Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Physical Sciences and Mathematics (14752)
- Computer Engineering (9173)
- Computer Sciences (8065)
- Electrical and Computer Engineering (6951)
- Operations Research, Systems Engineering and Industrial Engineering (4875)
-
- Materials Science and Engineering (4599)
- Artificial Intelligence and Robotics (3991)
- Systems Science (3929)
- Numerical Analysis and Scientific Computing (3891)
- Civil and Environmental Engineering (3655)
- Mechanical Engineering (2776)
- Engineering Science and Materials (2736)
- Environmental Sciences (2455)
- Chemistry (2280)
- Chemical Engineering (2277)
- Social and Behavioral Sciences (2126)
- Mining Engineering (2100)
- Sustainability (2098)
- Physical Chemistry (2037)
- Oil, Gas, and Energy (2013)
- Materials Chemistry (1979)
- Earth Sciences (1958)
- Architecture (1621)
- Power and Energy (1456)
- Life Sciences (1426)
- Construction Engineering and Management (1299)
- Civil Engineering (1252)
- Aerospace Engineering (1116)
- Education (1086)
- Institution
-
- China Simulation Federation (3880)
- TÜBİTAK (3106)
- Chinese Chemical Society | Xiamen University (2029)
- China Coal Technology and Engineering Group (CCTEG) (1799)
- National Taiwan Ocean University (1307)
-
- Chulalongkorn University (1101)
- Tashkent State Technical University (884)
- Universitas Indonesia (761)
- Embry-Riddle Aeronautical University (738)
- Rochester Institute of Technology (701)
- University of Dar es Salaam (689)
- Changsha University of Science and Technology (579)
- Association of Arab Universities (574)
- Ministry of Higher and Secondary Specialized Education of the Republic of Uzbekistan (546)
- Technological University Dublin (537)
- Brigham Young University (456)
- Faculty of Engineering, Mansoura University (432)
- Purdue University (391)
- Neutrosophic Systems with Applications (380)
- University of Alabama at Birmingham (378)
- Ohio University (336)
- Beirut Arab University (320)
- Universitas Negeri Malang (308)
- University of Nebraska at Omaha (281)
- California State University, San Bernardino (240)
- Al Iraqia University (235)
- Tashkent Institute of Chemical Technology (233)
- Central Mining Institute (220)
- University of Technology (218)
- University of Arkansas, Fayetteville (204)
- Keyword
-
- Engineering (1085)
- Building (461)
- Construction (423)
- Architecture (416)
- Conference (379)
-
- Proceedings (379)
- ASME (378)
- ECTC (378)
- Plumbing (340)
- Deep learning (221)
- Simulation (206)
- Machine learning (201)
- Numerical simulation (180)
- Optimization (161)
- Sustainability (149)
- Genetic algorithm (141)
- Classification (115)
- Architectural Engineering (110)
- Artificial intelligence (104)
- Particle swarm optimization (99)
- Heating (96)
- Civil and Environmental Engineering (94)
- Western Australia (91)
- Path planning (90)
- Technology (87)
- Modeling (85)
- Design (82)
- Corrosion (75)
- Electrocatalysis (75)
- Temperature (75)
- Publication Year
- Publication
-
- Journal of System Simulation (3880)
- Turkish Journal of Electrical Engineering and Computer Sciences (3106)
- Journal of Electrochemistry (2029)
- Coal Geology & Exploration (1799)
- Journal of Marine Science and Technology–Taiwan (1299)
-
- Journal of Metals, Materials and Minerals (788)
- Tanzania Journal of Engineering and Technology (TJET) (616)
- Journal of the Microelectronic Engineering Conference (593)
- Journal of China & Foreign Highway (576)
- Chemical Technology, Control and Management (536)
- Makara Journal of Technology (478)
- Building Services Engineering (476)
- Journal of Undergraduate Research (438)
- Mansoura Engineering Journal (432)
- Neutrosophic Systems with Applications (380)
- Early Career Technical Journal (ECTJ) (378)
- Technical science and innovation (348)
- Online Journal of Space Communication (336)
- Journal of Digital Forensics, Security and Law (301)
- Space and Defense (280)
- International Journal of Aviation, Aeronautics, and Aerospace (269)
- Journal of Engineering Research (249)
- Iraqi Journal for Computer Science and Mathematics (235)
- CHEMISTRY AND CHEMICAL ENGINEERING (233)
- Journal of International Technology and Information Management (226)
- Journal of Sustainable Mining (220)
- Engineering and Technology Journal (218)
- Applied Environmental Research (216)
- Journal of Mechanical Engineering Science and Technology (JMEST) (198)
- Journal of Tashkent Institute of Railway Engineers (185)
- File Type
Articles 21691 - 21720 of 27416
Full-Text Articles in Engineering
Apparatus To Measure The Performance And Manufacturability Of The Multiple-Layer Floating-Opposing Arm Centrifugal Force Clutch, Derek Wright, Dr. Robert Todd
Apparatus To Measure The Performance And Manufacturability Of The Multiple-Layer Floating-Opposing Arm Centrifugal Force Clutch, Derek Wright, Dr. Robert Todd
Journal of Undergraduate Research
Centrifugal force clutches are used around the globe in devices from washing machines to garden tillers. Considering methods of reducing the cost of such clutches, the Utah Center of Excellence for Compliant Mechanism Research developed a fully compliant version, known as the Floating- Opposing Arm Centrifugal Force (FOA) Clutch. Unfortunately, the thickness required for the FOA clutch to perform competitively with comparable clutches makes manufacturing solid FOA clutches slow and costly. To overcome this difficulty, the clutch may be produced as stackable thin layers that sum to the desired performance characteristics. A testing apparatus is required to quantify the performance …
Comparison Of The Variance In The R-Value Calculated Using The Power Law In If Steel To Experimental Measurements, Craig Przybyla, Dr. Brent Adams
Comparison Of The Variance In The R-Value Calculated Using The Power Law In If Steel To Experimental Measurements, Craig Przybyla, Dr. Brent Adams
Journal of Undergraduate Research
As advances in engineering and technology increasingly require engineers and scientists to work in smaller length scales, they must have a greater understanding about how materials and their properties behave at these scales. This is true particularly in the field of mechanical engineering with the development of MicroElectroMechanical Systems or MEMS. These are tiny mechanical systems that are only measured in micrometers and that can only be seen with the aid of high powered microscopes. In order to build MEMS that are reliable and perform as they should, engineers not only must have an understanding of the material properties of …
Static Stability Of Micro-Air Vehicles, Stephen Griffiths, Nathan Knoebel, Daniel Reimann, Jon Ostler, Dr. Jerry Bowman
Static Stability Of Micro-Air Vehicles, Stephen Griffiths, Nathan Knoebel, Daniel Reimann, Jon Ostler, Dr. Jerry Bowman
Journal of Undergraduate Research
The purpose of this research was to find the optimal combination of three static stabilityenhancing features: dihedral angle, vertical position of center of gravity, and tail volume ratio.
Calibration Of Seawinds On Adeos-Ii Via The Quikscat Calibration Ground Station, Spencer Haycock, Dr. David G. Long
Calibration Of Seawinds On Adeos-Ii Via The Quikscat Calibration Ground Station, Spencer Haycock, Dr. David G. Long
Journal of Undergraduate Research
A scatterometer is essentially an orbiting radar aimed at the Earth’s surface. It can be used to study weather patterns, track icebergs, observe polar sea ice, detect climatic changes, and estimate environmental factors such as vegetation and soil moisture. Correct calibration of the scatterometer is essential in order to yield accurate measurements of these data.
Black Liquor Pyrolysis, Jarom D. Webster, Dr. Thomas H. Fletcher
Black Liquor Pyrolysis, Jarom D. Webster, Dr. Thomas H. Fletcher
Journal of Undergraduate Research
The black liquor recovery boiler is the largest and most expensive piece of equipment in a modern pulp mill. Inside this boiler, black liquor is burned to produce electricity for the mill and also to recover spent chemicals. Black liquor combustion occurs in three stages: drying, pyrolysis, and char combustion. Understanding black liquor pyrolysis is an important step to controlling and improving the efficiency of the recovery boiler.
Mri Rf Receiver And Transmitter Design, David A. Thayer, Dr. Travis E. Oliphant
Mri Rf Receiver And Transmitter Design, David A. Thayer, Dr. Travis E. Oliphant
Journal of Undergraduate Research
Radiofrequency (RF) transmitters and receivers are a critical component in Magnetic Resonance Imaging (MRI). These are the components used for imaging. The goal of this project was to design an RF transmitter and receiver. Both were successfully designed and implemented.
Lemmings: A Student Animation, Craig Paul Van Dyke, Dr. Brent R. Adams
Lemmings: A Student Animation, Craig Paul Van Dyke, Dr. Brent R. Adams
Journal of Undergraduate Research
Lemmings brought together eighteen students for one full year to work on a 5 minute computer animation. Such a learning experience broke the bonds of a normal artistic and technical education; it became a lesson in teamwork, leadership and hard work. The entire animation was student run and directed.
Catalyst Regeneration/Wax Solubility, Steven Gale Smith, Dr. Calvin Bartholomew
Catalyst Regeneration/Wax Solubility, Steven Gale Smith, Dr. Calvin Bartholomew
Journal of Undergraduate Research
Catalysts are widely used throughout many industries to decrease reaction time and make processes economically favorable. In the synthetic fuels industry a catalyst is used to convert carbon monoxide gases (CO) to hydrocarbon liquids (CnH2n+2). In this process, the catalyst becomes coated with the heavier hydrocarbon products. This coating is a wax and deactivates the catalyst (inhibits the catalyst from reacting). The catalyst is currently one of the largest expenses for this process and prevents the process from being competitive with natural fuels. Hence, a method to remove the waxes from the catalysts was studied. The process of removing the …
Anisotropic Etching In Silicon And Other Materials Using A Reactive Ion Etcher, Justin Henrie, Dr. Aaron Hawkins
Anisotropic Etching In Silicon And Other Materials Using A Reactive Ion Etcher, Justin Henrie, Dr. Aaron Hawkins
Journal of Undergraduate Research
Microfabrication technology has been one of the major areas of advancement of technology from the latter half of the twentieth century until today. Initially, microfabrication wasn’t a new concept—it started as a way to make large, complex electronic circuits smaller, and therefore more durable and less power-consuming. With advances in microfabrication techniques, we are starting to be able to not only manufacture solid-state electronic devices on a microscopic scale, but also mechanical devices with moving parts that operate at incredible speeds.
New Constant-Force Mechanism Configurations, Bart D. Frischknecht, Dr. Larry L. Howell
New Constant-Force Mechanism Configurations, Bart D. Frischknecht, Dr. Larry L. Howell
Journal of Undergraduate Research
In machine design it is often desirable to correlate output force with displacement. Incorporating a translational spring into the design creates a linear relationship between force and displacement. In contrast, if a constant output force is desired independent of displacement, solutions include pneumatic or hydraulic systems or complicated systems of weights or springs. A simple lightweight mechanical device that exhibits constant-force output over a significant displacement would have the potential of replacing complicated current systems. It could also provide an improved solution for systems where a constant-force output is desirable but has not yet been proven feasible.
The Integration Of Small Diameter Isotrussô Structures To A Bicycle Frame, Rodney B. Boynton, Dr. David W. Jensen
The Integration Of Small Diameter Isotrussô Structures To A Bicycle Frame, Rodney B. Boynton, Dr. David W. Jensen
Journal of Undergraduate Research
In order to fully explore the capabilities of the IsoTrussÔ Structure in a light weight application it was decided to replace not only the main tubes of a bicycle frame, but the rear tubing as well. Several of the initially proposed steps to this process have been completed and show good sign of meeting the performance requirements necessary of a high end, light weight mountain bike frame.
The Graftsweep Tool: A Multi-Axis Multi-Sweep Tool For Creating An All-Hexahedral Finite Element Mesh, Matthew Earp, Dr. Stephen E. Benzley
The Graftsweep Tool: A Multi-Axis Multi-Sweep Tool For Creating An All-Hexahedral Finite Element Mesh, Matthew Earp, Dr. Stephen E. Benzley
Journal of Undergraduate Research
Finite Element Analysis (FEA) is a method of performing mathematical analysis on complex geometry used extensively by both scientists and engineers. An important step in performing the analysis is the mesh generation process. This is the process of dividing a volume into small individual elements (finite elements). Currently there are two common shapes for these elements: tetrahedrons and hexahedrons. Due to the fact that tetrahedrons are a much simpler geometric shape, many robust tetrahedral meshing algorithms have been produced and find a wide range of uses. For solid modeling problems however, hexahedrons are the element of choice. Unfortunately there has …
Behavior Of Stacked Ortho-Planar Springs In Cvt’S, Marc P. Christenson, Dr. Robert H. Todd
Behavior Of Stacked Ortho-Planar Springs In Cvt’S, Marc P. Christenson, Dr. Robert H. Todd
Journal of Undergraduate Research
Compliant mechanisms are mechanical devices that achieve their motion from the deflection of flexible members rather than rigid links and moveable joints. One such mechanism using compliant design is an ortho-planar spring.
Fatigue Testing A Laminated Compliant Clutch, Daniel Brown, Dr. Robert H. Todd
Fatigue Testing A Laminated Compliant Clutch, Daniel Brown, Dr. Robert H. Todd
Journal of Undergraduate Research
Compliant mechanisms derive motion from flexible segments, rather than from joints. A BYU student, Nathan Crane, used compliant design concepts to develop a prototype centrifugal clutch.1 Manufacturing considerations led to a design incorporating many layers rather than a single solid piece.2 Further testing verified the engagement RPM and torque capacity of the clutch.3
Dynasense: Remote Monitoring System, Bryce Ott, Mike Coleman, Tyler Monson, Janell Armstrong, Ben Tanner, Brad Anderson, Dr. Steven Renshaw
Dynasense: Remote Monitoring System, Bryce Ott, Mike Coleman, Tyler Monson, Janell Armstrong, Ben Tanner, Brad Anderson, Dr. Steven Renshaw
Journal of Undergraduate Research
DynaSense is a robust and modular remote monitoring system that can be incorporated into an existing network. Individual embedded hardware modules gather and log data from attached sensors. This data is web-accessible from each individual module or can be compiled and monitored by custom management software for additional processing and display. A variety of industries could benefit from the features provided in the DynaSense system, including hospitals and clinical centers, manufacturing plants and refineries, museums, grocery stores, and the military.
Integrated Optics – Coupling And Guiding, Josh Kvavle, Dr. Aaron Hawkins
Integrated Optics – Coupling And Guiding, Josh Kvavle, Dr. Aaron Hawkins
Journal of Undergraduate Research
The computer has changed every aspect of the modern world. It almost seems that this burst of technological advance in computers will continue without limit. One can go and buy a computer with more “gigahertz” today for less that another bought one for the week before. Gordon Moore, of Intel Corp., predicted this trend of scaling the transistor down every 18 months . This scaling is the reason we have seen prices continue to drop, number of transistors per chip to increase, and the personal computer become an everyday thing in most people’s lives. Though many have predicted an end …
Computer Simulated Multi-Component Aerosol Thermodynamics And Chemistry, Eric Halpenny, Dr. Larry Baxter
Computer Simulated Multi-Component Aerosol Thermodynamics And Chemistry, Eric Halpenny, Dr. Larry Baxter
Journal of Undergraduate Research
Aerosols are small (sub-micron) particles formed mainly in combustion processes by the vaporization and subsequent re-condensation of volatile, inorganic compounds. Cloud formation is an example of an aerosol process. However, unlike clouds, most aerosol-generating processes produce negative effects on both the process that forms them and the environment. Aerosols represent major process and emissions issues for essentially all systems employing low-grade fuel (coal, biomass, and black liquor). An accurate, predictive understanding of aerosol formation and chemistry would substantially improve the efficiency and environmental performance of many processes.
Streamline-Based Novel Dynamic Grid Reservoir Simulation, Bradley C. Bundy, Dr. Larry Lin Baxter, Dr. Hugh Bradley Hales
Streamline-Based Novel Dynamic Grid Reservoir Simulation, Bradley C. Bundy, Dr. Larry Lin Baxter, Dr. Hugh Bradley Hales
Journal of Undergraduate Research
Oil is one of the most important commodities we have. It provides energy, transportation, and chemicals to provide a better life for mankind. However, it is a depleting recourse that is getting harder and harder to find and recover. Simulation techniques have been used for many years to determine the best place to drill wells and when it is the best time economically to stop pumping slurry. Unfortunately, current simulators often take weeks to months to complete and are only an estimate of what may occur. The industry is currently limited by slow, inaccurate simulation techniques. Faster simulators with increased …
Three-Dimensional Cfd Model Of A Reacting Char Bed, Michael M. Choi, Dr. Larry Baxter
Three-Dimensional Cfd Model Of A Reacting Char Bed, Michael M. Choi, Dr. Larry Baxter
Journal of Undergraduate Research
Black liquor is a recycled byproduct formed during the pulping of wood in the papermaking industry. In this process, cellulose is used to form paper fibers while lignin is combined with water and chemical used for the extraction to form black liquor. Black liquor is burned in a recovery boiler to produce steam and electricity and is the second largest renewable energy next to hydro energy.
Investigation Of Pavement Patch Rehabilitation Bond Strength, Keith Woffinden, Dr. W. Spencer Guthrie
Investigation Of Pavement Patch Rehabilitation Bond Strength, Keith Woffinden, Dr. W. Spencer Guthrie
Journal of Undergraduate Research
The traditional construction method for asphalt removal and replacement uses a high-power saw to separate the damaged asphalt from the existing pavement. The remaining material is broken and removed from the site in a time-consuming and laborious process. The saw-cut leaves a smooth, vertical edge on the asphalt surface that can lead to poor mechanical interlock between the old and new pavement materials, a major catalyst for accelerated pavement deterioration.
Construction Of An On-Chip Microfluidic Pumping System, Ghassan Sanber, Dr. Aaron Hawkins
Construction Of An On-Chip Microfluidic Pumping System, Ghassan Sanber, Dr. Aaron Hawkins
Journal of Undergraduate Research
The fabrication and testing of micro-scale electroosmotic pumps, made with a thin-film deposition process compatible with standard silicon processing, is described. The fabrication method relies on chemical vapor deposition and chemical sacrificial etching to form long hollow fluid microchannels. Each pump consists of parallel narrow microchannels that deliver fluid to a larger wide sample handling microchannel. Flow rates were measured on these devices for different applied voltages using charge-coupled device (CCD) imaging. Pressures up to 1000 psi were produced. The pumps are based on the multiple open-channel electroosmotic pumping system described by Lazar et al [1]. However, instead of etching …
Analysis Of Electrical Current As An Agent For Bacterial Killing, Taylor Turner, Dr. William Pitt
Analysis Of Electrical Current As An Agent For Bacterial Killing, Taylor Turner, Dr. William Pitt
Journal of Undergraduate Research
Previously it has been shown that antibiotic killing of bacteria, especially biofilms, can be enhanced by various non-invasive treatments. Low-level electric current has been shown to increase killing of Streptococcus gordonii biofilms when applied during treatment with gentamicin.1 Others have partially tested the feasibility of electrically killing bacteria on prosthetic joints.2 Ultrasonic exposure has also been shown to increase killing of bacterial biofilms.3 Our group previously observed that ultrasound increased the transport of gentamicin through biofilms.4 Electrical treatment of S. gordonii in the absence of gentamicin also generates a 1.9 log reduction in biofilm cell counts.1 Our previous findings showed …
Establishing The Facility Capital Investment Laboratory, Tim Tucker, Dr. Jeffery Campbell
Establishing The Facility Capital Investment Laboratory, Tim Tucker, Dr. Jeffery Campbell
Journal of Undergraduate Research
One of the greatest difficulties a manager has in the current economy is being able to validly show the value that is being created by their efforts. After human resource and related issues the greatest expenses an organization faces is the total cost of ownership of their fixed assets. Many organizations both private and public are coming to the understanding that a plan must be developed for the care of facilities and other capital assets. As one looks for information on how to proceed in the development of these plans one thing becomes clear, there is no single source that …
Teacher Excellence At Brigham Young University, Naomi Nuttall, Dr. Jared Berrett
Teacher Excellence At Brigham Young University, Naomi Nuttall, Dr. Jared Berrett
Journal of Undergraduate Research
At a university, a professor’s first and foremost job is that of a teacher. In order to become a professor, one does have to have a doctorate degree, but does not have to go through the rigorous teaching courses required for elementary, middle school, or high school teachers. Still, many professors at Brigham Young University have become outstanding teachers. I decided that I wanted to know what things had contributed to their success. My goal was that by surveying some of those professors who have received awards for their teaching and learning about the things that have added to their …
The Effect Of Pre-Service Turbine Blade Surface Roughness On The Formation Of Deposits, John Pettitt, Dr. Jeffrey P. Bons
The Effect Of Pre-Service Turbine Blade Surface Roughness On The Formation Of Deposits, John Pettitt, Dr. Jeffrey P. Bons
Journal of Undergraduate Research
Land based Gas Turbine (GT) engines are used very widely in power generation plants. The performance of the turbine blades greatly influences the engine’s overall efficiency and service life. As turbine engines operate, the life and performance of the blades are degraded by the deposition of material. Deposits can come from dirty fuels or eroded components or from airborne particles in the environment.1 Filters have been created for GT engines in an effort to screen out such particles. When particles are ingested into the GT engine and infiltrate these filters they become molten and stick to the turbine blade surfaces. …
An Experimental Study Of The Mechanisms Of Fine Particle Deposition In Kraft Recovery Boilers, Larry Baxter
An Experimental Study Of The Mechanisms Of Fine Particle Deposition In Kraft Recovery Boilers, Larry Baxter
Journal of Undergraduate Research
Experiments on the deposition of fume (submicron) and particles produced during black liquor combustion indicate that deposit mass accumulation increases linearly with time and is independent of temperature gradient – results that are inconsistent with the classical explanation of thermophoresis as a driving force. Temperature-controlled, cylindrical probes in cross flow collected particles for periods up to ten hours and at Reynolds and Stokes numbers comparable to those in commercial boilers. Fume deposits appear dense and smooth to the unaided eye but under microscopic examination prove to have filamentary structures, with individual filaments radiating from the probe center and consisting of …
Configurable Multiprocessor System Design, Jordan Anderson, Dr. Doran Wilde
Configurable Multiprocessor System Design, Jordan Anderson, Dr. Doran Wilde
Journal of Undergraduate Research
The goal of this project was to write a hardware description of a new microprocessor in a language called VHDL that can be built inside a field-programmable gate array (FPGA). The processor will run real-time applications and take advantage of the programmability of FPGA hardware by implementing several functions that are typically done in software, such as task resource allocation. The description will be used to create multiple processors that function together in one FPGA.
An Analysis Of Safety Culture & Safety Training: Comparing The Impact Of Union, Non-Union, And Right To Work Construction Venues, Harry Miller Csp, Tara Hill, Kris Mason, John S. Gaal Edd
An Analysis Of Safety Culture & Safety Training: Comparing The Impact Of Union, Non-Union, And Right To Work Construction Venues, Harry Miller Csp, Tara Hill, Kris Mason, John S. Gaal Edd
Online Journal for Workforce Education and Development
The construction industry is one of the most dangerous sectors of the US economy. As such, the safety attitudes and climate within small (residential) contracting firms may play a role in providing a safe culture and working environment. The intent of this practitioner-based research study is to compare and determine if there is a difference in safety practices—based on documented field inspections and their related original number of violations observed by OSHA—between union residential carpentry contractors in the St. Louis area and:
1) non-union residential carpentry contractors in the St. Louis area;
2) non-union residential carpentry contractors across Missouri; and …
Money Laundering Detection Framework To Link The Disparate And Evolving Schemes, Murad Mehmet, Duminda Wijesekera, Miguel F. Buchholtz
Money Laundering Detection Framework To Link The Disparate And Evolving Schemes, Murad Mehmet, Duminda Wijesekera, Miguel F. Buchholtz
Journal of Digital Forensics, Security and Law
Money launderers hide traces of their transactions with the involvement of entities that participate in sophisticated schemes. Money laundering detection requires unraveling concealed connections among multiple but seemingly unrelated human money laundering networks, ties among actors of those schemes, and amounts of funds transferred among those entities. The link among small networks, either financial or social, is the primary factor that facilitates money laundering. Hence, the analysis of relations among money laundering networks is required to present the full structure of complex schemes. We propose a framework that uses sequence matching, case-based analysis, social network analysis, and complex event processing …
Bipedal Locomotion, Jamie Nichol, Dr. Paul Eastman
Bipedal Locomotion, Jamie Nichol, Dr. Paul Eastman
Journal of Undergraduate Research
Creating an artificial biped (two legged machine) has proven a challenge. The first stage of the project, designing and building the mechanical frame, has required that I study several engineering disciplines. I have also learned many lessons by trial and error.