Semilocal momentum-space regularized chiral two-nucleon potentials up to fifth order

We introduce new semilocal two-nucleon potentials up to fifth order in the chiral expansion. We employ a simple regularization approach for the pion-exchange contributions which (i) maintains the long-range part of the interaction, (ii) is implemented in momentum space and (iii) can be straightforwardly applied to regularize many-body forces and current operators. We discuss in detail the two-nucleon contact interactions at fourth order and demonstrate that three terms out of fifteen used in previous calculations can be eliminated via suitably chosen unitary transformations. The removal of the redundant contact terms results in a drastic simplification of the fits to scattering data and leads to interactions which are much softer (i.e. more perturbative) than our recent semilocal coordinate-space regularized potentials. Using the pion-nucleon low-energy constants from matching pion-nucleon Roy-Steiner equations to chiral perturbation theory, we perform a comprehensive analysis of nucleon-nucleon scattering and the deuteron properties up to fifth chiral order and study the impact of the leading F-wave two-nucleon contact interactions which appear at sixth order. The resulting chiral potentials lead to an outstanding description of the proton-proton and neutron-proton scattering data from the self-consistent Granada-2013 database below the pion production threshold, which is significantly better than for any other chiral potential. For the first time, the chiral potentials match in precision and even outperform the available high-precision phenomenological potentials, while the number of adjustable parameters is, at the same time, reduced by about ~40%. Last but not least, we perform a detailed error analysis and, in particular, quantify for the first time the statistical uncertainties of the fourth- and the considered sixth-order contact interactions.Comment: 57 pages, 17 figures, 19 table

Updating the Liability Regime in Outer Space: Why Spacefaring Companies Should Be Internationally Liable For Their Space Objects

Nothing inspires the human imagination quite like outer space. How many people have laid on their backs on a dark, clear night and gazed up at the stars above? The vast expanse of outer space seems endless. But satellite operators are increasingly realizing that space is not endless. Indeed, space is becoming more crowded with space objects, and the threat of these objects causing damage is rapidly growing. The space industry has changed dramatically in recent years, and the threats facing the industry have concurrently evolved. The world is experiencing the dawn of a new space race—only this time, private entities are leading the charge rather than government agencies. Companies like SpaceX and Virgin Galactic are revolutionizing human operations in outer space by developing groundbreaking new space technologies and by crafting ambitious plans for the future of human activity in space. The private sector’s ability to harness market forces has decisively decreased the costs of operating in space, which in turn has made outer space more accessible to private entities across the globe. As a result, the number of space objects in orbit will continue to skyrocket in the coming years as more private actors expand their operations in space. The probability of space objects causing damage, therefore, is only increasing. Yet, the law governing international liability for damage caused by space objects has remained shockingly stagnant. The process by which spacefaring parties are held liable under international space law has remained the same since the current liability regime was adopted in the Convention on International Liability for Damage Caused by Space Objects (Liability Convention) in 1972. The Liability Convention was drafted at a time when only two nationstates— the United States and the Soviet Union—had space-launch capabilities. Furthermore, the drafters “were neither expected nor ... required to [deal] with” private space actors at the time. As such, the Liability Convention establishes a notably state-centric framework to assign liability for damage involving space objects, in which national governments are held internationally liable for damage caused by any spacefaring actor from that country. Given the rapid privatization of the space industry, this Note argues that the international community should update the Liability Convention to reflect the modern reality that the private sector has taken the lead from the public sector in space activity. The Liability Convention is insufficient and ineffective as applied to companies, and an international liability regime that directly addresses private entities will promote certainty, investment, and development in the space industry for the benefit of all. Part I of this Note explores the current status of the space industry and further examines the rise of spacefaring companies. Part II reviews the treaty framework that establishes the current rules governing international liability for damage caused by space objects. Given this treaty framework, Part III assesses the weaknesses of this approach. First, gaps in the Liability Convention create uncertainty as to which State should be held liable in some cases involving spacefaring companies. Second, the treaty framework promotes the existence of flag states by encouraging national legislation to account for the incompleteness of the international treaties. Flag states foster a dangerous environment for the space industry. Third, the Liability Convention fails to establish effective enforcement mechanisms. The Convention lacks teeth as applied to companies, which renders it largely ineffective in certain instances. As such, Part IV articulates this Note’s two-part conclusion: the international community should (1) amend the Liability Convention and (2) assign liability for space object damage directly on spacefaring companies. This amendment would solve each problem described in Part III and would address the modern realities of today’s space industry. Indeed, these spacefaring companies no longer require insulation from liability by their national governments. Rather, these companies have attracted enormous investment in recent years and have enough resources in their corporate treasuries to cover their own liabilities. Moreover, a clearer liability regime would promote efficiency and certainty for spacefaring companies, which would benefit their business operations. Consequently, this Note argues that the international community should modernize the Liability Convention by amending it to place liability for space object damage directly on the companies involved

Structure and transport in multi-orbital Kondo systems

We consider Kondo impurity systems with multiple local orbitals, such as rare earth ions in a metallic host or multi--level quantum dots coupled to metallic leads. It is shown that the multiplet structure of the local orbitals leads to multiple Kondo peaks above the Fermi energy $E_F$, and to ``shadow'' peaks below $E_F$. We use a slave boson mean field theory, which recovers the strong coupling Fermi liquid fixed point, to calculate the Kondo peak positions, widths, and heights analytically at T=0, and NCA calculations to fit the temperature dependence of high--resolution photoemission spectra of Ce compounds. In addition, an approximate conductance quantization for transport through multi--level quantum dots or single--atom transistors in the Kondo regime due to a generalized Friedel sum rule is demonstrated.Comment: 4 pages, 3 figures. Invited article, 23rd International Conference on Low Temperature Physics LT23, Hiroshima, Japan 200

Variability and climate sensitivity of fast ice extent in the north-eastern Kara Sea

This work investigates the temporal and spatial variation of shore-fast ice extent in the north-eastern part of the Kara Sea during 1953–1990 and its sensitivity to interannual variability of the regional climate. The area of fast ice in spring months shows a bimodal distribution. This indicates the existence of two different regimes of fast ice formation driven by the system of prevailing winds. The westward wind transport during the cold season gives larger fast ice extent while the eastward wind transport suppresses the expansion of fast ice. There is a significant correlation (ca. –0.55) between the average winter temperature and the area of fast ice. Linear trends for time records of shore-fast ice area in spring show a decrease during 1953–1990. This decrease is most pronounced in April: the mean fast ice area in April is 12 % lower in 1988–1990 compared to 1953–55. A comparison of fast ice regimes for two particular years— 1979 and 1985—revealed a significant influence of cyclone activity on fast ice development over the course of the cold season. It is shown that partial break-ups of fast ice in spring 1985 are associated with the passage of cyclones across the area of fast ice

Sampling bias in systems with structural heterogeneity and limited internal diffusion

Complex systems research is becomingly increasingly data-driven, particularly in the social and biological domains. Many of the systems from which sample data are collected feature structural heterogeneity at the mesoscopic scale (i.e. communities) and limited inter-community diffusion. Here we show that the interplay between these two features can yield a significant bias in the global characteristics inferred from the data. We present a general framework to quantify this bias, and derive an explicit corrective factor for a wide class of systems. Applying our analysis to a recent high-profile survey of conflict mortality in Iraq suggests a significant overestimate of deaths

Momentum-resolved evolution of the Kondo lattice into 'hidden-order' in URu2Si2

We study, using high-resolution angle-resolved photoemission spectroscopy, the evolution of the electronic structure in URu2Si2 at the Gamma, Z and X high-symmetry points from the high-temperature Kondo-screened regime to the low-temperature `hidden-order' (HO) state. At all temperatures and symmetry points, we find structures resulting from the interaction between heavy and light bands, related to the Kondo lattice formation. At the X point, we directly measure a hybridization gap of 11 meV already open at temperatures above the ordered phase. Strikingly, we find that while the HO induces pronounced changes at Gamma and Z, the hybridization gap at X does not change, indicating that the hidden-order parameter is anisotropic. Furthermore, at the Gamma and Z points, we observe the opening of a gap in momentum in the HO state, and show that the associated electronic structure results from the hybridization of a light electron band with the Kondo-lattice bands characterizing the paramagnetic state.Comment: Updated published version. Mansucript + Supplemental Material (8 pages, 9 figures). Submitted 16 September 201

High Resolution Photoemission Study on Low-T_K Ce Systems: Kondo Resonance, Crystal Field Structures, and their Temperature Dependence

We present a high-resolution photoemission study on the strongly correlated Ce-compounds CeCu_6, CeCu_2Si_2, CeRu_2Si_2, CeNi_2Ge_2, and CeSi_2. Using a normalization procedure based on a division by the Fermi-Dirac distribution we get access to the spectral density of states up to an energy of 5 k_BT above the Fermi energy E_F. Thus we can resolve the Kondo resonance and the crystal field (CF) fine-structure for different temperatures above and around the Kondo temperature T_K. The CF peaks are identified with multiple Kondo resonances within the multiorbital Anderson impurity model. Our theoretical 4f spectra, calculated from an extended non-crossing approximation (NCA), describe consistently the observed photoemission features and their temperature dependence. By fitting the NCA spectra to the experimental data and extrapolating the former to low temperatures, T_K can be extracted quantitatively. The resulting values for T_K and the crystal field energies are in excellent agreement with the results from bulk sensitive measurements, e.g. inelastic neutron scattering.Comment: 16 two-column pages, 10 figure