27,017 research outputs found
Unsupervised machine learning for detection of phase transitions in off-lattice systems II. Applications
We outline how principal component analysis (PCA) can be applied to particle
configuration data to detect a variety of phase transitions in off-lattice
systems, both in and out of equilibrium. Specifically, we discuss its
application to study 1) the nonequilibrium random organization (RandOrg) model
that exhibits a phase transition from quiescent to steady-state behavior as a
function of density, 2) orientationally and positionally driven equilibrium
phase transitions for hard ellipses, and 3) compositionally driven demixing
transitions in the non-additive binary Widom-Rowlinson mixture
Cornering pseudoscalar-mediated dark matter with the LHC and cosmology
Models in which dark matter particles communicate with the visible sector through a pseudoscalar mediator are well-motivated both from a theoretical and from a phenomenological standpoint. With direct detection bounds being typically subleading in such scenarios, the main constraints stem either from collider searches for dark matter, or from indirect detection experiments. However., LHC searches for the mediator particles themselves can not only compete with — or even supersede — the reach of direct collider dark matter probes, but they can also test scenarios in which traditional monojet searches become irrelevant, especially when the mediator cannot decay on-shell into dark matter particles or its decay is suppressed. In this work we perform a detailed analysis of a pseudoscalar-mediated dark matter simplified model, taking into account a large set of collider constraints and concentrating on the parameter space regions favoured by cos-mological and astrophysical data. We find that mediator masses above 100-200 GeV are essentially excluded by LHC searches in the case of large couplings to the top quark, while forthcoming collider and astrophysical measurements will further constrain the available parameter space
Global monopoles and scalar fields as the electrogravity dual of Schwarzschild spacetime
We prove that both global monopole and minimally coupled static zero mass
scalar field are electrogravity dual of the Schwarzschild solution or flat
space and they share the same equation of state, . This
property was however known for the global monopole spacetime while it is for
the first time being established for the scalar field. In particular, it turns
out that the Xanthopoulos - Zannias scalar field solution is dual to flat
space.Comment: 5 pages, RevTe
The propensity of molecules to spatially align in intense light fields
The propensity of molecules to spatially align along the polarization vector
of intense, pulsed light fields is related to readily-accessible parameters
(molecular polarizabilities, moment of inertia, peak intensity of the light and
its pulse duration). Predictions can now be made of which molecules can be
spatially aligned, and under what circumstances, upon irradiation by intense
light. Accounting for both enhanced ionization and hyperpolarizability, it is
shown that {\it all} molecules can be aligned, even those with the smallest
static polarizability, when subjected to the shortest available laser pulses
(of sufficient intensity).Comment: 8 pages, 4 figures, to be submitted to PR
Digitized archive of the Kodaikanal images: Representative results of solar cycle variation from sunspot area determination
Photographic images are valuable data resources for studying long term
changes in the solar magnetic field and its influence on the Earth's climate
and weather.
We digitized more than 100 years of white light images stored in photographic
plates and films that are available at Kodaikanal observatory starting from
1904. The digitized images were calibrated for relative plate density and
aligned in such a way that the solar north is in upward direction. A
semi-automated sunspot detection technique was used to identify the sunspots on
the digitized images. In addition to describing the calibration procedure and
availability of the data, we here present preliminary results on the sunspot
area measurements and their variation with time. The results show that the
white-light images have a uniform spatial resolution throughout the 90 years of
observations. However, the contrast of the images decreases from 1968 onwards.
The images are circular and do not show any major geometrical distortions. The
measured monthly averaged sunspot areas closely match the Greenwich sunspot
area over the four solar cycles studied here. The yearly averaged sunspot area
shows a high degree of correlation with the Greenwich sunspot area. Though the
monthly averaged sunspot number shows a good correlation with the monthly
averaged sunspot areas, there is a slight anti-correlation between the two
during solar maximum The Kodaikanal data archive is hosted at
http://kso.iiap.res.in. The long time sequence of the Kodaikanal white light
images provides a consistent data set for sunspot areas and other proxies. Many
studies can be performed using Kodaikanal data alone without requiring
intercalibration between different data sources.Comment: 9 pages, A&A(accepted
Design and test of a magnetic thrust bearing
A magnetic thrust bearing can be employed to take thrust loads in rotating machinery. The design and construction of a prototype magnetic thrust bearing for a high load per weight application is described. The theory for the bearing is developed. Fixtures were designed and the bearing was tested for load capacity using a universal testing machine. Various shims were employed to have known gap thicknesses. A comparison of the theory and measured results is presented
Nonsingular static global string
A new solution for the spacetime outside the core of a U(1) static global
string has been presented which is nonsingular. This is the first example of a
nonsingular spacetime around a static global string.}}Comment: Minor corrections added. Accepted for publication in Phys.Rev.
- …