Yusuf Jafry

Yusuf Jafry

PhD MS BSc Aero/Astro

About

44
Publications
4,693
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667
Citations
Citations since 2016
0 Research Items
119 Citations
20162017201820192020202120220510152025
20162017201820192020202120220510152025
20162017201820192020202120220510152025
20162017201820192020202120220510152025

Publications

Publications (44)
Article
Full-text available
We present the solution that Hypo Real Estate Bank International (Hypo) implemented to perform Monte Carlo simulations of its commercial real estate credit risk. The solution uses Risk Integrated's proprietary software, the Specialized Finance System, which is supported by another Risk Integrated technology, the Enterprise Spread- sheet Platform. T...
Article
Full-text available
We present Risk Integrated's Enterprise Spreadsheet Platform (ESP), a technical approach to the near-elimination of spreadsheet risk in the enterprise computing environment, whilst maintaining the full flexibility of spreadsheets for modelling complex financial structures and processes. In its Basic Mode of use, the system comprises a secure and ro...
Article
Full-text available
STEP is one of a number of missions now being developed to take advantage of the quiet space environment to carry out very sensitive gravitational experiments. Using pairs of concentric free-falling proof-masses, STEP will be able to test the equivalence principle (EP) to a sensitivity at least five orders of magnitude better than currently achieva...
Article
Full-text available
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988. Bibliography: leaves 87-88. by Yusuf Rezah Jafry. M.S.
Article
Full-text available
Credit migration matrices are cardinal inputs to many risk management applications; their accurate estimation is therefore critical. We explore two approaches: cohort and two variants of duration – one imposing, the other relaxing time homogeneity – and the resulting differences, both statistically through matrix norms and economically using a cred...
Article
Experiments to test the Equivalence Principle in space are typically suggested for flight in low-Earth, circular, Sun-synchronous orbits at 400–600 km altitude. In these orbits the spacecraft routinely traverses the South Atlantic Anomaly (SAA), where the fluxes of trapped charged particles are enhanced. These particles, together with energetic sol...
Article
The MiniSTEP drag-free control system must reduce the atmospheric drag forces acting on the spacecraft by seven orders of magnitude, to yield an average residual acceleration of less than 3·10−14 m s−2 averaged over the measurement bandwidth. The origins of the drag-free requirements are discussed, and a control system is presented which meets the...
Article
Electrostatic charging of the LISA proof masses by penetrating cosmic rays and energetic solar particles in interplanetary space leads to two kinds of spurious forces: i) Lorentz interaction due to the motion of the charged proof masses through the interplanetary magnetic field, and ii) Coulomb interaction between the charged proof masses and surro...
Article
Full-text available
Credit migration or transition matrices, which characterize the expected changes in credit quality of obligors, are cardinal inputs to applications such as asset pricing and risk management. We propose a new metric for comparing these matrices (a mobility index) by first subtracting the identity matrix, focusing the analysis on the dynamics, and th...
Article
The detection of low-frequency gravitational radiation requires a space-borne detector, principally to escape the effects of seismic noise which plague ground-based detectors at low frequencies. Although the seismic disturbance is eliminated, the space environment introduces its own set of problems. For example, solar radiation pressure. This can b...
Article
Full-text available
The proposed Satellite Test of the Equivalence Principle (STEP) Mission aims to test the Equivalence Principle with higher accuracy than previously obtained by ground based experiments. The mission uses low thrust proportional thrusters for either 3-DOF or 6-DOF control in different phases. During the attitude acquisition sequence the thrusters can...
Article
Full-text available
Credit migration matrices are cardinal inputs to many risk management applications. Their accurate estimation is therefore critical. We explore three approaches, cohort and two variants of duration—time homogeneous and non-homogeneous—and the resulting differences, both statistically through matrix norms and economically through credit portfolio an...
Article
LISA will be the first space-home gravitational wave observatory. It aims to detect gravitational waves in the 0.1 mHz÷1 Hz range from sources including galactic binaries, super-massive black-hole binaries, capture of objects by super-massive black-holes and stochastic background. LISA is an ESA approved Cornerstone Mission foreseen as a joint ESA-...
Article
Full-text available
The Satellite Test of the Equivalence Principle (STEP) Mission aims at testing the Equivalence Principle with a very high accuracy. The paper presents a simple design of the drag free attitude control system (DFACS). The rotational and translational control laws are designed as multiple single-input-single output (SISO) loops using simple proportio...
Article
A limiting disturbance that affects high-precision weak-force experiments in space using proof-masses, such as MiniSTEP (MINImal Satellite Test of the Equivalence Principle) and LISA (Laser Interferometer Space Antenna), is due to charging of the proof-masses. Charging by an ambient flux of high-energy protons is inevitable in any orbit. Estimates...
Article
The build-up of electrical charge on the proof masses is an important disturbance for LISA. The charging is due to penetrating particle radiation (primarily protons) from cosmic rays, and from the Sun during solar flares. Estimates of charging rates have been computed using the GEANT Monte Carlo particle-transport code in combination with realistic...
Article
Various proposed space experiments to test the weak equivalence principle (EP) use ultra-precise differential accelerometers in Earth orbit. A common feature of these accelerometers is that their test masses are physically constrained in some manner, thus imposing a limit on the achievable sensitivity. An alternative approach, analogous to the fami...
Article
The MiniSTEP drag-free control system must reduce the atmospheric drag forces acting on the spacecraft by seven orders of magnitude, to yield an average residual acceleration of less than averaged over the measurement bandwidth. The origins of the drag-free requirements are discussed, and a control system is presented which meets the requirements u...
Article
Full-text available
The proposed space mission Galileo Galilei (GG) utilizes Earth-orbiting test masses in high-speed co-rotation to test the Weak Equivalence Principle (EP). This paper presents the results of a technical evaluation of the proposal, as it was presented in September 1996. Investigation of the dynamics and control aspects reveals that the experiment is...
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Space-borne physics experiments involving the measurement of small motions of test bodies are likely to be limited by disturbance forces. Of particular concern are forces arising from electrostatic charging of the test body due to interactions with particle radiation. Estimates of charging rates have been computed using Monte Carlo particle-transpo...
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Full-text available
There are many advantages of the space environment for fundamental physics experiments. A brief overview of the mission possibilities is presented. Spaceborne tests of the Weak Equivalence Principle are discussed in detail, illustrating the advantages of space, and highlighting the key concepts of accelerometry and drag-free control.
Article
STEP (Satellite Test of the Equivalence Principle) is a mission in the discipline area of "Fundamental Physics". The scientific objectives of the M3-STEP mission are to test the Equivalence Principle to 1 part in 1017, five orders of magnitude better than has been achieved on the ground; search for a new interaction between quantum-mechanical spin...
Article
Computational results are presented for the flow through a helium microthruster. This device is to be used for fine adjustments in attitude control for a proposed space experiment. The mass-flow rates used by the thruster are very low giving Knudsen numbers at the nozzle throat between 0.01 and 1 based on the stagnation conditions and the nozzle th...
Article
The goal with LISA (Laser Interferometer Space Antenna) is to detect and study low-frequency astrophysical gravitational radiation. LISA will complement the next-generation ground-based detectors (VIRGO, LIGO) by accessing the important low-frequency regime (10-4 to 10-1 Hz), which will never be observable from the Earth because of terrestrial dist...
Article
STEP - Satellite Test of the Equivalence Principle - is a 'fundamental-physics laboratory in space', combining four different experiments in one payload. The latter consists of eight differential accelerometers accommodated in a quartz block and cooled to 2 K in order to test the Equivalence Principle, search for a new interaction between quantum-m...
Chapter
Gravity Probe-B is the relativity gyroscope experiment being developed by NASA and Stanford University to test two extraordinary, unverified predictions of Albert Einstein's general theory of relativity. The experiment will check, very precisely, tiny changes in the directions of spin of four gyroscopes contained in an Earth satellite orbiting at 4...
Chapter
A new semi-empirical thruster plume model is presented based on recent experimental and numerical (Direct Simulation Monte Carlo) studies. The results are unique in that they pertain to unprecedentedly low flow rates (nozzle Reynolds numbers below 200). The model is used in computing the impingement forces acting on a spacecraft solar panel emersed...
Chapter
A general procedure to determine accurately the true relationship between the commanded and the actual force output of a set of thrusters is presented. This relationship is determined from data generated from a spacecraft while it is on orbit. On orbit thruster calibration measures the true outputs of the thrusters in the actual space environment i...
Article
A fundamental physics experiment has been proposed whereby a 200 kg cannon-ball is flown in close proximity to a drag-free spacecraft in low earth orbit. The spacecraft contains a cryogenically cooled superconducting differential accelerometer which can detect the gravitational field of the cannonball with a sensitivity of 10⁻¹⁶ m s⁻². By using dif...
Article
During Phase A, the STEP Study Team identified three types of experiments that can be accommodated on the STEP satellite within the mission constraints and whose performance is orders of magnitude better than any present or planned future experiment of the same kind on the ground. The scientific objectives of the STEP mission are to: test the Equiv...
Article
STEP, the Satellite Test of the Equivalence Principle, is a joint European-U.S. space program to investigate one the strangest phenomena in physics: the fact that gravity makes all bodies fall with the same acceleration. Interpreted by Isaac Newton as the outcome of an equivalence between two distinct properties of a body, weight and quantity of ma...
Article
The fundamental nature of the various experiments on STEP has profound implications for the most important areas of physics. STEP would be ESA's first mission in Fundamental Physics, opening up a third discipline area in space science, in addition to Solar-System Exploration and Astronomy. A very large community of physicists in numerous universiti...
Article
A general procedure to determine accurately the true relationship between the commanded and the actual force output of a set of thrusters is presented. This relationship is determined from data generated from a spacecraft while it is on orbit. On orbit thruster calibration measures the true outputs of the thrusters in the actual space environment i...
Article
A new semi-empirical thruster plume model is presented based on recent experimental and numerical (Direct Simulation Monte Carlo) studies. The results are unique in that they pertain to unprecedentedly low flow rates (nozzle Reynolds numbers below 200). The model is used in computing the impingement forces acting on a spacecraft solar panel emersed...
Article
Gravity Probe-B is the relativity gyroscope experiment being developed by NASA and Stanford University to test two extraordinary, unverified predictions of Albert Einstein's general theory of relativity. The experiment will check, very precisely, tiny changes in the directions of spin of four gyroscopes contained in an Earth satellite orbiting at 4...
Article
Full-text available
Gravity Probe‐B and the Satellite Test of the Equivalence Principle are two proposed experiments in basic physics which will utilize drag‐free satellites equipped with proportional helium thrusters. In order to calibrate the thrust systems for precise aeronomic measurements, it is necessary to model the effects of thruster plume impingement. Conven...
Article
GP-B and STEP are two proposed experiments in basic physics which will utilize drag-free spacecraft in 600 km polar orbits around the earth. By monitoring the activity of the drag-free compensators, it will be possible to obtain in situ drag measurements from which variations in atmospheric density and winds can be observed with unprecedented resol...
Article
Rather than a complete summary of the session, this paper reflects the closing remarks I made on the subject of performing a spaceborne test of the Equivalence Principle using unsupported test masses.
Article
Full-text available
A modular real-time PC-based audio processing software tool has been developed which offers a high degree of user control, intended for use by audio effect developers, signal processing engineers, sound designers, musicians, and educators. The key software features are described, followed by a range of example applications in audio effect design an...

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