465 research outputs found
Equilibrium hydrostatic equation and Newtonian limit of the singular f(R) gravity
We derive the equilibrium hydrostatic equation of a spherical star for any
gravitational Lagrangian density of the form . The Palatini
variational principle for the Helmholtz Lagrangian in the Einstein gauge is
used to obtain the field equations in this gauge. The equilibrium hydrostatic
equation is obtained and is used to study the Newtonian limit for
. The same procedure is carried out for the more
generally case giving a good
Newtonian limit.Comment: Revised version, to appear in Classical and Quantum Gravity
Towards a Relativistic Description of Exotic Meson Decays
This work analyses hadronic decays of exotic mesons, with a focus on the
lightest one, the , in a fully relativistic formalism,
and makes comparisons with non-relativistic results. We also discuss Coulomb
gauge decays of normal mesons that proceed through their hybrid components. The
relativistic spin wave functions of mesons and hybrids are constructed based on
unitary representations of the Lorentz group. The radial wave functions are
obtained from phenomenological considerations of the mass operator. Fully
relativistic results (with Wigner rotations) differ significantly from
non-relativistic ones. We also find that the decay channels are favored, in agreement with results obtained using
other models.Comment: 14 pages, 7 figure
A Discussion on Dirac Field Theory, No-Go Theorems and Renormalizability
We study Dirac field equations coupled to electrodynamics with metric and
torsion fields: we discuss how special spinorial solutions are incompatible
with torsion; eventually these results will be used to sketch a discussion on
the problem of renormalizability of point-like particles.Comment: 10 page
Medical Students’ Perceptions, Knowledge, and Competence in Treating Neurodivergent, Disability, and Chronic Illness (NDCI) Populations: Results from a Cross-Sectional Study
Background: Globally, Neurodivergent, Disability, and Chronic Illness (NDCI) populations face significant health disparities. Lack of physician knowledge about NDCI is a key mechanism underlying these disparities. The current study aimed to describe medical students’ perceptions, knowledge, and competence regarding NDCI.
Methods: A cross-sectional study was carried out using an online survey of medical students at a large public university with no NDCI-specific curriculum (n = 97; response rate = 18%). The survey asked about students’ perceptions, knowledge, and competence pertaining to NDCI populations.
Results: Most (n = 93, 96%) indicated it is important for physicians to understand the influence of NDCI on patient health and clinical encounters. Yet only seven (7%) and 15 (15%) reported that the NDCI curriculum in their medical school was sufficient, and they felt comfortable taking care of patients with NDCI respectively. Most (n = 87, 90%) wanted their medical school to provide additional NDCI training. Few reported high knowledge about ableism (n = 12, 12%), self-determination (n = 7, 7%), coordinating care (n = 4, 4%) and accommodations (n = 10, 10%). Few indicated high competence in cognitive, physical, social-emotional, and other NDCI types (n = 7 – 32, 7-33%). Existing knowledge often came from personal experiences or the news and media.
Conclusion: Findings demonstrated the gaps in medical education, as exemplified by medical students surveyed in one U.S. public university. Results can inform efforts to ameliorate global health disparities associated with a lack of physician knowledge about NDCI
Covariant conservation of energy momentum in modified gravities
An explicit proof of the vanishing of the covariant divergence of the
energy-momentum tensor in modified theories of gravity is presented. The
gravitational action is written in arbitrary dimensions and allowed to depend
nonlinearly on the curvature scalar and its couplings with a scalar field. Also
the case of a function of the curvature scalar multiplying a matter Lagrangian
is considered. The proof is given both in the metric and in the first-order
formalism, i.e. under the Palatini variational principle. It is found that the
covariant conservation of energy-momentum is built-in to the field equations.
This crucial result, called the generalized Bianchi identity, can also be
deduced directly from the covariance of the extended gravitational action.
Furthermore, we demonstrate that in all of these cases, the freely falling
world lines are determined by the field equations alone and turn out to be the
geodesics associated with the metric compatible connection. The independent
connection in the Palatini formulation of these generalized theories does not
have a similar direct physical interpretation. However, in the conformal
Einstein frame a certain bi-metricity emerges into the structure of these
theories. In the light of our interpretation of the independent connection as
an auxiliary variable we can also reconsider some criticisms of the Palatini
formulation originally raised by Buchdahl.Comment: 8 pages. v2: more discussio
Polymorphism of DNA mismatch repair genes in endometrial cancer
Endometrial cancer (EC) is the second most common malignancy associated with hereditary non-polyposis colorectal cancer (HNPCC) family. The development of HNPCC is associated with defects in DNA mismatch repair (MMR) pathway resulting in microsatellite instability (MSI). MSI is present in a greater number of EC than can be accounted for by inherited MMR mutations, therefore alternative mechanisms may underline defective MMR in EC, including polymorphic variation. Aim: We checked the association between EC occurrence and two polymorphisms of MMR genes: a 1032G>A (rs4987188) transition in the hMSH2 gene resulting in a Gly22Asp substitution and a –93G>A (rs1800734) transition in the promoter of the hMLH1 gene. Material and methods: These polymorphisms were genotyped in DNA from peripheral blood lymphocytes of 100 EC patients and 100 age-matched women by restriction fragment length polymorphism PCR. Results: A positive association (OR 4.18; 95% CI 2.23–7.84) was found for the G/A genotype of the –93G>A polymorphism of the hMLH1 gene and EC occurrence. On the other hand, the A allele of this polymorphism was associated with decreased EC occurrence. The Gly/Gly genotype slightly increased the effect of the –93G>A-G/A genotype (OR 4.52; CI 2.41–8.49). Our results suggest that the –93G>A polymorphism of the hMLH1 gene singly and in combination with the Gly322Asp polymorphism of the hMSH2 gene may increase the risk of EC. Key Words: hMSH2, hMLH1, endometrial cancer, genetic polymorphism, MMR
The Cauchy problem of f(R) gravity
The initial value problem of metric and Palatini f(R)gravity is studied by
using the dynamical equivalence between these theories and Brans-Dicke gravity.
The Cauchy problem is well-formulated for metric f(R)gravity in the presence of
matter and well-posed in vacuo. For Palatini f(R)gravity, instead, the Cauchy
problem is not well-formulated.Comment: 16 latex pages, to appear in Class. Quantum Grav; typographical
errors corrected, new references adde
Modified gravity and its reconstruction from the universe expansion history
We develop the reconstruction program for the number of modified gravities:
scalar-tensor theory, , and string-inspired, scalar-Gauss-Bonnet
gravity. The known (classical) universe expansion history is used for the
explicit and successful reconstruction of some versions (of special form or
with specific potentials) from all above modified gravities. It is demonstrated
that cosmological sequence of matter dominance, decceleration-acceleration
transition and acceleration era may always emerge as cosmological solutions of
such theory. Moreover, the late-time dark energy FRW universe may have the
approximate or exact CDM form consistent with three years WMAP data.
The principal possibility to extend this reconstruction scheme to include the
radiation dominated era and inflation is briefly mentioned. Finally, it is
indicated how even modified gravity which does not describe the
matter-dominated epoch may have such a solution before acceleration era at the
price of the introduction of compensating dark energy.Comment: LaTeX file, 24 pages, no figure, prepared for the proceedings of ERE
2006, minor correction
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