Dynamic diffracting trees

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 109-111).by Giovanni M. Della-Libera.M.Eng

Quiescent consistency: Defining and verifying relaxed linearizability

Concurrent data structures like stacks, sets or queues need to be highly optimized to provide large degrees of parallelism with reduced contention. Linearizability, a key consistency condition for concurrent objects, sometimes limits the potential for optimization. Hence algorithm designers have started to build concurrent data structures that are not linearizable but only satisfy relaxed consistency requirements. In this paper, we study quiescent consistency as proposed by Shavit and Herlihy, which is one such relaxed condition. More precisely, we give the first formal definition of quiescent consistency, investigate its relationship with linearizability, and provide a proof technique for it based on (coupled) simulations. We demonstrate our proof technique by verifying quiescent consistency of a (non-linearizable) FIFO queue built using a diffraction tree. © 2014 Springer International Publishing Switzerland

Using natural means to reduce surface transport noise during propagation outdoors

This paper reviews ways of reducing surface transport noise by natural means. The noise abatement solutions of interest can be easily (visually) incorporated in the landscape or help with greening the (sub)urban environment. They include vegetated surfaces (applied to faces or tops of noise walls and on building façades and roofs ), caged piles of stones (gabions), vegetation belts (tree belts, shrub zones and hedges), earth berms and various ways of exploiting ground-surface-related effects. The ideas presented in this overview have been tested in the laboratory and/or numerically evaluated in order to assess or enhance the noise abatement they could provide. Some in-situ experiments are discussed as well. When well-designed, such natural devices have the potential to abate surface transport noise, possibly by complementing and sometimes improving common (non-green) noise reducing devices or measures. Their applicability strongly depends on the available space reserved for the noise abatement and the receiver position

Development of a Spatial Filtering Apparatus

This thesis contains a discussion of the theoretical background for Fourier spatial filtering and a description of the design and construction of a portable in-class spatial filtering apparatus. A portable, in-class spatial filtering demonstration apparatus was designed and built. This apparatus uses liquid crystal display (LCD) panels from two projectors as the object and filter masks. The blue LCD panel from the first projector serves as the object mask, and the red panel from the second projector serves as the filter mask. The panels were extracted from their projectors and mounted onto aluminum blocks which are held in place by optical component mounts. Images are written to the LCD panels via custom open source software developed for this apparatus which writes independent monochromatic images to the video signal. The software has two monochromatic image windows, basic image manipulation tools, and two video feed input display windows. Two complementary metal-oxide semiconductor (CMOS) sensors are positioned to record the reconstructed image of the object mask and the diffraction pattern created by the object mask. The object and filter mask can be digitally changed and the effects on the filtered image and diffraction pattern can be observed in real-time. The entire apparatus is assembled onto a rolling cart which allows it to be easily taken into classrooms

Twisting structures and strongly homotopy morphisms

In an application of the notion of twisting structures introduced by Hess and Lack, we define twisted composition products of symmetric sequences of chain complexes that are degreewise projective and finitely generated. Let Q be a cooperad and let BP be the bar construction on the operad P. To each morphism of cooperads g from Q to BP is associated a P-co-ring, K(g), which generalizes the two-sided Koszul and bar constructions. When the co-unit from K(g) to P is a quasi-isomorphism, we show that the Kleisli category for K(g) is isomorphic to the category of P-algebras and of their morphisms up to strong homotopy, and we give the classifying morphisms for both strict and homotopy P-algebras. Parametrized morphisms of (co)associative chain (co)algebras up to strong homotopy are also introduced and studied, and a general existence theorem is proved. In the appendix, we study the particular case of the two-sided Koszul resolution of the associative operad.Comment: 54 page

A computational model for path loss in wireless sensor networks in orchard environments.

A computational model for radio wave propagation through tree orchards is presented. Trees are modeled as collections of branches, geometrically approximated by cylinders, whose dimensions are determined on the basis of measurements in a cherry orchard. Tree canopies are modeled as dielectric spheres of appropriate size. A single row of trees was modeled by creating copies of a representative tree model positioned on top of a rectangular, lossy dielectric slab that simulated the ground. The complete scattering model, including soil and trees, enhanced by periodicity conditions corresponding to the array, was characterized via a commercial computational software tool for simulating the wave propagation by means of the Finite Element Method. The attenuation of the simulated signal was compared to measurements taken in the cherry orchard, using two ZigBee receiver-transmitter modules. Near the top of the tree canopies (at 3 m), the predicted attenuation was close to the measured one-just slightly underestimated. However, at 1.5 m the solver underestimated the measured attenuation significantly, especially when leaves were present and, as distances grew longer. This suggests that the effects of scattering from neighboring tree rows need to be incorporated into the model. However, complex geometries result in ill conditioned linear systems that affect the solver's convergence

An in-depth analysis and modelling of the Shuttle to MILA S-band telemetry link

The S-Band radio frequency (RF) link between the Merritt Island (MILA) Tracking Station and the Space Shuttle launch pads is a critical communication path for prelaunch and launch operations. The proposed siting of the Center for Space Education (CSE) at the Visitor Center required a study to avoid RF line-of-sight blockage and reflection paths. The study revealed the trees near MILA's 9-meter (9-M) antennas are obstructing the optical line-of-sight. The studies found diffraction is the main propagation mechanism. This paper describes a link model based on the Geometric Theory of Diffraction

Internal composition, structure, and hydrological significance of rock glaciers in the Eastern Cascades, Washington

Low summer river base flow places a strain on natural and economic resources of the Eastern Cascades. A major contributor to stream flow in this region is snow pack which has declined over the past few decades because of a warming climate. In addition, glacial runoff, which contributes significantly to base flow in summer dry periods, will diminish from glacial recession. However, rock glaciers, because their internal ice (i.e., permafrost) is insulated by an outer debris layer, react slowly to climate change, thus acting as sinks for ice and liquid water storage in mountain environments. This study utilized ground penetrating radar (GPR) to investigate the internal structure, composition, and hydrological significance of a sample of nine Eastern Cascade rock glaciers. Analysis reveals that active layer thickness for all active rock glaciers are similar with an average of 3.4 meters (m). In addition, linear reflectors deeper in the profiles indicate bedrock and accurately depict the overall rock glacier depth. Other internal stratigraphic features show thrust planes throughout different sections of the profile which are closely tied to slope angle. Further, GPR shows the presence of massive (i.e., solid) or interstitial internal permafrost indicating glaciogenic or talus origins. Through measurements of rock glacier base depth and the active layer, this study was able to improve on previous research for estimating the total volume of ice-rich permafrost in these features. Results show a 64 percent over-estimation of permafrost-rich layer thickness using methods from previous studies. These show that previous studies over-estimate the hydrological significance of rock glaciers in comparison to ice glaciers. Results indicate a ratio of volume of rock glacier to ice glacier ice-water equivalence of 1:46 in the Eastern Cascades. In turn, results indicate Eastern Cascade rock glaciers rank similarly in terms of hydrological significance to other mountain ranges around the globe. While rock glaciers in this region will continue to contribute to base flow, they will not totally compensate for the inevitable loss of ice glaciers. This research provides insight for water management for the Eastern Cascades experiencing shifting water resources due to a warming climate