bluuebunny/crossref_metadata_2025 huggingface dataset:
Diurnal oscillation in the accumulation of Arabidopsis microRNAs, miR167, miR168, miR171 and miR398
Authors: Siré Christelle , Moreno Ana Beatriz , Garcia-Chapa Meritxell , López-Moya Juan José , Segundo Blanca San
Published: February 2009

MicroRNAs (miRNAs) are small RNAs acting as regulators of eukaryotic gene expression at the post‐transcriptional level. Plant miRNAs have been implicated in developmental processes and adaptation to the environment. We show that the accumulation of four Arabidopsis miRNAs (miR171, miR398, miR168 and miR167) oscillates during the diurnal cycle, their accumulation increasing during the light period of the daytime and decreasing in darkness. This oscillatory pattern of miRNA accumulation is not governed by the circadian clock. These results suggest a potential role of light in controlling miRNA accumulation while defining a new level of regulation of miRNA gene expression in Arabidopsis.
Regulation of chondrocytic phenotype by micro RNA 18a: Involvement of Ccn2/Ctgf as a major target gene
Authors: Ohgawara Toshihiro , Kubota Satoshi , Kawaki Harumi , Kondo Seiji , Eguchi Takanori , Kurio Naito , Aoyama Eriko , Sasaki Akira , Takigawa Masaharu
Published: February 2009

We searched for miRNAs that were down‐regulated in chondrocytic cells and predicted to target CCN2/connective tissue growth factor (CCN2/CTGF) that promotes endochondral ossification. Among them, expression of miR‐18a was most strongly repressed in chondrocytic cells. Reporter gene analysis confirmed the functionality of an miR‐18a target in the 3′‐untranslated region of Ccn2 mRNA, which was predicted in silico. Indeed, introduction of miR‐18a efficiently repressed the CCN2 production from chondrocytic cells. Finally, transfected miR‐18a significantly repressed the mature chondrocytic phenotype. Our present study revealed a regulatory role for miR‐18a in chondrocytic differentiation through CCN2.
Single‐channel study of the binding–gating coupling in the slowly desensitizing chimeric α7‐5HT3A receptor
Authors: Bernal José Antonio , Mulet José , Castillo Mar , Criado Manuel , Sala Francisco , Sala Salvador
Published: February 2009

We have studied the role of the highly conserved residue αLysine145 in the early steps of activation by acetylcholine of the nicotinic acetylcholine receptor (nAChR). Both macroscopic and single‐channel currents were recorded in the slowly desensitizing chimeric mutant receptor α7V201‐5HT3A/R432Q/R436D/R440A, made of α7 nAChRs and serotonin receptors of subtype 3A (ch1), and its corresponding mutant K145A (ch1/K145A) expressed inXenopusoocytes. Mutant ch1/K145A receptors had a reduced gating function similar to that produced by the same mutation in the wild type receptor α7. The mutated receptor has reduced opening rate constants,β, and increased closing rate constants,α.
Suppression of Tie‐1 in endothelial cells in vitro induces a change in the genome‐wide expression profile reflecting an inflammatory function
Authors: Chan Barden , Sukhatme Vikas P.
Published: February 2009

Tie‐1 is an endothelial specific receptor tyrosine kinase that is upregulated in diseases such as atherosclerosis and rheumatoid arthritis. We recently demonstrated that Tie‐1 induced a proinflammatory response when overexpressed in endothelial cells. Here, we used a complementary approach and suppressed endogenous Tie‐1 expression in endothelial cells to examine its function by microarray analysis. Tie‐1 appeared to govern expression of many genes involved in inflammation. Expression knockdown of Tie‐1 significantly reduced endothelial conditioned medium ability to stimulate MCP‐1 production in U937 cells. Collectively, our results support the notion that Tie‐1 has an inflammatory function in endothelial cells.
Ovine fetal hormonal and hypothalamic neuroendocrine responses to maternal water deprivation at late gestation
Authors: Zhu Liyan , Mao Caiping , Wu Jiawei , Guan Junchang , Wan Zhen , Liu Yujuan , Xu Feichao , Zhou Yun , Feng Xing , Xu Zhice
Published: February 2009

Angiotensin II (Ang II), aldosterone, and arginine‐vasopressin (AVP) are three major neuropeptides or hormones that are important in the control of body fluid regulation. Dehydration during pregnancy induces alterations in maternal–fetal fluid homeostasis. It is still not clear about effects and mechanisms of maternal water deprivation on fetal neuroendocine and hormonal responses. The present study deprived water from pregnant sheep at near‐term for 24 h and 48 h, and determined maternal and fetal blood osmolality and sodium levels before and immediately after water deprivation. Fetal renal excretion and plasma hormones were measured. Fetal forebrain was analyzed for cellular activation marked with Fos and Fos‐B. The results showed that maternal and fetal blood osmolality and sodium were increased by water deprivation. Maternal and fetal Ang II, aldosterone, and AVP levels were elevated by 24‐h and 48‐h water deprivation, while fetal plasma Ang I levels were increased only under the condition of 48‐h water deprivation. Intensive Fos and Fos‐B expression was detected in the median preoptic nuclei and paraventricular nuclei in the fetal brain following exposure to maternal water deprivation. Double labeling demonstrated that many Fos‐positive cells were AVP‐containing neurons in the fetal paraventricular nucleus. Together, the results suggest that neuroendocrine and hormonal regulatory mechanisms play a role in the control of body fluid homeostasis, and relatively matured and functional at the last third of gestation, as well as the fetal hypothalamus is functional in the control of the neuropeptide in response to maternal dehydration.
Technique and diagnostic utility of saline infusion sonohysterography
Authors: Elsayes Khaled M. , Pandya Amit , Platt Joel F. , Bude Ronald O.
Published: February 2009

The introduction of saline infusion sonohysterography has significantly improved sonographic diagnosis of various endometrial pathologies. This procedure entails instillation of warm saline into the uterine cavity transcervically to provide enhanced visualization of the endometrium during transvaginal ultrasound examination. This article reviews the sonohysterography technique and current utility, as well as the spectrum of imaging features of various endometrial pathologies.
Effects of visceral peritoneal closure on scar formation at cesarean delivery
Authors: Malvasi Antonio , Tinelli Andrea , Farine Dan , Rahimi Siavash , Cavallotti Carlo , Vergara Daniele , Martignago Roberta , Stark Michael
Published: February 2009

Objective

To determine the effect of closure or non‐closure of the visceral peritoneum at cesarean delivery on uterine scar formation assessed at repeat cesarean delivery.

Methods

Women undergoing initial cesarean delivery were allocated into 2 groups: group 1 underwent visceral peritoneal closure, while in group 2 the visceral peritoneum was not closed. At repeat cesarean delivery 4 specimens from the initial uterine scar were collected and assessed by light microscopy and scanning electron microscopy.

Results

In group 1, 57% of women had adhesions compared with 20.6% in group 2 (P < 0.05). Light microscopy revealed reactive mesothelial hyperplasia (51.8% vs 13.7%), submesothelial fibrosis (48.1% vs 6.8%), and neoangiogenesis of mesothelial stroma (44.4% vs 12%) in group 1 and group 2 patients, respectively (P < 0.05). Scanning electron microscopy showed more patients with pericytes on the surface of microvessels in group 1 compared with group 2 (26.3 ± 1.4 vs 11.5 ± 1.1 patients; P < 0.05).

Conclusion

Closure of the visceral peritoneum at cesarean delivery may produce an inflammatory reaction and adhesions, evidenced by reactive and regenerative mesothelial hyperplasia and submesothelial fibrosis.
Reducing maternal mortality among Afghan refugees in Pakistan
Authors: Purdin Susan , Khan Tila , Saucier Roxanne
Published: February 2009

Objective

The International Rescue Committee (IRC) strove to reduce maternal mortality among Afghan refugees in Hangu district of Pakistan by improving access to emergency obstetric care (EmOC), community knowledge of danger signs of pregnancy, and the use of health information.

Methods

IRC established EmOC centers, trained community members on safe motherhood, linked primary health care with education on danger signs of pregnancy and the importance of skilled attendance, and improved the health information system.

Results

The maternal mortality ratio among Afghan refugees in the area improved from 291 per 100 000 live births in 2000 to 102 per 100 000 live births in 2004. The proportion of refugee births attended by skilled staff increased from 5% in 1996 to 67% in 2007. Complete prenatal care coverage increased from 49% in 2000 to 90% in 2006, and postnatal coverage more than trebled from 27% in 2000 to 85% in 2006.

Conclusion

Improved services, community involvement and education, good coordination, and effective systems succeeded in reducing maternal mortality in a traditionally conservative environment.
Doppler analysis of uterine perfusion and ovarian stromal blood flow in polycystic ovary syndrome
Authors: Adali Ertan , Kolusari Ali , Adali Fulya , Yildizhan Recep , Kurdoglu Mertihan , Sahin Hanim Guler
Published: February 2009

Objective

To investigate blood flow velocity in the ovarian stromal artery and uterine artery in women with polycystic ovary syndrome (PCOS) and to correlate these velocities with clinical and biochemical parameters.

Methods

A prospective study was carried out in 55 patients with PCOS and 42 age‐matched women who did not have PCOS. Clinical, biochemical, and hormonal characteristics, and utero–ovarian Doppler ultrasound blood flow parameters were determined, and correlations between the parameters were evaluated.

Results

Ovarian stromal blood flow was higher (P < 0.01) and uterine perfusion was lower (P < 0.01) in women with PCOS compared with women who did not have PCOS. Ovarian stromal artery pulsatility index (PI) was inversely correlated with levels of dehydroepiandrosterone sulfate (DHEAS) and insulin‐like growth factor‐1, and with the luteinizing hormone/follicle‐stimulating hormone ratio. There was a positive correlation between uterine artery PI and DHEAS level.

Conclusion

Doppler analysis of the uterine and intraovarian arteries may provide additional information about the etiopathogenesis of PCOS and partly explain the clinical implications of the condition.
Evidence‐based maternal and perinatal healthcare practices in public hospitals in Argentina
Authors: Karolinski Ariel , Micone Paula , Mercer Raúl , Gibbons Luz , Althabe Fernando , Belizán José M. , Messina Analía , Lapidus Alicia , Correa Alberto , Taddeo Corina , Lambruschini Rodolfo , Bertin Marta , Dibiase Lucía , Montes Varela Dolores , Laterra Cristina
Published: February 2009

Objective

To investigate the use of beneficial maternal and perinatal healthcare practices in a network of public maternity hospitals in Argentina.

Method

A multicenter, prospective, descriptive study of 6661 deliveries in 9 hospitals. The use of 5 obstetric care practices that reduce maternal and perinatal morbidity and mortality was evaluated.

Results

Median use rates for the selected practices were: continuous support for women during childbirth (17.9%); corticosteroids for preterm birth (35.3%); avoidance of episiotomy in primiparous women (41.2%); iron and folate supplementation (52.5%); active management of third stage of labor (93.5%).

Conclusion

There is limited use of the selected evidence‐based maternal and perinatal practices in public hospitals in Argentina and a large variation in their use among and within hospitals. Efforts should be made to increase the use of these evidence‐based practices.
Uterine artery embolization versus laparoscopic occlusion of uterine vessels for management of symptomatic uterine fibroids
Authors: Ambat Sreekrishnakiran , Mittal Suneeta , Srivastava Deep N. , Misra Renu , Dadhwal Vatsla , Ghosh Bhaswati
Published: February 2009

Objective

To evaluate the efficacy and complications of uterine artery embolization (UAE) versus laparoscopic occlusion of uterine vessels (LOUV) in the management of symptomatic fibroids.

Methods

A pilot randomized clinical trial in which 20 patients with symptomatic fibroids were randomly allocated into two groups. Ten women underwent UAE, and 10 women underwent LOUV. Symptomatic improvement in menorrhagia and reduction in the volumes of the uterus and the fibroid were assessed at 3 and 6 months.

Results

The patients were comparable with regard to age and parity. At 6 months, there was no significant difference in the mean reduction in menstrual blood loss, uterine volume, and volume of the dominant fibroid between the two groups (P = 0.436, P = 0.796, P = 1.00, respectively). However, higher pain scores were recorded on day 1 in the UAE group compared with the LOUV group (P = 0.0002).

Conclusions

The effects of UAE and LOUV in the management of symptomatic fibroids are comparable. The main advantage of LOUV is less postoperative pain compared with UAE.
Breastfeeding and contraception use among women with unplanned pregnancies less than 2 years after delivery
Authors: Tilley Ian B. , Shaaban Omar M. , Wilson Melissa , Glasier Anna , Mishell Daniel R.
Published: February 2009

Objective

To examine breastfeeding and contraceptive use after the lactational amenorrhea method (LAM) criteria were no longer met.

Methods

Two hundred and thirty‐three parous Egyptian women with unplanned pregnancies less than 2 years after delivery completed a questionnaire examining breastfeeding practice and contraceptive use.

Results

The majority of women (81.5%) with unplanned pregnancies within 2 years of delivery were breastfeeding at conception. Of these women, 36.3% had used a method of contraception other than LAM compared with 60.5% of women who had weaned (P < 0.05). Among the breastfeeding women, 61.2% failed to use contraception because they believed breastfeeding would prevent pregnancy.

Conclusion

Breastfeeding women with unplanned pregnancies were less likely to have used contraception than women who had weaned, suggesting that prolonged breastfeeding contributes to unmet contraceptive need.
Obstetricians' opinions and attitudes toward maternal refusal of recommended cesarean delivery in Nigeria
Authors: Chigbu Chibuike O. , Ezenyeaku Cyril C. , Ezenkwele Eziamaka
Published: February 2009

Objective

To assess the opinions and attitudes of Nigerian obstetricians toward women's refusal of cesarean delivery.

Method

We used a questionnaire with 5 clinical scenarios drawn from published cases in which Nigerian women refused to undergo a recommended cesarean delivery.

Results

Most obstetricians (84.8%) advocated continuous counseling of these women but, from their response to the scenarios, few (13.7%–16.1%) would actually do so. Insufficient facilities and poor logistics for emergency obstetric care were their stated major reason for not respecting maternal choices in situations where vaginal delivery could have been given a chance.

Conclusion

The possibility of providing emergency obstetric care would remove many indications for cesarean delivery from the list of absolute indications in Nigeria; and management guidelines would protect obstetricians in the event of litigation, and improve their acceptance and respect of maternal choice.
Effect of treatment with dydrogesterone or calcium plus vitamin D on the severity of premenstrual syndrome
Authors: Khajehei Marjan , Abdali Khadijeh , Parsanezhad Mohammad Ebrahim , Tabatabaee Hamid Reza
Published: February 2009

Objective

To compare the effects of dydrogesterone and calcium plus vitamin D in women with severe premenstrual syndrome (PMS).

Method

In this randomized, double‐blind, placebo‐controlled study, 180 Shiraz University students with PMS used questionnaires daily to rate their symptoms for 2 menstrual cycles. Then, the students were randomly assigned to take a tablet containing either 5 mg of dydrogesterone, 500 mg of calcium plus 200 mg of vitamin D, or a placebo twice daily from the 15th to the 24th day of the cycle for 2 more cycles, and to use the same questionnaires during the intervention cycles. The collected data were then analyzed by repeated‐measurement design and multilevel modeling tests.

Result

Treatment with dydrogesterone or calcium plus vitamin D decreased symptom severity in a similar way (by 4.64% and 4.20%, respectively) and placebo was associated with a 3.42% decrease.

Conclusion

Treatment with dydrogesterone or calcium plus vitamin D had a similar effect on symptom severity in women with PMS.
Hereditary ovarian carcinoma: Heterogeneity, molecular genetics, pathology, and management
Authors: Lynch Henry T. , Casey Murray Joseph , Snyder Carrie L. , Bewtra Chhanda , Lynch Jane F. , Butts Matthew , Godwin Andrew K.
Published: February 2009

Hereditary ovarian cancer accounts for at least 5% of the estimated 22,000 new cases of this disease during 2009. During this same time, over 15,000 will die from malignancy ascribed to ovarian origin. The bulk of these hereditary cases fits the hereditary breast–ovarian cancer syndrome, while virtually all of the remainder will be consonant with the Lynch syndrome, disorders which are autosomal dominantly inherited. Advances in molecular genetics have led to the identification of BRCA1 and BRCA2 gene mutations which predispose to the hereditary breast–ovarian cancer syndrome, and mutations in mismatch repair genes, the most common of which are MSH2 and MLH1, which predispose to Lynch syndrome. These discoveries enable relatively certain diagnosis, limited only by their variable penetrance, so that identification of mutation carriers through a comprehensive cancer family history might be possible. This paper reviews the subject of hereditary ovarian cancer, with particular attention to its molecular genetic basis, its pathology, and its phenotypic/genotypic heterogeneity.
Epitympanoplasty with mastoid obliteration technique: A long‐term study of results
Authors: Kang Myung‐Koo , Ahn Joong‐Ki , Gu Tae‐Woo , Han Chi‐Sung
Published: February 2009

Objective

To report the long‐term results of epitympanoplasty with mastoid obliteration technique.

Subjects and Methods

Two hundred adult cases had undergone epitympanoplasty with mastoid obliteration from December 1994 to May 2003. The mean postoperative observation period was 91 months, with a minimum of five years. Epitympanoplasty with mastoid obliteration technique has four major procedures: the widening of the external auditory canal and removal of the scutum; preservation of the posterior canal wall; epitympanoplasty; and mastoid obliteration. We examined postoperative complications and hearing outcomes.

Results

There was no retraction pocket formation and recurrence of cholesteatoma. Residual cholesteatoma in the tympanic cavity was seen in 10 cases (5%) and three cases were seen in the mastoid cavity (1.5%). Other complications were otorrhea (15 cases), perforation (8 cases), material extrusion (6 cases), and posterior auricular infection (4 cases). The average preoperative pure tone air‐bone gap, postoperative pure tone air‐bone gap, and air‐bone gap closure were 31.5 ± 12.4 dB, 25.3 ± 12.2 dB, and 6.2 ± 12.6 dB, respectively. There were significant differences between the preoperative and postoperative values (P < 0.01).

Conclusions

The authors believe that epitympanoplasty with mastoid obliteration technique can combine the advantages of canal wall down and canal wall up techniques while improving their shortcomings.
Island arc–back-arc basin evolution: implications for Late Riphean–Early Paleozoic geodynamic history of the Sayan–Baikal folded area
Authors: Zorin Yu.A. , Sklyarov E.V. , Belichenko V.G. , Mazukabzov A.M.
Published: February 2009

We suggest a more rigorous approach to paleogeodynamic reconstructions of the Sayan-Baikal folded area proceeding from update views of the origin and evolution of island arcs and back-arc basins. Modern island arcs and attendant back-arc basins form mainly by trench rollback caused by progressive subduction of negatively buoyant thick and cold oceanic slabs. Slab stagnation upsets the dynamic equilibrium in the subduction system, which accelerates the rollback. As a result, a continental volcanic arc transforms into an island arc, with oceanic crust production in the back-arc basin behind it. As subduction progresses, the island arc and the back-arc basin may deform, and fold-thrust structures, with the involved back-arc basin and island arc complexes, may accrete to the continent (accretion and collision) without participation of large colliding blocks. When applied to the Sayan–Baikal area, the model predicts that the Riphean and Vendian–Early Paleozoic back-arc basins were more active agents in the regional geologic history than it was thought before. They were deposition areas of sedimentary and volcanosedimentary complexes and then became the scene of collision and accretion events, including folding, metamorphism, and plutonism.
Optimization fitting of the eccentric dipole models to the observed geomagnetic field
Authors: Ladynin A.V. , Popova A.A.
Published: February 2009

We have obtained formulas to calculate the field components of an eccentric dipole (ED) with an arbitrarily directed moment from specified coordinates of the dipole center and from its moment vector. With these formulas, the model dipole position was fitted to the observed geomagnetic field, and the approximation accuracy was estimated according to the standard deviation from IGRF along the X, Y, and Z components; the fitting procedure was checked in several tests.

We computed the ED parameters (position and moment orientation) and harmonic coefficients of the ED field for 50 years using surface IGRF components, discovered some changes, and compared them with those according to the Schmidt eccentric dipole model. It was found that the nondipolar contributions to the geomagnetic field increase as the dipole field decays with time, and the dipole center drifts northand eastward away from the Earth’s gravity center.

The main contribution of the dipole part in the Gaussian spherical harmonic expansion of the geomagnetic field turned out to come from the terms with n of 1 to 5 rather than from two first terms, and the contribution of higher harmonics increases with time. Therefore, the Schmidt ED approximation based on the first eight Gauss coefficients (n≤ 2) must have only relative significance indicating changes of the parameters. On the other hand, world magnetic anomalies (WMA) show up already in two first Gauss terms rather than since the third term as it has been commonly assumed.
Deformation and seismic effects in the ice cover of Lake Baikal
Authors: Ruzhich V.V. , Psakhie S.G. , Chernykh E.N. , Bornyakov S.A. , Granin N.G.
Published: February 2009

The mechanics of the ice cover of Lake Baikal has been studied through monitoring of its deformation and seismic effects and full-size uniaxial compression and shear tests in 2005–2007. We measured the shear strength of ice specimens and large in situ blocks (σ = 0.2−1.9 MPa) and investigated it as a function of air temperature and ice structure. Deformation was analyzed in terms of various natural controls, such as air temperature and pressure, wind, sub-ice currents, and local earthquakes. Precise strain measurements along ice cracks were used to explore the strain behavior of ice, including the cases of dynamic failure (ice shocks). Measurements by seismic station Baikal-12 were used to monitor diurnal background microseismicity variations and to record an ice quake with its magnitude (M = 0.3–0.8; E = 104–105 J) comparable to a medium-size rock burst or a small earthquake. Ice quakes were studied in terms of their nucleation, dynamics, and aftereffects, as well as the strain and seismic responses of the ice, using sub-ice explosions in the latter case. The natural conditions of deformation in the elastoviscoplastic Baikal ice are similar to lithospheric processes and thus can be employed in tectonophysical modeling with scientific and practical implications for hazard mitigation.
Gold in the weathering crust at the Suzdal’ deposit (Kazakhstan)
Authors: Kalinin Yu.A. , Kovalev K.R. , Naumov E.A. , Kirillov M.V.
Published: February 2009

A comparative analysis of morphology and geochemistry was made for gold from the primary ores and weathering crust of the Suzdal’ gold deposit, Eastern Kazakhstan. The deposit is localized in Carboniferous carbonaceous-terrigenous strata and is of gold-sulfide type. Study of gold from primary ores showed that it occurs mainly in two species: free and so-called invisible. Free gold is crystallomorphic segregations and irregular-shaped grains up to tens of microns in size; it occurs in intergrowths with sulfides, quartz, carbonate, and mica-chlorite aggregate. Most of gold particles have a fineness of 930–980‰, with some grains showing wide variations in composition. Invisible gold (probably chemically combined) is present in fine-acicular arsenopyrite and, less frequently, pyrite.

Being transported to the weathering crust, all this gold served as a source for “neogenic” gold of diverse morphologic forms. We recognized crystalline (isometric, prismatic, acicular, and tabular) particles and drusoid gold aggregates in the form of exotic intergrowths of crystallomorphic and sinter-shelly grains. The grains tend to coarsen from bottom to top of the weathering crust. Several generations of gold of different granulometric classes are observed. We have revealed seed and layer growth and dissolution structures in crystals of early generations overgrown with fine grains. All these gold varieties are associated with hypergene minerals. Most of this gold is of high fineness (on the average, 995‰). The hypergene gold particles are chemically homogeneous high-grade, without rims.

The results of studies suggest that the high-grade hypergene gold formed in the weathering crust as a result of the dissolution of invisible gold of sulfides and its local redistribution and deposition in oxidizing media. This is also evidenced from the tendency of gold to coarsen from bottom to top of the weathering crust. A distinctive feature of secondary gold is well-expressed crystals and their great diversity.
Applying the transmission line theory to study ungrounded horizontal loop self-transients
Authors: Kozhevnikov N.O.
Published: February 2009

Ungrounded horizontal loop responses at low frequencies and/or late times can be modeled in terms of an equivalent circuit with lumped elements, but a loop in a general case is a distributed system. At high frequencies and/or early times, the wire in combination with the underlying earth makes a transmission line in which current behaves according to the wave equation. Solving the equation for current turn-off is quite difficult because the primary parameters of the wire–earth system depend, in an intricate way, on earth conductivity (resistivity) and frequency (or time). In modeling the current turn-off process, the loop was simulated as a symmetrical combination of two identical transmission lines with shorted outputs. Modeling was performed in the frequency domain with subsequent transformation into the time domain. Comparison of measured and computed transient self responses showed that good fit requires taking into account (1) interaction of each line with its own image current, (2) mutual inductance of the two lines, and (3) skin effect in the wire. As a result of mutual inductance, the parameters of the lines and, hence, of the whole loop depend on local conductivity, which, at least in principle, may allow one to infer the resistivity of shallow subsurface from current turn-off responses. A real ungrounded horizontal loops lacks symmetry at early times and its magnetic field differs from that predicted by the conventional methods of induction soundings.
Preservation of heteronuclear multiple-quantum coherences in NMR by double-resonance irradiation
Authors: Verde Mariachiara , Ulzega Simone , Ferrage Fabien , Bodenhausen Geoffrey
Published: February 2009

A heteronuclear double-resonance (HDR) method based on MLEV-32 or WALTZ-32 pulse sequences has been designed for the investigation of relaxation of heteronuclear multiple-quantum (MQ) coherences. The theoretical analysis of this technique uses average Hamiltonian theory (AHT) to treat the effects of coherent evolution associated with scalar couplings, offsets, and inhomogeneous radiofrequency (rf) fields during the pulse sequence. Under most conditions, the dynamics of the MQ coherences during the HDR sequence is not affected by rf inhomogeneities and scalar couplings for offsets as large as the nutation frequency. The predictions drawn from AHT are supported by numerical simulations and experiments.
Time-resolved velocity map ion imaging study of NH3 photodissociation
Authors: Wells Kym L. , Perriam Gareth , Stavros Vasilios G.
Published: February 2009

Following excitation of the Ã state ν2′=4 mode in ammonia, we show how the time scale to dissociation of the N–H bond depends on the internal energy imparted to the NH2 photofragment. Using a combination of femtosecond pump/probe spectroscopy and velocity map ion imaging techniques, the time and energy resolved H-atom elimination can be directly related to the nonadiabatic nature of the photodissociation for high kinetic energy H atoms with evidence for adiabatic dynamics to dissociation giving the lowest energy H atoms. Extrapolation of the time scales for dissociation versus internal energy of the NH2 photofragment implies that dissociation to the vibrationless ground state of NH2 occurs in <50 fs, in very good agreement with frequency resolved measurements. The anisotropy of the H fragments with the highest kinetic energies seems to also suggest that the NH2 partner fragment comes off with very low rotational excitation.
Determining exciton coherence from the photoluminescence spectral line shape in poly(3-hexylthiophene) thin films
Authors: Spano Frank C. , Clark Jenny , Silva Carlos , Friend Richard H.
Published: February 2009

The photoluminescence (PL) spectral line shape of regioregular poly(3-hexylthiophene) thin films is analyzed using a model which treats the polymer π-stacks as H-aggregates with exciton-vibrational coupling and spatially correlated site disorder. The Stokes shift, linewidth, and relative vibronic peak intensities in the low-temperature PL spectrum (T=10K) are accurately reproduced, allowing the coherence function corresponding to the lowest energy (emitting) exciton to be determined from the ratio of the 0-0 to 0-1 peak intensities. The exciton migration length is determined from the N-dependent Stokes shift, where N is the number of segments comprising the stack. Based on the temperature dependence of the PL spectrum it is concluded that emission arises from a low concentration of aggregates which are more disordered than the dominant species responsible for absorption. The emissive aggregates are characterized by shorter average conjugation lengths and hence greater exciton bandwidths. The coherence length of the emitting exciton is estimated to be only three lattice spacings (≈1.1nm) along the π-stacking direction. By contrast, the exciton migration length for incoherent hopping between coherent domains is estimated to be approximately 15nm.
Periodic density functional theory and local-MP2 study of the librational modes of Ice XI
Authors: Erba Alessandro , Casassa Silvia , Dovesi Roberto , Maschio Lorenzo , Pisani Cesare
Published: February 2009

Two periodic codes, CRYSTAL and CRYSCOR, are here used to simulate and characterize the librational modes of the νR band of Ice XI: this band has been found experimentally to be the region of the vibrational spectrum of ordinary ice most affected by the transition from the proton-disordered (Ice Ih) to the proton-ordered (Ice XI) phase. With CRYSTAL, the problem is solved using Hartree–Fock (HF), pure Kohn–Sham (PW91) or hybrid (B3LYP) one-electron Hamiltonians: the harmonic approximation is employed to obtain the vibrational spectrum after optimizing the geometry. The B3LYP results are those in best agreement with the experiment. For a given crystalline geometry, CRYSCOR computes the energy per cell in an ab initio HF+MP2 approximation using a local-correlation approach; this technique is employed for recalculating the frequencies of the different modes identified by the B3LYP approach, by fully accounting for long range dispersive interactions. The effect of anharmonicity is evaluated separately for each mode both in the B3LYP and HF+MP2 case. The two approaches accurately reproduce the four-peak structure of the librational band. The harmonic B3LYP νR bandwidth of 70 meV is lowered to 60 meV by anharmonic corrections, and becomes 57 meV in the HF+MP2 anharmonic calculation, in excellent agreement with the experimental IINS data (56–59 meV). The assignment of the librational modes is discussed.
Evaporation into vacuum: Mass flux from momentum flux and the Hertz–Knudsen relation revisited
Authors: Hołyst Robert , Litniewski Marek
Published: February 2009

We performed molecular dynamics simulations of liquid film evaporation into vacuum for two cases: free evaporation without external supply of energy and evaporation at constant average liquid temperature. In both cases we found that the pressure inside a liquid film was constant, while temperature decreased and density increased as a function of distance from the middle of the film. The momentum flux in the vapor far from the liquid was equal to the liquid pressure in the evaporating film. Moreover the pseudopressure (stagnation pressure) was found to be constant in the evaporating vapor and equal to the liquid pressure. The momentum flux and its relation to the pressure determined the number of evaporating molecules per unit time and as a consequence the mass evaporation flux. We found a simple formula for the evaporation flux, which much better describes simulation results than the commonly used Hertz–Knudsen relation.
Enhanced light extraction efficiency of GaN-based light-emitting diodes with ZnO nanorod arrays grown using aqueous solution
Authors: Kim Kyoung-Kook , Lee Sam-dong , Kim Hyunsoo , Park Jae-Chul , Lee Sung-Nam , Park Youngsoo , Park Seong-Ju , Kim Sang-Woo
Published: February 2009

We report a dramatic increase in the light extraction efficiency of GaN-based blue light-emitting diodes (LEDs) by ZnO nanorod arrays on a planar indium tin oxide (ITO) transparent electrode. ZnO nanorods were grown into aqueous solution at the low temperature of 90 °C. With 20 mA current injection, the light output efficiency of the LED with ZnO nanorod arrays on ITO was increased by about 57% with no increase in a forward voltage over the conventional LEDs with planar ITO. The increased light extraction by the ZnO nanorod arrays is due to the formation of sidewalls and a rough surface, resulting in a multiple photon scattering at the LED surface.
An optimized replica exchange molecular dynamics method
Authors: Kamberaj Hiqmet , van der Vaart Arjan
Published: February 2009

We introduce a new way to perform swaps between replicas in replica exchange molecular dynamics simulations. The method is based on a generalized canonical probability distribution function and flattens the potential of mean force along the temperature coordinate, such that a random walk in temperature space is achieved. Application to a Gō model of protein A showed that the method is more efficient than conventional replica exchange. The method results in a constant probability distribution of the replicas over the thermostats, yields a minimum round-trip time between extremum temperatures, and leads to faster ergodic convergence.
Deforming glassy polystyrene: Influence of pressure, thermal history, and deformation mode on yielding and hardening
Authors: Vorselaars Bart , Lyulin Alexey V. , Michels M. A. J.
Published: February 2009

The toughness of a polymer glass is determined by the interplay of yielding, strain softening, and strain hardening. Molecular-dynamics simulations of a typical polymer glass, atactic polystyrene, under the influence of active deformation have been carried out to enlighten these processes. It is observed that the dominant interaction for the yield peak is of interchain nature and for the strain hardening of intrachain nature. A connection is made with the microscopic cage-to-cage motion. It is found that the deformation does not lead to complete erasure of the thermal history but that differences persist at large length scales. Also we find that the strain-hardening modulus increases with increasing external pressure. This new observation cannot be explained by current theories such as the one based on the entanglement picture and the inclusion of this effect will lead to an improvement in constitutive modeling.
Microphase separation of diblock copolymer poly(styrene-b-isoprene): A dissipative particle dynamics simulation study
Authors: Li Xuejin , Guo Jiayi , Liu Yuan , Liang Haojun
Published: February 2009

Dissipative particle dynamics (DPD) simulations have been employed to study the microphase separation of the poly(styrene-b-isoprene) (PS-b-PI) diblock copolymer. The DPD model is constructed to match the physical description and structural properties of the PS-b-PI diblock copolymer. A coarse-grained force field has been developed for the diblock copolymer system in DPD simulations. The new force field contains bonded and nonbonded interaction terms, which are derived from atomistic molecular dynamics simulations and determined by fitting experimental data of the compressibility of water at room temperature and interfacial tension values, respectively. The morphologies of the PS-b-PI diblock copolymer system obtained from DPD simulations are in agreement with experimental observations as well as previous simulated results.
Continuous and smooth potential energy surface for conductorlike screening solvation model using fixed points with variable areas
Authors: Su Peifeng , Li Hui
Published: February 2009

Rigorously continuous and smooth potential energy surfaces, as well as exact analytic gradients, are obtained for a conductorlike screening solvation model (CPCM, a variant of the general COSMO) with Hartree–Fock (RHF, ROHF, UHF, and MCSCF) and density functional theory (R-DFT, RO-DFT, and U-DFT) methods using a new tessellation scheme, fixed points with variable areas (FIXPVA). In FIXPVA, spheres centered at atoms are used to define the molecular cavity and surface. The surface of each sphere is divided into 60, 240, or 960 tesserae, which have positions fixed relative to the sphere center and areas scaled by switching functions of their distances to neighboring spheres. Analytic derivatives of the positions and areas of the surface tesserae with respect to atomic coordinates can be obtained and used to evaluate the solvation energy gradients. Due to the accurate analytic gradients and smooth potential energy surface, geometry optimization processes using these methods are stable and convergent.
Formation of holographic fringes on photochromic Ag/TiO2 nanocomposite films
Authors: Qiao Qian , Zhang Xintong , Lu Zifeng , Wang Lingling , Liu Yichun , Zhu Xingfu , Li Jixue
Published: February 2009

Silver nanoparticles deposited on TiO2 nanoporous films exhibited unique photochromic property under the irradiation of visible light. Here we investigated the application of photochromic Ag/TiO2 nanocomposite film in holographic data storage. Stable holographic fringes were formed on the Ag/TiO2 film using two coherent green lasers as writing beams, and these fringes could be erased with ultraviolet irradiation. These observations are consistent with the photochromism of Ag/TiO2 nanocomposite film and can be well explained by the visible light-stimulated dissolution and ultraviolet light-stimulated regeneration of silver nanoparticles in TiO2 matrix.
Free-running, room temperature operation of an InGaAs/InP single-photon avalanche diode
Authors: Warburton Ryan E. , Itzler Mark , Buller Gerald S.
Published: February 2009

Passive quenching operation of an InGaAs/InP single-photon avalanche diode detector at low excess bias is reported in terms of the key figures of merit including afterpulsing analysis. The reduced charge required to measure individual photon events meant that room temperature single-photon counting at 1550 nm wavelength was achievable without the requirement of electrical gating and with negligible afterpulsing effects evident.
Pseudomorphic growth of organic semiconductor thin films driven by incommensurate epitaxy
Authors: Sassella A. , Campione M. , Raimondo L. , Borghesi A. , Bussetti G. , Cirilli S. , Violante A. , Goletti C. , Chiaradia P.
Published: February 2009

A stable pseudomorphic phase of α-quaterthiophene, a well known organic semiconductor, is obtained by growing films with organic molecular beam epitaxy (OMBE) on a single crystal of another organic semiconductor, namely, tetracene. The structural characteristics of the new phase are investigated by monitoring in situ the OMBE process by reflectance anisotropy spectroscopy; thus assessing that incommensurate epitaxy is in this case, the driving force for tuning the molecular packing in organic molecular films and in turn, their solid state properties.
Phase-change oscillations in silicon microwires
Authors: Cywar A. , Bakan G. , Boztug C. , Silva H. , Gokirmak A.
Published: February 2009

We have observed liquid-solid phase-change oscillations in 2–5.5 μm long silicon wires biased through a load resistor. Molten silicon resistivity is approximately 30 times lower than that of the room temperature solid-state resistivity of the highly doped nanocrystalline-silicon thin film used to fabricate the wires. Wires typically melt with 15–20 V electrical stresses, draining the parasitic capacitance introduced by the experimental setup within 1 μs. The power dissipated in the wire is not sufficient to keep it in molten state after the discharge, leading to repeated melting and resolidification of the wires with 1 MHz, 2–20 mA current oscillations.
Current limiting effects of photoactivated charge domain in semi-insulating GaAs photoconductive switch
Authors: Shi Wei , Qu Guanghui , Xu Ming , Xue Hong , Ji Weili , Zhang Lin , Tian Liqiang
Published: February 2009

The photoactivated charge domain (PACD) plays an important role in the nonlinear modes of semi-insulating GaAs and LnP photoconductive switches. The formation and transporting process of photoactivated charge domain are discussed in this paper, which indicate that it is the shielded electric field that induced the unique distribution and evolution law of the PACD. The PACD restricts space-charge current in the photoconductor and the output current of the photoconductive switch by its shielded effect.
Carrier and phonon dynamics of wurtzite InN nanorods
Authors: Chang Y.-M. , Gwo S.
Published: February 2009

Time-resolved second harmonic generation is utilized to investigate the photoexcited carrier and phonon dynamics in wurtzite InN nanorods. The exponential decay response in the pump-induced second-harmonic generation curve reveals the carrier relaxation process via radiative and nonradiative recombination channels. Meanwhile, the generation and detection of the coherent A1(LO) phonon can reveal not only the phonon dynamics but also the crystalline quality in InN nanorods. It is found that the nonradiative structural defects play a dominant role in the transport and optical properties of InN nanorods.
Extremely low scattering cross section of a perforated silver film
Authors: Wang Haining , Zou Shengli
Published: February 2009

With a perforated silver film, we demonstrate that an extremely low scattering cross section with an efficiency of less than 1% can be achieved at tunable wavelengths with tunable widths. The resonance wavelength, width, and intensity are influenced by the size, shape, and arrangement pattern of the holes, as well as the distance separating the holes along the polarization direction. The discovered phenomenon holds promise for the development of photovoltaic devices with improved energy conversion efficiency.
Plasmonic thermal IR emitters based on nanoamorphous carbon
Authors: Tay Savaş , Kropachev Aleksandr , Araci Ismail Emre , Skotheim Terje , Norwood Robert A. , Peyghambarian N.
Published: February 2009

The development of plasmonic narrow-band thermal mid-IR emitters made from a conducting amorphous carbon composite is shown. These IR emitters have greatly improved thermal and mechanical stability compared to metallic emitters as they can be operated at 600 °C in air without any degradation in performance. The emitted thermal radiation has a bandwidth of 0.5 μm and can be set to the desired wavelength from 3 to 15 μm by changing the surface periodicity. The periodically patterned devices have in-band emissivities significantly exceeding that of the non-patterned devices, constituting simple yet efficient radiation sources at this important wavelength range.
Nanowire-templated microelectrodes for high-sensitivity pH detection
Authors: Antohe Vlad Andrei , Radu Adrian , Mátéfi-Tempfli Mária , Attout Anne , Yunus Sami , Bertrand Patrick , Duţu Constantin Augustin , Vlad Alexandru , Melinte Sorin , Mátéfi-Tempfli Stefan , Piraux Luc
Published: February 2009

A highly sensitive pH capacitive sensor has been designed by confined growth of vertically aligned nanowire arrays on interdigited microelectrodes. The active surface of the device has been functionalized with an electrochemical pH transducer (polyaniline). We easily tune the device features by combining lithographic techniques with electrochemical synthesis. The reported electrical LC resonance measurements show considerable sensitivity enhancement compared to conventional capacitive pH sensors realized with microfabricated interdigited electrodes. The sensitivity can be easily improved by changing only the thickness of the functional layer.
Vector holograms using radially polarized light
Authors: Ono Hiroshi , Wakabayashi Hiroyuki , Sasaki Tomoyuki , Emoto Akira , Shioda Tatsutoshi , Kawatsuki Nobuhiro
Published: February 2009

We have demonstrated the vector holograms using the radially polarized light. The inhomogeneous polarized light well controlled the spatial distribution of the optical anisotropy in the solid state polymeric materials. The theoretical calculation revealed formation mechanism and optical properties of the vector holograms.
Impacts of anisotropic lattice relaxation on crystal mosaicity and luminescence spectra of m-plane AlxGa1−xN films grown on m-plane freestanding GaN substrates by NH3 source molecular beam epitaxy
Authors: Hoshi T. , Hazu K. , Ohshita K. , Kagaya M. , Onuma T. , Fujito K. , Namita H. , Chichibu S. F.
Published: February 2009

In-plane anisotropic lattice relaxation was correlated with the crystal mosaicity and luminescence spectra for m-plane AlxGa1−xN films grown on a freestanding GaN substrate by NH3-source molecular beam epitaxy. The homoepitaxial GaN film exhibited A- and B-excitonic emissions at 8 K, which obeyed the polarization selection rules. For AlxGa1−xN overlayers, the m-plane tilt mosaic along c-axis was the same as the substrate as far as coherent growth was maintained (x≤0.25). However, it became more severe than along the a-axis for lattice-relaxed films (x≥0.52). The results are explained in terms of anisotropic lattice and thermal mismatches between the film and the substrate. Nonetheless, all the AlxGa1−xN films exhibited a near-band-edge emission peak and considerably weak deep emission at room temperature.