Numeric comparative study on Advanced Nozzles in subsonic counter-flows

openAl giorno d'oggi, la stragrande maggioranza dei razzi regolarmente commercializzati impiega convenzionali ugelli a campana, i quali si stanno avvicinando ai loro limiti di ottimizzazione. Alcuni concept di ugelli avanzati (ANC) offrono potenziali soluzioni alternative per la futura generazione di veicoli di lancio riutilizzabili (RLV). Nell'ottica migliorare le prestazioni delle manovre di recupero (Powered Descent and Landing), l'integrazione di queste tecnologie negli RLV sembra rivelarsi promettente, grazie alla loro capacità di auto-adattamento al variare dell'altitudine. In particolare, durante la fase finale della manovra -- nota come landing burn -- il veicolo affronta una fase di retro-propulsione subsonica, in cui il motore viene acceso in direzione opposta al contro-flusso ambientale. Questo studio mira a valutare e confrontare le prestazioni aerodinamiche e degli ugelli di un RLV durante quest'ultima fase. Ciò è condotto nell'ecosistema del software ANSYS Fluent, tramite simulazioni CFD di quattro distinti concept di ugello: convenzionale ugello a campana (due diversi design: un profilo Rao parabolico e un Truncated-Ideal-Contour), Aerospike, Expansion-Deflection e Dual-Bell. Ognuna di queste tipologie è sottoposta a sua volta a test in quattro scenari: static burn on- e off-design (rispettivamente motore funzionante al punto di progetto e a SLS, senza alcun controflusso), discesa aerodinamica (con motore spento ma contro-flusso attivato) e retro-propulsione subsonica (con motore e controflusso attivati). I risultati numerici vengono successivamente confrontati e convalidati con una parallela campagna sperimentale condotta sugli stessi casi in laboratorio.In the present era, the vast majority of regularly manufactured rockets employ conventional Bell Nozzles, which are approaching their limits of improvement. Advanced Nozzle Concepts (ANCs) offer potential alternative solutions for the future generation of Reusable Launch Vehicles (RLVs). Integrating these technologies into RLVs holds promise for enhancing the performance of Powered Descent and Landing (PDL) recovery maneuvers, owing to their capacity for altitude compensation. Specifically, during the final stage of PDL -- known as the landing burn maneuver -- the vehicle undergoes a subsonic retro-propulsion phase, wherein the engine is ignited against a low-speed counter-flow. This study aims to assess and compare the aerodynamic and nozzle performance of a reusable launch vehicle during this latter phase. The evaluation is conducted using the ANSYS Fluent software environment, employing Computational Fluid Dynamics (CFD) numerical simulations of four distinct nozzle concepts: conventional bell nozzle (including two different designs: Rao parabolic and Truncated-Ideal-Contour), Aerospike, Expansion-Deflection, and Dual Bell nozzles. Each of these concepts is subjected to testing under four scenarios: on- and off-design static burns (respectively with the engine operating at the design point and at SLS, without any counter-flow), aerodynamic descent (with the engine off and counter-flow activated), and subsonic retro-propulsion (with both the engine and counter-flow activated). The numerical results are subsequently compared and validated against a parallel experimental campaign conducted on the same cases

Characterization studies of Silicon Photomultipliers and crystals matrices for a novel time of flight PET detector

This paper describes the characterization of crystal matrices and silicon photomultiplier arrays for a novel Positron Emission Tomography (PET) detector, namely the external plate of the EndoTOFPET-US system. The EndoTOFPET-US collaboration aims to integrate Time-Of-Flight PET with ultrasound endoscopy in a novel multimodal device, capable to support the development of new biomarkers for prostate and pancreatic tumors. The detector consists in two parts: a PET head mounted on an ultrasound probe and an external PET plate. The challenging goal of 1 mm spatial resolution for the PET image requires a detector with small crystal size, and therefore high channel density: 4096 LYSO crystals individually readout by Silicon Photomultipliers (SiPM) make up the external plate. The quality and properties of these components must be assessed before the assembly. The dark count rate, gain, breakdown voltage and correlated noise of the SiPMs are measured, while the LYSO crystals are evaluated in terms of light yield and energy resolution. In order to effectively reduce the noise in the PET image, high time resolution for the gamma detection is mandatory. The Coincidence Time Resolution (CTR) of all the SiPMs assembled with crystals is measured, and results show a value close to the demanding goal of 200 ps FWHM. The light output is evaluated for every channel for a preliminary detector calibration, showing an average of about 1800 pixels fired on the SiPM for a 511 keV interaction. Finally, the average energy resolution at 511 keV is about 13 %, enough for effective Compton rejection.Comment: 12 pages, 31 figure

Safety of extended interval dosing immune checkpoint inhibitors:a multicenter cohort study

BACKGROUND: Real-life spectrum and survival implications of immune-related adverse events (irAEs) in patients treated with extended interval dosing (ED) immune checkpoint inhibitors (ICIs) are unknown. METHODS: Characteristics of 812 consecutive solid cancer patients who received at least 1 cycle of ED monotherapy (pembrolizumab 400 mg Q6W or nivolumab 480 mg Q4W) after switching from canonical interval dosing (CD; pembrolizumab 200 mg Q3W or nivolumab 240 mg Q2W) or treated upfront with ED were retrieved. The primary objective was to compare irAEs patterns within the same population (before and after switch to ED). irAEs spectrum in patients treated upfront with ED and association between irAEs and overall survival were also described. RESULTS: A total of 550 (68%) patients started ICIs with CD and switched to ED. During CD, 225 (41%) patients developed any grade and 17 (3%) G3 or G4 irAEs; after switching to ED, any grade and G3 or G4 irAEs were experienced by 155 (36%) and 20 (5%) patients. Switching to ED was associated with a lower probability of any grade irAEs (adjusted odds ratio [aOR] = 0.83, 95% confidence interval [CI] = 0.64 to 0.99; P = .047), whereas no difference for G3 or G4 events was noted (aOR = 1.55, 95% CI = 0.81 to 2.94; P = .18). Among patients who started upfront with ED (n = 232, 32%), 107 (41%) developed any grade and 14 (5%) G3 or G4 irAEs during ED. Patients with irAEs during ED had improved overall survival (adjusted hazard ratio [aHR] = 0.53, 95% CI = 0.34 to 0.82; P = .004 after switching; aHR = 0.57, 95% CI = 0.35 to 0.93; P = .025 upfront). CONCLUSIONS: Switching ICI treatment from CD and ED did not increase the incidence of irAEs and represents a safe option also outside clinical trials.</p

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum