bluuebunny/crossref_metadata_2025 huggingface dataset:
Variations in Photosystem I Properties in the Primordial Cyanobacterium Gloeobacter violaceus PCC 7421
Authors: Mimuro Mamoru , Yokono Makio , Akimoto Seiji
Published: September 2009

We compared the optical properties of the trimeric photosystem (PS) I complexes of the primordial cyanobacterium Gloeobacter violaceus PCC 7421 with those of Synechocystis sp. PCC 6803. Gloeobacter violaceus PS I showed (1) a shorter difference maximum of P700 by approximately 2 nm, (2) a smaller antenna size by approximately 10 chlorophyll (Chl) a molecules and (3) an absence of Red Chls. The energy transfer kinetics in the antennae at physiological temperatures were very similar between the two species due to the thermal equilibrium within the antenna; however, they differed at 77 K where energy transfer to Red Chls was clearly observed in Synechocystis sp. PCC 6803. Taken together with the lower P700 redox potential in G. violaceus by approximately 60 mV, we discuss differences in the optical properties of the PS I complexes with respect to the amino acid sequences of core proteins and further to evolution of cyanobacteria.
Pp IX Silica Nanoparticles Demonstrate Differential Interactions with In Vitro Tumor Cell Lines and In Vivo Mouse Models of Human Cancers
Authors: Simon Virginie , Devaux Corinne , Darmon Audrey , Donnet Thibault , Thiénot Edouard , Germain Matthieu , Honnorat Jérôme , Duval Alex , Pottier Agnès , Borghi Elsa , Levy Laurent , Marill Julie
Published: September 2009

Protoporphyrin IX (Pp IX) silica nanoparticles, developed for effective use in photodynamic therapy (PDT), were explored in in vitro and in vivo models with the ambition to improve knowledge on the role of biological factors in the photodamage. Pp IX silica nanoparticles are found efficient at temperature with extreme metabolic downregulation, which suggest a high proportion of passive internalization. For the first time, clearance of silica nanoparticles on tumor cells is established. Cell viability assessment in six tumor cell lines is reported. In all tumor types, Pp IX silica nanoparticles are more efficient than free Pp IX. A strong fluorescence signal of reactive oxygen species generation colocalized with Pp IX silica nanoparticles, correlates with 100% of cell death. In vivo studies performed in HCT 116, A549 and glioblastoma multiforme tumors‐bearing mice show tumor uptake of Pp IX silica nanoparticles with better tumor accumulation than the control alone, highlighting a high selectivity for tumor tissues. As observed in in vitro tests, tumor cell type is likely a major determinant but tumor microenvironment could more influence this differential time accumulation dynamic. The present results strongly suggest that Pp IX silica nanoparticles may be involved in new alternative local applications of PDT.
Report of Two Double‐Blind Randomized Placebo‐Controlled Pilot Studies of a Carbohydrate‐Rich Nutrient Mixture for Treatment of Seasonal Affective Disorder (SAD)
Authors: Mischoulon David , Pedrelli Paola , Wurtman Judith , Vangel Mark , Wurtman Richard
Published: September 2009

We investigated a carbohydrate‐rich nutrient‐drink mix for treatment of seasonal affective disorder (SAD). This mixture may contribute to brain serotonin synthesis, potentially exerting an antidepressant effect and controlling carbohydrate cravings. Two successive double‐blind placebo‐controlled studies were performed. In Study 1, 18 subjects (50% women; mean age 43 ± 15 years) with SCID‐diagnosed SAD were randomized to 12 days of twice daily carbohydrate beverage (CHO) containing mixed starches, or a placebo beverage (PRO) containing the CHO mix plus casein protein to dampen serotonin synthesis. Following a 2‐day washout, subjects were crossed over to the other treatment for 12 days. In Study 2, 32 subjects (63% women; mean age 46 ± 14 years) with SCID‐diagnosed SAD were randomized to 21 days of CHO or PRO. Efficacy in both studies was determined by the first 17 items of the Hamilton Depression Rating Scale (HAM‐D‐28), an appetite questionnaire, and regular weighing. In Study 1, response rates were 50% for both groups. Remission rates favored CHO (50% vs. 38%), as did the decrease in the HAM‐D‐17 score, but differences were nonsignificant. In Study 2, response rates were 71% for CHO and 76% for PRO, and remission rates were 71% for each group. Both treatment groups experienced significant improvement in HAM‐D‐17 scores within 1 week of treatment, which continued through the entire study period. Weight change did not differ significantly between treatment groups in either study. The drink mix was well tolerated and treatment adherence was high. Both the active and placebo intervention were effective in alleviating symptoms of SAD. Replication studies in larger samples appear warranted.
Neurological and Cardiovascular Adverse Events Associated with Antimanic Treatment in Children and Adolescents
Authors: Jerrell Jeanette M.
Published: September 2009

To identify the factors associated with incident neurological and cardiovascular adverse events in children and adolescents treated with antimanic agents, a retrospective, longitudinal study was conducted. Medicaid medical and pharmacy claims between January 1996 and December 2005 were used to identify 3657 children and adolescents prescribed antimanic medications, and a random sample of 4500 children not treated with psychotropic medications. All adverse events examined (sedation/drowsiness, headaches, involuntary movements/extrapyramidal symptoms (EPS), cardiovascular events, hypertension, and orthostatic hypotension) were more prevalent in the antimanic‐treated cohort. The odds of developing incident sedation/drowsiness and headaches were significantly higher for those prescribed carbamazepine, and co‐prescribed selective serotonin reuptake inhibitors or antipsychotics. The odds of incident involuntary movements/EPS were significantly higher for those co‐prescribed antimanic and antipsychotic agents, and those with comorbid central nervous system (CNS), organic brain disorders/mental retardation, or epilepsy. Incident cardiovascular events, hypertension, and orthostatic hypotension odds were significantly higher for those co‐prescribed antimanic agents and antipsychotics, or those with comorbid epilepsy or metabolic conditions. Co‐prescription of antimanic and antipsychotic agents is more likely associated with neurological and cardiovascular adverse reactions, especially in young patients with preexisting CNS/neurological disorders.
Transition Mechanisms in Separation Bubbles Under Low- and Elevated-Freestream Turbulence
Authors: McAuliffe Brian R. , Yaras Metin I.
Published: September 2009

Through numerical simulations, this paper examines the nature of instability mechanisms leading to transition in separation bubbles. The results of two direct numerical simulations are presented in which separation of a laminar boundary layer occurs over a flat surface in the presence of an adverse pressure gradient. The primary difference in the flow conditions between the two simulations is the level of freestream turbulence with intensities of 0.1% and 1.45% at separation. In the first part of the paper, transition under a low-disturbance environment is examined, and the development of the Kelvin–Helmholtz instability in the separated shear layer is compared to the well-established instability characteristics of free shear layers. The study examines the role of the velocity-profile shape on the instability characteristics and the nature of the large-scale vortical structures shed downstream of the bubble. The second part of the paper examines transition in a high-disturbance environment, where the above-mentioned mechanism is bypassed as a result of elevated-freestream turbulence. Filtering of the freestream turbulence into the laminar boundary layer results in streamwise streaks, which provide conditions under which turbulent spots are produced in the separated shear layer, grow, and then merge to form a turbulent boundary layer. The results allow identification of the structure of the instability mechanism and the characteristic structure of the resultant turbulent spots. Recovery of the reattached turbulent boundary layer is then examined for both cases. The large-scale flow structures associated with transition are noted to remain coherent far downstream of reattachment, delaying recovery of the turbulent boundary layer to an equilibrium state.
Experimental and Computational Fluid Dynamics Based Determination of Flutter Limits in Supersonic Space Turbines
Authors: Groth Pieter , Mårtensson Hans , Edin Niklas
Published: September 2009

Turbines operating at high pressure in high velocity flow are susceptible to flutter. As reduced frequencies become sufficiently low, negative aerodynamic damping will be found in some modes. Ensuring that the total system damping is positive over the entire turbine operating envelope for all modes is of utmost importance in any design since flutter in a turbine often causes blade failures. This is in contrast to the normal engineering approach, which is to require a positive aerodynamic damping. A unique test campaign with a 1.5 stage supersonic space turbine has been performed. The turbine was operated at simulated running conditions over a large operating envelope in order to map out flutter limits. During the test, flutter was intentionally triggered at seven different operating conditions. Unique data have been obtained during the test that supports validation of design tools and enables better understanding of flutter in this type of turbine. Based on the data the flutter boundary for the turbine could be established. Using computational fluid dynamics (CFD) tools flutter was predicted at all operating points where the flutter limit was crossed. Both in predictions and as evidenced in test the two nodal diameter backward traveling mode was the most unstable. In addition to this predicted values of aerodynamic damping at flutter agreed well with damping estimated from measured amplitude growth.
Design and Experimental Verification of Mistuning of a Supersonic Turbine Blisk
Authors: Groth Pieter , Mårtensson Hans , Andersson Clas
Published: September 2009

A rotor blisk of a supersonic space turbine has previously been designed to allow for free flutter to occur in an air test rig (Groth Mårtensson, and Edin, 2010, “Experimental and Computational Fluid Dynamics Based Determination of Flutter Limits in Supersonic Space Turbines,” 132(1), p. 011010). Flutter occurred at several operating conditions, and the flutter boundary for the test turbine was established. In this paper the rotor blisk is redesigned in order to inhibit flutter. The design strategy chosen is to introduce a mistuning concept. Based on aeroelastic analyses using a reduced order model a criterion for the required level of mistuning is established in order to stabilize the lower system modes. Proposals in literature suggest and analyze mistuning by varying blade mode frequencies in random patterns or by modifying blades in an odd-even pattern. Here a modification of sectors of the blisk is introduced in order to bring a sufficient split of the system mode frequencies. To verify that the redesigned blisk efficiently could inhibit flutter, an experiment similar to that in the work of Groth et al. is performed with the mistuned rotor blisk. By running the redesigned blisk at operating conditions deep into the unstable region of the tuned blisk, it is demonstrated that a relative low level of mistuning is sufficient to eliminate rotor flutter.
Investigation of Loss Generation in an Embedded Transonic Fan Stage at Several Gaps Using High-Fidelity, Time-Accurate Computational Fluid Dynamics
Authors: List Michael G. , Gorrell Steven E. , Turner Mark G.
Published: September 2009

The blade-row interaction (BRI) rig at the Air Force Research Laboratory, Compressor Aero Research Laboratory, has been simulated at three axial gaps between the highly loaded upstream stator row and the downstream transonic rotor using TURBO. Previous work with the stage matching investigation (SMI) demonstrated a strong dependence of mass flow rate, efficiency, and pressure ratio on the axial spacing between an upstream wake generator and the downstream rotor through the variation of the axial gap. Several loss producing mechanisms were discovered and related to the spacings, referred to as close, mid, and far. In the SMI work, far spacing had the best performance. The BRI experiments were a continuation of the SMI work with the wake generator replaced with a swirler row to turn the flow and a deswirler row to create a wake by diffusion. Results of the BRI experiments showed a performance degradation between mid- and far spacings, which was not observed in SMI. This trend is seen in the numerical work as well, and the time-averaged data show that the majority of this performance change occurred in the rotor. An unsteady separation bubble periodically forms and collapses as shocks reflect through the stator passage, creating additional aerodynamic blockage. The shed vortices induced by the unsteady loading and unloading of the stator trailing edge are chopped, with a frequency related to the spacing, by the rotor leading edge and ingested by the rotor. Once ingested the vortices interact in varying degrees with the rotor boundary layer. A treatment of the loss production in the BRI rig is given based on the time-accurate and time-averaged, high-fidelity TURBO results.
Three Dimensional Clocking Effects in a One and a Half Stage Transonic Turbine
Authors: Schennach O. , Woisetschläger J. , Paradiso B. , Persico G. , Gaetani P.
Published: September 2009

This paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three-dimensional aerodynamics of the second vane for different clocking positions. To give an overview of the time-averaged flow field, five-hole probe measurements were performed upstream and downstream of the second stator. Furthermore in these planes additional unsteady measurements were carried out with laser Doppler velocimetry in order to record rotor phase-resolved velocity, flow angle, and turbulence distributions at two different clocking positions. In the planes upstream of the second vane, the time-resolved pressure field has been measured by means of a fast response aerodynamic pressure probe. This paper shows that the secondary flows of the second vane are significantly modified by the different clocking positions, in connection with the first vane modulation of the rotor secondary flows. An analysis of the performance of the second vane is also carried out, and a 0.6% variation in the second vane loss coefficient has been recorded among the different clocking positions.
Transition Prediction on Turbine Blade Profile With Intermittency Transport Equation
Authors: Piotrowski Wladyslaw , Elsner Witold , Drobniak Stanisław
Published: September 2009

This paper presents the results of tests and validations of the γ-Reθ model proposed by Menter et al. (2006, “A Correlation-Based Transition Model Using Local Variables—Part I: Model Formation,” ASME J. Turbomach., 128, pp. 413–422), which was extended by in-house correlations for onset location and transition length. The tests performed were based on experimental data from the flat plate test cases available at the ERCOFTAC database as well as on experimental data from the turbine blade profile investigated at Czestochowa University of Technology. Further on, the model was applied for unsteady calculations of the blade profile test case, where chosen inlet conditions (turbulent intensity and wake parameters) were applied. For the selected case, numerical results were compared not only with the experimental data but also with the results obtained with other transition models. It was shown that the applied model was able to reproduce some essential flow features related to the bypass and wake-induced transition, and the simulations revealed good agreement with the experimental results in terms of localization and extent of wake-induced transition.
Aerodynamic Asymmetry Analysis of Unsteady Flows in Turbomachinery
Authors: Ekici Kivanc , Kielb Robert E. , Hall Kenneth C.
Published: September 2009

A nonlinear harmonic balance technique for the analysis of aerodynamic asymmetry of unsteady flows in turbomachinery is presented. The present method uses a mixed time-domain/frequency-domain approach that allows one to compute the unsteady aerodynamic response of turbomachinery blades to self-excited vibrations. Traditionally, researchers have investigated the unsteady response of a blade row with the assumption that all the blades in the row are identical. With this assumption the entire wheel can be modeled using complex periodic boundary conditions and a computational grid spanning a single blade passage. In this study, the steady/unsteady aerodynamic asymmetry is modeled using multiple passages. Specifically, the method has been applied to aerodynamically asymmetric flutter problems for a rotor with a symmetry group of 2. The effect of geometric asymmetries on the unsteady aerodynamic response of a blade row is illustrated. For the cases investigated in this paper, the change in the diagonal terms (blade on itself) dominated the change in stability. Very little mode coupling effect caused by the off-diagonal terms was found.
Application of Artificial Neural Networks in Investigations of Steam Turbine Cascades
Authors: Kosowski Krzysztof , Tucki Karol , Kosowski Adrian
Published: September 2009

We present the results of numerical tests of artificial neural networks (ANNs) applied in the investigations of flows in steam turbine cascades. Typical constant cross-sectional blades, as well as high-performance blades, were both considered. The obtained results indicate that ANNs may be used for estimating the spatial distribution of flow parameters, such as enthalpy, entropy, pressure, velocity, and energy losses, in the flow channel. Finally, we remark on the application of ANNs in the design process of turbine flow parts, as an extremely fast complementary method for many 3D computational fluid dynamics calculations. By using ANNs combined with evolutionary algorithms, it is possible to reduce by several orders of magnitude the time of design optimization for cascades, stages, and groups of stages.
Tip Clearance Effects on Inlet Hot Streak Migration Characteristics in High Pressure Stage of a Vaneless Counter-Rotating Turbine
Authors: Qingjun Zhao , Jianyi Du , Huishe Wang , Xiaolu Zhao , Jianzhong Xu
Published: September 2009

In this paper, three-dimensional multiblade row unsteady Navier–Stokes simulations at a hot streak temperature ratio of 2.0 have been performed to reveal the effects of rotor tip clearance on the inlet hot streak migration characteristics in high pressure stage of a vaneless counter-rotating turbine. The numerical results indicate that the migration characteristics of the hot streak in the high pressure turbine rotor are dominated by the combined effects of secondary flow, buoyancy, and leakage flow in the rotor tip clearance. The leakage flow trends to drive the hotter fluid toward the blade tip on the pressure surface and to the hub on the suction surface. Under the effect of the leakage flow, even partial hotter fluid near the pressure surface is also driven to the rotor suction surface through the tip clearance. Compared with the case without rotor tip clearance, the heat load of the high pressure turbine rotor is intensified due to the effects of the leakage flow. And the results indicate that the leakage flow effects trend to increase the low pressure turbine rotor inlet temperature at the tip region. The air flow with higher temperature at the tip region of the low pressure turbine rotor inlet will affect the flow and heat transfer characteristics in the downstream low pressure turbine.
Optimization of Nonaxisymmetric Endwalls in Compressor S-Shaped Ducts
Authors: Naylor Edward M. J. , Dueñas Cecilia Ortiz , Miller Robert J. , Hodson Howard P.
Published: September 2009

This paper presents a new design methodology for strutted S-shaped compressor ducts that allows for more aggressive designs while maintaining current levels of duct loss. A baseline duct geometry was selected, which had a radius change to length ratio that is 34% larger than current engine design limits. A large-scale low-speed model of the baseline duct was experimentally tested. The flow in the corner between the hub and the strut was found to separate due to the high local diffusion causing an increase in duct loss. Area ruling was applied to the baseline duct and was predicted to reduce the size and extent of the strut-hub corner separation, but the duct design was compromised. The duct loss coefficient at midpitch was predicted to increase compared with that of the baseline design. Nonaxisymmetric endwall profiling was then used on the duct wall, locally to the strut, to remove the strut-hub corner separation and thus reduce net duct loss, without compromising the duct design away from the strut. The endwall geometry was produced by numerical optimization. It was shown that the net duct loss was insensitive to casing profiling but highly sensitive to hub profiling. The optimal hub geometry was experimentally tested and shown to completely remove endwall strut-hub corner separation. The profiling was found to reduce the net duct loss by 16%. The paper shows that the key benefit to endwall profiling is that it can be used to safely increase the size of the design space in which aeroengine duct designers can operate.
Aerothermal Investigation of a Rib-Roughened Trailing Edge Channel With Crossing-Jets—Part I: Flow Field Analysis
Authors: Armellini Alessandro , Coletti Filippo , Arts Tony , Scholtes Christophe
Published: September 2009

The present contribution addresses the aerothermal, experimental, and computational studies of a trapezoidal cross-sectional model simulating a trailing edge cooling cavity with one rib-roughened wall. The flow is fed through tilted slots on one side wall and exits through straight slots on the opposite side wall. The flow field aerodynamics is investigated in Part I of the paper. The reference Reynolds number is defined at the entrance of the test section and set at 67,500 for all the experiments. A qualitative flow model is deduced from surface-streamline flow visualizations. Two-dimensional particle image velocimetry measurements are performed in several planes around midspan of the channel and recombined to visualize and quantify three-dimensional flow features. The crossing-jets issued from the tilted slots are characterized and the jet-rib interaction is analyzed. Attention is drawn to the motion of the flow deflected by the rib-roughened wall and impinging on the opposite smooth wall. The experimental results are compared with the numerical predictions obtained from the finite volume Reynolds-averaged Navier–Stokes solver, CEDRE.
Separated Flow Measurements on a Highly Loaded Low-Pressure Turbine Airfoil
Authors: Volino Ralph J.
Published: September 2009

Boundary layer separation, transition, and reattachment have been studied on a new, very high lift, low-pressure turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases, the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. This behavior contrasts with previous research on other airfoils, in which transition, if it occurred, always induced reattachment, regardless of Reynolds number.
Web-Based, Interactive Laboratory Experiment in Turbomachine Aerodynamics
Authors: Navarathna Nalin , Fedulov Vitalij , Martin Andrew , Fransson Torsten
Published: September 2009

Remote laboratory exercises are gaining popularity due to advances in communication technologies along with the need to provide realistic yet flexible educational tools for tomorrow’s engineers. Laboratory exercises in turbomachinery aerodynamics generally involve substantial equipment in both size and power, so the development of remotely controlled facilities has perhaps not occurred as quickly as in other fields. This paper presents an overview of a new interactive laboratory exercise involving aerodynamics in a linear cascade of stator blades. The laboratory facility consists of a high-speed fan that delivers a maximum of 2.5 kg/s of air to the cascade. Traversing pneumatic probes are used to determine pressure profiles at upstream and downstream locations, and loss coefficients are later computed. Newly added equipment includes cameras, stepper motors, and a data acquisition and control system for remote operation. This paper presents the laboratory facility in more detail and includes discussions related to user interface issues, the development of a virtual laboratory exercise as a complement to experiments, and comparative evaluation of virtual, remote, and local laboratory exercises.
Influence of Thermodynamic Models in Two-Dimensional Flow Simulations of Turboexpanders
Authors: Harinck John , Colonna P. , Guardone A. , Rebay S.
Published: September 2009

This paper presents a quantitative comparison of the effect of using thermodynamic models of various degrees of complexity if applied to fluid-dynamic simulations of turboexpanders operated at conditions affected by strong real-gas effects. The 2D flow field of a standard transonic turbine stator is simulated using the state-of-the-art inviscid ZFLOW computational fluid-dynamic solver coupled with a fluid property library containing the thermodynamic models. The considered thermodynamic models are, in order of increasing complexity, the polytropic ideal-gas (PIG) law, the Peng–Robinson–Stryjek–Vera (PRSV) cubic equation of state, and the highly accurate multiparameter equations of state (MPEoSs), which are adopted as benchmark reference. The fluids are steam, toluene, and R245fa. The two processes under scrutiny are a moderately nonideal subcritical expansion and a highly nonideal supercritical expansion characterized by the same pressure ratio. Using the PIG model for moderately nonideal subcritical expansions leads to large deviations with magnitudes of up to 18–25% in density, sound speed, velocity, and total pressure loss, and up to 4–10% in Mach number, pressure, temperature, and mass flow rate. The PIG model applied to highly nonideal supercritical expansions leads to a doubling of the deviations’ magnitudes. The advantage of the PIG model is that its computational cost is roughly 1/11 (or 1/3 if saturation-checks in the MPEoS are omitted) of the cost of the MPEoSs. For the subcritical expansion, adopting the physically more correct cubic PRSV model leads to comparatively smaller deviations, namely, <2% (toluene and R245fa) and <4% (steam) in all flow parameters, except for the total pressure loss error, which is comparable to that of the PIG model. The PRSV model is reasonably accurate even for the highly nonideal supercritical expansion, for which the errors are at most 4%. The computational cost of the PRSV model is roughly nine times higher than the cost of the PIG model (or twice as high if saturation-checks in the PRSV are omitted). Contrary to low-complexity fluids like water, for complex fluids like toluene and R245fa the deviations in density, speed of sound, and velocity ensuing from the use of the PIG model vary strongly along the isentropic expansions. This invalidates the approach commonly used in practice of correcting the PIG model with a properly chosen constant compressibility factor.
Oxygen effects on radiation hardness of ZnO thin films
Authors: Gür Emre , Asıl Hatice , Çınar Kübra , Coşkun C. , Tüzemen S. , Meral Kadem , Onganer Y. , Şerifoğlu Korkmaz
Published: September 2009

Six ZnO thin films were grown under different oxygen flow rates by electrochemical deposition onto commercial indium tin oxide substrates. X-ray diffraction (XRD), optical absorption, and photoluminescence (PL) measurements were performed on all films. XRD measurements showed that films are highly (0002) c-axis oriented. It has been observed that the growth rates of the films are highly dependent on the oxygen flow rates. High growth rate is obtained for the midoxygen flow rates in the cell. Calculated crystallite size values have an increasing trend as the oxygen flow rate increases. Absorption measurements have revealed that the band gap energy of ZnO thin films is about 3.4eV. PL measurements showed that two emissions are observed in all films: free exciton emission at about 3.37eV and so-called blue emission at 2.66eV in ZnO. Relatively low dose (5×1012e−∕cm2) and high-energy electron-irradiation (HEEI) (12MeV) experiments were performed on all films. Their effects on the optical and structural characteristics are discussed. In addition, an annealing process was applied to understand the effect on the recovery of the HEEI-induced defects.
Effect of magnetic field strength on deposition rate and energy flux in a dc magnetron sputtering system
Authors: Ekpe Samuel D. , Jimenez Francisco J. , Field David J. , Davis Martin J. , Dew Steven K.
Published: September 2009

Variations in the magnetic field strongly affect the plasma parameters in a magnetron sputtering system. This in turn affects the throughput as well as the energy flux to the substrate. The variation in the magnetic field in this study, for a dc magnetron process, is achieved by shifting the magnet assembly slightly away from the target. Measurements of the plasma parameters show that while the electron density at the substrate increases with decrease in magnetic field, the electron temperature decreases. The cooling of the electron temperature is consistent with results reported elsewhere. The deposition rate per input magnetron power is found to increase slightly with the decrease in magnetic field for the process conditions considered in this study. Results suggest that the energy flux to the substrate tends to show a general decrease with the shift in the magnet assembly.
Time of flight secondary ion mass spectroscopy studies of poly(allyl methacrylate-g-dimethylsiloxane) copolymers using cryogenic sample handling techniques: Effects of hydration on surface chemical structure and surface chain length distribution
Authors: Hook Daniel J. , Chen Lu , Valint Paul L. , Gardella Joseph A.
Published: September 2009

A series of amphiphilic graft copolymers having a poly(allyl methacrylate) [poly(AMA)] backbone and polydimethylsiloxane (PDMS) side chains were studied by time of flight secondary ion mass spectroscopy (ToF-SIMS) in both hydrated and dehydrated states using cryogenic sample handling methods. Both the copolymers and the PDMS macromers used for grafting to the acrylate backone were synthesized using anionic methods, yielding copolymers with a tightly controlled molecular weight distribution and a tightly controlled PDMS graft chain length in a polymer brush surface configuration. The effects of hydration on surface chemical structure and graft length distribution at the surface were examined. Low mass ToF-SIMS studies provided direct structural evidence that the polymer surface reorganized between hydrated and dehydrated states. High mass ToF-SIMS (1000–5000Da) studies detected oligomeric ion distributions of the PDMS macromer graft at both air and water exposed interfaces, but with a greatly decreased ion yield at the water exposed interface. This marks the first time that detection of high mass oligomeric ion distributions from water exposed (frozen) interfaces has been reported. The chain length distribution of PDMS at the surface was determined and no statistical difference in surface graft length distribution was detected between hydrated and dehydrated copolymers. The effects of polymer bulk structure and composition on graft length distribution at the surface were also examined. High mass ToF-SIMS (1000–5000Da) results indicated that shorter chain lengths were more prominently represented in distribution of graft chains at the surface, regardless of polymer bulk structure, composition, or hydration condition. This is the first report of quantitative and high mass ToF-SIMS study of the effect of water absorption on polymer surface structure in both hydrated and dehydrated states, with control of the polymer structure and composition.
Analysis of dielectric constant of a self-forming barrier layer with Cu–Mn alloy on TEOS-SiO2
Authors: Chung S.-M. , Koike J.
Published: September 2009

A Cu–Mn alloy film was deposited on SiO2 to self-form a diffusion barrier layer of MnOx at their interface. Transmission electron microscopy revealed that the barrier layer was formed not on the Cu alloy side but on the SiO2 side. Capacitance-voltage measurement revealed the decrease in the dielectric constant of the barrier layer from 11.4 to 5.1 with increasing annealing temperature. The obtained results indicated that the self-forming barrier layer with Cu–Mn is an excellent barrier layer without posing any negative influences on the interconnect line resistance and on the insulator capacitance.
Luminescence mechanisms in Si quantum dots-SiNx nanocomposite structures
Authors: Rezgui Béchir , Sibai Abel , Nychyporuk Tetyana , Lemiti Mustapha , Brémond Georges
Published: September 2009

Silicon quantum dots have been grown in situ in amorphous silicon nitride (SiNx) films on silicon substrate by plasma-enhanced chemical vapor deposition using ammonia (NH3) and silane (SiH4) as reactant gases. After deposition, films were annealed in N2 atmosphere at temperatures ranging from 700 to 1000 °C for 1 min using rapid thermal annealing system. The evolution of the Si quantum dots (QDs) and the chemical composition of the films have been investigated by Raman scattering and infrared absorption spectroscopy, and the correlation with the optical properties is presented. From the photoluminescence measurements, the position and the intensity of the photoluminescence peak were studied as a function of the annealing temperature (Ta), and the luminescence mechanism in Si QDs-SiNx composite structures is attributed to the quantum confinement in silicon clusters. These results lead to further understanding the physical and optical properties of Si QDs embedded in silicon nitride films and thus open up the possibility of realizing efficient Si-based tandem solar cells.
Mechanisms for plasma etching of HfO2 gate stacks with Si selectivity and photoresist trimming
Authors: Shoeb Juline , Kushner Mark J.
Published: September 2009

To minimize leakage currents resulting from the thinning of the insulator in the gate stack of field effect transistors, high-dielectric constant (high-k) metal oxides, and HfO2 in particular, are being implemented as a replacement for SiO2. To speed the rate of processing, it is desirable to etch the gate stack (e.g., metal gate, antireflection layers, and dielectric) in a single process while having selectivity to the underlying Si. Plasma etching using Ar/BCl3/Cl2 mixtures effectively etches HfO2 while having good selectivity to Si. In this article, results from integrated reactor and feature scale modeling of gate-stack etching in Ar/BCl3/Cl2 plasmas, preceded by photoresist trimming in Ar/O2 plasmas, are discussed. It was found that BCln species react with HfO2, which under ion impact, form volatile etch products such as BmOCln and HfCln. Selectivity to Si is achieved by creating Si–B bonding as a precursor to the deposition of a BCln polymer which slows the etch rate relative to HfO2. The low ion energies required to achieve this selectivity then challenge one to obtain highly anisotropic profiles in the metal gate portion of the stack. Validation was performed with data from literature. The effect of bias voltage and key reactant probabilities on etch rate, selectivity, and profile are discussed.
Hubisz Replies
Authors: Hubisz John
Published: September 2009

I want to thank Dr. Montalvo for his letter about my paper “A ‘Mathematics Background Check.’” I think I can assume that he is a regular reader of The Physics Teacher and thus realizes that it is not a research journal but one to help teachers in any way possible in their attempts to teach their students.
The Anatomy of a Pitch: Doing Physics with PITCHf/x Data
Authors: Kagan David
Published: September 2009

On Aug. 7, 2007, Barry Bonds of the San Francisco Giants was at bat waiting for a 3-2 pitch from Mike Bacsik of the Washington Nationals. The ball left the pitcher's hand at 84.7 mph and arrived at home plate traveling 77.2 mph. It was within 0.2 in of the center of home plate and 3.213 ft above the ground when Bonds swung and hit his 756th home run, making him the all-time leader for homers in a career. Thanks to a company called Sportvision and Major League Baseball, you can get kinematic data on any pitch thrown. Just think of the interesting and realistic physics problems you can generate from such a rich data set!
Are Most People Too Dumb for Physics?
Authors: Lasry Nathaniel , Finkelstein Noah , Mazur Eric
Published: September 2009

In last month's issue of TPT, Michael Sobel turns our attention to the increasing number and broader population of students taking physics courses and urges us to reconsider how to better cater to their needs. We applaud the author for focusing our attention on this important issue. However, we find his proposal for teaching physics to nonscience majors problematic.
Why Does the Goldfish Disappear in the Fishbowl?
Authors: Zhu Yuhua , Shi Fengliang
Published: September 2009

You may have observed that a small goldfish swimming in a spherical fishbowl can suddenly disappear. Why does this happen? The effect is due to total internal reflection. In this paper we find the locations of the fish and the observer's eye for which the fish cannot be seen.
The International Year of Astronomy 2009: New Approaches and Novel Resources for Physics Classrooms
Authors: Pompea Stephen M. , Isbell Douglas
Published: September 2009

The International Year of Astronomy 2009 (IYA2009) was conceived to honor the 400th anniversary of the first use of an astronomical telescope by Galileo Galilei in 1609, and has evolved into an engaging series of worldwide programs. IYA2009 is sponsored by the International Astronomical Union (IAU) and endorsed by the U.S. House of Representatives, UNESCO, and the United Nations. During this year, we are making great efforts to stimulate worldwide interest in astronomy and science, especially among young people and underserved populations. More than 145 countries and three dozen agencies are participating in this global effort, with the United States taking command of three large cornerstone projects described in this article, assisted by funding from the National Science Foundation and leadership from the American Astronomical Society and NASA.
Motion-Matching: A Challenge Game to Generate Motion Concepts
Authors: Schuster David , Adams Betty , Brookes David , Milner-Bolotin Marina , Undreiu Adriana
Published: September 2009

Motion is a topic that is taught from elementary grades through to university at various levels of sophistication. It is an area that can be challenging for learning in a conceptually meaningful way, and formal kinematics instruction can sometimes seem dry and boring. Thus, the nature of students' initial introduction to motion is important in sparking their interest, shaping their perspective, and developing conceptual understanding of motion. The kinematic concepts we want students to acquire for basic motions are: position, time, speed, direction, velocity, velocity change, change rate, and acceleration, all with respect to a frame of reference. In this article we describe a challenge game used as an “opener” to motion, in which students themselves essentially generate these concepts, in everyday language, from a perceived need for them.
Non-Zero Net Force and Constant Velocity: A Study in Mazur's Peer Instruction
Authors: Newburgh Ronald
Published: September 2009

A problem addressed infrequently in beginning physics courses is that of a moving body with changing mass. Elementary texts often have footnotes referring to jet planes and rockets but rarely do they go further. This omission is understandable because calculations with variable mass generally require the tools of calculus. This paper presents a changing mass problem that can be treated on an elementary level, thereby leading to an understanding of the role of changing mass on Newton's second law. It also illustrates Mazur's technique of Peer Instruction, a technique that demands active student participation.
Modeling the Compact Disc Read System in Lab
Authors: Hinaus Brad , Veum Mick
Published: September 2009

One of the great, engaging aspects of physics is its application to everyday technology. The compact disc player is an example of one such technology that applies fundamental principles from optics in order to efficiently store and quickly retrieve information. We have created a lab in which students use simple optical components to assemble a large-scale mockup of the compact disc player. In this lab, students are challenged to both “write” and “read” a word of their choice in order to demonstrate the way in which the principles of optics are applied in the design of a CD player. In particular, students actively apply the optics concepts of specular reflection, diffuse reflection, and ray tracing for lenses in building the apparatus. The laboratory also provides a vehicle for learning the fundamental principles of binary data storage.
The Real Prize Inside: Learning About Science and Spectra from Cereal Boxes
Authors: Kustusch Mary Bridget , Gaffney Jon D. H. , Beichner Robert
Published: September 2009

Opportunities to learn are everywhere, often in overlooked places, such as in the Universal Product Code (UPC) that is used for barcodes on nearly everything we buy. In this paper, we describe an engaging and meaningful activity in which these barcodes were used in an introductory calculus-based physics class.
Real 3-D: How Does It Work?
Authors: Schmitzer H. , Tierney D. , Toepker T.
Published: September 2009

The 3-D glasses that are now used with many of the new 3-D movies being released provide an excellent investigative opportunity for physics and mathematics students (and teachers).
Interacting Compasses
Authors: Riveros Héctor G. , Betancourt Julián
Published: September 2009

The use of multiple compasses to map and visualize magnetic fields is well-known. The magnetic field exerts a torque on the compasses aligning them along the lines of force. Some science museums show the field of a magnet using a table with many compasses in a closely packed arrangement. However, the very interesting interactions that occur between the compasses themselves are frequently neglected. In this paper we describe demonstrations, using arrays of compasses, that show these interactions and model magnetic domains in ferromagnetic materials.
Evaluation Strategies: Teaching Students to Assess Consistency
Authors: Warren Aaron
Published: September 2009

There is a growing consensus that introductory physics courses should help students develop general scientific reasoning abilities that transform them into lifelong learners, preparing them for careers and citizenship in a rapidly evolving world. Despite the sometimes daunting nature of this challenge, activities developed by various physics education researchers have demonstrated that it is, in fact, an achievable goal. Although some of these activities require specific course formats that may not be feasible for every instructor, this is not uniformly true. In this article, I describe the design and use of activities that may be used within an introductory algebra-based physics course of any format to encourage the development of students' evaluation abilities.
Broadcasting a Lab Measurement Over Existing Conductor Networks
Authors: Knipp Peter A.
Published: September 2009

Students learn about physical laws and the scientific method when they analyze experimental data in a laboratory setting. Three common sources exist for the experimental data that they analyze: (1) “hands-on” measurements by the students themselves, (2) electronic transfer (by downloading a spreadsheet, video, or computer-aided data-acquisition [DAQ] file filled with data that have been measured ahead of time by either the instructor or a third party), or (3) receipt in paper format (e.g, as graphs or tables) of measurements made by either the instructor or a third party. Hands-on experimentation is generally the optimal approach, in that the data's “ownership” by each student or student team makes the student(s) more inclined to appreciate the conclusions drawn from the analysis. However, this method is not always practical, because of the experiment's excessive length, difficulty, delicacy, danger, or expense. Methods (2) and (3) eliminate these technical difficulties, but the students miss out by not experiencing and observing the phenomenon for which they analyze the data. It is not generally appreciated that a solution to this data-procurement problem exists which is intermediate between methods (1) and (2). This hybrid approach involves the generation of data at a single location, in the presence of the students, and the simultaneous broadcast of these data to the students using readily available networks of conducting wires. This hybrid approach combines the experiential benefits of method (1) without its liabilities, and it includes the data-access benefits of methods (1) and (2). This approach is the subject of this paper.
Professional Learning Is a Lifelong Process
Authors: Blanton Patricia
Published: September 2009

At a recent conference sponsored by the National Science Teachers Association on Professional Learning Communities in Science, I was reminded how crucial it is for teachers to continually examine their practice. As one new to teaching physics, you may be overwhelmed by the task of helping your students develop accurate understanding of the concepts that are the essence of physics while still maintaining some semblance of order in your classroom. Consider your thoughts about some of the following questions as a way to begin to examine your practice: 1) Have you identified the most important models or ideas you want your students to develop or are you simply following the curriculum outlined in the chapters of your text or those mandated by your state or institution? 2) Have you developed a storyline on which you want the concepts to be built or are you presenting physics as a set of facts, formulas, and problems to be solved? 3) Are you confident in your content knowledge or do you feel that you are just staying one day ahead of your students? 4) Do you have assessment strategies developed to probe for understanding throughout the concept development or do you rely mainly on chapter tests and summative assessments? 5) Do you feel you work in isolation or are you collaborating with colleagues to examine the practices that are most effective for motivating learners while managing the day-to-day requirements of teaching?.
Fermi Questions
Authors: Weinstein Larry
Published: September 2009

How much energy could be extracted each year in the United States from the potential energy of water flowing off of roofs and down the gutters (rain spouts)?
A Wedge Issue
Authors: Korsunsky Boris
Published: September 2009

A wedge slides down a frictionless inclined plane that makes angle θ with the horizontal. A small block is placed at the horizontal top side of the wedge. During the slide, the block does not move relative to the wedge. Find the minimum possible coefficient of static friction μs between the block and the wedge.