2,318 research outputs found
Correlations and the relativistic structure of the nucleon self-energy
A key point of Dirac Brueckner Hartree Fock calculations for nuclear matter
is to decompose the self energy of the nucleons into Lorentz scalar and vector
components. A new method is introduced for this decomposition. It is based on
the dependence of the single-particle energy on the small component in the
Dirac spinors used to calculate the matrix elements of the underlying NN
interaction. The resulting Dirac components of the self-energy depend on the
momentum of the nucleons. At densities around and below the nuclear matter
saturation density this momentum dependence is dominated by the non-locality of
the Brueckner G matrix. At higher densities these correlation effects are
suppressed and the momentum dependence due to the Fock exchange terms is
getting more important. Differences between symmetric nuclear matter and
neutron matter are discussed. Various versions of the Bonn potential are
considered.Comment: 18 pages LaTeX, including 6 figure
Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets
The concept of local isotropy in a chemically reacting turbulent wall-jet
flow is addressed using direct numerical simulation (DNS) data. Different DNS
databases with isothermal and exothermic reactions are examined. The chemical
reaction and heat release effects on the turbulent velocity, passive scalar and
reactive species fields are studied using their probability density functions
(PDF) and higher order moments for velocities and scalar fields, as well as
their gradients. With the aid of the anisotropy invariant maps for the Reynolds
stress tensor the heat release effects on the anisotropy level at different
wall-normal locations are evaluated and found to be most accentuated in the
near-wall region. It is observed that the small-scale anisotropies are
persistent both in the near-wall region and inside the jet flame. Two
exothermic cases with different Damkohler number are examined and the
comparison revealed that the Damkohler number effects are most dominant in the
near-wall region, where the wall cooling effects are influential. In addition,
with the aid of PDFs conditioned on the mixture fraction, the significance of
the reactive scalar characteristics in the reaction zone is illustrated. We
argue that the combined effects of strong intermittency and strong persistency
of anisotropy at the small scales in the entire domain can affect mixing and
ultimately the combustion characteristics of the reacting flow
Network characteristics of financial networks
We embrace a fresh perspective to auditing by analyzing a large set of
companies as complex financial networks rather than static aggregates of
balance sheet data. Preliminary analyses show that network centrality measures
within these networks could significantly enhance auditors' insights into
financial structures. Utilizing data from over 300 diverse companies, we
examine the structure of financial statement networks through bipartite graph
analysis, exploring their scale-freeness by comparing degree distributions to
power-law and exponential models. Our findings indicate heavy-tailed degree
distribution for financial account nodes, networks that grow with the same
diameter, and the presence of influential hubs. This study lays the groundwork
for future auditing methodologies where baseline network statistics could serve
as indicators for anomaly detection, marking a substantial advancement in audit
research and network science
Relativistic Structure of the Nucleon Self-Energy in Asymmetric Nuclei
The Dirac structure of the nucleon self-energy in asymmetric nuclear matter
cannot reliably be deduced from the momentum dependence of the single-particle
energies. It is demonstrated that such attempts yield an isospin dependence
with even a wrong sign. Relativistic studies of finite nuclei have been based
on such studies of asymmetric nuclear matter. The effects of these isospin
components on the results for finite nuclei are investigated.Comment: 9 pages, Latex 4 figures include
The Sensitivity of Auditory-Motor Representations to Subtle Changes in Auditory Feedback While Singing
Singing requires accurate control of the fundamental frequency (F0) of the voice. This study examined trained singers’ and untrained singers’ (nonsingers’) sensitivity to subtle manipulations in auditory feedback and the subsequent effect on the mapping between F0 feedback and vocal control. Participants produced the consonant-vowel /ta/ while receiving auditory feedback that was shifted up and down in frequency. Results showed that singers and nonsingers compensated to a similar degree when presented with frequency-altered feedback (FAF); however, singers’ F0 values were consistently closer to the intended pitch target. Moreover, singers initiated their compensatory responses when auditory feedback was shifted up or down 6 cents or more, compared to nonsingers who began compensating when feedback was shifted up 26 cents and down 22 cents. Additionally, examination of the first 50 ms of vocalization indicated that participants commenced subsequent vocal utterances, during FAF, near the F0 value on previous shift trials. Interestingly, nonsingers commenced F0 productions below the pitch target and increased their F0 until they matched the note. Thus, singers and nonsingers rely on an internal model to regulate voice F0, but singers’ models appear to be more sensitive in response to subtle discrepancies in auditory feedback
Scalar and vector decomposition of the nucleon self-energy in the relativistic Brueckner approach
We investigate the momentum dependence of the nucleon self-energy in nuclear
matter. We apply the relativistic Brueckner-Hartree-Fock approach and adopt the
Bonn A potential. A strong momentum dependence of the scalar and vector
self-energy components can be observed when a commonly used pseudo-vector
choice for the covariant representation of the T-matrix is applied. This
momentum dependence is dominated by the pion exchange. We discuss the problems
of this choice and its relations to on-shell ambiguities of the T-matrix
representation. Starting from a complete pseudo-vector representation of the
T-matrix, which reproduces correctly the pseudo-vector pion-exchange
contributions at the Hartree-Fock level, we observe a much weaker momentum
dependence of the self-energy. This fixes the range of the inherent uncertainty
in the determination of the scalar and vector self-energy components. Comparing
to other work, we find that extracting the self-energy components by a fit to
the single particle potential leads to even more ambiguous results.Comment: 35 pages RevTex, 7 PS figures, replaced by a revised and extended
versio
The acoustic space of pain: cries as indicators of distress recovering dynamics in preverbal infants
Crying is a vital built-in survival mechanism for the Human baby. Yet both the information carried by cries and the factors driving the perception and reaction of adult listeners remain under-investigated. Here, we contrasted the relevance of psychoacoustic vs. acoustic evaluation for the assessment of distress levels in babies' cries recorded during baths and during an immunization event. Parents asked to rate the level of distress experienced by babies from listening to their cries attributed lower pain ratings to mild discomfort (bath) than to distress (vaccination) cries but failed to discriminate between different putative levels of pain experienced during different vaccination sequences. In contrast, vocal "roughness", a composite acoustic factor characterising the level of aperiodicity of the cries, not only differed between mild discomfort and distress cries but also between the levels of pain experienced during the different vaccination sequences. These observations suggest that acoustic analyses are more powerful than psychoacoustic evaluations for discriminating distress levels in babies’ cries, and opens the way for the design of a tool based on the acoustics of cries for assessing and monitoring pain levels in preverbal infants
The back reaction and the effective Einstein's equation for the Universe with ideal fluid cosmological perturbations
We investigate the back reaction of cosmological perturbations on the
evolution of the Universe using the renormalization group method. Starting from
the second order perturbed Einstein's equation, we renormalize a scale factor
of the Universe and derive the evolution equation for the effective scale
factor which includes back reaction due to inhomogeneities of the Universe. The
resulting equation has the same form as the standard Friedman-Robertson-Walker
equation with the effective energy density and pressure which represent the
back reaction effect.Comment: 16 pages, to appear in Phys. Rev.
Back Reaction Problem in the Inflationary Universe
We investigate the back reaction of cosmological perturbations on an
inflationary universe using the renormalization-group method. The second-order
zero mode solution which appears by the nonlinearity of the Einstein equation
is regarded as a secular term of a perturbative expansion, we renormalized a
constant of integration contained in the background solution and absorbed the
secular term to this constant in a gauge-invariant manner. The resultant
renormalization-group equation describes the back reaction effect of
inhomogeneity on the background universe. For scalar type classical
perturbation, by solving the renormalization-group equation, we find that the
back reaction of the long wavelength fluctuation works as a positive spatial
curvature, and the short wavelength fluctuation works as a radiation fluid. For
the long wavelength quantum fluctuation, the effect of back reaction is
equivalent to a negative spatial curvature.Comment: 17 page
Renormalization Group Approach to Cosmological Back Reaction Problems
We investigated the back reaction of cosmological perturbations on the
evolution of the universe using the second order perturbation of the Einstein's
equation. To incorporate the back reaction effect due to the inhomogeneity into
the framework of the cosmological perturbation, we used the renormalization
group method. The second order zero mode solution which appears by the
non-linearities of the Einstein's equation is regarded as a secular term of the
perturbative expansion, we renormalized a constant of integration contained in
the background solution and absorbed the secular term to this constant. For a
dust dominated universe, using the second order gauge invariant quantity, we
derived the renormalization group equation which determines the effective
dynamics of the Friedman-Robertson-Walker universe with the back reaction
effect in a gauge invariant manner. We obtained the solution of the
renormalization group equation and found that perturbations of the scalar mode
and the long wavelength tensor mode works as positive spatial curvature, and
the short wavelength tensor mode as radiation fluid.Comment: 18 pages, revtex, to appear in Phys. Rev.
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