Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTorsional refrigeration by twisted, coiled, and supercoiled fibers
94
0
0.0
(
0
)
Added by
Alexandre F. Fonseca
Publication date
2019
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Higher efficiency, lower cost refrigeration is needed for both large and small scale cooling. Refrigerators using entropy changes during cycles of stretching or hydrostatically compression of a solid are possible alternatives to the vapor-compression fridges found in homes. We show that high cooling results from twist changes for twisted, coiled, or supercoiled fibers, including those of natural rubber, NiTi, and polyethylene fishing line. By using opposite chiralities of twist and coiling, supercoiled natural rubber fibers and coiled fishing line fibers result that cool when stretched. A demonstrated twist-based device for cooling flowing water provides a high cooling energy and device efficiency. Theory describes the axial and spring index dependencies of twist-enhanced cooling and its origin in a phase transformation for polyethylene fibers.
rate research
Read More
The buckling and twisting of slender, elastic fibers is a deep and well-studied field. A slender elastic rod that is twisted with respect to a fixed end will spontaneously form a loop, or hockle, to relieve the torsional stress that builds. Further twisting results in the formation of plectonemes -- a helical excursion in the fiber that extends with additional twisting. Here we use an idealized, micron-scale experiment to investigate the energy stored, and subsequently released, by hockles and plectonemes as they are pulled apart, in analogy with force spectroscopy studies of DNA and protein folding. Hysteresis loops in the snapping and unsnapping inform the stored energy in the twisted fiber structures.
We have characterized the conductivity of carbon nanotubes (CNT) fibers enriched in semiconducting species as a function of temperature and pulsed laser irradiation of 266 nm wavelength. While at high temperatures the response approaches an Arrhenius law behavior, from room temperature down to 4.2 K the response can be framed, quantitatively, within the predictions of the fluctuation induced tunneling which occurs between the inner fibrils (bundles) of the samples and/or the elementary CNTs constituting the fibers. Laser irradiation induces an enhancement of the conductivity, and analysis of the resulting data confirms the (exponential) dependence of the potential barrier upon temperature as expected from the fluctuation induced tunneling model. A thermal map of the experimental configuration consisting of laser-irradiated fibers is also obtained via COMSOL simulations in order to rule out bare heating phenomena as the background of our experiments. (*) Author
NADH is a key biomolecule involved in many biocatalytic processes as cofactor and its quantification can be correlated to specific enzymatic activity. Many efforts have been taken to obtain clean electrochemical signals related to NADH presence and lower its redox overpotential to avoid interferences. Suppression of background and secondary signals can be achieved by including a switchable electroactive surface, for instance, by using semiconductors able to harvest light energy and drive the excited electrons only when irradiated. Here we present the combination of a n-type Si semiconductor with fibers made of carbon nanotubes as electroactive surface for NADH quantification at low potentials only upon irradiation. The resulting photoelectrode responded linearly to NADH concentrations from 50 {mu} M to 1.6 mM with high sensitivity (54 $mu$ A cm$^{-2}$ mM${-1}$). This system may serve as a biosensing platform for detection and quantification of dehydrogenases activity.
Atomically thin transition metal dichalcogenides are highly promising for integrated optoelectronic and photonic systems due to their exciton-driven linear and nonlinear interaction with light. Integrating them into optical fibers yields novel opportunities in optical communication, remote sensing, and all-fiber optoelectronics. However, scalable and reproducible deposition of high quality monolayers on optical fibers is a challenge. Here, we report the chemical vapor deposition of monolayer MoS2 and WS2 crystals on the core of microstructured exposed core optical fibers and their interaction with the fibers guided modes. We demonstrate two distinct application possibilities of 2D-functionalized waveguides to exemplify their potential. First, we simultaneously excite and collect excitonic 2D material photoluminescence with the fiber modes, opening a novel route to remote sensing. Then we show that third harmonic generation is modified by the highly localized nonlinear polarization of the monolayers, yielding a new avenue to tailor nonlinear optical processes in fibers. We anticipate that our results may lead to significant advances in optical fiber based technologies.
Colloidal quantum dots (cQDs) are now a mature nanomaterial with optical properties customizable through varying size and composition. However, their use in optical devices is limited as they are not widely available in convenient forms such as optical fibers. With advances in polymerization methods incorporating nanocrystals, nanocomposite materials suitable for processing into high quality hybrid active fibers can be achieved. We demonstrate a plastic optical fiber fabrication method which ensures homogeneous dispersion of cQDs within a polymer core matrix. Loading concentrations between 10$^{11}$-10$^{13}$ CdSe/CdS cQDs per cm$^{3}$ in polystyrene were electronically imaged, confirming only sporadic sub-wavelength aggregates. Rayleigh scattering losses are therefore dominant at energies below the semiconductors band gap, but are overtaken by a sharp CdS-related absorption onset around 525 nm facilitating cQD excitation. The redshifted photoluminescence emission is then minimally reabsorbed along the fiber with a spectrum barely affected by the polymerization and a quantum yield staying at $sim$65$%$ of its initial value. The latter, along with the glass transition temperature and refractive index, is independent of the cQD concentration hence yielding a proportionally increasing light output. Our cQD-doped fibers are photostable to within 5$%$ over days showing great promise for functional material applications.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
