20 research outputs found
Mitigation of crosstalk and noise in multicore fiber on quantum communication
The influence of crosstalk on quantum communication networks and its
mitigation is discussed. It was shown that choosing the parameters for the
network that uses the phase stochastic resonance phenomena can increase the
signal-to-noise ratio.Comment: QKD, phase stochastic resonance, multi-core fiber. arXiv admin note:
substantial text overlap with arXiv:2208.0855
Modulation of Negative Index Metamaterials in the Near-IR Range
Optical modulation of the effective refractive properties of a "fishnet"
metamaterial with a Ag/Si/Ag heterostructure is demonstrated in the near-IR
range and the associated fast dynamics of negative refractive index is studied
by pump-probe method. Photo excitation of the amorphous Si layer at visible
wavelength and corresponding modification of its optical parameters is found to
be responsible for the observed modulation of negative refractive index in
near-IR.Comment: 11 figures, 4 figure
Two-Phase Flow Modeling of Cryogenic Loading Operations
We consider problem of modeling and controlling two-phase cryogenic flows during ground loading operations. We introduce homogeneous moving front and separated two-phase flow solvers that are capable of fast and accurate online predictions of flow dynamics during chilldown and transfer under nominal conditions and in the presence of faults. Concise sets of cryogenic correlations are proposed in each case. We present results of application of proposed solvers to the analysis of chilldown in large-scale experimental cryogenic transfer line build in Kennedy Space Center. We discuss optimization of parameters of cryogenic models obtained using general inferential framework and an application of the solvers to the fault detection and evaluation based on D-matrix approach. It is shown that solver’s predictions are in good agreement with experimental data obtained for liquid nitrogen flow in nominal regime and in the presence of faults
Risk Assessment and Scaling for the SLS LH2 ET
In this report the main physics processes in LH2 tank during prepress and rocket flight are studied. The goal of this investigation is to analyze possible hazards and to make risk assessment in proposed LH2 tank designs for SLS with 5 engines (the situation with 4 engines is less critical). For analysis we use the multinode model (MNM) developed by us and presented in a separate report and also 3D ANSYS simulations. We carry out simulation and theoretical analysis the physics processes such as (i) accumulation of bubbles in LH2 during replenish stage and their collapsing in the liquid during the prepress; (ii) condensation-evaporation at the liquid-vapor interface and tank wall, (iv) heating the liquid near the interface and wall due to condensation and environment heat, (v) injection of hot He during prepress and of hot GH2 during flight, (vi) mixing and cooling of the injected gases due to heat transfer between the gases, liquid and the tank wall. We analyze the effects of these physical processes on the thermo- and fluid gas dynamics in the ullage and on the stratification of temperature in the liquid and assess the associated hazards. A special emphasize is put on the scaling predictions for the larger SLS LH2 tank
Achieving higher photoabsorption than group III-V semiconductors in silicon using photon-trapping surface structures
The photosensitivity of silicon is inherently very low in the visible
electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared
wavelengths. Herein, we have experimentally demonstrated a technique utilizing
photon-trapping surface structures to show a prodigious improvement of
photoabsorption in one-micrometer-thin silicon, surpassing the inherent
absorption efficiency of gallium arsenide for a broad spectrum. The
photon-trapping structures allow the bending of normally incident light by
almost ninety degrees to transform into laterally propagating modes along the
silicon plane. Consequently, the propagation length of light increases,
contributing to more than an order of magnitude improvement in absorption
efficiency in photodetectors. This high absorption phenomenon is explained by
FDTD analysis, where we show an enhanced photon density of states while
substantially reducing the optical group velocity of light compared to silicon
without photon-trapping structures, leading to significantly enhanced
light-matter interactions. Our simulations also predict an enhanced absorption
efficiency of photodetectors designed using 30 and 100-nanometer silicon thin
films that are compatible with CMOS electronics. Despite a very thin absorption
layer, such photon-trapping structures can enable high-efficiency and
high-speed photodetectors needed in ultra-fast computer networks, data
communication, and imaging systems with the potential to revolutionize on-chip
logic and optoelectronic integration.Comment: 24 pages, 4 figure
Mathematical and critical physics analysis of engineering problems:Old-new way of doing things
In a modern world, importance of computer modeling for solving complex engineering problems cannot be overstated. However, in a number of critical engineering problems computational models cannot provide unique answer and so further physical and analytical insight is required to guide computer simulations. Such an insight becomes even more valuable when off-nominal regimes of operation have to be considered. To deal with complexity of the physical process at the interface of multiple engineering systems a new discipline is emerging - operational physics of critical missions. This discipline combines an old-good physics based approach to modeling engineering problems with modern advanced technologies for analyzing continuous and discrete volving multiple modes of operation in uncertain environments, unknown state variables, heterogeneous software and hardware components. In this paper the new approach is illustrated using as an example analysis of the critical physics phenomena that lead to Challenger accident including physics of cryogenic explosion and propagation of detonation waves, internal ballistics of SRM's in the presence of the case breach fault, and monitoring of the structural integrity of the spacecraft
Explosion Hazard from a Propellant-Tank Breach in Liquid Hydrogen-Oxygen Rockets
An engineering risk assessment of the conditions for massive explosions of cryogenic liquid hydrogen-oxygen rockets during launch accidents is presented. The assessment is based on the analysis of the data of purposeful rupture experiments with liquid oxygen and hydrogen tanks and on an interpretation of these data via analytical semiquantitative estimates and numerical simulations of simplified models for the whole range of the physical phenomena governing the outcome of a propellant-tank breach. The following sequence of events is reconstructed: rupture of fuel tanks, escape of the fluids from the ruptured tanks, liquid film boiling, fragmentation of liquid flow, formation of aerosol oxygen and hydrogen clouds, mixing of the clouds, droplet evaporation, self-ignition of the aerosol clouds, and aerosol combustion. The power of the explosion is determined by a small fraction of the escaped cryogens that become well mixed within the aerosol cloud during the delay time between rupture and ignition. Several scenarios of cavitation-induced self-ignition of the cryogenic hydrogen/oxygen mixture are discussed. The explosion parameters in a particular accident are expected to be highly varied and unpredictable due to randomness of the processes of formation, mixing, and ignition of oxygen and hydrogen clouds. Under certain conditions rocket accidents may result in very strong explosions with blast pressures from a few atm up to 100 atm. The most dangerous situations and the foreseeable risks for space missions are uncovered
Fault diagnostics and evaluation in cryogenic loading system using optimization algorithm
Physics-based approach to the cryogenic flow health management is presented. It is based on fast and time-accurate physics models of the cryogenic flow in the transfer line. We discuss main features of one of these models - the homogeneous moving front model - and presents results of its validation. The main steps of the approach including fault detection, identification, and evaluation are discussed. A few examples of faults are presented. It is shown that dynamic features of the faults naturally form a number of ambiguity groups. A D-matrix approach to optimized identification of these faults is briefly outlined. An example of discerning and evaluating faults within one ambiguity group using optimization algorithm is considered in more details. An application of this approach to the Integrated Health Management of cryogenic loading is discussed