1,775 research outputs found
Self-aligned fabrication process for silicon quantum computer devices
We describe a fabrication process for devices with few quantum bits (qubits),
which are suitable for proof-of-principle demonstrations of silicon-based
quantum computation. The devices follow the Kane proposal to use the nuclear
spins of 31P donors in 28Si as qubits, controlled by metal surface gates and
measured using single electron transistors (SETs). The accurate registration of
31P donors to control gates and read-out SETs is achieved through the use of a
self-aligned process which incorporates electron beam patterning, ion
implantation and triple-angle shadow-mask metal evaporation
A comparative study of Type II-P and II-L supernova rise times as exemplified by the case of LSQ13cuw
We report on our findings based on the analysis of observations of the Type
II-L supernova LSQ13cuw within the framework of currently accepted physical
predictions of core-collapse supernova explosions. LSQ13cuw was discovered
within a day of explosion, hitherto unprecedented for Type II-L supernovae.
This motivated a comparative study of Type II-P and II-L supernovae with
relatively well-constrained explosion epochs and rise times to maximum
(optical) light. From our sample of twenty such events, we find evidence of a
positive correlation between the duration of the rise and the peak brightness.
On average, SNe II-L tend to have brighter peak magnitudes and longer rise
times than SNe II-P. However, this difference is clearest only at the extreme
ends of the rise time versus peak brightness relation. Using two different
analytical models, we performed a parameter study to investigate the physical
parameters that control the rise time behaviour. In general, the models
qualitatively reproduce aspects of the observed trends. We find that the
brightness of the optical peak increases for larger progenitor radii and
explosion energies, and decreases for larger masses. The dependence of the rise
time on mass and explosion energy is smaller than the dependence on the
progenitor radius. We find no evidence that the progenitors of SNe II-L have
significantly smaller radii than those of SNe II-P.Comment: 19 pages, 10 figures, accepted by A&
Early ultraviolet emission in the Type Ia supernova LSQ12gdj: No evidence for ongoing shock interaction
We present photospheric-phase observations of LSQ12gdj, a slowly-declining,
UV-bright Type Ia supernova. Classified well before maximum light, LSQ12gdj has
extinction-corrected absolute magnitude , and pre-maximum
spectroscopic evolution similar to SN 1991T and the super-Chandrasekhar-mass SN
2007if. We use ultraviolet photometry from Swift, ground-based optical
photometry, and corrections from a near-infrared photometric template to
construct the bolometric (1600-23800 \AA) light curve out to 45 days past
-band maximum light. We estimate that LSQ12gdj produced
of Ni, with an ejected mass near or slightly above the
Chandrasekhar mass. As much as 27% of the flux at the earliest observed phases,
and 17% at maximum light, is emitted bluewards of 3300 \AA. The absence of
excess luminosity at late times, the cutoff of the spectral energy distribution
bluewards of 3000 \AA, and the absence of narrow line emission and strong Na I
D absorption all argue against a significant contribution from ongoing shock
interaction. However, up to 10% of LSQ12gdj's luminosity near maximum light
could be produced by the release of trapped radiation, including kinetic energy
thermalized during a brief interaction with a compact, hydrogen-poor envelope
(radius cm) shortly after explosion; such an envelope arises
generically in double-degenerate merger scenarios.Comment: 18 pages, 10 figures, accepted to MNRAS; v2 accepted version. Spectra
available on WISEReP (http://www.weizmann.ac.il/astrophysics/wiserep/).
Natural-system photometry and bolometric light curve available as online
tables in MNRAS versio
Next Generation Very Large Array Memo No. 5 Science Working Groups Project Overview
We summarize the design, capabilities, and some of the priority science goals of a next generation Very Large Array (ngVLA). The ngVLA is an interferometric array with 10x larger effective collecting area and 10x higher spatial resolution than the current VLA and the Atacama Large Millimeter Array (ALMA), optimized for operation in the wavelength range 0.3cm to 3cm. The ngVLA opens a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcecond resolution, as well as unprecedented broad band continuum polarimetric imaging of non-thermal processes. The continuum resolution will reach 9mas at 1cm, with a brightness temperature sensitivity of 6K in 1 hour. For spectral lines, the array at 1" resolution will reach 0.3K surface brightness sensitivity at 1cm and 10 km s^(-1) spectral resolution in 1 hour. These capabilities are the only means with which to answer a broad range of critical scientific questions in modern astronomy, including direct imaging of planet formation in the terrestrial-zone, studies of dust-obscured star formation and the cosmic baryon cycle down to pc-scales out to the Virgo cluster, making a cosmic census of the molecular gas which fuels star formation back to first light and cosmic reionization, and novel techniques for exploring temporal phenomena from milliseconds to years. The ngVLA is optimized for observations at wavelengths between the superb performance of ALMA at submm wavelengths, and the future SKA1 at few centimeter and longer wavelengths. This memo introduces the project. The science capabilities are outlined in a parallel series of white papers. We emphasize that this initial set of science goals are simply a starting point for the project. We invite comment on these programs, as well as new ideas, through our public forum link on the ngVLA web page: https://science.nrao.edu/futures/ngvl
The Properties and Origins of Kuiper Belt Object Arrokoth's Large Mounds
We report on a study of the mounds that dominate the appearance of Kuiper
Belt Object (KBO) (486958) Arrokoth's larger lobe, named Wenu. We compare the
geological context of these mounds, measure and intercompare their shapes,
sizes/orientations, reflectance, and colors. We find the mounds are broadly
self-similar in many respects and interpret them as the original building
blocks of Arrokoth. It remains unclear why these building blocks are so similar
in size, and this represents a new constrain and challenge for solar system
formation models. We then discuss the interpretation of this interpretation.Comment: 24 pages, 8 figure
Failure of single-parameter scaling of wave functions in Anderson localization
We show how to use properties of the vectors which are iterated in the
transfer-matrix approach to Anderson localization, in order to generate the
statistical distribution of electronic wavefunction amplitudes at arbitary
distances from the origin of disordered systems. For
our approach is shown to reproduce exact diagonalization results
available in the literature. In , where strips of width sites
were used, attempted fits of gaussian (log-normal) forms to the wavefunction
amplitude distributions result in effective localization lengths growing with
distance, contrary to the prediction from single-parameter scaling theory. We
also show that the distributions possess a negative skewness , which is
invariant under the usual histogram-collapse rescaling, and whose absolute
value increases with distance. We find for the
range of parameters used in our study, .Comment: RevTeX 4, 6 pages, 4 eps figures. Phys. Rev. B (final version, to be
published
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