Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 105
Filtrar
1.
Opt Express ; 29(22): 35161-35171, 2021 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-34808955

RESUMO

We have designed a method of harvesting electrical energy using plasmon-enhanced light pressure. A device was fabricated as a cut cone structure that optimizes light collection so that the weak incident light pressure can be sufficiently enhanced inside the cut cone to generate electrical energy. An increase in the device's current output is a strong indication that the pressure of incident light has been enhanced by the surface plasmons on a platinum layer inside the cut cone. The electrical energy harvested in a few minutes by irradiating pulsed laser light on a single micro device was possible to illuminate a blue LED.

2.
ACS Photonics ; 8(9): 2699-2704, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34557568

RESUMO

The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nanolasers. While nonresonantly pumped lasing from all-inorganic lead-halide perovskites is now well-established as an attractive pathway to scalable low-power laser sources for nano-optoelectronics, here we showcase a resonant optical pumping scheme on a fast triplet-state in CsPbBr3 nanocrystals. The scheme allows us to realize a polarized triplet-laser source that dramatically enhances the coherent signal by 1 order of magnitude while suppressing noncoherent contributions. The result is a source with highly attractive technological characteristics, including a bright and polarized signal and a high stimulated-to-spontaneous emission signal contrast that can be filtered to enhance spectral purity. The emission is generated by pumping selectively on a weakly confined excitonic state with a Bohr radius ∼10 nm in the nanocrystals. The exciton fine-structure is revealed by the energy-splitting resulting from confinement in nanocrystals with tetragonal symmetry. We use a linear polarizer to resolve 2-fold nondegenerate sublevels in the triplet exciton and use photoluminescence excitation spectroscopy to determine the energy of the state before pumping it resonantly.

3.
Nano Lett ; 21(12): 5217-5224, 2021 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-34086468

RESUMO

Crystallographic point defects (PDs) can dramatically decrease the efficiency of optoelectronic semiconductor devices, many of which are based on quantum well (QW) heterostructures. However, spatially resolving individual nonradiative PDs buried in such QWs has so far not been demonstrated. Here, using high-resolution cathodoluminescence (CL) and a specific sample design, we spatially resolve, image, and analyze nonradiative PDs in InGaN/GaN QWs at the nanoscale. We identify two different types of PDs by their contrasting behavior with temperature and measure their densities from 1014 cm-3 to as high as 1016 cm-3. Our CL images clearly illustrate the interplay between PDs and carrier dynamics in the well: increasing PD concentration severely limits carrier diffusion lengths, while a higher carrier density suppresses the nonradiative behavior of PDs. The results in this study are readily interpreted directly from CL images and represent a significant advancement in nanoscale PD analysis.

4.
Biomicrofluidics ; 15(1): 014111, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33643513

RESUMO

The need for cell and particle sorting in human health care and biotechnology applications is undeniable. Inertial microfluidics has proven to be an effective cell and particle sorting technology in many of these applications. Still, only a limited understanding of the underlying physics of particle migration is currently available due to the complex inertial and impact forces arising from particle-particle and particle-wall interactions. Thus, even though it would likely enable significant advances in the field, very few studies have tried to simulate particle-laden flows in inertial microfluidic devices. To address this, this study proposes new codes (solved in OpenFOAM software) that capture all the salient inertial forces, including the four-way coupling between the conveying fluid and the suspended particles traveling a spiral microchannel. Additionally, these simulations are relatively (computationally) inexpensive since the arbitrary Lagrangian-Eulerian formulation allows the fluid elements to be much larger than the particles. In this study, simulations were conducted for two different spiral microchannel cross sections (e.g., rectangular and trapezoidal) for comparison against previously published experimental results. The results indicate good agreement with experiments in terms of (monodisperse) particle focusing positions, and the codes can readily be extended to simulate two different particle types. This new numerical approach is significant because it opens the door to rapid geometric and flow rate optimization in order to improve the efficiency and purity of cell and particle sorting in biotechnology applications.

5.
Sci Total Environ ; 767: 144181, 2021 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-33450590

RESUMO

Ultra-low pressure gravity-driven membrane (GDM) systems have the potential to be significantly less costly and complex than conventional membranes for water treatment applications. To build upon this inherent advantage, this study assesses the reuse of recycled membranes in GDM systems for producing drinking water. Two reverse osmosis spiral-wound modules were recycled into nanofiltration (NF)-like and ultrafiltration (UF)-like membranes via controlled exposure to free chlorine. To operate the recycled membranes, two housing devices, based on a simple fitting and an advanced end-caps design, were developed. The recycled membrane systems were tested under a range of conditions (submerged vs. external system configuration and continuous vs. intermittent filtration mode). Synthetic river water feed solutions were used in the tests where performance, fouling, and clogging were measured. NF-like recycled membranes resulted in poor salt rejection and low permeability (~1.7 L m-2 h-1 bar-1), but also in high rejection (>81%) of dissolved organic carbon. UF-like recycled membranes maintained their capacity to reject biopolymers (BP) (>74%) and featured up to 18-fold higher permeate rate than NF-like recycled membranes. The optimized operating conditions were found when the recycled membranes were housed in the end-caps device and operated intermittently (relaxation time plus forward flushing). Flushing reduced the fouling accumulation inside the membrane (only 12% and 40% of BP accumulation was observed in the NF-like and UF-like, respectively). However, the end-caps-based device was estimated to be more expensive during the economic analysis. To address this techno-economic trade-off, a decision-making tree was developed to select the appropriate configuration based upon the implementation context. Overall, this study concludes that these designs can serve as robust, low-cost (water production cost <1 USD ct. yr. L-1), and light-weight GDM alternatives. This study is beneficial for developing compact GDM systems based on recycled spiral-wound membranes for both rural areas and emergency response.

6.
Biomicrofluidics ; 14(6): 064106, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-33269035

RESUMO

A hydrocyclone is a macroscale separation device employed in various industries, with many advantages, including high-throughput and low operational costs. Translating these advantages to microscale has been a challenge due to the microscale fabrication limitations that can be surmounted using 3D printing technology. Additionally, it is difficult to simulate the performance of real 3D-printed micro-hydrocyclones because of turbulent eddies and the deviations from the design due to printing resolution. To address these issues, we propose a new experimental method for the direct observation of particle motion in 3D printed micro-hydrocyclones. To do so, wax 3D printing and soft lithography were used in combination to construct a transparent micro-hydrocyclone in a single block of polydimethylsiloxane. A high-speed camera and fluorescent particles were employed to obtain clear in situ images and to confirm the presence of the vortex core. To showcase the use of this method, we demonstrate that a well-designed device can achieve a 95% separation efficiency for a sample containing a mixture of (desired) stem cells and (undesired) microcarriers. Overall, we hope that the proposed method for the direct visualization of particle trajectories in micro-hydrocyclones will serve as a tool, which can be leveraged to accelerate the development of micro-hydrocyclones for biomedical applications.

7.
Light Sci Appl ; 9: 100, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32566170

RESUMO

We find that the emission from laterally coupled quantum dots is strongly polarized along the coupled direction [1 1 ¯ 0], and its polarization anisotropy can be shaped by changing the orientation of the polarized excitation. When the nonresonant excitation is linearly polarized perpendicular to the coupled direction [110], excitons (X1 and X2) and local biexcitons (X1X1 and X2X2) from the two separate quantum dots (QD1 and QD2) show emission anisotropy with a small degree of polarization (10%). On the other hand, when the excitation polarization is parallel to the coupled direction [1 1 ¯ 0], the polarization anisotropy of excitons, local biexcitons, and coupled biexcitons (X1X2) is enhanced with a degree of polarization of 74%. We also observed a consistent anisotropy in the time-resolved photoluminescence. The decay rate of the polarized photoluminescence intensity along the coupled direction is relatively high, but the anisotropic decay rate can be modified by changing the orientation of the polarized excitation. An energy difference is also observed between the polarized emission spectra parallel and perpendicular to the coupled direction, and it increases by up to three times by changing the excitation polarization orientation from [110] to [1 1 ¯ 0]. These results suggest that the dipole-dipole interaction across the two separate quantum dots is mediated and that the anisotropic wavefunctions of the excitons and biexcitons are shaped by the excitation polarization.

8.
IEEE Rev Biomed Eng ; 13: 261-279, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31395552

RESUMO

Globally, around 2.6 million people receive renal replacement therapy (RRT), and a further 4.9-9.7 million people need, but do not have access to, RRT [1]. The next generation RRT devices will certainly be in demand due to the increasing occurrence of diabetes, atherosclerosis and the growing population of older citizens. This review provides a comprehensive, yet concise overview of the cleared and remaining hurdles in the development of artificial kidneys to move beyond traditional dialysis technology-the current baseline of renal failure treatment. It compares and contrasts the state-of-the-art in 'cell-based' and 'non-cell-based' approaches. Based on this study, a new engineering perspective on the future of artificial kidneys is described. This review suggests that stem-cell-based artificial kidneys represent a long-term, complete solution but it can take years of development due to the limitations of current cell seeding technology, viability and complicated behaviour control. Alternatively, there is much potential for near- and medium- term solutions with the development of non-cell-based wearable and implantable devices to support current therapies. Based on recent fundamental advances in microfluidics, membranes and related research, it may be possible to integrate these technologies to enable implantable artificial kidneys (iAK) in the near future.


Assuntos
Rins Artificiais , Membranas Artificiais , Microfluídica , Animais , Humanos , Ratos , Terapia de Substituição Renal
9.
Nat Commun ; 10(1): 4421, 2019 09 27.
Artigo em Inglês | MEDLINE | ID: mdl-31562317

RESUMO

Photocatalytic water splitting is attracting enormous interest for the storage of solar energy but no practical method has yet been identified. In the past decades, various systems have been developed but most of them suffer from low activities, a narrow range of absorption and poor quantum efficiencies (Q.E.) due to fast recombination of charge carriers. Here we report a dramatic suppression of electron-hole pair recombination on the surface of N-doped TiO2 based nanocatalysts under enhanced concentrations of H+ and OH-, and local electric field polarization of a MgO (111) support during photolysis of water at elevated temperatures. Thus, a broad optical absorption is seen, producing O2 and H2 in a 1:2 molar ratio with a H2 evolution rate of over 11,000 µmol g-1 h-1 without any sacrificial reagents at 270 °C. An exceptional range of Q.E. from 81.8% at 437 nm to 3.2% at 1000 nm is also reported.

10.
Biomicrofluidics ; 13(3): 034117, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31431813

RESUMO

Inertial microfluidics represents a powerful new tool for accurately positioning cells and microparticles within fluids for a variety of biomedical, clinical, and industrial applications. In spite of enormous advancements in the science and design of these devices, particularly in curved microfluidic channels, contradictory experimental results have confounded researchers and limited progress. Thus, at present, a complete theory which describes the underlying physics is lacking. We propose that this bottleneck is due to one simple mistaken assumption-the locations of inflection points of the Dean velocity profile in curved microchannels are not fixed, but can actually shift with the flow rate. Herein, we propose that the dynamic distance (δ) between the real equilibrium positions and their nearest inflection points can clearly explain several (previously) unexplained phenomena in inertial microfluidic systems. More interestingly, we found that this parameter, δ, is a function of several geometric and operational parameters, all of which are investigated (in detail) here with a series of experiments and simulations of different spiral microchannels. This key piece of understanding is expected to open the door for researchers to develop new and more effective inertial microfluidic designs.

11.
Biomicrofluidics ; 13(3): 034118, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31431814

RESUMO

Curved microchannels allow controllable microparticle focusing, but a full understanding of particle behavior has been limited-even for simple rectangular and trapezoidal shapes. At present, most microfluidic particle separation literature is dedicated to adding "internal" complexity (via sheath flow or obstructions) to relatively simple cross-sectional channel shapes. We propose that, with sufficient understanding of particle behavior, an equally viable pathway for microparticle focusing could utilize complex "external" cross-sectional shapes. By investigating three novel, complex spiral microchannels, we have found that it is possible to passively focus (6, 10, and 13 µm) microparticles in the middle of a convex channel. Also, we found that in concave and jagged channel designs, it is possible to create multiple, tight focusing bands. In addition to these performance benefits, we report an "additive rule" herein, which states that complex channels can be considered as multiple, independent, simple cross-sectional shapes. We show with experimental and numerical analysis that this new additive rule can accurately predict particle behavior in complex cross-sectional shaped channels and that it can help to extract general inertial focusing tendencies for suspended particles in curved channels. Overall, this work provides simple, yet reliable, guidelines for the design of advanced curved microchannel cross sections.

12.
ACS Sens ; 4(8): 2181-2189, 2019 08 23.
Artigo em Inglês | MEDLINE | ID: mdl-31321976

RESUMO

Multiplexed analysis of biochemical analytes such as proteins, enzymes, and immune products using a microfluidic device has the potential to cut assay time, reduce sample volume, realize high-throughput, and decrease experimental error without compromising sensitivity. Despite these huge benefits, the need for expensive specialized equipment and the complex photolithography fabrication process for the multiplexed devices have, to date, prevented widespread adoption of microfluidic systems. Here, we present a simple method to fabricate a new microfluidic-based multiplexed biosensing device by taking advantage of 3D-printing. The device is an integration of normally closed (NC) microfluidic valving units which offer superior operational flexibility by using PDMS membrane (E ∼ 1-2 MPa) and require minimized energy input (1-5 kPa). To systematically engineer the device, we first report on the geometrical and operational analysis of a single 3D-printed valving unit. Based on the characterization, we introduce a full prototype multiplexed chip comprising several microfluidic valves. The prototype offers-for the first time in a 3D-printed microfluidic device-the capability of on-demand performce of both a sequential and a parallel biochemical assay. As a proof of concept, our device has been used to simultaneously measure the apoptotic activity of 5 different members of the caspase protease enzyme family. In summary, the 3D-printed valving system showcased in this study overcomes traditional bottlenecks of microfabrication, enabling a new class of sophisticated liquid manipulation required in performing multiplexed sensing for biochemical assays.


Assuntos
Apoptose , Técnicas Biossensoriais , Técnicas Eletroquímicas , Técnicas Analíticas Microfluídicas , Impressão Tridimensional , Técnicas Biossensoriais/instrumentação , Técnicas Eletroquímicas/instrumentação , Humanos , Células Jurkat , Técnicas Analíticas Microfluídicas/instrumentação , Impressão Tridimensional/instrumentação
13.
Chem Commun (Camb) ; 55(30): 4415-4418, 2019 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-30916081

RESUMO

The high activity of nanocrystallites is commonly attributed to the terminal high-energy facets. However, we demonstrate that the high activity of the anatase TiO2(001) facet in photocatalytic H2 evolution is not due to its high intrinsic surface energy, but local electronic effects created by surface features on the facet.

14.
Vet Surg ; 48(3): 388-400, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30758853

RESUMO

OBJECTIVE: Identify relevant electromyography (EMG), kinematic, and kinetic changes resulting from monopolar radiofrequency energy (MRFE)-induced cranial cruciate ligament (CCL) injury and eventual rupture in dogs. STUDY DESIGN: Experimental, repeated measures. ANIMALS: Five purpose-bred female dogs free of orthopedic and neurologic disease. METHODS: Surface EMG, joint kinematics, and ground reaction forces were assessed at a trot in the pelvic limbs at baseline, at 2 and 4 weeks after unilateral MRFE-induced CCL injury, and at 4, 8, and 16 weeks after CCL rupture (CCLR). RESULTS: After MRFE-induced injury, average hip joint range of motion (ROM) during stance decreased within the untreated pelvic limb. After CCLR, stifle flexion angles decreased within the treated limb at 8 weeks and within the untreated pelvic limb at all time points, whereas average tarsal joint ROM decreased in the treated limb and increased in the untreated limb. Peak vertical ground reaction force and impulse decreased within the treated limb. Qualitative alterations of many EMG values were noted after MRFE-induced injury and CCLR, although significant differences between limbs or from baseline values were not detected. CONCLUSION: Monopolar radiofrequency energy-induced injury altered contralateral hip kinematics, suggesting early regional compensatory gait alterations. After CCLR, additional compensatory gait patterns occurred in both pelvic limbs. CLINICAL IMPACT: The qualitative analysis of trial-averaged EMG data in this small population supports a relationship between neuromuscular function and induced CCL injury leading to rupture.


Assuntos
Lesões do Ligamento Cruzado Anterior/veterinária , Ligamento Cruzado Anterior/patologia , Doenças do Cão/patologia , Marcha , Joelho de Quadrúpedes/lesões , Animais , Lesões do Ligamento Cruzado Anterior/patologia , Lesões do Ligamento Cruzado Anterior/fisiopatologia , Fenômenos Biomecânicos , Doenças do Cão/fisiopatologia , Cães , Eletromiografia/veterinária , Feminino , Masculino , Projetos Piloto , Amplitude de Movimento Articular , Ruptura/veterinária , Articulações Tarsianas/patologia
15.
Nano Lett ; 18(10): 6188-6194, 2018 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-30223652

RESUMO

We found that optical Aharonov-Bohm oscillations in a single GaAs/GaAlAs quantum ring can be controlled by excitation intensity. With a weak excitation intensity of 1.2 kW cm-2, the optical Aharonov-Bohm oscillation period of biexcitons was observed to be half that of excitons in accordance with the period expected for a two-exciton Wigner molecule. When the excitation intensity is increased by an order of magnitude (12 kW cm-2), a gradual deviation of the Wigner molecule condition occurs with decreased oscillation periods and diamagnetic coefficients for both excitons and biexcitons along with a spectral shift. These results suggest that the effective orbit radii and rim widths of electrons and holes in a single quantum ring can be modified by light intensity via photoexcited carriers, which are possibly trapped at interface defects resulting in a local electric field.

16.
Water Res ; 144: 642-655, 2018 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-30096690

RESUMO

The consumption of saline groundwater has contributed to a growing incidence of renal diseases, particularly in coastal communities of India. Although reverse osmosis (RO) is routinely used to remove salt from groundwater, conventional RO systems (i.e. centralized systems using spiral wound RO elements) have limited utility in these communities due to high capital and maintenances costs, and lack of infrastructure to distribute the water. Consequently, there is a need to develop an appropriate solution for groundwater treatment based on small-scale, mobile and community-led systems. In this work, we designed a mobile desalination system to provide a simple platform for water treatment and delivery of goods to rural communities. The system employs tubular RO membranes packed in a single, low-profile vessel which fits below the cargo space. The low-profile enables minimal intrusion on the space available for the transportation of goods. Pressure is delivered by a belt driven clutch pump, powered by the engine. Water is treated locally by connecting the intake to the village well while the vehicle idles. A combined numerical and experimental approach was used to optimise the module/system design, resulting in ∼20% permeate flux enhancement. Experimental results revealed that the system can produce 16 L per square meter of membrane area per hour (LMH) at a salinity level of 80 ppm from a ∼2000 ppm groundwater when it is feed at 1 m3/h at 8 bars. This indicates that a vehicle equipped with 12 m2 of tubular RO membranes can deliver 1 m3 of drinkable water by using ∼0.9 L of diesel. Assuming eight such systems could be implemented in a community to fulfil the water demands for a village with 2000 residents, a social business study revealed that a payback time of 2.5 years is achievable, even if the sale price of the water is relatively low, USD 0.18 (Rs 12, which is half of the lowest market price) per 20 L, including providing a goods transportation service at price of USD 5.25 (Rs 350) per 100 km.


Assuntos
Água Subterrânea , Purificação da Água , Humanos , Índia , Membranas Artificiais , Osmose , População Rural
17.
Sci Rep ; 8(1): 8124, 2018 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-29802300

RESUMO

We have investigated the emission from InGaN/GaN quantum disks grown on the tip of GaN nanorods. The emission at 3.21 eV from the InGaN quantum disk doesn't show a Stark shift, and it is linearly polarized when excited perpendicular to the growth direction. The degree of linear polarization is about 39.3% due to the anisotropy of the nanostructures. In order to characterize a single nanostructure, the quantum disks were dispersed on a SiO2 substrate patterned with a metal reference grid. By rotating the excitation polarization angle from parallel to perpendicular relative to the nanorods, the variation of overall PL for the 3.21 eV peak was recorded and it clearly showed the degree of linear polarization (DLP) of 51.5%.

18.
Sci Rep ; 8(1): 5380, 2018 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-29599429

RESUMO

Photoluminescence measurements in mono- and bilayer-MoS2 on SiO2 were undertaken to determine the thermal effect of the MoS2/SiO2 interface on the optical bandgap. The energy and intensity of the photoluminescence from monolayer MoS2 were lower and weaker than those from bilayer MoS2 at low temperatures, whilst the opposite was true at high temperatures above 200 K. Density functional theory calculations suggest that the observed optical bandgap crossover is caused by a weaker substrate coupling to the bilayer than to the monolayer.

19.
Bioresour Technol ; 252: 91-99, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29306136

RESUMO

Microalgae represent the most promising new source of biomass for the world's growing demands. However, the biomass productivity and quality is significantly decreased by the presence of bacteria or other invading microalgae species in the cultures. We therefore report a low-cost spiral-microchannel that can effectively separate and purify Tetraselmis suecica (lipid-rich microalgae) cultures from Phaeodactylum tricornutum (invasive diatom). Fluorescent polystyrene-microbeads of 6 µm and 10 µm diameters were first used as surrogate particles to optimize the microchannel design by mimicking the microalgae cell behaviour. Using the optimum flowrate, up to 95% of the P. tricornutum cells were separated from the culture without affecting the cell viability. This study shows, for the first time, the potential of inertial microfluidics to sort microalgae species with minimal size difference. Additionally, this approach can also be applied as a pre-sorting technique for water quality analysis.


Assuntos
Microalgas , Microfluídica , Biomassa , Clorófitas , Diatomáceas
20.
Opt Express ; 26(24): 32332-32345, 2018 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-30650694

RESUMO

We present experimental and numerical investigations of photonic molecules obtained from laser patterned SU-8 photoresist strips on photonic crystal waveguides. Properties of cavities defined by a single strip are investigated and we show that two adjacent strips on a waveguide form a pair of optically coupled cavities. Simulation results and micro-photoluminescence mapping measurements demonstrate that the coupling strength is tunable by controlling the separation between the strips. Confocal mapping with decoupled collection and excitation points is used to explicitly show coupling between two cavities of a photonic molecule.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...