Integrated dual optical frequency comb source

A monolithically integrated dual-channel optical frequency comb source is demonstrated in this paper. Three lasers are integrated on a single chip using a regrowth-free fabrication process in a master-slave-slave configuration. The master laser’s power is split equally using a 1x2 multimode interference coupler and injection locks the two slave lasers. The slave lasers are gain-switched to produce dual optical frequency combs at 4.1 GHz and 5 GHz. To the best of our knowledge, this is the first demonstration of a dual optical frequency comb source with all light sources monolithically integrated in a photonic integrated circuit (PIC)

Exploring the relationship between media coverage and participation in entrepreneurship : initial global evidence and research implications

Using a set of variables measured in the Global Entrepreneurship Monitor (GEM) study, our empirical investigation explored the influence of mass media through national culture on national entrepreneurial participation rates in 37 countries over 4 years (2000 to 2003). We found that stories about successful entrepreneurs, conveyed in mass media, were not significantly associated with the rate of nascent (opportunity searching) or the rate of actual (business activities commenced up to 3 months old) start-up activity, but that there was a significant positive association between the volume of entrepreneurship media stories and a nation&rsquo;s volume of people running a young business (that is in GEM terminology, a business aged greater than 3 but less than 42 months old). More particularly, such stories had strong positive association with opportunity oriented operators of young businesses. Together, these findings are compatible with what in the mass communications theory literature may be called the &lsquo;reinforcement model&rsquo;. This argues that mass media are only capable of reinforcing their audience&rsquo;s existing values and choice propensities but are not capable of shaping or changing those values and choices. In the area covered by this paper, policy-makers are committing public resources to media campaigns of doubtful utility in the absence of an evidence base. A main implication drawn from this study is the need for further and more sophisticated investigation into the relationship between media coverage of entrepreneurship, national culture and the rates and nature of people&rsquo;s participation in the various stages of the entrepreneurial process.<br /

Deoxycholate induces COX-2 expression via Erk1/2-, p38-MAPK and AP-1-dependent mechanisms in esophageal cancer cells

<p>Abstract</p> <p>Background</p> <p>The progression from Barrett's metaplasia to adenocarcinoma is associated with the acquirement of an apoptosis-resistant phenotype. The bile acid deoxycholate (DCA) has been proposed to play an important role in the development of esophageal adenocarcinoma, but the precise molecular mechanisms remain undefined. The aim of this study was to investigate DCA-stimulated COX-2 signaling pathways and their possible contribution to deregulated cell survival and apoptosis in esophageal adenocarcinoma cells.</p> <p>Methods</p> <p>Following exposure of SKGT-4 cells to DCA, protein levels of COX-2, MAPK and PARP were examined by immunoblotting. AP-1 activity was assessed by mobility shift assay. DCA-induced toxicity was assessed by DNA fragmentation and MTT assay.</p> <p>Results</p> <p>DCA induced persistent activation of the AP-1 transcription factor with Fra-1 and JunB identified as the predominant components of the DCA-induced AP-1 complex. DCA activated Fra-1 via the Erk1/2- and p38 MAPK while Erk1/2 is upstream of JunB. Moreover, DCA stimulation mediated inhibition of proliferation with concomitant low levels of caspase-3-dependent PARP cleavage and DNA fragmentation. Induction of the anti-apoptotic protein COX-2 by DCA, via MAPK/AP-1 pathway appeared to balance the DCA mediated activation of pro-apoptotic markers such as PARP cleavage and DNA fragmentation. Both of these markers were increased upon COX-2 suppression by aspirin pretreatment prior to DCA exposure.</p> <p>Conclusion</p> <p>DCA regulates both apoptosis and COX-2-regulated cell survival in esophageal cells suggesting that the balance between these two opposing signals may determine the transformation potential of DCA as a component of the refluxate.</p

Regrowth-free monolithic vertical integration of passive and active waveguides

Data usage continues to rise exponentially with user demand, and the bandwidth of optical communications is reaching its limit. Spectrally efficient advanced modulation formats are being used to increase the data rate within the existing bandwidth. Mach-Zehnder Modulators achieve high spectral density by modulating both the phase and amplitude of light. At the moment, laser light sources and Mach-Zehnder Modulators are built discretely and packaged and coupled thereafter. Photonic Integrated Circuits (PICs) place multiple photonic components onto single chips, with the benefit of compactness resulting in lower cost through simpler coupling, lower power consumption, and volume manufacture. The difficulty faced by photonic integration is that different components require different material for their different functions, and so cannot be easily placed onto the same material substrate wafer. Existing methods use regrowth techniques to selectively replace material around the chip, but regrowth is expensive and time consuming. This work vertically integrated a passive waveguide above an active waveguide using regrowth-free monolithic integration. The passive and active waveguides are designed for Mach-Zehnder modulator and laser material. The waveguides were processed on an InP platform, and consisted of AlGaInAs alloys. To our knowledge this is the first time a passive waveguide has been vertically integrated above an active waveguide for III-V semiconductors, and the first time two AlGaInAs waveguides have been vertically integrated, using monolithic regrowth-free techniques on InP. Vertical coupling was performed through lateral tapers, and an isolation barrier between the stacked waveguides allows the vertical integration of already optimised discrete components without modification. As the isolation barrier deliberately reduces the coupling between the waveguides away from the transition region, a technique using a third passive waveguide in the barrier was used to increase the vertical coupling while maintaining isolation. A regrowth-free vertical monolithic PIC was conceived, designed, grown, fabricated and tested to prove its operation. The two vertically stacked waveguides provide a solution for integrating active and passive material, so that a laser and Mach-Zehnder Modulator can be monolithically integrated to create a low cost advanced modulator to meet today’s ever increasing data demands