Measurement of loss in superconducting microstrip at millimeter-wave frequencies

We have developed a new technique for accurate measurement of the loss of superconducting microstrips at mm-wave frequencies. In this technique, we optically couple power to slot antenna, which is connected to one port of a hybrid coupler. One of the output ports of the hybrid delivers power to a series of mm-wave microstrip resonators which are capacitively coupled to a feedline followed by an MKID (microwave kinetic inductance detector) that measures the transmitted power. Two other MKIDs are connected to the remaining ports of the hybrid to measure the total incident optical power and the power reflected from the mm-wave resonators, allowing |S_(21)|^2 and |S_(11)|^2 to be accurately determined and resonance frequency fr and quality factor Q to be retrieved. We have fabricated such a Nb/SiO_2/Nb microstrip loss test device which contains several mm- wave resonators with f_r~100 GHz and measured it at 30 mK. All the resonators have shown internal quality factor Qi~500–2000, suggesting a loss tangent of ~5×10^(−4)−2×10^(−3) for the SiO_2 in use. For comparison, we have also fabricated a 5 GHz microstrip resonator on the same chip and measured it with a network analyzer. The loss tangent at 5 GHz derived from fitting the f_0 and Q data to the two-level system (TLS) model is 6×10^(−4), about the same as from the mm-wave measurement. This suggests that the loss at both microwave and mm-wave frequencies is probably dominated by the TLS in SiO_2. Our results are of direct interest to mm/submm direct detection applications which use microstrip transmission lines (such as antenna-coupled MKIDs and transition-edge sensors), and other applications (such as on-chip filters). Our measurement technique is applicable up to approximately 1 THz and can be used to investigate a range of dielectrics

Quasiparticle Trapping in Microwave Kinetic Inductance Strip Detectors

Microwave Kinetic Inductance Detectors (MKIDs) are thin-film, superconducting resonators, which are attractive for making large detector arrays due to their natural frequency domain multiplexing at GHz frequencies. For X-ray to IR wavelengths, MKIDs can provide high-resolution energy and timing information for each incoming photon. By fabricating strip detectors consisting of a rectangular absorber coupled to MKIDs at each end, high quantum efficiency and spatial resolution can be obtained. A similar geometry is being pursued for phonon sensing in a WIMP dark matter detector. Various materials have been tested including tantalum, tin, and aluminum for the absorbing strip, and aluminum, titanium, and aluminum manganese for the MKID. Initial Ta/Al X-ray devices have shown energy resolutions as good as 62 eV at 6 keV. A Ta/Al UV strip detector with an energy resolution of 0.8 eV at 4.9 eV has been demonstrated, but we find the coupling of the MKIDs to the absorbers is unreliable for these thinner devices. We report on progress probing the thicknesses at which the absorber/MKID coupling begins to degrade by using a resonator to inject quasiparticles directly into the absorber. In order to eliminate the absorber/MKID interface, a modified design for implanted AlMn/Al UV strip detectors was developed, and results showing good transmission of quasiparticles from the absorber to MKID in these devices are presented

Two-level system noise reduction for Microwave Kinetic Inductance Detectors

Noise performance is one of the most crucial aspects of any detector. Superconducting Microwave Kinetic Inductance Detectors (MKIDs) have an "excess" frequency noise that shows up as a small time dependent jitter of the resonance frequency characterized by the frequency noise power spectrum measured in units of Hz^2/Hz. Recent studies have shown that this noise almost certainly originates from a surface layer of two-level system (TLS) defects on the metallization or substrate. Fluctuation of these TLSs introduces noise in the resonator due to coupling of the TLS electric dipole moments to the resonator's electric field. Motivated by a semi-empirical quantitative theory of this noise mechanism, we have designed and tested new resonator geometries in which the high-field "capacitive" portion of the CPW resonator is replaced by an interdigitated capacitor (IDC) structure with 10 - 20 micron electrode spacing, as compared to the 2 micron spacing used for our more conventional CPW resonators. Measurements show that this new IDC design has dramatically lower TLS noise, currently by about a factor of ~29 in terms of the frequency noise power spectrum, corresponding to an improvement of about a factor of 29^(1/2) in NEP. These new devices are replacing the CPW resonators in our next design iteration in progress for MKIDCam. Opportunities and prospects for future reduction of the TLS noise will be discussed.Comment: 4 pages, 5 figures, Proceedings of the 13th International Workshop on Low Temperature Detectors, Stanford July 20-24, 200

Netrin-3 and Netrin-4-Like Proteins are Secreted from \u3cem\u3eTetrahymena thermophila\u3c/em\u3e

Netrins are signaling proteins, acting as chemorepellants or chemoattractants, and their role is especially important in early growth in organisms. In studies involving Tetrahymena thermophila, netrin proteins often act as chemorepellants, so research centered around verifying if this was also true for Netrin-4 protein. Since Netrin-1 and Netrin-3 have been shown to influence neurological and developmental growth in organisms, the implications for discovering the cellular effects of Netrin-4 are significant for human health and research. Through behavioral assays, we were able to confirm that Netrin4 does act as a chemorepellant. In addition, our ELISA and Western blots also helped substantiate the idea that Tetrahymena produce Netrin-4 for physiological functions, as they possess receptors for these proteins. The exact purposes of Netrin-4 for this organism is unknown up to this point, so further testing is needed to determine the cellular mechanisms with which Netrin-4 is involved

Comparing temporal patterns in body condition of ringed seals living within their core geographic range with those living at the edge

Ecological theory suggests that demographic responses by populations to environmental change vary depending on whether individuals inhabit central or peripheral regions within the species’ geographic range. Here, we tested this prediction by comparing a population of ringed seals Pusa hispida located at high latitudes as part of their core range (core) with a population located at the southern extremity of their range (peripheral). First, we compared the two regions’ environmental trends in timing of sea-ice breakup and freeze-up, open-water duration and the North Atlantic Oscillation (NAO). We found that the core region shifted to progressively warmer conditions in the early 1990s; whereas, in the peripheral region, the warming trend shifted in 1999 to one with no warming trend but high inter-annual variability. Next, we examined how body condition, inferred from blubber depth, responded to temporal changes in sea-ice and climatic variables – variables that have been shown to influence ringed seal demography. Core seals displayed minimal seasonal changes in body condition; whereas peripheral seals displayed a 20–60% amplitude seasonal change in body condition with a phase shift to earlier initiation of fat accumulation and loss. Finally, we tested for interannual differences and found that both core and peripheral seals responded similarly with decreased body condition following more positive NAO. Environmental variables influenced body condition in opposite directions between the two regions with core seals declining in body condition with later spring breakup and shorter open-water duration, whereas peripheral seals showed opposite relationships. Seals living at the core likely benefit from an evolved match between adaptation and environmental variation resulting in dampened seasonal and interannual fluctuations in body condition. Knowledge of how different populations respond to environmental change depending on geographic location within a species range can assist in anticipating population specific responses to climate warming

Polarized Narrow-Line Emission from the Nucleus of NGC 4258

The detection of polarized continuum and line emission from the nucleus of NGC 4258 by Wilkes et al. (1995) provides an intriguing application of the unified model of Seyfert nuclei to a galaxy in which there is known to be an edge-on, rotating disk of molecular gas surrounding the nucleus. Unlike most Seyfert nuclei, however, NGC 4258 has strongly polarized narrow emission lines. To further investigate the origin of the polarized emission, we have obtained spectropolarimetric observations of the NGC 4258 nucleus at the Keck-II telescope. The narrow-line polarizations range from 1.0% for [S II] 6716 to 13.9% for the [O II] 7319,7331 blend, and the position angle of polarization is oriented nearly parallel to the projected plane of the masing disk. A correlation between critical density and degree of polarization is detected for the forbidden lines, indicating that the polarized emission arises from relatively dense (n_e > 10^4 cm^-3) gas. An archival Hubble Space Telescope narrow-band [O III] image shows that the narrow-line region has a compact, nearly unresolved core, implying a FWHM size of <2.5 pc. We discuss the possibility that the polarized emission might arise from the accretion disk itself and become polarized by scattering within the disk atmosphere. A more likely scenario is an obscuring torus or strongly warped disk surrounding the inner portion of a narrow-line region which is strongly stratified in density. The compact size of the narrow-line region implies that the obscuring structure must be smaller than ~2.5 pc in diameter.Comment: To appear in the Astronomical Journal. 13 pages, including 1 table and 4 figures. Uses emulateapj.st

Microwave Kinetic Inductance Detector (MKID) Camera Testing for Submillimeter Astronomy

Developing kilopixel focal planes for incoherent submm- and mm-wave detectors remains challenging due to either the large hardware overhead or the complexity of multiplexing standard detectors. Microwave kinetic inductance detectors (MKIDs) provide a efficient means to produce fully lithographic background-limited kilopixel focal planes. We are constructing an MKID-based camera for the Caltech Submillimeter Observatory with 576 spatial pixels each simultaneously sensitive in 4 bands at 230, 300, 350, and 400 GHz. The novelty of MKIDs has required us to develop new techniques for detector characterization. We have measured quasiparticle lifetimes and resonator Qs for detector bath temperatures between 200 mK and 400 mK. Equivalent lifetime measurements were made by coupling energy into the resonators either optically or by driving the third harmonic of the resonator. To determine optical loading, we use both lifetime and internal Q measurements, which range between 15,000 and 30,000 for our resonators. Spectral bandpass measurements confirm the placement of the 230 and 350 GHz bands. Additionally, beam maps measurements conform to expectations. The same device design has been characterized on both sapphire and silicon substrates, and for different detector geometries. We also report on the incorporation of new shielding to reduce detector sensitivity to local magnetic fields

Iron deposition is independent of cellular inflammation in a cerebral model of multiple sclerosis

<p>Abstract</p> <p>Background</p> <p>Perivenular inflammation is a common early pathological feature in multiple sclerosis (MS). A recent hypothesis stated that CNS inflammation is induced by perivenular iron deposits that occur in response to altered blood flow in MS subjects. In order to evaluate this hypothesis, an animal model was developed, called cerebral experimental autoimmune encephalomyelitis (cEAE), which presents with CNS perivascular iron deposits. This model was used to investigate the relationship of iron deposition to inflammation.</p> <p>Methods</p> <p>In order to generate cEAE, mice were given an encephalitogen injection followed by a stereotactic intracerebral injection of TNF-α and IFN-γ. Control animals received encephalitogen followed by an intracerebral injection of saline, or no encephalitogen plus an intracerebral injection of saline or cytokines. Laser Doppler was used to measure cerebral blood flow. MRI and iron histochemistry were used to localize iron deposits. Additional histological procedures were used to localize inflammatory cell infiltrates, microgliosis and astrogliosis.</p> <p>Results</p> <p>Doppler analysis revealed that cEAE mice had a reduction in cerebral blood flow compared to controls. MRI revealed T2 hypointense areas in cEAE animals that spatially correlated with iron deposition around vessels and at some sites of inflammation as detected by iron histochemistry. Vessels with associated iron deposits were distributed across both hemispheres. Mice with cEAE had more iron-labeled vessels compared to controls, but these vessels were not commonly associated with inflammatory cell infiltrates. Some iron-laden vessels had associated microgliosis that was above the background microglial response, and iron deposits were observed within reactive microglia. Vessels with associated astrogliosis were more commonly observed without colocalization of iron deposits.</p> <p>Conclusion</p> <p>The findings indicate that iron deposition around vessels can occur independently of inflammation providing evidence against the hypothesis that iron deposits account for inflammatory cell infiltrates observed in MS.</p

The Frequency of Polarized Broad Emission Lines in Type 2 Seyfert Galaxies

We have discovered polarized broad emission lines in five type 2 Seyfert galaxies (NGC 424, NGC 591, NGC 2273, NGC 3081, and NGC 4507), establishing that these objects are type 1 Seyferts obscured by dense circumnuclear material. The galaxies are part of a distance-limited sample of 31 Seyfert 2s, for which spectropolarimetric observations are now complete. Combined with published reports, our results indicate that at least 11 of the galaxies in this sample, or > 35%, possess hidden broad-line regions. This represents the first reliable estimate of the frequency of polarized broad emission lines in type 2 Seyferts, which has important implications for the general applicability of Seyfert unification models.Comment: 13 pages, including 5 figures. Accepted for publication in ApJ Letter