Microwave interferometer for phase and response time measurements.

We report the development of a microwave interferometer using a quadrature intermediate frequency (IQ) mixer designed to measure the relative phase change and response time of microwave devices tested in the Ka and upper K bands (22-40 GHz). The interferometer is currently used to test liquid crystal based devices. The system allows for the application of an AC bias beyond the amplitude/frequency limitations imposed on vector network analyzer bias ports. Our IQ mixer based design uses bias signals ranging from 0 to 100 V peak-to-peak in a frequency range from DC to 100 kHz. This range of bias signals is necessary to properly test the response of microwave devices designed with liquid crystal materials. The setup enables us to measure changes in the output phase of the device as a function of both the voltage and frequency of the applied bias signal. The setup also measures the phase difference as a function of microwave frequency and response times for the device under test. Our system can be integrated into a stand-alone test setup without the need for a vector network analyzer.

Why consistent completion criterion are required in childhood weight management programmes.

OBJECTIVES: Current research in the field of childhood weight management (WM) effectiveness is hampered by inconsistent terminology and criterion for WM programme completion, alongside other engagement-related concepts (e.g. adherence, dropout and attrition). Evidence reviews are not able to determine conclusive intervention effectiveness because of this issue. This study aims to quantify how various completion criterion impacts upon on: 1) the percentage of WM completers; 2) the standardised body mass index (BMI SDS) reduction; and 3) the predictors of WM completion. STUDY DESIGN: A methodological, sensitivity analysis to examine how differential completion criterion affect programme outcomes and predictors. METHODS: Secondary data of 2948 children were used. All children attended a MoreLife WM programme between 2009 and 2014. The completion criterion was incrementally adjusted by 10% (i.e. completer attends 10%, 20%, 30%... of sessions) for research aims 1-2, with the percentage of completers and change in BMI SDS calculated at each increment. For aim 3, the stability (strength, direction and significance) of the predictors were examined when using the completion criterion of four alternative studies against our previous study (completion ≥70% attendance). RESULTS: The volume of programme completers decreased in a linear manner as the completion criterion became more stringent (i.e. 70-100% attendance). The change in BMI SDS conversely became incrementally greater. The strength, direction and significance of the predictors was highly dependent on the completion criterion; the odds ratio varied by 24.2% across a single predictor variable (delivery period). The degree of change is evidenced in the paper. CONCLUSIONS: Inconsistent completion criterion greatly limits the synthesis of programme effectiveness and explains some of the inconsistency in the predictors of engagement. Standardised criterion for engagement-related terminology are called for.

Biasing vector network analyzers using variable frequency and amplitude signals.

We report the development of a test setup designed to provide a variable frequency biasing signal to a vector network analyzer (VNA). The test setup is currently used for the testing of liquid crystal (LC) based devices in the microwave region. The use of an AC bias for LC based devices minimizes the negative effects associated with ionic impurities in the media encountered with DC biasing. The test setup utilizes bias tees on the VNA test station to inject the bias signal. The square wave biasing signal is variable from 0.5 to 36.0 V peak-to-peak (VPP) with a frequency range of DC to 10 kHz. The test setup protects the VNA from transient processes, voltage spikes, and high-frequency leakage. Additionally, the signals to the VNA are fused to ½ amp and clipped to a maximum of 36 VPP based on bias tee limitations. This setup allows us to measure S-parameters as a function of both the voltage and the frequency of the applied bias signal.

Warm autoantibodies: time for a change.

Routine adsorption procedures to remove autoantibodies from patients' serum often require many hours to perform. This time-consuming process can create significant delays that affect patient care. This study modified the current adsorption method to reduce total adsorption time to 1 hour. A ratio of one part serum to three parts red blood cells (RBCs; 1:3 method) was maintained for all samples. The one part serum was split into three tubes. Each of these three aliquots of serum was mixed with one full part RBCs, creating three adsorbing tubes. All tubes were incubated for 1 hour with periodic mixing. Adsorbed serum from the three tubes was harvested, combined, and tested for reactivity. Fifty-eight samples were evaluated using both the current method and the 1:3 method. Forty-eight (83%) samples successfully adsorbed using both methods. Twenty (34.5%) samples contained underlying alloantibodies. The 1:3 method demonstrated the same antibody specificities and strengths in all 20 samples. Eight samples failed to adsorb by either method. The 1:3 method found previously undetected alloantibodies in three samples. Two samples successfully autoadsorbed but failed to alloadsorb by either method. The 1:3 method proved to be efficient and effective for quick removal of autoantibodies while allowing for the detection of underlying alloantibodies.

Changes in access to screening mammography, 2008-2011.

Screening mammography is a cornerstone of preventive health care for adult women in the United States. As rates of screening mammography have declined and plateaued in the past decade, access to services remains a concern. In 2011, we repeated a survey of mammography facilities initially surveyed in 2008 in six states. The availability of digital mammography increased and appointment wait times generally improved between the two survey periods, but more facilities required payment upfront. Provisions of the federal healthcare reform law that eliminate cost sharing for selected preventive health services may improve access to screening mammography and prevent further declines in the rate of breast cancer screening.