This paper describes the fabrication of free-standing high-carbon microstructures by soft-lithographic techniques; these structures ranged in complexity from simple beams to complex, suspended ...deflectors. Microstructures of polymeric precursors (copolymers of furfuryl alcohol−phenol) to high-carbon solids were fabricated using poly(dimethylsiloxane) (PDMS) molds. Carbonization of these microstructures under argon resulted in mass loss (up to 45%) and shrinkage (up to 20% linearly); the density increased to reach a plateau value of ∼1.5 g/cm3 at ∼900 °C. Microstructures pyrolyzed at 900 °C were electrically conductive, with a conductivity of ∼10-2 Ω cm. Elementary microelectromechanical functions were demonstrated in these microstructures: electrostatic actuation induced deflection or vibrations of suspended structures. The measurement of the frequency of resonance of high-carbon cantilevered beams allowed the determination of Young's modulus for the solid: typical values were ∼15−20 GPa. The microelectromechanical properties of more complex structures (microresonators, light deflectors) were also determined. This paper demonstrates that high-carbon microstructures can be easily fabricated that have potential use as the active components of MEMS.
Abstract Deep brain stimulation (DBS) is used to alleviate chronic pain. Using magnetoencephalography (MEG) to study the mechanisms of DBS for pain is difficult because of the artefact caused by the ...stimulator. We were able to record activity over the occipital lobe of a patient using DBS for phantom limb pain during presentation of a visual stimulus. This demonstrates that MEG can be used to study patients undergoing DBS provided control stimuli are used to check the reliability of the data. We then asked the patient to rate his pain during and off DBS. Correlations were found between these ratings and power in theta (6–9) and beta bands (12–30). Further, there was a tendency for frequencies under 25 Hz to correlate with each other after a period off stimulation compared with immediately after DBS. The results are interpreted as reflecting abnormal thalamocortical dynamics, previously implicated in painful syndromes.
A small, lightweight, space-filling truss structure is fabricated using soft lithography in combination with electrodeposition. The truss architecture is chosen so that three-dimensionality can be ...achieved simply by folding a two-dimensional grid at a specific angle. The mechanical performance and structural efficiency of the truss beam are assessed under four-point bending and compared to the bending behavior of a square box beam in terms of non-dimensional indexes for stiffness, weight, and load-bearing capacity.
Microcontact printing (μCP) and wet chemical etching generated two-dimensional (2D) patterns in thin silver films. Electroplating silver onto these patterns increased the structural integrity of the ...metal layer. Separating the metal film from the substrate resulted in free-standing, 2D structures. Folding of these structures along predesigned “hinges” produced three-dimensional (3D) objects. Additional electrodeposition of nickel welded hinges into position, strengthened the structure, and joined separate pieces. By printing onto cylindrical surfaces, it was possible to generate complex shapes efficiently and to minimize joining steps.
This paper describes a method for fabricating three-dimensional (3D) microstructures with complex topologiestrefoil, figure eight, and cinquefoil knots, a chain with complex links, Borromean rings, ...a Möbius strip, and a torus. This method is based on the strategy of decomposing these structures into figures that can be printed on the surfaces of cylinders and planes that contact one another. Any knot can be considered as a pattern of crossings of lines, in which one line crosses “over” or “under” the second. We map these “over” and “under” crossings onto the surface of a cylinder and show that only two cylinders, in tangential contact (with axes parallel) and with lines allowed to cross from the surface of one to the surface of the second, are required to make any knot (or, in a combinatorial mathematical sense, any graph) in a topography that consists only of smooth curves. To form free-standing metal microstructures, we begin by printing appropriate patterns onto a continuous metal film on two cylinders using microcontact printing: these patterns are developed into patterns of exposed metal by etching or by covering with polymer. The cylinders are aligned (using a new procedure) with a slight separation between them. The metallic patterns on them are used as cathodes for electrodeposition, which strengthens the metal features and also welds them into a continuous structure. When electrodeposition and welding are complete, the cylindrical templates are dissolved, and the topologically complex, 3D, free-standing metallic structures are released.
High‐carbin mcirostructures as components in microelectromechanical structures and microreactors are of particular interest because their mechanical, electrical, and chemical properties can be ...controlled by the temperature of preparation. The range of electrical properties is especially impressive. A method of fabricating microstructures of glassy carbon and other high‐carbon solids is presented, based on micromolding of polymers to form precursors to these structures and pyrolysis to yield the carbon solids. The advantages of the technique are discussed.
ABSTRACT We describe a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the ACS instrument on the Herschel Space ...Observatory. This Open Time Key program, known as GASPS (Gas Survey of Protoplanetary Systems), targeted ∼250 young stars in narrow wavelength regions covering the OI fine structure line at 63 μm the brightest far-infrared line in such objects. A subset of the brightest targets were also surveyed in OI145 μm, CII at 157 μm, as well as several transitions of H2O and high-excitation CO lines at selected wavelengths between 78 and 180 μm. Additionally, GASPS included continuum photometry at 70, 100 and 160 μm, around the peak of the dust emission. The targets were SED Class II-III T Tauri stars and debris disks from seven nearby young associations, along with a comparable sample of isolated Herbig AeBe stars. The aim was to study the global gas and dust content in a wide sample of circumstellar disks, combining the results with models in a systematic way. In this overview paper we review the scientific aims, target selection and observing strategy of the program. We summarise some of the initial results, showing line identifications, listing the detections, and giving a first statistical study of line detectability. The OI line at 63 μm was the brightest line seen in almost all objects, by a factor of ∼10. Overall OI63 μm detection rates were 49%, with 100% of HAeBe stars and 43% of T Tauri stars detected. A comparison with published disk dust masses (derived mainly from sub-mm continuum, assuming standard values of the mm mass opacity) shows a dust mass threshold for OI63 μm detection of ∼10-5 M⊙. Normalising to a distance of 140 pc, 84% of objects with dust masses ≥10-5 M⊙ can be detected in this line in the present survey; 32% of those of mass 10-6-10-5 M⊙, and only a very small number of unusual objects with lower masses can be detected. This is consistent with models with a moderate UV excess and disk flaring. For a given disk mass, OI detectability is lower for M stars compared with earlier spectral types. Both the continuum and line emission was, in most systems, spatially and spectrally unresolved and centred on the star, suggesting that emission in most cases was from the disk. Approximately 10 objects showed resolved emission, most likely from outflows. In the GASPS sample, OI detection rates in T Tauri associations in the 0.3-4 Myr age range were ∼50%. For each association in the 5-20 Myr age range, ∼2 stars remain detectable in OI63 μm, and no systems were detected in associations with age >20 Myr. Comparing with the total number of young stars in each association, and assuming a ISM-like gas/dust ratio, this indicates that ∼18% of stars retain a gas-rich disk of total mass ∼1 MJupiter for 1-4 Myr, 1-7% keep such disks for 5-10 Myr, but none are detected beyond 10-20 Myr. The brightest OI objects from GASPS were also observed in OI145 μm, CII157 μm and CO J = 18 - 17, with detection rates of 20-40%. Detection of the CII line was not correlated with disk mass, suggesting it arises more commonly from a compact remnant envelope.
We present new continuum and line observations, along with modelling, of the faint (6−8) Myr old T Tauri star ET Cha belonging to the η Chamaeleontis cluster. We have acquired Herschel/PACS ...photometric fluxes at 70 μm and 160 μm, as well as a detection of the OI 63 μm fine-structure line in emission, and derived upper limits for some other far-IR OI, CII, CO and o-H2O lines. These observations were carried out in the frame of the open time key programme GASPS, where ET Cha was selected as one of the science demonstration phase targets. The Herschel data is complemented by new simultaneous ANDICAM B − K photometry, new HST/COS and HST/STIS UV-observations, a non-detection of CO J = 3 → 2 with APEX, re-analysis of a UCLES high-resolution optical spectrum showing forbidden emission lines like OI 6300 Å, SII 6731 Å and 6716 Å, and NII 6583 Å, and a compilation of existing broad-band photometric data. We used the thermo-chemical disk code ProDiMo and the Monte-Carlo radiative transfer code MCFOST to model the protoplanetary disk around ET Cha. The paper also introduces a number of physical improvements to the ProDiMo disk modelling code concerning the treatment of PAH ionisation balance and heating, the heating by exothermic chemical reactions, and several non-thermal pumping mechanisms for selected gas emission lines. By applying an evolutionary strategy to minimise the deviations between model predictions and observations, we find a variety of united gas and dust models that simultaneously fit all observed line and continuum fluxes about equally well. Based on these models we can determine the disk dustmass with confidence, Mdust ≈ (2−5) × 10-8 M⊙ whereas the total disk gas mass is found to be only little constrained, Mgas ≈ (5 × 10-5−3 × 10-3) M⊙. Both mass estimates are substantially lower than previously reported. In the models, the disk extends from 0.022 AU (just outside of the co-rotation radius) to only about 10 AU, remarkably small for single stars, whereas larger disks are found to be inconsistent with the CO J = 3 → 2 non-detection. The low velocity component of the OI 6300 Å emission line is centred on the stellar systematic velocity, and is consistent with being emitted from the inner disk. The model is also consistent with the line flux of H2 v = 1 → 0 S(1) at 2.122 μm and with the OI 63 μm line as seen with Herschel/PACS. An additional high-velocity component of the OI 6300 Å emission line, however, points to the existence of an additional jet/outflow of low velocity 40−65 km s-1 with mass loss rate ≈ 10-9 M⊙/yr. In relation to our low estimations of the disk mass, such a mass loss rate suggests a disk lifetime of only ~0.05−3 Myr, substantially shorter than the cluster age. If a generic gas/dust ratio of 100 was assumed, the disk lifetime would be even shorter, only ~3000 yrs. The evolutionary state of this unusual protoplanetary disk is discussed.
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