16 research outputs found
Thermoelectric effects in a magnetic topological insulators
No full textReport of enhanced Seebeck effect in the antiferromagnetic topological insualtor MnBi2Te4 at high B field regim
Direct measurement of the local electrocaloric effect in 2D ferroelectric In 2 Se 3 by Scanning Electrocaloric Thermometry
No full textThe electrocaloric effect refers to the temperature change in a material when an electric field is applied or removed. Significant breakthroughs revealed its potential for solid-state cooling technologies in past decades. These devices offer a sustainable alternative to traditional vapor compression refrigeration, with advantages such as compactness, silent operation, and the absence of moving parts or refrigerants. Electrocaloric effects are typically studied using indirect methods using polarization data, and which suffer from inaccuracies related to assumptions about heat capacity. Direct methods, although more precise, require device fabrication and face challenges in studying meso- or nanoscale systems, like 2D materials, and materials with non-uniform polarization textures where high spatial resolution is required. In this study, a novel technique, Scanning Electrocaloric Thermometry, is introduced for characterizing the local electrocaloric effect in nanomaterials. This approach achieves high spatial resolution by locally applying electric fields and by simultaneously measuring the resulting temperature change. By employing AC excitation, the measurement sensitivity is further enhanced and the electrocaloric effect is disentangled from other heating mechanisms such as Joule heating and dielectric losses. The effectiveness of the method is demonstrated by examining electrocaloric and heat dissipation phenomena in two-dimensional In2Se3micrometer-sized flakes
Imaging the electrocaloric effect at the nanoscale
No full textThe electrocaloric effect (ECE) refers to the temperature change in a material when an electric field is applied or removed. Significant breakthroughs revealed its potential for solidstate cooling technologies in past decades. Electrocaloric effects are typically studied using indirect methods using polarization data, and which suffer from inaccuracies related to assumptions about heat capacity. Direct methods, although more precise, require device fabrication and face challenges in studying meso- or nanoscale systems, like 2D materials, and materials with non-uniform polarization textures where high spatial resolution is required. A novel technique, Scanning Electrocaloric Thermometry, is introduced for characterizing the local electrocaloric effect in nanomaterials. This approach achieves high spatial resolution by locally applying electric fields and by simultaneously measuring the resulting temperature change, as shown in Figure 1. By employing AC excitation, the measurement sensitivity is further enhanced and the electrocaloric effect is disentangled from other heating mechanisms such as Joule heating and dielectric losses. These losses appear at the first and third harmonic of the signal while the ECE dominates in the second harmonic, as shown at Figure 2. The effectiveness of the method is demonstrated by examining the local electrocaloric effect in two-dimensional In2Se3 μ-sized flakes
Quantum heat under the microscope: a perspective on cryogenic scanning thermal microscopy
No full textExploring thermal transport at cryogenic temperatures presents both significant challenges and valuable insights. By uncovering the thermal counterpart of well-known quantum phenomena, researchers investigated fascinating phenomena ranging from the violation of the Wiedemann–Franz law to the quantisation of phonons. One key frontier remains : no existing method can image local heat transport at the nanoscale under cryogenic conditions. In this Perspective, we review the current state of the art of local heat transport characterisation techniques and highlight their limitations. As a motivation for the development of cryogenic Scanning Thermal Microscopy, we provide five case studies illustrating how this approach could deepen our understanding of exotic quantum phases and enable the emergence of transformative technologies
IMCN PhD Day - Electrocaloric effect at the nanoscale
No full textThe electrocaloric effect (ECE) refers to the temperature change in a material when an electric field is applied or removed. Significant breakthroughs revealed its potential for solid-state cooling technologies in past decades. Electrocaloric effects are typically studied using indirect methods using polarization data, and which suffer from inaccuracies related to assumptions about heat capacity. Direct methods, although more precise, require device fabrication and face challenges in studying meso- or nanoscale systems, like 2D materials, and materials with non-uniform polarization textures where high spatial resolution is required. A novel technique, Scanning Electrocaloric Thermometry, is introduced for characterizing the local electrocaloric effect in nanomaterials. This approach achieves high spatial resolution by locally applying electric fields and by simultaneously measuring the resulting temperature change, as shown in Figure 1. By employing AC excitation, the measurement sensitivity is further enhanced and the electrocaloric effect is disentangled from other heating mechanisms such as Joule heating and dielectric losses. These losses appear at the first and third harmonic of the signal while the ECE dominates in the second harmonic, as shown at Figure 2. The effectiveness of the method is demonstrated by examining the local electrocaloric effect in two-dimensional In2Se3 μ-sized flakes
The trade-off between accuracy and accessibility of syphilis screening assays.
No full textThe availability of rapid and sensitive methods to diagnose syphilis facilitates screening of pregnant women, which is one of the most cost-effective health interventions available. We have evaluated two screening methods in Tanzania: an enzyme immunoassay (EIA), and a point-of-care test (POCT). We evaluated the performance of each test against the Treponema pallidum particle agglutination assay (TPPA) as the reference method, and the accessibility of testing in a rural district of Tanzania. The POCT was performed in the clinic on whole blood, while the other assays were performed on plasma in the laboratory. Samples were also tested by the rapid plasma Reagin (RPR) test. With TPPA as reference assay, the sensitivity and specificity of EIA were 95.3% and 97.8%, and of the POCT were 59.6% and 99.4% respectively. The sensitivity of the POCT and EIA for active syphilis cases (TPPA positive and RPR titer ≥ 1/8) were 82% and 100% respectively. Only 15% of antenatal clinic attenders in this district visited a health facility with a laboratory capable of performing the EIA. Although it is less sensitive than EIA, its greater accessibility, and the fact that treatment can be given on the same day, means that the use of POCT would result in a higher proportion of women with syphilis receiving treatment than with the EIA in this district of Tanzania
Characterization of heat transfer in 3D CMOS structures using Sideband Scanning Thermal Wave Microscopy
No full textEfficient thermal management is critical for cryogenic CMOS circuits, where local heating can compromise device performance and qubit coherence. Understanding heat flow at the nanoscale in these multilayer architectures requires localized, high-resolution thermal probing techniques capable of accessing buried structures. Here, we introduce a sideband thermal wave detection scheme for Scanning Thermal Microscopy, S-STWM, to probe deeply buried heater structures within CMOS dies. By extracting the phase of propagating thermal waves, this method provides spatially resolved insight into heat dissipation pathways through complex multilayer structures. Our approach enables quantitative evaluation of thermal management strategies, informs the design of cryo-CMOS circuits, and establishes a foundation for in situ thermal characterization under cryogenic operating conditions
Probing thermoelectric effects in MnBi2Te4
No full textEarly results of thermoelectric transport in an intrinsic magnetic topological insulator. Magnetoresistance and longitudinal thermocurrent measurements were performed on an exfoliated MnBi2Te4 flake using a microfabricated heating platform at a base temperature of 8mK. These early results show a correlation between the intensity of the thermoeletric response and the magnetic state of the magnetic topological insulator
Bases biológicas para a domesticação de uma alga vermelha nativa de valor econômico : Chondracanthus teedei
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Biológicas, Programa de Pós-graduação em Biologia de Fungos, Algas e Plantas, Florianópolis, 2013O gênero Chondracanthus (Gigartinaceae, Rhodophyta) tem despertado interesse das indústrias produtoras de carragenana e do mercado de alimentação humana por seu grande potencial econômico. No Brasil o gênero possui quatro espécies, dentre as quais se destaca Chondracanthus teedei, pelo seu porte, distribuição e abundância. Tendo em vista que as populações naturais não são suficientes para suportar uma explotação econômica, a alternativa para viabilizar o aproveitamento deste recurso é por meio da maricultura. Por outro lado, um programa de maricultura só terá chances de êxito se apoiado em fundamentos sólidos sobre a biologia da espécie, de tal modo que permiti- se sua domesticação. Este trabalho tem como objetivo o desenvolvimento de bases biológicas para apoiar a maricultura desta espécie de alga marinha no litoral brasileiro. Nesta fase inicial estudamos: i. a liberação de meiósporos e mitósporos; ii. a germinação de ambos tipos de esporos e seu desenvolvimento até plantas adultas; iii. a taxa de crescimento de plântulas haploides e diploides; iv. a influência da temperatura no crescimento das plântulas e v. a análise do desempenho de progênies derivadas de meiose nas condições de cultivo que utilizamos. Como resultados destacamos: i. tanto carpósporos como tetrásporos apresentaram o padrão Dumontia de desenvolvimento, com o surgimento do eixo ereto cerca de 100 horas após a liberação do esporo; ii. a taxa de liberação de esporos por grama de talo com cistocarpos foi 68% superior em relação a talos com tetrasporângios; iii. a taxa de germinação foi superior nos carpósporos (32%) em relação aos tetrásporos (29%); iv. não há diferenças significativas entre as taxas de crescimento relativo (TCR) de plântulas derivadas de tetrásporos e carpósporos; v. as melhores TCR ocorreram a 25ºC para ambas as fases e vi. houve ampla variação na morfologia e nas TCRs das linhagens obtidas a partir de tetrásporos evidenciando recombinação genética independente e mostrando ser este o caminho para a obtenção de linhagens mais produtivas. Acreditamos que os resultados obtidos fornecem informações relevantes para futuros programas de maricultura de Chondracanthus teedei no litoral brasileiro, a serem complementados por ensaios de cultivo no mar. Abstract: Species of the red algal genus Chondracanthus (Gigartinaceae, Rhodophyta) have been considered a target for exploitation because of its importance as a source of raw material for the carrageenan industry as well as food industry as a sea vegetable. Chondracanthus is represented in Brazil by four species, among which C. teedei is of special interest in view of its size, distribution and abundance. As the natural population are not large enough to support a commercial explotation the alternative remains on its mariculture. However, it is well known that success in a sustainable and commercial cultivation of a natural resource can only be achieved if based on solid biotechnological background, that leads to the domestication of the targeted species. This study aims at developing basic knowledge of the biology of C. teedei to support the mariculture of this species on the Brazilian coast. In this first approach we studied: i. the release of mitospores and meiospores; ii. spore´s germination and development until adult thalli; iii. relative growth rates (GR) of haploid and diploid germlings; iv. GR performance under different temperatures and v. the performance of strains of plantlets derived from meiotic spores in vitro. Among the results we highlight: i. both, tetraspores and carpospores germinate following the same pattern described for the genus Dumontia; an erect shoot is produced after about 96 hours since spore´s release; ii. release of spores per gram (fresh) of thalli with cystocarps was 68% higher than thalli with tetrasporangial sori; iii. germination rates of spores was higher in carpospores (32%) than in tetraspores (29%); iv. on a total mean basis there was no significant differences among GR of plantlets derived from tetraspores and carpospores; v. higher GR for plantlets derived from both spores types occurred at 25Cº and vi. there was a high variability in the morphology, as well as GR, in plantlets derived from tetraspores, showing independent gene segregation. This high variability will provide the genetic basis for strain selection in order to pick up the best strains for higher productivity. We believe that these results are a contribution towards the establishment of a biotechnological basis for the mariculture of this potentially important species on the Brazilian coasts. A follow up of this project is to develop pilot assays in the sea
