Microscale materials testing using MEMS actuators

Small size scale and high resolutions in force and displacement measurements make MEMS actuators appropriate for micromechanical testing. In this paper, for the first time, we present methodologies for uniaxial tensile and cantilever bending testing of both micrometer- and submicrometer-scale freestanding specimens using MEMS actuators. We also introduce dry fabrication processes for the specimens. The methodologies allow freestanding single or multilayered thin-film specimens to be fabricated separately from the MEMS actuators. For the uniaxial tension test, tensile forces are applied by lateral comb drive actuators capable of generating a total load of 383 μN at 40 V with resolutions on the order of 3 nN. A similar actuator is used in the bending test, with load resolution of 58 nN and spring constant of 0.78 N/m. The tensile testing methodology is demonstrated with the testing of a 110-nm-thick freestanding aluminum specimen. The cantilever bending experiment is performed on a 100-nm-thick aluminum specimen. The experimental setups can be mounted in a SEM (and also in a TEM after modifications for tensile testing) for in situ observation of materials behavior under different environmental conditions. Remarkable strengthening is observed in all the specimens tested compared to their bulk counterparts in both tensile and bending experiments. Experimental results highlight the potential of MEMS actuators as a new tool for materials research     

Vortex structure in high-T c ceramic superconductors

We consider penetration of magnetic flux in the rare earth ceramic superconductors within the framework of a generalized Ginzburg-Landau theory, based on the coexistence of antiferromagnetism and superconductivity. We study vortex structure produced for a magnetic field close to . We make a new prediction that may serve to test the theory experimentally.     

A survey on resource allocation in high performance distributed computing systems

An efficient resource allocation is a fundamental requirement in high performance computing (HPC) systems. Many projects are dedicated to large-scale distributed computing systems that have designed and developed resource allocation mechanisms with a variety of architectures and services. In our study, through analysis, a comprehensive survey for describing resource allocation in various HPCs is reported. The aim of the work is to aggregate under a joint framework, the existing solutions for HPC to provide a thorough analysis and characteristics of the resource management and allocation strategies. Resource allocation mechanisms and strategies play a vital role towards the performance improvement of all the HPCs classifications. Therefore, a comprehensive discussion of widely used resource allocation strategies deployed in HPC environment is required, which is one of the motivations of this survey. Moreover, we have classified the HPC systems into three broad categories, namely: (a) cluster, (b) grid, and (c) cloud systems and define the characteristics of each class by extracting sets of common attributes. All of the aforementioned systems are cataloged into pure software and hybrid/hardware solutions. The system classification is used to identify approaches followed by the implementation of existing resource allocation strategies that are widely presented in the literature.     

SRA-MSDU: Enhanced A-MSDU frame aggregation with selective retransmission in 802.11n wireless networks

The main goal of the IEEE 802.11n standard is to achieve more than 100 Mbps of throughput at the MAC service access point. This high throughput has been achieved via many enhancements in both the physical and MAC layers. One of the MAC enhancements is the frame aggregation in which multiple frames are concatenated into a single large frame before being transmitted. The 802.11n MAC layer defines two types of aggregation, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). The A-MPDU outperforms A-MSDU due to its large aggregation size and the subframes retransmission in erroneous channels. However, in error free channels and under the same aggregation size the A-MSDU performs better than the A-MPDU due to its smaller headers. Thus, adding a selective retransmission capability to the A-MSDU would improve the system performance. In this paper, we have proposed an MSDU frame aggregation scheme that enables selective retransmission at the MSDU level without altering the original MAC header. In this proposed scheme an implicit sequence control mechanism has been introduced in order to keep the frames in sequence and preserve their correct order at the receiver side. The results show that the proposed scheme improves the system performance in terms of throughput and delay even under highly erroneous channels.     

On a tunable bistable MEMS-theory and experiment

A tunable micromechanical bistable system is presented in this paper. It consists of a long slender micromechanical beam attached to an actuator. The beam is subjected to a transverse force at the middle and a residual stress developed during fabrication. The actuator generates a force along the axial direction of the beam, and is shared by the beam and springs of the actuator. If the total axial load on the beam is compressive and exceeds a critical value, then the beam buckles along the transverse direction and it has two possible equilibrium states. Thus, the actuator and beam together become a bistable system. An analytical model is presented to characterize the system. The model is based on the first mode of buckling of the beam. The model accounts for the elastic axial shortening of the beam and the nonlinear coupling between the beam and actuator. The main result of this paper is a closed-form relation between the transverse force and corresponding equilibrium transverse displacement of the beam for a given actuator force. An experimental micromechanical device is designed and fabricated to verify the theoretical model. Excellent correspondence is found between theory and experiment, as if the experimental device emulates the mathematical model, which is an important result of this paper, since now experimental studies, both quasi-static and dynamic, of bistable systems are possible, which are otherwise difficult to conduct with macrosystems. Several examples of possible applications of the bistable system are provided, including digital sensing of physical parameters     

Timely vs. delayed CEO turnover

This paper investigates changes in company performance following timely versus delayed CEO resignations due to financial wrongdoings. A timely resignation is proactively pushed by the company, and a delayed resignation is driven by investigations initiated by the SEC or other regulatory authorities. Our results show significant negative abnormal returns following the announcement of CEO resignations. In addition, compared with timely resignations, delayed resignations experience a larger and longer lasting negative stock market reaction. This suggests that CEO resignations due to financial wrongdoings are not perceived as good news by investors, and the delayed resignations could make investors lose more confidence, possibly because of worries about the ineffective corporate governance and supervision mechanism. We have found a significant negative relationship between CEO-chairman duality and the timeliness of CEO resignations. Our results have important implications for investors and policy makers.     

Effects of maternal antibodies on protection and development of antibody responses to human rotavirus in gnotobiotic pigs

Although maternal antibodies can protect against infectious disease in infancy, they can also suppress active immune responses. The effects of circulating maternal antibodies, with and without colostrum and milk antibodies, on passive protection and active immunity to human rotavirus (HRV) were examined in gnotobiotic pigs. Pigs received intraperitoneal injections of high-titer serum (immune pigs [groups 1 and 2]) from immunized sows, low-titer serum from naturally infected sows (control pigs [groups 3 and 4]), or no serum (group 5). Immune or control colostrum and milk were added to the diet of groups 2 and 4, respectively. After inoculation (3 to 5 days of age) and challenge (postinoculation day [PID] 21) with virulent HRV, the effects of maternal antibodies on protection (from diarrhea and virus shedding), and on active antibody responses (measured by quantitation of antibody-secreting cells [ASC] in intestinal and systemic lymphoid tissues by ELISPOT) were evaluated. Groups 1 and 2 had significantly less diarrhea and virus shedding after inoculation but higher rates of diarrhea and virus shedding after challenge than did groups 3 and 5. Group 1 and 2 pigs had significantly fewer immunoglobulin A (IgA) ASC in intestinal tissues at PID 21 and at postchallenge day (PCD) 7 compared to group 5. Significantly fewer IgG ASC were present in the intestines of group 2 pigs at PID 21 and PCD 7 compared to group 5. There was a trend towards fewer ASC in intestinal tissues of group 2 than group 1, from PID 21 on, with significantly fewer IgA ASC at PCD 7. IgG ASC in the duodenum and mesenteric lymph nodes of group 3 and 4 pigs were significantly fewer than in group 5 at PCD 7. These decreases in ASC emphasize the role of passive antibodies in impairing induction of ASC rather than in merely suppressing the function of differentiated B cells. To be successful, vaccines intended for populations with high titers of maternal antibodies (infants in developing countries) may require higher titers of virus, multiple doses, or improved delivery systems, such as the use of microencapsulation or immune stimulating complexes, to overcome the suppressive effects of maternal antibodies.     

Nonlinear dynamic study of a bistable MEMS: model and experiment

In the Journal of Microelectromechanical Systems (see vol. 11, pp. 574-583, Oct. 2002), we presented an actuation scheme for toggling a bistable MEMS, a buckled beam, from one stable state to the other using radiation pressure of light. The experiments revealed some anomalous behavior of the beam. While long duration laser pulses at a power level slightly above the toggle threshold reliably toggled the beam every time, short duration pulses of the same power toggled the beam only about two-thirds of the time. In addition, when excessively high power levels (far above the toggle threshold) were used, the beam would not reliably toggle regardless of the pulse duration. This paper resolves the anomaly. It presents a nonlinear dynamical analysis of the bistable beam device which explains the anomaly as follows: a slightly higher than threshold force, applied for sufficient time, toggles the beam. If the force duration is longer than the time of decay of the oscillation of the beam about the toggled state, then the beam remains in that state after the force is removed. Otherwise, the beam may return to the original state. On the other hand, if the beam is toggled by a force far above the threshold, then after removal of the force, the beam may oscillate spanning both the states until the motion decays and the beam settles down to one of the states, not necessarily the toggled state, which may appear to be an anomalous behavior. The theoretical model is validated by a series of toggling experiments.     

Image forgery detection using image similarity

Multimedia Tools and Applications - Ideally, sophisticated image forgery methods leave no perceptible evidence of tampering. In response to such stringent context, researchers have proposed digital...