The role of General Relativity in the evolution of Low Mass X-ray Binaries

We study the evolution of Low Mass X-ray Binaries (LMXBs) and of millisecond binary radio pulsars (MSPs), with numerical simulations that keep into account the evolution of the companion, of the binary system and of the neutron star. According to general relativity, when energy is released, the system loses gravitational mass. Moreover, the neutron star can collapse to a black hole if its mass exceeds a critical limit, that depends on the equation of state. These facts have some interesting consequences: 1) In a MSP the mass-energy is lost with a specific angular momentum that is smaller than the one of the system, resulting in a positive contribution to the orbital period derivative. If this contribution is dominant and can be measured, we can extract information about the moment of inertia of the neutron star, since the energy loss rate depends on it. Such a measurement can therefore help to put constraints on the equation of state of ultradense matter. 2) In LMXBs below the bifurcation period (\sim 18 h), the neutron star survives the period gap only if its mass is smaller than the maximum non-rotating mass when the companion becomes fully convective and accretion pauses. Therefore short period (P < 2h) millisecond X-ray pulsar like SAX J1808.4-3658 can be formed only if either a large part of the accreting matter has been ejected from the system, or the equation of state of ultradense matter is very stiff. 3) In Low Mass X-ray binaries above the bifurcation period, the mass-energy loss lowers the mass transfer rate. As side effect, the inner core of the companion star becomes 1% bigger than in a system with a non-collapsed primary. Due to this difference, the final orbital period of the system becomes 20% larger than what is obtained if the mass-energy loss effect is not taken into account.Comment: 7 pages, 3 figures, accepted by the MNRA

Simulation of the Melting Behavior of the UO2-Zircaloy Fuel Cladding System by Laser Heating

The current research focuses on laser melting and successive analysis of laboratory-scale uranium dioxide nuclear fuel samples in direct contact with Zircaloy-4 cladding. The goal was to characterize the melted and refrozen interfaces, in particular, observing local changes of the melting point and interdiffusion of fuel and cladding materials under inert gas (Ar), in the presence of hydrogen (Ar + 6% H2) or in air. Results obtained by laser heating UO2 pellets clad in a Zircaloy ring were interpreted in light of reference tests performed on pellets in which UO2 and zirconium were blended in a series of given compositions. The sample composition was analyzed by scanning electron microscopy to verify the occurrence of diffusion and segregation phenomena during the laser-heating cycles. Laser-melting experiments were performed on pellets of uranium dioxide clad in Zircaloy-4 rings to simulate the configuration of a light water reactor fuel rod. Under inert gas, the material interdiffusion resulted in consistent melting point depression (of up to 200 K below the melting point of pure UO2) at the interface between the fuel and the cladding. Experiments carried out in the presence of H2 displayed a more limited effect on the melting temperature, but they resulted in a remarkable embrittlement of the whole structure, with large fragmentation of the Zircaloy cladding. This was probably due to the formation of brittle and highly volatile Zr hydrides. The observed melting point decrease was even more pronounced (up to over 400 K) under air in uranium-rich samples, due to the change in the stoichiometry of UO2 in UO2+x

The BeppoSAX 0.1 - 100 keV Spectrum of the X-ray Pulsar 4U 1538-52

We report the results of temporal and spectral analysis performed on the X-ray pulsar 4U 1538-52 observed by BeppoSAX. We obtained a new estimate of the spin period of the neutron star P=528.24 \pm 0.01 s (corrected for the orbital motion of the X-ray source): the source is still in the spin-up state, as since 1988. The pulse profile is double peaked, although significant variations of the relative intensity of the peaks with energy are present. The broad band (0.12-100 keV) out-of-eclipse spectrum is well described by an absorbed power law modified by a high energy cutoff at \sim 16 keV (e-folding energy \sim 10 keV) plus an iron emission line at \sim 6.4 keV. A cyclotron line at \sim 21 keV is present. The width of the line is consistent with thermal Doppler broadening at the temperature of the exponential cutoff. We searched for the presence of the second harmonic, previously reported for this source. We found no evidence of lines at \sim 42 keV, although an absorption feature at 51 keV seems to be present (at 99% confidence level). A soft excess, modelled by a blackbody with a temperature of \sim 0.08 keV could be present, probably emitted by the matter at the magnetosphere. We also performed a spectral analysis during the X-ray eclipse. The spectral evolution during the eclipse can be well described by a progressive covering of the primary Comptonization spectrum that is scattered into the line of sight. During the deep eclipse this spectrum also softens, suggesting that the dust-scattered component becomes important. An alternative, more complex model, with an emission iron line and scattered components (as the one that has been used to fit the eclipse of Centaurus X-3), also gives a good fit of the deep-eclipse data

Chandra Observation of the Big Dipper X 1624-490

We present the results of a 73 ks long Chandra observation of the dipping source X 1624-490. During the observation a complex dip lasting 4 hours is observed. We analyse the persistent emission detecting, for the first time in the 1st-order spectra of X 1624-490, an absorption line associated to \ion{Ca}{xx}. We confirm the presence of the \ion{Fe}{xxv} K$_\alpha$ and \ion{Fe}{xxvi} K$_\alpha$ absorption lines with a larger accuracy with respect to a previous XMM observation. Assuming that the line widths are due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines have been produced in a photoionized absorber between the coronal radius and the outer edge of the accretion disk

Mechanical ventilation in patients with acute ischaemic stroke: From pathophysiology to clinical practice

Most patients with ischaemic stroke are managed on the ward or in specialty stroke units, but a significant number requires higher-acuity care and, consequently, admission to the intensive care unit. Mechanical ventilation is frequently performed in these patients due to swallowing dysfunction and airway or respiratory system compromise. Experimental studies have focused on stroke-induced immunosuppression and brain-lung crosstalk, leading to increased pulmonary damage and inflammation, as well as reduced alveolar macrophage phagocytic capability, which may increase the risk of infection. Pulmonary complications, such as respiratory failure, pneumonia, pleural effusions, acute respiratory distress syndrome, lung oedema, and pulmonary embolism from venous thromboembolism, are common and found to be among the major causes of death in this group of patients. Furthermore, over the past two decades, tracheostomy use has increased among stroke patients, who can have unique indications for this procedure - depending on the location and type of stroke - when compared to the general population. However, the optimal mechanical ventilator strategy remains unclear in this population. Although a high tidal volume (V T) strategy has been used for many years, the latest evidence suggests that a protective ventilatory strategy (V T = 6-8 mL/kg predicted body weight, positive end-expiratory pressure and rescue recruitment manoeuvres) may also have a role in brain-damaged patients, including those with stroke. The aim of this narrative review is to explore the pathophysiology of brain-lung interactions after acute ischaemic stroke and the management of mechanical ventilation in these patients

Transcranial Doppler Monitoring of Intracranial Pressure Plateau Waves

$\textbf{BACKGROUND}$: Transcranial Doppler (TCD) has been used to estimate ICP noninvasively (nICP); however, its accuracy varies depending on different types of intracranial hypertension. Given the high specificity of TCD to detect cerebrovascular events, this study aimed to compare four TCD-based nICP methods during plateau waves of ICP. $\textbf{METHODS}$: A total of 36 plateau waves were identified in 27 patients (traumatic brain injury) with TCD, ICP, and ABP simultaneous recordings. The nICP methods were based on: (1) interaction between flow velocity (FV) and ABP using a "black-box" mathematical model (\textit{nICP_BB}); (2) diastolic FV (\textit{nICP_FV}$_{d}$); (3) critical closing pressure (\textit{nICP_CrCP}), and (4) pulsatility index (\textit{nICP_PI}). Analyses focused on relative changes in time domain between ICP and noninvasive estimators during plateau waves and the magnitude of changes ($\textit{∆}$ between baseline and plateau) in real ICP and its estimators. A ROC analysis for an ICP threshold of 35 mmHg was performed. $\textbf{RESULTS}$: In time domain, \textit{nICP_PI, nICP_BB,} and \textit{nICP_CrCP} presented similar correlations: 0.80 ± 0.24, 0.78 ± 0.15, and 0.78 ± 0.30, respectively. \textit{nICP_FV}$_{d}$ presented a weaker correlation (R = 0.62 ± 0.46). Correlations between ∆ICP and ∆nICP were better represented by \textit{nICP_CrCP} and BB, R = 0.48, 0.44 (p < 0.05), respectively. \textit{nICP_FV}$_{d}$ and $\textit{PI}$ presented nonsignificant $\textit{∆}$ correlations. ROC analysis showed moderate to good areas under the curve for all methods: \textit{nICP_BB}, 0.82; \textit{nICP_FV}$_{d}$, 0.77; \textit{nICP_CrCP}, 0.79; and \textit{nICP_PI}, 0.81. $\textbf{CONCLUSIONS}$: Changes of ICP in time domain during plateau waves were replicated by nICP methods with strong correlations. In addition, the methods presented high performance for detection of intracranial hypertension. However, absolute accuracy for noninvasive ICP assessment using TCD is still low and requires further improvement

Ventilatory settings in the initial 72 h and their association with outcome in out-of-hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out-of-hospital cardiac arrest (TTM2) trial

Purpose: The optimal ventilatory settings in patients after cardiac arrest and their association with outcome remain unclear. The aim of this study was to describe the ventilatory settings applied in the first 72 h of mechanical ventilation in patients after out-of-hospital cardiac arrest and their association with 6-month outcomes. Methods: Preplanned sub-analysis of the Target Temperature Management-2 trial. Clinical outcomes were mortality and functional status (assessed by the Modified Rankin Scale) 6 months after randomization. Results: A total of 1848 patients were included (mean age 64 [Standard Deviation, SD = 14] years). At 6 months, 950 (51%) patients were alive and 898 (49%) were dead. Median tidal volume (VT) was 7 (Interquartile range, IQR = 6.2-8.5) mL per Predicted Body Weight (PBW), positive end expiratory pressure (PEEP) was 7 (IQR = 5-9) cmH20, plateau pressure was 20 cmH20 (IQR = 17-23), driving pressure was 12 cmH20 (IQR = 10-15), mechanical power 16.2 J/min (IQR = 12.1-21.8), ventilatory ratio was 1.27 (IQR = 1.04-1.6), and respiratory rate was 17 breaths/minute (IQR = 14-20). Median partial pressure of oxygen was 87 mmHg (IQR = 75-105), and partial pressure of carbon dioxide was 40.5 mmHg (IQR = 36-45.7). Respiratory rate, driving pressure, and mechanical power were independently associated with 6-month mortality (omnibus p-values for their non-linear trajectories: p < 0.0001, p = 0.026, and p = 0.029, respectively). Respiratory rate and driving pressure were also independently associated with poor neurological outcome (odds ratio, OR = 1.035, 95% confidence interval, CI = 1.003-1.068, p = 0.030, and OR = 1.005, 95% CI = 1.001-1.036, p = 0.048). A composite formula calculated as [(4*driving pressure) + respiratory rate] was independently associated with mortality and poor neurological outcome. Conclusions: Protective ventilation strategies are commonly applied in patients after cardiac arrest. Ventilator settings in the first 72 h after hospital admission, in particular driving pressure and respiratory rate, may influence 6-month outcomes

L-functions of Symmetric Products of the Kloosterman Sheaf over Z

The classical $n$-variable Kloosterman sums over the finite field ${\bf F}_p$ give rise to a lisse $\bar {\bf Q}_l$-sheaf ${\rm Kl}_{n+1}$ on ${\bf G}_{m, {\bf F}_p}={\bf P}^1_{{\bf F}_p}-\{0,\infty\}$, which we call the Kloosterman sheaf. Let $L_p({\bf G}_{m,{\bf F}_p}, {\rm Sym}^k{\rm Kl}_{n+1}, s)$ be the $L$-function of the $k$-fold symmetric product of ${\rm Kl}_{n+1}$. We construct an explicit virtual scheme $X$ of finite type over ${\rm Spec} {\bf Z}$ such that the $p$-Euler factor of the zeta function of $X$ coincides with $L_p({\bf G}_{m,{\bf F}_p}, {\rm Sym}^k{\rm Kl}_{n+1}, s)$. We also prove similar results for $\otimes^k {\rm Kl}_{n+1}$ and $\bigwedge^k {\rm Kl}_{n+1}$.Comment: 16 page