474 research outputs found
Atomic parity violation and the HERA anomaly
We show that the two scenarios able to explain the HERA anomaly --- a new
leptoquark coupling or a new contact interaction --- predict new contributions
to atomic parity violation. These corrections are sufficiently large and
different that a feasible reduction in the dominant atomic theory uncertainty
could give some hint in favour of one of the two scenarios.Comment: 4 pages. Reference added, PDG value of weak charge revise
Frequency-splitting estimators of single-propagator traces
Single-propagator traces are the most elementary fermion Wick contractions
which occur in numerical lattice QCD, and are usually computed by introducing
random-noise estimators to profit from volume averaging. The additional
contribution to the variance induced by the random noise is typically orders of
magnitude larger than the one due to the gauge field. We propose a new family
of stochastic estimators of single-propagator traces built upon a frequency
splitting combined with a hopping expansion of the quark propagator, and test
their efficiency in two-flavour QCD with pions as light as 190 MeV. Depending
on the fermion bilinear considered, the cost of computing these diagrams is
reduced by one to two orders of magnitude or more with respect to standard
random-noise estimators. As two concrete examples of physics applications, we
compute the disconnected contributions to correlation functions of two vector
currents in the isosinglet omega channel and to the hadronic vacuum
polarization relevant for the muon anomalous magnetic moment. In both cases,
estimators with variances dominated by the gauge noise are computed with a
modest numerical effort. Theory suggests large gains for disconnected three and
higher point correlation functions as well. The frequency-splitting estimators
and their split-even components are directly applicable to the newly proposed
multi-level integration in the presence of fermions.Comment: 26 pages, 8 figures, LaTe
A Fast Learning Algorithm for Image Segmentation with Max-Pooling Convolutional Networks
We present a fast algorithm for training MaxPooling Convolutional Networks to
segment images. This type of network yields record-breaking performance in a
variety of tasks, but is normally trained on a computationally expensive
patch-by-patch basis. Our new method processes each training image in a single
pass, which is vastly more efficient.
We validate the approach in different scenarios and report a 1500-fold
speed-up. In an application to automated steel defect detection and
segmentation, we obtain excellent performance with short training times
Learning Ground Traversability from Simulations
Mobile ground robots operating on unstructured terrain must predict which
areas of the environment they are able to pass in order to plan feasible paths.
We address traversability estimation as a heightmap classification problem: we
build a convolutional neural network that, given an image representing the
heightmap of a terrain patch, predicts whether the robot will be able to
traverse such patch from left to right. The classifier is trained for a
specific robot model (wheeled, tracked, legged, snake-like) using simulation
data on procedurally generated training terrains; the trained classifier can be
applied to unseen large heightmaps to yield oriented traversability maps, and
then plan traversable paths. We extensively evaluate the approach in simulation
on six real-world elevation datasets, and run a real-robot validation in one
indoor and one outdoor environment.Comment: Webpage: http://romarcg.xyz/traversability_estimation
Exotic atoms at extremely high magnetic fields: the case of neutron star atmosphere
The presence of exotic states of matter in neutron stars (NSs) is currently
an open issue in physics. The appearance of muons, kaons, hyperons, and other
exotic particles in the inner regions of the NS, favored by energetic
considerations, is considered to be an effective mechanism to soften the
equation of state (EoS). In the so-called two-families scenario, the softening
of the EoS allows for NSs characterized by very small radii, which become
unstable and convert into a quark stars (QSs). In the process of conversion of
a NS into a QS material can be ablated by neutrinos from the surface of the
star. Not only neutron-rich nuclei, but also more exotic material, such as
hypernuclei or deconfined quarks, could be ejected into the atmosphere. In the
NS atmosphere, atoms like H, He, and C should exist, and attempts to model the
NS thermal emission taking into account their presence, with spectra modified
by the extreme magnetic fields, have been done. However, exotic atoms, like
muonic hydrogen or the so-called Sigmium , could
also be present during the conversion process or in its immediate aftermath. At
present, analytical expressions of the wave functions and eigenvalues for these
atoms have been calculated only for H. In this work, we extend the existing
solutions and parametrizations to the exotic atoms and
, making some predictions on possible transitions. Their
detection in the spectra of NS would provide experimental evidence for the
existence of hyperons in the interior of these stars.Comment: 10 pages, 6 figures, proceedings of the "International Conference on
Exotic Atoms and Related Topics - EXA2017", Austrian Academy of Sciences,
Austria, September 11-15, 201
Challenges of tsunami and conflict affected rural water supply in Sri Lanka
The water supply of the rural coastal areas in Sri Lanka is provided by private open dug wells, most of which have been
flooded by sea water during the tsunami. The salinity of the well affected proved not to be the main problem, and early
attempts to rehabilitate wells failed. Salinity reduction can only be achieved naturally, through the recharge of the aquifer.
The true challenge for rural water supply is represented by bacteriological and agricultural contamination and sustainability
of handpumps. Constructing back better means also an exit strategy from water trucking that does not focus on
salinity, but introduces a new water quality awareness, and new water purification solutions, to the users. A lesson learned:
in case of tsunami, do not try to rehabilitate the well, just wait for the rainy season
Ein nichtlineares Modell fĂŒr das dynamische Verhalten von schwimmenden Offshore-Fundamenten
Among the renewable energies, the exploitation of offshore wind energy in deep waters is becoming more and more important, and it is expected to increase even more because of the intrinsic potential and the large availability of this resource. Deep-water wind turbines are usually installed over moored floating supports. Their dynamics depends on the complex interaction between the system and the environment making the use of numerical models almost inevitable for the design and optimization of such structures. In this context, a nonlinear model for the dynamics of moored floating platforms is developed. The dynamic problem of the platform is formulated in the framework of the dynamics of rigid bodies, referring to the mixed representation of the motion, which consists in the simultaneous use of two different bases. The formulation is developed for a wide range of loads (forces and torques) with particular attention to the transformations of the state variables. Both follower and non-follower loads are considered. The differential problem is solved with a recently developed time integration algorithm that considers the Lie group structure of the configuration space overcoming some critical aspects associated with the typical use of nautical angles and their time derivatives. The resulting formulation is very general and in principle can be exploited for the study of every system modelled as a rigid body, such as ships and hulls. The developed dynamic solver can be coupled with other models to study specific problems. In this work the assessment of the loads related to both the mooring system and the hydrodynamic action is addressed. In particular, mooring lines are modelled by means of a quasi-static formulation, whereas wave loads are evaluated with the linear hydrodynamic theory. In general, both the formulations guarantee a satisfying level of accuracy, even though in some specific cases the inertia and damping of the mooring lines as well as higher-order hydrodynamic terms should be included to improve the reliability of the model. The numerical model is tested against a number of dynamic problems for which the exact analytic solution is known, allowing a detailed assessment of the capabilities of the method. The dynamics of moored floating platforms is then investigated discussing the effect of different strategies of simulation on the system response and the role of the main parameters affecting the motion.Die Bedeutung von Offshore-Windenergie unter den erneuerbaren EnergietrĂ€gern nimmt momentan stark zu und weitere ZuwĂ€chse werden aufgrund der weiten VerfĂŒgbarkeit dieser Energiequelle und ihres intrinsischen Potenzials erwartet. Windkraftanlagen in Tiefwasser werden normalerweise mittels schwimmenden Offshore-Fundamenten am Meeresboden verankert. Ihr dynamisches Verhalten hĂ€ngt von der komplexen Interaktion zwischen dem System und der Umgebung ab, weshalb numerische Modelle unerlĂ€sslich fĂŒr die Entwicklung und Optimierung solcher Strukturen sind. Daher wird ein nichtlineares Modell zur Beschreibung des dynamischen Verhaltens von schwimmenden Offshore-Fundamenten vorgestellt. DafĂŒr wird ein analytischer Ansatz aus dem Bereich der Dynamik starrer Körper unter Verwendung einer gemischten Darstellung der Bewegung entwickelt. Dieser Ansatz berĂŒcksichtigt eine groĂe Bandbreite an Belastungen (KrĂ€fte und Momente) unter Beachtung der Transformation der Zustandsvariablen. Dabei werden sowohl Lasten mit raumfesten als auch mit verĂ€nderlichen Wirkrichtungen berĂŒcksichtigt. Die Lösung des Differentialgleichungssystems erfolgt mittels eines Zeitintegrationsverfahrens, das die Struktur der Lie-Gruppe des betrachteten Raumes berĂŒcksichtigt und eine Vereinfachung in Bezug auf die allgemein verwendeten Eulerschen Winkel darstellt. Der resultierende Ansatz ist allgemeingĂŒltig und kann prinzipiell auf jedes beliebige, als starrer Körper modellierte System angewendet werden. Der dynamische Gleichungslöser wird mit zusĂ€tzlichen Modellen zur Ermittlung der, von der Verankerung verursachten, ReaktionskrĂ€fte und -momente und der Beanspruchung durch hydrodynamische Lasten gekoppelt. Dabei werden die Ankertrossen mittels eines quasi-statischen Ansatzes modelliert und die Belastung durch Wellen wird nach der linearen hydrodynamischen Theorie bestimmt. Generell liefern beide AnsĂ€tze eine hohe Genauigkeit, in einigen SpezialfĂ€llen sollten die MassentrĂ€gheit und DĂ€mpfung der Verankerung sowie hydrodynamische Terme höherer Ordnung zur Verbesserung des Modells berĂŒcksichtigt werden. Das numerische Modell wird anhand einer Reihe dynamischer Problemstellungen mit exakten, analytischen Lösungen validiert, wodurch die allgemeingĂŒltige Anwendbarkeit der Methode belegt wird. AbschlieĂend wird das dynamische Verhalten von schwimmenden Offshore-Fundamenten hinsichtlich verschiedener Simulationsstrategien und des Einflusses der Hauptparameter auf die Bewegung untersucht
Resistenza di travi in cemento armato deteriorate dalla corrosione: confronto fra risultati sperimentali e teorici
La valutazione della resistenza di strutture in cemento armato dipende principalmente dalle proprietĂ dei materiali, dalla geometria e dalle incertezze legate al modello applicato. La corrosione delle armature Ăš generalmente considerata la principale causa del deterioramento di tali strutture e puĂČ influire sia sul comportamento allo stato limite ultimo sia allo stato limite di esercizio. Nella presente tesi si applicano le indicazioni per il calcolo delle incertezze di modello descritte nel Probabilistic Model Code of the Joint Committee on Structural Safety e si propone un procedimento per la valutazione di strutture in cemento armato deteriorate dalla corrosione. I parametri statistici delle incertezze dei modelli di resistenza sono stimati applicando le formulazioni dellâEurocodice UNI-EN 1992-1-1, relativamente al calcolo della resistenza a flessione, e del Model Code 2010 e del modello sperimentale di A. MĂĄri, relativamente al calcolo della resistenza a taglio, opportunamente modificate per tenere conto degli effetti della corrosione sulla resistenza degli elementi strutturali. Le informazioni inerenti alle proprietĂ dei materiali, alla geometria e allâaderenza sono state introdotte allâinterno dei suddetti modelli per stabilire la residua capacitĂ portante. Comparando i risultati teorici con quelli ottenuti a seguito di una campagna sperimentale su travi in cemento armato con armature corrose a causa dellâesposizione ad ambiente marino aggressivo durante 70 anni, sono stati individuati i modelli maggiormente affidabili, che peraltro presentano deviazioni leggermente maggiori rispetto a quelle riscontrate nel caso di strutture integre. Infine, Ăš stata implementata una procedura generale di valutazione di strutture deteriorate che prevede lâutilizzo dei modelli di flessione e di taglio maggiormente affidabili; mediante lâapplicazione di tale metodologia al campione di travi testate, Ăš stato verificato che tale metodo permette di compiere una stima affidabile del comportamento di strutture in cemento armato degradate dalla corrosione
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