90,493 research outputs found
Comment on Meir Dan-Cohen, Skirmishes on the Temporal Boundaries of States
Goldberg praises Meir Dan-Cohen\u27s creative thinking about state wrongdoing but argues that it is ultimately unclear how a nation gets relieved of responsibility for its past harms. Equally unclear is why as a normative matter nations should be permitted to obtain temporal shifts. Dyadic conflicts that redefine the wrongdoer might be easier to envision because the victim is empowered to redraw the boundary of the wrongdoer. When a nation commits wrong, the justification for redrawing its boundaries often must come from somewhere other than a single victim\u27s forgiveness
Excitation Mechanisms of the Nitrogen FirstāPositive and FirstāNegative Radiation at High Temperature
The kinetic mechanisms responsible for the excitation of the first-positive and first-negative emission
of nitrogen have been investigated in a re-examination of previously reported shock-tube measurements
of the nonequilibrium radiation for these systems. The rate coefficients of the collisional quenching reactions, N_2(A^(3)Ī£^(+)_u)(^(k^(N)_(-2))ā) N_2(X^(1)Ī£^(+)_g) + N(^(4)S) and N^(+)_2(B^(2)Ī£^(+)_u) + N_2(X^(1)Ī£^(+)_g)(^(k^(N)_(q))ā) N^(+)_2(X^(2)Ī£^(+)_g) or N^(+)_2(A(^(2)II_u)+N_2(X^(1)Ī£^(+)_g)
were found to be given by the empirical expressions, k_(2^(N))=5.1x10^(-3)T^(-2.23) cm^3 sec^(-1) and k_(q^(N_2))=1.9x10^(-2)T^(-2.33)cm^3 sec^(-1), respectively, over the approximate temperature range 6000-14 000Ā°K
Quantum tomography for collider physics: Illustrations with lepton pair production
Quantum tomography is a method to experimentally extract all that is
observable about a quantum mechanical system. We introduce quantum tomography
to collider physics with the illustration of the angular distribution of lepton
pairs. The tomographic method bypasses much of the field-theoretic formalism to
concentrate on what can be observed with experimental data, and how to
characterize the data. We provide a practical, experimentally-driven guide to
model-independent analysis using density matrices at every step. Comparison
with traditional methods of analyzing angular correlations of inclusive
reactions finds many advantages in the tomographic method, which include
manifest Lorentz covariance, direct incorporation of positivity constraints,
exhaustively complete polarization information, and new invariants free from
frame conventions. For example, experimental data can determine the
of the production process, which is a
model-independent invariant that measures the degree of coherence of the
subprocess. We give reproducible numerical examples and provide a supplemental
standalone computer code that implements the procedure. We also highlight a
property of that guarantees in a least-squares type fit
that a local minimum of a statistic will be a global minimum: There
are no isolated local minima. This property with an automated implementation of
positivity promises to mitigate issues relating to multiple minima and
convention-dependence that have been problematic in previous work on angular
distributions.Comment: 25 pages, 3 figure
Amalgams of Inverse Semigroups and C*-algebras
An amalgam of inverse semigroups [S,T,U] is full if U contains all of the
idempotents of S and T. We show that for a full amalgam [S,T,U], the C*-algebra
of the inverse semigroup amaglam of S and T over U is the C*-algebraic amalgam
of C*(S) and C*(T) over C*(U). Using this result, we describe certain
amalgamated free products of C*-algebras, including finite-dimensional
C*-algebras, the Toeplitz algebra, and the Toeplitz C*-algebras of graphs
Hydrodynamic Simulations of the Bardeen-Petterson Effect
We present SPH simulations of accretion discs in orbit about rotating compact
objects such as black holes and neutron stars, and study the structure of
warped discs produced by the Bardeen-Petterson effect. We calculate the
transition radius out to which the disc specific angular momentum vector is
aligned with that of the black hole. We focus on the parameter regime where the
warp dynamics are controlled by bending wave propagation, but also consider
models in which warps are subject to diffusion rather than wave transport, and
are able to consider the fully nonlinear regime. Because of hydrodynamic or
pressure effects, for the parameter range investigated, the transition radius
is always found to be much smaller than that obtained by Bardeen & Petterson
(1975). For discs with midplane Mach numbers of about 10, the transition occurs
between 10 - 16 gravitational radii, whereas for a Mach number of about 30 it
occurs at around 30 gravitational radii. A thicker disc with a Mach number of 5
is found to produce no discernible warped structure. The rate of black hole -
disc alignment is found to be consistent with the ideas of Ress (1978), with
the alignment torque behaving as if it arises from the accreted material
transferring its misaligned component of angular momentum at the larger
transition radius of Bardeen & Petterson (1975). The inclusion of Einstein
precession in the calculations modified both the warped disc structure and,
consistent with linear analysis, produced an increased alignment rate by up to
a factor of 4 because of the effect that a non Keplerian potential has on the
propagation of warps.Comment: 18 pages, 14 figures. Accepted for publication in M.N.R.A.S. A
version with posctcript figures included can be obtained from
http://www.maths.qmw.ac.uk/~rp
Compulsory Deep Mixing of 3He and CNO Isotopes in the Envelopes of low-mass Red Giants
Three-dimensional stellar modeling has enabled us to identify a deep-mixing
mechanism that must operate in all low mass giants. This mixing process is not
optional, and is driven by a molecular weight inversion created by the
3He(3He,2p)4He reaction. In this paper we characterize the behavior of this
mixing, and study its impact on the envelope abundances. It not only eliminates
the problem of 3He overproduction, reconciling stellar and big bang
nucleosynthesis with observations, but solves the discrepancy between observed
and calculated CNO isotope ratios in low mass giants, a problem of more than 3
decades' standing. This mixing mechanism, which we call `-mixing',
operates rapidly (relative to the nuclear timescale of overall evolution, ~
10^8 yrs) once the hydrogen burning shell approaches the material homogenized
by the surface convection zone. In agreement with observations, Pop I stars
between 0.8 and 2.0\Msun develop 12C/13C ratios of 14.5 +/- 1.5, while Pop II
stars process the carbon to ratios of 4.0 +/- 0.5. In stars less than
1.25\Msun, this mechanism also destroys 90% to 95% of the 3He produced on the
main sequence.Comment: Final accepted version (submitted to Astrophys J in Jan 2007...
- ā¦