6,502 research outputs found
Constraint on the Low Energy Constants of Wilson Chiral Perturbation Theory
Wilson chiral perturbation theory (WChPT) is the effective field theory
describing the long- distance properties of lattice QCD with Wilson or
twisted-mass fermions. We consider here WChPT for the theory with two light
flavors of Wilson fermions or a single light twisted-mass fermion.
Discretization errors introduce three low energy constants (LECs) into
partially quenched WChPT at O(a^2), conventionally called W'_6, W'_7 and W'_8 .
The phase structure of the theory at non-zero a depends on the sign of the
combination 2W'_6 + W'_8, while the spectrum of the lattice Hermitian
Wilson-Dirac operator depends on all three constants. It has been argued, based
on the positivity of partition functions of fixed topological charge, and on
the convergence of graded group integrals that arise in the epsilon-regime of
ChPT, that there is a constraint on the LECs arising from the underlying
lattice theory. In particular, for W'_6 = W'_7 = 0, the constraint found is
W'_8 \le 0. Here we provide an alternative line of argument, based on mass
inequalities for the underlying partially quenched theory. We find that W'_8
\le 0, irrespective of the values of W'_6 and W'_7. Our constraint implies that
2W'_6 > |W'_8| if the phase diagram is to be described by the first-order
scenario, as recent simulations suggest is the case for some choices of action.Comment: 10 pages, no figure
Ownership Structure and The Performance of Quoted Companies in Nigeria
Following the Berle-Means thesis ( 1932) which implies that diffuse ownership
adversely affects finn pe1jonnance, diverse researches have been carried out to obtain
an empirical evidence to support or nullify their position. This work, seeks to find out
whether the ownership structure of Nigerian finns results in systematic variations in
their pe1jormance. For the purpose of this study, ownership structure was classified as
inside or managerial ownership and outside ownership (those who are not directly
involved in management). The objective of the study is to ascertain the influence of each
of the classification onfirm 's pe1jonnance. The hypotheses were tested using datafor
20 Nigerian firms listed on the NSE. Empirical findings suggest that whereas a high
level of inside ownership negatively but significantly relates to higher firms'
performance, outside ownership was found to be positively and significantly related to
firm performanc
Dielectric properties of charge ordered LuFe2O4 revisited: The apparent influence of contacts
We show results of broadband dielectric measurements on the charge ordered,
proposed to be mul- tiferroic material LuFe2O4. The temperature and frequency
dependence of the complex permittivity as investigated for temperatures above
and below the charge-oder transition near T_CO ~ 320 K and for frequencies up
to 1 GHz can be well described by a standard equivalent-circuit model
considering Maxwell-Wagner-type contacts and hopping induced AC-conductivity.
No pronounced contribution of intrinsic dipolar polarization could be found and
thus the ferroelectric character of the charge order in LuFe2O4 has to be
questioned.Comment: 4 pages, 3 figure
Relativistic predictions of spin observables for exclusive proton knockout reactions
Within the framework of the relativistic distorted wave impulse approximation
(DWIA), we investigate the sensitivity of complete sets of polarization
transfer observables for exclusive proton knockout from the 3s,
2d and 2d states in Pb, at an incident laboratory
kinetic energy of 202 MeV, and for coincident coplanar scattering angles
(, ), to different distorting optical potentials,
finite-range (FR) versus zero-range (ZR) approximations to the DWIA, as well as
medium-modified meson-nucleon coupling constants and meson masses. Results are
also compared to the nonrelativistic DWIA predictions based on the
Schr\"{o}dinger equation.Comment: Submitted for publication to Physicical Review C, 23 pages, 7 figure
Sequential Strong Measurements and Heat Vision
We study scenarios where a finite set of non-demolition von-Neumann
measurements are available. We note that, in some situations, repeated
application of such measurements allows estimating an infinite number of
parameters of the initial quantum state, and illustrate the point with a
physical example. We then move on to study how the system under observation is
perturbed after several rounds of projective measurements. While in the finite
dimensional case the effect of this perturbation always saturates, there are
some instances of infinite dimensional systems where such a perturbation is
accumulative, and the act of retrieving information about the system increases
its energy indefinitely (i.e., we have `Heat Vision'). We analyze this effect
and discuss a specific physical system with two dichotomic von-Neumann
measurements where Heat Vision is expected to show.Comment: See the Appendix for weird examples of heat visio
Self-organized criticality in the intermediate phase of rigidity percolation
Experimental results for covalent glasses have highlighted the existence of a
new self-organized phase due to the tendency of glass networks to minimize
internal stress. Recently, we have shown that an equilibrated self-organized
two-dimensional lattice-based model also possesses an intermediate phase in
which a percolating rigid cluster exists with a probability between zero and
one, depending on the average coordination of the network. In this paper, we
study the properties of this intermediate phase in more detail. We find that
microscopic perturbations, such as the addition or removal of a single bond,
can affect the rigidity of macroscopic regions of the network, in particular,
creating or destroying percolation. This, together with a power-law
distribution of rigid cluster sizes, suggests that the system is maintained in
a critical state on the rigid/floppy boundary throughout the intermediate
phase, a behavior similar to self-organized criticality, but, remarkably, in a
thermodynamically equilibrated state. The distinction between percolating and
non-percolating networks appears physically meaningless, even though the
percolating cluster, when it exists, takes up a finite fraction of the network.
We point out both similarities and differences between the intermediate phase
and the critical point of ordinary percolation models without
self-organization. Our results are consistent with an interpretation of recent
experiments on the pressure dependence of Raman frequencies in chalcogenide
glasses in terms of network homogeneity.Comment: 20 pages, 18 figure
Why the Entanglement of Formation is not generally monogamic
Differently from correlation of classical systems, entanglement of quantum
systems cannot be distributed at will - if one system A is maximally entangled
with another system B, it cannot be entangled at all to a third system C. This
concept, known as the monogamy of entanglement, manifests when the entanglement
of A with a pair BC, can be divided as contributions of entanglement between A
and B and A and C, plus a term \tau_{ABC} involving genuine tripartite
entanglement and so expected to be always positive. A very important measure in
Quantum Information Theory, the Entanglement of Formation (EOF), fails to
satisfy this last requirement. Here we present the reasons for that and show a
set of conditions that an arbitrary pure tripartite state must satisfy for EOF
to become a monogamous measure, ie, for \tau_{ABC} \ge 0. The relation derived
is connected to the discrepancy between quantum and classical correlations,
being \tau_{ABC} negative whenever the quantum correlation prevails over the
classical one. This result is employed to elucidate features of the
distribution of entanglement during a dynamical evolution. It also helps to
relate all monogamous instances of EOF to the Squashed Entanglement, an always
monogamous entanglement measure.Comment: 7 pages, 3 figures. Extended versio
Anomalous Rotational Relaxation: A Fractional Fokker-Planck Equation Approach
In this study we obtained analytically relaxation function in terms of
rotational correlation functions based on Brownian motion for complex
disordered systems in a stochastic framework. We found out that rotational
relaxation function has a fractional form for complex disordered systems, which
indicates relaxation has non-exponential character obeys to
Kohlrausch-William-Watts law, following the Mittag-Leffler decay.Comment: Revtex4, 9 pages. Paper was revised. References adde
Comparison of tumour-based (Petersen Index) and inflammation-based (Glasgow Prognostic Score) scoring systems in patients undergoing curative resection for colon cancer
After resection, it is important to identify colon cancer patients, who are at a high risk of recurrence and who may benefit from adjuvant treatment. The Petersen Index (PI), a prognostic model based on pathological criteria is validated in Dukes' B and C disease. Similarly, the modified Glasgow Prognostic Score (mGPS) based on biochemical criteria has also been validated. This study compares both the scores in patients undergoing curative resection of colon cancer. A total of 244 patients underwent elective resection between 1997 and 2005. The PI was constructed from pathological reports; the mGPS was measured pre-operatively. The median follow-up was 67 months (minimum 36 months) during which 109 patients died; 68 of them from cancer. On multivariate analysis of age, Dukes' stage, PI and mGPS, age (hazard ratio, HR, 1.74, P=0.001), Dukes' stage (HR, 3.63, P<0.001), PI (HR, 2.05, P=0.010) and mGPS (HR, 2.34, P<0.001) were associated independently with cancer-specific survival. Three-year cancer-specific survival rates for Dukes' B patients with the low-risk PI were 98, 92 and 82% for the mGPS of 0, 1 and 2, respectively (P<0.05). The high-risk PI population is small, in particular for Dukes' B disease (9%). The mGPS further stratifies those patients classified as low risk by the PI. Combining both the scoring systems could identify patients who have undergone curative surgery but are at high-risk of cancer-related death, therefore guiding management and trial stratification
Refining the continuous tracking paradigm to investigate implicit motor learning.
In two experiments we investigated factors that undermine conclusions about implicit motor learning in the continuous tracking paradigm. In Experiment 1, we constructed a practice phase in which all three segments of the waveform pattern were random, in order to examine whether tracking performance decreased as a consequence of time spent on task. Tracking error was lower in the first segment than in the middle segment and lower in the middle segment than in the final segment, indicating that tracking performance decreased as a function of increasing time-on-task. In Experiment 2, the waveform pattern presented in the middle segment was identical in each trial of practice. In a retention test, tracking performance on the repeated segment was superior to tracking performance on the random segments of the waveform. Furthermore, substitution of the repeated pattern with a random pattern (in a transfer test) resulted in a significantly increased tracking error. These findings imply that characteristics of the repeated pattern were learned. Crucially, tests of pattern recognition implied that participants were not explicitly aware of the presence of a recurring segment of waveform. Recommendations for refining the continuous tracking paradigm for implicit learning research are proposed
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