Publications (12)18.57 Total impact
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Conference Proceeding: Message-Embedded Cryptosystems: Cryptanalysis and Identifiability
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ABSTRACT: The aim of this paper is to compare two encryption schemes, the standard stream cipher and a so-called message-embedded cryptosystem. The comparison is based on two main aspects. The first aspect deals with the synchronization of the time-varying keys at the transmission side and at the reception side. The second aspect focuses on the cryptanalysis of the encryption algorithms. The cryptanalysis is concerned with the system parameter retrieving. The key point of the paper is that, for message-embedded cryptosystems, the cryptanalysis can be treated as a parametric identifiability issue. Two methods, the local state isomorphism approach and the Gröbner bases method, are presented for systems including polynomial nonlinearities. It is shown that these systems are weak against algebraic attack.Decision and Control, 2005 and 2005 European Control Conference. CDC-ECC '05. 44th IEEE Conference on; 01/2006 -
Article: In Vivo31P NMR measurement of glucose‐6‐phosphate in the rat muscle after exercise
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ABSTRACT: Comparison of 31P NMR spectra of the rat gastrocnemius, obtained in vivo and from PCA extracts, after electrically induced contractions, demonstrates that glucose-6-phosphate (G6P) is the major metabolite in the low-field part of the PME spectral region. In vivo31P NMR can thus be used to measure the muscle G6P concentration after exercise.Magnetic Resonance in Medicine 12/2005; 30(3):347 - 350. · 2.96 Impact Factor -
Conference Proceeding: Global adaptive synchronization based upon polytopic observers
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ABSTRACT: A new adaptive synchronization scheme achieving a joint state and parameter estimation is proposed as an alternative to the well-known Extended Kalman Filter based on a first order approximation. It involves a polytopic observer which no longer requires a linearization. The resulting adaptive synchronization is global and holds for a large class of chaotic systems. The computation of the gain of the observer is performed in a systematic way and is derived from the solutions of a Linear Matrix Inequalities set.Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on; 06/2004 -
Article: In vivo regulation of muscle glycogen synthase and the control of glycogen synthesis.
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ABSTRACT: The activity of glycogen synthase (GSase; EC 2.4.1.11) is regulated by covalent phosphorylation. Because of this regulation, GSase has generally been considered to control the rate of glycogen synthesis. This hypothesis is examined in light of recent in vivo NMR experiments on rat and human muscle and is found to be quantitatively inconsistent with the data under conditions of glycogen synthesis. Our first experiments showed that muscle glycogen synthesis was slower in non-insulin-dependent diabetics compared to normals and that their defect was in the glucose transporter/hexokinase (GT/HK) part of the pathway. From these and other in vivo NMR results a quantitative model is proposed in which the GT/HK steps control the rate of glycogen synthesis in normal humans and rat muscle. The flux through GSase is regulated to match the proximal steps by "feed forward" to glucose 6-phosphate, which is a positive allosteric effector of all forms of GSase. Recent in vivo NMR experiments specifically designed to test the model are analyzed by metabolic control theory and it is shown quantitatively that the GT/HK step controls the rate of glycogen synthesis. Preliminary evidence favors the transporter step. Several conclusions are significant: (i) glucose transport/hexokinase controls the glycogen synthesis flux; (ii) the role of covalent phosphorylation of GSase is to adapt the activity of the enzyme to the flux and to control the metabolite levels not the flux; (iii) the quantitative data needed for inferring and testing the present model of flux control depended upon advances of in vivo NMR methods that accurately measured the concentration of glucose 6-phosphate and the rate of glycogen synthesis.Proceedings of the National Academy of Sciences 10/1995; 92(19):8535-42. · 9.68 Impact Factor -
Article: Proton NMR observation of glycogen in vivo.
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ABSTRACT: Our previous solution studies of the proton relaxation properties of glycogen H1 have shown significant dipolar cross-relaxation with intra-ring H2 and inter-ring H4' protons characterized by a correlation time tau c = 2.7 x 10(-9) s. This leads to a significant negative Nuclear Overhauser Enhancement (NOE) of glycogen H1 following either transient or steady state perturbations of the longitudinal magnetization of dipolar coupled protons, especially H2 and H4'. Here we use the NOE to edit selectively the H1 resonance of glycogen in the rat liver in vivo using a surface coil probe. The approach shows the possibility of measuring glycogen in vivo with high sensitivity using 1H NMR.Magnetic Resonance in Medicine 06/1994; 31(5):576-9. · 2.96 Impact Factor -
Article: In vivo regulation of rat muscle glycogen resynthesis after intense exercise.
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ABSTRACT: Time courses of the glycogen synthesis rate and of the glucose 6-phosphate (G-6-P) concentration after an electrically induced exercise were followed in the anesthetized rat gastrocnemius by in vivo 13C and 31P nuclear magnetic resonance (NMR) spectroscopy, respectively. The ratio of glycogen synthase I to glycogen synthase I and D (I/I+D) and allosteric activation by G-6-P were also studied in vitro on muscles sampled at rest and 10 min (early recovery) and 100 min (late recovery) after exercise. From early recovery to late recovery, the in vivo glycogen synthesis rate dropped from 0.46 +/- 0.06 to 0.11 +/- 0.04 mmol.kg wet tissue-1.min-1, the G-6-P concentration from 0.83 +/- 0.08 to 0.32 +/- 0.05 mmol/kg wet tissue, and I/I+D from 83 +/- 4 to 47 +/- 1%. The combination of the changes in G-6-P concentration and in I/I+D quantitatively describes the fourfold decrease in glycogen synthesis rate from early to late recovery. These results demonstrate that phosphorylation, determining glycogen synthase I/I+D, and allosteric control of glycogen synthase by G-6-P contribute approximately equally to the regulation of the postexercise in vivo glycogen synthesis rate.The American journal of physiology 02/1994; 266(1 Pt 1):E85-91. -
Article: In vivo 31P NMR measurement of glucose-6-phosphate in the rat muscle after exercise.
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ABSTRACT: Comparison of 31P NMR spectra of the rat gastrocnemius, obtained in vivo and from PCA extracts, after electrically induced contractions, demonstrates that glucose-6-phosphate (G6P) is the major metabolite in the low-field part of the PME spectral region. In vivo 31P NMR can thus be used to measure the muscle G6P concentration after exercise.Magnetic Resonance in Medicine 10/1993; 30(3):347-50. · 2.96 Impact Factor -
Article: Flow field in a low-speed axial fan: a DPIV investigation
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ABSTRACT: The characteristics of the flow in a low-speed axial fan were investigated using digital particle image velocimetry (DPIV). Instantaneous and time-averaged velocity measurements were made at the leading-edge, trailing-edge, and suction and pressure sides of the blade by synchronizing the passage of the blade with the laser and camera system. These measurements revealed steady and unsteady flow features at several operating points and allowed a composite DPIV image around the entire fan blade to be made. This composite image was compared with a panel code solution, and the main differences found between them were attributed to local viscous effects such as flow separation and wake unsteadiness that are not included in the present panel code implementation.Experimental Thermal and Fluid Science. -
Article: Experimental evaluation Celsior®, a new heart preservation solution
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ABSTRACT: An original heart preservation solution (Celsior) has been developed, the formulation of which has been designed to fulfil two major objectives: (1) to combine the general principles of hypothermic organ preservation with those specific for the myocardium, and (2) to offer the possibility of being used not only as a storage medium but also as a perfusion fluid during initial donor heart arrest, poststorage graft reimplantation and early reperfusion. The major principles addressed by the Celsior formulation include (1) prevention of cell swelling (by mannitol and lactobionate), (2) prevention of oxygen-derived free radical injury (by reduced glutathione, histidine and mannitol), and (3) prevention of contracture by enhancement of energy production (glutamate) and limitation of calcium overload (high magnesium content, slight degree of acidosis). Two experimental preparations were used: The isolated isovolumic buffer-perfused rat heart model and the heterotopic rabbit heart transplantation model. In isolated heart experiments, hearts were arrested with and stored in Celsior for 5 h at 4°C and subsequently reperfused for 1 h. A similar protocol was used in the transplantation experiments except that the total ischemic time was approximately longer (corresponding to 6 h of storage followed by the 25 additional minutes of cold ischemia required for graft implantation). In both models, the results were primarily assessed on isovolumic measurements of left ventricular diastolic pressure, developed pressure and peak positive rate of the rise of the left ventricular pressure (), and compared with those obtained in control hearts arrested with and stored in St Thomas' Hospital cardioplegic solution No 2 under similar experimental conditions. The isolated rat heart experiments show that Celsior-preserved hearts incurred significantly smaller losses of compliance after ischemia than hearts exposed to St Thomas' Hospital solution whereas they demonstrated significantly higher values of contractile indices throughout the period of reperfusion. Qualitatively similar patterns of recovery were seen in the rabbit transplantation experiments. We conclude that the functional preservation of cardioplegically arrested cold-stored cardiac allografts can be improved by their exposure to a single solution, the formulation of which combines the major protective features of cardioplegic perfusates with those of organ storage media.European Journal of Cardio-Thoracic Surgery. -
Article: Real-time video communication secured by a chaotic key stream cipher
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ABSTRACT: An improvement of the chaotic inverse system encryption approach is suggested by intro-ducing piecewise linearities. The usual design pro-cedure is adapted in order to achieve an Input In-dependent Global Synchronization. Experiment of the resulting chaotic key stream encryption setup is conducted on a real-time video transmission. The secrecy level is assessed through a linear cryptanal-ysis. -
Article: Considering the attractor structure of chaotic maps for observer-based synchronization problems
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ABSTRACT: The main purpose of this paper is to state some sufficient conditions for global synchronization of chaotic maps. The synchronization is viewed as a state reconstruction problem which is tackled by polytopic observers. Unlike most standard observers, polytopic observers can account for a special property of chaotic dynamics. Indeed, it is shown that many chaotic maps can be described in a so-called convexified form, involving a time-varying parameter which depends on the chaotic state vector. Such a form makes it possible to incorporate knowledge on the structure of the compact set wherein the parameter lies. This set depends implicitly on the structure of the chaotic attractor. It is proved that the conservatism of the polyquadratic stability conditions for the state reconstruction, stated in a companion paper, can be reduced when the corresponding Linear Matrix Inequalities involve the vertices of the minimal convex hull of this set. Theoretical developments along with special emphasis on computational aspects are provided and illustrated in the context of adaptive synchronization.Mathematics and Computers in Simulation. -
Article: period expression in the honey bee brain is developmentally regulated and not affected by light, flight experience, or colony type
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ABSTRACT: Changes in circadian rhythms of behavior are related to age-based division of labor in honey bee colonies. The expression of the clock gene period (per) in the bee brain is associated with age-related changes in circadian rhythms of behavior, but previous efforts to firmly associate per brain expression with division of labor or age have produced variable results. We explored whether this variability was due to differences in light and flight experience, which vary with division of labor, or differences in colony environment, which are known to affect honey bee behavioral development. Our results support the hypothesis that per mRNA expression in the bee brain is developmentally regulated. One-day-old bees had the lowest levels of expression and rarely showed evidence of diurnal fluctuation, while foragers and forager-age bees (>21 days of age) always had high levels of brain per and strong and consistent diurnal patterns. Results from laboratory and field experiments do not support the hypothesis that light, flight experience, and colony type influence per expression. Our results suggest that the rate of developmental elevation in per expression is influenced by factors other than the ones studied in our experiments, and that young bees are more sensitive to these factors than foragers.Insect Biochemistry and Molecular Biology.
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Institutions
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1993–2005
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Yale University
- Department of Molecular Biophysics and Biochemistry
New Haven, CT, USA
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