31,367 research outputs found
Pairing gaps in Hartree-Fock Bogoliubov theory with the Gogny D1S interaction
As part of a program to study odd-A nuclei in the Hartree-Fock-Bogoliubov
(HFB) theory, we have developed a new calculational tool to find the HFB minima
of odd-A nuclei based on the gradient method and using interactions of Gogny's
form. The HFB minimization includes both time-even and time-odd fields in the
energy functional, avoiding the commonly used "filling approximation". Here we
apply the method to calculate neutron pairing gaps in some representative
isotope chains of spherical and deformed nuclei, namely the Z=8,50 and 82
spherical chains and the Z=62 and 92 deformed chains. We find that the gradient
method is quite robust, permitting us to carry out systematic surveys involving
many nuclei. We find that the time-odd field does not have large effect on the
pairing gaps calculated with the Gogny D1S interaction. Typically, adding the
T-odd field as a perturbation increases the pairing gap by ~100 keV, but the
re-minimization brings the gap back down. This outcome is very similar to
results reported for the Skyrme family of nuclear energy density functionals.
Comparing the calculated gaps with the experimental ones, we find that the
theoretical errors have both signs implying that the D1S interaction has a
reasonable overall strength. However, we find some systematic deficiencies
comparing spherical and deformed chains and comparing the lighter chains with
the heavier ones. The gaps for heavy spherical nuclei are too high, while those
for deformed nuclei tend to be too low. The calculated gaps of spherical nuclei
show hardly any A-dependence, contrary to the data. Inclusion of the T-odd
component of the interaction does not change these qualitative findings
Mass Detection with Nonlinear Nanomechanical Resonator
Nanomechanical resonators having small mass, high resonance frequency and low
damping rate are widely employed as mass detectors. We study the performances
of such a detector when the resonator is driven into a region of nonlinear
oscillations. We predict theoretically that in this region the system acts as a
phase-sensitive mechanical amplifier. This behavior can be exploited to achieve
noise squeezing in the output signal when homodyne detection is employed for
readout. We show that mass sensitivity of the device in this region may exceed
the upper bound imposed by thermomechanical noise upon the sensitivity when
operating in the linear region. On the other hand, we show that the high mass
sensitivity is accompanied by a slowing down of the response of the system to a
change in the mass
ESTIMATING SITE-SPECIFIC NITROGEN CROP RESPONSE FUNCTIONS: A CONCEPTUAL FRAMEWORK AND GEOSTATISTICAL MODEL
Confirming the precision agriculture hypothesis for variable rate nitrogen applications (VRA) is challenging. To confront this challenge, researchers have used increasingly sophisticated statistical models to estimate and compare site-specific crop response functions (SSCRFs). While progress has been made, it has been hampered by the lack of a conceptual framework to guide the development of appropriate statistical models. This paper provides such a framework and demonstrates its utility by developing a heteroscedastic, fixed and random effects, geostatistical model to test if VRA can increase nitrogen returns. The novelty of the model is the inclusion of site, spatial, treatment, and treatment strip heteroscedasticity and correlation. Applied to data collected in 1995 from two corn nitrogen response experiments in South Central Minnesota, results demonstrate the importance of including site, spatial, treatment, and treatment strip effects in the estimation of SSCRFs. Results also indicate a significant potential for VRA to increase nitrogen returns and that these potential returns increase as the area of the management unit decreases. At one location, there was greater than a 95% chance that VRA could have increased profitability if the cost of implementing VRA was less than 14.5 ha-1, there was greater than a 95% chance of increased profitability.Crop Production/Industries,
High frequency electro-optic measurement of strained silicon racetrack resonators
The observation of the electro-optic effect in strained silicon waveguides
has been considered as a direct manifestation of an induced
non-linearity in the material. In this work, we perform high frequency
measurements on strained silicon racetrack resonators. Strain is controlled by
a mechanical deformation of the waveguide. It is shown that any optical
modulation vanishes independently of the applied strain when the applied
voltage varies much faster than the carrier effective lifetime, and that the DC
modulation is also largely independent of the applied strain. This demonstrates
that plasma carrier dispersion is responsible for the observed electro-optic
effect. After normalizing out free carrier effects, our results set an upper
limit of to the induced high-speed tensor
element at an applied stress of . This upper limit is about one
order of magnitude lower than the previously reported values for static
electro-optic measurements
A Lattice Study of the Gluon Propagator in Momentum Space
We consider pure glue QCD at beta=5.7, beta=6.0 and beta=6.3. We evaluate the
gluon propagator both in time at zero 3-momentum and in momentum space. From
the former quantity we obtain evidence for a dynamically generated effective
mass, which at beta=6.0 and beta=6.3 increases with the time separation of the
sources, in agreement with earlier results. The momentum space propagator G(k)
provides further evidence for mass generation. In particular, at beta=6.0, for
k less than 1 GeV, the propagator G(k) can be fit to a continuum formula
proposed by Gribov and others, which contains a mass scale b, presumably
related to the hadronization mass scale. For higher momenta Gribov's model no
longer provides a good fit, as G(k) tends rather to follow an inverse power
law. The results at beta=6.3 are consistent with those at beta=6.0, but only
the high momentum region is accessible on this lattice. We find b in the range
of three to four hundred MeV and the exponent of the inverse power law about
2.7. On the other hand, at beta=5.7 (where we can only study momenta up to 1
GeV) G(k) is best fit to a simple massive boson propagator with mass m. We
argue that such a discrepancy may be related to a lack of scaling for low
momenta at beta=5.7. {}From our results, the study of correlation functions in
momentum space looks promising, especially because the data points in Fourier
space turn out to be much less correlated than in real space.Comment: 19 pages + 12 uuencoded PostScript picture
Nonlocal Scalar Quantum Field Theory: Functional Integration, Basis Functions Representation and Strong Coupling Expansion
Nonlocal QFT of one-component scalar field in -dimensional
Euclidean spacetime is considered. The generating functional (GF) of complete
Green functions as a functional of external source , coupling
constant , and spatial measure is studied. An expression for GF
in terms of the abstract integral over the primary field
is given. An expression for GF in terms of integrals
over the primary field and separable Hilbert space (HS) is obtained by means of
a separable expansion of the free theory inverse propagator over the
separable HS basis. The classification of functional integration measures
is formulated, according to which trivial and
two nontrivial versions of GF are obtained. Nontrivial versions
of GF are expressed in terms of -norm and -norm,
respectively. The definition of the -norm generator is suggested.
Simple cases of sharp and smooth generators are considered. Expressions for GF
in terms of integrals over the separable HS with new integrands
are obtained. For polynomial theories and for
the nonpolynomial theory , integrals over the separable HS in
terms of a power series over the inverse coupling constant for
both norms (-norm and -norm) are calculated. Critical values of model
parameters when a phase transition occurs are found numerically. A
generalization of the theory to the case of the uncountable integral over HS is
formulated. A comparison of two GFs , one in the case of
uncountable HS integral and one obtained using the Parseval-Plancherel
identity, is given.Comment: 26 pages, 2 figures; v2: significant additions in the text; prepared
for the special issue "QCD and Hadron Structure" of the journal Particles;
v3: minimal corrections; v4: paragraphs added related to Reviewer comment
-Matrix of Nonlocal Scalar Quantum Field Theory in the Representation of Basis Functions
Nonlocal quantum theory of one-component scalar field in -dimensional
Euclidean spacetime is studied in representations of -matrix
theory for both polynomial and nonpolynomial interaction Lagrangians. The
theory is formulated on coupling constant in the form of an infrared smooth
function of argument for space without boundary. Nonlocality is given by
evolution of Gaussian propagator for the local free theory with ultraviolet
form factors depending on ultraviolet length parameter . By representation
of the -matrix in terms of abstract functional integral over
primary scalar field, the form of a grand canonical partition
function is found. And, by expression of -matrix in terms of the
partition function, the representation for in terms of basis
functions is obtained. Derivations are given for discrete case where basis
functions are Hermite functions, and for continuous case where basis functions
are trigonometric functions. The obtained expressions for the
-matrix are investigated within the framework of variational
principle based on Jensen inequality. Equations with separable kernels
satisfied by variational function are found and solved, yielding results
for both the polynomial theory and the nonpolynomial sine-Gordon
theory. A new definition of the -matrix is proposed to solve
additional divergences which arise in application of Jensen inequality for the
continuous case. Analytical results are illustrated numerically. For simplicity
of numerical calculation: the case is considered, and propagator for the
free theory is in the form of Gaussian function typically in the
Virton-Quark model. The formulation for nonlocal QFT in momentum space of
extra dimensions with subsequent compactification into physical spacetime is
discussed.Comment: 38 pages, 18 figures; v2: significant text editing; v3: text and
plots edited, references and acknowledgments added; prepared for the special
issue of the journal Particles in memory of G.V. Efimo
The origin of the LMC stellar bar: clues from the SFH of the bar and inner disk
We discuss the origin of the LMC stellar bar by comparing the star formation
histories (SFH) obtained from deep color-magnitude diagrams (CMDs) in the bar
and in a number of fields in different directions within the inner disk. The
CMDs, reaching the oldest main sequence turnoffs in these very crowded fields,
have been obtained with VIMOS on the VLT in service mode, under very good
seeing conditions. We show that the SFHs of all fields share the same patterns,
with consistent variations of the star formation rate as a function of time in
all of them. We therefore conclude that no specific event of star formation can
be identified with the formation of the LMC bar, which instead likely formed
from a redistribution of disk material that occurred when the LMC disk became
bar unstable, and shared a common SFH with the inner disk thereafter. The
strong similarity between the SFH of the center and edge of the bar rules out
significant spatial variations of the SFH across the bar, which are predicted
by scenarios of classic bar formation through buckling mechanisms.Comment: MNRAS Letters, accepte
Finite-volume two-pion energies and scattering in the quenched approximation
We investigate how L\"uscher's relation between the finite-volume energy of
two pions at rest and pion scattering lengths has to be modified in quenched
QCD. We find that this relation changes drastically, and in particular, that
``enhanced finite-volume corrections" of order and occur at
one loop ( is the linear size of the box), due to the special properties of
the in the quenched approximation. We define quenched pion scattering
lengths, and show that they are linearly divergent in the chiral limit. We
estimate the size of these various effects in some numerical examples, and find
that they can be substantial.Comment: 22 pages, uuencoded, compressed postscript fil
Pion-Nucleon Phase Shifts in Heavy Baryon Chiral Perturbation Theory
We calculate the phase shifts in the pion-nucleon scattering using the heavy
baryon formalism. We consider phase shifts for the pion energy range of 140 to
MeV. We employ two different methods for calculating the phase shifts -
the first using the full third order calculation of the pion-nucleon scattering
amplitude and the second by including the resonances and as
explicit degrees of freedom in the Lagrangian. We compare the results of the
two methods with phase shifts extracted from fits to the pion-nucleon
scattering data. We find good to fair agreement between the calculations and
the phase shifts from scattering data.Comment: 14 pages, Latex, 6figures. Revised version to appear in Phys.Rev.
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