13,094 research outputs found
A projective Dirac operator on CP^2 within fuzzy geometry
We propose an ansatz for the commutative canonical spin_c Dirac operator on
CP^2 in a global geometric approach using the right invariant (left action-)
induced vector fields from SU(3). This ansatz is suitable for noncommutative
generalisation within the framework of fuzzy geometry. Along the way we
identify the physical spinors and construct the canonical spin_c bundle in this
formulation. The chirality operator is also given in two equivalent forms.
Finally, using representation theory we obtain the eigenspinors and calculate
the full spectrum. We use an argument from the fuzzy complex projective space
CP^2_F based on the fuzzy analogue of the unprojected spin_c bundle to show
that our commutative projected spin_c bundle has the correct
SU(3)-representation content.Comment: reduced to 27 pages, minor corrections, minor improvements, typos
correcte
A study on job postures and musculoskeletal illnesses in dentists
Objectives: Musculoskeletal disorders (MSDs) compose a large part of occupational diseases in dental professionals, prevention of which is dependent on assessment and improvement of job postures by means of ergonomic interventions. This study was aimed at evaluation of ergonomic conditions of the profession of dentists and also at assessing the relationship between MSDs and conditions of work. Materials and Methods: This cross-sectional study was performed among 65 dentists using the method of Rapid Entire Body Assessment (REBA). The prevalence of MSDs was obtained by the use of the Nordic Musculoskeletal Questionnaire (NMQ). Results: In this investigation, the prevalence of MSDs for different body parts was: 75.9% for the neck, 58.6% for the shoulders, 56.9% for the upper back, 48.3% for the lower back and 44.8% for the wrist. Job analysis by the use of REBA showed that 89.6% of limbs in group A and 79.3% of limbs in group B had a score > 4. Only neck and lower back pain have significant relationship with the risk levels obtained using the REBA method. Conclusions: It can be concluded that work postures of dentists need to be improved. In addition to education, work station design, rest period during work and regular physical activities should be taken into account
Quantum Simulation of Spin Chains Coupled to Bosonic Modes with Superconducting Circuits
We propose the implementation of a digital quantum simulation of spin chains
coupled to bosonic field modes in superconducting circuits. Gates with high
fidelities allows one to simulate a variety of Ising magnetic pairing
interactions with transverse field, Tavis-Cummings interaction between spins
and a bosonic mode, and a spin model with three-body terms. We analyze the
feasibility of the implementation in realistic circuit quantum electrodynamics
setups, where the interactions are either realized via capacitive couplings or
mediated by microwave resonators.Comment: Chapter in R. S. Anderssen et al. (eds.), Mathematics for Industry 11
(Springer Japan, 2015
Quantum Simulation of Tunneling in Small Systems
A number of quantum algorithms have been performed on small quantum
computers; these include Shor's prime factorization algorithm, error
correction, Grover's search algorithm and a number of analog and digital
quantum simulations. Because of the number of gates and qubits necessary,
however, digital quantum particle simulations remain untested. A contributing
factor to the system size required is the number of ancillary qubits needed to
implement matrix exponentials of the potential operator. Here, we show that a
set of tunneling problems may be investigated with no ancillary qubits and a
cost of one single-qubit operator per time step for the potential evolution. We
show that physically interesting simulations of tunneling using 2 qubits (i.e.
on 4 lattice point grids) may be performed with 40 single and two-qubit gates.
Approximately 70 to 140 gates are needed to see interesting tunneling dynamics
in three-qubit (8 lattice point) simulations.Comment: 4 pages, 2 figure
Gravity and compactified branes in matrix models
A mechanism for emergent gravity on brane solutions in Yang-Mills matrix
models is exhibited. Newtonian gravity and a partial relation between the
Einstein tensor and the energy-momentum tensor can arise from the basic matrix
model action, without invoking an Einstein-Hilbert-type term. The key
requirements are compactified extra dimensions with extrinsic curvature M^4 x K
\subset R^D and split noncommutativity, with a Poisson tensor \theta^{ab}
linking the compact with the noncompact directions. The moduli of the
compactification provide the dominant degrees of freedom for gravity, which are
transmitted to the 4 noncompact directions via the Poisson tensor. The
effective Newton constant is determined by the scale of noncommutativity and
the compactification. This gravity theory is well suited for quantization, and
argued to be perturbatively finite for the IKKT model. Since no
compactification of the target space is needed, it might provide a way to avoid
the landscape problem in string theory.Comment: 35 pages. V2: substantially revised and improved, conclusion
weakened. V3: some clarifications, published version. V4: minor correctio
Scale Dependence of Dark Energy Antigravity
We investigate the effects of negative pressure induced by dark energy
(cosmological constant or quintessence) on the dynamics at various
astrophysical scales. Negative pressure induces a repulsive term (antigravity)
in Newton's law which dominates on large scales. Assuming a value of the
cosmological constant consistent with the recent SnIa data we determine the
critical scale beyond which antigravity dominates the dynamics () and discuss some of the dynamical effects implied. We show that
dynamically induced mass estimates on the scale of the Local Group and beyond
are significantly modified due to negative pressure. We also briefly discuss
possible dynamical tests (eg effects on local Hubble flow) that can be applied
on relatively small scales (a few ) to determine the density and equation
of state of dark energy.Comment: Contributed talk at the 2nd Hellenic Cosmology Workshop at NOA
(Athens) Jan. 2001.To appear in the proceedings. Based on work done in
collaboration with M. Axenides and E. Florato
A holographic model for the fractional quantum Hall effect
Experimental data for fractional quantum Hall systems can to a large extent
be explained by assuming the existence of a modular symmetry group commuting
with the renormalization group flow and hence mapping different phases of
two-dimensional electron gases into each other. Based on this insight, we
construct a phenomenological holographic model which captures many features of
the fractional quantum Hall effect. Using an SL(2,Z)-invariant
Einstein-Maxwell-axio-dilaton theory capturing the important modular
transformation properties of quantum Hall physics, we find dyonic diatonic
black hole solutions which are gapped and have a Hall conductivity equal to the
filling fraction, as expected for quantum Hall states. We also provide several
technical results on the general behavior of the gauge field fluctuations
around these dyonic dilatonic black hole solutions: We specify a sufficient
criterion for IR normalizability of the fluctuations, demonstrate the
preservation of the gap under the SL(2,Z) action, and prove that the
singularity of the fluctuation problem in the presence of a magnetic field is
an accessory singularity. We finish with a preliminary investigation of the
possible IR scaling solutions of our model and some speculations on how they
could be important for the observed universality of quantum Hall transitions.Comment: 86 pages, 16 figures; v.2 references added, typos fixed, improved
discussion of ref. [39]; v.3 more references added and typos fixed, several
statements clarified, v.4 version accepted for publication in JHE
High-energy scale revival and giant kink in the dispersion of a cuprate superconductor
In the present photoemission study of a cuprate superconductor
Bi1.74Pb0.38Sr1.88CuO6+delta, we discovered a large scale dispersion of the
lowest band, which unexpectedly follows the band structure calculation very
well. The incoherent nature of the spectra suggests that the hopping-dominated
dispersion occurs possibly with the assistance of local spin correlations. A
giant kink in the dispersion is observed, and the complete self-energy
containing all interaction information is extracted for a doped cuprate in the
low energy region. These results recovered significant missing pieces in our
current understanding of the electronic structure of cuprates.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. on May 21, 200
Hysteroscopy in the management of endometrial hyperplasia and cancer in reproductive aged women: new developments and current perspectives
Over the last twenty years, the incidence of early endometrial cancer (EC) and atypical endometrial hyperplasia (AEH) among women of reproductive age is increasing rapidly, likely due to a combination of factors including increased prevalence of obesity and delayed of childbirths. Regarding preoperative diagnosis of endometrial neoplasia, it is still debated which is the most accurate and reliable method to obtain endometrial histopathological samples with fractional dilatation and curettage (D&C) having been considered, for a long time, as the method of choice. Nowadays, the advent of in-office endometrial biopsy with or without hysteroscopy has radically changed the approach, giving the opportunity to perform the endometrial biopsy under direct visualization. However, the lack of agreement about its diagnostic accuracy is still relevant. Since a significant number of women with AEH and/or EC are of childbearing age, a fertility-sparing diagnostic and therapeutic approach should be considered in all cases. The feasibility, safety and efficacy of fertility-sparing strategies involving hysteroscopic focal resections in conjunction with hormonal therapies have been evaluated and beneficial effects have been confirmed in several studies and one meta-analysis. Both local and systemic administration of hormonal therapies are currently used. Oral progestin, including medroxyprogesterone acetate (MPA) and megestrol acetate, are the most commonly used therapies. Nowadays, new therapeutic approaches, such as levonorgestrel intrauterine systems (LNG-IUS), gonadotropin-releasing hormone (GnRH) agonists, combined megestrol acetate and metformin, and other combinations of therapies are also used as first line therapies or after the hysteroscopic resection of the lesion. However, it is still unclear which approach provides higher clinical response with lower relapse rate, in addition to preserving fertility in women desiring to conceive. The aim of this narrative review is to summarize the available evidence regarding the evaluation and management with fertility-sparing treatments options of women with AEC and EC
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