The exhaust plume, emanating from the spacecraft thruster and composed of hot gases, expansively extends into the vacuum of space, frequently interacting with the spacecraft's structure that are often inclined relative to the thruster. Therefore, the heat flux and pressure resulting from plume impingement on inclined spacecraft surfaces are required to be determined. In this study, we perform steady-state CFD modeling to analyze the plume expansion into vacuum and the effect of plate inclination on the impingement heat flux and pressure. The CFD model incorporates a temperature jump boundary with a partial slip condition at the plate. The investigation is conducted based on the experimental conditions reported in literature. The CFD model with partial slip predicts the peak heat flux within 1

Nucleotide fragmentation after photoexcitation in the ultraviolet is a potential cause for damage to DNA strands. Consequently, the fragmentation process needs to be explored to understand the stability of nucleotides on a molecular level. Here, we present wavelength-dependent relative photoabsorption cross section measurements of [dAMP-H]- below the photodetachment threshold, which lead to fragmentation along several different channels. Several spectral features are observed in the broad absorption peak in the range of 240 to 270 nm, the resolution of which we attribute to the low temperature of 3 K achieved in our cryogenic 16-pole radiofrequency wire trap. These features likely originate from different Franck-Condon-active vibrational bands in only one or two different conformers. Quantum chemical calculations predict that the spectrum originates from a strong ππ* excitation located at the adenine moiety. Furthermore, the wavelength-dependent yield of the five observed photofragments was studied. This revealed no preferred single photofragment, but showed different trends for different fragments as a function of photon energy. Finally, an absolute photofragmentation cross section of [dAMP-H]- was obtained by comparison with the photodetachment cross section of I-.

Numerical simulations of the firing of H2–O2 igniters in the presence of an air-O2 crossflow are conducted with a specific focus on air-heater configurations with faceplates. Simulations are conducted for three igniter chamber pressures (22, 41 and 55 bar) to investigate penetration lengths of igniter flames into the crossflow. Two alignments of the air-heater faceplate are assessed: one where the igniter-injector jets exhibit a direct interaction (Case 1), and one where the igniter jet is fired in-between two adjacent injector jets (Case 2). For all three igniter chamber pressures, air-heater faceplate heating is lesser for Case 1 compared to Case 2 because the igniter flame is naturally deflected away from the faceplate here. Moreover for Case 1, the 41 bar igniter chamber pressure shows the least peak heating of 68 W/cm2. For Case 2, with the 22 bar igniter chamber pressure, the igniter flame is deflected markedly towards the faceplate because of entrainment-instigated suction between two injector jets. This shows the highest peak heating on the faceplate of 467 W/cm2. When the igniter chamber pressure is increased, the extent of deflection reduces, as does the peak heating on the faceplate. Notwithstanding, hot-spots near the centre of the faceplate are still evident even at higher igniter chamber pressures.

In high-resolution mass spectrometry, an electrospray ionization source is often paired with an ion-funnel to enhance ion transmission. Although it is established that ions experience collision-induced dissociation as they pass through this device, the impact of gas-flow dynamics on ion fragmentation remains unexplored. The present work demonstrates that the gas-flow dynamics from the capillary interface of an electrospray ionization source into an ion-funnel significantly reduces ion fragmentation. This reduction stems from the substantial decrease in the rate of increase in the internal energy of the ions, resulting from the collisions with a supersonically expanding gas. The results of this study have significant consequences for systems that employ electrospray mass spectrometry and ion-mobility spectrometry as well as in interdisciplinary fields involving ion transport through a gaseous medium.

The optimization of injector dynamics is essential for enhancing performance, reliability, and safety in rocket engines. This study examines the dynamics of an in-house-designed, coaxial swirl injector for a high-pressure LOx-CH4 rocket system, presenting a novel methodology for a swirl injector design that incorporates both flow and geometric parameters. A comprehensive parametric study, based on Bazarov's analytical framework, is conducted to assess the influence of geometric design variables on injector dynamics. The findings indicate that increasing the vortex chamber length (Lv) reduces the dynamic response and shifts the resonance peak to lower frequencies. An optimal radius ratio (Rrt) between 1.2 and 1.8 is identified to achieve a balanced dynamic response. Additionally, variations in the convergence angle ((3) have minimal impact on the injector's overall dynamics, with a 45 degrees angle found to be optimal for manufacturing purposes.This study offers crucial design recommendations for developing stable swirl injectors with an optimized dynamic response, providing valuable insights for improving injector performance and ensuring stability in high-pressure rocket systems.

A stable three coordinate Cu(i)-radical complex with an S-3 donor set having the general formula of [Cu-I(S-NHCH)(SS-NHC=S)] (1) was isolated as dark blue needles. Interestingly, this complex possesses a zwitterionic ligand, S--NHCH+, which is coordinated to the central Cu(i) ion via its S-atom [S--NHCH+=C4-thiolate functionalized C2-protonated zwitterionic N-hetero cyclic carbene; SS-NHC=S center dot- =NHC-based dithiolene radical anion]. 1 has been structurally characterized by single-crystal X-ray diffraction, and further characterized by UV-vis, IR, XPS, and EPR spectroscopy. 1 has also been studied by quantum chemical calculations.

The motion of liquid hydrogen in a cryogenic stage tank under microgravity conditions is numerically simulated in the present paper. The fluid motion is studied for various tank maneuvers such as tank rotation, simultaneous tank pitching and rotation, and disturbance imparted during satellite separation. The effectiveness of thrusters to settle the propellant and the effect of their firing durations on propellant availability near the drain port are determined. The propellant motion is studied using time-dependent computational fluid dynamics (CFD) simulations carried out in ANSYS Fluent. The vapor-liquid interface is captured using the volume of fluid (VOF) method. The surface tension is modeled using the continuum surface force model. The present analysis shows that capillary rise of the liquid during tank rotation takes place at slow speeds, whereas the bulk liquid motion is seen when the tank undergoes pitching and rotation simultaneously. Increasing the firing duration of the propellant settling thrusters from 5 s to 10 s is found to increase the propellant volume fraction at the drain port location from 0.89 to 0.99. Analysis shows that during spacecraft separation, the liquid-vapor interface is disturbed due to the sudden deceleration felt during separation. The liquid hydrogen blobs separate from the bulk liquid and migrate towards the tank fore-end, unlike the cases of tank rotation and simultaneous pitching and rotation. The present work clearly shows that significant liquid movement happens during spacecraft separation and tank pitching, and thus, a sufficient impulse needs to be provided by firing thrusters for settling the propellant before subsequent engine operations.

The absolute photodetachment cross section characterizes the photostability of atomic and molecular anions against photodestruction by neutralization. The measurement of this quantity has been reported only for atomic and simple molecular ions. In 2006, Wester's group introduced a novel ion-trap-based technique to measure the absolute photodetachment cross section [Trippel et al., Phys. Rev. Lett. 97, 193003 (2006)] of OH-. In the present work, we propose a novel methodology to streamline this technique to reduce the measurement time by several orders of magnitude by combining a single experimental rate measurement with a simulated column density distribution of the trapped ions. We validated our approach by reproducing the cross section reported for OH- at 632.8 nm. Using this technique, we report the first such measurement for a molecule of biological interest, deprotonated indole, at a laser wavelength of 403 nm. The proposed scheme is anticipated to have a significant and transformative impact on the development of a comprehensive database for photodetachment and photodissociation cross sections of molecular ions. Furthermore, these measurements have the potential to drive the development of cutting-edge computational codes for cross section calculations, enabling an unprecedentedly detailed understanding of electron dynamics in large molecules and the light-matter interaction.

This paper investigates combustion dynamics in a complex multi-injector element combustor using a flamelet approach in a large eddy simulation (LES) framework. The capability of computationally less expensive chemistry tabulation method to capture the interaction between unsteady heat release and acoustics is investigated. A non-adiabatic steady flamelet-based tabulated chemistry closure is invoked to simulate hydrogen–oxygen reactions in mixture fraction space. The model incorporates flow-induced non-equilibrium flame effects through scalar dissipation rate and the turbulence-chemistry interaction using a probability density function (PDF). A multi-element combustor dynamic study captures the first tangential mode close to 4000 Hz and corresponding high-frequency harmonics appropriately. Spectral analysis of the pressure variation displays similar frequency features in chamber and injector sections, suggesting the possibility of injector-chamber coupling. The coupling of the transverse pressure waves in the combustion chamber with the longitudinal pressure oscillations in the oxidizer post was probed as the reason for the pressure dynamics observed in the combustor.

Fluorescein, one of the brightest fluorescent dye molecules, is a widely used fluorophore for various applications from biomedicine to industry. The dianionic form of fluorescein is responsible for its high fluorescence quantum yield. Interestingly, the molecule was found to be nonfluorescent in the gas phase. This characteristic is attributed to the photodetachment process, which out-competes the fluorescence emission in the gas phase. In this work, we show that the calculated vertical and adiabatic detachment energies of fluorescein dianion in the gas and solvent phases account for the drastic differences observed in their fluorescence characteristics. The functional dependence of these detachment energies on the dianion's microsolvation was systematically investigated. The performance of different solvent models was also assessed. The higher thermodynamic stability of fluorescein dianion over the monoanion doublet in the solvent phase plays a crucial role in quenching photodetachment and activating the radiative channel with a high fluorescence quantum yield.

Impingement of satellite thruster plume on the adjacent surfaces of the satellite generates disturbance torques and heat loads that are undesirable. It is therefore important to configure the spacecraft such that the impingement effects of the thruster plume are minimized. In the present work, Computational Fluid Dynamics (CFD) study of plume expansion in to low pressure environment is carried out, and the impact pressure and heat flux on the flat plate are determined. The simulations are carried out for the reported experimental conditions of plume impingent on a flat plate for various standoff distances of the plate from the nozzle. The Knudsen number distribution shows that the flow remains in continuum in the vicinity of the nozzle and at the impingement region on the plate. The results of the simulation are compared with the measured test data for model validation. Finally, the effect of incorporating temperature jump condition on the impingement heat flux estimation is presented. The CFD model predicts the peak pressure and heat flux within 1.6 and 11.9

Abiotic stresses, including thermal extremes, water scarcity, metal toxicity, and high salinity levels, pose significant challenges to agricultural sustainability and food security. These stresses, driven by climate change, soil degradation, and pollution, disrupt water and nutrient uptake, photosynthesis, and cellular integrity. Consequently, plant growth, production, and yield are significantly reduced, highlighting the need for sustainable techniques, like utilizing soil microbes, which is crucial for effectively alleviating abiotic stress in plants. Microbial inoculation, particularly with arbuscular mycorrhizal fungi (AMF) and plant growth-promoting bacteria (PGPB), significantly mitigates these stresses. These microorganisms enhance plant growth, nutrient uptake, and stress tolerance through mechanisms like nutrient solubilization, polyamine accumulation, and reactive oxygen species (ROS) scavenging. They improve plant physiological responses, such as photosynthesis rates and stomatal conductance, and contribute to ultrastructural stability by maintaining membrane integrity and promoting the accumulation of osmolytes like trehalose, proline, polyamines (PA), and glycine betaine (GB). The activation of antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) further reduces oxidative stress. Key signaling pathways, including the Mitogen-Activated Protein Kinase (MAPK) cascade and Salt Overly Sensitive (SOS) signaling, play critical roles in plant responses to osmotic and ionic stresses. Additionally, aquaporins (AQPs), Calcium-Dependent Protein Kinases (CDPKs) and Late Embryogenesis Abundant (LEA) proteins are integral to abiotic stress resistance. Microbial symbiosis enhances these pathways, promoting ion homeostasis and stress resilience. Overall, understanding the intricate interactions between plants and soil microbes, coupled with sustainable agricultural practices, is crucial for enhancing crop resilience to abiotic stresses and ensuring food security amidst climate change. This review paper emphasizes the detrimental impacts of abiotic stresses on agricultural sustainability and food security, highlighting the imperative for sustainable techniques like utilization of soil microbes to effectively mitigate these stresses and enhance crop resilience.

This paper presents the computational methodology developed to simulate monomethyl hydrazine/nitrogen tetroxide (MMH/NTO) combustion. A three-dimensional rocket scale combustor domain with multi-element triplet injectors is utilized to study hypergolic flow and flame features. A Eulerian–Lagrangian framework is invoked for continuous phase treatment of combustion gas and discrete phase treatment for both MMH and NTO droplets. A discrete particle-based method (DPM) with finite rate chemistry is employed to study droplet injection, evaporation, and combustion. A description of flow and flame characteristics in three-dimensional RANS framework is presented in this paper. The model captures impinging jets from multiple triplet injectors, and MMH film cooling injection appropriately. It presents physical trends on the core combustion process, as well as the global evolution of temperature, pressure, and droplet spray in the combustor. The focus of the study is to develop a hypergolic combustion model which can be used to predict combustion performance under off-nominal operating conditions. The aim is to extend the model to study the combustion instability aspects of MMH/NTO-based combustors.

A linear 16-pole ion trap-based experimental setup has been designed, implemented, and characterized to investigate the photophysics of biomolecules in the gas phase. Electrospray ionization is employed to generate the ions in the gas phase at atmospheric pressure. The voltage configuration on the ion funnel, the ion optic device in the first vacuum interface, is used to control the energy of the ions. A home-built quadrupole mass-filter is utilized for the mass-selection of the ions of interest. A 16-pole ion trap designed and built in-house is implemented for ion trapping. The instrument's versatility and capability are showcased by demonstrating the fragmentation patterns of protonated and deprotonated tryptophan, as well as describing the photodetachment decay of deprotonated indole.

The formation of nitrogen hydrides in the interstellar medium is initiated by the nearly thermoneutral reaction of N ^+ + H _2 → NH ^+ + H. Here, we experimentally determine the enthalpy of this reaction using the principle of detailed balance from a measurement of the rate coefficient of the reverse reaction NH ^+ + H → N ^+ + H _2 . The measurements were carried out in a linear radiofrequency 22-pole trap combined with an effusive beam source of atomic hydrogen at temperatures between 10 and 100 K. The resulting ground-state energy difference (or reaction enthalpy at 0 K) of Δ E ^0 = (18 ± 4) meV confirms that there are no significant energy barriers on the reaction path.

We present the comparison of a field-programmable-gate-array (FPGA) based digital servo module with an analog counterpart for the purpose of laser frequency stabilization to a high-finesse optical cavity. The transfer functions of both the digital and analog modules for proportional-integral-derivative control are measured. For the lasers stabilized to the cavity, we measure the singe-sideband power spectral density of fast phase noise by means of an optical beat with filtered light transmitted through the cavity. The comparison between the digital and analog modules is performed for two low-phase-noise diode lasers at 1120 and 665 nm wavelengths. The performance of the digital servo module compares well to the analog one for the lowest attained levels of 30 mrad for the integrated phase noise and 10(-3) for the relative noise power. The laser linewidth is determined to be in the sub-kHz regime, only limited by the high-finesse cavity. Our work exploits the versatility of the FPGA-based servo module (STEMlab) when used with open-source software and hardware modifications. We demonstrated that such modules are suitable candidates for remote-controlled low-phase-noise applications in the fields of laser spectroscopy and atomic, molecular, and optical physics.

Multipole radiofrequency ion traps are versatile tools for trapping and manipulating ions. The extraction of ions from such a trap leads to broad time-of-flight (ToF) distributions, which make it incompatible with ToF mass spectrometry. In this work, we conducted numerical simulations of biomolecular ions stored in 16-pole and 16-wire ion traps to analyze their extraction characteristics. We show that the ions extracted from a wire trap with a simple upgrade exhibit ToF distributions two orders of magnitude narrower than that typically results from conventional ion traps. Further, in the upgraded design, the ions can be confined within a much narrower region, which, together with higher optical access of the wire trap configuration, makes it compatible with fluorescence spectroscopy measurements.

This paper describes the experimental and numerical works conducted to decipher the phenomenon of direct contact condensation (DCC). DCC, being a homogeneous condensation process, is characterised by extremely high heat transfer coefficient and very high turbulence across the interface. The study was initiated with experiments of steam condensation in stagnant and flowing water and is being augmented to GN2 condensation in stagnant and flowing LN2. Studies on steam condensation in stagnant water were conducted by injecting steam at different Reynolds numbers, Re (3000 < Re < 20,000) into a stagnant pool of water, stored in a transparent cuboidal test rig (0.48 m × 0.48 m × 0.5 m). Study was carried out for three different pool subcooling, ∆Tsub (50–70) with three different injector orifice diameters, D (2, 4 and 6 mm). Flowing water experiments were implemented with Reynolds number of steam varied from 12,400 to 24,900 and injected perpendicularly into flowing water with Re varied from 14,000 to 74,400. Preliminary experiments were also conducted with GN2 and stagnant LN2, and more comprehensive works are planned for future. Numerical studies of DCC were performed using two-fluid Eulerian framework. A pressure-based coupled solver of ANSYS Fluent was used to solve the governing equations. The condensation of steam in a pool of water was modelled, and the pressure oscillations during the different events of condensation were studied. DCC in cryogenic media was also analysed by injecting gaseous oxygen into flowing liquid oxygen through discrete holes. Salient results of gaseous oxygen condensation in flowing liquid oxygen are reported.