3,081 research outputs found
Curvatures and potential of M-theory in D=4 with fluxes and twist
We give the curvatures of the free differential algebra (FDA) of M--theory
compactified to D=4 on a twisted seven--torus with the 4--form flux switched
on. Two formulations are given, depending on whether the 1--form field
strengths of the scalar fields (originating from the 3--form gauge field
) are included or not in the FDA. We also give the bosonic
equations of motion and discuss at length the scalar potential which emerges in
this type of compactifications. For flat groups we show the equivalence of this
potential with a dual formulation of the theory which has the full \rE_{7(7)}
symmetry.Comment: 14 pages, LaTeX source, typos correcte
Use of the Natural Circulation Flow Map for Natural Circulation Systems Evaluation
The aim of this paper is to collect and resume the work done to build and develop, at the University of Pisa, an engineering tool related to the natural circulation. After a brief description of the different loop flow regimes in single phase and two phase, the derivation of a suitable tool to judge the NC performance in a generic system is presented. Finally, an extensive comparison among the NC performance of various nuclear power plants having different design is done to show a practical application of the NC flow map
CFD Code Validation against Stratified Air-Water Flow Experimental Data
Pressurized thermal shock (PTS) modelling has been identified as one of the most important industrial needs related to nuclear reactor safety. A severe PTS scenario limiting the reactor pressure vessel (RPV) lifetime is the cold water emergency core cooling (ECC) injection into the cold leg during a loss of coolant accident (LOCA). Since it represents a big challenge for numerical simulations, this scenario was selected within the European Platform for Nuclear Reactor Simulations (NURESIM) Integrated Project as a reference two-phase problem for computational fluid dynamics (CFDs) code validation. This paper presents a CFD analysis of a stratified air-water flow experimental investigation performed at the Institut de MĂ©canique des Fluides de Toulouse in 1985, which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have been carried out with two commercial codes (Fluent and Ansys CFX), and a research code (NEPTUNE CFD). The aim of this work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in the codes against experimental data, and to perform code-to-code benchmarking. Obtained results suggest the relevance of three-dimensional effects and stress the importance of a suitable interface drag modelling
Maintenance bevacizumab beyond first-line paclitaxel plus bevacizumab in patients with Her2-negative hormone receptor-positive metastatic breast cancer. Efficacy in combination with hormonal therapy
Background: Data on efficacy of bevacizumab (B) beyond first-line taxane -including regimen (BT) as first-line treatment are lacking. Although preclinical results that anti-angiogenic agents combined with hormonal therapy (HT) could be active, no clinical data exist about combination of maintenance Bevacizumab (mBev) with HT.Methods: Thirty-five patients who experienced a response after first-line BT, were given mBev at the dose of 15 mg/kg every 3 weeks. Among 30 pts with hormonal receptor-positive metastatic breast cancer (MBC), 20 (66.6%) received HT with mBev (mHTBev). Objective of the study was the outcome and safety of mBev and in two groups of patients receiving HT or not.Results: Complete response and partial response was achieved/maintained in 4 (11.4%) and 13 (37.1%) patients, respectively (overall response rate: 48.5%). Clinical benefit was obtained on 23 patients (65.7%). Median of mBev PFS and clinical benefit were 6.8 months (95% CI: 0.8-12.7) and 17.1 months (95% CI :12.2-21.9), respectively. Median PFS of patients who received mHTBev was longer than mBev without HT (13 months and 4.1 months, respectively, p = 0.05). The most common severe toxicities were proteinuria (11.4%) and hypertension (8.5%). No additional toxicity was observed with HTBev.Conclusion: Maintenance bevacizumab with or without anti-hormonal therapy in patients with hormone receptor positive breast cancer is tolerable and associated with long-term clinical outcome; these results encourage the strategy of prolonging bevacizumab until progression in combination with anti-hormonal agents
Focus on Olea europaea L. pruning by-products: extraction techniques, biological activity, and phytochemical profile
The Olea europaea L. tree has played a central role in Mediterranean culture since
ancient times. Several studies have highlighted the health-promoting properties both of its primary
products (olives) and its by-products (leaves, pomace, husk, stone, mill wastes, and wood).
In this study, pruning residues from 25-year-old olive trees located in a Mediterranean region
(Basilicata, Italy) were analyzed. The antioxidant activity of hydro-alcoholic extracts from wood
samples were analyzed through three complementary in vitro assays. The molecular composition
of the extracts was thoroughly evaluated using a gas chromatography apparatus coupled with a
mass spectrometer (GC–MS). Our study demonstrated that all but three extracts had remarkable
antioxidant activity, which was likely due to the meaningful presence of phenolic compounds,
mostly derived from lignin. Moreover, the results showed that bark extracts obtained with
ultrasound-assisted extraction (UAE) had the highest antioxidant activity. In this extract, several
known compounds with demonstrated antioxidant activity were found, including hexylresorcinol,
1-methyl-N-vanillyl-2-phenethamine, and allopurinol. This research suggests that woody olive
by-products are a potential natural resource of antioxidants. These compounds could be useful
for functional foods and in industry, and could help to solve the problem of pruning residues,
increasing their potential economic valu
Superconformal field theories from IIB spectroscopy on
We report on tests of the AdS/CFT correspondence that are made possible by
complete knowledge of the Kaluza-Klein mass spectrum of type IIB supergravity
on with T^{11}=SU(2)^2/U(1). After briefly discussing
general multiplet shortening conditions in SU(2,2|1) and PSU(2,2|4), we compare
various types of short SU(2,2|1) supermultiplets on AdS_5 and different
families of boundary operators with protected dimensions. The supergravity
analysis predicts the occurrence in the SCFT at leading order in N and g_s N,
of extra towers of long multiplets whose dimensions are rational but not
protected by supersymmetry.Comment: 11 pages, To appear in the proceedings of the STRINGS '99 conference,
Potsdam (Germany), 19-25 July 199
Type-IIA flux compactifications and N=4 gauged supergravities
We establish the precise correspondence between Type-IIA flux
compactifications preserving an exact or spontaneously broken N=4 supersymmetry
in four dimensions, and gaugings of their effective N=4 supergravities. We
exhibit the explicit map between fluxes and Bianchi identities in the
higher-dimensional theory and generalized structure constants and Jacobi
identities in the reduced theory, also detailing the origin of gauge groups
embedded at angles in the duality group. We present AdS4 solutions of the
massive Type-IIA theory with spontaneous breaking to N=1, at small string
coupling and large volume, and discuss their dual CFT3.Comment: 43 pages, 1 figure. v2: refs added, v3: minor additions. Final
version to appear on JHE
The Scherk-Schwarz mechanism as a flux compactification with internal torsion
The aim of this paper is to make progress in the understanding of the
Scherk-Schwarz dimensional reduction in terms of a compactification in the
presence of background fluxes and torsion. From the eleven dimensional
supergravity point of view, we find that a general E6(6) S-S phase may be
obtained by turning on an appropriate background torsion, together with
suitable fluxes, some of which can be directly identified with certain
components of the four-form field-strength. Furthermore, we introduce a novel
(four dimensional) approach to the study of dualities between flux/torsion
compactifications of Type II/M-theory. This approach defines the action that
duality should have on the background quantities, in order for the E7(7)
invariance of the field equations and Bianchi identities to be restored also in
the presence of fluxes/torsion. This analysis further implies the
interpretation of the torsion flux as the T-dual of the NS three-form flux.Comment: Version published on J. High Energy Phy
Off-shell N=2 tensor supermultiplets
A multiplet calculus is presented for an arbitrary number n of N=2 tensor
supermultiplets. For rigid supersymmetry the known couplings are reproduced. In
the superconformal case the target spaces parametrized by the scalar fields are
cones over (3n-1)-dimensional spaces encoded in homogeneous SU(2) invariant
potentials, subject to certain constraints. The coupling to conformal
supergravity enables the derivation of a large class of supergravity
Lagrangians with vector and tensor multiplets and hypermultiplets. Dualizing
the tensor fields into scalars leads to hypermultiplets with hyperkahler or
quaternion-Kahler target spaces with at least n abelian isometries. It is
demonstrated how to use the calculus for the construction of Lagrangians
containing higher-derivative couplings of tensor multiplets. For the
application of the c-map between vector and tensor supermultiplets to
Lagrangians with higher-order derivatives, an off-shell version of this map is
proposed. Various other implications of the results are discussed. As an
example an elegant derivation of the classification of 4-dimensional
quaternion-Kahler manifolds with two commuting isometries is given.Comment: 36 page
Polarization entangled photon-pair source based on quantum nonlinear photonics and interferometry
We present a versatile, high-brightness, guided-wave source of polarization
entangled photons, emitted at a telecom wavelength. Photon-pairs are generated
using an integrated type-0 nonlinear waveguide, and subsequently prepared in a
polarization entangled state via a stabilized fiber interferometer. We show
that the single photon emission wavelength can be tuned over more than 50 nm,
whereas the single photon spectral bandwidth can be chosen at will over more
than five orders of magnitude (from 25 MHz to 4 THz). Moreover, by performing
entanglement analysis, we demonstrate a high degree of control of the quantum
state via the violation of the Bell inequalities by more than 40 standard
deviations. This makes this scheme suitable for a wide range of quantum optics
experiments, ranging from fundamental research to quantum information
applications. We report on details of the setup, as well as on the
characterization of all included components, previously outlined in F. Kaiser
et al. (2013 Laser Phys. Lett. 10, 045202).Comment: 16 pages, 7 figure
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