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S Popescu

Publications and source records attributed to S Popescu.

At least 19 recordsLinked to original sources
PubMed2006

Current-free double-layer formation in inductively coupled plasma in a uniform magnetic field.

The axial profiles of plasma parameters for low and moderate pressures, such as the plasma potential, electron temperature, and number density, have been evaluated in magnetized inductively coupled plasma. The experimental results revealed in both cases the existence of a genuine current-free double-layer structure, separating two plasma regions with different properties. Based on the experimental results, a physical scenario for the self-assembling of the double layer is proposed. Also, the axial profile of the electron number density downstream is analyzed, emphasizing the role of neutral metastable ionization, and a simple analytical model is developed to fit the experimental data. The model allows the estimation of neutral metastable number density downstream and the recombination rate coefficient.

Journal Article↗
PubMed2005

Simulating maximal quantum entanglement without communication.

It is known that all causal correlations between two parties which output each 1 bit, a and b, when receiving each 1 bit, x and y, can be expressed as convex combinations of local correlations (i.e., correlations that can be simulated with local random variables) and nonlocal correlations of the form a+b=xy mod 2. We show that a single instance of the latter elementary nonlocal correlation suffices to simulate exactly all possible projective measurements that can be performed on a maximally entangled state of two qubits, with no communication needed at all. This elementary nonlocal correlation thus defines some unit of nonlocality, which we call a nl bit.

Journal Article↗
PubMed2004

Fast light, slow light, and phase singularities: a connection to generalized weak values.

We demonstrate that Aharonov-Albert-Vaidman weak values have a direct relationship with the response function of a system, and have a much wider range of applicability in both the classical and quantum domains than previously thought. Using this idea, we have built an optical system, based on a birefringent photonic crystal, with an infinite number of weak values. In this system, the propagation speed of a polarized light pulse displays both superluminal and slow light behavior with a sharp transition between the two regimes. We show that this system's response possesses two-dimensional, vortex-antivortex phase singularities. Important consequences for optical signal processing are discussed.

Journal Article↗
PubMed2002

Almost every pure state of three qubits is completely determined by its two-particle reduced density matrices.

In a system of n quantum particles, we define a measure of the degree of irreducible n-way correlation, by which we mean the correlation that cannot be accounted for by looking at the states of n-1 particles. In the case of almost all pure states of three qubits, we show that there is no such correlation: almost every pure state of three qubits is completely determined by its two-particle reduced density matrices.

Journal Article↗
PubMed2001

Are all noisy quantum states obtained from pure ones?

We ask what type of mixed quantum states can arise when a number of separated parties start by sharing a pure quantum state and then this pure state becomes contaminated by noise. We show that not all mixed states arise in this way. This is even the case if the separated parties actively try to degrade their initial pure state by arbitrary local actions and classical communication.

Journal Article↗
PubMed2001

Entanglement capabilities of nonlocal Hamiltonians.

We quantify the capability of creating entanglement for a general physical interaction acting on two qubits. We give a procedure for optimizing the generation of entanglement. We also show that a Hamiltonian can create more entanglement if one uses auxiliary systems.

Journal Article↗
PubMed2001

Good dynamics versus bad kinematics: is entanglement needed for quantum computation?

We study the role of entanglement in quantum computation. We consider the case of a pure state contaminated by "white noise." This framework arises, for example, in pseudopure state implementations of quantum computing using NMR. We analyze quantum computational protocols which aim to solve exponential classical problems with polynomial resources and ask whether or not entanglement of the pseudopure states is needed to achieve this aim. We show that, for a large class of such protocols, including Shor's factorization, entanglement is necessary. We also show that achieving entanglement is not sufficient: If the state is sufficiently noisy, exponential resources are needed even if entanglement is present.

Journal Article↗
PubMed2000

Exercise-induced increase in circulating adrenomedullin is related to mean blood pressure in heart transplant recipients.

Adrenomedullin (ADM) is a newly discovered potent vasorelaxing and natriuretic peptide that recently has been shown to be increased after heart transplantation. To investigate the hemodynamic factors modulating its release and the eventual role of ADM in blood pressure regulation after heart transplantation, seven matched heart-transplant recipients (Htx) and seven normal subjects performed a maximal bicycle exercise test while monitoring for heart rate, blood pressure, and circulating ADM. Baseline heart rate and systemic blood pressure were higher in Htx; left ventricular mass index and ADM tended to be higher after heart transplantation and correlated positively in Htx (r = 0.79, P = 0.03). As expected, exercise-induced increase in heart rate was lower in Htx than in controls (60 +/- 11 % vs. 121 +/- 14 %, respectively) and blood pressure increase was similar in both groups. Maximal exercise increased significantly plasma ADM in both groups (from 25.3 +/- 3.1 to 30.7 +/- 3.5 pmol/L, P < 0.05 and from 15.2 +/- 1.4 to 29.1 +/- 4.4 pmol/L, P = 0.02 in Htx and controls, respectively), the hypotensive peptide level remaining elevated until the 30th min of recovery. A significant inverse relationship was observed between peak mean blood pressure and circulating ADM in Htx (r = -0.86, P < 0.02). Besides showing that circulating ADM is increased after heart transplantation, the present study demonstrates a positive relationship between baseline ADM and left ventricular mass index. Furthermore, maximal exercise-induced increase in ADM is inversely related to mean blood pressure in Htx, suggesting that ADM might participate in blood pressure regulation during exercise after heart transplantation.

Adrenomedullin↗
PubMed1999

A malignant primary cardiac pheochromocytoma.

We report the case of a malignant primary cardiac pheochromocytoma treated by adjuvant cytotoxic chemotherapy after surgical resection, with a 5-year survival. There is no specific chemotherapy for malignant pheochromocytoma, but because it has the same embryologic origin as neuroblastoma, we used similar chemotherapy. Because of unexpected malignancy potential, we think that total and meticulous resection of the tumor must be done.

Adult↗
PubMed1998

Is a prosthetic ring required for mitral repair of mitral insufficiency due to posterior leaflet prolapse? Long-term results in 96 patients submitted to repair with no ring.

OBJECTIVE: It is a common statement that every mitral repair should be stabilized by some type of prosthetic mitral ring. In the very specific situation of isolated prolapse of the posterior leaflet (PPL), this statement may be enhanced by the possible anatomically discontinuity of the mitral annulus. This article concerns 96 patients with 'isolated' PPL (IPPL) who were operated upon without ring insertion. Long-term follow-up was obtained in order to ascertain the survival, stability of the repair and the need for reoperation, thus justifying or not the lack of use of a ring. METHODS: A total of 96 patients, 70 male and 26 female, underwent mitral repair for mitral insufficiency (MI) almost exclusively caused by PPL. Age ranged from 33 to 81 years (mean 60.7+/-11.3). All underwent quadrangular resection of the prolapsed portion and plication of the annulus. In 69 cases local stabilization was achieved by four U stitches, two on each side of the plication, passed through and sutured on some flexible material, 2-3 cm in length. Twenty seven patients had no such local reinforcement. RESULTS: There was one case of early death (1%) caused by refractory hypoxemia in a patient with long lasting pre-operative pulmonary edema. Two patients were lost for follow-up after 2 months. Follow-up was from 0.2 to 14.7 years (mean 4.5), for a total of 422.7 patient-years. There were four late deaths at a mean of 6-year follow-up (0.9-10 years). Actuarial survival was 95.5 and 90.5% at 5 and 8 years, respectively. Event-free for recurrence of significant mitral insufficiency (MI) was 96 and 92% at 5 and 8 years. Event-free of thromboembolic or hemorrhagic events was 84.3 and 72.3% at 5 and 8 years. Event-free from reoperation was 97.8 and 94% at 5 and 8 years. CONCLUSION: One can conclude that (a) IPPL repair without insertion of a ring is safe and long-lasting (b) the incidence of late death, recurrence of MI, thromboembolic/hemorrhagic events, need for reoperation, is not higher in this subset of patients than in conventional repair (c) such repair might work better and for a longer time, as reaction and sclerosis resulting from ring insertion are avoided (d) minor advantages could be due to an easier surgical procedure, especially through a minimally invasive approach.

Actuarial Analysis↗
PubMed1997

Transaortic approach in double-outlet right ventricle with subaortic ventricular septal defect.

The standard approach (right ventriculotomy and atriotomy) for surgical repair of double-outlet right ventricle with subaortic ventricular septal defect and pulmonary stenosis may not give an adequate view of the intracardiac defect due-to the presence of anomalous coronary artery anatomy or unusual cavity spacial relationship. Thus, a transverse aortotomy was performed and the left ventricular outflow tract was well visualized through the aortic valve and could be reconstructed precisely. Therefore, the transaortic approach also should be considered for systemic route reconstruction in this group.

Aorta↗
PubMed1997

Clinical presentation and treatment options for mitral valve myxoma.

Myxomas rarely are located on the mitral valve. We report the case of a 44-year-old man operated on successfully with mitral valve conservation, which is the 21st case of mitral valve myxoma reported in the western literature. Among the cases reported in the literature, the diagnosis was made at the time of autopsy in 6 cases, with premortem heart failure in 1 case. A clinical diagnosis was made in 15 cases on the basis of the following symptoms: peripheral embolism in 9 cases, cardiac signs in 4 cases, and constitutional manifestations in 2 cases. The clinical presentation of mitral valve myxoma differs slightly from that of other cardiac myxomas in that it has a lower incidence of constitutional manifestations. The gold standard for noninvasive diagnosis and localization of cardiac myxomas is transesophageal echocardiography. It allows for the detection of early, small valvular tumors and may help to characterize better their location and echostructure, facilitating the choice of an optimal surgical approach through preoperative study of the integrity and mobility of the valve. Conservative operative treatment by resection of the area of implantation of the myxoma followed by suture repair of the valve and annuloplasty may be recommended as the most appropriate treatment option for this rare condition.

Adult↗
PubMed1997

[Carotid endarterectomy by eversion and reimplantation. Techniques and results].

Endarterectomy of the carotid bifurcation through a longitudinal arteriotomy of the common and internal carotid arteries followed by a direct closure is still accepted as the main surgical technique for carotid stenoses. However, this technique is complicated in about 10% of the cases by a restenosis. Mechanisms of myointimal hyperplasia leading to restenosis are not completely explained. The technique of eversion endarterectomy of the internal carotid artery has been said to be an alternate technique which could decrease the incidence of restenosis. We described the three main techniques of eversion endarterectomy and their results. The technique of eversion endarterectomy after proximal section of the internal carotid artery is the most frequently used. It allows to treat easily length excess of the internal carotid artery. Its results are good in terms of neurologic morbidity and mortality. However, randomized comparative studies are still required in order to determine its role on the incidence of restenosis despite the first encouraging results of first non comparative studies. The technique of eversion endarterectomy after distal section of the internal carotid artery has been proposed by Chevalier who reported also good short term results and no delayed restenosis.

Carotid Artery, Internal↗