bluuebunny/crossref_metadata_2025 huggingface dataset:
The Moderating Role of Social Support on the Relationship Between Impulsivity and Suicide Risk
Authors: Kleiman Evan M. , Riskind John H. , Schaefer Karen E. , Weingarden Hilary
Published: May 2012

Background: Suicide is the second leading cause of death among college students. There has been considerable research into risk factors for suicide, such as impulsivity, but considerably less research on protective factors. Aims: The present study examines the role that social support plays in the relationship between impulsivity and suicide risk. Methods: Participants were 169 undergraduates who completed self-report measures of impulsivity and social support. Suicide risk was assessed using an interview measure. Results: Social support moderates the relationship between impulsivity and suicide risk, such that those who are highly impulsive are less likely to be at risk for suicide if they also have high levels of social support. Conclusions: Social support can be a useful buffer to suicide risk for at-risk individuals who are highly impulsive.
An Adolescent Suicide Cluster and the Possible Role of Electronic Communication Technology
Authors: Robertson Lindsay , Skegg Keren , Poore Marion , Williams Sheila , Taylor Barry
Published: May 2012

Background: Since the development of Centers for Disease Control’s (CDC) guidelines for the management of suicide clusters, the use of electronic communication technologies has increased dramatically. Aims: To describe an adolescent suicide cluster that drew our attention to the possible role of online social networking and SMS text messaging as sources of contagion after a suicide and obstacles to recognition of a potential cluster. Methods: A public health approach involving a multidisciplinary community response was used to investigate a group of suicides of New Zealand adolescents thought to be a cluster. Difficulties in identifying and managing contagion posed by use of electronic communications were assessed. Results: The probability of observing a time-space cluster such as this by chance alone was p = .009. The cases did not belong to a single school, rather several were linked by social networking sites, including sites created in memory of earlier suicide cases, as well as mobile telephones. These facilitated the rapid spread of information and rumor about the deaths throughout the community. They made the recognition and management of a possible cluster more difficult. Conclusions: Relevant community agencies should proactively develop a strategy to enable the identification and management of suicide contagion. Guidelines to assist communities in managing clusters should be updated to reflect the widespread use of communication technologies in modern society.
Relationships Between Vocabulary Size, Working Memory, and Phonological Awareness in Spanish-Speaking English Language Learners
Authors: Gorman Brenda K.
Published: May 2012

Purpose

The goals of this study were to evaluate the impact of short-term phonological awareness (PA) instruction presented in children’s first language (L1; Spanish) on gains in their L1 and second language (L2; English) and to determine whether relationships exist between vocabulary size, verbal working memory, and PA in Spanish-speaking English language learners (ELLs).

Method

Participants included 25 kindergartners who received PA instruction and 10 controls. A 2-way within-subjects repeated measures multivariate analysis of variance (MANOVA) was conducted to evaluate gains. Relationships between PA gains, Spanish and English vocabulary, and memory, as measured using nonword repetition and experimental working memory tasks, were analyzed using correlation and regression analyses.

Results

Results indicated significant and equivalent gains in both languages of children in the experimental group and no gains in the control group. Spanish vocabulary size was significantly related to PA gains in both languages and was more strongly related to English gains than was English vocabulary size. The memory tasks predicted gains in each language in distinct ways.

Conclusion

Results support the conclusion that PA instruction and strong vocabulary skills in an individual’s L1 benefit PA development in both the L1 and L2. Results also indicate that dynamic relationships exist between vocabulary size, storage and processing components of working memory, and PA development in both languages of ELLs.

Supplemental Material

https://doi.org/10.23641/asha.6170195
Miranda Rights Comprehension in Young Adults With Specific Language Impairment
Authors: Rost Gwyneth C. , McGregor Karla K.
Published: May 2012

Purpose

The purpose of this study was to determine whether citizens with language impairment understand legal rights as conveyed in Miranda warnings.

Method

Grisso’s Instruments for Assessing Understanding and Appreciation of Miranda Rights (1998) was administered to 34 young adults, half of whom met the diagnostic criteria for specific language impairment (SLI). A correlational analysis of the relationship between language scores and Miranda rights comprehension was conducted, as were tests of differences between individuals with SLI (
n
= 17) and individuals without SLI.

Results

Language ability was positively correlated with overall performance on the Miranda measure. As a group, individuals with SLI were significantly poorer than their peers with normal language at defining Miranda vocabulary and applying Miranda rights in hypothetical situations. The group with SLI was also marginally less able to paraphrase Miranda sentences.

Conclusion

Language impairment limits comprehension of Miranda warnings. As a result, citizens with language impairment are at risk of being denied their constitutional rights.
The Role of Experience in the Perception of Phonetic Detail in Children’s Speech: A Comparison Between Speech-Language Pathologists and Clinically Untrained Listeners
Authors: Munson Benjamin , Johnson Julie M. , Edwards Jan
Published: May 2012

Purpose

This study examined whether experienced speech-language pathologists (SLPs) differ from inexperienced people in their perception of phonetic detail in children’s speech.

Method

Twenty-one experienced SLPs and 21 inexperienced listeners participated in a series of tasks in which they used a visual–analog scale (VAS) to rate children’s natural productions of target /s/–/θ/, /t/–/k/, and /d/–/ɡ/ in word-initial position. Listeners rated the perceived distance between individual productions and ideal productions.

Results

The experienced listeners' ratings differed from the inexperienced listeners' ratings in four ways: They had higher intrarater reliability, showed less bias toward a more frequent sound, and were more closely related to the acoustic characteristics of the children’s speech. In addition, the experienced listeners' responses were related to a different set of predictor variables.

Conclusion

Results suggest that experience working as an SLP leads to better perception of phonetic detail in children’s speech. Limitations and future research are discussed.

Supplemental Material

https://doi.org/10.23641/asha.6170198
Model Choice and Sample Size in Item Response Theory Analysis of Aphasia Tests
Authors: Hula William D. , Fergadiotis Gerasimos , Martin Nadine
Published: May 2012

Purpose

The purpose of this study was to identify the most appropriate item response theory (IRT) measurement model for aphasia tests requiring 2-choice responses and to determine whether small samples are adequate for estimating such models.

Method

Pyramids and Palm Trees (Howard & Patterson, 1992) test data that had been collected from individuals with aphasia were analyzed, and the resulting item and person estimates were used to develop simulated test data for 3 sample size conditions. The simulated data were analyzed using a standard 1-parameter logistic (1-PL) model and 3 models that accounted for the influence of guessing: augmented 1-PL and 2-PL models and a 3-PL model. The model estimates obtained from the simulated data were compared to their known true values.

Results

With small and medium sample sizes, an augmented 1-PL model was the most accurate at recovering the known item and person parameters; however, no model performed well at any sample size. Follow-up simulations confirmed that the large influence of guessing and the extreme easiness of the items contributed substantially to the poor estimation of item difficulty and person ability.

Conclusion

Incorporating the assumption of guessing into IRT models improves parameter estimation accuracy, even for small samples. However, caution should be exercised in interpreting scores obtained from easy 2-choice tests, regardless of whether IRT modeling or percentage correct scoring is used.
Apraxia of Speech: Perceptual Analysis of Trisyllabic Word Productions Across Repeated Sampling Occasions
Authors: Mauszycki Shannon C. , Wambaugh Julie L. , Cameron Rosalea M.
Published: May 2012

Purpose

Early apraxia of speech (AOS) research has characterized errors as being variable, resulting in a number of different error types being produced on repeated productions of the same stimuli. Conversely, recent research has uncovered greater consistency in errors, but there are limited data examining sound errors over time (more than one occasion). Furthermore, the influence of conditions of stimulus presentation (blocked vs. random) on sound errors remains uncertain. The purpose of this investigation was to examine the effects of repeated sampling and conditions of stimulus presentation on speech sound errors for 11 speakers with AOS/aphasia.

Method

Trisyllabic words consisting of 7 target phonemes in the initial position served as stimuli. On 3 occasions, stimuli were elicited under 2 conditions: blocked (by phoneme) and randomized presentation. Speech productions were analyzed via narrow phonetic transcription.

Results

Findings revealed a similar overall mean percentage of errors in both conditions and across sampling occasions. Distortions were the dominant error type.

Conclusion

There was no obvious pattern of responding across sampling occasions or conditions of stimulus presentation. The dominant error type differed among target phonemes, but there appeared to be some degree of consistency in the error types produced for the majority of target phonemes.
Orthographic Word Knowledge Growth in School-Age Children
Authors: Wagovich Stacy A. , Pak Youngju , Miller Margaret D.
Published: May 2012

Purpose

Natural reading experiences provide an opportunity for the development of orthographic word knowledge as well as other forms of partial word knowledge. The purpose of this study was to compare the orthographic word knowledge growth of school-age children with relatively low language skills (LL group) to that of age- and gender-matched peers with high language skills (HL group).

Method

Thirty-two children, 16 per group, read stories containing rare words 3 times, 2–3 days apart. Posttesting, completed at the end of each session, required participants to indicate recognition of the rare words encountered in the stories while not indicating recognition of orthographically similar nonwords.

Results

Over time, both groups showed significant growth in recognition of the orthographic forms of the rare words. However, the groups differed in the extent to which they indicated that the orthographically similar nonwords were words, with the LL group indicating that significantly more of the nonwords were words.

Conclusion

Results provide some preliminary evidence that children with relatively weaker language skills are able to develop orthographic knowledge of unfamiliar words through reading experiences, but their orthographic representations may not be as well defined as those of children with stronger language skills.
Effect of Fundamental Frequency on Judgments of Electrolaryngeal Speech
Authors: Nagle Kathy F. , Eadie Tanya L. , Wright Derek R. , Sumida Yumi A.
Published: May 2012

Purpose

To determine (a) the effect of fundamental frequency (f
0
) on speech intelligibility, acceptability, and perceived gender in electrolaryngeal (EL) speakers, and (b) the effect of known gender on speech acceptability in EL speakers.

Method

A 2-part study was conducted. In Part 1, 34 healthy adults provided speech recordings using electrolarynges set at 75 Hz, 130 Hz, and 175 Hz, and 36 listeners transcribed the recordings. In Part 2, 22 speech samples were presented to 16 listeners. First, listeners identified the gender of each speaker and judged his or her speech acceptability using rating scales. Second, listeners judged the same samples for speech acceptability when gender information was provided.

Results

In Part 1, speakers were significantly more intelligible when using 75-Hz devices. In Part 2, the f
0
of the speech signal significantly impacted listeners' accuracy in perceiving the speaker’s gender: In gender-incongruent conditions (males using 175-Hz devices, females using 75-Hz devices), listeners were unable to identify female speakers. Speech acceptability judgments were directly related to intelligibility. Finally, listeners differentially penalized female speakers who used 75-Hz devices when gender information was known.

Conclusion

Low f
0
facilitated speech intelligibility. However, at low f
0
, listeners were unable to identify females as female, and females were differentially penalized for speech acceptability. Results may have implications for rehabilitation.
A Comparison of Intention and Pantomime Gesture Treatment for Noun Retrieval in People With Aphasia
Authors: Ferguson Neina F. , Evans Kelli , Raymer Anastasia M.
Published: May 2012

Purpose

The effects of intention gesture treatment (IGT) and pantomime gesture treatment (PGT) on word retrieval were compared in people with aphasia.

Method

Four individuals with aphasia and word retrieval impairments subsequent to left-hemisphere stroke participated in a single-participant crossover treatment design. Each participant viewed target nouns on a computer screen in 2 counterbalanced training phases. Training included paired verbal + gesture treatment strategies to elicit verbal and/or gestural productions of target nouns. Treatment effects were measured using daily picture-naming probes for verbal naming and gesture productions for trained and untrained words as well as pre-/posttreatment standardized aphasia tests.

Outcomes and Results

IGT resulted in immediate effects on the verbal productions of 2 participants but lacked carryover to untrained words. PGT resulted in improved verbal production for 2 participants and immediate effects on the gesture productions of 3 participants, with carryover of gesture production to untrained words in 1 participant. Improvements on standardized aphasia tests were evident in 2 participants.

Conclusion

IGT and PGT had positive treatment effects, but for contrasting communication modalities. Two individuals with mild–moderate aphasia improved verbal production with both IGT and PGT, and 2 individuals with severe aphasia improved gesture use with PGT.
Effects of Syntactic Complexity, Semantic Reversibility, and Explicitness on Discourse Comprehension in Persons With Aphasia and in Healthy Controls
Authors: Levy Joshua , Hoover Elizabeth , Waters Gloria , Kiran Swathi , Caplan David , Berardino Alex , Sandberg Chaleece
Published: May 2012

Purpose

Prior studies of discourse comprehension have concluded that the deficits of persons with aphasia (PWA) in syntactically based comprehension of sentences in isolation are not predictive of deficits in comprehension of sentences in discourse (Brookshire & Nicholas, 1984; Caplan & Evans, 1990). However, these studies used semantically constrained sentences in discourse, which do not require syntactic analysis to be understood. A discourse task was developed to assess the effect of syntactic complexity, among other factors, on discourse comprehension in PWA.

Method

Thirty-eight PWA and 30 neurologically healthy control participants were presented with passages that contained 2–3 semantically reversible sentences that were either syntactically simple or syntactically complex. The passages were presented auditorily, and comprehension was assessed with the auditory and written presentation of 4 multiple-choice questions immediately following each passage.

Results

Passages with syntactically simple sentences were better understood than passages with syntactically complex sentences. Moreover, semantically constrained sentences were more likely to be accurately interpreted than semantically reversible sentences. Comprehension accuracy on our test correlated positively with comprehension accuracy on an existing test.

Conclusion

The presence of semantically reversible, syntactically complex sentences in a passage affects comprehension of the passage in both PWA and neurologically healthy individuals.
Constrained Versus Unconstrained Intensive Language Therapy in Two Individuals With Chronic, Moderate-to-Severe Aphasia and Apraxia of Speech: Behavioral and fMRI Outcomes
Authors: Kurland Jacquie , Pulvermüller Friedemann , Silva Nicole , Burke Katherine , Andrianopoulos Mary
Published: May 2012

Purpose

This Phase I study investigated behavioral and functional MRI (fMRI) outcomes of 2 intensive treatment programs to improve naming in 2 participants with chronic moderate-to-severe aphasia with comorbid apraxia of speech (AOS). Constraint-induced aphasia therapy (CIAT; Pulvermüller et al., 2001) has demonstrated positive outcomes in some individuals with chronic aphasia. Whether constraint to the speech modality or treatment intensity is responsible for such gains is still under investigation. Moreover, it remains to be seen whether CIAT is effective in individuals with persistent severe nonfluent speech and/or AOS.

Method

A single-subject multiple-baseline approach was used. Both participants were treated simultaneously, first with Promoting Aphasics' Communicative Effectiveness (PACE; Davis & Wilcox, 1985) and then with CIAT. Pre-/posttreatment testing included an overt naming fMRI protocol. Treatment effect sizes were calculated for changes in probe accuracy from baseline to posttreatment phases and maintenance where available.

Results

Both participants made more and faster gains in naming following CIAT. Treatment-induced changes in BOLD activation suggested that better naming was correlated with the recruitment of perilesional tissue.

Conclusion

Participants produced more target words accurately following CIAT than following PACE. Behavioral and fMRI results support the notion that the intense and repetitive nature of obligatory speech production in CIAT has a positive effect on word retrieval, even in participants with chronic moderate-to-severe aphasia with comorbid AOS.
Predicting Story Goodness Performance From Cognitive Measures Following Traumatic Brain Injury
Authors: Lê Karen , Coelho Carl , Mozeiko Jennifer , Krueger Frank , Grafman Jordan
Published: May 2012

Purpose

This study examined the prediction of performance on measures of the Story Goodness Index (SGI; Lê, Coelho, Mozeiko, & Grafman, 2011) from executive function (EF) and memory measures following traumatic brain injury (TBI). It was hypothesized that EF and memory measures would significantly predict SGI outcomes.

Method

One hundred sixty-seven individuals with TBI participated in the study. Story retellings were analyzed using the SGI protocol. Three cognitive measures—Delis-Kaplan Executive Function System (D-KEFS; Delis, Kaplan, & Kramer, 2001) Sorting Test, Wechsler Memory Scale—Third Edition (WMS–III; Wechsler, 1997) Working Memory Primary Index (WMI), and WMS–III Immediate Memory Primary Index (IMI)—were entered into a multiple linear regression model for each discourse measure. Two sets of regression analyses were performed, the first with the Sorting Test as the first predictor and the second with it as the last.

Results

The first set of regression analyses identified the Sorting Test and IMI as the only significant predictors of performance on measures of the SGI. The second set identified all measures as significant predictors when evaluating each step of the regression function.

Conclusion

The cognitive variables predicted performance on the SGI measures, although there were differences in the amount of explained variance. The results (a) suggest that storytelling ability draws on a number of underlying skills and (b) underscore the importance of using discrete cognitive tasks rather than broad cognitive indices to investigate the cognitive substrates of discourse.
Finiteness Marking in Boys With Fragile X Syndrome
Authors: Sterling Audra M. , Rice Mabel L. , Warren Steven F.
Published: May 2012

Purpose

The current study investigated finiteness marking (e.g., he walks, he walked) in boys with fragile X syndrome (FXS); the boys were grouped based on receptive vocabulary (i.e., borderline, impaired).

Method

Twenty-one boys with the full mutation of fragile X, between the ages of 8 and 16 years participated. The boys completed probes from the Test of Early Grammatical Impairment (TEGI; Rice & Wexler, 2001), a language sample, a nonverbal IQ test (Leiter–R; Roid & Miller, 1997), a receptive vocabulary test (the Pearson Picture Vocabulary Test—Fourth Edition [PPVT–IV]; Dunn & Dunn, 2007), and a measure of autistic symptoms (the Childhood Autism Rating Scale [CARS]; Schopler, Reichler, & Renner, 2002).

Results

There were group differences for finiteness responses on the 3rd person singular probe; the group with impaired vocabulary omitted markers with greater frequency compared to the borderline vocabulary group. There were not significant differences on the past tense probe, with both groups performing lower than expectations based on receptive vocabulary ability. Nonverbal IQ was not correlated with the measures of finiteness marking.

Conclusion

Boys with FXS demonstrate delays in finiteness marking, in particular, on past tense verbs. Boys with FXS show a unique profile, unlike children with SLI, in which their use of tense markers may exceed expectations benchmarked to clause length.
Aerodynamic and Nonlinear Dynamic Acoustic Analysis of Tension Asymmetry in Excised Canine Larynges
Authors: Devine Erin E. , Bulleit Erin E. , Hoffman Matthew R. , McCulloch Timothy M. , Jiang Jack J.
Published: May 2012

Purpose

To model tension asymmetry caused by superior laryngeal nerve paralysis (SLNP) in excised larynges and apply perturbation, nonlinear dynamic, and aerodynamic analyses.

Method

SLNP was modeled in 8 excised larynges using sutures and weights to mimic cricothyroid (CT) muscle function. Weights were removed from one side to create tension asymmetry, mimicking unilateral SLNP. Two sets of weights were used, 1 light and 1 heavy. Five conditions were evaluated: (a) no tension, (b) symmetrical light tension, (c) asymmetrical light tension, (d) symmetrical heavy tension, and (e) asymmetrical heavy tension.

Results

Perturbation parameters were not significantly different across conditions: percent jitter, χ
2
(4) = 3.70,
p
= .451; percent shimmer,
F
(4) = 0.95,
p
= .321. In addition, many measurements were invalid (error values >10). Second-order entropy was significantly different across conditions,
F
(4) = 5.432,
p
= .002, whereas correlation dimension was not,
F
(4) = 0.99,
p
= .428. Validity of these nonlinear dynamic parameters was demonstrated by low standard deviations. Phonation threshold pressure, χ
2
(4) = 22.50,
p
< .001, and power, χ
2
(4) = 9.50,
p
= .05, differed significantly across conditions, whereas phonation threshold flow did not, χ
2
(4) = 4.08,
p
= .396.

Conclusions

Nonlinear dynamic analysis differentiated between symmetrical and asymmetrical tension conditions, whereas traditional perturbation analysis was less useful in characterizing type 2 or 3 vocal signals. Supplementing acoustic with aerodynamic parameters may help distinguish among laryngeal disorders of neuromuscular origin.
Children With Specific Language Impairment and Resolved Late Talkers: Working Memory Profiles at 5 Years
Authors: Petruccelli Nadia , Bavin Edith L. , Bretherton Lesley
Published: May 2012

Purpose

The evidence of a deficit in working memory in specific language impairment (SLI) is of sufficient magnitude to suggest a primary role in developmental language disorder. However, little research has investigated memory in late talkers who recover from their early delay. Drawing on a longitudinal, community sample, this study compared the memory profiles of 3 groups of 5-year-olds: children with SLI who had been identified as late talkers, resolved late talkers (RLTs), and children with typical language development (TLD).

Method

Participants were 25 children with SLI, 45 RLTs, and 32 children with TLD. Subtests from the Working Memory Test Battery for Children and the Children’s Memory Scale plus recalling sentences and nonword repetition tasks were administered to test the components of Baddeley’s working memory model.

Results

The SLI group showed significantly poorer performance than the RLT and TLD groups on measures of the phonological loop and episodic buffer. The RLT and TLD groups scored similarly on all memory measures.

Conclusions

The results support previous findings that sentence recall and nonword repetition are markers of SLI. Although residual effects of late-talking status may emerge over time, RLTs do not necessarily show memory deficits at 5 years of age despite delayed early vocabulary development.
Large bubble entrapment during drop impacts on a restricted liquid surface
Authors: Zou Jun , Ji Chen , Yuan BaoGang , Ren YuLiang , Ruan XiaoDong , Fu Xin
Published: May 2012

The behavior of millimetric drops impacting on a gas-liquid interface restricted by surrounding walls is studied using a high-speed video camera. A novel phenomenon of large bubble entrapment is observed in experiments. It is found that the large bubble formation is not only dependent on the impact velocity of the drop, but also the shape of drop at the moment of contact with the liquid surface and the distance from the impact point to surrounding walls.
Landau-Levich flow visualization: Revealing the flow topology responsible for the film thickening phenomena
Authors: Mayer H. C. , Krechetnikov R.
Published: May 2012

An extensive body of experimental work has proven the validity of the analysis of Landau and Levich, who were the first to determine theoretically the thickness of the film deposited by the withdrawal of a flat substrate from a bath of liquid with a clean interface. However, there are a number of experimental investigations that have shown that surfactants in the liquid may result in a thickening of the deposited film. Marangoni phenomena have usually been considered responsible for this effect. However, some careful experiments and numerical simulations reported in the literature seemed to rule out this view as the cause of the observed behavior. Despite all these studies and the number of reports of film thickening, an experimental study of the flow field close to the coated substrate in the presence of surfactants has never been undertaken. In this paper we will present a set of flow visualization experiments on coating of a planar substrate in the range of capillary numbers 10−4 ≲ Ca ≲ 10−3 for sodium dodecyl sulfate solutions with bulk concentrations of 0.25 CMC ⩽ C ⩽ 5.0 CMC (critical micelle concentration). It was evident during experiments that the flow field near the meniscus region exhibits patterns that can only be explained with a stagnation point residing in the bulk and not at the interface. As opposed to patterns with an interfacial stagnation point, the observed flow fields allow for the increase in film thickness due to the presence of surfactants compared to the clean interface case.
On the representation of coupled adiabatic potential energy surfaces using quasi-diabatic Hamiltonians: A distributed origins expansion approach
Authors: Zhu Xiaolei , Yarkony David R.
Published: May 2012

In two previous papers we have introduced a method to generate coupled quasi-diabatic Hamiltonians (Hd) that are capable of representing adiabatic energies, energy gradients, and derivative couplings over a wide range of geometries including seams of conical intersection. In this work, two new synergistic features are introduced. Firstly, the functional form of Hd is generalized. Rather than requiring there to be a low energy point of high symmetry to serve as the unique origin, functions centered on points distributed in nuclear coordinate space are used in the polynomials that comprise the matrix elements in Hd. The use of functions with distributed origins, allows reproduction of the ab initio data with lower order expansions, and offers the possibility of describing multichannel dissociation. The fitting algorithm is combined with a three-step procedure in which the domain of Hd is extended from a core set of nuclear configurations to a region of nuclear coordinate space appropriate for nuclear dynamics, with a prescribed accuracy. This significant extension of the domain of definition compared to our original work, which is facilitated by the distributed origin approach, is achieved largely through the use of surface hopping trajectories. The 1,21A states of NH3, which provide an archetypical example of nonadiabatic dynamics, are used to demonstrate the utility of this approach. The representation describes 21 points on the 11A–21A seam of conical intersection and their local topography flawlessly and on the entire domain, the electronic structure data is represented to an accuracy of 77.00 (46.90) cm−1, as measured by the root mean square (mean unsigned) error for energies lower than 50 000 cm−1. This error is a factor of 10 lower than that of the most accurate representation of high quality ab initio data, on a comparable domain, previously reported for this system.
Vibrational quenching of excitonic splittings in H-bonded molecular dimers: The electronic Davydov splittings cannot match experiment
Authors: Ottiger Philipp , Leutwyler Samuel , Köppel Horst
Published: May 2012

The S1/S2 state exciton splittings of symmetric doubly hydrogen-bonded gas-phase dimers provide spectroscopic benchmarks for the excited-state electronic couplings between UV chromophores. These have important implications for electronic energy transfer in multichromophoric systems ranging from photosynthetic light-harvesting antennae to photosynthetic reaction centers, conjugated polymers, molecular crystals, and nucleic acids. We provide laser spectroscopic data on the S1/S2 excitonic splitting Δexp of the doubly H-bonded o-cyanophenol (oCP) dimer and compare to the splittings of the dimers of (2-aminopyridine)2, [(2AP)2], (2-pyridone)2, [(2PY)2], (benzoic acid)2, [(BZA)2], and (benzonitrile)2, [(BN)2]. The experimental S1/S2 excitonic splittings are Δexp = 16.4 cm−1 for (oCP)2, 11.5 cm−1 for (2AP)2, 43.5 cm−1 for (2PY)2, and <1 cm−1 for (BZA)2. In contrast, the vertical S1/S2 energy gaps Δcalc calculated by the approximate second-order coupled cluster (CC2) method for the same dimers are 10–40 times larger than the Δexp values. The qualitative failure of this and other ab initio methods to reproduce the exciton splitting Δexp arises from the Born-Oppenheimer (BO) approximation, which implicitly assumes the strong-coupling case and cannot be employed to evaluate excitonic splittings of systems that are in the weak-coupling limit. Given typical H-bond distances and oscillator strengths, the majority of H-bonded dimers lie in the weak-coupling limit. In this case, the monomer electronic-vibrational coupling upon electronic excitation must be accounted for; the excitonic splittings arise between the vibronic (and not the electronic) transitions. The discrepancy between the BO-based splittings Δcalc and the much smaller experimental Δexp values is resolved by taking into account the quenching of the BO splitting by the intramolecular vibronic coupling in the monomer S1 ← S0 excitation. The vibrational quenching factors Γ for the five dimers (oCP)2, (2AP)2, (2AP)2, (BN)2, and (BZA)2 lie in the range Γ = 0.03−0.2. The quenched excitonic splittings Γ·Δcalc are found to be in very good agreement with the observed splittings Δexp. The vibrational quenching approach predicts reliable Δexp values for the investigated dimers, confirms the importance of vibrational quenching of the electronic Davydov splittings, and provides a sound basis for predicting realistic exciton splittings in multichromophoric systems.
Ab initio calculation of the rotational spectrum of methane vibrational ground state
Authors: Cassam-Chenaï P. , Liévin J.
Published: May 2012

In a previous article we have introduced an alternative perturbation scheme to the traditional one starting from the harmonic oscillator, rigid rotator Hamiltonian, to find approximate solutions of the spectral problem for rotation-vibration molecular Hamiltonians. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the ab initio calculation of effective dipole moments for methane within the same theoretical frame. The first order of perturbation when applied to the electric dipole moment operator of a spherical top gives the expression used in previous spectroscopic studies. Higher orders of perturbation give corrections corresponding to higher centrifugal distortion contributions and are calculated accurately for the first time. Two potential energy surfaces of the literature have been used for solving the anharmonic vibrational problem by means of the vibrational mean field configuration interaction approach. Two corresponding dipole moment surfaces were calculated in this work at a high level of theory. The predicted intensities agree better with recent experimental values than their empirical fit. This suggests that our ab initio dipole moment surface and effective dipole moment operator are both highly accurate.
Multipartite entanglement in the Fenna-Matthews-Olson (FMO) pigment-protein complex
Authors: Thilagam A.
Published: May 2012

We investigate multipartite states in the Fenna-Matthews-Olson (FMO) pigment-protein complex of the green sulfur bacteria using a Lorentzian spectral density of the phonon reservoir fitted with typical parameter estimates of the species, Prosthecochloris aestuarii. The evolution of the entanglement measure of the excitonic W qubit states is evaluated in the picosecond time range, showing increased revivals in the non-Markovian regime. Similar trends are observed in the evolution dynamics of the Meyer-Wallach measure of the N-exciton multipartite state, with results showing that multipartite entanglement can last from 0.5 to 1 ps, between the bacteriochlorophylls of the FMO complex. The teleportation and quantum information splitting fidelities associated with the Greenberger-Horne-Zeilinger and W-like resource states formed by the excitonic qubit channels of the FMO complex show that revivals in fidelities increase with the degree of non-Markovian strength of the decoherent environment. Quantum information processing tasks involving teleportation followed by the decodification process involving W-like states of the FMO complex may play a critical role during coherent oscillations at physiological temperatures.
Transport in nanoporous zeolites: Relationships between sorbate size, entropy, and diffusivity
Authors: Borah Bhaskar J. , Maiti Prabal K , Chakravarty Charusita , Yashonath S.
Published: May 2012

Molecular dynamics simulations have been performed on monatomic sorbates confined within zeolite NaY to obtain the dependence of entropy and self-diffusivity on the sorbate diameter. Previously, molecular dynamics simulations by Santikary and Yashonath [J. Phys. Chem. 98, 6368 (1994)], theoretical analysis by Derouane et al. [J. Catal. 110, 58 (1988)] as well as experiments by Kemball [Adv. Catal. 2, 233 (1950)] found that certain sorbates in certain adsorbents exhibit unusually high self-diffusivity. Experiments showed that the loss of entropy for certain sorbates in specific adsorbents was minimum. Kemball suggested that such sorbates will have high self-diffusivity in these adsorbents. Entropy of the adsorbed phase has been evaluated from the trajectory information by two alternative methods: two-phase and multiparticle expansion. The results show that anomalous maximum in entropy is also seen as a function of the sorbate diameter. Further, the experimental observation of Kemball that minimum loss of entropy is associated with maximum in self-diffusivity is found to be true for the system studied here. A suitably scaled dimensionless self-diffusivity shows an exponential dependence on the excess entropy of the adsorbed phase, analogous to excess entropy scaling rules seen in many bulk and confined fluids. The two trajectory-based estimators for the entropy show good semiquantitative agreement and provide some interesting microscopic insights into entropy changes associated with confinement.
The role of axis embedding on rigid rotor decomposition analysis of variational rovibrational wave functions
Authors: Szidarovszky Tamás , Fábri Csaba , Császár Attila G.
Published: May 2012

Approximate rotational characterization of variational rovibrational wave functions via the rigid rotor decomposition (RRD) protocol is developed for Hamiltonians based on arbitrary sets of internal coordinates and axis embeddings. An efficient and general procedure is given that allows employing the Eckart embedding with arbitrary polyatomic Hamiltonians through a fully numerical approach. RRD tables formed by projecting rotational-vibrational wave functions into products of rigid-rotor basis functions and previously determined vibrational eigenstates yield rigid-rotor labels for rovibrational eigenstates by selecting the largest overlap. Embedding-dependent RRD analyses are performed, up to high energies and rotational excitations, for the H216O isotopologue of the water molecule. Irrespective of the embedding chosen, the RRD procedure proves effective in providing unambiguous rotational assignments at low energies and J values. Rotational labeling of rovibrational states of H216O proves to be increasingly difficult beyond about 10 000 cm−1, close to the barrier to linearity of the water molecule. For medium energies and excitations the Eckart embedding yields the largest RRD coefficients, thus providing the largest number of unambiguous rotational labels.
Controllable transport of water through nanochannel by rachet-like mechanism
Authors: Lu Hangjun , Nie Xuechuan , Wu Fengmin , Zhou Xiaoyan , Kou Jianlong , Xu Yousheng , Liu Yang
Published: May 2012

By using molecular dynamics simulation, we have investigated systematically the feasibility of continuous unidirectional water flux across a deformed single-walled carbon nanotube (SWNT) driven by an oscillating charge outside without osmotic pressure or hydrostatic drop. Simulation results indicate that the flux is dependent sensitively on the oscillating frequency of the charge, the distance of the charge from the SWNT, and the asymmetry of the water-SWNT system. A resonance-like phenomenon is found that the water flux is enhanced significantly when the period of the oscillation is close to twice the average hopping time of water molecules inside the SWNT. These findings are helpful in developing a novel design of efficient functional nanofluidic devices.
Exact expressions for ensemble functionals from particle number dependence
Authors: Joubert Daniel P.
Published: May 2012

Some properties of exact ensemble density functionals can be determined by examining the particle number dependence of ground state ensemble density matrices for systems where the integer ground state energies satisfy a convexity condition. The results include the observation that the integral of the product of the functional derivative and Fukui function of functionals that can be expressed as the trace of an operator is particle number independent for particle numbers between successive integers and the integral itself is equal to the difference between functionals evaluated at successive integer particle numbers. Expressions that must be satisfied by 2nd and higher order functional derivatives are formulated and equations that must be satisfied point by point in space are derived. Using the analytic Hooke's atom model, it is shown that commonly used correlation functional approximations do not bear any resemblance to a spatially dependent expression derived from the exact second order functional derivative of the correlation functional. It is also shown that two expressions for the mutual Coulomb energy are not equal when approximate exchange and correlation functionals are used.
Adsorption, mobility, and dimerization of benzaldehyde on Pt(111)
Authors: Rasmussen Anton M. H. , Hammer Bjørk
Published: May 2012

Building on results for the adsorption of benzene on Pt(111), the adsorption of benzaldehyde is investigated using density functional theory. Benzaldehyde is found to chemisorb preferentially with its aromatic ring in the flat-lying bridge geometry that is also preferred for benzene. Across the investigated geometries, adsorption is homogeneously weakened compared to corresponding benzene geometries. This is found to be true for very different adsorption modes, namely, η6 and η8 modes, the latter having metal atoms inserted in the carbonyl bond. Reorientation and diffusion of benzaldehyde is found to have low energy barriers. Aggregation of molecules in dimers bound by aryl C–H⋯O hydrogen bonds is investigated, and specific configurations are found to be up to 0.15 eV more favorable than optimally configured, separated adsorbates. The binding is significantly stronger than what is found for gas phase dimers, suggesting an enhancing effect of the metal interaction.
Self-assembly of model amphiphilic Janus particles
Authors: Rosenthal Gerald , Gubbins Keith E. , Klapp Sabine H. L.
Published: May 2012

We apply molecular dynamics simulations to investigate the structure formation of amphiphilic Janus particles in the bulk phase. The Janus particles are modeled as (soft) spheres composed of a hydrophilic and hydrophobic part. Their orientation is described by a vector representing an internal degree of freedom. Investigating energy fluctuations and cluster size distributions, we determine the aggregation line in a temperature-density-diagram, where the reduced temperature is an inverse measure for the anisotropic coupling. Below this aggregation line clusters of various sizes depending on density and reduced temperature are found. For low densities in the range ρ* ⩽ 0.3, the cluster size distribution has a broad maximum, indicating simultaneous existence of various cluster sizes between 5 and 10. We find no hint of a condensation transition of these clustered systems. In the case of higher densities (ρ* = 0.5 and 0.6), the cluster size distribution shows an extremely narrow peak at clusters of size 13. In these icosahedrons, the particles are arranged in a closed-packed manner, thereby maximizing the number of bonds. Analyzing the translational mean-square displacement we also observe indications of hindered diffusion due to aggregation.
In-situ oxygen x-ray absorption spectroscopy investigation of the resistance modulation mechanism in LiNbO2 memristors
Authors: Greenlee Jordan D. , Petersburg Cole F. , Laws Calley W. , Jaye Cherno , Fischer Daniel A. , Alamgir Faisal M. , Alan Doolittle W.
Published: May 2012

In situ near edge x-ray absorption fine structure spectroscopy (NEXAFS) is performed on LiNbO2 analog memristors to identify the underlying analog resistance modulation mechanism. Empty electronic state gradients in the NEXAFS difference spectra are observed in biased devices indicating a gradual movement of lithium. This movement of lithium supports the assertion that simple ion dopant drift and diffusion dominate the analog memristor’s resistance response. By identifying the physical memristance mechanism in analog LiNbO2 memristors, suggestions are made for additions to the memristor to modify device performance for both neuromorphic computing and memory applications.
Microwave spectroscopy of platinum monofluoride and platinum monochloride in the X 2Π3/2 states
Authors: Okabayashi Toshiaki , Kurahara Taku , Okabayashi Emi Y. , Tanimoto Mitsutoshi
Published: May 2012

Platinum monofluoride (PtF) and platinum monochloride (PtCl) were detected in the gas phase using a source-modulated microwave spectrometer. The PtF and PtCl radicals were generated in a free space cell using the sputtering reaction from a platinum sheet placed on the inner surface of a stainless steel cathode through a dc glow discharge plasma of CF4 and Cl2, respectively, diluted with Ar. Rotational transitions were measured in the region between 150 and 313 GHz. Rotational, centrifugal distortion, and several fine- and hyperfine-structure constants were determined by a least-squares analysis. The observed fine-structure spectral patterns indicate that both PtF and PtCl radicals have the 2Π3/2 electronic ground states, while the related cyanide PtCN and hydride PtH radicals have the 2Δ5/2 electronic ground states.
Flow properties of particles in a model annular shear cell
Authors: Wang X. , Zhu H. P. , Yu A. B.
Published: May 2012

In order to quantitatively investigate the mechanical and rheological properties of solid flow in a shear cell under conditions relevant to those in an annular cell, we performed a series of discrete particle simulations of slightly polydispersed spheres from quasi-static to intermediate flow regimes. It is shown that the average values of stress tensor components are uniformly distributed in the cell space away from the stationary walls; however, some degree of inhomogeneity in their spatial distributions does exist. A linear relationship between the (internal/external) shear and normal stresses prevails in the shear cell and the internal and external friction coefficients can compare well with each other. It is confirmed that annular shear cells are reasonably effective as a method of measuring particle flow properties. The so-called I-rheology proposed by Jop et al. [Nature (London) 441, 727 (2006)] is rigorously tested in this cell system. The results unambiguously display that the I-rheology can effectively describe the intermediate flow regime with a high correlation coefficient. However, significant deviations take place when it is applied to the quasi-static regime, which corresponds to very small values of inertial number.
Interaction of laser generated ultrasonic waves with wedge-shaped samples
Authors: Edwards R. S. , Dutton B. , Clough A. R.
Published: May 2012

Wedge-shaped samples can be used as a model of acoustic interactions with samples ranging from ocean wedges, to angled defects such as rolling contact fatigue, to thickness measurements of samples with non-parallel faces. We present work on laser generated ultrasonic waves on metal samples; one can measure the dominant Rayleigh-wave mode, but longitudinal and shear waves are also generated. We present calculations, models, and measurements giving the dependence of the arrival times and amplitudes of these modes on the wedge apex angle and the separation of generation and detection points, and hence give a measure of the wedge characteristics.
Li-doped BC3 sheet for high-capacity hydrogen storage
Authors: Yang Zailin , Ni Jun
Published: May 2012

Hydrogen storage on Li-doped BC3 sheet is studied by the first principles calculations. The Li atoms can be strongly adsorbed on the BC3 sheet without clustering. For one Li atom adsorbed on the (2 × 2) BC3 supercell, each Li atom could adsorb four hydrogen molecules. By adsorbing Li atoms on both sides of BC3 sheet to form the (1 × 1) pattern, the hydrogen capacity of 10.11 wt. % can be achieved and adsorption energy of each hydrogen molecule is in the range of 0.22–0.34 eV. The Li-doped BC3 sheet is the favorable candidate material for the reversible hydrogen adsorption and desorption at near ambient conditions.