Quasi-reciprocal mixer as an absolute vector signal standard at microwave frequencies

A reciprocal mixer has the potential to extend an absolute calibration of magnitude and phase relationships at baseband to an absolute calibration at microwave frequencies. Unfortunately, recent publications have shown that mixers are not in general reciprocal devices. The authors' tests have shown that the up- and down-conversion transmission responses for a mixer change with time and temperature. The ratio of the up- and down-conversion transmission responses, however, can be remarkably constant with time and temperature for some mixers. The authors refer to this ratio as the characterised non-reciprocal ratio (CNR) for the mixer. By using a new calibration circuit, they are able to utilise this CNR for a quasi- reciprocal mixer and provide an effective absolute vector calibration standard at microwave frequencies.     

Corneal endothelial damage associated with phacoemulsification

Ergonovine maleate (EM) is a powerful stimulant of human tubal motility. It has been therefore thought that EM could interfere with normal ovum transport and serve as a contraceptive. The tube activating effects of EM and methyl EM were evaluated in 14 women and results confirmed that both are powerful stimulants of the human Fallopian tube. EM immediately post coitus significantly reduces the conception rate.     

Anisotropy of hygrothermal damage in fiber/polymer composites: Effective elasticity measures and estimates

Measured elasticity moduli of a highly (68%) glass-fiber reinforced epoxy matrix for different amounts of fiber/matrix interface weakening and debonding, due to different hygrothermal ageing stages, are compared to estimated ones. Ultrasonic measurements provide seven of the nine elasticity moduli of the orthotropic material samples, including all the moduli significantly affected by damage. Theoretical estimates combine homogenization modeling techniques and Finite Element (FE) calculations, the latter when the effect of observed partial debonding on effective moduli is to be specified. These estimates are performed under different assumptions for the composite structure, with special attention to the existence of a fiber–matrix interphase. Analytical comparisons for the undamaged composite establish that matching US measurements with estimates cannot be obtained, regardless of the chosen model, without the assumption of an interphase layer of modified resin coating the fibers. This coating resin, when in relevant concentration with regard to literature data about fiber coating thickness, typically conserves the epoxy moduli transversally to the fiber orientation, while, in the fiber direction its moduli approach those of the fibers. The comparison of the US measurements on damaged samples to FE calculations assuming progressive one-directional debonding shows that most of the composite stiffness loss can preferentially be due to an initial interphase weakening, while the fiber/matrix debonding seems more likely delayed to long H-ageing times. This is consistent with physical interpretation of damage by water pooling through silane bridges bonding epoxy to glass. The calculations also provide the effective stiffness, at different damage stages, of the “Undamaged Equivalent Inhomogeneity” for this damaged inclusion type.     

Relating chemical activity to structure: An examination of ILP successes

Problems concerned with learning the relationships between molecular structure and activity have been important test-beds for Inductive Logic programming (ILP) systems. In this paper we examine these applications and empirically evaluate the extent to which a first-order representation was required. We compared ILP theories with those constructed using standard linear regression and a decision-tree learner on a series of progressively more difficult problems. When a propositional encoding is feasible for the feature-based algorithms, we show that such algorithms are capable of matching the predictive accuracies of an ILP theory. However, as the complexity of the compounds considered increased, propositional encodings becomes intractable. In such cases, our results show that ILP programs can still continue to construct accurate, understandable theories. Based on this evidence, we propose future work to realise fully the potential of ILP in structure-activity problem.     

Role of isotope methods in the evaluation of cardiac function in intensive care

Radioisotopic cardiac investigation techniques still have a limited role in intensive care units, mainly due to cumbersome traditional equipment, even if in some cases favourable local circumstances exist, such as the proximity of a nuclear medicine unit or the availability of a mobile gamma camera. Nevertheless, nuclear techniques show a number of interesting features, mainly related to the fact that measurements of cardiac chamber volumes and of their variations can be directly derived from activity counts, without any geometrical hypothesis as it is necessary for other methods such as contrast angiography or echocardiography. The whole cardiac cycle (its systolic part as well as its diastolic part) can therefore be evaluated. In addition, since the blood pool labelling remains stable for a long period after a single tracer injection, continuous monitoring of critically ill patients becomes possible. In this case it is no longer the gamma camera imaging system which may be used but rather a very sensitive miniature detector associated with a computerized data acquisition system, allowing beat-by-beat assessment of cardiac activity. The development of this device raises specific problems related to detection geometry, elimination of extracardiac background and stability of the probe positioning on the patient's thorax, but it is clear that such a system merits its place in an intensive care unit in the near future.     

Protein secondary structure prediction using logic-based machine learning

Protein Engineering, 5, 647–657 An error was found (Leberman, 1993) in the selection of non-homologousproteins used to train the machine learning program Golem. Theproteins 155C (cytochrome C550) and 2C2C (cytochrome C2 oxidized)have 43.5% sequence homology. Removal of the result for 2C2C(the most accurately predicted of the two proteins) producesa Q3 accuracy of 78% (no change) and a Matthew's correlationof 0.53 (a reduction of 0.04). Removal of 2C2C makes no differenceto results for the independent test set of non-homologous proteins. Reference. Leberman, R. (1993) Protein Engng, 6, 547.     

Editorial.

As he approaches the halfway mark in his role as Editor of the Psychological Bulletin, the author uses this editorial to take stock of where the Bulletin has gone during the first half of his editorship, and where he would still like to see it go. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Asbestos corrosion study in a caustic potash solution at several temperatures

Corrosion of chrysotile asbestos tissue (diaphragm material) was determined at 115–200°C in pressure vessels (1–20 bars). These tests have shown the good shape of this asbestos material for 2000/h with an unchanged solution of potash at 200°C under a 20 bars pressure, and a progressive elimination of the silica when potash solution is renewed and partial destruction of the samples.     

Epinephrine-induced learning under anesthesia: Retention performance at several training–testing intervals.

While under deep barbiturate anesthesia, 58 male Sprague-Dawley rats received a series of 10 classical conditioning trials in which white noise was paired with intramuscular shock. The anesthetized Ss received subcutaneous injections of saline or epinephrine bitartrate (.1 mg/kg) prior to the training trials. Independent sets of Ss were tested for retention performance 2, 7, or 15 days after training. In these test trials, a conditioned suppression measure was used in which the white noise was turned on while the Ss were drinking. Results indicate that the Ss that had received saline while trained under anesthesia exhibited no evidence of later retention. Ss that had received epinephrine injections prior to training under anesthesia suppressed their drinking in the presence of the white noise when tested 2 or 7, but not 15, days later. Findings demonstrate that epinephrine can enable learning under anesthesia and that forgetting occurs within 15 days. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Application of scaled particle theory to model the hydrophobic effect: implications for molecular association and protein stability

The energetics of alkane dissolution and partition between waterand organic solvent are described in terms of the energy ofcavity formation and solute-solvent interaction using scaledparticle theory. Thermodynamic arguments are proposed that allowcomparison of experimental measurements of the surface areawith values calculated from an all-atom representation of thesolute. While the surface tension relating to the accessiblesurface is shape dependent, it is found that for the molecularsurface it is not. This model rationalizes the change in surfacetension between the microscopic (20–30 cal/mol/A2) andmacroscopic (70–75 cal/mol/A2) regimes without the needto invoke Flory-Huggins theory or to apply other corrections.The difference in the values arises (i) to a small extent asa result of the curvature dependence of surface tension and(ii) to a large extent due to the difference in the molecularsurface derived from the experiment and that calculated froman extended all-atom model. The model suggests that the primarydriving force for alkane association in water is due to thetendency of water to reduce the solute cavity surface. It isargued that to model the energetics of alkane association, thesurface tension should be related to the molecular surface (ratherthan the accessible surface) with a surface tension near themacroscopic limit for water. This model is compared with resultsfrom theoretical simulations of the hydrophobic effect for twowell-studied systems. The implications for antibody– antigeninteractions and the effect of hydrophobic amino acid deletionon protein stability are discussed. The approach can be usedto model the solute cavity formation energy in solution as afirst step in the continuum modelling of biomolecular interactions