A research program in active control/aeroelasticity in the JIAFS at NASA Langley Research Center

A control law synthesis methodology for multifunctional active control system to satisfy root-mean-square load and response constraints as well as to meet stability robustness requirements at plant input and output was developed. Modern control theory, singular value analysis and optimization techniques were utilized. All stability and response derivative expressions were derived analytically for sensitivity study. The software is incorporated as an update to the AB/LAD general control design software package PADLOCS

Analytical method for determining the stability of linear retarded systems with two delays

The stability is considered of the solution differential-difference equations of the retarded type with constant coefficients and two constant time delays. A method that makes use of analytical expressions to determine stability boundaries, and the stability of the system, is derived. The method was applied to a system represented by a second-order differential equation with constant coefficients and time delays in the velocity and displacement terms. The results obtained is in agreement with those obtained by other investigators

Stability of neutral equations with constant time delays

A method was developed for determining the stability of a scalar neutral equation with constant coefficients and constant time delays. A neutral equation is basically a differential equation in which the highest derivative appears both with and without a time delay. Time delays may appear also in the lower derivatives or the independent variable itself. The method is easily implemented, and an illustrative example is presented

Cold Flow Determination of the Internal Flow Environment Around the Submerged TVC Nozzle for the Space Shuttle SRM

A series of subscale cold flow tests was performed to quantify the gas flow characteristics at the aft end of the Space Shuttle Solid Rocket Motor. This information was used to support the analyses of the redesigned nozzle/case joint. A portion of the thermal loads at the joint are due to the circumferential velocities and pressure gradients caused primarily by the gimbaling of the submerged nose TVC nozzle. When the nozzle centerline is vectored with respect to the motor centerline, asymmetries are set up in the flow field under the submerged nozzle and immediately adjacent to the nozzle/case joint. Specific program objectives included: determination of the effects of nozzle gimbal angle and propellant geometry on the circumferential flow field; measurement of the static pressure and gas velocities in the vicinity of the nozzle/case joint; use of scaling laws to apply the subscale cold flow data to the full scale SRM; and generation of data for use in validation of 3-D computational fluid dynamic, CFD, models of the SRM flow field. These tests were conducted in the NASA Marshall Space Flight Center Airflow Facility with a 7.5 percent scale model of the aft segment of the SRM. Static and dynamic pressures were measured in the model to quantify the flow field. Oil flow data was also acquired to obtain qualitative visual descriptions of the flow field. Nozzle gimbal angles of 0, 3.5, and 7 deg were used with propellant grain configurations corresponding to motor burn times of 0, 9, 19, and 114 seconds. This experimental program was successful in generating velocity and pressure gradient data for the flow field around the submerged nose nozzle of the Space Shuttle SRM at various burn times and gimbal angles. The nature of the flow field adjacent to the nozzle/case joint was determined with oil droplet streaks, and the velocity and pressure gradients were quantified with pitot probes and wall static pressure measurements. The data was applied to the full scale SRM thru a scaling analysis and the results compared well with the 3-D computational fluid dynamics computer model

Program of Research and Education in Aerospace Structures

Since its inception in January 2003, the program has provided support for 1 research professor and a total of 10 Graduate Research Scholar Assistants of these all 10 have completed their MS degree program. The program has generated 10 MS thesis. Final report lists papers presented in seminars for the period January 1, 2003 through June 30, 2005

Nanoscale fluid flows in the vicinity of patterned surfaces

Molecular dynamics simulations of dense and rarefied fluids comprising small chain molecules in chemically patterned nano-channels predict a novel switching from Poiseuille to plug flow along the channel. We also demonstrate behavior akin to the lotus effect for a nanodrop on a chemically patterned substrate. Our results show that one can control and exploit the behavior of fluids at the nanoscale using chemical patterning.Comment: Phys. Rev. Lett. in pres

Increasing the Net Charge and Decreasing the Hydrophobicity of Bovine Carbonic Anhydrase Decreases the Rate of Denaturation with Sodium Dodecyl Sulfate

AbstractThis study compares the rate of denaturation with sodium dodecyl sulfate (SDS) of the individual rungs of protein charge ladders generated by acylation of the lysine ε−NH3+ groups of bovine carbonic anhydrase II (BCA). Each acylation decreases the number of positively charged groups, increases the net negative charge, and increases the hydrophobic surface area of BCA. This study reports the kinetics of denaturation in solutions containing SDS of the protein charge ladders generated with acetic and hexanoic anhydrides; plotting these rates of denaturation as a function of the number of modifications yields a U-shaped curve. The proteins with an intermediate number of modifications are the most stable to denaturation by SDS. There are four competing interactions—two resulting from the change in electrostatics and two resulting from the change in exposed hydrophobic surface area—that determine how a modification affects the stability of a rung of a charge ladder of BCA to denaturation with SDS. A model based on assumptions about how these interactions affect the folded and transition states has been developed and fits the experimental results. Modeling indicates that for each additional acylation, the magnitude of the change in the activation energy of denaturation (ΔΔG‡) due to changes in the electrostatics is much larger than the change in ΔΔG‡ due to changes in the hydrophobicity, but the intermolecular and intramolecular electrostatic effects are opposite in sign. At the high numbers of acylations, hydrophobic interactions cause the hexanoyl-modified BCA to denature nearly three orders of magnitude more rapidly than the acetyl-modified BCA

Combinatorial Properties and Recognition of Unit Square Visibility Graphs

Unit square (grid) visibility graphs (USV and USGV, resp.) are described by axis-parallel visibility between unit squares placed (on integer grid coordinates) in the plane. We investigate combinatorial properties of these graph classes and the hardness of variants of the recognition problem, i.e., the problem of representing USGV with fixed visibilities within small area and, for USV, the general recognition problem

Deep Sequencing Analysis of Phage Libraries using Illumina Platform

This paper presents an analysis of phage-displayed libraries of peptides using Illumina. We describe steps for the preparation of short DNA fragments for deep sequencing and MatLab software for the analysis of the results. Screening of peptide libraries displayed on the surface of bacteriophage (phage display) can be used to discover peptides that bind to any target. The key step in this discovery is the analysis of peptide sequences present in the library. This analysis is usually performed by Sanger sequencing, which is labor intensive and limited to examination of a few hundred phage clones. On the other hand, Illumina deep-sequencing technology can characterize over 107 reads in a single run. We applied Illumina sequencing to analyze phage libraries. Using PCR, we isolated the variable regions from M13KE phage vectors from a phage display library. The PCR primers contained (i) sequences flanking the variable region, (ii) barcodes, and (iii) variable 5′-terminal region. We used this approach to examine how diversity of peptides in phage display libraries changes as a result of amplification of libraries in bacteria. Using HiSeq single-end Illumina sequencing of these fragments, we acquired over 2 × 107 reads, 57 base pairs (bp) in length. Each read contained information about the barcode (6 bp), one complimentary region (12 bp) and a variable region (36 bp). We applied this sequencing to a model library of 106 unique clones and observed that amplification enriches ∼150 clones, which dominate ∼20% of the library. Deep sequencing, for the first time, characterized the collapse of diversity in phage libraries. The results suggest that screens based on repeated amplification and small-scale sequencing identify a few binding clones and miss thousands of useful clones. The deep sequencing approach described here could identify under-represented clones in phage screens. It could also be instrumental in developing new screening strategies, which can preserve diversity of phage clones and identify ligands previously lost in phage display screens.Chemistry and Chemical Biolog

Chaotic flow and efficient mixing in a micro-channel with a polymer solution

Microscopic flows are almost universally linear, laminar and stationary because Reynolds number, $Re$, is usually very small. That impedes mixing in micro-fluidic devices, which sometimes limits their performance. Here we show that truly chaotic flow can be generated in a smooth micro-channel of a uniform width at arbitrarily low $Re$, if a small amount of flexible polymers is added to the working liquid. The chaotic flow regime is characterized by randomly fluctuating three-dimensional velocity field and significant growth of the flow resistance. Although the size of the polymer molecules extended in the flow may become comparable with the micro-channel width, the flow behavior is fully compatible with that in a table-top channel in the regime of elastic turbulence. The chaotic flow leads to quite efficient mixing, which is almost diffusion independent. For macromolecules, mixing time in this microscopic flow can be three to four orders of magnitude shorter than due to molecular diffusion.Comment: 8 pages,7 figure