Isotopic Composition of Fragments in Nuclear Multifragmentation

The isotope yields of fragments, produced in the decay of the quasiprojectile in Au+Au peripheral collisions at 35 MeV/nucleon and those coming from the disassembly of the unique source formed in Xe+Cu central reactions at 30 MeV/nucleon, were measured. We show that the relative yields of neutron-rich isotopes increase with the excitation energy in multifragmentation reaction. In the framework of the statistical multifragmentation model which fairly well reproduces the experimental observables, this behaviour can be explained by increasing N/Z ratio of hot primary fragments, that corresponds to the statistical evolution of the decay mechanism with the excitation energy: from a compound-like decay to complete multifragmentation.Comment: 10 pages. 4 Postscript figures. Submitted to Physical Review C, Rapid Communicatio

Plastic adjustments of biparental care behavior across embryonic development under elevated temperature in a marine ectotherm

Phenotypic plasticity in parental care investment allows organisms to promptly respond to rapid environmental changes by potentially benefiting offspring survival and thus parental fitness. To date, a knowledge gap exists on whether plasticity in parental care behaviors can mediate responses to climate change in marine ectotherms. Here, we assessed the plasticity of parental care investment under elevated temperatures in a gonochoric marine annelid with biparental care, Ophryotrocha labronica, and investigated its role in maintaining the reproductive success of this species in a warming ocean. We measured the time individuals spent carrying out parental care activities across three phases of embryonic development, as well as the hatching success of the offspring as a proxy for reproductive success, at control (24℃) and elevated (27℃) temperature conditions. Under elevated temperature, we observed: (a) a significant decrease in total parental care activity, underpinned by a decreased in male and simultaneous parental care activity, in the late stage of embryonic development; and (b) a reduction in hatching success that was however not significantly related to changes in parental care activity levels. These findings, along with the observed unaltered somatic growth of parents and decreased brood size, suggest that potential cost-benefit trade-offs between offspring survival (i.e., immediate fitness) and parents' somatic condition (i.e., longer-term fitness potential) may occur under ongoing ocean warming. Finally, our results suggest that plasticity in parental care behavior is a mechanism able to partially mitigate the negative effects of temperature-dependent impacts

Isotopic composition of fragments in multifragmentation of very large nuclear systems: effects of the chemical equilibrium

Studies on the isospin of fragments resulting from the disassembly of highly excited large thermal-like nuclear emitting sources, formed in the ^{197}Au + ^{197}Au reaction at 35 MeV/nucleon beam energy, are presented. Two different decay systems (the quasiprojectile formed in midperipheral reactions and the unique source coming from the incomplete fusion of projectile and target in the most central collisions) were considered; these emitting sources have the same initial N/Z ratio and excitation energy (E^* ~= 5--6 MeV/nucleon), but different size. Their charge yields and isotopic content of the fragments show different distributions. It is observed that the neutron content of intermediate mass fragments increases with the size of the source. These evidences are consistent with chemical equilibrium reached in the systems. This fact is confirmed by the analysis with the statistical multifragmentation model.Comment: 9 pages, 4 ps figure

Causal analysis of positive Reaction Systems

Cause/effect analysis of complex systems is instrumental in better understanding many natural phenomena. Moreover, formal analysis requires the availability of suitable abstract computational models that somehow preserve the features of interest. Our contribution focuses on the analysis of Reaction Systems (RSs), a qualitative computational formalism inspired by biochemical reactions in living cells. The primary challenge lies in dealing with inhibition mechanisms. On the one hand, inhibitors enhance the expressiveness of the computational abstraction; on the other hand, they can introduce nonmonotonic behaviors that can be computationally hard to deal with in the analysis. We propose an encoding of RSs into an equivalent formulation without inhibitors (called Positive RSs, PRSs for short) that is easier to handle, because PRSs exhibit monotonic behaviors. The effectiveness of our transformation is witnessed by its impact on two different techniques for cause/effect analysis. The first, called slicing, allows detecting the causes of some unforeseen phenomenon by reasoning backward along a given computation. Here, PRSs can be exploited to improve the quality of the analysis. The second technique, predictor analysis, is addressed by introducing a novel tool called MuMa, which is based on must/maybe sets, whence the tool name, an original abstraction for approximating ancestor formulas. MuMa exploits PRSs to improve the performance of the analysis

Quantitative extensions of reaction systems based on SOS semantics

Reaction systems (RSs) are a successful natural computing framework inspired by chemical reaction networks. A RS consists of a set of entities and a set of reactions. Entities can enable or inhibit each reaction and are produced by reactions or provided by the environment. In this paper, we define two quantitative variants of RSs: the first one is along the time dimension, to specify delays for making available reactions products and durations to protract their permanency, while the second deals with the possibility to specify different concentration levels of a substance in order to enable or inhibit a reaction. Technically, both extensions are obtained by modifying in a modular way the Structural Operational Semantics (SOS) for RSs that was already defined in the literature. Our approach maintains several advantages of the original semantics definition that were: (1) providing a formal specification of the RS dynamics that enables the reuse of many formal analysis techniques and favours the implementation of tools, and (2) making the RS framework extensible, by adding or changing some of the SOS rules in a compositional way. We provide a prototype logic programming implementation and apply our tool to three different case studies: the tumour growth, the Th cell differentiation in the immune system and neural communication

Causal analysis of positive Reaction Systems

Cause/effect analysis of complex systems is instrumental in better understanding many natural phenomena. Moreover, formal analysis requires the availability of suitable abstract computational models that somehow preserve the features of interest. Our contribution focuses on the analysis of Reaction Systems (RSs), a qualitative computational formalism inspired by biochemical reactions in living cells. The primary challenge lies in dealing with inhibition mechanisms. On the one hand, inhibitors enhance the expressiveness of the computational abstraction; on the other hand, they can introduce nonmonotonic behaviors that can be computationally hard to deal with in the analysis. We propose an encoding of RSs into an equivalent formulation without inhibitors (called Positive RSs, PRSs for short) that is easier to handle, because PRSs exhibit monotonic behaviors. The effectiveness of our transformation is witnessed by its impact on two different techniques for cause/effect analysis. The first, called slicing, allows detecting the causes of some unforeseen phenomenon by reasoning backward along a given computation. Here, PRSs can be exploited to improve the quality of the analysis. The second technique, predictor analysis, is addressed by introducing a novel tool called MuMa, which is based on must/maybe sets, whence the tool name, an original abstraction for approximating ancestor formulas. MuMa exploits PRSs to improve the performance of the analysis

Ejector characterization for refrigeration applications with natural refrigerants

Employing natural fluids in refrigerating plants at warm climate conditions sometimes impacts negatively on the system performance. Ejectors can play a key role in configurations aiming at improving the efficiency of such systems, however their geometry has to be optimized in order to gain the best benefit. Scope of this work is a numerical investigation on the geometry of the ejector in a cascade plant configuration with natural refrigerants, aiming at identifying the influence of various geometry aspects on the performance of the system. A one-dimensional model is employed for the ejector, while the performance of the refrigerating plant is evaluated in different operating conditions in order to seek the optimal configuration

Morphology, rheological and mechanical properties of isotropic and anisotropic PP/rPET/GnP nanocomposite samples

The effect of graphene nanoplatelets (GnPs) on the morphology, rheological, and mechanical properties of isotropic and anisotropic polypropylene (PP)/recycled polyethylene terephthalate (rPET)-based nanocomposite are reported. All the samples were prepared by melt mixing. PP/rPET and PP/rPET/GnP isotropic sheets were prepared by compression molding, whereas the anisotropic fibers were spun using a drawing module of a capillary viscometer. The results obtained showed that the viscosity of the blend is reduced by the presence of GnP due to the lubricating effect of the graphene platelets. However, the Cox–Merz rule is not respected. Compared to the PP/rPET blend, the GnP led to a slight increase in the elastic modulus. However, it causes a slight decrease in elongation at break. Morphological analysis revealed a poor adhesion between the PP and PET phases. Moreover, GnPs distribute around the droplets of the PET phase with a honey-like appearance. Finally, the effect of the orientation on both systems gives rise not only to fibers with higher modulus values, but also with high deformability and a fibrillar morphology of the dispersed PET phase. A fragile-ductile transition driven by the orientation was observed in both systems