Recent advances in X-ray science have witnessed the X-ray communication (XCOM), a new revolutionary technology first proposed by NASA since 2007. In combination with the advanced modulated X-ray source, XCOM shows a promising prospect for helping to alleviate the occurrence of inevitable blackout communication by using the regular radio frequency (RF) signal, paving the way towards realizing real-time communication during spacecraft reentry into atmosphere. Here, we acquired the detailed information of electron density distribution of plasma sheath encountered during vehicle reentry through Computational Fluid Dynamics simulation. Based on these derived parameters, Finite-difference Time-domain method was employed to investigate the transmission properties of X-rays through the plasma sheath, and the results indicated that X-ray transmission was not influenced by the reentry plasma sheath at different reentry altitudes and spacecraft surface positions compared with RF signal. In addition, 2D Particle-In-Cell simulation was also adopted to provide deeper insight into the transmission properties and physical mechanisms of X-ray carrier propagating through the plasma sheath, and results showed that the transmission coefficient was over 0.994 and the observation of plasma channel effect was also an important signature, which was of great importance to X-ray propagating through the plasma sheath.

X-ray communication (XCOM) offers important advantages to both civilian and military space projects. Rapid advance in high-intensity laser interaction with plasma has become a driving force for providing a new X-ray carrier generation based on the laser wakefield acceleration scheme. XCOM has the potential to eliminate RF shielding on the ground and communicate with the re-entry supersonic spacecraft during blackout occurrence. In this process, the plasma sheath is formed around the surface due to air compression and ablation, which blocks the traditional communication signals. In this paper, the hazardous substance was proactively exploited and coupled with the modulated laser. Particle-In-Cell simulation results indicate the ultra-bright controllable X-ray emission with a small angular divergence ($0.04\hspace{0.17em}\mathrm{rad}\times 0.03\hspace{0.17em}\mathrm{rad}$ ), a tunable X-ray energy range (4.60 keV to 321.48 keV), and high photon yields. Additionally, the data rate of the communication via the X-ray carrier during re-entry was estimated up to ∼20.7 Mbps by considering the transmission model, encoding schemes and photon information efficiency. Combined with an existing or developing X-ray detection technique, this regime can eliminate re-entry blackout and also provide a novel modulated X-ray source to acquire high-rate, low transmit power, and highly secure space-based data links.

Objective: Identifying high-risk children with a poor prognosis in pediatric intensive care units (PICUs) is critical. The aim of this study was to assess the predictive value of early plasma osmolality levels in determining the clinical outcomes of children in PICUs.Methods: We retrospectively assessed critically ill children in a pediatric intensive care database. The locally weighted-regression scatter-plot smoothing (LOWESS) method was used to explore the approximate relationship between plasma osmolality and in-hospital mortality. Linear spline functions and stepwise expansion models were applied in conjunction with a multivariate logistic regression to further analyze this relationship. A subgroup analysis by age and complications was performed.Results: In total, 5,620 pediatric patients were included in this study. An approximately “U”-shaped relationship between plasma osmolality and mortality was detected using LOWESS. In the logistic regression model using a linear spline function, plasma osmolality ≥ 290 mmol/L was significantly associated with in-hospital mortality [odds ratio (OR) 1.020, 95% confidence interval (CI) 1.010–1.031], while plasma osmolality <290 mmol/L was not significantly associated with in-hospital mortality (OR 0.990, 95% CI 0.966–1.014). In the logistic regression model with plasma osmolality as a tri-categorical variable, only high osmolality was significantly associated with in-hospital mortality (OR 1.90, 95% CI 1.38–2.64), whereas low osmolality was not associated with in-hospital mortality (OR 1.28, 95% CI 0.84–1.94). The interactions between plasma osmolality and age or complications were not significant.Conclusion: High osmolality, rather than low osmolality, can predict a poor prognosis in children in PICUs.

Irradiation damage is an important cause of material failure in in-service nuclear reactors. It is important to explore the resistance to irradiation of metals with different crystal structures. As the formation and evolution of point defects on the atomic scale caused by cascade collisions in the early stages of irradiation are currently difficult to observe experimentally, it is currently possible to simulate the dynamic process of irradiation damage on the atomic scale by means of molecular dynamics (MD) methods. In this paper, some atomic scale numerical simulations are performed to study the irradiation behaviour and displacement cascades in metals with different crystal structures of bcc-Fe, hcp-Ti, hcp-Zr and fcc-Ni by the MD methods. The effect of temperature and the magnitude of the primary knock-on atom (PKA) energy on the generation and evolution of point defects is mainly studied. Results show that an increase in cascade energies from 0.5 keV to 10 keV can significantly promote defect formation for different crystal structures, while ambient temperature (T) has a slight effect on the number of surviving defects. The simulations also illustrate that high-energy cascades can significantly promote the formation of defect clusters. Statistical results of the displacement cascades show that bcc-Fe produces a small number of stable defects, a small cluster size and number relative to fcc-Ni, hcp-Ti, and hcp-Zr structures, which indicates that the bcc-Fe structure has a good radiation resistance. These findings could provide an appropriate idea for obtaining potential radiation-resistant materials for nuclear reactors.