École Polytechnique de Montréal

About: École Polytechnique de Montréal is a education organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 8015 authors who have published 18390 publications receiving 494372 citations.

Spacetime Metamaterials—Part II: Theory and Applications

Abstract: The overall article presents the authors’ vision of the emerging field of spacetime metamaterials, and related systems, in a cohesive and pedagogical perspective, systematically building up the physics, modeling, and applications of these media upon the foundation of their pure-space and pure-time counterparts. Following the first part, dealing with the general concepts underpinning spacetime metamaterials, this part establishes the theory of spacetime metamaterials and overviews some of their current and potential applications. It first describes the scattering phenomenology of a spacetime interface, the building brick of any spacetime metamaterial, and deduces the corresponding electromagnetic boundary conditions. Upon this basis, it derives the spacetime interface scattering (Fresnel-like) coefficients and frequency transitions, and subsequently generalizes time reversal to spacetime compansion (compression and expansion). Then, it illustrates the new physics of spacetime metamaterials with the examples of spacetime mirrors and cavities, the inverse prism and chromatic birefringence, and spacetime crystals. Next, it discusses various applications—categorized as frequency multiplication and mixing, matching and filtering, nonreciprocity and absorption, cloaking, electromagnetic processing, and radiation. Finally, the conclusion section provides a list of eight items that concisely summarizes the key results of this article, in completion to the list related to the general concepts in Part I.

Reconfigurable pipelined 2-D convolvers for fast digital signal processing

Abstract: In order to make software applications simpler to write and easier to maintain, a software digital signal-processing library that performs essential signal- and image-processing functions is an important part of every digital signal processor (DSP) developer's toolset In general, such a library provides high-level interface and mechanisms, therefore, developers only need to know how to use algorithms, not the details of how they work Complex signal transformations then become function calls, eg, C-callable functions Considering the two-dimensional (2-D) convolver function as an example of great significance for DSP's, this paper proposes to replace this software function by an emulation on a field-programmable gate array (FPGA) initially configured by software programming Therefore, the exploration of the 2-D convolver's design space will provide guidelines for the development of a library of DSP-oriented hardware configurations intended to significantly speed up the performance of general DSP processors Based on the specific convolver, and considering operators supported in the library as hardware accelerators, a series of tradeoffs for efficiently exploiting the bandwidth between the general-purpose DSP and accelerators are proposed In terms of implementation, this paper explores the performance and architectural tradeoffs involved in the design of an FPGA-based 2-D convolution coprocessor for the TMS320C40 DSP microprocessor available from Texas Instruments Incorporated However, the proposed concept is not limited to a particular processor

Mixer-Duplexer-Antenna Leaky-Wave System Based on Periodic Space-Time Modulation

Abstract: We present a mixer-duplexer-antenna leaky-wave system based on periodic space-time modulation. This system operates as a full transceiver, where the upconversion and downconversion mixing operations are accomplished via space-time transitions; the duplexing operation is induced by the nonreciprocal nature of the structure, and the radiation operation is provided by the leaky-wave nature of the wave. A rigorous electromagnetic solution is derived for the dispersion relation and field distributions. The system is implemented in the form of a spatio-temporally modulated microstrip leaky-wave structure incorporating an array of subwavelengthly spaced varactors modulated by a harmonic wave. In addition to the overall mixer-duplexer-antenna operation, frequency beam scanning at fixed input frequency is demonstrated as one of the interesting features of the system. A prototype is realized and demonstrated by full-wave and experimental results.

What does value mean in business‐to‐business professional services?

Abstract: Addresses the value definition and conceptualization issues in a business‐to‐business professional services context. Finds that results of exploratory research reveal that providers and organizational customers do not perceive value as a static concept; rather, the value definition comprises a time aspect and is associated with the exchange value during the transaction itself and value in use after the transaction. Discovers that value exchange is made up of a set of quality and relational criteria, whereas value in use refers to financial, social, operational and strategic performance and furthermore, perceptual differences may be explained by the presence of causal ambiguity which refers to differences in competency level between providers and customers, between hierarchical levels and professional services.

Geometrical variations in white and gray matter affect the biomechanics of spinal cord injuries more than the arachnoid space

Abstract: Traumatic spinal cord contusions lead to loss of quality of life, but their pathomechanisms are not fully understood. Previous studies have underlined the contribution of the cerebrospinal fluid in spinal cord protection. However, it remains unclear how important the contribution of the cerebrospinal fluid is relative to other factors such as the white/gray matter ratio. A finite element model of the spinal cord and surrounding morphologic features was used to investigate the spinal cord contusion mechanisms, considering subarachnoid space and white/gray matter ratio. Two vertebral segments (T6 and L1) were impacted transversely at 4.5ms-1, which demonstrated three major results: While the presence of cerebrospinal fluid plays a significant contributory role in spinal cord protection (compression percentage decreased by up to 19%), the arachnoid space variation along the spine appears to have a limited (3% compression decrease) impact; Differences in the white and gray matter geometries from lumbar to thoracic spine levels decrease spinal cord compression by up to 14% at the thoracic level ; Stress distribution in the sagittal spinal cord section was consistent with central cord syndrome, and local stress concentration on the anterior part of the spinal cord being highly reduced by the presence of cerebrospinal fluid. The use of a refined spinal cord finite element method showed that all the geometrical parameters are involved in the spinal cord contusion mechanisms. Hence, spinal cord injury criteria must be considered at each vertebral level.