Shot Noise with Interaction Effects in Single Walled Carbon Nanotubes

We have measured shot noise in single walled carbon nanotubes (SWNT) with good contacts at 4.2 K at low frequencies ($f=600 - 850$ MHz). We find a strong modulation of shot noise over the Fabry-Perot pattern; in terms of differential Fano factor the variation ranges over 0.4 - 1.2. The shot noise variation, in combination with differential conductance, is analyzed using two (spin-degenerate) modes with different, energy-dependent transmission coefficients. No power law dependence of shot noise, as expected for Luttinger liquids, was found in our measurements.Comment: 5 pages, 4 figure

Rationality as the Rule of Reason

The demands of rationality are linked both to our subjective normative perspective (given that rationality is a person-level concept) and to objective reasons or favoring relations (given that rationality is non-contingently authoritative for us). In this paper, I propose a new way of reconciling the tension between these two aspects: roughly, what rationality requires of us is having the attitudes that correspond to our take on reasons in the light of our evidence, but only if it is competent. I show how this view can account for structural rationality on the assumption that intentions and beliefs as such involve competent perceptions of downstream reasons, and explore various implications of the account

Measurements of shot noise in single walled carbon nanotubes

We have measured shot noise in single walled carbon nanotubes (SWNT) at 4.2K over frequencies f = 600 – 850 MHz. Here we report results obtained on shot noise without DC bias by applying an AC modulation at ω0 and recording the noise variation at 2ω0: the Fano factor is obtained by extrapolating down to zero excitation amplitude. We also discuss the applicability of this method in samples which have strongly non‐linear IV characteristics like carbon nanotubes. The obtained results are compared with regular differential noise measurements where both DC and AC bias are employed.Peer reviewe

Teknologisen oppimisympäristön vaikutukset opettajiin ja oppilaisiin

Tiivistelmä. Kandidaatintyössä selvitetään kiihtyneen digitalisaation aiheuttamien oppimisympäristön muutoksien vaikutuksia opettajiin sekä oppilaisiin. Tutkielma koetaan tarpeelliseksi, sillä yhteiskunnassa on jatkuvaa keskustelua teknologian kuormittavasta vaikutuksesta opettajien keskuudessa, sekä useista teknologian haitallisista vaikutuksista lasten keskuudessa. Tavoitteenamme on selvittää mahdollisimman tuoretta lähdekirjallisuutta hyödyntäen useita teknologisen oppimisympäristön vaikutuksia pääsääntöisesti peruskouluikäisiin oppilaisiin sekä heidän opettajiinsa liittyen. Pohjustaaksemme vaikutuksien selvittämistä, tutkimme ensin lähdekirjallisuuden avulla myös teknologisen oppimisympäristön nykytilannetta Suomessa. Tutkielma on tehty kuvailevana kirjallisuuskatsauksena, jolloin se pohjaa aiemmin julkaistuun tutkimustietoon, sekä sen arvioimiseen. Teknologiaa ja digitalisaatiota käsitellessä lähdekirjallisuuden tuoreus on erityisen tärkeää, sillä aihe elää erittäin vilkkaasti digitalisaation liepeissä. Teknologia on erittäin nopeasti uusiutuvaa, joten aiheesta tehty tutkimuskin vanhenee erittäin nopeasti. Olemme huomioineet tämän lähdekirjallisuutta valitessa, keskittyen siksi mahdollisimman uuteen tutkimukseen. Tutkimukseen poimimme käsittelemämme lähdekirjallisuuden pohjalta muutamia pinnalle nousseita vaikutuksia opettajien ja oppilaiden keskuudessa, jotka koimme erityisen tärkeiksi. Teknologiset oppimisympäristöt ilmenivät opettajien ammatissa teknologisena kuormittavuutena ja -voimavarana, sekä teknostressin muodossa. Oppilailla digitalisoituneen oppimisympäristön lähdekirjallisuudesta pinnalle nousi ruutuajan lisääntyminen, nettikiusaamisen ilmeneminen sekä muuttuneiden oppimisympäristöjen vaikutukset. Molemmista kohderyhmistä löytyi sekä positiivisia, että negatiivisia vaikutteita teknologian pohjalta. On hankalaa puntaroida, onko positiivisten vaikutusten painoarvo suurempi kuin negatiivisten, mutta tutkimuksen tavoitteena ei olekaan selvittää kyseistä eroa. Keskitymme tutkimuksessa vain vaikutuksien ilmi tuomiseen, sekä niiden käsittelemiseen

Controlling supercurrents using single-walled carbon nanotube weak links

We have investigated proximity-induced supercurrents in single-walled carbon nanotubes. Phase diffusion is found to be present in the maximum measured supercurrent of 4.8 nA, which results in a minimum of 100Ω zero bias resistance in superconducting state. We also observe that the supercurrent is very sensitive to the measurement bandwidth and large phase fluctuations can even destroy the supercurrents. Our results shed light on the methods of how to improve the performance of high frequency superconducting single-walled nanotube devices.Peer reviewe

Single-walled carbon nanotube weak links in Kondo regime with zero-field splitting

We have investigated proximity-induced supercurrents in single-walled carbon nanotubes in the Kondo regime and compared them with supercurrents obtained on the same tube with Fabry-Pérot resonances. Our data display a wide distribution of Kondo temperatures TK=1–14 K, and the measured critical current ICM vs TK displays two distinct branches; these branches, distinguished by zero-field splitting of the normal-state Kondo conductance peak, differ by an order of magnitude at large values of TK. Evidence for renormalization of Andreev levels in Kondo regime is also found.Peer reviewe

A spatiotemporal theory for MRI T2 relaxation time and apparent diffusion coefficient in the brain during acute ischaemia:Application and validation in a rat acute stroke model

The objective of this study is to present a mathematical model which can describe the spatiotemporal progression of cerebral ischaemia and predict magnetic resonance observables including the apparent diffusion coefficient (ADC) of water and transverse relaxation time T(2). This is motivated by the sensitivity of the ADC to the location of cerebral ischaemia and T(2) to its time-course, and that it has thus far proven challenging to relate observations of changes in these MR parameters to stroke timing, which is of considerable importance in making treatment choices in clinics. Our mathematical model, called the cytotoxic oedema/dissociation (CED) model, is based on the transit of water from the extra- to the intra-cellular environment (cytotoxic oedema) and concomitant degradation of supramacromolecular and macromolecular structures (such as microtubules and the cytoskeleton). It explains experimental observations of ADC and T(2), as well as identifying the rate of spread of effects of ischaemia through a tissue as a dominant system parameter. The model brings the direct extraction of the timing of ischaemic stroke from quantitative MRI closer to reality, as well as providing insight on ischaemia pathology by imaging in general. We anticipate that this may improve patient access to thrombolytic treatment as a future application

Stroke onset time estimation from multispectral quantitative magnetic resonance imaging in a rat model of focal permanent cerebral ischaemia

Background Quantitative T2 relaxation magnetic resonance imaging allows estimation of stroke onset time. Aims We aimed to examine the accuracy of quantitative T1 and quantitative T2 relaxation times alone and in combination to provide estimates of stroke onset time in a rat model of permanent focal cerebral ischemia and map the spatial distribution of elevated quantitative T1 and quantitative T2 to assess tissue status. Methods Permanent middle cerebral artery occlusion was induced in Wistar rats. Animals were scanned at 9.4T for quantitative T1, quantitative T2, and Trace of Diffusion Tensor (Dav) up to 4 h post-middle cerebral artery occlusion. Time courses of differentials of quantitative T1 and quantitative T2 in ischemic and non-ischemic contralateral brain tissue (ΔT1, ΔT2) and volumes of tissue with elevated T1 and T2 relaxation times ( f1, f2) were determined. TTC staining was used to highlight permanent ischemic damage. Results ΔT1, ΔT2, f1, f2, and the volume of tissue with both elevated quantitative T1 and quantitative T2 (VOverlap) increased with time post-middle cerebral artery occlusion allowing stroke onset time to be estimated. VOverlap provided the most accurate estimate with an uncertainty of ±25 min. At all times-points regions with elevated relaxation times were smaller than areas with Dav defined ischemia. Conclusions Stroke onset time can be determined by quantitative T1 and quantitative T2 relaxation times and tissue volumes. Combining quantitative T1 and quantitative T2 provides the most accurate estimate and potentially identifies irreversibly damaged brain tissue. </jats:sec