Thick-film Piezoelectric Vibration Harvesting –A HUMS Application

A vibration energy scavenger, manufactured entirely by thick-film construction, has been developed to power autonomous subsystems in an embedded health and useage system. The device is constrained to a 2mm thickness and has been designed for a specific helicopter application. The resulting power output is capable of powering an ‘off-the-shelf’ microcontroller based system

Design and Construction of a Programmable Electroporation system for Biological Applications

Studies into electroporation have grown rapidly in biotechnology and medicine in recent years. This paper presents the design and construction of a low cost programmable electroporation system for biological applications. The system consists of a control module, a pulse generation circuit and a high voltage switch using a power MOSFET. The programmable electroporation has been designed, developed and tested. Using a standard commercial electroporation cuvette, it is possible to generate electric fields of 100 to 1000V/cm with programmed pulse lengths of 10?sec to 20msec. The system was evaluated with Hela cells and propidium dye to evaluate transfection rates under a variety of electroporation conditions. Initial results showed that the electroporation system achieved a peak cell transfection efficiency of 48.74% at 600V/cm with pulse lengths of 10 ms

Informing Writing: The Benefits of Formative Assessment

Examines whether classroom-based formative writing assessment - designed to provide students with feedback and modified instruction as needed - improves student writing and how teachers can improve such assessment. Suggests best practices

Survivor-complier effects in the presence of selection on treatment, with application to a study of prompt ICU admission

Pre-treatment selection or censoring (`selection on treatment') can occur when two treatment levels are compared ignoring the third option of neither treatment, in `censoring by death' settings where treatment is only defined for those who survive long enough to receive it, or in general in studies where the treatment is only defined for a subset of the population. Unfortunately, the standard instrumental variable (IV) estimand is not defined in the presence of such selection, so we consider estimating a new survivor-complier causal effect. Although this effect is generally not identified under standard IV assumptions, it is possible to construct sharp bounds. We derive these bounds and give a corresponding data-driven sensitivity analysis, along with nonparametric yet efficient estimation methods. Importantly, our approach allows for high-dimensional confounding adjustment, and valid inference even after employing machine learning. Incorporating covariates can tighten bounds dramatically, especially when they are strong predictors of the selection process. We apply the methods in a UK cohort study of critical care patients to examine the mortality effects of prompt admission to the intensive care unit, using ICU bed availability as an instrument

Vibration energy harvesting using the Halbach array

This paper studies the feasibility of vibration energy harvesting using a Halbach array. A Halbach array is a specific arrangement of permanent magnets that concentrates the magnetic field on one side of the array while cancelling the field to almost zero on the other side. This arrangement can improve electromagnetic coupling in a limited space. The Halbach array offers an advantage over conventional layouts of magnets in terms of its concentrated magnetic field and low-profile structure, which helps improve the output power of electromagnetic energy harvesters while minimizing their size. Another benefit of the Halbach array is that due to the existence of an almost-zero magnetic field zone, electronic components can be placed close to the energy harvester without any chance of interference, which can potentially reduce the overall size of a self-powered device. The first reported example of a low-profile, planar electromagnetic vibration energy harvester utilizing a Halbach array was built and tested. Results were compared to ones for energy harvesters with conventional magnet layouts. By comparison, it is concluded that although energy harvesters with a Halbach array can have higher magnetic field density, a higher output power requires careful design in order to achieve the maximum magnetic flux gradient

Panel Stationarity Tests with Cross-sectional Dependence

We present a test of the null hypothesis of stationarity against unit root alternatives for panel data that allows for arbitrary cross- sectional dependence. We treat the short run time series dynamics non- parametrically and thus avoid the need to fit separate models for the individual series. The statistic is simple to compute and is asymptotically normally distributed, even in the presence of a wide range of deterministic components. Taken together, these features provide a generally applicable solution to the problem of testing for stationarity versus unit roots in macro-panel based data. The test is applied to assess the validity of the purchasing power parity hypothesis and finds significant evidence against the hypothesis being true.