Conference Session

ChE: Innovation in the Laboratory

Collection

2006 Annual Conference & Exposition

Authors

Edgar Clausen, University of Arkansas; William Penney, University of Arkansas

Tagged Divisions

Chemical Engineering

2006-1488: LABORATORY DEMONSTRATIONS/EXPERIMENTS IN FREE ANDFORCED CONVECTION HEAT TRANSFEREdgar Clausen, University of Arkansas EDGAR C. CLAUSEN Dr. Clausen currently serves as Adam Professor of Chemical Engineering at the University of Arkansas. His research interests include bioprocess engineering (fermentations, kinetics, reactor design, bioseparations, process scale-up and design), gas phase fermentations, and the production of energy and chemicals from biomass and waste. Dr. Clausen is a registered professional engineer in the state of Arkansas.William Penney, University of Arkansas W. ROY PENNEY Dr. Penney currently serves as Professor of Chemical Engineering at the University

Conference Session

Laboratory Learning in Biomedical Engineering (Works in Progress) - June 24th

Collection

2020 ASEE Virtual Annual Conference Content Access

Authors

Scott Howard Seidman, University of Rochester

Tagged Divisions

Biomedical Engineering

Paper ID #30210Work In Progress: Interfacing with microcontrollers: an onlinelaboratory learning experienceDr. Scott Howard Seidman PhD, University of Rochester American c Society for Engineering Education, 2020 WORK IN PROGRESS: INTERFACING WITH MICROCONTROLLERS: AN ONLINE LEARNING EXPERIENCEAn online learning experience for resident students entitled “Interfacing with Microcontrollers” has beendesigned and implemented. This is a 2-credit laboratory course offered in online format using theBlackboard LMS. This course, offered within the Department of Biomedical Engineering and

Conference Session

Innovations in Experiments and Modeling

Collection

2024 ASEE Annual Conference & Exposition

Authors

Robert P. Hesketh, Rowan University; Barnabas Gao, Rowan University; Kirti M Yenkie, Rowan University; Swapana Subbarao Jerpoth, Rowan University; David Anthony Theuma, Rowan University; Sean Curtis, Rowan University; Michael Fracchiolla, Rowan University; C. Stewart Slater, Rowan University; Mariano Javier Savelski, Rowan University; Steven Roth, Rowan University; Emma Marie Padros, Rowan University

Tagged Divisions

Chemical Engineering Division (ChED)

research awards. He has made major contributions in laboratory methods that demonstrate chemical engineering practice and principles. These highly visual and effective experiments, the most notable using the vehicle of a coffeemaker, are used to introduce engineering design and science to university and pre-college students. This work has been presented at national meetings, workshops and published in journals and proceedingsMr. Barnabas Gao, Rowan University Barnabas Gao is a passionate chemical engineer currently pursuing his PhD at Rowan University in Glassboro, New Jersey. He received his Bachelor of Science degree from Kwame Nkrumah University of Science and Technology in Ghana. His research is centered around

Conference Session

Unique Laboratory Experiments & Programs

Collection

2003 Annual Conference

Authors

Hyun Kim

that reinforce students’ understanding on fundamentals of “Proceedings of the American Society for Engineering education Annual Conference & Exposition Copyright 2003, American Society for Engineering Education” 1thermodynamics and heat transfer. The course emphasizes design of thermal systems andcomponents and experiments that students create for themselves. The laboratory is equipped witha number of commercial bench-top, wall-mounted, and stand-alone experimental equipment whichallows students to conduct a variety of experiments on temperature measurement, calorimetry,heat conduction, forced and free convection, heat exchangers, radiation heat transfer

Conference Session

ECE Laboratory Design

Collection

2006 Annual Conference & Exposition

Authors

Dick Blandford, University of Evansville

Tagged Divisions

Electrical and Computer

2006-1313: DSP ON GENERIC MACHINESDick Blandford, University of Evansville Dr. Dick K. Blandford is the Chair of the Electrical Engineering and Computer Science Department at the University of Evansville. Page 11.499.1© American Society for Engineering Education, 2006 DSP on Generic MachinesAbstractMany electrical engineering classes which introduce digital signal processing at theundergraduate level include a laboratory component in which students implement systems ondedicated DSP boards. Many such boards are programmed in an unfamiliar assembly languageor they require cumbersome I/O drivers

Conference Session

How to Effectively Teach Using Teams

Collection

2007 Annual Conference & Exposition

Authors

Steven Burian, University of Utah; Pedro Romero, University of Utah; Steven Bartlett, University of Utah

Tagged Divisions

Civil Engineering

attributes of a leader periodically by the instructor orteaching assistant and is then assigned full responsibility for the laboratory including directingpreparations for the experiment (Fig. 1), designating experiment duties, and guiding the reportthrough completion. The team leader rates the team members and the team members rate theteam leader in specified categories. The team leader is also graded by the instructor based on theinformation contained in the memo or summary grade sheet (reflecting organization, efficientuse of resources, leading by example) and quality of the laboratory report. Introspective teamdiscussions are encouraged to self-analyze team dynamics and develop plan to improve.In Hydraulics, the report format, team dynamics, and

Conference Session

Lab Experiments in Materials Science

Collection

2002 Annual Conference

Authors

Terry Creasy; Richard Griffin

. Both of the prior courses had laboratory components, and the newmaterials/manufacturing course has been developing a set of laboratory activities that combineboth topics. The experiment to be described in this paper involves the rapid prototyping of acomponent, using that part as a mold for an aluminum casting, and finally the evaluation of thepart. The experiment is performed over a several week period. The students design a small partusing a solids modeling program (Currently, MEEN is using Solid Works.); the part is then usedas a mold for a green sand aluminum casting. The part is constrained by the volume of the rapidprototyping machine and the ability to make a mold for casting. The students must evaluate theresults to see if it meets

Conference Session

Unique Laboratory Experiments and Programs

Collection

2006 Annual Conference & Exposition

Authors

Shuvra Das, University of Detroit Mercy

Tagged Divisions

Division Experimentation & Lab-Oriented Studies

2006-1260: IMPLEMENTING A MULTI-MEDIA CASE STUDY IN ATRADITIONAL LABORATORY CLASSShuvra Das, University of Detroit Mercy Dr. Shuvra Das is Professor of Mechanical Engineering at UDM. He teaches mechanics of materials, mechanical design, mechatronics, and computer modeling and simulation courses such as finite elements and mechatronic system modeling using bond graphs. His current research interests and publications are in two broad areas: mechanistic modeling of manufacturing processes, and mechatronic systems. He received the Engineering Teacher of the Year Award in 1996, UDM Faculty Achievement Award in 2001, and the ASEE North-Central Section’s Best Teacher Award in 2002. Das earned his

Conference Session

Mechanical Engineering Laboratories II

Collection

2011 ASEE Annual Conference & Exposition

Authors

Anthony William Duva, Wentworth Institute of Technology; Ali Moazed, Wentworth Institute of Technology; Xiaobin Le, Wentworth Institute of Technology ; Richard L. Roberts, Wentworth Institute of Technology

Tagged Divisions

Mechanical Engineering

Balancing Theory, Simulation and Physical Experiments in Heat Transfer EducationAbstract: Some big problems for students studying heat transfer are (1) difficulty in visualizingboth basic and complex theoretical concepts, (2) unsure how to design changes effect heat flowor temperature distributions, (3) unclear how to apply theoretical concepts in the development ofcomponents / systems and (4) confusion with how to extend single point experiments to genericapplications. It is impossible for students to solve complex heat transfer problems throughtheoretical hand calculations or execute real experiments when the boundary conditions arecomplicated because of time and laboratory equipment cost constraints. During the

Conference Session

Electrical ET Laboratory Practicum

Collection

2004 Annual Conference

Authors

Glenn Blackwell

Session 2004 Experiences with the transition to Surface Mount Technology in ECET Labs Glenn R. Blackwell ECET – Purdue University West Lafayette, IN 47907-2021 gblack@purdue.eduabstractThe author has been actively involved with the use of surface mount technology (SMT) inPurdue’s ECET labs for 10 years. In that time the department has expanded its use of surfacemount devices (SMDs) from use solely in an undergraduate SMT class, to use of SMDs in halfof the

Conference Session

Unique Laboratory Experiments & Programs

Collection

2003 Annual Conference

Authors

Theodore Dibble; Carrie Hernandez; Abbie Wells; Steven Barrett

AbstractOften, engineering departments are faced with the need to update laboratory exercises andequipment. However, adequate funds do not always exist to accomplish these upgrades in atimely manner. Another challenge faced by departments are satisfying Accreditation Board forEngineering and Technology (ABET) requirements for a major design experience within thecurriculum. ABET guidelines state, “Students must be prepared for engineering practice throughthe curriculum culminating in a major design experience based on the knowledge and skillsacquired in earlier course work and incorporating engineering standards and realistic constraintsthat include most of the following considerations: economic; environmental; sustainability;manufacturability; ethical

Conference Session

Modern Software Measurement Techniques

Collection

2007 Annual Conference & Exposition

Authors

Gangbing Song, University of Houston; Claudio Olmi, University of Houston; Richard Bannerot, University of Houston

Tagged Divisions

Instrumentation

. Page 12.677.1© American Society for Engineering Education, 2007 Enhancing Vibration and Controls Teaching with Remote Lab ExperimentsAbstractThis paper describes the remote laboratory experiments and demonstrations developed in theDepartment of Mechanical Engineering at the University of Houston to enhance students’learning of vibrations control and their knowledge of smart materials. Two intelligent vibratingstructures utilizing smart materials to control and damp structural vibrations have been integratedinto an internet based virtual laboratory. The students are now able to control the experimentalvariables through a virtual instrument, created through the commercial virtual lab softwareLabView

Conference Session

Computers in Education General Technical Session I

Collection

2011 ASEE Annual Conference & Exposition

Authors

Yizhe Chang, Stevens Institute of Technology; El-Sayed Aziz, Stevens Institute of Technology; Sven K. Esche, Stevens Institute of Technology; Constantin Chassapis, Stevens Institute of Technology

Tagged Divisions

Computers in Education

subsequent analysis. The scriptedscenario11 for the first laboratory exercise was piloted in the fall 2007 semester in ‘ME 358Machine Dynamics and Mechanisms’, a junior level course for mechanical engineering majors atSIT.12 The laboratory exercise involved an industrial plant emulator13 designed for experimentswith different rotating bodies connected by a gear-belt mechanism. The experimental setupallowed students to determine the inertia of the device itself and of weights placed at variouslocations within the mechanism as well as to experiment with different gear ratios and beltstiffnesses.The purpose of this paper is to present another virtual experiment and asses its effectiveness as asupplementary learning tool for teaching the fundamental law

Conference Session

BME Laboratory Courses and Experiences

Collection

2009 Annual Conference & Exposition

Authors

Conrad Zapanta, Carnegie Mellon University; Warren Ruder, Carnegie Mellon University; Justin Newberg, Carnegie Mellon University; Paul Glass, Carnegie Mellon University; Davneet Minhas; Elvira Garcia Osuna, Carnegie Mellon University; Liang Tso Sun, Carnegie Mellon University; Alyssa Siefert, Carnegie Mellon University; Judy Shum, Carnegie Mellon University; Portia Taylor, Carnegie Mellon University; Arielle Drummond, Carnegie Mellon University; Bur Chu, Carnegie Mellon University

Tagged Divisions

Biomedical

advances in biology, continuum mechanics, imaging, applied mathematics, and scientific computing.The Biomedical Engineering Laboratory course described in this paper is designed to give theundergraduate students hands-on experiences in each of these tracks. The course has beenoffered every semester since its initial offering in the Fall of 2006. One instructor (Dr. Zapanta)developed the course and has taught it every semester since its inception. The co-authors haveserved as teaching assistants since the courses inception and have had a significant role in itsdevelopment. Over 150 students have completed this course to date.The class was initially offered in the Fall of 2006 with the cellular and molecular biotechnology,biomaterials, and

Conference Session

LabVIEW and Mindstorms Based Experiments

Collection

2008 Annual Conference & Exposition

Authors

Suxia Cui, Prairie View A&M University; Yonghui Wang, Prairie View A&M University; Yongpeng Zhang, Prairie View A&M University; Cajetan Akujuobi, Prairie View A&M University

Tagged Divisions

Division Experimentation & Lab-Oriented Studies

capabilities in both hardware and software. The details of the hardware andsoftware to be used in the related courses are listed as the above Table 2. • CPET (Computer Engineering Technology) Program:In the freshman and sophomore year, the departmental required courses are the same in bothCPET and ELET programs, thus the current situation and corresponding plan in CPET is also thesame as of ELET program in the lower level courses. (1) Same as of ELET program. (2) Same as of ELET program.In the upper level courses, there are three laboratories to be revamped. In CPET 3251 DigitalHardware Design Lab, experiments include design of digital computers and computer controlleddevices; the internal operation of a microprocessor and computer; register

Conference Session

Unique Laboratory Experiments and Programs

Collection

2006 Annual Conference & Exposition

Authors

Jed Marquart, Ohio Northern University; David Sawyers, Ohio Northern University

Tagged Divisions

Division Experimentation & Lab-Oriented Studies

interpersonal and written communication skills 5. Teach students to design their own experiments using available equipment to achieve a specified objective.The first four goals can be accomplished with traditional experiments1, in which studentsfollow a specified procedure to generate a clearly-defined set of data. During the first twoyears of their college careers, students encounter this approach numerous times. The fifthobjective, while often an essential skill in professional practice, is seldom considered inintroductory labs. This paper discusses efforts by the Mechanical Engineering faculty atONU to provide a laboratory experience which satisfies all five of these goals by integrating

Conference Session

BME Laboratory Courses and Experiences

Collection

2009 Annual Conference & Exposition

Authors

Melissa Micou, University of California, San Diego

Tagged Divisions

Biomedical

together twice per weekfor six weeks.Department Networking EventsEach Friday the program participants gathered for a research skills workshops followed by aprofessional networking event designed to integrate academic and social experiences, a hallmarkof a learning community. The networking events encouraged participants to meet as manycurrent undergraduate students, graduate students, and faculty members in the department aspossible. The networking events also provided opportunities to learn more about graduate schooland ongoing research in an informal setting. Electronic invitations were sent to guests and REUparticipants one week in advance to encourage attendance. Examples of networking eventsinclude a pizza party with current Bioengineering

Conference Session

Assessment in Laboratory and Project-based Courses: Experimentation and Laboratory-oriented Studies Division

Collection

2021 ASEE Virtual Annual Conference Content Access

Authors

Nebojsa I. Jaksic, Colorado State University, Pueblo

Tagged Topics

Diversity

Tagged Divisions

Experimentation and Laboratory-Oriented Studies

learning framework where two ormore peer groups interact and through those interactions increase the knowledge (or skills) of allgroup members. The simplest form of GGPL is pair-to-pair peer learning (PPPL) where each groupis limited to only two peers per group. This allows the greatest control of the experiments onGGPL. A PPPL method was implemented in an undergraduate engineering lab conducted in aface-to-face (f2f) manner as well as in a synchronous (and asynchronous) online manner. The twoare compared with respect to the knowledge gained (skills developed) and students’ learningperceptions.What follows are sections on previous work emphasizing online learning methods and PPPL,curricular context, description of the lab design problem for online

Conference Session

Experimentation and Laboratory-oriented Studies Division Technical Session 3

Collection

2020 ASEE Virtual Annual Conference Content Access

Authors

Hitesh D. Vora, Oklahoma State University; Brad Rowland, Oklahoma State University; Joe Conner, Oklahoma State University; Brian K. Norton P.E., Oklahoma State University; Qinang Hu, Oklahoma State University; Toni Ivey, Oklahoma State University

Tagged Divisions

Experimentation and Laboratory-Oriented Studies

paradigm shift that expands the instruction beyond theclassroom and increases undergraduate laboratory and exploratory time for interdisciplinary,hands-on and industry-aligned learning. Students (even in their freshman year) can experiencehands-on interdisciplinary design, applied experiments and training/use of the 5 makerspaceareas. ENDEAVOR is a college asset where all eight departments in the college may use thismultidisciplinary laboratory for undergraduate experiments, design, and research. The new72,000-square-foot facility opens the door in Fall 2018 contains state-of-the-art industry-relevanttechnology in an immersive glass environment that promotes undergraduate interdisciplinaryteaching, research, and training. ENDEAVOR facilities

Conference Session

Laboratory Experiences in Chemical Engineering

Collection

2015 ASEE Annual Conference & Exposition

Authors

Arshan Nazempour, Washington State University; Paul B. Golter, Washington State University; Cecilia Dianne Richards, Washington State University; Robert F. Richards, Washington State University; Bernard J. Van Wie, Washington State University

Tagged Divisions

Chemical Engineering

Paul B. Golter obtained an MS and PhD Washington State University and made the switch from Instruc- tional Laboratory Supervisor to Post-Doctoral Research Associate on an engineering education project. His research area has been engineering education, specifically around the development and assessment of technologies to bring fluid mechanics and heat transfer laboratory experiences into the classroom.Prof. Cecilia Dianne Richards, Washington State University Dr. Cecilia Richards is a professor in the School of Mechanical and Materials Engineering at Washington State University. Dr. Richards received her B.S. and M.S. degrees in Mechanical Engineering from the University of British Columbia, Canada. She earned her Ph.D

Conference Session

Division for Experimentation & Lab-oriented Studies Technical Session 2

Collection

2018 ASEE Annual Conference & Exposition

Authors

Stephen Schultz, Brigham Young University; Brad L. Hutchings, Brigham Young University

Tagged Divisions

Experimentation and Laboratory-Oriented Studies

-inventor for 60+ patents. c American Society for Engineering Education, 2018 Designing a Sustainable Large Scale Project-Based Learning (PBL) Experience for Juniors in Electrical and Computer EngineeringAbstractThis paper presents a large-scale Project-Based Learning (PBL) curriculum that can handle 200students per year without requiring an undue commitment of faculty or teaching-assistant time.The following strategies were used to attain the student benefits of the PBL curriculum whileaccommodating a large number of students and while keeping the faculty and teaching-assistantcommitments to reasonable levels. (1) A top-level hardware/software specification of the

Conference Session

ELOS Technical Session 1 - Fluids, Wind, and Flow

Collection

2024 ASEE Annual Conference & Exposition

Authors

Peter B. Johnson, Imperial College London; Christian Klettner, University College London

Tagged Divisions

Experimentation and Laboratory-Oriented Studies Division (DELOS)

Paper ID #43732Desktop Flow Visualisation Experiments for Guided Discovery of BoundaryLayersDr. Peter B. Johnson, Imperial College London Peter is a Principal Teaching Fellow (permanent academic staff with an education focused remit) in the Mechanical Engineering Department at Imperial College London. He teaches a fluid mechanics module to undergraduate students. He is also responsible for laboratory based learning, and plays a lead role in teaching administration within the department. Additionally, Peter has a remit to innovate in educational methods, with two main focuses: discovery based learning, including developing

Conference Session

BME Laboratory and Project Experiences

Collection

2012 ASEE Annual Conference & Exposition

Authors

Melissa Kurtis Micou, University of California, San Diego; Dawn M. Kilkenny Ph.D., University of Toronto

Tagged Divisions

Biomedical

tissue engineering(TE), yet very few offer a lab component or separate lab course. Given that engineering is anapplied field, the benefits of hands-on lab experience are clear. A new textbook entitled ALaboratory Course in Tissue Engineering will be published by Taylor Francis and CRC Press insummer 2012. The lab manual is appropriate for upper-division undergraduates or graduatestudents without prior hands-on TE experience, the content and structure are intended tofacilitate development of new TE lab courses, and an instructor’s manual is available. Theexperiments within the book are based on both classic TE experiments and modern TEtechniques and emphasize the importance of engineering analysis, mathematical modeling, andstatistical design of

Conference Session

Remote and Network-based Laboratories

Collection

2012 ASEE Annual Conference & Exposition

Authors

John Matthew Long, Deakin University; Ben P. Horan, Deakin University; Robynne Hall, Deakin University

Tagged Divisions

Division Experimentation & Lab-Oriented Studies

typical introductory electronicsexperiment consists in building a specific circuit, then testing that circuit while varying some keyparameter, such as an input signal or DC bias. Recreational kits and experiments in a universityelectronics course have very different purposes. The former is designed for building specificdevices (often for entertainment) and the latter is for teaching more systematic skills such ascircuit analysis, testing, and especially design. For example, a recreational electronics kit mayteach one how to build a working transistor amplifier that may drive a small speaker. Thecorresponding components in a university laboratory course would be used to investigate loadlines and the effect of DC bias on the performance of the

Conference Session

NSF Grantees Poster Session

Collection

2002 Annual Conference

Authors

Mary Stephen; Jerry Weinberg

Session 1526 A Laboratory Experience for Teaching Participatory Design in a Human-Computer Interaction Course Jerry B. Weinberg, Mary L. Stephen Southern Illinois University Edwardsville / Saint Louis UniversityI. IntroductionThe ability of computer technology to improve productivity and enhance quality of life restssquarely on how well the technology application fits our conceptual understanding of how thingswork1. While it is important for a software product to provide the necessary functionality toperform its intended use, it is also important that this

Conference Session

Web-Based Laboratory Experiments

Collection

2005 Annual Conference

Authors

Lars Håkansson; Ingvar Gustavsson; Henrik Åkesson

compared to a traditional educationon universities distant from the working place and thus increases the efficiency of the timeused to education. Hence, distance education is likely to be an advantageous choice for theindustrial research workers. A remote laboratory within the sound and vibration field is running at Blekinge Instituteof Technology (BTH). The students have the possibility to perform the experiment at anytime twenty-four hours a day, from anywhere in the world. Also other laboratories have beenset up previously on BTH3, 4 and also by other universities around the world.5, 6 The remotelaboratory at BTH is design to meet demands from both students on undergraduate educationsand development engineers from industry, providing

Conference Session

Multidisciplinary Capstone

Collection

2010 Annual Conference & Exposition

Authors

James Palmer, Louisiana Tech University; Hisham Hegab, Louisiana Tech University

Tagged Divisions

Multidisciplinary Engineering

in the capstone experience. However, there is little transition between the highlydefined problems provided in lecture and laboratory courses versus the open-ended projectstudents are asked to solve in their capstone design course. The capstone design projects for theNanosystems Engineering program is provided by faculty across a variety of disciplines.Therefore, it became evident that rather than expecting each faculty mentor to provide certainbasic skills, a more effective approach would be to have all Nanosystems Engineering students towork on a smaller open-ended project in the last quarter of the Junior year to teach all theelements that they would need to apply more deeply in their capstone project the following year.The educational

Conference Session

Virtual and Distance Experiments

Collection

2006 Annual Conference & Exposition

Authors

Prakash Kripakaran, North Carolina State University; Abhinav Gupta, North Carolina State University; Vernon Matzen, North Carolina State University

Tagged Divisions

Division Experimentation & Lab-Oriented Studies

the remote user when the allotted timeslot expires.Introduction In recent years, universities have witnessed a greater number of students enrolling indistance-education classes. But as the existing computing technologies are primarily designed forvideo-based lectures, rarely are laboratory experiments included in these classes. Laboratoryexperiments can be vital for students in visualizing various engineering concepts. For instance,remotely controlling a shaketable experiment may help students gain a better understanding ofvibration phenomena like resonance. There have been some suggestions to use simulations in theclasses to achieve the same goal. However, researchers 1 have pointed out that “There will alwaysbe an important place for

Conference Session

Laboratory Experiences for Env. Engineers

Collection

2002 Annual Conference

Authors

Jesse Condon; Chasity Williams; Benjamin Fratto; Kauser Jahan; C. Stewart Slater

Session 3451 Membrane Experiments for Pollution Prevention Kauser Jahan 1 , Jesse Condon 1, Chasity Williams1 and Benjamin Fratto 2 1 Civil and Environmental Engineering 2 Chemical Engineering Rowan University Glassboro, NJ 08028-1701AbstractA major objective of the Junior and Senior Engineering Clinics at Rowan University is tointroduce students to open-ended design projects. The purpose of the clinic classes is to provideengineering students with a hands-on, multidisciplinary experience throughout their collegeeducation

Conference Session

Mechanical Engineering Laboratory Innovations

Collection

2013 ASEE Annual Conference & Exposition

Authors

Goodarz Ahmadi, Clarkson University

Tagged Divisions

Mechanical Engineering

University. The course includes both lecture-based instruction on the theoryrelated to aerosol measurements and laboratory experiments for a hands-on experience.During the lectures, a wide-range of aerosol topics, as related to aerosol measurementsand instrumentation, were covered, including: a review of fundamental aerosolmechanics, particle statistics, size distributions, aerosol electrical properties, and aerosolsampling. The lectures helped provide students with a theoretical understanding of thebasics of popular aerosol measurement techniques, such as electrical mobilityinstruments, inertial samplers, mass measurement devices, and diffusion-basedinstruments.The experimental aspect of the course included four extended experiments where a