bluuebunny/crossref_metadata_2025 huggingface dataset:
Pathways of Early Fatherhood, Marriage, and Employment: A Latent Class Growth Analysis
Authors: Dariotis Jacinda K. , Pleck Joseph H. , Astone Nan M. , Sonenstein Freya L.
Published: April 2011

In the National Longitudinal Survey of Youth 1979 (NLSY79), young fathers include heterogeneous subgroups with varying early life pathways in terms of fatherhood timing, the timing of first marriage, and holding full-time employment. Using latent class growth analysis with 10 observations between ages 18 and 37, we derived five latent classes with median ages of first fatherhood below the cohort median (26.4), constituting distinct early fatherhood pathways representing 32.4% of NLSY men: (A) Young Married Fathers, (B) Teen Married Fathers, (C) Young Underemployed Married Fathers, (D) Young Underemployed Single Fathers, and (E) Young Later-Marrying Fathers. A sixth latent class of men who become fathers around the cohort median, following full-time employment and marriage (On-Time On-Sequence Fathers), is the comparison group. With sociodemographic background controlled, all early fatherhood pathways show disadvantage in at least some later-life circumstances (earnings, educational attainment, marital status, and incarceration). The extent of disadvantage is greater when early fatherhood occurs at relatively younger ages (before age 20), occurs outside marriage, or occurs outside full-time employment. The relative disadvantage associated with early fatherhood, unlike early motherhood, increases over the life course.
Medicaid Expansions and Fertility in the United States
Authors: DeLeire Thomas , Lopoo Leonard M. , Simon Kosali I.
Published: April 2011

Beginning in the mid-1980s and extending through the early to mid-1990s, a substantial number of women and children in the United States gained eligibility for Medicaid through a series of income-based expansions. Using natality data from the National Center for Health Statistics, we estimate fertility responses to these eligibility expansions. We follow Currie and Gruber (2001) and measure changes in state Medicaid-eligibility policy by simulating the fraction of a standard population that would qualify for benefits in different states and different time periods. From 1985 to 1996, the fraction of women aged 15–44 who were eligible for Medicaid coverage for a pregnancy increased more than 20 percentage points. When we use a state and year fixed-effects model with a limited set of covariates, our estimates indicate that fertility increases in response to Medicaid expansions. However, after we include fixed effects for demographic characteristics, the estimated relationship diminishes substantially in size and is no longer statistically significant. We conclude that there is no robust relationship between Medicaid expansions and fertility.
Air pollution is associated with brainstem auditory nuclei pathology and delayed brainstem auditory evoked potentials
Authors: Calderón‐Garcidueñas Lilian , D'Angiulli Amedeo , Kulesza Randy J. , Torres‐Jardón Ricardo , Osnaya Norma , Romero Lina , Keefe Sheyla , Herritt Lou , Brooks Diane M. , Avila‐Ramirez Jose , Delgado‐Chávez Ricardo , Medina‐Cortina Humberto , González‐González Luis Oscar
Published: April 2011

We assessed brainstem inflammation in children exposed to air pollutants by comparing brainstem auditory evoked potentials (BAEPs) and blood inflammatory markers in children age 96.3 ± 8.5 months from highly polluted (n = 34) versus a low polluted city (n = 17). The brainstems of nine children with accidental deaths were also examined. Children from the highly polluted environment had significant delays in wave III (t(50) = 17.038; p < 0.0001) and wave V (t(50) = 19.730; p < 0.0001) but no delay in wave I (p = 0.548). They also had significantly longer latencies than controls for interwave intervals I–III, III–V, and I–V (all t(50) > 7.501; p < 0.0001), consisting with delayed central conduction time of brainstem neural transmission. Highly exposed children showed significant evidence of inflammatory markers and their auditory and vestibular nuclei accumulated α synuclein and/or β amyloid1–42. Medial superior olive neurons, critically involved in BAEPs, displayed significant pathology. Children's exposure to urban air pollution increases their risk for auditory and vestibular impairment.
A Systematic Literature Review of the Applications of Q-Technique and Its Methodology
Authors: Dziopa Fiona , Ahern Kathy
Published: April 2011

Q-methodology is a technique incorporating the benefits of both qualitative and quantitative research. Q-method involves Q-sorting, a method of data collection and factor analysis, to assess subjective (qualitative) information. The use of Q-sorting and factor analysis has often resulted in the misconception that Q-methodology involves psychometric or quantitative assessment, although Q as a methodology actually enables the systematic assessment of qualitative data. Misconceptions regarding Q have resulted in a heterogeneous collection of Q-applications in the extant literature, which has obscured the fundamental principles of Q-methodology. The purpose of this paper is to present a systematic review of Q-based research to investigate the criteria researchers have used to develop Q-studies. Published research studies between January 2008 and December 2008 that employed Q-techniques and methodology were assessed. Data were extracted and synthesized through the development and use of the Assessment and Review Instrument for Q-methodology (ARIQ). Fourteen research studies met the inclusion criteria for the review. The Q-methodological studies were disparate in their application of terminology, instrument development, and factor analysis, although data extraction and synthesis processes revealed two types of studies: those which aimed to apply conventional Q-methodology and those which applied variations of Q-techniques. It is concluded that variations of Q-technique and its methodology are unavoidable. However, this does not obviate the need for researchers to explicitly state their rationale for decisions to deviate from conventional Q-methodology if they are to produce demonstrably valid research. The review instrument (ARIQ) developed for this review will facilitate this end.
A Simulation Procedure for the Generation of Samples to Evaluate Goodness of Fit Indices in Item Response Theory Models
Authors: Chacón Edixon , Alvarado Jesús M. , Santisteban Carmen
Published: April 2011

The LISREL8.8/PRELIS2.81 program can carry out ordinal factorial analysis (OFA command), with full information maximum likelihood methods, in a data set containing n samples obtained by simulation. Nevertheless, when the replication number is greater than 1, an error command is produced, which impedes reaching solutions that can execute normal (NOR) and logistic (POM) functions. This paper proposes a new procedure of data simulation in PRELIS-LISREL. This procedure permits the generation of n replications and the calculation of the goodness of fit (GOF) indices in the item response theory (IRT) models for each replication, thus allowing the execution of the OFA command for Monte Carlo simulations. The solutions using underlying variable (weighted least squares (WLS) estimation method) and IRT approaches are compared.
A Note on the Connection Between Knowledge Structures and Latent Class Models
Authors: Ünlü Ali
Published: April 2011

Schrepp (2005) points out and builds upon the connection between knowledge space theory (KST) and latent class analysis (LCA) to propose a method for constructing knowledge structures from data. Candidate knowledge structures are generated, they are considered as restricted latent class models and fitted to the data, and the BIC is used to choose among them. This article adds additional information about the relationship between KST and LCA. It gives a more comprehensive overview of the literature and the probabilistic models that are at the interface of KST and LCA. KST and LCA are also compared with regard to parameter estimation and model testing methodologies applied in their fields. This article concludes with an overview of KST-related publications addressing the outlined connection and presents further remarks about possible future research arising from a connection of KST to other latent variable modeling approaches.
Measurement Equivalence and Extreme Response Bias in the Comparison of Attitudes Across Europe
Authors: Kankaraš Miloš , Moors Guy
Published: April 2011

It is generally accepted that both measurement inequivalence and extreme response bias (ERB) can seriously distort measurement of attitudes and subsequent causal models. However, these two issues have rarely been investigated together. In this article we demonstrate the flexibility of a multigroup latent-class factor approach in both analyzing measurement equivalence and detecting ERB. Using data from the European Values Survey from 1999/2000, we identified an ERB in answering Likert-type questions on attitudes toward morals of compatriots. Furthermore, we found measurement inequivalence in the form of direct effects of countries on the attitude items. The model that included both these issues resulted in quite distinct findings regarding country difference in the latent attitude compared to the models that only included one of these effects – either measurement inequivalence or extreme response. It is suggested that the all-inclusive model provides the more valid estimates of country differences in the latent attitude.
Visual Cues and Listening Effort: Individual Variability
Authors: Picou Erin M. , Ricketts Todd A. , Hornsby Benjamin W. Y.
Published: April 2011

Purpose

To investigate the effect of visual cues on listening effort as well as whether predictive variables such as working memory capacity (WMC) and lipreading ability affect the magnitude of listening effort.

Method

Twenty participants with normal hearing were tested using a paired-associates recall task in 2 conditions (quiet and noise) and 2 presentation modalities (audio only [AO] and auditory–visual [AV]). Signal-to-noise ratios were adjusted to provide matched speech recognition across audio-only and AV noise conditions. Also measured were subjective perceptions of listening effort and 2 predictive variables: (a) lipreading ability and (b) WMC.

Results

Objective and subjective results indicated that listening effort increased in the presence of noise, but on average the addition of visual cues did not significantly affect the magnitude of listening effort. Although there was substantial individual variability, on average participants who were better lipreaders or had larger WMCs demonstrated reduced listening effort in noise in AV conditions.

Conclusions

Overall, the results support the hypothesis that integrating auditory and visual cues requires cognitive resources in some participants. The data indicate that low lipreading ability or low WMC is associated with relatively effortful integration of auditory and visual information in noise.
A Nationally Representative Study of the Association Between Communication Impairment at 4–5 Years and Children’s Life Activities at 7–9 Years
Authors: McCormack Jane , Harrison Linda J. , McLeod Sharynne , McAllister Lindy
Published: April 2011

Purpose

To examine the longitudinal association between communication impairment (primary or secondary diagnosis) and children’s Activities and Participation (International Classification of Functioning, Disability and Health—Children and Youth [ICF–CY]; World Health Organization [WHO], 2007).

Method

Participants were 4,329 children in the Longitudinal Study of Australian Children (LSAC; Australian Institute of Family Studies [AIFS], 2009): 1,041 (24.0%) of these children were identified with communication impairment at 4–5 years of age, and 3,288 (76.0%) of these children were not identified with a communication impairment. At age 7–9 years, Activities and Participation (WHO, 2007) outcomes across 5 ICF–CY domains were provided by (a) teachers (Academic Rating Scales [National Center for Education Statistics (NCES), 2002], Approach to Learning Scale [Gresham & Elliott, 1990], School Progress Scale (AIFS, 2009), Strengths and Difficulties Questionnaire [SDQ; Goodman, 1997], and Student–Teacher Relationship Scale [Pianta, 2001]); (b) parents (School-Age Inventory of Temperament [McClowry, 1995] and SDQ); (c) children (Marsh Self-Description Questionnaire–III [Marsh, 1992], School Liking [Ladd & Price, 1987], and Bullying [Kochenderfer & Ladd, 1997]); and (d) child assessment (Peabody Picture Vocabulary Test—III: Adapted; Rothman, 2003).

Results

Children identified with communication impairment at age 4–5 years performed significantly poorer at age 7–9 years on all outcomes. Parents and teachers reported slower progression in reading, writing, and overall school achievement than peers. Children reported more bullying, poorer peer relationships, and less enjoyment of school than did their peers. Analyses of covariance tests confirmed significant associations between communication impairment and outcomes, over and above the effects of sex, age, Indigenous status, and socioeconomic status.

Conclusion

Consideration of the breadth and longevity of Activities and Participation outcomes reveals the potential extent and severity of communication impairment and directs future research and practice.
Effects of Perceptual and Contextual Enrichment on Visual Confrontation Naming in Adult Aging
Authors: Rogalski Yvonne , Peelle Jonathan E. , Reilly Jamie
Published: April 2011

Purpose

The purpose of this study was to determine the effects of enriching line drawings with color/texture and environmental context as a facilitator of naming speed and accuracy in older adults.

Method

Twenty young and 23 older adults named high-frequency picture stimuli from the Boston Naming Test (Kaplan, Goodglass, & Weintraub, 2001) under three conditions: (a) black-and-white items, (b) colorized-texturized items, and (c) scene-primed colored items (e.g., “hammock” preceded 1,000 ms by a backyard scene).

Results

With respect to speeded naming latencies, mixed-model analyses of variance revealed that young adults did not benefit from colorization-texturization but did show scene-priming effects. In contrast, older adults failed to show facilitation effects from either colorized-texturized or scene-primed items. Moreover, older adults were consistently slower to initiate naming than were their younger counterparts across all conditions.

Conclusions

Perceptual and contextual enrichment of sparse line drawings does not appear to facilitate visual confrontation naming in older adults, whereas younger adults do tend to show benefits of scene priming. We interpret these findings as generally supportive of a processing speed account of age-related object picture-naming difficulty.
Relation of Structural and Vibratory Kinematics of the Vocal Folds to Two Acoustic Measures of Breathy Voice Based on Computational Modeling
Authors: Samlan Robin A. , Story Brad H.
Published: April 2011

Purpose

To relate vocal fold structure and kinematics to 2 acoustic measures: cepstral peak prominence (CPP) and the amplitude of the first harmonic relative to the second (H1–H2).

Method

The authors used a computational, kinematic model of the medial surfaces of the vocal folds to specify features of vocal fold structure and vibration in a manner consistent with breathy voice. Four model parameters were altered: degree of vocal fold adduction, surface bulging, vibratory nodal point, and supraglottal constriction. CPP and H1–H2 were measured from simulated glottal area, glottal flow, and acoustic waveforms and were related to the underlying vocal fold kinematics.

Results

CPP decreased with increased separation of the vocal processes, whereas the nodal point location had little effect. H1–H2 increased as a function of separation of the vocal processes in the range of 1.0 mm to 1.5 mm and decreased with separation > 1.5 mm.

Conclusions

CPP is generally a function of vocal process separation. H1*–H2* (see paragraph 6 of article text for an explanation of the asterisks) will increase or decrease with vocal process separation on the basis of vocal fold shape, pivot point for the rotational mode, and supraglottal vocal tract shape, limiting its utility as an indicator of breathy voice. Future work will relate the perception of breathiness to vocal fold kinematics and acoustic measures.
Effects of Computer System and Vowel Loading on Measures of Nasalance
Authors: Awan Shaheen N. , Omlor Kristin , Watts Christopher R.
Published: April 2011

Purpose

The purpose of this study was to determine similarities and differences in nasalance scores observed with different computerized nasalance systems in the context of vowel-loaded sentences.

Methodology

Subjects were 46 Caucasian adults with no perceived hyper- or hyponasality. Nasalance scores were obtained using the Nasometer 6200 (Kay Elemetrics Corp.), the Nasometer II 6400 (Kay Elemetrics Corp.), and the NasalView (Tiger DRS, Inc.) for sentences loaded with mixed, high front, high back, low front, or low back vowels.

Results

Measures of nasalance obtained with the NasalView were significantly higher than those obtained with the Nasometer 6200, and the measures of nasalance obtained with the Nasometer 6200 were significantly higher than those obtained with the Nasometer II 6400. However, similar effects of vowel loading on measures of nasalance were observed, regardless of system. For all systems, the high front vowel sentence tended to result in higher measures of nasalance than did the high back, low front, and low back vowel sentences—the mixed vowel sentence tended to have a higher degree of nasalance than did any of the other sentences.

Conclusions

Although nasalance data computed using different systems are not readily comparable, all three systems that were evaluated produced similar effects of vowel loading on nasalance. Increased nasalance for high front versus low back vowels may be due to factors such as increased oral impedance, reduced radiated oral sound pressure, possible increases in airflow via the nasal cavity, and increased transpalatal nasalance.
Bimodal Hearing and Speech Perception With a Competing Talker
Authors: Pyschny Verena , Landwehr Markus , Hahn Moritz , Walger Martin , von Wedel Hasso , Meister Hartmut
Published: April 2011

Purpose

The objective of the study was to investigate the influence of bimodal stimulation upon hearing ability for speech recognition in the presence of a single competing talker.

Method

Speech recognition was measured in 3 listening conditions: hearing aid (HA) alone, cochlear implant (CI) alone, and both devices together (CI + HA). To examine the use of low-frequency cues, the competing masker voice was manipulated with respect to fundamental frequency (F0) and formant frequencies. Twelve implanted adults were included in the study.

Results

Group results revealed only a relatively small benefit of CI + HA compared with the CI alone. A detailed analysis of errors, which was assumed to be an indicator for the release from masking, revealed that this benefit was not attributed to improved target–masker segregation. The variable determined to be responsible for segregating target and masker talkers was a large difference in F0 of the voices. This held true for all CI alone, HA alone, and CI + HA listening conditions.

Conclusions

Bimodal hearing improved overall speech recognition of both the target and the masker. No evidence for better target–masker separation with bimodal fitting could be found.
Accuracy of the NDI Wave Speech Research System
Authors: Berry Jeffrey J.
Published: April 2011

Purpose

This work provides a quantitative assessment of the positional tracking accuracy of the NDI Wave Speech Research System.

Method

Three experiments were completed: (a) static rigid-body tracking across different locations in the electromagnetic field volume, (b) dynamic rigid-body tracking across different locations within the electromagnetic field volume, and (c) human jaw-movement tracking during speech. Rigid-body experiments were completed for 4 different instrumentation settings, permuting 2 electromagnetic field volume sizes with and without automated reference sensor processing.

Results

Within the anthropometrically pertinent “near field” (< 200 mm) of the NDI Wave field generator, at the 300-mm
3
volume setting, 88% of dynamic positional errors were < 0.5 mm and 98% were < 1.0 mm. Extreme tracking errors (> 2 mm) occurred within the near field for < 1% of position samples. For human jaw-movement tracking, 95% of position samples had < 0.5 mm errors for 9 out of 10 subjects.

Conclusions

Static tracking accuracy is modestly superior to dynamic tracking accuracy. Dynamic tracking accuracy is best for the 300-mm
3
field setting in the 200-mm near field. The use of automated head correction has no deleterious effect on tracking. Tracking errors for jaw movements during speech are typically < 0.5 mm.
Effects of Voice Therapy on Relative Fundamental Frequency During Voicing Offset and Onset in Patients With Vocal Hyperfunction
Authors: Stepp Cara E. , Merchant Gabrielle R. , Heaton James T. , Hillman Robert E.
Published: April 2011

Purpose

The purpose of this study was to determine whether the relative fundamental frequency (RFF) surrounding a voiceless consonant in patients with hyperfunctionally related voice disorders would normalize after a successful course of voice therapy.

Method

Pre- and posttherapy measurements of RFF were compared in 16 subjects undergoing voice therapy for voice disorders associated with vocal hyperfunction.

Results

A 2-way analysis of variance showed a statistically significant effect of both cycle of vibration near the consonant and therapy phase (pre- vs. post-), with
p
< .001. A post hoc paired Student’s
t
test showed that posttherapy RFF measurements were significantly higher (more typical;
p
< .0001) than pretherapy measurements.

Conclusions

Prior to therapy, participants exhibited lowered RFF values, similar to those found previously (Stepp, Hillman, & Heaton, 2010). After successful completion of voice therapy, RFF values increased toward patterns seen previously in individuals with healthy typical voice. The goal of voice therapy in these patients was to reduce laryngeal muscle tension; therefore, the increase of RFF toward more typical values may be indicative of decreased baseline laryngeal muscle tension resulting from therapy. Results are discussed further in terms of necessary research to incorporate RFF as a clinical measure of vocal hyperfunction.
Structure of an exploding laser-produced plasma
Authors: Collette A. , Gekelman W.
Published: April 2011

Currents and instabilities associated with an expanding dense plasma embedded in a magnetized background plasma are investigated by direct volumetric probe measurements of the magnetic field and floating potential. A diamagnetic cavity is formed and found to collapse rapidly compared to the expected magnetic diffusion time. The three-dimensional current density within the expanding plasma includes currents along the background magnetic field, in addition to the diamagnetic current. Correlation measurements reveal that flutelike structures at the plasma surface translate with the expanding plasma across the magnetic field and extend into the current system that sustains the diamagnetic cavity, possibly contributing to its collapse.
Application of a renormalization-group treatment to the statistical associating fluid theory for potentials of variable range (SAFT-VR)
Authors: Forte Esther , Llovell Felix , Vega Lourdes F. , Trusler J. P. Martin , Galindo Amparo
Published: April 2011

An accurate prediction of phase behavior at conditions far and close to criticality cannot be accomplished by mean-field based theories that do not incorporate long-range density fluctuations. A treatment based on renormalization-group (RG) theory as developed by White and co-workers has proven to be very successful in improving the predictions of the critical region with different equations of state. The basis of the method is an iterative procedure to account for contributions to the free energy of density fluctuations of increasing wavelengths. The RG method has been combined with a number of versions of the statistical associating fluid theory (SAFT), by implementing White's earliest ideas with the improvements of Prausnitz and co-workers. Typically, this treatment involves two adjustable parameters: a cutoff wavelength L for density fluctuations and an average gradient of the wavelet function Φ. In this work, the SAFT-VR (variable range) equation of state is extended with a similar crossover treatment which, however, follows closely the most recent improvements introduced by White. The interpretation of White's latter developments allows us to establish a straightforward method which enables Φ to be evaluated; only the cutoff wavelength L then needs to be adjusted. The approach used here begins with an initial free energy incorporating only contributions from short-wavelength fluctuations, which are treated locally. The contribution from long-wavelength fluctuations is incorporated through an iterative procedure based on attractive interactions which incorporate the structure of the fluid following the ideas of perturbation theories and using a mapping that allows integration of the radial distribution function. Good agreement close and far from the critical region is obtained using a unique fitted parameter L that can be easily related to the range of the potential. In this way the thermodynamic properties of a square-well (SW) fluid are given by the same number of independent intermolecular model parameters as in the classical equation. Far from the critical region the approach provides the correct limiting behavior reducing to the classical equation (SAFT-VR). In the critical region the β critical exponent is calculated and is found to take values close to the universal value. In SAFT-VR the free energy of an associating chain fluid is obtained following the thermodynamic perturbation theory of Wertheim from the knowledge of the free energy and radial distribution function of a reference monomer fluid. By determining L for SW fluids of varying well width a unique equation of state is obtained for chain and associating systems without further adjustment of critical parameters. We use computer simulation data of the phase behavior of chain and associating SW fluids to test the accuracy of the new equation.
RgBF2+ complexes (Rg = Ar, Kr, and Xe): The cations with large stabilities
Authors: Lv Zhi , Chen Guang-Hui , Li Dan , Wu Di , Huang Xiao-Chun , Li Zhi-Ru , Liu Wen-Guang
Published: April 2011

Rare gas containing cations with general formula [Rg, B, 2F]+ have been investigated theoretically by second-order Møller–Plesset perturbation, coupled cluster, and complete active space self-consistent field levels of theory with correlation-consistent basis sets. Totally two types of minima, i.e., boron centered C2v symmetried RgBF2+ (Rg = Ar, Kr, and Xe) which can be viewed as loss of F− from FRgBF2 and linear FRgBF+ (Rg = Kr and Xe) are obtained at the CCSD(T)/aug-cc-pVTZ/SDD and CASSCF(10,8)/aug-cc-pVTZ/SDD levels, respectively. It is shown that the RgBF2+ are global minima followed by FRgBF+ at 170.9 and 142.2 kcal/mol on the singlet potential-energy surfaces of [Rg, B, 2F]+ (Rg = Kr and Xe) at the CASPT2(10,8) /aug-cc-pVTZ/SDD//CASSCF(10,8)/aug-cc-pVTZ/SDD, respectively. The interconversion barrier heights between RgBF2+ and FRgBF+ (Rg = Kr and Xe) are at least 39 kcal/mol. In addition, no dissociation transition state associated with RgBF2+ and FRgBF+ can be found. This suggests that RgBF2+ (Rg = Ar, Kr, and Xe) can exist as both thermodynamically and kinetically stable species, while linear FRgBF+ (Rg = Kr and Xe) can exist as metastable species compared with the lowest dissociation limit energies just like isoelectronic linear FRgBO and FRgBN−. From natural bond orbital and atoms-in-molecules calculations, it is found that the positive charge is mainly located on Rg and boron atoms for both types of minima, the Rg–B bonds of ArBF2+, KrBF2+, and XeBF2+ are mostly electrostatic, thus can be viewed as ion-induced dipole interaction; while that of linear FKrBF+ and FXeBF+ are covalent in nature. The previous experimental observation of ArBF2+ by Pepi et al. [J. Phys. Chem. B. 110, 4492 (2006)]10.1021/jp0560922 should correspond to C2v minimum. The presently predicted spectroscopies of KrBF2+, XeBF2+, FKrBF+, and FXeBF+ should be helpful for their experimental identification in the future.
Electron–cyclotron damping of helicon waves in low diverging magnetic fields
Authors: Lafleur T. , Charles C. , Boswell R. W.
Published: April 2011

Particle-in-cell simulations are performed to investigate wave propagation and absorption behavior of low-field (B0<5 mT) helicon waves in the presence of a diverging magnetic field. The 1D electromagnetic simulations, which include experimental external magnetic field profiles, provide strong evidence for electron–cyclotron damping of helicon waves in the spatially decaying nonuniform magnetic field. For a dipole-type magnetic field configuration, the helicon waves are absence in the downstream (lower field) region of the plasma and are observed to be completely absorbed. As the magnetic field is changed slightly however, wave damping decreases, and waves are able to propagate freely downstream, confirming previous experimental measurements of this phenomenon.
Single-cell assays
Authors: Ryan Declan , Ren Kangning , Wu Hongkai
Published: April 2011

This review presents an overview of literature that describes the applications of microfluidics to assay individual cells. We quantify the content of an individual mammalian cell, so that we can understand what criteria a single-cell assay must satisfy to be successful. We put in context the justification for single-cell assays and identify the characteristics that are relevant to single-cell assays. We review the literature from the past 24 months that describe the methods that use microfabrication—conventional or otherwise—and microfluidics in particular to study individual cells, and we present our views on how an increasing emphasis on three-dimensional cell culture and the demonstration of the first chemically defined cell might impact single-cell assays.
Generalized MICZ-Kepler problems and unitary highest weight modules
Authors: Meng Guowu , Zhang Ruibin
Published: April 2011

For each integer n ⩾ 1, we demonstrate that a (2n + 1)-dimensional generalized MICZ-Kepler problem has a Spin(2, 2n + 2) dynamical symmetry which extends the manifest Spin(2n + 1) symmetry. The Hilbert space of bound states is shown to form a unitary highest weight Spin(2, 2n + 2)-module with the minimal positive Gelfand–Kirillov dimension. As a byproduct, we obtain a simple geometric realization for such a unitary highest weight Spin(2, 2n + 2)-module.
A novel high resolution ion wide angle spectrometer
Authors: Jung D. , Hörlein R. , Gautier D. C. , Letzring S. , Kiefer D. , Allinger K. , Albright B. J. , Shah R. , Palaniyappan S. , Yin L. , Fernández J. C. , Habs D. , Hegelich B. M.
Published: April 2011

A novel ion wide angle spectrometer (iWASP) has been developed, which is capable of measuring angularly resolved energy distributions of protons and a second ion species, such as carbon C6 +, simultaneously. The energy resolution for protons and carbon ions is better than 10% at ∼50 MeV/nucleon and thus suitable for the study of novel laser-ion acceleration schemes aiming for ultrahigh particle energies. A wedged magnet design enables an acceptance angle of 30°(∼524 mrad) and high angular accuracy in the μrad range. First, results obtained at the LANL Trident laser facility are presented demonstrating high energy and angular resolution of this novel iWASP.
Control of nitromethane photoionization efficiency with shaped femtosecond pulses
Authors: Roslund Jonathan , Shir Ofer M. , Dogariu Arthur , Miles Richard , Rabitz Herschel
Published: April 2011

The applicability of adaptive femtosecond pulse shaping is studied for achieving selectivity in the photoionization of low-density polyatomic targets. In particular, optimal dynamic discrimination (ODD) techniques exploit intermediate molecular electronic resonances that allow a significant increase in the photoionization efficiency of nitromethane with shaped near-infrared femtosecond pulses. The intensity bias typical of high-photon number, nonresonant ionization is accounted for by reference to a strictly intensity-dependent process. Closed-loop adaptive learning is then able to discover a pulse form that increases the ionization efficiency of nitromethane by ∼150%. The optimally induced molecular dynamics result from entry into a region of parameter space inaccessible with intensity-only control. Finally, the discovered pulse shape is demonstrated to interact with the molecular system in a coherent fashion as assessed from the asymmetry between the response to the optimal field and its time-reversed counterpart.
On the convergence of the solution for a generalized Zakharov system
Authors: Zhang Jingjun , Guo Yanfeng
Published: April 2011

In this paper, we study the limit behavior of the smooth solution for the generalized Zakharov system with a magnetic field which describes the spontaneous generation of a magnetic field in a cold plasma. By showing uniform bounds of solutions for this system with suitable initial data, we prove that solution of the generalized Zakharov system converges to the solution of the nonlinear Schrödinger equation with a magnetic field.
Electromagnetic modes of an infinite cylindrical sample of two-level atoms
Authors: Friedberg Richard , Manassah Jamal T.
Published: April 2011

We find both the electromagnetic TE and TM transverse eigenmodes of an infinite cylindrical sample of two-level atoms. The TM modes are similar to those obtained in the “scalar photon” theory, while the TE series is new. The TE series possesses “anomalous modes,” which are absent in the TM series. We find the metric for the scalar product for the eigenfunctions in both series and numerically show the completeness of both these series. Using Fourier-like expansions of the initial excitation state of the atoms in these eigenfunctions, we are able to compute to arbitrary accuracy the polarization of the atomic state at an arbitrary time. We compare these accurate results with those obtained from the eikonal–slowly varying envelope approximation in space and find remarkable agreement in the results for a system which is initially weakly excited.
A density-functional theory study of water on clean and hydrogen preadsorbed Rh(111) surfaces
Authors: Hamada Ikutaro , Morikawa Yoshitada
Published: April 2011

We study the water bilayer on clean and hydrogen preadsorbed Rh(111) surfaces by means of density-functional theory with the generalized gradient approximation and the van der Waals density functional, to investigate the influence of adsorbed hydrogen on the adsorption state of water. We found that adsorbed hydrogen interacts repulsively with water through its 1b1 and 4a1 orbitals. The repulsion dominates at high hydrogen coverage, resulting in a hydrophobic Rh(111)-H surface.
On complete integrability of the Mikhailov–Novikov–Wang system
Authors: Vojčák Petr
Published: April 2011

In the present paper we consider a new two-component fifth-order integrable system recently found by Mikhailov, Novikov, and Wang, and show that this system possesses a hereditary recursion operator and infinitely many commuting symmetries and conservation laws, as well as infinitely many compatible Hamiltonian and symplectic structures, and is therefore completely integrable. The system in question admits a reduction to the Kaup–Kupershmidt equation.
Discovery of deep and shallow trap states from step structures of rutile TiO2 vicinal surfaces by second harmonic and sum frequency generation spectroscopy
Authors: Takahashi Hiroaki , Watanabe Ryosuke , Miyauchi Yoshihiro , Mizutani Goro
Published: April 2011

In this report, local electronic structures of steps and terraces on rutile TiO2 single crystal faces were studied by second harmonic and sum frequency generation (SHG/SFG) spectroscopy. We attained selective measurement of the local electronic states of the step bunches formed on the vicinal (17 18 1) and (15 13 0) surfaces using a recently developed step-selective probing technique. The electronic structures of the flat (110)-(1×1) (the terrace face of the vicinal surfaces) and (011)-(2×1) surfaces were also discussed. The SHG/SFG spectra showed that step structures are mainly responsible for the formation of trap states, since significant resonances from the trap states were observed only from the vicinal surfaces. We detected deep hole trap (DHT) states and shallow electron trap (SET) states selectively from the step bunches on the vicinal surfaces. Detailed analysis of the SHG/SFG spectra showed that the DHT and SET states are more likely to be induced at the top edges of the step bunches than on their hillsides. Unlike the SET states, the DHT states were observed only at the step bunches parallel to $[ {1\;\overline{ 1}\;1} ]$[11¯1] [equivalent to the step bunches formed on the (17 18 1) surface]. Photocatalytic activity for each TiO2 sample was also measured through methylene blue photodegradation reactions and was found to follow the sequence: (110) < (17 18 1) < (15 13 0) < (011), indicating that steps along [0 0 1] are more reactive than steps along $[ {1\;\bar 1\;1} ]$[11¯1]. This result implies that the presence of the DHT states observed from the step bunches parallel to $[ {1\;\bar 1\;1} ]$[11¯1] did not effectively contribute to the methylene blue photodegradation reactions.
Vapor–liquid surface tension of strong short-range Yukawa fluid
Authors: Odriozola G. , Bárcenas M. , Orea P.
Published: April 2011

The thermodynamic properties of strong short-range attractive Yukawa fluids, κ = 10, 9, 8, and 7, are determined by combining the slab technique with the standard and the replica exchange Monte Carlo (REMC) methods. A good agreement was found among the coexistence curves of these systems calculated by REMC and those previously reported in the literature. However, REMC allows exploring the coexistence at lower temperatures, where dynamics turns glassy. To obtain the surface tension we employed, for both methods, a procedure that yields the pressure tensor components for discontinuous potentials. The surface tension results obtained by the standard MC and REMC techniques are in good agreement.
Self-assembly of manganese phthalocyanine on Pb(111) surface: A scanning tunneling microscopy study
Authors: Hao Dan , Song Canli , Ning Yanxiao , Wang Yilin , Wang Lili , Ma Xu-Cun , Chen Xi , Xue Qi-Kun
Published: April 2011

The self-assembled structure of submonolayer manganese phthalocyanine (MnPc) on Pb(111) surface is investigated by using low-temperature scanning tunneling microscopy (STM). A “holelike” superlattice, which is superimposed on the self-assembled nearly quadratic network, is observed. High resolution STM images reveal that there are two distinct azimuthal orientations of MnPc molecules. It is found that by taking the two different orientations the self-assembly can further be optimized energetically by maximizing intermolecular orbital overlapping. It is this intralayer energy minimization process that leads to the characteristic holelike superlattice.
Structural modes of a polymer in the repton model
Authors: Barkema Gerard T. , Panja Debabrata , van Leeuwen J. M. J.
Published: April 2011

Using extensive computer simulations, the behavior of the structural modes—more precisely, the eigenmodes of a phantom Rouse polymer—are characterized for a polymer in the three-dimensional repton model and are used to study the polymer dynamics at time scales well before the tube renewal. Although these modes are not the eigenmodes for a polymer in the repton model, we show that numerically the modes maintain a high degree of statistical independence. The correlations in the mode amplitudes decay exponentially with (p/N)2A(t), in which p is the mode number, N is the polymer length, and A(t) is a single function shared by all modes. In time, the quantity A(t) causes an exponential decay for the mode amplitude correlation functions for times <1; a stretched exponential with an exponent 1/2 between times 1 and τR ∼ N2, the time-scale for diffusion of tagged reptons along the contour of the polymer; and again an exponential decay for times t > τR. Having assumed statistical independence and the validity of a single function A(t) for all modes, we compute the temporal behavior of three structural quantities: the vectorial distance between the positions of the middle monomer and the center-of-mass, the end-to-end vector, and the vector connecting two nearby reptons around the middle of the polymer. Furthermore, we study the mean-squared displacement of the center-of-mass and the middle repton, and their relation with the temporal behavior of the modes.
Analytical solution of the Poisson–Nernst–Planck equations in the linear regime at an applied dc-voltage
Authors: Golovnev Anatoly , Trimper Steffen
Published: April 2011

The analytical solution of the Poisson–Nernst–Planck equations is found in the linear regime as response to a dc-voltage. In deriving the results a new approach is suggested, which allows to fulfill all initial and boundary conditions and guarantees the absence of Faradaic processes explicitly. We obtain the spatiotemporal distribution of the electric field and the concentration of the charge carriers valid in the whole time interval and for an arbitrary initial concentration of ions. A different behavior in the short- and the long-time regime is observed. The crossover between these regimes is estimated.
Change in carbon nanofiber resistance from ambient to vacuum
Authors: Maeda Shusaku , Wilhite Patrick , Kanzaki Nobuhiko , Yamada Toshishige , Yang Cary Y.
Published: April 2011

The electrical properties of carbon nanofibers (CNFs) can be affected by adsorbed gas species. In this study, we compare the resistance values of CNF devices in a horizontal configuration in air and under vacuum. CNFs in air are observed to possess lower current capacities compared to those in vacuum. Further, Joule heating due to current stressing can result in desorption of gas molecules responsible for carrier trapping, leading to lower resistances and higher breakdown currents in vacuum, where most adsorbed gaseous species are evacuated before any significant re-adsorption can occur. A model is proposed to describe these observations, and is used to estimate the number of adsorbed molecules on a CNF device.
Fabrication of Li-intercalated bilayer graphene
Authors: Sugawara K. , Kanetani K. , Sato T. , Takahashi T.
Published: April 2011

We have succeeded in fabricating Li-intercalated bilayer graphene on silicon carbide. The low-energy electron diffraction from Li-deposited bilayer graphene shows a sharp \documentclass[12pt]{minimal}\begin{document}$\sqrt{3}$\end{document}3×\documentclass[12pt]{minimal}\begin{document}$\sqrt{3}$\end{document}3\documentclass[12pt]{minimal}\begin{document}$\it R$\end{document}R30° pattern in contrast to Li-deposited monolayer graphene. This indicates that Li atoms are intercalated between two adjacent graphene layers and take the same well-ordered superstructure as in bulk C6Li. The angle-resolved photoemission spectroscopy has revealed that Li atoms are fully ionized and the π bands of graphene are systematically folded by the superstructure of intercalated Li atoms, producing a snowflake-like Fermi surface centered at the Γ point. The present result suggests a high potential of Li-intercalated bilayer graphene for application to a nano-scale Li-ion battery.
Determination of the decay exponent in mechanically stirred isotropic turbulence
Authors: Perot J. Blair
Published: April 2011

Direct numerical simulation is used to investigate the decay exponent of isotropic homogeneous turbulence over a range of Reynolds numbers sufficient to display both high and low Re number decay behavior. The initial turbulence is generated by the stirring action of the flow past many small randomly placed cubes. Stirring occurs at 1/30th of the simulation domain size so that the low-wavenumber and large scale behavior of the turbulent spectrum is generated by the fluid and is not imposed. It is shown that the decay exponent in the resulting turbulence matches the theoretical predictions for a k2 low-wavenumber spectrum at both high and low Reynolds numbers. The transition from high Reynolds number behavior to low Reynolds number behavior occurs relatively abruptly at a turbulent Reynolds number of around 250 (${\mathop{\rm Re}\nolimits} _\lambda \approx 41$ Re λ≈41).
Nitrogen is a deep acceptor in ZnO
Authors: Tarun M. C. , Iqbal M. Zafar , McCluskey M. D.
Published: April 2011

Zinc oxide is a promising material for blue and UV solid-state lighting devices, among other applications. Nitrogen has been regarded as a potential p-type dopant for ZnO. However, recent calculations [Lyons, Janotti, and Van de Walle, Appl. Phys. Lett. 95, 252105 (2009)] indicate that nitrogen is a deep acceptor. This paper presents experimental evidence that nitrogen is, in fact, a deep acceptor and therefore cannot produce p-type ZnO. A broad photoluminescence (PL) emission band near 1.7 eV, with an excitation onset of ∼2.2 eV, was observed, in agreement with the deep-acceptor model of the nitrogen defect. The deep-acceptor behavior can be explained by the low energy of the ZnO valence band relative to the vacuum level.
Optimized photolithographic fabrication process for carbon nanotube devices
Authors: Khamis S. M. , Jones R. A. , Johnson A. T. Charlie
Published: April 2011

We have developed a photolithographic process for the fabrication of large arrays of single walled carbon nanotube transistors with high quality electronic properties that rival those of transistors fabricated by electron beam lithography. A buffer layer is used to prevent direct contact between the nanotube and the novolac-based photoresist, and a cleaning bake at 300C effectively removes residues that bind to the nanotube sidewall during processing. In situ electrical measurement of a nanotube transistor during a temperature ramp reveals sharp decreases in the ON-state resistance that we associate with the vaporization of components of the photoresist. Data from nearly 2000 measured nanotube transistors show an average ON-state resistance of 250 ± 100 kΩ. This new process represents significant progress towards the goal of high-yield production of large arrays of nanotube transistors for applications including chemical sensors and transducers, as well as integrated circuit components.
Laboratory technology and cosmochemistry
Authors: Zinner Ernst K. , Moynier Frederic , Stroud Rhonda M.
Published: April 2011

Recent developments in analytical instrumentation have led to revolutionary discoveries in cosmochemistry. Instrumental advances have been made along two lines: (i) increase in spatial resolution and sensitivity of detection, allowing for the study of increasingly smaller samples, and (ii) increase in the precision of isotopic analysis that allows more precise dating, the study of isotopic heterogeneity in the Solar System, and other studies. A variety of instrumental techniques are discussed, and important examples of discoveries are listed. Instrumental techniques and instruments include the ion microprobe, laser ablation gas MS, Auger EM, resonance ionization MS, accelerator MS, transmission EM, focused ion-beam microscopy, atom probe tomography, X-ray absorption near-edge structure/electron loss near-edge spectroscopy, Raman microprobe, NMR spectroscopy, and inductively coupled plasma MS.