14,626 research outputs found
Ceramic automotive Stirling engine study
A conceptual design study for a Ceramic Automotive Stirling Engine (CASE) is performed. Year 1990 structural ceramic technology is assumed. Structural and performance analyses of the conceptual design are performed as well as a manufacturing and cost analysis. The general conclusions from this study are that such an engine would be 10-26% more efficient over its performance map than the current metal Automotive Stirling Reference Engine (ASRE). Cost of such a ceramic engine is likely to be somewhat higher than that of the ASRE but engine cost is very sensitive to the ultimate cost of the high purity, ceramic powder raw materials required to fabricate high performance parts. When the design study is projected to the year 2000 technology, substantinal net efficiency improvements, on the order of 25 to 46% over the ASRE, are computed
Inflatonless Inflation
We consider a 4+N dimensional Einstein gravity coupled to a non-linear sigma
model. This theory admits a solution in which the N extra dimensions contract
exponentially while the ordinary space expand exponentially. Physically, the
non-linear sigma fields induce the dynamical compactification of the extra
dimensions, which in turn drives inflation. No inflatons are required.Comment: 12 pages, version to appear in IJMP
Interplay between antiferromagnetic order and spin polarization in ferromagnetic metal/electron-doped cuprate superconductor junctions
Recently we proposed a theory of point-contact spectroscopy and argued that
the splitting of zero-bias conductance peak (ZBCP) in electron-doped cuprate
superconductor point-contact spectroscopy is due to the coexistence of
antiferromagnetic (AF) and d-wave superconducting orders [Phys. Rev. B {\bf
76}, 220504(R) (2007)]. Here we extend the theory to study the tunneling in the
ferromagnetic metal/electron-doped cuprate superconductor (FM/EDSC) junctions.
In addition to the AF order, the effects of spin polarization, Fermi-wave
vector mismatch (FWM) between the FM and EDSC regions, and effective barrier
are investigated. It is shown that there exits midgap surface state (MSS)
contribution to the conductance to which Andreev reflections are largely
modified due to the interplay between the exchange field of ferromagnetic metal
and the AF order in EDSC. Low-energy anomalous conductance enhancement can
occur which could further test the existence of AF order in EDSC. Finally, we
propose a more accurate formula in determining the spin polarization value in
combination with the point-contact conductance data.Comment: 9 pages, 8 figure
Positivity of Quasilocal Mass
Motivated by the important work of Brown adn York on quasilocal energy, we
propose definitions of quasilocal energy and momentum surface energy of a
spacelike 2-surface with positive intrinsic curvature in a spacetime. We show
that the quasilocal energy of the boundary of a compact spacelike hypersurface
which satisfies the local energy condition is strictly positive unless the
spacetime is flat along the spacelike hypersurface.Comment: 4 pages; final published versio
Seventy-One New L and T Dwarfs from the Sloan Digital Sky Survey
We present near-infrared observations of 71 newly discovered L and T dwarfs,
selected from imaging data of the Sloan Digital Sky Survey (SDSS) using the
i-dropout technique. Sixty-five of these dwarfs have been classified
spectroscopically according to the near-infrared L dwarf classification scheme
of Geballe et al. and the unified T dwarf classification scheme of Burgasser et
al. The spectral types of these dwarfs range from L3 to T7, and include the
latest types yet found in the SDSS. Six of the newly identified dwarfs are
classified as early- to mid-L dwarfs according to their photometric
near-infrared colors, and two others are classified photometrically as M
dwarfs. We also present new near-infrared spectra for five previously published
SDSS L and T dwarfs, and one L dwarf and one T dwarf discovered by Burgasser et
al. from the Two Micron All Sky Survey. The new SDSS sample includes 27 T
dwarfs and 30 dwarfs with spectral types spanning the complex L-T transition
(L7-T3). We continue to see a large (~0.5 mag) spread in J-H for L3 to T1
types, and a similar spread in H-K for all dwarfs later than L3. This color
dispersion is probably due to a range of grain sedimentation properties,
metallicity, and gravity. We also find L and T dwarfs with unusual colors and
spectral properties that may eventually help to disentangle these effects.Comment: accepted by AJ, 18 pages, 10 figures, 5 tables, emulateapj layou
On Recognizing Transparent Objects in Domestic Environments Using Fusion of Multiple Sensor Modalities
Current object recognition methods fail on object sets that include both
diffuse, reflective and transparent materials, although they are very common in
domestic scenarios. We show that a combination of cues from multiple sensor
modalities, including specular reflectance and unavailable depth information,
allows us to capture a larger subset of household objects by extending a state
of the art object recognition method. This leads to a significant increase in
robustness of recognition over a larger set of commonly used objects.Comment: 12 page
Orbital Ferromagnetism and Quantum Collapse in Stellar Plasmas
The possibility of quantum collapse and characteristics of nonlinear
localized excitations is examined in dense stars with Landau orbital
ferromagnetism in the framework of conventional quantum magnetohydrodynamics
(QMHD) model including Bohm force and spin-orbit polarization effects.
Employing the concepts of effective potential and Sagdeev pseudopotential, it
is confirmed that the quantum collapse and Landau orbital ferromagnetism
concepts are consistent with the magnetic field and mass-density range present
in some white dwarf stars. Furthermore, the value of ferromagnetic-field found
in this work is about the same order of magnitude as the values calculated
earlier. It is revealed that the magnetosonic nonlinear propagations can behave
much differently in the two distinct non-relativistic and relativistic
degeneracy regimes in a ferromagnetic dense astrophysical object. Current
findings should help to understand the origin of the most important mechanisms
such as gravitational collapse and the high magnetic field present in many
compact stars.Comment: To appear in journal Physics of Plasma
Stops and MET: the shape of things to come
LHC experiments have placed strong bounds on the production of supersymmetric
colored particles (squarks and gluinos), under the assumption that all flavors
of squarks are nearly degenerate. However, the current experimental constraints
on stop squarks are much weaker, due to the smaller production cross section
and difficult backgrounds. While light stops are motivated by naturalness
arguments, it has been suggested that such particles become nearly impossible
to detect near the limit where their mass is degenerate with the sum of the
masses of their decay products. We show that this is not the case, and that
searches based on missing transverse energy (MET) have significant reach for
stop masses above 175 GeV, even in the degenerate limit. We consider direct
pair production of stops, decaying to invisible LSPs and tops with either
hadronic or semi-leptonic final states. Modest intrinsic differences in MET are
magnified by boosted kinematics and by shape analyses of MET or suitably-chosen
observables related to MET. For these observables we show that the
distributions of the relevant backgrounds and signals are well-described by
simple analytic functions, in the kinematic regime where signal is enhanced.
Shape analyses of MET-related distributions will allow the LHC experiments to
place significantly improved bounds on stop squarks, even in scenarios where
the stop-LSP mass difference is degenerate with the top mass. Assuming 20/fb of
luminosity at 8 TeV, we conservatively estimate that experiments can exclude or
discover degenerate stops with mass as large as ~ 360 GeV and 560 GeV for
massless LSPs.Comment: Version submitted to journal with improved analysis and small fixes,
27 pages, 11 figures, 2 table
Extended model of sport spectator goal-directed behavior: The role of event prestige in non-major sport events
Although the importance of destinations' image has been explored in the extant literature, little is known about the influence of event prestige on spectators' intention to attend recurring sport events, especially in the case of nonmajor international events. Given the situation, the current study incorporated spectators' perception of event prestige on the basis of the Model of Goal-directed Behavior (MGB) as a research framework to investigate their behavioral intention to attend nonmajor sport events. An on-site survey was conducted for spectators (N = 371) who attended the 2016 William Jones Cup Tournament held in Taipei, Taiwan. The results revealed that attitude, subjective norm, positive anticipated emotion, negative anticipated emotion, and perceived behavioral control played significant roles in influencing spectators' desire to attend sport events. Moreover, event prestige and desire have significant influences on spectators' intention. Theoretical and practical implications of the study results were discussed
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