scholarly journals Lifetime Estimation of the Upper Stage of GSAT-14 in Geostationary Transfer Orbit

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Jim Fletcher Jeyakodi David ◽  
Ram Krishan Sharma
Keyword(s):  
Initial Conditions ◽  
Lifetime Estimation ◽  
Eccentric Orbits ◽  
Solar Perturbations ◽  
Transfer Orbit ◽  
Upper Stage ◽  
Optimal Values ◽  
The Mean ◽  
Satellite Launch Vehicle ◽  
Earth’S Oblateness

The combination of atmospheric drag and lunar and solar perturbations in addition to Earth’s oblateness influences the orbital lifetime of an upper stage in geostationary transfer orbit (GTO). These high eccentric orbits undergo fluctuations in both perturbations and velocity and are very sensitive to the initial conditions. The main objective of this paper is to predict the reentry time of the upper stage of the Indian geosynchronous satellite launch vehicle, GSLV-D5, which inserted the satellite GSAT-14 into a GTO on January 05, 2014, with mean perigee and apogee altitudes of 170 km and 35975 km. Four intervals of near linear variation of the mean apogee altitude observed were used in predicting the orbital lifetime. For these four intervals, optimal values of the initial osculating eccentricity and ballistic coefficient for matching the mean apogee altitudes were estimated with the response surface methodology using a genetic algorithm. It was found that the orbital lifetime from these four time spans was between 144 and 148 days.

scholarly journals A modified fluctuation test for elucidating drug resistance in microbial and cancer cells

2020 ◽  
Author(s):  
Pavol Bokes ◽  
Abhyudai Singh
Keyword(s):  
Drug Resistance ◽  
Cancer Cells ◽  
Colony Size ◽  
Random Number ◽  
Initial Conditions ◽  
Fano Factor ◽  
Persister Cells ◽  
Efficient Treatment ◽  
Fluctuation Test ◽  
The Mean

AbstractClonal populations of microbial and cancer cells are often driven into a drug-tolerant persister state in response to drug therapy, and these persisters can subsequently adapt to the new drug environment via genetic and epigenetic mechanisms. Estimating the frequency with which drug-tolerance states arise, and its transition to drug-resistance, is critical for designing efficient treatment schedules. Here we study a stochastic model of cell proliferation where drug-tolerant persister cells transform into a drug-resistant state with a certain adaptation rate, and the resistant cells can then proliferate in the presence of the drug. Assuming a random number of persisters to begin with, we derive an exact analytical expression for the statistical moments and the distribution of the total cell count (i.e., colony size) over time. Interestingly, for Poisson initial conditions the noise in the colony size (as quantified by the Fano factor) becomes independent of the initial condition and only depends on the adaptation rate. Thus, experimentally quantifying the fluctuations in the colony sizes provides an estimate of the adaptation rate, which then can be used to infer the starting persister numbers from the mean colony size. Overall, our analysis introduces a modification of the classical Luria–Delbrück experiment, also called the “Fluctuation Test”, providing a valuable tool to quantify the emergence of drug resistance in cell populations.

scholarly journals Secular evolution of close-in planets: the effects of general relativity

2020 ◽  
Vol 493 (1) ◽  
pp. 427-436
Author(s):  
F Marzari ◽  
M Nagasawa
Keyword(s):  
General Relativity ◽  
Numerical Integration ◽  
Time Scales ◽  
Initial Conditions ◽  
Outer Planet ◽  
Secular Perturbations ◽  
Secular Evolution ◽  
Eccentric Orbits ◽  
Wide Range ◽  
Comparable Time

ABSTRACT Pairs of planets in a system may end up close to their host star on eccentric orbits as a consequence of planet–planet scattering, Kozai, or secular migration. In this scenario, general relativity and secular perturbations have comparable time-scales and may interfere with each other with relevant effects on the eccentricity and pericenter evolution of the two planets. We explore, both analytically and via numerical integration, how the secular evolution is changed by general relativity for a wide range of different initial conditions. We find that when the faster secular frequency approaches the general relativity precession rate, which typically occurs when the outer planet moves away from the inner one, it relaxes to it and a significant damping of the proper eccentricity of the inner planet occurs. The proper eccentricity of the outer planet is reduced as well due to the changes in the secular interaction of the bodies. The lowering of the peak eccentricities of the two planets during their secular evolution has important implications on their stability. A significant number of two-planet systems, otherwise chaotic because of the mutual secular perturbations, are found stable when general relativity is included.

The Service Time Properties of an Unreliable Server Characterize the Exponential Distribution

1994 ◽  
Vol 26 (01) ◽  
pp. 172-182 ◽  
Author(s):  
Z. Khalil ◽  
B. Dimitrov
Keyword(s):  
Exponential Distribution ◽  
Service Time ◽  
Initial Conditions ◽  
Mean Values ◽  
Unreliable Server ◽  
Service Disciplines ◽  
The Mean ◽  
Server Reliability ◽  
Preemptive Repeat Different

Consider the total service time of a job on an unreliable server under preemptive-repeat-different and preemptive-resume service disciplines. With identical initial conditions, for both cases, we notice that the distributions of the total service time under these two disciplines coincide, when the original service time (without interruptions due to server failures) is exponential and independent of the server reliability. We show that this fact under varying server reliability is a characterization of the exponential distribution. Further we show, under the same initial conditions, that the coincidence of the mean values also leads to the same characterization.

Optimal Reentry Time Estimation of an Upper Stage from Geostationary Transfer Orbit

2010 ◽  
Vol 47 (4) ◽  
pp. 686-690 ◽  
Author(s):  
M. Mutyalarao ◽  
Ram Krishnan Sharma
Keyword(s):  
Time Estimation ◽  
Transfer Orbit ◽  
Upper Stage

Effect of an Azimuthal Mean Flow On the Structure and Stability of Thermoacoustic Modes in an Annular Combustor Model with Electroacoustic Feedback

2020 ◽  
Author(s):  
Sylvain C. Humbert ◽  
Jonas Moeck ◽  
Alessandro Orchini ◽  
Christian Oliver Paschereit
Keyword(s):  
Mach Number ◽  
Initial Conditions ◽  
Mean Flow ◽  
Final State ◽  
Mean Velocity ◽  
Acoustic Damping ◽  
Annular Combustor ◽  
The Mean ◽  
High Mach ◽  
The Stability

Abstract Thermoacoustic oscillations in axisymmetric annular combustors are generally coupled by degenerate azimuthal modes, which can be of standing or spinning nature. Symmetry breaking due to the presence of a mean azimuthal flow splits the degenerate thermoacoustic eigenvalues, resulting in pairs of counter-spinning modes with close but distinct frequencies and growth rates. In this study, experiments have been performed using an annular system where the thermoacoustic feedback due to the flames is mimicked by twelve identical electroacoustic feedback loops. The mean azimuthal flow is generated by fans. We investigate the standing/spinning nature of the oscillations as a function of the Mach number for two types of initial states, and how the stability of the system is affected by the mean azimuthal flow. It is found that spinning, standing or mixed modes can be encountered at very low Mach number, but increasing the mean velocity promotes one spinning direction. At sufficiently high Mach number, spinning modes are observed in the limit cycle oscillations. In some cases, the initial conditions have a significant impact on the final state of the system. It is found that the presence of a mean azimuthal flow increases the acoustic damping. This has a beneficial effect on stability: it often reduces the amplitude of the self-sustained oscillations, and can even suppress them in some cases. However, we observe that the suppression of a mode due to the mean flow may destabilize another one. We discuss our findings in relation with an existing low-order model.

Uncertainty Analysis of Free Running Manoeuvring Model Test on a Modern Ferry, With Emphasis on Heel Angles

2019 ◽  
Author(s):  
Anton Kisjes ◽  
Frans Quadvlieg ◽  
Victor Ferrari
Keyword(s):  
Uncertainty Analysis ◽  
Model Test ◽  
Initial Conditions ◽  
Test Series ◽  
Confidence Bounds ◽  
Approach Speed ◽  
Twin Screw ◽  
Free Running ◽  
The Mean ◽  
The Stability

Abstract This paper presents an uncertainty study on the manoeuvring behaviour of a twin screw ferry. In particular, we are interested in heel angles that this ship achieves while manoeuvring. Earlier published uncertainty analysis has focused on the uncertainty of overshoot angles and tactical diameters see [1] and [2]. The heel angles of these ships are not large. However, there is a class of ships that may encounter large heel angles due to steering. Ferries are such ships. The present paper quantifies also the uncertainty of the measured heel angles due to manoeuvres. During the model test series, results are obtained for various values of the stability (GM), where large heel angles are observed. This provides a unique insight in the relation between the GM, approach speed, directional stability and the achieved heel angles. Because of the demonstrated large heel angles, it was important to make an uncertainty analysis of these tests. More publications have been written on the uncertainty of overshoot angles and dimensions of turning circle manoeuvres. However, the uncertainty of heel angles during manoeuvres hasn’t been published yet, which makes this a unique paper. The uncertainty analysis will be based on repeat tests for the zigzag 10°/10° and 35° turning circle manoeuvres. Repeat tests are carried out for these manoeuvres to verify the mean and the uncertainty of the experimentally obtained values. The methodology for estimating the uncertainty with 95% confidence bounds are derived by accounting for 1) uncertainty from measurement, 2) repeat tests and 3) the uncertainty from propagation of initial conditions and the error in check angle and rudder. The uncertainty results are compared with a previous study of uncertainty of manoeuvring characteristics of model tests with the KVLCC2 [1] and [2].

scholarly journals Suppressing cosmic variance with paired-and-fixed cosmological simulations: average properties and covariances of dark matter clustering statistics

2020 ◽  
Vol 496 (3) ◽  
pp. 3862-3869 ◽  
Author(s):  
Anatoly Klypin ◽  
Francisco Prada ◽  
Joyce Byun
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Initial Conditions ◽  
Cosmological Parameters ◽  
Average Density ◽  
Covariance Matrices ◽  
Acoustic Oscillations ◽  
Galaxy Clustering ◽  
The Mean ◽  
Statistical Noise

ABSTRACT Making cosmological inferences from the observed galaxy clustering requires accurate predictions for the mean clustering statistics and their covariances. Those are affected by cosmic variance – the statistical noise due to the finite number of harmonics. The cosmic variance can be suppressed by fixing the amplitudes of the harmonics instead of drawing them from a Gaussian distribution predicted by the inflation models. Initial realizations also can be generated in pairs with 180○ flipped phases to further reduce the variance. Here, we compare the consequences of using paired-and-fixed versus Gaussian initial conditions on the average dark matter clustering and covariance matrices predicted from N-body simulations. As in previous studies, we find no measurable differences between paired-and-fixed and Gaussian simulations for the average density distribution function, power spectrum, and bispectrum. Yet, the covariances from paired-and-fixed simulations are suppressed in a complicated scale- and redshift-dependent way. The situation is particularly problematic on the scales of Baryon acoustic oscillations where the covariance matrix of the power spectrum is lower by only $\sim 20{{\ \rm per\ cent}}$ compared to the Gaussian realizations, implying that there is not much of a reduction of the cosmic variance. The non-trivial suppression, combined with the fact that paired-and-fixed covariances are noisier than from Gaussian simulations, suggests that there is no path towards obtaining accurate covariance matrices from paired-and-fixed simulations – result, that is theoretically expected and accepted in the field. Because the covariances are crucial for the observational estimates of galaxy clustering statistics and cosmological parameters, paired-and-fixed simulations, though useful for some applications, cannot be used for the production of mock galaxy catalogues.

Orbit Plan Method for General Rendezvous Problems

2014 ◽  
Vol 543-547 ◽  
pp. 1385-1388
Author(s):  
Xu Min Song ◽  
Yong Chen ◽  
Qi Lin
Keyword(s):  
Optimization Problem ◽  
Planning Problem ◽  
Shooting Technique ◽  
Lambert Problem ◽  
Orbit Perturbation ◽  
Eccentric Orbits ◽  
Rendezvous Problem ◽  
Transfer Orbit ◽  
Adaptive Simulated Annealing ◽  
Annealing Method

The orbit plan method of rendezvous mission was studied in this paper. We are concerned with the general rendezvous problem between two satellites which may be in non-coplanar, eccentric orbits, considering orbit perturbation and rendezvous time limitation. The planning problem was modeled as a nonlinear optimization problem, and the adaptive simulated annealing method was used to get the global solution. The Lambert algorithm was used to compute the transfer orbit, so that the endpoint constraint of rendezvous was eliminated. A shooting technique was used to solve the perturbed lambert problem. The method was validated by simulation results.

Chaotic Balanced State in a Model of Cortical Circuits

1998 ◽  
Vol 10 (6) ◽  
pp. 1321-1371 ◽  
Author(s):  
C. van Vreeswijk ◽  
H. Sompolinsky
Keyword(s):  
Cortical Neurons ◽  
Initial Conditions ◽  
Single Cells ◽  
Network Size ◽  
Short Time Scale ◽  
Strong Nonlinearity ◽  
Large Network ◽  
Wide Range ◽  
The Mean

The nature and origin of the temporal irregularity in the electrical activity of cortical neurons in vivo are not well understood. We consider the hypothesis that this irregularity is due to a balance of excitatory and inhibitory currents into the cortical cells. We study a network model with excitatory and inhibitory populations of simple binary units. The internal feedback is mediated by relatively large synaptic strengths, so that the magnitude of the total excitatory and inhibitory feedback is much larger than the neuronal threshold. The connectivity is random and sparse. The mean number of connections per unit is large, though small compared to the total number of cells in the network. The network also receives a large, temporally regular input from external sources. We present an analytical solution of the mean-field theory of this model, which is exact in the limit of large network size. This theory reveals a new cooperative stationary state of large networks, which we term a balanced state. In this state, a balance between the excitatory and inhibitory inputs emerges dynamically for a wide range of parameters, resulting in a net input whose temporal fluctuations are of the same order as its mean. The internal synaptic inputs act as a strong negative feedback, which linearizes the population responses to the external drive despite the strong nonlinearity of the individual cells. This feedback also greatly stabilizes the system's state and enables it to track a time-dependent input on time scales much shorter than the time constant of a single cell. The spatiotemporal statistics of the balanced state are calculated. It is shown that the autocorrelations decay on a short time scale, yielding an approximate Poissonian temporal statistics. The activity levels of single cells are broadly distributed, and their distribution exhibits a skewed shape with a long power-law tail. The chaotic nature of the balanced state is revealed by showing that the evolution of the microscopic state of the network is extremely sensitive to small deviations in its initial conditions. The balanced state generated by the sparse, strong connections is an asynchronous chaotic state. It is accompanied by weak spatial cross-correlations, the strength of which vanishes in the limit of large network size. This is in contrast to the synchronized chaotic states exhibited by more conventional network models with high connectivity of weak synapses.

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