Aalto University

About: Aalto University is a education organization based out in Espoo, Finland. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 9969 authors who have published 32648 publications receiving 829626 citations. The organization is also known as: TKK & Aalto-korkeakoulu.

Three-fold rotational defects in two-dimensional transition metal dichalcogenides

Abstract: As defects frequently govern the properties of crystalline solids, the precise microscopic knowledge of defect atomic structure is of fundamental importance. We report a new class of point defects in single-layer transition metal dichalcogenides that can be created through 60° rotations of metal-chalcogen bonds in the trigonal prismatic lattice, with the simplest among them being a three-fold symmetric trefoil-like defect. The defects, which are inherently related to the crystal symmetry of transition metal dichalcogenides, can expand through sequential bond rotations, as evident from in situ scanning transmission electron microscopy experiments, and eventually form larger linear defects consisting of aligned 8-5-5-8 membered rings. First-principles calculations provide insights into the evolution of rotational defects and show that they give rise to p-type doping and local magnetic moments, but weakly affect mechanical characteristics of transition metal dichalcogenides. Thus, controllable introduction of rotational defects can be used to engineer the properties of these materials.

Water balance analysis for the Tonle Sap lake - floodplain system

Abstract: The Tonle Sap Lake of Cambodia is the largest freshwater body of Southeast Asia, forming an important part of the Mekong River system. The lake has an extremely productive ecosystem and operates as a natural floodwater reservoir for the lower Mekong Basin, offering flood protection and assuring the dry season flow to the Mekong Delta. In light of the accelerating pace of water resources development within the Mekong Basin and the anticipation of potentially significant hydrological impacts, it is critical to understand the overall hydrologic regime of Tonle Sap Lake. We present here a detailed water balance model based on observed data of discharges from the lake's tributaries, discharge between Mekong and the lake through the Tonle Sap River, precipitation, and evaporation. The overland flow between the Mekong and lake was modelled with the EIA 3D hydrodynamic model. We found that majority (53.5%) of the water originates from the Mekong mainstream but the lake's tributaries also play an important role contributing 34% of the annual flow, while 12.5% is derived from precipitation. The water level in the lake is mainly controlled by the water level in the Mekong mainstream. The Tonle Sap system is hence very vulnerable, from a water quantity point of view, to possible changes in the Mekong mainstream and thus, development activities in the whole Mekong basin. From a biogeochemical point of view, the possible changes in the lake's own catchment are equally important, together with the changes in the whole Mekong Basin. Based on our findings we recommend of continuing the monitoring programmes in lake's tributaries and urgently starting of groundwater measurement campaign within the floodplain, and including the groundwater modelling to be part of the hydrodynamic models applied for the lake. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis of Oscillator Phase-Noise Effects on Self-Interference Cancellation in Full-Duplex OFDM Radio Transceivers

Abstract: This paper addresses the analysis of oscillator phase-noise effects on the self-interference cancellation capability of full-duplex direct-conversion radio transceivers. Closed-form solutions are derived for the power of the residual self-interference stemming from phase noise in two alternative cases of having either independent oscillators or the same oscillator at the transmitter and receiver chains of the full-duplex transceiver. The results show that phase noise has a severe effect on self-interference cancellation in both of the considered cases, and that by using the common oscillator in upconversion and downconversion results in clearly lower residual self-interference levels. The results also show that it is in general vital to use high quality oscillators in full-duplex transceivers, or have some means for phase noise estimation and mitigation in order to suppress its effects. One of the main findings is that in practical scenarios the subcarrier-wise phase-noise spread of the multipath components of the self-interference channel causes most of the residual phase-noise effect when high amounts of self-interference cancellation is desired.

Driven by aspirations, but in what direction? Performance shortfalls, slack resources, and resource-consuming vs. resource-freeing organizational change

Abstract: Research summary: Prior literature drawing on the behavioral theory of the firm has not considered how resource constraints impact the direction of organizational change in response to performance shortfalls relative to aspirations We argue that decreasing financial resources resulting from substantial performance shortfalls and the absence or availability of slack resources together affect the emphasis on different types of organizational change in response to performance shortfalls Using data on the acquisition and divestment behavior of 530 companies in the information and communications technology sector from 1992 to 2014, we find that the frequency of resource-consuming acquisitions and of resource-freeing divestments are affected differently by performance below aspirations and that these relationships are moderated by the level of financial slack Managerial summary: This paper examines whether firms respond to performance shortfalls with acquisitions or divestments We argue and show that the closer the firm is to the aspired level of performance, the more likely it is to respond with resource-consuming acquisitions to close the performance gap, whereas the further it is from aspired performance, the more likely the firm is to respond with divestments to free resources Financial slack weakens these relationships between performance relative to aspirations and acquisitions or divestments such that it increases the likelihood of a response through acquisitions while it reduces the likelihood of a response through divestments Copyright © 2016 John Wiley & Sons, Ltd

Advantages of white LED lamps and new detector technology in photometry

Abstract: Light emitting diode (LED) lighting is becoming more and more popular, as incandescent lamps are being phased out globally. LEDs have several advantages over incandescent lamps, including energy efficiency, robustness, long lifetime, and good temporal stability. The three latter features make LEDs attractive candidates as new photometric standards. Because the spectra of white LEDs are limited to the visible wavelength range, a novel method for the realization of photometric units based on the predictable quantum efficient detector (PQED) can be utilized. The method eliminates the need of photometric filters that are traditionally used in photometry, and instead relies on carrying out the photometric weighting numerically based on the measured relative spectrum of the source. The PQED-based realization simplifies the traceability chain of photometric measurements significantly as compared with the traditional filter-based method. The measured illuminance values of a white LED deviate by only 0.03% when determined by the new and the traditional methods. The new PQED method has significantly lower expanded uncertainty of 0.26% (k = 2) as compared with that of the traditional filter-based method of 0.42% (k = 2). Furthermore, when filtered photometers that measure LED lighting are calibrated using LED lamps as calibration sources instead of incandescent lamps, a significant decrease in the uncertainty related to the spectral mismatch correction can be obtained. The maximum spectral mismatch errors of LED measurements decreased on average by a factor of 3 when switching from an incandescent lamp to an LED calibration source. White light-emitting diodes (LEDs) can be used to define photometric units and offer several advantages over conventional incandescent lamps. Tungsten-filament incandescent lamps are widely used as standard light sources in photometry, but LEDs have higher energy efficiencies, greater robustness, long lifetimes, and good temporal stability. Now, a team of scientists in Finland has demonstrated that a high accuracy can be achieved by using a new primary standard for optical power based on an induced junction photodiode trap as a broadband detector. By measuring the illuminance of a white LED lamp, they show that this detector is more accurate than photometers when LEDs are used as the light source. Furthermore, using LEDs does not require filters as photometric weighting is performed numerically based on the measured relative spectrum of the source.