bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of a Flattened Fundamental Frequency on Intelligibility at the Sentence Level
Authors: Laures Jacqueline S. , Weismer Gary
Published: July 2014

The purpose of this preliminary experiment was to evaluate the effect of a flattened fundamental frequency (F
0
) contour on sentence intelligibility. The perceptual dimension
monotone pitch
is frequently used to describe the speech of persons with dysarthria, and relatively flat F
0
contours have been noted in several acoustic studies of dysarthria. To determine the independent effect of a flattened F
0
contour on sentence intelligibility a resynthesis technique was used that held timing and spectral characteristics of utterances constant while allowing parametric control over successive pitch periods. Two male speakers produced low-probability utterances selected from the SPIN test, which were then resynthesized with a flattened F
0
contour. Speech intelligibility was assessed using two measures: one involving word transcription and the other interval scaling. These measures were collected from 10 listeners. The results showed that both measures were significantly lower when the F
0
contour was flattened, as compared with naturally varying contours. Several different explanations are proposed for this effect, which can and should be explored in greater detail using the resynthesis technique given the prominence of this characteristic in dysarthria.
Present and Future Possibilities for Defining a Phenotype for Specific Language Impairment
Authors: Tager-Flusberg Helen , Cooper Judith
Published: July 2014

This brief report summarizes a workshop that was held at the National Institutes of Health in April 1998. The goal of the workshop was to further the development of a definition for the phenotype of specific language impairment (SLI). The report includes a discussion of research recommendations that will refine our current views of the definition of the SLI phenotype and sets out priority areas that are in need of further study to help advance understanding of this complex languagebased disorder.
Optimality Theory in Phonological Acquisition
Authors: Barlow Jessica A. , Gierut Judith A.
Published: July 2014

This tutorial presents an introduction to the contemporary linguistic framework known as optimality theory (OT). The basic assumptions of this constraint-based theory as a general model of grammar are first outlined, with formal notation being defined and illustrated. Concepts unique to the theory, including “emergence of the unmarked,” are also described. OT is then examined more specifically within the context of phonological acquisition. The theory is applied in descriptions of children's common error patterns, observed inter- and intrachild variation, and productive change over time. The particular error patterns of fronting, stopping, final-consonant deletion, and cluster simplification are considered from an OT perspective. The discussion concludes with potential clinical applications and extensions of the theory to the diagnosis and treatment of children with functional phonological disorders.
Narrative Production by Children With and Without Specific Language Impairment
Authors: Kaderavek Joan N. , Sulzby Elizabeth
Published: July 2014

The research reported in this paper was based on the premise that oral and written language development are intertwined. Further, the research was motivated by research demonstrating that narrative ability is an important predictor of school success for older children with language impairment. The authors extended the inquiry to preschool children by analyzing oral narratives and "emergent storybook reading" (retelling of a familiar storybook) by two groups of 20 children (half with, half without language impairment) age 2;4 (years;months) to 4;2. Comparative analyses of the two narrative genres using a variety of language and storybook structure parameters revealed that both groups of children used more characteristics of written language in the emergent storybook readings than in the oral narratives, demonstrating that they were sensitive to genre difference. The children with language impairment were less able than children developing typically to produce language features associated with written language. For both groups, middles and ends of stories were marked significantly more often within the oral narratives than the emergent readings. The children with language impairment also had difficulty with other linguistic features: less frequent use of past-tense verbs in both contexts and the use of personal pronouns in the oral narratives. Emergent storybook reading may be a useful addition to language sampling protocols because it can reveal higher order language skills and contribute to understanding the relationship between language impairment and later reading disability.
Risk for Speech Disorder Associated With Early Recurrent Otitis Media With Effusion
Authors: Shriberg Lawrence D. , Flipsen Peter , Thielke Helen , Kwiatkowski Joan , Kertoy Marilyn K. , Katcher Murray L. , Nellis Robert A. , Block Michael G.
Published: July 2014

The goals of this two-part series on children with histories of early recurrent otitis media with effusion (OME) were to assess the risk for speech disorder with and without hearing loss and to develop a preliminary descriptive-explanatory model for the findings. Recently available speech analysis programs, lifespan reference data, and statistical techniques were implemented with three cohorts of children with OME and their controls originally assessed in the 1980s: 35 typically developing 3-year-old children followed since infancy in a university-affiliated pediatrics clinic, 50 typically developing children of Native American background followed since infancy in a tribal health clinic, and (in the second paper) 70 children followed prospectively from 2 months of age to 3 years of age and older. Dependent variables included information from a suite of 10 metrics of speech production (Shriberg, Austin, Lewis, McSweeny, & Wilson, 1997a, 1997b). Constraints on available sociodemographic and hearing status information limit generalizations from the comparative findings for each database, particularly data from the two retrospective studies. The present paper reports findings from risk analysis of conversational speech data from the first two cohorts, each of which included retrospective study of children for whom data on hearing loss were not available. Early recurrent OME was not associated with increased risk for speech disorder in the pediatrics sample but was associated with approximately 4.6 (CI=1.10–20.20) increased risk for subclinical or clinical speech disorder in the children of Native American background. Discussion underscores the appropriateness of multifactorial risk models for this subtype of child speech disorder.
Predicting Language Production in Children and Adolescents With Down Syndrome
Authors: Chapman Robin S. , Seung Hye-Kyeung , Schwartz Scott E. , Bird Elizabeth Kay-Raining
Published: July 2014

Predictors of language production skills in 12-minute narratives are investigated cross-sectionally in 48 children and adolescents with Down syndrome (trisomy 21), aged 5 to 20 years, in comparison to 48 control children aged 2 to 6 years matched statistically for nonverbal mental age and mother’s years of education. Two models were evaluated by hierarchical regression analyses using predictors drawn from the domains of group membership, chronological age, cognition, socioeconomic status, and hearing screening status (Model I) and, additionally, comprehension performance (Model II). Results showed that Model II was more successful. In the DS group, it explained 68% of the variability in number of different words, 80% in MLU, and 32% in intelligibility. Corresponding percentages for the control group were 72%, 71%, and 26%. A mechanism linking comprehension of input to early stages of production practice through activation of the early speech motor area is proposed.
Age Differences in the Use of Informative/Heuristic Communicative Functions in Young Children With and Without Hearing Loss Who Are Learning Spoken Language
Authors: Nicholas Johanna Grant
Published: July 2014

Previous research has suggested that the normal development of communicative functions proceeds from the directing or "instrumental" types to the informative or "heuristic" types with age. This paper describes a cross-sectional study of communicative function in children with profound hearing loss and children with normal hearing, from ages 12–54 months. The children with hearing loss were learning spoken English as their primary means of communication. The primary purpose of the study was to evaluate whether the pattern of age differences seen in the two groups of children (those with and without normal hearing) are similar patterns that occur at differing chronological ages, or whether they are dissimilar patterns altogether. A second purpose was to examine the relationship between the use of informative/heuristic functions and the acquisition of vocabulary and syntax. The data suggested a somewhat different pattern of communicative function development in children with and without hearing loss. In addition, the use of language for social purposes was closely related to the achievement of traditional language milestones. In both normally hearing children and in those with hearing loss, the correlations between the use of informative-heuristic functions and various measures of language development indicated that the more mature uses of language co-occur with increased frequency of communication, larger vocabulary, and longer utterance length. These results document that when linguistic improvements such as increasing vocabulary size and sentence length occur in deaf children learning spoken English, they are used for appropriate and informative social purposes that are commensurate with their language age.
Effect of Compression Ratio on Speech Recognition and Speech-Quality Ratings With Wide Dynamic Range Compression Amplification
Authors: Boike Kumiko T. , Souza Pamela E.
Published: July 2014

This project examined the effect of varying compression ratio on speech recognition and quality. Both listeners with mild-to-moderate sensorineural hearing loss and a control group of listeners with normal hearing participated. Test materials were sentences from the Connected Speech Test (R. M. Cox, G. C. Alexander, & C. Gilmore, 1987) which were digitally processed with linear amplification and wide dynamic range compression amplification with 3 compression ratios. Speech-recognition scores were obtained with sentences in quiet and in noise at a 10-dB signal-to-noise ratio for each amplification condition. Additionally, the participants rated each amplification condition in terms of clarity, pleasantness, ease of understanding, and overall impression. Results indicated that, for speech in quiet, compression ratio had no effect on speech-recognition scores; however, speech-quality ratings decreased as compression ratio increased. For speech in noise, both speech-recognition scores and ratings decreased with increasing compression ratio for the listeners with hearing loss. These results suggest that selection of compression ratio on the basis of speech-quality judgments does not compromise speech recognition.
Induced Fatigue Effects on Velopharyngeal Closure Force
Authors: Kuehn David P. , Moon Jerald B.
Published: July 2014

This investigation studied the effects of induced velopharyngeal fatigue in speakers with normal mechanisms. Five adult female and 5 adult male subjects were used. A force sensing bulb was placed in the velopharynx to measure velopharyngeal closure force and intramuscular electrodes were inserted in the levator veli palatini muscle to sample muscle activation levels. The subjects' task was to repeat the syllable /si/ 100 times while an external load was placed on the velopharyngeal mechanism. The external load consisted of various levels of air pressure (0 as a control, 5, 15, 25, and 35 cm H2O relative to atmospheric pressure) delivered to the nasal passages via a tube and nasal mask assembly. Fatigue was defined as a declination of force across the series of syllables within a pressure condition and was depicted as the slope of a linear regression line that was fit to the data. The more negative the slope, the greater was the rate of fatigue. Within each experimental pressure condition, small cyclic variations in force were noted about each regression line that corresponded to individual breath groups. This type of declination, within breath groups, has been reported in the literature previously. Overall declination in force over an entire series of syllables and over several breath groups is a new finding. It was possible to induce such fatigue in most subjects, and greater rates of fatigue generally occurred at the higher levels of external loading, i.e., at 25 and 35 cm H2O. Two subjects, 1 male and 1 female, reached exhaustion. The female subject could not perform the syllable repetition task at 25 cm H2O, and the male subject could not complete the task at 35 cm H2O. Three subjects, 1 female and 2 males, exhibited virtually no force declination even at the highest level (35 cm H2O) of external loading. There were no discernable differences in patterns of fatigue or in initial velopharygeal closure force values between the male and female subjects.
Bandwidth Effects on Children's Perception of the Inflectional Morpheme /s/
Authors: Kortekaas Reinier W. L. , Stelmachowicz Patricia G.
Published: July 2014

The goal of this study was to examine developmental effects in auditory perception of word-final /s/ in inflectional morpheme contexts as a function of high-frequency (HF) bandwidth. Such developmental effects may support the use of hearing aids with extended bandwidths in young children with impaired hearing. The first part of the study consisted of acoustical measurements on word-initial /s/ and inflectional morpheme /s/ in sentences recorded from a male speaker. For this speaker, recordings of inflectional morpheme /s/ on average were approximately 50 ms shorter and about 5 dB lower in level than word-initial /s/ sounds. They also had a lower spectral center of gravity, but not a higher coefficient of kurtosis. The second part consisted of measurements of psychometric functions relating detection of the inflectional morpheme /s/ sounds to HF bandwidth in normally hearing 5-, 7-, and 10-year-old children and adults. In speech-shaped noise, significant main effects of age were found for detection as a function of bandwidth for both the 30- and 10-dB signal-to-noise ratio (SNR) condition, although there was no interaction between age and SNR condition. The third part consisted of subjective clarity rating as a function of HF bandwidth for the same speech stimuli used in the second part. No differences were found between age groups in the shape of the clarity rating functions, but differences were found in the rating variance. No systematic effects of the spectral composition of inflectional morpheme /s/ sounds on either detection or clarity rating were found. The higher detection thresholds and larger clarity rating variances for the youngest participants support the use of extended high-frequency bandwidths for young children with impaired hearing. The extent to which the potential benefit of extended bandwidths is affected by hearing impairment in this population, however, deserves further investigation.
Segmental Timing in Amyotrophic Lateral Sclerosis
Authors: Tjaden Kris , Turner Greg
Published: July 2014

This study describes segmental timing patterns for a passage read by speakers with ALS and a group of age- and gender-matched neurologically healthy speakers. Segment durations for ALS speakers' habitual rates (ALS condition) were compared to segment durations for healthy speakers' habitual and slow reading rates (
Control Habitual
and
Control Slow
conditions). Temporal differences for pairs of sound classes (i.e., long-short vowels, voiceless-voiced fricatives, voiceless-voiced stop gaps, high-low vowels) and prepausal lengthening of vowels also were studied. The results of the ALS-Control Habitual comparison suggested that the slowed articulatory rate of ALS influences segmental timing for most phonetic events. The finding that local segmental cues for disordered speakers were broadly consistent with their overall (slow) articulatory rate suggests that duration likely does not contribute in a significant way to intelligibility deficits in ALS. A qualitative analysis further indicated that the slowed rate of ALS is not uniformly distributed across phonetic events, but influences segment durations of particular sound categories in ways consistent with the disease process. The analysis comparing segment durations for the ALS and Control Slow conditions suggested that the overall pattern of segmental timing for speakers with ALS was broadly similar to the pattern for voluntarily slowed speech of healthy talkers. Finally, temporal differences for sound classes (i.e., voiceless-voiced fricatives, long-short vowels) and prepausal lengthening for speakers with ALS typically were similar to healthy speakers' habitual and slow speech. There were substantial variability within speaker groups and reversals of expected effects, however. The implication is that temporal differences for sound classes, such as short and long vowels, are not a particularly reliable perceptual cue for listeners.
Personality Traits and Psychological Factors in Voice Pathology
Authors: Roy Nelson , Bless Diane M.
Published: July 2014

It has been argued that personality, emotions, and psychological problems contribute to or are primary causes of voice disorders and that voice disorders in turn create psychological problems and personality effects. This article (a) briefly reviews the literature surrounding the role of psychological and personality processes in individuals with functional dysphonia (FD), vocal nodules (VN), and spasmodic dysphonia (SD); (b) provides an overview of recent concepts in personality and trait structure; and (c) summarizes the fundamental tenets of a theoretical synthesis proposed by Roy and Bless (2000) to explain the dispositional bases of FD and VN. This theory links FD and VN to the signal sensitivities and behavioral response biases of neurotic introverts and neurotic extraverts, respectively. In a companion article, the merits of the Roy and Bless theory are evaluated.
The Dysphonia Severity Index
Authors: Wuyts Floris L. , Bodt Marc S. De , Molenberghs Geert , Remacle Marc , Heylen Louis , Millet Benoite , Lierde Kristiane Van , Raes Jan , Heyning Paul H. Van de
Published: July 2014

The vocal quality of a patient is modeled by means of a Dysphonia Severity Index (DSI), which is designed to establish an objective and quantitative correlate of the perceived vocal quality. The DSI is based on the weighted combination of the following selected set of voice measurements: highest frequency (F
0
-High in Hz), lowest intensity (I-Low in dB), maximum phonation time (MPT in s), and jitter (%). The DSI is derived from a multivariate analysis of 387 subjects with the goal of describing, purely based on objective measures, the perceived voice quality. It is constructed as DSI=0.13 x MPT + 0.0053 x F
0
-High – 0.26 x I-Low – 1.18 x Jitter (%) + 12.4. The DSI for perceptually normal voices equals +5 and for severely dysphonic voices –5. The more negative the patient's index, the worse is his or her vocal quality. As such, the DSI is especially useful to evaluate therapeutic evolution of dysphonic patients. Additionally, there is a high correlation between the DSI and the Voice Handicap Index score.
Swallowing and Tongue Function Following Treatment for Oral and Oropharyngeal Cancer
Authors: Lazarus Cathy L. , Logemann Jeri A. , Pauloski Barbara Roa , Rademaker Alfred W. , Larson Charles R. , Mittal Bharat B. , Pierce Margaret
Published: July 2014

This study examined tongue function and its relation to swallowing in 13 subjects with oral or oropharyngeal cancer treated with primary radiotherapy ± chemotherapy and 13 age- and sex-matched control subjects. Measures of swallowing and tongue function were obtained using videofluoroscopy, pretreatment and 2 months posttreatment. Maximum isometric strength and endurance at 50% of maximum strength were obtained with the Iowa Oral Performance Instrument (IOPI). Control subjects were tested once. All subjects with head and neck cancer were evaluated pretreatment and 2 months posttreatment. No significant differences were found for the tongue function measures pre- and 2 months posttreatment in the group with head and neck cancer. Significantly higher tongue strength was observed in the control than in the group with head and neck cancer both pre- and posttreatment. No significant differences were found for the 2 groups for tongue endurance measures. Significant correlations of tongue strength and endurance and some swallow measures were found pre- and posttreatment for the group with head and neck cancer and for the control group. These correlations included oral and pharyngeal temporal swallow measures and oropharyngeal swallow efficiency. Pretreatment differences between the 2 groups in tongue strength were likely related to tumor bulk, pain, and soreness. Two-month posttreatment differences were likely related to radiation ± chemotherapy changes to the oral and pharyngeal mucosa. This study provides support for the hypothesis that tongue strength plays a role in oropharyngeal swallowing, particularly related to the oral phase of the swallow.
Validity of a Parent-Report Measure of Vocabulary and Grammar for Spanish-Speaking Toddlers
Authors: Thal Donna , Jackson-Maldonado Donna , Acosta Dora
Published: July 2014

The validity of the Fundación MacArthur Inventario del Desarrollo de Habilidades Comunicativas: Palabras y Enunciados (IDHC:PE) was examined with twenty 20- and nineteen 28-month-old, typically developing, monolingual, Spanish-speaking children living in Mexico. One measure of vocabulary (number of words) and two measures of grammar (mean of the three longest utterances and grammatical complexity score) from the IDHC:PE were compared to behavioral measures of vocabulary (number of different words from a language sample and number of objects named in a confrontation naming task) and one behavioral measure of grammar (mean length of utterance from a language sample). Only vocabulary measures were assessed in the 20-month-olds because of floor effects on the grammar measures. Results indicated validity for assessing expressive vocabulary in 20-month-olds and expressive vocabulary and grammar in 28-month-olds.
Subjective Vs. Objective Intelligibility of Sentences in Listeners With Hearing Loss
Authors: Cienkowski Kathleen M. , Speaks Charles
Published: July 2014

The relation between rated intelligibility and correct key word repetitions of sentences was examined in listeners with normal hearing and listeners with hearing loss. Ten lists of 10 CID sentences were arranged in two randomly ordered groups. Listeners were asked to complete two tasks: (1) rate the intelligibility of 50 sentences on a scale of 0 to 100%, and (2) repeat each of the 50 sentences, which were scored as the number of key words repeated correctly. Sentences were presented at five signal-to-noise ratios. The start level for sentence presentation was established using the method of adjustment and the Revised Speech Intelligibility Rating passages. Correlations of rated intelligibility and correct repetition were 0.85 for listeners with normal hearing and 0.86 for listeners with hearing loss. This study confirms the earlier work of Speaks, Parker, Harris, and Kuhl (1972), and the findings demonstrate that listeners with hearing loss preserve the ability to rate the intelligibility of speech.
Ataxic Dysarthria
Authors: Kent Ray D. , Kent Jane Finley , Duffy Joe R. , Thomas Jack E. , Weismer Gary , Stuntebeck Sarah
Published: July 2014

Although ataxic dysarthria has been studied with various methods in several languages, questions remain concerning which features of the disorder are most consistent, which speaking tasks are most sensitive to the disorder, and whether the different speech production subsystems are uniformly affected. Perceptual and acoustic data were obtained from 14 individuals (seven men, seven women) with ataxic dysarthria for several speaking tasks, including sustained vowel phonation, syllable repetition, sentence recitation, and conversation. Multidimensional acoustic analyses of sustained vowel phonation showed that the largest and most frequent abnormality for both men and women was a long-term variability of fundamental frequency. Other measures with a high frequency of abnormality were shimmer and peak amplitude variation (for both sexes) and jitter (for women). Syllable alternating motion rate (AMR) was typically slow and irregular in its temporal pattern. In addition, the energy maxima and minima often were highly variable across repeated syllables, and this variability is thought to reflect poorly coordinated respiratory function and inadequate articulatory/voicing control. Syllable rates tended to be slower for sentence recitation and conversation than for AMR, but the three rates were highly similar. Formant-frequency ranges during sentence production were essentially normal, showing that articulatory hypometria is not a pervasive problem. Conversational samples varied considerably across subjects in intelligibility and number of words/ morphemes in a breath group. Qualitative analyses of unintelligible episodes in conversation showed that these samples generally had a fairly well-defined syllable pattern but subjects differed in the degree to which the acoustic contrasts typical of consonant and vowel sequences were maintained. For some individuals, an intelligibility deficit occurred in the face of highly distinctive (and contrastive) acoustic patterns.
Treating Stuttering in Young Children
Authors: Jones Mark , Onslow Mark , Harrison Elisabeth , Packman Ann
Published: July 2014

It is known that children may recover from stuttering without formal treatment during the first years after onset. Consequently, the timing of professional, early stuttering intervention is a pressing issue in speech-language pathology. This report presents data pertinent to this issue for 261 preschool-age children who received the Lidcombe Program of early stuttering intervention. Of these children, 250 completed the program and were considered by their clinicians to have been treated successfully. For the children who were treated successfully, logistical regression analyses were used to determine whether age, gender, period from onset to treatment, and stuttering severity related systematically to the time required for treatment. The present data confirmed previous reports that a median of 11 clinic visits was required to achieve zero or near-zero stuttering with the Lidcombe Program. Results were also consistent with a preliminary report of 14 children (C. W. Starkweather & S. R. Gottwald, 1993) showing a significant relation between stuttering severity and the time needed for treatment, with children with more severe stuttering requiring longer treatment times than children with less severe stuttering. However, results did not associate either increasing age or increased onset-to-treatment intervals with longer treatment times. This finding is not consistent with the Starkweather and Gottwald report, which linked advancing age with longer treatment time. In fact, the present data suggest that, for a short period after stuttering onset in the preschool years, a short delay in treatment does not appear to increase treatment time. An important caveat to these data is that they cannot be generalized to late childhood or early adolescence. The present findings are discussed in relation to natural recovery from stuttering.
Perceptual-Phonetic Predictors of Single-Word Intelligibility
Authors: Whitehill Tara L. , Ciocca Valter
Published: July 2014

This study investigated the perceptual-phonetic predictors of intelligibility in Cantonese speakers with dysarthria. The speakers were 20 young adults with cerebral palsy. The listener group consisted of 12 native Cantonese speakers. A single-word intelligibility test was constructed, based on 17 phonetic contrasts. There were no significant differences in intelligibility for gender, age, or type of cerebral palsy. A regression analysis showed that intelligibility could be predicted with 97% accuracy by 5 out of the 6 most problematic contrasts. Three contrasts (glottal vs. null, final vs. null, and long vs. short vowel) predicted variation on an independent intelligibility measure obtained for the same speakers with 84% accuracy. Principal components analysis derived 4 components, which accounted for 81% of the variance in the 17 contrasts. Physiological explanations and language-specific contributions to speech disorder in this group of speakers are discussed.
Cryptanalysis of two cryptosystems based on multiple intractability assumptions
Authors: Xu Jun , Hu Lei , Sun Siwei
Published: July 2014

Two public key cryptosystems based on the two intractable number‐theoretic problems, integer factorisation and simultaneous Diophantine approximation, were proposed in 2005 and 2009, respectively. In this study, the authors break these two cryptosystems for the recommended minimum parameters by solving the corresponding modular linear equations with small unknowns. For the first scheme, the public modulus is factorised and the secret key is recovered with the Gauss algorithm. By using the LLL basis reduction algorithm for a seven‐dimensional lattice, the public modulus in the second scheme is also factorised and the plaintext is recovered from a ciphertext. The author's attacks are efficient and verified by experiments which were done within 5s.
New secure channel coding scheme based on randomly punctured quasi‐cyclic‐low density parity check codes
Authors: Esmaeili Mostafa , Dakhilalian Mohammad , Gulliver T. Aaron
Published: July 2014

A new joint cryptography‐channel coding technique is introduced which employs punctured quasi‐cyclic‐low density parity check (QC‐LDPC) codes obtained from extended difference families. The absence of permutation and scrambling matrices reduces the key size compared with similar code‐based cryptosystems, while having an acceptable level of security. The main advantage of this system is that, provided the system parameters are chosen appropriately, even if the code employed is revealed the system remains secure. Performance results are presented which show that the punctured code outperforms a random low density parity check (LDPC) code of the same length and rate.
On optimally reducing search costs for placing replicas in Symphony P2P networks
Authors: Tsai Jichiang , Chang Tien‐Yu
Published: July 2014

Peer‐to‐peer (P2P) overlay networks are widely employed in distributed systems. Furthermore, the number of hops required by a node for searching an object is the fundamental search cost of a P2P network. Hence, since placing replicas can efficiently reduce such a cost of the whole system, how to deploy replicas to reduce it as much as possible becomes a critical problem of P2P networks. In this study, the authors investigate this centre problem for the randomised P2P network ‘Symphony’. Particularly, the authors present a stochastic analysis on optimal replica placements, in terms of number of total hops, as well as proposing an optimal replica placement algorithm to perform a simulation study on this issue. Both the theoretical and experimental results show that locations of optimal replica placements in Symphony are not necessarily closest to the target node in the identifier space. Hence, based on the results, the authors evaluate one existing simple but experimentally efficient replica placement strategy, which exactly allocates replicas at nodes closest to the target node, to provide some guidelines on designing more efficient strategy applicable to the real‐world Symphony.
Parallel continuous simulated tempering and its applications in large-scale molecular simulations
Authors: Zang Tianwu , Yu Linglin , Zhang Chong , Ma Jianpeng
Published: July 2014

In this paper, we introduce a parallel continuous simulated tempering (PCST) method for enhanced sampling in studying large complex systems. It mainly inherits the continuous simulated tempering (CST) method in our previous studies [C. Zhang and J. Ma, J. Chem. Phys. 130, 194112 (2009); C. Zhang and J. Ma, J. Chem. Phys. 132, 244101 (2010)], while adopts the spirit of parallel tempering (PT), or replica exchange method, by employing multiple copies with different temperature distributions. Differing from conventional PT methods, despite the large stride of total temperature range, the PCST method requires very few copies of simulations, typically 2–3 copies, yet it is still capable of maintaining a high rate of exchange between neighboring copies. Furthermore, in PCST method, the size of the system does not dramatically affect the number of copy needed because the exchange rate is independent of total potential energy, thus providing an enormous advantage over conventional PT methods in studying very large systems. The sampling efficiency of PCST was tested in two-dimensional Ising model, Lennard-Jones liquid and all-atom folding simulation of a small globular protein trp-cage in explicit solvent. The results demonstrate that the PCST method significantly improves sampling efficiency compared with other methods and it is particularly effective in simulating systems with long relaxation time or correlation time. We expect the PCST method to be a good alternative to parallel tempering methods in simulating large systems such as phase transition and dynamics of macromolecules in explicit solvent.
Accurate prediction of diradical chemistry from a single-reference density-matrix method: Model application to the bicyclobutane to gauche-1,3-butadiene isomerization
Authors: Bertels Luke W. , Mazziotti David A.
Published: July 2014

Multireference correlation in diradical molecules can be captured by a single-reference 2-electron reduced-density-matrix (2-RDM) calculation with only single and double excitations in the 2-RDM parametrization. The 2-RDM parametrization is determined by N-representability conditions that are non-perturbative in their treatment of the electron correlation. Conventional single-reference wave function methods cannot describe the entanglement within diradical molecules without employing triple- and potentially even higher-order excitations of the mean-field determinant. In the isomerization of bicyclobutane to gauche-1,3-butadiene the parametric 2-RDM (p2-RDM) method predicts that the diradical disrotatory transition state is 58.9 kcal/mol above bicyclobutane. This barrier is in agreement with previous multireference calculations as well as recent Monte Carlo and higher-order coupled cluster calculations. The p2-RDM method predicts the Nth natural-orbital occupation number of the transition state to be 0.635, revealing its diradical character. The optimized geometry from the p2-RDM method differs in important details from the complete-active-space self-consistent-field geometry used in many previous studies including the Monte Carlo calculation.
Ultrahigh vacuum and low-temperature cleaning of oxide surfaces using a low-concentration ozone beam
Authors: Pratt A. , Graziosi P. , Bergenti I. , Prezioso M. , Dediu A. , Yamauchi Y.
Published: July 2014

We present a novel method of delivering a low-concentration (<15%) ozone beam to an ultra-high vacuum environment for the purpose of cleaning and dosing experimental samples through oxidation processing. The system described is safe, low-cost, and practical and overcomes the limitations of ozone transport in the molecular flow environment of high or ultrahigh vacuum whilst circumventing the use of pure ozone gas which is potentially highly explosive. The effectiveness of this method in removing surface contamination is demonstrated through comparison of high-temperature annealing of a simple oxide (MgO) in ozone and oxygen environments as monitored using quadrupole mass spectroscopy and Auger electron spectroscopy. Additionally, we demonstrate the potential of ozone for obtaining clean complex oxide surfaces without the need for high-temperature annealing which may significantly alter surface structure.
Influence of the orientation of methylammonium lead iodide perovskite crystals on solar cell performance
Authors: Docampo Pablo , Hanusch Fabian C. , Giesbrecht Nadja , Angloher Philipp , Ivanova Alesja , Bein Thomas
Published: July 2014

Perovskite solar cells are emerging as serious candidates for thin film photovoltaics with power conversion efficiencies already exceeding 16%. Devices based on a planar heterojunction architecture, where the MAPbI3 perovskite film is simply sandwiched between two charge selective extraction contacts, can be processed at low temperatures (<150 °C), making them particularly attractive for tandem and flexible applications. However, in this configuration, the perovskite crystals formed are more or less randomly oriented on the surface. Our results show that by increasing the conversion step temperature from room temperature to 60 °C, the perovskite crystal orientation on the substrate can be controlled. We find that films with a preferential orientation of the long axis of the tetragonal unit cell parallel to the substrate achieve the highest short circuit currents and correspondingly the highest photovoltaic performance.
Reduced hierarchical equations of motion in real and imaginary time: Correlated initial states and thermodynamic quantities
Authors: Tanimura Yoshitaka
Published: July 2014

For a system strongly coupled to a heat bath, the quantum coherence of the system and the heat bath plays an important role in the system dynamics. This is particularly true in the case of non-Markovian noise. We rigorously investigate the influence of system-bath coherence by deriving the reduced hierarchal equations of motion (HEOM), not only in real time, but also in imaginary time, which represents an inverse temperature. It is shown that the HEOM in real time obtained when we include the system-bath coherence of the initial thermal equilibrium state possess the same form as those obtained from a factorized initial state. We find that the difference in behavior of systems treated in these two manners results from the difference in initial conditions of the HEOM elements, which are defined in path integral form. We also derive HEOM along the imaginary time path to obtain the thermal equilibrium state of a system strongly coupled to a non-Markovian bath. Then, we show that the steady state hierarchy elements calculated from the real-time HEOM can be expressed in terms of the hierarchy elements calculated from the imaginary-time HEOM. Moreover, we find that the imaginary-time HEOM allow us to evaluate a number of thermodynamic variables, including the free energy, entropy, internal energy, heat capacity, and susceptibility. The expectation values of the system energy and system-bath interaction energy in the thermal equilibrium state are also evaluated.
A dynamic forcing scheme incorporating backscatter for hybrid simulation
Authors: Xun Qian-Qiu , Wang Bing-Chen
Published: July 2014

In this paper, a dynamic forcing scheme incorporating backscatter is proposed in order to remove the artificial buffer layer in a hybrid Reynolds-averaged Navier-Stokes (RANS)/large-eddy simulation (LES) approach. In contrast to previous forcing techniques, the proposed forcing is determined dynamically from the flow field itself, and does not require any extraction of turbulent fields from reference direct numerical simulation (DNS) or high-resolution LES databases. Transport equations for the resolved turbulent stresses and kinetic energy are introduced to investigate the effects of dynamic forcing on reduction of the thickness and impact of the artificial buffer layer. The proposed forcing model has been tested in the context of turbulent channel flows with Reynolds numbers Reτ = 650 and 1020 (based on the wall friction velocity and half channel height). In order to validate the hybrid RANS/LES approach, flow statistics obtained from the simulations have been thoroughly compared against the available DNS data.
Diffusive and quantum effects of water properties in different states of matter
Authors: Yeh Kuan-Yu , Huang Shao-Nung , Chen Li-Jen , Lin Shiang-Tai
Published: July 2014

The enthalpy, entropy, and free energy of water are important physical quantities for understanding many interesting phenomena in biological systems. However, conventional approaches require different treatments to incorporate quantum and diffusive effects of water in different states of matter. In this work, we demonstrate the use of the two-phase thermodynamic (2PT) model as a unified approach to obtain the properties of water over the whole phase region of water from short (∼20 ps) classical molecular dynamics trajectories. The 2PT model provides an effective way to separate the diffusive modes (gas-like component) from the harmonic vibrational modes (solid-like component) in the vibrational density of states (DoS). Therefore, both diffusive and quantum effect can be properly accounted for water by applying suitable statistical mechanical weighting functions to the DoS components. We applied the 2PT model to systematically examine the enthalpy, entropy, and their temperature dependence of five commonly used rigid water models. The 2PT results are found to be consistent with those obtained from more sophisticated calculations. While the thermodynamic properties determined from different water models are largely similar, the phase boundary determined from the equality of free energy is very sensitive to the small inaccuracy in the values of enthalpy and absolute entropy. The enthalpy, entropy, and diffusivity of water are strongly interrelated, which challenge further improvement of rigid water model via parameter fitting. Our results show that the 2PT is an efficient method for studying the properties of water under various chemical and biological environments.
Radiative observables for linearized gravity on asymptotically flat spacetimes and their boundary induced states
Authors: Benini Marco , Dappiaggi Claudio , Murro Simone
Published: July 2014

We discuss the quantization of linearized gravity on globally hyperbolic, asymptotically flat, vacuum spacetimes, and the construction of distinguished states which are both of Hadamard form and invariant under the action of all bulk isometries. The procedure, we follow, consists of looking for a realization of the observables of the theory as a sub-algebra of an auxiliary, non-dynamical algebra constructed on future null infinity ℑ+. The applicability of this scheme is tantamount to proving that a solution of the equations of motion for linearized gravity can be extended smoothly to ℑ+. This has been claimed to be possible provided that a suitable gauge fixing condition, first written by Geroch and Xanthopoulos [“Asymptotic simplicity is stable,” J. Math. Phys. 19, 714 (1978)], is imposed. We review its definition critically, showing that there exists a previously unnoticed obstruction in its implementation leading us to introducing the concept of radiative observables. These constitute an algebra for which a Hadamard state induced from null infinity and invariant under the action of all spacetime isometries exists and it is explicitly constructed.
Classification of quadratic Lie algebras of low dimension
Authors: Benayadi Saïd , Elduque Alberto
Published: July 2014

In this paper, we give the classification of the irreducible nonsolvable Lie algebras of dimensions \documentclass[12pt]{minimal}\begin{document}$\le\hspace*{-2.5pt}13$\end{document}≤13 with nondegenerate, symmetric, and invariant bilinear forms.
Electronic, magnetic structure and water splitting reactivity of the iron-sulfur dimers and their hexacarbonyl complexes: A density functional study
Authors: Uzunova Ellie L. , Mikosch Hans
Published: July 2014

The iron sulfide dimers (FeS)2 and their persulfide isomers with S–S bonds are studied with the B3LYP density functional as bare clusters and as hexacarbonyls. The disulfides are more stable than the persulfides as bare clusters and the persulfide ground state lies at 3.2 eV above the global minimum, while in the hexacarbonyl complexes this order is reversed: persulfides are more stable, but the energy gap between disulfides and persulfides becomes much smaller and the activation barrier for the transition persulfide → disulfide is 1.11 eV. Carbonylation also favors a non-planar Fe2S2 ring for both the disulfides and the persulfides and high electron density in the Fe2S2 core is induced. The diamagnetic ordering is preferred in the hexacarbonyls, unlike the bare clusters. The hexacarbonyls possess low-lying triplet excited states. In the persulfide, the lowest singlet-to-triplet state excitation occurs by electron transition from the iron centers to an orbital located predominantly at S2 via metal-to-ligand charge transfer. In the disulfide this excitation corresponds to ligand-to-metal charge transfer from the sulfur atoms to an orbital located at the iron centers and the Fe–Fe bond. Water splitting occurs on the hexacarbonyls, but not on the bare clusters. The singlet and triplet state reaction paths were examined and activation barriers were determined: 50 kJ mol−1 for HO–H bond dissociation and 210 kJ mol−1 for hydrogen evolution from the intermediate sulfoxyl-hydroxyl complexes Fe2S(OH)(SH)(CO)6 formed. The lowest singlet-singlet excitations in the hexacarbonyls, the water adsorption complexes and in the reaction intermediates, formed prior to dihydrogen release, fall in the visible light region. The energy barrier of 210 kJ mol−1 for the release of one hydrogen molecule corresponds to one visible photon of 570 nm. The dissociation of a second water molecule, followed by H2 and O2 release via hydro-peroxide intermediate is a two-step process, with activation barriers of 218 and 233 kJ mol−1, which also fall in the visible light region. A comparison of the full reaction path with that on diiron dioxide hexacarbonyls Fe2O2(CO)6 is traced.
Predicting the stability of atom-like and molecule-like unit-charge Coulomb three-particle systems
Authors: King Andrew W. , Herlihy Patrick E. , Cox Hazel
Published: July 2014

Non-relativistic quantum chemical calculations of the particle mass, $m_2^ \pm $m2±, corresponding to the dissociation threshold in a range of Coulomb three-particle systems of the form $\{ {m_1^ \pm m_2^ \pm m_3^ \mp } \}${m1±m2±m3∓}, are performed variationally using a series solution method with a Laguerre-based wavefunction. These masses are used to calculate an accurate stability boundary, i.e., the line that separates the stability domain from the instability domains, in a reciprocal mass fraction ternary diagram. This result is compared to a lower bound to the stability domain derived from symmetric systems and reveals the importance of the asymmetric (mass-symmetry breaking) terms in the Hamiltonian at dissociation. A functional fit to the stability boundary data provides a simple analytical expression for calculating the minimum mass of a third particle required for stable binding to a two-particle system, i.e., for predicting the bound state stability of any unit-charge three-particle system.