30,856 research outputs found
The Operator form of 3H (3He) and its Spin Structure
An operator form of the 3N bound state is proposed. It consists of eight
operators formed out of scalar products in relative momentum and spin vectors,
which are applied on a pure 3N spin 1/2 state. Each of the operators is
associated with a scalar function depending only on the magnitudes of the two
relative momenta and the angle between them. The connection between the
standard partial wave decomposition of the 3N bound state and the operator form
is established, and the decomposition of these scalar function in terms of
partial wave components and analytically known auxiliary functions is given.
That newly established operator form of the 3N bound state exhibits the
dominant angular and spin dependence analytically. The scalar functions are
tabulated and can be downloaded. As an application the spin dependent nucleon
momentum distribution in a polarized 3N bound state is calculated to illustrate
the use of the new form of the 3N bound state.Comment: 21 pages, 1 table, 8 figures, revtex
Summary of all cycle II.5 shear and boundary layer measurements, aerodynamics
The two measurement systems were used to measure mean velocity and velocity, mass flux, and total temperature fluctuations in the turbulent boundary on the fuselage of a KC-135 aircraft. The boundary layer thickness ranged between about 20 and 30 cm for the range of flight Mach numbers from about 0.25 to 0.85 and Reynolds numbers between 3 and 6 x 10 to the 6th power/m. The adaptation of each system for use in airborne applications is discussed. The data obtained from each system are given and compared with each other and they indicate that the two systems represent viable ones for use in future airborne turbulence experiments
The Potential of Learned Index Structures for Index Compression
Inverted indexes are vital in providing fast key-word-based search. For every
term in the document collection, a list of identifiers of documents in which
the term appears is stored, along with auxiliary information such as term
frequency, and position offsets. While very effective, inverted indexes have
large memory requirements for web-sized collections. Recently, the concept of
learned index structures was introduced, where machine learned models replace
common index structures such as B-tree-indexes, hash-indexes, and
bloom-filters. These learned index structures require less memory, and can be
computationally much faster than their traditional counterparts. In this paper,
we consider whether such models may be applied to conjunctive Boolean querying.
First, we investigate how a learned model can replace document postings of an
inverted index, and then evaluate the compromises such an approach might have.
Second, we evaluate the potential gains that can be achieved in terms of memory
requirements. Our work shows that learned models have great potential in
inverted indexing, and this direction seems to be a promising area for future
research.Comment: Will appear in the proceedings of ADCS'1
High Accuracy Fuel Flowmeter, Phase 1
Technology related to aircraft fuel mass - flowmeters was reviewed to determine what flowmeter types could provide 0.25%-of-point accuracy over a 50 to one range in flowrates. Three types were selected and were further analyzed to determine what problem areas prevented them from meeting the high accuracy requirement, and what the further development needs were for each. A dual-turbine volumetric flowmeter with densi-viscometer and microprocessor compensation was selected for its relative simplicity and fast response time. An angular momentum type with a motor-driven, spring-restrained turbine and viscosity shroud was selected for its direct mass-flow output. This concept also employed a turbine for fast response and a microcomputer for accurate viscosity compensation. The third concept employed a vortex precession volumetric flowmeter and was selected for its unobtrusive design. Like the turbine flowmeter, it uses a densi-viscometer and microprocessor for density correction and accurate viscosity compensation
A fiber-optic current sensor for aerospace applications
A robust, accurate, broad-band, alternating current sensor using fiber optics is being developed for space applications at power frequencies as high as 20 kHz. It can also be used in low and high voltage 60 Hz terrestrial power systems and in 400 Hz aircraft systems. It is intrinsically electromagnetic interference (EMI) immune and has the added benefit of excellent isolation. The sensor uses the Faraday effect in optical fiber and standard polarimetric measurements to sense electrical current. The primary component of the sensor is a specially treated coil of single-mode optical fiber, through which the current carrying conductor passes. Improved precision is accomplished by temperature compensation by means of signals from a novel fiber-optic temperature sensor embedded in the sensing head. The technology contained in the sensor is examined and the results of precision tests conducted at various temperatures within the wide operating range are given. The results of early EMI tests are also given
Hot Populations in M87 Globular Clusters
We have obtained HST/STIS far- and near-UV photometry of globular clusters in
four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total
of 66 globular clusters (GCs) in common with the deep HST optical-band study of
Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the
M87 GCs have UV/optical properties that are distinct from clusters in the Milky
Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB
populations than do Milky Way analogues. Cluster mass is probably not a factor
in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun
and overlap the local E galaxy sample in estimated Mg_2 line indices.
Nonetheless, the clusters produce much more UV light at a given Mg_2, being up
to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear
to represent a transition between Milky Way-type clusters and E galaxies. The
differences are in the correct sense if the clusters are significantly older
than the E galaxies. Comparisons with Galactic open clusters indicate that the
hot stars lie on the extreme horizontal branch, rather than being blue
stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find
that 43 of our UV detections have no optical-band counterparts. Most appear to
be UV-bright background galaxies, seen through M87. Eleven NUV variable sources
detected at only one epoch in the central field are probably classical novae.
[Abridged]Comment: 70 pages, 25 figures (including 4 jpgs), 7 tables. To appear in AJ.
Full resolution version available at
http://www.astro.virginia.edu/~rwo/m87/m87-hotpops.pd
Fiber-optic sensors for aerospace electrical measurements: An update
Fiber-optic sensors are being developed for electrical current, voltage, and power measurements in aerospace applications. These sensors are presently designed to cover ac frequencies from 60 Hz to 20 kHz. The current sensor, based on the Faraday effect in optical fiber, is in advanced development after some initial testing. Concentration is on packaging methods and ways to maintain consistent sensitivity with changes in temperature. The voltage sensor, utilizing the Pockels effect in a crystal, has excelled in temperature tests. This paper reports on the development of these sensors, the results of evaluation, improvements now in progress, and the future direction of the work
Biofuel Growth: Global Greenhouse Gas Emissions Impacts from Changes in Forest Carbon Stocks
There is significant policy interest in liquid biofuels with appealing prospects for energy security, farm security, poverty alleviation, and climate change. Large-scale commercial biofuel production could have far reaching implications for regional and global markets – particularly those related to energy and land use. As such, large-scale biofuels growth is likely to have significant impacts on global greenhouse gas (GHG) emissions. This paper utilizes a CGE model with explicit biofuel, land, and energy markets. The model is able to estimate the effects on the broad range of input and output markets potentially affected globally by biofuels policies. One of the most controversial issues within the biofuels debate is potential indirect changes in land use and, in particular, the resulting changes in forest carbon stocks. To uncover consequences of biofuel policies for forest carbon, we link our CGE model with a dynamic forward looking model of the forest sector. Within this framework, we evaluate the potential effects of US and multinational biofuels growth on changes in land use and emissions from changes in forest carbon stocks.land use change, biofuels, CGE model, forest carbon stocks, GHG emissions, Resource /Energy Economics and Policy,
Unambiguous pure state identification without classical knowledge
We study how to unambiguously identify a given quantum pure state with one of
the two reference pure states when no classical knowledge on the reference
states is given but a certain number of copies of each reference quantum state
are presented. By the unambiguous identification, we mean that we are not
allowed to make a mistake but our measurement can produce an inconclusive
result. Assuming the two reference states are independently distributed over
the whole pure state space in a unitary invariant way, we determine the optimal
mean success probability for an arbitrary number of copies of the reference
states and a general dimension of the state space. It is explicitly shown that
the obtained optimal mean success probability asymptotically approaches that of
the unambiguous discrimination as the number of the copies of the reference
states increases.Comment: v3: 8 pages, minor corrections, journal versio
Photoconductance of a submicron oxidized line in surface conductive single crystalline diamond
We report on sub-bandgap optoelectronic phenomena of hydrogen-terminated
diamond patterned with a submicron oxidized line. The line acts as an energy
barrier for the two-dimensional hole gas located below the hydrogenated diamond
surface. A photoconductive gain of the hole conductivity across the barrier is
measured for sub-bandgap illumination. The findings are consistent with
photogenerated electrons being trapped in defect levels within the barrier. We
discuss the spatial and energetic characteristics of the optoelectronic
phenomena, as well as possible photocurrent effects
- …