An analytic method to predict the thermal map of cryosurgery iceballs in MR images

This paper presents a newly developed method to estimate, in magnetic resonance (MR) images, the temperatures reached within the volume of an iceball produced by a cryogenic probe. Building on the direct measurements of the MR signal intensity and its correlation with independent temperature variations at the phase transition from liquid to solid, the thermal information embedded in the images was accessed. The volume and diameter of the growing iceball were estimated from a time series of MR images. Using regressions over the volume in the time and thermal domains, this method predicted the cryogenic temperatures beyond the range of sensitivity of the MR signal itself. We present a validation of this method in samples of gelatin and ex vivo pig liver. Temperature predictions are shown to agree with independent thermosensor readings over a range extending from 20 degrees C down to -65 degrees C, with an average error of less than 6 degrees C.     

Automatic generation of noise-free time-activity curve with gated blood-pool emission tomography using deformation of a reference curve

This paper describes a new method for assessing clinical parameters from a noisy regional time-activity curve (TAC) in tomographic gated blood-pool ventriculography. This method is based on a priori knowledge on the shape of a TAC, and shape approximation. The rejection method was used to generate different random Poisson deviates, covering standard count levels, of six representative TACs in order to test and compare the proposed method with harmonic and multiharmonic reconstruction methods. These methods were compared by evaluating four clinical parameters: time of end systole, amplitude, peak ejection and filling rates. Overall, the accuracy of assessment of these parameters was found to be better with the method described in this paper than with standard multiharmonic fits.     

Towards trust management standardization

Recent research in the field of security has evolved into trust issues, which are now one of the interesting research topics. A majority of current approaches proposes techniques that support users' trust processes, while a minority of them addresses the essence of trust. The latter approaches form the basis for the work presented in this paper. Outer manifestations of trust phenomenon are formalized in order to facilitate the development in this field. The main goal is to provide means for computable trust that can be used in a standardized way for contemporary internet-based applications, independently of its cognitive principles.     

A mammalian genetic system to screen for small molecules capable of disrupting protein-protein interactions

A mammalian two-hybrid system was developed for high-throughput screening of compounds that disrupt specific protein-protein interactions. The existing mammalian systems are unsatisfactory for drug screening due to nonregulated expression of interacting proteins. To construct a tightly regulated system, the tetracycline repressor was fused with the inhibitory KRAB domain as a suppressor. The binding of the suppressor to the tet operator entirely blocked expression of two interacting proteins. When both the inducer doxycycline and drugs were added to the culture, the reporter gene was either activated by interaction of the paired proteins with ineffective drugs or remained silent due to disruption of the protein interactions by the effective drugs. We demonstrate that interactions of the type I receptor for TGFbeta with FKBP12 and the epidermal growth factor receptor (EGFR) with p85 are effectively disrupted by FK506 and EGFR kinase inhibitor AG1478, respectively. The power of this system for drug screening was further demonstrated by rapid identification of inhibitors from a druglike library for the receptor kinases.     

Intrinsic properties of the optical coupling between axisymmetric Gaussian beams

On the basis of the overlap integral method, an approximate analytical model is derived to estimate the coupled optical power between axisymmetric Gaussian beams when transverse, axial, and angular misalignments simultaneously exist in three dimensions. Seven optical properties are derived from a detailed analysis of the model. Because the model is an approximate analytical solution to the overlap integral method, the existence of each property is also investigated by a numerical solution. Results show that all seven properties are intrinsic to the optical coupling phenomenon between Gaussian beams. Because numerous single-mode device-to-fiber coupling systems can be well described by use of Gaussian beams, the seven properties provide a solid basis to develop model-based algorithms for single-mode device-to-fiber alignment automation.     

A model to describe the interaction between UO2 and zircaloy in the temperature range 1000–1700°C

During high temperature transients the Zircaloy claddings in a nuclear power reactor may chemically interact with their environment, either on the internal or on the external surfaces. The external oxidation due to the interaction with the coolant has been extensively studied and described in models. However, the internal oxide-metal interaction is less well known and has not yet been satisfactorily described in models. In this paper the internal oxidation, which results from the reduction of the UO₂ pellets by the Zircaloy cladding material is analyzed. A model is developed which solves only the oxygen diffusion problem in the five phases which are formed due to the UO₂/Zircaloy interaction, without taking into account zirconium and uranium diffusion. The oxygen diffusion coefficients of four of the phases are determined and the oxygen concentrations at some of the interfaces are adjusted in order that the interface movements be in accordance with the experimental data published in the literature for the temperature range 1000 to 1700°C. The model attempts only to simulate the kinetics of the system during the first stages of the process when all the interface movements obey parabolic rate laws.     

Nouveaux composes graphite-sodium-azote-hydrogene

Sodium reacts with graphite only with difficulty. However, in the presence of impurities, compounds of formula NaC₆₄ seem to have been observed by Asher. More recent work shows that products richer in sodium can be obtained by using new techniques. We have reacted graphite and sodium in the presence of nitrogen and hydrogen. The reaction was carried out in a sealed, stainless steel reactor at a temperature in the neighbourhood of 400°C. New quaternary compounds of graphite, sodium, nitrogen and hydrogen are obtained.Compounds of stages II, III and IV were identified, although only the third stage compound has been isolated. Of bluish-black colour, it may be kept exposed to the air for several hours without any apparent alteration. Chemical analysis allows attribute it a formula C₁₅₀Na₁₄Na₁₄N₇H₁₄. The average experimental mass increase, equal to 23%, is close to that deduced from chemical analysis (25%) (Table 1). A radiocrystallographic study of this compound has been carried out on pyrographite samples (PGCCL from Carbone Lorraine or HOPG from Union Carbide). Results are identical for the two types of samples (Figs. 1 and 2).A study of the 001 reflections of stage II, III and IV compounds gave the following values of c axis repeat periods: 10.88 and 17.57 Å (Table 3). These results allow to deduce the value of the interplanar distance, equal to 7.52 Å. Direct thickness measurements of the samples before and after intercalation give an average relative dilatation of 44%, close to the theoretical value of 41.5% deduced from the preceding X-ray analysis results.Examination of the rotating crystal diagram carried out for a third stage compound shows that the parameter c is equal to the identity period along the c axis. The kh0 reflections (Table 4) can be indexed in a hexagonal system and the parameter a calculated in the case of the third stage compound is equal to 12.30 Å, five times the parameter a of graphite.The resistivity in the later planes was measured at room temperature, using a noncontact method. It was found to be close to 10 μΩ cm, a value which is comparable to that of the first stage graphite-potassium compound.     

Study of the Action of Static and Dynamic Fusimotor Fibers With a Mechanical Model of the Mammalian Muscle Spindle

A model of the mammalian muscle spindle having three distinct parts is proposed. The three parts, which consist of a mechanical filter, a transducer, and an encoder, are closely related with their physiological counterparts. A study of the generator potentials for the primary and secondary endings of the spindle was performed by means of an analog computer simulation of the model. The afferent responses of the spindle under a phasic stretch with and without fusimotor fibers simulation are also studied. Finally, frequencygrams (see text) are obtained under the condition of ?1 (dynamic) stimulation acting on both nuclear bag and nuclear chain fibers. The model yields results that are directly comparable with physiological data obtained under similar conditions.     

Twin-sensitivity measurement by spatial multiplexing of digitally recorded holograms

We present an all-numeric multiplexing/demultiplexing technique for digitally recorded holograms that allow the simultaneous determination of the in-plane and the out-of-plane components of the displacement vector of an object submitted to some loading. The twin-sensitivity measurement is obtained from two different illumination directions that give two sensitivity vectors. The spatial multiplexing is achieved by an incoherent mixing of two duplets of coherent waves that produce holograms carried with orthogonal polarized reference waves. The spatial demultiplexing uses the autocorrelation function of the multiplexed holograms as a position estimator. The estimator then enables the determination of the pixel-to-pixel correspondence between the holograms for the double component determination. Results of the experiment are presented.     

Design and optical characterization of a large continuous phase plate for Laser Integration Line and Laser Megajoule facilities

For development of the French Laser Integration Line and the Laser Megajoule, we describe the design and the control of a first 383 mm x 398 mm continuous phase-plate prototype. Extensively used in laser fusion facilities for beam smoothing, this optical component was manufactured by deep etching onto a fused-silica substrate, which led to a phase plate engraved directly onto fused silica, with which good optical performance could be achieved. We demonstrate good agreement between the desired simulated component and the manufactured component in terms of focal spot shape. This demonstration was performed by both interferometric and photometric measurements.