The probability density function of a hardware performance parameter

Probability density function of hardware performance parameter and incentive contractin

Analytical developments for definition and prediction of USB noise

A systematic acoustic data base and associated flow data are used in identifying the noise generating mechanisms of upper surface blown flap configurations of short takeoff and landing aircraft. Theory is developed for the radiated sound field of the highly sheared flow of the trailing edge wake. An empirical method is also developed using extensive experimental data and physical reasonings to predict the noise levels

The Application of Convex Hull in Industrial X-Ray Computerized Tomography

In some x-ray CT situations, the x-ray data of the object are available only in a limited angular range. Limited-angle imaging occurs, for example, when scanning in an angular range is obstructed by other physical objects, or when the x-ray is attenuated too much in a particular angular range to serve any useful purpose. These situations are illustrated in Fig. 1. Under such circumstances limited-angle image reconstruction techniques could be employed to reconstruct the object from the x-ray data and other information about the object, such as (1) exterior boundary of the object; (2) upper bound of the object density; (3) lower bound of the object density. It has been shown that by using this information in addition to the limited-angle x-ray data, the object can be reconstructed uniquely [1]. The limited-angle reconstruction algorithm developed in the above reference is shown in Fig. 2; the image is transformed back and forth between the object space by filtered backprojection, and the projection space by projection, with corrections by the a priori information in the object space and the limited-angle known projections in the projection space

3-Dimensional Flaw Characterization Through 2-Dimensional Image Reconstructions

The 3-dimensional Born approximation is a powerful method for characterizing flaws because it can be applied to characterize flaws of any shape. Yet, the method has a number of difficulties, such as taking and processing a large amount of data, and the complications associated with 3-dimensional image reconstructions such as 3-dimensional interpolation, long computing time, etc. For these reasons the method is usually simplified and restricted to characterize symmetrically shaped flaws, which can be characterized by using only a small number of pulse echoes. Though this procedure is simple, it cannot be applied to characterize flaws of more general shape

Shock associated noise reduction from inverted-velocity-profile coannular jets

Acoustic measurements show that the shock noise from the outer stream is virtually eliminated when the inner stream is operated at a Mach number just above unity, regardless of all the other jet operating conditions. At this optimum condition, the coannular jet provides the maximum noise reduction relative to the equivalent single jet. The shock noise reduction can be achieved at inverted-as well as normal-velocity-profile conditions, provided the coannular jet is operated with the inner stream just slightly supersonic. Analytical models for the shock structure and shock noise are developed indicate that a drastic change in the outer stream shock cell structure occurs when the inner stream increases its velocity from subsonic to supersonic. At this point, the almost periodic shock cell structure of the outer stream nearly completely disappears the noise radiated is minimum. Theoretically derive formulae for the peak frequencies and intensity scaling of shock associated noise are compared with the measured results, and good agreement is found for both subsonic and supersonic inner jet flows

Stimuli Responsive Polymers for Enhanced Drug Release Applications

This talk will focus on the development of polymeric nano-structured systems for drug and gene delivery applications. Two major classes of polymer systems will be considered; namely poly(ethylene-oxide-b-propylene-oxide-b-ethylene-oxide) (Pluronics) tri-block copolymers (FDA approved) and methacrylic acid (MAA) block and random copolymers. These polymers were functionalised with biodegradable or stimuli-sensitive functional groups to produce stimuli-sensitive nano-structure for efficient delivery of drugs and DNAs. The atom transfer radical polymerisation (ATRP) was adopted to synthesize a range of mono-dispersed block copolymers (e.g. PEO-b-MAA, MMA-b-MAA). Ring opening polymerization method was used to functionalize Pulronics with degradable functional groups, such as lactide (LA), and caprolactone (CL). Other stimuli-sensitive functional groups such as methacrylic acid was used to impart pH sensitivity to the polymers. Various types of methacrylic acid block and random cross-linked copolymers and other novel systems, such as fullerene based block copolymers were synthesized. Detailed mechanism and physics that control the micellization, microstructure and drug/polymer interactions will be discussed.Singapore-MIT Alliance (SMA

Acoustic interactions between an altitude test facility and jet engine plumes: Theory and experiments

The overall objective of the described effort was to develop an understanding of the physical mechanisms involved in the flow/acoustic interactions experienced in full-scale altitude engine test facilities. This is done by conducting subscale experiments and through development of a theoretical model. Model cold jet experiments with an axisymmetric convergent nozzle are performed in a test setup that stimulates a supersonic jet exhausting into a cylindrical diffuser. The measured data consist of detailed flow visualization data and acoustic spectra for a free and a ducted plume. It is shown that duct resonance is most likely responsible by theoretical calculations. Theoretical calculations also indicate that the higher discrete tones observed in the measurements are related to the screech phenomena. Limited experiments on the sensitivity of a free 2-D, C-D nozzle to externally imposed sound are also presented. It is shown that a 2-D, C-D nozzle with a cutback is less excitable than a 2-D C-D nozzle with no cutback. At a pressure ratio of 1.5 unsteady separation from the diverging walls of the nozzle is noticed. This separation switches from one wall to the opposite wall thus providing an unsteady deflection of the plume. It is shown that this phenomenon is related to the venting provided by the cutback section

Gamma-ray emission from globular clusters

Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as Millisecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gamma-ray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed gamma-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that gamma-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.Comment: 11 pages, 7 figures, 2 tables, J. Astron. Space Sci., in pres

Local Density of the Bose Glass Phase

We study the Bose-Hubbard model in the presence of on-site disorder in the canonical ensemble and conclude that the local density of the Bose glass phase behaves differently at incommensurate filling than it does at commensurate one. Scaling of the superfluid density at incommensurate filling of $\rho=1.1$ and on-site interaction $U=80t$ predicts a superfluid-Bose glass transition at disorder strength of $\Delta_c \approx 30t$. At this filling the local density distribution shows skew behavior with increasing disorder strength. Multifractal analysis also suggests a multifractal behavior resembling that of the Anderson localization. Percolation analysis points to a phase transition of percolating non-integer filled sites around the same value of disorder. Our findings support the scenario of percolating superfluid clusters enhancing Anderson localization near the superfluid-Bose glass transition. On the other hand, the behavior of the commensurate filled system is rather different. Close to the tip of the Mott lobe ($\rho=1, U=22t$) we find a Mott insulator-Bose glass transition at disorder strength of $\Delta_c \approx 16t$. An analysis of the local density distribution shows Gaussian like behavior for a wide range of disorders above and below the transition.Comment: 12 pages, 14 figure

Study of off-diagonal disorder using the typical medium dynamical cluster approximation

We generalize the typical medium dynamical cluster approximation (TMDCA) and the local Blackman, Esterling, and Berk (BEB) method for systems with off-diagonal disorder. Using our extended formalism we perform a systematic study of the effects of non-local disorder-induced correlations and of off-diagonal disorder on the density of states and the mobility edge of the Anderson localized states. We apply our method to the three-dimensional Anderson model with configuration dependent hopping and find fast convergence with modest cluster sizes. Our results are in good agreement with the data obtained using exact diagonalization, and the transfer matrix and kernel polynomial methods.Comment: 10 pages, 8 figure