prognostic value of rest-redistribution single-photon emission computed tomographic imaging with thallium-201 in patients with coronary artery disease (CAD) and left ventricular (LV) dysfunction. Patients were divided into 2 groups: group 1 patients (n = 47) were treated medically and group 2 patients (n = 38) underwent coronary revascularization. The 2 groups were comparable in the extent of CAD and in LV ejection fraction. Thallium images showed normal tracer uptake in 1 group 1 and 3 group 2 patients, fixed defects in 26 group 1 and 18 group 2 patients, and both reversible and fixed defects in 20 group 1 and 17 group 2 patients (p = NS). Based on analysis of 20 segments/patient, reversible defects were seen in 4 +/- 4 segments/patient in group 1 and 5 +/- 5 segments/patient in group 2 (p = NS). Viable myocardium (defined as normal tracer uptake, reversible defects, or mild fixed defects) was seen in 14 +/- 4 segments/patient in group 1 and 15 +/- 5 segments/patient in group 2 (p = NS). During a mean follow-up of 31 months, there were 16 group 1 (34%) and 6 group 2 (16%) deaths. The annual mortality rate was 13% in group 1 and 6% in group 2. Actuarial survival analysis showed better survival in group 2 than in group 1 (p = 0.056). Thus, viable myocardium in patients with CAD and LV dysfunction is associated with poor prognosis with medical therapy. Coronary revascularization improves prognosis.

Actuarial Analysis↗

Use of a tantalum-178 generator and a multiwire gamma camera to study the effect of the Mueller maneuver on left ventricular performance: comparison to hemodynamics and single photon emission computed tomography perfusion patterns.

During the Mueller maneuver, there is a decrease in intrathoracic pressure and an increase in transmural left ventricular pressure. The changes in loading conditions cause transient left ventricular dysfunction. This study examined the effects of the Mueller maneuver on left ventricular performance using tantalum (Ta)-178 (half-life 9.3 min) and a multiwire gamma camera. First-pass radionuclide angiograms were obtained at baseline and during Mueller maneuver in 41 patients aged 58 +/- 10 years. In 34 patients, stress single photon emission computed tomography (SPECT) myocardial perfusion imaging with thallium-201 or sestamibi was also performed. Hemodynamic measurements during the Mueller maneuver (n = 10) showed a decrease in systemic pressure (139 +/- 25 mm Hg vs 123 +/- 24 mm Hg, p < 0.001) and pulmonary artery pressure (24 +/- 6 mm Hg vs 14 +/- 12 mm Hg, p = 0.01) and an increase in heart rate (67 +/- 10 bpm vs 75 +/- 14 beats/min, p = 0.001). Among the 34 patients who had perfusion imaging, the left ventricular ejection fraction remained unchanged or increased in 17 patients (group 1) (48% +/- 19% vs 49% +/- 21%, p not significant) and decreased (> or = 5%) in 17 patients (group 2) (55% +/- 13% vs 40% +/- 16%, p = 0.001). The stress SPECT images showed no or only fixed defects in 11 (65%) patients in group 1 and 3 (18%) patients in group 2 (p = 0.02), and reversible defects in 6 (35%) patients in group 1 and 14 (82%) patients in group 2 (p = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

Sex differences in cognitive processing in children treated with CNS prophylaxis for acute lymphoblastic leukemia.

Evaluated cognitive processing in 51 children (27 female, 24 male) who had been treated for acute lymphoblastic leukemia (ALL) with CNS prophylaxis (cranial radiation in combination with intrathecal chemotherapy) and were continuously disease-free for 5 to 12 years. The control group comprised 15 children treated for Wilm's tumor. Functions assessed included visuoperceptual skills, generation of organizational strategies, sensitivity to organizational structure, and attention. The ALL group showed performance deficits relative to the solid tumor controls in appreciating the organization inherent in complex visuospatial material and alertness, with females more severely affected than males. Sex differences favoring males on IQ and academic achievement were related to these cognitive processes.

Adolescent↗

Prevalence of non-specific vaginitis and correlation with isolation of Gardnerella vaginalis in Italian outpatients.

Among all subjects attending a Center for prevention of female genital tract cancer Gardnerella vaginalis was isolated from 57 out of 171 women affected by non-specific vaginitis (NSV), from 15 of 703 non-NSV vaginitis patients and from 10 of 338 healthy adults. Postmenopausal women showed an increased rate of asymptomatic carriage of G. vaginalis. The data suggest a relatively weak association between clinical diagnosis of NSV and isolation of G. vaginalis.

Adolescent↗

[Normal echo-Doppler values in Duromedics valvular prostheses].

To determine the value of Doppler echocardiography in the normal clinical use of functional diagnosis, and to define normal values of prosthetic mitral and aortic valves, of different sizes and in different positions, 48 patients (53 Duromedics prosthesis) were examined. Two groups were formed: the first group (12 patients) was studied soon after operation, i.e. less than 3 weeks; the second group (36 patients) was examined at a later stage i.e. 2-60 months later. This group did not present any associated valvular disease (i.e. there was no aortic disease in patients with mitral prostheses nor mitral disease in patients with aortic prostheses). In the first group the following results were found: DP max = 12.70 +/- 4 mmHg, DP mean = 4.0 +/- 3 mmHg, Half Time Pressure (T 1/2) = 79.57 +/- 17 ms in mitral prostheses; DP max = 25 +/- 10.9 mmHg, DP mean = 6.8 +/- 4 mmHg in aortic prostheses. In the second group the findings were as follows: mitral prostheses: DP max = 9.28 +/- 3.32 mmHg, DP mean = 3.0 +/- 1.0 mmHg, T 1/2 = 80 +/- 17.96 ms; aortic prostheses: DP max = 19.0 +/- 9.59 mmHg, DP mean = 6.0 +/- 3 mmHg. A trend towards higher DP values was noted in the first group of mitral prostheses (p = 0.05 only for DP max; for DP mean no statistic significance). No differences were noted either between the first and second group as regards aortic prostheses. For prosthetic mitral valves permissible upper limits of DP max, DP mean and T 1/2 in the first and second groups were respectively: 16.70 mmHg, 7.0 mmHg, 96.57 ms; and 12.26 mmHg, 4.0 mmHg, 105.96 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗