University of Crete

About: University of Crete is a education organization based out in Rethymno, Greece. It is known for research contribution in the topics: Population & Galaxy. The organization has 8681 authors who have published 21684 publications receiving 709078 citations. The organization is also known as: Panepistimio Kritis.

Direct laser writing of 3D scaffolds for neural tissue engineering applications.

Abstract: This study reports on the production of high-resolution 3D structures of polylactide-based materials via multi-photon polymerization and explores their use as neural tissue engineering scaffolds. To achieve this, a liquid polylactide resin was synthesized in house and rendered photocurable via attaching methacrylate groups to the hydroxyl end groups of the small molecular weight prepolymer. This resin cures easily under UV irradiation, using a mercury lamp, and under femtosecond IR irradiation. The results showed that the photocurable polylactide (PLA) resin can be readily structured via direct laser write (DLW) with a femtosecond Ti:sapphire laser and submicrometer structures can be produced. The maximum resolution achieved is 800 nm. Neuroblastoma cells were grown on thin films of the cured PLA material, and cell viability and proliferation assays revealed good biocompatibility of the material. Additionally, PC12 and NG108-15 neuroblastoma growth on bespoke scaffolds was studied in more detail to assess potential applications for neuronal implants of this material.

Atmospheric deposition of inorganic phosphorus in the Levantine Basin, eastern Mediterranean: Spatial and temporal variability and its role in seawater productivity

Abstract: Total and dissolved inorganic phosphorus (IP) was measured in both rainwater and aerosol samples collected from two remote coastal areas: on the island of Crete (Greece) and at Erdemli (Turkey). Particle size distributions of P, as well as total deposition were also measured. Wet and dry deposition of dissolved inorganic phosphorus (DIP) from Crete are compared with simultaneously obtained dissolved inorganic nitrogen (DIN) and with productivity data from the literature. Our results indicate that (1) in both wet and dry deposition, the DIN/DIP molar ratio ranges between 63 and 349, exceeding by a factor of up to 22 the N/P ratio observed in seawater (ranging from 25 to 28) and (2) atmospheric deposition of DIP could reasonably account for a significant part of the new production (up to 38%) observed during the summer and autumn period (i.e., when water stratification is at its maximum).

Adaptive Algorithms to Track the PARAFAC Decomposition of a Third-Order Tensor

Abstract: The PARAFAC decomposition of a higher-order tensor is a powerful multilinear algebra tool that becomes more and more popular in a number of disciplines. Existing PARAFAC algorithms are computationally demanding and operate in batch mode - both serious drawbacks for on-line applications. When the data are serially acquired, or the underlying model changes with time, adaptive PARAFAC algorithms that can track the sought decomposition at low complexity would be highly desirable. This is a challenging task that has not been addressed in the literature, and the topic of this paper. Given an estimate of the PARAFAC decomposition of a tensor at instant t, we propose two adaptive algorithms to update the decomposition at instant t+1, the new tensor being obtained from the old one after appending a new slice in the 'time' dimension. The proposed algorithms can yield estimation performance that is very close to that obtained via repeated application of state-of-art batch algorithms, at orders of magnitude lower complexity. The effectiveness of the proposed algorithms is illustrated using a MIMO radar application (tracking of directions of arrival and directions of departure) as an example.

The long-term X-ray spectral variability of AGN

Abstract: We present the results from the spectral analysis of more than 7500 Rossi X-ray Timing Explorer (RXTE) spectra of 10 active galactic nuclei (AGN). Our main goal was to study their long-term X-ray spectral variability. The sources in the sample are nearby, X-ray bright, and they have been observed by RXTE regularly over a long period of time (∼7–11 yr). High-frequency breaks have been detected in their power spectra, and these characteristic frequencies imply time-scales of the order of a few days or weeks. Consequently, the RXTE observations we have used most probably sample most of the flux and spectral variations that these objects exhibit. Thus, the RXTE data are ideal for our purpose. Fits to the individual spectra were performed in the 3–20 keV energy band. We modelled the data in a uniform way using simple phenomenological models (a power law with the addition of Gaussian line and/or edge to model the iron Kα emission/absorption features, if needed) to consistently parametrize the shape of the observed X-ray continuum of the sources in the sample. We found that the average spectral slope does not correlate with source luminosity or black hole mass, while it correlates positively with the average accretion rate. We have also determined the (positive) spectral slope–flux relation for each object, over a flux range larger than before. We found that this correlation is similar in all objects, except for NGC 5548 which displays limited spectral variations for its flux variability. We discuss this global spectral slope–flux trend in the light of current models for spectral variability. We consider (i) intrinsic variability, expected, for example, from Comptonization processes, (ii) variability caused by absorption of X-rays by a single absorber whose ionization parameter varies proportionally to the continuum flux variations, (iii) variability resulting from the superposition of a constant reflection component and an intrinsic power law which is variable in flux but constant in shape and (iv) variability resulting from the superposition of a constant reflection component and an intrinsic power law which is variable both in flux and in shape. Our final conclusion is that scenario (iv) provides the best fit to the data of all objects, except for NGC 5548.