Asymmetry Dependence of the Nuclear Caloric Curve

A basic feature of the nuclear equation of state is not yet understood: the dependence of the nuclear caloric curve on the neutron-proton asymmetry. Predictions of theoretical models differ on the magnitude and even the sign of this dependence. In this work, the nuclear caloric curve is examined for fully reconstructed quasi-projectiles around mass A=50. The caloric curve extracted with the momentum quadrupole fluctuation thermometer shows that the temperature varies linearly with quasi-projectile asymmetry (N-Z)/A. An increase in asymmetry of 0.15 units corresponds to a decrease in temperature on the order of 1 MeV. These results also highlight the importance of a full quasi-projectile reconstruction in the study of thermodynamic properties of hot nuclei

Forty Years of Change in Piute Cypress (Hesperocyparis nevadensis), a Rare California Tree, After Frequent Fire and Drought

Piute cypress (Hesperocyparis nevadensis) is a rare cypress species endemic to the Lake Isabella region in the southern Sierra Nevada in California. Piute cypress groves have not been quantitatively studied in the last 40 years and with recent fires (some in short succession) and observed mortality, we had questions surrounding conditions in groves recovering from fire compared to other groves with no recorded fire histories. Piute cypress rarely survive fire and are obligate seeders with serotinous cones and, as such, require sufficient time after fire to grow to reproductive maturity to be able to withstand future fire. We visited five of the 12 known groves of Piute cypress to evaluate current stand conditions and make comparisons with an assessment conducted 40 years ago. We evaluated two recently burned groves nine years post-fire. One grove with a shorter interval between fires (~20 years), has only limited regeneration and is at risk of local extinction. Based on our findings, we extrapolated to unstudied groves to conclude that five recently burned groves are vulnerable to immaturity risk if these stands were to reburn soon. We recommend aggressive fire suppression tactics to protect these groves if threatened by fire. Another recently burned grove with a longer period between fires (~90 years) appears to be recovering and capable of becoming a self-sustaining population that can survive another fire based on regeneration data. While the 90-year-old trees did not have nearly the level of canopy seed bank that older trees (~200 years old) did in another part of the grove, seedling and sapling regeneration after fire occurred at higher densities than tree densities in mature stands and were already developing cones. Though theoretically long-unburned groves also may be at risk, we found no evidence of age-related decline in this long-lived species and some non-fire induced regeneration. We did discover evidence of cedar bark beetle attack (Phloeosinus), particularly in smaller trees at two unburned groves. which was correlated to high tree mortality (31.6%) at one site. While we found no evidence of encroaching non-cypress tree species threatening long-unburned groves among mature cohorts, we did document relatively high densities of regenerating non-cypress tree species in groves. We strongly recommend further monitoring in groves to assess fire, insect, and disease vulnerability in cypress populations

Estimating the Energy Density of Fish: The Importance of Ontogeny

Ontogenetic patterns in the percent dry weight (%DW) and energy density (joules per gram of wet weight) were studied in the early life stages of the subtropical estuarine and marine gray snapper Lutjanus griseus and the warmtemperate estuarine and marine spotted seatrout Cynoscion nebulosus. The %DW was variable for individuals of both species but increased significantly through larval to juvenile stages (50 mm). The lipid percentage, which was determined only for gray snapper, was also variable between individuals but showed significant increase with body size. Strong relationships between percent dry weight and energy density were evident for both species; however, the slopes of regressions were significantly lower than in general multispecies models, demonstrating the need for species- and stagespecific energy density data in bioenergetics models

Measuring the Temperature of Hot Nuclear Fragments

A new thermometer based on fragment momentum fluctuations is presented. This thermometer exhibited residual contamination from the collective motion of the fragments along the beam axis. For this reason, the transverse direction has been explored. Additionally, a mass dependence was observed for this thermometer. This mass dependence may be the result of the Fermi momentum of nucleons or the different properties of the fragments (binding energy, spin etc..) which might be more sensitive to different densities and temperatures of the exploding fragments. We expect some of these aspects to be smaller for protons (and/or neutrons); consequently, the proton transverse momentum fluctuations were used to investigate the temperature dependence of the source

Genomic Data from NSCLC Tumors Reveals Correlation between SHP-2 Activity and PD-L1 Expression and Suggests Synergy in Combining SHP-2 and PD-1/PD-L1 Inhibitors

The identification of novel therapies, new strategies for combination of therapies, and repurposing of drugs approved for other indications are all important for continued progress in the fight against lung cancers. Antibodies that target immune checkpoints can unmask an immunologically hot tumor from the immune system of a patient. However, despite accounts of significant tumor regression resulting from these medications, most patients do not respond. In this study, we sought to use protein expression and RNA sequencing data from The Cancer Genome Atlas and two smaller studies deposited onto the Gene Expression Omnibus (GEO) to advance our hypothesis that inhibition of SHP-2, a tyrosine phosphatase, will improve the activity of immune checkpoint inhibitors (ICI) that target PD-1 or PD-L1 in lung cancers. We first collected protein expression data from The Cancer Proteome Atlas (TCPA) to study the association of SHP-2 and PD-L1 expression in lung adenocarcinomas. RNA sequencing data was collected from the same subjects through the NCI Genetic Data Commons and evaluated for expression of the PTPN11 (SHP-2) and CD274 (PD-L1) genes. We then analyzed RNA sequencing data from a series of melanoma patients who were either treatment naïve or resistant to ICI therapy. PTPN11 and CD274 expression was compared between groups. Finally, we analyzed gene expression and drug response data collected from 21 non-small cell lung cancer (NSCLC) patients for PTPN11 and CD274 expression. From the three studies, we hypothesize that the activity of SHP-2, rather than the expression, likely controls the expression of PD-L1 as only a weak relationship between PTPN11 and CD274 expression in either lung adenocarcinomas or melanomas was observed. Lastly, the expression of CD274, not PTPN11, correlates with response to ICI in NSCLC

Symmetry energy and the isoscaling properties of the fragments produced in 40^{40}Ar, 40^{40}Ca + 58^{58}Fe, 58^{58}Ni reactions at 25 −- 53 MeV/nucleon

The symmetry energy and the isoscaling properties of the fragments produced in the multifragmentation of $^{40}$Ar, $^{40}$Ca + $^{58}$Fe, $^{58}$Ni reactions at 25 - 53 MeV/nucleon were investigated within the framework of statistical multifragmentation model. The isoscaling parameters $\alpha$, from the primary (hot) and secondary (cold) fragment yield distributions, were studied as a function of excitation energy, isospin (neutron-to-proton asymmetry) and fragment symmetry energy. It is observed that the isoscaling parameter $\alpha$ decreases with increasing excitation energy and decreasing symmetry energy. The parameter $\alpha$ is also observed to increase with increasing difference in the isospin of the fragmenting system. The sequential decay of the primary fragments into secondary fragments, when studied as a function of excitation energy and isospin of the fragmenting system, show very little influence on the isoscaling parameter. The symmetry energy however, has a strong influence on the isospin properties of the hot fragments. The experimentally observed scaling parameters can be explained by symmetry energy that is significantly lower than that for the ground state nuclei near saturation density. The results indicate that the properties of hot nuclei at excitation energies, densities and isospin away from the normal ground state nuclei could be significantly different.Comment: 14 pages, 15 figure

Density determinations in heavy ion collisions

The experimental determination of freeze-out temperatures and densities from the yields of light elements emitted in heavy ion collisions is discussed. Results from different experimental approaches are compared with those of model calculations carried out with and without the inclusion of medium effects. Medium effects become of relevance for baryon densities above $\approx 5 \times 10^{-4}$ fm$^{-3}$. A quantum statistical (QS) model incorporating medium effects is in good agreement with the experimentally derived results at higher densities. A densitometer based on calculated chemical equilibrium constants is proposed.Comment: 5 pages, 3 figure

Analysis of fragment yield ratios in the nuclear phase transition

The critical phenomena of the liquid-gas phase transition has been investigated in the reactions 78,86Kr+58,64Ni at beam energy of 35 MeV/nucleon using the Landau free energy approach with isospin asymmetry as an order parameter. Fits to the free energy of fragments showed three minima suggesting the system to be in the regime of a first order phase transition. The relation m =-{\partial}F/{\partial}H, which defines the order parameter and its conjugate field H, has been experimentally verified from the linear dependence of the mirror nuclei yield ratio data, on the isospin asymmetry of the source. The slope parameter, which is a measure of the distance from a critical temperature, showed a systematic decrease with increasing excitation energy of the source. Within the framework of the Landau free energy approach, isoscaling provided similar results as obtained from the analysis of mirror nuclei yield ratio data. We show that the external field is primarily related to the minimum of the free energy, which implies a modification of the source concentration \Delta used in isospin studies