475 research outputs found
Comments on the classification of orientifolds
The simple current construction of orientifolds based on rational conformal
field theories is reviewed. When applied to SO(16) level 1, one can describe
all ten-dimensional orientifolds in a unified framework.Comment: 9 pages, Contribution to proceedings of RTN-workshop in Leuven,
Belgium, September 200
Demagnetization Analysis in Excel (DAIE). An open source workbook in Excel for viewing and analyzing demagnetization data from paleomagnetic discrete samples and u-channels
The Demagnetization Analysis in Excel (DAIE) program is a single Microsoft Excel file designed for viewing and analyzing stepwise demagnetization data of both discrete and u-channel samples in paleomagnetic studies. DAIE is an Excel workbook and has an open modular structure organized in 10 worksheets.
It is designed for easy use and interactive operation; all the commands and choices can be entered using drop-down menus associated to single cells.
The standard demagnetization diagrams and various parameters of common use are shown on the same worksheet including selectable parameters and user's choices. The characteristic remanence components may be computed by principal component analysis (PCA) on a selected interval of demagnetization steps. Saving of the PCA data can be done both sample by sample, and automatically by applying the selected choices to all the samples included in the file. The whole workbook is free both for use and editing and it is available for download on a dedicated website
¿CUÁNTO DURA UNA INVERSIÓN DEL CAMPO MAGNÉTICO TERRESTRE? Nuevos datos de la última inversión del campo magnético terrestre
CUÁNTO DURA UNA INVERSIÓN DEL CAMPO MAGNÉTICO TERRESTRE? El campo magnético terrestre (o campo geomagnético) está generado por el movimiento complejo que
tiene lugar en el núcleo externo de
la Tierra. En su mayor parte, este
campo es asimilable al que generaría
una barra de imán situada en el
centro del planeta
ENVIRONMENTAL MAGNETISM: APPLICATIONS TO PALEOCLIMATIC RECONSTRUCTIONS AND AIR POLLUTION MONITORING
This short course will be focused on environmental magnetism. In the first part I will present a general overview of the relevant rock magnetic techniques and parameters, briefly discussing
laboratory measurements and basic data analysis. Following this general introduction, I will address the application of rock magnetic techniques to two main lines of research
Evaluation of a long-time temperature drift in a commercial Quantum Design MPMS SQUID magnetometer using GdO as a standard
The long-time temperature drift in a commercial Quantum Design MPMS SQUID
magnetometer was evaluated using time-dependent magnetization measurements of
GdO. In contrast to earlier claims, the amplitude of the drift was
found not to exceed 1-1.5 K. 30 minutes after system stabilization the
temperature deviation did not exceed 0.2 K and the temperature was fully
stabilized in less than 3 hours
Mass scales, supersymmetry breaking and open strings
We review physical motivations and possible realizations of string vacua with
large internal volume and/or low string scale and discuss the issue of
supersymmetry breaking. In particular, we describe the key features of
Scherk-Schwarz deformations in type I models and conclude by reviewing the
phenomenon of ``brane supersymmetry breaking'': the tadpole conditions of some
type-I models require that supersymmetry be {\it broken at the string scale} on
a collection of branes, while being exact, to lowest order, in the bulk and on
other branes.Comment: Based on talks presented by the authors at STRINGS '99. Submitted to
Classical and Quantum Gravity. misprints correcte
Gauss-Bonnet gravity renders negative tension braneworlds unstable
We show that the Gauss-Bonnet correction to Einstein gravity induces a
gravitational tachyon mode, namely an unstable spin 2 fluctuation, in the
Randall-Sundrum I model. We demonstrate that this instability is generically
related to the presence of a negative tension brane in the set-up, with or
without -symmetry across it. Indeed it is shown that the tachyon mode is a
bound state localised on any negative tension brane of co-dimension one,
embedded in anti-de Sitter background. We discuss the possible resolution of
this instability by the inclusion of induced gravity terms on the branes or by
an effective four-dimensional cosmological constant.Comment: published versio
Paleomagnetic constraints on the Plio-Pleistocene geodynamic evolution of the external central-northern Apennines (Italy)
We report on new paleomagnetic results obtained from 27 sites sampled in the Plio-Pleistocene sequences at the external front of the central-northern Apennines. Previous analyses of Miocene (Messinian) sediments indicated that the present shape of the northern Apenninic arc is due to the oroclinal bending of an originally straight belt oriented around N320° and that vertical axis rotations accompanied the migration of the thrust fronts toward the Adriatic
foreland [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. We tried to provide new paleomagnetic constraints for the timing and rates of the oroclinal bending process during the Pliocene and the Pleistocene. The results suggest that CCW rotations observed in the northern part of the studied area are possibly younger than 3 Ma. No regional rotation is recorded in the Pliocene and Pleistocene sediments from the southern part of the study area, analogously to the Messinian sediments of the 'Acquasanta' domain of Speranza et al. [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. A local significant CCW rotation (23° ± 10°) is identified in the Early Pleistocene sediments that crop out along the Adriatic coast between Ascoli and Pescara, indicating differential motion of the thrust sheets. This rotation must be younger than 1.43 Ma
Degeneracy Between the Regge Slope of Mesons and Baryons from Supersymmetry
We consider the degeneracy between the Regge slope of mesons and baryons in
QCD. We argue that within the "orientifold large-N approximation"
asymptotically massive mesons and baryons become supersymmetric partners and
hence degenerate. To this end, we generalize QCD by a SU(N) theory with a quark
in the two-index antisymmetric representation. We show that in this framework
the meson is represented by an oriented bosonic QCD-string and the baryon is
represented by an un-oriented fermionic QCD-string. At large-N, due to an
equivalence with super Yang-Mills, the tensions of the bosonic and the
fermionic strings coincide. Our description of mesons and baryons as oriented
and un-oriented bosonic and fermionic QCD-strings is in full agreement with the
spectra of open strings in the dual type 0' string theory.Comment: v2: extended version. Appendices and references adde
Paleomagnetic dating of non-sulfide Zn-Pb ores in SW Sardinia (Italy): a first attempt
A first paleomagnetic investigation aimed at constraining the age of the non-sulfide Zn-Pb ore deposits in the
Iglesiente district (SW Sardinia, Italy) was carried out. In these ores, the oxidation of primary sulfides, hosted
in Cambrian carbonate rocks, was related to several paleoweathering episodes spanning from the Mesozoic onward.
Paleomagnetic analyses were performed on 43 cores from 4 different localities, containing: a) non-oxidized
primary sulfides and host rock, b) oxidized Fe-rich hydrothermal dolomites and (c) supergene oxidation
ore («Calamine»). Reliable data were obtained from 18 samples; the others show uninterpretable results due to
low magnetic intensity or to scattered demagnetization trajectories. Three of them show a scattered Characteristic
Remanent Magnetization (ChRM), likely carried by the original (i.e. Paleozoic) magnetic iron sulfides. The
remaining 15 samples show a well defined and coherent ChRM, carried by high-coercivity minerals, acquired
after the last phase of counterclockwise rotation of Sardinia (that is after 16 Myr), in a time interval long enough
to span at least one reversal of the geomagnetic field. Hematite is the main magnetic carrier in the limestone,
whereas weathered hydrothermal dolomite contains goethite or a mixture of both. The results suggest that paleomagnetism
can be used to constrain the timing of oxidation in supergene-enriched ores
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