NUMERICAL BENCHMARK OF STRONGLY TO LOOSELY COUPLED ASSEMBLIES USING THE TRANSIENT FISSION MATRIX METHOD

Advances in computational methods have given rise to the study and simulation of different aspects of reactor behavior. As such, topics associated with high computational costs become feasible candidates for further investigation and one of them is reactor space-time kinetics (STK). Until recently, STK simulation and point kinetics approximation were limited to deterministic codes, with Monte Carlo codes being too costly to start with. However, recent developments in this area have allowed the use of certain methods in stochastic codes. One such technique is based on the Transient Fission Matrix (TFM) model, a hybrid method that uses a system response obtained through Monte Carlo and stored in fission and time matrices as input for deterministic calculations. The result enables a view of the STK in terms of neutron propagation probability and propagation time across the system. The TFM method was applied to a simple coupled core configuration to generate a numerical benchmark. The Serpent 2 Monte Carlo code was used for the stochastic part of the calculation. The configuration consists of two fuel assemblies placed in a light water tank, with a water blade of varying width between them. TFM, flux and fission results were obtained for varying water blade widths, ranging between 0 cm and 20 cm. The data is then used to analyze the behavior of the system, as well as the effects of the coupling between the two assemblies. As the assemblies move further apart, the system slowly transitions from two tightly coupled assemblies that essentially form a single core, to two almost independent cores. This study enables to produce a benchmark for future calculations and predefine an innovative way of designing high dominant ratio configurations, required for tackling Monte Carlo residual problems. An actual experimental program could be led in ad hoc zero power reactor (ZPR), such as the KUCA reactor of Kyoto University.

[Unilateral pigmentary retinopathy : about 2 cases]

We present the case of two patients in whom unilateral retinal involvement with pigmentary lesions on the fundus examination was observed. Apart from the unilateral nature of the lesions, a diagnosis of retinitis pigmentosa could have been made in view of the morphological and functional aspects of the retina. However, in these two clinical cases, an association between retinal lesions and Bartonella in one case, and pre-existing multiple sclerosis in the other case, has been proposed with a final diagnosis of unilateral pigmentary retinopathy. Nevertheless, a sufficiently long period of patient follow-up is necessary to rule out delayed onset in the unaffected eye, suggesting an asymmetrical bilateral retinitis pigmentosa.

Tests and foreseen developments of fibered-OSLD gamma heating measurements in low-power reactors

In this paper are presented test measurements of a fibered-OSLD system performed during a dedicated experimental phase in EOLE zero-power reactor. The measurement setup consists of an OSLD crystal connected onto the extremity of an optical fiber and a laser stimulation system, manufactured by the CEA/LIST in Saclay. The OSL sensor is remotely stimulated via an optical fiber using a diode-pumped solid-state laser. The OSL light is collected and guided back along the same fiber to a photomultiplier tube. Results obtained using this system are compared to usual gamma heating measurement protocol using OSLD pellets. The presence of induced radio-luminescence in the OSLD during the irradiation was also observed and could be used to monitor the gamma flux.

The feasibility of remote measurements is achieved, whereas further developments could be conducted to improve this technique since the readout procedure still requires to withdraw the OSLD off the gamma flux (hence from the core) on account of the dose rate (around a few Gy.h-1), and the readout time remains quite long for on-line applications. Several improvements are foreseen, and will be tested in the forthcoming years.

The CANDELLE experiment for characterization of neutron sensitivity of LiF TLDs

As part of the design studies conducted at CEA for future power and research nuclear reactors, the validation of neutron and photon calculation schemes related to nuclear heating prediction are strongly dependent on the implementation of nuclear heating measurements. Such measurements are usually performed in low-power reactors, whose core dimensions are accurately known and where irradiation conditions (power, flux and temperature) are entirely controlled. Due to the very low operating power of such reactors (of the order of 100 W), nuclear heating is assessed by using dosimetry techniques such as thermoluminescent dosimeters (TLDs). However, although they are highly sensitive to gamma radiation, such dosimeters are also, to a lesser extent, sensitive to neutrons. The neutron dose depends strongly on the TLD composition, typically contributing to 10-30% of the total measured dose in a mixed neutron/gamma field. The experimental determination of the neutron correction appears therefore to be crucial to a better interpretation of doses measured in reactor with reduced uncertainties. A promising approach based on the use of two types of LiF TLDs respectively enriched with lithium-6 and lithium-7, precalibrated both in photon and neutron fields, has been recently developed at INFN (Milan, Italy) for medical purposes. The CANDELLE experiment is dedicated to the implementation of a pure neutron field “calibration” of TLDs by using the GENEPI-2 neutron source of LPSC (Grenoble, France). Those irradiation conditions allowed providing an early assessment of the neutron components of doses measured in EOLE reactor at CEA Cadarache with 10% uncertainty at 1σ.

[Posterior scleritis]

Posterior scleritis, a severe and painful inflammation of the sclera, is an often misdiagnosed pathology due to its clinical polymorphism. An accurate diagnosis is however needed in order to propose an appropriate treatment of the ophthalmologic symptoms and to exclude an associated systemic inflammatory or auto-immune pathology.

The role of the local chemical environment of Ag on the resistive switching mechanism of conductive bridging random access memories

Conductive bridging random access memories (CBRAMs) are one of the most promising emerging technologies for the next generation of non-volatile memory. However, the lack of understanding of the switching mechanism at the nanoscale level prevents successful transfer to industry. In this paper, Ag/GeSx/W CBRAM devices are analyzed using depth selective X-ray Absorption Spectroscopy before and after switching. The study of the local environment around Ag atoms in such devices reveals that Ag is in two very distinct environments with short Ag-S bonds due to Ag dissolved in the GeSx matrix, and longer Ag-Ag bonds related to an Ag metallic phase. These experiments allow the conclusion that the switching process involves the formation of metallic Ag nano-filaments initiated at the Ag electrode. All these experimental features are well supported by ab initio molecular dynamics simulations showing that Ag favorably bonds to S atoms, and permit the proposal of a model at the microscopic level that can explain the instability of the conductive state in these Ag-GeSx CBRAM devices. Finally, the principle of the nondestructive method described here can be extended to other types of resistive memory concepts.

[Clinical case of the month. Acute post-traumatic panophthalmitis]

Panophtalmitis is an intra-ocular and intra-orbital rare infection, but its consequences are often horrendous, with loss of both function and anatomy of the eye. The surgical approach and the antibiotherapy should be given as soon as possible, both by intra-vitreal and intra-venous injections. We report the case of a 49-year-old man who developed a Bacillus cereus panophtalmitis. A delay in the diagnosis lead to the loss of vision and the evisceration of the sick eye. Bacillus cereus panopthalmitis should be suspected in all cases of post-traumatic endophtalmitis with a soiled metallic foreign body, in patients with important local inflammatory signs as well as systemic signs. Vitrectomy, surgical extraction of the foreign body, intra-vitreal and systemic antibiotherapies should be given as soon as possible, even before the results of the bacteriological analysis.

Sudden sensorineural hearing loss: when ophthalmology meets otolaryngology

OBJECTIVES

Sudden sensorineural hearing loss is a perplexing entity in otology. Susac's syndrome (also called retinocochleocerebral vasculopathy) is a rare disorder that consists of microangiopathy of the brain, retina, and inner ear, and usually affects women in young adulthood. We describe the clinical aspects, radiographic findings, and management of one such case.

CASE REPORT

A 30-year-old woman was admitted to the hospital because of sudden onset of bilateral deafness and headache. During her hospitalization, she developed discrete right hemiparesis and hypoesthesia.

RESULTS

Magnetic resonance imaging revealed multiple signal hyperintensities and atrophy of the corpus callosum. The differential diagnosis was a myelinating condition, such as multiple sclerosis or acute demyelinating encephalomyelitis.

CONCLUSION

Retinal fluorescein angiography helped the diagnosis of Susac's syndrome.

[Clinical case of the month. A case of von Hippel-Lindau disease]

von Hippel-Lindau disease is an inherited multisystemic familial cancer syndrome caused by mutations of the VHL gene. The spectrum of clinical manifestations is broad and includes central nervous system hemangioblastomas and visual benign and malignant tumors. The various manifestations can be demonstrated by means of different imaging techniques such as magnetic resonance imaging, computed tomography, and fluorescein retinal hemangiography. A systematic approach must be followed for repeated screening in patients at risk, since many lesions in VHL disease are treatable.

Retinitis pigmentosa and bronchiectasis: a case report on a rare association suggestive of a common underlying primary ciliary dyskinesia (PCD)

We describe a case of retinitis pigmentosa, associated with bronchiectasis, as the first sign of primary ciliary dyskinesia (PCD). Only a few cases were described in the literature and the association of both diseases is not obvious at first sight, although a common ciliary dysfunction of both respiratory epithelium and photoreceptors of the retina seems to be the common factor. It is important to recognize the association and to question patients with retinitis pigmentosa about their respiratory functions, because an early diagnosis of PCD can prevent recurrent infections and development of bronchiectasis with daily physiotherapy.

Variations nycthémérales de la pression intraoculaire et leurs implications cliniques

Intraocular pressure follows a circadian rhythm like many of the body's parameters. These fluctuations in intraocular pressure were recently identified as a risk factor for visual field loss, in addition to intraocular pressure itself. Furthermore, the pressure curve seems to have a different profile in glaucomatous patients: the peak occurs later compared with normal subjects. Better knowledge of pressure fluctuations and their physiological mechanisms is essential for optimal management of glaucomatous patients not only to interpret the single ocular tension recordings, but also to use the available treatments rationally, both drugs and surgery. The authors review different studies that have contributed to the current knowledge on the circadian rhythm of intraocular pressure, aquous humor flow regulation, and the effects of topical hypotensive drugs on the pressure curve.

Les occlusions vasculaires rétiniennes : diagnostic et prise en charge

PURPOSE

The diagnosis of retinal venous and arterial occlusions is usually easily evoked on visual symptoms and ophthalmoscopic features. However, their management (etiologic explorations and treatment) has not been formally established and remains controversial.

CURRENT KNOWLEDGE AND KEY POINTS

Some retinal vascular occlusions may result of loco-regional ocular causes. They more often occur in patients with cardiovascular pathologies or risk factors, or sometimes other systemic diseases that need to be recognized for a proper treatment. Therefore, a comprehensive management of patients with retinal vascular occlusions is necessary to correct associated diseases or predisposing abnormalities that could lead to local recurrences or systemic events.

CONCLUSION

Along with a review of the literature, we suggest a practical approach for the management of retinal vascular occlusions, which requires a collaboration between the ophthalmologist and other physicians: general practitioner, cardiologist, internist... as appropriate according to each case.

A realistic approach to the evaluation of the quality management movement in health care systems: a comparison between European and African contexts based on Mintzberg's organizational models

The quality movement is gaining momentum worldwide in the field of health care. Initiated in industrialized countries, it steadily grows in Africa. However, there is no evidence that approaches designed to address issues in a given organizational context have the same effect in another one where issues present differently. Along the epistemological paradigm of realistic evaluation proposed by Pawson and Tilley, we use Mintzberg's organizational models to compare the configurations of European and African health care organizations and the trends followed by the quality management movement in both contexts. We illustrate how European health systems traditionally emphasize professional autonomy while African health systems are structured as command and control hierarchical systems. We illustrate how the quality movement in Europe emphasizes standardization of procedures, a characteristic of a mechanistic organization, while excessive standardization is part of the quality problem in Africa. We suggest that instilling professionalism may be a way forward for the quality movement in Africa to improve patient focus and responsiveness of responsible professionals. We also suggest that our interpretation of broad trends and contrasts may be used as a useful departure point to study the wide contextual diversity of the African experience with quality management.

[Anterior lenticonus: diagnostic aid in Alport syndrome]

Anterior lenticonus is a rare condition in which the lens presents a conical protrusion of its anterior cortex. Sometimes isolated, it may be an ocular manifestation of Alport syndrome, a hereditary nephritis accompanied by deafness and other ocular signs such as flecked retinopathy or posterior polymorphous corneal dystrophy. All these manifestations are a result of a genetic defect in type IV collagen, a major component of basal membranes in the human body. The clinical aspects and therapy of anterior lenticonus and Alport syndrome are described, as well as the exploration that must begin when anterior lenticonus is discovered. This exploration is essential so that this diagnosis can be made as soon as possible.

HIV resistance to antiretroviral drugs: mechanisms, genotypic and phenotypic resistance testing in clinical practice

HIV resistance to antiretroviral agents is a major contributory cause of treatment failure. The dynamics of HIV replication, together with patient-, physician-, and drug-related factors, lead to emergence of HIV resistant strains in most of the patients. Phenotypic assays look for an increase in the antiretroviral drug (ARV) concentration that inhibits 50% of the growth of the tested HIV strain (IC50), comparatively with a reference strain cultivated in parallel. Genotypic tests detect resistance mutations in the reverse transcriptase and protease genes by comparing the gene sequences of a resistant virus to those of a wild-type strain that has previously been described. The efficacy of each ARV class and each individual ARV is threatened by specific mutations and resistance mechanisms. In retrospective studies of genotypic or phenotypic resistance testing, baseline resistance tests results were correlated with virological outcomes. There is some evidence from prospective studies that resistance testing may have some benefits when used to choose salvage regimens. However, problems in the areas of test interpretation, patient compliance, availability of active drugs, and technical test performance limit the usefulness of resistance testing in clinical practice. This article reviews the mechanisms underlying HIV resistance, the principles of phenotypic and genotypic tests, and the use of these tests in clinical practice.

[Clinical case of the month. An unusual cause of bronchiectasis: primary ciliary dyskinesia]

We report a case of bronchiectasis due to primary ciliary dyskinesia.

[Update on hepatorenal syndrome]

The hepatorenal syndrome is a form of renal failure occurring in patients with advanced liver disease. The diagnosis is based both on the demonstration of low GFR and exclusion of other common causes of renal failure that may occur in patients with cirrhosis. Orthotopic liver transplantation remains the only curative treatment for this poor outcome disease; other modalities such as vasopressin analogues, transjugular intrahepatic portosystemic shunt or renal replacement therapies may serve as a bridge to transplantation. This article reviews the pathophysiology, diagnosis and current treatment of hepatorenal syndrome.

[Clinical case of the month. A caes of portopulmonary hypertension]

A case of portopulmonary hypertension discovered during exploration of an atypical faint is described and the pathophysiology and management are discussed.

Charge-induced fragmentation of sodium clusters

The fission of highly charged sodium clusters with fissilities X>1 is studied by ab initio molecular dynamics. Na4+24 is found to undergo predominantly sequential Na+3 emission on a time scale of 1 ps, while Na(Q+)(24) ( 5< or =Q< or =8) undergoes multifragmentation on a time scale > or =0.1 ps, with Na+ increasingly the dominant fragment as Q increases. All singly charged fragments Na(+)(n) up to size n = 6 are observed. The observed fragment spectrum is, within statistical error, independent of the temperature T of the parent cluster for T< or =1500 K. These findings are consistent with and explain recent trends observed experimentally.

[Idiopathic pulmonary fibrosis: a new histopathologic classification and clinical aspects]

Idiopathic pulmonary fibrosis (IPF) comprises different interstitial lung diseases of unknown origin. They are classified into four groups based on pathologic criteria: UIP, DIP, AIP and NSIP. This classification helps in terms of prognosis and treatment. In addition to history, physical examination and common investigations (chest X ray, pulmonary function testing), a bronchoalveolar lavage (BAL), a high-resolution CT scan and ideally a open-lung biopsy are needed to establish a precise diagnosis. The patients are usually treated by immunosuppressive agents, and mainly by corticoids. However, in UIP, lung transplantation is the only way to improve survival.

[Centralized purchasing of essential drugs, a priority for the health care systems of developing countries]

Health sector reform is a key priority of many governments throughout the world. Drug supply systems are a major element of public health policy design in Africa, where 90% of drugs are imported. The WHO Essential Drugs Program and the UNICEF sponsored Bamako Initiative have, since the late 1980s, promoted the rational use of essential drugs and attempted to ensure a sustainable drug supply through the implementation of cost recovery schemes and quality assurance mechanisms in public health services. A new market for drugs is emerging within this framework and there is growing competition for its control. Government medical stores are all too often bankrupt and the private sector is expensive, catering mainly for the middle to upper classes of urban areas. An intermediate alternative. Essential Drugs Purchasing Offices (EDPOs), has been proposed to balance social objectives and economic constraints. Some of the experimental strategies have given promising results. However, their implementation raises a number of questions: What is the role of the EDPO? Should it promote public health issues in general or focus purely on drug availability? What is the most appropriate legal status? Public or private? For profit or not? How should the investment capital be structured? In drugs or in funds? With ample provision or a tight budget? How should drug purchases be managed? Where should drugs be purchased? How much? How often? According to which procedures? How should the distribution of drugs be organized? Supplying everyone? Pushing supplies or pulling purchasers in? The answers to these questions, analysis of the reasons for success and failure and the dissemination of the information gathered should identify priorities for action and future research and define a framework for expansion. These are the objectives of the "Concerted Action for the Development of EDPO in Sub-Saharan African Countries" which is supported by the European Union (DG XII).

Chemoenzymatic synthesis of glucose fatty esters

D-Glucose fatty esters at C-6 were obtained by chemoenzymatic synthesis involving 1,2-O-cyclohexylidene-alpha-D-glucofuranose (1) followed by hydrolysis of the cyclohexylidene protecting group. The enzymatic esterification of 1 was performed with fatty acids of variable chain lengths (C8:0 to C18:0). The kinetic of the reaction was studied for each fatty acid and the structure of the octanoyl ester was determined by 1H and 13C NMR spectroscopy.

Geobase: a simple geographical information system on a personal computer

Spatially distributed data are often encountered in the biological sciences. Representation and analysis of such data requires specific tools. A simple geographical information system is presented, which allows representation and elementary analysis of geographically coded information. The system handles two kinds of data: maps and facts, where map data describe the basis on which the fact data are located. Maps consist of objects described through a set of coordinates, while for facts a coordinate pair is associated with an unlimited number of data records containing five fields: a date, an element from a list, a two-character code, an integer number and a real number. The input data can be displayed interactively on screen by logically combining selection criteria for each field. The facts corresponding to the selected criteria are either displayed as such, or are clustered and displayed as polygons or pies. A short example showing a possible application of the program is presented and advantages as well as limitations are discussed.

Quantitative determination of tertatolol in biological fluids by gas chromatography-mass spectrometry

Quantitative determination of tertatolol concentrations in plasma and urine was performed by gas chromatography-mass spectrometry in the chemical-ionization mode with ammonia after successive extractions of the beta-blocking drug in alkaline, acid and final alkaline medium. [2H9]Tertatolol, isotopically stable under the operating conditions employed, was used as an internal standard, thus allowing quantities of 1 ng/ml to be specifically determined. Overall analytical error was less than 10%. Prior to isothermal chromatography at 240 degrees C on a column packed with 3% SE-30, both compounds were silylated with bis(trimethylsilyl)trifluoroacetamide. Detection was performed by monitoring the quasimolecular ions of tertatolol, m/z 368 and m/z 377, for the [2H9]tertatolol in the chemical-ionization mode with ammonia. The calibration curves obtained had linear characteristics for the concentration range 1-1125 ng/ml.