A Cognitive Study of Problem Solving in Statics

Background Even as expectations for engineers continue to evolve to meet global challenges, analytical problem solving remains a central skill. Thus, improving students' analytical problem solving skills remains an important goal in engineering education. This study involves observation of students as they execute the initial steps of an engineering problem solving process in statics. Purpose (Hypothesis ) (1) What knowledge elements do statics students have the greatest difficulty applying during problem solving? (2) Are there differences in the knowledge elements that are accurately applied by strong and weak statics students? (3) Are there differences in the cognitive and metacognitive strategies used by strong and weak statics students during analysis? Design /Method These questions were addressed using think‐aloud sessions during which students solved typical textbook problems. We selected the work of twelve students for detailed analysis, six weak and six strong problem solvers, using an extreme groups split based on scores on the think‐aloud problems and a course exam score. The think‐aloud data from the two sets of students were analyzed to identify common technical errors and also major differences in the problem solving processes. Conclusions We found that the weak, and most of the strong problem solvers relied heavily on memory to decide what reactions were present at a given connection, and few of the students could reason physically about what reactions should be present. Furthermore, the cognitive analysis of the students' problems solving processes revealed substantial differences in the use of self‐explanation by weak and strong students.     

Laser synthesized TiO2-based nanoparticles and their efficiency in the photocatalytic degradation of linear carboxylic acids

Abstract

Titanium dioxide nanoparticles were synthesized by laser pyrolysis, their surface and electronic properties were modified by gold and/or nitrogen. These materials were characterized by different techniques like X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Time resolved conductivity (TRMC) was used to study the charge separation of electron/hole pairs. Altogether (XPS, EPR, TRMC), the physicochemical characterizations are well correlated with chemical photoactivity of the different samples. Their photocatalytic activity was evaluated for the degradation of linear carboxylic acids (C2-C3) under UV and visible illumination. The decomposition rate of acids was measured, it shows that the modification with gold increases the photoactivity while the presence of nitrogen slows down the process. Such observations are in good agreement with evolution of TRMC signals. A degradation pathway has been determined by identification of intermediate products by chromatography and EPR, results show different intermediate species. In particular EPR confirms the presence of NO^2? paramagnetic centers and shows two novel N centered paramagnetic centers. A decrease of the degradation rate is observed with increase of carboxylic acid chain length.     

Inlet ionization: a new highly sensitive approach for liquid chromatography/mass spectrometry of small and large molecules

Inlet ionization is a new approach for ionizing both small and large molecules in solids or liquid solvents with high sensitivity. The utility of solvent based inlet ionization mass spectrometry (MS) as a method for analysis of volatile and nonvolatile compounds eluting from a liquid chromatography (LC) column is demonstrated. This new LC/MS approach uses reverse phase solvent systems common to electrospray ionization MS. The first LC/MS analyses using this novel approach produced sharp chromatographic peaks and good quality full mass range mass spectra for over 25 peptides from injection of only 1 pmol of a tryptic digest of bovine serum albumin using an eluent flow rate of 55 μL min(-1). Similarly, full acquisition LC/MS/MS of the MH(+) ion of the drug clozapine, using the same solvent flow rate, produced a signal-to-noise ratio of 54 for the major fragment ion with injection of only 1 μL of a 2 ppb solution. LC/MS results were acquired on two different manufacturer's mass spectrometers using a Waters Corporation NanoAcquity liquid chromatograph.     

Improved electrochemical microsensor for the real-time simultaneous analysis of endogenous nitric oxide and carbon monoxide generation

An amperometric dual NO/CO microsensor was developed on the basis of a working electrode incorporating dual Pt microdisks (each diameter, 76 μm) and a Ag/AgCl reference electrode covered with a gas permeable membrane. One of the Pt disks was sequentially electrodeposited with Pt and Sn; the other Pt disk was deposited with Pt-Fe(III) oxide nanocomposites. The first showed activity for the oxidation of both NO and CO; the second showed activity only for NO oxidation. In the copresence of NO and CO, the currents measured at each electrode, respectively, represented the concentrations of CO and NO. The sensor showed high stability during the monitoring of organ tissue for at least 2.5 h and high selectivity to NO over CO at the Pt-Fe(III) oxide working electrode. Real-time coupled dynamic changes of NO and CO generated by a living C57 mouse kidney were monitored simultaneously and quantitatively in response to a NO synthase inhibitor (N(G)-nitro-l-arginine methyl ester), for the first time. CO was found to increase and NO decreased upon addition of the inhibitor, suggesting a possible reciprocal interaction between these endogenous gases.     

3D,Reconfigurable, Multimodal Electronic Whiskers via Directed Air Assembly

A batch‐assembly technique for forming 3D electronics on shape memory polymer substrates is demonstrated and is used to create dense, highly sensitive, multimodal arrays of electronic whiskers. Directed air flow at temperatures above the substrate's glass transition temperature transforms planar photolithographically defined resistive sensors from 2D precursors into shape‐tunable, deterministic 3D assemblies. Reversible 3D assembly and flattening is achieved by exploiting the shape memory properties of the substrate, enabling context‐driven shape reconfiguration to isolate/enhance specific sensing modes. In particular, measurement schemes and device configurations are introduced that allow for the sensing of temperature, stiffness, contact force, proximity, and surface texture and roughness. The assemblies offer highly spatiotemporally resolved, wide‐range measurements of surface topology (50 nm to 500 µm), material stiffness (200 kPa to 7.5 GPa), and temperature (0–100 °C), with response times of <250 µs. The development of a scalable process for 3D assembly of reconfigurable electronic sensors, as well as the large breadth and sensitivity of complex sensing modes demonstrated, has applications in the growing fields of 3D assembly, electronic skin, and human–machine interfaces.     

A novel porous scaffold fabrication technique for epithelial and endothelial tissue engineering

Porous scaffolds have the ability to minimize transport barriers for both two- (2D) and three-dimensional tissue engineering. However, current porous scaffolds may be non-ideal for 2D tissues such as epithelium due to inherent fabrication-based characteristics. While 2D tissues require porosity to support molecular transport, pores must be small enough to prevent cell migration into the scaffold in order to avoid non-epithelial tissue architecture and compromised function. Though electrospun meshes are the most popular porous scaffolds used today, their heterogeneous pore size and intense topography may be poorly-suited for epithelium. Porous scaffolds produced using other methods have similar unavoidable limitations, frequently involving insufficient pore resolution and control, which make them incompatible with 2D tissues. In addition, many of these techniques require an entirely new round of process development in order to change material or pore size. Herein we describe “pore casting,” a fabrication method that produces flat scaffolds with deterministic pore shape, size, and location that can be easily altered to accommodate new materials or pore dimensions. As proof-of-concept, pore-cast poly(ε-caprolactone) (PCL) scaffolds were fabricated and compared to electrospun PCL in vitro using canine kidney epithelium, human colon epithelium, and human umbilical vein endothelium. All cell types demonstrated improved morphology and function on pore-cast scaffolds, likely due to reduced topography and universally small pore size. These results suggest that pore casting is an attractive option for creating 2D tissue engineering scaffolds, especially when the application may benefit from well-controlled pore size or architecture.     

Study of lipid and apolipoprotein binding interactions using vesicle affinity capillary electrophoresis

Vesicle affinity capillary electrophoresis (VCE), a newly developed technique, was designed to assess the effect of physicochemical properties of apolipoprotein (apo) on the binding to lipoproteins, under physiological conditions (phosphate-saline buffer system at pH 7.4 and 37 degrees C), using vesicle as a model. The technique results in similar lipid binding properties of apo CIII (CIII) and its peptides compared to other techniques. It also offers a fast and more sensitive tool in determining the lipid affinity of apos in a unique system simulating the dynamic binding properties of apo in vivo. A noncompetitive binding model is used to determine the multiple binding properties of CIII and its peptides to vesicle. The VCE binding constants are dependent on temperature, physicochemical properties of the protein (hydrophobicity and charge), and nature of the vesicle. The vesicles used in the VCE experiments described here have been fully characterized and found to be stable under different temperatures (4 and 37 degrees C) and voltage conditions. Migration behavior of CIII and related peptides is reported in terms of relative mobility in order to correct for variability in viscosity at different vesicle concentrations. The VCE method provides very precise data on the migration time from 0.1 to 3.3% RSD at the highest concentration of vesicle. The model and current data have been used to determine VCE binding constants and protein-to-lipid binding ratios. The model predicts that higher lipid affinity (K(B)), protein-lipid binding ratio (n), and lower protein concentration result in a shift of the binding isotherm toward a lower concentration range of vesicle. A higher vesicle mobility, reflecting the size and charge of the vesicle, results in a larger separation window between the migration time of the free protein and the complex. The value of VCE for structure-function studies and drug design for peptides and proteins that are strongly bound to lipids has been illustrated.     

Safety effects of unsignalized superstreets in North Carolina

Arterials across the United States are experiencing far too many collisions. Agencies tasked with improving these arterials have few available effective solutions. Superstreets, called restricted crossing u-turns by the Federal Highway Administration (FHWA), are part of a menu of unconventional arterial intersection designs that may provide a promising solution. Up to this point, there is little valid information available on the safety effects of superstreets, as study results have been from basic analyses that only account for traffic volume changes. The purpose of this research was to determine the safety effects of the unsignalized superstreet countermeasure on existing arterials in North Carolina.     

Investigation of the joining zone of laser welded and cross wedge rolled hybrid parts

Most of today’s technical parts and components are made of monolithic materials. These mono-material components produced in established production processes reach their limits due to their respective material characteristics. Thus, a significant increase in production quality and efficiency can only be achieved by combining different materials in one part. Bulk forming of previously joined semi-finished products to net shape hybrid components that consist of two different materials is a promising method to produce parts with locally optimized characteristics. This new production process chain offers a number of advantages compared to conventional manufacturing technologies. Examples are the production of specific load-adapted forged parts with a high level of material utilization and an impact on the joining zone caused by the following forming process. This paper describes the production process of serially arranged hybrid steel parts, produced by combining a laser welding process with a subsequent cross wedge rolling process. The presented results are only a first approach in order to get first insights in the forming behaviour of laser welded and cross wedge rolled parts. The investigated material combination is C22 (1.0402) and 20MnCr5 (1.7147). This innovative process chain enables the production of hybrid parts. To evaluate the developed process chain, the weld and the joining zone is analysed before and after cross wedge rolling. Main results are that the joining process using laser welding enables a strong bonding between the two materials with a higher hardness in the joining zone than for the individual materials. After the forming process, the bonding of the joining zone is still present, while the hardness decreased but remains higher than of the materials themselves.