1,319 research outputs found
The light baryon spectrum in a relativistic quark model with instanton-induced quark forces I. The non-strange baryon spectrum and ground-states
This is the second of a series of three papers treating light baryon
resonances up to 3 GeV within a relativistically covariant quark model based on
the three-fermion Bethe-Salpeter equation with instantaneous two- and
three-body forces. In this paper we apply the covariant Salpeter framework
(which we developed in the first paper) to specific quark model calculations.
Quark confinement is realized by a linearly rising three-body string potential
with appropriate spinorial structures in Dirac-space. To describe the hyperfine
structure of the baryon spectrum we adopt 't Hooft's residual interaction based
on QCD-instanton effects and demonstrate that the alternative
one-gluon-exchange is disfavored phenomenological grounds. Our fully
relativistic framework allows to investigate the effects of the full Dirac
structures of residual and confinement forces on the structure of the mass
spectrum. In the present paper we present a detailed analysis of the complete
non-strange baryon spectrum and show that several prominent features of the
nucleon spectrum such as e.g. the Roper resonance and approximate ''parity
doublets'' can be uniformly explained due to a specific interplay of
relativistic effects, the confinement potential and 't Hooft's force. The
results for the spectrum of strange baryons will be discussed in a subsequent
paper.Comment: 59 p. postscript, including 24 figures and 25 tables, submitted to
Eur.Phys.J.
Search for Short-Term Periodicities in the Sun's Surface Rotation: A Revisit
The power spectral analyses of the Sun's surface equatorial rotation rate
determined from the Mt. Wilson daily Doppler velocity measurements during the
period 3 December 1985 to 5 March 2007 suggests the existence of 7.6 year, 2.8
year, 1.47 year, 245 day, 182 day and 158 day periodicities in the surface
equatorial rotation rate during the period before 1996.
However, there is no variation of any kind in the more accurately measured
data during the period after 1995. That is, the aforementioned periodicities in
the data during the period before the year 1996 may be artifacts of the
uncertainties of those data due to the frequent changes in the instrumentation
of the Mt. Wilson spectrograph. On the other hand, the temporal behavior of
most of the activity phenomena during cycles 22 (1986-1996) and 23 (after 1997)
is considerably different. Therefore, the presence of the aforementioned
short-term periodicities during the last cycle and absence of them in the
current cycle may, in principle, be real temporal behavior of the solar
rotation during these cycles.Comment: 11 pages, 6 figures, accepted for publication in Solar Physic
Strain driven fast osseointegration of implants
BACKGROUND: Although the bone's capability of dental implant osseointegration has clinically been utilised as early as in the Gallo-Roman population, the specific mechanisms for the emergence and maintenance of peri-implant bone under functional load have not been identified. Here we show that under immediate loading of specially designed dental implants with masticatory loads, osseointegration is rapidly achieved. METHODS: We examined the bone reaction around non- and immediately loaded dental implants inserted in the mandible of mature minipigs during the presently assumed time for osseointegration. We used threaded conical titanium implants containing a titanium2+ oxide surface, allowing direct bone contact after insertion. The external geometry was designed according to finite element analysis: the calculation showed that physiological amplitudes of strain (500–3,000 ustrain) generated through mastication were homogenously distributed in peri-implant bone. The strain-energy density (SED) rate under assessment of a 1 Hz loading cycle was 150 Jm-3 s-1, peak dislocations were lower then nm. RESULTS: Bone was in direct contact to the implant surface (bone/implant contact rate 90%) from day one of implant insertion, as quantified by undecalcified histological sections. This effect was substantiated by ultrastructural analysis of intimate osteoblast attachment and mature collagen mineralisation at the titanium surface. We detected no loss in the intimate bone/implant bond during the experimental period of either control or experimental animals, indicating that immediate load had no adverse effect on bone structure in peri-implant bone. CONCLUSION: In terms of clinical relevance, the load related bone reaction at the implant interface may in combination with substrate effects be responsible for an immediate osseointegration state
Neutron diffraction study of spin and charge ordering in SrFeO(3-delta)
We report a comprehensive neutron diffraction study of the crystal structure
and magnetic order in a series of single-crystal and powder samples of
SrFeO in the vacancy range . The data
provide detailed insights into the interplay between the oxygen vacancy order
and the magnetic structure of this system. In particular, a crystallographic
analysis of data on Sr8Fe8O23 revealed a structural transition between the
high-temperature tetragonal and a low-temperature monoclinic phase with a
critical temperature T = 75 K, which originates from charge ordering on the Fe
sublattice and is associated with a metal-insulator transition. Our experiments
also revealed a total of seven different magnetic structures of
SrFeO in this range of , only two of which (namely an
incommensurate helix state in SrFeO3 and a commensurate, collinear
antiferromagnetic state in Sr4Fe4O11) had been identified previously. We
present a detailed refinement of some of the magnetic ordering patterns and
discuss the relationship between the magneto-transport properties of
SrFeO samples and their phase composition and magnetic
microstructure.Comment: 37 page
Sprache und Ethik im technologischen Zeitalter : Bamberger Hegelwoche 1990
Sprache und Ethik im technologischen Zeitalter : Bamberger Hegelwoche 199
Testing in the incremental design and development of complex products
Testing is an important aspect of design and development which consumes significant time and resource in many companies. However, it has received less research attention than many other activities in product development, and especially, very few publications report empirical studies of engineering testing. Such studies are needed to establish the importance of testing and inform the development of pragmatic support methods. This paper combines insights from literature study with findings from three empirical studies of testing. The case studies concern incrementally developed complex products in the automotive domain. A description of testing practice as observed in these studies is provided, confirming that testing activities are used for multiple purposes depending on the context, and are intertwined with design from start to finish of the development process, not done after it as many models depict. Descriptive process models are developed to indicate some of the key insights, and opportunities for further research are suggested
Structural insight into SUMO chain recognition and manipulation by the ubiquitin ligase RNF4
The small ubiquitin-like modifier (SUMO) can form polymeric chains that are important signals in cellular processes such as meiosis, genome maintenance and stress response. The SUMO-targeted ubiquitin ligase RNF4 engages with SUMO chains on linked substrates and catalyses their ubiquitination, which targets substrates for proteasomal degradation. Here we use a segmental labelling approach combined with solution nuclear magnetic resonance (NMR) spectroscopy and biochemical characterization to reveal how RNF4 manipulates the conformation of the SUMO chain, thereby facilitating optimal delivery of the distal SUMO domain for ubiquitin transfer
The T Tauri star RY Tau as a case study of the inner regions of circumstellar dust disks
We study the inner region of the circumstellar disk around the TTauri star RY
Tau. Our aim is to find a physical description satisfying the available
interferometric data, obtained with the mid-infrared interferometric instrument
at the Very Large Telescope Interferometer, as well as the spectral energy
distribution. We also compare the findings with the results of similar studies,
including those of intermediate-mass stars. Our analysis is done within the
framework of a passive circumstellar disk, which is optionally supplemented by
the effects of accretion and an added envelope. To achieve a more consistent
and realistic model, we used our continuum transfer code MC3D. In addition, we
studied the shape of the 10um silicate emission feature in terms of the
underlying dust population, both for single-dish and for interferometric
measurements. We show that a modestly flaring disk model with accretion can
explain both the observed spectral energy distribution and the mid-infrared
visibilities obtained with the mid-infrared infrared instrument. We found an
interesting ambiguity: a circumstellar active disk model with an added
envelope, and a lower accretion rate than in the active disk model without
envelope, could represent the observations equally as well. This type of model
with the envelope should be considered a viable alternative in future models of
other TTauri stars. The approach of a disk with a puffed-up inner rim wall and
the influence of a stellar companion is also discussed. From the study of the
silicate emission feature we see evidence for dust evolution in a TTauri star,
with a decreasing fraction of small amorphous and an increasing fraction of
crystalline particles closer to the star.Comment: 19 pages, 23 figures; accepted by Astronomy & Astrophysic
Efficacy and safety of acupuncture for chronic pain caused by gonarthrosis: A study protocol of an ongoing multi-centre randomised controlled clinical trial [ISRCTN27450856]
BACKGROUND: Controlled clinical trials produced contradictory results with respect to a specific analgesic effect of acupuncture. There is a lack of large multi-centre acupuncture trials. The German Acupuncture Trial represents the largest multi-centre study of acupuncture in the treatment of chronic pain caused by gonarthrosis up to now. METHODS: 900 patients will be randomised to three treatment arms. One group receives verum acupuncture, the second sham acupuncture, and the third conservative standard therapy. The trial protocol is described with eligibility criteria, detailed information on the treatment definition, blinding, endpoints, safety evaluation, statistical methods, sample size determination, monitoring, legal aspects, and the current status of the trial. DISCUSSION: A critical discussion is given regarding the considerations about standardisation of the acupuncture treatment, the choice of the control group, and the blinding of patients and observers
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