bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐frequency response of the ocean to mountain gap winds in the northeastern tropical Pacific
Authors: Liang Jun‐Hong , McWilliams James C. , Gruber Nicolas
Published: December 2009

The wind jets generated by the three mountain gaps of Central America have a substantial impact on the mean state of the northeastern tropical Pacific. Here, we study the mean oceanic impact of individual high‐frequency wind events by synthesizing satellite and reanalysis products. Using daily sea level wind and sea level pressure (SLP) for the period from 1999 through 2007, we identified a total of 103 short‐term wind events for the Gulf of Tehuantepec, 59 events for the Gulf of Papagayo, and 36 events for the Gulf of Panama, most of them occurring between November and May. On the day of maximum wind, the composite peak wind speed reaches about 15 cm/s across nearly the entire Gulf of Tehuantepec, while the winds in the other two gulfs are somewhat weaker. Downwind of the gaps, the composite mean sea surface temperature (SST) drops substantially within one day in response to these wind events, but the spatial extent of the changes remains limited to the region of high wind speed. The high correlation with wind speed suggests that the cooling is mainly a response to wind‐driven turbulent mixing rather than wind stress curl induced upwelling. The boundary layer turbulence is strongly shear‐driven and weakly convectively driven in the Gulf of Tehuantepec and purely shear driven in the other two gulfs. Mean SST recovers quickly after the event, with the recovery largely being controlled by the anomalous surface heat flux induced by the SST disturbance. Each wind event is followed by a phytoplankton bloom, as evidenced by strong increases in satellite detected chlorophyll‐a(Chl‐a) and inferred net primary production (NPP). The initial response of chlorophyll and NPP is delayed relative to SST by only one day, likely owing to upward mixing of chlorophyll from the deep chlorophyll maximum. Chlorophyll remains elevated for several days after the SST has already recovered suggesting that the upward mixing of new nutrients has sustained the bloom. This is supported by the observation that the chlorophyll response remains also limited to the region of high wind speed. These wind events contribute substantially to the overall NPP in the northeastern tropical Pacific. In contrast to SST and Chl‐a, the response of sea surface height (SSH) to these wind events appears to involve both local coastal recirculations and regional mesoscale activities.
Working for the clampdown
Authors: Jacobs Howy
Published: December 2009

Howy Jacobs lampoons the pervasive spread of time management and organisation in academic research
Diamonds and rust: how transposable elements influence mammalian genomes
Authors: Moran John V. , Malik Harmit S.
Published: December 2009

Once dismissed as junk DNA, transposable elements have played a major role in shaping mammalian genomes. Moran and Malik discuss many of the latest discoveries reported at a recent meeting, with a particular focus on DNA transposon and LTR‐retrotransposon biology.
Me, myself and I
Authors: Hunter Philip
Published: December 2009

Flowering plants have diversified and conquered the land. To do so, they have evolved strategies to avoid incest and promote compatible outcrossing. Philip Hunter explores some of the latest research in this area and its application to agriculture and horticulture.
Crystal‐induced neutrophil activation
Authors: Popa‐Nita Oana , Naccache Paul H
Published: December 2009

Monosodium urate (MSU) crystals are among the most potent pro‐inflammatory stimuli and an innate immune inflammatory response to the crystal surface is intimately involved in the pathology of gouty arthritis. The responses of human neutrophils to MSU crystals represent an integral part of this innate response and a key component of the acute inflammatory response associated with gout. A significant, though incomplete, body of information concerning the implication of human neutrophils in MSU crystal‐induced inflammation and the signal transduction pathways activated in response to these agonists in neutrophils has accumulated over the last few years. This review focuses on the current state of knowledge concerning the activation of human neutrophils by MSU crystals specifically in the context of acute gout, as recent data begin to draw a comprehensive picture of the events leading to the often excessive functional responses of neutrophils to these particulate agonists. A non‐exhaustive list of the most important questions that remain to be assessed to further describe the physio‐pathological mechanisms of gouty arthritis is presented here.
Measuring Tinnitus Loudness Using Constrained Psychophysical Scaling
Authors: Ward Lawrence M. , Baumann Michael
Published: December 2009

Purpose

We measured tinnitus loudness using a new method of psychophysical scaling with the aim of introducing a potentially useful new procedure to the literature.

Method

Fourteen adults reporting tinnitus were trained to use a standardized loudness scale, and then they used that response scale to assess loudness of nonstandard stimuli and of their tinnitus. We also measured tinnitus loudness and pitch using a computer-based matching procedure, and we measured the impact of tinnitus on daily living using the Tinnitus Handicap Inventory (THI; C. W. Newman, G. P. Jacobson, & J. B. Spitzer, 1996) for those 14 individuals and an additional 2 participants.

Results and Conclusions

Our 14 trained participants judged loudness similarly to normal hearing participants for pure tones at normal hearing, nontinnitus frequencies—implying that their judgments of tinnitus loudness were valid. Constrained scaling of tinnitus loudness yielded measurements that were substantially greater than the sensation level of sounds matched to tinnitus loudness. Our total of 16 participants fell into 2 groups on the basis of hearing loss, extent of abnormal loudness growth at the tinnitus frequency, and several aspects of tinnitus experience. Finally, as previously found, there was little correlation between tinnitus loudness, no matter how measured, and the impact of tinnitus on daily life as measured by the THI.
Pediatricians’ Knowledge of, Experience With, and Comfort Levels for Cochlear Implants in Children
Authors: Mathews Melody R. , Johnson Carole E. , Danhauer Jeffrey L.
Published: December 2009

Purpose

Pediatricians are vital to early hearing detection and intervention programs (EHDIPs) and influence families’ decisions and compliance with recommendations for their children having hearing loss. Pediatricians need current, accurate knowledge about diagnostics and treatments including cochlear implants (CIs). This study assessed pediatricians’ knowledge about, experience with, and comfort levels for CIs in children.

Method

Questionnaires were mailed to a total of 220 pediatricians in 9 cities in Alabama.

Results

Nine questionnaires were undeliverable; of the remaining 211 surveys, 29 were returned (for a response rate of 13.7%), and 26 of those were usable. The results were consistent with other studies. All respondents focused on pediatrics; most were medical homes experienced with children having sensorineural hearing loss. Less than half had counseled families about CIs but had patients using them. Over half had not recommended CIs in 5 years. Several were unsure about current EHDIP goals and CIs in children. Over half were completely uncomfortable determining children’s CI candidacy but were comfortable referring them to specialists. About a third were completely uncomfortable discussing CIs with and counseling families about them; most were comfortable with CIs being used in children over other habilitative options.

Conclusions

These pediatricians demonstrated deficits in current, accurate knowledge about EHDIPs and CIs in children. Audiologists should help them obtain needed information.
Universal Newborn Hearing Screening Follow-Up: A University Clinic Perspective
Authors: Krishnan Lata A.
Published: December 2009

Purpose

To evaluate the referral and follow-up procedures at a university clinic to determine whether the early intervention program is achieving the goals of diagnosis of hearing loss by 3 months, amplification within 1 month of diagnosis, and intervention services by 6 months, as outlined in the Joint Committee on Infant Hearing (JCIH; 2007) position statement.

Method

Files for 142 infants were examined, and the following data were collected from each file: date of birth, birth hospital, hometown, parents' ages, ethnicity, nursery status (well baby or neonatal intensive care unit), medical history, age at initial evaluation and at diagnosis, results of evaluation(s), and age at hearing aid fitting and start of early intervention services.

Results

Results revealed that 17% of infants were older than 3 months at the initial evaluation, and 18% of infants who needed further evaluation were lost to follow-up. None of the infants identified with hearing loss received amplification within 1 month of diagnosis or early intervention services by the age of 6 months.

Conclusions

The findings provide further evidence of the challenges of early intervention programs as stated by the JCIH (2007), and they emphasize the importance of communication between practitioners and implementation of monitoring systems and checks and balances to improve the efficacy of early intervention programs.
Effects of Syntactic Complexity and Sentence-Structure Priming on Speech Initiation Time in Adults Who Stutter
Authors: Tsiamtsiouris Jim , Cairns Helen Smith
Published: December 2009

Purpose

To test the hypotheses that adults who stutter will be slower in producing syntactically complex sentences than fluent adults and will benefit more from sentence-structure priming than will fluent adults.

Method

Adults who stutter (n= 15) and fluent adults (n= 15) participated in 2 experiments. In Experiment 1, adults in both groups were administered a task that required memorization and production of sentences that varied in syntactic complexity. The same individuals who participated in Experiment 1 also participated in Experiment 2. The second experiment required all participants to create and produce sentences under primed and unprimed sentence-structure conditions.

Results

Relative to adults who do not stutter, the speech initiation time of fluent utterances of adults who stutter became increasingly slower as syntactic complexity increased, and they exhibited greater facilitative effects of sentence-structure priming. In addition, adults who stutter showed a significant correlation between syntactic complexity and priming facilitation.

Conclusion

Data from these experiments confirmed both hypotheses and provided evidence that a subgroup of adults who stutter have grammatical encoding differences when compared with adults who do not stutter.
Relief of Acquired Stuttering Associated With Parkinson’s Disease by Unilateral Left Subthalamic Brain Stimulation
Authors: Walker Harrison C. , Phillips Daniel E. , Boswell Deborah B. , Guthrie Barton L. , Guthrie Stephanie L. , Nicholas Anthony P. , Montgomery Erwin B. , Watts Ray L.
Published: December 2009

Purpose

In this article, the authors report a case of acquired stuttering associated with Parkinson’s disease (PD) that was responsive to unilateral subthalamic nucleus deep-brain stimulation (STN DBS) in the language-dominant hemisphere.

Method

A single-subject, masked, multiple baseline design was used to evaluate the effects of unilateral left STN DBS on stuttering associated with PD. The patient underwent 3 formal speech assessments of spontaneous speech and the reading of passages with DBS off and on. Speech samples were videotaped and placed in random order, and 2 independent speech-language pathologists calculated the percentage of stuttered syllables and classified individual stuttering events.

Results

Stuttering improved significantly in the DBS-on condition. In total, 10% of syllables were affected by stuttering events with DBS off, and less than 1% of syllables were affected by stuttering events with DBS on (n= 2,281 syllables,p< .00001, in a χ2test). The effect of unilateral STN DBS on stuttering was relatively independent of whether the patient was on or off dopaminergic medications.

Conclusion

This article emphasizes the important role of the subthalamic region in the motor control of speech and language.
Acoustic and Articulatory Features of Diphthong Production: A Speech Clarity Study
Authors: Tasko Stephen M. , Greilick Kristin
Published: December 2009

Purpose

The purpose of this study was to evaluate how speaking clearly influences selected acoustic and orofacial kinematic measures associated with diphthong production.

Method

Forty-nine speakers, drawn from the University of Wisconsin X-Ray Microbeam Speech Production Database (J. R. Westbury, 1994), served as participants. Samples of clear and conversational productions of the word
combine
were extracted for analysis. Analyses included listener ratings of speech clarity and a number of acoustic and articulatory kinematic measures associated with production of the diphthong /aI/.

Results

Key results indicate that speaking clearly is associated with (a) increased duration of diphthong-related acoustic and kinematic events, (b) larger F1 and F2 excursions and associated tongue and mandible movements, and (c) minimal evidence of change in formant transition rate.

Conclusions

Overall, the results suggest that clarity-related changes in diphthong production are accomplished through larger, longer, but not necessarily faster diphthong-related transitions. The clarity-related adjustments in diphthong production observed in this study conform to a simple model that assumes speech clarity arises out of reduced overlap of articulatory gestures.
A Comparative Study of Two Acoustic Measures of Hypernasality
Authors: Vogel Adam P. , Ibrahim Hasherah M. , Reilly Sheena , Kilpatrick Nicky
Published: December 2009

Purpose

This study aimed to compare 2 quantitative acoustic measures of nasality in children with cleft lip and palate (CLP) and healthy controls using formalized perceptual assessment as a guide.

Method

Fifty participants (23 children with CLP and 27 age- and gender-matched healthy controls) aged between 4 and 12 years produced a variety of high and low vowels that allowed perceptual ratings of nasal resonance severity as well as acoustic analysis of spectral changes. Two objective measures of nasality were used: 1/3 octave spectra analysis and the voice low tone high tone ratio. Each respective technique has been evaluated in previous research, and their potential as an effective means of detecting changes in nasal resonance has been demonstrated.

Results

Only 1/3 octave spectra analysis differentiated between participants with hypernasal speech and those perceived to have normal nasal resonance. Significant differences were also observed between varying levels of perceived severity on vowels within nonnasalized phonemic environments (/p
i
t/, /t
i
p/).

Conclusions

Perceptual judgment remains the primary means of evaluating levels of nasality in children with CLP. However, the development and validation of easy-to-use objective techniques remains an important goal for effective clinical and empirical practice.
The Perception of Lexical Tone Contrasts in Cantonese Children With and Without Specific Language Impairment (SLI)
Authors: Wong Anita M.-Y. , Ciocca Valter , Yung Sun
Published: December 2009

Purpose

This study examined the perception of fundamental frequency (f0) patterns by Cantonese children with and without specific language impairment (SLI).

Method

Participants were 14 five-year-old children with SLI, and 14 age-matched (AM) and 13 four-year-old vocabulary-matched (VM) controls. The children identified a word from familiar word pairs that illustrated the 8 minimally contrastive pairs of the 6 lexical tones. They discriminated the f0 patterns within contrastive tonal pairs in speech and nonspeech stimuli.

Results

In tone identification, the SLI group performed worse than the AM group but not the VM group. In tone discrimination, the SLI group did worse than the AM group on 2 contrasts and showed a nonsignificant trend of poorer performance on all contrasts combined. The VM group generally did worse than the AM group. There were no group differences in discrimination performance between speech and nonspeech stimuli. No correlation was found between identification and discrimination performance. Only the normal controls showed a moderate correlation between vocabulary scores and performance in the 2 perception tasks.

Conclusion

The SLI group’s poor tone identification cannot be accounted for by vocabulary knowledge alone. The group’s tone discrimination performance suggests that some children with SLI have a deficit in f0 processing.
Comparison of Two Methods of Voice Activity Detection in Field Studies
Authors: Lindstrom Fredric , Ren Keni , Li Haibo , Waye Kerstin Persson
Published: December 2009

Purpose

To evaluate and compare the performance of 2 methods of voice activity detection (neck-attached accelerometer vs. binaural recordings) in field studies in environments where voice activity normally occurs.

Method

A group of 11 healthy adults wore recording equipment during their lunch break. We used binary classification to analyze the results from the 2 methods. The output was compared to a gold standard, obtained through listening tests, and the probability for sensitivity (Ps) and false positive (Pf) was rated. The binary classifiers were set for consistent sensitivity of 99%; thus, the lower false positive rate would indicate the method with the better performance.

Results

The neck-attached accelerometer (Pf = 0.5%) performed significantly (
p
< .001) better than the binaural method (Pf = 7%).

Conclusion

The neck-attached accelerometer is more suitable than the binaural method for voice assessments in environments where people are speaking in close proximity to each other and where the signal-to-noise ratio is moderate to low.
Formant Centralization Ratio: A Proposal for a New Acoustic Measure of Dysarthric Speech
Authors: Sapir Shimon , Ramig Lorraine O. , Spielman Jennifer L. , Fox Cynthia
Published: December 2009

Purpose

The vowel space area (VSA) has been used as an acoustic metric of dysarthric speech, but with varying degrees of success. In this study, the authors aimed to test an alternative metric to the VSA—the
formant centralization ratio
(FCR), which is hypothesized to more effectively differentiate dysarthric from healthy speech and register treatment effects.

Method

Speech recordings of 38 individuals with idiopathic Parkinson’s disease and dysarthria (19 of whom received 1 month of intensive speech therapy [Lee Silverman Voice Treatment; LSVT LOUD]) and 14 healthy control participants were acoustically analyzed. Vowels were extracted from short phrases. The same vowel-formant elements were used to construct the FCR, expressed as (F2u + F2ɑ + F1i + F1u) / (F2i + F1ɑ), the VSA, expressed as ABS([F1i × (F2ɑ – F2u) + F1ɑ × (F2u – F2i) + F1u × (F2i – F2ɑ)] / 2), a logarithmically scaled version of the VSA (LnVSA), and the F2i/F2u ratio.

Results

Unlike the VSA and the LnVSA, the FCR and F2
i/F2
u ratio robustly differentiated dysarthric from healthy speech and were not gender sensitive. All metrics effectively registered treatment effects and were strongly correlated with each other.

Conclusion

Albeit preliminary, the present findings indicate that the FCR is a sensitive, valid, and reliable acoustic metric for distinguishing dysarthric from unimpaired speech and for monitoring treatment effects, probably because of reduced sensitivity to interspeaker variability and enhanced sensitivity to vowel centralization.
Using Laryngeal Electromyography to Differentiate Presbylarynges From Paresis
Authors: Stager Sheila V. , Bielamowicz Steven A.
Published: December 2009

Purpose

Differential diagnosis of patients over 64 years of age reporting hoarseness is challenging. Laryngeal electromyography (LEMG) was used to determine the status of the recurrent and superior laryngeal nerves. The authors hypothesized that individuals with hoarseness but normal LEMG would have measures similar to those of patients from previous studies with presbylarynges and significantly different from those of patients with abnormal LEMG.

Method

A retrospective chart review of acoustic, aerodynamic, endoscopic, and self-rating measures was completed for 52 individuals over 64 years of age reporting moderate to severe hoarseness.

Results

Individuals with normal LEMG had measures similar to those of patients from previous studies diagnosed with presbylarynges. The group with LEMG abnormalities was subcategorized by specific nerve(s) affected. Significant differences were found for measures between presbylarynges and unilateral but not bilateral paresis groups. Several endoscopic findings were observed more often than expected in the presbylarynges group. Using electromyography as a gold standard, the presence of any impairment in arytenoid movement had the most sensitivity (77%) in making the diagnosis of paresis, and the absence of any impairment had the most specificity (67%) in making the diagnosis of presbylarynges.

Conclusion

LEMG may be useful in differentially diagnosing hoarseness in older patients, especially to distinguish between bilateral paresis and presbylarynges.
The Effect of Delayed Auditory Feedback on Activity in the Temporal Lobe While Speaking: A Positron Emission Tomography Study
Authors: Takaso Hideki , Eisner Frank , Wise Richard J. S. , Scott Sophie K.
Published: December 2009

Purpose

Delayed auditory feedback is a technique that can improve fluency in stutterers, while disrupting fluency in many nonstuttering individuals. The aim of this study was to determine the neural basis for the detection of and compensation for such a delay, and the effects of increases in the delay duration.

Method

Positron emission tomography was used to image regional cerebral blood flow changes, an index of neural activity, and to assess the influence of increasing amounts of delay.

Results

Delayed auditory feedback led to increased activation in the bilateral superior temporal lobes, extending into posterior-medial auditory areas. Similar peaks in the temporal lobe were sensitive to increases in the amount of delay. A single peak in the temporal parietal junction responded to the amount of delay but not to the presence of a delay (relative to no delay).

Conclusions

This study permitted distinctions to be made between the neural response to hearing one’s voice at a delay and the neural activity that correlates with this delay. Notably, all the peaks showed some influence of the amount of delay. This result confirms a role for the posterior, sensorimotor “how” system in the production of speech under conditions of delayed auditory feedback.
Frontotemporal Lobar Degeneration: Characterizing Semantic Binding and Abstracted Meaning Abilities
Authors: Anand Raksha , Hart John , Moore Patricia S. , Chapman Sandra B.
Published: December 2009

Purpose: Frontotemporal lobar degeneration (FTLD) encompasses a group of neurodegenerative disorders characterized by gradual and progressive decline in behavior and/or language. Identifying the subtypes of FTLD can be challenging with traditional assessment tools. Growing empirical evidence suggests that language measures might be useful in differentiating FTLD subtypes.

Method: In this paper, we examined the performance of five individuals with FTLD (two with frontotemporal dementia, two with semantic dementia, and one with progressive nonfluent aphasia) and 10 cognitively normal older adults on measures of semantic binding (Semantic Object Retrieval Test and semantic problem solving) and abstracted meaning (generation of interpretive statement and proverb interpretation).

Results and Conclusion: A differential profile of impairment was observed in the three FTLD subtypes on these four measures. Further examination of these measures in larger groups will establish their clinical utility in differentiating the FTLD subtypes.
The Effects of Question Type on Conversational Discourse in Alzheimer's Disease
Authors: Petryk Megan , Hopper Tammy
Published: December 2009

Purpose: The purpose of this study was to investigate the effects of asking open-ended episodic memory questions versus open-ended semantic memory questions on the conversational discourse of individuals with Alzheimer's disease (AD).

Methods: Four females diagnosed with probable AD participated in the study. A within-subjects experimental design was employed to assess the effects of the different question types on participants’ spoken language. Transcripts were analyzed using specific discourse measures used in previous research involving individuals with AD.

Results: Participants in this study produced more meaningful and relevant statements, as measured by ratios of on-topic utterances, when responding to the semantic memory questions as compared to episodic memory questions. Participants made few negative comments overall; however, more negative self-evaluative statements were made in the episodic memory condition. When considered in conjunction with previous research, the results support the use of multiple question types in conversation with individuals with mild and moderate AD. However, communication partners should limit their use of open-ended questions that primarily tax episodic memory.
Superconducting properties of a boson-exchange model of doped graphene
Authors: Loktev V. M. , Turkowski V.
Published: December 2009

We study the superconducting properties of a doped one-layer graphene by using a model in which the interparticle attraction is caused by a boson (phonon-like) excitations. We study the dependence of the superconducting gap Δ and the mean-field critical temperature TcMF on the carrier density, attraction strength, and characteristic (Debye) bosonic frequency. In addition, we study the temperature-carrier density phase diagram of the model by taking into account the thermal fluctuations of the order parameter. We show that the fluctuations result in a significant suppression of TcMF, such that the real (Berezinskii-Kosterlitz-Thouless) critical temperature Tc is much lower than TcMF. The region Tc<T<TcMF is characterized by a finite density of states at the Fermi level (the pseudogap phase). We show that the width of the temperature interval of the pseudogap phase depends strongly on the model parameters—carrier concentration, attraction amplitude, and boson frequency.
Magnetic-field-induced effects in the electronic structure of itinerant d- and f-metal systems
Authors: Grechnev G. E.
Published: December 2009

A paramagnetic response of transition metals and itinerant d- and f-metal compounds in an external magnetic field is studied by employing ab initio full-potential LMTO method in the framework of the local spin density approximation. Within this method the anisotropy of the magnetic susceptibility in hexagonal close-packed transition metals is evaluated for the first time. This anisotropy is owing to the orbital Van Vleck-like paramagnetic susceptibility, which is revealed to be substantial in transition-metal systems due to hybridization effects in the electronic structure. It is demonstrated that compounds TiCo, Ni3Al, YCo2, CeCo2, YNi5, LaNi5, and CeNi5 are strong paramagnets close to the quantum critical point. For these systems the Stoner approximation underestimates the spin susceptibility, whereas the calculated field-induced spin moments provide a good description of the large paramagnetic susceptibilities and magnetovolume effects. It is revealed that an itinerant description of hybridized f electrons produces magnetic properties of the compounds CeCo2, CeNi5, UAl3, UGa3, USi3, and UGe3 in close agreement with experiment. In the uranium compounds UX3 the strong spin-orbit coupling together with hybridization effects give rise to peculiar magnetic states in which the field-induced spin moments are antiparallel to the external field, and the magnetic response is dominated by the orbital contribution.
Nonequilibrium and quantum coherent phenomena in the electromechanics of suspended nanowires (Review Article)
Authors: Shekhter Robert I. , Santandrea Fabio , Sonne Gustav , Gorelik Leonid Y. , Jonson Mats
Published: December 2009

Strong coupling between electronic and mechanical degrees of freedom is a basic requirement for the operation of any nanoelectromechanical device. In this review we consider such devices and in particular investigate the properties of small tunnel-junction nanostructures that contain a movable element in the form of a suspended nanowire. In these systems, electrical currents and charge can be concentrated to small spatial volumes, resulting in strong coupling between the mechanics and the charge transport. As a result, a variety of mesoscopic phenomena appear, which can be used for the transduction of electrical currents into mechanical operation. Here we will in particular consider nanoelectromechanical dynamics far from equilibrium and the effect of quantum coherence in both the electronic and mechanical degrees of freedom in the context of both normal and superconducting nanostructures.
Effect of defects on the quasiparticle spectra of graphite and graphene
Authors: Feher A. , Gospodarev I. A. , Grishaev V. I. , Kravchenko K. V. , Manzheliĭ E. V. , Syrkin E. S. , Feodos’ev S. B.
Published: December 2009

It is shown that in graphite the spectral density of phonons polarized along the c axis has a V shaped feature similar to the so-called Dirac singularity characteristic of the electron density of states in graphene. The formation of quasilocal states, which increase the occupation of the quasiparticle levels near this feature, is analyzed from a unified standpoint for the phonon spectrum of metal-intercalated graphite and the electronic spectrum of graphene with vacancies. It is determined that in the electronic spectrum of graphene with an isolated vacancy quasilocal states are characteristic only of atoms belonging to the sublattice that does not contain this vacancy.
Magnetic quantum oscillations in borocarbide superconductors
Authors: Bergk B. , Wosnitza J.
Published: December 2009

We report systematic de Haas-van Alphen (dHvA) investigations in the normal and superconducting state of RNi2B2C (R=Y and Lu). The observed rich frequency spectrum of the dHvA signals results from a rather complex electronic band structure with different open and closed Fermi-surface sheets. From our data in combination with full-potential local-orbital calculations we are able to extract the angular-resolved mass-enhancement factors λ for different bands. We find a strong anisotropy and band dependence of λ, clearly reflecting the multiband character of the superconductivity in RNi2B2C. We further were able to resolve dHvA oscillations deep into the superconducting state. The observed additional damping of the dHvA amplitudes is much less than expected from most theories. This hints at a reduced or even zero superconducting gap for the detected Fermi surface.
Superconductivity of electron–hole pairs in a bilayer graphene system in a quantizing magnetic field
Authors: Fil’ D. V. , Kravchenko L. Yu.
Published: December 2009

A state with spontaneous interlayer phase coherence in a bilayer quantum Hall system based on graphene is studied. This state can be regarded as a gas of superfluid electron–hole pairs whose components belong to different layers. A superfluid flow of such pairs is equivalent to two electric supercurrents in the layers. It is shown that in a graphene system a state with interlayer phase coherence arises if a definite unbalance of the filling factors of the Landau levels in neighboring layers is created. The temperature of the transition into a superfluid state, the maximum interlayer distance for which phase coherence is possible, and the critical values of the supercurrent are found. The advantages of using graphene systems instead of GaAs heterostructures to realize bilayer electron–hole superconductivity are discussed.
Electron sound in metals
Authors: Avramenko Yu. A. , Bezuglyĭ E. V. , Burma N. G. , Fil’ V. D.
Published: December 2009

This work is devoted to the investigation of electron sound—oscillations coupled with elastic deformation of the electron distribution function and propagating with the Fermi velocity. The amplitude-phase relations characterizing the behavior of electron sound in Ga single crystals are determined experimentally. A model problem of excitation of electron sound in a compensated metal with equivalent bands is solved for a finite sample with diffuse scattering of electrons at the interfaces. It is determined that the displacement amplitude of the receiving interface is two orders of magnitude greater than the elastic amplitude characteristic for the wave due to electron pressure. It is established that the changes occurring in the amplitude and phase of the electron sound waves at a superconducting transition do not depend on the path traversed by the wave, i.e. they refer only to the behavior of the conversion coefficient.
Possible observation of orbiton excitations in manganites by tunneling spectroscopy
Authors: Svistunov V. M. , Leonova V. N. , Belogolovskiĭ M. A. , Revenko Yu. F.
Published: December 2009

Experimental attempts to observe the elementary excitations of an orbitally ordered state (orbitons) in strongly correlated electronic systems by means of Raman scattering and by inelastic x-ray scattering are discussed for the Mott insulator LaMnO3. The results of investigations of the differential conductivity of heterostructures, consisting of a silver needle and manganite-doped La0.57Ca0.43MnO3, for voltages above the phonon and magnon frequencies of manganites are presented. Three peaks at energies corresponding to the peaks in the Raman scattering spectra of LaMnO3 are observed. It is assumed that these peaks are due to the interaction of tunneling electrons with excitations in the orbital subsystem of a degraded region adjoining the metal–manganite interface.
BCS-BEC crossover and nodal-points contribution in p-wave resonance superfluids
Authors: Kagan M. Yu. , Efremov D. V.
Published: December 2009

We solve the Leggett equations for BCS-BEC crossover of the resonance p-wave superfluid. We calculate sound velocity, specific heat and the normal density for the BCS domain (μ>0), the BEC domain (μ<0), and for the interesting interpolation point (μ=0) in the 100%-polarized A1 phase in 3D. We are especially interested in the quasiparticle contribution coming from the zeros of the superfluid gap in the A1 phase. We discuss the spectrum of orbital waves and the superfluid hydrodynamics at temperature T→0. In this context we elucidate the difficult problem of the chiral anomaly and mass-current nonconcervation appearing in the BCS domain. We present the different approaches taken to solve this problem. To clarify this problem experimentally we propose an experiment for measurement of the anomalous current in the superfluid A1 phase in the presence of aerogel for He3 and in the presence of Josephson tunneling structures for ultracold gases in magnetic traps.
Gamma-ray superconducting detector based on Abrikosov vortices: Principle of operation
Authors: Lisitskiy M. P.
Published: December 2009

The high atomic number of some superconducting elements such as niobium (Z=41) and tantalum (Z=73) and a high material thickness (e.g., t=300 μm) are emphasized as essential properties for development of a gamma-ray solid state detector with high intrinsic detection efficiency in the energy range up to 100 keV. To exploit these properties, a new detection principle based on the interaction of a single gamma-ray photon with Abrikosov vortex is proposed. The interaction of gamma-ray photon with a superconductor is discussed in terms of the photoelectric absorption and a hot-spot formation, the last acts as a short-time pinning center on an Abrikosov vortex and activates its motion, namely, a jump or damped vibration. Both types of vortex motion lead to variation (either static or dynamic) in the magnetic field on the absorber surface. The high sensitivity of the Josephson tunneling to weak magnetic field can be exploited for revealing the magnetic field variation and to make the readout of the detector. Main intrinsic properties of a gamma-ray detector based on Abrikosov vortices are evaluated, including the possibility to measure the energy deposited in the detector. A single Josephson tunnel junction configuration or a superconducting quantum interference device (SQUID) configuration is proposed and discussed as possible realization of working gamma-ray detector both in the counter operation mode and in the radiation spectroscopy operation mode.
The effect of angle of incidence on the optical field distribution within thin film organic solar cells
Authors: Meyer A. , Ade H.
Published: December 2009

The optical field within an organic solar cell is the result of thin film interference effects which become more complex at higher angles of incidence. We use optical modeling to study the optical field at oblique incidence. Our findings include an expansion of the interference pattern, a significant intensity of p-polarized light at the cathode interface, and a strong dependence on indium tin oxide and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) thicknesses for single wavelengths. Applications to current research are presented including recent misconceptions in the literature and suggestions for new research.
Monte Carlo calculations of electron transport in silicon and related effects for energies of 0.02–200 keV
Authors: Akkerman A. , Murat M. , Barak J.
Published: December 2009

We present results of systematic Monte Carlo calculations of electron transport in silicon for the wide energy range of 0.02–200 keV, obtained in the frame of a single model using verified input data. The results include characteristics of electron transport, such as backscattering coefficients, ranges, transmission, and deposited-energy distributions, which are quantities of importance for electron-beam applications. The calculations of the spatial and temporal evolution of the electron-initiated cascades of secondary electrons yield a better understanding of the electron and ion track structures and related effects in silicon.
Permeability and resonance characteristics of metamaterial constructed by a wire coil wound on a ferrite core
Authors: Li Z. W. , Huang R. F. , Kong L. B.
Published: December 2009

Metamaterial constructed by a Cu-wire coil wound on a ferrite core exhibits greatly enhanced imaginary permeability μmax″, large negative real permeability μ′−, and resonance frequency fR controlled through varying the number of coil turns, N. Based on an equivalent lumped parameter model, the special permeability spectrum shape and the dependence of permeability parameters on N are deduced for the metamaterial. The theoretical prediction is well consistent with the experimental results.
Effects of fatty acid surfactants on the magnetic and magnetohydrodynamic properties of ferrofluids
Authors: Regmi Rajesh , Black Correy , Sudakar C. , Keyes P. H. , Naik Ratna , Lawes G. , Vaishnava Prem , Rablau Cornel , Kahn David , Lavoie Melissa , Garg Vijayendra K. , Oliveira A. C.
Published: December 2009

We prepared Fe3O4 magnetic nanoparticles having diameters of approximately 12 nm by chemical coprecipitation, which were coated with three different fatty acid surfactants: oleic acid, lauric acid, and myristic acid. From x-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy measurements we confirmed that Fe3O4 is the only phase present in the samples. The zero field cooled magnetization curves for the nanoparticles exhibit broad peaks, consistent with superparamagnetic blocking for the polydisperse samples, and a saturation magnetization smaller than that for bulk Fe3O4. Although there are minimal differences in the magnetic properties of the nanoparticles having different surfactants, we find significant changes in the hydrodynamic response depending on chain length. Hyperthermia measurements show considerably larger response for oleic acid-coated samples, while magneto-optical studies indicate that these samples have slower dynamics of aggregation under the influence of a dc field. These results suggest that the magnetohydrodynamic response of ferrofluids can be controlled by judiciously selecting appropriate surfactants.
Strain effect analysis on phonon thermal conductivity of two-dimensional nanocomposites
Authors: Xu Y. , Li G.
Published: December 2009

In this paper, we present a model that combines lattice dynamics and the phonon Boltzmann transport equation (BTE) to analyze strain effect on the cross-plane phonon thermal conductivity of silicon wire-germanium host nanocomposites. For a given strain condition, mechanical strain is translated to crystal lattice deformation by using the Cauchy–Born rule. Strain-dependent phonon thermal properties of Si and Ge obtained from lattice dynamics with Tersoff empirical interatomic potential are then incorporated into the BTE, in which ballistic transport within one material and diffuse scattering between Si–Ge interface are employed. The strain-dependent BTE is solved numerically on an unstructured triangular mesh by using a finite volume method. Nanocomposites with different Si nanowire cross sections are also investigated. The results show that the phonon thermal conductivity of the nanocomposites can be significantly decreased (or increased) by a tensile (or compressive) strain. With the same length change, hydrostatic strain produces a larger variation in phonon thermal conductivity than uniaxial strain. In addition, it is shown that with the same atomic percentage, the cross-sectional shape makes little difference to the thermal conductivity except at very small characteristic lengths of the Si nanowire.
Electron field emission from wide bandgap semiconductors under intervalley carrier redistribution
Authors: Litovchenko V. , Grygoriev A. , Evtukh A. , Yilmazoglu O. , Hartnagel H. L. , Pavlidis D.
Published: December 2009

Electron field emission phenomena from semiconductors (and, in particular, wide band gap materials) are analyzed theoretically for the general case, i.e., by taking into consideration aspects that have not been considered earlier such as two (or more) valleys of the energy band structure, nondegenerated statistics for the free electrons, heating of conduction band electrons, intervalley carrier redistribution under applied electrical fields, size quantization of electron band spectra, and change in the field emission characteristics. Comparisons with experiments performed on the highly structured (micro- and nano) surfaces of the GaN wide bandgap semiconductor have been made. The influence of the above factors on the current-voltage Fowler–Nordheim characteristics was demonstrated by theory and experiment. From theoretical and experimental results the intervalley energy difference (ΔE) for GaN quantum-sized cathodes was estimated to be 0.8 eV, which is considerably less than that predicted for bulk semiconductor (ΔE=1.2–1.5 eV). Furthermore the field emission currents were several orders higher than for bulk material. This is in good agreement with the prediction of the proposed theoretical model.
Study of optical properties and effective three-photon absorption in Bi-doped ZnO nanoparticles
Authors: Karthikeyan B. , Sandeep C. S. Suchand , Philip Reji , Baesso M. L.
Published: December 2009

In this paper we report the linear and nonlinear optical properties of Bi-doped ZnO nanoparticles. Bi-doped ZnO nanoparticles were prepared through the wet chemical method at room temperature. Optical absorption measurements show that the exciton peaks are situated at 272 and 368 nm, which are attributed to the n=2 and n=1 exciton states, respectively. Transmission electron microscopy measurements reveal the size and shape of the particles and energy dispersive X-ray measurements confirm the doping of Bi in ZnO. Steady state photoluminescence measurements show that the emission is composed of five peaks. Open aperture z-scan measurements done at 532 nm using 5 ns, 300 μJ laser pulses reveal nonlinear absorption which arises from an effective three-photon absorption process.
Molecular dynamics study of energetics of graphene flakes
Authors: Nakajima Takaaki , Shintani K.
Published: December 2009

Molecular dynamics simulations for graphene flakes of various shapes are performed. The equilibrium structures of graphene flakes are obtained. Round, hexagonal, and rectangular graphene flakes are dealt with, and their sizes are varied from a few angstroms to 200 Å. It is shown that for round and hexagonal graphene flakes of small size, the edge configuration influences their energy in equilibrium. Graphene nanoribbons (GNRs) of various aspect ratios are equilibrated at low temperature. The energies of the equilibrated graphene flakes with zigzag (ZZ) edges are lower than the energies of the equilibrated graphene flakes with armchair (AC) edges. This result corresponds to the scanning tunneling microscopy observations in the literature. The atomic bonds on the edges of graphene flakes with both edge configurations are reconstructed. The bond lengths of such reconstructed edges are smaller than the lengths of the atomic bonds inside them. Therefore, free graphene flakes undergo compressive edge stress and vibrate at finite temperature. Constrained GNRs also vibrate, and the amplitudes of the vibrations of the GNRs with ZZ edges are smaller than those of the GNRs with AC edges. On designing and fabricating GNR devices, GNRs with ZZ edges are more favorable than GNRs with AC edges, and vibrations of GNRs should be taken into account.
Electrostatic manipulation of a dielectric microparticle considering surface conductivity using a single probe
Authors: Yamashima Atsushi , Saito Shigeki
Published: December 2009

In this study, we have developed the technique of electrostatic manipulation of a dielectric microparticle by a single probe. The manipulation system consists of three objects: a conductive probe as a manipulating tool, a conductive plate as a substrate, and a dielectric particle that dubs as a microparticle. In manipulating 60 μm in diameter particles of polystyrene, when a constant probe-substrate voltage was applied, we observed the phenomenon of the particle repeatedly moving up and down between the substrate and the probe tip, similarly to a “micro-dribble.” In order to understand the mechanism of the phenomenon, we have proposed a model with a resistor-capacitor circuit in consideration of the surface conductivity of the dielectric particle such that the model can explain the micro-dribble phenomenon in terms of the time constant of the circuit. By a single-pulse voltage the duration of which was designed (selected) on the basis of the frequency of the observed micro-dribble, we experimentally demonstrated the electrostatic micromanipulation by picking up/placing the polystyrene particle using the single probe. Although the success rate of 42% requires further improvement, the experimental result indicates the feasibility of the technique, which can be applied to future technology for microdevice packaging or assembly.
Nonuniform apparent relaxation from dephasing of magnetostatic wave modes in a confined microdisk
Authors: Lee Kyeong-Dong , Kim Ji-Wan , Jeong Jae-Woo , Shin Sung-Chul
Published: December 2009

We report the nonuniform apparent relaxation due to the spatially inhomogeneous dephasing of magnetostatic wave modes in a confined Permalloy microdisk investigated by picosecond time-resolved scanning Kerr microscopy. Spin precession in the disk shows a considerable nonuniformity in the relaxation time along the direction of a bias magnetic field. The nonuniform apparent relaxation is well reproduced by micromagnetic simulation using uniform values of damping constant. This implies that the spinwaves in the microdisk plays a significant role in the relaxation process. The simulation study, based on the analysis of spinwave modes, reveals that the spatial relaxation variation is mainly caused by the spatially inhomogeneous dephasing between the fundamental mode and magnetostatic backward volume wave mode.