1,887 research outputs found
The Structure on Invariant Measures of generic diffeomorphisms
Let be an isolated non-trival transitive set of a generic
diffeomorphism f\in\Diff(M). We show that the space of invariant measures
supported on coincides with the space of accumulation measures of
time averages on one orbit. Moreover, the set of points having this property is
residual in (which implies the set of irregular points is also
residual in ). As an application, we show that the non-uniform
hyperbolicity of irregular points in with totally 0 measure
(resp., the non-uniform hyperbolicity of a generic subset in )
determines the uniform hyperbolicity of
Superconducting Films for Absorber-Coupled MKID Detectors for Sub-Millimeter and Far-Infrared Astronomy
We describe measurements of the properties, at dc, gigahertz, and terahertz frequencies, of thin (10 nm) aluminum films with 10 ohm/{rm square}$ normal state sheet resistance. Such films can be applied to construct microwave kinetic inductance detector arrays for submillimeter and far-infrared astronomical applications in which incident power excites quasiparticles directly in a superconducting resonator that is configured to present a matched-impedance to the high frequency radiation being detected. For films 10 nm thick, we report normal state sheet resistance, resistance-temperature curves for the superconducting transition, quality factor and kinetic inductance fraction for microwave resonators made from patterned films, and terahertz measurements of sheet impedance measured with a Fourier Transform Spectrometer. We compare properties with similar resonators made from niobium 600 nm thick
Fabrication of an Absorber-Coupled MKID Detector and Readout for Sub-Millimeter and Far-Infrared Astronomy
We have fabricated absorber-coupled microwave kinetic inductance detector (MKID) arrays for sub-millimeter and far-infrared astronomy. Each detector array is comprised of lambda/2 stepped impedance resonators, a 1.5 micrometer thick silicon membrane, and 380 micrometer thick silicon walls. The resonators consist of parallel plate aluminum transmission lines coupled to low impedance Nb microstrip traces of variable length, which set the resonant frequency of each resonator. This allows for multiplexed microwave readout and, consequently, good spatial discrimination between pixels in the array. The Al transmission lines simultaneously act to absorb optical power and are designed to have a surface impedance and filling fraction so as to match the impedance of free space. Our novel fabrication techniques demonstrate high fabrication yield of MKID arrays on large single crystal membranes and sub-micron front-to-back alignment of the microstrip circuit
Micro-spec: an Integrated Direct-detection Spectrometer for Far-infrared Space Telescopes
The far-infrared and submillimeter portions of the electromagnetic spectrum provide a unique view of the astrophysical processes present in the early universe. Our ability to fully explore this rich spectral region has been limited, however, by the size and cost of the cryogenic spectrometers required to carry out such measurements.Micro-Spec (-Spec) is a high-sensitivity, direct-detection spectrometer concept working in the 450-1000 (micrometers) wavelength range which will enable a wide range of flight missions that would otherwise be challenging due tothe large size of current instruments with the required spectral resolution and sensitivity. The spectrometer design utilizes two internal antenna arrays, one for transmitting and one for receiving, superconducting microstrip transmission lines for power division and phase delay, and an array of microwave kinetic inductance detectors (MKIDs) to achieve these goals. The instrument will be integrated on a approximately 10 sq cm silicon chip and can therefore become an important capability under the low background conditions accessible via space and high-altitude borne platforms. In this paper, an optical design methodology for micro-Spec is presented, with particular attention given to its two-dimensional diffractive region, where the light of different wavelengths is focused on the different detectors. The method is based on the maximization of the instrument resolving power and minimization of the RMS phase error on the instrument focal plane. This two-step optimization can generate geometrical configurations given specific requirements on spectrometer size, operating spectral range and performance.Two point designs with resolving power of 260 and 520 and an RMS phase error less than approximately 0.004 radians were developed for initial demonstration and will be the basis of future instruments with resolving power up to about 1200
Micro-Spec: An Ultra-Compact, High-Sensitivity Spectrometer for Far-Infrared and Sub-Millimeter Astronomy
High-performance, integrated spectrometers operating in the far-infrared and sub-millimeter promise to be powerful tools for the exploration of the epochs of reionization and initial galaxy formation. These devices, using high-efficiency superconducting transmission lines, can achieve the performance of a meter-scale grating spectrometer in an instrument implemented on a four-inch silicon wafer. Such a device, when combined with a cryogenic telescope in space, provides an enabling capability for studies of the early universe. Here, the optical design process for Micro-Spec (mu-Spec) is presented, with particular attention given to its two-dimensional diffractive region, where the light of different wavelengths is focused on the different detectors. The method is based on the stigmatization and minimization of the light path function in this bounded region, which results in an optimized geometrical configuration. A point design with an efficiency of approx. 90% has been developed for initial demonstration, and can serve as the basis for future instruments. Design variations on this implementation are also discussed, which can lead to lower efficiencies due to diffractive losses in the multimode region
Study on the One-Proton Halo Structure in Al
The Glauber theory has been used to investigate the reaction cross section of
proton-rich nucleus Al. A core plus a proton structure is assumed for
Al. HO-type density distribution is used for the core while the density
distribution for the valence proton is calculated by solving the eigenvalue
problem of Woods-Saxon potential. The transparency function in an analytical
expression is obtained adopting multi-Gaussian expansion for the density
distribution. Coulomb correction and finite-range interaction are introduced.
This modified Glauber model is apt for halo nuclei. A dominate s-wave is
suggested for the last proton in Al from our analysis which is possible
in the RMF calculation.Comment: 4 pages, 4 figure
A draft human pangenome reference
Here the Human Pangenome Reference Consortium presents a first draft of the human pangenome reference. The pangenome contains 47 phased, diploid assemblies from a cohort of genetically diverse individual
Excitation spectrum of the homogeneous spin liquid
We discuss the excitation spectrum of a disordered, isotropic and
translationally invariant spin state in the 2D Heisenberg antiferromagnet. The
starting point is the nearest-neighbor RVB state which plays the role of the
vacuum of the theory, in a similar sense as the Neel state is the vacuum for
antiferromagnetic spin wave theory. We discuss the elementary excitations of
this state and show that these are not Fermionic spin-1/2 `spinons' but spin-1
excited dimers which must be modeled by bond Bosons. We derive an effective
Hamiltonian describing the excited dimers which is formally analogous to spin
wave theory. Condensation of the bond-Bosons at zero temperature into the state
with momentum (pi,pi) is shown to be equivalent to antiferromagnetic ordering.
The latter is a key ingredient for a microscopic interpretation of Zhang's
SO(5) theory of cuprate superconductivityComment: RevTex-file, 16 PRB pages with 13 embedded eps figures. Hardcopies of
figures (or the entire manuscript) can be obtained by e-mail request to:
[email protected]
Schr\"{o}dinger Fields on the Plane with Chern-Simons Interactions and Generalized Self-dual Solitons
A general non-relativistic field theory on the plane with couplings to an
arbitrary number of abelian Chern-Simons gauge fields is considered. Elementary
excitations of the system are shown to exhibit fractional and mutual
statistics. We identify the self-dual systems for which certain classical and
quantal aspects of the theory can be studied in a much simplified mathematical
setting. Then, specializing to the general self-dual system with two
Chern-Simons gauge fields (and non-vanishing mutual statistics parameter), we
present a systematic analysis for the static vortexlike classical solutions,
with or without uniform background magnetic field. Relativistic generalizations
are also discussed briefly.Comment: 49 pages including 4 figures, LATEX ( three LATEX figures and one
PICTEX figure), SNUTP 93-14, UMN-TH-113
Quasiparticle States around a Nonmagnetic Impurity in D-Density-Wave State of High- Cuprates
Recently Chakravarty {\em et al.} proposed an ordered -density wave (DDW)
state as an explanation of the pseudogap phase in underdoped high-temperature
cuprates. We study the competition between the DDW and superconducting ordering
based on an effective mean-field Hamiltonian. We are mainly concerned with the
effect of the DDW ordering on the electronic state around a single nonmagnetic
impurity. We find that a single subgap resonance peak appears in the local
density of state around the impurity. In the unitary limit, the position of
this resonance peak is always located at with respect to the Fermi
energy. This result is dramatically different from the case of the pure
superconducting state for which the impurity resonant energy is approximately
pinned at the Fermi level. This can be used to probe the existence of the DDW
ordering in cuprates.Comment: 4 pages, 4 figure
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