Semitransparent thermophotovoltaics for efficient utilization of moderate temperature thermal radiation.

Recent advances in thermophotovoltaic (TPV) power generation have produced notable gains in efficiency, particularly at very high emitter temperatures. However, there remains substantial room for improving TPV conversion of waste, solar, and nuclear heat streams at temperatures below 1,100°C. Here, we demonstrate the concept of transmissive spectral control that enables efficient recuperation of below-bandgap photons by allowing them to transmit through the cell to be absorbed by a secondary emitter. We fabricate a semitransparent TPV cell consisting of a thin InGaAs-InP heterojunction membrane supported by an infrared-transparent heat-conducting substrate. The device absorbs less than 1% of below-bandgap radiation, resulting in a TPV efficiency of 32.5% at an emitter temperature of 1,036°C. To our knowledge, this represents an 8% absolute improvement (~33% relative) in efficiency relative to the best TPV devices at such low temperatures. By enabling near-zero photon loss, the semitransparent architecture facilitates high TPV efficiencies over a wide range of applications.

Near-perfect photon utilization in an air-bridge thermophotovoltaic cell.

Thermophotovoltaic cells are similar to solar cells, but instead of converting solar radiation to electricity, they are designed to utilize locally radiated heat. Development of high-efficiency thermophotovoltaic cells has the potential to enable widespread applications in grid-scale thermal energy storage1,2, direct solar energy conversion3-8, distributed co-generation9-11 and waste heat scavenging12. To reach high efficiencies, thermophotovoltaic cells must utilize the broad spectrum of a radiative thermal source. However, most thermal radiation is in a low-energy wavelength range that cannot be used to excite electronic transitions and generate electricity. One promising way to overcome this challenge is to have low-energy photons reflected and re-absorbed by the thermal emitter, where their energy can have another chance at contributing towards photogeneration in the cell. However, current methods for photon recuperation are limited by insufficient bandwidth or parasitic absorption, resulting in large efficiency losses relative to theoretical limits. Here we demonstrate near-perfect reflection of low-energy photons by embedding a layer of air (an air bridge) within a thin-film In0.53Ga0.47As cell. This result represents a fourfold reduction in parasitic absorption relative to existing thermophotovoltaic cells. The resulting gain in absolute efficiency exceeds 6 per cent, leading to a very high power conversion efficiency of more than 30 per cent, as measured with an approximately 1,455-kelvin silicon carbide emitter. As the out-of-band reflectance approaches unity, the thermophotovoltaic efficiency becomes nearly insensitive to increasing cell bandgap or decreasing emitter temperature. Accessing this regime may unlock a range of possible materials and heat sources that were previously inaccessible to thermophotovoltaic energy conversion.

Design of thermophotovoltaics for tolerance of parasitic absorption.

With advances in thermophotovoltaic (TPV) cells enabling recycling of sub-bandgap photons, a key barrier to reaching high prototype efficiencies has become radiative losses to parasitic high-emissivity regions, such as heavily doped contact regions, defects in coatings, and inactive areas. Here, we examine the impact of such radiative losses on the performance of various candidate cell materials, including GaAs, Si, InGaAsP, InGaAs, GaSb, and InGaAsSb. The ability of a TPV design to resist this performance loss is termed "radiation-sink tolerance" (RST). We show that RST is directly proportional to the spectral overlap between the absorptance profile of the cell and the emission profile of the emitter, which can be improved by adding a lower-bandgap absorber, increasing the emitter temperature, and utilizing a selective emitter. Our RST expressions can be used to estimate the efficiency of a prototypical TPV generator based on a component-level measurement.

Simple and inexpensive micromachined aluminum microfluidic devices for acoustic focusing of particles and cells.

We introduce a new method to construct microfluidic devices especially useful for bulk acoustic wave (BAW)-based manipulation of cells and microparticles. To obtain efficient acoustic focusing, BAW devices require materials that have high acoustic impedance mismatch relative to the medium in which the cells/microparticles are suspended and materials with a high-quality factor. To date, silicon and glass have been the materials of choice for BAW-based acoustofluidic channel fabrication. Silicon- and glass-based fabrication is typically performed in clean room facilities, generates hazardous waste, and can take several hours to complete the microfabrication. To address some of the drawbacks in fabricating conventional BAW devices, we explored a new approach by micromachining microfluidic channels in aluminum substrates. Additionally, we demonstrate plasma bonding of poly(dimethylsiloxane) (PDMS) onto micromachined aluminum substrates. Our goal was to achieve an approach that is both low cost and effective in BAW applications. To this end, we micromachined aluminum 6061 plates and enclosed the systems with a thin PDMS cover layer. These aluminum/PDMS hybrid microfluidic devices use inexpensive materials and are simply constructed outside a clean room environment. Moreover, these devices demonstrate effectiveness in BAW applications as demonstrated by efficient acoustic focusing of polystyrene microspheres, bovine red blood cells, and Jurkat cells and the generation of multiple focused streams in flow-through systems. Graphical abstract The aluminum acoustofluidic device and the generation of multinode focusing of particles.

Metastatic type A thymoma: morphological and genetic correlation.

AIMS: The vast majority of type A thymomas are diagnosed in tumour stages 1 or 2, and metastatic cases are exceedingly rare. The histological and genetic features of such metastatic type A thymomas have not been described in detail. METHODS AND RESULTS: Five metastatic type A thymomas in tumour stage Masaoka IVb that had been reviewed by a panel of expert pathologists were analysed using comparative genomic hybridization (CGH). Cases 1, 2 and 3 showed the prototypical morphology of type A thymomas with mainly solid growth patterns. These cases displayed only very subtle nuclear irregularities and slight nuclear crowding, but no other atypical features. Mitoses were absent. Cases 3 and 4, in contrast, had a distinctly atypical morphology. CGH revealed partially recurrent alterations in four cases (with and without atypical morphology), including gains on chromosome 1q (one case), 17q (two cases), chromosome 19 (three cases) and 22q (one case) and losses on chromosome 17p (two cases) and 22q (one case). CONCLUSION: Rare metastatic type A thymomas, both with typical and 'atypical' histological features, show partially recurrent genomic alterations that differ from the much more frequent localized and indolent tumours. The fact that these alterations were recurring points to a link between clinical behaviour and molecular features. Our findings may have implications for the management and treatment of such tumours.

[Recurrent seizures of unknown aetiology]. / Rezidivierende zerebrale Krampfanfälle unklarer Genese.

History and admission findings | A 41year old woman presented at our internistic clinic after treatment by an emergency doctor because of confusion and amnesia accompanied by a hypoglycaemic episode while driving her car. Only by giving continuous glucose intravenously a stable clinical state could be achieved. In her medical history she took Lamotrigin for 12 years since she had seizures of unknown aetiology. 16 years ago she had similar sudden attacks with confusion and hypoglycaemia. At that time thorough diagnostics at the clinic for internal medicine did not reveal any evidence for hyperinsulinaemia. While taking Lamotrigin the patient had no seizures or similar symptoms for 12 years. Treatment and course | In the present case we detected a tumor in the pancreas and a two-fold increased insulin secretion. Histopathological work-up of the removed tissue confirmed the suspected diagnosis of insulinoma. Postoperatively, Lamotrigin treatment was terminated. Since then the patient remained asymptomatic.

Ovarian-type epithelial tumours of the testis: immunohistochemical and molecular analysis of two serous borderline tumours of the testis.

Tumours of ovarian-epithelial type of the testis, including serous borderline tumours, represent very rare entities. They are identical to the surface epithelial tumours of the ovary and have been reported in patients from 14 to 68 years of age. We describe two cases of a 46- and a 39-year old man with incidental findings of intratesticular masses of the left respectively right testis. Under the assumption of a malignant testicular tumour the patients were subjected to inguinal orchiectomy. Histologically, the tumours were identical to their ovarian counterparts: They showed a cystic configuration with a fibrous wall and irregular papillary structures lined by partially multistratified columnar cells and areas of hobnail cells. Furthermore, there was mild cytological atypia with a proliferative activity of below 5% as proved by Ki67 staining; mitoses could not be detected. Immunohistochemically, the tumour cells displayed expression of pan-cytokeratin AE3, progesterone receptor, Wilms' tumour protein (WT1), and PAX8 (Paired box gene 8). Estrogen receptor was expressed in one case. Octamer-binding transcription factor-4 (OCT4), calretinin, thrombomodulin, and D2-40 were not expressed. Mutation testing of BRAF revealed a BRAF V600E mutation in one case, while testing for KRAS mutations proved to be negative in both. The BRAF mutated tumour showed strong cytosolic and membranous positivity for B-Raf also on immunohistochemical analysis. Comparative genomic hybridization of one case could not reveal any chromosomal aberrations.

Variable aperture stop based on the design of a single chamber silicone membrane lens with integrated actuation.

In this Letter we report on the fabrication and testing of an extremely thin variable aperture stop based on the design of a single chamber adaptive membrane lens with integrated actuation. The aperture consists of a ring-shaped piezoelectric bending actuator with an elastic silicone membrane in the center. The formed cavity is filled with a nontransparent fluid and sealed with a glass platelet. In a voltage range up to 80 V, an opening of the aperture of 4.55 mm in diameter is obtained. The transmission in comparison to a standard mechanical aperture stop is maximum 6% lower.

On-chip three dimensional microcoils for MRI at the microscale.

We present for the first time a fully MEMS-integrated technology to manufacture 3D geometrically perfect solenoidal microcoils for microscale MRI applications. We report 25 microm isotropic resolution MR images of a copper sulfate aqueous phantom. These images are acquired using microcoils with 5 windings of insulated 25 microm diameter Au wire and with quality factors as high as 46 at the operating frequency (400 MHz).