787 research outputs found
Chiral perturbation theory for lattice QCD including O(a^2)
The O(a^2) contributions to the chiral effective Lagrangian for lattice QCD
with Wilson fermions are constructed. The results are generalized to partially
quenched QCD with Wilson fermions as well as to the "mixed'' lattice theory
with Wilson sea quarks and Ginsparg-Wilson valence quarks.Comment: 3 pages, Lattice2003 (spectrum
General N = 1 Supersymmetric Flux Vacua of (Massive) Type IIA String Theory
We derive conditions for the existence of four-dimensional \N=1
supersymmetric flux vacua of massive type IIA string theory with general
supergravity fluxes turned on. For an SU(3) singlet Killing spinor, we show
that such flux vacua exist only when the internal geometry is nearly-K\"ahler.
The geometry is not warped, all the allowed fluxes are proportional to the mass
parameter and the dilaton is fixed by a ratio of (quantized) fluxes. The
four-dimensional cosmological constant, while negative, becomes small in the
vacuum with the weak string coupling.Comment: 4 page
Twisted-mass QCD, O(a) improvement and Wilson chiral perturbation theory
We point out a caveat in the proof for automatic O(a) improvement in twisted
mass lattice QCD at maximal twist angle. With the definition for the twist
angle previously given by Frezzotti and Rossi, automatic O(a) improvement can
fail unless the quark mass satisfies m_q >> a^2 Lambda_QCD^3. We propose a
different definition for the twist angle which does not require a restriction
on the quark mass for automatic O(a) improvement. In order to illustrate
explicitly automatic O(a) improvement we compute the pion mass in the
corresponding chiral effective theory. We consider different definitions for
maximal twist and show explicitly the absence or presence of the leading O(a)
effect, depending on the size of the quark mass.Comment: 27 pages, no figure
Pion scattering in Wilson ChPT
We compute the scattering amplitude for pion scattering in Wilson chiral
perturbation theory for two degenerate quark flavors. We consider two different
regimes where the quark mass m is of order (i) a\Lambda_QCD^2 and (ii)
a^2\Lambda_QCD^3. Analytic expressions for the scattering lengths in all three
isospin channels are given. As a result of the O(a^2) terms the I=0 and I=2
scattering lengths do not vanish in the chiral limit. Moreover, additional
chiral logarithms proportional to a^2\ln M_{\pi}^2 are present in the one-loop
results for regime (ii). These contributions significantly modify the familiar
results from continuum chiral perturbation theory.Comment: 20 pages, 4 figures. V3: Comments on finite size effects and the
axial vector current added, one more reference. To be published in PR
Einfluss der Aufschlusstemperatur auf die morphologischen Eigenschaften von TMP aus Kiefernholz
Chips from pine wood were subjected to thermomechanical pulping (TMP) at 140 and 180 degrees C for 5 minutes, whereas the cooked chips were defibrated using a single disk pressurized refiner at the same temperatures (140 and 180 degrees C). The fibres were tested for some of their morphological properties including fibre length, fibre width, cell-wall thickness. Moreover, the fine fibre fraction (zero fibres) and the content of splinters were also estimated. The results reveal, that increasing the temperature during thermomechanical pulping decreases the fibre length, the cell width and the fibre wall thickness. It also increases the amount of fine fibres and increases the curl factor
Spiral waves in a surface reaction: Model calculations
A systematic study of spiral waves in a realistic reactionâdiffusion model describing the isothermal CO oxidation on Pt(110) is carried out. Spirals exist under oscillatory, excitable, and bistable (doubly metastable) conditions. In the excitable region, two separate meandering transitions occur, both when the time scales become strongly different and when they become comparable. By the assumption of surface defects of the order of 10 ÎŒm, to which the spirals can be pinned, the continuous distribution of wavelengths observed experimentally can be explained. An external periodic perturbation generally causes a meandering motion of a free spiral, while a straight drift results, if the period of the perturbation divided by the rotation period is a natural number
The Role of Bordetella Infections in Patients with Acute Exacerbation of Chronic Bronchitis
Abstract : Background: : Acute exacerbations of chronic bronchitis (AECB) are associated with a variety of viral and bacterial infectious agents, some of which are potentially preventable by immunization. Bordetella pertussis, which causes whooping cough, has not been studied in this context. We aimed to assess the role of Bordetella infections in patients with AECB. Patients and Methods: : Patients with AECB, who presented to participating private practices in Basel, Switzerland, between October 2000 and June 2002, were evaluated by a standardized questionnaire, nasopharyngeal swabs for culture (Bordetella spp.), and PCR (Bordetella spp. and selected other respiratory pathogens) and paired blood samples for serologic diagnosis of Bordetella infection. Results: : A total of 26 patients (34-86 years of age) were recruited. All culture and PCR samples were negative. Serology revealed Bordetella infection in eight (31%) patients. Duration of cough was shorter in patients with Bordetella infection compared to those without Bordetella infection (mean 15 days vs 41 days, p = 0.04). Cough â„ 21 days duration was present in three (43%) of seven patients with evidence of Bordetella infection compared to 17 (94%) of 18 controls (p = 0.012). Progression to convalescence from initial to follow-up visit after 4-6 weeks was comparable between both groups. Conclusion: : Bordetella infections appear to play a significant role in AECB and preventive measurements such as immunization with acellular pertussis vaccines should be considered. Extended investigations are necessary to confirm our preliminary and provocative finding
Alternative mechanisms of structuring biomembranes: Self-assembly vs. self-organization
We study two mechanisms for the formation of protein patterns near membranes
of living cells by mathematical modelling. Self-assembly of protein domains by
electrostatic lipid-protein interactions is contrasted with self-organization
due to a nonequilibrium biochemical reaction cycle of proteins near the
membrane. While both processes lead eventually to quite similar patterns, their
evolution occurs on very different length and time scales. Self-assembly
produces periodic protein patterns on a spatial scale below 0.1 micron in a few
seconds followed by extremely slow coarsening, whereas self-organization
results in a pattern wavelength comparable to the typical cell size of 100
micron within a few minutes suggesting different biological functions for the
two processes.Comment: 4 pages, 5 figure
A note about the t`Hooft`s ansatz for SU(N) real time guage theories
The t`Hooft's ansatz reduces the classical Yang--Mills theory to the
one. It is shown that in the frame of this ansatz the real-time
classical solutions for the arbitrary SU(N) gauge group is obtained by
embedding into SU(N). It is argued that this group
structure is the only possibility in the frame of the considered ansatz. New
explicit solutions for SU(3) and SU(5) gauge groups are shown
In system photoelectron spectroscopy study of tin oxide layers produced from tetrakis dimethylamino tin by plasma enhanced atomic layer deposition
Tin oxide SnO2 layers were deposited using plasma enhanced atomic layer deposition with tetrakis dimethylamino tin precursor and oxygen plasma. The deposited layers were analyzed by spectral ellipsometry, conductivity measurements, and in system photoelectron spectroscopy. Within a deposition temperature range of 90 210 amp; 8201; C, the resistivity of the SnO2 layers decreases by 5 orders of magnitude with increasing deposition temperature. At the same time, the refractive index at 632.8 amp; 8201;nm increases from 1.7 to 1.9. These changes in bulk layer properties are connected to results from photoelectron spectroscopy. It is found that decreasing carbon and nitrogen contaminations in the tin oxide layers lead to decreasing optical band gaps and increasing refractive index. Additionally, for the deposited SnO2 layers, a shoulder in the O 1s core level spectrum is observed that decreases with the deposition temperature and thus is proposed to be related to hydroxyl group
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