894 research outputs found
Low-energy Compton scattering on the nucleon and sum rules
The Gerasimov-Drell-Hearn and Baldin-Lapidus sum rules are evaluated in the
dressed K-matrix model for photon-induced reactions on the nucleon. For the
first time the sum of the electric and magnetic polarisabilities
and the forward spin polarisability are explicitly calculated in two
alternative ways -- from the sum rules and from the low-energy expansion of the
real Compton scattering amplitude -- within the {\em same} framework. The two
methods yield compatible values for but differ somewhat for
. Consistency between the two ways of determining the
polarisabilities is a measure of the extent to which basic symmetries of the
model are obeyed.Comment: 9 pages, 4 figures, using REVTeX. More concise version, results
unchanged. To appear in Phys. Rev.
Fracture characterisation of bone-cement bonded joints under mode I loading
Over the years, many techniques have been developed for the stabilisation of bone fractures. The study of the adhesion of bone-to-bone cement is an important step towards the development of new immobilization systems. Although bone cement has been used for more than fifty years, very few studies have been performed regarding the evaluation of fracture properties. In this work, numerical and experimental investigations were conducted to evaluate the strain energy release rate under mode I loading in a bone-cement bonded joint, using the Double Cantilever Beam (DCB) test. Cohesive zone laws were also measured combining the finite element method with non-linear elastic fracture mechanics. This has been made in a cortical bone bonded joint with poly- methylmethacrylate (PMMA). Consistent results have been obtained regarding fracture toughness in a widely used bone-to-bone cement joint in many biomedical applications.The first author acknowledges the Portuguese (FCT) for the conceded financial support through the reference grant PTDC/EME-SIS/28225/2017. M.F.S.M. de Moura acknowledges the ‘Laboratório Associado de Energia, Transportes e Aeronáutica’ (LAETA) for the financial support by the project UID/EMS/50022/2020. The corresponding author acknowledges FCT for the conceded financial support through the reference projects PTDC/EME-SIS/28225/2017 and UID/EEA/04436/2019.Funding: Portuguese Foundation for Science and Technology for MsC grant of the first author, and research project PTDC/EME-SIS/28225/2017
Neutron polarizabilities investigated by quasi-free Compton scattering from the deuteron
Measuring Compton scattered photons and recoil neutrons in coincidence,
quasi-free Compton scattering by the neutron has been investigated at MAMI
(Mainz) at in an energy range from 200 to 400 MeV.
From the data a polarizability difference of in units of has been
determined. In combination with the polarizability sum deduced from photo absorption data, the neutron electric and
magnetic polarizabilities, and ,
are obtained
SIHEM-UB: A scale to assess higher-education management skills
University management and governance is a complex matter and differs from the management and governance of other institutions, since the structure, organisation and complexity of the university make it a unique institution. Moreover, teaching staff members with individual management roles are not professional managers, as is the case in other institutions. This raises the question of whether all university teachers can be effective managers of their institutions. The goal of this paper is therefore to create a scale to assess highereducation management skills (SIHEM-UB). The initial scale consisted of 129 items, and after a review by expert judges and the pilot study, the final scale was reduced to 30 items and was administered to a sample of 690 university teachers. The scale was checked for reliability, internal consistency, and content, criterion, discriminant and construct validity. All indicators demonstrated the suitability of the proposed scale in relation to reliability and validity in all facets analysed
Cluster Transformation Coefficients for Structure and Dynamics Calculations in n-Particle Systems: Atoms, Nuclei, and Quarks
The structure and dynamics of an n-particle system are described with coupled
nonlinear Heisenberg's commutator equations where the nonlinear terms are
generated by the two-body interaction that excites the reference vacuum via
particle-particle and particle-hole excitations. Nonperturbative solutions of
the system are obtained with the use of dynamic linearization approximation and
cluster transformation coefficients. The dynamic linearization approximation
converts the commutator chain into an eigenvalue problem. The cluster
coefficients factorize the matrix elements of the (n)-particles or
particle-hole systems in terms of the matrix elements of the (n-1)-systems
coupled to a particle-particle, particle-hole, and hole-hole boson. Group
properties of the particle-particle, particle-hole, and hole-hole permutation
groups simplify the calculation of these coefficients. The particle-particle
vacuum-excitations generate superconductive diagrams in the dynamics of
3-quarks systems. Applications of the model to fermionic and bosonic systems
are discussed.Comment: 13 pages, 5 figures, Wigner Proceedings for Conference Wigner
Centenial Pecs, July 8-12, 200
Nucleon Spin-Polarisabilities from Polarisation Observables in Low-Energy Deuteron Compton Scattering
We investigate the dependence of polarisation observables in elastic deuteron
Compton scattering below the pion production threshold on the spin-independent
and spin-dependent iso-scalar dipole polarisabilities of the nucleon. The
calculation uses Chiral Effective Field Theory with dynamical Delta(1232)
degrees of freedom in the Small Scale Expansion at next-to-leading order.
Resummation of the NN intermediate rescattering states and including the Delta
induces sizeable effects. The analysis considers cross-sections and the
analysing power of linearly polarised photons on an unpolarised target, and
cross-section differences and asymmetries of linearly and circularly polarised
beams on a vector-polarised deuteron. An intuitive argument helps one to
identify kinematics in which one or several polarisabilities do not contribute.
Some double-polarised observables are only sensitive to linear combinations of
two of the spin-polarisabilities, simplifying a multipole-analysis of the data.
Spin-polarisabilities can be extracted at photon energies \gtrsim 100 MeV,
after measurements at lower energies of \lesssim 70 MeV provide high-accuracy
determinations of the spin-independent ones. An interactive Mathematica 7.0
notebook of our findings is available from [email protected]: 30 pages LaTeX2e, including 22 figures as 66 .eps file embedded with
includegraphicx; three errors in initial submission corrected. This
submission includes ot the erratum to be published in EPJA (2012) and the
corrections in the tex
Frozen cancellous bone allografts: positive cultures of implanted grafts in posterior fusions of the spine
We have carried out a study on the behaviour pattern of implanted allografts
initially stored in perfect conditions (aseptically processed, culture-negative
and stored at -80 degrees C) but which presented positive cultures at the
implantation stage. There is no information available on how to deal with this
type of situation, so our aim was to set guidelines on the course of action which
would be required in such a case. This was a retrospective study of 112 patients
who underwent a spinal arthrodesis and in whom a total of 189 allograft pieces
were used. All previous bone and blood cultures and tests for hepatitis B and C,
syphilis and HIV (via PCR techniques) were negative. The allografts were stored
by freezing them at -80 degrees C. A sample of the allograft was taken for
culture in the operating theatre just before its implantation in all cases. The
results of the cultures were obtained 3-5 days after the operation. There were 22
allografts with positive culture results (12%) after implantation. These
allografts were implanted in 16 patients (14%). Cultures were positive for
staphylococci coagulase negative (ECN) in 10 grafts (46%), Pseudomonas stutzeri
in two grafts (9%), Corynebacterium jeikeium in two grafts (9%), staphylococci
coagulase positive in two grafts (9%) and for each of the following organisms in
one case each (4%): Corynebacterium spp., Actinomyces odontolyticus,
Streptococcus mitis, Peptostreptococcus spp., Rhodococcus equi and Bacillus spp.
No clinical infection was seen in any of these patients. Positive cultures could
be caused by non-detected contamination at harvesting, storing or during
manipulation before implantation. The lack of clinical signs of infection during
the follow-up of our patients may indicate that no specific treatment different
from our antibiotic protocol is required in the case of positive culture results
of a graft piece after implantation
Nuclear medicine procedures and the evaluation of male sexual organs: a short review
Sexuality consists of three aspects that are interrelated and inseparable, biological, physiological and social. The biological aspect considers the individual's capability to give and to receive pleasure. In consequence, it covers the functionality of the sexual organs and the physiology of human sexual response cycle. Diagnostic imaging modalities, such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) have been used to evaluate clinical disorders of the male reproductive system. PET and SPECT procedures basically involve the administration of a radiopharmaceutical that has a higher uptake in a specific tumor or tissue. The aim of this brief review is to present some radiopharmaceuticals that have been used in the clinical evaluation of the male sexual organs (testes, prostate, seminal vesicles, penis) related with male sexuality. This information could be useful in better understanding the male sexual response cycle, as well as the sexual disorders, when considering the male sexual organs and the pelvic floor. Moreover, the findings obtained with PET and SPECT imaging could help to evaluate the efficacy of clinical results of therapeutic procedures. In conclusion, the knowledge from these images could aid in better understanding the physiology of the different organs related with sexuality. Furthermore, they could be important tools to evaluate the physiological integrity of the involved organs, to improve clinical strategies and to accompany the patients under treatment
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