Search results for "ORIENTATION"
showing 10 items of 1041 documents
Light-Driven Extremely Nonlinear Bulk Photogalvanic Currents
2021
We predict the generation of bulk photocurrents in materials driven by bichromatic fields that arc circularly polarized and corotating. The nonlinear photocurrents have a fully controllable directionality and amplitude without requiring carrier-envelope-phase stabilization or few-cycle pulses, and can be generated with photon energies much smaller than the band gap (reducing heating in the photoconversion process). We demonstrate with ab initio calculations that the photocurrent generation mechanism is universal and arises in gaped materials (Si, diamond, MgO, hBN), in semimetals (graphene), and in two- and three-dimensional systems. Photocurrents are shown to rely on sub-laser-cycle asymme…
The MORA project
2018
The MORA (Matter's Origin from the RadioActivity of trapped and oriented ions) project aims at measuring with unprecedented precision the D correlation in the nuclear beta decay of trapped and oriented ions. The D correlation offers the possibility to search for new CP-violating interactions, complementary to searches done at the LHC and with Electric Dipole Moments. Technically, MORA uses an innovative in-trap orientation method which combines the high trapping efficiency of a transparent Paul trap with laser orientation techniques. The trapping, detection, and laser setups are under development, for first tests at the Accelerator laboratory, JYFL, in the coming years.
Effects of emergency remote instruction during the COVID-19 pandemic on university physics students in Italy
2021
We surveyed a convenience sample of 362 Italian university physics students, asking them to retrospectively assess their experience of emergency remote instruction due to the COVID-19 outbreak. We looked at their psychological well being, motivation for physics, academic orientation, attitude towards physics and physicists, and tried to link these factors to their overall perception of the online instruction. Our results show a general appreciation for the organization and effectiveness of online courses. However, online teaching negatively impacted on engagement and interaction between peers and with the instructors. Only 22% of students in our sample complained of the psychological distre…
Study of Even Gd Nuclei by Decay of Oriented Tb, With Analysis by Simple Boson Models
1983
We have studied low-spin states of 150,152,154,156Gd by nuclear orientation of β-decaying Tb in a Gd host. Especially by means of multipole mixing ratios, including E0/E2, we have checked and revised spin-parities and assignments to (quasi) rotational ground, β and γ bands. For 150Gd we propose the new interpretation 1207.2 keV (0β+), 1518.5 keV (2β+), 1700.1 keV (4β+), 1430.5 keV (2γ+), 1988.0 keV (3γ+), 2080.0 keV (4γ+). For 152,154,156Gd we find agreement with recent literature. Our comparison with theory includes available data on 158,160Gd and on states up to 10g+, 10β+, 7γ+. We review our previously proposed "projection model", which is basically of the Bohr-Mottelson geometrical type…
Positioning systems in Minkowski space-time: from emission to inertial coordinates
2009
The coordinate transformation between emission coordinates and inertial coordinates in Minkowski space-time is obtained for arbitrary configurations of the emitters. It appears that a positioning system always generates two different coordinate domains, namely, the front and the back emission coordinate domains. For both domains, the corresponding covariant expression of the transformation is explicitly given in terms of the emitter world-lines. This task requires the notion of orientation of an emitter configuration. The orientation is shown to be computable from the emission coordinates for the users of a `central' region of the front emission coordinate domain. Other space-time regions a…
Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands
2018
We have studied a complete radio sample of active galactic nuclei with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high-precision phase-delay astrometry atQband (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique atUband (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1σlevel betweenUandQbands. With the benefit of quasi-simultaneousUandQband observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three d…
Spatiotemporal rotational dynamics of laser-driven molecules
2020
Molecular alignment and orientation by laser fields has attracted significant attention in recent years, mostly due to new capabilities to manipulate the molecular spatial arrangement. Molecules can now be efficiently prepared for ionization, structural imaging, orbital tomography, and more, enabling, for example, shooting of dynamic molecular movies. Furthermore, molecular alignment and orientation processes give rise to fundamental quantum and classical phenomena like quantum revivals, Anderson localization, and rotational echoes, just to mention a few. We review recent progress on the visualization, coherent control, and applications of the rich dynamics of molecular rotational wave pack…
Angular momentum spatial distribution symmetry breaking in Rb by an external magnetic field
2000
Excited state angular momentum alignment -- orientation conversion for atoms with hyperfine structure in presence of an external magnetic field is investigated. Transversal orientation in these conditions is reported for the first time. This phenomenon occurs under Paschen Back conditions at intermediate magnetic field strength. Weak radiation from a linearly polarized diode laser is used to excite Rb atoms in a cell. The laser beam is polarized at an angle of pi/4 with respect to the external magnetic field direction. Ground state hyperfine levels of the 5S_1/2 state are resolved using laser-induced fluorescence spectroscopy under conditions for which all excited 5P_3/2 state hyperfine com…
Global and Local Effects of Rotation: Observational Aspects
2011
In the paper we discussed the observational aspects of rotation in the Universe on different scales. We show dependence between the angular momentum of the structures and their size. The presented observational situation is that the galaxies, their pairs and compact groups have a non-vanishing angular momentum. In the structures of mass corresponding to groups of galaxies, this feature has not been found, while in the clusters and superclusters alignment of galaxy orientation has been actually found. Also we know that galaxies have net angular momentum due to the fact that we actually measure the rotation curves of galaxies. These facts lead to the conclusion that theories which connect gal…
Orientation of galaxies in structures
2014
The investigation of the orientation of galaxies is a standard test concerning to scenarios of galaxy formation, because different theories of galaxy formation make various predictions regarding to the angular momentum of galaxies. The new method of analysis of the alignment of galaxies in clusters was proposed in the paper Godlowski (2012) and now is improved. We analyzed the distribution of the position angles of the galaxy major axes, as well as the distribution of two angles describing the spatial orientation of galaxy plane, which gives the information about galaxy angular momenta. We discuss the orientation of galaxies in groups and clusters of galaxies. The results show the dependenc…