254 research outputs found
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 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 m at 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 tĂ€yttökerrosten kosteus- ja mikrobiologisia olosuhteita selvitettiin kenttĂ€mittauksin. YhteensĂ€ 46:sta satunnaisesti valitusta kohteesta eri puolilta Suomea otettiin maanĂ€ytteitĂ€ yhteensĂ€ 49 kappaletta, joista mÀÀritettiin laboratoriokokein kosteus- ja mikrobipitoisuudet. PÀÀosa nĂ€ytteistĂ€ otettiin vuonna 2005, osa vuonna 2006. NĂ€ytteet otettiin koekohteista kahdesti: talvella ja loppukesĂ€stĂ€. Mikrobianalyysit teetettiin Turun yliopiston Aerobiologian yksikössĂ€ STM:n SisĂ€ilmanohjeen mukaisena kvantitatiivisena analyysina, jossa suoritettiin viljelyyn perustuva suku- tai lajitason tunnistus kahdella eri kasvatusalustalla. Mittaustulosten perusteella tĂ€yttökerrosten ylĂ€osien vesipitoisuudet ylittivĂ€t lĂ€hes aina hygroskooppisen tasapainokosteuden RH 100 %:n suhteellisessa kosteudessa. TĂ€yttöjen huokosilman suhteellinen kosteus on siis pysyvĂ€sti hyvin korkea: RH â 100 %. Joissain kohteissa mitattu vesipitoisuus oli selvĂ€sti yli hygroskooppisen tasapainokosteuden ja tĂ€ytön ylĂ€osat toimivat osittain kapillaarisella alueella. Maanvastaisen alapohjan tĂ€yttökerrosten lĂ€mpötila lĂ€mmitetyn rakennuksen alapuolella vaihtelee vĂ€lillĂ€ +10âŠ+20 ÂșC. TĂ€yttökerrosten vallitsevat olosuhteet, korkea kosteuspitoisuus ja lĂ€mpötila, ovat suotuisat mikrobikasvulle. Jonkinasteista mikrobikasvustoa löydettiin 98 %:sta kaikista maanĂ€ytteistĂ€. Kosteusvaurioita indikoivia mikrobilajeja, joko homesienien indikaattorilajeja tai aktinomykeetti âbakteereja, löytyi 79 % nĂ€ytteistĂ€. Suurimmassa osassa tutkituista kohteista ei kuitenkaan ollut koskaan havaittu alapohjiin liittyviĂ€ kosteusvaurioita. Vastaavia lajeja lĂ€hes yhtĂ€ suurina pitoisuuksina oli myös referenssinĂ€ytteissĂ€, jotka otettiin hiekkakuopilta valmiiksi seulotusta ja lĂ€jitetystĂ€ salaojasorasta. Tulosten perusteella tĂ€yttöjen vesipitoisuudella tai kapillaarisuudella ja mikrobikasvuston mÀÀrĂ€llĂ€ ei ole suoraa yhteyttĂ€. Samoin indikaattorilajeja ja toksiineja tuottavia homekasvustoja kasvoi tĂ€yttökerroksissa kosteustasosta riippumatta. Mikrobikasvu on jossain mÀÀrin riippuvainen rakennuksen iĂ€stĂ€: pitoisuudet olivat alempia ja esiintyminen satunnaisempaa vanhimmissa rakennuksissa, eikĂ€ 30âluvulla rakennettujen tai sitĂ€ vanhempien kohteiden nĂ€ytteistĂ€ tavattu homesienikasvustoja lainkaan, vaikka vanhimmat alapohjarakenteet kapillaarisine alustĂ€yttöineen ovat kosteusteknisesti riskialttiimpia kuin uudet. YhtenĂ€isten materiaalikerrosten ja epĂ€jatkuvuuskohtien kykyĂ€ estÀÀ mikrobien kulkeutuminen materiaalin lĂ€pi tutkittiin laboratorio-olosuhteissa. Tutkimuksessa yhtenĂ€inen betonilaatta (h = 80 mm, w/c = 0,7 ... 1,0) tai EPS-eristekerros (EPS 100 Lattia 100 mm) ja SPU âeristekerros eivĂ€t lĂ€pĂ€isseet homesienten itiöitĂ€ (Aspergillus versicolor). Sen sijaan valusauma, joka ei ollut ilmanpitĂ€vĂ€ muodostui itiöiden tunkeutumisreitiksi. TĂ€yttökerroksista mitattu korkea suhteellinen kosteus ja runsas mikrobikasvu eivĂ€t ole merkki alapohjalaatan kosteusvaurioista, vaan ne ovat tĂ€yttökerroksen luonnolliset kĂ€yttötilan olosuhteet, jotka on otettava huomioon rakenteita suunniteltaessa. Mikrobien ja itiöiden kulkeutuminen sisĂ€ilmaan on estettĂ€vĂ€ tekemĂ€llĂ€ alapohjarakenne ja erityisesti liitokset muihin rakenneosiin ja laattojen lĂ€piviennit mahdollisimman ilmanpitĂ€viksi. Toimivat rakenneratkaisut ovat pÀÀosin samat kuin radon-tiivistyksessĂ€.<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 mLâ1 and 32.4 pg mLâ1 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
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