bluuebunny/crossref_metadata_2025 huggingface dataset:
Maternal occupational exposure to polycyclic aromatic hydrocarbons and risk of neural tube defect‐affected pregnancies
Authors: Langlois Peter H. , Hoyt Adrienne T. , Lupo Philip J. , Lawson Christina C. , Waters Martha A. , Desrosiers Tania A. , Shaw Gary M. , Romitti Paul A. , Lammer Edward J. ,   and the National Birth Defects Prevention Study
Published: July 2012

BACKGROUND

This study evaluated whether there is an association between maternal occupational exposure to polycyclic aromatic hydrocarbons (PAHs) and neural tube defects (NTDs) in offspring. This is the first such study of which the authors are aware.

METHODS

Data were analyzed from 1997 to 2002 deliveries in the National Birth Defects Prevention Study, a large population‐based case‐control study in the United States. Maternal interviews yielded information on jobs held in the month before through 3 months after conception. Three industrial hygienists blinded to case or control status assessed occupational exposure to PAHs. Crude and adjusted odds ratios (ORs) with 95% confidence intervals (CIs) were estimated using unconditional logistic regression.

RESULTS

Of the 520 mothers of children with NTDs, 5.0% were classified as exposed to occupational PAHs, as were 3.5% of the 2989 mothers of controls. The crude OR for PAH exposure was 1.43 (95% CI, 0.92–2.22) for any NTD and 1.71 (95% CI, 1.03–2.83) for spina bifida. Adjusted ORs were smaller in magnitude and not significant. Among women who were normal weight or underweight, the crude OR for spina bifida was 3.13 (95% CI, 1.63–6.03) and adjusted OR was 2.59 (95% CI, 1.32–5.07). Based on estimated cumulative exposure, a statistically significant dose‐response trend was observed for spina bifida; however, it was attenuated and no longer significant after adjustment.

CONCLUSION

Maternal occupational exposure to PAHs may be associated with increased risk of spina bifida in offspring among women who are normal weight or underweight. Other comparisons between PAHs and NTDs were consistent with no association. Birth Defects Research (Part A) 94:693–700, 2012. © 2012 Wiley Periodicals, Inc.
Sample size estimates for well‐powered cross‐sectional cortical thickness studies
Authors: Pardoe Heath R. , Abbott David F. , Jackson Graeme D. ,   The Alzheimer's Disease Neuroimaging Initiative
Published: July 2012

Introduction: Cortical thickness mapping is a widely used method for the analysis of neuroanatomical differences between subject groups. We applied power analysis methods over a range of image processing parameters to derive a model that allows researchers to calculate the number of subjects required to ensure a well‐powered cross‐sectional cortical thickness study. Methods: 0.9‐mm isotropic T1‐weighted 3D MPRAGE MRI scans from 98 controls (53 females, age 29.1 ± 9.7 years) were processed using Freesurfer 5.0. Power analyses were carried out using vertex‐wise variance estimates from the coregistered cortical thickness maps, systematically varying processing parameters. A genetic programming approach was used to derive a model describing the relationship between sample size and processing parameters. The model was validated on four Alzheimer's Disease Neuroimaging Initiative control datasets (mean 126.5 subjects/site, age 76.6 ± 5.0 years). Results: Approximately 50 subjects per group are required to detect a 0.25‐mm thickness difference; less than 10 subjects per group are required for differences of 1 mm (two‐sided test, 10 mm smoothing, α = 0.05). Sample size estimates were heterogeneous over the cortical surface. The model yielded sample size predictions within 2–6% of that determined experimentally using independent data from four other datasets. Fitting parameters of the model to data from each site reduced the estimation error to less than 2%. Conclusions: The derived model provides a simple tool for researchers to calculate how many subjects should be included in a well‐powered cortical thickness analysis. Hum Brain Mapp 34:3000–3009, 2013. © 2012 Wiley Periodicals, Inc.
Shoulder Injuries in the Skeletally Immature Baseball Pitcher and Recommendations for the Prevention of Injury
Authors: Zaremski Jason L. , Krabak Brian J.
Published: July 2012

Since 1996, when the first article on pitch restriction recommendations was published, the number of research articles involving skeletally immature pitchers has increased. Potential shoulder injuries in this age group are proximal humeral epiphysiolysis, glenohumeral instability, rotator cuff dysfunction, and superior labrum anteroposterior lesions. Fatigue, improper biomechanics, and overuse are the most common reasons for these injuries. In the hopes of preventing injury to young pitchers, numerous organizations, including the USA Baseball Medical & Safety Advisory Committee, The American Sports Medicine Institute, Little League Baseball & Softball, and the Long Term Athlete Development Program for Baseball Canada, have developed recommendations on pitching restrictions that include limits on pitch count, pitches per week, pitches per season, and rest between pitching. Awareness by sports medicine providers, coaches, and parents/guardians of the most up‐to‐date recommendations on injury prevention and return to play guidelines should reduce the incidence of acute and chronic injuries in adolescent baseball pitchers.
Quasi-steady states in natural displacement ventilation driven by periodic gusting of wind
Authors: Mott Richard W. , Woods Andrew W.
Published: July 2012

We investigate the natural displacement ventilation of a space connected to a body of warm fluid through high- and low-level vents. The space is subject to discrete periodic gusts of wind entering at high level from a cold exterior. The cold exterior air entering the space produces buoyancy differences between the space and the body of warm fluid, driving a ventilation flow. Initially we examine the case of a series of identical gusts of wind modelled as turbulent buoyant thermals. New laboratory experiments show that an approximately two-layer stratification is established and the height of the interface is quasi-steady if the period between thermals is much less than the draining time of the space but longer than the fall time of individual thermals. Experiments also show that the interface height depends on the average buoyancy flux associated with the wind gusts, the time between thermals as well as the geometric properties of the vents. This contrasts with the case of a continuous source of buoyancy where the interface height depends only on the geometric properties of the vents and is independent of the buoyancy flux. We develop a quasi-steady two-layer model of the flow based on the classical theory of turbulent thermals and show that it is consistent with our new experimental data. We generalize the model to explore the sensitivity of the results to temporal variations in the size of thermals. We then extend the model to explore the effects of longer interval times between successive thermals and find a two-layer stratification still develops but that the interface height now varies cyclically in time. We then discuss the implications of these results for the ventilation of a shopping mall subject to gusts of wind.
Micro-splashing by drop impacts
Authors: Thoroddsen S. T. , Takehara K. , Etoh T. G.
Published: July 2012

We use ultra-high-speed video imaging to observe directly the earliest onset of prompt splashing when a drop impacts onto a smooth solid surface. We capture the start of the ejecta sheet travelling along the solid substrate and show how it breaks up immediately upon emergence from the underneath the drop. The resulting micro-droplets are much smaller and faster than previously reported and may have gone unobserved owing to their very small size and rapid ejection velocities, which approach 100 m s−1, for typical impact conditions of large rain drops. We propose a phenomenological mechanism which predicts the velocity and size distribution of the resulting microdroplets. We also observe azimuthal undulations which may help promote the earliest breakup of the ejecta. This instability occurs in the cusp in the free surface where the drop surface meets the radially ejected liquid sheet.
An unusual location for a fungus ball: the concha bullosa
Authors: Ciger E , Demiray U , Onal K , Songu M
Published: July 2012

Objective:

We report an unusual case of a fungus ball in the concha bullosa, without involvement of the paranasal sinuses.

Case report:

A 29-year-old woman presented complaining of nasal obstruction and postnasal discharge. Paranasal computed tomography demonstrated that the concha bullosa in the right middle turbinate was filled with a high-density material. The patient underwent endoscopic resection of the concha bullosa, during which a dark brown, cheese-like material was found. Histopathological examination of the excised specimen revealed a fungus ball.

Conclusion:

Fungus balls are non-invasive accumulations of dense fungal concretions that generally affect healthy individuals. In the sinonasal region, they occur most frequently in the maxillary sinus. Although fungus ball formation in the concha bullosa is unusual, it should be considered in the differential diagnoses of middle turbinate and sinonasal pathology.
Nasolacrimal relapse of nasopharyngeal carcinoma
Authors: Sia K J , Tang I P , Kong C K L , Tan T Y
Published: July 2012

Objectives:

To describe three rare cases of nasolacrimal relapse of nasopharyngeal carcinoma, and to discuss the route of tumour spread from nasopharynx to lacrimal system as well as the relevant computed tomography findings.

Case report:

We report three cases of nasolacrimal relapse in patients with previously treated nasopharyngeal carcinoma. The common initial presentations in these cases were epiphora and medial canthal swelling. The tumour spread from the nasopharynx to the lacrimal sac along the lateral nasal wall and nasolacrimal canal. Computed tomography demonstrated nasolacrimal canal invasion and osteomeatal complex obliteration by the tumour. Distant metastasis was detected in two cases.

Conclusion:

More targeted radiotherapy should be delivered to prevent under-treatment of nasopharyngeal carcinoma. Nasolacrimal relapse of nasopharyngeal carcinoma is an advanced disease with a poor prognosis.
Typology of clinical course in bipolar disorder based on 18-month naturalistic follow-up
Authors: Uher R. , Mantere O. , Suominen K. , Isometsä E.
Published: July 2012

Background

Individual variation in the clinical course of bipolar disorder may have prognostic and therapeutic implications but is poorly reflected in current classifications. We aimed to establish a typology of the individual clinical trajectories based on detailed prospective medium-term follow-up.

Method

Latent class analysis (LCA) of nine characteristics of clinical course (time depressed, severity of depression, stability of depression, time manic, severity of mania, stability of mania, mixed symptoms, mania-to-depression and depression-to-mania phase switching) derived from life charts prospectively tracking the onsets and offsets of (hypo)manic, depressive, mixed and subsyndromal episodes in a representative sample of 176 patients with bipolar disorder.

Results

The best-fitting model separated patients with bipolar disorder into large classes of episodic bipolar (47%) and depressive type (32%), moderately sized classes characterized by prolonged hypomanias (10%) and mixed episodes (5%) and five small classes with unusual course characteristics including mania-to-depression and depression-to-mania transitions and chronic mixed affective symptoms. This empirical typology is relatively independent of the distinction between bipolar disorder type I and type II. Lifetime co-morbidity of alcohol use disorders is characteristic of the episodic bipolar course type.

Conclusions

There is potential for a new typology of clinical course based on medium-term naturalistic follow-up of a representative clinical sample of patients with bipolar disorder. Predictive validity and stability over longer follow-up periods remain to be established.
X-ray spectroscopy diagnoses of clusters surviving under prepulses of ultra-intense femtosecond laser pulse irradiation
Authors: Faenov A.Ya. , Skobelev I.Yu. , Pikuz T.A. , Pikuz S.A. , Fortov V.E. , Fukuda Y. , Hayashi Y. , Pirozhkov A. , Kotaki H. , Shimomura T. , Kiriyama H. , Kanazawa S. , Kato Y. , Colgan J. , Abdallah J. , Kando M. ,   J-KAREN Laser Operation Group
Published: July 2012

It is shown that various spectroscopic methods based on measurements of X-ray spectra radiated from cluster targets can be used for estimation of the destruction degree of clusters by laser prepulses. These methods allow insight to be gained regarding the important issue of preservation of the dense cluster core at the moment of the arrival of the main laser pulse. In addition, they can be used for quantitative estimation of the size of the undestroyed parts of the clusters and also for measuring the temperature and density of the preplasmas produced by the laser prepulses.
Iron-deficiency anaemia, gastric hyperplasia, and elevated gastrin levels due to potassium channel dysfunction in the Jervell and Lange-Nielsen Syndrome
Authors: Winbo Annika , Sandström Olof , Palmqvist Richard , Rydberg Annika
Published: July 2012

Aim

We investigated extra-cardiac clinical symptoms and signs in the rare Jervell and Lange-Nielsen Syndrome, characterised by impairedKCNQ1function, a gene essential for gastric acid secretion.

Methods

All Swedish Jervell and Lange-Nielsen cases with doubleKCNQ1mutations (14 cases) were investigated by medical record review, an interview, and were offered laboratory testing for iron-deficiency anaemia and gastrointestinal markers.

Results

A history of iron-deficiency anaemia in 12 of 14 patients and subjective gastrointestinal symptoms in 13 of 14 patients was revealed. Previous endoscopy in five cases had revealed no case of coeliac or inflammatory bowel disease but three cases of mucosal hyperplasia/dysplasia. Current signs of anaemia or iron substitution were present in 9 of 12 tested cases. Elevated levels of gastrin in seven of nine cases, pepsinogen in six of seven cases, and faecal calprotectin in nine of nine cases were present. A significant correlation between elevated gastrin levels and concurrent iron-deficiency and/or anaemia was revealed (p-value 0.039).

Conclusions

A high frequency of extra-cardiac clinical symptoms and previous medical investigations was found. We propose that the Jervell and Lange-Nielsen Syndrome phenotypically includes gastrointestinal symptoms/signs and secondary iron-deficiency anaemia owing to hypochlorhydria on the basis ofKCNQ1mutations. The resultant elevated gastrin level is a potential risk factor for later gastrointestinal cancer. Clinical monitoring with regard to developing anaemia and hypergastrinaemia should be considered in the Jervell and Lange-Nielsen Syndrome.
A numerical study of the laminar necklace vortex system and its effect on the wake for a circular cylinder
Authors: Kirkil Gokhan , Constantinescu George
Published: July 2012

Large eddy simulation (LES) is used to investigate the structure of the laminar horseshoe vortex (HV) system and the dynamics of the necklace vortices as they fold around the base of a circular cylinder mounted on the flat bed of an open channel for Reynolds numbers defined with the cylinder diameter, D, smaller than 4460. The study concentrates on the analysis of the structure of the HV system in the periodic breakaway sub-regime, which is characterized by the formation of three main necklace vortices. Over one oscillation cycle of the previously observed breakaway sub-regime, the corner vortex and the primary vortex merge (amalgamate) and a developing vortex separates from the incoming laminar boundary layer (BL) to become the new primary vortex. Results show that while the classical breakaway sub-regime, in which one amalgamation event occurs per oscillation cycle, is present when the nondimensional displacement thickness of the incoming BL at the location of the cylinder is relatively large (δ*/D > 0.1), a new type of breakaway sub-regime is present for low values of δ*/D. This sub-regime, which we call the double-breakaway sub-regime, is characterized by the occurrence of two amalgamation events over one full oscillation cycle. LES results show that when the HV system is in one of the breakaway sub-regimes, the interactions between the highly coherent necklace vortices and the eddies shed inside the separated shear layers (SSLs) are very strong. For the relatively shallow flow conditions considered in this study (H/D ≅ 1, H is the channel depth), at times, the disturbances induced by the legs of the necklace vortices do not allow the SSLs on the two sides of the cylinder to interact in a way that allows the vorticity redistribution mechanism to lead to the formation of a new wake roller. As a result, the shedding of large-scale rollers in the turbulent wake is suppressed for relatively large periods of time. Simulation results show that the wake structure changes randomly between time intervals when large-scale rollers are forming and are convected in the wake (von Karman regime), and time intervals when the rollers do not form. When the wake is in the von Karman regime, the shedding frequency of the rollers is close to that observed for flow past infinitely long cylinders.
An extended formula of site-site Smoluchowski-Vlasov equation for electrolyte solution and infinitely dilute solution
Authors: Iida Kenji , Sato Hirofumi
Published: July 2012

Solvation dynamics is one of the central subjects in solution chemistry. Site-site Smoluchowski-Vlasov (SSSV) equation is a diffusion equation for molecular liquid to analytically calculate the van Hove time correlation function. However, the application has been limited to simple solvent system such as liquid water because of the difficulty in solving the equation. In this study, an extended treatment of SSSV equation is proposed, which is applicable to a wide range of solution systems including mixed solution, electrolyte solution, and infinitely dilute solution. The present treatment realizes computation of the dynamics in LiCl aqueous solution, NaCl aqueous solution, and infinitely dilute aqueous solution of Li+ and Cs+ at the molecular level.
SPHERES, Jülich's high-flux neutron backscattering spectrometer at FRM II
Authors: Wuttke Joachim , Budwig Alfred , Drochner Matthias , Kämmerling Hans , Kayser Franz-Joseph , Kleines Harald , Ossovyi Vladimir , Pardo Luis Carlos , Prager Michael , Richter Dieter , Schneider Gerald J. , Schneider Harald , Staringer Simon
Published: July 2012

SPHERES is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Jülich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 μeV, a dynamic range of ± 31 μeV, and a signal-to-noise ratio of up to 1750:1.
A multi-frame soft x-ray pinhole imaging diagnostic for single-shot applications
Authors: Wurden G. A. , Coffey S. K.
Published: July 2012

For high energy density magnetized target fusion experiments at the Air Force Research Laboratory FRCHX machine, obtaining multi-frame soft x-ray images of the field reversed configuration (FRC) plasma as it is being compressed will provide useful dynamics and symmetry information. However, vacuum hardware will be destroyed during the implosion. We have designed a simple in-vacuum pinhole nosecone attachment, fitting onto a Conflat window, coated with 3.2 mg/cm2 of P-47 phosphor, and covered with a thin 50-nm aluminum reflective overcoat, lens-coupled to a multi-frame Hadland Ultra intensified digital camera. We compare visible and soft x-ray axial images of translating (∼200 eV) plasmas in the FRX-L and FRCHX machines in Los Alamos and Albuquerque.
A general nonlinear fluid model for reacting plasma-neutral mixtures
Authors: Meier E. T. , Shumlak U.
Published: July 2012

A generalized, computationally tractable fluid model for capturing the effects of neutral particles in plasmas is derived. The model derivation begins with Boltzmann equations for singly charged ions, electrons, and a single neutral species. Electron-impact ionization, radiative recombination, and resonant charge exchange reactions are included. Moments of the reaction collision terms are detailed. Moments of the Boltzmann equations for electron, ion, and neutral species are combined to yield a two-component plasma-neutral fluid model. Separate density, momentum, and energy equations, each including reaction transfer terms, are produced for the plasma and neutral equations. The required closures for the plasma-neutral model are discussed.
Large thermoelectric power factor in p-type Si (110)/[110] ultra-thin-layers compared to differently oriented channels
Authors: Neophytou Neophytos , Kosina Hans
Published: July 2012

Using atomistic electronic structure calculations and Boltzmann semi-classical transport, we compute the thermoelectric power factor of ultra-thin-body p-type Si layers of thicknesses from W = 3 nm up to 10 nm. We show that the power factor for channels in [110] transport orientation and (110) surface confinement largely outperforms all differently oriented channels by more than 2×. Furthermore, the power factor in this channel increases by ∼40% with layer thickness reduction. This increase, together with the large confinement effective mass of the (110) surface, make this particular channel less affected by the detrimental effects of enhanced surface roughness scattering and distortion at the nanoscale. Our results, therefore, point towards the optimal geometrical features regarding orientation and length scale for power factor improvement in 2D thin-layers of zincblende semiconductors.
Post-growth surface smoothing of thin films of diindenoperylene
Authors: Hinderhofer A. , Hosokai T. , Yonezawa K. , Gerlach A. , Kato K. , Broch K. , Frank C. , Novák J. , Kera S. , Ueno N. , Schreiber F.
Published: July 2012

We applied in situ x-ray reflectivity and ultraviolet photoelectron spectroscopy to study the impact of annealing on low temperature (200 K) deposited organic thin films of diindenoperylene (DIP) on SiO2 and indium tin oxide (ITO). At 200 K, DIP is crystalline on SiO2 and amorphous on ITO. Upon heating to room temperature, the roughness of DIP is reduced on both substrates, from 1.5 nm to 0.75 nm (SiO2) and from 0.90 nm to 0.45 nm (ITO). The smoothing is accompanied by crystallization of the surface molecules, whereas the bulk structure of the films does not strongly reorganize.
Generating self-organizing collective behavior using separation dynamics from experimental data
Authors: Dieck Kattas Graciano , Xu Xiao-Ke , Small Michael
Published: July 2012

Mathematical models for systems of interacting agents using simple local rules have been proposed and shown to exhibit emergent swarming behavior. Most of these models are constructed by intuition or manual observations of real phenomena, and later tuned or verified to simulate desired dynamics. In contrast to this approach, we propose using a model that attempts to follow an averaged rule of the essential distance-dependent collective behavior of real pigeon flocks, which was abstracted from experimental data. By using a simple model to follow the behavioral tendencies of real data, we show that our model can exhibit a wide range of emergent self-organizing dynamics such as flocking, pattern formation, and counter-rotating vortices.
How grain boundaries in Cu(In,Ga)Se2 thin films are charged: Revisit
Authors: Jiang C.-S. , Contreras M. A. , Repins I. , Moutinho H. R. , Yan Y. , Romero M. J. , Mansfield L. M. , Noufi R. , Al-Jassim M. M.
Published: July 2012

Potential measurements on Cu(In,Ga)Se2 thin films using scanning Kelvin probe force microscopy have been reported extensively to address grain-boundary (GB) recombination by examining GB charging. However, the results are highly inconsistent. We revisit this issue by measuring high- and low-quality wide-bandgap films and using a complementary method of scanning capacitance microscopy. Our results show consistent positively charged GBs in our high-quality films with minimal surface defects, except for the Σ3[112] GBs, which are charge neutral. We discuss possible artifacts due to surface defects when examining the GB charging and the role of GBs in the device performance.
Type-II GaSb/GaAs coupled quantum rings: Room-temperature luminescence enhancement and recombination lifetime elongation for device applications
Authors: Lin Wei-Hsun , Wang Kai-Wei , Chang Shu-Wei , Shih Min-Hsiung , Lin Shih-Yen
Published: July 2012

Type-II GaSb/GaAs coupled quantum rings have exhibited two-order-of-magnitude luminescence enhancement and ten-times elongation of recombination lifetime at room temperature as compared with regular rings. The longer lifetime suggests that a significant amount of electrons are confined in coupled rings rather than simply leaking away. These phenomena indicate that type-II nanostructures can be potentially utilized for room-temperature luminescence and carrier storage applications.
Role of InAs and GaAs terminated heterointerfaces at source/channel on the mixed As-Sb staggered gap tunnel field effect transistor structures grown by molecular beam epitaxy
Authors: Zhu Y. , Jain N. , Vijayaraghavan S. , Mohata D. K. , Datta S. , Lubyshev D. , Fastenau J. M. , Liu W. K. , Monsegue N. , Hudait M. K.
Published: July 2012

The structural, morphological, defect properties, and OFF state leakage current mechanism of mixed As-Sb type-II staggered gap GaAs-like and InAs-like interface heterostructure tunnel field effect transistors (TFETs) grown on InP substrates using linearly graded InxAl1-xAs buffer by molecular beam epitaxy are investigated and compared. Symmetric relaxation of >90% and >75% in the two orthogonal 〈110〉 directions with minimal lattice tilt was observed for the terminal GaAs0.35Sb0.65 and In0.7Ga0.3As active layers of GaAs-like and InAs-like interface TFET structures, respectively, indicating that nearly equal numbers of α and β dislocations were formed during the relaxation process. Atomic force microscopy reveals extremely ordered crosshatch morphology and low root mean square roughness of ∼3.17 nm for the InAs-like interface TFET structure compared to the GaAs-like interface TFET structure of ∼4.46 nm at the same degree of lattice mismatch with respect to the InP substrates. The GaAs-like interface exhibited higher dislocation density, as observed by cross-sectional transmission electron microscopy, resulting in the elongation of reciprocal lattice point of In0.7Ga0.3As channel and drain layers in the reciprocal space maps, while the InAs-like interface creates a defect-free interface for the pseudomorphic growth of the In0.7Ga0.3As channel and drain layers with minimal elongation along the Δω direction. The impact of the structural differences between the two interface types on metamorphic TFET devices was demonstrated by comparing p+-i-n+ leakage current of identical TFET devices that were fabricated using GaAs-like and InAs-like interface TFET structures. Higher OFF state leakage current dominated by band-to-band tunneling process due to higher degree of defects and dislocations was observed in GaAs-like interface compared to InAs-like interface where type-II staggered band alignment was well maintained. Significantly lower OFF state leakage current dominated by the field enhanced Shockley-Read-Hall generation-recombination process at different temperatures was observed in InAs-like TFET structure. The fixed positive charge at the source/channel heterointerface influences the band lineup substantially with charge density greater than 1 × 1012/cm2 and the band alignment is converted from staggered gap to broken gap at ∼6 × 1012/cm2. Clearly, InAs-like interface TFET structure exhibited 4× lower OFF state leakage current, which is attributed primarily to the impact of the layer roughness, defect properties on the carrier recombination rate, suggesting great promise for metamorphic TFET devices for high-performance, and ultra-low power applications.
Optical method of estimation of degree of atomic ordering within quaternary semiconductor alloys
Authors: Prutskij T. , Attolini G. , Lantratov V. , Kalyuzhnyy N.
Published: July 2012

It is well known that within metal-organic vapor-phase epitaxy grown semiconductor ternary alloys atomically ordered regions are spontaneously formed during the epitaxial growth. This ordering leads to bandgap reduction and to valence bands splitting, and therefore to anisotropy of the photoluminescence emission polarization. The same phenomenon occurs within quaternary semiconductor alloys. While the ordering in ternary alloys is widely studied, for quaternaries there have been only a few detailed experimental studies of it, probably because of the absence of appropriate methods of its detection. Here, we propose an optical method to reveal atomic ordering within quaternary alloys by measuring the photoluminescence (PL) emission polarization. The measured and calculated angular dependencies of the polarized PL emission intensity from (100) surface for two semiconductor alloys: Ga0.51In0.49P and (Al0.3Ga0.7)0.5In0.5P are compared in order to estimate the degree of atomic ordering within these alloys. The method shows that the quaternary (Al0.3Ga0.7)0.5In0.5P alloy is a highly ordered structure with the value of the atomic ordering degree close to 0.5.
Thermal rectification and phonon scattering in asymmetric silicon nanoribbons
Authors: Ju Shenghong , Liang Xingang
Published: July 2012

Thermal rectification is an interesting phenomenon and has important potential applications in improving the thermal management of electronics and saving energy. Exploring thermal rectification phenomena and understanding the mechanism are very necessary and important. This paper reports the investigation of the thermal conductivity and thermal rectification of asymmetric silicon nanoribbons by the non-equilibrium molecular dynamics simulation. The results indicate that the thermal conductivity of the nanoribbon is only on the order of 100 Wm−1K−1. Thermal rectification is observed in silicon nanoribbons at different temperatures, geometry aspects, and ribbon length. The thermal conductivity is apparently larger when heat flows from the thin end to the thick end. The larger the aspect ratio of the thick end to thin end is, the larger the thermal rectification. The rectification coefficient does not change much in the ribbon length ranges from 8.1 nm to 21.7 nm. The longitudinal phonon scattering in the silicon nanoribbon at different frequency is investigated by the phonon wave packet dynamic simulation. The results show that the phonon transmission coefficient is sensitive to frequency and transverse phonons are generated during the scattering. Decreasing the thin end width will reduce the transmission coefficient due to the scattering at the slope boundary.
Fast electrothermally activated micro-positioner using a high-aspect-ratio micro-machined polymeric composite
Authors: Lau Gih-Keong , Yang Jiaping , Thubthimthong Borriboon , Chong Nyok-Boon , Tan Cheng Peng , He Zhimin
Published: July 2012

Recently, silicon electrothermal micro-actuators have been developed for dual-stage micropositioning in hard disk drive. But, silicon with a low coefficient of thermal expansion (CTE) has a shortcoming of requiring a large temperature change (>300 °C) to expand adequately. This letter presented a high-CTE polymer composite to solve the shortcoming of silicon. The polymer composite consists of high-aspect-ratio micro-machined SU-8 thermal expander and silicon thermal conductor. A micro-positioner which embodies the proposed polymer composite can drive a slider to travel fast (>1 kHz) more than a 17 nm-pitch data track under a moderate temperature rise (<100 °C).
Electrical and thermoelectric properties of single-wall carbon nanotube doped Bi2Te3
Authors: Zhang Y. , Wang X. L. , Yeoh W. K. , Zheng R. K. , Zhang C.
Published: July 2012

The effects of single-wall carbon nanotube (SWCNT) doping in n-type Bi2Te3 bulk samples on the electrical and thermal transport properties have been studied. Bi2Te3 samples doped with 0–5 wt. % SWCNTs were fabricated using solid state reaction and investigated using x-ray diffraction, transmission electron microscopy, and magneto transport measurements. Results show that the 0.5% doping results in the significant enhancement of the Seebeck coefficience to as high as −231.8 μV/K, giant magneto resistance of up to 110%, reduction of thermal conductivity, and change of sign of the Seebeck coefficient from n to p type depending on the doping level and temperature. The figure of merit, ZT, of the optimum SWCNT doped Bi2Te3 was increased by 25%–40% over a wide temperature range compared to the undoped sample.
Micronewton electromagnetic thruster
Authors: Charrier D. S. H.
Published: July 2012

A low cost and light electromagnetic thruster, consisting in a disc rigidly attached with a coaxial coil, shows steady recoil by losing its linear momentum. The signal applied in the device is a square electric potential. A continuous thrust is observed on the center-of-mass in one single direction under electromagnetic excitation for various voltages and nominal high frequencies. At 1 kHz with 20 V amplitude, the recoil force reaches 4 μN (micronewton). The recoil is numerically quantified with induced electromotive and Lorentz forces. The presented device directly converts electric energy into kinetic energy.
Missing verbal inflections as a representational problem
Authors: VanPatten Bill , Keating Gregory D. , Leeser Michael J.
Published: July 2012

A continuing concern in second language acquisition (SLA) research is whether problems with inflectional morphology are representational or related somehow to performance. In this study, we examine 25 non-advanced learners of L2 Spanish and compare them with 18 native Spanish speakers on three grammatical structures: subject-verb inversion, adverb placement and person-number inflections on verbs. We use self-paced reading as a measure of underlying sensitivity to grammatical violations. Our results clearly show that the L2 learners pattern like the native speakers on the two syntactic structures; both groups demonstrate sensitivity to grammatical violations while reading sentences for meaning. For person-number on verbs, L2 learners did not show sensitivity to grammatical violations whereas the native speakers did. We argue that these results suggest a representational problem for morphology in our L2 population.
Critical transition between cohesive and population-dividing responses to change
Authors: Muneepeerakul Rachata , Qubbaj Murad R. , Aggarwal Rimjhim M. , Anderies John M. , Janssen Marco A.
Published: July 2012

Globalization and global climate change will probably be accompanied by rapid social and biophysical changes that may be caused by external forcing or internal nonlinear dynamics. These changes often subject residing populations (human or otherwise) to harsh environments and force them to respond. Research efforts have mostly focused on the underlying mechanisms that drive these changes and the characteristics of new equilibria towards which populations would adapt. However, the transient dynamics of how populations respond under these new regimes is equally, if not more, important, and systematic analysis of such dynamics has received less attention. Here, we investigate this problem under the framework of replicator dynamics with fixed reward kernels. We show that at least two types of population responses are possible—cohesive and population-dividing transitions—and demonstrate that the critical transition between the two, as well as other important properties, can be expressed in simple relationships between the shape of reward structure, shift magnitude and initial strategy diversity. Importantly, these relationships are derived from a simple, yet powerful and versatile, method. As many important phenomena, from political polarization to the evolution of distinct ecological traits, may be cast in terms of division of populations, we expect our findings and method to be useful and applicable for understanding population responses to change in a wide range of contexts.
Individual contributions to territory defence in a cooperative breeder: weighing up the benefits and costs
Authors: Mares Rafael , Young Andrew J. , Clutton-Brock Tim H.
Published: July 2012

While investment in territory defence is expected to be influenced by its benefits, the additional role that costs may play is rarely considered. Here, we quantify both benefits and costs of repelling prospecting males in cooperative meerkats, and demonstrate that both are required to explain the substantial variation in individual contributions to the defence observed. Males benefit more from repelling prospectors than females, as males may lose dominance and be expelled during intrusions. Accordingly, males invest the most in repelling prospectors. We also show that males experience an associated cost in the form of reduced weight gain and, as such, heavier males contribute more to chasing prospectors. Finally, we show evidence of a cost not restricted to individuals engaged in chasing: both males and females reduce their contributions to feeding dependent pups when prospectors are present, resulting in a reduction in pup weight gain in this context. Males appear to adjust their contributions to chasing in light of this cost, chasing at lower rates when their group contains dependent young. Our findings support the view that investment in cooperative behaviours can be attributed to benefits and costs, and highlight the additional importance of considering trade-offs in investment between cooperative behaviours.
Thermal transpirational flow in the transitional flow regime
Authors: Pharas Kunal , Miles Stephanie , McNamara Shamus
Published: July 2012

Pressure and mass flow rate due to thermal transpiration in the transitional flow regime is experimentally investigated for a wide range of Knudsen numbers, from 0.06 to 2.9, using a nanoporous membrane. A temperature gradient is created by heating one side of the membrane, and cooling the other side with a heat sink. The largest pressure difference and mass flow rates are found for the smallest pore size, 25 nm. It is found that a pressure difference and mass flow rate can still be observed for the largest pore size studied, 1.2 μm. This demonstrates that pressures due to thermal transpiration may be significant for certain MEMS devices with temperature gradients and sub-micron gaps. Using a fit for the temperature difference across the membrane, the experimental and theoretical results are in agreement.
An undergraduate measurement of radiative broadening in atomic vapor
Authors: Hachtel A. J. , Kleykamp J. D. , Kane D. G. , Marshall M. D. , Worth B. W. , Barkeloo J. T. , Kangara J. C. B. , Camenisch J. C. , Gillette M. C. , Bali S.
Published: July 2012

We show that one may quantitatively investigate radiative broadening of atomic transitions in the undergraduate laboratory using a traditional saturated absorption spectroscopy setup.
On energy transfers in reflection of light by a moving mirror
Authors: Goedecke G. , Toussaint V. , Cooper C.
Published: July 2012

Using independent wave and photon approaches, the energy transfers from a finite duration radiation pulse normally incident from vacuum on a mirror moving uniformly in the pulse propagation direction are derived. The classical sinusoidal wavetrain approach yields the quantum-like result that the ratio of the total energy in the reflected pulse to that in the incident pulse is equal to the corresponding ratio of their frequencies. Both approaches reveal that although the conventional sinusoidal plane wave reflection coefficient for the moving mirror does not have unit magnitude, there is no violation of energy conservation for pulses of finite duration. Instead, the energy in the incident pulse is partly transferred to the stretched or compressed Doppler-shifted reflected pulse, and partly converted to work done on the mirror. This work is negative if the mirror is moving toward the source/detector, resulting in a reflected pulse more energetic and shorter than the incident one, much more so as the relative speed approaches lightspeed.
Qualitative study of perfect-fluid Friedmann-Lemaître-Robertson-Walker models with a cosmological constant
Authors: Sonego Sebastiano , Talamini Vittorino
Published: July 2012

The evolution of spatially homogeneous and isotropic cosmological models containing a perfect fluid with equation of state p = wρ and a cosmological constant Λ is investigated for arbitrary combinations of w and Λ, using standard qualitative analysis borrowed from classical mechanics. This approach allows one to consider a large variety of situations, appreciating similarities and differences between models, without solving the Friedmann equation, and is suitable for an elementary course in cosmology.
Numerical calculations of scattering characteristics of inhomogeneities in biological tissue
Authors: Genis Vladimir I. , Oboznenko Igor L. , Zietz Stanley
Published: July 2012

Identification of inhomogeneities is one of the main problems in medical diagnosis, particularly in tissue characterization. Often the backscatter signal does not permit discrimination between inhomogeneities in the tissue. Despite high effectiveness of the B-mode diagnostic systems, at the present time ultrasonography does not provide a sufficient degree of diagnostic confidence in identification of pathology. Diffraction tomography promises to extend these observations quantitatively and provide information about tissue properties. The main goal of this work is to present a theoretical basis of the scattering process on inhomogeneities and provide some preliminary experimental results confirming theoretical investigations and numerical simulations. The method of integral equations for solving forward and inverse scattering problems is used, and scattering diagrams are presented. Experimental setup is based on one transmitting and seven receiving elements. Presented experimental resuls support numerical simulations.
An adaptive coupled range-dependent normal-mode method
Authors: Werby M. F. , Sidorovskaia N. A.
Published: July 2012

Based on the warping method and the generalized eigenvalue problem the range-independent solution is extended to that of range dependence. In this method, coupling in range is analytical and may be either one way or two way. Since the range steps are not dependent on finite-difference schemes, the optimal range step at each point is determined. This leads to two advantages: (1) There is no need for input of range step; and (2) the optimal range step is predetermined by several conditions, thus avoiding overkill and reruns to determine stability. Comparisons with other range-dependent methods are presented. [Work sponsored by ONR, the Naval Res. Lab., and the Univ. of New Orleans.]
Six-year study of IMSA road racing noise
Authors: Bricken Gordon , Jean Christopher
Published: July 2012

The Del Mar Fairgrounds, San Diego, hosted the IMSA Grand Prix for 6 years from 1987–1993. The project provides a unique long-term study of professional road racing noise in a unique setting, a narrow valley just east of the coastline and within an environmentally sensitive lagoon. Sponsors were required to perform community noise monitoring at selected locations in the adjacent hills and lagoon. Both human and bird responses were examined. The monitoring documented the hour by hour variations in the maximum and average noise levels at up to 12 separate locations. The results indicated the thresholds which would trigger community response, the sensitivity of the response to diurnal and short-term wind shift, the effect of the inversion layer, the effects on bird patterns, and the statistical distribution of vehicle noise levels for the IMSA class vehicle. Basic findings revealed community response was triggered when levels exceeded 70 dBA Lavg. Downwind levels tended to increase at 1 dBA/mph over 5 mph. When the track was within an inversion, levels increased 10 dBA. The mean vehicle level at 15 m was 105 dBA with a 4-dBA standard deviation.
Paul S. Veneklasen, contributions to psychological acoustics and speech communication systems
Authors: Christoff Jerry P. , Ortega Jose C.
Published: July 2012

Early in the authors’ careers working with Paul Veneklasen at the Western Electro-Acoustic Laboratory, the authors were involved with programs dealing with speech communication in high-noise fields and the development of a new ear plug, possibly to replace the venerable V51-R ear defender that was developed by Paul Veneklasen, Vern O. Knudsen, and others during World War II. His later interests were involved with the perception of lateral reflections in rooms, which Knudsen called ‘‘envelopment,’’ primarily through research in his patented Auditorium Synthesis demonstration room. Highlights of this work are recounted including the novel forehead, ear, and tooth microphones.
Single-bubble sonoluminescence in microgravity
Authors: Matula Thomas J. , Swalwell Jarred E. , Bezzerides Vassiloius , Hilmo Paul , Chittick Mike , Crum Lawrence A. , Kuhns David W. , Roy Ronald A.
Published: July 2012

A recent experiment involving single-bubble sonoluminescence aboard NASA’s parabolic research aircraft will be described. Measurements of the intensity of the light emission were performed during periods of microgravity (near 0 g) and hypergravity (near 2 g). Gravitational effects on the luminescence and extinction pressure thresholds were examined. In addition, the light emission was monitored under constant drive conditions as the gravitational acceleration varied during the parabolas. Measurements show some variability in the sonoluminescence intensity for both thresholds. However, during otherwise constant conditions in which the drive pressure amplitude did not change, the intensity from stable single-bubble sonoluminescence was observed to increase during periods of microgravity. There was an initial increase in intensity that occurred simultaneous with the decrease in the gravitational acceleration, followed by a slow increase in intensity that appeared to level off near the end of the microgravity period. The longer time scales over which the intensity changed during the microgravity period may be indicative of gas diffusion occurring as the bubble attains a new equilibrium condition. [Research supported by NSF and NASA.]
Active impedance control in a water-filled waveguide for low-frequency bioacoustic testing
Authors: Finneran James J. , Hastings Mardi C.
Published: July 2012

A challenging problem in studying low-frequency sound reception in aquatic animals is creating a suitable underwater acoustic testing environment. For studies of sound reception in fishes, a plane traveling wave is often a desirable stimulus because the relationship between acoustic pressure and particle velocity is well known. At low frequencies, the long acoustic wavelengths in water rule out obtaining traveling waves in rectangular aquaria. In this study, a cylindrical, water-filled acoustic waveguide, with an active termination was used to generate constant frequency, plane traveling waves in the 12–400-Hz frequency range. The waveguide was constructed of acrylic tubing with an NRL J-13 transducer flanged to each end. One J-13 was the primary source and generated continuous harmonic waves. The active control system measured the transfer function between two hydrophones located inside the tube and used a pattern search algorithm to adjust the secondary source amplitude and phase in order to drive the measured transfer function to that for an unbounded wave. The active control system was able to reduce the terminating reflection coefficient to below 0.05 within the frequency range 12–400 Hz. [Work supported by ONR, Grant No. N00014-94-1-0337.]