559 research outputs found
Kaon effective mass and energy from a novel chiral SU(3)-symmetric Lagrangian
A new chiral SU(3) Lagrangian is proposed to describe the properties of kaons
and antikaons in the nuclear medium, the ground state of dense matter and the
kaon-nuclear interactions consistently.
The saturation properties of nuclear matter are reproduced as well as the
results of the Dirac-Br\"{u}ckner theory. Our numerical results show that the
kaon effective mass might be changed only moderately in the nuclear medium due
to the highly non-linear density effects. After taking into account the
coupling between the omega meson and the kaon, we obtain similar results for
the effective kaon and antikaon energies as calculated in the
one-boson-exchange model while in our model the parameters of the kaon-nuclear
interactions are constrained by the SU(3) chiral symmetry.Comment: 13 pages, Latex, 3 PostScript figures included; replaced by the
revised version, to appear in Phys. Rev.
Abandonment of core knowledge areas and innovation performance
Within a constantly evolving technological environment, it is imperative for innovative organizations to be able to successfully respond and adapt to environmental changes. To achieve this, they must have the ability to efficiently and timely modify their innovation resources by divesting and reorganizing them, even if these are their core ones. Although divestiture of core innovation resources is an important managerial phenomenon, the literature is rather silent on this issue. To address this significant gap, this study examines how the abandonment of core knowledge areas is related to innovation performance and how this relationship is moderated by absorptive capacity. Two hypotheses are developed about these research questions and tested on a sample of firms from the pharmaceutical, biotechnology, and chemical industries. Findings suggest that the abandonment of core knowledge areas is a negative predictor of innovation performance; however, when the abandonment interacts with absorptive capacity the effect becomes positive
Human Papillomavirus in Endometrial Adenocarcinomas: Infectious Agent or a Mere âPassengerâ?
Aims. To investigate the possible association
of human papillomavirus (HPV) with endometrial hyperplasias and
neoplasia. Does HPV play any role in the initiation or
prognosis of endometrial adenocarcinomas?
Methods. Twenty-five endometrial adenocarcinomas
of the endometrioid cell type, with and without squamous
differentiation, and twenty-four endometrial hyperplasias of various
forms (simple, complex, and atypical) were analyzed for the
presence of type 16 and 18 HPV by the polymerase chain
reaction (PCR). The results were related to histopathological
features of the tumour, and the patients' age, and
prognosis. Results. Six of 25 endometrial
adenocarcinomas were HPV 16-positive
(24%),
and 5 of 25
(20%)
were HPV 18-positive. Simple endometrial hyperplasias was
associated somewhat more commonly with HPV 16 and 18 (2/8 and
1/8 cases, resp.) than hyperplasias progressing to
endometrial adenocarcinomas, namely, atypical endometrial
hyperplasia (1/8 and 0/8 cases, resp.). None of the
positive cases in the series, whether hyperplastic or
neoplastic, demonstrated cytological evidence of HPV
infection. There was no relation between HPV-positive cases
and squamous differentiation, depth of myometrial invasion,
lymphatic involvement, lymphocytic response, patients' age,
or prognosis. Conclusion. It appears that the
presence of HPV in the endometrium, as detected by PCR, does
not play any role in the initiation or prognosis of
endometrial adenocarcinoma
Hadrons in Dense Resonance-Matter: A Chiral SU(3) Approach
A nonlinear chiral SU(3) approach including the spin 3/2 decuplet is
developed to describe dense matter. The coupling constants of the baryon
resonances to the scalar mesons are determined from the decuplet vacuum masses
and SU(3) symmetry relations. Different methods of mass generation show
significant differences in the properties of the spin-3/2 particles and in the
nuclear equation of state.Comment: 28 pages, 9 figure
Biophysically motivated efficient estimation of the spatially isotropic R*2 component from a single gradientârecalled echo measurement
Purpose
To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientationâdependent part of R*2 using a single gradientârecalled echo (GRE) measurement.
Methods
The proposed method utilized a temporal secondâorder approximation of the hollowâcylinderâfiber model, in which the parameter describing the linear signal decay corresponded to the orientationâindependent part of R*2. The estimated parameters were compared to the classical, monoâexponential decay model for R*2 in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of R*2, it was compared to the established phenomenological method for separating R*2 into orientationâdependent and âindependent parts.
Results
Using the phenomenological method on the classical signal model, the wellâknown separation of R*2 into orientationâdependent and âindependent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed.
Conclusions
Since the proposed secondâorder model features orientationâdependent and âindependent components at distinct temporal orders, it can be used to remove the orientation dependence of R*2 using only a single GRE measurement
Fabrication and examination of oxidation resistance of zinc coated copper and brass components by chemical deposition
n this work, the structure and the oxidation resistance of Zn deposited Cu and brass metallic components are examined. The deposition was accomplished with pack cementation chemical deposition. The examination of the samples was performed with electron microscopy and X-ray diffraction analysis. It was found that coatings on Cu substrate consist of two layers with different Zn concentrations, while coatings on brass were single layered with almost constant Zn concentration. The presence of distinct ZnâCu phases was revealed in both cases. The subjection of the as coated samples together with the uncoated substrates in air at 400ÂșC showed that both Zn coated samples have enhanced resistivity in such atmospheres, as most of the coating remained mostly unoxidised, and the substrates were fully protected. On the contrary, the bare substrates appear to have undergone severe damage as brittle oxides were formed on their surface.Publicad
DIAGNOSTIC REVIEW OF A BLACKOUT IN RHODES
U radu se daje tehniÄka analiza jednog incidenta koji se dogodio 21. oĆŸujka 2007. godine u 00:50 sati u noÄi i doveo do dvosatnog potpunog raspada elektroenergetskog sustava na otoku Rodosu. Analiza dogaÄanja temelji se na registriranim operativnim podacima kao i nalazima na terenu. IzvrĆĄena je tehniÄka analiza smetnji kako bi se utvrdili vjerojatni uzroci i Äimbenici koji su pridonijeli pojavi smetnji. S obzirom da se radi o izoliranom sustavu koji je osobito je osjetljiv na poremeÄaje, ispitane su uloge zaĆĄtite sustava kao i kolebanja proizvodnje vjetroelektrana tijekom incidenta. IzvuÄeni su zakljuÄci od praktiÄnog znaÄenja i dane su preporuke korektivnih mjera koje valja provesti kako bi se u buduÄnosti sprijeÄile takve smetnje.A technical review of an incident on March 21, 2007 that began at 00:50 a.m. and led to a two-hour blackout of the island of Rhodes electric power system is presented with the complete sequence, including all the relevant registered operational data as well as the on-site field findings. A technical analysis of the disturbance was performed to determine the probable causes and factors that contributed to the duration of the disturbance. Since the system is an isolated one, it is particularly vulnerable to perturbations. The roles of system protection and wind power generation during the incident are examined. Conclusions of practical importance are drawn, including recommendations for corrective measures to be implemented for preventing disturbances of this kind from reoccurring in the future
Cosmological Evolution of a Purely Conical Codimension-2 Brane World
We study the cosmological evolution of isotropic matter on an infinitely thin
conical codimension-two brane-world. Our analysis is based on the boundary
dynamics of a six-dimensional model in the presence of an induced gravity term
on the brane and a Gauss-Bonnet term in the bulk. With the assumption that the
bulk contains only a cosmological constant Lambda_B, we find that the isotropic
evolution of the brane-universe imposes a tuned relation between the energy
density and the brane equation of state. The evolution of the system has fixed
points (attractors), which correspond to a final state of radiation for
Lambda_B=0 and to de Sitter state for Lambda_B>0. Furthermore, considering
anisotropic matter on the brane, the tuning of the parameters is lifted, and
new regions of the parametric space are available for the cosmological
evolution of the brane-universe. The analysis of the dynamics of the system
shows that, the isotropic fixed points remain attractors of the system, and for
values of Lambda_B which give acceptable cosmological evolution of the equation
of state, the line of isotropic tuning is a very weak attractor. The initial
conditions, in this case, need to be fine tuned to have an evolution with
acceptably small anisotropy.Comment: 20 pages, 4 figures, typo correcte
Strangeness Enhancement in Heavy Ion Collisions - Evidence for Quark-Gluon-Matter ?
The centrality dependence of (multi-)strange hadron abundances is studied for
Pb(158 AGeV)Pb reactions and compared to p(158 GeV)Pb collisions. The
microscopic transport model UrQMD is used for this analysis. The predicted
Lambda/pi-, Xi-/pi- and Omega-/pi- ratios are enhanced due to rescattering in
central Pb-Pb collisions as compared to peripheral Pb-Pb or p-Pb collisions. A
reduction of the constituent quark masses to the current quark masses m_s \sim
230 MeV, m_q \sim 10 MeV, as motivated by chiral symmetry restoration, enhances
the hyperon yields to the experimentally observed high values. Similar results
are obtained by an ad hoc overall increase of the color electric field strength
(effective string tension of kappa=3 GeV/fm). The enhancement depends strongly
on the kinematical cuts. The maximum enhancement is predicted around
midrapidity. For Lambda's, strangeness suppression is predicted at
projectile/target rapidity. For Omega's, the predicted enhancement can be as
large as one order of magnitude. Comparisons of Pb-Pb data to proton induced
asymmetric (p-A) collisions are hampered due to the predicted strong asymmetry
in the various rapidity distributions of the different (strange) particle
species. In p-Pb collisions, strangeness is locally (in rapidity) not
conserved. The present comparison to the data of the WA97 and NA49
collaborations clearly supports the suggestion that conventional (free)
hadronic scenarios are unable to describe the observed high (anti-)hyperon
yields in central collisions. The doubling of the strangeness to nonstrange
suppression factor, gamma_s \approx 0.65, might be interpreted as a signal of a
phase of nearly massless particles.Comment: published version, discussion on strange mesons and new table added,
extended discussion on strange baryon yields. Latex, 20 pages, including 5
eps-figure
Nuclei, Superheavy Nuclei and Hypermatter in a chiral SU(3)-Modell
A model based on chiral SU(3)-symmetry in nonlinear realisation is used for
the investigation of nuclei, superheavy nuclei, hypernuclei and multistrange
nuclear objects (so called MEMOs). The model works very well in the case of
nuclei and hypernuclei with one Lambda-particle and rules out MEMOs. Basic
observables which are known for nuclei and hypernuclei are reproduced
satisfactorily. The model predicts Z=120 and N=172, 184 and 198 as the next
shell closures in the region of superheavy nuclei. The calculations have been
performed in self-consistent relativistic mean field approximation assuming
spherical symmetry. The parameters were adapted to known nuclei.Comment: 19 pages, 11 figure
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