Biomedical subjects

M Saba

Publications and source records attributed to M Saba.

At least 19 recordsLinked to original sources

PubMed2006

Low velocity quantum reflection of Bose-Einstein condensates.

We study how interactions affect the quantum reflection of Bose-Einstein condensates. A patterned silicon surface with a square array of pillars resulted in high reflection probabilities. For incident velocities greater than 2.5 mm/s, our observations agreed with single-particle theory. At velocities below 2.5 mm/s, the measured reflection probability saturated near 60% rather than increasing towards unity as predicted by the accepted theoretical model. We extend the theory of quantum reflection to account for the mean-field interactions of a condensate which suppresses quantum reflection at low velocity. The reflected condensates show collective excitations as recently predicted.

Journal Article↗

PubMed2006

Temporal artery biopsy for diagnosing giant cell arteritis: the longer, the better?

OBJECTIVE: To investigate the relation between temporal artery biopsy (TAB) length and diagnostic sensitivity for giant cell arteritis. METHODS: Histological TAB reports generated from four hospital pathology departments were reviewed for demographics, histological findings, and formalin fixed TAB lengths. A biopsy was considered positive for giant cell arteritis if there was a mononuclear cell infiltrate predominating at the media-intima junction or in the media. RESULTS: Among 1821 TAB reports reviewed, 287 (15.8%) were excluded because of missing data, sampling errors, or age < 50 years. Mean TAB length of the 1520 datasets finally analysed (67.2% women; mean (SD) age, 73.1 (10.0) years) was 1.33 (0.73) cm. Histological evidence of giant cell arteritis was found in 223 specimens (14.7%), among which 164 (73.5%) contained giant cells. Statistical analyses, including piecewise logistic regression, identified 0.5 cm as the TAB length change point for diagnostic sensitivity. Compared with TAB length of < 0.5 cm, the respective odds ratios for positive TAB without and with multinucleated giant cells in samples > or = 0.5 cm long were 5.7 (95% confidence interval, 1.4 to 23.6) and 4.0 (0.97 to 16.5). CONCLUSIONS: A fixed TAB length of at least 0.5 cm could be sufficient to make a histological diagnosis of giant cell arteritis.

Aged↗

PubMed2005

[Whipple disease, initially diagnosed as sarcoidosis].

INTRODUCTION: Whipple disease is a multisystem infectious disease caused by Tropheryma whipplei. We report a case in which an initial diagnosis of sarcoidosis was changed to Whipple disease endocarditis. CASE: Based on clinical, radiographic, endoscopic and histologic findings, this 61-year-old man was diagnosed with sarcoidosis. Initial response to corticotherapy was good, but the patient required 35 mg of prednisone daily. The subsequent onset of clinical and laboratory signs of inflammation cast doubt on the diagnosis. After cardiac ultrasound revealed a mass 1 cm in diameter on the mitral valve, apparently vegetation, we diagnosed culture-negative infective endocarditis and ruled out most possible causes. PCR of a duodenal biopsy sample showed Tropheryma whipplei, thus confirming the diagnosis of Whipple disease, despite normal histological findings. After 3 weeks of intravenous gentamicin and amoxicillin treatment, oral cotrimoxazole was substituted. Follow-up transesophageal ultrasound showed no mitral vegetation. The patient, still under cotrimoxazole, has been off prednisone for 13 months and is completely asymptomatic. CONCLUSION: This case is an illustration of the difficulty in distinguishing Whipple disease from sarcoidosis in practice and of the importance of that distinction.

Anti-Bacterial Agents↗

PubMed2005

Optical weak link between two spatially separated Bose-Einstein condensates.

Two spatially separate Bose-Einstein condensates were prepared in an optical double-well potential. A bidirectional coupling between the two condensates was established by two pairs of Bragg beams which continuously outcoupled atoms in opposite directions. The atomic currents induced by the optical coupling depend on the relative phase of the two condensates and on an additional controllable coupling phase. This was observed through symmetric and antisymmetric correlations between the two outcoupled atom fluxes. A Josephson optical coupling of two condensates in a ring geometry is proposed. The continuous outcoupling method was used to monitor slow relative motions of two elongated condensates and characterize the trapping potential.

Journal Article↗

PubMed2005

Light scattering to determine the relative phase of two Bose-Einstein condensates.

We demonstrated an experimental technique based on stimulated light scattering to continuously sample the relative phase of two spatially separated Bose-Einstein condensates of atoms. The phase measurement process created a relative phase between two condensates with no initial phase relation, read out the phase, and monitored the phase evolution. This technique was used to realize interferometry between two trapped Bose-Einstein condensates without need for splitting or recombining the atom cloud.

Journal Article↗

PubMed2004

Quantum reflection from a solid surface at normal incidence.

We observed quantum reflection of ultracold atoms from the attractive potential of a solid surface. Extremely dilute Bose-Einstein condensates of 23Na, with peak density 10(11)-10(12) atoms/cm(3), confined in a weak gravitomagnetic trap were normally incident on a silicon surface. Reflection probabilities of up to 20% were observed for incident velocities of 1-8 mm/s. The velocity dependence agrees qualitatively with the prediction for quantum reflection from the attractive Casimir-Polder potential. Atoms confined in a harmonic trap divided in half by a solid surface exhibited extended lifetime due to quantum reflection from the surface, implying a reflection probability above 50%.

Journal Article↗

PubMed2004

Dynamical instability of a doubly quantized vortex in a Bose-Einstein condensate.

Doubly quantized vortices were topologically imprinted in /F=1> 23Na condensates, and their time evolution was observed using a tomographic imaging technique. The decay into two singly quantized vortices was characterized and attributed to dynamical instability. The time scale of the splitting process was found to be longer at higher atom density.

Journal Article↗

PubMed2004

Distillation of bose-einstein condensates in a double-well potential.

Bose-Einstein condensates of sodium atoms, prepared in an optical dipole trap, were distilled into a second empty dipole trap adjacent to the first one. The distillation was driven by thermal atoms spilling over the potential barrier separating the two wells and then forming a new condensate. This process serves as a model system for metastability in condensates, provides a test for quantum kinetic theories of condensate formation, and also represents a novel technique for creating or replenishing condensates in new locations.

Journal Article↗

PubMed2004

Atom interferometry with Bose-Einstein condensates in a double-well potential.

A trapped-atom interferometer was demonstrated using gaseous Bose-Einstein condensates coherently split by deforming an optical single-well potential into a double-well potential. The relative phase between the two condensates was determined from the spatial phase of the matter wave interference pattern formed upon releasing the condensates from the separated potential wells. Coherent phase evolution was observed for condensates held separated by 13 microm for up to 5 ms and was controlled by applying ac Stark shift potentials to either of the two separated condensates.

Journal Article↗

PubMed2003

Cooling Bose-Einstein condensates below 500 picokelvin.

Spin-polarized gaseous Bose-Einstein condensates were confined by a combination of gravitational and magnetic forces. The partially condensed atomic vapors were adiabatically decompressed by weakening the gravito-magnetic trap to a mean frequency of 1hertz, then evaporatively reduced in size to 2500 atoms. This lowered the peak condensate density to 5 x 10(10) atoms per cubic centimeter and cooled the entire cloud in all three dimensions to a kinetic temperature of 450 +/- 80 picokelvin. Such spin-polarized, dilute, and ultracold gases are important for spectroscopy, metrology, and atom optics.

Journal Article↗

PubMed2003

Coherent control of polariton parametric scattering in semiconductor microcavities.

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k=0, even for delays much longer than the pulse width. The control of a large population at k=0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the scattering get faster. Just above threshold the parametric scattering process shows unexpected long coherence times, whereas when pump power is risen the contrast decays due to a significant pump reservoir depletion. The weak pulses at normal incidence control the whole angular emission pattern of the microcavity.

Journal Article↗

PubMed2002

[Distal glue embolization in a patient with gastrointestinal hemorrhage].

This is a case report, concerning the endovascular use of N-butyl-2-cyanoacrylate, for treatment of a digestive hemorrhage from a distal branch of the superior mesenteric artery, leading to a successful outcome. This material, usually used in brain angiomas, constitutes an alternative for digestive embolization, which is quick, precise and definitive, without additional risk in experienced hands.

Aged↗

PubMed2001

High-temperature ultrafast polariton parametric amplification in semiconductor microcavities.

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons. Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton-polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures. Here we demonstrate polariton parametric amplification up to 120 K in GaAlAs-based microcavities and up to 220 K in CdTe-based microcavities. We show that the cut-off temperature for the amplification is ultimately determined by the binding energy of the exciton. A 5-micrometer-thick planar microcavity can amplify a weak light pulse more than 5,000 times. The effective gain coefficient of an equivalent homogeneous medium would be 107 cm-1. The subpicosecond duration and high efficiency of the amplification could be exploited for high-repetition all-optical microscopic switches and amplifiers. 105 polaritons occupy the same quantum state during the amplification, realizing a dynamical condensate of strongly interacting bosons which can be studied at high temperature.

Journal Article↗

PubMed2000

Crossover from exciton to biexciton polaritons in semiconductor microcavities

Pump-probe measurements in a microcavity containing a quantum well show that a population of circularly polarized ( sigma(+)) excitons can completely inhibit the transition to sigma(-) one-exciton states by transferring the oscillator strength to the biexcitonic resonance. With increasing pump intensity the linear exciton-polariton doublet evolves into a triplet polariton structure and finally into a shifted biexciton-polariton doublet. A theoretical model of interacting excitons demonstrates that the crossover from exciton to biexciton polaritons is driven by three-exciton Coulomb correlation.

Journal Article↗

PubMed2000

Advanced life support: retention of registered nurses' knowledge 18 months after initial training.

In 1996, The Wesley Hospital introduced a 2 day Advanced Life Support (ALS) course, targeted at all critical care registered nurses and medical officers. The purpose of this study was to explore the retention of theoretical knowledge and clinical skills of registered nurses who had successfully completed the 2 day ALS course 18 months previously and to establish effective retesting timeframes. The study utilised a repeated post-test measure design. Forty registered nurses participated in the study. Data were collected during ALS retesting using scores from a theoretical examination and from the results of four practical skill assessments (basic life support, airway management, defibrillation and code management). Using Wilcoxon test, data were analysed with and compared to the participant's original scores from the training program 18 months previously. The findings demonstrate that the participant's theoretical knowledge remained at an equivalent level over the 18 month timeframe. However, 18 months after successfully completing an ALS course, only 75 per cent (n = 30) of participants passed the practical skill assessment components, with the 25 per cent (n = 10) requiring a second attempt to pass. The implications from this study focus on the model of assessment utilised and the dichotomy between theoretical and practical skill assessment results. Additional study is required to determine the optimal timeframe for ALS retesting and educational strategies to help retain skills over time.

Adult↗

PubMed1997

Morphological and biochemical changes following acute unilateral testicular torsion in prepubertal rats.

PURPOSE: The role played by reactive oxygen species in the effects of testicular torsion and torsion/detorsion on ipsilateral and contralateral testis was investigated. MATERIALS AND METHODS: Prepubertal rats were submitted to unilateral testicular torsion alone or followed by detorsion for up to 1 week. Morphology and biochemical parameters (thiobarbituric reactive substances, superoxide dismutase-like and catalase-like activities) were evaluated. RESULTS: Torsion (1 or 2 h) alone induced time-dependent morphological damages that worsened progressively after detorsion in ipsilateral testis but had no effect on contralateral testis. The levels of antioxidants against the superoxide anion and hydrogen peroxide decreased in ipsilateral but not in contralateral testis. However, the level of thiobarbituric reactive substances (an indicator of lipid perioxidation) decreased after testicular torsion or torsion/detorsion in both testes. CONCLUSION: These data emphasize that oxidative stress may play a role in testicular damage caused by torsion/detorsion and that biochemical indicators of oxidative stress are more sensitive than histological techniques in detecting modifications in the contralateral testis.

Aging↗

PubMed1992

Gonadotropin secreting pituitary microadenoma.

FSH and LH secreting pituitary adenomas may not be as rare as has been previously thought. Women in their reproductive years with a normal estrogenic state and hypergonadotropic amenorrhea should be suspected to harbor a pituitary microadenoma secreting gonadotropins. A computerized tomogram of the pituitary confirms the diagnosis. Two such cases who underwent transphenoidal resection of their adenomas are presented. Pituitary dynamic testing is normal in both. Laparoscopic directed ovarian biopsies show primordial follicles in one and a corpus luteum in the other. Transphenoidal resection, with the risk of permanent hypopituitarism, should be weighed against expectant management, with periodic evaluation of pituitary functions, until the natural history of these adenomas is uncovered.

Adenoma↗

PubMed1988

Wandering intravascular missiles: report of five cases from the Lebanon war.

From 1980 to 1986, during the Lebanon war, five patients with missile embolization were seen at the American University of Beirut Medical Center. Three had entry in the heart or thoracic aorta with peripheral embolization, and two had entry in the internal carotid artery and inferior vena cava with embolization to the middle cerebral artery and heart, respectively. Embolization was suspected when, in the absence of an exit, routine x-ray films showed the missile in a distant location. Angiography and echocardiography confirmed the diagnosis. Peripheral arterial emboli were extracted while cerebral and venous emboli were kept, as they caused transient symptoms and remained silent.

Adolescent↗