17,363 research outputs found
Hidden Dangers to Researcher Safety While Sampling Freshwater Benthic Macroinvertebrates
Abstract
This paper reviews hidden dangers that threaten the safety of freshwater (FW) researchers of benthic macroinvertebrates (BMIs). Six refereed journals containing 2,075 papers were reviewed for field research resulting in 505 FW BMI articles. However, danger was reported in only 18% of FW BMI papers. I discussed: 1) papers that did not warn of existing danger and consider researcher safety, 2) metric threshold values (e.g., chemical hazards), and non-metric dangers, (e.g., caves and aquatic habitats), 3), the frequency of danger occurrence, 4) baseline and extreme values. Examples of 28 danger factors that posed a threat to BMI researchers in water were compared by frequency per journal papers. FW dangers identified by metric thresholds present a safety limit not to be exceeded, whereas non-metric dangers do not have a threshold as further explained. Also, discussed was a recent thesis on civil engineering hydraulics that identified low-head dams as deceptive and an increasing source of drownings in 39 states. A safe shallow water maximum depth to wade and collect BMIs is proposed based on researcher height and gender, compared to human height means in a large database. Practical safety recommendations were presented to help protect the FW researcher avoid and survive hidden dangers
SOCIAL CAPITAL, TAX MODIFICATIONS, AND RURAL ECONOMIC PROGRESS: DISCUSSION
Community/Rural/Urban Development,
Exponential Smoothing: A Prediction Error Decomposition Principle
In the exponential smoothing approach to forecasting, restrictions are often imposed on the smoothing parameters which ensure that certain components are exponentially weighted averages. In this paper, a new general restriction is derived on the basis that the one-step ahead prediction error can be decomposed into permanent and transient components. It is found that this general restriction reduces to the common restrictions used for simple, trend and seasonal exponential smoothing. As such, the prediction error argument provides the rationale for these restrictions.time series analysis, prediction, exponential smoothing, ARIMA models, state space models.
A Pedant's Approach to Exponential Smoothing
An approach to exponential smoothing that relies on a linear single source of error state space model is outlined. A maximum likelihood method for the estimation of associated smoothing parameters is developed. Commonly used restrictions on the smoothing parameters are rationalised. Issues surrounding model identification and selection are also considered. It is argued that the proposed revised version of exponential smoothing provides a better framework for forecasting than either the Box-Jenkins or the traditional multi-disturbance state space approaches.Time Series Analysis, Prediction, Exponential Smoothing, ARIMA Models, Kalman Filter, State Space Models
A comparison of integrated testlet and constructed-response question formats
Constructed-response (CR) questions are a mainstay of introductory physics
textbooks and exams. However, because of time, cost, and scoring reliability
constraints associated with this format, CR questions are being increasingly
replaced by multiple-choice (MC) questions in formal exams. The integrated
testlet (IT) is a recently-developed question structure designed to provide a
proxy of the pedagogical advantages of CR questions while procedurally
functioning as set of MC questions. ITs utilize an answer-until-correct
response format that provides immediate confirmatory or corrective feedback,
and they thus allow not only for the granting of partial credit in cases of
initially incorrect reasoning, but furthermore the ability to build cumulative
question structures. Here, we report on a study that directly compares the
functionality of ITs and CR questions in introductory physics exams. To do
this, CR questions were converted to concept-equivalent ITs, and both sets of
questions were deployed in midterm and final exams. We find that both question
types provide adequate discrimination between stronger and weaker students,
with CR questions discriminating slightly better than the ITs. Meanwhile, an
analysis of inter-rater scoring of the CR questions raises serious concerns
about the reliability of the granting of partial credit when this traditional
assessment technique is used in a realistic (but non optimized) setting.
Furthermore, we show evidence that partial credit is granted in a valid manner
in the ITs. Thus, together with consideration of the vastly reduced costs of
administering IT-based examinations compared to CR-based examinations, our
findings indicate that ITs are viable replacements for CR questions in formal
examinations where it is desirable to both assess concept integration and to
reward partial knowledge, while efficiently scoring examinations.Comment: 14 pages, 3 figures, with appendix. Accepted for publication in
PRST-PER (August 2014
Fibre imaging bundles for full-field optical coherence tomography
An imaging fibre bundle is incorporated into a full-field imaging OCT system,
with the aim of eliminating the mechanical scanning currently required at the
probe tip in endoscopic systems. Each fibre within the imaging bundle addresses
a Fizeau interferometer formed between the bundle end and the sample, a
configuration which ensures down lead insensitivity of the probe fibres,
preventing variations in sensitivity due to polarization changes in the many
thousand constituent fibres. The technique allows acquisition of information
across a planar region with single-shot measurement, in the form of a 2D image
detected using a digital CCD camera. Depth scanning components are now confined
within a processing interferometer external to the completely passive endoscope
probe. The technique has been evaluated in our laboratory for test samples, and
images acquired using the bundle-based system are presented. Data are displayed
either as en-face scans, parallel to the sample surface, or as slices through
the depth of the sample, with a spatial resolution of about 30 ï ÂÂm. The minimum
detectable reflectivity at present is estimated to be about 10-3, which is
satisfactory for many inorganic samples. Methods of improving the signal-to-
noise ratio for imaging of lower reflectivity samples are discuss
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