The Kepler Pixel Response Function

Kepler seeks to detect sequences of transits of Earth-size exoplanets orbiting Solar-like stars. Such transit signals are on the order of 100 ppm. The high photometric precision demanded by Kepler requires detailed knowledge of how the Kepler pixels respond to starlight during a nominal observation. This information is provided by the Kepler pixel response function (PRF), defined as the composite of Kepler's optical point spread function, integrated spacecraft pointing jitter during a nominal cadence and other systematic effects. To provide sub-pixel resolution, the PRF is represented as a piecewise-continuous polynomial on a sub-pixel mesh. This continuous representation allows the prediction of a star's flux value on any pixel given the star's pixel position. The advantages and difficulties of this polynomial representation are discussed, including characterization of spatial variation in the PRF and the smoothing of discontinuities between sub-pixel polynomial patches. On-orbit super-resolution measurements of the PRF across the Kepler field of view are described. Two uses of the PRF are presented: the selection of pixels for each star that maximizes the photometric signal to noise ratio for that star, and PRF-fitted centroids which provide robust and accurate stellar positions on the CCD, primarily used for attitude and plate scale tracking. Good knowledge of the PRF has been a critical component for the successful collection of high-precision photometry by Kepler.Comment: 10 pages, 5 figures, accepted by ApJ Letters. Version accepted for publication

Assessment of the phenotypic effects of Platelet Rich Fibrin on Mesenchymal Stem Cells derived from Minced Pulp

Our aim is to investigate the effects of autologous platelet-rich fibrin (PRF) on Mesenchymal Stem cell derived from Minced Pulp (MP-MSCs). We first developed a mouse model of PRF to study the phenotypic effects of PRF in cultured cells. We obtained PRF from the blood and prepared PRF-enriched culture media. The phenotypic effects of PRF on MP-MSCs were determined by assessing the changes in cell proliferation, differentiation and immunophenotypic profiling. The mRNA levels of ALP, OCN, DMP1 and DSPP were determined by qRT-PCR. It was found that PRF increased the proliferation capacity of MP-MSCs and reduced the cell doubling time. With PRF exposure, the MP-MSCs were able to retain their immunophenotypic characteristics defining them as MSCs, as the cells expressing surface markers CD105, CD146 and CD73 were higher. MP-MSCs were able to undergo osteogenic differentiation in the presence of PRF and the mRNA levels of OCN was significantly increased in the presence of PRF. To assess the odontogenic differentiation of cells in response to PRF, we prepared dentin-slice model in which we cultured MP-MSCs embedded in PRF. Histological sections of the dentin slice model revealed that there was increase in the cellularity of the pulp tissue along the edges of the pulp tissue. Based on our findings, PRF can act as a source of growth factors cell proliferation, migration and differentiation

Dublin City University at CLEF 2005: Experiments with the ImageCLEF St Andrew’s collection

The aim of the Dublin City University participation in the CLEF 2005 ImageCLEF St Andrew’s Collection task was to explore an alternative approach to exploiting text annotation and content-based retrieval in a novel combined way for pseudo relevance feedback (PRF). This method combines evidence from retrieved lists generated using text and content-based retrieval to determine which documents will be assumed relevant for the PRF process. Unfortunately the results show that while standard textbased PRF improves upon a no feedback text baseline, at present our new approach to combining evidence from text and content-based retrieval does not give further improve improvement

Biomimetic implant surface functionalization with liquid L-PRF products: in vitro study

Abstract Objective: Platelet-rich fibrin (PRF) clots and membranes are autologous blood concentrates widely used in oral surgical procedures; less is known, however, about the liquid formulations of such products. The aim of this in vitro study is to assess the behavior of different implant surfaces when in contact with two liquid leucocyte- and platelet-rich fibrin (L-PRF) products. Methods: Six commercial pure titanium discs, of 9.5 mm diameter and 1.5 mm thickness, were used. Three of these samples had a micro/nano-rough surface; three were machined. Three different protocols were tested. Protocols involved the immersion of the samples in (1) a platelets, lymphocytes, and fibrinogen liquid concentrate (PLyF) for 10 minutes, (2) an exudate obtained from L-PRF clots rich in fibronectin and vitronectin for 5 minutes, and (3) the fibronectin/vitronectin exudate for 2 minutes followed by immersion in the PLyF concentrate for further 8 minutes. After these treatments, the samples were fixed and observed using a scanning electron microscope (SEM). Results: Under microscopic observation, (1) the samples treated with the PLyF concentrate revealed a dense fibrin network in direct contact with the implant surface and a significant number of formed elements of blood; (2) in the samples treated with the fibronectin/vitronectin exudates, only a small number of white and red blood cells were detectable; and (3) in samples exposed to the combined treatment, there was an apparent increase in the thickness of the fibrin layer. When compared to the machined surface, the micro/nano-rough samples showed an overall increased retention of fibrin, leading to a thicker coating. Conclusions: Liquid L-PRF products promote the formation of a dense fibrin clot on micro/nano-rough implant surfaces in vitro. The adjunctive treatment of surfaces with the fibronectin/vitronectin exudate could provide support to contact of the fibrin with the surface, though it is not essential for the clot formation. Further studies are necessary to better elucidate the properties and benefits of liquid L-PRF products

Approximating Monetary Policy: Case Study for the ASEAN-5

Empirical studies on the process of monetary policy making in a number of advanced economies have shown that a simple policy reaction function (PRF) performs well in explaining the setting of monetary policy. This paper examines an application of a simple PRF in an attempt to broaden the understanding of monetary policy making processes in five developing ASEAN countries. As found to be the case in the more advanced economies, a simple PRF is also found to perform well in explaining the setting of monetary policy in these countries. Moreover, the findings uncover the main drivers behind the conduct of monetary policy and provide a relatively consistent explanation about the monetary policy episodes in the sample economies.Monetary policy, policy reaction function, ASEAN

Ultra-Wide Swath SAR Imaging With Continuous PRF Variation

Innovative multi-channel synthetic aperture radar (SAR) concepts enable high-resolution wide-swath imaging, but the antenna length typically restricts the achievable swath width. This limitation can be overcome by a novel technique which is based on a single azimuth channel but operates the system with a continuously varied pulse repetition frequency (PRF) by this allowing in principle for arbitrary wide swaths. This paper introduces the basic principles and discusses design constraints for such a PRF variation. Further, a systematic performance analysis of an L-band reflector antenna system is carried out with focus on the sensitivity versus different input parameters

NPRF: A Neural Pseudo Relevance Feedback Framework for Ad-hoc Information Retrieval

Pseudo-relevance feedback (PRF) is commonly used to boost the performance of traditional information retrieval (IR) models by using top-ranked documents to identify and weight new query terms, thereby reducing the effect of query-document vocabulary mismatches. While neural retrieval models have recently demonstrated strong results for ad-hoc retrieval, combining them with PRF is not straightforward due to incompatibilities between existing PRF approaches and neural architectures. To bridge this gap, we propose an end-to-end neural PRF framework that can be used with existing neural IR models by embedding different neural models as building blocks. Extensive experiments on two standard test collections confirm the effectiveness of the proposed NPRF framework in improving the performance of two state-of-the-art neural IR models.Comment: Full paper in EMNLP 201

External query reformulation for text-based image retrieval

In text-based image retrieval, the Incomplete Annotation Problem (IAP) can greatly degrade retrieval effectiveness. A standard method used to address this problem is pseudo relevance feedback (PRF) which updates user queries by adding feedback terms selected automatically from top ranked documents in a prior retrieval run. PRF assumes that the target collection provides enough feedback information to select effective expansion terms. This is often not the case in image retrieval since images often only have short metadata annotations leading to the IAP. Our work proposes the use of an external knowledge resource (Wikipedia) in the process of refining user queries. In our method, Wikipedia documents strongly related to the terms in user query (" definition documents") are first identified by title matching between the query and titles of Wikipedia articles. These definition documents are used as indicators to re-weight the feedback documents from an initial search run on a Wikipedia abstract collection using the Jaccard coefficient. The new weights of the feedback documents are combined with the scores rated by different indicators. Query-expansion terms are then selected based on these new weights for the feedback documents. Our method is evaluated on the ImageCLEF WikipediaMM image retrieval task using text-based retrieval on the document metadata fields. The results show significant improvement compared to standard PRF methods