66 research outputs found
Optimal Scaling transformations to model non-linear relations in GLMs with ordered and unordered predictors
In Generalized Linear Models (GLMs) it is assumed that there is a linear
effect of the predictor variables on the outcome. However, this assumption is
often too strict, because in many applications predictors have a nonlinear
relation with the outcome. Optimal Scaling (OS) transformations combined with
GLMs can deal with this type of relations. Transformations of the predictors
have been integrated in GLMs before, e.g. in Generalized Additive Models.
However, the OS methodology has several benefits. For example, the levels of
categorical predictors are quantified directly, such that they can be included
in the model without defining dummy variables. This approach enhances the
interpretation and visualization of the effect of different levels on the
outcome. Furthermore, monotonicity restrictions can be applied to the OS
transformations such that the original ordering of the category values is
preserved. This improves the interpretation of the effect and may prevent
overfitting. The scaling level can be chosen for each individual predictor such
that models can include mixed scaling levels. In this way, a suitable
transformation can be found for each predictor in the model. The implementation
of OS in logistic regression is demonstrated using three datasets that contain
a binary outcome variable and a set of categorical and/or continuous predictor
variables.Comment: 35 pages, 4 figure
Projected Images of Major Chinese Outbound Destinations
This study aimed to explore the projected images of major outbound destinations based on popular travel magazines in China. Travel articles on Hong Kong, Macau, Japan, South Korea, Vietnam and Taiwan from 2006 to 2008 were content analyzed. Japan was reported on most, and the projected images of the six destinations are dominated by leisure and recreation, and culture, history and art. Correspondence analysis was used to examine relationships between destinations and popular image attributes. The results showed that South Korea and Macau had distinct projected images, whereas Japan, Taiwan, Hong Kong and Vietnam shared many similar image attributes. Practical implications for destination marketing organizations are provided
Broadband Meter-Wavelength Observations of Ionospheric Scintillation
Intensity scintillations of cosmic radio sources are used to study
astrophysical plasmas like the ionosphere, the solar wind, and the interstellar
medium. Normally these observations are relatively narrow band. With Low
Frequency Array (LOFAR) technology at the Kilpisj\"arvi Atmospheric Imaging
Receiver Array (KAIRA) station in northern Finland we have observed
scintillations over a 3 octave bandwidth. ``Parabolic arcs'', which were
discovered in interstellar scintillations of pulsars, can provide precise
estimates of the distance and velocity of the scattering plasma. Here we report
the first observations of such arcs in the ionosphere and the first broad-band
observations of arcs anywhere, raising hopes that study of the phenomenon may
similarly improve the analysis of ionospheric scintillations. These
observations were made of the strong natural radio source Cygnus-A and covered
the entire 30-250\,MHz band of KAIRA. Well-defined parabolic arcs were seen
early in the observations, before transit, and disappeared after transit
although scintillations continued to be obvious during the entire observation.
We show that this can be attributed to the structure of Cygnus-A. Initial
results from modeling these scintillation arcs are consistent with simultaneous
ionospheric soundings taken with other instruments, and indicate that
scattering is most likely to be associated more with the topside ionosphere
than the F-region peak altitude. Further modeling and possible extension to
interferometric observations, using international LOFAR stations, are
discussed.Comment: 11 pages, 17 figure
Optimized Trigger for Ultra-High-Energy Cosmic-Ray and Neutrino Observations with the Low Frequency Radio Array
When an ultra-high energy neutrino or cosmic ray strikes the Lunar surface a
radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to
detect these pulses. In this work we propose an efficient trigger
implementation for LOFAR optimized for the observation of short radio pulses.Comment: Submitted to Nuclear Instruments and Methods in Physics Research
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Visualization of Genomic Changes by Segmented Smoothing Using an L0 Penalty
Copy number variations (CNV) and allelic imbalance in tumor tissue can show strong segmentation. Their graphical presentation can be enhanced by appropriate smoothing. Existing signal and scatterplot smoothers do not respect segmentation well. We present novel algorithms that use a penalty on the norm of differences of neighboring values. Visualization is our main goal, but we compare classification performance to that of VEGA
Going it alone wonât work! The relational imperative for social innovation in social enterprises
Shifts in the philosophy of the âstateâ and a growing emphasis on the âBig Societyâ have placed an increasing onus on a newly emerging organizational form, social enterprises, to deliver innovative solutions to ease societal issues. However, the question of how social enterprises manage the process of social innovation remains largely unexplored. Based on insights from both in-depth interviews and a quantitative empirical study of social enterprises, this research examines the role of stakeholder relationships in supporting the process of social innovation within social enterprises. We find that social enterprises are adept at working with their stakeholders in the ideation stage of social innovation. In contrast, they often fail to harness knowledge and expertise from their partners during the social innovation implementation phase. Consequently, we propose a social innovationâstakeholder relationship matrix that provides social enterprises in particular with insight for developing stakeholder relationships to achieve their social innovation missions
The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?
Using observations obtained with the LOw Fequency ARray (LOFAR), the Westerbork Synthesis Radio Telescope (WSRT) and archival Very Large Array (VLA) data, we have traced the radio emission to large scales in the complex source 4C 35.06 located in the core of the galaxy cluster Abell 407. At higher spatial resolution (~ 4âł), the source was known to have two inner radio lobes spanning 31 kpc and a diffuse, low-brightness extension running parallel to them, offset by about 11 kpc (in projection). At 62 MHz, we detect the radio emission of this structure extending out to 210 kpc. At 1.4 GHz and intermediate spatial resolution (~ 30âł), the structure appears to have a helical morphology. We have derived the characteristics of the radio spectral index across the source. We show that the source morphology is most likely the result of at least two episodes of AGN activity separated by a dormant period of around 35 Myr. The outermost regions of radio emission have a steep spectral index (α-1), similar to what is found in other clusters. The derived column density is NHI ~ 4 Ă 1020 cm-2 for a Tspin = 100 K. This detection supports the connection â already suggested for other restarted radio sources â between the presence of cold gas and restarting activity. The cold gas appears to be dominated by a blue-shifted component although the broad HâI profile could also include gas with different kinematics. Understanding the duty cycle of the radio emission as well as the triggering mechanism for starting (or restarting) the radio-loud activity can provide important constraints to quantify the impact of AGN feedback on galaxy evolution. The study of these mechanisms at low frequencies using morphological and spectral information promises to bring new important insights in this field
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