Alejandro López‐Ortiz

Centro de Investigación en Materiales Avanzados

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V. Collins-Martı́nez

Centro de Investigación en Materiales Avanzados

Reza Dorrigiv

Samsung (United States)

Shahin Kamali

York University

Alejandro Salinger

Systems, Applications & Products in Data Processing (Germany)

J. Ian Munro

University of Waterloo

Jesús Salinas Gutiérrez

Centro de Investigación en Materiales Avanzados

Miguel A. Escobedo-Bretado

Universidad Juárez del Estado de Durango

Erik D. Demaine

Vassar College

Virginia Hidalina Collins Martinez

Jesús M. Salinas-Gutiérrez

Centro de Investigación en Materiales Avanzados

Cooperative Institutions

University of Waterloo

Centro de Investigación en Materiales Avanzados

Saarland University

University of Alberta

Concordia University

University of Windsor

Concordia University

University of Regina

Centre National de la Recherche Scientifique

Max Planck Society

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Low temperature sugar cane bagasse pyrolysis for the production of high purity hydrogen through steam reforming and CO2 capture

International Journal of Hydrogen Energy (2013)

Alejandro López‐Ortiz F.J. Neri Segura Raúl Sandoval Jabalera Marcos Marques da Silva Paula E. Arias del Campo

Bagasse

Isothermal process

10.1016/j.ijhydene.2013.06.059

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Citations (9)

Comparative Study of Zn2Ti3O8 and ZnTiO3 Photocatalytic Properties for Hydrogen Production

Catalysts (2020)

Juan C. Pantoja-Espinoza Jorge L. Domínguez-Arvizu Jaime A. Jiménez-Miramontes Blanca C. Hernández-Majalca M.J. Meléndez-Zaragoza

In the present work, zinc titanates (ZTO) as photocatalysts were synthesized, characterized, and evaluated aiming to study their photocatalytic properties for hydrogen production under visible-light irradiation and employing MeOH (methanol) and TEOA (Triethanolamine) as sacrificial agents. ZTO were synthesized by modified Pechini method. Characterization of materials consisted in TGA, XRD, TEM, EELS, BET, and UV–Vis. Surface interaction studies consisted of FT-IR spectroscopy and determination of MeOH and TEOA adsorption–desorption capacities on the ZTO by TGA. Zinc titanates were evaluated as photocatalyst for H2 production using an artificial visible light and monitored by GC. TGA results led to establish calcination temperatures of 550 °C (Zn2Ti3O8) and 700 °C (ZnTiO3) to reach their crystalline phases. XRD analysis of sample cds-ZTO found cubic Zn2Ti3O8 and traces of the ZnO crystalline phase, while p-ZTO exhibited a mixture of cubic and hexagonal ZnTiO3 crystalline phases. Surface area for cds-ZTO was 88 m2/g, while ZnTiO3 had 13 m2/g. Photocatalytic H2 production for cds-ZTO and p-ZTO using TEOA as sacrificial agent showed the highest photocatalytic activities generating 548 and 441 µmolH2/h.gcat. TEOA adsorption–desorption capacity was found superior on cds-ZTO and p-ZTO than that for MeOH on both samples.

Triethanolamine

Visible spectrum

10.3390/catal10121372

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Citations (14)

Editorial for the XII-SMH International Congress special issue

International Journal of Hydrogen Energy (2013)

Alejandro López‐Ortiz

10.1016/j.ijhydene.2013.08.050

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Synthesis, characterization and photocatalytic evaluation of potassium hexatitanate (K2Ti6O13) fibers

International Journal of Hydrogen Energy (2018)

Miguel A. Escobedo-Bretado María Azucena González-Lozano V. Collins Martínez Alejandro López‐Ortiz Miguel Meléndez Zaragoza

Characterization

Specific surface area

10.1016/j.ijhydene.2018.06.085

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Citations (23)

Large Profits or Fast Gains: A Dilemma in Maximizing Throughput with Applications to Network Processors

arXiv (Cornell University) (2012)

Kirill Kogan Alejandro López‐Ortiz Gabriel Scalosub Michael Segal

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Fast string sorting using order-preserving compression

ACM Journal of Experimental Algorithmics (2005)

Alejandro López‐Ortiz Mehdi Mirzazadeh Mohammad Ali Safari Hossein Sheikhattar

We give experimental evidence for the benefits of order-preserving compression in sorting algorithms. While, in general, any algorithm might benefit from compressed data because of reduced paging requirements, we identified two natural candidates that would further benefit from order-preserving compression, namely string-oriented sorting algorithms and word-RAM algorithms for keys of bounded length. The word-RAM model has some of the fastest known sorting algorithms in practice. These algorithms are designed for keys of bounded length, usually 32 or 64 bits, which limits their direct applicability for strings. One possibility is to use an order-preserving compression scheme, so that a bounded-key-length algorithm can be applied. For the case of standard algorithms, we took what is considered to be the among the fastest nonword RAM string sorting algorithms, Fast MKQSort, and measured its performance on compressed data. The Fast MKQSort algorithm of Bentley and Sedgewick is optimized to handle text strings. Our experiments show that order-compression techniques results in savings of approximately 15% over the same algorithm on noncompressed data. For the word-RAM, we modified Andersson's sorting algorithm to handle variable-length keys. The resulting algorithm is faster than the standard Unix sort by a factor of 1.5 X . Last, we used an order-preserving scheme that is within a constant additive term of the optimal Hu--Tucker, but requires linear time rather than O ( m log m ), where m = |Σ| is the size of the alphabet.

Online algorithm

10.1145/1064546.1180611

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Citations (3)

TiO<sub>2</sub> Films Synthesis over Polypropylene by Sol-Gel Assisted with Hydrothermal Treatment for the Photocatalytic Propane Degradation

Green and Sustainable Chemistry (2014)

Vanessa Guzmán-Velderrain Yudith Ortega López Jesús Salinas Gutiérrez Alejandro López‐Ortiz V. Collins-Martı́nez

The present investigation shows experimental results obtained with TiO2 thin films synthesized by the sol-gel method assisted with hydrothermal treatment over polypropylene, using the dip coating technique. Obtained coatings were characterized through SEM, XRD, UV-Vis and the photo- catalytic activity was monitored by GC. According to results, the hydrothermal treatment facilitates the crystallization of the TiO2 anatase phase, which is present in all synthesized films. Crystal size formed from precursor solutions (estimated by the Scherrer's equation) depends on the time and temperature of the hydrothermal treatment, wherein solution exposed to a higher temperature treatment of 150。C for 1.5 h (H150/1.5) exhibited a larger crystal size compared to those synthesized at 80。C for 1.5 h and 3 h (H80/1.5 and H80/3). Sample H150/1.5 over polypropylene resulted in a uniform and crack free coating. This behavior was attributed to the precursor solution being denser than those synthesized at 80。C. Additionally, the photocatalytic activity of the coatings was evaluated through the degradation of propane. Coating H150/1.5 reached 100% conversion after 3 h of UV light irradiation.

Propane

Polypropylene

Degradation

Dip-coating

Hydrothermal Synthesis

10.4236/gsc.2014.43017

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Citations (5)

On the separation and equivalence of paging strategies

Symposium on Discrete Algorithms (2007)

Spyros Angelopoulos Reza Dorrigiv Alejandro López‐Ortiz

It has been experimentally observed that LRU and variants thereof are the preferred strategies for on-line paging. However, under most proposed performance measures for on-line algorithms the performance of LRU is the same as that of many other strategies which are inferior in practice. In this paper we first show that any performance measure which does not include a partition or implied distribution of the input sequences of a given length is unlikely to distinguish between any two lazy paging algorithms as their performance is identical in a very strong sense. This provides a theoretical justification for the use of a more refined measure. Building upon the ideas of concave analysis by Albers et al. [AFG05], we prove strict separation between LRU and all other paging strategies. That is, we show that LRU is the unique optimum strategy for paging under a deterministic model. This provides full theoretical backing to the empirical observation that LRU is preferable in practice.

Paging

10.5555/1283383.1283408

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Citations (74)

Combinatorial and Algorithmic Aspects of Networking

Lecture notes in computer science (2005)

Alejandro López‐Ortiz Angèle M. Hamel

10.1007/11527954

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Citations (10)

Capacity Provisioning a Valiant Load-Balanced Network

A. R. Curtis Alejandro López‐Ortiz

Valiant load balancing (VLB), also called two-stage load balancing, is gaining popularity as a routing scheme that can serve arbitrary traffic matrices. To date, VLB network design is well understood on a logical full-mesh topology, where VLB is optimal even when nodes can fail. In this paper, we address the design and capacity provisioning of arbitrary VLB network topologies. First, we introduce an algorithm to determine if VLB can serve all traffic matrices when a fixed number of arbitrary links fail, and we show how to find a min-cost expansion of the network - via link upgrades and installs - so that it is resilient to these failures. Additionally, we propose a method to design a new VLB network under the fixed-charge network design cost model. Finally, we prove that VLB is no longer optimal on unrestricted topologies, and can require more capacity than shortest path routing to serve all traffic matrices on some topologies. These results rely on a novel theorem that characterizes the capacity VLB requires of links crossing each cut, i.e., a partition, of the network's nodes.

Provisioning

Network partition

10.1109/infcom.2009.5062276

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Citations (5)