Mechanical and Industrial Engineering Faculty Publications

A nano-cheese-cutter to directly measure interfacial adhesion of freestanding nano-fibers

Xin Wang — Mon, 16 Apr 2012 13:49:12 PDT

A nano-cheese-cutter is fabricated to directly measure the adhesion between two freestanding nano-fibers. A single electrospun fiber is attached to the free end of an atomic force microscope cantilever, while a similar fiber is similarly prepared on a mica substrate in an orthogonal direction. External load is applied to deform the two fibers into complementary V-shapes, and the force measurement allows the elastic modulus to be determined. At a critical tensile load, “pull-off” occurs when the adhering fibers spontaneously detach from each other, yielding the interfacial adhesion energy. Loading-unloading cycles are performed to investigate repeated adhesion-detachment and surface degradation.

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Rules and limitations of building delay-tolerant topologies for coupled systems

Rifat Sipahi — Mon, 16 Apr 2012 13:49:09 PDT

This paper investigates the equilibrium behavior of broadly studied synchronization dynamics of coupled systems, among which shared information is delayed. The underlying relationship is established between graph structures and the largest amount of delay the dynamics can withstand without losing stability. In particular, based on Cartesian product of graphs, we present the rules and limitations for synthesizing the graphs of large-scale systems that can remain stable for as large delays as possible. Examples are provided to demonstrate the results.

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Supply network dynamics and delays; performance, synchronization, stability

Rifat Sipahi — Mon, 02 Apr 2012 14:18:47 PDT

Recent research results in operations research specifically emphasize the critical role of delays in the functionality of supply networks. Delays arise due to the time needed for material deliveries, information flow and human perception towards adjusting to new decisions. Delays contaminate decision-making and lead to poor performance, synchronization problems and fluctuations in inventory levels resulting in major economical losses. This paper surveys continuous time deterministic mathematical models developed at system-level for supply network dynamics along with standard delay models pertaining to material deliveries, information flows and human perception. Next, the analogy between such delay models arising in supply networks and...

A comparative survey in determining the imaginary characteristic roots of LTI time delayed systems

Rifat Sipahi — Mon, 02 Apr 2012 14:18:45 PDT

The aim of this study is to offer a comparison of the numerical procedures for an important problem, the determination of purely imaginary characteristic roots of LTITime Delayed Systems (LTI-TDS). This problem, in fact, has a crucial role in assessing the stability of the general class of vector LTI-TDS x = Ax + Bx(t -τ). There are many procedures discussed in the literature for this purpose. Those, which are exact, first determine the complete set of imaginary characteristic roots of the dynamics, as they constitute the only points where stability switching can take place. These approaches are, in fact, some...

Dependence of delay margin on network topology: single delay case

Wei Qiao — Mon, 02 Apr 2012 14:18:42 PDT

The main objective in this paper is to capture the indirect relationship between the delay margin τ* of coupled systems and different graphs G these systems form via their different topologies, τ* = τ*(G). A four-agent linear time invariant (LTI) consensus dynamics is taken as a benchmark problem with a single delay τ and second-order agent dynamics. In this problem, six possible topologies with graphs G1,...,G6 exist without disconnecting an agent from all others. To achieve the objectives of the paper, we start with a recently introduced stability analysis technique called Advanced Clustering with Frequency Sweeping (ACFS) and reveal the...

Controller design for delay-independent stability of multiple time-delay systems via Déscartes's rule of signs

Ismail Ilker Delice — Mon, 02 Apr 2012 14:18:39 PDT

A general class of multi-input linear time-invariant (LTI) multiple time-delay system (MTDS) is investigated in order to obtain a control law which stabilizes the LTI-MTDS independently of all the delays. The method commences by reformulating the infinite-dimensional analysis as a finite-dimensional algebraic one without any sacrifice of accuracy and exactness. After this step, iterated discriminant allows one to construct a single-variable polynomial, coefficients of which are the controller gains. This crucial step succinctly formulates the delay-independent stability (DIS) condition of the controlled MTDS based on the roots of the single-variable polynomial. Implementation of the Déscartes's rule of signs then reveals,...

Exact upper and lower bounds of crossing frequency set and delay independent stability test for multiple time delayed systems

Ismail Ilker Delice — Mon, 02 Apr 2012 14:18:35 PDT

A general class of linear time invariant (LTI) multiple time-delay system is investigated in order to (i) obtain exact lower and upper bounds of crossing frequency set (CFS), and (ii) test the necessary and sufficient conditions of delay independent stability (DIS). The method commences by deploying Rekasius substitution for the transcendental terms in the characteristic function, reducing it into a finite dimensional one. After substitution, utilization of elimination theory allows one to achieve the two nontrivial objectives (i)-(ii). The approach is new and novel as it does not require any parameter sweeping and graphical display; it is exact and can...

Exact stability analysis of neutral systems with cross-talking delays

Nejat Olgac — Mon, 02 Apr 2012 14:18:32 PDT

The stability of neutral systems with two cross-talking delays is investigated using the method of cluster treatment of characteristic roots (CTCR). here are two main outcomes of this study: (a) Generation of the well-known delay stabilizability condition as a by-product of the CTCR procedure. This is achieved by a small delay stability treatment over the system. We also demonstrate for the delay-stabilizable systems the exact bounds of the stability regions in the domain of the delays. (b) Validation of these stability regions using an alternative point-wise algorithm, which computes the right-most roots of the characteristic quasi-polynomial.

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Analytical stability study of a deterministic car following model under multiple delay interactions

Rifat Sipahi — Mon, 02 Apr 2012 14:18:29 PDT

Analytical stability study of some deterministic car following models under time-delay influences is presented and various case studies are demonstrated. Interestingly, for some control law deployed by human drivers, more than one stability interval in the domain of time delay is revealed. Physical interpretations along with comparisons conclude the study.

Complete stability map of first order - two time delay systems with delay cross-talk

Rifat Sipahi — Mon, 02 Apr 2012 14:18:25 PDT

First order linear time invariant dynamics is taken into account with two delays. A unique feature is included in this study, from the stability perspective: a term that represents the cross-talk between the two delays. This class of systems can be treated by a unique procedure, which is recently developed, known as Cluster Treatment of Characteristic Roots (CTCR). In the text we present several case studies to display the steps and the strengths of CTCR. We also include some comparison results with respect to a cornerstone study (Hale, and Huang, 1993), which gives a wonderful point of reference for this...

Complete stability analysis of neutral‐type first order two‐time‐delay systems with cross‐talking delays

Rifat Sipahi — Mon, 02 Apr 2012 14:18:21 PDT

The stability robustness of first order linear time invariant dynamics of neutral type with multiple time delays against delay uncertainties is taken into consideration. We depart from a simpler investigation of Hale and Huang [J. Math. Anal. Appl., 178 (1993), pp. 344–362], which studies the same problem for retarded‐type systems. On this basis we further introduce two challenging features by including (a) terms that add neutral dynamics and (b) an additional term that introduces cross‐talk between the multiple delays. To the best of the authors’ knowledge, the stability posture of this class of systems can be treated only by a...

Stability robustness of retarded LTI systems with single delay and exhaustive determination of their imaginary spectra

Rifat Sipahi — Mon, 02 Apr 2012 14:18:18 PDT

In this paper we consider the stability robustness of the general class of vector LTI (linear time invariant) equations with a single delay, $\dot{\bf x}(t) = {\bf A}{\bf x}(t) + {\bf B}{\bf x}(t-\tau)$, ${\bf x} \in {\bf R}^n$. The robustness is against the uncertain, but constant delay, $\tau \in {\bf R}^+$. We first present a set of novel propositions and state that the solution must start from the complete knowledge of imaginary spectra of the system, and the corresponding delays. The propositions claim that such spectra form a set of manageably small number of members, and this number is upper...

A new perspective in the stability assessment of neutral systems with multiple and cross-talking delays

Nejat Olgac — Mon, 02 Apr 2012 14:18:15 PDT

The stability of neutral systems with two cross-talking delays is investigated using the method of cluster treatment of characteristic roots (CTCR). There are two main outcomes of this study: (a) we create the “strong stabilizability” (also called the “delay stabilizability”) of the system directly from the CTCR procedure. This is achieved by a small-delay stability treatment while performing the steps of the CTCR. For the “delay-stabilizable systems,” we also arrive at the exact bounds of the stability regions in the domain of the delays. (b) We deploy a point-wise algorithm which computes the rightmost roots of the characteristic quasi polynomial...

A note on Taylor's stability rule

Gerald G. Kleinstein — Mon, 13 Feb 2012 07:11:07 PST

Analyzing the stability of the interface between two fluids of different densities which is accelerating normal to its surface, Taylor concluded a rule that "this surface is stable or unstable according to whether the acceleration is directed from the heavier to the lighter fluid or vice versa." We show by following Taylor's analysis that in the range where the acceleration of the interface is in the direction of the gravitational acceleration and its magnitude is smaller, this rule reverses direction. The interface is stable or unstable according to whether the acceleration is from the lighter to the heavier fluid or...

Thermal conductivity of bovine serum albumin: a tool to probe denaturation of protein

Byoung Kyoo Park — Tue, 06 Dec 2011 11:54:48 PST

We demonstrate a strong correlation between denaturation of bovine serum albumin (BSA) and the thermal conductivity k of aqueous solutions of BSA. When denaturation of BSA began, k dropped significantly. These results suggest that k, i.e., the ability of a protein to transport passively applied thermal energy, can be exploited to probe the conformational dynamics of BSA and potentially of other proteins. The technique of protein analysis demonstrated in this work is expected to be useful in micro-total-analysis systems because it is easier to miniaturize and to integrate into a device than is conventional differential scanning calorimetry analysis.

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Impulsive displacement of a liquid in a pipe at high Reynolds numbers

Gerald G. Kleinstein — Mon, 22 Aug 2011 13:43:39 PDT

We consider the problem of an impulsive displacement of a liquid, originally at rest in a circular pipe, which is displaced by another liquid. The purpose of this analysis is to show that at a sufficiently high inertia the initial essentially inviscid motion can be extended to cover the entire displacement process, thus creating an inviscid window to which an inviscid analysis can be applied. We simplify the problem first, by considering a 1-liquid problem where the displacing liquid and displaced liquid are the same. We identify two characteristic times in this problem: the time it takes an inviscid liquid...

On the derivation of boundary conditions from the global principles of continuum mechanics

Gerald G. Kleinstein — Thu, 12 May 2011 13:36:03 PDT

We consider the motion of a fluid exterior to a moving rigid obstacle, or interior to a moving rigid shell. The boundary conditions, such as the no-slip condition and the condition of an isothermal wall, applied in the solution of the system of differential equations describing these motions, are currently assumed to be an approximation derived from experimental observation rather than an exact law. It is the purpose of this paper to show that the boundary conditions at a material interface between a fluid and a solid are derivable from the global principles of balance of continuum mechanics and the...

The measurement of magnetostriction constants of thin films using planar microwave devices and ferromagnetic resonance

S. E. Bushnell — Mon, 20 Dec 2010 13:21:21 PST

In this paper we introduce a new technique for measuring the saturation magnetostriction constant (λ_s) for isotropic polycrystalline thin films. The technique makes use of nonresonant planar microwave structures together with a novel stressing mechanism to induce a shift in the resonant field of a magnetic thin film as measured by a ferromagnetic resonance (FMR) experiment. Measurement of the shift induced by a uniaxial stress allows for determination of λ_s via a magnetic resonance analysis. Either a slotline device or coplanar waveguide (CPW) was used as the source of the microwave excitation field depending upon the orientation of the dc...

Structural and magnetic characterization of amorphous Gd₂Fe₁₄B thin films

S. E. Bushnell — Mon, 20 Dec 2010 12:57:37 PST

Thin amorphous films of nominal composition Gd₂Fe₁₄B were fabricated on Si (100) substrates using ion‐beam sputtering for the purpose of establishing their structural and magnetic properties at room temperature. X‐ray‐diffraction scans performed on as‐deposited and annealed films revealed an amorphous structure. The as‐deposited saturation magnetization was found to be 8101 G at room temperature suggesting ferrimagnetic ordering with anti‐parallel coupling similar to other heavy rare earth‐transition metal systems. Results from in‐plane and perpendicular ferromagnetic resonance experiments conducted at 9.108 GHz showed the films to be inhomogeneous. This was evident from the presence of two in‐plane resonance lines and spin‐wave spectra...

Silicon oxide micromodule capacitors

W. B. Nowak — Mon, 20 Dec 2010 12:35:29 PST

Silicon oxide capacitors have been developed on micromodule wafers (0.310-in. sq. with three termination notches per side). Each microelement contains 1, 2, 3, or 4 capacitors with values of 1120 and 560, 180, 100 and 68 pf per capacitor, respectively. The 1120 pf capacitor is double layered. In addition to the general requirements of microelements and micromodules, some of the more important specifications these capacitors must meet are: dissipation factor (DF) not exceeding 0.015, insulation resistance (IR) at 50 volts exceeding 10,000 megohms (25°C) and 750 megohms (125°c), 50 WVDC and 150 volts dielectric withstanding voltage (DWV), Δ C not...