Helsinki University of Technology

About: Helsinki University of Technology is a based out in . It is known for research contribution in the topics: Thin film & Vortex. The organization has 8962 authors who have published 20136 publications receiving 723787 citations. The organization is also known as: TKK & Teknillinen korkeakoulu.

Review of stability for advanced dye solar cells

Abstract: The current status of the long-term stability of dye solar cells (DSCs) and factors affecting it is reviewed. The purpose is to clarify present knowledge of degradation phenomena and factors in these cells by critically separating the assumptions from the solid experimental evidence reported in the literature. Important degradation processes such as dye desorption, decrease in the tri-iodide concentration, degradation at the photoelectrode and counter electrode, affect of ultraviolet light and moisture, and issues related to the sealing, are covered. It is concluded that techniques giving chemical information are needed for the stability investigations of DSCs to reveal possible ways to improve their lifetime. In this regard, experimental methods suitable for separating degradation mechanisms in complete cells during long-term testing are proposed employing specifically designed sealed cell structures, called segmented cells, that provide windows to measure specific cell components without being obscured by the others.

Developing GIS-supported location-based services

Abstract: Mobile networking is developing and proliferating at a high speed. Many estimates say that the number of mobile telecom subscribers will exceed 1 billion in the year 2003. Among the terminals deployed, there will be hundreds of millions of Internet-enabled ones making Mobile Internet a reality for the big masses. The terminals and/or the mobile networks are now able to determine the position of the terminal on the earth with more and more precision. This is the basis for the new class of services called Location-Based Services (LBS). The paper discusses this new emerging application area that some people consider the central novel application class of Mobile Internet. The main topic of the paper is the question, how Geographic Information Systems (GIS) and the data hosted currently by them could be used in the context of LBS. We analyze their properties and relate them with the needs of LBS. We also present our LBS pilot system that is using XML-based vector formal for city maps and runs on Java-enabled mobile terminals, PDAs and smartphones.

Thermal Modifications in Softwood Studied by FT‐IR and UV Resonance Raman Spectroscopies

Abstract: Scots pine planks were heat‐treated under steam in a temperature range of 100–240°C at every 20°C. Changes in chemical structure of the wood samples were examined with UV resonance Raman (UVRR) and Fourier transform infrared (FT‐IR) spectroscopies. Prior to the FT‐IR and UVRR analysis, the heartwood part of wood samples were ground and extracted with acetone. Both the extracts and the extracted samples were analyzed. In addition, Klason lignin contents of the samples were determined. The FT‐IR and UVRR spectroscopy were powerful techniques to monitor chemical changes in the heat‐treated wood samples. Results confirmed most of what determined previously by other research groups using different techniques. The UVRR and FT‐IR spectra of acetone extracts showed that lignin became partly acetone soluble after a heat treatment of 180°C or greater. Increased levels of free phenolic hydroxyl groups were detected in lignin, probably due to cleavages of β‐O‐aryl ether interunit linkages. The amount of extr...

Single-mode heat conduction by photons

Abstract: A clever experiment that makes use of two metallic islands connected by superconducting leads now confirms that thermal conduction by photons is limited by the same quantum value. Although the result is mainly of fundamental importance, there are implications for the design of bolometers, detectors of far-infrared light that are used in astrophysical studies, and electronic micro-refrigerators. The thermal conductance of a single channel is limited by its unique quantum value GQ, as was shown theoretically1 in 1983. This result closely resembles the well-known quantization of electrical conductance in ballistic one-dimensional conductors2,3. Interestingly, all particles—irrespective of whether they are bosons or fermions—have the same quantized thermal conductance4,5 when they are confined within dimensions that are small compared to their characteristic wavelength. The single-mode heat conductance is particularly relevant in nanostructures. Quantized heat transport through submicrometre dielectric wires by phonons has been observed6, and it has been predicted to influence cooling of electrons in metals at very low temperatures due to electromagnetic radiation7. Here we report experimental results showing that at low temperatures heat is transferred by photon radiation, when electron–phonon8 as well as normal electronic heat conduction is frozen out. We study heat exchange between two small pieces of normal metal, connected to each other only via superconducting leads, which are ideal insulators against conventional thermal conduction. Each superconducting lead is interrupted by a switch of electromagnetic (photon) radiation in the form of a DC-SQUID (a superconducting loop with two Josephson tunnel junctions). We find that the thermal conductance between the two metal islands mediated by photons indeed approaches the expected quantum limit of GQ at low temperatures. Our observation has practical implications—for example, for the performance and design of ultra-sensitive bolometers (detectors of far-infrared light) and electronic micro-refrigerators9, whose operation is largely dependent on weak thermal coupling between the device and its environment.