Online gaming is a lucrative and growing industry but one that is slowed by cheating that compromises the gaming experience and hence drives away players (and revenue). In this paper we develop a technique by which game developers can enable game operators to validate the behavior of game clients as being consistent with valid execution of the sanctioned client software. Our technique employs symbolic execution of the client software to extract constraints on clientside state implied by each client-to-server message, and then uses constraint solving to determine whether the sequence of client-to-server messages can be "explained" by any possible user inputs, in light of the server-to-client messages already received. The requisite constraints and solving components can be developed either simultaneously with the game or retroactively for existing games. We demonstrate our approach in two case studies: one of the open-source game XPilot, and one of a game similar to Pac-Man of our own design.

In vivo molecular imaging enables non-invasive visualization of biological processes within living subjects, and holds great promise for diagnosis and monitoring of disease. The ability to create new agents that bind to molecular targets and deliver imaging probes to desired locations in the body is critically important to further advance this field. To address this need, phage display, an established technology for the discovery and development of novel binding agents, is increasingly becoming a key component of many molecular imaging research programs. This review discusses the expanding role played by phage display in the field of molecular imaging with a focus on in vivo applications. Furthermore, new methodological advances in phage display that can be directly applied to the discovery and development of molecular imaging agents are described. Various phage library selection strategies are summarized and compared, including selections against purified target, intact cells, and ex vivo tissue, plus in vivo homing strategies. An outline of the process for converting polypeptides obtained from phage display library selections into successful in vivo imaging agents is provided, including strategies to optimize in vivo performance. Additionally, the use To whom correspondence may be addressed (cochran1@stanford.edu) Abbreviations: scFv, single chain variable fragment; Fab, fragment antigen binding; ELISA, Enzyme-Linked Immunosorbent Assay; NEB, New England Biolabs; PET, positron emission tomography; SPECT, single photon emission computed tomography; NIR, near infrared; PEG, polyethylene glycol; SPARC, secreted protein acidic and rich in cysteine; VCAM-1, vascular cell adhesion molecule; MRI, magnetic resonance imaging; DOTA, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid; IC 50 , half maximal inhibitory concentration; CT, computed tomography; K D , equilibrium dissociation constant; EGFR, epidermal growth factor receptor; EGFR-ECD, EGFR extracellular domain; Aβ 42 , amyloid-beta; MMP, matrix metalloprotease; uPAR, urokinase-type plasminogen activator receptor; VEGF, vascular endothelial growth factor; IL-11, Interleukin-11; IL-11αR, Interleukin-11 α-receptor. 58F.V. CoChran and J.r. CoChran of phage particles as imaging agents is also described. In the latter part of the review, a survey of phage-derived in vivo imaging agents is presented, and important recent examples are highlighted. Other imaging applications are also discussed, such as the development of peptide tags for site-specific protein labeling and the use of phage as delivery agents for reporter genes. The review concludes with a discussion of how phage display technology will continue to impact both basic science and clinical applications in the field of molecular imaging.

In this paper, we investigate an approach to program synthesis that is based on crowd-sourcing. With the help of crowd-sourcing, we aim to capture the "wisdom of the crowds" to find good if not perfect solutions to inherently tricky programming tasks, which elude even expert developers and lack an easy-to-formalize specification. We propose an approach we call program boosting, which involves crowd-sourcing imperfect solutions to a difficult programming problem from developers and then blending these programs together in a way that improves their correctness. We implement this approach in a system called CROWDBOOST and show in our experiments that interesting and highly non-trivial tasks such as writing regular expressions for URLs or email addresses can be effectively crowd-sourced. We demonstrate that carefully blending the crowd-sourced results together consistently produces a boost, yielding results that are better than any of the starting programs. Our experiments on 465 program pairs show consistent boosts in accuracy and demonstrate that program boosting can be performed at a relatively modest monetary cost.

In this paper, we investigate an approach to program synthesis that is based on crowd-sourcing. With the help of crowd-sourcing, we aim to capture the "wisdom of the crowds" to find good if not perfect solutions to inherently tricky programming tasks, which elude even expert developers and lack an easy-to-formalize specification.We propose an approach we call program boosting, which involves crowd-sourcing imperfect solutions to a difficult programming problem from developers and then blending these programs together in a way that improves their correctness.We implement this approach in a system called CROWDBOOST and show in our experiments that interesting and highly non-trivial tasks such as writing regular expressions for URLs or email addresses can be effectively crowd-sourced. We demonstrate that carefully blending the crowd-sourced results together consistently produces a boost, yielding results that are better than any of the starting programs. Our experiments on 465 program pairs show consistent boosts in accuracy and demonstrate that program boosting can be performed at a relatively modest monetary cost.

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A calculation method for predicting the rate at which an oil slick will spread on water can also be used to predict the behavior of a slick that has been treated with a surface chemical collecting agent. Field and laboratory tests show that only a small quantity of the agent is needed to contain a slick for a considerable time. Introduction Highly important in designing an oil pollution control system is a knowledge of the growth rate of the oil slick. This information is particularly necessary if there is an impending spill so that a cleanup strategy can be planned before the spill occurs. This knowledge can also be applied to predict theoretically the behavior of an oil slick that has been treated with a surface chemical agent. A surface chemical agent is a compound that, when applied to the water surface, forms a thin layer that changes the surface tension characteristics of the water-air interface and thereby affects the spreading rate of oil on the water surface When a quantity of oil is added to a smooth water surface that has been treated by one of these compounds, the oil may form a stable circular lens. For such a stable lens to form, it is necessary that the spreading pressure, defined as w, - o, - ow, be negative. (Here w, o, and ow, represent the water-air, oil-air, and oil-water interfacial tensions, respectively.) Garrett and Barger have proposed the application of suitable surface chemical agents to prevent the uncontrolled spread of oil slicks on the open sea. If such slicks are left untreated, they will spread quickly, and on a calm sea several barrels of oil will spread as much as a mile a day. These large, thin oil slicks are very difficult to recover mechanically, but a suitable surface chemical agent applied to the perimeter will drastically affect their growth. If a slick is thicker than the stable lens, its growth decreases and eventually stops when the thickness equals that of the stable lens. If at first the slick is thinner than the stable lens, treating it with the agent mill cause it to shrink until its thickness equals that of the stable lens. For a typical crude oil the stable lens is about 1/2 cm thick, and for a 1,000-bbl spill this would correspond, assuming the slick is circular, to a stable diameter of only about 200 m. Because it is thicker, this slick can be removed by mechanical skimmers more easily than one that is left untreated. The chemicals used to control oil spills must be nontoxic and water insoluble and must have a high spreading pressure. Some chemicals that meet these requirements are the high-molecular-weight water-insoluble alcohols and acids such as steric acid and oleic acid. Additional substances are cited in Ref. 1. To understand how these surface chemical agents affect the spreading of oil on water it is necessary to identify and to understand the forces governing the growth of a slick. In the following sections we shall deal with the important forces, develop a related mathematical model, compare the model predictions with field test results, and predict the effects of surface chemical agents on the growth behavior of an oil slick. Forces Important in the Spreading of Oil Fig. 1 shows a cross-section of the oil-water-air interface of a growing oil slick. It shows that the forces acting on the slick are surface tension, pressure, and viscosity. pressure, and viscosity. JPT P. 781

A pulsed MPD arc has been operated to experimentally determine the occurrence of the rotating spoke mode of operation and to investigate voltage characteristics and spoke frequency of the MPD arc. It was found that the single rotating current spoke occurs at intermediate current levels above a critical magnetic field strength. A comparison of the spoke frequency measurements with the actuator-disk theory of Fay and Cochran shows that the actuatordisk model gives a satisfactory prediction of the behavior of the spoke frequency until a limiting frequency is reached after which the spoke approaches a constant rotational speed which is the same for all gases. The variation in the electrode voltage was found to obey the correlation of Patrick and Schneiderman when the arc was operated in the diffuse mode at lowpower levels. In the spoke mode voltages several times this prediction were measured and can be explained in terms of the EMF generated by the rotating spoke. Several criteria are suggested which predict the observed spoke/no-spoke boundaries. Nomenclature a 2 = sound speed of gas at arc exit A = channel cross-sectional area downstream of arc B -magnetic field strength CD = nondimensional drag coefficient d = radial electrode gap D = width of arc e = charge of an electron E = electric field 7 = total current j = current density I = mean electrode radius ra = mass flow rate m = mass of a molecule n e = electron number density n = molecule number flow rate T = gas temperature U = gas speed U c = critical speed V e = electrode voltage VQ = sum of voltage drops in electrode boundary layers /3= constant of order one CD = dissociation energy €i = ionization energy /io = permeability of free space p = density a--electrical conductivity co = angular velocity a)«T e -Hall parameter Subscripts r, z, 9 = radial, axial, and azimuthal components

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