Influence of water vapor pressure fluctuations on the spectral density of millimeter wave amplitude scintillations in an absorption region

Results are presented of scintillation spectra, measured at 54.5GHz on a 4.1 km line of sight path, when the variance of the water vapour pressure fluctuations (σ_e ²) is very much greater than the variance of the temperature fluctuations (σ_T ²). The effect of σ_e ² under these conditions is established both through the experimental results and the theoretical considerations which are also presented.     

Analysis of structural members under point loadings

Several problems of long, uniform-thickness, channel, rectangular tube, and I-beam sections subjected to concentrated loads are investigated by means of thin-plate elastic analysis. The loads are applied symmetrically on the edges of opposite flanges for the channel and I-beam, and symmetrically at the centers of opposite sides of the rectangular tube. Solutions are obtained using a Fourier integral approach and by considering the members as sets of plates joined together along adjacent edges. The coefficients in the Fourier integrals are determined from the individual plate boundary conditions, and using conditions of slope and moment continuity along the adjacent plate edges. Cramer's Rule is used to compute the integrals on the digital computer. Deflections, strains and stresses can be determined. Experiments were performed on a channel section to test the validity of the assumptions made theoretically in all three problems. The theoretical channel solution agrees well with the experimental results.     

Optimizing fiber coatings for interferometric acoustic sensors

The pressure sensitivity of the phase of light propagating in an optical fiber is studied both analytically and experimentally. The analysis, which takes into account the exact composition and geometry of multilayer fibers, is utilized to identify coating properties which optimize the fiber acoustic sensitivity. In order to predict the fiber acoustic sensitivity, the elastic parameters of commonly used coating materials, thermoplastics, and UV curable elastomers have been studied in bulk samples as a function of frequency (10^{2}-10^{4}Hz) and temperature (0-35degC). The analytically predicted frequency dependence of the acoustic sensitivity is found to be in agreement with that obtained experimentally from fibers with coatings of various materials.     

Mapping of potential gradients within the electrospray emitter

A novel electrochemical probe has been designed, built, and used to characterize the distribution in solution potential within the metal capillary and Taylor cone of the electrospray (ES) device. The measurement system consists of three electrodes-a counter electrode held at highly negative potential that serves as the cathode, and two anodes consisting of a disk-shaped, mobile, internal (working) electrode, and the internal surface of the surrounding ES capillary (auxiliary electrode, held at ground potential). One-dimensional differential electrospray emitter potential (DEEP) maps detailing solution potential gradients within the electrospray emitter and in the region of the Taylor cone are constructed by measuring the potential at the working electrode vs the ES capillary, as a function of working electrode position along the emitter axis. Results show that the measured potential difference increases as the internal probe travels toward the ES capillary exit, with values rising sharply as the base of the Taylor cone is penetrated. Higher conductivity solutions exhibit potentials of higher magnitude at longer distances away from the counter electrode, but these same solutions show lower potentials near the ES capillary exit. Removal of easily oxidizable species from the solution causes the measured potential difference to have nonzero values at distances further within the capillary, and the values measured at all points are raised. Results are consistent with the characterization of the electrospray system as a controlled-current electrolytic flow cell. Elucidation of the electrochemical details of the electrospray process can lead to mass spectrometric signal enhancement of certain species present in the spraying liquid and also allow the detection of molecules that are usually not observable due to their low ionization efficiencies.     

Computational and experimental simulations of the haemodynamics at cuffed arterial bypass graft anastomoses

The development of intimal hyperplasia at arterial bypass graft anastomoses is a major factor responsible for graft failure. A revised surgical technique, involving the incorporation of a small section of vein (vein cuff) into the distal anastomosis of polytetrafluoroethylene (PTFE) grafts, alters the distribution of intimal hyperplasia and improves graft performance. Numerical and in vitro flow visualization experiments have been conducted to identify the flow behaviour in the cuffed bypass model and to determine whether the improved performance of the cuffed system can be accounted for by haemodynamic factors. The flowfield at the cuffed anastomosis is characterized by an expansive recirculation. Separation occurs at the graft heel, and at the cuff toe as the blood enters the recipient artery. Wall shear stresses in the vicinity of the cuff heel are low, but high shear stresses and large spatial gradients in the shearing force act for a time on the artery floor. In the conventional model, a less disturbed flow prevails while the gradients of shear stress on the floor are smaller. Aspects of the anastomotic haemodynamics are worsened when the cuff is employed. The superior patency rates of cuffed bypasses may not be explained purely on the basis of local haemodynamic factors.     

Influence of Inelastic Tower Links on Cable-Supported Bridge Response

A new concept for bridge tower designs in seismic zones incorporates sacrificial link schemes that enable the tower shafts to remain elastic under large seismic excitation. In order to study the influence of inelastic tower links on the seismic response of cable-supported bridges, global seismic time history analyses were performed on models of the new San Francisco-Oakland Bay Bridge East Span self-anchored suspension bridge (SASB) and a cable-stayed bridge (CSB) alternative. The addition of inelastic links to the signature tower improved the behavior of both structures. The tower and overall bridge demands were reduced, including the tower drift and moments as well as the suspension cable, cable stay, and superstructure drifts and axial loads. The inelastic tower links protected the SASB and CSB tower shafts from nonlinear behavior under the 1,500-year Safety Evaluation Earthquake (SEE) event as well as a 2,500-year event. When the inelastic tower links were removed, the SASB tower shafts yielded under the SEE. It was shown that the inelastic tower links could be used to tune the dynamic response of bridge towers in regions of high seismicity.     

The Longitudinal Structure of the Children's Depression Inventory: Testing a Latent Trait-State Model.

In a 6-wave longitudinal study, children (Grades 4-6, n=648), adolescents (Grades 7-9, n=1,489), and their parents completed child-adolescent or parent versions of the Children's Depression Inventory (CDI; M. Kovacs, 1981). Using structural equation modeling, the authors conducted latent trait-state analyses to distinguish between a stable trait dimension of depression (in which individual differences are stable over time) and an autoregressive dimension (in which individual differences are less stable over time). Children's CDIs reflected the autoregressive dimension more than a stable trait dimension, whereas parents' CDIs reflected a stable trait dimension more than an autoregressive dimension. Reports from adolescents and their parents reflected a stable trait dimension more than an autoregressive dimension of depressive symptoms. Results suggest that the longitudinal structure of the CDI varies considerably depending on the age of the target and the type of informant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal-difference prediction errors and Pavlovian fear conditioning: Role of NMDA and opioid receptors.

Three experiments studied temporal-difference (TD) prediction errors during Pavlovian fear conditioning. In Stage I, rats received conditioned stimulus A (CSA) paired with shock. In Stage II, they received pairings of CSA and CSB with shock that blocked learning to CSB. In Stage III, a serial overlapping compound, CSB 3 CSA, was followed by shock. The change in intratrial durations supported fear learning to CSB but reduced fear of CSA, revealing the operation of TD prediction errors. N-methyl- D-aspartate (NMDA) receptor antagonism prior to Stage III prevented learning, whereas opioid receptor antagonism selectively affected predictive learning. These findings support a role for TD prediction errors in fear conditioning. They suggest that NMDA receptors contribute to fear learning by acting on the product of predictive error, whereas opioid receptors contribute to predictive error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in cardiovascular reactions to stress and cigarette smoking.

Examined the stability of cardiovascular (CDV) reactions to psychological stress and cigarette smoking and the extent to which CDV actions to stress were predictive of CDV reactions to smoking. 26 male Ss were given an initial test involving 2 repetitions of mental arithmetic stress and paced smoking while blood pressure and heart rate were measured. Ss were retested 2 mo later in the same paradigm. Large and stable individual differences were observed in CDV reactivity to both stress and smoking. For systolic and diastolic blood pressure, but not heart rate, reactions to stress were modestly correlated with reactions to cigarette smoking, suggesting that levels of reactivity to cigarette smoking may have significance for coronary heart disease and blood pressure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)