150 research outputs found
Low divergent, high-power, single-mode terahertz wire lasers
We devise arrays of surface emitting THz QCLs exploiting two novel lithographic configurations: a) a dual periodicity slit architecture and b) corrugated sinusoidal wire laser cavities. Extremely low divergent optical beams, with up to 85 mW of emitted optical powers and 245 mV/A slope efficiencies have been reached
Distributed feedback terahertz frequency quantum cascade lasers with dual periodicity gratings
We have developed terahertz frequency quantum cascade lasers that exploit a double-periodicity distributed feedback grating to control the emission frequency and the output beam direction independently. The spatial refractive index modulation of the gratings necessary to provide optical feedback at a fixed frequency, and simultaneously, a far-field emission pattern centered at controlled angles, was designed through use of an appropriate wavevector scattering model. Single mode terahertz (THz) emission at angles tuned by design between 0° and 50° was realized, leading to an original phase-matching approach for highly collimated THz quantum cascade lasers
Tuning a microcavity-coupled terahertz laser
Tunable oscillators are a key component of almost all electronic and photonic systems. Yet, a technology capable of operating in the terahertz (THz)-frequency range and fully suitable for widescale implementation is still lacking. This issue is significantly limiting potential THz applications in gas sensing, high-resolution spectroscopy, hyper-spectral imaging, and optical communications. The THz quantum cascade laser is arguably the most promising solution in terms of output power and spectral purity. In order to achieve reliable, repeatable, and broad tunability, here we exploit the strong coupling between two different cavity mode concepts: a distributed feedback one-dimensional photonic resonator (providing gain) and a mechanically actuated wavelength-size microcavity (providing tuning). The result is a continuously tunable, single-mode emitter covering a 162 GHz spectral range, centered on 3.2 THz. Our source has a few tens of MHz resolution, extremely high differential efficiency, and unprecedented compact and simple design architecture. By unveiling the large potential that lies in this technique, our results provide a robust platform for radically different THz systems exploiting broadly tunable semiconductor lasers
A General Model of Dynamics on Networks with Graph Automorphism Lumping
In this paper we introduce a general Markov chain model of dynamical processes on networks. In this model, nodes in the network can adopt a finite number of states and transitions can occur that involve multiple nodes changing state at once. The rules that govern transitions only depend on measures related to the state and structure of the network and not on the particular nodes involved. We prove that symmetries of the network can be used to lump equivalent states in state-space. We illustrate how several examples of well-known dynamical processes on networks correspond to particular cases of our general model. This work connects a wide range of models specified in terms of node-based dynamical rules to their exact continuous-time Markov chain formulation
Exact analysis of summary statistics for continuous-time discrete-state Markov processes on networks using graph-automorphism lumping
We propose a unified framework to represent a wide range of continuous-time discrete-state Markov processes on networks, and show how many network dynamics models in the literature can be represented in this unified framework. We show how a particular sub-set of these models, referred to here as single-vertex-transition (SVT) processes, lead to the analysis of quasi-birth-and-death (QBD) processes in the theory of continuous-time Markov chains. We illustrate how to analyse a number of summary statistics for these processes, such as absorption probabilities and first-passage times. We extend the graph-automorphism lumping approach [Kiss, Miller, Simon, Mathematics of Epidemics on Networks, 2017; Simon, Taylor, Kiss, J. Math. Bio. 62(4), 2011], by providing a matrix-oriented representation of this technique, and show how it can be applied to a very wide range of dynamical processes on networks. This approach can be used not only to solve the master equation of the system, but also to analyse the summary statistics of interest. We also show the interplay between the graph-automorphism lumping approach and the QBD structures when dealing with SVT processes. Finally, we illustrate our theoretical results with examples from the areas of opinion dynamics and mathematical epidemiology
Growth arrest-specific transcript 5 associated snoRNA levels are related to p53 expression and DNA damage in colorectal cancer
BACKGROUND
The growth arrest-specific transcript 5 gene (GAS5) encodes a long noncoding RNA (lncRNA) and hosts a number of small nucleolar RNAs (snoRNAs) that have recently been implicated in multiple cellular processes and cancer. Here, we investigate the relationship between DNA damage, p53, and the GAS5 snoRNAs to gain further insight into the potential role of this locus in cell survival and oncogenesis both in vivo and in vitro.
METHODS
We used quantitative techniques to analyse the effect of DNA damage on GAS5 snoRNA expression and to assess the relationship between p53 and the GAS5 snoRNAs in cancer cell lines and in normal, pre-malignant, and malignant human colorectal tissue and used biological techniques to suggest potential roles for these snoRNAs in the DNA damage response.
RESULTS
GAS5-derived snoRNA expression was induced by DNA damage in a p53-dependent manner in colorectal cancer cell lines and their levels were not affected by DICER. Furthermore, p53 levels strongly correlated with GAS5-derived snoRNA expression in colorectal tissue.
CONCLUSIONS
In aggregate, these data suggest that the GAS5-derived snoRNAs are under control of p53 and that they have an important role in mediating the p53 response to DNA damage, which may not relate to their function in the ribosome. We suggest that these snoRNAs are not processed by DICER to form smaller snoRNA-derived RNAs with microRNA (miRNA)-like functions, but their precise role requires further evaluation. Furthermore, since GAS5 host snoRNAs are often used as endogenous controls in qPCR quantifications we show that their use as housekeeping genes in DNA damage experiments can lead to inaccurate results
Systemic Risk: Fire-Walling Financial Systems Using Network-Based Approaches
The latest financial crisis has painfully revealed the dangers arising from a
globally interconnected financial system. Conventional approaches based on the
notion of the existence of equilibrium and those which rely on statistical
forecasting have seen to be inadequate to describe financial systems in any
reasonable way. A more natural approach is to treat financial systems as
complex networks of claims and obligations between various financial
institutions present in an economy. The generic framework of complex networks
has been successfully applied across several disciplines, e.g., explaining
cascading failures in power transmission systems and epidemic spreading. Here
we review various network models addressing financial contagion via direct
inter-bank contracts and indirectly via overlapping portfolios of financial
institutions. In particular, we discuss the implications of the
"robust-yet-fragile" nature of financial networks for cost-effective regulation
of systemic risk.Comment: 19 pages, 7 figure
Health-related quality of life in patients with metastatic renal cell carcinoma treated with sunitinib vs interferon-α in a phase III trial: final results and geographical analysis
Effect of Dietary Zinc Oxide on Morphological Characteristics, Mucin Composition and Gene Expression in the Colon of Weaned Piglets
The trace element zinc is often used in the diet of weaned piglets, as high
doses have resulted in positive effects on intestinal health. However, the
majority of previous studies evaluated zinc supplementations for a short
period only and focused on the small intestine. The hypothesis of the present
study was that low, medium and high levels of dietary zinc (57, 164 and 2,425
mg Zn/kg from zinc oxide) would affect colonic morphology and innate host
defense mechanisms across 4 weeks post-weaning. Histological examinations were
conducted regarding the colonic morphology and neutral, acidic, sialylated and
sulphated mucins. The mRNA expression levels of mucin (MUC) 1, 2, 13, 20,
toll-like receptor (TLR) 2, 4, interleukin (IL)-1β, 8, 10, interferon-γ
(IFN-γ) and transforming growth factor-β (TGF-β) were also measured. The
colonic crypt area increased in an age-depending manner, and the greatest area
was found with medium concentration of dietary zinc. With the high
concentration of dietary zinc, the number of goblet cells containing mixed
neutral-acidic mucins and total mucins increased. Sialomucin containing goblet
cells increased age-dependently. The expression of MUC2 increased with age and
reached the highest level at 47 days of age. The expression levels of TLR2 and
4 decreased with age. The mRNA expression of TLR4 and the pro-inflammatory
cytokine IL-8 were down-regulated with high dietary zinc treatment, while
piglets fed with medium dietary zinc had the highest expression. It is
concluded that dietary zinc level had a clear impact on colonic morphology,
mucin profiles and immunological traits in piglets after weaning. Those
changes might support local defense mechanisms and affect colonic physiology
and contribute to the reported reduction of post-weaning diarrhea
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