bluuebunny/crossref_metadata_2025 huggingface dataset:
Perspectives in electrical stimulation of the ear (Experimental studies)
Authors: Aran Jean-Marie , de Sauvage Renaud Charlet , Erre Jean-Paul
Published: May 2011

The use of electrical stimulation of the ear for artificial auditory stimulation of the profoundly deaf, as well as for the suppression of tinnitus when it is exceedingly annoying (Cazals et al., 1978) has been extensively discussed here, but I would like to present now other possible clinical applications of electrical stimulation. These concern its use as a new tool in objective audiometry
ABR and tinnitus—an overview
Authors: Shulman Abraham
Published: May 2011

This paper will present an overview of the clinical experience that has been accumu-lated by the Division of Otolaryngology Center for Communication Sciences, Downstate Medical Center, Brooklyn, New York, using auditory brainstem response (ABR) in the tinnitus patient. This work has been ongoing since 1977. Our observations of ABR in the tinnitus patient have been reported to stimulation with tone and broad band clicks. They are observations, not conclusions. We reported in 1981, a clinical test—“Simultaneous Binaural Auditory Brain Response” with monaural stimula-tion for attempts to locate central tinnitus (SABR).
Computer-assisted analysis of reported tinnitus sounds
Authors: Meikle Mary , Whitney Susan
Published: May 2011

Just as the various words used to describe pain are helpful to physicians in identifying the probable cause of the pain, the words used by tinnitus patients to describe their tinnitus sounds may prove useful for categorizing tinnitus and, eventually, for identifying the cause(s) of the tinnitus. We here report preliminary attempts to analyze verbal descriptions of tinnitus sensations obtained from a large population of tinnitus patients.
Autoimmune ear disease: animal models update A possible tinnitus model?
Authors: Yoo T. J. , Tomoda K. , Yazawa Y. , Floyd R. , Stuart J. M. , Cremer M. , Ishibe T. , Kang A. H. , Townes A. S.
Published: May 2011

Immunology and ear diseases finally have met each other. There are several ear diseases associated with hearing loss, vertigo, tinnitus. These include Menière's Disease, otosclerosis and autoimmune sensorineural hearing loss. These diseases have immunologic manifestations.
Pediatric tinnitus (a thesis revisited)
Authors: Nodar Richard H. , LeZak Mary H. W.
Published: May 2011

Although the literature teems with articles on tinnitus in adults, it appears that investigations on tinnitus in children are few and far between. A survey of the literature revealed that, spanning 11 years since our first article (Nodar, 1972), only the work of Graham (1981) specifically addressed tinnitus in children (Table I). In a recent publication, McFadden (1982) dedicated two paragraphs to tinnitus in children, citing the two studies mentioned above. It is apparent that McFadden either did not read or did not understand at least one of the articles (Nodar, 1972) since his figures are grossly erroneous. The previous observations, coupled with gentle prodding from Dr. A. Schulman (New York), led to this report which will address three issues: (1) our first study of tinnitus in children; (2) a recent study of tinnitus in children; and (3) a philosophical discussion of the phenomenon we call tinnitus, our approach to its investigation, and why relief from it is evasive, inconsistent and often non-existent.
Medical treatment of tinnitus with XylocaineTM and tocainideTH
Authors: Shea John J.
Published: May 2011

Medical treatment offers the best hope, we believe, of the various treatment methods available for the management of tinnitus.
Translabyrinthine nerve section: effect on tinnitus
Authors: Barrs David M. , Brackmann Derald E.
Published: May 2011

The effect on tinnitus in 110 patients undergoing translabyrinthine vestibular nerve section is presented. The effect on tinnitus of vestibular and cochlear nerve section (VCNS) together and vestibular nerve section (VNS) alone was studied. The number of patients improved with VCNS (61 per cent) was slightly better than with VNS alone (49 per cent). VNS alone worsened tinnitus more often than VCNS. Age, side involved, sex, etiology of vertigo, severity of tinnitus, interference with sleep and activities, slope of the pre-operative audiogram, and magnitude of the hearing loss had no value in predicting the change in tinnitus following either VNS or VCNS.
Neurotologic surgery and tinnitus
Authors: Gardner Gale
Published: May 2011

Otologic surgeons have long searched for a predictable surgical procedure for the control of tinnitus, but without success. Yet periodically, surgical procedures employed primarily for other purposes serendipitously produce relief of associated tinnitus. An effort will be made to study this aspect of tinnitus. The recent literature on the subject will be surveyed briefly. The effect upon tinnitus in 332 patients by the use of various neurotologic surgical procedures, performed primarily for other purposes, will be presented and discussed.
The lack of impact of peri-implantation or late gestation nutrient restriction on ovine fetal renal development and function
Authors: Braddick L. M. , Burrage D. M. , Cleal J. K. , Noakes D. E. , Hanson M. A. , Green L. R.
Published: May 2011

Unbalanced nutrition during critical windows of development is implicated in determining the susceptibility to hypertension and cardiovascular disease in adult life, but the underlying mechanisms during fetal life have not been fully elucidated. We investigated the effects of moderate nutritional restriction during critical windows in gestation on late gestation fetal sheep growth, cardiovascular and renal renin-angiotensin system function. Ewes were fed 100% nutrient requirements (control), or 40–50% nutrient requirements during the peri-implantation period (1–31 days gestation (dGA), PI40 and PI50), or 50% nutrient requirements in late gestation (104–127 dGA). At 125 ± 2 dGA, fetal cardiovascular and renal function were measured at baseline, and during frusemide, angiotensin II (Ang II), phenylephrine and hypoxia challenges. Maternal undernutrition had no effect on fetal biometry, kidney weight, nephron number, basal cardiovascular function or cardiovascular and renal responses to frusemide. Fetal blood pressure response to Ang II was blunted in PI50 (P< 0.05), but not in PI40 groups. There was no difference between groups in the cardiovascular or endocrine response to hypoxia. The lack of effect of moderate undernutrition within key developmental windows of fetal kidney development on fetal renal structure and function suggests that renal mechanisms do not underlie our previous observations of cardiovascular dysfunction in adulthood following early-life undernutrition.
Self-Report of Suicidal Thoughts and Behavior vs. School Nurse Evaluations in Dutch High-School Students
Authors: de Wilde Erik Jan , van de Looij Petra , Goldschmeding Judith , Hoogeveen Christina
Published: May 2011

Background: Systematic screening to identify adolescents at risk for suicidal behavior is crucial to suicide prevention. Aims: The current practice of screening and follow-up actions taken by school nurses in schools for secondary education in Rotterdam, the Netherlands, was studied. Methods: In Rotterdam, an approach was developed in which, as a standard routine, students are invited to an interview with a school nurse after filling out a youth health survey in classroom setting. This health survey comprised, among other subjects, the Strengths and Difficulties Questionnaire (SDQ) and questions about suicidal thoughts and behaviors. The results from the interviews and the self-report questionnaires of nearly 4000 first-grade students in secondary education were analyzed. Results: The vast majority of invitations were not followed by any action from the school nurse. Also, the majority of students whose self-report led to an “Attention Subject” for the nurse were not considered to be at risk by the nurse. The self-report of recent suicidal thoughts added to the predictive value of emotional distress as measured by the SDQ and other self-report conclusions. Conclusions: This study demonstrates the additional value of self-reported suicidal thoughts for Dutch preventive practices in youth health care.
Saturated‐unsaturated flow to a well with storage in a compressible unconfined aquifer
Authors: Mishra Phoolendra Kumar , Neuman Shlomo P.
Published: May 2011

Mishra and Neuman (2010) developed an analytical solution for flow to a partially penetrating well of zero radius in a compressible unconfined aquifer that allows inferring its saturated and unsaturated hydraulic properties from responses recorded in the saturated and/or unsaturated zones. Their solution accounts for horizontal as well as vertical flows in each zone. It represents unsaturated zone constitutive properties in a manner that is at once mathematically tractable and sufficiently flexible to provide much improved fits to standard constitutive models. In this paper we extend the solution of Mishra and Neuman [2010] to the case of a finite diameter pumping well with storage; investigate the effects of storage in the pumping well and delayed piezometer response on drawdowns in the saturated and unsaturated zones as functions of position and time; validate our solution against numerical simulations of drawdown in a synthetic aquifer having unsaturated properties described by the van Genuchten [1980]–Mualem [1976] model; use our solution to analyze 11 transducer‐measured drawdown records from a seven‐day pumping test conducted by University of Waterloo researchers at the Canadian Forces Base Borden in Ontario, Canada; validate our parameter estimates against manually‐measured drawdown records in 14 other piezometers at Borden; and compare (a) our estimates of aquifer parameters with those obtained on the basis of all these records by Moench [2008], (b) on the basis of 11 transducer‐measured drawdown records by Endres et al. [2007], (c) our estimates of van Genuchten–Mualem parameters with those obtained on the basis of laboratory drainage data from the site by Akindunni and Gillham [1992], and (d) our corresponding prediction of how effective saturation varies with elevation above the initial water table under static conditions with a profile based on water contents measured in a neutron access tube at a radial distance of about 5 m from the center of the pumping well. We also use our solution to analyze 11 transducer‐measured drawdown records from a 7 day pumping test conducted by University of Waterloo researchers at the Canadian Forces Base Borden in Ontario, Canada. We validate our parameter estimates against manually measured drawdown records in 14 other piezometers at Borden. We compare our estimates of aquifer parameters with those obtained on the basis of all these records by Moench (2008) and on the basis of 11 transducer‐measured drawdown records by Endres et al. (2007), and we compare our estimates of van Genuchten–Mualem parameters with those obtained on the basis of laboratory drainage data from the site by Akindunni and Gillham (1992); finally, we compare our corresponding prediction of how effective saturation varies with elevation above the initial water table under static conditions with a profile based on water contents measured in a neutron access tube at a radial distance of about 5 m from the center of the pumping well.
A member of the ETS family, EHF, and the ATPase RUVBL1 inhibit p53‐mediated apoptosis
Authors: Taniue Kenzui , Oda Takeaki , Hayashi Tomoatsu , Okuno Masumi , Akiyama Tetsu
Published: May 2011

Tumour cells are known to be dependent on, or ‘addicted to’, not only oncogenes, but also some non‐oncogenes. However, the mechanisms by which tumour cells are addicted to these genes have not been fully explained. Here, we show that overexpression of a member of the ETS family, EHF, is required for the survival of colon tumour cells that contain wild‐type p53. We found that EHF directly activates the transcription of RUVBL1, an ATPase associated with chromatin‐remodelling complexes. RUVBL1 blocks p53‐mediated apoptosis by repressing the expression of p53 and its target genes. Moreover, we found that RUVBL1 represses p53 transcription by binding to the p53 promoter, interfering with RNF20/hBRE1‐mediated histone H2B monoubiquitination and promoting PAF1‐mediated histone H3K9 trimethylation. These results indicate that EHF‐mediated RUVBL1 expression allows colon tumour cells to avoid p53‐mediated apoptosis. Thus, EHF and RUVBL1 might be promising molecular targets for the treatment of colon tumours.
A biochemical analysis of the constraints of tail-anchored protein biogenesis
Authors: Leznicki Pawel , Warwicker Jim , High Stephen
Published: May 2011

TA (tail-anchored) proteins utilize distinct biosynthetic pathways, including TRC40 (transmembrane domain recognition complex of 40 kDa)-mediated, chaperone-dependent and/or unassisted routes to the ER (endoplasmic reticulum) membrane. We have addressed the flexibility of cytosolic components participating in these pathways, and explored the thermodynamic constraints of their membrane insertion, by exploiting recombinant forms of Sec61β and Cytb5 (cytochrome b5) bearing covalent modifications within their TA region. In both cases, efficient membrane insertion relied on cytosolic factors capable of accommodating a surprising range of covalent modifications to the TA region. For Sec61β, we found that both SGTA (small glutamine-rich tetratricopeptide repeat-containing protein α) and TRC40 can bind this substrate with a singly PEGylated TA region. However, by introducing two PEG [poly(ethylene glycol)] moieties, TRC40 binding can be prevented, resulting in a block of subsequent membrane integration. Although TRC40 can bind Sec61β polypeptides singly PEGylated at different locations, membrane insertion is more sensitive to the precise location of PEG attachment. Modelling and experimentation indicate that this post-TRC40 effect results from an increased energetic cost of inserting different PEGylated TA regions into the lipid bilayer. We therefore propose that the membrane integration of TA proteins delivered via TRC40 is strongly dependent upon underlying thermodynamics, and speculate that their insertion is via a phospholipid-mediated process.
Inducing toxicity by introducing a leucine-zipper-like motif in frog antimicrobial peptide, magainin 2
Authors: Pandey Brijesh Kumar , Srivastava Saurabh , Singh Manish , Ghosh Jimut Kanti
Published: May 2011

Cytotoxicity, a major obstacle in therapeutic application of antimicrobial peptides, is controlled by leucine-zipper-like sequences in melittin and other naturally occurring antimicrobial peptides. Magainin 2 shows significantly lower cytotoxicity than many naturally occurring antimicrobial peptides and lacks this structural element. To investigate the consequences of introducing a leucine zipper sequence in magainin 2, a novel analogue (Mag-mut) was designed by rearranging only the positions of its hydrophobic amino acids to include this structural element. Both magainin 2 and Mag-mut showed appreciable similarities in their secondary structures in the presence of negatively charged lipid vesicles, in localizing and permeabilizing the selected bacteria and exhibiting bactericidal activities. However, Mag-mut bound and localized strongly on to the mammalian cells tested and exhibited significantly higher cytotoxicity than magainin 2. Only Mag-mut, but not magainin 2, permeabilized human red blood cells and zwitterionic lipid vesicles. In contrast with magainin 2, Mag-mut self-assembled in an aqueous environment and bound co-operatively on to zwitterionic lipid vesicles. The peptides formed pores of different sizes on to a selected mammalian cell. The results of the present study indicate an important role of the leucine zipper sequence in the cytotoxicity of Mag-mut and demonstrate that its introduction into a non-toxic peptide, without altering the amino acid composition, can render cytotoxicity.
Phosphoinositide 3-kinase signalling pathway involvement in a truncated apoptotic cascade associated with motility loss and oxidative DNA damage in human spermatozoa
Authors: Koppers Adam J. , Mitchell Lisa A. , Wang Ping , Lin Minjie , Aitken R. John
Published: May 2011

Human spermatozoa are characterized by poor functionality and abundant DNA damage that collude to generate the high incidences of male infertility and miscarriage seen in our species. Although apoptosis has been suggested as a possible cause of poor sperm quality, the ability of these cells to enter an apoptotic state and the factors that might trigger such an event are unresolved. In the present study we provide evidence that the commitment of these cells to apoptosis is negatively regulated by PI3K (phosphoinositide 3-kinase)/AKT. If PI3K activity is inhibited, then spermatozoa default to an apoptotic cascade characterized by rapid motility loss, mitochondrial reactive oxygen species generation, caspase activation in the cytosol, annexin V binding to the cell surface, cytoplasmic vacuolization and oxidative DNA damage. However, the specialized physical architecture of spermatozoa subsequently prevents endonucleases activated during this process from penetrating the sperm nucleus and cleaving the DNA. As a result, DNA fragmentation does not occur as a direct result of apoptosis in spermatozoa as it does in somatic cells, even though oxidative DNA adducts can clearly be detected. We propose that this unusual truncated apoptotic cascade prepares spermatozoa for silent phagocytosis within the female tract and prevents DNA-damaged spermatozoa from participating in fertilization.
GULP1 is a novel APP-interacting protein that alters APP processing
Authors: Hao Candy Yan , Perkinton Michael S. , Chan William Wai-Lun , Chan Ho Yin Edwin , Miller Christopher C. J. , Lau Kwok-Fai
Published: May 2011

Altered production of Aβ (amyloid-β peptide), derived from the proteolytic cleavage of APP (amyloid precursor protein), is believed to be central to the pathogenesis of AD (Alzheimer's disease). Accumulating evidence reveals that APPc (APP C-terminal domain)-interacting proteins can influence APP processing. There is also evidence to suggest that APPc-interacting proteins work co-operatively and competitively to maintain normal APP functions and processing. Hence, identification of the full complement of APPc-interacting proteins is an important step for improving our understanding of APP processing. Using the yeast two-hybrid system, in the present study we identified GULP1 (engulfment adaptor protein 1) as a novel APPc-interacting protein. We found that the GULP1–APP interaction is mediated by the NPTY motif of APP and the GULP1 PTB (phosphotyrosine-binding) domain. Confocal microscopy revealed that a proportion of APP and GULP1 co-localized in neurons. In an APP–GAL4 reporter assay, we demonstrated that GULP1 altered the processing of APP. Moreover, overexpression of GULP1 enhanced the generation of APP CTFs (C-terminal fragments) and Aβ, whereas knockdown of GULP1 suppressed APP CTFs and Aβ production. The results of the present study reveal that GULP1 is a novel APP/APPc-interacting protein that influences APP processing and Aβ production.
Conservation of targeting but divergence in function and quality control of peroxisomal ABC transporters: an analysis using cross-kingdom expression
Authors: Zhang Xuebin , De Marcos Lousa Carine , Schutte-Lensink Nellie , Ofman Rob , Wanders Ronald J. , Baldwin Stephen A. , Baker Alison , Kemp Stephan , Theodoulou Frederica L.
Published: May 2011

ABC (ATP-binding cassette) subfamily D transporters are found in all eukaryotic kingdoms and are known to play essential roles in mammals and plants; however, their number, organization and physiological contexts differ. Via cross-kingdom expression experiments, we have explored the conservation of targeting, protein stability and function between mammalian and plant ABCD transporters. When expressed in tobacco epidermal cells, the mammalian ABCD proteins ALDP (adrenoleukodystrophy protein), ALDR (adrenoleukodystrophy-related protein) and PMP70 (70 kDa peroxisomal membrane protein) targeted faithfully to peroxisomes and P70R (PMP70-related protein) targeted to the ER (endoplasmic reticulum), as in the native host. The Arabidopsis thaliana peroxin AtPex19_1 interacted with human peroxisomal ABC transporters both in vivo and in vitro, providing an explanation for the fidelity of targeting. The fate of X-linked adrenoleukodystrophy disease-related mutants differed between fibroblasts and plant cells. In fibroblasts, levels of ALDP in some ‘protein-absent’ mutants were increased by low-temperature culture, in some cases restoring function. In contrast, all mutant ALDP proteins examined were stable and correctly targeted in plant cells, regardless of their fate in fibroblasts. ALDR complemented the seed germination defect of the Arabidopsis cts-1 mutant which lacks the peroxisomal ABCD transporter CTS (Comatose), but neither ALDR nor ALDP was able to rescue the defect in fatty acid β-oxidation in establishing seedlings. Taken together, our results indicate that the mechanism for trafficking of peroxisomal membrane proteins is shared between plants and mammals, but suggest differences in the sensing and turnover of mutant ABC transporter proteins and differences in substrate specificity and/or function.
Clinical and haemodynamic correlates of heart rate turbulence as a non-invasive index of baroreflex sensitivity in chronic heart failure
Authors: La Rovere Maria Teresa , Maestri Roberto , Pinna Gian Domenico , Sleight Peter , Febo Oreste
Published: May 2011

HRT (heart rate turbulence), describing the heart rate changes following a premature ventricular contraction, has been regarded as an indirect index of baroreflex function. However, limited data are available on its relationship with invasive assessment by phenylephrine injection (Phe-slope). In the present study, we therefore compared these methodologies in a series of patients with HF (heart failure) in which both measures together with clinical and haemodynamic data were available. HRT parameters [TO (turbulence onset) and TS (turbulence slope)] were measured from 24-h Holter recordings obtained within 1 week of baroreflex sensitivity assessment and right heart haemodynamic evaluation (Swan-Ganz catheter). HRT was computable in 135 out of 157 (86%) patients who had both a phenylephrine test and haemodynamic evaluation. TO and TS significantly correlated with Phe-slope (r=−0.39, P<0.0001 and r=0.66, P<0.0001 respectively). Age, baseline heart rate, LVEF (left ventricular ejection fraction), PCP (pulmonary capillary pressure), CI (cardiac index) and sodium were significant and independent predictors of Phe-slope, accounting for 51% of its variability. Similarly, age, baseline heart rate and PCP, and NYHA (New York Heart Association) classes III–IV were independent predictors for TS and explained 48% of its variability, whereas only CI and LVEF were found to be significantly related to TO and explained a very limited proportion (20%) of the variability. In conclusion, these results suggest that HRT may be regarded as a surrogate measure of baroreflex sensitivity in clinical and prognostic evaluation in patients with HF.
A generic model for transport in turbulent shear flows
Authors: Newton Andrew P. L. , Kim Eun-Jin
Published: May 2011

Turbulence regulation by large-scale shear flows is crucial for a predictive modeling of transport in plasma. In this paper the suppression of turbulent transport by large-scale flows is studied numerically by measuring the turbulent diffusion Dt and scalar amplitude 〈n′2〉 of decaying passive scalar fields n′ advected by various turbulent flows. Both uniform flows and shear flows are shown to suppress turbulence causing the quenching in transport and turbulence amplitude. The uniform flows U0=Λy with the advection rate Λ in the case of a finite correlated forcing with τF=1 gives rise to the advection/sweeping effect which suppresses Dt, 〈u′2〉 and 〈n′2〉 as ∝Λ-2 for Λ>>τF-1. In contrast, no influence of the uniform flow is found in the case of a short correlated forcing τF→0 due to Galilean invariance. For the shear flow U0=Ωsinxy∧ (Ω= constant shearing rate) with the appropriate choice of the forcing (τF→0) the nature of transport suppression is shown to crucially depend on the properties of the turbulence. Specifically, for prescribed turbulence with a short correlation time τc=τF≪ Ω-1, the turbulence statistics scale as Dt∝Ω-0.02, 〈n′2〉∝Ω-0.62 and cross-phase cosθ∝Ω0.29. For consistently evolved turbulence with a finite correlation time τc≥Ω-1, turbulence statistics are suppressed more strongly as Dt∝Ω-1.75, 〈n′2〉∝Ω-2.41, 〈u'x2〉∝Ω-0.65 and 〈ω′2〉∝Ω-0.50. A novel renormalization scheme is then introduced to rescale our results into the regime within which the kinetic energy and enstrophy are unchanged by shear flow. This allows our numerical results to closely match previous analytical predictions [E. Kim, Mod. Phys. Lett. B 18, 1 (2004)] and to understand different experimental scalings observed in laboratory plasmas. Furthermore, Dt is found to be related to 〈n′2〉 by 〈n′2〉∝Dt/DΩ, where DΩ∝Ω23 is the shear accelerated diffusion of n′ with an interesting scaling cosθ∝DtDΩ.
Precision and accuracy in film stiffness measurement by Brillouin spectroscopy
Authors: Beghi M. G. , Di Fonzo F. , Pietralunga S. , Ubaldi C. , Bottani C. E.
Published: May 2011

The interest in the measurement of the elastic properties of thin films is witnessed by a number of new techniques being proposed. However, the precision of results is seldom assessed in detail. Brillouin spectroscopy (BS) is an established optical, contactless, non-destructive technique, which provides a full elastic characterization of bulk materials and thin films. In the present work, the whole process of measurement of the elastic moduli by BS is critically analyzed: experimental setup, data recording, calibration, and calculation of the elastic moduli. It is shown that combining BS with ellipsometry a fully optical characterization can be obtained. The key factors affecting uncertainty of the results are identified and discussed. A procedure is proposed to discriminate factors affecting the precision from those affecting the accuracy. By the characterization of a model transparent material, silica in bulk and film form, it is demonstrated that both precision and accuracy of the elastic moduli measured by BS can reach 1% range, qualifying BS as a reference technique.
Absolute magnetic helicity and the cylindrical magnetic field
Authors: Low B. C.
Published: May 2011

The different magnetic helicities conserved under conditions of perfect electrical conductivity are expressions of the fundamental property that every evolving fluid surface conserves its net magnetic flux. This basic hydromagnetic point unifies the well known Eulerian helicities with the Lagrangian helicity defined by the conserved fluxes frozen into a prescribed set of disjoint toroidal tubes of fluid flowing as a permanent partition of the entire fluid [B. C. Low, Astrophys. J. 649, 1064 (2006)]. This unifying theory is constructed from first principles, beginning with an analysis of the Eulerian and Lagrangian descriptions of fluids, separating the ideas of fluid and magnetic-flux tubes and removing the complication of the magnetic vector potential’s free gauge from the concept of helicity. The analysis prepares for the construction of a conserved Eulerian helicity, without that gauge complication, to describe a 3D anchored flux in an upright cylindrical domain, this helicity called absolute to distinguish it from the well known relative helicity. In a version of the Chandrasekhar-Kendall representation, the evolving field at any instant is a unique superposition of a writhed, untwisted axial flux with a circulating flux of field lines all closed and unlinked within the cylindrical domain. The absolute helicity is then a flux-weighted sum of the writhe of that axial flux and its mutual linkage with the circulating flux. The absolute helicity is also conserved if the frozen-in field and its domain are continuously deformed by changing the separation between the rigid cylinder-ends with no change of cylinder radius. This hitherto intractable cylindrical construction closes a crucial conceptual gap for the fundamentals to be complete at last. The concluding discussion shows the impact of this development on our understanding of helicity, covering (i) the helicities of wholly contained and anchored fields; (ii) the Eulerian and Lagrangian descriptions of field evolution; (iii) twist as a topological property of solenoidal fields versus the linkage properties of open and closed discrete curves treated by Gauss, Caligarneau, Berger, and Prior; and (iv) the change of absolute helicity by resistive diffusion. These are important hydromagnetic properties of twisted magnetic fields in the million-degree hot, highly conducting corona of the Sun.
Comment on “Chaotic electron trajectories in an electromagnetic wiggler free-electron laser with ion-channel guiding” [Phys. Plasmas 17, 093103 (2010)]
Authors: Nasr N. , Hasanbeigi A.
Published: May 2011

The chaotic electron dynamics in a free-electron laser with electromagnetic-wave wiggler and ion-channel has been recently reported by A. Taghavi et al. [Phys. Plasmas 17, 093103 (2010)]. We comment on the authors use of a set of initial condition that is not correct based on the dispersion relation and steady-state orbits.
Response to “Comment on ‘Chaotic electron trajectories in an electromagnetic wiggler free-electron laser with ion-channel guiding’” [Phys. Plasmas 17, 093103 (2010)]
Authors: Esmaeilzadeh Mahdi , Taghavi Amin
Published: May 2011

Nasr and Hasanbeigi in their comment [Phys. Plasmas 17, 093103 (2010)] have claimed that, in our recent paper [Phys. Plasmas 17, 093103 (2010)], incorrect initial conditions have been used based on dispersion relation (or normalized electromagnetic wave frequency ω−w) and mean axial velocity βb. We use a self-consistent method to calculate more accurate values of ω−w and βb and show that all results presented in our recent paper are correct.
Shear flow-driven electrostatic instabilities in low density and low temperature pair-ion plasmas with and without electrons
Authors: Saleem H. , Batool N. , Poedts S.
Published: May 2011

The shear flow-driven electrostatic instabilities are investigated in ideal low density, low temperature pair-ion-electron and pure pair-ion plasmas in several different cases, including homogeneous and inhomogeneous density effects. In uniform pair-ion-electron plasma, when the shear flow is of the order of the acoustic speed, the purely growing D’Angelo mode can give rise to electrostatic fields. In the case of an inhomogeneous plasma, the drift wave becomes unstable. The presence of negative ions, however, reduces the growth rate. If the positive and negative ions are not in thermal equilibrium with each other, then the shear flow also gives rise to an electrostatic instability in pure pair-ion plasma.
The plasma drag and dust motion inside the magnetized sheath
Authors: Pandey B. P. , Vladimirov S. V. , Samarian A.
Published: May 2011

The motion of micron size dust inside the sheath in the presence of an oblique magnetic field is investigated by self-consistently calculating the charge and various forces acting on the dust. It is shown that the dust trajectory inside the sheath, which is like an Archimedean spiral swinging back and forth between the wall and the plasma–sheath boundary, depends only indirectly on the orientation of the magnetic field. When the Lorentz force is smaller than the collisional momentum exchange, the dust dynamics is insensitive to the obliqueness of the magnetic field. Only when the magnetic field is strong enough, the sheath structure and, thus, the dust dynamics are significantly affected by the field orientation. Balance between the plasma drag, sheath electrostatic field, and gravity plays an important role in determining how far the dust can travel inside the sheath. The dust equilibrium point shifts closer to the wall in the presence of gravity and plasma drag. However, in the absence of plasma drag, dust can sneak back into the plasma if acted only by gravity. The implication of our results to the usability of dust as a sheath probe is discussed.
Many-body dissipative particle dynamics simulation of liquid/vapor and liquid/solid interactions
Authors: Arienti Marco , Pan Wenxiao , Li Xiaoyi , Karniadakis George
Published: May 2011

The combination of short-range repulsive and long-range attractive forces in many-body dissipative particle dynamics (MDPD) is examined at a vapor/liquid and liquid/solid interface. Based on the radial distribution of the virial pressure in a drop at equilibrium, a systematic study is carried out to characterize the sensitivity of the surface tension coefficient with respect to the inter-particle interaction parameters. For the first time, the approximately cubic dependence of the surface tension coefficient on the bulk density of the fluid is evidenced. In capillary flow, MDPD solutions are shown to satisfy the condition on the wavelength of an axial disturbance leading to the pinch-off of a cylindrical liquid thread; correctly, no pinch-off occurs below the cutoff wavelength. Moreover, in an example that illustrates the cascade of fluid dynamics behaviors from potential to inertial-viscous to stochastic flow, the dynamics of the jet radius is consistent with the power law predictions of asymptotic analysis. To model interaction with a solid wall, MDPD is augmented by a set of bell-shaped weight functions; hydrophilic and hydrophobic behaviors, including the occurrence of slip in the latter, are reproduced using a modification in the weight function that avoids particle clustering. The dynamics of droplets entering an inverted Y-shaped fracture junction is shown to be correctly captured in simulations parametrized by the Bond number, confirming the flexibility of MDPD in modeling interface-dominated flows.
Generation of ultraintense proton beams by multi-ps circularly polarized laser pulses for fast ignition-related applications
Authors: Badziak J. , Mishra G. , Gupta N. K. , Holkundkar A. R.
Published: May 2011

A scheme of generation of ultraintense proton beams relevant for proton fast ignition (PFI) which employs multi-ps, circularly polarized laser pulse irradiating a thick (≥ 10 μm) H-rich target is proposed and examined using one-dimensional particle-in cell-simulations. It is shown that a 5-ps laser pulse of intensity ∼ (2–5) × 1020W/cm2 irradiating the target of the areal proton density ∼ 2 × 1020cm−2 can produce – with a high energetic efficiency – a proton beam (plasma block) of parameters (intensity, energy fluence, pulse duration, proton energy spectrum) close to those required for PFI. At a fixed total laser energy, the proton beam parameters can be controlled and fitted to the PFI requirements by changing the laser intensity (energy fluence) and/or the target thickness as well as by using a shaped (curved) target inserted into a guiding cone.
Electromagnetic effects of kinetic geodesic acoustic mode in tokamak plasmas
Authors: Wang Lingfeng , Dong J. Q. , Shen Y. , He H. D.
Published: May 2011

Electromagnetic effects of the kinetic geodesic acoustic modes (KGAMs) are numerically studied in low β(= plasma pressure/magnetic pressure) tokamak plasmas. The parallel component of the perturbed vector potential is considered along with the electrostatic potential perturbation. The finite Larmor radius and finite orbit width of the ions as well as electron parallel dynamics are all taken into account. Systematic harmonic and ordering analysis is performed for collisionless damping of the KGAMs, assuming β~(κρi)2, where κand ρiare the radial component of the KGAM wave vector and the Larmor radius of the ions, respectively. It is found that the electron parallel dynamics enhances the damping of the electrostatic KGAM modes when the safety factor q is high. In addition, the electromagnetic (finite β effect is revealed to enhance and weaken the damping of the modes in plasmas of low and high safety factor q~2.0 and 5.5, respectively. The harmonic features of the KGAMs are discussed as well.
Domain engineered ferroelectric energy harvesters on a substrate
Authors: Münch I. , Krauß M. , Landis C. M. , Huber J. E.
Published: May 2011

Phase-field modeling is used to study the domain evolution of nano-scaled ferroelectric devices influenced by the mechanical strain of an underlying substrate. The investigations focus on the design of the energy harvesting systems to convert mechanical into electrical energy. Mechanical energy is provided by an alternating in-plane strain in the substrate through bending or unidirectional stretching. Additionally, lattice mismatch between the substrate and the ferroelectric material induces epitaxial strain and controls the polarization behavior within the system. Further, electrical boundary conditions are used to stabilize the domain topology. Finite element simulations are employed to explore the performance of the engineered domain topologies in delivering electrical charge from mechanical deformation.
Free radicals created by plasmas cause autohesive bonding in polymers
Authors: Awaja Firas , McKenzie David R. , Zhang Shengnan , James Natalie
Published: May 2011

We find that plasma immersion ion implantation of polymer surfaces enhances their autohesive bond strength when pressed together by more than a factor of five. Both polymerising (CH4/O2) and nonpolymerising (Ar) plasmas are effective. There is currently no satisfactory theory for predicting this remarkable phenomenon. We propose that free radicals created by the plasma treatment process diffuse to the interface and cause covalent bonds to form. This theory predicts the dependence of bond strength on plasma bias voltage, treatment time, and autohesive process conditions.
Vertical mixing in homogeneous sheared stratified turbulence: A one-dimensional-turbulence study
Authors: Gonzalez-Juez Esteban D. , Kerstein Alan R. , Shih Lucinda H.
Published: May 2011

We conduct a parametric study of diapycnal mixing using one-dimensional-turbulence (ODT) simulations. Homogeneous sheared stratified turbulence is considered. ODT simulations reproduce the intermediate and energetic regimes of mixing, in agreement with previous work, but do not capture important physics of the diffusive regime. ODT indicates Kρ~ɛ/N2 for the intermediate regime, and Kρ~(ɛh4)1/3 for the energetic regime and limit of near-zero stratification. Here Kρ is the turbulent diffusivity for mass, ɛ the dissipation rate, N the buoyancy frequency, and h the computational domain height, where h is relevant mainly in simulations with jump-periodic vertical boundary conditions. These scaling relationships suggest that Kρ is independent of the molecular diffusivity. ODT results for a wide range of parameters show that Kρ cannot be parametrized solely with the turbulent intensity parameter ɛ/(νN2), in contrast with the previous studies, but it is well predicted by correlations using the Ellison length scale.
Effective mobility of single-layer graphene transistors as a function of channel dimensions
Authors: Venugopal Archana , Chan Jack , Li Xuesong , Magnuson Carl W. , Kirk Wiley P. , Colombo Luigi , Ruoff Rodney S. , Vogel Eric M.
Published: May 2011

A detailed analysis of the extracted back gated FET mobility as a function of channel length, channel width, and underlying oxide thickness for both exfoliated and chemical vapor deposited (CVD) graphene is presented. The mobility increases with increasing channel length eventually saturating at a constant value for channel lengths of several micrometers. The length dependence is consistent with the transition from a ballistic to diffusive transport regime. The mobility as a function of channel width first increases and then decreases. The increase in mobility for very small channel widths is consistent with a reduction in edge scattering. The decrease in mobility for larger channel widths is observed to be strongly dependent on the oxide thickness suggesting that electrostatics associated with fringing fields is an important effect. This effect is further confirmed by a comparative analysis of the measured mobility of graphene devices with similar channel dimensions on oxides of different thicknesses. The observed electrical measurements are in excellent agreement with theoretical studies predicting the width dependence of conductivity and mobility. The mobility of CVD grown graphene is slightly lower than that of exfoliated graphene but shows similar trends with length and width. The mobility values reported in the literature are in agreement with the trend reported here.
Photorefractive space charge electric field in GaAs:Cr with external electric and magnetic fields
Authors: Sharma Dheeraj , Mohan Devendra , Gupta Umesh
Published: May 2011

Using band charge transport model, the effect of external dc electric (E0) and magnetic fields (B0) on photorefractive parameters, viz, space charge electric field (ESC) and gain coefficient in steady state regime is investigated for Cr doped GaAs. In particular, space charge electric field of ∼105 V/cm is obtained for E0=5.0×102 V/cm and B0=0.064 T. ESC obtained is nearly 103 times higher than, in absence of either E0 or B0. The gain coefficient exhibits considerable enhancement at above values of E0 and B0.
Molecular dynamics simulations of nucleation from vapor to solid composed of Lennard-Jones molecules
Authors: Tanaka Kyoko K. , Tanaka Hidekazu , Yamamoto Tetsuo , Kawamura Katsuyuki
Published: May 2011

We performed molecular dynamics (MD) simulations of nucleation from vapor at temperatures below the triple point for systems consisting of 104-105 Lennard-Jones (L-J) type molecules in order to test nucleation theories at relatively low temperatures. Simulations are performed for a wide range of initial supersaturation ratio (S0 ≃ 10 − 108) and temperature (kT = 0.2 − 0.6ε), where ε and k are the depth of the L-J potential and the Boltzmann constant, respectively. Clusters are nucleated as supercooled liquid droplets because of their small size. Crystallization of the supercooled liquid nuclei is observed after their growth slows. The classical nucleation theory (CNT) significantly underestimates the nucleation rates (or the number density of critical clusters) in the low-T region. The semi-phenomenological (SP) model, which corrects the CNT prediction of the formation energy of clusters using the second virial coefficient of a vapor, reproduces the nucleation rate and the cluster size distributions with good accuracy in the low-T region, as well as in the higher-T cases considered in our previous study. The sticking probability of vapor molecules onto the clusters is also obtained in the present MD simulations. Using the obtained values of sticking probability in the SP model, we can further refine the accuracy of the SP model.
Electromechanical wavelength tuning of double-membrane photonic crystal cavities
Authors: Midolo L. , van Veldhoven P. J. , Dündar M. A. , Nötzel R. , Fiore A.
Published: May 2011

We present a method for tuning the resonant wavelength of photonic crystal cavities (PCCs) around 1.55 μm. Large tuning of the PCC mode is enabled by electromechanically controlling the separation between two parallel InGaAsP membranes. A fabrication method to avoid sticking between the membranes is discussed. Reversible red/blueshifting of the symmetric/antisymmetric modes has been observed, which provides clear evidence of the electromechanical tuning, and a maximum shift of 10 nm with <6 V applied bias has been obtained.
Modeling the electrical resistance of gold film conductors on uniaxially stretched elastomeric substrates
Authors: Cao Wenzhe , Görrn Patrick , Wagner Sigurd
Published: May 2011

The electrical resistance of gold film conductors on polydimethyl siloxane substrates at stages of uniaxial stretching is measured and modeled. The surface area of a gold conductor is assumed constant during stretching so that the exposed substrate takes up all strain. Sheet resistances are calculated from frames of scanning electron micrographs by numerically solving for the electrical potentials of all pixels in a frame. These sheet resistances agree sufficiently well with values measured on the same conductors to give credence to the model of a stretchable network of gold links defined by microcracks.
A volume averaging approach for asymmetric diffusion in porous media
Authors: Valdés-Parada Francisco J. , Alvarez-Ramírez José
Published: May 2011

Asymmetric diffusion has been observed in different contexts, from transport in stratified and fractured porous media to diffusion of ions and macromolecular solutes through channels in biological membranes. Experimental and numerical observations have shown that diffusion is facilitated in the direction of positive void fraction (\documentclass[12pt]{minimal}\begin{document}$\text{i.e.}$\end{document}i.e., porosity) gradients. This work uses the method of volume averaging in order to obtain effective medium equations for systems with void fraction gradients for passive and diffusive mass transport processes. The effective diffusivity is computed from the solution of an associated closure problem in representative unit cells that allow considering porosity gradients. In this way, the results in this work corroborate previous findings showing that the effective diffusivity exhibits important directional asymmetries for geometries with void fraction gradients. Numerical examples for simple geometries (a section with an obstacle and a channel with varying cross section) show that the diffusion asymmetry depends strongly on the system configuration. The magnitude of this dependence can be quantified from the results in this work.
An extended study of the phase separation between phospholipids and grafted polymers on a bilayer biomembrane
Authors: Benhamou M , Joudar I , Kaidi H , Elhasnaoui K , Ridouane H , Qamar H
Published: May 2011

We re-examine here the phase separation between phospholipids and adsorbed polymer chains on a fluid membrane with a change in some suitable parameter (temperature). Our purpose is to quantify the significant effects of the solvent quality and of the polydispersity of adsorbed loops formed by grafted polymer chains on the segregation phenomenon. To this end, we elaborate on a theoretical model that allows us to derive the expression for the mixing free energy. From this, we extract the phase diagram shape in the composition–temperature plane. Our main conclusion is that the polymer chain condensation is very sensitive to the solvent quality and to the polydispersity of loops of adsorbed chains.