bluuebunny/crossref_metadata_2025 huggingface dataset:
RIM: A Random Item Mixture Model to Detect Differential Item Functioning
Authors: Frederickx Sofie , Tuerlinckx Francis , De Boeck Paul , Magis David
Published: April 2011

In this paper we present a new methodology for detecting differential item functioning (DIF). We introduce a DIF model, called the random item mixture (RIM), that is based on a Rasch model with random item difficulties (besides the common random person abilities). In addition, a mixture model is assumed for the item difficulties such that the items may belong to one of two classes: a DIF or a non‐DIF class. The crucial difference between the DIF class and the non‐DIF class is that the item difficulties in the DIF class may differ according to the observed person groups while they are equal across the person groups for the items from the non‐DIF class. Statistical inference for the RIM is carried out in a Bayesian framework. The performance of the RIM is evaluated using a simulation study in which it is compared with traditional procedures, like the likelihood ratio test, the Mantel‐Haenszel procedure and the standardized
p
‐DIF procedure. In this comparison, the RIM performs better than the other methods. Finally, the usefulness of the model is also demonstrated on a real life data set.
An Analysis of Variance Approach for the Estimation of Response Time Distributions in Tests
Authors: Attali Yigal
Published: April 2011

Generalizability theory and analysis of variance methods are employed, together with the concept of objective time pressure, to estimate response time distributions and the degree of time pressure in timed tests. By estimating response time variance components due to person, item, and their interaction, and fixed effects due to item types and examinee time pressure, one can predict the distribution (mean and variance) of total response time for a population of examinees and a particular time limit. Furthermore, these variance components and fixed effects can be used in a simulation approach to estimate the distributions of time pressure during the test to help test developers evaluate the appropriateness of specific time limits. I present theoretical considerations and empirical results from two tests.
Long‐Term Groundwater Monitoring Results at Large, Sudden Denatured Ethanol Releases
Authors: Spalding Roy F. , Toso Mark A. , Exner Mary E. , Hattan Gregory , Higgins Tom M. , Sekely Adam C. , Jensen Shane D.
Published: April 2011

Hundreds of groundwater samples were collected at E95 (95% ethanol, 5% gasoline) train derailment spills in Balaton and Cambria, Minnesota and South Hutchinson, Kansas. Most samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX), ethanol, methane, acetate, terminal electron acceptors, and field parameters. At each site, maximum groundwater ethanol concentrations at percent levels were restricted to the release area and downgradient ethanol transport was not detected. A shallow, anaerobic groundwater zone characterized by the absence of dissolved oxygen, low nitrate (less than 1 mg N/L), high Fe+2, and high dissolved methane (more than 10,000 μg/L) and BTEX formed and spread downgradient from each release area. BTEX appeared to be persistent. Methane appeared to be generated within the capillary fringe and very shallow groundwater and migrate laterally. Methane's high oxygen demand promotes anaerobic conditions within the shallow groundwater. Estimated and measured methane soil gas concentrations exceeded the lower explosive limit. Long‐term monitoring at South Hutchinson and Cambria using 1 to 5‐foot (0.3 to 1.5 m) well screens straddling the capillary fringe and the shallow water table effectively demonstrated the presence of high ethanol (∼1%) and benzene (more than 250 μg/L) concentrations 5 years after the release. The wells appear impacted by long‐term ethanol inputs from the vadose zone where ethanol has persisted for years after the initial release. Toxicity, volatile fatty acids, excess hydrogen production, and/or exudate coatings could be responsible for ethanol's preservation. High acetate and hydrogen concentrations at South Hutchinson indicated that fermentation was actively occurring in the very shallow groundwater and/or in the lower capillary fringe. Short‐screened (1 to 5 feet; 0.3 to 1.5 m) nested wells were pivotal to improving our understanding of ethanol's behavior.
Monitoring Lateral Transport of Ethanol and Dissolved Gasoline Compounds in the Capillary Fringe
Authors: Freitas Juliana G. , Barker James F.
Published: April 2011

Fuel mixtures composed of gasoline and ethanol are lighter than water and, if enough volume is released into the unsaturated zone, they accumulate in the capillary fringe, acting as a source for dissolved plumes. To evaluate different sampling techniques and transport in the capillary fringe, two controlled releases of gasoline and ethanol mixtures were conducted in the unsaturated zone at the CFB Borden aquifer. Lateral flow and transport in the capillary fringe is well documented, but this is the first field documentation of transport of organic compounds in the capillary fringe following fuel spills. Transport of both ethanol and hydrocarbon compounds in the capillary fringe was significant, ethanol being transported exclusively above the water table. Significant concentrations of benzene were found above the water table up to 6 m downgradient from the source. The groundwater sampling techniques evaluated were fully screened monitoring wells; multilevel wells constructed with ceramic porous cups located in both the capillary fringe and below the water table; and soil coring. The fully screened monitoring well was unable to draw water from the capillary fringe and so failed to adequately describe the contaminant distribution. Pore water concentrations obtained by sampling the multilevel porous cups and calculated based on analysis of soil core yielded similar results.
Esophageal cancer associated with right aortic arch and thyroid adenoma
Authors: Gu Jundong , Zhao Hui , Zhu Siwei , Wen Yanjun , Wang Shuchuan , Chen Jun , Zhou Qinghua
Published: April 2011

A 55‐year‐old Chinese woman with thoracic esophageal cancer associated with right aortic arch and thyroid adenoma was admitted to our hospital. Computed tomography revealed a right aortic arch with mirror‐image branching and a mass in the esophagus. The following barium‐coated esophagograms and esophagoscopy showed an ulcerative and infiltrative tumor in the upper thoracic esophagus. The patient also had an almost 10‐year history of thyroid adenoma.
Design of Flexible Multi‐Stage Processes
Authors: Eynan Amit , Dong Lingxiu
Published: April 2011

Faced with demand uncertainty across multiple product lines, many companies have recourse to flexible capacities which can process different products in order to better balance the trade‐off between capacity utilization and cost efficiency. Many studies demonstrated the potential benefit of using flexible capacity at the aggregate level by treating a whole plant or a whole process as a single stage. This paper extends these analyses by studying the benefits of flexible capacity while considering the multi‐stage structure of processes and consequently determining which stages should be flexible, which should be dedicated, and how much capacity to assign to each stage. We consider a two‐product firm which operates in a process‐to‐order environment and faces uncertain demand. Each stage of the process can be designed as dedicated or flexible. Dedicated resources are highly cost efficient but limited to the single product they are exclusively designed for, whereas flexible resources are versatile to handle several products but are more expensive. Using a general mathematical formulation our analysis shows that the optimal design may have some dedicated and some flexible stages along the process. Interestingly, this decision should be decoupled from the chronological order of the stages along the process.
A survey on the knowledge, beliefs and behaviour of a general adult population in Malaysia with respect to the adverse effects of medicines
Authors: Jose Jimmy , Chong David , Lynn Tay Szu , Jye Goh Ee , Jimmy Beena
Published: April 2011

Objective

The aim of the study was to explore, in the Malaysian general population: knowledge and beliefs of the characteristics in general of medication-related side effects and side effects associated with different types of medicines; behaviour related to the safe use of drugs before and after taking a medication; and behaviour in the event of a medication-related side effect.

Methods

A 24-item self-administered questionnaire was developed and used to survey the general public living or working in suburban Kuala Lumpur, Malaysia. Eight hundred questionnaires were distributed, face to face, by researchers using quota sampling. Respondents’ knowledge, belief and behaviour were analysed and correlated with demographics, medical history and experience of side effects.

Key findings

Six hundred and ten respondents completed the questionnaire giving a response rate of 76.3%. The mean knowledge score for the respondents was 18.4 ± 3.6 out of the maximum possible score of 26. Educational level and experience of side effect had an influence on the knowledge score obtained. Respondents had misconceptions regarding the safety of complementary and alternative medicines (CAMs) and over-the-counter medications. Medication history and previous experience with side effects had a significant influence on the higher behaviour score obtained.

Conclusion

The survey has shown moderate results with regard to the knowledge of public regarding safety of medications, and there was evidence of under-estimating the risk of medications, especially CAMs. The misconceptions among the public, and inappropriate behaviour on drug safety-related aspects, is a concern which needs to be addressed in the interventions designed.
Fatigue Properties of Narrow and Wide Gap Braze Repaired Joints
Authors: Henhoeffer Thomas , Huang Xiao , Yandt Scott , Au Peter
Published: April 2011

With the increasing utilization of braze repair in the gas turbine industry, the properties of braze joints under simulated service conditions become vital in selecting braze repair over other processes. While braze repair has often been claimed to deliver mechanical properties equivalent to that of the parent material, this is largely based on the results of tensile or accelerated creep tests for most gas turbine hot section components failure occurs as a result of thermal fatigue or thermomechanical fatigue. The damage that occurs under such conditions cannot be assessed from tensile or creep testing. This study was undertaken to characterize the fatigue properties of narrow and wide gap brazed X-40 cobalt-based superalloy and compare these properties to that of the X-40 parent material. Butt joint narrow gap and wide gap specimens were vacuum brazed using BNi-9 braze alloy. X-40 and IN-738 were used as additive materials in wide gap braze joints. To characterize the fatigue properties of the braze joints and parent material, isothermal fatigue tests were conducted at 950°C and under load control using a fully reversed sinusoidal wave form having stress amplitude of 75% of the yield strength of the parent material. The braze specimens were fatigue tested in the as-brazed condition. The fatigue test results showed that the fatigue lives of the brazed specimens were lower than that of the parent material, particularly for the narrow gap samples and wide gap samples containing IN-738 additive alloy. All fatigue failures in the brazed samples occurred in the braze joints. An analysis of the fracture surfaces using a scanning electron microscope revealed that porosity was the major contributing factor to fatigue failures in the wide gap braze joints. The testing life debit observed in the narrow gap braze samples can be attributed to the presence of brittle boride phases in the braze joint. This study also included examination of techniques for reducing the aforementioned porosity and presence of brittle intermetallic phases.
High-Temperature Performance of Cast CF8C-Plus Austenitic Stainless Steel
Authors: Maziasz Philip J. , Pint Bruce A.
Published: April 2011

Covers and casings of small to medium size gas turbines can be made from cast austenitic stainless steels, including grades such as CF8C, CF3M, or CF10M. Oak Ridge National Laboratory and Caterpillar have developed a new cast austenitic stainless steel, CF8C-Plus, which is a fully austenitic stainless steel, based on additions of Mn and N to the standard Nb-stabilized CF8C steel grade. The Mn addition improves castability, as well as increases the alloy solubility for N, and both Mn and N synergistically act to boost mechanical properties. CF8C-Plus steel has outstanding creep-resistance at 600–900°C, which compares well with Ni-based superalloys such as alloys X, 625, 617, and 230. CF8C-Plus also has very good fatigue and thermal fatigue resistance. It is used in the as-cast condition, with no additional heat-treatments. While commercial success for CF8C-Plus has been mainly for diesel exhaust components, this steel can also be considered for gas turbine and microturbine casings. The purposes of this paper are to demonstrate some of the mechanical properties, to update the long-term creep-rupture data, and to present new data on the high-temperature oxidation behavior of these materials, particularly in the presence of water vapor.
An Experimental Investigation of Low-Octane Gasoline in Diesel Engines
Authors: Ciatti Stephen , Subramanian Swami Nathan
Published: April 2011

Conventional combustion techniques struggle to meet the current emissions norms. In particular, oxides of nitrogen (NOx) and particulate matter (PM) emissions have limited the utilization of diesel fuel in compression ignition engines. Advance combustion concepts have proved the potential to combine fuel efficiency and improved emission performance. Low-temperature combustion (LTC) offers reduced NOx and PM emissions with comparable modern diesel engine efficiencies. The ability of premixed, low-temperature compression ignition to deliver low PM and NOx emissions is dependent on achieving optimal combustion phasing. Diesel operated LTC is limited by early knocking combustion, whereas conventional gasoline operated LTC is limited by misfiring. So the concept of using an unconventional fuel with the properties in between those two boundary fuels has been experimented in this paper. Low-octane (84 RON) gasoline has shown comparable diesel efficiencies with the lowest NOx emissions at reasonable high power densities (NOx emission was 1 g/kW h at 12 bar BMEP and 2750 rpm).
Optical Investigation Into Wall Wetting From Late-Cycle Post-Injections Used for Diesel Particulate Filter Regeneration
Authors: Bozic Goran , Kook Sanghoon , Ekoto Isaac W. , Petersen Ben R. , Miles Paul C.
Published: April 2011

Wall wetting phenomena were investigated in a light-duty diesel optical engine, operating under typical diesel particulate filter regeneration conditions, through the use of liquid spray imaging during late-cycle post-injections. Three post-injection timings were explored: (1) an “early” timing (44.5 deg after top dead center (aTDC)) where high ambient temperatures and densities were expected to decrease the liquid penetration, (2) a “conventional” timing (78.5 deg aTDC) that is typically used to produce the necessary aftertreatment regeneration exhaust conditions, and (3) a “late” timing (133.5 deg aTDC) where in-cylinder flows generated by exhaust valve opening-induced blowdown can disrupt the liquid penetration. In addition to a 2007 U.S. certification diesel fuel, a palm-derived B20 biodiesel blend and a soy-derived B100 biodiesel were examined since liquid spray impingement is thought to worsen for biodiesel blends due to higher fuel distillation temperature, density, and viscosity. No significant wall wetting was observed for the early post-injection. However, considerable impingement occurred for the conventional and late post-injections. Liquid penetration and persistence of liquid fuel in the cylinder were found to increase with biodiesel content, while exhaust blowdown flows were ineffective in reducing the severity of wall wetting. Negligible distortion of jet structure was observed for the liquid spray at the late post-injection. Short pulse durations decreased the severity of liquid penetration with the soy-derived biodiesel during the early post-injection but were otherwise ineffective.
Spark Advance Real-Time Optimization Based on Combustion Analysis
Authors: Corti Enrico , Forte Claudio
Published: April 2011

One of the most effective factors influencing performance, efficiency, and pollutant emissions of internal combustion engines is the combustion phasing: In gasoline engines, electronic control units (ECUs) manage the spark advance (SA) in order to set the optimal combustion phase. SA is usually optimized on the test bench by changing the ignition angle while monitoring brake mean effective pressure (BMEP) and indicated mean effective pressure (IMEP) and brake specific fuel consumption (BSFC). The optimization process relates BMEP, IMEP, and BSFC mean values with the control setting (SA). However, the effect of SA on combustion is not deterministic due to the cycle-to-cycle variation: The analysis of mean values requires many engine cycles to be significant in the performance obtained with the given control setting. This paper presents a novel approach to SA optimization, with the objective of improving the performance analysis robustness while reducing the test time. For a given running condition, IMEP can be considered a function of the combustion phase, represented by the 50% mass fraction burned (50% MFB). Due to cycle-to-cycle variation, different MFB50 and IMEP values are obtained during a steady state test carried out with constant SA, but these values are related by means of a unique relationship. The distribution on the plane IMEP-MFB50 forms a parabola; therefore, the optimization could be carried out by choosing SA values maintaining the scatter around the vertex. Unfortunately, the distribution shape is slightly influenced by heat losses: This effect must be taken into account in order to avoid overadvanced calibrations. SA is then controlled by means of a proportional-integer-derivative controller, fed by an error that is defined based on previous considerations: A contribution is related to the MFB50-IMEP distribution, and a second contribution is related to the net cumulative heat release-IMEP distribution. The latter is able to take into account for heat losses. First, the methodology has been tested on in-cylinder pressure data, collected from different SI engines; then, it has been implemented in real-time by means of a programmable combustion analyzer: The system performs a cycle-to-cycle combustion analysis, evaluating the combustion parameters necessary to calculate the target SA, which is then actuated by the ECU. The approach proved to be efficient, reducing the number of engine cycles necessary for the calibration to less than 1000 per operating condition.
A Nonlinear Model of a Slack Cable With Bending Stiffness and Moving Ends With Application to Elevator Traveling and Compensation Cables
Authors: Zhu W. D. , Ren H. , Xiao C.
Published: April 2011

A nonlinear, planar model of a slack cable with bending stiffness and arbitrarily moving ends is developed. The model uses the slope angle of the centroid line of the cable to describe the motion of the cable, and the resulting integropartial differential equation with constraints is derived using Hamilton’s principle. A new method is developed to obtain the spatially discretized equations, and the Baumgarte stabilization procedure is used to solve the resulting differential-algebraic equations. The model can be used to calculate the equilibria and corresponding free vibration characteristics of the cable, as well as the dynamic response of the cable under arbitrarily moving ends. The results for an equilibrium and free vibration characteristics around the equilibrium are experimentally validated on a laboratory steel band. The methodology is applied to elevator traveling and compensation cables. It is found that a vertical motion of the car can introduce a horizontal vibration of a traveling or compensation cable. The results presented are verified by a commercial finite element software. The current method is shown to be more efficient than the finite element method as it uses a much smaller number of elements to reach the same accuracy. Some other interesting features include the condition for a traveling or compensation cable equilibrium to be closest to a natural loop and a direct proof that the catenary solution is unique.
A Discrete Dislocation Plasticity Analysis of a Single-Crystal Half-Space Indented by a Rigid Cylinder
Authors: Yin X. , Komvopoulos K.
Published: April 2011

Elastic-plastic indentation of a single-crystal half-space by a rigid cylinder was analyzed by discrete dislocation plasticity. Short-range dislocation interactions were modeled by a set of constitutive rules of dislocation emission, glide, pinning (by obstacles), and annihilation. The occurrence of the first dislocation dipole, multiplication of dislocations, and evolution of subsurface stress field were examined in terms of contact load, dislocation source density, slip-plane distance and orientation angle, and indenter radius. In the presence of defects (dislocation sources), the critical load for dislocation initiation is less than that of a defect-free medium and depends on dislocation source density, slip-plane distance, and indenter radius. The critical indenter radius resulting in deformation under the theoretical material strength is determined from numerical results, and the role of dislocation obstacles is interpreted in terms of their spatial density. Simulations provide insight into yielding and plastic deformation of indented single-crystal materials, and establish a basis for developing coarse-grained plasticity models of localized contact deformation in polycrystalline solids.
Aeroelastic Control of Long-Span Suspension Bridges
Authors: Graham J. Michael R. , Limebeer David J. N. , Zhao Xiaowei
Published: April 2011

The modeling, control, and dynamic stabilization of long-span suspension bridges are considered. By employing leading- and trailing-edge flaps in combination, we show that the critical wind speeds for flutter and torsional divergence can be increased significantly. The relatively less well known aerodynamic properties of leading-edge flaps will be studied in detail prior to their utilization in aeroelastic stability and control system design studies. The optimal approximation of the classical Theodorsen circulation function will be studied as part of the bridge section model building exercise. While a wide variety of control systems is possible, we focus on compensation schemes that can be implemented using passive mechanical components such as springs, dampers, gearboxes, and levers. A single-loop control system that controls the leading- and trailing-edge flaps by sensing the main deck pitch angle is investigated. The key finding is that the critical wind speeds for flutter and torsional divergence of the sectional model of the bridge can be greatly increased, with good robustness characteristics, through passive feedback control. Static winglets are shown to be relatively ineffective.
Resonance hairpin and Langmuir probe-assisted laser photodetachment measurements of the negative ion density in a pulsed dc magnetron discharge
Authors: Bradley James W. , Dodd Robert , You S.-D. , Sirse Nishant , Karkari Shantanu Kumar
Published: April 2011

The time-resolved negative oxygen ion density n− close to the center line in a reactive pulsed dc magnetron discharge (10 kHz and 50% duty cycle) has been determined for the first time using a combination of laser photodetachment and resonance hairpin probing. The discharge was operated at a power of 50 W in 70% argon and 30% oxygen gas mixtures at 1.3 Pa pressure. The results show that the O− density remains pretty constant during the driven phase of the discharge at values typically below 5×1014 m−3; however, in the off-time, the O− density grows reaching values several times those in the on-time. This leads to the negative ion fraction (or degree of electronegativity) α=n−/ne being higher in the off phase (maximum value α∼1) than in the on phase (α=0.05–0.3). The authors also see higher values of α at positions close to the magnetic null than in the more magnetized region of the plasma. This fractional increase in negative ion density during the off-phase is attributed to the enhanced dissociative electron attachment of highly excited oxygen molecules in the cooling plasma. The results show that close to the magnetic null the photodetached electron density decays quickly after the laser pulse, followed by a slow decay over a few microseconds governed by the negative ion temperature. However, in the magnetized regions of the plasma, this decay is more gradual. This is attributed to the different cross-field transport rates for electrons in these two regions. The resonance hairpin probe measurements of the photoelectron densities are compared directly to photoelectron currents obtained using a conventional Langmuir probe. There is good agreement in the general trends, particularly in the off-time.
Preparation of clean Bi2Te3 and Sb2Te3 thin films to determine alignment at valence band maxima
Authors: Fang Fang , Opila Robert L. , Venkatasubramanian Rama , Colpitts Thomas
Published: April 2011

The thermoelectric application of Bi2Te3 and Sb2Te3 thin film structures relies on the relative alignment of the valence band maxima for good electrical conduction. In order to determine the valence band maxima of the bulk films, the authors propose a simple repeatable treatment of a chemical etching in dilute hydrochloric acid solution and a subsequent annealing at ∼150 °C under ultrahigh vacuum to prepare clean surfaces of Bi2Te3 and Sb2Te3 thin films. High-resolution photoemission spectroscopy using synchrotron radiation is used to investigate the chemical states of epitaxial Bi2Te3 and Sb2Te3 thin films grown on GaAs by low-temperature metal-organic chemical vapor deposition. The valence band and core-level photoemission spectra indicate that the surface contaminations and oxides were removed. After chemical etching in acid solution, elemental Te was observed on the surface; a follow-up anneal in ultrahigh vacuum creates a stoichiometric oxide-free surface.
Cryogenic thermal simulator for testing low temperature thermophotovoltaic cells
Authors: DeMeo Dante F. , Vandervelde Thomas E.
Published: April 2011

Thermophotovoltaic (TPV) devices convert infrared electromagnetic radiation into electricity. The authors’ research involves the use of strained-layer superlattices to enable TPV devices to operate at longer wavelengths than the current state of the art designs. To determine the performance of these devices, a novel test apparatus was designed and constructed. Here, the authors present a custom-built, cryogenic vacuum chamber for the testing and characterization of TPV samples. As TPV cells become sensitive to longer wavelength photons (lower source temperatures) in the infrared, the need to control the sample’s ambient temperature becomes critical for accurate testing; thus, the tester includes two copper heat shields cooled via conduction with two liquid nitrogen reservoirs. A calibrated blackbody source is used to illuminate a temperature controlled sample in high vacuum (∼10−6 Torr). The chamber temperature is extensively monitored and is designed to generate current-voltage (I-V) curves for TPV samples at different temperatures and input radiation in order to determine cell conversion efficiency. The system is evaluated based on the performance of its component systems.
A memorandum that changed the world
Authors: Bernstein Jeremy
Published: April 2011

We present an analysis of both the content and the influence of the 1940 memoir by Otto Frisch and Rudolf Peierls that showed that nuclear weapons were possible.
Improving students’ understanding of quantum mechanics via the Stern–Gerlach experiment
Authors: Zhu Guangtian , Singh Chandralekha
Published: April 2011

The Stern–Gerlach experiment can play an important role in teaching the formalism of quantum mechanics. In the context of a finite-dimensional Hilbert space students can learn how to prepare a specific quantum state starting from an arbitrary state, issues related to the time evolution of the wave function and quantum measurement. The Stern–Gerlach experiment can also be used to teach the distinction between the physical space where the experiment is performed and the Hilbert space where the state of the system lies, and how information about the state of the system in the Hilbert space can be exploited to interpret the possible outcomes of the experiment in physical space. Students can learn the advantages of choosing an appropriate basis to make predictions about the outcomes of experiments with different arrangements of Stern–Gerlach devices. The latter can also help students understand that an ensemble of identically prepared systems is not the same as a mixture. We discuss student difficulties with the Stern–Gerlach experiment based on written tests and interviews with advanced undergraduate and graduate students in quantum mechanics courses. We also discuss preliminary data which suggest that the Quantum Interactive Learning Tutorial on the Stern–Gerlach experiment is helpful in improving student understanding of these concepts.
Calibrating the frequency of tuning forks by means of Lissajous figures
Authors: Quereda Jorge , Ramón Marina , Silva Blanca , Hinarejos Juan José , Rodrigo José Gabriel , Farías Daniel
Published: April 2011

We produce Lissajous figures by modulating a laser beam along two perpendicular directions by means of two tuning forks. When the ratio of the resonant frequencies of the tuning forks is a small rational number, Lissajous figures are clearly resolved on a screen. Because the ratio of frequencies is never exactly a rational number, a phase drift of the Lissajous figures is observed as a function of time. If the period of this phase drift is measured, variations in the resonant frequencies as small as 0.01 Hz can be detected.
Equation of the field lines of an axisymmetric multipole with a source surface
Authors: Gregory S. G.
Published: April 2011

Optical spectropolarimeters can be used to produce maps of the surface magnetic fields of stars and hence to determine how stellar magnetic fields vary with stellar mass, rotation rate, and evolutionary stage. In particular, we now can map the surface magnetic fields of forming solar-like stars, which are still contracting under gravity and are surrounded by a disk of gas and dust. Their large scale magnetic fields are almost dipolar on some stars, and there is evidence for many higher order multipole field components on other stars. The availability of new data has renewed interest in incorporating multipolar magnetic fields into models of stellar magnetospheres. I describe the basic properties of axial multipoles of arbitrary degree ℓ and derive the equation of the field lines in spherical coordinates. The spherical magnetic field components that describe the global stellar field topology are obtained analytically assuming that currents can be neglected in the region exterior to the star, and interior to some fixed spherical equipotential surface. The field components follow from the solution of Laplace’s equation for the magnetostatic potential.
Absorption of a pulse by an optically dense medium: An argument for field quantization
Authors: Berman P. R. , Le Gouët J.-L.
Published: April 2011

The theory of the absorption of a weak optical pulse by an optically dense medium is shown to lead to unphysical results unless the radiation field is quantized. In contrast to the photoelectric effect, the atom-field dynamics for pulsed field absorption can be obtained using elementary quantum mechanics without imposing any assumptions on the nature of the detection process. As such, pulsed field absorption offers distinct advantages over the photoelectric effect as a proving ground for field quantization. If the classical field pulse is replaced by a quantized, multimode field state, many classical field results are recovered without the inconsistencies that arise in the classical field calculation.
Demonstration of optical spatial coherence using a variable width source
Authors: Sharpe J. P. , Collins D. A.
Published: April 2011

We describe an experiment that clearly shows the change in optical spatial coherence as a function of source size. The experiment is easy to set up, requires modest equipment, and gives a striking demonstration of the celebrated phase shift of the interference fringes. The experiment yields quantitative results that agree well with theory. Setup and data acquisition are suitable for a 3 h upper division undergraduate physics laboratory.
Dirac, Majorana, and Weyl fermions
Authors: Pal Palash B.
Published: April 2011

We discuss the Dirac, Majorana, and Weyl fermion fields. The definitions and motivations for introducing each kind of field is discussed, along with the connections between them. It is pointed out that these definitions have to do with the proper Lorentz group and not with any discrete symmetry. The action of discrete symmetries, such as charge conjugation and CP on various types of fermion fields, which are particularly important for Majorana fermions, is also clarified.
Radial motion in a central potential for singular mass densities
Authors: Zürcher Ulrich , Kaufman Miron
Published: April 2011

We study the radial motion of an object in the gravitational field produced by an isotropic mass density that is singular at the origin. This problem applies to elliptical galaxies and can be used to illustrate motion in a central field appropriate for an intermediate-level mechanics course.
Newton’s superb theorem: An elementary geometric proof
Authors: Schmid Christoph
Published: April 2011

Newton’s “superb theorem” for the gravitational 1/r2 force states that a spherically symmetric mass distribution attracts a body outside as if the entire mass were concentrated at the center. This theorem is crucial for Newton’s comparison of the Moon’s orbit with terrestrial gravity, which is evidence for the 1/r2 law. In this paper, we give an elementary geometric proof, which is simpler than Newton’s geometric proof and more elementary than proofs using calculus.
Five ways to the nonresonant dynamic Stark effect
Authors: Sussman Benjamin J.
Published: April 2011

The dynamic Stark effect is the quasistatic shift in energy levels due to the application of optical fields. The effect is in many ways similar to the static Stark effect. However, the dynamic Stark effect can be applied on rapid time scales and with high energies, comparable to those of atoms and molecules themselves. The dynamic Stark effect due to nonresonant laser fields is used in a myriad of contemporary experiments to hold and align molecules, to shape potential energy surfaces, and to make rapid transient birefringence. Five approaches of increasing sophistication are used to describe the dynamic Stark effect. One application, molecular alignment, is summarized and a comparison is made between the dynamic Stark effect and Stokes light generation in a Raman scattering process.
A double pendulum model of tennis strokes
Authors: Cross Rod
Published: April 2011

The physics of swinging a tennis racquet is examined by modeling the forearm and the racquet as a double pendulum. We consider differences between a forehand and a serve, and show how they differ from the swing of a bat and a golf club. It is also shown that the swing speed of a racquet, like that of a bat or a club, depends primarily on its moment of inertia rather than on its mass.
The implications of a robust curriculum in introductory mechanics
Authors: Hoellwarth Chance , Moelter Matthew J.
Published: April 2011

We have developed a curriculum for introductory mechanics that emphasizes interactive engagement and conceptual understanding using the studio format. As previously reported, we have shown in three different quarters that the curriculum much improved the students’ conceptual understanding compared to the traditional course without significantly affecting the scores on a traditional final exam. Here we report the results for the entire three-year period during which the course was taught, 34 sections of the course were taught with 11 different instructors to over 1200 students. In each term, these sections had common exams, syllabus, and schedule. Student experiences were very similar in terms of activities. Student performance was measured using the force and motion conceptual evaluation or the force concept inventory; the average pre/post normalized gain was 0.59. There was no significant correlation with any instructor characteristics, including teaching experience, knowledge of interactive-engagement methods, and attitudes. Because the instructor characteristics are not important, it is the structure of the course that promotes the learning gains.
Classical applications of the Klein–Gordon equation
Authors: Gravel Pierre , Gauthier Claude
Published: April 2011

The quantum mechanical origin of the Klein–Gordon equation hides its capability to model many classical systems. We consider three examples of vibrating systems whose mathematical descriptions lead to the Klein–Gordon equation. These examples are adapted to applications such as the motion of suspended cables and Inca rope suspension bridges. We also discuss the correspondence between the classical and quantum settings of this equation as a way to provide an explanation of the concept of mass.
Student understanding of wave behavior at a boundary: The limiting case of reflection at fixed and free ends
Authors: Kryjevskaia Mila , Stetzer MacKenzie R. , Heron Paula R. L.
Published: April 2011

We investigated student understanding of wave behavior at a boundary in the context of pulses and periodic waves in water and in elastic media. The participants were science and engineering majors in introductory calculus-based physics. We document several conceptual and reasoning difficulties and describe the refinement and assessment of our instructional materials. The results show significant improvements in student learning of some aspects of superposition and reflection, but some reasoning patterns that yield incorrect predictions persist. Among these difficulties is the tendency to employ simple rule-based approaches in cases in which a systematic application of the superposition principle is necessary to predict the motion of points in the medium over an interval of time.
Novel Biphenyl-Oxidizing Bacteria and Dioxygenase Genes from a Korean Tidal Mudflat
Authors: Lee Tae Kwon , Lee Jaejin , Sul Woo Jun , Iwai Shoko , Chai Benli , Tiedje James M. , Park Joonhong
Published: April 2011

Gene-targeted FLX titanium pyrosequencing integrated with stable isotope probing (SIP) using [
13
C]biphenyl substrate revealed that tidal mudflat sediments harbor novel aromatic ring hydroxylating dioxygenases (ARHD). More than 80% of the detected ARHD genes comprise four clades (0.5 distance) with 49 to 70% amino acid identity to sequences in public databases. The 16S rRNA sequences enriched in the
13
C fraction were from the
Betaproteobacteria
, bacilli (primarily
Paenibacillus
-like), and unclassified phyla.
Characterization of the Genome of the Polyvalent Lytic Bacteriophage GTE2, Which Has Potential for Biocontrol of Gordonia-, Rhodococcus-, and Nocardia-Stabilized Foams in Activated Sludge Plants
Authors: Petrovski Steve , Seviour Robert J. , Tillett Daniel
Published: April 2011

Hydrophobic
Actinobacteria
are commonly associated with the stabilization of foams in activated sludge systems. One possible attractive approach to control these foam-stabilizing organisms is the use of specific bacteriophages. We describe the genome characterization of a novel polyvalent DNA phage, GTE2, isolated from activated sludge. This phage is lytic for
Gordonia terrae
,
Rhodococcus globerulus
,
Rhodococcus erythropolis
,
Rhodococcus erythropolis
,
Nocardia otitidiscaviarum
, and
Nocardia brasiliensis
. Phage GTE2 belongs to the family
Siphoviridae
, possessing a characteristic icosahedral head encapsulating a double-stranded DNA linear genome (45,530 bp) having 10-bp 3′-protruding cohesive ends. The genome sequence is 98% unique at the DNA level and contains 57 putative genes. The genome can be divided into two components, where the first is modular and encodes phage structural proteins and lysis genes. The second is not modular, and the genes harbored there are involved in DNA replication, repair, and metabolism. Some have no known function. GTE2 shows promising results in controlling stable foam production by its host bacteria under laboratory conditions, suggesting that it may prove useful in the field as a biocontrol agent.
Genome-Wide Transcriptional and Physiological Responses of Bradyrhizobium japonicum to Paraquat-Mediated Oxidative Stress
Authors: Donati Andrew J. , Jeon Jeong-Min , Sangurdekar Dipen , So Jae-Seong , Chang Woo-Suk
Published: April 2011

The rhizobial bacterium
Bradyrhizobium japonicum
functions as a nitrogen-fixing symbiont of the soybean plant (
Glycine max
). Plants are capable of producing an oxidative burst, a rapid proliferation of reactive oxygen species (ROS), as a defense mechanism against pathogenic and symbiotic bacteria. Therefore,
B. japonicum
must be able to resist such a defense mechanism to initiate nodulation. In this study, paraquat, a known superoxide radical-inducing agent, was used to investigate this response. Genome-wide transcriptional profiles were created for both prolonged exposure (PE) and fulminant shock (FS) conditions. These profiles revealed that 190 and 86 genes were up- and downregulated for the former condition, and that 299 and 105 genes were up- and downregulated for the latter condition, respectively (>2.0-fold;
P
< 0.05). Many genes within putative operons for F
0
F
1
-ATP synthase, chemotaxis, transport, and ribosomal proteins were upregulated during PE. The transcriptional profile for the FS condition strangely resembled that of a bacteroid condition, including the FixK
2
transcription factor and most of its response elements. However, genes encoding canonical ROS scavenging enzymes, such as superoxide dismutase and catalase, were not detected, suggesting constitutive expression of those genes by endogenous ROS. Various physiological tests, including exopolysaccharide (EPS), cellular protein, and motility characterization, were performed to corroborate the gene expression data. The results suggest that
B. japonicum
responds to tolerable oxidative stress during PE through enhanced motility, increased translational activity, and EPS production, in addition to the expression of genes involved in global stress responses, such as chaperones and sigma factors.
Correlation of Borrelia burgdorferi Sensu Lato Prevalence in Questing Ixodes ricinus Ticks with Specific Abiotic Traits in the Western Palearctic
Authors: Estrada-Peña Agustín , Ortega Carmelo , Sánchez Nely , DeSimone Lorenzo , Sudre Bertrand , Suk Jonathan E. , Semenza Jan C.
Published: April 2011

This meta-analysis of reports examining ticks throughout the Western Palearctic region indicates a distinct geographic pattern for
Borrelia burgdorferi
sensu lato prevalence in questing nymphal
Ixodes ricinus
ticks. The greatest prevalence was reported between the 5°E and 25°E longitudes based on an analysis of 123 collection points with 37,940 nymphal tick specimens (87.43% of total nymphs; 56.35% of total ticks in the set of reports over the target area). Climatic traits, such as temperature and vegetation stress, and their seasonality correlated with
Borrelia
prevalence in questing ticks. The greatest prevalence was associated with mild winter, high summer, and low seasonal amplitude of temperatures within the range of the tick vector, higher vegetation indices in the May-June period, and well-connected vegetation patches below a threshold at which rates suddenly drop. Classification of the target territory using a qualitative risk index derived from the abiotic variables produced an indicator of the probability of finding infected ticks in the Western Palearctic region. No specific temporal trends were detected in the reported prevalence. The ranges of the different
B. burgdorferi
sensu lato genospecies showed a pattern of high biodiversity between 4°W and 20°E, partially overlapping the area of highest prevalence in ticks.
Borrelia afzelii
and
Borrelia garinii
are the dominant species in central Europe (east of ∼25°E), but
B. garinii
may appear alone at southern latitudes and
Borrelia lusitaniae
is the main indicator species for meridional territories.
Regulation of Cell Division, Biofilm Formation, and Virulence by FlhC in Escherichia coli O157:H7 Grown on Meat
Authors: Sule Preeti , Horne Shelley M. , Logue Catherine M. , Prüß Birgit M.
Published: April 2011

To understand the continuous problems that
Escherichia coli
O157:H7 causes as food pathogen, this study assessed global gene regulation in bacteria growing on meat. Since FlhD/FlhC of
E. coli
K-12 laboratory strains was previously established as a major control point in transducing signals from the environment to several cellular processes, this study compared the expression pattern of an
E. coli
O157:H7 parent strain to that of its isogenic
flhC
mutant. This was done with bacteria that had been grown on meat. Microarray experiments revealed 287 putative targets of FlhC. Real-time PCR was performed as an alternative estimate of transcription and confirmed microarray data for 13 out of 15 genes tested (87%). The confirmed genes are representative of cellular functions, such as central metabolism, cell division, biofilm formation, and pathogenicity. An additional 13 genes from the same cellular functions that had not been hypothesized as being regulated by FlhC by the microarray experiment were tested with real-time PCR and also exhibited higher expression levels in the
flhC
mutant than in the parent strain. Physiological experiments were performed and confirmed that FlhC reduced the cell division rate, the amount of biofilm biomass, and pathogenicity in a chicken embryo lethality model. Altogether, this study provides valuable insight into the complex regulatory network of the pathogen that enables its survival under various environmental conditions. This information may be used to develop strategies that could be used to reduce the number of cells or pathogenicity of
E. coli
O157:H7 on meat by interfering with the signal transduction pathways.
Occurrence of Thermotolerant Campylobacter spp. on Eggshells: a Missing Link for Food-Borne Infections?
Authors: Messelhäusser U. , Thärigen D. , Elmer-Englhard D. , Bauer H. , Schreiner H. , Höller C.
Published: April 2011

We analyzed the prevalence of thermotolerant
Campylobacter
spp. compared that of to
Salmonella
spp. in raw yolk and on eggshells. A total of 2,710 eggs were investigated for each bacterium. Viable bacteria were found in 4.1% (
Campylobacter
spp.) and 1.1% (
Salmonella
spp.) of the eggshell samples, whereas the egg yolk samples were negative for both bacteria.