Leontyev I.N.,Ecole Centrale Paris |
Leontyev I.N.,Southern Federal University |
Belenov S.V.,Southern Federal University |
Guterman V.E.,Southern Federal University |
And 3 more authors.
Journal of Physical Chemistry C | Year: 2011
Carbon-supported Pt catalysts prepared by the impregnation method in water-dimethyl sulfoxide (DMSO) solutions were investigated. Using X-ray diffraction (XRD) technique for estimation of the particle size and shapes, we show that morphology of the Pt/C catalysts depends strongly on the DMSO content in the solutions. The average particles size reduces and a shape of the Pt nanocrystals changes from a truncated octahedron to a cuboctahedron and eventually to a truncated cube with increasing DMSO concentration in the reaction mixture. Antibate effects of the size and shape cause nonmonotonic dependence of the catalytic activity for the oxygen reduction reaction (ORR) with electric current maximum at an average particle size of 2.7 nm. © 2011 American Chemical Society. Source
News Article | September 13, 2016
A team of researchers with Russia's Karadag Scientific Station–Nature Reserve of RAS has used specially developed underwater microphones to capture for the first time what they claim to be a human-like conversation between two Black Sea bottlenose dolphins. In their paper uploaded to the open access site St. Petersburg Polytechnical University Journal: Physics and Mathematics, the team, led by Vyacheslav Ryabov, describe the pulses generated by the sea creatures and why they believe what they heard was an actual conversation. Humans have suspected for centuries that dolphins have more advanced communications than other animals—tales of their conversational abilities have been reported by sailors from around the globe. More recently, scientists have been listening to sounds the underwater mammals produce and trying to decipher their meaning—some have claimed they have found that certain pulsed clicks and whistles correspond to certain activities or observations, but to date, none have been able to prove that the dolphins actually carry on conversations. In this new effort, the researchers believe they have come close. To gain a better perspective on dolphin communication, the researchers developed a two-channel hydrophone recording system in the frequency band up to 220 kHz with a dynamic range of 81 dB meant specifically to capture all the sounds produced by a pair of dolphins (named Yasha and Yana) housed in a research pool. They began by recording sounds from just one of the dolphins at a time to match the pulses made to each individual animal—capturing their unique voices. Then they recorded the two animals as they appeared to hold a conversation near the side of the pool. They noted that the animals took turns "speaking" while the other listened—back and forth emitting short pulses of clicks that varied in pitch and volume, which the researchers suggest were similar to words used in human communication—they describe the conversation as eerily reminiscent of two people having a chat. The researchers were not able to decipher the messages the dolphins relayed to one another, of course, but suggest their recordings indicate that dolphins are able to communicate in a highly developed spoken language.
News Article | June 6, 2006
Google has said it plans to release a free online spreadsheet program to compete with Microsofts Excel. Google Spreadsheets will allow users to import and export spreadsheets in the .xls format used by Microsoft Excel and the more generic .csv (common separated values) format. Through a Web browser, users in remote locations will be able to view and simultaneously edit data. The software is platform-neutral, meaning it can be accessed using a number of browsers, including the open-source Firefox, Microsoft's Internet Explorer or Apple's Safari. Google will accept sign-ups on its website from a limited number of beta testers starting at 9 a.m EDT/1 p.m. GMT Tuesday, a Google spokeswoman confirmed. "This further proves the legitimate usefulness of software-as-a-service applications," said Tom Snyder, president of iNetOffice. The startup makes a free Web-based word processor called iNetWord. Charlene Li, an analyst with Forrester Research, said next-generation Web applications such as Google Spreadsheets and Writely, an online word processor acquired by Google in March, provide much of the functionality of Microsoft Office but are not yet credible replacements. "Google Spreadsheets is not an effort to replace Excel. And if you tried to print out stuff you wrote in Writely, it would come out all ugly," she said. "Look at Web-based e-mail. We've had it for 10 years, but Outlook still reigns supreme. "Eventually these products will get there, but not today." Google was not the first company to release a Web 2.0 counterpart to Excel. A startup called iRows also offers a free online spreadsheet program. San Diego-based Ajax13, a startup founded by Internet entrepreneur Michael Robertson, also has a beta of a free Web spreadsheet editor called ajaxXLS. AJAX13 is the closest so far to having a full lineup of productivity applications that can challenge Microsoft Office. Besides ajaxXLS, the company also offers an online word processor called ajaxWrite, a drawing program called ajaxSketch and a hosted video editor called eyespot. It plans to release a PowerPoint-like presentation program by the middle of the year, according to Robertson, who founded MP3.com and is also chairman of desktop Linux provider, Linspire. Robertson said that AJAX's applications were gaining fans - more than 10,000 unique users a day - because Microsoft is stuck: reluctant to cannibalise existing Microsoft Office revenues by cutting prices or by beefing up its Office Live family of Web-based applications, which despite their name, don't yet provide any of the features of Microsoft Office. "The beauty is that we are attacking Microsoft right at their heart," Robertson said. Unlike AJAX13, which is marketing its wares directly at end users, Snyder hopes to sidestep competition from Microsoft and Google by inking partnerships with other hosted software providers who need word processing capabilities within their applications.
Sharapov D.,University of Cadiz |
Shkhinek K.,Polytechnical University
Advanced Materials Research | Year: 2013
Ice loads is one of the most important parameters which should be taken into consideration for arctic structures. Ice load highly depends on the ice thickness. It is always recommended to consider the ice thickness data from field observations. However if data is not available it is necessary to calculate the thicknesses of ice level. Calculation is also important for the areas where the thermal fluxes through structure should be taken into the consideration. In this work numerical simulation of Stefan problem for determining of ice level thickness is presented. The results show good correlation between empirical, experimental data and the results from finite element simulation of Stefan problem. © (2014)Trans Tech Publications,Switzerland. Source
Lateral photonic integration of oxide-confined leaky vertical-cavity surface-emitting lasers enables their application in data communications and sensing. Vertical-cavity surface-emitting lasers (VCSELs) that operate at 850nm and are based on oxide-confined apertures are widely used in optical interconnects in data centers, supercomputers, wireless backbone networks, and consumer applications.1 As the processor productivity in these applications increases, it is necessary to continuously improve performance and scale transmission speeds accordingly. In recent years, developers have produced a generation of devices capable of transmitting 40Gb/s at moderate current densities,2, 3 and they have recently demonstrated 54Gb/s non-return-to-zero transmission through 2.2km of multimode fiber.4 Now, 108Gb/s per wavelength transmission can be realized over 100–300m of multimode fiber through the use of advanced modulation formats: discrete multi-tone,5 multiCAP,6 and PAM4.7 All of these achievements are made possible through the use of VCSELs operating in a single transverse and longitudinal mode (SM VCSELs). When manufacturing SM VCSELs, developers typically make the oxide aperture in a VCSEL very small (around 2–3μm in diameter). This approach, however, may result in very low optical power, high resistance, and low manufacturing yield. To extend single-mode behavior toward more conventional aperture sizes (5–7μm), several alternative approaches have been proposed, including surface patterning, etching, overgrowth, and ion implantation in combination with photonic crystals.8, 9 These approaches require additional processing steps that must be precisely aligned (oxide aperture and surface pattern). The resulting complexity can reduce the yield and increase the cost of manufacturing. Our approach uses oxide-confined leaky VCSELs, which—through the application of proper epitaxial design—enable the generation of high optical leakage losses for high-order transverse modes. Using these devices, we extend the single-mode behavior of the laser toward large oxide aperture diameters. With our approach, we aim to create an additional cavity at a wavelength longer than the VCSEL cavity mode. Upon oxidation, the relative intensity distribution of the optical field between the coupled cavities can be strongly affected in the oxidized section. This induces a break in the orthogonality of the VCSEL mode and the second cavity mode (when at a certain tilt angle), which enables in-plane leakage to occur. High-order modes with the field intensity maxima close to the oxide periphery have thus much higher leakage losses.10 We have designed and manufactured oxide-confined leaky VCSELs and observed their leakage process through tilted narrow lobes in the far-field spectrum. The emission comes from the area outside the aperture, and thus does not suffer from diffraction-induced broadening. To model the VCSELs in 3D, we applied finite element analysis based on Maxwell's vector equations in a rotational symmetric system.11 Figure 1 shows a cross section of the simulated electric field of the fundamental and first excited optical modes of an oxide-confined aluminum gallium arsenide-based leaky VCSEL. A simulated far-field profile of the excited mode can be seen in Figure 2. The simulations show that the leakage effect results in a specific tilted emission over the VCSEL surface at ∼35–37°. Most of the intensity of the leaking light is channeled in the direction parallel to the surface. Figure 1. Radial distribution of the simulated electric field of oxide-confined leaky vertical-cavity surface-emitting laser (VCSEL) optical modes. (a) Fundamental optical mode. (b) First excited mode. An active region (magenta line) placed within the cavity is confined by aluminum gallium arsenide distributed Bragg reflectors. The structure contains oxide apertures (white lines). A semiconductor-air interface is shown as a dotted line in the figure. arb. u.: Arbitrary units. Figure 2. Far-field profile simulation of the excited VCSEL mode presented in Figure 1. We manufactured and tested VCSELs according to our design. The far-field measurements of the devices at two current densities can be seen in Figure 3, which shows that at high current densities during multimode operation, narrow lobes arise at ∼35° angles. These lobes are related to the leakage process (see Figure 2). Figure 3. Far-field profiles of a leaky VCSEL operating in fundamental mode (blue, 10kA/cm2) and multi-mode (red, >25kA/cm2). Electroluminescence spectra of the leaky VCSEL at different current densities are shown in Figure 4. We concluded that the VCSEL was predominantly single mode at all the current densities examined, despite the relatively large aperture diameter (5μm). In contrast, the non-leaky VCSEL with thick oxide apertures was heavily multimode, with the excited modes dominant even at small current densities.12 Figure 4. Electroluminescence spectra of an oxide leaky VCSEL with a 5μm aperture. The graph shows dominance of the fundamental mode up to high currents (5.5mA, red). Insert: An optical eye diagram (PRBS7) at 32Gb/s. To summarize, we have shown that it is possible to significantly improve VCSEL spectral quality without involving any additional processing steps. Furthermore, we confirmed the occurrence of in-plane leakage through leakage lobes in the far-field profile of the device. Our findings create opportunities for engineering photonic integrated circuits, for example, by coherent coupling of two or more devices. Therefore, it may be possible to use the technique for beam steering.13 By operating one VCSEL in a couple under reverse bias, it is possible to realize an on-chip integrated monitor photodiode, thus drastically reducing the cost of packaging (since fewer of the elements require alignment and assembly). Our future work will focus on optimization of the leakage effect in order to manufacture high- power and high-speed single-mode VCSELs. This project received funding from the European Union's Horizon 2020 research and innovation program under grant 666866. VI Systems GmbH Nikolay Ledentsov Jr. received his MSc in physics at the Technical University of Berlin while developing indium gallium arsenide-based LEDs. At VI Systems he is responsible for the design and numerical simulation of optoelectronic devices, and operates an automated testbed for spectral and high-speed characterization. Vitaly Shchukin received a diploma in physics and engineering in the field of semiconductor physics from St. Petersburg State Polytechnical University, St. Petersburg, Russia, and a PhD (1987) and doctor of science (1999) in physics and mathematics from the Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg. He is co-author of more than 190 published papers, and holds 22 patents and a monograph. Joerg Kropp holds a doctor of science in the field of atomic physics with optical spectroscopy and laser applications. He has more than 25 years' experience in industry in the field of optical communications through management positions with Siemens and Infineon. Mikel Agustin received a diploma in telecommunications engineering from the Public University of Navarra, Spain, and completed his education at the Institute of Telecommunications, Warsaw University of Technology, Poland. At VI Systems he is responsible for developing energy-efficient ultrafast vertical-cavity surface-emitting lasers and photodetectors. Nikolay N. Ledentsov received a diploma in electrical engineering from the Electrical Engineering Institute in Leningrad (LETI, now Electrotechnical University, St. Petersburg, Russia) in 1982. He obtained his PhD (1987) and doctor of science (1994) in physics and mathematics from the Ioffe Physical-Technical Institute. He has been professor of electrical engineering at LETI since 1994 and professor of physics and mathematics at the Ioffe Physical-Technical Institute since 2005. 1. T. R. Fanning, J. Wang, Z.-W. Feng, M. Keever, C. Chu, A. Sridhara, C. Rigo, et al., 28-Gbps 850-nm oxide VCSEL development and manufacturing progress at Avago, Proc. SPIE 9001, p. 900102, 2014. doi:10.1117/12.2039499 3. S. A. Blokhin, J. A. Lott, A. Mutig, G. Fiol, N. N. Ledentsov, M. V. Maximov, A. M. Nadtochiy, V. A. Shchukin, D. Bimberg, 850nm VCSELs operating at bit rates up to 40Gbit/s, Electron. Lett. 45, p. 501-503, 2009. 4. G. Stepniak, A. Lewandowski, J. R. Kropp, N. N. Ledentsov, V. A. Shchukin, N. Ledentsov, G. Schaefer, M. Agustin, J. P. Turkiewicz, 54 Gbit/s OOK transmission using single-mode VCSEL up to 2.2km MMF, Electron. Lett. 52, p. 633-635, 2016. 5. B. Wu, X. Zhou, Y. Ma, J. Luo, K. Zhong, S. Qiu, Z. Feng, et al., Close to 100 Gbps discrete multitone transmission over 100m of multimode fiber using a single transverse mode 850nm VCSEL, Proc. SPIE 9766, p. 97660K, 2016. doi:10.1117/12.2208901 6. R. Puerta, M. Agustin, L. Chorchos, J. Tonski, J.-R. Kropp, N. Ledentsov, V. A. Shchukin, et al., 107.5Gb/s 850nm multi- and single-mode VCSEL transmission over 10 and 100m of multi-mode fiber, OSA Opt. Fiber Commun. Conf. Th5B, p. Th5B.5, 2016. 7. G. Stepniak, L. Chorchos, M. Agustin, J.-R. Kropp, N. N. Ledentsov, V. A. Shchukin, N. N. Ledentsov, J. P. Turkiewicz, Up to 108Gb/s PAM 850nm multi and single mode VCSEL transmission over 100m of multi mode fiber, 2016. Paper accepted at the 42nd Euro. Conf. Opt. Commun. in Düsseldorf, 18-22 September 2016. 8. E. Haglund, A. Haglund, J. Gustavsson, B. Kögel, P. Westbergh, A. Larsson, Reducing the spectral width of high speed oxide confined VCSELs using an integrated mode filter, Proc. SPIE 8276, p. 82760L, 2012. doi:10.1117/12.908424 10. V. Shchukin, N. N. Ledentsov, J. Kropp, G. Steinle, N. Ledentsov, S. Burger, F. Schmidt, Single-mode vertical cavity surface emitting laser via oxide-aperture-engineering of leakage of high-order transverse modes, IEEE J. Quantum Electron. 50, p. 990-995, 2014. 11. N. Ledentsov, V. A. Shchukin, N. N. Ledentsov, J.-R. Kropp, S. Burger, F. Schmidt, Direct evidence of the leaky emission in oxide-confined vertical cavity lasers, IEEE J. Quantum Electron. 52, p. 1-7, 2016. 12. N. N. Ledentsov, J. Xu, J. A. Lott, Future Trends in Microelectronics: Frontiers and Innovations, ch. Ultrafast nanophotonic devices for optical interconnects, Wiley, 2013. doi:10.1002/9781118678107.ch11