2,601 research outputs found
Impedance Matched Absorptive Thermal Blocking Filters
We have designed, fabricated and characterized absorptive thermal blocking
filters for cryogenic microwave applications. The transmission line filter's
input characteristic impedance is designed to match and its
response has been validated from 0-to-50\,GHz. The observed return loss in the
0-to-20\,GHz design band is greater than dB and shows graceful
degradation with frequency. Design considerations and equations are provided
that enable this approach to be scaled and modified for use in other
applications
PAPPA: Primordial Anisotropy Polarization Pathfinder Array
The Primordial Anisotropy Polarization Pathfinder Array (PAPPA) is a
balloon-based instrument to measure the polarization of the cosmic microwave
background and search for the signal from gravity waves excited during an
inflationary epoch in the early universe. PAPPA will survey a 20 x 20 deg patch
at the North Celestial Pole using 32 pixels in 3 passbands centered at 89, 212,
and 302 GHz. Each pixel uses MEMS switches in a superconducting microstrip
transmission line to combine the phase modulation techniques used in radio
astronomy with the sensitivity of transition-edge superconducting bolometers.
Each switched circuit modulates the incident polarization on a single detector,
allowing nearly instantaneous characterization of the Stokes I, Q, and U
parameters. We describe the instrument design and status.Comment: 12 pages, 9 figures. Proceedings of the Fundamental Physics With CMB
workshop, UC Irvine, March 23-25, 2006, to be published in New Astronomy
Review
Cosmic Microwave Background Polarization Detector with High Efficiency, Broad Bandwidth, and Highly Symmetric Coupling to Transition Edge Sensor Bolometers
Four probe antennas transfer signals from waveguide to microstrip lines. The probes not only provide broadband impedance matching, but also thermally isolate waveguide and detector. In addition, we developed a new photonic waveguide choke joint design, with four-fold symmetry, to suppress power leakage at the interface. We have developed facilities to test superconducting circuit elements using a cryogenic microwave probe station, and more complete systems in waveguide. We used the ring resonator shown below to measure a dielectric loss tangent 99% coupling efficiency over 30% fractional bandwidth
Equation of state of resonance-rich matter in the central cell in heavy-ion collisions at =200 AGeV
The equilibration of hot and dense nuclear matter produced in the central
cell of central Au+Au collisions at RHIC ( AGeV) energies is
studied within a microscopic transport model. The pressure in the cell becomes
isotropic at fm/ after beginning of the collision. Within the
next 15 fm/ the expansion of matter in the cell proceeds almost
isentropically with the entropy per baryon ratio , and the
equation of state in the plane has a very simple form,
. Comparison with the statistical model of an ideal hadron gas
indicates that the time fm/c may be too short to reach the fully
equilibrated state. Particularly, the creation of long-lived resonance-rich
matter in the cell decelerates the relaxation to chemical equilibrium. This
resonance-abundant state can be detected experimentally after the thermal
freeze-out of particles.Comment: LATEX, 21 pages incl. 7 figure
Millennial Chinese Consumers’ Perceived Destination Brand Value
There has been a substantial rise in the number of Chinese tourists, with the Chinese millennials being important influencers. Yet very little is known about their tourism behavior, particularly how their perceived destination brand values influence their destination loyalty. This study brings in the consumers’ perceived brand value concept from the branding literature to investigate Chinese millennial tourists’ destination loyalty. An online survey was adopted to collect data from 287 Chinese millennial tourists. The findings offer insight into the relative effects of five dimensions of tourists’ perceived destination brand values on their destination loyalty. The findings also extend existing tourism literature, showing the moderating effects of destination brand globality, destination status (domestic vs. international) and national brand attitude on the said relationships. Managerial implications to better target Chinese millennials are discussed together with future research directions
Fabrication of an Antenna-Coupled Bolometer for Cosmic Microwave Background Polarimetry
We describe the development of a detector for precise measurements of the cosmic microwave background polarization. The detector employs a waveguide to couple light between a pair of Mo/Au superconducting transition edge sensors (TES) and a feedhorn. Incorporation of an on-chip ortho-mode transducer (OMT) results in high isolation. The OMT is micromachined and bonded to the microstrip and TES circuits in a low temperature wafer bonding process. The wafer bonding process incorporates a buried superconducting niobium layer with a single crystal silicon layer which serves as the leg isolated TES membrane and as the microstrip dielectric. We describe the micromachining and wafer bonding process and report measurement results of the microwave circuitry operating in the 29-43GHz band along with Johnson noise measurements of the TES membrane structures and development of Mo/Au TES operating under '00mK
A simple radionuclide-driven single-ion source
We describe a source capable of producing single barium ions through nuclear
recoils in radioactive decay. The source is fabricated by electroplating 148Gd
onto a silicon {\alpha}-particle detector and vapor depositing a layer of BaF2
over it. 144Sm recoils from the alpha decay of 148Gd are used to dislodge Ba+
ions from the BaF2 layer and emit them in the surrounding environment. The
simultaneous detection of an {\alpha} particle in the substrate detector allows
for tagging of the nuclear decay and of the Ba+ emission. The source is simple,
durable, and can be manipulated and used in different environments. We discuss
the fabrication process, which can be easily adapted to emit most other
chemical species, and the performance of the source
Properties of Superconducting Mo, Mo2n and Trilayer Mo2n-Mo-Mo2n Thin Films
We present measurements of the properties of thin film superconducting Mo, Mo2N and Mo2N/Mo/Mo2N trilayers of interest for microwave kinetic inductance detector (MKID) applications. Using microwave resonator devices, we investigate the transition temperature, energy gaps, kinetic inductance, and internal quality factors of these materials. We present an Usadel-based interpretation of the trilayer transition temperature as a function of trilayer thicknesses, and a 2-gap interpretation to understand the change in kinetic inductance and internal resonance quality factor (Q) as a function of temperature
Kinetic equation with exact charge conservation
We formulate the kinetic master equation describing the production of charged
particles which are created or destroyed only in pairs due to the conservation
of their Abelian charge.Our equation applies to arbitrary particle
multiplicities and reproduces the equilibrium results for both canonical (rare
particles) and grand canonical (abundant particles) systems. For canonical
systems, the equilibrium multiplicity is much lower and the relaxation time is
much shorter than the naive extrapolation from the grand canonical ensemble
results. Implications for particle chemical equilibration in heavy-ion
collisions are discussed.Comment: 4 Pages in RevTe
Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling
A planar slab of negative index material works as a superlens with
sub-diffraction-limited imaging resolution, since propagating waves are focused
and, moreover, evanescent waves are reconstructed in the image plane. Here, we
demonstrate a superlens for electric evanescent fields with low losses using
perovskites in the mid-infrared regime. The combination of near-field
microscopy with a tunable free-electron laser allows us to address precisely
the polariton modes, which are critical for super-resolution imaging. We
spectrally study the lateral and vertical distributions of evanescent waves
around the image plane of such a lens, and achieve imaging resolution of
wavelength/14 at the superlensing wavelength. Interestingly, at certain
distances between the probe and sample surface, we observe a maximum of these
evanescent fields. Comparisons with numerical simulations indicate that this
maximum originates from an enhanced coupling between probe and object, which
might be applicable for multifunctional circuits, infrared spectroscopy, and
thermal sensors.Comment: 20 pages, 6 figures, published as open access article in Nature
Communications (see http://www.nature.com/ncomms/
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