Efficient Peltier refrigeration by a pair of normal metal/ insulator/superconductor junctions

We suggest and demonstrate in experiment that two normal metal /insulator/ superconductor (NIS) tunnel junctions combined in series to form a symmetric SINIS structure can operate as an efficient Peltier refrigerator. Specifically, it is shown that the SINIS structure with normal-state junction resistances 1.0 and 1.1 k$\Omega$ is capable of reaching a temperature of about 100 mK starting from 300 mK. We estimate the corresponding cooling power to be 1.5 pW per total junction area of 0.8 $\mu$m$^2$ at $T= 300$ mK.Comment: 7 pages, revtex, 3 figures by fax/conventional mail upon reques

Effect of a thin AlO_x layer on transition-edge sensor properties

We have studied the physics of transition-edge sensor (TES) devices with an insulating AlOx layer on top of the device to allow implementation of more complex detector geometries. By comparing devices with and without the insulating film, we have observed significant additional noise apparently caused by the insulator layer. In addition, AlOx was found to be a relatively good thermal conductor. This adds an unforeseen internal thermal feature to the system.Comment: 6 pages, 5 figures, Low Temperature Detectors 14 conferenc

Maanvastaisten rakenteiden mikrobiologinen toimivuus

Maanvastaisen rakenteen alapuolisten täyttökerrosten kosteus- ja mikrobiologisia olosuhteita selvitettiin kenttämittauksin. Yhteensä 46:sta satunnaisesti valitusta kohteesta eri puolilta Suomea otettiin maanäytteitä yhteensä 49 kappaletta, joista määritettiin laboratoriokokein kosteus- ja mikrobipitoisuudet. Pääosa näytteistä otettiin vuonna 2005, osa vuonna 2006. Näytteet otettiin koekohteista kahdesti: talvella ja loppukesästä. Mikrobianalyysit teetettiin Turun yliopiston Aerobiologian yksikössä STM:n Sisäilmanohjeen mukaisena kvantitatiivisena analyysina, jossa suoritettiin viljelyyn perustuva suku- tai lajitason tunnistus kahdella eri kasvatusalustalla. Mittaustulosten perusteella täyttökerrosten yläosien vesipitoisuudet ylittivät lähes aina hygroskooppisen tasapainokosteuden RH 100 %:n suhteellisessa kosteudessa. Täyttöjen huokosilman suhteellinen kosteus on siis pysyvästi hyvin korkea: RH ≈ 100 %. Joissain kohteissa mitattu vesipitoisuus oli selvästi yli hygroskooppisen tasapainokosteuden ja täytön yläosat toimivat osittain kapillaarisella alueella. Maanvastaisen alapohjan täyttökerrosten lämpötila lämmitetyn rakennuksen alapuolella vaihtelee välillä +10…+20 ºC. Täyttökerrosten vallitsevat olosuhteet, korkea kosteuspitoisuus ja lämpötila, ovat suotuisat mikrobikasvulle. Jonkinasteista mikrobikasvustoa löydettiin 98 %:sta kaikista maanäytteistä. Kosteusvaurioita indikoivia mikrobilajeja, joko homesienien indikaattorilajeja tai aktinomykeetti –bakteereja, löytyi 79 % näytteistä. Suurimmassa osassa tutkituista kohteista ei kuitenkaan ollut koskaan havaittu alapohjiin liittyviä kosteusvaurioita. Vastaavia lajeja lähes yhtä suurina pitoisuuksina oli myös referenssinäytteissä, jotka otettiin hiekkakuopilta valmiiksi seulotusta ja läjitetystä salaojasorasta. Tulosten perusteella täyttöjen vesipitoisuudella tai kapillaarisuudella ja mikrobikasvuston määrällä ei ole suoraa yhteyttä. Samoin indikaattorilajeja ja toksiineja tuottavia homekasvustoja kasvoi täyttökerroksissa kosteustasosta riippumatta. Mikrobikasvu on jossain määrin riippuvainen rakennuksen iästä: pitoisuudet olivat alempia ja esiintyminen satunnaisempaa vanhimmissa rakennuksissa, eikä 30–luvulla rakennettujen tai sitä vanhempien kohteiden näytteistä tavattu homesienikasvustoja lainkaan, vaikka vanhimmat alapohjarakenteet kapillaarisine alustäyttöineen ovat kosteusteknisesti riskialttiimpia kuin uudet. Yhtenäisten materiaalikerrosten ja epäjatkuvuuskohtien kykyä estää mikrobien kulkeutuminen materiaalin läpi tutkittiin laboratorio-olosuhteissa. Tutkimuksessa yhtenäinen betonilaatta (h = 80 mm, w/c = 0,7 ... 1,0) tai EPS-eristekerros (EPS 100 Lattia 100 mm) ja SPU –eristekerros eivät läpäisseet homesienten itiöitä (Aspergillus versicolor). Sen sijaan valusauma, joka ei ollut ilmanpitävä muodostui itiöiden tunkeutumisreitiksi. Täyttökerroksista mitattu korkea suhteellinen kosteus ja runsas mikrobikasvu eivät ole merkki alapohjalaatan kosteusvaurioista, vaan ne ovat täyttökerroksen luonnolliset käyttötilan olosuhteet, jotka on otettava huomioon rakenteita suunniteltaessa. Mikrobien ja itiöiden kulkeutuminen sisäilmaan on estettävä tekemällä alapohjarakenne ja erityisesti liitokset muihin rakenneosiin ja laattojen läpiviennit mahdollisimman ilmanpitäviksi. Toimivat rakenneratkaisut ovat pääosin samat kuin radon-tiivistyksessä.<br/

Cloning, Expression, and Purification of a Nitric Oxide Synthase-Like Protein from Bacillus cereus

The nitric oxide synthase-like protein from Bacillus cereus (bcNOS) has been cloned, expressed, and characterized. This small hemeprotein (356 amino acids in length) has a mass of 43 kDa and forms a dimer. The recombinant protein showed similar spectral shifts to the mammalian NOS proteins and could bind the substrates L-arginine and NG-hydroxy-L-arginine as well as the ligand imidazole. Low levels of activity were recorded for the hydrogen peroxide-dependent oxidation of NG-hydroxy-L-arginine and L-arginine by bcNOS, while a reconstituted system with the rat neuronal NOS reductase domain showed no activity. The recombinant bcNOS protein adds to the complement of bacterial NOS-like proteins that are used for the investigation of the mechanism and function of NO in microorganisms

P-N JUNCTION THEORY AND THE JUNCTION TRANSISTOR

A theoretical discussion is presented of the P-N junction theory and the junction transistor. A P-N juncion is where the two regions of a Ge crystal meet, one side of which is P-type, the other N-type. An NPN junction transistor consists of a single crystal, one end of which is N-type, a middle section which is P-type, and the composite end which is N-type. Silicon and Ge are the semiconductors commonly used. (W.L.H.

Microrefrigeration by a pair of normal metal/insulator/superconductor junctions

We suggest and demonstrate experimentally that two normal metal/insulator/superconductor (NIS) tunnel junctions combined in series to form a symmetric SINIS structure can operate as an efficient Peltier refrigerator. Specifically, it is shown that the SINIS structure with normal-state junction resistences of 1.0 and 1.1 kOmega is capable of reaching a temperature of about 100 mK starting from 300 mK. We estimate the corresponding cooling power to be 1.5 pW per total junction area of 0.8 micrometers(exp 2) at T = 300 mK. This cooling power density implies that scaling of junction area up to about 1 mm(exp 2) should bring the cooling power into the microW range

Efficiency in nanostructured thermionic and thermoelectric devices

Advances in solid-state device design now allow the spectrum of transmitted electrons in thermionic and thermoelectric devices to be engineered in ways that were not previously possible. Here we show that the shape of the electron energy spectrum in these devices has a significant impact on their performance. We distinguish between traditional thermionic devices where electron momentum is filtered in the direction of transport only and a second type, in which the electron filtering occurs according to total electron momentum. Such 'total momentum filtered' kr thermionic devices could potentially be implemented in, for example, quantum dot superlattices. It is shown that whilst total momentum filtered thermionic devices may achieve efficiency equal to the Carnot value, traditional thermionic devices are limited to efficiency below this. Our second main result is that the electronic efficiency of a device is not only improved by reducing the width of the transmission filter as has previously been shown, but also strongly depends on whether the transmission probability rises sharply from zero to full transmission. The benefit of increasing efficiency through a sharply rising transmission probability is that it can be achieved without sacrificing device power, in contrast to the use of a narrow transmission filter which can greatly reduce power. We show that devices which have a sharply-rising transmission probability significantly outperform those which do not and it is shown such transmission probabilities may be achieved with practical single and multibarrier devices. Finally, we comment on the implications of the effect the shape of the electron energy spectrum on the efficiency of thermoelectric devices.Comment: 11 pages, 15 figure

Calorimetric readout of a superconducting proximity-effect thermometer

A proximity-effect thermometer measures the temperature dependent critical supercurrent in a long superconductor - normal metal - superconductor (SNS) Josephson junction. Typically, the transition from the superconducting to the normal state is detected by monitoring the appearance of a voltage across the junction. We describe a new approach to detect the transition based on the temperature increase in the resistive state due to Joule heating. Our method increases the sensitivity and is especially applicable for temperatures below about 300 mK.Comment: 10 pages, 5 figures. To appear in the proceedings of the Conference on Micro- and Nanocryogenics (LT25 satellite) organized in Espoo, Finland (2008

Development of anti-immunocomplex specific antibodies and non-competitive time-resolved fluorescence immunoassay for the detection of estradiol

Detection of circulatory estradiol has widespread use in various clinical applications. Particularly, the use of estradiol-specific antibodies in immunoassays is routinely used, mainly due to the cost efficiency and simplicity of the sample handling process. However, the circulatory levels of estradiol can be extremely low in some conditions, and beyond the current detection limit of existing competitive immunoassays. We describe the generation of anti-immunocomplex specific antibodies derived from synthetic antibody repertoire and the development of high-performance non-competitive immunoassay for the detection of estradiol. Phage display selections were used to isolate new antibodies from synthetic antibody library with the use of existing estradiol specific Fab fragment. The found antibodies were consecutively used to set up a time-resolved fluorescence-based immunoassay (TRFIA), which can be used to detect estradiol with exceptional sensitivity and specificity. The limit of detection and EC50 were shown to be 3.0 pg mL−1 and 32.4 pg mL−1 respectively.</p

Electronic and thermal sequential transport in metallic and superconducting two-junction arrays

The description of transport phenomena in devices consisting of arrays of tunnel junctions, and the experimental confirmation of these predictions is one of the great successes of mesoscopic physics. The aim of this paper is to give a self-consistent review of sequential transport processes in such devices, based on the so-called "orthodox" model. We calculate numerically the current-voltage (I-V) curves, the conductance versus bias voltage (G-V) curves, and the associated thermal transport in symmetric and asymmetric two-junction arrays such as Coulomb-blockade thermometers (CBTs), superconducting-insulator-normal-insulator-superconducting (SINIS) structures, and superconducting single-electron transistors (SETs). We investigate the behavior of these systems at the singularity-matching bias points, the dependence of microrefrigeration effects on the charging energy of the island, and the effect of a finite superconducting gap on Coulomb-blockade thermometry.Comment: 23 pages, 12 figures; Berlin (ISBN: 978-3-642-12069-5