The twin paradox in compact spaces

Twins travelling at constant relative velocity will each see the other's time dilate leading to the apparent paradox that each twin believes the other ages more slowly. In a finite space, the twins can both be on inertial, periodic orbits so that they have the opportunity to compare their ages when their paths cross. As we show, they will agree on their respective ages and avoid the paradox. The resolution relies on the selection of a preferred frame singled out by the topology of the space.Comment: to be published in PRA, 3 page

Flow-enhanced nucleation of poly(1-butene) : model application to short-term and continuous shear and extensional flow

A modeling framework for flow-enhanced nucleation of polymers is applied to a broad set of data from literature. Creation of flow-induced pointlike nuclei is coupled to chain stretch of the high-molecular weight tail of the material, calculated with a rheological constitutive model. As the flow-induced nuclei grow, the crystalline volume fraction increases and with it the viscosity of the material. This is accounted for by describing the material as a suspension of spheres in a viscoelastic matrix. Calculations are compared with a broad set of experimental data from literature on three grades of poly(1-butene). First, a parameter set is determined by fitting model results to flow-induced nucleation densities from short-term shear experiments. Next, this parameter set is used to validate the framework in continuous flow experiments in which viscosity is monitored during a constant flow rate. In this way, we demonstrate the approach is applicable to not only short-term shear but also continuous flow. It was observed in experiments that for continuous extensional flow, the viscosity shows an upturn at a constant strain, the value of which is independent of strain rate. We hypothesize that this upturn is related to long chains entering the chain stretch regime, as a result of the extension rate exceeding the inverse of the Rouse time of the longest chains

Local‐Regional Similarity in Drylands Increases During Multiyear Wet and Dry Periods and in Response to Extreme Events

Climate change is predicted to impact ecosystems through altered precipitation (PPT) regimes. In the Chihuahuan Desert, multiyear wet and dry periods and extreme PPT pulses are the most influential climatic events for vegetation. Vegetation responses are most frequently studied locally, and regional responses are often unclear. We present an approach to quantify correlation of PPT and vegetation responses (as Normalized Difference Vegetation Index [NDVI]) at the Jornada ARS‐LTER site (JRN; 550 km2 area) and the surrounding dryland region (from 0 to 500 km distance; 400,000 km2 study area) as a way to understand regional similarity to locally observed patterns. We focused on fluctuating wet and dry years, multiyear wet or dry periods of 3–4 yr, and multiyear wet periods that contained one or more extreme high PPT pulses or extreme low rainfall. In all but extreme high PPT years, JRN PPT was highly correlated... (See article for full abstract)

Length of Multi-Year Precipitation and Primary Production Relationships Vary Regionally Across Grasslands in the Central U.S.

Grasslands in the central United States span large temperature and aridity gradients and regionally differ in their drivers of water availability. These differences likely determine how drought event periodicity and duration can influence grassland growth, and are important to consider as global warming changes energy and water distribution across these systems. Here, we explored frequency patterns in annual grassland plant growth (aboveground net primary productivity (ANPP)) and precipitation (PPT) relationships for over 20 years at six long-term research sites spatially distributed across the central grassland region. We identified the periods (\u3e1 year) these relationships are strongest- and when they occur- with wavelet coherence analyses. We found disturbance events such as severe drought lowered ANPP and preceded strong coherence at 2-4 year periods at two sites, potentially by increasing ANPP sensitivity to PPT. All sites showed strong coherence at 1-2 years periods, however this coherence was not consistent through time for two sites, where declines in ANPP did not correspond with PPT variability. In addition to strong coherence at 1-2 year periods, at southern desert and central tallgrass grasslands there was also strong coherence at 5-10 year periods over the entire record, indicating that long-term PPT and ANPP dynamics are important. Pacific ocean-atmosphere drivers of regional precipitation were found to influence coherence at all sites, and could potentially explain the long-term 5- 10 year coherence at the sites mentioned above. Contextualizing ANPP-PPT relationships through time at sites with different drivers of precipitation requires understanding of site-dependent production dynamics and is key to forecasting grassland responses to climate change

Еколого-геохімічні дослідження ґрунтів в зоні впливу підприємств чорної металургії м. Маріуполя

Вивчено закономірності розподілу і форми знаходження важких металів у ґрунтах і компонентах оточуючого середовища поблизу комбінатів чорної металургії м. Маріуполь.Изучены закономерности распределения и формы нахождения тяжелых металлов в почвах и компонентах окружающей среды вблизи комбинатов черной металлургии г. Мариуполь.There was done investigation of distribution and deportment form of heavy metals in soils and environmental components nearby the group of ferrous metallurgy enterprises of Mariupol

Gravitational radiation reaction in compact binary systems: Contribution of the magnetic dipole-magnetic dipole interaction

We study the gravitational radiation reaction in compact binary systems composed of neutron stars with spin and huge magnetic dipole moments (magnetars). The magnetic dipole moments undergo a precessional motion about the respective spins. At sufficiently high values of the magnetic dipole moments, their interaction generates second post-Newtonian order contributions both to the equations of motion and to the gravitational radiation escaping the system. We parametrize the radial motion and average over a radial period in order to find the secular contributions to the energy and magnitude of the orbital angular momentum losses, in the generic case of \textit{eccentric} orbits. Similarly as for the spin-orbit, spin-spin, quadrupole-monopole interactions, here too we deduce the secular evolution of the relative orientations of the orbital angular momentum and spins. These equations, supplemented by the evolution equations for the angles characterizing the orientation of the dipole moments form a first order differential system, which is closed. The circular orbit limit of the energy loss agrees with Ioka and Taniguchi's earlier result

Parallelization, Special Hardware and Post-Newtonian Dynamics in Direct N - Body Simulations

The formation and evolution of supermassive black hole (SMBH) binaries during and after galaxy mergers is an important ingredient for our understanding of galaxy formation and evolution in a cosmological context, e.g. for predictions of cosmic star formation histories or of SMBH demographics (to predict events that emit gravitational waves). If galaxies merge in the course of their evolution, there should be either many binary or even multiple black holes, or we have to find out what happens to black hole multiples in galactic nuclei, e.g. whether they come sufficiently close to merge resulting from emission of gravitational waves, or whether they eject each other in gravitational slingshot interactions