2,771 research outputs found
Antiangular Ordering of Gluon Radiation in QCD Media
We investigate angular and energy distributions of medium-induced gluon
emission off a quark-antiquark antenna in the framework of perturbative QCD as
an attempt toward understanding, from first principles, jet evolution inside
the quark-gluon plasma. In-medium color coherence between emitters, neglected
in all previous calculations, leads to a novel mechanism of soft-gluon
radiation. The structure of the corresponding spectrum, in contrast with known
medium-induced radiation, retains some properties of the vacuum case; in
particular, it exhibits a soft divergency. However, as opposed to the vacuum,
the collinear singularity is regulated by the pair opening angle, leading to a
strict angular separation between vacuum and medium-induced radiation, denoted
as antiangular ordering. We comment on the possible consequences of this new
contribution for jet observables in heavy-ion collisions.Comment: 4 pages, 2 figures; v2. a number of minor improvements, figures
updated, accepted for publication in PR
Dynamical Coulomb Blockade Observed in Nano-Sized Electrical Contacts
Electrical contacts between nano-engineered systems are expected to
constitute the basic building blocks of future nano-scale electronics. However,
the accurate characterization and understanding of electrical contacts at the
nano-scale is an experimentally challenging task. Here we employ
low-temperature scanning tunneling spectroscopy to investigate the conductance
of individual nano-contacts formed between flat Pb islands and their supporting
substrates. We observe a suppression of the differential tunnel conductance at
small bias voltages due to dynamical Coulomb blockade effects. The differential
conductance spectra allow us to determine the capacitances and resistances of
the electrical contacts which depend systematically on the island--substrate
contact area. Calculations based on the theory of environmentally assisted
tunneling agree well with the measurements.Comment: 5 pages, 3 figures, to appear in PR
The gauging of two-dimensional bosonic sigma models on world-sheets with defects
We extend our analysis of the gauging of rigid symmetries in bosonic
two-dimensional sigma models with Wess-Zumino terms in the action to the case
of world-sheets with defects. A structure that permits a non-anomalous coupling
of such sigma models to world-sheet gauge fields of arbitrary topology is
analysed, together with obstructions to its existence, and the classification
of its inequivalent choices.Comment: 94 pages, 1 figur
Altimetry, gravimetry, GPS and viscoelastic modeling data for the joint inversion for glacial isostatic adjustment in Antarctica (ESA STSE Project REGINA)
The poorly known correction for the ongoing deformation of the solid Earth caused by glacial isostatic adjustment (GIA) is a major uncertainty in determining the mass balance of the Antarctic ice sheet from measurements of satellite gravimetry and to a lesser extent satellite altimetry. In the past decade, much progress has been made in consistently modeling ice sheet and solid Earth interactions; however, forward-modeling solutions of GIA in Antarctica remain uncertain due to the sparsity of constraints on the ice sheet evolution, as well as the Earth's rheological properties. An alternative approach towards estimating GIA is the joint inversion of multiple satellite data – namely, satellite gravimetry, satellite altimetry and GPS, which reflect, with different sensitivities, trends in recent glacial changes and GIA. Crucial to the success of this approach is the accuracy of the space-geodetic data sets. Here, we present reprocessed rates of surface-ice elevation change (Envisat/Ice, Cloud,and land Elevation Satellite, ICESat; 2003–2009), gravity field change (Gravity Recovery and Climate Experiment, GRACE; 2003–2009) and bedrock uplift (GPS; 1995–2013). The data analysis is complemented by the forward modeling of viscoelastic response functions to disc load forcing, allowing us to relate GIA-induced surface displacements with gravity changes for different rheological parameters of the solid Earth. The data and modeling results presented here are available in the PANGAEA database (https://doi.org/10.1594/PANGAEA.875745). The data sets are the input streams for the joint inversion estimate of present-day ice-mass change and GIA, focusing on Antarctica. However, the methods, code and data provided in this paper can be used to solve other problems, such as volume balances of the Antarctic ice sheet, or can be applied to other geographical regions in the case of the viscoelastic response functions. This paper presents the first of two contributions summarizing the work carried out within a European Space Agency funded study: Regional glacial isostatic adjustment and CryoSat elevation rate corrections in Antarctica (REGINA)
Violent Behavior During Psychiatric Inpatient Treatment in a German Prison Hospital
Violent behavior in correctional facilities is common and differs substantially in type, target, implication, and trigger. Research on frequency and characteristics of violent behavior in correctional facilities and psychiatric hospitals is limited. Results from recent research suggest that comorbidity of severe mental disorder, personality disorder, and diagnosis of substance abuse is related to a higher risk of violent behavior. In the Berlin prison hospital, a database was created to collect data from all violent incidences (n=210) between 1997 and 2006 and between 2010 and 2016. In a retrospective, case-control study, we analyzed specific socioeconomic data and psychiatric diagnosis and compared the group of prisoners with violent behavior with randomly selected prisoners of the same department without violent behavior (n = 210). Diagnosis of schizophrenia, non-German nationality, no use of an interpreter, no children, and no previous sentence remained significantly associated with the dependent variable violent behavior. There were no significant differences regarding age and legal statuses. Practical implications for clinical work are discussed
A deterministic detector for vector vortex states
Encoding information in high-dimensional degrees of freedom of photons has led to new avenues in various quantum protocols such as communication and information processing. Yet to fully benefit from the increase in dimension requires a deterministic detection system, e.g., to reduce dimension dependent photon loss in quantum key distribution. Recently, there has been a growing interest in using vector vortex modes, spatial modes of light with entangled degrees of freedom, as a basis for encoding information. However, there is at present no method to detect these non-separable states in a deterministic manner, negating the benefit of the larger state space. Here we present a method to deterministically detect single photon states in a four dimensional space spanned by vector vortex modes with entangled polarisation and orbital angular momentum degrees of freedom. We demonstrate our detection system with vector vortex modes from the |[Formula: see text]| = 1 and |[Formula: see text]| = 10 subspaces using classical and weak coherent states and find excellent detection fidelities for both pure and superposition vector states. This work opens the possibility to increase the dimensionality of the state-space used for encoding information while maintaining deterministic detection and will be invaluable for long distance classical and quantum communication
Pulsed squeezed light: simultaneous squeezing of multiple modes
We analyze the spectral properties of squeezed light produced by means of
pulsed, single-pass degenerate parametric down-conversion. The multimode output
of this process can be decomposed into characteristic modes undergoing
independent squeezing evolution akin to the Schmidt decomposition of the
biphoton spectrum. The main features of this decomposition can be understood
using a simple analytical model developed in the perturbative regime. In the
strong pumping regime, for which the perturbative approach is not valid, we
present a numerical analysis, specializing to the case of one-dimensional
propagation in a beta-barium borate waveguide. Characterization of the
squeezing modes provides us with an insight necessary for optimizing homodyne
detection of squeezing. For a weak parametric process, efficient squeezing is
found in a broad range of local oscillator modes, whereas the intense
generation regime places much more stringent conditions on the local
oscillator. We point out that without meeting these conditions, the detected
squeezing can actually diminish with the increasing pumping strength, and we
expose physical reasons behind this inefficiency
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