bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of SMA Helical Actuators: An Experimental Study
Authors: Czarnocki Isabel , Kim Wonhee , Utter Brent , Luntz Jonathan , Brei Diann , Alexander Paul
Published: February 2014

The Shape Memory Alloy (SMA) helical actuation architecture overcomes the typical strain limitations of straight wire SMA actuators by producing larger stroke in a small package size. SMA Helical actuators also provide design tailorability where the tightness of the coil can be used to make tradeoffs between force and displacement, along with the coupled tradeoff between package length and diameter. These are very attractive for industrial settings such as the automotive industry, but require models and design processes to support the needs of the quick, early design cycles typically required. This paper presents an experimentally-based parameter study from which a streamlined design process is extracted. SMA helical actuators with a range of wire diameters and coil diameters were fabricated and experimentally characterized. The functional dependence of performance metrics such as austenite stiffness, force level of the martensite plateau, and recoverable strain were evaluated. A two-step decoupled design procedure is presented based on the resulting empirical model where the kinematic design is first undertaken to select the spring index which provides the required strain within the available package space, and then the non-dimensionalized force is used to scale the design such that the required actuation force is achieved. The streamlined, systematic design framework presented in this paper provides the means for the design of compact, large stroke helical actuators in industrial settings.
Impact of Length Mismatch on the Fatigue Life of Parallel Shape Memory Alloy Wires
Authors: Churchill Christopher B. , Bedegi Anthony , Gao Xiujie
Published: February 2014

Shape memory alloy (SMA) actuator wires promise substantial size, weight, and potential cost advantages over their solenoid and electric motor counterparts. Designing actuators which fully realize these advantages is hampered by a limited understanding of how interactions between wires and their environment affect cyclic lifetime. For example, many devices use two SMA wires mechanically in parallel but electrically in series. This has practical advantages in simplified electrical routing and thermal lag. However, it complicates modeling in that wires interact both electrically and mechanically.

Here we study the effect of a mismatch in length between two SMA wires in parallel. We perform a series of fatigue experiments to show that mismatch of up to 0.75%, at the chosen set of conditions, has no measurable effect on cycle life. We also perform a series of simulations to show how the mechanical interaction between the two parallel wires tends to suppress, rather than amplify, any impact of length mismatch.
Vibration Analysis of Shrouded Turbine Blades for a 30 MW Gas Turbine
Authors: Tamai Ryoji , Tanaka Ryozo , Sato Yoshichika , Kusterer Karsten , Lin Gang , Kemper Martin , Panning-von Scheidt Lars
Published: February 2014

Turbine blades are subjected to high static and dynamic loads. In order to reduce the vibration amplitude means of friction damping devices have been developed, e.g. damping wires, interblade friction dampers and shrouds. This paper presents both numerical and experimental results for investigating the dynamical behavior of shrouded turbine blades. The studies are focused on the lowest family of the bladed disk.

The aspect of experimental studies, the effect of the shroud contact force on the resonance frequency of the blade was examined by using the simplified blade test stand. Based on the result of the simplified blade studies, the shroud contact force of the real blade was determined in order to stabilize the resonance frequencies of the bladed disk system. The resonance frequencies and mode shapes of the real bladed disk assembly were measured in no rotation and room temperature condition. Finally, the dynamic strains were measured in the actual engine operations by using a telemetry system.

The aspect of analytical studies, a non-linear vibration analysis code named DATES was applied to predict vibration behavior of a shrouded blade model which includes contact friction surfaces. The DATES code is a forced response analysis code that employs a 3-dimensional friction contact model. The Harmonic Balance Method (HBM) is applied to solve resulting nonlinear equations of motion in frequency domain. The simulated results show a good agreement with the experimental results.
Advanced Coating Systems for Future Shroudless Turbines
Authors: Gebhard Susanne , Wobst Tanja , Roth-Fagaraseanu Dan , Hancock Matthew
Published: February 2014

Shroudless turbine designs offer the advantages of weight reduction and lower mechanical loads on the one hand but bear challenges as high gap sensitivity and high temperatures of the static parts on the other hand. In the last years, a lot of work was carried out in order to develop a sealing system for a shroudless design consisting of an abrasive blade tip coating and an abradable segment coating addressing all the requirements defined. Aside from being abradable, the segment coatings have to be mechanically stable, withstand high thermo-mechanical loadings and have to work for thicknesses larger than 1 mm.

Due to the limited temperature capability of the currently used segment coating material yttria-stabilised zirconia, which combines advantageously a suitable thermal conductivity with a high thermal expansion coefficient, new ceramic materials for the segment coating had to be developed.

A very promising sealing system combines an abrasive blade tip coating with an yttria-stabilised zirconia / magnesia alumina spinel double-layer abradable coating system with a 3D interface structure between the bond coat and the ceramic coatings. The present work gives an overview of the development and the performance of this sealing system.
Impact of Wall Temperature on Turbine Blade Tip Aero-Thermal Performance
Authors: Zhang Q. , He L.
Published: February 2014

Currently, the aerodynamics and heat transfer over a turbine blade tip tend to be analyzed separately with the assumption that the wall thermal boundary conditions do not affect the Over-Tip-Leakage (OTL) flow field. There are some existing correlations for correcting the wall temperature effect on heat transfer. But they were mainly developed to account for the temperature dependence on fluid properties, and are inherently limited by the empirical nature. The questions arise with regard to: is the OTL aerodynamics significantly affected by the wall thermal condition? And if it is, how can we count this effect consistently in turbine blade tip design and analysis using modern CFD methods?

In the present study, the problem has been examined for typical HP turbine blade tip configurations. An extensively developed RANS code (HYDRA) is employed and validated against the experimental data from a high speed linear cascade testing rig. The numerical analysis reveals that the wall-gas temperature ratio could greatly affect the transonic OTL flow field and there is a strong two-way coupling between aerodynamics and heat transfer. The feedbacks of the thermal boundary condition to aerodynamics behave differently at different flow regimes over the tip, clearly indicating a highly localized dependence of the convective heat transfer coefficient (HTC) upon wall temperatures. This implies that to use HTC for blade metal temperature predictions without resorting a fully conjugate solution, the temperature dependence needs to be corrected locally. A nonlinear correction approach has been adopted in the present work, and the results demonstrate its effectiveness for the transonic turbine tip configurations studied.
Effects of Inlet Turbulence and End-Wall Boundary Layer on Aero-Thermal Performance of a Transonic Turbine Blade Tip
Authors: Zhang Q. , He L. , Rawlinson A.
Published: February 2014

Most of previous researches of inlet turbulence effects on blade tip have been carried out for low speed situations. Recent work has indicated that for a transonic turbine tip, turbulent diffusion tends to have distinctively different impact on tip heat transfer than for its subsonic counterpart. It is hence of interest to examine how inlet turbulence flow conditioning would affect heat transfer characteristics for a transonic tip.

This present work is aimed to identify and understand the effects of both inlet freestream turbulence and end-wall boundary layer on a transonic turbine blade tip aero-thermal performance. Spatially-resolved heat transfer data are obtained at aerodynamic conditions representative of a high-pressure turbine, using the transient infrared thermography technique with the Oxford High-Speed Linear Cascade research facility. With and without turbulence grids, the turbulence levels achieved are 7–9% and 1% respectively.

On the blade tip surface, no apparent change in heat transfer was observed with high and low turbulence intensity levels investigated. On the blade suction surface, however, substantially different local heat transfer for the suction side near tip surface have been observed, indicating a strong local dependence of the local vortical flow on the freestream turbulence. These experimentally observed trends have also been confirmed by CFD predictions using Rolls-Royce HYDRA. Further CFD analysis suggests that the level of inflow turbulence alters the balance between the passage vortex associated secondary flow and the OverTL flow. Consequently, enhanced inertia of near wall fluid at a higher inflow turbulence weakens the cross-passage flow. As such, the weaker passage vortex leads the tip leakage vortex to move further into the mid passage, with the less spanwise coverage on the suction surface, as consistently indicated by the heat transfer signature.

Different inlet end-wall boundary layer profiles are employed in the HYDRA numerical study. All CFD results indicate the inlet boundary layer thickness has little impact on the heat transfer over the tip surface as well as the pressure side near-tip surface. However, noticeable changes in heat transfer are observed for the suction side near-tip surface. Similar to the freestream turbulence effect, such changes are attributed to the interaction between the passage vortex and the OTL flow.
Experimental and Unsteady Numerical Investigation of the Tip Clearance Noise of an Axial Fan
Authors: Zhu Tao , Carolus Thomas H.
Published: February 2014

The aerodynamic and aeroacoustic performance of axial fans are strongly affected by the unavoidable tip clearance. Two identical fan impellers but with different tip clearance ratio were investigated. Unsteady wall pressure fluctuations in the tip region of the rotating blades and on the interior wall of the duct type shroud and the overall sound radiated were analysed by an unsteady numerical Scale-Adaptive Simulation (SAS) and unsteady surface pressure measurements in both, the stationary and rotating system. Based on SAS-predicted pressure fluctuations on the blade surfaces the acoustic analogy according to Ffowcs Williams and Hawkings (FWH) was employed to calculate the sound pressure in the far field.

In general, experimentally and numerically determined unsteady flow were found to be a tendentially good agreement. The spatial and temporal structure of the tip vortex system and the resulting unsteady pressure distribution on the surfaces in the vicinity of the blade tips was revealed in good detail. The vortices’ strength and trajectories as well as the unsteadiness are controlled by the size of the tip clearance and the operating point: As tip clearance is increased blade/vortex interaction becomes more prevalent and with it the unsteady surface pressure and eventually the sound radiated into the far field. The broadband tip clearance noise was acceptably predicted from the simulation results, while the prediction at discrete frequency should still be improved in the further work.
Effect of Common Blade Tip Squealer Designs in Terms of Tip Clearance Loss Control
Authors: Lomakin N. , Granovskiy A. , Belkanov V. , Szwedowicz J.
Published: February 2014

The increase of new gas turbine’s efficiency is connected with further rise of turbine inlet temperature and sometimes as well pressure. In these conditions, first cooled turbine stages of a gas turbine engine usually consist of freestanding airfoils, which do not use an integrated shroud, to avoid risk of shroud overheating. In order to better control the radial gap leakage flow between the rotating blade tip and turbine casing, special design features of the airfoil tip need to be considered in the design process to meet the best possible stage performance. In the general engineering practice, a blade tip squealer provides opportunities to control tip clearance loss. In this paper several simplified types of the tip squealer design are investigated to determine the most effective loss control. At this stage of the investigation, blade tip cooling was not taken into account, but aerodynamic effects were analysed in detail. Based on the most common designs of the blade tip in the literature, four geometry types were investigated: (i) a flat tip design as the reference baseline solution, (ii) full tip squealer, (iii) partial squealer along the pressure side (PS) wall with a cut-out at the pressure side near the trailing edge (TE) and (iv) partial squealer along the suction side (SS) wall with a cut-out at the suction side near TE. All these cases have been compared among each other for two relative radial gaps (gap to blade height) of 0.6% and 1.36%. The flow calculations were done with a full 3D Navier-Stokes CFD code. For the flat tip and for full squealer designs, numerical results were validated against well-known experimental data measured on the GE-E3 blade cascade test rig found in the open literature. By using the 3D numerical data, the special attention was considered to confirm reliability and predictive credibility of the blade tip flow obtained from the analytical model.

The obtained loss values and flow details were compared for all studied cases, providing insight into turbine stage aerodynamics with respect to minimal and maximal radial clearance.
The Influence of Boundary Conditions on Tip Leakage Flow
Authors: Coull John D. , Atkins Nicholas R.
Published: February 2014

Most of the current understanding of tip leakage flows has been derived from detailed cascade experiments. However, the cascade model is inherently approximate since it is difficult to simulate the boundary conditions present in a real machine, particularly the secondary flows convecting from the upstream stator row and the relative motion of the casing and blade. This problem is further complicated when considering the high pressure turbine rotors of aero engines, where the high Mach numbers must also be matched in order to correctly model the aerodynamics and heat transfer. More realistic tests can be performed on high-speed turbines, but the experimental fidelity and resolution achievable in such set-ups is limited.

In order to examine the differences between cascade models and real-engine behavior, the influence of boundary conditions on the tip leakage flow in an unshrouded high pressure turbine rotor is investigated using RANS calculations. This study examines the influence of the rotor inlet condition and relative casing motion. A baseline calculation with a simplified inlet condition and no relative endwall motion exhibits similar behavior to cascade studies. Only minor changes to the leakage flow are induced by introducing either a more realistic inlet condition or relative casing motion. However when both of these conditions are applied simultaneously the pattern of leakage flow is very different, with ingestion of flow over much of the early suction surface. The paper explores the physical processes driving this change and the impact on leakage losses and modeling requirements.
Modeling Approach to Calculate Redistributions of HPT-Shroud Cooling Channels Minimizing Thermal Stresses Including Some Turbine Blade Tip Effects
Authors: Rademaker Edward R. , Huls Rob A. , Soemarwoto Bambang I. , van Gestel Ron
Published: February 2014

A numerical case study on a HPT-shroud of a medium-sized commercial engine has been carried out to investigate the heat loading and the possible redistribution (number of channels, position and exit angle) of shroud cooling channels facing the turbine blade tip. A combination of modeling vehicles was used to quantify the aerodynamics, the thermodynamics and resulting heat loads on the shroud. This includes a 1-D gas turbine performance simulation model, engineering models for cooling flow distributions and heat loads, CFD modeling of the HPT flow including some tip flow effects and the finite element modeling to calculate the temperature and stress distribution in the solid shroud. Regions with high temperatures and/or maximum thermal stresses and the potential for reduction by relocating the cooling channels at equal amounts of cooling flow were identified. Although the physics involved in the processes is much more complicated than modeled, the parametric studies gave valuable insight and quantitative results in terms of differences in shroud temperatures and thermal stresses. A complementary experimental study on shroud maintenance and service experiences (not published yet) has delivered data for model input support and comparison with the numerical results.
Effect of the Tip Clearance on End Wall Heat-Transfer in a HP Turbine
Authors: Biester Marc H.-O. , Karapetrow Dimitri , Seume Joerg R.
Published: February 2014

The present investigation analyzes the effect of the extension of the radial gap on the heat transfer at the blade tip and the casing within a high-pressure turbine stage of an aircraft engine. Due to the rotation and the interaction of the adjacent blade-rows, the flow field in the tip region of an unshrouded rotor-blade is characterized by a high level of unsteadiness. Furthermore, the casing is exposed to the passing blade-gap and corresponding changes in the velocity-profile, the resulting near-wall velocity-gradients, and the resulting changes in heat transfer. In order to account for these effects, time-resolved RANS computations of three different radial gaps are performed and evaluated. The present analysis shows an influence of the radial gap on the characteristics of the steady and unsteady heat transfer and a correlation with the size of the tip-clearance vortex can be shown.
Aerodynamic Optimization of Axial Turbine Tip Cavity With Approximation Model
Authors: Kang Young-Seok , Rhee Dong-Ho , Kim Chun-Taek , Cha Bong-Jun
Published: February 2014

Design optimization of unshrouded rotor tip cavity of a high pressure turbine stage with low aspect ratio was carried out to maximize the turbine stage efficiency. Cavity shapes were parameterized with 4 design variables including rim thickness, cavity depth, cavity front blend radius and cavity aft blend radius. Initially the CCD method was utilized for sampling experimental points and the Kriging method was chosen to construct an approximation model. The optimum points derived from the approximation model were assessed by CFD analyses to verify the approximation model. The approximation model was refined repeatedly by adding more experiment points to minimize difference of CFD result and predicted value from the approximation model at the optimum point.

The optimization result showed that there is an optimum ratio of cavity depth to tip clearance height, while the optimum design suggests cavity front blend radius and cavity aft blend radius be as small as possible within the design range. As the tip clearance height increases, the optimized tip cavity depth increases. However, the rim thickness has little effect on the optimum tip cavity depth. Without the tip cavity, leakage flow at fore part of the blade suction surface develops large vortex flow from the starting point of the unguided turning region due to adverse pressure gradient. The tip cavity prevents the early leakage flow from flow to the suction surface, which suppresses the leakage flow dissipation to the loss. It results in efficiency improvement. The effect of the tip cavity on the efficiency increases at the larger tip clearance.

On the other hand, the cavity rim thickness effect on the efficiency becomes noticeable when the tip cavity depth is over than the optimum value. The rim thickness effect mainly appears on the tip leakage flow after the blade throat. The leaked flow after the blade throat generates a high loss region near the blade tip, especially when the rim thickness is small. The loss from the thick tip cavity rim gradually increases as the tip clearance increases. However, the rim thickness effect is most sensitive when the tip clearance is small. The loss generation mechanism due to the rim thickness is totally different to the tip cavity depth effects on the total pressure loss.
Effect of annealing treatment on the electrical characteristics of Pt/Cr-embedded ZnO/Pt resistance random access memory devices
Authors: Chang Li-Chun , Kao Hsuan-Ling , Liu Keng-Hao
Published: February 2014

ZnO/Cr/ZnO trilayer films sandwiched with Pt electrodes were prepared for nonvolatile resistive memory applications. The threshold voltage of a ZnO device embedded with a 3-nm Cr interlayer was approximately 50% lower than that of a ZnO monolayer device. This study investigated threshold voltage as a function of Cr thickness. Both the ZnO monolayer device and the Cr-embedded ZnO device structures exhibited resistance switching under electrical bias both before and after rapid thermal annealing (RTA) treatment, but resistive switching effects in the two cases exhibited distinct characteristics. Compared with the as-fabricated device, the memory cell after RTA demonstrated remarkable device parameter improvements, including a lower threshold voltage, a lower write current, and a higher Roff/Ron ratio. Both transmission electron microscope observations and Auger electron spectroscopy revealed that the Cr charge trapping layer in Cr-embedded ZnO dispersed uniformly into the storage medium after RTA, and x-ray diffraction and x-ray photoelectron spectroscopy analyses demonstrated that the Cr atoms lost electrons to become Cr3+ ions after dispersion. These results indicated that the altered status of Cr in ZnO/Cr/ZnO trilayer films during RTA treatment was responsible for the switching mechanism transition.
Novel high-throughput and maskless photolithography to fabricate plasmonic molecules
Authors: Bonakdar Alireza , Jang Sung Jun , Mohseni Hooman
Published: February 2014

Fabrication of nanostructures for applications such as plasmonics and metamaterials is typically low throughput, due to the required submicron feature sizes. Therefore, rapid production of optically engineered structures with low cost and large area is an enabling technology for many applications, such as light harvesting, solid state lighting, disposable biosensing, and metamaterials. Here, the authors propose a simple technique, based on microsphere nanolithography, to fabricate arrays of optical elements, or so-called plasmonic molecules, at about one third of exposure wavelength. This method is capable of producing many symmetric/asymmetric array of submicron arrangement of circles and is compatible with high-throughput nanomanufacturing schemes such as roll-to-roll production. The gap size between disks is precisely controllable by the angle of exposure. Here, the authors demonstrate the capabilities of this method in producing an array of complex plasmonic molecules over a large area. The periodicity of array and element's diameter can be tuned by microsphere size and exposure/develop time, respectively. Finite-difference time domain simulation agrees well with our experimental results and suggests that much smaller feature sizes can be achieved at shorter wavelengths.
Physiology, Biophysics, and Biomedical Engineering.
Authors: Gueye Paul
Published: February 2014

Physiology, Biophysics, and Biomedical Engineering. Wood A. W., CRC Press, Taylor & Francis Group, Boca Raton, FL, 2012, 782 pp. (hardcover). Price: $99.95. ISBN: 9781420065138
Prospective study evaluating the use of IV contrast on IMRT treatment planning for lung cancer
Authors: Li Hua , Bottani Beth , DeWees Todd , Low Daniel A. , Michalski Jeff M. , Mutic Sasa , Bradley Jeffrey D. , Robinson Clifford G.
Published: February 2014

Purpose:

To investigate the impact of exclusively using intravenous (IV) contrast x‐ray computed tomography (CT) scans on lung cancer intensity‐modulated radiation therapy (IMRT) treatment planning.

Methods:

Eight patients with lung cancer (one small cell, seven nonsmall cell) scheduled to receive IMRT consented to acquisition of simulation CT scans with and without IV contrast. Clinical treatment plans optimized on the noncontrast scans were recomputed on contrast scans and dose coverage was compared, along with the γ passing rates.

Results:

IV contrast enhanced scans provided better target and critical structure conspicuity than the noncontrast scans. Using noncontrast scan as a reference, the median absolute/relative differences in mean, maximum, and minimum doses to the planning target volume (PTV) were −4.5 cGy/−0.09%, 41.1 cGy/0.62%, and −19.7 cGy/−0.50%, respectively. Regarding organs‐at‐risk (OARs), the median absolute/relative differences of maximum dose to heart was −13.3 cGy/−0.32%, to esophagus was −63.4 cGy/−0.89%, and to spinal cord was −16.3 cGy/−0.46%. The median heart region of interest CT Hounsfield Unit (HU) number difference between noncontrast and contrast scans was 136.4 HU (range, 94.2–161.8 HU). Subjectively, the regions with absolute dose differences greater than 3% of the prescription dose were small and typically located at the patient periphery and/or at the beam edges. The median γ passing rate was 0.9981 (range, 0.9654–0.9999) using 3% absolute dose difference/3 mm distance‐to‐agreement criteria. Overall, all evaluated cases were found to be clinically equivalent.

Conclusions:

PTV and OARs dose differences between noncontrast and contrast scans appear to be minimal for lung cancer patients undergoing IMRT. Using IV contrast scans as the primary simulation dataset could increase treatment planning efficiency and accuracy by avoiding unnecessary scans, manually region overriding, and planning errors caused by nonperfect image registrations.
Noise correlation in CBCT projection data and its application for noise reduction in low‐dose CBCT
Authors: Zhang Hua , Ouyang Luo , Ma Jianhua , Huang Jing , Chen Wufan , Wang Jing
Published: February 2014

Purpose:

To study the noise correlation properties of cone‐beam CT (CBCT) projection data and to incorporate the noise correlation information to a statistics‐based projection restoration algorithm for noise reduction in low‐dose CBCT.

Methods:

In this study, the authors systematically investigated the noise correlation properties among detector bins of CBCT projection data by analyzing repeated projection measurements. The measurements were performed on a TrueBeam onboard CBCT imaging system with a 4030CB flat panel detector. An anthropomorphic male pelvis phantom was used to acquire 500 repeated projection data at six different dose levels from 0.1 to 1.6 mAs per projection at three fixed angles. To minimize the influence of the lag effect, lag correction was performed on the consecutively acquired projection data. The noise correlation coefficient between detector bin pairs was calculated from the corrected projection data. The noise correlation among CBCT projection data was then incorporated into the covariance matrix of the penalized weighted least‐squares (PWLS) criterion for noise reduction of low‐dose CBCT.

Results:

The analyses of the repeated measurements show that noise correlation coefficients are nonzero between the nearest neighboring bins of CBCT projection data. The average noise correlation coefficients for the first‐ and second‐order neighbors are 0.20 and 0.06, respectively. The noise correlation coefficients are independent of the dose level. Reconstruction of the pelvis phantom shows that the PWLS criterion with consideration of noise correlation (PWLS‐Cor) results in a lower noise level as compared to the PWLS criterion without considering the noise correlation (PWLS‐Dia) at the matched resolution. At the 2.0 mm resolution level in the axial‐plane noise resolution tradeoff analysis, the noise level of the PWLS‐Cor reconstruction is 6.3% lower than that of the PWLS‐Dia reconstruction.

Conclusions:

Noise is correlated among nearest neighboring detector bins of CBCT projection data. An accurate noise model of CBCT projection data can improve the performance of the statistics‐based projection restoration algorithm for low‐dose CBCT.
A Century-Old Question: Does a Crookes Paddle Wheel Cathode Ray Tube Demonstrate that Electrons Carry Momentum?
Authors: Humphrey T. E. , Calisa Vaishnavi
Published: February 2014

In 1879, in the midst of the debate between English and continental scientists about the nature of cathode rays, William Crookes conducted an experiment in which a small mill or “paddle wheel” was pushed along tracks inside a cathode ray tube (CRT) (similar to that shown in Fig. 1) when connected to a high-voltage induction coil. Crookes attributed the motion of the wheel to momentum transfer from the cathode rays (electrons) to the wheel,1 and interpreted the experiment as providing evidence that cathode rays were particles. In 1903 Thomson discounted Crookes' interpretation by calculating that the rate of momentum transfer (which he estimated at no more than 2×10−3 dyn, equivalent to 2×10−8 N) would be far too small to account for the observed motion of the wheel,2 instead attributing the motion to the radiometric effect. The misconception was not laid to rest, however, and despite an effort in 1961 to draw attention to Thomson's original work and so remove the error from textbooks,3 the notion that a Crookes paddle wheel CRT demonstrates that electrons carry momentum continues to be taught in high school physics courses4 and wheel. We then measured the actual acceleration of the wheel in the CRT by video analysis of its motion and determined the moment of inertia of the wheel along with its mass and dimensions. We could then compare the force, which really acts on the wheel to produce the observed motion to the maximum impulsive force that is supplied by the electrons. Our measurements yield a maximum impulsive force due to the electrons [Fel=(1.1±0.3)×10−8N], which is within a factor of two of Thomson's estimate, and which is more than two orders of magnitude smaller than the force that is responsible for the observed acceleration of the paddle wheel [FW=(6±2)×10−6N]. This means that the rotation of the wheel is certainly not due to transferred momentum from the electron beam, and the results of the experiment should not be taught to students as proof that electrons are particles with mass that carry momentum.
Analyzing Forces on Amusement Park Rides with Mobile Devices
Authors: Vieyra Rebecca E. , Vieyra Chrystian
Published: February 2014

Mobile device accelerometers are a simple and easy way for students to collect accurate and detailed data on an amusement park ride. The resulting data can be graphed to assist in the creation of force diagrams to help students explain their physical sensations while on the ride. This type of activity can help students overcome some of the conceptual difficulties often associated with understanding centripetal force and typical “elevator-type problems” that are inherent in so many amusement park rides that move, lift, and drop riders. This article provides some sample data and examples from a visit to Six Flags Great America.
Animating Energy: Stop-Motion Animation and Energy Tracking Representations
Authors: Atkins Leslie J. , Erstad Craig , Gudeman Paul , McGowan Jacob , Mulhern Kristin , Prader Kaitlyn , Rodriguez Gregoria , Showaker Amy , Timmons Adam
Published: February 2014

Energy is a topic that is often treated as an accounting process—a number that students are asked to calculate, but that is not particularly meaningful in itself. When we try to ascribe meaning to this number (“an ability to do work,” for example), we are met with caveats and hedges. As Feynman1 notes when lecturing on the conservation of energy, it “is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.” These calculations allow us to infer more meaningful quantities: how fast an object will move, how far it will travel, how compressed it will become, or how hot it will feel. But energy itself, particularly in introductory physics, rarely gives insights into physical problems.
An Arduino Investigation of Simple Harmonic Motion
Authors: Galeriu Calin , Edwards Scott , Esper Geoffrey
Published: February 2014

We cannot hope for a new generation of scientists and engineers if we don't let our young students take ownership of their scientific and engineering explorations, if we don't let them enjoy the hands-on cycle of design and production, and if we don't let them implant their creativity into a technologically friendly environment. With this educational philosophy in mind, Massimo Banzi1 and his team have developed and popularized the open source Arduino microcontroller board. The Arduino board has helped countless people in their science, electronics,robotics, or engineering projects, allowing them to build things that we have not even dreamed of. Physics instructors have also realized the advantages of using Arduino boards for lab experiments.2–4 The schools are saving money because the homemade experimental equipment is much cheaper than the commercial alternatives. The students are thankful for an educational experience that is more interesting, more loaded with STEM content, and more fun. As further proof of this new trend in physics education, Vernier5 is now documenting the use of their probes with Arduino boards. This is why we have developed an Arduino-based physics investigation of the simple harmonic motion (SHM) of a mass on a spring. The experimental data are collected with the help of an ultrasonic distance sensor and an Arduino Uno board. The data are then graphed and analyzed using Origin 9. This rich cross-curricular STEM activity integrates electronics,computer programming, physics, and mathematics in a way that is both experimentally exciting and intellectually rewarding.
Low-Cost Timer to Measure the Terminal Velocity of a Magnet Falling Through a Conducting Pipe
Authors: Pathare Shirish R. , Huli Saurabhee , Lahane Rohan , Sawant Sumedh
Published: February 2014

Dropping a magnet into a conductive pipe (made up of copper or brass or aluminum) is a very popular demonstration in many physics classrooms and laboratories. In this paper we present an inexpensive timer that can be used to measure the terminal velocity of the magnet falling through a conducting pipe. The timer assembly consists of Hall effect switches connected to a digital stopwatch. The timer assembly was then used to observe the variation in the terminal velocity of the falling magnet with respect to the thickness of the copper pipes.
Measuring the Drag Force on a Falling Ball
Authors: Cross Rod , Lindsey Crawford
Published: February 2014

The effect of the aerodynamic drag force on an object in flight is well known and has been described in this and other journals many times. At speeds less than about 1 m/s, the drag force on a sphere is proportional to the speed and is given by Stokes' law. At higher speeds, the drag force is proportional to the velocity squared and is usually small compared with the gravitational force if the object mass is large and its speed is low. In order to observe a significant effect, or to measure the terminal velocity, experiments are often conducted with very light objects such as a balloon1,2 or coffee filter3 or muffin cup,4 or are conducted in a liquid rather than in air. The effect of the drag force can also be increased by increasing the surface area of the object.
Rotational energy in a physical pendulum
Authors: Monteiro Martín , Cabeza Cecilia , Marti Arturo C.
Published: February 2014

Smartphone usage has expanded dramatically in recent years worldwide. This revolution also has impact in undergraduate laboratories where different experiences are facilitated by the use of the sensors usually included in these devices. Recently, in several articles published in the literature,1,2 the use of smartphones has been proposed for several physics experiments. Although most previous articles focused on mechanical experiments, an aspect that has received less attention is the use of rotation sensors or gyroscopes. Indeed, the use of these sensors paves the way for new experiments enabling the measurement of angular velocities. In a very recent paper the conservation of the angular momentum is considered using rotation sensors.3 In this paper we present an analysis of the rotational energy of a physical pendulum.
Reflections of a TPT enthusiast
Authors: Hicks Jim
Published: February 2014

Unparalleled academic journals not only provide a seaworthy vessel for the sharing and dissemination of innovative ideas, but also cause a perceptible wake with each new issue. For physics teaching enthusiasts, our flagship is The Physics Teacher (TPT), with its vibrant community of learners on board observing an extensive horizon. It is our signature through time.
Derivation of continuous wave mode output power from burst mode measurements in high-intensity ultrasound applications
Authors: Haller Julian , Wilkens Volker
Published: February 2014

Measurement of the acoustic output power of transducers in burst mode and derivation of the results to the continuous wave (CW) case reduces heating problems during power measurements with radiation force balances and absorbing targets at high power levels, but requires the knowledge of an “effective duty factor,” DReff. In this work, an alternative method for determining DReff is presented that allows the determination at any input voltage amplitude as it can be calculated from the input voltage rf signal in burst mode. Thus with this method, it is not necessary to apply CW signals at all.
Averting Lemur Extinctions amid Madagascar's Political Crisis
Authors: Schwitzer C. , Mittermeier R. A. , Johnson S. E. , Donati G. , Irwin M. , Peacock H. , Ratsimbazafy J. , Razafindramanana J. , Louis E. E. , Chikhi L. , Colquhoun I. C. , Tinsman J. , Dolch R. , LaFleur M. , Nash S. , Patel E. , Randrianambinina B. , Rasolofoharivelo T. , Wright P. C.
Published: February 2014

Community-based management, ecotourism, and researchers' presence are proposed to prevent lemur extinctions.
Rhodium-Catalyzed Intermolecular C–H Silylation of Arenes with High Steric Regiocontrol
Authors: Cheng Chen , Hartwig John F.
Published: February 2014

Silicon Siting

The synthesis of many pharmaceutical and agrochemical compounds requires selective functionalization of multiple different sites on aromatic ring frameworks. The size and electronic properties of the first substituent added can influence where the next one is likely to end up.
Cheng and Hartwig
(p.
853
, see the Perspective by

Tobisu and Chatani

) discovered a rhodium-catalyzed reaction that is particularly sensitive to size that places a silicon substituent as far away as possible from the largest group already on the ring. The silicon group can then be replaced with carbon, oxygen, nitrogen, or halide substituents as needed.
The Robustness and Evolvability of Transcription Factor Binding Sites
Authors: Payne Joshua L. , Wagner Andreas
Published: February 2014

Robust to Change

The variation in genetic sequences determining the binding of transcription factors is believed to be an important facet of evolution. However, the degree to which a genome is robust, that is, able to withstand changes and how robustness affects evolution is unclear.
Payne and Wagner
(p.
875
) investigated the empirical support for mutational robustness by examining transcription factor (TF) binding in the mouse and yeast genomes. A network analysis of the degree of variation revealed that the sites with the highest affinity for TF binding exhibit the greatest tolerance for nucleotide substitutions, whereas low-affinity sites exhibit greater sensitivity to mutation. Thus, while mutational robustness and evolvability are antagonistic at the genotypic level, they are synergistic at the phenotypic level.
From Past to Future Warming
Authors: Hegerl Gabi , Stott Peter
Published: February 2014

Analyses of past observations help to predict the human contribution to future climate change.
The Significance of “Frontier”
On the Frontier of Science
An American Rhetoric of Exploration and Exploitation

by Leah Ceccarelli

Michigan State University Press, East Lansing, MI, 2013. 218 pp. Paper, $44.95. ISBN 9781611861006.
Authors: Newell Catherine L.
Published: February 2014

Ceccarelli explores the uses and effects of the metaphor "frontier of science."
Remote Control by Steric Effects
Authors: Tobisu Mamoru , Chatani Naoto
Published: February 2014

A rhodium-catalyzed reaction places a silicon substituent on the site farthest away from the largest group present on an aromatic ring.

[Also see Research Article by
Cheng and Hartwig
]
Reach Out and Touch Someone
Authors: Rørth Pernille
Published: February 2014

Cellular extensions called cytonemes may allow nonneuronal cells to communicate directly with each other over long distances.

[Also see Research Article by

Roy
et al.

]
Keystone XL
Authors: McNutt Marcia
Published: February 2014

I drive a hybrid car and set my thermostat at 80°F in the Washington, DC, summer. I use public transportation to commute to my office, located in a building given “platinum” design status by the U.S. Green Building Council. The electric meter on my house runs backward most months of the year, thanks to a large installation of solar panels. I am committed to doing my part to cut greenhouse gas (GHG) emissions and minimize global warming. At the same time, I believe it is time to move forward on the Keystone XL pipeline to transport crude oil from the tar sands deposits of Alberta, Canada, and from the Williston Basin in Montana and North Dakota to refineries on the U.S. Gulf Coast.
New Neutrino May Have Heated Baby Universe
Authors: Cho Adrian
Published: February 2014

A new analysis of the way galaxies are distributed through space suggests that some of the universe's dark matter may consist of hitherto undiscovered particles known as sterile neutrinos.
LIFE SCIENCE TECHNOLOGIES: Miniaturizing Mass Spectrometry
Authors: Perkel Jeffrey M.
Published: February 2014

Time was when mass spectrometry was the province of white-coated chemistry Ph.D.s with a secret language all their own. Terms like ion trap and post-source decay, mass-to-charge, and MALDI made the field inaccessible to others. Today, the technique has pushed beyond those narrow confines and entered the biology lab, where it underlies proteomics and biomarker research. But you can also find mass specs in airports and warehouses, and even at the bottom of the ocean. In many cases those instruments are being run not by specially trained researchers, but by TSA agents, soldiers, and first responders. Chalk that up to miniaturization. Researchers have finally figured out how to compress benchtop systems into portable, sometimes handheld gadgets. In so doing, they have created devices that empower not only themselves, but the wider world.
Intranasal Administration of Retinyl Palmitate with a Respiratory Virus Vaccine Corrects Impaired Mucosal IgA Response in the Vitamin A-Deficient Host
Authors: Surman Sherri L. , Jones Bart G. , Rudraraju Rajeev , Sealy Robert E. , Hurwitz Julia L.
Published: February 2014

Our previous studies showed that intranasal vaccination of vitamin A-deficient (VAD) mice failed to induce normal levels of upper respiratory tract IgA, a first line of defense against respiratory virus infection. Here we demonstrate that the impaired responses in VAD animals are corrected by a single intranasal application of retinyl palmitate with the vaccine. Results encourage the clinical testing of intranasal vitamin A supplements to improve protection against respiratory viral disease in VAD populations.
Rapid Molecular Detection of Inducible Macrolide Resistance in Mycobacterium chelonae and M. abscessus Strains: a Replacement for 14-Day Susceptibility Testing?
Authors: Hanson Kimberly E. , Slechta E. Susan , Muir Haleina , Barker Adam P.
Published: February 2014

The
erm
(41) gene causes inducible macrolide resistance in
Mycobacterium abscessus
but not
Mycobacterium chelonae
.
erm
(41) sequencing of 285
M. abscessus
and 45
M. chelonae
isolates was compared to 14-day susceptibility; agreement percentages were 98.9% and 100%, respectively. Extended incubation may not be necessary for
M. chelonae
, and the
erm
(41) genotype is a useful adjunct for
M. abscessus
.
Characterization of Invasive Group B Streptococcus Strains from the Greater Toronto Area, Canada
Authors: Teatero Sarah , McGeer Allison , Low Donald E. , Li Aimin , Demczuk Walter , Martin Irene , Fittipaldi Nahuel
Published: February 2014

We determined the capsular polysaccharide (CPS) type of 600 group B
Streptococcus
(GBS) (also known as
Streptococcus agalactiae
) strains recovered from patients with invasive infections in the greater Toronto area, Canada, between 2009 and 2012. GBS strains of CPS type III were the most prevalent among infants (44% in those with early-onset disease, 75% in those with late-onset disease), while type V strains were most frequently isolated from adult patients (26% in patients ≥19 years old). We next investigated the presence in our collection of GBS strains belonging to the hypervirulent multilocus sequence typing clonal complex 17 (CC17). We used a PCR test described as specific for the detection of CC17 strains, which targets the gene encoding the major virulence factor HvgA. We identified 91
hvgA
-positive strains; of these, 88 were CPS type III, 2 were CPS type IV, and 1 was CPS type V. Using whole-genome sequencing, we showed that the two
hvgA
-positive CPS type IV strains are CC17 strains which underwent capsular switching. However, sequence analysis revealed that the
hvgA
-positive CPS type V strain does not belong to CC17 but instead is a bona fide CC1 strain which acquired
hvgA
, probably by recombination from a CC17 donor. Our findings underline the importance of recombination in GBS pathogenesis and caution against the use of single-gene-based PCR tests to detect CC17 GBS strains.