291 research outputs found
Measurement exchangeability and normal one-factor models
The one-factor model restricts the covariance structure of the observed variables on the basis of assumptions about their relationship with an unobserved variable. It is hard to justify these assumptions on substantive or empirical grounds. In this paper, alternative measurement models are proposed that are based on exchangeability of variables after admissible scale transformations. They provide an alternative interpretation of the model and do not involve unobserved variables. They also yield a new one-factor model for sum scales. © 2004 Biometrika Trust
Multimode waveguides of Photodefinable epoxy for optical backplane applications
We developed photodefined, multimode-fiber compatible waveguides based on epoxies. These waveguides will be embedded in backplane PCB’s for optical interconnect applications using 850 nm VCSELs as light sources. Apart from very low loss, the material selection took into account, PCB compatibility and low yellowing due to high temperature processing (for PCB lamination and soldering). The waveguides showed losses < 0.06 dB/cm at 832 nm and 633 nm. Their loss increase after aging (1 hr at 185 °C) was limited to 0.04 dB/cm at 850 nm. Waveguides realized on FR-4 (epoxyfiberglass)PCB material are demonstrated
Thermal wavelength-selective switch based on micro-ring resonators
A thermally driven wavelength-selective switch, based on integrated-optic micro-ring resonators is described. This configuration allows high ON/OFF ratios combined with small dimensions. Measurements of the thermal behaviour of a single resonator confirm the switching capability
Thermally Tuneable, Wide FSR Switch based on Micro-ring Resonators
A thermally tuneable, wide FSR switch, based on integrated-optic micro-ring resonators is described. This wavelength-selective switch allows high ON/OFF ratios combined with small dimensions. Furthermore allows the structure for a wide Free Spectral Range, since multiple resonators are used. This switch can be used in WDM filter arrays for a transceiver in an access network. Measurements of the thermal behaviour of a single resonator confirm the switching capability of the switch
Reconfigurable optical add-drop multiplexer using microring resonators
We report a reconfigurable four-channel optical add-drop multiplexer for use in access networks. The optical add-drop multiplexer (OADM) is based on vertically coupled thermally tunable Si/sub 3/N/sub 4/--SiO/sub 2/ microring resonators (MRs) and has been realized on a footprint of 0.25 mm/sup 2/. Individual MRs in the OADM can be tuned across the full free-spectral range of 4.18 nm and have a 3-dB bandwidth of 50 GHz
Response shifts in mental health interventions: An illustration of longitudinal measurement invariance.
The efficacy of treatments for depression is often measured by comparing observed total scores on self-report inventories, in both clinical practice and research. However, the occurrence of response shifts (changes in subjects' values, or their standards for measurement) may limit the validity of such comparisons. As most psychological treatments for depression are aimed at changing patients' values and frame of reference, response shifts are likely to occur over the course of such treatments. In this article, we tested whether response shifts occurred over the course of treatment in an influential randomized clinical trial. Using confirmatory factor analysis, measurement models underlying item scores on the Beck Depression Inventory (Beck & Beamesderfer, 1974) of the National Institute of Mental Health Treatment of Depression Collaborative Research Program (Elkin, Parloff, Hadley, & Autry, 1985) were analyzed. Compared with before treatment, after-treatment item scores appeared to overestimate depressive symptomatology, measurement errors were smaller, and correlations between constructs were stronger. These findings indicate a response shift, in the sense that participants seem to get better at assessing their level of depressive symptomatology. Comparing measurement models of patients receiving psychotherapy and medication suggested that the aforementioned effects were more apparent in the psychotherapy groups. Consequently, comparisons of observed total scores on self-report inventories may yield confounded measures of treatment efficacy. © 2013 American Psychological Association
Bends in polymeric multimode waveguides
We developed photodefined, multimode-fiber compatible waveguides based on epoxies. The waveguides showed losses <0.06 dB/cm at 832 nm and 633 nm. Propagation and bending losses are calculated and experimentally verified. The minimum allow-able radius that can be connected to a straight waveguides are modeled and experimentally verified
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