Star polymers as unit cells for coarse-graining cross-linked networks

Reducing the complexity of cross-linked polymer networks by preserving their main macroscale properties, is key to understanding them, and a crucial issue is to relate individual properties of the polymer constituents to those of the reduced network. Here we study polymer networks in a good solvent, by considering star polymers as their unit elements, and first quantify the interaction between their centers of masses. We then reduce the complexity of a network by replacing sets of its bridged star polymers by equivalent effective soft particles with dense cores. Our coarse graining allows us to approximate complex polymer networks by much simpler ones, keeping their relevant mechanical properties, as illustrated in computer experiments on an isotropic compression.Comment: 5 pages, 8 figure

Public finance, governance, and growth in transition economies : empirical evidence from 1992-2004

This paper revisits the early empirical literature on economic growth in transition economies, with particular focus on fiscal policy variables-fiscal balance and the size of government. The baseline model uses a parsimonious specification, drawn from Fischer and Sahay (2000), of economic growth as a function of initial conditions, stabilization, liberalization, and structural reform. The paper expands the data used in previous analyses by up to 10 years and finds unambiguous evidence that fiscal balance matters for growth, while confirming other previous findings on the correlates of economic growth in transition economies. In addition, the paper extends the baseline model and explores potential sources of nonlinearities in the relationship between growth and public finance. A key finding is that determinants of growth may vary in relative importance, depending on the underlying institutional quality. The evidence indicates that there could be higher growth payoffs from macroeconomic stability and public expenditure in countries characterized by relatively better public sector governance as measured by relevant indicators. In addition, the size of government matters for growth in a nonlinear manner: Beyond indicative thresholds of expenditure levels, public spending has a negative impact, while at levels below the threshold, there is no measurable impact on economic growth.Public Sector Expenditure Analysis&Management,Governance Indicators,Achieving Shared Growth,National Governance,Macroeconomic Management

The effects of short-lived radionuclides and porosity on the early thermo-mechanical evolution of planetesimals

The thermal history and internal structure of chondritic planetesimals, assembled before the giant impact phase of chaotic growth, potentially yield important implications for the final composition and evolution of terrestrial planets. These parameters critically depend on the internal balance of heating versus cooling, which is mostly determined by the presence of short-lived radionuclides (SLRs), such as aluminum-26 and iron-60, as well as the heat conductivity of the material. The heating by SLRs depends on their initial abundances, the formation time of the planetesimal and its size. It has been argued that the cooling history is determined by the porosity of the granular material, which undergoes dramatic changes via compaction processes and tends to decrease with time. In this study we assess the influence of these parameters on the thermo-mechanical evolution of young planetesimals with both 2D and 3D simulations. Using the code family I2ELVIS/I3ELVIS we have run numerous 2D and 3D numerical finite-difference fluid dynamic models with varying planetesimal radius, formation time and initial porosity. Our results indicate that powdery materials lowered the threshold for melting and convection in planetesimals, depending on the amount of SLRs present. A subset of planetesimals retained a powdery surface layer which lowered the thermal conductivity and hindered cooling. The effect of initial porosity was small, however, compared to those of planetesimal size and formation time, which dominated the thermo-mechanical evolution and were the primary factors for the onset of melting and differentiation. We comment on the implications of this work concerning the structure and evolution of these planetesimals, as well as their behavior as possible building blocks of terrestrial planets.Comment: 19 pages, 11 figures, 5 tables; accepted for publication in Icarus; for associated video files, see http://timlichtenberg.net/2015_porosity.html or http://dx.doi.org/10.1016/j.icarus.2016.03.00

The impact of energy price changes in Moldova

In January 2006 the price of natural gas supplied to Moldova increased from $80 to$110 per thousand cubic meters (mcm). Prices may increase further in the near future, putting additional pressure on the economy and leading to adverse effects on the poorest households. This study examines the potential impact of higher energy prices on the economy of Moldova by simulating the likely macroeconomic consequences of recent and future price increases. Moreover, it estimates the direct impact on individual households using data drawn from the 2004 Household Budget Survey. It assesses the distributional implications of the price shock, noting how the social impact may vary depending on the intensity of energy use, geographic location, and the relative share of energy in household expenditure. The results suggest that energy price changes could dampen economic growth while putting additional strains on the current account deficit. The impact on the poorest households could be significant and protecting them may require resources in the amount of 0.7 to 1.7 percent of GDP. This study identifies possible policy responses to dampen the shock of the energy price increase and to promote the longer-term objective of reducing energy vulnerability.Energy Production and Transportation,Environment and Energy Efficiency,Energy and Environment,Markets and Market Access,Transport and Environment

Laparoscopic Retrieval of Intrauterine Device Perforating the Sigmoid Colon

An infrequent complication of intrauterine device use is uterine perforation and migration of the device. The authors suggest that laparoscopic removal of a translocated intrauterine device is a preferred method of retrieval

Jordan-Wigner Approach to Dynamic Correlations in 2D Spin-1/2 Models

We discuss the dynamic properties of the square-lattice spin-1/2 XY model obtained using the two-dimensional Jordan-Wigner fermionization approach. We argue the relevancy of the fermionic picture for interpreting the neutron scattering measurements in the two-dimensional frustrated quantum magnet Cs_2CuCl_4.Comment: Presented at 12-th Czech and Slovak Conference on Magnetism, Ko\v{s}ice, 12-15 July 200

Impact splash chondrule formation during planetesimal recycling

Chondrules are the dominant bulk silicate constituent of chondritic meteorites and originate from highly energetic, local processes during the first million years after the birth of the Sun. So far, an astrophysically consistent chondrule formation scenario, explaining major chemical, isotopic and textural features, remains elusive. Here, we examine the prospect of forming chondrules from planetesimal collisions. We show that intensely melted bodies with interior magma oceans became rapidly chemically equilibrated and physically differentiated. Therefore, collisional interactions among such bodies would have resulted in chondrule-like but basaltic spherules, which are not observed in the meteoritic record. This inconsistency with the expected dynamical interactions hints at an incomplete understanding of the planetary growth regime during the protoplanetary disk phase. To resolve this conundrum, we examine how the observed chemical and isotopic features of chondrules constrain the dynamical environment of accreting chondrite parent bodies by interpreting the meteoritic record as an impact-generated proxy of planetesimals that underwent repeated collision and reaccretion cycles. Using a coupled evolution-collision model we demonstrate that the vast majority of collisional debris feeding the asteroid main belt must be derived from planetesimals which were partially molten at maximum. Therefore, the precursors of chondrite parent bodies either formed primarily small, from sub-canonical aluminum-26 reservoirs, or collisional destruction mechanisms were efficient enough to shatter planetesimals before they reached the magma ocean phase. Finally, we outline the window in parameter space for which chondrule formation from planetesimal collisions can be reconciled with the meteoritic record and how our results can be used to further constrain early solar system dynamics.Comment: 20 pages, 11 figures, 2 tables; accepted for publication in Icarus; associated blog article at goo.gl/5bDqG

Ill-Behaved Convergence of a Model of the Gd3Ga5O12 Garnet Antiferromagnet with Truncated Magnetic Dipole-Dipole Interactions

Previous studies have found that calculations which consider long-range magnetic dipolar interactions truncated at a finite cut-off distance Rc predict spurious (unphysical) long-range ordered phases for Ising and Heisenberg systems on the pyrochlore lattice. In this paper we show that, similar to these two cases, calculations that use truncated dipolar interactions to model the Gd3Ga5O12 garnet antiferromagnet also predict unphysical phases with incommensurate ordering wave vector q_ord that is very sensitive to the dipolar cut-off distance Rc.Comment: 7 pages, 2 color figures; Proceedings of the HFM2006 conference, to appear in a special issue of J. Phys.: Condens. Matte

Dynamic properties of quantum spin chains: Simple route to complex behavior

We examine dynamic structure factors of spin-1/2 chains with nearest-neighbor interactions of XX and Dzyaloshinskii-Moriya type, and with periodic and random changes in the sign of these interactions. This special kind of inhomogeneity can be eliminated from the Hamiltonian by suitable transformation of the spin variables. As a result, the dynamic structure factors of periodic or random chains can be computed from those of the uniform chains. Using the exact analytical and precise numerical results available for the uniform systems we illustrate the effects of regular alternation or random disorder on dynamic structure factors of quantum spin chains