A matrix perturbation view of the small world phenomenon

We use techniques from applied matrix analysis to study small world cutoff in a Markov chain. Our model consists of a periodic random walk plus uniform jumps. This has a direct interpretation as a teleporting random walk, of the type used by search engines to locate web pages, on a simple ring network. More loosely, the model may be regarded as an analogue of the original small world network of Watts and Strogatz [Nature, 393 (1998), pp. 440-442]. We measure the small world property by expressing the mean hitting time, averaged over all states, in terms of the expected number of shortcuts per random walk. This average mean hitting time is equivalent to the expected number of steps between a pair of states chosen uniformly at random. The analysis involves nonstandard matrix perturbation theory and the results come with rigorous and sharp asymptotic error estimates. Although developed in a different context, the resulting cutoff diagram agrees closely with that arising from the mean-field network theory of Newman, Moore, and Watts [Phys. Rev. Lett., 84 (2000), pp. 3201-3204]

Optimal VIA Placement in Under Filled Embedded Multimode Waveguides

The self-imaging property of multimode waveguides creates a challenging problem when finding the optimal placement position of an out-of-plane coupler for embedded waveguides. This problem is compounded when the waveguides are coupled using a small input such as a vertical cavity surface emitting laser (VCSEL) or a single mode fiber where only some of the modes are generated. When the waveguide system is under filled, the coupling efficiency for the optical vertical interconnect assembly (VIA) can vary by as much as 6.2 dB depending on the length of the proceeding waveguide due to different output fields from the self-imaging property. This requires sweeping each individual VIA over the entire range of possible coupler positions to find the total maximum coupling efficiency. This process increases in complexity when a VIA supports several parallel channels all having a different optical path length. If a VIA can be placed in a calculated position from the end of a terminated embedded waveguide dependent upon the modal structure then blind pick and place methods may be used. The optimal coupler placement was determined based on smallest average VIA attenuation, smallest attenuation variance, and worse-case alignment scenario

Finding optimal strategies for influencing social networks in two player games

Thesis (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, June 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 141).This thesis considers the problem of optimally influencing social networks in Afghanistan as part of ongoing counterinsurgency efforts. The social network is analyzed using a discrete time agent based model. Each agent has a belief [-0.5,0.5] and interacts stochastically pairwise with their neighbors. The network converges to a set of equilibrium beliefs in expectation. A 2-player game is formulated in which the players control a set of stubborn agents whose beliefs never change, and who wield significant influence in the network. Each player chooses how to connect their stubborn agents to maximally influence the network. Two different payoff functions are defined, and the pure Nash equilibrium strategy profiles are found in a series of test networks. Finding equilibrium strategy profiles can be difficult for large networks due to exponential increases in the strategy space but a simulated annealing heuristic is used to rapidly find equilibria using best response dynamics. We demonstrate through experimentation that the games formulated admit pure Nash equilibrium strategy profiles and that best response dynamics can be used to find them. We also test a scenario based on the author's experience in Afghanistan to show how nonsymmetric equilibria can naturally emerge if each player weights the value of agents in the network differently.by Nicholas J Howard.S.M

Research And Development Investment

The United States has long enjoyed a leadership role in research and development investment and they invest more in both basic and applied scientific research than any other country.  The U.S. preeminence in R&D investment, however, is at a critical point.  U.S. R&D investment has been declining as a percentage of the nation’s GDP since 2009, and in 2013, U.S. R&D investment is expected to decline in real dollars as well.  Declining investment in R&D is the result of budgetary constraints and the lack of political consensus as to the economic value of the government’s continued commitment to R&D programs.  This decline in U.S. investment comes at a time when global R&D investment is increasing significantly.  Economic rivals, led by China in particular, have made investment in R&D a core component of their plans for economic growth and have committed themselves to increasing and substantial R&D investment.  U.S. policymakers need to take action now to reverse what could become a policy trend of decreased government investment in R&D, which has both a short-term and long-term impact.  R&D spending is an “economic and employment driver” and ultimately employs 8.27 million U.S. workers, generating $1.238 trillion dollars to the U.S. economy.  In addition, government investment funds the majority of basic scientific research which, in the past, has led to such innovations as digital recording technology, communication satellites, global positioning systems (GPS), and the Internet.  It is unclear if the private sector alone can make up the difference in government R&D investment.  If the U.S. fails to protect its leadership position in R&D investment, it consequently risks its leadership in science, technology, productivity, and innovation which is the basis of the nation’s employment and economic activity

Direct load measurement of a wind turbine high speed shaft bearing in the field

Small piezoelectric transducers bonded to the outer raceway of a rolling element bearing can be used to send ultrasonic pulses to the element-raceway contact and receive reflections. Interpretation of the magnitude and time of flight (ToF) of the reflections can be used to deduce amount of load imparted between roller and raceway. The approach is most successful when the sensor is smaller than the area of contact. Then the sound field falls directly on the contact region. It is thus suited to large bearings, such as those found in wind turbines. In this work, we have used the approach on the rotor side high speed shaft bearing in a Vestas V42 600 kW wind turbine operating in the Barnesmore windfarm in Northern Ireland. The bearing is a SKF 32222 tapered roller bearing. The nature of the contact geometry meant that careful location of the transducer was required to ensure direct pulseecho reflection. The load directly imparted by the roller onto the raceway can be deduced from the change in time of flight of the reflected signal. This measurement is challenging because the change in time of flight is only a few nanoseconds. Nevertheless loads on each roller were determined and results were consistent with expectation. Functional over a period of 2 years, this validated method allows confident application in other sites such as pitch and main bearings to measure key inputs to prognostic algorithms derived from rig-based sensitivity studies, rather than optimistic ISO 281 calculations

Measurement of roller load, load variation, and lubrication in a wind turbine gearbox high speed shaft bearing in the field

The variability of applied load and the integrity of lubrication are crucial factors dictating the durability of wind turbine gearbox bearings. In this work, new ultrasonic reflectometry techniques have been implemented to measure both load and lubrication in the high-speed shaft bearing of a field operational Vestas V42 wind turbine gearbox. Miniature piezoelectric transducers were bonded onto the bearing outer raceway. The reflected pulses were used to infer bearing load and lubrication. Roller load measurements were seen to vary by 33% across the roller complement, with similar trend observed for reflection coefficient. Inspection of the reflection coefficient patterns were able to show whether the roller inlet region was fully flooded or partially starved, capturing the stochastic behaviour of bearing lubrication

Antisense Suppression of the Small Chloroplast Protein CP12 in Tobacco Alters Carbon Partitioning and Severely Restricts Growth

Abstract The thioredoxin-regulated chloroplast protein CP12 forms a multienzyme complex with the Calvin-Benson cycle enzymes phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). PRK and GAPDH are inactivated when present in this complex, a process shown in vitro to be dependent upon oxidized CP12. The importance of CP12 in vivo in higher plants, however, has not been investigated. Here, antisense suppression of CP12 in tobacco (Nicotiana tabacum) was observed to impact on NAD-induced PRK and GAPDH complex formation but had little effect on enzyme activity. Additionally, only minor changes in photosynthetic carbon fixation were observed. Despite this, antisense plants displayed changes in growth rates and morphology, including dwarfism and reduced apical dominance. The hypothesis that CP12 is essential to separate oxidative pentose phosphate pathway activity from Calvin-Benson cycle activity, as proposed in cyanobacteria, was tested. No evidence was found to support this role in tobacco. Evidence was seen, however, for a restriction to malate valve capacity, with decreases in NADP-malate dehydrogenase activity (but not protein levels) and pyridine nucleotide content. Antisense repression of CP12 also led to significant changes in carbon partitioning, with increased carbon allocation to the cell wall and the organic acids malate and fumarate and decreased allocation to starch and soluble carbohydrates. Severe decreases were also seen in 2-oxoglutarate content, a key indicator of cellular carbon sufficiency. The data presented here indicate that in tobacco, CP12 has a role in redox-mediated regulation of carbon partitioning from the chloroplast and provides strong in vivo evidence that CP12 is required for normal growth and development in plants.</jats:p

Plasma microRNA levels following resection of metastatic melanoma

Melanoma remains the leading cause of skin cancer–related deaths. Surgical resection and adjuvant therapies can result in disease-free intervals for stage III and stage IV disease; however, recurrence is common. Understanding microRNA (miR) dynamics following surgical resection of melanomas is critical to accurately interpret miR changes suggestive of melanoma recurrence. Plasma of 6 patients with stage III (n = 2) and stage IV (n = 4) melanoma was evaluated using the NanoString platform to determine pre- and postsurgical miR expression profiles, enabling analysis of more than 800 miRs simultaneously in 12 samples. Principal component analysis detected underlying patterns of miR expression between pre- vs postsurgical patients. Group A contained 3 of 4 patients with stage IV disease (pre- and postsurgical samples) and 2 patients with stage III disease (postsurgical samples only). The corresponding preoperative samples to both individuals with stage III disease were contained in group B along with 1 individual with stage IV disease (pre- and postsurgical samples). Group A was distinguished from group B by statistically significant analysis of variance changes in miR expression ( P < .0001). This analysis revealed that group A vs group B had downregulation of let-7b-5p, miR-520f, miR-720, miR-4454, miR-21-5p, miR-22-3p, miR-151a-3p, miR-378e, and miR-1283 and upregulation of miR-126-3p, miR-223-3p, miR-451a, let-7a-5p, let-7g-5p, miR-15b-5p, miR-16-5p, miR-20a-5p, miR-20b-5p, miR-23a-3p, miR-26a-5p, miR-106a-5p, miR-17-5p, miR-130a-3p, miR-142-3p, miR-150-5p, miR-191-5p, miR-199a-3p, miR-199b-3p, and miR-1976. Changes in miR expression were not readily evident in individuals with distant metastatic disease (stage IV) as these individuals may have prolonged inflammatory responses. Thus, inflammatory-driven miRs coinciding with tumor-derived miRs can blunt anticipated changes in expression profiles following surgical resection

Mineral Acquisition from Clay by Budongo Forest Chimpanzees

Chimpanzees of the Sonso community, Budongo Forest, Uganda were observed eating clay and drinking clay-water from waterholes. We show that clay, clay-rich water, and clay obtained with leaf sponges, provide a range of minerals in different concentrations. The presence of aluminium in the clay consumed indicates that it takes the form of kaolinite. We discuss the contribution of clay geophagy to the mineral intake of the Sonso chimpanzees and show that clay eaten using leaf sponges is particularly rich in minerals. We show that termite mound soil, also regularly consumed, is rich in minerals. We discuss the frequency of clay and termite soil geophagy in the context of the disappearance from Budongo Forest of a formerly rich source of minerals, the decaying pith of Raphia farinifera palms