4,341 research outputs found
Electromagnetic Moments of the Baryon Decuplet
We compute the leading contributions to the magnetic dipole and electric
quadrupole moments of the baryon decuplet in chiral perturbation theory. The
measured value for the magnetic moment of the is used to determine
the local counterterm for the magnetic moments. We compare the chiral
perturbation theory predictions for the magnetic moments of the decuplet with
those of the baryon octet and find reasonable agreement with the predictions of
the large-- limit of QCD. The leading contribution to the quadrupole
moment of the and other members of the decuplet comes from one--loop
graphs. The pionic contribution is shown to be proportional to (and so
will not contribute to the quadrupole moment of nuclei), while the
contribution from kaons has both isovector and isoscalar components. The chiral
logarithmic enhancement of both pion and kaon loops has a coefficient that
vanishes in the limit. The third allowed moment, the magnetic octupole,
is shown to be dominated by a local counterterm with corrections arising at two
loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using
uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5
Hadron Spectrum with Wilson fermions
We present results of a high statistics study of the quenched spectrum using
Wilson fermions at on lattices. We calculate the
masses of mesons and baryons composed of both degenerate and non-degenerate
quarks. Using non-degenerate quark combinations allows us to study baryon mass
splittings in detail. We find significant deviations from the lowest order
chiral expansion, deviations that are consistent with the expectations of
quenched chiral perturbation theory. We find that there is a
systematic error in the extracted value of , depending on the meson mass
ratio used to set its value. Using the largest estimate of we find that
the extrapolated octet mass-splittings are in agreement with the experimental
values, as is , while the decuplet splittings are 30% smaller
than experiment. Combining our results with data from the GF11 collaboration we
find considerable ambiguity in the extrapolation to the continuum limit. Our
preferred values are and , suggesting that the quenched approximation is good to only . We also analyze the discretization errors in heavy quark
masses.Comment: 52 pages. Tex. Modified "axis" source for figures also included.
Needs macro packages lanlmac and epsf. Uses hyperbasics if available.
Significant number of typographical errors correcte
Magnetic moments of the SU(3) decuplet baryons in the chiral quark-soliton model
Magnetic moments of baryons are studied within the chiral quark soliton model
with special emphasis on the decuplet of baryons. The model is used to identify
all symmetry breaking terms proportional to . Sum rules for the
magnetic moments are derived. A ``model-independent'' analysis of the symmetry
breaking terms is performed and finally model calculations are presented, which
show the importance of the rotational corrections for cranking of
the soliton.Comment: 22 pages, RevTex. The final version accepted for publication in Phys.
Rev.
Terahertz Magneto Optical Polarization Modulation Spectroscopy
We report the development of new terahertz techniques for rapidly measuring
the complex Faraday angle in systems with broken time-reversal symmetry using
the cyclotron resonance of a GaAs two-dimensional electron gas in a magnetic
field as a system for demonstration of performance. We have made polarization
modulation, high sensitivity (< 1 mrad) narrow band rotation measurements with
a CW optically pumped molecular gas laser, and by combining the distinct
advantages of terahertz (THz) time domain spectroscopy and polarization
modulation techniques, we have demonstrated rapid broadband rotation
measurements to < 5 mrad precision.Comment: 25 pages including 7 figures, introduces use of rotating polarizer
with THz TDS for Complex Faraday Angle determinatio
Understanding Unauthorized Access using Fine-Grained Human-Computer Interaction Data
Unauthorized Data Access (UDA) by an internal employee is a major threat to an organization. Regardless of whether the individuals engaged in UDA with malicious intent or not, real-time identification of UDA events and anomalous behaviors is extremely difficult. For example, various artificial intelligence methods for detecting insider threat UDA have become readily available; while useful, such methods rely on post hoc analysis of the past (e.g., unsupervised learning algorithms on access logs). This research-in-progress note reports on if the analysis of Human-Computer Interaction (HCI) behaviors, which have been empirically validated in various studies to reveal hidden cognitive state, can be utilized as a method to detect UDAs. To examine this, an experimental design was required that would grant the subjects an opportunity to engage in UDA events while tracking the HCI behaviors in an unobtrusive manner. Background, experimental design, study execution, preliminary results, and future research plans are presented
Nucleon axial charge from quenched lattice QCD with domain wall fermions
We present a quenched lattice calculation of the nucleon isovector vector and
axial-vector charges gV and gA. The chiral symmetry of domain wall fermions
makes the calculation of the nucleon axial charge particularly easy since the
Ward-Takahashi identity requires the vector and axial-vector currents to have
the same renormalization, up to lattice spacing errors of order O(a^2). The
DBW2 gauge action provides enhancement of the good chiral symmetry properties
of domain wall fermions at larger lattice spacing than the conventional Wilson
gauge action. Taking advantage of these methods and performing a high
statistics simulation, we find a significant finite volume effect between the
nucleon axial charges calculated on lattices with (1.2 fm)^3 and (2.4 fm)^3
volumes (with lattice spacing, a, of about 0.15 fm). On the large volume we
find gA = 1.212 +/- 0.027(statistical error) +/- 0.024(normalization error).
The quoted systematic error is the dominant (known) one, corresponding to
current renormalization. We discuss other possible remaining sources of error.
This theoretical first principles calculation, which does not yet include
isospin breaking effects, yields a value of gA only a little bit below the
experimental one, 1.2670 +/- 0.0030.Comment: 38 pages, 12 figures, 9 tables, Revtex. Version accepted for
publication in Physical Review
Quantifying the impact of climate change on drought regimes using the Standardised Precipitation Index
The study presents a methodology to characterise short- or long-term drought events, designed to aid understanding of how climate change may affect future risk. An indicator of drought magnitude, combining parameters of duration, spatial extent and intensity, is presented based on the Standardised Precipitation Index (SPI). The SPI is applied to observed (1955â2003) and projected (2003â2050) precipitation data from the Community Integrated Assessment System (CIAS). Potential consequences of climate change on drought regimes in Australia, Brazil, China, Ethiopia, India, Spain, Portugal and the USA are quantified. Uncertainty is assessed by emulating a range of global circulation models to project climate change. Further uncertainty is addressed through the use of a high-emission scenario and a low stabilisation scenario representing a stringent mitigation policy. Climate change was shown to have a larger effect on the duration and magnitude of long-term droughts, and Australia, Brazil, Spain, Portugal and the USA were highlighted as being particularly vulnerable to multi-year drought events, with the potential for drought magnitude to exceed historical experience. The study highlights the characteristics of drought which may be more sensitive under climate change. For example, on average, short-term droughts in the USA do not become more intense but are projected to increase in duration. Importantly, the stringent mitigation scenario had limited effect on drought regimes in the first half of the twenty-first century, showing that adaptation to drought risk will be vital in these regions
Shapes, contact angles, and line tensions of droplets on cylinders
Using an interface displacement model we calculate the shapes of
nanometer-size liquid droplets on homogeneous cylindrical surfaces. We
determine effective contact angles and line tensions, the latter defined as
excess free energies per unit length associated with the two contact lines at
the ends of the droplet. The dependences of these quantities on the cylinder
radius and on the volume of the droplets are analyzed.Comment: 26 pages, RevTeX, 10 Figure
High pressure transport properties of the topological insulator Bi2Se3
We report x-ray diffraction, electrical resistivity, and magnetoresistance
measurements on Bi2Se3 under high pressure and low temperature conditions.
Pressure induces profound changes in both the room temperature value of the
electrical resistivity as well as the temperature dependence of the
resistivity. Initially, pressure drives Bi2Se3 towards increasingly insulating
behavior and then, at higher pressures, the sample appears to enter a fully
metallic state coincident with a change in the crystal structure. Within the
low pressure phase, Bi2Se3 exhibits an unusual field dependence of the
transverse magnetoresistance that is positive at low fields and becomes
negative at higher fields. Our results demonstrate that pressures below 8 GPa
provide a non-chemical means to controllably reduce the bulk conductivity of
Bi2Se3
Scaling, Multiscaling, and Nontrivial Exponents in Inelastic Collision Processes
We investigate velocity statistics of homogeneous inelastic gases using the
Boltzmann equation. Employing an approximate uniform collision rate, we obtain
analytic results valid in arbitrary dimension. In the freely evolving case, the
velocity distribution is characterized by an algebraic large velocity tail,
P(v,t) ~ v^{-sigma}. The exponent sigma(d,epsilon), a nontrivial root of an
integral equation, varies continuously with the spatial dimension, d, and the
dissipation coefficient, epsilon. Although the velocity distribution follows a
scaling form, its moments exhibit multiscaling asymptotic behavior.
Furthermore, the velocity autocorrelation function decays algebraically with
time, A(t)= ~ t^{-alpha}, with a non-universal dissipation-dependent
exponent alpha=1/epsilon. In the forced case, the steady state Fourier
transform is obtained via a cumulant expansion. Even in this case, velocity
correlations develop and the velocity distribution is non-Maxwellian.Comment: 10 pages, 3 figure
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