Engineering camel single-domain antibodies and immobilization chemistry for human prostate-specific antigen sensing

The specificity and affinity characteristics of antibodies make them excellent probes in biosensor applications. Unfortunately, their large size, unstable behavior, and random immobilization properties create numerous problems. The single-domain antigen-binding fragment derived from heavy-chain antibodies of camelids (termed VHH) offers special advantages in terms of size, stability, and ease of generating different antibody constructs. In this study, we show the potential of those VHHs in sensing human prostate-specific antigen (hPSA) by SPR technology. Different VHH constructs were immobilized onto commercial and custom-built sensor surfaces by metal chelation, biotin-streptavidin interaction, or covalent coupling. The detection of subnanogram per milliliter hPSA concentrations could be attained on a covalently coupled three-dimensional dextran surface. Moreover, the ratio of different hPSA isoform concentrations could be assessed via a sandwich assay and resulted in the detection of clinically significant antigen concentrations within 15 min. In addition, for the first time, the intrinsic protein stability is presented as an important probe design factor, since our results reveal that higher intrinsic stability offers higher resistance to harsh regeneration conditions. In conclusion, we present VHHs as a novel class of biosensor probes rivaling conventional antibodies and their derived antibody fragments.     

Efficient March Test Procedure for Dynamic Read Destructive Fault Detection in SRAM Memories

This paper presents an analysis of dynamic faults in core-cell of SRAM memories. These faults may appear as the consequence of resistive-open defects that appear more and more frequently in VDSM technologies. In particular, the study concentrates on those defects that generate dynamic Read Destructive Faults, dRDFs. In this paper, we demonstrate that read or write operations on a cell involve a stress on the other cells of the same word line. This stress, called Read Equivalent Stress (RES), has the same effect than a read operation. On this basis, we propose to modify the well known March C-, which does not detect dRDFs, into a new version able to detect them. This is obtained by changing its addressing order with the purpose of producing the maximal number of RES. This modification does not change the complexity of the algorithm and its capability to detect the former target faults.This work has been partially funded by the French government under the framework of the MEDEA+ A503 “Associate“ European program.     

Phosphorus budget as a water quality management tool for closed aquatic mesocosms

Since the start-up of the St. Lawrence Mesocosm (SLM) at the Montreal Biodome in 1992, phosphorus has accumulated slowly, reaching about 18 mg P l(-1) in 2000. It was decided that this concentration should be lowered to about 2mg P l(-1) to maintain a safe nitrogen:phosporus (N:P) ratio of about 10. Before deciding what type of treatment to use for the removal of phosphorus, a P budget was estimated for 1998 in order to evaluate the different pathways of phosphorus in the mesocosm. The resulting budget had only a 1% difference between the inputs (CV = 12.9%) and the sum of the outputs and changes in P pools (CV = 12.5%). P inputs amounted to 40.5 kg for 1998: food for fish and invertebrates contributed 76% of the inputs while seabird guano contributed 20%. Filtration and general cleaning removed 51% of the inputs while water losses removed 22%. The slight but constant difference between total phosphorus and dissolved reactive phosphorus (DRP) in 1998 and previous years led us to believe that only DRP (mostly orthophosphate) accumulated in the system. The accumulation of DRP was 10% of the inputs in 1998. The budget showed that the importance of water losses is relative and depends on the DRP concentration in the SLM. Furthermore, it was possible to compare this P budget with an N budget of the SLM prepared in 1995. The comparison helped us understand why nitrate in closed-circuit mesocosms are characterized by a high, never-ending accumulation while DRP is characterized by a net increase in the first few years after start-up followed by a very small increase in the following years. Considering its low CV, this P budget was considered a useful water quality management tool in designing a P removal unit for the SLM. This budget may also serve as a guideline for managers of closed-circuit systems such as marine aquariums and aquacultures as well as for designers of P removal units.     

Study of NbGeSi films deposited by chemical vapour deposition

NbGeSi films were prepared by chemical vapour deposition. Results of X-ray diffraction, electron microscopy and chemical composition examinations are reported. The A15 phase was obtained over a wide composition range and a new Nb₃Si₂ structure was produced. The stability and the homogeneity of these materials are discussed.     

Layered double hydroxides: an attractive material for electrochemical biosensor design

Electrochemical biosensors for phenol determination were developed based on the immobilization of polyphenol oxidase (PPO) within two different clay matrixes, one anionic (layered double hydroxide, LDH) and the other cationic (Laponite). The biosensor based on the enzyme immobilized in [Zn-Al-Cl] LDH shows greater sensitivity (7807 mA M(-1) cm(-2)) and maximum current (492 microA cm(-2)). Biosensor characteristics, such as Michaelis-Menten constant, recycling constant, activation energy, and permeability highlight the advantages of LDH matrixes to immobilize PPO. It appears that LDH provides a favorable environment to PPO activity. The best PPO/[Zn-Al-Cl] configuration was used to determine five different phenol derivatives reaching extremely sensitive detection limits (< or = 1 nM).     

Finite-element modeling of needle electrodes in tissue from the perspective of frequent model computation

Information about electric field distribution in tissue is very important for effective electropermeabilization. In heterogeneous tissues with complex geometry, finite-element (FE) models provide one of alternative sources of such information. In the present study, modeling of needle electrode geometry in the FE model was investigated in order to determine the most appropriate geometry by considering the need for frequent FE model computation present in electroporation models. The 8-faceted needle electrode geometry proposed--determined on a model with a single needle electrode pair by means of criteria function--consisted of the weighted sum of relative difference between measured and computed total current, the relative difference in CPU time spent on solving model, and the relative difference in cross section surface of electrodes. Such electrode geometry was further evaluated on physical models with needle arrays by comparison of computed total current and measured current. The agreement between modeled and measured current was good (within 9% of measurement), except in cases with very thin gel. For voltage above 50 V, a linear relationship between current and voltage was observed in measurements. But at lower voltages, a nonlinear behavior was detected resulting from side (electrochemical) effects at electrode-gel interface. This effect was incorporated in the model by introducing a 50-V shift which reduced the difference between the model and the measurement to less than 3%. As long as material properties and geometry are well described by FE model, current-based validation can be used for a rough model validation. That is a routine assay compared with imaging of electric field, which is otherwise employed for model validation. Additionally, current estimated by model, can be preset as maximum in electroporator in order to protect tissue against damage.     

New phase-noise model for crystal oscillators: application to the Clapp oscillator

Leeson's is the basic model for predicting oscillator noise. A mathematical analysis of this "heuristic" model has been proposed. Both models do not detail the relative importance of the amplifier transfer function associated to its own noise with regard to that of the resonator. In this paper, an improved version of those previous models is presented. The phase noise generated by the amplifier and the one generated by the resonator are differentiated without considering their origins, such as the conversion of amplitude modulation noise into phase modulation noise. The power spectral densities of phase noise at various points of the oscillator loop are calculated from their respective correlation functions. As a consequence, the influence of the inner amplifier and resonator noises on the resulting oscillator noise is predictable. The model is especially attractive to the makers of widely used quartz oscillators. The resulting oscillator noise is easily obtained from the oscillator open-loop noise. An example of the phase-noise modeling of the Clapp quartz crystal oscillator is simulated and discussed.     

Cryogenic monolithic sapphire-rutile temperature compensated resonator oscillator

We have tested a new temperature-compensated sapphire resonator as frequency determining element for high-stability microwave oscillator. Temperature compensation has been obtained by coating the sapphire resonator with a thin rutile film. A 2-/spl mu/m rutile thickness is sufficient to reach turnover temperature higher than 40 K, and a 2/spl times/10/sup -12/ short-term frequency stability has been obtained.     

The power of languages for the manipulation of complex values

Various models and languages for describing and manipulating hierarchically structured data have been proposed. Algebraic, calculus-based, and logic-programming oriented languages have all been considered. This article presents a general model for complex values (i.e., values with hierarchical structures), and languages for it based on the three paradigms. The algebraic language generalizes those presented in the literature; it is shown to be related to the functional, style of programming advocated by Backus (1978). The notion of domain independence (from relational databases) is defined, and syntactic restrictions (referred to as safety conditions) on calculus queries are formulated to guarantee domain independence. The main results are: The domain-independent calculus, the safe calculus, the algebra, and the logic-programming oriented language have equivalent expressive power. In particular, recursive queries, such as the transitive closure, can be expressed in each of the languages. For this result, the algebra needs the powerset operation. A more restricted version of safety is presented, such that the restricted safe calculus is equivalent to the algebra without the powerset. The results are extended to the case where arbitrary functions and predicates are used in the languages.