2,483 research outputs found
Electrochemical machining of carbides and borides
The use of high rate anodic dissolution (electrochemical machining) for shaping titanium carbide, zirconium carbide, titanium boride and zirconium boride has been investigated in 2N potassium nitrate and 3N sodium chloride under current densities ranging from 20 to 120 A/cm{sup 2} (corresponding to cutting rates of 0.3 to 1.8 mm/min). The dissolution stoichiometry for all these materials is independent of the current density in the range 20 to 120 A/cm{sup 2}. Both titanium and zirconium appear to dissolve in the +4 state, boron in the +3 state and the weight loss measurements indicate that carbon is oxidized to CO and CO{sub 2}. The current voltage curves permit to establish that, over the entire current density and flow range investigated, dissolution occurs in the transpassive state. The surface roughness obtained on TiC and ZrC is within 3-5 {micro}m and is independent of current density, applied voltage or flow rate
Scalable background-limited polarization-sensitive detectors for mm-wave applications
We report on the status and development of polarization-sensitive detectors
for millimeter-wave applications. The detectors are fabricated on
single-crystal silicon, which functions as a low-loss dielectric substrate for
the microwave circuitry as well as the supporting membrane for the
Transition-Edge Sensor (TES) bolometers. The orthomode transducer (OMT) is
realized as a symmetric structure and on-chip filters are employed to define
the detection bandwidth. A hybridized integrated enclosure reduces the
high-frequency THz mode set that can couple to the TES bolometers. An
implementation of the detector architecture at Q-band achieves 90% efficiency
in each polarization. The design is scalable in both frequency coverage, 30-300
GHz, and in number of detectors with uniform characteristics. Hence, the
detectors are desirable for ground-based or space-borne instruments that
require large arrays of efficient background-limited cryogenic detectors.Comment: 7 pages, 3 figures, Presented at SPIE Astronomical Telescopes and
Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors
and Instrumentation for Astronomy VII. To be published in Proceedings of SPIE
Volume 915
Silicon-Based Antenna-Coupled Polarization-Sensitive Millimeter-Wave Bolometer Arrays for Cosmic Microwave Background Instruments
We describe feedhorn-coupled polarization-sensitive detector arrays that
utilize monocrystalline silicon as the dielectric substrate material.
Monocrystalline silicon has a low-loss tangent and repeatable dielectric
constant, characteristics that are critical for realizing efficient and uniform
superconducting microwave circuits. An additional advantage of this material is
its low specific heat. In a detector pixel, two Transition-Edge Sensor (TES)
bolometers are antenna-coupled to in-band radiation via a symmetric planar
orthomode transducer (OMT). Each orthogonal linear polarization is coupled to a
separate superconducting microstrip transmission line circuit. On-chip
filtering is employed to both reject out-of-band radiation from the upper band
edge to the gap frequency of the niobium superconductor, and to flexibly define
the bandwidth for each TES to meet the requirements of the application. The
microwave circuit is compatible with multi-chroic operation. Metalized silicon
platelets are used to define the backshort for the waveguide probes. This
micro-machined structure is also used to mitigate the coupling of out-of-band
radiation to the microwave circuit. At 40 GHz, the detectors have a measured
efficiency of 90%. In this paper, we describe the development of the 90 GHz
detector arrays that will be demonstrated using the Cosmology Large Angular
Scale Surveyor (CLASS) ground-based telescope
Distinct mesenchymal progenitor cell subsets in the adult human synovium
Objective. To analyse the heterogeneity at the single-cell level of human mesenchymal progenitor cells from SM. Methods. Cell populations were enzymatically released from the knee joint synovium of adult human individuals. Single cell-derived clonal populations were obtained by limiting dilution and serially passaged to determine growth rates. Phenotypic analysis was carried out by flow cytometry. Replicative senescence was assessed by the senescence-associated β-galactosidase staining. Telomere lengths were determined semiquantitatively by Southern blotting. Telomerase activity was measured using a real-time quantitative telomerase repeat amplification procedure. Culture-expanded clonal populations were subjected to in vitro differentiation assays to investigate their mesenchymal multipotency. Results. The 50 clones analysed displayed wide variations in the proliferation rates, even within the same donor sample. The time taken to reach 20 population doublings ranged from 44 to 130 days. The phenotype of the clones tested was compatible with that of mesenchymal stem cells. Mean telomere lengths ranged from 5.2 to 10.9 kb with positive linear trend with telomerase activity, but no correlation with proliferative rates or cell senescence. All clones tested were capable of chondrogenic and osteogenic differentiation, though with large variability in potency. In contrast, only 30% of the clones were adipogenic. Conclusions. We report for the first time the co-existence, within the synovium, of progenitor cell subsets with distinct mesenchymal differentiation potency. Our findings further emphasize the need for strategies to purify cell populations with the clinically desired tissue formation potential
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